Postprandial changes in plasma acylcarnitine concentrations as markers of fatty acid flux in overweight and obesity

The effects of free fatty acid-free bovine serum albumin and palmitate on pancreatic β-cell function

Pancreatic β-cells release insulin in response to fluctuations in plasma glucose, amino acids, and free fatty acids (FFA). Clonal cell lines and isolated islets serve as essential early models for studying the impact of nutrients and evaluating potential therapies to address β-cell dysfunction. Acute and chronic changes in FFA levels have been shown to have positive and negative effects on β-cell function both in vivo and in vitro. A key problem in comparing islet lipid studies from different laboratories is that a wide variety of methods are used to isolate, culture, and assess islet function. The current study compares bovine serum albumin (BSA) types and lipid preparation methods in clonal 832/13 cells and human islets. Changing the percentage and culture conditions when using FFA-free BSA can negatively affect β-cell function compared to regular BSA. Preparing palmitate with FFA-free BSA can rescue insulin secretion compared to treating cells alone with FFA-free BSA. Different methods of preparing palmitate can have unique effects on insulin secretion. Overall, interpreting the effects of lipids on β-cell function is complicated by a number of variables that need to be controlled for in islet experiments.

Isomer-resolved characterization of acylcarnitines reveals alterations in type 2 diabetes

BACKGROUND

Acylcarnitines (CARs) are metabolites of fatty acids that play crucial roles in various cellular energy metabolism pathways. The structural diversity of CAR species arises from several modifications localized on the fatty acyl chain and there is currently a lack of reports characterizing these detailed structures. High-performance liquid chromatography (HPLC)-electrospray mass spectrometry (ESI-MS) is the common tool for CARs analysis.

RESULTS

In this study, we improved the MS detection signals of CARs by adding NH4HCO3 as buffer in the mobile phase of LC system. We demonstrated that electron activated dissociation (EAD) on the ZenoTOF 7600 system is capable of localizing the hydroxyl group and methyl branching position in CARs. The benzophenone Paternò-Büchi (PB) reaction was used for derivatizing the carbon-carbon double bond (CC). The capability of profiling CARs with detailed structural information was demonstrated by analyzing complex lipid extracts from mouse plasma. Our results also provided visualization of isomers composition, including branched chain isomers of CAR 4:0 and CAR 5:0 and CC location isomers of unsaturated CARs. Notably, we observed significant changes in the relative compositions of branched-chain isomers of CAR 5:0 and CC location isomers of several unsaturated CARs in mouse plasma samples from type 2 diabetes (T2D) compared to normal controls, suggesting their potential as diagnostic indicators for T2D.

SIGNIFICANCE

In this work, we enhanced the limit of detection for acylcarnitine species by incorporating ammonium bicarbonate into the LC system. The CC positions in the acyl chain of CARs were identified using Paternò-Büchi (PB) derivatization coupled with tandem mass spectrometry. Modifications such as methyl branching and hydroxyl groups along the acyl chain were localized through Electron-Activated Dissociation (EAD) on the Zeno-TOF 7600 system.

Longitudinal characterization of the metabolome of dairy cows transitioning from one lactation to the next: Investigations in fecal samples

The fecal metabolome comprises metabolites that are excreted or not absorbed by the animal. This study examined the changes in the fecal metabolome of dairy cows from the end of one lactation period, through the dry period, and into the subsequent lactation. Twelve Holstein cows (BW = 745 ± 71 kg, BCS = 3.43 ± 0.66) were housed in a tiestall barn from 7 wk before to 15 wk after parturition, with dry-off occurring approximately 6 wk before the expected calving date (mean dry-off time = 42 d). Fecal samples were taken at wk -7, -5, -1, +1, +5, +10, and +15 relative to calving. Targeted metabolomics identified a total of 93 metabolites, including AA, biogenic amines, bile acids (BA), acylcarnitines (AcylCN), and some phospholipids. Principal component analysis (PCA) revealed clear metabolic shifts that showed a clear separation between the samples from the dry period and the samples from the end, early, and middle of lactation, indicating significant changes in the metabolic profiles in the feces. The transition from the dry period (wk -5, -1 relative to calving) to lactation (wk +1, +5, +10, +15, and -7 relative to calving) is characterized by an increase in fecal AA and metabolites, such as Glu, Met, β-alanine, and methionine sulfoxide, reflecting a shift in nitrogen metabolism to support increased protein metabolism for milk production. Higher concentrations of polyamines, such as spermidine and putrescine, were observed postpartum, indicating increased cell growth and improved tissue regeneration. Elevated gamma-aminobutyric acid levels during lactation indicate increased microbial activity driven by a nutrient-rich diet. Results showed significant adjustments in BA profiles as cows transitioned into lactation. Deoxycholic acid remained the predominant BA in feces, reflecting ongoing microbial transformation, whereas glycine- and taurine-conjugated BA increased postpartum, suggesting improved enterohepatic circulation and lipid absorption. Fecal AcylCN showed dynamic shifts with elevated levels during late gestation, a decrease in the dry period, and an increase postpartum, indicating increased fatty acid oxidation to meet energy demands. Results showed that phosphatidylcholines decreased prepartum but increased after calving. This indicates shifts in lipid metabolism reflecting energy requirements in lactation and suggests that fecal lipid composition is an indicator of metabolic adaptations in dairy cows. In particular, PCA revealed considerable overlap in the fecal metabolite profiles of multiparous and primiparous cows, indicating similar metabolic profiles. This was also confirmed by volcano plots, which showed no significant differences in fecal metabolism between the 2 groups across different weeks relative to calving (wk -7, -5, -1, +1, +5, +10, and +15). Overall, these results emphasize the complex interactions between dietary factors, liver and gastrointestinal function, and the gut microbiome in shaping the fecal metabolite profile of dairy cows. These results underscore the value of this data set in advancing the application of fecal metabolome profiling to investigate metabolic changes during critical transitions in the lactation cycle of dairy cows.

Two-dimensional Health State Map to define metabolic health using separated static and dynamic homeostasis features: a proof-of-concept study

Defining metabolic health is critical for the earlier reversing of metabolic dysfunction and disease, and fasting-based diagnosis may not adequately assess an individual's metabolic adaptivity under stress. We constructed a novel Health State Map (HSM) comprising a Health Phenotype Score (HPS) with fasting features alone and a Homeostatic Resilience Score (HRS) with five time-point features only (t = 30, 60, 90, 180, 240 min) following a standardized mixed macronutrient tolerance test (MMTT). Among 111 Chinese adults, when the same set of fasting and post-MMTT data as for the HSM was used, the mixed-score was highly correlated with the HPS. The HRS was significantly associated with metabolic syndrome prevalence, independently of the HPS (OR [95% CI]: 0.41 [0.18, 0.92]) and the mixed-score (0.34 [0.15, 0.69]). Moreover, the HRS could discriminate metabolic characteristics unseparated by the HPS and the mixed-score. Participants with higher HRSs had better metabolic traits than those with lower HRSs. Large interpersonal variations were also evidenced by evaluating postprandial homeostatic resiliencies for glucose, lipids and amino acids when participants had similar overall HRSs. Additionally, the HRS was positively associated with physical activity level and specific gut microbiome structure. Collectively, our HSM model might offer a novel approach to precisely define an individual's metabolic health and nutritional capacity.

Postprandial Metabolomic Profiling: Insights into Macronutrient-Specific Metabolic Responses in Healthy Individuals

BACKGROUND/OBJECTIVES

Understanding the metabolic responses to different macronutrients is crucial for assessing their impacts on health. This study aims to investigate the postprandial metabolomic profiles of healthy individuals following the consumption of glucose, protein, and lipids.

METHODS

Twenty-three healthy, normal-weight adults participated in the study, randomly assigned to consume 300 kcal from glucose, protein, or lipids after an overnight fast. Blood samples were collected at baseline and at 1, 2, and 3 h post-ingestion. An untargeted metabolomic approach using mass spectrometry was employed to analyze plasma metabolites.

RESULTS

In total, 21, 59, and 156 dysregulated metabolites were identified after glucose, protein, and lipid intake, respectively. Notably, 3'-O-methylguanosine levels decreased significantly after glucose consumption while remaining stable during lipid intake before increasing at 2 h. Common metabolites shared between glucose and lipid groups included 3'-O-methylguanosine, 3-oxotetradecanoic acid, poly-g-D-glutamate, and triglyceride (TG) (15:0/18:4/18:1).

CONCLUSIONS

The findings highlight distinct metabolic responses to macronutrient intake, emphasizing the role of specific metabolites in regulating postprandial metabolism. These insights contribute to understanding how dietary components influence metabolic health and insulin sensitivity.

Longitudinal characterization of serum metabolome and lipidome reveals that the ceramide profile is associated with metabolic health in early postpartum cows experiencing different lipolysis

Reduced feed intake in early lactation prompts increased fat mobilization to meet dairy cow energy needs for milk production. The increased lipolysis in cows presents significant health risks with unclear mechanisms. The objectives of our study were to compare the longitudinal profiles of metabolites and lipids of serum from high- and low-lipolysis cows. Forty multiparous Holstein dairy cows were enrolled in the retrospective study. Serum samples were collected on d 7 before expected calving, as well as on d 5, 7, 14, and 21 postpartum. Dairy cows were grouped according to mean serum nonesterified fatty acids on d 5 and 7 after parturition as low (<0.600 mmol/L; n = 8; LFM) and high (>0.750 mmol/L; n = 8; HFM), indicating fat mobilization during early lactation. Lactational performance and serum metabolic parameters related to glucose and lipid metabolism, liver functions, oxidative status, and inflammatory responses were determined. Serum samples were subjected to liquid chromatography-MS-based metabolomics and lipidomics. Despite differences in postpartum BW change, there were no observed variations in milk yield and composition between the 2 groups. Serum β-hydroxybutyric acid, glucose, leptin, aspartate aminotransferase, IL-6, and tumor necrosis factor alpha were greater in cows with HFM than in cows with LFM. Serum adiponectin, revised quantitative insulin sensitivity check index, and albumin were lower in cows with HFM than in cows with LFM. Intensified fat mobilization in the HFM cows came along with reduced estimated insulin sensitivity, impaired liver functions, and increased oxidative stress and inflammatory responses. Differences in metabolic patterns were observed across the transition period when comparing serum blood matrixes (e.g., in different amino acids, acylcarnitines, and sphingolipids). The serum metabolome of the HFM cows was characterized by higher concentrations of glycine, acylcarnitines, carnosine, Cer(d20:0/18:0), Cer(d18:1/16:0), and Cer(t18:0/24:0) compared with LFM cows. The differential serum metabolites and lipids at different sampling times during the peripartum period were enriched in the sphingolipid metabolism. Differences in serum metabolic status parameters suggest that cows adopt varied metabolic adaptation strategies to cope with energy deficits postpartum. Our investigation found a comprehensive remodeling of the serum metabolic profiles in transition dairy cattle, highlighting the significance of alterations in sphingolipid species, as they play a crucial role in insulin resistance and metabolic disorders.

Untargeted lipidomics analysis in women with morbid obesity and type 2 diabetes mellitus: A comprehensive study

There is a phenotype of obese individuals termed metabolically healthy obese that present a reduced cardiometabolic risk. This phenotype offers a valuable model for investigating the mechanisms connecting obesity and metabolic alterations such as Type 2 Diabetes Mellitus (T2DM). Previously, in an untargeted metabolomics analysis in a cohort of morbidly obese women, we observed a different lipid metabolite pattern between metabolically healthy morbid obese individuals and those with associated T2DM. To validate these findings, we have performed a complementary study of lipidomics. In this study, we assessed a liquid chromatography coupled to a mass spectrometer untargeted lipidomic analysis on serum samples from 209 women, 73 normal-weight women (control group) and 136 morbid obese women. From those, 65 metabolically healthy morbid obese and 71 with associated T2DM. In this work, we find elevated levels of ceramides, sphingomyelins, diacyl and triacylglycerols, fatty acids, and phosphoethanolamines in morbid obese vs normal weight. Conversely, decreased levels of acylcarnitines, bile acids, lyso-phosphatidylcholines, phosphatidylcholines (PC), phosphatidylinositols, and phosphoethanolamine PE (O-38:4) were noted. Furthermore, comparing morbid obese women with T2DM vs metabolically healthy MO, a distinct lipid profile emerged, featuring increased levels of metabolites: deoxycholic acid, diacylglycerol DG (36:2), triacylglycerols, phosphatidylcholines, phosphoethanolamines, phosphatidylinositols, and lyso-phosphatidylinositol LPI (16:0). To conclude, analysing both comparatives, we observed decreased levels of deoxycholic acid, PC (34:3), and PE (O-38:4) in morbid obese women vs normal-weight. Conversely, we found elevated levels of these lipids in morbid obese women with T2DM vs metabolically healthy MO. These profiles of metabolites could be explored for the research as potential markers of metabolic risk of T2DM in morbid obese women.

Longitudinal characterization of the metabolome of dairy cows transitioning from one lactation to the next: Investigations in blood serum

The objective of this study was to characterize changes in the serum metabolome and various indicators of oxidative balance in dairy cows starting 2 wk before dry-off and continuing until wk 16 of lactation. Twelve Holstein dairy cows (body weight 745 ± 71 kg, body condition score 3.43 ± 0.66; mean ± SD) were housed in a tiestall barn from 10 wk before to 16 wk after parturition. Cows were dried off 6 wk before the expected calving date (mean dry period length = 42 d). From 8 wk before calving to 16 wk after calving, blood samples were taken weekly to study redox metabolism by determining antioxidant capacity, measured as the ferric-reducing ability of plasma, reactive oxidative metabolites, oxidative stress index, oxidative damage of lipids, measured as thiobarbituric acid reactive substances, and glutathione peroxidase activity. According to these results, dairy cows had the lowest serum antioxidant capacity and greater levels of oxidative stress during the dry-off period and the early postpartum period. For metabolomics, a subset of serum samples including wk -7 (before dry-off), -5 (after dry-off), -1, 1, 5, 10, and 15 relative to calving were used. A targeted metabolomics approach was performed using liquid chromatography and flow injection with electrospray ionization triple quadrupole mass spectrometry using the MxP Quant 500 kit (Biocrates Life Sciences AG). A total of 240 metabolites in serum were used in the final data analysis. Principal component analysis revealed a clear separation by days of sampling, indicating a remarkable shift in metabolic phenotype between the dry period and late and early lactation. Changes in many non-lipid metabolites associated with one-carbon metabolism, the tricarboxylic acid cycle, the urea cycle, and AA catabolism were observed in the study, with changes in AA serum concentrations likely related to factors such as energy and nitrogen balance, digestive efficiency, and changing diets. The study confirmed an extensive remodeling of the serum lipidome in peripartum dairy cows, highlighting the importance of changes in acylcarnitine (acylCN), phosphatidylcholines (PC), and triacylglycerols (TG), as they play a crucial role in lipid metabolism. Results showed that short-chain acylCN increased after dry-off and decreased thereafter, whereas lipid-derived acylCN increased around parturition, suggesting that more fatty acids could enter mitochondria. Phospholipids and sphingolipids in serum showed changes during lactation. In particular, concentrations of sphingomyelins, PC, and lysoPC decreased around calving but increased in mid- and late lactation. In contrast, concentrations of TG remained consistently low after parturition. The serum concentrations of bile acids fluctuated during the dry period and lactation, with glycocholic acid, cholic acid, glycodeoxycholic acid, and taurocholic acid showing the greatest concentrations. These changes are likely due to the interplay of diet, liver function, and the ability of the gut microbiota to convert primary to secondary bile acids. Overall, these descriptive results may aid in hypothesis generation and in the design and interpretation of future metabolite-based studies in dairy cows. Furthermore, they contribute to our understanding of the physiological ranges in serum metabolites relative to the lactation cycle of the dairy cow.

Ceramide on the road to insulin resistance and immunometabolic disorders in transition dairy cows: driver or passenger?

Dairy cows must undergo profound metabolic and endocrine adaptations during their transition period to meet the nutrient requirements of the developing fetus, parturition, and the onset of lactation. Insulin resistance in extrahepatic tissues is a critical component of homeorhetic adaptations in periparturient dairy cows. However, due to increased energy demands at calving that are not followed by a concomitant increase in dry matter intake, body stores are mobilized, and the risk of metabolic disorders dramatically increases. Sphingolipid ceramides involved in multiple vital biological processes, such as proliferation, differentiation, apoptosis, and inflammation. Three typical pathways generate ceramide, and many factors contribute to its production as part of the cell's stress response. Based on lipidomic profiling, there has generally been an association between increased ceramide content and various disease outcomes in rodents. Emerging evidence shows that ceramides might play crucial roles in the adaptive metabolic alterations accompanying the initiation of lactation in dairy cows. A series of studies also revealed a negative association between circulating ceramides and systemic insulin sensitivity in dairy cows experiencing severe negative energy balance. Whether ceramide acts as a driver or passenger in the metabolic stress of periparturient dairy cows is an unknown but exciting topic. In the present review, we discuss the potential roles of ceramides in various metabolic dysfunctions and the impacts of their perturbations. We also discuss how this novel class of bioactive sphingolipids has drawn interest in extrahepatic tissue insulin resistance and immunometabolic disorders in transition dairy cows. We also discuss the possible use of ceramide as a new biomarker for predicting metabolic diseases in cows and highlight the remaining problems.

Metabolomics profiling of maternal and umbilical cord blood in normoglycemia macrosomia

Background: Macrosomia is a common disorder that occurs during pregnancy. We investigated the comprehensive metabolite profiles of pregnant maternal and fetal sera in normoglycemic macrosomia in a Chinese population. Methods: Forty pregnant women and their fetuses were included in the study (twenty macrosomia patients and twenty normal-weight controls). Maternal and umbilical cord serum metabolites were identified using ultra-performance liquid chromatography coupled with tandem mass spectrometry. Results: In total, 203 metabolites were identified. Lipids and lipid-like molecules were the predominant metabolites. Fifty-three metabolites with significant differences were obtained in the maternal samples. In the macrosomia group, the levels of docosahexaenoic acid, eicosapentaenoic acid, and arachidonic acid were significantly higher than those in the control group. Umbilical cord serum samples were obtained for 24 different metabolites. The maternal-fetal gradient of polyunsaturated fatty acids was decreased in the macrosomia group. Aconitic acid, citric acid, isocitric acid, 2-methylhexanoic acid, and 12-hydroxystearic acid were the common differential metabolites in the maternal and umbilical cord serum samples. Conclusion: There were obvious metabolic abnormalities in the sera of pregnant women and fetuses with macrosomia. Lipids and lipid-like molecules were the predominant differential metabolites but had different classifications in the maternal and umbilical cord serum. These results may provide new insights into the long-term metabolic disorders associated with macrosomia.

Advances of stable isotope technology in food safety analysis and nutrient metabolism research

Food quality, safety, and the regulatory metabolism of food nutrients in cells are primary factors in determining human health. However, residues of undesirable or hazardous compounds in food products and dysregulation in the nutrient metabolism inevitably occur occasionally. For years, chromatography-mass spectrometry technology has been recognized as an essential research tool in food analysis and nutrient metabolism research, and it is more accurate and robust when coupled with stable isotopes. In this study, we summarize the applications of stable isotope technology in the quantification of contaminant residues (pesticides, veterinary drugs, mycotoxins, polycyclic aromatic hydrocarbons, and other hazardous compounds) in foods and in the nutrients (glucose, lipids, amino acids and proteins) metabolism research. The aim of this review was to serve as a reference for providing effective analysis techniques for protecting food quality and human health, and to pave the way for the broader application of stable isotope technology.

Invited review: Assessment of body condition score and body fat reserves in relation to insulin sensitivity and metabolic phenotyping in dairy cows

The purpose of this article is to review body condition scoring and the role of body fat reserves in relation to insulin sensitivity and metabolic phenotyping. This article summarizes body condition scoring assessment methods and the differences between subcutaneous and visceral fat depots in dairy cows. The mass of subcutaneous and visceral adipose tissue (AT) changes significantly during the transition period; however, metabolism and intensity of lipolysis differ between subcutaneous and visceral AT depots of dairy cows. The majority of studies on AT have focused on subcutaneous AT, and few have explored visceral AT using noninvasive methods. In this systematic review, we summarize the relationship between body fat reserves and insulin sensitivity and integrate omics research (e.g., metabolomics, proteomics, lipidomics) for metabolic phenotyping of cows, particularly overconditioned cows. Several studies have shown that AT insulin resistance develops during the prepartum period, especially in overconditioned cows. We discuss the role of AT lipolysis, fatty acid oxidation, mitochondrial function, acylcarnitines, and lipid insulin antagonists, including ceramide and glycerophospholipids, in cows with different body condition scoring. Nonoptimal body conditions (under- or overconditioned cows) exhibit marked abnormalities in metabolic and endocrine function. Overall, reducing the number of cows with nonoptimal body conditions in herds seems to be the most practical solution to improve profitability, and dairy farmers should adjust their management practices accordingly.

Plasma Cholesterol- and Body Fat-Lowering Effects of Chicken Protein Hydrolysate and Oil in High-Fat Fed Male Wistar Rats

Rest raw materials provide a new source of bioactive dietary ingredients, and this study aimed to determine the health effects of diets with chicken protein hydrolysate (CPH) and chicken oil (CO) generated from deboned chicken meat. Male Wistar rats (n = 56) were divided into seven groups in three predefined sub-experiments to study the effects of protein source (casein, chicken fillet, pork fillet, and CPH), the dose-effect of CPH (50% and 100% CPH), and the effects of combining CPH and CO. Rats were fed high-fat diets for 12 weeks, and casein and chicken fillet were used as controls in all sub-experiments. While casein, chicken-, or pork fillet diets resulted in similar weight gain and plasma lipid levels, the CPH diet reduced plasma total cholesterol. This effect was dose dependent and accompanied with the reduced hepatic activities of acetyl-CoA carboxylase and fatty acid synthase. Further, rats fed combined CPH and CO showed lower weight gain, and higher hepatic mitochondrial fatty acid oxidation, plasma L-carnitine, short-chain acylcarnitines, TMAO, and acetylcarnitine/palmitoylcarnitine. Thus, in male Wistar rats, CPH and CO lowered plasma cholesterol and increased hepatic fatty acid oxidation compared to whole protein diets, pointing to potential health-beneficial bioactive properties of these processed chicken rest raw materials.

Untargeted muscle tissue metabolites profiling in young, adult, and old rats supplemented with tocotrienol-rich fraction

The greatest significant influence on human life span and health is inevitable ageing. One of the distinguishing characteristics of ageing is the gradual decrease of muscle mass and physical function. There has been growing evidence that tocotrienol can guard against age-associated chronic diseases and metabolic disorders. This study aimed to elucidate the effects of tocotrienol-rich fraction (TRF) on muscle metabolomes and metabolic pathways in ageing Sprague Dawley (SD) rats. Three months, 9 months, and 21 months old male SD rats were divided into control and treated groups with 10 rats per group. Rats in control and treated groups were given 60 mg/kg body weight/day of palm olein and 60 mg/kg body weight/day of TRF, respectively, via oral gavage for 3 months. Muscle performance was assessed at 0 and 3 months of treatment by measuring muscle strength and function. Our results showed that TRF treatment caused a significant increase in the swimming time of the young rats. Comparison in the control groups showed that metabolites involved in lipid metabolisms such as L-palmitoyl carnitine and decanoyl carnitine were increased in ageing. In contrast, several metabolites, such as 3-phosphoglyceric acid, aspartic acid and aspartyl phenylalanine were decreased. These findings indicated that muscle metabolomes involved in lipid metabolism were upregulated in aged rats. In contrast, the metabolites involved in energy and amino acid metabolism were significantly downregulated. Comparison in the TRF-supplemented groups showed an upregulation of metabolites involved in energy and amino acid metabolism. Metabolites such as N6-methyl adenosine, spermine, phenylalanine, tryptophan, aspartic acid, histidine, and N-acetyl neuraminic acid were up-regulated, indicating promotion of amino acid synthesis and muscle regeneration. Energy metabolism was also improved in adult and old rats with TRF supplementation as indicated by the upregulation of nicotinamide adenine dinucleotide and glycerol 3-phosphate compared to the control group. In conclusion, the mechanism underlying the changes in skeletal muscle mass and functions in ageing was related to carbohydrate, lipid and amino acid metabolism. Tocotrienol supplementation showed beneficial effects in alleviating energy and amino acid synthesis that may promote the regeneration and renewal of skeletal muscle in ageing rats.

Integrated omics analysis reveals differences in gut microbiota and gut-host metabolite profiles between obese and lean chickens

Abdominal fat is the major adipose tissue in chickens. In chicken, the deposition of abdominal fat affects meat yield and quality. Previous reports suggest that gut microbiota composition and function are associated with lipid metabolism. In this study, we used comparative metagenomics and metabolomics analysis to determine the gut microbiota and gut-host metabolite profiles in Shouguang (SG; a Chinese chicken breed with low-fat deposition) and Luqin (LQ; a fatty-type chicken breed with a fast growth rate) chickens. The results showed that LQ chickens had higher body weight, eviscerated yield, abdominal fat yield, abdominal fat ratio, and triglyceride (TG) content in the breast muscle than SG chickens. Untargeted metabolomics analyses showed a total of 11 liver metabolites, 19 plasma metabolites, and 30 cecal metabolites differentially enriched in LQ and SG chickens based on variable importance in the projection (VIP) ≥ 1 and P ≤ 0.05. These metabolites are involved in lipid and amino acid metabolism. The relative abundance of bacteria in the microbiota differed significantly between the 2 chicken breeds. The functional prediction of microbiota abundant in LQ chickens was starch and lactose degradation. Erysipelatoclostridium was abundant in LQ chickens and significantly positively correlated to palmitoyl ethanolamide (PEA), a key regulator of lipid metabolism. Our findings revealed differences in liver and plasma metabolites between chicken breeds with different adipose deposition capacities. Long-chain acylcarnitines might be important markers of adipose deposition differences in chickens. The cecum's microbial communities and metabolome profiles significantly differed between LQ and SG chickens. However, the relationship between cecal microbiota and their metabolites and liver and plasma metabolites is not thoroughly understood. Future research will focus on relating tissue metabolite changes to intestinal microbiota and their effects on body fat deposition.

Determinants of blood acylcarnitine concentrations in healthy individuals of the European Prospective Investigation into Cancer and Nutrition

BACKGROUND & AIMS

Circulating levels of acylcarnitines (ACs) have been associated with the risk of various diseases such as cancer and type 2 diabetes. Diet and lifestyle factors have been shown to influence AC concentrations but a better understanding of their biological, lifestyle and metabolic determinants is needed.

METHODS

Circulating ACs were measured in blood by targeted (15 ACs) and untargeted metabolomics (50 ACs) in 7770 and 395 healthy participants of the European Prospective Investigation into Cancer and Nutrition (EPIC), respectively. Associations with biological and lifestyle characteristics, dietary patterns, self-reported intake of individual foods, estimated intake of carnitine and fatty acids, and fatty acids in plasma phospholipid fraction and amino acids in blood were assessed.

RESULTS

Age, sex and fasting status were associated with the largest proportion of AC variability (partial-r up to 0.19, 0.18 and 0.16, respectively). Some AC species of medium or long-chain fatty acid moiety were associated with the corresponding fatty acids in plasma (partial-r = 0.24) or with intake of specific foods such as dairy foods containing the same fatty acid. ACs of short-chain fatty acid moiety (propionylcarnitine and valerylcarnitine) were moderately associated with concentrations of branched-chain amino acids (partial-r = 0.5). Intake of most other foods and of carnitine showed little association with AC levels.

CONCLUSIONS

Our results show that determinants of ACs in blood vary according to their fatty acid moiety, and that their concentrations are related to age, sex, diet, and fasting status. Knowledge on their potential determinants may help interpret associations of ACs with disease risk and inform on potential dietary and lifestyle factors that might be modified for disease prevention.

Insulin Sensitivity and Metabolic Flexibility Parallel Plasma TCA Levels in Early Chronotype With Metabolic Syndrome

CONTEXT

People characterized as late chronotype have elevated type 2 diabetes and cardiovascular disease risk compared to early chronotype. It is unclear how chronotype is associated with insulin sensitivity, metabolic flexibility, or plasma TCA cycle intermediates concentration, amino acids (AA), and/or beta-oxidation.

OBJECTIVE

This study examined these metabolic associations with chronotype.

METHODS

The Morningness-Eveningness Questionnaire (MEQ) was used to classify adults with metabolic syndrome (ATP III criteria) as either early (n = 15 [13F], MEQ = 64.7 ± 1.4) or late (n = 19 [16F], MEQ = 45.5 ± 1.3) chronotype. Fasting bloods determined hepatic (HOMA-IR) and adipose insulin resistance (Adipose-IR) while a 120-minute euglycemic clamp (40 mU/m2/min, 5 mmoL/L) was performed to test peripheral insulin sensitivity (glucose infusion rate). Carbohydrate (CHOOX) and fat oxidation (FOX), as well as nonoxidative glucose disposal (NOGD), were also estimated (indirect calorimetry). Plasma tricarboxylic acid cycle (TCA) intermediates, AA, and acyl-carnitines were measured along with VO2max and body composition (DXA).

RESULTS

There were no statistical differences in age, BMI, fat-free mass, VO2max, or ATP III criteria between groups. Early chronotype, however, had higher peripheral insulin sensitivity (P = 0.009) and lower HOMA-IR (P = 0.02) and Adipose-IR (P = 0.05) compared with late chronotype. Further, early chronotype had higher NOGD (P = 0.008) and greater insulin-stimulated CHOOX (P = 0.02). While fasting lactate (P = 0.01), TCA intermediates (isocitrate, α-ketoglutarate, succinate, fumarate, malate; all P ≤ 0.04) and some AA (proline, isoleucine; P = 0.003-0.05) were lower in early chronotype, other AA (threonine, histidine, arginine; all P ≤ 0.05) and most acyl-carnitines were higher (P ≤ 0.05) compared with late chronotype.

CONCLUSION

Greater insulin sensitivity and metabolic flexibility relates to plasma TCA concentration in early chronotype.

Acylcarnitines: Nomenclature, Biomarkers, Therapeutic Potential, Drug Targets, and Clinical Trials

Acylcarnitines are fatty acid metabolites that play important roles in many cellular energy metabolism pathways. They have historically been used as important diagnostic markers for inborn errors of fatty acid oxidation and are being intensively studied as markers of energy metabolism, deficits in mitochondrial and peroxisomal β -oxidation activity, insulin resistance, and physical activity. Acylcarnitines are increasingly being identified as important indicators in metabolic studies of many diseases, including metabolic disorders, cardiovascular diseases, diabetes, depression, neurologic disorders, and certain cancers. The US Food and Drug Administration-approved drug L-carnitine, along with short-chain acylcarnitines (acetylcarnitine and propionylcarnitine), is now widely used as a dietary supplement. In light of their growing importance, we have undertaken an extensive review of acylcarnitines and provided a detailed description of their identity, nomenclature, classification, biochemistry, pathophysiology, supplementary use, potential drug targets, and clinical trials. We also summarize these updates in the Human Metabolome Database, which now includes information on the structures, chemical formulae, chemical/spectral properties, descriptions, and pathways for 1240 acylcarnitines. This work lays a solid foundation for identifying, characterizing, and understanding acylcarnitines in human biosamples. We also discuss the emerging opportunities for using acylcarnitines as biomarkers and as dietary interventions or supplements for many wide-ranging indications. The opportunity to identify new drug targets involved in controlling acylcarnitine levels is also discussed. SIGNIFICANCE STATEMENT: This review provides a comprehensive overview of acylcarnitines, including their nomenclature, structure and biochemistry, and use as disease biomarkers and pharmaceutical agents. We present updated information contained in the Human Metabolome Database website as well as substantial mapping of the known biochemical pathways associated with acylcarnitines, thereby providing a strong foundation for further clarification of their physiological roles.

Comparative Evaluation of the Effect of Metformin and Insulin on Gut Microbiota and Metabolome Profiles of Type 2 Diabetic Rats Induced by the Combination of Streptozotocin and High-Fat Diet

Lately, an increasing number of studies have investigated the relationship between metformin and gut microbiota, suggesting that metformin exerts part of its hypoglycemic effect through the microbes. However, its underlying mechanism remains largely undetermined. In the present study, we investigated the effects of metformin on gut microbiota and metabolome profiles in serum and compared it with insulin treatment in rats with type 2 diabetes mellitus (T2DM). Diabetic rats (DM group) were induced by a combination of streptozotocin and high-fat diet (HFD). After 7 days, DM rats were treated with metformin (MET group) or insulin (INS group) for 3 weeks. The 16S rRNA sequencing of the gut microbiota and non-targeted metabolomics analysis of serum were conducted. A total of 13 bile acids (BAs) in serum were further determined and compared among different groups. The rat model of T2DM was well established with the typical diabetic symptoms, showing significantly increased blood glucose, AUC of OGTT, HOMA-IR, TC, TG, LDL-C and TBA. Metformin or insulin treatment could ameliorate symptoms of diabetes and partly recover the abnormal biochemical indicators. Compared with DM rats, the relative abundances of 13 genera were significantly changed after metformin treatment, while only three genera were changed after insulin treatment. The metformin and insulin treatments also exhibited different serum metabolome profiles in T2DM rats. Moreover, 64 differential metabolites were identified between MET and DM groups, whereas 206 were identified between INS and DM groups. Insulin treatment showed greater influence on amino acids, glycerophospholipids/glycerolipids, and acylcarnitine compared with the metformin treatment, while metformin had an important impact on BAs. Furthermore, metformin could significantly decrease the serum levels of CA, GCA, UDCA, and GUDCA, but increase the level of TLCA in DM rats. Insulin treatment significantly decreased the levels of CA, UDCA, and CDCA. Besides, several metabolites in serum or microbiota were positively or negatively correlated with some bacteria. Collectively, our findings indicated that metformin had a stronger effect on gut microbiota than insulin, while insulin treatment showed greater influence on serum metabolites, which provided novel insights into the therapeutic effects of metformin on diabetes.

Metabolite Signature of Physical Activity and the Risk of Type 2 Diabetes in 7271 Men

Large population-based studies investigating the association of physical activity (PA) with the metabolite signature contribute significantly to the understanding of the effects of PA on metabolic pathways associated with the risk of type 2 diabetes. Our study included 8749 Finnish men without diabetes at baseline recruited from the Metabolic Syndrome in Men (METSIM) cohort. We used a questionnaire to measure leisure-time PA. Metabolites were measured in 7271 men as a part of Metabolon’s untargeted Discovery HD4 platform using ultrahigh-performance liquid chromatography–tandem mass spectrometry. We found 198 metabolites significantly associated with PA. Several of these metabolites were novel including especially steroids, amino acids, imidazoles, carboxylic acids, and hydroxy acids. Increased PA was significantly associated with high levels of choline plasmalogens, lysophosphatidylcholines, polyunsaturated fatty acids, carotenoids, long chain acylcarnitines, imidazoles, bilirubins, aryl sulfates, hydroxy acids, indolepropionate, and indolelactate. Several of these metabolites have been previously associated with a decreased risk of type 2 diabetes and with a healthy diet. Our population-based study shows that the metabolite signature of increased PA includes multiple metabolic pathways and is associated with better adherence to a healthy lifestyle.

The metabolomics approach revealed a distinctive metabolomics pattern associated with hyperthyroidism treatment

BACKGROUND

Hyperthyroidism is characterized by increased thyroid hormone production, which impacts various processes, including metabolism and energy expenditure. Yet, the underlying mechanism and subsequent influence of these changes are unknown. Metabolomics is a broad analytical method that enables qualitative and quantitative examination of metabolite level changes in biological systems in response to various stimuli, pathologies, or treatments.

OBJECTIVES

This study uses untargeted metabolomics to explore the potential pathways and metabolic patterns associated with hyperthyroidism treatment.

METHODS

The study consisted of 20 patients newly diagnosed with hyperthyroidism who were assessed at baseline and followed up after starting antithyroid treatment. Two blood samples were taken from each patient, pre (hyperthyroid state) and post-treatment (euthyroid state). Hyperthyroid and euthyroid states were identified based on thyroxine and thyroid-stimulating hormone levels. The metabolic alteration associated with antithyroid therapy was investigated using liquid chromatography- high-resolution mass spectrometry. The untargeted metabolomics data was analyzed using both univariate and multivariate analyses using MetaboAnalyst v5.0. The significant metabolic pattern was identified using the lab standard pipeline, which included molecular annotation in the Human Metabolome Database, LipidMap, LipidBlast, and METLIN. The identified metabolites were examined using pathway and network analyses and linked to cellular metabolism.

RESULTS

The results revealed a strong group separation between the pre- and post-hyperthyroidism treatment (Q2 = 0.573, R2 = 0.995), indicating significant differences in the plasma metabolome after treatment. Eighty-three mass ions were significantly dysregulated, of which 53 and 30 characteristics were up and down-regulated in the post-treatment compared to the pre-treatment group, respectively. The medium-chain acylcarnitines, octanoylcarnitine, and decanoylcarnitine, previously found to rise in hyperthyroid patients, were among the down-regulated metabolites, suggesting that their reduction could be a possible biomarker for monitoring euthyroid restoration. Kynurenine is a downregulated tryptophan metabolite, indicating that the enzyme kynurenine 3-hydroxylase, inhibited in hyperthyroidism, is back functioning. L-cystine, a cysteine dimer produced from cysteine oxidation, was among the down-regulated metabolites, and its accumulation is considered a sign of oxidative stress, which was reported to accompany hyperthyroidism; L-cystine levels dropped, this suggests that the plasma level of L-cystine can be used to monitor the progress of euthyroid state restoration.

CONCLUSION

The plasma metabolome of patients with hyperthyroidism before and after treatments revealed differences in the abundance of several small metabolites. Our findings add to our understanding of hyperthyroidism's altered metabolome and associated metabolic processes and shed light on acylcarnitines as a new biomarker for treatment monitoring in conjunction with thyroxine and thyroid-stimulating hormone.

Serum Metabolite Profile Associated with Sex-Dependent Visceral Adiposity Index and Low Bone Mineral Density in a Mexican Population

Recent evidence shows that obesity correlates negatively with bone mass. However, traditional anthropometric measures such as body mass index could not discriminate visceral adipose tissue from subcutaneous adipose tissue. The visceral adiposity index (VAI) is a reliable sex-specified indicator of visceral adipose distribution and function. Thus, we aimed to identify metabolomic profiles associated with VAI and low bone mineral density (BMD). A total of 602 individuals from the Health Workers Cohort Study were included. Forty serum metabolites were measured using the targeted metabolomics approach, and multivariate regression models were used to test associations of metabolomic profiles with anthropometric, clinical, and biochemical parameters. The analysis showed a serum amino acid signature composed of glycine, leucine, arginine, valine, and acylcarnitines associated with high VAI and low BMD. In addition, we found a sex-dependent VAI in pathways related to primary bile acid biosynthesis, branched-chain amino acids, and the biosynthesis of pantothenate and coenzyme A (CoA). In conclusion, a metabolic profile differs by VAI and BMD status, and these changes are gender-dependent.

Acylcarnitine profile in Alaskan sled dogs during submaximal multiday exercise points out metabolic flexibility and liver role in energy metabolism

Alaskan sled dogs develop a particular metabolic strategy during multiday submaximal exercise, allowing them to switch from intra-muscular to extra-muscular energy substrates thus postponing fatigue. Specifically, a progressively increasing stimulus for hepatic glycogenolysis and gluconeogenesis provides glucose for both fueling exercise and replenishing the depleted muscle glycogen. Moreover, recent studies have shown that with continuation of exercise sled dogs increase their insulin-sensitivity and their capacity to transport and oxidize glucose and carbohydrates rather than oxidizing fatty acids. Carnitine and acylcarnitines (AC) play an essential role as metabolic regulators in both fat and glucose metabolism; they serve as biomarkers in different species in both physiologic and pathologic conditions. We assessed the effect of multiday exercise in conditioned sled dogs on plasma short (SC), medium (MC) and long (LC) chain AC by tandem mass spectrometry (MS/MS). Our results show chain-specific modification of AC profiles during the exercise challenge: LCACs maintained a steady increase throughout exercise, some SCACs increased during the last phase of exercise and acetylcarnitine (C2) initially increased before decreasing during the later phase of exercise. We speculated that SCACs kinetics could reflect an increased protein catabolism and C2 pattern could reflect its hepatic uptake for energy-generating purposes to sustain gluconeogenesis. LCACs may be exported by muscle to avoid their accumulation to preserve glucose oxidation and insulin-sensitivity or they could be distributed by liver as energy substrates. These findings, although representing a “snapshot” of blood as a crossing point between different organs, shed further light on sled dogs metabolism that is liver-centric and more carbohydrate-dependent than fat-dependent and during prolonged submaximal exercise.

Metabolic flexibility during normal pregnancy allows appropriate adaptation during gestation independently of BMI

BACKGROUND & AIMS

Overweight and obesity in reproductive-age women hasten the development of insulin resistance and increase risk for deterioration of pregnancy metabolism. These pregnancy-associated metabolic changes are similar to those of the metabolic syndrome. Thus, some metabolic flexibility must allow appropriate adaptation to the metabolic load that pregnancy imposes. We evaluated metabolic flexibility during uncomplicated pregnancy in women with pre-gestational normal weight or overweight.

METHODS

In 20 women with singleton pregnancies, pre-pregnancy BMI was categorized as normal-weight (Nw) or overweight (Ow). The women were seen quarterly, and fasting and postprandial blood samples were collected at each visit. Indirect fasting and/postprandial calorimetry was performed to evaluate metabolic flexibility (Δrespiratory quotient (RQ) = RQ_postprandial - RQ_fasting).

RESULTS

In the first trimester, metabolic flexibility was lower in the Ow group compared to the Nw group (0.031 ± 0.0131 vs 0.077 ± 0.018, respectively) without a statistically significant difference (p = 0.053). In the second trimester, the Ow group was significantly more flexible than the Nw group (0.190 ± 0.016 vs 0.077 ± 0.015, respectively (p = 0.004)). For the third trimester, the Ow and Nw groups did not differ in metabolic flexibility (0.074 ± 0.013 vs 0.087 ± 0.021, respectively) (p = 0.40). The most influential variables for metabolic flexibility during pregnancy were lactate, leptin, β-hydroxybutyrate, glycerol, aromatic amino acids, medium and long chain acylcarnitine's.

CONCLUSIONS

Our findings indicate that metabolic flexibility changes throughout pregnancy, independently of pre-pregnancy BMI. These changes maintain metabolic homeostasis between the mother and foetus, allowing for appropriate adjustments during pregnancy.

Advantages of Studying the Metabolome in Response to Mixed-Macronutrient Challenges and Suggestions for Future Research Designs

Evaluating the postprandial response to a dietary challenge containing all macronutrients-carbohydrates, lipids, and protein-may provide stronger insights of metabolic health than a fasted measurement. Metabolomic profiling deepens the understanding of the homeostatic and adaptive response to a dietary challenge by classifying multiple metabolic pathways and biomarkers. A total of 26 articles were identified that measure the human blood metabolome or lipidome response to a mixed-macronutrient challenge. Most studies were cross-sectional, exploring the baseline and postprandial response to the dietary challenge. Large variations in study designs were reported, including the macronutrient and caloric composition of the challenge and the delivery of the challenge as a liquid shake or a solid meal. Most studies utilized a targeted metabolomics platform, assessing only a particular metabolic pathway, however, several studies utilized global metabolomics and lipidomics assays demonstrating the expansive postprandial response of the metabolome. The postprandial response of individual amino acids was largely dependent on the amino acid composition of the test meal, with the exception of alanine and proline, 2 nonessential amino acids. Long-chain fatty acids and unsaturated long-chain acylcarnitines rapidly decreased in response to the dietary challenges, representing the switch from fat to carbohydrate oxidation. Studies were reviewed that assessed the metabolome response in the context of obesity and metabolic diseases, providing insight on how weight status and disease influence the ability to cope with a nutrient load and return to homeostasis. Results demonstrate that the flexibility to respond to a substrate load is influenced by obesity and metabolic disease and flexibility alterations will be evident in downstream metabolites of fat, carbohydrate, and protein metabolism. In response, we propose suggestions for standardization between studies with the potential of creating a study exploring the postprandial response to a multitude of challenges with a variety of macronutrients.

Metabolic adaptation characterizes short-term resistance to weight loss induced by a low-calorie diet in overweight/obese individuals

BACKGROUND

Low-calorie diet (LCD)-induced weight loss demonstrates response heterogeneity. Physiologically, a decrease in energy expenditure lower than what is predicted based on body composition (metabolic adaptation) and/or an impaired capacity to increase fat oxidation may hinder weight loss. Understanding the metabolic components that characterize weight loss success is important for optimizing weight loss strategies.

OBJECTIVES

We tested the hypothesis that overweight/obese individuals who had lower than expected weight loss in response to a 28-d LCD would be characterized by 1) impaired fat oxidation and 2) whole-body metabolic adaptation. We also characterized the molecular mechanisms associated with weight loss success/failure.

METHODS

This was a retrospective comparison of participants who met their predicted weight loss targets [overweight/obese diet sensitive (ODS), n = 23, females = 21, males = 2] and those that did not [overweight/obese diet resistant (ODR), n = 14, females = 12, males = 2] after a 28-d LCD (900-1000 kcal/d). We used whole-body (energy expenditure and fat oxidation) and tissue-specific measurements (metabolic proteins in skeletal muscle, gene expression in adipose tissue, and metabolites in serum) to detect metabolic properties and biomarkers associated with weight loss success.

RESULTS

The ODR group had greater mean ± SD metabolic adaptation (-175 ± 149 kcal/d; +119%) than the ODS group (-80 ± 108 kcal/d) after the LCD (P = 0.030). Mean ± SD fat oxidation increased similarly for both groups from baseline (0.0701 ± 0.0206 g/min) to day 28 (0.0869 ± 0.0269 g/min; P < 0.001). A principal component analysis factor comprised of serum 3-hydroxybutyric acid, citrate, leucine/isoleucine, acetyl-carnitine, and 3-hydroxylbutyrlcarnitine was associated with weight loss success at day 28 (std. β = 0.674, R2 = 0.479, P < 0.001).

CONCLUSIONS

Individuals who achieved predicted weight loss targets after a 28-d LCD were characterized by reduced metabolic adaptation. Accumulation of metabolites associated with acetyl-CoA excess and enhanced ketogenesis was identified in the ODS group.This trial was registered at clinicaltrials.gov as NCT01616082.

Metabolic Complications in Cardiac Aging

Aging is a process that can be accompanied by molecular and cellular alterations that compromise cardiac function. Although other metabolic disorders with increased prevalence in aged populations, such as diabetes mellitus, dyslipidemia, and hypertension, are associated with cardiovascular complications; aging-related cardiomyopathy has some unique features. Healthy hearts oxidize fatty acids, glucose, lactate, ketone bodies, and amino acids for producing energy. Under physiological conditions, cardiac mitochondria use fatty acids and carbohydrate mainly to generate ATP, 70% of which is derived from fatty acid oxidation (FAO). However, relative contribution of nutrients in ATP synthesis is altered in the aging heart with glucose oxidation increasing at the expense of FAO. Cardiac aging is also associated with impairment of mitochondrial abundance and function, resulting in accumulation of reactive oxygen species (ROS) and activation of oxidant signaling that eventually leads to further mitochondrial damage and aggravation of cardiac function. This review summarizes the main components of pathophysiology of cardiac aging, which pertain to cardiac metabolism, mitochondrial function, and systemic metabolic changes that affect cardiac function.

Acyl-Carnitine plasma levels and their association with metabolic syndrome in individuals with schizophrenia

The metabolic syndrome (MetS) affects individuals with schizophrenia at a higher rate when compared to individuals in the general population. Accumulating evidence indicated that subjects with MetS generally manifest elevated levels of acyl-carnitines, which are important carriers for transporting fatty acyl group. Abnormalities of acyl-carnitines in individuals with schizophrenia with or without MetS had not been sufficiently characterized. We conducted this post-hoc analysis with our published data to further evaluate the differences of 29 acyl-carnitines in 46 individuals with schizophrenia with MetS and 123 without MetS. The rate of MetS was 27.2% (46/169) in the individuals with schizophrenia. After FDR correction, the individuals with schizophrenia and MetS showed significantly higher levels of 17 plasma acyl-carnitines, compared to individuals without MetS. Eight acyl-carnitines (i.e., C3, C4, C5, C6: 1, C10: 1, C10: 2, C14: 2-OH, C16: 2-OH) were significantly different between two groups after adjusting for age and sex. The correlation analysis reported that acyl-carnitine concentrations have potential correlations with certain metabolic parameters. Our findings provide valuable new clues for exploring the roles of acyl-carnitines in the diagnosis and treatment of schizophrenia. More data and molecular biology evidences are needed to replicate our findings and elucidate relevant mechanisms.

Effect of conjugated estrogens and bazedoxifene on glucose, energy and lipid metabolism in obese postmenopausal women

OBJECTIVE

Combining conjugated estrogens (CE) with the selective estrogen receptor modulator bazedoxifene (BZA) is a novel, orally administered menopausal therapy. We investigated the effect of CE/BZA on insulin sensitivity, energy metabolism, and serum metabolome in postmenopausal women with obesity.

DESIGN

Randomized, double-blind, crossover pilot trial with washout was conducted at Pennington Biomedical Research Center. Eight postmenopausal women (age 50-60 years, BMI 30-40 kg/m2) were randomized to 8 weeks CE/BZA or placebo. Primary outcome was insulin sensitivity (hyperinsulinemic-euglycemic clamp). Secondary outcomes included body composition (DXA); resting metabolic rate (RMR); substrate oxidation (indirect calorimetry); ectopic lipids (1H-MRS); fat cell size, adipose and skeletal muscle gene expression (biopsies); serum inflammatory markers; and serum metabolome (LC/MS).

RESULTS

CE/BZA treatment produced no detectable effect on insulin sensitivity, body composition, ectopic fat, fat cell size, or substrate oxidation, but resulted in a non-significant increase in RMR (basal: P = 0.06; high-dose clamp: P = 0.08) compared to placebo. CE/BZA increased serum high-density lipoprotein (HDL)-cholesterol. CE/BZA also increased serum diacylglycerol (DAG) and triacylglycerol (TAG) species containing long-chain saturated, mono- and polyunsaturated fatty acids (FAs) and decreased long-chain acylcarnitines, possibly reflecting increased hepatic de novo FA synthesis and esterification into TAGs for export into very low-density lipoproteins, as well as decreased FA oxidation, respectively (P < 0.05). CE/BZA increased serum phosphatidylcholines, phosphatidylethanolamines, ceramides, and sphingomyelins, possibly reflecting the increase in serum lipoproteins (P < 0.05).

CONCLUSIONS

A short treatment of obese postmenopausal women with CE/BZA does not alter insulin action or ectopic fat but increases serum markers of hepatic de novo lipogenesis and TAG production.

Long-Chain Acylcarnitines and Cardiac Excitation-Contraction Coupling: Links to Arrhythmias

A growing number of metabolomic studies have associated high circulating levels of the amphiphilic fatty acid metabolites, long-chain acylcarnitines (LCACs), with cardiovascular disease (CVD) risk. These studies show that plasma LCAC levels can be correlated with the stage and severity of CVD and with indices of cardiac hypertrophy and ventricular function. Complementing these recent clinical associations is an extensive body of basic research that stems mostly from the twentieth century. These works, performed in cardiomyocyte and multicellular preparations from animal and cell models, highlight stereotypical derangements in cardiac electrophysiology induced by exogenous LCAC treatment that promote arrhythmic muscle behavior. In many cases, this is coupled with acute inotropic modulation; however, whether LCACs increase or decrease contractility is inconclusive. Linked to the electromechanical alterations induced by LCAC exposure is an array of effects on cardiac excitation-contraction coupling mechanisms that overload the cardiomyocyte cytosol with Na⁺ and Ca²⁺ ions. The aim of this review is to revisit this age-old literature and collate it with recent findings to provide a pathophysiological context for the growing body of metabolomic association studies that link circulating LCACs with CVD.

Correlation of plasma metabolites with glucose and lipid fluxes in human insulin resistance

OBJECTIVE

Insulin resistance develops prior to the onset of overt type 2 diabetes, making its early detection vital. Direct accurate evaluation is currently only possible with complex examinations like the stable isotope-based hyperinsulinemic euglycemic clamp (HIEC). Metabolomic profiling enables the detection of thousands of plasma metabolites, providing a tool to identify novel biomarkers in human obesity.

DESIGN

Liquid chromatography mass spectrometry-based untargeted plasma metabolomics was applied in 60 participants with obesity with a large range of peripheral insulin sensitivity as determined via a two-step HIEC with stable isotopes [6,6-2H2]glucose and [1,1,2,3,3-2H5]glycerol. This additionally enabled measuring insulin-regulated lipolysis, which combined with metabolomics, to the knowledge of this research group, has not been reported on before.

RESULTS

Several plasma metabolites were identified that significantly correlated with glucose and lipid fluxes, led by plasma (gamma-glutamyl)citrulline, followed by betaine, beta-cryptoxanthin, fructosyllysine, octanylcarnitine, sphingomyelin (d18:0/18:0, d19:0/17:0) and thyroxine. Subsequent machine learning analysis showed that a panel of these metabolites derived from a number of metabolic pathways may be used to predict insulin resistance, dominated by non-essential amino acid citrulline and its metabolite gamma-glutamylcitrulline.

CONCLUSION

This approach revealed a number of plasma metabolites that correlated reasonably well with glycemic and lipolytic flux parameters, measured using gold standard techniques. These metabolites may be used to predict the rate of glucose disposal in humans with obesity to a similar extend as HOMA, thus providing potential novel biomarkers for insulin resistance.

Identification and regulation of the xenometabolite derivatives cis- and trans-3,4-methylene-heptanoylcarnitine in plasma and skeletal muscle of exercising humans

Little is known about xenometabolites in human metabolism, particularly under exercising conditions. Previously, an exercise-modifiable, likely xenometabolite derivative, cis-3,4-methylene-heptanoylcarnitine, was reported in human plasma. Here, we identified trans-3,4-methylene-heptanoylcarnitine, and its cis-isomer, in plasma and skeletal muscle by liquid chromatography-mass spectrometry. We analyzed the regulation by exercise and the arterial-to-venous differences of these cyclopropane ring-containing carnitine esters over the hepatosplanchnic bed and the exercising leg in plasma samples obtained in three separate studies from young, lean and healthy males. Compared with other medium-chain acylcarnitines, the plasma concentrations of the 3,4-methylene-heptanoylcarnitine isomers only marginally increased with exercise. Both isomers showed a more than twofold increase in the skeletal muscle tissue of the exercising leg; this may have been due to the net effect of fatty acid oxidation in the exercising muscle and uptake from blood. The latter idea is supported by a more than twofold increased net uptake in the exercising leg only. Both isomers showed a constant release from the hepatosplanchnic bed, with an increased release of the trans-isomer after exercise. The isomers differ in their plasma concentration, with a four times higher concentration of the cis-isomer regardless of the exercise state. This is the first approach studying kinetics and fluxes of xenolipid isomers from tissues under exercise conditions, supporting the hypothesis that hepatic metabolism of cyclopropane ring-containing fatty acids is one source of these acylcarnitines in plasma. The data also provide clear evidence for an exercise-dependent regulation of xenometabolites, opening perspectives for future studies about the physiological role of this largely unknown class of metabolites.

Biomarkers of appetite: is there a potential role for metabolomics?

Knowing the biological signals associated with appetite control is crucial for understanding the regulation of food intake. Biomarkers of appetite have been defined as physiological measures that relate to subjective appetite ratings, measured food intake, or both. Several metabolites including amino acids, lipids and glucose were proposed as key molecules associated with appetite control over 60 years ago, and along with bile acids are all among possible appetite biomarker candidates. Additional metabolites that have been associated with appetite include endocannabinoids, lactate, cortisol and β-hydroxybutyrate. However, although appetite is a complex integrative process, studies often investigated a limited number of markers in isolation. Metabolomics involves the study of small molecules or metabolites present in biological samples such as urine or blood, and may present a powerful approach to further the understanding of appetite control. Using multiple analytical techniques allows the characterisation of molecules, such as carbohydrates, lipids, amino acids, bile acids and fatty acids. Metabolomics has proven successful in identifying markers of consumption of certain foods and biomarkers implicated in several diseases. However, it has been underexploited in appetite control or obesity. The aim of the present narrative review is to: (1) provide an overview of existing metabolites that have been identified in human biofluids and associated with appetite control; and (2) discuss the potential of metabolomics to deepen understanding of appetite control in humans.

Alterations of the acylcarnitine profiles in blood serum and in muscle from periparturient cows with normal or elevated body condition

The objective of the current study was to characterize muscle and blood serum acylcarnitine (AcylCN) profiles and to determine the mRNA abundance of muscle carnitine acyltransferases in periparturient dairy cows with high (HBCS) and normal body condition (NBCS). Fifteen weeks antepartum, 38 pregnant multiparous Holstein cows were assigned to 2 groups that were fed differently to reach the targeted BCS and backfat thickness (BFT) until dry-off at -49 d before calving (HBCS: BCS >3.75 and BFT >1.4 cm; NBCS: <3.5 and <1.2 cm). Thereafter, both groups were fed identical diets. Blood samples and biopsies from the semitendinosus muscle were collected on d -49, 3, 21, and 84 relative to calving. Actual BCS at d -49 were 3.02 ± 0.24 and 3.82 ± 0.33 (mean ± SD) for NBCS and HBCS, respectively. In both groups, serum profiles showed marked changes during the periparturient period, with decreasing concentrations of free carnitine and increasing concentrations of long-chain AcylCN. Compared with NBCS, HBCS had greater serum long-chain AcylCN in early lactation, which may point to an insufficient adaptation of their metabolism in response to the metabolic load of fatty acids around parturition. The muscle concentrations of C5-, C9-, C18:1-, and C18:2-AcylCN were lower and those of C14:2-AcylCN were greater in HBCS than in NBCS cows. The mRNA abundance of carnitine palmitoyltransferase (CPT)1, muscle isoform (CPT1b) and CPT2 increased from d -49 to early lactation (d 3, d 21), followed by a decline to nearly antepartum values by d 84; this change was not affected by group. In conclusion, over-conditioning around calving seems to be associated with mitochondrial overload, which can result in incomplete fatty acid oxidation in dairy cows.

Mass Spectrometric Analysis of L-carnitine and its Esters: Potential Biomarkers of Disturbances in Carnitine Homeostasis

PURPOSE

After a golden age of classic carnitine research three decades ago, the spread of mass spectrometry opened new perspectives and a much better understanding of the carnitine system is available nowadays. In the classic period, several human and animal studies were focused on various distinct physiological functions of this molecule and these revealed different aspects of carnitine homeostasis in normal and pathological conditions. Initially, the laboratory analyses were based on the classic or radioenzymatic assays, enabling only the determination of free and total carnitine levels and calculation of total carnitine esters' amount without any information on the composition of the acyl groups. The introduction of mass spectrometry allowed the measurement of free carnitine along with the specific and sensitive determination of different carnitine esters. Beyond basic research, mass spectrometry study of carnitine esters was introduced into the newborn screening program because of being capable to detect more than 30 metabolic disorders simultaneously. Furthermore, mass spectrometry measurements were performed to investigate different disease states affecting carnitine homeostasis, such as diabetes, chronic renal failure, celiac disease, cardiovascular diseases, autism spectrum disorder or inflammatory bowel diseases.

RESULTS

This article will review the recent advances in the field of carnitine research with respect to mass spectrometric analyses of acyl-carnitines in normal and various pathological states.

CONCLUSION

The growing number of publications using mass spectrometry as a tool to investigate normal physiological conditions or reveal potential biomarkers of primary and secondary carnitine deficiencies shows that this tool brought a new perspective to carnitine research.

Dysregulated Choline, Methionine, and Aromatic Amino Acid Metabolism in Patients with Wilson Disease: Exploratory Metabolomic Profiling and Implications for Hepatic and Neurologic Phenotypes

Wilson disease (WD) is a genetic copper overload condition characterized by hepatic and neuropsychiatric symptoms with a not well-understood pathogenesis. Dysregulated methionine cycle is reported in animal models of WD, though not verified in humans. Choline is essential for lipid and methionine metabolism. Defects in neurotransmitters as acetylcholine, and biogenic amines are reported in WD; however, less is known about their circulating precursors. We aimed to study choline, methionine, aromatic amino acids, and phospholipids in serum of WD subjects. Hydrophilic interaction chromatography-quadrupole time-of-flight mass spectrometry was employed to profile serum of WD subjects categorized as hepatic, neurologic, and pre-clinical. Hepatic transcript levels of genes related to choline and methionine metabolism were verified in the Jackson Laboratory toxic milk mouse model of WD (tx-j). Compared to healthy subjects, choline, methionine, ornithine, proline, phenylalanine, tyrosine, and histidine were significantly elevated in WD, with marked alterations in phosphatidylcholines and reductions in sphingosine-1-phosphate, sphingomyelins, and acylcarnitines. In tx-j mice, choline, methionine, and phosphatidylcholine were similarly dysregulated. Elevated choline is a hallmark dysregulation in WD interconnected with alterations in methionine and phospholipid metabolism, which are relevant to hepatic steatosis. The elevated phenylalanine, tyrosine, and histidine carry implications for neurologic manifestations and are worth further investigation.

Cord Blood Metabolomics: Association With Newborn Anthropometrics and C-Peptide Across Ancestries

CONTEXT

Newborn adiposity is associated with childhood obesity. Cord blood metabolomics is one approach that can be used to understand early-life contributors to adiposity and insulin resistance.

OBJECTIVE

To determine the association of cord blood metabolites with newborn adiposity and hyperinsulinemia in a multiethnic cohort of newborns.

DESIGN

Cross-sectional, observational study.

SETTING

Hyperglycemia and Adverse Pregnancy Outcome study.

PARTICIPANTS

One thousand six hundred multiethnic mother-newborn pairs.

MAIN OUTCOME MEASURE

Cord blood C-peptide, birthweight, and newborn sum of skinfolds.

RESULTS

Meta-analyses across four ancestry groups (Afro-Caribbean, Northern European, Thai, and Mexican American) demonstrated significant associations of cord blood metabolites with cord blood C-peptide, birthweight, and newborn sum of skinfolds. Several metabolites, including branched-chain amino acids (BCAAs), medium- and long-chain acylcarnitines, nonesterified fatty acids, and triglycerides were negatively associated with cord C-peptide but positively associated with birthweight and/or sum of skinfolds. 1,5-Anhydroglucitol, an inverse marker of recent maternal glycemia, was significantly inversely associated with birthweight and sum of skinfolds. Network analyses revealed groups of interrelated amino acid, acylcarnitine, and fatty acid metabolites associated with all three newborn outcomes.

CONCLUSIONS

Cord blood metabolites are associated with newborn size and cord blood C-peptide levels after adjustment for maternal body mass index and glucose during pregnancy. Negative associations of metabolites with C-peptide at birth were observed. 1,5-Anhydroglucitol appears to be a marker of adiposity in newborns. BCAAs were individually associated with birthweight and demonstrated possible associations with newborn adiposity in network analyses.

Urate and Nonanoate Mark the Relationship between Sugar-Sweetened Beverage Intake and Blood Pressure in Adolescent Girls: A Metabolomics Analysis in the ELEMENT Cohort

We sought to identify metabolites that mark the relationship of sugar-sweetened beverage (SSB) intake with adiposity and metabolic risk among boys (n = 114) and girls (n = 128) aged 8–14 years. We conducted the analysis in three steps: (1) linear regression to examine associations of SSB intake (quartiles) with adiposity, glycemia, lipids, and blood pressure (BP); (2) least absolute shrinkage and selection operator (LASSO) regression to identify SSB-associated metabolites from an untargeted dataset of 938 metabolites; and (3) linear regression to determine whether SSB-related metabolites are also associated with adiposity and metabolic risk. In girls, SSB intake was associated with marginally higher BP (Q2 vs, Q1: 1.11 [−3.90, 6.13], Q3 vs. Q1: 1.16 [−3.81, 6.13], Q4 vs. Q1: 4.65 [−0.22, 9.53] mmHg systolic blood pressure (SBP); P-trend = 0.07). In boys, SSB intake corresponded with higher C-peptide insulin resistance (Q2 vs. Q1: 0.06 [−0.06, 0.19], Q3 vs. Q1: 0.01 [−0.12, 0.14], Q4 vs. Q1: 0.17 [0.04, 0.30] ng/mL; P-trend = 0.03) and leptin (P-trend = 0.02). LASSO identified 6 annotated metabolites in girls (5-methyl-tetrohydrofolate, phenylephrine, urate, nonanoate, deoxyuridine, sn-glycero-3-phosphocholine) and 3 annotated metabolites in boys (2-piperidinone, octanoylcarnitine, catechol) associated with SSB intake. Among girls, urate and nonanoate marked the relationship of SSB intake with BP. None of the SSB-associated metabolites were related to health outcomes in boys.

Indication of metabolic inflexibility to food intake in spontaneously overweight Labrador Retriever dogs

Background

Obesity in dogs is an increasing problem associated with morbidity, shortened life span and poor life quality. Overweight dogs exhibit postprandial hyperlipidaemia, highlighting the need to identify potential dysregulations in lipid metabolism. This study investigated metabolites related to lipid metabolism (i.e. acylcarnitines and taurine) and phospholipids in a feed-challenge test and aimed to identify metabolic variations in spontaneously overweight dogs. Twenty-eight healthy male Labrador Retriever dogs were included, 12 of which were classified as lean (body condition score (BCS) 4–5 on a 9-point scale) and 16 as overweight (BCS 6–8). After overnight fasting (14–17 h), fasting blood samples were collected and dogs were fed a high-fat meal followed by postprandial blood sample collection hourly for 4 h. Liquid chromatography-time of flight mass spectrometry (LC-TOFMS) was used to identify plasma metabolites and phospholipids. Multivariate models, mixed model repeated measures and linear regression analyses were used for data interpretation.

Results

In all dogs, propionylcarnitine, stearoylcarnitine and nine phospholipids increased in response to food intake, while vaccenylcarnitine decreased (P ≤ 0.005 for all). Overall, carnitine and acetylcarnitine signal areas in the feed-challenge test were lower in overweight dogs (P ≤ 0.004). Notably, fasting plasma acetylcarnitine was lower in overweight dogs than in lean dogs (P = 0.001) and it did not change in response to feeding. The latter finding was in contrast to the decreased acetylcarnitine signal area found in lean dogs at one hour postprandially (P < 0.0001). One fasting phosphatidylcholine (PCaa C38:4) was higher in prominently overweight dogs (BCS > 6) than in lean dogs (P < 0.05).

Conclusions

Plasma carnitine status was overall lower in spontaneously overweight dogs than in lean dogs in this cohort of healthy Labrador Retriever dogs, indicating a potential carnitine insufficiency in the overweight group. The acetylcarnitine response in overweight dogs indicated decreased fatty acid oxidation at fasting and metabolic inflexibility to food intake. Further studies on metabolic inflexibility and its potential role in the metabolism of overweight dogs are warranted.

Electronic supplementary material

The online version of this article (10.1186/s12917-019-1845-5) contains supplementary material, which is available to authorized users.

Maternal metabolites during pregnancy are associated with newborn outcomes and hyperinsulinaemia across ancestries

AIMS/HYPOTHESIS

We aimed to determine the association of maternal metabolites with newborn adiposity and hyperinsulinaemia in a multi-ethnic cohort of mother-newborn dyads.

METHODS

Targeted and non-targeted metabolomics assays were performed on fasting and 1 h serum samples from a total of 1600 mothers in four ancestry groups (Northern European, Afro-Caribbean, Mexican American and Thai) who participated in the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study, underwent an OGTT at ~28 weeks gestation and whose newborns had anthropometric measurements at birth.

RESULTS

In this observational study, meta-analyses demonstrated significant associations of maternal fasting and 1 h metabolites with birthweight, cord C-peptide and/or sum of skinfolds across ancestry groups. In particular, maternal fasting triacylglycerols were associated with newborn sum of skinfolds. At 1 h, several amino acids, fatty acids and lipid metabolites were associated with one or more newborn outcomes. Network analyses revealed clusters of fasting acylcarnitines, amino acids, lipids and fatty acid metabolites associated with cord C-peptide and sum of skinfolds, with the addition of branched-chain and aromatic amino acids at 1 h.

CONCLUSIONS/INTERPRETATION

The maternal metabolome during pregnancy is associated with newborn outcomes. Maternal levels of amino acids, acylcarnitines, lipids and fatty acids and their metabolites during pregnancy relate to fetal growth, adiposity and cord C-peptide, independent of maternal BMI and blood glucose levels.

Decreases in Circulating Concentrations of Long-Chain Acylcarnitines and Free Fatty Acids During the Glucose Tolerance Test Represent Tissue-Specific Insulin Sensitivity

Background: Insulin plays a pivotal role in the regulation of both carbohydrate and lipid intermediate turnover and metabolism. In the transition from a fasted to fed state, insulin action inhibits lipolysis in adipocytes, and acylcarnitine synthesis in the muscles and heart. The aim of this study was to measure free fatty acid (FFA) and acylcarnitine levels during the glucose tolerance test as indicators of tissue-specific insulin resistance. Results: Insulin release in response to glucose administration decreased both FFA and long-chain acylcarnitine levels in plasma in healthy control animals by 30% (120 min). The glucose tolerance test and [³H]-deoxy-D-glucose uptake in tissues revealed that high fat diet-induced lipid overload in C57bl/6N mice evoked only adipose tissue insulin resistance, and plasma levels of FFAs did not decrease after glucose administration. In comparison, db/db mice developed type 2 diabetes with severely impaired insulin sensitivity and up to 70% lower glucose uptake in both adipose tissues and muscles (skeletal muscle and heart), and both plasma concentrations of FFAs and long-chain acylcarnitines did not decrease in response to glucose administration. Conclusions: These results link impaired adipose tissue insulin sensitivity with continuous FFA release in the transition from a fasted to postprandial state, while a blunted decrease in long-chain acylcarnitine levels is associated with muscle and heart insulin resistance.

Differential metabolomics analysis allows characterization of diversity of metabolite networks between males and females

Females and males are known to have different abilities to cope with stress and disease. This study was designed to investigate the effect of sex on properties of a complex interlinked network constructed of central biochemical metabolites. The study involved the blood collection and analysis of a large set of blood metabolic markers from a total of 236 healthy participants, which included 140 females and 96 males. Metabolic profiling yielded concentrations of 168 metabolites for each subject. A differential correlation network analysis approach was developed for this study that allowed detection and characterization of interconnection differences in metabolites in males and females. Through topological analysis of the differential network that depicted metabolite differences in the sexes, we identified metabolites with high centralities in this network. These key metabolites were identified as 10 phosphatidylcholines (PCaaC34:4, PCaaC36:6, PCaaC34:3, PCaaC42:2, PCaeC38:1, PCaeC38:2, PCaaC40:1, PCaeC34:1, PC aa C32:1 and PC aa C40:6) and 4 acylcarnitines (C3-OH, C7-DC, C3 and C0). Identification of these metabolites may help further studies of sex-specific differences in the metabolome that may underlie different responses to stress and disease in males and females.

Global testing of shifts in metabolic phenotype

INTRODUCTION

Current metabolomics approaches to unravel impact of diet- or lifestyle induced phenotype variation and shifts predominantly deploy univariate or multivariate approaches, with a posteriori interpretation at pathway level. This however often provides only a fragmented view on the involved metabolic pathways.

OBJECTIVES

To demonstrate the feasibility of using Goeman's global test (GGT) for assessment of variation and shifts in metabolic phenotype at the level of a priori defined pathways.

METHODS

Two intervention studies with identified phenotype variations and shifts were examined. In a weight loss (WL) intervention study obese subjects received a mixed meal challenge before and after WL. In a polyphenol (PP) intervention study obese subjects received a high fat mixed meal challenge (61E% fat) before and after a PP intervention. Plasma samples were obtained at fasting and during the postprandial response. Besides WL- and PP-induced phenotype shifts, also correlation of plasma metabolome with phenotype descriptors was assessed at pathway level. The plasma metabolome covered organic acids, amino acids, biogenic amines, acylcarnitines and oxylipins.

RESULTS

For the population of the WL study, GGT revealed that HOMA correlated with the fasting levels of the TCA cycle, BCAA catabolism, the lactate, arginine-proline and phenylalanine-tyrosine pathways. For the population of the PP study, HOMA correlated with fasting metabolite levels of TCA cycle, fatty acid oxidation and phenylalanine-tyrosine pathways. These correlations were more pronounced for metabolic pathways in the fasting state, than during the postprandial response. The effect of the WL and PP intervention on a priori defined metabolic pathways, and correlation of pathways with insulin sensitivity as described by HOMA was in line with previous studies.

CONCLUSION

GGT confirmed earlier biological findings in a hypothesis led approach. A main advantage of GGT is that it provides a direct view on involvement of a priori defined pathways in phenotype shifts.

Plasma metabolome analysis identifies distinct human metabotypes in the postprandial state with different susceptibility to weight loss-mediated metabolic improvements

Health has been defined as the capability of the organism to adapt to challenges. In this study, we tested to what extent comprehensively phenotyped individuals reveal differences in metabolic responses to a standardized mixed meal tolerance test (MMTT) and how these responses change when individuals experience moderate weight loss. Metabolome analysis was used in 70 healthy individuals. with profiling of ∼300 plasma metabolites during an MMTT over 8 h. Multivariate analysis of plasma markers of fatty acid catabolism identified 2 distinct metabotype clusters (A and B). Individuals from metabotype B showed slower glucose clearance, had increased intra-abdominal adipose tissue mass and higher hepatic lipid levels when compared with individuals from metabotype A. An NMR-based urine analysis revealed that these individuals also to have a less healthy dietary pattern. After a weight loss of ∼5.6 kg over 12 wk, only the subjects from metabotype B showed positive changes in the glycemic response during the MMTT and in markers of metabolic diseases. Our study in healthy individuals demonstrates that more comprehensive phenotyping can reveal discrete metabotypes with different outcomes in a dietary intervention and that markers of lipid catabolism in plasma could allow early detection of the metabolic syndrome.-Fiamoncini, J., Rundle, M., Gibbons, H., Thomas, E. L., Geillinger-Kästle, K., Bunzel, D., Trezzi, J.-P., Kiselova-Kaneva, Y., Wopereis, S., Wahrheit, J., Kulling, S. E., Hiller, K., Sonntag, D., Ivanova, D., van Ommen, B., Frost, G., Brennan, L., Bell, J. Daniel, H. Plasma metabolome analysis identifies distinct human metabotypes in the postprandial state with different susceptibility to weight loss-mediated metabolic improvements.

Weight loss moderately affects the mixed meal challenge response of the plasma metabolome and transcriptome of peripheral blood mononuclear cells in abdominally obese subjects

INTRODUCTION

The response to dietary challenges has been proposed as a more accurate measure of metabolic health than static measurements performed in the fasted state. This has prompted many groups to explore the potential of dietary challenge tests for assessment of diet and lifestyle induced shifts in metabolic phenotype.

OBJECTIVES

We examined whether the response to a mixed-meal challenge could provide a readout for a weight loss (WL)-induced phenotype shift in abdominally obese male subjects. The underlying assumption of a mixed meal challenge is that it triggers all aspects of phenotypic flexibility and provokes a more prolonged insulin response, possibly allowing for better differentiation between individuals.

METHODS

Abdominally obese men (n = 29, BMI = 30.3 ± 2.4 kg/m²) received a mixed-meal challenge prior to and after an 8-week WL or no-WL control intervention. Lean subjects (n = 15, BMI = 23.0 ± 2.0 kg/m²) only received the mixed meal challenge at baseline to have a benchmark for WL-induced phenotype shifts.

RESULTS

Levels of several plasma metabolites were significantly different between lean and abdominally obese at baseline as well as during postprandial metabolic responses. Genes related to oxidative phosphorylation in peripheral blood mononuclear cells (PBMCs) were expressed at higher levels in abdominally obese subjects as compared to lean subjects at fasting, which was partially reverted after WL. The impact of WL on the postprandial response was modest, both at the metabolic and gene expression level in PBMCs.

CONCLUSION

We conclude that mixed-meal challenges are not necessarily superior to measurements in the fasted state to assess metabolic health. Furthermore, the mechanisms accounting for the observed differences between lean and abdominally obese in the fasted state are different from those underlying the dissimilarity observed during the postprandial response.

Plasma acylcarnitine concentrations reflect the acylcarnitine profile in cardiac tissues

Increased plasma concentrations of acylcarnitines (ACs) are suggested as a marker of metabolism disorders. The aim of the present study was to clarify which tissues are responsible for changes in the AC pool in plasma. The concentrations of medium- and long-chain ACs were changing during the fed-fast cycle in rat heart, muscles and liver. After 60 min running exercise, AC content was increased in fasted mice muscles, but not in plasma or heart. After glucose bolus administration in fasted rats, the AC concentrations in plasma decreased after 30 min but then began to increase, while in the muscles and liver, the contents of medium- and long-chain ACs were unchanged or even increased. Only the heart showed a decrease in medium- and long-chain AC contents that was similar to that observed in plasma. In isolated rat heart, but not isolated-contracting mice muscles, the significant efflux of medium- and long-chain ACs was observed. The efflux was reduced by 40% after the addition of glucose and insulin to the perfusion solution. Overall, these results indicate that during fed-fast cycle shifting the heart determines the medium- and long-chain AC profile in plasma, due to a rapid response to the availability of circulating energy substrates.

Plasma Palmitoyl-Carnitine (AC16:0) Is a Marker of Increased Postprandial Nonesterified Incomplete Fatty Acid Oxidation Rate in Adults With Type 2 Diabetes

OBJECTIVES

Enhanced mitochondrial fatty acid utilization is known to increase radical oxidative stress and induce insulin resistance. An increased level of plasma acylcarnitine (AC) has been proposed to indicate mitochondrial energy substrate overload, a possible mechanism leading to insulin resistance. The aim of our study was to determine fasting and postprandial plasma acetyl-carnitine (AC2:0), palmitoyl-carnitine (AC16:0), oleoyl-carnitine (AC18:1) and linoleoyl-carnitine (AC18:2) levels and their relationships with plasma nonesterified fatty acid appearance and oxidation rates and insulin sensitivity in participants with type 2 diabetes and normoglycemic offspring of 2 parents with type 2 diabetes (FH+) compared to healthy participants without family histories of type 2 diabetes (FH-).

METHODS

All participants underwent 3 metabolic protocols: 1) a euglycemic hyperinsulinemic clamp at fasting; 2) a 6-hour steady-state oral standard liquid meal and 3) an identical 6-hour steady-state meal intake study with a euglycemic hyperinsulinemic clamp. AC levels were measured by liquid chromatography with tandem mass spectrometry, and fatty acid oxidation (FAO) rates were measured by stable isotopic tracer techniques with indirect respiratory calorimetry.

RESULTS

During the insulin clamp at fasting, AC16:0 was significantly higher in the group with type 2 diabetes vs. FH- (p<0.05). In the postprandial state, AC2:0, AC16:0 and AC18:1 decreased significantly, but this reduction was blunted in type 2 diabetes, even during normalization of postprandial glucose levels during the insulin clamp. Fasting AC16:0 correlated with FAO (ρ=+0.604; p=0.0002); triacylglycerol (ρ=+0.427; p<0.02) and waist circumference (ρ=+0.416; p=0.02).

CONCLUSIONS

Spillover of AC occurs in type 2 diabetes but is not fully established in FH+. AC16:0 can be a useful biomarker of excessive FAO.

Treatment of Swedish Patients with Graves' Hyperthyroidism Is Associated with Changes in Acylcarnitine Levels

BACKGROUND

Hyperthyroidism is associated with alterations in metabolism that are currently only partially understood. The objective of the study was to investigate changes in metabolism associated with reinstatement of euthyroidism in Swedish patients.

METHODS

Eighty metabolites in plasma were profiled from 10 subjects with Graves' disease (GD) at baseline and after 9 and 15 months of treatment to reinstate euthyroidism. Thyroid parameters, thyrotropin (TSH), TSH receptor antibodies, free triiodothyronine, and free thyroxine were followed. Main findings were validated in plasma from 20 subjects with GD at baseline and at three, six, and nine months. The study was conducted at the endocrinology clinic in Malmö, Sweden.

RESULTS

Euthyroidism was reinstated at three months, and thyroid status did not change further during the 15-month follow-up. This was paralleled by altered levels of 9/19 detected acylcarnitines (p < 0.05 after adjustment for multiple testing). Levels of short-chain acylcarnitines were decreased, intermediate-chain acylcarnitines elevated, and long-chain acylcarnitines unaltered.

CONCLUSIONS

GD and treatment of the disease is associated with pronounced acyl chain length-dependent alterations in acylcarnitine levels. These changes may be impacted by ethnicity and or dietary differences.

Effects of Soybean Lipid Infusion on Unbound Free Fatty Acids and Unbound Bilirubin in Preterm Infants

OBJECTIVE

To assess the effects of a soybean lipid emulsion infusions on levels of unbound (free) bilirubin (Bf) and unbound free fatty acids (FFAu) as well as changes in Bf and total serum bilirubin (TSB) during phototherapy in infants born preterm.

STUDY DESIGN

Ninety-seven infants born preterm (birth weight: 500-2000 g; gestational age: 23-34 weeks) were enrolled to investigate the effect of 0, 1, 2, and 3 g/kg/d of intralipid infusion on Bf and FFAu. Pre- and postphototherapy TSB, FFAu, and Bf also were analyzed in 91 infants to assess the effects of phototherapy. FFAu levels were measured with the fluorescent probe ADIFAB2 and Bf by the fluorescent Bf sensor BL22P1B11-Rh during intralipid infusion and at start and end of phototherapy. TSB and plasma albumin were measured by the diazo and bromcresol green techniques, respectively. Bilirubin-albumin dissociation constants were calculated based on Bf and plasma albumin.

RESULTS

Bf and FFAu increased with increasing intralipid dosage across all gestational ages. TSB and Bf were correlated significantly when infants received 0 or 1 g/kg/d of intralipid but not at greater doses of intralipid (2 and 3 g/kg/d). Although phototherapy effectively reduced both TSB and Bf in the total phototherapy group (by 32% and 12%, respectively), it reduced TSB, but not Bf, in infants less than 28 weeks of gestation.

CONCLUSIONS

Increasing intralipid doses result in increasing FFAu levels, which are associated with increased Bf independent of TSB. In infants born extremely preterm (<28 weeks of gestation), phototherapy effectively reduces TSB but not Bf.