Skeletal muscle membrane lipids and insulin resistance

Relevance of multilamellar and multicompartmental vesicles in biological fluids: understanding the significance of proportional variations and disease correlation

Extracellular vesicles (EVs) have garnered significant interest in the field of biomedical science due to their potential applications in therapy and diagnosis. These vesicles participate in cell-to-cell communication and carry a diverse range of bioactive cargo molecules, such as nucleic acids, proteins, and lipids. These cargoes play essential roles in various signaling pathways, including paracrine and endocrine signaling. However, our understanding of the morphological and structural features of EVs is still limited. EVs could be unilamellar or multilamellar or even multicompartmental structures. The relative proportions of these EV subtypes in biological fluids have been associated with various human diseases; however, the mechanism remains unclear. Cryo-electron microscopy (cryo-EM) holds great promise in the field of EV characterization due to high resolution properties. Cryo-EM circumvents artifacts caused by fixation or dehydration, allows for the preservation of native conformation, and eliminates the necessity for staining procedures. In this review, we summarize the role of EVs biogenesis and pathways that might have role on their structure, and the role of cryo-EM in characterization of EVs morphology in different biological samples and integrate new knowledge of the alterations of membranous structures of EVs which could be used as biomarkers to human diseases.

Bioactivity of Macronutrients from Chlorella in Physical Exercise

Chlorella is a marine microalga rich in proteins and containing all the essential amino acids. Chlorella also contains fiber and other polysaccharides, as well as polyunsaturated fatty acids such as linoleic acid and alpha-linolenic acid. The proportion of the different macronutrients in Chlorella can be modulated by altering the conditions in which it is cultured. The bioactivities of these macronutrients make Chlorella a good candidate food to include in regular diets or as the basis of dietary supplements in exercise-related nutrition both for recreational exercisers and professional athletes. This paper reviews current knowledge of the effects of the macronutrients in Chlorella on physical exercise, specifically their impact on performance and recovery. In general, consuming Chlorella improves both anaerobic and aerobic exercise performance as well as physical stamina and reduces fatigue. These effects seem to be related to the antioxidant, anti-inflammatory, and metabolic activity of all its macronutrients, while each component of Chlorella contributes its bioactivity via a specific action. Chlorella is an excellent dietary source of high-quality protein in the context of physical exercise, as dietary proteins increase satiety, activation of the anabolic mTOR (mammalian Target of Rapamycin) pathway in skeletal muscle, and the thermic effects of meals. Chlorella proteins also increase intramuscular free amino acid levels and enhance the ability of the muscles to utilize them during exercise. Fiber from Chlorella increases the diversity of the gut microbiota, which helps control body weight and maintain intestinal barrier integrity, and the production of short-chain fatty acids (SCFAs), which improve physical performance. Polyunsaturated fatty acids (PUFAs) from Chlorella contribute to endothelial protection and modulate the fluidity and rigidity of cell membranes, which may improve performance. Ultimately, in contrast to several other nutritional sources, the use of Chlorella to provide high-quality protein, dietary fiber, and bioactive fatty acids may also significantly contribute to a sustainable world through the fixation of carbon dioxide and a reduction of the amount of land used to produce animal feed.

Multimodal high-resolution nano-DESI MSI and immunofluorescence imaging reveal molecular signatures of skeletal muscle fiber types

The skeletal muscle is a highly heterogeneous tissue comprised of different fiber types with varying contractile and metabolic properties. The complexity in the analysis of skeletal muscle fibers associated with their small size (30-50 μm) and mosaic-like distribution across the tissue tnecessitates the use of high-resolution imaging to differentiate between fiber types. Herein, we use a multimodal approach to characterize the chemical composition of skeletal fibers in a limb muscle, the gastrocnemius. Specifically, we combine high-resolution nanospray desorption electrospray ionization (nano-DESI) mass spectrometry imaging (MSI) with immunofluorescence (IF)-based fiber type identification. Computational image registration and segmentation approaches are used to integrate the information obtained with both techniques. Our results indicate that the transition between oxidative and glycolytic fibers is associated with shallow chemical gradients (<2.5 fold change in signals). Interestingly, we did not find any fiber type-specific molecule. We hypothesize that these findings might be linked to muscle plasticity thereby facilitating a switch in the metabolic properties of fibers in response to different conditions such as exercise and diet, among others. Despite the shallow chemical gradients, cardiolipins (CLs), acylcarnitines (CAR), monoglycerides (MGs), fatty acids, highly polyunsaturated phospholipids, and oxidized phospholipids, were identified as molecular signatures of oxidative metabolism. In contrast, histidine-related compounds were found as molecular signatures of glycolytic fibers. Additionally, the presence of highly polyunsaturated acyl chains in phospholipids was found in oxidative fibers whereas more saturated acyl chains in phospholipids were found in glycolytic fibers which suggests an effect of the membrane fluidity on the metabolic properties of skeletal myofibers.

Analysis of fatty acid composition and sensitivity to dietary n-3 PUFA intervention of mouse n-3 PUFA-enriched tissues/organs

PURPOSE

n-3 polyunsaturated fatty acids (PUFAs), docosahexaenoic acid (DHA; C22:6 n3) and eicosapentaenoic acid (EPA; C20:5 n3), are of concern for their health-promoting effects such as anti-inflammatory, but the tissue selectivity for n-3 PUFA (i.e., which tissues and organs are rich in n-3 PUFA) is still not well known. In addition, it is unclear which tissues and organs are more sensitive to n-3 PUFA intervention. These unresolved issues have greatly hindered the exploring of the health benefits of n-3 PUFA.

METHODS

Twenty-four 7-week-old male C57BL/6 J mice were assigned to the control, fish oil, DHA, and EPA groups. The last three groups were given a 4-week oral intervention of fatty acids in ethyl ester (400 mg/kg bw). The fatty acid profiles in 27 compartments were determined by gas chromatography.

RESULTS

The proportion of long-chain n-3 PUFA (the total relative percentage of EPA, DPA n3, and DHA) was analyzed. Eight tissues and organs, including the brain (cerebral cortex, hippocampus, hypothalamus) and peripheral organs (tongue, quadriceps, gastrocnemius, kidney, and heart) were determined as being n-3 PUFA-enriched tissues and organs, owing to their high n-3 PUFA levels. The highest n-3 PUFA content was observed in the tongue for the first time. Notably, the content of linoleic acid (LA; C18:2 n6c) in peripheral organs was observed to be relatively high compared with that in the brain. Interestingly, the proportions of EPA in the kidney, heart, quadriceps, gastrocnemius, and tongue increased more markedly after the EPA intervention than after the DHA or fish oil intervention. As expected, the levels of proinflammatory arachidonic acid (AA; C20:4 n6) in the kidney, quadriceps, and tongue were markedly decreased after the three dietary interventions.

CONCLUSION

Peripheral tissues and organs, including the tongue, quadriceps, gastrocnemius, kidney, and heart, besides the brain, showed obvious tissue selectivity for n-3 PUFA. In the whole body of mice, the tongue exhibits the strongest preference for n-3 PUFA, with the highest proportion of n-3 PUFA. Moreover, these peripheral tissues and organs, especially the kidney, are more sensitive to dietary EPA administration in comparison with the brain.

Higher Intake of Vegetable Protein and Lower Intake of Animal Fats Reduce the Incidence of Diabetes in Non-Drinking Males: A Prospective Epidemiological Analysis of the Shika Study

Although nutrient intake and alcohol consumption are both closely associated with the incidence of diabetes, their interrelationships remain unclear. Therefore, we herein have investigated the interrelationships among nutrient intake, alcohol consumption, and the incidence of diabetes using longitudinal data. This study included 969 residents ≥40 years living in Japan. In 2011 and 2012, a baseline study was conducted using questionnaires on basic demographics, diabetes, nutrient intake, and lifestyle habits. In 2018 and 2019, a follow-up study was performed using questionnaires and medical records on diabetes. Two-way analysis of covariance (two-way ANCOVA) was used to test the interactions of drinking habits and diabetes incidence on nutrients intake. The prospective relationship between nutrient intake at baseline and the incidence of diabetes in the follow-up stratified by drinkers and non-drinkers was evaluated using multiple logistic regression analysis. Interactions were observed for vegetable protein intake (p = 0.023) and animal fat intake (p = 0.016) in males. Vegetable protein intake negatively correlated with the incidence of diabetes in non-drinkers (odds ratio (OR): 0.208; 95% confidence interval (95% CI): 0.046-0.935; p = 0.041). Furthermore, animal fat intake positively correlated with the incidence of diabetes in non-drinkers (OR: 1.625; 95% CI: 1.020-2.589; p = 0.041). Therefore, vegetable protein and animal fat intakes in combination with drinking habits need to be considered for the prevention of diabetes.

Nuts in the Prevention and Management of Type 2 Diabetes

Diabetes is a continuously growing global concern affecting >10% of adults, which may be mitigated by modifiable lifestyle factors. Consumption of nuts and their inclusion in dietary patterns has been associated with a range of beneficial health outcomes. Diabetes guidelines recommend dietary patterns that incorporate nuts; however, specific recommendations related to nuts have been limited. This review considers the epidemiological and clinical evidence to date for the role of nut consumption as a dietary strategy for the prevention and management of type 2 diabetes (T2D) and related complications. Findings suggest nut consumption may have a potential role in the prevention and management of T2D, with mechanistic studies assessing nuts and individual nut-related nutritional constituents supporting this possibility. However, limited definitive evidence is available to date, and future studies are needed to elucidate better the impact of nuts on the prevention and management of T2D.

Different Types of Dietary Fat and Fructose Interactions Result in Distinct Metabolic Phenotypes in Male Mice

Fat and fructose are the two major components over-represented in the Western diet. The aim of this study was to determine the combined effects of different types of dietary fat and fructose on the development of nonalcoholic fatty liver disease (NAFLD) in a murine model. Eight-week-old male C57BL/6J mice were fed with high-fat diet enriched with saturated fat (HSF), or omega-6 polyunsaturated fat (n6HUSF), or omega-3 polyunsaturated fat (n3HUSF) with 42% of calories derived from the fat. Fructose supplementation was given via 10% fructose (w/v) in the drinking water ad libitum for 20 weeks. While both HSF and n6HUSF fed mice developed obesity, HSF fed mice exhibited severe hepatic steatosis associated with hepatomegaly and liver injury. Fructose feeding promotes the development of liver fibrosis in HSF fed mice. n6HUSF fed mice were characterized with moderate hepatic steatosis, accompanied with hypertriglyceridemia and hyperlipidemia. Notably, fructose supplementation led to remarkable glucose intolerance in n6HUSF fed mice compared to controls. Hepatic lipidomic analysis revealed that the total saturated fatty acids and total monounsaturated fatty acids were significantly increased by fructose in the free fatty acid pool in HSF fed mice. Moreover, fructose supplementation increased hepatic and plasma cholesterol levels in the HSF fed mice. Our data suggest that excess energy from HSF intake results in fat storage in the liver, likely due to impaired triglyceride secretion; whereas excess energy from n6HUSF diet is stored in the periphery. Both effects are exacerbated by fructose supplementation. n3HUSF is beneficial, even consumed with fructose.

Fat Intake and High Triglyceride-Glucose Index in Individuals at Cardiometabolic Risk: An Isocaloric Substitution Analyses

Insulin resistance (IR) is an important risk factor for cardiovascular diseases, and the triglyceride-glucose index (TyG index) is a potential IR biomarker. Evidence also suggests that fat intake may modulate IR status, but this relationship remains unclear. Thus, the present study aimed to analyze the relationship between the TyG index and isocaloric replacement of macronutrients, including the profile of dietary fatty acids in individuals at cardiometabolic risk.

This cross-sectional study enrolled 264 individuals at cardiometabolic risk (age 43.1 ± 16.3 years) who participated in a nutritional intervention study (ReBEC, id: RBR-5n4y2g). The baseline demographic, anthropometric, clinical, dietary, and lifestyle data were used. The TyG index was calculated using the formula ln [fasting triglycerides (mg/dL) × fasting plasma glucose (mg/dL)/2]. Multivariate nutrient density models were used to analyze isocaloric replacement of fatty acids (as 5% of energy). The chance of having a high TyG index (TyG index >8.83, median value) was decreased by 60% after replacing 5% of the energy intake of polyunsaturated fatty acid (PUFA), saturated fatty acid (SFA), and trans fatty acid (TFA) with monounsaturated fatty acid (MUFA) or PUFA and SFA with protein.

Isocaloric replacement of PUFA, SFA, and TFA with MUFA and protein was associated with lower chances of having a high TyG index. These results indicate the importance of macronutrient and dietary fat profiles in the dietary planning of individuals at cardiometabolic risk.

Dietary Carbohydrate as Glycemic Load, Not Fat, Coupled with Genetic Permissiveness Favoring Rapid Growth and Extra Calories, Dictate Metabolic Syndrome and Diabetes Induction in Nile Rats (Arvicanthis niloticus)

Objective: Whether dietary carbohydrate (CHO) or fat is more involved in type 2 diabetes (T2DM) induction uncomplicated by dietary fiber was addressed in a spontaneous diabetic model, the diurnal Nile rat that mimics the human condition. Methods: A total of 138 male Nile rats were fed plant-based and animal-based saturated fat where 10% energy as CHO and fat were exchanged across 5 diets keeping protein constant, from 70:10:20 to 20:60:20 as CHO:fat:protein %energy. Diabetes induction was analyzed by: 1. diet composition, i.e., CHO:fat ratio, to study the impact of diet; 2. quintiles of average caloric intake per day to study the impact of calories; 3. quintiles of diabetes severity to study the epigenetic impact on diabetes resistance. Results: High glycemic load (GLoad) was most problematic if coupled with high caloric consumption. Diabetes severity highlighted rapid growth and caloric intake as likely epigenetic factors distorting glucose metabolism. The largest weanling rats ate more, grew faster, and developed more diabetes when the dietary GLoad exceeded their gene-based metabolic capacity for glucose disposal. Diabetes risk increased for susceptible rats when energy intake exceeded 26 kcal/day and the GLoad was >175/2000 kcal of diet and when the diet provided >57% energy as CHO. Most resistant rats ate <25 kcal/day independent of the CHO:fat diet ratio or the GLoad adjusted to body size. Conclusion: Beyond the CHO:fat ratio and GLoad, neither the type of fat nor the dietary polyunsaturated/saturated fatty acid (P/S) ratio had a significant impact, suggesting genetic permissiveness affecting caloric and glucose intake and glucose disposition were key to modulating Nile rat diabetes. Fat became protective by limiting GLoad when it contributed >40% energy and displaced CHO to <50% energy, thereby decreasing the number of diabetic rats and diabetes severity.

Effects of Sustained Hyperglycemia on Skeletal Muscle Lipids in Healthy Subjects

CONTEXT

Sustained increases in plasma glucose promote skeletal muscle insulin resistance independent from obesity and dyslipidemia (ie, glucotoxicity). Skeletal muscle lipids are key molecular determinants of insulin action, yet their involvement in the development of glucotoxicity is unclear.

OBJECTIVE

To explore the impact of mild physiologic hyperglycemia on skeletal muscle lipids.

DESIGN

Single group pretest-posttest.

PARTICIPANTS

Healthy males and females with normal glucose tolerance.

INTERVENTIONS

72-hour glucose infusion raising plasma glucose by ~50 mg/dL.

MAIN OUTCOME MEASURES

Skeletal muscle lipids, insulin sensitivity, lipid oxidation.

RESULTS

Despite impairing insulin-mediated glucose disposal and suppressing fasting lipid oxidation, hyperglycemia did not alter either the content or composition of skeletal muscle triglycerides, diacylglycerides, or phospholipids. Skeletal muscle ceramides decreased after glucose infusion, likely in response to a reduction in free fatty acid concentrations.

CONCLUSIONS

Our results demonstrate that the major lipid pools in skeletal muscle are unperturbed by sustained increases in glucose availability and suggest that glucotoxicity and lipotoxicity drive insulin resistance through distinct mechanistic pathways.

Innovative Use of Olive, Winery and Cheese Waste By-Products as Functional Ingredients in Broiler Nutrition

The purpose of this study was to evaluate the dietary use of novel silage that was created by combining three agro-industrial wastes produced in bulk, i.e., olive mill wastewater, grape pomace, and deproteinized feta cheese whey, in the diets of broiler chickens. A total of 216 one-day-old male Ross-308 chicks were randomly allocated to three treatment groups with six replications (12 chicks per pen). Three isocaloric and isonitrogenous diets were formulated to include the examined silage at 0%, 5%, or 10%. Commercial breeding and management procedures were employed throughout the trial. At the end of the trial (day 35), tissue samples were collected for analysis. Feeding 10% silage resulted in increased (p ≤ 0.001) final body weight (p ≤ 0.001) and feed intake. Jejunum and cecum microflora, as well as breast and thigh meat microflora, were modified (p ≤ 0.05) by the dietary inclusion. Thigh meat oxidative stability was improved (p < 0.01) by the silage supplementation. In addition, breast and thigh meat fatty acid profiles were different, respectively, (p < 0.05) in the supplemented treatments compared to the control. The examined silage was successfully tested in broiler diets with potential benefits for their performance and meat quality.

Short-Term Effects of Early Menopause on Adiposity, Fatty Acids Profile and Insulin Sensitivity of a Swine Model of Female Obesity

Menopause strongly increases incidence and consequences of obesity and non-communicable diseases in women, with recent research suggesting a very early onset of changes in lipid accumulation, dyslipidemia, and insulin resistance. However, there is a lack of adequate preclinical models for its study. The present trial evaluated the usefulness of an alternative method to surgical ovariectomy, the administration of two doses of a GnRH analogue-protein conjugate (Vacsincel^®), for inducing ovarian inactivity in sows used as preclinical models of obesity and menopause. All the sows treated with the compound developed ovarian stoppage after the second dose and, when exposed to obesogenic diets during the following three months, showed changes in the patterns of fat deposition, in the fatty acids profiles at the different tissues and in the plasma concentrations of fructosamine, urea, β-hydroxibutirate, and haptoglobin when compared to obese fed with the same diet but maintaining ovarian activity. Altogether, these results indicate that menopause early augments the deleterious effects induced by overfeeding and obesity on metabolic traits, paving the way for future research on physiopathology of these conditions and possible therapeutic targets using the swine model.

A Study on Insulin Levels and the Expression of Glut 4 in Streptozotocin (STZ) Induced Diabetic Rats Treated with Mustard Oil Diet

The study was undertaken to evaluate the therapeutic effect of mustard oil incorporated diet in streptozotocin (STZ)-induced type 1 diabetic rats. Dietary composition has shown to play a significant role in improving insulin sensitivity. Various authors have reported the hypoglycemic effect of mustard oil in experimentally induced diabetic rats. In the present study, reverse transcriptase polymerase chain reaction (RT-PCR) was done to analyze the Glut 4 expression in STZ induced diabetic rats as it is a key player in glucose homeostasis. The effect of mustard oil on serum biochemical parameter and insulin levels was also studied. Twenty-four male Wistar rats were randomly divided into three different groups with each containing eight animals. The first, second and third groups were control, diabetic control and treatment group with mustard oil respectively. All the rats in respective groups were fed for 60 days with iso-caloric mash diet containing 8% lipid. Diabetes was induced by intra-peritoneal administration of STZ (40 mg/kg body weight). A highly significant reduction in blood glucose level, with an increase in insulin activity was observed in mustard oil-treated diabetic rats when compared to control group indicating anti-hyperglycemic activity of mustard oil. Mustard oil-treated diabetic rats showed increased expression of  Glut 4 in muscle tissue when compared to diabetic control. A significant reduction in the levels of triacylglycerols, total cholesterol, VLDL and LDL and raised plasma HDL were noticed in mustard oil-treated diabetic rats when compared to diabetic control rats. Histopathological studies revealed a mild regeneration of β cells of pancreas in mustard oil-treated diabetic rats. The results from our investigation suggest that mustard oil elicits hypoglycemic effect by increased insulin activity and up-regulation of  Glut 4 gene expression in muscle tissue of STZ-induced diabetic rats.

Increasing Acyl CoA thioesterase activity alters phospholipid profile without effect on insulin action in skeletal muscle of rats

Increased lipid metabolism in muscle is associated with insulin resistance and therefore, many strategies have been employed to alter fatty acid metabolism and study the impact on insulin action. Metabolism of fatty acid requires activation to fatty acyl CoA by Acyl CoA synthases (ACSL) and fatty acyl CoA can be hydrolysed by Acyl CoA thioesterases (Acot). Thioesterase activity is low in muscle, so we overexpressed Acot7 in muscle of chow and high-fat diet (HFD) rats and investigated effects on insulin action. Acot7 overexpression modified specific phosphatidylcholine and phosphatidylethanolamine species in tibialis muscle of chow rats to levels similar to those observed in control HFD muscle. The changes in phospholipid species did not alter glucose uptake in tibialis muscle under hyperinsulinaemic/euglycaemic clamped conditions. Acot7 overexpression in white extensor digitorum longus (EDL) muscle increased complete fatty acid oxidation ex-vivo but was not associated with any changes in glucose uptake in-vivo, however overexpression of Acot7 in red EDL reduced insulin-stimulated glucose uptake in-vivo which correlated with increased incomplete fatty acid oxidation ex-vivo. In summary, although overexpression of Acot7 in muscle altered some aspects of lipid profile and metabolism in muscle, this had no major effect on insulin-stimulated glucose uptake.

Serum adiponectin and TNFα concentrations are closely associated with epicardial adipose tissue fatty acid profiles in patients undergoing cardiovascular surgery

BACKGROUND

Epicardial adipose tissue (EAT) releases both adiponectin and TNFα, and these two adipokines play important roles in heart diseases such as coronary arterial disease. The aim of the present study was to clarify whether fatty acid (FA) profiles in EAT are linked to the serum concentration of these adipokines. The relationships between serum adipokine levels and FA profiles in patients undergoing cardiovascular surgery were analyzed.

METHODS

Patients (n = 21) undergoing cardiovascular surgery (11 males, 70.4 ± 9.0 years, BMI 26.0 ± 5.1 kg/m2) were included. EAT samples were taken. We measured clinical biochemical data and FA profiles in venous blood and EAT samples using gas chromatography. Serum adiponectin and TNFα concentrations were also measured.

RESULTS

The adiponectin and TNFα levels were not correlated with any fatty acid concentration in serum lipids. In contrast, there was a positive correlation between the serum adiponectin level and epicardial level of nervonic acid (C24:1ω9, r = 0.525, P = 0.025). In multiple regression analysis, adiponectin showed a positive association with the epicardial C24:1ω9 concentration after controlling for age and BMI, or TG, non-HDL-C, and BNP. The serum TNFα concentration was negatively correlated with the epicardial C18:3ω3, C12:0 and C18:0 content. In multiple regression analysis, the serum TNFα concentration showed a positive association with the epicardial C18:3ω3 level (β = - 0.575, P = 0.015).

CONCLUSIONS

These results suggest that there is a close relationship between epicardial FA profiles and serum levels of adiponectin and TNFα. Dietary therapy to target FA profiles may be helpful to modulate inflammation.

Erythrocytes and Skeletal Muscle Unsaturated and Omega-6 Fatty Acids Are Positively Correlated after Caloric Restriction and Exercise

BACKGROUND

Nutritional intervention studies with fatty acid (FA) supplements assess the efficacy of the intervention by measuring the changes in erythrocyte membrane lipid profiles reflected in tissue composition changes. The aim was to determine the effects of caloric restriction (CR) on erythrocytes lipid composition and to compare and correlate these changes with skeletal muscle acid profiles after CR.

METHODS

Erythrocytes were obtained from 11 healthy men before and after 4 weeks of 33% CR in post-exercise conditions; muscle biopsies were obtained from the same athletes after 4 weeks of 33% CR in post-exercise conditions. Samples were used for FA determination by chromatography.

RESULTS

CR significantly modified erythrocyte FAs composition. Skeletal muscle FA profile was significantly different from that for the erythrocytes. The erythrocyte FA profile was more saturated (52.1 ± 1.5% and 32.8 ± 0.9%, respectively) and less monounsaturated (21.0 ± 0.8% and 39.0 ± 2.0%, respectively) than the skeletal muscle FA profile and similarly polyunsaturated.

CONCLUSIONS

CR modifies erythrocyte lipid composition, mainly omega-6 FAs. Erythrocyte monounsaturated, polyunsaturated and omega-6 FAs, but not the saturated and omega-3 FAs, were significantly positively correlated with skeletal muscle FAs. There is a discordance between saturated and omega-3 FAs from erythrocyte and from muscle, but monounsaturated, polyunsaturated and omega-6 fatty acids are positively correlated.

Association of muscle lipidomic profile with high-fat diet-induced insulin resistance across five mouse strains

Different mouse strains exhibit variation in their inherent propensities to develop metabolic disease. We recently showed that C57BL6, 129X1, DBA/2 and FVB/N mice are all susceptible to high-fat diet-induced glucose intolerance, while BALB/c mice are relatively protected, despite changes in many factors linked with insulin resistance. One parameter strongly linked with insulin resistance is ectopic lipid accumulation, especially metabolically active ceramides and diacylglycerols (DAG). This study examined diet-induced changes in the skeletal muscle lipidome across these five mouse strains. High-fat feeding increased total muscle triacylglycerol (TAG) content, with elevations in similar triacylglycerol species observed for all strains. There were also generally consistent changes across strains in the abundance of different phospholipid (PL) classes and the fatty acid profile of phospholipid molecular species, with the exception being a strain-specific difference in phospholipid species containing two polyunsaturated fatty acyl chains in BALB/c mice (i.e. a diet-induced decrease in the other four strains, but no change in BALB/c mice). In contrast to TAG and PL, the high-fat diet had a minor influence on DAG and ceramide species across all strains. These results suggest that widespread alterations in muscle lipids are unlikely a major contributors to the favourable metabolic profile of BALB/c mice and rather there is a relatively conserved high-fat diet response in muscle of most mouse strains.

FFA4 (GPR120) as a fatty acid sensor involved in appetite control, insulin sensitivity and inflammation regulation

Unsaturated long-chain fatty acids have been suggested to be beneficial in the context of cardiovascular disorders based in epidemiologic studies conducted in Greenland and Mediterranean. DHA and EPA are omega-3 polyunsaturated fatty acids that are plentiful in fish oil, and oleic acid is an omega-9 monounsaturated fatty acid, rich in olive oil. Dietary intake of these unsaturated long-chain fatty acids have been associated with insulin sensitivity and weight loss, which contrasts with the impairment of insulin sensitivity and weight gain associated with high intakes of saturated long-chain fatty acids. The recent discovery that free fatty acid receptor 4 (FFA4, also known as GPR120) acts as a sensor for unsaturated long-chain fatty acids started to unveil the molecular mechanisms underlying the beneficial functions played by these unsaturated long-chain fatty acids in various physiological processes, which include the secretions of gastrointestinal peptide hormones and glucose homeostasis. In this review, the physiological roles and therapeutic significance of FFA4 in appetite control, insulin sensitization, and inflammation reduction are discussed in relation to obesity and type 2 diabetes from pharmacological viewpoints.

Is There a Role for Bioactive Lipids in the Pathobiology of Diabetes Mellitus?

Inflammation, decreased levels of circulating endothelial nitric oxide (eNO) and brain-derived neurotrophic factor (BDNF), altered activity of hypothalamic neurotransmitters (including serotonin and vagal tone) and gut hormones, increased concentrations of free radicals, and imbalance in the levels of bioactive lipids and their pro- and anti-inflammatory metabolites have been suggested to play a role in diabetes mellitus (DM). Type 1 diabetes mellitus (type 1 DM) is due to autoimmune destruction of pancreatic β cells because of enhanced production of IL-6 and tumor necrosis factor-α (TNF-α) and other pro-inflammatory cytokines released by immunocytes infiltrating the pancreas in response to unknown exogenous and endogenous toxin(s). On the other hand, type 2 DM is due to increased peripheral insulin resistance secondary to enhanced production of IL-6 and TNF-α in response to high-fat and/or calorie-rich diet (rich in saturated and trans fats). Type 2 DM is also associated with significant alterations in the production and action of hypothalamic neurotransmitters, eNO, BDNF, free radicals, gut hormones, and vagus nerve activity. Thus, type 1 DM is because of excess production of pro-inflammatory cytokines close to β cells, whereas type 2 DM is due to excess of pro-inflammatory cytokines in the systemic circulation. Hence, methods designed to suppress excess production of pro-inflammatory cytokines may form a new approach to prevent both type 1 and type 2 DM. Roux-en-Y gastric bypass and similar surgeries ameliorate type 2 DM, partly by restoring to normal: gut hormones, hypothalamic neurotransmitters, eNO, vagal activity, gut microbiota, bioactive lipids, BDNF production in the gut and hypothalamus, concentrations of cytokines and free radicals that results in resetting glucose-stimulated insulin production by pancreatic β cells. Our recent studies suggested that bioactive lipids, such as arachidonic acid, eicosapentaneoic acid, and docosahexaenoic acid (which are unsaturated fatty acids) and their anti-inflammatory metabolites: lipoxin A4, resolvins, protectins, and maresins, may have antidiabetic actions. These bioactive lipids have anti-inflammatory actions, enhance eNO, BDNF production, restore hypothalamic dysfunction, enhance vagal tone, modulate production and action of ghrelin, leptin and adiponectin, and influence gut microbiota that may explain their antidiabetic action. These pieces of evidence suggest that methods designed to selectively deliver bioactive lipids to pancreatic β cells, gut, liver, and muscle may prevent type 1 and type 2 DM.

Ontogeny of Sex-Related Differences in Foetal Developmental Features, Lipid Availability and Fatty Acid Composition

Sex-related differences in lipid availability and fatty acid composition during swine foetal development were investigated. Plasma cholesterol and triglyceride concentrations in the mother were strongly related to the adequacy or inadequacy of foetal development and concomitant activation of protective growth in some organs (brain, heart, liver and spleen). Cholesterol and triglyceride availability was similar in male and female offspring, but female foetuses showed evidence of higher placental transfer of essential fatty acids and synthesis of non-essential fatty acids in muscle and liver. These sex-related differences affected primarily the neutral lipid fraction (triglycerides), which may lead to sex-related postnatal differences in energy partitioning. These results illustrate the strong influence of the maternal lipid profile on foetal development and homeorhesis, and they confirm and extend previous reports that female offspring show better adaptive responses to maternal malnutrition than male offspring. These findings may help guide dietary interventions to ensure adequate fatty acid availability for postnatal development.

Membrane lipid alterations in the metabolic syndrome and the role of dietary oils

The metabolic syndrome is a cluster of pathological conditions, including hypertension, hyperglycemia, hypertriglyceridemia, obesity and low HDL levels that is of great concern worldwide, as individuals with metabolic syndrome have an increased risk of type-2 diabetes and cardiovascular disease. Insulin resistance, the key feature of the metabolic syndrome, might be at the same time cause and consequence of impaired lipid composition in plasma membranes of insulin-sensitive tissues like liver, muscle and adipose tissue. Diet intervention has been proposed as a powerful tool to prevent the development of the metabolic syndrome, since healthy diets have been shown to have a protective role against the components of the metabolic syndrome. Particularly, dietary fatty acids are capable of modulating the deleterious effects of these conditions, among other mechanisms, by modifications of the lipid composition of the membranes in insulin-sensitive tissues. However, there is still scarce data based of high-level evidence on the effects of dietary oils on the effects of the metabolic syndrome and its components. This review summarizes the current knowledge on the effects of dietary oils on improving alterations of the components of the metabolic syndrome. It also examines their influence in the modulation of plasma membrane lipid composition and in the functionality of membrane proteins involved in insulin activity, like the insulin receptor, GLUT-4, CD36/FAT and ABCA-1, and their effect in the metabolism of glucose, fatty acids and cholesterol, and, in turn, the key features of the metabolic syndrome. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.

Total and subtypes of dietary fat intake and risk of type 2 diabetes mellitus in the Prevención con Dieta Mediterránea (PREDIMED) study

Background: The associations between dietary fat and cardiovascular disease have been evaluated in several studies, but less is known about their influence on the risk of diabetes.Objective: We examined the associations between total fat, subtypes of dietary fat, and food sources rich in saturated fatty acids and the incidence of type 2 diabetes (T2D).Design: A prospective cohort analysis of 3349 individuals who were free of diabetes at baseline but were at high cardiovascular risk from the PREvención con DIeta MEDiterránea (PREDIMED) study was conducted. Detailed dietary information was assessed at baseline and yearly during the follow-up using a food frequency questionnaire. Multivariable Cox proportional hazards models were used to estimate T2D HRs and 95% CIs according to baseline and yearly updated fat intake.Results: We documented 266 incident cases during 4.3 y of follow-up. Baseline saturated and animal fat intake was not associated with the risk of T2D. After multivariable adjustment, participants in the highest quartile of updated intake of saturated and animal fat had a higher risk of diabetes than the lowest quartile (HR: 2.19; 95% CI: 1.28, 3.73; and P-trend = 0.01 compared with HR: 2.00; 95% CI: 1.29, 3.09; and P-trend < 0.01, respectively). In both the Mediterranean diet and control groups, participants in the highest quartile of updated animal fat intake had an ∼2-fold higher risk of T2D than their counterparts in the lowest quartile. The consumption of 1 serving of butter and cheese was associated with a higher risk of diabetes, whereas whole-fat yogurt intake was associated with a lower risk.Conclusions: In a Mediterranean trial focused on dietary fat interventions, baseline intake of saturated and animal fat was not associated with T2D incidence, but the yearly updated intake of saturated and animal fat was associated with a higher risk of T2D. Cheese and butter intake was associated with a higher risk of T2D, whereas whole-fat yogurt intake was associated with a lower risk of T2D. This trial was registered at www.isrctn.com as ISRCTN35739639.

Alterations of fatty acid profiles in gestational diabetes and influence of the diet

Gestational diabetes mellitus (GDM) is a pregnancy-induced complication with increased prevalence, especially in overweight women. Fatty acid (FA) composition in tissues can reflect dietary fat intake, especially essential FA intake. Moreover, it has been shown that FA profiles in blood lipid fractions are altered in diabetic patients. Consequently, women with GDM may also have a distinctive FA profile. The objective of this review is compare FA profiles in different blood lipid fractions and the influence of dietary fat intake in women with GDM or normoglycemic pregnancies. Results show that women with GDM have more saturated and less polyunsaturated FA (PUFA) in their red blood cell (RBC) membranes than normoglycemic pregnant women. Moreover, some studies reported that women with GDM have a greater energy intake from total fat and saturated FA, along with a lower energy intake from PUFA, when compared to normoglycemic pregnancies. Clinical trials showed that omega-3 PUFA levels in RBC membranes of GDM women can be restored by a dietary intervention. Further research is required to determine whether FA profiles are altered prior to the diagnosis of GDM and can be prevented by diet.

Evaluation of treadmill exercise effect on muscular lipid profiles of diabetic fatty rats by nanoflow liquid chromatography-tandem mass spectrometry

We compare comprehensive quantitative profiling of lipids at the molecular level from skeletal muscle tissues (gastrocnemius and soleus) of Zucker diabetic fatty rats and Zucker lean control rats during treadmill exercise by nanoflow liquid chromatography-tandem mass spectrometry. Because type II diabetes is caused by decreased insulin sensitivity due to excess lipids accumulated in skeletal muscle tissue, lipidomic analysis of muscle tissues under treadmill exercise can help unveil the mechanism of lipid-associated insulin resistance. In total, 314 lipid species, including phospholipids, sphingolipids, ceramides, diacylglycerols (DAGs), and triacylglycerols (TAGs), were analyzed to examine diabetes-related lipid species and responses to treadmill exercise. Most lysophospholipid levels increased with diabetes. While DAG levels (10 from the gastrocnemius and 13 from the soleus) were >3-fold higher in diabetic rats, levels of most of these decreased after exercise in soleus but not in gastrocnemius. Levels of 5 highly abundant TAGs (52:1 and 54:3 in the gastrocnemius and 48:2, 50:2, and 52:4 in the soleus) displaying 2-fold increases in diabetic rats decreased after exercise in the soleus but not in the gastrocnemius in most cases. Thus, aerobic exercise has a stronger influence on lipid levels in the soleus than in the gastrocnemius in type 2 diabetic rats.

Ratio of dietary ω-3 and ω-6 fatty acids-independent determinants of muscle mass-in hemodialysis patients with diabetes

OBJECTIVE

ω-3 and ω-6 polyunsaturated fatty acids (PUFAs) are essential nutrients in the human diet and possibly affect muscle mass. We evaluated the association between the dietary ratios of ω-3 and ω-6 PUFAs and muscle mass, indicated as skeletal muscle mass (SMM) and appendicular skeletal muscle mass (ASM), in patients with diabetes undergoing hemodialysis (HD).

METHODS

In this cross-sectional study, data on 69 patients with diabetes who underwent standard HD therapy were analyzed. For estimating muscle mass, anthropometric and bioelectrical impedance analyses were conducted following dialysis. In addition, routine laboratory and 3-d dietary data were obtained. The adequate intake (AI) cut-off for ω-3 PUFAs was 1.6 g/d and 1.1 g/d for male and female patients, respectively.

RESULTS

The average age of the participants was 63.0 ± 10.4 y. The mean ratios of ω-3/ω-6 PUFA intake, ω-6/ω-3 PUFA intake, SMM, and ASM of the patients were 0.13 ± 0.07, 9.4 ± 6.4, 24.6 ± 5.4 kg, and 18.3 ± 4.6 kg, respectively. Patients who had AI of ω-3 PUFAs had significantly higher SMM and ASM than did their counterparts. Linear and stepwise multivariable adjustment analyses revealed that insulin resistance and the ω-6/ω-3 PUFA ratio were the independent deleterious determinants of ASM normalized to height in HD patients.

CONCLUSIONS

Patients with AI of ω-3 PUFAs had total-body SMM and ASM that were more appropriate. A higher dietary ratio of ω-6/ω-3 PUFAs was associated with reduced muscle mass in HD patients.

Nigella sativa Relieves the Altered Insulin Receptor Signaling in Streptozotocin-Induced Diabetic Rats Fed with a High-Fat Diet

The black cumin (Nigella sativa) "NS" or the black seeds have many pharmacological activities such as antioxidant, anticarcinogenic, antihypertensive, and antidiabetic properties. In this work, streptozotocin-induced diabetic rats fed with a high-fat diet were treated daily with NS oil (NSO) in order to study the effect on the blood glucose, lipid profile, oxidative stress parameters, and the gene expression of some insulin receptor-induced signaling molecules. This treatment was combined also with some drugs (metformin and glimepiride) and the insulin receptor inhibitor I-OMe-AG538. The administration of NSO significantly induced the gene expression of insulin receptor compared to rats that did not receive NSO. Also, it upregulated the expression of insulin-like growth factor-1 and phosphoinositide-3 kinase, whereas the expression of ADAM-17 was downregulated. The expression of ADAM-17 is corroborated by the analysis of TIMP-3 content. In addition, the NSO significantly reduced blood glucose level, components of the lipid profile, oxidative stress parameters, serum insulin/insulin receptor ratio, and the tumor necrosis factor-α, confirming that NSO has an antidiabetic activity. Thus, the daily NSO treatment in our rat model indicates that NSO has a potential in the management of diabetes as well as improvement of insulin-induced signaling.

Skeletal intramyocellular lipid metabolism and insulin resistance

Lipids stored in skeletal muscle cells are known as intramyocellular lipid (IMCL). Disorders involving IMCL and its causative factor, circulatory free fatty acids (FFAs), induce a toxic state and ultimately result in insulin resistance (IR) in muscle tissue. On the other hand, intramuscular triglyceride (IMTG), the most abundant component of IMCL and an essential energy source for active skeletal muscle, is different from other IMCLs, as it is stored in lipid droplets and plays a pivotal role in skeletal muscle energy homeostasis. This review discusses the association of FFA-induced ectopic lipid accumulation and IR, with specific emphasis on the relationship between IMCL/IMTG metabolism and IR.

Docosahexaenoic Acid Levels in Blood and Metabolic Syndrome in Obese Children: Is There a Link?

Prevalence of metabolic syndrome is increasing in the pediatric population. Considering the different existing criteria to define metabolic syndrome, the use of the International Diabetes Federation (IDF) criteria has been suggested in children. Docosahexaenoic acid (DHA) has been associated with beneficial effects on health. The evidence about the relationship of DHA status in blood and components of the metabolic syndrome is unclear. This review discusses the possible association between DHA content in plasma and erythrocytes and components of the metabolic syndrome included in the IDF criteria (obesity, alteration of glucose metabolism, blood lipid profile, and blood pressure) and non-alcoholic fatty liver disease in obese children. The current evidence is inconsistent and no definitive conclusion can be drawn in the pediatric population. Well-designed longitudinal and powered trials need to clarify the possible association between blood DHA status and metabolic syndrome.

Food sources of fat may clarify the inconsistent role of dietary fat intake for incidence of type 2 diabetes

BACKGROUND

Dietary fats could affect glucose metabolism and obesity development and, thereby, may have a crucial role in the cause of type 2 diabetes (T2D). Studies indicated that replacing saturated with unsaturated fats might be favorable, and plant foods might be a better choice than animal foods. Nevertheless, epidemiologic studies suggested that dairy foods are protective.

OBJECTIVE

We hypothesized that, by examining dietary fat and its food sources classified according to fat type and fat content, some clarification regarding the role of dietary fat in T2D incidence could be provided.

DESIGN

A total of 26,930 individuals (61% women), aged 45-74 y, from the Malmö Diet and Cancer cohort were included in the study. Dietary data were collected by using a modified diet-history method. During 14 y of follow-up, 2860 incident T2D cases were identified.

RESULTS

Total intake of high-fat dairy products (regular-fat alternatives) was inversely associated with incident T2D (HR for highest compared with lowest quintiles: 0.77; 95% CI: 0.68, 0.87; P-trend < 0.001). Most robust inverse associations were seen for intakes of cream and high-fat fermented milk (P-trend < 0.01) and for cheese in women (P-trend = 0.02). High intake of low-fat dairy products was associated with increased risk, but this association disappeared when low- and high-fat dairy were mutually adjusted (P-trend = 0.18). Intakes of both high-fat meat (P-trend = 0.04) and low-fat meat (P-trend < 0.001) were associated with increased risk. Finally, we did not observe significant association between total dietary fat content and T2D (P-trend = 0.24), but intakes of saturated fatty acids with 4-10 carbons, lauric acid (12:0), and myristic acid (14:0) were associated with decreased risk (P-trend < 0.01).

CONCLUSIONS

Decreased T2D risk at high intake of high- but not of low-fat dairy products suggests that dairy fat partly could have contributed to previously observed protective associations between dairy intake and T2D. Meat intake was associated with increased risk independently of the fat content.

Seasonal changes in minor membrane phospholipid classes, sterols and tocopherols in overwintering insect, Pyrrhocoris apterus

Ectotherm animals including insects are known to undergo seasonal restructuring of the cell membranes in order to keep their functionality and/or protect their structural integrity at low body temperatures. Studies on insects so far focused either on fatty acids or on composition of molecular species in major phospholipid classes. Here we extend the scope of analysis and bring results on seasonal changes in minor phospholipid classes, lysophospholipids (LPLs), free fatty acids, phytosterols and tocopherols in heteropteran insect, Pyrrhocoris apterus. We found that muscle tissue contains unusually high amounts of LPLs. Muscle and fat body tissues also contain high amounts of β-sitosterol and campesterol, two phytosterols derived from plant food, while only small amounts of cholesterol are present. In addition, two isomers (γ and δ) of tocopherol (vitamin E) are present in quantities comparable to, or even higher than phytosterols in both tissues. Distinct seasonal patterns of sterol and tocopherol concentrations were observed showing a minimum in reproductively active bugs in summer and a maximum in diapausing, cold-acclimated bugs in winter. Possible adaptive meanings of such changes are discussed including: preventing the unregulated transition of membrane lipids from functional liquid crystalline phase to non-functional gel phase; decreasing the rates of ion/solute leakage; silencing the activities of membrane bound enzymes and receptors; and counteracting the higher risk of oxidative damage to PUFA in winter membranes.

Plant oils were associated with low prevalence of impaired glucose metabolism in Japanese workers

Fatty acid has been suggested to be involved in development of diabetes. However, its association is unclear among Japanese populations, which consume large amounts of fish rich in n-3 polyunsaturated fatty acids. The present cross-sectional study examined the association of individual dietary fatty acids and dietary fatty acid patterns with abnormal glucose metabolism among 1065 Japanese employees, aged 18-69 years. Impaired glucose metabolism is defined if a person has a history of diabetes, current use of anti-diabetic drug, fasting plasma glucose of 110 mg/dl (≥6.1 mmol/L) or greater, or hemoglobin A1C of 6.0% (≥42 mmol/mol) or greater. Dietary intake was assessed with a self-administered diet history questionnaire. Dietary fatty acid patterns were extracted by principal component analysis. Odds ratios of impaired glucose metabolism according to tertile categories of each fatty acids and dietary fatty acid patterns were estimated using logistic regression with adjustment for potential confounding variables. A higher intake of polyunsaturated fatty acid, n-6 fatty acid, linoleic acid, and oleic acid were significantly associated with a decreased prevalence of impaired glucose metabolism (P for trend = 0.03, 0.01, 0.02, and 0.04, respectively). Alpha-linolenic acid was marginally significantly associated with a decreased prevalence of impaired glucose metabolism (P for trend = 0.12). Of three fatty acid patterns identified, a higher plant oil pattern score, which characterized by high intake of alpha-linolenic acid, linoleic acid, and oleic acid, was associated with a decreased prevalence of impaired glucose metabolism (P for trend = 0.03). No association was observed for other patterns. In conclusion, plant source fatty acids might be protectively associated with development of diabetes in Japanese adults.

Metabolic rates associated with membrane fatty acids in mice selected for increased maximal metabolic rate

Aerobic metabolism of vertebrates is linked to membrane fatty acid (FA) composition. Although the membrane pacemaker hypothesis posits that desaturation of FAs accounts for variation in resting or basal metabolic rate (BMR), little is known about the FA profiles that underpin variation in maximal metabolic rate (MMR). We examined membrane FA composition of liver and skeletal muscle in mice after seven generations of selection for increased MMR. In both liver and skeletal muscle, unsaturation index did not differ between control and high-MMR mice. We also examined membrane FA composition at the individual-level of variation. In liver, 18:0, 20:3 n-6, 20:4 n-6, and 22:6 n-3 FAs were significant predictors of MMR. In gastrocnemius muscle, 18:2 n-6, 20:4 n-6, and 22:6 n-3 FAs were significant predictors of MMR. In addition, muscle 16:1 n-7, 18:1 n-9, and 22:5 n-3 FAs were significant predictors of BMR, whereas no liver FAs were significant predictors of BMR. Our findings indicate that (i) individual variation in MMR and BMR appears to be linked to membrane FA composition in the skeletal muscle and liver, and (ii) FAs that differ between selected and control lines are involved in pathways that can affect MMR or BMR.

Ectopic overexpression of porcine DGAT1 increases intramuscular fat content in mouse skeletal muscle

The microsomal enzyme 1, 2-acyl CoA: diacylglyceroltransferase-1 (DGAT1) plays an important role in triglyceride storage in adipose tissue and expresses in skeletal muscle as well. The primary goal of the present study was to investigate the effect of porcine DGAT1 on intramuscular fat (IMF) content of transgenic mice produced by pronuclear microinjection with muscle specific promoter of porcine muscle creatine kinase (MCK). In normal chow-fed diet, 4 month-old male transgenic mice expressed more DGAT1, ACC1, UCP1, and FABP4 mRNAs and proteins in skeletal muscle than control mice by real-time PCR and western blot. No significant changes were detected for ACC2, CD36, ADRP, PPAR gamma and LPL. Triacylglycerol assay and soleus muscle sections showed overexpression of porcine DGAT1 in skeletal muscle increased intramyocellular triglyceride and percent of the total cell surface covered by lipid droplets. Thus, upregulation of porcine DGAT1 in skeletal muscle increases IMF content. The present study may further serve to develop transgenic pigs with higher IMF content and improved meat quality.

Gut bacteria profiles of Mus musculus at the phylum and family levels are influenced by saturation of dietary fatty acids

BACKGROUND

Mammalian gut microbiota have been implicated in a variety of functions including the breakdown of ingested nutrients, the regulation of energy intake and storage, the control of immune system development and activity, and the synthesis of novel chemicals. Previous studies have shown that feeding mammalian hosts a high-fat diet shifts gut bacteria at the phylum level to reduce the ratio of Bacteroidetes-to-Firmicutes, while feeding hosts a fat-restricted diet increases this ratio. However, few studies have investigated the differential effects of fatty acid type on gut bacterial profile.

METHODS

Over a 14-week period, Mus musculus were fed a diet rich in omega-3 polyunsaturated fatty acids (n-3 PUFAs), omega-6 polyunsaturated fatty acids (n-6 PUFAs), or saturated fatty acids (SFAs). Fecal pellets were collected before and after the treatment period from 12 randomly selected mice (4 per treatment group). Bacterial DNA was extracted from the pellets and characterized by analysis of the hypervariable V3 region of the 16S rRNA. Nominal logistic regression models were used to assess shifts in microbial profile at the phylum and family levels in response to diet.

RESULTS

A significant decrease in the proportion of phylum Bacteroidetes species was observed for mice fed any of the three diets over time. However, the SFA-rich diet group showed a significantly greater decrease in Bacteroidetes proportion (-28%) than did either the n-3 PUFA group (-10%) or the n-6 PUFA group (-12%). At the family level, a significant decrease in proportion of Porphyromonadaceae was observed for mice fed the n-6 PUFA-rich diet, and a significant decrease in proportion of Lachnospiraceae was observed for mice fed the SFA-rich diet. There was no significant effect of diet type on body mass change.

CONCLUSION

Our results indicate that SFAs have stronger effects than PUFAs in shifting gut microbiota profiles toward those typical of obese individuals, and that dietary fatty acid saturation influences shifts in gut microbiota independently of changes in body mass.

Recent insights into the relation of Δ5 desaturase and Δ6 desaturase activity to the development of type 2 diabetes

PURPOSE OF REVIEW

The Δ5 desaturase (D5D) and Δ6 desaturase (D6D) are key enzymes in the metabolism of polyunsaturated fatty acids. This review aims to summarize recent advances towards understanding the relation of the activities of D5D and D6D to the development of type 2 diabetes.

RECENT FINDINGS

Prospective studies that investigated fatty acid product-to-precursor ratios in blood as estimates of desaturase activity reported a clear inverse relation of D5D activity and a strong direct relation of D6D activity to diabetes incidence. Due to the prospective design and comprehensive confounder adjustment in these studies, confounding and reverse causation are unlikely explanations for these findings. Furthermore, studies on genetic variation in the FADS1 and FADS2 genes, which encode D5D and D6D, also point to an influence of D5D and D6D activity on glucose metabolism. The inverse relation of D5D activity and the direct relation of D6D activity to diabetes risk have been corroborated by a Mendelian randomization approach recently.

SUMMARY

These recent studies suggest an important role of D5D and D6D activities for the development of type 2 diabetes. Factors which influence the activities of these desaturases are likely to be of public health relevance.

A prospective study of prepregnancy dietary fat intake and risk of gestational diabetes

BACKGROUND

Fatty acids play a vital role in glucose homeostasis; however, studies on habitual dietary fat intakes and gestational diabetes mellitus (GDM) risk are limited and provide conflicting findings.

OBJECTIVE

We determined whether the total amount and the type and source of prepregnancy dietary fats are related to risk of GDM.

DESIGN

A prospective study was conducted in 13,475 women who reported a singleton pregnancy between 1991 and 2001 in the Nurses' Health Study II. In these women, 860 incident GDM cases were reported. The adjusted RR of GDM was estimated for quintiles of total fat, specific fat, and the source of fat intakes by pooled logistic regression.

RESULTS

Higher animal fat and cholesterol intakes were significantly associated with increased GDM risk. Across increasing quintiles of animal fat, RRs (95% CIs) for GDM were 1.00 (reference), 1.55 (1.20, 1.98), 1.43 (1.09, 1.88), 1.40 (1.04, 1.89), and 1.88 (1.36, 2.60) (P-trend = 0.05). Corresponding RRs (95% CIs) for dietary cholesterol were 1.00 (reference), 1.08 (0.84, 1.32), 1.02 (0.78, 1.29), 1.20 (0.93, 1.55), and 1.45 (1.11, 1.89) (P-trend = 0.04). The substitution of 5% of energy from animal fat for an equal percentage of energy from carbohydrates was associated with significantly increased risk of GDM [RR (95% CI): 1.13 (1.08, 1.18); P < 0.0001]. No significant associations were observed between dietary polyunsaturated fat, monounsaturated fat, or trans fat intakes and GDM risk.

CONCLUSION

Higher prepregnancy intakes of animal fat and cholesterol were associated with elevated GDM risk.

Foods for the prevention of diabetes: how do they work?

With the diabetes epidemic reaching menacing proportions worldwide, there is an urgent need for the development of cost-efficient prevention strategies to be effective at the population level. Great potential in this direction lies in properly designed, large-scale dietary interventions. The macronutrient composition and the caloric content of our diet are major determinants of glucose homeostasis and there is a continuously growing list of foods, nutrients or individual compounds that have been associated with an increased or reduced incidence of diabetes mellitus. These include fat, carbohydrates, fibre, alcohol, polyphenols and other micronutrients or individual dietary compounds, which have been shown to either promote or prevent a progression towards a (pre-)diabetic state. This review aims to briefly summarize relevant epidemiological data linking foods to diabetes and to provide insights into the mechanisms through which these effects are mediated. These include improvement of insulin sensitivity or promotion of insulin resistance, regulation of inflammatory pathways, regulation of glucose transport and tissue glucose uptake, aggravation or attenuation of postprandial glycaemia/insulinaemia, interactions with hormonal responses and β-cell-dependent mechanisms.

The role of diet in the prevention of type 2 diabetes

Type 2 diabetes mellitus is an important preventable disease and a growing public health problem. Epidemiologic and interventional studies suggest that weight loss is the main driving force to reduce diabetes risk. Landmark clinical trials of lifestyle changes in subjects with prediabetes have shown that diet and exercise leading to weight loss consistently reduce the incidence of diabetes. However, from these studies it cannot be established whether dietary changes alone play a significant role in preventing diabetes. Here we review epidemiologic and clinical trial evidence relating nutrients, foods and dietary patterns to diabetes risk and the possible mechanisms involved. The differential effects of carbohydrate and fat quantity and quality, and those of specific foods and whole diets are discussed. Importantly, most dietary components influencing diabetes risk have similar effects on biomarkers of cardiovascular risk and inflammation. The conclusion is that there is no universal dietary strategy to prevent diabetes or delay its onset. Together with the maintenance of ideal body weight, the promotion of the so-called prudent diet (characterized by a higher intake of food groups that are generally recommended for health promotion, particularly plant-based foods, and a lower intake of red meat, meat products, sweets, high-fat dairy and refined grains) or a Mediterranean dietary pattern rich in olive oil, fruits and vegetables, including whole grains, pulses and nuts, low-fat dairy, and moderate alcohol consumption (mainly red wine) appears as the best strategy to decrease diabetes risk, especially if dietary recommendations take into account individual preferences, thus enabling long-time adherence.

Effect of high-fat diets on body composition, lipid metabolism and insulin sensitivity, and the role of exercise on these parameters

Dietary fat composition can interfere in the development of obesity due to the specific roles of some fatty acids that have different metabolic activities, which can alter both fat oxidation and deposition rates, resulting in changes in body weight and/or composition. High-fat diets in general are associated with hyperphagia, but the type of dietary fat seems to be more important since saturated fats are linked to a positive fat balance and omental adipose tissue accumulation when compared to other types of fat, while polyunsaturated fats, omega-3 and omega-6, seem to increase energy expenditure and decrease energy intake by specific mechanisms involving hormone-sensitive lipase, activation of peroxisome proliferator-activated receptor α (PPARα) and others. Saturated fat intake can also impair insulin sensitivity compared to omega-3 fat, which has the opposite effect due to alterations in cell membranes. Obesity is also associated with impaired mitochondrial function. Fat excess favors the production of malonyl-CoA, which reduces GLUT4 efficiency. The tricarboxylic acid cycle and beta-oxidation are temporarily uncoupled, forming metabolite byproducts that augment reactive oxygen species production. Exercise can restore mitochondrial function and insulin sensitivity, which may be crucial for a better prognosis in treating or preventing obesity.

Dietary polyunsaturated fatty acid prevents hyperlipidemia and hepatic oxidant status in pregnant diabetic rats and their macrosomic offspring

A considerable amount of clinical and experimental evidence now exists and suggests the involvement of fatty acids and free radical-mediated oxidative processes in the pathogenesis of diabetic complications. Fetuses from diabetic mothers are at increased risk of developing neonatal macrosomia and oxidative stress. We investigated the modulation of antioxidant status and liver biochemical parameters in normal and diabetic pregnant rats and their offspring. Animals were randomly allocated into three groups of six rats each: a control group, a diabetic group and diabetic rats fed with flax and sesame seeds mixture group. The time course of changes in lipid metabolism and antioxidant status by dietary rich in ω3- and ω6-polyunsaturated fatty acids in alloxan-induced diabetic pregnant rats and their macrosomic offspring was studied. Glucose and insulin levels were also assessed in order to characterize the diabetic state of dams and their offspring. The diabetic rats presented a significant increase in glycemia, plasma and liver lipid parameters compared with those of control group. In addition, liver malonaldialdehyde levels significantly increased. Antioxidant enzyme activities such as catalase and superoxide dismutase and reduced glutathione levels significantly decreased in the liver of diabetic rats when compared with controls. Diet supplemented with flax and sesame seeds mixture in pregnant diabetic rats ameliorated lipid parameters, antioxidant enzyme activities, level of reduced glutathione and significantly decreased malonaldialdehyde levels. These ameliorations were also observed in pups whose pregnant diabetic mothers were fed seeds mixture. Our results suggested that flax and sesame seeds mixture supplemented to diet of pregnant diabetic rats might be helpful in preventing diabetic complications in adult dams and their offspring.

A grape polyphenol extract modulates muscle membrane fatty acid composition and lipid metabolism in high-fat--high-sucrose diet-fed rats

Accumulation of muscle TAG content and modification of muscle phospholipid fatty acid pattern may have an impact on lipid metabolism, increasing the risk of developing diabetes. Some polyphenols have been reported to modulate lipid metabolism, in particular those issued from red grapes. The present study was designed to determine whether a grape polyphenol extract (PPE) modulates skeletal muscle TAG content and phospholipid fatty acid composition in high-fat-high-sucrose (HFHS) diet-fed rats. Muscle plasmalemmal and mitochondrial fatty acid transporters, GLUT4 and lipid metabolism pathways were also explored. The PPE decreased muscle TAG content in HFHS/PPE diet-fed rats compared with HFHS diet-fed rats and induced higher proportions of n-3 PUFA in phospholipids. The PPE significantly up-regulated GLUT4 mRNA expression. Gene and protein expression of muscle fatty acid transporter cluster of differentiation 36 (CD36) was increased in HFHS diet-fed rats but returned to control values in HFHS/PPE diet-fed rats. Carnitine palmitoyltransferase 1 protein expression was decreased with the PPE. Mitochondrial β-hydroxyacyl CoA dehydrogenase was increased in HFHS diet-fed rats and returned to control values with PPE supplementation. Lipogenesis, mitochondrial biogenesis and mitochondrial activity were not affected by the PPE. In conclusion, the PPE modulated membrane phospholipid fatty acid composition and decreased muscle TAG content in HFHS diet-fed rats. The PPE lowered CD36 gene and protein expression, probably decreasing fatty acid transport and lipid accumulation within skeletal muscle, and increased muscle GLUT4 expression. These effects of the PPE are in favour of a better insulin sensibility.

Increased intake of dietary polyunsaturated fat does not promote whole body or preferential abdominal fat mass loss in overweight adults

OBJECTIVE

There is evidence that increasing the proportion of polyunsaturated fatty acids (PUFA) in a diet can enhance the rate of fat oxidation acutely. Higher PUFA in a diet has also been associated with greater abdominal fat loss in longer term studies. This study aimed to investigate if higher PUFA intake would result in greater fat mass loss over a 12-week period, mainly from the abdominal region.

METHODS

Data at the 12-week time point from two weight loss studies, both comparing high PUFA versus low PUFA diets was, accessed for 141 overweight subjects from the same area. Specifically, data on anthropometric measurements (weight, height, BMI, body composition, waist and hip circumference, SAT, VAT) and dietary intake were analyzed. The relationship between fat mass and VAT changes was examined using a differential equation.

RESULTS

Energy consumption decreased significantly in both study groups. The low fat groups decreased total dietary fat while the HPUFA groups increased PUFA intake significantly. All anthropometric measurements reduced significantly over time but there was no difference between the two dietary groups. The relationship between fat mass and visceral adipose tissue (VAT) loss was allometric.

CONCLUSION

A higher PUFA intake did not lead to greater fat mass loss and there was no additional preferential loss of VAT following higher PUFA consumption.

Dietary monounsaturated fatty acids but not saturated fatty acids preserve the insulin signaling pathway via IRS-1/PI3K in rat skeletal muscle

Saturated fatty acids (SFA) and monounsaturated fatty acids (MUFA) show different effects on the development of insulin resistance. In this study, we compared the effect of dietary SFA and MUFA on the insulin signaling pathway in the skeletal muscle of a type 2 diabetic animal model. Twenty-nine-week-old male Otsuka Long-Evans Tokushima fatty (OLETF) rats were randomly divided into three groups and fed one of the following diets for 3 weeks; a normal chow diet, an SFA (lard oil) enriched or a MUFA (olive oil) enriched high-fat diet. The vastus lateralis muscle was used for analyses. Insulin tolerance test showed improved insulin sensitivity in rats fed the MUFA diet, as compared to those fed the SFA diet (p < 0.001). The SFA diet reduced IRS-1 expression and phosphorylated PI3K levels in skeletal muscle, as compared with a chow diet (p < 0.001, respectively). On the contrary, muscle IRS-2 expression and phosphorylated ERK1/2 was significantly increased in rats fed the SFA diet (p < 0.001, respectively). Membrane translocation of glucose transporter type 4 decreased in the skeletal muscle of rats fed the SFA diet, as compared to those fed a chow diet (p < 0.001). These changes in insulin signaling pathway in skeletal muscle were not observed in rats fed the MUFA diet. In conclusion, the beneficial effect of dietary MUFA on insulin sensitivity is associated with a conserved IRS-1/PI3K insulin signaling pathway which was altered by dietary SFA.

The ω-3 and ω-6 fats in meals: a proposal for a simple new label

OBJECTIVE

The ω-3 and ω-6 polyunsaturated fatty acids (PUFAs) are separate essential dietary fatty acids that play a key role in many physiologic processes in higher animals. The content of these PUFAs is relatively well described for many individual food components. Our goal in this study was to analyze the PUFA content of whole meals and produce a simple measurement to estimate the intake of these fatty acids.

METHODS

The fatty acid profile and macronutrient composition were determined for a range of fast food, cuisine (restaurant-prepared), and home-prepared whole meals commonly consumed by Australians.

RESULTS

Across the different meals there was significant variation in protein (4-fold), fat (13-fold), and carbohydrate (23-fold) contents. With regard to the fatty acid profile, saturated and monounsaturated fatty acids made up approximately 80% of total fatty acids for most meals. The ω-6 PUFAs were substantially more abundant than ω-3 PUFAs for most meals. The balance of dietary ω-3 and ω-6 PUFAs is an important determinant of their metabolic effects within the body, and accordingly we calculated the percentage of the total PUFA comprised of ω-3 PUFAs and referred to this as the PUFA Balance. This parameter showed the greatest variation among the different meals (>45-fold).

CONCLUSION

The relative proportions of ω-3 and ω-6 PUFAs vary greatly across meals. PUFA Balance is a useful tool that will allow individuals to more easily monitor and balance their intake of ω-3 and ω-6 fats.