Plasma sphingolipids are biomarkers of metabolic syndrome in non-human primates maintained on a Western-style diet

Diet-Induced Obesity in the Rat Impairs Sphingolipid Metabolism in the Brain and This Metabolic Dysfunction Is Transmitted to the Offspring via Both the Maternal and the Paternal Lineage

Obesity leads to a number of health problems, including learning and memory deficits that can be passed on to the offspring via a developmental programming process. However, the mechanisms involved in the deleterious effects of obesity on cognition remain largely unknown. This study aimed to assess the impact of obesity on the production of sphingolipids (ceramides and sphingomyelins) in the brain and its relationship with the learning deficits displayed by obese individuals. We also sought to determine whether the effects of obesity on brain sphingolipid synthesis could be passed on to the offspring. Learning abilities and brain concentration of sphingolipids in male and female control and obese founder rats (F0) and their offspring (F1) were evaluated, respectively, by the novel object recognition test and by ultra-performance liquid chromatography tandem mass spectrometry. In addition, a global lipidome profiling of the cerebral cortex and hippocampus was performed. Both male and female F0 rats showed impaired learning and increased concentrations of ceramides and sphingomyelins in the hippocampus and frontal cortex compared to their control counterparts. However, the overall lipidome profile of these brain regions did not change with obesity. Remarkably, the alterations in brain sphingolipid synthesis, as well as the cognitive impairment induced by obesity, were also present in adult F1 male rats born to obese mothers or sired by obese fathers and were associated with enhanced expression of mRNAs coding for enzymes involved in the de novo synthesis of ceramides. These results show that the cognitive deficits and impaired sphingolipid metabolism induced by obesity can be transmitted to the offspring through both the maternal and paternal lineages and suggest that an increase in the brain concentration of sphingolipids could play a causal role in the cognitive deficits associated with obesity.

Combined diet and exercise training decreases serum lipids associated with insulin resistance

OBJECTIVE

Circulating lipids are linked with insulin resistance and increased cardiovascular disease risk. We previously reported that dihydroceramides, a specific type of sphingolipid, are elevated in insulin-resistant individuals; however, little is known regarding whether insulin-sensitizing lifestyle interventions can improve profiles of sphingolipids and other lipid species.

METHODS

A total of 21 individuals with obesity participated in a 3-month lifestyle intervention of combined weight loss and exercise training. Insulin sensitivity was assessed by hyperinsulinemic-euglycemic clamps, and serum lipidomics was conducted.

RESULTS

Following the intervention, BMI was significantly reduced by 10%; VO2peak and insulin sensitivity increased by 12% and 57%, respectively; and total serum triacylglycerol (TAG), diacylglycerol, dihydroceramides, sphingosine-1-phosphate, and sphinganine-1-phosphate were significantly reduced, as were specific species of dihydroceramides (C18:0 and C24:1). Individuals with higher preintervention TAG concentrations had significant decreases in serum lipids, which were not significantly changed in individuals with lower preintervention TAG.

CONCLUSIONS

These data show that serum sphingolipid species previously linked to insulin resistance in humans can be reduced with insulin-sensitizing lifestyle interventions. Furthermore, individuals with elevated serum TAG may significantly benefit from lifestyle interventions that increase insulin sensitivity due to a greater decrease in serum lipids related to insulin resistance.

Different time-restricted feeding patterns potentially modulate metabolic health by altering tryptophan metabolism of gut microbes in pigs

Time-restricted feeding has emerged as a preferred approach for alleviating metabolic disorders, but the potential microbiological mechanism remains poorly understood. This study used a growing pig model to mimic common-sense eating habits. Four feeding patterns were set up, including ad libitum feeding (ALF) for daily irregulated eating habits, time-restricted feeding (TRF) for three meals a day, early time-restricted feeding (eTRF) for skipping dinner and mid-day time-restricted feeding (mTRF) for skipping breakfast. The results showed that the three time-restricted feeding patterns (TRF, eTRF and mTRF) resulted in a reduction of hepatic fat accumulation and a decrease in hepatic function markers compared to the ALF pattern. However, this was independent of food consumption. Transcriptome analysis of the liver showed that the three time-restricted feeding patterns downregulated the expression of genes related to gluconeogenesis, β-oxidation, lipid accumulation, and urea cycle, and upregulated the expression of genes related to lipogenesis and glycolysis compared to the ALF pattern. Microbiome and metabolome analyses showed that Lactobacillus enriched in the colon of pigs in three time-restricted groups were negatively correlated with serum triglyceride. Meanwhile, three time-restricted feeding patterns elevated the levels of the microbial metabolite indole-3-lactic acid, which was further confirmed to reduce excessive hepatic lipid accumulation in vitro. Overall, time-restricted feeding potentially improved metabolic health by modulating gut microbiota and metabolites.

Ceramides as Biomarkers of Cardiovascular Diseases and Heart Failure

PURPOSE OF REVIEW

 Ceramides are lipid species that play several physiological roles in the body, including stress response, inflammation, and apoptosis, and their involvement in lipid metabolism and energy production makes them crucial in the pathophysiology of heart failure (HF).

RECENT FINDINGS

 Several species of ceramides and ceramide signatures have recently been investigated as possible biomarkers of cardiovascular disease (CVD), and risk scores have demonstrated prognostic value in stratifying patients by risk and possibly predicting adverse cardiac events. With growing interest in targeting metabolic dysfunction, understanding the role of ceramides in CVD also opens the possibility of novel therapeutics that target ceramide metabolism to improve cardiac function and cardiac outcomes in patients.  Understanding the role of ceramides in CVD opens the possibility of novel diagnostics and theragnostic targeting ceramide metabolism to improve cardiac function and cardiac outcomes in patients with heart failure.

Ceramides-Emerging Biomarkers of Lipotoxicity in Obesity, Diabetes, Cardiovascular Diseases, and Inflammation

Abnormalities in lipid homeostasis have been associated with many human diseases, and the interrelation between lipotoxicity and cellular dysfunction has received significant attention in the past two decades. Ceramides (Cers) are bioactive lipid molecules that serve as precursors of all complex sphingolipids. Besides their function as structural components in cell and mitochondrial membranes, Cers play a significant role as key mediators in cell metabolism and are involved in numerous cellular processes, such as proliferation, differentiation, inflammation, and induction of apoptosis. The accumulation of various ceramides in tissues causes metabolic and cellular disturbances. Recent studies suggest that Cer lipotoxicity has an important role in obesity, metabolic syndrome, type 2 diabetes, atherosclerosis, and cardiovascular diseases (CVDs). In humans, elevated plasma ceramide levels are associated with insulin resistance and impaired cardiovascular and metabolic health. In this review, we summarize the role of ceramides as key mediators of lipotoxicity in obesity, diabetes, cardiovascular diseases, and inflammation and their potential as a promising diagnostic tool.

Ceramides are fuel gauges on the drive to cardiometabolic disease

Ceramides are signals of fatty acid excess that accumulate when a cell's energetic needs have been met and its nutrient storage has reached capacity. As these sphingolipids accrue, they alter the metabolism and survival of cells throughout the body including in the heart, liver, blood vessels, skeletal muscle, brain, and kidney. These ceramide actions elicit the tissue dysfunction that underlies cardiometabolic diseases such as diabetes, coronary artery disease, metabolic-associated steatohepatitis, and heart failure. Here, we review the biosynthesis and degradation pathways that maintain ceramide levels in normal physiology and discuss how the loss of ceramide homeostasis drives cardiometabolic pathologies. We highlight signaling nodes that sense small changes in ceramides and in turn reprogram cellular metabolism and stimulate apoptosis. Finally, we evaluate the emerging therapeutic utility of these unique lipids as biomarkers that forecast disease risk and as targets of ceramide-lowering interventions that ameliorate disease.

Liraglutide reduces plasma dihydroceramide levels in patients with type 2 diabetes

BACKGROUND

Emerging evidence supports that dihydroceramides (DhCer) and ceramides (Cer) contribute to the pathophysiology of insulin resistance and liver steatosis, and that their circulating concentrations are independently associated with cardiovascular outcomes. Circulating DhCer levels are increased in patients with type 2 diabetes (T2D). On the other hand, the GLP-1 receptor agonist liraglutide reduces major adverse cardiac events, insulin resistance and liver steatosis in T2D patients. The main purpose of the present study was therefore to investigate whether liraglutide decreases circulating levels of DhCer and Cer in T2D patients, which could be a mechanism involved in its cardiometabolic benefits. The secondary purpose was to assess the relationship between liraglutide-induced changes in DhCer/Cer levels and insulin resistance and liver steatosis.

METHODS

Plasma concentrations of 11 DhCer and 15 Cer species were measured by a highly-sensitive mass spectrometry system in 35 controls and 86 T2D patients before and after 6 months of liraglutide (1.2 mg/day). Insulin resistance was estimated by the triglyceride-glucose (TyG) index. Liver fat content (LFC) was assessed in 53 patients by proton magnetic resonance spectroscopy.

RESULTS

Plasma levels of total DhCer, 7 DhCer and 7 Cer species were increased in T2D patients compared to controls. Liraglutide decreased total DhCer by 15.1% (p = 0.005), affecting 16:0 (p = 0.037), 18:0 (p < 0.0001), 18:1 (p = 0.0005), 20:0 (p = 0.0003), 23:0 (p = 0.005) and 24:1 (p = 0.04) species. Total plasma Cer did not significantly change after liraglutide (p = 0.18), but 5 Cer species decreased significantly, i.e. 18:0 and 18:1 (both p < 0.0001), 19:0 and 24:1 (both p < 0.01) and 26:1 (p = 0.04). In multivariate analysis, the reduction in DhCer after liraglutide was independently associated with the reduction in LFC (p = 0.0005) and in TyG index (p = 0.05).

CONCLUSIONS

Liraglutide reduces plasma levels of numerous DhCer and Cer species in T2D patients, which may contribute to the cardiovascular benefit observed in the LEADER trial. The independent association between the decrease in plasma DhCer level with the reduction in LFC and TyG index adds new insights regarding the relationship between DhCer, liver steatosis and insulin resistance. Trial registration ClinicalTrials.gov identifier: NCT02721888.

Fenretinide inhibits obesity and fatty liver disease but induces Smpd3 to increase serum ceramides and worsen atherosclerosis in LDLR-/- mice

Fenretinide is a synthetic retinoid that can prevent obesity and improve insulin sensitivity in mice by directly altering retinol/retinoic acid homeostasis and inhibiting excess ceramide biosynthesis. We determined the effects of Fenretinide on LDLR-/- mice fed high-fat/high-cholesterol diet ± Fenretinide, a model of atherosclerosis and non-alcoholic fatty liver disease (NAFLD). Fenretinide prevented obesity, improved insulin sensitivity and completely inhibited hepatic triglyceride accumulation, ballooning and steatosis. Moreover, Fenretinide decreased the expression of hepatic genes driving NAFLD, inflammation and fibrosis e.g. Hsd17b13, Cd68 and Col1a1. The mechanisms of Fenretinide's beneficial effects in association with decreased adiposity were mediated by inhibition of ceramide synthesis, via hepatic DES1 protein, leading to increased dihydroceramide precursors. However, Fenretinide treatment in LDLR-/- mice enhanced circulating triglycerides and worsened aortic plaque formation. Interestingly, Fenretinide led to a fourfold increase in hepatic sphingomyelinase Smpd3 expression, via a retinoic acid-mediated mechanism and a further increase in circulating ceramide levels, linking induction of ceramide generation via sphingomyelin hydrolysis to a novel mechanism of increased atherosclerosis. Thus, despite beneficial metabolic effects, Fenretinide treatment may under certain circumstances enhance the development of atherosclerosis. However, targeting both DES1 and Smpd3 may be a novel, more potent therapeutic approach for the treatment of metabolic syndrome.

The Impact of Phytochemicals in Obesity-Related Metabolic Diseases: Focus on Ceramide Metabolism

The prevalence of obesity and related metabolic diseases has increased dramatically worldwide. As obesity progresses, various lipid species accumulate in ectopic tissues. Amongst them, ceramides-a deleterious sphingolipid species-accumulate and cause lipotoxicity and metabolic disturbances. Dysregulated ceramide metabolism appears to be a key feature in the pathogenesis of obesity-related metabolic diseases. Notably, dietary modification might have an impact on modulating ceramide metabolism. Phytochemicals are plant-derived compounds with various physiological properties, which have been shown to protect against obesity-related metabolic diseases. In this review, we aim to examine the impact of a myriad of phytochemicals and their dietary sources in altering ceramide deposition and ceramide-related metabolism from in vitro, in vivo, and human clinical/epidemiological studies. This review discusses how numerous phytochemicals are able to alleviate ceramide-induced metabolic defects and reduce the risk of obesity-related metabolic diseases via diverse mechanisms.

Serum dihydroceramides correlate with insulin sensitivity in humans and decrease insulin sensitivity in vitro

Serum ceramides, especially C16:0 and C18:0 species, are linked to CVD risk and insulin resistance, but details of this association are not well understood. We performed this study to quantify a broad range of serum sphingolipids in individuals spanning the physiologic range of insulin sensitivity and to determine if dihydroceramides cause insulin resistance in vitro. As expected, we found that serum triglycerides were significantly greater in individuals with obesity and T2D compared with athletes and lean individuals. Serum ceramides were not significantly different within groups but, using all ceramide data relative to insulin sensitivity as a continuous variable, we observed significant inverse relationships between C18:0, C20:0, and C22:0 species and insulin sensitivity. Interestingly, we found that total serum dihydroceramides and individual species were significantly greater in individuals with obesity and T2D compared with athletes and lean individuals, with C18:0 species showing the strongest inverse relationship to insulin sensitivity. Finally, we administered a physiological mix of dihydroceramides to primary myotubes and found decreased insulin sensitivity in vitro without changing the overall intracellular sphingolipid content, suggesting a direct effect on insulin resistance. These data extend what is known regarding serum sphingolipids and insulin resistance and show the importance of serum dihydroceramides to predict and promote insulin resistance in humans.

The sphingolipidome of plasma, liver, and adipose tissues and its association with insulin response to oral glucose testing in Icelandic horses

Insulin dysregulation (ID) is a determinant of equine metabolic syndrome. Among the sphingolipids, ceramides contribute to the development of ID; however, the crosstalk between the liver and adipose tissue (AT) depots and the variation among AT depots in terms of ceramide metabolism are not well-understood. We aimed to characterize the sphingolipidome of plasma, liver, and AT (nuchal, NUAT; subcutaneous, SCAT; omental, OMAT; retroperitoneal, RPAT) and their associations with insulin response to oral glucose testing (OGT) in normoinsulinemic and hyperinsulinemic horses. Plasma, liver, and AT samples were collected from 12 Icelandic horses upon euthanasia and analyzed by liquid chromatography-mass spectrometry. Eighty-four targeted compounds were effectively quantified. Comparing the AT depots, greater (FDR < 0.05) ceramide, dihydroceramide, and sphingomyelin concentrations and lower glucosyl- and galactosyl-ceramides were found in RPAT and OMAT than in NUAT and SCAT. Hyperinsulinemic response to OGT was associated with sphingolipidome alterations primarily in the RPAT and OMAT, while the NUAT sphingolipidome did not show signs of ceramide accumulation, which was inconsistent with the previously proposed role of nuchal adiposity in ID. The plasma sphingolipidome was not significantly associated with the liver or AT sphingolipidomes, indicating that plasma profiles are determined by an interplay of various organs. Further, hepatic sphingolipid profiles were not correlated with the profiles of AT depots. Finally, statistically valid partial least square regression models predicting insulin response were found in the plasma (Q²= 0.58, R²= 0.98), liver (Q²= 0.64, R²= 0.74), and RPAT (Q²= 0.68, R²= 0.79) sphingolipidome, but not in the other adipose tissues.

Sphingomyelin profiling in patients with diabetes could be potentially useful as differential diagnostics biomarker: A pilot study

PURPOSE

Autoimmune diabetes (AD) in adults includes both the classical form of type 1 diabetes mellitus (T1DM) and latent autoimmune diabetes in adults (LADA). LADA shares clinical and metabolic features with type 1 and type 2 diabetes mellitus (T2DM). Ceramide (Cer) levels negatively correlate with insulin sensitivity in humans and animal models. However, only a few studies have focused on other sphingolipids, including sphingomyelin (SM). Therefore, we determined sphingolipids in patients with newly diagnosed diabetes as possible diagnostic biomarkers.

MATERIALS AND METHODS

We evaluated sphingolipids in a cohort of 59 adults with newly diagnosed diabetes without prior hypoglycemic pharmacotherapy to distinguish diabetes mellitus types and for precise LADA definition. All patients with newly diagnosed diabetes were tested for the concentrations of individual Cer and SM species by gas-liquid chromatography. The study included healthy controls and patients with T1DM, T2DM and LADA.

RESULTS

SM species were significantly altered in patients with newly diagnosed diabetes compared to healthy controls. SM-C16:0, C16:1, -C18:0, -C18:1, -C18:2, -C18:3, -C20:4, and -C22:6 species were found to be significantly elevated in LADA patients. In contrast, significant differences were observed for Cer species with saturated acyl chains, especially Cer-C14:0, -C16:0, -C18:0 (AD and T2DM), -C22:0, and -C24:0 (T1DM). Following ROC analysis, SM-C16:0, and particularly -C18:1, and -C20:4 may be supportive diagnostic markers for LADA.

CONCLUSION

SM profiling in patients with newly diagnosed diabetes could be potentially helpful for differential diagnosis of LADA, T1DM, and T2DM in more challenging cases.

Ceramides are early responders in metabolic syndrome development in rhesus monkeys

Metabolic syndrome increases risk of complicating co-morbidities. Current clinical indicators reflect established metabolic impairment, preventing earlier intervention strategies. Here we show that circulating sphingolipids are altered in the very early stages of insulin resistance development. The study involved 16 paired overweight but healthy monkeys, one-half of which spontaneously developed metabolic syndrome over the course of 2 years. Importantly, animals did not differ in adiposity and were euglycemic throughout the study period. Using mass spectrometry, circulating sphingolipids, including ceramides and sphingomyelins, were detected and quantified for healthy and impaired animals at both time points. At time of diagnosis, several ceramides were significantly different between healthy and impaired animals. Correlation analysis revealed differences in the interactions among ceramides in impaired animals at diagnosis and pre-diagnosis when animals were clinically indistinguishable from controls. Furthermore, correlations between ceramides and early-stage markers of insulin resistance, diacylglycerols and non-esterified fatty acids, were distinct for healthy and impaired states. Regression analysis identifies coordinated changes in lipid handling across lipid classes as animals progress from healthy to insulin resistant. Correlations between ceramides and the adipose-derived adipokine adiponectin were apparent in healthy animals but not in the metabolically impaired animals, even in advance of loss in insulin sensitivity. These data suggest that circulating ceramides are clinically relevant in identifying disease risk independent of differences in adiposity, and may be important in devising preventative strategies.

The Endocannabinoid System and Physical Activity—A Robust Duo in the Novel Therapeutic Approach against Metabolic Disorders

Rapidly increasing worldwide prevalence of obesity and related pathologies encompassing coronary heart disease, hypertension, metabolic syndrome, or type 2 diabetes constitute serious threats to global health and are associated with a significantly elevated risk of premature death. Considering the enormous burden of these pathologies, novel therapeutic and preventive patterns are indispensable. Dysregulation of one of the most complex biological systems in the human body namely, the endocannabinoid system (ECS) may result in metabolic imbalance and development of insulin resistance, type 2 diabetes, or non-alcoholic fatty liver disease. Furthermore, many studies showed that physical exercises, depending on their type, intensity, and frequency, exert various alterations within the ECS. Emerging evidence suggests that targeting the ECS via physical activity may produce robust beneficial effects on the course of metabolic pathologies. However, the data showing a direct correlation between the ECS and physical activity in the aspect of metabolic health are very scarce. Therefore, the aim of this review was to provide the most up-to-date state of knowledge about the interplay between the ECS activity and physical exercises in the novel therapeutic and preventive approach toward metabolic pathologies. We believe that this paper, at least in part, will fulfill the existing gap in knowledge and encourage researchers to further explore this very complex yet interesting link between the ECS, its action in physical activity, and subsequent positive outcomes for metabolic health.

1-Deoxysphinganine initiates adaptive responses to serine and glycine starvation in cancer cells via proteolysis of sphingosine kinase

Cancer cells may depend on exogenous serine, depletion of which results in slower growth and activation of adaptive metabolic changes. We previously demonstrated that serine and glycine (SG) deprivation causes loss of sphingosine kinase 1 (SK1) in cancer cells, thereby increasing the levels of its lipid substrate, sphingosine (Sph), which mediates several adaptive biological responses. However, the signaling molecules regulating SK1 and Sph levels in response to SG deprivation have yet to be defined. Here, we identify 1-deoxysphinganine (dSA), a noncanonical sphingoid base generated in the absence of serine from the alternative condensation of alanine and palmitoyl CoA by serine palmitoyl transferase, as a proximal mediator of SG deprivation in SK1 loss and Sph level elevation upon SG deprivation in cancer cells. SG starvation increased dSA levels in vitro and in vivo and in turn induced SK1 degradation through a serine palmitoyl transferase-dependent mechanism, thereby increasing Sph levels. Addition of exogenous dSA caused a moderate increase in intracellular reactive oxygen species, which in turn decreased pyruvate kinase PKM2 activity while increasing phosphoglycerate dehydrogenase levels, and thereby promoted serine synthesis. We further showed that increased dSA induces the adaptive cellular and metabolic functions in the response of cells to decreased availability of serine likely by increasing Sph levels. Thus, we conclude that dSA functions as an initial sensor of serine loss, SK1 functions as its direct target, and Sph functions as a downstream effector of cellular and metabolic adaptations. These studies define a previously unrecognized "physiological" nontoxic function for dSA.

Lipid Metabolism Disorders in the Comorbid Course of Nonalcoholic Fatty Liver Disease and Chronic Obstructive Pulmonary Disease

Non-alcoholic fatty liver disease (NAFLD) is currently among the most common liver diseases. Unfavorable data on the epidemiology of metabolic syndrome and obesity have increased the attention of clinicians and researchers to the problem of NAFLD. The research results allow us to emphasize the systemicity and multifactoriality of the pathogenesis of liver parenchyma lesion. At the same time, many aspects of its classification, etiology, and pathogenesis remain controversial. Local and systemic metabolic disorders are also a part of the pathogenesis of chronic obstructive pulmonary disease and can influence its course. The present article analyzes the metabolic pathways mediating the links of impaired lipid metabolism in NAFLD and chronic obstructive pulmonary disease (COPD). Free fatty acids, cholesterol, and ceramides are involved in key metabolic and inflammatory pathways underlying the pathogenesis of both diseases. Moreover, inflammation and lipid metabolism demonstrate close links in the comorbid course of NAFLD and COPD.

Sanye Tablet Ameliorates Insulin Resistance and Dysregulated Lipid Metabolism in High-Fat Diet-Induced Obese Mice

Sanye Tablet (SYT) is a patent prescription widely used in treating T2D and pre-diabetes, especially T2D comorbid with hypertriglyceridemia, for many years in China. However, the underlying mechanism that accounts for the anti-diabetic potential of SYT by regulating lipid-related intermediates remains to be elucidated. This study aimed to investigate the mechanism of SYT on lipid metabolism and insulin sensitivity in high-fat diet (HFD)-induced obese mice by means of combining lipidomics and proteomics. The obese mice models were developed via HFD feeding for 20 consecutive weeks. Mice in the treatment group were given metformin and SYT respectively, and the effects of SYT on body weight, blood glucose, insulin sensitivity, fat accumulation in the organs, and pathological changes in the liver were monitored. Lipid metabolism was examined by lipidomics. Further determination of signaling pathways was detected by proteomics. The biological contributions of the compounds detected in SYT’s chemical fingerprint were predicted by network pharmacology. SYT treatment reduced body weight, inhibited viscera and hepatic steatosis lipid accumulation, and prevented insulin resistance. Furthermore, it was found that circulatory inflammatory cytokines were reduced by SYT treatment. In addition, lipidomics analysis indicated that SYT targets lipid intermediates, including diacylglycerol (DAG) and Ceramide (Cer). Mechanistically, SYT positively affected these lipid intermediates by suppressing liver lipogenesis via downregulation of SREBP1/ACC and the JAK/STAT signaling pathway. Our results predicted that astragalin and rosmarinic acid might regulate the JAK-STAT pathway by targeting PIM2 and STAT1, respectively, while paeoniflorin and rosmarinic acid were likely to regulate inflammatory responses by targeting TNFα, IL-6, and IL-4 during T2D. Overall, our study provides supportive evidence for the mechanism of SYT’s therapeutic effect on dysregulated lipid metabolism in diabesity.

Cannabidiol - A phytocannabinoid that widely affects sphingolipid metabolism under conditions of brain insulin resistance

Obesity-related insulin resistance (IR) and attenuated brain insulin signaling are significant risk factors for neurodegenerative disorders, e.g., Alzheimer's disease. IR and type 2 diabetes correlate with an increased concentration of sphingolipids, a class of lipids that play an essential structural role in cellular membranes and cell signaling pathways. Cannabidiol (CBD) is a nonpsychoactive constituent of Cannabis sativa plant that interacts with the endocannabinoidome. Despite known positive effects of CBD on improvement in diabetes and its aftermath, e.g., anti-inflammatory and anti-oxidant effects, there are no studies evaluating the effect of phytocannabinoids on the brain insulin resistance and sphingolipid metabolism. Our experiment was carried out on Wistar rats that received a high-fat diet and/or intraperitoneal CBD injections. In our study, we indicated inhibition of de novo synthesis and salvage pathways, which resulted in significant changes in the concentration of sphingolipids, e.g., ceramide and sphingomyelin. Furthermore, we observed reduced brain IR and decreased tau protein phosphorylation what might be protective against neuropathologies development. We believe that our research will concern a new possible therapeutic approach with Cannabis -plant derived compounds and within a few years, cannabinoids would be considered as prominent substances for targeting both metabolic and neurodegenerative pathologies.

Lipid regulation of NLRP3 inflammasome activity through organelle stress

Inflammation driven by the NLRP3 inflammasome in macrophages is an important contributor to chronic metabolic diseases that affect growing numbers of individuals. Many of these diseases involve the pathologic accumulation of endogenous lipids or their oxidation products, which can activate NLRP3. Other endogenous lipids, however, can inhibit the activation of NLRP3. The intracellular mechanisms by which these lipids modulate NLRP3 activity are now being identified. This review discusses emerging evidence suggesting that organelle stress, particularly involving mitochondria, lysosomes, and the endoplasmic reticulum, may be key in lipid-induced modification of NLRP3 inflammasome activity.

Unwrapping the mechanisms of ceramide and fatty acid-initiated signals leading to immune-inflammatory responses in obesity

Obesity is considered a global epidemic developed in part as a consequence of the overconsumption of high fat diets. One of the main negative outcomes of obesity is the development of low-grade chronic systemic inflammation, induced by dysregulated immune responses, which can lead to multiple obesity-related diseases. Ceramides are a group of bioactive lipids known to be elevated in obesity and obesity-associated conditions, including cardiovascular disease and type II diabetes. Ceramides may be key players in promoting an obesity-induced inflammatory environment due to their ability to activate key pathways such as Toll-like receptor 4 (TLR4) and NLR pyrin domain containing receptor 3 (Nlrp3), while studies have shown that inhibition of ceramide synthesis gives rise to an anti-inflammatory environment. N-3 polyunsaturated fatty acids (n-3 PUFA) have been of interest due to their anti-inflammatory actions and shown to have beneficial effects in obesity-related diseases. This review will highlight the impact of ceramides in promoting an obesity-induced inflammatory microenvironment and discuss how n-3 PUFA could potentially counteract these responses and have a regulatory effect promoting immune homeostasis.

The Impact of Dietary Sphingolipids on Intestinal Microbiota and Gastrointestinal Immune Homeostasis

The large surfaces of gastrointestinal (GI) organs are well adapted to their diverse tasks of selective nutritional uptake and defense against the external environment. To maintain a functional balance, a vast number of immune cells is located within the mucosa. A strictly regulated immune response is required to impede constant inflammation and to maintain barrier function. An increasing prevalence of GI diseases has been reported in Western societies over the past decades. This surge in GI disorders has been linked to dietary changes followed by an imbalance of the gut microbiome, leading to a chronic, low grade inflammation of the gut epithelium. To counteract the increasing health care costs associated with diseases, it is paramount to understand the mechanisms driving immuno-nutrition, the associations between nutritional compounds, the commensal gut microbiota, and the host immune response. Dietary compounds such as lipids, play a central role in GI barrier function. Bioactive sphingolipids (SLs), e.g. sphingomyelin (SM), sphingosine (Sph), ceramide (Cer), sphingosine-1- phosphate (S1P) and ceramide-1-phosphate (C1P) may derive from dietary SLs ingested through the diet. They are not only integral components of cell membranes, they additionally modulate cell trafficking and are precursors for mediators and second messenger molecules. By regulating intracellular calcium levels, cell motility, cell proliferation and apoptosis, SL metabolites have been described to influence GI immune homeostasis positively and detrimentally. Furthermore, dietary SLs are suggested to induce a shift in the gut microbiota. Modes of action range from competing with the commensal bacteria for intestinal cell attachment to prevention from pathogen invasion by regulating innate and immediate defense mechanisms. SL metabolites can also be produced by gut microorganisms, directly impacting host metabolic pathways. This review aims to summarize recent findings on SL signaling and functional variations of dietary SLs. We highlight novel insights in SL homeostasis and SL impact on GI barrier function, which is directly linked to changes of the intestinal microbiota. Knowledge gaps in current literature will be discussed to address questions relevant for understanding the pivotal role of dietary SLs on chronic, low grade inflammation and to define a balanced and healthy diet for disease prevention and treatment.

Lipid profile disturbances may predispose psoriatic patients to liver dysfunction

INTRODUCTION

Psoriasis is a chronic inflammatory disease associated with metabolic disturbances and liver dysfunction. Both serum fatty acids (FA) and ceramides (Cer) have structural functions but also are signal molecules that could be involved in the pathogenesis of liver dysfunction.

AIM

To assess the concentration of the circulating FA and Cer in correlation with the alanine aminotransferase (ALT) blood level in psoriatic patients. In addition, we have examined the relationship between ALT concentration and severity of the disease and inflammation markers.

MATERIAL AND METHODS

Eighty-five patients with psoriasis and 32 healthy controls were enrolled in the study. Patients were divided into 2 groups according to ALT blood levels. Serum concentration of 14 FA and 14 Cer were measured by gas-liquid chromatography. The results were correlated with the Psoriasis Area and Severity Index (PASI), serum lipid profile, and inflammatory markers.

RESULTS

We observed higher PASI score (p = 0.01) and higher C-reactive protein (p = 0.02) concentration in the group of psoriatic patients with high ALT. Serum ALT positively correlated with saturated fatty acids (SFA) (p = 0.01, r = 0.27) and SFA/unsaturated fatty acids (UFA) ratio (p = 0.01, r = 0.26). ALT negatively correlated with UFA level (p = 0.008, r = -0.28). Lignoceric ceramide positively correlated with ALT level (r = 0.22; p = 0.045) in psoriatic patients.

CONCLUSIONS

Patients with severe psoriasis are predisposed to the development of liver dysfunction. We have demonstrated disturbances of serum fatty acid and sphingolipid profile in psoriatic patients, which may trigger liver disease.

Dihydroceramides: their emerging physiological roles and functions in cancer and metabolic diseases

Dihydroceramides (DhCers) are a type of sphingolipids that for a long time were regarded as biologically inactive. They are metabolic intermediates of the de novo sphingolipid synthesis pathway, and are converted into ceramides (Cers) with the addition of a double bond. Ceramides are abundant in tissues and have well-established biological functions. On the contrary, dihydroceramides are less prevalent, and despite their hitherto characterization as inert lipids, studies of the past decade began to unravel their implication in various biological processes distinct from those involving ceramides. These processes include cellular stress responses and autophagy, cell growth, pro-death or pro-survival pathways, hypoxia, and immune responses. In addition, their plasma concentration has been related to metabolic diseases and shown as a long-term predictor of type 2 diabetes onset. They are thus important players and potential biomarkers in pathologies ranging from diabetes to cancer and neurodegenerative diseases. The purpose of this mini-review is to highlight the emergence of dihydroceramides as a new class of bioactive sphingolipids by reporting recent advances on their biological characterization and pathological implications, focusing on cancer and metabolic diseases.

Circulating Ceramides- Are Origins Important for Sphingolipid Biomarkers and Treatments?

Biomarkers are important tools for describing the adequacy or inadequacy of biological processes (to allow for the early and accurate diagnosis) and monitoring the biological effects of intervention strategies (to identify and develop optimal dose and treatment strategies). A number of lipid biomarkers are implicated in metabolic disease and the circulating levels of these biomarkers are used in clinical settings to predict and monitor disease severity. There is convincing evidence that specific circulating ceramide species can be used as biological predictors and markers of cardiovascular disease, atherosclerosis and type 2 diabetes mellitus. Here, we review the existing literature that investigated sphingolipids as biomarkers for metabolic disease prediction. What are the advantages and disadvantages? Are circulating ceramides predominantly produced in the liver? Will hepatic sphingolipid inhibitors be able to completely prevent and treat metabolic disease? As sphingolipids are being employed as biomarkers and potential metabolic disease treatments, we explore what is currently known and what still needs to be discovered.

Dihydroceramides in Triglyceride-Enriched VLDL Are Associated with Nonalcoholic Fatty Liver Disease Severity in Type 2 Diabetes

Plasma dihydroceramides are predictors of type 2 diabetes and related to metabolic dysfunctions, but the underlying mechanisms are not characterized. We compare the relationships between plasma dihydroceramides and biochemical and hepatic parameters in two cohorts of diabetic patients. Hepatic steatosis, steatohepatitis, and fibrosis are assessed by their plasma biomarkers. Plasma lipoprotein sphingolipids are studied in a sub-group of diabetic patients. Liver biopsies from subjects with suspected non-alcoholic fatty liver disease are analyzed for sphingolipid synthesis enzyme expression. Dihydroceramides, contained in triglyceride-rich very-low-density lipoprotein (VLDL), are associated with steatosis and steatohepatitis. Expression of sphingolipid synthesis enzymes is correlated with histological steatosis and inflammation grades. In conclusion, association of plasma dihydroceramides with nonalcoholic fatty liver might explain their predictive character for type 2 diabetes. Our results suggest a relationship between hepatic sphingolipid metabolism and steatohepatitis and an involvement of dihydroceramides in the synthesis/secretion of triglyceride-rich VLDL, a hallmark of NAFLD and type 2 diabetes dyslipidemia.

Plasma dihydroceramides are associated with NAFLD severity in type 2 diabetic patients

Plasma dihydroceramides are found in triglyceride-enriched VLDL

A role for dihydroceramide in triglyceride-rich VLDL synthesis/secretion is suggested

Expression of enzymes of hepatic sphingolipid synthesis increases with NAFLD severity

Sample Preparation Methods for Lipidomics Approaches Used in Studies of Obesity

Obesity is associated with alterations in the composition and amounts of lipids. Lipids have over 1.7 million representatives. Most lipid groups differ in composition, properties and chemical structure. These small molecules control various metabolic pathways, determine the metabolism of other compounds and are substrates for the syntheses of different derivatives. Recently, lipidomics has become an important branch of medical/clinical sciences similar to proteomics and genomics. Due to the much higher lipid accumulation in obese patients and many alterations in the compositions of various groups of lipids, the methods used for sample preparations for lipidomic studies of samples from obese subjects sometimes have to be modified. Appropriate sample preparation methods allow for the identification of a wide range of analytes by advanced analytical methods, including mass spectrometry. This is especially the case in studies with obese subjects, as the amounts of some lipids are much higher, others are present in trace amounts, and obese subjects have some specific alterations of the lipid profile. As a result, it is best to use a method previously tested on samples from obese subjects. However, most of these methods can be also used in healthy, nonobese subjects or patients with other dyslipidemias. This review is an overview of sample preparation methods for analysis as one of the major critical steps in the overall analytical procedure.

Ceramides in Metabolism: Key Lipotoxic Players

The global prevalence of metabolic diseases such as type 2 diabetes mellitus, steatohepatitis, myocardial infarction, and stroke has increased dramatically over the past two decades. These obesity-fueled disorders result, in part, from the aberrant accumulation of harmful lipid metabolites in tissues not suited for lipid storage (e.g., the liver, vasculature, heart, and pancreatic beta-cells). Among the numerous lipid subtypes that accumulate, sphingolipids such as ceramides are particularly impactful, as they elicit the selective insulin resistance, dyslipidemia, and ultimately cell death that underlie nearly all metabolic disorders. This review summarizes recent findings on the regulatory pathways controlling ceramide production, the molecular mechanisms linking the lipids to these discrete pathogenic events, and exciting attempts to develop therapeutics to reduce ceramide levels to combat metabolic disease.

Metabolic shift favoring C18:0 ceramide accumulation in obese asthma

BACKGROUND

Obesity associated with various complications has increased worldwide. Body weight gain alters lipid metabolites (especially sphingolipids) contributing to obesity-induced inflammation. However, the significance of the metabolites in the development of obese asthma is not yet clear.

METHODS

The serum levels of sphingolipids were measured using liquid chromatography-tandem mass spectrometry in obese controls (n = 7) and patients with asthma: the obese group (BMI > 25 kg/m² , n = 13) vs the nonobese (n = 28) group. To examine the relationship between metabolic changes in sphingolipids and macrophage polarization, public microarray data were analyzed. In addition, the alteration in sphingolipid metabolism was investigated in wild-type BALB/c mice fed a high-fat diet.

RESULTS

The obese asthma had higher levels of serum C18:0 and C20:0 ceramides than the nonobese asthma group (P = .028 and P = .040, respectively). The value of the serum C18:0 ceramide (184.3 ng/mL) for discriminating the obese asthma from the nonobese asthma group showed 53.9% sensitivity and 85.7% specificity (AUC = 0.721, P = .024). The microarray data showed significantly increased ceramide synthesis and metabolic shift to ceramide accumulation during M1 macrophage polarization in humans. Increased airway hyperresponsiveness, M1 macrophage polarization, and C18:0 ceramide levels were noted in obese mice, but not in nonobese mice. Increased expression of ceramide synthase (CerS) 1 and CerS6 (not CerS2) was noted in lung tissues of obese mice.

CONCLUSION

Alteration in sphingolipid metabolism favoring ceramide accumulation (especially long-chain ceramides) may contribute to developing obese asthma.

The Role of Ceramides in Diabetes and Cardiovascular Disease Regulation of Ceramides by Adipokines

Metabolic dysfunction is intertwined with the pathophysiology of both diabetes and cardiovascular disease. Recently, one particular lipid class has been shown to influence the development and sustainment of these diseases: ceramides. As a subtype of sphingolipids, these species are particularly central to many sphingolipid pathways. Increased levels of ceramides are known to correlate with impaired cardiovascular and metabolic health. Furthermore, the interaction between ceramides and adipokines, most notably adiponectin and leptin, appears to play a role in the pathophysiology of these conditions. Adiponectin appears to counteract the detrimental effects of elevated ceramides, largely through activation of the ceramidase activity of its receptors. Elevated ceramides appear to worsen leptin resistance, which is an important phenomenon in the pathophysiology of obesity and metabolic syndrome.

Altered Metabolome of Lipids and Amino Acids Species: A Source of Early Signature Biomarkers of T2DM

Diabetes mellitus, a disease of modern civilization, is considered the major mainstay of mortalities around the globe. A great number of biochemical changes have been proposed to occur at metabolic levels between perturbed glucose, amino acid, and lipid metabolism to finally diagnoe diabetes mellitus. This window period, which varies from person to person, provides us with a unique opportunity for early detection, delaying, deferral and even prevention of diabetes. The early detection of hyperglycemia and dyslipidemia is based upon the detection and identification of biomarkers originating from perturbed glucose, amino acid, and lipid metabolism. The emerging “OMICS” technologies, such as metabolomics coupled with statistical and bioinformatics tools, proved to be quite useful to study changes in physiological and biochemical processes at the metabolic level prior to an eventual diagnosis of DM. Approximately 300–400 such metabolites have been reported in the literature and are considered as predicting or risk factor-reporting metabolic biomarkers for this metabolic disorder. Most of these metabolites belong to major classes of lipids, amino acids and glucose. Therefore, this review represents a snapshot of these perturbed plasma/serum/urinary metabolic biomarkers showing a significant correlation with the future onset of diabetes and providing a foundation for novel early diagnosis and monitoring the progress of metabolic syndrome at early symptomatic stages. As most metabolites also find their origin from gut microflora, metabolism and composition of gut microflora also vary between healthy and diabetic persons, so we also summarize the early changes in the gut microbiome which can be used for the early diagnosis of diabetes.

Use of preclinical models to identify markers of type 2 diabetes susceptibility and novel regulators of insulin secretion - A step towards precision medicine

BACKGROUND

Progression from pre-diabetes to type 2 diabetes (T2D) and from T2D to insulin requirement proceeds at very heterogenous rates among patient populations, and the risk of developing different types of secondary complications is also different between patients. The diagnosis of pre-diabetes and T2D solely based on blood glucose measurements cannot capture this heterogeneity, thereby preventing proposition of therapeutic strategies adapted to individual needs and pathogenetic mechanisms. There is, thus, a need to identify novel means to stratify patient populations based on a molecular knowledge of the diverse underlying causes of the disease. Such knowledge would form the basis for a precision medicine approach to preventing and treating T2D according to the need of identified patient subgroups as well as allowing better follow up of pharmacological treatment.

SCOPE OF REVIEW

Here, we review a systems biology approach that aims at identifying novel biomarkers for T2D susceptibility and identifying novel beta-cell and insulin target tissue genes that link the selected plasma biomarkers with insulin secretion and insulin action. This work was performed as part of two Innovative Medicine Initiative projects. The focus of the review will be on the use of preclinical models to find biomarker candidates for T2D prediction and novel regulators of beta-cell function. We will demonstrate that the study of mice with different genetic architecture and widely different adaptation to metabolic stress can be a powerful approach to identify biomarkers of T2D susceptibility in humans or for the identification of so far unrecognized genes controlling beta-cell function.

MAJOR CONCLUSIONS

The examples developed in this review will highlight the power of the systems biology approach, in particular as it allowed the discovery of dihydroceramide as a T2D biomarker candidate in mice and humans and the identification and characterization of novel regulators of beta-cell function.

Cumulative sugar-sweetened beverage consumption is associated with higher concentrations of circulating ceramides in the Framingham Offspring Cohort

BACKGROUND

Ceramides have been implicated in the pathogenesis of type 2 diabetes and cardiovascular disease. Limited data exist on how habitual dietary intake of foods that can alter hepatic lipid metabolism may influence circulating ceramide concentrations.

OBJECTIVES

We investigated the cross-sectional association of cumulative sugar-sweetened beverage (SSB) consumption with concentrations of 3 circulating ceramides and ceramide ratios.

METHODS

We examined participants from the Framingham Heart Study's Offspring Cohort who had 3 ceramides measured (n  = 1561, mean age 66 y, 59% women). SSB consumption was measured 4 times over ∼14 y. Participants were categorized by cumulative SSB intake as nonconsumers (0 to <1 SSB serving/mo) and occasional (1 SSB serving/mo to <1 serving/wk), frequent (1 SSB serving/wk to <1 serving/d), and daily (≥1 SSB serving/d) consumers. Multivariable linear regression models were used to relate cumulative SSB consumption (independent variable) to blood concentrations of ceramides (C16:0, C22:0, and C24:0) and ceramide ratios (C22:0/C16:0 and C24:0/C16:0).

RESULTS

In adjusted models, more frequent cumulative SSB consumption was positively associated with concentrations of the C16:0 and C22:0 ceramides (Ptrend < 0.05). Compared with nonconsumers, daily consumers had 0.01 μg/mL (95% CI: 0.002, 0.017 µg/mL) and 0.06 µg/mL (95% CI: 0.018, 0.092 µg/mL) higher mean concentrations of the C16:0 and C22:0 ceramides, respectively. Results were consistent when modeling continuous cumulative SSB consumption per 1 serving/d. We observed effect modification by diabetes status in the relation between cumulative SSB consumption and concentrations of the C24:0 ceramide (Pinteraction = 0.014). In a stratified analysis, more frequent cumulative SSB consumption was positively associated with concentrations of the C24:0 ceramide only in individuals with prediabetes or diabetes (Ptrend = 0.001).

CONCLUSIONS

Our study raises the possibility that higher concentrations of distinct ceramide species, previously associated with adverse metabolic health, may be one mechanism by which SSB consumption contributes to higher risk of cardiometabolic diseases.

Plasma Phospholipids with Long-Chain Polyunsaturated Fatty Acids and Dihydroceramides at the Crossroads of Iron Stores and Insulin Resistance

SCOPE

Iron plays an important role in the pathogenesis of insulin resistance (IR) and type 2 diabetes. Recent studies suggest a role of specific lipids in the induction of IR, but the potential relationships between iron and lipid metabolites in relation to IR have not been explored. Therefore, the aim of the study is to evaluate the association among iron, IR, and the lipidome.

METHODS AND RESULTS

The plasma lipidome, IR, parameters of iron metabolism, and several cytokines and adipokines in 65 overweight/obese participants are measured. Measurements of IR correlate positively with ferritin, a measure of iron storage (r = 0.35, p = 0.005), and negatively with adiponectin (r = -0.30, p = 0.02). The serum ferritin/adiponectin ratio has a stronger association with IR (r = 0.41, p < 0.001). From multivariate analyses adjusted for age, sex, and BMI, several phospholipids containing long chain polyunsaturated fatty acids (PUFA) with 20-22 carbons (phosphatidylcholines, phosphatidylethanolamines, phosphatidylinositols, and a phosphatidylserine), are positively associated with ferritin and the ferritin/adiponectin ratio. Two dihydroceramides (Cer(18:0/22:0), Cer(18:0/24:0)) and several diglycerides and triglycerides, mainly comprised of C14:0, C16:0, C18:0, C18:1, and C18:2, also have positive correlations with ferritin and the ferritin/adiponectin ratio.

CONCLUSIONS

The positive associations between these lipid species and ferritin or the ferritin/adiponectin ratio suggest a potential crosstalk between iron and lipid metabolism in obesity and IR.

Sphingolipid Metabolism and Signaling in Skeletal Muscle: From Physiology to Physiopathology

Sphingolipids represent one of the major classes of eukaryotic lipids. They play an essential structural role, especially in cell membranes where they also possess signaling properties and are capable of modulating multiple cell functions, such as apoptosis, cell proliferation, differentiation, and inflammation. Many sphingolipid derivatives, such as ceramide, sphingosine-1-phosphate, and ganglioside, have been shown to play many crucial roles in muscle under physiological and pathological conditions. This review will summarize our knowledge of sphingolipids and their effects on muscle fate, highlighting the role of this class of lipids in modulating muscle cell differentiation, regeneration, aging, response to insulin, and contraction. We show that modulating sphingolipid metabolism may be a novel and interesting way for preventing and/or treating several muscle-related diseases.

Sphingolipids in Obesity and Correlated Co-Morbidities: The Contribution of Gender, Age and Environment

This paper reviews our present knowledge on the contribution of ceramide (Cer), sphingomyelin (SM), dihydroceramide (DhCer) and sphingosine-1-phosphate (S1P) in obesity and related co-morbidities. Specifically, in this paper, we address the role of acyl chain composition in bodily fluids for monitoring obesity in males and females, in aging persons and in situations of environmental hypoxia adaptation. After a brief introduction on sphingolipid synthesis and compartmentalization, the node of detection methods has been critically revised as the node of the use of animal models. The latter do not recapitulate the human condition, making it difficult to compare levels of sphingolipids found in animal tissues and human bodily fluids, and thus, to find definitive conclusions. In human subjects, the search for putative biomarkers has to be performed on easily accessible material, such as serum. The serum “sphingolipidome” profile indicates that attention should be focused on specific acyl chains associated with obesity, per se, since total Cer and SM levels coupled with dyslipidemia and vitamin D deficiency can be confounding factors. Furthermore, exposure to hypoxia indicates a relationship between dyslipidemia, obesity, oxygen level and aerobic/anaerobic metabolism, thus, opening new research avenues in the role of sphingolipids.

Metabolic Messengers: ceramides

Ceramides are products of metabolism that accumulate in individuals with obesity or dyslipidaemia and alter cellular processes in response to fuel surplus. Their actions, when prolonged, elicit the tissue dysfunction that underlies diabetes and heart disease. Here, we review the history of research on these enigmatic molecules, exploring their discovery and mechanisms of action, the evolutionary pressures that have given them their unique attributes and the potential of ceramide-reduction therapies as treatments for cardiometabolic disease.

Beyond adiponectin and leptin: adipose tissue-derived mediators of inter-organ communication

The breakthrough discoveries of leptin and adiponectin more than two decades ago led to a widespread recognition of adipose tissue as an endocrine organ. Many more adipose tissue-secreted signaling mediators (adipokines) have been identified since then, and much has been learned about how adipose tissue communicates with other organs of the body to maintain systemic homeostasis. Beyond proteins, additional factors, such as lipids, metabolites, noncoding RNAs, and extracellular vesicles (EVs), released by adipose tissue participate in this process. Here, we review the diverse signaling mediators and mechanisms adipose tissue utilizes to relay information to other organs. We discuss recently identified adipokines (proteins, lipids, and metabolites) and briefly outline the contributions of noncoding RNAs and EVs to the ever-increasing complexities of adipose tissue inter-organ communication. We conclude by reflecting on central aspects of adipokine biology, namely, the contribution of distinct adipose tissue depots and cell types to adipokine secretion, the phenomenon of adipokine resistance, and the capacity of adipose tissue to act both as a source and sink of signaling mediators.

Mammalian sphingoid bases: Biophysical, physiological and pathological properties

Sphingoid bases encompass a group of long chain amino alcohols which form the essential structure of sphingolipids. Over the last years, these amphiphilic molecules were moving more and more into the focus of biomedical research due to their role as bioactive molecules. In fact, free sphingoid bases interact with specific receptors and target molecules and have been associated with numerous biological and physiological processes. In addition, they can modulate the biophysical properties of biological membranes. Several human diseases are related to pathological changes in the structure and metabolism of sphingoid bases. Yet, the mechanisms underlying their biological and pathophysiological actions remain elusive. Within this review, we aimed to summarize the current knowledge on the biochemical and biophysical properties of the most common sphingoid bases and to discuss their importance in health and disease.

Ceramide: a novel inducer for neural tube defects

BACKGROUND

Circulating plasma ceramides, a class of bioactive sphingolipids, are elevated in metabolic disorders, including obesity. Infants of women with these disorders are at 2- to 3-fold greater risk for developing a neural tube defect (NTD). This study aimed to test the effects of embryonic exposure to C2-ceramides (C2) during neural tube closure. Preliminary data shows an increase in NTDs in chick embryos after C2 exposure, and addresses potential mechanisms.

RESULTS

Cell and embryo models were used to examine redox shifts after ceramide exposure. While undifferentiated P19 cells were resistant to ceramide exposure, neuronally differentiated P19 cells exhibited an oxidizing shift. Consistent with these observations, GSH E _h curves revealed a shift to a more oxidized state in C2 treated embryos without increasing apoptosis or changing Pax3 expression, however cell proliferation was lower. Neural tube defects were observed in 45% of chick embryos exposed to C2, compared to 12% in control embryos.

CONCLUSIONS

C2 exposure during critical developmental stages increased the frequency of NTDs in the avian model. Increased ROS generation in cell culture, along with the more oxidative GSH E _h profiles of C2 exposed cells and embryos, support a model wherein ceramide affects neural tube closure via altered tissue redox environments.

Invited review: Sphingolipid biology in the dairy cow: The emerging role of ceramide

The physiological control of lactation through coordinated adaptations is of fundamental importance for mammalian neonatal life. The putative actions of reduced insulin sensitivity and responsiveness and enhanced adipose tissue lipolysis spare glucose for the mammary synthesis of milk. However, severe insulin antagonism and body fat mobilization may jeopardize hepatic health and lactation in dairy cattle. Interestingly, lipolysis- and dietary-derived fatty acids may impair insulin sensitivity in cows. The mechanisms are undefined yet have major implications for the development of postpartum fatty liver disease. In nonruminants, the sphingolipid ceramide is a potent mediator of saturated fat-induced insulin resistance that defines in part the mechanisms of type 2 diabetes mellitus and nonalcoholic fatty liver disease. In ruminants including the lactating dairy cow, the functions of ceramide had remained virtually undescribed. Through a series of hypothesis-centered studies, ceramide has emerged as a potential antagonist of insulin-stimulated glucose utilization by adipose and skeletal muscle tissues in dairy cattle. Importantly, bovine data suggest that the ability of ceramide to inhibit insulin action likely depends on the lipolysis-dependent hepatic synthesis and secretion of ceramide during early lactation. Although these mechanisms appear to fade as lactation advances beyond peak milk production, early evidence suggests that palmitic acid feeding is a means to augment ceramide supply. Herein, we review a body of work that focuses on sphingolipid biology and the role of ceramide in the dairy cow within the framework of hepatic and fatty acid metabolism, insulin function, and lactation. The potential involvement of ceramide within the endocrine control of lactation is also considered.

Targeting a ceramide double bond improves insulin resistance and hepatic steatosis

Ceramides contribute to the lipotoxicity that underlies diabetes, hepatic steatosis, and heart disease. By genetically engineering mice, we deleted the enzyme dihydroceramide desaturase 1 (DES1), which normally inserts a conserved double bond into the backbone of ceramides and other predominant sphingolipids. Ablation of DES1 from whole animals or tissue-specific deletion in the liver and/or adipose tissue resolved hepatic steatosis and insulin resistance in mice caused by leptin deficiency or obesogenic diets. Mechanistic studies revealed ceramide actions that promoted lipid uptake and storage and impaired glucose utilization, none of which could be recapitulated by (dihydro)ceramides that lacked the critical double bond. These studies suggest that inhibition of DES1 may provide a means of treating hepatic steatosis and metabolic disorders.

Mammalian sphingoid bases: Biophysical, physiological and pathological properties

Sphingoid bases encompass a group of long chain amino alcohols which form the essential structure of sphingolipids. Over the last years, these amphiphilic molecules were moving more and more into the focus of biomedical research due to their role as bioactive molecules. In fact, free sphingoid bases interact with specific receptors and target molecules, and have been associated with numerous biological and physiological processes. In addition, they can modulate the biophysical properties of biological membranes. Several human diseases are related to pathological changes in the structure and metabolism of sphingoid bases. Yet, the mechanisms underlying their biological and pathophysiological actions remain elusive. Within this review, we aimed to summarize the current knowledge on the biochemical and biophysical properties of the most common sphingoid bases and to discuss their importance in health and disease.

The role of dihydrosphingolipids in disease

Dihydrosphingolipids refer to sphingolipids early in the biosynthetic pathway that do not contain a C4-trans-double bond in the sphingoid backbone: 3-ketosphinganine (3-ketoSph), dihydrosphingosine (dhSph), dihydrosphingosine-1-phosphate (dhS1P) and dihydroceramide (dhCer). Recent advances in research related to sphingolipid biochemistry have shed light on the importance of sphingolipids in terms of cellular signalling in health and disease. However, dihydrosphingolipids have received less attention and research is lacking especially in terms of their molecular mechanisms of action. This is despite studies implicating them in the pathophysiology of disease, for example dhCer in predicting type 2 diabetes in obese individuals, dhS1P in cardiovascular diseases and dhSph in hepato-renal toxicity. This review gives a comprehensive summary of research in the last 10-15 years on the dihydrosphingolipids, 3-ketoSph, dhSph, dhS1P and dhCer, and their relevant roles in different diseases. It also highlights gaps in research that could be of future interest.

Obesity leads to distinct metabolomic signatures in follicular fluid of women undergoing in vitro fertilization

Although obesity negatively influences the metabolic homeostasis of cells within a broad range of tissues, its impact on oocyte metabolism is not fully understood. Prior evidence suggests that obesity increases expression of oocyte genes associated with inflammation, oxidative stress, and lipid metabolism; however, the metabolic impact of these genetic differences is not known. To address this gap, we conducted an exploratory assessment of the follicular fluid (FF) metabolome in eight overweight/obese (OW) and nine normal-weight (NW) women undergoing in vitro fertilization. FF and serum were collected and analyzed by untargeted metabolomics using gas chromatography-quadrupole time-of-flight mass spectrometry and charged-surface hybrid column-electrospray ionization quadrupole time-of-flight tandem mass spectrometry. Untargeted metabolomics identified obesity-associated changes in FF metabolites related to oxidative stress/antioxidant capacity, xenometabolism/amino acid biosynthesis, and lipid metabolism. Discriminant FF metabolites included elevated uric acid, isothreonic acid, one unknown primary metabolite, and six unknown complex lipids in OW compared with NW women. Conversely, 2-ketoglucose dimethylacetal, aminomalonate, two unknown primary metabolites, and two unknown complex lipids were decreased in FF of OW relative to NW women. Indole-3-propionic acid (IPA), a bacteria-derived metabolite, was also decreased in both FF and serum of OW women ( P < 0.05). The significant correlation between antioxidant IPA in serum and FF ( R = 0.95, P < 0.0001) suggests a potential serum biomarker of FF antioxidant status or reflection of the gut metabolism interaction with the follicle. These results suggest that obesity has important consequences for the follicular environment during the preconception period, a window of time that may be important for lifestyle interventions to ameliorate obesity-associated risk factors.

Genetic Architecture of Human Obesity Traits in the Rhesus Macaque

OBJECTIVE

Whereas the metabolic consequences of obesity have been studied extensively in the rhesus macaque, corollary genetic studies of obesity are nonexistent. This study assessed genetic contributions to spontaneous adiposity in this species.

METHODS

Phenotypic variation by age class and sex for BMI, waist to height ratio, waist to thigh ratio, and waist circumference was assessed in 583 macaques. Total and sex-specific heritability for all traits was estimated, including waist to thigh ratio adjusted for BMI, as well as genotypic and phenotypic correlations. In addition, functional genetic variation at BDNF, FTO, LEP, LEPR, MC4R, PCSK1, POMC, and SIM1 was assessed in four animals with extreme spontaneous adiposity.

RESULTS

Trait heritability in the combined sample was low to moderate (0.14-0.32), whereas sex-specific heritability was more substantial (0.20-0.67). Heritability was greater in females for all traits except BMI. All traits were robustly correlated, with genetic correlations of 0.63 to 0.93 indicating substantial pleiotropy. Likely functional variants were discovered in the four macaques at all eight human obesity genes, including six missense mutations in BDNF, FTO, LEP, LEPR, and PCSK1 and, notably, one nonsense mutation in LEPR.

CONCLUSIONS

A moderate polygenic contribution to adiposity in rhesus macaques was found, as well as mutations with potentially larger effects in multiple genes that influence obesity in humans.

Plasma metabolites predict both insulin resistance and incident type 2 diabetes: a metabolomics approach within the Prevención con Dieta Mediterránea (PREDIMED) study

BACKGROUND

Insulin resistance is a complex metabolic disorder and is often associated with type 2 diabetes (T2D).

OBJECTIVES

The aim of this study was to test whether baseline metabolites can additionally improve the prediction of insulin resistance beyond classical risk factors. Furthermore, we examined whether a multimetabolite model predicting insulin resistance in nondiabetics can also predict incident T2D.

METHODS

We used a case-cohort study nested within the Prevención con Dieta Mediterránea (PREDIMED) trial in subsets of 700, 500, and 256 participants without T2D at baseline and 1 and 3 y. Fasting plasma metabolites were semiquantitatively profiled with liquid chromatography-tandem mass spectrometry. We assessed associations between metabolite concentrations and the homeostasis model of insulin resistance (HOMA-IR) through the use of elastic net regression analysis. We subsequently examined associations between the baseline HOMA-IR-related multimetabolite model and T2D incidence through the use of weighted Cox proportional hazard models.

RESULTS

We identified a set of baseline metabolites associated with HOMA-IR. One-year changes in metabolites were also significantly associated with HOMA-IR. The area under the curve was significantly greater for the model containing the classical risk factors and metabolites together compared with classical risk factors alone at baseline [0.81 (95% CI: 0.79, 0.84) compared with 0.69 (95% CI: 0.66, 0.73)] and during a 1-y period [0.69 (95% CI: 0.66, 0.72) compared with 0.57 (95% CI: 0.53, 0.62)]. The variance in HOMA-IR explained by the combination of metabolites and classical risk factors was also higher in all time periods. The estimated HRs for incident T2D in the multimetabolite score (model 3) predicting high HOMA-IR (median value or higher) or HOMA-IR (continuous) at baseline were 2.00 (95% CI: 1.58, 2.55) and 2.24 (95% CI: 1.72, 2.90), respectively, after adjustment for T2D risk factors.

CONCLUSIONS

The multimetabolite model identified in our study notably improved the predictive ability for HOMA-IR beyond classical risk factors and significantly predicted the risk of T2D.

Impaired Skeletal Muscle Branched-Chain Amino Acids Catabolism Contributes to Their Increased Circulating Levels in a Non-Obese Insulin-Resistant Fructose-Fed Rat Model

Elevated plasma branched-chain amino acids (BCAA) levels are often observed in obese insulin-resistant (IR) subjects and laboratory animals. A reduced capacity of the adipose tissues (AT) to catabolize BCAA has been proposed as an explanation, but it seems restricted to obesity models of genetically modified or high fat⁻fed rodents. We aimed to determine if plasma BCAA levels were increased in a model of IR without obesity and to explore the underlying mechanisms. Rats were fed with a standard diet, containing either starch or fructose. BCAA levels, body weight and composition were recorded before and after 5, 12, 30, or 45 days of feeding. Elevated blood BCAA levels were observed in our IR model with unaltered body weight and composition. No changes were observed in the liver or the AT, but instead an impaired capacity of the skeletal muscle to catabolize BCAA was observed, including reduced capacity for transamination and oxidative deamination. Although the elevated blood BCAA levels in the fructose-fed rat seem to be a common feature of the IR phenotype observed in obese subjects and high fat⁻fed animals, the mechanisms involved in such a metabolic phenomenon are different, likely involving the skeletal muscle BCAA metabolism.

Chronic hyperandrogenemia in the presence and absence of a western-style diet impairs ovarian and uterine structure/function in young adult rhesus monkeys

STUDY QUESTION

Does chronic hyperandrogenemia beginning at menarche, in the absence and presence of a western-style diet (WSD), alter ovarian and uterine structure-function in young adult rhesus monkeys?

SUMMARY ANSWER

Phenotypic alterations in ovarian and uterine structure/function were induced by exogenous testosterone (T), and compounded in the presence of a WSD (T+WSD).

WHAT IS KNOWN ALREADY

Hyperandrogenemia is a well-established component of PCOS and is observed in adolescent girls, indicating a potential pubertal onset of disease symptoms. Obesity is often associated with hyperandrogenemia and it is hypothesized that metabolic dysfunction exacerbates PCOS symptoms.

STUDY DESIGN, SIZE, DURATION

Macaque females (n = 40) near the onset of menarche (~2.5 years of age) were assigned to a 2 by 2 factorial cohort design. Effects on reproductive characteristics were evaluated after 3 years of treatment.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Rhesus macaques (Macaca mulatta) were fed either a normal balanced diet (n = 20) or a WSD (n = 20). Additionally, implants containing cholesterol (n = 20) or T (n = 20) were implanted subcutaneously to elevate serum T approximately 5-fold. This resulted in treatment groups of controls (C), T, WSD and T+WSD (n = 10/group). Vaginal swabbing was performed daily to detect menses. After 3 years of treatment, daily serum samples from one menstrual cycle were assayed for hormone levels. Ovarian structure was evaluated in the early follicular phase by 3D/4D ultrasound. Uterine endometrial size and ovarian/luteal vascular function was also evaluated in subgroups (n = 6/group) in the late follicular and mid-luteal phases by 3D/4D ultrasound and contrast-enhanced ultrasound, respectively. Expression of steroid hormone receptors and markers of decidualization and endometrial receptivity were assessed in endometrial biopsies at mid-luteal phase.

MAIN RESULTS AND THE ROLE OF CHANCE

Approximately 90% of menstrual cycles appeared ovulatory with no differences in frequency or duration between groups. Serum estradiol (E2) levels during the early follicular phase were greatest in the T alone group, but reduced in T+WSD (P < 0.02). Serum LH was elevated in the T group (P < 0.04); however, there were no differences among groups in FSH levels (P > 0.13). Ovarian size at menses tended to be greater in the WSD groups (P < 0.07) and antral follicles ≥1 mm were more numerous in the T+WSD group (P < 0.05). Also, females in T and T+WSD groups displayed polycystic ovarian morphology (PCOM) at greater frequency than C or WSD groups (P < 0.01). Progesterone (P4) levels during the luteal phase were reduced in the T+WSD group compared to C and T groups (P < 0.05). Blood volume (BV) and vascular flow (VF) within the corpus luteum was reduced in all treatment groups compared to C (P < 0.01, P = 0.03), with the WSD alone group displaying the slowest BV and VF (P < 0.05). C and WSD groups displayed endometrial glands at mid-luteal phase with low estrogen receptor 1 (ESR1) and progesterone receptor (PGR) mRNA and immunohistochemical staining in the functionalis zone, but appreciable PGR in the stroma. In contrast, T and T+WSD treatment resulted in glands with less secretory morphology, high ESR1 expression in the glandular epithelium and low PGR in the stroma. Endometrial levels of TIMP3 and MMP26 mRNA and immunostaining were also decreased in the T and T+WSD groups, whereas AR expression was unchanged.

LARGE SCALE DATA

None.

LIMITATIONS, REASONS FOR CAUTION

Females are young adults, so effects could change as they reach prime reproductive age. The T level generated for hyperandrogenemia may be somewhat greater than the 3-4-fold increase observed in adolescent girls, but markedly less than those observed in male monkeys or adolescent boys.

WIDER IMPLICATIONS OF THE FINDINGS

Alterations to ovarian and uterine structure-function observed in T and, in particular, T+WSD-treated female macaques are consistent with some of the features observed in women diagnosed with polycystic ovary syndrome (PCOS), and suggest impaired fertility.

STUDY FUNDING/COMPETING INTEREST(S)

Research reported in this publication was supported by the Eunice Kennedy Shriver National Institute of Child Health & Human Development (NICHD) of the National Institutes of Health (NIH) under Award Number P50HD071836 (to RLS). The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH. Additional funding was provided by Office of the Director, NIH under Award Number P51OD011092 (Support for National Primate Research Center). Authors declare no competing interests.