Lysophosphatidylcholines activate PPARδ and protect human skeletal muscle cells from lipotoxicity

Inhibitory Effect and Mechanism of Epigallocatechin Gallate on the Differentiation of 3T3-L1 Preadipocytes

Green tea possesses a range of beneficial effects, including anti-obesity, antioxidant, and anti-inflammatory properties, owing to its biologically active components, primarily catechins such as epicatechin (EC), epicatechin gallate (ECG), epigallocatechin (EGC), and epigallocatechin gallate (EGCG). However, few studies have investigated the four catechin monomers simultaneously, and the molecular mechanisms of their anti-obesity effects have not been fully elucidated. In this study, we investigated the effects of four catechin monomers on the differentiation of 3T3-L1 preadipocytes of mice. Our findings demonstrated that four catechin monomers EC/ECG/EGC/EGCG (12, 25, 50 µM) dose-dependently inhibited the differentiation of 3T3-L1 preadipocytes and reduced triglyceride content. EGCG exhibited the most potent inhibitory effect with an optimal concentration of 50 µM. In addition, transcriptome sequencing and lipidomic analysis of EGCG-treated 3T3-L1 preadipocytes revealed that Ptgs2 and Pim1 were the most differentially expressed genes involved in regulating adipocyte differentiation. The results suggested that EGCG up-regulated the expression of the Pla2g2e gene and down-regulated the expression of the Pla2g4a and Pla2g2a genes via the glycerophospholipid metabolic pathway, which subsequently elevated lysophosphatidylcholine (LPC) levels, influencing the differentiation process of 3T3-L1 preadipocytes.

Integrated 16S rRNA sequencing and nontargeted metabolomics analysis to reveal the mechanisms of Yu-Ye Tang on type 2 diabetes mellitus rats

Introduction

Yu-Ye Tang (YYT) is a classical formula widely used in treatment of type 2 diabetes mellitus (T2DM). However, the specific mechanism of YYT in treating T2DM is not clear.

Methods

The aim of this study was to investigate the therapeutic effect of YYT on T2DM by establishing a rat model of T2DM. The mechanism of action of YYT was also explored through investigating gut microbiota and serum metabolites.

Results

The results indicated YYT had significant therapeutic effects on T2DM. Moreover, YYT could increase the abundance of Lactobacillus, Candidatus_Saccharimonas, UCG-005, Bacteroides and Blautia while decrease the abundance of and Allobaculum and Desulfovibrio in gut microbiota of T2DM rats. Nontargeted metabolomics analysis showed YYT treatment could regulate arachidonic acid metabolism, alanine, aspartate and glutamate metabolism, arginine and proline metabolism, glycerophospholipid metabolism, pentose and glucuronate interconversions, phenylalanine metabolism, steroid hormone biosynthesis, terpenoid backbone biosynthesis, tryptophan metabolism, and tyrosine metabolism in T2DM rats.

Discussion

In conclusion, our research showed that YYT has a wide range of therapeutic effects on T2DM rats, including antioxidative and anti-inflammatory effects. Furthermore, YYT corrected the altered gut microbiota and serum metabolites in T2DM rats. This study suggests that YYT may have a therapeutic impact on T2DM by regulating gut microbiota and modulating tryptophan and glycerophospholipid metabolism, which are potential key pathways in treating T2DM.

A High-Phosphorus Diet Moderately Alters the Lipidome and Transcriptome in the Skeletal Muscle of Adult Mice

A high phosphorus intake has been associated with various metabolic disorders, including chronic kidney disease, cardiovascular disease, and osteoporosis. Recent studies have demonstrated the effects of dietary phosphorus on lipid and glucose metabolism. This study investigated the impact of a high-phosphorus diet on mouse skeletal muscle lipid composition and gene transcription. Adult male mice (n = 12/group) received either a diet with an adequate (0.3%) or a high (1.2%) phosphorus concentration for 6 weeks. The lipidome analysis showed that among the 17 analyzed lipid classes, the concentrations of three classes were reduced in the high phosphorus group compared to the adequate phosphorus group. These classes were phosphatidylethanolamine (PE), phosphatidylglycerol (PG), and lysophosphatidylcholine (LPC) (p < 0.05). Out of the three hundred and twenty-three individual lipid species analyzed, forty-nine showed reduced concentrations, while three showed increased concentrations in the high phosphorus group compared to the adequate phosphorus group. The muscle transcriptome analysis identified 142 up- and 222 down-regulated transcripts in the high phosphorus group compared to the adequate phosphorus group. Gene set enrichment analysis identified that genes that were up-regulated in the high phosphorus group were linked to the gene ontology terms "mitochondria" and "Notch signaling pathway", whereas genes that were down-regulated were linked to the "PI3K-AKT pathway". Overall, the effects of the high-phosphorus diet on the muscle lipidome and transcriptome were relatively modest, but consistently indicated an impact on lipid metabolism.

Changes in Choline Metabolites and Ceramides in Response to a DASH-Style Diet in Older Adults

This feeding trial evaluated the impact of the Dietary Approaches to Stop Hypertension diet on changes in plasma choline, choline metabolites, and ceramides in obese older adults; 28 adults consumed 3oz (n = 15) or 6oz (n = 13) of beef within a standardized DASH diet for 12 weeks. Plasma choline, betaine, methionine, dimethylglycine (DMG), phosphatidylcholine (PC), lysophosphotidylcholine (LPC), sphingomyelin, trimethylamine-N-oxide (TMAO), L-carnitine, ceramide, and triglycerides were measured in fasted blood samples. Plasma LPC, sphingomyelin, and ceramide species were also quantified. In response to the study diet, with beef intake groups combined, plasma choline decreased by 9.6% (p = 0.012); DMG decreased by 10% (p = 0.042); PC decreased by 51% (p < 0.001); total LPC increased by 281% (p < 0.001); TMAO increased by 26.5% (p < 0.001); total ceramide decreased by 22.1% (p < 0.001); and triglycerides decreased by 18% (p = 0.021). All 20 LPC species measured increased (p < 0.01) with LPC 16:0 having the greatest response. Sphingomyelin 16:0, 18:0, and 18:1 increased (all p < 0.001) by 10.4%, 22.5%, and 24%, respectively. In contrast, we observed that sphingomyelin 24:0 significantly decreased by 10%. Ceramide 22:0 and 24:0 decreased by 27.6% and 10.9% (p < 0.001), respectively, and ceramide 24:1 increased by 36.8% (p = 0.013). Changes in choline and choline metabolites were in association with anthropometric and cardiometabolic outcomes. These findings show the impact of the DASH diet on choline metabolism in older adults and demonstrate the influence of diet to modify circulating LPC, sphingomyelin, and ceramide species.

Targeting PPARs for therapy of atherosclerosis: A review

Atherosclerosis, a chief pathogenic factor of cardiovascular disease, is associated with many factors including inflammation, dyslipidemia, and oxidative stress. Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors and are widely expressed with tissue- and cell-specificity. They control multiple genes that are involved in lipid metabolism, inflammatory response, and redox homeostasis. Given the diverse biological functions of PPARs, they have been extensively studied since their discovery in 1990s. Although controversies exist, accumulating evidence have demonstrated that PPAR activation attenuates atherosclerosis. Recent advances are valuable for understanding the mechanisms of action of PPAR activation. This article reviews the recent findings, mainly from the year of 2018 to present, including endogenous molecules in regulation of PPARs, roles of PPARs in atherosclerosis by focusing on lipid metabolism, inflammation, and oxidative stress, and synthesized PPAR modulators. This article provides information valuable for researchers in the field of basic cardiovascular research, for pharmacologists that are interested in developing novel PPAR agonists and antagonists with lower side effects as well as for clinicians.

Identification of potential biomarkers and metabolic insights for gestational diabetes prevention: A review of evidence contrasting gestational diabetes versus weight loss studies that may direct future nutritional metabolomics studies

Gestational diabetes mellitus (GDM) significantly increases maternal health risks and adverse effects for the offspring. Observational studies suggest that weight loss before pregnancy may be a promising GDM prevention method. Still, biochemical pathways linking preconception weight changes with subsequent development of GDM among women who are overweight or obese remain unclear. Metabolomic assessment is a powerful approach for understanding the global biochemical pathways linking preconception weight changes and subsequent GDM. We hypothesize that many of the alterations of metabolite levels associated with GDM will change in one direction in GDM studies but will change in the opposite direction in studies focusing on lifestyle interventions for weight loss. The present review summarizes available evidence from 21 studies comparing women with GDM with healthy participants and 12 intervention studies that investigated metabolite changes that occurred during weight loss using caloric restriction and behavioral interventions. We discuss 15 metabolites, including amino acids, lipids, amines, carbohydrates, and carbohydrate derivatives. Of particular note are the altered levels of branched-chain amino acids, alanine, palmitoleic acid, lysophosphatidylcholine 18:1, and hypoxanthine because of their mechanistic links to insulin resistance and weight change. Mechanisms that may explain how these metabolite modifications contribute to GDM development in those who are overweight or obese are proposed, including insulin resistance pathways. Future nutritional metabolomics preconception intervention studies in overweight or obese are necessary to investigate whether weight loss through lifestyle intervention can reduce GDM occurrence in association with these metabolite alterations and to test the value of these metabolites as potential diagnostic biomarkers of GDM development.

Action mechanism of hypoglycemic principle 9-(R)-HODE isolated from cortex lycii based on a metabolomics approach

The 9-(R)-HODE is an active compound isolated from cortex lycii that showed significant hypoglycemic effects in our previous in vitro study. In this study, 9-(R)-HODE’s in vivo hypoglycemic activity and effect on alleviating diabetic complications, together with its molecular mechanism, was investigated using a metabolomics approach. The monitored regulation on dynamic fasting blood glucose, postprandial glucose, body weight, biochemical parameters and histopathological analysis confirmed the hypoglycemic activity and attenuation effect, i.e., renal lesions, of 9-(R)-HODE. Subsequent metabolomic studies indicated that 9-(R)-HODE induced metabolomic alterations primarily by affecting the levels of amino acids, organic acids, alcohols and amines related to amino acid metabolism, glucose metabolism and energy metabolism. By mediating the related metabolism or single molecules related to insulin resistance, e.g., kynurenine, myo-inositol and the branched chain amino acids leucine, isoleucine and valine, 9-(R)-HODE achieved its therapeutic effect. Moreover, the mediation of kynurenine displayed a systematic effect on the liver, kidney, muscle, plasma and faeces. Lipidomic studies revealed that 9-(R)-HODE could reverse the lipid metabolism disorder in diabetic mice mainly by regulating phosphatidylinositols, lysophosphatidylcholines, lysophosphatidylcholines, phosphatidylserine, phosphatidylglycerols, lysophosphatidylglycerols and triglycerides in both tissues and plasma. Treatment with 9-(R)-HODE significantly modified the structure and composition of the gut microbiota. The SCFA-producing bacteria, including Rikenellaceae and Lactobacillaceae at the family level and Ruminiclostridium 6, Ruminococcaceae UCG 014, Mucispirillum, Lactobacillus, Alistipes and Roseburia at the genus level, were increased by 9-(R)-HODE treatment. These results were consistent with the increased SCFA levels in both the colon content and plasma of diabetic mice treated with 9-(R)-HODE. The tissue DESI‒MSI analysis strongly confirmed the validity of the metabolomics approach in illustrating the hypoglycemic and diabetic complications-alleviation effect of 9-(R)-HODE. The significant upregulation of liver glycogen in diabetic mice by 9-(R)-HODE treatment validated the interpretation of the metabolic pathways related to glycogen synthesis in the integrated pathway network. Altogether, 9-(R)-HODE has the potential to be further developed as a promising candidate for the treatment of diabetes.

The Effect of Metabolites on Mitochondrial Functions in the Pathogenesis of Skeletal Muscle Aging

Sarcopenia is an age-related systemic disease characterized by skeletal muscle aging that generally severely affects the quality of life of elderly patients. Metabolomics analysis is a powerful tool for qualitatively and quantitatively characterizing the small molecule metabolomics of various biological matrices in order to clarify all key scientific problems concerning cell metabolism. The discovery of optimal therapy requires a thorough understanding of the cellular metabolic mechanism of skeletal muscle aging. In this review, the relationship between skeletal muscle mitochondria, amino acid, vitamin, lipid, adipokines, intestinal microbiota and vascular microenvironment has been separately reviewed from the perspective of metabolomics, and a new therapeutic direction has been suggested.

Longitudinal associations between blood lysophosphatidylcholines and skeletal muscle mitochondrial function

Lysophosphatidylcholines (LPCs) are phospholipids critical in the synthesis of cardiolipin, an essential component of mitochondrial membranes. Lower plasma LPCs have been cross-sectionally associated with lower skeletal muscle mitochondrial function, but whether lower LPCs and their decline over time are longitudinally associated with an accelerated decline of mitochondria function is unknown. We analyzed data from 184 participants in the Baltimore Longitudinal Study of Aging (mean age: 74.5 years, 57% women, 25% black) who had repeated measures of plasma LPCs (16:0, 16:1, 17:0, 18:0, 18:1, 18:2, 20:3, 20:4, 24:0, and 28:1) by liquid chromatography-tandem mass spectrometry and repeated measures of skeletal muscle oxidative capacity (k_PCr) assessed by ³¹P magnetic resonance spectroscopy over an average of 2.4 years. Rates of change in k_PCr and each LPC were first estimated using simple linear regression. In multivariable linear regression models adjusted for baseline demographics and PCr % depletion, lower baseline LPC 16:1 and faster rates of decline in LPC 16:1 and 18:1 were significantly associated with a faster rate of decline in k_PCr (B =  - 0.169, 95% CI: - 0.328, - 0.010, p = 0.038; B = 0.209, 95% CI: 0.065, 0.352, p = 0.005; B = 0.156, 95% CI: 0.011, 0.301, p = 0.035, respectively). Rates of change in other LPCs were not significantly associated with change in k_PCr (all p > 0.05). Lower baseline concentrations and faster decline in selected plasma lysophosphatidylcholines over time are associated with faster decline in skeletal muscle mitochondrial function. Strategies to prevent the decline of plasma LPCs at an early stage may slow down mitochondrial function decline and impairment during aging.

Knockout of Stearoyl-CoA Desaturase 1 Decreased Milk Fat and Unsaturated Fatty Acid Contents of the Goat Model Generated by CRISPR/Cas9

Goat milk contains a rich source of nutrients, especially unsaturated fatty acids. However, the regulatory mechanism of milk fat and fatty acid synthesis remains unclear. Stearoyl-CoA desaturase 1 (SCD1) is the key enzyme catalyzing monounsaturated fatty acid synthesis and is essential for milk lipid metabolism. To explore milk lipid synthesis mechanism in vivo, SCD1-knockout goats were generated through CRISPR/Cas9 technology for the first time. SCD1 deficiency did not influence goat growth or serum biochemistry. Plasma phosphatidylcholines increased by lipidomics after SCD1 knockout in goats. Whole-blood RNA-seq indicated alterations in biosynthesis of unsaturated fatty acid synthesis, cAMP, ATPase activity, and Wnt signaling pathways. In SCD1-knockout goats, milk fat percentage and unsaturated fatty acid levels were reduced but other milk components were unchanged. Milk lipidomics revealed decreased triacylglycerols and diacylglycerols levels, and the differential abundance of lipids were enriched in glycerolipid, glycerophospholipids, and thermogenesis metabolism pathways. In milk fat globules, the expression levels of genes related to fatty acid and TAG synthesis including SREBP1 were reduced. ATP content and AMPK activity were promoted, and p-p70S6K protein level was suppressed in SCD1-knockout goat mammary epithelial cells, suggesting that SCD1 affected milk lipid metabolism by influencing AMPK-mTORC1/p70S6K-SREBP1 pathway. The integrative analysis of gene expression levels and lipidomics of milk revealed a crucial role of SCD1 in glycerolipids and glycerophospholipids metabolism pathways. Our observations indicated that SCD1 regulated the synthesis of milk fat and unsaturated fatty acid in goat by affecting lipid metabolism gene expression and lipid metabolic pathways. These findings would be essential for improving goat milk nutritional value which is beneficial to human health.

Lyso-Lipid-Induced Oligodendrocyte Maturation Underlies Restoration of Optic Nerve Function

Protein hyperdeimination and deficiency of lyso-phospholipids (LPC 18:1) has been associated with the pathology of demyelinating disease in both humans and mice. We uncovered interesting biology of LPC 18:1, in which LPC 18:1 induced optic nerve function restoration through oligodendrocyte maturation and remyelination in mouse model systems. Our in vitro studies show LPC 18:1 protection against neuron-ectopic hyperdeimination and stimulation of oligodendrocyte maturation, while in vivo investigations recorded optic nerve function improvement following optic nerve injections of LPC 18:1, in contrast with LPC 18:0. Thus, just a change in a single bond renders a dramatic alternation in biological function. The incorporation of isobaric C13-histidine in newly synthesized myelin proteins and quantitative proteome shifts are consistent with remyelination underlying restoration in optic nerve function. These results suggest that exogenous LPC 18:1 may provide a therapeutic avenue for stemming vision loss in demyelinating diseases.

Metabolomic profiling of ZrO2 nanoparticles in MC3T3-E1 cells

The authors' previous study showed that zirconium oxide nanoparticles (ZrO2 NPs) induce toxic effects in MC3T3-E1 cells; however, its toxicological mechanism is still unclear. Liquid chromatography-mass spectrometry/time-of-flight mass spectrometry was used to reveal the metabolite profile and toxicological mechanism of MC3T3-E1 cells in response to ZrO2 NPs. The results demonstrated that MC3T3-E1 cells treated with ZrO2 NPs for 24 and 48 h presented different metabolic characteristics. Following ZrO2 NP treatment for 24 h, 96 upregulated and 129 downregulated metabolites in the positive ion mode, as well as 91 upregulated and 326 downregulated metabolites in the negative ion mode were identified. Following ZrO2 NP treatment for 48 h, 33 upregulated and 174 downregulated metabolites were identified in the positive ion mode, whereas 37 upregulated and 302 downregulated metabolites were confirmed in the negative ion mode. Among them, 42 differential metabolites were recognised as potential metabolites contributing to the induced toxic effects of ZrO2 NPs in MC3T3-E1 cells. Most of the differential metabolites were lysophosphatidylcholine and lysophosphatidylethanolamide, indicating that exposure to ZrO2 NPs may have a profound impact on human cellular function by impairing the membrane system. The results also provide new clues for the toxicological mechanism of ZrO2 NP dental materials.

Identifying Codium fragile extract components and their effects on muscle weight and exercise endurance

Codium fragile (CF) is a type of green algae consumed as kimchi in Asia. UPLC-QTOF-MS/MS analysis showed that CF contain lysophosphatidyl choline, canthaxanthin, retinoic acid, α-tocopherol, and unsaturated fatty acids, which reportedly improve skeletal muscle health. However, the effect of CF on skeletal muscle mass and function remains to be elucidated. In mice fed with CF extracts, exercise endurance and muscle weight increased. CF extracts enhanced protein synthesis and myogenic differentiation through the mTORC1 pathway. CF extracts also promoted oxidative muscle fiber formation and mitochondrial biogenesis through the PGC-1α-related signaling pathway. Upregulation of PGC-1α by CF extracts was abolished by EX527 SIRT1 inhibitor treatment. Changed signaling molecules in the CF extracts were partially regulated by canthaxanthin, a new compound in CF extracts, suggesting that canthaxanthin contribute synergistically to the effect of CF extracts. Therefore, CF is a potential food source for sport nutrition or prevention of sarcopenia.

Diet-induced dyslipidemia induces metabolic and migratory adaptations in regulatory T cells

AIMS

A hallmark of advanced atherosclerosis is inadequate immunosuppression by regulatory T (Treg) cells inside atherosclerotic lesions. Dyslipidemia has been suggested to alter Treg cell migration by affecting the expression of specific membrane proteins, thereby decreasing Treg cell migration towards atherosclerotic lesions. Besides membrane proteins, cellular metabolism has been shown to be a crucial factor in Treg cell migration. We aimed to determine whether dyslipidemia contributes to altered migration of Treg cells, in part, by affecting cellular metabolism.

METHODS AND RESULTS

Dyslipidemia was induced by feeding Ldlr-/- mice a western-type diet for 16-20 weeks and intrinsic changes in Treg cells affecting their migration and metabolism were examined. Dyslipidemia was associated with altered mTORC2 signalling in Treg cells, decreased expression of membrane proteins involved in migration, including CD62L, CCR7, and S1Pr1, and decreased Treg cell migration towards lymph nodes. Furthermore, we discovered that diet-induced dyslipidemia inhibited mTORC1 signalling, induced PPARδ activation and increased fatty acid (FA) oxidation in Treg cells. Moreover, mass-spectrometry analysis of serum from Ldlr-/- mice with normolipidemia or dyslipidemia showed increases in multiple PPARδ ligands during dyslipidemia. Treatment with a synthetic PPARδ agonist increased the migratory capacity of Treg cells in vitro and in vivo in an FA oxidation-dependent manner. Furthermore, diet-induced dyslipidemia actually enhanced Treg cell migration into the inflamed peritoneum and into atherosclerotic lesions in vitro.

CONCLUSION

Altogether, our findings implicate that dyslipidemia does not contribute to atherosclerosis by impairing Treg cell migration as dyslipidemia associated with an effector-like migratory phenotype in Treg cells.

Sex Differences in Insulin Sensitivity are Related to Muscle Tissue Acylcarnitine But Not Subcellular Lipid Distribution

OBJECTIVE

Sex differences in insulin sensitivity are present throughout the life-span, with men having a higher prevalence of insulin resistance and diabetes compared with women. Differences in lean mass, fat mass, and fat distribution-particularly ectopic fat-have all been postulated to contribute to the sexual dimorphism in diabetes risk. Emerging data suggest ectopic lipid composition and subcellular localization are most relevant; however, it is not known whether they explain sex differences in obesity-induced insulin resistance.

METHODS

To address this gap, this study evaluated insulin sensitivity and subcellular localization of intramuscular triacylglycerol, diacylglycerol, and sphingolipids as well as muscle acylcarnitines and serum lipidomics in people with obesity.

RESULTS

Insulin sensitivity was significantly lower in men (P < 0.05); however, no sex differences were found in localization of intramuscular triacylglycerol, diacylglycerol, or sphingolipids in skeletal muscle. In contrast, men had higher total muscle acylcarnitine (P < 0.05) and long-chain muscle acylcarnitine (P < 0.05), which were related to lower insulin sensitivity (r = -0.42, P < 0.05). Men also displayed higher serum ceramide (P = 0.05) and lysophosphatidylcholine (P < 0.01).

CONCLUSIONS

These data reveal novel sex-specific associations between lipid species involved in the coupling of mitochondrial fatty acid transport, β-oxidation, and tricarboxylic acid cycle flux that may provide therapeutic targets to improve insulin sensitivity.

PPARs and Microbiota in Skeletal Muscle Health and Wasting

Skeletal muscle is a major metabolic organ that uses mostly glucose and lipids for energy production and has the capacity to remodel itself in response to exercise and fasting. Skeletal muscle wasting occurs in many diseases and during aging. Muscle wasting is often accompanied by chronic low-grade inflammation associated to inter- and intra-muscular fat deposition. During aging, muscle wasting is advanced due to increased movement disorders, as a result of restricted physical exercise, frailty, and the pain associated with arthritis. Muscle atrophy is characterized by increased protein degradation, where the ubiquitin-proteasomal and autophagy-lysosomal pathways, atrogenes, and growth factor signaling all play an important role. Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptor family of transcription factors, which are activated by fatty acids and their derivatives. PPARs regulate genes that are involved in development, metabolism, inflammation, and many cellular processes in different organs. PPARs are also expressed in muscle and exert pleiotropic specialized responses upon activation by their ligands. There are three PPAR isotypes, viz., PPARα, -β/δ, and -γ. The expression of PPARα is high in tissues with effective fatty acid catabolism, including skeletal muscle. PPARβ/δ is expressed more ubiquitously and is the predominant isotype in skeletal muscle. It is involved in energy metabolism, mitochondrial biogenesis, and fiber-type switching. The expression of PPARγ is high in adipocytes, but it is also implicated in lipid deposition in muscle and other organs. Collectively, all three PPAR isotypes have a major impact on muscle homeostasis either directly or indirectly. Furthermore, reciprocal interactions have been found between PPARs and the gut microbiota along the gut–muscle axis in both health and disease. Herein, we review functions of PPARs in skeletal muscle and their interaction with the gut microbiota in the context of muscle wasting.

Pre-diagnostic biomarkers of type 2 diabetes identified in the UAE's obese national population using targeted metabolomics

Currently, type 2 diabetes mellitus (T2DM) and obesity are major global public health issues, and their prevalence in the United Arab Emirates (UAE) are among the highest in the world. In 2019, The UAE diabetes national prevalence was 15.4%. In recent years there has been a considerable investigation of predictive biomarkers associated with these conditions. This study analysed fasting (8 h) blood samples from an obese, normoglycemic cohort and an obese, T2DM cohort of UAE nationals, employing clinical chemistry analysis, 1D ¹H NMR and mass spectroscopy (FIA-MS/MS and LC-MS/MS) techniques. The novel findings reported for the first time in a UAE population revealed significant differences in a number of metabolites in the T2DM cohort. Metabolic fingerprints identified by NMR included BCAAs, trimethylamine N-oxide, β-hydroxybutyrate, trimethyl uric acid, and alanine. A targeted MS approach showed significant differences in lysophosphatidylcholines, phosphatidylcholines, acylcarnitine, amino acids and sphingomyelins; Lyso.PC.a.C18.0, PC.ae.C34.2, C3.DC..C4.OH, glutamine and SM.C16.1, being the most significant metabolites. Pearson's correlation studies showed associations between these metabolites and the clinical chemistry parameters across both cohorts. This report identified differences in metabolites in response to T2DM in agreement with many published population studies. This contributes to the global search for a bank of metabolite biomarkers that can predict the advent of T2DM and give insight to its pathogenic mechanisms.

PPARδ and FOXO1 Mediate Palmitate-Induced Inhibition of Muscle Pyruvate Dehydrogenase Complex and CHO Oxidation, Events Reversed by Electrical Pulse Stimulation

The mechanisms behind the reduction in muscle pyruvate dehydrogenase complex (PDC)-controlled carbohydrate (CHO) oxidation during chronic high-fat dietary intake are poorly understood, as is the basis of CHO oxidation restoration during muscle contraction. C2C12 myotubes were treated with (300 μM) palmitate or without (control) for 16 h in the presence and absence of electrical pulse stimulation (EPS, 11.5 V, 1 Hz, 2 ms). Compared to control, palmitate reduced cell glucose uptake (p < 0.05), PDC activity (p < 0.01), acetylcarnitine accumulation (p < 0.05) and glucose-derived mitochondrial ATP production (p < 0.01) and increased pyruvate dehydrogenase kinase isoform 4 (PDK4) (p < 0.01), peroxisome proliferator-activated receptor alpha (PPARα) (p < 0.01) and peroxisome proliferator-activated receptor delta (PPARδ) (p < 0.01) proteins, and reduced the whole-cell p-FOXO1/t-FOXO1 (Forkhead Box O1) ratio (p < 0.01). EPS rescued palmitate-induced inhibition of CHO oxidation, reflected by increased glucose uptake (p < 0.01), PDC activity (p < 0.01) and glucose-derived mitochondrial ATP production (p < 0.01) compared to palmitate alone. EPS was also associated with less PDK4 (p < 0.01) and PPARδ (p < 0.01) proteins, and lower nuclear p-FOXO1/t-FOXO1 ratio normalised to the cytoplasmic ratio, but with no changes in PPARα protein. Collectively, these data suggest PPARδ, and FOXO1 transcription factors increased PDK4 protein in the presence of palmitate, which limited PDC activity and flux, and blunted CHO oxidation and glucose uptake. Conversely, EPS rescued these metabolic events by modulating the same transcription factors.

Untargeted Profiling of Bile Acids and Lysophospholipids Identifies the Lipid Signature Associated with Glycemic Outcome in an Obese Non-Diabetic Clinical Cohort

The development of high throughput assays for assessing lipid metabolism in metabolic disorders, especially in diabetes research, nonalcoholic fatty liver disease (NAFLD), and nonalcoholic steatohepatitis (NASH), provides a reliable tool for identifying and characterizing potential biomarkers in human plasma for early diagnosis or prognosis of the disease and/or responses to a specific treatment. Predicting the outcome of weight loss or weight management programs is a challenging yet important aspect of such a program’s success. The characterization of potential biomarkers of metabolic disorders, such as lysophospholipids and bile acids, in large human clinical cohorts could provide a useful tool for successful predictions. In this study, we validated an LC-MS method combining the targeted and untargeted detection of these lipid species. Its potential for biomarker discovery was demonstrated in a well-characterized overweight/obese cohort subjected to a low-caloric diet intervention, followed by a weight maintenance phase. Relevant markers predicting successful responses to the low-caloric diet intervention for both weight loss and glycemic control improvements were identified. The response to a controlled weight loss intervention could be best predicted using the baseline concentration of three lysophospholipids (PC(22:4/0:0), PE(17:1/0:0), and PC(22:5/0:0)). Insulin resistance on the other hand could be best predicted using clinical parameters and levels of circulating lysophospholipids and bile acids. Our approach provides a robust tool not only for research purposes, but also for clinical practice, as well as designing new clinical interventions or assessing responses to specific treatment. Considering this, it presents a step toward personalized medicine.

Knockout of butyrophilin subfamily 1 member A1 (BTN1A1) alters lipid droplet formation and phospholipid composition in bovine mammary epithelial cells

Background

Milk lipids originate from cytoplasmic lipid droplets (LD) that are synthesized and secreted from mammary epithelial cells by a unique membrane-envelopment process. Butyrophilin 1A1 (BTN1A1) is one of the membrane proteins that surrounds LD, but its role in bovine mammary lipid droplet synthesis and secretion is not well known.

Methods

The objective was to knockout BTN1A1 in bovine mammary epithelial cells (BMEC) via the CRISPR/Cas9 system and evaluate LD formation, abundance of lipogenic enzymes, and content of cell membrane phospholipid (PL) species. Average LD diameter was determined via Oil Red O staining, and profiling of cell membrane phospholipid species via liquid chromatography-tandem mass spectrometry (LC-MS/MS).

Results

Lentivirus-mediated infection of the Cas9/sgRNA expression vector into BMEC resulted in production of a homozygous clone BTN1A1^(−/−). The LD size and content decreased following BTN1A1 gene knockout. The mRNA abundance of fatty acid synthase (FASN) and peroxisome proliferator-activated receptor-gamma (PPARG) was downregulated in the BTN1A1^(−/−) clone. Subcellular analyses indicated that BTN1A1 and LD were co-localized in the cytoplasm. BTN1A1 gene knockout increased the percentage of phosphatidylethanolamine (PE) and decreased phosphatidylcholine (PC), which resulted in a lower PC/PE ratio.

Conclusions

Results suggest that BTN1A1 plays an important role in regulating LD synthesis via a mechanism involving membrane phospholipid composition.

Current metabolic perspective on malnutrition in obesity: towards more subgroup-based nutritional approaches?

Lifestyle intervention may be effective in reducing type 2 diabetes mellitus incidence and cardiometabolic risk. A more personalised nutritional approach based on an individual or subgroup-based metabolic profile may optimise intervention outcome. Whole body insulin resistance (IR) reflects defective insulin action in tissues such as muscle, liver, adipose tissue, gut and brain, which may precede the development of cardiometabolic diseases. IR may develop in different organs but the severity may vary between organs. Individuals with more pronounced hepatic IR have a distinct plasma metabolome and lipidome profile as compared with individuals with more pronounced muscle IR. Additionally, genes related to extracellular modelling were upregulated in abdominal subcutaneous adipose tissue in individuals with more pronounced hepatic IR, whilst genes related to inflammation as well as systemic low-grade inflammation were upregulated in individuals with primarily muscle IR. There are indications that these distinct IR phenotypes may also respond differentially to dietary macronutrient composition. Besides metabolic phenotype, microbial phenotype may be of importance in personalising the response to diet. In particular fibres or fibre mixtures, leading to a high distal acetate and SCFA production may have more pronounced effects on metabolic health. Notably, individuals with prediabetes may have a reduced response to diet-induced microbiota modulation with respect to host insulin sensitivity and metabolic health outcomes. Overall, we need more research to relate metabolic subphenotypes to intervention outcomes to define more optimal diets for individuals with or predisposed to chronic metabolic diseases.

PPARβ/δ recruits NCOR and regulates transcription reinitiation of ANGPTL4

In the absence of ligands, the nuclear receptor PPARβ/δ recruits the NCOR and SMRT corepressors, which form complexes with HDAC3, to canonical target genes. Agonistic ligands cause dissociation of corepressors and enable enhanced transcription. Vice versa, synthetic inverse agonists augment corepressor recruitment and repression. Both basal repression of the target gene ANGPTL4 and reinforced repression elicited by inverse agonists are partially insensitive to HDAC inhibition. This raises the question how PPARβ/δ represses transcription mechanistically. We show that the PPARβ/δ inverse agonist PT-S264 impairs transcription initiation by decreasing recruitment of activating Mediator subunits, RNA polymerase II, and TFIIB, but not of TFIIA, to the ANGPTL4 promoter. Mass spectrometry identifies NCOR as the main PT-S264-dependent interactor of PPARβ/δ. Reconstitution of knockout cells with PPARβ/δ mutants deficient in basal repression results in diminished recruitment of NCOR, SMRT, and HDAC3 to PPAR target genes, while occupancy by RNA polymerase II is increased. PT-S264 restores binding of NCOR, SMRT, and HDAC3 to the mutants, resulting in reduced polymerase II occupancy. Our findings corroborate deacetylase-dependent and -independent repressive functions of HDAC3-containing complexes, which act in parallel to downregulate transcription.

Targeted Metabolomics Shows Low Plasma Lysophosphatidylcholine 18:2 Predicts Greater Decline of Gait Speed in Older Adults: The Baltimore Longitudinal Study of Aging

Background

Gait speed is an important measure of lower extremity physical performance in older adults and is predictive of disability and mortality. The biological pathways involved in the decline of lower extremity physical performance are not well understood. We used a targeted metabolomics approach to identify plasma metabolites predictive of change in gait speed over time.

Methods

Gait speed was measured at baseline and over median follow-up of 50.5 months in 504 adults, aged ≥50 years, who had two or more study visits in the Baltimore Longitudinal Study of Aging (BLSA). Plasma metabolites were measured using targeted mass spectrometry (AbsoluteIDQ p180 Kit, Biocrates).

Results

Of 148 plasma metabolites (amino acids, biogenic amines, hexoses, glycerophospholipids) measured, eight were significantly associated with gait speed at baseline, independent of age and sex: hexoses (r = -0.148, p < .001), [sphingomyelin (SM) 16:1 (r = -0.091, p = .0009), SM 18:0 (r = -0.085, p = .002), SM 18:1 (r = -0.128, p < .0001], phosphatidylcholine aa 32:3 (r = -0.088, p = .001), lysophosphatidylcholine (LPC) 17:0 (r = 0.083, p = .003), LPC 18:1 (r = 0.089, p = .001), and LPC 18:2 (r = 0.104, p < .0001). Adjusting for baseline age, sex, and chronic diseases, baseline plasma LPC 18:2 was an independent predictor of the rate of change of gait speed over subsequent follow-up (p = .003). No other plasma metabolites were significantly associated longitudinal changes of gait speed over time.

Conclusions

Low plasma LPC 18:2, which has previously been shown to predict impaired glucose tolerance, insulin resistance, type 2 diabetes, coronary artery disease, and memory impairment, is an independent predictor of decline in gait speed in older adults.

Pre-meal protein intake alters postprandial plasma metabolome in subjects with metabolic syndrome

PURPOSE

We examined the effect on the postprandial plasma metabolome of protein pre-meals before a fat-rich main meal.

METHODS

Two randomized, cross-over meal studies were conducted to test the dose-response effect (0 g, 10 g, 20 g) of a pre-meal with whey protein (WP) (PREMEAL I), and the effect of protein quality (10 g WP, casein, or gluten) and timing (- 15 min vs - 30 min) of the pre-meal (PREMEAL II). Participants with metabolic syndrome received one of the test meals on each test day, - 15 min (or - 30 min) prior to a standardized fat-rich breakfast. Plasma samples were collected at - 15 min (or - 30 min), 0, 120, 240 a nd 360 min and analyzed using liquid chromatography-mass spectrometry with an untargeted method.

RESULTS

Pre-meal WP intake elevated plasma branched-chain amino acids (BCAA), aromatic amino acids and methionine and decreased plasma LPC (16:0) and PC (32:1) levels before the main meal. Early (- 15 to 0 min) aromatic amino acids and BCAA in response to pre-meal WP partially predict the glucose and insulin response after the main meal. A pre-meal with WP altered the postprandial plasma metabolic pattern of acyl-carnitines, specific PCs, LPCs and LPEs, betaine, citric acid, linoleic acid, and β-hydroxypalmitic acid compared to no pre-meal. The casein and WP pre-meals exhibited similar postprandial amino acid responses whereas a pre-meal with gluten resulted in lower levels of plasma amino acids and its metabolites.

CONCLUSION

A pre-meal with protein affects the postprandial metabolic pattern indicating facilitated glucose and lipid disposal from plasma in participants with metabolic syndrome.

A Metabolomics Approach to Investigate Kukoamine B-A Potent Natural Product With Anti-diabetic Properties

Due to the surge in type 2 diabetes mellitus (T2DM), treatments for chronic metabolic dysregulations with fewer side-effects are sought. Lycii Cortex (LyC), a traditional Chinese Medicine (TCM) herb has a long history of being widely prescribed to treat T2DM as alternative medicine; however, the bioactive molecules and working mechanism remained unknown. Previous studies revealed kukoamine B (KB) as a major and featured compound for LyC with bioactivities for anti-oxidation and acute inflammation, which may be related to anti-diabetes properties. This study aims to understand the efficacy and the mode of action of KB in the diabetic (db/db) mouse model using a metabolomics approach. Parallel comparison was conducted using the first-line anti-diabetic drugs, metformin and rosligtazone, as positive controls. The db/db mice were treated with KB (50 mg kg-1 day-1) for 9 weeks. Bodyweight and fasting blood glucose were monitored every 5 and 7 days, respectively. Metabolomics and high-throughput molecular approaches, including lipidomics, targeted metabolomics (Biocrates p180), and cytokine profiling were applied to measure the alteration of serum metabolites and inflammatory biomarkers between different treatments vs. control (db/db mice treated with vehicle). After 9 weeks of treatment, KB lowered blood glucose, without the adverse effects of bodyweight gain and hepatomegaly shown after rosiglitazone treatment. Lipidomics analysis revealed that KB reduced levels of circulating triglycerides, cholesterol, phosphatidylethanolamine, and increased levels of phosphatidylcholines. KB also increased acylcarnitines, and reduced systemic inflammation (cytokine array). Pathway analysis suggested that KB may regulate nuclear transcription factors (e.g., NF-κB and/or PPAR) to reduce inflammation and facilitate a shift toward metabolic and inflammatory homeostasis. Comparison of KB with first-line drugs suggests that rosiglitazone may over-regulate lipid metabolism and anti-inflammatory responses, which may be associated with adverse side effects, while metformin had less impact on lipid and anti-inflammation profiles. Our research from holistic and systemic views supports the conclusion that KB is the bioactive compound of LyC for managing T2DM, and suggests KB as a nutraceutical or a pharmaceutical candidate for T2D treatment. In addition, our research provides insights related to metformin and rosiglitazone action, beyond lowering blood glucose.

A comprehensive strategy for studying protein-metabolite interactions by metabolomics and native mass spectrometry

Protein-metabolite interactions play important roles in many cellular and physiological processes in biological systems. However, the lack of effective research approaches impedes the understanding of the protein-metabolite interactions. In this study, a novel comprehensive strategy by combining metabolomics platform with native mass spectrometry was developed for investigating the protein-metabolite interactions. Peroxisome proliferator-activated receptors gamma (PPARγ) is a lipid-binding nuclear receptors that plays a key role in regulating fatty-acid oxidation and lipid metabolism, which was selected as the model protein. Seven metabolites including lyso-phosphatidylcholine (LPC) 16:0, LPC18:0, LPC18:1, arachidonic acid, oleic acid, linoleic acid and palmitoleic acid (p < 0.05) were found to have the possible interactions with the PPARγ, these LPCs were discovered as candidate ligands for the first time by using untargeted metabolomics method. Native mass spectrometry based on 15 T Fourier transform ion cyclotron resonance mass spectrometer was employed to directly detect the PPARγ-LPCs complexes to obtain their stoichiometry and kinetic constants. Isothermal titration calorimetry, circular dichroism spectrum and molecular modeling were further utilized to investigate the thermodynamics, conformation and binding mechanism of the interaction between PPARγ and LPCs. It was found that the PPARγ-LPC interaction was an endothermic process, and these LPCs have similar binding constants with stoichiometric number of 1:1. The novel strategy can provide a very useful approach for mapping and identifying unknown protein-metabolite interactions in biological systems.

Plasma lipid profiling of tissue-specific insulin resistance in human obesity

BACKGROUND/OBJECTIVES

Obesity-associated insulin resistance (IR) may develop in multiple organs, representing different aetiologies towards cardiometabolic diseases. This study aimed to identify distinct plasma lipid profiles in overweight/obese individuals who show muscle-IR and/or liver-IR.

SUBJECTS/METHODS

Baseline data of the European multicenter DiOGenes project were used (n = 640; 401 women, nondiabetic BMI: 27-45 kg/m²). Muscle insulin sensitivity index (MISI) and hepatic insulin resistance index (HIRI) were derived from a 5-point oral glucose tolerance test. The 140 plasma lipids were quantified by liquid chromatography-mass spectrometry. Linear mixed models were used to evaluate associations between MISI, HIRI and plasma lipids.

RESULTS

MISI was comparable between sexes while HIRI and triacylglycerol (TAG) levels were lower in women than in men. MISI was associated with higher lysophosphatidylcholine (LPC) levels (standardized (std)β = 0.126; FDR-p = 0.032). Sex interactions were observed for associations between HIRI, TAG and diacylglycerol (DAG) lipid classes. In women, but not in men, HIRI was associated with higher levels of TAG (44 out of 55 species) and both DAG species (stdβ: 0.139-0.313; FDR-p < 0.05), a lower odd-chain/even-chain TAG ratio (stdβ = -0.182; FDR-p = 0.005) and a lower very-long-chain/long-chain TAG ratio (stdβ = -0.156; FDR-p = 0.037).

CONCLUSIONS

In overweight/obese individuals, muscle insulin sensitivity is associated with higher plasma LPC concentrations. Women have less hepatic IR and lower TAG than men. Nevertheless, hepatic IR is associated with higher plasma TAG and DAG concentrations and a lower abundance of odd-chain and very-long-chain TAG in women, but not in men. This suggests a more pronounced worsening of plasma lipid profile in women with the progression of hepatic IR.

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.

Obesity, adipokines, and C-peptide are associated with distinct plasma phospholipid profiles in adult males, an untargeted lipidomic approach

Obesity is associated with dysregulated lipid metabolism and adipokine secretion. Our group has previously reported obesity and adipokines are associated with % total fatty acid (FA) differences in plasma phospholipids. The objective of our current study was to identify in which complex lipid species (i.e., phosphatidylcholine, sphingolipids, etc) these FA differences occur. Plasma lipidomic profiling (n = 126, >95% Caucasian, 48–65 years) was performed using chromatographic separation and high resolution tandem mass spectrometry. The responses used in the statistical analyses were body mass index (BMI), waist circumference (WC), serum adipokines, cytokines, and a glycemic marker. High-dimensional statistical analyses were performed, all models were adjusted for age and smoking, and p-values were adjusted for false discovery. In Bayesian models, the lipidomic profiles (over 1,700 lipids) accounted for >60% of the inter-individual variation of BMI, WC, and leptin in our population. Across statistical analyses, we report 51 individual plasma lipids were significantly associated with obesity. Obesity was inversely associated lysophospholipids and ether linked phosphatidylcholines. In addition, we identify several unreported lipids associated with obesity that are not present in lipid databases. Taken together, these results provide new insights into the underlying biology associated with obesity and reveal new potential pathways for therapeutic targeting.

Angiopoietin-like 4 directs uptake of dietary fat away from adipose during fasting

Objective

Angiopoietin-like 4 (ANGPTL4) is a fasting-induced inhibitor of lipoprotein lipase (LPL) and a regulator of plasma triglyceride metabolism. Here, we examined the kinetics of Angptl4 induction and tested the hypothesis that ANGPTL4 functions physiologically to reduce triglyceride delivery to adipose tissue during nutrient deprivation.

Methods

Gene expression, LPL activity, and triglyceride uptake were examined in fasted and fed wild-type and Angptl4^−/− mice.

Results

Angptl4 was strongly induced early in fasting, and this induction was suppressed in mice with access to food during the light cycle. Fasted Angptl4^−/− mice manifested increased LPL activity and triglyceride uptake in adipose tissue compared to wild-type mice.

Conclusions

Angptl4 is induced early in fasting to divert uptake of fatty acids and triglycerides away from adipose tissues.

•Angptl4 is induced within the first few hours of fasting.

•Angptl4 expression is driven by fasting rather than circadian rhythms.

•Fasted Angptl4^−/− mice have increased triglyceride uptake in adipose tissue.

•Angptl4^−/− mice also have increased LPL activity specifically in adipose tissue.

•Data support a model where ANGPTL4 acts locally in adipose during fasting.

Roles of Peroxisome Proliferator-Activated Receptor β/δ in skeletal muscle physiology

More than two decades of studying Peroxisome Proliferator-Activated Receptors (PPARs) has led to an understanding of their implications in various physiological processes that are key for health and disease. All three PPAR isotypes, PPARα, PPARβ/δ, and PPARγ, are activated by a variety of molecules, including fatty acids, eicosanoids and phospholipids, and regulate a spectrum of genes involved in development, lipid and carbohydrate metabolism, inflammation, and proliferation and differentiation of many cell types in different tissues. The hypolipidemic and antidiabetic functions of PPARα and PPARγ in response to fibrate and thiazolidinedione treatment, respectively, are well documented. However, until more recently the functions of PPARβ/δ were less well defined, but are now becoming more recognized in fatty acid metabolism, energy expenditure, and tissue repair. Skeletal muscle is an active metabolic organ with high plasticity for adaptive responses to varying conditions such as fasting or physical exercise. It is the major site of energy expenditure resulting from lipid and glucose catabolism. Here, we review the multifaceted roles of PPARβ/δ in skeletal muscle physiology.