Branched Fatty Acid Esters of Hydroxy Fatty Acids (FAHFAs) Protect against Colitis by Regulating Gut Innate and Adaptive Immune Responses

Plasma fatty acid esters of hydroxy fatty acids and surrogate fatty acid esters of hydroxy fatty acids hydrolysis activity in children with or without obesity and in adults with or without coronary artery disease

AIM

Fatty acid esters of hydroxy fatty acids (FAHFA) are a class of bioactive lipids with anti-inflammatory, antidiabetic and cardioprotective properties. FAHFA hydrolysis into its fatty acid (FA) and hydroxy fatty acid (HFA) constituents can affect the bioavailability of FAHFA and its subsequent biological effects. We aimed to investigate FAHFA levels and FAHFA hydrolysis activity in children with or without obesity, and in adults with or without coronary artery disease (CAD).

MATERIALS AND METHODS

Our study cohort included 20 children without obesity, 40 children with obesity, 10 adults without CAD and 28 adults with CAD. We quantitated plasma levels of four families of FAHFA [palmitic acid hydroxy stearic acid (PAHSA), palmitoleic acid hydroxy stearic acid (POHSA), oleic acid hydroxy stearic acid (OAHSA), stearic acid hydroxy stearic acid] and their corresponding FA and HFA constituents using liquid chromatography-tandem mass spectrometry analysis. Surrogate FAHFA hydrolysis activity was estimated as the FA/FAHFA or HFA/FAHFA ratio.

RESULTS

Children with obesity had lower plasma PAHSA (p = .001), OAHSA (p = .006) and total FAHFA (p = .011) levels, and higher surrogate FAHFA hydrolysis activity represented by PA/PAHSA (p = .040) and HSA/OAHSA (p = .025) compared with children without obesity. Adults with CAD and a history of myocardial infarction (MI) had lower POHSA levels (p = .026) and higher PA/PAHSA (p = .041), POA/POHSA (p = .003) and HSA/POHSA (p = .038) compared with those without MI.

CONCLUSION

Altered FAHFA metabolism is associated with obesity and MI, and inhibition of FAHFA hydrolysis should be studied further as a possible therapeutic strategy in obesity and MI.

Beneficial metabolic effects of PAHSAs depend on the gut microbiota in diet-induced obese mice but not in chow-fed mice

Dietary lipids play an essential role in regulating the function of the gut microbiota and gastrointestinal tract, and these luminal interactions contribute to mediating host metabolism. Palmitic Acid Hydroxy Stearic Acids (PAHSAs) are a family of lipids with antidiabetic and anti-inflammatory properties, but whether the gut microbiota contributes to their beneficial effects on host metabolism is unknown. Here, we report that treating chow-fed female and male germ-free (GF) mice with PAHSAs improves glucose tolerance, but these effects are lost upon high fat diet (HFD) feeding. However, transfer of feces from PAHSA-treated, but not vehicle-treated, chow-fed conventional mice increases insulin sensitivity in HFD-fed GF mice. Thus, the gut microbiota is necessary for, and can transmit, the insulin-sensitizing effects of PAHSAs in HFD-fed GF male mice. Analyses of the cecal metagenome and lipidome of PAHSA-treated mice identified multiple lipid species that associate with the gut commensal Bacteroides thetaiotaomicron (Bt) and with insulin sensitivity resulting from PAHSA treatment. Supplementing live, and to some degree, heat-killed Bt to HFD-fed female mice prevented weight gain, reduced adiposity, improved glucose tolerance, fortified the colonic mucus barrier and reduced systemic inflammation compared to HFD-fed controls. These effects were not observed in HFD-fed male mice. Furthermore, ovariectomy partially reversed the beneficial Bt effects on host metabolism, indicating a role for sex hormones in mediating the Bt probiotic effects. Altogether, these studies highlight the fact that PAHSAs can modulate the gut microbiota and that the microbiota is necessary for the beneficial metabolic effects of PAHSAs in HFD-fed mice.

Fatty acid esters of hydroxy fatty acids: A potential treatment for obesity-related diseases

Obesity, a burgeoning worldwide health system challenge, is associated with multiple chronic diseases, including diabetes and chronic inflammation. Fatty acid esters of hydroxy fatty acids (FAHFAs) are newly identified lipids with mitigating and anti-inflammatory effects in diabetes. Increasing work has shown that FAHFAs exert antioxidant activity and enhance autophagy in neuronal cells and cardiomyocytes. We systematically summarized the biological activities of FAHFAs, including their regulatory effects on diabetes and inflammation, antioxidant activity, and autophagy augmentation. Notably, the structure-activity relationships and potential biosynthesis of FAHFAs are thoroughly discussed. FAHFAs also showed potential roles as diagnostic biomarkers. FAHFAs are a class of resources with promising applications in the biomedical field that require in-depth research and hotspot development, as their structure has not been fully resolved and their biological activity has not been fully revealed.

Inflammation causes insulin resistance in mice via interferon regulatory factor 3 (IRF3)-mediated reduction in FAHFA levels

Obesity-induced inflammation causes metabolic dysfunction, but the mechanisms remain elusive. Here we show that the innate immune transcription factor interferon regulatory factor (IRF3) adversely affects glucose homeostasis through induction of the endogenous FAHFA hydrolase androgen induced gene 1 (AIG1) in adipocytes. Adipocyte-specific knockout of IRF3 protects male mice against high-fat diet-induced insulin resistance, whereas overexpression of IRF3 or AIG1 in adipocytes promotes insulin resistance on a high-fat diet. Furthermore, pharmacological inhibition of AIG1 reversed obesity-induced insulin resistance and restored glucose homeostasis in the setting of adipocyte IRF3 overexpression. We, therefore, identify the adipocyte IRF3/AIG1 axis as a crucial link between obesity-induced inflammation and insulin resistance and suggest an approach for limiting the metabolic dysfunction accompanying obesity.

Comparative Metabolome and Transcriptome Analyses Reveal Differential Enrichment of Metabolites with Age in Panax notoginseng Roots

Panax notoginseng is a perennial plant well known for its versatile medicinal properties, including hepatoprotective, antioxidant, anti-inflammatory, anti-tumor, estrogen-like, and antidepressant characteristics. It has been reported that plant age affects the quality of P. notoginseng. This study aimed to explore the differential metabolome and transcriptome of 2-year (PN2) and 3-year-old (PN3) P. notoginseng plant root samples. Principal component analysis of metabolome and transcriptome data revealed major differences between the two groups (PN2 vs. PN3). A total of 1813 metabolites and 28,587 genes were detected in this study, of which 255 metabolites and 3141 genes were found to be differential (p < 0.05) between PN2 vs. PN3, respectively. Among differential metabolites and genes, 155 metabolites and 1217 genes were up-regulated, while 100 metabolites and 1924 genes were down-regulated. The KEGG pathway analysis revealed differentially enriched metabolites belonging to class lipids ("13S-hydroperoxy-9Z, 11E-octadecadionic acid", "9S-hydroxy-10E, 12Z-octadecadionic acid", "9S-oxo-10E, 12Z-octadecadionic acid", and "9,10,13-trihydroxy-11-octadecadionic acid"), nucleotides and derivatives (guanine and cytidine), and phenolic acids (chlorogenic acid) were found to be enriched (p < 0.05) in PN3 compared to PN2. Further, these differentially enriched metabolites were found to be significantly (p < 0.05) regulated via linoleic acid metabolism, nucleotide metabolism, plant hormone signal transduction, and arachidonic acid metabolism pathways. Furthermore, the transcriptome analysis showed the up-regulation of key genes MAT, DMAS, SDH, gallate 1-beta-glucosyltransferase, and beta-D-glucosidase in various plants' secondary metabolic pathways and SAUR, GID1, PP2C, ETR, CTR1, EBF1/2, and ERF1/2 genes observed in phytohormone signal transduction pathway that is involved in plant growth and development, and protection against the various stressors. This study concluded that the roots of a 3-year-old P. notoginseng plant have better metabolome and transcriptome profiles compared to a 2-year-old plant with importantly enriched metabolites and genes in pathways related to metabolism, plant hormone signal transduction, and various biological processes. These findings provide insights into the plant's dynamic biochemical and molecular changes during its growth that have several implications regarding its therapeutic use.

Susceptibility to febrile malaria is associated with an inflammatory gut microbiome

Malaria is a major public health problem, but many of the factors underlying the pathogenesis of this disease are not well understood. Here, we demonstrate in Malian children that susceptibility to febrile malaria following infection with Plasmodium falciparum is associated with the composition of the gut microbiome prior to the malaria season. Gnotobiotic mice colonized with the fecal samples of malaria-susceptible children had a significantly higher parasite burden following Plasmodium infection compared to gnotobiotic mice colonized with the fecal samples of malaria-resistant children. The fecal microbiome of the susceptible children was enriched for bacteria associated with inflammation, mucin degradation, gut permeability and inflammatory bowel disorders (e.g., Ruminococcus gauvreauii, Ruminococcus torques, Dorea formicigenerans, Dorea longicatena, Lachnoclostridium phocaeense and Lachnoclostridium sp. YL32). However, the susceptible children also had a greater abundance of bacteria known to produce anti-inflammatory short-chain fatty acids and those associated with favorable prognosis and remission following dysbiotic intestinal events (e.g., Anaerobutyricum hallii, Blautia producta and Sellimonas intestinalis). Metabolomics analysis of the human fecal samples corroborated the existence of inflammatory and recovery-associated features within the gut microbiome of the susceptible children. There was an enrichment of nitric oxide-derived DNA adducts (deoxyinosine and deoxyuridine) and long-chain fatty acids, the absorption of which has been shown to be inhibited by inflamed intestinal epithelial cells, and a decrease in the abundance of mucus phospholipids. Nevertheless, there were also increased levels of pseudouridine and hypoxanthine, which have been shown to be regulated in response to cellular stress and to promote recovery following injury or hypoxia. Overall, these results indicate that the gut microbiome may contribute malaria pathogenesis and suggest that therapies targeting intestinal inflammation could decrease malaria susceptibility.

The chemical and biological characteristics of fatty acid esters of hydroxyl fatty acids

With the continuous advancements in detection methods and the exploration of unknown substances, an increasing number of bioactive compounds are being discovered. Fatty acid esters of hydroxyl fatty acids (FAHFAs), a class of endogenous lipids found in 2014, exhibit various physiological activities, such as improving glucose tolerance and insulin sensitivity, stimulating insulin secretion, and demonstrating broad anti-inflammatory effects. Moreover, some FAHFAs are closely linked to intestinal health and can serve as potential biomarkers for gut health. Various FAHFAs have been observed in food, including palmitic acid esters of hydroxy stearic acids (PAHSA), oleic acid esters of hydroxy stearic acids (OAHSA), linoleic acid esters of hydroxy linoleic acid (LAHLA). As a type of lipid regularly consumed in the daily diet, it is highly important to ascertain the types and quantities of FAHFAs present in the diet. This article, based on existing research, provides a review of the analysis methods for FAHFAs, particularly focusing on the separation of chiral isomers. It also summarizes the sources and contents of dietary FAHFAs, emphasizing their bioavailability and impact on the gut. Understanding the beneficial effects of these lipids in the diet can serve as a valuable reference for the development of specific functional foods.

Synthesis and quantification of short-chain fatty acid esters of hydroxy fatty acids in rat intestinal contents and fecal samples by LC-MS/MS

Short-chain fatty acid esters of hydroxy fatty acids (SFAHFAs) are a new class of endogenous lipids belonging to the fatty acid esters of the hydroxy fatty acid family. We previously uncovered their chemical structure and discussed their potential biological significance. We anticipate an increased need for SFAHFA measurements as markers of metabolic and inflammatory health. In this study, we synthesized sixty isomeric SFAHFAs by combining 12 hydroxy fatty acids (C16-C24) and five short-chain fatty acids (C2-C6) including a labelled internal standard. SFAHFA enrichment was achieved by solid-phase extraction and established a sensitive method for their quantitation by targeted LC-MS/MS. The method was applied to profile SFAHFAs in intestinal contents and fecal samples collected from rats fed a high-fat diet (HFD). The results demonstrated a significant decrease in SFAHFAs in the intestinal contents of the HFD group compared with the control group. The fecal time course (0-8 weeks) profile of SFAHFAs showed significant downregulation of acetic and propanoic acid esters in just 2 weeks after HFD administration. This study offers the first synthesis and quantitation method for SFAHFAs, demonstrating their potential use in elucidating SFAHFA sources, their role in various diseases, and potential biochemical signalling pathways.

A Chemo-Enzymatic Cascade Strategy for the Synthesis of Phosphatidylcholine Incorporated with Structurally Diverse FAHFAs

Fatty acid esters of hydroxy fatty acids (FAHFAs), a newly discovered class of human endogenous complex lipids showing great promise for treating diabetes and inflammatory diseases, exist naturally in extremely low concentrations. This work reports a chemo-enzymatic approach for the comprehensive synthesis of phospholipids containing FAHFAs via sequential steps: hydratase-catalyzed hydration of unsaturated fatty acids to generate structurally diverse hydroxy fatty acids (HFAs), followed by the selective esterification of these HFAs with fatty acids mediated by secondary alcohol-specific Candida antarctica lipase A (CALA), resulting in the formation of a series of diverse FAHFA analogs. The final synthesis is completed through carbodiimide-based coupling of FAHFAs with glycerophosphatidylcholine. Optimal reaction conditions are identified for each step, and the substrate affinity of CALA, responsible for the catalytic mechanisms during FAHFA production, is evaluated through molecular docking. Compared to multistep lab-tedious chemical synthesis, this route, relying on natural building blocks and natural biocatalysts, is significantly facile, scalable, and highly selective, affording high yields (74-98 mol %) in each step for the construction of higher FAHFA-PC series (10/12/13-FAHFAs). The developed strategy aims to increase the availability of naturally occurring FAHFA species and provide the tools for the construction of versatile and novel analogs of FAHFA conjugates.

The impacts of biologic treatment on metabolic profiling in psoriasis

Psoriasis is an immune-mediated inflammatory disease commonly accompanied by various metabolic disorders. It is widely known that biologics could affect the metabolic status and comorbidities in psoriasis patients, however, the effects of biologics on metabolism in psoriasis patients remain poorly understood. The aim of this study was to elucidate the characteristic changes of metabolic profiling in psoriasis vulgaris (PsV) patients before and after applying biologics. Plasma samples were collected from a retrospective cohort of 43 PsV patients. Non-targeted metabolomics analyses were performed using liquid chromatography-mass spectrometry (LC-MS) to compare the metabolic profiles before and after applying adalimumab (ADA) or ixekizumab (IXE) for 4 weeks. Additionally, correlation analyses were conducted to investigate the associations between metabolite expression levels and clinical characteristics. The biologics significantly affected the metabolic profiles of PsV patients especially in glycerophospholipids (GPs). First, phosphatidylcholine (PC), unsaturated lysophosphatidylcholine (LPC), unsaturated lysophosphatidic acid (LPA) and unsaturated lysophosphatidylethanolamine (LPE) were significantly up-regulated, whereas phosphatidylethanolamine (PE), saturated LPC, saturated LPA and saturated LPE were predominantly down-regulated after biologic treatment. What is more, the changes in PE and LPA were mainly observed after applying IXE instead of ADA. Second, we also found GPs including PC, unsaturated LPC, unsaturated LPA and unsaturated LPE were primarily negatively correlated with disease severity, whereas, PE, saturated LPC, saturated LPA and saturated LPE displayed inverse correlations. Biologics could affect GP metabolism and facilitate the transition of metabolic status from a pro-inflammatory to an anti-inflammatory phenotype in PsV patients.

GPR120/FFAR4: A Potential New Therapeutic Target for Inflammatory Bowel Disease

Inflammatory bowel disease, whose major forms are Crohn's disease and ulcerative colitis, is characterized by chronic inflammation of the gut due to the loss of tolerance toward antigens normally contained in the gut lumen. G protein-coupled receptor (GPR) 120 has gained considerable attention as a potential therapeutic target for metabolic disorders due to its implication in the production of the incretin hormone glucagon-like peptide 1 and the secretion of cholecystokinin. Recent studies have also highlighted the role of GPR120 in regulating immune system activity and inflammation. GPR120, expressed by intestinal epithelial cells, proinflammatory macrophages, enteroendocrine L cells, and CD4+ T cells, suppresses proinflammatory and enhances anti-inflammatory cytokine production, suggesting that GPR120 might have a pivotal role in intestinal inflammation and represent a possible therapeutic target in inflammatory bowel disease. This narrative review aims at summarizing the role of GPR120 in the maintenance of intestinal homeostasis through the analysis of the most recent studies.

The Metabolomic Characteristics and Dysregulation of Fatty Acid Esters of Hydroxy Fatty Acids in Breast Cancer

Lipid reprogramming metabolism is crucial for supporting tumor growth in breast cancer and investigating potential tumor biomarkers. Fatty acid esters of hydroxy fatty acids (FAHFAs) are a class of endogenous lipid metabolites with anti-diabetic and anti-inflammatory properties that have been discovered in recent years. Our previous targeted analysis of sera from breast cancer patients revealed a significant down-regulation of several FAHFAs. In this study, we aimed to further explore the relationship between FAHFAs and breast cancer by employing chemical isotope labeling combined with liquid chromatography-mass spectrometry (CIL-LC-MS) for profiling of FAHFAs in tumors and adjacent normal tissues from breast cancer patients. Statistical analysis identified 13 altered isomers in breast cancer. These isomers showed the potential to distinguish breast cancer tissues with an area under the curve (AUC) value above 0.9 in a multivariate receiver operating curve model. Furthermore, the observation of up-regulated 9-oleic acid ester of hydroxy stearic acid (9-OAHSA) and down-regulated 9-hydroxystearic acid (9-HSA) in tumors suggests that breast cancer shares similarities with colorectal cancer, and their potential mechanism is to attenuate the effects of pro-apoptotic 9-HSA by enhancing the synthesis of FAHFAs, thereby promoting tumor survival and progression through this buffering system.

Beneficial metabolic effects of PAHSAs depend on the gut microbiota in diet-induced obese mice

Dietary lipids play an essential role in regulating the function of the gut microbiota and gastrointestinal tract, and these luminal interactions contribute to mediating host metabolism. PAHSAs are a class of lipids with anti-diabetic and anti-inflammatory properties, but whether the gut microbiota contributes to their beneficial effects on host metabolism is unknown. Here, we report that treating high fat diet (HFD)-fed germ-free mice with PAHSAs does not improve insulin sensitivity. However, transfer of feces from PAHSA-treated, but not Vehicle-treated, chow-fed mice increases insulin-sensitivity in HFD-fed germ free mice. Thus, the gut microbiota is necessary for and can transmit the insulin-sensitizing effects of PAHSAs in HFD-fed germ-free mice. Functional analyses of the cecal metagenome and lipidome of PAHSA-treated mice identified multiple lipid species that associate with the gut commensal Bacteroides thetaiotaomicron ( Bt ) and with insulin sensitivity resulting from PAHSA treatment. Bt supplementation in HFD-fed female mice prevented weight gain, reduced adiposity, improved glucose tolerance, fortified the colonic mucus barrier and reduced systemic inflammation versus chow-fed controls, effects that were not observed in HFD-fed male mice. Furthermore, ovariectomy partially reversed the beneficial Bt effects on host metabolism, indicating a role for sex hormones in mediating probiotic effects. Altogether, these studies highlight the fact that lipids can modulate the gut microbiota resulting in improvement in host metabolism and that PAHSA-induced changes in the microbiota result in at least some of their insulin-sensitizing effects in female mice.

Lipid remodeling of adipose tissue in metabolic health and disease

Adipose tissue is a dynamic and metabolically active organ that plays a crucial role in energy homeostasis and endocrine function. Recent advancements in lipidomics techniques have enabled the study of the complex lipid composition of adipose tissue and its role in metabolic disorders such as obesity, diabetes, and cardiovascular disease. In addition, adipose tissue lipidomics has emerged as a powerful tool for understanding the molecular mechanisms underlying these disorders and identifying bioactive lipid mediators and potential therapeutic targets. This review aims to summarize recent lipidomics studies that investigated the dynamic remodeling of adipose tissue lipids in response to specific physiological changes, pharmacological interventions, and pathological conditions. We discuss the molecular mechanisms of lipid remodeling in adipose tissue and explore the recent identification of bioactive lipid mediators generated in adipose tissue that regulate adipocytes and systemic metabolism. We propose that manipulating lipid-mediator metabolism could serve as a therapeutic approach for preventing or treating obesity-related metabolic diseases.

Polyunsaturated Fatty Acids: Conversion to Lipid Mediators, Roles in Inflammatory Diseases and Dietary Sources

Polyunsaturated fatty acids (PUFAs) are important components of the diet of mammals. Their role was first established when the essential fatty acids (EFAs) linoleic acid and α-linolenic acid were discovered nearly a century ago. However, most of the biochemical and physiological actions of PUFAs rely on their conversion to 20C or 22C acids and subsequent metabolism to lipid mediators. As a generalisation, lipid mediators formed from n-6 PUFAs are pro-inflammatory while those from n-3 PUFAs are anti-inflammatory or neutral. Apart from the actions of the classic eicosanoids or docosanoids, many newly discovered compounds are described as Specialised Pro-resolving Mediators (SPMs) which have been proposed to have a role in resolving inflammatory conditions such as infections and preventing them from becoming chronic. In addition, a large group of molecules, termed isoprostanes, can be generated by free radical reactions and these too have powerful properties towards inflammation. The ultimate source of n-3 and n-6 PUFAs are photosynthetic organisms which contain Δ-12 and Δ-15 desaturases, which are almost exclusively absent from animals. Moreover, the EFAs consumed from plant food are in competition with each other for conversion to lipid mediators. Thus, the relative amounts of n-3 and n-6 PUFAs in the diet are important. Furthermore, the conversion of the EFAs to 20C and 22C PUFAs in mammals is rather poor. Thus, there has been much interest recently in the use of algae, many of which make substantial quantities of long-chain PUFAs or in manipulating oil crops to make such acids. This is especially important because fish oils, which are their main source in human diets, are becoming limited. In this review, the metabolic conversion of PUFAs into different lipid mediators is described. Then, the biological roles and molecular mechanisms of such mediators in inflammatory diseases are outlined. Finally, natural sources of PUFAs (including 20 or 22 carbon compounds) are detailed, as well as recent efforts to increase their production.

Physiological and pathological roles of lipogenesis

Lipids are essential metabolites, which function as energy sources, structural components and signalling mediators. Most cells are able to convert carbohydrates into fatty acids, which are often converted into neutral lipids for storage in the form of lipid droplets. Accumulating evidence suggests that lipogenesis plays a crucial role not only in metabolic tissues for systemic energy homoeostasis but also in immune and nervous systems for their proliferation, differentiation and even pathophysiological roles. Thus, excessive or insufficient lipogenesis is closely associated with aberrations in lipid homoeostasis, potentially leading to pathological consequences, such as dyslipidaemia, diabetes, fatty liver, autoimmune diseases, neurodegenerative diseases and cancers. For systemic energy homoeostasis, multiple enzymes involved in lipogenesis are tightly controlled by transcriptional and post-translational modifications. In this Review, we discuss recent findings regarding the regulatory mechanisms, physiological roles and pathological importance of lipogenesis in multiple tissues such as adipose tissue and the liver, as well as the immune and nervous systems. Furthermore, we briefly introduce the therapeutic implications of lipogenesis modulation.

Immune regulation of poly unsaturated fatty acids and free fatty acid receptor 4

Fatty acid metabolism contributes to energy supply and plays an important role in regulating immunity. Free fatty acids (FFAs) bind to free fatty acid receptors (FFARs) on the cell surface and mediate effects through the intra-cellular FFAR signaling pathways. FFAR4, also known as G-protein coupled receptor 120 (GPR120), has been identified as the primary receptor of omega-3 polyunsaturated fatty acids (ω-3 PUFAs). FFAR4 is a promising target for treating metabolic and inflammatory disorders due to its immune regulatory functions and the discovery of highly selective and efficient agonists. This review summarizes the reported immune regulatory functions of ω-3 PUFAs and FFAR4 in immune cells and immune-related diseases. We also speculate possible involvements of ω-3 PUFAs and FFAR4 in other types of inflammatory disorders.

9-PAHPA long term intake in DIO and db/db mice ameliorates insulin sensitivity but has few effects on obesity and associated metabolic disorders

Branched fatty acid esters of hydroxy fatty acids are endogenous lipids reported to have antidiabetic and anti-inflammatory effects. Recently, we showed that 9-palmitic acid esters of hydroxypalmitic acid (9-PAHPA) and 9-oleic acid esters of hydroxypalmitic acid increased insulin sensitivity in mice when incorporated to a chow diet or to a high fat and high sucrose diet. However, preventive supplementation with 9-PAHPA and 9-oleic acid esters of hydroxypalmitic acid in high fat and high sucrose diet mice did not impair significant weight gain or the development of hyperglycemia. The aim of this work was therefore to study whether in two animal models of obesity, namely the classical diet-induced obesity (DIO) and the db/db mice, 9-PAHPA may have beneficial effects against obesity and liver and skeletal muscle metabolic dysfunction. In DIO mice, we observed that 9-PAHPA increased body weight and fat mass. In line with this observation, we found that 9-PAHPA supplementation decreased energy expenditure. In liver and in skeletal muscle, mitochondrial activities and oxidative stress parameters were not modified by 9-PAHPA supplementation. In db/db mice, 9-PAHPA had no effect on the dramatic weight gain and hyperglycemia. In addition, 9-PAHPA supplementation did not correct either the hepatomegaly and hepatic steatosis or the severe muscle atrophy recorded compared with db/+ animals. Likewise, supplementation with 9-PAHPA did not impact the different metabolic parameters analyzed, either in the liver or in the skeletal muscles. However, it decreased insulin resistance in DIO and db/db mice. In conclusion, our study indicated that a long-term intake of 9-PAHPA in DIO and db/db mice improved insulin sensitivity but had only few effects on obesity and associated metabolic disorders.

12-OAHSA is a component of olive oil and mitigates obesity-induced inflammation

Fatty acid esters of hydroxyl fatty acids (FAHFAs) are a new family of endogenous lipids that exert anti-inflammatory action. Among the various FAHFA isomers, the dietary source of oleic acid-hydroxy stearic acid (OAHSA) and its anti-inflammatory functions are poorly understood. This study investigated the composition of OAHSA isomers in dietary oils and the impact of 12-OAHSA on obesity-induced inflammation. Liquid chromatography with tandem mass spectrometry analysis revealed that various dietary oils, including fish oil, corn oil, palm oil, soybean oil, and olive oil, present a wide variation in OAHSA profiles and amounts. The highest amounts of total OAHSAs are present in olive oil including 12-OAHSA. Compared to vehicle-treated obese mice, administration of 12-OAHSA significantly improved glucose homeostasis, independent of body weight. 12-OAHSA-treated mice displayed significantly reduced accumulation of CD11c⁺ adipose tissue macrophages, and CD4⁺/CD8⁺ adipose tissue T lymphocytes. Concomitantly, the expression of pro-inflammatory cytokine genes and the nuclear factor kappa-light-chain-enhancer of activated B cells signaling pathway were significantly decreased in the 12-OAHSA-treated adipose tissue, while the expression of the anti-inflammatory gene Il10 was markedly increased. Moreover, in vitro cell culture experiments showed that 12-OAHSA significantly inhibited the lipopolysaccharides-induced inflammatory response in macrophages by suppressing the nuclear factor kappa-light-chain-enhancer of activated B cells signaling pathway. Collectively, these results indicated that 12-OAHSA, as a component of olive oil, mitigates obesity-induced insulin resistance by regulating AT inflammation. Therefore, 12-OAHSA could be used as a novel nutritional intervention against obesity-associated metabolic dysregulation.

PAHSAs reduce cellular senescence and protect pancreatic beta cells from metabolic stress through regulation of Mdm2/p53

Senescence in pancreatic beta cells plays a major role in beta cell dysfunction, which leads to impaired glucose homeostasis and diabetes. Therefore, prevention of beta cell senescence could reduce the risk of diabetes. Treatment of nonobese diabetic (NOD) mice, a model of type 1 autoimmune diabetes (T1D), with palmitic acid hydroxy stearic acids (PAHSAs), a novel class of endogenous lipids with antidiabetic and antiinflammatory effects, delays the onset and reduces the incidence of T1D from 82% with vehicle treatment to 35% with PAHSAs. Here, we show that a major mechanism by which PAHSAs protect islets of the NOD mice is by directly preventing and reversing the initial steps of metabolic stress-induced senescence. In vitro PAHSAs increased Mdm2 expression, which decreases the stability of p53, a key inducer of senescence-related genes. In addition, PAHSAs enhanced expression of protective genes, such as those regulating DNA repair and glutathione metabolism and promoting autophagy. We demonstrate the translational relevance by showing that PAHSAs prevent and reverse early stages of senescence in metabolically stressed human islets by the same Mdm2 mechanism. Thus, a major mechanism for the dramatic effect of PAHSAs in reducing the incidence of type 1 diabetes in NOD mice is decreasing cellular senescence; PAHSAs may have a similar benefit in humans.

The Effect of Supplemental Concentrate Feeding on the Morphological and Functional Development of the Pancreas in Early Weaned Yak Calves

Simple Summary

This study aimed to investigate the nutritional intake deficiency on rearing yak calves. We investigated supplemental concentrate feeding effects on the morphological and functional development of the pancreas in early weaned yak calves. In the study, we determined the apparent digestibility of nutrients by digestion trail, the morphological development of the pancreas in yak calves by tissue sectioning, the activity of main digestive enzymes and hormone levels by ELISA kits, and the content of major small molecule metabolites in the pancreas by non-targeted metabolomics techniques. The morphological and functional development of the pancreas and its small molecule metabolites are mainly presented in graphical form, which had positive regulatory effects on the development of the pancreas in early weaned yak calves. In summary, we found that supplemental concentrate feeding was crucial for the high-quality growth and development of early weaned yak calves and had a positive influence on the intrinsic relationship between the overall development level and physiological functions of the pancreas, which could provide an important reference for scientific rearing of early weaned yak calves.

Abstract

This experiment was conducted to investigate the effect of supplemental concentrate feeding on the pancreatic development of yak calves. Twenty one-month-old yak calves with healthy body condition and similar body weight were selected as experimental animals and randomly divided into two groups, five replicates in each group. The control group yak calves were fed milk replacer and alfalfa hay, the experimental group yak calves were fed milk replacer, alfalfa hay and concentrate. The pre-feeding period of this experiment was thirty days, the trial period was one hundred days. At the end of feeding trail, five yak calves from each group were selected and slaughtered and the pancreas tissues of yak calves were collected and determined. The results showed that: (1) Dry matter and body weight of yak calves in the test group were significantly higher than those of the control group. (2) The apparent nutrient digestibility of crude protein, crude fat, calcium and phosphorus in the test group of yak calves was significantly higher than that of the control group, while the apparent nutrient digestibility of neutral detergent fiber and acid detergent fiber in the test group was significantly lower than that of the control group. (3) Pancreatic weight, organ index, total ratio of exocrine part area and total ratio of endocrine area of yak calves in the test group were significantly higher than those in the control group, while the ratio of exocrine area was significantly lower in the test group than that of the control group. (4) The activities of the main pancreatic digestive enzymes: pancreatic amylase, pancreatic lipase, pancreatic protease and chymotrypsin were significantly higher in the test group than those of the control group, as were the hormonal contents of glucagon, insulin and pancreatic polypeptide. (5) The main differential metabolites of the pancreas in the test group were significantly higher than those of the control group, such as D-proline, hypoxanthine, acetylcysteine, gamma-glutamylcysteine, thiazolidine-4-carboxylic acid, piperidinic acid, ellagic acid, nicotinamide, tropolone, D-serine, ribulose-5-phosphate, (+/-)5(6)-epoxyeicosatrienoic acid(EET), 2-hydroxycinnamic acid, L-phenylalanine, creatinine, tetrahydrocorticosterone, pyridoxamine, xanthine, 5-oxoproline, asparagine, DL-tryptophan, in-dole-3-acrylic acid, thymine, trehalose, docosapentaenoic acid, docosahexaenoic acid, fatty acid esters of hydroxy fatty acids(FAHFA) (18:1/20:3), fatty acid esters of hydroxy fatty acids(FAHFA) (18:2/20:4), adrenic acid and xanthosine. In conclusion, supplemental concentrate feeding promoted the good development of morphological and functional properties of the pancreas in early weaned yak calves to improve the digestion and absorption of feed nutrients, so as to enhance the growth and development quality of early weaned yak calves.

Comparison of two anti-diabetic monoestolides regarding effects on intact murine liver tissue

CONTEXT

Monoestolides belonging to the fatty acid-hydroxy fatty acid (FAHFA) family have recently emerged as promising insulin sensitizers.

OBJECTIVE

To investigate and compare impact of two selected FAHFA isomers, namely 9-hexadecanoyloxy-octadecanoic acid [9-PAHSA] and 9-(9Z-octadecenoyloxy)-octadecanoic acid [9-OAHSA], on intact livers in C57BL/6J mice.

MATERIALS AND METHODS

Short-term in vivo study with intragastric gavage of 13 mg/kg of substances. Morphological, biochemical and high-resolution respirometric assessment of plasma and liver tissue or homogenates thereof.

RESULTS

The 9-OAHSA-gavaged mice had the highest final total body weight, the lowest free fatty acid circulating levels and the highest plasma activities of both ALT and AST. No significant changes of ambient glycaemia were found, however 9-PAHSA-gavaged mice tended to have lower glycaemia than other animals. Respirometry proved no substance-dependent differences.

DISCUSSION AND CONCLUSION

9-PAHSA was more metabolically beneficial and less hepatotoxic than 9-OAHSA. Bioenergetic machinery of liver homogenates seemed unaffected at our FAHFA dose.

ATGL is a biosynthetic enzyme for fatty acid esters of hydroxy fatty acids

Branched fatty acid (FA) esters of hydroxy FAs (HFAs; FAHFAs) are recently discovered lipids that are conserved from yeast to mammals1,2. A subfamily, palmitic acid esters of hydroxy stearic acids (PAHSAs), are anti-inflammatory and anti-diabetic1,3. Humans and mice with insulin resistance have lower PAHSA levels in subcutaneous adipose tissue and serum1. PAHSA administration improves glucose tolerance and insulin sensitivity and reduces inflammation in obesity, diabetes and immune-mediated diseases1,4-7. The enzyme(s) responsible for FAHFA biosynthesis in vivo remains unknown. Here we identified adipose triglyceride lipase (ATGL, also known as patatin-like phospholipase domain containing 2 (PNPLA2)) as a candidate biosynthetic enzyme for FAHFAs using chemical biology and proteomics. We discovered that recombinant ATGL uses a transacylation reaction that esterifies an HFA with a FA from triglyceride (TG) or diglyceride to produce FAHFAs. Overexpression of wild-type, but not catalytically dead, ATGL increases FAHFA biosynthesis. Chemical inhibition of ATGL or genetic deletion of Atgl inhibits FAHFA biosynthesis and reduces the levels of FAHFA and FAHFA-TG. Levels of endogenous and nascent FAHFAs and FAHFA-TGs are 80-90 per cent lower in adipose tissue of mice in which Atgl is knocked out specifically in the adipose tissue. Increasing TG levels by upregulating diacylglycerol acyltransferase (DGAT) activity promotes FAHFA biosynthesis, and decreasing DGAT activity inhibits it, reinforcing TGs as FAHFA precursors. ATGL biosynthetic transacylase activity is present in human adipose tissue underscoring its potential clinical relevance. In summary, we discovered the first, to our knowledge, biosynthetic enzyme that catalyses the formation of the FAHFA ester bond in mammals. Whereas ATGL lipase activity is well known, our data establish a paradigm shift demonstrating that ATGL transacylase activity is biologically important.

Investigation of the Therapeutic Potential of New Antidiabetic Compounds Using Islet-on-a-Chip Microfluidic Model

Nowadays, diabetes mellitus is one of the most common chronic diseases in the world. Current research on the treatment of diabetes combines many fields of science, such as biotechnology, transplantology or engineering. Therefore, it is necessary to develop new therapeutic strategies and preventive methods. A newly discovered class of lipids—Palmitic Acid Hydroxy Stearic Acid (PAHSA) has recently been proposed as an agent with potential therapeutic properties. In this research, we used an islet-on-a-chip microfluidic 3D model of pancreatic islets (pseudoislets) to study two isomers of PAHSA: 5-PAHSA and 9-PAHSA as potential regulators of proliferation, viability, insulin and glucagon expression, and glucose-stimulated insulin and glucagon secretion. Due to the use of the Lab-on-a-chip systems and flow conditions, we were able to reflect conditions similar to in vivo. In addition, we significantly shortened the time of pseudoislet production, and we were able to carry out cell culture, microscopic analysis and measurements using a multi-well plate reader at the same time on one device. In this report we showed that under microfluidic conditions PAHSA, especially 5-PAHSA, has a positive effect on pseudoislet proliferation, increase in cell number and mass, and glucose-stimulated insulin secretion, which may qualify it as a compound with potential therapeutic properties.

Artifactual FA dimers mimic FAHFA signals in untargeted metabolomics pipelines

FA esters of hydroxy FAs (FAHFAs) are lipokines with extensive structural and regional isomeric diversity that impact multiple physiological functions, including insulin sensitivity and glucose homeostasis. Because of their low molar abundance, FAHFAs are typically quantified using highly sensitive LC-MS/MS methods. Numerous relevant MS databases house in silico-spectra that allow identification and speciation of FAHFAs. These provisional chemical feature assignments provide a useful starting point but could lead to misidentification. To address this possibility, we analyzed human serum with a commonly applied high-resolution LC-MS untargeted metabolomics platform. We found that many chemical features are putatively assigned to the FAHFA lipid class based on exact mass and fragmentation patterns matching spectral databases. Careful validation using authentic standards revealed that many investigated signals provisionally assigned as FAHFAs are in fact FA dimers formed in the LC-MS pipeline. These isobaric FA dimers differ structurally only by the presence of an olefinic bond. Furthermore, stable isotope-labeled oleic acid spiked into human serum at subphysiological concentrations showed concentration-dependent formation of a diverse repertoire of FA dimers that analytically mimicked FAHFAs. Conversely, validated FAHFA species did not form spontaneously in the LC-MS pipeline. Together, these findings underscore that FAHFAs are endogenous lipid species.  However, nonbiological FA dimers forming in the setting of high concentrations of FFAs can be misidentified as FAHFAs. Based on these results, we assembled a FA dimer database to identify nonbiological FA dimers in untargeted metabolomics datasets.

Triacylglycerols containing branched palmitic acid ester of hydroxystearic acid (PAHSA) are present in the breast milk and hydrolyzed by carboxyl ester lipase

Breast milk is a complex mixture containing underexplored bioactive lipids. We performed an observational case-control study to compare the impact of delivery mode: caesarean section (CS) and vaginal birth (VB); and term (preterm and term delivery) on the levels of lipokines in human milk at different stages of lactation. Metabolomic analysis of the milk identified triacylglycerol estolides as a metabolic reservoir of the anti-inflammatory lipid mediator 5-palmitic acid ester of hydroxystearic acid (5-PAHSA). We found that triacylglycerol estolides were substrates of carboxyl ester lipase and 5-PAHSA-containing lipids were the least preferred substrates among tested triacylglycerol estolide isomers. This explained exceptionally high colostrum levels of 5-PAHSA in the VB group. CS and preterm birth negatively affected colostrum lipidome, including 5-PAHSA levels, but the lipidomic profiles normalized in mature milk. Mothers delivering term babies vaginally produce colostrum rich in 5-PAHSA, which could contribute to the prevention of intestinal inflammation in newborns.

Bioactive lipids and metabolic syndrome-a symposium report

Recent research has shed light on the cellular and molecular functions of bioactive lipids that go far beyond what was known about their role as dietary lipids. Bioactive lipids regulate inflammation and its resolution as signaling molecules. Genetic studies have identified key factors that can increase the risk of cardiovascular diseases and metabolic syndrome through their effects on lipogenesis. Lipid scientists have explored how these signaling pathways affect lipid metabolism in the liver, adipose tissue, and macrophages by utilizing a variety of techniques in both humans and animal models, including novel lipidomics approaches and molecular dynamics models. Dissecting out these lipid pathways can help identify mechanisms that can be targeted to prevent or treat cardiometabolic conditions. Continued investigation of the multitude of functions mediated by bioactive lipids may reveal additional components of these pathways that can provide a greater understanding of metabolic homeostasis.

Acute aerobic exercise reveals FAHFAs distinguish the metabolomes of overweight and normal weight runners

Background

Responses of the metabolome to acute aerobic exercise may predict maximum oxygen consumption (VO₂max) and longer-term outcomes, including the development of diabetes and its complications.

Methods

Serum samples were collected from overweight/obese trained (OWT) and normal-weight trained (NWT) runners prior to and immediately after a supervised 90-minute treadmill run at 60% VO₂max (NWT = 14, OWT = 11) in a cross-sectional study. We applied a liquid chromatography high-resolution–mass spectrometry–based untargeted metabolomics platform to evaluate the effect of acute aerobic exercise on the serum metabolome.

Results

NWT and OWT metabolic profiles shared increased circulating acylcarnitines and free fatty acids (FFAs) with exercise, while intermediates of adenine metabolism, inosine, and hypoxanthine were strongly correlated with body fat percentage and VO₂max. Untargeted metabolomics-guided follow-up quantitative lipidomic analysis revealed that baseline levels of fatty acid esters of hydroxy fatty acids (FAHFAs) were generally diminished in the OWT group. FAHFAs negatively correlated with visceral fat mass and HOMA-IR. Strikingly, a 4-fold decrease in FAHFAs was provoked by acute aerobic running in NWT participants, an effect that negatively correlated with circulating IL-6; these effects were not observed in the OWT group. Machine learning models based on a preexercise metabolite profile that included FAHFAs, FFAs, and adenine intermediates predicted VO₂max.

Conclusion

These findings in overweight human participants and healthy controls indicate that exercise-provoked changes in FAHFAs distinguish normal-weight from overweight participants and could predict VO₂max. These results support the notion that FAHFAs could modulate the inflammatory response, fuel utilization, and insulin resistance.

Trial registration

ClinicalTrials.gov, NCT02150889.

Funding

NIH DK091538, AG069781, DK098203, TR000114, UL1TR002494.

Glucose metabolism enhancement by 10-hydroxy-2-decenoic acid via the PI3K/AKT signaling pathway in high-fat-diet/streptozotocin induced type 2 diabetic mice

Here, we used high fat diet (HFD) combined with streptozotocin (STZ) injection to establish a diabetes model, with the aim of exploring the hypoglycemic effects of 10-hydroxy-2-decenoic acid (10-HDA), and...

Characterization of the Synergistic Effect between Ligands of Opioid and Free Fatty Acid Receptors in the Mouse Model of Colitis

Background: Recent studies suggest that lipids, including free fatty acids (FFAs), are necessary for proper μ opioid receptor (MOR) binding and that activation of opioid receptors (ORs) improves intestinal inflammation. The objective of the study was to investigate a possible interaction between the ORs and FFA receptors (FFARs) ligands in the colitis. Methods: The potential synergistic effect of ORs and FFARs ligands was evaluated using mouse model of acute colitis induced by dextran sulfate sodium (DSS, 4%). Compounds were injected intraperitoneally (i.p.) once or twice daily at the doses of 0.01 or 0.02 mg/kg body weight (BW) (DAMGO—an MOR agonist), 0.3 mg/kg BW (DPDPE—a δ OR (DOR) agonist) and 1 mg/kg BW (naloxone—a non-selective OR antagonist, GLPG 0974—a FFAR2 antagonist, GSK 137647—a FFAR4 agonist and AH 7614—a FFAR4 antagonist) for 4 days. Results: Myeloperoxidase (MPO) activity was significantly decreased after DAMGO (0.02 mg/kg BW) and GSK 137647 (1 mg/kg BW) administration and co-administration as compared to DSS group. Conclusions: Treatment with ligands of ORs and FFARs may affect the immune cells in the inflammation; however, no significant influence on the severity of colitis and no synergistic effect were observed.

Differences in Diet and Gut Microbiota Between Lactating and Non-lactating Asian Particolored Bats (Vespertilio sinensis): Implication for a Connection Between Diet and Gut Microbiota

In mammals, lactation is considered the most energetically costly phase for females. To meet nutritional and energy demands, lactating females usually change feeding patterns by eating food that is higher in protein and calories. Their gut microbes respond accordingly to help adapt to the changes in diet. In this study, we examined differences in diet and gut microbial composition between lactating and non-lactating Asian particolored bats (Vespertilio sinensis) using COI and 16S amplicon sequencing. When compared with non-lactating bats, we found that the diversity and composition of lactating bats' diets differed; the proportion of Diptera increased and Coleoptera and Orthoptera decreased significantly. This could be attributed to the easy availability and high protein content of Diptera. Comparative analysis of the gut microbiota of lactating and non-lactating females showed that although the diversity of gut microbiota did not change, the relative abundance of specific gut microbiota associated with a particular diet did change. For example, when the consumption of Coleoptera decreased in lactating bats, the relative abundance of Lactobacillaceae was also reduced. Lactobacillaceae are thought to be involved in the digestion of Coleopteran exoskeletons. This study suggests that during lactation, Asian particolored bats eat a diet that yields higher levels of protein, and at the same time, the abundance of specific gut microbes change to help their hosts adapt to these changes in diet.

The Therapeutic Efficacy of Adipose Tissue-Derived Mesenchymal Stem Cell Conditioned Medium on Experimental Colitis Was Improved by the Serum From Colitis Rats

Adipose derived mesenchymal stem cells (AD-MSCs) have shown therapeutic potential in treatments of inflammatory bowel disease (IBD). Due to the harsh host environment and poor survival of the cells, controversy concerning the homing, proliferation and differentiation of MSCs in lesion tissue still remains. It has been reported that conditioned media from MSCs could improve the colitis, whereas the therapeutic efficiency could be significantly elevated by the stimulation of pro-cytokines. In this study, we pre-treated the adipose derived MSCs with the serum from colitis rats and then the activated conditioned media (CM-AcMSC) were collected. To compare the therapeutic effects of CM-MSC and CM-AcMSC on IBD, we constructed dextran sodium sulphate (DSS)-induced colitis rat models. The colitis was induced in rats by administrating 5% DSS in drinking water for 10 days, and the disease symptoms were recorded daily. The colon histopathological changes were observed by different staining methods (H&E and PAS). The expression levels of MUC2 and tight junctions (TJs) were determined by RT-qPCR. The levels of inflammatory cytokines were analyzed by ELISA and western blot analysis. Our findings suggested that CM-AcMSC was more effective in ameliorating the clinical features and histological damage scores. Treatment with CM-AcMSC significantly increased the expression of MUC2 and TJs and suppressed the production of pro-inflammatory cytokines in colonic tissues of colitis rats. The inhibitory effects of CM-AcMSC on inflammatory responses of colitis rats were mediated by NF-κB signaling pathway. These results suggested that pre-activation of MSCs with serum from colitis rats could promote the production of paracrine factors and improve the therapeutic effects of conditioned medium on colitis rats.

Branched and linear fatty acid esters of hydroxy fatty acids (FAHFA) relevant to human health

Fatty acid esters of hydroxy fatty acids (FAHFAs) represent a complex lipid class that contains both signaling mediators and structural components of lipid biofilms in humans. The majority of endogenous FAHFAs share a common chemical architecture, characterized by an estolide bond that links the hydroxy fatty acid (HFA) backbone and the fatty acid (FA). Two structurally and functionally distinct FAHFA superfamilies are recognized based on the position of the estolide bond: omega-FAHFAs and in-chain branched FAHFAs. The existing variety of possible HFAs and FAs combined with the position of the estolide bond generates a vast quantity of unique structures identified in FAHFA families. In this review, we discuss the anti-diabetic and anti-inflammatory effects of branched FAHFAs and the role of omega-FAHFA-derived lipids as surfactants in the tear film lipid layer and dry eye disease. To emphasize potential pharmacological targets, we recapitulate the biosynthesis of the HFA backbone within the superfamilies together with the degradation pathways and the FAHFA regioisomer distribution in human and mouse adipose tissue. We propose a theoretical involvement of cytochrome P450 enzymes in the generation and degradation of saturated HFA backbones and present an overview of small-molecule inhibitors used in FAHFA research. The FAHFA lipid class is huge and largely unexplored. Besides the unknown biological effects of individual FAHFAs, also the enigmatic enzymatic machinery behind their synthesis could provide new therapeutic approaches for inflammatory metabolic or eye diseases. Therefore, understanding the mechanisms of (FA)HFA synthesis at the molecular level should be the next step in FAHFA research.

Distinct biological activities of isomers from several families of branched fatty acid esters of hydroxy fatty acids (FAHFAs)

Branched fatty acid esters of hydroxy fatty acids (FAHFAs) are endogenous lipids with antidiabetic and anti-inflammatory effects. Each FAHFA family consists of esters with different acyl chains and multiple isomers with branch points at different carbons. Some FAHFAs, including palmitic acid hydroxy stearic acids (PAHSAs), improve insulin sensitivity and glucose tolerance in mice by enhancing glucose-stimulated insulin secretion (GSIS), insulin-stimulated glucose transport, and insulin action to suppress hepatic glucose production and reducing adipose tissue inflammation. However, little is known about the biological effects of other FAHFAs. Here, we investigated whether PAHSAs, oleic acid hydroxy stearic acid, palmitoleic acid hydroxy stearic acid, and stearic acid hydroxy stearic acid potentiate GSIS in β-cells and human islets, insulin-stimulated glucose uptake in adipocytes, and anti-inflammatory effects in immune cells. We also investigated whether they activate G protein-coupled receptor 40, which mediates the effects of PAHSAs on insulin secretion and sensitivity in vivo. We show that many FAHFAs potentiate GSIS, activate G protein-coupled receptor 40, and attenuate LPS-induced chemokine and cytokine expression and secretion and phagocytosis in immune cells. However, fewer FAHFAs augment insulin-stimulated glucose uptake in adipocytes. S-9-PAHSA, but not R-9-PAHSA, potentiated GSIS and glucose uptake, while both stereoisomers had anti-inflammatory effects. FAHFAs containing unsaturated acyl chains with higher branching from the carboxylate head group are more likely to potentiate GSIS, whereas FAHFAs with lower branching are more likely to be anti-inflammatory. This study provides insight into the specificity of the biological actions of different FAHFAs and could lead to the development of FAHFAs to treat metabolic and immune-mediated diseases.

Activation of Free Fatty Acid Receptor 4 Affects Intestinal Inflammation and Improves Colon Permeability in Mice

Diet is considered an important trigger in inflammatory bowel diseases (IBD), as feeding habits can affect intestinal permeability and clearance of bacterial antigens, consequently influencing the immune system. Free fatty acid receptors (FFARs), expressed on the intestinal epithelial cells, belong to the family of luminal-facing receptors that are responsive to nutrients. The objective of this study was to characterize the anti-inflammatory activity and the effect on intestinal barrier function of synthetic FFAR agonists in mouse models of colitis. Therapeutic activity of GW9508 (FFAR1 agonist), 4-CMTB (FFAR2 agonist), AR420626 (FFAR3 agonist), and GSK137647 (FFAR4 agonist) was investigated in two models of semi-chronic colitis: induced by trinitrobenzenesulfonic acid (TNBS), mimicking Crohn's disease, as well as induced by dextran sulfate sodium (DSS), which recapitulates ulcerative colitis in humans. Moreover, we assessed the influence of FFARs agonists on epithelial ion transport and measured the ion flow stimulated by forskolin and veratridine. Administration of FFAR4 agonist GSK137647 attenuated both TNBS-induced and DSS-induced colitis in mice, as indicated by macroscopic parameters and myeloperoxidase activity. The action of FFAR4 agonist GSK137647 was significantly blocked by pretreatment with selective FFAR4 antagonist AH7614. Moreover, FFAR1 and FFAR4 agonists reversed the increase in the colon permeability caused by inflammation. FFAR4 restored the tight junction genes expression in mouse colon. This is the first evaluation of the anti-inflammatory activity of selective FFAR agonists, showing that pharmacological intervention targeting FFAR4, which is a sensor of medium and long chain fatty acids, attenuates intestinal inflammation.

Detection and Structural Characterization of SFAHFA Homologous Series in Mouse Colon Contents by LTQ-Orbitrap-MS and Their Implication in Influenza Virus Infection

Fatty acid esters of hydroxy fatty acids (FAHFAs) are a new class of endogenous lipids with promising physiological functions in mammals. We previously introduced a new type of lipids to this family called short-chain fatty acid esters of hydroxy fatty acids (SFAHFAs), branching specific to the C2 carbon of a long-chain fatty acid (≥C20). In this study, we discovered a homologous series of SFAHFAs comprising C16-C26 hydroxy fatty acids esterified with short-chain fatty acids (C2-C5) in mouse colon contents. The detected SFAHFAs were characterized by high-resolution mass spectrometry with MSn analysis. The double-bond position of monounsaturated SFAHFAs was determined by the epoxidation reaction of samples with m-chloroperoxybenzoic acid and their MSn analysis. Further, the measurement of SFAHFA concentration in the colon contents of mice infected with influenza A/Puerto Rico/8/34 (H1N1; PR8) virus revealed a significant increase in their levels compared to native control. A strong correlation was observed between hydroxy fatty acid and SFAHFAs. Detection, characterization, and profiling of these new SFAHFA levels in relation with pandemic H1N1; PR8 influenza virus will contribute to the in-depth study of their function and metabolism.

Docosahexaenoic Acid Esters of Hydroxy Fatty Acid Is a Novel Activator of NRF2

Fatty acid esters of hydroxy fatty acids (FAHFAs) are a new class of endogenous lipids with interesting physiological functions in mammals. Despite their structural diversity and links with nuclear factor erythroid 2-related factor 2 (NRF2) biosynthesis, FAHFAs are less explored as NRF2 activators. Herein, we examined for the first time the synthetic docosahexaenoic acid esters of 12-hydroxy stearic acid (12-DHAHSA) or oleic acid (12-DHAHOA) against NRF2 activation in cultured human hepatoma-derived cells (C3A). The effect of DHA-derived FAHFAs on lipid metabolism was explored by the nontargeted lipidomic analysis using liquid chromatography-mass spectrometry. Furthermore, their action on lipid droplet (LD) oxidation was investigated by the fluorescence imaging technique. The DHA-derived FAHFAs showed less cytotoxicity compared to their native fatty acids and activated the NRF2 in a dose-dependent pattern. Treatment of 12-DHAHOA with C3A cells upregulated the cellular triacylglycerol levels by 17-fold compared to the untreated group. Fluorescence imaging analysis also revealed the suppression of the degree of LDs oxidation upon treatment with 12-DHAHSA. Overall, these results suggest that DHA-derived FAHFAs as novel and potent activators of NRF2 with plausible antioxidant function.

Fatty Acid Esters of Hydroxy Fatty Acids (FAHFAs) Are Associated With Diet, BMI, and Age

Background: Fatty acid esters of hydroxy fatty acids (FAHFAs) are a group of fatty acids with potential anti-inflammatory and anti-diabetic effects. The blood levels of FAHFAs and their regulation in humans have hardly been studied.

Objective: We aimed to investigate serum FAHFA levels in well-characterized human cohorts, to evaluate associations with age, sex, BMI, weight loss, diabetic status, and diet.

Methods: We analyzed levels of stearic-acid-9-hydroxy-stearic-acid (9-SAHSA), oleic-acid-9-hydroxy-stearic-acid (9-OAHSA) and palmitic-acid-9-hydroxy-palmitic-acid (9-PAHPA) as well as different palmitic acid-hydroxy-stearic-acids (PAHSAs) by HPLC-MS/MS with the use of an internal standard in various cohorts: A cohort of different age groups (18–25y; 40–65y; 75–85y; Σn = 60); severely obese patients undergoing bariatric surgery and non-obese controls (Σn = 36); obese patients with and without diabetes (Σn = 20); vegetarians/vegans (n = 10) and omnivores (n = 9); and young men before and after acute overfeeding with saturated fatty acids (SFA) (n = 15).

Results: Omnivores had substantially higher FAHFA levels than vegetarians/vegans [median (25th percentile; 75th percentile) tFAHFAs = 12.82 (7.57; 14.86) vs. 5.86 (5.10; 6.71) nmol/L; P < 0.05]. Dietary overfeeding by supplementation of SFAs caused a significant increase within 1 week [median tFAHFAs = 4.31 (3.31; 5.27) vs. 6.96 (6.50; 7.76) nmol/L; P < 0.001]. Moreover, obese patients had lower FAHFA levels than non-obese controls [median tFAHFAs = 3.24 (2.80; 4.30) vs. 5.22 (4.18; 7.46) nmol/L; P < 0.01] and surgery-induced weight loss increased 9-OAHSA level while other FAHFAs were not affected. Furthermore, significant differences in some FAHFA levels were found between adolescents and adults or elderly, while no differences between sexes and between diabetic and non-diabetic individuals were detected.

Conclusions: FAHFA serum levels are strongly affected by high SFA intake and reduced in severe obesity. Age also may influence FAHFA levels, whereas there was no detectable relation with sex and diabetic status. The physiological role of FAHFAs in humans remains to be better elucidated.

Trial Registration: All studies referring to these analyses were registered in the German Clinical Trial Register (https://www.drks.de/drks_web/) with the numbers DRKS00009008, DRKS00010133, DRKS00006211, and DRKS00009797.

Lipidomic Analysis to Assess Oxidative Stress in Acute Coronary Syndrome and Acute Stroke Patients

Alterations in lipid metabolism mediated by oxidative stress play a key role in the process of atherosclerosis and superimposed thrombosis; these can lead to acute coronary syndrome (ACS) and acute ischemic stroke (AIS). Multiple studies have shown that the formation of atheromatous lesions is initiated by oxidation of low-density lipoproteins incorporated into the intima of the vessel wall. Here, we studied lipids in plasma samples from three cohorts: 61 patients with ACS (group A), 49 patients with AIS (group D), and 82 controls (group K). Untargeted lipidomics based on high-performance liquid chromatography coupled to mass spectrometry (UHPLC-HRMS) was employed to obtain comprehensive information on whether relationships exist between these patient categories based on lipid patterns. In addition, malondialdehyde (MDA) as a standard marker of oxidative stress was monitored. The most characteristic lipids in group K were fatty acyls of hydroxyfatty acids (FAHFAs). As expected, MDA concentrations were the lowest in group K. Our findings can better explain ongoing pathologies, both acute and chronic, with the potential for future diagnosis and treatment.

A Bi-Enzymatic Cascade Pathway towards Optically Pure FAHFAs*

Recently discovered endogenous mammalian lipids, fatty acid esters of hydroxy fatty acids (FAHFAs), have been proved to have anti-inflammatory and anti-diabetic effects. Due to their extremely low abundancies in vivo, forging a feasible scenario for FAHFA synthesis is critical for their use in uncovering biological mechanisms or in clinical trials. Here, we showcase a fully enzymatic approach, a novel in vitro bi-enzymatic cascade system, enabling an effective conversion of nature-abundant fatty acids into FAHFAs. Two hydratases from Lactobacillus acidophilus were used for converting unsaturated fatty acids to various enantiomeric hydroxy fatty acids, followed by esterification with another fatty acid catalyzed by Candida antarctica lipase A (CALA). Various FAHFAs were synthesized in a semi-preparative scale using this bi-enzymatic approach in a one-pot two-step operation mode. In all, we demonstrate that the hydratase-CALA system offers a promising route for the synthesis of optically pure structure-diverse FAHFAs.

Insights into the Functional Role of ADTRP (Androgen-Dependent TFPI-Regulating Protein) in Health and Disease

The novel protein ADTRP, identified and described by us in 2011, is androgen-inducible and regulates the expression and activity of Tissue Factor Pathway Inhibitor, the major inhibitor of the Tissue Factor-dependent pathway of coagulation on endothelial cells. Single-nucleotide polymorphisms in ADTRP associate with coronary artery disease and myocardial infarction, and deep vein thrombosis/venous thromboembolism. Some athero-protective effects of androgen could exert through up-regulation of ADTRP expression. We discovered a critical role of ADTRP in vascular development and vessel integrity and function, manifested through Wnt signaling-dependent regulation of matrix metalloproteinase-9. ADTRP also hydrolyses fatty acid esters of hydroxy-fatty acids, which have anti-diabetic and anti-inflammatory effects and can control metabolic disorders. Here we summarize and analyze the knowledge on ADTRP and try to decipher its functions in health and disease.

Insulin action in adipocytes, adipose remodeling, and systemic effects

On this 100th anniversary of the discovery of insulin, we recognize the critical role that adipocytes, which are exquisitely responsive to insulin, have played in determining the mechanisms for insulin action at the cellular level. Our understanding of adipose tissue biology has evolved greatly, and it is now clear that adipocytes are far more complicated than simple storage depots for fat. A growing body of evidence documents how adipocytes, in response to insulin, contribute to the control of whole-body nutrient homeostasis. These advances highlight adipocyte plasticity, heterogeneity, and endocrine function, unique features that connect adipocyte metabolism to the regulation of other tissues important for metabolic homeostasis (e.g., liver, muscle, pancreas).

Effects of Protein Restriction and Subsequent Realimentation on Body Composition, Gut Microbiota and Metabolite Profiles in Weaned Piglets

Simple Summary

Protein restriction strategies are often used in weaned piglets to reduce the incidence of intestinal disorders that are sensitive to dietary protein supply, but may lead to a decline in production performance. Subsequent protein realimentation can alleviate the detrimental effects of reduced dietary protein on growth. However, the effects of protein realimentation on the body composition, gut microbiota and metabolite profiles of piglets are poorly understood. The present study, combining comparative slaughter methods, microbiome and metabolome analyses, demonstrated that protein restriction and subsequent realimentation lead to compensatory growth and compensatory protein deposition in piglets, and contribute to animal intestinal health by altering the gut microbiota and metabolite profiles.

Abstract

The objective of this study was to evaluate the effects of protein restriction and subsequent protein realimentation on the body composition, gut microbiota and metabolite profiles of piglets. Fifty weaned piglets were randomly assigned to two treatments: a normal protein (NP) group (20% crude protein (CP)) or a low protein (LP) group (16% CP) with five animals per pen and five pens per group. Treatment diets were fed for 14 d during the protein restriction phase, and then all pigs were fed the same nursery diets with a normal CP level (19% CP) during the protein realimentation phase until they reached an average target body weight (BW) of 25 ± 0.15 kg. At day 14 and the end of the experiment, one piglet close to the average BW of each pen was slaughtered to determine body composition, microbial composition and microbial metabolites. Results showed that there was no difference (p > 0.05) in the experimental days to reach target BW between the LP and NP groups. The average daily gain (ADG) and gain:feed ratio (G:F) during the protein restriction phase as well as BW at day 14, were significantly decreased (p < 0.05) in the LP group compared with the NP group. However, there were no significant differences (p > 0.05) during the protein realimentation phase and the overall experiment. Similarly, piglets in the LP group showed a significantly decreased body protein content (p < 0.05) at day 14, but not (p > 0.05) at the end of the experiment. The relative abundance of Parabacteroides, Butyricicoccus, Olsenella, Succinivibrio and Pseudoramibacter were significantly increased (p < 0.05), while the relative abundance of Alloprevotella and Faecalicoccus were significantly decreased (p < 0.05) in the LP group at day 14. At the end of the experiment, the piglets in the LP group showed a higher (p < 0.05) colonic relative abundances of Parabacteroides, unidentified Christensenellaceae and Caproiciproducens, and a lower (p < 0.05) relative abundance of unidentified Prevotellaceae, Haemophilus, Marvinbryantia, Faecalibaculum, Neisseria and Dubosiella than those in the NP group. Metabolomics analyses indicated that tryptophan metabolism and vitamin metabolism were enriched in the LP group at day 14, and glycerophospholipid metabolism and fatty acid esters of hydroxy fatty acid metabolism were enriched at the end of the experiment. Moreover, Spearman’s correlation analysis demonstrated that the microbial composition was highly correlated with changes in colonic metabolites. Collectively, these results indicated that protein restriction and subsequent realimentation lead to compensatory growth and compensatory protein deposition in piglets and contribute to animal intestinal health by altering the gut microbiota and its metabolites.

Distinct roles of adipose triglyceride lipase and hormone-sensitive lipase in the catabolism of triacylglycerol estolides

Branched esters of palmitic acid and hydroxy stearic acid are antiinflammatory and antidiabetic lipokines that belong to a family of fatty acid (FA) esters of hydroxy fatty acids (HFAs) called FAHFAs. FAHFAs themselves belong to oligomeric FA esters, known as estolides. Glycerol-bound FAHFAs in triacylglycerols (TAGs), named TAG estolides, serve as metabolite reservoir of FAHFAs mobilized by lipases upon demand. Here, we characterized the involvement of two major metabolic lipases, adipose triglyceride lipase (ATGL) and hormone-sensitive lipase (HSL), in TAG estolide and FAHFA degradation. We synthesized a library of 20 TAG estolide isomers with FAHFAs varying in branching position, chain length, saturation grade, and position on the glycerol backbone and developed an in silico mass spectra library of all predicted catabolic intermediates. We found that ATGL alone or coactivated by comparative gene identification-58 efficiently liberated FAHFAs from TAG estolides with a preference for more compact substrates where the estolide branching point is located near the glycerol ester bond. ATGL was further involved in transesterification and remodeling reactions leading to the formation of TAG estolides with alternative acyl compositions. HSL represented a much more potent estolide bond hydrolase for both TAG estolides and free FAHFAs. FAHFA and TAG estolide accumulation in white adipose tissue of mice lacking HSL argued for a functional role of HSL in estolide catabolism in vivo. Our data show that ATGL and HSL participate in the metabolism of estolides and TAG estolides in distinct manners and are likely to affect the lipokine function of FAHFAs.

Potential physio-pathological effects of branched fatty acid esters of hydroxy fatty acids

Branched Fatty Acid Esters of Hydroxy Fatty Acids (FAHFAs) are a new endogenous lipid class with recently uncovered interesting biological effects and which have been detected in food of plant and animal origins. Some FAHFAs can improve glucose tolerance and insulin sensitivity, stimulate insulin secretion, and exert anti-inflammatory effects. Other beneficial health effects have also been suggested, in particular against some cancers. FAHFAs could therefore be a potential therapeutic target for the treatment of numerous metabolic disorders such as type II diabetes, hepatic steatosis, cardiovascular diseases and various cancers. Their recent discovery has generated a great interest in the field of human health. This short review aims at bringing together the information available to date in the literature concerning their chemical synthesis, biosynthesis and degradation pathways as well as their potential physio-pathological beneficial effects.

Pro-resolving lipid mediators: regulators of inflammation, metabolism and kidney function

Obesity, diabetes mellitus, hypertension and cardiovascular disease are risk factors for chronic kidney disease (CKD) and kidney failure. Chronic, low-grade inflammation is recognized as a major pathogenic mechanism that underlies the association between CKD and obesity, impaired glucose tolerance, insulin resistance and diabetes, through interaction between resident and/or circulating immune cells with parenchymal cells. Thus, considerable interest exists in approaches that target inflammation as a strategy to manage CKD. The initial phase of the inflammatory response to injury or metabolic dysfunction reflects the release of pro-inflammatory mediators including peptides, lipids and cytokines, and the recruitment of leukocytes. In self-limiting inflammation, the evolving inflammatory response is coupled to distinct processes that promote the resolution of inflammation and restore homeostasis. The discovery of endogenously generated lipid mediators - specialized pro-resolving lipid mediators and branched fatty acid esters of hydroxy fatty acids - which promote the resolution of inflammation and attenuate the microvascular and macrovascular complications of obesity and diabetes mellitus highlights novel opportunities for potential therapeutic intervention through the targeting of pro-resolution, rather than anti-inflammatory pathways.

Determination of Major Endogenous FAHFAs in Healthy Human Circulation: The Correlations with Several Circulating Cardiovascular-Related Biomarkers and Anti-Inflammatory Effects on RAW 264.7 Cells

Fatty acid esters of hydroxy fatty acids (FAHFAs) are newly discovered long-chain fatty acids. However, the major endogenous FAHFAs in healthy human circulation, their correlation with cardiovascular (CV) biomarkers, and their anti-inflammatory effects have not been investigated and remain unclear. In the present study, a total of 57 healthy subjects were recruited. Liquid chromatography–mass spectrometry (LC-MS) was developed for the simultaneous determination of seven FAHFAs, four long-chain fatty acids, and four non-traditional circulating CV-related biomarkers. We found two major types of FAHFAs in healthy human circulation, palmitoleic acid ester of 9-hydroxystearic acid (9-POHSA), and oleic acid ester of 9-hydroxystearic acid (9-OAHSA). Both 9-POHSA and 9-OAHSA had a strong positive correlation with each other and were negatively correlated with fasting blood glucose, S-adenosyl-l-homocysteine (SAH), and trimethylamine N-oxide (TMAO), but not with l-homocysteine. 9-POHSA was also positively correlated with l-carnitine. Moreover, we confirmed that both 9-POHSA and 9-OAHSA exhibited an anti-inflammatory effect by suppressing LPS stimulated cytokines, including IL-1β and IL-6 in RAW 264.7 cells. In addition, palmitoleic acid also had a positive correlation with 9-POHSA and 9-OAHSA. As far as we know, this is the first report showing the major endogenous FAHFAs in healthy subjects and their CV protection potential which might be correlated with SAH and TMAO reduction, l-Carnitine elevation, and their anti-inflammatory effects.

FAHFAs Regulate the Proliferation of C2C12 Myoblasts and Induce a Shift toward a More Oxidative Phenotype in Mouse Skeletal Muscle

Branched fatty acid esters of hydroxy fatty acids (FAHFAs) are endogenous lipids reported to have antidiabetic and anti-inflammatory effects. Since skeletal muscle is a major target for insulin, the aim of this study is to explore for the first time the influence of several FAHFAs in C2C12 myoblasts and in skeletal muscle phenotype in mice. Here, we show that eleven FAHFAs belonging to different families inhibit C2C12 myoblast proliferation. In addition, all FAHFAs decreased mitochondrial cytochrome c oxidase activity without affecting reactive oxygen species production and the mitochondrial network. During C2C12 myoblasts differentiation, we found that two of the most active lipids, 9-PAHPA and 9-OAHPA, did not significantly affect the fusion index and the expression of myosin heavy chains. However, we found that three months’ intake of 9-PAHPA or 9-OAHPA in mice increased the expression of more oxidative myosin in skeletal muscle without affecting skeletal muscle mass, number, and mean fiber area, mitochondrial activity, and oxidative stress parameters. In conclusion, our study indicated that the eleven FAHFAs tested decreased the proliferation rate of C2C12 myoblasts, probably through the inhibition of mitochondrial activity. In addition, we found that 9-PAHPA or 9-OAHPA supplementation in mice induced a switch toward a more oxidative contractile phenotype of skeletal muscle. These data suggest that the increase in insulin sensitivity previously described for these two FAHFAs is of muscular origin.