Diet-induced obesity up-regulates the abundance of GPR43 and GPR120 in a tissue specific manner

FFAR4 regulates cardiac oxylipin balance to promote inflammation resolution in HFpEF secondary to metabolic syndrome

Heart failure with preserved ejection fraction (HFpEF) is a complex clinical syndrome, but a predominant subset of HFpEF patients has metabolic syndrome (MetS). Mechanistically, systemic, nonresolving inflammation associated with MetS might drive HFpEF remodeling. Free fatty acid receptor 4 (Ffar4) is a GPCR for long-chain fatty acids that attenuates metabolic dysfunction and resolves inflammation. Therefore, we hypothesized that Ffar4 would attenuate remodeling in HFpEF secondary to MetS (HFpEF-MetS). To test this hypothesis, mice with systemic deletion of Ffar4 (Ffar4KO) were fed a high-fat/high-sucrose diet with L-NAME in their water to induce HFpEF-MetS. In male Ffar4KO mice, this HFpEF-MetS diet induced similar metabolic deficits but worsened diastolic function and microvascular rarefaction relative to WT mice. Conversely, in female Ffar4KO mice, the diet produced greater obesity but no worsened ventricular remodeling relative to WT mice. In Ffar4KO males, MetS altered the balance of inflammatory oxylipins systemically in HDL and in the heart, decreasing the eicosapentaenoic acid-derived, proresolving oxylipin 18-hydroxyeicosapentaenoic acid (18-HEPE), while increasing the arachidonic acid-derived, proinflammatory oxylipin 12-hydroxyeicosatetraenoic acid (12-HETE). This increased 12-HETE/18-HEPE ratio reflected a more proinflammatory state both systemically and in the heart in male Ffar4KO mice and was associated with increased macrophage numbers in the heart, which in turn correlated with worsened ventricular remodeling. In summary, our data suggest that Ffar4 controls the proinflammatory/proresolving oxylipin balance systemically and in the heart to resolve inflammation and attenuate HFpEF remodeling.

Novel Fat Taste Receptor Agonists Curtail Progressive Weight Gain in Obese Male Mice

BACKGROUND & AIMS

The spontaneous preference for dietary lipids is principally regulated by 2 lingual fat taste receptors, CD36 and GPR120. Obese animals and most of human subjects exhibit low orosensory perception of dietary fat because of malfunctioning of these taste receptors. Our aim was to target the 2 fat taste receptors by newly synthesized high affinity fatty acid agonists to decrease fat-rich food intake and obesity.

METHODS

We synthesized 2 fat taste receptor agonists (FTA), NKS-3 (CD36 agonist) and NKS-5 (CD36 and GPR120 agonist). We determined their molecular dynamic interactions with fat taste receptors and the effect on Ca²⁺ signaling in mouse and human taste bud cells (TBC). In C57Bl/6 male mice, we assessed their gustatory perception and effects of their lingual application on activation of tongue-gut loop. We elucidated their effects on obesity and its related parameters in male mice fed a high-fat diet.

RESULTS

The two FTA, NKS-3 and NKS-5, triggered higher Ca²⁺ signaling than a dietary long-chain fatty acid in human and mouse TBC. Mice exhibited a gustatory attraction for these compounds. In conscious mice, the application of FTA onto the tongue papillae induced activation of tongue-gut loop, marked by the release of pancreato-bile juice into collecting duct and cholecystokinin and peptide YY into blood stream. Daily intake of NKS-3 or NKS-5 via feeding bottles decreased food intake and progressive weight gain in obese mice but not in control mice.

CONCLUSIONS

Our results show that targeting fat sensors in the tongue by novel chemical fat taste agonists might represent a new strategy to reduce obesity.

Butyrate to combat obesity and obesity-associated metabolic disorders: Current status and future implications for therapeutic use

Evidence is increasing that disturbances in the gut microbiome may play a significant role in the etiology of obesity and type 2 diabetes. The short chain fatty acid butyrate, a major end product of the bacterial fermentation of indigestible carbohydrates, is reputed to have anti-inflammatory properties and positive effects on body weight control and insulin sensitivity. However, whether butyrate has therapeutic potential for the treatment and prevention of obesity and obesity-related complications remains to be elucidated. Overall, animal studies strongly indicate that butyrate administered via various routes (e.g., orally) positively affects adipose tissue metabolism and functioning, energy and substrate metabolism, systemic and tissue-specific inflammation, and insulin sensitivity and body weight control. A limited number of human studies demonstrated interindividual differences in clinical effectiveness suggesting that outcomes may depend on the metabolic, microbial, and lifestyle-related characteristics of the target population. Hence, despite abundant evidence from animal data, support of human data is urgently required for the implementation of evidence-based oral and gut-derived butyrate interventions. To increase the efficacy of butyrate-focused interventions, future research should investigate which factors impact treatment outcomes including baseline gut microbial activity and functionality, thereby optimizing targeted-interventions and identifying individuals that merit most from such interventions.

Mechanisms of Short-Chain Fatty Acids Derived from Gut Microbiota in Alzheimer's Disease

Short-chain fatty acids (SCFAs) are important metabolites derived from the gut microbiota through fermentation of dietary fiber. SCFAs participate a number of physiological and pathological processes in the human body, such as host metabolism, immune regulation, appetite regulation. Recent studies on gut-brain interaction have shown that SCFAs are important mediators of gut-brain interactions and are involved in the occurrence and development of many neurodegenerative diseases, including Alzheimer's disease. This review summarizes the current research on the potential roles and mechanisms of SCFAs in AD. First, we introduce the metabolic distribution, specific receptors and signaling pathways of SCFAs in human body. The concentration levels of SCFAs in AD patient/animal models are then summarized. In addition, we illustrate the effects and mechanisms of SCFAs on the cognitive level, pathological features (Aβ and tau) and neuroinflammation in AD. Finally, we analyze the translational value of SCFAs as potential therapeutic targets for the treatment of AD.

GPR120 modulates epileptic seizure and neuroinflammation mediated by NLRP3 inflammasome

Background

The complex pathophysiology of epilepsy hampers the development of effective treatments. Although more than ten kinds of anti-seizures drugs (ASDs) have good effects on seizure control worldwide, about 30% of patients still display pharmacoresistance against ASDs. Neuroinflammation seems to play a crucial role in disease progression. G protein-coupled receptor 120 (GPR120) has been shown to negatively regulate inflammation and apoptosis. However, the role of GPR120 in epilepsy remains unclear. In this study, we aimed to explore the mechanism of GPR120 in epilepsy.

Methods

Male adult C57BL/6 mice were intracranially injected with kainic acid (KA) to establish epilepsy model, and the adeno associated virus (AAV) was administered intracranially at 3 weeks before KA injection. VX765 was administered by intragastric administration at 30 min before KA induced and an equal dose administrated twice a day (10 a.m. and 4 p.m.) lasting 7 days until the mice were killed. Western blot analysis, immunofluorescence staining, video monitoring of seizure, LFP recording, Nissl staining were performed.

Results

GPR120 was increased in both the hippocampus and cortex in the KA-induced model with temporal lobe epilepsy (TLE), and both were most highly expressed at 7 days after KA injection. Overexpression of GPR120 significantly alleviated epileptic activity, reduced neuronal death after status epilepticus (SE), downregulated the expression of IL-1β, IL-6, IL-18, and pyrin domain-containing protein 3 (NLRP3) inflammasome, whereas knockdown GPR120 showed the opposite effect. The effects of GPR120 knockdown were reversed by VX765 inhibition cysteinyl aspartate specific proteinase-1 (Caspase-1).

Conclusion

GPR120 modulates epileptic seizure activity and affects neuronal survival in KA-induced mouse model of temporal lobe epilepsy. Furthermore, GPR120 regulated neuroinflammation in epileptic animals through NLRP3/Caspase-1/IL-1β signaling pathway.

GPR43 activation-mediated lipotoxicity contributes to podocyte injury in diabetic nephropathy by modulating the ERK/EGR1 pathway

Background: G-protein-coupled receptor 43 (GPR43) is a posttranscriptional regulator involved in cholesterol metabolism. This study aimed to investigate the possible roles of GPR43 activation in podocyte lipotoxicity in diabetic nephropathy (DN) and explore the potential mechanisms.

Methods: The experiments were conducted by using diabetic GPR43-knockout mice and a podocyte cell culture model. Lipid deposition and free cholesterol levels in kidney tissues were measured by BODIPY staining and quantitative cholesterol assays, respectively. The protein expression of GPR43, LC3II, p62, beclin1, low-density lipoprotein receptor (LDLR) and early growth response protein 1 (EGR1) in kidney tissues and podocytes was measured by real-time PCR, immunofluorescent staining and Western blotting.

Results: There were increased LDL cholesterol levels in plasma and cholesterol accumulation in the kidneys of diabetic mice. However, GPR43 gene knockout inhibited these changes. An in vitro study further demonstrated that acetate treatment induced cholesterol accumulation in high glucose-stimulated podocytes, which was correlated with increased cholesterol uptake mediated by LDLR and reduced cholesterol autophagic degradation, as characterized by the inhibition of LC3 maturation, p62 degradation and autophagosome formation. Gene knockdown or pharmacological inhibition of GPR43 prevented these effects on podocytes. Furthermore, GPR43 activation increased extracellular regulated protein kinases 1/2 (ERK1/2) activity and EGR1 expression in podocytes, which resulted in an increase in cholesterol influx and autophagy inhibition. In contrast, after GPR43 deletion, these changes in podocytes were improved, as shown by the in vivo and in vitro results.

Conclusion: GPR43 activation-mediated lipotoxicity contributes to podocyte injury in DN by modulating the ERK/EGR1 pathway.

Effect of Ginseng Extracts on the Improvement of Osteopathic and Arthritis Symptoms in Women with Osteopenia: A Randomized, Double-Blind, Placebo-Controlled Clinical Trial

Ginsenosides are active compounds that are beneficial to bone metabolism and have anti-osteoporosis properties. However, very few clinical investigations have investigated the effect of ginseng extract (GE) on bone metabolism. This study aims to determine the effect of GE on improving bone metabolism and arthritis symptoms in postmenopausal women with osteopenia. A 12-week randomized, double-blind, placebo-controlled clinical trial was conducted. A total of 90 subjects were randomly divided into a placebo group, GE 1 g group, and GE 3 g group for 12 weeks based on the random 1:1:1 assignment to these three groups. The primary outcome is represented by bone metabolism indices consisting of serum osteocalcin (OC), urine deoxypyridinoline (DPD), and DPD/OC measurements. Secondary outcomes were serum CTX, NTX, Ca, P, BsALP, P1NP, OC/CTX ratio, and WOMAC index. The GE 3 g group had a significantly increased serum OC concentration. Similarly, the GE 3 g group showed a significant decrease in the DPD/OC ratio, representing bone resorption and bone formation. Moreover, among all the groups, the GE 3 g group demonstrated appreciable improvements in the WOMAC index scores. In women with osteopenia, intake of 3 g of GE per day over 12 weeks notably improved the knee arthritis symptoms with improvements in the OC concentration and ratios of bone formation indices like DPD/OC.

FFAR4: A New Player in Cardiometabolic Disease?

Free fatty acids (FFAs) are implicated in the pathogenesis of metabolic diseases that includes obesity, type 2 diabetes mellitus, and cardiovascular disease (CVD). FFAs serve as ligands for free fatty acid receptors (FFARs) that belong to the family of rhodopsin-like G protein-coupled receptors (GPCRs) and are expressed throughout the body to maintain energy homeostasis under changing nutritional conditions. Free fatty acid receptor 4 (FFAR4), also known as G protein-coupled receptor 120, is a long-chain fatty acid receptor highly expressed in adipocytes, endothelial cells, and macrophages. Activation of FFAR4 helps maintain metabolic homeostasis by regulating adipogenesis, insulin sensitivity, and inflammation. Furthermore, dysfunction of FFAR4 is associated with insulin resistance, obesity, and eccentric remodeling in both humans and mice, making FFAR4 an attractive therapeutic target for treating or preventing metabolic diseases. While much of the previous literature on FFAR4 has focused on its role in obesity and diabetes, recent studies have demonstrated that FFAR4 may also play an important role in the development of atherosclerosis and CVD. Most notably, FFAR4 activation reduces monocyte-endothelial cell interaction, enhances cholesterol efflux from macrophages, reduces lesion size in atherogenic mouse models, and stimulates oxylipin production in myocytes that functions in a feed-forward cardioprotective mechanism. This review will focus on the role of FFAR4 in metabolic diseases and highlights an underappreciated role of FFAR4 in the development of atherosclerosis and CVD.

Fish oil attenuated dystrophic muscle markers of inflammation via FFA1 and FFA4 in the mdx mouse model of DMD

In the present study we investigated the involvement of free fatty acid (FFA) receptors in the anti-inflammatory role of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in dystrophic muscles, by administering FFA blockers in the mdx mouse model of dystrophy. Mdx mice (3 months-old) were treated with fish oil capsules (FDC Vitamins; 0.4 g EPA and 0.2 g DHA; gavage) alone or concomitant to FFA1 and FFA4 blockers (GW1100 and AH7614; i.p.). C57BL/10 mice (3 months-old) and untreated-mdx mice received mineral oil and were used as controls. After 1 month of treatment, plasma markers of myonecrosis (total and cardiac creatine kinase; CK), the levels of FFA1 and FFA4 and of the markers of inflammation, nuclear transcription factor kappa B (NFkB), tumor necrosis factor alpha (TNF-α) and interleukin 1β (IL-1β) were analyzed in the diaphragm muscle and heart by western blot. Fish oil significantly reduced total CK, cardiac CK and the levels of NFkB (diaphragm), and of TNF-α and IL-1β (diaphragm and heart) in mdx. In the dystrophic diaphragm, FFA1 was increased compared to normal. Blockers of FFA1 and FFA4 significantly inhibited the effects of fish oil treatment in both dystrophic muscles. The anti-inflammatory effects of fish oil in dystrophic diaphragm muscle and heart were mediated through FFA1 and FFA4.

The Gut Microbial Endocrine Organ in Type 2 Diabetes

Historically, the focus of type II diabetes mellitus (T2DM) research has been on host metabolism and hormone action. However, emerging evidence suggests that the gut microbiome, commensal microbes that colonize the gastrointestinal tract, also play a significant role in T2DM pathogenesis. Specifically, gut microbes metabolize what is available to them through the host diet to produce small molecule metabolites that can have endocrine-like effects on human cells. In fact, the meta-organismal crosstalk between gut microbe-generated metabolites and host receptor systems may represent an untapped therapeutic target for those at risk for or suffering from T2DM. Recent evidence suggests that gut microbe-derived metabolites can impact host adiposity, insulin resistance, and hormone secretion to collectively impact T2DM progression. Here we review the current evidence that structurally diverse gut microbe-derived metabolites, including short chain fatty acids, secondary bile acids, aromatic metabolites, trimethylamine-N-oxide, polyamines, and N-acyl amides, that can engage with host receptors in an endocrine-like manner to promote host metabolic disturbance associated with T2DM. Although these microbe-host signaling circuits are not as well understood as host hormonal signaling, they hold untapped potential as new druggable targets to improve T2DM complications. Whether drugs that selectively target meta-organismal endocrinology will be safe and efficacious in treating T2DM is a key new question in the field of endocrinology. Here we discuss the opportunities and challenges in targeting the gut microbial endocrine organ for the treatment of diabetes and potentially many other diseases where diet-microbe-host interactions play a contributory role.

Microbiota, a New Playground for the Omega-3 Polyunsaturated Fatty Acids in Cardiovascular Diseases

Several cardioprotective mechanisms attributed to Omega-3 polyunsaturated fatty acids (PUFAs) have been studied and widely documented. However, in recent years, studies have supported the concept that the intestinal microbiota can play a much larger role than we had anticipated. Microbiota could contribute to several pathologies, including cardiovascular diseases. Indeed, an imbalance in the microbiota has often been reported in patients with cardiovascular disease and produces low-level inflammation. This inflammation contributes to, more or less, long-term development of cardiovascular diseases. It can also worsen the symptoms and the consequences of these pathologies. According to some studies, omega-3 PUFAs in the diet could restore this imbalance and mitigate its harmful effects on cardiovascular diseases. Many mechanisms are involved and included: (1) a reduction of bacteria producing trimethylamine (TMA); (2) an increase in bacteria producing butyrate, which has anti-inflammatory properties; and (3) a decrease in the production of pro-inflammatory cytokines. Additionally, omega-3 PUFAs would help maintain better integrity in the intestinal barrier, thereby preventing the translocation of intestinal contents into circulation. This review will summarize the effects of omega-3 PUFAs on gut micro-biota and the potential impact on cardiac health.

Targeting FFA1 and FFA4 receptors in cancer-induced cachexia

Free fatty acid (FFA) receptors FFA1 and FFA4 are omega-3 molecular targets in metabolic diseases; however, their function in cancer cachexia remains unraveled. We assessed the role of FFA1 and FFA4 receptors in the mouse model of cachexia induced by Lewis lung carcinoma (LLC) cell implantation. Naturally occurring ligands such as α-linolenic acid (ALA) and docosahexaenoic acid (DHA), the synthetic FFA1/FFA4 agonists GW9508 and TUG891, or the selective FFA1 GW1100 or FFA4 AH7614 antagonists were tested. FFA1 and FFA4 expression and other cachexia-related parameters were evaluated. GW9508 and TUG891 decreased tumor weight in LLC-bearing mice. Regarding cachexia-related end points, ALA, DHA, and the preferential FFA1 agonist GW9508 rescued body weight loss. Skeletal muscle mass was reestablished by ALA treatment, but this was not reflected in the fiber cross-sectional areas (CSA) measurement. Otherwise, TUG891, GW1100, or AH7614 reduced the muscle fiber CSA. Treatments with ALA, GW9508, GW1100, or AH7614 restored white adipose tissue (WAT) depletion. As for inflammatory outcomes, ALA improved anemia, whereas GW9508 reduced splenomegaly. Concerning behavioral impairments, ALA and GW9508 rescued locomotor activity, whereas ALA improved motor coordination. Additionally, DHA improved grip strength. Notably, GW9508 restored abnormal brain glucose metabolism in different brain regions. The GW9508 treatment increased leptin levels, without altering uncoupling protein-1 downregulation in visceral fat. LLC-cachectic mice displayed FFA1 upregulation in subcutaneous fat, but not in visceral fat or gastrocnemius muscle, whereas FFA4 was unaltered. Overall, the present study shed new light on FFA1 and FFA4 receptors' role in metabolic disorders, indicating FFA1 receptor agonism as a promising strategy in mitigating cancer cachexia.

Mechanistic insights into cardiovascular protection for omega-3 fatty acids and their bioactive lipid metabolites

Patients with well-controlled low-density lipoprotein cholesterol levels, but persistent high triglycerides, remain at increased risk for cardiovascular events as evidenced by multiple genetic and epidemiologic studies, as well as recent clinical outcome trials. While many trials of low-dose ω3-polyunsaturated fatty acids (ω3-PUFAs), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) have shown mixed results to reduce cardiovascular events, recent trials with high-dose ω3-PUFAs have reignited interest in ω3-PUFAs, particularly EPA, in cardiovascular disease (CVD). REDUCE-IT demonstrated that high-dose EPA (4 g/day icosapent-ethyl) reduced a composite of clinical events by 25% in statin-treated patients with established CVD or diabetes and other cardiovascular risk factors. Outcome trials in similar statin-treated patients using DHA-containing high-dose ω3 formulations have not yet shown the benefits of EPA alone. However, there are data to show that high-dose ω3-PUFAs in patients with acute myocardial infarction had reduced left ventricular remodelling, non-infarct myocardial fibrosis, and systemic inflammation. ω3-polyunsaturated fatty acids, along with their metabolites, such as oxylipins and other lipid mediators, have complex effects on the cardiovascular system. Together they target free fatty acid receptors and peroxisome proliferator-activated receptors in various tissues to modulate inflammation and lipid metabolism. Here, we review these multifactorial mechanisms of ω3-PUFAs in view of recent clinical findings. These findings indicate physico-chemical and biological diversity among ω3-PUFAs that influence tissue distributions as well as disparate effects on membrane organization, rates of lipid oxidation, as well as various receptor-mediated signal transduction pathways and effects on gene expression.

The Role of Atypical Cannabinoid Ligands O-1602 and O-1918 on Skeletal Muscle Homeostasis with a Focus on Obesity

O-1602 and O-1918 are atypical cannabinoid ligands for GPR55 and GPR18, which may be novel pharmaceuticals for the treatment of obesity by targeting energy homeostasis regulation in skeletal muscle. This study aimed to determine the effect of O-1602 or O-1918 on markers of oxidative capacity and fatty acid metabolism in the skeletal muscle. Diet-induced obese (DIO) male Sprague Dawley rats were administered a daily intraperitoneal injection of O-1602, O-1918 or vehicle for 6 weeks. C₂C₁₂ myotubes were treated with O-1602 or O-1918 and human primary myotubes were treated with O-1918. GPR18 mRNA was expressed in the skeletal muscle of DIO rats and was up-regulated in red gastrocnemius when compared with white gastrocnemius. O-1602 had no effect on mRNA expression on selected markers for oxidative capacity, fatty acid metabolism or adiponectin signalling in gastrocnemius from DIO rats or in C₂C₁₂ myotubes, while APPL2 mRNA was up-regulated in white gastrocnemius in DIO rats treated with O-1918. In C₂C₁₂ myotubes treated with O-1918, PGC1α, NFATc1 and PDK4 mRNA were up-regulated. There were no effects of O-1918 on mRNA expression in human primary myotubes derived from obese and obese T2DM individuals. In conclusion, O-1602 does not alter mRNA expression of key pathways important for skeletal muscle energy homeostasis in obesity. In contrast, O-1918 appears to alter markers of oxidative capacity and fatty acid metabolism in C₂C₁₂ myotubes only. GPR18 is expressed in DIO rat skeletal muscle and future work could focus on selectively modulating GPR18 in a tissue-specific manner, which may be beneficial for obesity-targeted therapies.

Effect of icosapent ethyl on susceptibility to ventricular arrhythmias in postinfarcted rat hearts: Role of GPR120-mediated connexin43 phosphorylation

The ω‐3 fatty acids exert as an antioxidant via the G protein‐coupled receptor 120 (GPR120). Icosapent ethyl, a purified eicosapentaenoic acid, showed a marked reduction in sudden cardiac death. Connexin43 is sensitive to redox status. We assessed whether icosapent ethyl attenuates fatal arrhythmias after myocardial infarction, a status of high oxidative stress, through increased connexin43 expression and whether the GPR120 signalling is involved in the protection. Male Wistar rats after ligating coronary artery were assigned to either vehicle or icosapent ethyl for 4 weeks. The postinfarction period was associated with increased oxidative‐nitrosative stress. In concert, myocardial connexin43 levels revealed a significant decrease in vehicle‐treated infarcted rats compared with sham. These changes of oxidative‐nitrosative stress and connexin43 levels were blunted after icosapent ethyl administration. Provocative arrhythmias in the infarcted rats treated with icosapent ethyl were significantly improved than vehicle. Icosapent ethyl significantly increased GPR120 compared to vehicle after infarction. The effects of icosapent ethyl on superoxide and connexin43 were similar to GPR120 agonist GW9508. Besides, the effects of icosapent ethyl on oxidative‐nitrosative stress and connexin43 phosphorylation were abolished by administering AH‐7614, an inhibitor of GPR120. SIN‐1 abolished the Cx43 phosphorylation of icosapent ethyl without affecting GPR120 levels. Taken together, chronic use of icosapent ethyl after infarction is associated with up‐regulation of connexin43 phosphorylation through a GPR120‐dependent antioxidant pathway and thus plays a beneficial effect on arrhythmogenic response to programmed electrical stimulation.

Short-term but not long-term high-fat diet induces an increase in gene expression of gonadotropic hormones and GPR120 in the male mouse pituitary gland

High-fat diet (HFD) is associated with the regulation of reproductive functions. This study aimed to investigate the effects of short-term HFD on the mRNA expression levels of follicle-stimulating hormone β subunit (FSHβ), luteinizing hormone β subunit (LHβ), gonadotropin-releasing hormone receptor, and long-chain fatty acid receptor, GPR120, in the matured male mouse pituitary gland. Adult male mice were fed either control chow or HFD for 1, 2, 5, 10, 30 and 150 days. Fshb and Gpr120 mRNA expression levels in the pituitary glands were significantly increased during 2 to 30 days of HFD feeding. Gnrh-r mRNA in the 30 days HFD fed group and body weight in the 30 and 150 days HFD fed groups were higher than control. However, there were no significant differences in plasma non-esterified fatty acids or glucose levels during the 150 days of HFD feeding. These results suggest that male mice feeding a short-term HFD induces FSHβ synthesis and GPR120 expression in their pituitary gonadotropes.

Oral Administration of Compound Probiotics Ameliorates HFD-Induced Gut Microbe Dysbiosis and Chronic Metabolic Inflammation via the G Protein-Coupled Receptor 43 in Non-alcoholic Fatty Liver Disease Rats

The aim of this study was to investigate how the effects of compound probiotics modulate the gut microbiota, short-chain fatty acid (SCFA), body composition, serum and liver lipids, and inflammatory markers in non-alcoholic fatty liver disease (NAFLD) rats. Twenty-four male SD rats were randomly divided into 3 groups: normal control group (standard feed), high-fat diet (HFD) feeding group (83% standard feed + 10% lard oil + 1.5% cholesterol + 0.5% cholate + 5% sucrose), and compound probiotics intervention group (HFD + 0.6 g × kg^-1 × d^-1 compound probiotics). The microbial population was assessed by 16S rDNA amplification and sequence analysis. Body composition, serum and liver lipids, serum inflammatory markers, colonic SCFAs, and relative proteins were assessed. The results showed that compound probiotics significantly reduced body weight, visceral and total fat mass, and the levels of hepatic TC and TG and serum TG, FFA, ALT, LPS, IL-1β, and IL-18 (P < 0.05). The proportions of TM7 phylum (0.06 vs 1.57%, P < 0.05) clearly increased, while that of Verrucomicrobia phylum (5.69 vs 2.61%, P < 0.05) clearly decreased. Compound probiotics also increased the representation of Ruminococcus genus (0.95 vs 1.83%, P < 0.05), while the proportion of Veillonella genus decreased (0.10 vs 0.03%, P < 0.05). The levels of colonic SCFAs and GPR43, NLRP3, ASC, and CASPASE-1 proteins also changed significantly (P < 0.05). Compound probiotics modulated gut microbiota, SCFAs, and their receptor GPR43 in NAFLD rats. These changes might inhibit lipid deposition and chronic metabolic inflammation in response to the insult of HFD.

Marine-Derived Omega-3 Polyunsaturated Fatty Acids and Heart Failure: Current Understanding for Basic to Clinical Relevance

Heart failure (HF) is a rapidly growing global public health problem. Since HF results in high mortality and re-hospitalization, new effective treatments are desired. Although it remains controversial, omega 3 polyunsaturated fatty acids (n-3 PUFAs), such as the eicosapentaenoic acid and docosahexaenoic acid, have been widely recognized to have benefits for HF. In a large-scale clinical trial regarding secondary prevention of HF by n-3 PUFA (GISSI-HF trial), the supplementation of n-3 PUFA significantly reduced cardiovascular mortality and hospitalization. Other small clinical studies proposed that n-3 PUFA potentially suppresses the ventricular remodeling and myocardial fibrosis, which thereby improves the ventricular systolic and diastolic function both in ischemic and non-ischemic HF. Basic investigations have further supported our understanding regarding the cardioprotective mechanisms of n-3 PUFA against HF. In these reports, n-3 PUFA has protected hearts through (1) anti-inflammatory effects, (2) intervention of cardiac energy metabolism, (3) modification of cardiac ion channels, (4) improvement of vascular endothelial response, and (5) modulation of autonomic nervous system activity. To clarify the pros and cons of n-3 PUFA on HF, we summarized recent evidence regarding the beneficial effects of n-3 PUFA on HF both from the clinical and basic studies.

Gut Microbiota-Derived Components and Metabolites in the Progression of Non-Alcoholic Fatty Liver Disease (NAFLD)

Human gut microbiota has been increasingly recognized as a pivotal determinant of non-alcoholic fatty liver disease (NAFLD). Apart from the changes in the composition of gut microbiota, the components and metabolites derived from intestinal microbiota have emerged as key factors in modulating the pathological process of NAFLD. Compelling evidences have revealed that gut microbiota generates a variety of bioactive substances that interact with the host liver cells through the portal vein. These substances include the components derived from bacteria such as lipopolysaccharides, peptidoglycan, DNA, and extracellular vesicles, as well as the metabolites ranging from short-chain fatty acids, indole and its derivatives, trimethylamine, secondary bile acids, to carotenoids and phenolic compounds. The mechanisms underlying the hepatic responses to the bioactive substances from gut bacteria have been associated with the regulation of glycolipid metabolism, immune signaling response, and redox homeostasis. Illuminating the interplay between the unique factors produced from gut microbiome and the liver will provide a novel therapeutical target for NAFLD. The current review highlights the recent advances on the mechanisms by which the key ingredients and metabolites from gut microbiota modulate the development and progression of NAFLD.

Sodium Butyrate Improves Liver Glycogen Metabolism in Type 2 Diabetes Mellitus

Liver plays a central role in modulating blood glucose level. Our most recent findings suggested that supplementation with microbiota metabolite sodium butyrate (NaB) could ameliorate progression of type 2 diabetes mellitus (T2DM) and decrease blood HbA1c in db/db mice. To further investigate the role of butyrate in homeostasis of blood glucose and glycogen metabolism, we carried out the present study. In db/db mice, we found significant hypertrophy and steatosis in hepatic lobules accompanied by reduced glycogen storage, and expression of GPR43 was significantly decreased by 59.38 ± 3.33%; NaB administration significantly increased NaB receptor G-protein coupled receptor 43 (GPR43) level and increased glycogen storage in both mice and HepG2 cells. Glucose transporter 2 (GLUT2) and sodium-glucose cotransporter 1 (SGLT1) on cell membrane were upregulated by NaB. The activation of intracellular signaling Protein kinase B (PKB), also known as AKT, was inhibited while glycogen synthase kinase 3 (GSK3) was activated by NaB in both in vivo and in vitro studies. The present study demonstrated that microbiota metabolite NaB possessed beneficial effects on preserving blood glucose homeostasis by promoting glycogen metabolism in liver cells, and the GPR43-AKT-GSK3 signaling pathway should contribute to this effect.

Unsaturated fatty acids from flaxseed oil and exercise modulate GPR120 but not GPR40 in the liver of obese mice: a new anti-inflammatory approach

GPR120 and GPR40 were recently reported as omega-3 (ω3) receptors with anti-inflammatory properties. Physical exercise could increase the expression of these receptors in the liver, improving hepatic metabolism in obesity and type 2 diabetes. Our aim was to investigate GPR120/40 in the liver of lean and obese mice after acute or chronic physical exercise, with or without the supplementation of ω3 rich flaxseed oil (FS), as well as assess the impact of exercise and FS on insulin signaling and inflammation. Mice were fed a high-fat diet (HF) for 4 weeks to induce obesity and subsequently subjected to exercise with or without FS, or FS alone. Insulin signaling, inflammatory markers and GPR120/40 and related cascades were measured. Chronic, but not acute, exercise and FS increased GPR120, but not GPR40, activating β-arrestin-2 and decreasing the inflammatory response, as well as reducing fat depots in liver and adipose tissue. Exercise or a source of ω3 led to a higher tolerance to fatigue and an increased running distance and speed. The combination of physical exercise and ω3 food sources could provide a new strategy against obesity through the modulation of hepatic GPR120 and an increase in exercise performance.

Extracorporeal shockwave against inflammation mediated by GPR120 receptor in cyclophosphamide-induced rat cystitis model

BACKGROUND

We tested the hypothesis that extracorporeal shockwave treatment (ESWT) can abolish inflammation and restore urothelial barrier integrity in acute interstitial cystitis by upregulating the fatty acid receptor GPR120.

METHODS

A total of 30 female Sprague-Dawley rats were categorized into five groups: (1) sham-operated rats (SC); (2) rats treated with ESWT (SC + ESWT); (3) rats with bladder irritation using 150 mg/kg cyclophosphamide through intraperitoneal injection; (4) cyclophosphamide rats treated with ESWT (cyclophosphamide+ESWT); (5) cyclophosphamide rats treated with GPR120 agonist (cyclophosphamide+GW9508).

RESULTS

On Day 3, urine and bladder specimens were collected for biochemical, histopathological, immunological, and immunoblotting analysis. Following stimulation with cyclophosphamide, the inhibition of the elevated levels of TAK1/NF-κB and phospho-TAK1/NF-κB by ESWT and GPR120 agonists in RT4 cells was associated with a suppression of NF-κB translocation from the cytosol to the nucleus. Accordingly, this anti-inflammatory effect was abolished by GPR120 antagonist and knockdown of GPR120. Histologically, bladder inflammation in cyclophosphamide-treated rats was suppressed by GW9508 or ESWT. Masson's trichrome and Sirius red staining revealed that cyclophosphamide treatment enhanced synthesis of extracellular matrix in rats that was reversed by GW9508 or ESWT. Upregulated pro-inflammatory mediators and cytokines in the cyclophosphamide-treated rats were also suppressed in the GW9508- or ESWT-treated rats. The significantly increased inflammatory cell infiltration as well as the impaired urothelial integrity of the bladder after cyclophosphamide treatment were reversed by treatment with GW9508 or ESWT.

CONCLUSIONS

These findings suggest that GPR120, the sensing receptor for ESWT, may be useful in the treatment of interstitial cystitis by inhibiting inflammatory response in bladder cells.

Cardioprotective Effects of Omega-3 Polyunsaturated Fatty Acids: Dichotomy between Experimental and Clinical Studies

The high-fat diet of North Americans has a major impact on cardiovascular disease occurrence. Notably, fatty acids have been identified as important factors that could modulate such diseases, especially myocardial infarction (MI). Experimentally, omega-3 polyunsaturated fatty acids (PUFA) have demonstrated positive effects on cardiovascular disorders and have also shown cardioprotection by decreasing MI size. Although many animal experiments have clearly established the benefits of omega-3 PUFA, clinical studies have not reached similar conclusions. In fact, the findings of recent clinical investigations indicate that omega-3 PUFA play only a minor role in cardiovascular health. This dichotomy between experimental and clinical studies may be due to different parameters that are not taken into account in animal experiments. We have recently observed that the high consumption of omega-6 PUFA results in significant attenuation of the beneficial effect of omega-3 PUFA on MI. We believe that part of the dichotomy between experimental and clinical research may be related to the quantity of omega-6 PUFA ingested. This review of the data indicates the importance of considering omega-6 PUFA consumption in omega-3 PUFA studies.

A high omega-3 fatty acid diet rapidly changes the lipid composition of cardiac tissue and results in cardioprotection

The present study was designed to ascertain the effects of 3 diets with different omega-3/6 fatty acid ratios on infarct size and the modifications that these diets induce in the lipid composition of cardiac tissue. Sprague-Dawley rats were fed omega-3/6 fatty acid diets with 1:1, 1:5, or 1:20 ratios for at least 10 days, followed by occlusion of the left anterior descending artery for 40 min and 24 h of reperfusion. Infarct size was significantly smaller in the 1:1 group than in the other groups. Significantly higher concentrations of the omega-3 fatty acids eicosapentaenoic acid, docosapentaenoic acid, and docosahexaenoic acid were found in the 1:1 group than in the other groups. Omega-6 polyunsaturated fatty acid levels were similar between groups, although they were higher in the 1:5 and 1:20 groups than in the 1:1 group. Margaric acid concentrations were higher in the 1:1 group than in the other groups. Docosahexaenoic acid levels in cardiac tissue and infarct size were significantly correlated with no other significant links being apparent. The present study indicated that a 1:1 omega-3/6 fatty acid ratio protected against ischemia and was associated with increased omega-3 fatty acid composition of cardiac tissue.

Expression of GPR43 in Brown Adipogenesis Is Enhanced by Rosiglitazone and Controlled by PPARγ/RXR Heterodimerization

GPR43, a G-protein coupled receptor recognizing short-chain fatty acids, has been reported to participate in many biological functions of white adipocytes, such as adipogenesis and lipolysis. However, the functional role of GPR43 in brown adipocytes is still not clear. In this study, we investigated the effects of the PPARγ agonist rosiglitazone on GPR43 expression in brown adipogenesis. The results demonstrated that GPR43 was expressed during the late phase of brown adipocyte differentiation, which could be further augmented by adipogenic agent rosiglitazone treatment. The PPARγ/RXR heterodimerization was found to be the key transcription factor for this enhancing effect of rosiglitazone on GPR43 expression. Taken together, these results suggested GPR43 levels might be regulated by PPARγ-activated events during brown adipocytes differentiation and reflect the adipogenesis status of brown adipocytes.

Docosahexaenoic acid (DHA) effects on proliferation and steroidogenesis of bovine granulosa cells

BACKGROUND

Docosahexaenoic acid (DHA) is a n-3 polyunsaturated fatty acid (PUFA) belonging to a family of biologically active fatty acids (FA), which are known to have numerous health benefits. N-3 PUFAs affect reproduction in cattle, and notably directly affect follicular cells. In terms of reproduction in cattle, n-3 PUFA-enriched diets lead to increased follicle size or numbers.

METHODS

The objective of the present study was to analyze the effects of DHA (1, 10, 20 and 50 μM) on proliferation and steroidogenesis (parametric and/or non parametric (permutational) ANOVA) of bovine granulosa cells in vitro and mechanisms of action through protein expression (Kruskal-Wallis) and signaling pathways (non parametric ANOVA) and to investigate whether DHA could exert part of its action through the free fatty acid receptor 4 (FFAR4).

RESULTS

DHA (10 and 50 μM) increased granulosa cell proliferation and DHA 10 μM led to a corresponding increase in proliferating cell nuclear antigen (PCNA) expression level. DHA also increased progesterone secretion at 1, 20 and 50 μM, and estradiol secretion at 1, 10 and 20 μM. Consistent increases in protein levels were also reported for the steroidogenic enzymes, cytochrome P450 family 11 subfamily A member 1 (CYP11A1) and hydroxy-delta-5-steroid dehydrogenase, 3 beta- and steroid delta-isomerase 1 (HSD3B1), and of the cholesterol transporter steroidogenic acute regulatory protein (StAR), which are necessary for production of progesterone or androstenedione. FFAR4 was expressed in all cellular types of bovine ovarian follicles, and in granulosa cells it was localized close to the cellular membrane. TUG-891 treatment (1 and 50 μM), a FFAR4 agonist, increased granulosa cell proliferation and MAPK14 phosphorylation in a similar way to that observed with DHA treatment. However, TUG-891 treatment (1, 10 and 50 μM) showed no effect on progesterone or estradiol secretion.

CONCLUSIONS

These data show that DHA stimulated proliferation and steroidogenesis of bovine granulosa cells and led to MAPK14 phosphorylation. FFAR4 involvement in DHA effects requires further investigation, even if our data might suggest FFAR4 role in DHA effects on granulosa cell proliferation. Other mechanisms of DHA action should be investigated as the steroidogenic effects seemed to be independent of FFAR4 activation.

Impact of a single bout of high-intensity interval exercise and short-term interval training on interleukin-6, FNDC5, and METRNL mRNA expression in human skeletal muscle

BACKGROUND

Exercise promotes numerous phenotypic adaptations in skeletal muscle that contribute to improved function and metabolic capacity. An emerging body of evidence suggests that skeletal muscle also releases a myriad of factors during exercise, termed "myokines". The purpose of this study was to examine the effects of high-intensity interval training (HIIT) on the acute regulation of the mRNA expression of several myokines, including the prototypical myokine interleukin-6 (IL-6), and recently identified myokines fibronectin type III domain-containing protein 5 (FNDC5) (irisin) and meteorin-like protein (METRNL).

METHODS

Both before and after a 20-day period of twice-daily high-volume HIIT, 9 healthy males (20.5 ± 1.5 years performed a standardized bout of high-intensity interval exercise (HIIE; 5 × 4 min at ~80% pretraining peak power output) with skeletal muscle biopsy samples (vastus lateralis) obtained at rest, immediately following exercise, and at 3 h recovery.

RESULTS

Before training, a single bout of HIIE increased IL-6 (p < 0.05) and METRNL (p < 0.05) mRNA expression measured at 3 h recovery when compared to rest. Following 20 days of HIIT, IL-6 and FNDC5 mRNA were increased at 3 h recovery from the standardized HIIE bout when compared to rest (both p < 0.05). Resting METRNL and FNDC5 mRNA expression were higher following training (p < 0.05), and there was an overall increase in FNDC5 mRNA post-training (main effect of training, p < 0.05).

CONCLUSION

In human skeletal muscle (1) an acute bout of HIIE can induce upregulation of skeletal muscle IL-6 mRNA both before and after a period of intensified HIIT; (2) Resting and overall FNDC5 mRNA expression is increased by 20 days of HIIT; and (3) METRNL mRNA expression is responsive to both acute HIIE and short-term intense HIIT. Future studies are needed to confirm these findings at the protein and secretion level in humans.

Effect of different levels of feed restriction and fish oil fatty acid supplementation on fat deposition by using different techniques, plasma levels and mRNA expression of several adipokines in broiler breeder hens

Background

Reproductive hens are subjected to a restricted diet to limit the decline in fertility associated with change in body mass. However, endocrine and tissue responses to diet restriction need to be documented.

Objective

We evaluated the effect of different levels of feed restriction, with or without fish oil supplementation, on metabolic parameters and adipokine levels in plasma and metabolic tissues of reproductive hens.

Methods

We designed an in vivo protocol involving 4 groups of hens; RNS: restricted (Rt) unsupplemented, ANS: ad libitum (Ad, receiving an amount of feed 1.7 times greater than animals on the restricted diet) unsupplemented, RS: Rt supplemented, and AS: Ad supplemented. The fish oil supplement was used at 1% of the total diet composition.

Results

Hens fed with the Rt diet had a significantly (P < 0.0001) lower growth than Ad hens, while the fish oil supplementation had no effect on these parameters. Furthermore, the bioelectrical impedance analysis (BIA) and the fat ultrasonographic examinations produced similar results to the other methods that required animals to be killed (carcass analysis and weight of adipose tissue). In addition, the Rt diet significantly (P < 0.05) decreased plasma levels of triglycerides, phospholipids, glucose and ADIPOQ, and fish oil supplementation decreased plasma levels of RARRES2. We also showed a positive correlation between insulin values and ADIPOQ or NAMPT or RARRES2 values, and a negative correlation of fat percentage to RARRES2 values. Moreover, the effects of the Rt diet and fish oil supplementation on the mRNA expression depended on the factors tested and the hen age.

Conclusions

Rt diet and fish oil supplementation are able to modulate metabolic parameters and the expression of adipokines and their receptors in metabolic tissue.

Short-Term Microbiota Manipulation and Forearm Substrate Metabolism in Obese Men: A Randomized, Double-Blind, Placebo-Controlled Trial

OBJECTIVE

To investigate the impact of gut microbiota manipulation on fasting and postprandial skeletal muscle metabolism in humans.

METHODS

40 obese, insulin-resistant males were randomized to amoxicillin (broad-spectrum antibiotic), vancomycin (narrow-spectrum antibiotic), or placebo (7 days, 1,500 mg/day). Before and after treatment, forearm blood flow and metabolite fluxes across forearm muscle were measured under fasting and postprandial (high-fat mixed-meal) conditions.

RESULTS

Vancomycin decreased bacterial diversity, reduced the abundance of Gram-positive Firmicutes, and increased the abundance of Gram-negative Proteobacteria, whereas amoxicillin did not affect microbial composition. Neither vancomycin nor amoxicillin treatment affected fasting and postprandial plasma glucose, free fatty acid (FFA), triacylglycerol (TAG), glycerol, lactate, and insulin concentrations or forearm blood flow. Fasting and postprandial net forearm muscle glucose uptake and the release of lactate were not significantly altered by antibiotic treatment as compared to placebo. Finally, antibiotic treatment did not change fasting and postprandial glycerol, FFA, and TAG fluxes across forearm muscle.

CONCLUSION

The present study demonstrates that short-term antibiotic treatment has no effects on fasting and postprandial forearm substrate metabolism and blood flow in obese men with impaired glucose metabolism. These data suggest that short-term strategies targeting the gut microbiota to improve metabolic health may not be effective in obese humans.

GPR120: a critical role in adipogenesis, inflammation, and energy metabolism in adipose tissue

It is well known that adipose tissue has a critical role in the development of obesity and metabolic diseases and that adipose tissue acts as an endocrine organ to regulate lipid and glucose metabolism. Accumulating in the adipose tissue, fatty acids serve as a primary source of essential nutrients and act on intracellular and cell surface receptors to regulate biological events. G protein-coupled receptor 120 (GPR120) represents a promising target for the treatment of obesity-related metabolic disorders for its involvement in the regulation of adipogenesis, inflammation, glucose uptake, and insulin resistance. In this review, we summarize recent studies and advances regarding the systemic role of GPR120 in adipose tissue, including both white and brown adipocytes. We offer a new perspective by comparing the different roles in a variety of homeostatic processes from adipogenic development to adipocyte metabolism, and we also discuss the effects of natural and synthetic agonists that may be potential agents for the treatment of metabolic diseases.

GPR43 activation enhances psoriasis-like inflammation through epidermal upregulation of IL-6 and dual oxidase 2 signaling in a murine model

The gut is densely inhabited by commensal bacteria, which metabolize dietary fibers/undigested carbohydrates and produce short-chain fatty acids such as acetate. GPR43 is one of the receptors to sense short-chain fatty acids, and expressed in various immune and non-immune cells. Acetate/GPR43 signaling has been shown to affect various inflammatory diseases through Th17 responses and NADPH oxidase (NOX)-derived reactive oxygen species (ROS) generation. However, no study has previously explored the effects of GPR43 activation during psoriasis-like inflammation. Therefore, this study investigated the effect of acetate/phenylacetamide (GPR43 agonists) on imiquimod induced skin inflammation in mice. Mice were administered phenylacetamide/acetate followed by assessment of skin inflammation, NOXs (NOX-2, NOX-4, dual oxidases), and Th17 related signaling. Our study showed induction of epidermal GPR43 after imiquimod treatment, i.e. psoriasis-like inflammation. Acetate administration in psoriatic mice led to further increase in skin inflammation (ear thickness/myeloperoxidase activity) with concurrent increase in Th17 immune responses and epidermal dual oxidase-2 signaling. Further, topical application of GPR43 agonist, phenylacetamide led to enhanced ear thickness with concomitant epidermal IL-6 signaling as well as dual oxidase-2 upregulation which may be responsible for increased psoriasis-like inflammation. Taken together, dual oxidase-2 and IL-6 play important roles in GPR43-mediated skin inflammation. The current study suggests that GPR43 activation in psoriatic patients may lead to aggravation of psoriatic inflammation.

Host-Microbiota Mutualism in Metabolic Diseases

The intestinal microbiota is a plastic ecosystem that is shaped by environmental and genetic factors, interacting with virtually all tissues of the host. Many signals result from the interplay between the microbiota with its mammalian symbiont that can lead to altered metabolism. Disruptions in the microbial composition are associated with a number of comorbidities linked to the metabolic syndrome. Promoting the niche expansion of beneficial bacteria through diet and supplements can improve metabolic disorders. Reintroducing bacteria through probiotic treatment or fecal transplant is a strategy under active investigation for multiple pathological conditions. Here, we review the recent knowledge of microbiota's contribution to host pathology, the modulation of the microbiota by dietary habits, and the potential therapeutic benefits of reshaping the gut bacterial landscape in context of metabolic disorders such as obesity.

Insulinotropic effects of GPR120 agonists are altered in obese diabetic and obese non-diabetic states

G-protein-coupled receptor 120 (GPR120) is a putative target for obesity and diabetes therapies. However, it remains controversial whether resident GPR120 plays a direct regulatory role in islet β-cell insulin secretion. The present study examined this issue in isolated rodent islets and rat β-cell line INS-1E, and assessed the role of GPR120 in islet insulin secretion in obese non-diabetic (OND) and diabetic states. GPR120 expression was detected in rodent islet β-cells. Docosahexaenoic acid (DHA) and synthetic GPR120 agonist GSK137647 (GSK) augmented insulin release from rat/mouse islets and INS-1E; DHA effects were partially mediated by GPR40. GPR120 knockdown and overexpression attenuated and enhanced DHA effects in INS-1E respectively. DHA and GSK improved postprandial hyperglycaemia of diabetic mice. Inhibition of calcium signalling in INS-1E reduced GPR120 activation-induced insulinotropic effects. The insulinotropic effects of DHA/GSK were amplified in OND rat islets, but diminished in diabetic rat islets. GPR120 and peroxisome proliferator-activated receptor γ (PPARγ) expression were elevated in OND islets and palmitic acid (PA)-treated INS-1E, but reduced in diabetic islets and high glucose-treated INS-1E. PPARγ activation increased GPR120 expression in rat islets and INS-1E. DHA and GSK induced protein kinase B (Akt)/extracellular signal-regulated kinase (ERK) phosphorylation in rodent islets and INS-1E, and these effects were altered in OND and diabetic states. Taken together, the present study indicates that (i) GPR120 activation has an insulinotropic influence on β-cells with the involvement of calcium signalling; (ii) GPR120 expression in β-cells and GPR120-mediated insulinotropic effects are altered in OND and diabetic states in distinct ways, and these alterations may be mediated by PPARγ.

ω3-Polyunsaturated fatty acids for heart failure: Effects of dose on efficacy and novel signaling through free fatty acid receptor 4

Heart failure (HF) affects 5.7 million in the U.S., and despite well-established pharmacologic therapy, the 5-year mortality rate remains near 50%. Furthermore, the mortality rate for HF has not declined in years, highlighting the need for new therapeutic options. Omega-3 polyunsaturated fatty acids (ω3-PUFAs), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are important regulators of cardiovascular health. However, questions of efficacy and mechanism of action have made the use of ω3-PUFAs in all cardiovascular disease (CVD) controversial. Here, we review recent studies in animal models of HF indicating that ω3-PUFAs, particularly EPA, are cardioprotective, with the results indicating a threshold for efficacy. We also examine clinical studies suggesting that ω3-PUFAs improve outcomes in patients with HF. Due to the relatively small number of clinical studies of ω3-PUFAs in HF, we discuss EPA concentration-dependency on outcomes in clinical trials of CVD to gain insight into the perceived questionable efficacy of ω3-PUFAs clinically, with the results again indicating a threshold for efficacy. Ultimately, we suggest that the main failing of ω3-PUFAs in clinical trials might be a failure to reach a therapeutically effective concentration. We also examine mechanistic studies suggesting that ω3-PUFAs signal through free fatty acid receptor 4 (Ffar4), a G-protein coupled receptor (GPR) for long-chain fatty acids (FA), thereby identifying an entirely novel mechanism of action for ω3-PUFA mediated cardioprotection. Finally, based on mechanistic animal studies suggesting that EPA prevents interstitial fibrosis and diastolic dysfunction, we speculate about a potential benefit for EPA-Ffar4 signaling in heart failure preserved with ejection fraction.

Uptake of leptin and albumin via separate pathways in proximal tubule cells

The adipokine leptin and oncotic protein albumin are endocytosed in the proximal tubule via the scavenger receptor megalin. Leptin reduces megalin expression and activates cell signalling pathways that upregulate fibrotic protein expression. The aim of this study was to investigate if leptin uptake in proximal tubule cells was via the albumin-megalin endocytic complex. In immortalised proximal tubule Opossum kidney cells (OK) fluorescent leptin and albumin co-localised following 5min exposure, however there was no co-localisation at 10, 20 and 30min exposure. In OK cells, acute exposure to leptin for 2h did not alter NHE3, ClC-5, NHERF1 and NHERF2 mRNA. However, acute leptin exposure increased NHERF2 protein expression in proximal tubule cells. In OK cells, immunoprecipitation experimentation indicated leptin did not bind to ClC-5. Leptin uptake in OK cells was enhanced by bafilomycin and ammonium chloride treatment, demonstrating that uptake was not dependent on lysosomal pH. Thus, it is likely that two pools of megalin exist in proximal tubule cells to facilitate separate uptake of leptin and albumin by endocytosis.

Gut microbiota are linked to increased susceptibility to hepatic steatosis in low-aerobic-capacity rats fed an acute high-fat diet

Poor aerobic fitness is linked to nonalcoholic fatty liver disease and increased all-cause mortality. We previously found that rats with a low capacity for running (LCR) that were fed an acute high-fat diet (HFD; 45% kcal from fat) for 3 days resulted in positive energy balance and increased hepatic steatosis compared with rats that were highly aerobically fit with a high capacity for running (HCR). Here, we tested the hypothesis that poor physiological outcomes in LCR rats following acute HFD feeding are associated with alterations in cecal microbiota. LCR rats exhibited greater body weight, feeding efficiency, 3 days of body weight change, and liver triglycerides after acute HFD feeding compared with HCR rats. Furthermore, compared with HCR rats, LCR rats exhibited reduced expression of intestinal tight junction proteins. Cecal bacterial 16S rDNA revealed that LCR rats had reduced cecal Proteobacteria compared with HCR rats. Microbiota of HCR rats consisted of greater relative abundance of Desulfovibrionaceae and unassigned genera within this family, suggesting increased reduction of endogenous mucins and proteins. Although feeding rats an acute HFD led to reduced Firmicutes in both strains, short-chain fatty acid-producing Phascolarctobacterium was reduced in LCR rats. In addition, Ruminococcae and Ruminococcus were negatively correlated with energy intake in the LCR/HFD rats. Predicted metagenomic function suggested that LCR rats had a greater capacity to metabolize carbohydrate and energy compared with HCR rats. Overall, these data suggest that the populations and metabolic capacity of the microbiota in low-aerobically fit LCR rats may contribute to their susceptibility to acute HFD-induced hepatic steatosis and poor physiologic outcomes.

Diet induced obesity in rats reduces NHE3 and Na(+) /K(+) -ATPase expression in the kidney

The consumption of a high fat diet (HFD) is associated with proteinuria and altered sodium handling and excretion, which can lead to kidney disease. In the proximal tubule, the Na(+) /H(+) Exchanger 3 (NHE3) is responsible for normal protein reabsorption and the reabsorption of approximately 70% of the renal sodium load. It is the Na(+) /K(+) -ATPase that provides the driving force for the reabsorption of sodium and its exit across the basolateral membrane. This study investigates the effects that consumption of a HFD for 12 weeks has on NHE3 and Na(+) /K(+) -ATPase expression in the kidney. Western blot analysis identified a significant reduction in NHE3 and its modulator, phosphorylated protein kinase B, in renal lysate from obese rats. In the obese rats, a reduction in NHE3 expression in the proximal tubule may impact on the acidification of endosomes which are responsible for albumin uptake, suggesting a key role for the exchanger in protein endocytosis in obesity. Western blot analysis identified a reduction in Na(+) /K(+) -ATPase which could also potentially impact on albumin uptake and sodium reabsorption. This study demonstrates that consumption of a HFD for 12 weeks reduces renal NHE3 and Na(+) /K(+) -ATPase expression, an effect that may contribute to the albuminuria associated with obesity. Furthermore the reduction in these transporters is not likely to contribute to the reduced sodium excretion in obesity. These data highlight a potential link between NHE3 and Na(+) /K(+) -ATPase in the pathophysiological changes in renal protein handling observed in obesity.

Dietary Fatty Acids and Their Potential for Controlling Metabolic Diseases Through Activation of FFA4/GPR120

It is well known that the amount and type of ingested fat impacts the development of obesity and metabolic diseases, but the potential for beneficial effects from fat has received less attention. It is becoming clear that the composition of the individual fatty acids in diet is important. Besides acting as precursors of potent signaling molecules, dietary fatty acids act directly on intracellular and cell surface receptors. The free fatty acid receptor 4 (FFA4, previously GPR120) is linked to the regulation of body weight, inflammation, and insulin resistance and represents a potential target for the treatment of metabolic disorders, including type 2 diabetes and obesity. In this review, we discuss the various types of dietary fatty acids, the link between FFA4 and metabolic diseases, the potential effects of the individual fatty acids on health, and the ability of fatty acids to activate FFA4. We also discuss the possibility of dietary schemes that implement activation of FFA4.

Epigenetic regulation of gene expression and M2 macrophage polarization as new potential omega-3 polyunsaturated fatty acid targets in colon inflammation and cancer

INTRODUCTION

It has become increasingly clear that dietary habits may affect the risk/progression of chronic diseases with a pathogenic inflammatory component, such as colorectal cancer. Considerable attention has been directed toward the ability of nutritional agents to target key molecular pathways involved in these inflammatory-related diseases.

AREAS COVERED

ω-3 Polyunsaturated fatty acids (PUFA) and their oxidative metabolites have attracted considerable interest as possible anti-inflammatory and anti-cancer agents, especially in areas such as the large bowel, where the influence of orally introduced substances is high and tumors show deranged PUFA patterns. On this basis, we have analyzed pre-clinical findings that have recently revealed new insight into the molecular pathways targeted by ω-3 PUFA.

EXPERT OPINION

The findings analyzed herein demonstrate that ω-3 PUFA may exert beneficial effects by targeting the epigenetic regulation of gene expression and altering M2 macrophage polarization during the inflammatory response. These mechanisms need to be better explored in the large bowel, and further studies could better clarify their role and the potential of dietary interventions with ω-3 PUFA in the large bowel. The epigenomic mechanism is discussed in view of the potential of ω-3 PUFA to enhance the efficacy of other agents used in the therapy of colorectal cancer.

Free-fatty acid receptor-4 (GPR120): Cellular and molecular function and its role in metabolic disorders

Over the last decade, a subfamily of G protein-coupled receptors that are agonized by endogenous and dietary free-fatty acids (FFA) has been discovered. These free-fatty acid receptors include FFA2 and FFA3, which are agonized by short-chained FFA, as well as FFA1 and FFA4, which are agonized by medium-to-long chained FFA. Ligands for FFA1 and FFA4 comprise the family of long chain polyunsaturated omega-3 fatty acids including α-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), suggesting that many of the long-known beneficial effects of these fats may be receptor mediated. In this regard, FFA4 has gathered considerable interest due to its role in ameliorating inflammation, promoting insulin sensitization, and regulating energy metabolism in response to FFA ligands. The goal of this review is to summarize the body of evidence in regard to FFA4 signal transduction, its mechanisms of regulation, and its functional role in a variety of tissues. In addition, recent endeavors toward discovery of small molecules that modulate FFA4 activity are also presented.

Fish oil and flax seed oil supplemented diets increase FFAR4 expression in the rat colon

BACKGROUND AND OBJECTIVE

Omega-3 fatty acids, such as α-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), are polyunsaturated fatty acids (PUFA) that have long been associated with anti-inflammatory activity and general benefit toward human health. Over the last decade, the identification of a family of cell-surface G protein-coupled receptors that bind and are activated by free-fatty acids, including omega-3 fatty acids, suggest that many effects of PUFA are receptor-mediated. One such receptor, free-fatty acid receptor-4 (FFAR4), previously described as GPR120, has been shown to modulate anti-inflammatory and insulin-sensitizing effects in response to PUFA such as ALA and DHA. Additionally, FFAR4 stimulates secretion of the insulin secretagogue glucagon-like peptide-1 (GLP-1) from the GI tract and acts as a dietary sensor to regulate energy availability. The aim of the current study was to assess the effects of dietary omega-3 fatty acid supplementation on FFAR4 expression in the rat colon.

METHODS

Sprague-Dawley rats were fed control soybean oil diets or alternatively, diets supplemented with either fish oil, which is enriched in DHA and EPA, or flaxseed oil, which is enriched in ALA, for 7 weeks. GLP-1 and blood glucose levels were monitored weekly and at the end of the study period, expression of FFAR4 and the inflammatory marker TNF-α was assessed.

RESULTS

Our findings indicate that GLP-1 and blood glucose levels were unaffected by omega-3 fatty acid supplementation, however, animals that were fed fish or flaxseed oil-supplemented diets had significantly heightened colonic FFAR4 and actin expression, and reduced expression of the pro-inflammatory cytokine TNF-α compared to animals fed control diets.

CONCLUSIONS

These results suggest that similar to ingestion of other fats, dietary-intake of omega-3 fatty acids can alter FFAR4 expression within the colon.

Endogenous Ligand for GPR120, Docosahexaenoic Acid, Exerts Benign Metabolic Effects on the Skeletal Muscles via AMP-activated Protein Kinase Pathway

Docosahexaenoic acid (DHA) is an endogenous ligand of G protein-coupled receptor 120 (GPR120). However, the mechanisms underlying DHA action are poorly understood. In this study, DHA stimulated glucose uptake in the skeletal muscles in an AMP-activated protein kinase (AMPK)-dependent manner. GPR120-mediated increase in intracellular Ca(2+) was critical for DHA-mediated AMPK phosphorylation and glucose uptake. In addition, DHA stimulated GLUT4 translocation AMPK-dependently. Inhibition of AMPK and Ca(2+)/calmodulin-dependent protein kinase kinase blocked DHA-induced glucose uptake. DHA and GW9508, a GPR120 agonist, increased GPR120 expression. DHA-mediated glucose uptake was not observed in GPR120 knockdown conditions. DHA increased AMPK phosphorylation, glucose uptake, and intracellular Ca(2+) concentration in primary cultured myoblasts. Taken together, these results indicated that the beneficial metabolic role of DHA was attributed to its ability to regulate glucose via the GPR120-mediated AMPK pathway in the skeletal muscles.

Renal effects of chronic pharmacological manipulation of CB2 receptors in rats with diet-induced obesity

BACKGROUND AND PURPOSE

In diabetic nephropathy agonism of CB2 receptors reduces albuminuria and podocyte loss; however, the role of CB2 receptors in obesity-related nephropathy is unknown. The aim of this study was to determine the role of CB2 receptors in a model of diet-induced obesity (DIO) and characterize the hallmark signs of renal damage in response to agonism (AM1241) and antagonism (AM630) of CB2 receptors.

EXPERIMENTAL APPROACH

Male Sprague Dawley rats were fed a high-fat diet (HFD: 40% digestible energy from lipids) for 10 weeks. In another cohort, after 9 weeks on a HFD, rats were injected daily with either 3 mg·kg(-1) AM1241, 0.3 mg·kg(-1) AM630 or saline for 6 weeks.

KEY RESULTS

Ten weeks on a HFD significantly reduced renal expression of CB2 receptors and renal function. Treatment with AM1241 or AM630 did not reduce weight gain or food consumption in DIO. Despite this, AM1241 significantly reduced systolic BP, peri-renal adipose accumulation, plasma leptin, urinary protein, urinary albumin, urinary sodium excretion and the fibrotic markers TGF-β1, collagen IV and VEGF in kidney lysate. Treatment with AM630 of DIO rats significantly reduced creatinine clearance and increased glomerular area and kidney weight (gross and standardized for body weight). Diastolic BP, glucose tolerance, insulin sensitivity, plasma creatinine, plasma TGF-β1 and kidney expression of fibronectin and α-smooth muscle actin were not altered by either AM1241 or AM630 in DIO.

CONCLUSIONS

This study demonstrates that while agonism of CB2 receptors with AM1241 treatment for 6 weeks does not reduce weight gain in obese rats, it leads to improvements in obesity-related renal dysfunction.

LINKED ARTICLES

This article is part of a themed section on Endocannabinoids. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v173.7/issuetoc.

Direct activation of the proposed anti-diabetic receptor, GPR119 in cardiomyoblasts decreases markers of muscle metabolic activity

GPR119 agonists are emerging rapidly as a pharmaceutical treatment of diabetes. Diabetes is a known risk factor for cardiovascular disease yet the cardiac-specific consequences of GPR119 activation are unknown. This study demonstrated that GPR119 agonism in cardiac myoblasts reduces metabolic activity in high and low concentrations of fatty acids, with high concentrations of palmitate largely attenuating the effects of the GPR119 agonist, PSN632408. The effects of GPR119 activation on gene and protein markers of metabolism were dependent on fatty acid exposure. Activating GPR119 did not affect cell hypertrophy of lipid accumulation regardless of lipid exposure. These results suggest that the pathways activated in response to GPR119 modulation in cardiac muscle cells differ between healthy and metabolically dysregulated states. However regardless of the pathway activated by GPR119, these effects may cause detrimental reductions to oxidative/metabolic capacity under both conditions. Thus further development of GPR119 agonists for treating metabolic diseases is warranted.

Expression of the long-chain fatty acid receptor GPR120 in the gonadotropes of the mouse anterior pituitary gland

G-protein-coupled receptor 120 (GPR120) has been known to be a receptor of long-chain fatty acids. Here, we investigated GPR120 expression in the mouse pituitary gland via real-time PCR, in situ hybridization, and immunohistochemistry. GPR120 mRNA was abundantly expressed in the pituitary gland of ad-lib fed animals. In situ hybridization and immunohistochemistry revealed GPR120 expression in the gonadotropes of the anterior pituitary gland, but not in thyrotropes, somatotropes, lactotropes, corticotropes, melanotropes, and the posterior pituitary gland. Furthermore, 24 h of fasting induced an increase in GPR120 mRNA expression in the pituitary gland. These results demonstrate that GPR120 in mouse pituitary gonadotropes is upregulated by fasting and that it may play a role in controlling gonadotropin secretion.

Potential roles of GPR120 and its agonists in the management of diabetes

Free fatty acids (FFAs) serve not only as nutrients that provide energy but also as extracellular signaling molecules that manipulate intracellular physiological events through FFA receptors (FFARs) such as FFAR4. FFAR4 is also known as G-protein coupled receptor 120 (GPR120). The main role of GPR120 is to elicit FFA regulation on metabolism homeostasis. GPR120 agonism correlates with prevention of the occurrence and development of metabolic disorders such as obesity and diabetes. GPR120 activation directly or indirectly inhibits inflammation, modulates hormone secretion from the gastrointestinal tract and pancreas, and regulates lipid and/or glucose metabolism in adipose, liver, and muscle tissues, which may help prevent obesity and diabetes. This review summarizes recent advances in physiological roles of GPR120 in preventing insulin resistance and protecting pancreatic islet function, and examines how resident GPR120 in the pancreas may be involved in modulating pancreatic islet function.