Short chain fatty acids and their receptors: new metabolic targets

Short-chain fatty acids: a link between prebiotics and microbiota in chronic kidney disease

Under physiologic conditions, the human gut microbiota performs several activities essential to the body health. In contrast, their imbalances exacerbate some actions which can promote a cascade of metabolic abnormalities, and vice versa. Numerous diseases, including chronic kidney disease, are associated with gut microbiota imbalance, and among several strategies to re-establish gut symbiosis, prebiotics seem to represent an effective nonpharmacological approach. Prebiotics fermentation by gut microbiota produce short-chain fatty acids, which improve the gut barrier integrity and function, and modulate the glucose and lipid metabolism as well as the inflammatory response and immune system. Therefore, this literature review intends to discuss the beneficial effects of prebiotics in human health through short-chain fatty acids production, with a particular interest on chronic kidney disease.

High Resolution NMR Spectroscopy as a Structural and Analytical Tool for Unsaturated Lipids in Solution

Mono- and polyunsaturated lipids are widely distributed in Nature, and are structurally and functionally a diverse class of molecules with a variety of physicochemical, biological, medicinal and nutritional properties. High resolution NMR spectroscopic techniques including 1H-, 13C- and 31P-NMR have been successfully employed as a structural and analytical tool for unsaturated lipids. The objective of this review article is to provide: (i) an overview of the critical 1H-, 13C- and 31P-NMR parameters for structural and analytical investigations; (ii) an overview of various 1D and 2D NMR techniques that have been used for resonance assignments; (iii) selected analytical and structural studies with emphasis in the identification of major and minor unsaturated fatty acids in complex lipid extracts without the need for the isolation of the individual components; (iv) selected investigations of oxidation products of lipids; (v) applications in the emerging field of lipidomics; (vi) studies of protein-lipid interactions at a molecular level; (vii) practical considerations and (viii) an overview of future developments in the field.

Targeting Innate Immunity for Type 1 Diabetes Prevention

PURPOSE OF REVIEW

Despite immense research efforts, type 1 diabetes (T1D) remains an autoimmune disease without a known trigger or approved intervention. Over the last three decades, studies have primarily focused on delineating the role of the adaptive immune system in the mechanism of T1D. The discovery of Toll-like receptors in the 1990s has advanced the knowledge on the role of the innate immune system in host defense as well as mechanisms that regulate adaptive immunity including the function of autoreactive T cells.

RECENT FINDINGS

Recent investigations suggest that inflammation plays a key role in promoting a large number of autoimmune disorders including T1D. Data from the LEW1.WR1 rat model of virus-induced disease and the RIP-B7.1 mouse model of diabetes suggest that innate immune signaling plays a key role in triggering disease progression. There is also evidence that innate immunity may be involved in the course of T1D in humans; however, a small number of clinical trials have shown that interfering with the function of the innate immune system following disease onset exerts only a modest effect on β-cell function. The data implying that innate immune pathways are linked with mechanisms of islet autoimmunity hold great promise for the identification of novel disease pathways that may be harnessed for clinical intervention. Nevertheless, more work needs to be done to better understand mechanisms by which innate immunity triggers β-cell destruction and assess the therapeutic value in blocking innate immunity for diabetes prevention.

The lauric acid-activated signaling prompts apoptosis in cancer cells

The saturated medium-chain fatty-acid lauric acid (LA) has been associated to certain health-promoting benefits of coconut oil intake, including the improvement of the quality of life in breast cancer patients during chemotherapy. As it concerns the potential to hamper tumor growth, LA was shown to elicit inhibitory effects only in colon cancer cells. Here, we provide novel insights regarding the molecular mechanisms through which LA triggers antiproliferative and pro-apoptotic effects in both breast and endometrial cancer cells. In particular, our results demonstrate that LA increases reactive oxygen species levels, stimulates the phosphorylation of EGFR, ERK and c-Jun and induces the expression of c-fos. In addition, our data evidence that LA via the Rho-associated kinase-mediated pathway promotes stress fiber formation, which exerts a main role in the morphological changes associated with apoptotic cell death. Next, we found that the increase of p21^Cip1/WAF1 expression, which occurs upon LA exposure in a p53-independent manner, is involved in the apoptotic effects prompted by LA in both breast and endometrial cancer cells. Collectively, our findings may pave the way to better understand the anticancer action of LA, although additional studies are warranted to further corroborate its usefulness in more comprehensive therapeutic approaches.

Sodium butyrate has context-dependent actions on dipeptidyl peptidase-4 and other metabolic parameters

Sodium butyrate (SB) has various metabolic actions. However, its effect on dipeptidyl peptidase 4 (DPP-4) needs to be studied further. We aimed to evaluate the metabolic actions of SB, considering its physiologically relevant concentration. We evaluated the effect of SB on regulation of DPP-4 and its other metabolic actions, both in vitro (HepG2 cells and mouse mesangial cells) and in vivo (high fat diet [HFD]-induced obese mice). Ten-week HFD-induced obese C57BL/6J mice were subjected to SB treatment by adding SB to HFD which was maintained for an additional 16 weeks. In HepG2 cells, SB suppressed DPP-4 activity and expression at sub-molar concentrations, whereas it increased DPP-4 activity at a concentration of 1,000 µM. In HFD-induced obese mice, SB decreased blood glucose, serum levels of insulin and IL-1β, and DPP-4 activity, and suppressed the increase in body weight. On the contrary, various tissues including liver, kidney, and peripheral blood cells showed variable responses of DPP-4 to SB. Especially in the kidney, although DPP-4 activity was decreased by SB in HFD-induced obese mice, it caused an increase in mRNA expression of TNF-α, IL-6, and IL-1β. The pro-inflammatory actions of SB in the kidney of HFD-induced obese mice were recapitulated by cultured mesangial cell experiments, in which SB stimulated the secretion of several cytokines from cells. Our results showed that SB has differential actions according to its treatment dose and the type of cells and tissues. Thus, further studies are required to evaluate its therapeutic relevance in metabolic diseases including diabetes and obesity.

The dynamic plasticity of insulin production in β-cells

BACKGROUND

Although the insulin-producing pancreatic β-cells are quite capable of adapting to both acute and chronic changes in metabolic demand, persistently high demand for insulin will ultimately lead to their progressive dysfunction and eventual loss. Recent and historical studies highlight the importance of 'resting' the β-cell as a means of preserving functional β-cell mass.

SCOPE OF REVIEW

We provide experimental evidence to highlight the remarkable plasticity for insulin production and secretion by the pancreatic β-cell alongside some clinical evidence that supports leveraging this unique ability to preserve β-cell function.

MAJOR CONCLUSIONS

Treatment strategies for type 2 diabetes mellitus (T2DM) targeted towards reducing the systemic metabolic burden, rather than demanding greater insulin production from an already beleaguered β-cell, should be emphasized to maintain endogenous insulin secretory function and delay the progression of T2DM.

β-Hydroxybutyrate: A Signaling Metabolite

Various mechanisms in the mammalian body provide resilience against food deprivation and dietary stress. The ketone body β-hydroxybutyrate (BHB) is synthesized in the liver from fatty acids and represents an essential carrier of energy from the liver to peripheral tissues when the supply of glucose is too low for the body's energetic needs, such as during periods of prolonged exercise, starvation, or absence of dietary carbohydrates. In addition to its activity as an energetic metabolite, BHB is increasingly understood to have cellular signaling functions. These signaling functions of BHB broadly link the outside environment to epigenetic gene regulation and cellular function, and their actions may be relevant to a variety of human diseases as well as human aging.

A place for host-microbe symbiosis in the comparative physiologist's toolbox

Although scientists have long appreciated that metazoans evolved in a microbial world, we are just beginning to appreciate the profound impact that host-associated microbes have on diverse aspects of animal biology. The enormous growth in our understanding of host-microbe symbioses is rapidly expanding the study of animal physiology, both technically and conceptually. Microbes associate functionally with various body surfaces of their hosts, although most reside in the gastrointestinal tract. Gut microbes convert dietary and host-derived substrates to metabolites such as short-chain fatty acids, thereby providing energy and nutrients to the host. Bacterial metabolites incorporated into the host metabolome can activate receptors on a variety of cell types and, in doing so, alter host physiology (including metabolism, organ function, biological rhythms, neural activity and behavior). Given that host-microbe interactions affect diverse aspects of host physiology, it is likely that they influence animal ecology and, if they confer fitness benefits, the evolutionary trajectory of a species. Multiple variables - including sampling regime, environmental parameters, host metadata and analytical methods - can influence experimental outcomes in host-microbiome studies, making careful experimental design and execution crucial to ensure reproducible and informative studies in the laboratory and field. Integration of microbiomes into comparative physiology and ecophysiological investigations can reveal the potential impacts of the microbiota on physiological responses to changing environments, and is likely to bring valuable insights to the study of host-microbiome interactions among a broad range of metazoans, including humans.

Fenugreek galactomannan and citrus pectin improve several parameters associated with glucose metabolism and modulate gut microbiota in mice

OBJECTIVE

Galactomannans derived from fenugreek confer known health benefits; however, there is little information regarding health benefits of citrus pectin (CP) and its association with gut microbiome metabolites. The aim of this study was to examine links between galactomannan and CP consumption, microbiota development, and glucose metabolism.

DESIGN

Male C57 BL/6 J mice ages 7 to 8 wk were fed ad libitum with a normal diet or one supplemented with 15% of either galactomannan or CP. At 3 wk, an oral glucose tolerance test was performed. Animals were sacrificed at 4 wk and relevant organs were harvested.

RESULTS

Fiber enrichment led to reductions in weight gain, fasting glucose levels, and total serum cholesterol (P < 0.05). Compared with mice fed the normal diet, microbiota populations were altered in both fiber groups and were found to be richer in Bacteroidetes rather than Firmicutes (P < 0.05). The modification was significantly greater in galactomannan-fed than in CP-fed mice (P < 0.0001). Also, enhanced levels of the short-chain fatty acid (SCFA) propionate were found in the cecal contents of CP-fed animals (P < 0.05). Protein expression levels of monocarboxylate transporter 1, which may promote transport of SCFA, were measured in the large intestines after fiber consumption. Enhanced adenosine monophosphate-activated protein kinase (AMPK) activation was observed in livers of galactomannan-fed mice (P < 0.05).

CONCLUSION

Consumption of diets containing soluble fibers, as used in this study, resulted in gut microbiota comprising a healthier flora, and led to positive effects on weight, glycemic control, and liver β oxidation via AMPK.

Epigenetic Metabolite Acetate Inhibits Class I/II Histone Deacetylases, Promotes Histone Acetylation, and Increases HIV-1 Integration in CD4+ T Cells

In this study, we investigated the effect of acetate, the most concentrated short-chain fatty acid (SCFA) in the gut and bloodstream, on the susceptibility of primary human CD4⁺ T cells to HIV-1 infection. We report that HIV-1 replication is increased in CD3/CD28-costimulated CD4⁺ T cells upon acetate treatment. This enhancing effect correlates with increased expression of the early activation marker CD69 and impaired class I/II histone deacetylase (HDAC) activity. In addition, acetate enhances acetylation of histones H3 and H4 and augments HIV-1 integration into the genome of CD4⁺ T cells. Thus, we propose that upon antigen presentation, acetate influences class I/II HDAC activity that transforms condensed chromatin into a more relaxed structure. This event leads to a higher level of viral integration and enhanced HIV-1 production. In line with previous studies showing reactivation of latent HIV-1 by SCFAs, we provide evidence that acetate can also increase the susceptibility of primary human CD4⁺ T cells to productive HIV-1 infection.IMPORTANCE Alterations in the fecal microbiota and intestinal epithelial damage involved in the gastrointestinal disorder associated with HIV-1 infection result in microbial translocation that leads to disease progression and virus-related comorbidities. Indeed, notably via production of short-chain fatty acids, bacteria migrating from the lumen to the intestinal mucosa could influence HIV-1 replication by epigenetic regulatory mechanisms, such as histone acetylation. We demonstrate that acetate enhances virus production in primary human CD4⁺ T cells. Moreover, we report that acetate impairs class I/II histone deacetylase activity and increases integration of HIV-1 DNA into the host genome. Therefore, it can be postulated that bacterial metabolites such as acetate modulate HIV-1-mediated disease progression.

Arachidonic acid sex-dependently affects obesity through linking gut microbiota-driven inflammation to hypothalamus-adipose-liver axis

Unraveling the role of dietary lipids is beneficial to treat obesity and metabolic dysfunction. Nonetheless, how dietary lipids affect existing obesity remains unknown. Arachidonic acid (AA), a derivative of linoleic acid, is one of the crucial n-6 fatty acids. The aim of this study was to investigate whether AA affects obesity through associating microbiota-driven inflammation with hypothalamus-adipose-liver axis. Four-week old C57BL/6J mice were fed with a high-fat diet (HFD, 45% fat) for 10weeks to induce obesity, and then fed a HFD enriched with 10g/kg of AA or a continuous HFD in the following 15weeks. Systemic adiposity and inflammation, metabolic profiles, gut microbiota composition, short-chain fatty acids production, hypothalamic feeding regulators, browning process of adipocytes, hepatosteatosis, and insulin resistance in adipose were investigated. The results indicated that AA aggravates obesity for both genders whereas sex-dependently affects gut microbiota composition. Also, AA favors pro-inflammatory microbiota and reduces butyrate production and circulating serotonin, which augments global inflammation and triggers hypothalamic leptin resistance via microglia accumulation in male. AA exacerbates non-alcoholic steatohepatitis along with amplified inflammation through TLR4-NF-κB pathway and induces insulin resistance. Reversely, AA alleviates obesity-related disorders via rescuing anti-inflammatory and butyrate-producing microbiota, up-regulating GPR41 and GPR109A and controlling hypothalamic inflammation in female. Nevertheless, AA modifies adipocyte browning and promotes lipid mobilization for both genders. We show that AA affects obesity likely through a gut-hypothalamus-adipose-liver axis. Our findings formulate recommendations of n-6 fatty acids like AA from dietary intake for obese subjects preferably in a sexually dimorphic way.

Minor Constituents in Rice Bran Oil and Sesame Oil Play a Significant Role in Modulating Lipid Homeostasis and Inflammatory Markers in Rats

The effects of feeding rats with groundnut oil (GNO), rice bran oil (RBO), and sesame oil (SESO) on serum lipids, liver lipids, and inflammatory markers were evaluated in rats. Male Wistar rats were fed with AIN-93 diet supplemented with 10 wt% of GNO, RBO, and SESO in the form of native (N) and minor constituent-removed (MCR) oils. Rats given RBO and SESO showed significant reduction in serum and liver lipids, 8-hydroxy-2-deoxyguanosine, cytokines in liver, and eicosanoids in leukocytes as compared with the rats given GNO and MCR oils. The rats fed with native oils of RBO and SESO showed an upregulation of sterol regulatory element-binding protein (SREBP)-2 and peroxisome proliferator-activated receptor gamma (PPARγ) and downregulation of nuclear factor-kappa B (NF-κB) p65. These effects of native oil were significantly compromised when rats were given MCR oils. In conclusion, the minor constituents significantly support the hypolipidemic and anti-inflammatory properties of RBO and SESO.

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.

Regulation of Connexin-Based Channels by Fatty Acids

In this mini-review, we briefly summarize the current knowledge about the effects of fatty acids (FAs) on connexin-based channels, as well as discuss the limited information about the impact FAs may have on pannexins (Panxs). FAs regulate diverse cellular functions, some of which are explained by changes in the activity of channels constituted by connexins (Cxs) or Panxs, which are known to play critical roles in maintaining the functional integrity of diverse organs and tissues. Cxs are transmembrane proteins that oligomerize into hexamers to form hemichannels (HCs), which in turn can assemble into dodecamers to form gap junction channels (GJCs). While GJCs communicate the cytoplasm of contacting cells, HCs serve as pathways for the exchange of ions and small molecules between the intra and extracellular milieu. Panxs, as well as Cx HCs, form channels at the plasma membrane that enable the interchange of molecules between the intra and extracellular spaces. Both Cx- and Panx-based channels are controlled by several post-translational modifications. However, the mechanism of action of FAs on these channels has not been described in detail. It has been shown however that FAs frequently decrease GJC-mediated cell-cell communication. The opposite effect also has been described for HC or Panx-dependent intercellular communication, where, the acute FA effect can be reversed upon washout. Additionally, changes in GJCs mediated by FAs have been associated with post-translational modifications (e.g., phosphorylation), and seem to be directly related to chemical properties of FAs (e.g., length of carbon chain and/or degree of saturation), but this possible link remains poorly understood.

Wheat Bran Does Not Affect Postprandial Plasma Short-Chain Fatty Acids from 13C-inulin Fermentation in Healthy Subjects

Wheat bran (WB) is a constituent of whole grain products with beneficial effects for human health. Within the human colon, such insoluble particles may be colonized by specific microbial teams which can stimulate cross-feeding, leading to a more efficient carbohydrate fermentation and an increased butyrate production. We investigated the extent to which WB fractions with different properties affect the fermentation of other carbohydrates in the colon. Ten healthy subjects performed four test days, during which they consumed a standard breakfast supplemented with 10 g ¹³C-inulin. A total of 20 g of a WB fraction (unmodified WB, wheat bran with a reduced particle size (WB RPS), or de-starched pericarp-enriched wheat bran (PE WB)) was also added to the breakfast, except for one test day, which served as a control. Blood samples were collected at regular time points for 14 h, in order to measure ¹³C-labeled short-chain fatty acid (SCFA; acetate, propionate and butyrate) concentrations. Fermentation of ¹³C-inulin resulted in increased plasma SCFA for about 8 h, suggesting that a sustained increase in plasma SCFA can be achieved by administering a moderate dose of carbohydrates, three times per day. However, the addition of a single dose of a WB fraction did not further increase the ¹³C-SCFA concentrations in plasma, nor did it stimulate cross-feeding (Wilcoxon signed ranks test).

Exploration of phenylpropanoic acids as agonists of the free fatty acid receptor 4 (FFA4): Identification of an orally efficacious FFA4 agonist

The long chain free fatty acid receptor 4 (FFA4/GPR120) has recently been recognized as lipid sensor playing important roles in nutrient sensing and inflammation and thus holds potential as a therapeutic target for type 2 diabetes and metabolic syndrome. To explore the effects of stimulating this receptor in animal models of metabolic disease, we initiated work to identify agonists with appropriate pharmacokinetic properties to support progression into in vivo studies. Extensive SAR studies of a series of phenylpropanoic acids led to the identification of compound 29, a FFA4 agonist which lowers plasma glucose in two preclinical models of type 2 diabetes.

Evaluating the Contribution of Gut Microbiota to the Variation of Porcine Fatness with the Cecum and Fecal Samples

Microbial community in gastrointestinal tract participates in the development of the obesity as well as quite a few metabolic diseases in human. However, there are few studies about the relationship between gut microbiota and porcine fatness. Here, we used high-throughput sequencing to perform 16S rRNA gene analysis in 256 cecum luminal samples from Erhualian pigs and 244 stools from Bamaxiang pigs, and adopted a two-part model statistical method to evaluate the association of gut microbes with porcine fatness. As the results, we identified a total of 6 and 108 operational taxonomic units (OTUs), and 9 and 10 bacterial taxa which showed significant associations with fatness traits in the stool and cecum samples, respectively. Cross-validation analysis indicated that gut microbiome showed the largest effect on abdominal adipose by explaining 2.73% phenotypic variance of abdominal fat weight. Significantly more fatness-associated OTUs were identified in the cecum samples than that in the stools, suggesting that cecum luminal samples were better used for identification of fatness-associated microbes than stools. The fatness-associated OTUs were mainly annotated to Lachnospiraceae, Ruminococcaceae, Prevotella, Treponema, and Bacteroides. These microbes have been reported to produce short-chain fatty acids by fermenting dietary indigested polysaccharide and pectin. The short-chain fatty acids can regulate host body energy homeostasis, protect host from inflammation and inhibit fat mass development. Our findings suggested that the gut microbiome may be an important factor modulating fatness in pigs.

FFA2 Contribution to Gestational Glucose Tolerance Is Not Disrupted by Antibiotics

During the insulin resistant phase of pregnancy, the mRNA expression of free fatty acid 2 receptor (Ffar2) is upregulated and as we recently reported, this receptor contributes to insulin secretion and pancreatic beta cell mass expansion in order to maintain normal glucose homeostasis during pregnancy. As impaired gestational glucose levels can affect metabolic health of offspring, we aimed to explore the role of maternal Ffar2 expression during pregnancy on the metabolic health of offspring and also the effects of antibiotics, which have been shown to disrupt gut microbiota fermentative activity (the source of the FFA2 ligands) on gestational glucose homeostasis. We found that maternal Ffar2 expression and impaired glucose tolerance during pregnancy had no effect on the growth rates, ad lib glucose and glucose tolerance in the offspring between 3 and 6 weeks of age. To disrupt short chain fatty acid production, we chronically treated WT mice and Ffar2^-/- mice with broad range antibiotics and further compared their glucose tolerance prior to pregnancy and at gestational day 15, and also quantified cecum and plasma SCFAs. We found that during pregnancy antibiotic treatment reduced the levels of SCFAs in the cecum of the mice, but resulted in elevated levels of plasma SCFAs and altered concentrations of individual SCFAs. Along with these changes, gestational glucose tolerance in WT mice, but not Ffar2^-/- mice improved while on antibiotics. Additional data showed that gestational glucose tolerance worsened in Ffar2^-/- mice during a second pregnancy. Together, these results indicate that antibiotic treatment alone is inadequate to deplete plasma SCFA concentrations, and that modulation of gut microbiota by antibiotics does not disrupt the contribution of FFA2 to gestational glucose tolerance.

Branched short-chain fatty acids modulate glucose and lipid metabolism in primary adipocytes

Short-chain fatty acids (SCFAs), e.g. acetic acid, propionic acid and butyric acid, generated through colonic fermentation of dietary fibers, have been shown to reach the systemic circulation at micromolar concentrations. Moreover, SCFAs have been conferred anti-obesity properties in both animal models and human subjects. Branched SCFAs (BSCFAs), e.g., isobutyric and isovaleric acid, are generated by fermentation of branched amino acids, generated from undigested protein reaching colon. However, BSCFAs have been sparsely investigated when referring to effects on energy metabolism. Here we primarily investigate the effects of isobutyric acid and isovaleric acid on glucose and lipid metabolism in primary rat and human adipocytes. BSCFAs inhibited both cAMP-mediated lipolysis and insulin-stimulated de novo lipogenesis at 10 mM, whereas isobutyric acid potentiated insulin-stimulated glucose uptake by all concentrations (1, 3 and 10 mM) in rat adipocytes. For human adipocytes, only SCFAs inhibited lipolysis at 10 mM. In both in vitro models, BSCFAs and SCFAs reduced phosphorylation of hormone sensitive lipase, a rate limiting enzyme in lipolysis. In addition, BSCFAs and SCFAs, in contrast to insulin, inhibited lipolysis in the presence of wortmannin, a phosphatidylinositide 3-kinase inhibitor and OPC3911, a phosphodiesterase 3 inhibitor in rat adipocytes. Furthermore, BSCFAs and SCFAs reduced insulin-mediated phosphorylation of protein kinase B. To conclude, BSCFAs have effects on adipocyte lipid and glucose metabolism that can contribute to improved insulin sensitivity in individuals with disturbed metabolism.

Faecalibacterium prausnitzii phylotypes in type two diabetic, obese, and lean control subjects

Faecalibacterium prausnitzii is one of the main butyrate producers in the healthy human gut. Information on its genetic diversity is lacking, although two genetic phylotypes have been differentiated. In the present study, F. prausnitzii phylotypes were examined in faeces of obese and type two diabetes with similar eating behaviour compared to a lean control group. The purpose of the study was to analyse if an excessive butyrate production induced by different F. prausnitzii phylotypes discriminates between obese developing type two diabetes or not. The faecal samples were analysed for the total abundance of F. prausnitzii 16S rRNA copies, fragment lengths polymorphism, high resolution melt curve analysis (HRM) and the butyryl-CoA:acetate CoA-transferase gene copies and melt curve variances. The diabetic group was found to differ significantly from the lean control group in the results of qPCR, butyryl-CoA:acetyate CoA-transferase gene melt curve, and HRM. F. prausnitzii phylotypes differed in obese with and without developed diabetes type two. Different phylotypes of F. prausnitzii may lead to differences in the inflammatory genesis in the host. F. prausnitzii phylotypes may have an influence on developing type two diabetes and might also act as starting points for prevention and therapy of obesity associated disease.

SCFA Receptors in Pancreatic β Cells: Novel Diabetes Targets?

Nutrient sensing receptors are key metabolic mediators of responses to dietary and endogenously derived nutrients. These receptors are largely G-protein-coupled receptors (GPCRs) and many are gaining significant interest as drug targets with a potential therapeutic role in metabolic diseases. A distinct subclass of nutrient sensing GPCRs, two short chain fatty acid (SCFA) receptors (FFA2 and FFA3) are uniquely responsive to gut microbiota derived nutrients (such as acetate, propionate, and butyrate). Pharmacological, molecular, and genetic studies have investigated their role in organismal glucose metabolism and recently in pancreatic β cell biology. Here, we summarize the present knowledge on the role of these receptors as metabolic sensors in β cell function and physiology, revealing new therapeutic opportunities for type 2 diabetes.

Communicating systems in the body: how microbiota and microglia cooperate

Microglia are tissue macrophages of the central nervous system (CNS). Their key tasks are immune surveillance as well as responding to infections or other pathological states such as neurological diseases or injury. In recent years it has been discovered that microglia are additionally crucial for the maintenance of brain homeostasis during development and adulthood by adjusting the neuronal network and phagocytosing neuronal debris. Microglia persist in the CNS throughout the life of the organism and self-renew without engraftment of bone-marrow-derived cells. Until recently it remained unknown what controls their maturation and activation under homeostatic conditions. In this review we discuss new aspects of the interaction between host microbiota and brain function with special focus on the brain-resident innate immune cells, the microglia.

Agavins Increase Neurotrophic Factors and Decrease Oxidative Stress in the Brains of High-Fat Diet-Induced Obese Mice

BACKGROUND

Fructans obtained from agave, called agavins, have recently shown significant benefits for human health including obesity. Therefore, we evaluated the potential of agavins as neuroprotectors and antioxidants by determining their effect on brain-derived neurotrophic factor (BDNF) and glial-derived neurotrophic factor (GDNF) as well as oxidative brain damage in of obese mice.

METHODS

Male C57BL/6J mice were fed a high-fat diet (HFD) and treated daily with 5% (HFD/A5) or 10% (HFD/A10) of agavins or a standard diet (SD) for 10 weeks. The levels of BDNF and GDNF were evaluated by ELISA. The oxidative stress was evaluated by lipid peroxidation (TBARS) and carbonyls. SCFAs were also measured with GC-FID. Differences between groups were assessed using ANOVA and by Tukey's test considering p < 0.05.

RESULTS

The body weight gain and food intake of mice HFD/A10 group were significantly lower than those in the HFD group. Agavins restored BDNF levels in HFD/A5 group and GDNF levels of HFD/A5 and HFD/A10 groups in cerebellum. Interestingly, agavins decreased TBARS levels in HFD/A5 and HFD/A10 groups in the hippocampus, frontal cortex and cerebellum. Carbonyl levels were also lower in HFD/A5 and HFD/A10 for only the hippocampus and cerebellum. It was also found that agavins enhanced SCFAs production in feces.

CONCLUSION

Agavins may act as bioactive ingredients with antioxidant and protective roles in the brain.

Role of bioactive fatty acids in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is characterized by fat deposition in hepatocytes, and a strong association with nutritional factors. Dietary fatty acids are classified according to their biochemical properties, which confer their bioactive roles. Monounsaturated fatty acids have a dual role in various human and murine models. In contrast, polyunsaturated fatty acids exhibit antiobesity, anti steatosic and anti-inflammatory effects. The combination of these forms of fatty acids—according to dietary type, daily intake and the proportion of n-6 to n-3 fats—can compromise hepatic lipid metabolism. A chemosensory rather than a nutritional role makes bioactive fatty acids possible biomarkers for NAFLD. Bioactive fatty acids provide health benefits through modification of fatty acid composition and modulating the activity of liver cells during liver fibrosis. More and better evidence is necessary to elucidate the role of bioactive fatty acids in nutritional and clinical treatment strategies for patients with NAFLD.

Short Chain Fatty Acids (SCFA) Reprogram Gene Expression in Human Malignant Epithelial and Lymphoid Cells

The effect of short chain fatty acids (SCFAs) on gene expression in human, malignant cell lines was investigated, with a focus on signaling pathways. The commensal microbial flora produce high levels of SCFAs with established physiologic effects in humans. The most abundant SCFA metabolite in the human microflora is n-butyric acid. It is well known to activate endogenous latent Epstein-Barr virus (EBV), that was used as a reference read out system and extended to EBV+ epithelial cancer cell lines. N-butyric acid and its salt induced inflammatory and apoptotic responses in tumor cells of epithelial and lymphoid origin. Epithelial cell migration was inhibited. The n-butyric gene activation was reduced by knock-down of the cell membrane transporters MCT-1 and -4 by siRNA. N-butyric acid show biologically significant effects on several important cellular functions, also with relevance for tumor cell phenotype.

Vinegar as a functional ingredient to improve postprandial glycemic control-human intervention findings and molecular mechanisms

Type 2 diabetes prevalence worldwide is increasing and the burden is particularly high in Asian countries. Identification of functional food ingredients to curb the rise of diabetes among various Asian population groups is warranted. Vinegar is widely consumed throughout Asia, where the principle bioactive component is acetic acid. This review has collated data from human intervention trials to show that vinegar consumption seems more effective in modulating glycemic control in normal glucose-tolerant individuals than in either type 2 diabetics or in those with impaired glucose tolerance. The molecular mechanisms by which vinegar can improve glycemic control have been presented using human, animal and cell culture data. These mechanisms include (i) activation of the free fatty acid receptor 2 (FFAR2) receptors localized in the enteroendocrine L-cells of the intestinal lumen, leading to increased glucagon like peptide 1 (GLP-1) secretion, (ii) increased 5'adenosine monophosphate-activated protein kinase (AMPK) activation, leading to increased fatty acid oxidation and decreased hepatic gluconeogenesis, (iii) lowering of free fatty acid in circulation, potentially leading to improved insulin sensitivity, (iv) increased blood flow to the peripheral tissues and (v) increased satiety, leading to lower food intake. The review also discusses why these mechanisms appear more effective in nondiabetics than in diabetics.

Loss of Free Fatty Acid Receptor 2 leads to impaired islet mass and beta cell survival

The regulation of pancreatic β cell mass is a critical factor to help maintain normoglycemia during insulin resistance. Nutrient-sensing G protein-coupled receptors (GPCR) contribute to aspects of β cell function, including regulation of β cell mass. Nutrients such as free fatty acids (FFAs) contribute to precise regulation of β cell mass by signaling through cognate GPCRs, and considerable evidence suggests that circulating FFAs promote β cell expansion by direct and indirect mechanisms. Free Fatty Acid Receptor 2 (FFA2) is a β cell-expressed GPCR that is activated by short chain fatty acids, particularly acetate. Recent studies of FFA2 suggest that it may act as a regulator of β cell function. Here, we set out to explore what role FFA2 may play in regulation of β cell mass. Interestingly, Ffar2(-/-) mice exhibit diminished β cell mass at birth and throughout adulthood, and increased β cell death at adolescent time points, suggesting a role for FFA2 in establishment and maintenance of β cell mass. Additionally, activation of FFA2 with Gαq/11-biased agonists substantially increased β cell proliferation in in vitro and ex vivo proliferation assays. Collectively, these data suggest that FFA2 may be a novel therapeutic target to stimulate β cell growth and proliferation.

Investigation of proteome changes in osteoclastogenesis in low serum culture system using quantitative proteomics

Background

RAW 264.7 cells can differentiate into osteoclasts when cultured in medium supplemented with 1 % FBS. However, the proteomic changes in the development of RAW 264.7 cells into osteoclasts in low serum culture system have not been elucidated. Therefore, we conducted quantitative proteomics analysis to investigate proteomic changes during osteoclastogenesis in low serum culture system.

Results

Our study confirmed that mature multinucleated osteoclasts were generated in a low serum culture system, validated by upregulated expression of 15 characteristic marker proteins, including TRAP, CTSK, MMP9, V-ATPase and ITGAV. Proteomics results demonstrated that 549 proteins expressed differentially in osteoclastogenesis in low serum culture system. In-depth bioinformatics analysis suggested that the differentially expressed proteins were mainly involved in mitochondrial activities and energy metabolism, including the electron transport chain pathway, TCA cycle pathway, mitochondrial LC-fatty acid beta-oxidation pathway and fatty acid biosynthesis pathway. The data have been deposited to the ProteomeXchange with identifier PXD001935.

Conclusion

Osteoclast formation is an ATP consuming procedure, whether occurring in a low serum culture system or a conventional culture system. In contrast to osteoclasts formed in conventional culture system, the fatty acid biosynthesis pathway was upregulated in osteoclasts cultured in low serum condition.

Electronic supplementary material

The online version of this article (doi:10.1186/s12953-016-0097-6) contains supplementary material, which is available to authorized users.

Study on Dendrobium officinale O-Acetyl-glucomannan (Dendronan). 7. Improving Effects on Colonic Health of Mice

This research was aimed to study the effect of Dendrobium officinale polysaccharide (Dendronan) on colonic health. Mice were fed Dendronan at doses of 40, 80, and 160 mg/kg body weight for 0, 10, 20, and 30 days, respectively. Results showed that Dendronan, which has a special structure formed by mannose and glucose, rich in O-acetyl groups, exhibited improving effects on colonic and fecal parameters of Balb/c mice. After Dendronan feeding, the content of short-chain fatty acids (SCFAs), colon length and index, and fecal moisture were increased, whereas colonic pH was decreased and defecation time was shortened. All of these changes were significantly different between polysaccharide-treated groups and the control group (p < 0.05). These findings suggested that an adequate intake of Dendronan is beneficial to the process of fermentation and regulation of colonic microenvironment, thus playing a role in the maintenance of colonic health.

Gut Microbiota and Nonalcoholic Fatty Liver Disease: Insights on Mechanism and Application of Metabolomics

Gut microbiota are intricately involved in the development of obesity-related metabolic diseases such as nonalcoholic fatty liver disease (NAFLD), type 2 diabetes, and insulin resistance. In the current review, we discuss the role of gut microbiota in the development of NAFLD by focusing on the mechanisms of gut microbiota-mediated host energy metabolism, insulin resistance, regulation of bile acids and choline metabolism, as well as gut microbiota-targeted therapy. We also discuss the application of a metabolomic approach to characterize gut microbial metabotypes in NAFLD.

Role of the Gut Microbiome in Uremia: A Potential Therapeutic Target

Also known as the "second human genome," the gut microbiome plays important roles in both the maintenance of health and the pathogenesis of disease. The symbiotic relationship between host and microbiome is disturbed due to the proliferation of dysbiotic bacteria in patients with chronic kidney disease (CKD). Fermentation of protein and amino acids by gut bacteria generates excess amounts of potentially toxic compounds such as ammonia, amines, thiols, phenols, and indoles, but the generation of short-chain fatty acids is reduced. Impaired intestinal barrier function in patients with CKD permits translocation of gut-derived uremic toxins into the systemic circulation, contributing to the progression of CKD, cardiovascular disease, insulin resistance, and protein-energy wasting. The field of microbiome research is still nascent, but is evolving rapidly. Establishing symbiosis to treat uremic syndrome is a novel concept, but if proved effective, it will have a significant impact on the management of patients with CKD.

Butyrate, neuroepigenetics and the gut microbiome: Can a high fiber diet improve brain health?

As interest in the gut microbiome has grown in recent years, attention has turned to the impact of our diet on our brain. The benefits of a high fiber diet in the colon have been well documented in epidemiological studies, but its potential impact on the brain has largely been understudied. Here, we will review evidence that butyrate, a short-chain fatty acid (SCFA) produced by bacterial fermentation of fiber in the colon, can improve brain health. Butyrate has been extensively studied as a histone deacetylase (HDAC) inhibitor but also functions as a ligand for a subset of G protein-coupled receptors and as an energy metabolite. These diverse modes of action make it well suited for solving the wide array of imbalances frequently encountered in neurological disorders. In this review, we will integrate evidence from the disparate fields of gastroenterology and neuroscience to hypothesize that the metabolism of a high fiber diet in the gut can alter gene expression in the brain to prevent neurodegeneration and promote regeneration.

A Critical Look at Prebiotics Within the Dietary Fiber Concept

This article reviews the current knowledge of the health effects of dietary fiber and prebiotics and establishes the position of prebiotics within the broader context of dietary fiber. Although the positive health effects of specific fibers on defecation, reduction of postprandial glycemic response, and maintenance of normal blood cholesterol levels are generally accepted, other presumed health benefits of dietary fibers are still debated. There is evidence that specific dietary fibers improve the integrity of the epithelial layer of the intestines, increase the resistance against pathogenic colonization, reduce the risk of developing colorectal cancer, increase mineral absorption, and have a positive impact on the immune system, but these effects are neither generally acknowledged nor completely understood. Many of the latter effects are thought to be particularly elicited by prebiotics. Although the prebiotic concept evolved significantly during the past two decades, the line between prebiotics and nonprebiotic dietary fiber remains vague. Nevertheless, scientific evidence demonstrating the health-promoting potential of prebiotics continues to accumulate and suggests that prebiotic fibers have their rightful place in a healthy diet.

Evaluating the Contribution of Gut Microbiota to the Variation of Porcine Fatness with the Cecum and Fecal Samples

Microbial community in gastrointestinal tract participates in the development of the obesity as well as quite a few metabolic diseases in human. However, there are few studies about the relationship between gut microbiota and porcine fatness. Here, we used high-throughput sequencing to perform 16S rRNA gene analysis in 256 cecum luminal samples from Erhualian pigs and 244 stools from Bamaxiang pigs, and adopted a two-part model statistical method to evaluate the association of gut microbes with porcine fatness. As the results, we identified a total of 6 and 108 operational taxonomic units (OTUs), and 9 and 10 bacterial taxa which showed significant associations with fatness traits in the stool and cecum samples, respectively. Cross-validation analysis indicated that gut microbiome showed the largest effect on abdominal adipose by explaining 2.73% phenotypic variance of abdominal fat weight. Significantly more fatness-associated OTUs were identified in the cecum samples than that in the stools, suggesting that cecum luminal samples were better used for identification of fatness-associated microbes than stools. The fatness-associated OTUs were mainly annotated to Lachnospiraceae, Ruminococcaceae, Prevotella, Treponema, and Bacteroides. These microbes have been reported to produce short-chain fatty acids by fermenting dietary indigested polysaccharide and pectin. The short-chain fatty acids can regulate host body energy homeostasis, protect host from inflammation and inhibit fat mass development. Our findings suggested that the gut microbiome may be an important factor modulating fatness in pigs.

The short-chain fatty acid receptor, FFA2, contributes to gestational glucose homeostasis

The structure of the human gastrointestinal microbiota can change during pregnancy, which may influence gestational metabolism; however, a mechanism of action remains unclear. Here we observed that in wild-type (WT) mice the relative abundance of Actinobacteria and Bacteroidetes increased during pregnancy. Along with these changes, short-chain fatty acids (SCFAs), which are mainly produced through gut microbiota fermentation, significantly changed in both the cecum and peripheral blood throughout gestation in these mice. SCFAs are recognized by G protein-coupled receptors (GPCRs) such as free fatty acid receptor-2 (FFA2), and we have previously demonstrated that the fatty acid receptor-2 gene (Ffar2) expression is higher in pancreatic islets during pregnancy. Using female Ffar2-/- mice, we explored the physiological relevance of signaling through this GPCR and found that Ffar2-deficient female mice developed fasting hyperglycemia and impaired glucose tolerance in the setting of impaired insulin secretion compared with WT mice during, but not before, pregnancy. Insulin tolerance tests were similar in Ffar2-/- and WT mice before and during pregnancy. Next, we examined the role of FFA2 in gestational β-cell mass, observing that Ffar2-/- mice had diminished gestational expansion of β-cells during pregnancy. Interestingly, mouse genotype had no significant impact on the composition of the gut microbiome, but did affect the observed SCFA profiles, suggesting a functional difference in the microbiota. Together, these results suggest a potential link between increased Ffar2 expression in islets and the alteration of circulating SCFA levels, possibly explaining how changes in the gut microbiome contribute to gestational glucose homeostasis.

Non-equivalence of Key Positively Charged Residues of the Free Fatty Acid 2 Receptor in the Recognition and Function of Agonist Versus Antagonist Ligands

Short chain fatty acids (SCFAs) are produced in the gut by bacterial fermentation of poorly digested carbohydrates. A key mediator of their actions is the G protein-coupled free fatty acid 2 (FFA2) receptor, and this has been suggested as a therapeutic target for the treatment of both metabolic and inflammatory diseases. However, a lack of understanding of the molecular determinants dictating how ligands bind to this receptor has hindered development. We have developed a novel radiolabeled FFA2 antagonist to probe ligand binding to FFA2, and in combination with mutagenesis and molecular modeling studies, we define how agonist and antagonist ligands interact with the receptor. Although both agonist and antagonist ligands contain negatively charged carboxylates that interact with two key positively charged arginine residues in transmembrane domains V and VII of FFA2, there are clear differences in how these interactions occur. Specifically, although agonists require interaction with both arginine residues to bind the receptor, antagonists require an interaction with only one of the two. Moreover, different chemical series of antagonist interact preferentially with different arginine residues. A homology model capable of rationalizing these observations was developed and provides a tool that will be invaluable for identifying improved FFA2 agonists and antagonists to further define function and therapeutic opportunities of this receptor.

Re-discovering periodontal butyric acid: New insights on an old metabolite

The oral microbiome is composed of detrimental and beneficial microbial communities producing several microbial factors that could contribute to the development of the oral microbiome and, likewise, may lead to the development of host diseases. Metabolites, like short-chain fatty acids, are commonly produced by the oral microbiome and serve various functions. Among the periodontal short-chain fatty acids, butyric acid is mainly produced by periodontopathic bacteria and, attributable to the butyrate paradox, is postulated to exhibit a dual function depending on butyric acid concentration. A better understanding of the interconnecting networks that would influence butyric acid function in the oral cavity may shed a new light on the current existing knowledge and view regarding butyric acid.

Modulation of Gut Microbiota-Brain Axis by Probiotics, Prebiotics, and Diet

There exists a bidirectional communication system between the gastrointestinal tract and the brain. Increasing evidence shows that gut microbiota can play a critical role in this communication; thus, the concept of a gut microbiota and brain axis is emerging. Here, we review recent findings in the relationship between intestinal microbes and brain function, such as anxiety, depression, stress, autism, learning, and memory. We highlight the advances in modulating brain development and behavior by probiotics, prebiotics, and diet through the gut microbiota-brain axis. A variety of mechanisms including immune, neural, and metabolic pathways may be involved in modulation of the gut microbiota-brain axis. We also discuss some future challenges. A deeper understanding of the relationship between the gut bacteria and their hosts is implicated in developing microbial-based therapeutic strategies for brain disorders.

Colonic Fermentation of Unavailable Carbohydrates from Unripe Banana and its Influence over Glycemic Control

The aim of this study was to evaluate the effect of the colonic fermentation of unavailable carbohydrates from unripe banana (mass - UBM - and starch - UBS) over parameters related to glucose and insulin response in rats. Wistar male rats were fed either a control diet, a UBM diet (5 % resistant starch - RS) or a UBS diet (10 % RS) for 28 days. In vivo (oral glucose tolerance test) and in vitro (cecum fecal fermentation, pancreatic islet insulin secretion) analyses were performed. The consumption of UBM and UBS diets by Wistar rats for 28 days improved insulin/glucose ratio. Also, pancreatic islets isolated from the test groups presented significant lower insulin secretion compared to the control group, when the same in vitro glucose stimulation was done. Total short chain fatty acids produced were higher in both experimental groups in relation to the control group. These findings suggest that UBM and UBS diets promote colonic fermentation and can influence glycemic control, improving insulin sensitivity in rats.

Altered Colonic Bacterial Fermentation as a Potential Pathophysiological Factor in Irritable Bowel Syndrome

OBJECTIVES

Dysbiosis leading to abnormal intestinal fermentation has been suggested as a possible etiological mechanism in irritable bowel syndrome (IBS). We aimed to investigate the location and magnitude of altered intestinal bacterial fermentation in IBS and its clinical subtypes.

METHODS

IBS patients who satisfied the Rome III criteria (114) and 33 healthy controls (HC) were investigated. Intestinal fermentation was assessed using two surrogate measures: intestinal intraluminal pH and fecal short-chain fatty acids (SCFAs). Intraluminal pH and intestinal transit times were measured in the small and large bowel using a wireless motility capsule (SmartPill) in 47 IBS and 10 HC. Fecal SCFAs including acetate, propionate, butyrate, and lactate were analyzed by capillary gas chromatography in all enrolled subjects. Correlations between intestinal pH, fecal SCFAs, intestinal transit time, and IBS symptom scores were analyzed.

RESULTS

Colonic intraluminal pH levels were significantly lower in IBS patients compared with HC (total colonic pH, 6.8 for IBS vs. 7.3 for HC, P=0.042). There were no differences in total and segmental pH levels in the small bowel between IBS patients and HC (6.8 vs. 6.8, P=not significant). The intraluminal colonic pH differences were consistent in all IBS subtypes. Total SCFA level was significantly lower in C-IBS patients than in D-IBS and M-IBS patients and HC. The total SCFA level in all IBS subjects was similar with that of HC. Colonic pH levels correlated positively with colon transit time (CTT) and IBS symptoms severity. Total fecal SCFAs levels correlated negatively with CTT and positively with stool frequency.

CONCLUSIONS

Colonic intraluminal pH is decreased, suggesting higher colonic fermentation, in IBS patients compared with HC. Fecal SCFAs are not a sensitive marker to estimate intraluminal bacterial fermentation.

Effect of short-chain fatty acids on triacylglycerol accumulation, lipid droplet formation and lipogenic gene expression in goat mammary epithelial cells

Short-chain fatty acids (SCFAs) are the major energy sources for ruminants and are known to regulate various physiological functions in other species. However, their roles in ruminant milk fat metabolism are still unclear. In this study, goat mammary gland epithelial cells (GMECs) were treated with 3 mmol/L acetate, propionate or butyrate for 24 h to assess their effects on lipogenesis. Data revealed that the content of triacylglycerol (TAG) and lipid droplet formation were significantly stimulated by propionate and butyrate. The expression of FABP3, SCD1, PPARG, SREBP1, DGAT1, AGPAT6 and ADRP were upregulated by propionate and butyrate treatment. In contrast, the messenger RNA (mRNA) expression of FASN and LXRα was not affected by propionate, but reduced by butyrate. Acetate had no obvious effect on the content of TAG and lipid droplets but increased the mRNA expression of SCD1 and FABP3 in GMECs. Additionally, it was observed that propionate significantly increased the relative content of mono-unsaturated fatty acids (C18:1 and C16:1) at the expense of decreased saturated fatty acids (C16:0 and C18:0). Butyrate and acetate had no significant effect on fatty acid composition. Overall, the results from this work help enhance our understanding of the regulatory role of SCFAs on goat mammary cell lipid metabolism.

Shifts in microbiota species and fermentation products in a dietary model enriched in fat and sucrose

The gastrointestinal tract harbours a 'superorganism' called the gut microbiota, which is known to play a crucial role in the onset and development of diverse diseases. This internal ecosystem, far from being a static environment, can be manipulated by diet and dietary components. Feeding animals with high-fat sucrose (HFS) diets entails diet-induced obesity, a model which is usually used in research to mimic the obese phenotype of Western societies. The aim of the present study was to identify gut microbiota dysbiosis and associated metabolic changes produced in male Wistar rats fed a HFS diet for 6 weeks and compare it with the basal microbial composition. For this purpose, DNA extracted from faeces at baseline and after treatment was analysed by amplification of the V4-V6 region of the 16S ribosomal DNA (rDNA) gene using 454 pyrosequencing. Short-chain fatty acids, i.e. acetate, propionate and butyrate, were also evaluated by gas chromatography-mass spectrometry. At the end of the treatment, gut microbiota composition significantly differed at phylum level (Firmicutes, Bacteroidetes and Proteobacteria) and class level (Erisypelotrichi, Deltaproteobacteria, Bacteroidia and Bacilli). Interestingly, the class Clostridia showed a significant decrease after HFS diet treatment, which correlated with visceral adipose tissue, and is likely mediated by dietary carbohydrates. Of particular interest, Clostridium cluster XIVa species were significantly reduced and changes were identified in the relative abundance of other specific bacterial species (Mitsuokella jalaludinii, Eubacterium ventriosum, Clostridium sp. FCB90-3, Prevotella nanceiensis, Clostridium fusiformis, Clostridium sp. BNL1100 and Eubacterium cylindroides) that, in some cases, showed opposite trends to their relative families. These results highlight the relevance of characterising gut microbial population differences at species level and contribute to understand the plausible link between diet and specific gut bacterial species that are able to influence the inflammatory status, intestinal barrier function and obesity development.

An Acetate-Specific GPCR, FFAR2, Regulates Insulin Secretion

G protein-coupled receptors have been well described to contribute to the regulation of glucose-stimulated insulin secretion (GSIS). The short-chain fatty acid-sensing G protein-coupled receptor, free fatty acid receptor 2 (FFAR2), is expressed in pancreatic β-cells, and in rodents, its expression is altered during insulin resistance. Thus, we explored the role of FFAR2 in regulating GSIS. First, assessing the phenotype of wild-type and Ffar2(-/-) mice in vivo, we observed no differences with regard to glucose homeostasis on normal or high-fat diet, with a marginally significant defect in insulin secretion in Ffar2(-/-) mice during hyperglycemic clamps. In ex vivo insulin secretion studies, we observed diminished GSIS from Ffar2(-/-) islets relative to wild-type islets under high-glucose conditions. Further, in the presence of acetate, the primary endogenous ligand for FFAR2, we observed FFAR2-dependent potentiation of GSIS, whereas FFAR2-specific agonists resulted in either potentiation or inhibition of GSIS, which we found to result from selective signaling through either Gαq/11 or Gαi/o, respectively. Lastly, in ex vivo insulin secretion studies of human islets, we observed that acetate and FFAR2 agonists elicited different signaling properties at human FFAR2 than at mouse FFAR2. Taken together, our studies reveal that FFAR2 signaling occurs by divergent G protein pathways that can selectively potentiate or inhibit GSIS in mouse islets. Further, we have identified important differences in the response of mouse and human FFAR2 to selective agonists, and we suggest that these differences warrant consideration in the continued investigation of FFAR2 as a novel type 2 diabetes target.