GPR41 and GPR43 in Obesity and Inflammation - Protective or Causative?

Butyrate Shapes Immune Cell Fate and Function in Allergic Asthma

The microbiome plays a fundamental role in how the immune system develops and how inflammatory responses are shaped and regulated. The “gut-lung axis” is a relatively new term that highlights a crucial biological crosstalk between the intestinal microbiome and lung. A growing body of literature suggests that dysbiosis, perturbation of the gut microbiome, is a driving force behind the development, and severity of allergic asthma. Animal models have given researchers new insights into how gut microbe-derived components and metabolites, such as short-chain fatty acids (SCFAs), influence the development of asthma. While the full understanding of how SCFAs influence allergic airway disease remains obscure, a recurring theme of epigenetic regulation of gene expression in several immune cell compartments is emerging. This review will address our current understanding of how SCFAs, and specifically butyrate, orchestrates cell behavior, and epigenetic changes and will provide a detailed overview of the effects of these modifications on immune cells in the context of allergic airway disease.

Pharmacology of Free Fatty Acid Receptors and Their Allosteric Modulators

The physiological function of free fatty acids (FFAs) has long been regarded as indirect in terms of their activities as educts and products in metabolic pathways. The observation that FFAs can also act as signaling molecules at FFA receptors (FFARs), a family of G protein-coupled receptors (GPCRs), has changed the understanding of the interplay of metabolites and host responses. Free fatty acids of different chain lengths and saturation statuses activate FFARs as endogenous agonists via binding at the orthosteric receptor site. After FFAR deorphanization, researchers from the pharmaceutical industry as well as academia have identified several ligands targeting allosteric sites of FFARs with the aim of developing drugs to treat various diseases such as metabolic, (auto)inflammatory, infectious, endocrinological, cardiovascular, and renal disorders. GPCRs are the largest group of transmembrane proteins and constitute the most successful drug targets in medical history. To leverage the rich biology of this target class, the drug industry seeks alternative approaches to address GPCR signaling. Allosteric GPCR ligands are recognized as attractive modalities because of their auspicious pharmacological profiles compared to orthosteric ligands. While the majority of marketed GPCR drugs interact exclusively with the orthosteric binding site, allosteric mechanisms in GPCR biology stay medically underexploited, with only several allosteric ligands currently approved. This review summarizes the current knowledge on the biology of FFAR1 (GPR40), FFAR2 (GPR43), FFAR3 (GPR41), FFAR4 (GPR120), and GPR84, including structural aspects of FFAR1, and discusses the molecular pharmacology of FFAR allosteric ligands as well as the opportunities and challenges in research from the perspective of drug discovery.

Goals in Nutrition Science 2020-2025

Five years ago, with the editorial board of Frontiers in Nutrition, we took a leap of faith to outline the Goals for Nutrition Science - the way we see it (1). Now, in 2020, we can put ourselves to the test and take a look back. Without a doubt we got it right with several of the key directions. To name a few, Sustainable Development Goals (SDGs) for Food and Nutrition are part of the global public agenda, and the SDGs contribute to the structuring of international science and research. Nutritional Science has become a critical element in strengthening work on the SDGs, and the development of appropriate methodologies is built on the groundwork of acquiring and analyzing big datasets. Investigation of the Human Microbiome is providing novel insight on the interrelationship between nutrition, the immune system and disease. Finally, with an advanced definition of the gut-brain-axis we are getting a glimpse into the potential for Nutrition and Brain Health. Various milestones have been achieved, and any look into the future will have to consider the lessons learned from Covid-19 and the sobering awareness about the frailty of our food systems in ensuring global food security. With a view into the coming 5 years from 2020 to 2025, the editorial board has taken a slightly different approach as compared to the previous Goals article. A mind map has been created to outline the key topics in nutrition science. Not surprisingly, when looking ahead, the majority of scientific investigation required will be in the areas of health and sustainability. Johannes le Coutre, Field Chief Editor, Frontiers in Nutrition.

Sodium butyrate attenuated neuronal apoptosis via GPR41/Gβγ/PI3K/Akt pathway after MCAO in rats

Sodium butyrate, a short-chain fatty acid, is predominantly produced by gut microbiota fermentation of dietary fiber and serves as an important neuromodulator in the central nervous system. Recent experimental evidence has suggested that sodium butyrate may be an endogenous ligand for two orphan G protein-coupled receptors, GPR41 and GP43, which regulate apoptosis and inflammation in ischemia-related pathologies, including stroke. In the present study, we evaluated the potential efficacy and mechanism of action of short-chain fatty acids in a rat model of middle cerebral artery occlusion (MCAO). Fatty acids were intranasally administered 1 h post MCAO. Short-chain fatty acids, especially sodium butyrate, reduced infarct volume and improved neurological function at 24 and 72 h after MCAO. At 24 h, the effects of MCAO, increased apoptosis, were ameliorated after treatment with sodium butyrate, which increased the expressions of GPR41, PI3K and phosphorylated Akt. To confirm these mechanistic links and characterize the GPR active subunit, PC12 cells were subjected to oxygen-glucose deprivation and reoxygenation, and pharmacological and siRNA interventions were used to reverse efficacy. Taken together, intranasal administration of sodium butyrate activated PI3K/Akt via GPR41/Gβγ and attenuated neuronal apoptosis after MCAO.

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.

Citrulline supplementation attenuates the development of non-alcoholic steatohepatitis in female mice through mechanisms involving intestinal arginase

Non-alcoholic fatty liver disease (NAFLD) is by now the most prevalent liver disease worldwide. The non-proteogenic amino acid l-citrulline (L-Cit) has been shown to protect mice from the development of NAFLD. Here, we aimed to further assess if L-Cit also attenuates the progression of a pre-existing diet-induced NAFLD and to determine molecular mechanisms involved. Female C57BL/6J mice were either fed a liquid fat-, fructose- and cholesterol-rich diet (FFC) or control diet (C) for 8 weeks to induce early stages of NASH followed by 5 more weeks with either FFC-feeding +/- 2.5 g L-Cit/kg bw or C-feeding. In addition, female C57BL/6J mice were either pair-fed a FFC +/- 2.5 g L-Cit/kg bw +/- 0.01 g/kg bw i.p. N(ω)-hydroxy-nor-l-arginine (NOHA) or C diet for 8 weeks.

The protective effects of supplementing L-Cit on the progression of a pre-existing NAFLD were associated with an attenuation of 1) the increased translocation of bacterial endotoxin and 2) the loss of tight junction proteins as well as 3) arginase activity in small intestinal tissue, while no marked changes in intestinal microbiota composition were prevalent in small intestine. Treatment of mice with the arginase inhibitor NOHA abolished the protective effects of L-Cit on diet-induced NAFLD. Our results suggest that the protective effects of L-Cit on the development and progression of NAFLD are related to alterations of intestinal arginase activity and intestinal permeability.

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l-citrulline diminished progression of non-alcoholic fatty liver disease (NAFLD).

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l-citrulline protects from fructose-induced small intestinal barrier dysfunction.

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NASH development is associated with a loss of arginase activity in small intestine.

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l-citrulline improves intestinal arginase activity in diet-induced NAFLD.

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Arginase inhibitor attenuates effects of l-citrulline on NAFLD development.

Chemogenetic Approaches to Explore the Functions of Free Fatty Acid Receptor 2

Short-chain fatty acids are generated in large amounts by the intestinal microbiota. They activate both the closely related G protein-coupled receptors free fatty acid receptor 2 (FFA2) and free fatty acid receptor 3 (FFA3) that are considered therapeutic targets in diseases of immuno-metabolism. Limited and species-selective small-molecule pharmacology has restricted our understanding of the distinct roles of these receptors. Replacement of mouse FFA2 with a designer receptor exclusively activated by designer drug form of human FFA2 (hFFA2-DREADD) has allowed definition of specific roles of FFA2 in pharmacological and physiological studies conducted both ex vivo and in vivo, whilst overlay of murine disease models offers opportunities for therapeutic validation prior to human studies. Similar approaches can potentially be used to define roles of other poorly characterised receptors.

Potential type 2 diabetes mellitus drug HMPA promotes short-chain fatty acid production by improving carbon catabolite repression effect of gut microbiota

BACKGROUND AND PURPOSE

Gut microbiota plays an important role in type 2 diabetes mellitus (T2DM) progression. From our previous work N-(4-Hydroxyphenethyl)-3-mercapto-2-methylpropanamide (HMPA) is a potential T2DM drug. We evaluated the effect of HMPA on gut microbiota and studied the molecular mechanism underlying HMPA's regulation of gut microbiota.

EXPERIMENTAL APPROACH

The pseudo germ-free (PGF) T2DM model and faecal microbiota transplantation method were used to study whether gut microbiota mediates the actions of HMPA. The composition of gut microbiota was detected by using 16S rRNA sequence. Short-chain fatty acids (SCFAs) content was detected by gas chromatography. The HMPA probe was synthesised for finding and identifying the target protein of HMPA. The effect of HMPA on the utilisation of carbon sources in Bifidobacterium was evaluated.

KEY RESULTS

HMPA has a slight effect on the PGF T2DM model. The gut microbiota changed by HMPA can also alleviate the symptoms of T2DM. HMPA can regulate gut microbiota structure, increase SCFAs production and reduce nitrate content in the intestinal tissues. The thickness of the mucus on colon tissues increases after HMPA treatment. The target protein of HMPA in gut microbiota is the nitrogen metabolism global transcriptional regulator (GlnR). HMPA promotes the utilisation of less preferred carbon source in the gut microbiota and increases the fermentation product of SCFAs.

CONCLUSION AND IMPLICATIONS

HMPA plays a hypoglycaemic role through the gut microbiota. HMPA improves the carbon catabolite repression effect of gut microbiota and increases SCFAs production by targeting GlnR. GlnR may be a target for gut microbiota regulation.

Effect of Dietary Acetic Acid Supplementation on Plasma Glucose, Lipid Profiles, and Body Mass Index in Human Adults: A Systematic Review and Meta-analysis

BACKGROUND

Acetic acid is a short-chain fatty acid that has demonstrated biomedical potential as a dietary therapeutic agent for the management of chronic and metabolic illness comorbidities. In human beings, its consumption may improve glucose regulation and insulin sensitivity in individuals with cardiometabolic conditions and type 2 diabetes mellitus. Published clinical trial evidence evaluating its sustained supplementation effects on metabolic outcomes is inconsistent.

OBJECTIVE

This systematic review and meta-analysis summarized available evidence on potential therapeutic effects of dietary acetic acid supplementation via consumption of acetic acid-rich beverages and food sources on metabolic and anthropometric outcomes.

METHODS

A systematic search was conducted in Medline, Scopus, EMBASE, CINAHL Plus, and Web of Science from database inception until October 2020. Randomized controlled trials conducted in adults evaluating the effect of dietary acetic acid supplementation for a minimum of 1 week were included. Meta-analyses were performed using a random-effects model on fasting blood glucose (FBG), triacylglycerol (TAG), high-density lipoprotein (HDL), low-density lipoprotein (LDL), glycated hemoglobin (HbA1c), body mass index (BMI), and body fat percentage. Statistical heterogeneity was assessed by calculation of Q and I² statistics, and publication bias was assessed by calculation of Egger's regression asymmetry and Begg's test.

RESULTS

Sixteen studies were included, involving 910 participants who consumed between 750 and 3600 mg acetic acid daily in interventions lasting an average of 8 weeks. Dietary acetic acid supplementation resulted in significant reductions in TAG concentrations in overweight and obese but otherwise healthy individuals (mean difference [MD] = -20.51 mg/dL [95% confidence intervals = -32.98, -8.04], P = .001) and people with type 2 diabetes (MD = -7.37 mg/dL [-10.15, -4.59], P < .001). Additionally, acetic acid supplementation significantly reduced FBG levels (MD = -35.73 mg/dL [-63.79, -7.67], P = .01) in subjects with type 2 diabetes compared with placebo and low-dose comparators. No other changes were seen for other metabolic or anthropometric outcomes assessed. Five of the 16 studies did not specify the dose of acetic acid delivered, and no studies measured blood acetate concentrations. Only one study controlled for background acetic acid-rich food consumption during intervention periods. Most studies had an unclear or high risk of bias.

CONCLUSION

Supplementation with dietary acetic acid is well tolerated, has no adverse side effects, and has clinical potential to reduce plasma TAG and FBG concentrations in individuals with type 2 diabetes, and to reduce TAG levels in people who are overweight or obese. No significant effects of dietary acetic acid consumption were seen on HbA1c, HDL, or anthropometric markers. High-quality, longer-term studies in larger cohorts are required to confirm whether dietary acetic acid can act as an adjuvant therapeutic agent in metabolic comorbidities management.

Design and Application of Receptor-Targeted Fluorescent Probes Based on Small Molecular Fluorescent Dyes

In recent years, a variety of receptor-targeted fluorescent probes have been developed and widely used to realize the visualization of certain receptors, which facilitates the early diagnosis and treatment of diseases. In this Review, we focus on the recent achievements in design, chemical structure, imaging characterization, and potential applications of receptor-targeted fluorescent probes from the past 10 years. The development and application of receptor-targeted fluorescent probes will expand our knowledge of the distribution and function of disease-related receptors, shed light on the drug discovery for clinical diseases where receptors are implicated, and feed into the diagnosis and treatment of a plethora of diseases, including tumors.

A cross-talk between gut microbiome, salt and hypertension

Cardiac disorders contribute to one of the major causes of fatality across the world. Hypertensive patients, even well maintained on drugs, possess a high risk to cardiovascular diseases. It is, therefore, highly important to identify different factors and pathways that lead to risk and progression of cardiovascular disorders. Several animals and human studies suggest that taxonomical alterations in the gut are involved in the cardiovascular physiology. In this article, with the help of various experimental evidences, we suggest that the host gut-microbiota plays an important in this pathway. Short chain fatty acids (SCFAs) and Trimethyl Amine -n-Oxide (TMAO) are the two major products of gut microbiome. SCFAs present a crucial role in regulating the blood pressure, while TMAO is involved in pathogenesis of atherosclerosis and other coronary artery diseases, including hypertension. We prove that there exists a triangular bridge connecting the gap between dietary salt, hypertension and gut microbiome. We also present some of the dietary interventions which can regulate and control microbiota that can prevent cardiovascular complications.We strongly believe that this article would improve the understanding the role of gut microbiota in hypertension, and will be helpful in the development of novel therapeutic strategies for prevention of hypertension through restoring gut microbiome homeostasis in the near future.

Effect of Oral Tributyrin Treatment on Lipid Mediator Profiles in Endotoxin-Induced Hepatic Injury

Eicosanoid modulation by butyrate has been reported in various cells and conditions. Recently, comprehensive analyses of lipid mediators using liquid chromatography/tandem mass spectrometry has been reported. We hypothesized that tributyrin, a prodrug of butyrate, may attenuate LPS-induced liver injury in rats by suppressing the production of pro-inflammatory lipid mediators and/or by inducing anti-inflammatory specialized proresolving mediators. To test this, groups of Wistar rats were orally administered tributyrin (1 g/kg body weight) or vehicle 1 h before intraperitoneal injection of LPS. The livers were collected at 0, 1.5, 6, and 24 h later and analyzed: lipid mediators were profiled by liquid chromatography/tandem mass spectrometry; expression of cyclooxygenase-2, 5-lipoxygenase (LOX), 12/15-LOX, and leukotriene (LT) A₄ hydrolase, and nuclear translocation of 5-LOX were evaluated by western blot analysis; and induction of liver injury was assessed by immunostaining for 8-hydroxy-2'-deoxyguanosine, an indicator of oxidative DNA damage. We found that tributyrin treatment attenuated LPS-induced production of pro-inflammatory LTB₄ (p < 0.05) and decreased oxidative stress levels in the liver. Tributyrin also attenuated the nuclear translocation of 5-LOX in response to LPS, suggesting a possible mechanism for the LTB₄ reduction. LPS-induced changes in other lipid mediators were not significantly affected by tributyrin treatment up to 24 h after LPS injection. Our results suggest that oral tributyrin administration protects against endotoxemia-associated liver damage by reducing production of the pro-inflammatory eicosanoid LTB₄.

Morphological elucidation of short-chain fatty acid receptor GPR41-positive enteric sensory neurons in the colon of mice with dextran sulfate sodium-induced colitis

Although the etiology of inflammatory bowel disease (IBD) remains unclear, it has generally been accepted that abnormalities in the intestinal immune system and dysbiosis of the gut microbiota are involved in the pathology of IBD. Recently, short-chain fatty acids (SCFAs) produced by gut microbiota were reported to maintain intestinal homeostasis through their receptors, such as GPR41. However, there are contradictory reports about the role of GPR41 in intestinal inflammation. Consequently, the roles of GPR41 in dysbiosis induced by intestinal inflammation remain unclear. Thus, we investigated the distribution of GPR41 in the colonic mucosa of mice with dextran sulfate sodium (DSS)-induced colitis. GPR41-immunoreactive fibrous structures were observed in the colonic lamina propria and muscularis layer of normal mice. In addition, GPR41-immunoreactive fibrous structures partly colocalized with calcitonin gene-related peptide (CGRP; a neurotransmitter of cholinergic enteric sensory neurons)-immunoreactive nerve fibers in the colonic lamina propria, indicating that GPR41 is expressed in cholinergic intrinsic sensory neurons. Furthermore, both GPR41-immunoreactivities and CGRP-immunoreactivities were significantly increased in the lamina propria of the colon in mice with DSS-induced colitis. Interestingly, GPR41-immunoreactivities were often found in close proximity to F4/80⁺ macrophages in the colonic mucosa of normal mice, and their frequency was elevated in the colonic mucosa of mice with DSS-induced colitis. Therefore, the crosstalk between SCFA-sensing intrinsic sensory neurons and macrophages might be involved in the pathology of acute colitis.

Metabolic networks of the human gut microbiota

The human gut microbiota controls factors that relate to human metabolism with a reach far greater than originally expected. Microbial communities and human (or animal) hosts entertain reciprocal exchanges between various inputs that are largely controlled by the host via its genetic make-up, nutrition and lifestyle. The composition of these microbial communities is fundamental to supply metabolic capabilities beyond those encoded in the host genome, and contributes to hormone and cellular signalling that support the dynamic adaptation to changes in food availability, environment and organismal development. Poor functional exchange between the microbial communities and their human host is associated with dysbiosis, metabolic dysfunction and disease. This review examines the biology of the dynamic relationship between the reciprocal metabolic state of the microbiota-host entity in balance with its environment (i.e. in healthy states), the enzymatic and metabolic changes associated with its imbalance in three well-studied diseases states such as obesity, diabetes and atherosclerosis, and the effects of bariatric surgery and exercise.

COVID-19: Is there a role for immunonutrition in obese patient?

On December 12, 2019 a new coronavirus (SARS-CoV-2) emerged in Wuhan, China, triggering a pandemic of severe acute respiratory syndrome in humans (COVID-19). Today, the scientific community is investing all the resources available to find any therapy and prevention strategies to defeat COVID-19. In this context, immunonutrition can play a pivotal role in improving immune responses against viral infections. Immunonutrition has been based on the concept that malnutrition impairs immune function. Therefore, immunonutrition involves feeding enriched with various pharmaconutrients (Omega 3 Fatty Acids, Vitamin C, Arginine, Glutamine, Selenium, Zinc, Vitamin, E and Vitamin D) to modulate inflammatory responses, acquired immune response and to improve patient outcomes. In literature, significant evidences indicate that obesity, a malnutrition state, negatively impacts on immune system functionality and on host defense, impairing protection from infections. Immunonutrients can promote patient recovery by inhibiting inflammatory responses and regulating immune function. Immune system dysfunction is considered to increase the risk of viral infections, such as SARS-CoV-2, and was observed in different pathological situations. Obese patients develop severe COVID-19 sequelae, due to the high concentrations of TNF-α, MCP-1 and IL-6 produced in the meantime by visceral and subcutaneous adipose tissue and by innate immunity. Moreover, leptin, released by adipose tissue, helps to increase inflammatory milieu with a dysregulation of the immune response. Additionally, gut microbiota plays a crucial role in the maturation, development and functions of both innate and adaptive immune system, as well as contributing to develop obese phenotype. The gut microbiota has been shown to affect lung health through a vital crosstalk between gut microbiota and lungs, called the "gut-lung axis". This axis communicates through a bi-directional pathway in which endotoxins, or microbial metabolites, may affect the lung through the blood and when inflammation occurs in the lung, this in turn can affect the gut microbiota. Therefore, the modulation of gut microbiota in obese COVID-19 patients can play a key role in immunonutrition therapeutic strategy. This umbrella review seeks to answer the question of whether a nutritional approach can be used to enhance the immune system's response to obesity in obese patients affected by COVID-19.

Prebiotics can change immunomodulatory properties of probiotics

Beneficial effects of probiotics and prebiotics are mainly related to modulation of compositions and activities of gut microbiota as well as manipulation of immunological reactivity in autoimmune diseases. In the present study, we examined whether metabolic products from different strains of Lactobacillus brevis cultured with different prebiotics have similar immunomodulating properties on immune cells under normal and inflammatory conditions, using mouse model of collagen-induced arthritis (CIA). Two strains of Lactobacillus brevis (3448 and 8429) were cultured with four different prebiotics, such as xylooligosaccharides, inulin, pectin, and chitosan. Sterile supernatants containing different metabolic products have been used for direct treatment of cell cultures prepared from CII-immunized mice and non-immunized (control mice). Our results showed that metabolic products from XOS decreased levels of IFN-γ, IL-6, IL-17, and TNF-α in both cultures from immunized and non-immunized mice. In contrast, metabolic products from inulin, pectin, and chitosan increased concentrations of these cytokines with highest values for pectin. Neither of investigated prebiotics influenced the secretion of IL-10. In addition, we found changes in the percentage of macrophages, which were different for the tested prebiotics. Also, metabolic products from pectin and chitosan caused loss of T-cells (CD3+) and increased percentages of CD4⁺CD25⁺ regulatory T cells and CD8⁺CD279⁺ anergic T cells. Hence, our data indicate that immunomodulating properties of probiotics are strain-specific and prebiotic-dependent.

Can You Trust Your Gut? Implicating a Disrupted Intestinal Microbiome in the Progression of NAFLD/NASH

Non-alcoholic fatty liver disease (NAFLD) is a spectrum of disorders, ranging from fatty liver to a more insulin resistant, inflammatory and fibrotic state collectively termed non-alcoholic steatohepatitis (NASH). In the United States, 30%-40% of the adult population has fatty liver and 3%-12% has NASH, making it a major public health concern. Consumption of diets high in fat, obesity and Type II diabetes (T2D) are well-established risk factors; however, there is a growing body of literature suggesting a role for the gut microbiome in the development and progression of NAFLD. The gut microbiota is separated from the body by a monolayer of intestinal epithelial cells (IECs) that line the small intestine and colon. The IEC layer is exposed to luminal contents, participates in selective uptake of nutrients and acts as a barrier to passive paracellular permeability of luminal contents through the expression of tight junctions (TJs) between adjacent IECs. A dysbiotic gut microbiome also leads to decreased gut barrier function by disrupting TJs and the gut vascular barrier (GVB), thus exposing the liver to microbial endotoxins. These endotoxins activate hepatic Toll-like receptors (TLRs), further promoting the progression of fatty liver to a more inflammatory and fibrotic NASH phenotype. This review will summarize major findings pertaining to aforementioned gut-liver interactions and its role in the pathophysiology of NAFLD.

GPR43 regulates marginal zone B-cell responses to foreign and endogenous antigens

Marginal zone (MZ) B cells are innate‐like B cells that produce polyreactive antibodies with an affinity for microbial molecular patterns and carbohydrate ligands. MZ B cells have been shown to be important in mediating immunity to various bacteria including Streptococcus pneumoniae and are also implicated in inflammatory syndromes including lupus erythematosus. The intestinal microbiota is responsible for producing short‐chain fatty acids, which can regulate immune cell function by several mechanisms including ligation of the G‐protein‐coupled receptor (GPR)43. Herein, we show that MZ B cells express Gpr43 messenger RNA and that the absence of this receptor impacts on MZ B‐cell surface marker expression and antibody production. In T‐cell‐independent responses to the hapten 4‐hydroxy‐3‐nitrophenylacetic acid (NP), mice deficient in GPR43 displayed higher serum titers of NP‐specific antibodies. Moreover, in response to a pneumococcal polysaccharide vaccine, GPR43‐deficient mice developed robust serum antibody responses and had markedly increased numbers of splenic antibody‐secreting cells, compared with control mice. Finally, serum immunoglobulin M autoantibodies to double‐stranded DNA and phosphatidylcholine were increased in resting 10–15‐week‐old mice lacking GPR43. Taken together, mice lacking GPR43 have heightened antibody responses to T‐cell‐independent antigens, which may be a result of impaired regulation of MZ B cells.

Impact of a Moderately Hypocaloric Mediterranean Diet on the Gut Microbiota Composition of Italian Obese Patients

Although it is known that the gut microbiota (GM) can be modulated by diet, the efficacy of specific dietary interventions in determining its composition and diversity in obese patients remains to be ascertained. The present work aims to evaluate the impact of a moderately hypocaloric Mediterranean diet on the GM of obese and overweight patients (OB). The GM of 23 OB patients (F/M = 20/3) was compared before (T0) and after 3 months (T3) of nutritional intervention (NI). Fecal samples were analyzed by Illumina MiSeq sequencing of the 16S rRNA gene. At baseline, GM characterization confirmed typical obesity-associated dysbiosis. After 3 months of NI, patients presented a statistically significant reduction in body weight and fat mass, along with changes in the relative abundance of many microbial patterns. In fact, an increase in the abundance of several Bacteroidetes taxa (i.e., Sphingobacteriaceae, Sphingobacterium, Bacteroides spp., Prevotella stercorea) and a depletion of many Firmicutes taxa (i.e., Lachnospiraceae members, Ruminococcaceae and Ruminococcus, Veillonellaceae, Catenibacterium, Megamonas) were observed. In addition, the phylum Proteobacteria showed an increased abundance, while the genus Sutterella, within the same phylum, decreased after the intervention. Metabolic pathways, predicted by bioinformatic analyses, showed a decrease in membrane transport and cell motility after NI. The present study extends our knowledge of the GM profiles in OB, highlighting the potential benefit of moderate caloric restriction in counteracting the gut dysbiosis.

Short-Chain Fatty Acid Production by Gut Microbiota from Children with Obesity Differs According to Prebiotic Choice and Bacterial Community Composition

Pediatric obesity remains a public health burden and continues to increase in prevalence. The gut microbiota plays a causal role in obesity and is a promising therapeutic target. Specifically, the microbial production of short-chain fatty acids (SCFA) from the fermentation of otherwise indigestible dietary carbohydrates may protect against pediatric obesity and metabolic syndrome. Still, it has not been demonstrated that therapies involving microbiota-targeting carbohydrates, known as prebiotics, will enhance gut bacterial SCFA production in children and adolescents with obesity (age, 10 to 18 years old). Here, we used an in vitro system to examine the SCFA production by fecal microbiota from 17 children with obesity when exposed to five different commercially available over-the-counter (OTC) prebiotic supplements. We found microbiota from all 17 patients actively metabolized most prebiotics. Still, supplements varied in their acidogenic potential. Significant interdonor variation also existed in SCFA production, which 16S rRNA sequencing supported as being associated with differences in the host microbiota composition. Last, we found that neither fecal SCFA concentration, microbiota SCFA production capacity, nor markers of obesity positively correlated with one another. Together, these in vitro findings suggest the hypothesis that OTC prebiotic supplements may be unequal in their ability to stimulate SCFA production in children and adolescents with obesity and that the most acidogenic prebiotic may differ across individuals.IMPORTANCE Pediatric obesity remains a major public health problem in the United States, where 17% of children and adolescents are obese, and rates of pediatric "severe obesity" are increasing. Children and adolescents with obesity face higher health risks, and noninvasive therapies for pediatric obesity often have limited success. The human gut microbiome has been implicated in adult obesity, and microbiota-directed therapies can aid weight loss in adults with obesity. However, less is known about the microbiome in pediatric obesity, and microbiota-directed therapies are understudied in children and adolescents. Our research has two important findings: (i) dietary prebiotics (fiber) result in the microbiota from adolescents with obesity producing more SCFA, and (ii) the effectiveness of each prebiotic is donor dependent. Together, these findings suggest that prebiotic supplements could help children and adolescents with obesity, but that these therapies may not be "one size fits all."

Gut microbiota modulate dendritic cell antigen presentation and radiotherapy-induced antitumor immune response

Alterations in gut microbiota impact the pathophysiology of several diseases, including cancer. Radiotherapy (RT), an established curative and palliative cancer treatment, exerts potent immune modulatory effects, inducing tumor-associated antigen (TAA) cross-priming with antitumor CD8+ T cell elicitation and abscopal effects. We tested whether the gut microbiota modulates antitumor immune response following RT distal to the gut. Vancomycin, an antibiotic that acts mainly on gram-positive bacteria and is restricted to the gut, potentiated the RT-induced antitumor immune response and tumor growth inhibition. This synergy was dependent on TAA cross presentation to cytolytic CD8+ T cells and on IFN-γ. Notably, butyrate, a metabolite produced by the vancomycin-depleted gut bacteria, abrogated the vancomycin effect. In conclusion, depletion of vancomycin-sensitive bacteria enhances the antitumor activity of RT, which has important clinical ramifications.

Dietary fiber and its associations with depression and inflammation

Dietary fiber is a crucial component of a healthy diet, with benefits that can be attributed to processes in the gut microbiota and the resulting by-products. Observational studies support associations between dietary fiber intake and depression and inflammation, but the potential mechanisms are poorly understood. This review examines evidence of the effects of dietary fiber on depression and inflammation and considers plausible mechanisms linking dietary fiber and depression, including microbiota-driven modification of gene expression and increased production of neurotransmitters. Additionally, inflammation may mediate the relationship between dietary fiber intake and depression. A high-fiber diet potentially lowers inflammation by modifying both the pH and the permeability of the gut. The resultant reduction in inflammatory compounds may alter neurotransmitter concentrations to reduce symptoms of depression. Further research into the link between dietary fiber intake and inflammation and depression is essential, as findings could potentially provide guidance for improvement in or prevention of inflammatory and depressive disorders.

Postnatal growth retardation is associated with intestinal mucosa mitochondrial dysfunction and aberrant energy status in piglets

Individuals with postnatal growth retardation (PGR) are prone to developing chronic disease. Abnormal development in small intestine is casually implicated in impaired growth performance. However, the exact mechanism is still unknown. In this present study, PGR piglets (aged 42 days) were employed as a good model to analyse changes in nutrient absorption and energy metabolism in the intestinal mucosa. The results showed lower serum concentrations of free amino acids, and lipid metabolites in PGR piglets, which were in accordance with the down‐regulated mRNA expressions involved in fatty acid and amino acid transporters in the jejunal and ileal mucosa. The decreased activities of digestive enzymes and the marked swelling in mitochondria were also observed in the PGR piglets. In addition, it was found that lower ATP production, higher AMP/ATP ratio, deteriorated mitochondrial complex III and ATP synthase, and decreased manganese superoxide dismutase activity in the intestinal mucosa of PGR piglets. Furthermore, altered gene expression involved in energy metabolism, accompanied by decreases in the protein abundance of SIRT1, PGC‐1α and PPARγ, as well as phosphorylations of AMPKα, mTOR, P70S6K and 4E‐BP1 were observed in intestinal mucosa of PGR piglets. In conclusion, decreased capability of nutrient absorption, mitochondrial dysfunction, and aberrant energy status in the jejunal and ileal mucosa may contribute to PGR piglets.

The canine gastrointestinal microbiota: early studies and research frontiers

The canine gut microbiota is a complex microbial population that is potentially related to metabolism, immunologic activity and gastrointestinal (GI) diseases. Early studies revealed that the canine gut microbiota was dynamic, and bacterial populations in the adjacent gut segments were similar, with anaerobes predominating. Metagenomics analysis revealed that nutrient contents in the diet modulated bacterial populations and metabolites in the canine gut. Further research revealed significant correlations between dietary factors and canine gut core microbiomes. Canine GI diseases are closely correlated with gut microbiota dysbiosis and metabolic disorders. Probiotic-related therapies can effectively treat canine GI diseases. Recent studies have revealed that the canine gut microbiota is similar to the human gut microbiota, and dietary factors affect both. Studying canine intestinal microorganisms enables clarifying changes in the canine intestinal bacteria under different conditions, simulating human diseases in dog models, and conducting in-depth studies of the interactions between intestinal bacteria and disease.

Helminth-Induced and Th2-Dependent Alterations of the Gut Microbiota Attenuate Obesity Caused by High-Fat Diet

BACKGROUND & AIMS

Epidemiological and animal studies have indicated an inverse correlation between the rising prevalence of obesity and metabolic syndrome and exposure to helminths. Whether helminth-induced immune response contributes to microbiota remodeling in obesity remains unknown. The aim of this study is to explore the immune-regulatory role of helminth in the prevention of HFD-induced obesity through remodeling gut microbiome.

METHODS

C57BL/6J WT and STAT6-/- mice were infected with Heligmosomoides polygyrus and followed by high fat diet (HFD) feeding for 6 weeks. The host immune response, body weight, and fecal microbiota composition were analyzed. We used adoptive transfer of M2 macrophages and microbiota transplantation approaches to determine the impact of these factors on HFD-obesity. We also examined stool microbiota composition and short chain fatty acids (SCFAs) concentration and determined the expression of SCFA-relevant receptors in the recipient mice.

RESULTS

Helminth infection of STAT6-/- (Th2-deficient) mice and adoptive transfer of helminth-induced alternatively activated (M2) macrophages demonstrated that the helminth-associated Th2 immune response plays an important role in the protection against obesity and induces changes in microbiota composition. Microbiota transplantation showed that helminth-induced, Th2-dependent alterations of the gut microbiota are sufficient to confer protection against obesity. Collectively, these results indicate that helminth infection protects against HFD-induced obesity by Th2-dependent, M2 macrophage-mediated alterations of the intestinal microbiota.

CONCLUSION

Our findings provide new mechanistic insights into the complex interplay between helminth infection, the immune system and the gut microbiota in a HFD-induced obesity model and holds promise for gut microbiome-targeted immunotherapy in obesity prevention.

The impact of metabolites derived from the gut microbiota on immune regulation and diseases

The gut microbiota strongly impacts the physiology and pathology in the host. To understand the complex interactions between host and gut microbiota, an 'integrated omics' approach has been employed, where exhaustive analyses for the different layers of cellular functions, such as epigenomics, transcriptomics and metabolomics, in addition to metagenomics, are combined. With this approach, the mechanisms whereby short-chain fatty acids (SCFAs) regulate host defense and the immune system have been elucidated. In a gnotobiotic mouse model of enterohemorrhagic Escherichia coli infection, Bifidobacterium-derived acetate can protect from infection-mediated death by changing the gene expression profile of colonic epithelial cells. It has also been shown that gut microbiota-derived butyrate enhances colonic regulatory T-cell differentiation through its epigenetic modulatory ability via histone deacetylase inhibition. SCFAs are involved in many other immunomodulatory effects as well as host pathophysiological conditions. Dysbiosis in the gut has been implicated in the pathogenesis of many diseases. Although the causal relationship of gut microbial dysbiosis and/or metabolites with pathogenesis is mostly unknown, mechanistic insights have been elucidated in some cases. Metabolism in the gut microbiota and host liver produces trimethylamine N-oxide, which is known to aggravate atherosclerosis, and a secondary bile acid deoxycholate, which reportedly induces non-alcoholic steatohepatitis-related hepatocellular carcinoma. It has been reported that secondary bile acids could also induce the differentiation of peripherally derived regulatory T cells in the gut. Further studies on the interactions between the host and gut microbiota could lead to the development of new therapeutic strategies as well as in preventive medicine.

Microbiota Modulating Nutritional Approaches to Countering the Effects of Viral Respiratory Infections Including SARS-CoV-2 through Promoting Metabolic and Immune Fitness with Probiotics and Plant Bioactives

Viral respiratory infections (VRIs) can spread quickly and cause enormous morbidity and mortality worldwide. These events pose serious threats to public health due to time lags in developing vaccines to activate the acquired immune system. The high variability of people's symptomatic responses to viral infections, as illustrated in the current COVID-19 pandemic, indicates the potential to moderate the severity of morbidity from VRIs. Growing evidence supports roles for probiotic bacteria (PB) and prebiotic dietary fiber (DF) and other plant nutritional bioactives in modulating immune functions. While human studies help to understand the epidemiology and immunopathology of VRIs, the chaotic nature of viral transmissions makes it difficult to undertake mechanistic study where the pre-conditioning of the metabolic and immune system could be beneficial. However, recent experimental studies have significantly enhanced our understanding of how PB and DF, along with plant bioactives, can significantly modulate innate and acquired immunity responses to VRIs. Synbiotic combinations of PB and DF potentiate increased benefits primarily through augmenting the production of short-chain fatty acids (SCFAs) such as butyrate. These and specific plant polyphenolics help to regulate immune responses to both restrain VRIs and temper the neutrophil response that can lead to acute respiratory distress syndrome (ARDS). This review highlights the current understanding of the potential impact of targeted nutritional strategies in setting a balanced immune tone for viral clearance and reinforcing homeostasis. This knowledge may guide the development of public health tactics and the application of functional foods with PB and DF components as a nutritional approach to support countering VRI morbidity.

Effects of Inulin Propionate Ester on Obesity-Related Metabolic Syndrome and Intestinal Microbial Homeostasis in Diet-Induced Obese Mice

Short-chain fatty acid (SCFA) plays an important role in improving obesity and related metabolic syndrome induced by high-fat diet. We used the prepared inulin propionate ester (IPE) as a system for the targeted release of propionate to the colon to elucidate the role of IPE in regulating obesity and metabolic syndrome, and intestinal microbial homeostasis, in diet-induced obese mice. With this strategy, IPE significantly increased the SCFA contents in the colon and resulted in significant body weight reduction, insulin resistance amelioration, and gastrointestinal hormone (glucagon-like peptide and peptide YY) secretion (P < 0.05). The IPE intervention reduced liver fatty accumulation, which improved obesity-related fatty liver disease (P < 0.05). IPE supplementation increased the richness and diversity of the microbial community and altered bacterial population at both the phylum and family level. Intestinal microbial results showed that the relative abundance of Desulfovibrionaceae and Erysipelotrichaceae, which promote the production of inflammatory factors, was reduced. Our results demonstrate that IPE can be used as an effective strategy for delivering propionate to obese mice colon, which can ameliorate obesity and associated metabolic syndrome and modify intestinal microbial homeostasis.

Egg oil from Portunus trituberculatus alleviated obesity and regulated gut microbiota in mice

Egg oil from Portunus trituberculatus (Pt-egg oil) can overcome insulin resistance resulting from abundant bioactive lipids. However, its effects on obesity and gut microbiota were unclear. Here, we evaluated whether Pt-egg oil could improve obesity and gut microbiota or not in high-fat diet feeding mice. Results exhibited that Pt-egg oil markedly reduced body weight and adipose weight gain, improved lipid accumulation and circulatory cytokines, inhibited epididymal adipose cell size. Moreover, Pt-egg oil modified gut microbiota, involving decreases in the ratio of Firmicutes to Bacteroidetes, Proteobacteria, Actinobacteria, and increase in Verrucomicrobia phylum. Pt-egg oil reduced serum and fecal lipopolysaccharide (LPS) levels and down-regulated Toll-like receptor 4 pathway in both epididymal adipose and liver tissues. Meanwhile, Pt-egg oil increased short chain fatty acids and up-regulated of G-protein-coupled receptors in both epididymal adipose and liver tissues. These suggest that Pt-egg oil could be alternative food supplement for the prophylactic effects on anti-obesity and improvement in human gut health.

Niacin Alleviates Dairy Cow Mastitis by Regulating the GPR109A/AMPK/NRF2 Signaling Pathway

Mastitis is one of three bovine diseases recognized as a cause of substantial economic losses every year throughout the world. Niacin is an important feed additive that is used extensively for dairy cow nutrition. However, the mechanism by which niacin acts on mastitis is not clear. The aim of this study is to investigate the mechanism of niacin in alleviating the inflammatory response of mammary epithelial cells and in anti-mastitis. Mammary glands, milk, and blood samples were collected from mastitis cows not treated with niacin (n = 3) and treated with niacin (30 g/d, n = 3) and healthy cows (n = 3). The expression of GPR109A, IL-6, IL-1β, and TNF-α in the mammary glands of the dairy cows with mastitis was significantly higher than it was in the glands of the healthy dairy cows. We also conducted animal experiments in vivo by feeding rumen-bypassed niacin. Compared with those in the untreated mastitis group, the somatic cell counts (SCCs) and the expression of IL-6, IL-1β, and TNF-α in the blood and milk were lower. In vitro, we isolated the primary bovine mammary epithelial cells (BMECs) from the mammary glands of the healthy cows. The mRNA levels of IL-6, IL-1β, TNF-α, and autophagy-related genes were detected after adding niacin, shRNA, compound C, trans retinoic acid, 3-methyladenine to BMECs. Then GPR109A, AMPK, NRF-2, and autophagy-related proteins were detected by Western blot. We found that niacin can activate GPR109A and phosphorylate AMPK, and promote NRF-2 nuclear import and autophagy to alleviate LPS-induced inflammatory response in BMECs. In summary, we found that niacin can reduce the inflammatory response of BMECs through GPR109A/AMPK/NRF-2/autophagy. We also preliminarily explored the alleviative effect of niacin on mastitis in dairy cows.

Protective Effects of Short-Chain Fatty Acids on Endothelial Dysfunction Induced by Angiotensin II

Short-chain fatty acids (SCFAs) are among the main classes of bacterial metabolic products and are mainly synthesized in the colon through bacterial fermentation. Short-chain fatty acids, such as acetate, butyrate, and propionate, reduce endothelial activation induced by proinflammatory mediators, at least in part, by activation of G protein–coupled receptors (GPRs): GPR41 and GPR43. The objective of the study was to analyze the possible protective effects of SCFAs on endothelial dysfunction induced by angiotensin II (AngII). Rat aortic endothelial cells (RAECs) and rat aortas were incubated with AngII (1 μM) for 6 h in the presence or absence of SCFAs (5–10 mM). In RAECs, we found that AngII reduces the production of nitric oxide (NO) stimulated by calcium ionophore A23187; increases the production of reactive oxygen species (ROS), both from the nicotinamide adenine dinucleotide phosphate oxidase system and the mitochondria; diminishes vasodilator-stimulated phosphoprotein (VASP) phosphorylation at Ser²³⁹; reduces GPR41 and GPR43 mRNA level; and reduces the endothelium-dependent relaxant response to acetylcholine in aorta. Coincubation with butyrate and acetate, but not with propionate, increases both NO production and pSer²³⁹-VASP, reduces the concentration of intracellular ROS, and improves relaxation to acetylcholine. The beneficial effects of butyrate were inhibited by the GPR41 receptor antagonist, β-hydroxybutyrate, and by the GPR43 receptor antagonist, GLPG0794. Butyrate inhibited the down-regulation of GPR41 and GPR43 induced by AngII, being without effect acetate and propionate. Neither β-hydroxybutyrate nor GLPG0794 affects the protective effect of acetate in endothelial dysfunction. In conclusion, acetate and butyrate improve endothelial dysfunction induced by AngII by increasing the bioavailability of NO. The effect of butyrate seems to be related to GPR41/43 activation, whereas acetate effects were independent of GPR41/43.

Modulation of Pectin on Mucosal Innate Immune Function in Pigs Mediated by Gut Microbiota

The use of prebiotics to regulate gut microbiota is a promising strategy to improve gut health. Pectin (PEC) is a prebiotic carbohydrate that enhances the health of the gut by promoting the growth of beneficial microbes. These microbes produce metabolites that are known to improve mucosal immune responses. This study was conducted to better understand effects of PEC on the microbiome and mucosal immunity in pigs. Pigs were fed two diets, with or without 5% apple PEC, for 72 days. Effects of PEC on the microbiota, cytokine expression, short-chain fatty acids (SCFAs) concentration and barrier function were examined in the ileum and cecum of the pigs. An integrative analysis was used to determine interactions of PEC consumption with bacterial metabolites and microbiome composition and host mucosal responses. Consumption of PEC reduced expression of pro-inflammatory cytokines such as IFN-γ, IL-6, IL-8, IL-12 and IL-18, and the activation of the pro-inflammatory NF-κB signaling cascade. Expression of MUC2 and TFF and the sIgA content was upregulated in the mucosa of PEC-fed pigs. Network analysis revealed that PEC induced significant interactions between microbiome composition in the ileum and cecum on mucosal immune pathways. PEC-induced changes in bacterial genera and fermentation metabolites, such as Akkermansia, Faecalibacterium, Oscillibacter, Lawsonia and butyrate, correlated with the differentially expressed genes and cytokines in the mucosa. In summary, the results demonstrate the anti-inflammatory properties of PEC on mucosal immune status in the ileum and cecum effected through modulation of the host microbiome.

Effects of gut microbiota on leptin expression and body weight are lessened by high-fat diet in mice

Aberration in leptin expression is one of the most frequent features in the onset and progression of obesity, but the underlying mechanisms are still unclear and need to be clarified. This study investigated the effects of the absence of gut microbiota on body weight and the expression and promoter methylation of the leptin. Male C57 BL/6 J germ-free (GF) and conventional (CV) mice (aged 4-5 weeks) were fed either a normal-fat diet (NFD) or a high-fat diet (HFD) for 16 weeks. Six to eight mice from each group, at 15 weeks, were administered exogenous leptin for 7 d. Leptin expression and body weight gain in GF mice were increased by NFD with more CpG sites hypermethylated at the leptin promoter, whereas there was no change with HFD, compared with CV mice. Adipose or hepatic expression of genes associated with fat synthesis (Acc1, Fas and Srebp-1c), hydrolysis and oxidation (Atgl, Cpt1a, Cpt1c, Ppar-α and Pgc-1α) was lower, and hypothalamus expression of Pomc and Socs3 was higher in GF mice than levels in CV mice, particularly with NFD feeding. Exogenous leptin reduced body weight in both types of mice, with a greater effect on CV mice with NFD. Adipose Lep-R expression was up-regulated, and hepatic Fas and hypothalamic Socs3 were down-regulated in both types of mice. Expression of fat hydrolysis and oxidative genes (Atgl, Hsl, Cpt1a, Cpt1c, Ppar-α and Pgc-1α) was up-regulated in CV mice. Therefore, the effects of gut microbiota on the leptin expression and body weight were affected by dietary fat intake.

Effects of Nondigestible Oligosaccharides on Obesity

Obesity is a major public health concern that has almost reached the level of pandemic and is rapidly progressing. The gut microbiota has emerged as a crucial regulator involved in the etiology of obesity, and the manipulation of it by dietary intervention has been widely used for reducing the risk of obesity. Nondigestible oligosaccharides (NDOs) are attracting increasing interests as prebiotics, as the indigestible ingredients can induce compositional or metabolic improvement to the gut microbiota, thereby improving gut health and giving rise to the production of short-chain fatty acids (SCFAs) to elicit metabolic effects on obesity. In this review, the role NDOs play in obesity intervention via modification of the gut microecology, as well as the physicochemical and physiological properties and industrial manufacture of NDOs, is discussed. Our goal is to provide a critical assessment of and stimulate comprehensive research into NDO use in obesity.

The short-chain free fatty acid receptor FFAR3 is expressed and potentiates contraction in human airway smooth muscle

Emerging evidence suggests that gut microbiota-derived short-chain fatty acids (SCFAs; acetate, propionate, and butyrate) are important modulators of the inflammatory state in diseases such as asthma. However, the functional expression of the G_i protein-coupled free fatty acid receptors (FFAR2/GPR43 and FFAR3/GPR41) has not been identified on airway smooth muscle (ASM). Classically, acute activation of G_i-coupled receptors inhibits cyclic AMP (cAMP) synthesis, which impairs ASM relaxation and can also induce crosstalk between G_i- and G_q-signaling pathways, potentiating increases in intracellular Ca²⁺ concentration ([Ca²⁺]_i), favoring ASM contraction. In contrast, chronic activation of G_i-coupled receptors can sensitize adenylyl cyclase resulting in increased cAMP synthesis favoring relaxation. We questioned whether the G_i-coupled FFAR2 or FFAR3 is expressed in human ASM, whether they modulate cAMP and [Ca²⁺]_i, and whether SCFAs modulate human ASM tone. We detected the protein expression of FFAR3 but not FFAR2 in native human ASM and primary cultured human airway smooth muscle (HASM) cells. In HASM cells, acute activation of FFAR3 with SCFAs inhibited forskolin-stimulated cAMP accumulation, but chronic activation did not sensitize cAMP synthesis. SCFAs induced [Ca²⁺]_i increases that were attenuated by pertussis toxin, gallein, U73122, or xestospongin C. Acute treatment with SCFAs potentiated acetylcholine-stimulated [Ca²⁺]_i increases and stress fiber formation in cells and contraction of ex vivo human airway tissues. In contrast, chronic pretreatment of human ASM with propionate did not potentiate airway relaxation. Together, these findings demonstrate that FFAR3 is expressed in human ASM and contributes to ASM contraction via reduced cAMP and increased [Ca²⁺]_i.

The small chain fatty acid butyrate antagonizes the TCR-stimulation-induced metabolic shift in murine epidermal gamma delta T cells

The metabolic requirements change during cell proliferation and differentiation. Upon antigen-stimulation, effector T cells switch from adenosine-triphospate (ATP)-production by oxidative phosphorylation in the mitochondria to glycolysis. In the gut it was shown that short chain fatty acids (SCFA), fermentation products of the microbiota in colon, ameliorate inflammatory reactions by supporting the differentiation of regulatory T cells. SCFA are a major energy source, but they are also anabolic metabolites, histone-deacetylase-inhibitors and activators of G protein receptors. Recently, it was reported that a topical application of the SCFA butyrate promotes regulatory T cells in the skin. Here we ask if the SCFA butyrate, propionate and acetate affect the energy metabolism and inflammatory potential of dendritic epidermal T cells (DETC), the innate resident skin γδ T cell population. Using the Seahorse™ technology, we measured glycolysis and oxidative phosphorylation (OXPHOS) in a murine DETC cell line, 7-17, upon TCR-stimulation by CD3/CD28 crosslinking, with or without SCFA addition. TCR engagement resulted in a change of the ratio glycolysis/OXPHOS. A similar metabolic shift has been described for activated CD4 T cells. Addition of 5 mM SCFA, in particular butyrate, antagonized the effect. Stimulated DETC secrete cytokines, e.g. the pro-inflammatory cytokine interferon-gamma (IFNγ), and thereby regulate skin homeostasis. Addition of butyrate and propionate to the cultures at non-toxic concentrations decreased secretion of IFNγ by DETC and increased the expression of the immunoregulatory surface receptor CD69. We hypothesize that SCFA can dampen the inflammatory activity of DETC.

The olfactory G protein-coupled receptor (Olfr-78/OR51E2) modulates the intestinal response to colitis

Olfactory receptor-78 (Olfr-78) is a recently identified G protein-coupled receptor activated by short-chain fatty acids acetate and propionate. A suggested role for this receptor exists in the prostate where it may influence chronic inflammatory response leading to intraepithelial neoplasia. Olfr-78 has also been shown to be expressed in mouse colon. Short-chain fatty acids and their receptors are well known to modulate inflammation in the gut. Considering this possibility, we first explored if colitis regulated Olfr-78 expression in the gut, where we observed a significant reduction in the expression of Olfr-78 transcript in mouse models of dextran sodium sulfate (DSS)- and 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced colitis. To more directly test this, mice deficient in Olfr-78 were administered with DSS in water for 7 days and were found to have increased expression of IL-1β and inflammatory signs in colon compared with control mice. Next, we explored the expression of its human counterpart olfactory receptor family 51, subfamily E, member 2 (OR51E2) in human intestinal samples and observed that it was in fact also expressed in human colon samples. RNA sequence analysis revealed significant changes in the genes involved in infection, immunity, inflammation, and colorectal cancer between wild-type and Olfr-78 knockout mice. Collectively, our findings show that Olfr-78 is highly expressed in colon and downregulated in DSS- and TNBS-induced colitis, and DSS-treated Olfr-78 null mice had increased colonic expression of cytokine RNA levels, suggesting a potential role for this receptor in intestinal inflammation. Future investigations are needed to understand how Olfr-78/OR51E2 in both mouse and human intestine modulates gastrointestinal pathophysiology.

Acetate attenuates perioperative neurocognitive disorders in aged mice

Perioperative neurocognitive disorders are common in elderly patients who have undergone surgical procedures. Neuroinflammation induced by microglial activation is a hallmark of these neurological disorders. Acetate can suppress inflammation in the context of inflammatory diseases. We employed an exploratory laparotomy model with isoflurane anesthesia to study the effects of acetate on perioperative neurocognitive disorders in aged mice. Neurocognitive function was assessed with open-field tests and Morris water maze tests 3 or 7 days post-surgery. Acetate ameliorated the surgery-induced cognitive deficits of aged mice and inhibited the activation of IBA-1, a marker of microglial activity. Acetate also reduced expression of inflammatory proteins (tumor necrosis factor-α, interleukin-1β and interleukin-6), oxidative stress factors (NADPH oxidase 2, inducible nitric oxide synthase and reactive oxygen species), and signaling molecules (nuclear factor kappa B and mitogen-activated protein kinase) in the hippocampus. BV2 microglial cells were used to verify the anti-inflammatory effects of acetate in vitro. Acetate suppressed inflammation in lipopolysaccharide-treated BV2 microglial cells, but not when GPR43 was silenced. These results suggest that acetate may bind to GPR43, thereby inhibiting microglial activity, suppressing neuroinflammation, and preventing memory deficits. This makes acetate is a promising therapeutic for surgery-induced neurocognitive disorders and neuroinflammation.

Short-chain fatty acid mitigates adenine-induced chronic kidney disease via FFA2 and FFA3 pathways

Short-chain fatty acids (SCFAs), including acetate, butyrate, and propionate, are produced when colonic bacteria in the human gastrointestinal tract ferment undigested fibers. Free fatty acid receptor 2 (FFA2) and FFA3 are G-protein-coupled receptors recently identified as SCFA receptors that may modulate inflammation. We previously showed through in vitro experiments that SCFAs activate FFA2 and FFA3, thereby mitigating inflammation in human renal cortical epithelial cells. This study used a murine model of adenine-induced renal failure to investigate whether or not SCFAs can prevent the progression of renal damage. We also examined whether or not these FFA2 and FFA3 proteins have some roles in this protective mechanism in vivo. Immunohistochemical analyses of mouse kidneys showed that FFA2 and FFA3 proteins were expressed mainly in the distal renal tubules and collecting tubules. First, we observed that the administration of propionate mitigated the renal dysfunction and pathological deterioration caused by adenine. Consistent with this, the expression of inflammatory cytokines and fibrosis-related genes was reduced. Furthermore, the mitigation of adenine-induced renal damage by the administration of propionate was significantly attenuated in FFA2^-/- and FFA3^-/- mice. Therefore, the administration of propionate significantly protects against adenine-induced renal failure, at least in part, via the FFA2 and FFA3 pathways. Our data suggest that FFA2 and FFA3 are potential new therapeutic targets for preventing or delaying the progression of chronic kidney disease.

Changes in Plasma Short-Chain Fatty Acid Levels after Dietary Weight Loss Among Overweight and Obese Adults over 50 Weeks

Gut microbial-derived short-chain fatty acids (SCFAs) may regulate energy homeostasis and exert anti-carcinogenic, immunomodulatory and anti-inflammatory effects. Smaller trials indicate that dietary weight loss may lead to decreased SCFA production, but findings have been inconclusive. SCFA concentrations were measured by HPLC-MS/MS in plasma samples of 150 overweight or obese adults in a trial initially designed to evaluate the metabolic effects of intermittent (ICR) versus continuous (CCR) calorie restriction (NCT02449148). For the present post hoc analyses, participants were classified by quartiles of weight loss, irrespective of the dietary intervention. Linear mixed models were used to analyze weight-loss-induced changes in SCFA concentrations after 12, 24 and 50 weeks. There were no differential changes in SCFA levels across the initial study arms (ICR versus CCR versus control) after 12 weeks, but acetate concentrations significantly decreased with overall weight loss (mean log-relative change of −0.7 ± 1.8 in the lowest quartile versus. −7.6 ± 2 in the highest, p = 0.026). Concentrations of propionate, butyrate and other SCFAs did not change throughout the study. Our results show that weight-loss, achieved through calorie restriction, may lead to smaller initial decreases in plasma acetate, while plasma SCFAs generally remain remarkably stable over time.

Impact of maternal dietary gut microbial metabolites on an offspring's systemic immune response in mouse models

The gut microbiota has a great impact on the host immune systems. Recent evidence suggests that the maternal gut microbiota affects the immune systems of offspring. Metabolites produced by the gut microbiota play crucial roles in the immune system. Previous studies have also revealed that metabolites such as short-chain fatty acids (SCFAs) and the aryl hydrocarbon receptor (AhR) ligands are involved in host health and diseases. Great progress has been made in understanding the roles of diet-derived SCFAs in the offspring’s immune system. The findings to date raise the possibility that maternal dietary soluble fiber intake may play a role in the development of the offspring’s systemic immune response. In this review, we summarize the present knowledge and discuss future therapeutic possibilities for using dietary soluble fiber intake against inflammatory diseases.

Short chain fatty acids could prevent fat deposition in pigs via regulating related hormones and genes

Short chain fatty acids (SCFAs) are produced when indigestible carbohydrates, such as fiber and resistant starch, undergo fermentation by specific microbiota in the hindgut.

Influence of Maternal Prepregnancy Obesity and Excessive Gestational Weight Gain on Maternal and Child Gastrointestinal Microbiome Composition: A Systematic Review

BACKGROUND

Maternal obesity is a well-known risk factor for significant obstetric and neonatal complications. The influence of the gastrointestinal microbiome in the setting of maternal obesity during pregnancy is less understood. The purpose of this systematic review is to synthesize the literature on the relationships between maternal obesity and excessive gestational weight gain (EGWG) and the composition of maternal and child gastrointestinal microbiomes.

METHOD

We searched CINHAL, OVID Medline, Web of Science, and PubMed for relevant literature using medical subject heading terms related to obesity, pregnancy, and the gastrointestinal microbiome. We assessed 249 articles for potential inclusion using the preferred reporting items for systematic review and meta-analyses framework and deemed 11 articles as relevant for this review.

RESULTS

Maternal obesity was associated with significant microbial changes in both maternal and infant fecal microbiome biospecimens including increases in Bacteroidetes, Firmicutes, and the Actinobacteria phyla and decreases in Bifidobacteria. However, inconsistencies in uniform taxonomic results across all studies mean that evidence of specific microbial associations with obesity and EGWG is inconclusive.

CONCLUSION

Our findings suggest that both maternal and child gastrointestinal microbiome composition is altered in the setting of maternal obesity and EGWG during pregnancy. Future microbiome studies should concentrate on the investigation of metagenomic sequencing to elucidate microbial function rather than solely taxonomic composition. More diverse populations of mothers should be sampled to address health disparities and adverse outcomes of underrepresented populations. Finally, analytic pipelines should be standardized across studies to aid in reproducibility.

Gut Microbiota and Cancer of the Host: Colliding Interests

Cancer develops in multicellular organisms from cells that ignore the rules of cooperation and escape the mechanisms of anti-cancer surveillance. Tumorigenesis is jointly encountered by the host and microbiota, a vast collection of microorganisms that live on the external and internal epithelial surfaces of the body. The largest community of human microbiota resides in the gastrointestinal tract where commensal, symbiotic and pathogenic microorganisms interact with the intestinal barrier and gut mucosal lymphoid tissue, creating a tumor microenvironment in which cancer cells thrive or perish. Aberrant composition and function of the gut microbiota (dysbiosis) has been associated with tumorigenesis by inducing inflammation, promoting cell growth and proliferation, weakening immunosurveillance, and altering food and drug metabolism or other biochemical functions of the host. However, recent research has also identified several mechanisms through which gut microbiota support the host in the fight against cancer. These mechanisms include the use of antigenic mimicry, biotransformation of chemotherapeutic agents, and other mechanisms to boost anti-cancer immune responses and improve the efficacy of cancer immunotherapy. Further research in this rapidly advancing field is expected to identify additional microbial metabolites with tumor suppressing properties, map the complex interactions of host-microbe 'transkingdom network' with cancer cells, and elucidate cellular and molecular pathways underlying the impact of specific intestinal microbial configurations on immune checkpoint inhibitor therapy.

Effect of Diet on the Gut Microbiota Associated with Obesity

Obesity is abnormal or excessive fat accumulation that is associated with progression of metabolic diseases including type 2 diabetes mellitus, cardiovascular disease, nonalcoholic fatty liver disease, and cancer. Gut microbiota (GM) have received much attention as essential factors in development and progression of obesity. The diversity, composition, and metabolic activity of GM are closely associated with nutrient intake and dietary pattern. Scientific evidence supports the idea that dietary pattern directly changes the GM profile; therefore, diet is a crucial component related to interactions between GM and obesity progression. A literature review showed that dietary factors such as probiotics, prebiotics, fat, fatty acids, and fiber dramatically alter the GM profile related to obesity. Furthermore, different dietary patterns result in different GM composition and activity that can contribute to amelioration of obesity.

Obesity-induced asthma: Role of free fatty acid receptors

Obesity is a major risk factor for the development of asthma, and worsens the key features of asthma including airway hyperresponsiveness, inflammation, and airway remodeling. Although pro- and anti-inflammatory adipocytokines may contribute to the pathogenesis of asthma in obesity, the mechanistic basis for the relationship between asthma and obesity remains unclear. In obese individuals, the increased amount of adipose tissue results in the release of more long-chain free fatty acids as compared to lean individuals, causing an elevation in plasma long-chain free fatty acid concentrations. Recent findings suggest that the free fatty acid receptor 1 (FFAR1), which is a sensor of medium- and long-chain free fatty acids, is expressed on airway smooth muscle and plays a pivotal role in airway contraction and airway smooth muscle cell proliferation. In contrast, FFAR4, which is a sensor for long-chain n-3 polyunsaturated fatty acids and also expressed on airway smooth muscle, does not contribute to airway contraction and airway smooth muscle cell proliferation. Functional roles for short-chain fatty acid receptors FFAR2 and FFAR3 in the pathogenesis of asthma is still under debate. Taken together, adipose-derived long-chain free fatty acids may contribute to the pathogenesis of asthma in obesity through FFAR1.

Gut microbiotas and immune checkpoint inhibitor therapy response: a causal or coincidental relationship?

As the largest immune organ, human gut microbiome could influence the efficacy of immune checkpoint inhibitor therapy (ICI). However, identifying contributory microbes from over 35,000 species is virtually impossible and the identified microbes are not consistent among studies. The reason for the disparity may be that the microbes found in feces are markers of other factors that link immune response and microbiotas. Notably, gut microbiome is influenced by stool consistency, diet and other lifestyle factors. Therefore, the ICI and microbiotas relationship must be adjusted for potential confounders and analyzed longitudinally. Moreover, a recent study where 11 low-abundance commensal bacteria induced interferon-γ-producing CD8 T cells, challenges the validity of the abundance-oriented microbiotas investigations. This study also confirmed the hierarchy in immunogenic roles among microbiotas. Fecal transplantation trials in germ-free mice provided “the proof of principle” that germ-free mice reproduce the donor’s microbiome and corresponding ICI efficacy. However, species-specific biological differences prevent direct extrapolation between the results in murine and human models. Fecal transplantation or supplementation with microbes found in ICI responders requires caution due to potential adverse events.

Free Fatty Acid Receptors in Health and Disease

Fatty acids are metabolized and synthesized as energy substrates during biological responses. Long- and medium-chain fatty acids derived mainly from dietary triglycerides, and short-chain fatty acids (SCFAs) produced by gut microbial fermentation of the otherwise indigestible dietary fiber, constitute the major sources of free fatty acids (FFAs) in the metabolic network. Recently, increasing evidence indicates that FFAs serve not only as energy sources but also as natural ligands for a group of orphan G protein-coupled receptors (GPCRs) termed free fatty acid receptors (FFARs), essentially intertwining metabolism and immunity in multiple ways, such as via inflammation regulation and secretion of peptide hormones. To date, several FFARs that are activated by the FFAs of various chain lengths have been identified and characterized. In particular, FFAR1 (GPR40) and FFAR4 (GPR120) are activated by long-chain saturated and unsaturated fatty acids, while FFAR3 (GPR41) and FFAR2 (GPR43) are activated by SCFAs, mainly acetate, butyrate, and propionate. In this review, we discuss the recent reports on the key physiological functions of the FFAR-mediated signaling transduction pathways in the regulation of metabolism and immune responses. We also attempt to reveal future research opportunities for developing therapeutics for metabolic and immune disorders.

Metabolites as regulators of insulin sensitivity and metabolism

The cause of insulin resistance in obesity and type 2 diabetes mellitus (T2DM) is not limited to impaired insulin signalling but also involves the complex interplay of multiple metabolic pathways. The analysis of large data sets generated by metabolomics and lipidomics has shed new light on the roles of metabolites such as lipids, amino acids and bile acids in modulating insulin sensitivity. Metabolites can regulate insulin sensitivity directly by modulating components of the insulin signalling pathway, such as insulin receptor substrates (IRSs) and AKT, and indirectly by altering the flux of substrates through multiple metabolic pathways, including lipogenesis, lipid oxidation, protein synthesis and degradation and hepatic gluconeogenesis. Moreover, the post-translational modification of proteins by metabolites and lipids, including acetylation and palmitoylation, can alter protein function. Furthermore, the role of the microbiota in regulating substrate metabolism and insulin sensitivity is unfolding. In this Review, we discuss the emerging roles of metabolites in the pathogenesis of insulin resistance and T2DM. A comprehensive understanding of the metabolic adaptations involved in insulin resistance may enable the identification of novel targets for improving insulin sensitivity and preventing, and treating, T2DM.