Propionate lowers blood glucose and alters lipid metabolism in healthy subjects

Interactions between host and gut microbiota in gestational diabetes mellitus and their impacts on offspring

Gestational diabetes mellitus (GDM) is characterized by insulin resistance and low-grade inflammation, and most studies have demonstrated gut dysbiosis in GDM pregnancies. Overall, they were manifested as a reduction in microbiome diversity and richness, depleted short chain fatty acid (SCFA)-producing genera and a dominant of Gram-negative pathogens releasing lipopolysaccharide (LPS). The SCFAs functioned as energy substance or signaling molecules to interact with host locally and beyond the gut. LPS contributed to pathophysiology of diseases through activating Toll-like receptor 4 (TLR4) and involved in inflammatory responses. The gut microbiome dysbiosis was not only closely related with GDM, it was also vital to fetal health through vertical transmission. In this review, we summarized gut microbiota signature in GDM pregnancies of each trimester, and presented a brief introduction of microbiome derived SCFAs. We then discussed mechanisms of microbiome-host interactions in the physiopathology of GDM and associated metabolic disorders. Finally, we compared offspring microbiota composition from GDM with that from normal pregnancies, and described the possible mechanism.

A Long-Chain Dextran Produced by Weissella cibaria Boosts the Diversity of Health-Related Gut Microbes Ex Vivo

Long-chain dextrans are α-glucans that can be produced by lactic acid bacteria. NextDextTM, a specific long-chain dextran with a high degree of polymerisation, produced using Weissella cibaria, was recently shown to exert prebiotic potential in vitro. In this study, the ex vivo SIFR® technology, recently validated to provide predictive insights into gut microbiome modulation down to the species level, was used to investigate the effects of this long-chain dextran on the gut microbiota of six human adults that altogether covered different enterotypes. A novel community modulation score (CMS) was introduced based on the strength of quantitative 16S rRNA gene sequencing and the highly controlled ex vivo conditions. This CMS overcomes the limitations of traditional α-diversity indices and its application in the current study revealed that dextran is a potent booster of microbial diversity compared to the reference prebiotic inulin (IN). Long-chain dextran not only exerted bifidogenic effects but also consistently promoted Bacteroides spp., Parabacteroides distasonis and butyrate-producing species like Faecalibacterium prausnitzii and Anaerobutyricum hallii. Further, long-chain dextran treatment resulted in lower gas production compared to IN, suggesting that long-chain dextran could be better tolerated. The additional increase in Bacteroides for dextran compared to IN is likely related to the higher propionate:acetate ratio, attributing potential to long-chain dextran for improving metabolic health and weight management. Moreover, the stimulation of butyrate by dextran suggests its potential for improving gut barrier function and inflammation. Overall, this study provides a novel tool for assessing gut microbial diversity ex vivo and positions long-chain dextran as a substrate that has unique microbial diversity enhancing properties.

Multiple micronutrient deficiencies alter energy metabolism in host and gut microbiome in an early-life murine model

Introduction

Micronutrients perform a wide range of physiological functions essential for growth and development. However, most people still need to meet the estimated average requirement worldwide. Globally, 2 billion people suffer from micronutrient deficiency, most of which are co-occurring deficiencies in children under age five. Despite decades of research, animal models studying multiple micronutrient deficiencies within the early-life period are lacking, which hinders our complete understanding of the long-term health implications and may contribute to the inefficacy of some nutritional interventions. Evidence supporting the Developmental Origins of Health and Disease (DOHaD) theory demonstrates that early-life nutritional deficiencies carry life-long consequences mediated through various mechanisms such as abnormal metabolic programming, stunting, altered body composition, and the gut microbiome. However, this is largely unexplored in the multiple micronutrient deficient host.

Methods

we developed a preclinical model to examine undernutrition's metabolic and functional impact on the host and gut microbiome early in life. Three-week-old weanling C57BL/6N male mice were fed a low-micronutrient diet deficient in zinc, folate, iron, vitamin A, and vitamin B12 or a control diet for 4-weeks.

Results

Our results showed that early-life multiple micronutrient deficiencies induced stunting, altered body composition, impaired glucose and insulin tolerance, and altered the levels of other micronutrients not depleted in the diet within the host. In addition, functional metagenomics profiling and a carbohydrate fermentation assay showed an increased microbial preference for simple sugars rather than complex ones, suggestive of a less developed microbiome in the low-micronutrient-fed mice. Moreover, we found that a zinc-only deficient diet was not sufficient to induce these phenotypes, further supporting the importance of studying co-occurring deficiencies.

Discussion

Together, these findings highlight a previously unappreciated role of early-life multiple micronutrient deficiencies in shaping the metabolic phenome of the host and gut microbiome through altered glucose energy metabolism, which may have implications for metabolic disease later in life in micronutrient-deficient survivors.

Effects of gut microbiota on neurodegenerative diseases

A progressive degradation of the brain's structure and function, which results in a reduction in cognitive and motor skills, characterizes neurodegenerative diseases (NDs) such as Alzheimer's disease (AD), Parkinson's disease (PD), Amyotrophic lateral sclerosis (ALS), and Huntington's disease (HD). The morbidity linked to NDs is growing, which poses a severe threat to human being's mental and physical ability to live well. The gut-brain axis (GBA) is now known to have a crucial role in the emergence of NDs. The gut microbiota is a conduit for the GBA, a two-way communication system between the gut and the brain. The myriad microorganisms that make up the gut microbiota can affect brain physiology by transmitting numerous microbial chemicals from the gut to the brain via the GBA or neurological system. The synthesis of neurotransmitters, the immunological response, and the metabolism of lipids and glucose have all been demonstrated to be impacted by alterations in the gut microbiota, such as an imbalance of helpful and harmful bacteria. In order to develop innovative interventions and clinical therapies for NDs, it is crucial to comprehend the participation of the gut microbiota in these conditions. In addition to using antibiotics and other drugs to target particular bacterial species that may be a factor in NDs, this also includes using probiotics and other fecal microbiota transplantation to maintain a healthy gut microbiota. In conclusion, the examination of the GBA can aid in understanding the etiology and development of NDs, which may benefit the improvement of clinical treatments for these disorders and ND interventions. This review indicates existing knowledge about the involvement of microbiota present in the gut in NDs and potential treatment options.

Bacterial Metabolites: A Link between Gut Microbiota and Dermatological Diseases

Dysbiosis has been identified in many dermatological conditions (e.g., psoriasis, atopic dermatitis, systemic lupus erythematosus). One of the ways by which the microbiota affect homeostasis is through microbiota-derived molecules (metabolites). There are three main groups of metabolites: short-chain fatty acids (SCFAs), tryptophan metabolites, and amine derivatives including trimethylamine N-oxide (TMAO). Each group has its own uptake and specific receptors through which these metabolites can exert their systemic function. This review provides up-to-date knowledge about the impact that these groups of gut microbiota metabolites may have in dermatological conditions. Special attention is paid to the effect of microbial metabolites on the immune system, including changes in the profile of the immune cells and cytokine disbalance, which are characteristic of several dermatological diseases, especially psoriasis and atopic dermatitis. Targeting the production of microbiota metabolites may serve as a novel therapeutic approach in several immune-mediated dermatological diseases.

Treatment of Dyslipidemia through Targeted Therapy of Gut Microbiota

Dyslipidemia is a multifaceted condition with various genetic and environmental factors contributing to its pathogenesis. Further, this condition represents an important risk factor for its related sequalae including cardiovascular diseases (CVD) such as coronary artery disease (CAD) and stroke. Emerging evidence has shown that gut microbiota and their metabolites can worsen or protect against the development of dyslipidemia. Although there are currently numerous treatment modalities available including lifestyle modification and pharmacologic interventions, there has been promising research on dyslipidemia that involves the benefits of modulating gut microbiota in treating alterations in lipid metabolism. In this review, we examine the relationship between gut microbiota and dyslipidemia, the impact of gut microbiota metabolites on the development of dyslipidemia, and the current research on dietary interventions, prebiotics, probiotics, synbiotics and microbiota transplant as therapeutic modalities in prevention of cardiovascular disease. Overall, understanding the mechanisms by which gut microbiota and their metabolites affect dyslipidemia progression will help develop more precise therapeutic targets to optimize lipid metabolism.

Short Chain Fatty Acid Metabolism in Relation to Gut Microbiota and Genetic Variability

It is widely accepted that the gut microbiota plays a significant role in modulating inflammatory and immune responses of their host. In recent years, the host-microbiota interface has gained relevance in understanding the development of many non-communicable chronic conditions, including cardiovascular disease, cancer, autoimmunity and neurodegeneration. Importantly, dietary fibre (DF) and associated compounds digested by the microbiota and their resulting metabolites, especially short-chain fatty acids (SCFA), were significantly associated with health beneficial effects, such as via proposed anti-inflammatory mechanisms. However, SCFA metabolic pathways are not fully understood. Major steps include production of SCFA by microbiota, uptake in the colonic epithelium, first-pass effects at the liver, followed by biodistribution and metabolism at the host's cellular level. As dietary patterns do not affect all individuals equally, the host genetic makeup may play a role in the metabolic fate of these metabolites, in addition to other factors that might influence the microbiota, such as age, birth through caesarean, medication intake, alcohol and tobacco consumption, pathogen exposure and physical activity. In this article, we review the metabolic pathways of DF, from intake to the intracellular metabolism of fibre-derived products, and identify possible sources of inter-individual variability related to genetic variation. Such variability may be indicative of the phenotypic flexibility in response to diet, and may be predictive of long-term adaptations to dietary factors, including maladaptation and tissue damage, which may develop into disease in individuals with specific predispositions, thus allowing for a better prediction of potential health effects following personalized intervention with DF.

Beneficial effect of the short-chain fatty acid propionate on vascular calcification through intestinal microbiota remodelling

BACKGROUND

Vascular calcification is a major cause of the high morbidity and mortality of cardiovascular diseases and is closely associated with the intestinal microbiota. Short-chain fatty acids (SCFAs) are derived from the intestinal microbiota and can also regulate intestinal microbiota homeostasis. However, it remains unclear whether exogenous supplementation with propionate, a SCFA, can ameliorate vascular calcification by regulating the intestinal microbiota. This study was conducted to explore the roles of propionate and the intestinal microbiota in the process of vascular calcification.

METHODS

In total, 92 patients were enrolled consecutively as the observational cohort to analyse the relationship between SCFAs and vascular calcification in both blood and faecal samples. A rat model of vascular calcification was induced by vitamin D3 and nicotine (VDN) to validate the effect of propionate. Differences in the intestinal microbiota were analysed by 16S ribosomal RNA gene sequencing. Faecal microbiota transplantation and Akkermansia muciniphila transplantation experiments were performed to evaluate the functions of the intestinal microbiota.

RESULTS

The results of the observational cohort study revealed that the levels of SCFAs (particularly propionate) in both blood and faecal samples independently correlated negatively with calcification scores (P < 0.01). To verify the activities of propionate, it was provided to VDN-treated rats, and oral or rectal propionate delivery reshaped the intestinal microbiota, resulted in elevated SCFA production, improved intestinal barrier function and alleviated inflammation, ultimately ameliorating vascular calcification. Furthermore, we demonstrated that transplantation of the propionate-modulated intestinal microbiota induced beneficial outcomes similar to those with oral or rectal propionate administration. Interestingly, linear discriminant analysis (LDA) effect size (LEfSe) revealed that oral or rectal propionate administration and propionate-modulated intestinal microbiota transplantation both enriched primarily Akkermansia. Subsequently, we demonstrated that Akkermansia supplementation could ameliorate VDN-induced vascular calcification in rats.

CONCLUSIONS

Propionate can significantly ameliorate vascular calcification in VDN-treated rats, and this effect is mediated by intestinal microbiota remodelling. The findings in our study indicate that the intestinal tract-vessel axis is a promising target for alleviating vascular calcification. Video Abstract.

Effects of hawthorn seed oil on plasma cholesterol and gut microbiota

Background

Hypercholesterolemia and gut microbiota dysbiosis are associated with the risk of cardiovascular diseases. Hawthorn fruits has shown to be cardioprotective and hypocholesterolemic. However, no studies to date have studied the biological activity of hawthorn seed oil (HSO). The present study was to investigate if HSO could favourably reduce plasma cholesterol and modulate gut microbiota in hypercholesterolemia hamsters.

Methods

Golden Syrian hamsters (age, 8 weeks) were randomly divided into five groups (n = 8, each) and fed one of the following five diets, namely a non-cholesterol diet, a high cholesterol diet containing 0.15% cholesterol (HCD); a HCD diet with addition of 4.75% HSO (LHSO), a HCD diet with addition of 9.5% HSO (HHSO), a HCD diet with addition of 0.50% cholestyramine as positive control diet. After 6-week dietary intervention, plasma lipids, inflammatory markers, atherosclerosis plaque, hepatic and fecal lipids were quantified. Microbiota in fresh feces were analysed by sequencing 16S rRNA genes, while RT-PCR and Western blot analyses were employed to quantify the expression of genes involved in cholesterol homeostasis.

Results

HSO at a dose of 9.5% HSO could decrease plasma cholesterol and non-HDL-cholesterol by 15%. Additionally, both HSO experimental groups also suppressed mRNA of 3-Hydroxy-3-Methylglutaryl-CoA Reductase (HMG-CoA-R). Supplementation of HSO at 4.75% could significantly increase the excretion of fecal acidic sterols, accompanied by elevation of short-chain fatty acid levels in feces. The analyses of gut microbiome indicated that HSO supplementation could selectively alter the genera abundance of gut bacteria that were correlated with cholesterol metabolism including unclassified_f__Christensenellaceae, Ruminococcaceae_NK4A214_ group, norank_o_Gastranaerophilales, Faecalibaculum, Peptococcus, norank_f__Clostridiales_vadinBB60_group and Ruminococcus_2.

Conclusions

HSO supplementation was able to decrease plasma cholesterol by favourably modulating gut microbiota composition and gut-derived metabolites associated with cholesterol regulation.

Graphical Abstract

The effects of SCFAs on glycemic control in humans: a systematic review and meta-analysis

BACKGROUND

Noncommunicable disease development is related to impairments in glycemic and insulinemic responses, which can be modulated by fiber intake. Fiber's beneficial effects upon metabolic health can be partially attributed to the production of SCFAs via microbial fermentation of fiber in the gastrointestinal tract.

OBJECTIVES

We aimed to determine the effects of SCFAs, acetate, propionate, and butyrate on glycemic control in humans.

METHODS

The CENTRAL, Embase, PubMed, Scopus, and Web of Science databases were searched from inception to 7 December 2021. Papers were included if they reported a randomized controlled trial measuring glucose and/or insulin compared to a placebo in adults. Studies were categorized by the type of SCFA and intervention duration. Random-effects meta-analyses were performed for glucose and insulin for those subject categories with ≥3 studies, or a narrative review was performed.

RESULTS

We identified 43 eligible papers, with 46 studies within those records (n = 913), and 44 studies were included in the meta-analysis. Vinegar intake decreased the acute glucose response [standard mean difference (SMD), -0.53; 95% CI, -0.92 to -0.14; n = 67] in individuals with impaired glucose tolerance or type 2 diabetes and in healthy volunteers (SMD, -0.27; 95% CI, -0.54 to 0.00; n = 186). The meta-analyses for acute acetate, as well as acute and chronic propionate studies, showed no significant effect.

CONCLUSIONS

Vinegar decreased the glucose response acutely in healthy and metabolically unhealthy individuals. Acetate, propionate, butyrate, and mixed SCFAs had no effect on blood glucose and insulin in humans. Significant heterogeneity, risks of bias, and publication biases were identified in several study categories, including the acute vinegar glucose response. As evidence was very uncertain, caution is urged when interpreting these results. Further high-quality research is required to determine the effects of SCFAs on glycemic control.

Urolithins: Diet-Derived Bioavailable Metabolites to Tackle Diabetes

Diabetes remains one of the leading causes of deaths and co-morbidities in the world, with tremendous human, social and economic costs. Therefore, despite therapeutics and technological advancements, improved strategies to tackle diabetes management are still needed. One of the suggested strategies is the consumption of (poly)phenols. Positive outcomes of dietary (poly)phenols have been pointed out towards different features in diabetes. This is the case of ellagitannins, which are present in numerous foodstuffs such as pomegranate, berries, and nuts. Ellagitannins have been reported to have a multitude of effects on metabolic diseases. However, these compounds have high molecular weight and do not reach circulation at effective concentrations, being metabolized in smaller compounds. After being metabolized into ellagic acid in the small intestine, the colonic microbiota hydrolyzes and metabolizes ellagic acid into dibenzopyran-6-one derivatives, known as urolithins. These low molecular weight compounds reach circulation in considerable concentrations ranging until micromolar levels, capable of reaching target tissues. Different urolithins are formed throughout the metabolization process, but urolithin A, isourolithin A, and urolithin B, and their phase-II metabolites are the most frequent ones. In recent years, urolithins have been the focus of attention in regard to their effects on a multiplicity of chronic diseases, including cancer and diabetes. In this review, we will discuss the latest advances about the protective effects of urolithins on diabetes.

Gut Microbiota Regulation and Their Implication in the Development of Neurodegenerative Disease

In recent years, human gut microbiota have become one of the most promising areas of microorganism research; meanwhile, the inter-relation between the gut microbiota and various human diseases is a primary focus. As is demonstrated by the accumulating evidence, the gastrointestinal tract and central nervous system interact through the gut–brain axis, which includes neuronal, immune-mediated and metabolite-mediated pathways. Additionally, recent progress from both preclinical and clinical studies indicated that gut microbiota play a pivotal role in gut–brain interactions, whereas the imbalance of the gut microbiota composition may be associated with the pathogenesis of neurological diseases (particularly neurodegenerative diseases), the underlying mechanism of which is insufficiently studied. This review aims to highlight the relationship between gut microbiota and neurodegenerative diseases, and to contribute to our understanding of the function of gut microbiota in neurodegeneration, as well as their relevant mechanisms. Furthermore, we also discuss the current application and future prospects of microbiota-associated therapy, including probiotics and fecal microbiota transplantation (FMT), potentially shedding new light on the research of neurodegeneration.

Gut-microbiota derived bioactive metabolites and their functions in host physiology

Every individual harbours a complex, diverse and mutualistic microbial flora in their intestine and over the time it became an integral part of the body, affecting a plethora of activities of the host. Interaction between host and gut-microbiota affects several aspects of host physiology. Gut-microbiota affects host metabolism by fermenting unabsorbed/undigested carbohydrates in the large intestine. Not only the metabolic functions, any disturbances in the composition of the gut-microbiota during first 2-3 years of life may impact on the brain development and later affects cognition and behaviour. Thus, gut-dysbiosis causes certain serious pathological conditions in the host including metabolic disorders, inflammatory bowel disease and mood alterations, etc. Microbial-metabolites in recent times have emerged as key mediators and are responsible for microbiota induced beneficial effects on host. This review provides an overview of the mechanism of microbial-metabolite production, their respective physiological functions and the impact of gut-microbiome in health and diseases. Metabolites from dietary fibres, aromatic amino acids such as tryptophan, primary bile acids and others are the potential substances and link microbiota to host physiology. Many of these metabolites act as signalling molecules to a number of cells types and also help in the secretion of hormones. Moreover, interaction of microbiota derived metabolites with their host, immunity boosting mechanisms, protection against pathogens and modulation of metabolism is also highlighted here. Understanding all these functional attributes of metabolites produced from gut-microbiota may lead to the opening of a new avenue for preventing and developing potent therapies against several diseases.

The Role of the Gut Microbiome in Diabetes and Obesity-Related Kidney Disease

Diabetic kidney disease (DKD) is a progressive disorder, which is increasing globally in prevalence due to the increased incidence of obesity and diabetes mellitus. Despite optimal clinical management, a significant number of patients with diabetes develop DKD. Hence, hitherto unrecognized factors are likely to be involved in the initiation and progression of DKD. An extensive number of studies have demonstrated the role of microbiota in health and disease. Dysregulation in the microbiota resulting in a deficiency of short chain fatty acids (SCFAs) such as propionate, acetate, and butyrate, by-products of healthy gut microbiota metabolism, have been demonstrated in obesity, type 1 and type 2 diabetes. However, it is not clear to date whether such changes in the microbiota are causative or merely associated with the diseases. It is also not clear which microbiota have protective effects on humans. Few studies have investigated the centrality of reduced SCFA in DKD development and progression or the potential therapeutic effects of supplemental SCFAs on insulin resistance, inflammation, and metabolic changes. SCFA receptors are expressed in the kidneys, and emerging data have demonstrated that intestinal dysbiosis activates the renal renin-angiotensin system, which contributes to the development of DKD. In this review, we will summarize the complex relationship between the gut microbiota and the kidney, examine the evidence for the role of gut dysbiosis in diabetes and obesity-related kidney disease, and explore the mechanisms involved. In addition, we will describe the role of potential therapies that modulate the gut microbiota to prevent or reduce kidney disease progression.

Mechanistic and physiological approaches of fecal microbiota transplantation in the management of NAFLD

Non-alcoholic fatty liver disease (NAFLD) is a multifaceted disease allied with various metabolic disorders, obesity and dysbiosis. Gut microbiota plays an influential role in the pathogenesis of NAFLD and other metabolic disorders. However, recent scientific upsurge emphasizes on the utility of beneficial gut microbiota and bacteriotherapy in the management of NAFLD. Fecal microbiota transplantation (FMT) is the contemporary therapeutic approach with state-of-the-art methods for the treatment of NAFLD. Other potential therapies include probiotics and prebiotics supplements which are based on alteration of gut microbes to treat NAFLD. In this review, our major focus is on the pathological association of gut microbiota with progression of NAFLD, historical aspects and recent advances in FMT with possible intervention to combat NAFLD and its associated metabolic dysfunctions.

Nutritional, Medicinal, and Cosmetic Value of Bioactive Compounds in Button Mushroom (Agaricus bisporus): A Review

Fungi are vital to numerous industrial and household processes, especially producing cheeses, beer, wine, and bread, and they are accountable for breaking down organic matter. The remarkable medicinal and nutritional values of the mushrooms have increased their consumption. Agaricus bisporus belongs to the Agaricaceae family, and it is a top-ranked cultivated mushroom that is well known for its edibility. A. bisporus is rich in nutrients such as carbohydrates, amino acids, fats, and minerals and has potential anticancer, antioxidant, anti-obesity, and anti-inflammation properties. The bioactive compounds extracted from this mushroom can be used for the treatment of several common human diseases including cancer, bacterial and fungal infections, diabetes, heart disorder, and skin problems. A. bisporus has opened new horizons for the world to explore mushrooms as far as their culinary and medicinal values are concerned. In recent years, tyrosinase and ergothioneine have been extracted from this mushroom, which has made this mushroom worth considering more for nutritional and medicinal purposes. To emphasize various aspects of A. bisporus, a comprehensive review highlighting the nutritional, medicinal, and cosmetic values and finding out the research gaps is presented. In this way, it would be possible to improve the quality and quantity of bioactive compounds in A. bisporus, ultimately contributing to the discovery of new drugs and the responsible mechanisms. In the present review, we summarize the latest advancements regarding the nutritional, pharmaceutical, and cosmetic properties of A. bisporus. Moreover, research gaps with future research directions are also discussed.

Food Matrix Effects for Modulating Starch Bioavailability

As the prevalence of obesity and diabetes has continued to increase rapidly in recent years, dietary approaches to regulating glucose homeostasis have gained more attention. Starch is the major source of glucose in the human diet and can have diverse effects, depending on its rate and extent of digestion in the small intestine, on postprandial glycemic response, which over time is associated with blood glucose abnormalities, insulin sensitivity, and even appetitive response and food intake. The classification of starch bioavailability into rapidly digestible starch, slowly digestible starch, and resistant starch highlights the nutritional values of different starches. As starch is the main structure-building macroconstituent of foods, its bioavailability can be manipulated by selection of food matrices with varying degrees of susceptibility to amylolysis and food processing to retain or develop new matrices. In this review, the food factors that may modulate starch bioavailability, with a focus on food matrices, are assessed for a better understanding of their potential contribution to human health. Aspects affecting starch nutritional properties as well as production strategies for healthy foods are also reviewed, e.g., starch characteristics (different type, structure, and modification), food physical properties (food form, viscosity, and integrity), food matrix interactions (lipid, protein, nonstarch polysaccharide, phytochemicals, organic acid, and enzyme inhibitor), and food processing (milling, cooking, and storage).

A rational approach to COVID-19

It is crucial to use the wealth of information emerging from the ongoing SARS-CoV-2 pandemic and confront COVID-19 with a rational approach. There are proactive steps to prevent and fight COVID-19. Management of the disease should be according to clinical features and laboratory test markers and personalized therapeutic targets.

Understanding connections and roles of gut microbiome in cardiovascular diseases

The gut microbiome encompasses trillions of residing microbes, mainly bacteria, which play a crucial role in maintaining the physiological and metabolic health of the host. The gut microbiome has been associated with several diseases, including cardiovascular disease (CVD). A growing body of evidence suggests that an altered gut environment and gut-microbiome-derived metabolites are associated with CVD events. The gut microbiome communicates with host physiology through different mechanisms, including trimethylamine N-oxide generation, primary and secondary bile acid metabolism pathways, and short-chain fatty acids production. The main focus of this review is to understand the association of the gut microbiome with CVD and its implications on the interactions between the gut microbiome and the host. Manipulation of the gut microbiome through specific dietary intervention is a simple approach to identifying novel targets for therapy or better dietary recommendations, and new preventive measures for screening biomarkers to reduce CVD risk in humans.

Short-Chain Fatty Acids and Their Association with Signalling Pathways in Inflammation, Glucose and Lipid Metabolism

Short-chain fatty acids (SCFAs), particularly acetate, propionate and butyrate, are mainly produced by anaerobic fermentation of gut microbes. SCFAs play an important role in regulating energy metabolism and energy supply, as well as maintaining the homeostasis of the intestinal environment. In recent years, many studies have shown that SCFAs demonstrate physiologically beneficial effects, and the signalling pathways related to SCFA production, absorption, metabolism, and intestinal effects have been discovered. Two major signalling pathways concerning SCFAs, G-protein-coupled receptors (GPRCs) and histone deacetylases (HDACs), are well recognized. In this review, we summarize the recent advances concerning the biological properties of SCFAs and the signalling pathways in inflammation and glucose and lipid metabolism.

Short chain fatty acids in human gut and metabolic health

Evidence is accumulating that short chain fatty acids (SCFA) play an important role in the maintenance of gut and metabolic health. The SCFA acetate, propionate and butyrate are produced from the microbial fermentation of indigestible carbohydrates and appear to be key mediators of the beneficial effects elicited by the gut microbiome. Microbial SCFA production is essential for gut integrity by regulating the luminal pH, mucus production, providing fuel for epithelial cells and effects on mucosal immune function. SCFA also directly modulate host metabolic health through a range of tissue-specific mechanisms related to appetite regulation, energy expenditure, glucose homeostasis and immunomodulation. Therefore, an increased microbial SCFA production can be considered as a health benefit, but data are mainly based on animal studies, whereas well-controlled human studies are limited. In this review an expert group by ILSI Europe’s Prebiotics Task Force discussed the current scientific knowledge on SCFA to consider the relationship between SCFA and gut and metabolic health with a particular focus on human evidence. Overall, the available mechanistic data and limited human data on the metabolic consequences of elevated gut-derived SCFA production strongly suggest that increasing SCFA production could be a valuable strategy in the preventing gastro-intestinal dysfunction, obesity and type 2 diabetes mellitus. Nevertheless, there is an urgent need for well controlled longer term human SCFA intervention studies, including measurement of SCFA fluxes and kinetics, the heterogeneity in response based on metabolic phenotype, the type of dietary fibre and fermentation site in fibre intervention studies and the control for factors that could shape the microbiome like diet, physical activity and use of medication.

The short-chain fatty acid propionate increases glucagon and FABP4 production, impairing insulin action in mice and humans

The short-chain fatty acid propionate is a potent inhibitor of molds that is widely used as a food preservative and endogenously produced by gut microbiota. Although generally recognized as safe by the U.S. Food and Drug Administration, the metabolic effects of propionate consumption in humans are unclear. Here, we report that propionate stimulates glycogenolysis and hyperglycemia in mice by increasing plasma concentrations of glucagon and fatty acid-binding protein 4 (FABP4). Fabp4-deficient mice and mice lacking liver glucagon receptor were protected from the effects of propionate. Although propionate did not directly promote glucagon or FABP4 secretion in ex vivo rodent pancreatic islets and adipose tissue models, respectively, it activated the sympathetic nervous system in mice, leading to secretion of these hormones in vivo. This effect could be blocked by the pharmacological inhibition of norepinephrine, which prevented propionate-induced hyperglycemia in mice. In a randomized, double-blind, placebo-controlled study in humans, consumption of a propionate-containing mixed meal resulted in a postprandial increase in plasma glucagon, FABP4, and norepinephrine, leading to insulin resistance and compensatory hyperinsulinemia. Chronic exposure of mice to a propionate dose equivalent to that used for food preservation resulted in gradual weight gain. In humans, plasma propionate decreased with weight loss in the Dietary Intervention Randomized Controlled Trial (DIRECT) and served as an independent predictor of improved insulin sensitivity. Thus, propionate may activate a catecholamine-mediated increase in insulin counter-regulatory signals, leading to insulin resistance and hyperinsulinemia, which, over time, may promote adiposity and metabolic abnormalities. Further evaluation of the metabolic consequences of propionate consumption is warranted.

Supplementation of a propionate-producing consortium improves markers of insulin resistance in an in vitro model of gut-liver axis

Gut-liver cross talk is an important determinant of human health with profound effects on energy homeostasis. While gut microbes produce a huge range of metabolites, specific compounds such as short-chain fatty acids (SCFAs) can enter the portal circulation and reach the liver (Brandl K, Schnabl B. Curr Opin Gastroenterol 33: 128-133, 2017), a central organ involved in glucose homeostasis and diabetes control. Propionate is a major SCFA involved in activation of intestinal gluconeogenesis (IGN), thereby regulating food intake, enhancing insulin sensitivity, and leading to metabolic homeostasis. Although microbiome-modulating strategies may target the increased microbial production of propionate, it is not clear whether such an effect spreads through to the hepatic cellular level. Here, we designed a propionate-producing consortium using a selection of commensal gut bacteria, and we investigated how their delivered metabolites impact an in vitro enterohepatic model of insulin resistance. Glycogen storage on hepatocyte-like cells and inflammatory markers associated with insulin resistance were evaluated to understand the role of gut metabolites on gut-liver cross talk in a simulated scenario of insulin resistance. The metabolites produced by our consortium increased glycogen synthesis by ~57% and decreased proinflammatory markers such as IL-8 by 12%, thus elucidating the positive effect of our consortium on metabolic function and low-grade inflammation. Our results suggest that microbiota-derived products can be a promising multipurpose strategy to modulate energy homeostasis, with the potential ability to assist in managing metabolic diseases due to their adaptability.

Effects of dietary grape pomace on the intestinal microbiota and growth performance of weaned piglets

Grape pomace (GP) is an abundant by-product from wine production and is rich in phenolic compounds, unsaturated fatty acids, dietary fibre and beneficial bacteria. In this study, weaned piglets were fed a basic diet supplemented with 5% GP for 4 weeks. Compared with those in the control (CON) group, it was found that the proportion of Lactobacillus delbrueckii, Olsenella umbonata and Selenomonas bovis in the caecum and the villus height and villus height/crypt depth ratio (VCR) of the jejunum were both significantly increased in the GP group (p < 0.05). Meanwhile, at the mRNA expression level, several proinflammatory cytokines (IL-1β, IL-8, IL-6 and TNF-α) were significantly downregulated (p < 0.05) in piglet caecal tissue, and the short-chain fatty acid receptors (GPR41 and GPR43) were not significantly upregulated. In contrast, the levels of IgG was significantly increased (p < 0.05) in the sera of weaned piglets in the GP group. However, no difference in growth performance between the two groups of piglets was detected. These results show that GP had no adverse effects on the growth performance of piglets, but GP can promote the content of some beneficial bacteria in the caecum; this effect is conducive to improving the disease resistance potential of piglets.

The Relationship between Circulating Acetate and Human Insulin Resistance before and after Weight Loss in the DiOGenes Study

Microbially-produced acetate has been reported to beneficially affect metabolic health through effects on satiety, energy expenditure, insulin sensitivity, and substrate utilization. Here, we investigate the association between sex-specific concentrations of acetate and insulin sensitivity/resistance indices (Homeostatic Model Assessment of Insulin Resistance (HOMA-IR), circulating insulin and Matsuda Index) in the Diet, Obesity and Genes (DiOGenes) Dietary study at baseline and after a low-calorie diet (LCD, 800 kcal/d). In this analysis, 692 subjects (Body Mass Index >27 kg/m²) were included, who underwent an LCD for 8 weeks. Linear mixed models were performed, which were adjusted for mean acetate concentration, center (random factor), age, weight loss, and fat-free mass (FFM). At baseline, no associations between plasma acetate and insulin sensitivity/resistance indices were found. We found a slight positive association between changes in acetate and changes in HOMA-IR (std 0.130, p = 0.033) in women, but not in men (std -0.072, p = 0.310) independently of age, weight loss and FFM. We were not able to confirm previously reported associations between acetate and insulin sensitivity in this large European cohort. The mechanisms behind the sex-specific relationship between LCD-induced changes in acetate and insulin sensitivity require further study.

The Gut Microbiota Affects Host Pathophysiology as an Endocrine Organ: A Focus on Cardiovascular Disease

It is widely recognized that the microorganisms inhabiting our gastrointestinal tract-the gut microbiota-deeply affect the pathophysiology of the host. Gut microbiota composition is mostly modulated by diet, and gut microorganisms communicate with the different organs and tissues of the human host by synthesizing hormones and regulating their release. Herein, we will provide an updated review on the most important classes of gut microbiota-derived hormones and their sensing by host receptors, critically discussing their impact on host physiology. Additionally, the debated interplay between microbial hormones and the development of cardiovascular disease will be thoroughly analysed and discussed.

The impact of dietary fiber and probiotics in infectious diseases

Although antibiotics are commonly used to treat infectious diseases, emergence of antibiotic resistant strains highlights the necessity for developing novel alternative approaches. Meanwhile, clinically, antibiotics can destroy the gut microbes balance, which is not conducive to the recovery of infectious disorders. As a result, recent studies have begun to explore potential prevention and treatment methods for infectious diseases, starting with more readily available dietary fiber and probiotics. Moreover, researches have shown the personalized nature of host responses to dietary fiber intervention, with outcomes being dependent on individual pre-treatment gut microbes. In this review, we will focus on the roles of dietary fiber and probiotics on infectious diseases, how probiotics and dietary fiber work on infectious diseases and then explore their mechanisms, so as to guide clinical consideration of new therapies for infectious diseases.

The Cholesterol-Lowering Effect of Oats and Oat Beta Glucan: Modes of Action and Potential Role of Bile Acids and the Microbiome

Consumption of sufficient quantities of oat products has been shown to reduce host cholesterol and thereby modulate cardiovascular disease risk. The effects are proposed to be mediated by the gel-forming properties of oat β-glucan which modulates host bile acid and cholesterol metabolism and potentially removes intestinal cholesterol for excretion. However, the gut microbiota has emerged as a major factor regulating cholesterol metabolism in the host. Oat β-glucan has been shown to modulate the gut microbiota, particularly those bacterial species that influence host bile acid metabolism and production of short chain fatty acids, factors which are regulators of host cholesterol homeostasis. Given a significant role for the gut microbiota in cholesterol metabolism it is likely that the effects of oat β-glucan on the host are multifaceted and involve regulation of microbe-host interactions at the gut interface. Here we consider the potential for oat β-glucan to influence microbial populations in the gut with potential consequences for bile acid metabolism, reverse cholesterol transport (RCT), short-chain fatty acid (SCFA) production, bacterial metabolism of cholesterol and microbe-host signaling.

Mitochondrial Substrate-Level Phosphorylation as Energy Source for Glioblastoma: Review and Hypothesis

Glioblastoma multiforme (GBM) is the most common and malignant of the primary adult brain cancers. Ultrastructural and biochemical evidence shows that GBM cells exhibit mitochondrial abnormalities incompatible with energy production through oxidative phosphorylation (OxPhos). Under such conditions, the mitochondrial F0-F1 ATP synthase operates in reverse at the expense of ATP hydrolysis to maintain a moderate membrane potential. Moreover, expression of the dimeric M2 isoform of pyruvate kinase in GBM results in diminished ATP output, precluding a significant ATP production from glycolysis. If ATP synthesis through both glycolysis and OxPhos was impeded, then where would GBM cells obtain high-energy phosphates for growth and invasion? Literature is reviewed suggesting that the succinate-CoA ligase reaction in the tricarboxylic acid cycle can substantiate sufficient ATP through mitochondrial substrate-level phosphorylation (mSLP) to maintain GBM growth when OxPhos is impaired. Production of high-energy phosphates would be supported by glutaminolysis—a hallmark of GBM metabolism—through the sequential conversion of glutamine → glutamate → alpha-ketoglutarate → succinyl CoA → succinate. Equally important, provision of ATP through mSLP would maintain the adenine nucleotide translocase in forward mode, thus preventing the reverse-operating F0-F1 ATP synthase from depleting cytosolic ATP reserves. Because glucose and glutamine are the primary fuels driving the rapid growth of GBM and most tumors for that matter, simultaneous restriction of these two substrates or inhibition of mSLP should diminish cancer viability, growth, and invasion.

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.

Propionate suppresses hepatic gluconeogenesis via GPR43/AMPK signaling pathway

Short-chain fatty acids (SCFAs) such as acetate, propionate, and butyrate are generated by gut microbial fermentation of dietary fiber. SCFAs may exert multiple beneficial effects on human lipid and glucose metabolism. However, their actions and underlying mechanisms are not fully elucidated. In this study, we examined the direct effects of propionate on hepatic glucose and lipid metabolism using human HepG2 hepatocytes. Here, we demonstrate that propionate at a physiologically-relevant concentration effectively suppresses palmitate-enhanced glucose production in HepG2 cells but does not affect intracellular neutral lipid levels. Our results indicated that propionate can decline in gluconeogenesis by down-regulation of glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK) through activation of AMP-activated protein kinase (AMPK), which is a major regulator of the hepatic glucose metabolism. Mechanistic studies also revealed that propionate-stimulated AMPK phosphorylation can be ascribed to Ca²⁺/calmodulin-dependent protein kinase kinase β (CaMKKβ) activation in response to an increase in intracellular Ca²⁺ concentration. Moreover, siRNA-mediated knockdown of the propionate receptor GPR43 prevented propionate-inducible activation of AMPK and abrogates the gluconeogenesis-inhibitory action. Thus, our data indicate that the binding of propionate to hepatic GPR43 elicits CaMKKβ-dependent activation of AMPK through intracellular Ca²⁺ increase, leading to suppression of gluconeogenesis. The present study suggests the potential efficacy of propionate in preventive and therapeutic management of diabetes.

Obesity, Motility, Diet, and Intestinal Microbiota-Connecting the Dots

PURPOSE OF REVIEW

The goal of the present review is to explore the relationship between dietary changes and alterations in gut microbiota that contribute to disorders of gut motility and obesity.

RECENT FINDINGS

We review the microbiota changes that are seen in obesity, diarrhea, and constipation and look at potential mechanisms of how dysbiosis can predispose to these. We find that microbial metabolites, particularly short chain fatty acids, can lead to signaling changes in the host enterocytes. Microbial alteration leading to both motility disorders and obesity may be mediated by the release of hormones including glucagon-like peptides 1 and 2 (GLP-1, GLP-2) and polypeptide YY (PYY). These pathways provide avenues for microbiota-targeted interventions that can treat both disorders of motility and obesity. In summary, multiple mechanisms contribute to the interplay between the microbial dysbiosis, obesity, and dysmotility.

Review article: dietary fibre in the era of microbiome science

BACKGROUND

Explanations for the health benefits of dietary fibre have, in the past, been inconsistent and studies of the physiological effects of dietary fibre were, perhaps, directed at the wrong read-outs. Confounding factors included a failure to appreciate the molecular diversity and varied properties of fibre-types and the role of fibre as a substrate for microbial metabolism in the gut.

AIM

To present a modern perspective on fibre science and to encourage clinicians to re-consider the health impact of dietary fibre and how best to approach adjustments in dietary consumption.

METHODS

This perspective is drawn selectively from recent microbiome science; no attempt was made to perform an exhaustive review of all articles related to every aspect of dietary fibre.

RESULTS

Advances in microbiome science have revealed not only the functional impact of dietary fibre on the composition and function of the microbiota but have also demonstrated the physiologic responses to microbial-derived metabolites from fibre digestion. Moreover, studies have shown the personalised nature of host responses to dietary fibre intervention, with outcomes being dependent on individual pre-treatment gut ecology.

CONCLUSIONS

The physical properties of dietary fibres are important for homeostasis within the gut, but the predominant health benefits extend beyond the gut to enhanced metabolic welfare, including protection against obesity and related metabolic diseases. Fibre is a form of functional food joining a growing list of examples of diet-microbe-host interactions which link microbe-host metabolic and immune cascades.

Interorgan Metabolic Crosstalk in Human Insulin Resistance

Excessive energy intake and reduced energy expenditure drive the development of insulin resistance and metabolic diseases such as obesity and type 2 diabetes mellitus. Metabolic signals derived from dietary intake or secreted from adipose tissue, gut, and liver contribute to energy homeostasis. Recent metabolomic studies identified novel metabolites and enlarged our knowledge on classic metabolites. This review summarizes the evidence of their roles as mediators of interorgan crosstalk and regulators of insulin sensitivity and energy metabolism. Circulating lipids such as free fatty acids, acetate, and palmitoleate from adipose tissue and short-chain fatty acids from the gut effectively act on liver and skeletal muscle. Intracellular lipids such as diacylglycerols and sphingolipids can serve as lipotoxins by directly inhibiting insulin action in muscle and liver. In contrast, fatty acid esters of hydroxy fatty acids have been recently shown to exert a series of beneficial effects. Also, ketoacids are gaining interest as potent modulators of insulin action and mitochondrial function. Finally, branched-chain amino acids not only predict metabolic diseases, but also inhibit insulin signaling. Here, we focus on the metabolic crosstalk in humans, which regulates insulin sensitivity and energy homeostasis in the main insulin-sensitive tissues, skeletal muscle, liver, and adipose tissue.

A selective gut bacterial bile salt hydrolase alters host metabolism

The human gut microbiota impacts host metabolism and has been implicated in the pathophysiology of obesity and metabolic syndromes. However, defining the roles of specific microbial activities and metabolites on host phenotypes has proven challenging due to the complexity of the microbiome-host ecosystem. Here, we identify strains from the abundant gut bacterial phylum Bacteroidetes that display selective bile salt hydrolase (BSH) activity. Using isogenic strains of wild-type and BSH-deleted Bacteroides thetaiotaomicron, we selectively modulated the levels of the bile acid tauro-β-muricholic acid in monocolonized gnotobiotic mice. B. thetaiotaomicron BSH mutant-colonized mice displayed altered metabolism, including reduced weight gain and respiratory exchange ratios, as well as transcriptional changes in metabolic, circadian rhythm, and immune pathways in the gut and liver. Our results demonstrate that metabolites generated by a single microbial gene and enzymatic activity can profoundly alter host metabolism and gene expression at local and organism-level scales.

Microbial Fermentation of Starch: Its Impact on the Range of Acceptable Carbohydrate Intake

Starch, a major source of carbohydrates in human nutrition, is extensively hydrolyzed in the gastrointestinal tract of children and adults. A small fraction of the ingested starch reaches the cecum and colon where it is fermented by the gut microbiome into short-chain fatty acids (SCFA) and other products. Recent data in humans and in animal models have demonstrated the extensive effects of short-chain fatty acids on whole body energy metabolism, appetite, insulin resistance, fatty acid oxidation, fat accretion, obesity, and diabetes. Clear discernible effects of SCFA on the rates of production of glucose, its oxidation and uptake in the fasting state were, however, not observed. In the fed state, the effects on glucose metabolism are related to the effects of SCFA on insulin sensitivity, possibly the consequence of their influence on lipid metabolism. The suggested limits of carbohydrate intake were based upon the kinetics and metabolism of glucose in the basal state and on the responses to glucose administration. It is postulated that in healthy subjects, the present data do not suggest any significant impact of microbial fermentation of starch on the range of acceptable intake of carbohydrates.

Differential metabolic effects of oral butyrate treatment in lean versus metabolic syndrome subjects

Background

Gut microbiota-derived short-chain fatty acids (SCFAs) have been associated with beneficial metabolic effects. However, the direct effect of oral butyrate on metabolic parameters in humans has never been studied. In this first in men pilot study, we thus treated both lean and metabolic syndrome male subjects with oral sodium butyrate and investigated the effect on metabolism.

Methods

Healthy lean males (n = 9) and metabolic syndrome males (n = 10) were treated with oral 4 g of sodium butyrate daily for 4 weeks. Before and after treatment, insulin sensitivity was determined by a two-step hyperinsulinemic euglycemic clamp using [6,6-²H₂]-glucose. Brown adipose tissue (BAT) uptake of glucose was visualized using ¹⁸F-FDG PET-CT. Fecal SCFA and bile acid concentrations as well as microbiota composition were determined before and after treatment.

Results

Oral butyrate had no effect on plasma and fecal butyrate levels after treatment, but did alter other SCFAs in both plasma and feces. Moreover, only in healthy lean subjects a significant improvement was observed in both peripheral (median Rd: from 71 to 82 µmol/kg min, p < 0.05) and hepatic insulin sensitivity (EGP suppression from 75 to 82% p < 0.05). Although BAT activity was significantly higher at baseline in lean (SUVmax: 12.4 ± 1.8) compared with metabolic syndrome subjects (SUVmax: 0.3 ± 0.8, p < 0.01), no significant effect following butyrate treatment on BAT was observed in either group (SUVmax lean to 13.3 ± 2.4 versus metabolic syndrome subjects to 1.2 ± 4.1).

Conclusions

Oral butyrate treatment beneficially affects glucose metabolism in lean but not metabolic syndrome subjects, presumably due to an altered SCFA handling in insulin-resistant subjects. Although preliminary, these first in men findings argue against oral butyrate supplementation as treatment for glucose regulation in human subjects with type 2 diabetes mellitus.

Microbiome-host systems interactions: protective effects of propionate upon the blood-brain barrier

BACKGROUND

Gut microbiota composition and function are symbiotically linked with host health and altered in metabolic, inflammatory and neurodegenerative disorders. Three recognised mechanisms exist by which the microbiome influences the gut-brain axis: modification of autonomic/sensorimotor connections, immune activation, and neuroendocrine pathway regulation. We hypothesised interactions between circulating gut-derived microbial metabolites, and the blood-brain barrier (BBB) also contribute to the gut-brain axis. Propionate, produced from dietary substrates by colonic bacteria, stimulates intestinal gluconeogenesis and is associated with reduced stress behaviours, but its potential endocrine role has not been addressed.

RESULTS

After demonstrating expression of the propionate receptor FFAR3 on human brain endothelium, we examined the impact of a physiologically relevant propionate concentration (1 μM) on BBB properties in vitro. Propionate inhibited pathways associated with non-specific microbial infections via a CD14-dependent mechanism, suppressed expression of LRP-1 and protected the BBB from oxidative stress via NRF2 (NFE2L2) signalling.

CONCLUSIONS

Together, these results suggest gut-derived microbial metabolites interact with the BBB, representing a fourth facet of the gut-brain axis that warrants further attention.

The regulation of host cellular and gut microbial metabolism in the development and prevention of colorectal cancer

Metabolism regulation is crucial in colorectal cancer (CRC) and has emerged as a remarkable field currently. The cellular metabolism of glucose, amino acids and lipids in CRC are all reprogrammed. Each of them changes tumour microenvironment, modulates bacterial composition and activity, and eventually promotes CRC development. Metabolites such as short chain fatty acids, secondary bile acids, N-nitroso compounds, hydrogen sulphide, polyphenols and toxins like fragilysin, FadA, cytolethal distending toxin and colibactin play a dual role in CRC. The relationship of gut microbe-metabolite is essential in remodelling intestinal microbial ecology composition and metabolic activity. It regulates the metabolism of colonic epithelial cells and changes the tumour microenvironment in CRC. Microbial metabolism manipulation has been considered to be potentially preventive in CRC, but more large-scale clinical trials are required before their application in clinical practice in the near future.

Physical exercise, gut, gut microbiota, and atherosclerotic cardiovascular diseases

Arteriosclerotic cardiovascular diseases (ASCVDs) are the leading cause of morbidity and mortality worldwide and its risk can be independently decreased by regular physical activity. Recently, ASCVD and its risk factors were found to be impacted by the gut microbiota through its diversity, distribution and metabolites. Meanwhile, several experiments demonstrated the relationship between physical exercise and diversity, distribution, metabolite of the gut microbiota as well as its functions on the lipid metabolism and chronic systematic inflammation. In this review, we summarize the current knowledge on the effects of physical exercise on ASCVD through modulation of the gut microbiota and intestinal function.

Anthropometric and metabolic improvements in human type 2 diabetes after introduction of an Okinawan-based Nordic diet are not associated with changes in microbial diversity or SCFA concentrations

The Okinawan-based Nordic (O-BN) diet improves anthropometry and metabolism in type 2 diabetes mellitus (T2DM) patients. The aim of this study was to study mechanisms behind improvements by examining Enterobacteriaceae abundance, microbial diversity, and concentrations of short-chain fatty acids (SCFAs). A secondary aim was exploring if metformin treatment affects microbiota or SCFAs. Thirty T2DM patients received the O-BN diet for 12 weeks. Faecal and blood samples were collected at baseline, 12 and 28 weeks. Although patients experienced weight loss and improved metabolic parameters, there were no significant changes in Enterobacteriaceae abundance or microbial diversity. Patients on metformin displayed higher Enterobacteriaceae abundance throughout the study (p = .008, p = .038, and p = .001, respectively). Isovaleric acid was decreased after 12 weeks (p = .018). Butyric acid was decreased at follow-up (p = .007). Improved anthropometry and metabolism in T2DM after introduction of the O-BN diet is not associated with changes in Enterobacteriaceae abundance, microbial diversity or SCFA concentrations.

Evaluating the contribution of gut microbiome to the variance of porcine serum glucose and lipid concentration

Serum glucose and lipids are important indicators for host metabolic condition. Interaction of host and gut microbes regulates the metabolism process. However, how much the gut microbiome contributes to the variance of serum glucose and lipids is largely unknown. Here we carried out a 16S rRNA gene based association study between cecum microbiome and the concentration of serum glucose and lipids in 240 Chinese Erhualian pigs. We identified tens of bacterial taxa associated with serum glucose and lipids. The butyrate-producing bacteria were significantly associated with serum glucose level. The pathogenic bacteria belonging to Proteobacteria and Fusobacteria showed significant associations with increased serum lipid levels, while the bacteria Lactobacillus and Bacilli had negative correlations with serum lipids. Cross-validation analysis revealed that 23.8% variation of serum glucose and 1.6%~6.0% variations of serum lipids were explained by gut microbiome. Furthermore, predicted function capacities related to nutrition intake, transport and carbohydrate metabolism were significantly associated with serum glucose level, while the pathways related to antioxidant metabolism and bile synthesis tended to be associated with serum lipid level. The results provide meaningful information to get insight into the effect of gut microbiome on serum glucose and lipid levels in pigs.

Microbiome, probiotics and neurodegenerative diseases: deciphering the gut brain axis

The gut microbiota is essential to health and has recently become a target for live bacterial cell biotherapies for various chronic diseases including metabolic syndrome, diabetes, obesity and neurodegenerative disease. Probiotic biotherapies are known to create a healthy gut environment by balancing bacterial populations and promoting their favorable metabolic action. The microbiota and its respective metabolites communicate to the host through a series of biochemical and functional links thereby affecting host homeostasis and health. In particular, the gastrointestinal tract communicates with the central nervous system through the gut-brain axis to support neuronal development and maintenance while gut dysbiosis manifests in neurological disease. There are three basic mechanisms that mediate the communication between the gut and the brain: direct neuronal communication, endocrine signaling mediators and the immune system. Together, these systems create a highly integrated molecular communication network that link systemic imbalances with the development of neurodegeneration including insulin regulation, fat metabolism, oxidative markers and immune signaling. Age is a common factor in the development of neurodegenerative disease and probiotics prevent many harmful effects of aging such as decreased neurotransmitter levels, chronic inflammation, oxidative stress and apoptosis-all factors that are proven aggravators of neurodegenerative disease. Indeed patients with Parkinson's and Alzheimer's diseases have a high rate of gastrointestinal comorbidities and it has be proposed by some the management of the gut microbiota may prevent or alleviate the symptoms of these chronic diseases.

Distinct patterns in the gut microbiota after surgical or medical therapy in obese patients

Bariatric surgery is highly successful in improving health compared to conventional dietary treatments. It has been suggested that the gut microbiota is a relevant factor in weight loss after bariatric surgery. Considering that bariatric procedures cause different rearrangements of the digestive tract, they probably have different effects on the gut microbiota. In this study, we compared the impact of medical treatment, sleeve gastrectomy and Roux-en-Y gastric bypass on the gut microbiota from obese subjects. Anthropometric and clinical parameters were registered before, 6 and 12 months after treatment. Fecal samples were collected and microbiota composition was studied before and six months post treatment using 16S rRNA gene sequencing and qPCR. In comparison to dietary treatment, changes in intestinal microbiota were more pronounced in patients subjected to surgery, observing a bloom in Proteobacteria. Interestingly, Bacteroidetes abundance was largely different after six months of each surgical procedure. Furthermore, changes in weight and BMI, or glucose metabolism, correlated positively with changes in these two phyla in these surgical procedures. These results indicate that distinct surgical procedures alter the gut microbiota differently, and changes in gut microbiota might contribute to health improvement. This study contributes to our understanding of the impact of weight loss surgery on the gut microbiota, and could be used to replicate this effect using targeted therapies.

Odd-chain fatty acids as a biomarker for dietary fiber intake: a novel pathway for endogenous production from propionate

Background: The risk of type 2 diabetes is inversely correlated with plasma concentrations of odd-chain fatty acids [OCFAs; pentadecanoic acid (15:0) and heptadecanoic acid (17:0)], which are considered as biomarkers for dairy fat intake in humans. However, rodent studies suggest that OCFAs are synthesized endogenously from gut-derived propionate. Propionate increases with dietary fiber consumption and has been shown to improve insulin sensitivity.Objective: We hypothesized that OCFAs are produced in humans from dietary fibers by a novel endogenous pathway.Design: In a randomized, double-blind crossover study, 16 healthy individuals were supplemented with cellulose (30 g/d), inulin (30 g/d), or propionate (6 g/d) for 7 d. In addition, human hepatoma cells were incubated with different propionate concentrations. OCFAs were determined in plasma phospholipids and hepatoma cells by gas chromatography.Results: Cellulose did not affect plasma OCFA levels, whereas inulin and propionate increased pentadecanoic acid by ∼17% (P < 0.05) and 13% (P = 0.05), respectively. The effect on heptadecanoic acid was even more pronounced, because it was elevated in almost all participants by inulin (11%; P < 0.01) and propionate (13%; P < 0.001). Furthermore, cell culture experiments showed a positive association between propionate and OCFA levels (R² = 0.99, P < 0.0001), whereas palmitate (16:0) was negatively correlated (R² = 0.83, P = 0.004).Conclusions: Our data show that gut-derived propionate is used for the hepatic synthesis of OCFAs in humans. The association of OCFAs with a decreased risk of type 2 diabetes may therefore also relate to dietary fiber intake and not only dairy fat. This trial was registered at www.germanctr.de as DRKS00010121.

The interplay between host immune cells and gut microbiota in chronic inflammatory diseases

Many benefits provided by the gut microbiota to the host rely on its intricate interactions with host cells. Perturbations of the gut microbiota, termed gut dysbiosis, affect the interplay between the gut microbiota and host cells, resulting in dysregulation of inflammation that contributes to the pathogenesis of chronic inflammatory diseases, including inflammatory bowel disease, multiple sclerosis, allergic asthma and rheumatoid arthritis. In this review, we provide an overview of how gut bacteria modulates host metabolic and immune functions, summarize studies that examined the roles of gut dysbiosis in chronic inflammatory diseases, and finally discuss measures to correct gut dysbiosis as potential therapeutics for chronic inflammatory diseases.

Deacetylated Konjac Glucomannan Is Less Effective in Reducing Dietary-Induced Hyperlipidemia and Hepatic Steatosis in C57BL/6 Mice

Konjac gel foods that mainly consist of deacetylated konjac glucomannan (Da-KGM) are considered to have the same health benefits as native konjac glucomannan (KGM); however, no definitive data support this notion. The objective of this study was to compare the effects of Da-KGM and KGM on the hyperlipidemia and liver steatosis induced by high-fat diet feeding and to investigate the underlying molecular mechanisms. C57BL/6 mice were fed (1) normal chow diet, (2) high-fat diet, (3) HFD with KGM, or (4) HFD with Da-KGM for 10 weeks. KGM, but not Da-KGM, showed decreased fat accumulation, improved blood and liver lipid profiles, and prevention of liver lipid droplet deposition compared with HFD. Compared with Da-KGM, KGM increased the outputs of fecal bile acid (KGM 22.5 ± 2.34 mg/g vs Da-KGM 19.3 ± 1.87 mg/g), fat (KGM 5.56 ± 0.68 mg/g vs Da-KGM 4.42 ± 0.57 mg/g) and cholesterol (KGM2.67 ± 0.43 mg/g vs Da-KGM 1.78 ± 0.28 mg/g), fecal concentrations of total short-chain fatty acids (KGM 103 ± 14.8 μmol/g vs Da-KGM 74.5 ± 8.49 μmol/g), and improved hepatic antioxidant status and upregulated CYP7A1 and LDLR gene expression. These findings suggest that deacetylation of KGM negatively affects its fermentation characteristics and its inhibition of lipid absorption, which thereby reduces Da-KGM's health benefits.

Fecal microbiota transplantation in metabolic syndrome: History, present and future

The history of fecal microbiota transplantation (FMT) dates back even to ancient China. Recently, scientific studies have been looking into FMT as a promising treatment of various diseases, while in the process teaching us about the interaction between the human host and its resident microbial communities. Current research focuses mainly on Clostridium difficile infections, however interest is rising in other areas such as inflammatory bowel disease (IBD) and the metabolic syndrome. With regard to the latter, the intestinal microbiota might be causally related to the progression of insulin resistance and diabetes. FMT in metabolic syndrome has proven to be an intriguing method to study the role of the gut microbiota and open the way to new therapies by dissecting in whom insulin resistance is driven by microbiota. In this article we review the history of FMT, the present evidence on its role in the pathophysiology of metabolic syndrome and its efficacy, limitations and future prospects.

The Effects of Moderate Whole Grain Consumption on Fasting Glucose and Lipids, Gastrointestinal Symptoms, and Microbiota

This study was designed to determine if providing wheat, corn, and rice as whole (WG) or refined grains (RG) under free-living conditions will change parameters of health over a six-week intervention in healthy, habitual non-WG consumers. Measurements of body composition, fecal microbiota, fasting blood glucose, total cholesterol, high density lipoprotein (HDL), low density lipoprotein (LDL), and triglycerides were made at baseline and post intervention. Subjects were given adequate servings of either WG or RG products based on their caloric need and asked to keep records of grain consumption, bowel movements, and GI symptoms weekly. After six weeks, subjects repeated baseline testing. Significant decreases in total, LDL, and non-HDL cholesterol were seen after the WG treatments but were not observed in the RG treatment. During Week 6, bowel movement frequency increased with increased WG consumption. No significant differences in microbiota were seen between baseline and post intervention, although, abundance of order Erysipelotrichales increased in RG subjects who ate more than 50% of the RG market basket products. Increasing consumption of WGs can alter parameters of health, but more research is needed to better elucidate the relationship between the amount consumed and the health-related outcome.