Faecal microbial metabolites of proteolytic and saccharolytic fermentation in relation to degree of insulin resistance in adult individuals

Association of branched-chain fatty acids with metabolic syndrome: a systematic review and meta-analysis of observational studies

Background: branched-chain fatty acids (BCFAs) have recently emerged as a group of functional fatty acids that are widely distributed in various foodstuffs, including dairy products, ruminant meat products, and fermented foods. Several studies have investigated the differences in the levels of BCFAs among individuals with varying risks of metabolic syndrome (MetS). In this study, we conducted a meta-analysis to explore the relationship between BCFAs and MetS, and to assess the feasibility of BCFAs as potential biomarkers for diagnosing MetS. Methods: in accordance with the PRISMA guidelines, we conducted a systematic literature search on PubMed, Embase, and the Cochrane Library up to March 2023. Both longitudinal and cross-sectional studies were included. The quality of the longitudinal and cross-sectional studies was evaluated using the Newcastle-Ottawa Scale (NOS) and the Agency for Healthcare Research and Quality (AHRQ) criteria, respectively. Heterogeneity detection and sensitivity analysis of the included research literature were carried out using R 4.2.1 software with a random-effects model. Results: Our meta-analysis included 685 participants and revealed a significant negative correlation between the endogenous BCFAs (serum BCFAs and adipose tissue BCFAs) and the risk of developing MetS, with lower BCFA levels found in individuals at a high risk of MetS (WMD: -0.11%, 95% CI: [-0.12, -0.09] %, P < 0.0001). However, there was no difference in fecal BCFAs among different MetS risk groups (SMD: -0.36, 95% CI: [-1.32, 0.61], P = 0.4686). Conclusion: our study provides insights into the relationship between BCFAs and the risk of developing MetS, and lays the groundwork for the development of novel biomarkers for diagnosing MetS in the future.

Circulating Short-Chain Fatty Acids and Non-Alcoholic Fatty Liver Disease Severity in Patients with Type 2 Diabetes Mellitus

(1) Background: Non-alcoholic fatty liver disease (NAFLD) is a major global health concern. The increasing prevalence of NAFLD has been related to type 2 diabetes mellitus (T2D). However, the relationship between short-chain fatty acids (SCFAs) and NAFLD severity is ambiguous in T2D subjects. This study aimed to explore the association of SCFAs with the severity of NAFLD in T2D patients. (2) Methods: We employed echography to examine the severity of hepatic steatosis. The serum levels of nine SCFAs, namely, formate, acetate, propionate, butyrate, isobutyrate, methylbutyrate, valerate, isovalerate, and methylvalerate, were measured using gas chromatography mass spectrometry. (3) Results: A total of 259 T2D patients was enrolled in this cross-sectional study. Of these participants, 117 with moderate to severe NAFLD had lower levels of formate, isobutyrate, and methylbutyrate than the 142 without NAFLD or with mild NAFLD. Lower circulating levels of isobutyrate and methylbutyrate were associated with an increased severity of NAFLD. A relationship between NAFLD severity and circulating isobutyrate and methylbutyrate levels was found independently of a glycated hemoglobin (HbA1C) level of 7.0%. (4) Conclusion: Circulating levels of isobutyrate and methylbutyrate were significantly and negatively correlated with NAFLD severity in the enrolled T2D patients. SCFAs may be related to NAFLD severity in T2D patients.

A Combination of Acetate, Propionate, and Butyrate Increases Glucose Uptake in C2C12 Myotubes

BACKGROUND

Dietary fibers are subjected to saccharolytic fermentation by the gut microbiota, leading to the production of short chain fatty acids (SCFAs). SCFAs act as signaling molecules to different cells in the human body including skeletal muscle cells. The ability of SCFAs to induce multiple signaling pathways, involving nuclear erythroid 2-related factor 2 (Nrf2), may contribute to the redox balance, and thereby may be involved in glucose homeostasis. The aim of this study is to investigate whether SCFAs increase glucose uptake by upregulating the endogenous antioxidant glutathione (GSH) in C2C12 myotubes.

METHODS

C2C12 myotubes were exposed to 1, 5, or 20 mM of single (acetate, propionate, or butyrate) or mixtures of SCFAs for 24 h. Cytotoxicity, glucose uptake, and intracellular GSH levels were measured.

RESULTS

20 mM of mixture but not separate SCFAs induced cytotoxicity. Exposure to a mixture of SCFAs at 5 mM increased glucose uptake in myotubes, while 20 mM of propionate, butyrate, and mixtures decreased glucose uptake. Exposure to single SCFAs increased GSH levels in myotubes; however, SCFAs did not prevent the menadione-induced decrease in glucose uptake in myotubes.

CONCLUSIONS

The effect of SCFAs on modulating glucose uptake in myotubes is not associated with the effect on endogenous GSH levels.

Gut microbial response to host metabolic phenotypes

A large number of studies have proved that biological metabolic phenotypes exist objectively and are gradually recognized by humans. Gut microbes affect the host's metabolic phenotype. They directly or indirectly participate in host metabolism, physiology and immunity through changes in population structure, metabolite differences, signal transduction and gene expression. Obtaining comprehensive information and specific identification factors associated with gut microbiota and host metabolic phenotypes has become the focus of research in the field of gut microbes, and it has become possible to find new and effective ways to prevent or treat host metabolic diseases. In the future, precise treatment of gut microbes will become one of the new therapeutic strategies. This article reviews the content of gut microbes and carbohydrate, amino acid, lipid and nucleic acid metabolic phenotypes, including metabolic intermediates, mechanisms of action, latest research findings and treatment strategies, which will help to understand the relationship between gut microbes and host metabolic phenotypes and the current research status.