Capsaicin Improves Glucose Tolerance and Insulin Sensitivity Through Modulation of the Gut Microbiota‐Bile Acid‐FXR Axis in Type 2 Diabetic db/db Mice

Effects of Capsicum annuum supplementation on the components of metabolic syndrome: a systematic review and meta-analysis

Metabolic syndrome (MetS) has increasingly gained importance as the main risk factor for cardiovascular diseases and type II diabetes mellitus. Various natural compounds derived from plants are associated with beneficial effects on the incidence and progression of MetS. This study aimed to evaluate the effects of Capsicum annuum on factors related to MetS by assessing randomized controlled trials (written in English). We searched the online databases of PubMed, Embase, Google scholar, and Cochrane Library up to April 2020. 'Patient/Population, Intervention, Comparison and Outcomes' format was used to determine whether intervention with C. annuum supplementation compared with placebo supplementation had any effect on the components of MetS among participants. We considered standardized mean differences (SMD) with 95% confidence intervals (CI) as effect size measures using random-effects model. Analysis of the included 11 studies (n = 609) showed that C. annuum supplementation had significant effect on low density lipoprotein-cholesterol [SMD = - 0.39; 95% CI - 0.72, - 0.07; P = 0.02; prediction interval, - 1.28 to 0.50] and marginally significant effect on body weight [SMD = - 0.19; 95% CI - 0.40, 0.03; P = 0.09]. However, larger and well-designed clinical trials are needed to investigate the effects of C. annuum on MetS.

Hypoglycemic Effect of Prolamin from Cooked Foxtail Millet (Setaria italic) on Streptozotocin-Induced Diabetic Mice

Millet proteins have been demonstrated to possess glucose-lowering and lipid metabolic disorder modulation functions against diabetes; however, the molecular mechanisms underlying their anti-diabetic effects remain unclear. The present study aimed to investigate the hypoglycemic effect of prolamin from cooked foxtail millet (PCFM) on type 2 diabetic mice, and explore the gut microbiota and serum metabolic profile changes that are associated with diabetes attenuation by PCFM. Our diabetes model was established using a high-fat diet combined with streptozotocin before PCFM or saline was daily administrated by gavage for 5 weeks. The results showed that PCFM ameliorated glucose metabolism disorders associated with type 2 diabetes. Furthermore, the effects of PCFM administration on gut microbiota and serum metabolome were investigated. 16S rRNA gene sequencing analysis indicated that PCFM alleviated diabetes-related gut microbiota dysbiosis in mice. Additionally, the serum metabolomics analysis revealed that the metabolite levels disturbed by diabetes were partly altered by PCFM. Notably, the decreased D-Glucose level caused by PCFM suggested that its anti-diabetic potential can be associated with the activation of glycolysis and the inhibition of gluconeogenesis, starch and sucrose metabolism and galactose metabolism. In addition, the increased serotonin level caused by PCFM may stimulate insulin secretion by pancreatic β-cells, which contributed to its hypoglycemic effect. Taken together, our research demonstrated that the modulation of gut microbiota composition and the serum metabolomics profile was associated with the anti-diabetic effect of PCFM.

Microbiota-governed microRNA-204 impairs endothelial function and blood pressure decline during inactivity in db/db mice

An impaired decline in blood pressure at rest is typical in people with diabetes, reflects endothelial dysfunction, and increases the risk of end-organ damage. Here we report that microRNA-204 (miR-204) promotes endothelial dysfunction and impairment in blood pressure decline during inactivity. We show that db/db mice overexpress miR-204 in the aorta, and its absence rescues endothelial dysfunction and impaired blood pressure decline during inactivity despite obesity. The vascular miR-204 is sensitive to microbiota, and microbial suppression reversibly decreases aortic miR-204 and improves endothelial function, while the endothelial function of mice lacking miR-204 remained indifferent to the microbial alterations. We also show that the circulating miR-122 regulates vascular miR-204 as miR-122 inhibition decreases miR-204 in endothelial cells and aorta. This study establishes that miR-204 impairs endothelial function, promotes impairment in blood pressure decline during rest, and opens avenues for miR-204 inhibition strategies against vascular dysfunction.

Capsaicin improves glucose homeostasis by enhancing glucagon-like peptide-1 secretion through the regulation of bile acid metabolism via the remodeling of the gut microbiota in male mice

Mounting evidence has linked dietary capsaicin (CAP) consumption to the improvement of glucose homeostasis; however, the underlying mechanisms still need to be further elucidated. Male mice were fed a high-fat diet (HFD) with CAP administration for 8 weeks, gut microbiota, bile acid (BA) profiles and markers for BA, and glucose metabolism were investigated. CAP improved glucose homeostasis partially by enhancing the secretion of glucagon-like peptide 1 (GLP-1). The gut microbiota was remodeled by CAP and was characterized by the increased abundance of Bacteroides genera, which is related with lithocholic acid (LCA) production. LCA is an endogenous agonist of Takeda G-protein coupled receptor 5 (TGR5); it may enhance GLP-1 secretion in intestinal L cells. Meanwhile, antibiotics experiment abolished the effects of CAP on glucose homeostasis and microbiota transplantation experiments demonstrated that the CAP-induced beneficial effects were transferable, indicating that the effects of CAP on glucose homeostasis were largely dependent on the gut microbiota. Additionally, we further identified that the improvements induced by CAP were attenuated by the antagonist of GLP-1 receptor, indicating that the activation of GLP-1 signaling contributes to the CAP-induced improvement in glucose homeostasis.

Resveratrol enhances brown adipose tissue activity and white adipose tissue browning in part by regulating bile acid metabolism via gut microbiota remodeling

OBJECTIVE

Current evidence has linked dietary resveratrol (RSV) intake to the activation of brown adipose tissue (BAT) and induction of white adipose tissue (WAT) browning, which may be a potential means of improving glucose homeostasis. However, the underlying mechanisms remain unclear.

METHODS

A diet containing RSV was fed to db/db mice for 10 weeks, following which the body weight, adipose tissue accumulation, bile acid (BA) profiles, and markers of BA metabolism were analyzed. Oral glucose tolerance testing, immunohistochemistry, and gut microbiota sequencing were also performed.

RESULTS

RSV intervention improved glucose homeostasis in db/db mice, which was linked to the enhanced BAT activity and WAT browning. Moreover, RSV-treated mice exhibited altered plasma and fecal BA compositions and significant remodeling of the gut microbiota, the latter confirmed by a higher level of lithocholic acid (LCA) in the plasma and feces. LCA was identified to be the agonist of Takeda G-protein coupled receptor 5 (TGR5), which mediated the BAT activation and WAT browning by upregulating uncoupling protein 1 (UCP1) expression. Furthermore, depletion of the gut microbiota using antibiotics partially abolished the beneficial effects of RSV against glucose intolerance. Finally, microbiota transplantation experiments demonstrated that the RSV-induced beneficial effects were transferable, indicating that these effects were largely dependent on the gut microbiota.

CONCLUSIONS

These data indicate that RSV administration improves glucose homeostasis by enhancing BAT activation and WAT browning, a mechanism that might partially be mediated by the gut microbiota-BA-TGR5/UCP1 pathway.

Antidiabetic Effect of Casein Glycomacropeptide Hydrolysates on High-Fat Diet and STZ-Induced Diabetic Mice via Regulating Insulin Signaling in Skeletal Muscle and Modulating Gut Microbiota

This study evaluated the effects and the underlying mechanisms of casein glycomacropeptide hydrolysate (GHP) on high-fat diet-fed and streptozotocin-induced type 2 diabetes (T2D) in C57BL/6J mice. Results showed that 8-week GHP supplementation significantly decreased fasting blood glucose levels, restored insulin production, improved glucose tolerance and insulin tolerance, and alleviated dyslipidemia in T2D mice. In addition, GHP supplementation reduced the concentration of lipopolysaccharides (LPSs) and pro-inflammatory cytokines in serum, which led to reduced systematic inflammation. Furthermore, GHP supplementation increased muscle glycogen content in diabetic mice, which was probably due to the regulation of glycogen synthase kinase 3 beta and glycogen synthase. GHP regulated the insulin receptor substrate-1/phosphatidylinositol 3-kinase/protein kinase B pathway in skeletal muscle, which promoted glucose transporter 4 (GLUT4) translocation. Moreover, GHP modulated the overall structure and diversity of gut microbiota in T2D mice. GHP increased the Bacteroidetes/Firmicutes ratio and the abundance of S24-7, Ruminiclostridium, Blautia and Allobaculum, which might contribute to its antidiabetic effect. Taken together, our findings demonstrate that the antidiabetic effect of GHP may be associated with the recovery of skeletal muscle insulin sensitivity and the regulation of gut microbiota.