The gut microbiota benefits humans via short-chain fatty acid (SCFA) production from carbohydrate fermentation, and deficiency in SCFA production is associated with type 2 diabetes mellitus (T2DM). We conducted a randomized clinical study of specifically designed isoenergetic diets, together with fecal shotgun metagenomics, to show that a select group of SCFA-producing strains was promoted by dietary fibers and that most other potential producers were either diminished or unchanged in patients with T2DM. When the fiber-promoted SCFA producers were present in greater diversity and abundance, participants had better improvement in hemoglobin A1c levels, partly via increased glucagon-like peptide-1 production. Promotion of these positive responders diminished producers of metabolically detrimental compounds such as indole and hydrogen sulfide. Targeted restoration of these SCFA producers may present a novel ecological approach for managing T2DM.

Polycystic ovary syndrome (PCOS) is a common endocrine and metabolic disorder in women. Gut microbiota has been implicated to play a critical role in metabolic diseases and may modulate the secretion of mediators of the brain–gut axis. Interaction between gut microbiota and the endocrine and biochemical disturbances in PCOS still remains elusive. Here, we showed an altered gut microbiota significantly correlated with PCOS phenotype. There were 33 patients with PCOS (non-obese PCOS individuals, PN, n = 12; obese PCOS individuals, PO, n = 21) as well as 15 control subjects (non-obese control individuals, CN, n = 9; obese control individuals, CO, n = 6) enrolled in our study. The plasma levels of serotonin, ghrelin, and peptide YY (PYY) were significantly decreased in patients with PCOS compared with controls, and have a significantly negative correlation with waist circumference and testosterone. Sequencing of the V3–V4 region of the 16S rRNA gene in fecal samples revealed the substantial differences of gut microbial species between the PCOS and non-obese controls. Bacterial species were clustered into 23 co-abundance groups (CAGs) based on the SparCC correlation coefficients of their relative abundance. The CAGs increased in PCOS, including the bacteria belonging to Bacteroides, Escherichia/Shigella and Streptococcus, were negatively correlated with ghrelin, and positively correlated with testosterone and BMI. Furthermore, the CAGs that were decreased in PCOS, including the bacteria from Akkermansia and Ruminococcaceae, showed opposite relationship with body-weight, sex-hormone, and brain–gut peptides. In conclusion, gut microbial dysbiosis in women with PCOS is associated with the disease phenotypes.

Spexin mRNA and protein are widely expressed in rat tissues and associate with weight loss in rodents of diet-induced obesity. Its location in endocrine and epithelial cells has also been suggested. Spexin is a novel peptide that involves weight loss in rodents of diet-induced obesity. Therefore, we aimed to examine its expression in human tissues and test whether spexin could have a role in glucose and lipid metabolism in type 2 diabetes mellitus (T2DM). The expression of the spexin gene and immunoreactivity in the adrenal gland, skin, stomach, small intestine, liver, thyroid, pancreatic islets, visceral fat, lung, colon, and kidney was higher than that in the muscle and connective tissue. Immunoreactive serum spexin levels were reduced in T2DM patients and correlated with fasting blood glucose (FBG, r=-0.686, P<0.001), hemoglobin A1c (HbA1c, r=-0.632, P<0.001), triglyceride (TG, r=-0.236, P<0.001) and low density lipoprotein-cholesterol (LDL-C, r=-0.382, P<0.001). A negative correlation of blood glucose with spexin was observed during oral glucose tolerance test (OGTT). Spexin is intensely expressed in normal human endocrine and epithelial tissues, indicating that spexin may be involved in physiological functions of endocrine and in several other tissues. Circulating spexin levels are low in T2DM patients and negatively related to blood glucose and lipids suggesting that the peptide may play a role in glucose and lipid metabolism in T2DM.