Chitosan alleviated menopausal symptoms and modulated the gut microbiota in estrogen-deficient rats

Menopause disturbs energy, glucose, and lipid metabolisms and changes the composition of the gut microbiota, but dietary fibers without phytoestrogens may ameliorate menopausal metabolic disorders. The objective of the present study was to assess whether consuming the prebiotics chitosan and citrus pectin can improve postmenopausal symptoms, possibly by modulating the gut microbiota in ovariectomized (OVX) rats, and the mechanism of action was examined. The OVX rats were given 4.5% cellulose (OVX-Control), chitosan (OVX-Chitosan), or citrus pectin (OVX-Pectin) in a 43% fat diet and the sham rats were given the same diet as the OVX-Control for 12 weeks. Sham-operated rats had the same diet as OVX-Control (Normal-Control). Body-weight, visceral fat mass, tail skin temperature, serum 17β-estradiol, glucose intolerance, and insulin tolerance were determined. Gut microbiota in the fecal samples was measured by NGS and analyzed with PICRUSt2. Short-chain fatty acids (SCFA) and metabolomic characteristics of serum were also measured with UPLC-mass spectrometry. Chitosan and citrus pectin were selected because the incubation of rat feces with these two prebiotics in vitro had shown increased butyrate production. OVX-Chitosan reduced the weight, visceral fat content, and tail skin temperature, and OVX-Chitosan and OVX-Pectin improved glucose tolerance, compared to the OVX-Control. Both alleviated dyslipidemia, compared to the OVX-Control. OVX-Chitosan and OVX-Pectin elevated serum propionate and butyrate concentrations but only OVX-Chitosan lowered serum acetate concentrations. In PICRUSt2, chitosan upregulated the functional genes of gut microbiota involved in valine, leucine, and isoleucine biosynthesis, whereas the OVX-Control exhibited significantly upregulated lipopolysaccharide biosynthesis. OVX-Pectin exhibited increased α-diversity in the fecal bacteria. Metabolomic analysis revealed higher serum urate concentrations in the OVX-Control group than the other groups, and serum arginine and leucine concentrations were higher in the OVX-Chitosan group (P < 0.05). Chitosan and citrus pectin consumptions improved menopausal symptoms by improving the diversity and composition of the gut microbiota, and serum metabolites and SCFA originating from fecal bacteria. Chitosan was more effective for improving menopausal symptoms than citrus pectin.