Sex differences in alcohol inhibits bone formation and promotes bone resorption in young male and female rats by altering intestinal flora, metabolites, and bone microenvironment.

BACKGROUND: Long-term alcohol intake has toxic effects on osteoblasts and osteoclasts, resulting in decreased bone density, which directly disrupts the composition of the gut microbiota and affects bone metabolism and immune activity. The effects of alcohol on the bones may be closely related to sex. This study investigated the effects of long-term alcohol consumption on bone status in different sexes by examining the gut microbiota, bone metabolism, and immune activity. METHODS: Young male and female rats were administered a Bio-Serv liquid diet containing 5% alcohol. The effects of alcohol metabolism capacity, bone morphology, bone formation, bone resorption, bone marrow immune activity, gut microbiota, and metabolite differences were analyzed in male and female rats using hematoxylin and eosin staining, micro-computed tomography, enzyme-linked immunosorbent assay, western blotting, 16S rRNA sequencing, and untargeted metabolomics. RESULTS: Chronic alcohol consumption resulted in excessive osteoclast activation and decreased bone mineral density. Furthermore, alcohol reduced bone metabolism and formation while increasing bone resorption. Bone loss was significantly more severe in female rats than in male rats, indicating that the effects of alcohol on rat bones are related to sex. Chronic alcohol consumption also led to polarization of bone marrow immunoreactivity toward the M1 phenotype. In addition, chronic alcohol consumption affected the composition of gut microbiota, reduced the richness and diversity of intestinal microbiota, and decreased the ratio of Firmicutes/Bacteroidetes. Long-term alcohol consumption also affected fecal metabolites, and 754 differentially expressed metabolites were identified. CONCLUSIONS: Chronic alcohol consumption increased bone resorption, inhibited bone formation, and affected bone marrow immunoreactivity in young male and female rats. Alcohol can also affect gut microbiota composition and fecal metabolism. Female rats were more susceptible to alcohol, possibly because young female rats have a lower alcohol metabolism, immunomodulatory capacity, and gut microbiota diversity than young male rats.