Single supplement of calcium carbonate aggravated intestinal microenvironment disorder in senile osteoporosis mice

Calcium carbonate supplementation for the prevention and treatment of senile osteoporosis is increasingly being questioned. The gut microbiome plays an important role in the pathogenesis of bone loss and mineral absorption. Currently, it is not well understood whether the bone metabolic status of patients after oral calcium carbonate supplementation is related to the intestinal flora. In this study, we utilized an aged mouse model of senile osteoporosis (18-month-old female C57BL/6 mice) to elucidate whether calcium carbonate supplementation aggravated the already aberrant gut microbiome of osteoporotic mice using 16S rDNA gene and metagenomic high-throughput sequencing. By analyzing intestinal wall structures and the inflammatory state, we proved that calcium carbonate supplementation increased intestinal wall permeability and systemic inflammatory responses in aged mice. We found that oral calcium carbonate supplementation mildly alleviated aging-induced bone loss, downregulated expression of intestinal junction proteins (including glucagon-like peptide 2 receptor, zonula occludens-1, Occludin, and Claudin 1), increased proinflammatory cytokines TNF-α, IL-17A, decreased anti-inflammatory cytokines IL-10, IL-4, and exacerbated dyshomeostasis of the intestinal microbiome (manifested as the enhanced ratio of Firmicutes-to-Bacteroidetes, increased harmful gut microbiome, and decreased the beneficial species). Our study verified calcium carbonate supplementation mildly promoted bone mass to inhibit senile osteoporosis, but further reduced intestinal mucosal integrity by disordering the types and richness of gut microbiota, decreasing tight binding proteins (GLP-2R, ZO-1, occludin, and claudin 1) related mRNA and increasing systemic inflammatory responses. We provided new insights into the usefulness of calcium carbonate supplementation in senile osteoporosis.