Linagliptin-metformin combination: A novel approach to mitigate 4-vinyl cyclohexene di epoxide and dexamethasone-induced osteoporosis in mice

Elevated levels of dipeptidyl-peptidase (DPP-4) enzyme, associated with accelerated bone resorption, are linked to both post-menopausal osteoporosis (PMO) and glucocorticoid-induced osteoporosis (GIO). Consequently, DPP-4 inhibitors, a class of anti-diabetic drugs, emerge as potential candidates for repurposing as anti-osteoporotic agents. In this study, we explored the effect of 4-week treatment with linagliptin (a DPP-4 inhibitor) and its combination with metformin on PMO and GIO in mice. PMO was induced in Balb/c mice by injecting 4-vinyl cyclohexene diepoxide (VCD), 160 mg/kg, ip for 15 days while GIO was induced by administering dexamethasone (DEX) 5 mg/kg, ip for 21 days. A significant improvement in bone architectural parameters and bone mineral density (BMD) was observed following the linagliptin-metformin combination, which was consistent with the altered bone turnover markers i.e., increased ALP, osteocalcin, BMP-2, and reduced serum calcium, TRAP, sclerostin and pro-inflammatory cytokines. Results from bone immunohistochemistry (IHC) demonstrated that the combination led to an increase in immunopositive OPG cells, while RANKL expression was diminished. Linagliptin, however, demonstrated only partial improvement in the PMO model. Conversely, in the GIO model, linagliptin did not show a significant effect except for improved BMD and sclerostin levels. Treatment with metformin did not show significant changes in either model. These findings suggest that the combination of linagliptin with metformin could alleviate the PMO and GIO, possibly through targeting AMPK and Wnt signaling pathway and thereby modulating BMP-2, sclerostin and RANKL/OPG.