Pym-18a, a novel pyrimidine derivative ameliorates glucocorticoid induced osteoblast apoptosis and promotes osteogenesis via autophagy and PINK 1/Parkin mediated mitophagy induction.

Glucocorticoid-induced osteoporosis (GIOP) is the most common type of secondary osteoporosis, marked by reduced bone density and impaired osteoblast function. Current treatments have serious side effects, highlighting the need for new drug candidates. Pyrimidine derivatives have been noted for their potential in suppressing osteoclastogenesis, but their effects on osteogenesis and GIOP remain underexplored. Our recent study identified a novel pyrimidine derivative, Pym-18a, which enhances osteoblast functions. In this study, Pym-18a was found to mitigate the detrimental effects of Dexamethasone (Dex) in osteoblast cells and in GIOP in Balb/C mice. Pretreatment with Pym-18a followed by Dex (100 µM) for 24 h restored osteoblast alkaline phosphatase activity and viability. Pym-18a reduced Dex-induced apoptosis and reactive oxygen species (ROS) generation at cellular and mitochondrial levels and preserved mitochondrial membrane potential. Dex impaired autophagy and mitophagy, but Pym-18a pretreatment increased expression of autophagy markers (LC3II) and mitophagy markers (PINK1, Parkin, TOM20) while decreasing P62 expression. The osteogenic effects of Pym-18a were diminished in the presence of 3-MA (an autophagy inhibitor). In silico studies showed mTOR inhibition by Pym-18a, corroborated by its suppression of Dex-induced mTOR activation. In vivo, Pym-18a (10 mg/kg) significantly improved bone microarchitecture, trabecular connectivity, and strength, and corrected P1NP and CTX levels altered by Dex. Pym-18a also promoted autophagy, mitophagy, and suppressed mTOR activation in GIOP mice. Overall, Pym-18a mitigates detrimental effect of Dex by modulating autophagy and PINK/Parkin-mediated mitophagy through mTOR inhibition, suggesting it as a potential novel therapeutic option for GIOP.