To investigate the effects of Tonglagat-5, a Mongolian drug, on bone microstructure and bone metabolism in osteoporotic mice, and to explore the possible mechanisms of action based on phosphatase and tensin homologue-induced kinase 1 (PINK1)/Parkin-mediated mitophagy.

Osteoporotic mouse model was established by ovariectomy (OVX). Osteoporotic model mice were randomly divided into model group (equal volume 0.9% NaCl by gavage), control group (estradiol valerate 1 mg·kg^-1 by gavage), experimental group (0.05 g·kg^-1 Tonglagat-5 solution by gavage) and combined group (0.05 g·kg^-1 Tonglagat-5 solution by gavage + 50 mg·kg^-1 Mdivi-1 by intraperitoneal injection), with 10 mice per group; ten mice were randomly selected as the sham-operation group. After 10 consecutive weeks of treatment, the bone mineral density (BMD) was measured by Micor-CT assay, the bone metabolism marker assay [C-terminal telopeptide of type Ⅰ collagen (CTx-Ⅰ), alkaline phosphatase (ALP) and bone Gla-protein (BGP)] were detected by kit, and the protein expression levels of translocase of outer mitochondrial membrane 20 (Tomm20), p62, PINK1 and Parkin were performed by Western blot.

The BMD in the sham-operation, model, control, experimental and combined groups were (0.23±0.02), (0.09±0.01), (0.22±0.03), (0.23±0.01) and (0.11±0.02) g·mm^-3; the levels of CTx-Ⅰ were (14.58±1.22), (26.62±2.04), (16.44±2.31), (12.31±1.98) and (22.76±2.52) ng·mL^-1; the levels of ALP were (4.87±1.12), (1.41±1.10), (3.03±1.07), (4.44±1.15) and (2.05±1.41) U·L^-1; the levels of BGP were (9.35±1.06), (5.28±0.84), (7.76±0.35), (8.34±0.87) and (6.12±0.81) ng·mL^-1; the relative expression levels of Tomm20 protein were 0.93±0.08, 0.10±0.01, 0.37±0.03, 0.84±0.06 and 0.28±0.03; the relative expression levels of p62 protein were 0.15±0.02, 0.93±0.09, 0.65±0.06, 0.37±0.04 and 0.86±0.06; the relative expression levels of PINK1 protein were 0.87±0.09, 0.14±0.02, 0.32±0.03, 0.69±0.06 and 0.26±0.03; the relative expression levels of Parkin protein were 0.79±0.08, 0.12±0.02, 0.26±0.04, 0.58±0.05 and 0.23±0.03, respectively. The above indexes in model group were compared those in sham-operation, control and experimental groups, the differences were statistically significant (all P<0.05).

Tonglagat-5 is able to improve bone microstructure and bone metabolism and reduce bone loss in OVX mice, and the mechanism may be related to the activation of PINK1/Parkin pathway-mediated mitophagy to exert osteoprotective effects.