Fructus ligustri lucidi Ethanol Extract Improves Bone Mineral Density and Properties Through Modulating Calcium Absorption-Related Gene Expression in Kidney and Duodenum of Growing Rats

Optimizing peak bone mass in early life is one of key preventive strategies against osteoporosis. Fructus ligustri lucidi (FLL), the fruit of Ligustrum lucidum Ait., is a commonly prescribed herb in many kidney-tonifying traditional Chinese medicinal formulas to alleviate osteoporosis. Previously, FLL extracts have been shown to have osteoprotective effect in aged or ovariectomized rats. In the present study, we investigated the effects of FLL ethanol extract on bone mineral density (BMD) and mechanical properties in growing male rats and explored the underlying mechanisms. Male weaning Sprague–Dawley rats were randomized into four groups and orally administrated for 4 months an AIN-93G formula-based diet supplementing with different doses of FLL ethanol extract (0.40, 0.65, and 0.90 %) or vehicle control, respectively. Then calcium balance, serum level of Ca, P, 25(OH)₂D₃, 1,25(OH)₂D₃, osteocalcin (OCN), C-terminal telopeptide of type I collagen (CTX-I), and parathyroid hormone, bone microarchitecture, and calcium absorption-related genes expression in duodenum and kidney were analyzed. The results demonstrated that FLL ethanol extract increased BMD of growing rats and improved their bone microarchitecture and mechanical properties. FLL ethanol extract altered bone turnover, as evidenced by increasing a bone formation maker, OCN, and decreasing a bone resorption maker, CTX-I. Intriguingly, both Ca absorption and Ca retention rate were elevated by FLL ethanol extract treatment, possibly through the mechanisms of up-regulating the transcriptions of calcitropic genes in kidney (1α-hydroxylase) and duodenum (vitamin D receptor, calcium transporter calbindin-D9k, and transient receptor potential vanilloid 6). In conclusion, FLL ethanol extract increased bone mass gain and improved bone properties via modulating bone turnover and up-regulating calcium absorption-related gene expression in kidney and duodenum, which could then activate 1,25(OH)₂D₃-dependent calcium transport in male growing rats.