[Mechanism of Zuogui Pills in regulating bone metabolism through OXT/OXTR feed-forward loop based on theory of "all...

Grounded in the theory of "all marrows dominated by brain", this study explored the therapeutic mechanism of Zuogui Pills in modulating the oxytocin(OXT)/oxytocin receptor(OXTR) feed-forward loop in the treatment of postmenopausal osteoporosis(PMOP). A PMOP rat model was established using ovariectomy, and 70 Sprague-Dawley female rats were randomly divided into the following groups: sham operation group, model group, estradiol group(17β-estradiol, 0.05 mg·kg~(-1)·d~(-1)), Zuogui Pills low, medium, and high dose groups(0.2, 0.4, 0.8 g·kg~(-1)·d~(-1), respectively), and an antagonist group(atosiban 0.9 mg·kg~(-1)·d~(-1) + 17β-estradiol 0.05 mg·kg~(-1)·d~(-1) + Zuogui Pills 0.4 g·kg~(-1)·d~(-1)). After 12 weeks of model establishment, treatment was administered by gavage once daily for another 12 weeks, followed by sample collection. Enzyme-linked immunosorbent assay(ELISA) was used to measure serum levels of estrogen(E_2), OXT, tartrate-resistant acid phosphatase(TRACP-5b), and bone alkaline phosphatase(BALP). Histopathological changes in the left distal femur were observed through hematoxylin and eosin(HE) staining. Micro-computed tomography(micro-CT) was used to analyze the microstructure of the right distal femur. Western blot was employed to detect the expression levels of OXTR, small GTP-binding protein Ras, Raf1 proto-oncogene(Raf1), mitogen-activated protein kinase kinase 1/2(MEK1/2), and extracellular signal-regulated kinase 1/2(ERK1/2), and their phosphorylated forms in tibial tissues. Compared with the model group, the Zuogui Pills medium and high dose groups showed significantly increased levels of E_2, OXT, and BALP, with a notable decrease in TRACP-5b levels. Morphologically, the trabeculae in the left distal femur were more tightly arranged. The fibrous structure in the right distal femur was significantly improved in the Zuogui Pills high dose group. Additionally, the expression of OXTR, Ras, p-Raf1, p-MEK1/2, and p-ERK1/2 proteins in tibial tissues was significantly increased. The therapeutic effect of the Zuogui Pills high dose group was partially inhibited when an OXTR antagonist was administered. These findings suggest that Zuogui Pills can regulate the OXT/OXTR feed-forward loop, activate the phosphorylation of the downstream Ras/Raf1/MEK/ERK signaling pathway, and ultimately improve bone mineral density, thereby exerting therapeutic effects in PMOP.