Abstract

Postmenopausal osteoporosis caused by estrogen deficiency often requires hormone replacement therapy (HRT), but its systemic side effects limit clinical application. Here, we developed a bone-targeted Poly (lactic-co-glycolic acid) (PLGA) nanocarrier modified with Alendronic acid (ADA) to co-deliver 17β-Estradiol (E2) and Vitamin D3 (VitD3), aiming to enhance efficacy and safety. The ADA-functionalized nanoparticles (E2+VD@PLGA IR780 ADA) showed high drug loading (7.2 wt% for E2 and 2.3 wt% for VitD3), sustained release (>90% over 48 h). In ovariectomized (OVX) mice, targeted delivery significantly improved bone mineral density, restored trabecular structure, and reduced serum bone resorption markers, while markedly alleviating E2-induced endometrial thickening. In vivo imaging confirmed selective bone accumulation. Mechanistically, co-administration of VitD3 and E2 elicits enhanced pro-osteogenic effects by virtue of VitD3-mediated Vitamin D Receptor (VDR) upregulation and amplified E2-induced estrogen receptor (ER) expression, which collectively drive robust activation of the PI3K/AKT/mTOR signaling cascade.This bone-specific nanoplatform offers a promising and safer strategy for osteoporosis therapy beyond conventional HRT.