Functional Effects of Sericin on Bone Health and D-Serine Regulation in Estrogen-Deficient Rats

Postmenopausal osteoporosis is characterized by progressive bone loss and deterioration of trabecular microarchitecture, yet safe and effective nutritional interventions remain limited. This study investigated the skeletal effects of whole sericin compared to isolated L-serine and calcium-only formulations in an ovariectomized (OVX) rat model. Forty female Sprague–Dawley rats underwent either sham surgery or OVX, followed by 8 weeks of daily oral administration with vehicle (calcium + vitamin D, NS), sericin formulation (S55), or L-serine. Sham and untreated OVX groups served as controls. Serum D-serine concentrations and femoral trabecular microarchitecture were assessed using fluorometric assays and micro-computed tomography (μCT), respectively. OVX significantly decreased bone volume fraction (BV/TV), bone mineral density (BMD), and trabecular number, while increasing trabecular separation. Sericin supplementation markedly improved BV/TV, BMD, trabecular thickness, and trabecular number, and reduced trabecular separation compared to both vehicle and untreated OVX controls. Sericin improved multiple trabecular parameters compared with L-serine. Serum D-serine levels were significantly elevated in the sericin group relative to calcium-only controls, though comparable to sham. These findings suggest that whole sericin exerts skeletal benefits beyond those attributable to its primary amino acid component, supporting its potential as a functional food ingredient for enhancing postmenopausal bone health.