Intake of eggshell membrane enhances bone mass and suppresses bone marrow adiposity in normal growing rats

Eggshell membrane intake is considered to have beneficial effects on bone health; however, relevant evidence remains scant. Therefore, we aimed to explore the direct effects of eggshell membrane intake on osteogenic function in normal growing rats. Six-week-old male Wistar rats were divided into control (CO) and eggshell membrane (EM) groups. The experiment was conducted over 8 weeks. Visual observation and micro-computed tomography analysis revealed a significant increase in bone mass in the EM group compared with that in the CO group. Histological analysis showed thick and long trabeculae in the EM group, accompanied by an increase in the number of osteoblasts and suppression of adipocyte accumulation. Furthermore, Col1a1 expression was significantly higher in the EM group than in the CO group, although no significant differences were found in the number of TRAP-positive osteoclasts or Ctsk expression. Immunohistochemical analysis demonstrated a notable increase in the number of Col1-positive osteoblasts but a significant decrease in the number of Dlk1-positive adipocytes in the EM group. Gene expression analysis revealed no difference in the expression of Runx2 (the master regulator of osteoblast differentiation) between the groups. However, the expression of Sp7, which functions downstream of Runx2, was significantly upregulated, whereas that of Pparg, the master regulator of adipocyte differentiation, was significantly downregulated in the EM group compared with those in the CO group. Overall, the intake of eggshell membranes may enhance osteogenic function and suppress bone marrow adiposity. These findings support the beneficial effects of eggshell membrane intake on bone health.