Immobilization is commonly used in the treatment of fractures. Prolonged immobilization may cause many health problems, especially osteoporosis. Green apple peels include flavonoids and phenols, and may be protective against many chronic diseases. This research aimed to examine alterations in the bone of immobilized rats and investigate, for the first time to our knowledge, the beneficial preventive effect of the apple peel extract (APE) against immobilization osteoporosis. The rats were divided into four groups; control, APE treated, immobilization and immobilization + APE. The immobilization was done in a shortened position for 2 successive weeks, and APE was administrated in a dose of (500mg/kg/day) orally for 3 weeks. Biochemical analysis was done for evaluation of bone markers and oxidative stress biomarkers. The tibias were dissected out for histological study (light and scanning electron microscopic) and immunohistochemical assessment (Osteopontin (OPN), Receptor activator of nuclear factor kappa beta ligand (RANKL), High mobility group box 1(HMGB1) and Becline-1). Histological examination of bone tissue showed that APE administration effectively restored normal histological structure compared to the immobilized untreated group, with significant increase in cortical thickness while Haversian canals’ perimeters were significantly decreased. This positive impact is provided via the considerable reduction in malondialdehyde (MDA), and by rise in superoxide dismutase (SOD) and catalase. APE protected against osteoporotic changes by significant increase in OPN and decrease in RANKL and HMGB1 immunoreaction compared to the immobilized group. APE also promotes autophagy by significant up-regulation of Becline-1 immunoreaction. These findings demonstrate the protective effect of APE to guard against immobilization osteoporosis.
