Ergothioneine prevents ovariectomy-induced osteoporosis by suppressing NF-κB/p65 signalling to attenuate osteoclastogenesis and bone marrow inflammation.

Aims: Osteoporosis (OP), an age-related skeletal disorder, is characterized by excessive bone resorption driven by osteoclast overactivation, reactive oxygen species (ROS) accumulation, and chronic inflammation. Although the mitochondria-targeted antioxidant ergothioneine (EGT) has shown potential in regulating bone metabolism, its specific preventive mechanism in oestrogen-deficient osteoporosis remains unclear. Therefore, this study aimed to elucidate the preventive effects of EGT and its underlying mechanisms when administered early after ovariectomy. Methods: Using an oestrogen-deficient mouse model, EGT was administered immediately after modelling to evaluate its preventive effects against bone loss and microstructural deterioration. In vivo analyses included assessments of bone resorption parameters, B-cell precursor populations, and the bone marrow inflammatory status. Complementary in vitro experiments were conducted to examine the influence of EGT on mitochondrial ROS levels, p65 phosphorylation, NF-κB/NFATc1 signalling pathway activity, and osteoclast differentiation. Results: Preventive administration of EGT significantly mitigated ovariectomy-induced bone loss and preserved bone microstructure. This was achieved through the suppression of osteoclast activity, modulation of B-cell precursors, and reversal of the pro-inflammatory bone marrow microenvironment. Mechanistically, EGT reduced mitochondrial ROS generation, inhibited p65 phosphorylation and nuclear translocation, and consequently disrupted the nuclear factor κB (NF-κB)/NFATc1 signalling axis, ultimately inhibiting osteoclastogenesis. Conclusion: The findings of this study indicate that ergothioneine has the potential to prevent osteoporosis. It bidirectionally regulates bone homeostasis by targeting the ROS-NF-κB axis, systemically remodelling a protective anti-inflammatory bone marrow microenvironment while directly inhibiting osteoclast activation and differentiation. These results underscore the translational value of EGT as an early preventive strategy for oestrogen-deficient osteoporosis.