ABSTRACT
Activating Nrf2 by small molecules is a promising strategy to treat postmenopausal osteoporosis. However, there is currently no Nrf2 activator approved for treating chronic diseases, and the downstream mechanism underlying the regulation of Nrf2 on osteoclast differentiation remains unclear. Here, we found that bitopertin, a clinical-stage glycine uptake inhibitor, suppresses osteoclast differentiation and ameliorates ovariectomy-induced bone loss by activating Nrf2. Mechanistically, bitopertin interacts with the Keap1 Kelch domain and decreases Keap1-Nrf2 binding, leading to reduced Nrf2 ubiquitination and degradation. Bitopertin is associated with less adverse events than clinically approved Nrf2 activators in both mice and human subjects. Furthermore, Nrf2 transcriptionally activates ferroportin-coding gene Slc40a1 to reduce intracellular iron levels in osteoclasts. Loss of Nrf2 or iron supplementation upregulates ornithine-metabolizing enzyme Odc1, which decreases ornithine levels and thereby promotes osteoclast differentiation. Collectively, our findings identify a novel clinical-stage Nrf2 activator and propose a novel Nrf2-iron-ornithine metabolic axis in osteoclasts.
Subject(s)
Cell Differentiation , Iron , Mice, Inbred C57BL , NF-E2-Related Factor 2 , Osteoclasts , NF-E2-Related Factor 2/metabolism , Animals , Cell Differentiation/drug effects , Osteoclasts/metabolism , Osteoclasts/drug effects , Osteoclasts/cytology , Mice , Iron/metabolism , Humans , Kelch-Like ECH-Associated Protein 1/metabolism , Female , Cation Transport ProteinsABSTRACT
OBJECTIVES: Shaoyao Gancao Decoction (SGD) is a well-known Chinese herbal prescription used to treat ulcerative colitis (UC). This study was designed to evaluate the effect of SGD in dextran sulfate sodium-induced UC and to reveal the potential mechanism. METHODS: A UC mouse model was established by the administration of dextran sulfate sodium. The mice were given SGD extract intragastrically for 7 days. Histological pathology, inflammatory factors, and ferroptosis regulators were determined in vivo. In addition, ferroptotic Caco-2 cells were prepared to investigate the underlying mechanism of the effects of SGD. KEY FINDINGS: The results showed that SGD reduced the disease activity index, the level of inflammatory factors, and histological damage in mice with UC. Moreover, SGD down-regulated the level of ferroptosis in cells in colon tissue, as evidenced by a reduced iron overload, decreased glutathione depletion, and a lower level of malondialdehyde production, compared with the model group. Correspondingly, similar effects of SGD on ferroptosis were observed in Erastin-treated Caco-2 cells. The results of our in vitro reactive oxygen species assays and the changes in mitochondrial structure observed by scanning electron microscopy also supported these results. CONCLUSION: Taken together, these findings suggest that SGD protected against UC by down-regulating ferroptosis in colonic tissue.