Osteoporosis is a common bone imbalance disease that threatens the health of postmenopausal women. Estrogen deficiency accelerates the aging of women. Oxidative stress damage is regarded as the main pathogenesis of postmenopausal osteoporosis. The accumulation of reactive oxygen species in the bone microenvironment plays a role in osteoblast and osteoclast apoptosis. Improving the oxidative state is essential for the prevention and treatment of postmenopausal osteoporosis. There are three classes of antioxidant defense systems in the body to eliminate free radicals and peroxides including antioxidant substances, antioxidant enzymes, and repair enzymes. In our review, we demonstrated the mechanism of antioxidants and their effect on bone metabolism in detail. We concluded that glutathione/oxidized glutathione (GSH/GSSG) conversion involved the PI3K/Akt-Nrf2/HO-1 signaling pathway and that the antioxidant enzyme-mediated mitochondrial apoptosis pathway of osteoblasts was necessary for the development of postmenopausal osteoporosis. Since the current therapeutic effects of targeting bone cells are not significant, improving the systemic peroxidation state and then regulating bone homeostasis will be a new method for the treatment of postmenopausal osteoporosis.
At present, the drug treatment of osteoporosis is mostly focused on inhibiting osteoclastogenesis, which has relatively poor effects. Metformin is a drug that can potentially promote osteogenic differentiation and improve bone mass in postmenopausal women. We aimed to detect the molecular mechanism underlying the osteogenic effect of metformin. Our study indicated that metformin obviously increased the Alkaline phosphatase activity and expression of osteogenic marker genes at the mRNA and protein levels. The PI3K/AKT signaling pathway was revealed to play an essential role in the metformin-induced osteogenic process, as shown by RNA sequencing. We added LY294002 to inhibit the PI3K/AKT pathway, and the results indicated that the osteogenic effect of metformin was also blocked. Additionally, the sequencing data also indicated oxidation-reduction reaction was involved in the osteogenic process of osteoblasts. We used H2O2 to mimic the oxidative damage of osteoblasts, but metformin could attenuate it. Antioxidative Nrf2/HO-1 pathway, regarded as the downstream of PI3K/AKT pathway, was modulated by metformin in the protective process. We also revealed that metformin could improve bone mass and oxidative level of OVX mice. In conclusion, our study revealed that metformin promoted osteogenic differentiation and H2O2-induced oxidative damage of osteoblasts via the PI3K/AKT/Nrf2/HO-1 pathway.
Oxidative stress is one of the main causes of osteoblast apoptosis induced by post-menopausal osteoporosis. The authors previously found that metformin can reverse the loss of bone mass in post-menopausal osteoporosis. The present study aimed to further clarify the effects and mechanisms of action of metformin in post-menopausal osteoporosis under conditions of oxidative stress. Combined with an in-depth investigation using the transcriptome database, the association between oxidative stress and mitochondrial dysfunction in post-menopausal osteoporosis was confirmed. A pre-osteoblast model of oxidative stress was constructed, and the apoptotic rate following the addition of hydrogen peroxide and metformin was detected using CCK-8 assay and Annexin V-FITC/PI staining. Mitochondrial membrane potential was detected using the JC-1 dye, the intracellular calcium concentration was detected using Fluo-4 AM, the intracellular reactive oxygen species (ROS) level was observed using DCFH-DA, and the mitochondrial superoxide level was observed using MitoSOX Red. Bay K8644 was used to increase the level of intracellular calcium. siRNA was used to interfere with the expression of glycogen synthase kinase (GSK)-3β. Western blot analysis was used to detect the expression of mitochondrial dysfunction-related proteins. The results revealed that oxidative stress decreased mitochondrial membrane potential and increased intracellular ROS, mitochondrial superoxide and cytoplasmic calcium levels in pre-osteoblasts; however, metformin improved mitochondrial dysfunction and reversed oxidative stress-induced injury. Metformin inhibited mitochondrial permeability transition pore opening, suppressed the cytoplasmic calcium influx and reversed pre-osteoblast apoptosis by promoting GSK-3β phosphorylation. Moreover, it was found that EGFR was the cell membrane receptor of metformin in pre-osteoblasts, and the EGFR/GSK-3β/calcium axis played a key role in metformin reversing the oxidative stress response of pre-osteoblasts in post-menopausal osteoporosis. On the whole, these findings provide a pharmacological basis for the use of metformin for the treatment of post-menopausal osteoporosis.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.