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Objective To investigate the effect of boldine isolated from Litsea cubeba on collagen-induced arthritis (CIA) rats and explore the molecular mechanism predicted by network pharmacology. Material and methods CIA rats were orally administered with boldine. The bone destruction of paws was analyzed by histologic examination, tartrate-resistant acid phosphatase (TRACP) staining and micro-computed tomography. Prediction of signal pathway associated with boldine network molecules and CIA genes was applied by the network pharmacology analysis. The expressions of osteoprotegerin (OPG), receptor activator of nuclear factor-κB (RANK) and its ligand (RANKL) in the ankle were detected by immunohistochemistry. In vitro osteoclasts were cultured in the presence of variable doses of boldine and the RANK expressions were evaluated using Real-time polymerase chain reaction and western blot. Results Boldine reduced ankle swelling, alleviated pathological damage and significantly prevented bone destruction in CIA rats. Consistent with this, enzyme linked immunosorbent assay revealed boldine decreased serum TRACP5b levels and osteoclast number in the ankle region by TRACP staining from CIA rats. The network pharmacology analysis indicated that RANK signaling in osteoclasts was the most significant canonical pathway associated with boldine network molecules and CIA genes, which was verified by the increased expression of OPG, reduced expression of RANK, RANKL and RANKL/OPG in boldine-treated CIA rats. The in vitro study further confirmed that boldine inhibited osteoclastogenesis by inhibiting the RANKL/RANK signaling pathway. Conclusion Taken together, our study first indicates that boldine from Litsea cubeba suppresses osteoclastogenesis, improves bone destruction by down-regulating the OPG/RANKL/RANK signal pathway and may be a potential therapeutic agent for rheumatoid arthritis. [ABSTRACT FROM AUTHOR]

Cadmium (Cd) is a widespread environmental contaminant that causes severe bone metabolism disease, such as osteoporosis, osteoarthritis, and osteomalacia. The present review aimed to explore the molecular mechanisms of Cd-induced bone injury starting from bone cell function and teeth development. Cd inhibits the differentiation of bone marrow mesenchymal stem cells (BMSCs) into osteoblasts, and directly causes BMSC apoptosis. In the case of osteoporosis, Cd mainly affects the activation of osteoclasts and promotes bone resorption. Cd-induces osteoblast injury and oxidative stress, which causes DNA damage, mitochondrial dysfunction, and endoplasmic reticulum stress, resulting in apoptosis. In addition, the development of osteoarthritis (OA) might be related to Cd-induced chondrocyte damage. The high expression of metallothionein (MT) might reduce Cd toxicity toward osteocytes. The toxicity of Cd toward teeth mainly focuses on enamel development and dental caries. Understanding the effect of Cd on bone cell function and teeth development could contribute to revealing the mechanisms of Cd-induced bone damage. This review explores Cd-induced bone disease from cellular and molecular levels, and provides new directions for removing this heavy metal from the environment. Cd exposure causes severe bone metabolism disease. Apoptosis and differentiation play an essential role in Cd-induced osteoporosis. The development of osteoarthritis (OA) might be related to Cd-induced chondrocyte damage. The expression of MT may affect Cd-induced osteocytes damage. The toxicity of Cd toward teeth is mainly focused on enamel development and dental caries. Therefore, bone cells function and teeth development is mainly present manner of Cd toxicity. Unlabelled Image • Cd causes severe bone metabolism disease. • Cd-induces bone injury via affecting bone cell formation and function. • Apoptosis is main death manner by Cd-induced bone cell. • The toxicity of Cd toward teeth is mainly affected enamel development and dental caries. [ABSTRACT FROM AUTHOR]

Cadmium (Cd), an environmental pollutant, induces osteoporosis by directly destroying bone tissue, but its direct damaging effect on bone cells is not fully illustrated. Here, we treated mouse bone marrow stem cells (BMSC) and bone marrow macrophages (BMM) with Cd, and gave BALB/c mice Cd in water. Long-term Cd exposure significantly inhibited BMSC osteogenesis and osteoclast differentiation in vitro , and induced osteoporosis in vivo. Cd exposure also reduced P2X7 expression dramatically. However, P2X7 deletion significantly inhibited osteoblast and osteoclast differentiation; P2X7 overexpression obviously reduced the suppression effect of Cd on osteoblast and osteoclast differentiation. The suppression of P2X7–PI3K–AKT signaling aggravated the effect of Cd. In mice, short-term Cd exposure did not result in osteoporosis, but bone formation was inhibited, RANKL expression was increased, and osteoclasts were significantly increased in vivo. In vitro , short-term Cd exposure not only increased osteoclast numbers, but also promoted osteoclast adhesion function at late-stage osteoclast differentiation. Cd exposure also reduced P2X7 expression in vivo and in vitro. Our results demonstrate that short-term Cd exposure does not affect osteoblast and osteoclast apoptosis in vivo and in vitro , but long-term Cd exposure significantly increases bone tissue apoptosis. Overall, our results describe a novel mechanism for Cd-induced osteoporosis. ga1 • Long-term Cd exposure induced osteoporosis in mice. • Cd exposure decreased P2X7 greatly in vitro and in vivo. • In vitro , deleting P2X7 inhibited osteoblast and osteoclast differentiation. • Cd exposure inhibited osteogenesis and osteoclast differentiation in vitro. • P2X7 overexpression decreased this suppressive effect of Cd. [ABSTRACT FROM AUTHOR]

Schematic representation of the proposed Cd-induced signaling pathway in osteoclasts. Treatment of osteoclasts with Cd leads to a transient increase in intracellular calcium concentration ([Ca2+] i). Cd-induces the elevation of [Ca2+] i and activation of CaM/CaMKII/CaMKIV signaling. CaM/CaMKII/CaMKIV signaling induces the expression of NFATc1, leading to osteoclast differentiation. ER Ca2+ release, the elevation of [Ca2+] I , and the activation of CaM, CaMKII, and CaMKIV can be inhibited by 2-APB, BAPTA-AM, W-7, KN93 and STO-609, respectively. Environmental cadmium (Cd) pollution can ultimately lead to chronic toxicity via food consumption. Previous studies have demonstrated that long-term low-dose Cd exposure decreases bone mineral density and bone mineralization. Cd may increase receptor activator of nuclear factor-κ B ligand (RANKL) expression by osteoclasts, and inhibit the expression of osteoprotegerin. However, the molecular mechanism underlying Cd toxicity toward osteoclasts is unclear. In this study, bone marrow monocytes were isolated from C57BL/6 mice and treated with macrophage colony-stimulating factor and RANKL to induce the formation of osteoclasts. The results show that low-dose Cd exposure induced osteoclast differentiation. Cd also increased the intracellular calcium concentration of osteoclasts by triggering release of calcium ions from the endoplasmic reticulum into the cytoplasm. Furthermore, the elevation of intracellular calcium levels was shown to activate the calmodulin (CaM)/calmodulin-dependent protein kinase (CaMK) pathway. NFATc1 is a downstream protein of CaM/CaMK signaling, as well as a key player in osteoclast differentiation. Overall, we conclude that Cd activates the CaM/CaMK/NFATc1 pathway and regulates osteoclast differentiation by increasing intracellular calcium concentration. Our data provide new insights into the mechanisms underlying osteoclast differentiation following Cd exposure. This study provides a theoretical basis for future investigations into the therapeutic application of CaMK inhibitors in osteoporosis induced by Cd exposure. [ABSTRACT FROM AUTHOR]