We previously demonstrated that magnesium ions (Mg2+) was a novel therapeutic alternative for osteoarthritis (OA) through promoting the hypoxia inducible factor-1α (HIF-1α)-mediated cartilage matrix synthesis. However, oxidative stress can inhibit the expression of HIF-1α, amplify the inflammation that potentially impairs the therapeutic efficacy of Mg2+ in OA. Vitamin (VC), a potent antioxidant, may enhance the efficacy of Mg2+ in OA treatment. This study aims to investigate the efficacy of combination of Mg2+ and VC on alleviating joint destruction and pain in OA. Anterior cruciate ligament transection with partial medial meniscectomy induced mice OA model were randomly received intra-articular injection of either saline, MgCl2 (0.5 mol/L), VC (3 mg/ml) or MgCl2 (0.5 mol/L) plus VC (3 mg/ml) at week 2 post-operation, twice weekly, for 2 weeks. Joint pain and pathological changes were assessed by gait analysis, histology, western blotting and micro-CT. Mg2+ and VC showed additive effects to significantly alleviate the joint destruction and pain. The efficacy of this combined therapy could sustain for 3 months after the last injection. We demonstrated that VC enhanced the promotive effect of Mg2+ on HIF-1α expression in cartilage. Additionally, combination of Mg2+ and VC markedly promoted the M2 polarization of macrophages in synovium. Furthermore, combination of Mg2+ and VC inhibited osteophyte formation and expressions of pain-related neuropeptides. Intra-articular administration of Mg2+ and VC additively alleviates joint destruction and pain in OA. Our current formulation may be a cost-effective alternative treatment for OA.

Distraction osteogenesis (DO) is a well-established surgical technique for treating bone defect and limb lengthening. The major drawback of DO is the long treatment period as the external fixator has to be kept in place until consolidation is completed. Calcitonin gene-related peptide (CGRP) has been reported to promote angiogenesis by affecting endothelial progenitor cells (EPCs) in limb ischemia and wound healing. Thus, the goal of this study was to evaluate the angiogenic effect of exogenous CGRP on bone regeneration in a rat DO model. Exogenous CGRP was directly injected into the bone defect after each cycle of distraction in vivo. Micro-computed tomography, biomechanical test and histological analysis were performed to assess the new bone formation. Angiography and immunofluorescence were performed to assess the formation of blood vessels. CD31+CD144+ EPCs in the bone defect were quantified with flow cytometry. In in vitro study, bone marrow stem cells (BMSCs) were used to investigate the effect of CGRP on EPCs production during endothelial differentiation. Our results showed that CGRP significantly promoted bone regeneration and vessel formation after consolidation. CGRP significantly increased the fraction of CD31+CD144+EPCs and the density of capillary density in the bone defect at the end of distraction phase. CGRP increased EPCs population in the endothelial differentiation of BMSCs in vitro by activating PI3K/AKT signaling pathway. Furthermore, differentiated EPCs rapidly assembled into tube-like structures and promoted osteogenic differentiation of BMSCs. In conclusion, CGRP increased EPCs population and promoted blood vessel formation and bone regeneration at the defect region in a DO model.

Magnesium metal and its alloys are being developed as effective orthopedic implants; however, the mechanisms underlying the actions of magnesium on bones remain unclear. Cystic fibrosis, the most common genetic disease in Caucasians caused by the mutation of CFTR, has shown bone disorder as a key clinical manifestation, which currently lacks effective therapeutic options. Here we report that implantation of magnesium-containing implant stimulates bone formation and improves bone fracture healing in CFTR-mutant mice. Wnt/β-catenin signaling in the bone is enhanced by the magnesium implant, and inhibition of Wnt/β-catenin by iCRT14 blocks the magnesium implant to improve fracture healing in CFTR-mutant mice. We further demonstrate that magnesium ion enters osteocytes, increases intracellular cAMP level and activates ATF4, a key transcription factor known to regulate Wnt/β-catenin signaling. In vivo knockdown of ATF4 abolishes the magnesium implant-activated β-catenin in bones and reverses the improved-fracture healing in CFTR-mutant mice. In addition, oral supplementation of magnesium activates ATF4 and β-catenin as well as enhances bone volume and density in CFTR-mutant mice. Together, these results show that magnesium implantation or supplementation may serve as a potential anabolic therapy for cystic fibrosis-related bone disease. Activation of ATF4-dependent Wnt/β-catenin signaling in osteocytes is identified as a previously undefined mechanism underlying the beneficial effect of magnesium on bone formation.

Elevated bone resorption and diminished bone formation have been recognized as the primary features of glucocorticoid-associated skeletal disorders. However, the direct effects of excess glucocorticoids on bone turnover remain unclear. Here, we explored the outcomes of exogenous glucocorticoid treatment on bone loss and delayed fracture healing in mice and found that reduced bone turnover was a dominant feature, resulting in a net loss of bone mass. The primary effect of glucocorticoids on osteogenic differentiation was not inhibitory; instead, they cooperated with macrophages to facilitate osteogenesis. Impaired local nutrient status — notably, obstructed fatty acid transportation — was a key factor contributing to glucocorticoid-induced impairment of bone turnover in vivo. Furthermore, fatty acid oxidation in macrophages fueled the ability of glucocorticoid-liganded receptors to enter the nucleus and then promoted the expression of BMP2 , a key cytokine that facilitates osteogenesis. Metabolic reprogramming by localized fatty acid delivery partly rescued glucocorticoid-induced pathology by restoring a healthier immune-metabolic milieu. These data provide insights into the multifactorial metabolic mechanisms by which glucocorticoids generate skeletal disorders, thus suggesting possible therapeutic avenues.

Magnesium (Mg) has a prophylactic potential against the onset of hyperlipidemia. Similar to statin, Mg is recommended as lipid-lowering medication for hypercholesterolemia and concomitantly exhibits an association with increased bone mass. The combination of statin with Mg ions (Mg²⁺) may be able to alleviate the high-fat diet (HFD)-induced bone loss and reduce the side-effects of statin. This study aimed to explore the feasibility of combined Mg²⁺ with simvastatin (SIM) for treating HFD-induced bone loss in mice and the involving mechanisms. C57BL/6 male mice were fed with a HFD or a normal-fat diet (NFD). Mice were intraperitoneally injected SIM and/or orally received water with additional Mg²⁺ until sacrificed. Enzyme-linked immunosorbent assay was performed to measure cytokines and cholesterol in serum and liver lysates. Bone mineral density (BMD) and microarchitecture were assessed by micro-computed tomography (μCT) in different groups. The adipogenesis in palmitate pre-treated HepG2 cells was performed under various treatments. μCT analysis showed that the trabecular bone mass was significantly lower in the HFD-fed group than that in NFD-fed group since week 8. The cortical thickness in HFD-fed group had a significant decrease at week 24, as compared with NFD-fed group. The combination of Mg²⁺ and SIM significantly attenuated the trabecular bone loss in HFD-fed mice via arresting the osteoclast formation and bone resorption. Besides, such combination also reduced the hepatocytic synthesis of cholesterol and inhibited matrix metallopeptidase 13 (Mmp13) mRNA expression in pre-osteoclasts. The combination of Mg²⁺ and SIM shows a synergistic effect on attenuating the HFD-induced bone loss. Our current formulation may be a cost-effective alternative treatment to be indicated for obesity-related bone loss.