Alterations in osteoclast morphology following osteoprotegerin administration in the magnesium-deficient mouse

The Role of Trace Elements and Minerals in Osteoporosis: A Review of Epidemiological and Laboratory Findings

The objective of the present study was to review recent epidemiological and clinical data on the association between selected minerals and trace elements and osteoporosis, as well as to discuss the molecular mechanisms underlying these associations. We have performed a search in the PubMed-Medline and Google Scholar databases using the MeSH terms "osteoporosis", "osteogenesis", "osteoblast", "osteoclast", and "osteocyte" in association with the names of particular trace elements and minerals through 21 March 2023. The data demonstrate that physiological and nutritional levels of trace elements and minerals promote osteogenic differentiation through the up-regulation of BMP-2 and Wnt/β-catenin signaling, as well as other pathways. miRNA and epigenetic effects were also involved in the regulation of the osteogenic effects of trace minerals. The antiresorptive effect of trace elements and minerals was associated with the inhibition of osteoclastogenesis. At the same time, the effect of trace elements and minerals on bone health appeared to be dose-dependent with low doses promoting an osteogenic effect, whereas high doses exerted opposite effects which promoted bone resorption and impaired bone formation. Concomitant with the results of the laboratory studies, several clinical trials and epidemiological studies demonstrated that supplementation with Zn, Mg, F, and Sr may improve bone quality, thus inducing antiosteoporotic effects.

Magnesium deficiency results in an increased formation of osteoclasts

Magnesium (Mg(2+)) deficiency is a frequently occurring disorder that leads to loss of bone mass, abnormal bone growth and skeletal weakness. It is not clear whether Mg(2+) deficiency affects the formation and/or activity of osteoclasts. We evaluated the effect of Mg(2+) restriction on these parameters. Bone marrow cells from long bone and jaw of mice were seeded on plastic and on bone in medium containing different concentrations of Mg(2+) (0.8 mM which is 100% of the normal value, 0.4, 0.08 and 0 mM). The effect of Mg(2+) deficiency was evaluated on osteoclast precursors for their viability after 3 days and proliferation rate after 3 and 6 days, as was mRNA expression of osteoclastogenesis-related genes and Mg(2+)-related genes. After 6 days of incubation, the number of tartrate resistant acid phosphatase-positive (TRACP(+)) multinucleated cells was determined, and the TRACP activity of the medium was measured. Osteoclastic activity was assessed at 8 days by resorption pit analysis. Mg(2+) deficiency resulted in increased numbers of osteoclast-like cells, a phenomenon found for both types of marrow. Mg(2+) deficiency had no effect on cell viability and proliferation. Increased osteoclastogenesis due to Mg(2+) deficiency was reflected in higher expression of osteoclast-related genes. However, resorption per osteoclast and TRACP activity were lower in the absence of Mg(2+). In conclusion, Mg(2+) deficiency augmented osteoclastogenesis but appeared to inhibit the activity of these cells. Together, our in vitro data suggest that altered osteoclast numbers and activity may contribute to the skeletal phenotype as seen in Mg(2+) deficient patients.

Reduction of dietary magnesium by only 50% in the rat disrupts bone and mineral metabolism

INTRODUCTION

The objective of this study was to determine the effect of a moderate reduction of dietary magnesium [50% of nutrient requirement (50% NR)] on bone and mineral metabolism in the rat, and to explore possible mechanisms for the resultant reduced bone mass.

METHODS

Female rats were 6 weeks of age at the start of study. Serum magnesium (Mg), calcium (Ca), parathyroid hormone (PTH), 1,25(OH)(2)-vitamin D, alkaline phosphatase, osteocalcin, and pyridinoline were measured during the study at 3- and 6-month time points in control (dietary Mg of 100% NR) and Mg-deficient animals (dietary Mg at 50% NR). Femurs and tibias were also collected for mineral content analyses, micro-computerized tomography, histomorphometry, and immunohistochemical localization of substance P, TNFalpha, and IL-1beta at 3 and 6 months.

RESULTS

Although no significant change in serum Mg was observed, Mg deficiency developed, as assessed by the reduction in bone Mg content at the 3- and 6-month time points (0.69+/-0.05 and 0.62+/-0.04% ash, respectively, in the Mg depletion group compared to 0.74+/-0.04 and 0.67+/-0.04% ash, respectively, in the control group; p=0.0009). Hypercalcemia did not develop. Although serum Ca level remained in the normal range, it fell significantly with Mg depletion at 3 and 6 months (10.4+/-0.3 and 9.6+/-0.3 mg/dl, respectively, compared to 10.5+/-0.4 and 10.1+/-0.6 mg/dl, respectively, in the control group; p=0.0076). The fall in serum Ca in the Mg-depleted animals was associated with a fall in serum PTH concentration between 3 and 6 months (603+/-286 and 505+/-302 pg/ml, respectively, although it was still higher than the control). The serum 1,25(OH)(2)-vitamin D level was significantly lower in the Mg depletion group at 6 months (10.6+/-7.1 pg/ml) than in the control (23.5+/- 12.7 pg/ml) (p<0.01 by the t-test). In Mg-deficient animals, no difference was noted in markers of bone turnover. Trabecular bone mineral content gain was less over time in the distal femur with Mg deficiency at 3 and 6 months (0.028+/-0.005 and 0.038+/-0.007 g, respectively, compared to 0.027+/-0.004 and 0.048+/-0.006 g, respectively, in the control group; p<0.005). Histomorphometry at these time points demonstrated decreased trabecular bone volume (15.76+/-1.93 and 14.19+/-1.85%, respectively, compared to 19.24+/-3.10 and 17.30+/-2.59%, respectively, in the control group; p=0.001). Osteoclast number was also significantly increased with Mg depletion (9.07+/-1.21 and 13.84+/-2.06, respectively, compared to 7.02+/-1.89 and 10.47+/-1.33, respectively, in the control group; p=0.0003). Relative to the control, immunohistochemical staining intensity of the neurotransmitter substance P and of the cytokines TNFalpha and IL-1beta was increased in cells of the bone microenvironment in the Mg depletion group, suggesting that inflammatory cytokines may contribute to bone loss.

CONCLUSION

These data demonstrate that Mg intake of 50% NR in the rat causes a reduced bone mineral content and reduced volume of the distal femur. These changes may be related to altered PTH and 1,25(OH)(2)-vitamin D formation or action as well as to an increase release of substance P and the inflammatory cytokines TNFalpha and IL-1beta.