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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.

Insufficient dietary magnesium (Mg) intake has been associated in humans with low bone mass. Mg deficiency in the rat has suggested bone loss is due to increased bone resorption and/or inadequate bone formation during remodeling. The purpose of this study was to assess the effect of a low Mg diet on bone and mineral metabolism in the young and mature BALB/c mouse and explore the hypothesis that inflammatory cytokines may contribute to Mg deficiency-induced osteoporosis. Using an artificial diet, we induced targeted Mg depletion (0.002% Mg) with all other nutrients maintained at the normal level. In all Mg-depleted mice, hypomagnesemia developed and skeletal Mg content fell significantly. The serum Ca in Mg-deficient mice was higher than in control mice; however, serum PTH levels were not significantly different. Osteoprotegerin (OPG) in dosages that inhibit osteoclastic bone resorption did not prevent hypercalcemia in Mg-deficient animals. No significant difference in serum Ca was observed between groups when dietary Ca was reduced by 50%, suggesting that a compensatory increase in intestinal absorption might account for the hypercalcemia. Growth plate width decreased 33% in young Mg-deficient animals and chondrocyte columns decreased in number and length, suggesting that Mg deficiency reduced bone growth. Trabecular bone volume in the metaphysis of the tibia in these animals was decreased and osteoclast number was increased by 135%. Osteoblast number was significantly reduced. Immunohistochemistry revealed that substance P increased 230% and 200% in megakaryocytes and lymphocytes, respectively, after 1 day of Mg depletion. IL-1 increased by 140% in osteoclasts by day 3 and TNF alpha increased in osteoclasts by 120% and 500% in megakaryocytes on day 12. This study demonstrates a profound effect of Mg depletion on bone characterized by impaired bone growth, decreased osteoblast number, increased osteoclast number in young animals, and loss of trabecular bone with stimulation of cytokine activity in bone.

Magnesium (Mg) intake has been linked to bone mass and/or rate of bone loss in humans. Experimental Mg deficiency in animal models has resulted in impaired bone growth, osteopenia, and increased skeletal fragility. In order to assess changes in bone and mineral homeostasis that may be responsible, we induced dietary Mg deficiency in adult Simonsen albino rats for 16 weeks. Rats were fed either a low Mg diet (0.002 percent) or a normal control Mg diet (0.063 percent). Blood was obtained at baseline, 4 weeks, 8 weeks, 12 weeks and 16 weeks in both groups for serum Mg, calcium, PTH, and 1.25(OH)2-vitamin D determinations. Femora were harvested at 4 weeks and 16 weeks for mineral analysis and histomorphometry. Serum Mg fell in the Mg depleted group to 0.6 mg/dl (mean) by 16 weeks (controls = 2.0 mg/dl). The serum calcium (Ca) concentration was higher in the Mg depleted animals at 16 weeks, 10.8 mg/dl (controls = 8.9 mg/dl). Serum PTH concentration fell progressively in the Mg deficient rats to 30 pg/ml by week 16 (control = 96 pg/ml). Serum concentration of 1.25(OH)2-vitamin D also fell progressively in the Mg deficient animals by 16 weeks to 14 pg/ml (control = 30 pg/ml). While the percent ash weights of Ca and phosphorus in the femur were not different at any time point, the percent ash weight of Mg progressively fell to 0.54 percent vs control (0.74 percent) by 16 weeks. The percent ash weight of potassium also fell progressively in the Mg deficient group to approximately 30 percent of control by 16 weeks. Histomorphometric analyses showed a significant drop in trabecular bone volume in Mg deficient animals by 16 weeks (percent BV/TV = 13.2 percent vs 17.3 percent in controls). Evaluation of the endosteal bone surface features showed significantly greater bone resorption in the Mg depleted group as reflected in increased number of tartrate-resistant positive osteoclasts/mm bone surface (7.8 vs 4.0 in controls) and an elevated percent of bone surface occupied by osteoclasts (percent OcS/BS = 12.2 percent vs 6.7 percent in controls. This increased resorption occurred in the presence of an inappropriate lowered bone forming surface relative to controls; a decreased number of osteoblasts per mm bone surface (0.23 vs 0.94 in control) and a decrease in percent trabecular surface lined by osteoid (percent OS/BS = 0.41 vs 2.27 percent in controls) were also noted. Our findings demonstrate a Mg-deficiency induced uncoupling of bone formation and bone resorption resulting in a loss of bone mass. While the fall in PTH and/or 1.25(OH)2-D may explain a decrease in osteoblast activity, the mechanism for increased osteoclast activity is unclear. These data suggest that Mg deficiency may be a risk factor for osteoporosis.

Osteoblasts arise from partially differentiated osteogenic progenitor cells (OPCs) which in turn arise from undifferentiated marrow stromal mesenchymal stem cells (MSCs). It has been postulated that age-related defects in osteoblast number and function may be due to quantitative and qualitative stem cell defects. To examine this possibility, we compared osteogenic stem cell number and in vitro function in marrow cells from 4-month-old and 24-month-old male BALB/c mice. Histologic studies demonstrated that these mice undergo age-related bone loss resembling that seen in humans. In primary MSC cultures grown in media supplemented with 10 nM dexamethasone, cultures from older animals yielded an average of 41% fewer OPC colonies per given number of marrow cells plated (p < 0.001). This implies that for a given number of marrow cells there are fewer stem cells with osteogenic potential in older animals than there are in younger animals. The basal proliferative rate in cultures from older animals, as measured by 3H-thymidine uptake, was more than three times that observed in cultures from young animals (p < 0.005). However, the increase in proliferative response to serum stimulation was 10-fold in the younger cultures (p <0.001) and insignificant (p <0.4) in the older cultures. Colonies in both age groups became alkaline phosphatase positive at the same rate, and virtually all colonies were positive after 12 days of culture. Cultures from both age groups produced abundant type I collagen. These studies suggest that defects in the number and proliferative potential of MSCs may underlie age-related defects in osteoblast number and function.

Glucocorticoid excess results in osteoporosis by inhibiting bone formation as well as by increasing bone resorption. The cellular mechanism for the glucocorticoid effect is unknown but has been postulated to be due to enhancement of the cyclic AMP response to PTH. This study examined the effect of in vivo administration of a glucocorticoid on adenylate cyclase activity in plasma membranes isolated from mineralized bone. Glucocorticoid excess was induced by implanting cortisone subcutaneously in adult female guinea pigs. At the end of 3 weeks skeletal plasma membranes were obtained, and adenylate cyclase activity was compared with that of normal age-matched guinea pigs. The specific activity of basal adenylate cyclase activity was significantly greater in the cortisone-treated animals (77.7 +/- 10 vs. 41.9 +/- 4.4 pmol cAMP/mg protein/15 min, p < 0.005), but PTH stimulated both to an equal degree. In contrast to the increased specific activity of intact adenylate cyclase, the specific activity of the catalytic unit was lower in the membranes from cortisone-treated animals. We also examined the effect of cortisone treatment on the modulation of adenylate cyclase by divalent cations. Neither the KaMg or the ability of Ca2+ to inhibit enzyme activity was found to differ between normal and cortisone-treated animals. In addition, PTH caused an increase in Mg2+ affinity in both sets of membranes to a comparable degree. The effect of cortisone could not be attributed to altered amounts of Ni present in these membranes; we were unable to satisfactorily quantitate the amounts of Ns.(ABSTRACT TRUNCATED AT 250 WORDS)

This study evaluates osteoblast and osteoclast cell numbers and cell activities determined from quantitative histology of trabecular bone in human iliac crest bone biopsies. Subjects studied were postmenopausal osteoporotic patients (aged 53-81) for whom total body calcium and urine and serum clinical data were also available. Only 39% of the osteoclasts identified by acid phosphatase content were multinucleate; however, a significant correlation between multinucleate osteoclasts and the total number of osteoclasts was found (r = 0.87; p less than 0.001). The mean number of osteoclasts per square millimeter of total tissue area was 0.96 (+/- 0.14, SEM, n = 36); the mean number of osteoblasts was 6.8 (+/- 1.5, n = 14)/mm2 tissue area. Computed osteoclast activity (square millimeter bone resorbed per osteoclast nucleus per day) was 2.6 X 10(-4) +/- 1.0 X 10(-4) (n = 13). Computed osteoblast activity (square millimeter bone formed per osteoblast per day) was 2.9 X 10(-5) +/- 8.8 X 10(-6) (n = 13). Calculated mean rate of bone resorption was 1.6 X 10(-4) +/- 3.4 X 10(-5) mm2 bone resorbed per mm2 total tissue area per day (n = 19). These data indicate that although osteoclasts are not numerous in the iliac crest of postmenopausal osteoporotics, the individual osteoclast activity (in square millimeter bone resorbed osteoclast cell unit per day) is significantly greater (p less than 0.001) than the osteoblast activity (in square millimeter matrix deposited per cell per day). These data also point out that greater consideration should be given to the role that osteoclast cell activity may play in human postmenopausal osteoporosis.

A rational approach to the diagnosis of osteoporosis by the primary care physician is outline, with emphasis on the patient who presents with chronic back pain and a vertebral compression fracture. The basic information includes data from the patient's history and physical examination, laboratory, x-ray and bone biopsy studies, and determination of bone mineral content (BMC) by photon absorptiometry. Characteristic radiologic features associated with bone loss, BMC changes, and bone biopsy findings are illustrated. This diagnostic approach, summarized in a flow diagram, poses a series of questions; the answer to each question leads either ot a diagnostic conclusion or to further questions which must be answered. This permits decision as to whether a compression fracture is due to trauma, local osteoporosis, osteomalacia, secondary osteoporosis or primary osteoporosis. In te study population (150 subjects), 80 percent of patients presenting with vertebral compression fractures had primary osteoporosis.

To assess the efficacy of the anabolic steroid stanozolol in the treatment of osteoporosis, a 29-month double-blind study was performed with 23 treated and 23 control postmenopausal osteoporotic women. Drug efficacy was assessed by serial determinations of total body calcium (TBC--total bone mass) by neutron activation analysis, regional bone mass (RBM) by single-photon absorptiometry, and by spinal roentgenograms. Total body calcium increased 4.4% from baseline values (P less than 0.01) in the treated group and remained unchanged in the control group; the difference in the change in TBC between the treated and control groups was significant (P less than 0.03). The effect of the drug on TBC persisted throughout the 29-month period. In contrast to TBC, measurements of RBM indicated no significant differences between the treated and placebo groups, suggesting a possible differential response to therapy at various skeletal sites. No new spinal compression fractures were noted in the treated group (compared with three new fractures in the control group). Assessment of serum and urine values indicated a decrease in the level of urinary calcium and an increase in the level of total urinary cyclic AMP in the treated group. These changes were observed even though the level of serum iPTH was significantly decreased during the study. An analysis of changes in bone biopsy specimens revealed no significant differences between the treated and control groups. Seventy-six percent of the treated subjects developed SGOT elevations or other side effects from the stanozolol therapy; at no time were these effects sufficiently severe to cause termination of medication. The data suggest that long-term use of stanozolol increases the net total bone mass above pretreatment levels.

Case reports of three young patients who developed vertebral fractures and skeletal complications during pregnancy and/or lactation are presented. Radiologic features are described. All three had severe disease with three to nine vertebral fractures at presentation postpartum. In two patients, follow-up for 5-7.8 yr (including further pregnancy in each) revealed no further fractures. In general, serum and urine features were normal, the exceptions being a low serum 25-hydroxyvitamin D level (plus intermittent elevation of serum parathyroid hormone) in one, a tendency to low plasma alkaline phosphatase in another, and in the third (the most severely affected patient) a transient rise in urinary hydroxyproline and plasma alkaline phosphatase during a phase of bone loss following her second and third pregnancies. Bone biopsies performed 1 to 6-1/2 yr after parturition showed quantitative bone histologic features and bone formation rates that, as a group, were not significantly different from either normal or postmenopausal osteoporotic subjects. These patients did not have osteomalacia and did not show high turnover osteoporotic features. It is possible that this type of osteoporosis may be somewhat self-limiting, although this hypothesis is subject to great influence by any adaptive lifestyle changes introduced by the patient. The severe fracture history of these patients emphasizes the gravity of their bone disease and stresses the need for further study on the etiology and treatment of this form of osteoporosis.

Results are presented from a 2-year controlled study evaluating the efficacy of 100 units synthetic salmon calcitonin/d in the treatment of postmenopausal osteoporosis. All patients received 400 units D2 po qd and 1200 mg CaCO3 po qd. The 21 control and 24 treated patients (mean age 65) were not statistically different at baseline. Although mean total body calcium (TBCa) was not significantly different between treated and control patients throughout the study, mean differences in the change in TBCa from baseline (treated minus control) were significant at 12, 18, and 26 months. The mean slope of TBCa for treated patients, but not for controls, was significantly positive through 18 months. Iliac crest bone biopsies showed (1) a significantly greater percent total bone area in treated compared to control patients at 2 years, and (2) a significantly decreased percent resorbing surface in treated patients when evaluated by paired difference from baseline. At 4 months, serum calcium values were significantly lower in treated patients than in controls (mean difference, treated minus controls), but were not statistically different from controls at study completion. Urine calcium increased significantly for the first 4 months in treated subjects and then declined to baseline levels. Since urinary calcium increased, the increase in TBCa was probably associated with an increase in net intestinal calcium absorption.

The present study is a retrospective examination of osteoblast indices in human iliac crest bone biopsies from a study on the long-term efficacy of calcitonin. Paired baseline and 2-year biopsies were examined from eight control subjects and 10 treated subjects; treated subjects received 100 MRC units synthetic salmon calcitonin (Calcimar, Armour Pharmaceutical Co, Scottsdale, AZ) injected i.m. sub Q at bedtime. Control patients did not receive a placebo injection. All subjects received 400 units vitamin D(2) p.o. q.d. and 1200 mg CaCO(3) p.o. q.d. When the differences in baseline and 2-year values were analyzed, subjects receiving calcitonin showed no decrease compared with control subjects for the fraction of osteoid surface lined by osteoblasts (ObS/OS) (but were in fact significantly greater, P = 0.04). There was no difference from control subjects in the number of osteoblasts/mm bone surface (NOb/BPm), or mean mineral apposition rate (MAR). Since calcitonin is receiving renewed interest for osteoporosis therapy, these data (derived from paired human biopsies) are valuable since they show that no decrease in osteoblast cell number resulted from long-term calcitonin therapy. Results point to the need for renewed investigation concerning the effect of calcitonin on osteoblast-osteoclast interactions. [ABSTRACT FROM AUTHOR]