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In comparison with calcium, magnesium is an "orphan nutrient" that has been studied considerably less heavily. Low magnesium intakes and blood levels have been associated with type 2 diabetes, metabolic syndrome, elevated C-reactive protein, hypertension, atherosclerotic vascular disease, sudden cardiac death, osteoporosis, migraine headache, asthma, and colon cancer. Almost half (48%) of the US population consumed less than the required amount of magnesium from food in 2005-2006, and the figure was down from 56% in 2001-2002. Surveys conducted over 30 years indicate rising calcium-to-magnesium food-intake ratios among adults and the elderly in the United States, excluding intake from supplements, which favor calcium over magnesium. The prevalence and incidence of type 2 diabetes in the United States increased sharply between 1994 and 2001 as the ratio of calcium-to-magnesium intake from food rose from <3.0 to >3.0. Dietary Reference Intakes determined by balance studies may be misleading if subjects have chronic latent magnesium deficiency but are assumed to be healthy. Cellular magnesium deficit, perhaps involving TRPM6/7 channels, elicits calcium-activated inflammatory cascades independent of injury or pathogens. Refining the magnesium requirements and understanding how low magnesium status and rising calcium-to-magnesium ratios influence the incidence of type 2 diabetes, metabolic syndrome, osteoporosis, and other inflammation-related disorders are research priorities., (© 2012 International Life Sciences Institute.)

Epidemiologic studies have linked low dietary magnesium (Mg) intake to osteoporosis. Dietary Mg restriction in animal models has demonstrated a decrease in bone mass and an increase in skeletal fragility. The exact mechanism for the decrease in bone mass is not clear but a decrease in osteoblast number and an increase in osteoclast number (Oc.No/B.Pm) suggests an uncoupling of bone formation and bone resorption favoring skeletal loss. Mg depletion results in an increase in inflammatory cytokines, which could explain the increase in bone resorption. We have previously demonstrated an increase in TNFalpha in bone from Mg deficient rodents. Here we report results of a 3 week study of a low magnesium (LM) diet and normal Mg diet in 35-day-old TNFalpha receptor knockout mice (TNF-r-KO) versus wild type (WT) control mice. Our results indicated that a LM diet resulted in a greater increase in Oc.No/B.Pm in the WT mice, with a trend toward greater eroded bone perimeter, as compared to TNF-r-KO. These findings suggest that TNFalpha may play a role in Mg deficiency-induced bone loss.

Magnesium (Mg) is the second most abundant intracellular cation where it plays an important role in enzyme function and trans-membrane ion transport. Mg deficiency has been associated with a number of clinical disorders including osteoporosis. Osteoporosis is common problem accounting for 2 million fractures per year in the United States at a cost of over $17 billion dollars. The average dietary Mg intake in women is 68% of the RDA, indicating that a large proportion of our population has substantial dietary Mg deficits. The objective of this paper is to review the evidence for Mg deficiency-induced osteoporosis and potential reasons why this occurs, including a cumulative review of work in our laboratories and well as a review of other published studies linking Mg deficiency to osteoporosis. Epidemiological studies have linked dietary Mg deficiency to osteoporosis. As diets deficient in Mg are also deficient in other nutrients that may affect bone, studies have been carried out with select dietary Mg depletion in animal models. Severe Mg deficiency in the rat (Mg at <0.0002% of total diet; normal = 0.05%) causes impaired bone growth, osteopenia and skeletal fragility. This degree of Mg deficiency probably does not commonly exist in the human population. We have therefore induced dietary Mg deprivation in the rat at 10%, 25% and 50% of recommended nutrient requirement. We observed bone loss, decrease in osteoblasts, and an increase in osteoclasts by histomorphometry. Such reduced Mg intake levels are present in our population. We also investigated potential mechanisms for bone loss in Mg deficiency. Studies in humans and and our rat model demonstrated low serum parathyroid hormone (PTH) and 1,25(OH)(2)-vitamin D levels, which may contribute to reduced bone formation. It is known that cytokines can increase osteoclastic bone resorption. Mg deficiency in the rat and/or mouse results in increased skeletal substance P, which in turn stimulates production of cytokines. With the use of immunohistocytochemistry, we found that Mg deficiency resulted in an increase in substance P, TNFalpha and IL1beta. Additional studies assessing the relative presence of receptor activator of nuclear factor kB ligand (RANKL) and its decoy receptor, osteoprotegerin (OPG), found a decrease in OPG and an increase in RANKL favoring an increase in bone resorption. These data support the notion at dietary Mg intake at levels not uncommon in humans may perturb bone and mineral metabolism and be a risk factor for osteoporosis.

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.

Background: Epidemiological studies have linked low dietary magnesium (Mg) to low bone mineral density and osteoporosis. Mg deficiency in animal models has demonstrated a reduction in bone mass and increase in skeletal fragility. One major mechanism appears to be an increase in osteoclast number and bone resorption. The final pathway of osteoclastogenesis involves three constituents of a cytokine system: receptor activator of nuclear factor kB ligand (RANKL); its receptor, receptor activator of nuclear factor kB (RANK); and its soluble decoy receptor, osteoprotegerin (OPG). The relative presence of RANKL and OPG dictates osteoclastogenesis. The objective of this study was to assess the presence of RANKL and OPG in rats on a low Mg diet., Methods: RANKL and OPG were assessed by immunocytochemistry staining in the tibia for up to 6 months in control rats on regular Mg intake (0.5 g/kg) and experimental rats on reduction of dietary Mg (.04%, 25% and 50% of this Nutrient Requirement)., Results: At all dietary Mg intakes, alteration in the presence of immunocytochemical staining of RANKL and OPG was observed. In general, OPG was decreased and RANKL increased, reflecting an alteration in the RANKL/OPG ratio toward increased osteoclastogenesis., Conclusion: We have, for the first time demonstrated that a reduction in dietary Mg in the rat alters the presence of RANKL and OPG and may explain the increase in osteoclast number and decrease in bone mass in this animal model. As some of these dietary intake reductions in terms of the RDA are present in a large segment of or population, Mg deficiency may be another risk factor for osteoporosis.

Low dietary magnesium (Mg) may be a risk factor for osteoporosis. In animals, severe Mg deficiency (0.04% of nutrient requirement [NR]) results in bone loss. We have also found that a more moderate dietary Mg restriction (10% of NR) also resulted in loss of bone. We now report the effect of Mg intake of 25% NR on bone and mineral metabolism in the rat. Serum Mg, Ca, PTH, 1,25(OH)2-vitamin D, alkaline phosphatase, osteocalcin, and pyridinoline were measured at 2, 4, and 6 months in control and Mg-deficient animals. Femurs and tibias were collected for mineral content, micro-computerized tomography, histomorphometry, and immunocytochemical localization. Profound Mg deficiency developed as assessed by marked hypomagnesemia and 27% reduction in bone Mg content. Serum calcium was not significantly different between groups. Mg depletion resulted in a significantly lower serum PTH concentrations. Serum 1,25(OH)2-vitamin D was also significantly lower. No difference was noted in markers of bone turnover. Histomorphometry and micro-computerized tomography demonstrated decreased bone volume and trabecular thickness. No difference was observed for osteoclast or osteoblast number. Inflammatory cytokines may contribute to bone loss. We found that immunocytochemical localization of TNFalpha in osteoclasts was increased 138-150%. This increase in TNFalpha may be due to increased substance P as it was found to be elevated from 179% to 432%. These data demonstrate that Mg intake of 25% NR in the rat causes lower bone mass which may be related to increased release of substance P and TNFalpha.

Magnesium (Mg) deficiency commonly occurs in critical illness and correlates with a higher mortality and worse clinical outcome in the intensive care unit (ICU). Magnesium has been directly implicated in hypokalemia, hypocalcemia, tetany, and dysrhythmia. Moreover, Mg may play a role in acute coronary syndromes, acute cerebral ischemia, and asthma. Magnesium regulates hundreds of enzyme systems. By regulating enzymes controlling intracellular calcium, Mg affects smooth muscle vasoconstriction, important to the underlying pathophysiology of several critical illnesses. The principle causes of Mg deficiency are gastrointestinal and renal losses; however, the diagnosis is difficult to make because of the limitations of serum Mg levels, the most common assessment of Mg status. Magnesium tolerance testing and ionized Mg2+ are alternative laboratory assessments; however, each has its own difficulties in the ICU setting. The use of Mg therapy is supported by clinical trials in the treatment of symptomatic hypomagnesemia and preeclampsia and is recommended for torsade de pointes. Magnesium therapy is not supported in the treatment of acute myocardial infarction and is presently undergoing evaluation for the treatment of severe asthma exacerbation, for the prevention of post-coronary bypass grafting dysrhythmias, and as a neuroprotective agent in acute cerebral ischemia.

Although osteoporosis is a major health concern for our growing population of the elderly, there continues to be a need for well-designed clinical and animal studies on the link between dietary magnesium (Mg) intake and osteoporosis. Relatively few animal studies have assessed the skeletal and hormonal impact of long-term low Mg intake; however, these studies have demonstrated that Mg deficiency results in bone loss. Potential mechanisms include a substance P-induced release of inflammatory cytokines as well as impaired production of parathyroid hormone and 1,25-dihydroxyvitamin D. Abnormal mineralization of bones may also contribute to skeletal fragility. Clinical studies have often varied greatly in study design, subject age, menopausal status and outcome variables that were assessed. Most studies focused on female subjects, thus pointing to the great need for studies on aging males. According to the U.S. Department of Agriculture, the mean Mg intake for males and females is 323 and 228 mg/day, respectively. These intake levels suggest that a substantial number of people may be at risk for Mg deficiency, especially if concomitant disorders and/or medications place the individual at further risk for Mg depletion. In this paper, we will review animal and human evidence of the association of Mg deficiency with osteoporosis and explore possible mechanisms by which this may occur.

Dietary Mg intake has been linked to osteoporosis. Previous studies have demonstrated that severe Mg deficiency [0.04% of nutrient requirement (NR)] results in osteoporosis in rodent models. We assessed the effects of more moderate dietary Mg restriction (10% of NR) on bone and mineral metabolism over a 6-mo experimental period in rats. At 2, 4 and 6 mo, serum Mg, Ca, parathyroid hormone (PTH), 1,25-dihydroxy-vitamin D, alkaline phosphatase, osteocalcin and urine pyridinoline were measured. Femurs and tibiae were collected for measurement of mineral content, microcomputerized tomography, histomorphometry, and immunocytochemical localization. By 2 mo, profound Mg deficiency had developed as assessed by marked hypomagnesemia and up to a 51% reduction in bone Mg content. These features continued through 6 mo of study. Serum Ca was slightly but significantly higher in Mg-deficient rats than in controls at all time points. At 2 mo, serum PTH was elevated in Mg-deficient rats but was significantly decreased at 6 mo in contrast to control rats in which PTH rose. Serum 1,25-dihydroxy-vitamin D was significantly lower than in controls at 4 and 6 mo. A significant fall in both serum alkaline phosphatase and osteocalcin suggested decreased osteoblast activity. Histomorphometry demonstrated decreased bone volume and trabecular thickness. This was confirmed by microcomputerized tomography analysis, which also showed that trabecular volume, thickness and number were significantly lower in Mg-deficient rats. Increased bone resorption was suggested by an increase in osteoclast number over time compared with controls as well as surface of bone covered by osteoclasts and eroded surface, but there was no difference in osteoblast numbers. The increased bone resorption may be due to an increase in TNF-alpha because immunocytochemical localization of TNF-alpha in osteoclasts was 199% greater than in controls at 2 mo, 75% at 4 mo and 194% at 6 mo. The difference in TNF-alpha may be due to substance P, which was 250% greater than in controls in mononuclear cells at 2 mo and 266% at 4 mo. These data demonstrated that a Mg intake of 10% of NR in rats causes bone loss that may be secondary to the increased release of substance P and TNF-alpha.

Background: Dietary magnesium (Mg) deficiency in the mouse perturbs bone and mineral homeostasis. The objective of the present study was to evaluate bone mineral density of the femur in control and Mg-deficient mice., Methods: BALB/c mice aged 28 days at study initiation were maintained on a normal or Mg deficient (0.0002% Mg) diet, and at time points 0, 2, 4 or 6 weeks bones were harvested for bone mineral density analysis. Peripheral quantitative computed tomography (pQCT) was used to assess the trabecular metaphyseal compartment and the cortical midshaft., Results: Although mean total bone density of the femoral midshaft in Mg deficient mice did not differ significantly from controls throughout the study, the trabecular bone compartment showed significantly decreased mineral content after 4 (p < 0.001) and 6 weeks (p < 0.001) of Mg depletion., Conclusions: This study demonstrates the profound effect of Mg depletion on the trabecular compartment of bone, which, with its greater surface area and turnover, was more responsive to Mg depletion than cortical bone in the appendicular skeleton of the mouse.

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.

Objective: To assess the effect of bone mineral density (BMD) screening on the decision to initiate preventive or therapeutic measures for osteoporosis., Methods: We offered low-cost BMD screening by dual-energy x-ray absorptiometry of the lumbar spine and proximal femur in conjunction with National Osteoporosis Week. In an effort to assess whether the availability of the BMD measurements resulted in any medical action by the participants of the screening, we conducted a retrospective telephone survey 9 to 12 months after the screening., Results: In response to a newspaper promotion, 350 subjects underwent BMD screening during a 3- to 4-month period. Of these 332 female and 18 male participants, 83% were Caucasian, 10% were Asian, 5% were Hispanic, and 2% were African American. The mean age was 60 +/- 11 years (range, 29 to 93). Osteoporosis (T-score > or = -2.5) was present in 24% and osteopenia (T-score of -1 to -2.49) in 47% of the subjects. A report was sent to the participant and, if requested, also to a specified physician. Of the 350 participants, 249 (238 women and 11 men) responded to the telephone survey. Of these respondents, 63% had sought medical consultation after the BMD screening. Results of the BMD study led to an increase in calcium intake in 32% of female respondents (48% of those with osteoporosis). After BMD measurement, use of osteoporosis therapy approved by the US Food and Drug Administration increased from 38% to 78% of those with osteoporosis., Conclusion: These results suggest that low-cost BMD screening is highly effective in increasing awareness of osteoporosis, prompting medical consultation, and initiating measures for prevention and treatment of osteoporosis.

Isolated hereditary renal magnesium (Mg) wasting may result from mutations in the renal tubular epithelial cell tight junction protein paracellin-1 gene or the tubular Na(+),K(+)-ATPase gamma-subunit gene FXYD2. The FXYD2 gene mutation was discovered in two Dutch families as an autosomal dominant disorder. It is characterized by isolated renal Mg wasting with resultant symptomatic hypomagnesemia. The defective FXYD2 gene in these families mapped to chromosome 11q23. Here, we describe an American family with a similar phenotype but without linkage to the 11q23 locus; in testing 22 individuals in the pedigree multipoint LOD scores for five different loci from the 11q23 region were equal to -2.97. Compared with unaffected family members and normal controls, affected family members harbored significant reductions in the serum and lymphocyte Mg concentrations and in the serum immunoreactive PTH level with a 4-fold increase in the mean fractional urinary Mg excretion rate during a normomagnesemic clamp. Bone mineral density at the lumbar spine and proximal femur was significantly reduced in affected family members. In conclusion, our data demonstrate locus heterogeneity for the phenotype of isolated renal Mg wasting with hypomagnesemia and suggest that hypomagnesemia, at least in this pedigree, may be associated with low bone mass.

The use of magnesium in the treatment of acute myocardial infarction remains controversial despite preliminary experimental evidence that magnesium plays a beneficial role as a regulator of thrombosis. The aim of our study was to determine whether oral magnesium treatment inhibits platelet-dependent thrombosis (PDT) in stable patients with coronary artery disease (CAD). In a randomized prospective, double-blind, cross-over and placebo controlled study, 42 patients with stable CAD (37 men, 5 women, mean age 68 +/- 9 years) on aspirin received either magnesium oxide tablets (800-1,200 mg/day) or placebo for 3 months (Phase 1) followed by a 4-week washout period, and the cross-over treatment for 3 months (Phase 2). PDT, platelet aggregation, platelet P-selectin flow-cytometry, monocyte tissue factor procoagulant activity (TF-PCA) and adhesion molecules density were assessed before and after each phase. PDT was evaluated by an ex-vivo perfusion model using the Badimon chamber. Median PDT was significantly reduced by 35 percent in patients who received magnesium versus placebo (D change from baseline: -24 vs. 26 microm2/mm; p = 0.02, respectively). There was no significant effect of magnesium treatment on platelet aggregation, P-selectin expression, monocyte TF-PCA or adhesion molecules. Oral magnesium treatment inhibits PDT in patients with stable CAD. This effect appears to be independent of platelet aggregation or P-selectin expression, and is evident despite aspirin therapy. These findings suggest a potential mechanism whereby magnesium may beneficially alter outcomes in patients with CAD.

Background: Although reduced intracellular levels of magnesium have been described in patients with acute myocardial infarction, its significance as a regulator of thrombosis remains unknown., Methods and Results: To determine whether reduced intracellular levels of magnesium enhance platelet-dependent thrombosis, we evaluated 42 patients with coronary artery disease (CAD) by exposing porcine aortic media to their flowing unanticoagulated venous blood for 5 minutes by using an ex vivo perfusion (Badimon) chamber. Baseline analysis demonstrated significant associations between intracellular levels of magnesium, platelet-dependent thrombosis (P =.02), and platelet P-selectin (CD62P) expression (P <.05). Patients were divided into 2 groups: below (n = 22) and above (n = 20) the median intracellular levels of magnesium (1.12 microg/mg protein). There were no significant differences in age, body mass index, serum lipids, fibrinogen, platelet count, or serum magnesium levels between the two groups. Platelet-dependent thrombosis was significantly higher in patients with intracellular levels of magnesium below compared with above median (150 +/- 128 vs 45 +/- 28 microm(2)/mm, P <.004). Neither platelet aggregation nor CD62P expression was significantly different between the two groups., Conclusions: Platelet-dependent thrombosis was significantly increased in patients with stable CAD with low intracellular levels of magnesium, suggesting a potential role for magnesium supplementation in CAD.

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.

The use of magnesium in the treatment of acute myocardial infarction remains controversial despite preliminary experimental evidence that magnesium plays a beneficial role as a regulator of thrombosis. This study examines whether oral magnesium treatment inhibits platelet-dependent thrombosis (PDT) in patients with coronary artery disease (CAD). In a randomized prospective, double-blind, crossover, and placebo-controlled study, 42 patients with CAD (37 men, 5 women, mean age 68 +/- 9 years) on aspirin received either magnesium oxide tablets (800 to 1,200 mg/day) or placebo for 3 months (phase 1) followed by a 4-week wash-out period, and the crossover treatment for 3 months (phase 2). PDT, platelet aggregation, platelet P-selectin flow cytometry, monocyte tissue factor procoagulant activity (TF-PCA), and adhesion molecule density were assessed before and after each phase. PDT was evaluated by an ex vivo perfusion model using the Badimon chamber. Median PDT was significantly reduced by 35% in patients who received magnesium versus placebo (delta change from baseline -24 vs 26 mm2/mm; p = 0.02, respectively). There was no significant effect of magnesium treatment on platelet aggregation, P-selectin expression, monocyte TF-PCA, or adhesion molecules. Oral magnesium treatment inhibited PDT in patients with stable CAD. This effect appears to be independent of platelet aggregation or P-selectin expression, and is evident despite aspirin therapy. These findings suggest a potential mechanism whereby magnesium may beneficially alter outcomes in patients with CAD.

Vitamin D3 analogs and paclitaxel (Taxol) are able to inhibit the in vitro growth of a variety of malignant cells including breast cancer cells. These two compounds decrease growth by different mechanisms and they have nonoverlapping toxicities. We examined the abilities of three vitamin D3 compounds to inhibit growth of a human mammary cancer (MCF-7) in BNX triple immunodeficient mice either alone or with Taxol. Vitamin D3 analogs were 1,25(OH)2D3 (code name, Compound C), 1,25(OH)2-16-ene-23-yne-19-nor-26,27-F6-D3 (Compound LH), and 24a,26a,27a,-trihomo-22,24-diene-1,25(OH)2D3 (EB1089). At the doses chosen, the antitumor effect of vitamin D3 analogs alone was greater than that of Taxol alone, and an additive effect was observed when a vitamin D3 analog and Taxol were administered together. EB1089 was the most potent compound, and the EB1089 plus Taxol was the most active combination, decreasing the tumor mass nearly 4-fold compared to controls. Weight-gain in each of the experimental cohorts at the end of the study was less than the control group, but the gain was significantly less in only two experimental groups (those receiving either EB1089 or Compound C plus Taxol). None of the animals became hypercalcemic, and their complete blood counts, serum electrolyte analyses, and liver and renal functions were all fairly similar and within the normal range. In summary, this combination of a vitamin D3 analog and Taxol has the potential to be a therapy for breast cancer.

To determine whether increased intracellular levels of magnesium ([Mg]i) are associated with enhanced functional capacity, we performed symptom-limited exercise treadmill testing on 42 stable coronary artery disease (CAD) patients (37 men, 5 women, mean age 68 +/- 9 years). [Mg]i was found to be an independent and significant predictor of exercise duration (R = 0.31, p = 0.02) in a multivariate stepwise regression model. Patients with > normal [Mg]i of 1.23 microg/mg protein (n = 13) had a significantly greater mean functional capacity, measured in higher achieved metabolic equivalents (10.6 +/- 2.5 vs. 8.9 +/- 2.3, p < 0.05) and exercise duration (9.4 +/- 2.3 vs. 7.9 +/- 2.2 min, p < 0.05) compared to patients with [Mg]i

Eleven femurs with press-fit titanium hip components were retrieved at autopsy for clinical, radiographic, and histologic evaluation. Back-scattered electron microscopy (BEM), bone densitometry, and appositional bone index studies also were performed. The average patient age was 87 years; the average time in situ was 22 months (range: 2 to 60). All patients were functioning well and pain free. Radiographs and bone mineral density studies (BMD) showed mild proximal stress shielding in five cases. No cases of osteolysis or pedestal formation were observed. Histologic sections revealed an average of 26% bone-prosthesis contact. Bone surrounding the prosthesis appeared viable, and osteoclastic activity in the interfacial bone was minimal; the presence of macrophages and inflammatory cells was rare. The appositional bone index averaged 40%. Bone-prosthesis contact was seen consistently at the corners of the component in the multiple regions, mostly were prosthesis-endosteal cortical contact was made. BEM demonstrated intimate contact of bone with the rough titanium surface. Bone mineral density was lower in the lesser trochanter and medial proximal regions of the implanted femur than in the contralateral femur. Evidence of bone on-growth fixation in 11 femoral components suggests that cementless, stable bone fixation may be achievable in senior individuals and that "complete fit and fill," porous-coated, cementless prostheses may not be required for prosthesis stability.

Disorders in which magnesium (Mg) depletion is common have an associated high incidence of osteoporosis. Mg depletion in humans results in hypocalcemia, low serum parathyroid hormone (PTH) and 1, 25(OH)2-vitamin D levels, as well as PTH and vitamin D resistance which may serve as mechanisms for the development of osteoporosis. In order to determine if isolated Mg depletion will result in bone loss, we have induced dietary Mg deficiency in the rat. Adult (290 g) female rats were given either a low-Mg diet (2 mg/100 g chow; n = 6) or a normal control Mg diet (63 mg/100 g chow; n = 6). Dietary calcium (Ca) was normal in both groups (592 mg/100 g chow). At 12 weeks, blood was obtained for serum Mg, Ca, PTH, 1,25(OH)2-vitamin D, and osteocalcin determinations. The rats were then euthanized and the femurs obtained for mineral analysis and histomorphometry. Serum Mg in the low-Mg group was less than control (0.4 +/- 0.2 vs. 1.9 +/- 0.2 mg/dl, p < 0.001; mean +/- SD) while serum Ca was higher (11. 7 +/- 0.5 vs. 9.3 +/- 0.4 mg/dl, p < 0.001). PTH was suppressed in the Mg-deficient group (36 +/- 16 vs. 109 +/- 30 pg/ml in controls, p < 0.002). Serum 1,25(OH)2-vitamin D was also suppressed in the Mg-deficient animals (7.1 +/- 4.8 vs. 28.5 +/- 8.2 pg/ml in controls, p < 0.002). Serum osteocalcin levels were not different (19.8 +/- 2.5 ng/ml in Mg-deficient rats vs. 15.3 +/- 3.4 ng/ml in controls). While the ash weight of Ca and phosphorus in the femur did not change, the ash weight of Mg fell (low-Mg group 0.55 +/- 0.01%, controls 0.65 +/- 0.02%, p < 0.001). Histomorphometry demonstrated reduction in bone mass; the trabecular bone volume in the femur of the low-Mg group was reduced from control (7.7 +/- 0.2 vs. 13.7 +/- 1.9%, p < 0.002). A surprising new observation was an increase in osteoclast (OC) bone resorption with Mg depletion. The number of OC per millimeter bone surface was 16.9 +/- 1.3 in the low-Mg group versus 7.8 +/- 1.5 in controls (p < 0.001). The percentage of bone surface occupied by OC was 38.3 +/- 3.7 in the low-Mg group versus 17.7 +/- 2.4 in controls (p < 0.001). This increased resorption occurred with an inappropriate non-altered bone-forming surface relative to control (% osteoid surface: low-Mg group 2.4 +/- 0.7 vs. controls 2.6 +/- 0.4; % osteoid volume: low-Mg group 0.25 +/- 0.09 vs. controls 0.38 +/- 0.06; number of osteoblasts per millimeter bone surface: low-Mg group 0.9 +/- 0.3 vs controls 1.3 +/- 0.3). No increase in bone-forming surface or osteoblast number despite an increase in OC-resorbing surface and OC number strongly suggests impaired activation of osteoblasts and an uncoupling of bone formation and bone resorption. Our data demonstrate that Mg depletion in the rat alters bone and mineral metabolism which results in bone loss.

Leptin, the obese (ob) gene product, is thought to be a lipostatic hormone that contributes to body weight regulation through modulating feeding behavior and/or energy expenditure. The determinants of plasma leptin concentration were evaluated in 267 subjects (106 with normal glucose tolerance, 102 with impaired glucose tolerance, and 59 with noninsulin-dependent diabetes). Fasting plasma leptin levels ranged from 1.8-79.6 ng/mL (geometric mean, 12.4), were higher in the obese subjects, and were not related to glucose tolerance. Women had approximately 40% higher leptin levels than men at any level of adiposity. After controlling for body fat, postmenopausal women had still higher leptin levels than men of similar age, and their levels were not different from those in younger women. Multiple regression analysis showed that adiposity, gender, and insulinemia were significant determinants of leptin concentration, explaining 42%, 28%, and 2% of its variance, respectively. Neither age nor the waist/hip ratio was significantly related to leptin concentration. Thus, our data indicate that gender is a major determinant of the plasma leptin concentration. This sex difference is not apparently explained by sex hormones or body fat distribution. Leptin's sexual dimorphism suggests that women may be resistant to its putative lipostatic actions and that it may have a reproductive function.

The working group on magnesium considered a number of issues relevant to establishing allowances and to providing other pertinent information on this ion for the next edition of the Recommended Dietary Allowances (RDA). An accurate and specific marker for assessing the importance of magnesium nutriture in health and disease remains to be identified. Thus, it is unknown whether marginal magnesium depletion results in a disease. Although it is apparent that abnormal serum concentrations are unusual and obvious signs of acute depletion of magnesium are absent in the U.S. populace, one cannot assume that the associated cellular and intracellular pool sizes are optimal for health. There is a need for systematic studies of these and other parameters in healthy individuals with controlled intakes and during depletion. To address the question of how magnesium allowances should be set, previous editions of the RDA that included magnesium were reviewed; this review indicated the need for the adoption of objective criteria for acceptance of published balance studies and the inclusion in the discussion of an analysis of the balance studies and the specific calculations used in establishing the RDA. Such criteria and evaluations should be placed in a technical addendum to allow readers to evaluate the data. It is recommended that future RDA Committees consider expressing metabolic balance data on a basis other than weight, e.g., energy expenditure, lean body mass or body cell mass. Claims that magnesium nutriture has a role in preventing or ameliorating chronic disease such as heart disease and hypertension need to be critically evaluated if they are to be used to set the next RDA. The pharmacologic effects of magnesium are significant and need to be recognized. Because excess oral magnesium can be toxic to persons with advanced renal disease, more attention should be given to this topic by future RDA Committees.

Primary hyperparathyroidism is the most prevalent cause of hypercalcemia. Although renal stone disease and osteitis fibrosis were prominent complications of this disorder in the past, the advent of biochemical screening has resulted in earlier detection. This has changed the clinical presentation of primary hyperparathyroidism, so that as many as 80% of patients do not have any sign or symptom that can be attributed solely to the disease. Improvement in assays for PTH has allowed for accurate bio-chemical diagnosis in over 90% of cases. Neck exploration is the treatment of choice for any patient who presents with signs, symptoms, or complications of hypercalcemia or hyperparathyroidism. Medical therapy is indicated in patients who either cannot undergo surgery because of medical contraindication, failed prior neck surgery, unresectable parathyroid carcinoma or simply refuse surgery. Medical therapy is not optimal, although sex steroid replacement therapy in the postmenopausal woman has met with some success. Calcitonin, phosphate, and bisphosphonates may be used, but their long-term efficacy is not clear. Recent studies have suggested that a large proportion of patients with asymptomatic primary hyperparathyroidism do not demonstrate progression of disease in terms of renal dysfunction, bone disease, or biochemical changes in calcium or PTH. Guidelines have been established for medical follow-up of such patients. If any such patient develops signs or symptoms during medical follow-up, surgery is then indicated.

Osteoporosis and magnesium (Mg) deficiency often occur in malabsorption syndromes such as gluten-sensitive enteropathy (GSE). Mg deficiency is known to impair parathyroid hormone (PTH) secretion and action in humans and will result in osteopenia and increased skeletal fragility in animal models. We hypothesize that Mg depletion may contribute to the osteoporosis associated with malabsorption. It was our objective to determine Mg status and bone mass in GSE patients who were clinically asymptomatic and on a stable gluten-free diet, as well as their response to Mg therapy. Twenty-three patients with biopsy-proven GSE on a gluten-free diet were assessed for Mg deficiency by determination of the serum Mg, red blood cell (RBC) and lymphocyte free Mg2+, and total lymphocyte Mg. Fourteen subjects completed a 3-month treatment period in which they were given 504-576 mg MgCl2 or Mg lactate daily. Serum PTH, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D and osteocalcin were measured at baseline and monthly thereafter. Eight patients who had documented Mg depletion (RBC Mg2+ < 150 microM) underwent bone density measurements of the lumbar spine and proximal femur, and 5 of these patients were followed for 2 years on Mg therapy. The mean serum Mg, calcium, phosphorus and alkaline phosphatase concentrations were in the normal range. Most serum calcium values fell below mean normal and the baseline serum PTH was high normal or slightly elevated in 7 of the 14 subjects who completed the 3-month treatment period. No correlation with the serum calcium was noted, however. Mean serum 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D and osteocalcin concentrations were also normal. Despite only 1 patient having hypomagnesemia, the RBC Mg2+ (153 +/- 6.2 microM; mean +/- SEM) and lymphocyte Mg2+ (182 +/- 5.5 microM) were significantly lower than normal (202 +/- 6.0 microM, p < 0.001, and 198 +/- 6.8 microM, p < 0.05, respectively). Bone densitometry revealed that 4 of 8 patients had osteoporosis of the lumbar spine and 5 of 8 had osteoporosis of the proximal femur (T-scores < or = -2.5). Mg therapy resulted in a significant rise in the mean serum PTH concentration from 44.6 +/- 3.6 pg/ml to 55.9 +/- 5.6 pg/ml (p < 0.05). In the 5 patients given Mg supplements for 2 years, a significant increased in bone mineral density was observed in the femoral neck and total proximal femur. This increase in bone mineral density correlated positively with a rise in RBC Mg2+. This study demonstrates that GSE patients have reduction in intracellular free Mg2+, despite being clinically asymptomatic on a gluten-free diet. Bone mass also appears to be reduced. Mg therapy resulted in a rise in PTH, suggesting that the intracellular Mg deficit was impairing PTH secretion in these patients. The increase in bone density in response to Mg therapy suggests that Mg depletion may be one factor contributing to osteoporosis in GSE.

Diabetes mellitus may be associated with magnesium depletion, which in turn may contribute to metabolic complications of diabetes including vascular disease and osteoporosis. Intracellular depletion is thought to be due to osmotically induced renal magnesium loss; however, impaired ability of insulin to increase intracellular magnesium during insulin deficiency or insulin resistance could also play a role. Magnesium deficiency per se has also been reported to result in insulin resistance. In order to determine if magnesium transport is altered in non-insulin-dependent diabetes mellitus (NIDDM), we measured intracellular Mg(2+) in circulating lymphocytes obtained from nine normal subjects and seven patients with NIDDM. Ionized intracellular Mg(2+) was determined by fluorescent spectroscopy using Mg-fura-2. A 30 min incubation of insulin with lymphocytes obtained from normal subjects resulted in an increase in Mg(2+) of 8.6 +/- 3.6 percent (mean +/- SEM) at 100 mu U/ml which reached a plateau at approximately 250 mu U/ml (11.0 +/- 1.7 percent). The mean lymphocyte Mg(2+) in the patients (0.198 +/- 0.011 mM) was not significantly lower than normal (0.218 +/- 0.017). Insulin (500 mU/ml) added acutely during the fluorescence reading caused a rapid 31 +/- 3.9 percent rise in intracellular Mg(2+) in the normal subjects, which was significantly greater than the 18 +/- 1.6 percent rise observed in the NIDDM subjects (P < 0.01). The effect of magnesium deficiency was also studied in 3 normal subjects experimentally Mg deficient for 3 weeks. The mean lymphocyte Mg(2+) fell from 0.198 +/- 0.009 mM pre-diet to 0.153 +/- 0.006 mM post-diet. and the insulin-induced rise in Mg(2+) fell from 27.2 percent pre-magnesium depletion to 12.7 percent post-magnesium depletion. These data suggest that insulin resistance and magnesium depletion may result in a vicious cycle of worsening insulin resistance and decrease in intracellular Mg(2+) which may limit the role of magnesium in vital cellular processes.

Magnesium depletion is more common than previously thought. It seems to be especially prevalent in patients with diabetes mellitus. It is usually caused by losses from the kidney or gastrointestinal tract. A patient with magnesium depletion may present with neuromuscular symptoms, hypokalemia, hypocalcemia, or cardiovascular complication. Physicians should maintain a high index of suspicion for magnesium depletion in patients at high risk and should implement therapy early.

To examine potential mechanisms for the blood pressure-lowering action of the thiazolidinedione compound, pioglitazone (PIO), we studied the effects of the drug on blood pressure and insulin action in vivo and on vascular tissue in vitro. In vivo, PIO lowered blood pressure in fructose-fed and chow-fed rats to an extent that could not be explained by alterations in fasting plasma insulin or free magnesium concentrations or by alterations in whole-body insulin sensitivity. In vitro, PIO caused significant blunting of the contractile responses of aortic rings to NE, arginine vasopressin (AVP), and potassium chloride; the blunting of responses to NE was maintained after removal of the endothelium. To assess the potential importance of extracellular calcium to the vasodepressor effect of PIO, we measured contractile responses to NE in the absence of calcium, and then after acute restoration of calcium in the presence of NE. PIO had no effect on the contractile response in the absence of calcium. By contrast, PIO blunted by 42% the contractile response that occurred when the extracellular calcium supply was acutely restored in the presence of NE, suggesting that the blunting was mediated by blockade of calcium uptake by vascular smooth muscle. Such an effect was confirmed in cultured a7r5 vascular smooth muscle cells, which exhibited a brisk increase in intracellular calcium in response to AVP that was blocked by PIO in a dose-dependent fashion. Our data indicate that PIO has a direct vascular effect that appears to be mediated at least in part by inhibition of agonist-mediated calcium uptake by vascular smooth muscle. The direct vascular effect may contribute to the blood pressure-lowering actions of PIO in vivo, because that effect could not be explained by alterations in whole-body insulin sensitivity.

In vitro, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) induces differentiation of HL-60 cells and inhibits their proliferation as well as the proliferation of leukemic cells from patients. In vivo, the survival of mice challenged with syngeneic leukemic cells is enhanced by treatment with 1,25(OH)2D3. Patients treated with 1,25(OH)2D3 develop hypercalcemia at a serum level of 2 x 10(-10) mol/l which is a concentration too low to achieve an antileukemic effect in vitro. Several interesting vitamin D3 analogs have recently been developed. We initially examined the effect of 1,25(OH)2-16ene-23yne-19-nor-26,27-F6-D3 and 24a,26a,27a-tri-homo-22,24-diene-1-alpha,25-(OH)2-D3 on clonal growth and differentiation of HL-60 cells. Each of the analogs had comparable effects on clonal growth with 50% inhibition (ED50) at concentrations of 0.2-0.5 x 10(-9) M; 1,25(OH)2D3 was about 20- to 50-fold less active in inhibiting growth. Differentiation was determined by induction of superoxide production, as measured by nitroblue tetrazolium (NBT) reduction and by expression of a macrophage-specific enzyme (alpha napthyl acetate esterase (ANAE)). The 24a,26a,27a-tri-homo-22,24-diene-1-alpha,25-(OH)2-D3 and 1,25(OH)2-16ene-23yne-19-nor-26,27-F6-D3 were about 5- to 14-fold more potent than 1,25(OH)2D3. The hypercalcemia inducing side-effects of these analogs and three other previously identified, extremely potent vitamin D3 compounds, as well as 1,25(OH)2D3, were studied. The analogs were administered intraperitoneally every other day (qod) for 5 weeks; serum was collected weekly and Ca2+ measured by atomic absorption spectrophotometry. The highest tolerated dose of each analog leaving all mice alive was for 1,25(OH)2D3: 0.25 micrograms; 1,25(OH)2-24a,26a,27a-tri-homo-22,24-diene-D3: 0.25 micrograms; and 1,25(OH)2-16ene-23yne-19-nor-26,27-F6-D3: 0.0625 micrograms. Another hexafluoro compound with potent abilities to induce differentiation (1,25(OH)2-16ene-23yne-26,27-F6-D3) was very toxic, all mice died in the second week while receiving 0.0625 micrograms qod. Prior studies showed that the most potent compound in inducing differentiation of HL-60 was 1,25(OH)2-20-epi-D3; but it is very toxic as only one mouse survived a dose of > or = 0.0125 micrograms qod for 5 weeks. 1,25(OH)2-16ene-23yne-D3 is an extremely active inducer of differentiation but, on the other hand, it has low potential to produce hypercalcemia; mice maintained normal serum calcium levels even while receiving 2 micrograms qod for 5 weeks.(ABSTRACT TRUNCATED AT 400 WORDS)

Magnesium (Mg) deficiency occurs frequently in chronic alcoholism and may contribute to the increased incidence of osteoporosis and cardiovascular disease seen in this population. Mg deficiency is primarily due to renal Mg-wasting and is exacerbated by dietary Mg deprivation, gastrointestinal losses with diarrhea or vomiting, as well as concomitant use of drugs such as diuretics and aminoglycosides. Osteoporosis is prevalent in the alcoholic population. Mg deficiency may contribute to increased bone loss by its effects on mineral homeostasis. In Mg depletion, there is often hypocalcemia due to impaired parathyroid hormone (PTH) secretion, as well as renal and skeletal resistance to PTH action. Serum concentrations of 1,25-vitamin D are also low. These changes are seen with even mild degrees of Mg deficiency and may contribute to the metabolic bone disease seen in chronic alcoholics. Hypomagnesemia in alcoholics may also contribute to increased cardiovascular disease by altering platelet function. Mg deficiency has been demonstrated to enhance platelet reactivity. In these studies, Mg was shown to inhibit platelet aggregation against various aggregation agents. Patients with Mg deficiency were shown to have increased platelet aggregation that was normalized with Mg therapy. The antiplatelet effect of Mg may be related to the finding that Mg inhibits the synthesis of thromboxane A2 and 12-hydroxyeicosatetraenoic acid, eicosanoids thought to be involved in platelet aggregation. Mg also inhibits the thrombin-induced Ca2+ influx in platelets, as well as stimulates synthesis of prostaglandin I2, the potent antiaggregatory eicosanoid. Therefore, Mg deficiency may increase platelet aggregation and cause increased hypertension and atherosclerotic cardiovascular disease in alcoholics.

Increased dietary fructose may produce insulin insensitivity and elevate blood pressure in rats. It is possible that the reduced magnesium content of the high-fructose commercial diet used in some studies may play a role in these abnormalities because it is known that magnesium deficiency can produce insulin insensitivity and increased angiotensin II action in humans. To study this, we maintained rats for 9 weeks on either a normal control diet, a standard high-fructose diet, or the same high-fructose diet supplemented with magnesium. Glucose uptake was assessed using a perfused rat hindquarter preparation sequentially with 0, 900, and 120,000 pmol/L of added insulin. Basal serum glucose, plasma insulin, and basal glucose uptake in the absence of insulin were similar among all three groups. However, insulin sensitivity, defined as glucose uptake in the presence of 900 pmol/L insulin minus basal, was depressed in the high-fructose compared with the control group (1.02 +/- 0.38 to 1.77 +/- 0.57 mumol/g per hour, P < .05). In contrast, the high-fructose group supplemented with normal magnesium had similar insulin sensitivity as the control group (2.09 +/- 0.69 mumol/g per hour). Total serum magnesium was reduced in the high-fructose group compared with control or high-fructose plus magnesium-supplemented groups. Blood pressure and fasting insulin levels were also lower in the magnesium-supplemented group. These results suggest that magnesium deficiency and not fructose ingestion per se leads to insulin insensitivity in skeletal muscle and changes in blood pressure.

Background: Hypercalcemia is a serious and common complication of malignancy. Etidronate, a known inhibitor of osteoclastic bone resorption, is approved in the therapy of hypercalcemia of malignancy (HCM) at a dose of 7.5 mg/kg/day infused during a period of 2-4 hours on 3 consecutive days. A multicenter study was conducted to evaluate the safety and efficacy of a single 24-hour infusion of etidronate disodium in patients with HCM., Methods: Selected patients with HCM had disease refractory to at least 24-hours of intravenous fluid (more than 3 l/day) with two albumin-adjusted serum calcium concentrations greater than 11.5 mg/dl drawn 24 hours apart before etidronate treatment. Thirty patients were enrolled; 13 received 25 mg/kg for 24 hours, 12 received 30 mg/kg for 24-hours, 3 received incorrect doses (2 overdoses, and 1 underdose) and 2 died of disease-related complications before day 7. Of the 25 evaluable patients, 15 were men and 10 were women. Median age was 53 years (range, 20-75 years). Twelve patients (6 in each treatment group) had confirmed skeletal metastases., Results: During the week after treatment, the 25 mg/kg group had adjusted serum calcium levels fall from a mean preinfusion baseline of 13.3 +/- 0.3 mg/dl (plus or minus the standard error of the mean) to a mean nadir of 10.9 +/- 0.4 mg/dl (the average of each patient's lowest calcium values). The 30 mg/kg group had adjusted serum calcium levels fall from a mean preinfusion baseline of 13.8 +/- 0.4 mg/dl to a mean nadir of 10.5 +/- 0.3 mg/dl. The average day that nadir occurred was day 5.7 for the 25 mg/kg group and day 5.6 for the 30 mg/kg group. The mean maximum reduction (delta) derived from the patients' nadirs in the 25 mg/kg dose group was 2.5 +/- 0.4 mg/dl and 3.3 +/- 0.3 mg/dl for the 30 mg/kg dose. Time to effect (either a partial response defined as a 15% or greater decrease in the adjusted serum calcium from the preinfusion value or a complete eucalcemic response defined as a reduction to the laboratory's eucalcemic range) occurred on average on day 4.6 in the 25 mg/kg group and day 3.7 in the 30 mg/kg group. Nine of the 13 (69%) patients in the 25 mg/kg treatment group had either partial or complete response to the 24-hour infusion. Five of these patients (38% of the 13 patients) of the 25 mg/kg group had serum calcium levels fall to their laboratory's eucalcemic range before day 7 (a complete response), 4 (31%) had partial response only, and 4 had no response. In the 30 mg/kg group, 11 of 12 (92%) patients had at least partial responses. Eight of the 12 (67%) patients had adjusted serum calcium concentrations fall to the eucalcemic range by day 7, 3 (25%) had a partial response, and 1 had no response. Reported adverse experiences generally were attributable to the underlying disease. The reduction in the serum calcium throughout the week for the 30 mg/kg dose group was significantly greater than that for the 25 mg/kg group (analysis of variance, P < 0.0001)., Conclusions: Etidronate, when administered intravenously at 30 mg/kg during a period of 24 hours, apparently was safe and effective in this study for treatment of hypercalcemia in patients with a wide variety of tumor types. This regimen may offer a more convenient method of administration than does standard etidronate therapy for the treatment of HCM.

Magnesium (Mg) deficiency is a common yet underdiagnosed problem in the ICU. Since only 1% of total body Mg is in the extracellular fluid, serum Mg concentrations may not adequately reflect Mg status. Utilizing techniques to measure intracellular Mg concentrations, Mg depletion has been shown to be present in about one half of all ICU patients. These patients have significantly higher morbidity and mortality rates than Mg-replete patients. Accurate identification of patients with Mg depletion requires a knowledge of the risk factors associated with Mg deficiency. These factors include poorly controlled diabetes mellitus, alcohol ingestion, severe diarrhea and steatorrhea, and the use of a number of pharmacologic agents that induce renal Mg wasting. Manifestations of Mg deficiency include hypokalemia, hypocalcemia, neuromuscular hyperexcitability, respiratory muscle weakness, and intractable arrhythmias. Mg deficiency may also play a role in the genesis of myocardial ischemia. In this article, we review the assessment, causes, and manifestations of Mg deficiency and suggest guidelines for adequate treatment.

Magnesium is a prominent intracellular cation required for the function of hundreds of enzyme systems. Magnesium depletion is observed frequently in hospitalized patients and is usually secondary to renal or intestinal magnesium loss. Clinically, magnesium deficiency may present with neuromuscular hyperexcitability, hypocalcemia, hypokalemia, and cardiac arrhythmias. Magnesium therapy appears to improve survival in patients with myocardial infarction. The diagnosis of magnesium deficiency is usually made by a low-serum magnesium concentration, although the magnesium tolerance test may be more indicative of low magnesium states. In acutely ill patients, magnesium is usually give parenterally; oral magnesium may be given for long-term repletion.

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)

Magnesium (Mg) is critical for the function of numerous enzyme systems. Mg deficiency thereby may result in many and varied clinical manifestations. Mg deficiency is common as approximately 10% of patients admitted to city hospitals are hypomagnesemic. Mg deficiency is usually due to losses from the gastrointestinal tract or from the kidney. A serum Mg concentration of < 1.5 mEq/l usually indicates Mg deficiency, however, intracellular Mg deletion may be present despite a normal serum Mg concentration. Acute clinical manifestations of Mg deficiency include neuromuscular hyperexcitability, cardiac arrhythmias, and biochemical abnormalities of hypokalemia and hypocalcemia. Chronic Mg depletion may contribute to hypertension, atherosclerotic vascular disease, altered glucose homeostasis, and metabolic bone disease. Therapy of the acute manifestations usually requires parenteral Mg administration of 24-48 mEq Mg/day for 3-5 days. Long-term Mg repletion may be accomplished by the administration of 300-600 mg of Mg orally/day.

A large body of evidence demonstrates the prevalence and adverse clinical consequences of magnesium deficiency in patients with diabetes mellitus. It would be prudent for physicians who treat these patients to consider magnesium deficiency as a contributing factor in many diabetic complications and in exacerbation of the disease itself. Repletion of the deficiency or prophylactic supplementation with oral magnesium may help avoid or ameliorate such complications as arrhythmias, hypertension, and sudden cardiac death and may even improve the course of the diabetic condition.

Both estrogen and androgen have been reported to attenuate cyclic AMP responses to parathyroid hormone stimulation in cultured bone cells. The present study examines the effect of in vivo estrogen deficiency on skeletal adenylate cyclase (AC) activity. The AC activity was compared in bone membranes prepared from normal female guinea pigs and from age-matched guinea pigs 3 weeks after ovariectomy. Histomorphometric analysis of femoral specimens from the ovariectomized guinea pigs demonstrated significant decreases in percentage bone volume, the percentage eroded surfaces and osteoclast numbers, and increased osteoid thickness, compared with the normal controls. No differences were found in basal AC activity, the ability of bone AC to be stimulated by parathyroid hormone (bPTH(1-34)) or isoproterenol, or in the regulation of AC activity by calcium and magnesium. We conclude that bone AC is not a direct target for estrogen effects on bone cells and that the reported effects of sex steroids on cAMP levels in bone cells probably act via an indirect mechanism.

Objective: Mg deficiency may be an important factor leading to cardiovascular disease. Diabetic subjects show an increase in platelet reactivity that can enhance the risks of vascular disease. In addition, diabetic patients have been reported to be at risk of developing extracellular Mg deficiency. However, the intracellular free Mg concentration and its role in the enhanced platelet reactivity in diabetes is not known., Research Design and Methods: We evaluated the intracellular erythrocyte (RBC) Mg2+ concentration in 20 non-insulin-dependent (type II) diabetics. In addition, the effects of intravenous 3-h drip or 8 wk of oral Mg supplementation on intracellular RBC Mg2+ levels and platelet reactivity was studied. To more clearly evaluate the direct role of Mg in these effects, we induced isolated Mg deficiency in 16 nondiabetic control subjects with an Mg-free liquid diet for 3 wk., Results: The intracellular RBC Mg2+ concentration of diabetic patients was significantly reduced compared with values in nondiabetic control subjects (166 +/- 7 vs. 204 +/- 7 microM, P less than 0.01). Serum Mg levels were also reduced in the diabetic patients compared with the control subjects (1.59 +/- 0.04 vs. 1.9 +/- 0.1 mEq/L, P less than 0.05). Oral Mg supplementation for 8 wk (400 mg/day) restored RBC Mg2+ concentration to normal without significantly changing serum Mg concentration. Both intravenous and oral Mg supplementation markedly reduced platelet reactivity in response to the thromboxane A2 analog, U46619. The Mg-free diet resulted in a significant reduction in RBC Mg2+ concentration and markedly enhanced the sensitivity of platelet aggregation to U46619 and ADP., Conclusions: These results suggest that type II diabetic patients have intracellular Mg2+ deficiency and that Mg deficiency may be a key factor in leading to enhanced platelet reactivity in type II diabetes. Therefore, Mg supplementation may provide a new therapeutic approach to reducing vascular disease in patients with diabetes.

Hypercalcemia of malignancy is a commonly encountered serious clinical problem that often requires aggressive therapy. In order to combine the rapid hypocalcemic effects of calcitonin with the more delayed effect of a bisphosphonate, we administered etidronate, 7.5 mg/kg/day intravenously and salmon calcitonin, 100 IU subcutaneously, every 12 hours for 3 days in 9 patients with hypercalcemia associated with malignancy. The mean serum calcium concentration fell from 3.33 +/- 0.1 mmol/liter (mean +/- SEM) to 2.88 +/- 0.1 mmol/liter within 24 hours (P less than 0.001). All patients had a fall in the serum calcium concentration of greater than 0.5 mmol/liter and it returned to normal in 7 of the 9 patients. We conclude that the combination of salmon calcitonin with etidronate more effectively lowers the serum calcium concentration in patients with hypercalcemia of malignancy then the use of either agent alone.

Magnesium (Mg) deficiency in man may result in hypocalcemia, impaired PTH secretion, and low serum concentrations of 1,25-dihydroxyvitamin D [1,25-(OH)2D]. To determine whether these changes are due to selective Mg depletion, we studied 26 normal subjects before and after a 3-week low Mg (less than 1 meq/day) diet. This diet induced Mg deficiency, as demonstrated by a fall in pre- to postdiet serum Mg levels from 0.80 +/- 0.01 to 0.61 +/- 0.02 mmol/L (P less than 0.001), an increase in Mg retention from 11 +/- 4% to 62 +/- 4% (P less than 0.001), and a fall in red blood cell free Mg2+ from 205 +/- 10 to 162 +/- 7 microM (P less than 0.001). Serum calcium (Ca) fell significantly from 2.36 +/- 0.02 to 2.31 +/- 0.03 mmol/L (P less than 0.05), and serum 1,25-(OH)2D fell from 55 +/- 4 to 43 +/- 3 pmol/L (P less than 0.05). PTH secretion was impaired, as demonstrated by a fall or no change in serum PTH in 20 of 26 subjects despite a fall in the serum Ca and Mg. In addition, an iv injection of Mg in eight subjects after the diet resulted in a significant rise in PTH from 15 +/- 2 to 19 +/- 2 ng/L (P less than 0.01), whereas a similar injection given to six of the subjects before the diet resulted in a significant fall from 28 +/- 5 to 13 +/- 3 ng/L (P less than 0.001). The fall in serum 1,25-(OH)2D may be due to both the decrease in PTH secretion and a renal resistance to PTH. PTH resistance was suggested, as no increase in serum 1,25-(OH)2D was observed in the six subjects in which the PTH concentration rose by mean of 68% after the diet. Also, the rise in serum 1,25-(OH)2D after a 6-h human PTH-(1-34) infusion was significantly less after Mg deprivation. The results demonstrate that mild Mg depletion can impair mineral homeostasis and may be implicated as risk factor for osteoporosis in disorders such as chronic alcoholism and diabetes mellitus, in which Mg deficiency and osteoporosis are both common.

Red blood (RBC) ionized magnesium (Mg2+) was determined by nuclear magnetic resonance (NMR) in order to assess the usefulness of this technique as an index of magnesium depletion. Twenty-four normal subjects underwent a 3-week low-Mg diet. The RBC Mg2+ fell from 209 +/- 9.8 microM before diet to 162 +/- 9.3 microM at the end of the 3 weeks (p < 0.001). In patient populations, 22 hypomagnesemic hospitalized patients had a significantly lower RBC Mg than normal (146 +/- 7.1 microM, p < 0.002), and 37 outpatients with diabetes mellitus had a mean RBC Mg2+ of 172 +/- 7.1 microM which was also significantly lower than normal (p < 0.001). These data suggest that determination of RBC Mg2+ may be used to reflect intracellular Mg status.

A dose-ranging, baseline-controlled study was undertaken to assess the safety and effectiveness of a 24-hour infusion of etidronate disodium in treating patients with hypercalcemia of malignant disease. Patients with hypercalcemia refractory to at least 48 h of saline loading (greater than 3 1/day) with two albumin-adjusted serum calcium values between 11.1 and 12.0 mg/dl or one albumin-adjusted serum calcium greater than 12.0 mg/dl within 48 h of therapy were admitted to the study. A total of 26 patients were treated in a dose-escalating fashion with 5, 10, 15, 20 or 25 mg/kg of intravenous etidronate disodium over 24 h. Patients treated with 5, 10 or 15 mg/kg did not have significant reductions in albumin-adjusted serum calcium during the first 7 days. In the 6 patients who made up the 20 mg/kg group, adjusted serum calcium levels fell from an average of 13.8 +/- 0.5 mg/dl on day 1 before infusion to 11.7 +/- 0.3 mg/dl (p less than 0.05) by day 7. In the 8 patients in the 25 mg/kg group, adjusted serum calcium levels decreased from an average of 12.9 +/- 0.5 mg/dl on day 1 before infusion to 10.9 +/- 0.4 mg/dl (p less than 0.05) by day 7. All 8 patients in the 25 mg/kg group achieved a fall in albumin-adjusted serum calcium to less than 11.1 mg/dl within the 1 week with a minimum decrement of 0.6 mg/dl and a maximum of 5.5 mg/dl.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypomagnesemia is a common clinical finding in hospitalized patients and can cause hypocalcemia, cardiac arrhythmias, muscular weakness, and hypokalemia. Hypomagnesemia usually implies cellular magnesium (Mg) depletion, but stress and some clinical conditions which raise serum catecholamine concentrations may lower serum Mg (sMg) concentrations. To help investigate the mechanism and degree of the effect of catecholamines on sMg concentration, we gave intravenous epinephrine (0.1 microgram/kg/min) to 12 normal volunteers for 2 hours. The sMg concentration fell from 1.86 +/- 0.04 mg/dl to 1.63 +/- 0.05 mg/dl (mean +/- SEM, p less than 0.01). Pre-infusion intracellular free Mg (Mg++) in red blood cells (RBC) as measured by nuclear magnetic resonance spectrophotometry (NMR) was 171 +/- 7.6 microM and did not differ significantly from post-infusion RBC Mg++, 186 +/- 12.6 microM. Total blood mononuclear cell Mg content and urine Mg excretion also did not change. These data suggest that epinephrine has a small but significant effect on the lowering of sMg concentrations. Endogenous catecholamine release during stress or acute illness may therefore contribute to the hypomagnesemia seen in acutely ill patients. Our data also suggest that hypomagnesemia seen under conditions of acute stress may not always imply depleted tissue Mg stores. As no absolute change in cellular Mg or in urinary Mg excretion was demonstrated, acute intracellular shifts of Mg into blood cells and/or urinary Mg losses may not account for the hypomagnesemia. The prevalence and clinical consequences of stress hypomagnesemia require further investigation.

To determine the role of magnesium deficiency in the pathogenesis of hypocalcemia in acute pancreatitis, we measured magnesium levels in serum and in peripheral blood mononuclear cells in 29 patients with acute pancreatitis, 14 of whom had hypocalcemia and 15 of whom had normal calcium levels. Only six patients had overt hypomagnesemia (serum magnesium less than 0.70 mmol per liter [1.7 mg per dl]). The mean serum magnesium concentration in hypocalcemic patients was not significantly lower than in normocalcemic patients, but the mononuclear cell magnesium content in hypocalcemic patients with pancreatitis was significantly lower than in normocalcemic patients with pancreatitis (P less than .01). The serum magnesium level did not correlate with that of serum calcium or the mononuclear cell magnesium content, but the latter did significantly correlate with the serum calcium concentration (r = .81, P less than .001). Most patients with hypocalcemia had a low intracellular magnesium content. Three normomagnesemic, hypocalcemic patients with alcoholic pancreatitis also underwent low-dose parenteral magnesium tolerance testing and showed increased retention of the magnesium load. We conclude that patients with acute pancreatitis and hypocalcemia commonly have magnesium deficiency despite normal serum magnesium concentrations. Magnesium deficiency may play a significant role in the pathogenesis of hypocalcemia in patients with acute pancreatitis.

Magnesium deficiency is a common clinical condition, frequently present even with normal serum magnesium (S-Mg) concentrations. We have studied retention of a low-dose (0.2 mEq/kg lean body weight), intravenously administered magnesium load in 6 hypomagnesemic patients and 18 normomagnesemic alcoholics as compared with 16 normal subjects. Both normomagnesemic and hypomagnesemic subjects retained significantly greater amounts of the administered magnesium than did the normal subjects. In patients who were restudied following parenteral magnesium repletion, retention of the magnesium load normalized. We conclude that increased retention of a magnesium load is a more sensitive index of magnesium deficiency than is the S-Mg concentration, and suggest that low-dose magnesium tolerance testing be used more frequently as a clinical tool in the evaluation of states of normomagnesemic magnesium deficiency.