The effect of moderately and severely restricted dietary magnesium intakes on bone composition and bone metabolism in the rat

Spheroids as a 3D in vitro model to study bone and bone mineralization

Traumas, fractures, and diseases can severely influence bone tissue. Insight into bone mineralization is essential for the development of therapies and new strategies to enhance bone regeneration. 3D cell culture systems, in particular cellular spheroids, have gained a lot of interest as they can recapitulate crucial aspects of the in vivo tissue microenvironment, such as the extensive cell-cell and cell-extracellular matrix (ECM) interactions found in tissue. The potential of combining spheroids and various classes of biomaterials opens also new opportunities for research within bone tissue engineering. Characterizing cellular organization, ECM structure, and ECM mineralization is a fundamental step for understanding the biological processes involved in bone tissue formation in a spheroid-based model system. Still, many experimental techniques used in this field of research are optimized for use with monolayer cell cultures. There is thus a need to develop new and improving existing experimental techniques, for applications in 3D cell culture systems. In this review, bone composition and spheroids properties are described. This is followed by an insight into the techniques that are currently used in bone spheroids research and how these can be used to study bone mineralization. We discuss the application of staining techniques used with optical and confocal fluorescence microscopy, molecular biology techniques, second harmonic imaging microscopy, Raman spectroscopy and microscopy, as well as electron microscopy-based techniques, to evaluate osteogenic differentiation, collagen production and mineral deposition. Challenges in the applications of these methods in bone regeneration and bone tissue engineering are described. STATEMENT OF SIGNIFICANCE: 3D cell cultures have gained a lot of interest in the last decades as a possible technique that can be used to recreate in vitro in vivo biological process. The importance of 3D environment during bone mineralization led scientists to use this cell culture to study this biological process, to obtain a better understanding of the events involved. New and improved techniques are also required for a proper analysis of this cell model and the process under investigation. This review summarizes the state of the art of the techniques used to study bone mineralization and how 3D cell cultures, in particular spheroids, are tested and analysed to obtain better resolved results related to this complex biological process.

Influence of Magnesium Source on the Mechanochemical Synthesis of Magnesium-Substituted Hydroxyapatite

Magnesium, as one of the most abundant cations in the human body, plays an important role in both physiological and pathological processes. In this study, it was shown that a promising biomedical material, Mg-substituted hydroxyapatite (Mg-HA), can be synthesized via a fast mechanochemical method. For this method, the nature of magnesium-containing carriers was shown to be important. When using magnesium oxide as a source of magnesium, the partial insertion of magnesium cations into the apatite structure occurs. In contrast, when magnesium hydroxide or monomagnesium phosphate is used, single-phase Mg-HA is formed. Both experimental and theoretical investigations showed that an increase in the Mg content leads to a decrease in the lattice parameters and unit cell volume of Mg-HA. Density functional theory calculations showed the high sensitivity of the lattice parameters to the crystallographic position of the calcium site substituted by magnesium. It was shown experimentally that the insertion of magnesium cations decreases the thermal stability of hydroxyapatite. The thermal decomposition of Mg-HA leads to the formation of a mixture of stoichiometric HA, magnesium oxide, and Mg-substituted tricalcium phosphate phases.

Long-term use of proton pump inhibitors adversely affects minerals and vitamin metabolism, bone turnover, bone mass, and bone strength

Notwithstanding, proton pump inhibitors (PPIs) are one of the most excellent options for different anti-secretory therapy in terms of improved symptomatic outcomes, numerous epidemiological and cohort studies provide evidence of an association between long-term proton PPIs use and increased fracture risk among users. The present attempt aimed to summarize the effect of long-term use of PPIs on musculoskeletal systems by considering the recent claims of different research groups to understand the risk of osteopenia and osteoporosis and to determine the risk factors associated with these complications. We extracted data from various systematic reviews and meta-analyses, cross-sectional studies, prospective studies, case-control studies, cohort studies, and in-vivo and in-vitro studies to observe the consequence of long-term PPIs uses over the patient's bone health. Recent findings suggested that long-term use of PPIs plays an introductory and cabalistic role in the development of osteoporosis mostly hip fractures by disturbing numerous biological pathways and thus able to set up a link between over-prescription of PPIs and bone loss. Frequent administration of PPIs is associated with a significantly worse outcome to bone mineral density (BMD) profile and produce a negative impression on bone health. Since, there are limited data to determine the association of PPIs use and change in BMD, recommending further studies to find out this dissertation.

Cross-Talks between the Cardiovascular Disease-Sarcopenia-Osteoporosis Triad and Magnesium in Humans

Magnesium (Mg) is a pivotal and very complex component of healthy aging in the cardiovascular-muscle-bone triad. Low Mg levels and low Mg intake are common in the general aging population and are associated with poorer outcomes than higher levels, including vascular calcification, endothelial dysfunction, osteoporosis, or muscle dysfunction/sarcopenia. While Mg supplementation appears to reverse these processes and benefit the triad, more randomized clinical trials are needed. These will allow improvement of preventive and curative strategies and propose guidelines regarding the pharmaceutical forms and the dosages and durations of treatment in order to optimize and adapt Mg prescription for healthy aging and for older vulnerable persons with comorbidities.

Impact of serum magnesium and bone mineral density on systemic fractures in chronic hemodialysis patients

Introduction

Bone mineral density (BMD) measured with dual-energy X-ray absorptiometry (DXA) can be used to predict fractures, but its clinical utility has not been fully established in chronic kidney disease (CKD) patients. Magnesium is an essential trace element. Although magnesium is associated with the risk of fractures in non-CKD populations, the relationship is unknown in CKD patients.

Methods

BMD and serum magnesium levels were measured in 358 stable outpatients undergoing maintenance hemodialysis therapy. The primary outcome was fragility fracture. Patients were divided into groups according to the median level of magnesium and the normal threshold value of lumbar spine BMD.

Results

During the median follow-up period of 36 months, 36 (10.0%) fractures occurred. The cumulative incidence rates of fractures were 17.6% and 5.2% [adjusted hazard ratio (aHR) 2.31, 95% confidence interval (CI) 1.03–5.17, P = 0.030] in the lower (<2.6 mg/dL) and higher (≥2.6 mg/dL) magnesium (Mg) groups, respectively, and 21.2% and 7.3% (aHR 2.59, 95% CI 1.09–6.16, P = 0.027) in the low- and high-BMD groups, respectively. The lower-Mg and low-BMD group had a 9.21-fold higher risk of fractures (95% CI; 2.35–47.00; P = 0.0010) than the higher-Mg and high-BMD group. Furthermore, adding both magnesium levels and lumbar spine BMD levels to the established risk factors significantly improved the prediction of fractures (C-index: 0.784 to 0.830, p = 0.041).

Discussion/Conclusions

The combination of serum magnesium and lumbar spine BMD can be used for fracture risk stratification and synergistically improves the prediction of fractures in CKD patients.

Dietary magnesium restriction affects hematopoiesis and triggers neutrophilia by increasing STAT-3 expression and G-CSF production

BACKGROUND & AIMS

Magnesium (Mg²⁺) is able to modulate the differentiation and proliferation of cells. Mg²⁺ restriction can trigger neutrophilia, but the processes that result in this change have yet to be investigated and are not fully understood. Hematopoiesis is a complex process that is regulated by many factors, including cytokines and growth factors, and is strongly influenced by nutrient availability. In this context, our objective was to investigate the impact of the short-term restriction of dietary Mg²⁺ on bone marrow hematopoietic and peripheral blood cells, especially in processes related to granulocyte differentiation and proliferation.

METHODS

Male C57BL/6 mice were fed a Mg²⁺ restricted diet (50 mg Mg²⁺/kg diet) for 4 weeks. Cell blood count and bone marrow cell count were evaluated. Bone marrow cells were also characterized by flow cytometry. Gene expression and cytokine production were evaluated, and a colony-forming cell assay related to granulocyte differentiation and proliferation was performed.

RESULTS

Short-term dietary restriction of Mg²⁺ resulted in peripheral neutrophilia associated with an increased number of granulocytic precursors in the bone marrow. Additionally, Mg²⁺ restriction resulted in an increased number of granulocytic colonies formed in vitro. Moreover, the Mg²⁺ restricted group showed increased expression of CSF3 and CEBPα genes as well as increased production of G-CSF in association with increased expression of STAT3 protein.

CONCLUSION

Short-term dietary restriction of Mg²⁺ induces granulopoiesis by increasing G-CSF production and activating the CEBPα and STAT-3 pathways, resulting in neutrophilia in peripheral blood.

The associations between serum trace elements and bone mineral density in children under 3 years of age

We examined the associations of age and serum magnesium, iron, lead, copper, and zinc levels with bone mineral density (BMD) in 2412 children under 3 years of age in order to find a tool to monitor BMD in children without the use of expensive imaging techniques. One-way ANOVA and chi-square tests were used to determine the associations of age and serum trace elements with BMD. Multivariable logistic regression analysis was used to test the correlation of five serum trace elements with BMD after adjustments for potential confounding factors in children under 3 years of age. Significant associations between age and four serum trace elements and BMD were found. Compared to the group with the lowest serum levels detected, the adjusted odds ratio (OR) for the incidence of normal bone mineral density in the third magnesium concentration tertile, the third iron concentration tertile, the fifth copper concentration quintile, the third zinc concentration quintile, and the fifth zinc concentration quintile were 1.30 (95% confidence interval (CI) 1.02–1.67), 1.43 (95% CI 1.11–1.84), 1.42 (95% CI 1.04–1.94), 1.46 (95% CI 1.05–2.04), and 1.48 (95% CI 1.06–2.06), respectively. However, there was no significant correlation between serum lead level and BMD in this study. Age and serum magnesium, iron, copper, and zinc levels are positively associated with BMD in children under 3 years old.

Proton Pump Inhibitors and Fractures in Adults: A Critical Appraisal and Review of the Literature

Despite the large number of patients worldwide being on proton pump inhibitors (PPIs) for acid-related gastrointestinal disorders, uncertainty remains over their long-term safety. Particularly, the potential side effects of these drugs on bone health have been evaluated in the last years. The purpose of our narrative review is to gather and discuss results of clinical studies focusing on the interactions between PPIs and fracture risk. Data generated mainly from nested case-control studies and meta-analysis suggest that long-term/high-dose PPIs users are characterized by an increased risk of fragility fractures, mainly hip fractures. However, in these studies, the PPIs-induced bone impairment is often not adjusted for different confounding variables that could potentially affect bone health, and exposure to PPIs was reported using medical prescriptions without adherence evaluation. The mechanisms of the PPI-related bone damage are still unclear, but impaired micronutrients absorption, hypergastrinemia, and increased secretion of histamine may play a role. Clinicians should pay attention when prescribing PPIs to subjects with a preexistent high risk of fractures and consider antiosteoporotic drugs to manage this additive effect on the bone. However, further studies are needed to clarify PPIs action on the bone.

Magnesium: The recent research and developments

Magnesium is the fourth most abundant mineral in the human body, which facilitates more than 300 enzymatic reactions. Magnesium is essential for nucleic material and protein synthesis, neuromuscular conduction, cardiac contractility, energy metabolism, and immune system function. Gastrointestinal system and kidneys closely regulate magnesium absorption and elimination to maintain adequate storage of magnesium. Magnesium deficiency has been linked to many diseases and poor health outcomes. Magnesium has also been proven to be an effective therapeutic agent in many diseases, such as bronchial asthma, cardiac arrhythmia, and pre-eclampsia.

Biochemical activity of magnesium ions on human osteoblast migration

Magnesium is well known as a biodegradable biomaterial that has been reported to promote bone remodeling in several studies; however, the underlying biological mechanism remains unclear. In the present study, the role of magnesium ions in the migration of U-2 OS cells, which are osteoblast-like cell lines, was investigated. Magnesium treatment did not significantly alter the global transcriptome of U-2 OS cells, but increased the protein expression level of SNAI2, an epithelial-mesenchymal transition (EMT) marker. In addition, it was confirmed that the junctional site localization of Zona-occludens 1 (ZO-1), a representative tight junction protein, was destroyed by magnesium treatment; furthermore, it was determined that cytoplasmic localization increased, and alkaline phosphatase (ALP) activity increased. The obtained results on the mechanism by which magnesium is involved in osteoblast migration, which is important for fracture healing, will contribute to the understanding of the bone-formation process in patients with osteoporosis and musculoskeletal injury.

Calcium Deficiency in Diet Decreases the Magnesium Content in Bone and Affects Femur Physicochemical Properties in Growing Rats

This study evaluates the effect of three calcium levels in the diet (normal, moderate, and severe calcium depletion) on bone metabolism of male Wistar rats during their growth period. Bone mineral density (BMD) and femur length were determined in vivo during the growth stage using a single X-ray transmission system. The apparent calcium absorption was calculated in the rat adolescent and adulthood stages. At the end of the experiment, calcium concentrations in serum and urine were analyzed. The bones were evaluated postmortem to corroborate in vivo analyses. Microstructural properties of cortical and trabecular tissues of femurs bones were assessed using scanning electron microscopy. Bone mineral contents (Mg, Ca, P, and K) were quantified by inductively coupled plasma. Severe calcium depletion in the diets in the development stage affects the bone quality parameters such as bone mineral density and mineral content. Moreover, it was found thinner cortical and trabecular bone areas. Additionally, it was found that severe calcium depletion increased the apparent absorption of calcium as a defense mechanism, but with the decrease of the BMD peak, and the thickness of cortical bone as well as trabecular bone porosity. The severe calcium depletion increased the efficiency of apparent absorption calcium as a defense mechanism, but, even so, decreases the BMD peak as well as the thickness of cortical bone and trabecular bone porosity.

The Association Between the Concentration of Serum Magnesium and Postmenopausal Osteoporosis

Background: Osteoporosis is the most common and widespread chronic skeletal metabolic disease in the world and can lead to catastrophic fractures. Therefore, it is important to look for factors that can be modified or controlled to prevent osteoporosis. Although serum Mg is believed to be associated with osteoporosis in many individuals, there are conflicting reports on the association between serum Mg and osteoporosis. Therefore, this meta-analyses aimed to explore the association between the concentration of serum Mg and osteoporosis as well as that between the concentration of serum Mg and osteopenia.

Methods: Articles were searched in PubMed. We also reviewed the reference lists of the relevant publications and reviews as of December 2019. Finally, 11 eligible studies involving 2,776 postmenopausal women were selected. We performed subgroup analysis, and publication bias was assessed.

Results: According to the forest plot analysis, postmenopausal women with osteoporosis had a lower concentration of serum Mg than normal controls [standardized mean difference (SMD) = −0.56, 95% confidence interval (CI) = −1.02 to −0.09]. However, this result was not applicable to those with osteopenia (SMD = −0.30, 95% CI = −0.69 to 0.09). The subgroup analysis by geographical location found a similar pattern in European postmenopausal women with osteoporosis (SMD = −0.73, 95% CI = −1.322 to −0.143), but not in Asian (SMD = −0.007, 95% CI = −0.381 to 0.394). The subgroup analysis by site of bone mineral density (BMD) showed the serum Mg concentration of postmenopausal women with osteoporosis (BMD of femur) was lower than in healthy controls (SMD = −0.44, 95% CI = −0.77 to −0.12), and BMD of the spine group had the same conclusion (SMD = −0.78, 95% CI = −1.36 to −0.19). Besides, the serum Mg concentration of postmenopausal women with osteoporosis was lower than that of the normal bone mass group in the studies those included more than 50 postmenopausal women with osteoporosis (SMD = −0.57, 95% CI = −1.04 to −0.11). We also found postmenopausal women under the age of 60 with osteoporosis had a lower concentration of serum Mg than the healthy controls (SMD = −0.61, 95% CI = −1.09 to −0.13).

Conclusion: Postmenopausal women with osteoporosis have a lower concentration of serum Mg. However, the association between the concentration of serum Mg and osteopenia needs further confirmation.

The effect of dietary magnesium and caseinphosphopeptides on bone metabolism in rats

The effect of dietary magnesium (Mg) or caseinphosphopeptides (CPPs) on bone metabolism has been reported. However, few studies have investigated the effects of simultaneous supplementation of Mg and CPPs. Sixty-three 3-week-old Sprague-Dawley male rats were divided into seven groups and fed a specified diet for 45 days. Body characteristics, bone physicochemical indicators, and bone metabolism indicators relative to bone metabolism were analyzed. We found that, first, a dietary Mg deficiency resulted in increased bone formation and decreased bone resorption. Second, dietary Mg or CPP supplementation promoted bone formation and prevented bone resorption. Third, dietary Mg supplementation with CPPs also functioned to enhance bone formation and prevent bone resorption. There were synergistic effects on femur length, serum parathyroid hormone level and urinary deoxypyridinoline of the HS-Mg-CPP group (0.2% Mg, 0.1% CPPs). The increase in the femur length of the HS-Mg-CPP group compared with the control group was 6% which was much higher than that of HS-Mg (1%) or CPPs (5%). The induction in serum parathyroid hormone content in the HS-Mg-CPP group was 33% compared with the control group which was higher than that of the induction of the HS-Mg (19%) or CPP (23%) group. The induction in the deoxypyridinoline content of the HS-Mg-CPP (43%) group compared with the control group was remarkably higher than that of HS-Mg (8%) or CPPs (16%). Overall our results demonstrated that high doses of Mg (0.2%) and CPPs (0.1%) in combination produced synergistic effects on femur length, serum parathyroid hormone level and urinary deoxypyridinoline in rats, which is important for a better understanding of the effect of Mg and CPPs on bone metabolism.

Magnesium and Risk of Hip Fracture among Patients Undergoing Hemodialysis

Magnesium is an essential mineral for bone metabolism. However, little is known about the relationship between magnesium and the risk of fractures. In this cohort study, we elucidated the association between serum magnesium level and the risk of incident hip fracture among patients undergoing hemodialysis. We identified 113,683 patients undergoing hemodialysis with no history of hip fracture from a nation-wide database of patients undergoing dialysis in Japan. During a 2-year follow-up, a total of 2305 (2%) new hip fractures occurred. The crude incidence rate was significantly higher among patients in the lower quartiles of serum magnesium levels (2.63%, 2.08%, 1.76%, and 1.49% in Q1-Q4, respectively; P<0.001 for trend). The range of serum magnesium levels (in milligrams per deciliter) in each quartile was as follows: Q1, <2.3; Q2, 2.4-2.6; Q3, 2.7-2.8, and Q4, >2.9. After adjustment for demographic and clinical factors, patients in Q1 had a 1.23-fold higher risk for hip fracture than those in Q4 (95% confidence interval, 1.06 to 1.44; P<0.01). Similarly, an inverse probability weighting analysis showed an increased risk of hip fracture among patients in the lower magnesium quartiles. We did not observe significant effect modifications in subgroup analyses. The population-attributable fraction of serum magnesium level for incident hip fractures was 13.7% (95% confidence interval, 3.7% to 22.7%), which was much higher than that of serum calcium, serum phosphate, and parathyroid hormone levels. Thus, mild hypermagnesemia is associated with a lower risk of hip fracture among patients undergoing hemodialysis.

* Extracellular Matrices for Bone Regeneration: A Literature Review

The gold standard material for bone regeneration is still autologous bone, a mesenchymal tissue that consists mainly of extracellular matrix (ECM) (90% v/v) and little cellular content (10% v/v). However, the fact that decellularized allogenic bone grafts often present a clinical performance comparable to autologous bone grafts demonstrates the crucial role of ECM in bone regeneration. For long, the mechanism by which bone allografts function was not clear, but recent research has unveiled many unique characteristics of ECM that seem to play a key role in tissue regeneration. This is further confirmed by the fact that synthetic biomaterials with composition and properties resembling bone ECM present excellent bone regeneration properties. In this context, ECM molecules such as glycosaminoglycans (GAGs) and self-assembly peptides (SAPs) can improve the performance of bone regeneration biomaterials. Moreover, decellularized ECM derived either from native tissues such as bone, cartilage, skin, and tooth germs or from cells such as osteoblasts, chondrocytes, and stem cells has shown promising results in bone regeneration applications. Understanding the role of ECM in bone regeneration is crucial for the development of the next generation of biomaterials for bone tissue engineering. In this sense, this review addresses the state-of-the-art on this subject matter.

Attenuating trabecular morphology associated with low magnesium diet evaluated using micro computed tomography

OBJECTIVE

The literature shows that bone mineral density (BMD) and the geometric architecture of trabecular bone in the femur may be affected by inadequate dietary intake of Mg. In this study, we used microcomputed tomography (micro-CT) to characterize and quantify the impact of a low-Mg diet on femoral trabecular bones in mice.

MATERIALS AND METHODS

Four-week-old C57BL/6J male mice were randomly assigned to 2 groups and supplied either a normal or low-Mg diet for 8weeks. Samples of plasma and urine were collected for biochemical analysis, and femur tissues were removed for micro-CT imaging. In addition to considering standard parameters, we regarded trabecular bone as a cylindrical rod and used computational algorithms for a technical assessment of the morphological characteristics of the bones. BMD (mg-HA/cm3) was obtained using a standard phantom.

RESULTS

We observed a decline in the total tissue volume, bone volume, percent bone volume, fractal dimension, number of trabecular segments, number of connecting nodes, bone mineral content (mg-HA), and BMD, as well as an increase in the structural model index and surface-area-to-volume ratio in low-Mg mice. Subsequently, we examined the distributions of the trabecular segment length and radius, and a series of specific local maximums were identified. The biochemical analysis revealed a 43% (96%) decrease in Mg and a 40% (71%) decrease in Ca in plasma (urine excretion).

CONCLUSIONS

This technical assessment performed using micro-CT revealed a lower population of femoral trabecular bones and a decrease in BMD at the distal metaphysis in the low-Mg mice. Examining the distributions of the length and radius of trabecular segments showed that the average length and radius of the trabecular segments in low-Mg mice are similar to those in normal mice.

Bone Mineral Density, Mechanical, Microstructural Properties and Mineral Content of the Femur in Growing Rats Fed with Cactus Opuntia ficus indica (L.) Mill. (Cactaceae) Cladodes as Calcium Source in Diet

Mechanical, microstructural properties, mineral content and bone mineral density (BMD) of the femur were evaluated in growing rats fed with Opuntia ficus indica (L.) Mill. (Cactaceae) cladodes at different maturity stages as calcium source. Male weanling rats were fed with cladodes at early maturity stage (25 and 60 days of age, belonging to groups N-60 and N-200, respectively) and cladodes at late maturity stage (100 and 135 days of age, belonging to groups N-400 and N-600, respectively) for 6 weeks. Additionally, a control group fed with calcium carbonate as calcium source was included for comparative purposes. All diets were fitted to the same calcium content (5 g/kg diet). The failure load of femurs was significantly lower (p ≤ 0.05) in groups N-60 and N-200 in comparison to N-400, N-600 and control groups. The cortical width (Ct.Wi) and trabecular thickness (Tb.Th) of the femurs in control and N-600 groups were significantly higher (p ≤ 0.05) than Ct.Wi and Tb.Th of femurs in groups N-60 and N-200. Trabecular separation of the femurs in N-60 and N-200 groups showed the highest values compared with all experimental groups. The highest calcium content in the femurs were observed in control, N-600 and N-400 groups; whereas the lowest phosphorus content in the bones were detected in N-200, N-600 and N-400 groups. Finally, the BMD in all experimental groups increased with age; nevertheless, the highest values were observed in N-600 and control groups during pubertal and adolescence stages. The results derived from this research demonstrate, for the first time, that the calcium found in Opuntia ficus indica cladodes is actually bioavailable and capable of improving mineral density and mechanical and microstructural properties of the bones. These findings suggest that the consumption of cladodes at late maturity stage within the diet might have a beneficial impact on bone health.

Role of Magnesium Transporter Subtype 1 (MagT1) in the Osteogenic Differentiation of Rat Bone Marrow Stem Cells

In the present study, we investigated the role of magnesium transporter subtype 1 (MagT1), a selective Mg transporter protein, in the osteogenic differentiation of rat bone marrow stem cells (rBMSCs). Osteogenic differentiation was monitored by the expressions of alkaline phosphatase (ALP), osteocalcin (OCN), collagen-1 (COL-1) and runt-related transcription factor 2 (RUNX2), and extracellular matrix mineralization of rBMSCs. The expression of MagT1 increased with osteogenic differentiation of rBMSCs, suggesting the importance of intracellular Mg homeostasis to cell differentiation. Alteration of intracellular Mg homeostasis by culture condition with low extracellular Mg significantly reduced the osteogenic differentiation markers ALP, OCN, COL-1, and RUNX2 gene expressions. MagT1 knockdown during the differentiation period also reduced osteogenic differentiation and the extent of matrix mineralization of rBMSCs. In conclusion, our results indicate that Mg and MagT1 play an important role in osteogenic differentiation of rBMSCs and may be involved in the bone regeneration.

Effects of vanadium (V) and magnesium (Mg) on rat bone tissue: mineral status and micromorphology. Consequences of V-Mg interactions

The extent to which the 12 week separate and combined administration of vanadium (as sodium metavanadate--SMV, 0.125 mg V per ml) and magnesium (as magnesium sulphate--MS, 0.06 mg Mg per ml) affects bone mineral status and micromorphology as well as the alkaline phosphatase (ALP) activity in femoral diaphysis (FD) was examined in male rats. The bone chemical composition of SMV-exposed rats was also investigated. SMV alone or in combination with MS (as SMV-MS) reduced the levels of MgFD (by 21% and 20%) and PFD (by 12% and 9%), lowered the CaFD content (by 7% and 10%), and caused a rise of the FeFD concentration (by 22.5% and 17%), compared with the control; SMV alone also reduced and enhanced the KFD and ZnFD concentrations (by 19% and 15%, respectively) but remained without significant effect on the femoral bone surface roughness (FBSR), whereas MS alone lowered the VFD, PFD, and CuFD levels (by 42%, 10%, and 20.6%), reduced FBSR, and created the regular femoral bone surface shape. The SMV-MS combination also induced a decline and rise in the levels of CuFD (by 30%) and NaFD (by 15%), respectively, compared with the control and the MS-supplemented rats; elevated ALPFD activity (by 24%, 35%, and 40%), compared with the control, SMV-exposed, and MS-supplemented animals; and increased FBSR. Relationships between the root mean square roughness (Sq) and skewness (Ssk): Sq [MS < SMV < Control < SMV-MS] ⇔ Ssk [SMV-MS > Control > SMV > MS], ALPFD and Sq: ALPFD⇔ Sq [SMV-MS > Control > SMV > MS], and between other variables were demonstrated. A partial limitation of the drop in the PFD and KFD levels and normalization of the ZnFD concentration were a consequence of the V-Mg antagonistic interaction whereas a consequence of the V-Mg synergistic interaction was the increase in the NaFD level, ALPFD activity, and FBSR. Ca10(PO4)5(SiO4)(OH) was part of the inorganic component of the bone of the SMV-exposed rats.

Association between serum level of magnesium and postmenopausal osteoporosis: a meta-analysis

There are conflicting reports as to the association between serum level of magnesium (Mg) and postmenopausal osteoporosis (OP). The purpose of the present study is to clarify the association between serum level of Mg and postmenopausal OP using a meta-analysis approach. We searched articles indexed in Pubmed and the Chinese Journal Full-text Database (CJFD) published as of October 2013 that met our predefined criteria. Seven eligible studies involving 1,349 postmenopausal women from 12 case-control study arms were identified. Overall, pooled analysis indicated that postmenopausal osteoporotic women had a lower serum level of Mg than the healthy controls (standardized mean difference [SMD]=-0.55, 95 % confidence interval [CI]=-0.83 to -0.26). Further subgroup analysis found a similar pattern in Turkey (SMD=-0.66, 95% CI=-0.99 to -0.32) and Belgium (SMD=-0.98, 95% CI=-1.91 to -0.05), but not in China (SMD=0.02, 95% CI=-0.21 to 0.26). And the difference of serum level of Mg between postmenopausal osteoporotic women and healthy controls below the age of 60 years (SMD=-0.61, 95% CI=-1.09 to -0.13) was similar to that among the population over 60 years (SMD=-0.49, 95% CI=-0.80 to -0.18).In conclusion, this meta-analysis suggests that the low serum level of Mg seems to be a risk factor for OP among the postmenopausal women. However, the subgroup analysis found that there was contradiction regarding races and geography, like China and Turkey. Thus, this finding needs further confirmation by trans-regional multicenter study to obtain better understanding of causal relationships between serum Mg and postmenopausal OP.

Potential Osteoporosis Recovery by Deep Sea Water through Bone Regeneration in SAMP8 Mice

The aim of this study is to examine the therapeutic potential of deep sea water (DSW) on osteoporosis. Previously, we have established the ovariectomized senescence-accelerated mice (OVX-SAMP8) and demonstrated strong recovery of osteoporosis by stem cell and platelet-rich plasma (PRP). Deep sea water at hardness (HD) 1000 showed significant increase in proliferation of osteoblastic cell (MC3T3) by MTT assay. For in vivo animal study, bone mineral density (BMD) was strongly enhanced followed by the significantly increased trabecular numbers through micro-CT examination after a 4-month deep sea water treatment, and biochemistry analysis showed that serum alkaline phosphatase (ALP) activity was decreased. For stage-specific osteogenesis, bone marrow-derived stromal cells (BMSCs) were harvested and examined. Deep sea water-treated BMSCs showed stronger osteogenic differentiation such as BMP2, RUNX2, OPN, and OCN, and enhanced colony forming abilities, compared to the control group. Interestingly, most untreated OVX-SAMP8 mice died around 10 months; however, approximately 57% of DSW-treated groups lived up to 16.6 months, a life expectancy similar to the previously reported life expectancy for SAMR1 24 months. The results demonstrated the regenerative potentials of deep sea water on osteogenesis, showing that deep sea water could potentially be applied in osteoporosis therapy as a complementary and alternative medicine (CAM).

Magnesium and osteoporosis: current state of knowledge and future research directions

A tight control of magnesium homeostasis seems to be crucial for bone health. On the basis of experimental and epidemiological studies, both low and high magnesium have harmful effects on the bones. Magnesium deficiency contributes to osteoporosis directly by acting on crystal formation and on bone cells and indirectly by impacting on the secretion and the activity of parathyroid hormone and by promoting low grade inflammation. Less is known about the mechanisms responsible for the mineralization defects observed when magnesium is elevated. Overall, controlling and maintaining magnesium homeostasis represents a helpful intervention to maintain bone integrity.

Nanostructured magnesium has fewer detrimental effects on osteoblast function

Efforts have been made recently to implement nanoscale surface features on magnesium, a biodegradable metal, to increase bone formation. Compared with normal magnesium, nanostructured magnesium has unique characteristics, including increased grain boundary properties, surface to volume ratio, surface roughness, and surface energy, which may influence the initial adsorption of proteins known to promote the function of osteoblasts (bone-forming cells). Previous studies have shown that one way to increase nanosurface roughness on magnesium is to soak the metal in NaOH. However, it has not been determined if degradation of magnesium is altered by creating nanoscale features on its surface to influence osteoblast density. The aim of the present in vitro study was to determine the influence of degradation of nanostructured magnesium, created by soaking in NaOH, on osteoblast density. Our results showed a less detrimental effect of magnesium degradation on osteoblast density when magnesium was treated with NaOH to create nanoscale surface features. The detrimental degradation products of magnesium are of significant concern when considering use of magnesium as an orthopedic implant material, and this study identified a surface treatment, ie, soaking in NaOH to create nanoscale features for magnesium that can improve its use in numerous orthopedic applications.

MgO-doped tantalum coating on Ti: microstructural study and biocompatibility evaluation

Pure and MgO incorporated Ta coatings were prepared on Cp-Ti substrate using laser engineered net shaping (LENS), which resulted in diffuse coating-substrate interface. MgO was found along the Ta grain boundaries in the Ta matrix that increased the coating hardness from 185 ± 2.7 HV to 794 ± 93 HV. In vitro biocompatibility study showed excellent early cellular attachment and later stage proliferation in MgO incorporated coatings. The results indicated that although Ta coatings had higher biocompatibility than Ti, it could further be improved by incorporating MgO in the coating, while simultaneously improving the mechanical properties.

Nitric oxide mediates low magnesium inhibition of osteoblast-like cell proliferation

An adequate intake of magnesium (Mg) is important for bone cell activity and contributes to the prevention of osteoporosis. Because (a) Mg is mitogenic for osteoblasts and (b) reduction of osteoblast proliferation is detected in osteoporosis, we investigated the influence of different concentrations of extracellular Mg on osteoblast-like SaOS-2 cell behavior. We found that low Mg inhibited SaOS-2 cell proliferation by increasing the release of nitric oxide through the up-regulation of inducible nitric oxide synthase (iNOS). Indeed, both pharmacological inhibition with the iNOS inhibitor l-N(6)-(iminoethyl)-lysine-HCl and genetic silencing of iNOS by small interfering RNA restored the normal proliferation rate of the cells. Because a moderate induction of nitric oxide is sufficient to potentiate bone resorption and a relative deficiency in osteoblast proliferation can result in their inadequate activity, we conclude that maintaining Mg homeostasis is relevant to ensure osteoblast function and, therefore, to prevent osteoporosis.

Role of melastatin transient receptor potential 7 channels in the osteoblastic differentiation of murine MC3T3 cells

Adequate bone formation is assured by the coordinated proliferation, migration, differentiation, and secretory functions of osteoblasts. Epidemiological studies have linked insufficient dietary magnesium (Mg) intake to osteoporosis. Here, we investigated the role of melastatin-like transient receptor potential 7 (TRPM7), a calcium (Ca) and Mg channel, in osteoblastic differentiation of the murine MC3T3 cell line. Osteoblastic differentiation was monitored by alkaline phosphatase activity, osteocalcin gene expression, and extracellular matrix mineralization. Gene expression of TRPM7 increased with osteoblastic differentiation, suggesting the importance of intracellular Ca/Mg homeostasis to cell differentiation. Alteration of intracellular Ca/Mg homeostasis by culture conditions with low extracellular Ca or Mg significantly reduced the osteoblastic differentiation markers alkaline phosphatase activity and osteocalcin gene expression. In accordance, matrix mineralization was reduced under low extracellular Ca or Mg levels. Nevertheless, expression of collagen type I, the predominant matrix protein, was increased in low-Mg culture conditions, indicating that dysfunction of matrix protein production cannot account for the reduced mineralization. Silencing TRPM7 expression during the differentiation period also reduced osteoblastic differentiation and the extent of matrix mineralization. Gene expression of osteoblastic transcription factor Runx2 was reduced by conditions of culture under low extracellular Ca or Mg levels, as well as by TRPM7 silencing. Our results indicate that intracellular Ca and Mg homeostasis ensured by TRPM7 expression is important for the osteoblastic differentiation of MC3T3 cells. Thus, Mg deficiency, a common condition among the population, may be associated with altered osteoblastic differentiation leading to inadequate bone formation and the development of osteoporosis.

Effects of magnesium intake deficiency on bone metabolism and bone tissue around osseointegrated implants

OBJECTIVES

This study evaluated the effect of magnesium dietary deficiency on bone metabolism and bone tissue around implants with established osseointegration.

MATERIALS AND METHODS

For this, 30 rats received an implant in the right tibial metaphysis. After 60 days for healing of the implants, the animals were divided into groups according to the diet received. Control group (CTL) received a standard diet with adequate magnesium content, while test group (Mg) received the same diet except for a 90% reduction of magnesium. The animals were sacrificed after 90 days for evaluation of calcium, magnesium, osteocalcin and parathyroid hormone (PTH) serum levels and the deoxypyridinoline (DPD) level in the urine. The effect of magnesium deficiency on skeletal bone tissue was evaluated by densitometry of the lumbar vertebrae, while the effect of bone tissue around titanium implants was evaluated by radiographic measurement of cortical bone thickness and bone density. The effect on biomechanical characteristics was verified by implant removal torque testing.

RESULTS

Magnesium dietary deficiency resulted in a decrease of the magnesium serum level and an increase of PTH and DPD levels (P ≤ 0.05). The Mg group also presented a loss of systemic bone mass, decreased cortical bone thickness and lower values of removal torque of the implants (P ≤ 0.01).

CONCLUSIONS

The present study concluded that magnesium-deficient diet had a negative influence on bone metabolism as well as on the bone tissue around the implants.

Short-term oral magnesium supplementation suppresses bone turnover in postmenopausal osteoporotic women

Magnesium has been shown to increase bone mineral density when used in the treatment of osteoporosis, yet its mechanism of action is obscure. In this study, the effects of daily oral magnesium supplementation on biochemical markers of bone turnover were investigated. Twenty postmenopausal women have been divided into two groups. Ten patients were given magnesium citrate (1,830 mg/day) orally for 30 days. Ten postmenopausal women of matching age, menopause duration, and BMI were recruited as the control group and followed without any medication. Fasting blood and first-void urine samples were collected on days 0, 1, 5, 10, 20, and 30, respectively. Total magnesium, calcium, phosphorus, iPTH and osteocalcin were determined in blood samples. Deoxypyridinoline levels adjusted for creatinine were measured in urine samples. Thirty consecutive days of oral magnesium supplementation caused significantly decrease in serum iPTH levels in the Mg-supplemented group (p < 0.05). Serum osteocalcin levels were significantly increased (p < 0.001) and urinary deoxypyridinoline levels were decreased (p < 0.001) in the Mg-supplemented group. This study has demonstrated that oral magnesium supplementation in postmenopausal osteoporotic women suppresses bone turnover.

Importance of melastatin-like transient receptor potential 7 and magnesium in the stimulation of osteoblast proliferation and migration by platelet-derived growth factor

Bone is a dynamic tissue that is continuously being remodeled throughout life. Specialized cells called osteoclasts transiently break down old bone (resorption process) at multiple sites as other cells known as osteoblasts are replacing it with new tissue (bone formation). Usually, both resorption and formation processes are in balance and thereby maintain skeletal strength and integrity. This equilibrium is assured by the coordination of proliferation, migration, differentiation, and secretory functions of the osteoblasts, which are essential for adequate formation and resorption processes. Disturbances of this equilibrium may lead to decreased bone mass (osteoporosis), increased bone fragility, and susceptibility to fractures. Epidemiological studies have linked insufficient dietary magnesium (Mg2+) intake in humans with low bone mass and osteoporosis. Here, we investigated the roles of Mg2+ and melastatin-like transient receptor potential 7 (TRPM7), known as Mg2+ channels, in human osteoblast cell proliferation and migration induced by platelet-derived growth factor (PDGF), which has been involved in the bone remodeling process. PDGF promoted an influx of Mg2+, enhanced cell migration, and stimulated the gene expression of TRPM7 channels in human osteoblast MG-63 cells. The stimulation of osteoblast proliferation and migration by PDGF was significantly reduced under culture conditions of low extracellular Mg2+ concentrations. Silencing TRPM7 expression in osteoblasts by specific small interfering RNA prevented the induction by PDGF of Mg2+ influx, proliferation, and migration. Our results indicate that extracellular Mg2+ and TRPM7 are important for PDGF-induced proliferation and migration of human osteoblasts. Thus Mg2+ deficiency, a common condition among the general population, may be associated with altered osteoblast functions leading to inadequate bone formation and the development of osteoporosis.

Structural characterization and biological fluid interaction of Sol-Gel-derived Mg-substituted biphasic calcium phosphate ceramics

Sol-Gel chemistry has been used to prepare undoped and Mg-substituted biphasic calcium phosphate (BCP) ceramics composed of hydroxyapatite (HAp) and whitlockite (beta-TCP) phases. Different series of samples have been synthesized with different Mg-doping levels (from 0 to 5 atomic % of Ca atoms substituted) and different temperatures of calcination (from 500 to 1100 degrees C). All of the powdered samples were systematically treated by Rietveld refinement to extract the quantitative phase analysis and the structural and microstructural parameters, to locate the Mg crystallographic sites, and to refine the composition of the Mg-substituted phases. The temperature dependence of the weight amount ratio between HAp and beta-TCP is not monotonic because of the formation of minor phases such as Ca(2)P(2)O(7), CaO, MgO, and CaCO(3) and certainly an amorphous phase. On the other hand, the Mg stabilizing feature on the beta-TCP phase has been evidenced and explained. The mechanism of stabilization by small Mg(2+) is different from that by large Sr(2+). Nevertheless, in both cases, the beta-TCP stabilization is realized by an improvement of the environment of the Ca4 site unusually face-coordinated to a PO(4) tetrahedron. The substitution of a Mg atom in the Ca5 site allows considerable improvement of the bond valence sum of the unusual Ca4 polyhedron. The temperatures of calcination combined with the amount of Mg atoms introduced allow monitoring of the phase composition of the BCP ceramics as well as their microstructural properties. The bioactivity properties of the BCP samples are improved by the presence of Mg atoms in the structure of the beta-TCP phase. The mechanism of improvement is mainly attributed to an accelerated kinetic of precipitation of a calcium phosphate layer at the surface comprising HAp and/or beta-TCP phases.

Effects of high magnesium intake on bone mineral status and lipid metabolism in rats

Effects of magnesium (Mg)-intake on mineral levels in bone, blood and various tissues, bone density and plasma lipids were examined in 4-wk-old, female Wistar rats fed diets of five different Mg-contents of 1/10, 1 (standard diet (Mg 47 mg/100 g diet): control group), 2, 5 and 10-fold of the standard content for 4 wk. In rats fed the 1/10-fold Mg diet, the body weight gain declined with a statistical significance compared to control rats, while no significant differences were observed in rats fed on the 2-, 5-, and 10-fold Mg diets. The imbalance of mineral concentrations in the rats fed 1/10 Mg diet was induced, but in the rats fed high Mg diets were not induced except in tibia. Mg concentration in tibia of rats fed the 10-fold Mg diet significantly increased compared to the control group. All groups (1/10-fold, 2-, 5-, and 10-fold Mg groups) showed no significant changes in tibial mineral levels, except Mg in the 10-fold group, compared to the control group. With increase in Mg-intake, decline of plasma lipid parameters such as cholesterol, triglycerides and phospholipids are induced. Based on these results, it was suggested that a higher Mg-intake (around 5-fold of the standard Mg-content) might have a prophylactic potential against the onset of hyperlipidemia and cardiovascular disease by reducing lipid indices, and Mg decline in bone.

Infrared analysis of bones in magnesium-deficient rats treated with vitamin K2

In this study, we compared the effects of vitamin K(2) menatetrenone on bone mechanical properties in rats fed a low-magnesium (Mg) diet. In addition, the mechanism of bone quality was examined using Fourier transform infrared imaging (FTIRI). Thirty 4-week-old male Wistar rats were divided into three groups: intact, low-Mg-control, and low-Mg-MK-4 groups. Rats in the low-Mg groups were given a diet containing 6 mg/100 g Mg (intact, 90 mg/100 g). After an 8-week-treatment, the cortical bone mineral content (CtBMC), outer perimeter, and endo perimeter of the femoral diaphysis in the low-Mg-control group were significantly higher, while the maximum load (ML) and elastic modulus (EM) were 81% and 50% of those in the intact group, respectively (respectively, P < 0.05). In the low-Mg-MK-4 group, ML and EM were significantly higher than in the low-Mg-control group (P < 0.05), with no differences in CtBMC. The mineral/matrix ratios for the periosteal and central regions in the low-Mg-control group were 162% and 120% of those in the intact group (both, P < 0.05), respectively. MK-4 significantly inhibited these increases (P < 0.05). We found that the mineral/matrix ratios for the periosteal region of the femoral diaphysis were negatively correlated with EM, suggesting that an increase in the mineral/matrix ratio may be involved in the reduction of EM and that MK-4 may improve EM by improving the mineral/matrix ratio.

Dietary magnesium reduction to 25% of nutrient requirement disrupts bone and mineral metabolism in the rat

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 deficiency and osteoporosis: animal and human observations

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.

Histopathologic changes in metabolic bone disease

Metabolic bone disease encompasses a heterogeneous group of disorders that influence skeletal metabolism and structure. They are generally diagnosed at an advanced stage and manifest clinically with stunted skeletal growth in children and pathologic fractures in adults. Biochemical markers for bone metabolism are equivocal and microscopic examination of labeled bone remains the gold standard for the diagnosis and accurate monitoring of the response to therapy. This article reviews the role of microscopic bone changes in the diagnosis and management of metabolic bone disease.

Bone loss induced by dietary magnesium reduction to 10% of the nutrient requirement in rats is associated with increased release of substance P and tumor necrosis factor-alpha

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.

The effect of polyunsaturated fatty acids, including conjugated linoleic acid, on calcium absorption and bone metabolism and composition in young growing rats

The effect of polyunsaturated fatty acids (PUFA), in particular conjugated linoleic acid (CLA), on Ca and bone metabolism is unclear. In a 2x2 factorial design study, forty male 4-week-old rats were fed a control diet containing 70 g added fat (soyabean oil (SBO; n-6 PUFA-rich diet) or menhaden oil-safflower oil (MSO; n-3 PUFA-rich diet))/kg diet with 0 or 10 g CLA/kg for 8 weeks. Ex vivo prostaglandin E2 biosynthesis by bone organ culture was significantly higher (P<0.001) in rats consuming SBO compared with MSO, irrespective of CLA. Addition of the CLA treatment to either diet further lowered (P<0.05) ex vivo prostaglandin E2 production. Neither PUFA type nor CLA altered circulating or femoral mRNA levels of osteocalcin (a marker of bone formation) or insulin-like growth factor-I (a mediator of bone metabolism). While urinary pyridinium crosslinks levels (markers of bone resorption) were unaffected by CLA irrespective of PUFA type, they were significantly higher (P<0.05) in rats consuming SBO compared with MSO irrespective of CLA. Net fractional (%) and absolute (mg) Ca absorption were significantly (P<0.01 and P<0.05 respectively) higher in CLA-supplemented than unsupplemented animals fed on the n-3 PUFA-rich diet, whereas CLA had no effect in animals fed the n-6 PUFA-rich diet. There was no effect of CLA supplementation on bone mineral mass. In conclusion, CLA supplementation over 8 weeks appeared to enhance Ca absorption in young growing rats fed an n-3 PUFA-rich diet, but had no measurable effect on bone metabolism or bone mass over this time frame.

Cisplatin nephrotoxicity affects magnesium and calcium metabolism

Cisplatin is not directly toxic to bone, but cisplatin nephrotoxicity leading to magnesium wasting may affect magnesium and calcium metabolism, both of which contribute to bone integrity. The specificity of the magnesium lesion suggests that cisplatin may have an affinity for proteins that regulate magnesium absorption. Sulfhydryls such as amifostine can reduce the toxicity of cisplatin in adults, but current pediatric data do not indicate a role for sulfhydryl therapy to reduce cisplatin toxicity in children.

Acute effect of high-calcium milk with or without additional magnesium, or calcium phosphate on parathyroid hormone and biochemical markers of bone resorption

OBJECTIVE

To assess whether there are any differences in the postprandial physiological responses to apple drink (control), calcium phosphate (tricalcium phosphate, TCP) and high-calcium skim milk (HCSM) with or without additional magnesium in postmenopausal women.

DESIGN

Randomized, controlled, cross-over. Measurements after overnight fast before each drink, and subsequently every hour for 8 h postprandially.

SETTING

Human Nutrition Studies Laboratory, Milk and Health Research Centre, Massey University, Palmerston North, New Zealand.

SUBJECTS

Twenty-one healthy postmenopausal women.

INTERVENTION

Four drinks, each 400 ml. (1) Apple drink (25% fruit juice). (2) TCP dispersed in water containing 1200 mg Ca. (3) HCSM containing 1200 mg Ca and 65.5 mg Mg. (4) HCSM containing 1200 mg Ca and 172 mg Mg.

RESULTS

There was no difference in baseline serum calcium, PTH or C-telopeptide levels between drinks. There were no overall differences in serum calcium after apple or after either milk, but after TCP serum calcium increased from a baseline value of 2.12+/-0.08 to a mean peak of 2.21+/-0.12 mmol/l (s.d.) (P=0.0001) after 2 h. There were no significant differences in serum PTH after either apple or HCSM+Mg. In contrast, after TCP, serum PTH decreased from 2.76+/-0.69 to a mean nadir of 2.23+/-0.65 pmol/l (P=0.0001) after 1 h, and after HCSM, it decreased from 2.71+/-0.78 to a mean nadir of 2.51+/-0.87 pmol/l (P=0.007) after 2 h. Serum C-telopeptides decreased after each drink, reaching nadirs after 5 h. At this time the serum values for each of the high calcium drinks were not different from each other, but were significantly less than for apple (P=0.001 for each), being 0.22+/-0.09 ng/ml for apple, 0.15+/-0.08 for TCP, 0.14+/-0.07 for HCSM and 0.16+/-0.07 for HCSM+Mg.

CONCLUSION

Despite differences in serum calcium and PTH responses to the three high-calcium drinks that we tested, there was no distinguishable difference in serum C-telopeptides between high calcium drinks.

[Effect of menatetrenone (V.K2) on bone mineral density and bone strength in Ca/Mg deficient rats]

Two experiments were carried out using 7-week-old male Wistar rats. Exp. 1: Rats in the intact group were fed with normal diet (0.5% Ca, 0.09% Mg). Ca/Mg deficient rats were fed low Ca (0.01%) diets containing 0.003, 0.015 or 0.09% Mg for 4 weeks. After 4 weeks, the bone mineral density (BMD) and maximum load in the femur were decreased in Ca/Mg deficient rats, but this was not dependent on dietary Mg concentration. The elasticity, stiffness, and Mg concentration in the femur of these rats were also decreased and Ca deposition in the kidney were increased, compared to those of normal rats, which were related to Mg concentration in the diet. From these results, Mg may play an important role in qualitative changes in bone (i.e., reduced stiffness). Exp. 2: We investigated the effects of V.K2 on the changes in BMD and bone strength in femur induced by low Ca/Mg (0.01%/0.003%) diet for 8 weeks. Compared to the intact group, Ca and Mg levels in serum and femur and cortical thickness, cortical area, and maximum load of the femoral midshaft were decreased in the Ca/Mg-deficient group. In these rats, PTH in the serum and renal Ca concentration were increased. In V.K2-treated rats, these changes in the serum Ca, Mg and PTH levels and the renal Ca concentration were improved. V.K2 also improved the decrease in maximum load in spite of no influence on the cortical thickness, cortical area and Mg concentration in the femur. These findings suggest that V.K2 may affect the qualitative change in bone.

Bone morphology, strength and density are compromised in iron-deficient rats and exacerbated by calcium restriction

Rats fed an iron-deficient diet develop decreased bone mass and increased fragility. This study documents that rats fed two minerals likely to be low in American diets, calcium and iron, had dramatic changes in bone density and morphometry. Weanling male Long-Evans rats were fed a diet that was either deficient in iron (5-8 mg/kg or 89-143 micro mol/kg diet), low in calcium (1.0 g/kg Ca or 0.025 mol/kg diet) or deficient in both minerals or a control diet with adequate iron and calcium. Eight rats in each of the four groups were fed their respective diets for 5 wk. Total femur and tibia widths were decreased in all experimental groups and iron-deficient rats had decreased medullary widths compared with the other three groups. Cortical width was decreased in all experimental groups, with either the calcium-restricted group or the iron-deficient + calcium-restricted group showing the greatest impact. Both calcium restriction and iron deficiency, either singly or in combination with one another, had reduced cortical bone area. Analysis by dual-energy X-ray absorptiometry revealed a pattern of significant reductions in bone density for iron-deficient, calcium-restricted and the combination of calcium-restricted+ iron-deficient rats, respectively, as compared with controls. These data suggest that a commonly deficient trace element in American diets, iron, has a negative impact upon bone health, and this impact is exacerbated by a calcium-restricted diet.