Media calcification, low erythrocyte magnesium, altered plasma magnesium, and calcium homeostasis following grafting of the thoracic aorta to the infrarenal aorta in the rat—differential preventive effects of long-term oral magnesium supplementation alone and in combination with alkali

Relationship between Serum Magnesium, Parathyroid Hormone, and Vascular Calcification in Patients on Dialysis: A Literature Review

Secondary hyperparathyroidism is present in most patients with end-stage renal disease and has been linked to uremic bone disease, vascular calcification, and mortality. Current literature suggests an association between hypomagnesemia and cardiovascular disease in the general population. We reviewed all published studies on the relationship between serum magnesium and parathyroid hormone and the relationship between serum Mg and vascular calcification in dialysis patients. Of these, 10 of 12 studies of patients on hemodialysis and 4 of 5 studies of patients on peritoneal dialysis showed a significant inverse relationship between serum Mg and serum intact parathyroid hormone. Hyperparathyroidism develops in peritoneal dialysis patients dialyzed with a solution containing normal calcium (1.25 mmol/L) and low Mg (0.25 mmol/L), even though serum calcium is maintained at a normal level. Four of the hemodialysis studies and one of the peritoneal dialysis studies indicated that there is an inverse relationship between serum Mg and vascular calcification in these patients. Potential benefits have been attributed to magnesium carbonate as a phosphate binder and it may possibly be an effective, less toxic, less expensive phosphate binder. We believe that the role of Mg in secondary hyperparathyroidism and vascular calcification merits further investigation.

Magnesium as a Calcification Inhibitor

Vascular calcification (VC) is associated with elevated cardiovascular mortality rates in patients with CKD. Recent clinical studies of patients with advanced CKD have observed an association between low serum magnesium (Mg) levels on one hand and elevated VC and cardiovascular mortality on the other. These findings have stimulated interest in understanding Mg's impact on CKD in general and the associated VC in particular. In vitro and preclinical in vivo data indicate that Mg has the potential to protect vascular smooth muscle cells against calcification via several different molecular mechanisms. Accordingly, data from pilot interventional studies in the clinic suggest that oral Mg supplementation reduces VC in patients with CKD. The present review provides an overview of our current understanding of the impact of Mg on the development of VC in patients with CKD.

Metal Ion-Loaded Nanofibre Matrices for Calcification Inhibition in Polyurethane Implants

Pathologic calcification leads to structural deterioration of implant materials via stiffening, stress cracking, and other structural disintegration mechanisms, and the effect can be critical for implants intended for long-term or permanent implantation. This study demonstrates the potential of using specific metal ions (MI)s for inhibiting pathological calcification in polyurethane (PU) implants. The hypothesis of using MIs as anti-calcification agents was based on the natural calcium-antagonist role of Mg²⁺ ions in human body, and the anti-calcification effect of Fe³⁺ ions in bio-prosthetic heart valves has previously been confirmed. In vitro calcification results indicated that a protective covering mesh of MI-doped PU can prevent calcification by preventing hydroxyapatite crystal growth. However, microstructure and mechanical characterisation revealed oxidative degradation effects from Fe³⁺ ions on the mechanical properties of the PU matrix. Therefore, from both a mechanical and anti-calcification effects point of view, Mg²⁺ ions are more promising candidates than Fe³⁺ ions. The in vitro MI release experiments demonstrated that PU microphase separation and the structural design of PU-MI matrices were important determinants of release kinetics. Increased phase separation in doped PU assisted in consistent long-term release of dissolved MIs from both hard and soft segments of the PU. The use of a composite-sandwich mesh design prevented an initial burst release which improved the late (>20 days) release rate of MIs from the matrix.

Magnesium and outcomes in patients with chronic kidney disease: focus on vascular calcification, atherosclerosis and survival

Patients with chronic kidney disease (CKD) have a high prevalence of vascular calcification, and cardiovascular disease is the leading cause of death in this population. However, the molecular mechanisms of vascular calcification, which are multifactorial, cell-mediated and dynamic, are not yet fully understood. We need to address ways to improve outcomes in CKD patients, both in terms of vascular calcification and cardiovascular morbidity and mortality—and to these ends, we investigate the role of magnesium. Magnesium’s role in the pathogenesis of vascular calcification has not been extensively studied. Nonetheless, several in vitro and animal studies point towards a protective role of magnesium through multiple molecular mechanisms. Magnesium is a natural calcium antagonist and both human and animal studies have shown that low circulating magnesium levels are associated with vascular calcification. Clinical evidence from observational studies of dialysis patients has shown that low-magnesium levels occur concurrently with mitral annular calcification, peripheral arterial calcification and increased carotid intima–media thickness. Few interventional studies have been performed. Two interventional studies suggest that there may be benefits such as retardation of arterial calcification and/or reductions in carotid intima–media thickness in response to magnesium supplementation in CKD patients, though both studies have limitations. Finally, observational studies have shown that low serum magnesium may be an independent risk factor for premature death in CKD patients, and patients with mildly elevated serum magnesium levels could have a survival advantage over those with lower magnesium levels.

Low Magnesium Levels and FGF-23 Dysregulation Predict Mitral Valve Calcification as well as Intima Media Thickness in Predialysis Diabetic Patients

Background. Mitral valve calcification and intima media thickness (IMT) are common complications of chronic kidney disease (CKD) implicated with high cardiovascular mortality. Objective. To investigate the implication of magnesium and fibroblast growth factor-23 (FGF-23) levels with mitral valve calcification and IMT in CKD diabetic patients. Methods. Observational, prospective study involving 150 diabetic patients with mild to moderate CKD, divided according to Wilkins Score. Carotid-echodoppler and transthoracic echocardiography were used to assess calcification. Statistical tests used to establish comparisons between groups, to identify risk factors, and to establish cut-off points for prediction of mitral valve calcification. Results. FGF-23 values continually increased with higher values for both IMT and calcification whereas the opposite trend was observed for magnesium. FGF-23 and magnesium were found to independently predict mitral valve calcification and IMT (P < 0.05). Using Kaplan-Meier analysis, the number of deaths was higher in patients with lower magnesium levels and poorer Wilkins score. The mean cut-off value for FGF-23 was 117 RU/mL and for magnesium 1.7 mg/dL. Conclusions. Hypomagnesemia and high FGF-23 levels are independent predictors of mitral valve calcification and IMT and are risk factors for cardiovascular mortality in this population. They might be used as diagnostic/therapeutic targets in order to better manage the high cardiovascular risk in CKD patients.

Can antihypertensive medication interfere with the vicious cycle between hypertension and vascular calcification?

Vascular calcification is a phenomenon of disturbed calcium deposition, as part of the calcium that is supposed to be deposited to our bones, is lodged to our vessels. There are two forms of vascular calcification, each with a distinct anatomical distribution and clinical relevance, namely the intimal and medial calcification. Studies have demonstrated that hypertension may cause vascular calcification but also that both types of calcification, especially medial, promote arterial rigidity and hence hypertension. Implications of this two-way road are largely unknown as there is no consensus yet on their exact clinical value. However, several antihypertensive medications seem to be able to interfere with the cycle of high blood pressure and vascular calcium deposits. The present review summarizes the up-to-date data regarding the effect of antihypertensive medication on vascular calcification.

Magnesium retards the progress of the arterial calcifications in hemodialysis patients: a pilot study

BACKGROUND

The aim of the study was to evaluate the impact of magnesium (Mg) on the evolution of arterial calcifications in hemodialysis patients.

PATIENTS AND METHODS

Seventy-two stable hemodialysis patients were randomly allocated to two groups: 36 administered a regimen containing magnesium carbonate plus calcium acetate as a phosphate binder (Mg group), while the rest 36 received calcium acetate alone (Ca group). The presence and the progression of arterial calcifications were evaluated in plain X-rays using a simple vascular calcification score. The duration of the follow-up period was 12 months.

RESULTS

Thirty-two patients of the Mg group and 27 of the Ca group completed the study. The mean time average values of the biochemical laboratories did not differ between the two groups, except serum Mg: 2.83 + 0.38 in the Mg group versus 2.52 + 0.27 mg/dl in the Ca group, p = 0.001. In 9/32 (28.12 %) patients of the Mg group and in 12/27 (44.44 %) patients of the Ca group, the arterial calcifications were worsened, p = 0.276. Moreover, in 4/32 (15.6 %) patients of the Mg group and in 0/27 (0 %) patients of the Ca group, they were improved, p = 0.040. The multivariate logistic regression analysis revealed that serum magnesium was an independent predictor for no progression of the arterial calcifications, p = 0.047.

CONCLUSIONS

Magnesium probably retards the arterial calcifications in hemodialysis patients. Further clinical studies are needed to clarify whether magnesium provides cardiovascular protection to this group of patients.

Vascular smooth muscle cell differentiation to an osteogenic phenotype involves TRPM7 modulation by magnesium

Arterial calcification, common in vascular diseases, involves vascular smooth muscle cell (VSMC) transformation to an osteoblast phenotype. Clinical studies suggest that magnesium may prevent this, but mechanisms are unclear. We assessed whether increasing magnesium levels reduce VSMC calcification and differentiation and questioned the role of the Mg(2+) transporter, transient receptor potential melastatin (TRPM)7 cation channels in this process. Rat VSMCs were exposed to calcification medium in the absence and presence of magnesium (2.0 to 3.0 mmol/L) or 2-aminoethoxy-diphenylborate (2-APB) (TRPM7 inhibitor). VSMCs from mice with genetically low (MgL) or high-normal (MgH) [Mg(2+)](i) were also studied. Calcification was assessed by von Kossa staining. Expression of osteocalcin, osteopontin, bone morphogenetic protein (BMP)-2, BMP-4, BMP-7, and matrix Gla protein and activity of TRPM7 (cytosol:membrane translocation) were determined by immunoblotting. Calcification medium induced osteogenic differentiation, reduced matrix Gla protein content, and increased expression of the sodium-dependent cotransporter Pit-1. Magnesium prevented calcification and decreased osteocalcin expression and BMP-2 activity and increased expression of calcification inhibitors, osteopontin and matrix Gla protein. TRPM 7 activation was decreased by calcification medium, an effect reversed by magnesium. 2-APB recapitulated the VSMC osteoblastic phenotype in VSMCs. Osteocalcin was increased by calcification medium in VSMCs and intact vessels from MgL but not MgH, whereas osteopontin was increased in MgH, but not in MgL mice. Magnesium negatively regulates vascular calcification and osteogenic differentiation through increased/restored TRPM7 activity and increased expression of anticalcification proteins, including osteopontin, BMP-7, and matrix Gla protein. New molecular insights are provided whereby magnesium could protect against VSMC calcification.

Mechanisms of vascular calcification

Vascular calcification is highly prevalent and correlated with high rates of cardiovascular mortality in chronic kidney disease patients. Recent evidence suggests that mineral, hormonal, and metabolic imbalances that promote phenotype change in vascular cells as well as deficiencies in specific mineralization inhibitory pathways may be important contributory factors for vascular calcification in these patients. This article reviews current mechanisms proposed for the regulation of vascular calcification and data supporting their potential contribution to this process in chronic kidney disease.