Magnesium Inhibits Wnt/β-Catenin Activity and Reverses the Osteogenic Transformation of Vascular Smooth Muscle Cells

Magnesium reduces vascular smooth muscle cell (VSMC) calcification in vitro but the mechanism has not been revealed so far. This work used only slightly increased magnesium levels and aimed at determining: a) whether inhibition of magnesium transport into the cell influences VSMC calcification, b) whether Wnt/β-catenin signaling, a key mediator of osteogenic differentiation, is modified by magnesium and c) whether magnesium can influence already established vascular calcification. Human VSMC incubated with high phosphate (3.3 mM) and moderately elevated magnesium (1.4 mM) significantly reduced VSMC calcification and expression of the osteogenic transcription factors Cbfa-1 and osterix, and up-regulated expression of the natural calcification inhibitors matrix Gla protein (MGP) and osteoprotegerin (OPG). The protective effects of magnesium on calcification and expression of osteogenic markers were no longer observed in VSMC cultured with an inhibitor of cellular magnesium transport (2-aminoethoxy-diphenylborate [2-APB]). High phosphate induced activation of Wnt/β-catenin pathway as demonstrated by the translocation of β-catenin into the nucleus, increased expression of the frizzled-3 gene, and downregulation of Dkk-1 gene, a specific antagonist of the Wnt/β-catenin signaling pathway. The addition of magnesium however inhibited phosphate-induced activation of Wnt/β-catenin signaling pathway. Furthermore, TRPM7 silencing using siRNA resulted in activation of Wnt/β-catenin signaling pathway. Additional experiments were performed to test the ability of magnesium to halt the progression of already established VSMC calcification in vitro. The delayed addition of magnesium decreased calcium content, down-regulated Cbfa-1 and osterix and up-regulated MGP and OPG, when compared with a control group. This effect was not observed when 2-APB was added. In conclusion, magnesium transport through the cell membrane is important to inhibit VSMC calcification in vitro. Inhibition of Wnt/β-catenin by magnesium is one potential intracellular mechanism by which this anti-calcifying effect is achieved

Serum magnesium and sudden death in European hemodialysis patients

Despite suggestions that higher serum magnesium (Mg) levels are associated with improved outcome, the association with mortality in European hemodialysis (HD) patients has only scarcely been investigated. Furthermore, data on the association between serum Mg and sudden death in this patient group is limited. Therefore, we evaluated Mg in a posthoc analysis using pooled data from the CONvective TRAnsport STudy (CONTRAST, NCT00205556), a randomized controlled trial (RCT) evaluating the survival risk in dialysis patients on hemodiafiltration (HDF) compared to HD with a mean follow-up of 3.1 years. Serum Mg was measured at baseline and 6, 12, 24 and 36 months thereafter. Cox proportional hazards models, adjusted for confounders using inverse probability weighting, were used to estimate hazard ratios (HRs) of baseline serum Mg on all-cause mortality, cardiovascular mortality, non-cardiovascular mortality and sudden death. A generalized linear mixed model was used to investigate Mg levels over time. Out of 714 randomized patients, a representative subset of 365 (51%) were analyzed in the present study. For every increase in baseline serum Mg of 0.1 mmol/L, the HR for all-cause mortality was 0.85 (95% CI 0.77-94), the HR for cardiovascular mortality 0.73 (95% CI 0.62-0.85) and for sudden death 0.76 (95% CI 0.62-0.93). These findings did not alter after extensive correction for potential confounders, including treatment modality. Importantly, no interaction was found between serum phosphate and serum Mg. Baseline serum Mg was not related to non-cardiovascular mortality. Mg decreased slightly but statistically significant over time (Ä -0.011 mmol/L/year, 95% CI -0.017 to -0.009, p = 0.03). In short, serum Mg has a strong, independent association with all-cause mortality, cardiovascular mortality and sudden death in European HD patients. Serum Mg levels decrease slightly over time

Structure-based redesign of the dimerization interface reduces the toxicity of zinc-finger nucleases

Artificial endonucleases consisting of a Fokl cleavage domain tethered to engineered zinc-finger DNA-binding proteins have proven useful for stimulating homologous recombination in a variety of cell types. Because the catalytic domain of zinc-finger nucleases (ZFNs) must dimerize to become active, two subunits are typically assembled as heterodimers at the cleavage site. The use of ZFNs is often associated with significant cytotoxicity, presumably due to cleavage at off- target sites. Here we describe a structure- based approach to reducing off- target cleavage. Using in silico protein modeling and energy calculations, we increased the specificity of target site cleavage by preventing homodimerization and lowering the dimerization energy. Cell-based recombination assays confirmed that the modified ZFNs were as active as the original ZFNs but elicit significantly less genotoxicity. The improved safety profile may facilitate therapeutic application of the ZFN technology

Structure-based redesign of the dimerization interface reduces the toxicity of zinc-finger nucleases

Artificial endonucleases consisting of a Fokl cleavage domain tethered to engineered zinc-finger DNA-binding proteins have proven useful for stimulating homologous recombination in a variety of cell types. Because the catalytic domain of zinc-finger nucleases (ZFNs) must dimerize to become active, two subunits are typically assembled as heterodimers at the cleavage site. The use of ZFNs is often associated with significant cytotoxicity, presumably due to cleavage at off- target sites. Here we describe a structure- based approach to reducing off- target cleavage. Using in silico protein modeling and energy calculations, we increased the specificity of target site cleavage by preventing homodimerization and lowering the dimerization energy. Cell-based recombination assays confirmed that the modified ZFNs were as active as the original ZFNs but elicit significantly less genotoxicity. The improved safety profile may facilitate therapeutic application of the ZFN technology

Characterisation of Calcium Phosphate Crystals on Calcified Human Aortic Vascular Smooth Muscle Cells and Potential Role of Magnesium

International audienceBackgroundCardiovascular disease including vascular calcification (VC) remains the leading cause of death in patients suffering from chronic kidney disease (CKD). The process of VC seems likely to be a tightly regulated process where vascular smooth muscle cells are playing a key role rather than just a mere passive precipitation of calcium phosphate. Characterisation of the chemical and crystalline structure of VC was mainly led in patients or animal models with CKD. Likewise, Mg2+ was found to be protective in living cells although a potential role for Mg2+ could not be excluded on crystal formation and precipitation. In this study, the crystal formation and the role of Mg2+ were investigated in an in vitro model of primary human aortic vascular smooth muscle cells (HAVSMC) with physical techniques.Methodology/Principal FindingsIn HAVSMC incubated with increased Ca x Pi medium, only calcium phosphate apatite crystals (CPA) were detected by Micro-Fourier Transform InfraRed spectroscopy (µFTIR) and Field Effect Scanning Electron Microscope (FE — SEM) and Energy Dispersive X-ray spectrometry (EDX) at the cell layer level. Supplementation with Mg2+ did not alter the crystal composition or structure. The crystal deposition was preferentially positioned near or directly on cells as pictured by FE — SEM observations and EDX measurements. Large µFTIR maps revealed spots of CPA crystals that were associated to the cellular layout. This qualitative analysis suggests a potential beneficial effect of Mg2+ at 5 mM in noticeably reducing the number and intensities of CPA µFTIR spots.Conclusions/SignificanceFor the first time in a model of HAVSMC, induced calcification led to the formation of the sole CPA crystals. Our data seems to exclude a physicochemical role of Mg2+ in altering the CPA crystal growth, composition or structure. Furthermore, Mg2+ beneficial role in attenuating VC should be linked to an active cellular role

Altered serum levels of FGF-23 and magnesium are independent risk factors for an increased albumin-to-creatinine ratio in type 2 diabetics with chronic kidney disease

Aims: To investigate the role of FGF-23 and magnesium in relation to the albumin-to-creatinine ratio in type 2 diabetics with chronic kidney disease (CKD) stages 2-4.Methods: In a cross-sectional study we included all eligible type 2 diabetic patients with CKD stages 2-4, followed in our outpatient Diabetic Kidney clinic. We used descriptive statistics, the Student's t-test, ANOVA and the chi-square tests. Our population was divided according to the UACR (G1 30-300 mg/g and G2 >= 300 mg/g), and compared these groups regarding several biological and laboratorial parameters. We employed a multiple regression model to identify risk factors of increased UACR.Results: The patients in G2 displayed a lower eGFR (p = 0.0001) and, had lower levels of magnesium (p = 0.004) as well as higher levels of FGF-23 (p = 0.043) compared to patients in Gl.FGF-23 (beta = 0.562, P = 0.0001) and the magnesium (beta = - 8.916, p = 0.0001) were associated with increased UACR.Conclusions: A dysregulation of mineral metabolism, reflected by altered levels of magnesium and FGF-23, correlates with an increased UACR in type 2 diabetic patients with CKD stages 2-4. (C) 2016 Elsevier Inc. All rights reserved

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

Typical optical image and mapping (scale from blue to red with increasing concentration), and FTIR spectra of crystals generated in Pi 4 or PiCa samples without or in presence of a total concentration of 2 mM of Mg²⁺.

<p>Ia) Optical image, and corresponding Ib) typical FTIR spectra, Ic) Optical image and corresponding Id) typical FTIR spectra of sample PiCa. IIa) Optical image and corresponding IIb) typical FTIR spectra, IIc) Optical image and corresponding IId) typical FTIR spectra of sample PiCa Mg2.</p

Identification of the samples studied through µFTIR experiments.

<p>Samples nomenclature</p><p><b>Ct</b> = samples incubated in 1% FBS DMEM</p><p><b>Pi3</b> = samples incubated in 1% FBS DMEM with Pi set to 3 mM</p><p><b>Pi4</b> = samples incubated in 1% FBS DMEM with Pi set to 4 mM</p><p><b>Pi3 Mg2</b> = incubated in 1% FBS DMEM with Pi set to 3 mM and Mg²⁺ set to 2 mM</p><p><b>Pi4 Mg1.5</b> = incubated in 1% FBS DMEM with Pi set to 4 mM and Mg²⁺ set to 1.5 mM</p><p><b>Pi4 Mg2</b> = incubated in 1% FBS DMEM with Pi set to 4 mM and Mg²⁺ set to 2 mM</p><p><b>Pi4 Mg5</b> = incubated in 1% FBS DMEM with Pi set to 4 mM and Mg²⁺ set to 5 mM</p><p><b>PiCa</b> = samples incubated in 1% FBS DMEM with Pi set to 3 mM and Ca²⁺ set to 2.4 mM</p><p><b>PiCa Mg1.5</b> = samples incubated in 1% FBS DMEM with Pi set to 3 mM, Ca²⁺ set to 2.4 mM and Mg²⁺ set to 1.5 mM</p><p><b>PiCa Mg2</b> = samples incubated in 1% FBS DMEM with Pi set to 3 mM, Ca²⁺ set to 2.4 mM and Mg²⁺ set to 2 mM</p><p><b>PiCa Mg5</b> = samples incubated in 1% FBS DMEM with Pi set to 3 mM, Ca²⁺ set to 2.4 mM and Mg²⁺ set to 5 mM</p><p>It is of note that these experiments were conducted concomitantly with and without cells. The table is indicating the presence of apatite in experiments with cells. Data of passive Ca / Pi deposition on MirrIR slides are discussed in a proper section.</p><p>Identification of the samples studied through µFTIR experiments.</p

µFTIR maps obtained with calcium phosphate apatite features were collected for samples: PiCa, PiCa Mg2, PiCa Mg5, Pi4, Pi4 Mg2, Pi4 Mg5.

<p>The scale bar corresponds to 500 µm while the amplitude is between 0 and 10. Due to extended acquisition times, some maps were divided in 2 areas. The map size is 2000 µm x 4500 µm.</p