Effect of a magnesium-based phosphate binder on medial calcification in a rat model of uremia

Vascular, valvular and kidney calcification manifested in mouse models of adenine-induced chronic kidney disease

BACKGROUND

Ectopic calcification (EC) involves multiple organ systems in chronic kidney disease (CKD). Previous CKD-animal models primarily focused on a certain histological abnormality but did not show the correlation with calcified development among various tissues. This study compared calcified deposition in various tissues during CKD progression in mice.

METHODS

Male 8-week-old C57BL/6J mice were randomly allocated to the seven groups: a basic, adenine, high-phosphorus, or adenine and high-phosphorus diet for 12-16 weeks (Ctl16, A12, P16, or AP16, respectively); an adenine diet for 4-6 weeks; and a high-phosphorus or adenine and high-phosphorus diet for 10-12 weeks (A6 + P10, A4 + P12, or A4 + AP12, respectively).

RESULTS

Compared to the Ctl16 mice, the P16 mice only displayed a slight abnormality in serum calcium and phosphorus; the A12 mice had the most serious kidney impairment; the A4 + P12 and A6 + P10 mice had similar conditions of CKD, mineral abnormalities, and mild calcification in the kidney and aortic valves; the A4 + AP12 and AP16 groups had severe kidney impairment, mineral abnormalities and calcification in the kidneys, aortic valves and aortas. Furthermore, calcium-phosphate particles were deposited not only in the tubulointerstitial compartment but in the glomerular and tubular basement membrane. The elemental composition of EC in various tissues matched the calcification of human cardiovascular tissue as determined by energy dispersive spectroscopy.

CONCLUSIONS

The severity of CKD was unparalleled with the progression of mineral metabolism disorder and EC. Calcification was closely related in different tissues and observed in the glomerular and tubular basement membranes.

Correlative light and electron microscopic observation of calcium phosphate particles in a mouse kidney formed under a high-phosphate diet

Calcium phosphate forms particles under excessive urinary excretion of phosphate in the kidney. While the formation of calcium phosphate particles (CaPs) has been implicated in the damage to renal tubular cells and renal dysfunction, clarifying the ultrastructural information and the elemental composition of the small CaPs in the wide areas of kidney tissue has been technically difficult. This study introduces correlative and sequential light as well as electron microscopic CaP observation in the kidney tissue by combining fluorescent staining for CaPs and energy-dispersive X-ray spectroscopy (EDS) in scanning electron microscopy (SEM) on resin sections prepared using high-pressure freezing and freeze substitution. CaPs formed in mouse kidneys under long-term feeding of a high-phosphate diet were clearly visualized on resin sections by fluorescence-conjugated alendronate derivatives and toluidine blue metachromasia. These CaPs were verified by correlative observation with EDS. Furthermore, small CaPs formed in the kidney under short-term feeding were detected using fluorescent probes. The elemental composition of the particles, including calcium and magnesium, was identified following EDS analyses. These results suggest that the correlative microscopy approach is helpful for observing in situ distribution and elemental composition of CaPs in the kidney and contributing to studies regarding CaP formation-associated pathophysiology.

Attenuating effect of magnesium on pulmonary arterial calcification in rodent models of pulmonary hypertension

OBJECTIVE

Vascular calcification has been considered as a potential therapeutic target in pulmonary hypertension. Mg2+ has a protective role against calcification. This study aimed to investigate whether Mg2+ could alleviate pulmonary hypertension by reducing medial calcification of pulmonary arteries.

METHODS

Monocrotaline (MCT)-induced and chronic hypoxia-induced pulmonary hypertension rats were given an oral administration of 10% MgSO4 (10 ml/kg per day). Additionally, we administered Mg2+ in calcified pulmonary artery smooth muscle cells (PASMCs) after incubating with β-glycerophosphate (β-GP, 10 mmol/l).

RESULTS

In vivo, MCT-induced and chronic hypoxia-induced pulmonary hypertension indexes, including right ventricular systolic pressure, right ventricular mass index, and arterial wall thickness, as well as Alizarin Red S (ARS) staining-visualized calcium deposition, high calcium levels, and osteochondrogenic differentiation in pulmonary arteries, were mitigated by dietary Mg2+ intake. In vitro, β-GP-induced calcium-rich deposits stained by ARS, calcium content, as well as the detrimental effects of calcification to proliferation, migration, and resistance to apoptosis of PASMCs were alleviated by high Mg2+ but exacerbated by low Mg2+. Expression levels of mRNA and protein of β-GP-induced osteochondrogenic markers, RUNX Family Transcription Factor 2, and Msh Homeobox 2 were decreased by high Mg2+ but increased by low Mg2+; however, Mg2+ did not affect β-GP-induced expression of SRY-Box Transcription Factor 9. Moreover, mRNA expression and protein levels of β-GP-reduced calcification inhibitor, Matrix GLA protein was increased by high Mg2+ but decreased by low Mg2+.

CONCLUSION

Mg2+ supplement is a powerful strategy to treat pulmonary hypertension by mitigating pulmonary arterial calcification as the calcification triggered physiological and pathological changes to PASMCs.

Uremic mouse model to study vascular calcification and "inflamm-aging"

Calcification and chronic inflammation of the vascular wall is a high-risk factor for cardiovascular mortality, especially in patients with chronic uremia. For the reduction or prevention of rapid disease progression, no specific treatment options are currently available. This study aimed to evaluate an adenine-based uremic mouse model for studying medial vessel calcification and senescence-associated secretory phenotype (SASP) changes of aortic tissue to unravel molecular pathogenesis and provide a model for therapy testing. The dietary adenine administration induced a stable and similar degree of chronic uremia in DBA2/N mice with an increase of uremia blood markers such as blood urea nitrogen, calcium, creatinine, alkaline phosphatase, and parathyroid hormone. Also, renal fibrosis and crystal deposits were detected upon adenine feeding. The uremic condition is related to a moderate to severe medial vessel calcification and subsequent elastin disorganization. In addition, expression of osteogenic markers as Bmp-2 and its transcription factor Sox-9 as well as p21 as senescence marker were increased in uremic mice compared to controls. Pro-inflammatory uremic proteins such as serum amyloid A, interleukin (Il)-1β, and Il-6 increased. This novel model of chronic uremia provides a simple method for investigation of signaling pathways in vascular inflammation and calcification and therefore offers an experimental basis for the development of potential therapeutic intervention studies.

Magnesium—A More Important Role in CKD–MBD than We Thought

Chronic kidney disease (CKD) is associated with different complications, including chronic kidney disease–mineral and bone disorder (CKD–MBD), which represents a systemic disorder that involves the presence of different mineral or bone structure abnormalities (i.e., modification of bone turnover, strength, volume, etc.), including even vascular calcification development. Even if, over the years, different pathophysiological theories have been developed to explain the onset and progression of CKD–MBD, the influence and importance of serum magnesium level on the evolution of CKD have only recently been highlighted. So far, data are inconclusive and conflicting; therefore, further studies are necessary to validate these findings, which could be useful in developing a better, more adequate, and personalized management of CKD patients.

Combining phosphate binder therapy with vitamin K2 inhibits vascular calcification in an experimental animal model of kidney failure

BACKGROUND

Hyperphosphataemia is strongly associated with cardiovascular disease and mortality. Recently, phosphate binders (PBs), which are used to bind intestinal phosphate, have been shown to bind vitamin K, thereby potentially aggravating vitamin K deficiency. This vitamin K binding by PBs may offset the beneficial effects of phosphate reduction in reducing vascular calcification (VC). Here we assessed whether combining PBs with vitamin K2 supplementation inhibits VC.

METHODS

We performed 3/4 nephrectomy in rats, after which warfarin was given for 3 weeks to induce vitamin K deficiency. Next, animals were fed a high phosphate diet in the presence of low or high vitamin K2 and were randomized to either control or one of four different PBs for 8 weeks. The primary outcome was the amount of thoracic and abdominal aorta VC measured by high-resolution micro-computed tomography (µCT). Vitamin K status was measured by plasma MK7 levels and immunohistochemically analysed in vasculature using uncarboxylated matrix Gla protein (ucMGP) specific antibodies.

RESULTS

The combination of a high vitamin K2 diet and PB treatment significantly reduced VC as measured by µCT for both the thoracic (P = 0.026) and abdominal aorta (P = 0.023), compared with MK7 or PB treatment alone. UcMGP stain was significantly more present in the low vitamin K2-treated groups in both the thoracic (P < 0.01) and abdominal aorta (P < 0.01) as compared with high vitamin K2-treated groups. Moreover, a high vitamin K diet and PBs led to reduced vascular oxidative stress.

CONCLUSION

In an animal model of kidney failure with vitamin K deficiency, neither PB therapy nor vitamin K2 supplementation alone prevented VC. However, the combination of high vitamin K2 with PB treatment significantly attenuated VC.

Greater Dietary Inflammatory Potential Is Associated With Higher Likelihood of Abdominal Aortic Calcification

Aims: We aimed to assess the association between dietary inflammation index (DII) and abdominal aortic calcification (AAC) in US adults aged ≥40 years. Methods: Data were obtained from the 2013-2014 National Health and Nutrition Examination Survey (NHANES). Participants who were <40 years old and missing the data of DII and AAC were excluded. DII was calculated based on a 24-h dietary recall interview for each participant. AAC score was quantified by assessing lateral spine images and severe AAC was defined as AAC score >6. Weighted multivariable regression analysis and subgroup analysis were preformed to estimate the independent relationship between DII with AAC score and severe AAC. Results: A total of 2,897 participants were included with the mean DII of -0.17 ± 2.80 and the mean AAC score of 1.462 ± 3.290. The prevalence of severe AAC was 7.68% overall, and participants in higher DII quartile tended to have higher rates of severe AAC (Quartile 1: 5.03%, Quartile 2: 7.44%, Quartile 3: 8.38%, Quartile 4: 10.46%, p = 0.0016). A positive association between DII and AAC score was observed (β = 0.055, 95% CI: 0.010, 0.101, p = 0.01649), and higher DII was associated with an increased risk of severe AAC (OR = 1.067, 95% CI: 1.004, 1.134, p = 0.03746). Subgroup analysis indicated that this positive association between DII and AAC was similar in population with differences in gender, age, BMI, hypertension status, and diabetes status and could be appropriate for different population settings. Conclusion: Higher pro-inflammatory diet was associated with higher AAC score and increased risk of severe AAC. Anti-inflammatory dietary management maybe beneficial to reduce the risk of AAC.

The Cell Origin and Role of Osteoclastogenesis and Osteoblastogenesis in Vascular Calcification

Arterial calcification refers to the abnormal deposition of calcium salts in the arterial wall, which results in vessel lumen stenosis and vascular remodeling. Studies increasingly show that arterial calcification is a cell mediated, reversible and active regulated process similar to physiological bone mineralization. The osteoblasts and chondrocytes-like cells are present in large numbers in the calcified lesions, and express osteogenic transcription factor and bone matrix proteins that are known to initiate and promote arterial calcification. In addition, osteoclast-like cells have also been detected in calcified arterial walls wherein they possibly inhibit vascular calcification, similar to the catabolic process of bone mineral resorption. Therefore, tilting the balance between osteoblast-like and osteoclast-like cells to the latter maybe a promising therapeutic strategy against vascular calcification. In this review, we have summarized the current findings on the origin and functions of osteoblast-like and osteoclast-like cells in the development and progression of vascular progression, and explored novel therapeutic possibilities.

Phosphate, Microbiota and CKD

Phosphate is a key uremic toxin associated with adverse outcomes. As chronic kidney disease (CKD) progresses, the kidney capacity to excrete excess dietary phosphate decreases, triggering compensatory endocrine responses that drive CKD-mineral and bone disorder (CKD-MBD). Eventually, hyperphosphatemia develops, and low phosphate diet and phosphate binders are prescribed. Recent data have identified a potential role of the gut microbiota in mineral bone disorders. Thus, parathyroid hormone (PTH) only caused bone loss in mice whose microbiota was enriched in the Th17 cell-inducing taxa segmented filamentous bacteria. Furthermore, the microbiota was required for PTH to stimulate bone formation and increase bone mass, and this was dependent on bacterial production of the short-chain fatty acid butyrate. We review current knowledge on the relationship between phosphate, microbiota and CKD-MBD. Topics include microbial bioactive compounds of special interest in CKD, the impact of dietary phosphate and phosphate binders on the gut microbiota, the modulation of CKD-MBD by the microbiota and the potential therapeutic use of microbiota to treat CKD-MBD through the clinical translation of concepts from other fields of science such as the optimization of phosphorus utilization and the use of phosphate-accumulating organisms.

Uremic Vascular Calcification: The Pathogenic Roles and Gastrointestinal Decontamination of Uremic Toxins

Uremic vascular calcification (VC) commonly occurs during advanced chronic kidney disease (CKD) and significantly increases cardiovascular morbidity and mortality. Uremic toxins are integral within VC pathogenesis, as they exhibit adverse vascular influences ranging from atherosclerosis, vascular inflammation, to VC. Experimental removal of these toxins, including small molecular (phosphate, trimethylamine-N-oxide), large molecular (fibroblast growth factor-23, cytokines), and protein-bound ones (indoxyl sulfate, p-cresyl sulfate), ameliorates VC. As most uremic toxins share a gut origin, interventions through gastrointestinal tract are expected to demonstrate particular efficacy. The “gastrointestinal decontamination” through the removal of toxin in situ or impediment of toxin absorption within the gastrointestinal tract is a practical and potential strategy to reduce uremic toxins. First and foremost, the modulation of gut microbiota through optimizing dietary composition, the use of prebiotics or probiotics, can be implemented. Other promising strategies such as reducing calcium load, minimizing intestinal phosphate absorption through the optimization of phosphate binders and the inhibition of gut luminal phosphate transporters, the administration of magnesium, and the use of oral toxin adsorbent for protein-bound uremic toxins may potentially counteract uremic VC. Novel agents such as tenapanor have been actively tested in clinical trials for their potential vascular benefits. Further advanced studies are still warranted to validate the beneficial effects of gastrointestinal decontamination in the retardation and treatment of uremic VC.

Targeting Uremic Toxins to Prevent Peripheral Vascular Complications in Chronic Kidney Disease

Chronic kidney disease (CKD) exhibits progressive kidney dysfunction and leads to disturbed homeostasis, including accumulation of uremic toxins, activated renin-angiotensin system, and increased oxidative stress and proinflammatory cytokines. Patients with CKD are prone to developing the peripheral vascular disease (PVD), leading to poorer outcomes than those without CKD. Cumulative evidence has showed that the synergy of uremic milieu and PVD could exaggerate vascular complications such as limb ischemia, amputation, stenosis, or thrombosis of a dialysis vascular access, and increase mortality risk. The role of uremic toxins in the pathogenesis of vascular dysfunction in CKD has been investigated. Moreover, growing evidence has shown the promising role of uremic toxins as a therapeutic target for PVD in CKD. This review focused on uremic toxins in the pathophysiology, in vitro and animal models, and current novel clinical approaches in reducing the uremic toxin to prevent peripheral vascular complications in CKD patients.

Magnesium but not nicotinamide prevents vascular calcification in experimental uraemia

BACKGROUND

Optimal phosphate control is an unmet need in chronic kidney disease (CKD). High serum phosphate increases calcification burden and is associated with mortality and cardiovascular disease in CKD. Nicotinamide (NA) alone or in combination with calcium-free phosphate binders might be a strategy to reduce phosphate levels and calcification and thus impact cardiovascular disease in CKD.

METHODS

We studied the effect of NA alone and in combination with magnesium carbonate (MgCO3) as a potential novel treatment strategy. CKD was induced in dilute brown non-agouti/2 mice by subtotal nephrectomy followed by a high-phosphate diet (HP) and 7 weeks of treatment with NA, MgCO3 or their combination. Control mice underwent subtotal nephrectomy and received an HP or underwent sham surgery and received standard chow plus NA.

RESULTS

CKD mice showed increased serum fibroblast growth factor 23 and calcium-phosphate product that was normalized by all treatment regimes. NA alone increased soft tissue and vascular calcification, whereas any treatment with MgCO3 significantly reduced calcification severity in CKD. While MgCO3 supplementation alone resulted in decreased calcification severity, it resulted in increased intestinal expression of the phosphate transporters type II sodium-dependent phosphate transporter 1 (Pit-1). Combined therapy of MgCO3 and NA reduced tissue calcification and normalized expression levels of intestinal phosphate transporter proteins.

CONCLUSIONS

In conclusion, the data indicate that NA increases while MgCO3 reduces ectopic calcification severity. Augmented expression of intestinal phosphate transporters by MgCO3 treatment was abolished by the addition of NA. However, the clinical relevance of the latter remains to be explored. Importantly, the data suggest no benefit of NA regarding treatment of calcification in addition to MgCO3.

Pharmacological TNAP inhibition efficiently inhibits arterial media calcification in a warfarin rat model but deserves careful consideration of potential physiological bone formation/mineralization impairment

Arterial media calcification is frequently seen in elderly and patients with chronic kidney disease (CKD), diabetes and osteoporosis. Pyrophosphate is a well-known calcification inhibitor that binds to nascent hydroxyapatite crystals and prevents further incorporation of inorganic phosphate into these crystals. However, the enzyme tissue-nonspecific alkaline phosphatase (TNAP), which is expressed in calcified arteries, degrades extracellular pyrophosphate into phosphate ions, by which pyrophosphate loses its ability to block vascular calcification. Here, we aimed to evaluate whether pharmacological TNAP inhibition is able to prevent the development of arterial calcification in a rat model of warfarin-induced vascular calcification. To investigate the effect of the pharmacological TNAP inhibitor SBI-425 on vascular calcification and bone metabolism, a 0.30% warfarin rat model was used. Warfarin exposure resulted in distinct calcification in the aorta and peripheral arteries. Daily administration of the TNAP inhibitor SBI-425 (10 mg/kg/day) for 7 weeks significantly reduced vascular calcification as indicated by a significant decrease in calcium content in the aorta (vehicle 3.84 ± 0.64 mg calcium/g wet tissue vs TNAP inhibitor 0.70 ± 0.23 mg calcium/g wet tissue) and peripheral arteries and a distinct reduction in area % calcification on Von Kossa stained aortic sections as compared to vehicle. Administration of SBI-425 resulted in decreased bone formation rate and mineral apposition rate, and increased osteoid maturation time and this without significant changes in osteoclast- and eroded perimeter. Administration of TNAP inhibitor SBI-425 significantly reduced the calcification in the aorta and peripheral arteries of a rat model of warfarin-induced vascular calcification. However, suppression of TNAP activity should be limited in order to maintain adequate physiological bone mineralization.

Cardiovascular Calcification in Chronic Kidney Disease-Therapeutic Opportunities

Patients with chronic kidney disease (CKD) are highly susceptible to cardiovascular (CV) complications, thus suffering from clinical manifestations such as heart failure and stroke. CV calcification greatly contributes to the increased CV risk in CKD patients. However, no clinically viable therapies towards treatment and prevention of CV calcification or early biomarkers have been approved to date, which is largely attributed to the asymptomatic progression of calcification and the dearth of high-resolution imaging techniques to detect early calcification prior to the 'point of no return'. Clearly, new intervention and management strategies are essential to reduce CV risk factors in CKD patients. In experimental rodent models, novel promising therapeutic interventions demonstrate decreased CKD-induced calcification and prevent CV complications. Potential diagnostic markers such as the serum T50 assay, which demonstrates an association of serum calcification propensity with all-cause mortality and CV death in CKD patients, have been developed. This review provides an overview of the latest observations and evaluates the potential of these new interventions in relation to CV calcification in CKD patients. To this end, potential therapeutics have been analyzed, and their properties compared via experimental rodent models, human clinical trials, and meta-analyses.

Inhibition of vascular calcification by inositol phosphates derivatized with ethylene glycol oligomers

Myo-inositol hexakisphosphate (IP6) is a natural product known to inhibit vascular calcification (VC), but with limited potency and low plasma exposure following bolus administration. Here we report the design of a series of inositol phosphate analogs as crystallization inhibitors, among which 4,6-di-O-(methoxy-diethyleneglycol)-myo-inositol-1,2,3,5-tetrakis(phosphate), (OEG2)2-IP4, displays increased in vitro activity, as well as more favorable pharmacokinetic and safety profiles than IP6 after subcutaneous injection. (OEG2)2-IP4 potently stabilizes calciprotein particle (CPP) growth, consistently demonstrates low micromolar activity in different in vitro models of VC (i.e., human serum, primary cell cultures, and tissue explants), and largely abolishes the development of VC in rodent models, while not causing toxicity related to serum calcium chelation. The data suggest a mechanism of action independent of the etiology of VC, whereby (OEG2)2-IP4 disrupts the nucleation and growth of pathological calcification.

Mechanisms of Vascular Calcification in Kidney Disease

The increase in prevalence and severity of vascular calcification in chronic kidney disease is a result of complex interactions between changes in the vascular bed, mineral metabolites, and other uremic factors. Vascular calcification can occur in the intima and the media of arterial wall. Under permissive conditions, vascular smooth muscle cells (VSMCs) can transform to osteoblast-like phenotype. The membrane-bound vesicles released from transformed VSMCs and the apoptotic bodies derived from dying VSMCs serve as nucleating structures for calcium crystal formation. Alterations in the quality and the quantity of endogenous calcification inhibitors also give rise to an environment that potentiates calcification.

Hyperphosphatemia is required for initiation but not propagation of kidney failure-induced calcific aortic valve disease

High serum levels of phosphate are associated with uremia-induced calcific aortic valve disease (CAVD). However, it is not clear whether hyperphosphatemia is required in all phases of the process. Our aim was to determine the effects of phosphate and phosphate depletion at different phases of valve disease. The experimental design consisted of administering a uremia-inducing diet, with or without phosphate enrichment, to rats for 7 wk. Forty-two rats were fed with a phosphate-enriched uremic regimen that caused renal insufficiency and hyperphosphatemia. Another 42 rats were fed with a phosphate-depleted uremic regimen, which induces similar severity of renal insufficiency, but without its related mineral disorder. Aortic valves were evaluated at several points during the time of diet administration. In the second part, additional 54 rats were fed a phosphate-enriched diet for various time periods and were then switched to a phosphate-depleted diet to complete 7 wk of uremic diet. Osteoblast-like phenotype, inflammation, and eventually valve calcification were observed only in rats that were fed with a phosphate-enriched regimen. Significant valve calcification was observed only in rats that were fed a phosphate-enriched diet for at least 4 wk. Valve calcification was observed only when the switch to a phosphate-depleted regimen occurred after osteoblast markers and activation of Akt and ERK intracellular signaling pathways had already been found in the valve. Phosphate is essential for the initiation of the calcification process. However, when osteoblast markers are already expressed in valve tissue, phosphate depletion will not halt the disease.NEW & NOTEWORTHY High serum levels of phosphate are associated with uremia-induced calcific aortic valve disease. However, it is not clear whether hyperphosphatemia is required in all phases of the process. Our aim was to determine the effects of phosphate and phosphate depletion at different phases of valve disease. Our findings indicated that phosphate is essential for the initiation of the process that includes macrophage accumulation and osteoblast phenotype. Furthermore, hyperphosphatemia is dispensable beyond a certain phase of the process, a point of "no return" after which phosphate depletion does not prevent calcification. This point is relatively early in the course of calcification, when no calcification is apparent, but the inflammation, osteoblast markers, and activation of ERK and Akt pathways have already been identified. Our findings emphasize the complexity of the calcification process and suggest that different mediators might be required during different phases and that the role of phosphate precedes the actual calcification.

Magnesium Citrate Protects Against Vascular Calcification in an Adenine-induced Chronic Renal Failure Rat Model

BACKGROUND

Hypomagnesemia was identified as a strong risk factor for cardiovascular disease in patients with chronic renal failure (CRF). However, the effects of magnesium (Mg) on vascular calcification (VC) have not been fully elucidated. Thus, we aim to determine the effects of Mg citrate (MgCit) on VC in CRF rats.

METHODS

Rats were divided into 5 groups: group 1 (normal diet), group 2 (normal diet with MgCit), group 3 (the VC model of CRF induced by 0.75% adenine and 0.9% phosphorus diet from day 1 to day 28), group 4 (group 3 treated with low-dose MgCit from day 1 to day 42), and group 5 (same as group 3 except the high-dose MgCit). All rats were killed at day 43 with collection of blood and aortas. Then, serum biochemical parameters, VC-related staining, calcium and P contents, alkaline phosphatase contents and activity, expression of alpha smooth muscle actin, and runt-related transcription factor 2 (RUNX2) in aortas were assessed.

RESULTS

Group 3 had extensive VC. The VC degree decreased in groups 4 and 5 in a dose-depended manner with reduced calcium content, P levels, alkaline phosphatase content and activity, and protein levels of RUNX2 and increased protein levels of alpha smooth muscle actin in aortas.

CONCLUSIONS

MgCit exerted a protective role in VC in adenine-induced CRF rats; thus, it may be a potential drug for the prevention of VC in patients with CRF.

Strategies for Phosphate Control in Patients With CKD

Hyperphosphatemia is a common complication in patients with chronic kidney disease (CKD), particularly in those requiring renal replacement therapy. The importance of controlling serum phosphate has long been recognized based on observational epidemiological studies that linked increased phosphate levels to adverse outcomes and higher mortality risk. Experimental data further supported the role of phosphate in the development of bone and cardiovascular diseases. Recent advances in our understanding of the mechanisms involved in phosphate homeostasis have made it clear that the serum phosphate concentration depends on a complex interplay among the kidneys, intestinal tract, and bone, and is tightly regulated by a complex endocrine system. Moreover, the source of dietary phosphate and the use of phosphate-based additives in industrialized foods are additional factors that are of particular importance in CKD. Not surprisingly, the management of hyperphosphatemia is difficult, and, despite a multifaceted approach, it remains unsuccessful in many patients. An additional issue is the fact that the supposedly beneficial effect of phosphate lowering on hard clinical outcomes in interventional trials is a matter of ongoing debate. In this review, we discuss currently available treatment approaches for controlling hyperphosphatemia, including dietary phosphate restriction, reduction of intestinal phosphate absorption, phosphate removal by dialysis, and management of renal osteodystrophy, with particular focus on practical challenges and limitations, and on potential benefits and harms.

Magnesium: A Magic Bullet for Cardiovascular Disease in Chronic Kidney Disease?

Magnesium is essential for many physiological functions in the human body. Its homeostasis involves dietary intake, absorption, uptake and release from bone, swifts between the intra- and extracellular compartment, and renal excretion. Renal excretion is mainly responsible for regulation of magnesium balance. In chronic kidney disease (CKD), for a long time the general policy has been limiting magnesium intake. However, this may not be appropriate for many patients. The reference ranges for magnesium are not necessarily optimal concentrations, and risks for insufficient magnesium intake exist in patients with CKD. In recent years, many observational studies have shown that higher (in the high range of “normal” or slightly above) magnesium concentrations are associated with better survival in CKD cohorts. This review gives an overview of epidemiological associations between magnesium and overall and cardiovascular survival in patients with CKD. In addition, potential mechanisms explaining the protective role of magnesium in clinical cardiovascular outcomes are described by reviewing evidence from in vitro studies, animal studies, and human intervention studies with non-clinical endpoints. This includes the role of magnesium in cardiac arrhythmia, heart failure, arterial calcification, and endothelial dysfunction. Possible future implications will be addressed, which will need prospective clinical trials with relevant clinical endpoints before these can be adopted in clinical practice.

Effect of cross-linked chitosan iron (III) on vascular calcification in uremic rats

Cross-linked chitosan iron (III) is a chitin-derived polymer with a chelating effect on phosphorus, but it is untested in vascular calcification. We evaluated this compound's ability to reduce hyperphosphatemia and its effect on vascular calcification in uremic rats using an adenine-based, phosphorus-rich diet for seven weeks. We used a control group to characterize the uremia. Uremic rats were divided according the treatment into chronic kidney disease, CKD-Ch-Fe(III)CL (CKD-Ch), CKD-calcium carbonate, or CKD-sevelamer groups. We measured creatinine, phosphorus, calcium, alkaline phosphatase, phosphorus excretion fraction, parathyroid hormone, and fibroblast growth factor 23. Vascular calcification was assessed using the aortic calcium content, and a semi-quantitative analysis was performed using Von Kossa and hematoxylin-eosin staining. At week seven, rats in the chronic kidney disease group had higher creatinine, phosphorus, phosphorus excretion fraction, calcium, alkaline phosphatase, fibroblast growth factor 23, and aortic calcium content than those in the Control group. Treatments with cross-linked chitosan iron (III) and calcium carbonate prevented phosphorus increase (20%-30% reduction). The aortic calcium content was lowered by 88% and 85% in the CKD-Ch and CKD-sevelamer groups, respectively. The prevalence of vascular changes was higher in the chronic kidney disease and CKD-calcium carbonate (62.5%) groups than in the CKD-Ch group (37.5%). In conclusion, cross-linked chitosan iron (III) had a phosphorus chelating effect similar to calcium carbonate already available for clinical use, and prevented calcium accumulation in the aorta. Impact statement Vascular calcification (VC) is a common complication due to CKD-related bone and mineral disorder (BMD) and is characterized by deposition of calcium in vessels. Effective therapies are not yet available but new phosphorus chelators can prevent complications from CV. We tested the effect of chitosan, a new phosphorus chelator, on the VC of uremic animals. It has recently been proposed that chitosan treatment may be effective in the treatment of hyperphosphataemia. However, its action on vascular calcification has not been investigated yet. In this study, we demonstrated that chitosan reduced the calcium content in the aorta, suggesting that this may be a therapeutic approach in the treatment of hyperphosphatemia by preventing CV.

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.

Association between Dietary Intake and Coronary Artery Calcification in Non-Dialysis Chronic Kidney Disease: The PROGREDIR Study

Coronary artery calcification (CAC) is a widespread condition in chronic kidney disease (CKD). Diet may play an important role in CAC, but this role is not clear. This study evaluated the association between macro-and micronutrient intakes and CAC in non-dialysis CKD patients. We analyzed the baseline data from 454 participants of the PROGREDIR study. Dietary intake was evaluated by a food frequency questionnaire. CAC was measured by computed tomography. After exclusion of participants with a coronary stent, 373 people remained for the analyses. The highest tertile of CAC was directly associated with the intake of phosphorus, calcium and magnesium. There was a higher intake of pantothenic acid and potassium in the second tertile. After adjustments for confounding variables, the intake of pantothenic acid, phosphorus, calcium and potassium remained associated with CAC in the generalized linear mixed models. In order to handle the collinearity between these nutrients, we used the LASSO (least absolute shrinkage and selection operator) regression to evaluate the nutrients associated with CAC variability. In this approach, the nutrients that most explained the variance of CAC were phosphorus, calcium and potassium. Prospective studies are needed to confirm these findings and assess the role of interventions regarding these micronutrients on CAC prevention and progression.

A rat model of SHPT with bone abnormalities in CKD induced by adenine and a high phosphorus diet

The study of parathyroid hyperplasia with bone disease as a critical manifestation of chronic kidney disease-mineral and bone disorders (CKD-MBDs) is challenging due to the lack of a suitable research model. Here, we established a rat model with secondary hyperparathyroidism (SHPT) and bone disease induced by adenine and a high phosphorous diet and analyzed the skeletal characteristics. We performed blood analysis, emission computed tomography (ECT), dual energy X-ray absorptiometry (DEXA), micro-computed tomography (micro-CT), bone histomorphometry, and bone mechanical tests. The CKD rats with SHPT induced by adenine and a high phosphorus diet showed severe abnormalities in calcium and phosphorus metabolism and exhibited parathyroid hyperplasia. The bone mineral density (BMD) of femurs and lumbar vertebrae was significantly lower in the CKD rats than in the control (CTL) rats. The cortical and trabecular bone parameters of femurs showed significant bone loss. In addition, we found decreases in ultimate force, work to failure, stiffness, and elastic modulus in the CKD rats. In conclusion, our findings demonstrated that the CKD rats with SHPT induced by adenine and a high phosphorus diet may serve as a useful model for skeletal analysis in CKD with SHPT.

Magnesium Replacement to Protect Cardiovascular and Kidney Damage? Lack of Prospective Clinical Trials

Patients with advanced chronic kidney disease exhibit an increase in cardiovascular mortality. Recent works have shown that low levels of magnesium are associated with increased cardiovascular and all-cause mortality in hemodialysis patients. Epidemiological studies suggest an influence of low levels of magnesium on the occurrence of cardiovascular disease, which is also observed in the normal population. Magnesium is involved in critical cellular events such as apoptosis and oxidative stress. It also participates in a number of enzymatic reactions. In animal models of uremia, dietary supplementation of magnesium reduces vascular calcifications and mortality; in vitro, an increase of magnesium concentration decreases osteogenic transdifferentiation of vascular smooth muscle cells. Therefore, it may be appropriate to evaluate whether magnesium replacement should be administered in an attempt to reduce vascular damage and mortality in the uremic population In the present manuscript, we will review the magnesium homeostasis, the involvement of magnesium in enzymatic reactions, apoptosis and oxidative stress and the clinical association between magnesium and cardiovascular disease in the general population and in the context of chronic kidney disease. We will also analyze the role of magnesium on kidney function. Finally, the experimental evidence of the beneficial effects of magnesium replacement in chronic kidney disease will be thoroughly described.

Magnesium prevents vascular calcification in vitro by inhibition of hydroxyapatite crystal formation

Magnesium has been shown to effectively prevent vascular calcification associated with chronic kidney disease. Magnesium has been hypothesized to prevent the upregulation of osteoblastic genes that potentially drives calcification. However, extracellular effects of magnesium on hydroxyapatite formation are largely neglected. This study investigated the effects of magnesium on intracellular changes associated with transdifferentiation and extracellular crystal formation. Bovine vascular smooth muscle cells were calcified using β-glycerophosphate. Transcriptional analysis, alkaline phosphatase activity and detection of apoptosis were used to identify transdifferentiation. Using X-ray diffraction and energy dispersive spectroscopy extracellular crystal composition was investigated. Magnesium prevented calcification in vascular smooth muscle cells. β-glycerophosphate increased expression of osteopontin but no other genes related to calcification. Alkaline phosphatase activity was stable and apoptosis was only detected after calcification independent of magnesium. Blocking of the magnesium channel TRPM7 using 2-APB did not abrogate the protective effects of magnesium. Magnesium prevented the formation of hydroxyapatite, which formed extensively during β-glycerophosphate treatment. Magnesium reduced calcium and phosphate fractions of 68% and 41% extracellular crystals, respectively, without affecting the fraction of magnesium. This study demonstrates that magnesium inhibits hydroxyapatite formation in the extracellular space, thereby preventing calcification of vascular smooth muscle cells.

Pharmacotherapy in chronic kidney disease hyperphosphatemia – effects on vascular calcification and bone health

Hyperphosphatemia (HP) in patients with chronic kidney disease (CKD) leads to complications such as renal osteodistrophy, cardiovascular calcification and hemodynamic abnormalities, all of them having a serious impact on the survival rate and quality of life. Also, HP is a key pathogenic factor in the development of secondary hyperparathyroidism (SHPT) in CKD. Having in regard the significance of controlling serum phosphorus levels (Pi), in this paper, the needs and obstacles to successful pharmacological management of HP in CKD are presented, with an overview of major classes of phosphate binders (PBs) and other drugs affecting Pi level, such as active vitamin D sterols and calcimimetics (CMs). In addition, their effects on progression of cardiovascular calcification and bone health are elaborated. In this regard, a PubMed search was carried out to capture all abstracts and articles relevant to the topic of CKD, HP and mineral metabolism, bone disorders and vascular/valvular calcification (VC), published from January 2007 to August 2017. The search was limited to English language, with the search terms including drug name AND hyperphosphatemia or cardiovascular calcification or bone disorder. Comparative studies, clinical studies/trials and meta-analyses related to different classes/representatives of PBs, vitamin D analogues and CMs were reviewed and research data related to their efficacy and safety compared. Keywords: chronic kidney disease, hyperphosphatemia, phosphate binders, active vitamin D sterols, calcimimetics, bone disorders, cardiovascular calcification

Dose-response relationship between lower serum magnesium level and higher prevalence of knee chondrocalcinosis

Background

The aim was to assess serum magnesium levels in relation to prevalence of knee chondrocalcinosis in two population-based Chinese studies.

Methods

Data included in this analysis consisted of two population-based cross-sectional studies, i.e., the Xiangya Hospital Health Management Center Study and the Xiangya Osteoarthritis (XO) Study I. A bilateral knee anteroposterior radiograph was obtained from each subject. Radiographic knee chondrocalcinosis was present if there was definite linear cartilage calcification. Serum magnesium concentration was measured using the chemiluminescence method. We examined the relation of serum magnesium levels to prevalence of knee chondrocalcinosis using generalized estimating equations.

Results

The prevalence of knee chondrocalcinosis was 1.4% in the Xiangya Hospital Health Management Center Study (n = 12,631). Compared with the lowest tertile, the age, sex and body mass index (BMI)-adjusted odds ratios (ORs) of chondrocalcinosis were 0.59 (95% CI 0.40–0.87) and 0.49 (95% CI 0.33–0.72) in the second and the third tertiles of serum magnesium, respectively (P for trend <0.001). The prevalence of knee chondrocalcinosis in the XO Study I (n = 1316) was 4.1%. The age, sex and BMI-adjusted ORs of chondrocalcinosis were 0.67 (95% CI 0.34–1.30) in the second and 0.45 (95% CI 0.21–0.94) in the third tertile of serum magnesium when compared with the lowest tertile (P for trend = 0.030). Similar results were observed in men and women in both studies. Adjusting for additional potential confounders did not change the results materially.

Conclusions

Subjects with lower levels of serum magnesium, even within the normal range, had higher prevalence of knee chondrocalcinosis in a dose-response relationship manner, suggesting that magnesium may have a preventive or therapeutic potential for knee chondrocalcinosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-017-1450-6) contains supplementary material, which is available to authorized users.

Magnesium Counteracts Vascular Calcification: Passive Interference or Active Modulation?

Over the last decade, an increasing number of studies report a close relationship between serum magnesium concentration and cardiovascular disease risk in the general population. In end-stage renal disease, an association was found between serum magnesium and survival. Hypomagnesemia was identified as a strong predictor for cardiovascular disease in these patients. A substantial body of in vitro and in vivo studies has identified a protective role for magnesium in vascular calcification. However, the precise mechanisms and its contribution to cardiovascular protection remain unclear. There are currently 2 leading hypotheses: first, magnesium may bind phosphate and delay calcium phosphate crystal growth in the circulation, thereby passively interfering with calcium phosphate deposition in the vessel wall. Second, magnesium may regulate vascular smooth muscle cell transdifferentiation toward an osteogenic phenotype by active cellular modulation of factors associated with calcification. Here, the data supporting these major hypotheses are reviewed. The literature supports both a passive inorganic phosphate-buffering role reducing hydroxyapatite formation and an active cell-mediated role, directly targeting vascular smooth muscle transdifferentiation. However, current evidence relies on basic experimental designs that are often insufficient to delineate the underlying mechanisms. The field requires more advanced experimental design, including determination of intracellular magnesium concentrations and the identification of the molecular players that regulate magnesium concentrations in vascular smooth muscle cells.

Effects of Magnesium on the Phosphate Toxicity in Chronic Kidney Disease: Time for Intervention Studies

Magnesium, an essential mineral for human health, plays a pivotal role in the cardiovascular system. Epidemiological studies in the general population have found an association between lower dietary magnesium intake and an elevated risk of cardiovascular events. In addition, magnesium supplementation was shown to improve blood pressure control, insulin sensitivity, and endothelial function. The relationship between magnesium and cardiovascular prognosis among patients with chronic kidney disease (CKD) has been increasingly investigated as it is becoming evident that magnesium can inhibit vascular calcification, a prominent risk of cardiovascular events, which commonly occurs in CKD patients. Cohort studies in patients receiving dialysis have shown a lower serum magnesium level as a significant risk for cardiovascular mortality. Interestingly, the cardiovascular mortality risk associated with hyperphosphatemia is alleviated among those with high serum magnesium levels, consistent with in vitro evidence that magnesium inhibits high-phosphate induced calcification of vascular smooth muscle cells. Furthermore, a harmful effect of high phosphate on the progression of CKD is also attenuated among those with high serum magnesium levels. The potential usefulness of magnesium as a remedy for phosphate toxicity should be further explored by future intervention studies.

Electrolyte and Acid-Base Disorders in Chronic Kidney Disease and End-Stage Kidney Failure

The kidneys play a pivotal role in the regulation of electrolyte and acid-base balance. With progressive loss of kidney function, derangements in electrolytes and acid-base inevitably occur and contribute to poor patient outcomes. As chronic kidney disease (CKD) has become a worldwide epidemic, medical providers are increasingly confronted with such problems. Adequate diagnosis and treatment will minimize complications and can potentially be lifesaving. In this review, we discuss the current understanding of the disease process, clinical presentation, diagnosis and treatment strategies, integrating up-to-date knowledge in the field. Although electrolyte and acid-base derangements are significant causes of morbidity and mortality in CKD and end-stage renal disease patients, they can be effectively managed through a timely institution of combined preventive measures and pharmacological therapy. Exciting advances and several upcoming outcome trials will provide further information to guide treatment and improve patient outcomes.

The role of phosphate in kidney disease

The importance of phosphate homeostasis in chronic kidney disease (CKD) has been recognized for decades, but novel insights - which are frequently relevant to everyday clinical practice - continue to emerge. Epidemiological data consistently indicate an association between hyperphosphataemia and poor clinical outcomes. Moreover, compelling evidence suggests direct toxicity of increased phosphate concentrations. Importantly, serum phosphate concentration has a circadian rhythm that must be considered when interpreting patient phosphate levels. Detailed understanding of dietary sources of phosphate, including food additives, can enable phosphate restriction without risking protein malnutrition. Dietary counselling provides an often underestimated opportunity to target the increasing exposure to dietary phosphate of both the general population and patients with CKD. In patients with secondary hyperparathyroidism, bone can be an important source of serum phosphate, and adequate appreciation of this fact should impact treatment. Dietary and pharmotherapeutic interventions are efficacious strategies to lower phosphate intake and serum concentration. However, strong evidence that targeting serum phosphate improves patient outcomes is currently lacking. Future studies are, therefore, required to investigate the effects of modern dietary and pharmacological interventions on clinically meaningful end points.

Cinacalcet ameliorates aortic calcification in uremic rats via suppression of endothelial-to-mesenchymal transition

AIM

Experimental studies found that cinacalcet (CINA) markedly attenuated vascular calcification in uremic rats, but its underlying mechanisms are still largely unknown. Recent evidence have demonstrated that endothelial cells (ECs) participate in ectopic calcification in part by mediating endothelial-to-mesenchymal transition (EndMT). In this study, we investigated whether CINA ameliorated aortic calcification in uremic rats via suppression of EndMT.

METHODS

Uremia was induced in rats by feeding rats a 0.75% adenine diet for 4 weeks. After adenine withdrawal, the rats were maintained on a 1.03% phosphorus diet for next 8 weeks. At initiation of the adenine diet, rats were orally administered CINA (10mg/kg one day) for 12 weeks. The aortic expression of EndMT- and chondrocyte- markers was examined. The effect of elevated PTH on EndMT was also studied in aortic ECs.

RESULTS

In uremic rats, CINA treatment significantly decreased the serum PTH concentrations, but did not affect the elevated levels of serum calcium (Ca), phosphorus (P) and Ca×P product. Besides, CINA significantly attenuated aortic calcification, and inhibited the expression of chondrocyte markers (SOX9 and COL2A1) and chondrocyte proteoglycan in uremic aortas. Moreover, CINA treatment largely abolished the up-regulation of mesenchymal markers (FSP1 and α-SMA) and down-regulation of the endothelial marker (CD31), which accompanied aortic calcification in uremic aorta samples. In vitro, PTH increased the expression of EndMT-markers in a concentration- and time-dependent manner.

CONCLUSION

These findings suggest that strategies aiming at reducing serum PTH might prevent uremic aortic calcification by abrogating EndMT.

Can Intestinal Phosphate Binding or Inhibition of Hydroxyapatite Growth in the Vascular Wall Halt the Progression of Established Aortic Calcification in Chronic Kidney Disease?

Vascular calcification significantly contributes to mortality in chronic kidney disease (CKD) patients. Sevelamer and pyrophosphate (PPi) have proven to be effective in preventing vascular calcification, the former by controlling intestinal phosphate absorption, the latter by directly interfering with the hydroxyapatite crystal formation. Since most patients present with established vascular calcification, it is important to evaluate whether these compounds may also halt or reverse the progression of preexisting vascular calcification. CKD and vascular calcification were induced in male Wistar rats by a 0.75 % adenine low protein diet for 4 weeks. Treatment with PPi (30 or 120 µmol/kg/day), sevelamer carbonate (1500 mg/kg/day) or vehicle was started at the time point at which vascular calcification was present and continued for 3 weeks. Hyperphosphatemia and vascular calcification developed prior to treatment. A significant progression of aortic calcification in vehicle-treated rats with CKD was observed over the final 3-week period. Sevelamer treatment significantly reduced further progression of aortic calcification as compared to the vehicle control. No such an effect was seen for either PPi dose. Sevelamer but not PPi treatment resulted in an increase in both osteoblast and osteoid perimeter. Our study shows that sevelamer was able to reduce the progression of moderate to severe preexisting aortic calcification in a CKD rat model. Higher doses of PPi may be required to induce a similar reduction of severe established arterial calcification in this CKD model.

Calcium Acetate/Magnesium Carbonate and Cardiovascular Risk Factors in Chronic Hemodialysis Patients

BACKGROUND/AIM

Calcium acetate/magnesium carbonate (CaMg) is a recent phosphate binder that has been shown to have protective cardiovascular (CV) effects in animal models. The aim of this study was to evaluate the relationship between CaMg therapy and CV risk markers like pulse pressure (PP), left ventricular mass index (LVMI) and valvular calcifications compared to sevelamer or no phosphate binder (NPB) therapy in chronic hemodialysis (HD) patients.

METHODS

We performed a 48-month prospective study in 138 HD patients under hemodiafiltration with a dialysate Mg concentration of 0.5 mmol/l. Patients underwent treatment with CaMg or sevelamer for at least 36 months or NPB therapy. Demographic, clinical, biochemical and echocardiographic parameters were evaluated at baseline and after a 48-month period.

RESULTS

At the end of the study, patients who had taken CaMg showed a significant reduction in PP (p < 0.001), LVMI (p = 0.003), aortic (p = 0.004) and mitral valve calcifications (p = 0.03) compared with NPB patients. Patients under CaMg showed a significant reduction of PP (p < 0.001), LVMI (p = 0.01) and aortic valve calcifications (p = 0.02) compared to sevelamer patients. In a multivariable analysis, CaMg therapy was negatively associated with progression of LVMI (p = 0.02) and aortic valve calcifications (p = 0.01). Patients under CaMg showed higher serum Mg levels (0.93 ± 0.14 mmol/l) compared to patients under sevelamer (0.87 ± 0.13) or NPB patients (0.82 ± 0.12; p < 0.001).

CONCLUSIONS

In prevalent HD patients, the use of CaMg over 48 months was associated with a reduction of PP and LVMI and with a stabilization of aortic valve calcifications. These protective and promising results of this new phosphate binder need to be confirmed in randomized controlled studies.

Effect of parathyroid hormone on serum magnesium levels: the neglected relationship in hemodialysis patients with secondary hyperparathyroidism

Chronic kidney disease-mineral and bone disorder (CKD-MBD) is an important complication in patients with end-stage renal disease. Since recent studies have shown that magnesium (Mg) disturbance plays an important role in CKD-MBD and cardiovascular mortality, the interest on magnesium has grown recently. Although much concern focused on the effect of Mg on parathyroid hormone (PTH) levels, however, the influence of PTH on serum Mg levels is nearly unexplored. To evaluate the effect of PTH on serum Mg levels, we first described the relationship between serum Mg and PTH in secondary hyperparathyroidism. Besides, we also monitored the changes of serum Mg concentration after parathyroidectomy (PTX) in 23 patients. In our study, we found that hypermagnesemia (>2.5 mg/dL) occurred in up to 44% of cases and hypomagnesemia did not present. No statistically significant correlations were found between serum Mg levels and PTH (r = -0.143, p = 0.134). Correlation analysis and regression analysis suggested that the derangement of magnesium homeostasis was consistent with the derangement of calcium/phosphorus homeostasis. However, after PTX, serum magnesium levels dropped immediately after the surgery, minimally at the first day and gradually restored from the third day. The changes of serum Mg after surgery was positive correlated with the changes of serum phosphate (r = 0.558, p = 0.003). Taken altogether, our data suggested that the therapeutic strategies to achieve optimum serum magnesium levels in CKD-MBD should take into account the varying stages of disease development since PTH could also influence magnesium metabolism and this problem might be important in severe secondary hyperparathyroidism.

Disturbances in Bone Largely Predict Aortic Calcification in an Alternative Rat Model Developed to Study Both Vascular and Bone Pathology in Chronic Kidney Disease

Because current rat models used to study chronic kidney disease (CKD)-related vascular calcification show consistent but excessive vascular calcification and chaotic, immeasurable, bone mineralization due to excessive bone turnover, they are not suited to study the bone-vascular axis in one and the same animal. Because vascular calcification and bone mineralization are closely related to each other, an animal model in which both pathologies can be studied concomitantly is highly needed. CKD-related vascular calcification in rats was induced by a 0.25% adenine/low vitamin K diet. To follow vascular calcification and bone pathology over time, rats were killed at weeks 4, 8, 10, 11, and 12. Both static and dynamic bone parameters were measured. Vascular calcification was quantified by histomorphometry and measurement of the arterial calcium content. Stable, severe CKD was induced along with hyperphosphatemia, hypocalcemia as well as increased serum PTH and FGF23. Calcification in the aorta and peripheral arteries was present from week 8 of CKD onward. Four and 8 weeks after CKD, static and dynamic bone parameters were measurable in all animals, thereby presenting typical features of hyperparathyroid bone disease. Multiple regression analysis showed that the eroded perimeter and mineral apposition rate in the bone were strong predictors for aortic calcification. This rat model presents a stable CKD, moderate vascular calcification, and quantifiable bone pathology after 8 weeks of CKD and is the first model that lends itself to study these main complications simultaneously in CKD in mechanistic and intervention studies.

Association of hypermagnesemia and blood pressure in the critically ill

BACKGROUND

Although magnesium is important in the biology of blood pressure regulation, little clinical data exist on the association of hypermagnesemia and blood pressure.

METHOD

We examined the association of hypermagnesemia and SBP in a cross-sectional study of 10 521 ICU patients from a single tertiary care medical center, 6% of whom had a serum magnesium above 2.6 mg/dl at time of admission.

RESULTS

In a multivariable analysis, hypermagnesemia was associated with SBP 6.2 mmHg lower [95% confidence interval (CI) -8.2, -4.2, P < 0.001] than in patients with admission values of serum magnesium 2.6 mg/dl or less. Each mg/dl increase in serum magnesium was associated with a decrease in SBP of 4.3 mmHg (95% CI -5.5, -3.1, P < 0.001). In addition, hypermagnesemic patients had a 2.48-fold greater likelihood (95% CI 2.06, 3.00, P < 0.001) of receiving intravenous vasopressors during the first 24 h of ICU care, independent of admission SBP.

CONCLUSION

Our findings add support to the biologic importance of magnesium regulation in blood pressure control.

Serum Magnesium and Mortality in Hemodialysis Patients in the United States: A Cohort Study

BACKGROUND

Low serum magnesium levels in patients with kidney disease have been linked to increased mortality. This study investigated whether similar associations existed in maintenance hemodialysis (HD) patients.

STUDY DESIGN

Cohort study.

SETTING & PARTICIPANTS

All Fresenius Medical Care North America in-center HD patients with available serum magnesium measurements were studied. The initial exploratory study in 21,534 HD patients evaluated associations among serum magnesium level, dialysate magnesium concentration, and mortality from April 2007 through June 2008. The follow-up study in 27,544 HD patients evaluated associations between serum magnesium levels and mortality over 1 year (January through December 2008).

PREDICTORS

The primary predictor was serum magnesium level, with adjustment for case-mix (age, sex, race, diabetes, and dialysis vintage and additionally for follow-up study: body surface area and vascular access) and laboratory variables (albumin, hemoglobin, phosphorus, equilibrated Kt/V, potassium, calcium, and intact parathyroid hormone values).

OUTCOME

Primary outcome variable was 1-year mortality risk, evaluated using Cox proportional hazards models.

RESULTS

Among 21,534 HD patients in the exploratory study, there were 3,682 deaths. Higher dialysate magnesium level was associated with higher serum magnesium level (R=0.22; P<0.001). Patients with the lowest serum magnesium levels (<1.30 mEq/L) were at highest risk for death (HR, 1.63; 95% CI, 1.30-1.96; reference serum magnesium, 1.60-<1.90 mEq/L). Among 27,544 HD patients in the follow-up study, there were 4,531 deaths. In Cox proportional hazards models, there was a linear decline in death risk from the lowest to the highest serum magnesium category, with the best survival at serum magnesium levels ≥ 2.50 mEq/L (HR, 0.68; 95% CI, 0.56-0.82). However, risk estimates were attenuated with case-mix and lab adjustment. This pattern was consistent within diabetes subgroups and for cardiovascular or noncardiovascular causes of death.

LIMITATIONS

Observational study with cross-sectional serum magnesium measurements and no information for oral magnesium intake.

CONCLUSIONS

Elevated serum magnesium levels > 2.10 mEq/L were associated with better survival than low serum magnesium levels < 1.30 mEq/L in HD patients. Prospective studies may determine whether manipulation of low serum magnesium levels affects survival.

Cellular and Molecular Mechanisms of Chronic Kidney Disease with Diabetes Mellitus and Cardiovascular Diseases as Its Comorbidities

Chronic kidney disease (CKD), diabetes mellitus (DM), and cardiovascular diseases (CVD) are complex disorders of partly unknown genesis and mostly known progression factors. CVD and DM are the risk factors of CKD and are strongly intertwined since DM can lead to both CKD and/or CVD, and CVD can lead to kidney disease. In recent years, our knowledge of CKD, DM, and CVD has been expanded and several important experimental, clinical, and epidemiological associations have been reported. The tight cellular and molecular interactions between the renal, diabetic, and cardiovascular systems in acute or chronic disease settings are becoming increasingly evident. However, the (patho-) physiological basis of the interactions of CKD, DM, and CVD with involvement of multiple endogenous and environmental factors is highly complex and our knowledge is still at its infancy. Not only single pathways and mediators of progression of these diseases have to be considered in these processes but also the mutual interactions of these factors are essential. The recent advances in proteomics and integrative analysis technologies have allowed rapid progress in analyzing complex disorders and clearly show the opportunity for new efficient and specific therapies. More than a dozen pathways have been identified so far, including hyperactivity of the renin–angiotensin (RAS)–aldosterone system, osmotic sodium retention, endothelial dysfunction, dyslipidemia, RAS/RAF/extracellular-signal-regulated kinase pathway, modification of the purinergic system, phosphatidylinositol 3-kinase (PI 3-kinase)-dependent signaling pathways, and inflammation, all leading to histomorphological alterations of the kidney and vessels of diabetic and non-diabetic patients. Since a better understanding of the common cellular and molecular mechanisms of these diseases may be a key to successful identification of new therapeutic targets, we review in this paper the current literature about cellular and molecular mechanisms of CKD.

Magnesium and cardiovascular complications of chronic kidney disease

Cardiovascular complications are the leading cause of death in patients with chronic kidney disease (CKD). Abundant experimental evidence suggests a physiological role of magnesium in cardiovascular function, and clinical evidence suggests a role of the cation in cardiovascular disease in the general population. The role of magnesium in CKD-mineral and bone disorder, and in particular its impact on cardiovascular morbidity and mortality in patients with CKD, is however not well understood. Experimental studies have shown that magnesium inhibits vascular calcification, both by direct effects on the vessel wall and by indirect, systemic effects. Moreover, an increasing number of epidemiologic studies in patients with CKD have shown associations of serum magnesium levels with intermediate and hard outcomes, including vascular calcification, cardiovascular events and mortality. Intervention trials in these patients conducted to date have had small sample sizes and have been limited to the study of surrogate parameters, such as arterial stiffness, vascular calcification and atherosclerosis. Randomized controlled trials are clearly needed to determine the effects of magnesium supplementation on hard outcomes in patients with CKD.

Phosphate binders prevent phosphate-induced cellular senescence of vascular smooth muscle cells and vascular calcification in a modified, adenine-based uremic rat model

Clinical and experimental studies have reported that phosphate overload plays a central role in the pathogenesis of vascular calcification in chronic kidney disease. However, it remains undetermined whether phosphate induces cellular senescence during vascular calcification. We established a modified uremic rat model induced by a diet containing 0.3% adenine that showed more slowly progressive kidney failure, more robust vascular calcification, and longer survival than the conventional model (0.75% adenine). To determine the effect of phosphate on senescence of vascular smooth muscle cells (VSMCs) and the protective effect of phosphate binders, rats were divided into four groups: (1) normal control rats; (2) rats fed with the modified adenine-based diet (CKD); (3) CKD rats treated with 6% lanthanum carbonate (CKD-LaC); and (4) CKD rats treated with 6% calcium carbonate (CKD-CaC). After 8 weeks, CKD rats showed circumferential arterial medial calcification, which was inhibited in CKD-LaC and CKD-CaC rats. CKD rats showed increased protein expression of senescence-associated β-galactosidase, bone-related proteins, p16 and p21, and increased oxidative stress levels in the calcified area, which were inhibited by both phosphate binders. However, serum levels of oxidative stress and inflammatory markers, serum fibroblast growth factor 23, and aortic calcium content in CKD-CaC rats were higher than those in CKD-LaC rats. In conclusion, phosphate induces cellular senescence of VSMCs in the modified uremic rat model, and phosphate binders can prevent both cellular senescence and calcification of VSMCs via phosphate unloading. Our modified adenine-based uremic rat model is useful for evaluating uremia-related complications, including vascular calcification.

Characterisation of calcium phosphate crystals on calcified human aortic vascular smooth muscle cells and potential role of magnesium

Background

Cardiovascular 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 Findings

In 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/Significance

For 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.

Magnesium in CKD: more than a calcification inhibitor?

Magnesium fulfils important roles in multiple physiological processes. Accordingly, a tight regulation of magnesium homeostasis is essential. Dysregulated magnesium serum levels, in particular hypomagnesaemia, are common in patients with chronic kidney disease (CKD) and have been associated with poor clinical outcomes. In cell culture studies as well as in clinical situations magnesium levels were associated with vascular calcification, cardiovascular disease and altered bone-mineral metabolism. Magnesium has also been linked to diseases such as metabolic syndrome, diabetes, hypertension, fatigue and depression, all of which are common in CKD. The present review summarizes and discusses the latest clinical data on the impact of magnesium and possible effects of higher levels on the health status of patients with CKD, including an outlook on the use of magnesium-based phosphate-binding agents in this context.

A magnesium based phosphate binder reduces vascular calcification without affecting bone in chronic renal failure rats

The alternative phosphate binder calcium acetate/magnesium carbonate (CaMg) effectively reduces hyperphosphatemia, the most important inducer of vascular calcification, in chronic renal failure (CRF). In this study, the effect of low dose CaMg on vascular calcification and possible effects of CaMg on bone turnover, a persistent clinical controversy, were evaluated in chronic renal failure rats. Adenine-induced CRF rats were treated daily with 185 mg/kg CaMg or vehicle for 5 weeks. The aortic calcium content and area% calcification were measured to evaluate the effect of CaMg. To study the effect of CaMg on bone remodeling, rats underwent 5/6th nephrectomy combined with either a normal phosphorus diet or a high phosphorus diet to differentiate between possible bone effects resulting from either CaMg-induced phosphate deficiency or a direct effect of Mg. Vehicle or CaMg was administered at doses of 185 and 375 mg/kg/day for 8 weeks. Bone histomorphometry was performed. Aortic calcium content was significantly reduced by 185 mg/kg/day CaMg. CaMg ameliorated features of hyperparathyroid bone disease. In CRF rats on a normal phosphorus diet, the highest CaMg dose caused an increase in osteoid area due to phosphate depletion. The high phosphorus diet combined with the highest CaMg dose prevented the phosphate depletion and thus the rise in osteoid area. CaMg had no effect on osteoblast/osteoclast or dynamic bone parameters, and did not alter bone Mg levels. CaMg at doses that reduce vascular calcification did not show any harmful effect on bone turnover.