1,25-Dihydroxyvitamin D3 but not cinacalcet HCl (Sensipar/Mimpara) treatment mediates aortic calcification in a rat model of secondary hyperparathyroidism

Chronic Cinacalcet improves skin flap survival in rats: the suggested role of the nitric oxide pathway

Cinacalcet is a calcimimetic medicine that has been used to treat secondary hyperparathyroidism and parathyroid cancer. Various studies have proposed the positive role of calcium and its receptor in skin wound healing. Furthermore, Cinacalcet interacts with other skin repair-related mechanisms, including inflammation and nitric oxide pathways. The present study evaluated the effect of Cinacalcet on the random-pattern skin flap survival. Eighty-four Wistar male rats were used. Multiple doses of Cinacalcet (30, 3, 1, 0.3, and 0.05 mg/kg) were used in 3 different routes of administration before the surgery. Histopathological evaluations, quantitative assessment of IL-6, TNF-α, and nitric oxide (NO), and the expression of calcium-sensing receptor (CaSR) and E-cadherin were evaluated in the skin tissue. To assess the role of NO, a NO synthase inhibitor, N-nitro-L-arginine methyl ester hydrochloride (L-NAME), was used, and histopathological effects were investigated. Cinacalcet pretreatment at the IP chronic 1 mg/kg dose significantly increased the skin flap survival rate and enhanced the NO tissue level compared to the control. However, the administration of L-NAME abolished its protective effects. IP Chronic 1 mg/kg of Cinacalcet could also decline the levels of IL-6 and TNF-α and also increase the expression of CaSR and E-cadherin in the flap tissue compared with the control group. Chronic Cinacalcet at 1 mg/kg could improve skin flap survival, probably mediated by the CaSR, NO, and inflammation-related pathways.

Food to Prevent Vascular Calcification in Chronic Kidney Disease

Vascular calcification (VC) is a consequence of chronic kidney disease (CKD) which is of paramount importance regarding the survival of CKD patients. VC is far from being controlled with actual medication; as a result, in recent years, diet modulation has become more compelling. The concept of medical nutritional therapy points out the idea that food may prevent or treat diseases. The aim of this review was to evaluate the influence of food habits and nutritional intervention in the occurrence and progression of VC in CKD. Evidence reports the harmfulness of ultra-processed food, food additives, and animal-based proteins due to the increased intake of high absorbable phosphorus, the scarcity of fibers, and the increased production of uremic toxins. Available data are more supportive of a plant-dominant diet, especially for the impact on gut microbiota composition, which varies significantly depending on VC presence. Magnesium has been shown to prevent VC but only in experimental and small clinical studies. Vitamin K has drawn considerable attention due to its activation of VC inhibitors. There are positive studies; unfortunately, recent trials failed to prove its efficacy in preventing VC. Future research is needed and should aim to transform food into a medical intervention to eliminate VC danger in CKD.

Methotrexate Chemotherapy Causes Growth Impairments, Vitamin D Deficiency, Bone Loss, and Altered Intestinal Metabolism-Effects of Calcitriol Supplementation

Vitamin D deficiency or insufficiency is prevalent in childhood cancer patients and survivors after chemotherapy; further studies are needed to investigate the underlying aetiology and effectiveness of vitamin D supplementation in preventing chemotherapy-induced bone loss. This study used a rat model of treatment with antimetabolite methotrexate to investigate whether methotrexate chemotherapy causes vitamin D deficiency and if vitamin D supplementation attenuates the resultant bone loss. Methotrexate treatment (five daily injections) decreased serum vitamin D levels (from 52 to <30 ng/mL), reduced body and bone lengthening and tibial trabecular bone volume, and altered intestinal vitamin D metabolism, which was associated with intestinal mucosal damage known to cause malabsorption of nutrients, including dietary vitamin D and calcium. During the early stage after chemotherapy, mRNA expression increased for vitamin D activation enzyme CYP27B1 and for calcium-binding protein TRPV6 in the intestine. During the intestinal healing stage, expression of vitamin D catabolism enzyme CYP24 increased, and that of TRPV6 was normalised. Furthermore, subcutaneous calcitriol supplementation diminished methotrexate-induced bone loss due to its effect suppressing methotrexate-induced increased bone resorption. Thus, in young rats, methotrexate chemotherapy causes vitamin D deficiency, growth impairments, bone loss, and altered intestinal vitamin D metabolism, which are associated with intestinal damage, and vitamin D supplementation inhibits methotrexate-induced bone loss.

Vitamin D Analogues and Fracture Risk in Chronic Kidney Disease: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Vitamin D receptor agonists (VDRAs) are commonly prescribed in chronic kidney disease (CKD). However, their protective effects on bone remain controversial. We performed a systematic review and meta-analysis of randomized controlled trials (RCTs) to evaluate the effect of VDRAs on fracture risk and bone mineral density (BMD) in adult patients with CKD. We searched MEDLINE, EMBASE, CENTRAL, ClinicalTrials.gov, and the WHO's International Clinical Trials Registry Platform databases from inception to June 19, 2021. We included RCTs comparing VDRAs, to placebo or another medication, in adults with CKD requiring or not dialysis. Conference abstracts and trials involving kidney transplant recipients and/or comparing VDRAs to antiresorptive or anabolic bone therapy were excluded. Primary outcome was fracture at any anatomical site. Secondary outcomes were BMD at femoral neck, lumbar spine, and/or total hip. Prespecified subgroup analyses were conducted according to baseline demographics, overall risk of bias, and follow-up time. From 6868 references retrieved, eight RCTs were eligible: five reported fracture, two reported BMD, and one reported both outcomes. As comparator, one study used no VDRAs, one used nutritional intervention and no medication, and six used placebo. In meta-analysis, VDRAs were not associated with a significant reduction in total fractures in overall (risk ratio = 0.79, 95% confidence interval 0.38-1.65, I2 = 0%, six trials, 1507 participants, 27 fractures) or in prespecified subgroup analyses. Three trials reported BMD at different sites and with different BMD measurements; thus, a meta-analysis could not be performed. Two RCTs were at high risk of bias, notably because of deviations from the intended interventions. As limitation, we have to mention the low total number of fractures included in our meta-analysis. In conclusion, current evidence from RCTs is insufficient to associate VDRAs with bone protection in CKD. Further large and long-term studies specifically designed to evaluate the efficacy of VDRAs on bone outcomes are thus required. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Vascular Calcification in Rodent Models-Keeping Track with an Extented Method Assortment

Simple Summary

Arterial vessel diseases are the leading cause of death in the elderly and their accelerated pathogenesis is responsible for premature death in patients with chronic renal failure. Since no functioning therapy concepts exist so far, the identification of the main signaling pathways is of current research interest. To develop therapeutic concepts, different experimental rodent models are needed, which should be subject to the 3R principle of Russel and Burch: “Replace, Reduce and Refine”. This review aims to summarize the current available experimental rodent models for studying vascular calcification and their quantification methods.

Abstract

Vascular calcification is a multifaceted disease and a significant contributor to cardiovascular morbidity and mortality. The calcification deposits in the vessel wall can vary in size and localization. Various pathophysiological pathways may be involved in disease progression. With respect to the calcification diversity, a great number of research models and detection methods have been established in basic research, relying mostly on rodent models. The aim of this review is to provide an overview of the currently available rodent models and quantification methods for vascular calcification, emphasizing animal burden and assessing prospects to use available methods in a way to address the 3R principles of Russel and Burch: “Replace, Reduce and Refine”.

Vitamin D Analogues and Coronary Calcification in CKD Stages 3 and 4: A Randomized Controlled Trial of Calcitriol Versus Paricalcitol

Rationale & Objective

Mineral and bone disorder in chronic kidney disease (CKD) is associated with progression of coronary artery calcification (CAC). Mineral and bone disorder often is treated with calcitriol and other vitamin D receptor activators, including paricalcitol, agents that may have differential effects on calcium, phosphate, and parathyroid hormone levels. Accordingly, we investigated whether these agents have differential effects on CAC progression in patients with CKD.

Study Design

Randomized, double-concealed, 48-week clinical trial.

Setting & Participants

CKD stage 3 or 4 with secondary hyperparathyroidism with CAC score > 0 and no prior treatment with activated vitamin D.

Intervention

Calcitriol versus paricalcitol.

Outcomes

The primary outcome was log-transformed CAC change. Secondary outcomes included percent change in CAC volume, valvular calcifications, and bone mineral metabolism markers.

Results

Among 44 individuals randomly assigned, mean age was 65 years and mean estimated glomerular filtration rate was 27 mL/min/1.73 m². Median CAC score was 140 (IQR, 55-277) Agatston units at baseline. There was no significant difference in CAC progression between treatment arms (P = 0.06). After adjustment for baseline CAC score (log), treatment group remains nonsignificant (P = 0.08). Further adjustment for creatinine level and/or CKD stage did not change the association. In secondary analyses adjusting for dose level of activated vitamin D, treatment group was significant (P = 0.01), and when dose level was also included in the model, the coefficient for individuals in the paricalcitol group was significantly associated with CAC progression (P = 0.02). An interaction term between dosing level and CKD stage was significant at the highest dosing level (P = 0.04).

Limitations

Pilot single-center study.

Conclusions

In patients with CKD with secondary hyperparathyroidism naive to activated vitamin D therapy, there was no difference in CAC or valvular progression in participants receiving calcitriol compared with paricalcitol during a 48-week period.

Funding

Abbvie, Inc.

Trial Registration

NCT00752102.

Reduction of Secreted Frizzled-Related Protein 5 Drives Vascular Calcification through Wnt3a-Mediated Rho/ROCK/JNK Signaling in Chronic Kidney Disease

Vascular calcification (VC) is commonly associated with bone loss in patients with chronic kidney disease (CKD). The Wingless-related integration site (Wnt) regulates osteoblast activation through canonical signaling pathways, but the common pathophysiology of these pathways during VC and bone loss has not been identified. A rat model of adenine-induced CKD with VC was used in this study. The rats were fed 0.75% adenine (2.5% protein, 0.92% phosphate) with or without intraperitoneal injection of calcitriol (0.08 µg/kg/day) for 4 weeks. Angiotensin II (3 µM)-induced VC was achieved in high phosphate medium (3 mM) through its effect on vascular smooth muscle cells (VSMCs). In an mRNA profiler polymerase chain reaction assay of the Wnt signaling pathway, secreted frizzled-related protein 5 (sFRP5) levels were significantly decreased in the CKD rat model compared with the control group. The repression of sFRP5 on VSMC trans-differentiation was mediated through Rho/Rho-associated coiled coil containing protein kinase (ROCK) and c-Jun N-terminal kinase (JNK) pathways activated by Wnt3a. In a proof of concept study conducted with patients with CKD, serum sFRP5 concentrations were significantly lower in subjects with VC than in those without VC. Our findings suggest that repression of sFRP5 is associated with VC in the CKD environment via activation of the noncanonical Wnt pathway, and thus that sFRP5 might be a novel therapeutic target for VC in CKD.

Research Models for Studying Vascular Calcification

Calcification of the vessel wall contributes to high cardiovascular morbidity and mortality. Vascular calcification (VC) is a systemic disease with multifaceted contributing and inhibiting factors in an actively regulated process. The exact underlying mechanisms are not fully elucidated and reliable treatment options are lacking. Due to the complex pathophysiology, various research models exist evaluating different aspects of VC. This review aims to give an overview of the cell and animal models used so far to study the molecular processes of VC. Here, in vitro cell culture models of different origins, ex vivo settings using aortic tissue and various in vivo disease-induced animal models are summarized. They reflect different aspects and depict the (patho)physiologic mechanisms within the VC process.

Trimethylamine-N-Oxide Promotes Vascular Calcification Through Activation of NLRP3 (Nucleotide-Binding Domain, Leucine-Rich-Containing Family, Pyrin Domain-Containing-3) Inflammasome and NF-κB (Nuclear Factor κB) Signals

Objectives:

Vascular calcification is highly prevalent in patients with chronic kidney disease. Increased plasma trimethylamine N-oxide (TMAO), a gut microbiota-dependent product, concentrations are found in patients undergoing hemodialysis. However, a clear mechanistic link between TMAO and vascular calcification is not yet established. In this study, we investigate whether TMAO participates in the progression of vascular calcification using in vitro, ex vivo, and in vivo models.

Approach and Results:

Alizarin red staining revealed that TMAO promoted calcium/phosphate-induced calcification of rat and human vascular smooth muscle cells in a dose-dependent manner, and this was confirmed by calcium content assay. Similarly, TMAO upregulated the expression of bone-related molecules including Runx2 (Runt-related transcription factor 2) and BMP2 (bone morphogenetic protein-2), suggesting that TMAO promoted osteogenic differentiation of vascular smooth muscle cells. In addition, ex vivo study also showed the positive regulatory effect of TMAO on vascular calcification. Furthermore, we found that TMAO accelerated vascular calcification in rats with chronic kidney disease, as indicated by Mico-computed tomography analysis, alizarin red staining and calcium content assay. By contrast, reducing TMAO levels by antibiotics attenuated vascular calcification in chronic kidney disease rats. Interestingly, TMAO activated NLRP3 (nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3) inflammasome and NF-κB (nuclear factor κB) signals during vascular calcification. Inhibition of NLRP3 inflammasome and NF-κB signals attenuated TMAO-induced vascular smooth muscle cell calcification.

Conclusions:

This study for the first time demonstrates that TMAO promotes vascular calcification through activation of NLRP3 inflammasome and NF-κB signals, suggesting the potential link between gut microbial metabolism and vascular calcification. Reducing the levels of TMAO could become a potential treatment strategy for vascular calcification in chronic kidney disease.

Pharmacologic Therapies for Aortic Stiffness in End-Stage Renal Disease: A Systematic Review and Meta-Analysis

Background:

Increased carotid-femoral pulse wave velocity (cf-PWV), a surrogate of increased aortic stiffness, is a risk factor for cardiovascular events and all-cause mortality in end-stage renal disease (ESRD). To minimize the deleterious effects of an increased aortic stiffness in ESRD patients, several interventions have been developed and cf-PWV has been used to monitor responses.

Objective:

The aim of this study was to determine the effects of pharmacologic interventions that target aortic stiffness on cf-PWV and systolic blood pressure (SBP) in adults with ESRD.

Study design:

This study implements a systematic review and meta-analysis.

Data sources:

MEDLINE, EMBASE, Cochrane Central, Health Technology Assessment, and EBM databases were searched.

Study eligibility, participants, and interventions:

Randomized and non-randomized studies involving adults (>18 years) with ESRD of any duration, receiving or not renal replacement therapy (hemodialysis, peritoneal dialysis) and exposed to a pharmacologic intervention whose effects were assessed by cf-PWV.

Methods:

Study screening, selection, data extraction, and quality assessments were performed by 2 independent reviewers. Narrative synthesis and quantitative data analysis summarized the review.

Results:

We included 1027 ESRD participants from 13 randomized and 5 non-randomized studies. Most pharmacologic interventions targeted bone mineral metabolism disorder or hypertension. Treatment with vitamin D analogues or cinacalcet did not decrease cf-PWV or SBP over placebo or matched controls (P > .05). Calcium-channel blockers (CCB) decreased cf-PWV and SBP compared with placebo or standard care (P < .05). Renin-angiotensin system inhibitors did not show any advantage over placebo in decreasing cf-PWV (P > .05).

Limitations:

Quality of evidence ranged from very low to moderate. Overall evidence was limited by the low number of studies, small sample sizes, and methodological inconsistencies.

Conclusions:

Pharmacologic interventions targeting aortic stiffness in ESRD have mixed effects on reducing cf-PWV, with some strategies suggesting potential benefit. The quality of evidence, however, is insufficient to draw definitive conclusions on their use to slow progression of aortic stiffness in ESRD. Further well-designed studies are needed to confirm these associations and their impact on cardiovascular outcomes in ESRD.

Registered in PROSPERO (CRD42016033463)

Cinacalcet attenuated bone loss via inhibiting parathyroid hormone-induced endothelial-to-adipocyte transition in chronic kidney disease rats

Background

Recently, cinacalcet (CINA) has been shown to be effective for attenuating bone loss in the treatment of secondary hyperparathyroidism (SHPT) in patients with chronic kidney disease (CKD), which might be associated with the reduction in serum parathyroid hormone (PTH) levels. However, the exact mechanism is largely unclear. Emerging studies have revealed that an increased number of bone marrow adipocytes (BMAs) are involved in bone loss and the endothelial-to-adipocyte transition via the endothelial-to-mesenchymal transition (EndMT) might play a key role in this pathological process. Here, we assessed whether CINA could attenuate bone loss via inhibiting endothelial-to-adipocyte transition in CKD rats.

Methods

A rat model of CKD was induced by adenine and a high phosphorus diet. CINA was orally administrated to CKD animals (10 mg/kg once a day). Dual energy X-ray absorptiometry, micro-computed tomography, bone histomorphometry, and bone mechanical tests were used to determine the skeletal changes. The bone marrow expression of EndMT markers was also examined. The effect of elevated PTH levels on the endothelial-to-adipocyte transition was studied in endothelial cells (ECs).

Results

Elevation of serum PTH levels, remarkable bone loss and increased numbers of BMAs were observed in rats with CKD compared with the controls, and these changes were attenuated after treatment with CINA. Furthermore, the CINA treatment abolished the upregulation of mesenchymal markers (FSP1 and α-SMA) and the downregulation of an endothelial marker (CD31) in bone tissues from rats with CKD. The serum PTH concentrations were correlated with the bone marrow protein levels of these EndMT-related proteins. An in vitro treatment in ECs demonstrated that PTH induced the EndMT in a concentration- and time-dependent manner. Accordingly, ECs treated with PTH exhibited adipogenic potential following growth in adipogenic culture medium.

Conclusions

Our study indicated CINA treatment attenuated bone loss in CKD rats, which might be associated with inhibiting PTH-induced endothelial-to-adipocyte transition in CKD rats.

Supplementary nutrients for prevention of vascular calcification in patients with chronic kidney disease

Vascular calcification (VC) and malnutrition associated with cardiovascular disease are common in patients with chronic kidney disease (CKD) treated with dialysis. VC, which reflects vascular aging, and malnutrition are also encountered in the non-CKD elderly population. This similarity of clinical findings suggests that the progression of CKD is related to aging and the existence of a causal relationship between VC and malnutrition. To retard renal progression, a low- or very-low-protein diet is usually recommended for CKD patients. Dietary education may induce malnutrition and deficiency of important nutrients, such as vitamins K and D. Menaquinone-7, a type of vitamin K2, is under investigation for inhibiting VC in elderly patients without CKD, as well as for prevention of VC in patients with CKD. Nutritional vitamin D, such as cholecalciferol, may be considered to decrease the required dose of active vitamin D, which increases the risk of VC due to increased calcium and phosphate loads. Omega-3 fatty acids are important nutrients and their ability to inhibit VC needs to be evaluated in clinical trials. This review focuses on the ability of supplementary nutrients to prevent VC in patients with CKD, in whom dietary restriction is essential.

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.

High-phosphorus diet maximizes and low-dose calcitriol attenuates skeletal muscle changes in long-term uremic rats

Although disorders of mineral metabolism and skeletal muscle are common in chronic kidney disease (CKD), their potential relationship remains unexplored. Elevations in plasma phosphate, parathyroid hormone, and fibroblastic growth factor 23 together with decreased calcitriol levels are common features of CKD. High-phosphate intake is a major contributor to progression of CKD. This study was primarily aimed to determine the influence of high-phosphate intake on muscle and to investigate whether calcitriol supplementation counteracts negative skeletal muscle changes associated with long-term uremia. Proportions and metabolic and morphological features of myosin-based muscle fiber types were assessed in the slow-twitch soleus and the fast-twitch tibialis cranialis muscles of uremic rats (5/6 nephrectomy, Nx) and compared with sham-operated (So) controls. Three groups of Nx rats received either a standard diet (0.6% phosphorus, Nx-Sd), or a high-phosphorus diet (0.9% phosphorus, Nx-Pho), or a high-phosphorus diet plus calcitriol (10 ng/kg 3 day/wk ip, Nx-Pho + Cal) for 12 wk. Two groups of So rats received either a standard diet or a high-phosphorus diet (So-Pho) over the same period. A multivariate analysis encompassing all fiber-type characteristics indicated that Nx-Pho + Cal rats displayed skeletal muscle phenotypes intermediate between Nx-Pho and So-Pho rats and that uremia-induced skeletal muscle changes were of greater magnitude in Nx-Pho than in Nx-Sd rats. In uremic rats, treatment with calcitriol preserved fiber-type composition, cross-sectional size, myonuclear domain size, oxidative capacity, and capillarity of muscle fibers. These data demonstrate that a high-phosphorus diet potentiates and low-dose calcitriol attenuates adverse skeletal muscle changes in long-term uremic rats.

Pathophysiologic and treatment strategies for cardiovascular disease in end-stage renal disease and kidney transplantations

The inextricable link between the heart and the kidneys predestines that significant cardiovascular disease ensues in the face of end-stage renal disease (ESRD). As a point of fact, the leading cause of mortality of patients on dialysis is still from cardiovascular etiologies, albeit differing in particular types of disease from the general population. For example, sudden cardiac death outnumbers coronary artery disease in patients with ESRD, which is the reverse for the general population. In this review, we will focus on the pathophysiology and treatment options of important traditional and nontraditional risk factors for cardiovascular disease in ESRD patients such as hypertension, anemia, vascular calcification, hyperparathyroidism, uremia, and oxidative stress. The evidence of erythropoietin-stimulating agents, phosphate binders, calcimimetics, and dialysis modalities will be presented. We will then discuss how these risk factors may be changed and perhaps exacerbated after renal transplantation. This is largely due to the immunosuppressive agents that are both crucial yet potentially detrimental in the posttransplant state. Calcineurin inhibitors, corticosteroids, and mammalian target of rapamycin inhibitors, the mainstay of transplant immunosuppression, are all known to increase the risks of developing new onset diabetes as well as the metabolic syndrome. Thus, we need to carefully negotiate between patients' cardiovascular profile and their risks of rejection. Finally, we end by considering strategies by which we may minimize cardiovascular disease in the transplant population, as this modality still confers the highest chance of survival in patients with ESRD.

Pharmacological induction of ferritin prevents osteoblastic transformation of smooth muscle cells

Vascular calcification is a frequent complication of atherosclerosis, diabetes and chronic kidney disease. In the latter group of patients, calcification is commonly seen in tunica media where smooth muscle cells (SMC) undergo osteoblastic transformation. Risk factors such as elevated phosphorus levels and vitamin D3 analogues have been identified. In the light of earlier observations by our group and others, we sought to inhibit SMC calcification via induction of ferritin. Human aortic SMC were cultured using β-glycerophosphate with activated vitamin D3 , or inorganic phosphate with calcium, and induction of alkaline phosphatase (ALP) and osteocalcin as well as accumulation of calcium were used to monitor osteoblastic transformation. In addition, to examine the role of vitamin D3 analogues, plasma samples from patients on haemodialysis who had received calcitriol or paricalcitol were tested for their tendency to induce calcification of SMC. Addition of exogenous ferritin mitigates the transformation of SMC into osteoblast-like cells. Importantly, pharmacological induction of heavy chain ferritin by 3H-1,2-Dithiole-3-thione was able to inhibit the SMC transition into osteoblast-like cells and calcification of extracellular matrix. Plasma samples collected from patients after the administration of activated vitamin D3 caused significantly increased ALP activity in SMC compared to the samples drawn prior to activated vitamin D3 and here, again induction of ferritin diminished the osteoblastic transformation. Our data suggests that pharmacological induction of ferritin prevents osteoblastic transformation of SMC. Hence, utilization of such agents that will cause enhanced ferritin synthesis may have important clinical applications in prevention of vascular calcification.

Clinical outcomes in secondary hyperparathyroidism and the potential role of calcimimetics

Cinacalcet, a type II calcimimetic agent that interacts with the calcium-sensing receptor on the parathyroid gland and increases its sensitivity to calcium, has proved an effective therapy for the treatment of the biochemical derangements that comprise uraemic secondary hyperparathyroidism. These patients experience high cardiovascular attrition with evidence that this is associated with vascular calcification, arterial stiffening and increased pulse wave velocity, and with some of the disturbances of bone and mineral metabolism in uraemia. Thus, it is possible that improved biochemical control in calcimimetic-treated patients might lead to better clinical outcomes. This hypothesis was investigated by retrospective analyses of randomized placebo-controlled phase 3 studies. The addition of cinacalcet to standard therapy with active vitamin D and phosphate binders was found to result in a 93% reduction in the rate of parathyroidectomy, a 54% reduction in fracture rate and 39% reduction in the rate of cardiovascular hospitalization, as well as improvements in some measures of quality of life. These encouraging results point to the need for a more robust assessment of the impact of cinacalcet on cardiovascular and skeletal outcomes.

Active vitamin D and accelerated progression of aortic stiffness in hemodialysis patients: a longitudinal observational study

BACKGROUND

We hypothesized that high-dose active vitamin D therapy in the form of alphacalcidol (α-calcidol), used to treat secondary hyperparathyroidism in chronic kidney disease, could lead to vascular calcification and accelerated progression of aortic stiffness.

METHODS

We conducted an observational study in 85 patients on chronic hemodialysis, among which 70 were taking a weekly dose of α-calcidol of <2 µg and 15 were taking a weekly dose of ≥2 µg (pharmacological dose). Parathyroid hormone, 25-hydroxyvitamin D, fibroblast growth factor 23, and α-klotho were determined. Aortic stiffness was assessed by determination of carotid-femoral pulse wave velocity (cf-PWV) at baseline and after a mean follow-up of 1.2 years. A multivariable regression model was used to evaluate the impact of pharmacological dose of α-calcidol on the progression of aortic stiffness.

RESULTS

At baseline, clinical, biological, and hemodynamic parameters were similar. At follow-up, cf-PWV increased more in patients with pharmacological dose of α-calcidol (0.583±2.291 m/s vs. 1.948±1.475 m/s; P = 0.04). After adjustment for changes in mean blood pressure and duration of follow-up, pharmacological dose of α-calcidol was associated with a higher rate of progression of cf-PWV (0.969 m/s; 95% confidence interval = 0.111-1.827; P = 0.03), and this association persisted after further adjustments for parameters of mineral metabolism.

CONCLUSIONS

In this study, pharmacological dose of α-calcidol was associated with accelerated progression of aortic stiffness. This study suggest that the vascular safety of active vitamin D posology may need to be specifically addressed in the treatment of chronic kidney disease-related bone mineral disorder.

Comparison of AMG 416 and cinacalcet in rodent models of uremia

Background

AMG 416 is a novel peptide agonist of the calcium-sensing receptor (CaSR). This report describes the activity of AMG 416 in two different rodent models of uremia, compared in each case to cinacalcet, an approved therapeutic for secondary hyperparathyroidism (SHPT) in patients with chronic kidney disease on dialysis.

Methods

AMG 416 was administered as a single intravenous (IV) bolus in a severe, acute model of renal insufficiency (the “1K1C” model) and plasma parathyroid hormone (PTH) and serum calcium levels were monitored for 24 hours. In a chronic, less severe model of renal dysfunction, the 5/6 nephrectomy (5/6 Nx) model, AMG 416 was administered as a once-daily IV bolus for 28 days. Both studies included a control (vehicle) group and a comparison cinacalcet group (po dosing at 30 mg/kg and 10 mg/kg for the 1K1C and 5/6 Nx studies, respectively).

Results

Administration of AMG 416 by IV bolus injection into rats with acute renal dysfunction (1K1C model) resulted in a sustained reduction in plasma PTH from the initial elevated values. Following a single IV bolus (0.5 mg/kg), AMG 416 caused a substantial drop in PTH levels which remained approximately 50% below their initial level at 24 hrs. In the same model, oral treatment with cinacalcet (30 mg/kg) resulted in an acute drop in PTH which almost returned to the starting level by 24 hours after dosing. In the 5/6 Nx chronic uremia model, daily IV dosing of AMG 416 over 4 weeks (1 mg/kg) resulted in a sustained reduction in PTH, with approximately 50% of the initial level observed 48 hours post treatment throughout the study. Cinacalcet treatment (10 mg/kg) in the same model resulted in acutely lowered plasma PTH levels which returned to placebo levels by 24 hours post-dose. Consistent with the reductions in plasma PTH, reductions in serum calcium were observed in both AMG 416- and cinacalcet-treated animals.

Conclusions

As a long-acting CaSR agonist suitable for administration by the IV route, AMG 416 is a potential new therapy for the treatment of CKD patients with SHPT receiving hemodialysis.

Cinacalcet attenuates the renal endothelial-to-mesenchymal transition in rats with adenine-induced renal failure

Elevated serum parathyroid hormone (PTH) is an important complicated phenomenon in patients with chronic kidney disease (CKD). Emerging evidence indicates the involvement of PTH in organ fibrosis, and suppression of PTH by cinacalcet (CINA) ameliorates the progression of fibrotic disorders. However, the underlying mechanisms are largely unknown. The endothelial-to-mesenchymal transition (EndMT) has been shown to be an important mechanism involved in renal fibrosis. The present study aimed to investigate whether CINA treatment attenuated renal EndMT in rats with adenine-induced chronic renal failure (CRF). Compared with the control group, serum PTH was significantly higher in the CRF group and was suppressed after CINA treatment. Serum calcium, phosphorus, and calcium × phosphorus product levels were similar in the CRF group and CINA-treated CRF group. Renal collagen accumulation was significantly increased in the CRF group, which was markedly ameliorated by CINA treatment. Expression of the endothelial marker CD31 was significantly downregulated in rats with CRF, whereas expression of the mesenchymal markers fibroblast specific-protein 1 and α-smooth muscle actin was markedly upregulated. These changes were inhibited by CINA treatment. The protein levels of these EndMT-related markers were strongly correlated with serum PTH concentrations. Furthermore, the in vitro study showed that PTH could significantly increase the expression of fibroblast specific-protein 1 and α-smooth muscle actin and decrease CD31 in mRNA and protein levels in a concentration- and time-dependent manner. In conclusion, our study suggests that reducing serum PTH by CINA treatment could attenuate renal fibrosis via suppression of EndMT in the adenine-induced CRF rat model.

Role of local versus systemic vitamin D receptors in vascular calcification

OBJECTIVE

Calcitriol and various analogs are commonly used to suppress secondary hyperparathyroidism in chronic kidney disease but may also exacerbate vascular calcification. Although this could be because of increased intestinal calcium and phosphate absorption, direct effects through vitamin D receptors (VDRs) on vascular smooth muscle have also been proposed.

APPROACH AND RESULTS

The role of these receptors was investigated by examining gene regulation in rat aortas treated with calcitriol ex vivo and in vivo and by transplanting aortas from VDR-null (VDR(-/-)) mice into wild-type mice before induction of uremia and treatment with calcitriol. In cultured rat aortas, calcitriol increased the expression of mRNA for CYP24A1 but not mRNA for any bone-related or calcification-related genes. Gene expression in aortas in vivo was not altered by doses of calcitriol that promote calcification. Calcitriol markedly increased aortic calcification in uremic mice and this did not differ between VDR(-/-) aortic allografts and VDR(+/+) recipient aortas.

CONCLUSIONS

Calcitriol promotes vascular calcification through a systemic action rather than through a direct vascular action.

Echocardiographic integrated backscatter for assessing reduction of aortic valve calcifications by R-568 in a rat model of chronic kidney disease

Chronic kidney disease (CKD) and secondary hyper-parathyroidism are associated with calcific aortic valve disease (CAVD). Innovative modalities for imaging CAVD are warranted. Our aim was to use echocardiographic calibrated integrated backscatter (cIB) to quantitatively determine the preventive effect of the calcimimetic R-568 on CAVD in a CKD rat model, and to compare the results with those of micro-computed tomography and histology. Thirty-six male Wistar rats were followed for 7 wk. Rats were divided into four groups with respect to treatment: (1) adenine 0.5% to induce CKD + vehicle; (2) adenine + R-568 (30 mg/kg/d); (3) control, normal diet + vehicle; (4) controls, normal diet + R-568. At week 7, cIB values of the aortic valve were significantly lower in R-568-treated group 2 than in vehicle-treated group 1. This was confirmed by the significantly lower calcified volume observed on micro-computed tomography and the calcified area observed on histology. There were no significant differences in fractional area change and aortic valve area between groups. In conclusion, echocardiographic cIB was able to quantitatively assess a reduction in CAVD by R-568 in a rat model of CKD.

Lowering vascular calcification burden in chronic kidney disease: Is it possible?

High prevalence of atherosclerosis and arterial calcification in chronic kidney disease is far beyond the explanation by common cardiovascular risk factors such as aging diabetes, hypertension and dyslipidemia. The magnitude of coronary artery calcification is independently and inversely associated with renal function. In addition to cardiovascular risk factors, other chronic kidney disease-related risks such as phosphate retention, excess of calcium and prolonged dialysis vintage also contribute to the development of vascular calcification. Strategies to lower vascular calcification burden in chronic kidney disease population should include minimizing chronic kidney disease and atherosclerotic risk factors. Current therapies available are non-calcium containing phosphate binders, low dose active vitamin D and calcimimetic agent. The role of bisphosphonates in vascular calcification in chronic kidney disease population remains unclear. Preliminary data on sodium thiosulfate are promising, however, larger studies on efficacy and patient outcomes are necessary. Several large randomized controlled trials have confirmed the lack of benefit of statin in attenuating the progression of vascular calcification.

Treatment with oral active vitamin D is associated with decreased risk of peritonitis and improved survival in patients on peritoneal dialysis

Peritonitis is a major complication of peritoneal dialysis (PD) being associated with hospitalization, catheter loss, technique failure, and increased mortality. Data on incidence rates and risk factors for peritonitis episodes vary between centers. In seven Austrian PD units clinical and laboratory data on each peritonitis episode were collected from all patients (n = 726) who performed PD between January 2000 and December 2009. The peritonitis incidence rate was 0.32 episodes/patient-year. In a multivariate analysis the risk of peritonitis was decreased by 57% in patients treated with oral active vitamin D (HR 0.43; 95% CI 0.28–0.64). Renal disease classified as “other or unknown” (HR 1.65; 95% CI 1.08–2.53) and serum albumin <3500 mg/dl (HR 1.49; 95% CI 1.04–2.15) were also associated with an increased risk of peritonitis. Albumin levels <3500 mg/dl (HR 1.89; 95% CI 1.13–3.17), age (HR 1.06 per year; 95% CI 1.03–1.09), and cardiomyopathy (HR 3.01; 95% CI 1.62–5.59) were associated with increased mortality, whereas treatment with oral active vitamin D was associated with a significantly lower risk of death (HR 0.46; 95% CI 0.27–0.81). In this retrospective multi-center study we identified several factors being related to increased risk of peritonitis in PD patients. Treatment with oral active vitamin D was identified as being independently associated with decreased risk of peritonitis, and decreased all-cause mortality in PD patients.

Submaximal suppression of parathyroid hormone ameliorates calcitriol-induced aortic calcification and remodeling and myocardial fibrosis in uremic rats

BACKGROUND AND OBJECTIVE

In subtotally nephrectomized rats, we studied to what extent high-dose calcitriol-induced cardiovascular disease can be modulated by almost complete suppression of parathyroid hormone (PTH), mediated by either cinacalcet (CINA) or parathyroidectomy (PTX).

METHODS

Five groups were studied: sham-operated controls, uremic (U), uremic with calcitriol (U+1,25D), uremic and calcitriol with CINA (U+1,25D+CINA) and uremic and calcitriol with PTX (U+1,25D+PTX). Treatments lasted 14 weeks.

RESULTS

Compared with U group animals, PTH was significantly lower with calcitriol treatment and almost completely suppressed in animals treated with either PTX or CINA. Serum calcium and phosphorus levels were similarly elevated in all groups receiving calcitriol. Renal function in uremic animals was significantly more impaired in the U+1,25D group. Aortic calcifications were pronounced in U+1,25D animals and reduced by more than 50% by concomittant treatment with CINA or PTX. Chondrocytes were observed near areas of calcification (>90%) and endochondral bone formation was confirmed by positive immunofluorescence for chondrocytic transcription factor sox9 and matrix protein collagen X. Altered arterial (aneurysmatic) geometry with a significant increase in wall/lumen and lumen/body weight ratio was found only in the U+1,25D group. Myocardial fibrosis was present in all uremic groups with a significant increase in the U+1,25D group. Connective tissue growth factor messenger RNA was significantly upregulated only in the U+1,25D group.

CONCLUSION

Submaximal suppression of PTH by either CINA or PTX reduced vascular calcifications, arterial remodeling and myocardial fibrosis to a similar degree and independent of the serum calcium and phosphorus levels. These data do not indicate vasculotropic effects of calcimimetics independent of PTH suppression.

Effects of cholecalciferol on functional, biochemical, vascular, and quality of life outcomes in hemodialysis patients

BACKGROUND AND OBJECTIVES

Observational studies suggest that calciferol supplementation may improve laboratory and patient-level outcomes of hemodialysis patients with reduced 25-hydroxyvitamin D [25(OH)D] levels. This randomized controlled trial examined effects of cholecalciferol supplementation in patients on hemodialysis.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Sixty patients with 25(OH)D levels ≤24 ng/ml (≤60 nmol/L) were randomized to receive 50,000 IU oral cholecalciferol or placebo, once weekly for 8 weeks and then monthly for 4 months. At baseline (autumn 2011) and 6 months, testing evaluated muscle strength, functional capacity, laboratory parameters, pulse wave velocity (PWV), and health-related quality of life (HRQOL) using the Kidney Disease Quality of Life-36 survey.

RESULTS

Patients were well matched by treatment allocation. Median age was 62 years (range, 20-86), 52% were women, 55% had a history of diabetes, and mean serum 25(OH)D was 17±5 ng/ml (43±13 nmol/L). Patients were assessed over 6 months by repeated-measures ANOVA. Patients allocated to cholecalciferol had significantly higher values of 25(OH)D (P<0.001), 1,25-dihydroxyvitamin D (P=0.04), and tartrate-resistant acid phosphatase-5b) (P=0.04) and a greater reduction in phosphorus values (P=0.03) than placebo-treated patients Values of serum calcium, intact parathyroid hormone, and episodes of hypercalcemia and hyperphosphatemia did not differ significantly between the groups. No significant differences were detected in muscle strength, functional capacity, PWV, or HRQOL.

CONCLUSIONS

In this randomized controlled trial, patients supplemented with cholecalciferol had higher 25(OH)D, 1,25-dihydroxyvitamin D, and tartrate-resistant acid phosphatase-5b levels, without increased calcium or phosphorus values. However, no effects were detected in muscle strength, functional capacity, PWV, or HRQOL.

Restoration of bone mineralization by cinacalcet is associated with a significant reduction in calcitriol-induced vascular calcification in uremic rats

The present study investigated to what extent normalization of bone turnover goes along with a reduction of high-dose calcitriol-induced vascular calcifications in uremic rats. Five groups of male Sprague-Dawley rats were studied: sham-operated controls (n = 7), subtotally nephrectomized (SNX) uremic (CRF) animals (n = 12), CRF + calcitriol (vitD) (0.25 μg/kg/day) (n = 12), CRF + vitD + cinacalcet (CIN) (10 mg/kg/day) (n = 12), and CRF + vitD + parathyroidectomy (PTX) (n = 12). Treatment started 2 weeks after SNX and continued for the next 14 weeks. High-dose calcitriol treatment in hyperparathyroid rats went along with the development of distinct vascular calcification, which was significantly reduced by >50 %, in both CIN-treated and PTX animals. Compared to control animals and those of the CRF group, calcitriol treatment either in combination with CIN or PTX or not was associated with a significant increase in bone area comprising ±50 % of the total tissue area. However, whereas excessive woven bone accompanied by a dramatically increased osteoid width/area was seen in the CRF + vitD group, CIN treatment and PTX resulted in significantly reduced serum PTH level, which was accompanied by a distinct reduction of both the bone formation rate and the amount of osteoid. These data indicate that less efficient calcium and phosphorus incorporation in bone inherent to the severe hyperparathyroidism in vitamin D-treated uremic rats goes along with excessive vascular calcification, a process which is partially reversed by CIN treatment in combination with a more efficacious bone mineralization, thus restricting the availability of calcium and phosphate for being deposited in the vessel wall.

Arterial calcification and bone physiology: role of the bone-vascular axis

Bone never forms without vascular interactions. This simple statement of fact does not adequately reflect the physiological and pharmacological implications of the relationship. The vasculature is the conduit for nutrient exchange between bone and the rest of the body. The vasculature provides the sustentacular niche for development of osteoblast progenitors and is the conduit for egress of bone marrow cell products arising, in turn, from the osteoblast-dependent haematopoietic niche. Importantly, the second most calcified structure in humans after the skeleton is the vasculature. Once considered a passive process of dead and dying cells, vascular calcification has emerged as an actively regulated form of tissue biomineralization. Skeletal morphogens and osteochondrogenic transcription factors are expressed by cells within the vessel wall, which regulates the deposition of vascular calcium. Osteotropic hormones, including parathyroid hormone, regulate both vascular and skeletal mineralization. Cellular, endocrine and metabolic signals that flow bidirectionally between the vasculature and bone are necessary for both bone health and vascular health. Dysmetabolic states including diabetes mellitus, uraemia and hyperlipidaemia perturb the bone-vascular axis, giving rise to devastating vascular and skeletal disease. A detailed understanding of bone-vascular interactions is necessary to address the unmet clinical needs of an increasingly aged and dysmetabolic population.

In vascular smooth muscle cells paricalcitol prevents phosphate-induced Wnt/β-catenin activation

The present study investigates the differential effect of two vitamin D receptor agonists, calcitriol and paricalcitol, on human aortic smooth muscle cells calcification in vitro. Human vascular smooth muscle cells were incubated in a high phosphate (HP) medium alone or supplemented with either calcitriol 10(-8)M (HP + CTR) or paricalcitol 3·10(-8) M (HP + PC). HP medium induced calcification, which was associated with the upregulation of mRNA expression of osteogenic factors such as bone morphogenetic protein 2 (BMP2), Runx2/Cbfa1, Msx2, and osteocalcin. In these cells, activation of Wnt/β-catenin signaling was evidenced by the translocation of β-catenin into the nucleus and the increase in the expression of direct target genes as cyclin D1, axin 2, and VCAN/versican. Addition of calcitriol to HP medium (HP + CTR) further increased calcification and also enhanced the expression of osteogenic factors together with a significant elevation of nuclear β-catenin levels and the expression of cyclin D1, axin 2, and VCAN. By contrast, the addition of paricalcitol (HP + PC) not only reduced calcification but also downregulated the expression of BMP2 and other osteoblastic phenotype markers as well as the levels of nuclear β-catenin and the expression of its target genes. The role of Wnt/β-catenin on phosphate- and calcitriol-induced calcification was further demonstrated by the inhibition of calcification after addition of Dickkopf-related protein 1 (DKK-1), a specific natural antagonist of the Wnt/β-catenin signaling pathway. In conclusion, the differential effect of calcitriol and paricalcitol on vascular calcification appears to be mediated by a distinct regulation of the BMP and Wnt/β-catenin signaling pathways.

25-hydroxyvitamin D levels and vascular calcification in predialysis and dialysis patients with chronic kidney disease

BACKGROUND/AIMS

The role of vitamin D in the process of vascular calcification is unclear in patients with chronic kidney disease. We investigated whether serum 25-hydroxyvitamin D [25(OH)D] is associated with vascular calcification in predialysis and dialysis patients.

METHODS

We included 86 predialysis and 139 dialysis patients. The simple vascular calcification score (SVCS) was evaluated by examining plain X-rays of the pelvis and hands as described previously. The carotid-to-femoral pulse wave velocity (CF-PWV) was assessed with a commercially available device.

RESULTS

We found a high prevalence of vitamin D deficiency in our population (78.2%). Vascular calcification was present in 46.2% of all patients. Higher calcification (SVCS >3) was significantly associated with lower 25(OH)D levels in predialysis and dialysis patients. Multiple logistic regression analysis for SVCS >3 showed that 25(OH)D levels were negative independent predictors in predialysis (OR: 0.781; 95% CI: 0.623-0.908, p = 0.019) and dialysis patients (OR: 0.805; 95% CI: 0.749-0.853, p = 0.009). Lower 25(OH)D levels were associated with higher CF-PWV in predialysis patients, but this inverse relationship was no longer present in multivariate analysis.

CONCLUSION

We showed an independent relationship between low serum 25(OH)D levels and vascular calcification in both predialysis and dialysis patients.

Effect of alfacalcidol therapy on the survival of chronic hemodialysis patients

The aim of this study was to determine the relationship between alfacalcidol therapy and the outcomes of chronic hemodialysis (HD) patients. We collected demographic and clinical baseline data from 190 prevalent HD patients in a regional Japanese cohort. A 5-year survival analysis was performed according to whether the patients were receiving calcitriol analog therapy. Alfacalcidol therapy at a mean dose of 5.2 ± 1.8 µg/week was performed in 89 (46.8%) of the 190 patients. We recorded 38 deaths during the follow-up period, including 19 deaths from cardiovascular events. A Kaplan-Meier analysis demonstrated that the alfacalcidol users had a significantly lower rate of all-cause mortality and cardiovascular mortality than the non-users. According to a multivariate Cox proportional hazards model, in addition to the use of alfacalcidol (HR=0.347 [0.155-0.714]; P = 0.0035), serum CRP levels (HR= 1.746 [1.184-2.442]; P = 0.0071) and non-HDL-cholesterol levels (HR=1.012 [1.001-1.022]; P = 0.0267) were identified as independent predictors of all-cause mortality, and the presence of diabetes mellitus (HR=3.720 [1.182-12.398]; P = 0.0246) was identified as an independent predictor of cardiovascular mortality. These findings suggest that low-dose alfacalcidol therapy provides a survival advantage to chronic HD patients.

The calcium-sensing receptor and calcimimetics in blood pressure modulation

Calcium is a crucial second messenger in the cardiovascular system. However, calcium may also be an extracellular first messenger through a G-protein-coupled receptor that senses extracellular concentration (Ca(2+)(o)), the calcium-sensing receptor (CaR). The most prominent physiological function of the CaR is to maintain the extracellular Ca(2+) level in a very tight range by regulating the circulating levels of parathyroid hormone (PTH). This control over PTH and Ca(2+) levels is partially lost in patients suffering from primary and secondary hyperparathyroidism. Allosteric modulators of the CaR (calcimimetics) are the first drugs in their class to become available for clinical use and have been shown to successfully treat certain forms of primary and secondary hyperparathyroidism. In addition, several studies suggest beneficial effects of calcimimetics on cardiovascular risk factors associated with hyperparathyroidism. Although a plethora of studies demonstrated the CaR in heart and blood vessels, exact roles of the receptor in the cardiovascular system still remain to be elucidated. However, several studies point toward a possibility that the CaR might be involved in the regulation of vascular tone. This review will summarize the current knowledge on the possible functions of the CaR and calcimimetics on blood pressure regulation.

Cinacalcet: will it play a role in reducing cardiovascular events?

Secondary hyperparathyroidism is a common complication of chronic kidney disease and it is associated with high morbidity and mortality. It is characterized by high parathyroid hormone levels and bone turnover leading to bone pain, deformity and fragility. Furthermore, secondary hyperparathyroidism adversely affects the cardiovascular system and has been associated with cardiovascular calcification and cardiomyopathy. Cinacalcet, a type II calcimimetic, is an effective and well-tolerated oral therapy for the management of secondary hyperparathyroidism. It is an allosteric activator of the calcium-sensing receptor enhancing sensitivity of parathyroid cells to extracellular calcium, which leads to inhibition of parathyroid hormone secretion. The calcium-sensing receptor expression in cardiomyocytes, endothelial cells and vascular smooth muscle cells raises the possibility that this receptor may be implicated in the pathophysiology of cardiovascular disease and constitute a potential therapeutic target. This article reviews the role of the calcimimetic agent cinacalcet in the prevention and progression of cardiovascular calcification and uremic cardiomyopathy in the chronic kidney disease setting.

Vitamin d and stage 5 chronic kidney disease: a new paradigm?

Vitamin D receptor agonists (VDRA) are currently recommended for the treatment of secondary hyperparathyroidism in stage 5 CKD. They are considered to be contraindicated in the presence of low or normal (for a dialysis patient) levels of PTH due to the risk of developing adynamic bone disease, with consequent vascular calcification. However, these recommendations are increasingly at odds with the epidemiological evidence, which consistently shows a large survival advantage for patients treated with low-dose VDRAs, regardless of plasma calcium, phosphate, or PTH. A large number of pleiotropic effects of vitamin D have been described, including inhibition of renin activity, anti-inflammation, and suppression of vascular calcification stimulators and stimulation of vascular calcification inhibitors present in the uremic milieu. Laboratory studies suggest that a normal cellular vitamin D level is necessary for normal cardiomyocyte and vascular smooth muscle function. While pharmacological doses of VDRA can be harmful, the present evidence suggests that the level of 1,25-dihydroxycholecalciferol should also be more physiological in stage 5 CKD, and that widespread use of low-dose VDRA would be beneficial. A randomized controlled trial to test this hypothesis is warranted.

Vitamin D and vascular calcification in chronic kidney disease

Vascular calcification is common in patients with chronic kidney disease (CKD) and contributes to the increased rate of cardiovascular morbidity and mortality. The mechanisms regulating vascular calcification are under investigation; it is accepted that vascular calcification is an active and complex process involving many factors that promote or inhibit calcification. Vascular smooth muscle cells undergo transformation into osteogenic cells. This transformation is being stimulated by high phosphate, and more recently the role of the calcium phosphate nanocrystals has gained attention. Experimental models of uremia and in vitro studies have shown that an excess of calcitriol accelerates vascular calcification. However, observational studies suggest that vitamin D provides a survival advantage for patients with CKD. Experimental work shows that for similar serum concentrations of calcium and phosphate paricalcitol produces less vascular calcification than calcitriol suggesting a differential effect at the cellular level. Important issues regarding the role of vitamin D compounds on vascular calcification will be commented in this review.

The effect of cinacalcet on bone remodeling and renal function in transplant patients with persistent hyperparathyroidism

BACKGROUND

Parathyroidectomy is associated with renal functional losses in transplant patients; cinacalcet offers an attractive alternative.

METHODS

We performed a prospective observational study in 58 patients with persisting hyperparathyroidism after renal transplantation (Ca≥2.6 mmol/L) and impaired renal transplant function (estimated glomerular filtration rate [eGFR] <50 mL/min). The patients received 30 to 90 mg cinacalcet for 12 months with the target to normalize serum Ca. We measured parathyroid hormone (PTH), serum Ca, serum phosphorus, alkaline phosphatase, bone-specific alkaline phosphatase, osteocalcin, and telopeptide at 0, 1, 2, 3, 6, 9, and 12 months of cinacalcet treatment. Fractional excretion of calcium and phosphorus (n=24) were monitored at 0 and 1 month.

RESULTS

At inclusion, creatinine was 181±70 μmol/L, eGFR 43±19 mL/min, PTH 371±279 pg/mL, and Ca 2.73±0.22 mmol/L. We observed nephrocalcinosis in 58% of biopsied patients at enrollment. After cinacalcet, Ca decreased significantly and normalized at nearly any measurement. Phosphorus increased significantly at months 1, 9, and 12. PTH decreased significantly, but only at months 9 and 12 and did not normalize. Bone-specific alkaline phosphatase increased significantly (>normal) by month 12. eGFR decreased and serum creatinine increased at all time points. The Δ(creatinine) % increase correlated significantly with the Δ(PTH) % decrease at month 1 and 12. Telopeptide and alkaline phosphatase correlated with PTH and telopeptide also correlated with serum creatinine.

CONCLUSION

Calcium-phosphorus homeostasis in hypercalcemic renal transplant patients normalizes under cinacalcet and PTH decreases, albeit not to normal. The renal functional decline could be PTH mediated, analogous to the effects observed after parathyroidectomy.

Chondro/osteoblastic and cardiovascular gene modulation in human artery smooth muscle cells that calcify in the presence of phosphate and calcitriol or paricalcitol

Vitamin D sterol administration, a traditional treatment for secondary hyperparathyroidism, may increase serum calcium and phosphorus, and has been associated with increased vascular calcification (VC). In vitro studies suggest that in the presence of uremic concentrations of phosphorus, vitamin D sterols regulate gene expression associated with trans-differentiation of smooth muscle cells (SMCs) to a chondro/osteoblastic cell type. This study examined effects of vitamin D sterols on gene expression profiles associated with phosphate-enhanced human coronary artery SMC (CASMC) calcification. Cultured CASMCs were exposed to phosphate-containing differentiation medium (DM) with and without calcitriol, paricalcitol, or the calcimimetic R-568 (10(-11)-10(-7) M) for 7 days. Calcification of CASMCs, determined using colorimetry following acid extraction, was dose dependently increased (1.6- to 1.9-fold) by vitamin D sterols + DM. In contrast, R-568 did not increase calcification. Microarray analysis demonstrated that, compared with DM, calcitriol (10(-8) M) + DM or paricalcitol (10(-8) M) + DM similarly and significantly (P < 0.05) regulated genes of various pathways including: metabolism, CYP24A1; mineralization, ENPP1; apoptosis, GIP3; osteo/chondrogenesis, OPG, TGFB2, Dkk1, BMP4, BMP6; cardiovascular, HGF, DSP1, TNC; cell cycle, MAPK13; and ion channels, SLC22A3 KCNK3. R-568 had no effect on CASMC gene expression. Thus, SMC calcification observed in response to vitamin D sterol + DM may be partially mediated through targeting mineralization, apoptotic, osteo/chondrocytic, and cardiovascular pathway genes, although some gene changes may protect against calcification. Further studies to determine precise roles of these genes in development of, or protection against VC and cardiovascular disease are required.

Vascular Calcification in Chronic Renal Failure

Accelerated atherosclerotic plaque calcification and extensive medial calcifications are common and highly detrimental complications of chronic kidney disease. Valid murine models have been developed to investigate both pathologically distinguishable complications, which allow for better insight into the cellular mechanisms underlying these vascular pathologies and evaluation of compounds that might prevent or retard the onset or progression of vascular calcification. This review describes various experimental models that have been used for the study of arterial intimal and/or medial calcification and discusses the extent to which this experimental research has contributed to our current understanding of vascular calcification, particularly in the setting of chronic renal failure.

The ADVANCE study: a randomized study to evaluate the effects of cinacalcet plus low-dose vitamin D on vascular calcification in patients on hemodialysis

BACKGROUND

This prospective, randomized, controlled trial compared the progression of vascular and cardiac valve calcification in 360 prevalent adult hemodialysis patients with secondary hyperparathyroidism treated with either cinacalcet plus low-dose vitamin D sterols or flexible doses of vitamin D sterols alone.

METHODS

Eligible subjects were on hemodialysis for ≥ 3 months with parathyroid hormone (PTH) > 300 pg/mL or PTH 150-300 pg/mL with calcium-phosphorus product > 50 mg(2)/dL(2) while receiving vitamin D. All subjects received calcium-based phosphate binders. Coronary artery calcification (CAC) and aorta and cardiac valve calcium scores were determined both by Agatston and volume scoring using multi-detector computed tomography. Subjects with Agatston CAC scores ≥ 30 were randomized to cinacalcet (30- 180 mg/day) plus low-dose calcitriol or vitamin D analog (≤ 2 μg paricalcitol equivalent/dialysis), or flexible vitamin D therapy. The primary end point was percentage change in Agatston CAC score from baseline to Week 52.

RESULTS

Median (P10, P90) Agatston CAC scores increased 24% (-22%, 119%) in the cinacalcet group and 31% (-9%, 179%) in the flexible vitamin D group (P = 0.073). Corresponding changes in volume CAC scores were 22% (-12%, 105%) and 30% (-6%, 133%; P = 0.009). Increases in calcification scores were consistently less in the aorta, aortic valve and mitral valve among subjects treated with cinacalcet plus low-dose vitamin D sterols, and the differences between groups were significant at the aortic valve.

CONCLUSIONS

In hemodialysis patients with moderate to severe secondary hyperparathyroidism, cinacalcet plus low-dose vitamin D sterols may attenuate vascular and cardiac valve calcification.

Treatment with pyrophosphate inhibits uremic vascular calcification

Pyrophosphate, which may be deficient in advanced renal failure, is a potent inhibitor of vascular calcification. To explore its use as a potential therapeutic, we injected exogenous pyrophosphate subcutaneously or intraperitoneally in normal rats and found that their plasma pyrophosphate concentrations peaked within 15 min. There was a single exponential decay with a half-life of 33 min. The kinetics were indistinguishable between the two routes of administration or in anephric rats. The effect of daily intraperitoneal pyrophosphate injections on uremic vascular calcification was then tested in rats fed a high-phosphate diet containing adenine for 28 days to induce uremia. Although the incidence of aortic calcification varied and was not altered by pyrophosphate, the calcium content of calcified aortas was significantly reduced by 70%. Studies were repeated in uremic rats given calcitriol to produce more consistent aortic calcification and treated with sodium pyrophosphate delivered intraperitoneally in a larger volume of glucose-containing solution to prolong plasma pyrophosphate levels. This maneuver significantly reduced both the incidence and amount of calcification. Quantitative histomorphometry of bone samples after double-labeling with calcein indicated that there was no effect of pyrophosphate on the rates of bone formation or mineralization. Thus, exogenous pyrophosphate can inhibit uremic vascular calcification without producing adverse effects on bone.