Vitamin D analogs modulate the expression of plasminogen activator inhibitor-1, thrombospondin-1 and thrombomodulin in human aortic smooth muscle cells

Shining D' light on chronic kidney disease: mechanisms that may underpin the cardiovascular benefit of vitamin D

Hypovitaminosis D is a significant health-care burden worldwide, particularly in susceptible populations such as those with chronic kidney disease (CKD). Recent epidemiological studies have identified that both higher serum vitamin D concentrations and use of vitamin D supplements may confer a survival benefit both in terms of all-cause and cardiovascular mortality. There is potential to investigate this inexpensive therapy for the CKD population, which suffers excessive cardiovascular events, although the mechanisms explaining this link have yet to be fully elucidated. This review discusses potential mechanisms identified in the basic science literature that may provide important insights into how vitamin D may orchestrate a change in cardiovascular risk profile through such diverse mechanisms as inflammation, atherogenesis, glucose homeostasis, vascular calcification, renin-angiotensin regulation and alterations in cardiac physiology. Where available, the clinical translation of these concepts to intervention trials in the CKD population will be reviewed.

1,25-Dihydroxyvitamin D₃ suppresses inflammation-induced expression of plasminogen activator inhibitor-1 by blocking nuclear factor-κB activation

Plasminogen activator inhibitor (PAI)-1 is a major fibrinolytic inhibitor. High PAI-1 is associated with increased renal and cardiovascular disease risk. Previous studies demonstrated PAI-1 down-regulation by 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃), but the molecular mechanism remains unknown. Here we show that exposure of mouse embryonic fibroblasts to TNFα or LPS led to a marked induction of PAI-1, which was blunted by 1,25(OH)₂D₃, NF-κB inhibitor or p65 siRNA, suggesting the involvement of NF-κB in 1,25(OH)₂D₃-induced repression. In mouse Pai-1 promoter a putative cis-κB element was identified at -299. EMSA and ChIP assays showed that TNF-α increased p50/p65 binding to this κB site, which was disrupted by 1,25(OH)₂D₃. Luciferase reporter assays showed that PAI-1 promoter activity was induced by TNFα or LPS, and the induction was blocked by 1,25(OH)₂D₃. Mutation of the κB site blunted TNFα, LPS or 1,25(OH)₂D₃ effects. 1,25(OH)₂D₃ blocked IκBα degradation and arrested p50/p65 nuclear translocation. In mice LPS stimulated PAI-1 expression in the heart and macrophages, and the stimulation was blunted by pre-treatment with a vitamin D analog. Together these data demonstrate that 1,25(OH)₂D₃ down-regulates PAI-1 by blocking NF-κB activation. Inhibition of PAI-1 production may contribute to the reno- and cardio-protective effects of vitamin D.

Vitamin D deficiency and toxicity in chronic kidney disease: in search of the therapeutic window

Both vitamin D deficiency and vitamin D toxicity are associated with cardiovascular complications in chronic kidney disease (CKD). Clinical and experiment data indicate that the association of vitamin D levels with cardiovascular disease is best illustrated as a biphasic, or U-shaped, curve. Children and adolescents with CKD need vitamin D due to the demands of a growing skeleton, to prevent renal rickets. However, this therapy carries the risk of severe side effects and chronic toxicity. Observational studies show that vitamin D deficiency and toxicity are frequently present in patients with CKD. In view of the importance of cardiovascular complications for the long-term survival of young patients, these findings demand a judicious use of vitamin D preparations. In clinical practice, the therapeutic window is rather small, presenting a therapeutic challenge to avoid both vitamin D deficiency and toxicity.

Vitamin D and cardiometabolic health: a review of the evidence

The cardiometabolic syndrome (MetS) is a clustering of related metabolic abnormalities including abdominal adiposity, insulin resistance, hypertension, dyslipidaemia and increased inflammatory and thrombotic markers, which is linked to increased risk of type 2 diabetes, CVD and overall mortality. Several cross-sectional and prospective studies have shown an association between low vitamin D status, as indicated by concentrations of serum 25-hydroxyvitamin D (s25(OH)D), and increased prevalence of the MetS and individual CVD risk factors. These epidemiological observations are supported by mechanistic studies but experimental data are limited. The available data from intervention studies are largely confounded as most vitamin D supplementation trials were mainly carried out to explore the role of Ca in CVD and include Ca in the treatment arms. Inadequate consideration of seasonal effects on s25(OH)D concentrations is also a common design flaw in most studies. Further complications arise from shared risk factors such as adiposity and ageing, which predispose individuals to exhibit both a more pronounced risk profile and relatively lower s25(OH)D concentrations. In conclusion, while epidemiological associations are promising and a rationale for low vitamin D status as a potentially modifiable risk factor for CVD is supported by mechanistic data, suitable experimental data from appropriately designed trials are just beginning to emerge. As yet, this body of literature is too immature to draw firm conclusions on the role of vitamin D in CVD prevention. Carefully controlled vitamin D trials in well-described population groups using intervention doses that are titrated against target s25(OH)D concentrations could yield potentially valuable outcomes that may have a positive impact on CVD risk modification.

Simvastatin does not affect vitamin d status, but low vitamin d levels are associated with dyslipidemia: results from a randomised, controlled trial

Objectives. Statin drugs act as inhibitors of the 3-hydroxy-3methylglutaryl coenzyme A (HMG-CoA) reductase enzyme early in the mevalonate pathway, thereby reducing the endogenous cholesterol synthesis. In recent studies, it has been suggested from epidemiological data that statins also may improve vitamin D status, as measured by increased plasma 25-hydroxyvitamin D (25OHD) levels. We now report the results from a randomised controlled trial on effects of simvastatin on plasma 25OHD levels. Design and Methods. We randomised 82 healthy postmenopausal women to one year of treatment with either simvastatin 40 mg/d or placebo and performed measurement at baseline and after 26 and 52 weeks of treatment. The study was completed by 77 subjects. Results. Compared with placebo, plasma levels of cholesterol and low-density lipoproteins decreased in response to treatment with simvastatin, but our study showed no effect of simvastatin on vitamin D status. However, plasma levels of triglycerides were inversely associated with tertiles of plasma 25OHD levels and changes in plasma triglycerides levels correlated inversely with seasonal changes in vitamin D status. Conclusion. Our data do not support a pharmacological effect of statins on vitamin D status, but do suggest that vitamin D may influence plasma lipid profile and thus be of importance to cardiovascular health.

Vitamin D and the vasculature: can we teach an old drug new tricks?

BACKGROUND

Vitamin D is a steroid hormone known for its role in regulating levels of calcium and phosphorus. Vitamin D has important autocrine/paracrine roles and it is involved in vascular biology. Clinical studies have shown a relationship between vitamin D levels and cardiovascular health, and low levels of vitamin D metabolites have been associated with higher incidence of congestive heart failure and increases in mortality.

OBJECTIVE

To summarise the effect of vitamin D on cardiovascular pathology, the leading cause of death in chronic kidney disease patients.

CONCLUSIONS

All results indicate a potential effect of vitamin D on cardiovascular health. Therefore, maintaining optimum levels of circulating vitamin D is critical for a healthy cardiovascular system. In patients with low vitamin D status, like renal patients, supplementation with vitamin D metabolites has shown beneficial cardiovascular effects.

Vitamin D and human health: lessons from vitamin D receptor null mice

The vitamin D endocrine system is essential for calcium and bone homeostasis. The precise mode of action and the full spectrum of activities of the vitamin D hormone, 1,25-dihydroxyvitamin D [1,25-(OH)(2)D], can now be better evaluated by critical analysis of mice with engineered deletion of the vitamin D receptor (VDR). Absence of a functional VDR or the key activating enzyme, 25-OHD-1alpha-hydroxylase (CYP27B1), in mice creates a bone and growth plate phenotype that mimics humans with the same congenital disease or severe vitamin D deficiency. The intestine is the key target for the VDR because high calcium intake, or selective VDR rescue in the intestine, restores a normal bone and growth plate phenotype. The VDR is nearly ubiquitously expressed, and almost all cells respond to 1,25-(OH)(2)D exposure; about 3% of the mouse or human genome is regulated, directly and/or indirectly, by the vitamin D endocrine system, suggesting a more widespread function. VDR-deficient mice, but not vitamin D- or 1alpha-hydroxylase-deficient mice, and man develop total alopecia, indicating that the function of the VDR and its ligand is not fully overlapping. The immune system of VDR- or vitamin D-deficient mice is grossly normal but shows increased sensitivity to autoimmune diseases such as inflammatory bowel disease or type 1 diabetes after exposure to predisposing factors. VDR-deficient mice do not have a spontaneous increase in cancer but are more prone to oncogene- or chemocarcinogen-induced tumors. They also develop high renin hypertension, cardiac hypertrophy, and increased thrombogenicity. Vitamin D deficiency in humans is associated with increased prevalence of diseases, as predicted by the VDR null phenotype. Prospective vitamin D supplementation studies with multiple noncalcemic endpoints are needed to define the benefits of an optimal vitamin D status.

Race, gender, and socioeconomic disparities in CKD in the United States

Chronic kidney disease (CKD) is a national public health problem beset by inequities in incidence, prevalence, and complications across gender, race/ethnicity, and socioeconomic status. As health care providers, we can directly address some factors crucial for closing the disparities gap. Other factors are seemingly beyond our reach, entrenched within the fabric of our society, such as social injustice and human indifference. Paradoxically, the existence of health inequities provides unique, unrecognized opportunities for understanding biologic, environmental, sociocultural, and health care system factors that can lead to improved clinical outcomes. Several recent reports documented that structured medical care systems can reduce many CKD-related disparities and improve patient outcomes. Can the moral imperative to eliminate CKD inequities inspire the nephrology community not only to advocate for but also to demand high-quality, structured health care delivery systems for all Americans in the context of social reform that improves the ecology, health, and well-being of our communities? If so, then perhaps we can eliminate the unacceptable premature morbidity and mortality associated with CKD and the tragedy of health inequities. By so doing, we could become global leaders not only in medical technology, as we currently are, but also in health promotion and disease prevention, truly leaving no patient behind.

Elevated phosphorus modulates vitamin D receptor-mediated gene expression in human vascular smooth muscle cells

Clinical observations show that an increase in serum inorganic phosphorus (Pi) is linked to higher cardiovascular (CV) mortality, while vitamin D receptor (VDR) agonist therapy is associated with survival benefit in stage 5 chronic kidney disease. Smooth muscle cells (SMCs) play an important role in CV pathophysiology, but the interaction between Pi and the VDR signaling pathway in SMCs is not known. Real-time RT-PCR studies revealed that elevated Pi (2.06 mM) modulated VDR-mediated regulation of a panel of genes including thrombomodulin and osteopontin in SMCs. DNA microarray results demonstrated that increasing Pi from 0.9 to 2.06 mM exerted a widespread modulating effect on VDR-mediated gene expression. A total of 325 target genes were affected by paricalcitol at 0.9 mM Pi, with 195 up- and 130 downregulated. The number of target genes affected by paricalcitol at 2.06 mM Pi decreased to 86, with 55 up- and 31 downregulated. VDR-mediated gene expression in As4.1 cells (a juxtaglomerular cell-like cell line derived from kidney tumors in SV40 T-antigen transgenic mice) and peroxisome proliferator-activated receptor (PPAR)gamma-mediated gene expression in SMCs were also altered by elevated Pi, suggesting that the observation is not unique to VDR in SMCs. Mechanism analysis showed that elevated Pi had no significant effect on VDR or PPARgamma protein level but altered the cytosolic vs. nuclear distribution of NF-kappaB or nuclear receptor corepressor 1 (NCoR1). Our results demonstrate for the first time that elevated Pi affects VDR-mediated gene expression in human coronary artery SMCs and the effect is not limited to VDR in SMCs.