A Novel Vitamin D Receptor Agonist, VS-105, Improves Bone Mineral Density without Affecting Serum Calcium in a Postmenopausal Osteoporosis Rat Model.

BACKGROUND AND OBJECTIVES: VS-105, a novel vitamin D receptor agonist with significantly less hypercalcemic side effects than calcitriol, is a useful tool to investigate whether or not a vitamin D receptor agonist at non-hypercalcemic doses could improve bone mineral density (BMD). METHODS: VS-105 and calcitriol were evaluated in an ovariectomized (OVX) osteoporosis rat model and in calvariae bone organ culture. RESULTS: Treatment of OVX rats by VS-105 (0.1, 0.2 or 0.5 µg/kg, intraperitoneal, 3×/week, for 90 days) significantly improved BMD in the L3 lumbar vertebra in a dose-dependent manner (sham vs. OVX/vehicle: 324 ± 14 vs. 279 ± 10 mg/cm2; VS-105 at 0.1, 0.2 and 0.5 µg/kg: 306 ± 9, 329 ± 12, and 327 ± 10 mg/cm2, respectively) without affecting serum calcium (Ca). Calcitriol at 0.1 µg/kg significantly increased BMD but it also increased serum Ca. VS-105 and calcitriol at the test doses significantly suppressed serum parathyroid hormone and promoted tibia bone growth. With respect to biomarkers of bone remodeling, calcitriol and VS-105 both significantly elevated serum osteocalcin. In the calvariae bone organ culture, net Ca release was significantly less in VS-105-treated groups (vs. calcitriol). CONCLUSIONS: VS-105 is efficacious in improving BMD in a dose range that does not affect serum Ca in OVX rats; the improvement in BMD by VS-105 is attributable to increased osteoblastic activity and reduced osteoclastic bone resorption.

Vitamin D receptor agonist VS-105 directly modulates parathyroid hormone expression in human parathyroid cells and in 5/6 nephrectomized rats.

Vitamin D receptor (VDR) agonists (VDRAs) are commonly used to treat secondary hyperparathyroidism (SHPT) associated with chronic kidney disease (CKD). Current VDRA therapy often causes hypercalcemia, which is a critical risk for vascular calcification. Previously we have shown that a novel VDRA, VS-105, effectively suppresses serum parathyroid hormone (PTH) without affecting serum calcium levels in 5/6 nephrectomized (NX) uremic rats. However, it is not known whether VS-105 directly regulates PTH gene expression. To study the direct effect of VS-105 on modulating PTH, we tested VS-105 and paricalcitol in the spheroid culture of parathyroid cells from human SHPT patients, and examined the time-dependent effect of the compounds on regulating serum PTH in 5/6 NX uremic rats (i.p. 3x/week for 14days). In human parathyroid cells, VS-105 (100nM) down-regulated PTH mRNA expression (to 3.6% of control) and reduced secreted PTH (to 43.9% of control); paricalcitol was less effective. VS-105 effectively up-regulated the expression of VDR (1.9-fold of control) and CaSR (1.8-fold of control) in spheroids; paricalcitol was also less effective. In 5/6 NX rats, one single dose of 0.05-0.2µg/kg of VS-105 or 0.02-0.04µg/kg of paricalcitol effectively reduced serum PTH by >40% on Day 2. Serum PTH remained suppressed during the dosing period, but tended to rebound in the paricalcitol groups. These data indicate that VS-105 exerts a rapid effect on suppressing serum PTH, directly down-regulates the PTH gene, and modulates PTH, VDR and CaSR gene expression more effectively than paricalcitol.

Preclinical studies of VS-505: a non-absorbable highly effective phosphate binder.

BACKGROUND AND PURPOSE: Phosphate imbalance is often present in chronic kidney disease (CKD), and it contributes to a higher cardiovascular mortality rate. A phosphate binder is typically part of a treatment strategy for controlling phosphate imbalance. However, safety concerns and low compliance are two well-recognized disadvantages of on-market phosphate binders. This report describes the preclinical studies of VS-505, a non-absorbable, calcium- and aluminum-free, plant-derived polymer currently being evaluated in haemodialysis patients in Australia. EXPERIMENTAL APPROACH: Normal Sprague Dawley (SD) rats or uraemic SD rats induced by 5/6 nephrectomy fed a high-phosphate diet were treated with VS-505 or sevelamer (0.05-10% in food) for 5 and 28 days respectively. KEY RESULTS: Urinary and serum phosphate levels were significantly elevated in untreated rats, and were decreased by VS-505 and sevelamer. VS-505 increased faecal phosphate levels in a dose-dependent manner. High-phosphate diet also caused an increase in serum FGF-23 and parathyroid hormone in nephrectomized (NX) rats, effects prevented by VS-505 or sevelamer. Significant aortic calcification was observed in NX rats treated with 5% sevelamer, whereas VS-505 at all doses tested did not show effects. VS-505 had no effects on small intestine histomorphology and intestinal sodium-dependent phosphate cotransporter gene expression. In vitro characterizations showed that VS-505 has a relatively high density and low expansion volume when exposed to simulated gastric fluid. CONCLUSIONS AND IMPLICATIONS: VS-505 is a safe and effective phosphate binder and may offer the advantage of having a reduced pill burden and minimal GI side effects for CKD patients.

Vitamin D receptor agonist VS-105 improves cardiac function in the presence of enalapril in 5/6 nephrectomized rats.

Vitamin D receptor (VDR) agonists (VDRAs) are commonly used to manage hyperparathyroidism secondary to chronic kidney disease (CKD). Patients with CKD experience extremely high risks of cardiovascular morbidity and mortality. Clinical observations show that VDRA therapy may be associated with cardio-renal protective and survival benefits in patients with CKD. The 5/6 nephrectomized (NX) Sprague-Dawley rat with established uremia exhibits elevated serum parathyroid hormone (PTH), hypertension, and abnormal cardiac function. Treatment of 5/6 NX rats with VS-105, a novel VDRA (0.05 and 0.5 µg/kg po by gavage), once daily for 8 wk in the presence or absence of enalapril (30 mg/kg po via drinking water) effectively suppressed serum PTH without raising serum calcium. VS-105 alone reduced systolic blood pressure (from 174 ± 6 to 145 ± 9 mmHg, P < 0.05) as effectively as enalapril (from 174 ± 6 to 144 ± 7 mmHg, P < 0.05). VS-105 improved cardiac functional parameters such as E/A ratio, ejection fraction, and fractional shortening with or without enalapril. Enalapril or VS-105 alone significantly reduced left ventricular hypertrophy (LVH); VS-105 plus enalapril did not further reduce LVH. VS-105 significantly reduced both cardiac and renal fibrosis. The lack of hypercalcemic toxicity of VS-105 is due to its lack of effects on stimulating intestinal calcium transport and inducing the expression of intestinal calcium transporter genes such as Calb3 and TRPV6. These studies demonstrate that VS-105 is a novel VDRA that may provide cardiovascular benefits via VDR activation. Clinical studies are required to confirm the cardiovascular benefits of VS-105 in CKD.

Different vitamin D receptor agonists exhibit differential effects on endothelial function and aortic gene expression in 5/6 nephrectomized rats.

Endothelial dysfunction, common in chronic kidney disease (CKD), significantly increases cardiovascular disease risk in CKD patients. This study investigates whether different vitamin D receptor agonists exhibit different effects on endothelial function and on aortic gene expression in an animal CKD model. The 5/6 nephrectomized (NX) rat was treated with or without alfacalcidol (0.02, 0.04 and 0.08µg/kg), paricalcitol (0.04 and 0.08µg/kg), or VS-105 (0.004, 0.01 and 0.16µg/kg). All three compounds at the test doses suppressed serum parathyroid hormone effectively. Alfacalcidol at 0.08µg/kg raised serum calcium significantly. Endothelial function was assessed by pre-contracting thoracic aortic rings with phenylephrine, followed by treatment with acetylcholine or sodium nitroprusside. Uremia significantly affected endothelial-dependent aortic relaxation, which was improved by all three compounds in a dose-dependent manner with alfacalcidol and paricalcitol exhibiting a lesser effect. DNA microarray analysis of aorta samples revealed that uremia impacted the expression of numerous aortic genes, many of which were normalized by the vitamin D analogs. Real-time RT-PCR analysis confirmed that selected genes such as Abra, Apoa4, Fabp2, Hsd17b2, and Hspa1b affected by uremia were normalized by the vitamin D analogs with alfacalcidol exhibiting less of an effect. These results demonstrate that different vitamin D analogs exhibit different effects on endothelial function and aortic gene expression in 5/6 NX rats. This article is part of a Special Issue entitled '17th Vitamin D Workshop'.

VS-501: A NOVEL, NON-ABSORBED, CALCIUM- AND ALUMINUM-FREE, HIGHLY EFFECTIVE PHOSPHATE BINDER DERIVED FROM NATURAL PLANT POLYMER.

Inadequate control of serum phosphate in chronic kidney disease can lead to pathologies of clinical importance. Effectiveness of on-market phosphate binders is limited by safety concerns and low compliance due to high pill size/burden and gastrointestinal discomfort. VS-501 is a non-absorbed, calcium- and aluminum-free, chemically-modified, plant-derived polymer. In vitro studies show that VS-501 has a high density and a low swell volume when exposed to simulated gastric fluid (vs. sevelamer). When male Sprague Dawley (SD) rats on normal diet were treated with VS-501 or sevelamer, serum phosphate was not significantly altered, but urinary phosphate levels decreased by >90%. VS-501 had no effect on serum calcium (Ca) or urinary Ca, while 3% sevelamer significantly increased serum and urine Ca. In 5/6 nephrectomized (NX) uremic SD rats on high-phosphate diet, increasing dietary phosphate led to an increase in serum and urine phosphate, which was prevented in rats treated with VS-501 or sevelamer (0.2-5% in food). High phosphate diet also increased serum FGF-23 and parathyroid hormone in 5/6 NX rats, which was prevented by VS-501 or sevelamer. VS-501 or sevelamer increased fecal phosphate in a dose-dependent manner. More aortic calcification was observed in 5/6 NX rats treated with 5% sevelamer, while VS-501 and sevelamer did not show significant effects on cardiac parameters, fibrosis, intestine histology and intestinal sodium-dependent phosphate cotransporter gene expression. These results suggest that VS-501 is effective in binding phosphate with no effects on calcium homeostasis, and may have improved pill burden and gastrointestinal side effects.

Mechanistic analysis for time-dependent effects of cinacalcet on serum calcium, phosphorus, and parathyroid hormone levels in 5/6 nephrectomized rats.

This study investigates the time-dependent effects of cinacalcet on serum calcium, phosphorus, and parathyroid hormone (PTH) levels in 5/6 nephrectomized (NX) rats with experimental chronic renal insufficiency. In this study, 5/6 NX male, Sprague-Dawley rats were treated with vehicle or cinacalcet (10 mg/kg, oral, 1× daily). On Day 0 (before treatment), Day 12 and 13 after treatment (to approximate the clinical practice), and also at 0, 1, 4, 8, 16, and 24 hours after the last dosing, blood was collected for analysis. After 12 or 13 days of cinacalcet treatment, modest changes were observed in serum Ca and phosphorus (Pi), while PTH decreased by >45% to Sham levels (152 ± 15 pg/mL). Detailed mapping found that cinacalcet caused a significant time-dependent decrease in serum Ca following dosing, reaching a lowest point at 8 hours (decrease by 20% to 8.43 ± 0.37 mg/dL), and then returning to normal at 24 hours. Cinacalcet also caused a significant increase in serum Pi levels (by 18%). To investigate the potential mechanism of action, a broad approach was taken by testing cinacalcet in a panel of 77 protein-binding assays. Cinacalcet interacted with several channels, transporters, and neurotransmitter receptors, some of which are involved in brain and heart, and may impact Ca homeostasis. Cinacalcet dose-dependently increased brain natriuretic peptide (BNP) mRNA expression by 48% in cardiomyocytes, but had no significant effects on left ventricular hypertrophy and cardiac function. The results suggest that cinacalcet's hypocalcemic effect may be due to its nonspecific interaction with other receptors in brain and heart.

Synthesis of VS-105: A novel and potent vitamin D receptor agonist with reduced hypercalcemic effects.

We have synthesized a novel vitamin D receptor agonist VS-105 ((1R,3R)-5-((E)-2-((3αS,7αS)-1-((R)-1-((S)-3-hydroxy-2,3-dimethylbutoxy)ethyl)-7α-methyldihydro-1H-inden-4(2H,5H,6H,7H,7αH)-ylidene)ethylidene)-2-methylenecyclohexane-1,3-diol). Preparation of a-ring phenylphosphine oxide 11, followed by Wittig-Horner coupling of 11 with the protected 25-hydroxy Grundmann's ketone 22 generated the precursor 12. Deprotection of the TBDMS groups of 12 produced the target compound VS-105. The biological profiles of VS-105 were evaluated using in vitro assays (VDR receptor binding, VDR reporter gene and HL-60 differentiation) in comparison to calcitriol (the endogenous hormone) or paricalcitol. Furthermore, the PTH suppressing potency and hypercalcemic side effects of VS-105 were evaluated in the 5/6 nephrectomized uremic rats in comparison to paricalcitol. Combining various changes at 20-epi, 22-oxa, 24-methyl, and 2-methylene yielded VS-105 that not only is highly potent in inducing functional responses in vitro, but also effectively suppresses PTH in a dose range that does not affect serum calcium in the 5/6 nephrectomized uremic rats.

Two novel vitamin D receptor modulators with similar structures exhibit different hypercalcemic effects in 5/6 nephrectomized uremic rats.

BACKGROUND/AIMS: Vitamin D receptor modulators (VDRMs) are indicated for secondary hyperparathyroidism in chronic kidney disease (CKD). Clinical observations demonstrate that VDRM therapy provides cardiovascular (CV) benefit in CKD. Current on-market VDRMs have a narrow therapeutic index at 1- to 4-fold [hypercalcemic toxicity vs. parathyroid hormone (PTH)-suppressing efficacy]. Hypercalcemia leads to the need for frequent drug dose titration and serum calcium (Ca) monitoring. A VDRM with a wider therapeutic index and beneficial CV effects will be clinically useful. METHODS: Two structurally similar VDRMs were tested in the 5/6 nephrectomized (NX) rats with elevated PTH, endothelial dysfunction and left ventricular hypertrophy. RESULTS: VS-110 and VS-411 at 0.01-1 µg/kg (i.p. 3 times/week for 2 weeks) suppressed serum PTH effectively. VS-411 raised serum Ca with an 11% increase at 0.01 µg/kg (therapeutic index = ~1-fold), while VS-110 did not raise serum Ca even at 1 µg/kg (therapeutic index >50-fold). VS-110 improved endothelium-dependent aortic relaxation in a dose-dependent manner and significantly reduced left ventricular fibrosis without affecting serum Ca. VS-411 also exhibited effects on the CV parameters, but was less potent at the high doses with severe hypercalcemia. VS-110 and VS-411 specifically activated the reporter gene via a chimeric receptor containing the VDR ligand binding domain with EC(50) <0.1 nM. CONCLUSIONS: Structurally similar VDRMs can exhibit distinctly different hypercalcemic effects in 5/6 NX uremic rats. While differences exist for the Ca and CV effects of VS-110 and VS-411, the clinical implications are unclear. VS-110's results are promising but clinical outcome studies need to be performed.

Mapping the time-dependent effects of paricalcitol on serum calcium, phosphorus and parathyroid hormone levels in 5/6 nephrectomized uremic rats.

AIMS: To investigate whether the frequency of monitoring paricalcitol's impact on serum calcium (Ca), phosphorus and PTH in current clinical practice is sufficient by mapping the time-dependent effects of paricalcitol on these parameters. MAIN METHODS: The 5/6 nephrectomized (NX) male, Sprague-Dawley rats with established uremia were treated with vehicle or paricalcitol (0.16 µg/kg, i.p., 3×/week). On Day 0 (before treatment), Days 12 and 13 after treatment, and also at 0, 1, 4, 8, 16, 24 h after the last dosing, blood and small intestine samples were collected. KEY FINDINGS: Serum creatinine and blood urea nitrogen levels were significantly elevated in 5/6 NX rats. Significant increases were observed in serum Ca while PTH decreased by >90% when the parameters were determined at 12 or 13 days after paricalcitol dosing. Paricalcitol caused a step-wise increase in serum Ca levels at 1-24 h following dosing, reduced serum PTH levels with PTH values ranging from 1.06±0.06 to 26.7±25.7 pg/ml (vs. 152±15 pg/ml in Sham rats), but did not affect serum phosphorus in a time-dependent manner. Consistent with the serum Ca data, paricalcitol significantly induced the intestinal expression of Calb3 and TRPV6, genes involved in intestinal Ca transport, and also significantly induced the intestinal calcium absorption. SIGNIFICANCE: Our results suggest that the frequency of monitoring paricalcitol's effect on serum Ca, phosphorus and PTH in current clinical practice seems adequate. Additional clinical trials may be needed to resolve the inconsistent clinical observations about the impact of paricalcitol on serum Ca.

Vitamin D therapy in cardiac hypertrophy and heart failure.

Vitamin D3 is made in the skin, modified in the liver to form 25(OH)D, and then further hydroxylated in the kidney to form the active hormone, 1,25-dihydroxyvitamin D3 (calcitriol). Calcitriol binds to and activates the vitamin D receptor (VDR), a nuclear receptor, to regulate numerous downstream signaling pathways in different cells and tissues. Emerging evidence suggests that VDR plays an important role in modulating cardiovascular, immunological, metabolic and other functions. Data from preclinical, epidemiological and clinical studies have shown that deficiency in VDR activation is associated with an increased risk for cardiovascular disease (CVD). Results from interventional trials using either nutritional vitamin D or VDR agonists (VDRAs) support the idea that VDR activation is beneficial for improving the underlying factors of CVD such as hypertension, endothelial dysfunction, atherosclerosis, vascular calcification, cardiac hypertrophy and progressive renal dysfunction. Furthermore, a majority of chronic kidney disease (CKD) patients die of CVD and VDRA therapy is associated with a survival benefit in both pre-dialysis and dialysis CKD patients. Most of the studies measured serum 25(OH)D as an indication for vitamin D deficiency, which does not truly reflect the VDR activation status. Although VDR plays an important role in regulating cardiovascular function and VDRAs may be potentially useful for treating CVD, at present VDRAs are not indicated for the treatment of CVD.

VS-105: a novel vitamin D receptor modulator with cardiovascular protective effects.

BACKGROUND AND PURPOSE: Vitamin D receptor (VDR) modulators (VDRMs) such as calcitriol, paricalcitol and doxercalciferol are commonly used to manage hyperparathyroidism secondary to chronic kidney disease (CKD). CKD patients experience extremely high risks of cardiovascular morbidity and mortality. Clinical observations show that VDRM therapy may be associated with cardio-renal protective and survival benefits for CKD patients. However, hypercalcaemia remains a serious side effect for current VDRMs, which leads to the need for frequent dose titration and serum Ca (calcium) monitoring. Significant clinical benefits can be derived from a VDRM with cardiovascular protective effects without the hypercalcaemic liability. EXPERIMENTAL APPROACH: Male Sprague-Dawley rats were 5/6 nephrectomized and 6 weeks later, after they had established uraemia, elevated parathyroid hormone levels, endothelial dysfunction and left ventricular hypertrophy, the rats were treated with VS-105, a novel VDRM. The effects of VS-105 were also tested in cultured HL-60 cells. KEY RESULTS: VS-105 induced HL-60 cell differentiation with an EC50 value at 11.8 nM. Treatment (i.p., 3× a week over a period of 2 weeks) of the 5/6 nephrectomized rats by VS-105 (0.004-0.64 µg·kg⁻¹) effectively suppressed serum parathyroid hormone without raising serum Ca or phosphate levels. Furthermore, 2 weeks of treatment with VS-105 improved endothelium-dependent aortic relaxation and attenuated left ventricular abnormalities in a dose range that did not affect serum Ca levels. Similar results were obtained when VS-105 was administered i.p. or by oral gavage. CONCLUSIONS AND IMPLICATIONS: VS-105 exhibits an overall therapeutic product profile that supports expanded use in CKD to realize the cardiovascular protective effects of VDR activation.

Differential effects of vitamin d receptor agonists on gene expression in neonatal rat cardiomyocytes.

PURPOSE: Vitamin D receptor (VDR) activation is associated with cardiovascular benefits in chronic kidney disease patients, but whether VDR's hormone and prehormone exhibit similar effects requires more studies. METHODS: Neonatal rat cardiomyocytes were treated with VDR agonists (calcitriol and/or paricalcitol) and the prehormone calcidiol in the presence of aldo (1 µM). The expression of VDR target genes were determined by real-time PCR and Western blotting. The expression and activity of CYP27B1 (the enzyme responsible for converting calcidiol to calcitriol) was measured. RESULTS: Treating cells with aldo (1 µM) for 24 h significantly reduced the VDR mRNA (29%) and protein levels (>90%). Calcitriol and calcidiol induced VDR expression in the presence of aldo with EC(50) at 0.3 and 7,952 nM, respectively. Calcitriol, paricalcitol and calcidiol stimulated CYP24A1 (EC(50) at 6.4, 4.5 and 992 nM, respectively) and suppressed NPPB expression (IC(50) at 1.9, 0.1 and 210 nM, respectively) in the presence of 1 µM aldo. Neonatal rat cardiomyocytes expressed CYP27B1 and converted calcidiol to calcitriol at a low rate (~10% in 24 h). CONCLUSIONS: VDR hormone calcitriol and its analog paricalcitol exhibit more potent effects than the prehormone calcidiol in cardiomyocytes.

Comparison of the pharmacological effects of paricalcitol and doxercalciferol on the factors involved in mineral homeostasis.

Vitamin D receptor agonists (VDRAs) directly suppress parathyroid hormone (PTH) mRNA expression. Different VDRAs are known to have differential effects on serum calcium (Ca), which may also affect serum PTH levels since serum Ca regulates PTH secretion mediated by the Ca-sensing receptor (CaSR). In this study, we compared the effects of paricalcitol and doxercalciferol on regulating serum Ca and PTH, and also the expression of PTH, VDR, and CaSR mRNA. The 5/6 nephrectomized (NX) Sprague-Dawley rats on a normal or hyperphosphatemia-inducing diet were treated with vehicle, paricalcitol, or doxercalciferol for two weeks. Both drugs at the tested doses (0.042-0.33 mug/kg) suppressed PTH mRNA expression and serum PTH effectively in the 5/6 NX rats, but paricalcitol was less potent in raising serum Ca than doxercalciferol. In pig parathyroid cells, paricalcitol and the active form of doxercalciferol induced VDR translocation from the cytoplasm into the nucleus, suppressed PTH mRNA expression and inhibited cell proliferation in a similar manner, although paricalcitol induced the expression of CaSR mRNA more effectively. The multiple effects of VDRAs on modulating serum Ca, parathyroid cell proliferation, and the expression of CaSR and PTH mRNA reflect the complex involvement of the vitamin D axis in regulating the mineral homeostasis system.

Vitamin d receptor activation mitigates the impact of uremia on endothelial function in the 5/6 nephrectomized rats.

Endothelial dysfunction increases cardiovascular disease risk in chronic kidney disease (CKD). This study investigates whether VDR activation affects endothelial function in CKD. The 5/6 nephrectomized (NX) rats with experimental chronic renal insufficiency were treated with or without paricalcitol, a VDR activator. Thoracic aortic rings were precontracted with phenylephrine and then treated with acetylcholine or sodium nitroprusside. Uremia significantly affected aortic relaxation (-50.0 +/- 7.4% in NX rats versus -96.2 +/- 5.3% in SHAM at 30 muM acetylcholine). The endothelial-dependent relaxation was improved to -58.2 +/- 6.0%, -77.5 +/- 7.3%, and -90.5 +/- 4.0% in NX rats treated with paricalcitol at 0.021, 0.042, and 0.083 mug/kg for two weeks, respectively, while paricalcitol at 0.042 mug/kg did not affect blood pressure and heart rate. Parathyroid hormone (PTH) suppression alone did not improve endothelial function since cinacalcet suppressed PTH without affecting endothelial-dependent vasorelaxation. N-omega-nitro-L-arginine methyl ester completely abolished the effect of paricalcitol on improving endothelial function. These results demonstrate that VDR activation improves endothelial function in CKD.

Are vitamin D receptor activators useful for the treatment of thrombosis?

Vitamin D3 is produced in the skin and modified in the liver and kidneys to form the active metabolite 1,25-dihydroxyvitamin D3 (calcitriol). Calcitriol binds to the vitamin D receptor (VDR), a nuclear receptor. The binding of calcitriol to the VDR activates the recruitment of cofactors that form a transcriptional complex that binds vitamin D response elements in the promoter region of target genes. During the past three decades, VDR research has focused mainly on the role of the receptor in the regulation of parathyroid hormone, intestinal calcium and phosphate absorption, and bone metabolism, and several VDR activators have been developed for the treatment of osteoporosis, psoriasis and hyperparathyroidism secondary to chronic kidney diseases. Emerging evidence suggests that VDR activators may be useful for treating cardiovascular, immunological, inflammatory and renal diseases. In addition, the VDR may have a role in modulating thrombogenicity. For example, VDR-/- mice display a phenotype of increased thrombogenic activity. VDR activators modulate the expression of various factors involved in thrombogenicity. Calcitriol was demonstrated to reduce the rate of oncology-related thrombosis in a clinical trial. This review discusses evidence from preclinical and clinical studies to investigate the potential role of VDR in thrombogenicity, and assesses whether VDR activators can be useful in the treatment of thrombosis.

Endothelial dysfunction and chronic kidney disease: treatment options.

Endothelial cells detect physical and chemical changes in the blood vessels, and release various factors to counter these changes to maintain homeostasis. Traditional cardiovascular disease risk factors, such as hypertension, dyslipidemia and diabetes, cause endothelial dysfunction characterized by off-balanced vasodilation/vasoconstriction, increased oxidative stress and inflammation, deregulation of thrombosis and fibrinolysis, abnormal smooth muscle cell proliferation, and a deficient repair mechanism. Patients with chronic kidney disease (CKD) have a much higher risk of cardiovascular disease and mortality than the general population. Endothelial dysfunction is commonly observed in CKD, likely preceding other cardiovascular complications. Lipid-lowering agents, such as statins, improve endothelial functions and are effective in reducing cardiovascular disease risk in the general population, but have not demonstrated comparable efficacy in the CKD patient population. Similarly, antidiabetic agents, such as thiazolidinediones, that improve endothelial function in the general population are less efficacious than expected in slowing disease progression and reducing cardiovascular disease risk in CKD patients. Interestingly, agents that activate the vitamin D receptor (VDR) for the treatment of hyperparathyroidism secondary to CKD are associated with a survival benefit in CKD patients that is likely mediated through the effects of the VDR on modulating key components involved in endothelial dysfunction. However, a randomized, clinical study is required to confirm the survival benefit of VDR activation therapy for CKD patients. Results from clinical studies suggest that managing hypertension alone may not be adequate in slowing CKD progression and its related cardiovascular complications. Angiotensin-converting enzyme inhibitors and angiotensin receptor blockers that target the renin-angiotensin system slow CKD progression, possibly due to their effects on improving endothelial function, independent of controlling blood pressure.

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.

Differential inhibition of renin mRNA expression by paricalcitol and calcitriol in C57/BL6 mice.

BACKGROUND/AIMS: Vitamin D receptor activators (VDRAs) may suppress renin expression and VDR-mediated renin inhibitors may offer a novel mechanism to control the RAS. METHODS: We delineated the effects of paricalcitol and calcitriol on PTH, renin, and iCa(2+) in C57/BL6 mice administered vehicle, paricalcitol, or calcitriol (0.01, 0.03, 0.10, 0.33, 1.0 microg/kg s.c.) 3 days/week for 9 days. RESULTS: Paricalcitol produced PTH suppression from 0.03 to 1.0 microg/kg (values between 9.7 +/- 3.3 and 20.7 +/- 4.7 pg/ml; vehicle = 88.0 +/- 16.9) and elicited dose-dependent reductions in renin/GAPDH expression at 0.33 and 1.0 microg/kg (0.037 +/- 0.002, 0.027 +/- 0.003; vehicle = 0.054 +/- 0.003) but produced no increases iCa(2+) at any dose tested. Calcitrol produced PTH suppression at all doses tested (between 6.4 +/- 1.2 and 29.5 +/- 17.2 pg/ml) and renin suppression at 0.10, 0.33, and 1.0 microg/kg (0.029 +/- 0.002, 0.031 +/- 0.003, and 0.038 +/- 0.02). However, at 0.33 and 1.0 mg/kg, calcitriol produced increases iCa(2+) (1.31 +/- 0.03 and 1.48 +/- 0.02 mmol/l; vehicle = 1.23 +/- 0.02 mmol/l). CONCLUSIONS: Paricalcitol produces significant, dose-dependent suppression of renin expression in the absence of hypercalcemia at doses 10-fold above those necessary for PTH suppression. Calcitriol also produced suppression of renin at doses at least 10-fold above those required for PTH suppression, but increases in iCa(2+) were observed at doses only 3-fold above those necessary to elicit renin suppression.