The selective vitamin D receptor activator for albuminuria lowering (VITAL) study: study design and baseline characteristics

The Emerging Role of Vitamin D and Vitamin D Receptor in Diabetic Nephropathy

Diabetic nephropathy (DN), one of the most common and severe microvascular complications of diabetes mellitus (DM), is an important risk factor for DM patient's death. Nowadays, DN has become the leading cause of end-stage renal disease (ESRD) in most countries without effective therapeutic methods. Recently, the renoprotective effects mediated by vitamin D (VD) and vitamin D receptor (VDR) have been evidenced. VD, a kind of steroid with the active form 1,25(OH)₂D₃, has been known for the crucial roles in the modulation of serum calcium and phosphorus concentrations. It exerts important functions by binding with its receptor VDR.VDR, a transcription factor located at chromosome 12 containing 9 exons, is one of the nonsteroid nuclear hormone receptor superfamily, which participates in transcriptional regulation of genes in tissue- and cell-specific ways. Increasing evidences have demonstrated that VD/VDR signaling pathway possesses a variety of kidney-protective effects in DN patients, such as antiproteinuria, antifibrosis, anti-inflammatory, and preventing podocyte damage. Although there are many studies on the role of the VD/VDR signaling pathway in DN, the effects and mechanisms still need to be further explained. This review summarized the multiple roles of VD/VDR in podocyte injury, tubule lesions, interstitial fibrosis, and inflammation, as well as the clinical applications about DN to explore much more and effective therapeutic methods for DN.

Present and future in the treatment of diabetic kidney disease

Diabetic kidney disease is the leading cause of end-stage renal disease. Albuminuria is recognized as the most important prognostic factor for chronic kidney disease progression. For this reason, blockade of renin-angiotensin system remains the main recommended strategy, with either angiotensin converting enzyme inhibitors or angiotensin II receptor blockers. However, other antiproteinuric treatments have begun to be studied, such as direct renin inhibitors or aldosterone blockers. Beyond antiproteinuric treatments, other drugs such as pentoxifylline or bardoxolone have yielded conflicting results. Finally, alternative pathogenic pathways are being explored, and emerging therapies including antifibrotic agents, endothelin receptor antagonists, or transcription factors show promising results. The aim of this review is to explain the advances in newer agents to treat diabetic kidney disease, along with the background of the renin-angiotensin system blockade.

Effects of paricalcitol on calcium and phosphate metabolism and markers of bone health in patients with diabetic nephropathy: results of the VITAL study

Background

Chronic kidney disease (CKD) is associated with elevations in serum phosphate, calcium–phosphorus product and bone-specific alkaline phosphatase (BAP), with attendant risks of cardiovascular and bone disorders. Active vitamin D can suppress parathyroid hormone (PTH), but may raise serum calcium and phosphate concentrations. Paricalcitol, a selective vitamin D activator, suppressed PTH in CKD patients (stages 3 and 4) with secondary hyperparathyroidism (SHPT) with minimal changes in calcium and phosphate metabolism.

Methods

The VITAL study enrolled patients with CKD stages 2–4. We examined the effect and relationship of paricalcitol to calcium and phosphate metabolism and bone markers in a post hoc analysis of VITAL. The study comprised patients with diabetic nephropathy enrolled in a double-blind, placebo-controlled, randomized trial of paricalcitol (1 or 2 μg/day). Urinary and serum calcium and phosphate, serum BAP, and intact PTH (iPTH) concentrations were measured throughout the study.

Results

Baseline demographics and calcium, phosphate, PTH (49% with iPTH <70 pg/mL), and BAP concentrations were similar between groups. A transient, modest yet significant increase in phosphate was observed for paricalcitol 2 μg/day (+0.29 mg/dL; P < 0.001). Dose-dependent increases in serum and urinary calcium were observed; however, there were few cases of hypercalcemia: one in the 1-μg/day group (1.1%) and three in the 2-μg/day group (3.2%). Significant reductions in BAP were observed that persisted for 60 days after paricalcitol discontinuation (P < 0.001 for combined paricalcitol groups versus placebo). Paricalcitol dose-dependent reductions in iPTH were observed. Paricalcitol in CKD patients (±SHPT) was associated with modest increases in calcium and phosphate.

Conclusion

Paricalcitol reduces BAP levels, which may be beneficial for reducing vascular calcification.

Trial registration

Trial is registered with ClinicalTrials.gov, number NCT00421733.

Effect of acute and chronic vitamin D administration on systemic renin angiotensin system in essential hypertensives and controls

AIM

To investigate the systemic renin-angiotensin system (RAS) in essential hypertensives (EH) and controls (C) after short- and long-term vitamin D receptor activation.

DESIGN

Ten consecutive EH (under controlled low-salt diet) and 10 C underwent calcitriol administration (0.25 μg bid) for 1 week (Group A). Eighteen consecutive EH under angiotensin II receptor antagonist therapy received a single oral dose of 300,000 IU of cholecalciferol and were followed up for 8 weeks (Group B).

METHODS

In basal conditions and at the end of the study (1 week in Group A and 8 weeks in Group B), plasma renin activity (PRA), plasma active renin, aldosterone, and angiotensin II were evaluated, as well as blood pressure, plasma 25-hydroxyvitamin D [25(OH)D], 1,25-dihydroxyvitamin D [1,25(OH)2D], and PTH.

RESULTS

In Group A, plasma 25(OH)D levels in EH and C were below the normal range, although lower levels were found in the former. No association between basal plasma 25(OH)D or 1,25(OH)2D levels and blood pressure values or RAS components was observed either in the whole group or in the two subgroups. Calcitriol administration did not affect any RAS parameter either in EH or in C. In Group B, cholecalciferol significantly increased 25(OH)D and 1,25(OH)2D levels without interfering with the angiotensin II receptor antagonist-induced increase in RAS components. No correlation was found between plasma 25(OH)D or 1,25(OH)2D levels and blood pressure values or RAS parameters before and after cholecalciferol administration.

CONCLUSIONS

The present data suggest that, in our experimental conditions, vitamin D receptor activation is unable to influence systemic RAS activity.

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.

Meta-analysis: the efficacy and safety of paricalcitol for the treatment of secondary hyperparathyroidism and proteinuria in chronic kidney disease

Introduction. Previous studies have demonstrated the safety and efficacy of using Paricalcitol for the treatment of secondary hyperparathyroidism (SHPT) in patients on dialysis. The aim of the current meta-analysis was to assess the safety and efficacy of Paricalcitol for the management of SHPT in patients with chronic kidney disease (CKD) not yet on dialysis. A secondary aim was to determine if sufficient data was available to assess the effect of Paricalcitol for the management of proteinuria. Methods. A meta-analysis was conducted using the Cochrane Collaboration's RevMan 4.2 software. Results. Paricalcitol is effective in lowering PTH in patients with CKD not yet on dialysis and is also effective in lowering proteinuria in diabetic CKD patients. However, we uncovered a safety signal identifying an elevated calcium phosphate product and a trend towards the development of hypercalcemia. A phosphate elevation was not demonstrated because the target used in the clinical studies was a P > 5.5 mg/dl, a value appropriate for dialysis patients and not CKD patients. Conclusion. Although Paricalcitol is effective in lowering PTH, we advise caution in the use of any active Vitamin D analogues in patients with CKD because of the potential risk of exacerbating vascular calcification.

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.

Two thioredoxin reductases, trxr-1 and trxr-2, have differential physiological roles in Caenorhabditis elegans

Thioredoxin reductase (TrxR) is a member of the pyridine nucleotide-disulfide reductase family, which mainly functions in the thioredoxin system. TrxR is found in all living organisms and exists in two major ubiquitous isoenzymes in higher eukaryotic cells; One is cytosolic and the other mitochondrial. Mitochondrial TrxR functions to protect mitochondria from oxidative stress, where reactive oxidative species are mainly generated, while cytosolic TrxR plays a role to maintain optimal oxido-reductive status in cytosol. In this study, we report differential physiological functions of these two TrxRs in C. elegans. trxr-1, the cytosolic TrxR, is highly expressed in pharynx, vulva and intestine, whereas trxr-2, the mitochondrial TrxR, is mainly expressed in pharyngeal and body wall muscles. Deficiency of the non-selenoprotein trxr-2 caused defects in longevity and delayed development under stress conditions, while deletion mutation of the selenoprotein trxr-1 resulted in interference in acidification of lysosomal compartment in intestine. Interestingly, the acidification defect of trxr-1(jh143) deletion mutant was rescued, not only by selenocystein-containing wild type TRXR-1, but also cysteine-substituted mutant TRXR-1. Both trxr-1 and trxr-2 were up-regulated when worms were challenged by environmental stress such as heat shock. These results suggest that trxr-1 and trxr-2 function differently at organismal level presumably by their differential sub-cellular localization in C. elegans.

The kidney in type 2 diabetes therapy

Renal and cardiovascular complications make type 2 diabetes one of the most morbid conditions in medicine. The kidney frequently gets involved in this "multi-organ disease". Of the large proportion of patients who progress with further loss of renal function, most prematurely die or end up in dialysis. Many interventions have targeted a decelerated progression of renal function loss, including metabolic control, blood pressure, and lipid management. Recently, modulation of the renin-angiotensin-aldosterone-system (RAAS) have been combined with the existing therapeutic armamentarium. RAAS inhibitors lower blood pressure and decrease albuminuria which leads to additionally protective renal and cardiovascular effects. Although this has been the success story of the last two decades, it has still made a relatively small contribution to patient welfare, since the residual risk in patients that received this optimal care remains extremely high. New treatment strategies are required that further slow the progression of renal and cardiovascular functions. Recently, several pathways have been investigated, targeting traditional risk factors such as blood pressure- and lipid-lowering strategies with unexpected results. Furthermore, novel targets and drugs have been identified. Preliminary studies on surrogate markers for renal outcome show a great potential for additive renal protection, such that in many cases hard endpoint trials are initiated. Novel interventions, which are reviewed here, include vitamin D receptor activators, RAASi with direct renin inhibitors or aldosterone antagonists, endothelin-antagonist, inflammation suppression with pentoxyfillin, MCP-1 synthesis inhibitors, or with Nrf2 agonists. Despite the current depressing situation of type 2 diabetic patients with nephropathy, new treatment options are under development to reduce the high morbidity and mortality associated with this universal ever-increasing disease threat.

Short-term vitamin D receptor activation increases serum creatinine due to increased production with no effect on the glomerular filtration rate

Vitamin D receptor activation has been associated with increased serum creatinine and reduced estimated glomerular filtration rates, raising concerns that its use may be detrimental to kidney function. Here we studied the effect of vitamin D receptor activation on serum creatinine, creatinine generation, and its clearance. We measured baseline serum creatinine and 24-h urine creatinine in 16 patients with chronic kidney disease. The measurements were repeated every day for 7 days, during which time the patients received 2 μg paricalcitol, an orally active vitamin D receptor activator, every morning. At 4 days after stopping the vitamin analog, measurements were continued for 3 days. Geometric mean parathyroid hormone levels decreased from 77 pg/ml at baseline to 43 pg/ml at the end of treatment and significantly rebounded to 87 pg/ml following paricalcitol withdrawal, thereby supporting the biological efficacy of the analog dose used. With this therapy, the serum creatinine significantly increased at a rate of 0.010 mg/dl/day and urine creatinine at a rate of 17.6 mg/day. Creatinine and iothalamate clearances did not change, whereas urine albumin decreased insignificantly. Thus, short-term vitamin D receptor activation increases creatinine generation and serum creatinine, but it does not influence the glomerular filtration rate.

Selective vitamin D receptor activation with paricalcitol for reduction of albuminuria in patients with type 2 diabetes (VITAL study): a randomised controlled trial

BACKGROUND

Despite treatment with renin–angiotensin–aldosterone system (RAAS) inhibitors, patients with diabetes have increased risk of progressive renal failure that correlates with albuminuria. We aimed to assess whether paricalcitol could be used to reduce albuminuria in patients with diabetic nephropathy.

METHODS

In this multinational, placebo-controlled, double-blind trial, we enrolled patients with type 2 diabetes and albuminuria who were receiving angiotensin-converting enzyme inhibitors or angiotensin receptor blockers. Patients were assigned (1:1:1) by computer-generated randomisation sequence to receive 24 weeks’ treatment with placebo,1 μg/day paricalcitol, or 2 μg/day paricalcitol. The primary endpoint was the percentage change in geometric mean urinary albumin-to-creatinine ratio (UACR) from baseline to last measurement during treatment for the combined paricalcitol groups versus the placebo group. Analysis was by intention to treat. This trial is registered with ClinicalTrials.gov, number NCT00421733.

FINDINGS

Between February, 2007, and October, 2008, 281 patients were enrolled and assigned to receive placebo(n=93), 1 μg paricalcitol (n=93), or 2 μg paricalcitol (n=95); 88 patients on placebo, 92 on 1 μg paricalcitol, and 92 on2 μg paricalcitol received at least one dose of study drug, and had UACR data at baseline and at least one timepoint during treatment, and so were included in the primary analysis. Change in UACR was: –3% (from 61 to 60 mg/mmol;95% CI –16 to 13) in the placebo group; –16% (from 62 to 51 mg/mmol; –24 to –9) in the combined paricalcitol groups, with a between-group difference versus placebo of –15% (95% CI –28 to 1; p=0.071); –14% (from 63 to 54 mg/mmol; –24 to –1) in the 1 μg paricalcitol group, with a between-group difference versus placebo of –11%(95% CI –27 to 8; p=0.23); and –20% (from 61 to 49 mg/mmol; –30 to –8) in the 2 μg paricalcitol group, with a between-group difference versus placebo of –18% (95% CI –32 to 0; p=0.053). Patients on 2 μg paricalcitol showed a nearly, sustained reduction in UACR, ranging from –18% to –28% (p=0.014 vs placebo). Incidence of hypercalcaemia,adverse events, and serious adverse events was similar between groups receiving paricalcitol versus placebo.

INTERPRETATION

Addition of 2 μg/day paricalcitol to RAAS inhibition safely lowers residual albuminuria in patients with diabetic nephropathy, and could be a novel approach to lower residual renal risk in diabetes.

FUNDING

Abbott.

Vitamin D levels and mortality in type 2 diabetes

OBJECTIVE

To evaluate vitamin D as a predictor of all-cause and cardiovascular mortality and risk of progression to micro- or macroalbuminuria in type 2 diabetic patients.

RESEARCH DESIGN AND METHODS

In a longitudinal observational follow-up study, 289 type 2 diabetic patients with normoalbuminuria (n = 172), microalbuminuria (n = 73), and macroalbuminuria (n = 44) at baseline were followed for a median (range) of 15.0 (0.2-23) years. Mean ± SD age was 54 ± 9 years. Plasma 25-hydroxyvitamin D(3) levels were determined by high-performance liquid chromatography/tandem mass spectrometry on baseline samples. Severe vitamin D deficiency was defined as the lower 10th percentile (<13.9 nmol/l).

RESULTS

Median (range) vitamin D level was 35.7 (5-136.7) nmol/l. Vitamin D levels were not associated with age, sex, estimated glomerular filtration rate, urinary albumin excretion rate (UAER), or A1C at baseline, but low levels were weakly associated with elevated systolic blood pressure (R = 0.13, P = 0.03). During follow-up, 196 (68%) patients died. All-cause mortality was increased in patients with severe vitamin D deficiency (hazard ratio 1.96 [95% CI 1.29-2.98]). The association persisted after adjustment for UAER, A1C, diabetes duration, and conventional cardiovascular risk factors (2.03 [1.31-3.13]). Severe vitamin D deficiency was associated with increased cardiovascular mortality (1.95 [1.11-3.44]), and the association persisted after adjustment (1.90 [1.15-3.10]). Severe vitamin D deficiency at baseline did not predict progression to micro- or macroalbuminuria.

CONCLUSIONS

In type 2 diabetic patients, severe vitamin D deficiency predicts increased risk of all-cause and cardiovascular mortality, independent of UAER and conventional cardiovascular risk factors. Whether vitamin D substitution improves prognosis remains to be investigated.

Vitamin D deficiency, inflammation, and albuminuria in chronic kidney disease: complex interactions

OBJECTIVE

Vitamin D may promote cardiovascular health in general population and in chronic kidney disease (CKD) through inhibition of the renin-angiotensin system and anti-inflammatory effects. Although proteinuria is a marker of kidney and cardiovascular disease, few studies have examined vitamin D levels, inflammation, and proteinuria simultaneously in CKD. We evaluated the relationship between calcidiol (25D), calcitriol (1,25D), inflammation, and albuminuria in Study of Early Evaluation of Kidney Disease, a multicenter CKD cohort.

DESIGN

A cross-sectional study was carried out.

PARTICIPANTS

A total of 1,847 participants were studied, of which 387 were randomly selected for inflammatory biomarker assessment. PREDICTORS AND OUTCOMES: The primary predictors were 25D and 1,25D. The outcome was albuminuria (urine albumin to creatinine ratio [UACR]: >30 mg/g).

RESULTS

Albuminuric patients were more likely to have decreased 25D and 1,25D levels and higher interleukin-6 (IL-6) levels compared with normoalbuminuric patients. The lowest tertiles of 25D and 1,25D were associated with 2 to 3 times increased odds of albuminuria compared with the highest tertiles when adjusted for age, gender, race, systolic blood pressure, and diabetes (OR for 25D: 3.0; 95% CI: 1.3 to 7.0; OR for 1,25D: 2.6; 95% CI: 1.7 to 3.9). In analogous linear regression models, 25D and 1,25D were significantly associated with log UACR (P < .0001, for both). In participants for whom inflammatory markers were measured, demographics-adjusted linear regression models that included IL-6 described attenuation of the relationship between 25D, 1,25D, and UACR.

CONCLUSIONS

Low 25D and 1,25D levels are independently associated with albuminuria. IL-6 may be an important intermediary between vitamin D deficiency and albuminuria, or vitamin D deficiency may contribute to inflammation and subsequent albuminuria.

Globotriaosylsphingosine actions on human glomerular podocytes: implications for Fabry nephropathy

BACKGROUND

Transforming growth factor-β1 (TGF-β1) and the macrophage inhibitory factor receptor CD74 link the metabolic disorder with tissue injury in diabetic nephropathy. Fabry disease is an X-linked lysosomal glycosphingolipid storage disorder resulting from a deficient activity of α-galactosidase A that leads to proteinuric renal injury. However, the link between the metabolic abnormality and renal injury is poorly characterized. Globotriaosylsphingosine (lyso-Gb3) was recently identified as a bioactive molecule accumulating in Fabry disease. We hypothesized that lyso-Gb3 could modulate the release of secondary mediators of injury in glomerular podocytes and that recently described nephroprotective actions of vitamin D receptor activation in diabetic nephropathy may apply to lyso-Gb3.

METHODS

Real time RT-PCR, ELISA and Western blot were used to study the biological activity of lyso-Gb3 in cultured human podocytes and potential modulation by vitamin D receptor activation.

RESULTS

In human podocytes, lyso-Gb3 dose and time dependently increased the expression of TGF-β1, extracellular matrix proteins (fibronectin and type IV collagen) and CD74. TGF-β1 mediated lyso-Gb3 effects on extracellular matrix production. Vitamin D receptor activation with paricalcitol or calcitriol prevented the increase in TGF-β1, CD74 and extracellular matrix induced by lyso-Gb3.

CONCLUSIONS

Lyso-Gb3 may have a role in glomerular injury in Fabry disease by promoting the release of secondary mediators of glomerular injury common to diabetic nephropathy. These effects are prevented by paricalcitol, raising the issue of vitamin D receptor activation as potential adjunctive therapy in Fabry nephropathy.

Nuclear hormone receptors in diabetic nephropathy

Diabetes is the leading cause of end-stage renal disease in developed countries. In spite of glucose and blood pressure control, for example by use of angiotensin II receptor blockers, diabetic nephropathy still develops and progresses in affected patients and the development of additional protective therapeutic interventions is, therefore, required. Nuclear hormone receptors are transcription factors that regulate carbohydrate metabolism, lipid metabolism, the immune response, and inflammation. These receptors also modulate the development of fibrosis. As a result of their diverse biological effects, nuclear hormone receptors have become major pharmaceutical targets for the treatment of a host of diseases. The increasing prevalence of diabetic nephropathy has led intense investigation into the role that nuclear hormone receptors may have in slowing or preventing the progression of renal disease. This role of nuclear hormone receptors would be associated with improvements in metabolism, the immune response, and inflammation. Eight nuclear receptors have shown a renoprotective effect in the context of diabetic nephropathy. This Review discusses the evidence regarding the beneficial effects of the activation of these receptors in preventing the progression of diabetic nephropathy and describes how the discovery and development of compounds that modulate the activity of nuclear hormone receptors may provide potential additional therapeutic approaches in the management of diabetic nephropathy.