Vitamin D slows the progression of chronic kidney disease. Furthermore, activators of vitamin D receptors (VDR) have suppressant effects on the renin-angiotensin system, as well as anti-inflammatory and antifibrotic actions. This study aimed to evaluate the cytoprotective effects of paricalcitol, a VDR activator, at the mitochondrial level using an obstructive nephropathy model [unilateral ureteral obstruction (UUO)]. Rats subjected to UUO and controls were treated daily with vehicle or paricalcitol. The control group underwent a sham surgery. The treatment was done for 15 days (30 ng/kg). The following were determined: biochemical parameters; fibrosis; apoptosis; mitochondrial morphology; VDR, AT(1) receptor, and NADPH oxidase 4 expression; and NADPH oxidase activity (in total and in mitochondrial fractions from the renal cortex). VDR activation prevented fibrosis (20 ± 5 vs. 60 ± 10%) and the number of TUNEL-positive apoptotic cells (10 ± 3 vs. 25 ± 4) in UUO. Biochemical, histological, and molecular studies suggest mitochondrial injury. Electron microscopy revealed in UUO electronically luminous material in the nucleus. Some mitochondria were increased in size and contained dilated crests and larger than normal spaces in their interiors. These changes were not present with paricalcitol treatment. Additionally, high AT(1)-receptor mRNA and NADPH activity was reverted in mitochondrial fractions from obstructed paricalcitol-treated animals (0.58 ± 0.06 vs. 0.95 ± 0.05 relative densitometry units and 9,000 ± 800 vs. 15,000 ± 1,000 relative fluorescence units·μg protein(-1)·min(-1), respectively). These changes were consistent with an improvement in VDR expression (0.75 ± 0.05 vs. 0.35 ± 0.04 relative densitometry units). These results suggest that paricalcitol confers a protective effect and reveal, as well, a possible AT(1) receptor-dependent protective effect that occurs at the mitochondrial level.

Previous hypertension studies have shown that low levels of vitamin D are linked to elevated renin-angiotensin system. The heat shock protein 70 regulates signaling pathways for cellular oxidative stress responses. Hsp70 has been shown to protect against angiotensin II-induced hypertension and exert a cytoprotective effect. Here, we wanted to evaluate whether the vitamin D receptor (VDR) associated with Hsp70/ AT 1 expression may be involved in the mechanism by which paricalcitol provides renal protection in spontaneously hypertensive rats (SHRs). One-month-old female SHRs were treated for 4 months with vehicle, paricalcitol, enalapril, or a combination of both paricalcitol and enalapril. The following were determined: blood pressure; biochemical parameters; fibrosis; apoptosis; mitochondrial morphology; and VDR, AT 1 receptor, and Hsp70 expression in the renal cortex. Blood pressure was markedly reduced by enalapril or the combination but not by paricalcitol alone. However, VDR activation, enalapril or combination, prevented fibrosis, the number of TUNEL-positive apoptotic cells, mitochondrial damage, and NADPH oxidase activity in SHRs. Additionally, high AT 1 receptor expression, like low Hsp70 expression (immunohistochemical/immunofluorescence studies), was reversed in the renal cortices of paricalcitol-and/or enalapriltreated animals (SHRs), and these changes were most marked in the combination therapy group. Finally, all of the recovery parameters were consistent with an improvement in VDR expression. Data suggest that Hsp70/AT 1 modulated by VDR is involved in the mechanism by which paricalcitol provides renal protection in SHRs. We propose that low AT 1 expression through VDR induction could be a consequence of the heat shock response Hsp70-mediated cell protection.

Background/Aims: Unilateral ureteric obstruction (UUO) in neonatal rodents can be used as a paradigm for in utero obstruction in humans and a platform for studying the potential of novel therapies for congenital obstructive nephropathy. The present study examined the effect of rosuvastatin (Ros) on key morphometric measures of renal injury and corresponding gene expression correlates following neonatal UUO in the rat. Methods: Neonatal rats subjected to UUO and controls were treated daily with vehicle or Ros for 14 days. Quantification of tubular dilatation, glomerular size and number and tubulointerstitial fibrotic area was performed and changes validated by reference to appropriate renal gene expression correlates. Results: UUO increased tubular diameter and interstitial fibrosis by 2.7- and 7-fold, respectively, in parallel with increases in renal transforming growth factor-β₁ (TGF-β₁) and tumor necrosis factor-α (TNF-α) mRNA levels. Glomerular number and size were reduced by 52 and 33%, respectively. Reductions in WT-1 mRNA and protein expression were noted following obstruction occurring in tandem with reduced mRNA levels for BMP-7 and E-cadherin. Ros attenuated tubular dilatation (33%) and interstitial fibrosis (72%) in association with the normalization of renal TGF-β₁ and TNF-α mRNA levels. Ros improved glomerular number and size (30 and 50%), and preserved mRNA and protein expression levels of WT-1 and normalized mRNA levels for BMP-7 and E-cadherin. Conclusions: Ros treatment attenuated all changes, most notably the increase in interstitial fibrosis. Notably, Ros treatment was unable to completely salvage glomerular development. Together these data highlight the therapeutic potential and limitations of Ros in neonatal obstruction.

Cardiovascular disease is often associated with chronic kidney disease and vice versa; myocardial vitamin D receptors (VDRs) are among the probable links between the 2 disorders. The vitamin D receptor activator paricalcitol protects against some renal and cardiovascular complications. However, the structural and electrophysiological effects of myocardial vitamin D receptor modification and its impact on the response to ischemia-reperfusion are currently unknown. This work attempted to determine whether obstructive nephropathy induced myocardial changes (in rats) linked to vitamin D receptor deficiency and to ventricular arrhythmias in Langendorff-perfused hearts. Unilateral ureteral-obstructed and Sham-operated rats were treated with either paricalcitol (30 ng/kg/d intraperitoneal) or vehicle for 15 days. In 5 hearts from each group, we found that obstructed rats showed a reduction in VDRs and an increase in angiotensin II type 1 receptor expression (messenger RNA and protein), suffered fibrosis (determined by Masson trichrome stain) and myofibril reduction with an increase in mitochondrial size, and had dilated crests (determined by electron microscopy). These changes were reversed by paricalcitol. In 8 additional hearts per group, we found that obstructed rats showed a higher incidence of ventricular fibrillation during reperfusion (after 10 minutes of regional ischemia) than did those treated with paricalcitol. The action potential duration was prolonged throughout the experiment in paricalcitol-treated rats. We conclude that the reduction in myocardial vitamin D receptor expression in obstructed rats might be related to myocardial remodeling associated with an increase in arrhythmogenesis and that paricalcitol protects against these changes by restoring myocardial vitamin D receptor levels and prolonging action potentials.

Background: Chronic kidney disease is highly prevalent and is associated with cardiovascular disease. Paricalcitol protects individuals from some of the renal and cardiovascular complications associated with kidney disease. However, its electrophysiological effect during myocardial ischemia-reperfusion is currently unknown. Aims: Using an obstructive nephropathy (ON) model, we plan to investigate the potential, structural, and functional changes of the heart that are linked to vitamin D deficiency. Methods: The ureters of adult rats (n = 10) were unilaterally obstructed. An inductor of the vitamin D receptor (VDR) was administered for 15 days (30ng/Kg/day, ip). We evaluated histological, molecular, and biochemical parameters, as well, cardiac electrophysiological activity with ischemia-reperfusion protocol. Results: we found changes in the action potential duration (APD) at 90% (* P<0.05 vs. C, +P<0.05 vs. O). The analysis revealed arrhythmias, ventricular tachycardia (VT), and ventricular fibrillation (VF). Arrhythmias were quantified in the following ways: 0 − sinus rhythm, 1 – premature ventricular complex, 2 - salvos, 3 - no sustained VT, and 4 – sustained VT or VF (>30 seconds). * P<0.05 vs. C, +P<0.05 vs. O. Of interest was the finding that appears to prolong Pari ischemia DPA in both the controls and the obstructed animals. Also, a significant bradycardia was established in the ischemic phase of the animals obstructed with Pari, which reversed completely during reperfusion. In hearts from ON model animals, we found high AT 1 expression and marked low VDR expression; these changes were reversed by paricalcitol treatment. Conclusions: The reduction of VDR expression in ON hearts could be related to increased arrhythmogenesis. The recovery induced by paricalcitol could protect against ventricular fibrillation by the lengthening of the action potential. Further studies will be necessary to elucidate these interesting kidney-heart interactions.