APOL1 Modulates Renin-Angiotensin System

Patients carrying APOL1 risk alleles (G1 and G2) have a higher risk of developing Focal Segmental Glomerulosclerosis (FSGS); we hypothesized that escalated levels of miR193a contribute to kidney injury by activating renin-angiotensin system (RAS) in the APOL1 milieus. Differentiated podocytes (DPDs) stably expressing vector (V/DPD), G0 (G0/DPDs), G1 (G1/DPDs), and G2 (G2/DPDs) were evaluated for renin, Vitamin D receptor (VDR), and podocyte molecular markers (PDMMs, including WT1, Podocalyxin, Nephrin, and Cluster of Differentiation [CD]2 associated protein [AP]). G0/DPDs displayed attenuated renin but an enhanced expression of VDR and Wilms Tumor [WT]1, including other PDMMs; in contrast, G1/DPDs and G2/DPDs exhibited enhanced expression of renin but decreased expression of VDR and WT1, as well as other PDMMs (at both the protein and mRNA levels). G1/DPDs and G2/DPDs also showed increased mRNA expression for Angiotensinogen and Angiotensin II Type 1 (AT1R) and 2 (AT2R) receptors. Protein concentrations of Brain Acid-Soluble Protein [BASP]1, Enhancer of Zeste Homolog [EZH]2, Histone Deacetylase [HDAC]1, and Histone 3 Lysine27 trimethylated [H3K27me3] in WT1-IP (immunoprecipitated proteins with WT1 antibody) fractions were significantly higher in G0/DPDs vs. G1/DPD and G2/DPDs. Moreover, DPD-silenced BASP1 displayed an increased expression of renin. Notably, VDR agonist-treated DPDs showed escalated levels of VDR and a higher expression of PDMMs, but an attenuated expression of renin. Human Embryonic Kidney (HEK) cells transfected with increasing APOL1(G0) plasmid concentrations showed a corresponding reduction in renin mRNA expression. Bioinformatics studies predicted the miR193a target sites in the VDR 3'UTR (untranslated region), and the luciferase assay confirmed the predicted sites. As expected, podocytes transfected with miR193a plasmid displayed a reduced VDR and an enhanced expression of renin. Renal cortical section immunolabeling in miR193a transgenic (Tr) mice showed renin-expressing podocytes. Kidney tissue extracts from miR193aTr mice also showed reduced expression of VDR and PDMMs, but enhanced expression of Renin. Blood Ang II levels were higher in miR193aTr, APOLG1, and APOL1G1/G2 mice when compared to control mice. Based on these findings, miR193a regulates the activation of RAS and podocyte molecular markers through modulation of VDR and WT1 in the APOL1 milieu.

Pathways of hepatic and renal damage through non-classical activation of the renin-angiotensin system in chronic liver disease

In liver cirrhosis, renin-angiotensin system (RAS) activation sustains renal sodium retention and hepatic fibrogenesis. New information has recently enlivened the traditional concept of RAS. For instance, renin and prorenin bind their ubiquitous receptors, resulting in the local production of angiotensin (Ang) II; increased serum calcium and calcimimetic agents, through stimulation of extracellular calcium-sensing receptors (CaSR), blunt renin production and lead to natriuretic effects in human and experimental cirrhosis. Alongside systemic production, there is Ang II tissue production within various organs through RAS enzymes different from angiotensin-converting enzyme (ACE), that is chymase, tissue plasminogen activator and several cathepsins. In experimental cirrhosis, inhibition of chymase leads to natriuretic and hepatic antifibrotic effects, without changes in systemic haemodynamics. In the kidney, local RAS coordinates proximal and distal tubular sodium reabsorption. However, renalase, whose plasma and tissue levels are severely altered in experimental cirrhosis, degrades systemic and renal tubule catecholamines, antagonizing the effects of renal RAS. Angiotensinogen-derived natriuretic and vasodilating peptides (Ang1-9, Ang1-7, Ang3-8) and their receptors have been described. Receptor agonists or antagonists are available to affect portal hypertension and sodium retention in cirrhosis. ACE2-dependent generation of Ang1-7 may inhibit experimental liver fibrosis. inhibition of Ang1-7 clearance by means of neprilysin blockade has portal hypotensive and natriuretic effects. Ang1-12, whose production renin does not regulate, is converted to several different angiotensin peptides via chymase. Finally, Ang II behaves as either an antinatriuretic or a natriuretic agent, based on the tissue content of AT₁ R and AT₂ R receptors, their ratio being prone to pharmacological modulation.

Association of Vitamin D Status with Chronic Disease Risk Factors and Cognitive Dysfunction in 50⁻70 Year Old Adults

Vitamin D deficiency/insufficiency has been primarily associated with skeletal disorders, however, since vitamin D receptors are found on multiple types of cells, there is also a link to increased chronic disease risk and all-cause mortality. The aim of this study was to examine whether deficient/insufficient vitamin D levels are associated with risk factors of chronic diseases and cognitive dysfunction in 50 to 70 year old adults. Participants completed the health status, three-day dietary record and vitamin D food frequency, sun exposure, and international physical activity questionnaires. Cognitive function of the participants was assessed using the Automated Neuropsychological Assessment Metrics while body composition (percent body fat, android/gynoid ratio) was assessed using Dual Energy X-ray Absorptiometry. Applanation tonometry was used to obtain pressure wave forms at the radial artery to examine arterial stiffness and central pressures. A fasting blood draw was taken to measure vitamin D, blood lipid and glucose levels. Fifty percent of the participants (36/72) were vitamin D deficient/insufficient. Individuals in the low physical activity (PA) group had lower serum vitamin D concentration compared to those in the high PA group (p = 0.04). Moreover, serum vitamin D levels were negatively related to risk factors of chronic diseases; blood glucose (r = -0.38; p = 0.01), triglycerides (r = -0.27; p = 0.02), and android/gynoid ratio (r = -0.32; p = 0.01). Deficient/insufficient vitamin D levels are linked to the risk factors of chronic diseases in men and women aged 50 to 70 years.

Raising awareness on the therapeutic role of cholecalciferol in CKD: a multidisciplinary-based opinion

Vitamin D is recognized to play an essential role in health and disease. In kidney disease, vitamin D analogs have gained recognition for their involvement and potential therapeutic importance. Nephrologists are aware of the use of oral native vitamin D supplementation, however, uncertainty still exists with regard to the use of this treatment option in chronic kidney disease as well as clinical settings related to chronic kidney disease, where vitamin D supplementation may be an appropriate therapeutic choice. Two consecutive meetings were held in Florence in July and November 2016 comprising six experts in kidney disease (N = 3) and bone mineral metabolism (N = 3) to discuss a range of unresolved issues related to the use of cholecalciferol in chronic kidney disease. The panel focused on the following six key areas where issues relating to the use of oral vitamin D remain controversial: (1) vitamin D and parathyroid hormone levels in the general population, (2) cholecalciferol in chronic kidney disease, (3) vitamin D in cardiovascular disease, (4) vitamin D and renal bone disease, (5) vitamin D in rheumatological diseases affecting the kidney, (6) vitamin D and kidney transplantation.

CYP3A4 is a crosslink between vitamin D and calcineurin inhibitors in solid organ transplant recipients: implications for bone health

The use of calcineurin inhibitors (CNIs) and vitamin D deficiency may contribute to the pathogenesis of post-transplant bone disease. CNIs and 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) are substrates of the drug-metabolizing enzyme CYP3A4. This review summarizes the indications for the use of activated vitamin D analogs in post-transplant care and the current knowledge on the impact of CNIs on bone. We searched for clinical evidence of the interaction between CNIs and 1,25(OH)₂D₃. We also provide an overview of the literature on the interplay between vitamin D metabolism and CYP3A4 in experimental and clinical settings and discuss its possible implications for solid organ transplant recipients. In conclusion, there is a body of evidence on the interplay between vitamin D and the drug-metabolizing enzyme CYP3A4, which may have therapeutic implications.

Estrogen Receptor α Is Required for Maintaining Baseline Renin Expression

Enzymatic cleavage of angiotensinogen by renin represents the critical rate-limiting step in the production of angiotensin II, but the mechanisms regulating the initial expression of the renin gene remain incomplete. The purpose of this study is to unravel the molecular mechanism controlling renin expression. We identified a subset of nuclear receptors that exhibited an expression pattern similar to renin by reanalyzing a publicly available microarray data set. Expression of some of these nuclear receptors was similarly regulated as renin in response to physiological cues, which are known to regulate renin. Among these, only estrogen receptor α (ERα) and hepatic nuclear factor α have no known function in regulating renin expression. We determined that ERα is essential for the maintenance of renin expression by transfection of small interfering RNAs targeting Esr1, the gene encoding ERα, in renin-expressing As4.1 cells. We also observed that previously characterized negative regulators of renin expression, Nr2f2 and vitamin D receptor, exhibited elevated expression in response to ERα inhibition. Therefore, we tested whether ERα regulates renin expression through an interaction with Nr2f2 and vitamin D receptor. Renin expression did not return to baseline when we concurrently suppressed both Esr1 and Nr2f2 or Esr1 and vitamin D receptor mRNAs, strongly suggesting that Esr1 regulates renin expression independent of Nr2f2 and vitamin D receptor. ERα directly binds to the hormone response element within the renin enhancer region. We conclude that ERα is a previously unknown regulator of renin that directly binds to the renin enhancer hormone response element sequence and is critical in maintaining renin expression in renin-expressing As4.1 cells.

Causes of Vitamin D Deficiency and Effect of Vitamin D Supplementation on Metabolic Complications in Obesity: a Review

Obese subjects are often characterized by low plasma 25-hydroxy-vitamin D (25OHD) levels. Many explanations for this association have been proposed. Low plasma 25OHD is associated with obesity-related comorbidities such as insulin resistance, type 2 diabetes mellitus, and low-grade inflammation. In this review, we discuss the proposed mechanisms for low 25OHD in obesity and explore the results of recent RCTs on vitamin D (VD) supplementation on obesity and its metabolic complications such as insulin resistance and type 2 diabetes. Although the results from these clinical randomized controlled trials vary, the general picture is that VD treatment of obese individuals does not seem to be an effective treatment of obesity-related metabolic complications.

The effects of maternal vitamin D on neonatal growth parameters

Vitamin D facilitates calcium absorption and bone building. Presence of vitamin D is highly important in pregnant women due to its effect on the development of the fetal skeleton. The study population comprised 208 low-risk pregnant women of a heterogeneous population. Maternal and fetal serum concentrations of vitamin D were measured using the Liaison 25(OH)D Assay (DiaSorin, Italy).

CONCLUSION

Maternal vitamin D serum concentrations correlate with neonatal vitamin D serum concentrations but do not affect neonatal weight and/or head circumference. WHAT IS KNOWN? • Vitamin D is known to be also involved in immunomodulation and cellular proliferation and differentiation. • Vitamin D is highly important in pregnant women for its effect on fetal musculoskeletal and neurological development. WHAT IS NEW? • No association was detected between maternal or neonatal vitamin D concentration with neonatal growth parameters or obstetrical complications, and no association was found between maternal vitamin D serum concentrations and maternal obstetrical complication rate. • A strong correlation was demonstrated between maternal and neonatal serum vitamin D concentrations.

Uric acid, hypertension, and cardiovascular and renal complications

Over the last decade, the biologic interference of uric acid with the cardiovascular (CV) system and the kidney has been intensively investigated, and several experimental studies in animal models and in vitro documented that hyperuricemia may trigger hypertension and incite endothelial dysfunction, vascular damage and renal disease. A substantial proportion of epidemiological studies are compatible with the hypothesis that hyperuricemia may be noxious to the CV system and the kidney as well. However, there are still no well-powered trials testing whether uric acid-lowering interventions may reduce BP or attenuate the risk for adverse CV and renal outcomes. Evidence still remains largely insufficient to recommend changes in the current policy of not prescribing uric acid-lowering drugs to individuals with asymptomatic hyperuricemia.

Vitamin D deficiency is independently associated with the extent of coronary artery disease

BACKGROUND

Vitamin D (25-OH D3) deficiency represents a rising social and economic problem in Western countries. Vitamin D has been recently reported to modulate inflammatory processes, endothelium and smooth muscle cell proliferation and even platelet function, thus potentially modulating atherothrombosis. Great interest has been addressed on its impact on cardiovascular outcome, with contrasting results. The aim of current study was to evaluate the relationship between 25-OH D3 and the extent of coronary artery disease (CAD) in a consecutive cohort of patients undergoing coronary angiography.

MATERIALS AND METHODS

Patients undergoing elective coronary angiography were included in a cross-sectional study. Fasting samples were collected for 25-OH D3 levels assessment. Significant CAD was defined as at least 1 vessel stenosis > 50%, while severe CAD as left main and/or trivessel disease, as evaluated by quantitative coronary angiography.

RESULTS

Hypovitaminosis D was observed in 70·4% of 1484 patients. Patients were divided according to vitamin D tertiles (< 9·6; 9·6-18·4; ≥ 18·4). Lower vitamin D levels were associated with age, female gender (P < 0·001), renal failure (P = 0·05), active smoking (P = 0·001), acute coronary syndrome at presentation (P < 0·001), therapy with calcium antagonists (P = 0·02) and diuretics (P < 0·001), less beta-blockers (P = 0·02) and statins (P = 0·001) use. Vitamin D was directly related to haemoglobin (P < 0·001) and inversely with platelet count (P = 0·002), total and low-density-lipoprotein cholesterol (P = 0·002 and P < 0·001) and triglycerides (P = 0·01). Vitamin D did not influence angiographic features of coronary lesions, but was associated with higher prevalence of left main or right CAD (P = 0·03). Vitamin D deficiency was significantly associated with higher prevalence of CAD (adjusted OR [95%CI] = 1·32[1·1-1·6], P = 0·004) and severe CAD (adjusted OR [95%CI] = 1·18[1-1·39], P = 0·05).

CONCLUSION

Hypovitaminosis D was observed in the vast majority of patients undergoing coronary angiography. Vitamin D deficiency is significantly associated with the prevalence and extent of CAD, especially for patients with values < 10 ng/mL. Therefore, future large studies are needed to evaluate whether vitamin D supplementation may prevent CAD and its progression.

Is the renin-angiotensin system actually hypertensive?

The historical view of the renin-angiotensin system (RAS) is that of an endocrine hypertensive system that is controlled by renin and mediated via the action of angiotensin II on its type 1 receptor. Numerous new angiotensins (Ang) and receptors have been described, the majority being hypotensive and natriuretic, namely Ang-(1-7) and its receptor rMas. Renin and its precursor (pro-renin) can bind their common receptor. In addition to the production of Ang II, this receptor triggers intracellular effects. Given the control of renin production by intracellular calcium, calcium homeostasis is of particular importance. Ang-(1-12), which is not controlled by renin, is converted to several different angiotensin peptides and is a new pathway of the RAS. Local RAS enzymes produce or transform the different hyper- or hypotensive angiotensin within vessels and organs, but also in blood through circulating forms of the enzymes. In the kidney, a powerful local vascular RAS allows for the independence of renal vascularization from systemic control. Moreover, the kidney also contains an independent urinary RAS, which counterbalances the systemic RAS and coordinates proximal and distal sodium reabsorption. The systemic and local effects of renal RAS cannot be analyzed without taking into account the antagonistic effect of renalase. Our concept of RAS needs to evolve to take into account its dual potentiality (hyper- or hypotensive).

Short-term vitamin D3 supplementation lowers plasma renin activity in patients with stable chronic heart failure: an open-label, blinded end point, randomized prospective trial (VitD-CHF trial)

BACKGROUND

Many chronic heart failure (CHF) patients have low vitamin D (VitD) and high plasma renin activity (PRA), which are both associated with poor prognosis. Vitamin D may inhibit renin transcription and lower PRA. We investigated whether vitamin D3 (VitD3) supplementation lowers PRA in CHF patients.

METHODS AND RESULTS

We conducted a single-center, open-label, blinded end point trial in 101 stable CHF patients with reduced left ventricular ejection fraction. Patients were randomized to 6 weeks of 2,000 IU oral VitD3 daily or control. At baseline, mean age was 64 ± 10 years, 93% male, left ventricular ejection fraction 35% ± 8%, and 56% had VitD deficiency. The geometric mean (95% CI) of 25-hydroxyvitamin D3 increased from 48 nmol/L (43-54) at baseline to 80 nmol/L (75-87) after 6 weeks in the VitD3 treatment group and decreased from 47 nmol/L (42-53) to 44 nmol/L (39-49) in the control group (P < .001). The primary outcome PRA decreased from 6.5 ng/mL per hour (3.8-11.2) to 5.2 ng/mL per hour (2.9-9.5) in the VitD3 treatment group and increased from 4.9 ng/mL per hour (2.9-8.5) to 7.3 ng/mL per hour (4.5-11.8) in the control group (P = .002). This was paralleled by a larger decrease in plasma renin concentration in the VitD3 treatment group compared to control (P = .020). No significant changes were observed in secondary outcome parameters, including N-terminal pro-B-type natriuretic peptide natriuretic peptide and fibrosis markers.

CONCLUSIONS

Most CHF patients had VitD deficiency and high PRA levels. Six weeks of supplementation with 2,000 IU VitD3 increased 25-hydroxyvitamin D3 levels and decreased PRA and plasma renin concentration.

New roles for renin and prorenin in heart failure and cardiorenal crosstalk

The renin-angiotensin-aldosterone-system (RAAS) plays a central role in the pathophysiology of heart failure and cardiorenal interaction. Drugs interfering in the RAAS form the pillars in treatment of heart failure and cardiorenal syndrome. Although RAAS inhibitors improve prognosis, heart failure–associated morbidity and mortality remain high, especially in the presence of kidney disease. The effect of RAAS blockade may be limited due to the loss of an inhibitory feedback of angiotensin II on renin production. The subsequent increase in prorenin and renin may activate several alternative pathways. These include the recently discovered (pro-) renin receptor, angiotensin II escape via chymase and cathepsin, and the formation of various angiotensin subforms upstream from the blockade, including angiotensin 1–7, angiotensin III, and angiotensin IV. Recently, the direct renin inhibitor aliskiren has been proven effective in reducing plasma renin activity (PRA) and appears to provide additional (tissue) RAAS blockade on top of angiotensin-converting enzyme and angiotensin receptor blockers, underscoring the important role of renin, even (or more so) under adequate RAAS blockade. Reducing PRA however occurs at the expense of an increase plasma renin concentration (PRC). PRC may exert direct effects independent of PRA through the recently discovered (pro-) renin receptor. Additional novel possibilities to interfere in the RAAS, for instance using vitamin D receptor activation, as well as the increased knowledge on alternative pathways, have revived the question on how ideal RAAS-guided therapy should be implemented. Renin and prorenin are pivotal since these are at the base of all of these pathways.

Modulation of hypovitaminosis D-induced islet dysfunction and insulin resistance through direct suppression of the pancreatic islet renin-angiotensin system in mice

AIMS/HYPOTHESIS

Vitamin D is necessary for normal insulin action and suppresses renin production. Increased renin-angiotensin system (RAS) activity causes islet damage, including reduced insulin secretion. We therefore sought to determine whether hypovitaminosis D-induced upregulation of islet RAS in vivo impairs islet cell function and increases insulin resistance, and whether pharmacological suppression of the RAS during continuing vitamin D deficiency might correct this.

METHODS

C57BL/6 mice were rendered vitamin D-deficient by diet, and glucose and insulin tolerance was assessed. The expression and translation of islet functional, and islet RAS, genes were measured and the effects of pharmacological renin suppression examined.

RESULTS

Mice with diet-induced hypovitaminosis D developed impaired glucose tolerance, increased RAS component expression and impaired islet function gene transcription. Treatment with pharmacological renin inhibition (aliskiren), without vitamin D status correction, reduced islet RAS over-reactivity, islet dysfunction and insulin resistance, and improved glucose tolerance.

CONCLUSIONS/INTERPRETATION

Upregulation of islet RAS genes can contribute to hypovitaminosis D-induced impairment of islet function and increase insulin resistance independently of vitamin D status. Thus, our findings support the use of RAS inhibitors in impaired glucose homeostasis or early diabetes. They also suggest that combining RAS inhibition with correction of hypovitaminosis D might be useful in treating impaired glycaemic control and also in type 2 diabetes prevention. However, the use of aliskiren in established diabetes is contraindicated due to the increased risk of side effects such as hyperkalaemia, so other more suitable RAS blockers need to be identified.

Regulation of mouse-renin gene by apurinic/apyrimidinic-endonuclease 1 (APE1/Ref-1) via recruitment of histone deacetylase 1 corepressor complex

OBJECTIVES

Apurinic/apyrimidinic-endonuclease 1 (APE1) heterozygous mice have chronically elevated blood pressure. Renin of the renin-angiotensin (ANG) system for blood pressure maintenance regulates production of ANG II, a vasoactive hormone. Renin expression and secretion from kidney juxtaglomerular cells are regulated by intracellular calcium. Our objective in this study is to investigate APE1's regulatory role in renin expression.

METHODS

Effect of APE1 on calcium-mediated modulation of renin expression was examined by real-time reverse transcriptase-PCR, Western analysis and renin promoter-dependent luciferase activity in APE1-knockdown, APE1-overexpressing or control mouse kidney As4.1 cells. Furthermore, coimmunoprecipitation and chromatin immunoprecipitation assays were utilized to examine the association of APE1 with histone deacetylase (HDAC)1 corepressor complex and their recruitment to renin enhancer. Finally, kidney renin mRNA level and plasma-renin activity were measured in wild-type and APE1-heterozygous mice.

RESULTS

Here we show that APE1 is involved in calcium-mediated repression of renin gene. Our results further indicate that APE1 is a component of HDAC1 corepressor complex bound to renin-enhancer region. Increase in intracellular calcium ion concentration enhances the association of APE1 with HDAC1 corepressor complex and their recruitment to the enhancer region. Furthermore, APE1's N-terminal region is critical for formation and recruitment of the enhancer-bound corepressor complex. Increased renin expression in kidneys and higher plasma-renin activity in APE1 heterozygous mice further supports APE1's corepressor role in vivo.

CONCLUSION

This study uncovers APE1's function as a novel negative regulator of renin expression, and thereby in blood pressure maintenance.

Does vitamin D deficiency contribute to erectile dysfunction?

Erectile dysfunction (ED) is a multifactorial disease, and its causes can be neurogenic, psychogenic, hormonal and vascular. ED is often an important indicator of cardiovascular disease (CVD) and a powerful early marker for asymptomatic CVD. Erection is a vascular event, and ED is often a vascular disease caused by endothelial damage and subsequent inhibition of vasodilation. We show here that risk factors associated with a higher CVD risk also associate with a higher ED risk. Such factors include diabetes mellitus, hypertension, arterial calcification and Inflammation in the vascular endothelium. Vitamin D deficiency is one of several dynamics that associates with increased CVD risk, but to our knowledge, it has not been studied as a possible contributor to ED. Here we examine research linking ED and CVD and discuss how vitamin D influences CVD and its classic risk factors-factors that also associate to increased ED risk. We also summarize research indicating that vitamin D associates with reduced risk of several nonvascular contributing factors for ED. We conclude that VDD contributes to ED. This hypothesis should be tested through observational and intervention studies.

Vitamin d therapy and cardiovascular health

Vitamin D belongs to the family of nuclear steroid hormones, which has pleiotropic effects on several organ systems. Different vitamin D compounds have been studied as potential cardioprotective agents over the past 20 years. The results of these clinical studies vary based on the form and dosage of vitamin D administered during the trial. In the past 5 years, many have described an association of vitamin D compounds and cardiovascular health through reduction in blood pressure, reduction in inflammatory biomarkers, improved insulin sensitivity, and reduction in cardiovascular disease complications and death. Because there are several vitamin D compounds, it is important to consider the full breadth of the literature when examining vitamin D and cardiovascular health, to assist in hypothesis generation and understanding of the current state of the science. Although a growing body of evidence suggests that nutritional vitamin D supplementation and potentially even treatment with synthetic analogues of vitamin D may be cardioprotective, relatively few studies have examined either of these compounds in a randomized, controlled fashion. Studies examining the benefit of vitamin D supplementation are now beginning, but future studies considering calcitriol and analogue therapy also seem warranted.

The effect of different doses of vitamin D(3) on markers of vascular health in patients with type 2 diabetes: a randomised controlled trial

AIMS/HYPOTHESIS

Low 25-hydroxyvitamin D levels predict future cardiovascular events and are common in patients with type 2 diabetes. We compared the effect of 100,000 and 200,000 IU doses of vitamin D(3) on endothelial function, blood pressure and markers of glycaemic control in patients with type 2 diabetes.

METHODS

This was a randomised, parallel group, placebo-controlled trial. Patients with type 2 diabetes and baseline 25-hydroxyvitamin D levels <100 nmol/l were enrolled from community and hospital-based diabetes clinics. Participants were assessed in a university department of clinical pharmacology and received a single oral dose of placebo or vitamin D(3) (100,000 IU or 200,000 IU) at baseline, randomly allocated via numbered bottles prepared offsite; participants and investigators were both blinded to treatment allocation. Endothelial function, office blood pressure, B-type natriuretic peptide, insulin resistance and glycosylated haemoglobin were measured at baseline, and at 8 and 16 weeks.

RESULTS

We randomised 61 participants to the three groups (placebo 22, 100,000 IU vitamin D(3) 19, 200,000 IU vitamin D(3) 20). There was no significant difference in the primary outcome of endothelial function at 8 weeks (placebo 5.2%, n = 22; 100,000 IU 4.3%, n = 19; 200,000 IU 4.9%, n = 17) or at 16 weeks. Insulin resistance and glycosylated haemoglobin did not improve with either dose of vitamin D(3). On covariate analysis, systolic blood pressure was significantly lower in both treatment arms than in the placebo group at 8 weeks (placebo 146.4 mmHg, 100,000 IU 141.4 mmHg [p = 0.04 vs placebo], 200,000 IU 136.8 mmHg [p = 0.03 vs placebo]). B-type natriuretic peptide levels were significantly lower in the 200,000 IU group by 16 weeks (placebo 34 pg/ml, 200,000 IU 21 pg/ml, p = 0.02). No significant excess of adverse effects was noted in the treatment arms.

CONCLUSIONS/INTERPRETATION

High-dose vitamin D(3) improved systolic blood pressure and B-type natriuretic peptide levels, but not endothelial function, insulin resistance or glycosylated haemoglobin in patients with type 2 diabetes.

[Effect of vitamin D deficiency on cardiovascular risk]

Vitamin D deficiency affects almost 50 % of the population worldwide. Besides its classical effects on bone and calcium metabolism, vitamin D displays a wide spectrum of non classical effects. Among these effects, those targeting the cardiovascular system are mostly documented by observational, experimental and small intervention trials that most often evaluated intermediate parameters. The time has now come for large placebo-controlled trials targeting clinical endpoints such as the incidence of major cardiovascular events and mortality.

The Effects of Vitamin D Supplementation on Physical Function and Quality of Life in Older Patients With Heart Failure

Background— Low 25-hydroxyvitamin D levels, commonly found in older patients with heart failure, may contribute to the chronic inflammation and skeletal myopathy that lead to poor exercise tolerance. We tested whether vitamin D supplementation of patients with heart failure and vitamin D insufficiency can improve physical function and quality of life.

Methods and Results— In a randomized, parallel group, double-blind, placebo-controlled trial, patients with systolic heart failure aged ≥70 years with 25-hydroxyvitamin D levels <50 nmol/L (20 ng/mL) received 100 000 U of oral vitamin D2 or placebo at baseline and 10 weeks. Outcomes measured at baseline, 10 weeks, and 20 weeks were 6-minute walk distance, quality of life (Minnesota score), daily activity measured by accelerometry, Functional Limitations Profile, B-type natriuretic peptide, and tumor necrosis factor-α. Participants in the vitamin D group had an increase in their 25-hydroxyvitamin D levels compared with placebo at 10 weeks (22.9 versus 2.3 nmol/L [9.2 versus 0.9 ng/mL]; P <0.001) and maintained this increase at 20 weeks. The 6-minute walk did not improve in the treatment group relative to placebo. No significant benefit was seen on timed up and go testing, subjective measures of function, daily activity, or tumor necrosis factor. Quality of life worsened by a small, but significant amount in the treatment group relative to placebo. B-type natriuretic peptide decreased in the treatment group relative to placebo (−22 versus +78 pg/mL at 10 weeks; P =0.04).

Conclusions— Vitamin D supplementation did not improve functional capacity or quality of life in older patients with heart failure with vitamin D insufficiency.

Clinical Trial Registration— www.controlled-trials.com. Identifier: ISRCTN51372896.

Metabólitos séricos da vitamina D não se correlacionam com pressão arterial em adolescentes

OBJETIVO: O objetivo deste estudo foi avaliar a associação entre o estado nutricional da vitamina D, a adiposidade e a pressão arterial (PA) em adolescentes. MÉTODOS: Foi realizada avaliação antropométrica, da composição corporal, da ingestão alimentar, de medidas bioquímicas e aferição da PA de 205 adolescentes, com média de idade de 18,2 anos. RESULTADOS: Destes, 12,19% apresentaram PA elevada. O nível sérico médio da 25OHD foi 29,2(0,8) ng/mL, e 62% dos adolescentes apresentaram insuficiência de vitamina D. Não foi encontrada correlação significativa entre a PAS e a PAD com a 25OHD e a 1,25(OH)2D. Houve correlação negativa entre a PAD com os níveis séricos de adiponectina, e tanto a PAS quanto a PAD apresentaram correlação positiva com a circunferência da cintura em ambos os sexos. CONCLUSÃO: Não houve relação entre os níveis séricos de vitamina D e a PA. Porém, a gordura visceral apresenta risco potencial para elevação da PA em adolescentes.

Wilms' tumor protein (-KTS) modulates renin gene transcription

Renin plays a crucial role in the control of various physiological processes such as blood pressure and body fluid homeostasis. Here, we show that a splice variant of the Wilms' tumor protein lacking three amino acids WT1(-KTS) suppresses renin gene transcription. Using bioinformatics tools, we initially predicted that a WT1-binding site exists in a regulatory region about 12 kb upstream of the renin promoter; this was confirmed by reporter gene assays and gel shift experiments in heterologous cells. Co-expression of Wt1 and renin proteins was found in rat kidney sections, mouse kidney blood vessels, and a cell line derived from the juxtaglomerular apparatus that produces renin. Knockdown of WT1 protein by siRNA significantly increased the cellular renin mRNA content, while overexpression of WT1(-KTS) reduced renin gene expression in stable and transiently transfected cells. A mutant WT1(-KTS) protein found in Wilms' tumors failed to suppress renin gene reporter activity and endogenous renin expression. Our findings show that renin gene transcription is regulated by the WT1(-KTS) protein and this may explain findings in patients with WT1 gene mutations of increased plasma renin and hypertension.

Optimal vitamin D status attenuates the age-associated increase in systolic blood pressure in white Americans: results from the third National Health and Nutrition Examination Survey

BACKGROUND

The prevalences of both hypertension and vitamin D insufficiency are high in the United States. Recent clinical trials and animal studies have suggested that vitamin D insufficiency may be associated with elevated blood pressure.

OBJECTIVE

With cross-sectional data, we sought to determine whether vitamin D concentrations were related to systolic blood pressure (SBP) in the third National Health and Nutrition Examination Survey (1988-1992).

DESIGN

Blood pressure was classified with 5 categories from the Joint National Committee 7 with a sixth category added to distinguish participants with normotensive SBP (<110 mm Hg) from those with high-normal SBP (110-119 mm Hg). We used predicted marginals to estimate the conditional means of serum 25 hydroxyvitamin D [25(OH)D] and to test for trend across blood pressure categories. We used linear regression to explore the association between vitamin D, blood pressure, and age.

RESULTS

Lower 25(OH)D concentrations were associated with a higher blood pressure category in whites (P<0.001); however, when controlling for age, the association was no longer significant. Concentrations of 25(OH)D>80 nmol/L decreased the age-related increase in SBP by 20% compared with participants having 25(OH)D concentrations<50 nmol/L (P<0.001). Only 8% of blacks had 25(OH)D concentrations>80 nmol/L.

CONCLUSIONS

SBP is inversely associated with serum vitamin D concentrations in nonhypertensive white persons in the United States. This observation provides a rationale for studies on the potential effects of vitamin D supplementation as a method to reduce SBP in persons at risk of hypertension.

Dissecting the action of an evolutionary conserved non-coding region on renin promoter activity

Elucidating the mechanisms of the human transcriptional regulatory network is a major challenge of the post-genomic era. One important aspect is the identification and functional analysis of regulatory elements in non-coding DNA. Genomic sequence comparisons between related species can guide the discovery of cis-regulatory sequences. Using this technique, we identify a conserved region CNSmd of ∼775 bp in size, ∼14 kb upstream of the renin gene. Renin plays a pivotal role for mammalian blood pressure regulation and electrolyte balance. To analyse the cis-regulatory role of this region in detail, we perform 132 combinatorial reporter gene assays in an in vitro Calu-6 cell line model. To dissect the role of individual subregions, we fit several mathematical models to the experimental data. We show that a multiplicative switch model fits best the experimental data and that one subregion has a dominant effect on promoter activity. Mapping of the sub-sequences on phylogenetic conservation data reveals that the dominant regulatory region is the one with the highest multi-species conservation score.

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.

Multiple potential clinical benefits for 1alpha,25-dihydroxyvitamin D3 analogs in kidney transplant recipients

Therapeutic trials of 1alpha,25(OH)(2)D(3) and related synthetic analogs are merited in diverse clinical fields, including treatment or prevention of bone disease, cancer, immune-mediated diseases, cardiovascular diseases, and prostatic hypertrophy. Potential difficulties of carrying out such trials successfully, include experimental data suggesting relatively modest therapeutic effects of 1alpha,25(OH)(2)D(3) analogs as stand-alone intervention and the likely requirement for large study group size and lengthy follow-up periods, if individual prophylactic effects are to be proven. Thus, it may be wise to identify patient groups with multiple potential benefits, accelerated disease risks, and the possibility for exploring synergistic pharmacological effects, in whom to carry out clinical trials of 1alpha,25(OH)(2)D(3) analogs. With this consideration in mind, the suitability of kidney transplant recipients for such studies is discussed. Although, highly effective in reversing end-stage renal disease, kidney transplantation continues to be limited by heightened risk of osteoporosis, persistent hyperparathyroidism, acute and chronic immunological injury, new cancer diagnosis, and cardiovascular events. In addition, kidney transplant recipients generally receive multiple immunosuppressants with a high prevalence of medication-related toxicities. Finally, it is pointed out that clinical trials carried out in organ transplant recipients provide a unique opportunity for longitudinal comparison of target tissue structural and gene expression profiles among treated and control patient groups. It is proposed that addition of a 1alpha,25(OH)(2)D(3) analog to conventional post-kidney transplant medication regimens is likely to be associated with measurable effects to prevent or retard multiple important complications and that this patient group is especially suitable for carrying out clinical trials of these compounds.

Nutritional modulation of parathyroid hormone secretion may influence risk for left ventricular hypertrophy

Recent studies demonstrate low serum levels of 25-hydroxyvitamin D in patients with congestive heart failure (CHF). Although this may in part reflect reduced capacity for outdoor exercise, the possibility that poor vitamin D status increases risk for left ventricular hypertrophy (LVH), and its common sequel CHF, merits consideration. In cardiomyocytes, hormones which activate protein kinase C (PKC) -- including norepinephrine, angiotensin II, and endostatin, implicated in the pathogenesis of LVH -- induce a hypertrophic response analogous to that seen in LVH. Transgenic mice overexpressing PKC-beta2 or its upstream activator Galphaq in cardiac myofibers develop a syndrome similar to LVH. Parathyroid hormone (PTH) also activates Galphaq and PKC in cardiomyocytes, and provokes the expected hypertrophic response. Both primary and secondary hyperparathyroidism are associated with high risk for LVH. Moreover, in uncomplicated essential hypertension, left ventricular mass index has been shown to correlate very tightly with serum PTH levels, independent of blood pressure. This latter finding suggests that variations of PTH within the normal range can influence induction of LVH in at-risk subjects. If so, nutritional and lifestyle measures which modulate PTH secretion may have an impact on LVH risk. PTH secretion should be down-regulated by good vitamin D status -- achieved through supplementation or regular uv exposure -- and by vegan diets moderately low in bioavailable phosphate. Although high calcium intakes can likewise suppress PTH, they also boost renin secretion, which could have a countervailing effect on risk for LVH. Whether these nutritional measures do indeed influence LVH risk could be examined in prospective studies targeting patients at high risk, such as hypertensives.

Osteogenic regulation of vascular calcification: an early perspective

Cardiovascular calcification is a common consequence of aging, diabetes, hypercholesterolemia, mechanically abnormal valve function, and chronic renal insufficiency. Although vascular calcification may appear to be a uniform response to vascular insult, it is a heterogenous disorder, with overlapping yet distinct mechanisms of initiation and progression. A minimum of four histoanatomic variants-atherosclerotic (fibrotic) calcification, cardiac valve calcification, medial artery calcification, and vascular calciphylaxis-arise in response to metabolic, mechanical, infectious, and inflammatory injuries. Common to the first three variants is a variable degree of vascular infiltration by T cells and macrophages. Once thought benign, the deleterious clinical consequences of calcific vasculopathy are now becoming clear; stroke, amputation, ischemic heart disease, and increased mortality are portended by the anatomy and extent of calcific vasculopathy. Along with dystrophic calcium deposition in dying cells and lipoprotein deposits, active endochondral and intramembranous (nonendochondral) ossification processes contribute to vascular calcium load. Thus vascular calcification is subject to regulation by osteotropic hormones and skeletal morphogens in addition to key inhibitors of passive tissue mineralization. In response to oxidized lipids, inflammation, and mechanical injury, the microvascular smooth muscle cell becomes activated. Orthotopically, proliferating stromal myofibroblasts provide osteoprogenitors for skeletal growth and fracture repair; however, in valves and arteries, vascular myofibroblasts contribute to cardiovascular ossification. Current data suggest that paracrine signals are provided by bone morphogenetic protein-2, Wnts, parathyroid hormone-related polypeptide, osteopontin, osteoprotegerin, and matrix Gla protein, all entrained to endocrine, metabolic, inflammatory, and mechanical cues. In end-stage renal disease, a "perfect storm" of vascular calcification often occurs, with hyperglycemia, hyperphosphatemia, hypercholesterolemia, hypertension, parathyroid hormone resistance, and iatrogenic calcitriol excess contributing to severe calcific vasculopathy. This brief review recounts emerging themes in the pathobiology of vascular calcification and highlights some fundamental deficiencies in our understanding of vascular endocrinology and metabolism that are immediately relevant to human health and health care.

Identification of a novel region in the proximal promoter of the mouse renin gene critical for expression

An enhancer at -2.6 kb and a HOX.PBX-binding site at -60 bp have been demonstrated to be critical to expression of the mouse renin gene (Ren-1(c)) in As4.1 cells. In this report, we show that a region (-197 to -70) immediately 5' to the HOX.PBX-binding site is also critical for Ren-1(c) expression. Deletion of this region in a construct containing 4.1 kb of the Ren-1(c) 5'-flanking sequence resulted in a 99% reduction in Ren-1(c) promoter activity in As4.1 cells, suggesting the pivotal role for the region in the regulation of the mouse renin gene. Electrophoretic mobility shift and supershift assays have identified two nuclear factor I-binding sites and a Sp1/Sp3-binding site within the distal portion of the region (-197 to -103). Mutation of these three sites caused a 90% decrease in Ren-1(c) promoter activity. Mutational analysis and electrophoretic mobility shift assays have also identified three additional transcription factor-binding sites within the region from -103 to -69, each of which contributes to high-level expression of Ren-1(c) in As4.1 cells. Finally, we have shown that the Ren-1(c) enhancer is the target for endothelin-1 (ET-1)-induced inhibition of Ren-1(c) expression and the transcription factor-binding sites in the proximal promoter are required for the maximal ET-1 inhibitory effect.

Aldosterone potentiates 1,25-dihydroxyvitamin D3 action in renal thick ascending limb via a nongenomic, ERK-dependent pathway

Recently, we demonstrated that aldosterone inhibits HCO3- absorption in the rat medullary thick ascending limb (MTAL) via a nongenomic pathway blocked by inhibitors of extracellular signal-regulated kinase (ERK) activation. Here we examined the effects on the MTAL of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], which regulates cell functions through nongenomic mechanisms in nonrenal systems. Addition of 1 nM 1,25(OH)2D3 to the bath decreased HCO3- absorption by 24%, from 15.0 +/- 0.3 to 11.4 +/- 0.5 pmol. min-1. mm-1 (P < 0.001). This inhibition was maximal within 60 min and was eliminated by pretreatment with actinomycin D, cycloheximide, or inhibitors of protein kinase C. In MTAL bathed with 1 nM aldosterone [added 15-20 min before 1,25(OH)2D3], the absolute (5.6 +/- 0.3 vs. 3.6 +/- 0.3 pmol. min-1. mm-1) and fractional (49 +/- 2 vs. 24 +/- 2%) decreases in HCO3- absorption induced by 1,25(OH)2D3 were significantly greater than those in the absence of aldosterone (P < 0.05). The effect of aldosterone to potentiate inhibition by 1,25(OH)2D3 was not affected by spironolactone but was eliminated by the MAPK kinase/ERK inhibitor U-0126. U-0126 did not affect inhibition of HCO3- absorption by 1,25(OH)2D3 alone. Aldosterone induced rapid activation of ERK via a transcription-independent pathway. We conclude that 1) 1,25(OH)2D3 inhibits HCO3- absorption in the MTAL via a genomic pathway involving protein kinase C, which may contribute to 1,25(OH)2D3-induced regulation of urinary net acid and/or Ca2+ excretion and 2) aldosterone potentiates inhibition by 1,25(OH)2D3 through an ERK-dependent, nongenomic pathway. These results identify a novel regulatory interaction whereby aldosterone acts via nongenomic mechanisms to enhance the genomic response to 1,25(OH)2D3. Aldosterone may influence a broad range of biological processes, including epithelial transport, by modifying the response of target tissues to 1,25(OH)2D3 stimulation.

Control of renin synthesis

Studies published recently have considerably enhanced our understanding of the mechanisms controlling renin production. With regard to the control of renin transcription, two enhancer regions have been identified that markedly augment renin synthesis in cell lines. In the absence of this enhancer activity, the basic promoter of the renin gene increases transcription only two- to threefold. The location of one (Jones CA, Sigmund CD, McGowan RA, Kane-Haas CM, and Gross KW. Mol Endocrinol 4: 375-383, 1990) transcription enhancer in the mouse gene is at about -2.7 kb and in humans at roughly -11 kb. A second important region has been identified in a chorionic cell line to be located approximately 5 kb upstream of the transcription start site in humans. Another potentially important regulatory region may lie within approximately 3.9 kb upstream of the -11 kb enhancer, as suggested by several conserved sequences among species in this region. In addition to the control of renin transcription, it seems that renin translation and the stability of renin mRNA are also effectively regulated. This occurs via the 3'-untranslated region, to which several proteins can bind. The binding proteins were identified as hnRNP K and E1, dynamin, nucleolin, MINT homologous protein, and Y-Box 1.

Identification of a nuclear orphan receptor (Ear2) as a negative regulator of renin gene transcription

A potent transcriptional enhancer was previously identified upstream of the mouse renin gene. Within the enhancer is a TGACCT direct-repeat motif, required for enhancer activity, that is the consensus sequence recognized by members of the thyroid hormone subfamily of steroid hormone receptors. We previously reported that RAR/RXR bind to this sequence and mediate the induction of renin promoter activity by retinoids. However, gel mobility shift assays clearly show that other as yet unidentified factors also bind to this motif. In order to identify some of these TGACCT binding factors, we screened a yeast one-hybrid cDNA library derived from mouse As4.1 cells. One of these encoded the orphan nuclear receptor Ear2. Recombinant Ear2 was purified from Escherichia coli and an antipeptide antisera was generated. EMSA showed that purified recombinant Ear2 specifically binds the TGACCT direct-repeat motif. Transfection assays showed that Ear2 potently decreases both baseline and retinoid-induced mouse renin promoter activity in a dose-dependent, enhancer-dependent, and sequence-specific manner. Mutations in Ear2, which abolish its binding to the TGACCT motif, also abolish transcriptional repression. Ear2 was identified as a nuclear protein in As4.1 cells, is one of the proteins binding to the TGACCT repeat motif, and its overexpression can repress transcription of the endogenous renin gene in As4.1 cells. These data suggest that Ear2 is a negative modulator of renin gene transcription in As4.1 cells, and that the renin enhancer may actually encode a complex positive and negative regulator of transcription.

An evolutionary approach for identifying potential transcription factor binding sites: the renin gene as an example

Evolutionary pressure has resulted in the conservation of certain nucleotide sequences. These conserved regions are potentially important for certain functions. Here we give an example of a comparison between noncoding sequences combined with other independent database information to shed light onto the regulation of the renin gene, a gene that has great importance for cardiovascular and renal homeostasis. To combine the information regarding conservation and weight matrices of transcription factor (TF) binding sites, an algorithm was developed (TFprofile). Notably, a local peak in the resulting binding profile coincides with a previously experimentally identified regulatory region for the renin gene. The existence of further peaks in the binding profile in the conserved 3.9-kb-long hRENc DNA block upstream of the renin gene suggests additional regions of potential importance for gene regulation. The algorithm TFprofile may be used to integrate information on cross-species evolutionary conservation and aspects of TF binding characteristics to provide putative regulatory DNA regions for experimental verification.

Vitamin D regulation of the renin-angiotensin system

The renin-angiotensin system (RAS) plays a central role in the regulation of blood pressure, electrolyte, and volume homeostasis. Epidemiological and clinical studies have long suggested an association of inadequate sunlight exposure or low serum 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] levels with high blood pressure and/or high plasma renin activity, but the mechanism is not understood. Our recent discovery that 1,25(OH)(2)D(3) functions as a potent negative endocrine regulator of renin gene expression provides some insights into the mechanism. The concept of vitamin D regulation of blood pressure through the RAS opens a new avenue to our understanding of the physiological functions of the vitamin D endocrine system, and provides a basis for exploring the potential use of vitamin D analogues in prevention and treatment of hypertension.