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Exposure of rats to elevated dietary salt following recovery from acute kidney injury (AKI) accelerates the transition to chronic kidney disease (CKD), and is dependent on lymphocyte activity. Here we tested whether high salt diet triggers lymphocyte activation in postischemic kidneys to worsen renal inflammation and fibrosis. Male Sprague-Dawley rats on a 0.4% salt diet were subjected to left unilateral ischemia-reperfusion and allowed to recover for 5 weeks. This resulted in a mild elevation of CD4(+) T cells relative to sham animals. Contralateral unilateral nephrectomy and elevated dietary salt (4%) for 4 extra weeks hastened CKD and interstitial fibrosis. Activated T cells were increased in the kidney threefold after 4 weeks of elevated dietary salt exposure relative to post-AKI rats before salt feeding. The T cell subset was largely positive for IL-17, indicative of Th-17 cells. Because angiotensin II activity may influence lymphocyte activation, injured rats were given the AT1R antagonist, losartan, along with high salt diet. This significantly reduced the number of renal Th-17 cells to levels of sham rats, and significantly reduced the salt-induced increase in fibrosis to about half. In vitro studies in AKI-primed CD4(+) T cells indicated that angiotensin II and extracellular sodium enhanced, and losartan inhibited, IL-17 expression. Thus, dietary salt modulates immune cell activity in postischemic recovering kidneys because of the activity of local RAS, suggesting the participation of these cells in CKD progression post-AKI. [ABSTRACT FROM AUTHOR]

Proteinuria is a central component of chronic kidney disease and an independent risk factor for cardiovascular disease. Kidney podocytes have an essential role as a filtration barrier against proteinuria. Kruppel-like Factor 4 (KLF4) is expressed in podocytes and decreased in glomerular diseases leading to methylation of the nephrin promoter, decreased nephrin expression and proteinuria. Treatment with an angiotensin receptor blocker (ARB) reduced methylation of the nephrin promoter in murine glomeruli of an adriamycin nephropathy model with recovery of KLF4 expression and a decrease in albuminuria. In podocyte-specific KLF4 knockout mice, the effect of ARB on albuminuria and the nephrin promoter methylation was attenuated. In cultured human podocytes, angiotensin II reduced KLF4 expression and caused methylation of the nephrin promoter with decreased nephrin expression. In patients, nephrin promoter methylation was increased in proteinuric kidney diseases with decreased KLF4 and nephrin expression. KLF4 expression in ARB-treated patients was higher in patients with than without ARB treatment. Thus, angiotensin II can modulate epigenetic regulation in podocytes and ARB inhibits these actions in part via KLF4 in proteinuric kidney diseases. This study provides a new concept that renin-angiotensin system blockade can exert therapeutic effects through epigenetic modulation of the kidney gene expression. [ABSTRACT FROM AUTHOR]

We elucidate the underlying mechanisms of bidirectional cardiorenal interaction, focusing on the sympathetic nerve driving disruption of the local renin-angiotensin system (RAS). A rat model of Nω-nitro-L-arginine methyl ester (L-NAME; a nitric oxide synthase inhibitor) administration was used to induce damage in the heart and kidney, similar to cardiorenal syndrome. L-NAME induced sympathetic nerve-RAS overactivity and cardiorenal injury accompanied by local RAS elevations. These were suppressed by bilateral renal denervation, but not by hydralazine treatment, despite the blood pressure being kept the same between the two groups. Although L-NAME induced angiotensinogen (AGT) protein augmentation in both organs, AGT mRNA decreased in the kidney and increased in the heart in a contradictory manner. Immunostaining for AGT suggested that renal denervation suppressed AGT onsite generation from activated resident macrophages of the heart and circulating AGT excretion from glomeruli of the kidney. We also examined rats treated with L-NAME plus unilateral denervation to confirm direct sympathetic regulation of intrarenal RAS. The levels of urinary AGT and renal angiotensin II content and the degrees of renal injury from denervated kidneys were less than those from contralateral innervated kidneys within the same rats. Thus, renal denervation has blood pressure-independent beneficial effects associated with local RAS inhibition. [ABSTRACT FROM AUTHOR]

Agents blocking the renin-angiotensin-aldosterone system are frequently used in patients with end-stage renal disease, but whether they exert beneficial cardiovascular effects is unclear. Here the long-term effects of the angiotensin II receptor blocker, irbesartan, were studied in hemodialysis patients in a double-blind randomized placebo-controlled 1-year intervention trial using a predefined systolic blood pressure target of 140 mm Hg (SAFIR study). Each group of 41 patients did not differ in terms of age, blood pressure, comorbidity, antihypertensive treatment, dialysis parameters, and residual renal function. Brachial blood pressure decreased significantly in both groups, but there was no significant difference between placebo and irbesartan. Use of additional antihypertensive medication, ultrafiltration volume, and dialysis dosage were not different. Intermediate cardiovascular end points such as central aortic blood pressure, carotid-femoral pulse wave velocity, left ventricular mass index, N-terminal brain natriuretic prohormone, heart rate variability, and plasma catecholamines were not significantly affected by irbesartan treatment. Changes in systolic blood pressure during the study period significantly correlated with changes in both left ventricular mass and arterial stiffness. Thus, significant effects of irbesartan on intermediate cardiovascular end points beyond blood pressure reduction were absent in hemodialysis patients. [ABSTRACT FROM AUTHOR]

Angiotensin II type 1 receptor (AT1R)-associated protein (ATRAP) promotes AT1R internalization along with suppression of pathological activation of tissue AT1R signaling. However, the functional significance of ATRAP in renal sodium handling and blood pressure regulation under pathological stimuli is not fully resolved. Here we show the blood pressure of mice with a gene-targeted disruption of ATRAP was comparable to that of wild-type mice at baseline. However, in ATRAP-knockout mice, angiotensin II-induced hypertension was exacerbated and the extent of positive sodium balance was increased by angiotensin II. Renal expression of the sodium-proton antiporter 3, a major sodium transporter in the proximal tubules, urinary pH, renal angiotensinogen production, and angiotensin II content was unaffected. Stimulation of the renal expression and activity of the epithelial sodium channel (ENaC), a major sodium transporter in the distal tubules, was significantly enhanced by chronic angiotensin II infusion. The circulating and urinary aldosterone levels were comparable. The blood pressure response and renal ENaC expression by aldosterone were not affected. Thus, ATRAP deficiency exacerbated angiotensin II-mediated hypertension by pathological activation of renal tubular AT1R by angiotensin II. This directly stimulates ENaC in the distal tubules and enhances sodium retention in an aldosterone-independent manner. [ABSTRACT FROM AUTHOR]

Little is known about the risk of venous thrombosis following kidney transplant. To determine this we estimated the risk of thromboembolic events (TEs) in a cohort of consecutive patients who underwent kidney transplantation at a single tertiary care center over an 11-year period and calculated standardized incidence ratios (SIRs) for a first TE in kidney transplant recipients compared with the general population. We then performed a nested case-control study and compared patients with and without TEs to identify risk factors for thrombosis. Among 913 kidney transplant recipients (KTRs), 68 patients developed these events. The SIR for TEs in KTRs compared with the general population was 7.9 over the duration of follow-up. The risk was particularly higher in the first post-transplant year (SIR 26.1) but remained elevated afterward (SIR 5.2). Hospitalization, use of sirolimus, low hemoglobin level, and use of renin-angiotensin system inhibitors were independently associated with these events. When cases of TEs that occurred during hospitalization were excluded, the risk of these events remained elevated. The risk of TEs in KTRs was eightfold higher than in the general population but not fully explained by the increased risk associated with hospitalization. Our results underscore the important risk of thrombosis in patients who received a kidney transplant, making vigilance mandatory especially during hospitalization. [ABSTRACT FROM AUTHOR]

The level of the renin-angiotensin-aldosterone system (RAAS) activity in kidney transplant recipients has not been extensively studied or serially profiled. To describe this axis and to determine its association with glomerular filtration rate (GFR) change, interstitial expansion, and end-stage renal disease (ESRD), we measured plasma renin activity (PRA) and plasma aldosterone levels annually for 5 years in 153 kidney transplant recipients randomly assigned to losartan or placebo. PRA and plasma aldosterone levels were in the normal range at all times and did not vary by immunosuppression regimen. Those on losartan exhibited higher PRA but similar plasma aldosterone levels. Neither baseline nor serial PRA or plasma aldosterone levels were associated with GFR decline, proteinuria, or interstitial expansion. Losartan use (hazard ratio (HR) 0.48 (95% confidence interval (CI) 0.21-1.0), insignificant) and Caucasian donor (HR 0.18 (95% CI 0.07-0.4) significant) were associated with less doubling of serum creatinine, death, or ESRD. Hypertension, <3 human leukocyte antigen matches, the combination of tacrolimus-rapamycin, and acute rejection were associated with more events. Neither PRA nor plasma aldosterone levels were independently associated with this outcome. Higher serial plasma aldosterone levels were associated, however, with a significantly higher risk of ESRD (HR 1.01 (95% CI 1.00-1.02)). Thus, systemic RAAS is not overly activated in kidney transplant recipients, but this may not reflect the intrarenal system. Importantly, plasma aldosterone levels may be associated with more ESRD. [ABSTRACT FROM AUTHOR]

In follow-up to a recently published randomized controlled clinical trial, Issa et al. provide evidence that systemic activity and physiological responsiveness of the renin aldosterone angiotensin system (RAAS) are well within normal limits in most kidney recipients during the first 5 years post-transplant. Implications of the results include the need to better understand intra-renal RAAS activity in transplanted kidneys and to identify patients in which the graft-protective effects of RAAS blockade are most relevant. [ABSTRACT FROM AUTHOR]

Animal studies suggest temporary renin-angiotensin system (RAS) blockade enhances long-term vascular protective effects; however, this is not established in humans. Here we evaluated the long-term effects of prior RAS blockade on hemodynamic function, urinary measures of inflammation, and tissue antioxidant mRNA expression in patients with type 1 diabetes mellitus (T1DM) who participated in the 5-year Renin Angiotensin System Study (RASS). At 4 years after completing the RASS and discontinuing study medication, renal hemodynamic responses to clamped hyperglycemia were significantly greater in 18 patients in the RAS blockade group compared to 9 patients of the placebo-treated group. Individuals who had received RAS blockade also exhibited higher flow-mediated vasodilatation, reduced urinary cytokine excretion in response to hyperglycemia, and increased skin mRNA expression of superoxide dismutase-1 and catalase. Thus, patients with uncomplicated T1DM who received prior RAS blockade for 5 years maintain long-term effects on renal hemodynamic and systemic vascular function, inflammatory pathways in the kidney, and antioxidant enzyme expression in skin 4 years after discontinuation of therapy. Our findings suggest that sustained long-term protective effects of finite RAS inhibition requires further study. [ABSTRACT FROM AUTHOR]

We studied here the clinical course of heterozygous carriers of X-linked Alport syndrome and a subgroup of patients with thin basement membrane disease due to heterozygous autosomal recessive Alport mutations whose prognosis may be worse than formerly thought. We analyzed 234 Alport carriers, including 29 with autosomal recessive mutations. Using Kaplan-Meier estimates and log-rank tests, autosomal and X-linked carriers were found to have similar incidences of renal replacement therapy, proteinuria, and impaired creatinine clearance. Further, age at onset of renal replacement therapy did not differ between X-chromosomal and autosomal carriers. Both groups showed an impaired life expectancy when reaching renal replacement therapy. RAAS inhibition significantly delayed the onset of end-stage renal failure. Not only carriers of X-linked Alport mutations but also heterozygous carriers of autosomal recessive mutations were found to have an increased risk for worse renal function. The risk of end-stage renal disease in both groups affected life expectancy, and this should cause a greater alertness toward patients presenting with what has been wrongly termed 'familial benign hematuria.' Timely therapy can help to delay onset of end-stage renal failure. Thus, yearly follow-up by a nephrologist is advised for X-linked Alport carriers and patients with thin basement membrane nephropathy, microalbuminuria, proteinuria, or hypertension. [ABSTRACT FROM AUTHOR]

Renin-angiotensin-aldosterone system inhibitors prevent the progression of kidney disease in patients with diabetic nephropathy, and we studied how that benefit varies by the type of diabetes and baseline urinary albumin. We pooled data from 49 randomized controlled trials in a meta-analysis using the ratio of endpoint urinary albumin levels in those treated compared to those untreated with renin-angiotensin-aldosterone system inhibitors in both fixed- and random-effects models. The urinary albumin excretion for treated microalbuminuric patients with Type 1 diabetes was on average 60% lower at the end of the trial compared with patients not treated with renin-angiotensin-aldosterone system inhibitors using the fixed-effects model and 67% lower using the random-effects model. There was no significant effect of treatment in patients with normal albumin excretion. For normoalbuminuric patients with Type 2 diabetes, urinary albumin excretion was on average 12% lower after treatment using the fixed-effects model compared to 21% lower using the random-effects model. For microalbuminuric patients, urinary albumin excretion was on average 23% lower using the fixed-effects model and 27% lower using the random-effects model. Thus, renin-angiotensin-aldosterone system inhibition reduced urinary albumin excretion for Type 1 diabetic patients with micro-, but not those with normoalbuminuria. Treatment reduced urinary albumin excretion for Type 2 diabetic patients with and without microalbuminuria. [ABSTRACT FROM AUTHOR]

HALT PKD consists of two ongoing randomized trials with the largest cohort of systematically studied patients with autosomal dominant polycystic kidney disease to date. Study A will compare combined treatment with an angiotensin-converting inhibitor and receptor blocker to inhibitor alone and standard compared with low blood pressure targets in 558 early-stage disease patients with an eGFR over 60 ml/min per 1.73 m2. Study B will compare inhibitor-blocker treatment to the inhibitor alone in 486 late-stage patients with eGFR 25-60 ml/min per 1.73 m2. We used correlation and multiple regression cross-sectional analyses to determine associations of baseline parameters with total kidney, liver, or liver cyst volumes measured by MRI in Study A and eGFR in both studies. Lower eGFR and higher natural log-transformed urine albumin excretion were independently associated with a larger natural log-transformed total kidney volume adjusted for height (ln(HtTKV)). Higher body surface area was independently associated with a higher ln(HtTKV) and lower eGFR. Men had larger height-adjusted total kidney volume and smaller liver cyst volumes than women. A weak correlation was found between the ln(HtTKV) and natural log-transformed total liver volume adjusted for height or natural log liver cyst volume in women only. Women had higher urine aldosterone excretion and lower plasma potassium. Thus, our analysis (1) confirms a strong association between renal volume and functional parameters, (2) shows that gender and other factors differentially affect the development of polycystic disease in the kidney and liver, and (3) suggests an association between anthropomorphic measures reflecting prenatal and/or postnatal growth and disease severity. [ABSTRACT FROM AUTHOR]

Chan et al. report increased mortality with angiotensin-converting enzyme inhibitors and angiotensin type 1 receptor blockers in hemodialysis patients, supporting emerging evidence that such dual therapy may be detrimental. We speculate that effects of reactive renin and prorenin release on the (pro)renin receptor may explain this apparent paradox, either through membrane-bound generation of angiotensin II or via stimulation of signal transduction pathways. Potential benefits of direct renin inhibitors and yet-to-be-developed (pro)renin receptor blockers are discussed. [ABSTRACT FROM AUTHOR]

The anti-inflammatory, antifibrotic, and antiproteinuric properties of vitamin D have been defined in studies using active vitamin D analogs. In this prospective observational study we determined whether nutritional vitamin D repletion can have additional beneficial effects in patients with type 2 diabetic nephropathy already established on renin-angiotensin-aldosterone system inhibition. During a 7-month period, 63 patients were enrolled and those with low levels of 25(OH)D were treated with oral cholecalciferol for 4 months. Baseline serum 25(OH)D and 1,25(OH)2D showed no significant correlation with baseline urinary MCP-1, TGF-β1, or albuminuria measured as the urinary albumin-to-creatinine ratio. Of the 63 patients, 54 had insufficient or deficient levels of serum 25(OH)D and 49 complied with cholecalciferol therapy and follow-up. Both 25(OH)D and 1,25(OH)2D were significantly increased at 2 and 4 months of treatment. Albuminuria and urinary TGF-β1 decreased significantly at both time points compared to their baseline values, while urinary MCP-1 did not change. Thus, in the short term, dietary vitamin D repletion with cholecalciferol had a beneficial effect in delaying the progression of diabetic nephropathy above that due to established renin-angiotensin-aldosterone system inhibition. [ABSTRACT FROM AUTHOR]

Angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers are considered the standard of care for treatment of cardiovascular disease and chronic kidney disease. Combination therapy with both angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers effectively inhibits the renin-angiotensin system as well as potentiates the vasodilatory effects of bradykinin. It has been advocated that this dual blockade approach theoretically should result in improved clinical outcomes in both cardiovascular disease and chronic kidney disease. Clinical trial evidence for the use of combination therapy with angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers in cardiovascular disease has provided conflicting results in hypertension, congestive heart failure, and ischemic heart disease. Clinical trial evidence to support combination therapy with angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers in chronic kidney disease has largely been based on proteinuria reduction as a surrogate marker for clinically meaningful outcomes. Recent large-scale randomized clinical trials have not been able to validate protection in halting progression in chronic kidney disease with a dual blockade approach. This review serves as an appraisal on the clinical evidence of combination angiotensin-converting enzyme inhibition and angiotensin II receptor blockade in both cardiovascular disease and chronic kidney disease. [ABSTRACT FROM AUTHOR]

Diabetes mellitus is the most common and rapidly growing cause of end-stage renal disease. A classic hallmark of diabetes pathology is the activation of the intrarenal renin-angiotensin system (RAS), which may lead to hypertension and renal tissue injury, but the mechanism of RAS activation has been elusive. Recently, we described the intrarenal localization of the novel metabolic receptor GPR91 and established some of its functions in diabetes. These include the triggering of renin release in early diabetes via both vascular (endothelial) and tubular (macula densa) sites in the juxtaglomerular apparatus as well as the activation of MAP kinases in the distal nephron-collecting duct, which are important signaling mechanisms in diabetic nephropathy (DN) and renal fibrosis. GPR91 is a cell surface receptor for succinate and during the past few years it has provided a new paradigm for the mechanism of cell stress response in many organs. Beyond its traditional role in the tricarboxylic acid cycle, succinate now has an unexpected hormone-like signaling function, which may provide a feedback between local tissue metabolism, mitochondrial stress, and organ functions. Succinate accumulation in the local tissue environment and GPR91 signaling appear to be important early mechanisms by which cells detect and respond to hyperglycemia and trigger tissue injury in DN. Also, the distal nephron-collecting duct system, which is the major source of (pro)renin in diabetes and has the highest level of GPR91 expression in the kidney, may have an important, active, and early role in the pathogenesis of DN in contrast to the existing glomerulus-centric paradigm. [ABSTRACT FROM AUTHOR]

Renin-producing juxtaglomerular cells are connected to each other and to endothelial cells of afferent arterioles by gap junctions containing Connexin 40 (Cx40), abundantly expressed by these two cell types. Here, we generated mice with cell-specific deletion of Cx40 in endothelial and in renin-producing cells, as its global deletion caused local dissociation of renin-producing cells from endothelial cells, renin hypersecretion, and hypertension. In mice lacking endothelial Cx40, the blood pressure, renin-producing cell distribution, and the control of renin secretion were similar to wild-type mice. In contrast, mice deficient for Cx40 in renin-producing cells were hypertensive and these cells were ectopically localized. Although plasma renin activity and kidney renin mRNA levels of these mice were not different from controls, the negative regulation of renin secretion by pressure was inverted to a positive feedback in kidneys lacking Cx40 in renin-producing cells. Thus, our findings show that endothelial Cx40 is not essential for the control of renin expression and/or release. Cx40 in renin-producing cells is required for their correct positioning in the juxtaglomerular area and the control of renin secretion by pressure. [ABSTRACT FROM AUTHOR]

We recently showed that losartan and paricalcitol are synergistic in the treatment of diabetic nephropathy in a model of type 1 diabetes. To test this strategy in a model of type 2 diabetes, we treated 2-month-old diabetic Lprdb/db mice with losartan, paricalcitol, or a combination of losartan and paricalcitol for 3 months. Vehicle-treated diabetic mice developed progressive albuminuria and glomerular abnormalities with mesangial expansion and glomerulosclerosis compared to their non-diabetic littermate control mice. Accompanying damage of the glomerular filtration barrier was a marked reduction in podocyte number as well as reduced expression of slit diaphragm proteins. Further, there was increased glomerular expression of extracellular matrix proteins, monocyte chemoattractant protein-1 and transforming growth factor-β. Losartan or paricalcitol each alone moderately ameliorated albuminuria and glomerular damage. However, their combined use showed a dramatic therapeutic synergism, manifested by prevention of progressive albuminuria, restoration of the glomerular filtration barrier, reversal of the decline in slit diaphragm proteins, reduced synthesis of extracellular matrix proteins, and reduction of glomerulosclerosis. These effects were accompanied by blockade of the compensatory increase of renin production and angiotensin I/II accumulation in the kidney. Thus, our study further shows that vitamin D analogs can increase the efficacy of AT1 receptor blockade, leading to a more effective prevention of kidney disease in type 2 diabetes. [ABSTRACT FROM AUTHOR]

Autosomal recessive renal tubular dysgenesis (RTD) is a severe disorder of renal tubular development characterized by early onset and persistent fetal anuria leading to oligohydramnios and the Potter sequence. At birth, blood pressure is dramatically low and perinatal death occurs in most cases. Skull ossification defects are frequently associated with RTD. The disease is genetically heterogeneous and linked to mutations in the genes encoding any of the components of the renin–angiotensin system (RAS). An intense stimulation of renin production is noted in the kidneys of patients with mutations in the genes encoding angiotensinogen, angiotensin-converting enzyme, or AT1 receptor, whereas absence or increased renin production is associated with REN defects depending on the type of mutation. The severity of the disease underlines the importance of a functional RAS in the maintenance of blood pressure and renal blood flow during fetal life. The absence or poor development of proximal tubules, as well as renal vascular changes, may be attributable to renal hypoperfusion rather than to a morphogenic property of the RAS. The less severe phenotype in mice devoid of RAS may be linked to differences between mice and humans in the time of nephrogenesis and maturation of the RAS. The identification of the disease on the basis of precise clinical and histological analyses and the characterization of the genetic defects allow genetic counseling and early prenatal diagnosis. [ABSTRACT FROM AUTHOR]

[Arg8]-vasopressin (AVP) has several functions via its three distinct receptors, V1a, V1b, and V2. The V1a vasopressin receptor (V1aR) is expressed in blood vessels and involved in vascular contraction. Recently, we generated V1a receptor–deficient (V1aR−/−) mice and found that they were hypotensive. In addition, V1aR−/− mice exhibited (1) blunted AVP-induced vasopressor response, (2) impaired arterial baroreceptor reflex, (3) decreased sympathetic nerve activity, and (4) decreased blood volume, all of which could contribute to the observed hypotension. In relation to their decreased blood volume, V1aR−/− mice had decreased plasma aldosterone levels, which could result not only from decreased activity of the renin–angiotensin system (RAS), but also from impaired AVP-stimulated aldosterone release in the adrenal glands. V1aR was found to specifically co-express at the macula densa cells with cyclooxygenase (COX)-2 and with neuronal nitric oxide synthase, which produces potent stimulators of renin, PGE2, and NO. The expression levels of renin, COX-2, and nNOS were significantly decreased in V1aR−/− mice, which led to the suppression of RAS activity and consequent decreases in aldosterone and blood volume. Furthermore, V1aR is also expressed in collecting duct cells and involved in regulating water reabsorption by affecting V2/aquaporin 2 function. Thus, AVP regulates blood pressure and volume via V1aR by exerting diverse functions in vivo. [ABSTRACT FROM AUTHOR]

Many agents constrict isolated afferent arterioles only at concentrations higher than their physiological levels. Here we determined if norepinephrine, as released by sympathetic nerve activity, could influence the angiotensin II responsiveness of isolated mouse afferent arterioles. Pretreatment of the arterioles for short periods with norepinephrine significantly increased the ability of 10 picomolar angiotensin II to constrict the vessels, an effect inhibited by the alpha receptor blockers prazosin (α-1) or yohimbine (α-2). Although the intracellular calcium transients induced by angiotensin were not different, phosphorylation of the 20 kDa myosin light chain was significantly increased in the presence of norepinephrine. Phosphorylation of the p38 mitogen-activated protein kinase was not changed. Phosphorylation of the myosin phosphatase targeting subunit at Thr696, but not at Thr850, was significantly enhanced by, norepinephrine pretreatment, thus increasing the calcium sensitivity of the arteriolar smooth muscle. Our results show that norepinephrine increases afferent arteriolar sensitivity to angiotensin II by means of alpha receptor activation, causing increased calcium sensitivity through phosphorylation of the myosin phosphatase targeting subunit. [ABSTRACT FROM AUTHOR]

Blockade of the renin–angiotensin system (RAS), the standard treatment for chronic proteinuric nephropathy, slows but may not halt progression of the disease, particularly when therapy is started late. Because vasopressin may also play a role in the progression of renal disease, we measured the effect of a dual V1a and V2 vasopressin receptor antagonist (RWJ-676070) alone or combined with angiotensin-converting enzyme inhibition or angiotensin II type 1 receptor blockade on proteinuria and renal disease progression during overt nephropathy. Twenty-one days after renal mass reduction, a time of established injury, rats were given vehicle, RWJ-676070, enalapril, losartan, RWJ-676070 plus enalapril, or losartan in drinking water for an additional 39 days. RWJ-676070 returned the blood pressure to pre-treatment levels, which were significantly lower than those in vehicle-treated rats. Enalapril, losartan, and the combined therapies reduced blood pressure to a greater extent. RWJ-676070 afforded a partial antiproteinuric effect, which was enhanced by the addition of enalapril or losartan. Renal functional impairment, and glomerular and tubular changes were partially ameliorated by RWJ-676070; parameters significantly improved with either enalapril or losartan alone and improved to a greater extent with the combined therapies. Our findings suggest that vasopressin receptor antagonists could be of additional therapeutic value in the treatment of chronic proteinuric nephropathy. [ABSTRACT FROM AUTHOR]

Tissue kallikrein is the main kinin-forming enzyme in mammals, and differences in kinin levels are thought to be a contributing factor to diabetic nephropathy. Here, we determined the role of the kallikrein-kinin system in the pathogenesis of streptozotocin-induced diabetic nephropathy in wild-type and tissue kallikrein–knockout mice. All diabetic mice developed similar hyperglycemia, but the knockout mice had a significant two-fold increase in albuminuria compared to the wild-type mice before and after blood pressure elevation. Ezrin mRNA, a podocyte protein potentially implicated in albuminuria, was downregulated in the kidney of knockout mice. One month after induction of diabetes, the mRNAs of kininogen, tissue kallikrein, kinin B1, and B2 receptors were all increased up to two-fold in the kidney in both genotypes. Diabetes caused a 50% decrease in renal angiotensin-converting enzyme expression and a 20-fold increase in kidney injury molecule-1 reflecting tubular dysfunction, but there was no genotype difference. Our study found an early activation of the kallikrein-kinin system in the kidney and that this has a protective role against the development of diabetic nephropathy. The effect of tissue kallikrein deficiency on microalbuminuria in diabetic mice is similar to the effect of genetically high angiotensin-converting enzyme levels, suggesting that both observations, in part, result from a deficiency in kinins.Kidney International (2009) 76, 395–403; doi:10.1038/ki.2009.208; published online 10 June 2009 [ABSTRACT FROM AUTHOR]

Chronic inhibition of nitric oxide synthase by Nω-nitro- L-arginine methyl ester (L-NAME) causes progressive renal injury with systemic hypertension and interstitial macrophage infiltration. We have previously shown that there is local activation of the renin–angiotensin–aldosterone system in the renal cortex as a major pathogenic feature of macrophage infiltration. In this study, we measured the effects of the aldosterone antagonist, spironolactone, on renal injury in L-NAME-treated male Wistar rats. After 12 weeks of L-NAME-treatment, rats had increased systolic blood pressure, urinary protein excretion, and serum creatinine and histological analysis showed glomerulosclerosis, interstitial fibrosis, and macrophage infiltration. Treatment with spironolactone significantly prevented these renal changes, whereas treatment with hydralazine had no effect. The cortical expression of osteopontin was significantly elevated in L-NAME-treated rats, and expression of its mRNA significantly correlated with the number of infiltrating macrophages and degree of interstitial fibrosis. Spironolactone treatment markedly suppressed osteopontin expression. Our results suggest that reduced nitric oxide bioavailability caused renal inflammation and fibrosis through an aldosterone receptor–dependent mechanism associated with osteopontin expression independent of its systemic hemodynamic effects.Kidney International (2009) 75, 147–155; doi:10.1038/ki.2008.507; published online 15 October 2008 [ABSTRACT FROM AUTHOR]

Glomerular podocyte integrity is essential to limit protein filtration in the urine. Hayashi et al. report that epigenetic mechanisms control podocyte differentiation and that activation of the renin-angiotensin system in kidney disease affects podocyte differentiation and proteinuria by resetting the podocyte epigenome. These findings suggest that modulation of DNA methylation could be a promising target for the control of proteinuric kidney disease. [ABSTRACT FROM AUTHOR]

The renal renin–angiotensin system plays a major role in determining the rate of chronic renal disease progression. Treatment with activators of the vitamin D receptor retards the progression of experimental chronic renal disease, and vitamin D is known to suppress the renin–angiotensin system in other organs. Here we determined if the beneficial effects of paricalcitol (19-nor 1,25-dihydroxyvitamin D2) were associated with suppression of renin–angiotensin gene expression in the kidney. Rats with the remnant kidney model of chronic renal failure (5/6 nephrectomy) were given two different doses of paricalcitol thrice weekly for 8 weeks. Paricalcitol was found to decrease angiotensinogen, renin, renin receptor, and vascular endothelial growth factor mRNA levels in the remnant kidney by 30–50 percent compared to untreated animals. Similarly, the protein expression of renin, renin receptor, the angiotensin type 1 receptor, and vascular endothelial growth factor were all significantly decreased. Glomerular and tubulointerstitial damage, hypertension, proteinuria, and the deterioration of renal function resulting from renal ablation were all similarly and significantly improved with both treatment doses. These studies suggest that the beneficial effects of vitamin D receptor activators in experimental chronic renal failure are due, at least in part, to down-regulation of the renal renin-angiotensin system.Kidney International (2008) 74, 1394–1402; doi:10.1038/ki.2008.408; published online 27 August 2008 [ABSTRACT FROM AUTHOR]

To determine whether the cardiovascular effect of 1,25(OH)2D is dependent on calcium and/or phosphorus, mice with targeted deletion of the 25(OH)D 1α-hydroxylase and their wild-type littermates were fed a normal diet or a diet to rescue the ambient serum calcium and phosphorus levels. Mice on the normal diet were treated daily with vehicle or 1,25(OH)2D3 while mice on the rescue diet received vehicle, captopril or losartan. After four weeks the vehicle-treated knockout mice developed hypertension, cardiac hypertrophy and impaired cardiac function along with an up-regulation of the renin-angiotensin system in both renal and cardiac tissues. Although the serum calcium and phosphorus levels were normalized in knockout mice on the rescue diet, abnormalities in blood pressure, cardiac structure-function and the renin-angiotensin system remained. In contrast, 1,25(OH)2D3 not only normalized serum calcium and phosphorus levels but also normalized blood pressure, cardiac structure-function and the renin-angiotensin system. Treatment of the knockout mice with either captopril or losartan normalized blood pressure and cardiac structure and function although renin expression remained elevated. This study shows that 1,25(OH)2D plays a protective role in the cardiovascular system by repressing the renin-angiotensin system independent of extracellular calcium or phosphorus.Kidney International (2008) 74, 170–179; doi:10.1038/ki.2008.101; published online 2 April 2008 [ABSTRACT FROM AUTHOR]

Aliskiren represents the first member in a new class of antihypertensive drugs. Inhibiting the renin–angiotensin system at its rate-limiting step is an idea that has been pursued for >30 years; however, earlier compounds failed because of problems related to efficacy, bioavailability, and/or side effects. Aliskiren, a 610 Da nonpeptide molecule, has exceptional affinity for the human renin enzymatic site and a half-life of about 40 h, which make its 3% bioavailability clinically unimportant with continued administration. The drug is not metabolized by CYP P450 enzymes and is excreted >90% unchanged by the fecal route. No adjustments are necessary for renal function, liver function, age, ethnicity, or other prescribed drugs. Blood pressure reductions are similar to those provided by other monotherapies. Interestingly, aliskiren combined with angiotensin receptor blocker or angiotensin-converting enzyme inhibitor therapy leads to a further blood pressure reduction as does combination with a diuretic or calcium channel blocker. The fact that plasma renin activity is reduced to low levels with aliskiren could provide a theoretical advantage over other treatments, while increases in total renin (prorenin) after the drug poses additional food for thought. Studies with primary cardiovascular and renal end points to address these possibilities are in progress.Kidney International (2008) 73, 679–683; doi:10.1038/sj.ki.5002732; published online 26 December 2007 [ABSTRACT FROM AUTHOR]

Connexins form intercellular channels that span two plasma membranes and directly couple the cytoplasm of adjacent cells. This morphological contact enables the exchange of ions, second messengers, and metabolites, which act to regulate several biological functions. This review focuses on the significance of connexins in the renal circulation. Cells of the renal vasculature are coupled and express connexins in a vessel and cell-specific pattern. This finding indicates that renal connexins likely play an important role in renal autoregulatory mechanisms (Bayliss effect, tubuloglomerular feedback) and in the control of vasomotor responses. The described coupling of endothelial and vascular smooth muscle cells in the afferent arterioles may also contribute to the communication of neighboring nephrons, called ‘nephron coupling.’ Furthermore, deletion of the Cx40 and Cx43 genes results in an altered functional behavior of the renin-producing cells, suggesting involvement of these connexin isoforms in the regulation of renin secretion and synthesis. In addition, this review discusses the role of renal connexin expression in the pathogenesis of hypertension or diabetes.Kidney International (2008) 73, 547–555; doi:10.1038/sj.ki.5002720; published online 12 December 2007 [ABSTRACT FROM AUTHOR]

Gap junctions are present in the juxtaglomerular apparatus enabling intercellular communication. Our study determined the location of different connexin subtypes within the juxtaglomerular apparatus of the rat, and the role of these subtypes in renal hemodynamics through the use of specific mimetic peptides. Immunohistochemical analysis showed connexins 37 and 40 expression in the endothelial and renin-secreting cells of the afferent arteriole, while connexin 40 was also found in extra- and intraglomerular mesangial cells. In contrast, connexin 43 was weakly expressed in endothelial cells of the afferent arteriole and within the glomerulus. Intra-renal infusion of the peptides (GAP) reported to block specific gap junctions (Cx37,43GAP27 or Cx40GAP27), elevated blood pressure, plasma renin activity, and angiotensin II levels, while decreasing renal plasma flow without a significant change in the glomerular filtration rate. Subsequent restoration of blood pressure reduced both renal plasma flow and glomerular filtration rate. In contrast, Cx43GAP26 reduced glomerular filtration rate without alterations in blood pressure, renal plasma flow, plasma renin activity, or angiotensin II levels. Hence, connexins 37 and 40 are expressed in the rat juxtaglomerular apparatus and these proteins control, in part, the renin–angiotensin system and renal autoregulation.Kidney International (2008) 73, 415–422; doi:10.1038/sj.ki.5002673; published online 28 November 2007 [ABSTRACT FROM AUTHOR]

1,25-Dihydroxyvitamin D3 negatively regulates the renin–angiotensin system (RAS), which plays a critical role in the development of diabetic nephropathy. We tested if mice lacking the vitamin D receptor (VDR) are more susceptible to hyperglycemia-induced renal injury. Diabetic VDR knockout mice developed more severe albuminuria and glomerulosclerosis due to increased glomerular basement membrane thickening and podocyte effacement. More fibronectin (FN) and less nephrin were expressed in the VDR knockout mice compared to diabetic wild-type mice. In receptor knockout mice, increased renin, angiotensinogen, transforming growth factor-β (TGF-β), and connective tissue growth factor accompanied the more severe renal injury. 1,25-Dihydroxyvitmain D3 inhibited high glucose (HG)-induced FN production in cultured mesangial cells and increased nephrin expression in cultured podocytes. 1,25-Dihydroxyvitmain D3 also suppressed HG-induced activation of the RAS and TGF-β in mesangial and juxtaglomerular cells. Our study suggests that receptor-mediated vitamin D actions are renoprotective in diabetic nephropathy.Kidney International (2008) 73, 163–171; doi:10.1038/sj.ki.5002572; published online 10 October 2007 [ABSTRACT FROM AUTHOR]

Microalbuminuria independently predicts increased cardiovascular risk in hypertensive patients, especially in those with concomitant diabetes or established cardiovascular disease. Drugs that target the renin–angiotensin–aldosterone system reduce microalbuminuria regardless of diabetic status. The Irbesartan in the Management of PROteinuric patients at high risk for Vascular Events was a multicenter, randomized, double-blind, placebo-controlled paralleled group study in which hypertensive patients with microalbuminuria and increased cardiovascular risk were randomized to 20 weeks treatment with ramipril plus irbesartan or to ramipril plus placebo. Patients discontinued or tapered previous antihypertensive therapy during a 14-day placebo lead-in period. Change in albumin excretion rate from baseline to week 20 was the primary end point. Adjusted week 20 baseline geometric ratios for ramipril plus irbesartan and ramipril plus placebo were not significantly different. Although differences in blood pressure reductions were observed between the two treatments, these changes did not affect microalbuminuria. More patients on dual therapy achieved target blood pressure goals at week 20 than with monotherapy. The incidence of adverse effects and treatment-related adverse effects was similar in both groups. Our results suggest that patients with cardiovascular risk and relatively low albumin excretion rates in early-stage disease may only require monotherapy with renin–angiotensin–aldosterone blocking agents.Kidney International (2007) 72, 879–885; doi:10.1038/sj.ki.5002455; published online 1 August 2007 [ABSTRACT FROM AUTHOR]

The autocrine and paracrine activation of the renin–angiotensin system (RAS) within cells of the kidney plays a role in the overall pathophysiology of the renal disease due to diabetes. In this study, we focus on components of the RAS in the podocyte as these cells are important in the pathogenesis of glomerulosclerosis and proteinuria. Immortalized mouse podocytes were exposed to media containing normal glucose (NG) or high glucose (HG) for in vitro studies. In vivo studies utilized kidney tissue obtained from rats treated for 3 months with streptozotocin to induce diabetes. Angiotensinogen (AGT) and the angiotensin II (AII) type 1 receptor mRNA and protein were significantly increased in the podocytes cultured under the high glucose conditions. Both angiotensins I and II levels were significantly higher in cell lysates and the conditioned media of cells grown in high glucose. There were no differences in renin activity, angiotensin-converting enzyme level, or AII type 2 receptor level. Glomerular AGT and AII type 1 receptor assessed by means of immunohistochemistry were increased in diabetic rats compared with the control rats. Other measured components of the RAS within the glomeruli were not different. We suggest that increased AGT, an attendant increase in AII and increased AII type 1 receptor in podocytes experiencing diabetic conditions play an important role in the pathogenesis of diabetic nephropathy.Kidney International (2007) 71, 1019–1027. doi:10.1038/sj.ki.5002195; published online 14 March 2007 [ABSTRACT FROM AUTHOR]

The circadian blood pressure (BP) rhythm is associated with worsened cardiovascular outcomes in patients who have an excessive morning BP surge and in those who lack the normal nocturnal BP fall (non-dippers). There are multiple pathophysiologic mechanisms underlying abnormalities in circadian BP, most importantly abnormalities in sympathetic nervous system activity, salt and volume balance, and activation of the renin–angiotensin system. Several of these factors can be modified by clinical interventions, either related to lifestyle changes and/or antihypertensive drug therapy. The timing of drug administration or specific drug delivery systems that lead to a greater effect at night and/or mitigate the early morning BP surge can correct abnormal circadian rhythms. Although these strategies have not yet been shown to alter clinical outcomes, it is reasonable to understand their biologic basis and take them into consideration when designing antihypertensive therapy.Kidney International (2007) 71, 855–860. doi:10.1038/sj.ki.5002130; published online 21 March 2007 [ABSTRACT FROM AUTHOR]

Intrarenally synthesized angiotensin II (Ang II) may be involved in the progression of glomerulonephritis, leading to irreversible glomerulosclerosis. There is increasing evidence that systemic angiotensin receptor blocker (ARB) treatment has beneficial effect on the prognosis of progressive glomerulonephritis and diabetic nephropathy. However, the cellular and molecular mechanisms behind this therapeutic effect of ARB remain unclear. In this study, we used a novel strategy of local ARB delivery via type-1 collagen sponge, to treat progressive glomerulonephritis that would result in irreversible glomerulosclerosis in our previously established rat model. At days 9 and 14 after disease induction, mild proteinuria, 20.7±4.7 and 10±1.3 mg/day, was found. Local ARB treatment reduced proteinuria significantly to 3.19±3.2 and 5.25±0.95 mg/day (P<0.01), respectively. Scoring of glomerular matrix expansion and sclerotic index revealed that local ARB treatment significantly ameliorated glomerular pathology. Ang II type 1 receptor mRNA expression was remarkably enhanced in the Ang II group and ARB treatment reversed this effect at 14 days. Local delivery of ARB significantly improved glomerular blood flow levels, compared to the untreated disease control group, from 710±18.25 to 859.44±22.86 μm/s, respectively. Local delivery of ARB into the kidney affected local RAS and thus improved the renal injury and function in the potentially progressive glomerulosclerosis of rat model.Kidney International (2006) 70, 1591–1598. doi:10.1038/sj.ki.5001872; published online 20 September 2006 [ABSTRACT FROM AUTHOR]

The abnormal development of the intrarenal renin–angiotensin system (RAS) is thought contribute to adult-onset hypertension in the spontaneously hypertensive rat (SHR). Angiotensin-converting enzyme 2 (ACE2) is a novel enzyme with complementary actions to that of ACE. Recent studies have shown that ACE2 expression is reduced in the adult SHR. However, its regulation in pre-hypertensive animals is unknown. In this study, we examine the developmental expression of ACE2 in the rodent kidney and its temporal expression, as it relates to the development of hypertension in the SHR model. Kidneys from SHR and normotensive Wistar Kyoto (WKY) rats (n=8–12/group) at birth, 6 weeks of age, and adulthood (80 days) were examined. Gene expression and activity of ACE2 were determined by real-time reverse transcription-polymerase chain reaction and quenched fluorescence assays, respectively. Renal expression was localized by in situ hybridization and immunohistochemistry. The expression and ACE2 activity are significantly increased in the SHR kidney at birth. With the onset of hypertension, the tubular expression of ACE2 falls in SHR compared to WKY and remains reduced in the adult SHR kidney. Glomerular expression is paradoxically increased in the SHR glomerulus. The overall developmental pattern of ACE2 expression in the SHR kidney is also modified, with declining expression over the course of renal development. The developmental pattern of ACE2 expression in the SHR kidney is altered before the onset of hypertension, consistent with the key role of the RAS in the pathogenesis of adult-onset hypertension. Further research is required to distinguish the contribution of these changes to the development and progression of hypertension in this model.Kidney International (2006) 70, 34–41. doi:10.1038/sj.ki.5000428; published online 17 May 2006 [ABSTRACT FROM AUTHOR]

Angiotensin-converting enzyme 2 (ACE2) is a homolog of ACE, which is not blocked by ACE inhibitors. High amounts of ACE2 are present in the proximal tubule, and ACE2 catalyzes generation of angiotensin 1–7 (Ang-(1–7)) by this segment. Ang-(1–7) binds to a receptor distinct from the AT1 or AT2 Ang II receptor, identified as the mas receptor. We studied the effects of Ang-(1–7) on Ang II-mediated cell signaling pathways in proximal tubule. In primary cultures of rat proximal tubular cells, activation of mitogen-activated protein kinases (MAPK) was detected by immunoblotting, in the presence or absence of agonists/antagonists. Transforming growth factor-β1 (TGF-β1) was measured by enzyme-linked immunosorbent assay. Ang II (5 min, 10−7 M) stimulated phosphorylation of the three MAPK (p38, extracellular signal-related kinase (ERK 1/2), and c-Jun N-terminal kinase (JNK)). While incubation of proximal tubular cells with Ang-(1–7) alone did not significantly affect MAPK phosphorylation, Ang-(1–7) (10−7 M) completely inhibited Ang II-stimulated phosphorylation of p38, ERK 1/2, and JNK. This inhibitory effect was reversed by the Ang-(1–7) receptor antagonist, D-Ala7-Ang-(1–7). Ang II significantly increased production of TGF-β1 in proximal tubular cells, an effect that was partly inhibited by Ang-(1–7). Ang-(1–7) had no significant effect on cyclic 3′,5′-adenosine monophosphate production in these cells. In summary, Ang-(1–7) inhibits Ang II-stimulated MAPK phosphorylation in proximal tubular cells. Generation of Ang-(1–7) by proximal tubular ACE2 could thereby serve a protective role by counteracting the effects of locally generated Ang II.Kidney International (2006) 69, 2212–2218. doi:10.1038/sj.ki.5001509; published online 3 May 2006 [ABSTRACT FROM AUTHOR]

The existence of a tissue renin–angiotensin (RAS) system independent of the circulating RAS has prompted the search for cellular binding sites for angiotensinogen and for renin in order to explain their tissue uptake. Two receptors that bind with similar affinity mature renin and prorenin were identified, the mannose-6-phosphate receptor (M6P-R) and a specific receptor. The M6P-R is a clearance receptor that binds exclusively the glycosylated forms of renin and prorenin. Binding of renin and prorenin to the M6P-R is followed by internalization and degradation, and the intracellular proteolysis of prorenin in mature renin did not provoke any generation of intracellular angiotensins. In contrast to the M6P-R, (pro)renin bound to the specific receptor was not degraded. Instead, receptor-bound renin showed increased catalytic activity, and receptor-bound prorenin exhibited full catalytic activity. This ‘gain of activity’ was explained by a conformational change of the (pro)renin molecule upon binding. Furthermore, (pro)renin binding provoked a rapid activation of the mitogen-activated protein kinases p44/p42, indicating that the receptor has mediated specific, angiotensin II-independent effects of (pro)renin. This receptor represents an elegant concept to explain the existence of active prorenin in vivo, and it provides a pathological role for prorenin in situations with paradoxical low renin and high prorenin concentrations such as in diabetes. Experimental models of rats overexpressing the receptor either in vascular smooth muscle cells and developing high blood pressure or with ubiquitous expression associated with glomerulosclerosis and proteinuria confirm a role for the receptor in cardiovascular and renal diseases.Kidney International (2006) 69, 1503–1506. doi:10.1038/sj.ki.5000265; published online 1 March 2006 [ABSTRACT FROM AUTHOR]

Type 2 diabetes is becoming the leading cause of end-stage renal disease (ESRD) worldwide. Prevalence of ESRD and the antihypertensive response to renin–angiotensin system intervention are suggested to vary among different ethnicities. The Reduction in Endpoints in Non-insulin dependent diabetes mellitus with the Angiotensin II Antagonist Losartan (RENAAL) study, which included different ethnic groups, demonstrated a renoprotective effect of losartan. A post hoc analysis from RENAAL was performed where we examined in each ethnic group the ESRD risk, identified independent predictors for ESRD, effect of degree of baseline albuminuria, effect of 6-month antiproteinuric response to therapy on ESRD, and renoprotective effect of losartan assessed by albuminuria reduction and ESRD. Baseline albuminuria was the strongest predictor for ESRD in every ethnic group. Albuminuria reduction was associated with reduced risk of ESRD while losartan reduced albuminuria in every ethnic group. When accounting for independent predictors of ESRD, losartan exhibited renoprotection in all ethnic groups. In this type 2 diabetic population with nephropathy, baseline albuminuria is the predominant risk parameter for ESRD; early antiproteinuric effect of losartan predicts long-term renoprotection; and losartan appears to be renoprotective in all ethnic groups. Since the RENAAL study was not powered to determine ethnic responses, these results underline the need for prospective trials where the aim is renal protection among different ethnic groups.Kidney International (2006) 69, 1675–1682. doi:10.1038/sj.ki.5000326; published online 29 March 2006 [ABSTRACT FROM AUTHOR]

Although structural and functional changes of resistance arteries have been proposed to participate in arterial hypertension (HTA) outcome, not all therapies may correct these alterations, even if they normalize the blood pressure (BP). The aim of this study was to investigate the mechanisms of the protection afforded by the angiotensin receptor antagonist losartan in resistance arteries from patients with essential HTA. In all, 22 untreated hypertensive patients were randomized to receive losartan or amlodipine for 1 year and the morphological characteristics of resistance vessels from subcutaneous biopsies were evaluated. Protein expression of connective tissue growth factor (CTGF), transforming growth factor β (TGF-β), and collagens III and IV was detected by immunohistochemistry. In comparison with normotensive subjects, resistance arteries from hypertensive patients showed a significant media:lumen (M/L) ratio increment and a higher protein expression of CTGF, TGF-β, and collagens. After 1 year of treatment, both losartan and amlodipine similarly controlled BP. However, M/L only decreased in patients under losartan treatment, whereas in the amlodipine-treated group this ratio continued to increase significantly. The administration of losartan prevented significant increments in CTGF, TGF-β, and collagens in resistance arteries. By contrast, amlodipine-treated patients showed a higher vascular CTGF, TGF-β, and collagen IV staining than before treatment. Our results show that the administration of losartan, but not amlodipine, to hypertensive patients improves structural abnormalities and prevents the production of CTGF and TGF-β in small arteries, despite similar BP lowering. These data may explain the molecular mechanisms of the better vascular protection afforded by drugs interfering with the renin–angiotensin system.Kidney International (2006) 69, 1237–1244. doi:10.1038/sj.ki.5000034; published online 15 February 2006 [ABSTRACT FROM AUTHOR]

Hyperactivation of systemic renin–angiotensin system (RAS) during sepsis is well documented. However, the behavior of intrarenal RAS in the context of endotoxemia is yet to be defined. The present study evaluates the direct effect of Escherichia coli lipopolysaccharide (LPS) on immortalized human mesangial cell (HMC) RAS. Quiescent HMC were incubated with vehicle or LPS (1–100 μg/ml), and levels of angiotensin I and II (Ang I and II) and their metabolites were analyzed by high-performance liquid chromatography. In addition, angiotensin-converting enzyme (ACE) and renin activity were also investigated. Cell lysate and extracellular medium levels of Ang II were rapidly reduced (1 h) in a time- and concentration-dependent manner, reaching a significant −9 fold-change (P<0.001) after 3 h of LPS incubation. Similar results were obtained for Ang I levels (−3 fold-change, P<0.001). We ruled out Ang I and II degradation, as levels of their metabolic fragments were also significantly decreased by LPS. ACE activity was slightly increased following LPS incubation. On the other hand, renin activity was significantly inhibited, as Ang I concentration elevation following exogenous angiotensinogen administration was blunted by LPS (−60% vs vehicle, P<0.001). Renin and angiotensinogen protein levels were not affected by LPS according to Western blot analysis. Taken together, these data demonstrate for the first time that LPS significantly downregulates HMC RAS through inhibition of renin or renin-like activity. These findings are potentially related to the development of and/or recovery from acute renal failure in the context of sepsis.Kidney International (2006) 69, 974–980. doi:10.1038/sj.ki.5000134; published online 22 February 2006 [ABSTRACT FROM AUTHOR]

Progression of diabetic nephropathy appears directly related to renal tubulointerstitial injury, but the involved genes are incompletely delineated. To identify such genes, DNA microarray analysis was performed with RNA from renal proximal tubules (RPTs) of streptozotocin-induced diabetic Wistar rats, spontaneously diabetic BioBreeding rats, and rat immortalized renal proximal tubular cells (IRPTCs) exposed to high glucose (25 mM) medium for 2 weeks. Osteopontin (OPN) mRNA expression was quantified by real time-quantitative polymerase chain reaction (RT-qPCR) or conventional reverse transcriptase-polymerase chain reaction (RT-PCR). OPN mRNA expression was upregulated (5–70-fold increase) in diabetic rat RPTs and in IRPTCs chronically exposed to high glucose compared to control RPTs and IRPTCs. High glucose, angiotensin II, phorbol 12-myristate 13-acetate and transforming growth factor-beta 1 (TGF-β1) stimulated OPN mRNA expression in IRPTCs in a dose- and time-dependent manner. This effect was inhibited by tiron, taurine, diphenylene iodinium, losartan, perindopril, calphostin C, or LY 379196 but not PD123319. IRPTCs overexpressing dominant-negative protein kinase C-beta 1 (PKC-β1) cDNA or antisense TGF-β1 cDNA prevented the high glucose effect on OPN mRNA expression. We concluded that high glucose-mediated increases in OPN gene expression in diabetic rat RPTs and IRPTCs are mediated, at least in part, via reactive oxygen species generation, intrarenal rennin–angiotensin system activation, TGF-β1 expression, and PKC-β1 signaling.Kidney International (2006) 69, 1005–1015. doi:10.1038/sj.ki.5000206; published online 1 February 2006 [ABSTRACT FROM AUTHOR]

The renin–angiotensin system in the kidney plays a critical role in the regulation of renal hemodynamics and sodium handling through the activation of vascular, glomerular and tubular angiotensin II type 1 (AT1) receptor-mediated signaling. We previously cloned a molecule that specifically bound to the AT1 receptor and modulated AT1 receptor signaling in vitro, which we named ATRAP (for AT1 receptor-associated protein). The purpose of this study is to analyze the renal distribution of ATRAP and to examine whether ATRAP is co-expressed with the AT1 receptor in the mouse kidney. We performed in situ hybridization, Western blot analysis, and immunohistochemistry to investigate the expression of ATRAP mRNA and protein in the mouse kidney. The results of Western blot analysis revealed the ATRAP protein to be abundantly expressed in the kidney. Employing in situ hybridization and immunohistochemistry, we found that both ATRAP mRNA and the protein were widely distributed along the renal tubules from Bowman's capsules to the inner medullary collecting ducts. ATRAP mRNA was also detected in the glomeruli, vasculature, and interstitial cells. In all tubular cells, the ATRAP protein colocalized with the AT1 receptor. Finally, we found that the dietary salt depletion significantly decreased the renal expression of ATRAP as well as AT1 receptor. These findings show ATRAP to be abundantly and broadly distributed in nephron segments where the AT1 receptor is expressed. Furthermore, this is the first report demonstrating a substantial colocalization of ATRAP and AT1 receptor in vivo.Kidney International (2006) 69, 488–494. doi:10.1038/sj.ki.5000130; published online 6 January 2006 [ABSTRACT FROM AUTHOR]

Background. Aldosterone has been suggested to play a role in the initiation and progression of diabetic nephropathy. Currently recommended treatment with angiotensin-converting enzyme (ACE) inhibitors or angiotensin II receptor blockers [renin-angiotensin system (RAS) blockade] does not suppress circulating aldosterone sufficiently. We therefore aimed to evaluate the short-term effect of aldosterone antagonism with spironolactone on albuminuria and blood pressure in diabetic nephropathy. Methods. Twenty Caucasian type 1 diabetic patients with persistent macroalbuminuria despite antihypertensive treatment, including RAS blockade, completed this double-masked, randomized cross-over trial. Patients were treated in random order with spironolactone 25 mg once daily and matched placebo for two months, respectively, on top of usual antihypertensive treatment. After each treatment period albuminuria, 24-hour blood pressure, and glomerular filtration rate (GFR) were determined. Results. Spironolactone on top of usual antihypertensive treatment induced a 30% (95% CI 17 to 41) reduction in albuminuria from [geometric mean (95% CI)] 831 (624 to 1106) mg/24-hour on placebo treatment ( P < 0.001), and a reduction in fractional albumin clearance of 35% (20 to 46, P < 0.001). Twenty-four–hour blood pressure showed an insignificant reduction of [mean reduction (95% CI)] 8 (−1 to 17)/3 (−0.2 to 7) mm Hg ( P < 0.10). There was an insignificant reversible reduction in GFR during treatment with spironolactone. On spironolactone treatment, one patient was excluded due to hyperkalemia (plasma potassium 5.7 mmol/L) and one due to orthostatic dizziness. Otherwise treatment was well tolerated. Conclusion. Our results suggest that spironolactone treatment on top of recommended antihypertensive treatment reduces blood pressure and may offer additional renoprotection in type 1 diabetic patients with diabetic nephropathy. [ABSTRACT FROM AUTHOR]

Background. Patients with chronic kidney disease (CKD) are at high risk for cardiovascular disease, and despite recent advances in hypertension control, anemia management, and dialysis adequacy, mortality remains high. Improved understanding of nontraditional risk factors, including those present at early phases in CKD, may lead to novel therapeutic strategies. CKD has been demonstrated to be an independent risk factor for cardiovascular disease in the general population, but data are lacking as to the associated potential abnormalities that occur in association with reduced glomerular filtration rate (GFR), which may contribute to this increased risk. Data are accumulating regarding the role of abnormalities of calcium, phosphorus, vitamin D, and parathyroid hormone (PTH) in cardiovascular disease. Vitamin D deficiency is present even in the early stages of CKD. Vitamin D plays a central role in calcium-phosphorus homeostasis, regulation of PTH, and formation and maintenance of bone. However, until recently, vitamin D has not been considered to have a biologic role in CKD beyond mineral regulation, or has been considered as a negative factor contributing to soft tissue and cardiovascular calcification. In light of recent observational studies showing an association of vitamin D therapy and survival benefit in hemodialysis patients, the effects of vitamin D on cardiovascular system have become a heavily debated issue. Methods. A Medline search was performed to identify relevant literature describing the role of vitamin D in the pathogenesis of cardiovascular disease. Both the experimental and clinical literatures in English were reviewed. Results. The accumulating published data demonstrate both associative relationships and mechanisms for biologic plausibility. The following three potential mechanisms may be important for the protective effects of vitamin D against cardiovascular disease mortality: vitamin D can inhibit various aspects of inflammation, which have been established as a key pathogenic mechanism in atherosclerosis; vitamin D exerts an antiproliferative effect on myocardial cell hypertrophy and proliferation, which underlies the pathogenesis of congestive heart failure; and vitamin D acts as a negative endocrine regulator for the renin-angiotensin system, which itself plays an important independent role in hypertension and cardiovascular health. Conclusion. Vitamin D deficiency might be an underestimated nonclassical risk factor for cardiovascular disease in CKD. Based on a review of the evidence, from both basic science and clinical studies, this article supports the possible protective role of vitamin D beyond its effect on mineral metabolism, and suggests the need for ongoing evaluation of the role of vitamin D in cardiovascular health in the CKD population. [ABSTRACT FROM AUTHOR]

Background. The renin-angiotensin system plays a critical role in cardiovascular function, but little is known about the effects of specific cyclooxygenase 2 (COX-2) inhibition on this system in healthy humans under physiologic conditions. Methods. Twenty-one healthy female volunteers received, in a randomized, double-blind, crossover study, celecoxib 200 mg twice a day, indomethacin 50 mg three times a day, or placebo for 4 days and a single dose, each, on day 5. On day 5 of each treatment, the following parameters were assessed with subjects in an upright position before and after administration of 20 mg furosemide intravenously: plasma renin activity (PRA), plasma aldosterone, serum and urine electrolytes, and creatinine. Index metabolites of prostanoids were analyzed by gas chromatography-tandem mass spectrometry in 24-hour urine on day 4 and in 2-hour urines before and after furosemide administration. Results. Baseline and furosemide-stimulated PRA were reduced to a similar degree by celecoxib and indomethacin. Plasma aldosterone and urinary excretion of potassium showed changes consistent with the alteration of PRA. Urinary excretion rates of prostaglandin E2, (PGE2), 7α-hydroxy-5, 11-diketotetranor-prosta-1,16-dioic acid (PGE-M), and 2,3-dinor-thromboxane B2 (TxB2) were not reduced by celecoxib, whereas indomethacin led to a decrease of 40%, 45%, and 80%, respectively. Both active treatments inhibited urinary excretion of 2,3-dinor-6-keto-PGF1α and 6-keto-PGF1α by 60% and 40%, respectively. Conclusion. Renin-release in healthy humans with normal salt intake is COX-2 dependent. While COX-1 is critical for renal and systemic PGE2 production, renal prostacyclin synthesis is apparently COX-2 dependent. Finally, the previously demonstrated shift of the thromboxane-prostacyclin balance toward prothrombotic thromboxane by specific COX-2 inhibition is confirmed. [ABSTRACT FROM AUTHOR]

Background: Angiotensin-converting enzyme (ACE)2, a homologue of ACE, which is insensitive to ACE inhibitors and forms angiotensin-(1-7) [Ang-(1-7)] from angiotensin II (Ang II) with high efficiency was investigated in response to chronic blockade with lisinopril, losartan, and both drugs combined.Methods: Thirty-six adult Lewis rats were assigned to receive these medications in their drinking water for 2 weeks while their arterial pressure, water intake, and urine volume were recorded throughout the study. Measures of renal excretory variables included assessing excretion rates of angiotensin I (Ang I), Ang II and Ang-(1-7) while blood collected at the completion of the study was used for measures of plasma angiotensin concentrations. Samples from renal cortex were assayed for renin, angiotensinogen (Aogen), neprilysin, angiotensin types 1 and 2 (AT(1) and AT(2)) and mas receptor mRNAs by semiquantitative reverse transcriptase (RT) real-time polymerase chain reaction (PCR). ACE2 activity was determined as the rate of Ang II conversion into Ang-(1-7).Results: Comparable blood pressure reductions were obtained in rats medicated with either lisinopril or losartan, whereas both drugs produced a greater decrease in arterial pressure. Polyuria was recorded in all three forms of treatment associated with reduced osmolality but no changes in creatinine excretion. Lisinopril augmented plasma levels and urinary excretion rates of Ang I and Ang-(1-7), while plasma Ang II was reduced with no effect on urinary Ang II. Losartan produced similar changes in plasma and urinary Ang-(1-7) but increased plasma Ang II without changing urinary Ang II excretion. Combination therapy mimicked the effects obtained with lisinopril on plasma and urinary Ang I and Ang-(1-7) levels. Renal cortex Aogen mRNA increased in rats medicated with either lisinopril or the combination, whereas all three treatments produced a robust increase in renal renin mRNA. In contrast, ACE, ACE2, neprilysin, AT(1), and mas receptor mRNAs remained unchanged with all three treatments. Renal cortex ACE2 activity was significantly augmented in rats medicated with lisinopril or losartan but not changed in those given the combination.Conclusion: Our data revealed a role for ACE2 in Ang-(1-7) formation from Ang II in the kidney of normotensive rats as primarily reflected by the increased ACE2 activity measured in renal membranes from the kidney of rats given either lisinopril or losartan. The data further indicate that increased levels of Ang-(1-7) in the urine of animals after ACE inhibition or AT(1) receptor blockade reflect an intrarenal formation of the heptapeptide. [ABSTRACT FROM AUTHOR]

Background. Diabetes mellitus reduces female gender-mediated protection against progression of renal disease but the mechanisms responsible for this loss of protection are unknown. The impact of gender on the diabetic hyperfiltration state has not previously been studied. Since hyperfiltration is a factor in the development of diabetic renal disease, and is influenced by hyperglycemia and renin-angiotensin system (RAS) blockade, we examined gender differences in the renal response to hyperglycemia and angiotensin-converting enzyme (ACE) inhibition in young males and females with uncomplicated type 1 diabetes mellitus. Methods. Ten male and 12 female normoalbuminuric, normotensive, adolescents with type 1 diabetes mellitus were studied before ACE inhibition during clamped euglycemia and hyperglycemia, and then after 21 days treatment with enalapril (0.1 mg/kg daily × 1 week and then 0.1 mg/kg twice a day × 2 weeks). Results. During clamped euglycemia, males exhibited significantly higher effective renal plasma flow (ERPF) and renal blood flow (RBF) and a lower renal vascular resistance (RVR). During clamped hyperglycemia, females exhibited reductions in ERPF and RBF, and increased RVR and filtration fraction (FF). Males exhibited no significant renal hemodynamic changes during hyperglycemia. After ACE inhibition treatment, both genders exhibited significant declines in arterial pressure, but only females displayed a reduction in glomerular filtration rate (GFR) and FF. Conclusion. The renal responses to hyperglycemia and ACE inhibition appear to differ between male and female adolescents with uncomplicated type 1 diabetes mellitus. Hyperglycemia-induced changes in RVR and FF in women may account, at least in part, for the loss of gender-based protection in diabetic renal disease. [ABSTRACT FROM AUTHOR]

The prevalence of chronic renal diseases is increasing worldwide. There is a great need to identify therapies that arrest disease progression to end-stage renal failure. Inhibition of renin-angiotensin system both by ACE inhibitors and angiotensin II receptor antagonists is probably the best therapeutic option available. Several large, multicenter studies have indeed shown a significant reduction in the risk of doubling baseline serum creatinine or progression toward end-stage renal failure in diabetic and nondiabetic patients with chronic nephropathies treated with ACE inhibitors or angiotensin II receptor antagonists. However, the number of patients that reach end-stage renal failure is still considerably high. Significant reduction of the incidence of end-stage renal disease is likely to be achieved in the next future for chronic nephropathies, provided that we can improve the degree of renoprotection.This goal may be attainable with a more complex strategy than with a single or dual pharmacologic intervention on the renin-angiotensin system. Strict control of blood pressure and protein excretion rate, lowering of blood lipids, tight glucose control for diabetics, and lifestyle changes form part of the future multimodal protocol for management of patients with chronic nephropathies. [ABSTRACT FROM AUTHOR]

Renin-angiotensin polymorphisms and QTc interval prolongation in end- stage renal disease. Background. Polymorphisms of renin-angiotensin system (RAS) genes in patients with end-stage renal disease (ESRD) on chronic hemodialysis may be associated with QTc interval prolongation, leading to fatal arrhythmias. The objective of this study was to determine ( 1) the prevalence of QTc prolongation in hemodialysis patients, and (2) the association of a prolonged QTc in these patients with RAS polymorphisms [angiotensin-converting enzyme-insertion/deletion ( ACE-I/D), angiotensin type 1 receptor- A1166C ( AT1R-A1166C), and angiotensinogen- M235T ( AGT-M235T)]. Methods. Twelve-lead electrocardiograms (ECGs), serum electrolytes (sodium, potassium, and calcium), and ACE and angiotensin II levels were obtained 10 to 12 hours after a hemodialysis session in 43 patients with ESRD on chronic hemodialysis [mean age (±SD), 55 ± 14 years]. Using polymerase chain reaction (PCR), the presence of polymorphisms of the ACE-I/D, AT1R-A1166C, and AGT-M235T genes was determined from the buccal cells. A maximum QT interval in patients with sinus rhythm and normal QRS duration was corrected for heart rate using Hodges' formula. Results. Fifty-eight percent of the patients had QTc interval prolongation (>440 msec). The ACE-DD genotype ( P= 0.002) and the C allele of the AT1R-A1166C gene ( P= 0.004), but not the AGT-M235T gene, contributed to QTc prolongation. Conclusion. Polymorphisms of ACE and AT1R genes additively contribute to QTc prolongation found in a great majority of ESRD patients. Therefore, ESRD patients with both or one of these polymorphisms may be at a higher risk for sudden cardiac death. [ABSTRACT FROM AUTHOR]