Achieving maximal renal protection in nondiabetic chronic renal disease

Losartan treating podocyte injury induced by Ang II via downregulation of TRPC6 in podocytes

OBJECTIVE

In this study, we investigated the molecule mechanisms of podocyte injury and proteinuria and the protective effects of losartan.

METHODS

This study set up three groups: a control group; an Ang II group (Ang II 10(-6) mol/l, Sigma); and a losartan group (losartan 10(-6) mol/l, Sigma). We used RT-PCR assay to detect TRPC6 mRNA expression, and Western blot to detect TRPC6 protein expression.

RESULTS

TRPC6 overexpression was the basic change of podocyte injury and proteinuria occurrence. Losartan can treat podocyte injury and proteinuria induced by Ang II via downregulation of TRPC6 in podocytes.

CONCLUSION

These findings maybe provide an ideal drug target for the diagnosis and treatment of acquired glomerular diseases.

Losartan reverses glomerular podocytes injury induced by AngII via stabilizing the expression of GLUT1

Podocyte impairment is a key pathogenic even in the initiation and development of glomerular diseases associated with proteinuria. The type 2 diabetic patients is characterized by progressive increases in albuminuria which are associated with the development of characteristic histopathological features. Losartan had a benefit in decreasing albuminuria in type 2 diabetic patients,suggesting that losartan may have another effect other than blockade of the traditional renin-angiotensin system (RAS). However, the mechanism has remained undetermined. Glucose transporter 1 (GLUT1) is the predominant basal glucose transporter. In the kidney, GLUT1 was overexpressed predominantly in glomerular mesangial cells and in small vessels, rather than in podocytes. The increased glomerular GLUT1 mimicked diabetes-induced glomerular GLUT1 expression. In this study, we hypothesized that increased GLUT1 expression induced by angiotensinII (AngII) contributes to the progression of podocytes injury, losartan can block the effect of AngII and protect podocytes via stabilizing the expression of GLUT1, our results strongly suggest that losartan has a direct and protective effect on podocytes. This represents a novel mechanism by which losartan may protect podocyte from apoptotic death and improve podocyte function via stabilizing the expression of GLUT1. This finding underlines the crucial role of GLUT1 in the pathogenesis of podocyte injury and proteinuria.

Nephron-deficient Fvb mice develop rapidly progressive renal failure and heavy albuminuria involving excess glomerular GLUT1 and VEGF

Reduced nephron numbers may predispose to renal failure. We hypothesized that glucose transporters (GLUTs) may contribute to progression of the renal disease, as GLUTs have been implicated in diabetic glomerulosclerosis and hypertensive renal disease with mesangial cell (MC) stretch. The Os (oligosyndactyly) allele that typically reduces nephron number by approximately 50%, was repeatedly backcrossed from ROP (Ra/+ (ragged), Os/+ (oligosyndactyly), and Pt/+ (pintail)) Os/+ mice more than six times into the Fvb mouse background to obtain Os/+ and +/+ mice with the Fvb background for study. Glomerular function, GLUT1, signaling, albumin excretion, and structural and ultrastructural changes were assessed. The FvbROP Os/+ mice (Fvb background) exhibited increased glomerular GLUT1, glucose uptake, VEGF, glomerular hypertrophy, hyperfiltration, extensive podocyte foot process effacement, marked albuminuria, severe extracellular matrix (ECM) protein deposition, and rapidly progressive renal failure leading to their early demise. Glomerular GLUT1 was increased 2.7-fold in the FvbROP Os/+ mice vs controls at 4 weeks of age, and glucose uptake was increased 2.7-fold. These changes were associated with the activation of glomerular PKCbeta1 and NF-kappaB p50 which contribute to ECM accumulation. The cyclic mechanical stretch of MCs in vitro, used as a model for increased MC stretch in vivo, reproduced increased GLUT1 at 48 h, a stimulus for increased VEGF expression which followed at 72 h. VEGF was also shown to act in a positive feedback manner on MC GLUT1, increasing GLUT1 expression, glucose uptake and fibronectin (FN) accumulation in vitro, whereas antisense suppression of GLUT1 largely blocked FN upregulation by VEGF. The FvbROP Os/+ mice exhibited an early increase in glomerular GLUT1 leading to increased glomerular glucose uptake PKCbeta1, and NF-kappaB activation, with excess ECM accumulation. A GLUT1-VEGF-GLUT1 positive feedback loop may play a key role in contributing to renal disease in this model of nondiabetic glomerulosclerosis.

Emerging drugs for renal failure

Renal failure involves a significant impairment of the essential functions of the kidney, which can be either acute with sudden and rapid onset (acute renal failure [ARF]) or chronic with gradual onset (chronic renal failure [CRF]). ARF, if detected early, may be halted or reversed, whereas CRF is generally irreversible. Without treatment or intervention, both forms of renal failure lead to end stage renal failure (ESRF) or end stage renal disease (ESRD), requiring renal replacement therapy (RRT) in the form of dialysis or renal transplantation for survival. However, provision of RRT requires expert teams working in specialised units, making therapy of patients with renal failure expensive; furthermore, RRT is complex, with its own complications. Although pharmacological interventions have shown promise in experimental models, these have not been as successful in the clinical setting (e.g., administration of atrial natriuretic peptide, low-dose dopamine). At present, drugs are administered during CRF to either reduce one of the many risk factors of CRF (e.g., angiotensin-converting enzyme inhibitors, statins) or to deal with the consequences of CRF (e.g., erythropoietin, calcitriol). Recent evidence suggests that some of these interventions may provide further direct beneficial effects via reduction of renal inflammation. Although these interventions have greatly improved the prospects for patients suffering ESRF, the development of novel drugs and therapies with which to reduce the consequences of renal failure and ESRD remain topics of great interest. This article reviews the therapies available for the prevention and management of renal failure in adults and describes, in detail, emerging drugs and novel interventions that may soon become available for the treatment or prevention of ESRF.

Sodium glomerulopathy: tubuloglomerular feedback and renal injury in African Americans

African Americans are prone to develop not only essential hypertension but also progressive renal injury. We present a simple model to explain salt-induced renal injury (sodium glomerulopathy) in African Americans, the central features of which are the tubuloglomerular feedback and the balance/imbalance between the vascular tones of the afferent and efferent glomerular arterioles. We propose that in African Americans, habitual consumption of high salt causes chronic intermittent tubular hyperperfusion of the macula densa, resulting in a rightward and upward resetting of the operating point for the tubuloglomerular feedback. The resetting of the operating point causes an imbalance between the vascular tones of the afferent/efferent arterioles, a rise in the glomerular capillary hydraulic pressure, and consequent hyperfiltration. Increased susceptibility to glomerular hyperfiltration of African Americans on a high salt intake may explain their proclivity to progressive renal injury associated with essential hypertension.

Low-dose radiation modifies the progression of chronic renal failure

Previous studies have indicated that the application of low dose radiation to an arterial ligation has the potential to subsequently reduce or eliminate restenosis caused by smooth muscle cell proliferation. Sufficient kidney irradiation causes a radiation nephropathy and often leads to renal failure. In order to evaluate the effect of low-dose irradiation on the kidney we hypothesized that this particular therapy modifies renal injury in rats with renal ablation and subsequently slows the rate of the progression. For further clarification of the effect of irradiation at low doses, we determined proliferating cell nuclear antigen (PCNA) and monocyte chemoattractant protein-1 (MCP-1) expression in remnant kidneys after low-dose radiation. Adult Wistar rats (n = 10) were studied during the two weeks after renal ablation. The left kidney was irradiated 24 hours after an operation in anaesthetised animals with 3 Grey in a single dose. Ablated rats without irradiation (n = 9) served as nephrectomized animals group. Rats without surgery and without radiation (n = 10) served as healthy controls. Renal damage was assessed using the following parameters: urine protein excretion rate (UprotV, mg/day), awake systolic blood pressure (SBP, mm Hg), serum creatinine (SCr, micromol/l). The indirect immunofluorescence method was used for the detection of PCNA and MCP-1 expression. Glomerular and tubular immunostaining was scored semiquantitatively. Numerous PCNA positive cells and MCP-1 expression were present in the glomerulus and tubulointerstitium in nephrectomized rat kidneys. Low-dose radiation application was associated with a significant reduction in PCNA and low MCP-1 expression. This study shows that the application of low-dose irradiation has the potential to modify the progression of chronic renal failure in rats.

[Sympathetic overactivity and the kidney]

Hypertension is present in the majority of patients with chronic renal failure and constitutes a major risk factor for the very high cardiovascular morbidity and mortality in this patient population. Furthermore hypertension is known to be a substantial progression factor in renal disease. In the past, it had been presumed that hypertension in chronic renal failure is due to enhanced sodium retention, chronic hypervolemia and increased activity of the renin-angiotensin-aldosterone-system. Recent studies now provide evidence that sympathetic overactivity plays an additional important role and also promotes progression of renal failure. The treatment goal in renal patients is to delay or even prevent progression of renal failure and to reduce the cardiovascular risk. Recent studies have investigated the respective impact of sympatholytic drugs, e.g. inhibitors of the renin-angiotensin-aldosterone-system, beta-blockers or I1-Imidazolin-receptor-agonists in fulfilling these aims. The present report will review experimental and clinical studies on the role of sympathetic overactivity in hypertension and chronic renal failure and possible new therapeutic options.

Proteinuria and its consequences in renal disease

Chronic renal diseases that involve proteinuria are typically characterized by an inexorable progression to end-stage renal failure. Many studies suggest that this progression may be the result of factors, such as intraglomerular hypertension and glomerular hypertrophy, that are unrelated to the initial disease. This paper reviews the mechanisms of progression of chronic renal diseases and discusses therapeutic strategies that should prevent or minimize further renal damage and the applicability of these strategies to patients with the rare X-linked lysosomal storage disorder Fabry disease. Renal involvement is a major feature of Fabry disease, which is characterized by vacuolated epithelial cells in the glomerulus and distal tubules, resulting from lipid inclusions within these cells. Although enzyme replacement therapy is the key strategy to halt the progression of Fabry disease, additional therapeutic options include blood pressure control, reduction of proteinuria, lipid control and inhibition of the renin-angiotensin system.

CONCLUSION

A range of therapeutic options, used in conjunction with enzyme replacement therapy, may have beneficial effects on the renal manifestations of Fabry disease.

Long-term renal survival in HIV-associated nephropathy with angiotensin-converting enzyme inhibition

BACKGROUND

Human immunodeficiency virus (HIV)-associated nephropathy (HIVAN) is the most common cause of end-stage renal disease (ESRD) in HIV-infected patients. Angiotensin-converting enzyme (ACE) inhibition has previously shown a short-term benefit in HIVAN. This study examines the long-term effects of ACE inhibition on renal survival in HIVAN.

METHODS

In this single-center prospective cohort study, 44 patients with biopsy-proven HIVAN were enrolled prior to the onset of severe renal insufficiency (serum creatinine <or=2.0 mg/dL), throughout the study period of 1890 days (5.1 years). Twenty-eight patients received fosinopril, 10 mg/day, and 16 were followed as controls. End points included ESRD and death. Treatment effects on survival were evaluated with Kaplan-Meier product-limit estimates. Survival is also described as absolute median number of days.

RESULTS

Median renal survival of treated patients was 479.5 days, with only one patient developing ESRD. All untreated controls progressed to ESRD, with a median renal survival of 146.5 days (P < 0.0001). There were no significant differences between treatment and control groups in age, significant exposure to antiretroviral therapy, defined as >or=two antiviral drugs for >or=30 consecutive days, CD4 lymphocyte count, initial median serum creatinine concentration, or proteinuria. Risk of renal failure was reduced with ACE inhibitors (RR = 0.003, P < 0.0001). Exposure to antiretroviral therapy did not have a significant impact on the risk of renal failure. Of the ACE inhibitor-treated group, 87.5% survived compared with 21.4% of the control group (P < 0.001).

CONCLUSION

ACE inhibition initiated prior to severe renal insufficiency may offer long-term renal survival benefits in HIVAN. Diagnosis should be sought early in patients with clinical signs suggestive of HIVAN.

A comprehensive public health approach to address the burden of renal disease in singapore

With the epidemic rise of ESRD in multiple regions of the world, there is an urgent need to implement programs to address this increasing burden of kidney disease. We illustrate a public health approach using the program of the National Kidney Foundation of Singapore that incorporates stepwise primary, secondary, and tertiary strategies for prevention. Components of the program include an aggressive public education program, routine surveillance for kidney disease and associated chronic diseases, the implementation of a disease management program to improve physician practice patterns, and the provision of comprehensive services in the community through a network of Prevention Centers designed to optimize the care of patients at risk for kidney disease. Finally, an equally important aspect is the clinical and epidemiologic research component, because this will provide clear benchmarks to determine the program's effect on ESRD as well as generate information that can be used to identify future directions for this evolving program.

Beneficial effects of water-based exercise in patients with chronic kidney disease

The possible beneficial effect of regular aquatic exercise on cardiorespiratory, renal lipid parameters and oxidative stress status was studied in patients with mild to moderate renal failure. The exercise group did low-intensity aerobic exercise in the pool during a period of 12 weeks, twice a week, with sessions lasting for 30 min. Matched control participants remained sedentary. The results showed that in the exercise group all cardiorespiratory functional parameters improved and resting blood pressure lowered significantly. Proteinuria and cystatin-C were diminished significantly and glomerular filtration rate was enhanced. To evaluate the changes in oxidative stress status in the serum, products of lipid peroxidation (LPO) and serum glutathione values were measured. LPO was reduced significantly and reduced glutathione levels showed significant improvement after the exercise-conditioning programme. In the control group the data either remained the same or worsened in the same period of time. In conclusion, regular water-based exercise has beneficial effects on the cardiorespiratory, renal functional parameters and oxidative stress status in patients with moderate renal failure, and can be used in the complex rehabilitation of chronic renal failure patients, together with blood pressure control, dietary consultation, encouragement and education to prevent physical worsening and to postpone cardiovascular and renal atherosclerotic complications.