Angiotensin II and L-arginine in tissue fibrosis: more than blood pressure

Mechanisms and management of edema in pediatric nephrotic syndrome

Edema is the abnormal accumulation of fluid in the interstitial compartment of tissues within the body. In nephrotic syndrome, edema is often seen in dependent areas such as the legs, but it can progress to cause significant accumulation in other areas leading to pulmonary edema, ascites, and/or anasarca. In this review, we focus on mechanisms and management of edema in children with nephrotic syndrome. We review the common mechanisms of edema, its burden in pediatric patients, and then present our approach and algorithm for management of edema in pediatric patients. The extensive body of experience accumulated over the last 5 decades means that there are many options, and clinicians may choose among these options based on their experience and careful monitoring of responses in individual patients.

Darkness at the end of the tunnel: poststenotic kidney injury

Renal artery stenosis remains an important contributor to renal failure in the elderly population, but uncertainty continues to surround the mechanisms underlying progressive renal dysfunction. Here, we present the current understanding of the pathogenic mechanisms responsible for renal injury in these patients, with emphasis on those involved in disease progression.

Dioscorea alata attenuates renal interstitial cellular fibrosis by regulating Smad- and epithelial-mesenchymal transition signaling pathways

Renal interstitial fibrosis is characterized by increased extracellular matrix (ECM) synthesis. Epithelial-mesenchymal transition (EMT) in kidneys is driven by regulated expression of fibrogenic cytokines such as transforming growth factor-beta (TGF-β). Yam, or Dioscorea alata (DA) is an important herb in Chinese medicine widely used for the treatment of clinical diabetes mellitus. However, the fibrosis regulatory effect of DA is unclear. Thus, we examined TGF-β signaling mechanisms against EMT in rat fibroblast cells (NRK-49F). The characterization of DA water-extracts used various methods; after inducing cellular fibrosis in NRK-49F cells by treatment with β-hydroxybutyrate (β-HB) (10 mM), we used Western blotting to examine the protein expression in the TGF-β-related signal protein type I and type II TGF-β receptors, Smads2 and Smad3 (Smad2/3), pSmad2 and Smad3 (pSmad2/3), Smads4, Smads7, and EMT markers. These markers included E-cadherin, alpha-smooth muscle actin (α-SMA), and matrix metalloproteinase-2 (MMP-2). Bioactive TGF-β and fibronectin levels in the culture media were determined using ELISA. Expressions of fibronectin and Snail transcription factor, an EMT-regulatory transcription factor, were assessed by immunofluorescence staining. DA extract dose-dependently (50–200 µg/mL) suppressed β-HB-induced expression of fibronectin in NRK-49F cells concomitantly with the inhibition of Smad2/3, pSmad2/3, and Smad4. By contrast, Smad7 expression was significantly increased. DA extract caused a decrease in α-SMA (α-smooth muscle actin) and MMP-2 levels, and an increase in E-cadherin expression. We propose that DA extract might act as a novel fibrosis antagonist, which acts partly by down regulating the TGF-β/smad signaling pathway and modulating EMT expression.

Losartan chemistry and its effects via AT1 mechanisms in the kidney

Besides the importance of the renin-angiotensin system (RAS) in the circulation and other organs, the local RAS in the kidney has attracted a great attention in research in last decades. The renal RAS plays an important role in the body fluid homeostasis and long-term cardiovascular regulation. All major components and key enzymes for the establishment of a local RAS as well as two important angiotensin II (Ang II) receptor subtypes, AT1 and AT2 receptors, have been confirmed in the kidney. In additional to renal contribution to the systemic RAS, the intrarenal RAS plays a critical role in the regulation of renal function as well as in the development of kidney disease. Notably, kidney AT1 receptors locating at different cells and compartments inside the kidney are important for normal renal physiological functions and abnormal pathophysiological processes. This mini-review focuses on: 1) the local renal RAS and its receptors, particularly the AT1 receptor and its mechanisms in physiological and pathophysiological processes; and 2) the chemistry of the selective AT1 receptor blocker, losartan, and the potential mechanisms for its actions in the renal RAS-mediated disease.

Moderate alcohol intake has no impact on acute and chronic progressive anti-thy1 glomerulonephritis

Moderate alcohol consumption has shown beneficial effects in experimental and human cardiovascular disease. With the use of rat models of acute and chronic progressive anti-thy1 glomerulonephritis (GN), we tested the hypothesis that moderate alcohol intake is protective in renal fibrotic disease. In acute anti-thy1 GN, untreated nephritic rats showed marked mesangial cell lysis and induced nitric oxide production at day 1 and high proteinuria, glomerular matrix accumulation, and transforming growth factor (TGF)-beta(1), fibronectin, and plasminogen activator inhibitor (PAI)-1 expression at day 7 after disease induction, respectively. In animals 15 wk after induction of chronic progressive anti-thy1 GN, disease was characterized by significantly reduced renal function, persisting albuminuria as well as increased glomerular and tubulointerstitial matrix expansion, TGF-beta(1), fibronectin, and PAI-1 protein expression. In both anti-thy1 GN models, an ethanol intake of approximately 2 ml per day and animal was achieved, however, disease severity was not significantly altered by moderate alcohol consumption in any of the protocols. In conclusion, moderate alcohol intake does not influence renal matrix protein production and accumulation in acute and chronic progressive anti-thy1 glomerulofibrosis. The study suggests that, in contrast to cardiovascular disorders, moderate alcohol consumption might not provide specific protection in renal fibrotic disease.

L-arginine supplementation accelerates renal fibrosis and shortens life span in experimental lupus nephritis

BACKGROUND

Inducible, high-output nitric oxide (NO) production has been identified as a central mediator of cell injury in immune-mediated renal disease. In acute anti-thy-1 glomerulonephritis prefeeding with the NO precursor L-arginine increases mesangial cell injury and the subsequent fibrosis. The present study tested the hypothesis that L-arginine supplementation may also be detrimental in chronic, NO-mediated murine lupus nephritis.

METHODS

Groups (N = 18) of female MRL/lpr mice with lupus nephritis were fed the following diets: (1) normal protein (22% casein); (2) normal protein and 1.0% L-arginine in the drinking water; (3) low protein (6% casein); (4) low protein + 0.4%l-arginine; and (5) low protein + 1.0% L-arginine. After 40 days mouse survival, albuminuria, matrix accumulation, inflammatory cell infiltration, immunoglobulin G (IgG) deposition, expression of transforming growth factor-beta 1 (TGF-beta 1), fibronectin and plasminogen activator inhibitor-1 (PAI-1) mRNA and protein, anti-DNA antibody titer, inducible nitric oxide synthase (iNOS) mRNA expression, blood amino acid levels, blood urea nitrogen (BUN) concentrations and blood and urinary NOx (nitrite + nitrate) levels were assessed.

RESULTS

L-Arginine supplementation increased mortality significantly (P < 0.02). The death rate increased from 0% in the lowest to 50% in the highest L-arginine intake group (normal protein + 1.0% L-arginine). L-Arginine administration increased albuminuria, renal matrix accumulation, TGF-beta 1, fibronectin, PAI-1, blood L-arginine, L-citrulline, BUN and blood and urine NOx levels, while protein restriction reduced these parameters. Renal cell infiltration and iNOS mRNA expression were decreased in the low protein group only. Anti-ds DNA-IgG and renal IgG deposition were comparable in all groups

CONCLUSIONS

Increasing L-arginine intake increases the severity of renal fibrosis and the likelihood of death in MRL/lpr mice. The results appear to be at least in part mediated through enhanced cytotoxic NO generation via iNOS. The data suggest that L-arginine restriction should be considered in human immune-mediated renal diseases.

Angiotensin-converting enzyme inhibition but not beta-adrenergic blockade limits transforming growth factor-beta overexpression in acute normotensive anti-thy1 glomerulonephritis

OBJECTIVE

Recent experimental studies in chronic kidney disease have suggested that sympathicolytic drugs, similar to angiotensin II antagonism, limit renal fibrosis independent of blood pressure control. Using the model of acute and normotensive anti-thy1 glomerulonephritis, we analysed the action of beta-adrenergic blockade (as compared with angiotensin-converting enzyme inhibition) on renal overexpression of the profibrotic cytokine transforming growth factor (TGF)-beta.

METHODS

One day after induction of anti-thy1 glomerulonephritis, rats were given increasing doses of the beta-blockers metoprolol or nebivolol (0.1-fold, one-fold, 10-fold and 20-fold of the known blood pressure dose) until day 6 and the 20-fold dose until day 12. Additional animals were treated with a high dose of the angiotensin-converting enzyme inhibitor enalapril. At the end of each experiment, blood pressure and heart rate were recorded, glomerular matrix expansion was scored histologically, and protein expression of TGF-beta(1), fibronectin and plasminogen activator inhibitor-1 was determined in the supernatant of cultured glomeruli.

RESULTS

Metoprolol and nebivolol reduced heart rate in a dose-dependent manner. Blood pressure was normal in untreated animals and not significantly affected by either treatment. Compared with untreated nephritic rats, TGF-beta(1) overexpression was not significantly changed by metoprolol or nebivolol in any dose or treatment period. In contrast, TGF-beta(1) levels were significantly reduced by enalapril both 6 and 12 days after disease induction (-52 and -63%, respectively). The changes in glomerular matrix score, fibronectin and plasminogen activator inhibitor-1 production closely followed expression of TGF-beta(1).

CONCLUSIONS

In a model of acute and normotensive glomerular fibrosis, beta-adrenergic antagonism does not reduce TGF-beta overexpression, suggesting that its pressure-independent antifibrotic action may be limited to chronic renal diseases. The beneficial effect of angiotensin II inhibition even on acute matrix expansion may be a relevant mechanism as to the explanation of its superiority in treating fibrotic renal diseases.

Epidemiological study of kidney survival in autosomal dominant polycystic kidney disease

BACKGROUND

It is unknown whether the substantial increase in research, identification of risk factors for renal progression, greater antihypertensive armamentarium including inhibitors of the renin-angiotensin-aldosterone system (RAAS) and enhanced educational information have impacted the progression of autosomal dominant polycystic kidney disease (ADPKD) renal disease.

METHODS

An epidemiological study involving 513 ADPKD subjects was performed. The hypothesis tested was that over two separate periods, 1985 to 1992 versus 1992 to 2001, a significant slowing of renal function loss in ADPKD patients would be demonstrated in association with improved blood pressure (BP) control and inhibition of the RAAS as instituted by their primary care physicians.

RESULTS

ADPKD males and females in the later cohort (1992 to 2001) had longer mean and median survival times to ESRD than males and females in the earlier cohort (1985 to 1992). Analysis revealed that both males and females in the later cohort had significantly lower diastolic blood pressure (DBP) and mean arterial pressure (MAP) values than males and females in the earlier cohort. ADPKD male and female patients in the later cohort used significantly more angiotensin converting enzyme inhibitors (ACEIs) than ADPKD male and female patients in the earlier cohort.

CONCLUSIONS

These results demonstrate a significant slowing of ADPKD renal progression in both male and female patients that was associated with a significantly lower MAP and increased use of ACEIs in the later cohort (1992 to 2001) as compared to the early cohort (1985-1992).

Renal artery stenosis: a common, treatable cause of renal failure?

Chronic azotemic renovascular disease is common in patients with atherosclerosis. Its prevalence appears to be increasing in the aging population. How often it is the primary cause of end-stage renal disease (ESRD) is not yet certain. Some studies suggest that 10%-40% of elderly hypertensive patients with newly documented ESRD and no demonstrable primary renal disease have significant renal artery stenosis (RAS). Atherosclerotic vascular occlusive disease of the renal arteries does progress, but current rates of progression and occlusion are lower than those reported a decade ago. Methods of identifying patients whose renal function is at true risk from vascular occlusive disease and determining who will benefit from intervention remain elusive. The presence of RAS in an azotemic patient can be assessed with noninvasive and risk-free radiologic techniques, including Duplex doppler velicometry and magnetic resonance angiography. Functional tests that predict the change in renal function after revascularization are not yet available. However, a renal length of greater than 7.5 cm in the absence of renal cysts and a short history of renal functional deterioration indicate a good prognosis. Patients with recent deterioration in renal function, those with bilateral renal artery stenosis or stenosis to a single functioning kidney, those with flash pulmonary edema, advanced chronic renal failure, or ESRD (who have much to gain), those with reversible azotemia during angiotensin-converting enzyme inhibitor (ACEI) or angiotensin receptor antagonist (ARB) therapy, and those whose conditions cannot be managed medically should be considered for revascularization. Results from recent controlled clinical trials of the response to percutaneous transluminal renal artery angioplasty (PTRA) and stenting indicate that improvement in blood pressure control or renal function is not a predictable outcome of renal revascularization. In azotemic groups, 25%-30% of patients achieve important recovery of renal function. Thus, significant progress has been made recently in determining whether RAS is a frequent, treatable cause of renal failure. The decision to recommend revascularization remains a difficult balance between the risks and expense of the procedure and the undoubted benefits that accrue if renal function is successfully stabilized.

Acute simultaneous stimulation of nitric oxide and oxygen radicals by angiotensin II in humans in vivo

Angiotensin II is a powerful vasoconstrictor and proatherogenic factor. It was recently suggested that the endothelium may influence the actions of angiotensin II by production of, for example, nitric oxide and superoxide. By using venous occlusion plethysmography, forearm blood flow was measured in 26 healthy subjects during intraarterial cumulative infusion of angiotensin II. In 14 subjects, the interaction between angiotensin II and NO was studied by infusion of angiotensin II before and after clamping NO availability at a fixed basal level by using N(G)-monomethyl-L-arginine (L-NMMA) and nitroprusside. During a "free" NO system, blood flow decreased on angiotensin II infusion from 2.70+/-0.30 ml/100 ml forearm/min to 1.38+/-0.15 ml/100 ml forearm/min, whereas during NO-clamp vasoconstriction was significantly enhanced (blood flow from 2.56+/-0.25 to 1.19+/-0.13; p<0.05 saline vs. NO clamp). In 12 other subjects, the interaction between angiotensin II and superoxide was evaluated by comparison of the effects of angiotensin II before and after coinfusion of vitamin C. Angiotensin II-induced vasoconstriction was significantly attenuated by vitamin C at higher dosages of angiotensin (saline, blood flow from 3.08+/-0.33 to 1.12+/-0.09; vitamin C, blood flow from 3.01+/-0.23 to 1.61+/-0.13; p<0.05 saline vs. vitamin C). Vitamin C had no effect on baseline forearm blood flow. In conclusion, this study demonstrates that the constrictor actions of angiotensin II are enhanced during NO clamp and attenuated during vitamin C, suggesting direct angiotensin II-associated stimulation of endothelial NO and of oxygen radicals, respectively, in humans in vivo.

The transforming growth factor beta system in kidney disease and repair: recent progress and future directions

Transforming growth factor beta is a multifunctional polypeptide growth factor implicated in a variety of renal diseases. The expression of transforming growth factor beta is enhanced in renal diseases and available evidence suggests that its activity in promoting the synthesis of extracellular matrix plays a crucial role in fibrotic deposition and the decline in renal function. Transforming growth factor beta is, however, also expressed in response to renal injury and may play an important role in normal repair processes. It appears that renal diseases may result from the inappropriate regulation of transforming growth factor beta expression. The determination of the factors that mediate transforming growth factor beta activity will be of primary importance in elucidating the mechanisms leading to renal disease or repair after injury. Both in-vitro and in-vivo studies have demonstrated that proteolytic activity, thrombospondin-1, elevated glucose, angiotensin II, oxidant stress and hemodynamic forces regulate transforming growth factor beta activity through both transcriptional and post-transcriptional mechanisms. In some cases, therapies that may partly disrupt renal transforming growth factor beta activity have shown promise in slowing the progression to end-stage renal disease.

Progression of renal failure and hypertensive nephrosclerosis

Data provided by end-stage renal disease (ESRD) registries document a progressive and striking increase in the incidence of hypertension-related ESRD over the years, and its prevalence supports the classic statement that the kidney may be a victim of hypertension. Two clinical conditions should be considered separately when the role of hypertension in progressive renal disease is discussed: (a) hypertension and primary renal disease and (b) progressive renal disease in essential hypertension. The appearance of systemic hypertension is one of the major risk factors for the progressive deterioration of primary renal disease both in experimental models and in humans. Strict blood pressure control is able to significantly reduce the disease progression to renal failure. Angiotensin-converting enzyme inhibitors probably show a better nephroprotective action than other antihypertensive agents. Long-lasting hypertension may induce ESRD in some patients through hypertensive nephrosclerosis. In many cases of progressive renal disease associated with essential hypertension, particularly in elderly Caucasians, atheromatous renovascular disease via renal artery stenosis and/or cholesterol microembolization represent the main cause of ESRD.

Nephroprotective effect of antihypertensive drugs in essential hypertension

BACKGROUND

Effective antihypertensive treatment has prevented target-organ involvement in hypertension, markedly reducing morbidity and mortality from strokes, coronary heart disease, cardiac failure, and hypertensive emergencies. However, the incidence of hypertension-related end-stage renal disease continues to increase, suggesting that therapeutic reduction in arterial pressure by itself is not sufficient to prevent the development of hypertensive renal failure.

OBJECTIVE

To examine experimental and clinical data concerning the protective effect of reduction of arterial pressure on the progression of hypertension-related renal disease, and the evidence indicating that some antihypertensive agents may afford more nephroprotection, over and above that attributable to reduction of arterial pressure.

RESULTS

Results of numerous studies clearly indicate that adequate control of arterial pressure, irrespective of the antihypertensive agent used, slowed the progression of renal disease. Results of some studies suggest that lowering arterial pressure below the level that is usually considered adequate has an additional beneficial effect by slowing the progression of renal injury.

CONCLUSION

Results of a number of studies evaluating nephroprotective effects of various drugs and regimens have indicated that certain agents, most notably angiotensin converting enzyme inhibitors and their combination with calcium antagonists, afford more protection than do others at similar levels of reduction of arterial pressure. Results of still other studies suggest that certain agents that exert greater nephroprotection are more efficient at controlling arterial pressure. Therefore, further data are needed before any final conclusion can be drawn. However, it is clear that, in order to establish nephroprotection in patients with essential hypertension, the problem should not be further complicated by additional comorbid diseases such as diabetes mellitus.