Local renal aldosterone system and its regulation by salt, diabetes, and angiotensin II type 1 receptor

Non-adrenal synthesis of aldosterone: a reality check

Advances in the sensitivity of molecular techniques during the 1990s led to a flurry of studies that supported the existence of extra-adrenal sites of aldosterone production in various tissues including the brain and the heart. Subsequent work was often conflicting or ambiguous, leading many to question whether extra-adrenal aldosterone was of any physiological importance, or whether it even existed. In this article, we review these studies and, in light of this evidence, discuss whether the current lack of interest in extra-adrenal aldosterone biosynthesis is justified.

Aldosterone blockade and the mineralocorticoid receptor in the management of chronic kidney disease: current concepts and emerging treatment paradigms

The past two decades have witnessed a striking paradigm shift with respect to our understanding of the widespread effects of aldosterone. There is substantive evidence that mineralocorticoid receptor (MR) activation promotes myriad 'off target' effects on the heart, the vasculature, and importantly the kidney. In the present review, we summarize the expanding role of MR activation in promoting both vascular and renal injury. We review the recent clinical studies that investigated the efficacy of MR antagonism (MRA) in reducing proteinuria and attenuating progressive renal disease. We also review in-depth both the utility and safety of MRA in the end-stage renal disease (ESRD) patient undergoing dialysis. Because the feasibility of add-on MRA is critically dependent on our ability to minimize or avoid hyperkalemia, and because controversy centers on the incidence of hyperkalemia, we critically review the risk of hyperkalemia with add-on MRA. Our present analysis suggests that hyperkalemia supervening in MRA-treated patients is overstated. Furthermore, recent studies demonstrating the efficacy of new non-absorbed, orally administered, potassium [K+]-binding polymers suggest that a multi-pronged approach encompassing adequate surveillance, moderate or low-dose MRA, and K-binding polymers may adequately control serum K in both chronic kidney disease and ESRD patients.

Role of the renin-angiotensin-aldosterone system in the enhancement of salt sensitivity caused by prenatal protein restriction in stroke-prone spontaneously hypertensive rats

We previously demonstrated that maternal protein restriction during pregnancy enhanced salt sensitivity and shortened life span in stroke-prone spontaneously hypertensive rats (SHRSP). The present study was conducted to investigate the participation of the renin-angiotensin-aldosterone system in the development of salt sensitivity in the offspring of dams fed a low-protein diet during pregnancy. We used SHRSP offspring from dams fed a 20% casein diet (CN) or a 9% casein diet (LP) during pregnancy. The CN and LP SHRSP offspring were further subdivided into tap-water-drinking and 1%-saline-drinking groups from the postnatal 10th week. A remarkable elevation in blood pressure in response to salt loading was observed in the LP SHRSP offspring. The protein levels of CYP11B2, an enzyme for aldosterone synthesis, were markedly elevated in response to salt loading in the kidneys of LP offspring. Treatment of the LP offspring with an aldosterone receptor antagonist prevented the blood pressure from elevating and lengthened the average life span in LP offspring in response to the drinking of 1% saline. No difference in the activity of angiotensin-converting enzyme or in the protein level of the angiotensin type 1 receptor was found between the CN and LP offspring in either the tap-water-drinking or saline-drinking conditions. In conclusion, the increment of aldosterone production in response to high-salt loading may contribute to the elevated salt sensitivity of the offspring of protein-restricted dams.

Extra-adrenal glucocorticoids and mineralocorticoids: evidence for local synthesis, regulation, and function

Glucocorticoids and mineralocorticoids are steroid hormones classically thought to be secreted exclusively by the adrenal glands. However, recent evidence has shown that corticosteroids can also be locally synthesized in various other tissues, including primary lymphoid organs, intestine, skin, brain, and possibly heart. Evidence for local synthesis includes detection of steroidogenic enzymes and high local corticosteroid levels, even after adrenalectomy. Local synthesis creates high corticosteroid concentrations in extra-adrenal organs, sometimes much higher than circulating concentrations. Interestingly, local corticosteroid synthesis can be regulated via locally expressed mediators of the hypothalamic-pituitary-adrenal (HPA) axis or renin-angiotensin system (RAS). In some tissues (e.g., skin), these local control pathways might form miniature analogs of the pathways that regulate adrenal corticosteroid production. Locally synthesized glucocorticoids regulate activation of immune cells, while locally synthesized mineralocorticoids regulate blood volume and pressure. The physiological importance of extra-adrenal glucocorticoids and mineralocorticoids has been shown, because inhibition of local synthesis has major effects even in adrenal-intact subjects. In sum, while adrenal secretion of glucocorticoids and mineralocorticoids into the blood coordinates multiple organ systems, local synthesis of corticosteroids results in high spatial specificity of steroid action. Taken together, studies of these five major organ systems challenge the conventional understanding of corticosteroid biosynthesis and function.

Mineralocorticoid receptor activation: a major contributor to salt-induced renal injury and hypertension in young rats

Excessive salt intake is known to preferentially increase blood pressure (BP) and promote kidney damage in young, salt-sensitive hypertensive human and animal models. We have suggested that mineralocorticoid receptor (MR) activation plays a major role in kidney injury in young rats. BP and urinary protein were compared in young (3-wk-old) and adult (10-wk-old) uninephrectomized (UNx) Sprague-Dawley rats fed a high (8.0%)-salt diet for 4 wk. The effects of the MR blocker eplerenone on BP and renal injury were examined in the high-salt diet-fed young UNx rats. Renal expression of renin-angiotensin-aldosterone (RAA) system components and of inflammatory and oxidative stress markers was also measured. The effects of the angiotensin receptor blocker olmesartan with or without low-dose aldosterone infusion, the aldosterone synthase inhibitor FAD286, and the antioxidant tempol were also studied. Excessive salt intake induced greater hypertension and proteinuria in young rats than in adult rats. The kidneys of young salt-loaded rats showed marked histological injury, overexpression of RAA system components, and an increase in inflammatory and oxidative stress markers. These changes were markedly ameliorated by eplerenone treatment. Olmesartan also ameliorated salt-induced renal injury but failed to do so when combined with low-dose aldosterone infusion. FAD286 and tempol also markedly reduced urinary protein. UNx rats exposed to excessive salt at a young age showed severe hypertension and renal injury, likely primarily due to MR activation and secondarily due to angiotensin receptor activation, which may be mediated by inflammation and oxidative stress.

Drug of choice in the management of hypertension in diabetes and diabetic nephropathy: angiotensin-converting enzyme inhibitors

Hypertension is common in patients with diabetes mellitus and is a main cause of renal and cardiovascular complications. There has been recent controversy on what should be considered the optimal blood pressure goal and the optimal antihypertensive agent. It has become apparent that one blood pressure does not fit all in diabetic patients. Major confounders are preexisting cardiovascular disease and presence or absence of proteinuric kidney disease. In proteinuric diabetic nephropathy, renin-angiotensin system blockade is clearly indicated, but monotherapy is practically always insufficient to achieve target blood pressure values.

Inhibition of the renal renin-angiotensin system and renoprotection by pitavastatin in type1 diabetes

1. The aim of the present study was to investigate whether or not pitavastatin ameliorates diabetic nephropathy and if inhibition of the rennin-angiotensin-aldosterone system (RAAS) is associated with any renoprotective effects. Pitavastatin (10mg/ kg/day) and/or spironolactone (100mg/kg/day) were given by gavage for 3weeks to uninephrectomized rats with streptozotocin-induced diabetes. 2. Pitavastatin or spironolactone significantly reduced proteinuria and collagen deposition, and normalized creatinine clearance, serum creatinine levels and blood urea nitrogen concentrations. 3. Reverse transcription polymerase chain reaction analysis showed that the renal expression of collagenI, transforming growth factor-β and monocyte chemoattractant-1 were increased in diabetic rats and reduced by the pitavastatin and/or spironolactone treatment. 4. These agents also decreased angiotensin converting enzyme expression and aldosterone concentrations in the renal homogenate, but had no effect on blood glucose, haemoglobinA(1c) , and plasma total cholesterol, Na(+) , K(+) , aldosterone and NOx levels, or on systolic blood pressure measured by the tail-cuff method. Interestingly, cotreatment with pitavastatin and spironolactone did not result in additional normalization. 5. These results suggest that pitavastatin shows renoprotective effects against diabetic nephropathy mediated in part by inhibition of the renal RAAS, including the suppression of angiotensin-converting enzyme expression and aldosterone production.

The role of aldosteronism in causing obesity-related cardiovascular risk

A large body of evidence strongly links aldosterone to development and progression of cardiovascular disease, including vascular stiffness, left ventricular hypertrophy, congestive heart failure, chronic kidney disease, and, especially, hypertension. Emerging data suggest that adipocytes may serve as a source of aldosterone, either directly or indirectly, through the release of aldosterone-stimulating factors. If adipocytes are confirmed to have an important contribution to hyperaldosteronism, it would have significant clinical implications in linking aldosterone to obesity-related increases in cardiovascular risk. Such a cause-and-effect situation would then provide the opportunity to reverse that risk with preferential use of aldosterone antagonists in obese patients.

Role of the intrarenal renin-angiotensin-aldosterone system in chronic kidney disease

The existence of local or tissue-based renin-angiotensin-aldosterone systems (RAAS) is well documented and has been implicated as a key player in the pathogenesis of cardiovascular and renal diseases. The kidney contains all elements of the RAAS, and intrarenal formation of angiotensin II not only controls glomerular hemodynamics and tubule sodium transport, but also activates a number of inflammatory and fibrotic pathways. Experimental and clinical studies have shown that the intrarenal RAAS is activated early in diabetic nephropathy, the leading cause of chronic kidney disease (CKD). Although angiotensin-converting enzyme inhibitors and angiotensin receptor blockers decrease the rate of decline in kidney function in patients with diabetic and non-diabetic nephropathy, many patients still progress to end-stage renal disease or die from cardiovascular events. There is still a clear need for additional strategies to block the RAAS more effectively to reduce progression of CKD. The focus of this paper is to review the importance of the intrarenal RAAS in CKD and recent findings in renin-angiotensin biology pertinent to the kidney. We also discuss additional strategies to inhibit the RAAS more effectively and the potential impact of direct renin inhibition on the prevention and management of CKD.

Role of aldosterone in the progression of chronic kidney disease and potential use of aldosterone blockade in children

Much focus has been placed on the role of the renin-angiotensin system as a mediator of the progression of chronic kidney disease. Novel therapeutic strategies to inhibit the negative impact of renin-angiotensin activation, including dual therapy with an angiotensin-converting enzyme inhibitor and an angiotensin-receptor blocker, have been suggested to achieve more complete disruption of the renin-angiotensin system. The role played by aldosterone, a target of angiotensin II, in the progression of chronic kidney disease has become a subject of significant interest over the past decade. Experimental studies in animals have shown that persistently elevated aldosterone levels lead to pathohistological changes in the kidney, along with renal and cardiac fibrosis. Incomplete suppression of aldosterone may, therefore, contribute to the deleterious effects of the renin-angiotensin system in the setting of chronic kidney disease. Clinical trials in adults have shown a potential role for mineralocorticoid receptor blockers to delay further the development of end-stage renal disease by completing renin-angiotensin blockade. In adults, mineralocorticoid receptor blockade produces a significant anti-proteinuric effect and has minimal risk of causing hyperkalemia if the condition of the patients is closely monitored. Further studies will need to be conducted to determine whether mineralocorticoid receptor blockers are equally effective and safe for the treatment of chronic kidney disease in children.

Mineralocorticoid receptor blockade enhances the antiproteinuric effect of an angiotensin II blocker through inhibiting podocyte injury in type 2 diabetic rats

Treatment with angiotensin II type 1 receptor blockers (ARBs) is the first-line therapy for hypertensive patients with diabetic nephropathy. However, emerging clinical evidence indicates that mineralocorticoid receptor (MR) blockers have blood pressure-independent antiproteinuric effects. We sought to determine whether treatment with an MR blocker, eplerenone, enhances the effects of an ARB, telmisartan, on podocyte injury and proteinuria in type 2 diabetic Otsuka-Long-Evans-Tokushima-Fatty (OLETF) rats. From 20 to 50 weeks old, diabetic OLETF rats showed higher systolic blood pressure (SBP) and urinary protein excretion (U(protein)V) than nondiabetic control Long-Evans-Tokushima-Otsuka rats. At 50 weeks old, OLETF rats also showed glomerular sclerosis and podocyte injury, whereas nephrin and podocin mRNA levels in isolated glomeruli were significantly decreased. Treatment with telmisartan (3 mg/kg/day p.o.) decreased SBP and U(protein)V, increased nephrin and podocin mRNA levels, and attenuated glomerular sclerosis and podocyte injury. Eplerenone (100 mg/kg/day p.o.) did not alter SBP but elicited similar changes in renal parameters. However, greater reductions in U(protein)V and podocyte injury and greater increases in nephrin and podocin mRNA levels were observed in the combination treatment group. Hydralazine (25 mg/kg/day p.o.) decreased SBP but did not alter any renal parameters. These data indicate that MR blockade enhances the SBP-independent antiproteinuric effect of an ARB through inhibiting podocyte injury in type 2 diabetic rats.

Activation of local aldosterone system within podocytes is involved in apoptosis under diabetic conditions

Previous studies have shown that mineralocorticoid receptor (MCR) blocker reduces proteinuria in diabetic nephropathy (DN), but the role of aldosterone in podocyte injury has never been explored in DN. This study was undertaken to elucidate whether a local aldosterone system existed in podocytes and to examine its role in podocyte apoptosis under diabetic conditions. In vitro, immortalized podocytes were exposed to 5.6 mM glucose (NG), NG + 24.4 mM mannitol, and 30 mM glucose (HG) with or without 10(-7) M spironolactone (SPR). In vivo, 32 Sprague-Dawley rats were injected with diluent (C, n = 16) or streptozotocin intraperitoneally [diabetes mellitus (DM), n = 16], and 8 rats from each group were treated with SPR for 3 mo. Aldosterone synthase (CYP11B2) and MCR mRNA and protein expression were determined by real-time PCR and Western blot, respectively, and aldosterone levels by radioimmunoassay. Western blot for apoptosis-related molecules, Hoechst 33342 staining, and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay were performed to determine apoptosis. CYP11B2 and MCR expression were significantly higher in HG-stimulated podocytes and DM glomeruli compared with NG cells and C glomeruli, respectively, along with increased aldosterone levels. Western blot analysis revealed that cleaved caspase-3 and Bax expression was significantly increased, whereas Bcl-2 expression was significantly decreased in HG-stimulated podocytes and in DM glomeruli. Apoptosis determined by Hoechst 33342 staining and TUNEL assay were also significantly increased in podocytes under diabetic conditions. These changes in the expression of apoptosis-related proteins and the increase in apoptotic cells were inhibited by SPR treatment. These findings suggest that a local aldosterone system is activated and is involved in podocyte apoptosis under diabetic conditions.

Mineralocorticoid receptor antagonism attenuates glomerular filtration barrier remodeling in the transgenic Ren2 rat

Recent evidence suggests that mineralocorticoid receptor (MR) antagonism has beneficial effects on tissue oxidative stress and insulin metabolic signaling as well as reducing proteinuria. However, the mechanisms by which MR antagonism corrects both renin-angiotensin-aldosterone system (RAAS) impairments in renal insulin metabolic signaling and filtration barrier/podocyte injury remain unknown. To explore this potential beneficial interactive effect of MR antagonism we used young transgenic (mRen2)27 (Ren2) rats with increased tissue RAAS activity and elevated serum aldosterone levels. Ren2 and age-matched Sprague-Dawley (SD) control rats (age 6-7 wk) were implanted with a low dose of the MR antagonist spironolactone (0.24 mg/day) or vehicle, both delivered over 21 days. Albuminuria, podocyte-specific proteins (synaptopodin, nephrin, and podocin), and ultrastructural analysis of the glomerular filtration barrier were measured in relation to RAAS activation of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, reactive oxygen species (ROS), and the redox-sensitive Rho kinase (ROK). Insulin metabolic signaling was determined via measurement of insulin receptor substrate-1 (IRS-1) phosphorylation, IRS-1 ubiquitin/proteasomal degradation, and phosphorylation of Akt. Ren2 rats exhibited albuminuria, loss of podocyte-specific proteins, and podocyte foot process effacement contemporaneous with reduced renal IRS-1 and protein kinase B/Akt phosphorylation compared with SD control rats (each P < 0.05). Ren2 kidneys also manifested increased NADPH oxidase/ROS/ROK in conjunction with enhanced renal tissue levels of angiotensin II (ANG II), ANG-(1-12), and angiotensin type 1 receptor. Low-dose spironolactone treatment reduced albuminuria and tissue RAAS activity and improved podocyte structural and protein integrity with improvements in IRS-1/Akt phosphorylation. Thus, in this model of RAAS activation, MR antagonism attenuates glomerular/podocyte remodeling and albuminuria, in part through reductions in redox-mediated impairment of insulin metabolic signaling.

Aldosterone and progression of kidney disease

Experimental evidence indicates that aldosterone, besides its mineralcorticoid properties, directly contributes to accelerate renal damage through promotion of cell growth, fibrosis and inflammation. As a consequence, attenuation of growth-promoting and fibroproliferative effects of aldosterone might contribute to slow progression of chronic renal injury. Preliminary clinical observations have documented that aldosterone blockers added to angiotensin-converting enzyme inhibitor- and/or angiotensin receptor blocker-based regimens exerted significant antiproteinuric effects in patients with diabetic and nondiabetic nephropathies. Further studies in larger cohorts are now required to definitively address the safety and efficacy of aldosterone antagonism in patients with chronic kidney diseases.

Present and future drug treatments for chronic kidney diseases: evolving targets in renoprotection

At present, there are no specific cures for most of the acquired chronic kidney diseases, and renal transplantation is limited by organ shortage, therefore present efforts are concentrated on the prevention of progression of renal diseases. There is robust experimental and clinical evidence that progression of chronic nephropathies is multifactorial; however, intraglomerular haemodynamic changes and proteinuria play a key role in this process. With a focus on renoprotection, we first examine more established therapies--such as those that modulate the renin-angiotensin-aldosterone system--that can be used for the treatment of proteinuric renal diseases. We then discuss examples of novel drugs and biologics that might be used to target the inflammatory and profibrotic process, and glomerular injury, highlighting results from recent clinical trials.

Evidence for benefits of angiotensin receptor blockade beyond blood pressure control

Elevated levels of angiotensin II result in oxidative stress and endothelial dysfunction, which initiate atherogenic pathologic processes that are important in cardiovascular disease development. Angiotensin II induces its deleterious effects primarily through the type 1 receptor; these effects are inhibited by angiotensin II receptor blockers (ARBs) directly at the receptor level. Angiotensin II may potentiate protective mechanisms through stimulation of the type 2 receptor, which is not blocked by ARBs. Accumulating data suggest that blockade of angiotensin II production or activity provides vascular and cardioprotective benefits, such as reduction of atrial fibrillation, acute myocardial infarction, and heart failure events. Moreover, blockade of the renin-angiotensin system has been shown to offer renal protection in subjects with and without diabetes mellitus and to reduce the risk of new-onset diabetes.

Spironolactone exhibits direct renoprotective effects and inhibits renal renin-angiotensin-aldosterone system in diabetic rats

Aldosterone itself has been reported to participate in mediating renal injury, and it was confirmed that the aldosterone synthase CYP11B2 gene, protein, and aldosterone production are locally present in the kidney. To test the hypothesis that a mineralocorticoid receptor antagonist might ameliorate diabetic nephropathy and the inhibition of renal CYP11B2 expression might be associated with these renoprotective effects, spironolactone (50 mg/kg/day) was administered by gavage to uninephrectomized diabetic rats for 3 weeks. Streptozotocin (55 mg/kg, i.v.) significantly increased urinary protein excretion and collagen deposition in glomerular and tubulointerstitial areas in the kidney, which were attenuated by spironolactone treatment. RT-PCR and Western blot analysis revealed that the expression of mRNA for collagen I/IV, transforming growth factor-beta, NADPH oxidase and mineralocorticoid receptor and the mineralocorticoid receptor protein in the kidney was enhanced in the uninephrectomized diabetic rat kidney and that the overexpression of these molecules was suppressed by spironolactone. Renal angiotensin converting enzyme was activated and overexpressed in diabetic rats, and spironolactone inhibited these changes. We demonstrated that spironolactone prevented the streptozotocin-induced increase in the renal CYP11B2 mRNA content. Controlling blood glucose level with insulin also attenuated the renal expression of mRNA for CYP11B2. On the other hand, the treatment of spironolactone in the present study did not affect blood glucose level or blood pressure in uninephrectomized streptozotocin-induced diabetic rats. These results suggest that spironolactone exerted renoprotective effects in uninephrectomized streptozotocin-induced diabetic rats and inhibited local renin-angiotensin-aldosterone system, such as the ACE expression and the hyperglycemia-induced overexpression of CYP11B2, in the kidney.

Local renal aldosterone production induces inflammation and matrix formation in kidneys of diabetic rats

Recently, we reported the presence of a local renal aldosterone production. In the present study, we tested the hypothesis that local aldosterone production in the kidney contributes to renal inflammation, matrix formation and albuminuria associated with diabetes. We evaluated changes in renal aldosterone content (RAC), aldosterone synthase expression, nuclear factor kappaB (NFkappaB), tumour necrosis factor alpha (TNFalpha), interleukin-6 (IL-6), transforming growth factor beta (TGFbeta), glomerular fibronectin, collagen type IV and urinary albumin extraction (UAE) in response to the aldosterone synthase inhibitor FAD286. Studies were conducted in adrenalectomized, normoglycaemic (control) or diabetic rats for 14 weeks. The FAD286 was administered during the last 10 weeks of the study. Plasma aldosterone levels were not detectable in any of the study groups. Compared with control rats, diabetic rats had higher levels of RAC by 488% (P < 0.01), NFkappaB by 293% (P < 0.01), TNFalpha by 356% (P < 0.01), IL-6 by 378% (P < 0.01), TGFbeta by 337% (P < 0.01) and UAE by 1122% (P < 0.01), and increased glomerular fibronectin and collagen type IV immunostaining. In diabetic rats, FAD286 reduced RAC (P < 0.01), UAE (P < 0.05), NFkappaB mRNA, TNFalpha mRNA, IL-6 mRNA and TGFbeta mRNA by 51, 41, 41 and 52% and also their proteins and decreased glomerular fibronectin and collagen type IV immunostaining. In conclusion, diabetes increases local aldosterone production in the kidney, which contributes to development of renal inflammation, matrix formation and albuminuria. Inhibition of aldosterone production in the kidney could be helpful in management of diabetic nephropathy.

Aliskiren, a novel renin inhibitor, is renoprotective in a model of advanced diabetic nephropathy in rats

AIMS/HYPOTHESIS

Blockade of the renin-angiotensin system (RAS) with either ACE inhibitors or angiotensin receptor blocker is a key therapeutic strategy in slowing progression of diabetic nephropathy. Interruption of the RAS may also be achieved by blocking the activity of renin, the rate-limiting step in angiotensin II biosynthesis. However, it is not known whether drugs in this class also reduce the structural and functional manifestations of diabetic nephropathy.

METHODS

Using diabetic transgenic (mRen-2)27 rats, a rodent model of advanced diabetic nephropathy, we compared the efficacy of the renin inhibitor, aliskiren (10 mg kg(-1) day(-1) by osmotic mini-pump), with the ACE inhibitor, perindopril (0.2 mg kg(-1) day(-1) in drinking water), over a 16 week period.

RESULTS

Both perindopril and aliskiren reduced blood pressure, albuminuria and structural injury in experimental diabetic nephropathy, although not to the same extent. Aliskiren, at the dose used, did not reduce systemic blood pressure as much as perindopril, but both compounds were equally effective in reducing albuminuria and glomerulosclerosis in diabetic animals. The magnitude of interstitial fibrosis was attenuated to a greater degree by aliskiren than by perindopril.

CONCLUSIONS/INTERPRETATION

These findings suggest that therapies aimed at different targets within the RAS may not have identical effects in attenuating structural injury in experimental diabetic nephropathy.

Altered Regulation of Renin-Angiotensin, Endothelin and Natriuretic Peptide Systems in Rat Kidney with Chronic Unilateral Ureteral Obstruction

BACKGROUND

The present study was designed to investigate the role of the local renin-angiotensin-aldosterone system (RAAS), endothelin (ET) and the natriuretic peptide system (NPS) for the development of renal fibrosis and progressive renal disease in experimental unilateral ureteral obstructed (UUO) rats.

METHODS

Male Sprague-Dawley rats (180-200 g) were unilaterally obstructed by ligation of the proximal ureters for 14 days. Control rats were treated in the same way, except that no ligature was made. The mRNA expressions of local renin-angiotensin system, aldosterone synthase (CYP11B2), ET-1 and NPS was determined in the cortex by real-time polymerase chain reaction.

RESULTS

Following the unilateral ureteral obstruction, the mRNA expressions of angiotensin-converting enzyme 1, ET-1 and transforming growth factor-beta1 (TGF-beta1) were increased, while angiotensin-converting enzyme 2 was decreased in the obstructed kidney compared with the controls. Angiotensin II type 1 receptor was decreased and TGF-beta1 was not changed in contralateral kidney compared with the controls. Atrial natriuretic peptide, brain natriuretic peptide, and C-type natriuretic peptide expressions were increased in UUO kidneys compared with the controls, while natriuretic peptide receptor-A was decreased in UUO kidneys.

CONCLUSION

The local RAAS and ET-1 was upregulated which may play a role in the progressive renal fibrosis in obstructed kidneys in rats with UUO. The enhanced activity of NPS in UUO kidney may play a role to compensate against progressive renal fibrosis in chronic obstructive uropathy.

NO and cGMP mediate angiotensin AT2 receptor-induced renal renin inhibition in young rats

We hypothesized that angiotensin subtype-2 receptor (AT(2)R) inhibits renal renin biosynthesis in young rats via nitric oxide (NO). We monitored changes in renal NO, cGMP, renal renin content (RRC), and ANG II in 4-wk-old rats in response to low sodium (LNa(+)) intake alone and combined with 8-h direct renal cortical administration of AT(1) receptor blocker valsartan (VAL), AT(2)R blocker PD123319 (PD), NO synthase inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME), NO donor S-nitroso-N-acetyl penicillamine (SNAP), or guanylyl cyclase inhibitor 1H-[1,2,4] oxadiazolo[4,2-alpha] quinoxaline-1-one (ODQ). In addition, we monitored renal endothelial nitric oxide synthase (eNOS) and neuronal nitric oxide synthase (nNOS) in response to VAL or PD. LNa(+), VAL, PD, l-NAME, and ODQ increased RRC, ANG II, and renin mRNA. PD and l-NAME decreased NO and cGMP, while SNAP reduced RRC, ANG II, renin mRNA, and reversed the effects of PD. PD also reduced eNOS and nNOS protein and mRNA. Combined treatment with PD, l-NAME, or ODQ and VAL reversed the effects of VAL and caused further increase in RRC, ANG II, renin mRNA, and protein. ODQ reversed the effects of SNAP. These data demonstrate that the renal AT(2) receptor decreases renal renin biosynthesis and ANG II production in young rats. Reversal of the PD effects by SNAP and SNAP effects by ODQ confirms that NO and cGMP mediate the AT(2) receptor inhibition of renal renin production.

Aldosterone upregulates vascular endothelial growth factor expression in mouse cortical collecting duct epithelial cells through classic mineralocorticoid receptor

Accumulating evidence shows that aldosterone plays an important role in the pathogenesis of renal fibrosis but its mechanism has not been completely defined. Recently, exogenous administration of aldosterone significantly alleviated ischemic states in a model of femoral artery ligated rats, accompanied by an obvious enhancement of VEGF upregulation. We hypothesized that aldosterone may also regulate the expression of VEGF in the kidney. To confirm this, cultured cortical collecting duct epithelial cells (M-1 cell line) were incubated with aldosterone and control media, respectively. The pathway by which aldosterone regulates VEGF expression was tested by the administration of spironolactone, a specific mineralocorticoid receptor (MR) antagonist. VEGF expression was detected by immunofluorescence staining, ELISA, Western blot and RT-PCR. Aldosterone induced an elevation of VEGF excretion in a time- and dose-dependent manner. Western blotting showed a 1.4-fold elevation in cytosolic VEGF expression following aldosterone (10(-8) M) incubation for 48 h (p<0.01). After aldosterone (10(-7) M) incubation for 48 h, the mRNA level of VEGF164 and VEGF120 showed 1.8- and 1.7-fold increases, respectively (p<0.01). This upregulation was almost completely blocked by spironolactone as shown both by mRNA levels and cytosolic protein levels. In addition, the mRNA of aldosterone receptor was detected in M-1 cells. We demonstrated for the first time that aldosterone induced VEGF expression in M-1 cells, an effect mediated by classic mineralocorticoid receptor. This finding provides experimental evidence for the local non-hemodynamic action of aldosterone.

Increase in DPP-IV in the intestine, liver and kidney of the rat treated with high fat diet and streptozotocin

High fat diet or insulin deficiency is commonly seen in Type II diabetes, while the mechanism remains unclear. To test our hypothesis that DPP-IV contributes to Type II diabetes, we examined the expression and activity of DPP-IV in rats (n=8 to each group) treated for 12 weeks with 3 separate diets: a) normal control; b) a high fat diet; and c) a high fat diet plus streptozotocin, a chemical for induction of insulin-deficient diabetes. Compared to rats on the normal diet, the rats with a high fat diet significantly increased DPP-IV's expression and activity about 142-152% in the intestine (P<0.05) and 153-240% in kidneys (P<0.05), but there was no change in the liver. Administration of streptozotocin to the rats treated with the high fat diet showed an insufficient insulin secretion and higher blood glucose in response to glucose/insulin tolerance test, and an increase in expression of DPP-IV and activity by 188-242% in the intestine (P<0.01); 191-225% in liver (P<0.01); and 211-321% in the kidneys (P<0.01). Immunohistochemistry studies confirmed the above results, showing increased DPP-IV immunostaining localized primarily in intestinal epithelium, hepatocytes and renal tubular cells. This study, for the first time reports an increase in DPP-IV associated with a high fat diet, as well as in the combination of a high fat diet with an insulin deficiency. Since both high fat diet and insulin deficiency are closely linked with etiology of Type II diabetes, the evidence in this study suggests a role of DPP-IV in development of Type II diabetes.

Aldosterone, mineralocorticoid receptors, and vascular inflammation

PURPOSE OF REVIEW

Aldosterone and its mineralocorticoid receptor represent an ancient signaling system. Indeed, the mineralocorticoid receptor is older than its agonist. Both have probably served various functions through the eons and salt preservation may be relatively recent. A large body of evidence suggests that aldosterone conducts signaling in vascular cells and contributes substantially to vascular remodeling and target organ damage. A blood pressure and salt balance-independent effect was first observed in two large heart failure trials.

RECENT FINDINGS

Mineralocorticoid receptor blockade has now been shown to reduce proteinuria even in the face of angiotensin converting enzyme inhibition and AT1 receptor blockade. Mineralocorticoid receptor blockade effectively reduces target organ damage in every hypertensive model tested, irrespective of circulating renin and aldosterone levels. Protection is also observed in nonhypertensive diabetic and hyperlipidemic models. Signaling in vascular cells involves primarily the mitogen activated protein kinase pathway with participation of the epidermal growth factor receptor. Novel signaling molecules have been shown to participate in aldosterone-mediated actions including the murine double-minute type 2 protein that participates in antiapoptotic and proliferative effects. Clinically, mutations in the mineralocorticoid receptor have shed additional light on its importance.

SUMMARY

A resurgence of interest in aldosterone reflects its importance and clinical relevance for vascular remodeling and target organ damage.

Mechanisms of disease: The role of aldosterone in kidney damage and clinical benefits of its blockade

In the past 10 years, many widely accepted concepts relating to aldosterone production and its pathogenetic role have changed. We now know that aldosterone is produced not only by the zona glomerulosa of the adrenal cortex, but also in the heart, blood vessels, kidney and brain; such extra-epithelial production occurs mainly during tissue repair. Also, increased aldosterone levels contribute to vessel inflammation, oxidative stress, endothelial dysfunction and organ damage. As such, aldosterone has a key role in the development of myocardial fibrosis. Anti-aldosterone treatment has proven effective in patients with heart failure. Experimental evidence regarding the role of aldosterone in kidney damage has accumulated. Aldosterone infusion can counteract the beneficial effects of treatment with angiotensin-converting-enzyme inhibitors, causing more-severe proteinuria and an increased number of vascular and glomerular lesions; treatment with aldosterone antagonists can reverse these alterations. Preliminary observations in pilot studies in humans confirm the experimental findings, supporting the hypothesis that aldosterone antagonists are renoprotective in clinical practice. Studies in larger populations with longer follow-up are needed to confirm this theory.

Losartan-hydrochlorothiazide association promotes lasting blood pressure normalization and completely arrests long-term renal injury in the 5/6 ablation model

The possible long-term renoprotective effects of treatment with thiazides, either as monotherapy or associated with renin-angiotensin suppressors, have not been assessed. We investigated the effect of hydrochlorothiazide (H), alone or combined with losartan (L), in the 5/6 renal ablation model (Nx). Adult male Munich-Wistar rats underwent Nx, remaining untreated for 1 mo. At this time, functional and morphological studies were performed in 21 rats (group Nx(pre)). The remaining rats were distributed among groups: Nx, no treatment; Nx+L, receiving L, 50 mg kg(-1) day(-1) in the drinking water; Nx+H, receiving H, 6 mg kg(-1) day(-1) in drinking water; and Nx+L+H, receiving both L and H as described. At 30 days of treatment, systemic and glomerular pressures were markedly elevated in group Nx. Both H and L attenuated hypertension, whereas combined L+H treatment completely normalized both pressures. Eight months after Nx, mortality approached 70% in untreated rats, whereas severe albuminuria, hypertension, glomerulosclerosis, and interstitial expansion were observed. H and L attenuated, but did not prevent, mortality, hypertension, and renal injury. Combined L+H treatment completely prevented mortality, normalized albuminuria and blood pressure, and arrested renal injury at levels found 1 mo after ablation, despite the unusually long period of observation. Combined L+H treatment may represent an effective therapeutic alternative to prevent progression of chronic nephropathies.

Association Study With 33 Single-Nucleotide Polymorphisms in 11 Candidate Genes for Hypertension in Chinese

Essential hypertension is considered to be a typical complex disease with multifactorial etiology, which leads to inconsistent findings in genetic studies. One possibility of failure to replicate some single-locus results is that the underlying genetics of hypertension are not only based on multiple genes with minor effects but also on gene-gene interactions. To test this hypothesis, a case-control study was constructed in Chinese subjects, detecting both single locus and multilocus effects. Eleven candidate genes were selected from biochemical pathways that have been implicated in the development and progression of hypertension, and 33 polymorphisms were evaluated in 503 hypertension patients and 490 age- and gender-matched controls. Single-locus associations, using traditional logistic regression analyses, and multilocus associations, using classification and regression trees and multivariate adaptive regression splines, were both explored in this study. Final models were selected using either Bonferroni correction or cross-validation. Three polymorphisms, TH*rs2070762, ADRB2*Q27E, and GRK4*A486V, were found to be independently associated with essential hypertension in Chinese subjects. In addition to these individual predictors, a potential interaction of CYP11B2-AGTR1 is also involved in the etiology of hypertension. These findings support the multigenic nature of the etiology of essential hypertension and propose a potential gene-gene interactive model for future studies.