Modulation of incipient glomerular lesions in experimental diabetic nephropathy by hypotensive and subhypotensive dosages of an ACE inhibitor

RhoA/ROCK inhibition attenuates endothelin-1-induced elevated glomerular permeability to albumin, inflammation, and fibrosis

Endothelin-1 (ET-1) contributes to the development of kidney diseases. However, the underlying molecular mechanism is largely undefined. Here we sought to investigate the potential role of ET-1 receptors, ET_A and ET_B in the regulation of increased glomerular permeability and underlying signaling pathways post-ET-1 infusion. Male Sprague-Dawley rats were infused with ET-1 (2 pmol/kg per minute, i.v.) for four weeks, and the effect on glomerular permeability to albumin (P_alb) and albuminuria was measured. The selective ROCK-1/2 inhibitor, Y-27632, was administered to a separate group of rats to determine its effect on ET-1-induced P_alb and albuminuria. The role of ET_A and ET_B receptors in regulating RhoA/ROCK activity was determined by incubating isolated glomeruli from normal rats with ET-1 and with selective ET_A and ET_B receptor antagonists. ET-1 infusion for four weeks significantly elevated P_alb and albuminuria. Y-27632 significantly reduced the elevation of P_alb and albuminuria. The activities of both RhoA and ROCK-1/2 were increased by ET-1 infusion. Selective ET_B receptor antagonism had no effect on the elevated activity of both RhoA and ROCK-1/2 enzymes. Selective ET_A receptor and combined ET_A/ET_B receptors blockade restored the activity of RhoA and ROCK-1/2 to normal levels. In addition, chronic ET-1 infusion increased the levels of glomerular inflammatory and fibrotic markers. These effects were all attenuated in rats following ROCK-1/2 inhibition. These observations suggest that ET-1 contributes to increased albuminuria, inflammation, and fibrosis by modulating the activity of the ET_A-RhoA/ROCK-1/2 pathway. Selective ET_A receptor blockade may represent a potential therapeutic strategy to limit glomerular injury and albuminuria in kidney disease.

A Salt-Induced Reno-Cerebral Reflex Activates Renin-Angiotensin Systems and Promotes CKD Progression

Salt intake promotes progression of CKD by uncertain mechanisms. We hypothesized that a salt-induced reno-cerebral reflex activates a renin-angiotensin axis to promote CKD. Sham-operated and 5/6-nephrectomized rats received a normal-salt (0.4%), low-salt (0.02%), or high-salt (4%) diet for 2 weeks. High salt in 5/6-nephrectomized rats increased renal NADPH oxidase, inflammation, BP, and albuminuria. Furthermore, high salt activated the intrarenal and cerebral, but not the systemic, renin-angiotensin axes and increased the activity of renal sympathetic nerves and neurons in the forebrain of these rats. Renal fibrosis was increased 2.2-fold by high versus low salt, but intracerebroventricular tempol, losartan, or clonidine reduced this fibrosis by 65%, 69%, or 59%, respectively, and renal denervation or deafferentation reduced this fibrosis by 43% or 38%, respectively (all P<0.05). Salt-induced fibrosis persisted after normalization of BP with hydralazine. These data suggest that the renal and cerebral renin-angiotensin axes are interlinked by a reno-cerebral reflex that is activated by salt and promotes oxidative stress, fibrosis, and progression of CKD independent of BP.

Antidiabetic and renoprotective effects of Cladophora glomerata Kützing extract in experimental type 2 diabetic rats: a potential nutraceutical product for diabetic nephropathy

Cladophora glomerata extract (CGE) has been shown to exhibit antigastric ulcer, anti-inflammatory, analgesic, hypotensive, and antioxidant activities. The present study investigated antidiabetic and renoprotective effects of CGE in type 2 diabetes mellitus (T2DM) rats. The rats were induced by high-fat diet and streptozotocin and supplemented daily with 1 g/kg BW of CGE for 12 weeks. The renal transport function was assessed by the uptake of para-aminohippurate mediated organic anion transporters 1 (Oat1) and 3 (Oat3), using renal cortical slices. These two transporters were known to be upregulated by insulin and PKCζ while they were downregulated by PKCα activation. Compared to T2DM, CGE supplemented rats had significantly improved hyperglycaemia, hypertriglyceridemia, insulin resistance, and renal morphology. The baseline uptake of para-aminohippurate was not different among experimental groups and was correlated with Oat1 and 3 mRNA expressions. Nevertheless, while insulin-stimulated Oat1 and 3 functions in renal slices were blunted in T2DM rats, they were improved by CGE supplementation. The mechanism of CGE-restored insulin-stimulated Oat1 and 3 functions was clearly shown to be associated with upregulated PKCζ and downregulated PKCα expressions and activations. These findings indicate that CGE has antidiabetic effect and suggest it may prevent diabetic nephropathy through PKCs in a T2DM rat model.

Antioxidant and renoprotective effects of Spirogyra neglecta (Hassall) Kützing extract in experimental type 2 diabetic rats

Spirogyra neglecta extract (SNE) has shown antihyperglycemia and antihyperlipidemia in type 2 diabetic mellitus (T2DM) rats. This study investigated the antioxidant and renoprotective effects of SNE in T2DM rats induced by high-fat diet with low-single dose streptozotocin. T2DM rats were fed daily with SNE (0.25, 0.5, and 1 g/kg BW) for 12 weeks. Renal morphology, malondialdehyde levels, qPCR, and western blotting were analyzed. Renal cortical slices were used to determine renal transport of organic anions, which are estrone sulfate and para-aminohippurate, mediated through organic anion transporter 3-Oat3. Insulin and PKCζ were known to activate Oat3 function while it was inhibited by PKCα. Compared to T2DM, plasma glucose, triglyceride, insulin resistance, renal morphology, and malondialdehyde levels were significantly improved by SNE supplementation. Reduced glutathione peroxidase and nuclear factor κB expressions were related to antioxidant effect of SNE. Oat3 mRNA and protein were not different among groups, but insulin-stimulated rOat3 followed by anion uptakes was abolished in T2DM. This was restored in the slices from SNE treatment. The mechanism of SNE-improved Oat3 was associated with PKCα and PKCζ expressions and activities. These findings indicate that SNE has beneficial effects on renal transport through antioxidant enzymes and PKCs in T2DM rats.

Chronic endothelin-1 infusion elevates glomerular sieving coefficient and proximal tubular albumin reuptake in the rat

AIM

We have previously found that chronic endothelin-1 (ET-1) infusion in Sprague-Dawley rats increases glomerular permeability to albumin (P(alb)) as assessed in vitro independent of blood pressure with no observed albuminuria. In this study, we hypothesized that ET-1 increases glomerular albumin filtration with accompanied increase in albumin uptake via the proximal tubule, which masks the expected increase in urinary albumin excretion.

MAIN METHODS

Nonfasting Munich-Wistar Fromter rats were surgically prepared for in vivo imaging (n=6). Rats were placed on the microscope stage with the exposed kidney placed in a cover slip-bottomed dish bathed in warm isotonic saline. Rats were then injected i.v. with rat serum albumin conjugated to Texas Red that was observed to enter capillary loops of superficial glomeruli, move into Bowman's space, bind to the proximal tubular cell brush border and reabsorbed across the apical membrane. Glomerular sieving coefficient (GSC) was calculated as the ratio of conjugated albumin within the glomerular capillary versus that in Bowman's space. Rats were again studied after 2 weeks of chronic ET-1 (2 pmol/kg/min; i.v. osmotic minipump).

KEY FINDINGS

Glomerular sieving coefficient was significantly increased in rats following chronic ET-1 infusion (0.025 ± 0.005 vs. 0.017 ± 0.003, p<0.05). Mean fluorescence intensity for conjugated albumin within proximal tubules was increased by ET-1 infusion: 118.40 ± 6.34 vs. 74.27 ± 4.45 pixel intensity (p<0.01).

SIGNIFICANCE

These data provide in vivo evidence that ET-1 directly increases glomerular permeability to albumin and that albuminuria is prevented by increased PT albumin uptake in the rat.

Endothelin-1 increases glomerular permeability and inflammation independent of blood pressure in the rat

Endothelin (ET) 1 is a potent vasoactive peptide implicated in the pathogenesis of hypertension and renal disease. The aim of the current study was to test the hypotheses that ET-1 increases albumin permeability of glomeruli isolated from normal rats and that chronic ET-1 infusion will increase glomerular permeability and inflammation independent of blood pressure. Glomerular permeability to albumin was determined from the change in glomerular volume induced by exposing isolated glomeruli to oncotic gradients. Incubation of glomeruli taken from normal rats with ET-1 at a concentration that did not produce direct glomerular contraction (1 nmol/L) significantly increased glomerular permeability to albumin, reaching a maximum after 4 hours. Chronic ET-1 infusion for 2 weeks in Sprague-Dawley rats significantly increased glomerular permeability to albumin and nephrin excretion rate, effects that were attenuated in rats given an ET(A) receptor antagonist (ABT-627, 5 mg/kg per day). Urinary protein and albumin excretion and mean arterial pressure (telemetry) were not changed by ET-1 infusion. Acute incubation of glomeruli isolated from ET-1-infused rats with the selective ET(A) antagonist significantly reduced glomerular permeability to albumin, an effect not observed with acute treatment with a selective ET(B) antagonist. Chronic ET-1 infusion increased glomerular and plasma soluble intercellular adhesion molecule 1 and monocyte chemoattractant protein 1 and elevated the number of macrophages and lymphocytes in renal cortices (ED-1 and CD3-positive staining, respectively). These effects were all attenuated in rats given an ET(A) selective antagonist. These data support the hypothesis that ET-1 directly increases glomerular permeability to albumin and renal inflammation via ET(A) receptor activation independent of changes in arterial pressure.

Endothelin A receptor blockade reduces diabetic renal injury via an anti-inflammatory mechanism

Endothelin (ET) receptor blockade delays the progression of diabetic nephropathy; however, the mechanism of this protection is unknown. Therefore, the aim of this study was to test the hypothesis that ET(A) receptor blockade attenuates superoxide production and inflammation in the kidney of diabetic rats. Diabetes was induced by streptozotocin (diabetic rats with partial insulin replacement to maintain modest hyperglycemia [HG]), and sham rats received vehicle treatments. Some rats also received the ETA antagonist ABT-627 (sham+ABT and HG+ABT; 5 mg/kg per d; n = 8 to 10/group). During the 10-wk study, urinary microalbumin was increased in HG rats, and this effect was prevented by ET(A) receptor blockade. Indices of oxidative stress, urinary excretion of thiobarbituric acid reactive substances, 8-hydroxy--deoxyguanosine, and H2O2 and plasma thiobarbituric acid reactive substances were significantly greater in HG rats than in sham rats. These effects were not prevented by ABT-627. In addition, renal cortical expression of 8-hydroxy--deoxyguanosine and NADPH oxidase subunits was not different between HG and HG+ABT rats. ETA receptor blockade attenuated increases in macrophage infiltration and urinary excretion of TGF-beta and prostaglandin E2 metabolites in HG rats. Although ABT-627 did not alleviate oxidative stress in HG rats, inflammation and production of inflammatory mediators were reduced in association with prevention of microalbuminuria. These observations indicate that ETA receptor activation mediates renal inflammation and TGF-beta production in diabetes and are consistent with the postulate that ETA blockade slows progression of diabetic nephropathy via an anti-inflammatory mechanism.

Role of endoethelin-1 in development of neprhopathy induced with streptozocin

The main aim of our study was to detect changes in plasma level of endoethelin-1 after experimentally induced diabetes and diabetic nephropathy with streptozocin in rats. The effects of ACE inhibitors are well known and thus, we wanted to analyze the influence of enalapril (ACE inhibitor) on plasma concentrations of endoethelin-1 as well as its effects in the treatment of diabetic nephropathy. Single i.p. administration of streptozocin (STZ) caused a significant increase of endoethelin-1 plasma concentrations associated with distinct signs and symptoms of diabetic nephropathy (microalbuminuria, increased urine N-acetyl-D-glucosamidase, increased serum concentrations of urea and creatinine, polyuria). Four-week treatment with endoethelin-1 resulted in significant reduction of endoethelin-1 plasma concentrations and improved sings and symptoms of diabetic nephropathy. The results obtained have confirmed that endoethelin-1 may play an important role in development and progression of diabetic nephropathy and ACE inhibitors, that is enalapril, may alleviate and delay the progression of diabetic nephropathy

The effect of proteinase inhibitors on glomerular albumin permeability induced in vitro by serum from patients with idiopathic focal segmental glomerulosclerosis

BACKGROUND

The putative circulating factor responsible for the glomerular permeability alterations induced in vitro by serum from patients affected by focal segmental glomerulosclerosis (FSGS) remains unidentified. We have observed that a serine proteinase isolated from patient serum increases albumin permeability in isolated glomeruli. The objective of the present study was to determine the effect of various proteinase inhibitors on glomerular albumin permeability (P(alb)) in isolated glomeruli incubated with FSGS serum.

METHODS

The study population consisted of 12 FSGS patients (eight males; mean age: 21+/-10 years) previously shown to have elevated serum albumin permeability activity. P(alb) was determined by measuring the change in glomerular volume induced by applying oncotic gradients to isolated healthy rat glomeruli treated with patient serum in comparison to control serum. Solutions of seven different proteinase inhibitors (0.5 mg/ml) were added to the incubation media with the sera (1:1 vol/vol): serine proteinase inhibitors (PMSF, leupeptin, aprotinin, gabexate mesylate), the cysteine proteinase inhibitor E-64, the metalloproteinase inhibitor EDTA and the aspartate proteinase inhibitor pepstatin. Sera from the same patients were also tested with the addition to the incubation media of quinaprilat, an inhibitor of the metalloproteinase angiotensin-converting enzyme.

RESULTS

Mean P(alb) of the sera was 0.86+/-0.11, with the addition of PMSF 0.41+/-0.09, leupeptin 0.30+/-0.17, aprotinin 0.09+/-0.14, gabexate mesylate 0.27+/-0.25, E-64 0.81+/-0.09, EDTA 0.68+/-0.10 or pepstatin 0.76+/-0.11. The mean P(alb) of the sera combined with quinaprilat was reduced to 0.34+/-0.35. Thus, only the serine proteinase inhibitors consistently blocked the increased P(alb) induced by the FSGS sera.

CONCLUSIONS

In the cascade of events that lead to the initiation of glomerular fibrosis in FSGS, the putative glomerular permeability factor associated with FSGS may require a serine proteinase to effect its activity.

Haemodynamics in microvascular complications in type 1 diabetes

Type 1 diabetes is commonly associated with microvascular complications. Most of the microvascular blood vessels are involved but those in the kidney, retina and large nerves exhibit the more significant pathology. Haemodynamic and metabolic factors both alone and through the activation of a common pathway contribute to the characteristic dysfunction observed in diabetic vasculopathy. The haemodynamic abnormalities in type 1 diabetes are characterized by increased systemic blood pressure and altered blood flow with subsequent activation of various vasoactive factors, which can contribute to the maintenance of the haemodynamic alterations and to the development and progression of the microvascular complications. These vasoactive factors include vasoconstrictors such as angiotensin II, and endothelin, as well as vasodilators such as nitric oxide (NO). Systemic hypertension and vasoactive factors independently and in interaction with the metabolic pathway activate intracellular second messengers, nuclear transcription factors and various growth factors which lead to the typical functional and structural alterations of diabetic microvascular complications. Therapeutic strategies involved in the management and prevention of diabetic complications currently include antihypertensive agents, particularly those that interrupt the renin-angiotensin system. Further understanding of the interactions among the vasoactive factors, the intracellular second messengers and the growth factors may help to identify novel strategies to influence the action of the vasoactive factors. These novel therapies, together with specific inhibitors of the metabolic pathway or the common pathway, may provide the possibility of preventing or even reversing the progression of diabetic microvascular complications.