Angiotensin II receptor blockade limits kidney injury in two-kidney, one-clip Goldblatt hypertensive rats with special reference to phenotypic changes

Genetic Deletion of AT1a Receptor or Na+/H+ Exchanger 3 Selectively in the Proximal Tubules of the Kidney Attenuates Two-Kidney, One-Clip Goldblatt Hypertension in Mice

The roles of angiotensin II (Ang II) AT1 (AT1a) receptors and its downstream target Na+/H+ exchanger 3 (NHE3) in the proximal tubules in the development of two-kidney, 1-clip (2K1C) Goldblatt hypertension have not been investigated previously. The present study tested the hypothesis that deletion of the AT1a receptor or NHE3 selectively in the proximal tubules of the kidney attenuates the development of 2K1C hypertension using novel mouse models with proximal tubule-specific deletion of AT1a receptors or NHE3. 2K1C Goldblatt hypertension was induced by placing a silver clip (0.12 mm) on the left renal artery for 4 weeks in adult male wild-type (WT), global Agtr1a−/−, proximal tubule (PT)-specific PT-Agtr1a−/− or PT-Nhe3−/− mice, respectively. As expected, telemetry blood pressure increased in a time-dependent manner in WT mice, reaching a maximal response by Week 3 (p < 0.01). 2K1C hypertension in WT mice was associated with increases in renin expression in the clipped kidney and decreases in the nonclipped kidney (p < 0.05). Plasma and kidney Ang II were significantly increased in WT mice with 2K1C hypertension (p < 0.05). Tubulointerstitial fibrotic responses were significantly increased in the clipped kidney (p < 0.01). Whole-body deletion of AT1a receptors completely blocked the development of 2K1C hypertension in Agtr1a−/− mice (p < 0.01 vs. WT). Likewise, proximal tubule-specific deletion of Agtr1a in PT-Agtr1a−/− mice or NHE3 in PT-Nhe3−/− mice also blocked the development of 2K1C hypertension (p < 0.01 vs. WT). Taken together, the present study provides new evidence for a critical role of proximal tubule Ang II/AT1 (AT1a)/NHE3 axis in the development of 2K1C Goldblatt hypertension.

Cardiorenal dysfunction and hypertrophy induced by renal artery occlusion are normalized by galangin treatment in rats

Galangin is a polyphenolic compound found in Alpinia officinarum and propolis. This study investigated the effect of galangin on blood pressure, the renin angiotensin system (RAS), cardiac and kidney alterations and oxidative stress in two-kidney one-clipped (2K-1C) hypertensive rats. Hypertension was induced in male Sprague Dawley rats (180-220 g), and the rats were given galangin (30 and 60 mg/kg) and losartan (10 mg/kg) for 4 weeks (n = 8/group). Galangin decreased hypertension and cardiac dysfunction and hypertrophy, which was related to the reducing circulation angiotensin converting enzyme (ACE) activity and angiotensin II concentration (p < 0.05). These effects were consistent with the reduced overexpression of angiotensin II receptor type 1 (AT₁R), transforming growth factor beta 1 (TGF-β1) and collagen type I (Col I) protein in cardiac tissue (p < 0.05). Additionally, renal artery occlusion, procedure-induced kidney dysfunction and fibrosis were attenuated in the galangin-treated group. Galangin treatment normalized the overexpression of AT₁R and NADPH oxidase 4 (Nox-4) protein and normalized the downregulation of nuclear factor-erythroid Factor 2-related Factor 2 (Nrf-2) and haem oxygenase 1 (HO-1) in 2K-1C rats (p < 0.05). Galangin exhibited antioxidative effects, as it reduced systemic and tissue oxidative stress markers and increased catalase activity in 2K-1C rats (p < 0.05). In conclusion, galangin attenuated hypertension, renin-angiotensin system activation, cardiorenal damage and oxidative stress induced by renal artery stenosis in rats. These effects might be associated with modulation of the expression of AT₁R, TGF-β1 and Col I protein in the heart as well as AT₁R/Nox-4 and Nrf-2/HO-1 protein in renal tissue in hypertensive rats.

Comparative analysis of hypertensive nephrosclerosis in animal models of hypertension and its relevance to human pathology. Glomerulopathy

Current research on hypertension utilizes more than fifty animal models that rely mainly on stable increases in systolic blood pressure. In experimental hypertension, grading or scoring of glomerulopathy in the majority of studies is based on a wide range of opinion-based histological changes that do not necessarily comply with lesional descriptors for glomerular injury that are well-established in clinical pathology. Here, we provide a critical appraisal of experimental hypertensive glomerulopathy with the same approach used to assess hypertensive glomerulopathy in humans. Four hypertensive models with varying pathogenesis were analyzed–chronic angiotensin II infused mice, mice expressing active human renin in the liver (TTRhRen), spontaneously hypertensive rats (SHR), and Goldblatt two-kidney one-clip rats (2K1C). Analysis of glomerulopathy utilized the same criteria applied in humans–hyalinosis, focal segmental glomerulosclerosis (FSGS), ischemic, hypertrophic and solidified glomeruli, or global glomerulosclerosis (GGS). Data from animal models were compared to human reference values. Kidneys in TTRhRen mice, SHR and the nonclipped kidneys in 2K1C rats had no sign of hyalinosis, FSGS or GGS. Glomerulopathy in these groups was limited to variations in mesangial and capillary compartment volumes, with mild increases in collagen deposition. Histopathology in angiotensin II infused mice corresponded to mesangioproliferative glomerulonephritis, but not hypertensive glomerulosclerosis. The number of nephrons was significantly reduced in TTRhRen mice and SHR, but did not correlate with severity of glomerulopathy. The most substantial human-like glomerulosclerotic lesions, including FSGS, ischemic obsolescent glomeruli and GGS, were found in the clipped kidneys of 2K1C rats. The comparison of affected kidneys to healthy control in animals produces lesion values that are numerically impressive but correspond to mild damage if compared to humans. Animal studies should be standardized by employing the criteria and classifications established in human pathology to make experimental and human data fully comparable for comprehensive analysis and model improvements.

Canonical Wnt signaling in the kidney in different hypertension models

There is a close relationship between the kidney and blood pressure. On the one hand, kidney dysfunction causes an increase in blood pressure; on the other hand, high blood pressure causes kidney dysfunction. Wnt/β-catenin signaling is a key pathway that regulates various cellular processes and tissue homeostasis and is also involved in damage and repair processes. In healthy organs, Wnt/β-catenin signaling is muted, but it is activated in pathological states. The purpose of the present study was to immunohistochemically evaluate and compare the expression of WNT4, WNT10A, Fzd8, β-catenin, and GSK-3ß (glycogen synthase kinase 3β) in the kidneys of rats with essential arterial hypertension (SHR), renal-renal hypertension (2K1C), and DOCA-salt-induced hypertension. The study was performed on five male WKY rats, seven SHRs, and twenty-four (n = 24) young male Wistar rats. The main results showed that during hypertension, there are changes in Wnt/β-catenin signaling in the kidneys of rats, and the severity of these changes depends on the type of hypertension. This study is the first to assess the levels of some elements of the canonical Wnt/β-catenin signal transduction pathway in various types of arterial hypertension by immunohistochemistry and may form the basis for further molecular and functional studies of this pathway in hypertension.

Role of stimulated intrarenal angiotensinogen in hypertension

Experimental models of hypertension and patients with inappropriately increased renin formation due to a stenotic kidney, arteriosclerotic narrowing of the renal arterioles or a rare juxtaglomerular cell tumor have shown a progressive augmentation of the intrarenal/intratubular renin-angiotensin system (RAS). The increased intrarenal angiotensin II (Ang II) elicits renal vasoconstriction and enhanced tubular sodium reabsorption in proximal and distal nephron segments. The enhanced intrarenal Ang II levels are due to both increased Ang II type 1 (AT1) receptor mediated Ang II uptake and AT1 receptor dependent stimulation of renal angiotensinogen (AGT) mRNA and augmented AGT production. The increased AGT formation and secretion into the proximal tubular lumen leads to local formation of Ang II, which stimulates proximal transporters such as the sodium/hydrogen exchanger. Enhanced AGT production also leads to spillover of AGT into the distal nephron segments as reflected by AGT in the urine, which provides an index of intrarenal RAS activity. There is also increased Ang II concentration in distal nephron with stimulation of distal sodium transport. Increased urinary excretion of AGT has been demonstrated in patients with hypertension, type 1 and type 2 diabetes mellitus, and several types of chronic kidney diseases indicating an upregulation of intrarenal RAS activity.

The role of oxidative stress in renal injury induced in rats by losartan exposure during lactation

INTRODUCTION

Rats exposed to angiotensin II (AII) receptor antagonists during lactation present progressive disturbances in renal development that lead to progressive alterations in renal function and structure. This study evaluates the role of oxidative stress in the renal changes induced by exposure to losartan, a type 1 AII receptor antagonist, in rats during lactation.

MATERIALS AND METHODS

Male Wistar pups were divided into: Control, pups of dams that received 2% sucrose solution; Control-tempol, pups of dams that received tempol (0.34 g/l), a superoxide dismutase mimetic compound; Losartan, pups of dams that received losartan (100 mg/kg/day), and Losartan-tempol, pups of dams that received losartan and tempol. Losartan and/or tempol were administered during lactation. Blood and urine samples were collected at 21 or 60 days, and the kidneys were removed.

RESULTS

Losartan-treated pups exhibited disturbances in renal function and structure that persisted into adulthood. Tempol treatment reduced oxidative stress and attenuated the changes induced by losartan in the glomerular filtration rate, desmin expression at the glomerular edge, vimentin in tubular cells, as well as apoptosis and inflammatory infiltration in the renal cortex.

CONCLUSION

Oxidative stress contributes at least in part to the renal injury observed in pups exposed to losartan during lactation.

Renal vascular and tubulointerstitial inflammation and proliferation in Cyp1a1-Ren2 transgenic rats with inducible ANG II-dependent malignant hypertension

Transgenic rats with inducible ANG II-dependent malignant hypertension [TGR(Cyp1a1Ren2)] were generated by inserting the mouse Ren2 renin gene into the genome of the rat. The present study was performed to assess renal morphological changes occurring during the development of ANG II-dependent malignant hypertension in these rats. Male Cyp1a1-Ren2 rats (n = 10) were fed normal rat food containing indole-3-carbinol (I3C; 0.3%) for 10 days to induce malignant hypertension. Rats induced with I3C had higher mean arterial pressures (173 +/- 9 vs. 112 +/- 11 mmHg, P < 0.01) than noninduced normotensive rats (n = 9). Glomerular damage was evaluated by determination of the glomerulosclerosis index (GSI) in tissue sections stained with periodic acid-Schiff. Kidneys of hypertensive rats had a higher GSI than normotensive rats (21.3 +/- 5.6 vs. 3.5 +/- 1.31 units). Quantitative analysis of macrophage ED-1-positive cells and proliferating cell nuclear antigen using immunohistochemistry demonstrated increased macrophage numbers in the renal interstitium (106.4 +/- 11.4 vs. 58.7 +/- 5.0 cells/mm(2)) and increased proliferating cell number in cortical tubules (37.8 +/- 5.7 vs. 24.2 +/- 2.1 cells/mm(2)), renal cortical vessels (2.2 +/- 0.5 vs. 0.13 +/- 0.07 cells/vessel), and the cortical interstitium (33.6 +/- 5.7 vs. 4.2 +/- 1.4 cells/mm(2)) of hypertensive rat kidneys. These findings demonstrate that the renal pathological changes that occur during the development of malignant hypertension in Cyp1a1-Ren2 rats are characterized by inflammation and cellular proliferation in cortical vessels and tubulointerstitium.

The autoimmune response to vimentin after renal transplantation in nonhuman primates is immunosuppression dependent

BACKGROUND

Chronic allograft nephropathy (CAN) is a common late complication of kidney transplantation. Antibodies to both human leukocyte antigen and nonhuman leukocyte antigen antigens have been implicated in the development of this condition. Here we investigated the presence of antivimentin antibodies in nonhuman primate recipients of kidney allografts as a possible predictor of CAN and the effects of immunosuppression.

METHODS

Thirty seven rhesus monkeys received a kidney allograft to study the potency of several different immunosuppressive regimens (conventional immunosuppression, n=19, vs. costimulatory blockade, n=18). Monkeys were tested for antivimentin antibody by enzyme-linked immunosorbent assay and for anti-donor antibody by staining donor spleen cells with recipient serum. The appearance of antibodies was correlated with the graft pathology in biopsy and necropsy material.

RESULTS

Antivimentin antibodies were found in 31 of 37 animals, whereas only 15 of 32 animals made anti-donor antibodies. Conventional immunosuppression did not prevent antivimentin antibody formation. Costimulation blockade, in particular blocking CD40 and CD86, significantly delayed or prevented antivimentin antibody formation, but did not prevent CAN. Antivimentin antibodies were not significantly associated with development of CAN.

CONCLUSIONS

We postulate that vimentin acts as an autoantigen after renal transplantation; it elicits an autoimmune response that is not regulated by cyclosporine. This autoimmune response may be part of the complex immunologic events occurring posttransplantation and may contribute to the development of CAN, but cannot be considered as a major cause of CAN because this condition also develops without antivimentin antibodies.

Effects of chronic quercetin treatment in experimental renovascular hypertension

The aims of the present study were to analyse the effects of an oral daily dose (10 mg/kg) of the dietary flavonoid quercetin for five weeks in two-kidney, one-clip (2K1C) Goldblatt (GB) hypertensive rats. The evolution of systolic blood pressure was followed by weekly measurements, and morphological variables, proteinuria, plasma nitrates plus nitrites (NOx) and thiobarbituric acid reactive substances (TBARS), liver oxidative stress markers and endothelial function were determined at the end of the experimental period. Quercetin treatment reduced systolic blood pressure of GB rats, producing no effect in control animals. It also reduced cardiac hypertrophy and proteinuria developed in GB hypertensive rats. Decreased endothelium-dependent relaxation to acetylcholine of aortic rings from GB rats was improved by chronic quercetin treatment, as well as increased endothelium-dependent vasoconstrictor response to acetylcholine and overproduction of TXB2 by aortic vessels of GB rats, being without effect in normotensive animals. Increased plasma NOx and TBARS, and decreased liver total glutathione (GSH) levels and glutathione peroxidase (GPX) activity were observed in GB hypertensive rats compared to the control animals. Normalisation of plasma NOx and TBARS concentrations and improvement of the antioxidant defences system in liver accompanied the antihypertensive effect of quercetin. We conclude that chronic oral treatment with quercetin shows both antihypertensive and antioxidant effects in this model of renovascular hypertension.

Oxidative stress, renal infiltration of immune cells, and salt-sensitive hypertension: all for one and one for all

Recent evidence indicates that interstitial infiltration of T cells and macrophages plays a role in the pathogenesis of salt-sensitive hypertension. The present review examines this evidence and summarizes the investigations linking the renal accumulation of immune cells and oxidative stress in the development of hypertension. The mechanisms involved in the hypertensive effects of oxidant stress and tubulointerstitial inflammation, in particular intrarenal ANG II activity, are discussed, focusing on their potential for sodium retention. The possibility of autoimmune reactivity in hypertension is raised in the light of the proinflammatory and immunogenic pathways stimulated by the interrelationship between oxidant stress and inflammatory response. Finally, we present some clinical considerations derived from the recognition of this interrelationship.

Vimentin and heat shock protein expression are induced in the kidney by angiotensin and by nitric oxide inhibition

BACKGROUND

Angiotensin II (Ang II) infusion and nitric oxide synthesis (NOS) inhibition with Nomega-nitro-l-arginine-methyl-ester (l-NAME) are experimental models of hypertension associated with renal inflammation and oxidative stress. To gain insight into the nature of the tubulointerstitial injury induced in these models, we studied lectin-binding specificities, vimentin expression, and heat shock protein (HSP) 60 and 70 in these experimental models.

METHODS

Sprague-Dawley rats received Ang II infusion (435 ng/kg/min) for 2 weeks by subcutaneous minipumps (Ang II group, N = 5) or l-NAME in the drinking water (70 mg/100 mL) for 3 weeks (l-NAME group N = 7). The control group consisted of 10 rats. Systolic blood pressure (tail-cuff plethysmography), serum creatinine, and proteinuria were determined weekly. At the end of the treatment period, rats were sacrificed and kidneys studied. Binding specificities of fluorescein-labeled lectins were examined in frozen sections, and cellular infiltrates were identified by immunohistology and expression of vimentin and HSP 60 and 70 with immunohistochemistry and computer image analysis.

RESULTS

Tubulointerstitial accumulation of macrophages, lymphocytes, and Ang II-positive cells were present in the Ang II group and l-NAME group. Vimentin, HSP 60, and HSP 70 were increased 8 to 20 times in the cortex of the rats of the Ang II group and the l-NAME groups. Neoexpression of vimentin and HSPs was found primarily in proximal tubular cells.

CONCLUSION

Ang II infusion and NOS inhibition induce tubular injury with epithelial cell transdifferentiation and expression of stress proteins. The role of these changes in the accumulation and activation of the interstitial inflammatory infiltrate merits further investigation.

Successfully treated "accelerated" renovascular hypertension with intravascular stenting

A 76-year-old man developed progressive renal dysfunction with refractory hypertension. Bilateral renal artery stenosis due to atherosclerosis was revealed. Both the hypertension and renal dysfunction were improved by percutaneous transluminal renal angioplasty with stenting. Based on the rapidly progressive elevation of plasma renin activity and the improvement of both renal dysfunction and hypertension after stenting, this was considered a case of "accelerated" renovascular hypertension. There have been an increasing number of patients with bilateral renal artery stenosis due to atherosclerosis. The present case reminds us that a rapid progression of renal dysfunction suggests, in addition to besides rapidly progressive glomerulonephritis with crescent formation, bilateral renal artery stenosis, the incidence of which is on the rise. In the present case, angioplasty with stenting was effective for blood pressure control and preservation of renal function.

Chronic renal ischemia: pathophysiologic mechanisms of cardiovascular and renal disease

Chronic renal ischemia caused by renal artery stenosis (RAS) elicits a complex biologic response. Although the traditional pathophysiologic pathways underlying renal ischemia have been well studied, there is emerging evidence that additional mechanisms may be responsible for producing many of the hemodynamic alterations and end-organ injury seen in patients with RAS, including persistent hypertension, renal insufficiency, and cardiac disturbance syndromes. A better understanding of these mechanisms may allow earlier identification of RAS, provide markers to predict the response to revascularization, or allow unique therapeutic targets for drug development. This and a subsequent article will explore the pathophysiologic and clinical implications of chronic renal ischemia.

Angiotensin II and IGF-I may interact to regulate tubulointerstitial cell kinetics and phenotypic changes in hypertensive rats

Angiotensin II and insulin-like growth factor-I (IGF-I) are known to be actively involved in the pathogenesis of progressive renal injury, particularly in cell proliferation and phenotypic changes that contribute to tubulointerstitial injury. To investigate the possible mechanisms by which angiotensin II type 1 receptor antagonist (AIIA) ameliorates renal injury in a renal ablation model and to determine the contribution of phenotypic changes and IGF-I to morphological changes, we examined 1) whether AIIA attenuated phenotypic changes as markers of alpha-smooth muscle actin (SMA) and vimentin, 2) whether AIIA altered renal IGF-I expression, and 3) the changes of tubulointerstitial cell kinetics between apoptosis (tested via terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end labeling, TUNEL) and cell proliferation (a test of proliferating cell nuclear antigen, PCNA). Following a sham operation (sham) or 5/6 nephrectomy (Nx), we administered E4177, a potent, selective competitive angiotensin II type 1 receptor antagonist (AIIA), for 10 weeks. In Nx rats, SMA and vimentin expressions developed in injured tubulointerstitium, particularly in hypoperfused scar-adjacent areas, and there was an increase in renal IGF-I expressions. The TUNEL score increased 5-fold and PCNA increased 8-fold, compared with TUNEL and PCNA measurements in sham-operated rats. Renin expression in the juxtaglomerular apparatus was markedly suppressed in the Nx group, although de novo tubular renin expression appeared in Nx, compared with that in the sham group. E4177, both 10 mg/kg (AIIA 10) and 1 mg/kg (AIIA 1), markedly ameliorated renal injury, although blood pressure was less affected in AIIA 1. Both AIIA 10 and AIIA 1 suppressed the neoexpressions of SMA and vimentin in an association with decreased IGF-I expression. Regarding cell kinetics, neither AIIA 10 nor AIIA 1 decreased the TUNEL score; rather, tended to increase, while PCNA was significantly suppressed by AIIA. In conclusion, one of the underlying protective mechanisms of AIIA in this model may be related to the modulations of angiotensin II-induced phenotypic changes and tubulointerstitial cell kinetics through IGF-I.

Effect of insulin and heparin on glucose-induced vascular damage in cell culture

BACKGROUND

Clinical trials have shown that tight glycemic control reduces the risk of diabetic microvascular complications, namely retinopathy, nephropathy, and neuropathy. The mechanism of these microvascular complications is not yet fully elucidated. The present study describes the effect of different concentrations of glucose on vascular endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) in cell culture. Our objective was to shed some light through this biological study on the mechanism and prevention of diabetic microvascular complications.

METHODS

ECs and VSMCs were treated with 5 mmol/L (90 mg/dL) or 30 mmol/L (540 mg/dL) D-glucose or D-glucose plus insulin or D-glucose plus insulin and heparin in culture. ECs were studied with light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) for surface changes. The cultured ECs were treated with vimentin antibodies and VSMCs with actin antibodies for immunoflourescence microscopy (IFM) study. Endothelin-1 (ET-1) assay was done on ECs culture medium using enzyme-linked immunosorbent assay (ELISA).

RESULTS

LM, SEM, and TEM of ECs treated with a physiological concentration (90 mg/dL) of D-glucose appeared the same as control. However, LM and SEM of ECs treated with a high concentration of D-glucose (540 mg/dL) showed pronounced intercellular gaps. This finding was further confirmed by TEM study. These gaps were minimally or not at all discernible when insulin, heparin, or a combination of both was added to the culture medium. IFM showed increased vimentin expression with a high concentration of D-glucose. Vimentin expression was attenuated with the addition of insulin or heparin in the medium and more markedly with combined insulin and heparin. Significant correlations were obtained between glucose levels, vimentin expression, and ET-1 levels. The higher the glucose level, the higher is the ET-1 production and the greater vimentin expression in ECs. Cultured VSMCs treated with a high concentration of D-glucose showed enhanced actin expression. Actin expression was blunted with the addition of insulin or heparin in the culture medium.

CONCLUSIONS

These biological findings indicate the salutary effect of insulin or insulin and heparin in the mitigation of vascular disorganization caused by a high concentration of D-glucose.

Antihypertensive therapy and progression of chronic renal disease

This paper reviews findings on the relationship between blood pressure control and the progression of renal disease. Experimental studies demonstrate a correlation between systemic blood pressure and histologic glomerular injury and the delay in progression of renal disease with antihypertensive therapy, particularly with angiotensin-converting enzyme inhibitors. Recent clinical findings are reviewed, including epidemiologic data linking hypertension to subsequent renal disease, and clinical studies showing a beneficial effect on progression of renal disease with lower than usual blood pressure targets.