Chronic blockade of angiotensin II action prevents glomerulosclerosis, but induces graft vasculopathy in experimental kidney transplantation

Salt-deficient diet exacerbates cystogenesis in ARPKD via epithelial sodium channel (ENaC)

Background

Autosomal Recessive Polycystic Kidney Disease (ARPKD) is marked by cyst formation in the renal tubules, primarily in the collecting duct (CD) system, ultimately leading to end-stage renal disease. Patients with PKD are generally advised to restrict their dietary sodium intake. This study was aimed at testing the outcomes of dietary salt manipulation in ARPKD.

Methods

PCK/CrljCrlPkhd1pck/CRL (PCK) rats, a model of ARPKD, were fed a normal (0.4% NaCl; NS), high salt (4% NaCl; HS), and sodium-deficient (0.01% NaCl; SD) diets for 8 weeks. Immunohistochemistry, GFR measurements, balance studies, and molecular biology approaches were applied to evaluate the outcomes of the protocol. Renin-angiotensin-aldosterone system (RAAS) levels were assessed using LC-MS/MS, and renal miRNA profiles were studied.

Findings

Both HS and SD diets resulted in an increase in cystogenesis. However, SD diet caused extensive growth of cysts in the renal cortical area, and hypertrophy of the tissue; RAAS components were enhanced in the SD group. We observed a reduction in epithelial Na⁺ channel (ENaC) expression in the SD group, accompanied with mRNA level increase. miRNA assay revealed that renal miR-9a-5p level was augmented in the SD group; we showed that this miRNA decreases ENaC channel number in CD cells.

Interpretation

Our data demonstrate a mechanism of ARPKD progression during salt restriction that involves activity of ENaC. We further show that miR-9a-5p potentially implicated in this mechanism and that miR-9a-5p downregulates ENaC in cultured CD cells. Our findings open new therapeutic possibilities and highlight the importance of understanding salt reabsorption in ARPKD.

Dissecting recipient from donor contribution in experimental kidney transplantation: focus on endothelial proliferation and inflammation

Kidney transplantation (Tx) is considered the only definite treatment for end-stage kidney disease (ESKD) patients. The increasing prevalence of ESKD has necessitated the introduction of transplantation with kidneys from suboptimal donors. There is, however, still a lack of fundamental and longitudinal research on suboptimal kidney transplants. Specifically, there is a demand for accurate pre-Tx predictors of donor kidney function and injury to predict post-Tx outcome. In the present study, we combine rat models of chronic kidney disease (CKD) and renal Tx to dissect the effects of healthy and CKD renal grafts on healthy and CKD recipients. We show that renal function at 6 weeks post-Tx is exclusively determined by donor graft quality. Using cell tracking within enhanced green fluorescent protein-positive (eGFP⁺) recipients, we furthermore show that most inflammatory cells within the donor kidney originate from the donor. Oxidative and vascular extra-renal damage were, in contrast, determined by the recipient. Post- versus pre-Tx evaluation of grafts showed an increase in glomerular and peritubular capillary rarefaction in healthy but not CKD grafts within a CKD environment. Proliferation of glomerular endothelium was similar in all groups, and influx of eGFP⁺ recipient-derived cells occurred irrespective of graft or recipient status. Glomerular and peritubular capillary rarefaction, severity of inflammation and macrophage subtype data post-Tx were, however, determined by more complicated effects, warranting further study. Our experimental model could help to further distinguish graft from recipient environment effects, leading to new strategies to improve graft survival of suboptimal Tx kidneys.

This article has an associated First Person interview with the first author of the paper.

Summary: Using experimental kidney transplantation, we dissected donor graft from recipient environment effects, focusing on the endothelium and inflammation. These results can direct strategies to improve graft survival after suboptimal transplantation.

Renal transplantation induces mitochondrial uncoupling, increased kidney oxygen consumption, and decreased kidney oxygen tension

Hypoxia is an acknowledged pathway to renal injury and ischemia-reperfusion (I/R) and is known to reduce renal oxygen tension (Po2). We hypothesized that renal I/R increases oxidative damage and induces mitochondrial uncoupling, resulting in increased oxygen consumption and hence kidney hypoxia. Lewis rats underwent syngenic renal transplantation (TX) and contralateral nephrectomy. Controls were uninephrectomized (1K-CON) or left untreated (2K-CON). After 7 days, urinary excretion of protein and thiobarbituric acid-reactive substances were measured, and after 14 days glomerular filtration rate (GFR), renal blood flow, whole kidney Qo2, cortical Po2, kidney cortex mitochondrial uncoupling, renal oxidative damage, and tubulointerstitial injury were assessed. TX, compared with 1K-CON, resulted in mitochondrial uncoupling mediated via uncoupling protein-2 (16 ± 3.3 vs. 0.9 ± 0.4 pmol O2 · s(-1)· mg protein(-1), P < 0.05) and increased whole kidney Qo2 (55 ± 16 vs. 33 ± 10 μmol O2/min, P < 0.05). Corticomedullary Po2 was lower in TX compared with 1K-CON (30 ± 13 vs. 47 ± 4 μM, P < 0.05) whereas no significant difference was observed between 2K-CON and 1K-CON rats. Proteinuria, oxidative damage, and the tubulointerstitial injury score were not significantly different in 1K-CON and TX. Treatment of donors for 5 days with mito-TEMPO reduced mitochondrial uncoupling but did not affect renal hemodynamics, Qo2, Po2, or injury. Collectively, our results demonstrate increased mitochondrial uncoupling as an early event after experimental renal transplantation associated with increased oxygen consumption and kidney hypoxia in the absence of increases in markers of damage.

Proliferative changes of renal arteriolar walls induced by administration of angiotensin II receptor blocker are frequent in juvenile rats

INTRODUCTION

Our previous study of angiotensin II receptor blocker (ARB) administration in rats induced unusual proliferative changes of smooth muscle cells in renal arteriolar walls. The present study examined if the incidence of the changes depended on the rats' age, and how long it would take to find changes.

MATERIALS AND METHODS

Six-week-old (juvenile spontaneous hypertensive rats (SHRs)+ARB group, n=15) and 20-week-old (adult SHRs+ARB group, n=10) male SHRs were fed a standard diet (0.4% NaCl) containing valsartan (10 mg/kg/day; Novartis Co.). Fifteen age-matched SHRs were studied as controls. After 4, 8, and 12 weeks, the rat kidneys were examined under light and electron microscopes and through immunohistochemical studies.

RESULTS

Extremely concentric proliferative changes in afferent arteriolar walls were frequently observed in the juvenile SHR+ARB group compared to the adult SHR+ARB group (48.7±6.8% vs 19.3±6.9%; p=0.0307) at the 12(th) week. Increased renin expression and arteriolar changes were found from the 4(th) week in the juvenile SHR+ARB group.

CONCLUSION

This study indicates that ARB administration induces unusual proliferative changes and a marked renin-producing cell increase in afferent arterioles more frequently in juveniles than adult rats. It is suggested that the treatment of ARB in juveniles might have a higher risk of changes in renal afferent arterioles.

Attenuation of renovascular damage in Zucker diabetic fatty rat by NWT-03, an egg protein hydrolysate with ACE- and DPP4-inhibitory Activity

Background

Dipeptidyl peptidase 4 (DPP4) and angiotensin-converting enzyme (ACE) are important target enzymes in glycemic control and renovascular protection. Here, we studied the effect of NWT-03, an egg protein hydrolysate with DPP4- and ACE-inhibitory activity, on renovascular damage in Zucker diabetic fatty (ZDF) rats. Comparisons were made to rats treated with vildagliptin (VIL), included as a positive control for the effect of DPP4 inhibition.

Methods

ZDF rats received NWT-03 (1 g/kg/day) or VIL (3 mg/kg/day) from 10 to 25 weeks of age. Metabolic and renal functions were assessed; the kidney was removed for histological analysis of glomerulosclerosis and expression of pro-inflammatory/fibrotic markers (RT-PCR and Western blotting); and the aorta was removed for studies of endothelium-dependent relaxation (EDR).

Findings

Hyperinsulinemic ZDF rats typically developed signs of type-2 diabetes and renovascular damage, as evidenced by albuminuria, glomerulosclerosis, and impaired EDR. Neither NWT-03 nor VIL improved metabolic parameters; for VIL, this was despite a 5-fold increase in glucagon-like peptide (GLP)-1 levels. NWT-03 and VIL both reduced renal interleukin (Il)-1β/Il-13 mRNA expression and glomerulosclerosis. However, only NWT-03 additionally decreased renal tumor necrosis factor (TNF)-α mRNA and P22^phox protein expression, reduced albuminuria, and restored aortic EDR. Indomethacin added to the organ bath instantly improved aortic EDR, indicating a role for cyclooxygenase (COX)-derived contractile prostanoids in opposing relaxation in ZDF rats. This indomethacin effect was reduced by NWT-03, but not by VIL, and coincided with decreased renal COX-1/2 protein expression.

Conclusion and Interpretation

Long-term supplementation with the egg protein hydrolysate NWT-03 attenuated renovascular damage in this preclinical rat model of type 2 diabetes. A comparison to the DPP4-inhibitor VIL suggests that the effects of NWT-03 were related to both ACE- and DPP4-inhibitory properties. The development of protein hydrolysates with a multiple-targeting strategy may be of benefit to functional food formulations.

ACE Inhibition in Anti-Thy1 Glomerulonephritis Limits Proteinuria but Does Not Improve Renal Function and Structural Remodeling

Background/Aims

ACE inhibitor (ACE-I) treatment effectively inhibits proteinuria and ameliorates the course of various renal diseases. In experimental glomerulonephritis, however, angiotensin II (AngII) infusion has also been shown to be renoprotective. We evaluated the long-term (28 days) course of anti-Thy1 glomerulonephritis in animals with suppressed AngII formation by ACE-I treatment.

Methods

Brown Norway rats received perindopril (2.8 mg/kg/day, n = 12), dihydropyridine calcium-antagonist amlodipine (Ca-A; 13 mg/kg/day, n = 6) or were left untreated (n = 14). All animals were monitored for blood pressure, proteinuria, and creatinine clearance after anti-Thy1 injection. Renal histology was assessed at day 7 and 28.

Results

Systolic blood pressure was equally reduced by ACE-I and Ca-A treatment. AngII suppression prevented development of proteinuria, but did not protect against glomerular microaneurysm formation or reduction in creatinine clearance. After resolution of the microaneurysms, animals with suppressed AngII production showed a modest increase in glomerulosclerosis and vasculopathic thickening of intrarenal vessels.

Conclusions

In anti-Thy1 glomerulonephritis, suppression of AngII formation does not protect against the induction of glomerular damage and is associated with mild aggravation of adverse renal fibrotic remodeling. Proteinuria, however, is effectively prevented by ACE-I treatment. Ca-A treatment did not affect the course of glomerulonephritis, indicating that ACE-I effects are blood pressure independent.

Rat Ace allele variation determines susceptibility to AngII-induced renal damage

INTRODUCTION

Ace b/l polymorphism in rats is associated with differential tissue angiotensin-converting enzyme (ACE) expression and activity, and susceptibility to renal damage. Same polymorphism was recently found in outbred Wistar rat strain with b allele accounting for higher renal ACE, and provided a model for studying renin-angiotensin-aldosterone system (RAAS) response behind the innate high or low ACE conditions.

METHODS

We investigated the reaction of these alleles on chronic angiotensin II (AngII) infusion. Wistar rats were selected to breed male homozygotes for the b (WU-B) or l allele (WU-L) (n = 12). For each allele, one group (n = 6) received AngII infusion via an osmotic minipump (435 ng/kg/min) for 3 weeks. The other group (n = 6) served as a control.

RESULTS

WU-B had higher ACE activity at baseline then WU-L. Interestingly, baseline renal ACE2 expression and activity were higher in WU-L. AngII infusion induced the same increase in blood pressure in both genotypes, no proteinuria, but caused tubulo-interstitial renal damage with increased α-SMA and monocyte/macrophage influx only in WU-B (p < 0.05). Low ACE WU-L rats did not develop renal damage.

CONCLUSION

AngII infusion causes proteinuria-independent renal damage only in rats with genetically predetermined high ACE while rats with low ACE seemed to be protected against the detrimental effect of AngII. Differences in renal ACE2, mirroring those in ACE, might be involved.

The renin-angiotensin system: an old, newly discovered player in immunoregulation

Clinical and experimental studies that discuss the different immune functions of the renin-angiotensin system (RAS) in kidney diseases were reviewed, with emphasis on studies of kidney transplantation. The RAS has been shown to affect both the innate and adaptive immune responses and has a well-established role in fibrinogenesis. Of special clinical interest is the ability of the RAS to activate the transforming growth factor beta(1) and the Smad pathways leading to fibrinogenesis. In addition to the RAS enhancing effect on the activity of T cells, several components of the RAS have also been shown to be chemotactic to macrophages, T cells, and natural killer cells. Experimental studies have found that RAS blockade decreases the histologic lesions of chronic allograft nephropathy but can enhance acute graft vasculopathy. Although the blockade of RAS has been commonly practiced to reduce posttransplantation hypertension, proteinuria, and erythrocytosis, however, its role in prolonging graft survival is not well established.

Donor and recipient origin of mesenchymal and endothelial cells in chronic renal allograft remodeling

Chronic transplant dysfunction (CTD) is the leading cause for limited kidney graft survival. Renal CTD is characterized by interstitial and vascular remodeling leading to interstitial fibrosis, tubular atrophy and transplant vasculopathy (TV). The origin of cells and pathogenesis of interstitial and vascular remodeling are still unknown. To study graft-versus-recipient origin of interstitial myofibroblasts, vascular smooth muscle cells (SMCs) and endothelial cells (ECs), we here describe a new rat model for renal CTD using Dark Agouti kidney donors and R26 human placental alkaline phosphatase transgenic Fischer344 recipients. This model showed the development of CTD within 12 weeks after transplantation. In interstitial remodeling, both graft- and recipient-derived cells contributed to a similar extent to the accumulation of myofibroblasts. In arteries with TV, we observed graft origin of neointimal SMCs and ECs, whereas in peritubular and glomerular capillaries, we detected recipient EC chimerism. These data indicate that, within the interstitial and vascular compartments of the transplanted kidney, myofibroblasts, SMCs and ECs involved in chronic remodeling are derived from different sources and suggest distinct pathogenetic mechanisms within the renal compartments.

Spironolactone ameliorates transplant vasculopathy in renal chronic transplant dysfunction in rats

Chronic transplant dysfunction (CTD) is the leading cause of long-term renal allograft loss and is characterized by specific histological lesions including transplant vasculopathy, interstitial fibrosis, and focal glomerulosclerosis. Increasing evidence indicates that aldosterone is a direct mediator of renal damage via the mineralocorticoid receptor (MR). The MR antagonist spironolactone is renoprotective in native chronic kidney disease, but its effects on CTD are unknown. We studied the effects of spironolactone treatment on CTD development in the Dark Agouti-to-Wistar-Furth renal allograft transplant model, by treatment with 20 mg/kg spironolactone or vehicle daily by oral gavage from 2 days before transplantation (donors and recipients) throughout the experiment (12 wk, recipients). Dark Agouti-to-Dark Agouti isografts served as negative controls. Spironolactone significantly ameliorated the development of transplant vasculopathy in allografts by reducing the number of affected intrarenal arteries. In addition, spironolactone treatment showed a trend toward reduced proteinuria and focal glomerulosclerosis, and significantly reduced glomerular macrophage influx. However, spironolactone treatment did not affect interstitial fibrosis, interstitial macrophage influx, creatinine clearance, and systolic blood pressure. We conclude that spironolactone selectively ameliorates transplant vasculopathy and glomerular lesions in renal CTD in rats. These results suggest that spironolactone may have renoprotective potential as an adjunct treatment in renal transplantation to ameliorate CTD.

Reduction of proteinuria in adriamycin-induced nephropathy is associated with reduction of renal kidney injury molecule (Kim-1) over time

Tubulointerstitial lesions are important in the progression of proteinuric renal disease. Tubular kidney injury molecule-1 (Kim-1) is induced in acute renal injury and reversible as a natural course. Kim-1 is also present in chronic renal damage; however, the dynamics of Kim-1 in chronic renal damage and effects of antiproteinuric treatment on Kim-1 are unknown. We studied Kim-1 in adriamycin nephrosis (AN) before and after renin-angiotensin system blockade. A renal biopsy was taken 6 wk after adriamycin injection to study renal damage and Kim-1 expression. Subsequently, ACE inhibition (ACEi; n = 23), angiotensin II antagonist (AT(1A); n = 23), or vehicle (n = 10) was given for 6 wk; healthy rats served as controls (CON; n = 8). In AN, renal Kim-1 mRNA was induced 26-fold vs. CON at week 6, with further increase in vehicle to week 12 (40-fold) but was reduced by ACEi and AT(1A) to 10- and 12-fold vs. CON (P < 0.05 vs. week 6). Kim-1 protein was undetectable in CON; in AN, it was present in brush border of dilated tubules in areas with adjacent interstitial lesions. Renal Kim-1 protein levels increased from weeks 6-12 in vehicle and decreased in ACEi- and AT(1A)-treated groups (P < 0.05). In vehicle, urinary Kim-1 was increased (P < 0.05 vs. CON), with a reduction by ACEi and AT(1A) (P < 0.05 vs. vehicle). Renal and urinary Kim-1 correlated with proteinuria and interstitial damage cross-sectionally. Reductions in proteinuria and renal Kim-1 correlated, which was not associated by corresponding changes in tubulointerstitial fibrosis. In conclusion, on longitudinal follow-up during antiproteinuric treatment increased renal Kim-1 expression is reversible in proportion to proteinuria reduction, likely reflecting reversibility of early tubular injury, supporting its potential as a biomarker for tubulointerstitial processes of damage and repair.

Macrophage Infiltration Detected at MR Imaging in Rat Kidney Allografts: Early Marker of Chronic Rejection?

PURPOSE

To evaluate detection of iron-loaded macrophages at magnetic resonance (MR) imaging as a noninvasive means to monitor early signs of chronic allograft rejection in the life-supporting Fisher-to-Lewis rat kidney transplantation model.

MATERIALS AND METHODS

Experiments followed the Swiss federal regulations of animal protection. Male Fisher (n = 37) and Lewis (n = 77) rats were used. After removal of a native recipient kidney and transplantation of a donor kidney, the recipient rat's contralateral kidney was removed. Allografts and control syngeneic grafts comprised, respectively, kidneys from Fisher and Lewis donors transplanted into Lewis rats. Recipients were imaged by using a gradient-echo MR sequence 24 hours after intravenous administration of superparamagnetic iron oxide (SPIO) particles. Biochemical analyses of blood and urine, as well as assessments of Banff scores (reference standard for histologic classification of graft rejection), were performed. Statistical tests used were analysis of variance for multiple comparisons with Bonferroni tests, Mann-Whitney tests, and Pearson correlations with Bonferroni corrections.

RESULTS

A SPIO dose-dependent decrease in cortical MR signal intensity occurred in allografts between 8 and 16 weeks after transplantation. A strong significant negative correlation (P = .005 for 0.3 mL/kg SPIO dose, P = .003 for 1.0 mL/kg SPIO dose) was found between MR signal intensity and Banff scores, which deteriorated over the experimental period. Proteinuria occurred at 16 weeks. Blood and urine creatinine levels remained unchanged up to week 28.

CONCLUSION

This MR imaging method is more robust than the usually adopted creatinine clearance method for the detection of early signs of allograft chronic rejection in the Fisher-to-Lewis rat kidney transplantation model.

ACE inhibition and glomerular repair: restructuring or regeneration?

In this issue of Kidney International, Andrea Remuzzi et al. convincingly demonstrate glomerular repair in spontaneous renal disease by ACE inhibition. These findings provoke questions about how ACE inhibition (or AT1R blockade) can on the one hand actually repair some diseased kidneys while on the other interfering with normal renal development or the recovery of other diseased kidneys.

ACE inhibition has adverse renal effects during dietary sodium restriction in proteinuric and healthy rats

Angiotensin-converting enzyme inhibitors (ACEi) provide renoprotection. A low sodium diet enhances their efficacy. However, the added effect of sodium restriction on proteinuria and blood pressure is not invariably associated with better preservation of renal morphology, suggesting that the combination of ACEi with a low sodium diet can elicit renal structural abnormalities. To test this hypothesis, the effects of ACEi in combination with a control (CS) or a low sodium (LS) diet were investigated in healthy rats and in adriamycin nephrotic rats. After 3 weeks of treatment, rats were sacrificed and kidneys examined for renal structural abnormalities. In healthy rats, ACEi reduced blood pressure: the fall in blood pressure was significantly greater in the ACEi/LS group. Renal morphology was normal in the ACEi/CS group but severe interstitial damage was found in the ACEi/LS group. This was associated with increased interstitial macrophage influx and up-regulation of osteopontin, alpha-smooth muscle actin, and collagen III expression. In addition, ACEi/LS induced an increase in the total medial area of afferent arterioles. In nephrotic rats, ACEi/LS reduced both blood pressure and proteinuria, whereas only blood pressure was reduced in the ACEi/CS group. Mild interstitial damage was present in the ACEi/CS group but, strikingly, pronounced tubulo-interstitial abnormalities occurred in the ACEi/LS group, similar to those seen in ACEi/LS healthy rats, with similar changes in afferent arteriolar walls. In conclusion, the combination of ACEi/LS elicits pronounced renal interstitial abnormalities in healthy and nephrotic rats, despite a significant reduction of proteinuria in the latter. Considering their occurrence in healthy rats, these renal adverse effects cannot be due to specific characteristics of adriamycin nephrosis. Further studies should elucidate the mechanisms underlying these observations and their impact on long-term renoprotection.

Enhanced transduction of fibroblasts in transplanted kidney with an adenovirus having an RGD motif in the HI loop

Application of gene therapy to the renal graft has a powerful potential to improve the outcome of kidney transplantation and eliminate detrimental side effects associated with systemic therapy, through local expression of immunoregulatory or other protective molecules. However, the search for the optimal vector is still ongoing. In this study, we used a modified adenovirus that has an Arg-Gly-Asp (RGD) motif inserted in the HI loop of the fiber knob, as a successful strategy to transduce the renal graft. Donor Lewis rat kidneys were infused via the renal artery with a solution containing either a fiber-modified adenovirus (AdTL-RGD) or an unmodified adenovirus (AdTL), or with saline. Syngeneic recipients were killed after 3, 7 or 14 days. Efficiency, selectivity, localization, time course of gene expression and side effects were studied using biochemical and immunohistological techniques. Enhanced gene expression was achieved selectively in the transplanted kidney by AdTL-RGD, when compared to AdTL. Transgene expression lasted for at least 2 weeks. With the AdTL-RGD vector, the transgene was abundantly expressed in the renal interstitial fibroblasts. An increase in the number of cytotoxic T lymphocytes accompanied the use of either vector, when compared to saline. These data convincingly show enhanced and selective gene transfer to the fibroblasts of transplanted kidneys using an RGD-modified adenovirus, providing a highly efficient vector system for future therapeutic interventions.

Reduced Cyclooxygenase Involvement in Vascular Endothelial Function in Rat Renal Transplantation

BACKGROUND

Cardiovascular disease is a major cause of death following renal transplantation. Mechanisms leading to vascular dysfunction outside the transplanted organ involve common risk factors such as hypertension, hypercholesterolemia, proteinuria, but immune-mediated factors may also be involved. We hypothesized that transplantation-associated risk factors are involved in the development of vascular dysfunction following renal transplantation.

METHODS

Vascular function was studied in Fisher to Lewis allografts. Lewis to Lewis syngrafted rats served as controls. All rats received cyclosporin A for 10 days. Allografts were treated with ACE inhibition or AT1 receptor blockade or left untreated. After 34 weeks, aorta rings were studied for contractile and dilator responses in the presence or absence of L-NMMA and/or indomethacin. Tissue sections were immunostained for COX-1 and COX-2.

RESULTS

In contrast to syngrafts and treated allografts, untreated allografts developed proteinuria and hypercholesterolemia. In aortic rings, NOS inhibition similarly increased contractile responses and decreased dilator responses in syngrafts and allografts, indicating comparable NO pathways. In contrast, indomethacin affected contractile and dilator responses in syngrafts, but not in treated and untreated allografts, indicating absence of COX-derived prostanoids in control over vascular tone in allografts. This was in line with immunohistologic analysis demonstrating reduced aortic COX-2 expression in allografts. COX-1 expression was unaltered. Interestingly, RAS blockade quantitatively increased endothelium-dependent dilation without qualitatively altering COX function and expression.

CONCLUSION

Involvement of COX-derived prostaglandins in vascular endothelial function outside the transplanted organ is strongly diminished after allogeneic renal transplantation. RAS blockade improves common cardiovascular risk factors and endothelium-dependent dilation, but fails to restore prostaglandin function.

Temporary losartan or captopril in young SHR induces malignant hypertension despite initial normotension

BACKGROUND

Exposure of normotensive rats to angiotensin-converting enzyme (ACE) inhibitors in early life causes hypertrophy of intrarenal arteries. Similar defects have been found in knockout mice lacking angiotensinogen, ACE, or angiotensin II type 1 (AT1) receptors. On the other hand, transient inhibition of the renin-angiotensin system from 2 weeks of age in spontaneously hypertensive rats (SHR), either with ACE inhibitors or with AT1 receptor antagonists partially prevents the increase in blood pressure. However, permanent treatment of SHR from conception onwards with ACE inhibitors completely prevents hypertension. Although these studies demonstrated protection from hypertension-induced changes in the heart and large arteries, renal arteries were not studied and follow-up did not extend beyond 6 months of age. We postulated that while brief exposure to ACE inhibitors or AT1 receptor antagonists in young SHR would temporarily decrease blood pressure, it would also be associated with development of intrarenal arterial malformation, and ultimately have deleterious effects.

METHODS

Direct effects on intrarenal arterial morphology of an ACE inhibitor (captopril, 100 mg/kg/day) and an AT1 receptor antagonist (losartan, 50 mg/kg/day), administered from the last week of gestation until 8 weeks of age were examined in SHR. After stopping treatment at 8 weeks, we continued to monitor blood pressure until spontaneous death.

RESULTS

Systolic blood pressure at 8 weeks was normalized by captopril and losartan (SHR control 187 +/- 8 mm Hg; captopril 118 +/- 5 mm Hg; and losartan 120 +/- 9 mm Hg). However, by 30 weeks, blood pressure had increased to control SHR levels. At 4 weeks, the media of renal arteries and arterioles was hypertrophied. Marked smooth muscle cell hyperplasia of cortical arteries resulted in significantly increased wall thickness by 8 weeks, despite similar external diameter. Arterial wall structure was disrupted, with fragmentation of elastic fibers and irregular distribution of collagen type I fibers. After stopping treatment, the rats gradually began to show poor health and all had died by 1 year of age, while all 1-year-old control SHR females were in good health. The cause of morbidity and mortality in the rats treated in early life was clearly malignant hypertension. Severe hypertrophy of renal arterioles was found, as well as cerebral hemorrhage.

CONCLUSION

Despite initial normalization of blood pressure interference with the renin-angiotensin system during a crucial stage of development in SHR can initiate marked smooth muscle cell hyperplasia and disruption of the wall structure of the intrarenal arteries. Subsequent progression of this intrarenal process after cessation of treatment suggests an independent process that eventually results in malignant hypertension and early death.

Inter-individual differences in anti-proteinuric response to ACEi in established adriamycin nephrotic rats are predicted by pretreatment renal damage

ACE inhibition (ACEi) reduces proteinuria and provides reno-protection, but not all subjects benefit from ACEi. Individual differences in the reduction in proteinuria at the onset of treatment and in residual proteinuria during therapy predict differences in renal outcome. The present study investigated whether individual differences in the anti-proteinuric efficacy of ACEi are explained by differences in the severity of pretreatment renal structural damage and whether differences in the level of residual proteinuria during therapy are explained by the severity of renal structural damage at that time, in adriamycin nephrosis in the rat. Pretreatment renal structural damage was assessed in biopsies 6 weeks after exposure to adriamycin (2 mg/kg iv). Then ACEi (75 mg/l lisinopril, n = 23) or vehicle (n = 10) was administered; renal biopsies were repeated after stabilization of the anti-proteinuric response (week 8). Early renal damage (interstitial alpha-smooth muscle actin expression and macrophage accumulation) and established lesions [focal glomerulosclerosis (FGS) and interstitial fibrosis] were scored. During ACEi, proteinuria fell from 834 (487-851) mg/24 h pretreatment to 153 (66-265) mg/24 h at week 8 (p < 0.05); FGS stabilized from 27 (4-70) arbitrar units (AU) pretreatment to 26 (4-84) at week 12, whereas the vehicle did not affect proteinuria, resulting in progressive FGS: 18 (10-26) AU pretreatment versus 88 (46-130) at week 12 (p < 0.05). All parameters of pretreatment damage significantly predicted the anti-proteinuric response. Residual proteinuria during ACEi correlated significantly with renal structural damage parameters at that time. Pretreatment renal damage also predicted renal outcome during extended treatment. Thus, in this experimental setting, in rats with the same renal disorder and the same duration of disease, individual differences in pretreatment renal damage, albeit relatively modest, explain individual differences in renal responsiveness to ACEi. This implies that the limits of the efficacy of ACEi are set by prevalent renal damage. Further studies into the mechanisms of individual resistance to the anti-proteinuric action of ACEi are needed to develop additive intervention strategies.

Long-term dietary L-arginine supplementation attenuates proteinuria and focal glomerulosclerosis in experimental chronic renal transplant failure

Glomerular endothelial nitric oxide synthase expression is decreased in humans during acute rejection and chronic renal transplant failure (CRTF). This may contribute to vascular damage through changes in the renal hemodynamics and enhanced endothelial adhesion of leukocytes and platelets. Dietary supplementation of L-arginine may increase endothelial NO production, thereby protecting the vascular wall and improving renal hemodynamics. We tested the hypothesis that long-term L-arginine supplementation attenuates the development of CRTF in an experimental model for renal transplantation. In the Fisher 344 to Lewis rat model for renal transplantation, renal function and histology of untreated rats was compared with rats receiving L-arginine in the drinking water (10g/L), starting 2 days before transplantation. Every 4 weeks systolic blood pressure was measured and serum and urine were collected for measurement of nitrite and nitrate (NO(x)), creatinine, and proteinuria. At 34 weeks the histological renal damage was assessed by scoring focal glomerulosclerosis and measurement of alpha-smooth muscle actin (alpha-SMA) expression. Urinary NO(x) was significantly increased in treated animals. Proteinuria was significantly lower in L-arginine-treated animals from week 24 onward (p<0.05). Plasma creatinine and creatinine clearance did not differ between the groups. The focal and segmental glomerulosclerosis (FGS) score (max 400) at week 34 was also significantly lower in treated rats arbitrary U (20+/-21 vs 61+/-67 arbitrary U; p<0.05). The expression of alpha-SMA was lower in L-arginine-treated rats than in untreated rats (1.93+/-0.8% area surface vs 3.64+/-2.5% area surface). In conclusion, in this experimental model for CRTF, L-arginine administration significantly reduced FGS and proteinuria, without affecting renal function. Our data suggest that dietary L-arginine supplementation attenuates progression of CRTF and may therefore be an additional therapeutic option in human renal allograft recipients.

Strain differences in angiotensin-converting enzyme and angiotensin II type I receptor expression. Possible implications for experimental chronic renal transplant failure

BACKGROUND

The Fisher to Lewis (F-L) model of renal transplantation (Rtx) is widely used. Rtx from F to L without immunosuppressive treatment results in 50% survival, whereas L to F results in survival rates similar to syngrafts. When treated with an angiotensin-converting enzyme (ACE) inhibitor or antihypertensive triple therapy, renal damage is markedly reduced in F-L allografts. Despite similar reductions in blood pressure, the ACE inhibitor (ACE-I) is more effective than antihypertensive triple therapy, suggesting that the inhibition of intrarenal ACE plays an additional role in the attenuation of renal damage.

METHODS

In the present study, we investigated strain-related differences in intrarenal ACE activity between F and L rats and whether treatment with ACE-I in F-L allografted rats results in reduction of intrarenal ACE. Intrarenal ACE was measured by activity assays, immunohistochemistry and PCR.

RESULTS

In control kidneys from healthy F rats (n=8), we found a four-fold higher ACE activity than in native L rats (n=8, p<0.01). This was confirmed by a three-fold difference in ACE mRNA expression (n=5 for both, p<0.01). Using immunohistochemistry, we found strong tubular ACE expression in the F rat, whereas the L rat had no tubular ACE at all. In F-L allografts (n=9) we noted significant glomerulosclerosis and proteinuria after 34 weeks. Treatment with ACE-I in F-L (n=8) prevented the development of these changes. Although ACE mRNA and ACE protein expression were similar in treated and untreated allografts, intrarenal ACE activity was reduced by 50% in allografts with ACE-I.

CONCLUSION

In conclusion, intrarenal levels of ACE may play a role in the development of renal damage in experimental chronic renal transplant failure.