Angiotensin-converting enzyme is upregulated in the proximal tubules of rats with intense proteinuria.
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Persistent proteinuria is considered a deleterious prognostic factor in most progressive renal diseases. However, the mechanisms by which proteinuria induces renal damage remain undetermined. Since proximal tubular cells possess all the machinery to generate angiotensin II (Ang II), we approached the hypothesis that proteinuria could elicit the renal activation of the renin-angiotensin system in a model of intense proteinuria and interstitial nephritis induced by protein overload. After uninephrectomy (UNX), Wistar-Kyoto rats received daily injections of 1 g BSA or saline for 8 days. The mean peak of proteinuria was observed at the fourth day (538+/-89 versus 3+/-1 mg/24 h in UNX controls; n=12; P<0.05) and was increased during the whole study period (at the eighth day: 438+/-49 mg/24 h; n=12; P=NS). Morphological examination of the kidneys at the end of the study showed marked tubular lesions (atrophy, vacuolization, dilation, and casts), interstitial infiltration of mononuclear cells, and mesangial expansion. In relation to UNX control rats, renal cortex of BSA-overloaded rats showed an increment in the gene expression of angiotensinogen (2.4-fold) and angiotensin-converting enzyme (ACE) (2.1-fold), as well as a diminution in renin gene expression. No changes were observed in angiotensin type 1 (AT1) receptor mRNA expression in both groups of rats. By in situ reverse transcription-polymerase chain reaction and immunohistochemistry, ACE expression (gene and protein) was mainly localized in proximal and distal tubules and in the glomeruli. By immunohistochemistry, angiotensinogen was localized only in proximal tubules, and AT1 receptor was localized mainly in proximal and distal tubules. In the tubular brush border, an increase in ACE activity was also seen (5. 5+/-0.5 versus 3.1+/-0.7 U/mg protein x10(-4) in UNX control; n=7; P<0.05). Our results show that in the kidney of rats with intense proteinuria, ACE and angiotensinogen were upregulated, while gene expression of renin was inhibited and AT1 was unmodified. On the whole, these data suggest an increase in Ang II intrarenal generation. Since Ang II can elicit renal cell growth and matrix production through the activation of AT1 receptor, this peptide may be responsible for the tubulointerstitial lesions occurring in this model. These results suggest a novel mechanism by which proteinuria may participate in the progression of renal diseases. (+info)
Up-regulation of glomerular extracellular matrix and transforming growth factor-beta expression in RF/J mice.
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BACKGROUND: RF/J mice were first reported as a murine model of spontaneous glomerulosclerosis by Gude and Lupton in 1960, but the precise histologic characteristics and immunopathological background of this mouse have not been investigated further. METHODS: Measurements of serum levels of immunoglobulins, anti-single strand DNA (anti-ss-DNA) antibody, complement (C3), and circulating immune complex (IC) were performed. Analyses of glomerular histological and immunopathological lesions in association with the detection of mRNA expression of collagen IV, TGF-beta, matrix protein turnover related enzymes, matrix metalloproteinase-2 (MMP-2), tissue inhibitor of metalloproteinase-2 (TIMP-2) and platelet-derived growth factor (PDGF) were also performed in young (10-week-old) and elderly (60-week-old) RF/J mice with age-matched BALB/C mice as the controls. RESULTS: High levels of serum IgA and IgG from as early as 20 weeks of age were noted in the RF/J mice. Serum anti-ss-DNA antibody of aged RF/J mice increased up to 23% of that of aged MRL-lpr/lpr mice, and serum C3 concentration significantly decreased with age, reaching lower levels than that of BALB/c mice. IgA-IC levels were significantly high compared to BALB/C mice both in the early and late stages of life, whereas IgG-IC levels were high only in mice younger than 20 weeks. Semiquantitative and quantitative analyzes of renal histopathological findings revealed significantly marked and age-related mesangial matrix expansion in RF/J mice, with increasing frequency of global glomerular sclerosis and tubulointerstitial damage. On the other hand, although precise measurements of glomerular cell numbers also showed an apparent augmentation in both young and old RF/J mice compared to BALB/C mice, glomerular cellularity decreased with age in RF/J mice. Immunohistochemical study revealed massive immunoglobulin deposition from a young age in association with significantly higher accumulation of matrix proteins, such as types I and IV collagen and laminin from the early stage of life. In addition, in these glomeruli, transforming growth factor-beta1 (TGF-beta1) was highly expressed both in young and old mice. The mRNA expression of MMP-2 was up-regulated only in the early stage of life. Although PDGF mRNA of RF/J mice was significantly up-regulated in the early stage of life, the differences between the mice disappeared in the late stage of life. CONCLUSIONS: These findings suggest that in RF/J mice, an immunopathological background inducing high serum immunoglobulin and IC levels from the early stage of life is closely related to mesangioproliferative glomerular lesions mediated by PDGF, and that development of massive extracellular matrix accumulation in glomeruli was induced by up-regulated expression of TGF-beta with inappropriate regulation of protein turnover-related enzyme production. (+info)
Blocking angiotensin II ameliorates proteinuria and glomerular lesions in progressive mesangioproliferative glomerulonephritis.
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BACKGROUND: The renin-angiotensin system is thought to be involved in the progression of glomerulonephritis (GN) into end-stage renal failure (ESRF) because of the observed renoprotective effects of angiotensin-converting enzyme inhibitors (ACEIs). However, ACEIs have pharmacological effects other than ACE inhibition that may help lower blood pressure and preserve glomerular structure. We previously reported a new animal model of progressive glomerulosclerosis induced by a single intravenous injection of an anti-Thy-1 monoclonal antibody, MoAb 1-22-3, in uninephrectomized rats. Using this new model of progressive GN, we examined the hypothesis that ACEIs prevent the progression to ESRF by modulating the effects of angiotensin II (Ang II) on the production of transforming growth factor-beta (TGF-beta) and extracellular matrix components. METHODS: We studied the effect of an ACEI (cilazapril) and an Ang II type 1 receptor antagonist (candesartan) on the clinical features and morphological lesions in the rat model previously reported. After 10 weeks of treatment with equihypotensive doses of cilazapril, cilazapril plus Hoe 140 (a bradykinin receptor B2 antagonist), candesartan, and hydralazine, we examined systolic blood pressure, urinary protein excretion, creatinine clearance, the glomerulosclerosis index, and the tubulointerstitial lesion index. We performed a semiquantitative evaluation of glomerular immunostaining for TGF-beta and collagen types I and III by immunofluorescence study and of these cortical mRNA levels by Northern blot analysis. RESULTS: Untreated rats developed massive proteinuria, renal dysfunction, and severe glomerular and tubulointerstitial injury, whereas uninephrectomized control rats did not. There was a significant increase in the levels of glomerular protein and cortical mRNA for TGF-beta and collagen types I and III in untreated rats. Cilazapril and candesartan prevented massive proteinuria, increased creatinine clearance, and ameliorated glomerular and tubulointerstitial injury. These drugs also reduced levels of glomerular protein and cortical mRNA for TGF-beta and collagen types I and III. Hoe 140 failed to blunt the renoprotective effect of cilazapril. Hydralazine did not exhibit a renoprotective effect. CONCLUSION: These results indicate that ACEIs prevent the progression to ESRF by modulating the effects of Ang II via Ang II type 1 receptor on the production of TGF-beta and collagen types I and III, as well as on intrarenal hemodynamics, but not by either increasing bradykinin activity or reducing blood pressure in this rat model of mesangial proliferative GN. (+info)
Proteinuria induces tubular cell turnover: A potential mechanism for tubular atrophy.
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BACKGROUND: Proteinuria and tubular atrophy have both been closely linked with progressive renal failure. We hypothesized that apoptosis may be induced by tubular cell exposure to heavy proteinuria, potentially leading to tubular atrophy. Apoptosis was studied in a rat model of "pure" proteinuria, which does not induce renal impairment, namely protein-overload proteinuria. METHODS: Adult female Lewis rats underwent intraperitoneal injection of 2 g of bovine serum albumin (BSA, N = 16) or sham saline injections (controls, N = 8) daily for seven days. Apoptosis was assessed at day 7 in tissue sections using in situ end labeling (ISEL) and electron microscopy. ISEL-positive nuclei (apoptotic particles) were counted in blinded fashion using image analysis with NIH Image. Cell proliferation was assessed by detection of mRNA for histone by in situ hybridization, followed by counting of positive cells using NIH Image. RESULTS: Animals injected with saline showed very low levels of apoptosis on image analysis. BSA-injected rats had heavy proteinuria and showed both cortical and medullary apoptosis on ISEL. This was predominantly seen in the tubules and, to a lesser extent, in the interstitial compartment. Overall, the animals injected with BSA showed a significant 30-fold increase in the number of cortical apoptotic particles. Electron microscopy of tubular cells in a BSA-injected animal showed a progression of ultrastructural changes consistent with tubular cell apoptosis. The BSA-injected animals also displayed a significant increase in proximal tubular cell proliferation. This increased proliferation was less marked than the degree of apoptosis. CONCLUSION: Protein-overload proteinuria in rats induces tubular cell apoptosis. This effect is only partially balanced by proliferation and potentially provides a direct mechanism whereby heavy proteinuria can induce tubular atrophy and progressive renal failure. (+info)
Mycophenolate mofetil prevents the progressive renal failure induced by 5/6 renal ablation in rats.
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BACKGROUND: Extensive renal ablation is associated with progressive sclerosis of the remnant kidney. Because lymphocytes and monocytes accumulate in the remnant kidney, it is likely that they play a role in the renal scarring. Therefore, we treated rats with 5/6 nephrectomy (5/6Nx) with mycophenolate mofetil (MMF), a drug that has an antiproliferative effect and that suppresses the expression of intercellular adhesion molecules. METHODS: Sprague-Dawley rats with 5/6Nx received MMF (30 mg. kg-1. day-1 by daily gastric gavage, N = 15) or vehicle (N = 16). Ten additional rats were sham operated. All rats were fed a 30% protein diet. Body weight, serum creatinine, and urinary protein excretion were determined weekly. Lipid peroxidation, as a measure of oxidative stress observed by urinary malondialdehyde determinations, was performed every two weeks. Histologic studies were done in the remnant kidney four weeks (9 rats from the vehicle-treated group, 7 rats from the MMF group, and 5 sham-operated rats) and eight weeks after surgery (the remaining rats). Glomerular volume, sclerosis in glomeruli (segmental and global) and interstitium (semiquantitative scale), infiltrating lymphocytes and macrophages (CD43- and ED1-positive cells), and expression of adhesion molecules (CD54, CD18, and CD11b) were analyzed. RESULTS: MMF treatment prevented the progressive increment in serum creatinine and the proteinuria observed in the 5/6 nephrectomized rats during the eight weeks of observation (P < 0.01). Weight gain was comparable in the MMF-treated and sham-operated rats, whereas weight gain was decreased in untreated 5/6 nephrectomized rats. Excretion of malondialdehyde increased after surgery but returned sooner to control levels in the MMF-treated rats. Increments in glomerular size and mean arterial blood pressure induced by renal ablation were not modified by MMF treatment. Eight weeks after surgery, segmental sclerosis was present in 48.4 +/- 8.35% (+/- sd) glomeruli in the vehicle-treated group versus 25 +/- 10.5% in the MMF-treated group (P < 0.001). Interstitial fibrosis was reduced significantly with MMF treatment (P < 0.001). Infiltration with CD43- and ED1-positive cells in glomeruli and interstitium was two to five times lower in MMF-treated rats (P < 0.01). Expression of adhesion molecules CD18 and CD11b was similarly reduced. CONCLUSION: MMF ameliorates the progressive renal damage in the remnant kidney after 5/6Nx. This effect is associated with a reduction in the infiltration of lymphocytes and monocytes, whereas glomerular hypertrophy and systemic hypertension are unchanged. (+info)
HIV-associated nephropathy is a late, not early, manifestation of HIV-1 infection.
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BACKGROUND: Human immunodeficiency virus-associated nephropathy (HIVAN) can be the initial presentation of HIV-1 infection. As a result, many have assumed that HIVAN can occur at any point in the infection. This issue has important implications for appropriate therapy and, perhaps, for pathogenesis. Since the development of new case definitions for acquired immunodeficiency syndrome (AIDS) and better tools to assess infection, the relationship of HIVAN to the time of AIDS infection has not been addressed. In this study, we reassessed the stage of infection at the time of HIVAN diagnosis in 10 patients, and we reviewed all previously published cases applying the new case definitions to assess stage of infection. METHODS: HIVAN was confirmed by kidney biopsy in HIV seropositive patients with azotemia and/or proteinuria. CD4+ cell count and plasma HIV-1 RNA copy number were measured. We also reviewed all published cases of HIVAN to determine if AIDS-defining conditions, by current Centers for Disease Control definitions, were present in patients with biopsy-proven HIVAN. RESULTS: Twenty HIV-1 seropositive patients with proteinuria and an elevated creatinine concentration were biopsied. HIVAN was the single most common cause of renal disease. CD4+ cell count was below 200/mm3 in all patients with HIVAN, fulfilling Centers for Disease Control criteria for an AIDS-defining condition. HIV-1 plasma RNA was detectable in all patients with HIVAN. In reviewing previous reports, an AIDS-defining condition was present in virtually all patients with HIVAN. CONCLUSION: HIVAN develops late, not early, in the course of HIV-1 infection following the development of AIDS. This likely accounts for the poor prognosis noted in previous publications and has implications for pathogenesis. In addition, given the detectable viral RNA levels, highly active antiretroviral therapy is indicated in HIVAN. Highly active antiretroviral therapy may improve survival as well as alter the natural history of HIVAN. (+info)
Long-term effects of cyclosporine A in Alport's syndrome.
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BACKGROUND: In 1991, our initial results of cyclosporine A (CsA) administration in eight patients with Alport's syndrome were published. A significant decrease in or disappearance of proteinuria and apparently good tolerance to CsA were observed in all patients. METHODS: CsA administration has been maintained in these eight patients with the aim of obtaining further information about the clinical course of the disease. The ages of these eight patients currently range from 15 to 27 years, and the mean duration of treatment is from 7 to 10 years (x = 8.4 years). RESULTS: Renal function has remained stable, with no evaluable changes in serum creatinine levels compared with pre-CsA treatment values. Proteinuria in all patients has either remained negative or are values far lower than pretreatment levels. A second renal biopsy was performed in all patients after five years of CsA administration. No aggravation of the lesion present at the first biopsy or lesions typical of cyclosporine intoxication was observed. CONCLUSIONS: After a mean duration of 8.4 years and with no deterioration in renal function, we found possible beneficial effects of the continued treatment of CsA in patients with Alport's syndrome who present evidence of progression to renal insufficiency. (+info)
Circulating vascular endothelial growth factor is not increased during relapses of steroid-sensitive nephrotic syndrome.
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BACKGROUND: An uncharacterized circulating factor that increases vascular permeability has previously been described in childhood steroid-sensitive nephrotic syndrome (SSNS). The aim of this study was to determine whether this factor is vascular endothelial growth factor (VEGF), the recently described endothelial cell mitogen and enhancer of vascular permeability. METHODS: Plasma and urine VEGF levels were measured in children with SSNS in both relapse and remission and in normal age- and sex-matched controls. Semiquantitative reverse transcriptase-polymerase chain reaction studies investigating VEGF mRNA expression were performed on peripheral blood mononuclear cells isolated from children with SSNS in relapse and controls. In two experimental models (one-hour and three-day follow-up postinfusion), Sprague-Dawley rats were intravenously administered 50 microg rVEGF to determine whether this induced either proteinuria or glomerular histologic change. RESULTS: Plasma VEGF levels and urine VEGF/creatinine ratios were not elevated in SSNS relapse compared with remission and control samples. Peripheral blood mononuclear cell VEGF mRNA expression was no different in SSNS patients compared with controls. The administration of VEGF to rats induced an acute reversible fall in systemic blood pressure but did not result in the development of either proteinuria or glomerular histologic change. CONCLUSION: Increased circulating VEGF levels are not responsible for the proteinuria observed during relapses of SSNS. Further studies are warranted to investigate intrarenal VEGF expression. (+info)