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Experimental nephrotic syndrome induced by several immunologic and biochemical methods is associated with the development of tubulointerstitial nephritis (TIN). To investigate the hypothesis that severe sustained proteinuria plays a role in the pathogenesis of TIN, the renal interstitium in a model of protein-overload proteinuria was studied. After uninephrectomy, rats received daily injections of 1.0 g of bovine serum albumin (BSA) or saline (controls) until killing at 1, 2, 4, or 7 weeks. Sections of frozen renal cortex were stained with a panel of monoclonal antibodies reactive with subsets of rat lymphohemopoietic cells, and positive tubulointerstitial cells (TIC) were quantitated by epifluorescence microscopy. BSA rats developed proteinuria, with mean rat urinary albumin excretion rates at 1, 2, 3, and 6 weeks of 35.6 +/- 21.8, 97.2 +/- 46.1, 63.6 +/- 40.8, and 58.6 +/- 24.4 mg/24 hours, respectively (controls, 0.17 +/- 0.16 mg/24 hours). BSA was detectable in the plasma of experimental animals at all periods, with mean values of 26.8 +/- 3.8, 27.8 +/- 2.7, 20.3 +/- 6.2, and 7.0 +/- 1.1 mg/ml (controls, 0.03 +/- 0.04 mg/ml) at 1, 2, 4, and 7 weeks, respectively, whereas plasma anti-BSA antibodies were never detected. A significant mononuclear cell infiltrate was present in the interstitium of experimental animals at all periods. At 1 week, an influx of macrophages was evident that was identified by surface markers OX42 (75+/1000 TIC) (P less than 0.01) and Ia (58+/1000 TIC) (P less than 0.01). Macrophages dominated the infiltrate at all periods. By 2 weeks, a significant population of lymphocytes was also present that was identified by the surface marker OX19 (54+/1000 TIC) (P less than 0.01). This early lymphocytic infiltrate was a mixed lesion of T helper and T cytotoxic cells. However, at 4 and 7 weeks, most lymphocytes expressed the OX8 cytotoxic T cell marker. The proximal tubules of proteinuric rats expressed vimentin intermediate filaments, a marker of tubular epithelial cell regeneration after injury. In BSA rats, C3 and neoantigens of the membrane attack complex of complement without IgG were present along the luminal border of many tubular epithelial cells. The interstitial infiltrate was confirmed by light microscopy. By 4 weeks, focal areas of chronic interstitial disease were evident consisting of tubular atrophy and interstitial fibrosis. In a second study, one group of BSA-treated rats was depleted of circulating T lymphocytes by daily parenteral injections of monoclonal antibody OX19.(ABSTRACT TRUNCATED AT 400 WORDS)
The efficacy and safety of lovastatin as a hypolipidemic agent were evaluated in ten adult patients with secondary hypercholesterolemia due to proteinuria (greater than 2 g/d) and (in seven patients) concurrent corticosteroid therapy. Patients were on a low-cholesterol diet throughout the study. After a 4-week baseline period, patients were randomized to receive either placebo or 10 mg lovastatin twice daily for a period of 6 weeks. The dose of lovastatin was increased to 20 mg twice daily for 6 weeks, and 40 mg twice daily for 6 weeks in the latter group. Those patients who received placebo for the first 6 weeks subsequently received 10, 20, and 40 mg of lovastatin twice daily in a stepped dose regimen, with each dose given for 6 weeks. Lovastatin was well tolerated by all patients and none withdrew from the study. Baseline plasma cholesterol concentrations (390 +/- 20 mg/dL; mean +/- SEM) decreased 22% (P less than 0.003) at the lowest dose of 10 mg twice daily, 27% at 20 mg twice daily, and 33% at 40 mg twice daily. Baseline plasma triglycerides decreased by 25% (P less than 0.05) at the highest dosage. Concentrations of low-density lipoprotein (LDL) cholesterol fell by 29%, 34%, and 45% on doses of 10, 20, and 40 mg of lovastatin twice daily. Concentrations of high-density lipoprotein (HDL) cholesterol increased slightly. Serum creatinine concentrations and proteinuria were not affected by lovastatin therapy. We conclude that lovastatin was a well-tolerated and extremely effective hypocholesterolemic agent in patients with persistent secondary hypercholesterolemia associated with proteinuria or proteinuria and concurrent corticosteroid therapy.
Although circulating phagocytic cells are important mediators of glomerular injury, their recruitment mechanisms are not completely understood. In this study, the intraglomerular trafficking of leukocytes was characterized in a rat model of acute glomerular injury induced by nephrotoxic serum (NTS). Polymorphonuclear (PMN) cells infiltrated, then disappeared rapidly, reaching a peak at 2 hr. By 6 hr the PMN migration had almost reversed but small numbers persisted until Day 7. The monocyte influx began almost simultaneously but was of lesser magnitude. However, the number of ED-1+ monocytes increased progressively from 60 min to reach a plateau by Day 2 and persisted to the end of the study (Day 28). Quantitation of intraglomerular Ia+ cells suggested in situ activation of monocytes within the glomeruli. Increased Ia+ cells were first evident on Day 2. By Day 5, 80% of the intraglomerular macrophages were Ia+. Complement depletion with cobra venom factor abrogated early albuminuria, delayed the initial PMN influx, but failed to attenuate monocyte migration. T lymphocytes appeared briefly between 10 min and 2 hr. In vitro proliferation study failed to demonstrate lymphocyte sensitization to glomerular basement membrane (GBM) antigens. A unique population of cells (OX19 OX8+), possibly representing natural killer cells, was present from Day 1 to Day 14. During the secondary wave of proteinuria (autologous phase), all leukocytes had disappeared except for macrophages and a small number of OX19-, OX8+ cells. A complex intraglomerular migration of leukocytes was triggered by the binding of nephrotoxic antibodies to GBM antigens. We speculate that this cascade involves several cell-to-cell interactions necessary for the full expression of glomerular injury.
The relationship between tubulointerstitial nephritis and proteinuria was characterized in experimental nephrosis in rats. In one group, proteinuria induced by aminonucleoside of puromycin (PAN) was reduced by using an 8% protein diet and adding the angiotensin I-converting enzyme (ACE) inhibitor enalapril to the drinking water. Two control groups were injected with saline and PAN, respectively, and fed a 27% protein diet. The first group had significantly reduced albuminuria and a definite attenuation of tubular cell injury. There was a strong positive correlation between the number of interstitial macrophages and albuminuria. The beneficial effect was reproduced by dietary-protein restriction alone, whereas ACE inhibition alone had an insignificant effect on the degree of proteinuria. Depletion of circulating T lymphocytes in one group of nephrotic rats eliminated interstitial lymphocytes but did not affect interstitial macrophage influx. Inhibition of the in situ proliferation of resident interstitial macrophages by unilateral kidney irradiation failed to change the intensity of the macrophage infiltration. Treatment of rats with sodium maleate produced proximal tubular cell toxicity but interstitial inflammation did not develop, suggesting that the latter is not a nonspecific response to tubular injury. These studies demonstrate a strong relationship between tubulointerstitial nephritis and the severity of proteinuria in experimental nephrosis.
We examined the effect of glucocorticoid on intrinsic glomerular antioxidant enzyme (AOE) activities. Munich-Wistar rats were treated with daily i.p. injection of vehicle or methylprednisolone [MP, 15 mg/kg body wt, (MP15)] either for three days or nine days. Glomeruli isolated from rats given MP15 had significantly higher activities of total (T-) and manganese (Mn-) superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase than vehicle-treated rats (P less than 0.05). MP15-treated rats were subjected to intrarenal arterial infusion of hydrogen peroxide (35 mumol over 1 hr). Values for urinary protein excretion rate (UprV) after hydrogen peroxide infusion were markedly lower in rats pretreated with MP15 for both three days and nine days than in untreated rats (109 +/- 18 and 55 +/- 24 vs. 416 +/- 73 micrograms/min, respectively, both P less than 0.005). To test whether the same therapeutic intervention attenuates reactive oxygen species (ROS)-mediated glomerular injury in another model, rats given a single i.v. dose of puromycin aminonucleoside (PAN) (50 mg/kg body wt) were treated with daily i.p. injection of vehicle or MP15. Two days after PAN administration, when compared to vehicle-treated controls, PAN rats given MP15 had significantly higher activities of Mn-SOD, GSH-Px and catalase. After eight days of PAN injection, T- and Mn-SOD activities were, likewise, significantly higher in MP15- than vehicle-treated PAN rats. PAN rats given MP15 also had substantially less proteinuria, compared to PAN rats given vehicle alone, UprV averaging 32.3 +/- 9.4 versus 159.0 +/- 13.8 mg/24 hr (P less than 0.05). Elevated glomerular malondialdehyde (MDA) level characteristic of PAN rats was absent in rats treated with MP15. Moreover, epithelial foot process fusion and cell vacuolization seen in vehicle-treated PAN rats were markedly attenuated in MP15-treated PAN rats. These data indicate that the mechanism for therapeutic effect of glucocorticoids on ROS-mediated renal injuries includes an enhancement of endogenous glomerular AOE activities, which attenuates lipid peroxidation of glomerular tissue.
To identify the specific in vivo renal effect of reactive oxygen species (ROS), hydrogen peroxide (H2O2) was infused directly into the left renal artery in Munich-Wistar rats. H2O2 (5 to 50 mumol over 1 h) induced a dose-dependent increase in urine protein excretion rate in infused kidneys, reaching a maximum at the dose of 35 mumol (on average, a 60-fold increase from baseline). The H2O2 (35 mumol)-induced proteinuria peaked over 1 h and completely normalized by 24 h after the infusion. Electrophoresis revealed that the urine protein is primarily of glomerular origin. Fractional clearances of graded-size neutral dextran of larger molecular radii, an index of glomerular size selectivity, were significantly and substantially elevated immediately but normalized by 24 h after the infusion. GFR and RPF rate remained unchanged throughout the entire time course examined. The H2O2-induced proteinuria was largely prevented by pretreatment with catalase (20 mg, iv) or deferoxamine (30 mg/100 g body wt, iv). Thus, iron-dependent metabolites of hydrogen peroxide appear to be involved in this proteinuria and glomerular size-selective defect. Light and electron microscopy, including determination of anionic site density at lamina rara externa of glomerular capillary wall by polyethyleneimine staining, did not reveal any appreciable abnormality throughout the study period, including at the peak of proteinuria. Thus, ROS can cause massive, reversible proteinuria by inducing a molecular size-selectivity defect of the glomerular capillary wall without apparent ultrastructural abnormalities. The results raise the possibilities: (1) that persistent proteinuria of a variety of renal diseases may reflect persistence of pathogenic ROS acting on glomeruli because the potent proteinuric effect of ROS can be transient (2) that the light and electron microscopy abnormalities in glomeruli of ROS-induced renal injuries reported thus far may have no direct causal linkage to proteinuria; and, finally, (3) ROS-induced reversible proteinuria may relate to the mechanism of clinical functional proteinuria, which involves increased oxygen and ROS metabolism, e.g., exercise-induced proteinuria.