Growth of rat mesangial cells on oxidized extracellular matrix increases inducible nitric oxide synthase activity.

Biochemical modification of extracellular matrix (ECM) proteins can alter the function in overlying cells. We tested the hypothesis that metal-catalyzed oxidation of native ECM and individual matrix proteins modulates the activity of inducible nitric oxide synthase (iNOS) in cultured rat mesangial cells (RMC). Oxidized modification of native ECM resulted in a 32% increase in iNOS activity (P<0.01) without influencing the response to supplemental L-arginine or to the addition of the iNOS inhibitor, L-NAME. Immunoblot analysis indicated that enhanced iNOS activity was not associated with a parallel rise in the cytosolic content of iNOS. Synthesis of type IV collagen was unaffected by growth of RMC on oxidized native ECM. Oxidation of three normal constituents of the mesangial matrix - type IV collagen, laminin, and fibronectin - also stimulated iNOS activity in overlying RMC by 18-32% (P<0.05). Growth of RMC on oxidized type I collagen or Vitrogel had no effect on NO production. We conclude that oxidized modification of the mesangial matrix promotes increased iNOS activity and NO production by mesangial cells. Further work is required to determine whether this response limits glomerular injury or promotes damage to the mesangium in oxygen free radical-mediated diseases such as chronic renal failure, atherosclerosis and diabetes.

Vitamin E ameliorates renal injury in an experimental model of immunoglobulin A nephropathy.

IgA nephropathy is one of the most common forms of glomerular disease. Nearly 25% of affected patients progress to end-stage renal disease over a 20-25-y follow-up period. IgA-containing immune complexes stimulate oxygen-free radical production by mesangial cells in vitro. The excessive oxidant stress may mediate glomerular injury in this disorder. Therefore, we studied whether dietary supplementation with the antioxidant agent, vitamin E, attenuates renal disease in an experimental model of incipient IgA nephropathy with mild kidney inflammation. IgA nephropathy was induced in male Lewis rats by oral immunization with 0.1% bovine gamma-globulin (BGG)-containing drinking water for 8 wk. At the completion of this period, animals received BGG, 1 mg/dose i.v., on three successive days. Experimental rats (n = 10) received a specially formulated diet containing 100 IU of vitamin E/kg of chow, whereas control animals (n = 10) were fed chow containing 30 IU of vitamin/kg of chow. The BGG immunization regimen induced mesangial IgA deposition in all rats. Vitamin E supplementation resulted in a nearly 5-fold increase in the serum vitamin E concentration. Vitamin E-treated rats gained more weight and had a lower incidence of hematuria, 20% versus 80% (p < 0.03). Moreover, proteinuria was decreased by 50%, and reduced renal plasma flow was restored to normal, compared with untreated rats with IgA nephropathy. Glomerular hypertrophy occurred in animals with IgA nephropathy, but less so in those receiving vitamin E supplementation. Renal cortical malondialdehyde content was reduced from 1.55 +/- 0.10 to 1.22 +/- 0.09 nmol/mg of protein (p < 0.01) in rats fed the vitamin E-enriched diet. Finally, renal transforming growth factor-beta 1 gene expression was reduced by 34% in rats with IgA nephropathy receiving vitamin E treatment (p < 0.05). We conclude that experimental IgA nephropathy is associated with increased renal oxidant injury. Dietary treatment with the antioxidant agent, vitamin E, attenuated renal functional and structural changes in this experimental glomerulopathy. These studies support the importance of clinical trials for the evaluation of the efficacy of antioxidant therapy in patients with IgA nephropathy.

Taurine ameliorates chronic streptozocin-induced diabetic nephropathy in rats.

We examined the effect of two endogenous antioxidant agents, taurine and vitamin E, on renal function in experimental diabetes. Male Sprague-Dawley rats, rendered diabetic with streptozocin (STZ), were assigned to one of the following groups: 1) untreated; 2) insulin treatment with 6 U Ultralente insulin/day in two doses; 3) taurine supplementation by 1% taurine in drinking water; and 4) vitamin E supplementation at 100 IU vitamin E/kg chow. Animals were kept for 52 wk. The survival rate was similar (70-90%) in all groups except vitamin E-treated animals, of which 84% died by 6 mo. At 52 wk, glomerular filtration rate was elevated in untreated and taurine-treated STZ rats compared with normal or insulin-treated diabetic rats. Taurine supplementation reduced total proteinuria and albuminuria by nearly 50%. This treatment also prevented glomerular hypertrophy, preserved immunohistochemical staining for type IV collagen in glomeruli, and diminished glomerulosclerosis and tubulointerstitial fibrosis in diabetic animals. The changes in renal function and structure in taurine-treated diabetic rats were associated with normalization of renal cortical malondialdehyde content, lowering of serum free Fe2+ concentration, and decreased formation of the advanced glycooxidation products, pentosidine, and fluorescence in skin collagen. Administration of the vitamin E-enriched diet exacerbated the nephropathy in STZ-diabetic rats. In addition, vitamin E supplementation increased serum free Fe2+ concentration, enhanced renal lipid peroxidation, and accelerated the accumulation of advanced glycosylation end products (AGEs) in skin collagen. We conclude that administration of taurine, but not vitamin E, to rats with STZ-diabetes ameliorates diabetic nephropathy. The beneficial effect of taurine is related to reduced renal oxidant injury with decreased lipid peroxidation and less accumulation of AGEs within the kidney.

Taurine attenuates renal disease in chronic puromycin aminonucleoside nephropathy.

Repeated administration of low doses of puromycin aminonucleoside (PAMN) to rats induces a proteinuric renal disease that resembles focal segmental glomerulosclerosis (FSGS). Reactive oxygen molecules may be involved in the progressive course of this nephropathy. Therefore we evaluated whether taurine, an endogenous antioxidant, could limit the extent of renal injury. Sprague-Dawley rats received low-dose injections of PAMN, 2 mg/100 g body wt, over a 12-wk period. Two groups were studied: 1) controls given tap water (n = 23), and 2) an experimental group that drank 1% taurine-supplemented water (n = 22). Taurine-treated nephrotic rats had a reduction in albuminuria, as assessed by the urinary albumin-to-creatinine ratio (26 +/- 4 vs. 44 +/- 4, P less than 0.0001). After 12 wk, creatinine clearance was 0.33 +/- 0.03 (experimental) vs. 0.17 +/- 0.03 ml.min-1.100 g body wt-1 (control) (P less than 0.001), and inulin clearance (n = 6 pairs) was 0.26 +/- 0.04 (experimental) vs. 0.13 +/- 0.02 ml.min-1.100 g body wt-1 (control) (P less than 0.025). Administration of taurine reduced the percentage of segmentally sclerosed glomeruli (9.8 +/- 1.7 vs. 16.2 +/- 1.8%, P less than 0.02) and the tubulointerstitial injury score (1.36 +/- 0.19 vs. 2.61 +/- 0.25, P less than 0.0025) in experimental vs. control rats. Taurine treatment normalized the elevated renal cortical malondialdehyde level in rats with PAMN nephropathy (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)