Recent evidence has suggested that increased protein concentration in the urine can be toxic to renal proximal tubular cell function. In cases of proteinuric renal disease, the protein itself may be responsible for interstitial fibrosis and progressive deterioration in renal function. Oxidant stress has been implicated as a mechanism of disease in puromycin aminonucleoside (PA) nephropathy. This study investigates the NADPH oxidase activity in the renal cortex of rats with acute PA nephropathy in comparison to control animals.
Methods PA-treated adult male Sprague-Dawley rats (n = 8) were given a single intraperitoneal (IP) injection of 15 mg PA/100 g body weight. Control rats (n = 8) were given an equivalent IP injection of normal saline. Rats from each group were sacrificed on days 2, 6, 9, and 21 after initial injection. NADPH-dependent superoxide anion generation was assessed in renal cortical homogenates using lucigenin-enhanced chemiluminescence. 24-hour urine samples were obtained from each rat prior to days 2, 6, 9, and 21.
Results Proteinuria was greatest in the PA-treated rats on day 9, which is consistent with the known course of this disease. NADPH oxidase activity, expressed as relative light units (RLU)/mg protein, was similar between the two groups of animals on day 2. NADPH oxidase activity was significantly elevated on day 6 in the PA-treated rats as compared to the control animals. NADPH oxidase activity remained elevated in the PA-treated rats compared to controls on days 9 and 21.
Conclusions We found that in acute PA nephropathy, NADPH-dependent reactive oxygen species (ROS) production occurs shortly after the onset of clinical proteinuria. The fact that the two groups showed similar ROS generation at day 2 suggests that the proteinuria is responsible for these findings rather than the PA itself. Our results suggest that ROS production by NADPH-dependent superoxide generating enzymes may be stimulated by elevated concentrations of protein within the proximal tubule. This may represent one of the mechanisms by which the renal cortex becomes damaged in proteinuric states.
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