Tempol, a membrane-permeable radical scavenger, reduces oxidant stress-mediated renal dysfunction and injury in the rat

Background. The generation of reactive oxygen species (ROS) contributes to the pathogenesis of renal ischemia-reperfusion injury. The aim of this stud y was to investigate the effects of tempol in (1) an in vivo rat model of r enal ischemia/ reperfusion injury and on (2) cellular injury and death of r at renal proximal tubular (PT) cells exposed to oxidant stress in the form of hydrogen peroxide (H2O2). Method's. Male Wistar rats underwent bilateral renal pedicle clamping for 4 5 minutes followed by reperfusion for six hours. Tempol (30 mg/kg/h), desfe rrioxamine (DEF; 40 mg/kg/h), or a combination of tempol (30 mg/kg/h) and D EF (40 mg/kg/h) were administered prior to and throughout reperfusion. Plas ma concentrations of urea. creatinine, Na+, gamma-glutamyl transferase (gam ma GT), aspartate aminotransferase (AST), and urinary Na+ and N-acetyl-beta -D-glucosaminidase (NAG) were measured for the assessment of renal function and reperfusion injury. Kidney myeloperoxidase (MPO) activity and malondia ldehyde (MDA) levels were measured for assessment of polymorphonuclear (PMN ) cell infiltration and lipid peroxidation, respectively. Renal sections we re used for histologic grading of renal injury and for immunohistochemical localization of nitrotyrosine and poly(ADP-ribose) synthetase (PARS). Prima ry cultures of rat PT cells were incubated with H2O2 (1 mmol/L for 4 h) eit her in the absence or presence of increasing concentrations of tempol (0.03 to 10 mmol/L), DEF (0.03 to 10 mmol/L), or a combination of tempol (3 mmol /L) or DEF (3 mmol/L). PT cell injury and death were determined by evaluati ng mitochondrial respiration and lactate dehydrogenase (LDH) release, respe ctively. Results. In vivo, tempol significantly reduced the increase in urea, creati nine, gamma GT, AST, NAG, and FENa produced by renal ischemia/reperfusion, suggesting an improvement in both renal function and injury. Tempol also si gnificantly reduced kidney MPO activity and MDA levels, indicating a reduct ion in PMN infiltration and lipid peroxidation, respectively. Tempol reduce d the histologic evidence of renal damage associated with ischemia/reperfus ion and caused a substantial reduction in the staining for nitrotyrosine an d PARS, suggesting reduced nitrosative and oxidative stress. In vitro, temp ol significantly attenuated H2O2-mediated decrease in mitochondrial respira tion and increase in LDH release from rat PT cells, indicating a reduction in cell injury and death. Both in vivo and in vitro, the beneficial actions of tempol were similar to those obtained using the Fe2+ chelator DEF. Howe ver, coadministration of DEF and tempol did not produce any additional bene ficial actions against renal ischemia/reperfusion injury or against oxidati ve stress-mediated PT cell injury/death. Conclusion. Our results suggest that the membrane-permeable radical scaveng er, tempol, reduces the renal dysfunction and injury associated with ischem ia/reperfusion of the kidney.