The goal of the present study was directed to examine the potential role of a membranepermeable SOD-mimetic agent, tempol, in alleviating mitochondrial dysfunction in cisplatin-induced nephrotoxicity and to evaluate the effect of tempol on cisplatin antineoplastic efficacy. Cisplatin induced weight loss might be due to gastrointestinal toxicity and reduction of food ingestion. The present data show that administration of cisplatin to mice caused marked elevation of serum creatinine and urea levels as well as significant glucosuria and proteinuria. Cisplatin causes acute renal failure due to its preferential accumulation within the proximal tubular cells in the outer medulla of the kidney. The alterations in glomerular function in cisplatin-treated mice may be secondary to the oxidative stress status observed in the present study, which induces mesangial cells contraction, alteration of filtration surface area and modification of ultrafiltration coefficient factors that decrease the glomerular filtration rate. Pretreatment with tempol normalized serum creatinine level and caused significant reduction of serum urea, glucosuria and proteinuria compared to cisplatin group, indicating improvement of glomerular and tubular functions. The present results clearly indicate a significant degree of oxidative stress in both mitochondrial and postmitochondrial fractions in renal tissues of cisplatin-treated mice. This was demonstrated by a significant elevation of TBARS content and a significant reduction of GSH content along with inhibition of SOD and catalase activities in both mitochondrial and postmitochondrial fractions. The enhanced state of oxidative stress in cisplatin-treated group was associated with significant reduction of mitochondrial oxidative phosphorylation capacity and complexes I and III activities together with significant elevation of mNOS protein expression and caspase-3 activity. This was correlated with a pronounced reduction of ATP content indicating marked deterioration of mitochondrial respiration and energy production. GSH is one of the essential components for maintaining cell integrity because of its reducing properties and participation in the cell metabolism. The depletion of the renal GSH level has been observed in response to oxidative stress caused by cisplatin treatment. Platinum was shown to preferentially bind to GSH and protein thiol in kidneys after cisplatin treatment. The concentration of platinum-bound proteins was higher in the mitochondrial fraction than in the cytosolic fraction. Formation of these complexes limits the amount of drug available for DNA binding and therefore, a positive correlation has been AB1010 reported between GSH levels and resistance to cisplatin. Cisplatin affects many enzymes that protect the cells from oxidative damage, among which Cu, Zn-SOD, Mn-SOD and catalase. SOD plays an important role in the dismutation of superoxide anions. Decreased SOD activity as observed in this study could lead to incomplete scavenging of superoxide anions that are produced during the normal metabolic process with further initiation and propagation.