Vitamin E suppresses cyclosporine A–induced increase in the urinary excretion of arachidonic acid metabolites including F2-isoprostanes in the rat model

ESPITE a large body of research, the exact mechanism by which cyclosporine (CsA) causes nephrotoxicity remains unclear. A consistent finding following CsA administration is the increase in urinary excretion of arachidonic acid metabolites. 1‐3 Although experimental studies with thromboxane synthase inhibitors suggested a role for TXA2 in CsA-induced renal dysfunction, chronic administration of thromboxane synthase inhibitors in renal transplant patients treated with CsA had little effect on improving renal function. 4,5 One possible explanation would be that arachidonic acid metabolites other than TXA2 might also be involved in the mediation of renal vasoconstriction and dysfunction. This possibility deserves consideration, because recent studies suggest that free radical-catalyzed lipid peroxidation, independent of the enzymatic pathway, may produce vasoactive prostaglandins, F2-isoprostanes and E2-isoprostanes, as well as thromboxane and isothromboxane. 6‐ 9 We have reported that dosedependent renal lipid peroxidation occurs with CsA-induced renal toxicity and that vitamin E and Lazaroid compounds suppress lipid peroxidation and protect the kidney against CsA-mediated functional and structural injury. 10,11 Recent findings from others are consistent with these observations, thus providing further support for an important role for free radical-catalyzed lipid peroxidation in the pathogenesis of CsA-induced nephrotoxicity. 12‐14 Because CsA induces lipid peroxidation and this in turn can catalyze the formation of prostaglandin- and thromboxane-like molecules, 6‐ 9 we examined whether the excessive production of arachidonic acid metabolites by CsA might be linked to heightened lipid peroxidation. Compared to vehicle, 12 weeks of CsA administration was associated with a significant reduction in renal function and an increase in urinary excretion of vasoconstrictive TBX-B2 and F2-IP and vasodilatory PGF1a. Administration of vitamin E along with CsA was accompanied by marked preservation of GFR and significant suppression of urinary TBX-B2 ,F 2-IP and PGF1a. In another experiment, vitamin E administration in normal rats did not have any effect on renal function or arachidonic acid metabolite excretion. Our new findings suggest that part of the CsA-induced increase in urinary arachidonic acid metabolites may arise from free radicalcatalyzed lipid peroxidation, and that the renoprotective effect of vitamin E may arise in part from the suppression of two potent vasoconstrictors, TBX and F2-IP. METHODS Effect of Vitamin E on CsA-Induced Increase in Urinary Excretion of Arachidonic Acid Metabolites Two weeks after subcostal right nephrectomy to simulate the single kidney model of transplant, male Sprague Dawley rats, matched for body weight and serum creatinine, were assigned to 3 groups: the control (n 5 5), CsA (n 5 6), and CsA plus vitamin E (n 5 6). The initial body weights of these rats were between 250 to 275 g. The control rats received olive oil vehicle by gavage (1 mL/kg/d) and by subcutaneous injections (0.5 mL/kg/d). The CsA group received CsA 15 mg/kg/d in olive oil subcutaneously and plain olive oil by gavage. The CsA plus vitamin E group received CsA as in the CsA group, and additionally, received vitamin E 25 mg/kg/d in olive oil by gavage. Rats were pair-fed with standard laboratory rat chow and their food intake and body weights were monitored once a week. Serial hematocrit (microcapillary method) and serum protein (refractory method) were measured from tail vein blood. Using metabolic cages, 24-hour urine was collected into containers containing antioxidant (100 mL of 2% butylated hydroxytoluene in ethanol). Urine samples were spun down and aliquots were saved at 284° until the time of assay. Creatinine in the plasma and urine were measured using an auto-analyzer based on the Jaffe reaction.