Thromboxane receptor blockade attenuates chronic cyclosporine nephrotoxicity and improves survival in rats with renal isograft

The question of whether pharmacological inhibition of the thromboxane A₂ activity prevents cyclosporine-induced chronic renal dysfunction in a Lewis rat model of renal isograft was addressed. Transplanted animals were given a daily oral dose of cyclosporine (20 mg/kg; N= 15), cyclosporine (20 mg/kg) and the thromboxane A₂ receptor antagonist GR32191 (3 mg/kg twice daily, by gavage; N= 15), or the vehicle alone (N= 12). Treatments were started the day of kidney transplant, and animals were monitored for 1 year. Cyclosporine-treated animals developed renal insufficiency, as documented by serum creatinine levels of 0.49 ± 0.09, 0.95 ± 0.12, and 1.38 ± 0.15 mg/dL before and after 6 and 12 months of observation, respectively. Cyclosporine and GR32191 used in combination partially but significantly prevented the deterioration of renal function (serum creatinine, basal, 0.52 ± 0.06; month 6, 0.68 ± 0.04; month 12, 0.93 ± 0.10 mg/dL). At the end of the study, GFR, as inulin clearance, was significantly lower in rats given cyclosporine (0.28 ± 0.09 mL/min/ 100 g) than in rats given cyclosporine plus GR32191 (0.45 ± 0.05 mL/min/100 g) or than in vehicle-treated animals (0.56 ± 0.07 mL/min/100 g). Similar results were obtained for the effective RPF, measured as p-aminohippurate clearance. At the same time points, comparable to whole-blood cyclosporine levels were found in rats receiving cyclosporine alone and in those given cyclosporine plus GR32191. More than 50% of the animals on cyclosporine alone died from uremia before the end of the observation period. By contrast, rats receiving cyclosporine in combination with GR32191 had a prolonged survival. These findings indicate that limiting the functional consequence of excessive thromboxane A₂ synthesis in a rat isograft model prevents the long-term consequences of cyclosporine renal toxicity and increases the survival of transplanted animals.