Different Effect of Cyclosporine A and Mycophenolate Mofetil on Passive Heymann Nephritis in the Rat

Abstract

Background: While cyclosporine A (CsA) is an effective therapy for nephrotic syndrome, it has nephrotoxic side effects. We compared the anti-proteinuric effects and nephrotoxicity in rats with passive Heymann nephritis (PHN) of CsA and mycophenolate mofetil (MMF). Methods: PHN was induced in female Wistar rats. Two treatment groups consisting of 8 rats each received either 25 mg of CsA or 25 mg of MMF/kg body weight/day and were compared with untreated controls. Kidney function and proteinuria were monitored over 4 weeks. Western blots were used for densitometric analysis of renal cyclooxygenase-2 (COX-2) protein expression. Thromboxane B₂ (TxB₂) and 6-keto-PGF_1α were determined by radioimmunoassays (RIAs) in renal tissue and urine. Results: Rats with PHN exhibited a marked proteinuria of 12.76 ± 4.42 vs. 0.73 ± 0.28 mg/24 h (p < 0.01) and showed increased glomerular concentrations of TxB₂ and 6-keto-PGF_1α (992.6 ± 216.9 and 1,187.0 ± 54.2 pg/mg protein, respectively) compared with healthy controls (595 ± 196.17 and 729 ± 297.84, respectively) and a strongly induced COX-2 protein expression. CsA and MMF treatment reduced PHN-related proteinuria to 2.10 ± 1.47 and 1.47 ± 7.2 mg/24 h, respectively. In rats with PHN, CsA induced a significant deterioration of renal function and enhanced urine excretion of thromboxane A₂, paralleled by a significant, twofold increase in COX-2 protein expression and renal prostaglandins. By contrast, MMF treatment in rats with PHN was not nephrotoxic and had no effect on prostaglandin production. COX-2 protein expression under MMF was suppressed. Conclusion: While the antiproteinuric efficacy of MMF and CsA in PHN was comparable, the absence of nephrotoxicity might favor MMF in the treatment of nephrotic syndrome. The CsA-induced increase in COX-2 expression and COX-2-dependent prostacyclin may indicate a mechanism that compensates nephrotoxicity in the diseased and CsA-exposed kidney.