Analysis of the immunosuppressive and nephrotoxic effects of cyclosporin G.

Nephrotoxicity has limited the effectiveness of cyclosporine in transplantation therapy and has precipitated the need to develop a new immunosuppressive agent that lacks this nephrotoxicity or has a higher therapeutic index. Prior studies have suggested that cyclosporin G may be equally effective immunosuppressively, but less nephrotoxic than cyclosporine. To compare the immunosuppressive effects of the two agents, graft survival was analyzed in Lewis-Brown Norway rats, which received heterotopic ACl heart allografts and were treated orally with cyclosporin G or cyclosporine at 5 and 10 mg/kg/day. To compare nephrotoxicity the group of rats that had transplantations and an additional group of surgically intact Lewis-Brown Norway rats, treated orally with cyclosporin G or cyclosporine at dosages ranging from 10 to 50 mg/kg/day and for durations ranging from 50 to 180 days, were analyzed in terms of kidney morphology (fibrosis, glomerular damage, interstitial infiltrate, and tubular dilation) and kidney function (blood urea nitrogen and serum creatinine levels) in this model cyclosporin G was significantly less effective than cyclosporine in prolonging graft survival at 5 mg/kg/day but equally effective at 10 mg/kg/day. In addition, cyclosporin G was substantially less nephrotoxic both morphologically and functionally at low (10 mg/kg/day) and high (50 mg/kg/day) dosages. Further studies are indicated to determine the therapeutic index of cyclosporin G and to evaluate its use in combination with other immunosuppressive agents.