Production of less chronic nephrotoxicity by cyclosporine G than cyclosporine a in a low-salt rat model

Chronic tubulointerstitial nephropathy during long-term cyclosporine A (CsA) use has led to a search for equally effective but safer analogues. In this study we evaluated one of these analogues, cyclosporine G (CsG), in a rat model of chronic cyclosporine nephrotoxicity. CsG has immunosuppressive effects equivalent to CsA when dosed on a weight basis. Pair-fed Sprague-Dawley rats kept on a low-salt rice diet were given CsA 15 mg/kg, CsG 15 mg/kg, CsG 25 mg/kg, or vehicle subcutaneously. After 21 days, CsA animals had a lower glomerular filtration rate, measured by inulin clearance (0.16±0.04 ml/min/100 g) and higher serum creatinine (0.94±0.06 mg/dl) than CsG 15 mg/kg (GFR: 0.41±0.10 ml/min/100 g and serum creatinine: 0.68±0.09 mg/dl), CsG 25 mg/kg (GFR: 0.39±0.16 ml/min/100 g) or control rats (GFR: 0.62±0.06 ml/min/100 g; serum creatinine: 0.56±0.03 mg/dl), respectively (P<0.05). The CsA group had considerable cortical and medullary injury (interstitial fibrosis and tubular atrophy), whereas both groups of CsG animals had more limited changes. Despite the same or larger doses of CsG on a weight basis, cyclosporine blood levels were significantly lower in CsG than CsA rats. We conclude that CsG, an analogue of cyclosporine with immunosuppressive activity equivalent to that of CsA, produced less nephrotoxicity in a model of chronic renal injury in rats, using both functional and structural parameters.