Prolongation of islet allograft survival in mice by combined treatment with pravastatin and low-dose cyclosporine.

Pravastatin, a 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor, is known to have suppressive effects on immune and inflammatory cells. We have previously shown in mice and dogs that this agent prevents primary nonfunction of islet iso- and autografts by reducing inflammation at the graft site. The present study was designed to further investigate whether pravastatin has a synergistic effect with cyclosporine (Cs) to prolong islet allograft survival in mice. Unpurified 3000 BALB/c newborn islets were transplanted under the renal capsule of a streptozotocin-diabetic C57BL/6 mouse. Pravastatin and Cs were administered for 10 days starting on the day of grafting (day 0). Five groups were set up based on the treatment protocol: group 1, treatment with 40 mg/kg pravastatin; group 2, 30 mg/kg Cs; group 3, 50 mg/kg Cs; group 4, 40 mg/kg pravastatin and 30 mg/kg Cs; group 5, vehicle alone. Graft survival was indicated by blood glucose levels sustained at <200 mg/dl, and graft rejection by >250 mg/dl for 2 consecutive days. Hyperglycemia persisted in six of the eight (75%) mice and grafts were rejected in 3.6 +/- 0.5 days (mean +/- SD) in group 5. In group 1, grafts were also rejected in 3.8 +/- 0.8 days, but blood glucose was transiently <200 mg/dl in three of the five mice. Despite Cs, grafts were rejected between 7 and 15 days (10.3 +/- 2.4 days) in group 2. Among six mice in group 3, one maintained euglycemia for >60 days, the other rejected the graft on day 15, and the remaining four died with functioning grafts between 9 and 13 days due to Cs toxicity. A combination of a low dose of Cs and pravastatin (group 4) prolonged graft survival for >19 days in five of the eight mice, and for 7-13 days in the remaining three mice. Histological examination of the grafts in this group showed significantly reduced local inflammation. Results indicate a synergistic effect of pravastatin and Cs on prevention of islet allograft rejection.