The effect of combined rapamycin/cyclosporine on the changes in pro‐fibrotic gene expression that occur during the development of allograft vasculopathy in rats, compared with cyclosporine or rapamycin in isolation

Abstract Chronic allograft dysfunction, the leading cause of solid‐organ transplant failure, is characterised by histological evidence of extracellular matrix (ECM) accumulation (fibrosis). The aim of this study was to compare the effect of combined rapamycin and cyclosporine therapy on fibrosis‐associated gene expression and ECM turnover during the development of allograft vasculopathy, compared with either agent alone. Lewis recipients of F344 rat thoracic‐to‐abdominal aorta transplants were administered rapamycin, cyclosporine, combined rapamycin and cyclosporine or no treatment. F344‐to‐F344 isografts served as controls. Six grafts in each group were harvested at 16 weeks. Vascular remodelling and ECM accumulation (Sirius red) were measured by computerised histomorphometry of aortic sections. Messenger RNA was extracted from frozen tissue, and expression of fibrosis‐associated genes was studied by means of semiquantitative reverse transcription polymerase chain reaction (RT‐PCR). Rapamycin (0.5 mg/kg per day) or cyclosporine (5 mg/kg per day) inhibited intimal hyperplasia, medial ECM accumulation and expansive vascular remodelling (increasing vessel circumference) in rat aortic allografts. This was associated with attenuation of the graft inflammatory infiltrate and a reduction in intra‐graft gelatinase, collagen III and tissue inhibitor of metalloproteinase (TIMP)‐1 mRNA levels. Combined rapamycin and cyclosporine inhibited intimal hyperplasia; however, there was a lesser effect on vascular remodelling and medial ECM accumulation. Combined‐treatment aortic allografts were also seen to have a moresevere inflammatory infiltrate and larger amounts of intra‐graft matrix metalloproteinase (MMP)‐9, transforming growth factor (TGF)‐β and TIMP‐1 mRNA than those treated with monotherapy. Rapamycin and cyclosporine act synergistically to inhibit intimal hyperplasia but not the inflammatory infiltrate, allograft fibrosis or vessel remodelling. In the high‐responder F344‐to‐Lewis rat model, effective immunosuppression is required to reduce graft fibrosis.

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