CYCLOSPORINE-A HAS NO DIRECT EFFECT ON COLLAGEN-METABOLISM BY CARDIAC FIBROBLASTS INVITRO

Background. Cyclosporine A has been implicated in the pathogenesis of myocardial interstitial fibrosis observed in heart transplant recipients. However, other confounding variables such as posttransplantation hypertension and rejection episodes may also be responsible for interstitial fibrosis development and associated abnormalities in ventricular diastolic function. Therefore, we examined whether cyclosporine A directly or indirectly affects fibrillar collagen metabolism by cardiac fibroblasts in vitro. Methods and Results. Rat cardiac fibroblasts were isolated by collagenase digestion. Subconfluent cultures were then maintained (24 hours) in serum-containing or serum-free medium before addition of cyclosporine A (50-1,000 ng/mL). After an additional 24 hours, total procollagen synthesis, accumulation, and degradation were analyzed by measuring hydroxyproline content in the cell monolayer and in the ethanol-soluble and ethanol-precipitable fractions of the culture medium. mRNA levels for alpha1(I) and alpha1(III) procollagen polypeptides were assessed 2, 6, 12, and 24 hours after cyclosporine A treatment using Northern blot analysis. The results were compared with control cultures maintained in the absence of cyclosporine A. There were no differences in procollagen gene expression, total procollagen synthesis, accumulation, or degradation in cardiac fibroblasts treated directly with cyclosporine A, in concentrations up to 1,000 ng/mL, compared with untreated cells. In additional experiments, we examined whether cyclosporine A might stimulate the production of collagen regulatory substances by cardiac myocytes in culture. However, addition of conditioned media from neonatal myocytes maintained in the presence and absence of cyclosporine A (1,000 ng/mL) also had no effect on collagen deposition by cardiac fibroblasts. Conclusions. We conclude that cyclosporine A has no direct effect on collagen metabolism by cultured cardiac fibroblasts in vitro. In addition, we have excluded a paracrine effect of ventricular myocytes on collagen production in the presence of cyclosporine A. These results suggest that factors other than cyclosporine A are responsible for the interstitial fibrosis observed in cardiac allografts.