Cardiac allograft vasculopathy is a major cause of morbidity and mortality of cardiac transplant recipients. The underlying cause of this disease remains unclear. Histological studies have implicated accelerated hemostasis and intravascular fibrin deposition in its pathogenesis. In the present study a defined model of this disease in the rat was used to elucidate the implication of tissue factor in the production of the hypercoagulable state observed in cardiac allograft vessels. Tissue factor protein and mRNA expression were studied in rat heart allografts developing allograft vasculopathy resembling human disease. Immunohistochemistry demonstrated tissue-factor-positive cells present in the allograft coronary intima and adventitia. Significant staining for tissue factor was detected in the endothelium lining coronary lesions in cardiac allografts and in interstitial mononuclear cells, respectively. Both transplant coronary endothelial cells and mononuclear cells contained tissue factor mRNA as indicated by oligo-cell reverse transcription polymerase chain reaction after laser-assisted cell picking. In contrast, tissue factor mRNA and protein were not or negligibly detectable within the coronary intima of nontransplanted control hearts. Thus, the present study clearly demonstrates that aberrant tissue factor expression occurs within the coronary intima after cardiac transplantation. Tissue factor, activating downstream coagulation mechanisms, may account for the intravascular clotting abnormalities observed in cardiac allografts and may represent a key factor in transplant atherogenesis.

Background-Intravascular clotting has been implicated in the pathogenesis of cardiac allograft vasculopathy (CAV). We previously identified the expression of tissue factor (TF), the primary cellular initiator of blood coagulation, within the coronary intima, which was associated with neointimal thickening. In the present study, the effect of recombinant hirudin on CAV was assessed in Lewis to Fisher rat heterotopic cardiac allografts. Methods and Results-Transplant recipients were randomized to a control group (nϭ10) and a hirudin-treated group (nϭ12; 2 mg ⅐ kg Ϫ1 ⅐ d Ϫ1 SC). Histological evaluations of rejection, CAV, and TF staining were performed 120 days after transplantation. No significant differences were observed between the 2 groups with respect to the degree of rejection. Hirudin significantly (PϽ0.05) suppressed the development of CAV in the graft microvessels, but it was less effective in large coronary arteries. Graft intimal cells, isolated by laser-assisted cell picking, showed a marked upregulation of TF gene transcription, which was prevented by hirudin (PϽ0.01). As demonstrated by immunohistochemistry and quantitative analyses of TF mRNA levels by real-time polymerase chain reaction, hirudin treatment resulted in a significant reduction of TF protein and mRNA expression (PϽ0.001). Conclusions-Treatment with hirudin in this rat cardiac transplant model inhibited TF expression and decreased neointimal hyperplasia. These results suggest that TF inhibition by hirudin, in addition to its direct effect on thrombin, may attenuate the hypercoagulable state and prevent the development of CAV at least in restricted sites of the graft coronary vasculature.