Local delivery of a tissue factor antibody reduces early leukocyte infiltration but fails to limit intimal hyperplasia in experimental vein grafts

Background. Tissue Factor-mediated thrombin generation involves the generation of VII(a) and X(a) and has been implicated in the pathogenesis of intimal hyperplasia. In experimental vein grafts, Tissue Factor protein is increased over the first 3 days and colocalized with CD18-positive leukocytes; this increase in Tissue Factor precedes the development of intimal hyperplasia. This study further evaluates the potential role of Tissue Factor in vein graft intimal hyperplasia by directly inhibiting Tissue Factor protein. Methods. New Zealand white rabbits underwent interpositional bypass grafting of the common carotid artery using the external jugular vein. Perioperatively, murine anti-rabbit Tissue Factor antibody (109 μg/ml gel, 12,500 x IC₅₀ of Tissue Factor activity) was applied to the adventitial surface of the graft, using a pluronic gel (30% soln.). Tissue Factor antibody treated vein grafts were compared to control and empty gel-treated vein grafts. Vein grafts were examined at 3 days to assess CD18-positive leukocyte infiltration and the presence of residual antibody by Western blotting. At 28 days, intimal and medial dimensions were quantified using videomorphometry. Results. At day 3, there was marked reduction in CD18- positive leukocytes in the Tissue Factor antibody versus control vein grafts (6.3 ± 4.7 vs 20.8 ± 7.4 per 200x field, P < 0.05). At 28 days, intimal hyperplasia was similar for the control (70 ± 4 μm, mean ± SEM), gel (73 ± 4 μm), and Tissue Factor antibody (75 ± 4 μm) vein grafts. However, medial thickness (76 ± 4 μm;, P < 0.05) was significantly increased compared to the gel treated vein graft (61 ± 5 μm). Conclusion. Local delivery of pharmacologic doses of an anti-rabbit Tissue Factor antibody decreased CD18-positive leukocyte infiltration but failed to limit intimal hyperplasia in experimental vein grafts. The results suggest that inhibition of Tissue Factor protein modulates polymorphonuclear leukocyte-endothelial interactions but not in the subsequent development of intimal hyperplasia. It implies that the relationship between the extrinsic coagulation cascade and intimal hyperplasia in vein grafts is complex.