Prevention of hyperacute xenograft rejection through direct thrombin inhibition with hirudin

Hyperacute xenograft rejection (HXR) is characterized by complement activation and intravascular thrombosis. The pathogenesis of HXR is attributed to antibodies binding to α-Gal-epitopes on the endothelial cells (EC) of the xenograft, activating complement and thrombin-mediated coagulation mechanisms. Our aim was to evaluate the influence of thrombin inhibition upon HXR and tissue integrity in an ex-vivo working heart model.

Eighteen isolated porcine hearts were perfused with human whole blood in a working heart model. The blood was treated with heparin (n=9) in group G-I and with heparin and additionally recombinant hirudin (0.012 mg/ml bolus, afterwards 4.5 µg/ml/h continuously) in group G-II (n=9). The experiments were terminated at end of cardiac output. Histological analysis was performed after the experiments.

Working heart time of G-II was significantly longer (712.0±37.8 vs. 125.0±31.4 min, p<0.01). Heart weight increase in G-II was lower (0.05±0.01 vs. 0.30±0.06%/min, p<0.01). Stroke work index and specific coronary flow improved significantly in G-II after 120 minutes. Histological analysis revealed increased tissue damage and thrombosis phenomena in G-I. Moreover, immunohistochemistry showed increased C3 and C5b-C9 upon EC of G-I.

Direct thrombin inhibition with Hirudin could be a successful strategy in primate xenotransplantation experiments to prevent tissue damage thus improving the graft survival.