Monocyte procoagulant activity induced by adherence to an artificial surface is reduced by end-point immobilized heparin-coating of the surface.

Heparin-coating improves the biocompatibility of blood contacting artificial surfaces. This led us to investigate the impact of heparin-coating (Carmeda AB, Stockholm) of polymetylmetacrylate on the expression of monocyte tissue factor procoagulant activity (TF-PCA) by surface adhesion. Also, the anticoagulant effect of heparin-coating in the presence or absence of adherent procoagulant monocytes was assessed. This is of particular interest, since activation of extrinsic coagulation by adherent monocyte TF-PCA may play a significant role in thrombin generation during extracorporeal circulation. Monocytes exposed to heparin-coated or non-coated polymetylmetacrylate expressed TF-PCA. The heparin coat did not affect the rate of monocyte adhesion. However, heparin-coating reduced the induction of TF-PCA of non-adherent and adherent monocytes by 17 and 33% (p <0.001 and p <0.0003), respectively. Heparin-coating in the absence of monocytes, totally inhibited the clotting of recalcified plasma (p <0.003). In contrast, in the presence of adherent monocytes expressing TF-PCA, surface-bound heparin did not inhibit clotting. However, inclusion of heparin in a plasma concentration of 8.9 IU/ml totally inhibited the activation of coagulation. It is apparent that heparin-coating of an artificial surface is an efficient means to inhibit coagulation of recalcified plasma, but much less so when procoagulant monocytes are adherent to the coated surface. The present findings are of clinical relevance, since monocytes will adhere to blood contacting surfaces of extracorporeal circuits or to implanted vascular prostheses and subsequently express TF-PCA, and this may promote thromboembolism.