Thrombomodulin activity of fat-derived microvascular endothelial cells seeded on expanded polytetrafluorethylene

Lining the luminal surface of prosthetic vascular grafts with endothelial c ells (cell seeding) will lower its thrombogenicity. Commonly used macrovasc ular human adult endothelial cells (HAEC) require in vitro cultivation befo re large enough numbers are obtained to cover grafts confluently. Fat-deriv ed microvascular endothelial cells (MVEC) prove to be a good alternative as they can be harvested in much larger numbers while showing similar antithr ombotic and fibrinolytic characteristics. An important anticoagulant functi on of macrovascular endothelial cells is due to the activity of thrombomodu lin (TM) on their surface. In this study, the presence and functional activ ity of TM on fat-derived microvascular cells used in cell seeding was inves tigated. The expression and localization of TM on MVEC was studied using im munohistochemistry. Functional activity of TM on MVEC was measured by the g eneration of activated protein C (APC) and was compared to human umbilical vein endothelial cells (HUVEC). TM activity was studied in MVEC seeded on e xpanded polytetrafluorethylene (ePTFE) vascular prostheses and compared to blank prostheses. We found that TM was expressed on the surface of MVEC, bo th in vivo and vitro. TM-dependent generation of APC differed significantly between MVEC and HUVEC (3.98 +/- 1.2 vs. 3.0 +/- 0.7 nM, respectively). Af ter seeding MVEC on vascular prostheses, TM activity did not change. APC ge neration was significantly higher on MVEC-seeded vascular grafts compared t o blank grafts (4.0 +/- 0.7 vs. 1.7 +/- 0.5 nM, respectively). We conclude that TM is present and highly active on cultured MVEC. When seeded on ePTFE , MVEC retain the possibility to inhibit thrombin coagulant activity and to activate protein C. Therefore, since MVEC are readily available, the antic oagulant properties demonstrated here indicate that this cell type is suita ble for cell seeding of vascular prostheses.