CYCLOSPORINE-INDUCED DETACHMENT OF VASCULAR ENDOTHELIAL-CELLS INITIATES THE INTRINSIC COAGULATION SYSTEM IN PLASMA AND WHOLE-BLOOD

Cyclosporine A (CsA) is supposed to alter the metabolism of vascular e ndothelial cells, leading to a prothrombotic state. We examined by whi ch mechanism human umbilical vein endothelial cells (HUVECs) treated w ith CsA would promote coagulation in human plasma and in whole blood. Treatment of HUVECs with CsA at concentrations clinically used led to dose-dependent cell detachment, with the subsequent exposure of the hi ghly procoagulant connective tissue. As determined by scanning electro n microscopy, cell counting of detached and adherent cells, and antige nic measurement of collagen exposure, HUVECs treated with 0.4 mu g/ml CsA (or more) for 4 days exhibited significant amounts of subendotheli al areas. On CsA-treated HUVEC monolayers, the clotting time of recalc ified citrated platelet-rich plasma (PRP), but not platelet-poor plasm a (PPP), was dose-dependently shortened. Likewise, the onset of thromb in generation was significantly earlier. Except at a high concentratio n of 8.0 mu g/ml CsA, there was no procoagulant effect when PPP was us ed. To investigate CsA-treated HUVECs in whole blood, cells were culti vated on globular microcarriers and were incubated with nonanticoagula ted whole blood. When untreated cells were used, generation of factor Xa, thrombin, and kallikrein was completely suppressed for 30 minutes. HUVEC beads treated with 0.4 and 0.8 mu g/ml CsA, however, led to a d ose-dependent generation of all three coagulation factors, with peak v alues at 2.5 to 5 minutes. Extrinsic activation was excluded, since Cs A treatment did not induce tissue factor activity in HUVECs. Furthermo re, the thrombomodulin activity of HUVECs was not altered by CsA. In c onclusion, treatment of HUVECs with CsA for 4 days at concentrations c linically used leads to the exposure of subendothelial areas that indu ce activation of the intrinsic coagulation in recalcified PRP and nona nticoagulated whole blood.