Ethanol-induced increased surface-localized fibrinolytic activity in cultured human endothelial cells: Kinetic analysis

Background: Moderate alcohol consumption is associated with reduced risk fo r coronary heart disease and this cardioprotection may be due, in part, to increased fibrinolysis. We have previously demonstrated that low concentrat ions of ethanol (0.1%, v/v) induce the short-term (il hr) and sustained, lo ng-term (24 hr) increase in surface-localized fibrinolytic activity; it up- regulates t-PA, u-PA, and the candidate plasminogen receptor (PmgR), annexi n II, and gene transcription in cultured human umbilical vein endothelial c ells (HUVECs). These studies describe the short- and long-term effects of l ow concentrations of ethanol on the kinetics of cell-bound I-125-labeled Gl u-plasminogen (Glu-Pmg) activation by receptor (R)-bound t-PA, resulting in increased fibrinolytic activity in cultured HUVECs. Methods: Live cultured HUVECs were incubated with varying concentrations of Glu-Pmg (0.25-2 muM) and ethanol (0.025-0.1%, v/v) (in the presence of Apr otinin and alpha (2)-antiplasmin) and the direct activation of cell-bound I -125-labeled Glu-Pmg quantitated by measurement of I-125-labeled M-r 20 kDa plasmin light-chain, after reduction/SDS-PAGE. The effects of ethanol on I -125-labeled Glu-Pmg and I-PA ligand binding were determined by Scatchard a nalysis (B-max sites/cell). Results: Cell-bound t-PA (endogenous/exogenous) activation of cultured HUVE C-bound I-125-labeled Glu-Pmg (short- and long-term) obeyed Michaelis-Mente n kinetics, both in the absence/presence of low ethanol. as shown by Linewe aver-Burke plot analysis. In the short-term, ethanol (at 0.1%) increased th e V-max (2.5-fold), k(cat) (2-fold) and the apparent k(cat)/K-m (4-fold), c ommensurate with a significant decrease in the apparent K-m (6-fold) and in crease in I-125-labeled Glu-Pmg ligand binding, B-max (2-fold). In the long term, ethanol increased the V-max (2- to 3-fold), k(cat) (2.5-fold), appare nt k(cat)/K-m (5-fold), and Bmax (2-fold) for I-125-labtled Glu-Pmg ligand binding, without significantly affecting the apparent K-m. Conclusions: Low concentrations of ethanol induce the short- versus long-te rm increase in surface-localized fibrinolytic activity in cultured HUVECs v ia different mechanisms. Short-term effects may be mediated by ethanol-indu ced membrane conformational changes that simultaneously facilitate increase d surface-localized HUVEC PmgR availability and fibrinolytic protein/recept or interactions, resulting in the increased affinity of t-PA for Glu-Pmg an d the accelerated activation of Glu-Pmg (increased B-max, decreased apparen t K-m). The long-term effects may be attributed primarily to the ethanol-in duced increased availability of both newly synthesized t-PA and PmgR and, h ence, the accelerated activation of Glu-Pmg (increased B-max).