Human plasma contains a multivalent, Kunitz-type proteinase inhibitor termed tissue factor pathway inhibitor (TFPI), which is a specific inhibitor of the action of the factor VII(a)-tissue factor complex in coagulation. A major fraction of plasma TFPI is transported in association with LDL. Because LDL may undergo oxidation in the arterial wall during atherogenesis, we examined the effect of copper- and cell-mediated oxidative modification on TFPI activity associated with LDL. Oxidation mediated by copper ions resulted in a significant inactivation of LDL-associated TFPI (60% to 72% at 24 hours with 2.5 mumol/l CuCl2). The inactivation of TFPI was strongly negatively correlated with both an increase in the net electrical charge of LDL (r = -.80, P < or = .0001) and with the production of thiobarbituric acid-reactive substances (r = -.78, P < or = .0001) and lipid peroxides (r = -.80, P < or = .0001). Cell-mediated oxidation, involving incubation of LDL for 48 hours with either monocyte-like THP1 cells or human monocytes in Ham's F-10 medium, effected a significant decrease (64% and 75%, respectively) in LDL-associated TFPI activity. By contrast, prolonged exposure of LDL to purified soybean lipoxygenase (5000 U/mL) was less effective in inactivating TFPI (47% reduction after incubation for 72 hours at 37 degrees C). We subsequently investigated the mechanism(s) that may underlie such inactivation. Oxidation of LDL is accompanied by the generation of various aldehydes, including malondialdehyde and 4-hydroxynonenal. Chemical modification with these aldehydes revealed a significant inverse correlation between the progressive loss of TFPI activity and both the increase in net electrical charge (r = -.90, P < or = .0001) and the derivatization of free amino acid residues of LDL (r = -.90, P < or = .0001). Specific chemical modification of lysine amino groups by acetylation similarly led to inactivation of LDL-associated TFPI activity. TFPI activity was almost totally abolished (< 1.4%) when the TNBS reactivities of acetylated LDL, malondialdehyde-modified LDL, and 4-hydroxynonenal-modified LDL were 31%, 21%, and 43% that of native LDL, respectively. Our data demonstrate that expression of LDL-associated anticoagulant activity is markedly decreased as a consequence of the oxidative process, and suggest that the progressive aldehydic derivatization of apo B of LDL, and of the associated TFPI protein, may contribute to this phenomenon. Because tissue factor is overexpressed in the atheromatous plaque, it may exert a marked local procoagulant effect.(ABSTRACT TRUNCATED AT 400 WORDS)