Investigation of the Influence of Lipoprotein(a) and Oxidized Lipoprotein(a) on Plasminogen Activation and Fibrinolysis.

OBJECTIVE: In the present study, we compare the influence of oxidized lipoprotein(a) [Lp(a)] and unoxidized Lp(a) on plasminogen activation in the process of fibrinolysis and elucidate the potential atherogenic mechanisms of oxidized Lp(a), focusing on its role in thrombosis. METHODS: Chromogenic substrate assays were conducted to study the kinetics of plasminogen activation. Fibrin clots were generated by incubating fibrinogen with thrombin, and plasminogen activation was triggered with tissue plasminogen activator (tPA). Experiments were performed in low and high concentrations of Lp(a) or oxidized Lp(a) to evaluate their respective effects on plasmin generation. Oxidized Lp(a) was prepared by chemical oxidation of isolated Lp(a) samples. RESULTS: Low concentrations of Lp(a) enhanced plasminogen activation and fibrinolysis, reflecting its physiological role. However, at higher concentrations, oxidized Lp(a) exhibited a significant inhibitory effect on plasminogen activation. Compared to unoxidized Lp(a), oxidized Lp(a) led to earlier plateauing of plasmin generation and reduced overall plasmin levels. The inhibitory effects of oxidized Lp(a) are likely due to its structural similarity to plasminogen and higher oxidized phospholipid content, which competes with plasminogen for fibrin binding-the enhanced competition with fibrin fragments and tPA by oxidized Lp(a) further impaired fibrinolysis. CONCLUSION: This study demonstrates that while low levels of Lp(a) may support fibrinolysis, oxidized Lp(a) impairs this process by inhibiting plasminogen activation through structural and functional competition. These findings highlight the atherogenic potential of oxidized Lp(a) and its contribution to thrombotic cardiovascular risk.