Hypofibrinolysis in diabetes: a therapeutic target for the reduction of cardiovascular risk

An enhanced thrombotic environment and premature atherosclerosis are key factors for the increased cardiovascular risk in diabetes. The occlusive vascular thrombus, formed secondary to interactions between platelets and coagulation proteins, is composed of a skeleton of fibrin fibres with cellular elements embedded in this network. Diabetes is characterised by quantitative and qualitative changes in coagulation proteins, which collectively increase resistance to fibrinolysis, consequently augmenting thrombosis risk. Current long-term therapies to prevent arterial occlusion in diabetes are focussed on anti-platelet agents, a strategy that fails to address the contribution of coagulation proteins to the enhanced thrombotic milieu. Moreover, antiplatelet treatment is associated with bleeding complications, particularly with newer agents and more aggressive combination therapies, questioning the safety of this approach. Therefore, to safely control thrombosis risk in diabetes, an alternative approach is required with the fibrin network representing a credible therapeutic target. In the current review, we address diabetes-specific mechanistic pathways responsible for hypofibrinolysis including the role of clot structure, defects in the fibrinolytic system and increased incorporation of anti-fibrinolytic proteins into the clot. Future anti-thrombotic therapeutic options are discussed with special emphasis on the potential advantages of modulating incorporation of the anti-fibrinolytic proteins into fibrin networks. This latter approach carries theoretical advantages, including specificity for diabetes, ability to target a particular protein with a possible favourable risk of bleeding. The development of alternative treatment strategies to better control residual thrombosis risk in diabetes will help to reduce vascular events, which remain the main cause of mortality in this condition

Pivotal role of PAI-1 in a murine model of hepatic vein thrombosis

Hepatic veno-occlusive disease (VOD) is a common complication of high-dose chemotherapy associated with bone marrow transplantation. While the pathogenesis of VOD is uncertain, plasminogen activator inhibitor-1 (PAI-1) has emerged as a diagnostic marker and predictor of VOD in humans. In this study, we investigated the role of PAI-1 in a murine model of VOD produced by long-term nitric oxide synthase inhibition using L-NAME. After 6 weeks, wild-type (WT) mice developed extensive fibrinoid hepatic venous thrombi and biochemical evidence of hepatic injury and dysfunction. In contrast, PAI-1–deficient mice were largely protected from the development of hepatic vein thrombosis. Furthermore, WT mice that received tiplaxtinin, an antagonist of PAI-1, were effectively protected from L-NAME–induced thrombosis. Taken together, these data indicate that NO and PAI-1 play pivotal and antagonistic roles in hepatic vein thrombosis and that PAI-1 is a potential target in the prevention and treatment of VOD in humans

Enhanced clearance of Aβ in brain by sustaining the plasmin proteolysis cascade

The amyloid hypothesis states that a variety of neurotoxic β-amyloid (Aβ) species contribute to the pathogenesis of Alzheimer's disease. Accordingly, a key determinant of disease onset and progression is the appropriate balance between Aβ production and clearance. Enzymes responsible for the degradation of Aβ are not well understood, and, thus far, it has not been possible to enhance Aβ catabolism by pharmacological manipulation. We provide evidence that Aβ catabolism is increased after inhibition of plasminogen activator inhibitor-1 (PAI-1) and may constitute a viable therapeutic approach for lowering brain Aβ levels. PAI-1 inhibits the activity of tissue plasminogen activator (tPA), an enzyme that cleaves plasminogen to generate plasmin, a protease that degrades Aβ oligomers and monomers. Because tPA, plasminogen and PAI-1 are expressed in the brain, we tested the hypothesis that inhibitors of PAI-1 will enhance the proteolytic clearance of brain Aβ. Our data demonstrate that PAI-1 inhibitors augment the activity of tPA and plasmin in hippocampus, significantly lower plasma and brain Aβ levels, restore long-term potentiation deficits in hippocampal slices from transgenic Aβ-producing mice, and reverse cognitive deficits in these mice