H. Pannekoek

Bio: H. Pannekoek is an academic researcher from University of Amsterdam. The author has contributed to research in topics: Plasminogen activator inhibitor-1 & Plasminogen activator. The author has an hindex of 7, co-authored 12 publications receiving 334 citations. Previous affiliations of H. Pannekoek include Queen's University.

Novel low-molecular-weight inhibitor of PAI-1 (XR5118) promotes endogenous fibrinolysis and reduces postthrombolysis thrombus growth in rabbits

Abstract: Background Elevated levels of plasminogen activator inhibitor 1 (PAI-1) have been associated with the occurrence of thrombotic disease, and inhibition of PAI-1 activity in vivo resulted in enhanced thrombolysis and a reduction in reocclusion. Besides monoclonal antibodies and peptides, no suitable agents that are able to block PAI-1 activity are available to date. The present study was designed to test the interaction between a nonantibody, nonpeptide, diketopiperazine-based inhibitor of PAI-1, XR5118, and PAI-1 and to assess the effect of XR5118 on PAI-1 activity in vitro and on in vivo thrombolysis and thrombus growth in an experimental thrombosis model in rabbits. Methods and results The binding site of XR5118 on the PAI-1 molecule was studied by competitive binding experiments with mapped anti-PAI-1 monoclonal antibodies by use of surface plasmon resonance experiments. XR5118 selectively and competitively inhibited binding of the PAl-1-inhibiting monoclonal antibody CLB-2C8, indicating that binding of XR5118 to PAI-1 takes place at the area between amino acids 110 and 145 of the PAI-1 molecule, which is known to be involved with the binding of PAI-1 to tissue plasminogen activator (TPA). Incubation of plasma or platelet releasate with XR5118 resulted in a dose-dependent inhibition of PAI-1 activity. Systemic infusion of XR5118 induced a significant reduction in plasma PAI-1 activity levels from 23.7+/-4.9 to 10.9+/-3.4 IU/mL. Administration of XR5118 resulted in a significant, twofold increase in endogenous thrombolysis compared with the control. Thrombus growth in rabbits receiving both XR5118 and rTPA was significantly attenuated compared with rabbits receiving rTPA alone (13.5+/-2.7% versus 19.9+/-3.8%, respectively). Conclusions XR5118 binds to PAI-1 and reduces plasma PAI-1 activity levels. Furthermore, XR5118 promotes endogenous thrombolysis and inhibits thrombus accretion and is the first nonpeptide compound with significant anti-PAI-1 activity in vivo in these models.

The plasminogen activation system in tumor growth, invasion, and metastasis.

Abstract: Generation of the serine proteinase plasmin from the extracellular zymogen plasminogen can be catalyzed by either of two other serine proteinases, the urokinase- and tissue-type plasminogen activators (uPA and tPA). The plasminogen activation system also includes the serpins PAI-1 and PAI-2, and the uPA receptor (uPAR). Many findings, gathered over several decades, strongly suggest an important and causal role for uPA-catalyzed plasmin generation in cancer cell invasion through the extracellular matrix. Recent evidence suggests that the uPA system is also involved in cancer cell-directed tissue remodeling. Moreover, the system also supports cell migration and invasion by plasmin-independent mechanisms, including multiple interactions between uPA, uPAR, PAI-1, extracellular matrix proteins, integrins, endocytosis receptors, and growth factors. These interactions seem to allow temporal and spatial reorganizations of the system during cell migration and a selective degradation of extracellular matrix proteins during invasion. The increased knowledge about the plasminogen activation system may allow utilization of its components as targets for anti-invasive therapy.

Structural basis of substrate specificity in the serine proteases

Abstract: Structure-based mutational analysis of serine protease specificity has produced a large database of information useful in addressing biological function and in establishing a basis for targeted design efforts. Critical issues examined include the function of water molecules in providing strength and specificity of binding, the extent to which binding subsites are interdependent, and the roles of polypeptide chain flexibility and distal structural elements in contributing to specificity profiles. The studies also provide a foundation for exploring why specificity modification can be either straightforward or complex, depending on the particular system.

C-Reactive Protein Increases Plasminogen Activator Inhibitor-1 Expression and Activity in Human Aortic Endothelial Cells Implications for the Metabolic Syndrome and Atherothrombosis

Abstract: Background— Inflammation plays a pivotal role in atherosclerosis. In addition to being a risk marker for cardiovascular disease, much recent data suggest that C-reactive protein (CRP) promotes atherogenesis via effects on monocytes and endothelial cells. The metabolic syndrome is associated with significantly elevated levels of CRP. Plasminogen activator inhibitor-1 (PAI-1), a marker of atherothrombosis, is also elevated in the metabolic syndrome and in diabetes, and endothelial cells are the major source of PAI-1. However, there are no studies examining the effect of CRP on PAI-1 in human aortic endothelial cells (HAECs). Methods and Results— Incubation of HAECs with CRP results in a time- and dose-dependent increase in secreted PAI-1 antigen, PAI-1 activity, intracellular PAI-1 protein, and PAI-1 mRNA. CRP stabilizes PAI-1 mRNA. Inhibitors of endothelial NO synthase, blocking antibodies to interleukin-6 and an endothelin-1 receptor blocker, fail to attenuate the effect of CRP on PAI-1. CRP additionally ...