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CARDIOVASCULAR

The Glycocalyx Protects Erythrocyte-Bound Tissue-Type Plasminogen Activator from Enzymatic Inhibition

Institute for Environmental Medicine (K.G., J.L., V.R.M.), Department of Pathology and Laboratory Medicine (D.B.C.), and Department of Pharmacology and Targeted Therapeutics Program, Institute for Translational Medicine and Therapeutics (V.R.M.); University of Pennsylvania, Philadelphia, Pennsylvania; Centro Nacional de Investigaciones Cardiovasculares, Madrid, Spain (J.-C.M.); Howard Hughes Medical Institute, University of Michigan, Ann Arbor, Michigan (R.W.); and Los Alamos National Laboratory, Bio Division, Los Alamos, New Mexico (K.G.)

Coupling tissue-type plasminogen activator (tPA) to carrier red blood cells (RBC) prolongs its intravascular life span and permits its use for thromboprophylaxis. Here, we studied the susceptibility of RBC/tPA to PA inhibitors including plasminogen activator inhibitor-1 (PAI-1) that constrain its activity and may reduce the duration of its effect. Despite lesser spatial and diffusional limitations, soluble tPA was far less effective than RBC/tPA in dissolving clots formed in vitro from blood of wild-type (WT) mice (40 versus 80% lysis at equal doses of tPA). Furthermore, after i.v. injection, soluble tPA lost activity faster in transgenic mice expressing a high level of PAI-1 than in WT mice, whereas the activity of RBC/tPA was unaffected. PAI-1 inactivated soluble tPA at equimolar ratios in vitro, but it had no effect on the amidolytic or fibrinolytic activity of RBC/tPA. RBC/tPA was also more resistant than soluble tPA to in vitro inhibition by other serpins (₂-macroglobulin and ₁-antitrypsin) and pathologically high levels of glucose. However, coupling to RBC did not protect a truncated tPA mutant, Retavase, from plasma inhibitors. Chemical removal of the RBC glycocalyx negated tPA protection from inhibitors: tPA coupled to glycocalyx-stripped RBC bound twice as much ¹²⁵I-PAI-1 as did tPA coupled to naive RBC, and susceptibility of the bound tPA to inhibition by PAI-1 was restored. Thus, the RBC glycocalyx protects RBC-coupled tPA against inhibition. Resistance to high levels of inhibitors in vivo contributes to the potential utility of RBC/tPA for thromboprophylaxis.

Address correspondence to: Dr. Vladimir R. Muzykantov, Institute for Environmental Medicine, 1 John Morgan Bldg., University of Pennsylvania Medical Center, 3620 Hamilton Walk, Philadelphia, PA 19104-6068. E-mail: muzykant{at}mail.med.upenn.edu

This article has been cited by other articles:

				K. Danielyan, K. Ganguly, B.-S. Ding, D. Atochin, S. Zaitsev, J.-C. Murciano, P. L. Huang, S. E. Kasner, D. B. Cines, and V. R. Muzykantov Cerebrovascular Thromboprophylaxis in Mice by Erythrocyte-Coupled Tissue-Type Plasminogen Activator Circulation, September 30, 2008; 118(14): 1442 - 1449. [Abstract] [Full Text] [PDF]