RT Journal Article SR Electronic T1 The Glycocalyx Protects Erythrocyte-Bound Tissue-Type Plasminogen Activator from Enzymatic Inhibition JF Journal of Pharmacology and Experimental Therapeutics JO J Pharmacol Exp Ther FD American Society for Pharmacology and Experimental Therapeutics SP 158 OP 164 DO 10.1124/jpet.106.114405 VO 321 IS 1 A1 Kumkum Ganguly A1 Juan-Carlos Murciano A1 Randal Westrick A1 John Leferovich A1 Douglas B. Cines A1 Vladimir R. Muzykantov YR 2007 UL http://jpet.aspetjournals.org/content/321/1/158.abstract AB 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 (α2-macroglobulin and α1-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. The American Society for Pharmacology and Experimental Therapeutics