Inhibition of heparin activity in plasma by soluble fibrin: evidence for
ternary thrombin-fibrin-heparin complex formation
KA Hotchkiss, CN Chesterman and PJ Hogg
Centre for Thrombosis and Vascular Research, School of Pathology,
University of New South Wales, S[dney, Australia.
The ability of heparin to dramatically enhance the inactivation of thrombin
(IIa) by antithrombin III (ATIII) in buffer is negated through formation of
a IIa-fibrin-heparin ternary complex (Hogg and Jackson, Proc Natl Acad Sci
USA 86:3619, 1989; Hogg and Jackson, J Biol Chem 265:241, 1990). IIa, in
this ternary complex, is protected from inactivation by ATIII. Our aim was
to determine whether fibrin also compromises heparin efficacy in plasma. We
found that soluble fibrin ablated the heparin-mediated prolongation of the
thrombin time with half-maximal effect at 60 nmol/L fibrin. The
heparin-mediated prolongation of the activated partial thromboplastin time
(APTT) was also reduced by fibrin with half-maximal effects at 140 nmol/L
fibrin using 0.12 U/mL heparin and 500 nmol/L fibrin using 0.25 U/mL
heparin. The mechanism of inhibition of heparin activity by fibrin in
plasma was determined by measuring IIa-ATIII complexes by enzyme-linked
immunosorbent assay (ELISA). Fibrin was found to inhibit the heparin-
catalyzed inactivation of IIa by ATIII with half-maximal effect at 97 +/-
19 nmol/L fibrin. Fibrin had no effect on the heparin-catalyzed
inactivation of factor Xa by ATIII in plasma, using either standard
heparin, a heparinoid preparation (Orgaran; Organon, Lane Cove, Sydney,
Australia), or low-molecular weight heparin. These findings imply that
fibrin is a potent modulator of heparin activity in vivo by inhibiting
heparin-catalyzed IIa-ATIII complex formation through formation of ternary
IIa-fibrin-heparin complexes.
Volume 84,
Issue 2,
pp. 498-503,
07/15/1994
Copyright © 1994 by The American Society of Hematology
