Alpha 2-macroglobulin enhances prothrombin activation and thrombin potential by inhibiting the anticoagulant protein C/protein S system in cord and adult plasma.
Protein S (PS) is a vitamin K-dependent plasma protein and serves as a cofactor for the anticoagulant activities of activated protein C (APC). We investigated the effects of different PS concentrations on prothrombin activation and thrombin generation in cord and adult plasma containing APC and different amounts of alpha 2-macroglobulin (a2-M). Prothrombin activation was assessed by monitoring the time-course of prothrombin fragment 1+2 (F1+2) generation. Thrombin generation curves were determined by means of a subsampling technique using the chromogenic substrate S-2238. We demonstrate a dose-dependent inhibition of the anticoagulant action of PS by a2-M: suppression of F1+2 and thrombin generation due to addition of PS was stronger in plasma containing low amounts of a2-M than in plasma with elevated a2-M levels. Since no complex formation between a2-M and PS was observed by means of SDS-PAGE, we attribute decreased anticoagulant action of PS at high a2-M levels to enhanced complex formation between APC and a2-M. Thereby, APC is subtracted from its cofactor PS, resulting in suppressed formation of the anticoagulant APC/PS complex. Thus, our data suggest that a2-M, besides its well-known anticoagulant effects, also acts as a procoagulant by suppressing the formation of the anticoagulant APC/PS complex. Our findings have implications particularly on thrombin generation and inhibition in cord plasma, since a2-M levels in newborns are elevated over adult values and the antithrombotic APC/PS pathway is up-regulated at birth. Therefore, elevated levels of a2-M might restrict the up-regulation of the APC/PS pathway.
Cvirn
Gerhard
G
Ludwig Boltzmann Research Institute for Pediatric Hemostasis and Thrombosis, Graz, Austria. gerhard.cvirn@klinikum-graz.at
Gallistl
Siegfried
S
Koestenberger
Martin
M
Kutschera
Joerg
J
Leschnik
Bettina
B
Muntean
Wolfgang
W
D000328:Adult; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D005312:Fetal Blood; D006801:Humans; D007231:Infant, Newborn; D007700:Kinetics; D011486:Protein C / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D017293:Protein S / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D011516:Prothrombin / Q000378:metabolism*; D013917:Thrombin / Q000378:metabolism*; D000511:alpha-Macroglobulins / Q000494:pharmacology*
D011486:Protein C; D017293:Protein S; D000511:alpha-Macroglobulins; D011516:Prothrombin; D013917:Thrombin