The catalytic role of anionic phospholipids in the activation of protein C by factor Xa and expression of its anticoagulant function in human plasma.
Phospholipids bearing a proportion of anionic species such as phosphatidylserine are necessary to promote the anticoagulant potential of the protein C pathway. Factor Xa (200 or 350 pM) was found to activate protein C in a thrombomodulin-independent reaction requiring only phospholipids in Al(OH)3,-adsorbed plasma resupplemented with physiological concentrations of protein C (70 nM) and protein S (130 nM). All experiments were performed in the presence of an excess of hirudin. The activity of activated protein C was assessed by the survival of factor Va. The optimal phospholipid concentration range was 5 to 25 microM with a proportion of phosphatidylserine of 50% (mol/mol) resulting in a half-life of factor Va of 7.5 min in the absence of protein S and 4.2 min in its presence. Dns-EGR-Xa, an inactive derivative of factor Xa, behaved as an apparent protector of factor Va. When replacing factor Xa, thrombin at 10 nM was not an efficient protein C activator in the absence of purified human placenta thrombomodulin. In the presence of 100 pM activated protein C, factor Va half-life was 2 min in the absence of protein S and 1.1 min in its presence in the above optimal phospholipid concentration range. The presence of protein S allowed reduction of phospholipid requirements. Annexin-V (placental anticoagulant protein-I), a potent phospholipid antagonist, fully protected factor Va from degradation by phospholipid-dependent mechanisms. Factor Va was partially protected in the plasma of a patient having experienced thrombosis associated with lupus-like anticoagulant and anti-phospholipid auto-antibodies.(ABSTRACT TRUNCATED AT 250 WORDS)
Freyssinet
J M
JM
Institut d'Hématologie et d'Immunologie, Faculté de Médecine Strasbourg, France.
Toti-Orfanoudakis
F
F
Ravanat
C
C
Grunebaum
L
L
Gauchy
J
J
Cazenave
J P
JP
Wiesel
M L
ML
D000838:Anions; D016736:Antiphospholipid Syndrome / Q000097:blood*; D001711:Biotransformation / Q000187:drug effects; D001777:Blood Coagulation / Q000502:physiology*; D015943:Factor Va / Q000032:analysis; D015951:Factor Xa / Q000494:pharmacology*; D006207:Half-Life; D006801:Humans; D010718:Phosphatidylserines / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism*; D011486:Protein C / Q000378:metabolism*; D013927:Thrombosis / Q000097:blood
D000838:Anions; D010718:Phosphatidylserines; D010743:Phospholipids; D011486:Protein C; D015943:Factor Va; D015951:Factor Xa