Protein C

A soluble vitamin K dependent plasma serine protease.

Other factors can raise the risk of abnormal blood clots in people with mild protein C deficiency including: increasing age, surgery, immobility, or pregnancy.

Most people with mild protein C deficiency never develop abnormal blood clots, however.

In severe cases of protein C deficiency, infants develop a life-threatening blood clotting disorder called purpura fulminans soon after birth.

Purpura fulminans is characterized by the formation of blood clots within small blood vessels throughout the body.

Mild protein C deficiency affects approximately 1 in 500 individuals.

Protein C half life of 6- to 10-hours.

Activated protein C is formed when thrombin, bound to cofactor thrombomodulin, interacts with and cleaves the zymogen protein C.

Activated protein C is a potent anticoagulant and profibrinolytic enzyme able to inactivate clotting cofactors Va and VIIIa and plasminogen-activator inhibitor 1.

Cytokines such as TNF-alpha cause a decline in thrombomodulin activity and thereby decrease the generation of activated protein C.

Activated protein C (aPC), together with its cofactor protein S, serves multiple anticoagulant and antiinflammatory functions, one of which is to inactivate factors Va and VIIIa by proteolytic cleavage at specific sites on the substrate proteins.

Activated protein C also indirectly increases fibrinolytic activity by decreasing thrombin generation and the subsequent formation of thrombin-activatable fibrinolysis inhibitor.

Resistance to aPC is measured by comparison of standard clotting times in the presence and absence of aPC.

Proteolysis of activated factor V by aPC is usually rapid.

Activated Factor V Leiden molecule remains intact much longer because aPC cannot cleave it at its principal location.

Plasma clots in approximately 28–35 seconds when exposed to a contact pathway activator, creating the activated partial thromboplastin time (aPTT) and when aPC is added to the plasma, the anticoagulant effect of aPC increases the aPTT, usually by a factor of 2.0 or more: to 70–100 seconds.

Reduced levels of protein C in patients with sepsis is correlated with increased risk of death.

Abnormalities should be treated with warfarin but requires the use of heparin or low-molecular weight heparin before the initiation of warfarin.

The initiation of warfarin alone may deplete protein C levels rapidly enough to cause increased hypercoaguability.

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