Interference of factor V Leiden on protein S activity: evaluation of a new prothrombin time-based assay

The natural anticoagulant protein S; hemostatic functions and deficiency

Protein S (PS) is a vital endogenous anticoagulant. It plays a crucial role in regulating coagulation by acting as a cofactor for the activated protein C (APC) and tissue factor pathway inhibitor (TFPI) pathways. Additionally, it possesses direct anticoagulant properties by impeding the intrinsic tenase and prothrombinase complexes. Protein S oversees the coagulation process in both the initiation and propagation stages through these roles. The significance of protein S in regulating blood clotting can be inferred from the significant correlation between deficits in protein S and an elevated susceptibility to venous thrombosis. This is likely because activated protein C and tissue factor pathway inhibitor exhibit low efficacy as anticoagulants when no cofactors exist. The precise biochemical mechanisms underlying the roles of protein S cofactors have yet to be fully elucidated. Nevertheless, recent scientific breakthroughs have significantly enhanced comprehension findings for these functions. The diagnosis of protein S deficiency, both from a technical and genetic standpoint, is still a subject of debate due to the complex structural characteristics of the condition. This paper will provide an in-depth review of the molecular structure of protein S and its hemostatic effects. Furthermore, we shall address the insufficiency of protein S and its methods of diagnosis and treatment.

Low borderline plasma levels of antithrombin, protein C and protein S are risk factors for venous thromboembolism

BACKGROUND

Inherited deficiencies of antithrombin (AT), protein C (PC) and protein S (PS) are risk factors for venous thromboembolism (VTE). They are usually defined by laboratory cut-offs (in our setting 81, 70 and 63 IU dL(-1), respectively), which give only a rough idea of the VTE risk associated with plasma levels of these proteins.

OBJECTIVES

 We investigated whether the risk of VTE associated with the plasma deficiencies of AT, PC or PS has a dose-response effect, and whether low borderline levels of these proteins are associated with an increased risk of VTE, both in the whole study population and separately in carriers of either factor V Leiden or G20210A prothrombin gene mutation.

PATIENTS/METHODS

A case-control study of 1401 patients with a first objectively-documented VTE and 1847 healthy controls has been carried out.

RESULTS

A dose-response effect on the VTE risk was observed for all the three anticoagulant proteins. Compared with individuals with AT, PC or PS levels > 100 IU/dL, the adjusted odds ratio (95% CI) of VTE was 2.00 (1.44-2.78) for AT levels between 76 and 85 IUdL(-1) , 2.21 (1.54-3.18) and 1.84 (1.31-2.59) for PC and PS levels between 61 and 75 IUdL(-1) . The risk of unprovoked VTE in factor V Leiden or prothrombin G20210A carriers appears 2 to 3-fold increased when levels of AT or PS are low borderline.

CONCLUSIONS

 Low borderline plasma levels of AT, PC and PS are associated with a 2-fold increased risk of VTE and should be considered in the assessment of the individual VTE risk.