Protein Z Levels Could Help To Predict Obstetrical Complications and Arterial Thrombosis in Patients with Antiphospholipid Antibodies.

Introduction: Protein Z (PZ) is a vitamin K dependant plasma protein synthesized by the liver. The precise physiological function of PZ is still unclear: - anticoagulant, the PZ-dependant protease inhibitor complex inhibits factor Xa and acts as a naturally occurring anticoagulant; - procoagulant, PZ promote the assembly of thrombin with PL vesicles- and promote coagulation. In clinical situations, low PZ plasma levels have been associated with bleeding and thrombotic tendency while elevated PZ plasma levels have been linked with ischemic stroke. Antiphospholipid syndrome (APS) is a complex autoimmune thrombotic disorder. Despite specific clinical and laboratory criteria, diagnostic and prognostic tools in patients with APS are limited in their ability to predict adverse outcome in patients with antiphospholipid antibodies (aPLA). Therefore, we hypothesized that PZ could play a role in the thrombotic tendency.

Study: to evaluate our hypothesis, we measured PZ plasma concentrations in a case control study including 61 patients with confirmed aPLA with or without APS versus 53 controls. Among the group of patients with APS, 15 had obstetrical complications (OC), 16 had arterial thrombosis (AT) and 11 venous thrombosis (VT). Nineteen patients had aPLA without APS defining the APS(−) group. Plasma PZ antigen concentrations were measured on citrated plasma using the commercial ELISA kit, Asserachrom protein Z, (Diagnostica Stago).

Results: PZ plasma levels were normally distributed. Normal PZ concentrations defined as mean ±2 SD were contained between 0.4 and 2.6 μg/mL. No difference was found in mean+ SD between male and female. Two per cents of controls and 18% of patients with venous thrombosis had PZ under 0.4 μg/mL. Forty per cents of patients with OC, 25% with AT and 18% with VT had PZ above 2.6 μg/mL. Plasma protein Z levels measured at least 6 month after any clinical event were significantly higher in APS patients than in controls and APS(−) patients [mean ± SD μg/mL, 2.0 ± 0.9 vs 1.5 ± 0.5 and 1.3 ± 0.5 respectively). According to the clinical complications, PZ concentrations were significantly greater in the group with OC (2.4+0.6 μg/mL) and AT (2.05+0.8 μg/mL) than in controls (1.5+0.5 μg/mL), VT(1.3+0.9 μg/mL) and APS(−) (1.3+0.5 μg/mL) patients [OC vs Controls: p<0.0001; AT vs Controls: p= 0.0047; OC vs AT: p= NS; OC vs APS(−):p< 0.0001; OC vs VT: p= 0.0016, APS(−) vs controls: NS; APS(−) vs VT: NS; VT vs Controls: NS; APS(−) vs AT: p=0.0034; AT vs VT: p= 0.05]. We found an increased relative risk of OC and AT with increasing PZ levels with odds ratios of 7.1 [95% CI: 2.1–23.7] for OC and 2.4 [95% CI: 1.1–5.4] for AT.

Conclusion: our study retrospective on a small size sample, indicates that high protein Z plasma could be a high risk for obstetrical complications and a lower risk for arterial thrombosis in aPLA patients. Measure of PZ could help to evaluate obstetrical and thrombotic risk of patients with aPLA. Further prospective studies are needed to confirm our results.