A dedicated system for standardized measurement of VASP phosphorylation in blood platelets and detection of thienopyridine resistance

Abstract number: P1811

Poncelet^* P., Maunier^* T., Boulay-Moine^* D., Barragan† P., Pons^* C., Nedelec^* J.

^*BioCytex, France; †Private Hospital Center Beauregard, France

Thienopyridine (Ticlid^®, Plavix^®) resistance is still associated with a residual risk for stent thrombosis of about 2%. The level of Vasodilator Stimulated Phosphoprotein (VASP) phosphorylation in blood platelets is a hallmark of their activation status. Its measurement has been proposed for monitoring individual patient's response and for detecting the few cases of drug resistance (Barragan, Catheter. Cardiovasc. Interv., 2003). VASP-P level can be assessed by immuno-staining of permeabilized platelets with a specific monoclonal antibody. The index calculated by comparing VASP-P level after ADP-activation (ADP + PGE1) with the maximum level obtained in the basal state (PGE1 alone) is inversely related to each patient's drug sensitivity. Although flow cytometry has been initially proposed for measuring VASP-P levels (Schwartz, Thromb. Haemost., 1999), this clinically important parameter deserved a more user-friendly and accessible measurement system. We thus developed a dedicated platelet analyzer (Platelet Station, BioCytex, Marseille, F) which addresses the needs for easy access, limited cost, reliability as well as lab-to-lab and instrument-to-instrument reproducibility. This instrument may be assimilated to an optical blood cell counter, using a fluorescence detector for immuno-staining quantitation. Using this system, an excellent reproducibility was obtained for any sample with high index (CV < 3%) and low index values (CV < 5%). VASP-P index in healthy donors or coronary disease patients receiving only aspirin was always high (>60%). In contrast, most patients receiving thienopyridin showed a low value ranging from 20 to 60% and only a few cases had higher levels. This wide range illustrates the individual variability of response and includes the data from a few “bad responders” who may be at higher risk of stent thrombosis. With the help of this assay system, clinical studies are underway to determine the VASP cutoff index value under which patients can be considered at low risk of thrombosis. In addition to easy routine VASP measurement, the system also permits evaluation of more classical platelet function parameters such as fibrinogen binding capacity and surface P-selectin expression.