Vasodilator-stimulated phosphoprotein

Overview
Vasodilator-stimulated phosphoprotein, also known as VASP, is a human gene.

VASP-P
The phosphorylation (P) of vasodilator-stimulated phosphoprotein (VASP) is a test based on flow cytometry which is very specific to the P2Y12 signaling pathway. It is commercially available as a kit marketed as PLT VASP/P2Y12 (BioCytex, Marseilles, France).

VASP is an intracellular platelet protein that is not phosphorilated at baseline. VASP-P is mediated by the cAMP cascade, which is enhanced by prostaglandin E1 (PGE1) and inhibited by the link between ADP and P2Y12 receptors. Therefore, VASP-P is a marker of P2Y12receptor inhibition, whereas its non-phosphorylated counterpart correlates with the non-inhibited form of the P2Y12 receptor.

By using the PLT VASP/P2Y12 kit, the effect of clopidogrel can be demonstrated by the persistence of VASP in its phosphorylated state (VASP-P) induced by PGE1 despite the simultaneous addition of ADP.

More in detail, the blood sample is first incubated with PGE1 alone or PGE1 + ADP. Subsequently, after a cellular permeabilization, VASP-P is labeled by indirect no wash immunofluorescence using a specific monoclonal antibody. The two tested conditions are then evaluated by means of dual color flow cytometry analysis. Final results are usually expressed in terms of platelet reactivity index (PRI), which is calculated using corrected mean fluorescence intensities (MFIc) in the presence of PGE1 alone or PGE1 and ADP simultaneously, according to the following formula:

PRI = [(MFIcPGE1 - MFIc PGE1+ADP)/ MFIcPGE1]x100

Assessment of VASP-P requires a low sample volume and is performed on whole blood. Another advantage is the opportunity to ship blood samples at room temperature to a central core laboratory. Ultimately, it correlates well with light transmittance aggregometry and VerifyNow technologies. However, sample preparation is time consuming and the reliability of the results is highly dependent from the presence of a skilled technician. Also, a flow cytometer is required.