Individual Platelet Adhesion (iPA): A novel assay of platelet function
Cardiovascular disease is the leading cause of mortality in the developed countries and platelet related thrombosis the main complication in this condition. Anti-platelet agents are commonly used in the prevention of acute cardiovascular events. According to the American Heart Association and the American College of Cardiology (Circulation 2012), a class IIb recommendation is given for the use of platelet function test. This approach has been implemented in several clinical trials in order to improve outcomes in cardiovascular patients . There are a number of platelet function tests available for clinical use but there is a lack of correlation between the different tests and none of them are routinely used to assess anti-platelet therapy effect. We report a rapid and accurate methodology to quantify platelet-protein interactions termed iPA. This novel technique contains a micro-array of 6-μm fibrinogen dots which can capture platelets from whole blood, one platelet per dot. The fractional occupancy of an array of fibrinogen dots after a predefined incubation time (specifically 30 minutes) quantitatively assays platelet adhesion to the protein matrix. We demonstrated that iPA enables detection of the effects of aspirin, P2Y12 inhibitors and αIIbβ3 receptor inhibitors in vitro. The mechanism of iPA to detect the effectiveness of anti-platelet therapy is based on a decrease of platelet adhesion upon addition of an agonist. An important factor to note regarding iPA is that in comparison to a fibrinogen coated array, the profile of platelet adhesion is different. On a static fibrinogen coated array platelet agonists would normally increase adhesion and spreading due to an increase in platelet activation. However the same is not true for iPA. Platelet activation induces aggregation and the aggregates thus are unable to bind during the assay. The reasoning behind these events is that firstly iPA is performed on a rocker, thus not allowing platelet aggregates to adhere gravitationally. Secondly the size of the dot is optimized to capture a single platelet. This agonist induced decrease in adhesion is inhibited by the specific anti-platelet drug and this is in fact the mechanism of detection.
To summarise, in iPA normal resting platelets adhere maximally. Platelets that are in the presence of a platelet inhibitor also adhere normally to the 6-μm fibrinogen dots. Platelets stimulated with agonists show a marked reduction in fibrinogen occupancy. Platelets in the presence of antagonists and agonists show an occupancy value that is dependent on the effectiveness of the anti-platelet agent over the agonist.
Furthermore we showed that iPA can specifically detect the effect of each drug in patients treated with these anti-platelet agents. iPA correlated well with the standard techniques of flow cytometry and light transmission aggregometry. Furthermore, iPA can be easily integrated with microfluidic platforms.
Overall it promises to be more effective and rapid in the assessment of drug effects of anti-platelet agents during the treatment of cardiovascular disease.