ELEVATED PLATELET-DERIVED MICROPARTICLE LEVELS DURING UNSTABLE ANGINA

OBJECTIVE: To use fluorescent-activated flow cytometry coupled with ac tivation-dependent and -independent platelet-specific monoclonal antib odies in a pilot study to assess the degree and time course of platele t activation events in patients presenting within 24 h of onset of Can adian Cardiovascular Society class 4 angina. BACKGROUND: Although acti vated platelets play a key role in the pathogenesis of unstable angina , the development of simple assays to quantify platelet activation eve nts directly is lacking. METHODS: Blood samples were drawn from six un stable angina patients from the coronary care every 4 h over a 24 h pe riod into a fixative adn analyzed the following day. All patients were on acetylsalicylic acid and heparin. Comparisons were made with six h ealthy, medication-free volunteers. Platelets were defined by flow cyt ometry as positive for fluorochrome-labelled monoclonal antibody to gl ycoprotein lb (API) and within the single intact platelet window defin ed be scatter characteristics. The presence of the fluorochrome-labell ed activation-specific monoclonal antibody (KC4.1 for anto-P-selectin, PAC-1 for activated glycoprotein IIb/IIIa) was used to determine micr oparticles were identified by gating on AP1-positive events and defini ng microparticles (percentage of total platelet events) as being small er (forward size scatter) than single intact platelets. RESULTS: There was a marked, sixfold increase in microparticles generation (17 +/- 7 % versus 2.8 +/- 1.4%) in the unstable angina patients (P = 0.001) com pared with healthy volunteers. Further assessment of six coronary care unit patients with nonischemic cardiac disorders demonstrated a highl y variable intermediate level of microparticle generation (11 +/- 7%). No differences in activated glycoprotein IIb/IIIa expression were not ed for the various groups and P-selectin expression was lower in the u nstable angina patients (6 +/- 2% versus 12 +/- 3%, P = 0.007). CONCLU SIONS: This pilot study suggests that measuring circulating platelet m icroparticle levels is a simple yet useful parameter for the assessmen t of platelet activation in unstable angina compared with activation m arkers on intact whole platelets. Despite antiplatelet and antithrombi n therapy, significant platelet activation occurred in these patients over the initial 24 h, flow cytometry may be a useful tool in assessin g the efficacy of newer therapeutic modalities.