Insensitivity to the α2-adrenergic receptor blocker yohimbine hydrochloride and occurrence of spontaneous platelet macroaggregation (SPMA) in diabetes

Incidence and characteristics of spontaneous platelet macro-aggregation in acute ischemic stroke

Spontaneous platelet aggregation is a trigger for additional development of larger thrombi. Micro-aggregation is observed in 10% of diabetes approximately and blocked by P2Y12 inhibitors, whereas macro-aggregation is associated with overexpression of platelet α₂-adrenoreceptors and is not blocked by conventional anti-platelet medicines. We examined the incidence of spontaneous platelet macro-aggregation (SPMA) in acute ischemic stroke and analyzed its clinical characteristics. Out of 665 consecutive acute ischemic strokes, SPMA was found in 10 patients (1.5%, one tenth of micro-aggregation) despite no detection in 588 control subjects. Types of ischemic stroke were 4 atherothrombotic, 4 cardioembolic, and 2 lacunar strokes. Stroke with SPMA exhibited higher (worse) values of modified Rankin Scales (mRS) at discharge (3.00 ± 0.53 vs 1.93 ± 0.07, p = 0.042 by Wilcoxon) compared with stroke without SPMA despite no difference at admission. The proportion of patients who were functionally independent (score 0-2 on the mRS) at discharge was lower in stroke with SPMA compared with stroke without SPMA (p < 0.05 by chi-square test; OR 3.60, 95% CI 1.08-12.03; RR 2.04, 95% CI 1.05-2.86). It was intriguing that severe (high magnitude) SPMA was observed in 4 atherothrombotic stroke. Although anti-platelet therapy underwent, the proportion of atherothrombotic patients who were functionally improved and independent at discharge was lower in the presence of SPMA compared with the absence of SPMA (p < 0.05 by chi-square test). The patients with SPMA were more likely to be older, having major disabilities, being less functionally improved during hospitalization, and being less functionally independent at discharge.

Platelet responsiveness to yohimbine hydrochloride and MRS2179 in the context of the interaction between collagen and epinephrine in acute coronary syndrome

Acute coronary syndrome (ACS) covers a spectrum of clinical conditions ranging from unstable angina, Non-ST segment elevation myocardial infarction (NSTEMI), or ST segment elevation myocardial infarction (STEMI). This study encompasses patients with acute coronary syndrome, who were receiving the dual antiplatelet therapy of aspirin and clopidogrel. The focus of the study was to gain insight into the role of selective P2Y1 antagonism using MRS2179 in such cases as well as its effects, if any, on collagen-epinephrine interaction. All the cases showed greater potency of inhibition of the interaction when yohimbine hydrochloride (YH), a blocker of alpha2A-adrenoreceptor, was used compared to MRS2179, a P2Y1 antagonist, although there was variability in responsiveness to the antiplatelet drugs. These findings indicate that alpha2A-adrenoreceptors of platelets in this group play a major role in precipitating the interactive effect of collagen and epinephrine. The dose-response effect as studied by platelet aggregometry showed that the required molar concentration to block the interactive effect in the case of YH was less than that of MRS2179. Hence, it is postulated that although there may be an impairment of collagen-induced aggregation by MRS2179, the interactive effect of collagen-epinephrine may not be impaired by MRS2179 as efficaciously as YH.