Greater Collagen-Induced Platelet Aggregation Following Cyclooxygenase 1 Inhibition Predicts Incident Acute Coronary Syndromes Rehan Qayyum, M.D.1, Diane M. Becker, Sc.D.1, Lisa R. Yanek, M.P.H.1, Nauder Faraday, M.D.2, Dhananjay Vaidya, Ph.D.1, Rasika Mathias, Sc.D.1, Brian G. Kral, M.D.1, and Lewis C. Becker, M.D.1 Abstract Greater ex vivo platelet aggregation to agonists may identify individuals at risk of acute coronary syndromes (ACS). However, increased aggregation to a specific agonist may be masked by inherent variability in other activation pathways. In this study, we inhibited the cyclooxygenase-1 (COX1) pathway with 2-week aspirin therapy and measured residual aggregation to collagen and ADP to determine whether increased aggregation in a non-COX1 pathway is associated with incident ACS. We assessed ex vivo whole blood platelet aggregation in 1,699 healthy individuals with a family history of early-onset coronary artery disease followed for 6±1.2 years. Incident ACS events were observed in 22 subjects. Baseline aggregation was not associated with ACS. After COX1 pathway inhibition, collagen-induced aggregation was significantly greater in participants with ACS compared with those without (29.0 vs. 23.6 ohms, p < 0.001). In Cox proportional hazards models, this association remained significant after adjusting for traditional cardiovascular risk factors (HR = 1.10, 95%CI = 1.06–1.15; p < 0.001). In contrast, ADP-induced aggregation after COX1 inhibition was not associated with ACS. After COX1 pathway inhibition, subjects with greater collagen-induced platelet aggregation demonstrated a significant excess risk of incident ACS. These data suggest that platelet activation related to collagen may play an important role in the risk of ACS. Clin Trans Sci 2015; Volume 8: 17–22
Keywords: platelet aggregation, acute coronary syndromes, aspirin, collagen Introduction
Acute coronary syndromes (ACS) are the most common presentation of coronary artery disease (CAD). 1 Platelet activation with subsequent thrombus formation in the culprit coronary artery most likely creates the ultimate substrate for ACS.2 Given the thrombotic nature of ACS, greater in vitro platelet aggregability might be expected to be associated with incident ACS in populations at increased risk. Although some studies have attempted to examine associations between spontaneous and agonist-induced platelet aggregation and incident CAD in preclinical populations, these studies are plagued by design flaws such as limited platelet aggregation phenotyping, mixed cardiovascular disease phenotypes, and small sample sizes, resulting in a strong bias toward the null.3–9 Thus, few if any studies have examined this premise in an initially healthy population with robust designs and sufficient sample sizes. Certainly, antiplatelet agents are highly successful in the prevention of ACS, highlighting the essential role that platelets play in the pathogenesis of atherothrombotic disease events.10 Examining whether CAD events can be predicted by the extent of platelet aggregation to different agonists in a preclinical population thus remains an open question worthy of query given the widespread use of antiplatelet agents for primary prevention. We have previously reported significant interindividual variation in ex vivo platelet function in activation pathways related to known agonists including collagen, ADP, and thromboxane.11,12 In addition, we have followed individuals with measured ex vivo platelet aggregation phenotypes for the development of a first ACS event. Our aim was thus to examine the association of incident ACS with agonist-specific platelet aggregability in individuals who were free of CAD at baseline. We further hypothesized that blocking the cyclooxygenase 1 (COX1) pathway, which is responsible for the potent well-known thromboxane-dependent feedback
activation, might unmask variability in other pathways that are related to incident CAD events. Specifically, we determined whether greater platelet aggregation to collagen or ADP after COX1 inhibition with aspirin could identify individuals at risk of developing incident ACS from a population of healthy subjects with a family history of early-onset CAD.13 This population is particularly salient to the research question given their higher than average risk status and the large number of persons already taking aspirin for primary prevention. Methods
Study Sample: The study population consisted of 1,699 subjects who had participated in the Genetic Study of Aspirin Responsiveness (GeneSTAR) between 2003 and 2006. The detailed description of the GeneSTAR study design has been previously published.12,14 Briefly, healthy family members of probands with documented CAD events before 60 years of age, including siblings, adult offspring of probands and siblings, and the coparents of all adult offspring were enrolled. Eligible participants were initially free of CAD, cerebrovascular disease, peripheral vascular disease, bleeding disorders, or serious gastrointestinal disorders. Individuals were excluded if they were aspirin intolerant, had a history of aspirin allergy, abnormal blood counts (platelet count 500,000 per μL, hematocrit 20,000 per μL) or were taking aspirin, other antiplatelet agents, or anticoagulants that could not be safely discontinued for 2 weeks. The trial was approved by the Institutional Review Board of the Johns Hopkins University School of Medicine and was monitored by a data and safety monitoring board appointed by the National Heart, Lung and Blood Institute. Written informed consent was obtained from all participants.
GeneSTAR Research Program, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA ; 2Department of Anesthesiology and Critical Care Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA .
1
Correspondence: Rehan Qayyum ([email protected]) DOI: 10.1111/cts.12195
WWW.CTSJOURNAL.COM
VOLUME 8 • ISSUE 1
17
Qayyum et al. Platelet Aggregation after COX1 Blockade and ACS ■
Data collection: Age, sex, and race were determined by selfreport. All participants underwent a detailed medical history and physical examination. Subjects brought all prescription and over the counter medications with them for review, and a detailed medication history was assessed. Blood pressure was measured at rest with the patient seated and hypertension was defined as the average of 4 blood pressure measurements >140/90 mmHg and/or the use of antihypertensive medication. Current cigarette smoking was defined as any self-reported smoking within the past 30 days; nonsmoking status was verified by exhaled carbon monoxide levels >8 ppm. Serum glucose, total cholesterol, high-density lipoprotein cholesterol, and triglyceride levels were measured in the Clinical Chemistry Laboratory. Low-density lipoprotein cholesterol levels were estimated with the Friedewald formula15 for triglyceride levels 50% stenosis of coronary arteries on an angiogram, and 8 were stable or chronic angina. In the primary analysis, subjects with non-ACS events were combined with those without any events, but the analyses were also repeated after elimination of subjects with non-ACS events. At baseline and before COX1 inhibition with aspirin, individuals who developed ACS and those who did not had similar collagen, arachidonic acid, and ADP-induced platelet aggregation. After COX1 inhibition, there were no differences in ADP- or arachidonic acid-induced platelet aggregation between individuals who developed ACS and those who did not. There were only 111 (6.5%) subjects with any measureable aggregation to arachidonic acid following aspirin, consistent with potent suppression of the COX1 pathway in nearly all subjects. Only one of these 111 individuals had an ACS event during follow-up (0.9%). Collagen-induced aggregation was greater in individuals who developed ACS during follow-up than in those who did not (29.0±6.5 vs 23.6±7.0 ohms, p < 0.001). The results were the same when subjects with non-ACS events were combined with those without any events or when 12 subjects with non-ACS events were eliminated from the analysis. When examined across tertiles of collagen-induced platelet aggregation after COX1 inhibition, a graded relationship was seen between platelet aggregation and incidence of ACS (N = 1, 8, 13 events in first, second, and third tertile respectively). The incidence of ACS, per 1,000 person-years, was only 0.3 events in the first tertile compared to 4.25 events in the third tertile (Figure 1). Compared to the first tertile, participants in the third tertile WWW.CTSJOURNAL.COM
Qayyum et al. Platelet Aggregation after COX1 Blockade and ACS ■
No ACS (N = 1677)
ACS (N = 22)
p Value
Age (years)
42.7 (12.2)
53.0 (10.6)
Keywords: platelet aggregation, acute coronary syndromes, aspirin, collagen Introduction
Acute coronary syndromes (ACS) are the most common presentation of coronary artery disease (CAD). 1 Platelet activation with subsequent thrombus formation in the culprit coronary artery most likely creates the ultimate substrate for ACS.2 Given the thrombotic nature of ACS, greater in vitro platelet aggregability might be expected to be associated with incident ACS in populations at increased risk. Although some studies have attempted to examine associations between spontaneous and agonist-induced platelet aggregation and incident CAD in preclinical populations, these studies are plagued by design flaws such as limited platelet aggregation phenotyping, mixed cardiovascular disease phenotypes, and small sample sizes, resulting in a strong bias toward the null.3–9 Thus, few if any studies have examined this premise in an initially healthy population with robust designs and sufficient sample sizes. Certainly, antiplatelet agents are highly successful in the prevention of ACS, highlighting the essential role that platelets play in the pathogenesis of atherothrombotic disease events.10 Examining whether CAD events can be predicted by the extent of platelet aggregation to different agonists in a preclinical population thus remains an open question worthy of query given the widespread use of antiplatelet agents for primary prevention. We have previously reported significant interindividual variation in ex vivo platelet function in activation pathways related to known agonists including collagen, ADP, and thromboxane.11,12 In addition, we have followed individuals with measured ex vivo platelet aggregation phenotypes for the development of a first ACS event. Our aim was thus to examine the association of incident ACS with agonist-specific platelet aggregability in individuals who were free of CAD at baseline. We further hypothesized that blocking the cyclooxygenase 1 (COX1) pathway, which is responsible for the potent well-known thromboxane-dependent feedback
activation, might unmask variability in other pathways that are related to incident CAD events. Specifically, we determined whether greater platelet aggregation to collagen or ADP after COX1 inhibition with aspirin could identify individuals at risk of developing incident ACS from a population of healthy subjects with a family history of early-onset CAD.13 This population is particularly salient to the research question given their higher than average risk status and the large number of persons already taking aspirin for primary prevention. Methods
Study Sample: The study population consisted of 1,699 subjects who had participated in the Genetic Study of Aspirin Responsiveness (GeneSTAR) between 2003 and 2006. The detailed description of the GeneSTAR study design has been previously published.12,14 Briefly, healthy family members of probands with documented CAD events before 60 years of age, including siblings, adult offspring of probands and siblings, and the coparents of all adult offspring were enrolled. Eligible participants were initially free of CAD, cerebrovascular disease, peripheral vascular disease, bleeding disorders, or serious gastrointestinal disorders. Individuals were excluded if they were aspirin intolerant, had a history of aspirin allergy, abnormal blood counts (platelet count 500,000 per μL, hematocrit 20,000 per μL) or were taking aspirin, other antiplatelet agents, or anticoagulants that could not be safely discontinued for 2 weeks. The trial was approved by the Institutional Review Board of the Johns Hopkins University School of Medicine and was monitored by a data and safety monitoring board appointed by the National Heart, Lung and Blood Institute. Written informed consent was obtained from all participants.
GeneSTAR Research Program, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA ; 2Department of Anesthesiology and Critical Care Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA .
1
Correspondence: Rehan Qayyum ([email protected]) DOI: 10.1111/cts.12195
WWW.CTSJOURNAL.COM
VOLUME 8 • ISSUE 1
17
Qayyum et al. Platelet Aggregation after COX1 Blockade and ACS ■
Data collection: Age, sex, and race were determined by selfreport. All participants underwent a detailed medical history and physical examination. Subjects brought all prescription and over the counter medications with them for review, and a detailed medication history was assessed. Blood pressure was measured at rest with the patient seated and hypertension was defined as the average of 4 blood pressure measurements >140/90 mmHg and/or the use of antihypertensive medication. Current cigarette smoking was defined as any self-reported smoking within the past 30 days; nonsmoking status was verified by exhaled carbon monoxide levels >8 ppm. Serum glucose, total cholesterol, high-density lipoprotein cholesterol, and triglyceride levels were measured in the Clinical Chemistry Laboratory. Low-density lipoprotein cholesterol levels were estimated with the Friedewald formula15 for triglyceride levels 50% stenosis of coronary arteries on an angiogram, and 8 were stable or chronic angina. In the primary analysis, subjects with non-ACS events were combined with those without any events, but the analyses were also repeated after elimination of subjects with non-ACS events. At baseline and before COX1 inhibition with aspirin, individuals who developed ACS and those who did not had similar collagen, arachidonic acid, and ADP-induced platelet aggregation. After COX1 inhibition, there were no differences in ADP- or arachidonic acid-induced platelet aggregation between individuals who developed ACS and those who did not. There were only 111 (6.5%) subjects with any measureable aggregation to arachidonic acid following aspirin, consistent with potent suppression of the COX1 pathway in nearly all subjects. Only one of these 111 individuals had an ACS event during follow-up (0.9%). Collagen-induced aggregation was greater in individuals who developed ACS during follow-up than in those who did not (29.0±6.5 vs 23.6±7.0 ohms, p < 0.001). The results were the same when subjects with non-ACS events were combined with those without any events or when 12 subjects with non-ACS events were eliminated from the analysis. When examined across tertiles of collagen-induced platelet aggregation after COX1 inhibition, a graded relationship was seen between platelet aggregation and incidence of ACS (N = 1, 8, 13 events in first, second, and third tertile respectively). The incidence of ACS, per 1,000 person-years, was only 0.3 events in the first tertile compared to 4.25 events in the third tertile (Figure 1). Compared to the first tertile, participants in the third tertile WWW.CTSJOURNAL.COM
Qayyum et al. Platelet Aggregation after COX1 Blockade and ACS ■
No ACS (N = 1677)
ACS (N = 22)
p Value
Age (years)
42.7 (12.2)
53.0 (10.6)
