Keith Tanner

The functional G143E variant of carboxylesterase 1 is associated with increased clopidogrel active metabolite levels and greater clopidogrel response

Introduction Carboxylesterase 1 (CES1) is the primary enzyme responsible for converting clopidogrel into biologically inactive carboxylic acid metabolites. Methods We genotyped a functional variant in CES1, G143E, in participants of the Pharmacogenomics of Anti-Platelet Intervention (PAPI) study (n=566) and in 350 patients with coronary heart disease treated with clopidogrel, and carried out an association analysis of bioactive metabolite levels, on-clopidogrel ADP-stimulated platelet aggregation, and cardiovascular outcomes. Results The levels of clopidogrel active metabolite were significantly greater in CES1 143E-allele carriers (P=0.001). Consistent with these findings, individuals who carried the CES1 143E-allele showed a better clopidogrel response as measured by ADP-stimulated platelet aggregation in both participants of the PAPI study (P=0.003) and clopidogrel-treated coronary heart disease patients (P=0.03). No association was found between this single nucleotide polymorphism and baseline measures of platelet aggregation in either cohort. Conclusion Taken together, these findings suggest, for the first time, that genetic variation in CES1 may be an important determinant of the efficacy of clopidogrel.

Paraoxonase 1 (PON1) Gene Variants Are Not Associated With Clopidogrel Response

A common functional variant in paraoxonase 1 (PON1), Q192R, was recently reported to be a major determinant of clopidogrel response. This variant was genotyped in 566 participants of the Amish Pharmacogenomics of Anti–Platelet Intervention (PAPI) study and in 227 percutaneous coronary intervention (PCI) patients. Serum paraoxonase activity was measured in a subset of 79 PAPI participants. PON1 Q192R was not associated with pre– or post–clopidogrel platelet aggregation in the PAPI study (P = 0.16 and P = 0.21, respectively) or the PCI cohort (P = 0.47 and P = 0.91, respectively). The Q192 allele was not associated with cardiovascular events (hazard ratio (HR) 0.46, 95% confidence interval (CI) 0.20–1.06; P = 0.07). No correlation was observed between paraoxonase activity and post–clopidogrel platelet aggregation (r2 < 0.01, P = 0.78). None of 49 additional PON1 variants evaluated was associated with post–clopidogrel platelet aggregation. These findings do not support a role for PON1 as a determinant of clopidogrel response.

Genetic Variation in PEAR1 Is Associated With Platelet Aggregation and Cardiovascular Outcomes

Background—Aspirin or dual antiplatelet therapy with aspirin and clopidogrel is a standard therapy for patients who are at increased risk for cardiovascular events. However, the genetic determinants of variable response to aspirin (alone and in combination with clopidogrel) are not known. Methods and Results—We measured ex vivo platelet aggregation before and after dual antiplatelet therapy in individuals (n=565) from the Pharmacogenomics of Anti-Platelet Intervention (PAPI) Study and conducted a genome-wide association study of drug response. Significant findings were extended by examining genotype and cardiovascular outcomes in 2 independent aspirin-treated cohorts: 227 percutaneous coronary intervention patients and 1000 patients of the International Verapamil SR/Trandolapril Study (INVEST) Genetic Substudy (INVEST-GENES). Results from the genome-wide association study revealed a strong association between single-nucleotide polymorphisms on chromosome 1q23 and post–dual antiplatelet therapyplatelet aggregation. Further genotyping revealed rs12041331 in the platelet endothelial aggregation receptor-1 (PEAR1) gene to be most strongly associated with dual antiplatelet therapy response (P=7.66×10−9). In white and black patients undergoing percutaneous coronary intervention, A-allele carriers of rs12041331 were more likely to experience a cardiovascular event or death compared with GG homozygotes (hazard ratio, 2.62; 95% confidence interval, 0.96–7.10; P=0.059; and hazard ratio, 3.97; 95% confidence interval, 1.10–14.31; P=0.035, respectively). In aspirin-treated INVEST-GENES patients, rs12041331 A-allele carriers had significantly increased risk of myocardial infarction compared with GG homozygotes (odds ratio, 2.03; 95% confidence interval, 1.01–4.09; P=0.048). Conclusion—Common genetic variation in PEAR1 may be a determinant of platelet response and cardiovascular events in patients on aspirin alone or in combination with clopidogrel. Clinical Trial Registration—URL: http://www.clinicaltrials.gov. Unique identifiers: NCT00799396 and NCT00370045

Association between bilirubin and cardiovascular disease risk factors: using Mendelian randomization to assess causal inference

BackgroundElevated serum bilirubin has been associated with reduced risk of cardiovascular disease (CVD). However, serum bilirubin is also related with several potential confounders related to CVD, such as obesity. Mendelian randomization has been proposed as a method to address challenges to validity from confounding and reverse causality. It utilizes genotype to estimate causal relationships between a gene product and physiological outcomes. In this report, we demonstrate its use in assessing direct causal relations between serum bilirubin levels and CVD risk factors, including obesity, cholesterol, measures of vascular function and blood pressure.MethodsStudy subjects included 868 asymptomatic individuals. Study subjects were genotyped at the UGT1A1*28 locus, which is strongly associated with bilirubin levels.ResultsSerum bilirubin levels were inversely associated with levels of several cardiovascular disease risk factors, including body mass index (p = 0.003), LDL (p = 0.0005) and total cholesterol (p = 0.0002). In contrast, UGT1A1*28 genotype, a known cause of elevated bilirubin levels, was not significantly associated with any of these traditional CVD risk factors. We did observe an association between genotype and brachial artery diameter (p = 0.003) and cold pressor reactivity (p = 0.01).ConclusionsOur findings imply that the observed association of serum bilirubin levels with body mass index and cholesterol are likely due to confounding and suggest that previously established CVD benefits of increased bilirubin may in part be mediated by the early regulation of vascular structure and reactivity.

Circulating CD34+ Cell Count is Associated with Extent of Subclinical Atherosclerosis in Asymptomatic Amish Men, Independent of 10-Year Framingham Risk.

Background Bone-marrow derived progenitor cells (PCs) may play a role in maintaining vascular health by actively repairing damaged endothelium. The purpose of this study in asymptomatic Old Order Amish men (n = 90) without hypertension or diabetes was to determine if PC count, as determined by CD34+ cell count in peripheral blood, was associated with 10-year risk of cardiovascular disease (CVD) and measures of subclinical atherosclerosis. Methods and Results CD34+ cell count by fluorescence-activated cell sorting, coronary artery calcification (CAC) by electron beam computed tomography, and CVD risk factors were obtained. Carotid intimal-medial thickness (CIMT) also was obtained in a subset of 57 men. After adjusting for 10-year CVD risk, CD34+ cell count was significantly associated with CAC quantity (p =0.03) and CIMT (p < 0.0001). A 1-unit increase in natural-log transformed CD34+ cell count was associated with an estimated 55.2% decrease (95% CI: −77.8% to −9.3%) in CAC quantity and an estimated 14.3% decrease (95% CI: −20.1% to −8.1%) in CIMT. Conclusions Increased CD34+ cell count was associated with a decrease in extent of subclinical atherosclerosis in multiple arterial beds, independent of 10-year CVD risk. Further investigations of associations of CD34+ cell count with subclinical atherosclerosis in asymptomatic individuals could provide mechanistic insights into the atherosclerotic process.

Genome-wide analysis of clopidogrel active metabolite levels identifies novel variants that influence antiplatelet response.

Clopidogrel is one of the most commonly used therapeutics for the secondary prevention of cardiovascular events in patients with acute coronary syndromes. However, considerable interindividual variation in clopidogrel response has been documented, resulting in suboptimal therapy and an increased risk of recurrent events for some patients. In this investigation, we carried out the first genome-wide association study of circulating clopidogrel active metabolite levels in 513 healthy participants to directly measure clopidogrel pharmacokinetics. We observed that the CYP2C19 locus was the strongest genetic determinant of active metabolite formation (P=9.5×10). In addition, we identified novel genome-wide significant variants on chromosomes 3p25 (rs187941554, P=3.3×10) and 17q11 (rs80343429, P=1.3×10), as well as six additional loci that showed suggestive evidence of association (P≤1.0×10). Four of these loci showed nominal associations with on-clopidogrel ADP-stimulated platelet aggregation (P≤0.05). Evaluation of clopidogrel active metabolite concentration may help identify novel genetic determinants of clopidogrel response, which has implications for the development of novel therapeutics and improved antiplatelet treatment for at-risk patients in the future.

Epigenetic Signature of Impaired FastingGlucose in the Old Order Amish

Introduction Type 2 Diabetes (T2D) is a common chronic disease with substantial disease burden and economic impact. Lifestyle changes can significantly alter the course of the disease, if detected at an early stage. DNA methylation signature may serve as a biomarker for early detection of increased T2D risk. Design DNA methylation profiling was performed using the Illumina Infinium Human Methylation 450K Bead chip array in 24 normoglycemic Old Order Amish (OOA) individuals who later developed Impaired Fasting Glucose (IFG) (cases), and 24 OOA individuals who remained normoglycemic after an average follow up of 10 years (controls). Cases and controls were matched on age, sex, BMI, baseline fasting glucose, and glucose level after 2 h from 75 g Oral Glucose Tolerance Test (OGTT). Results Association analysis found no significant difference in either global methylation or individual probe methylation between cases and controls, however, the top 34 suggestive significant sites were located in genes with interesting biological links to T2D and glycemic traits. These genes include BTC that plays a role in pancreatic cell proliferation and insulin secretion, ITGA1 a known bone mineral density gene that was recently found to be associated also with T2D and glycemic traits, and may explain the link between T2D and BMD, and RPTOR and TSC2 both of which are part of insulin signaling pathway. Conclusions These results may shed light on the initiation and development of hyperglycemia and T2D and help to identify high risk individuals for early intervention; however, further studies are required for validation.