Supplementary Material for: Influence of Cyclooxygenase-1 Genotype on ex vivo Aspirin Response in Patients at Risk for Stroke

Background: We sought to determine whether cyclooxygenase-1 (PTGS1) genotype is associated with the ability of aspirin to inhibit platelet aggregation in patients at risk for stroke. Methods: Blood and urine samples were collected from 60 subjects, including 28 African Americans, who were taking aspirin for primary or secondary stroke prevention. Samples were analyzed for the PTGS1 A–707G, PTGS1 P17L, and glycoprotein IIIa (ITGB3)P1^A1/A2 genotypes, ex-vivo platelet aggregation, serum cholesterol, plasma salicylate levels, and urinary 11-dehydrothromboxane B₂ (11-dhTxB₂) concentrations. The association between PTGS1 A–707G and P17L genotypes and aspirin response, as assessed by ex vivo studies and 11-dhTxB₂ concentrations, was evaluated by statistical testing and nonlinear mapping. Results: Salicylate concentrations, ITGB3 genotype distribution and 11-dhTxB₂ concentrations were similar among PTGS1 genotype groups. More subjects with the PTGS1 17PP versus PL genotype had incomplete ex-vivo inhibition of platelet aggregation by aspirin (57 vs. 20%; p = 0.04). Fifty-nine percent of subjects homozygous for both the PTGS –707A and 17P alleles, but none with both the PTGS1 –707G and 17L alleles had incomplete inhibition with aspirin; p = 0.04. Similarly, nonlinear mapping showed a direct relationship between the PTGS1 17P allele and decreased aspirin response. When analyzed separately by ethnicity, the association with the P17L genotype and aspirin response persisted in African Americans, but not Caucasians. Conclusions: Our data suggest that the PTGS1 P17L genotype contributes to response to aspirin as assessed by ex-vivo platelet aggregation. Our data further suggest that the association between PTGS1 genotype and aspirin response might vary by ethnicity.