Ticagrelor responsive platelet genes are associated with platelet function and bleeding
Authors: Myers Rachel A , Ortel Thomas L , Waldrop Alexander , Dave Sandeep , Ginsburg Geoffrey S , Voora Deepak 
Published: March 2022

Structured AbstractImportanceTicagrelor inhibits platelet function, prevents myocardial infarction, and causes bleeding. A comprehensive analysis of the on- and off-target platelet effects of ticagrelor that underlie its clinical effects is lacking.ObjectiveTo test the hypothesis that platelet transcripts that change in response to ticagrelor exposure are associated with platelet function or bleeding.DesignA discovery cohort of healthy volunteers were sequentially exposed to aspirin, aspirin washout, and ticagrelor. Messenger RNA sequencing (mRNAseq) of purified platelets was performed pre/post each exposure. We defined the ticagrelor exposure signature (TES) as the ratio of mean expression of up-vs. down-regulated genes by ticagrelor that were prioritized based on lasso regression, weighted gene co-expression networks, and isoform level analyses. A separate healthy cohort was recruited to validate ticagrelor’s effects on TES genes measured using Nanostring. Platelet function was measured at baseline and in response to ticagrelor exposure in all participants. Self-reported bleeding was systematically queried during periods of ticagrelor exposure.SettingAn early phase, academic, clinical research unit.ParticipantsSelf-reported, healthy volunteers age > 30 and < 75, non-smoking, taking no daily prescribed medications.ExposuresTicagrelor (90 mg twice daily) and aspirin (81 mg/day and 325 mg/day) each for 4 weeks.Main outcomes and measuresExpression levels of platelet messenger RNA, platelet count, mean platelet volume, and 9 different measures of ex vivo platelet function (aggregated into a previously described platelet function score), and self-reported bleeding at baseline and after each exposure.ResultsIn the discovery cohort (n = 58, mean age 43, 39 female) platelet mRNAseq identified (FDR < 5%) 1820 up- and 1589 down-regulated genes associated with ticagrelor exposure. We prioritized 84 of these transcripts to calculate a TES score, which was increased by ticagrelor and unaffected by either dose of aspirin. In an independent cohort (n = 49, mean age 44, 24 female) we validated that ticagrelor exposure (beta = 0.48, SE = 0.08, p < 0.0001) increases TES scores. In combined analyses of discovery and validation cohorts, when TES levels were calculated using baseline platelet RNA, higher TES levels were associated with lower levels of baseline platelet function (meta-analysis beta = -0.60, standard error [SE] 0.29, P = 0.04) and self-reported bleeding during ticagrelor exposure (meta-analysis beta = 0.28, standard error [SE] = 0.14, P = 0.04). In contrast, we found no associations between bleeding with baseline platelet count, platelet volume, or platelet function.Conclusions and RelevanceTicagrelor exposure reproducibly and specifically changes a set of platelet transcripts, the baseline levels of which are a biomarker for platelet function and bleeding tendency on ticagrelor.Key PointsQuestionWhat are the global effects of ticagrelor exposure on platelets beyond platelet inhibition?FindingsIn an experimental human study of different antiplatelet therapies, we comprehensively characterized the effects of ticagrelor on platelet messenger RNA (mRNA). We found that 4 weeks of 90mg twice daily ticagrelor therapy specifically and reproducibly changes the levels of selected platelet mRNA. At baseline, volunteers with levels of platelet gene expression that mimic ticagrelor exposure had lower levels of platelet function and when exposed to ticagrelor a greater tendency for minor bleeding.MeaningBy using ticagrelor exposure as a molecular probe, we identified a platelet RNA biomarker that may identify patients at higher risk for ticagrelor-associated bleeding.