Genetic variability in response to clopidogrel therapy and its clinical implications

The Intriguing Relationships of von Willebrand Factor, ADAMTS13 and Cardiac Disease

von Willebrand factor (VWF) is an adhesive protein involved in primary hemostasis and facilitates platelet adhesion to sites of vascular injury, thereby promoting thrombus formation. VWF exists in plasma as multimers of increasing size, with the largest (high molecular weight; HMW) expressing the greatest functional activity. A deficiency of VWF is associated with a bleeding disorder called von Willebrand disease (VWD), whereas an excess of VWF, in particular the HMW forms, is associated with thrombosis. ADAMTS13 (a disintegrin and metalloproteinase with thrombospondin type 1 motif-13), also known as VWF-cleaving protease, functions to moderate the activity of VWF by cleaving multimers of VWF and limiting the expression of the largest multimers of VWF. A deficiency of ADAMTS13 is therefore associated with an excess of (HMW forms of) VWF, and thus thrombosis. Indeed, any disturbance of the VWF/ADAMTS13 ratio or ‘axis’ may be associated with pathophysiological processes, including prothrombotic tendency. However, both thrombosis or bleeding may be associated with such disturbances, depending on the presenting events. This review evaluates the relationship of VWF and ADAMTS13 with cardiac disease, including cardiac failure, and associated pathophysiology.

Predictive Value of Methods Measuring Platelet Activation for Ischemic Events in Patients Receiving Clopidogrel: A Systematic Review and Meta-analysis

This study investigates the efficiency and predictive value of light-transmission aggregometry (LTA), vasodilator-stimulated phosphoprotein (VASP) and VerifyNow for ischemia in patients undergoing percutaneous coronary intervention (PCI). Studies that used LTA, VASP or VerifyNow to predict ischemia were included, and their quality and efficiency were analyzed using Review Manager 5.3. The sensitivity and specificity of subgroup studies based on the outcome, cut-off value, and follow-up days were calculated and the summary ROC (sROC) curves were compared after having been fitted. Thirty-one studies including a total of 17,314 participants were analyzed. LTA, VASP and VerifyNow presented a considerable efficiency in predicting ischemic clinical events. In the subgroup analysis, the sensitivities of LTA, VASP and VerifyNow in predicting cardiac death, all-cause death, myocardial infarction, stent thrombosis, stroke, and revascularization were 0.40/0.63/0.62, 0.47/0.56/0.39, 0.40/0.48/0.60, 0.44/0.58/0.70, 0.29/not applicable/0.60 and 0.44/0.57/0.37, respectively and the specificities of LTA, VASP, and VerifyNow were 0.85/0.48/0.63, 0.73/0.52/0.63, 0.74/0.55/0.64, 0.75/0.47/0.61, 0.72/not applicable/ 0.61, and 0.70/0.47/0.67, respectively. LTA showed a higher sensitivity in predicting the outcomes over six months than those within six months, while VerifyNow prediction sensitivity was found to be higher within six months. Meanwhile, VerifyNow showed no statistically significant higher AUC of sROC in comparison to LTA and VASP in predicting ischemic events in patients undergoing clopidogrel treatment. The cut-off values of LTA, VASP and VerifyNow were suggested to be 56%, 50% and 235 respectively according to our study.

P2Y12-receptor-inhibiting antiplatelet strategies in acute coronary syndromes

Antiplatelet therapy in acute coronary syndromes is essential for preventing stent thrombosis and for reducing major adverse cardiovascular events. Treatment strategy has changed over the last years by frequent use of more active agents inhibiting the ADP mediated activation of platelets instead of clopidogrel, such as prasugrel and ticagrelor. Compared to clopidogrel these modern antiplatelet drugs showed a significant reduction of efficacy endpoints as well as an acceptable safety profile in large multicenter randomized trials (TRITON TIMI 38, PLATO). Going in with higher efficacy a generally higher bleeding risk of prasugrel could be reduced by optimizing the maintenance dose in elderly and underweight patients (TRILOGY-ACS). However even prasugrel and ticagrelor have shown a delayed onset of action in special patient populations (e.g. STEMI) suggesting that the optimal ADP inhibitor has not been found yet. Results of the CHAMPION PHOENIX trial indicate that cangrelor, an intravenous agent, might fulfill these high expectations of an ideal platelet inhibitor in the first hours of an ACS in special patient cohorts. This review summarizes the results of most important clinical studies investigating the novel P2Y12 receptor inhibiting antiplatelet drugs.

Oral antiplatelet therapy in acute coronary syndromes: update 2012

Dual antiplatelet therapy (DAPT), usually consisting of clopidogrel and acetylsalicylic acid (ASA), has come into discussion in recent years due to an increasing number of major adverse cardiac events based on insufficient ADP-mediated platelet inhibition with clopidogrel, mainly explained by drug interactions or genetic variants slowing or hindering the bioactivation of the prodrug clopidgrel into an active metabolite. Accordingly, new antiplatelet agents like prasugrel and ticagrelor were investigated in large prospective randomized clinical trials in patients with different entities of acute coronary syndromes (ACS). Based on their beneficial results in comparison to clopidogrel, these agents have found their way into the recent international guidelines for treatment of patients with acute coronary syndromes. Both antiplatelet agents demonstrated superiority with respect to the primary composite endpoint (cardiovascular death/non-lethal myocardial infarction/stroke). Ticagrelor even exhibited a mortality benefit over the comparator, but both compounds also increased the risk of spontaneous major bleedings to a significant extent. However, the efficacy/safety ratio of prasugrel and ticagrelor compared to clopidogrel is better. This article widens the insight into the recent changes in antiplatelet therapy in ACS by discussing the clinically most important data derived from the TRITON-TIMI 38 trial and the PLATO trial, including also the retrospective and pre-defined subgroup analyses. This article also gives information about the recommended duration of DAPT and the situation when patients who need permanent anticoagulation (e.g. in case of non-valvular atrial fibrillation) deserve also DAPT after coronary stenting ('triple therapy').

CYP2C19*2/ABCB1-C3435T polymorphism and risk of cardiovascular events in coronary artery disease patients on clopidogrel: is clinical testing helpful?

BACKGROUND

Studies evaluating CYP2C19*2 and ABCB1-C3435T polymorphisms have shown conflicting results. We performed this meta-analysis to evaluate role of clinical testing for these polymorphisms in CAD patients on clopidogrel.

METHODS

19,601 patients from 14 trials were analyzed. The endpoints were major adverse cardiovascular events (MACE), cardiovascular (CV) death, stent thrombosis (ST), myocardial infarction (MI), stroke and major bleeding. Combined relative risks (RR) with 95% confidence intervals (CI) were computed for each outcome by using standard methods of meta-analysis and test parameters were computed.

RESULTS

CYP2C19*2 polymorphism was associated with higher risk of MACE [RR: 1.28, CI: 1.06-1.54; p=0.009], CV death [RR: 3.21, CI: 1.65-6.23; p=0.001], MI [RR: 1.36, CI: 1.12-1.65; p=0.002], ST [RR: 2.41, CI: 1.69-3.41; p<0.001]. No difference was seen in major bleeding events [RR: 1.02, CI: 0.86-1.20; p=0.83]. Subgroup analysis showed similar results for elective PCI [RR: 1.34, CI: 1.01-1.76; p=0.03], and PCI with DES [RR: 1.53, CI: 1.029-1.269; p=0.03]. CYP2C19*2 polymorphism has very low sensitivity (28-58%), specificity (71-73%), positive predictive value (3-10%) but good negative predictive value (92-99%). ABCB1-C3435T polymorphism analysis revealed similar MACE [RR: 1.13, CI: 0.99-1.29; p=0.06], ST [RR: 0.88, CI: 0.52-1.47; p=0.63] and major bleeding [RR: 1.04, CI: 0.87-1.25; p=0.62] in both groups.

CONCLUSION

In CAD patients on clopidogrel therapy, CYP2C19*2 polymorphism is associated with significantly increased adverse cardiovascular events. However, due to the low positive predictive value, routine genetic testing cannot be recommended at present.