Genetic determinants of drug response in heart failure

Toxicogenetics: population-based testing of drug and chemical safety in mouse models

The rapid decline in the cost of dense genotyping is paving the way for new DNA sequence-based laboratory tests to move quickly into clinical practice, and to ultimately help realize the promise of 'personalized' therapies. These advances are based on the growing appreciation of genetics as an important dimension in science and the practice of investigative pharmacology and toxicology. On the clinical side, both the regulators and the pharmaceutical industry hope that the early identification of individuals prone to adverse drug effects will keep advantageous medicines on the market for the benefit of the vast majority of prospective patients. On the environmental health protection side, there is a clear need for better science to define the range and causes of susceptibility to adverse effects of chemicals in the population, so that the appropriate regulatory limits are established. In both cases, most of the research effort is focused on genome-wide association studies in humans where de novo genotyping of each subject is required. At the same time, the power of population-based preclinical safety testing in rodent models (e.g., mouse) remains to be fully exploited. Here, we highlight the approaches available to utilize the knowledge of DNA sequence and genetic diversity of the mouse as a species in mechanistic toxicology research. We posit that appropriate genetically defined mouse models may be combined with the limited data from human studies to not only discover the genetic determinants of susceptibility, but to also understand the molecular underpinnings of toxicity.

High loading dose of clopidogrel is unable to satisfactorily inhibit platelet reactivity in patients with glycoprotein IIIA gene polymorphism: a genetic substudy of PRAGUE-8 trial

The study aimed to assess the impact of nine polymorphisms of genes encoding platelet receptors, enzymes, and hemostatic factors on clopidogrel efficacy to inhibit platelet reactivity in patients with stable coronary artery disease undergoing elective coronary angiography either with or without ad hoc percutaneous coronary intervention. The study was performed as a genetic substudy of the PRAGUE-8 trial. Ninety-five patients pretreated with 600 mg clopidogrel at least 6 h prior to coronary angiography were tested. Baseline platelet reactivity to ADP was assessed before the drug was administered. Clopidogrel efficacy was tested again at 12 and 28 h after administration. Polymorphisms of platelet receptors, glycoprotein (GP) Ia (807C/T), GPVI (13254C/T), GPIIIa (PlA1/PlA2), PAR-1 (IVSn-14A/T), P2Y12 (32C/T), P2Y12 (H1/H2) haplotype, gene variations of cyclooxygenase-1, Leiden, and factor II mutations were studied. Flow cytometric tests of vasodilator-stimulated phosphoprotein phosphorylation states were used as a measure of drug efficacy. None of the gene polymorphisms influenced baseline ADP-induced platelet reactivity significantly. Twenty-eight hours after drug administration, differences in suppression of ADP-induced platelet reactivity were observed between polymorphism-positive and polymorphism-negative patients. Inhibition of platelet reactivity, after 600 mg of clopidogrel, was significantly less in carriers of PlA2 (P=0.009) for mean decrease in platelet reactivity index. The proportion of clopidogrel nonresponders (platelet reactivity index >50%) was apparently higher in PlA2 carriers in comparison with PlA1/PlA1 patients (54 vs. 24%, P=0.082). A 600 mg loading dose of clopidogrel failed to acceptably inhibit platelet reactivity in patients who were positive for the PlA2 polymorphism.