Racial differences in resistance to P2Y12 receptor antagonists in type 2 diabetic subjects.

Although resistance to the P2Y12 antagonist clopidogrel is linked to altered drug metabolism, some studies suggest that these pharmacokinetic abnormalities only partially account for drug resistance. To circumvent pharmacokinetic complications and target P2Y12 receptor function we applied the direct P2Y12 antagonist 2-methylthio-AMP (2-methylthioadenosine 5'-monophosphate triethylammonium salt) to purified platelets ex vivo. Platelets were purified from healthy and type 2 diabetes mellitus (T2DM) patients and stimulated with thrombin or the selective protease-activated receptor agonists, protease-activated receptor 1-activating peptide (PAR1-AP), or PAR4-AP. Platelet activation as measured by αIIbß3 activation, and P-selectin expression was monitored in 141 subjects. Our results demonstrate that, compared with healthy subjects, platelets from diabetic patients are resistant to inhibition by 2-methylthio-AMP, demonstrating P2Y12 pharmacodynamic defects among diabetic patients. Inhibition of thrombin-mediated αIIbß3 activation by 2-methylthio-AMP was lower in diabetic platelets versus healthy platelets. Subgroup analysis revealed a racial difference in the resistance to 2-methylthio-AMP. We found no resistance in platelets from diabetic African Americans; they were inhibited by 2-methylthio-AMP equally as well as platelets from healthy African Americans. In contrast, platelets from Caucasian patients with diabetes were resistant to P2Y12 antagonism compared with healthy Caucasians. Multivariable analysis demonstrated that other variables, such as obesity, age, or gender, could not account for the differential resistance to 2-methylthio-AMP among races. These results suggest that in addition to altered drug metabolism, P2Y12 receptor function itself is altered in the Caucasian diabetic population. The racial difference in platelet function in T2DM is a novel finding, which may lead to differences in treatment as well as new targets for antiplatelet therapy.

Dichotomous effects of exposure to bivalirudin in patients undergoing percutaneous coronary intervention on protease-activated receptor-mediated platelet activation.

Bivalirudin is a direct thrombin inhibitor that is increasingly used in percutaneous coronary intervention (PCI) and has been previously shown to lack inherent platelet activation. Thrombin works through activation of protease activated receptor-1 (PAR1) and PAR4 on human platelets to initiate signaling cascades leading to platelet aggregation. Despite the increasing usage of bivalirudin, the effects on platelet function have not been well defined. Bivalirudin exposure during PCI was therefore assessed for its potential short-term effects on washed platelet function through PAR1 and PAR4. Bivalirudin significantly inhibited low-dose thrombin-mediated platelet aggregation, dense granule secretion, integrin αIIbß3 activation and Rap1 activation and high dose thrombin-mediated dense granule secretion and Rap1 activation. Exposure to bivalirudin did not alter PAR1 or 4 agonist peptide (PAR1-AP or PAR4-AP) induced aggregation, dense granule secretion, integrin glycoprotein IIbIIIa activation or Rap1 activation. However, exposure to bivalirudin significantly potentiated surface expression of P-selectin following stimulation with high dose thrombin and PAR1-AP, and both low and high dose PAR4-AP. Hence, our data are the first to show that exposure to bivalirudin increased P-selectin expression with certain conditions demonstrating that bivalirudin can increase inherent platelet activity.

Novel inhibitors of the trypanosome alternative oxidase inhibit Trypanosoma brucei brucei growth and respiration.

African trypanosomiasis is a deadly disease for which few chemotherapeutic options are available. The causative agents, Trypanosoma brucei rhodesiense and T. b. gambiense, utilize a non-cytochrome, alternative oxidase (AOX) for their cellular respiration. The absence of this enzyme in mammalian cells makes it a logical target for therapeutic agents. We designed three novel compounds, ACB41, ACD15, and ACD16, and investigated their effects on trypanosome alternative oxidase (TAO) enzymatic activity, parasite respiration, and parasite growth in vitro. All three compounds contain a 2-hydroxybenzoic acid moiety, analogous to that present in SHAM, and a prenyl side chain similar to that found in ubiquinol. ACD15 and ACD16 are further differentiated by the presence of a solubility-enhancing carbohydrate moiety. Kinetic studies with purified TAO show that all three compounds competitively inhibit TAO, and two compounds, ACB41 and ACD15, have inhibition constants five- and three-fold more potent than SHAM, respectively. All three compounds inhibited the respiration and growth of continuously cultured T. b. brucei bloodstream cells in a dose-dependent manner. None of the compounds interfered with respiration of rat liver mitochondria, nor did they inhibit the growth of a continuously cultured mammalian cell line. Collectively, the results suggest we have identified a new class of compounds that are inhibitors of TAO, have trypanocidal properties in vitro, and warrant further investigation in vivo.