Are Immature Platelets Growing Up?: Toward a New Marker of Antiplatelet Drug Resistance

Is platelet responsiveness to clopidogrel attenuated in overweight or obese patients and why? A reverse translational study in mice

BACKGROUND AND PURPOSE

Overweight or obese patients exhibit poorer platelet responses to clopidogrel. However, the mechanisms behind this phenotype remain to be elucidated. Here, we sought to discover whether and why obesity could affect the metabolic activation of and/or platelet response to clopidogrel in obese patients and high-fat diet-induced obese mice.

EXPERIMENTAL APPROACH

A post hoc stratified analysis of an observational clinical study was performed to investigate changes in residual platelet reactivity with increasing body weight in patients taking clopidogrel. Furthermore, high-fat diet-induced obese mice were used to reveal alterations in systemic exposure of clopidogrel thiol active metabolite H4, ADP-induced platelet activation and aggregation, the expression of genes involved in the metabolic activation of clopidogrel, count of circulating reticulated and mature platelets, and proliferation profiles of megakaryocytes in bone marrow. The relevant genes and potential signalling pathways were predicted and enriched according to the GEO datasets available from obese patients.

KEY RESULTS

Obese patients exhibited significantly attenuated antiplatelet effects of clopidogrel. In diet-induced obese mice, systemic exposure of clopidogrel active metabolite H4 was reduced but that of its hydrolytic metabolite was increased due to down-regulation of certain P450s but up-regulation of carboxylesterase-1 in the liver. Moreover, enhanced proliferation of megakaryocytes and elevated platelet count also contributed.

CONCLUSION AND IMPLICATIONS

Obesity attenuated metabolic activation of clopidogrel and increased counts of circulating reticulated and mature platelets, leading to impaired platelet responsiveness to the drug in mice, suggesting that clopidogrel dosage may need to be adjusted adequately in overweight or obese patients.

Correlation of Cardiovascular Risk Factors and Biomarkers With Platelet Reactivity in Coronary Artery Disease

BACKGROUND

Low response to aspirin, aspirin resistance, and high platelet reactivity on aspirin treatment are similar names for lack of response to block arachidonic acid-induced aggregation with aspirin therapy and have an important role in the evolution of coronary artery disease (CAD) with thromboembolic events.

STUDY QUESTION

Was to evaluate the correlation between cardiovascular risk factors, biomarkers, and low response to aspirin in patients (pts) with CAD.

STUDY DESIGN

Four hundred pts with CAD were divided into 8 groups of study, consistent with the type of CAD and low response to aspirin. Cardiovascular risk factors and biomarkers-including some of high platelet reactivity, endothelial dysfunction, hypercoagulability, and oxidative stress-were evaluated in correlation with low response to aspirin, defined as on treatment aspirin test (ASPItest) >30U by multiple electrode platelet aggregometry.

RESULTS

In patients with CAD, low response to aspirin was significantly correlated with age older than 65 years, smoking, presence of diabetes mellitus, body mass index >25, hypertension, previous aspirin treatment, low response to clopidogrel, high mean platelets volume and von Willebrand factor activity, low flow-mediated vasodilation, and total antioxidant status (P < 0.01). In unstable angina patients, low response to aspirin was significantly correlated with male sex (P < 0.03). Incidence of other hypercoagulability biomarkers-S Protein, C Protein, Antithrombin III, and V Factor Leiden resistance to activated protein C-was low and not correlated with low response to aspirin.

CONCLUSIONS

In CAD, low response to aspirin was significantly correlated with age older than 65 years, smoking, presence of diabetes mellitus, body mass index I >25, hypertension, previous aspirin treatment, and only in unstable angina with male sex. Low response to aspirin was also statistically associated with low response to clopidogrel, high mean platelets volume, high von Willebrand factor activity, low flow-mediated vasodilation, and low total antioxidant status values.

Neutrophil-derived S100 calcium-binding proteins A8/A9 promote reticulated thrombocytosis and atherogenesis in diabetes

Platelets play a critical role in atherogenesis and thrombosis-mediated myocardial ischemia, processes that are accelerated in diabetes. Whether hyperglycemia promotes platelet production and whether enhanced platelet production contributes to enhanced atherothrombosis remains unknown. Here we found that in response to hyperglycemia, neutrophil-derived S100 calcium-binding proteins A8/A9 (S100A8/A9) interact with the receptor for advanced glycation end products (RAGE) on hepatic Kupffer cells, resulting in increased production of IL-6, a pleiotropic cytokine that is implicated in inflammatory thrombocytosis. IL-6 acts on hepatocytes to enhance the production of thrombopoietin, which in turn interacts with its cognate receptor c-MPL on megakaryocytes and bone marrow progenitor cells to promote their expansion and proliferation, resulting in reticulated thrombocytosis. Lowering blood glucose using a sodium-glucose cotransporter 2 inhibitor (dapagliflozin), depleting neutrophils or Kupffer cells, or inhibiting S100A8/A9 binding to RAGE (using paquinimod), all reduced diabetes-induced thrombocytosis. Inhibiting S100A8/A9 also decreased atherogenesis in diabetic mice. Finally, we found that patients with type 2 diabetes have reticulated thrombocytosis that correlates with glycated hemoglobin as well as increased plasma S100A8/A9 levels. These studies provide insights into the mechanisms that regulate platelet production and may aid in the development of strategies to improve on current antiplatelet therapies and to reduce cardiovascular disease risk in diabetes.