Towards a greater understanding of reduced response to aspirin in children with congenital heart disease post-cardiac surgery using immature platelet fraction

OBJECTIVE

A high platelet turnover rate may produce a population of platelets that confers an inadequate response to aspirin. We aimed to investigate the relationship between residual platelet aggregation and platelet turnover in paediatric cardiology patients on aspirin monotherapy by evaluating the fraction of immature platelets as a marker for turnover and secondly to test the predictive value of the immature platelet fraction (IPF) to classify patients as responsive or non-responsive to aspirin.

METHODS

Sixty patients divided into two age categories (≤90 days, >90 days of age) were included in this prospective observational study. Patients were then stratified into tertiles using their IPF level. Platelet studies included thromboelastography with platelet mapping (TEGPM).

RESULTS

The overall incidence of 'inadequate response to aspirin' was 38 % in our patient cohort recently post-cardiac surgery a consequence that warrants further study. The frequency of inadequate response to aspirin was higher in the upper tertile of IPF when compared to the lower tertile, (88 %) versus (4 %) respectively (p < 0.05). The 'cut off' for IPF was determined to be 3.9 % with a sensitivity of 95.7 %, and a specificity of 92.9 % (area under the curve of 0.955 [CI 0.896-1.014, p < 0.05]).

CONCLUSION

This study demonstrates that inadequate response to aspirin occurs in approximately 38 % of patients undergoing specific high-risk congenital cardiac procedures using the dosing practice of a national centre. This study supports the hypothesis that an elevated platelet turnover may result in aspirin being less effective in patients who are recently post cardiac surgery. These data are of direct translational relevance.

Effect of remote ischaemic conditioning on platelet aggregation and platelet turnover

Remote ischaemic conditioning (RIC) is a new beneficial treatment for patients with ST-elevation myocardial infarction. RIC may inhibit thrombus formation and, therefore, we investigated whether RIC affects platelet aggregation and turnover. 30 healthy male volunteers were subjected to intervention on day 1 (sham intervention, no aspirin), day 2 (RIC, no aspirin), and day 16 (RIC, treated 7 days with aspirin 75 mg/day). RIC was performed as four cycles of 5 min interchangeable inflation and deflation using an automated cuff. Blood samples were collected 5 min before, as well as 5 and 45 min after RIC. Platelet aggregation was measured by Multiplate® using collagen (COLtest), adenosine diphosphate (ADPtest), and arachidonic acid (ASPItest) as agonists. Platelet turnover was evaluated by flow cytometry. Serum thromboxane B₂ was determined by ELISA to confirm aspirin compliance. We found no significant change in platelet aggregation at visit 1 (COLtest: p = 0.32; ADPtest: p = 0.24; ASPItest: p = 0.07), visit 2, except for ADP-induced platelet aggregation evaluated 5 min after RIC (COLtest: p = 0.39; ADPtest: p = 0.02; ASPItest: p = 0.39), or visit 3 (COLtest: p = 0.48; ADPtest: p = 0.61; ASPItest: p = 0.90). Platelet turnover was not influenced by RIC, neither on nor off aspirin (all p-values > 0.07). (1) RIC did not affect platelet aggregation in healthy young men. (2) RIC did not affect platelet turnover in healthy young men. (3) Aspirin did not influence the effect of RIC on platelet aggregation and turnover. (4) Future studies exploring the effect of RIC on platelet aggregation and turnover in patients with ischaemic heart disease are warranted.

Antiplatelet effect of aspirin during 24h in patients with type 2 diabetes without cardiovascular disease

INTRODUCTION

The antiplatelet effect of low-dose aspirin in patients with type 2 diabetes (T2DM) without cardiovascular disease (CVD) has not been thoroughly explored. We investigated if platelet aggregation increased during the standard 24-hour aspirin dosing interval in patients with T2DM compared to non-diabetic controls. Furthermore, we evaluated baseline platelet aggregation, the acute effects of aspirin on platelet aggregation and platelet turnover.

MATERIALS AND METHODS

We included 21 patients with T2DM and 21 age and sex-matched controls. Platelet aggregation was measured by impedance aggregometry (Multiplate® Analyzer) and markers of platelet turnover by flow cytometry (Sysmex® XE-5000). Blood samples were obtained at baseline and 1h after administration of 75mg of aspirin. Participants were then treated for 6days with once-daily aspirin, and blood sampling was repeated 1h and 24h after aspirin intake.

RESULTS

After 6days of treatment, platelet aggregation levels increased during the 24-hour aspirin dosing interval in both patients and controls (p<0.001) with no difference between patients and controls. At baseline, patients with diabetes had increased platelet aggregation compared to controls (p=0.03). Platelet aggregation was reduced after the first dose of aspirin and significantly further reduced after six days of treatment (p<0.001). Patients with T2DM had numerically higher immature platelet count compared to controls (p=0.09), indicating an increased platelet turnover.

CONCLUSION

Patients with T2DM without a history of CVD and controls had increased platelet aggregation at the end of the standard 24-hour dosing interval of aspirin. Further, aspirin-naïve T2DM patients had increased platelet aggregation compared to controls.

Platelet indices and glucose control in type 1 and type 2 diabetes mellitus: A case-control study

BACKGROUND AND AIMS

The relationship between platelet indices and glucose control may differ in type 1 (T1DM) and type 2 (T2DM) diabetes. We aimed to investigate differences in mean platelet volume (MPV), platelet count, and platelet mass between patients with T1DM, T2DM, and healthy controls and to explore associations between these platelet indices and glucose control.

METHODS AND RESULTS

A total of 691 T1DM and 459 T2DM patients and 943 control subjects (blood donors) were included. HbA1c was measured in all subjects with diabetes and 36 T1DM patients further underwent 24 h-continuous glucose monitoring to estimate short-term glucose control (glucose mean and standard deviation). Adjusting for age and sex, platelet count was higher and MPV lower in both T1DM and T2DM patients vs control subjects, while platelet mass (MPV × platelet count) resulted higher only in T2DM. Upon further adjustment for HbA1c, differences in platelet count and mass were respectively 19.5 × 10⁹/L (95%CI: 9.8-29.3; p < 0.001) and 101 fL/nL (12-191; p = 0.027) comparing T2DM vs T1DM patients. MPV and platelet count were significantly and differently related in T2DM patients vs both T1DM and control subjects; this difference was maintained also accounting for HbA1c, age, and sex. Platelet mass and the volume-count relationship were significantly related to HbA1c only in T1DM patients. No associations were found between platelet indices and short-term glucose control.

CONCLUSION

By accounting for confounders and glucose control, our data evidenced higher platelet mass and different volume-count kinetics in subjects with T2DM vs T1DM. Long-term glucose control seemed to influence platelet mass and the volume-count relationship only in T1DM subjects. These findings suggest different mechanisms behind platelet formation in T1DM and T2DM patients with long-term glycaemic control being more relevant in T1DM than T2DM.

Antiplatelet drugs in patients with enhanced platelet turnover: biomarkers versus platelet function testing

Platelets are key players in atherothrombosis. Antiplatelet therapy comprising aspirin alone or with P2Y12-inhibitors are effective for prevention of atherothrombotic complications. However, there is interindividual variability in the response to antiplatelet drugs, leaving some patients at increased risk of recurrent atherothrombotic events. Several risk factors associated with high on-treatment platelet reactivity (HTPR), including elevated platelet turnover, have been identified. Platelet turnover is adequately estimated from the fraction of reticulated platelets. Reticulated platelets are young platelets, characterised by residual messenger RNA. They are larger, haemostatically more active and there is evidence that platelet turnover is a causal and prognostic factor in atherothrombotic disease. Whether platelet turnover per se represents a key factor in pathogenesis, progression and prognosis of atherothrombotic diseases (with focus on acute coronary syndromes) or whether it merely facilitates insufficient platelet inhibition will be discussed in this state-of-the art review.

Platelets and diabetes mellitus

Platelet activation plays a key role in atherothrombosis in type 2 diabetes mellitus (T2DM) and increased in vivo platelet activation with enhanced thromboxane (TX) biosynthesis has been reported in patients with impairment of glucose metabolism even in the earlier stages of disease and in the preclinical phases. In this regards, platelets appear as addresses and players carrying and transducing metabolic derangement into vascular injury. The present review critically addresses key pathophysiological aspects including (i) hyperglycemia, glycemic variability and insulin resistance as determinants and predictors of platelet activation, (ii) inflammatory mediators derived from platelets, such as soluble CD40 ligand, soluble CD36, Dickkopf-1 and probably soluble receptor for advanced glycation-end-products (sRAGE), which expand the functional repertoire of platelets from players of hemostasis and thrombosis to powerful amplifiers of inflammation by promoting the release of cytokines and chemokines, cell activation, and cell-cell interactions; (iii) molecular mechanisms underpinning the less-than-expected antithrombotic protection by aspirin (ASA), despite regular antiplatelet prophylaxis at the standard dosing regimen, and (iv) stratification of patients deserving different antiplatelet strategies, based on the metabolic phenotype. Taken together, these pathophysiological aspects may contribute to the development of promising mechanism-based therapeutic strategies to reduce the progression of atherothrombosis in diabetic subjects.

24-hour antiplatelet effect of aspirin in patients with previous definite stent thrombosis

OBJECTIVE

Once-daily aspirin is standard treatment, but recent studies point towards increased platelet function at the end of the dosing interval. Stent thrombosis (ST) has been linked with reduced antiplatelet effect of aspirin, so we investigated if platelet inhibition by aspirin declines through 24 h in patients with previous definite ST. Furthermore, we explored whether increased levels of immature platelets and thrombopoietin are associated with a particularly rapid recovery of platelet function.

METHODS

This case-control study included 50 patients with previous definite ST matched with 100 patients with stable coronary artery disease and 50 healthy volunteers. All participants were on aspirin 75 mg/day mono antiplatelet therapy. Platelet aggregation was measured 1 and 24 h after aspirin intake using platelet aggregometry (Multiplate® Analyzer). Cyclooxygenase-1 activity, platelet activation, immature platelets, and thrombopoietin were measured.

RESULTS

Platelet aggregation increased by 109±150 (arachidonic acid) and 47±155 (collagen) aggregation units per minute from 1 to 24 h after aspirin intake (p-values <0.0001) with corresponding increases in thromboxane B2 (5.6±5.1 ng/ml, p<0.0001) and soluble P-selectin (6.2±15.5 ng/ml, p<0.0001). Platelet aggregation increased equally in all groups, but patients with previous ST displayed the highest levels of platelet aggregation at 24 h (p-values≤0.05) and the highest levels of immature platelets (p<0.01) and thrombopoietin (p<0.0001).

CONCLUSIONS

Platelet inhibition declined significantly during the 24-hour dosing interval in aspirin-treated patients with previous definite ST or stable coronary artery disease and in healthy individuals. Increased levels of immature platelets and thrombopoietin were observed in patients with previous definite ST.