Reticulated platelets and antiplatelet therapy response in diabetic patients

Immature platelet dynamics are associated with clinical outcomes after major trauma

BACKGROUND

Major trauma results in dramatic changes in platelet behavior. Newly formed platelets are more reactive than older platelets, but their contributions to hemostasis and thrombosis after severe injury have not been previously evaluated.

OBJECTIVES

To determine how immature platelet metrics and plasma thrombopoietin relate to clinical outcomes after major injury.

METHODS

A prospective observational cohort study was performed in adult trauma patients. Platelet counts and the immature platelet fraction (IPF) were measured at admission and 24 hours, 72 hours, and 7 days after injury. Thromboelastometry was performed at admission. Plasma thrombopoietin, c-Mpl, and GPIbα were quantified in a separate cohort. The primary outcome was in-hospital mortality; secondary outcomes were venous thromboembolic events and multiple organ dysfunction syndrome (MODS).

RESULTS

On admission, immature platelet counts (IPCs) were significantly lower in nonsurvivors (n = 40) than in survivors (n = 236; 7.3 × 109/L vs 10.6 × 109/L; P = .009), but IPF did not differ. Similarly, impaired platelet function on thromboelastometry was associated with lower admission IPC (9.1 × 109/L vs 11.9 × 109/L; P < .001). However, at later time points, we observed significantly higher IPF and IPC in patients who developed venous thromboembolism (21.0 × 109/L vs 11.1 × 109/L; P = .02) and prolonged MODS (20.9 × 109/L vs 11 × 109/L; P = .003) than in those who did not develop complications. Plasma thrombopoietin levels at admission were significantly lower in nonsurvivors (P < .001), in patients with MODS (P < .001), and in those who developed venous thromboembolism (P = .04).

CONCLUSION

Lower levels of immature platelets in the acute phase after major injury are associated with increased mortality, whereas higher immature platelet levels at later time points may predispose to thrombosis and MODS.

Platelet ageing: A review

Platelet ageing is an area of research which has gained much interest in recent years. Newly formed platelets, often referred to as reticulated platelets, young platelets or immature platelets, are defined as RNA-enriched and have long been thought to be hyper-reactive. This latter view is largely rooted in associations and observations in patient groups with shortened platelet half-lives who often present with increased proportions of newly formed platelets. Evidence from such groups suggests that an increased proportion of newly formed platelets is associated with an increased risk of thrombotic events and a reduced effectiveness of standard anti-platelet therapies. Whilst research has highlighted the existence of platelet subpopulations based on function, size and age within patient groups, the common intrinsic changes which occur as platelets age within the circulation are only just being explored. By understanding the changes that occur during the natural ageing processes of platelets, we may be able to identify the triggers for alterations in platelet life span and platelet reactivity. Here we review research on platelet ageing in the context of health and disease, paying particular attention to the experimental approaches taken and the robustness of conclusions that can be drawn.

Higher body mass index raises immature platelet count: potential contribution to obesity-related thrombosis

Higher body mass index (BMI) is a risk factor for thrombosis. Platelets are essential for hemostasis but contribute to thrombosis when activated pathologically. We hypothesized that higher BMI leads to changes in platelet characteristics, thereby increasing thrombotic risk. The effect of BMI on platelet traits (measured by Sysmex) was explored in 33 388 UK blood donors (INTERVAL study). Linear regression showed that higher BMI was positively associated with greater plateletcrit (PCT), platelet count (PLT), immature platelet count (IPC), and side fluorescence (SFL, a measure of mRNA content used to derive IPC). Mendelian randomization (MR), applied to estimate a causal effect with BMI proxied by a genetic risk score, provided causal estimates for a positive effect of BMI on both SFL and IPC, but there was little evidence for a causal effect of BMI on PCT or PLT. Follow-up analyses explored the functional relevance of platelet characteristics in a pre-operative cardiac cohort (COPTIC). Linear regression provided observational evidence for a positive association between IPC and agonist-induced whole blood platelet aggregation. Results indicate that higher BMI raises the number of immature platelets, which is associated with greater whole blood platelet aggregation in a cardiac cohort. Higher IPC could therefore contribute to obesity-related thrombosis.

Proteome and functional decline as platelets age in the circulation

BACKGROUND

Platelets circulate in the blood of healthy individuals for approximately 7-10 days regulated by finely balanced processes of production and destruction. As platelets are anucleate we reasoned that their protein composition would change as they age and that this change would be linked to alterations in structure and function.

OBJECTIVE

To isolate platelets of different ages from healthy individuals to test the hypothesis that changes in protein content cause alterations in platelet structure and function.

METHODS

Platelets were separated according to thiazole orange fluorescence intensity as a surrogate indicator of mRNA content and so a marker of platelet age and then subjected to proteomics, imaging, and functional assays to produce an in-depth analysis of platelet composition and function.

RESULTS

Total protein content was 45 ± 5% lower in old platelets compared to young platelets. Predictive proteomic pathway analysis identified associations with 28 biological processes, notably higher hemostasis in young platelets whilst apoptosis and senescence were higher in old platelets. Further studies confirmed platelet ageing was linked to a decrease in cytoskeletal protein and associated capability to spread and adhere, a reduction in mitochondria number, and lower calcium dynamics and granule secretion.

CONCLUSIONS

Our findings demonstrate changes in protein content are linked to alterations in function as platelets age. This work delineates physical and functional changes in platelets as they age and serves as a base to examine differences associated with altered mean age of platelet populations in conditions such as immune thrombocytopenia and diabetes.

Impact of gender on immature platelet count and its relationship with coronary artery disease

The impact of platelet parameters on the cardiovascular risk is still debated. Gender differences in platelet volume indexes and turnover have been previously reported, potentially conditioning their role in the development of coronary artery disease (CAD). However, few studies have addressed, so far, the impact of gender on the immature platelet fraction (IPF) and count (IPC) and their relationship with CAD. We enrolled consecutive patients undergoing coronary angiography in a single centre. IPF and platelet indexes were measured at admission. Significant CAD was defined as the presence of at least one coronary stenosis more than 50%. A total of 2550 patients were included, 1835 (72%) were males, and 715 (28%) were females. Female patients were older (p < 0.001), with lower BMI (p = 0.002), lower prevalence of active smoking (p < 0.001), previous MI, previous PCI and CABG (p = 0.001, p = 0.001, p < 0.001), whilst a higher prevalence of renal failure (p = 0.02), acute presentation (p < 0.001) and CAD (p < 0.001). Platelet count was higher in females (p < 0.001), as well as the IPC levels (838.38 ± 562.05 vs 792.24 ± 535.66, p = 0.05) with no difference in the levels of immature platelet fraction (3.67 ± 2.68% vs 3.74 ± 2.6%, p = 0.55) or the prevalence of patients with IPF ≥ 3rd tertile (33.7% vs 35.2%, p = 0.26). At multivariate analysis, after correction for baseline confounders, gender did not emerge as an independent predictor of higher IPF (adjusted OR [95% CI] = 0.82 [0.64-1.06], p = 0.13). When dividing our patients according to the levels of IPF, in women we observed an inverse association between IPF ≥ 3rd tertile and coronary calcifications (p = 0.025) and a higher prevalence of restenosis (p = 0.003), but no difference in CAD (65.6% vs 66.9%, p = 0.71) or severe CAD (28.1% vs 24.7%, p = 0.31). In males, the IPF ≥ 3rd tertile related with a lower TIMI flow (p = 0.001). Males with lower IPF had a significantly higher percentage of CAD (87.7% vs 83.3%, p = 0.007; adjusted OR: 0.699 [95% CI] = [0.54-0.91], p = 0.008) but not for severe CAD (36.5% vs 39.9%, p = 0.134). The present study shows that among patients undergoing coronary angiography, gender is not associated to the levels of immature platelet fraction. Moreover, we found no association between IPF and the prevalence and extent of CAD in female gender, whereas in male gender the IPF was inversely related with the prevalence of CAD.

The multifaceted contribution of platelets in the emergence and aftermath of acute cardiovascular events

Atherosclerosis is an underlying cause of a broad array of cardiovascular diseases characterized by plaques, arterial wall thickening initiated by hyperlipidemia, pro-inflammatory signals, endothelial dysfunction and the influx of inflammatory cells. By still incompletely characterized mechanisms, these plaques can destabilize or erode, leading to thrombosis and blood vessel occlusion and becomes clinically manifest as angina pectoris, myocardial infarction (MI) or stroke. Among the several blood cell types that are involved in the development of atherosclerosis, the role of platelets during the thrombotic occlusion of ruptured or eroded plaques is well established and clinically exploited as evident by the extensive use of platelet inhibitors. However, there is increasing evidence that platelets are also involved in the earlier stages of atheroma development by exhibiting pro-inflammatory activities. The scope of this review is to describe the role of platelets in the initiation and propagation stages of atherosclerosis and beyond; in atherothrombotic complications.

Impact of diabetes mellitus on immature platelet fraction and its association with coronary artery disease

BACKGROUND

Higher prothrombotic status and alterations in platelet function and thrombopoiesis are associated with diabetes mellitus (DM). We assessed the impact of diabetes and glucose control on the immature platelet fraction (IPF) and their relationship with prevalence and extent of coronary artery disease (CAD).

METHODS

Consecutive patients undergoing coronary angiography were included. Significant CAD was defined as at least one vessel stenosis greater than 50%. IPF levels were measured at admission by routine blood cells count (A Sysmex XE-2100).

RESULTS

We included 1781 patients, of whom 660 (37.1%) suffered from diabetes. Diabetes was associated with advanced age and a higher cardiovascular risk profile. No difference in the mean values of IPF were observed between patients with or without DM (3.6 ± 2.5 vs 3.5 ± 2.5, P = 0.39) and neither in the rate of patients with IPF above the median (2.9%) (51.6% vs 50.6%, P = 0.73). In patients with DM, the IPF levels did not relate with glucose control parameters (glycaemia: r = -0.024, P = 0.54, glycosylated haemoglobin: r = 0.11, P = 0.72). The prevalence of CAD was significantly lower in patients with DM and IPF greater than the median (80.5% vs 86.5%, P = 0.04, adjusted odds ratio [OR] [95% confidence interval {CI}] = 0.57[0.36-0.91], P = 0.02), while not left main/three-vessel CAD (36.9% vs 38.2%, P = 0.75, adjusted OR [95%CI] = 0.91[0.64-1.28], P = 0.90).

CONCLUSION

In the present study, neither DM nor glucose control are independent predictors of IPF above the median. In patients with DM, higher IPF levels were associated with a lower prevalence of CAD and with a similar extent of severe CAD and angiographic findings. Therefore, until new data become available, elevated IPF should not be systematically applied on a large scale as cardiovascular risk marker in patients with diabetes.

Impact of aging on platelet reactivity in diabetic patients receiving dual antiplatelet therapy

Advanced age and diabetes represent summative conditions in the determination of cardiovascular risk, and especially for the management of dual antiplatelet therapy (DAPT), often requiring balancing between bleeding and thrombotic complications. However, few studies have so far evaluated the impact of age on platelet reactivity and suboptimal platelet inhibition (high-on treatment platelet reactivity-HRPR) on DAPT among diabetic patients, that was, therefore the aim of the present study. In diabetic patients treated with DAPT (ASA + clopidogrel or ticagrelor) platelet reactivity was assessed at 30-90 days post-discharge for an acute coronary syndrome or elective PCI. Aggregation was assessed by multiple-electrode aggregometry. HRPR was defined for values above the lower limit of normality (in non-treated patients). Elderly patients were considered ≥ 75 years of age. We included 462 patients, among them 149 (32.2%) were ≥ 75 years. Elderly patients were more often females (p = 0.006), with lower body size (p = 0.04), acute coronary syndrome at presentation and renal failure (p < 0.001), non-smokers (p = 0.002), in therapy with insulin (p = 0.02) and diuretics (p < 0.001) and lower rate of betablockers (p = 0.02). Age directly related with C reactive protein (p = 0.01), creatinine levels and inversely with hemoglobin (p < 0.001) and triglycerides (p = 0.003). No association was found at linear regression analysis for platelet reactivity and age with different activating stimuli, but for ASPI test (r = 0.12; p = 0.03). No significant difference in HAPR was found in elderly patients (2.4 vs. 3.2%, p = 0.76, OR[95% CI] = 0.45[0.1-2.11], p = 0.31). HRPR for ADP antagonists was similarly not affected by age (30.1% vs. 35.7%, p = 0.28, adjusted OR[95% CI] = 0.78[0.47-1.29], p = 0.33). Comparable results were obtained when considering separately the DAPT strategies with clopidogrel or ticagrelor, or when adjusting our results according to propensity score values. Among diabetic patients receiving dual antiplatelet therapy for an acute coronary syndrome or elective percutaneous coronary intervention, age does not affect platelet reactivity or the rate of high-on treatment platelet reactivity. Similar results were obtained for ASA and clopidogrel or ticagrelor.

Reticulated platelets – clinical application and future perspectives

Reticulated platelets are immature platelets freshly released from the bone marrow into the circulation and contain vestigial amounts of ribonucleic acid. Thus, they can serve as an indicator for the activity of thrombopoiesis. Despite the current lack of a standardized reference method, two types of hematology analyzers have incorporated a fully automated measurement of reticulated platelets. The “immature platelet fraction” (IPF; Sysmex XE-/XN-series) has some clinical utility in the differential diagnosis of thrombocytopenia. This is less clear for “reticulated platelets” (retPLT; Abbott CELL-DYN Sapphire/Alinity HQ). The usefulness of these parameters in the prediction of platelet recovery after chemotherapy or stem cell transplantation and as a decision aid for platelet transfusions has not been unequivocally confirmed. Recent findings have shown an association of reticulated platelets with an adverse risk in patients with coronary artery disease and stroke as well as resistance to anti-platelet therapy. Furthermore, a role of reticulated platelets for the prediction of sepsis was indicated. However, validation in larger prospective trials is necessary to establish the clinical benefit of reticulated platelets in these conditions. This review gives an overview of the available analytical methods and summarizes the current knowledge regarding the clinical application of reticulated platelets.

Impact of aging on immature platelet count and its relationship with coronary artery disease

Despite the fact that elderly patients represent a prevalent and challenging population in the current practice, few data exist on the impact of platelet parameters on cardiovascular risk in these patients. Therefore, the aim of the present study was to evaluate the impact of age on the immature platelet count (IPC) and their relationship with CAD. We included a total of 2236 consecutive patients undergoing coronary angiography in a single center. Elderly patients (age ≥ 75 years) were 756 (33.7%). IPC was measured at admission. Elderly patients were more often females (p < .001), with lower BMI and prevalence of smokers (p < .001), and a more complex cardiovascular risk profile and coronary disease (p = .02). Platelet count decreased with aging (p = .05), whereas no difference in the mean IPC was found between patients < or ≥75 years. In fact, advanced age did not emerge as an independent predictor of IPC above III tertile (≥8.6*10^6/ml), (adjusted OR[95%CI] = 0.97[0.78-1.21], p = .79). When considering elderly patients according to tertiles values of IPC (<5.1,5.1-8.59; ≥8.6*10^6/ml), we found no impact of IPC on the prevalence of CAD (81.1% vs 84.5% vs 81.5%, p = .92; adjusted OR[95%CI] = 1.08[0.67-1.72], p = .75) and its extent (37.7% vs 34.5% vs 40.2%, p = .57; adjusted OR[95%CI] = 1.22[0.85-1.73], p = .28). However, we observed a higher rate of calcified and type C lesions in elderly patients with higher IPC (p = .03 and p < .001, respectively). Therefore, advanced age is not associated with higher immature platelet count and the prevalence and severity of CAD. Moreover, IPC does not contribute to explain the higher prevalence and extent of coronary artery disease observed in elderly patients.

Prognostic significance of reticulated platelet levels in diabetic patients with stable coronary artery disease

Levels of reticulated platelets (RP) increase during high platelet turnover conditions, and have been shown to correlate with diabetes mellitus (DM) status. Little is known regarding the prognostic significance of levels of RP among patients with stable coronary artery disease (SCAD). The study consisted of patients with SCAD and DM, who visited our cardiology outpatient clinic between June 2016 and February 2017. RP levels were measured at baseline as immature platelet fraction (IPF)%, using flow cytometry. Outcomes at 2 years consisted of bleeding events and major adverse cardiovascular events (MACE), which included death, myocardial infarction, cerebrovascular accident and urgent revascularization. The study included 104 patients (mean age - 71.2 ± 9.5 years, 76.9% were male, and 83.7% had hypertension). IPF was significantly higher at baseline among patients who had suffered from a MACE (4.57% vs. 2.53%, p < .001), and lower in patients who had suffered from bleeding events, compared with those who had not (1.57% vs. 3.00%, p = .004). There were higher rates of MACE at higher IPF quartiles (p < .001, AUC-0.770), and higher rates of bleeding at the lowest quartiles (p = .007, AUC-0.781). In SCAD patients with DM, levels of RP are associated with a higher risk of MACE, and inversely correlated with the risk of bleeding.

Influence of antiretroviral therapy and cardiovascular disease on the immature platelet fraction in patients living with HIV

Cardiovascular disease is an important contributor to morbidity and mortality in people living with HIV . The immature platelet fraction (IPF) is increased in HIV-negative patients with cardiovascular disease and evidence suggests that an enlarged IPF is associated with adverse cardiovascular events. In this multi-center observational study, we aimed to investigate how the IPF in people living with HIV is influenced by antiretroviral therapy and cardiovascular disease. Subjects without cardiovascular disease that received antiretroviral therapy showed a smaller IPF accompanied by lower D-dimer and C-reactive protein (CRP) levels compared to therapy-naïve subjects (mean IPF: 2.9% vs. 3.9%, p = .016; median D-dimer: 252 µg/L vs. 623 µg/L, p < .001; median CRP: 0.2 mg/dL vs. 0.5 mg/dL, p = .004). No significant differences for the IPF, D-dimer or CRP were found between subjects on antiretroviral therapy with documented cardiovascular disease and therapy-naïve subjects. In conclusion, we observed a reduction in the IPF among subjects on therapy only in the absence of cardiovascular disease. In contrast, subjects receiving therapy that had documented cardiovascular disease showed an IPF comparable to therapy-naïve subjects. Future studies are needed to investigate if an enlarged IPF may serve as a biomarker in predicting adverse cardiovascular events in people living with HIV.

Clopidogrel utilization in patients with coronary artery disease and diabetes mellitus: should we determine CYP2C19*2 genotype?

PURPOSE

Clopidogrel non-responsiveness is multifactorial; several genetic and non-genetic factors may contribute to impaired platelet inhibition. The goal of this study is to determine the effect of the cytochrome P450 CYP2C19*2 polymorphism on the platelet response to clopidogrel in patients with and without diabetes mellitus (DM).

METHODS

We conducted an observational study in patients with coronary artery disease and consequent exposure to clopidogrel therapy (75 mg/day for at least 7 consecutive days). We have analyzed two groups of patients: group I (DM patients) and group II (non-diabetes mellitus patients). Platelet reactivity was assessed by the VerifyNow P2Y12 assay and high on clopidogrel platelet reactivity (HPR) was defined as P2Y12 reaction units (PRU) ≥ 208. Genotyping for CYP2C19*2 polymorphism was performed by PCR-RFLP.

RESULTS

We have included 150 subjects (76 DM and 74 non-diabetes mellitus patients). The carriage of CYP2C19*2 allele, in DM patients, was significantly associated to HPR (odds ratio (OR) 4.437, 95% confidence interval (CI) 1.134 to 17.359; p = 0.032). Furthermore, 8.4% of the variability in percent inhibition by clopidogrel could be attributed to CYP2C19*2 carrier status. However, in non-diabetes mellitus patients, there was no significant difference in platelet response to clopidogrel according to the presence or absence of CYP2C19*2 allele carriage (OR 1.260, 95% CI 0.288 to 5.522; p = 0.759).

CONCLUSIONS

Our study suggests that the carriage of CYP2C19*2 polymorphism, in DM patients, might be a potential predictor of persisting HPR in these high-risk individuals.

TRIAL REGISTRATION

Clinical Trials.gov NCT03373552 (Registered 13 December 2017).

Aspirin in the prevention of cardiovascular events in patients with diabetes

Diabetes imparts a substantial increased risk for cardiovascular disease-related mortality and morbidity. Because of this, current medical guidelines recommend prophylactic treatment with once-daily, low-dose aspirin (acetylsalicylic acid) for primary and secondary prevention of cardiovascular (CV) events in high-risk patients. However, only modest reductions in CV events and mortality have been observed with once-daily aspirin treatment in patients with diabetes, including patients with a previous CV event, perhaps because of disparity between aspirin pharmacokinetics and diabetes-related platelet abnormalities. Once-daily aspirin irreversibly inactivates platelets for only a short duration (acetylsalicylic acid half-life, approximately 15-20 minutes), after which time newly generated, active platelets enter the circulation and weaken aspirin's effect. Platelets from patients with diabetes are more reactive and are turned over more rapidly than platelets from normal individuals; the short inhibitory window provided by once-daily aspirin may therefore be insufficient to provide 24-h protection against CV events. Alternative conventional aspirin regimens (e.g. higher daily dose, twice-daily dosing, combination with clopidogrel) and newer formulations (e.g. 24-h, extended-release) have been proposed to overcome the apparent limited efficacy of conventional aspirin in patients with diabetes; however, tolerability concerns and limited clinical efficacy data need to be taken into account when considering the use of such regimens.

Drug delivery and therapeutic impact of extended-release acetylsalicylic acid

Current treatment guidelines recommend once-daily, low-dose acetylsalicylic acid (ASA; aspirin) for secondary prevention of cardiovascular events. However, the anti-thrombotic benefits of traditional ASA formulations may not extend over a 24-h period, especially in patients at high risk for a recurrent cardiovascular event. A next-generation, extended-release ASA formulation (ER-ASA) has been developed to provide 24-h anti-thrombotic coverage with once-daily dosing. The pharmacokinetics of ER-ASA indicates slower absorption and prolonged ASA release versus immediate-release ASA, with a favorable safety profile. ER-ASA minimizes systemic ASA absorption and provides sustained antiplatelet effects over a 24-h period.

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.