Leukocyte count is associated with increased platelet reactivity and diminished response to aspirin in healthy individuals with a family history of coronary artery disease

The association between platelet reactivity and lipoprotein levels in Framingham Heart Study participants

BACKGROUND

Hypertriglyceridemia is an independent risk factor for major adverse cardiovascular events, though the mechanisms linking triglycerides and platelet function with thrombosis, remain elusive. The aim of this study was to assess the association between platelet function and triglyceride levels.

METHODS

We included participants from the Framingham Heart Study Third Generation cohort, OMNI, and New Offspring Spouse cohort who attended the third examination cycle (2016-2019). Eligible participants were categorized into four triglyceride subgroups.

RESULTS

The study comprised a total of 1897 (55.53 %) participants with normal TG levels; 883 (25.85 %) participants with high-normal TGs; 378 (11.07 %) with borderline high TGs; and 258 (7.55 %) participants with hypertriglyceridemia. After adjusting for age, sex, alcohol consumption, aspirin, statin and P2Y₁₂ inhibitors, the levels of ADP-induced platelet aggregation were inversely associated with total cholesterol levels (P < 0.0001). Platelet disaggregation was associated with low-density lipoprotein and high-density lipoprotein cholesterol levels (P < 0.0001). Lastly, in a shear-stress chamber assay mimicking arterial flow velocities, TG levels in the normal-high group were associated with increased levels of collagen-dependent thrombogenicity (β = 24.16, SE = 6.65, P < 0.0001).

CONCLUSION

Triglyceride levels are associated with altered platelet activation and aggregation. Furthermore, increased platelet-driven thrombogenicity is directly associated with triglyceride levels after adjusting for medications and other covariates.

Platelet aggregation in whole blood is not impaired by a platelet-sparing leukoreduction filter and instead depends upon the presence of leukocytes

BACKGROUND

Recent studies characterizing in vitro hemostatic properties of whole blood (WB) leukoreduced (LR) with a platelet-sparing filter have described subtle, if any, changes to viscoelastic clotting; however, reductions in platelet (PLT) content and impedance aggregometry (IA) responses have been noted. The effects of filtration of WB (i.e., filter-contact effects, reduction in platelet and leukocyte count) have not been rigorously investigated as to their individual impacts on platelet IA responses.

STUDY DESIGN AND METHODS

WB units from healthy donors were collected and characterized to assess the effects of platelet-sparing leukoreduction (LR) upon the in vitro hemostatic measures of platelet IA and thromboelastometry. Further characterization of platelet IA responses was carried out in WB samples to delineate the effects of platelet count and leukocyte presence/absence upon the response.

RESULTS

WB filtration reduced the platelet count and IA responses but had no impact on viscoelastic clotting measures in fresh WB. Experiments revealed that IA responses have a linear correlation with platelet count in both apheresis platelets and WB and that passage of platelets through the WB-LR filter has no impact upon the strength of this response. Further experiments in LR WB showed that addition of autologous leukocytes back to the platelets fully restored the platelet aggregation response to pre-filtration levels.

CONCLUSION

WB filtration results in platelet count reduction and leukocyte removal; however, platelet IA is not degraded by passage through the filter. Apparent declines in platelet IA responses can be fully attributed to the reduction in platelet count and the removal of leukocytes.

White blood cell count and clustered components of metabolic syndrome: A study in western Iran

Background

White blood cell count (WBC) is one of the objective parameters of systemic inflammation. The aim of present study was to evaluate the relationship between WBC count and metabolic syndrome.

Methods

In this study on Lor population in Borujerd province (West of Iran), from 2011 to 2013, 800 persons were enrolled. MetS was defined based on ATP III criteria. Differences among the quartiles of WBC were examined by one-way analysis of variance.

Results

Only 14.7% did not have any of the five components and 43% of all subjects had metabolic syndrome. The means of WBC count in MetS group were significantly higher than the control group (p<0.0001). In subjects without any MetS components, the means of WBC was 5.321 /µL, and it was 5.664, 5.714, 5.961, 6.302, and 6.572 /µL in subjects with 1, 2, 3, 4, and 5 components, respectively. These differences show a significant increasing trend (p<0.0001).

Conclusion

WBC count was associated with clustered components of metabolic syndrome. It seems that WBC counts could be considered as a predictive factor for metabolic syndrome in preventive medicine.

Effect of leukoreduction and pathogen reduction on the hemostatic function of whole blood

BACKGROUND

There is renewed interest in the use of whole blood (WB) for resuscitation of patients in hemorrhagic shock. Leukoreduction with platelet-sparing filters and pathogen reduction may be used to improve the safety profile of WB, yet the effects of leukoreduction and pathogen reduction on WB hemostatic function are not well characterized.

STUDY DESIGN AND METHODS

Blood from 32 healthy group O donors was divided into treatment groups (n = 8 for each group): untreated, pathogen reduced (PR⁺ ), leukoreduced using an in-line filter (LR⁺ ), or PR⁺ LR⁺ . Units were stored without agitation for 21 days between 1° and 6°C, with sampling on days 0 (pre- and post-treatments), 1, 3, 5, 10, 15, and 21 for hemostatic function as assessed by thromboelastometry, thrombin generation, platelet activation factors, and platelet impedance aggregometry.

RESULTS

From day 3 (D3) to D15 of storage, platelet count was reduced in PR⁺ /LR⁺ units compared to PR^- /LR^- units. From D10 to D21 of storage, maximum clot firmness (MCF) was reduced in PR⁺ /LR⁺ units compared to PR^- /LR^- units. From D3 to D21 of storage, platelet aggregation was reduced in PR⁺ /LR⁺ units compared to PR^- /LR^- units. Total thrombin generation was similar in all groups from D0 to D21.

CONCLUSIONS

The combination of LR with a platelet-sparing filter and PR significantly reduces hemostatic function compared to either treatment alone or untreated WB. The clinical consequences of LR and PR of WB in patients with severe bleeding should be examined in trials before both are used in combination in patients.

The role of platelet hyperreactivity in venous thromboembolism after total knee arthroplasty in elderly population without pharmacologic prophylaxis: A single-center study

INTRODUCTION

While it is suggested that platelet hyperreactivity plays a role in the arterial thrombi, its link with venous thromboembolism (VTE) is not well defined. Aggregometry using low concentrations of agonists is proposed as a reliable method to detect hyperreactivity. The aim of this study was to examine whether platelet hyperreactivity affects the development of VTE after total knee arthroplasty (TKA).

METHODS

Total 150 elderly patients without VTE history were enrolled. Mechanical prophylaxis was used for VTE after TKA. We performed platelet aggregation using Chrono-log (Chrono-log Corporation, USA) in the presence of low concentrations of ADP (1.0 μmol/L) and epinephrine (0.4, 1.0 μmol/L), and measured maximal aggregation (%).

RESULTS

At 0.4 μmol/L epinephrine, 69.3%, 15.3%, and 15.3% displayed low (<40%), moderate (40-60%), and high (>60%) levels of aggregation, respectively. The proportion of high level of aggregation was 36.7%, 30.7% at 1.0 μmol/L of epinephrine and ADP, respectively. The incidence of VTE was higher in the moderate/high aggregation group (10/46, 21.7%) than in the low aggregation group (1/104, 1.0%) at 0.4 μmol/L epinephrine (P < 0.0001). In predicting postoperative VTE, sensitivity and specificity of ≥40% aggregation at 0.4 μmol/L epinephrine were 90.9% and 74.1%. Higher mean platelet volume and lower volume of blood loss were seen in the high aggregation group than in the low aggregation group.

CONCLUSION

Aggregation response to 0.4 μmol/L epinephrine is an optimal assay to classify platelet activity. Platelet hyperreactivity may increase the risk of postoperative VTE in an elderly population, and can be an indication of pharmacologic prophylaxis.

Impact of acute exacerbations on platelet reactivity in chronic obstructive pulmonary disease patients

Background

A higher risk of atherothrombotic cardiovascular events, which are platelet-driven processes, has been described during acute exacerbations of chronic obstructive pulmonary disease (AECOPD). However, the relevance of platelet reactivity during AECOPD and whether this is affected by antiplatelet agents are not fully elucidated to date. This study aimed to evaluate whether platelet reactivity is augmented during an exacerbation in COPD patients with and without antiplatelet therapy and its association with systemic inflammatory parameters.

Materials and methods

Prospective, observational, ex vivo investigation was conducted in consecutive patients suffering an exacerbation of COPD. Platelet reactivity was assessed during AECOPD and at stable state. Platelet function assays included: 1) vasodilator-stimulated phosphoprotein assay expressed as P2Y₁₂ reactivity index (PRI), 2) multiple electrode aggregometry and 3) optical aggregometry. Systemic inflammatory parameters such as leukocyte count, interleukin-6 and fibrinogen were also assessed.

Results

Higher platelet reactivity was observed during AECOPD compared to stability measured by vasodilator-stimulated phosphoprotein (PRI: 75.2%±1.9% vs 68.8%±2.4%, p=0.001). This augmented platelet aggregability was also observed in the subset of patients on antiplatelet therapy (PRI: 72.8%±3.1% vs 61.7%±7.5%, p=0.071). Consistent findings were observed with all other platelet function tests. Patients with greater enhancement of inflammatory markers during AECOPD were more likely to present a higher increase in platelet reactivity.

Conclusion

Platelet reactivity is increased during AECOPD, which may contribute to the augmented cardiovascular risk of these patients. Additionally, the increase in platelet reactivity might be associated with an increment in inflammatory markers during exacerbations.

Whole exome sequencing in the Framingham Heart Study identifies rare variation in HYAL2 that influences platelet aggregation

Inhibition of platelet reactivity is a common therapeutic strategy in secondary prevention of cardiovascular disease. Genetic and environmental factors influence inter-individual variation in platelet reactivity. Identifying genes that contribute to platelet reactivity can reveal new biological mechanisms and possible therapeutic targets. Here, we examined rare coding variation to identify genes associated with platelet reactivity in a population-based cohort. To do so, we performed whole exome sequencing in the Framingham Heart Study and conducted single variant and gene-based association tests against platelet reactivity to collagen, adenosine diphosphate (ADP), and epinephrine agonists in up to 1,211 individuals. Single variant tests revealed no significant associations (p<1.44×10^-7), though we observed a suggestive association with previously implicated MRVI1 (rs11042902, p = 1.95×10^-7). Using gene-based association tests of rare and low-frequency variants, we found significant associations of HYAL2 with increased ADP-induced aggregation (p = 1.07×10^-7) and GSTZ1 with increased epinephrine-induced aggregation (p = 1.62×10^-6). HYAL2 also showed suggestive associations with epinephrine-induced aggregation (p = 2.64×10^-5). The rare variants in the HYAL2 gene-based association included a missense variant (N357S) at a known N-glycosylation site and a nonsense variant (Q406*) that removes a glycophosphatidylinositol (GPI) anchor from the resulting protein. These variants suggest that improper membrane trafficking of HYAL2 influences platelet reactivity. We also observed suggestive associations of AR (p = 7.39×10^-6) and MAPRE1 (p = 7.26×10^-6) with ADP-induced reactivity. Our study demonstrates that gene-based tests and other grouping strategies of rare variants are powerful approaches to detect associations in population-based analyses of complex traits not detected by single variant tests and possible new genetic influences on platelet reactivity.

Integrity of Induced Pluripotent Stem Cell (iPSC) Derived Megakaryocytes as Assessed by Genetic and Transcriptomic Analysis

Previously, we have described our feeder-free, xeno-free approach to generate megakaryocytes (MKs) in culture from human induced pluripotent stem cells (iPSCs). Here, we focus specifically on the integrity of these MKs using: (1) genotype discordance between parent cell DNA to iPSC cell DNA and onward to the differentiated MK DNA; (2) genomic structural integrity using copy number variation (CNV); and (3) transcriptomic signatures of the derived MK lines compared to the iPSC lines. We detected a very low rate of genotype discordance; estimates were 0.0001%-0.01%, well below the genotyping error rate for our assay (0.37%). No CNVs were generated in the iPSCs that were subsequently passed on to the MKs. Finally, we observed highly biologically relevant gene sets as being upregulated in MKs relative to the iPSCs: platelet activation, blood coagulation, megakaryocyte development, platelet formation, platelet degranulation, and platelet aggregation. These data strongly support the integrity of the derived MK lines.

Genome-wide association study of platelet aggregation in African Americans

BACKGROUND

We have previously shown that platelet aggregation has higher heritability in African Americans than European Americans. However, a genome-wide association study (GWAS) of platelet aggregation in African Americans has not been reported. We measured platelet aggregation in response to arachidonic acid, ADP, collagen, or epinephrine by optical aggregometry. The discovery cohort was 825 African Americans from the GeneSTAR study. Two replication cohorts were used: 119 African Americans from the Platelet Genes and Physiology Study and 1221 European Americans from GeneSTAR. Genotyping was conducted with Illumina 1 M arrays. For each cohort, age- and sex-adjusted linear mixed models were used to test for association between each SNP and each phenotype under an additive model.

RESULTS

Six SNPs were significantly associated with platelet aggregation (P<5×10(-8)) in the discovery sample. Of these, three SNPs in three different loci were confirmed: 1) rs12041331, in PEAR1 (platelet endothelial aggregation receptor 1), replicated in both African and European Americans for collagen- and epinephrine-induced aggregation, and in European Americans for ADP-induced aggregation; 2) rs11202221, in BMPR1A (bone morphogenetic protein receptor type1A), replicated in African Americans for ADP-induced aggregation; and 3) rs6566765 replicated in European Americans for ADP-induced aggregation. The rs11202221 and rs6566765 associations with agonist-induced platelet aggregation are novel.

CONCLUSIONS

In this first GWAS of agonist-induced platelet aggregation in African Americans, we discovered and replicated, novel associations of two variants with ADP-induced aggregation, and confirmed the association of a PEAR1 variant with multi-agonist-induced aggregation. Further study of these genes may provide novel insights into platelet biology.

Greater collagen-induced platelet aggregation following cyclooxygenase 1 inhibition predicts incident acute coronary syndromes

Greater ex vivo platelet aggregation to agonists may identify individuals at risk of acute coronary syndromes (ACS). However, increased aggregation to a specific agonist may be masked by inherent variability in other activation pathways. In this study, we inhibited the cyclooxygenase-1 (COX1) pathway with 2-week aspirin therapy and measured residual aggregation to collagen and ADP to determine whether increased aggregation in a non-COX1 pathway is associated with incident ACS. We assessed ex vivo whole blood platelet aggregation in 1,699 healthy individuals with a family history of early-onset coronary artery disease followed for 6±1.2 years. Incident ACS events were observed in 22 subjects. Baseline aggregation was not associated with ACS. After COX1 pathway inhibition, collagen-induced aggregation was significantly greater in participants with ACS compared with those without (29.0 vs. 23.6 ohms, p < 0.001). In Cox proportional hazards models, this association remained significant after adjusting for traditional cardiovascular risk factors (HR = 1.10, 95%CI = 1.06-1.15; p < 0.001). In contrast, ADP-induced aggregation after COX1 inhibition was not associated with ACS. After COX1 pathway inhibition, subjects with greater collagen-induced platelet aggregation demonstrated a significant excess risk of incident ACS. These data suggest that platelet activation related to collagen may play an important role in the risk of ACS.

A contemporary viewpoint on 'aspirin resistance'

Aspirin is an irreversible inhibitor of platelet prostaglandin synthase activity, and is the most widely prescribed drug for the secondary prevention of cardiovascular disease. In recent years, clinical and laboratory evidence has shown significant individual variability in the response to aspirin and its link to clinical outcome. The term 'aspirin resistance' has been introduced to describe situations when clinical or ex-vivo effects of aspirin are less than expected. The accumulating evidence of increased risk of major adverse clinical events (MACE) associated with 'aspirin resistance' in the settings of acute coronary syndrome (ACS), stroke, and peripheral arterial disease has stimulated the search for ways of overcoming aspirin resistance. Existence of the link between high on-treatment platelet reactivity and atherothrombotic events suggests the common mechanisms for atherosclerosis progression and thrombotic complications with the platelets, being a key cellular interface between coagulation and inflammation. This review article provides a contemporary view on 'aspirin resistance' and discusses its definition, clinical importance, and possible mechanisms in light of recent data on the role of platelets in atherothrombosis.

Evaluation of platelet function and pharmacological platelet inhibition in patients with myeloproliferative disorders using multiple electrode aggregometry

BACKGROUND

The aim of this study was to describe platelet aggregation characteristics by multiple electrode aggregometry (MEA) and to evaluate MEA for its potential to detect platelet dysfunction and response to anti-aggregatory drugs in patients with myeloproliferative disorders (MPD).

METHODS

We compared the platelet response to arachidonic acid (ASPI test), adenosine diphosphate (ADP test) and thrombin receptor activating peptide (TRAP test) in hirudin-anticoagulated blood of 55 patients with polycythaemia vera and essential thrombocythaemia and 75 controls.

RESULTS

Comparing MPD patients and controls no statistically significant difference indicative of platelet dysfunction was found in MPD patients. Analysis of covariance revealed platelet- and leukocyte count as a significant influencing factor on MEA function. Furthermore we could demonstrate that ASA and clopidogrel treatment results in a statistically significant lower ASPI (Controls: p<0.0001, MPD: p<0.0001) and ADPtest value (MPD: p=0.00125) compared to untreated patients thereby validating the method for monitoring of anti-aggregatory therapy.

CONCLUSION

In this study MEA was confirmed as a valid method for monitoring of ASA and clopidogrel treatment in patients with MPD and normal control subjects. The platelet and leukocyte count were identified as major influencing factors on MEA aggregation tests both in MPD patients and controls. No functional platelet abnormalities were detected in MPD patients.