Individual variations in platelet reactivity towards ADP, epinephrine, collagen and nitric oxide, and the association to arterial function in young, healthy adults

Platelet inhibition by hypochlorous acid involves cAMP signalling

Hypochlorous acid (HOCl), made by neutrophil-derived myeloperoxidase, has been suggested to inhibit platelets, however, the mechanisms involved have not been described. Here we confirm that HOCl exposure changes platelet morphology and inhibits platelet spreading and aggregation. HOCl effects could be reversed by glutathione suggesting a role for cysteine oxidation. Mass spectrometry-based proteomics of HOCl-exposed platelets revealed oxidised cysteine residues in 37 proteins including adenylate cyclase 6 and Rap1B. Adenylate cyclase is involved in the inhibitory cAMP pathway triggered by endothelium-derived prostacyclin and Rap1 is a small G protein required for integrin αIIbβ3 activation and platelet aggregation. We show that HOCl exposure stimulates cAMP production and phosphorylation of the cAMP-dependent protein kinase substrate VASP in platelets and transfected HEK293T cells. In addition, HOCl inhibited Rap1-GTP formation. These data suggest that HOCl inhibits platelets at least in part through the cAMP pathway and by regulating Rap1. Thus, this study provides new insights into HOCl mediated crosstalk between neutrophils and platelets.

Observational Analyses of Ex Vivo Native American Platelet Responses

Platelet activation plays an essential role in clot formation to prevent blood loss following vascular damage. In pathologic conditions, platelet activation can lead to obstructive clots, disrupting blood flow and resulting in thrombosis. Native Americans suffer disproportionately from arterial disease and previous research has shown that Blacks are enriched in genetic polymorphisms that correlate with higher platelet reactivity contributing to an increased risk for thrombosis. Therefore, the current study sought to determine phenotypic variations in Native American platelet responses following stimulation with agonists, simulating vascular damage. Several donors from a small cohort of Native Americans showed atypical robust platelet aggregation when stimulated with submaximal concentrations of agonists. Further, when comparing α-granule secretion, a specific marker of platelet activation, Native Americans were more likely to have elevated responses to multiple agonist conditions of stimulation compared to Whites. Interestingly, there were no noticeable differences in integrin activation between Native Americans and Whites. Our study is the first to observe elevated Native American platelet responses compared to Whites, supporting further mechanistic studies and investigation of treatment approaches for the prevention of thrombosis.

Assessment of ADRB1 polymorphism in patients with acute coronary syndrome treated with ticagrelor and aspirin

Background: This study investigated the influence of ADRB1 gene rs1801253 polymorphism on the treatment response of ticagrelor and aspirin in patients with acute coronary syndrome (ACS). Methods: Genetic typing was detected by Sanger sequencing. Platelet inhibition was assessed using thromboelastography. Kaplan-Meier and Cox regression were applied for prognosis analysis. Results: Out of 200 participants, 94 cases with rs1801253-CC genotype and 106 cases with CG+GG genotype were found. There was no significant difference between the rs1801253-CC and CG+GG groups in the number of ST-segment elevation myocardial infarction, non-ST-segment elevation myocardial infarction and unstable angina patients. There was no statistical difference in the basic data of patients in the two groups in terms of age, sex, medical history and medicine use in the dominant model. The rs1801253-CC genotype was a risk prognostic factor for ACS patients based on the Cox regression analysis results. Conclusion: Detecting ADRB1 polymorphism is crucial for ACS patients undergoing treatment with ticagrelor and aspirin.

Elevated IL-1β and Comparable IL-1 Receptor Antagonist Levels Are Characteristic Features of L-PRP in Female College Athletes Compared to Male Professional Soccer Players

Autologous platelet-rich plasma (PRP) therapy has been becoming popular for the treatment of musculotendinous injuries among athletes. However, for individual and practical variations, clinical success is hardly predictable. To overcome this difficulty, we have been exploring possible criterion candidates for monitoring its clinical effectiveness. In this study, we focused on sex-based differences in young elite athletes and compared the biochemical compositions of their PRP. Leukocyte-rich PRP (L-PRP) was manually prepared from blood samples collected from male professional soccer players (mPSPs) (n = 25) and female college athletes (fCAs) (n = 36). Platelet-derived growth factor-BB (PDGF-BB), transforming-growth factor-β1 (TGFβ1), platelet factor-4 (PF4), interleukin-1β (IL-1β), and IL-1 receptor antagonist (IL-1RA) were quantified using an enzyme-linked immunosorbent assay. The levels of PDGF-BB, TGFβ1, and PF4 in L-PRP were significantly higher in mPSPs than in fCAs. Conversely, IL-1β and IL-1RA were detected at significantly and slightly higher levels, respectively, in fCAs than in mPSPs. Our findings suggest that, even though L-PRP from fCAs may have lower potential to induce cell growth and differentiation than that of mPSPs, due to the latter's higher capacity to control inflammation, it does not necessarily imply that PRP treatment in fCAs is less effective. Thus, these cytokine levels should be checked before PRP therapy.

Effects of ticagrelor monotherapy vs. clopidogrel monotherapy on platelet reactivity: a randomized, crossover clinical study (SINGLE study)

Increasing clinical trials demonstrated that the discontinuation of aspirin while maintaining a P2Y₁₂ inhibitor monotherapy could decrease the risk of bleeding without losing the antithrombotic effect. However, no data are available on the platelet reactivity of patients undergoing ticagrelor monotherapy vs. clopidogrel. Therefore, we performed this study to observe the efficacy of ticagrelor monotherapy vs. clopidogrel in Chinese patients with chronic coronary syndrome. This randomized, single-blinded, crossover trial enrolled 50 patients who were administered with ticagrelor (90 mg twice daily for 2 weeks) or clopidogrel (75 mg once daily for 2 weeks). Followed by a 2-week washout period, the two groups of patients underwent a crossover trial. Light transmission aggregometry (LTA) and thromboelastography (TEG) assays were used to test platelet reactivity. The platelet aggregation rate (PAgR) of ADP and AA was significantly lower with ticagrelor than clopidogrel (PAgR of ADP, 27.30% (7.30%-42.635%) vs. 35.55% (12.03%-69.25%), P = .0254; PAgR of AA, 77.80% (21.60%-86.43%) vs. 83.10% (67.13%-87.20%), P = .0400). There was no significant difference in PAgR of collagen and epinephrine between the two groups. The TEG assay showed that ADP and AA, which induced the inhibition of platelet aggregation, were significantly higher in the ticagrelor group than those in the clopidogrel group [ADP%, 69.00% (59.68%-88.95%) vs. 60.55% (35.98%-78.35%), P = .0020; AA%, 53.65% (22.75%-79.28%) vs. 15.15% (5.75%-70.25%), P = .0127]. High on-treatment platelet reactivity (HTPR) on ADP was 2.17% with ticagrelor and 19.57% with clopidogrel. HTPR on AA was 50.00% with ticagrelor and 69.57% with clopidogrel. Ticagrelor and clopidogrel caused the inhibition of ADP and AA-induced platelet aggregation. Moreover, ticagrelor monotherapy had a stronger inhibitory effect than clopidogrel monotherapy (except on collagen and epinephrine).

Untargeted Plasma Metabolomics and Gut Microbiome Profiling Provide Novel Insights into the Regulation of Platelet Reactivity in Healthy Individuals

BACKGROUND

Considerable variation exists in platelet reactivity to stimulation among healthy individuals. Various metabolites and metabolic pathways influence platelet reactivity, but a comprehensive overview of these associations is missing. The gut microbiome has a strong influence on the plasma metabolome. Here, we investigated the association of platelet reactivity with results of untargeted plasma metabolomics and gut microbiome profiling.

METHODS

We used data from a cohort of 534 healthy adult Dutch volunteers (the 500 Functional Genomics study). Platelet activation and reactivity were measured by the expression of the alpha-granule protein P-selectin and the binding of fibrinogen to the activated integrin αIIbβ3, both in unstimulated blood and after ex vivo stimulation with platelet agonists. Plasma metabolome was measured using an untargeted metabolic profiling approach by quadrupole time-of-flight mass spectrometry. Gut microbiome data were measured by shotgun metagenomic sequencing from stool samples.

RESULTS

Untargeted metabolomics yielded 1,979 metabolites, of which 422 were identified to play a role in a human metabolic pathway. Overall, 92/422 (21.8%) metabolites were significantly associated with at least one readout of platelet reactivity. The majority of associations involved lipids, especially members of eicosanoids, including prostaglandins and leukotrienes. Dietary-derived polyphenols were also found to inhibit platelet reactivity. Validation of metabolic pathways with functional microbial profiles revealed two overlapping metabolic pathways ("alanine, aspartate, and glutamate metabolism" and "arginine biosynthesis") that were associated with platelet reactivity.

CONCLUSION

This comprehensive overview is an resource for understanding the regulation of platelet reactivity by the plasma metabolome and the possible contribution of the gut microbiota.

Versatile New Reagent for Nitrosation under Mild Conditions

Here we report a new chemical reagent for transnitrosation under mild experimental conditions. This new reagent is stable to air and moisture across a broad range of temperatures and is effective for transnitrosation in multiple solvents. Compared with traditional nitrosation methods, our reagent shows high functional group tolerance for substrates that are susceptible to oxidation or reversible transnitrosation. Several challenging nitroso compounds are accessed here for the first time, including ¹⁵N isotopologues. X-ray data confirm that two rotational isomers of the reagent are configurationally stable at room temperature, although only one isomer is effective for transnitrosation. Computational analysis describes the energetics of rotamer interconversion, including interesting geometry-dependent hybridization effects.

Adrenaline May Contribute to Prothrombotic Condition via Augmentation of Platelet Procoagulant Response, Enhancement of Fibrin Formation, and Attenuation of Fibrinolysis

Background: Adrenaline is believed to play a role in thrombosis and hemostasis. The complex effect of its clinically relevant concentrations on thrombus formation, coagulation and fibrinolysis in human blood has never been specifically studied. Methods: Confocal microscopy was used to study thrombus formation under flow, exposure of phosphatidylserine (PS) in adhered platelets, to evaluate clots density, and to measure kinetics of fibrin formation and external fibrinolysis under flow. Flow cytometry was utilized to assess PS exposure in non-adhered platelets. Kinetics of clot formation and internal fibrinolysis was evaluated by thromboelastometry. Platelet aggregation was measured by optical aggremometry. Kinetics of clot retraction was assessed by using digital camera. Results: We found that adrenaline (1-10 nM) is able to enhance platelet activation evoked by subthreshold collagen (150 ng/ml), resulting in augmentation of platelet aggregation, thrombus formation under arterial flow conditions, platelet PS exposure, and formation of platelet-fibrin clots. The development of platelet procoagulant response evoked by adrenaline + low collagen was associated with the formation of denser platelet-fibrin clots and the decrease in rate of fibrinolysis despite whether lysis was initiated inside (internal fibrinolysis) or outside the clot (external fibrinolysis). The above phenomena were abolished by the α₂-adrenergic receptor antagonist, rauwolscine. Adrenaline-collagen synergism, expressed as PS exposure, was significantly reduced by cyclooxygenase inhibitor (acetylsalicic acid), GPIIb/IIIa receptor blocker (tirofiban), and P2Y₁₂ receptor antagonist (PSB 0739). Conclusion: Clinically relevant concentrations of adrenaline may significantly augment responses of human platelets in the presence of subthreshold concentrations of collagen, which should be considered during therapies involving adrenaline infusion. Routinely used antiplatelet drugs may reduce the prothrombotic state evoked by adrenaline-collagen synergism.

Effects of nitrite and far-red light on coagulation

Nitric oxide, NO, has been explored as a therapeutic agent to treat thrombosis. In particular, NO has potential in treating mechanical device-associated thrombosis due to its ability to reduce platelet activation and due to the central role of platelet activation and adhesion in device thrombosis. Nitrite is a unique NO donor that reduces platelet activation in that it's activity requires the presence of red blood cells whereas NO activity of other NO donors is blunted by red blood cells. Interestingly, we have previously shown that red blood cell mediated inhibition of platelet activation by adenosine diphosophate (ADP) is dramatically enhanced by illumination with far-red light that is likely due to photolysis of red cell surface bound NO congeners. We now report the effects of nitrite, far-red light, and their combination on several measure of blood coagulation using a variety of agonists. We employed turbidity assays in platelet rich plasma, platelet activation using flow cytometry analysis of a fluorescently labeled antibody to the activated platelet fibrinogen binding site, multiplate impedance-based platelet aggregometry, and assessment of platelet adhesion to collagen coated flow-through microslides. In all cases, the combination of far-red light and nitrite treatment decreased measures of coagulation, but in some cases mono-treatment with nitrite or light alone had no effect. Perhaps most relevant to device thrombosis, we observed that platelet adhesions was inhibited by the combination of nitrite and light treatment while nitrite alone and far-red light alone trended to decrease adhesion, but the results were mixed. These results support the potential of combined far-red light and nitrite treatment for preventing thrombosis in extra-corporeal or shallow-tissue depth devices where the far-red light can penetrate. Such a combined treatment could be advantageous due to the localized treatment afforded by far-red light illumination with minimal systemic effects. Given the role of thrombosis in COVID 19, application to treatment of patients infected with SARS Cov-2 might also be considered.

Spectrophotometric Determination of the Aggregation Activity of Platelets in Platelet-Rich Plasma for Better Quality Control

Although platelet-rich plasma (PRP) is now widely used in regenerative medicine and dentistry, contradictory clinical outcomes have often been obtained. To minimize such differences and to obtain high quality evidence from clinical studies, the PRP preparation protocol needs to be standardized. In addition, emphasis must be placed on quality control. Following our previous spectrophotometric method of platelet counting, in this study, another simple and convenient spectrophotometric method to determine platelet aggregation activity has been developed. Citrated blood samples were collected from healthy donors and used. After centrifugation twice, platelets were suspended in phosphate buffered saline (PBS) and adenosine diphosphate (ADP)-induced aggregation was determined using a spectrophotometer at 615 nm. For validation, platelets pretreated with aspirin, an antiplatelet agent, or hydrogen peroxide (H₂O₂), an oxidative stress-inducing agent, were also analyzed. Optimal platelet concentration, assay buffer solution, and representative time point for determination of aggregation were found to be 50–100 × 10⁴/μL, PBS, and 3 min after stimulation, respectively. Suppressed or injured platelets showed a significantly lower aggregation response to ADP. Therefore, it suggests that this spectrophotometric method may be useful in quick chair-side evaluation of individual PRP quality.