Platelet ageing: A review

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.

Causal relationship between physical activity and platelet traits: a Mendelian randomization study

Introduction: The purpose of this study was to discuss the causal relationship between physical activity and platelet traits. Methods: A dataset from a large-scale European physical activity and platelet traits was collected by using Mendelian randomization of the study. For the analysis, the inverse variance weighting method, weighted median and MR-Egger were used to estimate causal effects. The sensitivity analyses were also performed using Cochran's Q test, funnel plots and Leave-one-out analysis. Results: Light DIY, other exercises, strenuous sports, walking for pleasure were significantly associated with a decrease in platelet crit. But none of the heavy /light DIY was associated with increase in platelet crit. Other exercises and strenuous sports were associated with decrease in platelet count. Conclusion: Some types of physical activity have a causal relationship with platelet crit and platelet count. However, the types of physical activity we studied have not supported a causal relationship with mean platelet volume and platelet distribution width.

Heterogeneity of platelets and their responses

There has been increasing recognition of heterogeneity in blood platelets and their responses, particularly in recent years, where next-generation technologies and advanced bioinformatic tools that interrogate "big data" have enabled large-scale studies of RNA and protein expression across a growing list of disease states. However, pioneering platelet biologists and clinicians were already hypothesizing upon and investigating heterogeneity in platelet (and megakaryocyte) activity and platelet metabolism and aggregation over half a century ago. Building on their foundational hypotheses, in particular Professor Marian A. Packham's pioneering work and a State of the Art lecture in her memoriam at the 2023 International Society on Thrombosis and Haemostasis Congress by Anandi Krishnan, this review outlines the key features that contribute to the heterogeneity of platelets between and within individuals. Starting with important epidemiologic factors, we move stepwise through successively smaller scales down to heterogeneity revealed by single-cell technologies in health and disease. We hope that this overview will urge future scientific and clinical studies to recognize and account for heterogeneity of platelets and aim to apply methods that capture that heterogeneity. Finally, we summarize other exciting new data presented on this topic at the 2023 International Society on Thrombosis and Haemostasis Congress.

The shear rate promotes pinocytosis of extracellular dextran in platelets

BACKGROUND

Several conventional studies focused on platelet pinocytosis for possible utilization as drug delivery systems. Although platelet pinocytosis is important in such utilization, the impact of the shear rate on pinocytosis is unclear.

OBJECTIVE

Our objective was to investigate the relationship between shear rate and platelet pinocytosis in vitro. In addition, this study addressed the change in platelet aggregation reactivity with adenosine diphosphate (ADP) stimulation after pinocytosis.

METHOD

Porcine platelet-rich plasma was mixed with fluorescein isothiocyanate (FITC)-conjugated dextran and incubated for 15 min under shear conditions of 0, 500, and 1500 s-1. After incubation, confocal microscopic scanning and three-dimensional rendering were performed to confirm the internalization of FITC-dextran into platelets. The amount of FITC-dextran accumulated via platelet pinocytosis was compared using flow cytometry at each shear rate. In addition, light transmission aggregometry by ADP stimulation was applied to platelets after pinocytosis.

RESULTS

The amount of intracellular FITC-dextran increased with higher shear rates. Platelets with increased amounts of intracellular FITC-dextran did not show changes in the aggregation reactivity to ADP.

CONCLUSIONS

A higher shear rate promotes platelet pinocytosis, but enhanced pinocytosis does not affect aggregation sensitivity, which is stimulated by ADP.