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Abstract
In contrast to red blood cells, platelets float rather than sediment when a column of blood is placed in the gravitational field. By the analogy of erythrocyte sedimentation (ESR), it can be expressed with the platelet antisedimentation rate (PAR), which quantitates the difference in platelet count between the upper and lower halves of the blood column after 1 h of 1 g sedimentation. Venous blood samples from 21 healthy subjects were analyzed for PAR. After a 1-h sedimentation, the upper and lower fractions of blood samples were analyzed for platelet count, mean platelet volume (MPV), immature platelet fraction (IPF), and high-fluorescence IPF (H-IPF). The mechanisms behind platelet flotation were explored by further partitioning of the blood column, time-dependent measurements of platelet count and comparison with ESR. The structure and function of the platelets were assessed by electron microscopy (EM) and atomic force microscopy (AFM), and platelet aggregometry, respectively. Platelet antisedimentation is driven by density differences and facilitated by a size-exclusion mechanism caused by progressive erythrocyte sedimentation. The area under the curve (AUC) of the whole blood adenosine diphosphate (ADP) aggregation curves showed significant differences between the upper and lower samples (p < .005). AUC in the upper samples of 38% of healthy subjects exceeded the top of the normal range (53–122) suggesting that ascending platelets show an intensified ADP-induced aggregability ex vivo. H-IPF was significantly higher in the upper samples (p < .05). EM and AFM revealed that platelets in the upper samples were larger in volume and contained 1.6 times more alpha granules compared to platelets in the lower samples. Our results indicate that antisedimentation is able to differentiate platelet populations based on their structural and functional properties. Therefore, PAR may be a suitable laboratory parameter in various thromboinflammatory disorders.
Plain Language Summary
It is less known that platelets do not sediment in response to gravitational force but float on the top of the blood column. This phenomenon is called antisedimentation, the rate of which, however, can be different, yet this feature has not been widely studied and used in clinical practice or diagnosis. We tested the idea that antisedimentation of platelets from venous blood samples can be a potential biomarker. We have found that platelet antisedimentation is driven by density differences and facilitated by a size-exclusion mechanism caused by progressive erythrocyte sedimentation and after 1-h upper and lower fractions develop. Interestingly, the aggregation curves showed significant differences between the upper and lower samples, suggesting that the ascending platelets show ex vivo hyperaggregability. Electron and atomic force microscopy revealed that platelets in the upper samples were larger in volume and contained more alpha granules than platelets in the lower samples. Subsequently, antisedimentation can be used to differentiate platelet populations based on their structural and functional properties; thus, it may be a promising biomarker for various thromboinflammatory disorders.
Acknowledgments
The authors are thankful for valuable comments and EM images of Professor László Seres.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Author contributions
Conceptualization, E.E., M.K., A.K., and T.M.; methodology, J.H., M.T., A.M., H.A., R.B., I.P.; validation, M.K., A.K., and T.M.; formal analysis, T.M.; investigation, E.E., D.S., A.M., H.A., J.H., R.B., I.P., and M.T.; resources, M.K.; data curation, T.M.; writing–original draft preparation, T.M.; writing–review and editing, M.K. and A.K.; visualization, J.H. and H.A.; supervision, M.K. All authors have read and agreed to the published version of the manuscript.
Data availability statement
The data presented in this study are available on request from the corresponding author.
Supplementary material
Supplemental data for this article can be accessed online at https://doi.org/10.1080/09537104.2023.2298341
Institutional review board statement
The study was conducted in accordance with the Declaration of Helsinki and was approved by the University of Pécs Clinical Centre Regional and Institutional Research Ethics Committee (Ref. number: 6735, Clinical Trial No: NTC03679858).
Informed consent statement
Informed consent was obtained from all subjects involved in the study.