Tehran University Medical Journal

Background: Major platelet adhesive receptors that contribute significantly to thrombus formation include platelet receptor glycoprotein Ibα (GPIbα) of the GPIb-IX-V complex and platelet glycoprotein VI (GPVI). GPIbα plays a crucial role in platelet tethering to sub-endothelial matrix, which initiates thrombus formation at arterial shear rates, whereas GPVI is critically involved in platelets firm adhesion to the site of injury regardless of shear condition. During storage, platelets experience some changes that deleteriously affect the expression levels of platelet receptors, which in turn can alter platelet functional behaviors. Considering the important roles of GPIbα and GPVI in platelet adhesion, it seems that any dramatic changes in the expression levels of these receptors can influence adhesive function of transfused platelets. Thereby examining GPIbα and GPVI expression during the storage of platelet concentrates may provide some useful information about the functional quality of these products after transfusion.

Methods: In our experimental study, 5 PRP-platelet concentrates were randomly obtained from Iranian Blood Transfusion Organization (IBTO). All the platelet products met the standard quality assessment based on AABB (American Association of Blood Banks) guidelines. Washed platelets were subjected to flowcytometry analysis for the evaluation of GPIbα and GPVI receptor expression in day 1, 3 and 5 after storage. Data were presented as mean fluorescence intensity (MFI) and analyzed by Kruskal-Wallis test with Dunn’s multiple comparison test.

Results: The GPIbα expression on first day (MFI=86±5.9) was reduced three days after storage (MFI= 69±6.9). The expression levels continued to reduce until day 5 in which GPIbα expression was markedly decreased to (MFI= 61±7.7) (P= 0.0094). GPVI expression on the days 1, 3 and 5 after storage were 20.6±3.3, 24±2.5 and 14±4.9, respectively. The results showed a significant decrease of expression on day 5, compared to that in day 3 after storage (P= 0.0213).

Conclusion: Our study showed significant decreases in the expression of platelet receptors GPIbα and GPVI after 5 days storage, suggesting a major defect in adhesive function of platelets during this term.

Background: Platelet adhesion typically occurs by the critical role of GPIb-V-IX in capturing free-flowing platelets to the injured vessel wall where its rapid binding kinetics enables platelet tethering even under conditions of high shear through the interaction of the major ligand-binding subunit of GPIb-V-IX, GPIbα with subendothelial-bound vWF. During storage, platelet undesired activation may lead to platelet storage lesion (PSL) which changes the expression levels of platelet functional receptors including GPIbα. This study investigates the levels of expression and ectodomain shedding of platelet adhesive receptor GPIbα during the storage of platelet rich plasma (PRP) concentrates (PRP- PCs).

Methods: Five PRP-platelet concentrates were obtained from Iranian Blood Transfusion Organization (IBTO). The GPIbα expressions of platelets were analyzed on day 1, 3 and 5 after storage using flowcytometry. To examine the ectodomain shedding of this receptor the microparticle free supernatants obtained from stored platelets were subjected to western blot analysis. For control study, blood specimens was drawn from healthy consenting individuals and resting platelets were isolated while resuspended in Tyrode buffer.

Results: Our results indicated a continuous decrease of GPIbα expression during storage where the expression from fist day (Mean fluorescence intensity=86±5.9) was significantly reduced compared to that of fifth day (mean fluorescence intensity=61±7.7) after storage (P=0.0094). Conversely, shed GPIbα (Glycocalicin) demonstrated continuous elevation during five-day storage (P=0.0098). According to the results the shedding levels for the first day were increased from 0.31± 0.3 to 1.5± 0.4 by the day 5 after storage.  

Conclusion: Our study has demonstrated significant loss of platelet GPIbα during storage mostly due to receptor ectodomain shedding that leads to significant increase of soluble GPIbα in stored platelets. Considering the high levels of shed GPIbα in long stored platelets whether the transfusion of such products might be associated with defective adhesive function of platelets or possible proinflammatory effects could be of interests for future investigation.