The effect of storage on the expression of platelet membrane phosphatidylserine and the subsequent impacton the coagulant function of stored platelets

The effect of short-term refrigeration on platelet responsiveness

Storage of platelet concentrates (PC) at cold temperature (CT) is discussed as an alternative to the current standard of storage at room temperature (RT). Recently, we could show that cold-induced attenuation of inhibitory signaling is an important mechanism promoting platelet reactivity. For developing strategies in blood banking, it is required to elucidate the time-dependent onset of facilitated platelet activation. Thus, freshly prepared platelet-rich-plasma (PRP) was stored for 1 and 2 h at CT (2-6 °C) or at RT (20-24 °C), followed by subsequent comparative analysis. Compared to RT, basal and induced vasodilator-stimulated phosphoprotein (VASP) phosphorylation levels were decreased under CT within 1 h by approximately 20%, determined by Western blot analysis and flow cytometry. Concomitantly, ADP- and collagen-induced threshold aggregation values were enhanced by up to 30-40%. Furthermore, platelet-covered areas on collagen-coated slides and aggregate formation under flow conditions were increased after storage at CT, in addition to induced activation markers. In conclusion, a time period of 1-2 h for refrigeration is sufficient to induce an attenuation of inhibitory signaling, accompanied with an enhancement of platelet responsiveness. Short-term refrigeration may be considered as a rational approach to obtain PC with higher functional reactivity for the treatment of hemorrhage.

MicroRNA 320a and Membrane Antigens as Tools to Evaluate the Pathophysiology of Platelets Stored in Blood Banks

Our research group, through the analysis of miRNomes in platelet concentrates (PCs) stored in blood banks, identified and validated the miR-127 and miR-320a miRNAs as biomarkers of platelet storage lesions (PSLs) in PCs. In order to validate the miRNAs 127 and 320a methodologically, as PSL biomarkers in a large number of PC bags, we also evaluated important immunological markers involved in the platelet activation/aggregation process—the CD62P receptor (P-selectin), the surface glycoproteins (GP) IIb/IIIa, and the purinergic P2Y12 receptor—via flow cytometry. The miRNAs miR-127 and miR-320a were quantified by real-time quantitative PCR (RT-qPCR). To carry out this study, 500 collection tubes were used at the upper edge of the PC bags containing platelets. Each tube was divided into seven equal parts (totaling 3500 samples) for platelet analysis from 7 different storage days, where the 1st day represents the high-quality control, and the 7th day corresponds to the low-quality control of the platelets. After analyzing all parameters during storage days, it was concluded that the relative quantification of miR-320a below 0.50 and the CD62P receptor below 27.92% are reliable indicators of the absence of storage lesions in blood banks. We believe that the values found in the expression of the CD62P receptor legitimize the use of the miR-320a and miR-127 miRNAs to build a kit capable of accurately measuring whether the stored platelets are suitable for transfusion.

Cofilin-1-induced actin reorganization in stored platelets

BACKGROUND

During platelet storage, there are extensive changes in cytoskeleton and phosphatidylserine exposure. The intrinsic mitochondrial pathway of apoptosis, activated in stored platelets, is a major mediator these changes. Cofilin-1 is an effector of actin reorganization. We examined the effect of cofilin-1 deficiency on cytoskeleton and phosphatidylserine exposure during storage and following activation of apoptosis.

METHODS AND RESULTS

We assessed actin filaments by Alexa-647-phalloidin and phosphatidylserine exposure by fluorescein isothiocyanate-lactadherin by fluorescence microscopy. In fresh platelets, actin filaments are distributed in the subcortical region, and they do not express phosphatidylserine in the outer surface. In stored platelets, there is retraction of actin filaments from the subcortical region with increased phosphatidylserine expression. These changes are seen in 20% of platelets of 6 days old and increases further with storage. Treatment with ABT-737, which activates the mitochondrial apoptosis, induces similar cytoskeletal changes in actin filaments with increased phosphatidylserine. Cofilin-1 is activated in stored platelets as well as in ABT-737 treated platelets by dephosphorylation. In cofilin-1 deficient murine platelets actin filaments are abnormal and ABT-737 induces less phosphatidylserine. Despite these changes in vitro, platelet survival of cofilin-1 deficient platelets in mice was not significantly different from their wild-type controls.

CONCLUSION

These results show that cofilin-1 plays a role in apoptosis-induced actin rearrangement and phosphatidylserine exposure during storage. Despite the defects in platelet cytoskeleton and phosphatidylserine exposure in cofilin-1-deficient platelets, the in vivo life span of platelets is similar to littermate controls, indicating multiple redundant pathways for the clearance of platelets in vivo.

The Effect of Autophagic Activity on the Function of Apheresis Platelets and on the Efficacy of Clinical Platelet Transfusion

Platelet activation and survival jointly determine the efficacy of clinical platelet transfusion. This study aimed to discuss the effect of autophagic activity on activation and aggregation of apheresis platelets and on the efficacy of clinical platelet transfusion. In this study, we investigated the effects of autophagic activity of apheresis platelets for different blood types and after different storage durations on platelet activation and aggregation functions. By Western blot, immunofluorescence, and RT-qPCR detection, we found that with the prolongation of the storage duration, the expressions of both autophagy-related proteins and genes were upregulated in apheresis platelets and their expressions were insignificantly higher in the apheresis platelets of type A and O blood than in those of type B and type AB blood. After RAPA/IGF-1 pretreatment, there was a significant increase/reduction in autophagic activity. After RAPA and IGF-1 pretreatment, an opposite variation trend was observed with platelet activation and aggregation. Autophagic activity of platelets correlated negatively with the efficacy of clinical platelet transfusion. These research findings provide a theoretical basis for effective clinical platelet transfusion.

Not all (N)SAID and done: Effects of nonsteroidal anti-inflammatory drugs and paracetamol intake on platelets

Platelets are key mediators of hemostasis and thrombosis and can be inhibited by nonsteroidal anti-inflammatory drugs (NSAIDs). As a result, platelet donors are temporarily deferred from donating if they have recently taken NSAIDs such as aspirin or ibuprofen. Despite these measures, a proportion of platelet donations show exposure to these drugs; however, little is known about the effect of NSAIDs and their metabolites on platelet quality in vivo and during storage. In this review, the effect of NSAIDs on platelet function is summarized, with a focus on the widely consumed over-the-counter (OTC) medications aspirin, ibuprofen, and the non-NSAID paracetamol. Aspirin and ibuprofen have well-defined antiplatelet effects. In comparison, studies regarding the effect of paracetamol on platelets report variable findings. The timing and order of NSAID intake is important, as concurrent NSAID use can inhibit or potentiate platelet activation depending on the drug taken. NSAID deferral periods and maximum platelet shelf-life is set by each country and are revised regularly. Reduced donor deferral periods and longer platelet storage times may affect the quality of platelet products, and it is therefore important to identify the possible impact of NSAID intake on platelet quality before and after storage.

Platelet Function Changes during Neonatal Cardiopulmonary Bypass Surgery: Mechanistic Basis and Lack of Correlation with Excessive Bleeding

Thrombocytopenia and platelet dysfunction induced by extracorporeal blood circulation are thought to contribute to postsurgical bleeding complications in neonates undergoing cardiac surgery with cardiopulmonary bypass (CPB). In this study, we examined how changes in platelet function relate to changes in platelet count and to excessive bleeding in neonatal CPB surgery. Platelet counts and platelet P-selectin exposure in response to agonist stimulation were measured at four times before, during, and after CPB surgery in neonates with normal versus excessive levels of postsurgical bleeding. Relative to baseline, platelet counts were reduced in patients while on CPB, as was platelet activation by the thromboxane A2 analog U46619, thrombin receptor activating peptide (TRAP), and collagen-related peptide (CRP). Platelet activation by adenosine diphosphate (ADP) was instead reduced after platelet transfusion. We provide evidence that thrombocytopenia is a likely contributor to CPB-associated defects in platelet responsiveness to U46619 and TRAP, CPB-induced collagen receptor downregulation likely contributes to defective platelet responsiveness to CRP, and platelet transfusion may contribute to defective platelet responses to ADP. Platelet transfusion restored to baseline levels platelet counts and responsiveness to all agonists except ADP but did not prevent excessive bleeding in all patients. We conclude that platelet count and function defects are characteristic of neonatal CPB surgery and that platelet transfusion corrects these defects. However, since CPB-associated coagulopathy is multifactorial, platelet transfusion alone is insufficient to treat bleeding events in all patients. Therefore, platelet transfusion must be combined with treatment of other factors that contribute to the coagulopathy to prevent excessive bleeding.

Apoptosis of Platelets Inhibited By Herba Sarcandrae Extract through the Mitochondria Pathway

The purpose of the present study is to decode the underlying mechanism of Herba Sarcandrae that indicated antipurpuric effect and to unveil one of its primary components, flavonoids, which play an important role. An immune mediated bone marrow failure (BMF) model in mouse was established by infusion thymus suspension cells after radiation in vivo. Platelets isolated in vitro were prepared from normal mice and BMF mice, respectively. The expressions of PS, P-selectin, PAC-1, Bax, Bad, Bid, and caspase-9 were examined by flow cytometry, and alteration of morphology of platelets under different conditions was observed. Our results indicated that the number of platelets was increased by addition of total flavonoids, and some of apoptotic markers such as Bax, Bad, Bid, and Caspase-9 were downregulated. In addition, the phosphatidylserine (PS) exposure on platelets was inhibited by total flavonoids, and the expressions of PAC-1 and P-selectin were decreased. In conclusion, it is suggested that the total flavonoids of Herba Sarcandrae may inhibit the excessive platelet apoptosis through mitochondrial pathway. In addition, activation of platelets may be also involved in mediating apoptosis of platelets.

Generation of procoagulant collagen- and thrombin-activated platelets in platelet concentrates derived from buffy coat: the role of processing, pathogen inactivation, and storage

BACKGROUND

Collagen- and thrombin-activated (COAT) platelets (PLTs), generated by dual-agonist stimulation with collagen and thrombin (THR), enhance THR generation at the site of vessel wall injury. There is evidence that higher amounts of procoagulant COAT PLTs are associated with stroke, while a decreased ability to generate them is associated with bleeding diathesis. Our aim was to study PLT functions, particularly the ability to generate COAT PLTs, in PLT concentrates (PCs) from buffy coat. Thus, we investigated the effect of processing, pathogen inactivation treatment (amotosalen-UVA), and PC storage.

STUDY DESIGN AND METHODS

Two PCs from five donors each were pooled and split in two bags; one of them was pathogen inactivated and the other one was left untreated (n = 5). Flow cytometric analyses were performed immediately after PC preparation (Day 1) and thereafter on Days 2, 5, 7, and 9 in treated and untreated PCs to measure the reactivity of PLTs (CD62P and PAC-1), the content and secretion of dense granule after stimulation with different agonists, and the percentage of COAT PLTs after dual stimulation with convulxin (agonist of the collagen receptor GPVI) and THR.

RESULTS

Preparation of PCs resulted in a significant decrease of COAT PLTs and in an impaired response to adenosine 5'-diphosphate sodium (ADP). Storage further decreased ADP response. Minor differences were observed between untreated or amotosalen-UVA-treated PCs.

CONCLUSION

Preparation of PCs from buffy coats decreased the ability to generate COAT PLTs and impaired PLT response to ADP.

Ultraviolet-Based Pathogen Inactivation Systems: Untangling the Molecular Targets Activated in Platelets

Transfusions of platelets are an important cornerstone of medicine; however, recipients may be subject to risk of adverse events associated with the potential transmission of pathogens, especially bacteria. Pathogen inactivation (PI) technologies based on ultraviolet illumination have been developed in the last decades to mitigate this risk. This review discusses studies of platelet concentrates treated with the current generation of PI technologies to assess their impact on quality, PI capacity, safety, and clinical efficacy. Improved safety seems to come with the cost of reduced platelet functionality, and hence transfusion efficacy. In order to understand these negative impacts in more detail, several molecular analyses have identified signaling pathways linked to platelet function that are altered by PI. Because some of these biochemical alterations are similar to those seen arising in the context of routine platelet storage lesion development occurring during blood bank storage, we lack a complete picture of the contribution of PI treatment to impaired platelet functionality. A model generated using data from currently available publications places the signaling protein kinase p38 as a central player regulating a variety of mechanisms triggered in platelets by PI systems.

Platelet Storage Lesions: What More Do We Know Now?

Platelet concentrate (PC) transfusions are a lifesaving adjunct to control and prevent bleeding in cancer, hematologic, surgical, and trauma patients. Platelet concentrate availability and safety are limited by the development of platelet storage lesions (PSLs) and risk of bacterial contamination. Platelet storage lesions are a series of biochemical, structural, and functional changes that occur from blood collection to transfusion. Understanding of PSLs is key for devising interventions that prolong PC shelf life to improve PC access and wastage. This article will review advancements in clinical and mechanistic PSL research. In brief, exposure to artificial surfaces and high centrifugation forces during PC preparation initiate PSLs by causing platelet activation, fragmentation, and biochemical release. During room temperature storage, enhanced glycolysis and reduced mitochondrial function lead to glucose depletion, lactate accumulation, and product acidification. Impaired adenosine triphosphate generation reduces platelet capacity to perform energetically demanding processes such as hypotonic stress responses and activation/aggregation. Storage-induced alterations in platelet surface proteins such as thrombin receptors and glycoproteins decrease platelet aggregation. During storage, there is an accumulation of immunoactive proteins such as leukocyte-derive cytokines (tumor necrosis factor α, interleukin (IL) 1α, IL-6, IL-8) and soluble CD40 ligand which can participate in transfusion-related acute lung injury and nonhemolytic transfusion reactions. Storage-induced microparticles have been linked to enhanced platelet aggregation and immune system modulation. Clinically, stored PCs have been correlated with reduced corrected count increment, posttransfusion platelet recovery, and survival across multiple meta-analyses. Fresh PC transfusions have been associated with superior platelet function in vivo; however, these differences were abrogated after a period of circulation. There is currently insufficient evidence to discern the effect of PSLs on transfusion safety. Various bag and storage media changes have been proposed to reduce glycolysis and platelet activation during room temperature storage. Moreover, cryopreservation and cold storage have been proposed as potential methods to prolong PC shelf life by reducing platelet metabolism and bacterial proliferation. However, further work is required to elucidate and manage the PSLs specific to these storage protocols before its implementation in blood banks.

Current status of blood 'pharming': megakaryoctye transfusions as a source of platelets

PURPOSE OF REVIEW

Donor-derived platelets have proven to be of hemostatic value in many clinical settings. There is a fear that the need for platelets may outgrow the donor pool in first-world countries. Moreover, there are other challenges with donor platelets that add to the impetus to find an alternative platelet source, especially after the megakaryocyte cytokine thrombopoietin was identified. Megakaryocytes have since been differentiated from numerous cell sources and the observed released platelet-like particles (PLPs) have led to calls to develop such products for clinical use. The development of megakaryocytes from embryonic stem cell also supported the concept of developing nondonor-based platelets.

RECENT FINDINGS

Several groups have claimed that nondonor-based platelets derived from in-vitro grown megakaryocytes may soon become available to supplement or replace donor-derived products, but their number and quality has been wanting. A possible alternative of directly infusing megakaryocytes that release platelets in the lungs - similar to that recently shown for endogenous megakaryocytes - has been proposed.

SUMMARY

This present review will describe the present state-of-the-art in generating and delivering nondonor-derived platelets. Progress has been slow, but advances in our ability to generate human megakaryocytes in culture, generate PLPs from these cells, and test the functionality of the resultant platelets in vitro and in vivo have identified important remaining challenges and raised alternative potential solutions.

Platelet function in reconstituted whole blood variants: An observational study over 5 days of storage time

BACKGROUND

Platelet concentrates (PCs) are usually stored at room temperature under constant gentle agitation. Risk of bacterial contamination limits maximum storage time to 5 days. The objective of the study was to investigate platelet function with regard to storage time in different reconstituted whole blood (RWB) variants.

METHODS

Donated apheresis PCs were stored at 22°C over 5 days. To obtain RWB, apheresis PCs were mixed with plasma-free packed red blood cells (RBCs) and either prethawed fresh frozen plasma (PT) or solvent-detergent plasma (SD) [1:1:1 ratio], or with leukocyte- and platelet-depleted whole blood (LD-WB) as control. Platelet function in RWB variants was assessed by impedance aggregometry (Multiplate) on Days 0, 1, 3, and 5 following platelet donation.

RESULTS

Platelet aggregometry did not reach the lower limits determined from healthy volunteers in any of the RWB variants. Platelet aggregability measured by ASPI test, ADP test, and COL test declined over storage time in all RWB variants. No differences were observed in the TRAP test. At most measurement time points, LD-RWB provided significantly higher platelet aggregability compared with SD-RWB and PT-RWB (p < 0.01). SD-RWB demonstrated higher platelet aggregability on Day 0 in the ASPI test, ADP test, and TRAP test compared with PT-RWB.

CONCLUSION

Apheresis PCs stored for 5 days at 22°C demonstrated reduced platelet aggregability, as measured by multiple electrode aggregometry when mixed with RBCs and plasma. As platelet aggregation in LD-RWB was superior compared with SD-RWB and PT-RWB variants, it might be possible that additives in RBCs or plasma are responsible for the observed depressed platelet function. Critical evaluation of current massive transfusion recommendations proposing early platelet transfusion is indicated.

Resveratrol preserves the function of human platelets stored for transfusion

Stored platelets undergo biochemical, structural and functional changes that lead to decreased efficacy and safety of platelet transfusions. Not only do platelets acquire markers of activation during storage, but they also fail to respond normally to agonists post-storage. We hypothesized that resveratrol, a cardioprotective antioxidant, could act as a novel platelet storage additive to safely prevent unwanted platelet activation during storage, while simultaneously preserving normal haemostatic function. Human platelets treated with resveratrol and stored for 5 d released less thromboxane B2 and prostaglandin E2 compared to control platelets. Resveratrol preserved the ability of platelets to aggregate, spread and respond to thrombin, suggesting an improved ability to activate post-storage. Utilizing an in vitro model of transfusion and thromboelastography, clot strength was improved with resveratrol treatment compared to conventionally stored platelets. The mechanism of resveratrol's beneficial actions on stored platelets was partly mediated through decreased platelet apoptosis in storage, resulting in a longer half-life following transfusion. Lastly, an in vivo mouse model of transfusion demonstrated that stored platelets are prothrombotic and that resveratrol delayed vessel occlusion time to a level similar to transfusion with fresh platelets. We show resveratrol has a dual ability to reduce unwanted platelet activation during storage, while preserving critical haemostatic function.

Expression and function of purinergic receptors in platelets from apheresis-derived platelet concentrates

BACKGROUND

The storage of platelets affects platelet integrity and functionality, a process named platelet storage lesion (PSL). Reduced adenosine diphosphate (ADP)-induced platelet aggregation is a typical manifestation of PSL. However, the role of ADP receptors in this context has not been evaluated yet. The aim of this study was, therefore, to investigate surface expression and function of the purinergic receptors P2Y1, P2Y12 and P2X1 in stored platelet concentrates.

MATERIAL AND METHODS

Platelets were obtained from venous whole blood and from apheresis-derived platelet concentrates stored for 0, 2 and 5 days. Purinergic receptor expression was measured by flow cytometry and western blot analysis. Receptor function was determined by calcium-induced fluorescence (P2Y1 and P2X1) or by flow cytometric measurement of the platelet reactivity index (P2Y12).

RESULTS

The basal surface expression and total content of purinergic receptors remained unchanged throughout storage. After an initial reduction during apheresis, P2X1-mediated calcium flux was maintained, whereas the P2Y1-mediated increase of calcium flux gradually decreased during the course of storage. In contrast, the platelet reactivity index was comparable in freshly obtained and stored platelets.

DISCUSSION

The function of the P2Y12 receptor is maintained during storage of apheresis-derived platelet concentrates. However, the impairment of P2X1 and especially of P2Y1 receptor function indicated by decreased receptor-mediated calcium flux is an important mechanism contributing to reduced ADP responsiveness of stored platelets.

Storage of Blood Components Does Not Decrease Haemostatic Potential: In vitro Assessment of Fresh versus Stored Blood Components Using Thromboelastography

SUMMARY: BACKGROUND: Major surgery and severe trauma typically lead to massive blood loss requiring rapid transfusion of large amounts of blood products. It has been suggested that fresh, unrefrigerated whole blood provides a haemostatic advantage in this setting. The aim of the current study was to compare the clot formation parameters of fresh, unrefrigerated whole blood and whole blood reconstituted from components stored for varying periods of time, using rotational thromboelastography (ROTEM®). METHODS: Fresh whole blood and reconstituted whole blood using combinations of non-leucoreduced red cell units (stored for 7, 14, 21, 28, or 35 days), platelet concentrates (stored for 1, 3 or 5 days), and fresh frozen plasma (stored for 6 months) were analysed using ROTEM. Measurements of the clotting time (CT), clot formation time (CFT), and maximal clot firmness (MCF) were compared between units of fresh whole blood and reconstituted whole blood samples. RESULTS: There was no difference in the haemostatic parameters measured of fresh whole blood and reconstituted whole blood using red cell units stored for less than 21 days. ROTEM demonstrated that the CT and CFT were significantly shorter for reconstituted whole blood samples using red cells stored for longer than 21 days when compared to fresh whole blood and to reconstituted whole blood samples using red cell units stored for less than 21 days. The CT was inversely correlated to the duration of platelet storage. The MCF was unchanged regardless of duration of blood product storage. CONCLUSION: Fresh unrefrigerated whole blood and blood products stored for short duration (less than 21 days) were not superior to those stored for longer durations.

Biomarker analysis of stored blood products: emphasis on pre-analytical issues

Millions of blood products are transfused every year; many lives are thus directly concerned by transfusion. The three main labile blood products used in transfusion are erythrocyte concentrates, platelet concentrates and fresh frozen plasma. Each of these products has to be stored according to its particular components. However, during storage, modifications or degradation of those components may occur, and are known as storage lesions. Thus, biomarker discovery of in vivo blood aging as well as in vitro labile blood products storage lesions is of high interest for the transfusion medicine community. Pre-analytical issues are of major importance in analyzing the various blood products during storage conditions as well as according to various protocols that are currently used in blood banks for their preparations. This paper will review key elements that have to be taken into account in the context of proteomic-based biomarker discovery applied to blood banking.

Effects of storage duration and volume on the quality of leukoreduced apheresis-derived platelets: implications for pediatric transfusion medicine

BACKGROUND

Platelet (PLT) storage adversely affects PLT structure and function in vitro and is associated with decreased PLT recovery and function in vivo. In pediatric transfusion medicine, it is not uncommon for small residual volumes to remain in parent units after aliquot preparation of leukoreduced apheresis-derived PLTs (LR-ADP). However, limited data exist regarding the impact of storage on residual small-volume LR-ADP.

STUDY DESIGN AND METHODS

Standard metabolic testing was performed on residual volumes of LR-ADP after aliquot removal and PLT aggregometry using a dual agonist of ADP and collagen was performed on stored, small-volume aliquots (10-80mL) created from an in vitro model of PLT storage.

RESULTS

Seventy-seven LR-ADP underwent metabolic (n=67) or metabolic and aggregation (n=10) studies. All products maintained a pH value of more than 6.89 throughout storage. Lactate and pCO(2) increased proportionally with longer storage time. Regardless of acceptable metabolism during storage, aggregation in 10- to 20-mL aliquots was impaired by Day 4 and aliquots less than 40 mL demonstrated the most dramatic decrease in aggregation from baseline.

CONCLUSIONS

Despite maintenance of acceptable metabolic conditions, residual volumes of LR-ADP develop impaired aggregation in vitro that may adversely affect PLT survival and function in vivo. At volumes below 40mL, LR-ADP revealed reduced aggregation. As a result, it is recommended to monitor and record volumes of LR-ADP used for pediatric transfusion. Moreover, once LR-ADP attain a volume of 50mL or less on Day 4 or Day 5 of storage, consider discarding these products until their in vivo efficacy can be studied.

Platelet senescence and phosphatidylserine exposure

BACKGROUND

The exposure of phosphatidylserine occurs during platelet (PLT) activation and during in vitro storage. Phosphatidylserine exposure also occurs during apoptosis after the release of mitochondrial cytochrome c. We have examined the role of cytochrome c release, mitochondrial membrane potential (ΔΨm), and cyclophilin D (CypD) in phosphatidylserine exposure due to activation and storage.

STUDY DESIGN AND METHODS

The exposure of phosphatidylserine and the loss of ΔΨm were determined in a flow cytometer using fluorescein isothiocyanate-lactadherin and JC-1, a lipophilic cationic reporter dye. The role of CypD was determined with cyclosporin A and CypD-deficient murine PLTs. Cytochrome c-induced caspase-3 and Rho-associated kinase I (ROCK1) activation were determined by immunoblotting and using their inhibitors.

RESULTS

Collagen- and thrombin-induced exposure of phosphatidylserine was accompanied by a decrease in ΔΨm. Cyclosporin A inhibited the phosphatidylserine exposure and the loss of ΔΨm. CypD(-/-) mice had decreased loss of ΔΨm and impaired phosphatidylserine exposure. Collagen and thrombin did not induce the release of cytochrome c nor the activation of caspase-3 and ROCK1. In contrast, in PLTs stored for more than 5 days, the phosphatidylserine exposure was associated with cytochrome c-induced caspase-3 and ROCK1 activation. ABT737, a BH3 mimetic that induces mitochondrial pathway of apoptosis, induced cytochrome c release and activation of caspase-3 and ROCK1 and phosphatidylserine exposure independent of CypD.

CONCLUSION

These results show that in stored PLTs cytochrome c release and the subsequent activation of caspase-3 and ROCK1 mediate phosphatidylserine exposure and it is distinct from activation-induced phosphatidylserine exposure.

Cell integrity and mitochondrial function after Mirasol-PRT treatment for pathogen reduction of apheresis-derived platelets: Results of a three-arm in vitro study

BACKGROUND

Mirasol pathogen reduction technology (PRT) treatment uses riboflavin (vitamin B(2)) in combination with ultraviolet light (UV) to inactivate pathogens in platelet concentrates (PCs). This treatment has been reported to increase glycolytic flux, which could result from damage to mitochondria and/or increased ATP demand.

DESIGN

Triple-dose PCs were collected by the Trima Accel device. Immediately after splitting, single units were designated to Mirasol-PRT treatment (M), gamma irradiation (X) or remained untreated (C). Platelet (PLT) mitochondrial transmembrane potential (Deltapsi) was evaluated (JC-1 assay) as well as mitochondrial enzymatic activity (MTS assay). LDH release, p selectin expression, glucose/oxygen consumption and lactate production rates were quantified and compared among study groups during 7days of storage.

RESULTS

Immediately after PRT treatment, no significant changes were found in JC-1 signal, MTS activity, and LDH release indicating that PRT treatment did not alter functional/structural cell or mitochondrial integrity as evidenced by LDH release comparable to untreated study groups. In parallel to significantly higher p selectin expression, treated PLTs exhibited significantly accelerated oxygen and glucose consumption rates associated with increased acidity due to higher lactate production rates throughout storage. Despite larger cell populations with depolarized Deltapsi particularly at days 5 and 7, mitochondrial reduction activity of M units as measured by the MTS assay was maintained and appeared to be up-regulated relative to untreated and irradiated controls.

CONCLUSION

Mirasol-PRT treated PLTs increased both glycolytic flux as well as respiratory/enzymatic mitochondrial activity. An increased demand for ATP due to increased alpha granule degranulation may be the driving force for these observations.

Erythrocyte-derived ectosomes have immunosuppressive properties

Several clinical studies have suggested that blood transfusions are immunosuppressive. Whereas there have been reports describing immunosuppression induced by leukocytes or fragments thereof, the possibility that microparticles, released by erythrocytes during storage, are also involved was not investigated. We present evidence here that such microparticles have all the properties of ectosomes including size, the presence of a lipid membrane, and the specific sorting of proteins. These erythrocyte-derived ectosomes (E-ecto) fixed C1q, which was followed by activation of the classical pathway of complement with binding of C3 fragments. Similarly to ectosomes released by PMN, they express phosphatidylserine on their surface membrane, suggesting that they may react with and down-regulate cells of the immune system. In vitro, they were taken up by macrophages, and they significantly inhibited the activation of these macrophages by zymosan A and LPS, as shown by a significant drop in TNF-alpha and IL-8 release (respectively, 80% and 76% inhibitions). In addition, the effect of E-ecto was not transient but lasted for at least 24 h. In sum, E-ecto may interfere with the innate immune system/inflammatory reaction. Therefore, E-ecto transfused with erythrocytes may account for some of the immunosuppressive properties attributed to blood transfusions.

Freezing of buffy coat-derived, leukoreduced platelet concentrates in 6 percent dimethyl sulfoxide

BACKGROUND

There has recently been renewed interest in freezing platelets (PLTs) in dimethyl sulfoxide (DMSO) for the treatment of major traumatic injuries, especially in military situations. This study examined PLTs that were frozen in small volumes of 6 percent DMSO at -80 degrees C.

STUDY DESIGN AND METHODS

Buffy coat-derived pooled leukoreduced PLT concentrates were frozen in 6 percent DMSO and stored at -80 degrees C. Assays included hypotonic shock response (HSR); aggregation; glycoprotein (GP)Ibalpha and P-selectin binding sites; annexin V binding to phosphatidylserine, glycocalicin, and lactate dehydrogenase (LDH). Cone and plate technology (DiaMed Impact-R, DiaMed) was used to test PLT function under near physiologic conditions.

RESULTS

The freeze-thaw loss of PLTs was 23 percent. HSR was 17 +/- 7 percent. Cytometry demonstrated two populations of PLTs: one with normal levels of GPIbalpha binding sites (27 x 10(3) +/- 3 x 10(3)/PLT) and one with reduced levels (5.5 x 10(3) +/- 1.2 x 10(3)/PLT). There were 1.4 x 10(3) +/- 0.2 x 10(3) P-selectin binding sites per PLT. Annexin V binding to phosphatidylserine was 50 +/- 9 percent and LDH was 496 +/- 207 IU per 10(12) PLTs. Surface coverage and aggregate size, as measured by the DiaMed Impact-R, were similar to those observed with PLTs stored for 2 days at 22 degrees C.

CONCLUSION

Some degree of activation was demonstrated by the proportion of PLTs with reduced levels of GPIbalpha binding sites, increased P-selectin expression, and increased Annexin V binding. LDH concentrations indicated a degree of lysis. The DiaMed Impact-R results showed that the PLTs were still capable of adhering to surfaces and forming aggregates under shear force.

Hemostatic and signaling functions of transfused platelets

Metabolic studies have revealed a gradual impairment in platelet integrity during storage, a process termed the platelet storage lesion. Recent evidence shows that stored platelets also lose signaling responses to physiological agonists with impaired integrin activation, secretion, and aggregation of the cells. On the other hand, storage leads to a gain in platelet activation properties, such as release of microparticles and appearance of surface epitopes for their clearance by macrophages. New techniques for measuring flow-induced thrombus formation and platelet-dependent coagulation provide evidence that the hemostatic activity of platelets decreases during storage. Besides pharmacological inhibition, novel storage strategies, like metabolic suppression, should be considered to better preserve platelet functionality while limiting the expression of clearance markers. Understanding the changes that occur in association with the platelet storage lesion and the use of updated storage methods will help to generate platelets for transfusion with optimal hemostatic function and a long circulation time after transfusion.

Paraformaldehyde induces elevation of intracellular calcium and phosphatidylserine externalization in platelets

Paraformaldehyde fixation of platelets stabilizes surface antigens while altering some that are associated with cellular activation. Present experiments show that the asymmetric distribution of phosphatidylserine in platelets was especially sensitive to paraformaldehyde treatment. It was found that this reagent induced a dose- and time-dependent translocation of phosphatidylserine to the membrane surface as measured by annexin V binding and flow cytometry. The percent phosphatidylserine-positive cells increased from about 5% to >90%. Chelation of extracellular Ca(2+) with EGTA partially blocked this translocation. Spectrofluorimetric analysis of fluo-3 loaded platelets indicates that paraformaldehyde caused a concomitant elevation of intracellular Ca(2+) concentrations, [Ca(2+)](i). ATP levels also declined in paraformaldehyde-treated cells, suggesting that the rise in [Ca(2+)](i) ensued in part from decreased activity of calcium pumps. Previous studies indicate that phosphatidylserine externalization arises from Ca(2+)-activated randomization of membrane phospholipids and decreased transport of phosphatidylserine from the outer to the inner leaflet of the plasma membrane. In light of present results, paraformaldehyde fixation is best avoided particularly in studies involving platelet apoptosis or activation.

Stored platelets contain residual amounts of tissue factor: evidence from studies on platelet concentrates stored for prolonged periods

BACKGROUND

The advent of new strategies for pathogen reduction has raised the question of whether platelet (PLT) concentrates (PCs) exposed to longer periods of storage retain adequate hemostatic function.

STUDY DESIGN AND METHODS

The effects of prolonged storage on adhesive and procoagulant functions of PLTs in PCs have been analyzed. The ability of PLTs to interact with surfaces was assessed by en face electron microscopy. Exposure of anionic phospholipids or tissue factor (TF) antigen on PLTs was assessed by flow cytometry and by immunocytochemical methods at the ultrastructural level. Studies were performed in six different PCs followed 0, 3, 5, 7, and 11 days of storage.

RESULTS

A progressive impairment of PLT-adhesive functions was observed after 5 days of storage. A progressive increase in expression of anionic phospholipids and development of procoagulant activity (PCA) measured by a modified prothrombin time (mPT) was observed along the storage. Incubation of PLTs with a specific anti-TF resulted in prolongation of the mPT by approximately 10 to 15 percent. Flow cytometry revealed minimal TF expression at later storage times. Immunocytochemical studies showed minimal TF labeling when studies were performed on PLT whole mounts. Labeling was markedly improved when PLTs were previously exposed to sonication.

CONCLUSION

Prolonged storage of PCs was associated with decreased PLT-adhesive capacities and enhanced PCA. Current preparation procedures and storage media have important limitations for preserving PCs for longer than 1 week. PLTs in PCs retain residual amounts of TF as assessed by immunocytochemical and functional assays. The origin and hemostatic significance of this TF should be investigated further.

Clinical implications of red blood cell and platelet storage lesions: an overview

Both red blood cells and platelets undergo lesions upon storage which affect their function and possibly their clinical outcome. Some of these lesions are reversible, others not. Improved additive solutions and leukocyte depletion can delay the appearance of storage lesions. In addition, cellular apoptosis leads to numerous mitochondrial and surface changes during storage which have the potential to induce immune suppression by tuning down the innate immune system. This overview highlights some laboratory and clinical aspects of red cell and platelet storage lesions.

Increased platelet phosphatidylserine exposure and caspase activation in chronic uremia

Platelet activation is associated with exposure of the aminophospholipid phosphatidylserine (PS) to the outer hemi-leaflet of the plasma membrane bilayer, which seems to be involved in the coagulation process. Because platelet activation may occur in patients suffering from chronic uremia, which is frequently associated with a thrombophilic tendency, we studied whether uremic platelets show an increased propensity to expose PS on the outer membrane leaflet and whether this process is linked with important functional and molecular changes. Flow cytometric percentage of annexin V-positive platelets, a measure of PS externalization, was significantly elevated (P < 0.001) in uremic patients when compared to normal controls under both unstimulated and agonist-stimulated conditions. Uremic platelet procoagulant activity, as measured by thrombin generation, was more than twice as high (4.13 +/- 0.3 micro mL(-1)) as that found in normal controls (1.86 +/- 0.2 micro mL(-1)). Two independent assays showed that the enzymatic activity of caspase-3, a protease involved in the loss of membrane PS asymmetry, was significantly greater in the platelets of uremic subjects than in those of healthy controls. PS exposure in agonist-stimulated platelets was markedly reduced by inhibition of caspase-3 activity but was not affected by inhibition of calpain activity. These results support the view that the thrombophilic susceptibility of uremic patients may be partly ascribed to increased PS exposure to the outer membrane leaflet of platelets. This process seems to be causally linked to an increase in caspase-3 activity, particularly during platelet activation.

Decreased platelet aggregation of platelet concentrate during storage recovers in the body after transfusion

BACKGROUND

Previous reports have shown that storage decrease the ability of PLTs to aggregate in the form of PLT concentrate (PC). Nevertheless, there are few reports that have studied the PLT function in blood samples obtained from recipients after PLT transfusion. In this study, this issue was addressed by examining the ability of PLTs to aggregate after being transfused into the blood stream.

STUDY DESIGN AND METHODS

PC was transfused to the patients with extremely low PLT counts resulting from chemotherapy. The maximum extent of PLT aggregation and size of the aggregates were compared between PLT in stored PC before transfusion with the PLT-rich plasma (PRP) from the recipients after transfusion and with PRP from patients with moderate decrease in PLT counts after chemotherapy.

RESULTS

The maximum extent of PLT aggregation was significantly higher in PRP collected from the patients after transfusion compared to the extent obtained before transfusion. There were no significant differences in the maximum extents of PLT aggregation between the PRP collected from the recipients after PC transfusion and, in the same patients, when PLT counts were moderately low.

CONCLUSION

These results suggest that the observed decreased in PLT aggregation after storage can improve in the body after transfusion, and transfused PLTs have similar aggregation ability compared to the PLTs derived from the patient.

Procoagulant surface exposure and apoptosis in rabbit platelets: association with shortened survival and steady-state senescence

BACKGROUND

The signal(s) for removal of senescent platelets from the circulation are not fully understood; phosphatidylserine (PS) expression on platelets and another marker of apoptosis, loss of mitochondrial inner membrane potential (DeltaPsim), have been implicated in platelet clearance.

OBJECTIVE

To investigate whether shortened platelet survival and steady-state platelet senescence are associated with increased surface exposure of PS and DeltaPsim collapse.

METHODS

Survival of in-vitro biotinylated rabbit platelets treated with thrombin or Ca(2+)-ionophore A23187 was tracked by flow cytometry after injection. Steady-state platelet senescence was investigated by infusing biotin to label a platelet cohort. PS expression and DeltaPsim of in-vitro biotinylated platelets and of the aging platelet cohort biotinylated in-vivo were measured by flow cytometry using annexin V-FLUOS and the DeltaPsim-sensitive dye CMXRos, respectively.

RESULTS

Although PS expression, DeltaPsim and survival of thrombin-degranulated platelets were similar to those of control platelets, increasing concentrations of A23187 caused increased surface exposure of PS and progressive shortening of platelet survival; only one-sixth of PS-expressing platelets also exhibited DeltaPsim loss. The cohort of senescent, biotinylated platelets remaining in the circulation at 96 h had increased exposure of PS and collapsed DeltaPsim; of the 17% of PS-expressing platelets, one-third did not exhibit DeltaPsim loss. There was also an increase in platelets with collapsed DeltaPsim but not expressing PS.

CONCLUSIONS

Platelets with shortened survival and senescent platelets have increased surface exposure of PS, that may be involved in their clearance. PS expression can occur independently of DeltaPsim collapse and conversely, in aged platelets, DeltaPsim loss can occur independently of PS expression.

Effect of holding buffy coats 4 or 18 hours before preparing pooled filtered PLT concentrates in plasma

BACKGROUND

Filtered PLT concentrates (PCs) were prepared in plasma pooling three (for children) or six buffy coats (BCs; for adults) after holding them a maximum of 4 hours (blood bags collected in the afternoon) or 18 hours (blood bags collected in the morning).

STUDY DESIGN AND METHODS

With flow cytometry, PCs prepared after holding BCs 4 or 18 hours were compared. BCs removed from whole-blood donations in quadruple bag packs ("top-top") were held 4 or 18 hours before pooling them with a sterile connecting device. After the BCs were centrifuged, the supernatant was transferred through a BC filter (Autostop, Pall Medical) to a CLX bag. Samples for analysis were collected from the whole-blood bag, BCs, and PCs immediately after preparation and after 1, 3, 5, and 7 days of storage on a flat-bed agitator at 22 +/- 2 degrees C. The main PLT membrane glycoproteins (GPs, IIb-IIIa, IV, and Ibalpha), some of their ligands (fibrinogen, fibronectin, and VWF), activation-dependent antigens (CD62P and CD63), and procoagulant activity markers (annexin V and bound coagulation FV-Va) have been studied.

RESULTS

In the 12 PCs (six pools of 3 units each group) studied, a minor increase in activation markers during preparation was observed. During the storage, a significant increase in the expression of GPIIb-IIIa, CD62P, CD63, annexin V, and FVa was measured. After 5 days of storage, only the percentage of PLTs with bound fibrinogen was significantly greater in PCs prepared after holding BCs for 4 hours.

CONCLUSION

In PCs prepared after holding BCs 4 or 18 hours before pooling and filtering, only a minor significant difference in the percentage of PLTs with bound fibrinogen was found after 5 days of storage. This difference is probably of little, if any, transfusional significance.

Functional characteristics of photochemically treated platelets

BACKGROUND

A photochemical treatment (PCT) process using the psoralen compound amotosalen HCL (S59) and long wavelength UVA light was developed for inactivation of infectious pathogens and WBCs. In this study the effect of PCT on functional characteristics of the platelets was evaluated in vitro.

STUDY DESIGN AND METHODS

Platelet concentrates were treated photochemically using the experimental clinical processing system T-bag S59 Reduction Device (SRD) (n = 4) or the commercially available integral processing system Wafer SRD (n = 4) and compared with control platelet concentrates in plasma/PAS III alone (n = 4). The evaluation included variables with respect to the overall quality of the product (e.g., HSR, pH), the function (aggregation and activation tests), apoptosis (annexin V and caspase 3), and lysis.

RESULTS

No differences were found in the product quality variables, in P-selectin expression, and the apoptosis variables. PCT using the T-bag SRD led to a significant decrease in aggregation capacity with collagen and thrombin and a significant increase in plasma LDH, whereas no differences for the Wafer SRD were found.

CONCLUSION

PCT using the experimental T-bag SRD led to a significant decrease in platelet function. However, the commercially available Wafer SRD had only minor in vitro effects on the quality of the platelets.

Decreased responsiveness and development of activation markers of PLTs stored in plasma

BACKGROUND

Circulating PLTs have a low activation state and high responsiveness, which ensures adequate hemostatic activity at sites of vessel wall damage. PLTs collected for transfusion purposes preferably have retained these properties to restore impaired hemostasis with thrombocytopenia.

STUDY DESIGN AND METHODS

We determined activation properties and coagulant activity of PLT-plasma preparations that were pooled or collected from single donors via apheresis.

RESULTS

In comparison to freshly isolated PLTs, both apheresis and pooled PLTs exhibited slow exposure of CD62 upon storage, followed by surface appearance of procoagulant phosphatidylserine (PS) but not activated integrin alpha IIb beta 3. During storage, thrombin- and ADP-induced Ca2+ signal generation consistently decreased in apheresis and pooled PLTs, which was accompanied by lower agonist-induced CD62 exposure and alpha IIb beta 3 activation. In flowing whole blood, stored apheresis PLTs showed lower collagen-induced Ca2+ responses and strikingly diminished participation in thrombus formation. Both apheresis and pooled PLT-plasma concentrates exhibited high tissue factor-triggered thrombin generation, which was insensitive to PLT inhibition and attributable to PS-exposing microparticles.

CONCLUSION

PLTs stored in plasma develop surface activation markers but, simultaneously, show markedly decreased responsiveness toward physiologic agonists. The plasma contains high coagulant activity, which is no longer PLT (activation)-dependent.

Quality of intraoperative autologous blood withdrawal used for retransfusion after cardiopulmonary bypass

BACKGROUND

Intraoperative autologous blood withdrawal protects the pooled blood from the deleterious effects of cardiopulmonary bypass. Following reinfusion after cardiopulmonary bypass, the fresh autologous blood contributes to less coagulation abnormalities and reduces postoperative bleeding and the need for allogeneic blood products. However, few data have been available concerning the quality and potential activation of fresh blood stored at room temperature in the operating room.

METHODS

Forty coronary artery bypass grafting patients undergoing a consistent intraoperative and postoperative autotransfusion protocol had a median of 1,000 mL of autologous blood withdrawn before cardiopulmonary bypass. After heparinization the blood was drained from the venous catheter via venous cannula into standard blood bags and stored in the operating room until termination of cardiopulmonary bypass. Samples for hemostatic and inflammatory markers were taken from the pooled blood immediately before it was returned to the patient.

RESULTS

There was some activation of platelets in the stored autologous blood, as measured by an increase of beta-thromboglobulin. Indications of thrombin formation, as assessed by plasma levels of thrombin-antithrombin complex and prothrombin fragment 1.2 were not seen, and there was no fibrinolytic activity. The red blood cells remained intact, indicated by the absence of plasma free hemoglobin. As for the inflammatory response, the levels of the terminal complement complex remained stable, and the cytokines tumor necrosis factor-alpha and interleukin 6 levels were not increased during storage. The complement activation products increased minimally, but remained within normal ranges.

CONCLUSIONS

Except for slight activation of platelets, there was no indication of coagulation, hemolysis, fibrinolysis, or immunologic activity in the autologous blood after approximately 1 hour of operating room storage. The autologous blood was preserved in a condition of high quality, and retransfusion after cardiopulmonary bypass represents an uncomplicated and almost costless procedure for blood conservation.

Reversibility of severe metabolic stress in stored platelets after in vitro plasma rescue or in vivo transfusion: restoration of secretory function and maintenance of platelet survival

BACKGROUND

Determining reversible aspects of the platelet storage lesion may result in improved function and survival of transfused platelets.

STUDY DESIGN AND METHODS

Using a model of high-dose (apheresis-derived) platelet concentrates (PC), functional changes imposed by transient adverse metabolic conditions (pH < 6.0 for 1-2 hr) that could be reversed by autologous plasma rescue followed by standard platelet storage were investigated. Whole-blood-derived PCs were transfused into a small number of normal volunteers to determine platelet recovery and survival.

RESULTS

Without rescue, high-dose PCs developed severe in vitro functional derangements at the time of the pH nadir including 1) loss of resting morphology; 2) complete abrogation of osmotic recovery and platelet aggregation and glycoprotein IIb/IIIa up-regulation to agonist; and 3) decreased alpha-granule release. By contrast, spontaneous and agonist-induced binding of annexin V were unaffected by adverse metabolic conditions. Plasma rescue to an optimal pH improved morphology scores, stabilized osmotic recovery, and completely restored platelet secretory responses, as measured by aggregation, glycoprotein IIb/IIIa up-regulation, and alpha-granule release. In a limited number of studies, plasma rescue was accompanied by preserved in vivo platelet recovery and survival after autologous transfusion after 5 days of storage.

CONCLUSION

Transient derangement of platelet metabolism, which does not increase membrane phosphatidylserine exposure, causes in vitro functional abnormalities that are fully reversed or stabilized by metabolic rescue. Preliminary data suggest that such rescued platelets may have normal posttransfusion recovery and survival.

Rational use of blood products

Blood product transfusions can be life saving and must be considered in the supportive care of children of any age with underlying oncological or haematological problems, as well as after major surgery or after serious trauma. Paediatric transfusions are particularly challenging because life-long effects of transfusion complications are more durable and serious in children than in adults, in whom the median age at transfusion is >70 years (Tynell E, Norda R, Shanwell A, Björkman A. Long-term survival in transfusion recipients in Sweden, 1993. Transfusion 2001, 41, 251-255). While the general indications for transfusions in paediatric patients are similar to adults, the threshold, volumes and infusion rates for transfusions vary with age. In this Update, we discuss current blood products, then suggest transfusion "triggers" in major surgery and haematological and oncologic practice. Finally, future developments and new possibilities are considered.