In vitro platelet ageing at 22 degrees C is reduced compared to in vivo ageing at 37 degrees C

Effects of room temperature and cold storage on the metabolic and haemostatic properties of whole blood for acute normovolaemic haemodilution

Background

Acute normovolaemic haemodilution (ANH), as a blood-conservation technique, avoids the need for allogeneic blood transfusions. The historic practice of cold-storing type-O whole blood (WB) in military fields popularised the transfusion of refrigerated WB to treat acute bleeding. In this study, we compared the effects of room temperature (RT) and refrigeration up to 24 hours on the coagulation properties of WB for ANH.

Materials and methods

Each WB sample, collected from 12 male volunteers, was divided into two parts, one stored at RT and the other refrigerated for 24 hours. Complete blood counts (CBC), blood gas levels, and coagulation profiles were measured, and rotational thromboelastometry (ROTEM) measurements were performed at the initial collection time point (baseline) and at 6, 12, and 24 hours after initial collection.

Results

The preservation of platelet aggregation response induced by arachidonic acid and adenosine diphosphate was better in cold-stored WB compared to that in RT-stored WB. The platelet aggregation response induced by thrombin receptor-activating peptide 6 was significantly decreased in all samples after 24 hours of storage when compared with that at baseline. The lactate levels in WB stored at RT increased significantly after 6 hours of storage compared to that of cold-stored samples. There were no significant differences in CBC, coagulation parameters, and ROTEM variables between the cold-stored and RT-stored WB samples.

Conclusion

WB for ANH stored in the refrigerator showed better metabolic characteristics after 6 hours of storage and better aggregation response after 12 hours of storage than WB stored at RT.

The contribution of oxidative stress to platelet senescence during storage

BACKGROUND

Platelets for transfusion become senescent and dysfunctional during storage, resulting in a markedly short shelf life (5 days). We hypothesized that oxidative stress might account for this decline.

STUDY DESIGN AND METHODS

Human platelets were treated with or without antioxidants before storage, and samples were collected and analyzed at different time points. Platelet senescence was determined by senescence-associated β-galactosidase assay, and senescence-related platelet qualities were also analyzed.

RESULTS

Sign of senescence became evident after Day 3 and continued to increase over time. We also found that chemical induction of platelet activation did not affect senescence level, whereas apoptosis inducers showed a stimulative effect on platelet senescence. Moreover, this effect was not prevented by a pan-caspase inhibitor. Meanwhile, cellular and mitochondrial reactive oxygen species were found elevated during storage, and treatments with antioxidants successfully prevented this increase and also mitigated senescence levels of stored platelets. Finally, resveratrol, a natural antioxidant, was utilized as a novel storage additive to safely extend platelet shelf time. We showed that the addition of resveratrol efficiently postponed platelet senescence and ameliorated platelet storage lesion.

CONCLUSIONS

Platelets during storage became senescent and dysfunctional over time, and we found that oxidative stress might account for this decline. The addition of antioxidants effectively postponed senescence and ameliorated platelet storage lesion, which might provide a valuable reference to future platelet storage methodologies.

Lyophilised reconstituted human platelets increase thrombus formation in a clinical ex vivo model of deep arterial injury

Platelets are the principal component of the innate haemostatic system that protect from traumatic bleeding. We investigated whether lyophilised human platelets (LHPs) could enhance clot formation within platelet-free and whole blood environments using an ex vivo model of deep arterial injury. Lyophilised human platelets were produced from stored human platelets and characterised using conventional, fluorescent and electron microscopic techniques. LHPs were resuspended in platelet-free plasma (PFP) obtained from citrated whole human blood to form final concentrations of 0,20 and 200 × 109 LHPs/L. LHPs with recalcified PFP or whole blood were perfused through the chamber at low (212 s-1) and high (1,690 s-1) shear rates with porcine aortic tunica media as thrombogenic substrate. LHPs shared morphological characteristics with native human platelets and were incorporated into clot generated from PFP or whole blood. Histomorphometrically measured mean thrombus area increased in a dose-dependent manner following the addition of LHPs to PFP under conditions of high shear [704 μm2 ± 186 μm2 (mean ± SEM), 1,511 μm2 ± 320 μm2 and 2,378 μm2 ± 315 μm2, for LHPs at 0, 20 and 200 × 109 /l, respectively (p= 0.012)]. Lyophil-ised human platelets retain haemostatic properties when reconstituted in both PFP and whole blood, and enhance thrombus formation in a model of deep arterial injury. These data suggest that LHPs have the potential to serve as a therapeutic intervention during haemorrhage under circumstances of trauma, and platelet depletion or dysfunction.

The role of adenosine diphosphate mediated platelet responsiveness for the stability of platelet integrity in citrated whole blood under ex vivo conditions

Background

Platelets are important for effective hemostasis and considered to be involved in pathophysiological processes, e.g. in cardiovascular diseases. Platelets provided for research or for therapeutic use are frequently separated from citrated whole blood (WB) stored for different periods of time. Although functionally intact platelets are required, the stability of platelet integrity, e.g. adenosine diphosphate (ADP) mediated responsiveness, has never been thoroughly investigated in citrated WB under ex vivo conditions.

Objectives

Platelet integrity was evaluated at different time points in citrated WB units, collected from healthy donors and stored for 5 days at ambient temperature. The analysis included the measurement of activation markers, of induced light transmission aggregometry and of purinergic receptor expression or function. Inhibitory pathways were explored by determination of basal vasodilator-stimulated phosphoprotein (VASP)-phosphorylation, intracellular cyclic nucleotide levels and the content of phosphodiesterase 5A. Fresh peripheral blood (PB) samples served as controls.

Results

On day 5 of storage, thrombin receptor activating peptide-6 (TRAP-6) stimulated CD62P expression and fibrinogen binding were comparable to PB samples. ADP induced aggregation continuously decreased during storage. Purinergic receptor expression remained unchanged, whereas the P2Y1 activity progressively declined in contrast to preserved P2Y12 and P2X1 function. Inhibitory pathways were unaffected except for a slight elevation of VASP phosphorylation at Ser²³⁹ on day 5.

Conclusion

After 5 days of storage in citrated WB, platelet responsiveness to TRAP-6 is sufficiently maintained. However, ADP-mediated platelet integrity is more sensitive to deterioration, especially after storage for more than 2 days. Decreasing ADP-induced aggregation is particularly caused by the impairment of the purinergic receptor P2Y1 activity. These characteristics should be considered in the use of platelets from stored citrated WB for experimental or therapeutic issues.

Secretome profiling of apheresis platelet supernatants during routine storage via antibody-based microarray

Platelet storage lesions (PSLs) occur during platelet concentrate (PC) storage. Adverse transfusion reactions (ATRs) have been demonstrated to be more frequent in older PCs and removal of the supernatant prior to transfusion reduces their occurrence. Proteomic profiling of PC supernatants was thus performed to identify proteins associated with PSLs and ATRs. Twenty-four PCs were investigated daily from day 0 to day 9 for platelet pre-activation (PPA), platelet-derived extracellular vesicles (PEVs), and platelet function. Using antibody microarrays, 673 extracellular proteins were analysed in PC supernatants on days 0, 3, 5, 7, and 9. During 5days of storage, PPA and PEVs continuously increased (P<0.0001). Platelet function was observed to remain stable within the first 5days (P=0.1751) and decreased thereafter. Comparison of all time points to day 0 revealed the identification of 136 proteins that were significantly changed in abundance during storage, of which 72 were expressed by platelets. Network analysis identified these proteins to be predominantly associated with exosomes (P=4.61×10^-8, n=45 genes) and two clusters with distinct functions were found with one being associated with haemostasis and the other with RNA binding. These findings may provide an explanation for ATRs.

SIGNIFICANCE

Changes in platelet concentrate (PC) supernatants during storage have been so far only poorly addressed and high abundant proteins burden the identification of quantitative changes in the secretome. We applied a high-throughput antibody microarray allowing for the sensitive quantification of 673 extracellular factors. PCs account for the highest number of adverse transfusion reactions (ATRs). ATRs have been demonstrated to be more frequent in older PCs and removal of the supernatant prior to transfusion reduces their occurrence. Comprehensive interpretation of the changing proteins in the secretome during platelet storage under blood banking conditions may help to identify mechanisms leading to the occurrence of adverse transfusion reactions.

Development of a computational model for macroscopic predictions of device-induced thrombosis

While cardiovascular device-induced thrombosis is associated with negative patient outcomes, the convoluted nature of the processes resulting in a thrombus makes the full thrombotic network too computationally expensive to simulate in the complex geometries and flow fields associated with devices. A macroscopic, continuum computational model is developed based on a simplified network, which includes terms for platelet activation (chemical and mechanical) and thrombus deposition and growth in regions of low wall shear stress (WSS). Laminar simulations are performed in a two-dimensional asymmetric sudden expansion geometry and compared with in vitro thrombus size data collected using whole bovine blood. Additionally, the predictive power of the model is tested in a flow cell containing a series of symmetric sudden expansions and contractions. Thrombi form in the low WSS area downstream of the asymmetric expansion and grow into the nearby recirculation region, and thrombus height and length largely remain within 95 % confidence intervals calculated from the in vitro data for 30 min of blood flow. After 30 min, predicted thrombus height and length are 0.94 and 4.32 (normalized by the 2.5 mm step height). Importantly, the model also correctly predicts locations of thrombus deposition observed in the in vitro flow cell of expansions and contractions. As the simulation results, which rely on a greatly reduced model of the thrombotic network, are still able to capture the macroscopic behavior of the full network, the model shows promise for timely predictions of device-induced thrombosis toward optimizing and expediting the device development process.

Aging of platelets stored for transfusion

A goal of platelet storage is to maintain the quality of platelets from the point of donation to the point of transfusion - to suspend the aging process. This effort is judged by clinical and laboratory measures with varying degrees of success. Recent work gives encouragement that platelets can be maintained ex vivo beyond the current 5 -7 day shelf life whilst maintaining their quality, as measured by posttransfusion recovery and survival. However, additional measures are needed to validate the development of technologies that may further reduce the aging of stored platelets, or enhance their hemostatic properties.

In vitro quantification of time dependent thrombus size using magnetic resonance imaging and computational simulations of thrombus surface shear stresses

Thrombosis and thromboembolization remain large obstacles in the design of cardiovascular devices. In this study, the temporal behavior of thrombus size within a backward-facing step (BFS) model is investigated, as this geometry can mimic the flow separation which has been found to contribute to thrombosis in cardiac devices. Magnetic resonance imaging (MRI) is used to quantify thrombus size and collect topographic data of thrombi formed by circulating bovine blood through a BFS model for times ranging between 10 and 90 min at a constant upstream Reynolds number of 490. Thrombus height, length, exposed surface area, and volume are measured, and asymptotic behavior is observed for each as the blood circulation time is increased. Velocity patterns near, and wall shear stress (WSS) distributions on, the exposed thrombus surfaces are calculated using computational fluid dynamics (CFD). Both the mean and maximum WSS on the exposed thrombus surfaces are much more dependent on thrombus topography than thrombus size, and the best predictors for asymptotic thrombus length and volume are the reattachment length and volume of reversed flow, respectively, from the region of separated flow downstream of the BFS.

Hemostatic function of apheresis platelets stored at 4°C and 22°C

INTRODUCTION

Platelet refrigeration decreases the risk of bacterial contamination and may preserve function better than standard-of-care room temperature (RT) storage. Benefits could include lower transfusion-related complications, decreased costs, improved hemostasis in acutely bleeding patients, and extended shelf life. In this study, we compared the effects of 22°C and 4°C storage on the functional and activation status of apheresis platelets.

METHODS

Apheresis platelets (n = 5 per group) were stored for 5 days at 22°C with agitation (RT) versus at 4°C with agitation (4°C + AG) and without (4°C). Measurements included platelet counts, mean platelet volume, blood gas analytes, aggregation response, thromboelastography, thromboxane B2 and soluble CD40 ligand release, activation markers, and microparticle formation.

RESULTS

Sample pH levels were within acceptable limits for storage products (pH 6.2-7.4). Platelet glucose metabolism (P < 0.05), aggregation response (adenosine diphosphate: RT 0; 4°C + AG 5.0 ± 0.8; 4°C 5.6 ± 0.9; P < 0.05), and clot strength (maximum amplitude: RT 58 ± 2; 4°C + AG 63 ± 2; 4°C 67 ± 2; P < 0.05) were better preserved at 4°C compared with RT storage. Refrigerated samples were more activated compared with RT (P < 0.05), although thromboxane B2 (P < 0.05) and soluble CD40 ligand release (P < 0.05) were higher at RT. Agitation did not improve the quality of 4°C-stored samples.

CONCLUSIONS

Apheresis platelets stored at 4°C maintain more viable metabolic characteristics, are hemostatically more effective, and release fewer proinflammatory mediators than apheresis platelets stored at RT over 5 days. Given the superior bacteriologic safety of refrigerated products, these data suggest that cold-stored platelets may improve outcomes for acutely bleeding patients.

Effect of cold storage on shear-induced platelet aggregation and clot strength

BACKGROUND

Platelets (PLTs) participate in hemostasis and save lives following trauma. PLTs for transfusion are maintained at room temperature (RT, 22°C), limiting viability to 5 days because of metabolic compromise and high risk of bacterial contamination. RT storage may result in weaker clots, delaying hemorrhage control, whereas cold storage (4°C) could permit longer PLT shelf life and result in a more hemostatic product. In this study, we characterized the effect of storage temperature on shear-induced PLT aggregation, clot formation, and strength.

METHODS

PLTs obtained from phlebotomized blood or by apheresis were stored at RT or 4°C for 5 days, and PLT aggregation and clot strength were assessed at 37°C. We studied PLT aggregation at steady and complex patterns of shear rates (500-2,500 per second) by flow cytometry, and the kinetics of clot formation and strength were measured using turbidity and dynamic mechanical analysis, respectively.

RESULTS

PLT aggregation was higher in 4°C-stored samples on Day 5 compared with fresh or RT-stored samples at all shear rates tested (fresh vs. 4°C and RT vs. 4°C, p < 0.05). PLTs stored at 4°C for 5 days formed significantly stronger clots compared with fresh or RT-stored samples as quantified by turbidity and elastic moduli measurements (fresh vs. 4°C and RT vs. 4°C, p < 0.05).

CONCLUSION

Our results show that cold-stored PLTs are more responsive to aggregation stimuli and form stronger clots, presumably because of thicker fibrin strands. These data suggest that the superior functionality of cold-stored PLTs may support faster hemostasis for acutely bleeding in trauma patients compared with RT-stored PLTs.

Separation of in-vitro-derived megakaryocytes and platelets using spinning-membrane filtration

In-vitro-derived platelets (PLTs) could potentially overcome problems associated with donated PLTs, including contamination and alloimmunization. Although several groups have produced functional PLTs from stem cells in vitro, the challenge of developing this technology to yield transfusable PLT units has yet to be addressed. The asynchronous nature of in vitro PLT generation makes a single harvest point infeasible for collecting PLTs as soon as they are formed. The current standard of performing manual centrifugations to separate PLTs from nucleated cells at multiple points during culture is labor-intensive, imprecise, and difficult to standardize in accordance with current Good Manufacturing Practices (cGMP). In an effort to develop a more effective method, we adapted a commercially-available, spinning-membrane filtration device to separate in-vitro-derived PLTs from nucleated cells and recover immature megakaryocytes (MKs), the precursor cells to PLTs, for continued culture. Processing a mixture of in-vitro-derived MKs and PLTs on the adapted device yielded a pure PLT population and did not induce PLT pre-activation. MKs recovered from the separation process were unaffected with respect to viability and ploidy, and were able to generate PLTs after reseeding in culture. Being able to efficiently harvest in-vitro-derived PLTs brings this technology one step closer to clinical relevance.

Selective triggering of platelet apoptosis, platelet activation or both

Anucleate platelets perform two fundamental processes, activation and apoptosis. We elaborated an approach for selective and concurrent stimulation of platelet apoptosis and/or activation, processes important in haemostasis and platelet clearance. Human platelets were treated with BH3 mimetic ABT-737, thrombin, calcium ionophore A23187 and matched diluents. Apoptosis was determined as mitochondrial inner membrane potential (ΔΨm) depolarization and activation as P-selectin exposure. At optimal treatment conditions (90-180 min, 37°C), ABT-737 predominantly induced apoptosis, when 77-81% platelets undergo only ΔΨm depolarization. The ABT-737 impact on ΔΨm depolarization is strongly time- and temperature-dependent, and much higher at 37°C than at room temperature. In contrast, when platelets were treated with thrombin for 15-90 min at either temperature, activation-only was predominantly (79-85%) induced, whereas A23187 triggers both apoptosis and activation (73-81%) when platelets were treated for 15-60 min at 37°C or 15-90 min at room temperature. These data demonstrate that, depending on the triggering stimulus, platelets predominantly undergo ΔΨm depolarization-only, P-selectin exposure-only, or both responses, indicating that platelet apoptosis and activation are different phenomena driven by different mechanisms. The described model provides a basis for studying differential pharmacological manipulation of platelet apoptosis and activation and their role in haemostasis, thrombosis and platelet clearance.

Determination of thromboxane formation, soluble CD40L release and thrombopoietin clearance in apheresis platelet concentrates

All deleterious changes in platelet morphology, structure and function that occur in platelet concentrates (PC) during storage are titled as the 'platelet storage lesion'. No single in vitro test currently available is sufficient in assessing these changes of platelet quality. The release of soluble CD40 Ligand (sCD40L), the formation of thromboxane (TXB2) and the thrombopoietin (TPO) clearance reflect different aspects of platelet metabolism and activitiy, and were used to examine platelet quality in apheresis platelet products. At days 1, 3 and 5, in single-donor apheresis platelet products (n = 10) under routine storage conditions, sCD40L (measured by ELISA) and TXB2 (measured by RIA) were determined after platelet stimulation (recalcification and clot formation). TPO (measured by ELISA) was determined after an incubation time of 5 h at 37°C with platelet-rich plasma (adjusted initial TPO concentration of about 500 pg/mL). Results were related to a therapeutic unit (TU = 2 × 10(11) platelets). Immediately after platelet preparation, sCD40L release was 41 ± 7.6 ng/TU, TXB2 formation 1688 ± 374 ng/TU and TPO clearance 1.22 ± 0.32 ng/h/TU. At days 1, 3 and 5, sCD40L was reduced to 89 ± 7%, 71 ± 12% and 57 ± 9%, TXB2 release to 91 ± 6%, 74 ± 12% and 58 ± 9% and TPO clearance to 90 ± 15%, 84 ± 5% and 79 ± 10% of the respective control values. In conclusion, in single-donor apheresis PC, sCD40L release and TXB2 formation as well as TPO clearance by the platelets were dependent on storage duration and reduced to about 60% to 80% of the respective control values after a storage period for 5 days. These findings are in line with literature data, indicating that a loss of platelet functionality of about 30% will occur after 5 days of storage.

Current practice and future directions for optimization of platelet transfusions in patients with severe therapy-induced cytopenia

Platelet transfusions are mainly used for patients with thrombocytopenia due to bone marrow failure, especially cancer patients developing severe chemotherapy-induced thrombocytopenia (e.g. patients with acute leukemia or other hematologic malignancies). A prophylactic transfusion strategy is now generally accepted in developed countries. Some clinical data, however, support the use of a therapeutic transfusion strategy at least for certain subsets of these patients. Several methodological approaches can then be used to evaluate the outcome of platelet transfusions, including peripheral blood platelet increments and bleeding assessments. Several factors will influence the efficiency of platelet transfusions; fever and ongoing hemorrhage are among the most important patient-dependent factors, but the number and quality of the transfused platelets are also important. The quality of transfused platelets can be evaluated by analyzing platelet activation, metabolism or senescence/apoptosis. Only evaluation of metabolism is included in international guidelines, but high-throughput methods for evaluation of activation and senescence/apoptosis are available and should be incorporated into routine clinical practice if future studies demonstrate that they reflect clinically relevant platelet characteristics. Finally, platelet transfusions have additional biological effects that may cause immunomodulation or altered angioregulation; at present it is not known whether these effects will influence the long-time prognosis of cancer patients. Thus, several questions with regard to the optimal use of platelet transfusions in cancer patients still need to be answered.

p38 mitogen-activated protein kinase activation during platelet storage: consequences for platelet recovery and hemostatic function in vivo

Platelets undergo several modifications during storage that reduce their posttransfusion survival and functionality. One important feature of these changes, which are known as platelet storage lesion, is the shedding of the surface glycoproteins GPIb-alpha and GPV. We recently demonstrated that tumor necrosis factor-alpha converting enzyme (TACE/ADAM17) mediates mitochondrial injury-induced shedding of adhesion receptors and that TACE activity correlates with reduced posttransfusion survival of these cells. We now confirm that TACE mediates receptor shedding and clearance of platelets stored for 16 hours at 37 degrees C or 22 degrees C. We further demonstrate that both storage and mitochondrial injury lead to the phosphorylation of p38 mitogen-activated kinase (MAPK) in platelets and that TACE-mediated receptor shedding from mouse and human platelets requires p38 MAP kinase signaling. Protein kinase C, extracellular regulated-signal kinase MAPK, and caspases were not involved in TACE activation. Both inhibition of p38 MAPK and inactivation of TACE during platelet storage led to a markedly improved posttransfusion recovery and hemostatic function of platelets in mice. p38 MAPK inhibitors had only minor effects on the aggregation of fresh platelets under static or flow conditions in vitro. In summary, our data suggest that inhibition of p38 MAPK or TACE during storage may significantly improve the quality of stored platelets.

Markers of platelet activation and apoptosis during storage of apheresis- and buffy coat-derived platelet concentrates for 7 days

BACKGROUND

The different production methods for platelet concentrates (PCs) result in products with variable in vitro quality and in vivo viability. The aim of this study was to compare in vitro variables of PCs produced by apheresis (AP-PC) or the buffy coat (BC-PC) method by applying a number of new and established assays.

STUDY DESIGN AND METHODS

Standard TRIMA Accel (Gambro BCT) AP-PCs (n = 20) and BC-PCs (n = 20) were stored in 100 percent plasma and changes in mitochondrial membrane potential (DeltaPsi(m)) were assessed using 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethlybenzimidazolcarbocyanine iodide (JC-1) dye on Days 1, 3, 5, and 7. The capacity of platelets (PLTs) for oxidative phosphorylation was also monitored by measuring oxygen consumption using a Clark-type electrode. PLT viability was measured using a new assay that utilizes the vital stains calcein-AM and FM4-64. Expression of phosphatidylserine (PS), CD42b, CD47, CD61, and CD62P was also assessed.

RESULTS

Although the JC-1 ratio (FL2/FL1) decreased significantly in both preparations, the percentage of PLTs with depolarized DeltaPsi(m) increased significantly in BC-PCs but not in AP-PCs. However, no significant change was detected in the PLTs' ability to consume oxygen in both preparations. PLTs in BC-PCs also showed significantly lower GPIb, CD47, and CD61 expression than AP-PCs on Day 1. PLTs in both preparations, however, showed a similar increase in CD62P and PS expression during storage, without significant loss of viability.

CONCLUSIONS

PLTs in AP-PCs and BC-PCs undergo different degrees of deterioration in mitochondrial integrity and thus may undergo different degrees of apoptosis. Interventions that maintain mitochondrial integrity may improve PLT viability in vitro.

Impairment of the hemostatic potential of platelets during storage as evaluated by flow cytometry, thrombin generation, and thrombelastography under conditions promoting formation of coated platelets

BACKGROUND

The increasing demand for platelet (PLT) transfusions has focused attention on appropriate use. Coated PLTs are a subpopulation of highly procoagulant PLTs formed by simultaneous stimulation by the agonist's collagen and thrombin hypothesized to drive clot formation at the site of vascular injury. Prolonged storage of PLTs may reduce their ability to support optimal hemostasis upon transfusion.

STUDY DESIGN AND METHODS

PLT concentrates (PCs) stored for 1, 4, 6, and 8 days were costimulated with thrombin and the collagen glycoprotein VI (GPVI) receptor agonist convulxin, and their ability to form coated PLTs was determined by flow cytometry. Further, a plasma-based thrombin generation assay and thrombelastography were used to evaluate the aged PCs' capacity to support thrombin generation and clot formation, respectively. The stored PCs were additionally tested by standard quality control methods.

RESULTS

PLT quality as measured by standard analyses was acceptable according to current practice. The hemostatic potential, however, was impaired with increasing storage time. The formation of coated PLTs decreased significantly from approximately 85 to 55 percent with increasing storage time (p<0.05). The velocity of clot formation was significantly increased from Day 4 (p<0.05). The velocity of thrombin generation and resistance against fibrinolysis were significantly reduced on Day 8 compared to Day 1 of storage (p<0.05).

CONCLUSION

Data in the present study suggest that storage significantly reduced the stored PLTs' ability to respond to conditions expected to exist at the site of vascular injury and that storage-induced reduction in PLT activation sensitivity correlated with a loss of hemostatic potential.

In vitro evaluation of platelet concentrates during storage: Platelet counts and markers of platelet destruction

BACKGROUND

Differences in platelet counts are observed by use of automated haematology analyzers making interlaboratory comparison difficult.

MATERIALS AND METHODS

Twenty-eight single-donor platelet concentrates (PCs) were collected. Platelet concentration and markers of platelet destruction were investigated during storage for 11/12 days.

RESULTS

Increasing impedance-immunoplatelet ratio was observed during storage, correlating to platelet fragments, large platelets, platelet density and cell-lysis. High variability was observed for optical-immunoplatelet ratio.

CONCLUSION

Immunoplatelet count or correction factor calculated by impedance-immunoplatelet ratio should be used to confirm that platelet unit meets platelet count requirements or to compare results from clinical trials. Optical platelet count is not recommended.

In vitro evaluation of metabolic changes and residual platelet responsiveness in photochemical treated and gamma-irradiated single-donor platelet concentrates during long-term storage

BACKGROUND

Photochemical treatment (PCT) prevents replication of pathogens in platelet concentrates (PCs) by cross-linking nucleic acids and thus affects all cells containing DNA or RNA.

STUDY DESIGN AND METHODS

Fourteen double-dose single-donor PCs were divided into two study arms. The double-dose PCs were split in two identical units, PCT and conventional control PCs. Study Arm A consisted of seven PCT PCs with corresponding untreated controls, whereas Study Arm B consisted of seven PCT PCs with corresponding gamma-irradiated control. Metabolic changes and agonist-induced platelet (PLT) response were evaluated during storage for up to 12 days.

RESULTS

Higher rate of PLT destruction, illustrated by reduced PLT content, increased lactate dehydrogenase levels, and higher CD61+ microparticle formation rate, were observed after PCT. Generally PCT accelerated metabolic changes in PCs and reduced agonist-induced (collagen or thrombin receptor activator peptide [TRAP]) aggregation responses. Flow cytometric analysis of CD62P and CD42b (GPIbalpha) expression showed higher spontaneous PLT activation in PCT PCs from 5 days of storage. Correspondingly, a reduced capacity for up regulation of CD62P expression and down regulation of CD42b was observed in PCT PLTs after stimulation by the agonists ADP or TRAP.

CONCLUSION

Generally reduced in vitro PLT quality was observed after PCT during storage for up to 12 days, with marked reduction from 5 days of storage. Compared to conventional PCs, reduced agonist-induced aggregation and glycoprotein expression were observed after PCT during storage, corresponding to significantly higher level of spontaneous PLT activation in PCT PCs. Clinical studies of efficacy and safety of PCT PCs stored for more than 5 days are recommended.

Platelet Transfusion Therapy

This article provides guidelines for the appropriate use of platelet transfusions to reduce unnecessary transfusions, thereby avoiding transfusion-related risks to the patients and the costs of platelet therapy. Platelet products available for transfusion are whole blood derived platelet concentrates and apheresis platelets. Leukoreduced platelets can be used to reduce platelet alloimmunization, cytomegalovirus transmission, and febrile transfusion reactions, while gamma irradiation prevents transfusion-associated graftversus-host disease. Other topics discussed are the expected response to transfused platelets and reasons for poor responses related to alloimmunization, underlying disease state, clinical conditions, and drugs. Appropriate transfusion guidelines based on pretransfusion platelet count, platelet dose, and whether the transfusion is prophylactic or therapeutic are outlined. Identification, prevention, and management of adverse consequences of platelet transfusions and platelet refractoriness are discussed.

Storage of buffy coat-derived platelets in additive solutions: in vitro effects of storage at 4oC

BACKGROUND

The aims of this in vitro study were to compare the storage of platelets (PLTs) at 4 degrees C with those stored at 22 degrees C and to determine the in vitro effects of preincubation at 37 degrees C for 1 hour before the analysis on the basis of the maintenance of PLT metabolic and cellular integrity.

STUDY DESIGN AND METHODS

PLT concentrates (PCs) were prepared from pooled buffy coats (BCs) for paired studies (total eight pools from 160 BCs). Each pool was divided into four PCs and stored under different conditions: at 20 to 24 degrees C on a flatbed agitator, at 20 to 24 degrees C on a flatbed agitator and with incubation of the samples at 37 degrees C for 1 hour before the analysis, at 4 degrees C, and at 4 degrees C and with incubation of the samples at 37 degrees C for 1 hour before the analysis.

RESULTS

Storage of PLTs at 4 degrees C resulted in reductions in the rate of glycolysis and better retention of pH after Day 10 than in PCs stored at 22 degrees C (Day 14, 7.003 +/- 0.047 vs. 7.201 +/- 0.146). Hypotonic shock response and extent of shape change were higher at 22 degrees C than at 4 degrees C and in preincubated PCs stored at 22 degrees C than in reference PCs stored at the same temperature (Day 5, 45.6 +/- 2.7 vs. 36.5 +/- 3.9 and 24.1 +/- 2.0 vs. 15.5 +/- 1.8). The concentration of RANTES was higher in PCs stored at 22 degrees C than at 4 degrees C (Day 7, 179 +/- 25 vs. 79 +/- 32).

CONCLUSION

PLTs stored at 4 degrees C without agitation maintain metabolic and cellular characteristics to a great extent during 21 days of storage. These studies confirm the view that PLTs lose their discoid shape and that this loss with storage at 4 degrees C is associated with reductions in metabolic rate and in their release of alpha-granule content.

Recovery and life span of 111 indium-radiolabeled platelets treated with pathogen inactivation with amotosalen HCl (S-59) and ultraviolet A light

BACKGROUND

A photochemical treatment (PCT) method to inactivate pathogens in platelet concentrates has been developed. The system uses a psoralen, amotosalen HCl, coupled with ultraviolet A (UVA) illumination.

STUDY DESIGN AND METHODS

Three sequential clinical trials evaluated viability of PCT platelets prepared with a prototype device. Posttransfusion recovery and lifespan of (111)Indium-labeled autologous 5 day-old platelets in healthy subjects was assessed. In the first study, 23 subjects received transfusions of autologous PCT and/or control platelets. In a second study, 16 of these subjects received PCT platelets processed with a Compound Adsorption Device (CAD) (PCT-CAD) to reduce patient exposure to residual amotosalen. In the third study, the effect of gamma-irradiation on PCT platelets was studied. Data from control transfusions from Study A were used for paired comparisons in the latter 2 studies.

RESULTS

Mean PCT-CAD platelet recovery for the 16 subjects with paired data was 42.5 +/- 8.7% versus 50.3 +/- 7.7% for control platelets, mean difference of 7.8% (p < 0.01). Mean lifespan for PCT-CAD platelets was 4.8 days (+/-1.3) versus 6.0 days (+/-1.2) for control platelets, mean difference of 1.3 days (p < 0.01). Platelet recovery and lifespan were similar to PCT-CAD for PCT without CAD treatment and PCT-CAD with gamma-irradiation.

CONCLUSION

Viability of 5 day-old PCT platelets was less than for control platelets. However, both were within ranges reported for 5 day-old platelets.

Role of platelet surface glycoprotein Ibα and P-selectin in the clearance of transfused platelet concentrates

BACKGROUND

Role of P-selectin (CD62) and glycoprotein (GP) Ibalpha in posttransfusion clearance of platelet concentrates (PCs) is unclear.

STUDY DESIGN AND METHODS

Platelet (PLT) activation in vitro was determined by flow cytometry using anti-CD62 and anti-GPIbalpha. PC clearance in vivo was evaluated in an animal model using rabbits with an inhibited reticuloendothelial system, as measured by 0.5-hour (R(0.5)), 24-hour (R(24)), and total (R( summation operator )) PLT recoveries, and survival time (ST). Correlations were analyzed between in vitro assays of PLT activation and in vivo clearance of conventional (Days 2-5), outdated (Days 7-8), and refrigerated PCs.

RESULTS

Binding of anti-CD62 to the PLT surface was significantly increased and of anti-GPIbalpha decreased in outdated and refrigerated PCs compared to conventional PCs. Negative correlation was observed between in vitro anti-CD62 binding and the fast (R(0.5)) PLT clearance, but not with delayed (R(24) and ST) clearance. In contrast, anti-GPIbalpha binding showed positive correlations with delayed but not with fast PLT clearance. Overall (R( summation operator )) clearance correlated better with anti-GPIbalpha than with anti-CD62 binding. CD62 density on the PLT surface was decreased after PC transfusion, whereas GPIbalpha density remained unchanged.

CONCLUSION

These data suggest that CD62 exposure on the PLT surface during PC storage triggers fast CD62-mediated PC clearance, whereas in vitro GPIbalpha changes are involved in delayed GPIbalpha-mediated PC clearance.

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.

L-carnitine improves pH and decreases surface phosphatidylserine expression in extended stored apheresis platelets

Extension of the storage period of apheresis platelets to seven or ten days may be possible with the implementation of screening for bacteria. This, however, may impair platelet quality, and additive compounds that improve storage parameters would be desirable. Apheresis platelets were harvested using the Cobe LRS device. Part of the product was aliquoted into two CLX bags, 60 ml into each, on day 0. L-carnitine (LC) to a final concentration of 5 mM was added to one container and saline to the other. pH, morphology score, and surface expression of phosphatidylserine were measured on day 1, and, in addition, hypotonic shock response (HSR) and the extent of shape change (ESC) on days 5, 10, and 13. Differences between test and controls were analyzed using paired t-tests. The addition of LC improved pH by day 5, but was more evident by days 10 and 13. By day 10, significant differences (<0.01) were observed in pH (6.54 +/- 0.3 vs. 6.75 +/- 0.3), lactate (176 +/- 31 vs. 150 +/- 24 mg %), morphology score (213 +/- 27 vs. 229 +/- 35) and ESC (7 +/- 6 vs. 11 +/- 6). Percent surface phosphatidylserine expression was less in the LC treated platelets (16 +/- 7 vs. 12 +/- 4, P<0.03). Much of the benefit observed was attributable to improved parameters in some donors. LC improves the quality of extended stored apheresis platelets.

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.

Defining the optimal storage conditions for the long-term storage of platelets

Aging of platelets after in vitro storage at 22 degrees C is significantly slower than aging of platelets in vivo at 37 degrees C, a situation that may make long-term storage of platelets possible. Three approaches appear to be of specific importance: (1) to reduce the activation of platelets during collection of blood and the preparation and storage of platelet concentrates, (2) to reduce the metabolic rate of glucose consumption and lactate production, and (3) to make sure that glucose is available in the storage medium during the entire storage period. The activation of platelets can be counteracted either by the addition of platelet activation inhibitors or the availability of certain components such as potassium and magnesium in the synthetic storage media. The use of synthetic media offers the possibility to include additional platelet-specific components in the storage environment. A number of effects have been observed that can be assigned to certain added components. Reducing platelet activation and the inclusion of key components in the platelet storage environment, such as glucose, acetate, citrate, phosphate, potassium, and magnesium, may optimize storage conditions for the long-term storage of platelets.

Apoptotic markers are increased in platelets stored at 37 degrees C

BACKGROUND

PLTs for transfusion lose viability during storage in blood banking. This loss of viability is accelerated at 37 degrees C, as is the risk of bacterial contamination, and has led to the selection of 22 degrees C as the routine storage temperature. Because PLTs contain an intact apoptotic mechanism, we sought to determine whether PLTs undergo apoptosis during storage and whether storage at 37 degrees C accelerated this process.

STUDY DESIGN AND METHODS

PLT-rich plasma from PLT concentrates was stored at 37 or 22 degrees C in small aliquots or whole bags, with and without cell-permeable caspase inhibitors. Number of PLTs, pH, LDH level, and 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium activity were analyzed over time. PLT lysates were prepared and tested for the presence and activation of apoptotic proteins by enzyme assay and Western blotting.

RESULTS

PLT viability was greatly reduced after 1 to 2 days of storage at 37 degrees C; however, signs of apoptosis were evident by 3 hours after temperature shift. In temperature-stressed PLTs only, a gradual rise in caspase-3 activity was detected that correlated with the appearance of the 17- to 20-kDa cleavage products of caspase-3. Gelsolin, a caspase-3 substrate, underwent cleavage within the same time frame. Bcl-xL and caspase-2 also declined significantly; caspase-9 activity rose. Specific caspase inhibitors could prevent caspase activation but did not improve PLT cellular viability at 37 degrees C.

CONCLUSIONS

PLTs contain apoptotic proteins that are activated during PLT storage at 37 degrees C and may account for the rapid decline in PLT cellular viability. Although ineffective here, inhibition of PLT apoptosis may improve PLT cellular viability.

L-carnitine decreases glycolysis in liquid-stored platelets

BACKGROUND

The platelet storage lesion is characterized metabolically by a pH decrease associated with lactic acid generation; a change in platelet morphology from discoid to spherical; a diminished response to in vitro challenge tests, such as the hypotonic shock response (HSR) and extent of shape change (ESC); increased surface P-selectin expression; and decreased in vivo recovery and survival. Altering storage conditions to improve these measures could allow for extension of the duration of in vitro storage.

STUDY DESIGN AND METHODS

ABO-identical paired platelet concentrates were pooled and then equally divided into two plastic bags. Either L-carnitine (LC) or an equal volume of saline (control) was added to one container of each pair. Platelets were stored at 20 to 24 degrees C for 5 to 10 days or at 1 to 6 degrees C for 5 days at various concentrations of LC between 0.1 and 15 mM: At the end of storage, pH, glucose consumption, lactate generation, HSR, ESC, and surface P-selectin expression were measured. In different experiments, paired platelet concentrates were spiked with a Staphylococcus epidermidis suspension in the presence and absence of L-carnitine at a concentration of 5 mM:

RESULTS

At 20 to 24 degrees C and concentrations of LC between 0.1 and 5 mM:, there was evidence of better pH preservation, less glucose consumption, and less lactate generation. Only with storage beyond 5 days was a difference present in either surface P-selectin expression or HSR. An L-carnitine concentration of 5 mM: appeared optimal. L-carnitine did not enhance the growth of bacteria after 7 to 8 days of storage.

CONCLUSION

LC at 5 mM: may improve the quality of platelet concentrates that are stored beyond 5 days. There was no indication that LC at this concentration would promote bacterial growth. It may be a useful additive to platelet preservation.

Platelet membrane early activation markers during prolonged storage

The relationship between platelet aging and early markers of membrane activation have not been defined clearly. Activation markers expressed during prolonged storage are similar if not identical to those that appear after exposure to thrombin. Using flow cytometry, we investigated platelet membrane expression of CD62P, CD63, and annexin V binding (i.e., loss of membrane asymmetry) in platelets stored for up to 11 days under standard blood banking conditions. We compared five apheresis platelets to two random donor platelet concentrates, and to one pooled platelet preparation from six single platelet concentrates before and after exposure to thrombin. CD62P, CD63 expression, and annexin V binding increased during storage albeit with different kinetics. The differential increments observed between resting and thrombin (1 unit/ml) activated platelets showed an inverse correlation to storage time for CD62P, CD63, and annexin V binding, which was identical to published survival curves. A difference between apheresis platelets and platelet concentrates was observed only on day 1. Our data indicate that the in vitro platelet reserve activity to thrombin activation mirrors that of radiolabeled platelet survival in vivo and that platelet cross-sectional residual life span can explain their diminished capacity to respond to thrombin as a function of viability.

Fuel choices by human platelets in human plasma

Despite the fact that homogeneous preparations of isolated cells are now being used very effectively to study a range of important biochemical questions, it is still not known what combination of fuels and energy-producing pathways is used by cells when offered the complex mixture characteristic of plasma or extracellular fluid. We have developed an in vitro system whereby highly purified and functional human platelets are incubated in human plasma that has been minimally modified from its native state. The concentration of platelets and fuels, and the complexity of fuels in the incubation are similar to those in vivo. The preparation thus represents a reasonable approximation of the physiological condition, considering the complex nature of the system being studied. Measurements carried out simultaneously during the incubation are rates of oxygen consumption, lactate production and fuel oxidation. The data allow the calculation of total ATP turnover, and contributions to this turnover by lactate production and the oxidation of individual fuels. Lactate production accounts for 24% of the ATP turnover. The oxidation of glucose and 3-hydroxybutyrate each account for under 5%, palmitate for 21%, oleate for 7% and acetate for 9%, leaving 32% of the ATP turnover as yet unaccounted for. The results confirm some previous measurements in the literature, but show that data collected under non-physiological experimental conditions can be misleading.