In vitro variables of apheresis platelets are stably maintained for 7 days with 5% residual plasma in a glucose and bicarbonate salt solution, PAS-5

Platelet storage: Progress so far

There is a crucial need for platelet transfusion during an emergency-surgery and treatment of platelet disorders. The unavailability of donors has furthermore increased the demand for platelet storage. Platelets have limited shelf life due to bacterial contamination and storage lesions. Temperature, materials, oxygen availability, media, platelet processing and manufacturing methods influence the platelet quality and viability during storage. The conception of various platelet additive solutions along with the advent of plastic storage during the 1980s led to enormous developments in platelet storage strategies. Cold storage of platelets gained attention despite its inability to contribute to platelet survival post-transfusion as it offers faster haemostasis. Several developments in platelet storage strategies over the years have improved the quality and shelf-life of stored platelets. Despite the progress, the efficacy of platelets during storage beyond a week has not been achieved. Antioxidants as additives have been explored in platelet storage and have proven to enhance the efficacy of platelets during prolonged storage. However, the molecular interactions of antioxidants in platelets can provide a better understanding of their mechanism of action. Optimization of dosage concentrations of antioxidants is also a critical parameter to be considered as they tend to exhibit toxicity at certain levels. This review provides comprehensive insights into the critical factors affecting platelet storage and the evolution of platelet storage. It also emphasizes the role of antioxidants as additives in platelet storage solutions and their future prospects towards better platelet banking.

Platelet Transfusion-Insights from Current Practice to Future Development

Since the late sixties, therapeutic or prophylactic platelet transfusion has been used to relieve hemorrhagic complications of patients with, e.g., thrombocytopenia, platelet dysfunction, and injuries, and is an essential part of the supportive care in high dose chemotherapy. Current and upcoming advances will significantly affect present standards. We focus on specific issues, including the comparison of buffy-coat (BPC) and apheresis platelet concentrates (APC); plasma additive solutions (PAS); further measures for improvement of platelet storage quality; pathogen inactivation; and cold storage of platelets. The objective of this article is to give insights from current practice to future development on platelet transfusion, focusing on these selected issues, which have a potentially major impact on forthcoming guidelines.

Platelet storage in more than 90% additive solution containing glucose and bicarbonate has the potential to increase shelf life

BACKGROUND

Platelet concentrates (PCs) suspended in more than 90% additive solution (AS) are recommended for patients with reactions to platelets stored in plasma. Next-generation AS containing glucose and bicarbonate might enable storage of these PCs for longer than those in current-generation AS, which was therefore evaluated in this study.

STUDY DESIGN AND METHODS

Five buffy coat or apheresis-derived PCs were pooled and split into identical units. All units except the control were centrifuged, the plasma removed and replaced with AS (SSP+, PAS-5, or PAS-G), or resuspended in the same plasma and sampled 96 hours after resuspension for analysis.

RESULTS

Plasma carryover was less than 10%, total protein less than 1 g/unit, and immunoglobulin A levels lower than 0.1 mg/mL for all PCs in AS. The pH of all the platelets during storage was higher than 6.4. PAS containing glucose maintained superior in vitro platelet function during storage compared with those resuspended in SSP+. Compared with storage in SSP+, storage in PAS-5 or PAS-G resulted in better preservation of platelet adenosine triphosphate and hypotonic shock response, lower annexin V binding, and improved mitochondrial membrane potential.

CONCLUSION

Platelets resuspended in PAS-5 and PAS-G maintained in vitro function and metabolism during storage compared with SSP+ platelets. Elevated platelet metabolic activity was noticed in PAS-G, and higher platelet activation was detected with PAS-5. Platelets resuspended in PAS containing glucose has the potential to increase the shelf life of PC in more than 90% AS.

Influence of apheresis collection device and container on the storage properties of platelets in 90% PAS-5/10% plasma

BACKGROUND

The storage properties of apheresis platelets suspended in the experimental additive solution PAS-5 and 10% plasma may be affected by the collection instrument or storage container.

METHODS AND EXPERIMENTAL DESIGN

The same consenting 12 donors provided A or T platelets with concurrent plasma on four occasions in 100% plasma. Following collection and resting, the platelets were centrifuged, and plasma was expressed and resuspended in PAS-5 to yield units with 10% plasma. Platelets were either maintained in the original storage container or transferred to another of the manufacturer's storage containers. On days 1, 5 and 7, units were assayed for an array of in vitro tests.

RESULTS

Average unit volume, yield and percent plasma was 291±11 mL, 3.7±0.4×10¹¹, and 10.3±0.7%, respectively, and were comparable between collections with either of the apheresis instruments and stored with either of the manufacturer's containers. Day 1 platelet activation (CD62P+) was 40±22% and was similar in either of the collection instruments or containers. Except for pH (days 1, 5), CO₂ (days 1, 5, 7), and extent of shape change (day 5), every other in vitro parameter was similar between apheresis platforms or the manufacturer's container. pH values of all units on all days of storage were ≥6.8, except one unit that was collected on T and stored in an A container, which had pH values of 6.8 and 5.7 on days 5 and 7, respectively.

DISCUSSION

Storage of platelets suspended in PAS-5 with 10% plasma is feasible in the original manufacturer's container for seven days. Based on CO₂ levels, T containers have greater gas exchange than A containers.

Value of calcium and phosphate in a bicarbonate-containing platelet additive solution with low plasma levels in maintaining key in vitro platelet storage parameters

BACKGROUND

Use of recently developed platelet (PLT) additive solutions (PAS) with 5% plasma levels may reduce the frequency and/or severity of transfusion reactions attributed to plasma. PLTs suspended in bicarbonate-containing PAS-5 with 5% plasma levels can maintain key PLT parameters during 7-day storage. This study evaluates the role of calcium and phosphate, as constituents of PAS-5, in maintaining PLT parameters.

STUDY DESIGN AND METHODS

An Amicus apheresis PLT unit (n = 13) was equally divided into four 60-mL aliquots in CF-250 polyolefin bags. Four different formulations of PAS-5 were prepared: PAS-5, PAS-5 without phosphate (-PO₄ ), PAS-5 without calcium (-Ca), and PAS-5 without Ca and phosphate (-Ca/-PO₄ ). PLTs were centrifuged, and the supernatant was expressed and replaced with the respective PAS, yielding PLTs suspended in 95% PAS and 5% plasma. PLTs were stored at 20 to 24ºC with agitation for 7 days. PLT in vitro parameters were evaluated on Days 1, 5, and 7.

RESULTS

In PLT PAS-5 aliquots, pH levels were maintained better compared with those in -Ca and -Ca/-PO₄ aliquots. Glycolysis was greater in -Ca and -Ca/-PO₄ PLT aliquots compared with PAS-5 aliquots. Hypotonic stress response and morphology were less and p-selectin (CD62P) binding was greater in -Ca/-PO₄ PLT aliquots. The accumulation of reactive oxygen species was greater in -Ca/-PO₄ PLTs. Phosphorylation of p38 mitogen-activated protein kinase (MAPK) was greater in -Ca and -Ca/-PO₄ PLT aliquots during storage.

CONCLUSION

The removal of calcium and phosphate from PAS-5 leads to the activation of p38 MAPK and deterioration of key PLT storage parameters.

Novel platelet storage conditions: additive solutions, gas, and cold

PURPOSE OF REVIEW

Platelets are a frequently requested blood product today and are often in limited supply because of a shelf life of 5-7 days, depending on the country. Room temperature storage is associated with an increased risk of transfusion-transmitted infection. Plasma used for platelet storage is unavailable for other uses, and allogeneic plasma carries with it risks for adverse transfusion reactions. This review looks at recent activities evaluating alternative conditions for the storage of platelets.

RECENT FINDINGS

New-generation platelet additive solutions are being evaluated and applied as a strategy to reduce the volume of allogeneic plasma transfused and to support storage following pathogen reduction treatments. There is a renewed interest in refrigerator temperature and frozen storage of platelets to improve availability, to reduce septic transfusion risk, and to enhance hemostatic efficacy in the bleeding patient.

SUMMARY

Use of platelet additive solutions has been shown to reduce the incidence of allergic and nonhemolytic febrile transfusion reactions in two large studies. Results of ongoing research and new clinical trials in cold storage methods will be forthcoming and may present solutions for platelet availability problems and new choices for therapeutic transfusion of the bleeding patient.

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.

Platelet storage media

Present platelet storage media often designated platelet additive solutions (PAS) basically contain acetate, citrate and phosphate and recently also potassium and magnesium. However, there seems to be an increasing interest in developing PASs that can be used also after further reduction of residual plasma content below 15-20% plasma. Inclusion of glucose but also calcium and bicarbonate in such solutions have been suggested to improve platelet (PLT) storage, especially when plasma content is reduced to very low levels. Results from a limited number of studies using novel PAS alternatives have been presented during the last years, such as InterSol-G, PAS-5, M-sol, PAS-G and SAS. Most of them are experimental solutions. The combined results presented in those studies suggest that presence of glucose may be necessary during PLT storage, primarily to maintain ATP at acceptable levels. At plasma inclusion below 15-20%, the content of glucose will generally be too low to support PLT metabolism for more than a few days making glucose addition in PAS necessary. Significant effects associated with presence of calcium was observed in PLTs stored in PAS with 5% inclusion but not with 20-35% plasma inclusion, suggesting that the content of plasma could be of importance. Bicarbonate only seems to be of importance for pH regulation, primarily when plasma inclusion is reduced to about 5%. Reduction in rate of glycolysis was observed in some PAS alternatives containing potassium and magnesium but not in others. Differences in pH or in concentrations of the various compounds included in PAS may be possible explanations. Additionally, novel PAS containing glucose, calcium and bicarbonate does not seem to be associated with improved in vitro results as compared to SSP+ or CompoSol when PLTs are stored with 35% plasma inclusion. The results would then also suggest that excess of glucose in novel PAS environment may not be associated with additional positive effects on PLT metabolism. This review is based on the few publications on novel PAS available, and additional studies would be needed in the future.

Evaluation of in vitro storage properties of apheresis platelets suspended in a bicarbonate-containing additive solution with low levels of plasma and stored with a 24-hour interruption of agitation

BACKGROUND AND OBJECTIVES

PLT additive solutions (PAS) are useful for reducing the frequency and/or severity of plasma-associated transfusion reactions. A new PAS solution, PAS-5, containing 5% plasma, maintains in vitro PLT properties during 7-day storage. Periods with interruption of agitation (IA) ≤24 h routinely occur during PLT shipment and do not usually compromise platelet quality. The aim of the study was to evaluate the properties of PLTs stored for 7 days in 95% PAS-5/5% plasma subjected to a 24-h IA.

MATERIALS AND METHODS

Double apheresis Amicus units (n = 12) were collected using a manual PAS-5 addition to hyperconcentrated PLTs. PLT units were equally divided in two containers. Control and test PLTs were stored with continuous agitation at 20-24°C except for 24-h IA period for test units between days 2-3.

RESULTS

During storage, levels of glucose, lactate, mitochondrial membrane potential and aggregation significantly differed in test units compared to those of control. The pH levels of test PLTs were less than those of control units with 7/12 test units having pHs <6·2 on Day 7 compared to 1/12 control units. Morphology score, GP1bα expression, ESC values, superoxide production were also less, and activation was greater in test PLTs than those of control. All other parameters were similar between test and control units.

CONCLUSION

PLTs stored in PAS-5 solution containing 5% plasma with a 24-h IA results in marked decrements in many in vitro PLT quality parameters during 7-day storage.

ABO incompatible platelets: risks versus benefit

PURPOSE OF REVIEW

The importance of ABO blood group system compatibility in platelet transfusion is a subject of ongoing debate. Although there are theoretical advantages to pursuing a strict policy of providing exclusively ABO-compatible products, resource challenges may make this untenable for many transfusion services. Moreover, data supporting a net clinical benefit for this practice have been lacking. This review summarizes recent developments in the area of ABO compatibility and platelet transfusion and examines the risks and benefits associated with transfusion practices allowing for platelet ABO incompatibility.

RECENT FINDINGS

ABO-major incompatible transfusions are associated with lower platelet count increments than either ABO identical or minor incompatible transfusions and may lead to decreased intervals between platelet transfusions in thrombocytopenic patients. ABO-minor incompatible transfusions may rarely result in acute hemolytic reactions that are not predicted by isohemagglutinin titers. Yet published evidence to date does not clearly demonstrate improvements in clinical outcomes for patients receiving ABO-identical or ABO-compatible platelets. Adherence to a strict policy of transfusing exclusively ABO-identical platelets may lead to an increase in product wastage and challenges in maintaining adequate platelet availability.

SUMMARY

There is presently limited data and no consensus on the best approach for managing ABO compatibility in platelet transfusions. Well designed, sufficiently powered randomized clinical trials are urgently needed. These studies must examine not only safety and efficacy of various ABO matching strategies but also clinical benefit and resource utilization in order to identify optimal platelet transfusion strategies.

Impact of glucose and acetate on the characteristics of the platelet storage lesion in platelets suspended in additive solutions with minimal plasma

BACKGROUND AND OBJECTIVES

Glucose and acetate have been proposed to be required elements in platelet storage media. This study investigated the role of these compounds on the varied elements that comprise the platelet storage lesion.

MATERIALS AND METHODS

For each replicate, four pooled and split ABO group-specific buffy coat-derived platelet concentrates were suspended in an in-house additive solution with minimal plasma and varying final concentrations of acetate or glucose. Units were sampled on days 2, 3, 6, 8 and 10 and tested for markers of platelet morphology, activation, function, metabolism and indicators of cell death.

RESULTS

The absence of glucose was associated with a decrease in ATP, falling to a mean of 1·1 ± 0·1 μmol/10(11) plts in units with no added glucose compared with 4·2 ± 0·6 μmol/10(11) plts (P < 0·001) in units with 30 mm glucose. As glucose became depleted, the decrease in ATP to levels below 3 μmol/10(11) plts was associated with an increase in both annexin V binding and intracellular free calcium. In units lacking exogenous acetate, ATP levels on day 10 were 5·2 ± 1·5 μmol/10(11) plts compared with 2·7 ± 0·9 μmol/10(11) plts in units with 56 mm acetate (P = 0·006). Higher concentrations of exogenous acetate were associated with a lower hypotonic shock response and higher surface expression of CD62P suggestive of a dose dependency.

CONCLUSION

Under current physical storage conditions, glucose appears necessary for the maintenance of platelets stored as concentrates in minimal volumes of plasma. The addition of acetate was associated with increased platelet activation and reduced ATP levels.

The role of bicarbonate in platelet additive solution for apheresis platelet concentrates stored with low residual plasma

BACKGROUND

Complex platelet additive solutions (PASs) are required to store platelet (PLT) concentrates with plasma levels below 30%. Previously, apheresis PLTs stored with 5% plasma in acetate- and bicarbonate-containing PAS maintained stable pH and bicarbonate levels during 7-day storage. Due to this observation, the necessity of added bicarbonate in PAS was investigated and whether the concurrent increase in PAS pH after bicarbonate addition had any effect on PLT storage.

STUDY DESIGN AND METHODS

Apheresis PLTs were stored in 5% plasma-95% high- or low-pH PAS, with or without bicarbonate (n=10 per arm). Bicarbonate PAS PLTs were paired and nonbicarbonate PAS PLTs were paired (split from same double-dose collection). PLTs were evaluated for in vitro variables on Days 1 and 7 and up to Day 14 if the Day 7 pH was higher than 6.2.

RESULTS

PLT pH was maintained above 7.3 to Day 14 in bicarbonate PAS PLTs while pH failures below 6.2 were observed in 4 of 10 and 2 of 10 units on Day 7 in low- and high-pH nonbicarbonate PAS arms, respectively. Day 7 in vitro variables in nonbicarbonate PAS PLTs with pH values of higher than 6.2 were comparable to Day 7 variables in bicarbonate PAS PLTs. The pH of bicarbonate PAS did have a small effect on pH and bicarbonate levels in PLT units, but did not have an effect on functional variables and metabolism.

CONCLUSION

Bicarbonate was not required to maintain in vitro PLT function in 5% plasma-95% PAS, but was required as a pH buffer and increased PAS pH did not significantly contribute to this effect.