Quality assessment of platelet concentrates supplemented with second-messenger effectors

Morphology of platelet Golgi apparatus and their significance after acute cerebral infarction

Blood samples were harvested from the antecubital vein of 20 fasting patients with acute cerebral infarction at 1, 7 and 15 days after onset to prepare blood platelet suspension. Fasting antecubital vein blood was collected from an additional 20 normal adults as controls. Under transmission tron microscope, platelet Golgi tubules and vesicles became significantly thickened, enlarged, and irregular after acute cerebral infarction. Alpha granules in platelets significantly reduced in number, especially 1 day after cerebral infarction. Under immunoelectron microscopy, a few alpha granules aggregated around Golgi tubules and vesicles after infarction. These results suggested that platelet Golgi apparatus displayed significant morphological changes, which were possibly associated with enhanced synthetic and secretory functions of activated platelets after acute cerebral infarction. This study used Golgi apparatus blocking agent Brefeldin A to block Golgi apparatus in an aim to study the effects of Golgi apparatus on CD40L expression on the surface of activated platelets. Flow cytometry revealed that CD40L expression on activated platelet surfaces decreased significantly when Golgi apparatus was blocked, which indicated that Golgi apparatus participated in the synthesis and transport of CD40L to the platelet surface.

Addition of sialidase or p38 MAPK inhibitors does not ameliorate decrements in platelet in vitro storage properties caused by 4 °C storage

BACKGROUND AND OBJECTIVES

Bacterial proliferation is inhibited in platelets (PLTs) stored at refrigerated temperatures, but also dramatically decreases PLT in vivo survival. Recent studies have demonstrated that cold temperature (CT) stored PLTs secrete sialidases upon re-warming, removing sialic acid from the PLT surface, which may be responsible for clustering of GPIbα and PLT clearance from circulation. In this study, the influence of a sialidase inhibitor or a p38 MAP kinase inhibitor was evaluated in units stored at 4 °C.

MATERIALS AND METHODS

After collection of a single Trima apheresis unit (n = 12), PLTs were aliquoted into four 60-ml CLX storage bags. One bag was stored at 20-24 °C (RT) with continuous agitation; a second bag was stored at 4 °C without agitation; a third bag was held at 4 °C without agitation with sialidase inhibitor, a fourth bag was incubated at 4 °C with a p38 MAPK inhibitor without agitation.

RESULTS

Beginning from Day 1, all in vitro PLT parameters were adversely affected by CT compared to those of RT. Similar in vitro storage properties were observed in CT PLT in the presence or absence of sialidase or p38 MAPK inhibitors. P38 MAPK phosphorylation inhibition was not observed at CT. Decrease of sialidase activity was observed for 2 days in PLTs stored in additive solution but not in plasma.

CONCLUSION

Addition of either sialidase or p38 MAPK inhibitors do not improve any in vitro parameters of PLTs stored at 4 °C in 100% plasma.

High-density lipoprotein 3 and apolipoprotein A-I alleviate platelet storage lesion and release of platelet extracellular vesicles

BACKGROUND

Stored platelet (PLT) concentrates (PLCs) for transfusion develop a PLT storage lesion (PSL), decreasing PLT viability and function with profound lipidomic changes and PLT extracellular vesicle (PL-EV) release. High-density lipoprotein 3 (HDL3 ) improves PLT homeostasis through silencing effects on PLT activation in vivo. This prompted us to investigate HDL3 and apolipoprotein A-I (apoA-I) as PSL-antagonizing agents.

STUDY DESIGN AND METHODS

Healthy donor PLCs were split into low-volume standard PLC storage bags and incubated with native (n)HDL3 or apoA-I from plasma ethanol fractionation (precipitate IV) for 5 days under standard blood banking conditions. Flow cytometry, Born aggregometry, and lipid mass spectrometry were carried out to analyze PL-EV release, PLT aggregation, agonist-induced PLT surface marker expression, and PLT and plasma lipid compositions.

RESULTS

Compared to control, added nHDL3 and apoA-I significantly reduced PL-EV release by up to -62% during 5 days, correlating with the added apoA-I concentration. At the lipid level, nHDL3 and apoA-I antagonized PLT lipid loss (+12%) and decreased cholesteryl ester (CE)/free cholesterol (FC) ratios (-69%), whereas in plasma polyunsaturated/saturated CE ratios increased (+3%) and CE 16:0/20:4 ratios decreased (-5%). Administration of nHDL3 increased PLT bis(monoacylglycero)phosphate/phosphatidylglycerol (+102%) and phosphatidic acid/lysophosphatidic acid (+255%) ratios and improved thrombin receptor-activating peptide 6-induced PLT aggregation (+5%).

CONCLUSION

nHDL3 and apoA-I improve PLT membrane homeostasis and intracellular lipid processing and increase CE efflux, antagonizing PSL-related reduction in PLT viability and function and PL-EV release. We suggest uptake and catabolism of nHDL3 into the PLT open canalicular system. As supplement in PLCs, nHDL3 or apoA-I from Fraction IV of plasma ethanol fractionation have the potential to improve PLC quality to prolong storage.

Carbohydrate clearance receptors in transfusion medicine

BACKGROUND

Complex carbohydrates play important functions for circulation of proteins and cells. They provide protective shields and refraction from non-specific interactions with negative charges from sialic acids to enhance circulatory half-life. For recombinant protein therapeutics carbohydrates are especially important to enhance size and reduce glomerular filtration loss. Carbohydrates are, however, also ligands for a large number of carbohydrate-binding lectins exposed to the circulatory system that serve as scavenger receptors for the innate immune system, or have more specific roles in targeting of glycoproteins and cells.

SCOPE OF REVIEW

Here we provide an overview of the common lectin receptors that play roles for circulating glycoproteins and cells, and present a discussion of ways to engineer glycosylation of recombinant biologics and cells to improve therapeutic effects.

MAJOR CONCLUSIONS

While the pharmaceutical industry has learned how to exploit carbohydrates to improve pharmacokinetic properties of recombinant therapeutics, our understanding of how to improve cell-based therapies by manipulation of complex carbohydrates is still at its infancy. Progress with the latter has recently been achieved with cold-stored platelets, where exposure of uncapped glycans lead to rapid clearance from circulation by several lectin-mediated pathways.

GENERAL SIGNIFICANCE

Understanding lectin-mediated clearance pathways is essential for progress in development of biological pharmaceuticals.

Procoagulant platelets: are they necrotic?

Apoptosis and necrosis represent distinct cell death processes that regulate mammalian development, physiology and disease. Apoptosis characteristically leads to the silent destruction and removal of cells in the absence of an inflammatory response. In contrast, necrotic cell death can induce physiologic inflammatory responses linked to tissue defense and repair. Although anucleate, platelets undergo programmed cell death, with apoptosis playing an important role in clearing effete platelets from the circulation. While it has long been recognized that procoagulant platelets exhibit characteristic features of dying cells, recent studies have demonstrated that platelet procoagulant function can occur independent of apoptosis. A growing body of evidence suggest that the biochemical, morphologic and functional changes underlying agonist-induced platelet procoagulant function are broadly consistent with cell necrosis, raising the possibility that distinct death pathways regulate platelet function and survival. In this article, we will discuss the mechanisms underlying apoptotic and necrotic cell death pathways and examine the evidence linking these pathways to the platelet procoagulant response. We will also discuss the potential contribution of these pathways to the platelet storage lesion and propose a simplified nomenclature to describe procoagulant platelets.

Glycans and glycosylation of platelets: current concepts and implications for transfusion

PURPOSE OF REVIEW

Platelet products are currently stored at room temperature, because refrigeration causes their rapid clearance from the circulation upon transfusion. Glycans have recently been emphasized as important determinants for the clearance of refrigerated platelets. The present review addresses the current knowledge of platelet glycans and the potential of glycosylation for improving platelet storage.

RECENT FINDINGS

Removal of refrigerated platelets from the circulation is partly mediated by recognition of clustered beta-N-acetylglucosamine on platelet surface glycoproteins by the alphaMbeta2 hepatic lectin receptor. Capping the exposed beta-N-acetylglucosamine residues by enzymatic galactosylation restored the circulation of short-term chilled murine platelets, introducing a novel method that allows for cold storage of platelet. Recent studies have, however, shown that galactosylation is not sufficient to restore circulation of long-term refrigerated platelets. Additional data indicate that differential carbohydrate-mediated mechanisms may exist for clearance of short-term and long-term cold-stored platelets.

SUMMARY

Room temperature storage of platelet products increases the risk of transfusion-mediated sepsis and accelerates platelet deterioration, limiting platelet shelf life. Recent evidence suggests that glycoengineering of platelets might allow for their cold storage, significantly improving the quality of platelet products.

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.

Freeze-dried platelet-rich plasma shows beneficial healing properties in chronic wounds

Fresh platelet concentrates are used in many centers to treat recalcitrant wounds. To extend the therapeutic shelf-life of platelets, we analyzed the wound-healing effects of fresh-frozen and freeze-dried (FD) platelet-rich plasma (PRP) using a diabetic mouse model. Db/db mice with 1.0 cm2 dorsal excisional wounds (n = 15/group) were treated with a single application of FD PRP (1.2 x 10(6) platelets/microL) with or without a stabilization solution, and compared with wounds treated with fresh-frozen, sonicated PRP, and untreated wounds. Granulation tissue area, thickness, and wound size were analyzed 9 days posttreatment. Immunostained sections were quantified for vascularity and proliferation using antiplatelet endothelial cell adhesion molecule I and antiproliferating cell nuclear antigen antibodies. The results showed that all PRP preparations increased granulation tissue formation as assessed by surface coverage, thickness, and angiogenic response, when compared with untreated wounds. In addition, wounds treated with FD PRP, and biochemically stabilized FD PRP, exhibited higher proliferative levels. The possibility to deliver growth factors using platelets, and the potential to extend the shelf-life of platelet concentrates makes freeze-drying methods particularly suitable for enhanced wound care.

Flavonoids inhibit platelet function through binding to the thromboxane A2 receptor

BACKGROUND

Dietary flavonoids are known for their antiplatelet activity resulting in cardiovascular protection, although the specific mechanisms by which this inhibition occurs has not been fully established.

OBJECTIVE

The aim of this study was to investigate the interaction of nine flavonoids representative of various chemical classes, with platelet responses dependent on thromboxane A(2) (TxA(2)) generation and on receptor antagonism, and to analyze the structural requirements for such effects.

METHODS

The effect of several types of flavonoids on platelet aggregation, serotonin release, and TxA(2) generation was investigated. Competitive radioligand binding assays were used to screen for affinity of these compounds to TxA(2) receptors.

RESULTS

Flavones (apigenin and luteolin) and isoflavones (genistein) abrogated arachidonic acid and collagen-induced platelet responses, such as aggregation and secretion, with a less substantial effect on TxA(2) synthesis. These compounds were identified as specific ligands of the TxA(2) receptor in the micromol L(-1) range, this effect accounting for antiplatelet effects related to stimulation with those agonists. Tight binding of flavonoids to the human TxA(2) receptor relies on structural features such as the presence of the double bond in C2-C3, and a keto group in C4.

CONCLUSIONS

The inhibition by specific flavonoids of in vitro platelet responses induced by collagen or arachidonic acid seems to be related, to a great extent, to their ability to compete for binding to the TxA(2) receptor. Therefore, antagonism of this TxA(2) receptor may represent an additional mechanism for the inhibitory effect of these compounds in platelet function.

Evaluation of refrigerated platelet concentrates supplemented with low doses of second messenger effectors

With the goal of producing haemostatically effective platelet concentrates (PCs) with a longer shelf-life, we aimed to identify a simple combination of platelet inhibitors, with a low pharmacological load, which could avoid the unacceptable loss of platelets stored under refrigerated conditions. PCs stored with different combinations of second messenger effectors were analysed at days 5, 10 and 15 of storage and compared with those supplemented with ThromboSol--a combination of six platelet inhibitors that protects cells from cold damage. The following parameters were analysed: platelet counts, biochemical parameters (glucose, pH, bicarbonate, lactate), cell lysis (lactic dehydrogenase, LDH), membrane glycoproteins (GPs), platelet aggregation, fibrinogen binding and hypotonic shock response. We characterized the combination of amiloride and sodium nitroprusside (at 1/2 the dose included in ThromboSol). This was found to be similar to ThromboSol and superior to nontreated units in the prevention of cold-induced platelet aggregation at day 15 of storage (maintenance of 78% and 80% of initial platelet counts, respectively), preservation of GPIbalpha (11% and 12% better maintenance of mean fluorescence intensity compared with control units, respectively), and reduced cell lysis (13% and 11% decrease in supernatant LDH, respectively). The reduced pharmacological load with the identified solution compared with ThromboSol is an argument in favour of the potential use of these agents when designing strategies to improve PC storage.

Nitric oxide infusion alleviates cellular activation during preparation, leukofiltration and storage of platelets

Nitric oxide (NO) is a reversible inhibitor of platelet activation that generates S-nitrosylated compounds in plasma. Since platelets are activated during processing to platelet concentrates and storage, NO is anticipated to dampen the rate of lesion development. Platelet-rich plasma (PRP) was separated into aliquots that were unfiltered, filtered to remove leukocytes, or treated with NO or nitrite before filtration. Platelets were resuspended and stored up to four days at 22 degrees C. Samples removed were measured for S-nitrosylation of plasma, P-Selectin release, complement activation, and cGMP levels. Direct infusion of a NO solution (authentic NO) to PRP before filtration decreased adherence of platelets and improved yields. An infusion rate resulting in 1/1000 dilution of a saturated NO solution was optimal. C3a formation and soluble P-Selectin released from NO-treated-filtered platelets were about half that in unfiltered and filtered controls after four days (p<0.05 by Student-Newman-Keuls method after ANOVA for repeated measures). Plasma isolated from NO-treated PRP combined with untreated platelets protected the latter to a similar extent. Increases in S-nitrosylated compounds in PRPs were correlated with NO effects on platelet recovery and storage. Sodium nitrite failed to inhibit platelet activation and cyclic GMP levels were significantly increased in NO-treated cells. Results indicate that NO inhibited platelet activation associated with processing and storage and suggest that slow release of NO from S-nitrosylated plasma components afforded long-term protection. The infusion of authentic NO into PRPs is potentially an efficacious method for generating anti-platelet compounds to inhibit storage lesions.

Evaluation of a new whole-blood filter that allows preparation of platelet concentrates by platelet-rich plasma methods

BACKGROUND

A novel WBC-reduction in-line whole-blood (WB) filter that does not retain platelets was evaluated to assess the filtration performance and, after processing WB by the platelet-rich plasma (PRP) method, to analyze the storage quality of filtered platelet concentrate (PC) units.

STUDY DESIGN AND METHODS

To analyze the filter retention, blood was collected from random donors into quadruple blood packs with an integral in-line filter (Imuflex WB-SP, Terumo; n = 25) or in standard triple bag systems (n = 30). To assess the in vitro storage characteristics of platelets, 26 WB units were pooled in pairs and redistributed into 13 units that underwent WBC reduction and 13 units that were not WBC reduced. In all cases, WB was separated into RBCs, PCs, and plasma by the PRP method and platelet function was compared.

RESULTS

The filtration procedure led to RBC and PC WBC-reduced products that met the AABB and European requirements. The average filtration time was 30 minutes, the filter retained about 45 mL of WB, and there was no further loss of RBCs during the fractionation procedure. In vitro PC storage characteristics of the filtered units were similar to those of the nonfiltered units.

CONCLUSION

A 4- and 3-log WBC reduction was observed in RBC and PC units that were produced by the PRP method, with a mean residual WBC content of 0.24 +/- 0.38 x 106 and 0.02 +/- 0.03 x 106 per unit, respectively. The procedure, performed under relatively simple logistics, results in good-quality, standard components that may reduce costs and ease the process of WBC reduction in transfusion services.

Loss of phosphotyrosine phosphatase activity and changes in the tyrosine phosphorylation state of proteins after storage of sheep platelets in plasma or Seto solution at 4 degrees C

BACKGROUND AND OBJECTIVES

During platelet storage an array of deleterious changes occur, through mechanisms not fully understood, which impair platelet haemostasis. Transfused platelets should maintain the integrated networks of signalling pathways that regulate platelet activation and functionality. We hypothesized that protein phosphorylation and dephosphorylation, which play a fundamental role in these pathways, might be affected by platelet storage. We therefore investigated whether the activity of phosphotyrosine phosphatase (PTP), which belongs to an oxidant-susceptible group of enzymes involved in the platelet signal-transduction pathways that ensure platelet functionality, is affected by platelet storage.

MATERIALS AND METHODS

Using sheep platelet species as a model system, we conducted serial studies on the membranes of platelets and microparticles shed during platelet storage, in their own plasma or in a synthetic medium called Seto, for up to 5 days at 4 degrees C.

RESULTS

A progressive decrease in both total and specific membrane-associated PTP activities from whole platelets (but not from microparticles) located within each platelet storage bag was observed from day 1 onwards in both types of storage media. These decreases could be partly avoided by the addition of vitamin E. Additionally, the observed decrease in PTP activity was accompanied with increases in the tyrosine phosphorylation of proteins from whole platelets or crude platelet membranes, the tyrosine phosphorylation state of proteins from microparticles remaining basically unchanged.

CONCLUSION

Our findings suggest that alterations of at least the tyrosine phosphorylation balance might be one of the reasons for the decrease in the haemostatic function of stored platelets.

Renal changes induced by a cyclooxygenase-2 inhibitor during normal and low sodium intake

Cyclooxygenase-2 (COX-2) has been identified in renal tissues under normal conditions, with its expression enhanced during sodium restriction. To evaluate the role of COX-2-derived metabolites in the regulation of renal function, we infused a selective inhibitor (nimesulide) in anesthetized dogs with normal or low sodium intake. The renal effects elicited by nimesulide and a non-isozyme-specific inhibitor (meclofenamate) were compared during normal sodium intake. In ex vivo assays, meclofenamate, but not nimesulide, prevented the platelet aggregation elicited by arachidonic acid. During normal sodium intake, nimesulide infusion (n=6) had no effects on arterial pressure or renal hemodynamics but did reduce urinary sodium excretion, urine flow rate, and fractional lithium excretion. In contrast, nimesulide administration increased arterial pressure and decreased renal blood flow, urine flow rate, and fractional lithium excretion during low sodium intake (n=6). COX-2 inhibition reduced urinary prostaglandin E(2) excretion in both groups but did not modify plasma renin activity in dogs with low (8.1+/-1.1 ng angiotensin I. mL(-1). h(-1)) or normal (1.8+/-0.4 ng angiotensin I. mL(-1). h(-1)) sodium intake. Meclofenamate infusion in dogs with normal sodium intake (n=8) induced a greater renal hemodynamic effect than nimesulide infusion. These results suggest that COX-2-derived metabolites (1) are involved in the regulation of sodium excretion in dogs with normal sodium intake, (2) play an important role in the regulation of renal hemodynamic and excretory function in dogs with low sodium intake, and (3) are not involved in the maintenance of the high renin levels during a long-term decrease in sodium intake.

Effects of the addition of second-messenger effectors to platelet concentrates separated from whole-blood donations and stored at 4 degrees C or -80 degrees C

BACKGROUND

Platelet concentrates (PCs) are currently stored at 22 degrees C under continuous agitation. Because of the potential risk of the overgrowth of bacteria in case of contamination, PC shelf life is limited to 5 days. A mixture of second-messenger effectors is being evaluated to determine if it has benefits for cold liquid storage and cryopreservation of platelets.

STUDY DESIGN AND METHODS

PCs separated from whole-blood donations by the buffy coat method were randomly assigned (n = 6 each) to be stored for 5 days at 22 degrees C under continuous agitation or at 4 degrees C after treatment with a platelet storage medium (ThromboSol, LifeCell Corp. ). PCs were also cryopreserved with 6-percent DMSO (final concentration) or with ThromboSol plus 2-percent DMSO (final concentration) (TC). After storage, platelets were analyzed by flow cytometry, transmission electron microscopy, and aggregation and perfusion techniques.

RESULTS

Cold liquid storage of ThromboSol-treated platelets resulted in a lower binding of coagulation factor Va on the platelet surface than on platelets stored at 22 degrees C. In transmission electron microscopy, a conversion to spherical morphology was seen in the case of cold liquid storage. No difference between ThromboSol-treated platelets stored at 4 degrees C and platelets stored at 22 degrees C was seen in perfusion studies. Cryopreservation in the presence of TC prevented the reduction in glycoprotein Ib and IV expression on platelet surface that is seen in 6-percent DMSO-cryopreserved platelets. Platelets cryopreserved in TC covered, by thrombus, a significantly greater percentage of the perfused surface after the freezing and thawing process.

CONCLUSION

ThromboSol-treated PCs separated from whole-blood donations by the buffy coat method, stored at 4 degrees C for 5 days, or cryopreserved in the presence of TC, maintained in vitro functional activity comparable to that achieved by current methods of storage, although discoid morphology was not preserved during cold liquid storage with ThromboSol.

Platelet substitutes and novel platelet products

Despite many advances in the safety, processing and storage of conventional 22 degrees C liquid-stored allogeneic platelet concentrates, there are still significant drawbacks to standard platelet concentrates used in transfusions for patients with thrombocytopenia. Efforts to overcome these shortcomings have been undertaken in both academic and commercial settings, resulting in an array of novel platelet products and substitutes that are currently at various stages of development. This review summarises the recent developments in lyophilised platelets, infusible platelet membranes (IPM), red cells bearing arginine-glycine-aspartic acid (RGD) ligands, fibrinogen-coated albumin microcapsules and liposome-based agents as putative alternatives to conventional transfusions involving allogeneic platelet concentrates. These various products are designed to replace the use of allogeneic donor platelets with modified or artificial platelets, to augment the function of existing platelets and/or provide a procoagulant material capable of achieving primary haemostasis in patients with thrombocytopenia. Preclinical studies have been encouraging for several of these platelet substitutes and novel platelet products, however, to date, only a few of these products have entered human trials. With the ongoing development of these diverse products, properties necessary for haemostatic effectiveness will become apparent. Safety and efficacy, however, must be demonstrated in preclinical and Phase I - III clinical trials, before these novel agents can be used clinically for patients with thrombocytopenia.

In vitro analysis of platelet concentrates stored in the presence of modulators of 3',5' adenosine monophosphate, and organic anions

The storage of conventional platelet concentrates (PCs) under standard blood bank conditions is limited to five days, in part because longer storage periods lead to increasing damage in platelet integrity and functionality. The growing demand of PCs for clinical use, raises the interest to develop agents that would potentially permit a more extended period of storage. We have evaluated and compared the in vitro quality of PCs treated with: (1) Modulators of levels of cAMP (PGE1, foskolin, theophylline and isobutyl-methyl-xanthine [IBMX]); and (2) organic anions that function as alternative substrates of platelets (pyruvate and acetate). Platelet rich plasma (PRP) from pools (n = 6) of PCs was distributed into storage bags, and the agents to be tested were added, using saline as a control substance. PCs were stored at 22 degrees C with continuous agitation for up to 10 days. At 0, 5 and 10 days of storage, samples were analyzed for platelet counts, mean platelet volume (MPV), metabolic markers, and expression of glycoproteins (GPs). The addition of modulators of levels of cAMP, at the concentration used in the study, did not lead to substantial improvement in the parameters being evaluated, with respect to those in control units. The supplementation with organic anions, while not affecting the surface levels of GPs, favored the maintenance of metabolic values, such as pH, PCO2, and bicarbonate concentrations, as well as the preservation of MPV (p values < 0.05 respect to control units both at 5 and 10 days of storage). Our results indicate that while the use of modulators of levels of cAMP do not provide substantial benefit in the prevention of platelet storage lesions, organic anions have some advantageous effect in the storage promoted metabolic changes of PCs. These data might be considered when designing strategies to improve PC storage.

Platelet cryopreservation using a reduced dimethyl sulfoxide concentration and second-messenger effectors as cryopreserving solution

Cryopreservation of platelets is of great interest since it could extend to years the shelf life of therapeutic platelet concentrates (PCs) and facilitate stockpiling and inventory control in blood banking. We have compared the cryopreservation of PCs by the standard method using 6% Me(2)SO as cryoprotectant with the method of freezing employing low concentrations of Me(2)SO (2%) plus ThromboSol, a mixture of second-messenger effectors that protect platelets from cold damage. PC pools were treated either with 6% Me(2)SO or with ThromboSol and 2% Me(2)SO and then placed directly in a -80 degrees C freezer or in the vapor phase of a liquid nitrogen freezer (-120 degrees C). After storage for 1 week or for 3 months, samples were removed, thawed, and analyzed. Measurements included cell recovery, biochemical parameters, membrane glycoproteins (GPs), platelet aggregation, and binding of radiolabeled von Willebrand factor (vWF) and fibrinogen. PCs cryopreserved with ThromboSol and 2% Me(2)SO displayed a platelet recovery (90%) equivalent to those frozen with 6% Me(2)SO. Following either cryopreservation procedure, platelets showed increased surface expression of P-selectin and moderate loss of GP Ibalpha in comparison to fresh platelets. The aggregatory response to ristocetin and the binding of vWF were similar in platelets frozen by either procedure. Finally, both methods promoted comparable impairment of the reactivity of platelets to thrombin, aggregation and binding of fibrinogen and vWF, compared to that of fresh platelets. In summary, cryopreservation of PCs using reduced Me(2)SO concentration and ThromboSol yields platelets with in vitro functional characteristics equivalent to those of cells frozen with the conventional method using 6% Me(2)SO.