Platelet membrane glycoproteins: alteration during storage of human platelet concentration

Influence of Oxidative Stress on Stored Platelets

Platelet storage and its availability for transfusion are limited to 5-6 days. Oxidative stress (OS) is one of the causes for reduced efficacy and shelf-life of platelets. The studies on platelet storage have focused on improving the storage conditions by altering platelet storage solutions, temperature, and materials. Nevertheless, the role of OS on platelet survival during storage is still unclear. Hence, this study was conducted to investigate the influence of storage on platelets. Platelets were stored for 12 days at 22°C. OS markers such as aggregation, superoxides, reactive oxygen species, glucose, pH, lipid peroxidation, protein oxidation, and antioxidant enzymes were assessed. OS increased during storage as indicated by increments in aggregation, superoxides, pH, conjugate dienes, and superoxide dismutase and decrements in glucose and catalase. Thus, platelets could endure OS till 6 days during storage, due to the antioxidant defense system. An evident increase in OS was observed from day 8 of storage, which can diminish the platelet efficacy. The present study provides an insight into the gradual changes occurring during platelet storage. This lays the foundation towards new possibilities of employing various antioxidants as additives in storage solutions.

Platelet additive solution - electrolytes

Recent attention to solutions that replace most or all plasma in platelet concentrates, while maintaining satisfactory platelet function, is motivated by the potential of plasma reduction or depletion to mitigate various transfusion-related adverse events. This report considers the electrolytic composition of previously described platelet additive solutions, in order to draw general conclusions about what is required for platelet function and longevity. The optimal concentrations of Na(+) and Cl(-) are 69-115 mM. The presence of both K(+) and Mg(2+) in platelet suspension at nearly physiological concentrations (3-5mM and 1.5-3mM, respectively) is indispensable for good preservation capacity because both electrolytes are required to prevent platelet activation. In contrast to K(+) and Mg(2+), Ca(2+) may not be important because no free Ca(2+) is available in M-sol, which showed excellent platelet preservation capacity at less than 5% plasma concentration. The importance of bicarbonate (approximately 40 mM) can be recognized when the platelets are suspended in additive solution under less than 5% residual plasma concentration.

The platelet storage lesion

The continuous increase in the demand for platelet transfusion has necessitated the need to establish standards for determining the quality of platelets during storage. Bacterial contamination of platelet products and deleterious changes in structure and function referred to as the platelet storage lesion (PSL), have restricted the platelet shelf life to 5 days. The PSL and platelet health variables have been well studied and documented. The precise correlation between in vitro assays and in vivo platelet recovery and survival is yet to be established. This review presents an overview of the current understanding of PSL and the novel approaches being developed to negate the storage lesion.

Oxidative stress activates ADAM17/TACE and induces its target receptor shedding in platelets in a p38-dependent fashion

AIMS

Oxidative stress accompanies inflammatory and vascular diseases. The objective of this study was to explore whether reactive oxygen species can activate shedding of platelet receptors and thus suppress platelet function.

METHODS AND RESULTS

Hydrogen peroxide and glucose oxidase were chosen to model oxidative stress in vitro. We demonstrate that oxidative damage activated tumour necrosis factor-alpha-converting enzyme (TACE) and induced shedding of its targets, glycoprotein (GP) Ibalpha and GPV, in murine and human platelets. Also, 12-HpETE, a peroxide synthesized in the platelet lipoxygenase pathway, induced TACE-mediated receptor cleavage. The TACE activation was independent of platelet activation, as alpha-granule secretion, activation of alphaIIbbeta3, or phosphatidylserine expression was not observed. TACE activation induced by hydrogen peroxide was dependent on p38 mitogen-activated protein kinase signalling, whereas protein kinase C, phosphoinositide 3-kinase, and caspases were not involved. Inhibition of p38 cytoplasmic targets, phospholipase A(2) and heat shock protein 27, did not prevent shedding, whereas blocking 12-lipoxygenase or Src kinase slightly inhibited TACE activation. The loss of the GPIbalpha receptor induced by oxidative stress rendered platelets unable to incorporate into a growing thrombus in vivo.

CONCLUSION

Oxidative stress can render platelets functionally less active by shedding key adhesion receptors via the activation of p38. This suggests that oxidative injury of platelets may attenuate their function.

Preservation of Platelets by Adding Epigallocatechin-3-O-Gallate to Platelet Concentrates

The effect of epigallocatechin-3- O-gallate (EGCG), a major component of green tea, on platelet preservation was evaluated. Single donor platelets ( N = 10) were collected and preserved by the standard method. EGCG was added to the platelet concentrates before preservation and then the functional and biochemical parameters were monitored throughout the storage period. After 6 days of preservation, the aggregability of the platelets was significantly maintained by addition of 50 and 100 μg/ml of EGCG. Platelet prothrombinase activity was also significantly retained by the addition of EGCG. The accumulation of P-selectin and RANTES in the plasma preserved with EGCG was less than those preserved without EGCG, which indicated that EGCG might inhibit platelet activation. Furthermore, EGCG reduced the increase of LDH in plasma during preservation and inhibited the activation of caspase-3 and cleavage of gelsolin, thereby showing that EGCG could inhibit the apoptosis of platelets. These results suggest that EGCG may play an effective role in preserving platelets by inhibiting the activation and apoptosis of platelets.

Platelet storage lesion: a new understanding from a proteomic perspective

Platelet storage and availability for the purposes of transfusion are currently restricted by a markedly short shelf life of 5 to 7 days owing to an increased risk of bacterial growth and storage-related deterioration called the platelet storage lesion. Because most bacteria grow to confluence within 5 days during storage at room temperature, there is little increased risk of bacterial overgrowth with testing in place, and the only remaining issue is the quality of platelets during the extended storage. Although the manifestations of the storage lesion have been well studied using a variety of in vitro measures, the precise biochemical pathways involved in the initiation and progression of this process have yet to be identified. Proteomics has emerged as a powerful tool to identify and monitor changes during platelet storage and, in combination with biochemical and physiologic studies, facilitates the development of a sophisticated mechanistic view. In this review, we summarize recent experimental work that has led to a detailed overview of protein changes linked to platelet functions and signaling pathways, providing potential targets for inhibitors to ameliorate the storage lesion.

Platelet storage solution improves the in vitro function of preserved platelet concentrate

BACKGROUND AND OBJECTIVES

Stored platelets develop biochemical lesions, manifest as depressed haemostatic function, clot retraction and wound healing. ViaCyte trade mark, a proprietary experimental preservative solution (comprising D-ribose, D-glucose, Hanks solution, Hepes solution, bovine serum albumin, tic anticoagulant peptide and sterile water), was tested in comparison with the presently accepted storage solution, citrate-dextrose-phosphate-plasma (CDP-P), to evaluate its ability to preserve platelet function during storage.

MATERIALS AND METHODS

Platelets stored in ViaCyte and platelets suspended in CDP-P were transferred to polypropylene tubes with PL732 covers and analysed for adenine nucleotide levels (ATP molecules), in vitro agonist-mediated P-selectin expression and aggregation.

RESULTS

After 5 days of storage at room temperature, 12.2% of platelets stored in ViaCyte exhibited P-selectin expression at rest, and 64.2% exhibited P-selectin expression upon activation with thrombin challenge, an increase of 52%. Platelets stored in CDP-P exhibited 44.4% P-selectin expression at rest, suggesting significant activation during storage, and thrombin stimulation resulted in P-selectin expression of 47.9%, an increase of only 2.5% (P< or =0.002, untreated vs. treated). ViaCyte also maintained ATP levels throughout the storage period, while these levels became depressed in platelets stored in CDP-P (P< or =0.02, untreated vs. treated). Storing platelets in the experimental preservative solution maintained their ability to aggregate, while control platelets lost their ability to aggregate in response to agonist.

CONCLUSIONS

ViaCyte appears to protect platelets during storage, reflected by a low level of induced lesions. Platelets stored in ViaCyte maintain energy levels at their resting state, which preserves their ability to aggregate and secrete granule contents, and ensures the availability of additional platelets for activation upon in vitro challenge.

Flow cytometry of platelets for clinical analysis

Platelets are small, non-homogenous cells with distinctive surface features important to their essential role in hemostasis. The surface membrane is dynamic, and changes remarkably in lipid asymmetry and receptor expression on triggering of the activation process. There are also extensive and rapid intracellular changes in platelets as a result of biochemical activation through calcium fluxes, phospholipase activity, kinase activity, and phosphorylation mechanisms that lead to release of storage granule contents and generation of fast-acting prostaglandins, all in a matter of seconds after stimulation with a strong agonist. These characteristics make the platelet an interesting but difficult cell to study, and the explosion of knowledge over the last two decades has been fueled in large part by the application of flow cytometry techniques. Clinical applications of flow cytometry analysis of platelets have been pursued in individual specialized medical centers, but have not found widespread practice in clinical laboratories, mostly because of difficulties in standardization of techniques and the inherent biovariability in comparing normal to abnormal platelets. Despite these hurdles, it seems certain that flow cytometry analysis of platelets in pathological states will continue to evolve into more practical and robust procedures that will eventually become standard hematologic assays rather than specialized research tools.

Annexin V and platelet antigen expression is not altered during storage of platelet concentrates obtained with the AMICUS cell separator

During storage of platelet concentrate the so-called "storage lesion" occurs. During this time, platelets loose their morphological and functional capacities that are necessary for proper in vivo efficacy following transfusion. Annexin V represents a marker for apoptosis. In this study, Annexin V and additional antigens were analyzed by flow cytometry. Platelet concentrates were obtained with a new cell separator (AMICUS Separator, Fenwal). Following apheresis, platelet units were stored for an experimentally prolonged time of seven days. Daily aliquots of the platelet-rich plasma were obtained to measure Annexin V and platelet antigens CD62p, CD63, CD41a, CD42b, and the binding of fibrinogen. All analyses were performed using flow cytometry. During storage, no significant changes in mean channel fluorescence intensity (MCFI) of CD41a (P = 0.99) and CD42b (P = 0.29), percentage of CD62p+ and CD63+ platelets (P = 0.23 for CD62p; P = 0.52 for CD63), and the binding of fibrinogen to platelets occurred (P = 0.85). Also, the expression of Annexin V remained constant with no significant change (P = 0.36). This study shows that antigens of platelets, obtained with the AMICUS cell separator are well preserved during storage. Regarding Annexin V, no obvious signs of apoptosis can be detected by flow cytometry. These findings demonstrate the high degree of biocompatibility of the apheresis device and storage container.

Von Willebrand factor availability in platelet concentrates stored for 5 days

Von Willebrand factor (vWF) availability was assessed in platelet concentrates (PCs). After 5 days of storage, 82 +/- 9% of basal levels of ristocetin cofactor activity (vWF:RCo) remained in PCs. vWF antigen (vWF:Ag) increased up to 166 +/- 38% (P < 0.05) in the same period. Autoradiograph pattern of vW:Ag showed an increase in low molecular weight multimers, and fast migrating multimeric forms were visualized by crossed immunoelectrophoresis on day 5. Studies carried out in platelet free plasma stored as PCs showed similar changes in vWF:RCo but increments in vWF:Ag were not detected. These data indicate that PCs maintain vWF:RCo levels of clinical value even after 5 days of storage and suggest that vWF comes out from platelets to plasma during storage.

Role of lactate in platelet storage lesion

It is known that lactate accumulation may cause a pH fall in platelet concentrates (PC) during storage, and this phenomenon causes platelet morphological lesions and loss of platelet in vivo viability. In this study, we added increasing amounts of lactate to identical PC in order to evaluate the role of hydrogen ion accumulation in determining platelet activation and lesion during storage. Six hours after PC preparation, lactate was added to PC1 and PC2 at 20 and 12 mM final concentrations, respectively, while PC3 served as control. In PC1, pH was lower than 6.3, and platelet function and discoid morphology were lost. PC2 were stored for 7 days at pH values ranging from 6.4 to 6.6, and most results of in vitro measurements reflecting platelet function such as osmotic reversal, ATP release and aggregation in response to different stimuli were not significantly inferior when compared to controls. The addition of lactate had no apparent effect on the rise of platelet activation markers P-Selectin, lysosome-like protein gp 53, platelet-bound fibrinogen and granulophysin, while a reduction of borderline significance was observed in glycoprotein Ib expression after pH reduction to values lower than 6.6. It is concluded that the rise of platelet activation markers during storage reflects platelet lesions different from those determined by lactate per se.

Quality of platelet concentrates irradiated with UVB light: effect of UV dose and dose rate on glycocalicin release and correlation with other markers of the platelet storage lesion

The amount of membrane-associated glycoprotein Ib in platelet concentrates (PCs) irradiated with a high dose of UVB light has been shown to be significantly reduced after 48 h storage. We recently corroborated this finding when we noted an increase in the supernatant levels of glycocalicin (GC, a major segment of glycoprotein Ib) in UVB-treated PCs during storage. The aim of the present study was to determine whether GC release was related to both the UV dose and the rate of dose delivery. Plateletpheresis concentrates obtained from five donors were pooled and split into five equal parts. Four of these were treated with 7500 and 15,000 mJ/cm2 UVB using two prototype UV sources with differing rates of dose delivery; namely, Baxter (BAT) and British Aerospace (BAC) cabinets, with the latter having the slower rate of delivery. On days 1 and 5 of storage, GC levels in the supernatants of PCs were determined by ELISA. Moreover, the following parameters were also assessed: platelet and WBC count; hypotonic shock response (HSR) and platelet aggregation response to ADP, ADP+collagen, ADP+arachidonic acid and ristocetin; pH; supernatant levels of lactate, glucose, von Willebrand factor (vWf) and beta-thromboglobulin (beta TG). The results revealed an association of GC release with UVB dose using both UV sources, although this was more apparent in the BAC system, in which glycocalicin release at day 5 of storage was as follows (microgram/ml, mean +/- SD): 4.8 +/- 0.3 and 9.5 +/- 3.6 at 7500 and 15,000 mJ/cm2 respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Correlation of light transmission changes to changes of platelet glycoprotein Ib during storage of platelet concentrates

The present study compares some properties of platelet concentrates, i.e. their ability to transmit light and the degree of platelet lysis and the deterioration of the platelet membrane glycoprotein Ib (GPIb). Extracellular levels of glycocalicin and lactate dehydrogenase (LDH) served as indicators for the proteolytic cleavage of GPIb and platelet lysis, respectively. The light transmission of 16 platelet apheresis concentrates was monitored continuously during storage using a specially designed apparatus. Determination of platelet counts and extracellular glycocalicin levels was carried out on day 1. In addition, after 7 days of storage extracellular concentrations of LDH and glycocalicin were determined. After 7 days highly significant correlations were found both when comparing light transmission changes and extracellular glycocalicin levels (r = 0.78; p < 0.001) and when comparing light transmission changes and extracellular concentrations of LDH (r = 0.83; p < 0.001).

Alterations of the levels of glycoproteins Ib-IX and IIb-IIIa in platelets stored at 22 degrees C

Platelets stored in CLX blood bags, under normal blood banking conditions, were studied for up to 7 days to determine if changes occurred in the levels of membrane glycoproteins (GP) Ib-IX and IIb-IIIa. Radiolabeled monoclonal antibodies (MAB) were used to estimate the number of glycoprotein molecules on the surface membrane of intact platelets. GP IX and GP IIb-IIIa levels remained essentially unaltered during storage. In contrast, the content of GP Ib at day 7 decreased by 45% of the total when fresh. The aggregation response to ristocetin, which requires GP Ib, was also diminished after 7 days. Addition of protease inhibitors, leupeptin and/or aprotinin did not appear to influence the degradation of this glycoprotein. We conclude that storage at 22 degrees C had deleterious effects on the GP Ib content of platelets.

Platelet membrane glycoproteins and platelet functions during storage in the presence of a proteinase inhibitor

The effect of the proteinase inhibitor aprotinin on membrane glycoproteins and functions of platelets stored for 5 days in platelet-rich plasma was tested. Platelet membrane glycoprotein content was determined by flow cytometry or immunoblot techniques using different monoclonal antibodies. ADP- and ristocetin-induced platelet aggregation and adhesion to collagen were tested in parallel. Using the flow-cytometry technique i) a progressive decrease in the percentage of platelets reacting with the different monoclonal antibodies was observed during storage ii) a 30% reduction of the GPIb mean fluorescence intensity (MFI) was observed after 5 days storage while the MFI of the GP IIb-IIIa complex was not modified. Using the immunoblot technique, a decrease in the amount of both the GPIb alpha and the component of Mr 100,000 was observed, while a 50,000 Mr fragment appeared progressively. Platelet adhesion and aggregation were reduced after 24 hours of storage. Aprotinin prevented neither the GPIb alpha reduction nor the modifications of the functions of human platelets stored in their autologous plasma.

The preparation of platelet concentrates by the light-spin/hard-spin technique

For at least two decades the light-spin/hard-spin (LS/HS) method for preparation of platelet concentrates (PC) has been the standard of platelet support. With concern over the detrimental effects of platelet activation during component preparation and with increased recognition of the adverse consequences resulting from residual donor leukocytes in PC, new approaches to the production of PC have begun. This review addresses two aspects of the traditional LS/HS method of platelet preparation: platelet activation and residual leukocyte content. Studies of platelet activation are reviewed which focus on the second (hard-spin) centrifugation step during which pelleting of platelets occurs. Platelets studied immediately after the hard-spin exhibit evidence of alpha-granule release, expression of activation antigens, and decreased aggregation. There is a suggestion that some degree of reversal of platelet activation routinely occurs during the rest period following the hard-spin. The residual leukocyte content of PC prepared by the LS/HS method ranges from 10 7 to 10 9 leukocytes/unit. The residual donor leukocytes are predominantly lymphocytes and monocytes. Degeneration of residual donor leukocytes may release soluble cytokines resulting in febrile transfusion reactions. It remains controversial whether or not the cell-membrane fragments and microvesicles of degenerating donor leukocytes are capable of HLA allosensitization or viral transmission. Release of leukocyte elastase from degenerating leukocytes during platelet storage has been proposed as contributing to the platelet storage lesion. More research is needed to address the question of whether or not pre-storage leukocyte reduction during component preparation will result in improved PC. It appears likely that within the next few years radical changes will occur in the method of preparation of PC with the aim of providing the greatest degree of hemostatic effectiveness with the least toxicity to patients.

A new competitive binding enzyme-linked immunosorbent assay for glycocalicin in plasma and platelet concentrate supernatants

A new competitive binding enzyme-linked immunosorbent assay (CB ELISA) for glycocalicin (GC) was developed using GC coated wells and a monoclonal antibody (MAb) to glycoprotein Ib (AN51). The principal stages of the CB ELISA consisted of coating the plate with GC extract overnight, blocking with 3% BSA, incubating the wells with test or standard sample dilution and AN51, and a final incubation with horseradish peroxidase-conjugated goat anti-mouse IgG. Serial dilutions of purified GC, starting in 2% BSA, yielded standard curves which were linear between 10 and 0.4 micrograms/ml. Parallel curves were obtained for platelet concentrate supernatants and for citrated plasma. We used the ELISA to measure GC levels in platelet concentrates during storage. The results indicated that soluble GC increased progressively during storage from 3.3 to 6.7 micrograms/ml, while GC levels in platelet-poor plasma remained at 1.9-2.2 micrograms/ml. These results show that the new CB ELISA is a simple and short assay for the direct measurement of GC in plasma solutions, and may be of use in clinical studies.

Arachidonic acid metabolism in platelets stored for 5 days

(C-14)-Arachidonic acid [(C-14)-AA] metabolism was studied in platelet concentrates (PCs) stored for 5 d. There was a gradual decrease in uptake of radioactivity from day 0 to 3 (P less than 0.01). On day 0, distribution of radioactivity in platelet phospholipids (PLs), and formation of phosphatidic acid, HETE and cyclooxygenase products, when platelets were exposed to thrombin (5 U/ml), were similar to that reported for fresh platelets. On day 3 there was a change in the distribution of (C-14)-AA in platelet PLs which consisted of an increase in the percentage of radioactivity bound to phosphatidylserine, from 5.3 +/- 0.9% on day 0 to 8.8 +/- 1.5% on day 3 (P less than 0.001), and a decrease in (C-14)-AA in phosphatidylinositol (PI), from 12.4 +/- 1.5% on day 0, to 7.9 +/- 0.9% on day 3 (P less than 0.001). Phosphatidic acid generated by thrombin-stimulated platelets on day 0, comprised 2.6 +/- 0.5% of total radioactivity, but dropped to 1.4 +/- 0.3% on day 3 (P less than 0.001), and 0.9 +/- 0.2% on day 5 (P less than 0.01). These values showed a good correlation with the percentage of (C-14)-AA released from PI on the same days (r = 0.9). On day 0, 13.4 +/- 4.4% of platelet radioactivity was released from phosphatidylcholine by thrombin, but this amount was reduced to 6.8 +/- 3.4% on day 5 (P less than 0.05). Generation of radioactive 12-hydroxy-5,8,10,14-eicosatetraynoic acid (HETE) also dropped from 7.2 +/- 2.9 on day 0, to 2.1 +/- 1 on day 5 (P less than 0.01). We could not detect changes in cyclooxygenase metabolites. In conclusion, we suggest that various enzymatic pathways implicated in AA metabolism by platelets are impaired by storage.

Altered expression of platelet surface glycoproteins during storage

Human blood platelets were stored in autologous plasma at 4 degrees C or 22 degrees C and their surface changes were probed with three lectins--wheat germ agglutinin, lentil lectin and concanavalin A. Platelets stored at either temperature for different times showed increased sensitivity to lectins. Lectins which were nonagglutinating to fresh platelets readily agglutinated stored platelets. The platelets stored for 24 h or longer lost their ability to respond to thrombin but demonstrated enhanced aggregation with wheat germ agglutinin. Surface labelling experiments revealed progressive loss of a glycoprotein of Mr 150,000 (GPIb) together with the appearance of components with Mr 69,000, 60,000 and 25,000 respectively. New high molecular weight glycoproteins were detected only in stored platelets. These findings illustrate the usefulness of lectins for the detection of altered expression of surface glycoconjugates which may be a factor in storage related dysfunction of platelets.

Platelet storage results in a redistribution of glycoprotein Ib molecules. Evidence for a large intraplatelet pool of glycoprotein Ib

Platelet membrane glycoprotein (GP) Ib contains receptor for von Willebrand factor and thrombin. Its proteolytic fragment, glycocalicin, circulates in normal plasma. In this study, storage of platelet concentrates for 5 d resulted in a 221% increase in plasma glycocalicin (1.3 times the total amount of glycocalicin present on the surface of all platelets), an 8% overall increase in platelet surface GPIb, and the appearance of a surface GPIb-negative subpopulation of platelets. Total platelet GPIb content of fresh washed platelets, determined by gel electrophoresis and immunoassay of Triton X-100 lysates, averaged 159,740 molecules per platelet. There were 36,360 surface GPIb molecules per platelet, determined by immunoassay of the supernatant of fresh washed platelets whose surface GPIb had been completely plasmin-cleaved. In summary, these studies provide evidence for (a) a redistribution of GPIb molecules with platelet storage, and (b) a large intraplatelet pool of GPIb (approximately threefold larger than the platelet surface pool of GPIb).

Platelet membrane glycoprotein changes during the preparation and storage of platelet concentrates

Previous studies of platelet membrane glycoproteins during blood bank storage have reported conflicting results. This study assessed two major plasma membrane glycoproteins (GP Ib and GP IIb), an alpha-granule membrane protein (GMP-140), and the concentration of platelet membrane microparticles in cell-free plasma during routine hospital blood bank platelet storage. 125I-monoclonal antibody binding was used to measure membrane glycoproteins on the surface of intact platelets and to measure the concentration of membrane microparticles in cell-free plasma. Platelet concentrates were stored at room temperature in polyolefin bags for 7 days. In this blood bank, two types of rotators are routinely used for platelet concentrate storage: a 2-rpm circular tumbler rotator and a 6-rpm elliptical rotator. Different results were obtained with the rotators. With the tumbler rotator, there was no loss of platelets and antibody binding to GP Ib remained normal. With the elliptical rotator, one third of platelets were lost into clumps during storage, and a 50 percent decrease of antibody binding to GP Ib occurred in the remaining single platelets. There was no loss of antibody binding to GP IIb with either rotator. Antibody binding to GMP-140 increased equally in both rotators indicating that the remaining single platelets had secreted about 16 percent of their alpha-granule contents. The plasma concentration of platelet membrane microparticles was greater in the bags stored in the elliptical rotator. These results indicate that it is possible to maintain the normal concentration of platelet membrane glycoproteins Ib and IIb during 7 days of room-temperature blood bank storage.(ABSTRACT TRUNCATED AT 250 WORDS)

Lateral diffusion of lipid probes in the surface membrane of human platelets. An electron-electron double resonance (ELDOR) study

Electron-electron double resonance (ELDOR) techniques employing [14N], [15N] 16-Doxylstearate spin-label pairs have been used to measure the lateral diffusion constant, D, of lipids in the surface membrane of intact human blood platelets. For freshly prepared platelets, D is 1.0 X 10(-8) cm2/s at 37 degrees C and for platelets stored for 3 d at room temperature under accepted routine blood bank conditions, D is 2.6 X 10(-8) cm2/s at 37 degrees C. This is the first time that D in the surface membrane of platelets is reported. The marked increase in D for stored platelets may be attributed at least partly to loss of cholesterol during storage, suggesting a correlation between lipid lateral diffusion and cholesterol levels in cell membranes.

Purification and preliminary characterization of the glycoprotein Ib complex in the human platelet membrane

Human platelet glycoprotein Ib (GP Ib) is a major integral membrane protein that has been identified as the platelet-binding site mediating the factor VIII/von Willebrand-factor-dependent adhesion of platelets to vascular subendothelium. Recent evidence suggests that GP Ib is normally complexed with another platelet membrane protein, GP IX. In this study, human platelet plasma membranes were selectively solubilized with a buffer containing 0.1% (v/v) Triton X-100. The GP Ib complex (GP Ib plus GP IX) was purified to homogeneity in approximately 30% yield by immunoaffinity chromatography of the membrane extract using the anti-(glycoprotein Ib complex) murine monoclonal antibody, WM 23, coupled to agarose. GP Ib and GP IX were subsequently isolated as purified components by immunoaffinity chromatography of the GP Ib complex using a second anti-(glycoprotein Ib complex) monoclonal antibody, FMC 25, coupled to agarose. As assessed by dodecyl sulphate/polyacrylamide gel electrophoresis, purified GP Ib was identical to the molecule on intact platelets and had an apparent relative molecular mass of 170 000 under nonreducing conditions and 135 000 (alpha subunit) and 25 000 (beta subunit) under reducing conditions. GP IX had an apparent Mr of 22 000 under both nonreducing and reducing conditions. Purified Gb Ib complex and GP Ib inhibited the ristocetin-mediated, human factor VIII/von Willebrand-factor-dependent and bovine factor VIII/von Willebrand-factor-dependent agglutination of washed human platelets suggesting the proteins had been isolated in functionally active form. GP Ib alpha had a similar amino acid composition to that previously reported for its proteolytic degradation product, glycocalicin. The amino acid compositions of GP Ib beta and GP IX were similar but showed marked differences in the levels of glutamic acid, alanine, histidine and arginine. The N-termini of GP Ib alpha and GP IX were blocked; GP Ib beta had the N-terminal sequence, Ile-Pro-Ala-Pro-. On crossed immunoelectrophoresis, both GP Ib and GP IX were found to occur in the same immunoprecipitin arc(s) whether the platelets had been solubilized in the absence or presence of the calcium-dependent protease inhibitor, leupeptin. Binding studies in platelet-rich plasma indicated a similar number of binding sites (means +/- SD) for three anti-(glycoprotein Ib complex) monoclonal antibodies: AN 51, epitope on GP Ib alpha (22 000 +/- 2700, n = 3), WM 23, epitope on GP Ib alpha (21 000 +/- 3400, n = 3), FMC 25, epitope on GP IX (20 100 +/- 2700, n = 3), and FMC 25 (Fab')2 (27 100 +/- 800, n = 2).(ABSTRACT TRUNCATED AT 400 WORDS)

Evidence that glycocalicin circulates in normal plasma

By using a combination of a heterologous antiserum to GPIb/glycocalicin and a radiolabeled monoclonal antibody to GPIb/glycocalicin, we were able to develop a sensitive and specific radioimmunoelectrophoretic assay that can distinguish small amounts of glycocalicin from GPIb. Normal plasmas were found to contain glycocalicin, even in samples treated with protease inhibitors and centrifuged extensively to remove platelets and platelet fragments. Confirmation that the plasma antigen had a relative molecular weight similar or identical to glycocalicin was obtained from studies employing gel chromatography and affinity chromatography. An immunoradiometric assay was developed to quantify plasma glycocalicin, and normal plasma was found to contain approximately 1-3 micrograms/ml. The plasma of a patient with severe thrombocytopenia due to aplastic anemia had less than 12.5% of the normal level of glycocalicin, whereas two patients with thrombocytopenia due to diseases of increased platelet destruction (idiopathic thrombocytopenic purpura and hemolytic-uremic syndrome) had normal levels. Thus, there appears to be ongoing catabolism of platelet GPIb in vivo, and we postulate that the plasma level of glycocalicin reflects a complex function of factors, including platelet count, platelet turnover, and the site of platelet destruction.

The calcium-dependent neutral protease of human blood platelets: a comparison of its effects on the receptors for von Willebrand factor and for the Fc-fragment derived from IgG

Glycocalicin (Gc) is the large, water soluble fragment, obtained by cleavage of one of the major membrane glycoproteins, GP Ib, of human platelets by means of the endogenous, calcium-dependent neutral protease (CNP) obtained from lysed platelets. GP Ib has been proposed as the receptor for von Willebrand factor (vWF) as well as for the Fc-receptor of the platelet surface. We have investigated, whether Gc was involved in a receptor function for aggregated human IgG, which is a powerful activator of platelets. Neither Gc nor asialo-Gc inhibited the stimulation of human blood platelets by bisdiazoniumbenzidine-aggregated human IgG (BDB-IgG). Moreover, platelets, after treatment with a crude preparation of CNP, which removes Gc, could be stimulated by BDB-IgG as well as or better than control platelets, but were unreactive with bovine vWF. We conclude that the Gc-moiety of GP Ib, which is involved in the bovine vWF binding site, is not the Fc-receptor on platelets. Thus, the inhibition, by human or rabbit IgG aggregates or monomeric rabbit IgG, of vWF-induced platelet agglutination, as reported by other authors, is either due to a steric effect resulting from a vicinal position of both receptors or involves the residual part of GP Ib after cleavage of Gc.

Effect of storage on platelet release and aggregation responses

The effect of storage conditions on the aggregation and release responses of platelets have been investigated, using ADP as activating agent and beta-thromboglobulin (BTG) as a measure of the release reaction. Spontaneous release of BTG during storage was also investigated. Platelets held at room temperature maintained their ability to aggregate and release BTG in response to ADP after 3 days storage. After storage for 1 day at 4 degrees C platelets showed normal aggregation in response to ADP but did not release BTG. After 4-6 days, platelets stored at room temperature showed a smaller spontaneous loss of BTG than those stored at 4 degrees C. Spontaneous release of BTG from platelets in whole blood stored at 4 degrees C was significantly lower than from platelets stored as concentrates, although platelets prepared from whole blood stored for 1 day showed neither release nor aggregation in response to ADP stimulation. We suggest that ADP-stimulated BTG release may be a sensitive tests of platelet function during storage.

Prostacyclin prolongs viability of washed human platelets

The functional viability of stored human platelets, washed in the presence and absence of prostacyclin, was examined over a 96 h period. Platelet counts, aggregation responses and cyclic AMP levels were monitored as well as the spontaneous generation of thromboxane B2 and the liberation of labelled oleate from cellular phosphatides. In suspensions prepared without prostacyclin in the medium, platelet counts declined rapidly as did the sensitivity to aggregating agents. In addition, substantial amounts of thromboxane B2 were generated during preparation and storage and oleate liberation occurred at a rapid rate. In contrast, in prostacyclin-washed platelets, aggregation was maintained throughout the study period and there was little generation of thromboxane B2. Moreover, only a gradual decrease in platelet count and a slow increase in the rate of oleate liberation was observed when compared with controls. However, cyclic AMP levels rapidly declined when platelets were resuspended in prostacyclin-free medium.

The loss of sialic acid and its prevention in stored human platelets

The loss of sialic acid was determined in human platelets stored during a seven day period in their homologous plasma. Approximately 30% of the sialic acid was lost during the first three days of incubation at room temperature and a total of 73% was lost after seven days. The rapid in vitro loss of sialic acid may mimic a slower in vivo loss. It was found that platelets with a greater density had a higher sialic acid content than the less dense platelets. The loss of sialic acid from stored platelets could be completely inhibited by the addition of silyl compounds to the incubation plasma. The trisaccharide, N-acetylneuramin-lactose, gave a greater degree of protection than fetuin at comparable concentrations.

A platelet defect in a patient with eosinophilic leukaemia: absent ristocetin-induced platelet aggregation associated with a reduced platelet sialic acid content

Platelets from a patient with eosinophilic leukaemia were not aggregated by ristocetin. The defect was not corrected by normal human plasma and was due to a platelet abnormality. The patient's platelets also showed a diminished sensitivity to aggregation by bovine factor VIIIVWF. The defect was not associated with a prolonged bleeding time. No abnormalities were detected in ADP, collagen or thrombin-induced platelet aggregation. Biochemical studies showed that the platelets were deficient in sialic acid. This deficiency was associated with a reduced staining for glycoprotein I following SDS-polyacrylamide gel electrophoresis. The results suggest an acquired platelet surface abnormality.