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BACKGROUND: Pathogen reduction technologies (PRTs) were developed to improve the safety of platelet concentrates (PCs) for transfusion purposes; however, several studies report a negative impact on the in vitro and in vivo platelet (PLT) quality. Therefore, analyses of the underlying molecular processes triggered by PRT treatments are necessary to understand their effects on PLT function. STUDY DESIGN AND METHODS: In two separate two-arm studies PCs prepared in plasma for storage either by the leukoreduced buffy coat (BC-PCs) or by the leukoreduced apheresis (AP-PCs) method were treated with or without riboflavin and ultraviolet (UV) light (Mirasol; 6.24 J/mL; 265-375 nm). Samples were drawn after treatment and after 1, 4, and 6 days of storage with subsequent analyses performed using in vitro measurements for PLT quality monitoring. Semiquantitative proteomic studies identified proteins that changed in band intensities in response to treatment or storage. Protein validation and subsequent biochemical studies were carried out by immunoblot analyses. RESULTS: The proteomic results identified changes mainly of proteins associated with the structure and regulation of the cytoskeleton. Focusing on the vasodilator-stimulated phosphoprotein (VASP) in AP-PCs revealed a storage-dependent, but treatment-independent, delocalization and a strong treatment-dependent phosphorylation at Ser-239 that was also present, but to a much lesser degree in BC-PCs. This modification correlated exponentially with PLT activation as determined by P-selectin expression. CONCLUSION: Treatment of PCs with Mirasol leads to the amplification of VASP Ser-239 phosphorylation, which is linked to actin dynamics and regulation of integrin αIIbβ3 activation. This change offers one explanation for Mirasol's impact on PLT in vitro quality measures. The Ser-239 phosphorylation level of VASP might be a useful protein marker for riboflavin and UV light–mediated PLT compromise.

The metabolic conversion of glucose to energy and reducing power by platelets is examined. Although platelets concurrently metabolize glucose aerobically and anaerobically, the balance between the cytosolic and mitochondrial pathways is affected not only by physiological activation but also by conditions prevailing during in vitro storage. The development of platelet additive solutions and pathogen reduction technologies point to increased glucose metabolism and consequent high levels of lactate production as the effect of platelet damage, rather than the cause. Consequently a different perspective of the data suggests that reduction rather than support of platelet metabolism in vitro would result in a better quality of stored platelets.

Background In Europe, buffy-coat processing allows for the use of platelet additive solutions (PAS). These solutions, however, have long been questioned for their lack of glucose, a potentially essential nutrient for platelet storage. Using a novel, practical, two-part system for incorporation of glucose into an additive solution (PAS-G), this study compares platelet storage in plasma to storage in PAS-G. Study Design and Methods A paired study design of platelet concentrates (PC) were prepared from leucoreduced pools of eight buffy coats (BCP) split into two equal pools, with suspension in autologous plasma, or PAS-G. On days 2, 5, 7 and 9 of storage, samples were tested using standard in vitro platelet parameters. Data were analysed by paired Student's t-tests. Results During storage, PCs in PAS-G maintain a quality profile that is strikingly similar to PCs stored in plasma in terms of platelet activation (CD62) morphology score, swirl, glucose metabolism and pH. However, PCs in PAS-G perform lower (P

Although the disaccharide trehalose has been shown to protect cells during freezing and desiccation when present intracellularly, a major obstacle to using intracellular sugars for biopreservation applications is the impermeability of plasma membranes. We are investigating the use of liposomes, which are synthetic, microscopic vesicles, for the intracellular delivery of stabilizing sugars into mammalian cells. Previous work has shown that the mechanism of red blood cell (RBC)–liposome interaction includes both liposome fusion with the RBC membranes, as well as tight adsorption of the vesicles onto the RBC surface. However, the fusion efficiency of liposomes was low, with only micromolar concentrations of trehalose delivered to the RBC cytosol. The purpose of this study is to enhance the efficacy of liposomes’ delivery of trehalose into RBCs with minimal detrimental effects on RBC membrane quality, by manipulating liposome physical properties and liposome–RBC incubation conditions. Charged and uncharged un...

A major obstacle in using intracellular sugars for the cryopreservation of mammalian cells is the inability of cells to synthesize or actively accumulate these sugars. We are investigating the use ...

RGD (arginine-glycine-aspartic acid) is a known peptide sequence that binds platelet integrin GPIIbIIIa and disrupts platelet-fibrinogen binding and platelet cross-linking during thrombosis. RGD peptides are unsuitable for clinical applications due to their high 50% inhibitory concentration (IC50) and low in vivo residence times. We addressed these issues by conjugating RGD peptides to biocompatible macromolecular carriers: hyperbranched polyglycerols (HPG) via divinyl sulfone. The GPIIbIIIa binding activity of RGD was maintained after conjugation and the effectiveness of the HPG-RGD conjugate was dependent upon molecular weight and the number of RGD peptides attached to each HPG molecule. These polyvalent inhibitors of platelet aggregation decreased the IC50 of RGD in an inverse linear manner based on the number of RGD peptides per HPG. Since HPG-RGD conjugates do not cause platelet activation by degranulation and certain substitution ratios do not increase fibrinogen binding to resting platelets, HPG-RGD may serve as a model for a novel class of antithrombotics.

Background and Objectives We developed a viscous platelet additive solution (PAS) based on MacoPharma's SSP+ but containing hydroxyethyl starch to address the poor osmotic balance and low yield associated with conventional PAS for the storage of buffy-coat platelet concentrates (PC). Materials and Methods Pools of four buffy-coats were made into leucoreduced PCs (n = 5) suspended either in plasma or viscous PAS. After determination of platelet recoveries, the PCs were stored under standard conditions. On days 1, 2, 3, 5, 7 and 9, PCs were tested for mean platelet volume, platelet concentration, soluble protein concentration, CD62 expression, platelet morphology, partial pressure of oxygen and partial pressure of carbon dioxide, glucose and lactate concentration, pH, extent of shape change, and hypotonic shock response (HSR). Results Platelets were prepared with greater ease using the viscous PAS and had improved platelet yield. PCs stored in either plasma or viscous PAS displayed similar storage characteristics to day 9. On days 7 and 9 of storage, platelets stored in viscous PAS displayed significantly lower (P

We investigated the effect on in vitro platelet function of hirutonin, a modified hirutonin with an RGD-like motif, a pseudo-RGDS peptide and a linear RGDS peptide. Inhibition of expression of surface fibrinogen on ADP-activated platelets with 40 μM of the peptide was as follows: hirutonin 10±3%, modified chimeric peptide 26±5%, pseudo-RGDS 66±11% and linear RGDS 93±13%. Both hirutonin and the chimeric peptide significantly inhibited ADP-induced platelet activation as detected by CD62 expression. Unlike the RGDS and pseudo-RGDS controls, neither the chimeric peptide nor the parent hirutonin inhibited ADP-induced platelet aggregation even at 140 μM. The chimeric hirutonin peptide reduced ATP release from ADP-stimulated platelets by 40±4%. This inhibition was stronger than that caused by hirutonin (23±13%), but less than the RGDS (90±2%) and pseudo RGDS-peptides (59±11%). Primary platelet haemostasis was slightly but not significantly affected by the peptide at 40 and 80 μM. However, shear-induced platelet adhesion to vWF and especially subsequent aggregate formation was interrupted after the addition of the chimeric peptide. Similar results were obtained with hirutonin. This inhibition was not as marked as with the RGDS- and pseudo-RGDS peptides. Both the parent hirutonin and the chimeric peptide caused prolongation of the clinical coagulation assays aPTT and TT. In conclusion, the chimeric hirutonin peptide with introduction of the RGD motif retained its anticoagulant effect but had little formal disintegrin activity. Instead, it appeared to have novel anti-platelet effects that may be of therapeutic use.

BACKGROUND: The introduction of prestorage white cell (WBC) reduction in random-donor platelet concentrates in Canada has increased the occurrence of particulate material in PCs. The effects of filtration on platelet activation state and the activation of plasma enzyme systems were assessed. STUDY DESIGN AND METHODS: Particulate material was examined by light microscopy, electron microscopy, protein electrophoresis, and biochemical analysis. Thirty PCs (10 unfiltered, 20 filtered) were examined during processing and 5-day storage for pH, platelet count and mean volume, morphology, activation marker expression, and hypotonic shock response. Complement activation, thrombin generation, and fibrinolysis were assessed by using specific enzyme immunoassays or chromogenic assays. RESULTS: By all analyses, the particulate material appeared to be platelet aggregates. Platelets exposed to WBC-reduction filters expressed a significantly higher level of activation markers CD62 and CD63, altered morphology, and increased platelet microparticles throughout the storage period than did unfiltered platelets. Complement activation at the C3 level was significantly increased in filtered units with little evidence of coagulation or fibrinolytic system activation. CONCLUSION: Exposure of platelets to filters during prestorage WBC reduction increased platelet activation and mildly increased complement activation over the levels during the storage period. These alterations can contribute to the formation of irreversible platelet aggregates during processing.

To assess alterations in coagulation proteins in stored platelet concentrates, we used a series of platelet parameters and measures of coagulation activation to compare samples collected before unit donation, during the processing of platelet concentrates (PC) from CPDA-1 blood, and in storage up to 5 days as well as stored platelet-poor plasma (PPP). Storage-dependent increases in activated partial thromboplastin time and prothrombin time were seen in both PC and PPP. However, FVII, FXI, FXII, kallikrein activity and prothrombin F1.2 levels remained unchanged in stored PC. Surprisingly, in stored PPP, significant alterations in FXII, FVII, kallikrein and prothrombin F1.2 levels were seen. Platelet morphology and surface marker studies demonstrated platelet activation during storage. These data suggest that the presence of platelets in the CLX storage container partially suppresses coagulation activation at significant cost to platelet viability.

Conventional antithrombotic drug discovery requires testing of large numbers of drug candidates. We used computer-aided macromolecular interaction assessment (MIAX) to select antithrombotic molecules that mimic and therefore block platelet GPIb’s binding to von Willebrand factor (vWf), an early step in thrombus formation. We screened a random array of 15-mer D-amino acid peptides for binding vWf. Structures of 4 candidate peptides were inferred by comparison to sequences in protein databases, conversion from the L to D conformations and molecular dynamics (MD) determinations of those most energetically stable. By MIAX, we deduced the amino acids and intermolecular hydrogen bonds contributing to the GPIb-vWf interaction interface. We docked the peptides onto vWf in silico to localize their binding sites and consequent potential for preventing GPIb-vWf binding. In vitro inhibition of ristocetin-initiated platelet agglutination confirmed peptide function and suitability for antithrombotic development, thereby validating this novel approach to drug discovery.

BACKGROUND: Buffy-coat processing allows for the use of platelet additive solutions (PASs). PASs reduce plasma-associated transfusion reactions and conserve plasma for transfusion or fractionation. Platelet (PLT) storage in plasma was compared to storage in three commercially available PASs compared to assess their influence on in vitro laboratory variables. STUDY DESIGN AND METHODS: Platelet concentrates (PCs) were prepared from leukoreduced pools of four buffy coats (BCPs) suspended in autologous plasma or one of PASs (Composol, Fresenius-Kabi; T-Sol, Baxter Corp.; or SSP+, MacoPharma). On Days 1, 2, 3, 5, and 7 of storage, samples were tested for PLT concentration, mean PLT volume (MPV), CD62P, morphology, pO2, pCO2, glucose, lactate and total protein concentration, pH, extent of shape change (ESC), and hypotonic shock response (HSR). Data were analyzed by analysis of variance (ANOVA) with repeated measures and t tests. RESULTS: PLT recoveries from BCPs were higher (p

With the advent of liposomes as drug carriers, there arises a need for efficient targeted delivery in vivo. Proteins coupled to liposomes usually yield heterogeneous products that are ill-defined both chemically and in terms of spatial orientation. We now report on the disulfide linkage to the surface of intact liposomes of a peptide representing one-half of a ligand-receptor pair. An RGD-motif-containing peptide was coupled to the phospholipid PDP-DOPE of the liposomes by a thiol-disulfide exchange. The resulting lipopeptides were amenable to definition by TLC, HPLC, and MS and found to be in a functional orientation allowing biochemical interaction with their receptor, the integrin glycoprotein IIb-IIIa.

Peptides containing Arg-Gly-Asp (RGD) sequences are known to bind to integrins which mediate cell adhesion and therefore have been utilized in applications such as antithrombotics and tissue engineering. Although RGD and related peptides show promise, their unfavourable pharmacokinetic profiles and susceptibility to in vivo proteolysis hinder their clinical usefulness. Peptide-polymer conjugates can address one of these challenges by extending the peptide’s residence in plasma. Hyperbranched polyglycerols (HPGs) are biocompatible polyether polyols with very long plasma circulation half-lives (t1/2 ∼ 60h) and as such are ideally suited to be carriers in such conjugates. HPGs of three different molecular weights were conjugated with RGD peptides at various substitution levels. Some of the terminal hydroxyl groups of polyglycerols were converted to vinyl sulfone groups which were subsequently utilized to couple cysteine terminated RGD peptides. The following conjugates were made: 515 kDa with substitution levels of 100:1, 500:1 and 1000:1; 100 kDa with substitution levels of 100:1 and 1000:1; and 3 kDa with substitution levels of 1:1, and 10:1. RGD-coupled HPG inhibited fibrinogen binding to platelet glycoprotein IIb-IIIa as detected by flow cytometry using anti-fibrinogen. Compared to free RGD (Ic50 = 5 x 10-5 M), inhibition of fibrinogen binding increased with increasing HPG molecular weight and increasing RGD-substitution for the high MW conjugates: Ic50 for the 515 kDa conjugates were 6.3 x 10−8 M for the 100:1 substitution, 4.7 x 10-8 M for the 500:1 substitution, and 4.1 x 10−8 M for 1000:1 substitution; Ic50 for the 100 kDa conjugates were 7.0 x 10−7 M for the 100:1 substitution and 1.2 x 10−7 M for the 1000:1 substitution. Ic50 for the 3 kDa conjugates were 2 x 10−5 M for the 1:1 substitution, 2 x 10−4 M for 10:1 substitution. Similarly, platelet function, as demonstrated by MnCl2-initated aggregation was inhibited in a dose- and molecular weight-dependent manner by HPG-RGD conjugates. Platelet aggregate formation and aggregate size were confirmed by microscopy. However, unsubstituted HPG had no effect on platelet fibrinogen binding and neither conjugated nor unconjugated HPG increased platelet CD62 surface expression. Trypsin digestion (but not SBTI-treated trypsin) removed the inhibitory activity of the conjugates and thus confirmed that both fibrinogen binding and aggregation-inhibition were dependent on the RGD peptide sequence. Such multi-determinant peptide-HPG conjugates represent a new approach to the development of antithrombotic drugs.

T-2 toxin is taken up by lymphocytes in 10-15 min in a saturable manner. Uptake is dependent on temperature and partially on the availability of energy. Approx. 10(5) molecules of T-2 toxin are bound per cell, having a mean affinity constant, Ka = 1.6 X 10(7) M-1. The toxin is rapidly dissociated from the cell to leave approx. 10-15% of the original loading in 1 h. It is concluded that T-2 toxin uptake and release do not follow conventional mechanisms.

The tricothecene mycotoxin, T-2 toxin interacts differently with mammalian erythrocytes. Pig, man, rabbit, guinea pig, horse, dog, rat, and mouse erythrocytes are all lysed to a varying degree by T-2 toxin. But cow, sheep, goat, buffalo, and deer erythrocytes are all resistant to hemolysis by T-2 toxin. Since erythrocytes from ruminant animals contain little or no phosphatidylcholine, perhaps the presence of phosphatidylcholine in the membrane is required for the hemolytic action of T-2 toxin. Sheep erythrocytes were used to encapsulate T-2 toxin further confirming the resistance of erythrocytes from animals with ruminant physiology to T-2 toxin lysis.

Although T-2 toxin intoxications have been described as radiomimetic, we find that T-2 toxin does not preferentially affect multiplying cells. Among the targets of T-2 toxin toxicity, DNA, RNA and protein synthesis inhibition are analysed. All three types of macromolecular syntheses are affected by a threshold dose of T-2 toxin which corresponds to the interaction of approx. 1·105 T-2 toxin molecules with the same number of T-2 toxin receptors (Gyongyossy-Issa, M.I.C. and Kachatourians, G.G. (1984) Biochim. Biophys. Acta 803, 197–202). Since toxic effects occur faster at higher toxin concentrations than at lower levels, the time-toxic effect relationship may be defined by a constant. Based on these observations, we hypothesize that complete receptor-occupation is the critical first step in the course of T-2 toxin toxicity events.

The erythrocyte constitutes a good model system for the study of membrane-associated toxicity events caused by the trichothecene mycotoxin, T-2. This study confirms that T-2 has a direct lytic effect on erythrocytes. Lysis of guinea pig red cells requires approx. 10(10) molecules/cell and reaches plateau values after 4-6 h. An activation energy, Ea approximately equal to 4.5 kcal was derived from the Arrhenius equation. By use of osmotic blockers of differing Stokes' radii, the functional size of the membrane lesion caused by T-2 toxin was shown to be smaller than 5.5 A. It is concluded that T-2 toxin may exert its toxic effects via the cell membrane.

The interaction of the trichothecene mycotoxin T-2 with guinea-pig erythrocytes was studied. In a time- and dose-dependent manner, T-2 toxin showed a protective antihaemolytic effect in hypotonic solutions. In isotonic environments, T-2 toxin caused membrane changes resulting in an increase in cell volume and a dramatic alteration in red-cell morphology from the biconcave disc to an echinocyte. These results demonstrate that T-2 toxin, in line with other amphipaths, distributes into the outer half of the cell membrane's phospholipid bilayer. This constitutes the first direct demonstration of an initially amphipathic mechanism of action for this toxin. Therefore, it is suggested that the degree of the final toxic effect of T-2 may be influenced by the targeted cell's membrane.