The role of lectins and glycans in platelet clearance

The role of platelet desialylation as a biomarker in primary immune thrombocytopenia: mechanisms and therapeutic perspectives

Primary immune thrombocytopenia (ITP) is an acquired autoimmune disorder characterized by the destruction of platelets. Although it was long believed that the critical role of autoantibodies in platelet destruction, primarily through the Fc-dependent platelet clearance pathway, recent findings indicate that the significance of the Fc-independent platelet clearance pathway mediated by hepatocytes, thus shedding light on a previously obscure aspect of ITP pathogenesis. Within this context, the desialylation of platelets has emerged as a pivotal biochemical marker. Consequently, targeting platelet desialylation emerges as a novel therapeutic strategy in the pathogenesis of ITP. Notably, prevailing research has largely focused on antiplatelet antibodies and the glycosylation-associated mechanisms of platelet clearance, while comprehensive analysis of platelet desialylation remains scant. In response, we retrospectively discuss the historical progression, inducing factors, generation process, and molecular regulatory mechanisms underlying platelet desialylation in ITP pathogenesis. By systematically evaluating the most recent research findings, we contribute to a comprehensive understanding of the intricate processes involved. Moreover, our manuscript delves into the potential application of desialylation regulatory strategies in ITP therapy, heralding novel therapeutic avenues. In conclusion, this manuscript not only fills a critical void in existing literature but also paves the way for future research by establishing a systematic theoretical framework. By inspiring new research ideas and offering insights into the development of new therapeutic strategies and targeted drugs, our study is poised to significantly advance the clinical management of ITP.

Viruses and thrombocytopenia

Thrombocytopenia, characterized by a decrease in platelet count, is a multifaceted clinical manifestation that can arise from various underlying causes. This review delves into the intriguing nexus between viruses and thrombocytopenia, shedding light on intricate pathophysiological mechanisms and highlighting the pivotal role of platelets in viral infections. The review further navigates the landscape of thrombocytopenia in relation to specific viruses, and sheds light on the diverse mechanisms through which hepatitis C virus (HCV), measles virus, parvovirus B19, and other viral agents contribute to platelet depletion. As we gain deeper insights into these interactions, we move closer to elucidating potential therapeutic avenues and preventive strategies for managing thrombocytopenia in the context of viral infections.

Study of platelet kinetics in immune thrombocytopenia to predict splenectomy response

Despite the efficacy of splenectomy for chronic immune thrombocytopenia (ITP), its considerable failure rate and its possible related complications prove the need for further research into potential predictors of response. The platelet sequestration site determined by 111 In-labelled autologous platelet scintigraphy has been proposed to predict splenectomy outcome, but without standardisation in clinical practice. Here, we conducted a single-centre study by analysing a cohort of splenectomised patients with ITP in whom 111 In-scintigraphy was performed at La Paz University Hospital in Madrid to evaluate the predictive value of the platelet kinetic studies. We also studied other factors that could impact the splenectomy outcome, such as patient and platelet characteristics. A total of 51 patients were splenectomised, and 82.3% responded. The splenic sequestration pattern predicted a higher rate of complete response up to 12 months after splenectomy (p = 0.005), with 90% sensitivity and 77% specificity. Neither age, comorbidities, therapy lines nor previous response to them showed any association with response. Results from the platelet characteristics analysis revealed a significant loss of sialic acid in platelets from the non-responding patients compared with those who maintained a response (p = 0.0017). Our findings highlight the value of splenic sequestration as an independent predictor of splenectomy response.

Direct and indirect effects of Puumala hantavirus on platelet function

Thrombocytopenia is a cardinal symptom of hantavirus-induced diseases including Puumala virus (PUUV)-induced hemorrhagic fever with renal syndrome (HFRS), which is associated with impaired platelet function, bleeding manifestations and augmented thrombotic risk. However, the underlying mechanisms causing thrombocytopenia and platelet hypo-responsiveness are unknown. Thus, we investigated the direct and indirect impact of PUUV on platelet production, function and degradation. Analysis of PUUV-HFRS patient blood revealed that platelet hypo-responsiveness in PUUV infection was cell-intrinsic and accompanied by reduced platelet-leukocyte aggregates (PLAs) and upregulation of monocyte tissue factor (TF), whereas platelet vasodilator-stimulated phosphoprotein (VASP) phosphorylation was comparable to healthy controls. Plasma CXCL4 levels followed platelet count dynamics throughout disease course. PUUV activated both neutrophils and monocytes in vitro, but platelet desialylation, degranulation and GPIIb/IIIa activation as well as PLA formation and endothelial adhesion under flow remained unaltered in the presence of PUUV. Further, MEG-01 megakaryocytes infected with PUUV displayed unaltered polyploidization, expression of surface receptors and platelet production. However, infection of endothelial cells with PUUV significantly increased platelet sequestration. Our data thus demonstrate that although platelet production, activation or degradation are not directly modulated, PUUV indirectly fosters thrombocytopenia by sequestration of platelets to infected endothelium. Upregulation of immunothrombotic processes in PUUV-HFRS may further contribute to platelet dysfunction and consumption. Given the pathophysiologic similarities of hantavirus infections, our findings thus provide important insights into the mechanisms underlying thrombocytopenia and highlight immune-mediated coagulopathy as potential therapeutic target.

Cold stored platelets in the management of bleeding: is it about bioenergetics?

When platelet concentrates (PCs) were first introduced in the 1960s as a blood component therapy, they were stored in the cold. As platelet transfusion became more important for the treatment of chemotherapy-induced thrombocytopenia, research into ways to increase supply intensified. During the late 1960s/early 1970s, it was demonstrated through radioactive labeling of platelets that room temperature platelets (RTP) had superior post-transfusion recovery and survival compared with cold-stored platelets (CSP). This led to a universal switch to room temperature storage, despite CSP demonstrating superior hemostatic effectiveness upon being transfused. There has been a global resurgence in studies into CSP over the last two decades, with an increase in the use of PC to treat acute bleeding within hospital and pre-hospital care. CSP demonstrate many benefits over RTP, including longer shelf life, decreased bacterial risk and easier logistics for transport, making PC accessible in areas where they have not previously been, such as the battlefield. In addition, CSP are reported to have greater hemostatic function than RTP and are thus potentially better for the treatment of bleeding. This review describes the history of CSP, the functional and metabolic assays used to assess the platelet storage lesion in PC and the current research, benefits and limitations of CSP. We also discuss whether the application of new technology for studying mitochondrial and glycolytic function in PC could provide enhanced understanding of platelet metabolism during storage and thus contribute to the continued improvements in the manufacturing and storage of PC.

Hibernation and hemostasis

Hibernating mammals have developed many physiological adaptations to accommodate their decreased metabolism, body temperature, heart rate and prolonged immobility without suffering organ injury. During hibernation, the animals must suppress blood clotting to survive prolonged periods of immobility and decreased blood flow that could otherwise lead to the formation of potentially lethal clots. Conversely, upon arousal hibernators must be able to quickly restore normal clotting activity to avoid bleeding. Studies in multiple species of hibernating mammals have shown reversible decreases in circulating platelets, cells involved in hemostasis, as well as in protein coagulation factors during torpor. Hibernator platelets themselves also have adaptations that allow them to survive in the cold, while those from non-hibernating mammals undergo lesions during cold exposure that lead to their rapid clearance from circulation when re-transfused. While platelets lack a nucleus with DNA, they contain RNA and other organelles including mitochondria, in which metabolic adaptations may play a role in hibernator's platelet resistance to cold induced lesions. Finally, the breakdown of clots, fibrinolysis, is accelerated during torpor. Collectively, these reversible physiological and metabolic adaptations allow hibernating mammals to survive low blood flow, low body temperature, and immobility without the formation of clots during torpor, yet have normal hemostasis when not hibernating. In this review we summarize blood clotting changes and the underlying mechanisms in multiple species of hibernating mammals. We also discuss possible medical applications to improve cold preservation of platelets and antithrombotic therapy.

Platelets from 13-lined ground squirrels are resistant to cold storage lesions

During torpor in a 13-lined ground squirrel heart rate and blood flow decrease, increasing the risk of blood clot formation. In response, cells involved in clotting called platelets are sequestered in the liver, stored in the cold for months, and released back into circulation upon arousal. This is in contrast to non-hibernating mammals, including humans, in which chilled platelets undergo cold storage lesions and phagocytosis, leading to rapid clearance from circulation post-transfusion. Because of this, human platelets must be stored at room temperature, limiting their shelf life to 7 days due to the increased risk of microbial contamination at warmer temperatures. Human and ground squirrel platelets were stored at room temperature or 4 °C before being analyzed for cold storage lesions. Human platelets stored at 4 °C displayed progressive increases in phosphatidylserine surface exposure and caspase activation, while ground squirrel platelets showed minimal change. Following cold storage, sialic acid residues on human platelets were cleaved, leading to increased phagocytosis of human platelets by HepG2 cells. Ground squirrel platelets stored in the cold showed no changes in desialylation and phagocytosis, with Taxol-treated ground squirrel platelets showing the lowest phagocytosis rates between both species and all treatments. These results suggest that ground squirrel platelets may be resistant to cold storage lesions seen in human platelets. Although these experiments were done in vitro, they suggest a mechanism by which ground squirrel platelets are adapted to be stored during hibernation and remain functional following arousal. Other hibernating species may employ similar adaptations to retain functional platelets following torpor.

Platelet-Derived Extracellular Vesicles in Arterial Thrombosis

Blood platelets are necessary for normal haemostasis but also form life-threatening arterial thrombi when atherosclerotic plaques rupture. Activated platelets release many extracellular vesicles during thrombosis. Phosphatidylserine-exposing microparticles promote coagulation. Small exosomes released during granule secretion deliver cargoes including microRNAs to cells throughout the cardiovascular system. Here, we discuss the mechanisms by which platelets release these extracellular vesicles, together with the possibility of inhibiting this release as an antithrombotic strategy.

Clinical and Diagnostic Significance of Sialic Acids Determination in Biological Material

Sialic acids (SA) are neuraminic acid derivatives, located at the terminal position in the chains of monosaccharide residues of various glycoconjugates. SA play a dual role: they either mask recognition sites, or, on the contrary, represent biological targets that can be recognized by receptor proteins and serve as ligands. The desialylation/sialylation processes can be considered as a dynamic modification regulated by sialyltransferases and sialidases in response to external or internal stimuli. This review describes the structural and functional diversity and the potential use of SA fractions as biomarkers for various pathological conditions. Almost any extreme impact on the body and inflammatory processes are accompanied by an increase in the level of both total and free SA in the blood and tissues. Possible reasons for the increase of sialoglycoconjugate metabolism indicators in biological material include: (i) activation of the hepatocyte synthesis and secretion of various acute-phase proteins, many of which are sialoglycoproteins, (ii) impaired membrane integrity and destruction of body cells, (iii) high activity of sialidases (neurominidases) and sialyltransferases. Most acute and chronic liver diseases are characterized by the decrease in the total level of SA in the blood serum (because many plasma proteins are synthesized and glycosylated in hepatocytes). Aberrant sialylation results in changes of sialoglycoconjugate structure, its ability to perform biological functions and sialoglycoconjugate half-life. Glycosylation is the most common post-translational modification of proteins in the virus, which not only promotes the formation of specific conformation of viral proteins, but also modulates their interaction with receptors and affects host cell recognition, viral replication and infectivity. Serum total SA concentration increases in some benign and inflammatory conditions, which indicates a lack of specificity and limits their use for early detection and screening of neoplastic diseases. Clinical and diagnostic value of determining the sialoglycoconjugate metabolic indicators, including changes in the content of both SA fractions and specific proteins in various biological fluids and tissues, consists in establishing the causes and mechanisms of biochemical changes in the body in certain diseases. In combination with the measurement of existing markers, they can be used to improve diagnosis, staging and monitoring of therapeutic response in some pathological conditions where the need for specificity is less than for specific diagnostics.

[Clinical and diagnostic significance of sialic acids determination in biological material]

Sialic acids (SA) are derivatives of neuraminic acid; they are located at the terminal position in the chains of monosaccharide residues of various glycoconjugates. SA play a dual role, they either mask recognition sites, or, on the contrary, represent biological targets that can be recognized by receptor proteins and serve as ligands. The desialylation/sialylation processes can be viewed as a dynamic modification regulated by sialyltransferases and sialidases in response to external or internal stimuli. This review describes the structural and functional diversity and the potential use of SA fractions as biomarkers for various pathological conditions. Almost any extreme effects on the body and inflammatory processes lead to an increase in the level of both total and free SA in the blood and tissues. Possible reasons for the increase of sialoglycoconjugate metabolism indicators in biological material include activation of the hepatocyte synthesis and secretion of various acute-phase proteins, many of which are sialoglycoproteins, violation of the membrane integrity and destruction of body cells, and also high activity of sialidases (neurominidases) and sialyltransferases. Most acute and chronic liver diseases are characterized by the decrease in the total level of SA in the blood serum (because many plasma proteins are synthesized and glycosylated in hepatocytes). Aberrant sialylation results in changes of sialoglycoconjugate structure, its ability to perform biological functions and half-life. Glycosylation is the most common post-translational modification of proteins in the virus, which not only promotes the formation of specific conformation of viral proteins, but also modulates their interaction with receptors and affects host cell recognition, viral replication and infectivity. Serum total SA concentration increases in some benign and inflammatory conditions, which indicates a lack of specificity and limits their use for early detection and screening of neoplastic diseases. Nevertheless, determining blood SA level and measuring concentration of existing biomarkers can be used to improve diagnostic indicators, to stage and monitor therapeutic response in some types of cancer, when the need for specificity is less than for diagnosis. Clinical and diagnostic value of determining the sialoglycoconjugate metabolic indicators, including changes in the content of both SA fractions and specific proteins in various biological fluids and tissues, lies in establishing the causes and mechanisms of biochemical changes in the body in certain diseases.

Primary Immune Thrombocytopenia and Essential Thrombocythemia: So Different and yet Somehow Similar-Cases Series and a Review of the Literature

This article collects several published cases in which immune thrombocytopenic purpura (ITP) is followed by essential thrombocythemia (ET) and vice versa. This surprising clinical condition is possible, but very rare and difficult to diagnose and manage. We have made an attempt to analyse the possible causes of the sequential appearance of ITP and ET taking into consideration the following: alteration of the thrombopoietin (TPO) receptor, the role of autoimmunity and inflammation, and cytokine modulation. A better understanding of these interactions may provide opportunities to determine predisposing factors and aid in finding new treatment modalities both for ITP and ET patients.

Soluble Platelet Release Factors as Biomarkers for Cardiovascular Disease

Platelets are the main players in thrombotic diseases, where activated platelets not only mediate thrombus formation but also are involved in multiple interactions with vascular cells, inflammatory components, and the coagulation system. Although in vitro reactivity of platelets provides information on the function of circulating platelets, it is not a full reflection of the in vivo activation state, which may be relevant for thrombotic risk assessment in various disease conditions. Therefore, studying release markers of activated platelets in plasma is of interest. While this type of study has been done for decades, there are several new discoveries that highlight the need for a critical assessment of the available tests and indications for platelet release products. First, new insights have shown that platelets are not only prominent players in arterial vascular disease, but also in venous thromboembolism and atrial fibrillation. Second, knowledge of the platelet proteome has dramatically expanded over the past years, which contributed to an increasing array of tests for proteins released and shed from platelets upon activation. Identification of changes in the level of plasma biomarkers associated with upcoming thromboembolic events allows timely and individualized adjustment of the treatment strategy to prevent disease aggravation. Therefore, biomarkers of platelet activation may become a valuable instrument for acute event prognosis. In this narrative review based on a systematic search of the literature, we summarize the process of platelet activation and release products, discuss the clinical context in which platelet release products have been measured as well as the potential clinical relevance.

Evolution and Utility of Antiplatelet Autoantibody Testing in Patients with Immune Thrombocytopenia

To this day, immune thrombocytopenia (ITP) remains a clinical diagnosis made by exclusion of other causes for thrombocytopenia. Reliable detection of platelet autoantibodies would support the clinical diagnosis, but the lack of specificity and sensitivity of the available methods for platelet autoantibody testing limits their value in the diagnostic workup of thrombocytopenia. The introduction of methods for glycoprotein-specific autoantibody detection has improved the specificity of testing and is acceptable for ruling in ITP but not ruling it out as a diagnosis. The sensitivity of these assays varies widely, even between studies using comparable assays. A review of the relevant literature combined with our own laboratory's experience of testing large number of serum and platelet samples makes it clear that this variation can be explained by variations in the characteristics of the tests, including in the glycoprotein-specific monoclonal antibodies, the glycoproteins that are tested, the platelet numbers used in the assay and the cutoff levels for positive and negative results, as well as differences in the tested patient populations. In our opinion, further standardization and optimization of the direct autoantibody detection methods to increase sensitivity without compromising specificity seem possible but will still likely be insufficient to distinguish the often very weak specific autoantibody signals from background signals. Further developments of autoantibody detection methods will therefore be necessary to increase sensitivity to a level acceptable to provide laboratory confirmation of a diagnosis of ITP.

Platelet storage and functional integrity

Platelet transfusion is a topic of common interest for many specialists involved in patient care, from laboratory staff to clinical physicians. Various aspects make this type of transfusion different from those of other blood components. In this review, the challenges in platelet transfusion practice that are relevant for laboratory colleagues will be discussed, highlighting how the biochemical and structural characteristics of these blood elements directly affect their function and consequently the clinical outcome. More than 1,300 platelet concentrates are transfused in Germany every day, and several types are offered by their respective manufacturers. We describe the technological advances in platelet concentrate production, with a focus on how the storage conditions of platelets can be improved. Laboratory quality assessment procedures for a safe transfusion are discussed in detail. For this purpose, we will refer to the Hemotherapy Directives (Richtlinie Hämotherapie) of the German Medical Association.

Measuring beta-galactose exposure on platelets: Standardization and healthy reference values

BACKGROUND

Correct diagnosis of the cause of thrombocytopenia is crucial for the appropriate management of patients. Hyposialylation/desialylation (characterized by abnormally high β-galactose exposure) accelerates platelet clearance and can lead to thrombocytopenia. However, the reference range for β-galactose exposure in healthy individuals has not been defined previously.

OBJECTIVE

The objective of the present study was to develop a standardized assay of platelet β-galactose exposure for implementation in a clinical laboratory.

METHODS

β-Galactose exposure was measured in platelet-rich plasma by using flow cytometry and Ricinus communis agglutinin (RCA). A population of 120 healthy adults was recruited to study variability.

RESULTS

We determined an optimal RCA concentration of 12.5 μg/mL. The measure was stable for up to 4 hours (mean fluorescence intensity [MFI]-RCA: 1233 ± 329 at 0 hour and 1480 ± 410 at 4 hours). The platelet count did not induce a variation of RCA and the measure of RCA was stable when tested up to 24 hours after blood collection (MFI-RCA: 1252 ± 434 at day 0 and 1140 ± 297 24 hours after blood sampling). To take into account the platelet size, results should be expressed as RCA/forward scatter ratio. We used the assay to study variability in 120 healthy adults, and we found that the ratio is independent of sex and blood group.

CONCLUSION

We defined a normal range in a healthy population and several preanalytical and analytical variables were evaluated, together with positive and negative controls. This assay may assist in the diagnosis of thrombocytopenic diseases linked to changes in β-galactose exposure.

Label-free on chip quality assessment of cellular blood products using real-time deformability cytometry

Without cellular blood products such as platelet concentrates (PC), red blood cell concentrates (RCC), and hematopoietic stem cells (HPSC) modern treatments in medicine would not be possible. An unresolved challenge is the assessment of their quality with minimal cell manipulation. Minor changes in production, storage conditions, or blood bag composition may impact cell function, which can have important consequences on product integrity. This is especially relevant for personalized medicine, such as autologous T-cell therapy. Today a robust methodology that globally determines cell status directly before transfusion or transplantation is lacking. We demonstrate that measuring viscoelastic characteristics of peripheral blood cells using real-time deformability cytometry (RT-DC) provides comprehensive information on product quality, which is not accessible using conventional quality control tests. In addition, RT-DC requires few cells, a minimal sample volume and has a rapid turnaround time. We compared RT-DC to standard in vitro quality assays assessing: i) PC after storage at 4 °C and room temperature; ii) magnetic nanoparticle labeled platelets; iii) RCC stored in blood bags with different plasticizers; iv) RCC after gamma irradiation; and v) HPSC after cryopreservation with 5% or 10% dimethyl sulfoxide, respectively. Additionally, we evaluated the engraftment time of patients' platelets and leukocytes after transplantation of HPSC products. Our results demonstrate that label-free mechano-phenotyping can be used as a potential biomarker for quality assessment of cell-based pharmaceutical products.

The Birth and Death of Platelets in Health and Disease

Blood platelets are involved in a wide range of physiological responses and pathological processes. Recent studies have considerably advanced our understanding of the mechanisms of platelet production and clearance, revealing new connections between the birth and death of these tiny, abundant cells. Key insights have also been gained into how physiological challenges such as inflammation, infection, and chemotherapy can affect megakaryocytes, the cells that produce platelets.

Mechanisms of receptor shedding in platelets

The ability to upregulate and downregulate surface-exposed proteins and receptors is a powerful process that allows a cell to instantly respond to its microenvironment. In particular, mobile cells in the bloodstream must rapidly react to conditions where infection or inflammation are detected, and become proadhesive, phagocytic, and/or procoagulant. Platelets are one such blood cell that must rapidly acquire and manage proadhesive and procoagulant properties in order to execute their primary function in hemostasis. The regulation of platelet membrane properties is achieved via several mechanisms, one of which involves the controlled metalloproteolytic release of adhesion receptors and other proteins from the platelet surface. Proteolysis effectively lowers receptor density and reduces the reactivity of platelets, and is a mechanism to control robust platelet activation. Recent research has also established clear links between levels of platelet receptors and platelet lifespan. In this review, we will discuss the current knowledge of metalloproteolytic receptor regulation in the vasculature with emphasis on the platelet receptor system to highlight how receptor density can influence both platelet function and platelet survival.

Refrigeration, cryopreservation and pathogen inactivation: an updated perspective on platelet storage conditions

Conventional storage of platelet concentrates limits their shelf life to between 5 and 7 days due to the risk of bacterial proliferation and the development of the platelet storage lesion. Cold storage and cryopreservation of platelets may facilitate extension of the shelf life to weeks and years, and may also provide the benefit of being more haemostatically effective than conventionally stored platelets. Further, treatment of platelet concentrates with pathogen inactivation systems reduces bacterial contamination and provides a safeguard against the risk of emerging and re-emerging pathogens. While each of these alternative storage techniques is gaining traction individually, little work has been done to examine the effect of combining treatments in an effort to further improve product safety and minimize wastage. This review aims to discuss the benefits of alternative storage techniques and how they may be combined to alleviate the problems associated with conventional platelet storage.

Targeted Measurements of O- and N-Glycopeptides Show That Proteins in High Density Lipoprotein Particles Are Enriched with Specific Glycosylation Compared to Plasma

High density lipoprotein (HDL) particles are believed to be protective due to their inverse correlation with the prevalence of cardiovascular diseases. However, recent studies show that in some conditions such as heart disease and diabetes, HDL particles can become dysfunctional. Great attention has been directed toward HDL particle composition because the relative abundances of HDL constituents determine HDL's functional properties. A key factor to consider when studying the structure and composition of plasma particles is the protein glycosylation. Here, we profile the O- and N-linked glycosylation of HDL associated-proteins including the truncated form of Apo CIII and their glycan heterogeneity in a site-specific manner. Apolipoprotein CIII, fetuin A, and alpha 1 antitrypsin are glycoproteins associated with lipoproteins and are implicated in many cardiovascular and other disease conditions. A targeted method (UHPLC-QQQ) was used to measure the glycoprotein concentrations and site-specific glycovariations of the proteins in human plasma and compared with HDL particles isolated from the same plasma samples. The proteins found in the plasma are differentially glycosylated compared to those isolated in HDL. The results of this study suggest that glycosylation may play a role in protein partitioning in the blood, with possible functional implications.

Clinical updates in adult immune thrombocytopenia

Immune thrombocytopenia (ITP) occurs in 2 to 4/100 000 adults and results in variable bleeding symptoms and thrombocytopenia. In the last decade, changes in our understanding of the pathophysiology of the disorder have led to the publication of new guidelines for the diagnosis and management of ITP and standards for terminology. Current evidence supports alternatives to splenectomy for second-line management of patients with persistently low platelet counts and bleeding. Long-term follow-up data suggest both efficacy and safety, in particular, for the thrombopoietin receptor agonists and the occurrence of late remissions. Follow-up of patients who have undergone splenectomy for ITP reveals significant potential risks that should be discussed with patients and may influence clinician and patient choice of second-line therapy. Novel therapeutics are in development to address ongoing treatment gaps.

Specific and Differential Binding of N-Acetylgalactosamine Glycopolymers to the Human Macrophage Galactose Lectin and Asialoglycoprotein Receptor

A range of glycopolymers composed of N-acetylgalactosamine were prepared via sequential Cu(I)-mediated polymerization and alkyne-azide click (CuAAC). The resulting polymers were shown, via multichannel surface plasmon resonance, to interact specifically with human macrophage galactose lectin (MGL; CD301) with high affinity (K_D = 1.11 μM), but they did not bind to the mannose/fucose-selective human lectin dendritic-cell-specific intercellular adhesion molecule-3-grabbing nonintegrin (DC-SIGN; CD209). The effect of sugar ligand valency on the binding (so-called "glycoside cluster effect") of poly(N-acetylgalactosamine) to MGL was investigated by varying first the polymer chain length (DP: 100, 64, 40, 23, 12) and then the architecture (4- and 8-arm star glycopolymers). The chain length did not have a significant effect on the binding to MGL (K_D = 0.17-0.52 μM); however, when compared to a hepatic C-type lectin of a similar monosaccharide specificity, the asialoglycoprotein receptor (ASGPR), the binding affinity was more noticeably affected (K_D = 0.37- 6.65 μM). These data suggest that known differences in the specific configuration/orientation of the carbohydrate recognition domains of MGL and ASGPR are responsible for the differences in binding observed between the different polymers of varied chain length and architecture. In the future, this model has the potential to be employed for the development of tissue-selective delivery systems.

Platelet clearance by the hepatic Ashwell-Morrell receptor: mechanisms and biological significance

The daily production of billions of platelets must be regulated to avoid spontaneous bleeding or arterial occlusion and organ damage. Complex mechanisms control platelet production and clearance in physiological and pathological conditions. This review will focus on the mechanisms of platelet senescence with specific emphasis on the role of post-translational modifications in platelet life-span and thrombopoietin production downstream of the hepatic Ashwell-Morrell receptor.

Mice Lacking the Inhibitory Collagen Receptor LAIR-1 Exhibit a Mild Thrombocytosis and Hyperactive Platelets

OBJECTIVE

Leukocyte-associated immunoglobulin-like receptor-1 (LAIR-1) is a collagen receptor that belongs to the inhibitory immunoreceptor tyrosine-based inhibition motif-containing receptor family. It is an inhibitor of signaling via the immunoreceptor tyrosine-based activation motif-containing collagen receptor complex, glycoprotein VI-FcRγ-chain. It is expressed on hematopoietic cells, including immature megakaryocytes, but is not detectable on platelets. Although the inhibitory function of LAIR-1 has been described in leukocytes, its physiological role in megakaryocytes and in particular in platelet formation has not been explored. In this study, we investigate the role of LAIR-1 in megakaryocyte development and platelet production by generating LAIR-1-deficient mice.

APPROACH AND RESULTS

Mice lacking LAIR-1 exhibit a significant increase in platelet counts, a prolonged platelet half-life in vivo, and increased proplatelet formation in vitro. Interestingly, platelets from LAIR-1-deficient mice exhibit an enhanced reactivity to collagen and the glycoprotein VI-specific agonist collagen-related peptide despite not expressing LAIR-1, and mice showed enhanced thrombus formation in the carotid artery after ferric chloride injury. Targeted deletion of LAIR-1 in mice results in an increase in signaling downstream of the glycoprotein VI-FcRγ-chain and integrin αIIbβ3 in megakaryocytes because of enhanced Src family kinase activity.

CONCLUSIONS

Findings from this study demonstrate that ablation of LAIR-1 in megakaryocytes leads to increased Src family kinase activity and downstream signaling in response to collagen that is transmitted to platelets, rendering them hyper-reactive specifically to agonists that signal through Syk tyrosine kinases, but not to G-protein-coupled receptors.

Metalloproteolytic receptor shedding…platelets "acting their age"

Whilst significant effort has been focused on development of tools and approaches to clinically modulate activation processes that consume platelets, the platelet receptors that initiate activation processes remain untargeted. The modulation of receptor levels is also linked to underlying platelet aging processes which influence normal platelet lifespan and also the functionality and survival of stored platelets that are used in transfusion. In this review, we will focus on platelet adhesion receptors initiating thrombus formation, and discuss how regulation of levels of these receptors impact platelet function and platelet survival.

Platelets: handle with care

Platelets are delicate cells that require careful handling between collection, preparation and transfusion. This review addresses practical questions relating to platelet concentration, resting time after collection, total time and number of periods without agitation and temperature. The bags in which platelets are stored are made from gas-permeable plastic to allow sufficient oxygen for the platelets to maintain aerobic respiration. Manufacturers have assigned limits for platelet content and concentration, and these must not be exceeded. There is no strong evidence for or against the resting of platelets post-collection and pre-agitation, but platelets should not be over-wrapped during this period as this compromises gas exchange; a short rest period of up to 1 h may allow the separation of minor aggregates. It is necessary to transport platelet concentrates (e.g. from manufacturing site to hospital), but these periods without gas exchange must be limited to avoid excessive damage to the platelets. Current data support a total of 24 h of transportation per component but with no individual period lasting more than 8 h. Platelets need to be stored at 20-24 °C based on evidence that colder storage leads to irreversible changes on the platelet membrane, resulting in phagocytosis of the platelets following transfusion. Storage at warmer temperatures may lead to an increase in bacterial risk. On the basis of this review, the UK Guidelines for Blood Transfusion Services have been updated to ensure that platelets are handled in the most appropriate way to ensure that efficacious components are provided for patients.

The role of leukocytes in thrombosis

In recent years, the traditional view of the hemostatic system as being regulated by a coagulation factor cascade coupled with platelet activation has been increasingly challenged by new evidence that activation of the immune system strongly influences blood coagulation and pathological thrombus formation. Leukocytes can be induced to express tissue factor and release proinflammatory and procoagulant molecules such as granular enzymes, cytokines, and damage-associated molecular patterns. These mediators can influence all aspects of thrombus formation, including platelet activation and adhesion, and activation of the intrinsic and extrinsic coagulation pathways. Leukocyte-released procoagulant mediators increase systemic thrombogenicity, and leukocytes are actively recruited to the site of thrombus formation through interactions with platelets and endothelial cell adhesion molecules. Additionally, phagocytic leukocytes are involved in fibrinolysis and thrombus resolution, and can regulate clearance of platelets and coagulation factors. Dysregulated activation of leukocyte innate immune functions thus plays a role in pathological thrombus formation. Modulation of the interactions between leukocytes or leukocyte-derived procoagulant materials and the traditional hemostatic system is an attractive target for the development of novel antithrombotic strategies.

CD8(+) T cells induce platelet clearance in the liver via platelet desialylation in immune thrombocytopenia

In addition to antiplatelet autoantibodies, CD8⁺ cytotoxic T lymphocytes (CTLs) play an important role in the increased platelet destruction in immune thrombocytopenia (ITP). Recent studies have highlighted that platelet desialylation leads to platelet clearance via hepatocyte asialoglycoprotein receptors (ASGPRs). Whether CD8⁺ T cells induce platelet desialylation in ITP remains unclear. Here, we investigated the cytotoxicity of CD8⁺ T cells towards platelets and platelet desialylation in ITP. We found that the desialylation of fresh platelets was significantly higher in ITP patients with positive cytotoxicity of CD8⁺ T cells than those without cytotoxicity and controls. In vitro, CD8⁺ T cells from ITP patients with positive cytotoxicity induced significant platelet desialylation, neuraminidase-1 expression on the platelet surface, and platelet phagocytosis by hepatocytes. To study platelet survival and clearance in vivo, CD61 knockout mice were immunized and their CD8⁺ splenocytes were used. Platelets co-cultured with these CD8⁺ splenocytes demonstrated decreased survival in the circulation and increased phagocytosis in the liver. Both neuraminidase inhibitor and ASGPRs competitor significantly improved platelet survival and abrogated platelet clearance caused by CD8⁺ splenocytes. These findings suggest that CD8⁺ T cells induce platelet desialylation and platelet clearance in the liver in ITP, which may be a novel mechanism of ITP.

Evaluation of the role of the GPIb-IX-V receptor complex in development of the platelet storage lesion

BACKGROUND AND OBJECTIVES

In mice, loss of sialic acid resulting in shedding of glycoprotein (GP) Ibα and GPV has been linked to platelet survival. The aim of this study was to determine whether loss of sialic acid and the GPIb-IX-V complex contributes to development of the platelet storage lesion (PSL) in human platelet concentrates (PCs).

MATERIALS AND METHODS

PCs (stored in plasma (with or without Mirasol treatment); PAS-C or PAS-E) were stored at room temperature. Flow cytometry was used to monitor membrane expression of the GPIb-IX-V complex, CD62P, surface glycans and PS exposure. The functionality of stored platelets was determined employing aggregometry and ristocetin-induced VWF binding.

RESULTS

Storage time of PCs in blood banks is limited to 7 days. During this time period, a minor but gradually increasing subpopulation of GPIbα-negative platelets was observed. Also, ristocetin-induced VWF binding was impaired in a small population of platelets. Mean surface expression of GPIbα and GPV remained stable until day 9, whereas CD62P expression increased; also a rapid decrease in ADP-induced aggregation was observed for PAS-C, PAS-E and Mirasol-treated PCs. Upon prolonged storage (>9 days), a slow decline in surface expression of GPIbα and GPV was observed; no major changes were observed in surface sialylation with the exception of Mirasol-treated platelets.

CONCLUSION

In a small population of stored platelets, changes in GPIbα occur from day 2 onwards. Loss of sialic acid and subsequent shedding of GPIbα and GPV is not an early event during the development of the PSL.

Glycans and the platelet life cycle

Platelet numbers are intricately regulated to avoid spontaneous bleeding or arterial occlusion and organ damage. The growth factor thrombopoietin (TPO) drives platelet biogenesis by inducing megakaryocyte production. A recent study in mice identified a feedback mechanism by which clearance of aged, desialylated platelets stimulates TPO synthesis by hepatocytes. This new finding generated renewed interest in platelet clearance mechanisms. Here, different established and emerging mechanisms of platelet senescence and clearance will be reviewed with specific emphasis on the role of posttranslational modifications.

Novel mechanisms of platelet clearance and thrombopoietin regulation

PURPOSE OF REVIEW

The human body produces and removes 10 platelets daily to maintain a normal steady-state platelet count. Platelet production must be tightly regulated to avoid spontaneous bleeding or arterial occlusion and organ damage. Multifaceted and complex mechanisms control platelet removal and production in physiological and pathological conditions. This review will focus on different mechanisms of platelet clearance, with focus on the biological significance of platelet glycans.

RECENT FINDINGS

The Ashwell-Morrell receptor (AMR) recognizes senescent, desialylated platelets under steady state conditions. Desialylated platelets and the AMR are the physiological ligand-receptor pair regulating hepatic thrombopoietin (TPO) mRNA production, resolving the longstanding mystery of steady state TPO regulation. The AMR-mediated removal of desialylated platelets regulates TPO synthesis in the liver by recruiting JAK2 and STAT3 to increase thrombopoiesis.

SUMMARY

Inhibition of TPO production downstream of the hepatic AMR-JAK2 signaling cascade could additionally contribute to the thrombocytopenia associated with JAK1/2 treatment, which is clinically used in myeloproliferative neoplasms.

Regulation of platelet lifespan by apoptosis

The lifespan of platelets in circulation is brief, close to 10 days in humans and 5 days in mice. Bone marrow residing megakaryocytes produce around 100 billion platelets per day. In a healthy individual, the majority of platelets are not consumed by hemostatic processes, but rather their lifespan is controlled by programmed cell death, a canonical intrinsic apoptosis program. In the last decade, insights from genetically manipulated mouse models and pharmacological developments have helped to define the components of the intrinsic, or mitochondrial, apoptosis pathway that controls platelet lifespan. This review focuses on the molecular regulation of apoptosis in platelet survival, reviews thrombocytopenic conditions linked to enhanced platelet death, examines implications of chemotherapy-induced thrombocytopenia through apoptosis-inducing drugs in cancer therapy as well as discusses ex vivo aging of platelets.

Evaluation of in vitro storage characteristics of cold stored platelet concentrates with N acetylcysteine (NAC)

Platelets play a vital role in hemostasis and thrombosis, and their demand and usage has multiplied many folds over the years. However, due to the short life span and storage constraints on platelets, it is allowed to store them for up to 7 days at room temperature (RT); thus, there is a need for an alternative storage strategy for extension of shelf life. Current investigation involves the addition of 50 mM N acetylcysteine (NAC) in refrigerated concentrates. Investigation results revealed that addition of NAC to refrigerated concentrates prevented platelet activation and reduced the sialidase activity upon rewarming as well as on prolonged storage. Refrigerated concentrates with 50 mM NAC expressed a 23.91 ± 6.23% of CD62P (P-Selectin) and 22.33 ± 3.42% of phosphotidylserine (PS), whereas RT-stored platelets showed a 46.87 ± 5.23% of CD62P and 25.9 ± 6.48% of phosphotidylserine (PS) after 5 days of storage. Further, key metabolic parameters such as glucose and lactate accumulation indicated reduced metabolic activity. Taken together, investigation and observations indicate that addition of NAC potentially protects refrigerated concentrates by preventing platelet activation, stabilizing sialidase activity, and further reducing the metabolic activity. Hence, we believe that NAC can be a good candidate for an additive solution to retain platelet characteristics during cold storage and may pave the way for extension of storage shelf life.

The effect of stationary versus rocked storage of whole blood on red blood cell damage and platelet function

BACKGROUND

Increasingly, cold-stored whole blood (WB) is being considered for the resuscitation of civilian trauma patients. It is unclear whether the WB should be agitated to enhance the function of the platelets (PLTs) or whether agitation will cause RBC damage.

STUDY DESIGN AND METHODS

WB units were collected by standard procedures using a PLT-sparing inline leukoreduction filter and stored between 1 and 6°C. On Storage Day 3 each unit was divided into 4 subunits that were stored under one of the following conditions for 21 days: unrocked, manually rocked once daily, continuously rocked end over end, or continuously rocked horizontally. From Day 3 to Day 10, hemolysis and the mechanical fragility index (MFI) for RBC injury were measured daily and again on Days 15 and 21 (n = 9-16 units tested each time). On Days 4 and 10, rapid thromboelastogram (rTEG) measurements were performed (n = 8-10 units tested each time).

RESULTS

Hemolysis and MFI increased significantly between Day 3 and Day 21 (p < 0.0001) for all RBC rocking conditions, as well as the unrocked units. Only the manually and horizontally rocked units demonstrated higher hemolysis (on Day 21) and MFI (starting on Day 10) compared to the unrocked units. Only the α-angle and maximum amplitude in the end-over-end rocked units increased significantly between Day 4 and Day 10. There were no significant differences between the rocked and unrocked units on Day 10 for any rTEG variable.

CONCLUSIONS

Rocking does not appear to enhance in vitro PLT activity in cold-stored WB and can lead to increased hemolysis.

Numerical analysis of in vivo platelet consumption data from ITP patients

Background

Numerical methods have recently allowed quantitative interpretation of in vivo murine platelet consumption data in terms of values for the random destruction rate constant (RD), intrinsic lifespan (LS), and the standard deviation of ln LS (SD), as well as the platelet production rate (PR) and age distribution (AD). But application of these methods to data obtained in thrombocytopenic patients is problematic for two reasons. First, such data has in all cases been obtained with radiolabeled platelets, and uptake of the radio-isotope by long lived cells complicates the analysis. Second, inferred values of the platelet production rate (PR) and random destruction rate (RD) are difficult to interpret, since increased RD can occur either as a cause or a consequence of thrombocytopenia.

Methods

We used a numerical method to analyze in vivo platelet consumption data from a series of 41 patients with immune thrombocytopenic purpura (ITP). An additional parameter, the fraction of labeled long-lived cells (LL), was evaluated concurrently with RD, LS, and SD. To provide a basis for interpreting these values, we used an iterative interpolation process to predict their response to different pathophysiologic mechanisms. The process also generates predicted effects on the widely used immature platelet fraction (IPF).

Results

Optimal parameter value sets were identified in 76 % (31 of 41) of the data sets. 27 of 31 ITP patients showed no substantial homeostatic increase in platelet production, with the remaining 4 showing both augmented platelet consumption and a compensatory increase in PR. Up to 1/3 of the patients showed the degree of increased RD expected to result from reduced thrombopoiesis only. “Jacknife” resampling yielded CV values of <0.5 in over 75 % of the evaluable data sets. Predicted platelet age distributions indicate that interpretation of the IPF and absolute IPF (aIPF) is a complex function of platelet count. We found, counter-intuitively, that reduced PR can increase the IPF, and increased RD can reduce the aIPF.

Conclusions

Our findings support the feasibility of using numerical analysis to quantitatively interpret in vivo platelet consumption data, to identify likely etiologies of thrombocytopenias, and to assess the utility of IPF measurements in that context.

Electronic supplementary material

The online version of this article (doi:10.1186/s12878-015-0034-4) contains supplementary material, which is available to authorized users.

Regulating billions of blood platelets: glycans and beyond

The human body produces and removes 10(11) platelets daily to maintain a normal steady state platelet count. Platelet production must be regulated to avoid spontaneous bleeding or arterial occlusion and organ damage. Multifaceted and complex mechanisms control platelet production and removal in physiological and pathological conditions. This review will focus on different mechanisms of platelet senescence and clearance with specific emphasis on the role of posttranslational modifications. It will also briefly address platelet transfusion and the role of glycans in the clearance of stored platelets.

Horizontal RNA transfer mediates platelet-induced hepatocyte proliferation

Liver regeneration is stimulated by blood platelets, but the molecular mechanisms involved are largely unexplored. Although platelets are anucleate, they do contain coding or regulatory RNAs that can be functional within the platelet or, after transfer, in other cell types. Here, we show that platelets and platelet-like particles (PLPs) derived from the megakaryoblastic cell line MEG-01 stimulate proliferation of HepG2 cells. Platelets or PLPs were internalized within 1 hour by HepG2 cells and accumulated in the perinuclear region of the hepatocyte. Platelet internalization also occurred following a partial hepatectomy in mice. Annexin A5 blocked platelet internalization and HepG2 proliferation. We labeled total RNA of MEG-01 cells by incorporation of 5-ethynyluridine (EU) and added EU-labeled PLPs to HepG2 cells. PLP-derived RNA was detected in the cytoplasm of the HepG2 cell. We next generated PLPs containing green fluorescent protein (GFP)-tagged actin messenger RNA. PLPs did not synthesize GFP, but in coculture with HepG2 cells, significant GFP protein synthesis was demonstrated. RNA-degrading enzymes partly blocked the stimulating effect of platelets on hepatocyte proliferation. Thus, platelets stimulate hepatocyte proliferation via a mechanism that is dependent on platelet internalization by hepatocytes followed by functional transfer of RNA stored in the anucleate platelet. This mechanism may contribute to platelet-mediated liver regeneration.

The Ashwell-Morell receptor regulates hepatic thrombopoietin production via JAK2-STAT3 signaling

The hepatic Ashwell-Morell receptor (AMR) can bind and remove desialylated platelets. Here we demonstrate that platelets become desialylated as they circulate and age in blood. Binding of desialylated platelets to the AMR induces hepatic expression of thrombopoietin (TPO) mRNA and protein, thereby regulating platelet production. Endocytic AMR controls TPO expression through Janus kinase 2 (JAK2) and the acute phase response signal transducer and activator of transcription 3 (STAT3) in vivo and in vitro. Recognition of this newly identified physiological feedback mechanism illuminates the pathophysiology of platelet diseases, such as essential thrombocythemia and immune thrombocytopenia, and contributes to an understanding of the mechanisms of thrombocytopenia observed with JAK1/2 inhibition.

Platelets are efficient and protective depots for storage, distribution, and delivery of lysosomal enzyme in mice with Hurler syndrome

Use of megakaryocytes/platelets for transgene expression may take advantage of their rapid turnover and protective storage in platelets and reduce the risk of activating oncogenes in hematopoietic stem and progenitor cells (HSCs). Here, we show that human megakaryocytic cells could overexpress the lysosomal enzyme, α-l-iduronidase (IDUA), which is deficient in patients with mucopolysaccharidosis type I (MPS I). Upon megakaryocytic differentiation, the amount of released enzyme increased rapidly and steadily by 30-fold. Using a murine MPS I model, we demonstrated that megakaryocyte/platelets were capable of producing, packaging, and storing large amounts of IDUA with proper catalytic activity, lysosomal trafficking, and receptor-mediated uptake. IDUA can be released directly into extracellular space or within microparticles during megakaryocyte maturation or platelet activation, while retaining the capacity for cross-correction in patient's cells. Gene transfer into 1.7% of HSCs led to long-term normalization of plasma IDUA and preferential distribution of enzyme in liver and spleen with complete metabolic correction in MPS I mice. Detection of GFP (coexpressed with IDUA) in Kupffer cells and hepatocytes suggested liver delivery of platelet-derived IDUA possibly via the clearance pathway for senile platelets. These findings provide proof of concept that cells from megakaryocytic lineage and platelets are capable of generating and storing fully functional lysosomal enzymes and can also lead to efficient delivery of both the enzymes released into the circulation and those protected within platelets/microparticles. This study opens a door for use of the megakaryocytes/platelets as a depot for efficient production, delivery, and effective tissue distribution of lysosomal enzymes.

Dietary α-linolenic acid increases the platelet count in ApoE-/- mice by reducing clearance

Previously we reported that dietary intake of alpha-linolenic acid (ALA) reduces atherogenesis and inhibits arterial thrombosis. Here, we analyze the substantial increase in platelet count induced by ALA and the mechanisms of reduced platelet clearance. Eight-week-old male apolipoprotein E knockout (ApoE(-/-)) mice were fed a 0.21g% cholesterol diet complemented by either a high- (7.3g%) or low-ALA (0.03g%) content. Platelet counts doubled after 16 weeks of ALA feeding, whereas the bleeding time remained similar. Plasma glycocalicin and glycocalicin index were reduced, while reticulated platelets, thrombopoietin, and bone marrow megakaryocyte colony-forming units remained unchanged. Platelet contents of liver and spleen were substantially reduced, without affecting macrophage function and number. Glycoprotein Ib (GPIb) shedding, exposure of P-selectin, and activated integrin αIIbβ3 upon activation with thrombin were reduced. Dietary ALA increased the platelet count by reducing platelet clearance in the reticulo-endothelial system. The latter appears to be mediated by reduced cleavage of GPIb by tumor necrosis factor-α-converting enzyme and reduced platelet activation/expression of procoagulant signaling. Ex vivo, there was less adhesion of human platelets to von Willebrand factor under high shear conditions after ALA treatment. Thus, ALA may be a promising tool in transfusion medicine and in high turnover/high activation platelet disorders.

Temperature cycling improves in vivo recovery of cold-stored human platelets in a mouse model of transfusion

BACKGROUND

Platelet (PLT) storage at room temperature (RT) is limited to 5 days to prevent growth of bacteria, if present, to high levels. Storage in cold temperatures would reduce bacterial proliferation, but cold-exposed PLTs are rapidly cleared from circulation by the hepatic Ashwell-Morell (AM) receptor, which recognizes PLT surface carbohydrates terminated by β-galactose. We cycled storage temperature between 4 and 37°C to preserve PLT function and reduce bacterial growth.

STUDY DESIGN AND METHODS

Temperature-cycled (TC) human PLTs were stored at 4°C for 12 hours and then incubated at 37°C for 30 minutes before returning back to cold storage. PLTs stored at RT or at 4°C (COLD) or TC for 2, 5, and 7 days were infused into SCID mice and the in vivo recovery was determined at 5, 20, and 60 minutes after transfusion.

RESULTS

PLTs stored for 2 days in COLD had significantly lower in vivo recoveries than RT PLTs. TC PLTs had improved recoveries over COLD and comparable to RT PLTs. After 5- and 7-day storage, TC PLTs had better recoveries than RT and COLD PLTs. PLT surface β-galactose was increased significantly for both COLD and TC PLTs compared to RT. Blocking of the AM receptor by asialofetuin increased COLD but not TC PLT recovery.

CONCLUSION

TC cold storage may be an effective method to store PLTs without loss of in vivo recovery. The increased β-galactose exposure in TC PLTs suggests that mechanisms in addition to AM receptors may mediate clearance of cold-stored PLTs.

Development of orally active inhibitors of protein and cellular fucosylation

The key role played by fucose in glycoprotein and cellular function has prompted significant research toward identifying recombinant and biochemical strategies for blocking its incorporation into proteins and membrane structures. Technologies surrounding engineered cell lines have evolved for the inhibition of in vitro fucosylation, but they are not applicable for in vivo use and drug development. To address this, we screened a panel of fucose analogues and identified 2-fluorofucose and 5-alkynylfucose derivatives that depleted cells of GDP-fucose, the substrate used by fucosyltransferases to incorporate fucose into protein and cellular glycans. The inhibitors were used in vitro to generate fucose-deficient antibodies with enhanced antibody-dependent cellular cytotoxicity activities. When given orally to mice, 2-fluorofucose inhibited fucosylation of endogenously produced antibodies, tumor xenograft membranes, and neutrophil adhesion glycans. We show that oral 2-fluorofucose treatment afforded complete protection from tumor engraftment in a syngeneic tumor vaccine model, inhibited neutrophil extravasation, and delayed the outgrowth of tumor xenografts in immune-deficient mice. The results point to several potential therapeutic applications for molecules that selectively block the endogenous generation of fucosylated glycan structures.

Primary hemostatic capacity of whole blood: a comprehensive analysis of pathogen reduction and refrigeration effects over time

BACKGROUND

Whole blood (WB) has been used in combat since World War I as it is readily available and replaces every element of shed blood. Component therapy has become standard; however, recent military successes with WB resuscitation have revived the debate regarding wider WB use. Characterization of optimal WB storage is needed. We hypothesized that refrigeration preserves WB function and that a pathogen reduction technology (PRT) based on riboflavin and ultraviolet light has no deleterious effect over 21 days of storage.

STUDY DESIGN AND METHODS

WB units were stored for 21 days either at 4°C or 22°C. Half of each temperature group underwent PRT, yielding four final treatment groups (n = 8 each): CON 4 (WB at 4°C); CON 22 (WB at 22°C); PRT 4 (PRT WB at 4°C); and PRT 22 (PRT WB at 22°C). Testing was at baseline, Days 1-7, 10, 14, and 21. Assays included coagulation factors; platelet activation, aggregation, and adhesion; and thromboelastography (TEG).

RESULTS

Prothrombin time (PT) and partial thromboplastin time increased over time; refrigeration attenuated the effects on PT (p ≤ 0.009). Aggregation decreased over time (p ≤ 0.001); losses were attenuated by refrigeration (p ≤ 0.001). Refrigeration preserved TEG parameters (p ≤ 0.001) and PRT 4 samples remained within normal limits throughout the study. Refrigeration in combination with PRT inhibited fibrinolysis (p ≤ 0.001) and microparticle formation (p ≤ 0.031). Cold storage increased shear-induced platelet aggregation and ristocetin-induced platelet agglutination (p ≥ 0.032), as well as GPIb-expressing platelets (p ≤ 0.009).

CONCLUSION

The in vitro hemostatic function of WB is largely unaffected by PRT treatment and better preserved by cold storage over 21 days. Refrigerated PRT WB may be suitable for trauma resuscitation. Clinical studies are warranted.