Platelet storage lesion: an update on the impact of various leukoreduction processes on the biological response modifiers

The Effect of Leukocyte Removal and Matrix Metalloproteinase Inhibition on Platelet Storage Lesions

The reasons for unfavorable changes in platelet concentrate (PC) quality during storage are not fully understood yet. We aimed to evaluate whether leukocytes and matrix metalloproteinases (MMPs) lead to a decrease in the quality of PCs and examine whether MMP inhibition will slow down the platelets' aging. Nine PCs were divided into three parts: (1) leukocyte-depleted (F) PCs, (2) PCs with no additional procedures (NF), and (3) PCs with the addition of an MMP inhibitor-doxycycline (D). Each PC was stored for 144 h, and a sample for testing was separated from each part on the day of preparation and after 24, 48, 72 and 144 h of storage. Blood morphological analysis, platelet aggregation, and the expression of activation markers were evaluated. MMP-2 and MMP-9 concentration, activity, and gene expression were assessed. Platelet aggregation decreased, and platelet activation marker expression increased during the storage. D concentrates showed the lowest level of platelet activation. In turn, leukocyte-depleted PCs showed the highest level of platelet activation in general. MMP-9 platelet activity was higher in leukocyte-containing concentrates at the end of the storage period. We concluded that the filtration process leads to a higher platelet activation level. The presence of doxycycline in PCs reduces the expression of the activation markers as compared to leukocyte-depleted concentrates.

The platelet storage lesion, what are we working for?

BACKGROUND

Platelet concentrate (PC) transfusions are crucial in prevention and treatment of bleeding in infection, surgery, leukemia, and thrombocytopenia patients. Although the technology for platelet preparation and storage has evolved over the decades, there are still challenges in the demand for platelets in blood banks because the platelet shelf life is limited to 5 days due to bacterial contamination and platelet storage lesions (PSLs) at 20-24°C under constant horizontal agitation. In addition, the relations between some adverse effects of platelet transfusions and PSLs have also been considered. Therefore, understanding the mechanisms of PSLs is conducive to obtaining high quality platelets and facilitating safe and effective platelet transfusions.

OBJECTIVE

This review summarizes developments in mechanistic research of PSLs and their relationship with clinical practice, providing insights for future research.

METHODS

Authors conducted a search on PubMed and Web of Science using the professional terms "PSL" and "platelet transfusion." The obtained literature was then roughly categorized based on their research content. Similar studies were grouped into the same sections, and further searches were conducted based on the keywords of each section.

RESULTS

Different studies have explored PSLs from various perspectives, including changes in platelet morphology, surface molecules, biological response modifiers (BMRs), metabolism, and proteins and RNA, in an attempt to monitor PSLs and identify intervention targets that could alleviate PSLs. Moreover, novel platelet storage conditions, including platelet additive solutions (PAS) and reconsidered cold storage methods, are explored. There are two approaches to obtaining high-quality platelets. One approach simulates the in vivo environment to maintain platelet activity, while the other keeps platelets at a low activity level in vitro under low temperatures.

CONCLUSION

Understanding PSLs helps us identify good intervention targets and assess the therapeutic effects of different PSLs stages for different patients.

Donor citrate reactions influence the phenotype of apheresis platelets following storage

BACKGROUND

Platelet collection and processing methods, as well as donor attributes, can influence platelet function and quality during ex vivo storage. In this study, activation and procoagulant responses in platelets collected from donors experiencing a citrate reaction (CR) were investigated.

STUDY DESIGN AND METHODS

Apheresis platelet components (n = 54) were stored in 100% autologous plasma and tested on days 1 and 5 post-collection. Platelet components were categorized into two groups according to whether the donor had experienced a CR during donation (n = 10; non-CR group, n = 44). Platelet aggregation was initiated with collagen and thrombin. Platelet phenotype was characterized by flow cytometry. Fibrinogen binding was assessed following collagen + thrombin stimulation (COATed platelets), and procoagulant activity was assessed using a procoagulant phospholipid assay (PPL). Platelet microparticle (PMP) subsets were enumerated by flow cytometry.

RESULTS

Basal von Willebrand factor (VWF) binding was higher in the CR donations when compared with the non-CR group. Collagen aggregation was significantly higher in platelets from CR donations, in contrast to aggregation induced by thrombin. The proportion of phosphatidylserine (PS) positive PMP and PPL clotting time were higher in the CR group, in contrast to the number of basal PS⁺ platelets and COATed platelets following stimulation.

CONCLUSION

Platelets donated by donors who experienced a CR during donation had higher platelet activation response and possibly a more procoagulant PMP phenotype, suggesting that this donor reaction might lead to increased platelet activation.

The platelet proteasome and immunoproteasome are stable in buffy-coat derived platelet concentrates for up to 7 days

OBJECTIVES

Characterization of the proteasome and its stability in buffy-coat derived platelet concentrates (PCs) during storage.

BACKGROUND

The proteasome plays a key role in cell homeostasis by processing misfolded or abnormal proteins and regulating the levels and activities of a high number of proteins contributing to cell cycle, survival, and proliferation. Controversial data exist, whether inhibition of the proteasome affects platelet function. Little is known about function, expression, and stability of the proteasome in PCs during storage, and the potential role of the platelet proteasome in storage lesions.

STUDY DESIGN AND METHODS

PCs were produced by the buffy-coat method in additive solution and stored at room temperature under agitation. Platelet aggregation was monitored by light transmission aggregometry. Proteasome complexes were assessed by immunoprecipitation and immunoblotting, and proteasome activity was measured using fluorogenic substrates specific for the three different proteolytic activities over 7 days of storage.

RESULTS

Proteasome inhibition led to a decreased platelet aggregation response after activation with collagen, ADP, TRAP-6, and thrombin. There were no changes in the expression of the catalytic active subunits as well as the proteasome activity during storage of PCs, comparing baseline and day 7.

DISCUSSION

Platelet proteasome function is relevant for platelet aggregation in response to various agonists. The constitutive and stable expression of the active standard- and immunoproteasome in platelets makes it unlikely that loss of proteasome function is a relevant cause of storage lesions.

Platelet Storage Lesions: What More Do We Know Now?

Platelet concentrate (PC) transfusions are a lifesaving adjunct to control and prevent bleeding in cancer, hematologic, surgical, and trauma patients. Platelet concentrate availability and safety are limited by the development of platelet storage lesions (PSLs) and risk of bacterial contamination. Platelet storage lesions are a series of biochemical, structural, and functional changes that occur from blood collection to transfusion. Understanding of PSLs is key for devising interventions that prolong PC shelf life to improve PC access and wastage. This article will review advancements in clinical and mechanistic PSL research. In brief, exposure to artificial surfaces and high centrifugation forces during PC preparation initiate PSLs by causing platelet activation, fragmentation, and biochemical release. During room temperature storage, enhanced glycolysis and reduced mitochondrial function lead to glucose depletion, lactate accumulation, and product acidification. Impaired adenosine triphosphate generation reduces platelet capacity to perform energetically demanding processes such as hypotonic stress responses and activation/aggregation. Storage-induced alterations in platelet surface proteins such as thrombin receptors and glycoproteins decrease platelet aggregation. During storage, there is an accumulation of immunoactive proteins such as leukocyte-derive cytokines (tumor necrosis factor α, interleukin (IL) 1α, IL-6, IL-8) and soluble CD40 ligand which can participate in transfusion-related acute lung injury and nonhemolytic transfusion reactions. Storage-induced microparticles have been linked to enhanced platelet aggregation and immune system modulation. Clinically, stored PCs have been correlated with reduced corrected count increment, posttransfusion platelet recovery, and survival across multiple meta-analyses. Fresh PC transfusions have been associated with superior platelet function in vivo; however, these differences were abrogated after a period of circulation. There is currently insufficient evidence to discern the effect of PSLs on transfusion safety. Various bag and storage media changes have been proposed to reduce glycolysis and platelet activation during room temperature storage. Moreover, cryopreservation and cold storage have been proposed as potential methods to prolong PC shelf life by reducing platelet metabolism and bacterial proliferation. However, further work is required to elucidate and manage the PSLs specific to these storage protocols before its implementation in blood banks.

Transfusion as an Inflammation Hit: Knowns and Unknowns

Transfusion of blood cell components is frequent in the therapeutic arsenal; it is globally safe or even very safe. At present, residual clinical manifestations are principally inflammatory in nature. If some rare clinical hazards manifest as acute inflammation symptoms of various origin, most of them linked with conflicting and undesirable biological material accompanying the therapeutic component (infectious pathogen, pathogenic antibody, unwanted antigen, or allergen), the general feature is subtler and less visible, and essentially consists of alloimmunization or febrile non-hemolytic transfusion reaction. The present essay aims to present updates in hematology and immunology that help understand how, when, and why subclinical inflammation underlies alloimmunization and circumstances characteristic of red blood cells and – even more frequently – platelets that contribute inflammatory mediators. Modern transfusion medicine makes sustained efforts to limit such inflammatory hazards; efforts can be successful only if one has a clear view of each element’s role.

Molecular mechanisms of erythrocyte aging

Anemia and hemorrhagic shock are leading causes of morbidity and mortality worldwide, and transfusion of human blood products is the ideal treatment for these conditions. As human erythrocytes age during storage in blood banks they undergo many biochemical and structural changes, termed the red blood cell 'storage lesion'. Specifically, ATP and pH levels decrease as metabolic end products, oxidative stress, cytokines, and cell-free hemoglobin increase. Also, membrane proteins and lipids undergo conformational and organizational changes that result in membrane loss, viscoelastic changes and microparticle formation. As a result, transfusion of aged blood is associated with a host of adverse consequences such as decreased tissue perfusion, increased risk of infection, and increased mortality. This review summarizes current research detailing the known parts of the erythrocyte storage lesion and their physiologic consequences.

The association between platelet transfusion and idiopathic pneumonia syndrome is unaffected by platelet product type

BACKGROUND

Methods used to produce platelet (PLT) components, pooling of PLT-rich plasma (PRP-PLT) and apheresis (AP-PLT), may variably contribute to the pathogenesis and severity of idiopathic pneumonia syndrome (IPS).

STUDY DESIGN AND METHODS

We performed a retrospective cohort study of 906 allogeneic hematopoietic cell transplant recipients to examine associations between PLT product type and risks of developing IPS and dying after IPS onset. Proportional hazards models included separate terms for the sum of all PLT transfusions and the sum of PRP-PLT units received in the 3 or 7 days before IPS onset. Similarly constructed models analyzed the outcome of time to death after IPS onset. All analyses were adjusted for known IPS risk factors.

RESULTS

Patients received a median of three PRP-PLT transfusions (interquartile range [IQR], 0-6) and five AP-PLT transfusions (IQR, 1-13) while at risk for IPS. Seventy-five patients (8%) developed IPS by Posttransplant Day 120. The proportion of PRP-PLT transfusions was not associated with risk of developing IPS (3-day hazard ratio [HR] 0.98, 95% CI 0.74-1.29, p = 0.86; 7-day HR 1.00, 95% CI 0.86-1.15, p = 0.95) or dying after IPS onset (3-day HR 0.99, 95% CI 0.75-1.31, p = 0.97; 7-day HR 0.98, 95% CI 0.78-1.12, p = 0.47).

CONCLUSION

The association between PLT transfusions and risk of developing IPS or dying after IPS onset does not differ according to PLT product type. Further research is required to identify potentially modifiable steps in PLT component production that contribute to IPS.

Soluble Mediators in Platelet Concentrates Modulate Dendritic Cell Inflammatory Responses in an Experimental Model of Transfusion

The transfusion of platelet concentrates (PCs) is widely used to treat thrombocytopenia and severe trauma. Ex vivo storage of PCs is associated with a storage lesion characterized by partial platelet activation and the release of soluble mediators, such as soluble CD40 ligand (sCD40L), RANTES, and interleukin (IL)-8. An in vitro whole blood culture transfusion model was employed to assess whether mediators present in PC supernatants (PC-SNs) modulated dendritic cell (DC)-specific inflammatory responses (intracellular staining) and the overall inflammatory response (cytometric bead array). Lipopolysaccharide (LPS) was included in parallel cultures to model the impact of PC-SNs on cell responses following toll-like receptor-mediated pathogen recognition. The impact of both the PC dose (10%, 25%) and ex vivo storage period was investigated [day 2 (D2), day 5 (D5), day 7 (D7)]. PC-SNs alone had minimal impact on DC-specific inflammatory responses and the overall inflammatory response. However, in the presence of LPS, exposure to PC-SNs resulted in a significant dose-associated suppression of the production of DC IL-12, IL-6, IL-1α, tumor necrosis factor-α (TNF-α), and macrophage inflammatory protein (MIP)-1β and storage-associated suppression of the production of DC IL-10, TNF-α, and IL-8. For the overall inflammatory response, IL-6, TNF-α, MIP-1α, MIP-1β, and inflammatory protein (IP)-10 were significantly suppressed and IL-8, IL-10, and IL-1β significantly increased following exposure to PC-SNs in the presence of LPS. These data suggest that soluble mediators present in PCs significantly suppress DC function and modulate the overall inflammatory response, particularly in the presence of an infectious stimulus. Given the central role of DCs in the initiation and regulation of the immune response, these results suggest that modulation of the DC inflammatory profile is a probable mechanism contributing to transfusion-related complications.

Are Platelets Cells? And if Yes, are They Immune Cells?

Small fragments circulating in the blood were formally identified by the end of the nineteenth century, and it was suggested that they assisted coagulation via interactions with vessel endothelia. Wright, at the beginning of the twentieth century, identified their bone-marrow origin. For long, platelets have been considered sticky assistants of hemostasis and pollutants of blood or tissue samples; they were just cell fragments. As such, however, they were acknowledged as immunizing (to specific HPA and HLA markers): the platelet’s dark face. The enlightened face showed that besides hemostasis, platelets contained factors involved in healing. As early as 1930s, platelets entered the arsenal of medicines were transfused, and were soon manipulated to become a kind of glue to repair damaged tissues. Some gladly categorized platelets as cells but they were certainly not fully licensed as such for cell physiologists. Actually, platelets possess almost every characteristic of cells, apart from being capable of organizing their genes: they have neither a nucleus nor genes. This view prevailed until it became evident that platelets play a role in homeostasis and interact with cells other than with vascular endothelial cells; then began the era of physiological and also pathological inflammation. Platelets have now entered the field of immunity as inflammatory cells. Does assistance to immune cells itself suffice to license a cell as an “immune cell”? Platelets prove capable of sensing different types of signals and organizing an appropriate response. Many cells can do that. However, platelets can use a complete signalosome (apart from the last transcription step, though it is likely that this step can be circumvented by retrotranscribing RNA messages). The question has also arisen as to whether platelets can present antigen via their abundantly expressed MHC class I molecules. In combination, these properties argue in favor of allowing platelets the title of immune cells.

Use of a cytokine-release assay to demonstrate loss of platelet secretory capacity during blood bank processing and storage

CONTEXT

The extent to which changes in secretory function contribute to the storage lesion of platelets (PLTs) prepared for transfusion is not well described.

OBJECTIVE

To develop a cytokine-release assay for the assessment of PLT secretory capacity during the preparation and storage of PLTs.

DESIGN

Small volumes of PLT-rich plasma and PLT concentrate (PC) were prepared from whole blood (WB; N = 4 donors). Aliquots of WB, PLT-rich plasma, and PC were treated with 20 μM adenosine diphosphate or saline (control). Samples of WB-derived PCs obtained from a regional blood center were similarly stimulated at various storage times (N = 10 units). Plasma levels of RANTES (chemokine ligand 5; regulated on activation, normal T cell expressed and secreted) and PLT aggregation were measured following agonist addition.

RESULTS

Adenosine diphosphate stimulated RANTES release from PLTs in fresh WB on average by 4.1-fold (P < .001), in PLT-rich plasma by 4.7-fold (P = .002), and in PC by 1.3-fold (P < .001). For blood center PCs, adenosine diphosphate failed to stimulate RANTES release at day 2 of storage or later (P ≥ .31). Baseline RANTES levels in the plasma/supernatant increased 660% during PC preparation (P = .02) and an additional 30% during subsequent storage (P < .001). Mean PLT aggregation decreased during processing from WB (95.6%) to PC (60.5%; P = .04). For blood center PCs, mean PLT aggregation decreased substantially from days 2 (41.0%) to 7 (2.3%; P < .001).

CONCLUSIONS

A cytokine-release assay revealed a diminution in PLT secretory capacity during PC processing and storage, with complete elimination by day 2 of storage. Loss of PLT aggregability occurred more slowly. The cytokine-release assay may be a useful endpoint for optimizing PLT preparation and storage.

Role of Siglec-7 in apoptosis in human platelets

Background

Platelets participate in tissue repair and innate immune responses. Sialic acid-binding immunoglobulin-like lectins (Siglecs) are well-characterized I-type lectins, which control apoptosis.

Methodology/Principal Findings

We characterized the expression of Siglec-7 in human platelets isolated from healthy volunteers using flow cytometry and confocal microscopy. Siglec-7 is primarily expressed on α granular membranes and colocalized with CD62P. Siglec-7 expression was increased upon platelet activation and correlated closely with CD62P expression. Cross-linking Siglec-7 with its ligand, ganglioside, resulted in platelet apoptosis without any significant effects on activation, aggregation, cell morphology by electron microscopy analysis or secretion. We show that ganglioside triggered four key pathways leading to apoptosis in human platelets: (i) mitochondrial inner transmembrane potential (ΔΨm) depolarization; (ii) elevated expression of pro-apoptotic Bax and Bak proteins with reduced expression of anti-apoptotic Bcl-2 protein; (iii) phosphatidylserine exposure and (iv), microparticle formation. Inhibition of NAPDH oxidase, PI3K, or PKC rescued platelets from apoptosis induced by Siglec-7 recruitment, suggesting that the platelet receptors P2Y1 and GPIIbIIIa are essential for ganglioside-induced platelet apoptosis.

Conclusions/Significance

The present work characterizes the role of Siglec-7 and platelet receptors in regulating apoptosis and death. Because some platelet pathology involves apoptosis (idiopathic thrombocytopenic purpura and possibly storage lesions), Siglec-7 might be a molecular target for therapeutic intervention/prevention.

The effects of pneumatic tube transport on fresh and stored platelets in additive solution

BACKGROUND

Limited scientific work has been conducted on potential in vitro effects of transport on pneumatic tube systems on blood components, in particular platelets.

MATERIALS AND METHODS

To evaluate the possible effects of the Swisslog TranspoNet system on the cellular, metabolic, phenotypic and secreting properties of fresh and stored platelets, we set up a four-arm paired study comparing transported and non-transported platelets. Platelets were aliquoted, prepared with the OrbiSac system and suspended in 70% SSP+ (n=8). All in vitro parameters were monitored over a 7-day storage period.

RESULTS

Throughout storage, no differences were observed in glucose consumption, lactate production, pH, pCO2, ATP, hypotonic shock response reactivity, CD62P, PAC-1, platelet endothelial cell adhesion molecule-1 or CD42b. The release of sCD40L increased (p<0.01) in all units but without any significant differences between groups.

CONCLUSION

The storage stability of all platelets conveyed by the Swisslog TranspoNet system was not impaired throughout 7 days of storage. The Swisslog TranspoNet system does not, therefore, seem to be a risk for increased metabolic activity, activation or release reactions from the platelets. This lack of effect of the pneumatic tube transport system did not seem to be affected by the age of the platelets or repeated transport.

Inflammatory response, immunosuppression, and cancer recurrence after perioperative blood transfusions

Debate on appropriate triggers for transfusion of allogeneic blood products and their effects on short- and long-term survival in surgical and critically ill patients continue with no definitive evidence or decisive resolution. Although transfusion-related immune modulation (TRIM) is well established, its influence on immune competence in the recipient and its effects on cancer recurrence after a curative resection remains controversial. An association between perioperative transfusion of allogeneic blood products and risk for recurrence has been shown in colorectal cancer in randomized trials; whether the same is true for other types of cancer remains to be determined. This article focuses on the laboratory, animal, and clinical evidence to date on the mechanistic understanding of inflammatory and immune-modulatory effects of blood products and their significance for recurrence in the cancer surgical patient.

Increased platelet storage time is associated with mitochondrial dysfunction and impaired platelet function

BACKGROUND

Hemorrhagic shock is a leading cause of death following severe trauma, and platelet transfusions are frequently necessary to achieve hemostasis. Platelets, however, require special storage conditions, and storage time has been associated with loss of platelet quality. We hypothesized that standard storage conditions have a deleterious effect on platelet mitochondrial function and platelet activation.

MATERIALS AND METHODS

Platelet donations were collected from healthy donors (n = 5) and stored in gas-permeable collection bags according to American Association of Blood Bank recommendations. Platelet units were sampled from day of collection (day 0) until day 7. High-resolution respirometry was used to assess baseline mitochondrial respiration, maximal oxygen utilization, and individual mitochondrial complex-dependent respiration. Fluorescence-activated cell sorting was performed to analyze mitochondrial content, mitochondrial reactive oxygen species, the expression of P-selectin (both before and after challenge with thrombin receptor-activating peptide), and apoptosis. Data were analyzed using analysis of variance and Pearson correlation (P < 0.05 significant).

RESULTS

Mitochondrial respiration decreased significantly in platelets stored longer than 2 d (P < 0.05). Platelets also demonstrated a persistent decrease in response to stimulation with thrombin receptor-activating peptide by the third day of storage (P < 0.05) as well as an increase in mitochondrial reactive oxygen species and apoptosis (P < 0.05). Mitochondrial respiration significantly correlated with platelet capacity to activate (r = 0.8, P < 0.05).

CONCLUSIONS

Platelet mitochondrial respiratory function and activation response decrease significantly in platelets stored for 3 d or more. Because platelet transfusions almost universally occur between the third and fifth day of storage, our findings may have significant clinical importance and warrant further in vivo analysis.

Comparison of cytokine levels and metabolic parameters of stored platelet concentrates of the Fundação Hemominas, Belo Horizonte, Brazil

Background

Prolonged storage of platelets could improve availability and logistical management and decrease wastage. Immunobiochemical methods can be used to guarantee the quality of platelets after prolonged storage.

Objective

The aim of this study was to compare storage-related changes in buffy coat-derived platelet concentrations versus platelet-rich plasmal.

Methods

Units of whole blood were drawn using a quadruple-bag blood container system. Platelet-rich plasma and buffy coat prepared from whole blood following standard methods were stored for 9 days. During this period test samples were aseptically collected for analysis on Days 1, 2, 3, 5, 7 and 9.

Results

The highest CD42b expression was greater than 95%. The percentage of CD62p was significantly lower than the CD42b expression. The pH remained fairly stable during storage. Measurement of pO₂ and pCO₂ showed that oxygen levels were significantly higher than carbon dioxide levels. There were no significant differences in bicarbonate levels, glucose consumption and lactate production between the groups. The swirling effect with platelet-rich plasma samples decreased after 5 days of storage and after 7 days of storage for buffy coat samples. There was a significant twenty-fold increase in the mean IL-1β after 5 days of storage for both groups. Slight increases in IL-6 and IL-8 levels were seen at 5 days.

Conclusion

The quality of platelet concentrates remained acceptable during 7 days of storage in respect to the swirling effect, pH and platelet activation. There were no significant differences between buffy coat-derived platelets and platelet-rich plasma in this study.

Effects of blood products on inflammatory response in endothelial cells in vitro

BACKGROUND

Transfusing blood products may induce inflammatory reactions within the vascular compartment potentially leading to a systemic inflammatory response. Experiments were designed to assess the inflammatory potential of different blood products in an endothelial cell-based in vitro model and to compare baseline levels of potentially activating substances in transfusion products.

METHODS

The inflammatory response from pre-activated (endotoxin-stimulated) and non-activated endothelial cells as well as neutrophil endothelial transmigration in response to packed red blood cells (PRBC), platelet concentrates (PC) and fresh frozen plasma (FFP) was determined. Baseline inflammatory mediator and lipid concentrations in blood products were evaluated.

RESULTS

Following incubation with all blood products, an increased inflammatory mediator release from endothelial cells was observed. Platelet concentrates, and to a lesser extent also FFP, caused the most pronounced response, which was accentuated in already pre-stimulated endothelial cells. Inflammatory response of endothelial cells as well as blood product-induced migration of neutrophils through the endothelium was in good agreement with the lipid content of the according blood product.

CONCLUSION

Within the group of different blood transfusion products both PC and FFP have a high inflammatory potential with regard to activation of endothelial cells. Inflammation upon blood product exposure is strongly accentuated when endothelial cells are pre-injured. High lipid contents in the respective blood products goes along with an accentuated inflammatory reaction from endothelial cells.

Red blood cell age and potentiation of transfusion-related pathology in trauma patients

The specific negative clinical manifestations associated with the transfusion of stored red blood cells (RBCs) and the corresponding mechanisms responsible for such phenomena remain poorly defined. Our recent studies document that leukoreduced older RBC units potentiate transfusion-related toxicity in trauma patients. It is our hypothesis that the transfusion of relatively older blood impedes microvascular perfusion. The central mechanisms proposed to mediate this microcirculatory alteration include: 1) the loss of RBC-dependent control of nitric oxide-mediated homeostasis concerning vasodilation and 2) immune cell and complement activation. In this review, we outline the background for our hypothesis and detail our current investigations toward the understanding of this pathophysiology.

[Blood platelets and biological response to 'danger' signals and subsequent inflammation: towards a new paradigm?]

Blood platelets are cellular elements of primary haemostasis. During the last decade research on platelets has been subsequently based on this paradigm, with separate observations on issues such as the ability for platelets to bind infectious agents or even engulf them, to drop in counts in case of evolving infectious processes, etc. More recently, novel work has set up bases for novel functions for platelets, as members of functional immune cells, principally in innate immunity but capable of influencing adaptive immunity. Platelets are thus essential to haemostasis and to inflammation, questioning their essential functionality and the set up of a novel paradigm: could platelets be tissue-repairing cells? Such an assumption would open an entire new field of investigations. The present "State of the Art" essay attempts to discuss the main arguments on this.

An association between decreased cardiopulmonary complications (transfusion-related acute lung injury and transfusion-associated circulatory overload) and implementation of universal leukoreduction of blood transfusions

BACKGROUND

Cardiopulmonary adverse events after transfusion include transfusion-related acute lung injury (TRALI) and transfusion-associated circulatory overload (TACO), which are potentially lethal and incompletely understood.

STUDY DESIGN AND METHODS

To determine whether the incidence of TRALI and TACO was affected by leukoreduction we conducted a retrospective, before-and-after study of acute transfusion reactions for the 7years before and after introduction of universal leukoreduction in 2000, involving 778,559 blood components.

RESULTS

Substantial decreases occurred in the rates of TRALI (-83%; from 2.8 cases per 100,000 components before to 0.48 after universal leukoreduction; p=0.01), TACO (-49%; 7.4 to 3.8 cases per 100,000; p=0.03), and febrile reactions (-35%; 11.4 to 7.4 cases per 10,000; p<0.0001). The incidence of allergic reactions remained unchanged (7.0 per 100,000 before and after universal leukoreduction). These outcomes were primarily attributable to decreased TRALI and/or TACO associated with red blood cell (RBC) and platelet (PLT) transfusions (-64%) with notably smaller decreases associated with fresh-frozen plasma or cryoprecipitate transfusions (-29%). The incidence of TRALI and/or TACO after 28,120 washed RBC and 69,325 washed transfusions was zero.

CONCLUSION

These data suggest novel hypotheses for further testing in animal models, in prospective clinical trials, and via the new US hemovigilance system: 1) Is TACO or TRALI mitigated by leukoreduction? 2) Is the mechanism of TACO more complex than excessive blood volume? and 3) Does washing mitigate TRALI and TACO due to PLT and RBC transfusions?

Impact of platelets and fresh frozen plasma in contrast to red cell concentrate on unstimulated and stimulated cytokine release in an in vitro model of transfusion

Transfusion of blood may contribute to immunomodulation. Leuco-depleted standard blood products are supposed to result in less immunomodulation compared with whole blood. To determine the influence of leuco-depleted blood products on the cytokine response, red blood cell concentrates (RBC), fresh frozen plasma (FFP) and platelet concentrates (PC) were investigated in an in vitro model of blood transfusion. Leuco-depleted standard blood bank RBC, FFP and PC were mixed in vitro with AB0 compatible venous blood from healthy volunteers in ratios of 3:1, 1:1 and 1:3. Specimens were incubated in presence or absence of lipopolysaccharide, 1 mug/ml. After 24 h of incubation cytokine release of tumour necrosis factor (TNF)-alpha and interleukin-10 (IL-10) was measured in cell culture supernatants by means of enzyme-linked immunsorbent assay. Addition of RBC, FFP and PC to venous blood from healthy volunteers led to a significant and dose-dependent increase in spontaneous TNF-alpha and IL-10 release. After endotoxin stimulation, RBC, FFP and PC significantly suppressed the TNF-alpha response, while the stimulated release of IL-10 tended to increase, reaching significance only after high doses of FFP. Addition of leuco-depleted blood products changed the spontaneous and stimulated cytokine response in an in vitro model of transfusion. These data may suggest a possible contribution of transfused FFP and PC to immunomodulation after transfusion similar to RBC.

Cell integrity and mitochondrial function after Mirasol-PRT treatment for pathogen reduction of apheresis-derived platelets: Results of a three-arm in vitro study

BACKGROUND

Mirasol pathogen reduction technology (PRT) treatment uses riboflavin (vitamin B(2)) in combination with ultraviolet light (UV) to inactivate pathogens in platelet concentrates (PCs). This treatment has been reported to increase glycolytic flux, which could result from damage to mitochondria and/or increased ATP demand.

DESIGN

Triple-dose PCs were collected by the Trima Accel device. Immediately after splitting, single units were designated to Mirasol-PRT treatment (M), gamma irradiation (X) or remained untreated (C). Platelet (PLT) mitochondrial transmembrane potential (Deltapsi) was evaluated (JC-1 assay) as well as mitochondrial enzymatic activity (MTS assay). LDH release, p selectin expression, glucose/oxygen consumption and lactate production rates were quantified and compared among study groups during 7days of storage.

RESULTS

Immediately after PRT treatment, no significant changes were found in JC-1 signal, MTS activity, and LDH release indicating that PRT treatment did not alter functional/structural cell or mitochondrial integrity as evidenced by LDH release comparable to untreated study groups. In parallel to significantly higher p selectin expression, treated PLTs exhibited significantly accelerated oxygen and glucose consumption rates associated with increased acidity due to higher lactate production rates throughout storage. Despite larger cell populations with depolarized Deltapsi particularly at days 5 and 7, mitochondrial reduction activity of M units as measured by the MTS assay was maintained and appeared to be up-regulated relative to untreated and irradiated controls.

CONCLUSION

Mirasol-PRT treated PLTs increased both glycolytic flux as well as respiratory/enzymatic mitochondrial activity. An increased demand for ATP due to increased alpha granule degranulation may be the driving force for these observations.

Proteomics and transfusion medicine: Future perspectives

Limited number of important discoveries have greatly contributed to the progresses achieved in the blood transfusion; ABO histo-blood groups, citrate as anticoagulant, fractionation of plasma proteins, plastic bags and apheresis machines. Three major types of blood products are transfused to patients: red cell concentrates, platelet concentrates and fresh frozen plasma. Several parameters of these products change during storage process and they have been well studied over the years. However, several aspects have completely been ignored; in particular those related to peptide and protein changes. This review presents what has been done using proteomic tools and the potentials of proteomics for transfusion medicine.