Platelet apoptosis and activation in platelet concentrates stored for up to 12 days in plasma or additive solution

A Divergent Platelet Transcriptome in Patients with Lipedema and Lymphedema

Lipedema and lymphedema are physically similar yet distinct diseases that are commonly misdiagnosed. We previously reported that lipedema and lymphedema are associated with increased risk for venous thromboembolism (VTE). The underlying etiology of the prothrombotic profile observed in lipedema and lymphedema is unclear, but may be related to alterations in platelets. Our objective was to analyze the platelet transcriptome to identify biological pathways that may provide insight into platelet activation and thrombosis. The platelet transcriptome was evaluated in patients with lymphedema and lipedema, then compared to control subjects with obesity. Patients with lipedema were found to have a divergent transcriptome from patients with lymphedema. The platelet transcriptome and impacted biological pathways in lipedema were surprisingly similar to weight-matched comparators, yet different when compared to overweight individuals with a lower body mass index (BMI). Differences in the platelet transcriptome for patients with lipedema and lymphedema were found in biological pathways required for protein synthesis and degradation, as well as metabolism. Key differences in the platelet transcriptome for patients with lipedema compared to BMI-matched subjects involved metabolism and glycosaminoglycan processing. These inherent differences in the platelet transcriptome warrant further investigation, and may contribute to the increased risk of thrombosis in patients with lipedema and lymphedema.

High fragmentation in platelet concentrates impacts the activation, procoagulant, and aggregatory capacity of platelets

Platelets are transfused to patients to prevent bleeding. Since both preparation and storage can impact the hemostatic functions of platelets, we studied platelet concentrates (PCs) with different initial composition in regard to platelet fragmentation and its impact on storage-induced changes in activation potential. Ten whole blood derived PCs were assessed over 7 storage days. Using flow cytometry, platelet (CD41+) subpopulations were characterized for activation potential using activation markers (PAC-1, P-selectin, and LAMP-1), phosphatidylserine (Annexin V), and mitochondrial integrity (DiIC₁(5)). Aggregation response, coagulation, and soluble activation markers (cytokines and sGPVI) were also measured. Of the CD41+ events, the PCs contained a median of 82% normal-sized platelets, 10% small platelets, and 8% fragments. The small platelets exhibited procoagulant hallmarks (increased P-selectin and Annexin V and reduced DiIC₁(5)). Normal-sized platelets responded to activation, whereas activation potential was decreased for small and abolished for fragments. Five PCs contained a high proportion of small platelets and fragments (median of 28% of CD41+ events), which was significantly higher than the other five PCs (median of 9%). A high proportion of small platelets and fragments was associated with procoagulant hallmarks and decreased activation potential, but, although diminished, they still retained some activation potential throughout 7 days storage.

Requirements for successful mitochondrial transplantation

Maintenance of mitochondrial oxidative phosphorylation capacity and other mitochondrial functions are essential for the prevention of mitochondrial dysfunction-related diseases such as neurodegenerative, cardiovascular, and liver diseases. To date, no well-known treatment modality has been developed to prevent or reduce mitochondrial dysfunction. However, a novel approach that transplants fully functional mitochondria directly into defective cells has recently caught the attention of scientists. In this review, we provide an overview of the cell/tissue source of the mitochondria to prompt cell regeneration or tissue repair in vitro and in vivo applications. The animal and human models entail that effective procedures should be used in the isolation and confirmation of mitochondrial membrane potential and function. We believe that these procedures for mitochondrial transplantation for tissue or cell culture will confirm intact, viable, and free from contamination isolated mitochondria from the appropriate sources.

N-acetylcysteine reduce the stress induced by cold storage of platelets: A potential way to extend shelf life of platelets

The room temperature storage used for platelets worldwide leads to platelet storage lesion (PSL) and risk of bacterial growth, limiting platelet shelf life and safety in transfusion. Thus, there is a need for an alternative storage method that can serve as effective temperature storage for platelet concentrates (PCs). In the previous investigation, we have shown that N-acetylcysteine (NAC) is a potential candidate for an additive solution to retain platelet characteristics during cold storage for up to 5 days. However, the study partially describes the efficacy and has drawbacks to address. Here, we used the apheresis platelet product with 50 mM NAC and stored up to 10 days under refrigerated condition (4 ± 1 °C). Stored platelet concentrates were analyzed for critical parameters such as platelet activation, annexin V binding, sialic acid, reactive oxygen species (ROS), neuraminidase activity, and in vivo efficacy using Prkdc^scid mice. Investigation observations revealed that PCs with NAC showed reduced platelet activation, annexin V binding, ROS production, and sialic acid levels. in vivo recovery of PCs showed similar recovery rates stored PCs irrespective of treatment or storage condition. However, on the tenth day after 24 h, recovery in room temperature stored concentrates was about 32 %, whereas in NAC treated refrigerated concentrates, it stands at 47 %. These observations indicate that NAC addition protects refrigerated concentrates during long-term storage retaining the platelet integrity. The study also suggests that extending PC storage beyond 10 days is practically accomplishable with efficacy similar to room temperature (RT) stored PCs.

Computational Identification and Characterization of New microRNAs in Human Platelets Stored in a Blood Bank

Platelet concentrate (PC) transfusions are widely used to save the lives of patients who experience acute blood loss. MicroRNAs (miRNAs) comprise a class of molecules with a biological role which is relevant to the understanding of storage lesions in blood banks. We used a new approach to identify miRNAs in normal human platelet sRNA-Seq data from the GSE61856 repository. We identified a comprehensive miRNA expression profile, where we detected 20 of these transcripts potentially expressed in PCs stored for seven days, which had their expression levels analyzed with simulations of computational biology. Our results identified a new collection of miRNAs (miR-486-5p, miR-92a-3p, miR-103a-3p, miR-151a-3p, miR-181a-5p, and miR-221-3p) that showed a sensitivity expression pattern due to biological platelet changes during storage, confirmed by additional quantitative real-time polymerase chain reaction (qPCR) validation on 100 PC units from 500 healthy donors. We also identified that these miRNAs could transfer regulatory information on platelets, such as members of the let-7 family, by regulating the YOD1 gene, which is a deubiquitinating enzyme highly expressed in platelet hyperactivity. Our results also showed that the target genes of these miRNAs play important roles in signaling pathways, cell cycle, stress response, platelet activation and cancer. In summary, the miRNAs described in this study, have a promising application in transfusion medicine as potential biomarkers to also measure the quality and viability of the PC during storage in blood banks.

Comparison of the platelet activation status of single-donor platelets obtained with two different cell separator technologies

BACKGROUND

The microparticle content (MP%) of apheresis platelets-a marker of platelet activation-is influenced by donor factors and by external stressors during collection and storage. This study assessed the impact of apheresis technology and other factors on the activation status (MP%) of single-donor apheresis platelets.

STUDY DESIGN AND METHODS

Data from six US hospitals that screened platelets by measuring MP% through dynamic light scattering (ThromboLUX) were retrospectively analyzed. Relative risks (RRs) were derived from univariate and multivariable regression models, with activation rate (MP% ≥15% for plasma-stored platelets; ≥10% for platelet additive solution [PAS]-stored platelets) and MP% as outcomes. Apheresis platform (Trima Accel vs Amicus), storage medium (plasma vs PAS), pathogen reduction, storage time, and testing location were used as predictors.

RESULTS

Data were obtained from 7511 platelet units collected using Trima (from 16 suppliers, all stored in plasma, 20.0% were pathogen-reduced) and 2456 collected using Amicus (from four different collection facilities of one supplier, 65.0% plasma-stored, 35.0% PAS-stored, none pathogen-reduced). Overall, 30.0% of Trima platelets were activated compared to 45.6% of Amicus platelets (P < .0001). Multivariable analysis identified apheresis platform as significantly associated with platelet activation, with a lower activation rate for Trima than Amicus (RR: 0.641, 95% confidence interval [CI]: 0.578; 0.711, P < .0001) and a 6.901% (95% CI: 5.926; 7.876, P < .0001) absolute reduction in MP%, when adjusting for the other variables.

CONCLUSION

Trima-collected platelets were significantly less likely to be activated than Amicus-collected platelets, irrespective of the storage medium, the use of pathogen reduction, storage time, and testing site.

Protective effect of L-carnitine on platelet apoptosis during storage of platelet concentrate

BACKGROUND

Platelet apoptosis is considered as one of the important factors involved in platelet storage lesion (PSL) and affect the quality of platelets during storage. The beneficial effect of L-carnitine (LC) on platelet apoptosis during platelet concentrates (PCs) storage has not been fully investigated. The aim of this study was to evaluate the effects of LC on platelets of PC regarding their apoptosis markers during storage.

METHODS

Ten PCs from healthy donors were investigated in this study. PCs were prepared by platelet rich plasma (PRP) method and stored at 22±2°C with gentle agitation during storage. The effects of LC (15mM) on the platelet apoptosis were assessed by analyzing different indicative presence or absence of LC. Sampling was performed to evaluate apoptosis markers during platelet storage.

RESULTS

The results indicated significantly higher mitochondrial membrane potential for LC-treated platelets than the untreated on the days 2 and 5 of storage (P_day2=0.001, P_day5=0.001). Phosphatidylserine (PS) exposure significantly increased on the untreated compared with LC-treated platelets on the second and third days of storage (P_day2=0.014, P_day3=0.012). Also, active caspase 3 was lower in the LC- treated platelets than the control group on the day 5 of storage (P_day5=0.004). Cytosolic cytochrome C was so significantly lower in LC-treated compared to the untreated platelets during storage time (P_day2=0.002, P_day3=0.001, Pday5=0.001).

CONCLUSION

The results of this study indicate that the use of LC as an additive solution in platelets may be useful to reduce PSL by decreasing platelet apoptosis via mitochondrial pathway and increase platelet quality during storage.

Quality control in veterinary blood banks: evaluation of canine platelet concentrates stored for five days

Background

Platelets undergo structural, biochemical and functional alterations when stored, and platelet storage lesions reduce platelet function and half-life after transfusion. The objective of this study was to evaluate stored canine platelet concentrates with platelet aggregation, flow cytometry and biochemistry assays. Twenty-two bags of canine platelet concentrates were obtained by the platelet-rich plasma method and were assessed on days 1, 3 and 5 after collection. Parameters such as platelet counts, residual leukocytes, platelet swirling, glucose, lactate, pH, CD62P expression (platelet activation), JC-1 (mitochondrial function) and annexin V (apoptosis and cell death) were assessed.

Results

Over the five days of storage there was a significant decrease in glucose, HCO₃, pCO₂, ATP, pH, swirling and mitochondrial function, associated with a significant increase in lactate levels and pO₂. At the end of storage pH was 5.9 ± 0.6 and lactate levels were 2.8 ± 1.2 mmol/L. Results of the quality parameters evaluated were similar to those reported in human platelets studies. The deleterious effects of storage were more pronounced in bags with higher platelet counts (> 7.49 × 10¹⁰/unit), suggesting that canine platelet concentrates should not contain an excessive number of platelets.

Conclusions

Quality parameters of canine platelets under standard storage conditions were similar to those observed in human platelets. Our results have potential to be used for the routine evaluation and quality control in veterinary blood banks.

Acute bilirubin ditaurate exposure attenuates ex vivo platelet reactive oxygen species production, granule exocytosis and activation

Background

Bilirubin, a by-product of haem catabolism, possesses potent endogenous antioxidant and platelet inhibitory properties. These properties may be useful in inhibiting inappropriate platelet activation and ROS production; for example, during storage for transfusion. Given the hydrophobicity of unconjugated bilirubin (UCB), we investigated the acute platelet inhibitory and ROS scavenging ability of a water-soluble bilirubin analogue, bilirubin ditaurate (BRT) on ex vivo platelet function to ascertain its potential suitability for inclusion during platelet storage.

Methods

The inhibitory potential of BRT (10–100 μM) was assessed using agonist induced platelet aggregation, dense granule exocytosis and flow cytometric analysis of P-selectin and GPIIb/IIIa expression. ROS production was investigated by analysis of H₂DCFDA fluorescence following agonist simulation while mitochondrial ROS production investigated using MitoSOX™ Red. Platelet mitochondrial membrane potential and viability was assessed using TMRE and Zombie Green™ respectively.

Results

Our data shows ≤35 μM BRT significantly inhibits both dense and alpha granule exocytosis as measured by ATP release and P-selectin surface expression, respectively. Significant inhibition of GPIIb/IIIa expression was also reported upon ≤35 μM BRT exposure. Furthermore, platelet exposure to ≤10 μM BRT significantly reduces platelet mitochondrial ROS production. Despite the inhibitory effect of BRT, platelet viability, mitochondrial membrane potential and agonist induced aggregation were not perturbed.

Conclusions

These data indicate, for the first time, that BRT, a water-soluble bilirubin analogue, inhibits platelet activation and reduces platelet ROS production ex vivo and may, therefore, may be of use in preserving platelet function during storage.

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The impact of conjugated bilirubin on platelet function has not been investigated to date.

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Bilirubin ditaurate (BDT) is a water-soluble analogue of conjugated bilirubin.

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BDT attenuates ex vivo platelet activation and ROS generation.

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Conjugated forms of bilirubin might inhibit platelet activation during storage.

Platelet storage in more than 90% additive solution containing glucose and bicarbonate has the potential to increase shelf life

BACKGROUND

Platelet concentrates (PCs) suspended in more than 90% additive solution (AS) are recommended for patients with reactions to platelets stored in plasma. Next-generation AS containing glucose and bicarbonate might enable storage of these PCs for longer than those in current-generation AS, which was therefore evaluated in this study.

STUDY DESIGN AND METHODS

Five buffy coat or apheresis-derived PCs were pooled and split into identical units. All units except the control were centrifuged, the plasma removed and replaced with AS (SSP+, PAS-5, or PAS-G), or resuspended in the same plasma and sampled 96 hours after resuspension for analysis.

RESULTS

Plasma carryover was less than 10%, total protein less than 1 g/unit, and immunoglobulin A levels lower than 0.1 mg/mL for all PCs in AS. The pH of all the platelets during storage was higher than 6.4. PAS containing glucose maintained superior in vitro platelet function during storage compared with those resuspended in SSP+. Compared with storage in SSP+, storage in PAS-5 or PAS-G resulted in better preservation of platelet adenosine triphosphate and hypotonic shock response, lower annexin V binding, and improved mitochondrial membrane potential.

CONCLUSION

Platelets resuspended in PAS-5 and PAS-G maintained in vitro function and metabolism during storage compared with SSP+ platelets. Elevated platelet metabolic activity was noticed in PAS-G, and higher platelet activation was detected with PAS-5. Platelets resuspended in PAS containing glucose has the potential to increase the shelf life of PC in more than 90% AS.

Intrinsic apoptosis circumvents the functional decline of circulating platelets but does not cause the storage lesion

BAK/BAX depletion in murine platelets reveals that intrinsic apoptosis is not required for the development of the platelet storage lesion. Restriction of platelet life span by intrinsic apoptosis is pivotal to maintain a functional, hemostatically reactive platelet population.

Evaluation of platelet activation in leukocyte-depleted platelet concentrates during storage

Structural and functional changes in platelets during storage can lead to the loss of platelet reactivity and response. Our aim was to evaluate leukocyte-depleted platelet concentrates on storage days 0, 3 and 5, obtained by in-line filtration. In non-filtered platelet concentrates (NF-PC) group, 180 whole blood units were collected with quadruple blood bags and then compared to another group of 180 whole blood units (leukocyte-depleted platelet concentrates [LD-PC]), collected in Imuflex Whole Blood Filter Saving Platelets (WB-SP) bags with an integrated leukoreduction filter, with regard to the platelet quality and characteristics. The efficacy of the two techniques for platelet concentrate preparation was evaluated by white blood cell (WBC) and platelet count on day 0. The partial pressure of oxygen (pO2), pH, platelets positive for P-selectin (CD62P), CD63, cluster of differentiation 42b (CD42b), phosphatidylserine (PS), and mitochondrial membrane potential (MMP) were analyzed during the storage in both groups. A significantly lower WBC count and higher platelet count was observed in LD-PC compared to NF-PC group, indicating the overall efficacy of the first technique. During the 5-day storage, pH and pO2 decreased in both groups. In LD-PC group, higher pH, increased pO2 and decreased platelet surface expression of CD62P, CD63 and PS were observed compared to NF-PC group. In both groups, the percentage of CD42b positive platelets and MMP did not change significantly during the 5-day period. The assessment of different markers of platelet activation may be an effective tool in evaluating the quality of platelets during storage. A better understanding of platelet activation may provide new insights for developing a novel therapeutic approach in the manipulation of platelet aggregation.

Regulation of platelet membrane protein shedding in health and disease

Extracellular proteolysis of platelet plasma membrane proteins is an event that ensues platelet activation. Shedding of surface receptors such as glycoprotein (GP) Ibα, GPV and GPVI as well as externalized proteins P-selectin and CD40L releases soluble ectodomain fragments that are subsequently detectable in plasma. This results in the irreversible functional downregulation of platelet receptor-mediated adhesive interactions and the generation of biologically active fragments. In this review, we describe molecular insights into the regulation of platelet receptor and ligand shedding in health and disease. The scope of this review is specially focused on GPIbα, GPV, GPVI, P-selectin and CD40L where we: (1) describe the basic physiological regulation of expression and shedding of these proteins in hemostasis illustrate alterations in receptor expression during (2) apoptosis and (3) ex vivo storage relevant for blood banking purposes; (4) discuss considerations to be made when analyzing and interpreting shedding of platelet membrane proteins and finally; (5) collate clinical evidence that quantify these platelet proteins during disease.

Secretome profiling of apheresis platelet supernatants during routine storage via antibody-based microarray

Platelet storage lesions (PSLs) occur during platelet concentrate (PC) storage. Adverse transfusion reactions (ATRs) have been demonstrated to be more frequent in older PCs and removal of the supernatant prior to transfusion reduces their occurrence. Proteomic profiling of PC supernatants was thus performed to identify proteins associated with PSLs and ATRs. Twenty-four PCs were investigated daily from day 0 to day 9 for platelet pre-activation (PPA), platelet-derived extracellular vesicles (PEVs), and platelet function. Using antibody microarrays, 673 extracellular proteins were analysed in PC supernatants on days 0, 3, 5, 7, and 9. During 5days of storage, PPA and PEVs continuously increased (P<0.0001). Platelet function was observed to remain stable within the first 5days (P=0.1751) and decreased thereafter. Comparison of all time points to day 0 revealed the identification of 136 proteins that were significantly changed in abundance during storage, of which 72 were expressed by platelets. Network analysis identified these proteins to be predominantly associated with exosomes (P=4.61×10^-8, n=45 genes) and two clusters with distinct functions were found with one being associated with haemostasis and the other with RNA binding. These findings may provide an explanation for ATRs.

SIGNIFICANCE

Changes in platelet concentrate (PC) supernatants during storage have been so far only poorly addressed and high abundant proteins burden the identification of quantitative changes in the secretome. We applied a high-throughput antibody microarray allowing for the sensitive quantification of 673 extracellular factors. PCs account for the highest number of adverse transfusion reactions (ATRs). ATRs have been demonstrated to be more frequent in older PCs and removal of the supernatant prior to transfusion reduces their occurrence. Comprehensive interpretation of the changing proteins in the secretome during platelet storage under blood banking conditions may help to identify mechanisms leading to the occurrence of adverse transfusion reactions.

Refrigerated storage of platelets initiates changes in platelet surface marker expression and localization of intracellular proteins

BACKGROUND

Platelets (PLTs) are currently stored at room temperature (22°C), which limits their shelf life, primarily due to the risk of bacterial growth. Alternatives to room temperature storage include PLT refrigeration (2-6°C), which inhibits bacterial growth, thus potentially allowing an extension of shelf life. Additionally, refrigerated PLTs appear more hemostatically active than conventional PLTs, which may be beneficial in certain clinical situations. However, the mechanisms responsible for this hemostatic function are not well characterized. The aim of this study was to assess the protein profile of refrigerated PLTs in an effort to understand these functional consequences.

STUDY DESIGN AND METHODS

Buffy coat PLTs were pooled, split, and stored either at room temperature (20-24°C) or under refrigerated (2-6°C) conditions (n = 8 in each group). PLTs were assessed for changes in external receptor expression and actin filamentation using flow cytometry. Intracellular proteomic changes were assessed using two-dimensional gel electrophoresis and Western blotting.

RESULTS

PLT refrigeration significantly reduced the abundance of glycoproteins (GPIb, GPIX, GPIIb, and GPIV) on the external membrane. However, refrigeration resulted in the increased expression of high-affinity integrins (αIIbβ3 and β1) and activation and apoptosis markers (CD62P, CD63, and phosphatidylserine). PLT refrigeration substantially altered the abundance and localization of several cytoskeletal proteins and resulted in an increase in actin filamentation, as measured by phalloidin staining.

CONCLUSION

Refrigerated storage of PLTs induces significant changes in the expression and localization of both surface-expressed and intracellular proteins. Understanding these proteomic changes may help to identify the mechanisms resulting in the refrigeration-associated alterations in PLT function and clearance.

Aging of platelets stored for transfusion

A goal of platelet storage is to maintain the quality of platelets from the point of donation to the point of transfusion - to suspend the aging process. This effort is judged by clinical and laboratory measures with varying degrees of success. Recent work gives encouragement that platelets can be maintained ex vivo beyond the current 5 -7 day shelf life whilst maintaining their quality, as measured by posttransfusion recovery and survival. However, additional measures are needed to validate the development of technologies that may further reduce the aging of stored platelets, or enhance their hemostatic properties.

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.

Responsiveness of platelets during storage studied with flow cytometry--formation of platelet subpopulations and LAMP-1 as new markers for the platelet storage lesion

BACKGROUND AND OBJECTIVES

Storage lesions may prevent transfused platelets to respond to agonists and arrest bleeding. The aim of this study was to evaluate and quantify the capacity of platelet activation during storage using flow cytometry and new markers of platelet activation.

MATERIALS AND METHODS

Activation responses of platelets prepared by apheresis were measured on days 1, 5, 7 and 12. In addition, comparisons were made for platelet concentrates stored until swirling was affected. Lysosome-associated membrane protein-1 (LAMP-1), P-selectin and phosphatidylserine (PS) exposure were assessed by flow cytometry on platelets in different subpopulations in resting state or following stimulation with platelet agonists (cross-linked collagen-related peptide (CRP-XL), PAR1- and PAR4-activating peptides).

RESULTS

The ability to form subpopulations upon activation was significantly decreased already at day 5 for some agonist combinations. The agonist-induced exposure of PS and LAMP-1 also gradually decreased with time. Spontaneous exposure of P-selectin and PS increased with time, while spontaneous LAMP-1 exposure was unchanged. In addition, agonist-induced LAMP-1 expression clearly discriminated platelet concentrates with reduced swirling from those with retained swirling. This suggests that LAMP-1 could be a good marker to capture changes in activation capacity in stored platelets.

CONCLUSION

The platelet activation potential seen as LAMP-1 exposure and fragmentation into platelet subpopulations is potential sensitive markers for the platelet storage lesion.

p38MAPK is involved in apoptosis development in apheresis platelet concentrates after riboflavin and ultraviolet light treatment

BACKGROUND

Pathogen inactivation (PI) accelerates the platelet (PLT) storage lesion, including apoptotic-like changes. Proteomic studies have shown that phosphorylation levels of several kinases increase in PLTs after riboflavin and UV light (RF-PI) treatment. Inhibition of p38MAPK improved in vitro PLT quality, but the biochemical basis of this kinase's contribution to PLT damage requires further analysis.

STUDY DESIGN AND METHODS

In a pool-and-split design, apheresis PLT concentrates were either treated or kept untreated with or without selected kinase inhibitors. Samples were analyzed throughout 7 days of storage, monitoring in vitro quality variables including phosphatidylserine exposure, degranulation, and glucose metabolism. Changes in the protein expression of Bax, Bak, and Bcl-xL and the activities of caspase-3 and -9 were determined by immunoblot analysis and flow cytometry, respectively.

RESULTS

The expression levels of the proapoptotic proteins Bax and Bak, but not the antiapoptotic protein Bcl-xL, were significantly increased after the RF-PI treatment. This trend was reversed in the presence of p38MAPK inhibitor SB203580. As a result of increasing proapoptotic protein levels, caspase-3 and -9 activities were significantly increased in RF-PI treatment during storage compared with control (p < 0.05). Similarly, p38MAPK inhibition significantly reduced these caspase activities compared with vehicle control after RF-PI treatment (p < 0.05).

CONCLUSION

These findings revealed that p38MAPK is involved in signaling leading to apoptosis triggered by RF-PI. Elucidation of the biochemical processes influenced by PI is a necessary step in the development of strategies to improve the PLT quality and ameliorate the negative effects of PI treatment.

In vitro evaluation of pathogen-inactivated buffy coat-derived platelet concentrates during storage: psoralen-based photochemical treatment step-by-step

BACKGROUND

The Intercept Blood SystemTM (Cerus) is used to inactivate pathogens in platelet concentrates (PC). The aim of this study was to elucidate the extent to which the Intercept treatment modifies the functional properties of platelets.

MATERIAL AND METHODS

A two-arm study was conducted initially to compare buffy coat-derived pathogen-inactivated PC to untreated PC (n=5) throughout storage. A four-arm study was then designed to evaluate the contribution of the compound adsorbing device (CAD) and ultraviolet (UV) illumination to the changes observed upon Intercept treatment. Intercept-treated PC, CAD-incubated PC, and UV-illuminated PC were compared to untreated PC (n=5). Functional characteristics were assessed using flow cytometry, hypotonic shock response (HSR), aggregation, adhesion assays and flow cytometry for the detection of CD62P, CD42b, GPIIb-IIIa, phosphatidylserine exposure and JC-1 aggregates.

RESULTS

Compared to fresh platelets, end-of-storage platelets exhibited greater passive activation, disruption of the mitochondrial transmembrane potential (Δψm), and phosphatidylserine exposure accompanied by a decreased capacity to respond to agonist-induced aggregation, lower HSR, and CD42b expression. The Intercept treatment resulted in significantly lower HSR and CD42b expression compared to controls on day 7, with no significant changes in CD62P, Δψm, or phosphatidylserine exposure. GPIIbIIIa expression was significantly increased in Intercept-treated platelets throughout the storage period. The agonist-induced aggregation response was highly dependent on the type and concentration of agonist used, indicating a minor effect of the Intercept treatment. The CAD and UV steps alone had a negligible effect on platelet aggregation.

DISCUSSION

The Intercept treatment moderately affects platelet function in vitro. CAD and UV illumination alone make negligible contributions to the changes in aggregation observed in Intercept-treated PC.

Platelet adhesion changes during storage studied with a novel method using flow cytometry and protein-coated beads

The aim of the present study was to set up and evaluate a novel method for studies of platelet adhesion and activation in blood and platelet suspensions such as platelet concentrate (PC) samples using protein-coated polystyrene beads and flow cytometry. To demonstrate its usefulness, we studied PCs during storage. PCs were prepared by aphaeresis technique (n = 7). Metabolic variables and platelet function was measured on day 1, 5, 7 and 12 of storage. Spontaneous and TRAP-6-induced adhesion to fibrinogen- and collagen-coated beads was analyzed by flow cytometry. P-selectin and phosphatidyl serine (PS) expression was assessed on platelets bound to beads as well as on non-adherent platelets. Platelet adhesion to fibrinogen beads had increased by day 12 and adhesion to collagen beads at day 7 of storage (p < 0.05). TRAP-6 stimulation significantly increased the platelet adhesion to fibrinogen beads (p < 0.05) as well as the P-selectin and PS exposure on platelets bound to beads (p < 0.01) during the first 7 days of storage, but by day 12, significant changes were no longer induced by TRAP-6 stimulation. We demonstrate that our adhesion assay using protein-coated polystyrene beads can be used to assess the adhesion properties of platelets during storage without the addition of red blood cells. Therefore it may offer a useful tool for future studies of platelet adhesive capacity in transfusion medicine and other settings.

Omi/HtrA2 and XIAP are components of platelet apoptosis signalling

Although platelets possess the hallmarks of apoptosis such as activation of caspases, cytochrome c release and depolarisation of the mitochondrial transmembrane potential (∆Ψm), their entire apoptotic-signalling pathway is not totally understood. Therefore we studied the expression of various apoptotic proteins and found that platelets contain the pro-apoptotic proteins Omi/HtrA2 and Smac/Diablo, as well as their target the X-linked inhibitor of apoptosis XIAP. Omi/HtrA2 and Smac/Diablo were released from mitochondria into the platelet cytosol together with cytochrome c after induction of apoptosis by the Ca2+ ionophore A23187 or the BH3 mimetic ABT-737, and to a lesser extent, after platelet stimulation with collagen and thrombin. Inhibition of Omi/HtrA2 led to decreased levels of activated caspase-3/7 and caspase-9, but did not abolish loss of ∆Ψm or prevent release of Omi/HtrA2 from mitochondria. These results indicate that platelets have a functional intrinsic apoptotic-signalling pathway including the pro-apoptotic protease Omi/HtrA2 and its target protein XIAP.

Pathogen inactivation of platelets using ultraviolet C light: effect on in vitro function and recovery and survival of platelets

BACKGROUND

We evaluated the effect of treating platelets (PLTs) using ultraviolet (UV)C light without the addition of any photosensitizing chemicals on PLT function in vitro and PLT recovery and survival in an autologous radiolabeled volunteer study.

STUDY DESIGN AND METHODS

For in vitro studies, pooled or single buffy coat-derived PLT concentrates (PCs) were pooled and split to obtain identical PCs that were either treated with UVC or untreated (n = 6 each) and stored for 7 days. PLT recovery and survival were determined in a two-arm parallel autologous study in healthy volunteers performed according to BEST guidelines. UVC-treated or untreated PCs (n = 6 each) were stored for 5 days and were compared to fresh PLTs from the same donor.

RESULTS

There were no significant differences on Day 7 of storage between paired UVC-treated and control PC units for pH, adenosine triphosphate, lactate dehydrogenase, CD62P, CD63, PLT microparticles, and JC-1 binding, but annexin V binding, lactate accumulation, and expression of CD41/61 were significantly higher in treated units (p < 0.05). Compared with control units, the recovery and survival of UVC-treated PC were reduced after 5 days of storage (p < 0.05) and when expressed as a percentage of fresh values, survival was reduced by 20% (p = 0.005) and recovery by 17% (p = 0.088).

CONCLUSION

UVC-treated PLTs stored for 5 days showed marginal changes in PLT metabolism and activation in vitro and were associated with a degree of reduction in recovery and survival similar to other pathogen inactivation systems that are licensed and in use.

Phosphatidylserine-expressing cell by-products in transfusion: A pro-inflammatory or an anti-inflammatory effect?

Labile blood products contain phosphatidylserine-expressing cell dusts, including apoptotic cells and microparticles. These cell by-products are produced during blood product process or storage and derived from the cells of interest that exert a therapeutic effect (red blood cells or platelets). Alternatively, phosphatidylserine-expressing cell dusts may also derived from contaminating cells, such as leukocytes, or may be already present in plasma, such as platelet-derived microparticles. These cell by-products present in labile blood products can be responsible for transfusion-induced immunomodulation leading to either transfusion-related acute lung injury (TRALI) or increased occurrence of post-transfusion infections or cancer relapse. In this review, we report data from the literature and our laboratory dealing with interactions between antigen-presenting cells and phosphatidylserine-expressing cell dusts, including apoptotic leukocytes and blood cell-derived microparticles. Then, we discuss how these phosphatidylserine-expressing cell by-products may influence transfusion.

Pathogen reduction treatment of buffy coat platelet concentrates in additive solution induces proapoptotic signaling

BACKGROUND

Pathogen reduction technology (PRT) can potentially reduce the risk of transfusion-transmitted infections. However, PRT treatment of platelet (PLT) concentrates also results in reduced PLT quality and increased markers of apoptosis during storage. The aim of this study was to investigate changes to the expression and activation of proteins involved in apoptosis signaling.

STUDY DESIGN AND METHODS

Samples from riboflavin and ultraviolet light PRT-treated and untreated (control) buffy coat-derived PCs in 70% SSP+ and 30% plasma were taken on Days 1, 5, and 7 of storage. Phosphatidylserine (PS) exposure, expression of Bcl-2 family proteins, cytochrome c release, and cleavage of caspase-3 and caspase-3 substrates were analyzed using flow cytometry and Western blotting.

RESULTS

Compared to untreated controls, markers of apoptosis signaling were increased after PRT and subsequent storage. PS exposure on the PLT outer membrane was significantly higher after PRT on Days 5 and 7 of storage (p < 0.05). Expression of proapoptotic Bak and Bax was higher after PRT and subsequent storage. Cytochrome c release and caspase-3 cleavage were also greater and occurred earlier in the PRT-treated PLTs. The cleavage of caspase-3 substrates gelsolin and ROCK I were also increased after PRT, compared to untreated controls.

CONCLUSIONS

This study demonstrated an increase in proapoptotic signaling during PLT storage, which was exacerbated by PRT. Many of these differences emerged outside the current 5-day storage period. These changes may not currently influence PLT transfusion quality, but will need to be carefully evaluated when considering extending PLT storage beyond 5 days.

Validation of flow cytometric detection of platelet microparticles and liposomes by atomic force microscopy

BACKGROUND

Platelet microparticles (PMPs) are a promising prognostic marker for thrombotic disorders because of their release during platelet activation. The use of flow cytometry for the enumeration of PMPs in plasma has generated controversy due to their size, which is below the stated detection limits of conventional flow cytometry instruments. The potential impact of this is an underestimation of PMP counts.

OBJECTIVES/METHODS

To address this possibility, we used a combination of fluorescence-activated cell sorting (FACS) and atomic force microscopy (AFM) to determine the size distribution of PMPs present in plasma from acute myocardial infarction (AMI) patients and normal volunteers, and PMPs generated by expired platelet concentrates and washed platelets treated with agonists such as thrombin and calcium ionophore (A23187).

RESULTS

According to AFM image analysis, there was no statistically significant difference in height or volume distributions in PMPs from thrombin-activated, calcium ionophore-activated, expired platelet concentrates and plasma from healthy volunteers and AMI patients. Based on volume, expired platelets released the greatest proportion of exosomes (< 1.0 × 10(-22) L(3) in volume) in relation to the entire PMP population (29.7%) and the smallest proportion of exosomes was observed in AMI patient plasma (1.8%). Moreover, AFM imaging revealed that PMPs from expired platelets exhibited smooth surfaces compared with other PMP types but this was not statistically significant.

CONCLUSIONS

We confirm that flow cytometry is capable of analyzing PMPs from plasma by using AFM to perform nanoscale measurements of individual PMP events isolated by FACS. This method also provided the first quantitative nanoscale images of PMP ultrastructure.

Apoptosis in the anucleate platelet

For many years, programmed cell death, known as apoptosis, was attributed exclusively to nucleated cells. Currently, however, apoptosis is also well-documented in anucleate platelets. This review describes extrinsic and intrinsic pathways of apoptosis in nucleated cells and in platelets, platelet apoptosis induced by multiple chemical stimuli and shear stresses, markers of platelet apoptosis, mitochodrial control of platelet apoptosis, and apoptosis mediated by platelet surface receptors PAR-1, GPIIbIIIa and GPIbα. In addition, this review presents data on platelet apoptosis provoked by aging of platelets in vitro during platelet storage, platelet apoptosis in pathological settings in humans and animal models, and inhibition of platelet apoptosis by cyclosporin A, intravenous immunoglobulin and GPIIbIIIa antagonist drugs.