Apoptosis in platelets during ex vivo storage

Removal of citrate from PAS-III additive solution improves functional and biochemical characteristics of buffy-coat platelet concentrates stored for 7 days, with or without INTERCEPT pathogen reduction

BACKGROUND

Deterioration in quality of platelet concentrates (PCs) during storage results from the appearance of storage lesions affecting the hemostatic functions and posttransfusion survival of platelets. These lesions depend on the preparation and pathogen inactivation methods used, duration of storage, and platelet additive solutions (PASs) present in storage bags.

METHODS

We investigated the effects of citrate contained in third-generation PAS (PAS-III) on storage lesions in buffy-coat PCs with or without photochemical (amotosalen-ultraviolet A) treatment over 7 days.

RESULTS

Platelet counts were conserved in all groups during storage, as was platelet swirling without appearance of macroscopic aggregates. Glycoprotein (GP) IIbIIIa and GPVI expression remained stable, whereas GPIbα declined similarly in all groups during storage. Removal of citrate from PAS-III, resulting in global reduction of citrate from 11 to 5 mM, led to a significant decrease in glucose consumption, which largely countered a modest deleterious effect of photochemical treatment. Citrate reduction also resulted in decreased lactate generation and better maintenance of pH during storage, while photochemical treatment had no impact on these parameters. Moreover, citrate-free storage significantly reduced exposure of P-selectin and the apoptosis signal phosphatidylserine, thereby abolishing the activating effect of photochemical treatment on both parameters. Citrate reduction benefited platelet aggregation to various agonists up to Day 7, whereas PCT had no impact on these responses.

CONCLUSION

Removal of citrate from PAS-III has a beneficial impact on platelet metabolism, spontaneous activation, and apoptosis, and improves platelet aggregation, irrespective of photochemical treatment, which should allow transfusion of platelets with better and longer-lasting functional properties.

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.

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.

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 caspase-3 inhibitor (peptide Z-DEVD-FMK) affects the survival and function of platelets in platelet concentrate during storage

Background

Although apoptosis occurs in nucleated cells, studies show that this event also occurs in some anucleated cells such as platelets. During storage of platelets, the viability of platelets decreased, storage lesions were observed, and cells underwent apoptosis. We investigated the effects of caspase-3 inhibitor on the survival and function of platelets after different periods of storage.

Methods

Platelet concentrates were obtained from the Iranian Blood Transfusion Organization in plastic blood bags. Caspase-3 inhibitor (Z-DEVD-FMK) was added to the bags. These bags along with control bags to which no inhibitor was added were stored in a shaking incubator at 22℃ for 7 days. The effects of Z-DEVD-FMK on the functionality of platelets were analyzed by assessing their ability to bind to von Willebrand factor (vWF) and to aggregate in the presence of arachidonic acid and ristocetin. Cell survival was surveyed by MTT assay.

Results

At day 4 of storage, ristocetin-induced platelet aggregation was significantly higher in the inhibitor-treated (test) than in control samples; the difference was not significant at day 7. There was no significant difference in arachidonic acid-induced platelet aggregation between test and control samples. However, at day 7 of storage, the binding of platelets to vWF was significantly higher in test than in control samples. The MTT assay revealed significantly higher viability in test than in control samples at both days of study.

Conclusion

Treatment of platelets with caspase-3 inhibitor could increase their functionality and survival.

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.

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.

Dendritic cells of immune thrombocytopenic purpura (ITP) show increased capacity to present apoptotic platelets to T lymphocytes

OBJECTIVE

Altered self-antigen processing/presentation of apoptotic cells by DCs and/or modifications of autoantigens may lead to the development of autoantibodies. Increasing evidence indicates that platelets may undergo apoptosis. Therefore, in the present study we investigated whether platelet apoptosis and/or dendritic cells (DCs) may play a role in the stimulation of the immuno-mediated anti-platelet response in chronic immune thrombocytopenic purpura (ITP).

METHODS AND RESULTS

Twenty-nine patients with active ITP and 29 healthy adult volunteers were enrolled into the study. Freshly washed platelets and platelets aged in a plasma-free buffer for 72 hours at 37 degrees C were assessed by flow cytometry for phosphatidylserine exposure using annexin V-FITC, caspase activation, and platelet activation markers. CD14-derived DCs were characterized by immunophenotyping, cytokine production, and ability to present fresh and aged platelets to T lymphocytes. We demonstrated that platelets from ITP patients, either fresh or in vitro aged, show increased apoptosis (with low levels of activation) in comparison to their normal counterparts. We also found that immature DCs readily ingest apoptotic platelets. Furthermore, in ITP patients DCs, prepulsed with autologous/allogeneic fresh and aged platelets, are highly efficient in stimulating autologous T-cell proliferation as compared to DCs derived from healthy donors. This finding may be related to the upregulated expression of CD86 in DCs from ITP patients and not to higher phagocytic activity.

CONCLUSION

These results suggest that DC dysfunction, together with increased propensity of platelets to undergo apoptosis, may play a role in the stimulation of the immune system in ITP.

Improved extension of platelet storage in a polyolefin container with higher oxygen permeability

This study evaluated a newly developed polyolefin bag, which has a 50%/m(2) higher oxygen permeability to extend the shelf-life of platelets. Single-donor aphaeresis platelets were pooled, separated equally into two bags, PO-80 (0.8 l capacity) and KBP-PO (1 l capacity) for control, and stored in plasma for up to 7 d. Platelet biochemical and functional parameters were monitored in bags containing high (4.2 x 10(11)/250 ml/bag, n = 9) and low (2.0 x 10(11)/200 ml/bag, n = 3) concentrations of platelets over the storage period. After 7 d of storage, the PO-80 bags containing high concentrations of platelets had a better pH (mean pH 6.74) than those stored in KBP-PO (pH 6.32, P < 0.01); none of the nine PO-80 bags with a high platelet concentration had a pH below 6.2, compared with four of nine controls (P < 0.05). Similarly, lactate values were 20.19 mmol/l and 28.09 mmol/l respectively (P < 0.05). Aerobic metabolism was maintained better with greater O(2) consumption and less lactate generation in high-platelet concentration PO-80 bags than in the control bags. A significant difference was also found in pH, pCO(2) and lactate levels between the two bags containing low concentrations of platelets during the 7-d period. The in vitro characteristics of platelets declined less over 7 d when stored in a higher oxygen permeable container than in a marketed bag.

Platelet apoptosis in stored platelet concentrates and other models

Apoptosis or programmed cell death was discovered in nucleate cells 30 years ago and has been well documented. In contrast, apoptosis in anucleate platelets has only a five-year research history and as yet but few publications related to it. In this review, we will present the data on platelet apoptosis in several models. These include in vitro models where platelet apoptosis was induced by calcium ionophores, natural platelet agonists, storage in capped tubes at 37 degrees C and storage at room temperature under standard blood banking conditions, and in vivo models where apoptosis was provoked by suppression of thrombopoiesis, malaria infection and injection of tumor necrosis factor or anti-platelet antibodies. Understanding of platelet apoptosis and its role in the platelet storage lesion is an exciting challenge; future research is likely to provide us with further insight into this field.