Identification of platelet subpopulations in cryopreserved platelet components using multi-colour imaging flow cytometry

Platelets retain function and can be stored following disruption of human leucocyte antigens

BACKGROUND AND OBJECTIVES

Antibodies to human leucocyte antigen (HLA) Class-I antigens can lead to refractoriness to platelet transfusion. Although this can be overcome by transfusion of HLA-compatible platelets, they are not always available. Disruption of HLA antigens on platelets by acid treatment may be a suitable alternative when no other components are available. The aim of this study was to assess the effect of HLA disruption and subsequent storage of platelet components.

MATERIALS AND METHODS

Platelet components were treated with 0.9% saline or citric acid solution (pH 3.0), and then stored until expiry (Day 7). HLA and platelet glycoprotein expression, platelet viability, activation and sialylation were measured by flow cytometry. Release of soluble factors was measured by ELISA and metabolism by biochemistry analyser. Reactivity to patient anti-sera containing anti-HLA antibodies was measured using platelet immunofluorescence tests (PIFTs) and monoclonal antibody immobilization of platelet antigen (MAIPA) assays. Platelet function was measured using aggregometry and thromboelastography (TEG).

RESULTS

Acid treatment reduced detection of HLA Class-I on platelets by 75%, with significant reductions in reactivity to patient anti-sera. Acid treatment reduced platelet content and viability, increased platelet activation and accelerated metabolism. Glycan cleavage was increased by acid treatment. Treatment reduced platelet activation following agonist stimulation by ADP and TRAP-6, but platelets remained functional, displaying increased aggregation response and reduced time to clot formation by TEG.

CONCLUSION

Although HLA disruption had some detrimental effects, acid-treated platelets remained functional, retaining their capacity to respond to agonists and form clots, and with further development could be used to support refractory patients.

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.

Heterogeneity of platelets and their responses

There has been increasing recognition of heterogeneity in blood platelets and their responses, particularly in recent years, where next-generation technologies and advanced bioinformatic tools that interrogate "big data" have enabled large-scale studies of RNA and protein expression across a growing list of disease states. However, pioneering platelet biologists and clinicians were already hypothesizing upon and investigating heterogeneity in platelet (and megakaryocyte) activity and platelet metabolism and aggregation over half a century ago. Building on their foundational hypotheses, in particular Professor Marian A. Packham's pioneering work and a State of the Art lecture in her memoriam at the 2023 International Society on Thrombosis and Haemostasis Congress by Anandi Krishnan, this review outlines the key features that contribute to the heterogeneity of platelets between and within individuals. Starting with important epidemiologic factors, we move stepwise through successively smaller scales down to heterogeneity revealed by single-cell technologies in health and disease. We hope that this overview will urge future scientific and clinical studies to recognize and account for heterogeneity of platelets and aim to apply methods that capture that heterogeneity. Finally, we summarize other exciting new data presented on this topic at the 2023 International Society on Thrombosis and Haemostasis Congress.

cGMP modulates hemin-mediated platelet death

BACKGROUND AND AIMS

Hemolysis is a known risk factor for thrombosis resulting in critical limb ischemia and microcirculatory disturbance and organ failure. Intravasal hemolysis may lead to life-threatening complications due to uncontrolled thrombo-inflammation. Until now, conventional antithrombotic therapies failed to control development and progression of these thrombotic events. Thus, the pathophysiology of these thrombotic events needs to be investigated to unravel underlying pathways and thereby identify targets for novel treatment strategies.

METHODS

Here we used classical experimental set-ups as well as high-end flow cytometry, metabolomics and lipidomic analysis to in-depth analyze the effects of hemin on platelet physiology and morphology.

RESULTS

Hemin does strongly and swiftly induce platelet activation and this process is modulated by the sGC-cGMP-cGKI signaling axis. cGMP modulation also reduced the pro-aggregatory potential of plasma derived from patients with hemolysis. Furthermore, hemin-induced platelet death evokes distinct platelet subpopulations. Typical cell death markers, such as ROS, were induced by hemin-stimulation and the platelet lipidome was specifically altered by high hemin concentration. Specifically, arachidonic acid derivates, such as PGE2, TXB2 or 12-HHT, were significantly increased. Balancing the cGMP levels by modulation of the sGC-cGMP-cGKI axis diminished the ferroptotic effect of hemin.

CONCLUSION

We found that cGMP modulates hemin-induced platelet activation and thrombus formation in vitro and cGMP effects hemin-mediated platelet death and changes in the platelet lipidome. Thus, it is tempting to speculate that modulating platelet cGMP levels may be a novel strategy to control thrombosis and critical limb ischemia in patients with hemolytic crisis.

Cryopreservation affects platelet macromolecular composition over time after thawing and differently impacts on cancer cells behavior in vitro

Cryopreservation affects platelets' function, questioning their use for cancer patients. We aimed to investigate the biochemical events that occur over time after thawing to optimize transfusion timing and evaluate the effect of platelet supernatants on tumor cell behavior in vitro. We compared fresh (Fresh-PLT) with Cryopreserved platelets (Cryo-PLT) at 1 h, 3 h and 6 h after thawing. MCF-7 and HL-60 cells were cultured with Fresh- or 1 h Cryo-PLT supernatants to investigate cell proliferation, migration, and PLT-cell adhesion. We noticed a significant impairment of hemostatic activity accompanied by a post-thaw decrease of CD42b+ , which identifies the CD62P--population. FTIR spectroscopy revealed a decrease in the total protein content together with changes in their conformational structure, which identified two sub-groups: 1) Fresh and 1 h Cryo-PLT; 2) 3 h and 6 h cryo-PLT. Extracellular vesicle shedding and phosphatidylserine externalization (PS) increased after thawing. Cryo-PLT supernatants inhibited cell proliferation, impaired MCF-7 cell migration, and reduced ability to adhere to tumor cells. Within the first 3 hours after thawing, irreversible alterations of biomolecular structure occur in Cryo-PLT. Nevertheless, Cryo-PLT should be considered safe for the transfusion of cancer patients because of their insufficient capability to promote cancer cell proliferation, adhesion, or migration.

Cryopreserved Platelets in a Non-Toxic DMSO-Free Solution Maintain Hemostatic Function In Vitro

Dimethyl sulfoxide (DMSO) is regularly used as a cryoprotectant agent for the cryopreservation of platelets. However, DMSO is considered toxic. We therefore hypothesized that saline could be used as a non-toxic medium for the cryopreservation of platelets. Double-dose buffy coat platelets (n = 10) were divided and cryopreserved at -80 °C using 5-6% dimethyl sulfoxide (DMSO) or in NaCl (9 mg/mL). Paired testing was conducted pre-freeze, post-thaw (PT 1 h). Upon analysis, each bag was thawed and reconstituted in fresh plasma. Analyses included cell counts and the metabolic, phenotypic, and functional properties of the platelets together with thromboelastometry. The cryopreserved platelets showed several biochemical and ultrastructural changes compared to pre-freezing. Platelet recovery was approximately 17% higher in DMSO-free units (p < 0.001), but the platelet viability was reduced (p < 0.001). However, using controlled freezing (n = 6), the platelet viability was improved. The clot formation time (CFT) was comparable, but DMSO-free platelets showed slightly decreased maximum clot firmness (MCF) (p = 0.034). By reducing the reconstituted plasma volume, a reduced CFT and increased MCF were obtained (p < 0.001). This study demonstrates that platelets can be cryopreserved in saline without the addition of DMSO, with high recovery and maintained hemostatic function. However, controlled freezing is required to optimize platelet quality.

Platelets for advanced drug delivery in cancer

INTRODUCTION

Cancer-related drug expenses are rising with the increasing cancer incidence and cost may represent a severe challenge for drug access for patients with cancer. Consequently, strategies for increasing therapeutic efficacy of already available drugs may be essential for the future health-care system.

AREAS COVERED

In this review, we have investigated the potential for the use of platelets as drug-delivery systems. We searched PubMed and Google Scholar to identify relevant papers written in English and published up to January 2023. Papers were included at the authors' discretion to reflect an overview of state of the art.

EXPERT OPINION

It is known that cancer cells interact with platelets to gain functional advantages including immune evasion and metastasis development. This platelet-cancer interaction has been the inspiration for numerous platelet-based drug delivery systems using either drug-loaded or drug-bound platelets, or platelet membrane-containing hybrid vesicles combining platelet membranes with synthetic nanocarriers. Compared to treatment with free drug or synthetic drug vectors, these strategies may improve pharmacokinetics and selective cancer cell targeting. There are multiple studies showing improved therapeutic efficacy using animal models, however, no platelet-based drug delivery systems have been tested in humans, meaning the clinical relevance of this technology remains uncertain.