Platelet-derived microparticles analysis: Techniques, challenges and recommendations

An Investigation of Size Distribution and Calcium Signaling in Human Platelets

Background Platelets are thin disc-shaped blood cells that play a major role in hemostasis, maintenance of vascular integrity, and blood coagulation. Large platelets are more reactive and seen in patients with cardiovascular disease. This study aims to analyze the changes in platelet size of ex vivo activated platelets which phenotypically simulates that of a patient at risk of cardiovascular disease and elucidate the calcium signaling pathway responsible for this change. Methodology Platelets were isolated from adult human blood by differential centrifugation. Calcium was mobilized into platelets by treatment with calcium ionophore A23187 in the presence of Ca2+. Platelet size distribution was analyzed using Coulter Counter Multisizer 4. The following signaling parameters were studied: intracellular Ca2+ measurement (using Fura-2/AM by fluorescence spectrophotometry), Ca2+-dependent thiol protease calpain assay (using fluorogenic substrate t-butoxycarbonyl-Leu-metchloromethylcoumarin in fluorescence microplate reader), platelet-derived microparticles (using FACS Calibur flow cytometry), and cytoskeletal protein talin expression (by western immunoblotting). Results When adult platelets were treated with A23187 and Ca2+, two subcellular populations (<2 µm and between 2-4 µm) were noted. The mean size of the second cell population was significantly higher than that of resting platelets (2.94 ± 0.13 µm vs. 2.82 ± 0.15 µm, t = 4.605, p = 0.00). A23187 treatment led to elevated intracellular Ca2+, release of platelet-derived microparticles, increase in calpain activity, and cytoskeletal talin degradation. These events were inhibited by calpeptin (a specific calpain inhibitor). Conclusions Elevated calcium caused talin degradation by calpain activity. Breakdown of this cytoskeletal protein leads to relative swelling of cells reflected by the increase in platelet size.

Platelet-derived microparticles and their cargos: The past, present and future

All eukaryotic cells can secrete extracellular vesicles, which have a double-membrane structure and are important players in the intercellular communication involved in a variety of important biological processes. Platelets form platelet-derived microparticles (PMPs) in response to activation, injury, or apoptosis. This review introduces the origin, pathway, and biological functions of PMPs and their importance in physiological and pathological processes. In addition, we review the potential applications of PMPs in cancer, vascular homeostasis, thrombosis, inflammation, neural regeneration, biomarkers, and drug carriers to achieve targeted drug delivery. In addition, we comprehensively report on the origin, biological functions, and applications of PMPs. The clinical transformation, high heterogeneity, future development direction, and limitations of the current research on PMPs are also discussed in depth. Evidence has revealed that PMPs play an important role in cell-cell communication, providing clues for the development of PMPs as carriers for relevant cell-targeted drugs. The development history and prospects of PMPs and their cargos are explored in this guidebook.

Platelet functions in lymphatic filariasis patients

Filariasis is a chronic disease where parasitic worms survive in human hosts even for decades and lead to complications like lymphedema and elephantiasis. Despite the persistent existence of filarial parasites in human hosts, fatal and thrombotic complications are not known, unlike other parasitic diseases like malaria. This suggests that filarial parasites might be affecting the host's platelet functions. This study was conducted to examine platelet functions in confirmed filariasis patients and healthy controls. Results showed that filariasis patients had larger platelets, inhibited aggregation, and slower speed of aggregation, compared to controls. However, in vivo markers of platelet activation and degranulation (beta thromboglobulin and soluble P-selectin) were not affected. Observations suggested that there is increased platelet turnover, cellular apoptosis and inhibited platelet functions in filariasis patients compared to controls. Platelet function inhibition was not associated with the duration of disease, lymphedema-affected organs, or gender of patients. This study confirms that filarial parasites modulate platelet functions in human hosts.

Buyang Huanwu Decoction alleviates blood stasis, platelet activation, and inflammation and regulates the HMGB1/NF-κB pathway in rats with pulmonary fibrosis

ETHNOPHARMACOLOGICAL RELEVANCE

Qi deficiency and blood stasis are identified to be pathological factors of pulmonary fibrosis (PF) in traditional Chinese medicine (TCM) theory. Buyang Huanwu Decoction (BYHWD) is a traditional Chinese prescription ameliorating Qi deficiency and blood stasis.

AIM OF THE STUDY

The objective of this study was to investigate the anti-fibrosis effect of BYHWD and the potential molecular mechanism in rats.

MATERIALS AND METHODS

Bleomycin was used to construct PF rat models. 27 PF rats were randomly divided into three groups based on treatments: model group (saline solution, n = 9), low-dose BYHWD group (3.5 g/kg, n = 9), and high-dose BYHWD group (14.0 g/kg, n = 9). Moreover, 9 normal rats were used as the blank group. The blood viscosity, coagulation indexes (APTT, TT, PT, and FIB), platelet-related parameters (PLT, PDW, MPV, PCT, and PLCR), platelet microparticles (PMPs), and inflammatory factors (IL-2, IL-10, IL-1β, IL-6, IL-8, IL-17, IFN-γ, TNF-α, PAC-1, HMGB1, NF-κB, and TF) were determined. The lung tissue samples of rats were observed after hematoxylin-eosin (HE) staining. The full component analysis of the BYHWD extract was performed using the ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method. The signaling pathway included into the study was selected on the basis of bioinformatics analysis and the results of the phytochemical analysis. The expression levels of genes and proteins involved in the selected signaling pathway were detected.

RESULTS

Compared to the blank group, the whole blood viscosity, PLR, PDW, MPV, PCT, PLCR, PMPs, and the levels of IL-1β, IL-6, IL-8, IL-17, TNF-α, PAC-1, HMGB1, NF-κB, and TF were increased, while the levels of IL-2 and IL-10 were decreased in the model group. Both low-dose BYHWD and high-dose BYHWD reversed these PF-induced effects in spite of the fact that low-dose BYHWD had no significant effect on the level of NF-κB. In addition, BYHWD ameliorated PF-induced inflammation in the rat lung tissue. The phytochemical analysis of the BYHWD extract combined with the bioinformatics analysis suggested that the therapeutical effect of BYHWD on PF was related to the HMGB1/NF-κB pathway, which consisted of NF-κB, IKBKB, ICAM1, VCAM1, HMGB1, and TLR4. Both RT-qPCR and western blot analyses showed that PF induced increases in the expression levels of NF-κB, ICAM1, VCAM1, HMGB1, and TLR4, but a decrease in the expression level of IKBKB. Moreover, both low-dose BYHWD and high-dose BYHWD exerted the opposite effects, and recovered the expression levels of NF-κB, ICAM1, VCAM1, HMGB1, TLR4, and IKBKB, despite the fact that low-dose BYHWD had no effects on the mRNA expression levels of NF-κB or TLR4.

CONCLUSIONS

In summary, BYHWD alleviated PF-induced blood stasis, platelet activation, and inflammation in the rats. Our study suggested BYHWD had a therapeutic effect on PF and was a good alternative for the complementary therapy of PF, and the potential molecular mechanism was modulation of HMGB1/NF-κB signaling pathway, and it needs further study.

Platelet membrane-derived microparticles may be biomarkers in patients with hepatocellular carcinoma and can promote the invasion and metastasis of hepatoma carcinoma cells

BACKGROUND

Platelet membrane-derived microparticles (PMPs) released by apheresis platelets (APs) during storage are involved in immunomodulatory and tumor processes. However, few studies have emphasized the relationship between PMPs and hepatocellular carcinoma (HCC).

METHODS

Enzyme-linked immunosorbent assay (ELISA) was used to detect PMPs in the plasma of HCC patients and healthy individuals. ELISA and flow cytometry were separately applied to analyze the variation in PMPs from APs prepared after 0, 3, 5, and 7 days of storage. Transwell was used to demonstrate the effects of PMPs on the invasion and migration of HCC cells. HCC-related indicators and invasion and migration-related markers were detected in vivo.

RESULTS

We found the amount of PMPs was significantly increased in HCC patients. There was also a significant difference in the amount of PMPs in APs with prolonged storage time. Further, the PMPs in D5 promoted the invasion and migration of HepG2 and Huh7 cells. Transcriptomics revealed striking differences in the expression of many tumor metastasis associated genes with PMPs treatment. PMPs promoted tumor growth and weight loss in HCC-bearing mice, and Western blot results showed that invasion and migration-related indicators also increase.

CONCLUSION

The content of PMPs in the plasma of HCC patients increases, and it can also promote the invasion and migration of HCC.

Bidirectional Communication Between the Brain and Other Organs: The Role of Extracellular Vesicles

A number of substances released by the brain under physiological and pathological conditions exert effects on other organs. In turn, substances produced primarily by organs such as bone marrow, adipose tissue, or the heart may have an impact on the metabolism and function and metabolism of the healthy and diseased brain. Despite a mounting amount of evidence supports such bidirectional communication between the brain and other organs, research on the function of molecular mediators carried by extracellular vesicles (EVs) is in the early stages. In addition to being able to target or reach practically any organ, EVs have the ability to cross the blood-brain barrier to transport a range of substances (lipids, peptides, proteins, and nucleic acids) to recipient cells, exerting biological effects. Here, we review the function of EVs in bidirectional communication between the brain and other organs. In a small number of cases, the role has been explicitly proven; yet, in most cases, it relies on indirect evidence from EVs in cell culture or animal models. There is a dearth of research currently available on the function of EVs-carrying mediators in the bidirectional communication between the brain and bone marrow, adipose tissue, liver, heart, lungs, and gut. Therefore, more studies are needed to determine how EVs facilitate communication between the brain and other organs.

Platelets at the Vessel Wall in Non-Thrombotic Disease

Platelets are small, anucleate entities that bud from megakaryocytes in the bone marrow. Among circulating cells, platelets are the most abundant cell, traditionally involved in regulating the balance between thrombosis (the terminal event of platelet activation) and hemostasis (a protective response to tissue injury). Although platelets lack the precise cellular control offered by nucleate cells, they are in fact very dynamic cells, enriched in preformed RNA that allows them the capability of de novo protein synthesis which alters the platelet phenotype and responses in physiological and pathological events. Antiplatelet medications have significantly reduced the morbidity and mortality for patients afflicted with thrombotic diseases, including stroke and myocardial infarction. However, it has become apparent in the last few years that platelets play a critical role beyond thrombosis and hemostasis. For example, platelet-derived proteins by constitutive and regulated exocytosis can be found in the plasma and may educate distant tissue including blood vessels. First, platelets are enriched in inflammatory and anti-inflammatory molecules that may regulate vascular remodeling. Second, platelet-derived microparticles released into the circulation can be acquired by vascular endothelial cells through the process of endocytosis. Third, platelets are highly enriched in mitochondria that may contribute to the local reactive oxygen species pool and remodel phospholipids in the plasma membrane of blood vessels. Lastly, platelets are enriched in proteins and phosphoproteins which can be secreted independent of stimulation by surface receptor agonists in conditions of disturbed blood flow. This so-called biomechanical platelet activation occurs in regions of pathologically narrowed (atherosclerotic) or dilated (aneurysmal) vessels. Emerging evidence suggests platelets may regulate the process of angiogenesis and blood flow to tumors as well as education of distant organs for the purposes of allograft health following transplantation. This review will illustrate the potential of platelets to remodel blood vessels in various diseases with a focus on the aforementioned mechanisms.

A narrative review for platelets and their RNAs in cancers: New concepts and clinical perspectives

Recent years have witnessed a growing body of evidence suggesting that platelets are involved in several stages of the metastatic process via direct or indirect interactions with cancer cells, contributing to the progression of neoplastic malignancies. Cancer cells can dynamically exchange components with platelets in and out of blood vessels, and directly phagocytose platelets to hijack their proteome, transcriptome, and secretome, or be remotely regulated by metabolites or microparticles released by platelets, resulting in phenotypic, genetic, and functional modifications. Moreover, platelet interactions with stromal and immune cells in the tumor microenvironment lead to alterations in their components, including the ribonucleic acid (RNA) profile, and complicate the impact of platelets on cancers. A deeper understanding of the roles of platelets and their RNAs in cancer will contribute to the development of anticancer strategies and the optimization of clinical management. Encouragingly, advances in high-throughput sequencing, bioinformatics data analysis, and machine learning have allowed scientists to explore the potential of platelet RNAs for cancer diagnosis, prognosis, and guiding treatment. However, the clinical application of this technique remains controversial and requires larger, multicenter studies with standardized protocols. Here, we integrate the latest evidence to provide a broader insight into the role of platelets in cancer progression and management, and propose standardized recommendations for the clinical utility of platelet RNAs to facilitate translation and benefit patients.

Annexin V- and tissue factor+ microparticles as biomarkers for predicting deep vein thrombosis in patients after joint arthroplasty

OBJECTIVE

Venous thromboembolism (VTE) is a common and severe complication of joint arthroplasty. Microparticles (MPs) containing phosphatidylserine (PS) and tissue factor (TF) can trigger coagulation in VTE. This study aims to measure and compare MP levels in joint arthroplasty patients with and without VTE.

METHODS

This prospective cohort study enrolled 181 patients who underwent joint arthroplasty. Ultrasound examination was used to diagnose VTE on preoperative day 0 and postoperative day 6. MPs were analysed using transmission electron microscopy (TEM), nanoparticle tracking analysis (NTA), and flow cytometry. The levels of platelet-derived microparticles (PMPs), endothelial cell-derived microparticles (EMPs), granulocyte-derived microparticles (GMPs), red cell-derived microparticles (RMPs), monocyte-derived microparticles (MMPs), Annexin V⁺ MPs (AV⁺ MPs), and tissue factor⁺ MPs (TF⁺ MPs) derived from five kinds of MPs were measured on day 0 (before surgery), 1, 2, 3, 4, 5, and 6 after surgery.

RESULTS

The levels of AV^-TF⁺ EMPs and AV^-TF⁺ MMPs were significantly increased in patients with VTE on postoperative day 5 compared to those without VTE (P=0.031 and P=0.031, respectively).

CONCLUSION

AV^-TF⁺ MPs may indicate the development of VTE and serve as predictive markers in joint arthroplasty patients.

Bleeding During Veno-Venous ECMO: Prevention and Treatment

Veno-venous extracorporeal membrane oxygenation (vvECMO) has become a routine treatment for severe lung failure in specialized centers. Spontaneous bleeding complications, however, are observed in 30–60% of patients during vvECMO treatment. Bleeding increases mortality by factors 2–3. Anticoagulation in combination with several acquired bleeding disorders caused by the mechanical pump and the foreign layer of the extracorporeal system contribute to the risk of bleeding. In this review, the mechanisms of the underlying pathologies and the route from diagnosis to treatment are described.

Immune Thrombocytopenic Purpura as a Hemorrhagic Versus Thrombotic Disease: An Updated Insight into Pathophysiological Mechanisms

Immune thrombocytopenic purpura (ITP) is a blood disorder characterized by a low platelet count of (less than 100 × 109/L). ITP is an organ-specific autoimmune disease in which the platelets and their precursors become targets of a dysfunctional immune system. This interaction leads to a decrease in platelet number and, subsequently, to a bleeding disorder that can become clinically significant with hemorrhages in skin, on the mucous membrane, or even intracranial hemorrhagic events. If ITP was initially considered a hemorrhagic disease, more recent studies suggest that ITP has an increased risk of thrombosis. In this review, we provide current insights into the primary ITP physiopathology and their consequences, with special consideration on hemorrhagic and thrombotic events. The autoimmune response in ITP involves both the innate and adaptive immune systems, comprising both humoral and cell-mediated immune responses. Thrombosis in ITP is related to the pathophysiology of the disease (young hyperactive platelets, platelets microparticles, rebalanced hemostasis, complement activation, endothelial activation, antiphospholipid antibodies, and inhibition of natural anticoagulants), ITP treatment, and other comorbidities that altogether contribute to the occurrence of thrombosis. Physicians need to be vigilant in the early diagnosis of thrombotic events and then institute proper treatment (antiaggregant, anticoagulant) along with ITP-targeted therapy. In this review, we provide current insights into the primary ITP physiopathology and their consequences, with special consideration on hemorrhagic and thrombotic events. The accumulated evidence has identified multiple pathophysiological mechanisms with specific genetic predispositions, particularly associated with environmental conditions.

A panel of platelet-associated circulating long non-coding RNAs as potential biomarkers for colorectal cancer

Evidence has suggested the potential of tumor-educated platelets as a biomarker trove for cancer diagnostics, but the difficulty in isolation limits its application. Since most of the circulating RNAs are derived from platelets, the change of RNA profile in platelets may lead to altered RNA expression in serum. Here, we identified a panel of platelet-associated long non-coding RNAs (lncRNAs) and evaluated its diagnostic capacity in serum of colorectal cancer (CRC) patients. Four lncRNAs, LNCAROD, SNHG20, LINC00534, and TSPOAP-AS1, were upregulated in both platelets and serum of CRC patients. A binary logistic model derived from them has validated area under roc curve of 0.78 indicating great performance. Furthermore, the expression levels of LNCAROD and TSPOAP-AS1 were correlated with cancer staging and tumor location. Together, our results add novel lncRNA biomarkers to the list of blood tests for CRC diagnostics and provide molecular evidence for the cross-talk between CRC platelets and serum.

Platelets in ITP: Victims in Charge of Their Own Fate?

Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder. The pathophysiological mechanisms leading to low platelet levels in ITP have not been resolved, but at least involve autoantibody-dependent and/or cytotoxic T cell mediated platelet clearance and impaired megakaryopoiesis. In addition, T cell imbalances involving T regulatory cells (Tregs) also appear to play an important role. Intriguingly, over the past years it has become evident that platelets not only mediate hemostasis, but are able to modulate inflammatory and immunological processes upon activation. Platelets, therefore, might play an immuno-modulatory role in the pathogenesis and pathophysiology of ITP. In this respect, we propose several possible pathways in which platelets themselves may participate in the immune response in ITP. First, we will elaborate on how platelets might directly promote inflammation or stimulate immune responses in ITP. Second, we will discuss two ways in which platelet microparticles (PMPs) might contribute to the disrupted immune balance and impaired thrombopoiesis by megakaryocytes in ITP. Importantly, from these insights, new starting points for further research and for the design of potential future therapies for ITP can be envisioned.

Platelet extracellular vesicles enhance the proangiogenic potential of adipose-derived stem cells in vivo and in vitro

BACKGROUND

Adipose-derived mesenchymal stem cells (ADSC)-based therapy is an outstanding treatment strategy for ischaemic disease. However, the therapeutic efficacy of this strategy is not ideal due to the poor paracrine function and low survival rate of ADSCs in target regions. Platelet extracellular vesicles (PEVs) are nanoparticles derived from activated platelets that can participate in communication between cells. Accumulating evidence indicates that PEVs can regulate the biological functions of several cell lines. In the present study, we aimed to investigate whether PEVs can modulate the proangiogenic potential of ADSCs in vitro and in vivo.

METHODS

PEVs were identified using scanning electron microscope (SEM), flow cytometry (FCM) and nanoparticle tracking analysis (NTA). The CCK8 assay was performed to detect proliferation of cells. Transwell and wound healing assays were performed to verify migration capacity of cells. AnnexinV-FITC/PI apoptosis kit and live/dead assay were performed to assess ADSCs apoptosis under Cocl₂-induced hypoxia condition. The underlying mechanisms by which PEVs affected ADSCs were explored using real time-PCR(RT-PCR) and Western blot. In addition, matrigel plug assays were conducted and mouse hindlimb ischaemic models were established to investigate the proangiogenic potential of PEV-treated ADSCs in vivo.

RESULTS

We demonstrated that ADSC could internalize PEVs, which lead to a series of biological reactions. In vitro, dose-dependent effects of PEVs on ADSC proliferation, migration and antiapoptotic capacity were observed. Western blotting results suggested that multiple proteins such as ERK, AKT, FAK, Src and PLCγ1 kinase may contribute to these changes. Furthermore, PEVs induced upregulation of several growth factors expression in ADSCs and amplified the proliferation, migration and tube formation of HUVECs induced by ADSC conditioned medium (CM). In in vivo experiments, compared with control ADSCs, the injection of PEV-treated ADSCs resulted in more vascularization in matrigel plugs, attenuated tissue degeneration and increased blood flow and capillary density in ischaemic hindlimb tissues.

CONCLUSION

Our data demonstrated that PEVs could enhance the proangiogenic potential of ADSCs in mouse hindlimb ischaemia. The major mechanisms of this effect included the promotion of ADSC proliferation, migration, anti-apoptosis ability and paracrine secretion.

Characterization and Therapeutic Use of Extracellular Vesicles Derived from Platelets

Autologous blood products, such as platelet-rich plasma (PRP), are gaining increasing interest in different fields of regenerative medicine. Although growth factors, the main components of PRP, are thought to stimulate reparation processes, the exact mechanism of action and main effectors of PRP are not fully understood. Plasma contains a high amount of extracellular vesicles (EVs) produced by different cells, including anucleated platelets. Platelet-derived EVs (PL-EVs) are the most abundant type of EVs in circulation. Numerous advantages of PL-EVs, including their ability to be released locally, their ease of travel through the body, their low immunogenicity and tumourigenicity, the modulation of signal transduction as well as the ease with which they can be obtained, has attracted increased attention n. This review focuses briefly on the biological characteristics and isolation methods of PL-EVs, including exosomes derived from platelets (PL-EXOs), and their involvement in the pathology of diseases. Evidence that shows how PL-EVs can be used as a novel tool in medicine, particularly in therapeutic and regenerative medicine, is also discussed in this review.

Platelets induce free and phospholipid-esterified 12-hydroxyeicosatetraenoic acid generation in colon cancer cells by delivering 12-lipoxygenase

Platelets promote tumor metastasis by inducing promalignant phenotypes in cancer cells and directly contributing to cancer-related thrombotic complications. Platelet-derived extracellular vesicles (EVs) can promote epithelial-mesenchymal transition (EMT) in cancer cells, which confers high-grade malignancy. 12S-hydroxyeicosatetraenoic acid (12-HETE) generated by platelet-type 12-lipoxygenase (12-LOX) is considered a key modulator of cancer metastasis through unknown mechanisms. In platelets, 12-HETE can be esterified into plasma membrane phospholipids (PLs), which drive thrombosis. Using cocultures of human platelets and human colon adenocarcinoma cells (line HT29) and LC-MS/MS, we investigated the impact of platelets on cancer cell biosynthesis of 12S-HETE and its esterification into PLs and whether platelet ability to transfer its molecular cargo might play a role. To this aim, we performed coculture experiments with CFSE[5-(and-6)-carboxyfluorescein diacetate, succinimidyl ester]-loaded platelets. HT29 cells did not generate 12S-HETE or express 12-LOX. However, they acquired the capacity to produce 12S-HETE mainly esterified in plasmalogen phospholipid forms following the uptake of platelet-derived medium-sized EVs (mEVs) expressing 12-LOX. 12-LOX was detected in plasma mEV of patients with adenomas/adenocarcinomas, implying their potential to deliver the protein to cancer cells in vivo. In cancer cells exposed to platelets, endogenous but not exogenous 12S-HETE contributed to changes in EMT gene expression, mitigated by three structurally unrelated 12-LOX inhibitors. In conclusion, we showed that platelets induce the generation of primarily esterified 12-HETE in colon cancer cells following mEV-mediated delivery of 12-LOX. The modification of cancer cell phospholipids by 12-HETE may functionally impact cancer cell biology and represent a novel target for anticancer agent development.

Sphingolipidomics in Translational Sepsis Research-Biomedical Considerations and Perspectives

Scientific Background: Sphingolipids are a highly diverse group of lipids with respect to physicochemical properties controlling either structure, distribution, or function, all of them regulating cellular response in health and disease. Mass spectrometry, on the other hand, is an analytical technique characterizing ionized molecules or fragments thereof by mass-to-charge ratios, which has been prosperingly developed for rapid and reliable qualitative and quantitative identification of lipid species. Parallel to best performance of in-depth chromatographical separation of lipid classes, preconditions of precise quantitation of unique molecular species by preprocessing of biological samples have to be fulfilled. As a consequence, “lipid profiles” across model systems and human individuals, esp. complex (clinical) samples, have become eminent over the last couple of years due to sensitivity, specificity, and discriminatory capability. Therefore, it is significance to consider the entire experimental strategy from sample collection and preparation, data acquisition, analysis, and interpretation.

Areas Covered: In this review, we outline considerations with clinical (i.e., human) samples with special emphasis on sample handling, specific physicochemical properties, target measurements, and resulting profiling of sphingolipids in biomedicine and translational research to maximize sensitivity and specificity as well as to provide robust and reproducible results. A brief commentary is also provided regarding new insights of “clinical sphingolipidomics” in translational sepsis research.

Expert Opinion: The role of mass spectrometry of sphingolipids and related species (“sphingolipidomics”) to investigate cellular and compartment-specific response to stress, e.g., in generalized infection and sepsis, is on the rise and the ability to integrate multiple datasets from diverse classes of biomolecules by mass spectrometry measurements and metabolomics will be crucial to fostering our understanding of human health as well as response to disease and treatment.

Platelets in Healthy and Disease States: From Biomarkers Discovery to Drug Targets Identification by Proteomics

Platelets are a heterogeneous small anucleate blood cell population with a central role both in physiological haemostasis and in pathological states, spanning from thrombosis to inflammation, and cancer. Recent advances in proteomic studies provided additional important information concerning the platelet biology and the response of platelets to several pathophysiological pathways. Platelets circulate systemically and can be easily isolated from human samples, making proteomic application very interesting for characterizing the complexity of platelet functions in health and disease as well as for identifying and quantifying potential platelet proteins as biomarkers and novel antiplatelet therapeutic targets. To date, the highly dynamic protein content of platelets has been studied in resting and activated platelets, and several subproteomes have been characterized including platelet-derived microparticles, platelet granules, platelet releasates, platelet membrane proteins, and specific platelet post-translational modifications. In this review, a critical overview is provided on principal platelet proteomic studies focused on platelet biology from signaling to granules content, platelet proteome changes in several diseases, and the impact of drugs on platelet functions. Moreover, recent advances in quantitative platelet proteomics are discussed, emphasizing the importance of targeted quantification methods for more precise, robust and accurate quantification of selected proteins, which might be used as biomarkers for disease diagnosis, prognosis and therapy, and their strong clinical impact in the near future.

Polyphenols: Modulators of Platelet Function and Platelet Microparticle Generation?

Platelets and platelet microparticles (PMPs) play a key role in the pathophysiology of vascular disorders such as coronary artery disease and stroke. In atherosclerosis, for example, the disruption of the plaque exposes endogenous agonists such as collagen, which activates platelets. Platelet hyper-activation and the high levels of PMPs generated in such situations pose a thrombotic risk that can lead to strokes or myocardial infarctions. Interestingly, dietary polyphenols are gaining much attention due to their potential to mimic the antiplatelet activity of treatment drugs such as aspirin and clopidogrel that target the glycoprotein VI (GPVI)-collagen and cyclooxygenease-1 (COX-1)-thromboxane platelet activation pathways respectively. Platelet function tests such as aggregometry and flow cytometry used to monitor the efficacy of antiplatelet drugs can also be used to assess the antiplatelet potential of dietary polyphenols. Despite the low bioavailability of polyphenols, several in vitro and dietary intervention studies have reported antiplatelet effects of polyphenols. This review presents a summary of platelet function in terms of aggregation, secretion, activation marker expression, and PMP release. Furthermore, the review will critically evaluate studies demonstrating the impact of polyphenols on aggregation and PMP release.

Platelet-Derived Extracellular Vesicles as Target of Antiplatelet Agents. What Is the Evidence?

Platelet-derived large extracellular vesicles (often referred to as microparticles in the field of cardiovascular disease) have been identified as effector in the atherothrombotic process, therefore representing a target of pharmacological intervention of potential interest. Despite that, limited evidence is so far available concerning the effects of antiplatelet agents on the release of platelet-derived extracellular vesicles. In the present narrative review, the mechanisms leading to vesiculation in platelets and the pathophysiological processes implicated will be discussed. This will be followed by a summary of the present evidence concerning the effects of antiplatelet agents under experimental conditions and in clinical settings.

Engineered human platelet-derived microparticles as natural vectors for targeted drug delivery

Drug targeting has opened a new paradigm in therapeutics with development of delivery vectors like liposomes and polymeric nanoparticles. Although their clinical application is crippled by limited biological adaptability. Off-target toxicity and biocompatibility still remains one of the critical problems in anticancer therapeutics that can be life-threatening. Here we report a quick, simple and facile method of engineering human platelets to generate drug loaded platelet-derived microparticles (PMPs) by top-down approach, which are biocompatible and naturally target leukemia cells. Drug loaded PMPs and cancer cell uptake were characterized by flow cytometry, confocal microscopy, Nanoparticle Tracking Analysis and fluorimetry. Effective drug delivery was tested in cancer cell lines as well as in clinical samples from leukemia patients. We explored that PMPs are capable of carrying multiple drug payloads, have long shelf life and can be harvested in large quantity in short period. Importantly, PMPs exhibited remarkably higher toxicity towards cancer cells than free drug and had lower escape into extravascular spaces. Transfer of drug to cancer cells of leukemia patients was significantly higher than free drug, when delivered through PMPs. Our experiments validated therapeutic application of PMPs as biocompatible drug delivery vector against cancer cells with minimal off-target delivery.

Platelet-derived microparticles promote phagocytosis of oxidized low-density lipoprotein by macrophages, potentially enhancing foam cell formation

Background

The interaction between platelets and macrophages plays an important role in the development and progression of atherosclerosis (AS). This study aimed to investigate the role of platelet microparticles (PMPs) in the development of foam cells.

Methods

PMPs are generated by activating platelets with thrombin and separated by ultracentrifugation. The macrophages were treated with PMPs, the phagocytosis of oxidized low-density lipoprotein (Ox-LDL) and formation of foam cells were evaluated by flow cytometry and confocal microscopy, respectively, and the inflammatory factors cytokines in the supernatant were detected by ELISA.

Results

PMPs significantly increase the phagocytosis of Ox-LDL and elevated foam cell formation of macrophages. IL-1β content in the supernatant of macrophages peaked around 2-4 h and declined to normal level after 6-8 h; IL-6 content peaked at 4 h and then decreased to normal level. TNF-α content peaked at 2-4 h.

Conclusions

The microparticles from activated platelets can increase the phagocytosis of Ox-LDL and the production of inflammatory cytokines by macrophages, which is related to the development of AS.

Extraction and identification of platelet‑derived microparticles

Microparticles are carriers of signals for intracellular signal transduction. These carriers include proteins, mRNAs, microRNAs and other bioactive substances. Platelets are a major source of circulating microparticles, and microparticles are closely associated with the development of certain cardiovascular diseases. In the present study, a method for separating, extracting and identifying platelet‑derived microparticles was developed and differences in the expression of surface proteins on microparticles harvested from platelets stimulated by vortexing or treatment with thrombin was investigated. The counts, composition, sizes and inner structures of microparticles were determined using flow cytometry and transmission electron microscopy. Additionally, it was demonstrated that platelets could be readily activated, and a large quantity of microparticles with varying complex compositions, structures and sizes were derived from activated platelets. High purity platelet‑derived microparticles were obtained by gradient centrifugation. However, the microparticles derived from platelets stimulated by thrombin treatment or vortexing differed significantly in the levels of CD63. The present study aimed to provide improved options for the extraction and identification of microparticles.

Large Extracellular Vesicles: Have We Found the Holy Grail of Inflammation?

The terms microparticles (MPs) and microvesicles (MVs) refer to large extracellular vesicles (EVs) generated from a broad spectrum of cells upon its activation or death by apoptosis. The unique surface antigens of MPs/MVs allow for the identification of their cellular origin as well as its functional characterization. Two basic aspects of MP/MV functions in physiology and pathological conditions are widely considered. Firstly, it has become evident that large EVs have strong procoagulant properties. Secondly, experimental and clinical studies have shown that MPs/MVs play a crucial role in the pathophysiology of inflammation-associated disorders. A cardinal feature of these disorders is an enhanced generation of platelets-, endothelial-, and leukocyte-derived EVs. Nevertheless, anti-inflammatory effects of miscellaneous EV types have also been described, which provided important new insights into the large EV-inflammation axis. Advances in understanding the biology of MPs/MVs have led to the preparation of this review article aimed at discussing the association between large EVs and inflammation, depending on their cellular origin.

Microparticles as autoantigens in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a prototypic autoimmune disease characterized by the production of antibodies to components of the cell nucleus (antinuclear antibodies or ANAs) and the formation of immune complexes with nuclear antigens. These complexes can drive pathogenesis by depositing in the tissue to incite inflammation or induce cytokine production by cells of the innate immune system. While ANAs can bind to purified nuclear molecules, nuclear autoantigens in vivo most likely exist attached to other molecules or embedded in larger structures. Among these structures, microparticles (MPs) are membrane bound vesicles that are released from dead and dying cells by a blebbing process; MPs can also be released during activation of platelets. The presence of MPs in the blood or tissue culture media can be assayed by flow cytometry on the basis of light scattering as well as binding of marker antibodies to identify the cell of origin. As shown by biochemical analyses, MPs contain an ensemble of intracellular components including nuclear, cytoplasmic and membrane molecules. Because of the display of these molecules on the particle surface or in an otherwise accessible form, ANAs, including anti-DNA, can bind to particles. Levels of MPs are increased in the blood of patients with SLE, with flow cytometry demonstrating the presence of IgG-containing particles. In addition to forming immune complexes, MPs can directly stimulate immune responses. Together, these findings suggest an important role of particles in the pathogenesis of SLE and their utility as biomarkers.