Microparticles: biomarkers and beyond. Clin Sci (Lond). 2013;124:423-441. [PMID: 23249271 DOI: 10.1042/cs20120309]

Urinary podocyte microparticles identify prealbuminuric diabetic glomerular injury

Microparticles (MPs) are small (0.1-1.0 µm) vesicles shed from the surface of cells in response to stress. Whether podocytes produce MPs and whether this production reflects glomerular injury are unclear. We examined MP formation in cultured human podocytes (hPODs) and diabetic mice. hPODs were exposed to cyclical stretch, high glucose (HG; 25 mM), angiotensin II, or TGF-β. Urinary podocyte MPs were assessed in three mouse models of diabetic nephropathy: streptozotocin (STZ)-treated, OVE26, and Akita mice. Cyclic stretch and HG increased MP release as assessed by flow cytometry (P<0.01 and P<0.05, respectively, versus controls). Inhibition of Rho-kinase (ROCK) with fasudil blocked HG-induced podocyte MP formation. STZ-treated (8 weeks) mice exhibited increased urinary podocyte MPs compared with age-matched nondiabetic mice. Similarly, 16-week-old OVE26 mice had elevated levels of urinary podocyte MPs compared with wild-type littermates (P<0.01). In 1 week post-STZ-treated and 6- and 12-week-old Akita mice, urinary podocyte MPs increased significantly compared with those MPs in nondiabetic mice, despite normal urinary albumin levels. Our results indicate that podocytes produce MPs that are released into urine. Podocyte-derived MPs are generated by exposure to mechanical stretch and high glucose in vitro and could represent early markers of glomerular injury in diabetic nephropathy.

Production, fate and pathogenicity of plasma microparticles in murine cerebral malaria

In patients with cerebral malaria (CM), higher levels of cell-specific microparticles (MP) correlate with the presence of neurological symptoms. MP are submicron plasma membrane-derived vesicles that express antigens of their cell of origin and phosphatidylserine (PS) on their surface, facilitating their role in coagulation, inflammation and cell adhesion. In this study, the in vivo production, fate and pathogenicity of cell-specific MP during Plasmodium berghei infection of mice were evaluated. Using annexin V, a PS ligand, and flow cytometry, analysis of platelet-free plasma from infected mice with cerebral involvement showed a peak of MP levels at the time of the neurological onset. Phenotypic analyses showed that MP from infected mice were predominantly of platelet, endothelial and erythrocytic origins. To determine the in vivo fate of MP, we adoptively transferred fluorescently labelled MP from mice with CM into healthy or infected recipient mice. MP were quickly cleared following intravenous injection, but microscopic examination revealed arrested MP lining the endothelium of brain vessels of infected, but not healthy, recipient mice. To determine the pathogenicity of MP, we transferred MP from activated endothelial cells into healthy recipient mice and this induced CM-like brain and lung pathology. This study supports a pathogenic role for MP in the aggravation of the neurological lesion and suggests a causal relationship between MP and the development of CM.

Cerebral malaria (CM) is a potentially fatal neurological syndrome characterised by unrousable coma. Since the detection of high levels of plasma microparticles (MP) in patients with CM, it has been demonstrated that inhibition of MP production confers protection from murine CM. However, the precise mechanisms of action of these MP during CM have not been completely deciphered. In this study, we used experimental models of CM to measure the production and origins of MP over the course of infection. We found low baseline circulating MP in healthy mice and these were subsequently raised at the time of the neurological syndrome. Phenotypic analyses showed that circulating MP were predominantly from activated host cells that have previously been established to participate in CM pathogenesis. We show for the first time transferred MP impairing endothelial integrity and inducing CM-like pathology in the brain and lung of healthy animals. Our study dissects what tissues these MP localise to exert their effects, as little is known about their fate following the initial release. These data suggest a causal relationship between MP and the development of CM and also warrant further investigation into the representation of MP as a marker of CM risk.

Smoking alters circulating plasma microvesicle pattern and microRNA signatures

Circulating plasma microvesicles (PMVs) and their microRNA content are involved in the development of atherosclerosis and could serve as biomarkers for cardiovascular disease (CVD) progression. However, little is known on how smoking influences the levels of PMVs and microRNA signatures in vivo. Therefore, we aimed to investigate the effects of smoking on circulating PMV levels and CVD-related PMV-derived microRNAs in young, healthy smokers. Twenty young (10 female, 10 male; 25 ± 4 years) healthy smokers (16 ± 6 cigarettes per day for 8 ± 4 years) and age- and sex-matched controls were included in this study. While complete blood count revealed no differences between both groups, smoking significantly enhanced intracellular reactive oxygen species in platelets and leukocytes as well as platelet-leukocyte aggregate formation. Total circulating PMV counts were significantly reduced in smokers, which could be attributed to decreased platelet-derived PMVs. While the number of endothelial PMVs remained unaffected, smoking propagated circulating leukocyte-derived PMVs. Despite reduced total PMVs, PMV-derived microRNA-profiling of six smoker/control pairs revealed a decrease of only a single microRNA, the major platelet-derived microRNA miR-223. Conversely, miR-29b, a microRNA associated with aortic aneurysm and fibrosis, and RNU6-2, a commonly used reference-RNA, were significantly up-regulated. Smoking leads to alterations in the circulating PMV profile and changes in the PMV-derived microRNA signature already in young, healthy adults. These changes may contribute to the development of smoking-related cardiovascular pathologies. Moreover, these smoking-related changes have to be considered when microRNA or PMV profiles are used as disease-specific biomarkers.

Circulating levels of cell-derived microparticles are reduced by mild hypobaric hypoxia: data from a randomised controlled trial

PURPOSE

Hypoxia is known to induce the release of microparticles in vitro. However, few publications have addressed the role of hypoxia in vivo on circulating levels of microparticles. This randomised, controlled, crossover trial aimed to determine the effect of mild hypoxia on in vivo levels of circulating microparticles in healthy individuals.

METHODS

Blood was obtained from 51 healthy male volunteers (mean age of 26.9 years) at baseline altitude (490 m) and after 24 and 48 h at moderate altitude (2,590 m). The order of altitude exposure was randomised. Flow cytometry was used to assess platelet-poor plasma for levels of circulating microparticles derived from platelets, endothelial cells, leucocytes, granulocytes, monocytes, red blood cells and procoagulant microparticles.

RESULTS

Mean (standard deviation) oxygen saturation was significantly lower on the first and second day after arrival at 2,590 m, 91.0 (2.0) and 92.0 (2.0) %, respectively, compared to 490 m, 96 (1.0) %, p < 0.001 for both comparisons. A significant decrease in the levels of procoagulant microparticles (annexin V+ -221/μl 95 % CI -370.8/-119.0, lactadherin+ -202/μl 95 % CI -372.2/-93.1), platelet-derived microparticles (-114/μl 95 % CI -189.9/-51.0) and red blood cell-derived microparticles (-81.4 μl 95 % CI -109.9/-57.7) after 48 h at moderate altitude was found. Microparticles derived from endothelial cells, granulocytes, monocytes and leucocytes were not significantly altered by exposure to moderate altitude.

CONCLUSIONS

In healthy male individuals, mild hypobaric hypoxia, induced by a short-term stay at moderate altitude, is associated with lower levels of procoagulant microparticles, platelet-derived microparticles and red blood cell-derived microparticles, suggesting a reduction in thrombotic potential.

Therapeutic drug-induced platelet apoptosis: an overlooked issue in pharmacotoxicology

The surfacing of the applied fields of biology such as, biotechnology, pharmacology and drug discovery was a boon to the modern man. However, it had its share of disadvantages too. The indiscriminate use of antibiotics and other biological drugs resulted in numerous adverse reactions including thrombocytopenia. One of the reasons for drug-induced thrombocytopenia could be attributed to an enhanced rate of platelet apoptosis, which is a less investigated aspect. The present essay sheds light on the adverse (pro-apoptotic) effects of some of the commonly used drugs and antibiotics on platelets viz. cisplatin, aspirin, vancomycin and balhimycin. Furthermore, the undesirable reactions resulting from chemotherapy could be attributed at least to some extent to the systemic stress induced by microparticles, which in turn are the byproducts of platelet apoptosis. Thereby, the essay aims to highlight the challenges in the emerging trend of cross-disciplinary implications, i.e., drug-induced platelet apoptosis, which is a nascent field. Thus, the different mechanisms through which drugs induce platelet apoptosis are discussed, which also opens up a new perspective through which the adverse effects of commonly used drugs could be dealt. The drug-associated platelet toxicity is of grave concern and demands immediate attention. Besides, it would also be appealing to examine the platelet pro-apoptotic effects of other commonly used therapeutic drugs.

Evaluation of plasma endothelial microparticles in pre-eclampsia

Objective

To compare the antepartum and postpartum plasma concentrations of endothelial microparticles (EMPs) in patients with pre-eclampsia with those of healthy control subjects with normal pregnancies.

Methods

Plasma concentrations of EMPs were measured using specific antibody labelling and flow cytometry prior to delivery by caesarean section (antepartum), and again at 24 h and 72 h postpartum. The correlations between EMP concentration and mean arterial pressure (MAP), and between EMP concentration and 24-h urine protein were analysed.

Results

A total of 59 patients with pre-eclampsia and 60 healthy control subjects participated in the study. The antepartum plasma EMP concentration was significantly higher in patients with pre-eclampsia than in healthy control subjects with normal pregnancies (2863.5 ± 1543.1 versus 1703.0 ± 592.2 EMPs/ml, respectively); similar findings were observed at 24 h postpartum (1836.7 ± 1153.8 versus 1421.8 ± 760.2 EMPs/ml, respectively). There was no significant difference between the two groups at 72 h postpartum. The antepartum plasma EMP concentration in patients with pre-eclampsia demonstrated a significant positive correlation with MAP ( r = 0.716) and with 24-h urine protein ( r = 0.770).

Conclusion

Plasma EMP concentration might serve as a biomarker to evaluate the severity of pre-eclampsia in the future.

Using annexin V-coated magnetic beads to capture active tissue factor-bearing microparticles from body fluids

Microparticles, found in all body fluids including peripheral blood, are important elements that regulate cellular interactions under both physiological and pathological conditions. They play an important role in blood clot formation and increased cell aggregation. However, little is known about the components of the microparticles and their mechanism of action. A method to quantify and assess the underlying mechanism of action of microparticles in pathologies is therefore desirable. We present a specific method to isolate cell-derived microparticles from malignant effusions using annexin V-coated magnetic microbeads. The microparticles can be detected by flow cytometry. Our results show that the microparticles can be isolated with >80% specificity when bound to annexin V-coated magnetic beads, which was originally developed for the detection of apoptotic cells. We also show that the isolated microparticles were still functionally active and can be used for further analysis. Thus, our method enables isolation as well as structural and functional characterisation of the microparticles which are produced in numerous patho-physiological situations. This should help gain a deeper insight into various disease situations, which in turn should pave the way for the development of novel drugs and specific therapy strategies.

Pancreatic cancer diagnosis by free and exosomal miRNA

Patients with pancreatic adenocarcinoma (PaCa) have a dismal prognosis. This is in part due to late diagnosis prohibiting surgical intervention, which provides the only curative option as PaCa are mostly chemo- and radiation resistance. Hope is raised on a reliable non-invasive/minimally invasive diagnosis that is still missing. Recently two diagnostic options are discussed, serum MicroRNA (miRNA) and serum exosomes. Serum miRNA can be free or vesicle-, particularly, exosomes-enclosed. This review will provide an overview on the current state of the diagnostic trials on free serum miRNA and proceed with an introduction of exosomes that use as a diagnostic tool in serum and other body fluids has not received sufficient attention, although serum exosome miRNA in combination with protein marker expression likely will increase the diagnostic and prognostic power. By their crosstalk with host cells, which includes binding-initiated signal transduction, as well as reprogramming target cells via the transfer of proteins, mRNA and miRNA exosomes are suggested to become a most powerful therapeutics. I will discuss which hurdles have still to be taken as well as the different modalities, which can be envisaged to make therapeutic use of exosomes. PaCa are known to most intensely crosstalk with the host as apparent by desmoplasia and frequent paraneoplastic syndromes. Thus, there is hope that the therapeutic application of exosomes brings about a major breakthrough.

Effects of endothelial progenitor cell-derived microvesicles on hypoxia/reoxygenation-induced endothelial dysfunction and apoptosis

Oxidative stress-induced endothelial dysfunction plays a key role in ischemia/reperfusion injury. Recent evidence indicates that endothelial progenitor cell-derived microvesicles (EPC-MVs) can promote angiogenesis of endothelial cells (ECs). Here, we investigated the potential effects of EPC-MVs on hypoxia/reoxygenation (H/R) injury in human brain microvascular ECs (hb-ECs). MVs were prepared from EPCs cultured in a serum deprivation (SD) medium (starving stress, sEPC-MVs) or SD medium containing tumor necrosis factor-α (TNFα) (apoptotic stress, aEPC-MVs). H/R injury model of hb-ECs was produced by 6 hr hypoxia (1% O₂) and 24 hr reoxygenation. The H/R hb-ECs were co-cultured with EPC-MVs. Results showed that (1) H/R hb-ECs were dysfunctional and coupled with increased apoptosis and ROS overproduction; (2) under two different conditions, EPCs displayed remarkable difference in caspase 3 and miR126 expression, which were carried by the corresponsive EPC-MVs; (3) functionally, sEPC-MVs had beneficial effects on H/R hb-ECs, whereas aEPC-MVs had detrimental effects; (4) the diverse effects of sEPC-MVs and aEPC-MVs were associated with the changes in miR126 and eNOS expression and were abolished by PI3K inhibitor. In conclusion, sEPCs-MVs and aEPC-MVs are functionally different on hb-EC apoptosis and dysfunction via their carried RNAs associated with ROS production and PI3K/eNOS/NO pathway.

Circulating CD45+/CD3+ lymphocyte-derived microparticles map lipid-rich atherosclerotic plaques in familial hypercholesterolaemia patients

Circulating microparticles (cMPs) seem to play important roles in vascular function. Beyond markers of activated cells, cMPs may have potential paracrine functions and influence atherosclerosis. Here, our objective was to characterise a) the abundance and phenotype of cMPs in stable statin-treated heterozygous familial hypercholesterolaemia (FH) patients exposed to life-long hypercholesterolaemia and b) the principal phenotype associated to lipid-rich atherosclerotic plaques in hFH-patients with significant atherosclerotic plaque burden. An age/gender/treatment-matched group of adult-onset non-FH hypercholesterolaemic patients (n=37/group) was comparatively analysed. cMPs were characterised by flow cytometry using annexin-V and cell surface-specific antibodies. Our study shows that LLT-FH patients had higher overall cMP-numbers (p<0.005) than LLT-non-FH patients. Endothelial cell-shed cMPs were also significantly higherin FH (p<0.0005). Within the leukocyte-derived cMP-subpopulations, FH-patients had significantly higher lymphocyte- and monocyte-derived cMP-numbers as well as cMPs carrying leukocyte-activation markers. Normalisation of cMPs by LDL levels did not affect cMP number or phenotype, indicating that the proinflammatory effect was derived from chronic vascular damage. Levels of AV+-total, CD45+-pan-leukocyte and CD45+/CD3+-lymphocyte-derived cMPs were significantly higher in FH-patients with subclinical lipid-rich atherosclerotic plaques than fibrous plaques. Levels of CD45+/CD3+-lymphocyte-MPs above 20,000/ml could differentiate between FH-patients with lipidic or non-lipidic plaques (area under the ROC curve of 0.803, 95%CI: 0.641-0.965, p=0.008). In summary, in this snapshot cross-sectional study cMP concentration and phenotype in FH differed markedly from non-FH hypercholesterolaemia. Patients with life-long high LDL exposure have higher endothelial activation and higher proinflammatory profile, even under current state-of-the-art LLT. cMPs carrying lymphocyte-epitopes appear as markers of lipid-rich atherosclerotic plaques in FH.

Exocrine cell-derived microparticles in response to lipopolysaccharide promote endocrine dysfunction in cystic fibrosis

BACKGROUND

Diabetes in cystic fibrosis (CF) is a result of exocrine pancreas alteration followed by endocrine dysfunction at a later stage. Microparticles (MPs) are plasma membrane fragments shed from stimulated or damaged cells that act as cellular effectors. Our aim was to identify a new form of interaction between exocrine and endocrine pancreatic cells mediated by exocrine MPs, in the context of recurrent infection in CF.

METHODS

MPs from either human exocrine CFTRΔF508-mutated (CFPAC-1) cells or exocrine normal pancreatic (PANC-1) cells were collected after treatment by LPS from Pseudomonas aeruginosa and applied to rat endocrine normal insulin-secreting RIN-m5F cells. MP membrane integration in target cells was established by confocal microscopy and flow cytometry using PKH26 lipid probe. Apoptosis, lysosomal activity, insulin secretion were measured after 18 h. MP-mediated NF-κB activation was measured in HEK-Blue reporter cells by SEAP reporter gene system and in RIN-m5F cells by Western blot. In endocrine normal cells, CFTR inhibition was achieved using Inhibitor-172.

RESULTS

Compared to PANC-1, MPs from CFPAC-1 significantly reduced insulin secretion and lysosomal activity in RIN-m5F. MPs induced NF-κB activation by increasing the level of IκB phosphorylation. Moreover, the inhibition of NF-κB activation using specific inhibitors was associated with a restored insulin secretion. Interestingly, CFTR inhibition in normal RIN-m5F cells promoted apoptosis and decreased insulin secretion.

CONCLUSIONS

During recurrent infections associated with CF, exocrine MPs may contribute to endocrine cell dysfunction via NF-κB pathways. Membrane CFTR dysfunction is associated with decreased insulin secretion.

Melatonin elevates apoptosis in human platelets via ROS mediated mitochondrial damage

Melatonin is a pineal hormone that regulates circadian and seasonal rhythms. The chronobiotic role of melatonin corresponds with a repertoire of pharmacological properties. Besides, it has a wide range of therapeutic applications. However, recent studies have demonstrated its direct interaction with platelets: at physiological concentration it promotes platelet aggregation; on the other hand, at pharmacological doses it raises intracellular Ca(2+) leading to platelet activation, thrombus formation and cardiovascular disorders. In order to further probe its effects on platelets, the current study targeted platelet apoptosis and melatonin was found to stimulate apoptosis. The mitochondrial pathway of apoptosis was mainly investigated because of its susceptibility to oxidative stress-inducing factors including therapeutic and dietary elements. Melatonin significantly increased the generation of intracellular ROS and Ca(2+), facilitating mitochondrial membrane depolarization, cytochrome c release, caspase activation, protein phosphorylation and phosphatidylserine externalization. Further, the overall toxicity of melatonin on platelets was confirmed by MTT and lactate dehydrogenase assays. The elevated rate of platelet apoptosis has far reaching consequences including thrombocytopenia. Besides, platelets undergoing apoptosis release microparticles, which fuel thrombus formation and play a significant role in the pathophysiology of a number of diseases. In many parts of the world melatonin is an over-the-counter dietary supplement and alternative medicine. Since, melatonin displays platelet proapoptotic effect at a concentration attainable through therapeutic dosage, the present study sends a warning signal to the chronic use of melatonin as a therapeutic drug and questions its availability without a medical prescription.

A glimpse of the glomerular milieu: from endothelial cell to thrombotic disease in nephrotic syndrome

Patients with nephrotic syndrome (NS) carry a high risk of venous thromboembolism (VTE) due to the abnormalities in coagulation and fibrinolysis. Although massive urine protein loss is considered to trigger the cascade of hypercoagulation, the exact nature of VTE in NS patients still remains obscure, especially in some cases when VTE occurs far before the presence of nephrotic proteinuria. Recent findings illustrate that loss of local glomerular homeostasis, like disturbance of cytokine profiles in endothelial cells or aberrant cellular crosstalks in glomerulus, is sufficient to initiate the development of thrombotic disease in glomerulonephropathy. Emerging data have highlighted the glomerular endothelial cell as a key regulator of local homeostasis, which might mediate the haemostatic derangement in the beginning of glomerular disease by expression of numerous prothrombotic factors and result in the subsequent predilection of VTE in NS. As the glomerulus-derived circulating factors are all collected and flushed into the renal vein directly, it is reasonable to suggest that increased release of glomerulus-derived thrombotic regulators, particularly from endothelial cells, may play a significant role in the highest proclivity for the renal vein as the site of thrombosis in NS. In this review, we thus discuss the current understandings of thromboembolism in NS with focus on how the glomerular endothelial cell involves in the pathogenesis of VTE, which may help to increase our understandings in the anti-thrombotic therapy for patients with NS.