Maternal extracellular vesicles and platelets promote preeclampsia via inflammasome activation in trophoblasts

microRNA-520c-3p suppresses NLRP3 inflammasome activation and inflammatory cascade in preeclampsia by downregulating NLRP3

BACKGROUND

The pathogenesis of preeclampsia (PE) is suggested to be a consequence of inflammation. Previously conducted investigations on nod-like receptor pyrin domain-containing 3 (NLRP3) have shed light to its crucial role in PE. Furthermore, microRNA-520c-3p (miR-520c-3p) is observed to be implicated in inflammation. Therefore, the current study aimed to explore the role of miR-520c-3p in inflammatory cascade of PE by targeting NLRP3.

METHODS

Microarray analyses were performed to screen differentially expressed genes associated with PE, and the potential relationship between miR-520c-3p and NLRP3 was analyzed. PE and normal placenta tissues were collected to determine the levels of inflammatory cytokines (IL-18, IL-33, IL-1β, IL-10, and TNF-α), miR-520c-3p and NLRP3. Hypoxic HTR8/SVneo cells were transfected with oe-NLRP3, si-NLRP3 or miR-520c-3p mimic to elucidate the functional role of NLRP3 or miR-520c-3p in the inflammatory cascade in PE, followed by the evaluation of levels of inflammatory cytokines and NLRP3 inflammasomes (NLRP3, ASC and caspase-1). Additionally, the HTR8/SVneo cell migration and invasion were evaluated.

RESULTS

An upregulation of NLRP3, IL-18, IL-1β and TNF-α, and downregulation of miR-520c-3p, IL-33 and IL-10 were observed in PE placenta tissues. NLRP3 was found to be a target gene of miR-520c-3p. HTR8/SVneo cells after hypoxia transfected with si-NLRP3 or miR-520c-3p mimic exhibited decreased levels of inflammatory cytokines and NLRP3 inflammasomes, in addition to increased IL-10 and IL-33 levels. Moreover, enhanced migration and invasion abilities were observed in cells transfected with si-NLRP3.

CONCLUSION

Collectively, miR-520c-3p could potentially inhibit NLRP3 inflammasome activation and inflammatory cascade in PE by downregulating NLRP3, highlighting the potential of miR-520c-3p as a therapeutic target for PE treatment.

Assessment of Time-Dependent Platelet Activation Using Extracellular Vesicles, CD62P Exposure, and Soluble Glycoprotein V Content of Platelet Concentrates with Two Different Platelet Additive Solutions

Novel analytical measures are needed to accurately monitor the properties of platelet concentrates (PCs). Since activated platelets produce platelet-derived extracellular vesicles (EVs), analyzing EVs of PCs may provide additional information about the condition of platelets. The prospect of using EVs as an auxiliary measure of platelet activation state was investigated by examining the effect of platelet additive solutions (PASs) on EV formation and platelet activation during PC storage. The time-dependent activation of platelets in PCs with PAS-B or with the further developed PAS-E was compared by measuring the exposure of CD62P by flow cytometry and the content of soluble glycoprotein V (sGPV) of PCs by an immunoassay. Changes in the concentration and size distribution of EVs were determined using nanoparticle tracking analysis. A time-dependent increase in platelet activation in PCs was demonstrated by increased CD62P ex-posure, sGPV content, and EV concentration. Using these strongly correlating parameters, PAS-B platelets were shown to be more activated compared to PAS-E platelets. Since the EV concentration correlated well with the established platelet activation markers CD62P and sGPV, it could potentially be used as a complementary parameter for platelet activation for PCs. More detailed characterization of the resulting EVs could help to understand how the PC components contribute the functional effects of transfused PCs.

Hydrogen peroxide-mediated oxidative stress induces inflammasome activation in term human placental explants

BACKGROUND

The placenta is a multifunctional organ that can suffer with imbalances between pro- and antioxidant molecules, contributing for inflammatory imbalance. The inflammation generated by oxidative stress may induce inflammasome activation, an essential complex for pro-inflammatory cytokine production.

OBJECTIVE

The aim of this study was to evaluate whether hydrogen peroxide (H₂O₂) mediated oxidative stress induces inflammasome activation on placental explants.

STUDY DESIGN

Tissue cultures of placental explants obtained from normotensive pregnant women were performed in different concentrations of H₂O₂. Gene expressions of NLRP3, caspase-1, IL-1β, TNF-α and IL-10 were evaluated by qPCR. Superoxide dismutase (SOD), catalase, Heat shock protein 70 (Hsp70), Caspase-1, TNF-α, IL-1β, IL-10 and human Chorionic Gonadotropin (hCG) were determined by ELISA.

RESULTS

Concentrations of catalase, Hsp70, hCG and SOD were higher in cultures with 100 and 1000 µM H₂O₂ compared to controls. Gene and protein expressions of TNF-α and IL-1β were elevated in cultures with 1000 μM H₂O₂ compared to controls. This concentration led to inflammasome activation, by increasing gene expressions of NLRP3, caspase-1 and IL-1β. In contrast, gene and protein expressions of IL-10 were reduced at 100 and 1000 μM H₂O₂. Protein expression of caspase-1 was higher in cultures of 100 μM H₂O₂ compared to controls. Treatment with Glybenclamide at 200 μM was used to prevent NLRP3 inflammasome activation. This concentration reduced protein expression of caspase-1 compared to culture with only H₂O₂ and control cultures.

CONCLUSIONS

Our results confirm that H₂O₂ induces oxidative stress on placental explants and demonstrate that cell responses to this stress involve inflammasome activation.

High-Mobility Group Box 1 From Hypoxic Trophoblasts Promotes Endothelial Microparticle Production and Thrombophilia in Preeclampsia

OBJECTIVE

Thrombophilia is a major complication in preeclampsia, a disease associated with placental hypoxia and trophoblast inflammation. Preeclampsia women are known to have increased circulating microparticles that are procoagulant, but the underlying mechanisms remain unclear. In this study, we sought to understand the mechanism connecting placental hypoxia, circulating microparticles, and thrombophilia.

APPROACH AND RESULTS

We analyzed protein markers on plasma microparticles from preeclampsia women and found that the increased circulating microparticles were mostly from endothelial cells. In proteomic studies, we identified HMGB1 (high-mobility group box 1), a proinflammatory protein, as a key factor from hypoxic trophoblasts in stimulating microparticle production in human umbilical vein endothelial cells. Immunodepletion or inhibition of HMGB1 in the conditioned medium from hypoxic human trophoblasts abolished the endothelial microparticle-stimulating activity. Conversely, recombinant HMGB1 stimulated microparticle production in cultured human umbilical vein endothelial cells. The microparticles from recombinant HMGB1-stimulated human umbilical vein endothelial cells promoted blood coagulation and neutrophil activation in vitro. Injection of recombinant HMGB1 in pregnant mice increased plasma endothelial microparticles and promoted blood coagulation. In preeclampsia women, elevated placental HMGB1 expression was detected and high levels of plasma HMGB1 correlated with increased plasma endothelial microparticles.

CONCLUSIONS

Our results indicate that placental hypoxia-induced HMGB1 expression and release from trophoblasts are important mechanism underlying increased circulating endothelial microparticles and thrombophilia in preeclampsia.

Extracellular Vesicles in Human Reproduction in Health and Disease

Extensive evidence suggests that the release of membrane-enclosed compartments, more commonly known as extracellular vesicles (EVs), is a potent newly identified mechanism of cell-to-cell communication both in normal physiology and in pathological conditions. This review presents evidence about the formation and release of different EVs, their definitive markers and cargo content in reproductive physiological processes, and their capacity to convey information between cells through the transfer of functional protein and genetic information to alter phenotype and function of recipient cells associated with reproductive biology. In the male reproductive tract, epididymosomes and prostasomes participate in regulating sperm motility activation, capacitation, and acrosome reaction. In the female reproductive tract, follicular fluid, oviduct/tube, and uterine cavity EVs are considered as vehicles to carry information during oocyte maturation, fertilization, and embryo-maternal crosstalk. EVs via their cargo might be also involved in the triggering, maintenance, and progression of reproductive- and obstetric-related pathologies such as endometriosis, polycystic ovarian syndrome, preeclampsia, gestational diabetes, and erectile dysfunction. In this review, we provide current knowledge on the present and future use of EVs not only as biomarkers, but also as therapeutic targeting agents, mainly as vectors for drug or compound delivery into target cells and tissues.

Placental inflammation in pre-eclampsia by Nod-like receptor protein (NLRP)3 inflammasome activation in trophoblasts

Pre-eclampsia is associated with increased levels of cholesterol and uric acid and an inflamed placenta expressing danger-sensing pattern recognition receptors (PRRs). Crystalline cholesterol and uric acid activate the PRR Nod-like receptor protein (NLRP)3 inflammasome to release interleukin (IL)-1β and result in vigorous inflammation. We aimed to characterize crystal-induced NLRP3 activation in placental inflammation and examine its role in pre-eclampsia. We confirmed that serum total cholesterol and uric acid were elevated in pre-eclamptic compared to healthy pregnancies and correlated positively to high sensitivity C-reactive protein (hsCRP) and the pre-eclampsia marker soluble fms-like tyrosine kinase-1 (sFlt-1). The NLRP3 inflammasome pathway components (NLRP3, caspase-1, IL-1β) and priming factors [complement component 5a (C5a) and terminal complement complex (TCC)] were co-expressed by the syncytiotrophoblast layer which covers the placental surface and interacts with maternal blood. The expression of IL-1β and TCC was increased significantly and C5a-positive regions in the syncytiotrophoblast layer appeared more frequent in pre-eclamptic compared to normal pregnancies. In-vitro activation of placental explants and trophoblasts confirmed NLRP3 inflammasome pathway functionality by complement-primed crystal-induced release of IL-1β. This study confirms crystal-induced NLRP3 inflammasome activation located at the syncytiotrophoblast layer as a mechanism of placental inflammation and suggests contribution of enhanced NLRP3 activation to the harmful placental inflammation in pre-eclampsia.

Pravastatin therapy during preeclampsia prevents long-term adverse health effects in mice

Preeclampsia (PE), associates with long-term increased risk for cardiovascular disease in women, suggesting that PE is not an isolated disease of pregnancy. It is not known if increased risk for long-term diseases is due to PE-specific factors or to prepregnancy renal and cardiovascular risk factors. We used a mouse model in which a WT female with normal prepregnancy health develops PE to investigate if preeclampsia causes long-term cardiovascular consequences after pregnancy for mothers and offspring. Mothers exhibited endothelial dysfunction and hypertension after PE and had glomerular injury that not only persisted but deteriorated, leading to fibrosis. Left ventricular (LV) remodeling characterized by increased collagen deposition and MMP-9 expression and enlarged cardiomyocytes were also detected after PE. Increased LV internal wall thickness and mass, increased end diastolic and end systolic volumes, and increased stroke volume were observed after PE in the mothers. Placenta-derived bioactive factors that modulate vascular function, markers of metabolic disease, vasoconstrictor isoprostane-8, and proinflammatory mediators were increased in sera during and after a preeclamptic pregnancy in the mother. Offspring of PE mice developed endothelial dysfunction, hypertension, and signs of metabolic disease. Microglia activation was increased in the neonatal brains after PE, suggesting neurogenic hypertension in offspring. Prevention of placental insufficiency with pravastatin prevented PE-associated cardiovascular complications in both mothers and offspring. In conclusion, factors that develop during PE have long-term, cardiovascular effects in the mother and offspring independent of prepregnancy risk factors.

Immune activation by nucleic acids: A role in pregnancy complications

Cell-free self-DNA or RNA may induce an immune response by activating specific sensing receptors. During pregnancy, placental nucleic acids present in the maternal circulation further activate these receptors due to the presence of unmethylated CpG islands. A higher concentration of cell-free foetal DNA is associated with pregnancy complications and a higher risk for foetal rejection. Cell-free foetal DNA originates from placental trophoblasts. It appears in different forms: free, bound to histones in nucleosomes, in neutrophil extracellular traps (NETs) and in extracellular vesicles (EVs). In several pregnancy complications, cell-free foetal DNA triggers the production of proinflammatory cytokines, and this production results in a cellular and humoral immune response. This review discusses preeclampsia, systemic lupus erythematosus, foetal growth restriction, gestational diabetes, rheumatoid arthritis and obesity in pregnancy from an immunological point of view and closely examines the different pathways that result in maternal inflammation. Understanding the role of cell-free nucleic acids, as well as the biogenesis of NETs and EVs, will help us to specify their functions or targets, which seem to be important in pregnancy complications. It is still not clear whether higher concentrations of cell-free nucleic acids in the maternal circulation are the cause or consequence of various complications. Therefore, further clinical studies and, even more importantly, animal experiments that focus on the involved immunological pathways are needed.

Extracellular vesicles and their immunomodulatory functions in pregnancy

Extracellular vesicles (EVs) are membrane-bound vesicles released into the extracellular space by almost all types of cells. EVs can cross the physiological barriers, and a variety of biological fluids are enriched in them. EVs are a heterogeneous population of vesicles, including exosomes, microvesicles, and apoptotic bodies. The different subpopulations of vesicles can be differentiated by size and origin, in which exosomes (~100 nm and from endocytic origin) are the most studied so far. EVs have essential roles in cell-to-cell communication and are critical modulators of immune response under normal and pathological conditions. Pregnancy is a unique situation of immune-modulation in which the maternal immune system protects the fetus from allogenic rejection and maintains the immunosurveillance. The placenta is a vital organ that performs a multitude of functions to support the pregnancy. The EVs derived from the human placenta have crucial roles in regulating the maternal immune response for successful pregnancy outcome. Placenta-derived vesicles perform a myriad of functions like suppression of immune reaction to the developing fetus and establishment and maintenance of a systemic inflammatory response to combat infectious intruders. A fine-tuning of these mechanisms is quintessential for successful completion of pregnancy and healthy outcome for mother and fetus. Dysregulation in the mechanisms mentioned above can lead to several pregnancy disorders. In this review, we summarize the current literature regarding the critical roles played by the EVs in immunomodulation during pregnancy with particular attention to the placenta-derived exosomes.

The impact of circulating preeclampsia-associated extracellular vesicles on the migratory activity and phenotype of THP-1 monocytic cells

Intercellular communication via extracellular vesicles (EVs) and their target cells, especially immune cells, results in functional and phenotype changes that consequently may play a significant role in various physiological states and the pathogenesis of immune-mediated disorders. Monocytes are the most prominent environment-sensing immune cells in circulation, skilled to shape their microenvironments via cytokine secretion and further differentiation. Both the circulating monocyte subset distribution and the blood plasma EV pattern are characteristic for preeclampsia, a pregnancy induced immune-mediated hypertensive disorder. We hypothesized that preeclampsia-associated EVs (PE-EVs) induced functional and phenotypic alterations of monocytes. First, we proved EV binding and uptake by THP-1 cells. Cellular origin and protein cargo of circulating PE-EVs were characterized by flow cytometry and mass spectrometry. An altered phagocytosis-associated molecular pattern was found on 12.5 K fraction of PE-EVs: an elevated CD47 "don't eat me" signal (p < 0.01) and decreased exofacial phosphatidylserine "eat-me" signal (p < 0.001) were found along with decreased uptake of these PE-EVs (p < 0.05). The 12.5 K fraction of PE-EVs induced significantly lower chemotaxis (p < 0.01) and cell motility but accelerated cell adhesion of THP-1 cells (p < 0.05). The 12.5 K fraction of PE-EVs induced altered monocyte functions suggest that circulating EVs may have a role in the pathogenesis of preeclampsia.

Increased circulating microparticles in women with preeclampsia

INTRODUCTION

Preeclampsia (PE) is associated with hypercoagulability, endothelial dysfunction and inflammation, which generate microparticles (MPs). Therefore, MPs may be important for PE.

METHODS

We established a verified MP measurement procedure to detect MPs in nonpregnant women (n = 25), healthy pregnant women (n = 29) and PE women (n = 73) and compared their MP levels.

RESULTS

Microparticles prepared from platelets (PMPs), endothelial cells (EMPs) and leucocytes (LMPs) were confirmed by transmission electron microscopy and were analysed by our established flow cytofluorimetric approach, which showed good specificity for determining the cell origin and level of MPs. The levels of total MPs (tMPs) and PMPs in the healthy pregnant group were significantly higher than those in the nonpregnant group (158.78 vs 93.00 and 45.04 vs 17.41, P = .004 and P = .007, respectively) but were not significantly different from those of the PE group. However, EMPs and LMPs were significantly higher in the PE group than in the healthy pregnant group (14.62 vs 11.48 and 8.94 vs 5.03, P = .015 and P < .001, respectively). Furthermore, the area under the receiver operating characteristic curves (AUC) for EMPs, LMPs and the combined sum of EMPs and LMPs were 0.661, 0.746 and 0.718, respectively (P < . 05); at their optimal cut-off values, the sensitivities were 50.68%, 87.67% and 46.58%, respectively, and the specificities were 80.77%, 58.33% and 95.65%, respectively.

CONCLUSION

Determining the MP level, especially that of EMPs and LMPs, by a specificity-verified method may reflect the endothelial dysfunction and inflammation involved in PE pathogenesis.

Thrombocytopenia in pregnancy

Thrombocytopenia develops in 5% to 10% of women during pregnancy or in the immediate postpartum period. A low platelet count is often an incidental feature, but it might also provide a biomarker of a coexisting systemic or gestational disorder and a potential reason for a maternal intervention or treatment that might pose harm to the fetus. This chapter reflects our approach to these issues with an emphasis on advances made over the past 5 to 10 years in understanding and managing the more common causes of thrombocytopenia in pregnancy. Recent trends in the management of immune thrombocytopenia translate into more women contemplating pregnancy while on treatment with thrombopoietin receptor agonists, rituximab, or mycophenylate, which pose known or unknown risks to the fetus. New criteria to diagnose preeclampsia, judicious reliance on measurement of ADAMTS13 to make management decisions in suspected thrombotic thrombocytopenic purpura, new evidence supporting the efficacy and safety of anticomplement therapy for atypical hemolytic uremic syndrome during pregnancy, and implications of thrombotic microangiopathies for subsequent pregnancies are evolving rapidly. The goals of the chapter are to help the hematology consultant work through the differential diagnosis of thrombocytopenia in pregnancy based on trimester of presentation, severity of thrombocytopenia, and coincident clinical and laboratory manifestations, and to provide guidance for dealing with some of the more common and difficult diagnostic and management decisions.

Thrombocytopenia in pregnancy

Thrombocytopenia develops in 5% to 10% of women during pregnancy or in the immediate postpartum period. A low platelet count is often an incidental feature, but it might also provide a biomarker of a coexisting systemic or gestational disorder and a potential reason for a maternal intervention or treatment that might pose harm to the fetus. This chapter reflects our approach to these issues with an emphasis on advances made over the past 5 to 10 years in understanding and managing the more common causes of thrombocytopenia in pregnancy. Recent trends in the management of immune thrombocytopenia translate into more women contemplating pregnancy while on treatment with thrombopoietin receptor agonists, rituximab, or mycophenylate, which pose known or unknown risks to the fetus. New criteria to diagnose preeclampsia, judicious reliance on measurement of ADAMTS13 to make management decisions in suspected thrombotic thrombocytopenic purpura, new evidence supporting the efficacy and safety of anticomplement therapy for atypical hemolytic uremic syndrome during pregnancy, and implications of thrombotic microangiopathies for subsequent pregnancies are evolving rapidly. The goals of the chapter are to help the hematology consultant work through the differential diagnosis of thrombocytopenia in pregnancy based on trimester of presentation, severity of thrombocytopenia, and coincident clinical and laboratory manifestations, and to provide guidance for dealing with some of the more common and difficult diagnostic and management decisions.

Advanced glycation end products regulate interleukin-1β production in human placenta

Maternal obesity is a major risk factor for pregnancy complications, causing inflammatory cytokine release in the placenta, including interleukin-1β (IL-1β), IL-6, and IL-8. Pregnant women with obesity develop accelerated systemic and placental inflammation with elevated circulating advanced glycation end products (AGEs). IL-1β is a pivotal inflammatory cytokine associated with obesity and pregnancy complications, and its production is regulated by NLR family pyrin domain-containing 3 (NLRP3) inflammasomes. Here, we investigated whether AGEs are involved in the activation of NLRP3 inflammasomes using human placental tissues and placental cell line. In human placental tissue cultures, AGEs significantly increased IL-1β secretion, as well as IL-1β and NLRP3 mRNA expression. In human placental cell culture, although AGE treatment did not stimulate IL-1β secretion, AGEs significantly increased IL-1β mRNA expression and intracellular IL-1β production. After pre-incubation with AGEs, nano-silica treatment (well known as an inflammasome activator) increased IL-1β secretion in placental cells. However, after pre-incubation with lipopolysaccharide to produce pro-IL-1β, AGE treatment did not affect IL-1β secretion in placental cells. These findings suggest that AGEs stimulate pro-IL-1β production within placental cells, but do not activate inflammasomes to stimulate IL-1β secretion. Furthermore, using pharmacological inhibitors, we demonstrated that AGE-induced inflammatory cytokines are dependent on MAPK/NF-κB/AP-1 signaling and reactive oxygen species production in placental cells. In conclusion, AGEs regulate pro-IL-1β production and inflammatory responses, resulting in the activation of NLRP3 inflammasomes in human placenta. These results suggest that AGEs, as an endogenous and sterile danger signal, may contribute to chronic placental cytokine production.

Comparative proteomic analysis of trophoblast cell models reveals their differential phenotypes, potential uses, and limitations

Trophoblastic cell lines are widely used in in vitro studies of placental function as a surrogate for primary trophoblasts. To date, no reference proteomics dataset exists to directly compare the shared and unique characteristics of these cells. Here, we performed comparative proteomic profiling of the BeWo and HTR8/SVneo cell lines using label-free quantitative MS. A total of 1557 proteins were identified, which included 338 uniquely attributed to BeWo cells, and a further 304 specifically identified in HTR8/SVneo cells. Raw data are available via ProteomeXchange, identifier PDX005045. Of the 915 proteins expressed by both cell lines, 105 were of higher abundance in BeWo cells, while 199 proteins had a significantly higher expression in HTR8/SVneo cells. Comparative GO of unique and upregulated proteins revealed principal differences in cell junction/adhesion, catenin complex, spindle and microtubule associated complex, as well as cell differentiation. Our data indicate that BeWo cells express an epithelial proteome more characteristic of villous trophoblasts, whereas HTR8/SVneo cells embrace a mesenchymal phenotype, more characteristic of extravillous trophoblasts. This novel comparative proteomic profiling of these trophoblastic cell lines provides a useful platform for future investigations of placental function.

Placental hemostasis and sterile inflammation: New insights into gestational vascular disease

Activation of the coagulation and inflammatory systems are physiologically occurring during pregnancy. However, excess activation of either system is well documented in gestational vascular diseases (GVD). GVD are placenta-mediated pregnancy complications and a major cause of feto-maternal morbidity and mortality. The causal relevance of excess coagulation and inflammatory responses for GVD remains largely unknown. Deciphering the causal relationship of excess coagulation and inflammation in GVD may allow conceptualizing new therapeutic approaches to combat GVD. Platelet activation and procoagulant extracellular vesicles (EVs) provide a link between coagulation and inflammation and their activation or generation in GVD is well established. As recently shown EVs cause sterile placental inflammation by activating maternal platelets that release ATP and activate purinergic receptor signaling and NLRP3 inflammasome in the embryonic trophoblast. This thrombo-inflammatory mechanism suggests a novel link between coagulation activation and sterile inflammation in GVD. These findings highlight a role of anti-platelet therapies in GVD. In addition, targeting the inflammasome alone or in combination with platelet inhibition may provide a new therapeutic strategy in GVD.

Impact of haemostatic mechanisms on pathophysiology of preeclampsia

Preeclampsia (PE) is disorder of new onset hypertension and proteinuria during the second half of pregnancy. There is increasing evidence to implicate placental over-expression of tissue factor and PAR-1 in the pathophysiology of PE. Excessive activation of platelets, neutrophils and the complement system may also contribute to the placental pathology and maternal endothelial responsible for the symptoms of PE. Increased knowledge in this field may identify new therapeutic strategies for the treatment of PE.

Review: Eicosanoids in preterm labor and delivery: Potential roles of exosomes in eicosanoid functions

Preterm delivery is a major obstetric health problem contributing to poor neonatal outcome including low birth weight, respiratory distress syndrome, gastrointestinal, immunologic, central nervous system, hearing, and vision problems. Worldwide, approximately 15 million babies are born prematurely each year. The critical question which remains is how to identify women destined to deliver preterm from those who will achieve a term delivery. Prostaglandins, in all mammals, are important in the parturient process. Increased intrauterine prostaglandin production is associated with labor and in fact prostaglandin E₂ (PGE₂) or analogs are widely used clinically for cervical ripening and labor induction. Measurements of circulating eicosanoids have been problematic because of the rapid and major clearance by the lungs and then kidneys resulting in very low concentrations in plasma. Moreover, since eicosanoids are produced by all mammalian tissues, the sources of the measured eicosanoids are unknown. Our understanding of how cells communicate has undergone a paradigm shift with the recognition of the role of exosomes in intercellular signaling. Recent publications have identified enzymes and products of arachidonic acid metabolism (eicosanoids) within exosomes. This review will explore the potential roles of exosomes in eicosanoid functions that are critical in preterm labor and delivery.