Effect of the DASH diet on the sodium-chloride cotransporter and aquaporin-2 in urinary extracellular vesicles

The Dietary Approach to Stop Hypertension (DASH) diet, with its low sodium and high potassium content, acts like a diuretic by reducing sodium reabsorption in the kidney's distal convoluted tubule but without the side effects. Previous studies based on animal models didn't explore changes in human ion channel proteins. Recent insights into urinary extracellular vesicles (uEVs) suggest they reflect kidney tissue and physiological modifications. In our inpatient study, we shifted hypertensive volunteers from an American diet to the DASH diet, examining changes in those with stage 1 untreated hypertension. We analyzed a large range of pure uEVs, from small to large, in urine samples from nine volunteers over three time points. Mass spectrometry of these uEVs identified 1,800 proteins, revealing an increase in SCL12A3 (NCC) and a decrease in aquaporin 2 (AQP2). Immunoblotting showed an increase in activated (phosphorylated) NCC ratio to total NCC and a decrease in AQP2 from day 5 to 11, indicating the DASH diet induces measurable kidney responses via uEV protein abundance changes. This non-invasive method offers new insights into the diet's renal mechanism. Future studies should confirm these findings in a larger cohort, clarify the drivers behind NCC and AQP2 changes, their impact on hypertension, and investigate if uEVs also act as a waste pathway for inactive proteins, expanding our understanding of dietary effects on kidney physiology.

Extracellular Vesicles in Metabolic and Vascular Insulin Resistance

BACKGROUND

Insulin resistance is a major etiological factor in obesity, type 2 diabetes, and cardiovascular disease (CVD). Endothelial dysfunction may precede impairments in insulin-stimulated glucose uptake, thereby making it a key feature in development of CVD. However, the mechanism by which vascular tissue becomes dysfunctional is not clear.

SUMMARY

Extracellular vesicles (EVs) have emerged as potential mediators of insulin resistance and vascular dysfunction. EVs are membrane-bound particles released by tissues following cellular stress or activation. They carry "cargo" (e.g., insulin signaling proteins, eNOS-nitric oxide, and miRNA) that are believed to promote inter-cellular and interorgan communications. Herein, we review the underlying physiology of EVs in relation to type 2 diabetes and CVD risk. Specifically, we discuss how EVs may modulate metabolic (e.g., skeletal muscle, liver, and adipose) insulin sensitivity, and propose that EVs may modulate vascular insulin action to influence both endothelial function and arterial stiffness. We lastly identify how EVs may play a unique role following exercise to promote metabolic and vascular insulin sensitivity changes.

KEY MESSAGE

Gaining insight toward insulin-mediated EV mechanism has potential to identify novel pathways regulating cardiometabolic health and provide foundation for examining EVs as unique biomarkers and targets to prevent and/or treat chronic diseases.

Minimal information for studies of extracellular vesicles (MISEV2023): From basic to advanced approaches

Extracellular vesicles (EVs), through their complex cargo, can reflect the state of their cell of origin and change the functions and phenotypes of other cells. These features indicate strong biomarker and therapeutic potential and have generated broad interest, as evidenced by the steady year-on-year increase in the numbers of scientific publications about EVs. Important advances have been made in EV metrology and in understanding and applying EV biology. However, hurdles remain to realising the potential of EVs in domains ranging from basic biology to clinical applications due to challenges in EV nomenclature, separation from non-vesicular extracellular particles, characterisation and functional studies. To address the challenges and opportunities in this rapidly evolving field, the International Society for Extracellular Vesicles (ISEV) updates its 'Minimal Information for Studies of Extracellular Vesicles', which was first published in 2014 and then in 2018 as MISEV2014 and MISEV2018, respectively. The goal of the current document, MISEV2023, is to provide researchers with an updated snapshot of available approaches and their advantages and limitations for production, separation and characterisation of EVs from multiple sources, including cell culture, body fluids and solid tissues. In addition to presenting the latest state of the art in basic principles of EV research, this document also covers advanced techniques and approaches that are currently expanding the boundaries of the field. MISEV2023 also includes new sections on EV release and uptake and a brief discussion of in vivo approaches to study EVs. Compiling feedback from ISEV expert task forces and more than 1000 researchers, this document conveys the current state of EV research to facilitate robust scientific discoveries and move the field forward even more rapidly.

Acute exercise decreases insulin-stimulated extracellular vesicles in conjunction with augmentation index in adults with obesity

Extracellular vesicles (EVs) are often elevated in obesity and may modulate disease risk. Although acute exercise reduces fasting EVs in adults with obesity, no data exist on insulin-mediated EV responses. This study evaluated the effects of exercise on EV responses to insulin in relation to vascular function. Ten (5M/5F) sedentary adults with obesity (34.3 ± 3.7 kg/m2 ) completed an evening control and acute exercise condition (70%V ̇ O 2 max ${\dot{V}_{{{\rm{O}}_{\rm{2}}}{\rm{max}}}}$ to expend 400 kcal). Following an overnight fast, participants underwent a 2 h euglycaemic-hyperinsulinaemic clamp (90 mg/dl; 40 mU/m2 /min) to determine metabolic insulin sensitivity (M-value), phenotypes of medium- to large-sized EVs, and aortic waveform measures. Endothelial (CD105+ , CD41- /CD31+ )-, leukocyte (CD45+ )-, platelet (CD41+ , CD41+ /31+ )- and tetraspanin (TX+ )-derived EVs, as well as platelet endothelial cell adhesion molecule (CD31+ ), were determined before and after the clamp using high resolution spectral flow cytometry. Although exercise did not alter fasting haemodynamics, it lowered the augmentation index (AIx75, P = 0.024) and increased the M-value (P = 0.042). Further, exercise decreased all fasting EVs (P < 0.01) and decreased insulin-stimulated TX+ (P = 0.060), CD31+ (P = 0.060) and CD41- /31+ (P = 0.045) compared to rest. Interestingly, greater insulin-stimulated decreases in CD41- /31+ were associated with reduced AIx75 during the clamp (r = 0.62, P = 0.059), while insulin-stimulated decreases in CD41+ (r = -0.68, P = 0.031), CD41+ /31+ (r = -0.69, P = 0.262), TX+ (r = -0.66, P = 0.037) and CD31+ (r = -0.69, P = 0.028) correlated with M-value following exercise. Thus, acute exercise may decrease fasting and insulin-stimulated medium- to large-size EVs in conjunction with improved M-value and AIx75. More research is needed to understand effects of exercise on EVs in the regulation of glucose homeostasis and vascular function. KEY POINTS: Extracellular vesicles (EVs) are increased in states of obesity and may play a role in altered insulin sensitivity and blood pressure; aerobic exercise decreases fasting EV concentrations the following day in adults with obesity. This study directly tested the effects of insulin on EVs and how a single bout of exercise impacts these responses. Together, these data highlight the positive effects of a single bout of exercise on fasting and insulin-stimulated EVs, with the latter relating to increased insulin sensitivity and decreased augmentation index. These results support future research identifying EVs as mechanistic factors in glucose regulation and vascular function as well as clinical use of exercise to reduce cardiovascular disease risk.

Tracking Biomarker Responses to Exercise in Hypertension

PURPOSE OF REVIEW

Strong evidence is evolving that physical exercise prevents hypertension and reduces blood pressure in patients with pre- and manifest HTN. Yet, identifying and confirming the effectiveness of exercise are challenging. Herein, we discuss conventional and novel biomarkers such as extracellular vesicles (EVs) which may track responses to HTN before and after exercise.

RECENT FINDINGS

Evolving data shows that improved aerobic fitness and vascular function as well as lowered oxidative stress, inflammation, and gluco-lipid toxicity are leading biomarkers considered to promote HTN, but they explain only about a half of the pathophysiology. Novel biomarkers such as EVs or microRNA are providing additional input to understand the complex mechanisms involved in exercise therapy for HTN patients. Conventional and novel biomarkers are needed to fully understand the integrative "cross-talk" between tissues to regulate vasculature physiology for blood pressure control. These biomarker studies will lead to more specific disease markers and the development of even more personalized therapy in this field. However, more systematic approaches and randomized controlled trials in larger cohorts are needed to assess exercise effectiveness across the day and with different exercise types.

Extracellular Vesicles in Kidney Diseases: Moving Forward

Extracellular vesicles (EVs) are evolving as novel cell mediators, biomarkers, and therapeutic targets in kidney health and disease. They are naturally derived from cells both within and outside the kidney and carry cargo which mirrors the state of the parent cell. Thus, they are potentially more sensitive and disease-specific as biomarkers and messengers in various kidney diseases. Beside their role as novel communicators within the nephron, they likely communicate between different organs affected by various kidney diseases. Study of urinary EVs (uEVs) can help to fill current knowledge gaps in kidney diseases. However, separation and characterization are challenged by their heterogeneity in size, shape, and cargo. Fortunately, more sensitive and direct EV measuring tools are in development. Many clinical syndromes in nephrology from acute to chronic kidney and glomerular to tubular diseases have been studied. Yet, validation of biomarkers in larger cohorts is warranted and simpler tools are needed. Translation from in vitro to in vivo studies is also urgently needed. The therapeutic role of uEVs in kidney diseases has been studied extensively in rodent models of AKI. On the basis of the current exponential growth of EV research, the field of EV diagnostics and therapeutics is moving forward.

Extracellular vesicles and insulin-mediated vascular function in metabolic syndrome

Metabolic Syndrome (MetS) raises cardiovascular disease risk. Extracellular vesicles (EVs) have emerged as important mediators of insulin sensitivity, although few studies on vascular function exist in humans. We determined the effect of insulin on EVs in relation to vascular function. Adults with MetS (n = 51, n = 9 M, 54.8 ± 1.0 years, 36.4 ± 0.7 kg/m2 , ATPIII: 3.5 ± 0.1 a.u., VO2 max: 22.1 ± 0.6 ml/kg/min) were enrolled in this cross-sectional study. Peripheral insulin sensitivity (M-value) was determined during a euglycemic clamp (40 mU/m2 /min, 90 mg/dl), and blood was collected for EVs (CD105+, CD45+, CD41+, TX+, and CD31+; spectral flow cytometry), inflammation, insulin, and substrates. Central hemodynamics (applanation tonometry) was determined at 0 and 120 min via aortic waveforms. Pressure myography was used to assess insulin-induced arterial vasodilation from mouse 3rd order mesenteric arteries (100-200 μm in diameter) at 0.2, 2 and 20 nM of insulin with EVs from healthy and MetS adults. Adults with MetS had low peripheral insulin sensitivity (2.6 ± 0.2 mg/kg/min) and high HOMA-IR (4.7 ± 0.4 a.u.) plus Adipose-IR (13.0 ± 1.3 a.u.). Insulin decreased total/particle counts (p < 0.001), CD45+ EVs (p = 0.002), AIx75 (p = 0.005) and Pb (p = 0.04), FFA (p < 0.001), total adiponectin (p = 0.006), ICAM (p = 0.002), and VCAM (p = 0.03). Higher M-value related to lower fasted total EVs (r = -0.40, p = 0.004) while higher Adipose-IR associated with higher fasted EVs (r = 0.42, p = 0.004) independent of VAT. Fasting CD105+ and CD45+ derived total EVs correlated with fasting AIx75 (r = 0.29, p < 0.05) and Pb (r = 0.30, p < 0.05). EVs from MetS participants blunted insulin-induced vasodilation in mesenteric arteries compared with increases from healthy controls across insulin doses (all p < 0.005). These data highlight EVs as potentially novel mediators of vascular insulin sensitivity and disease risk.

Extracellular Vesicles in Acute Kidney Injury

Extracellular vesicles (EVs) are promising novel cellular communicators and biomarkers in acute kidney injury (AKI). These submicron vesicles derive from all cell types along the urinary tract and reflect molecular processes of their parent cells and physiological and pathological conditions in AKI. Several EV protein and RNA biomarker candidates have been identified. They have shown to differentiate AKI etiology and pinpoint to disease mechanisms. In fact, EV research has opened up a new frontier of biomarker discovery since some less abundant biomarkers are concentrated in EVs, which makes them more easily detectable. EVs are also functional and are involved in intra-nephron communication. Tubular-interstitial communication is current focus in EV research in AKI as it can help to understand maladaptive processes in AKI. EVs are also promising therapeutic tools and have been shown to be regenerative in many different models of AKI. Rigorous studies are needed to validate these findings, and more sensitive EV detection and characterization tools need to be developed to dissect EV biology in renal disease and AKI.

Insulin infusion decreases medium-sized extracellular vesicles in adults with metabolic syndrome

Elevated extracellular vesicles (EVs) are associated with glucose dysmetabolism. However, the effects of insulin on EVs and subsequent relationships with insulin sensitivity, substrate oxidation, and inflammation are unknown. We tested the hypothesis that insulin would lower EVs and relate to insulin action. Fifty-one sedentary adults (54.8 ± 1.0 yr; V̇o2peak : 22.1 ± 0.6 mL/kg/min) with metabolic syndrome (MetS) and obesity (36.4 ± 0.65 kg/m2) underwent a 2-h euglycemic-hyperinsulinemic clamp (5 mmol/L; 40 mU/m2/min). Count and size (medium: 200-624 nm; larger: 625-1,000 nm) for total particle count, endothelial- (CD105+), leukocyte- (CD45+), platelet- (CD41+), and tetraspanin- (TX+: CD9/CD81/CD63), as well as platelet endothelial cell adhesion molecule- (CD31+) derived EVs were determined before and following the clamp using Full Spectrum Profiling (FSPM). Size and MESF (molecules of equivalent soluble fluorochrome) data were generated using FCMPASS Software. Fat and carbohydrate oxidation, in addition to high-sensitivity c-reactive protein (hsCRP), were measured to understand insulin effects and associations between EVs, metabolic flexibility, and inflammation. Despite low metabolic insulin sensitivity (M-Value = 2.56 ± 0.17 mg/kg/min), insulin increased carbohydrate (P = 0.015) and decreased fat oxidation (P = 0.048) and hsCRP (P = 0.016) compared with fasting. Insulin also decreased total particle count (P < 0.001), attributable to decreased medium-sized CD105+ (P = 0.052) and CD45+ EVs (P < 0.001). Elevated fasting insulin was associated with reduced insulin-stimulated changes in all EVs phenotypes (P < 0.001). Interestingly, fasting EVs were associated with increased fasting carbohydrate oxidation (all P < 0.05). These findings suggest that insulin decreases medium-sized EVs in conjunction with metabolic flexibility under euglycemic conditions in adults with MetS. More research is needed to determine how therapies alter EV phenotype/size and consequent cardiometabolic risk.NEW & NOTEWORTHY This study is one of the first to investigate the effects of insulin on medium and larger extracellular vesicles (EVs) in relation to metabolic insulin sensitivity and fuel use in adults with metabolic syndrome. Our data suggest that insulin infusion decreases the concentration of total particle counts, mainly due to reductions in medium-sized EVs. Furthermore, EVs, predominantly medium-sized, are inversely associated with metabolic flexibility.

Extracellular Vesicles and Their Emerging Roles as Cellular Messengers in Endocrinology: An Endocrine Society Scientific Statement

During the last decade, there has been great interest in elucidating the biological role of extracellular vesicles (EVs), particularly, their hormone-like role in cell-to-cell communication. The field of endocrinology is uniquely placed to provide insight into the functions of EVs, which are secreted from all cells into biological fluids and carry endocrine signals to engage in paracellular and distal interactions. EVs are a heterogeneous population of membrane-bound vesicles of varying size, content, and bioactivity. EVs are specifically packaged with signaling molecules, including lipids, proteins, and nucleic acids, and are released via exocytosis into biofluid compartments. EVs regulate the activity of both proximal and distal target cells, including translational activity, metabolism, growth, and development. As such, EVs signaling represents an integral pathway mediating intercellular communication. Moreover, as the content of EVs is cell-type specific, it is a "fingerprint" of the releasing cell and its metabolic status. Recently, changes in the profile of EV and bioactivity have been described in several endocrine-related conditions including diabetes, obesity, cardiovascular diseases, and cancer. The goal of this statement is to highlight relevant aspects of EV research and their potential role in the field of endocrinology.

In sickness and in health: The functional role of extracellular vesicles in physiology and pathology in vivo: Part I: Health and Normal Physiology: Part I: Health and Normal Physiology

Previously thought to be nothing more than cellular debris, extracellular vesicles (EVs) are now known to mediate physiological and pathological functions throughout the body. We now understand more about their capacity to transfer nucleic acids and proteins between distant organs, the interaction of their surface proteins with target cells, and the role of vesicle‐bound lipids in health and disease. To date, most observations have been made in reductionist cell culture systems, or as snapshots from patient cohorts. The heterogenous population of vesicles produced in vivo likely act in concert to mediate both beneficial and detrimental effects. EVs play crucial roles in both the pathogenesis of diseases, from cancer to neurodegenerative disease, as well as in the maintenance of system and organ homeostasis. This two‐part review draws on the expertise of researchers working in the field of EV biology and aims to cover the functional role of EVs in physiology and pathology. Part I will outline the role of EVs in normal physiology.

In sickness and in health: The functional role of extracellular vesicles in physiology and pathology in vivo: Part II: Pathology: Part II: Pathology

It is clear from Part I of this series that extracellular vesicles (EVs) play a critical role in maintaining the homeostasis of most, if not all, normal physiological systems. However, the majority of our knowledge about EV signalling has come from studying them in disease. Indeed, EVs have consistently been associated with propagating disease pathophysiology. The analysis of EVs in biofluids, obtained in the clinic, has been an essential of the work to improve our understanding of their role in disease. However, to interfere with EV signalling for therapeutic gain, a more fundamental understanding of the mechanisms by which they contribute to pathogenic processes is required. Only by discovering how the EV populations in different biofluids change-size, number, and physicochemical composition-in clinical samples, may we then begin to unravel their functional roles in translational models in vitro and in vivo, which can then feedback to the clinic. In Part II of this review series, the functional role of EVs in pathology and disease will be discussed, with a focus on in vivo evidence and their potential to be used as both biomarkers and points of therapeutic intervention.

Updating MISEV: Evolving the minimal requirements for studies of extracellular vesicles

The minimal information for studies of extracellular vesicles (EVs, MISEV) is a field-consensus rigour initiative of the International Society for Extracellular Vesicles (ISEV). The last update to MISEV, MISEV2018, was informed by input from more than 400 scientists and made recommendations in the six broad topics of EV nomenclature, sample collection and pre-processing, EV separation and concentration, characterization, functional studies, and reporting requirements/exceptions. To gather opinions on MISEV and ideas for new updates, the ISEV Board of Directors canvassed previous MISEV authors and society members. Here, we share conclusions that are relevant to the ongoing evolution of the MISEV initiative and other ISEV rigour and standardization efforts.

Urinary extracellular vesicles: A position paper by the Urine Task Force of the International Society for Extracellular Vesicles

Urine is commonly used for clinical diagnosis and biomedical research. The discovery of extracellular vesicles (EV) in urine opened a new fast-growing scientific field. In the last decade urinary extracellular vesicles (uEVs) were shown to mirror molecular processes as well as physiological and pathological conditions in kidney, urothelial and prostate tissue. Therefore, several methods to isolate and characterize uEVs have been developed. However, methodological aspects of EV separation and analysis, including normalization of results, need further optimization and standardization to foster scientific advances in uEV research and a subsequent successful translation into clinical practice. This position paper is written by the Urine Task Force of the Rigor and Standardization Subcommittee of ISEV consisting of nephrologists, urologists, cardiologists and biologists with active experience in uEV research. Our aim is to present the state of the art and identify challenges and gaps in current uEV-based analyses for clinical applications. Finally, recommendations for improved rigor, reproducibility and interoperability in uEV research are provided in order to facilitate advances in the field.

T cell-derived extracellular vesicles are elevated in essential HTN

Extracellular vesicles (EVs) are novel mediators of cell-to-cell communication and appear to mediate the pathogenesis of hypertension (HTN). However, the mechanisms underlying the involvement of EVs in HTN remain unclear. The adaptive and innate immune systems play an important role affecting the kidney and vasculature in animal models of HTN. Evolving evidence shows that immune cell-derived EVs can modulate the immune system in a paracrine fashion and therefore may mediate the effects of inflammation in the pathogenesis of HTN. Therefore, we aimed to understand if specific subtypes of leukocyte/immune cell-derived EVs are altered in essential HTN using an in vivo model of angiotensin II (ANG II)-induced HTN. After 4 wk of ANG II treatment, EVs were isolated from the blood and kidney. EV origin and counts were characterized with Imaging Flow Cytometry, antibody panels targeting platelets, endothelial cells, and leukocytes including B and T cells, monocytes, and neutrophils. Leukocyte-derived EVs (CD45+) were elevated in the circulation and kidney tissue in ANG II-induced HTN. Subgroup analysis depicted T cell-derived EVs (CD3+) to be significantly elevated in ANG II-induced HTN (3.50e+5 particles/mL) compared with control groups (9.16e+4 particles/mL, P = 0.0106). T cell-derived EVs also significantly correlated with systolic blood pressure levels (r2 = 0.898, P = 0.0012). In summary, leukocyte-derived EVs, and more specifically T cell-derived EVs (CD3+), are elevated in ANG II-induced HTN in the circulation and kidney tissue and correlate well with blood pressure severity. EVs from the circulation and kidney may be sensitive biomarkers for HTN and end-organ damage and may lead to new mechanistic insights in this silent disease.

Extracellular Vesicles in Essential Hypertension: Hidden Messengers

PURPOSE OF REVIEW

Hypertension affects about half of all Americans, yet in the vast majority of cases, the factors causing the hypertension cannot be clearly delineated. Developing a more precise understanding of the molecular pathogenesis of HTN and its various phenotypes is therefore a pressing priority. Circulating and urinary extracellular vesicles (EVs) are potential novel candidates as biomarkers and bioactivators in HTN. EVs are a heterogeneous population of small membrane fragments shed from various cell types into various body fluids. As EVs carry protein, RNA, and lipids, they also play a role as effectors and novel cell-to-cell communicators. In this review, we discuss the diagnostic, functional, and regenerative role of EVs in essential HTN and focus on EV protein and RNA cargo as the most extensively studied EV cargo.

RECENT FINDINGS

The field of EVs in HTN is still a young one and earlier studies have not used the novel EV detection tools currently available. More rigor and transparency in EV research are needed. Current data suggest that EVs represent potential novel biomarkers in HTN. EVs correlate with HTN severity and possibly end-organ damage. However, it has yet to be discerned which specific subtype(s) of EV reflects best HTN pathophysiology. Evolving studies are also showing that EVs might be novel regulators in vascular and renal tubular function and also be therapeutic. RNA in EVs has been studied in the context of hypertension, largely in the form of studies of miRNA, which are reviewed herein. Beyond miRNAs, mRNA in urinary EVs changed in response to sodium loading in humans. EVs represent promising novel biomarkers and bioactivators in essential HTN. Novel tools are being developed to apply more rigor in EV research including more in vivo models and translation to humans.

Rigorous characterization of urinary extracellular vesicles (uEVs) in the low centrifugation pellet - a neglected source for uEVs

Urinary extracellular vesicles (uEVs) provide bio-markers for kidney and urogenital diseases. Centrifugation is the most common method used to enrich uEVs. However, a majority of studies to date have focused on the ultracentrifugation pellet, potentially losing a novel source of important biomarkers that could be obtained at lower centrifugation. Thus, the aim of this study is to rigorously characterize for the first time uEVs in the low speed pellet and determine the minimal volume of urine required for proteomic analysis (≥9.0 mL urine) and gene ontology classification identified 75% of the protein as extracellular exosomes. Cryo-Transmission Electron Microscopy (≥3.0 mL urine) provided evidence of a heterogeneous population of EVs for size and morphology independent of uromodulin filaments. Western blot detected several specific uEV kidney and EV markers (≥4.5 mL urine per lane). microRNAs quantification by qPCR was possible with urine volume as low as 0.5 mL. Particle enumeration with tunable resistive pulse sensing, nano particles tracking analysis and single EV high throughput imaging flow cytometry are possible starting from 0.5 and 3.0 mL of urine respectively. This work characterizes a neglected source of uEVs and provides guidance with regard to volume of urine necessary to carry out multi-omic studies and reveals novel aspects of uEV analysis such as autofluorescence of podocyte origin.

Circulating Extracellular Vesicles in Normotension Restrain Vasodilation in Resistance Arteries

Extracellular vesicles (EVs) have been described as novel biomarkers and bioactivators in vascular dysfunction in hypertension. However, the mechanism(s) by which EVs affect vascular function is unknown. To examine the effects of EVs on endothelial-dependent vasodilation (acetylcholine), we isolated circulating EVs from platelet-poor plasma using a low centrifugation speed (17 000g) and mesenteric resistance arteries from 12-week-old normotensive WKYs (Wistar-Kyoto rats) and SHRs (spontaneously hypertensive rats). Arteries were cannulated on a pressure myograph, and EVs were added to the vessel lumen and circulating bath. We found that circulating EVs from normotensive WKY reduced vasodilation of normotensive WKY arteries but had no effect on hypertensive SHR arteries. In contrast, EVs from hypertensive SHR failed to reduce vasodilation of arteries from both WKY and SHR. The restraining effect on vasodilation by EVs from normotensive WKY may be mediated by inhibition of eNOS (endothelial NO synthase), as addition of L-nitro-arginine methyl ester did not provide any additive effect. Moreover, circulating EVs from normotensive 6-week-old SHR-an age where SHRs have not yet developed hypertension-had similar restraining effect on vasodilation. In addition, delipidation of EVs did not alter the restraining effect of EVs from WKY but did restore the restraining effect of EVs from SHR. Finally, EVs from normotensive humans also restrained vasodilation of normotensive mouse arteries-an effect not observed in EVs from hypertensive humans. Taken together, our data support a vasoactive role of EVs that is altered in hypertension.

Biological membranes in EV biogenesis, stability, uptake, and cargo transfer: an ISEV position paper arising from the ISEV membranes and EVs workshop

Paracrine and endocrine roles have increasingly been ascribed to extracellular vesicles (EVs) generated by multicellular organisms. Central to the biogenesis, content, and function of EVs are their delimiting lipid bilayer membranes. To evaluate research progress on membranes and EVs, the International Society for Extracellular Vesicles (ISEV) conducted a workshop in March 2018 in Baltimore, Maryland, USA, bringing together key opinion leaders and hands-on researchers who were selected on the basis of submitted applications. The workshop was accompanied by two scientific surveys and covered four broad topics: EV biogenesis and release; EV uptake and fusion; technologies and strategies used to study EV membranes; and EV transfer and functional assays. In this ISEV position paper, we synthesize the results of the workshop and the related surveys to outline important outstanding questions about EV membranes and describe areas of consensus. The workshop discussions and survey responses reveal that while much progress has been made in the field, there are still several concepts that divide opinion. Good consensus exists in some areas, including particular aspects of EV biogenesis, uptake and downstream signalling. Areas with little to no consensus include EV storage and stability, as well as whether and how EVs fuse with target cells. Further research is needed in these key areas, as a better understanding of membrane biology will contribute substantially towards advancing the field of extracellular vesicles.

Abstract P120: Leukocyte and Lymphocyte-Derived Extracellular Vesicles are Elevated in Angiotensin-Induced Hypertension

Infiltration of macrophages and T cells in kidneys and vasculature may play a role in the development of hypertension (HTN) and extracellular vesicles (EVs) have emerged as novel cell-to-cell communicators in the pathogenesis HTN. Immune cell-derived EVs can reflect the pathophysiological activity of the parental cell and mediate immune stimulation or inhibition in paracrine fashion. We investigated subgroups of circulating leukocyte-derived EVs (LEVs) in angiotensin II (Ang II)-induced HTN with or without candesartan (C) or hydralazine, hydrochlorothiazide, and reserpine (HHR).

Ang II was delivered via osmotic mini pumps (500 ng/kg/min; n=15) and with C (10 mg/kg/day, n=5) or HHR (30 mg/kg/day, n=5) in drinking water for 4 weeks to 129S6 mice. Systolic blood pressure (SBP) was measured daily by tail-cuff manometry. After 4 weeks, mice were euthanized and citrated blood collected. EV isolation was performed by differential centrifugation, followed by EV phenotyping with imaging flow cytometry. We used EV surface markers for leukocyte (CD45), T- and B-cells (CD3,CD19), neutrophils (Ly6g+/CD11b-) and monocytes/macrophages (Ly6g-/CD11b+).

Ang II infused mice had significantly higher SBP compared to normotensive controls (NC) (n=5) (173.79 ± 4.9mmHg vs 129.8 ± 6.2mmHg, p <0.0001) and C/HHR treated mice (134.42 ± 7.5mmHg (C) and 138.21 ± 5.2mmHg (HHR), p = NS). Leukocyte-derived EV counts (CD45+ EVs for Ang II: 2.16E+06 particles/ml; NC: 6.15E+05 particles/mL; p=0.0001) and T cell-derived EV counts (CD3+) (Ang II: 2.14E+06 particles/ml, NC: 4.46E+05 particles/mL; p=0.0001] increased after 4 weeks in Ang II-infused mice compared to NC. In C and HHR treated groups, leukocyte- and T cell-derived EV concentrations were similar to NC, suggesting a BP effect rather than drug class effect. CD45+ and CD3+ EV concentrations correlated significantly with SBP [(r2=0.9343; p= 0.0004) and (r2= 0.8982; p= 0.0012), respectively]. In conclusion, leukocyte- and T cell-derived EVs were increased in Ang II-induced HTN and correlated significantly with SBP. Therefore, leukocyte- and T cell-derived EVs are potential bio-markers in HTN. Further studies are required to understand the functional role of leukocyte- and T cell-derived EVs in the pathogenesis of HTN.

Extracellular vesicles as a novel diagnostic and research tool for patients with HTN and kidney disease

Hypertension (HTN) affects one in three adults in the United States and is a major risk factor for cardiovascular disease and kidney failure. There is emerging evidence that more intense blood pressure lowering reduces mortality in patients with kidney disease who are at risk of cardiovascular disease and progression to end-stage renal disease. However, the ideal blood pressure threshold for patients with kidney disease remains a question of debate. Novel tools to more precisely diagnose HTN, tailor treatment, and predict the risk of end-organ damage such as kidney disease are needed. Analysis of circulating and urinary extracellular vesicles (EVs) and their cargo (protein and RNA) has the potential to identify novel noninvasive biomarkers that can also reflect a specific pathological mechanism of different HTN phenotypes. We will discuss the use of extracellular vesicles as markers of HTN severity and explain their profile change with antihypertensive medicine and potential to detect early end-organ damage. However, more studies with enhanced rigor in this field are needed to define the blood pressure threshold to prevent or delay kidney disease progression and decrease cardiovascular risk.

Optimisation of imaging flow cytometry for the analysis of single extracellular vesicles by using fluorescence-tagged vesicles as biological reference material

Extracellular vesicles (EVs) mediate targeted cellular interactions in normal and pathophysiological conditions and are increasingly recognised as potential biomarkers, therapeutic agents and drug delivery vehicles. Based on their size and biogenesis, EVs are classified as exosomes, microvesicles and apoptotic bodies. Due to overlapping size ranges and the lack of specific markers, these classes cannot yet be distinguished experimentally. Currently, it is a major challenge in the field to define robust and sensitive technological platforms being suitable to resolve EV heterogeneity, especially for small EVs (sEVs) with diameters below 200 nm, i.e. smaller microvesicles and exosomes. Most conventional flow cytometers are not suitable for the detection of particles being smaller than 300 nm, and the poor availability of defined reference materials hampers the validation of sEV analysis protocols. Following initial reports that imaging flow cytometry (IFCM) can be used for the characterisation of larger EVs, we aimed to investigate its usability for the characterisation of sEVs. This study set out to identify optimal sample preparation and instrument settings that would demonstrate the utility of this technology for the detection of single sEVs. By using CD63eGFP-labelled sEVs as a biological reference material, we were able to define and optimise IFCM acquisition and analysis parameters on an Amnis ImageStreamX MkII instrument for the detection of single sEVs. In addition, using antibody-labelling approaches, we show that IFCM facilitates robust detection of different EV and sEV subpopulations in isolated EVs, as well as unprocessed EV-containing samples. Our results indicate that fluorescently labelled sEVs as biological reference material are highly useful for the optimisation of fluorescence-based methods for sEV analysis. Finally, we propose that IFCM will help to significantly increase our ability to assess EV heterogeneity in a rigorous and reproducible manner, and facilitate the identification of specific subsets of sEVs as useful biomarkers in various diseases.

Minimal information for studies of extracellular vesicles 2018 (MISEV2018): a position statement of the International Society for Extracellular Vesicles and update of the MISEV2014 guidelines

The last decade has seen a sharp increase in the number of scientific publications describing physiological and pathological functions of extracellular vesicles (EVs), a collective term covering various subtypes of cell-released, membranous structures, called exosomes, microvesicles, microparticles, ectosomes, oncosomes, apoptotic bodies, and many other names. However, specific issues arise when working with these entities, whose size and amount often make them difficult to obtain as relatively pure preparations, and to characterize properly. The International Society for Extracellular Vesicles (ISEV) proposed Minimal Information for Studies of Extracellular Vesicles ("MISEV") guidelines for the field in 2014. We now update these "MISEV2014" guidelines based on evolution of the collective knowledge in the last four years. An important point to consider is that ascribing a specific function to EVs in general, or to subtypes of EVs, requires reporting of specific information beyond mere description of function in a crude, potentially contaminated, and heterogeneous preparation. For example, claims that exosomes are endowed with exquisite and specific activities remain difficult to support experimentally, given our still limited knowledge of their specific molecular machineries of biogenesis and release, as compared with other biophysically similar EVs. The MISEV2018 guidelines include tables and outlines of suggested protocols and steps to follow to document specific EV-associated functional activities. Finally, a checklist is provided with summaries of key points.

Abstract P365: Circulating and Kidney EVs in Angiotensin-induced HTN In Mice

There is emerging evidence that extracellular vesicles (EVs) may be novel bio-markers and bio-activators in the pathogenesis of HTN. We hypothesize that the phenotypes of EVs from the circulation and kidney are altered in Angiotensin II (AII) induced HTN and normalize with anti-hypertensive treatment (Rx). AII was delivered via osmotic mini pumps (500 ng/kg/min) alone, or with candesartan (C) @ 10 mg/kg/day, or with hydralazine, hydrochlorothiazide, reserpine (HHR) @ 30/10/0.2 mg/kg/day in drinking water for 2 weeks to 129S6 mice (n = 5 each). Systolic blood pressure (SBP) was measured daily for 2 weeks by tail-cuff manometry. After 2 weeks, mice were euthanized and citrated blood and kidneys collected. Kidney EVs (KEVs) were isolated after incubation with Collagenase type A and subsequent DC. Both circulating EVs and KEVs were isolated through differential centrifugation and characterized by imaging flow cytometry (AmnisImage-StreamX Mark II) using PECAM-1 (CD31), leukocyte (CD45), platelet (CD41) and endothelial (CD105) markers. AII treated mice had significantly higher SBP (mmHg) (162.05 ± 7.20) than normotensive controls ((N) 120.25 ± 7.12), p=0.02. SBP was similarly reduced with C and HHR (134.12 ± 6.15 and 122.45 ± 5.20, respectively, p=NS), and significantly lower than AII, p=0.0026 and =0.03, respectively). Circulating leukocyte derived EVs (LEVs, CD31+/CD45+) increased after 2 weeks in AII treated mice compared to N (AII 2.01E+0.3, N 2.04E+0.4 particles/mL; p=0.0130). This effect was not observed with endothelial and platelet derived EVs. Numbers of circulating LEVs correlated significantly with SBP [(r 2 =0.675); p=0.0029]. Circulating LEVs were reduced after equal normalization of SBP, though no difference in EVs was observed between Rx with C and HHR. CD45+ KEVs in AII treated mice were significantly increased compared to N (AII 7.52E+05 vs N 4.79E+04; p= 0.0257). KEVs also correlated significantly with SBP [(r 2 =0.682); p=0.0032]. In conclusion, circulating and kidney derived EVs may play a role in the immune response in HTN and may be influenced by blood pressure threshold, independent of AT 1 receptor activation. Further studies are needed to confirm and to characterize specific subtype(s) of LEVs and dissect their functional role.

Higher levels of SDMA and not ADMA are associated with poorer survival of trial patients with systemic ANCA-associated vasculitis

OBJECTIVE

Endothelial dysfunction, increased cardiovascular events (CVE), and accelerated atherosclerosis have been described in patients with small vessel vasculitis and collagen vascular disease. Identifying predictors of cardiovascular risk will help to optimize short- and long-term care of patients with vasculitis. The present study investigates the predictive role of the endogenous nitric oxide synthase (NOS) inhibitor asymmetric dimethylarginine (ADMA) and its stereoisomer symmetric dimethylarginine (SDMA) for cardiovascular risk, all-cause mortality, and renal function in patients with anti-neutrophil-cytoplasmic antibodies-associated small vessel vasculitis (AASV) subjected to standardized treatment regimens in four European Vasculitis Study Group trials representing all stages of renal disease.

METHODS

Sera from 89 patients with AASV were available for measuring SDMA, ADMA, and arginine using liquid chromatography/mass spectrometry at the time of active disease and remission. Clinical data on disease activity, remission, relapse rate, and 5-year follow-up data for CVE and renal outcome were collected.

RESULTS

Symmetric dimethylarginine and ADMA levels were not predictive of CVE at 5 years of follow-up. The overall CVE rate was low in the present cohort of AASV (8%). However, SDMA, and not ADMA, levels were significantly associated with poorer survival (death/ESRD) independent of entry glomerular filtration rate.

CONCLUSION

This novel outcome in a well-defined group of patients with AASV might indicate a different mechanism of endothelial response in AASV as compared with atherosclerosis. This should be further explored in a larger cohort of AASV patients with a higher CVE rate and/or a longer follow-up. Moreover, these findings should be correlated to other markers of vascular damage.

Low cardiorespiratory fitness is associated with higher extracellular vesicle counts in obese adults

Low cardiorespiratory fitness (CRF) is associated with cardiovascular disease (CVD) independent of obesity. Extracellular vesicles (EVs) are a novel target of CVD, however, it remains unknown if obese individuals with very poor fitness (VPF) have elevated EVs versus people with poor fitness (PF). Thus, we tested whether VPF was associated with greater EV subtypes in obese adults. Subjects with VPF (n = 13, VO2 peak: 15.4 ± 0.6 mL/kg/min, BMI: 34.1 ± 1.7 kg/m2 ) and PF (n = 13, VO2 peak: 25.9 ± 3.0 mL/kg/min, BMI: 32.1 ± 1.2 kg/m2 ) were compared in this cross-sectional study. After an overnight fast, AnnexinV (AV) +/- platelet (CD31+ /CD41+ ), leukocyte (CD45+ /CD41- ), and endothelial EVs (CD105+ , CD31+ /CD41- ) were analyzed from fresh platelet poor plasma via imaging flow cytometry. Body fat, blood pressure (BP), and glucose tolerance (OGTT) were also tested. Body weight, BP, and circulating glucose were similar between groups, although VPF subjects were older than PF (64.0 ± 2.1 vs. 49.8 ± 4.2 year; P < 0.05). People with VPF, compared with PF, had higher total AV- EVs (P = 0.04), AV- platelet EVs (CD31+ /CD41+ ; P = 0.006), and AV- endothelial EVs (CD31+ /CD41- ; P = 0.005) independent of age and body fat. Higher AV- platelet and endothelial EVs were associated with lower VO2 peak (r = -0.56, P = 0.006 and r = -0.55, P = 0.005, respectively). Endothelial-derived AV- /CD31+ /CD41- EVs were also related to pulse pressure (r = 0.45, P = 0.03), whereas AV- /CD105 was linked to postprandial glucose (r = 0.41, P = 0.04). VPF is associated with higher AnnexinV- total, endothelial, and platelet EVs in obese adults, suggesting that subtle differences in fitness may reduce type 2 diabetes and CVD risk through an EV-related mechanism.

Extracellular Vesicles: A Novel Target for Exercise-Mediated Reductions in Type 2 Diabetes and Cardiovascular Disease Risk

Regular exercise is important for reducing type 2 diabetes (T2D) and/or cardiovascular disease (CVD) risk. However, only about 40-50% of this CVD risk reduction is accounted for by adiposity, hyperglycemia, hypertension, and dyslipidemia. Herein, we present the novel hypothesis that extracellular vesicles (EVs) are candidate biomarkers that may relate to impaired endothelial function and insulin resistance independent of obesity risk factors. EVs are small membrane-bound particles that are generated by cells following stimulation, stress, or activation. They carry markers of their parent cell and are thought to be potent bioactivators and communicators. We discuss the underlying physiology of specific cell type EVs, as well as examine how acute and chronic exercise interventions impact EV count and phenotype. We also propose that current gaps in the field are in part related to use of different detection techniques and the lack of standardized measurements of EV affecting the pre- and postanalytical phase. Ultimately, improving the understanding of how EVs impact cardiometabolic health and their function will lead to improved approaches for enhancing diagnostic options as well as designing exercise interventions that treat and/or prevent T2D and CVD.

Macrophages redirect phagocytosis by non-professional phagocytes and influence inflammation

Professional phagocytes (such as macrophages) and non-professional phagocytes (such as epithelial cells) clear billions of apoptotic cells and particles on a daily basis. Although professional and non-professional macrophages reside in proximity in most tissues, whether they communicate with each other during cell clearance, and how this might affect inflammation, is not known. Here we show that macrophages, through the release of a soluble growth factor and microvesicles, alter the type of particles engulfed by non-professional phagocytes and influence their inflammatory response. During phagocytosis of apoptotic cells or in response to inflammation-associated cytokines, macrophages released insulin-like growth factor 1 (IGF-1). The binding of IGF-1 to its receptor on non-professional phagocytes redirected their phagocytosis, such that uptake of larger apoptotic cells was reduced whereas engulfment of microvesicles was increased. IGF-1 did not alter engulfment by macrophages. Macrophages also released microvesicles, whose uptake by epithelial cells was enhanced by IGF-1 and led to decreased inflammatory responses by epithelial cells. Consistent with these observations, deletion of IGF-1 receptor in airway epithelial cells led to exacerbated lung inflammation after allergen exposure. These genetic and functional studies reveal that IGF-1- and microvesicle-dependent communication between macrophages and epithelial cells can critically influence the magnitude of tissue inflammation in vivo.

Analytical challenges of extracellular vesicle detection: A comparison of different techniques

The interest in extracellular vesicles (EVs) has grown exponentially over the last decade. Evolving evidence is demonstrating that these EVs are playing an important role in health and disease. They are involved in intercellular communication and have been shown to transfer proteins, lipids, and nucleic acids. This review focuses on the most commonly used techniques for detection of EVs, to include microparticles, 100-1,000 nm in size, and exosomes, 50-100 nm in size. Conventional flow cytometry is the most prevalent technique, but nanoparticle tracking analysis (NTA), dynamic light scattering (DLS), and resistive pulse sensing have also been used to detect EVs. The accurate measurement of these vesicles is challenged by size heterogeneity, low refractive index, and the lack of dynamic measurement range for most of the available technologies. Sample handling during the preanalytical phase can also affect the accuracy of measurements. Currently, there is not one single method which allows phenotyping, sizing, and enumerating the whole range of EVs and, therefore, providing all the necessary information to truly understand the biology of these particles. A combination of methods is probably needed which might also include electron and atomic force microscopy and full RNA, lipid, and protein profiling.

Long-term impact of CMV infection on allografts and on patient survival in renal transplant patients with protocol biopsies

Cytomegalovirus (CMV) infection is a frequent complication of early posttransplantation. This study examines its impact on chronic allograft changes, long-term graft loss, and patient survival. We studied 594 patients who had protocol biopsies at 6 wk, and 3 and 6 mo posttransplantation. Chronic allograft changes were evaluated according to the updated Banff classification [interstitial fibrosis/tubular atrophy (IF/TA), vascular and glomerular lesions]. Follow-up data were available for up to 10 yr. CMV infection was diagnosed in 153 of 594 patients (26%) in the first year after transplantation, mostly within the first 3 mo. Graft survival was reduced in patients with CMV ( P = 0.03) as well as the combined allograft/patient survival ( P = 0.008). Prevalence of IF/TA at 6 wk after transplantation was already threefold higher in patients who experienced CMV infection later on compared with patients without CMV ( P = 0.005). In multivariate analyses, CMV viremia or disease was not a significant factor for graft loss or death. In conclusion, patients with CMV infection posttransplantation show more chronic allograft changes early on, even before CMV infection, and development of IF/TA is not more prevalent in patients with CMV. Our data do not support a significant role of CMV in patient and graft outcomes.

Extracellular Vesicles in Renal Diseases: More than Novel Biomarkers?

Extracellular vesicles from the urine and circulation have gained significant interest as potential diagnostic biomarkers in renal diseases. Urinary extracellular vesicles contain proteins from all sections of the nephron, whereas most studied circulating extracellular vesicles are derived from platelets, immune cells, and the endothelium. In addition to their diagnostic role as markers of kidney and vascular damage, extracellular vesicles may have functional significance in renal health and disease by facilitating communication between cells and protecting against kidney injury and bacterial infection in the urinary tract. However, the current understanding of extracellular vesicles has derived mostly from studies with very small numbers of patients or in vitro data. Moreover, accurate assessment of these vesicles remains a challenge, in part because of a lack of consensus in the methodologies to measure extracellular vesicles and the inability of most techniques to capture the entire size range of these vesicles. However, newer techniques and standardized protocols to improve the detection of extracellular vesicles are in development. A clearer understanding of the composition and biology of extracellular vesicles will provide insights into their pathophysiologic, diagnostic, and therapeutic roles.

Imaging flow cytometry elucidates limitations of microparticle analysis by conventional flow cytometry

Microparticles (MPs) are submicron vesicles released from cell membranes in response to activation, cell injury, or apoptosis. The clinical importance of MPs has become increasingly recognized, although no standardized method exists for their measurement. Flow cytometry (FCM) is the most commonly used technique, however, because of the small size of MPs, and the limitations of current FCM instrumentation, accurate identification is compromised by this methodology. We decided to investigate whether the use of FCM combined with imaging, such as is possible with the ImagestreamX imaging FC (ISX), would be a more sensitive approach to characterizing MPs. Combining FCM with imaging eliminates some of the limitations demonstrated by conventional FCM, whereas also providing morphological confirmation and the ability to distinguish true single events from aggregates and cell debris. The detection limit of standard nonspecialized FCM is suboptimal when compared to ISX. Evaluating MPs below 0.200 µm and sizing remain a challenge as some MPs remain below the detection limit of ISX. Standardized calibrators, that more closely reflect the physical characteristics of MPs, need further development.

[Is methotrexate nephrotoxic? Dose-dependency, comorbidities and comedication]

Methotrexate (MTX) in low-doses is an important component of anti-inflammatory therapy of rheumatoid arthritis and other inflammatory joint diseases. In contrast to high-dose administration of MTX in oncology, which can lead to direct tubulus toxicity and subsequent renal failure, renal side-effects are a rare exception for low-dose MTX. The biggest problem under low-dose MTX is that an already limited renal function due to comorbidities or an increasing, sometimes clinically insufficiently monitored renal insufficiency due to comedications, such as non-steroidal antirheumatics (NSAR) and antibiotics, leads to a reduced excretion of MTX and therefore to an accumulation in serum. This is primarily accompanied by gastrointestinal mucositis and bone marrow depression. For this reason low-dose MTX should never be administered once the glomerular filtration rate (GFR) is less than <30 ml/min and only 50% of the original dosage should be administered if the GFR is between 30 and 60 ml/min.

Endothelial microparticles as a diagnostic aid in Churg-Strauss vasculitis-induced cardiomyopathy

Churg-Strauss Syndrome (CSS) is characterized by allergic rhinitis, asthma and prominent blood and tissue eosinophilia. Although CSS can affect any organ system, isolated cardiac manifestation is a rare feature that is often characterized by rapidly progressive congestive heart failure. We present the case of a 48-year-old woman with acute dyspnoea and chest pain. Her past medical history was significant for asthma and frequently relapsing minimal-change glomerulonephritis. Echocardiogram and coronary angiography revealed cardiomyopathy and coronary small-vessel vasculitis in the presence of blood eosinophilia and elevated IgE. In the absence of infective agents, neoplastic diseases and further vasculitic manifestations, a flow cytometry-based analysis of markedly elevated endothelial microparticles supported the diagnosis of CSS. Cardiomyopathy resolved completely after initiation of immunosuppressive treatment with corticosteroids and cyclophosphamide pulses. Elevated endothelial, leukocytic and platelet-derived microparticles decreased during follow-up and closely paralleled vasculitic activity. Endothelial microparticles might be an additional tool to diagnose and monitor cases of suspected vasculitic cardiac involvement in CSS.

Mapping of myeloperoxidase epitopes recognized by MPO-ANCA using human-mouse MPO chimers

Myeloperoxidase (MPO) is one of the major target antigens of antineutrophil cytoplasmic autoantibodies (ANCA) found in patients with small-vessel vasculitis and pauci-immune necrotizing glomerulonephritis. To date, the target epitopes of MPO-ANCA remain poorly defined. Human MPO-ANCA do not typically bind mouse MPO. We utilized the differences between human and mouse MPO to identify the target regions of MPO-ANCA. We generated five chimeric MPO molecules in which we replaced different segments of the human or mouse molecules with their homologous counterpart from the other species. Of serum samples from 28 patients screened for this study, 43 samples from 14 patients with MPO-ANCA-associated vasculitis were tested against recombinant human and mouse MPO and the panel of chimeric molecules. Sera from 64 and 71% of patients bound to the carboxy-terminus of the heavy chain, in the regions of amino acids 517-667 or 668-745, respectively. No patient serum bound the MPO light chain or the amino-terminus of the heavy chain. All sera bound to only one or two regions of MPO. Although the pattern of MPO-ANCA binding changed over time (4-27 months) in 6 of 10 patients with several serum samples, such changes were infrequent. Other target regions of MPO-ANCA may not have been detected due to conformational differences between the native and recombinant forms of MPO. MPO-ANCA do not target a single epitope, but rather a small number of regions of MPO, primarily in the carboxy-terminus of the heavy chain.