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The importance of extracellular vesicle purification for downstream analysis: A comparison of differential centrifugation and size exclusion chromatography for helminth pathogens.

ABSTRACT: BACKGROUND:Robust protocols for the isolation of extracellular vesicles (EVs) from the rest of their excretory-secretory products are necessary for downstream studies and application development. The most widely used purification method of EVs for helminth pathogens is currently differential centrifugation (DC). In contrast, size exclusion chromatography (SEC) has been included in the purification pipeline for EVs from other pathogens, highlighting there is not an agreed research community 'gold standard' for EV isolation. In this case study, Fasciola hepatica from natural populations were cultured in order to collect EVs from culture media and evaluate a SEC or DC approach to pathogen helminth EV purification. METHODOLOGY/PRINCIPAL FINDINGS:Transmission electron and atomic force microscopy demonstrated that EVs prepared by SEC were both smaller in size and less diverse than EV resolved by DC. Protein quantification and Western blotting further demonstrated that SEC purification realised a higher EV purity to free excretory-secretory protein (ESP) yield ratio compared to DC approaches as evident by the reduction of soluble free cathepsin L proteases in SEC EV preparations. Proteomic analysis further highlighted DC contamination from ESP as shown by an increased diversity of protein identifications and unique peptide hits in DC EVs as compared to SEC EVs. In addition, SEC purified EVs contained less tegumental based proteins than DC purified EVs. CONCLUSIONS/SIGNIFICANCE:The data suggests that DC and SEC purification methods do not isolate equivalent EV population profiles and caution should be taken in the choice of EV purification utilised, with certain protocols for DC preparations including more free ES proteins and tegumental artefacts. We propose that SEC methods should be used for EV purification prior to downstream studies.

SUBMITTER: Davis CN

PROVIDER: S-EPMC6411213 | biostudies-literature | 2019 Feb

REPOSITORIES: biostudies-literature

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The importance of extracellular vesicle purification for downstream analysis: A comparison of differential centrifugation and size exclusion chromatography for helminth pathogens.

Davis Chelsea N CN Phillips Helen H Tomes John J JJ Swain Martin T MT Wilkinson Toby J TJ Brophy Peter M PM Morphew Russell M RM

PLoS neglected tropical diseases 20190227 2

<h4>Background</h4>Robust protocols for the isolation of extracellular vesicles (EVs) from the rest of their excretory-secretory products are necessary for downstream studies and application development. The most widely used purification method of EVs for helminth pathogens is currently differential centrifugation (DC). In contrast, size exclusion chromatography (SEC) has been included in the purification pipeline for EVs from other pathogens, highlighting there is not an agreed research communi ...[more]

PMID: 30811394

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Project description:Fascioliasis is a major neglected tropical disease that infects humans and ruminant species worldwide. Recent discoveries have identified that liver fluke extracellular vesicles are released into the host’s internal environment. To understand extracellular vesicle biology further, isolation of the extracellular vesicle is necessary for downstream applications. The most widely used purification method involves differential centrifugation however; there is no ‘gold standard’ to date of extracellular vesicle isolation. Recently, size exclusion chromatography has been used to successfully purify EVs. In this study, liver flukes were collected to compare size exclusion chromatography EV purification, to the widely accepted method of differential centrifugation. Transmission electron microscopy and atomic force microscopy showed that size exclusion chromatography extracellular vesicles were smaller in size and diversity than differential centrifugation purified extracellular vesicles. Protein concentration and western blotting suggested that size exclusion chromatography purification had a high EV purity to protein yield ratio in comparison to differential centrifugation. Mass spectrometry analysis discovered a greater amount of protein identifications and unique peptide hits in differential centrifugation purified EVs with less diverse functionality, than size exclusion chromatography purified EVs. However, gene enrichment analysis against the Fasciola hepatica genome showed comparable results between purification methods. Furthermore, western blotting revealed that glutathione s-transferase sigma could be a potential marker for liver fluke EVs. These results suggest that size exclusion chromatography purification produces a higher EV purity to protein yield ratio and maintains extracellular vesicle composition, so therefore is a better suited method for further downstream experimentation with liver fluke extracellular vesicles, compared to differential centrifugation.

Project description:Extracellular vesicles (EVs) are a heterogeneous population of biological particles released by cells. They represent an attractive source of potential biomarkers for early detection of diseases such as cancer. However, it is critical that sufficient amounts of EVs can be isolated and purified in a robust and reproducible manner. Several isolation methods that seem to produce distinct populations of vesicles exist, making data comparability difficult. While some methods induce cellular stress that may affect both the quantity and function of the EVs produced, others involve expensive reagents or equipment unavailable for many laboratories. Thus, there is a need for a standardized, feasible and cost-effective method for isolation of EVs from cell culture supernatants. Here we present the most common obstacles in the production and isolation of small EVs, and we suggest a combination of relatively simple strategies to avoid these. Three distinct cell lines were used (human oral squamous cell carcinoma (PE/CA-PJ49/E10)), pancreatic adenocarcinoma (BxPC3), and a human melanoma brain metastasis (H3). The addition of 1% exosome-depleted FBS to Advanced culture media enabled for reduced presence of contaminating bovine EVs while still ensuring an acceptable cell proliferation and low cellular stress. Cells were gradually adapted to these new media. Furthermore, using the Integra CELLine AD1000 culture flask we increased the number of cells and thereby EVs in 3D-culture. A combination of ultrafiltration with different molecular weight cut-offs and size-exclusion chromatography was further used for the isolation of a heterogeneous population of small EVs with low protein contamination. The EVs were characterized by nanoparticle tracking analysis, immunoaffinity capture, flow cytometry, Western blot and transmission electron microscopy. We successfully isolated a significant amount of small EVs compatible with exosomes from three distinct cell lines in order to demonstrate reproducibility with cell lines of different origin. The EVs were characterized as CD9 positive with a size between 60-140 nm. We conclude that this new combination of methods is a robust and improved strategy for the isolation of EVs, and in particular small EVs compatible with exosomes, from cell culture media without the use of specialized equipment such as an ultracentrifuge.

Dataset Information

The importance of extracellular vesicle purification for downstream analysis: A comparison of differential centrifugation and size exclusion chromatography for helminth pathogens.

Publications

The importance of extracellular vesicle purification for downstream analysis: A comparison of differential centrifugation and size exclusion chromatography for helminth pathogens.

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