Exosomes are small extracellular vesicles with diameters of 30-150 nm. In both physiological and pathological conditions, nearly all types of cells can release exosomes, which play important roles in cell communication and epigenetic regulation by transporting crucial protein and genetic materials such as miRNA, mRNA, and DNA. Consequently, exosome-based disease diagnosis and therapeutic methods have been intensively investigated. However, as in any natural science field, the in-depth investigation of exosomes relies heavily on technological advances. Historically, the two main technical hindrances that have restricted the basic and applied researches of exosomes include, first, how to simplify the extraction and improve the yield of exosomes and, second, how to effectively distinguish exosomes from other extracellular vesicles, especially functional microvesicles. Over the past few decades, although a standardized exosome isolation method has still not become available, a number of techniques have been established through exploration of the biochemical and physicochemical features of exosomes. In this work, by comprehensively analyzing the progresses in exosome separation strategies, we provide a panoramic view of current exosome isolation techniques, providing perspectives toward the development of novel approaches for high-efficient exosome isolation from various types of biological matrices. In addition, from the perspective of exosome-based diagnosis and therapeutics, we emphasize the issue of quantitative exosome and microvesicle separation.

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Progress, opportunity, and perspective on exosome isolation - efforts for efficient exosome-based theranostics.

The isolation and characterization of exosomes

Exosomes are small (∼30–140 nm) lipid bilayer-enclosed particles of endosomal origin. They are a subset of extracellular vesicles (EVs) that are secreted by most cell types. There has been growing interest in exosome research in the last decade due to their emerging role as intercellular messengers and their potential in disease diagnosis. Indeed, exosomes contain proteins, lipids, and RNAs that are specific to their cell origin and could deliver cargo to both nearby and distant cells. As a result, investigation of exosome cargo contents could offer opportunities for disease detection and treatment. Moreover, exosomes have been explored as natural drug delivery vehicles since they can travel safely in extracellular fluids and deliver cargo to destined cells with high specificity and efficiency. Despite significant efforts made in this relatively new field of research, progress has been held back by challenges such as inefficient separation methods, difficulties in characterization, and lack of specific biomarkers. In this review, we summarize the current knowledge in exosome biogenesis, their roles in disease progression, and therapeutic applications and opportunities in bioengineering. Furthermore, we highlight the established and emerging technological developments in exosome isolation and characterization. We aim to consider critical challenges in exosome research and provide directions for future studies.

Challenges and opportunities in exosome research—Perspectives from biology, engineering, and cancer therapy

Diabetes mellitus is characterized by a lack of insulin causing elevated blood glucose, often with associated insulin resistance. Over time, especially in genetically susceptible individuals, such chronic hyperglycemia can cause tissue injury. One pathological response to tissue injury is the development of fibrosis, which involves predominant extracellular matrix (ECM) accumulation. The main factors that regulate ECM in diabetes are thought to be pro-sclerotic cytokines and protease/anti-protease systems. This review will examine the key markers and regulators of tissue fibrosis in diabetes and whether their levels in biological fluids may have clinical utility.

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Fibrosis in diabetes complications: Pathogenic mechanisms and circulating and urinary markers

Extracellular vesicles (EVs) are membranous vesicles secreted by both prokaryotic and eukaryotic cells and play a vital role in intercellular communication. EVs are classified into several subtypes based on their origin, physical characteristics, and biomolecular makeup. Exosomes, a subtype of EVs, are released by the fusion of multivesicular bodies (MVB) with the plasma membrane of the cell. Several methods have been described in literature to isolate exosomes from biofluids including blood, urine, milk, and cell culture media, among others. While differential ultracentrifugation (dUC) has been widely used to isolate exosomes, other techniques including ultrafiltration, precipitating agents such as poly-ethylene glycol (PEG), immunoaffinity capture, microfluidics, and size-exclusion chromatography (SEC) have emerged as credible alternatives with pros and cons associated with each. In this review, we provide a summary of commonly used exosomal isolation techniques with a focus on SEC as an ideal methodology. We evaluate the efficacy of SEC to isolate exosomes from an array of biological fluids, with a particular focus on its application to adipose tissue-derived exosomes. We argue that exosomes isolated via SEC are relatively pure and functional, and that this methodology is reproducible, scalable, inexpensive, and does not require specialized equipment or user expertise. However, it must be noted that while SEC is a good candidate method to isolate exosomes, direct comparative studies are required to support this conclusion.

A Review of Exosomal Isolation Methods: Is Size Exclusion Chromatography the Best Option?

Exosomes are discrete populations of small (40-200 nm in diameter) membranous vesicles that are released into the extracellular space by most cell types, eventually accumulating in the circulation. As molecular messengers, exosomes exert a broad array of vital physiologic functions by transporting information between different cell types. Because of these functional properties, they may have potential as biomarker sources for prognostic and diagnostic disease. Recent research has found that exosomes have potential to be utilized as drug delivery agents for therapeutic targets. However, basic researches on exosomes and researches on their therapeutic potential both require the existence of effective and rapid methods for their separation from human samples. In the current absence of a standardized method, there are several methods available for the separation of exosomes, but very few studies have previously compared the efficiency and suitability of these different methods. This review summarized and compared the available traditional and novel methods for the extraction of exosomes from human samples and considered their advantages and disadvantages for use in clinical laboratories and point-of-care settings.

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A Comparison of Traditional and Novel Methods for the Separation of Exosomes from Human Samples.

S100A11, a member of S100 calcium-binding protein family, is associated with the numerous processes of tumorigenesis and metastasis. In the present study, the role of S100A11, and its possible underlying mechanisms in cell proliferation, apoptosis and cell cycle distribution in human pancreatic cancer were explored. Immunohistochemical analyses of S100A11 and phosphorylated (p)-AKT serine/threonine kinase (AKT) were performed in 30 resected specimens from patients with pancreatic cancer. PANC-1 cells were transfected with pcDNA3.1-S100A11 or treated with 50 µmol/l LY294002 for 48 h. Cell proliferation was determined using a cell counting kit-8 assay, whereas apoptosis and cell cycle distribution were determined by flow cytometry analysis. The mRNA and protein levels of S100A11, and AKT were determined using semi quantitative reverse transcription-polymerase chain reaction and western blot analyses, respectively. Pearson correlation analysis revealed that the expression levels of S100A11 and p-AKT were positively correlated (r, 0.802; P<0.05). Compared with the control group, S100A11 overexpression significantly promoted PANC-1 cell proliferation and reduced the percentage of early apoptotic cells. Flow cytometric analysis indicated that the proportion of PANC-1 cells in the S phase was significantly elevated and cell percentage in the G0/G1 phase declined in response to S100A11 overexpression (all P<0.05). S100A11 overexpression also significantly increased AKT mRNA and p-AKT protein expression levels (both P<0.05). The phosphoinositide 3-kinase (PI3K) inhibitor, LY294002, significantly inhibited PANC-1 cell proliferation, promoted apoptosis and caused G1/S phase arrest in PANC-1 cells (all P<0.05). These findings together suggest that S100A11 promotes the viability and proliferation of human pancreatic cancer PANC-1 cells through the upregulation of the PI3K/AKT signaling pathway. Thus, S100A11 may be considered as a novel drug target for targeted therapy of pancreatic cancer.

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S100A11 promotes human pancreatic cancer PANC-1 cell proliferation and is involved in the PI3K/AKT signaling pathway.

γ-glutamyl transferase isoenzyme II (GGT-II) is a sensitive biomarker of hepatocellular carcinoma (HCC). However, numerous disadvantages of the traditional manual method affected its application. The commercial kit provided a convenient and fast method for the determination of GGT-II levels. The purposes of the present study were to compare the reproducibility and sensitivity between the manual and commercial kit methods and to evaluate the diagnostic efficiency for HCC with the combined analysis of GGT-II, α-L-fucosidase (AFU) and α-fetoprotein (AFP). In patients with various liver diseases (HCC, liver cirrhosis and chronic hepatitis) and normal subjects, GGT-II was detected by manual and commercial polyacrylamide gel electrophoresis (PAGE). The levels of AFU and AFP were assayed by colorimetry and a chemiluminescence immunoassay, respectively. The commercial PAGE had equal diagnostic efficiency with traditional manual PAGE and no significant differences were observed in intra- and average-gel reproducibility and GGT-II sensitivities between the manual and commercial PAGE (P>0.05). The incidence of GGT-II detected by commercial PAGE in HCC patients was 84.1% and 636.5 μmol/l h and AFP >44.0 μg/l, respectively. There were no significant correlations between GGT-II and AFU or AFP. Combined detection of GGT-II with AFU or AFP increased the diagnostic sensitivity to 92.9 and 93.8%, respectively. These results suggest that commercial PAGE provides a simple and reproducible method for GGT-II detection. Combined determination of GGT-II with AFU or AFP exhibited superior sensitivity and specificity for the diagnosis of HCC.

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Combined analysis of serum γ-glutamyl transferase isoenzyme II, α-L-fucosidase and α-fetoprotein detected using a commercial kit in the diagnosis of hepatocellular carcinoma

Effect of serum hepatitis B surface antigen levels on predicting the clinical outcomes of chronic hepatitis B infection: A meta-analysis.

Effect of combined mutations in the enhancer II and basal core promoter of hepatitis B virus on development of hepatocellular carcinoma in Qidong, China

Jing Zhu

Papers

A Comparison of Traditional and Novel Methods for the Separation of Exosomes from Human Samples.

S100A11 promotes human pancreatic cancer PANC-1 cell proliferation and is involved in the PI3K/AKT signaling pathway.

Combined analysis of serum γ-glutamyl transferase isoenzyme II, α-L-fucosidase and α-fetoprotein detected using a commercial kit in the diagnosis of hepatocellular carcinoma

Effect of serum hepatitis B surface antigen levels on predicting the clinical outcomes of chronic hepatitis B infection: A meta-analysis.

Effect of combined mutations in the enhancer II and basal core promoter of hepatitis B virus on development of hepatocellular carcinoma in Qidong, China