The Majority of MicroRNAs Detectable in Serum and Saliva Is Concentrated in Exosomes

By A. Gallo, M. Tandon, I. Alevizos, G. Illei. PLoS ONE, 2012

1,049 citations recorded by the source corpus.

There is an increasing interest in using microRNAs (miRNA) as biomarkers in autoimmune diseases. They are easily accessible in many body fluids but it is controversial if they are circulating freely or are encapsulated in microvesicles, particularly exosomes. We investigated if the majority of miRNas in serum and saliva are free-circulating or concentrated in exosomes. Exosomes were isolated by ultracentrifugation from fresh and frozen human serum and saliva. The amount of selected miRNAs extracted from the exosomal pellet and the exosome-depleted serum and saliva was compared by quantitative RT-PCR. Some miRNAs tested are ubiquitously expressed, others were previously reported as biomarkers. We included miRNAs previously reported to be free circulating and some thought to be exosome specific. The purity of exosome fraction was confirmed by electronmicroscopy and western blot. The concentration of miRNAs was consistently higher in the exosome pellet compared to the exosome-depleted supernatant. We obtained the same results using an equal volume or equal amount of total RNA as input of the RT-qPCR. The concentration of miRNA in whole, unfractionated serum, was between the exosomal pellet and the exosome-depleted supernatant. Selected miRNAs, which were detectable in exosomes, were undetectable in whole serum and the exosome-depleted supernantant. Exosome isolation improves the sensitivity of miRNA amplification from human biologic fluids. Exosomal miRNA should be the starting point for early biomarker studies to reduce the probability of false negative results involving low abundance miRNAs that may be missed by using unfractionated serum or saliva.

Subfields: Cancer Research, Molecular Biology

View Paper: https://www.semanticscholar.org/paper/449dedf520b95d036c98ce398d2706b693c9da2f

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Citations in the corpus

Exosomes in Cancer Development, Metastasis and Drug Resistance: A Comprehensive Review (2013, neutral): “A recent study showed that most of the miRNAs detected in human saliva were concentrated in exosomes [109].”
Characterization of human plasma-derived exosomal RNAs by deep sequencing (2013, background): “Therefore, RNAs (at least miRNAs) in the blood stream are protected by multiple mechanisms and may be more stable than previously believed [53].”
Standardization of sample collection, isolation and analysis methods in extracellular vesicle research (2013, neutral): “So far, most EV have been analyzed from whole saliva (35,51,161).”
Overview of MicroRNA Biogenesis, Mechanisms of Actions, and Circulation (2018, background): “While several studies found that the majority of extracellular miRNAs are not associated with exosomes/microvesicles but are instead bound to AGO2 (118, 125), another study reported that extracellular miRNAs are present predominantly in exosomes in human serum and saliva (120).”
Exosome and Exosomal MicroRNA: Trafficking, Sorting, and Function (2015, background): “Accumulating evidence has shown that miRNAs can stably exist in body ﬂuids, including saliva [11,12], urine [13], breast milk [14], and blood [11,15,16].”
Circulating microRNAs in exosomes indicate hepatocyte injury and inflammation in alcoholic, drug-induced and inflammatory liver diseases (2012, background): “However, a recent study suggests that a majority of miRNAs in the serum and saliva is concentrated in exosomes.(37) Our results indicate that extracellular distribution of miRNA is distinct in different pathological conditions in the liver.”
Exosomes in Tumor Microenvironment Influence Cancer Progression and Metastasis (2013, background): “Apart from serum, exosomes can be detected in further body fluids such as urine or saliva and provide non-invasive diagnostic markers for cancer [60, 61].”
Exosomes provide a protective and enriched source of miRNA for biomarker profiling compared to intracellular and cell-free blood (2014, background): “Therefore, these exosomes may house a disease-specific miRNA signature (13), which could be useful for diagnostic purposes.”