Published online May 28, 2020. doi: 10.3748/wjg.v26.i20.2570
Peer-review started: January 1, 2020
First decision: January 19, 2020
Revised: March 2, 2020
Accepted: May 13, 2020
Article in press: May 13, 2020
Published online: May 28, 2020
Small extracellular vesicles (sEVs), including exosomes, are shed from tumors into the blood circulation. These circulating sEVs are an excellent source of microRNA (miRNA) biomarkers for cancer research. Blood serum and blood plasma both contain sEVs, however at present there is no consensus on which of these two blood sample types is most useful for biomarker analysis.
Extracellular vesicle preparations derived from serum and plasma are known to be enriched in sEVs, but they also contain significant amounts of non-vesicle associated miRNAs derived from sources such as blood cells and protein-bound miRNAs. These non-vesicles associated miRNAs could interfere with cancer biomarker discovery. Our study was motivated by the need to determine which blood sample contains the least amount of non-vesicle associated miRNAs. This knowledge has the potential to improve cancer biomarker discovery and translation.
We sought to compare the miRNA profiles between serum and plasma sEV preparations to determine their suitability for biomarker studies. We also sought to compare the diagnostic performance of these two sample types using a previously established multi-miRNA biomarker panel for esophageal adenocarcinoma.
Matched serum and plasma samples from 10 healthy controls and 10 patients with esophageal adenocarcinoma were used for this study. sEVs were isolated with using ExoquickTM. RNA extracted from the vesicles was profiled using the Taqman Openarray qPCR.
The overall miRNA content was higher in plasma sEV preparations (480 miRNAs) and contained 97.5% of the miRNAs found in the serum sEV preparations (412 miRNAs). The expression of commonly expressed miRNAs was highly correlated (Spearman’s R = 0.87, P < 0.0001) between the plasma and serum sEV preparations but was consistently higher in the plasma sEV preparations. Specific blood-cell miRNAs (hsa-miR-223-3p, hsa-miR-451a, miR-19b-3p, hsa-miR-17-5p, hsa-miR-30b-5p, hsa-miR-106a-5p, hsa-miR-150-5p and hsa-miR-92a-3p) were expressed at 2.7 to 9.6 fold higher levels in the plasma sEV preparations compared to serum sEV preparations (P < 0.05). In plasma sEV preparations, the percentage of protein-associated miRNAs expressed at relatively higher levels (cycle threshold 20-25) was greater than serum sEV preparations (50% vs 31%). While the percentage of vesicle-associated miRNAs expressed at relatively higher levels was greater in the serum sEV preparations than plasma sEV preparations (70% vs 44%). A 5-miRNA biomarker panel produced a higher cross validated accuracy for discriminating patients with esophageal adenocarcinoma from healthy controls using serum sEV preparations compared with plasma sEV preparations (AUROC 0.80 vs 0.54, P < 0.05).
Although plasma sEV preparations contained more miRNAs than serum sEV preparations, they also contained more miRNAs from non-vesicle origins.
Serum appears to be more suitable than plasma for sEV miRNAs biomarkers studies. Future studies on sEV associated cancer biomarkers may benefit from using serum as the sample type for analysis.