Background Exosomes are nano-sized extracellular vesicles containing different biomolecules such as proteins and microRNAs (miRNAs) that mediate intercellular communication. Recently, numerous studies have reported the important functions of exosomal miRNAs in disease development and the potential clinical application as diagnostic biomarkers. Up to now, the most commonly used methods to extract exosomes are ultracentrifugation (UC) and precipitation-based commercial kit (e.g., ExoQuick). Generally, both UC and ExoQuick method could co-isolate contaminating proteins along with exosomes, with the UC method yielding even purer exosomes than ExoQuick. However, the comparison of these two methods on co-precipitated free miRNAs is still unknown. Methods In this study, we isolated exosomes from the human serum with exogenously added cel-miR-39 by UC and ExoQuick and compared the proportion of cel-miR-39 co-precipitated with exosomes extracted by these two methods. Results Using exogenous cel-miR-39 as free miRNAs in serum, we concluded that ExoQuick co-isolates a small proportion of free miRNAs while UC hardly precipitates any free miRNAs. We also found that incubation at 37 °C for 1 h could decrease the proportion of free miRNAs, and exosomal miRNAs like miR-126 and miR-152 also decreased when RNase A was used. In conclusion, our findings provide essential information about the details of serum exosome isolation methods for further research on exosomal miRNAs.

Background Esophageal squamous cell carcinoma (ESCC) is the leading cause of cancer death in men and women worldwide. The poor prognosis and rapid increase in ESCC incidence highlight the need to promote early detection and prediction. Identifying key molecular targets involved in ESCC monitoring and progression is critical for ESCC patients. Methods This study examined miR-25/miR-203 as a biomarker for ESCC patients. Real-time quantitative polymerase chain reaction (PCR) was used to detect miR-25/miR-203 expression levels in tissues and serum exosomes, and MiR-25/miR-203 upregulation was confirmed in ESCC. Results We found that the miR-25/miR-203 ratio in cancer tissues from 36 ESCC patients was significantly enhanced compared with that in adjacent tissues. Moreover, the serum level of miR-25/miR-203 in 57 ESCC patients was higher than that in 31 healthy volunteers. Intriguingly, in 38 ESCC patients, the level of miR-25/miR-203 decreased significantly after surgery. Using ROC curve statistical analysis, we found that each group of miR-25/miR-203 had obvious sensitivity and high specificity. The miR-25/miR-203 relationship with the clinicopathological features of ESCC patients was also analyzed. MiR-25/miR-203 was significantly associated with the ESCC TNM-stage and lymph node metastasis, which predicts the prognosis of ESCC and reflects tumor progression. Conclusions This study highlights the feasibility of using exosome-mediated miR-25/miR-203 as a vital noninvasive biomarker for the detection and treatment monitoring of ESCC.