MicroRNAs (miRNAs) are small, non-coding RNA molecules that regulate gene expression at the post-transcriptional level. Since aberrant expression of miRNAs has been proposed as usage for blood-based biomarkers, hence reliable techniques for miRNA isolation as well as stability of miRNAs in various stored conditions needs to be explored. This present study aimed to investigate the efficacy of the Trizol-based isolation technique and the stability of miRNAs in stored serum and cDNA derivatives. Total RNA, including miRNAs, was isolated from human serum and a comparison of the efficiency of the Trizol ® LS reagent isolation method against the miRNeasy ® mini kit was conducted. Expression of RNU6, miR-145, and miR-20a was determined by quantitative real-time polymerase chain reaction (qRT-PCR). We showed that Trizol ® LS isolation yielded significantly lower RNA concentrations than that of the miRNeasy ® mini kit by approximately 35%. Purity of the isolated RNAs by both methods was similar. RNU6, miR-145, and miR-20a degraded at room temperature, but all genes were stable at 4ºC, -20ºC and -80ºC for a 72-hrs period, in both serum and cDNA storage conditions. In the stored cDNA derivatives, we observed the stability of RNU6, miR-145, and miR-20a for 3 months at -20ºC, and all genes also resisted 4 repeated freeze-thaw cycles at -20ºC. In conclusion, the Trizol-based method is efficient as well as economical to use for quantification of circulating miRNAs. In addition, we proposed that the storage of miRNA-derived cDNAs may be an alternative choice to avoid the stability effect.

Tumor-promoting cytokines are a cause of tumor progression; therefore, identifying key regulatory microRNAs (miRNAs) for controlling their production is important. The aim of this study is to identify promising miRNAs associated with tumor-promoting cytokines in non-small cell lung cancer (NSCLC). We identified circulating miRNAs from 16 published miRNA profiles. The selected miRNAs were validated in the serum of 32 NSCLC patients and compared with 33 patients with other lung diseases and 23 healthy persons using quantitative real-time PCR. The cytokine concentration was investigated using the enzyme-linked immunoassay in the same sample set, with clinical validation of the miRNAs. The correlation between miRNA expression and cytokine concentration was evaluated by Spearman’s rank correlation. For consistent direction, one up-regulated miRNA (miR-145) was found in four studies, and seven miRNAs were reported in three studies. One miRNA (miR-20a) and four miRNAs (miR-25-3p, miR-223, let-7f, and miR-20b) were reported in six and five studies. However, their expression was inconsistent. In the clinical validation, serum miR-145 was significantly down-regulated, whereas serum miR-20a was significantly up-regulated in NSCLC, compared with controls. Regarding serum cytokine, all cytokines [vascular endothelial growth factor (VEGF), interleukin-6 (IL-6), and transforming growth factor β (TGF-β)], except tumor necrosis factor-α (TNF-α), had a higher level in NSCLC patients than controls. In addition, we found a moderate correlation between the TGF-β concentration and miR-20a (r = −0.537, p = 0.002) and miR-223 (r = 0.428, p = 0.015) and a weak correlation between the VEGF concentration with miR-20a (r = 0.376, p = 0.037) and miR-223 (r = −0.355, p = 0.046). MiR-145 and miR-20a are potential biomarkers for NSCLC. In addition, the regulation of tumor-promoting cytokine, through miR-20a and miR-223, might be a new therapeutic approach for lung cancer.

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