Determination of plasmatic microRNA levels by ddPCR as peripheral biomarkers for IDH-wild type glioblastomas: a pilot study

BACKGROUND: Glioblastoma (GBM) is the most frequent malignant brain tumour in adults with a dismal prognosis. Peripheral biomarkers may be useful and effective in managing patients affected by GBM. The aim of our study was to analyse the plasmatic levels of three miRNAs as possible GBM-specific biomarkers. We focused on miR-21-5p – an onco-miR overexpressed in blood, tumour tissue and cell cultures derived from patients affected by GBM – miR-23b-3p – overexpressed in GBM, especially under hypoxic conditions – and miR-34a-5p – a tumour suppressor miR downregulated in tumour tissue and serum of patients with GBM. MATERIALS AND METHODS: Eight patients presenting with firstly-diagnosed IDH-wild type GBM and 10 age- and gender-matched healthy volunteers (hV) have been enrolled in the study. Peripheral blood samples were collected at diagnosis and one month after surgery. Total RNA was isolated from plasma by means of miRNeasy Serum/Plasma Kit (Qiagen), according to the manufacturer’s instructions. Digital droplet PCR (ddPCR) was performed for each miRNA according to the QX200 EvaGreen ddPCR protocol. RESULTS: The circulating concentrations of miR-21-5p were in mean 24.00 (28.44) and 72.40 (147.88) copies/L in patients with GBM at diagnosis and one month after surgery (p=0.38), respectively, compared with 98.74 copies/L ( 123.60) quantified in hV (p=0.09; p=0.69). The mean peripheral levels of miR-23b-3p were 0.49 copies/L (0.49) at diagnosis and 3.02 copies/L (6.88) one month after surgery (p=0.32) in patients with GBM, and 2.56 copies/L (5.57) in hV (p=0.31; p=0.88). Analysing plasmatic expression of miR-34a-5p, 1.11 (1.55) and 1.85 copies/L (1.87) were measured on average at diagnosis and one month after surgery in patients with GBM (p=0.41), while 0.73 copies/L (0.85) in hV (p=0.52; p=0.11). CONCLUSIONS: We preliminarily reported higher concentrations of circulating miR-21-5p, miR-23b-3p and miR-34a-5p in plasma of patients affected by IDH-wild type GBM one month after surgery compared to the levels at diagnosis.