Circulating microRNAs as potential biomarkers of occupational exposure to low dose organic solvents

Abstract

Circulating microRNAs (miRNAs) have been recently acknowledged as novel and non-invasive biomarkers of exposure to environmental and occupational hazardous substances. This preliminary study investigates the potential role of blood miRNAs as molecular biomarkers of exposure to the most common organic solvents (ethylbenzene, toluene, xylene) used in the shipyard painting activity. Despite the low number of recruited workers, a two-tail standard Students' test with Holm-Bonferroni adjusted p-value shows a significant up-regulation of two miRNAs (miR_6819_5p and miR_6778_5p) in exposed workers with respect to controls. A correlation analysis between miRNA, differentially expressed in exposed workers and in controls and urinary dose biomarkers i.e. methylhyppuric acid (xylenes metabolite), phenylglyoxylic and mandelic acid (ethylbenzene metabolites) S-benzyl mercapturic acid (toluene metabolite) and S-phenylmercapturic acid (benzene metabolite) measured at the end of the work-shift, allowed the identification of high correlation (0.80-0.99) of specific miRNAs with their respective urinary metabolites. MiRNA_671_5p correlated with methylhippuric, S-phenylmercapturic and S-benzyl mercapturic acid while the miRNA best correlating with the phenylglioxylic acid was miRNA_937_5p. These findings suggest miRNA as sensitive biomarkers of low dose exposure to organic chemicals used at workplace. Urinary DNA and RNA repair biomarkers coming from the oxidation product of guanine have been also associated to the different miRNAs. A significant negative association was found between 8-oxo-7,8-dihydroguanine (8-oxoGua) urinary concentration and miR_6778_5p. The findings of the present pilot study deserve to be tested on a larger population with the perspective of designing a miRNA based test of low dose exposure to organic solvents.

Keywords: Biological monitoring; Occupational exposure; Organic solvent; microRNA.

Graphical abstract

Fig. 1

Hierarchical clustering analysis with respect to the miRNA most differently expressed between exposed and control.

Fig. 2

Expression matrix for the selected miRNA. The miRNAs are grouped as up and down-regulated in exposed with respect to control subjects.

Fig. 3

Principal component analysis (PCA) performed on the miRNA of all samples of the dataset. The N1 subject is much more similar to the controls than to the exposed workers.

Fig. 4

Principal component analysis (PCA) performed on the exposure biomarkers of all samples of the dataset. The N1 subject is much more similar to the controls than to the exposed subjects.

Fig. 5

Exponential function of the (miRNA_671_5p) expression value versus the end shift concentration of Methylhyppuric acid.

Fig. 6

Exponential function of the (miRNA_6778_5p) expression value versus the concentration of the 8oxoGua. The best fitting linear regression is also shown.