Effects of microplastics on head kidney gene expression and enzymatic biomarkers in adult zebrafish

Due to massive production, improper use, and disposal of plastics, microplastics have become global environmental pollutants affecting both freshwater and marine ecosystems. Several studies have documented the uptake of microplastics in wild species and the correlated biological effects, such as epithelial damage, inflammation, metabolic alterations, and neurotoxicity. However, the effects of microplastics are not fully understood yet. In this study, adult zebrafish have been exposed for twenty days to two concentrations of a mix of polystyrene and high-density polyethylene microplastics. The biological effects were investigated through the expression levels of a set of selected genes in head kidney samples and two enzymatic biomarkers, acetylcholinesterase and lactate dehydrogenase, in head and body homogenates respectively. The lowest microplastic concentration up-regulated genes involved in xenobiotics catabolic processes (cyp2p8), and adaptive immunity (tcra). Acetylcholinesterase activity was inhibited by the highest microplastics exposure, while a weaker and no significant inhibition was induced by the lowest concentration. No significant effects on lactate dehydrogenase activity were observed. The results presented in this study support the hypothesis that MPs exposure could induce the activation of an immune response and the xenobiotic metabolism, suggesting also that the cytochrome P450 enzyme cyp2p8 and acetylcholinesterase may be sensitive to MPs contamination.