Oxidative stress biomarkers, physiological responses and proteomic profiling in oyster (Crassostrea gigas) exposed to microplastics with irregular-shaped PE and PET microplastic

Microplastics (MPs) are currently one of the major environmental problems due to the large amount released in aquatic and terrestrial ecosystems as well as their potential impacts on organisms and human health. However, the molecular mechanisms underlying MP toxicity remain elusive and insufficiently understood. In this study, oysters were exposed to irregular MPs composed of polyethylene and polyethylene terephthalate at concentrations of 10 and 1000 μg L−1 for 21 days under static conditions, and physiological responses and changes in antioxidant enzymatic activity were investigated. Moreover, the protein expression profiles in the digestive glands were analyzed by using the isobaric tags for relative and absolute quantitation (iTRAQ) method. And the expression of ten potentially regulated genes was analyzed by qRT-PCR in different tissues under MP exposure. It was demonstrated that PE and PET MP exposure had no distinct adverse effects on physiological rates, while inducing oxidative stresses in the oyster. Kyoto encyclopedia of genes and genomes (KEGG) enrichment analysis of DEPs revealed that MP exposure mainly disturbed the “arachidonic acid metabolism”, “linoleic acid metabolism” and “glycerophospholipid metabolism” processes in oysters. Gene Ontology enrichment analysis revealed that MPs affected the oxidation-reduction process, lipid metabolism process and pentose phosphate pathway. Moreover, a significant increase in the mRNA expression of genes related to lipid and aerobic metabolism and apoptosis pathways was observed after MP exposure. In summary, our results indicated that MPs could induce oxidative stress and alter lipid and glucose metabolism processes in oysters. Additionally, the weight of evidence (WOE) model analysis suggested that high concentrations of MPs were more hazardous than low concentrations and typically higher for PET than PE. This study provided the effects of PE and PET MP toxicity on oysters at the molecular level, which will contribute to better understanding the defense mechanisms of oysters against MP exposure.