Subchronic Exposure to Polystyrene Microplastic Differently Affects Redox Balance in the Anterior and Posterior Intestine of Sparus aurata

SIMPLE SUMMARY: Plastics are among the most widely distributed pollutants in the sea, where they break down into microplastic particles that undergo bioaccumulation and biomagnification processes along the trophic chain. Such particles can cause toxic effects in aquatic organisms, such as cytotoxicity, inflammation, and oxidative stress. Gilthead seabream (Sparus aurata) is one of the most spread species in Mediterranean aquaculture fish. It is a species at the top of the trophic chain and is considered a good sentinel species for toxicological and bioaccumulation studies. This study aimed to investigate the adverse effects of the oral exposure to polystyrene microplastics on intestinal redox balance. We demonstrated that microplastics ingestion increases the intestinal oxidative and nitrosative stress and impairs the antioxidant defense system. This evidence confirms that the gut is a target organ for the toxic effects of ingested microplastics in fish. The observed impairment may damage the organ function, leading to the alteration of fish health status. ABSTRACT: Microplastics (MPs) are pollutants widely distributed in aquatic ecosystems. MPs are introduced mainly by ingestion acting locally or in organs far from the gastroenteric tract. MPs-induced health consequences for fish species still need to be fully understood. We aimed to investigate the effects of the subchronic oral exposure to polystyrene microplastics (PS-MPs) (1–20 μm) in the gilthead seabreams (Sparus aurata) used as the experimental model. We studied the detrimental impact of PS-MPs (25 and 250 mg/kg b.w./day) on the redox balance and antioxidant status in the intestine using histological analysis and molecular techniques. The research goal was to examine the anterior (AI) and posterior intestine (PI) tracts, characterized by morphological and functional differences. PS-MPs caused an increase of reactive oxygen species and nitrosylated proteins in both tracts, as well as augmented malondialdehyde production in the PI. PS-MPs also differently affected gene expression of antioxidant enzymes (i.e., superoxide dismutase, catalase, glutathione reductase). Moreover, an increased up-regulation of protective heat shock proteins (HSPs) (i.e., hsp70 and hsp90) was observed in PI. Our findings demonstrate that PS-MPs are responsible for oxidative/nitrosative stress and alterations of detoxifying defense system responses with differences in AI and PI of gilthead seabreams.