Polylactic acid microplastics and fish species intestinal inflammation risk: Associated with mitochondrial function mediated by Sesn2/Nrf2 pathway

The polylactic acid (PLA), a kind of biodegradable plastic (BP), is widely used in various industries due to its environmental friendliness. Microplastics (MPs) derived from incomplete degradation of PLA presents significant ecological and health risks to aquatic organisms. However, the potential toxic mechanism of PLA MPs on intestines is still unclear. In the present study, rare minnows (Gobiocypris rarus) were exposed to 0 µg/L, 4.5 µg/L and 18 µg/L PLA MPs for 15 d. The results showed that PLA MPs exerted slight influence on intestinal growth in rare minnows, but caused intestinal damage as evidenced by intestinal villous epithelial cells eroded and necrotic, gap of edematous mucosal layer increased and fibrosis, and significantly increased inflammatory related genes expression. Moreover, the incidence and severity of intestinal damage escalated in a concentration-dependent manner, accompanied with the severe deterioration at distal intestines. Additionally, PLA MPs exposure caused intestinal mitochondrial dysfunction, as evidenced by significantly increased mitochondrial reactive oxygen species (ROS) and markedly decreased adenosine triphosphate (ATP) contents and mitochondrial respiratory enzymes activities (p < 0.05). The further studies found that PLA MPs exposure activated intestinal oxidative stress, as evidenced by significantly increased intestinal ROS and malondialdehyde (MDA), markedly decreased antioxidative stress enzyme activities and decreased antioxidative related genes expression. And then, the expression of pro-apoptotic related genes was significantly increased in PLA MPs exposure groups compared with the control levels, but decreased in the anti-apoptotic gene. Moreover, inhibited Sesn2/Nrf2 pathway may promote mitochondrial dysfunction by amplifying oxidant responses and apoptosis under PLA MPs exposure. Taken together, environmental PLA MPs aggravated intestinal damage through Sesn2/Nrf2 pathway-mediated mitochondrial dysfunction. These findings reveal a specific molecular pathway for PLA MPs to induce intestinal damage, which will contribute to assessing the ecological risks of BMPs to aquatic organisms.