Long-term exposure to tire-derived 6-PPD quinone causes intestinal toxicity by affecting functional state of intestinal barrier in Caenorhabditis elegans

Abstract

2-((4-Methylpentan-2-yl)amino)-5-(phenylamino)cyclohexa-2,5-diene-1,4-dione (6-PPDQ) is the ozonation product of 6-PPD, a commonly used tire preservative. Although the 6-PPDQ has been frequently detected in different environmental ecosystems, its long-term effects on organisms remain still largely unknown. We here used Caenorhabditis elegans as an experimental animal to investigate the toxic effect of prolonged exposure to 6-PPDQ (0.1–100 μg/L). After the exposure, we found that 100 μg/L 6-PPDQ caused the lethality. We further selected concentrations of 0.1–10 μg/L to examine the possible intestinal toxicity induced by 6-PPDQ. Although 0.1–10 μg/L 6-PPDQ could not influence intestinal morphology, the intestinal permeability was significantly enhanced by 1–10 μg/L 6-PPDQ as indicated by erioglaucine disodium staining. In addition, the expression of intestinal fatty acid transporter ACS-22 governing functional state of intestinal barrier was decreased by exposure to 1–10 μg/L 6-PPDQ. Meanwhile, intestinal reactive oxygen species (ROS) production was induced by 0.1–10 μg/L 6-PPDQ and lipofuscin accumulation reflected by intestinal autofluorescence was activated by 1–10 μg/L 6-PPDQ. Accompanied with activation of intestinal oxidative stress, expressions of some anti-oxidation related genes (ctl-2, sod-2, sod-3, and sod-4) were significantly increased by 0.1–10 μg/L 6-PPDQ. Moreover, intestinal RNAi of acs-22 strengthened the susceptibility of nematodes to intestinal toxicity of 6-PPDQ. Therefore, considering that the environmentally relevant concentrations of 6-PPDQ were ≤10 μg/L, our data suggested that long-term exposure to 6-PPDQ at environmentally relevant concentrations potentially results in intestinal toxicity by disrupting functional state of intestinal barrier in organisms.