Exposure to 6-PPD quinone causes ferroptosis activation associated with induction of reproductive toxicity in Caenorhabditis elegans

Exposure to N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6-PPDQ) caused toxicity on Caenorhabditis elegans, including reproductive toxicity. However, the underlying mechanisms for this induced reproductive toxicity by 6-PPDQ remain largely unclear. We examined possible association of ferroptosis activation with reproductive toxicity of 6-PPDQ. In 1-100 μg/L 6-PPDQ exposed nematodes, Fe2+ content was increased, which was accompanied with enhanced lipid peroxidation, increased MDA (malonydialdehyde) content, and decreased GSH (L-glutathione) content. Exposure to 1-100 μg/L 6-PPDQ decreased expressions of ftn-1 encoding ferritin, ads-1 encoding AGPS, and gpx-6 encoding GPX4 and increased expression of bli-3 encoding dual oxidase. After 6-PPDQ exposure, RNAi of ftn-1 decreased ads-1 and gpx-6 expressions and increased bli-3 expression. RNAi of ftn-1, ads-1, and gpx-6 strengthened alterations in ferroptosis related indicators, and RNAi of bli-3 suppressed changes of ferroptosis related indicators in 6-PPDQ exposed nematodes. Meanwhile, RNAi of ftn-1, ads-1, and gpx-6 induced susceptibility, and RNAi of bli-3 caused resistance to 6-PPDQ reproductive toxicity. Moreover, expressions of DNA damage checkpoint genes (clk-2, mrt-2, and hus-1) could be increased by RNAi of ftn-1, ads-1, and gpx-6 in 6-PPDQ exposed nematodes. Therefore, our results demonstrated activation of ferroptosis in nematodes exposed to 6-PPDQ at environmentally relevant concentrations, and this ferroptosis activation was related to reproductive toxicity of 6-PPDQ. 6-PPD quinone (6-PPDQ) is a derivate of 6-PPD, an antioxidant added into tires. 6-PPDQ is widely distributed in different environments, including aquatic environment. Using C. elegans as an animal model, we recently observed that 6-PPDQ could cause some toxicities on organisms, including reproductive toxicity. In this study, we further found that 6-PPDQ exposure at environmentally relevant concentrations could activate ferroptosis as indicated by elevated Fe2+ content, increased lipid peroxidation, and decreased GSH content. Alteration in some molecular signals, including FTN-1, ADS-1, BLI-3, and GPX-6, mediated this ferroptosis activation. Moreover, this activated ferroptosis was associated with 6-PPDQ reproductive toxicity in nematodes.