AO168=O at environmentally relevant concentrations induces reproductive toxicity by causing germline apoptosis and cell cycle arrest in Caenorhabditiselegans.

Tris(2,4-di-tert-butylphenyl) phosphate (AO168=O) is an oxidized derivative of the widely used organophosphite antioxidant tris(2,4-di-tert-butylphenyl) phosphite (AO168). AO168=O, frequently detected in environments, represents a novel organophosphate ester, the toxicity of which is poorly known. We report the effects of exposure to AO168=O on reproductive characteristics of the nematode Caenorhabditis elegans. Exposure to 1 and 10 μg/L AO168=O decreases brood size, fertilized egg number, germ cell number, and length and area of gonad arms, and enhances germline apoptosis and expressions of genes ced-3, ced-4, ced-9, and egl-1 that regulate apoptosis; apoptosis was altered by RNAi of these apoptotic regulatory genes. Additionally, AO168=O (1 and 10 μg/L) reduced germ cell number in the meiotic zone of the gonad and decreased expressions of gld-2 and gld-3 and increased those of fbf-1, cye-1, and cdk-2, suggesting that cell-cycle arrest was induced. This cell-cycle arrest could be altered by RNAi of these five genes; expression of gld-2 and gld-3 was increased by fbf-1, cye-1, and cdk-2 RNAi. AO168=O (10 μg/L) also decreased expressions of germline rho-1, let-502, and cyk-4 required for maintenance of the gonadal sheath, leading to formation of an abnormal gonadal sheath. After exposure to concentrations of 1 and 10 μg/L, AO168=O also accumulated in the nematode body. Therefore, we demonstrate that exposure to AO168=O at environmentally relevant concentrations can induce reproductive damage in a species.