Benzo[a]pyrene (BaP) exposure generates persistent reactive oxygen species (ROS) to inhibit the NF-κB pathway in medaka (Oryzias melastigma)

Benzo[a]pyrene (BaP), a common environmental pollutant, can modulate the immune-associated signal pathway NF-kappa B, which is one of the critical signal pathways involved in various immune responses. BaP exposure usually generates reactive oxygen species (ROS), but whether ROS are predominantly involved in the modulation mechanism of the NF-kappa B pathway has not been clearly understood. In this study, an in vivo examination of Oryzias melastigma demonstrated that BaP exposure led to a down-regulation of the NF-kappa B pathway and increased levels of ROS. Conversely, in vitro results using the medaka liver cell line DIT-29 and a widely applied H2O2 method showed the opposite: up-regulation of the NF-kappa B pathway. However, the down-regulation of NF-kappa B upon BaP exposure in vitro was inhibited by the addition of a ROS inhibitor, indicating ROS are involved in the modulation of NF-kappa B. The discrepancy between in vivo and in vitro results of ROS impacts on NF-kappa B activation might be related to the concentration and persistence of ROS. Using a modified luminol detection system, BaP was found to generate sustained physiological concentrations of ROS for 24 h, while an H2O2 bolus generated ROS for less than 30 min. Furthermore, a steady-state sub-micromolar H2O2 system (H(2)O(2)ss) was developed in parallel as a positive control of ROS, by which H2O2 could be maintained for 24 h. Comparative evaluation using H2O2, H(2)O(2)ss and BaP exposures on the medaka cell line with pGL4.32 demonstrated that the persistent physiological concentrations of ROS generated upon BaP exposure or treatment with H(2)O(2)ss inhibited the NF-kappa B pathway, but direct H2O2 exposure had the opposite effect. Moreover, a western-blot assay and EMSA detectidn further confirmed the modulation of the NF-kappa B pathway in DIT-29. Taken together, this study shows that BaP exposure inhibits the NF-kappa B pathway by generating sustained physiological concentrations of ROS. (C) 2019 Elsevier Ltd. All rights reserved.