Organic Extract Contaminants from Drinking Water Activate Nrf2-Mediated Antioxidant Response in a Human Cell Line

Traditional risk assessment methods face challenges in estimating risks from drinking waters that contain low-levels of large numbers of contaminants. Here, we evaluate the toxicity of organic contaminant (OC) extracts from drinking water by examining activation of nuclear factor E2-related factor 2 (Nrf2)-mediated antioxidant response. In HepG2 cells, the Nrf2-mediated antioxidant response measured as Nrf2 protein accumulation, expression of antioxidant response element (ARE)-regulated genes and ARE-luciferase reporter gene assays were activated by OC extracts from drinking water sources that detected 25 compounds in 9 classification groups. Individual OCs induced oxidative stress at concentrations much higher than their environmental levels; however, mixtures of contaminants induced oxidative stress response at only 8 times the environmental levels. Additionally, a synthetic OC mixture prepared based on the contamination profiling of drinking water induced ARE activity to the same extent as the real world mixture, reinforcing our conclusion that these mixture exposures produce responses relevant for human exposure situations. Our study tested the possibility of assessing toxicity of OCs of drinking water using a specific ARE-pathway measurement. This approach should be broadly useful in assisting risk assessment of mixed environmental