Examination of the mechanism of phenanthrenequinone toxicity to Vibrio fischeri: evidence for a reactive oxygen species-mediated toxicity mechanism.

Phenanthrenequinone (PHQ) is a photoproduct of phenanthrene, one of the most prevalent polycyclic aromatic hydrocarbons in the environment. Phenanthrenequinone is a compound of substantial interest, because its toxicity can be much greater than its parent chemical to aquatic organisms. The toxicity mechanisms of PHQ to the luminescent marine bacterium Vibrio fischeri were examined in the present study. Phenanthrenequinone can redox cycle in bacterial cells and transfer electrons to O2, enhancing the production of superoxide (O*2-), hydrogen peroxide (H2O2), and other reactive oxygen species (ROS). Exposure of cells to PHQ increased activity of superoxide dismutase (SOD), which detoxifies the ROS superoxide. Concentrations of PHQ that induced the production of H2O2 and other ROS, as well as the elevated levels of Fe-SOD, were correlated with its toxicity as measured by luminescence. Furthermore, toxicity of PHQ to V. fischeri was lowered under the anaerobic conditions, suggesting that the absence of oxygen, which would limit the production of ROS, alleviated toxicity of PHQ. Thus, a ROS-mediated toxicity mechanism of PHQ is highly implicated by in the present study.

Effect of copper on the cytotoxicity of phenanthrene and 9,10-phenanthrenequinone to the human placental cell line, JEG-3.

The trophoblast cell line, JEG-3, was used to study the cytotoxicity of phenanthrene, 9,10-phenanthrenequinone (PHEQ), anthracene, and 9,10-anthracenedione alone and with copper. The endpoints were the capacity of cultures to reduce alamar Blue (AB), a measure of energy metabolism, and to convert carboxyfluorescein diacetate acetoxymethyl ester (CFDA AM) to carboxyfluorescein, an indication of membrane integrity. Only PHEQ elicited a cytotoxic response. PHEQ caused a concentration-dependent decline in AB but not in CFDA AM readings, suggesting an impairment to energy metabolism. In the presence of copper, PHEQ concentration-response curves were shifted to the left for AB and were obtained with CFDA AM. The Cu/PHEQ synergy is attributed to an increase in redox cycling and production of reactive oxygen species (ROS), which overwhelm antioxidant defenses, damaging energy metabolism first and then membrane integrity. The impermeable copper chelator, bathocuproine, reduced the PHEQ/copper interaction, but the permeable chelator, neocuproine, and copper together were cytotoxic.