Biological Evaluation of the Environmental Pollution Based on the Induction of ECOD Activity in Human Hepatoma HepG2 Cells

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The extents of pollution of the rivers flowing into Tokyo Bay as well as the Sagami River draining into Sagami Bay were studied comparatively using river sediment extracts in an assay system based on the aryl hydrocarbon receptor (AhR)-dependent induction of 7-ethoxycoumarin O-deethylase (ECOD) activity in HepG2 cells. The Tsurumi River located in the middle of Keihin Industrial District was considered most polluted. The extract of heavily polluted river sediments sampled at Namamugi on the Tsurumi River showed a reverse U-shaped dose-response curve, for which polycyclic aromatic hydrocarbons (PAHs) might be mainly responsible, in a range of non-toxic concentrations. The pollution of the Namamugi sample was roughly estimated to be 2 to 20 μg as PAHs/g soil. Based on the longitudinal study on the pollution of the Tsurumi River, the former open-air industrial waste incineration site located in the midstream was found not to be a cause for the heavy pollution at the river mouth.The reverse U-shaped dose-response curve in terms of ECOD activity shown by the river sediment extracts as well as 3-methylcholanthrene (3-MC) was reflected in the dose-response curve for the CYP1A protein, whereas the expression of CYP1A1 mRNA in HepG2 cells remained roughly stationary at higher concentrations, implying translational suppression at higher AhR agonist levels.The XRE-luciferase gene reporter assay based on the transient transfection was found to be superior to the ECOD assay, in which time-wasting deglycosylation step was unavoidable, with respects to quantitativeness and reliability.