Aryl hydrocarbon receptor-mediated activity of mutagenic polycyclic aromatic hydrocarbons determined using in vitro reporter gene assay

Activation of aryl hydrocarbon receptor (AhR) by 30 polycyclic aromatic hyd rocarbons (PAHs) was determined in the chemical-activated luciferase expres sion (CALUX) assay, using two exposure times (6 and 24 h), in order to refl ect the metabolization of PAHs. AhR-inducing potencies of PAHs were express ed as induction equivalency factors (IEFs) relative to benzo[a]pyrene and 2 ,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In 24h exposure assay, the highe st IEFs were found for benzo[k]fluoranthene, dibenzo[a,h]anthracene and dib enzo[a,k]fluoranthene (approximately three orders of magnitude lower than T CDD) followed by dibenzo[a,j]anthracene, benzo[j]fluoranthene, indeno[1,2,3 -cd]pyrene, and naphtho[2,3-a]pyrene. The 6 h exposure to PAHs led to a sig nificantly higher AhR-mediated activity than the 24 h exposure (generally b y two orders of magnitude), probably due to the high rate of PAH metabolism . The strongest AhR inducers showed IEFs approaching that of TCDD. Several PAHs, including some strong mutagens, such as dibenzo[a,l]pyrene, cyclopent a[cd]pyrene, and benzo[a]perylene, elicited only partial agonist activity. Calculation of IEFs based on EC25 values and/or 6 h exposure data is sugges ted as an alternative approach to estimation of toxic potencies of PAHs wit h high metabolic rates and/or the weak AhR agonists. The IEFs, together wit h the recently reported relative mutagenic potencies of PAHs [Mutat. Res. 3 71 (1996) 123; Mutat, Res. 446 (1999) 1] were combined with data on concent rations of PAHs in extracts of model environmental samples (river sediments ) to calculate AhR-mediated induction equivalents and mutagenic equivalents . The highest AhR-mediated induction equivalents were found for benzo[k]flu oranthene and benzo[j]fluoranthene, followed by indeno[1,2,3-cd]pyrene, dib enzo[a,h]anthracene, benzo[a]pyrene, dibenzo[a,j]anthracene, chrysene, and benzo [b]fluoranthene. High mutagenic equivalents in the river sediments we re found for benzo[a]pyrene, dibenzo[a,e]pyrene, and naphtho[2,3-a]pyrene a nd to a lesser extent also for benzo[a] anthracene, benzo[b]fluoranthene, i ndeno[1,2,3-cd]pyrene, benzo[j]fluoranthene, dibenzo[a,e]fluoranthene and d ibenzo[a,i]pyrene. These data illustrate that AhR-mediated activity of PAHs , including the highly mutagenic compounds, occurring in the environment bu t not routinely monitored, could significantly contribute to their adverse effects. (C) 2001 Elsevier Science B.V. All rights reserved.