In vitro Evaluation of Environmental Polycyclic Aromatic Hydrocarbon Compound (PAC) Mixtures
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Recently, multiple states have explored treatment and monitoring procedures for water reuse. Advisory panels from states such as California and Texas have recommended using effects-based bioassays to screen for emerging contaminants. Due to the presence of polycyclic aromatic hydrocarbon compound (PAC) mixtures in environmental matrices, and the activation of the Aryl hydrocarbon Receptor (AhR) by PACs, effects-based bioassays for quantifying AhR activation have been identified as useful tools to screen for emerging contaminants and mixtures with potential biological activity. To understand potential discrepancies between in vivo relative potency factors (RPF) and in vitro responses from PAC mixtures with different chemical concentration ratios, as well as compare relative potency and efficacy in vitro and in vivo, we used a commercially available assay; INDIGO Biosciences™ human AhR reporter assay, to determine relative potency (EC50 values) and efficacy (percent maximal response of MeBio positive control) of 13 individual PACs (Benzo[a]pyrene, Benzo[k]fluoranthene, Dibenz[a,h]anthracene, Chrysene, Benz[j]aceanthrylene, Benzo[b]fluoranthene, Indeno[1,2,3-cd]pyrene, Phenanthrene, Pyrene, Dibenzo[a,l]pyrene, and Dibenzothiophene), 2 equipotent PAC mixtures and 1 equimolar PAC mixture. Cells were plated in a 96 well plate and measured for luminescence (AhR activity) and cytotoxicity. Individual PAC EC50 values ranged from 4.44x10-12M to 1.65x10-8M with Acenaphthenequinone having the highest relative potency. Phenanthrene, Pyrene, Dibenzo[a,l]pyrene, and Dibenzothiophene did not activate AhR activity. Benzo[b]fluoranthene had the highest efficacy (111.6% response). The two equipotent mixtures’ 95% confidence intervals overlapped (EC50 = 1.97x10-6M – 3.90x 10-6M) which demonstrates all PACs contributed equally to the mixture response. Based on differences between potency and efficacy values of the individual compounds from in vitro and in vivo RPF, future aims include address discrepancies that may have contributed to these differences such as compound degradation, metabolite production, or adherence to in vitro wells. The views expressed in this abstract are those of the author(s) and do not necessarily represent the view or policies of the U.S. Environmental Protection Agency.