CHEMICAL-ACTIVATED LUCIFERASE GENE-EXPRESSION (CALUX) - A NOVEL IN-VITRO BIOASSAY FOR AH RECEPTOR ACTIVE COMPOUNDS IN SEDIMENTS AND PORE-WATER

This study demonstrates that the novel in vitro CALUX (chemical-activa ted luciferase expression) assay is a rapid, sensitive assay for asses sing the toxic potency of (mixtures of) aryl hydrocarbon receptor (AhR )-active compounds in sediments and pore waters. A rat hepatoma (H4IIE ) cell line, stably transfected with a construct containing the dioxin -responsive element (DRE) sequence and the luciferase reporter gene, w as used to determine the relative potency or the total activities of A hR-active compounds in sediment and pore water extracts. This novel CA LUX assay had a detection limit of 0.5 fmol of 2,3,7,8-tetrachlorodibe nzo-p-dioxin (TCDD). The sensitivity and linear working range was slig htly better than for the ethoxyresorufin O-deethylase (EROD) assay in H4IIE wild type cells. The primary improvement of the CALUX assay comp ared to the EROD assay, however, is that the CALUX assay is insensitiv e to substrate inhibition. The CALUX activity induced by organic extra cts from 450-mg aliquots of sediment or 250-mu l aliquots of pore wate r corresponded with the instrumentally analyzed degree of pollution of the sediment. Using pore water, only a simple and rapid extraction pr ocedure was needed, without additional clean-up to prevent cell death. The response from pore water samples in an 8-day early life stage tes t with zebra fish (Branchydanio rerio) corresponded with the CALUX ind uction, although the correlation was sometimes disturbed by heavy meta ls. Two polychlorinated terphenyl mixtures, the PCB-substitute Ugilec 141, polybrominated diphenylethers, and the PCB-mixture Clophen A50 we re tested in the CALUX assay and had induction potencies that were 10( -4)-10(-7) compared to TCDD. (C) 1996 Society of Toxicology