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In a recent survey of pesticide concentrations in aquatic ecosystemsof Central America, the antifungal triazole compound propiconazole was found to be the most widely distributed pesticide. Previously, technical grade propiconazole (TGP) has been shown to modulate cytochrome P450 activity in mammals and birds. The present study investigated the concentration- and time-dependent effects of TGP on hepatic cytochrome CYP1A gene expression and catalytic activity in rainbow trout (Oncorhyncus mykiss). The TGP produced both a mixed-pattern response and a biphasic response for CYP1A expression following waterborne exposure. Evidence for inhibitory complex formation with cytochrome P450 may explain the occurrence of the mixed-pattern response. To further characterize the influence of TGP on CYP1A expression, a comparison was made between TGP and analytical grade propiconazole (AGP) with in vivo and in vitro assays. This comparison demonstrated that inductionof the CYP1A gene resulted from unidentified compounds in TGP. SinceTGP can be coapplied with other agricultural pesticides, either inhibition or induction of CYP1A protein activity by TGP and potentially other cytochrome P450 isoenzymes may lead to unexpected toxicologicalinteractions. [ABSTRACT FROM AUTHOR]

A method was developed to isolate lipophilic compounds efficiently from small aliquots of blood plasma and test these for total dioxin-like toxic potency using recombinant rat (H4IIE) and mouse (Hepa1c1c7) hepatoma cell lines, containing the firefly (Photinus pyralis) luciferase gene under trans-activational control of the aryl hydrocarbon receptor (AhR). For this experiment, blood plasma was used originating from eider ducks (Somateria mollissima) that had been dosed with 3,3',4,4'-tetrachlorobiphenyl (PCB-77) or with the technical PCB-mixture Clophen A50. For each sample the CALUX (chemical -activated luciferase expression) response of both the fat-containing organic extract andthe fat-free, cleaned extract were compared with data from chemical analyses of these samples. The CALUX responses for the extracts were converted into so-called CALUX TEQs (TCDD equivalents), using a 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) standard curve. The CALUX TEQs in both fatty and cleaned extracts correlated significantly with PCB-77 or PCB-153 levels (depending on the dosage group) determined in blood plasma using gas chromatography-mass spectrometry (GC-MS). For PCB-77 a toxic equivalency factor (TEF) of 1.5 X 10 -3 was calculated based on these correlations. In addition, PCB-118 and PCB-156 levels in abdominal fat (assessed with GC with electron capture detection) and hepatic ethoxyresorufin O-deethylase activities correlated well with the CALUX TEQs in both fatty and cleaned blood plasma extracts, suggesting the TEQ levels in blood offer a good measure for internal dose. Plasma cholesterol and triglyceride levels were determined as a measure of lipid content, in 10-mu l aliquots of blood plasma using enzymatic spcctrophotometric determination. In conclusion, wehave demonstrated that the CALUX assay is a rapid, sensitive assay for assessing the toxic potency of (mixtures of) AhR-active compounds in small aliquots of blood plasma. The limit of detection for the CALUX [ABSTRACT FROM AUTHOR]

Halogenated aromatic hydrocarbons (HAHs) and other chemicals that act as aryl hydrocarbon (Ah) receptor (AhR) agonists cause a variety oftoxic effects. in sac fry of many fish species, these effects include blue-sac disease and mortality. Because HAHs occur in complex mixtures, their toxicity in the environment is difficult to predict. A bioassay useful in predicting AhR-mediated toxicity to fish was developed using the RTH-149 rainbow trout hepatoma cell line. Stable transfection of this cell line with the pGudLuc1.1 plasmid, which contains a firefly luciferase reporter gene under the transcriptional regulationof dioxin responsive enhancers, has produced a recombinant cell linedesignated Remodulated Lightning Trout (RLT 2.0). The RLT 2.0 bioassay method detection limit for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is 4 pM. The responses of the RLT 2.0 bioassay to TCDD and several HAH congeners closely matched the responses observed in vivo in fish. The RLT 2.0 bioassay can provide an integrative measure of the total AhR-mediated toxic activity of complex mixtures to fish. The assaywill be useful in screening environmental extracts, guiding chemicalanalysis, and interpreting the AhR-mediated mechanism of toxicity. [ABSTRACT FROM AUTHOR]