Cytochrome P4501A Induction in Avian Hepatocyte Cultures: A Promising Approach for Predicting the Sensitivity of Avian Species to Toxic Effects of Halogenated Aromatic Hydrocarbons

Abstract

Concentration-dependent effects of halogenated aromatic hydrocarbons (HAHs) on cytochrome P4501A (CYP1A) induction in primary hepatocyte cultures prepared from embryos of chickens (four breeds), pheasants, turkeys, ducks (three breeds), and herring gulls were determined. CYP1A activity was estimated by measuring ethoxyresorufin O-deethylase (EROD) activity and the concentration of immunodetectable CYP1A was estimated using mouse monoclonal antibody 1-12-3 that was prepared against scup (Stenotomus chrysops) CYP1A1. The HAHs studies were 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,7,8-tetrachlorodibenzofuran (TCDF), 3,3',4,4'-tetrachlorobiphenyl (PCB 77, IUPAC nomenclature), 3,4,4',5-tetrachlorobiphenyl (PCB 81), 3,3',4,4',5-pentachlorobiphenyl (PCB 126), 3,3',4,4',5,5'-hexachlorobiphenyl (PCB 169), 2,3,3',4,4'-pentachlorobiphenyl (PCB 105), and 2,3',4,4',5-pentachlorobiphenyl (PCB 118). Two general types of comparisons were made: (1) relative potencies of compounds within a species (expressed relative to TCDD as induction equivalency factors, IEFs) and (2) relative sensitivity of each species to EROD induction by each compound. Three methods for estimating potency were compared. These were: (1) the concentration of inducer that produced a half-maximal (EC50) EROD response, (2) the concentration producing a response equivalent to 10% of the maximal response produced by TCDD (ECTCDD 10%), and (3) a slope ratio method. For each method, the rank order in potency was TCDD > or = TCDF > PCB 126 > PCB 81 > PCB 77 > PCB 169 in chicken, pheasant, and turkey hepatocytes. The rank order was similar in duck and herring gull hepatocytes with the following exceptions: TCDF was approximately 2- to 4-fold more potent than TCDD in duck hepatocytes; PCB 169 induced EROD in gulls, but PCB 77 had no measurable effect in this species. PCB 118 was a relatively weak EROD inducer in most species/breeds, but it did not induce EROD in Pekin ducks or gulls. PCB 105 was a weak inducer in White Leghorn chicken and turkey hepatocytes, but it did not induce EROD in other species. The EC50, ECTCDD10% and slope ratio methods for estimating potencies generally gave similar IEFs for compounds that produced a maximal response that was at least 60% of the maximal response produced by TCDD. For compounds that caused a response that was 50% or lower than that produced by TCDD, EC50-based IEFs were greater (10- to 100-fold) than ECTCDD10%-based IEFs or slope-ratio-based IEFs. Among species, the rank order in sensitivity to EROD induction was chicken > pheasant > turkey > or = duck > or = herring gull. The relative sensitivity of avian hepatocyte cultures to EROD induction by PCB 77 was similar to the relative sensitivity of these species (reported elsewhere) to lethality after in ovo injection of PCB 77. Chicken hepatocyte cultures were 5-10 times more sensitive to EROD induction by TCDD than were pheasant hepatocyte cultures, which is identical to the difference in sensitivity of these species to the lethal effect of TCDD after in ovo injection. M...

The role of selected cytochrome P450 enzymes on the bioactivation of aflatoxin B1 by duck liver microsomes

“…Our findings support previous studies where CYP1A1/2 and CYP3A4 activities were reported in ducks. Dealkylation of substituted alkylresorufins (CYP1A1/2 activity) has been reported in Mallard ducks by Riviere (1992), whereas Kennedy et al (1996) reported basal EROD (CYP1A1/2) activity in Campbell and Pekin ducks. Raynal et al (2001) reported EROD, MROD (CYP1A2), and ethylmorphine and erythromycin N-demethylase enzymatic activities (CYP3A4) in Mallard ducks.…”

Effects of in ovo exposure to 3,3′,4,4′‐tetrachlorobiphenyl (PCB 77) on heart development in tree swallow (Tachycineta bicolor)

“…However, despite the aryl hydrocarbon receptor (AhR) activity and TEQ of PCB 77, no adverse effects had been observed on embryonic survival in treated or environmentally exposed tree swallows. This lack of lethality may be ascribed to interspecific differences of PCB congeners on the activation of the AhR; according to these data, tree swallows have lower sensitivity to PCBs than other avian species [5,7,8,40]. Similarly, the potency of dioxin-like PCBs with similar chemical structures to dioxins (e.g., 2,3,7,8-tetrachlorodibenzodioxin) is toxicologically categorized by TEFs [41,42].…”

“…Avian species are variable in their sensitivity to PCB congeners, but it has been well established that coplanar dioxin-like congeners such as PCBs 77, 81, and 126 induce toxicity at higher rates than non-dioxin-like congeners [4][5][6][7][8]. Recent contaminant analysis has shown that concentrations of PCBs 77, 81, and 126 account for approximately 86, 9, and 3% respectively, of the total PCB toxic equivalents (TEQs) in tree swallow eggs collected along the Upper Hudson River in 2004 [9].…”

“…Moreover, contaminant analysis of bird eggs and nestlings collected from the Upper Hudson River showed that PCBs were detectable; in one report, geometric means of concentrations were 6.8 mg/g wet weight in tree swallows, 11.7 mg/g wet weight in kingfisher, and 12.6 mg/g wet weight in sandpiper; however, the PCB TEQs were greater in the tree swallows because of high PCB 77 concentrations [1,9,10,25,30,31]. Dioxin-like characteristics are found in PCB 77, as well as a relatively high toxicity equivalency factor (TEF) of 0.05 in chickens (TEF factors for PCB 77 in birds range from 0.0004 to 0.05), which suggests that PCB 77 may be a principal congener linked to adverse health effects mediated by the aryl hydrocarbon receptor [5,32]. Thus the high relative concentration of PCB 77 measured in eggs collected from the Hudson River environs and the high TEF of this PCB would predict adverse effects, especially with environmental exposure or injected treatment during embryonic development.…”

Relationships between environmental organochlorine contaminant residues, plasma corticosterone concentrations, and intermediary metabolic enzyme activities in Great Lakes herring gull embryos.

“…The method described by Wise and Ball (28) (31). Based on a previous study in which the relative cytochrome P4501A (CYP1A)-inducing potencies (induction equivalency factors; IEFs) of specific organochlorine contaminants in primary hepatocyte cultures prepared from herring gull embryos were reported (32), yolk sac residue data were also expressed as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) equivalents (TEQs). Expression of contaminant residue data in this manner allows estimation of the potential toxicity of complex environmental mixtures by taking into account the extreme range of potencies of specific isomers and congeners to induce CYPIA, their specific concentrations in a given sample, and interspecies differences in sensitivity to these chemicals (33 …”