CYTOCHROME P4501A INDUCTION IN AVIAN HEPATOCYTE CULTURES - A PROMISING APPROACH FOR PREDICTING THE SENSITIVITY OF AVIAN SPECIES TO TOXIC EFFECTS OF HALOGENATED AROMATIC-HYDROCARBONS

Concentration-dependent effects of halogenated aromatic hydrocarbons ( HAHs) on cytochrome P4501A (CYP1A) induction in primary hepatocyte cul tures prepared from embryos of chickens (four breeds), pheasants, turk eys, ducks (three breeds), and herring gulls were determined. CYP1A ac tivity 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 studied were 2,3,7,8-tetrachlo rodibenzo-p-dioxin (TCDD), 2,3,7,8-tetrachlorodibenzofuran (TCDF), 3,3 ',4,4'-tetrachlorobiphenyl (PCB 77, IUPAC nomenclature), 3,4,4',5-tetr achlorobiphenyl (PCB 81), 3,3',4,4',5-pentachlorobiphenyl (PCB 126), 3 ,3',4,4',5,5'-hexachlorobiphenyl (PCB 169), 2,3,3',4,4'-pentachlorobip henyl (PCB 105), and 2,3',4,4',5-pentachlorobiphenyl (PCB 118). Two ge neral types of comparisons were made: (1) relative potencies of compou nds within a species (expressed relative to TCDD as induction equivale ncy factors, IEFs) and (2) relative sensitivity of each species to ERO D induction by each compound. Three methods for estimating potency wer e 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 (ECTCDD10%), and (3) a slope ratio method. For each method, the rank o rder in potency was TCDD greater than or equal to TCDF > PCB 126 > PCB 81 > PCB 77 > PCB 169 in chicken, pheasant, and turkey hepatocytes. T he rank order was similar in duck and herring gull hepatocytes with th e following exceptions: TCDF was approximately 2- to 4-fold more poten t than TCDD in duck hepatocytes; PCB 169 induced EROD in gulls, but PC B 77 had no measurable effect in this species. PCB 118 was a relativel y 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 sp ecies. The EC50, ECTCDD10% and slope ratio methods for estimating pote ncies generally gave similar IEFs for compounds that produced a maxima l response that was at least 60% of the maximal response produced by T CDD. For compounds that caused a response that was 50% or lower than t hat produced by TCDD, EC50-based IEFs were greater (10- to 100-fold) t han ECTCDD10%-based IEFs or slope-ratio-based IEFs. Among species, the rank order in sensitivity to EROD induction was chicken > pheasant > turkey greater than or equal to duck greater than or equal to herring gull. The relative sensitivity of avian hepatocyte cultures to EROD in duction by PCB 77 was similar to the relative sensitivity of these spe cies (reported elsewhere) to lethality after in ovo injection of PCB 7 7. Chicken hepatocyte cultures were 5-10 times more sensitive to EROD induction by TCDD than were pheasant hepatocyte cultures, which is ide ntical to the difference in sensitivity of these species to the lethal effect of TCDD after in ovo injection. Measuring the sensitivity of h epatocyte cultures to EROD induction might be useful for estimating th e sensitivity of avian species (including rare or endangered species, where it is impossible to conduct in vivo studies) to the embryotoxic effects of TCDD, non-ortho substituted PCBs, and other aryl hydrocarbo n receptor agonists. (C) 1996 Academic Press, Inc.