Development of basal and induced aryl hydrocarbon (benzo[a]pyrene) hydroxylase activity in the chicken embryo in ovo.

Abstract

The development of the hepatic microsomal mixed-function oxidase system was studied to determine the basal level of embryonic enzyme activity and the inducibility of this system throughout growth and differentiation. Chicken embryo livers were assayed for basal and inducible hepatic aryl hydrocarbon hydroxylase (AHHase; designated elsewhere as AHH) activity from the first appearance of the liver as a discrete organ at 5 days of incubation (DI) through day 10 after hatching. In addition, wholeembryo and viscera preparations were assayed at 3 and 4 DI. Basal AHHase activity was equal to or greater than adult levels from 3 DI through hatching in all preparations (approximately 0.3-0.5 nmol/min per mg). A 3-fold increase in basal activity above adult values occurred at hatching. The onset of inducibility in chicken embryo liver between 5 and 6 DI was concomitant with hepatocyte differentiation. A developmental profile of 24-hr 3,4,3',4'-tetrachlorobiphenyl-induced AHHase activity showed 15-to 30-fold induction over controls from 7 DI through day 10 after hatching, with a maxmum of 15 nmol/min per mg at 14 DI and day 1 after hatching, a specific activity >50% greater than maximal induction in the adult. Embryonic AHHase activity was also induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin, 3-methylcholanthrene, 3-naphthoflavone, and sodium phenobarbital. Induction kinetics throughout embryonic development were similar to those reported for the adult chicken and other animals. These findings demonstrate development of a mixed-function oxidase system in very early embryogenesis and then in the liver as it differentiates. Liver AHHase activity is inducible throughout development and perinatally but such activity is under strict developmental regulation. The chicken embryo has adult levels of AHHase activity which would be sufficient to achieve metabolic activation of promutagens /carcinogens before and after hepatocyte differentiation.The chicken embryo is a sensitive indicator of the teratogenic (1) and mutagenic (2) capacity of xenobiotics. Since its development as the first in vivo sister chromatid exchange (SCE) assay (3), it has been used to screen more than 50 compounds for mutagenic activity, including both direct-and indirect-acting compounds (4, 5). The induction of SCEs at 3 days of incubation (DI) by compounds known to require activation to mutagenic metabolites indicates the presence of a xenobiotic-metabolizing system very early in chicken embryo development (4, 5). Furthermore, there was an increase in the frequency of SCEs at 6 DI from the same dose of an indirect-acting mutagen/carcinogen compared to the SCE frequency at 3 DI, in spite of a 17-fold increase in embryo weight, whereas the same dose of direct-acting mutagen at 6 DI as at 3 DI caused a decrease in SCEs in the older embryo (6). This differential response between 3 DI and 6 DI potentially could be explained by either an increase in basal enzyme levels or an increased inducibility of xenobiotic-metabolizing enzymes.Drummond et aL (7) report...

Cytochrome P-450 metabolic activity in embryonic and extraembryonic tissue lineages of mouse embryos.

“…Metabolism of benzo[a]pyrene by cytochrome P-450-mediated oxidation is thus the only system known to be active very early in gestation. Similar cytochrome P-450 metabolic activities are also detectable at very early stages (day 3 of incubation) of chicken embryo development (44) and in fish embryos at later stages (45). This early expression may be evidence for a role of the Ah locus in normal mammalian development other than metabolism of xenobiotics.…”

Protective effect ofBacopa monniera L. on cytarabine induced biochemical changes in chick embryo

“…In this study we observed the amniotic fluid as an indicator for drug toxicity in developing fetus of chick as model. The use of chick model for toxicological and pharmacological studies is promoted, as the mother does not influence the pharmacokinetics of the drug (8)(9).…”

Molecular basis for effects of carcinogenic heavy metals on inducible gene expression.

“…The chick embryo also possesses an active, highly inducible hepatic mixed-function oxidase enzyme system capable of metabolizing indirectacting mutagen-carcinogens to active forms (20,21,26,37,38,40). The chick embryo can also be used to specifically examine the developmental effects of agents on an embryonic system and mimics the human fetus in many important aspects with regard to its toxicology (21,37,38,40,41). Thus, this system represents an excellent nonmammalian whole animal toxicology model.…”

“…Arsenic induces phosphorylation of hsp27, increases expression of hsp27, hsp70, and hsp90 through the heat-shock factor, induces heme oxygenase, mdrl, and quinone reductase gene expression, and induces metallothionein expression by both a transcriptional and posttranscriptional mechanism, although arsenic is not a ligand for metallothionein protein binding (3,18,19). Arsenic exhibits a strong preferential binding to the vicinal dithiol of the glucocorticoid receptor, inhibiting binding of glucocorticoid hormone but not altering hsp9O binding (16,17 (10,14,21,(37)(38)(39). The chick embryo also possesses an active, highly inducible hepatic mixed-function oxidase enzyme system capable of metabolizing indirectacting mutagen-carcinogens to active forms (20,21,26,37,38,40).…”

“…Arsenic exhibits a strong preferential binding to the vicinal dithiol of the glucocorticoid receptor, inhibiting binding of glucocorticoid hormone but not altering hsp9O binding (16,17 (10,14,21,(37)(38)(39). The chick embryo also possesses an active, highly inducible hepatic mixed-function oxidase enzyme system capable of metabolizing indirectacting mutagen-carcinogens to active forms (20,21,26,37,38,40). The chick embryo can also be used to specifically examine the developmental effects of agents on an embryonic system and mimics the human fetus in many important aspects with regard to its toxicology (21,37,38,40,41).…”