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D W Nebert

Publications and source records attributed to D W Nebert.

At least 307 records · Page 17Linked to original sources
PubMed1976

Importance of genetic factors influencing the metabolism of foreign compounds.

Gene differences may alter an individual's response to foreign compounds by affecting their absorption, binding, distribution, excretion, biotransformation, or drug-drug interactions. Genetic differences in the metabolism of xenobiotics among inbred strains of various laboratory animals and model systems are reviewed. The inbred mouse has been studied most extensively. Genetic differences in toxicity are shown to be caused by various environmental pollutants in several inbred strains of mice and in siblings of the (C57BL/6N)(DBA/2N)F1 X DBA/2N backcross, in which the phenotypes "aromatic hydrocarbon responsiveness" or "nonresponsiveness" had been predetermined. This trait of "responsiveness"--which refers to the capacity for induction of cytochrome P1450 and numerous monooxygenase activities by certain aromatic compounds--segregates almost exclusively as a single gene among offspring of this backcross. All nonresponsive mice ingesting benzo/a/pyrene (about 125 mg/kg per day) die within 4 weeks, whereas the survival of responsive mice receiving the chemical orally is not significantly different from that of control mice; the apparent cause of early death in these experiments in toxic depression of the bone marrow. The life span of animals exposed to certain environmental pollutants can therefore be markedly influenced by a single gene or a very small number of genes. The same genetic trait can be either beneficial or detrimental to the animal, depending on whether detoxification or metabolic potentiation occurs. There also may exist genetic differences in man's susceptibility to toxicity or cancer caused by the numerous foreign compounds in his environment.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1976

Inducible monooxygenase activities and 3-methyl-cholanthrene-initiated tumorigenesis in mouse recombinant inbred sublines.

The induction of a certain group of hepatic monooxygenase activities by polycyclic aromatic compounds is regulated by the same locus or gene cluster controlling the formation of cytochrome P1-450 (P-448) in mice. Certain inbred strains of mice are "responsive" (Ahb) to such induction, whereas others are "nonresponsive" (Ahd). A pair of closely related sublines that differ with respect to the Ah locus (for aromatic hydrocarbon responsiveness) were used to identify or confirm the pleiotropic effects of this gene. The lines were derived by sibling-mating without selection from (C57L/J x AKR/J)F2 mice; the two sublines were separated at the F12 generation. Ten microsomal monooxygenase activities and one cytosol enzyme activity known to be associated with the Ah locus were similarly associated with cytochrome P1-450 formation in these recombinant inbred sublines as well. Nine additional hepatic monooxygenase activities studied were found not to be associated with the Ah locus; certain of these activities were increased slightly, following treatment of nonresponsive as well as responsive mice with polycyclic aromatic compounds. The Ahb-containing subline was highly susceptible to 3-methylcholanthrene-induced subcutaneous sarcomas, whereas the Ah-d-containing subline was relatively resistant. These results emphasize the potential importance of this particular enzyme for the study of coordinated regulation in mammals.

Animals↗
PubMed1975

Mutagenesis of certain activated carcinogens in vitro associated with genetically mediated increases in monooxygenase activity and cytochrome P 1-450.

A bacterial mutagenesis assay and genetic differences in microsomal CO-binding cytochromes were combined in vitro to evaluate the metabolic activation of several known carcinogens to frameshift mutagens. With the use of liver fractions from C57BL/6N and DBA/2N control mice and mice treated in vivo with 3-methylcholanthrene, beta-naphthoglavone, phenobarbital, or 2,3,7,,-tetrachlorodibenzo-p-dioxin, the in vitro mutagenicity of 3-methylcholanthrene, 6-aminochrysene, and 2-acetylaminofluorene --but not benzo[a]pyrene==is closely associated with the genetically mediated difference in both aromatic hydrocarbon-inducible aryl hydrocarbon (benzo[a]pyrene) hydroxylase activity and new cytochrome P1-450 formation; such an association between 7,12-dimethylbenz[a]anthracene or benz[a]anthracene activation to mutagens in vitro and these genetic differences between C57BL/6N and DBA/2N mouse strains in uncertain. The Salmonella typhimurium histidine mutant TA1538 is more effective than tester strains TA1537 and TA1535 in the determination of 3-methylcholanthrene mutagenesis in vitro. The relationships between the histidine revertant rate as a function of both liver protein concentration per plate and mutagen concentration per plate are illustrated for 3-methylcholanthrene, benzo[a]pyrene, 6-aminochrysene, and 2-acetylaminofluorene. With the use of offspring from the appropriate genetic crosses, the aromatic hydrocarbon-inducible hydroxylase activity appears to be expressed as an autosomal dominant trait, whereas the mutagenesis of 3-methylcholanthrene in vitro appears to be expressed additively; this apparent discrepancy probably reflects different proportional amounts of phenolic benzo[a]pyrene, compared with mutagenic 3-methylcholanthrene metabolites, formed by the monooxygenase(s). 3-Methylcholanthrene, 6-aminochrysene, and 2-acetylaminofluorene--but not benzo[a]pyrene--are each more mutagenic in vitro per molecule of cytochrome P1-450 than per molecule of CO-binding cytochrome other than P1450. Diethylmaleate, a compound which depletes flutathione content in liver, and 1,1,1-trichloropropene-2,3-epoxide, an inhibitor of epoxide hydrase (EC 4.2.1.63), were also studied in vitro. Diethylmaleate, and especially 1,1,1-trichloropropene-2,3-epoxide, increases the mutagenicity of benzo[a]pyrene, whereas no increases occur with 3-methylcholanthrene, 6-aminochrysene, or 2-acetylaminofluorene activation to mutagens in vitro. Both diethylmaleate and 1,1,1-trichloropropene-2,3-epoxide cause decreases in 2-acetylaminofluorene mutagenesis in vitro when liver fractions from phenobarbital-treated mice are used.

2-Acetylaminofluorene↗
PubMed1975

Genetic expression of aryl hydrocarbon hydroxylase activity in the mouse.

Monooxygenases require NADPH and molecular oxygen during the metabolism of numerous endogenous hydrophobic substrates and carcinogenic and toxic exogenous chemicals. The complexity of these membrane-bound multicomponent drug-metabolizing enzyme systems is reviewed. What "aryl hydrocarbon (benzo[a]pyrene) hydroxylase activity" actually represents is reviewed and discussed. At least two forms of the hydroxylase activity exist and we suggest that they are associated with different molecular species of membrane-bound CO-binding hemoprotein (i.e., they are associated with different enzyme active-sties). At least two, and probably more than two, nonlinked loci are responsible for the genetic expression of new cytochrome P1450 formation and aryl hydrocarbon hydroxylase induction--and the stimulation of 10 other monooxygenase "activities"--in the mouse treated with certain aromatic hydrocarbons. The individual variability of hydroxylase activity in an inbred and in a random-bred strain of micr is illustrated. The basal hydroxylase activity appears to be inherited differently from the aromatic hydrocarbon-inducible hydroxylase activity. The potent inducer 2,3,7,8-tetrachlorodibenzo-p-dioxin can stimulate increases in these hepatic monooxygenase activities and p1450 formation in so-called "nonresponsive" mice, whereas inducers such as beta-naphthoflavone and 3-methylcholanthrene cannot. Thus, the genetically "nonresponsive" micr apparently possess the structural and regulatory genes necessary for expression of these inducible monooxygenase activities and associated new formation of cytochrome P1450. We suggest that a mutation has occurred in the "nonresponsive" inbred strains that results in production of an inducer-binding receptor having a diminished affinity for aromatic hydrocarbons.

Animals↗
PubMed1975

Evidence for the activation of 3-methylcholanthrene as a carcinogen in vivo and asa mutagen in vitro by P1 -450 from inbred strains of mice.

Genetic differences in aromatic hydrocarbon "responsiveness" exist among various mouse strains. New formation of cytochrome P1-450 and the induction aryl hydrocarbon (benzo [a ])pyrene) hydroxylase (as well as numerous other monooxygenase activities) appear to be associated ultimately with genes that cosegregate at a small number of genetic loci. By comparing "responsive" and "nonresponsive" siblings, we can evaluate the susceptibility of each individual to various mutagenic chemicals in vitro or carcinogenic agents in vivo.

Animals↗