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Biomedical subjects

D W Nebert

Publications and source records attributed to D W Nebert.

At least 235 records · Page 13Linked to original sources
PubMed1981

Genetic differences in susceptibility to chemically induced myelotoxicity and leukemia.

The Ah locus represents a complex "cluster" of genese controlling the induction of numerous drug-metabolizing enzyme "activities" by polycyclic aromatic compounds. Allelic differences at the Ah locus are reflected in the large differences in inducibility of cytochrome P1-450 and benzo[a]pyrene metabolism in numerous tissues when the mice receive the chemical daily in their diet. This experimental model system offers to the hematologist and clinical pharmacologist a means to study genetic differences in toxic chemical depression of the bone marrow, as well as a potential model to study aplastic anemia and leukemia explainable on a single-gene basis. The genetically "responsive" individual who is at increased risk for cancer caused by subcutaneous or topical or intratracheal polycyclic hydrocarbons is at decreased risk for toxicity of the bone marrow and leukemia caused by oral benzo[a]pyrene (when compared with the genetically "nonresponsive" individual receiving the same dose of the same xenobiotic). In other words, tissue sites in direct contact with the carcinogen develop cancer in responsive animals because of induced P1-450; tissues in distant sites of the body may develop malignancy in nonresponsive animals because more carcinogen reaches that tissue due to decreased P1-450 induction all over the body and therefore decreased detoxication. Not only the dct with the carcinogen develop cancer in responsive animals because of induced P1-450; tissues in distant sites of the body may develop malignancy in nonresponsive animals because more carcinogen reaches that tissue due to decreased P1-450 induction all over the body and therefore decreased detoxication. Not only the dct with the carcinogen develop cancer in responsive animals because of induced P1-450; tissues in distant sites of the body may develop malignancy in nonresponsive animals because more carcinogen reaches that tissue due to decreased P1-450 induction all over the body and therefore decreased detoxication. Not only the dose but the route of administration and the tissue in which the malignancy or toxicity develops are therefore very important in the interpretation of data from tumorigenesis or toxicity experiments involving P1-450 inducers such as polycyclic hydrocarbons. There exists sufficient evidence that heritable variation of the Ah locus occurs in man. Growing evidence indicates that persons with higher aryl hydrocarbon hydroxylase inducibility in their cultured mitogen-activated lymphocytes may have a statistically significantly increased risk for certain types of cancer and drug toxicity. It remains to be determined at the present time, however, whether this genotype can be used as a biochemical marker in the individual patient for predicting increased susceptibility to certain types of environmentally caused cancers or toxicity in man.

Animals↗
PubMed1981

Structural gene products of the murine Ah complex. Differences in ontogenesis and glucosamine incorporation between liver microsomal cytochromes P1-450 and P-448 induced by polycyclic aromatic compounds.

Antibodies against mouse-liver microsomal cytochromes P1-450 and P-448, two polycyclic aromatic inducible cytochromes, were previously developed [Negishi, M. and Nebert, D.W. (1979) J. Biol. Chem. 254, 11015-11023]. Liver microsomes from 3-methylcholanthrene-treated and phenobarbital-treated and control adult mice and 2,3,7,8-tetrachlorodibenzo-p-dioxin-treated adult and fetal mice were examined. Immunoprecipitable radioactivity was measured, following labeling with pyridoxal phosphate/NaB[3H]4 or with 125I-labeled p-aminosulfobenzoic acid/NaNO2 in vitro or with [3H]leucine, [14C]glucosamine, or [32P]O4 in vivo. (a) Induction of cytochrome P1-450 occurs developmentally earlier in gestation than induction of cytochrome P-448 when the mother is treated with polycyclic aromatic compounds. (b) There appears to be a basal form of cytochrome P-448 but no cytochrome P1-450 in control liver microsomes; inducibility of cytochrome P-448 thus ranges between 5--12-fold, whereas that of P1-450 is infinite. (c) Phenobarbital pretreatment induces no detectable P1-450 or P-448. (d) P-448 appears to be either greater in concentration than P1-450 in the membrane or more exposed than P1-450 on the microsomal membrane surface. (e) By the radioimmunoassay methods used, 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced P1-450 and P-448 in Ah-nonresponsive mice are indistinguishable from those in Ah-responsive mice; this is true in both the fetus and the adult. (f) Compared with P-448 expression, the expression of P1-450 is more closely associated with 3-methylcholanthrene-induced aryl hydrocarbon hydroxylase activity, and these two structural gene products are apparently regulated independently. (g) P-448 but not P1-450 appears to be a glycoprotein. These data illustrate further differences between two forms of polycyclic aromatic-inducible P-450 in mouse liver. Neither P1-450 nor P-448 appears to be a phosphoprotein. Neither anti-(P1-450) nor anti-(P-448) precipitates any forms of liver microsomal P-450 from beta-naphthoflavone-treated adult rabbits and, conversely, anti-LM4 (the antibody to rabbit liver microsomal P-450 form 4) does not precipitate any forms of liver microsomal P-450 from 3-methylcholanthrene-treated C57BL/6N mice.

Animals↗
PubMed1981

Birth defects and the potential role of genetic differences in drug metabolism.

A study of genetic differences in the metabolism of certain drugs can be made quite simple with the use of inbred mouse strains. Highly inducible levels of a drug-metabolizing enzyme (called cytochrome P1-450) reflect a mendelian dominant trait over low inducible levels, similar to brown eyes being a dominant trait over blue eyes. It is shown in these mice that the tendency to develop birth defects (and other intrauterine toxicity) depends upon the genetic predisposition of the individual embryo, rather than that of the maternal tissues. The experimental model system presented here provides an example that might explain clinically why sometimes only one child is affected with an apparent "drug-induced syndrome" although the mother has taken the same dose of the particular drug during each of 2 or more pregnancies. Of special interest in this study is the fact that the mother and the father both must be of a particular genotype before differences in birth defects among fetuses (due to their genotype) will be expressed.

Abnormalities, Drug-Induced↗
PubMed1980

The Ah locus. A gene with possible importance in cancer predictability.

The Ah locus represents a complex "cluster" of genes controlling the induction of numerous drug-metabolizing enzyme "activities". Regulation involves a cytosolic receptor similar in many ways to the steroid receptors. Allelic differences at the Ah locus have been shown to be associated in the mouse with increased individual risk for cancer, mutation, drug toxicity, and birth defects. Aryl hydrocarbon (benzo[a]pyrene) hydroxylase (EC 1.14.14.2) (AHH) is an inducible drug-metabolizing enzyme activity which reflects allelic differences at the Ah locus. The exists sufficient evidence that heritable variation of the Ah locus occurs in man. Growing evidence indicates that persons with higher AHH inducibility in their cultured mitogen-activated lymphocytes may have a statistically significantly increased risk for certain cancers. Experimental difficulties in the day-to-day variability of the AHH assay with cultured lymphocytes or monocytes, however, make it impossible at this time to be certain of whether this induction process is controlled principally by a single gene. It also remains to be determined at the present time whether this genotype can be used as a biochemical marker in the individual patient for predicting increased susceptibility to certain types of environmentally caused cancers or toxicity in man.

Animals↗
PubMed1980

Cultured mouse embryos metabolize benzo[a]pyrene during early gestation: genetic differences detectable by sister chromatid exchange.

Mouse embryos explanted at 7 1/2 or 8 1/2 days of gestation were cultured in medium containing benzo[a]pyrene and supplemented with 5-bromodeoxyuridine to allow detection of sister chromatid exchanges. The murine Ah locus regulates the inducible metabolism of polycyclic hydrocarbons such as benzo[a]pyrene. A high frequency of sister chromatid exchange was induced by benzo[a]pyrene in embryos from three Ah-"responsive" inbred strains (BALB/cDub, C3H/AnfCum, and C57BL/6N); there was little or no increase in two Ah-"nonresponsive" inbred strains (AKR/J and DBA/2J). Benzo[a]pyrene also induced sister chromatid exchanges in the Ah-responsive recombinant inbred line B6NXAKN-12 but not in the Ah-nonresponsive recombinant inbred line B6NXAKN-3. Sister chromatid exchange in cultured Ah-responsive mouse embryos was thus shown to be a sensitive assay. These data provide direct evidence that genetically responsive mouse embryos (early postimplantation stage) possess the subcellular processes necessary for induction of enzymes that metabolize benzo[a]pyrene to its chemically active forms(s). Both the Ah regulatory gene product (a cytoslic receptor) and the structural gene product (inducible cytochrome P1-450) therefore appear to be functional at an early embryonic age. Furthermore, this metabolic capacity may play an important role in the damage to embryonic cells by polycyclic hydracarbons.

Animals↗
PubMed1980

Differing degrees of coal-tar shampoo-induced mutagenesis in the Salmonella/liver test system in vitro.

Hexane extracts of four commercial preparations of coal tar shampoos were studied for their mutagenic properties in the Salmonella/liver test system in vitro. Three of the four shampoos were highly mutagenic, whereas the fourth was not - under our experimental conditions. By high-performance liquid chromatographic, gas-liquid chromatographic, and gas-liquid chromatography-mass spectrometric analyses, more than 35 distinct fractions could be resolved; seven polycyclic aromatic chemicals believed to be present in coal tar were tentatively assigned as the major component of some of these fractions. The shampoo extract that was most mutagenic had a greater number of distinct fractions and contained approximately 50 times more benzo[a]pyrene, compared with the one shampoo extract that was not mutagenic under our experimental conditions. The possible clinical hazards of this observed mutagenicity of certain coal tar shampoos are presently not known.

Animals↗
PubMed1980

DNA binding of benzo[a]pyrene metabolites. Effects of substrate and microsomal protein concentration in vitro, dietary contaminants, and tissue differences.

The binding of reactive benzo[a]pyrene metabolites to deproteinized DNA in vitro can be drastically changed, both quantitatively and qualitatively, in vitro by changes in the substrate concentration or the substrate/P-450 ratio, and in the intact animal by starvation or substitution of a 'purified protein test diet' for the regular laboratory chow. Liver, lung, and bowel microsomes from C57BL/6N and DBA/2N mice were examined. These data demonstrate the importance of dietary contaminants or nutrition during benzo[a]pyrene tumorigenesis. The profile of DNA binding of benzo[a]pyrene metabolites is also shown to be an extremely sensitive test for detecting minute amounts of induced cytochrome P1-450 and its associated aryl hydrocarbon (benzo[a]pyrene) hydroxylase (EC 1.14.14.2) activity. A direct correlation is not necessarily observed, however, between 'aryl hydrocarbon hydroxylase activity' and the amount of benzo[a]pyrene metabolites bound covalently to DNA. 'Untreated' genetically responsive mice are shown to have greater 'control' levels of benzo[a]pyrene metabolism in their various tissues than genetically nonresponsive mice simply on the basis that responsive mice have a lower threshold for 'responsiveness' to exogenous inducers inhaled and/or ingested in their crude diet, i.e., responsive 'control' animals already have partially induced enzymes.

Animals↗
PubMed1980

Ontogenetic expression of regulatory and structural gene products associated with the Ah locus. Comparison of rat, mouse, rabbit and Sigmoden hispedis.

The murine Ah complex represents a 'cluster' of genes controlling the induction of numerous cytochrome P-450-mediated monooxygenase 'activities' by polycyclic aromatic compounds. These forms of cytochrome represent structural gene products. A major regulatory gene product is a cytosolic receptor to which radiolabeled 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD) binds with very high affinity. Developmental differences in mouse, rat and rabbit liver have been previously reported, indicating that some form of temporal control exists during the induction of enzymes associated with the ah locus. The cytosolic receptor levels were determined by sucrose density gradient centrifugation after dextran-charcoal treatment. Hepatic receptor levels, beta-naphthoflavone-inducible and control aryl hydrocarbon hydroxylase (EC 1.14.14.2) and acetanilide 4-hydroxylase activities and total P-450 content were studied in the Sprague-Dawley rat, C57BL/6N mouse, New Zealand White rabbit and Sigmoden hispedis (cotton rat) as a function of age. 3-Methylcholanthrene-inducible and control aryl hydrocarbon hydroxylase and acetanilide 4-hydroxylase activities in nonhepatic tissues of the neonatal and adult rabbit were examined. beta-Naphthoflavone-inducible hepatic microsomal proteins detectable by sodium dodecyl sulfate-polyacrylamide gel electrophoresis were also studied in the four species. Taken altogether, the developmental data indicate that: the form of P-450 responsible for induced aryl hydrocarbon hydroxylase activity is not the same as that for induced acetanilide 4-hydroxylase, and neither one is the same as induced cytochrome P-448; the presence of the TCDD-specific cytosolic receptor per se (detected as a distinct high-specificity saturable peak on sucrose density gradients) does not guarantee the expression of inducible aryl hydrocarbon hydroxylase or acetanilide 4-hydroxylase activity; although interesting developmental differences exist among all four species examined, the TCDD-specific receptor is maximal between the neonatal and weaning period, is considerably decreased in the adult, and is suppressed even more during the latter half of pregnancy; in general, the times at which the cytosolic receptor is highest or lowest parallels quite closely the well-known increases in inducible drug-metabolizing enzymes that have been commonly observed in the rat, mouse and other laboratory animals, and more studies are necessary before we understand what the 'TCDD-specific binding peak' (as observed on the sucrose density gradients) actually represents.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗