Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P00492 (hypoxanthine-guanine phosphoribosyltransferase)
 2,385 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

When 7,12-dimethylbenz[a]anthracene (DMBA) and aflatoxin B1 (AFB1) were activated by hepatocytes from Fischer 344 rats fed a diet containing 2% butylated hydroxyanisole (BHA), frequencies of mutation to 6-thioguanine resistance (TGR) at the HGPRTase gene locus and to ouabain resistance (OuR) at the Na+,K(+)-ATPase gene locus in V79 cells were 30-70% less than those obtained with hepatocytes from untreated controls. A difference in the mutation frequency did not occur when dimethylnitrosamine (DMN) was activated by BHA induced- rather than control-hepatocytes. Analysis of hepatocytes from rats fed 2% BHA showed a small (1.5-fold), but significant, increase in glutathione levels over that in the controls but no change in activity of cytochrome P450. Cytosolic glutathione S-transferase (GST) activity was increased 2-3-fold in hepatocytes from rats fed the 2% BHA diet. These results suggest that mutagenic response to DMBA and AFB1 is reduced, at least in part, because of BHA-induction of hepatocyte GST activity; while activation of DMN can occur by pathway(s) unaffected by BHA-induction of these liver enzymes. In contrast to mutation frequencies, significant differences between BHA- and control-activation in the production of sister-chromatid exchange (SCE) and micronucleus formation (MN) were not detected with any of the genotoxins. It was concluded that the mechanism(s) by which SCE and MN occur are likely unrelated to the capacity of BHA to induced activity of hepatic enzymes, e.g. the GSH S-transferases, that directly or indirectly affect mutation end-points.
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PMID:Comparative genotoxicity of 3 procarcinogens in V79 cells as related to glutathione S-transferase activity of hepatocytes from untreated rats and those fed 2% butylated hydroxyanisole. 216 83

The CHO mutant UV61 was previously assigned to complementation group 6 of UV-sensitive rodent cell mutants. UV61 is less sensitive to killing by UV radiation than mutants such as UV5, which is highly defective in the incision process that acts on UV-induced lesions. The D37 for cell survival is approximately 4 J/m2 for UV61, compared with 10 J/m2 for the parental AA8 line and approximately 2 J/m2 for UV5. Similarly, mutation induction at the hprt and aprt loci shows an intermediate response to UV61. In a post-replication recovery assay, the kinetics of maturation of pulse-labelled nascent DNA were normal after UV irradiation in UV61. Data from alkaline elution and alkaline unwinding assays showed that the rates of break accumulation and resealing, measured 0-120 min after irradiation, were also normal in the mutant. This repair incision correlated with the rapid, normal removal of pyrimidine(6-4)pyrimidone photoproducts in UV61 measured using a radioimmunoassay that is specific for this class of damage. In contrast, after exposure to 10 or 15 J/m2, no detectable removal of cyclobutane dimers from DNA was found in UV61 while AA8 cells removed 32% by 24 h. We suggest that the mutation in UV61 specifically lowers the affinity of a repair protein for cyclobutane dimers, which are also inefficiently removed from the bulk DNA of normal CHO cells. The resistance of UV61 to killing by the direct acting chemical 7-bromomethylbenz[a]anthracene was only slightly greater than that of UV5, indicating defective repair of bulky chemical adducts in addition to cyclobutane dimers.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:CHO mutant UV61 removes (6-4) photoproducts but not cyclobutane dimers. 265 25

The metabolic activation of promutagens by freshly isolated and cryopreserved rat hepatocytes was compared using the Chinese hamster ovary/hypoxanthine-guanine phosphoribosyltransferase assay (CHO/HGPRT). Cryopreserved rat hepatocytes were equivalent to freshly isolated hepatocytes in their ability to metabolize dimethylbenz(a)anthracene (DMBA) and dimethylnitrosamine (DMN) to active mutagens. Similar dose-response curves were observed using either freshly isolated or cryopreserved hepatocytes as activating systems after treatment with DMBA (0.1-1 micrograms/ml) and DMN (0.075-0.6 mg/ml). Our results suggest that cryopreserved hepatocytes are similar to freshly isolated hepatocytes as an experimental system for studies on promutagen activation.
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PMID:Promutagen activation by freshly isolated and cryopreserved rat hepatocytes. 313 8

The antioxidant butylated hydroxyanisole (BHA) and the promutagen/carcinogen 7,12-dimethylbenz[a] anthracene (DMBA) were examined for mutagenicity and the induction of sister chromatid exchanges (SCE) in a hepatocyte-mediated mutation assay with V79 Chinese hamster lung cells. Rat and hamster hepatocytes, prepared by in situ collagenase perfusion, were compared in the mutation assay to determine whether there are species differences in the ability to activate BHA and DMBA to ultimate mutagens. At the marginally cytotoxic concentration of 1.0 microM (2.6 micrograms/ml), DMBA induced a significant increase in the frequency of SCE and in the number of mutations to 6-thioguanine resistance (6-TGR) at the hypoxanthine-guanine phosphoribosyltransferase (HGPRT) locus with either rat or hamster hepatocyte-mediated activation, but induced highest mutation frequencies with rat hepatocytes. These findings support the contention that species differences can affect mutational response in hepatocyte-mediated assays with V79 cells. BHA was strongly cytotoxic to V79 cells at dose levels in excess of 0.3 mM (54 micrograms/ml). In contrast to DMBA, BHA showed no evidence of genotoxicity at marginally cytotoxic concentrations up to and including 0.3 mM as shown by the inability of this antioxidant to increase the frequency of sister chromatid exchanges or to induce mutations to 6-thioguanine resistance when activation was provided by rat or hamster hepatocytes.
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PMID:Lack of induction of sister chromatid exchanges and of mutation to 6-thioguanine resistance in V79 cells by butylated hydroxyanisole with and without activation by rat or hamster hepatocytes. 392 92

Sister chromatid exchange (SCE) is recognized as a sensitive indicator of genetic damage, and this has led numerous investigators to suggest that the analysis of SCE can provide a useful step toward the identification of environmental mutagens and/or carcinogens. To explore this approach, we measured SCE induction in V79 Chinese hamster lung cells and the frequency of mutation to 6-thioguanine resistance at the hypoxanthine-guanine phosphoribosyltransferase (HGPRT) locus in a cell-mediated mutation assay. Karyotypic analysis of V79 cells showed a stable modal chromosome number of 22 and an XY chromosome complement. When exposed to the procarcinogen 7,12-dimethylbenz[a]anthracene (DMBA) at marginally cytotoxic dose levels of 1.0, 0.5 and 0.25 microM (2.6, 1.3 and 0.65 micrograms/ml), SCE frequencies were highest within the first 24 h of activation with rat or hamster hepatocytes, showed somewhat lower values after 48 h of activation, and, following withdrawal of the chemical, declined to background levels during the period of expression. While this decline may involve several factors, the possibility is not excluded that DNA repair can contribute to the progressive elimination of SCE. The induction of SCE in V79 cells appeared unrelated to the expression of single-point mutation at the HGPRT locus. These findings demonstrate the advantage of multiple endpoint analysis which enabled cytotoxicity, mutagenicity and conditions optimal for the induction of SCE to be determined concurrently in a hepatocyte-mediated assay with V79 cells.
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PMID:In vitro short-term testing systems as prescreens for potential carcinogens: simultaneous detection of sister chromatid exchanges and mutation response in a cell-mediated assay with V79 cells. 392 93

We have developed a culture system for detecting and isolating rare hypoxanthine phosphoribosyltransferase-deficient mutants of human epidermal keratinocytes. A thioguanine-resistant variant, 3T3M1, of the Swiss mouse fibroblast line 3T3 was used as a feeder layer to support clonal growth of mutant keratinocytes. A near-diploid, epidermal squamous cell carcinoma line, SCC-13Y, was used as a prototype to determine mutagen treatment conditions, plating density, and phenotypic expression time for maximum mutant recovery. To extend this system to normal keratinocytes, we improved the culture conditions by adding insulin, adenine, and Ham's nutrient mixture F-12, which increased colony-forming efficiencies to 30% in early passage and made feasible the detection of rare mutants in normal epidermal keratinocyte populations. We have quantitated mutation in SCC-13Y and three strains of normal human epidermal keratinocytes after exposure to polycyclic aromatic hydrocarbons, which are activated to their mutagenic forms by cellular mixed-function oxidases. 7,12-Dimethylbenz[a]anthracene and benzo[a]pyrene caused almost no cytotoxicity, but induced thioguanine-resistant mutants at frequencies as much as 50-fold higher than the spontaneous frequency of approximately 10(-6). The mutants were aminopterin-sensitive and possessed no measurable hypoxanthine phosphoribosyltransferase activity; their behavior was indistinguishable from that of keratinocytes cultured from individuals with Lesch-Nyhan syndrome. This mutagenesis assay system should also be applicable to other feeder layer-dependent human epithelial cell types, such as urothelial, mammary, and tracheal epithelial cells.
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PMID:Polycyclic aromatic hydrocarbon mutagenesis of human epidermal keratinocytes in culture. 644 Jan 45

A strain of Chinese hamster ovary cells that is deficient in nucleotide excision repair, strain UV5, was compared with the normal parental CHO cells in terms of cytotoxicity and mutagenesis after exposure to several chemical carcinogens that are known to produce bulky, covalent adducts in DNA. Induced mutations were measured at the hprt locus using thioguanine resistance and at the aprt locus using azaadenine resistance. The compounds tested that required metabolic activation (using rat or hamster microsomal fractions) were 7,12-dimethylbenz(a)anthracene, 3-methylcholanthrene, benzo(a)pyrene, aflatoxin B1, 2-acetylaminofluorene, and 2-naphthylamine. The direct-acting compounds (+/-)-r-7,t-8-dihydroxy-t-9,10-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene, N-acetoxy-2-acetylaminofluorene, and N-OH-2-naphthylamine were also studied. For all compounds except 2-naphthylamine and its active metabolite, the repair-deficient cells were significantly more sensitive to killing than the normal CHO cells. Mutation induction at both loci was also more efficient in UV5 cells in each instance where enhanced cytotoxicity was observed. By using tritium-labeled N-acetoxy-2-acetylaminofluorene, normal and mutant cells were shown to bind mutagen to their nuclear DNA with similar efficiency, and a greater amount of adduct removal occurred in the normal cells. From this study it is concluded that the use of excision repair-deficient CHO cells provides enhanced sensitivity for detecting mutagenesis and that a positive differential cytotoxicity response gives an indication of repairable, potentially lethal genetic damage.
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PMID:Hypersensitivity to cell killing and mutation induction by chemical carcinogens in an excision repair-deficient mutant of CHO cells. 665 96

A murine keratinocyte cell-mediated mutagenesis assay was characterized and examined as an in vitro model system for studying the biotransformation of promutagens/procarcinogens by mouse skin. The assay used living cultured newborn SENCAR keratinocytes for the metabolic activation of promutagens and Chinese hamster lung V-79 fibroblasts for detection of resulting mutagens. Mutations at, or affecting, the hypoxanthine-guanine phosphoribosyltransferase locus were scored by resistance to 6-thioguanine. The relative mutagenicities of several polycyclic aromatic hydrocarbons (PAHs) in the cell-mediated assay correlated with the in vivo skin tumorigenicity of the PAHs determined in a two-stage carcinogenesis protocol. Metabolic activation of the promutagenic PAHs to ultimate mutagens was dependent upon the presence of the cultured keratinocyte feeder layer. 7,8-Benzoflavone, a potent inhibitor of 7,12-dimethylbenz[a]anthracene (DMBA)-dependent initiation in mouse skin, inhibited DMBA-dependent mutagenesis in the cell-mediated assay in a concentration responsive manner. The non-PAH promutagens, dimethylnitrosamine (DMN) and sterigmatocystin (STC) were both activated by cultured keratinocytes to cytotoxic derivatives. DMN was neither mutagenic in the cell-mediated assay nor tumorigenic in mouse skin when tested in a two-stage carcinogenesis protocol. STC was weakly mutagenic and tumorigenic in mouse skin.
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PMID:Keratinocyte cell-mediated mutagenesis assay: correlation with in vivo tumor studies. 683 37

Treatment of female Sprague-Dawley rats with the potent mammary gland carcinogen 7,12-dimethylbenz[a]anthracene (DMBA) results in the formation of DNA adducts with dG and dA and in the induction of 6-thioguanine-resistant (TGr) lymphocyte mutants. In this study, we have examined the types of mutations induced in TGr lymphocytes from DMBA-treated rats. DNA from 263 TGr lymphocyte clones was screened for mutations in exons 2, 3, and 8 of the hprt gene by polymerase chain reaction (PCR) amplification of the exons followed by heteroduplex analysis using denaturing gradient-gel electrophoresis. Twenty-five of the clones produced heteroduplexes in exon 2, 35 produced heteroduplexes in exon 3, and 36 produced heteroduplexes in exon 8. Direct sequence analysis of the heteroduplexes revealed 96 mutations, and at least 74 of these mutations were produced independently. Eighty-five of the total mutations were simple base pair (bp) substitutions, with A --> T and G --> T transversions being the predominant types. Seven mutations were deletions, three were complex bp substitutions, and one was an insertion. The results suggest that the types of mutations produced by DMBA in rat lymphocytes are specific to the DNA adducts produced by this compound.
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PMID:DNA sequence analysis of hprt mutations in lymphocytes from Sprague-Dawley rats treated with 7,12-dimethylbenz[a]anthracene. 869 46

The ability of the rat lymphocyte hprt assay to detect tissue-specific carcinogens was evaluated using 7,12-dimethylbenz[a]anthracene (DMBA) administered under conditions that result in mammary gland tumors. Fifty-day-old female Sprague-Dawley rats were given single doses of 5 and 20 mg/kg DMBA by gavage, and the frequency of 6-thioguanine-resistant (TGr) T-lymphocytes was measured over a period of 21 weeks. A time- and dose-dependent increase in mutant frequency was found, with a maximum frequency found 9-15 weeks after treatment with 20 mg/kg of DMBA. Rats were also dosed with 1, 2.5, 5, 10, 15 and 20 mg/kg of DMBA and assayed for TGr mutant frequency 10 weeks after treatment. A significant linear dose-response was found, with all the DMBA doses resulting in significant increases in mutant frequency. To determine whether or not DMBA-induced mutants in rat lymphocytes reflected the DNA damage in the target tissue, rats were treated with 5 and 20 mg/kg of DMBA and spleen lymphocytes and mammary gland tissue were assayed for DNA adduct formation 1, 3 and 7 days later. A similar pattern of 32P- postlabeled adducts, involving both dG and dA nucleotides, was found in DNA from both the target tissue and the surrogate lymphocytes. Adduct formation was dose responsive in both tissues, with a 2.3- to 4-fold higher concentration in mammary gland as compared with lymphocytes. These results indicate that the rat lymphocyte hprt assay is sensitive to a mammary gland carcinogen and that similar types of DNA adducts are associated with both the lymphocyte mutants and the mammary gland tumors induced by DMBA.
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PMID:Lymphocyte mutant frequency in relation to DNA adduct formation in rats treated with tumorigenic doses of the mammary gland carcinogen 7,12-dimethylbenz[a]anthracene. 887 84


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