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

The genotoxic risks from exposure to polycyclic aromatic hydrocarbons (PAH) have long been recognized. Less well understood are the potential genotoxic risks of the atmospheric reaction products of this class of compounds. In this investigation, we have utilized several human cell genotoxicity assays to evaluate naphthalene, phenanthrene, and their atmospheric reaction products 1-nitronaphthalene, 2-nitronaphthalene, 1-hydroxy-2-nitronaphthalene, 2-hydroxy-1-nitronaphthalene, 1,4-naphthoquinone and 2-nitrodibenzopyranone. In addition, reaction products of naphthalene were generated in a 6700-1 Teflon environmental chamber, collected on a solid adsorbent, extracted and fractionated by normal-phase HPLC. Individual fractions were then analyzed using GC-MS, and tested for genotoxicity. Genotoxicity was determined using the human B-lymphoblastoid cell line, MCL-5, which expresses several transfected P450 and epoxide hydrolase genes. Mutagenicity was evaluated at both the heterozygous tk locus and the hemizygous hprt locus, permitting detection of both intragenic and chromosomal scale mutational events. Test compounds were also screened using the CREST modified micronucleus assay. Genotoxicity results indicate that 2-nitronaphthalene and 2-nitrodibenzopyranone possess greater mutagenic potency than their parent compounds, and interestingly, both compounds induced significant increases in mutation frequency at tk but not hprt. These results suggest a mechanistic difference in human cell response as compared to bacteria, where both compounds were previously shown to induce point mutations in the Salmonella reversion assay. The genotoxicity of 2-nitronaphthalene and 2-nitrodibenzopyranone in human cells, together with their high concentrations in ambient air relative to nitro-PAH directly emitted from combustion sources, emphasizes the need to consider atmospheric reaction products of PAH in genotoxicity assessments.
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PMID:Genotoxicity induced in human lymphoblasts by atmospheric reaction products of naphthalene and phenanthrene. 935 59

Dihydrodiol epoxides (DEs) are important carcinogenic metabolites of polycyclic aromatic hydrocarbons (PAHs). The metabolic formation of four stereoisomeric DEs (a pair of optically active diastereomers termed as syn- and anti-form) is possible. Glutathione tranferases (GSTs) have been demonstrated to catalyze the detoxification of DEs. Purified GSTs display remarkable differences in catalytic efficiencies towards bay- and fjord-region DEs along with a high degree of regio- and stereoselectivity. Here we determined to which extent heterologously expressed human GSTP1-1, a major GST isoform in lung, affects the mutagenicity of stereoisomeric bay-region DEs of benzo[a]pyrene in Chinese hamster V79 cells. To evaluate the influence of sterical crowding in the substrate on the activity of GSTP-1, the study was extended to the strongly mutagenic fjord-region (-)-anti-DEs of benzo[c]phenanthrene and dibenzo[a,l]pyrene. GSTP1-1,reduced preferentially the mutagenicity (studied at the hprt locus) of (+)-anti and (+)-syn-DEs of benzo[a]pyrene (by 66 and 67%) as compared with the corresponding (-)-anti- and (-)-syn-enantiomers (by 15 and 13%). These results are in line with previous studies on the enantioselectivity of purified GSTP1-1 towards the DE isomers of benzo[a]pyrene and benzo[c]phenanthrene showing that enantiomers with (R)-configuration at the benzylic oxiranyl carbon are better substrates than those with (S)-configuration. Interestingly, the (-)-anti-DEs of benzo[c]phenanthrene and dibenzo[a,l]pyrene were efficiently detoxified by GSTP-1-1 in the constructed cell line (reduction of mutagenicity by 66 and 64%). This study demonstrates that differences in the caalytic activity seen for purified GST towards individual mutagens do not necessarily reflect the detoxification of DEs by the same enzyme in a living cell and provides further evidence that specific human GSTs play a role in the detoxification of DEs of PAHs.
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PMID:Detoxification of optically active bay- and fjord-region polycyclic aromatic hydrocarbon dihydrodiol epoxides by human glutathione transferase P1-1 expressed in Chinese hamster V79 cells. 985 12

LC-MS and LC-MS/MS analyses were used to investigate the chemoselectivity of the carcinogenic diol epoxide metabolite, (-)-(1R,2S,3S,4R)-1,2-epoxy-3,4-dihydroxy-1,2,3, 4-tetrahydrobenzo[c]phenanthrene [(-)-(R,S,S,R)-BcPh DE-2], on reaction in vitro with an oligonucleotide dodecamer derived from the HPRT gene. The sequence of this dodecamer, 5'-T(1)A(2)G(3)T(4)C(5)A(6)A(7)G(8)G(9)G(10)C(11)A(12)-3', contains a base (corresponding to A(7)) which is a hot spot for mutagenesis in the hprt gene induced by the carcinogenic (R,S,S,R)-enantiomer of benzo[a]pyrene 7,8-diol 9,10-epoxide, and an adjacent base (corresponding to A(6)) which gave no mutations with this diol epoxide. Modified oligonucleotides were generated by reaction of (-)-BcPh DE-2 with both the single-stranded and duplex forms of the dodecamer. Multiple purine targets in both strands led to the formation of complex reaction mixtures of regioisomeric BcPh DE-modified oligonucleotides, which were partially separated by reverse phase HPLC on a polystyrene-divinylbenzene column. On-line LC-MS data allowed facile distinction between adducts on the two strands of the duplex, and MS/MS analysis permitted unambiguous assignment of the major sites of modification in the regioisomeric, adducted strands. In the duplex, these sites were at A(6), A(7), and G(8). Interestingly, the "hot spot" A(7)w as about 3 times more reactive with the BcPh DE than the "cold spot" A(6). Adduct formation from the single-stranded dodecamer was less selective, and resulted in more extensive alkylation of G residues.
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PMID:HPLC-MS/MS identification of positionally isomeric benzo[c]phenanthrene diol epoxide adducts in duplex DNA. 1112 77

Chinese hamster V79 cells were exposed to a high or low concentration of the highly carcinogenic (R,S,S,R) or the less active (S,R,R,S) bay- or fjord-region diol epoxides of benzo[a]pyrene, benzo[c]phenanthrene or dibenz[c,h]acridine. Independent 8-azaguanine-resistant clones were isolated, and base substitutions at the hypoxanthine (guanine) phosphoribosyltransferase (hprt) locus were determined. For the three (R,S,S,R) diol epoxides studied, the proportion of mutations at AT base pairs increased as the concentration of diol epoxide decreased. Concentration-dependent differences in the mutational profile were not observed, however, for the three (S,R,R,S) diol epoxides. In studies, with V-H1 cells (a DNA repair deficient variant of V79 cells), a concentration-dependent difference in the profile of mutations for the (R,S,S,R) diol epoxide of benzo[a]pyrene was not observed. These results suggest that concentration-dependent differences in the mutational profile are dependent on an intact DNA repair system. In additional studies, we initiated mouse skin with a high or low dose of benzo[a]pyrene and promoted the mice for 26 weeks with 12-O-tetradecanoylphorbol-13-acetate. Papillomas were examined for mutations in the c-Ha-ras proto-oncogene. Dose-dependent differences in the profile of c-Ha-ras mutations in the tumors were observed. In summary, (i) dose-dependent differences in mutational profiles at the hprt locus were observed in Chinese hamster V79 cells treated with several highly mutagenic and carcinogenic (R,S,S,R) bay- or fjord-region diol epoxides but not with their less active (S,R,R,S) diol epoxide enantiomers, (ii) a dose-dependent difference in the mutational profile was not observed for the (R,S,S,R) diol epoxide of benzo[a]pyrene in a DNA-repair defective V79 cell line, and (iii) a dose-dependent difference in the mutational profile in the c-Ha-ras proto-oncogene was observed in tumors from mice treated with a high or low dose of benzo[a]pyrene.
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PMID:Dose-dependent differences in the profile of mutations induced by carcinogenic (R,S,S,R) bay- and fjord-region diol epoxides of polycyclic aromatic hydrocarbons. 1176 16