Environmental and Molecular Mutagenesis - Legacy Tobacco ...

224 1989 EMS Abstracts 79
ACTIVATION OF MUTAGENS BY HUMAN CYTOCHROME P-450 ENZYMES . F .P . Guengerich, T. Notes
Shimada, M . Iwasakl. and M .V. Martin. Dept. of Biochemistry and Center in Molecular Toxicology .
Vanderbilt University, Nashville . Tennessee 37232
Cytochrome P-450 (P-450) enzymes have been implicated in the In otbro bloactivation of mutagens
and carcinogens (Cancer Res . 48. 2946, 1988) . The specificity of a series of the major human liver P-450
enzymes towards a series of pro-mutagens was examined tn vitro using the approaches of enzyme
reconstitution, correlation with marker activities in liver samples . selecUve inhibition and
sttmulation, and Immuno-inhibition . The endpoint used was activation of a chimeric umuC'lacZcontaining
plasmid (pSK1002) in Salmonella typhtmurtum TA1535, which is Indicative of DNA
alkylation. P-45OpA, the low Km phenacetin O-deethylase . is the major enzyme involved in the
activation of 2-aminoanthracene . 2-acetylaminofluorene . 4-amtnobiphenyl. 2-amlrtoAuorene, and the
food pyrrolysates Glu-P-1, Glu-P-2, IQ, Me1Q, MEIQx, and Trp-P-2 . P-45oNF . the nifedipine oxidase, is
the major enzyme involved in the activation of 6-aminochrysene, trls(2,3-dibrompropyl)phosphate,
aflatoxins B1 and G1 . stertgmatocystin, benzo(a)pyrene-7,8-diol . benzo(b)tluoranthene-9 .10-diol, and
7,12-dlmethyl-benz(a)anthracene-3 .4-diol. The umu system is not responsive to N-nitroaamines but
other studies (Cancer Res. 88, 1499 . 1988) suggest that P-450J is involved in the activation of
N.N-dimethyl, N-benzyl-N-methyl-, N-butyl-N-methyl- . and N,N-diethylnltrosamine. Our studies
suggest that human P-45ODB (debrisoquine 4-hydroxylase) . P-450Mp (mephenytoin 4'-hydroxylase, and
P-45OTB (tolbutamide hydroxylase) do not contribute to the activation of the compounds studied . Rat
P-450 enzymes are generally not unreasonable models for human orthologs, although a number of
results suggest cauuon in making interspectes comparisons among P-450 gene products with regard to
catalytic specificity. (Supported in part by USPHS grants CA44353 and ES00267)
225
MUTAGENICITY OF NITROSCANATE AND ITS PUTATIVE METABOLITES IN
SAIA4JNELLA MJfATION ASSAY
_R .L . Gupta, I .P. Kaur and T .R . Juneja, Department of Pharmaceutical
Sciences, Panjab University, Chandigarh-160014, INDIA .
Nitroscanate, 4-Nitrodiphenyl ether, an anthelmintic drug, belongs
to nitroarenes which have been reported to possess mutagenlcity
and carcinogenicity and their toxicity is considered to be mediated
through metabolic reduction of the nitro group . We have investigated
nitroscanate (1) and its hydrolytic product amino (2) and the corresponding
acetamido (3) including its reduction products formohydroxamic
acid (4), nitroso (5), hydroxylamine (6) and its N-acetyl
(7) and N,O-diacetyl (8) for their mutagenicity in TA98,TA98NR
(nitroreductase deficient) and TA98/1,8DNP 6 (arylhydroxylamine
esterifying deficient) . Nitroscanate was direct acting mutagen to
only TA98 suggesting that bacterial nitroreductases and esterifyinenzymes are necessary for its activation in vitro
. However, 4,9
and 6 showed direct mutagenicity to TA98 and . TA98NR and the activity
increased after mammalian S9 activation . In contrast, strain TA98/1,-
8DNP6 was markedly resistant to these compounds . It would, therefore,
appear that arylhydroxylamine esterifying bacterial enzyme Is
necessary for their activation . To conclude that nitroscanate and
its hydrolytic product are mutagenic only after reduction and subsequent
esterification .
226
Mtl1'ATIONAL SPECIFICITIES OF N-NITRC50 COMPOUBIDS• J .B. t;uttenplan ., Dept . of
Biochemistry ., N .Y . University Dental School,, and Dept . of Environmental Medicine,,
N.Y . University Medical School,~ New York,, NY (U .S .A .) .
The mutational specificities of a group of N-nitroso compounds were examined in
Salmonella using the system of Levin and Ames (Environ . Mutag .#, 8., 9-28 (1986) which
assays the six different point mutations . All strains were uvrB and harbored pia1101 .
Direct acting N-nitroso-N-alkyl derivatives of ureas anitroguanidines .. with
increasing chain length ., were compared . Additionally, N-nitcosodimethylamine (NDMA)
and nitrosomethylphenylamine [nitrosanethylaniline (NMA)j were studied . Consistent
with previous reports, methylnitrosourea (IRiU) induced predominantly GC--AT
transitions . Ethylnitrosourea induced mainly three base changes, . GC-AT,, AT--GC and
AT-GC with only the latter two detected at low doses . Both the propyl and butyl
con4ounds also induced these three mutations,, but the fraction resulting from AT--CG
transversions was somewhat reduced . The fraction of GC-CG tcansversions ., although
small, also increased with chain length . The fractions of GC-TA, and AT-TA
transversions increased with chain length and were quite significant for the butyl
compound . NMA induced exclusively AT--CG transversions . NDMA surprisingly exhibited
a much different profile than MNU at the doses examined . It induced both AT-TA and
GC-AT base changes when metabolized by rat or hamster S-9 fraction . Bowever ., when
metabolized by microsomes, it exhibited the same specificity as lRNU . This study
demonstrates (1) that even relatively similar compounds have their own unique
mutational profiles and (2) that the comparison of mutational profiles can be
valuable to a tool in determining whether similar compounds induce mutations by
coamon or different pathways . Supported by Grant #ES03332 .
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