Environmental and Molecular Mutagenesis - Legacy Tobacco ...

34 1989 EMS Abstracts
Notes exposed to fractionated doses of 6000 1=raya (1 .7 Gy weekly and an accumulated
dose of 6 .8 (}y) . Mice were sacrificed at various time during 1-
195 days after irradiation . Some changes in histopathology, cytogenetics
ultrastructure and trace element were observed . The results indicated
that radiation could induce thymoma in treated mice (66 .3%), none of it
occurred in control . By histopathological and ultrastructural studies,
4 steps appeared clearly after irradiations thymic cortex atrophy, hyperplasia,
precancerous and cancerous phenomena . Some round viruslike
particles could be seen in lymphoma cells of exposed mice . The most frequent
type of chromosomal aberration was reciprocal translocation and
the abnormal clones appeared in some cells of thymus, spleen and tone
marrow in exposed mice . But there was no significant difference on the
frequency of SCE between two groups . Both the contents of Zn and Cu
have risen after irradiation . The results suggest radiation itself is a
potential mutagen, radiation induced mutation in the target cells may
be responsible for the development of tumor and leukemia in an irradiation
subject .
http://legacy.library.ucsf.edu/tid/clb93d00/pdf
METABOLIC ACTIVATION OF 6-NITROCBRYSENE IN ISOLATED RAT HEPATOCYTES DERIVED FROM
UNINDUCED AND INDUCED SPRAGUE-DAWLEY RAT LIVERS . D .A . Casciano, K .B . Delclos,
R.P . Walker, and J .G . Shaddock . National Center for Toxicological Research,
Jefferson, AR 72079 .
It has previously been shown that 6-nitrochrysene (6-NC) can be activated to
electrophilic species capable of reacting with DNA through metabolic pathways that
form N-hydroxy-6-aminochrysene (N-hydroxy-AC) or trans-1,2-hydroxy-1,2-dihydroxy-6aminochrysene
(AC-1,2-dihydrodiol) . We have alsoemonstrated that when N-hydroxy-AC
is reacted with DNA in cell-free systems, three major adducts are formed, N-(deoxyinosin-8-yl)-6-aminochrysene
(I) . 5-(deoxyguanosin-N2-yl)-6-aminochrysene (II), and N-
(deoxyguanosin-8-yl)-6-aminochrysene (III) ; while an as yet unidentified adduct (IV)
is formed from the in vitro reaction of a microsomal metabolite of AC-1,2-dihydrodiol .
In order to test the influence of microsomal enzyme induction on the activation pathway
in an intact cell system, 6-NC was incubated with freshly isolated hepatocytes
from rats that were either untreated or pretreated with phenobarbital (PB), 3-methylcholanthrene
(3-MC) or Aroclor 1254 (ARO) . Hepatocytea isolated from untreated or PBtreated
rats formed adducts derived from N-hydroxy-AC (predominately I . II, and III),
whereas hepatocytes isolated from rats pretreated with 3-MC or ARO formed adducts
derived from AC-1,2-dihydrodiol (predominately adduct IV) . Our results provide the
first clear demonstration that exposure to inducers of drug metabolizing enzymes can
profoundly alter the qualitative pattern of adducts formed in the DNA of cells treated
with a nitro PAH .
USE OF POLYMERASE CHAIN REACTION (PCR), DIRECT SEQUENCING, AND DNA
COLONY HYBRIDIZATION IN THE CHARACTERIZATION OF SdIJKONBI .L4
?YPHIMURIUM REVERTANTS. T.A. Cebula and W.H. Koch. Food and Drug Administration,
200 C Street, S.W., Washington, D.C. 20204 .
The S. typbLnuriuas reverse mutation assay Is widely used to assess the mutagenicity and
potential carcinogenicity of a large variety of chemical compounds . Elucidation of the molecular
events anderlying the reversion of the kLsG46, 6ttD30S2, and bisC3076 mutations by well
characterized carcinogenic and mutagenic agents should provide valuable insights Into the
mechanistic relationship between bacterial mutagenesls and oncogenic potential in higher
organisms . Thus, we have developed a battery of synthetic DNA probes, discriminating single
base-pair mismatches, for use in DNA colony hybrldiatbn to study spontaneous and mutageninduced
revertants of S. &phimu.Lrsi strains harboring each of the aforementioned mutations .
Using PCR, we have selectively amplified a single 400 bp fragment encompassing the bLsC3076
locus from total genomic DNA of strain TA2637 . Direct sequencing of this fragment showed the
mutation to be a GG Insertion in a run of four C residues ; DNA sequence near the hisC3076
locus Is S'- ...TTAAAAGTGATCGCCCC=ATCCGCTIT...4'. Southern analysis, using synthetic
probes (18 men) designed to discriminate between rrild-type and hisC3076 DNA, confirmed the
sequence tindings . We are currently using PCR and direct sequencing to characterize mutant
sequences of hisD3052 and hisC3076 revertants unidentitled by the probing analysis . Thus far,
approximately 1000 A1s* revertants have been characterized using these combined methods .
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