Environmental and Molecular Mutagenesis - Legacy Tobacco ...

206 1989 EMS Abstracts . r -- - .-
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http://legacy.library.ucsf.edu/tid/clb93d00/pdf
of~-the adducts:Z in target tissues is ecarse . We visualized the DNA adducts Osmethylguanine
and 7- ethylguanine in tissue sections of rats and hamsters six hours
after treatment-asic3ff= .ag (i .v .) resp . 100 mg (s .c .) NNK/kg . Adducts were observed
in all target tissues for tumor formation except rat liver and pancreas . Nuclear
staining was strongest in the nasal cavity, particularly in cells of Bowman glands .
Staining was weaker in sustentacular and basal cells of the olfactory epithelium,
the respiratory epithelium and serous glands . DNA adducts were also present in the
trachea (epithelial and glandular cells) and in the bronchiolar lining of the lung
(Clara cells) . Accumulation of adducts was observed after twice weekly applications
of NNK for 8 weeks (rats : 3 .5 mg/kg, i .v . ; hamsters : 10 mg/kg, s .c ., each) in Bowman
glands, serous glands and respiratary epithelium of the nasal cavity and in Clarti"
cells . These adducts disappeared within 4 weeks after the cessation of NNK
treatment . The immunocytochemical approach permits to study the distributiun,
accumulation, persistence and repair of DNA adducts at the level of the single cell .
One of the potential applications is the detection of adducts in human tissues, e .g .
in buccal or bronchiolar cells of tobacco users .
METABOLISM OF DIETARY OENOTOXIN9 BY THE RUMAN COLONIC MICROFLORA R .L . Van Tassellt,
D .G .I Kingeton2 and T .D . Yilkinst . Departments of Anaerobic Miorobiologyt and
Chemistry2 . Virginia Polytechnic Institute and State University Blacksburg, VA . 24061
598
The microflora of the human colon is a complex ecosystem of anaerobic bacteria
which have the capability of enaymatically transforming a variety of dietary (or
biliary) compounds to genotoxic metabolites . In the past, most investigators studying
the interplay between diet and colonic flora and its role in the etiology of cancers
focused on the reductive and glycosidie potential of the bacterial enzymes - many of
which reverse the oxidative and conjugative reactions performed by the liver . Recent
work in our laboratory has focused on the metabolism of two relatively new classes of
genotoxine, the heterocyclic amines (pyrolysis carcinogens) and the fecapentaenes .
The heterocyclic amines, which originate from fried or broiled proteinaoeous foods,
normally require activation by the liver before being potent mutagens or carcinogens .
However, the "IQ" subclass (IQ . MeIQ and MeIQx) can be activated in the colon by
Eubacterium and Clostridium spp . to a 7-hydroxy form which is directly mutagenic and
thus may react directly with the adjaoent oolonic epithelium . The fecapentaenes
(conjugated ether lipids) are produced in the colon by 8aoteroides epp . from
polyunsaturated ether phospholipids (plasmalogens) whose origin is unknown . The
fecapentaenes are potent direct-aoting genotoxins that are detected in the feces of
over 75% of individuals on normal western diets . Although there is no direct evidence
that the 7-hydroxy "IQ" compounds or the fecapentaenes influence risk for colon
cancer, the potency and prevalence of these bacterial metabolites is cause for concern
- they may be carcinogens or somehow affect risk levels for cancers, particularly
colo-rectal cancer, by some other means .
599
INFLUENCE OF DNA EXCISION REPAIR ON UV-INDUCED MUTATION SPECTRA IN CHINESE
HAMSTER CELLS. H . Vricfing, M .L. van Rooijen . J . Venema, M .Z. Zdaenicka, J.W.IM. Simons, , L.H .F.
Mullenders, P .H .M . Lobman and AA. van Zeeland. Department of Radiation Genetics and Chemical Mutagenesis,
State University of Leiden, P .O . Box 9503, 2300 RA Lciden, The Netherlands .
The molecular nature of mutations induced by UV light was investigated in Aprt mutants from V79 Chinese
hamster cells isolated after exposure to a high (12 J/ms) or a low (2 J/mY) dose . The nature of point mutations in
hpn exon sequences was determined by sequence analysis of in virro amplified Apx CDNA (PCR method) . Among
the mutants analyzed all possible classes of base pair changes were present, 70% being transversions . Since all
mutations except one did occur at dipyrimidine sites, the assumption was made that they were caused by UVinduced
photoproducts at these sites . At the low dose g0% of the mutations were caused by photoproducts in nontranscribed
strand of the hpit gene . This was 64% at the high dose . We propose that the strand bias for mutation
induction towards the non-transcribed strand is caused by preferential repair of photoproducts from the transcribed
strand of the Apn gene . Removal of pyrimidino dimers from an ig kb EooRI fisgment of the hprt gene was
determined after digestion with T4 endonuclease V and analysis on alkaline agarose gels. Pyrimidine dimer removal
in the Aprt gene was 80% in 24 hours whereas this was 18% in the genome overall . UV-induced mutations were
also analyzed in a repair deficient cell line V-Hi, which is a UV sensitive derivative of V79 . UV-induced mutation
induction in V-Hl was 7 times higher per unit dase than in normal V79 cells. All UV-iaduced (2 J/ms) single base
pair changes in V-Hl were GC to AT transitions . Furthermore, 90% of the base pair changes were caused by
photoproducta in the transcribed strand of the Irpr gese . Removal of pyrimidine dimers from the hpt gene is
completely deficient in V-HI cells. We propose that most UV-induced mutations in V-Hi are caused by pyria8dine
duners and that in normal V79 cells a relatively large part of the mutations are caused by 6-4 photoproducts . The
extreme strand specificity of mutation induction in V-Hl might be due to differences in fidelity of DNA replication
of the leading and the lagging strand .