Environmental and Molecular Mutagenesis - Legacy Tobacco ...

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GENOTOXIC AND EPIGENETIC MECHANISMS OF CHEMICAL CARCINOGENESIS s IN VITRO AND IN VIVO
STUDIES . L . Orfila, C . La ~ne, I . Chouroulinkov . Cancer Research Institute, C .N .R .S .,
94802 Villejuif Cedex, France .
Genotoxicity of chemicals ia generally considered as the only mechanism of carcinogenesis
. However, it was found chemicals which are mutagenic and carcinogenic, or which
are mutagenic but not carcinogenic, and finally which are not mutagenic but carcinogenic,
such as TPA (PMA) . It is obvious that epigenetic mechanisms of carcinogenesis
are clearly involved . The question is to know the'respective importance of each of
those mechanisms in carcinogenesis . To give some answer,we have studied the effects of
benzo(a)pyrene (BaP) 12-0-dimethylbenz(aYaT :thracene (DMBA), TPA (PMA),4-NQO, 3Me-4-NQO,
testosterone and trembolone in the Syrian hamster embryo (SHE) cell transformation
system, induction of ODC and epidermal hyperplasia as well as evaluation of BaP-DNA
covalent binding in SHE and epidermal cells . Moreover, dexamethasone (D)040) was used
as inhibitor of epigenetic effects in the different systems . The results showed that
DXMO inhibits cell transformation,ODC and hyperplasia induction without inhibition of
BaP-DNA covalent binding . From these results and data from long term skin tests we can
classify the chemical carcinogens in 3 classes : with double activity,genotoxic and
epigenetic activity (BaP,DMBA,4-NQO), only epigenetic activity (TPA,testosterone,
trembolone) and only genotoxic activity (3Me-4-NQO) . The genotoxic effect appears to
play a less important role in carcinogenesis than the epigenetic one .
426
IMMUNOHISTOCHEMICAL LOCALIZATION OF DNA-ADDUCTS FORMED DURING DNA R6PLICATION .
Ofelia A . Olivero and Miriam Poirier . Laboratory of Cellular Carcinogenesis and Tumor
Promotion, National Cancer Institute . Bethesda, MD 20892 .
It has been previously reported that synchronized CHO cells exposed to H-acetoxyacetylaminoflurene(N-Ac-AAF)show
a consistent pattern of preferential adduct formation
in specific regions of metaphase chromosomes . Preliminary experiments suggested that
chromosomal adduct localization correlated with the phase of the cell cycle in which
the exposure took place . To further investigate this phenomenon, shake synchronized
CHO cells were given simultaneous non toxic doses of 5-bromodeoxyuridine(BraU)and
N-AC-AAF for 15 and 30 min periods respectively at times either early or late during
the 8 hours of S phase . Cells were allowed to complete replication and were arrested
in metaphase with colchicine . Metaphase chromosome spreads were processed for immunofluorescence
using anti-BrdU antisera and a fluorescein :ltagged second antibody to localize
sites of HrdU incorporation by DNA replicative synthesis . An antiserum specific
for guanosin-(8-yl)-aminofluorene and a streptavidin-biotin second antibody system
tagged with Texas red were used to localize DNA-adducts .The immunofluorescence staining
showed evidence of adduct formation throughout the whole of each chromosome, but bright
spots indicated regions of high adduct concentration . The BrdU incorporation sites were
coincident with the areas of high adduct concentration, indicating a correlation of DNA
damage and DNA replication . These results suggest that the most concentrated DNA-adduct
formation is a cell cycle dependent phenomenon and occurs in those regions of the
chromosome that were replicating during carcinogen exposure .
427
FORMATION OF MUTAGFNIC COMPOUNDS BY INTESTINAL BACTSRIA
T .Osawa, M .Namiki, S .Kawakishi, K .Suzuki and T .Mitsuoka, Dept . of Food Science &
Technology, Nagoya University, Chikusa, Nagoya 464-01(Japan), and The Institute of
Physical and Chemical Research, Wako, Saitama 350-01(Japan) .
In the past several years much attention has been given to the correlation between
intestinal microflora and the formation of colonic cancer . One area of specific
interest has been the correlation of microflora to cocarcinogens produced from
dietary components through interference with intestinal bacteria, however, no clear
evidence for this correlation has yet been obtained .
Preliminary experiments showed that high mutagenic activity exists in the cellfree
homogenates prepared from the six strains of intestinal bacteria in the fortyfive
strains . High DNA damaging activity has been observed in the ethyl acetate
extracts obtained from Streptococcus faecium IB 37 and Veillonella parvula ATCC 10790
as shown by the differential growth inhibition between the Bacillus subtilis strains
H17 rec+ and M45 rec- . After a large scale incubation of the strain S . faecium IB
37, isolation and purification of the active principles have been carried out .
Instrumental analyses confirmed the structures of two of DNA-damaging substances as
indole and streptindle, respectively . Streptindole is the first genotoxic di-indole
derivative found in the metabolites produced by intestinal bacteria . Streptindole
was found to be negative by bacterial reversion assays with Salmonella typhimurium
strains TA98, TA100 and TA104, however, positive in the colonic nuclear aberration
assay using C57BL/6J mouse .
http://legacy.library.ucsf.edu/tid/clb93d00/pdf
1989 EMS Abstracts 147
Notes