Environmental and Molecular Mutagenesis - Legacy Tobacco ...

16 1989 EMS Abstracts
Notes
http://legacy.library.ucsf.edu/tid/clb93d00/pdf
ELECTROPHILICITY'OF NONGENOTOXIC CARCINOGENS AND GENOTOXIC NONCARCINOGENS AS MEASURED
BY THE ke TEST. G . Bakale and R .D . McCreary, Case Western Reserve University,
Cleveland, OH (USA)
The results of applying a physico-chemical short-term carcinogen-screeaing test,
the ke test, to probe the elctrophilic properties of nonganotoxic carcinogens and
genotoxic noncarcinogens will be presented . The electrophilicity of a test chemical
as measured by the ke test is based upon the reaction rate constant, ke, at which
excess electrons attach to the chemical in a nonpolar liquid (e .g., cyclohexane) ; a
diffusion-controlled ke is regarded as a positive indication that the test chemical
is an electrophile, whereas the ke of a chemical that is less than diffusioncontrolled
indicates an activation barrier to attachment and a non-electrophilic test
chemical . The pulse-conductivity syste∎ used to measure ke's in the nanosecond time
regime will be described as well as the results of screening with the ke test those
chemicals that yield conflicting rodent carcinogeniclty and bacterial mutagenicity as
determined, respectively, by National Toxicology Program (NTP) long-term animal
studies and by the Ames Salmonella test . Of 47 chemicals that are NTP rodent
carcinogens but which yield negative Ames test reponses, 26 are k-test
electrophiles. Of 23 chemicals that are noncarcinogenic in the NTP animal teits but
are mutagenic to the Ames Salmonella strains, 17 also yield positive electrophilicity
responses in the ke test . The implications of the ke-electrophilicity/bacterial
mutagenicity/rodent carcinogenicity rel}tionship to short-term screening of
carcinogens will be discussed as well as the rationale for the k test yielding
positive electrophilicity responses to procareinogens that 4have not been
metabolically activated .
PAN OBTAIIPRD BY HPLC FRACTIOd1ATION OF DIRSEL-SQGINg-EXU1UST-PARTICLE ERTRACTS ARE NOT
ACTIVATED BY 59 TISSUE HOMOGHiATE . James C . Ball and Irving Salmeen, Research Staff,
Ford Motor Company, Dearborn, MI 41821-2053 .
Diesel-sngine-exhaust-particle extracts are active in the Ames assay without the
addition of S9 . However, the interpretation of the indirect-acting mutagenicity (i .e .
mutagenicity in the presence of S9 tissue hosogenate) of these samples is difficult
because of the unknown effect of the S9 enzymes on the direct-acting mutagens . lie
carried out Ames assays on an HPLC-fractionated methylene chloride extract of a
diessl-engine-exhaust-particle aample using both TA98 and TA100 with and without the
addition of exogenous tissue homogenate . These resulta (shown below) suggest that the
"classic" PAN fraction (e .g . pyrene, chrysene, and benzo(a)pyrene) is not mutagenic
even with the addition of exogenous metabolizing enzymes and cofactors . These results
have implications for the interpretation of Ames assays of diesel-engine-exhaustparticle
extracts .
Bacterial Unfract . Fraction Number ; Rev/ug
Strain Extract 1 2 3 4 5 6 7 8
TA98 ; -S9 13 nm Q .8 5 180 66 20 39 6
+S9 8 nm znl 27 120 56 15 60 4
TA100 ;-59 1S mm Tm 7 130 70 21 38 8
_ +S9 11 r~m nl SO 130 42 22 31 6
1nm-not mutagenic ; nl~non-linear and less than 2x spont . rev .
F.FFECT OF PROTEIN A ON DRUG META90LISIKG ENZYMES
M .R .Bansal and Deepika Khanna
Department of Biophysics, Panjab University, Chandigarh 160 014, India
The phase I and phase II enzyme systems are responsible for conversion of the
carcinogen into a reactive metabolite and for its detoxification . Protein A is
known to regenerate cytochrome P-450 activity . To study the effect of protein A
on drug metabolising enzymes, female Swiss Porten rata were fed Ja'3A (24 mg in
olive oil) which caused 50% tumor incidence after five months . The palpable
tumor-bearing rats and the DMBA-fed rata without any morphological sign of tumor
were treated with 12 ug protein A in normal saline s .c . twice a week for 6 weeks .
Cytochrame P-450 levels increased significantly after protein A treatment whereas
there was no significant change in cytochrome b5 activity . DM3A-fed rate revealed
increased glutathione and glutathione-S-transferase activities . Protein A
edministration to non-tumor bearing rate showed that glutathione levels decreaseo
and glutathione-S-transferase activity increased . However, no significant change
in phase II system was observed in tumor-bearing rats treated with protein A .
It is concluded that cytochrome P-450 activities are regenerated by protein A
and hence metabolism of the carcinogen .
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