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R C Garner

Publications and source records attributed to R C Garner.

At least 19 recordsLinked to original sources
PubMed1992

Smoking-related DNA adducts in human gastric cancers.

DNA was extracted from the tumour tissue of 26 patients (18 smokers, 8 non-smokers) undergoing surgery for gastric cancer, and analyzed for the presence of DNA adducts by the 32P-post-labelling method. Adducts were detected in all samples tested, and adduct levels ranged from 2 adducts/10(8) nucleotides to 60 adducts/10(8) nucleotides. In male subjects, adduct levels were significantly greater in the DNA of smokers than in that of non-smokers. These results support epidemiological data suggesting that smoking is a risk factor for gastric cancer.

Aged↗
PubMed1992

32P-postlabelling analysis of DNA from human tissues.

DNA extracted from human lung, bladder, liver, pancreas, cervix and breast tissue samples taken at autopsy (37 sample sets) was analysed by the nuclease P1 enhancement modification of the 32P-postlabelling assay for levels of aromatic carcinogen DNA adducts. Results were combined with those from a previous study for statistical analysis of 56 sample sets (32 male+24 female). A strong trend was seen for increased adduct levels in the lung DNA of smokers and a weak association for the bladder DNA of smokers compared to non-smokers. Aromatic adducts were also detected in other tissues.

Carcinogens↗
PubMed1992

Comparison of 32P-postlabelling and cytogenetic analysis of human blood treated in vitro with melphalan.

Various 32P-postlabelling methods have been evaluated for the detection of melphalan-DNA (mel-DNA) adducts in melphalan treated calf thymus DNA and human blood treated in vitro with melphalan. When the butanol extraction procedure was used for the postlabelling studies, increasing adduct levels were seen between 0.01 and 1.0 micrograms/ml melphalan (maximum adduct value = 3.29/10(8) nucleotides at 1.5 micrograms/ml melphalan). The labelling efficiency, however, was thought to be low. Human blood treated in vitro with a dose range of melphalan from 0.01 to 1.5 micrograms/ml was analysed for micronuclei, sister chromatid exchanges, chromosome aberrations and DNA adducts. A correlation was seen between mel-DNA adducts and cytogenetic damage for each of the endpoints studied.

Animals↗
PubMed1991

DNA binding, adduct characterisation and metabolic activation of aflatoxin B1 catalysed by isolated rat liver parenchymal, Kupffer and endothelial cells.

In vitro studies with rat liver parenchymal, Kupffer and endothelial cells isolated from male Sprague-Dawley rats were undertaken to investigate cell-specific bioactivation of aflatoxin B1, DNA binding and adduct formation. In the mutagenicity studies, using homogenates of all three separated liver cell populations (co-incubated with NADP+ and glucose-6-phosphate as cofactors for the cytochrome P-450 monooxygenase system) parenchymal, Kupffer and endothelial cells were able to activate aflatoxin B1 to a metabolite mutagenic to Salmonella typhimurium TA 98. In the case of nonparenchymal cells (i.e. Kupffer and endothelial cells) 10-fold higher concentrations of aflatoxin B1 had to be used to obtain a similar number of revertants to that observed with parenchymal cells. Induction studies with Aroclor 1254 led to a striking decrease in the activation of aflatoxin B1 in parenchymal cells, whereas nonparenchymal cells had a slightly enhanced metabolic activation capacity for aflatoxin B1. Metabolism studies with microsomes from induced and noninduced cells using testosterone as substrate revealed comparable results: after induction with Aroclor 1254, parenchymal cells showed a 60% decrease in the formation rate of 2 alpha-hydroxytestosterone, whereas the formation rate of this metabolite remained unchanged in nonparenchymal cells; 2 alpha-hydroxytestosterone is specifically formed by cytochrome P-450 IIC11, which also catalyses the activation of aflatoxin B1 to its epoxide. When freshly isolated, intact cells were incubated with tritiated aflatoxin B1, a dose-dependent aflatoxin B1 binding to DNA in parenchymal and nonparenchymal cells was observed. HPLC analysis of DNA acid hydrolysates of all three cell types showed the major adduct to be 8,9-dihydro-8-(N7-guanyl)-9-hydroxy-aflatoxin B1.

Aflatoxin B1↗
PubMed1991

Immunological and HPLC detection of aflatoxin adducts in human tissues after an acute poisoning incident in S.E. Asia.

Acid hydrolysed, purified DNA, extracted from formalin fixed human tissues from persons acutely exposed to aflatoxins during a poisoning incident, was found to inhibit antibody binding in a competitive aflatoxin inhibition ELISA both before and after immunoaffinity column purification. HPLC analysis of acid hydrolysates of the DNA revealed a peak with a retention time 3 min earlier than 8,9-dihydro-2-(N7-guanyl)-9-hydroxy AFB1 synthesized either by peracid activation or direct reaction of the 8,9-oxide with DNA. The major peak seen when DNA was extracted from formalin fixed tissues from rats treated with aflatoxin B1 was identical to that seen in the formalin fixed human tissues. Adduct levels ranged from 0 to 170 x 10(6) nucleotides depending on tissue type and individual examined.

Adolescent↗
PubMed1990

O6-alkyltransferase activity in normal human gastric mucosa.

The spectrum of activity of the DNA repair enzyme O6-alkyltransferase has been studied in a large series of normal stomachs in order to establish the baseline range of values for this enzyme. Sixty-eight patients with histologically normal stomachs were biopsied during the course of upper gastrointestinal endoscopy and the biopsies assayed for O6-alkyl-transferase activity. A wide spectrum of activity was found with values ranging from 38 fmol O6-guanine extracted/mg protein to over 400 fmol/mg. This suggests that there may be wide inter-individual differences in susceptibility to alkylating actions in the human gastric mucosa.

Adult↗
PubMed1990

DNA adducts in different tissues of smokers and non-smokers.

Purified DNA from human lung, liver, bladder, pancreas, breast and cervix has been analysed for DNA adducts using the nuclease P1 modification of the 32P post-labelling technique. Tissues were obtained at autopsy from 13 men and 6 women. Relatives were asked to provide information on smoking history for deceased subjects. All tissues examined except the breast had detectable adducts. In lung, bladder and pancreatic tissue a characteristic pattern of adducts was seen which has previously been reported as typical of cigarette-smoke-induced damage. Smokers and former smokers tended to have higher adduct levels than non-smokers in the tissues examined but this was only significant for the lung. There appeared to be considerable variation in adduct levels among smokers which could not be accounted for by duration or daily consumption level. Certain smokers had high adduct levels in all tissues examined, whilst in others high levels were only seen in some tissues. All cervical samples examined had detectable adducts. These results confirm the finding that cigarette smoking is associated with DNA damage in the lung and suggest that similar damage may be related to tobacco-induced neoplasms of other tissues.

Aged↗
PubMed1990

Effect of tumour promoters and non-genotoxic carcinogens on terminal differentiation and proliferation in mouse teratoma XB2 cells cultured in low calcium medium.

XB2 cells, a teratocarcinoma derived cell line of keratinocyte lineage, have been shown to proliferate and differentiate in low calcium medium (0.03 mM Ca2+) at a density of 500 cells/9.6 cm2 without the need for fibroblast feeder layers or conditioned medium. The degree of differentiation can be assessed by measurements of keratin production and stratification of colonies of cells. Both of these parameters, as well as the proliferative capacity of the cells, can be altered by treatment of the cultures with various promoting agents and non-genotoxic carcinogens. Treatment with teleocidin and 12-O-tetradecanoyl phorbol-13-acetate induced large increases in proliferation, stratification and keratinization; mezerein-treated cells showed increased stratification at higher doses; butylated hydroxyanisole treatment resulted in hyperkeratinization and hyperstratification to lower levels than that seen with the phorbol-ester-like promoters; butylated hydroxytoluene had purely hyperproliferative effects. We suggest that this culture system may provide a useful model for studies of the mechanism of promotion and non-genotoxic carcinogenesis in epithelial tissues.

Animals↗
PubMed1990

Effect of butylated hydroxyanisole on the level of DNA adduction by aristolochic acid in the rat forestomach and liver.

Administration of butylated hydroxyanisole (BHA) orally at either 0.5 g or 1 g/kg daily for 14 days to rats did not produce any DNA adducts in the forestomach as measured by the 32P-postlabeling method using (1) limiting concentrations of 32P-ATP; (2) nuclease P1 enhancement; or (3) butanol extraction. Experiments were conducted to establish the effects of BHA administration on aristolochic acid (AA) DNA adduct formation in the forestomach and liver, when BHA was administered prior to, together with or after AA administration. Adduct levels per 10(9) nucleotides in the liver after oral dosing daily for 5 days with 1 mg/kg AA and BHA (1 g/kg) or corn oil (5 ml/kg) for 7 days were as follows: (a) BHA and AA given simultaneously; 235 +/- 71, (b) AA + corn oil; 63 +/- 39, (c) AA followed by BHA; 57 +/- 13, (d) AA followed by corn oil; 91 +/- 38, (e) BHA followed by AA; 90 +/- 12, (f) corn oil followed by AA; 83 +/- 24. For the forestomach the values were: (a) 236 +/- 86, (b) 77 +/- 25, (c) 367 +/- 97, (d) 296 +/- 47, (e) 217 +/- 81, (f) 70 +/- 64. These data suggest that BHA could have an enhancing effect on AA-induced lesions in the forestomach if dosed together with, or prior to, AA as adduct levels are significantly higher than in controls.

Animals↗
PubMed1990

The mutagenic activity of ethylmethanesulphonate, benzidine and benzo[a]pyrene at the hprt locus of wild-type L5178Y mouse lymphoma cells.

Ethylmethanesulphonate (EMS), benzidine (BZD) and benzo[a]pyrene (B[a]P) were assayed for ability to induce mutation at the hprt locus of wild-type L5178Y mouse lymphoma cells. EMS was assayed in the absence of metabolic activation, B[a]P in the presence of metabolic activation (S-9 mix) and BZD both in the absence and presence of S-9. Treatment with EMS minus S-9 and B[a]P plus S-9, especially when the S-9 content of the incubation was 2% (v/v), produced strong dose-related increases in mutant frequency. BZD failed to induce mutation at the hprt locus, either in the absence or presence of S-9.

Animals↗
PubMed1990

Linear relationship between DNA adducts in human lung and cigarette smoking.

Human lung and bladder DNA has been isolated and purified from either surgical or autopsy specimens. Smoking history details were obtained from patients or their close relatives. Each DNA sample was investigated using the nuclease P1 digestion modification of the 32P-postlabelling procedure. Data are presented for 48 lung and 19 bladder specimens. The samples were subdivided into three groups for data analysis, viz. smokers, former smokers and nonsmokers. The mean adduct levels (adducts per 10(8) nucleotides) in lung samples were: [see text] The chromatographic pattern of bladder DNA adducts for smokers was similar to that for smokers' lung DNA, although less intense. Adduct levels in former smokers tended to be lower than in smokers, although loss of adducts appeared to require several years after cessation of smoking. These findings support a link between DNA adduct levels and cigarette smoking, for both the lung and the bladder. For the former tissue there was a strong linear correlation between adduct levels and the number of cigarettes smoked.

Aged↗
PubMed1979

Carcinogen prediction in the laboratory: a personal view.

Although carcinogens can be divided into various categories, i.e. viruses, physical agents and synthetic and naturally occurring chemicals, it is the latter that give rise to the greatest concern because of their number, quantity and distribution. Present methods of testing chemicals for potential carcinogenicity rely in the main on administration of these at maximally tolerated dose levels to animals, usually rodents, for the animals' lifetime. Such tests would be economically impractical for all chemicals to which man is exposed. New methods have recently been introduced to screen large numbers of chemicals quickly and cheaply which rely on the unifying hypothesis that all carcinogenic chemicals are electrophiles or must be converted to such by metabolism. These methods will be reviewed and compared with traditional methods of carcinogenicity testing, particularly as to their role in attempting to predict hazard to man.

Alkylating Agents↗
PubMed1979

Mutagenicity of methyl-, ethyl-, propyl- and butylnitrosourea towards Escherichia coli WP2 strains with varying DNA repair capabilities.

Methyl- (MNUA), ethyl- (ENUA), propyl- (PNUA) and butylnitrosourea (BNUA) have been tested for toxicity and mutation in a liquid suspension assay towards Escherichia coli WP2 and some of its repair deficient derivatives. A comparison of survival rates after nitrosourea exposure between WP2 and WP2 uvrA showed no difference between the two strains but a consistent difference in potency between the various nitrosoureas studied. Toxicity increased in the order MNUA less than PNUA less than ENUA less than BNUA. ENUA and PNUA induced a greater number of trp+ revertants in both strains than did MNUA and BNUA, particularly at low survival rates. None of these differences in biological potency could be accounted for by differences in rates of hydrolysis. ENUA, PNUA and BNUA were non-mutagenic towards WP2 lexA, WP2 recA and WP2 uvrA lexA, whereas MNUA did induce mutations. Ethyl methanesulphonate (EMS) was able to mutate WP2 lexA. These results are discussed in the light of current theories regarding the mechanism of action of these compounds.

DNA Repair↗
PubMed1979

Comparison of aflatoxin B1 and aflatoxin G1 binding to cellular macromolecules in vitro, in vivo and after peracid oxidation; characterisation of the major nucleic acid adducts.

A comparison between [14C]aflatoxin B1 (AFB1) and [14C]aflatoxin G1 (AFG1) binding to rat liver and kidney cellular macromolecules has shown AFG1-DNA and-ribosomal RNA binding to be lower in both organs. For both mycotoxins more was bound to nucleic acids than to protein. Two hours after intraperitoneal injection (60 microgram/100 g) of [14C] AFB1, 40 ng, 151 ng/mg. Loss of radioactivity bound to liver DNA for both [14C]AFB1 and protein respectively and for [14C]AFG1 the respective figures were 10, 7 and 1 ng/mg. Loss of liver bound radioactivity to DNA for both [14C]AFG1 and [14C]AFG1 appeared to be biphasic indicating that an enzymic DNA repair process may be operating. In vitro binding studies also showed less AFG1 was bound to exogenous DNA after microsomal activation than AFB1. This difference was not a result of differences in the chemical reactivity of the "ultimate" electrophilic species, the respective expoxides, since chemical activation studies using 3-chloroperbenzoic acid showed similar amounts of AFG1 and AFB1 to be converted to the epoxides and to bind to DNA. Studies on the distribution coefficients of the two mycotoxins showed AFB1 to be more lipophilic than AFG1 and this may be an important factor in determining the weaker carcinogenicity of the latter compound. Characterisation of the major AFG1-DNA adduct formed in vitro, in vivo and after peracid oxidation showed it to have the structure trans-9,10-dihydro-9-(7-guanyl)-10-hydroxy-aflatoxin G1. This adduct is similar to that obtained from AFB1 by activation in vivo, in vitro and after peracid oxidation.

Aflatoxins↗
PubMed1978

Testing of known carcinogens and noncarcinogens for their ability to induce unscheduled DNA synthesis in HeLa cells.

The ability of 51 compounds, of known carcinogenic potential, to induce "unscheduled DNA synthesis" in HeLa cells has been tested in the presence or absence of a rat liver mixed-function oxidase preparation. Chemicals tested included those giving erroneous results in bacterial mutagenicity assays as well as representative compounds from various classes of chemical carcinogens including nitrosamines, polycyclic aromatic hydrocarbons, aromatic amines, and mycotoxins. Of the compounds assayed, all noncarcinogens failed to induce DNA repair; of 38 compounds of demonstrated carcinogenicity, 34 were active; safrole, N-propyl-N-nitrosourea, aflatoxin B2 and N-butyl-N-nitrosourea were, however, inactive. Six compounds for which carcinogenicity data are incomplete were active, namely, 4-nitro-o-phenylenediamine, 2-nitro-p-phenylenediamine, formaldehyde, 2,2'-dichlorobenzidine, 3,3',5,5'-tetrafluorobenzidine, and 3,3',5,5'-tetrachlorobenzidine. Three carcinogens that are weakly active or inactive in bacterial mutagenicity assays, i.e., urethan, N-dimethyl-p-aminoazobenzene, and diethylstilbestrol were active in our assay. The bacterial mutagens sodium azide and 9-aminoacridine were both inactive. The use of this assay in a tier scheme for the short-term testing of potential chemical carcinogens is discussed.

Biotransformation↗