Showing papers in "Carcinogenesis in 1992"
TL;DR: The results suggest that smoking increases oxidative DNA damage by approximately 50%.
Abstract: Oxidative DNA damage may be implicated in ageing, carcinogenesis and other degenerative diseases. Oxidative DNA damage can be assessed in humans in vivo from the urinary excretion of the DNA-repair product 8-hydroxydeoxyguanosine (8OHdG). We investigated factors influencing the excretion of 8OHdG in 24 h urine from 83 randomly selected healthy subjects (52 women) aged 40-64 years. For 2 weeks prior to urine collection the subjects kept a weighed diet record. 8OHdG was quantified by an automatic three-dimensional HPLC analysis with electrochemical detection. The 8OHdG excretion was 252 +/- 103 (mean +/- SD) pmol kg body weight/24 h with a range from 78 to 527. Multiple regression analysis identified three factors, smoking, body mass index (BMI) and gender, as significant predictors of the 8OHdG excretion. In 30 smokers the 8OHdG excretion was 320 +/- 99 pmol/kg/24 h opposed to 213 +/- 84 pmol/kg/24 h in 53 non-smokers. According to multiple regression analysis smokers excreted 50% (31-69%; 95% confidence interval) more 8OHdG than non-smokers. In 52 women the 8OHdG excretion was 240 +/- 106 pmol/kg/24 h opposed to 271 +/- 96 pmol/kg/24 h in 31 men. According to the multiple regression analysis men excreted 29% (10-48%) more 8OHdG than women. According to multiple regression analysis the 8OHdG excretion decreased with 4% (2-6%) per increment in BMI measured in kg/m2. The dietary distribution of energy demonstrated no important predictive value with respect to 8OHdG excretion. The intake of the antioxidant vitamins C and E and of vitamin A equivalents, including beta-carotene, was not associated with 8OHdG excretion. The results suggest that smoking increases oxidative DNA damage by approximately 50%. This effect implies potential serious health effects adding to the other well-known health hazards of smoking. The higher 8OHdG excretion in men and lean subjects may be related to a higher rate of metabolism with increased availability of reactive oxygen species. The apparent 7-fold individual variation in oxidative DNA damage carries implications regarding the rate of ageing and the risk of cancer and other degenerative diseases. The excretion of 8OHdG into urine offers a valuable tool for testing such hypotheses in humans.
628 citations
TL;DR: It is indicated that several P450 enzymes, particularly P450 2E1 and 2A6, catalyze metabolic activation of nitrosamine derivatives including N-nitrosodialkylamines and tobacco-smoke-related nitrosamines in human liver microsomes.
Abstract: An acetyltransferase-overexpressing strain of Salmonella typhimurium (NM2009) has been used to investigate roles of human liver microsomal cytochrome P450 (P450) enzymes in the activation of carcinogenic nitrosamine derivatives, including N-nitrosodialkylamines and tobacco-smoke-related nitrosamines, to genotoxic products. Studies employing correlation of activities with several P450-dependent monooxygenase reactions in different human liver samples, inhibition of microsomal activities by antibodies raised against human P450 enzymes and by specific P450 inhibitors, and reconstitution of activities with purified P450 enzymes suggest that the tobacco-smoke-related nitrosamines 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and N-nitrosonornicotine (NNN) as well as N-nitrosodimethylamine (NDMA) and N-nitrosodiethylamine (NDEA) are oxidized to genotoxic products by different P450 enzymes, particularly P450 2E1 and 2A6. The activation of NDMA and NNN by liver microsomes was suggested to be catalyzed more actively by P450 2E1 than by other P450 enzymes because the activities were well correlated with NDMA N-demethylation and aniline p-hydroxylation in different human samples, and purified P450 2E1 had the highest activities in reconstituted monooxygenase systems. The relatively high contribution of P450 2A6 to the activation of NDEA and NNK was supported by the correlation seen with coumarin 7-hydroxylation in human liver microsomes, and antibodies raised against P450 2A6 inhibited both activities by approximately 50%. P450 3A4, 2D6 and 2C enzymes appear not to be extensively involved in the activation of these nitrosamines as judged by several criteria examined. Thus, this work indicates that several P450 enzymes, particularly P450 2E1 and 2A6, catalyze metabolic activation of nitrosamine derivatives including N-nitrosodialkylamines and tobacco-smoke-related nitrosamines in human liver microsomes.
371 citations
325 citations
TL;DR: The effects of topical administration of curcumin on the formation of benzo,[a]pyrene (B[a]P)-DNA adducts and the tumorigenic activities of B[a?]P and 7,12-dimethylbenz[a].anthracene (DMBA) in epidermis were evaluated in female CD-1 mice.
Abstract: The effects of topical administration of curcumin on the formation of benzo[a]pyrene (B[a]P)-DNA adducts and the tumorigenic activities of B[a]P and 7,12-dimethylbenz[a]anthracene (DMBA) in epidermis were evaluated in female CD-1 mice. Topical application of 3 or 10 mumol curcumin 5 min prior to the application of 20 nmol [3H]B[a]P inhibited the formation of [3H]B[a]P-DNA adducts in epidermis by 39 or 61% respectively. In a two-stage skin tumorigenesis model, topical application of 20 nmol B[a]P to the backs of mice once weekly for 10 weeks followed a week later by promotion with 15 nmol 12-O-tetradecanoylphorbol-13-acetate (TPA) twice weekly for 21 weeks resulted in the formation of 7.1 skin tumors per mouse, and 100% of the mice had tumors. In a parallel group of mice, in which the animals were treated with 3 or 10 mumol curcumin 5 min prior to each application of B[a]P, the number of tumors per mouse was decreased by 58 or 62% respectively. The percentage of tumor-bearing mice was decreased by 18-25%. In an additional study, topical application of 3 or 10 mumol curcumin 5 min prior to each application of 2 nmol DMBA once weekly for 10 weeks followed a week later by promotion with 15 nmol TPA twice weekly for 15 weeks decreased the number of tumors per mouse by 37 or 41% respectively.
286 citations
TL;DR: The results validate the use of ACF with four or more crypts, as an intermediate biomarker for tumor incidence in this system, and are consistent with the hypothesis that the development of larger ACF (with four ormore crypts) is predictive of the tumor incidence.
Abstract: Aberrant crypts are putative preneoplastic lesions that have been proposed as intermediate biomarkers for colon cancer. The goals of these studies were to determine (i) if the colon cancer chemopreventive agent, sodium phytate, when started 1 week after a single dose of carcinogen, has any effect on the development of aberrant crypt foci (ACF) in treated rats; and (ii) if ACF at an early time period under these conditions correlate with the later formation of tumors in similarly treated animals. The number of ACF with four or more crypts was greater (P = 0.02, Mann-Whitney test) in rats with tumors compared with rats without tumors killed at 36 weeks after the injection of azoxymethane (AOM); the total number of ACF was not significantly different in these two groups. The incidence of tumors in F344 rats treated with AOM without phytate was 83% (10/12) compared to 25% (3/12) in rats treated with AOM plus phytate (P = 0.0045, two-tail Fisher's exact test). The finding of more (P = 0.005, Mann-Whitney test) ACF with four or more crypts in rats without phytate than in rats with phytate at 12 weeks after the injection of AOM is consistent with the hypothesis that the development of larger ACF (with four or more crypts) is predictive of the tumor incidence. These results validate the use of this parameter, i.e. ACF with four or more crypts, as an intermediate biomarker for tumor incidence in this system.
285 citations
TL;DR: It is demonstrated that it is possible not only to study mitochondrial DNA repair, but also directly to compare mitochondrial and nuclear DNA repair in the same biological sample and that repair capacity of mitochondrial DNA damage depends upon the type of lesion produced by the damaging agent.
Abstract: Using methodology recently developed to assess gene-specific DNA repair, we have demonstrated that it is possible not only to study mitochondrial DNA repair, but also directly to compare mitochondrial and nuclear DNA repair in the same biological sample. Complex enzymatic mechanisms recognize and repair nuclear DNA damage, but it has long been thought that there was no DNA repair in mitochondria. Therefore, in an attempt to delineate more clearly which DNA repair mechanisms, if any, are functioning in mitochondria, we have investigated the repair of several specific DNA lesions in mitochondrial DNA. They include cyclobutane dimers, cisplatin intrastrand adducts, cisplatin interstrand crosslinks and alkali-labile sites. We find that pyrimidine dimers and complex alkylation damage are not repaired in mitochondrial DNA, and that there is minimal repair of cisplatin intrastrand crosslinks. In contrast, there is efficient repair of cisplatin interstrand crosslinks as evidenced by approximately 70% of the lesions being removed by 24 h. Additionally, there is efficient repair of N-methylpurines following exposure to methylnitrosourea with approximately 70% of the lesions being removed by 24 h. The results of these studies reveal that repair capacity of mitochondrial DNA damage depends upon the type of lesion produced by the damaging agent. We speculate that a process similar to the base excision mechanism for nuclear DNA exists for mitochondrial DNA but that there is no nucleotide excision repair mechanism to remove more bulky lesions in this organelle.
262 citations
TL;DR: Tamoxifen induced a significant increase in micronucleus formation in a dose dependent manner in cultures of MCL-5 cells, a human cell line that expresses 5 different human cytochrome P450 isoenzymes, as well as epoxide hydrolase.
Abstract: Chronic administration of tamoxifen to female rats causes hepatocellular carcinomas. We have investigated damage to liver DNA caused by the administration of tamoxifen to female Fischer F344/N rats or C57B1/6 or DBA/2 mice using 32P-postlabelling. Following the administration of tamoxifen for 7 days (45 mg/kg/day) and extraction of hepatic DNA, up to 7 radiolabelled adduct spots could be detected after PEI-cellulose chromatography of the 32P-labelled DNA digests. Tamoxifen caused a time-dependent increase in the level of adduct detected up to a value of at least 1 adduct/10(6) nucleotides after 7 days dosing. A dose response relationship was demonstrated over the range of 5-45 mg/kg/day (0.013-0.12 mmol/kg/day). On cessation of dosing there was a loss of adducts from the liver DNA. These adducts were not detected in DNA from vehicle-dosed controls or in DNA from kidney, lung, spleen, uterus or peripheral lymphocytes. Pyrrolidinotamoxifen caused a similar level of adduct formation as tamoxifen. In contrast, no significant adduct formation could be detected in liver DNA from rats given droloxifene or toremifene. Mice given tamoxifen (45 mg/kg/day for 4 days) showed levels of adducts in the liver which were 30-40% of those present in rats. Exposure of rat hepatocytes to tamoxifen in vitro, resulted in induction of unscheduled DNA synthesis, when preparations from rats which had been pretreated with tamoxifen in vivo were used. No such increase could be detected in hepatocytes from control rats, suggesting tamoxifen may induce enzymes responsible for its own activation. Tamoxifen induced a significant increase in micronucleus formation in a dose dependent manner in cultures of MCL-5 cells, a human cell line that expresses 5 different human cytochrome P450 isoenzymes, as well as epoxide hydrolase.
255 citations
TL;DR: In vitro species differences in the oxidation of BD and B MO by cytochrome P450-dependent monooxygenases and the inactivation of BMO by epoxide hydrolases and glutathione S-transferases were quantitated using microsomal and cytosolic preparations of livers and lungs obtained from Sprague-Dawley rats, B6C3F1 mice and humans.
Abstract: 1,3-Butadiene (BD), a widely used monomer in the production of synthetic rubber and other resins, is one of the 189 hazardous air pollutants identified in the 1990 Clean Air Act Amendments. BD induces tumors at multiple organ sites in B6C3F1 mice and Sprague-Dawley rats; mice are much more susceptible to the carcinogenic action of BD than are rats. Previous in vivo studies have indicated higher circulating blood levels of butadiene monoepoxide (BMO), a potential carcinogenic metabolite of BD, in mice compared to rats, suggesting that species differences in the metabolism of BD may be responsible for the observed differences in carcinogenic susceptibility. The metabolic fate of BD in humans is unknown. The objective of these studies was to quantitate in vitro species differences in the oxidation of BD and BMO by cytochrome P450-dependent monooxygenases and the inactivation of BMO by epoxide hydrolases and glutathione S-transferases using microsomal and cytosolic preparations of livers and lungs obtained from Sprague-Dawley rats, B6C3F1 mice and humans. Maximum rates for BD oxidation (Vmax) were highest for mouse liver microsomes (2.6 nmol/mg protein/min) compared to humans (1.2) and rats (0.6). The Vmax for BD oxidation by mouse lung microsomes was similar to that of mouse liver but greater than 10-fold higher than the Vmax for the reaction in human or rat lung microsomes. Correlation analysis revealed that P450 2E1 is the major P450 enzyme responsible for oxidation of BD to BMO. Only mouse liver microsomes displayed quantifiable rates for metabolism of BMO to butadiene diepoxide (Vmax = 0.2 nmol/mg protein/min), a known rodent carcinogen. Human liver microsomes displayed the highest rate of BMO hydrolysis by epoxide hydrolases. The Vmax in human liver microsomes ranged from 9 to 58 nmol/mg protein/min and was at least 2-fold higher than the Vmax observed in mouse and rat liver microsomes. The Vmax for glutathione S-transferase-catalyzed conjugation of BMO with glutathione was highest for mouse liver cytosol (500 nmol/mg protein/min) compared to human (45) or rat (241) liver cytosol. In general, the KMs for the detoxication reactions were 1000-fold higher than the KMs for the oxidation reaction. Because of the low solubility of the BD and the relatively high KM for oxidation, it is likely that the Vmax/KM ratio will be important for BD and BMO metabolism in vivo. In vivo clearance constants were calculated from in vitro data for BD oxidation and BMO oxidation, hydrolysis and GSH conjugation.(ABSTRACT TRUNCATED AT 400 WORDS)
235 citations
TL;DR: The K--SDS assay was also successfully utilized to determine DNA--protein crosslinks in rat and mouse white blood cells exposed in vivo to chromate and cis-platinum, with sensitivity similar to the alkaline elution procedure.
Abstract: Addition of potassium chloride to sodium dodecyl sulfate (SDS) resulted in the formation of an insoluble precipitate that was easily recovered by low-speed centrifugation. Since SDS tightly binds to proteins but not DNA, all proteins and detergent-resistant DNA--protein complexes were also effectively co-precipitated in the presence of potassium--SDS leaving free DNA in the supernatant. The amount of SDS-precipitable DNA represented a measure of DNA--protein crosslinks. We have adapted this method for determining DNA--protein crosslinks formed in cells following their exposure in culture or in vivo to crosslinking agents such as chromate, cis-Pt(II) diammine dichloride and formaldehyde. The critical parameters for application of the K--SDS assay to cells were rigorously reproducible shearing of chromosomal DNA and effective washing steps. We have found that freeze-thawing SDS lysed cells followed by vortexing and repeated resuspensions of the precipitate by pipeting resulted in a low background and high reproducibility of the assay. The method detected in a dose-dependent manner DNA--protein crosslinks induced in CHO cells by chromate, cis-platinum and formaldehyde, with sensitivity similar to the alkaline elution procedure. The K--SDS assay was also successfully utilized to determine DNA--protein crosslinks in rat and mouse white blood cells exposed in vivo to chromate. Its sensitivity and simplicity in sample handling and DNA--protein complex isolation potential allows wide application of the assay to measure formation of DNA--protein crosslinks. The ease of recovery of DNA--protein complexes allows for a more thorough investigation of this lesion.
231 citations
TL;DR: Topical application of green tea polyphenol fraction inhibited TPA-induced inflammation, ornithine decarboxylase activity, hyperplasia and hydrogen peroxide formation, studies with individual polyphenolic compounds in green tea indicated.
Abstract: A green tea polyphenol fraction was evaluated for its ability to inhibit tumor initiation by polycyclic aromatic hydrocarbons and tumor promotion by a phorbol ester in the skin of CD-1 mice Topical application of the green tea polyphenol fraction inhibited benzo[a]pyrene- and 7,12-dimethylbenz[a]-anthracene-induced tumor initiation as well as 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced tumor promotion Topical application of the green tea polyphenol fraction also inhibited TPA-induced inflammation, ornithine decarboxylase activity, hyperplasia and hydrogen peroxide formation Studies with individual polyphenolic compounds in green tea indicated that topical application of (-)-epigallocatechin gallate, (-)-epigallocatechin and (-)-epicatechin gallate inhibited TPA-induced inflammation in mouse epidermis
218 citations
TL;DR: The relationship between intracellular glutathione levels and the inducibility of the human heme oxygenase gene after treatment of populations of cultured skin fibroblasts with either UVA radiation or hydrogen peroxide is investigated.
Abstract: Induction of the expression of the mammalian heme oxygenase gene appears to be a general response to oxidant stress. In view of the role of glutathione in protecting cells against solar UVA radiation and other forms of oxidant stress, we have investigated the relationship between intracellular glutathione levels and the inducibility of the human heme oxygenase gene after treatment of populations of cultured skin fibroblasts with either UVA radiation or hydrogen peroxide. We observe a clear relationship between cellular glutathione status and both the constitutive and oxidant-inducible accumulation of heme oxygenase mRNA. Glutathione depletion may lead to enhanced gene expression either as a result of the potentiated accumulation of active oxygen intermediates or as a result of the direct influence of glutathione on a critical target involved in signal transduction.
TL;DR: Three model systems of plasmacytomagenesis that are associated with mutations that affect c-myc transcription were discussed and fundamental unanswered questions are whether these inflammatory tissues provide products such as oxidants in vivo that damage DNA and promote mutagenesis.
Abstract: Three model systems of plasmacytomagenesis that are associated with mutations that affect c-myc transcription were discussed. Plasmacytoma induction by chronic peritoneal irritation induced by non-metabolized paraffin oils or plastic objects is strongly influenced by the immune status of the host. BALB/cAn mice must be exposed to natural environmental antigens to develop a high incidence of plasmacytomas. This may be related to T-cell priming. BALB/cAn mice raised under strict SPF conditions are refractory to plasmacytoma induction by pristane. The genotype of the mouse plays an important role in the chronic peritoneal irritation model of plasmacytomagenesis in mice. Only a few of the standard inbred strains are susceptible, notably BALB/cAn and NZB/B1. The genetic basis of susceptibility and resistance has been studied in crosses and congenic strains involving the susceptible BALB/cAn and resistant DBA/2 strains. While several genes play a role in determining resistance at least one resistance gene located on the distal end of Chr 4 reduces the incidence by at least 50% as determined in the BALB/cAn.DBA/2 Fv-1n/n congenic strain. The action of susceptibility and resistance genes is not known; hypothetically these genes could play a role in plasmacytomagenesis by increasing the probabilities of illegitimate exchanges between genes or by influencing the formation of mutations in genes that regulate mitotic cycling. Plasmacytomas appear to develop in the chronic inflammatory tissues induced by these agents. Fundamental unanswered questions are whether these inflammatory tissues provide products such as oxidants in vivo that damage DNA and promote mutagenesis. In the mouse there is a resident self-renewing B cell population that is CD5+. These B cells, which are known to be precursors of normal lamina propria IgA-secreting plasma cells, are directly in contact with the chronic inflammatory process induced by pristane; they may be targets in plasmacytomagenesis. The plasmacytomas that develop by the peritoneal mode of induction all have chromosomal translocations that directly or indirectly activate c-myc. The predominant MACTR found in 90% of these tumors is T(12;15) in which a heavy-chain switch region sequence is joined to the 5' region of c-myc. The evidence strongly suggests that the translocation develops in a late mature B cell that is in the process of isotype switching. An unanswered question is whether the switching associated T(12;15) takes place in a B cell that is exposed to the inflammatory microenvironment.(ABSTRACT TRUNCATED AT 400 WORDS)
TL;DR: The ratios of metabolites from dietary caffeine in spot urine samples offer ethical, non-invasive and reliable estimates of CYP1A2, NAT and XO, which are highly relevant for the bioactivation of potentially toxic compounds and the formation of oxygen radicals.
Abstract: Caffeine is sequentially metabolized by cytochrome P4501A2 (CYP1A2), N-acetyltransferase (NAT) and/or xanthine oxidase (XO). In the present study the activity of these three enzymes was estimated from ratios of the metabolites formed from dietary caffeine and excreted into the urine collected as spot samples. In the urine samples from 10 out of 377 subjects concentrations of caffeine metabolites were too low to allow reliable measurements of the ratios. In 335 healthy subjects the NAT activity showed a typically bimodal distribution with 47% fast acetylators and 53% slow acetylators, consistent with a Danish population. The ratios reflecting CYP1A2 and XO activities were log normal and normal distributed, respectively. In 103 non-smoking men and 90 non-smoking women the ratio of caffeine metabolites expressing CYP1A2 activity was 4.7 +/- 1.6 and 4.3 +/- 1.9 as compared to 7.8 +/- 2.5 and 7.3 +/- 3.0 in 31 male and 25 female subjects smoking 10 cigarettes/day or more respectively, verifying induction of CYP1A2 by tobacco (P less than 0.05), but minimal sex-related differences. In 12 non-smoking pregnant women and in 28 women using oral contraceptives the CYP1A2 ratio was 29 and 20% reduced respectively (P less than 0.05). In a multivariate analysis the only significant predictor of the XO ratio was the consumption of caffeine with an increase of 2% per cup of coffee or equivalent (P less than 0.05). In 23 healthy male subjects 30 days of vigorous exercise increased the CYP1A2 ratio by 70% and the XO ratio by 42% (P less than 0.05), but left the NAT ratio unchanged. In nine healthy volunteers daily ingestion of 500 g of broccoli for 10 days increased the CYP1A2 ratio by an average of 12% (P less than 0.05), compared to a control period with ingestion of an equivalent weight of non-cruciferous green vegetables. The ratios of metabolites from dietary caffeine in spot urine samples offer ethical, non-invasive and reliable estimates of CYP1A2, NAT and XO. These enzymes are highly relevant for the bioactivation of potentially toxic compounds and the formation of oxygen radicals. The method is applicable in large-scale epidemiological studies, allowing, for example, prospective testing of the relationship between these enzyme activities and the development of disease. Exercise may increase CYP1A2 activity to a magnitude corresponding to heavy smoking, as well as XO by mechanisms that remain to be clarified.
TL;DR: The study demonstrates that PEITC selectively affects xenobiotic-metabolizing enzymes in the liver, lung and nasal mucosa and it is especially effective in inhibiting the P450-dependent oxidation of NNK in the lung and of NDMA in the Liver.
Abstract: Phenethyl isothiocyanate (PEITC), a constituent of cruciferous vegetables, has been shown to inhibit chemical carcinogenesis, possibly due to its ability to block the activation or to enhance the detoxification of chemical carcinogens. The present study was conducted to elucidate the biochemical mechanisms involved by characterizing the effects of PEITC on phase I and phase II xenobiotic-metabolizing enzymes. A single dose of PEITC to F344 rats (1 mmol/kg) decreased the liver N-nitrosodimethylamine demethylase (NDMAd) activity (mainly due to P450 2E1) by 80% at 2 h and the activity of NDMAd remained decreased by 40% at 48 h after treatment. The liver pentoxyresorufin O-dealkylase (PROD) activity and P450 2B1 protein level were elevated 10- and 7-fold at 24 h after treatment respectively. The liver microsomal ethoxyresorufin O-dealkylase (EROD) (mainly due to P450 1A) and erythromycin N-demethylase (mainly due to P450 3A) activities were decreased at 2-12 h after treatment and recovered afterwards. The lung microsomal PROD and EROD activities were not significantly affected; whereas, the nasal microsomal PROD and EROD activities were decreased by 40-50%. After a treatment with PEITC, the rates of oxidative metabolism of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) were decreased in liver microsomes by 40-60% at 2 h and recovered gradually; the rates in lung microsomes were markedly decreased by 60-70% at 2 h and remained at the decreased level at 24 h; and the rates in nasal mucosa microsomes were decreased gradually with the lowest activities observed at 18 h (50%) followed by a gradual recovery. Furthermore, the treatment with PEITC resulted in a maximal 5-fold increase of NAD(P)H:quinone oxidoreductase and 1.5-fold increase of glutathione S-transferase activities in the liver, but the activities of these two enzymes were not significantly affected in the lung and nasal mucosa. The sulfotransferase activity in the liver was decreased by 32-48% at 24-48 h after treatment; the nasal activity was increased by 1.8- to 2.5-fold, but the lung activity was not significantly changed. The hepatic UDP glucuronosyltransferase activity was slightly decreased at 2 h but slightly increased at 48 h after treatment, but no changes were observed for the lung and nasal activities. The study demonstrates that PEITC selectively affects xenobiotic-metabolizing enzymes in the liver, lung and nasal mucosa and it is especially effective in inhibiting the P450-dependent oxidation of NNK in the lung and of NDMA in the liver.
TL;DR: Results analyzed by the linear regression method suggested a dose-dependent inhibition of colon carcinogenesis with increasing levels of piroxicam or ibuprofen, while glycyrrhetinic acid had no measurable chemopreventive effect on Colon carcinogenesis.
Abstract: The inhibitory effect of 40 and 80% maximum tolerated dose (MTD) levels of piroxicam, ibuprofen, ketoprofen and glycyrrhetinic acid on colon carcinogenesis was investigated in male F344 rats. The MTD levels of piroxicam, ibuprofen, ketoprofen and glycyrrhetinic acid as determined in male F344 rats were 500, 500, 250 and 3000 p.p.m. respectively. At 5 weeks of age, groups of male F344 rats were fed the control (AIN-76A) diet and 40 and 80% MTD levels of each test agent in AIN-76A diet. At 7 weeks of age, all animals except the vehicle (saline)-treated controls received azoxymethane (AOM) at a dose rate of 15 mg/kg body wt, once weekly for 2 weeks. All animals were necropsied 50 weeks after the second AOM injection and colon tumor incidences were compared among the groups fed the control diet and chemopreventive agents. Animals fed 400 (80% MTD) and 200 p.p.m. (40% MTD) of piroxicam, 400 p.p.m. (80% MTD) of ibuprofen and 200 p.p.m. (80% MTD) of ketoprofen showed a significant inhibition of colon tumorigenesis as compared to those fed the control diet. Results analyzed by the linear regression method suggested a dose-dependent inhibition of colon carcinogenesis with increasing levels of piroxicam or ibuprofen. In contrast, glycyrrhetinic acid had no measurable chemopreventive effect on colon carcinogenesis.
TL;DR: Compared to the sulfur structural analogs, selenium compounds are much more active in cancer protection and may have a multi-modal mechanism in preventing cellular transformation as well as in delaying or inhibiting the expression of malignancy after carcinogen exposure.
Abstract: Several organoselenium compounds have been shown to have powerful anticarcinogenic activity. In view of certain similarities between selenium and sulfur biochemistry, we have evaluated the chemopreventive efficacy of three pairs of analogs using the 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary tumor model in rats. The compounds tested were selenocystamine/cysteamine, Semethylselenocysteine/S-methylcysteine, selenobetaine/sulfobetaine. In the first study, each agent was added to the basal AIN-76A diet and was given before and continued after DMBA treatment until the end. All three selenium compounds were active; a 50% inhibition was achieved at approximately 25 x 10(-6) mol/kg with Se-methylselenocysteine and selenobetaine and at approximately 40 x 10(-6) mol/kg with selenocystamine. In the sulfur series, only cysteamine and S-methylcysteine produced anticancer activity, and the levels required for comparable responses were 500- to 750-fold higher compared to the corresponding selenium analogs. Sulfobetaine was inactive even when present at near maximally tolerated levels. In the second study, Se-methylselenocysteine and S-methylcysteine were chosen for further examination during the initiation and post-initiation phases of mammary carcinogenesis. Se-Methylselenocysteine was effective when it was given either before or after DMBA administration. In contrast, S-methylcysteine was effective only after DMBA treatment. Thus, compared to the sulfur structural analogs, selenium compounds are much more active in cancer protection and may have a multi-modal mechanism in preventing cellular transformation as well as in delaying or inhibiting the expression of malignancy after carcinogen exposure.
TL;DR: The interpretation of the data is that damaged cells in the stem cell region of the small bowel are removed by the activation of a cell suicide programme, which effectively removes potentially harmful genetic alterations in the colonic stem cell population and this may explain in part, the higher incidence of cancers observed in the large bowel.
Abstract: The ability of four mutagenic/carcinogenic chemicals administered as single doses to induce a programmed form of cell death (apoptosis) in the BDF1 mouse large bowel was studied and compared with a previous study on the small intestine using the same mice. The number of apoptotic cells was counted following treatment with the direct-acting agents N-nitroso-N-methylurea (NMU) and N-nitroso-N-ethylurea (NEU) and two agents which require metabolic activation 1,2-dimethylhydrazine (DMH) and N-nitrosodimethylamine (NDMA). DMH (80 mg/kg) was the most effective at inducing acute cell death and this was closely followed by NMU (200 mg/kg). The least effective agent in the large bowel was NDMA. The peak yield of apoptosis occurred between 4 h (NEU) and 8 h (DMH) after treatment. An analysis of the changing shapes of the frequency plots of apoptosis at each cell position in the crypt at various times after exposure permits an estimate to be made of the position in the crypt of the primary target cells for the cytotoxic action at time t = 0. For the agents studied, this is in the range of the 5th to the 10th position from the base of the crypt. This distribution for the target cells for apoptotic cell death is not coincident with that for the presumptive stem cells, which is at cell position 1 or 2. Comparisons with results previously obtained in the small intestine (ileum) of the same mice show that the relative cytotoxic effectiveness of the four agents differs. Furthermore, the position of the target cells is at about the 4th position from the bottom of the crypt in the ileum, and here the distribution is coincident with that presumed for the stem cells. Our interpretation of the data is that damaged cells in the stem cell region of the small bowel are removed by the activation of a cell suicide programme, which effectively removes potentially harmful genetic alterations. In contrast, in the large bowel, cell death is not initiated particularly strongly in the stem cell region but tends to occur higher in the crypt. The absence of this selective deletion process may result in the perpetuation of deleterious mutations in the colonic stem cell population and this may explain in part, the higher incidence of cancers observed in the large bowel.
TL;DR: Although FB1 primarily affects the liver, it is not very cytotoxic to primary hepatocytes when compared to aflatoxin B1, indicating that the fumonisins are poor cancer initiators.
Abstract: The cancer-initiating potential of the fumonisin B (FB) mycotoxins produced by Fusarium moniliforme was screened in rat liver for their ability to induce rare hepatocytes with an acquired resistance to the mitoinhibitory effect of 2-acetyl-aminofluorene (2-AAF). Two different initiating protocols were used: a feeding regimen during which FB1 was fed at a dietary level of 0.1% for 26 days, and another where single or multiple doses of FB1 and FB2 (varying from 200 to 50 mg/kg) were administered (by gavage) to hepatectomized rats. In both cases promotion was effected by a 2-acetylamino-fluorene/carbontetrachloride treatment. Cancer initiation was only obtained after the prolonged feeding regimen, indicating that the fumonisins are poor cancer initiators. FB1 and FB2 also lack genotoxic effects in the in vivo and in vitro DNA repair assays in primary hepatocytes. Although FB1 primarily affects the liver, it is not very cytotoxic to primary hepatocytes when compared to aflatoxin B1.
TL;DR: The activities of several flavonoids and the related nonflavonoid compound epicatechin were compared with respect to Cu(II)-induced strand scission of DNA by using two different assays and analysis of the data led to a discussion of alternative Cu( II)-sequestering mechanisms.
Abstract: The activities of several flavonoids and the related nonflavonoid compound epicatechin were compared with respect to Cu(II)-induced strand scission of DNA by using two different assays. The same series of compounds was used to study the stoichiometry of Cu(II) reduction in the absence of DNA. The compounds were compared for their ability to generate superoxide, hydrogen peroxide and the Cu(II)-dependent production of hydroxyl radicals. Flavonoids were examined to assess the production of a charge-transfer complex with Cu and the rate of decay of the complexes were compared. All the compounds tested had some ability to cause DNA strand scission in the presence of Cu(II), with myricetin being the most active and galangin the least active. The ability to cause such scission correlated with the rate of decay of the charge-transfer complex, the ability to generate active oxygen species and with the stoichiometry of Cu(II) binding. Analysis of the data in the light of the structural differences between the flavonoids led to a discussion of alternative Cu(II)-sequestering mechanisms.
TL;DR: The results suggest that factors which increase the generation of reactive oxygen species by UV light may be potent cofactors of UV-radiation carcinogenesis.
Abstract: Exposure to UV light contributes to the development of skin cancer. The importance of reactive oxygen species in UV-radiation carcinogenesis has been recognized for some time and several associated DNA base modifications have been identified. In particular, 8-hydroxydeoxyguanosine (8-OHdG) has been well studied as an indicator of oxidative damage to calf thymus DNA exposed to a variety of oxygen-generating systems, including UV light. However, to date, few studies of 8-OHdG have been conducted in cell or animal systems and those in vitro investigations that studied UV exposure have used UVC (< 290 nm), not the UVB (290-320 nm) or UVA (320-400 nm) ranges to which organisms are exposed through sunlight. The objective of this study was to measure 8-OHdG formation in the DNA of cultured mouse keratinocytes exposed to UVB. Using HPLC with electrochemical detection, background levels of 8-OHdG were approximately 6 fmol/micrograms DNA in DNA isolated and digested to the nucleoside level. UVB induced 8-OHdG up to 100% above that for mock-treated cells at a dose of 630 mJ/cm2 (dose-response range: 210-630 mJ/cm2). UVB exposure at 630 mJ/cm2 combined with 5 mM H2O2 elevated 8-OHdG formation up to 280% above that in control cells, whereas H2O2 alone had no effect. These results suggest that factors which increase the generation of reactive oxygen species by UV light may be potent cofactors of UV-radiation carcinogenesis.
TL;DR: HPLC separation followed by liquid scintillation counting of hydrolyzed liver DNA from a rat dosed with [3H]PhIP showed that radioactivity coeluted with the hydrolysis product of the synthetic PhIP-2-deoxyguanosine adduct, indicating that PhIP in vivo also forms an N2-(2'-de oxygenguanosin-8-yl)-PhIP adduct.
Abstract: The direct acting mutagenic N2-hydroxylated metabolite of the food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) does not react with DNA Upon acetylation of the N2-hydroxy-PhIP with acetic anhydride two products could be detected Mass spectrometric analysis showed that both products were monoacetyl derivatives of N2-hydroxy-PhIP One of the products did not show any reactivity towards DNA and is probably the N-acetyl derivative of N2-hydroxy-PhIP The other product which is most likely to be N2-acetoxy-PhIP reacted with DNA and 2'-deoxyguanosine but not with 2'-deoxycytidine, 2'-deoxyadenosine or 2'-deoxythymidine The PhIP-2'-deoxyguanosine adduct was purified and characterized by mass spectral, 1H and [13C]NMR analysis, showing that PhIP like the other cooked food mutagen 2-amino-3-methylimidazo[4,5-f]quinoline, had reacted with C-8 of guanine forming N2-(2'-deoxyguanosin-8-yl)-PhIP HPLC analysis of enzymatically hydrolyzed calf thymus DNA which had been reacted with N2-acetoxy-PhIP showed one adduct which was chromatographically and spectroscopically identical to N2-(2'-deoxyguanosin-8-yl)-PhIP HPLC separation followed by liquid scintillation counting of hydrolyzed liver DNA from a rat dosed with [3H]PhIP showed that radioactivity coeluted with the hydrolysis product of the synthetic PhIP-2-deoxyguanosine adduct, indicating that PhIP in vivo also forms an N2-(2'-deoxyguanosin-8-yl)-PhIP adduct
TL;DR: Sobrerol is 5-fold more potent than limonene in both enhancing carcinogen excretion and in preventing tumor formation, andHydroxylation of monoterpenes affects chemopreventive potential, with 2 hydroxyl groups greater than 1 greater than 0.05%.
Abstract: The monoterpene d-limonene has been shown to an effective, non-toxic chemopreventive agent in mammary and other rodent tumor models. The studies reported here investigated structure-activity relationships among limonene and three hydroxylated derivatives in the prevention of dimethylbenz[a]anthracene (DMBA)-induced mammary cancer. Rats were fed control or 1% limonene, carveol, uroterpenol or sobrerol diets from 2 weeks before to one week after carcinogen administration. Carveol, uroterpenol and sobrerol significantly prolonged tumor latency and decreased tumor yield. Sobrerol was the most potent of the monoterpenes tested, decreasing tumor yield to half that of the control, a level previously achieved with 5% limonene diets. Excretion of radioactivity from [3H]DMBA was doubled in rats fed 5% limonene and nearly tripled in rats fed 1% sobrerol. Sobrerol is thus 5-fold more potent than limonene in both enhancing carcinogen excretion and in preventing tumor formation. These data demonstrate that hydroxylation of monoterpenes affects chemopreventive potential, with 2 hydroxyl groups greater than 1 greater than 0. Sobrerol, carveol and uroterpenol are novel cancer chemopreventive agents with little or no toxicity.
TL;DR: In this paper, the effects of 3-methylcholanthrene (MC) on cell proliferation and [3H]thymidine uptake were investigated in MCF-7 cells.
Abstract: Treatment of MCF-7 cells with 1.0 microM 3-methylcholanthrene (MC) caused a decrease in cell proliferation and [3H]thymidine uptake whereas no effects were observed at a lower (0.1 microM) concentration. Co-treatment of the cells with 1 nM 17 beta-estradiol plus 0.1 or 1.0 mu MC resulted in a significant inhibition of 17 beta-estradiol-induced growth and [3H]thymidine uptake. MC also inhibited the 17 beta-estradiol-induced secretion of the 52 kDa protein (procathepsin D) in MCF-7 cells and caused a concentration-dependent decrease in the nuclear estrogen receptor (ER) as determined by either velocity sedimentation analysis or immunoquantitation with human ER antibodies. The effects of several different polynuclear aromatic hydrocarbon (PAH) congeners on the nuclear ER in MCF-7 cells were also determined. Only those congeners which bound to the aryl hydrocarbon (Ah) receptor, namely benzo[a]pyrene, benz[a]anthracene, 7,12-dimethylbenz[a]anthracene and MC, caused a decrease in nuclear ER levels. In contrast, benzo[ghi]perylene, a congener which did not bind to the Ah receptor did not affect nuclear ER levels in MCF-7 cells. Moreover, with some congeners the decrease in nuclear ER levels could be observed without any significant induction of ethoxyresorufin O-deethylase activity, a P4501A1-dependent monooxygenase. These data suggest that the Ah receptor liganded with MC and related PAHs induced a broad spectrum of antiestrogenic responses in MCF-7 cells and complements the results of previous studies which report the antiestrogenic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin and other halogenated aromatics which are also Ah receptor agonists.
TL;DR: The influence of aspirin on 1,2-dimethylhydrazine (1 2 -DMH)-induced colonic carcinogenesis was examined in weanling Sprague-Dawley rats as discussed by the authors.
Abstract: The influence of aspirin (ASA) on 1,2-dimethylhydrazine (1,2-DMH)-induced colonic carcinogenesis was examined in weanling Sprague-Dawley rats. The incidence of adenocarcinomas in response to a single dose of 1,2-DMH was reduced 60% in rats receiving ASA for 1 week before and after the carcinogen. However, ASA had no effect on tumor incidence when initiated 4 weeks after a single dose of 1,2-DMH and continuing until the animals were killed at 36 weeks. The doses of ASA employed suppressed by 95% or more ex vivo colonic prostaglandin E2 (PGE2) production and reduced colonic mucosal cAMP levels in both rats exposed to 1,2-DMH and in age-matched controls. Proliferative activity of colonic mucosa as assessed from tritiated thymidine ([3H]dThd) incorporation into mucosal DNA was increased at 1 week but suppressed by 36 weeks after 1,2-DMH exposure. ASA significantly increased colonic mucosal DNA synthesis, suppressed colonic PGE2 production and reduced mucosal cAMP levels at both 1 and 36 weeks in rats given the 1,2-DMH vehicle. However, ASA failed to alter the enhanced mucosal DNA synthesis observed at 1 week or the suppressed DNA synthesis observed at 36 weeks after a single dose of 1,2-DMH, despite significant inhibition of colonic PGE2 production and reduction in mucosal cAMP levels by ASA. Treatment of rats for 1 week with ASA significantly inhibited basal and arachidonate stimulated decomposition of the 1,2-DMH intermediary metabolite methylazoxy-methanol, assessed ex vivo in colonic mucosal homogenates. Thus, while other mechanisms are not excluded, suppression of 1,2-DMH induced colonic carcinoma by concurrent administration of ASA may be linked in part to altered metabolic activation of this carcinogen via cyclooxygenase-dependent co-oxidation. By contrast, the previously reported suppression of the promotional phase of colonic carcinogenesis in rats by the delayed introduction of cyclooxygenase inhibitors may not be linked to inhibition of local colonic prostanoid production, since (i) inhibition of colonic prostanoid synthesis by ASA did not mimic this antipromotional effect, and (ii) the doses of non-steroidal anti-inflammatory drugs employed in some earlier studies may not significantly inhibit colonic prostanoid synthesis.
TL;DR: It is shown that routine phenol-based DNA purification procedures can increase 8-hydroxydeoxyguanosine (8-OHdG) levels 20-fold in samples that are exposed to air after the phenol is removed from the solutions, and phenol treatments of DNA are shown to sensitize DNA to 8- OHdG formation by subsequent exposures to air.
Abstract: The DNA base adduct, 8-hydroxyguanine (8-OHGua), has been reported to be a key biomarker relevant to carcinogenesis and cellular oxidative stress important in tumor promotion. Although investigators often report artificially high levels of 8-OHGua in DNA samples that have been exposed to phenol solutions and/or air during processing, few quantitative results are available. We show that routine phenol-based DNA purification procedures can increase 8-hydroxydeoxyguanosine (8-OHdG) levels 20-fold in samples that are exposed to air after the phenol is removed from the solutions. Surprisingly, air exposure alone accounts for a significant portion of this increase (4-fold) when compared to dG or DNA samples that have been solubilized in buffers purged with nitrogen. Most importantly, phenol treatments of DNA are shown to sensitize DNA to 8-OHdG formation by subsequent exposures to air. The sensitization of DNA occurs even though extensive dialysis is used between phenol treatment and enzymatic DNA digestion. Alternate procedures, including chloroform:isoamyl-alcohol extractions, also yield air-sensitive DNA samples. Other artifacts of organic extraction prior to air exposure include alterations in DNA base ratios after nuclease digestions. Overall, these results strongly suggest that studies of 8-OHdG in carcinogenesis should avoid dry conditions, such as lyophilization followed by exposure to air, and that all four of the bases should be monitored before 8-OHdG concentrations are normalized by undamaged deoxynucleoside concentrations. Failure to heed these precautions can lead to 2- to 20-fold overestimates of 8-OHdG in target tissues or in vitro models.
TL;DR: The treatment of rat hepatocytes with microcystin-LR induced hyperphosphorylation of cytokeratins 8 and 18 associated with morphological changes, indicating that intermediate filament networks were rearranged in the cytoplasm.
Abstract: Microcystin-LR (MC-LR), an inhibitor of protein phosphatases 1 and 2A, is a potent tumor promoter in rat liver initiated with diethylnitrosamine. To understand its biochemical process in hepatocytes, primary cultured rat hepatocytes were treated with MC-LR. MC-LR (1 microM) induced phosphorylation of various proteins. Two 55 and 49 kDa proteins were phosphorylated at a 3-fold higher rate than other proteins, and these proteins were identified to be cytokeratins 8 and 18 respectively, by immunoprecipitation and Western blot analysis using monoclonal anti-cytokeratin 8 and 18 antibodies. The basic cytokeratins 8 and 18 showed pI 6.4 and 5.4 respectively, in two-dimensional gel electrophoresis. MC-LR dose dependently increased phosphorylation of cytokeratins 8 and 18 in a cell-free system by incubation with a cytosolic fraction of rat liver containing both protein kinases and protein phosphatases 1 and 2A, and with [gamma-32P]ATP. Cytokeratins 8 and 18 were target proteins for phosphorylation induced by inhibition of protein phosphatases 1 and 2A, in vitro and in rat hepatocytes. Thus, the treatment of rat hepatocytes with MC-LR induced hyperphosphorylation of cytokeratins 8 and 18 associated with morphological changes, indicating that intermediate filament networks were rearranged in the cytoplasm. The hyperphosphorylation of cytokeratins is a significant biochemical process associated with liver tumor promotion.
TL;DR: Results demonstrate that DAS is an effective chemopreventive agent against NNK-induced lung tumorigenesis, probably by inhibiting the metabolic activation of NNK.
Abstract: Diallyl sulfide (DAS), a component of garlic oil, has been shown to inhibit tumorigenesis by several chemical carcinogens. Our previous work demonstrated that DAS inhibited the metabolic activation of carcinogenic nitrosamines, including the tobacco-specific 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), in rat lung and nasal mucosa microsomes. In the present study, the effects of DAS on the tumorigenicity and the metabolism of NNK in A/J mouse lung were examined. Female A/J mice at 7 weeks of age were pretreated with DAS (200 mg/kg body wt in corn oil, p.o) daily for 3 days. Two hours after the final DAS treatment, the mice were either given a single dose of NNK (2 mg/mouse, i.p.) and kept for an additional 16 weeks for determining the production of pulmonary tumors, or were killed immediately so as to measure the microsomal activity in metabolizing NNK. In comparison to the vehicle control group, DAS pretreatment significantly decreased the incidence of NNK-induced lung tumors (37.9 versus 100%) and the tumor multiplicity (0.6 versus 7.2 tumors/mouse). In pulmonary metabolism of NNK, DAS pretreatment reduced the rates of formation of keto aldehyde, keto alcohol, NNAL-N-oxide, and NNK-N-oxide by 70-90%. In addition, the formation of NNK oxidative metabolites from NNK in the liver microsomes from DAS-pretreated mice was remarkably reduced. DAS also inhibited the metabolism of NNK in mouse lung microsomes in vitro. These results demonstrate that DAS is an effective chemopreventive agent against NNK-induced lung tumorigenesis, probably by inhibiting the metabolic activation of NNK.
TL;DR: The results indicate that the increase in colonic proliferation is mediated by diet-dependent increases in soluble colonic bile acid concentration and luminal lytic activity, which illustrates how diet could influence the risk for colon cancer.
Abstract: The proposed intermediate steps in the relationship between a diet-dependent increase in colonic bile acids and proliferation of colonic cells were studied in rats. Male Wistar rats were fed diets supplemented with increasing amounts of steroids to increase the bile acid concentration of the colon. After 2 weeks, in vivo colonic proliferation was measured using tritiated thymidine incorporation into DNA. Luminal lytic activity was measured as lysis of erythrocytes by fecal water. To quantify hemolysis in the presence of fecal water, a method was developed which measures Fe-release using atomic absorption spectrophotometry. This method proved to be superior to the cell-counter method published earlier. Our results showed that steroid supplementation increased, in a dose-dependent manner, the total fecal and the soluble bile acid concentration as well as lytic activity of fecal water and colonic proliferation. A highly significant correlation between lytic activity of fecal water and colonic proliferation (r = 0.85, n = 24, P less than 0.001) was observed. These results indicate that the increase in colonic proliferation is mediated by diet-dependent increases in soluble colonic bile acid concentration and luminal lytic activity. This sequence of effects illustrates how diet could influence the risk for colon cancer.
TL;DR: Data indicate that a rapid methodology exists to assess the levels of AFM1 excretion in human milk and to use this approach as a biomarker for exposure of children to this carcinogen.
Abstract: Maternal-to-child exposure of aflatoxin Ml in breast milk is an underevaluated risk factor from dietary exposure to aflatoxin B1. A molecular dosimetry study in the Gambia West Africa was initiated to explore the relationships between dietary intake of aflatoxins during a 1-week period and a number of aflatoxin biomarkers including aflatoxin metabolite excretion into breast milk. For the breast milk study 5 lactating women were identified and milk samples were collected by hand expression once a day during days 3-7 for 3 women and during days 3-6 for the 2 other women. Aflatoxin M1 (AFM1) in human milk was measured in all 5 subjects by a preparative monoclonal antibody immunoaffinity column/HPLC method. In 3 of 5 women aflatoxin G1 was found. Estimates of the percentage of aflatoxin in the diet excreted as AFM1 in milk ranged from 0.09% to 0.43%. Thus these data indicate that a rapid methodology exists to assess the levels of AFM1 excretion in human milk and to use this approach as a biomarker for exposure of children to this carcinogen. (authors)
TL;DR: While DDS may act as a chemopreventive agent, DS may promote hepatocarcinogenesis because it demonstrated clear enhancing effects on the development of glutathione S-transferase placental form positive foci in both experiments.
Abstract: It has been reported that diallyl sulfide (DS) and diallyl disulfide (DDS), major volatile compounds in garlic (Allium sativum), exert anticarcinogenic activity in several organs in rodents. The modifying effects of these two chemicals were therefore assessed using two-step liver and multi-organ carcinogenesis models. In experiment 1, male F344 rats were given a single i.p. injection of N-diethylnitrosamine (200 mg/kg body wt) and then received DS or DDS by intragastric intubation at doses of 200 and 50 mg/kg body wt, respectively, three times a week for 6 weeks. All rats were subjected to two-thirds partial hepatectomy at experimental week 3. In experiment 2, male F344 rats were sequentially treated with five carcinogens with different organ target sites for 4 weeks, and then administered DS or DDS as in experiment 1 for 24 weeks. DS demonstrated clear enhancing effects on the development of glutathione S-transferase placental form positive foci in both experiments. On the other hand, an inhibitory potential in colon and renal carcinogenesis was observed in rats treated with DDS. Therefore, while DDS may act as a chemopreventive agent, DS may promote hepatocarcinogenesis.