Effects of 3-Aminobenzamide on Induction of Multiorgan Carcinogenesis by N-Nitrosobis(2-hydroxypropyl)amine in Hamsters

The effects of an inhibitor of poly(ADP-ribose)polymerase, 3-aminobenzamide (ABA), on N-nitrosobis(2-hydroxypropyl)amine (BHP)-induced pancreas, liver, gallbladder and lung carcinogenesis in Syrian golden hamsters were investigated. Animals were given either BHP alone, by subcutaneous injection at a dose of 500 mg/kg body weight, or in combination with an intraperitoneal injection of ABA 30 min after the BHP at a dose of 300 or 600 mgAg body weight once a week for 5 weeks, and then killed 35 weeks after the commencement of the experiment. ABA exerted inhibitory effects on pancreas and lung carcinogenesis induced by BHP, with mean numbers of lesions (including hyperplasias and carcinomas) being significantly decreased compared with the BHP-alone group values, while no significant effect was observed on liver or gallbladder carcinogenesis. These results suggest that the effects of ABA on carcinogenesis depend on the target organ as well as the chemical carcinogen examined.     

Modulation of A N-nitrosobis(2-hydroxypropyl)amine-induced carcinogenesis by clofibrate in hamsters

The effects of clofibrate treatment on N-nitrosobis(2-hydroxy-propyl)amine(BHP) induced liver, gall bladder, pancreas, lung and kidneycarcinogenesis in hamsters were studied. Animals were givenBHP as an initiator at a dose of 500 mg/kg body weight subcutaneouslyonce a week for 5 weeks followed by diet containing 0.25 or0.5% clofibrate for 30 weeks. Both doses of clofibrate promotedhepatocarcino-genesis as judged from the associated multiplicityof liver lesions including hyperplastic nodules and hepatocellularcarcinomas. -Glutamyltranspeptidase (-GTP) activity was notexpressed in those lesions in the liver of hamsters given BHPfollowed by a basal diet or diets containing clofibrate. Clofibrateat a dose of 0.5% in the diet, in contrast, inhibited the developmentof pancreatic adenocarcinomas and lung neoplasms, includingadenomas and adenocarcinomas, without affecting carcinogenesisin the gall bladder and kidney. These results clearly indicatedifferectial modification potential of clofibrate for BHP-inducedliver, pancreas and lung carcinogenesis in Syrian hamsters.     

Effects of phenobarbital and secondary bile acids on liver, gallbladder, and pancreas carcinogenesis initiated by N-nitrosobis (2-hydroxypropyl)amine in hamsters

The effects of dietary administration of phenobarbital [(PB) CAS: 50-06-6] or the secondary bile acids, deoxycholic acid [(DCA) CAS: 83-44-3] and lithocholic acid [(LCA) CAS: 434-13-9], on tumorigenesis in the liver, gallbladder, and pancreas were investigated in male Syrian golden hamsters after carcinogenic initiation by N-nitrosobis(2-hydroxypropyl)amine [(BHP) CAS: 53609-64-6]. BHP [500 mg/kg (body wt)] was injected sc once weekly for 5 weeks. The animals were then maintained on a basal diet or a diet containing either 0.05% PB, 0.1% DCA, 0.5% DCA, or 0.5% LCA for 30 weeks. DCA enhanced the development of cholangiocarcinomas without influencing that of hepatocellular lesions. PB promoted the induction of hepatocellular carcinomas but not that of cholangiocarcinomas. LCA was without effect on the induction of either hepatocellular carcinomas or cholangiocarcinomas. DCA at a dose of 0.5% enhanced the induction of polyps in the gallbladder. Both DCA, at a dose of 0.1%, and LCA significantly enhanced the induction of pancreas carcinomas. PB had no effect on the induction of polyps in the gallbladder or of pancreas carcinomas. These data document that different tumors may be differentially promoted following initiation with a common carcinogen.     

Combined effects of cholecystectomy and lithocholic acid on pancreatic carcinogenesis of N-nitrosobis(2-hydroxypropyl)amine in Syrian golden hamsters

The effects of cholecystectomy and/or lithocholic acid (LCA) on the composition of biliary bile acid and on pancreatic carcinogenesis by N-nitrosobis(2-hydroxypropyl)amine (BHP) were examined in male Syrian golden hamsters. Cholecystectomy was performed 1 wk before BHP initiation. BHP (250 mg/kg of body weight) was injected s.c. once a wk for 5 wk. A diet containing 0.5% LCA was begun 1 wk after the final BHP injection. All hamsters were sacrificed 36 wk after cholecystectomy, and the pancreas was examined histologically. Only the LCA treatment but no other treatment influenced the bile acid composition, i.e., the increase in LCA and decrease in cholic acid. The incidence of pancreatic carcinoma was 23 of 30 (76.7%) in hamsters receiving cholecystectomy plus BHP followed by LCA diet. The tumor incidence was five of 18 (27.8%) with BHP followed by basal diet, ten of 18 (55.6%) with cholecystectomy plus BHP followed by basal diet, and six of 18 (33.3%) with BHP followed by LCA diet, respectively. The total number of pancreatic carcinomas in hamsters receiving cholecystectomy and BHP followed by LCA diet also increased significantly. These results indicate that combined treatments of cholecystectomy and dietary LCA enhanced BHP-inducing pancreatic carcinogenesis in hamsters.     

Effects of 3-aminobenzamide on the post-initiation phase of N-nitrosobis(2-oxopropyl)amine induced pancreatic carcinogenesis in Syrian hamsters.

Effects of 3-aminobenzamide (ABA) on pancreatic carcinogenesis after initiation by N-nitrosobis(2-oxopropyl)amine (BOP) were investigated in Syrian hamsters. Animals were given BOP at a dose of 70 mg/kg body weight by subcutaneous injection and following a 2-week recovery period, were administered basal diet or basal diet containing 0.5, 0.75 and 1.5% ABA for 30 weeks. While the incidences of resultant pancreatic lesions, including hyperplasia, atypical hyperplasia and carcinoma, induced by BOP were not significantly influenced by ABA treatment, the mean numbers of those pancreatic lesions were significantly decreased in a dose-dependent way. The results therefore suggested the possible involvement of poly(ADP-ribosyl)ation in the post-initiation phase of pancreatic carcinogenesis in hamsters.     

Distribution, metabolism and excretion of N-nitrosobis(2-hydroxypropyl)amine in Wistar rats

The metabolic fate of the carcinogen N-nitrosobis(2-hydroxypropyl)amine(BHP) in male Wistar rats was studied. The blood level of [1-¹⁴C]BHPafter a single intraperitoneal injection, administered at acarcinogenic dose of 3 g/kg body weight, reached a maximum within1 h. Whereas a relatively high concentration of ¹⁴C was foundin the blood and target organs, such as the lung, liver, thyroidgland and kidney 1 h after the treatment, most of the radioactivelabelling had disappeared from the tissues by 24 h after injection.Most of the administered ¹⁴C was eliminated via the urine; 90.8%was excreted in the urine within the 24 h period, 5.5% in thefeces and 3.2% by way of expired air. Studies in rats with exteriorizedbile flow demonstrated that about 11% of the intraperitoneallyadministered ¹⁴C was excreted via the bile in 24 h. Analysisby h.p.l.c. detected BHP (78.1% of the dose), HPOP (1.5%), glucuronidesof BHP (4.3%) and HPOP (0.16%), MHP (0.03%) and unknown metabolites(6.0%) in the urine 24 h after the treatment. Besides thesemetabolites, BOP and two unidentified metabolites were alsodetected in the blood, lung, liver or kidney of rats 3 h afterthe treatment. These results suggest the involvement of BHPmetabolites, HPOP, MHP and BOP, in carcinogenesis and in particularlung carcinogenesis induced by BHP in rats.     

Modifying effects of simultaneous treatment with butylated hydroxyanisole (BHA) on rat tumor induction by 3,2'-dimethyl-4-aminobiphenyl, 2,2'-dihydroxy-di-n-propylnitrosamine and N-methylnitrosourea

The modifying effects of concurrent treatment with high or low doses of butylated hydroxyanisole (BHA) on wide-spectrum carcinogen-induced carcinogenesis were studied in male F344 rats. Groups of 20 animals were treated with 2 or 0.04% BHA for 24 weeks. Starting 2 weeks after the commencement of BHA treatment, they were given s.c. injection of 50 mg/kg body weight 3,2'-dimethyl-4-aminobiphenyl (DMAB) once a week, i.g. administrations of 200 mg/kg body weight 2,2'-dihydroxy-di-n-propylnitrosamine (DHPN) once every 2 weeks, or i.p. injection of 15 mg/kg body weight N-methylnitrosourea (MNU) once every 2 weeks for 22 weeks. Further groups of rats were treated with DMAB, DHPN, MNU, or 2 or 0.04% BHA alone. All surviving animals were killed 24 weeks after the beginning of the experiment and the target organs examined histopathologically. The BHA treatment dose-dependently decreased the incidence of DMAB-induced liver preneoplastic lesions but was associated with significant tumor induction in the forestomach (papillomas, 40%, P less than 0.01) and urinary bladder (papillomas, 53%, P less than 0.001; carcinomas, 80%, P less than 0.001), where no lesions were observed in the group given only DMAB. Concurrent administration of 2% BHA also significantly inhibited the development of alveolar hyperplasia (P less than 0.001) of the lung in DHPN-treated animals, while enhancing induction of forestomach papillomas (P less than 0.05) and simple hyperplasia in the urinary bladder. Neither MNU nor 2% BHA alone induced forestomach carcinoma or papillary or nodular hyperplasia (PN hyperplasia) in the urinary bladder. However, these lesions were observed in 100% (P less than 0.001) and 55% (P less than 0.001) of animals respectively, receiving the two compounds in combination. These results demonstrated that concurrent treatment with BHA not only inhibits but can also strongly enhance carcinogenesis depending on the organ, irrespective of whether the carcinogens act directly or require metabolism. The finding that BHA potently modified carcinogenesis at 0.04% in diet, 1/50 of the carcinogenic dose, suggests that actual dietary levels close to the human situation might play a significant role in tumor development in man.     

Promoting effects of both dietary cholesterol and cholestyramine on pancreatic carcinogenesis initiated by N-nitrosobis(2-oxopropyl)amine in Syrian golden hamsters.

The effects of dietary cholesterol and cholestyramine on pancreatic carcinogenesis initiated with N-nitrosobis(2-oxopropyl)amine (BOP) were investigated in 120 female Syrian golden hamsters. BOP (70 mg/kg body weight) was injected s.c. once at the beginning of the experiment. Starting 2 weeks later, the animals were then maintained on basal diet or diets containing either 0.5% cholesterol or 1% cholestyramine for a further 16 weeks. All surviving hamsters were killed at week 18, and the pancreas tissues examined histologically. The incidences of pancreatic carcinomas in hamsters fed cholesterol and the cholestyramine supplement were 40.0 and 30.0% respectively; in both cases significantly higher than the 6.9% incidence in the basal diet group. Cholesterol contents of the serum, pancreas and liver were significantly increased by cholesterol feeding and significantly decreased by the cholestyramine diet. The cholesterol diet also significantly increased pancreatic protein and DNA contents, and the concentration of total bile acids and the level of lithocholic acid in gallbladder bile. The cholestyramine diet significantly increased total pancreatic DNA and protein contents, and pancreatic weight. The results thus indicated that both dietary cholesterol and cholestyramine can enhance BOP-initiated pancreatic carcinogenesis in hamsters.     

Nitrosamine-induced pancreatic carcinogenesis in outbred and inbred Syrian hamsters

Pancreatic carcinogenesis was investigated in outbred and infive strains of inbred Syrian golden hamsters utilizing thenitrosamines N-nitrosobis(2-hydroxypropyl)amine (BHP) and N-nitrosobis(2-oxopropyl)amine(BOP). Thirty eight outbred hamsters were treated for an averageof 15 weeks with weekly s.c. inoculations of BHP at doses of250, 500, or 1000 mg/kg. Pancreatic carcinomas developed in19%. Eighty nine inbred hamsters of strains CB, LHC, and PD4were given BHP at 250 mg/kg weekly for an average of 25 weeks.Pancreatic carcinomas developed in 61%. Pancreatic inflammation,fibrosis, and ductal hyperplasia were prominent. Toxic changesin the liver, biliary hyperplasia, and pulmonary interstitialinflammation were also prominent features of BHP-treated hamsters,along with occasional carcinomas of the liver and respiratorytract. One hundred and sixteen inbred hamsters of strains CB,LHC, LSH, MHA, and PD4 were treated with BOP at a dose of 5mg/kg weekly for 15 weeks. The incidence of pancreatic carcinomawas 51%. BHP-treated hamsters exhibited pancreatic fibrosisand ductal hyperplasia. Livers of BHP-treated animals showedbiliary hyperplasia, and lungs exhibited chronic inflammation.Occasional carcinomas of the liver and lung developed. From243 hamsters treated with nitroso carcinogens, eight pancreaticductal adenocarcinoma lines were derived that can be transplantedand propagated in inbred hamsters.     

Species and organ differences in DNA adduct formation and repair after treatment with 4-hydroxyaminoquinoline 1-oxide

4-Hydroxyaminoquinoline 1-oxide (4HAQO) demonstrates obvious organotropic and species specificity in its carcinogenesis and the present investigation concerns 4HAQO DNA adduct formation and repair as studied in various organs of four animal species (rats, mice, guinea pigs and hamsters). Three hours after an iv injection of 10 mg per kg body weight of tritium-labeled 4HAQO, the major organs were removed and used for assessment of label incorporation in the DNA. The results showed that the DNA binding levels generally correlated well with the reported species and organ specificity of 4HAQO tumorigenesis. For example, rats showed highest DNA binding in the pancreas and kidney, major target organs. The levels of DNA binding in the liver were invariably low in all 4 animal species, in agreement with the lack of hepatocarcinogenicity associated with 4HAQO exposure. A clear relationship between DNA adduct formation and carcinogen dose was also found after treatment of mice with 4HAQO at doses of 1, 5, 10 and 20 mg per kg body weight in all tissues (pancreas, kidney and lung) except for the liver. Comparison of DNA repair processes in rats, a highly susceptible species, and hamsters, a resistant species in terms of 4HAQO carcinogenicity, revealed highest formation and slowest removal of adducts in the target organs of the rat. In the hamster organs and the rat lung and liver, DNA adduct formation was generally low and in the case of elevation in the initial phase, quickly removed.     

Species and Organ Differences in DNA Adduct Formation and Repair after Treatment with 4-Hydroxyaminoquinoline 1-Oxide

4-Hydroxyaminoquinoline 1-oxide (4HAQO) demonstrates obvious organotropic and species specificity in its carcinogenesis and the present investigation concerns 4HAQO DNA adduct formation and repair as studied in various organs of four animal species (rats, mice, guinea pigs and hamsters). Three hours after an iv injection of 10 mg per kg body weight of tritium-labeled 4HAQO, the major organs were removed and used for assessment of label incorporation in the DNA. The results showed that the DNA binding levels generally correlated well with the reported species and organ specificity of 4HAQO tumorigenesis. For example, rats showed highest DNA binding in the pancreas and kidney, major target organs. The levels of DNA binding in the liver were invariably low in all 4 animal species, in agreement with the lack of hepatocarcinogenicity associated with 4HAQO exposure. A clear relationship between DNA adduct formation and carcinogen dose was also found after treatment of mice with 4HAQO at doses of 1, 5, 10 and 20 mg per kg body weight in all tissues (pancreas, kidney and lung) except for the liver. Comparison of DNA repair processes in rats, a highly susceptible species, and hamsters, a resistant species in terms of 4HAQO carcinogenicity, revealed highest formation and slowest removal of adducts in the target organs of the rat. In the hamster organs and the rat lung and liver, DNA adduct formation was generally low and in the case of elevation in the initial phase, quickly removed.     

Alkylation of rodent tissue DNA induced by N-nitrosobis(2-hydroxypropyl)amine.

Levels of methyl and hydroxypropyl adducts induced by single s.c. injections of various doses of tritium-labeled N-nitrosobis(2-hydroxypropyl)amine ([1-3H]BHP) were determined in the liver, pancreas, kidney and lung of hamsters and rats. At doses of BHP used in carcinogenesis studies (100-500 mg/kg), methylation of DNA was more extensive than its hydroxypropylation; however, it did not increase proportionally with the dose and gradually became secondary to hydroxypropylation at higher doses of the carcinogen. Ratios of hydroxypropyl versus methyl adducts also varied significantly depending on the tissue and species. In both species ratios of N7-hydroxypropylguanine (N7-HpG) versus N7-methylguanine (N7-MeG) were greater in kidney and pancreas than in liver or lung. Due to apparent differences in the repair of O6-methylguanine (O6-MeG) and O6-hydroxypropylguanine (O6-HpG), and the propensity of 2-hydroxypropylating as compared to methylating agents to yield a greater percentage of oxygen adducts, ratios of O6-HpG versus O6-MeG were markedly greater than those of N7-HpG versus N7-MeG. Levels of O6-HpG were greater than those of O6-MeG in rat liver, pancreas and kidney and also in hamster kidney, while such levels were similar in rat lung and also in hamster liver, pancreas and lung. Like N-nitrosobis(2-oxopropyl)amine (BOP) and N-nitroso(2-hydroxypropyl) (2-oxopropyl)amine (HPOP), BHP was activated primarily in the liver and induced substantially greater DNA damage in this than in any other tissue examined. However, unlike BOP and HPOP, which induced similar levels of hepatic DNA damage in the above two species, BHP methylated and hydroxypropylated hamster liver DNA more extensively than that of the rat. Differences between BOP and BHP were also observed regarding levels and distribution of DNA adducts in extrahepatic tissues. In rats, BHP induced greater levels of methylation and hydroxypropylation in lung than in kidney, while the reverse was observed with BOP. Apparently reduction of the beta-carbon of pancreas-specific nitrosamine carcinogens results in a shift of alkylation from kidney to the lung. Excretion of HPOP in the urine of BHP-treated animals and the observed saturation of DNA methylation at high doses of BHP, supported the hypothesis that the BHP-induced methylation of DNA proceeded via the intermediate formation of HPOP. This was further supported by the observation that both excretion of HPOP and levels of methyl adducts were greater in hamsters than in rats.(ABSTRACT TRUNCATED AT 400 WORDS)     

Epoprostenol sodium, a prostaglandin I2, lacks tumor promoting effects in a medium-term liver carcinogenesis bioassay in rats

Potential modifying effects of epoprostenol sodium administration on liver carcinogenesis were investigated in male F344/DuCrj rats initially treated with N-nitrosodiethylamine (DEN). Two weeks after a single dose of DEN (200 mg/kg, intraperitoneally), rats daily received subcutaneously epoprostenol sodium at doses of 0, 1, 10 and 100 microg/kg, or were fed phenobarbital sodium (PB) at a dietary level of 500 parts per million (ppm) as positive control for 6 weeks. All animals were subjected to partial hepatectomy at week 3, and were killed at week 8. Prominent flushing of extremis and signs of behavioural depression occurred after injection and lasted for 1 h in rats given 100 microg/kg epoprostenol sodium. Such clinical signs were slight in rats treated with 10 microg/kg, but not observed with 1 microg/kg. Marked decrease in body weight gain was noted in rats given 100 microg/kg. Statistically significant changes in relative liver weights were not found in any group given the test chemical. Epoprostenol sodium did not significantly increase the quantitative values for glutathione S-transferase placental form (GST-P) positive liver cell foci observed after DEN initiation, in clear contrast to the positive control. The results thus demonstrate that epoprostenol sodium lacks modifying potential for liver carcinogenesis in our medium-term bioassay system.     

Modifying effects of various chemicals on preneoplastic and neoplastic lesion development in a wide-spectrum organ carcinogenesis model using F344 rats

Modifying potentials of various chemicals on tumor development were investigated in a wide-spectrum organ carcinogenesis model using male F344/DuCrj rats. The animals were treated with N-nitrosodiethylamine (100 mg/kg body weight, ip, single injection at the commencement of the study), N-methyl-N-nitrosourea (20 mg/kg body weight, ip, 4 times during weeks 1 and 2) and N-bis(2-hydroxypropyl)nitrosamine (0.1% in drinking water, during weeks 3 and 4) for multi-organ initiation and then were given one of 14 test chemicals including 6 hepatocarcinogens, 7 non-hepatocarcinogens and 1 non-carcinogen, or basal diet for 16 weeks. All rats were killed at the end of week 20, and the major organs were carefully examined for preneoplastic and neoplastic lesions. Immunohistochemical demonstration of glutathione S-transferase-positive foci was also used for quantitative assessment of liver preneoplastic lesion development. Modifying effects were shown for 11 out of 14 test agents in the liver, forestomach, glandular stomach, lung, urinary bladder or thyroid, 7 of them targeting more than two organs. This was the first demonstration to our knowledge that clofibrate possesses enhancing potential for urinary bladder carcinogenesis and an inhibiting effect on thyroid carcinogenesis. Caprolactam showed no effect in any organ, in agreement with its established inactivity. The results indicated that the system could be reliably applied as a medium-term multiple organ bioassay for assessment of the modification potential of test agents in unknown target sites.     

Modifying Effects of Various Chemicals on Preneoplastic and Neoplastic Lesion Development in a Wide-spectrum Organ Carcinogenesis Model Using F344 Rats

Modifying potentials of various chemicals on tumor development were investigated in a wide-spectrum organ carcinogenesis model using male F344/DuCrj rats. The animals were treated with N-nitroso-diethylamine (100 mg/kg body weight, ip, single injection at the commencement of the study), N-methyl-N-nitrosourea (20 mg/kg body weight, ip, 4 times during weeks 1 and 2) and N-bis(2-hydroxypropyl)nitrosamine (0.1% in drinking water, during weeks 3 and 4) for multi-organ initiation and then were given one of 14 test chemicals including 6 hepatocarcinogens, 7 non-hepatocarcinogens and 1 non-carcinogen, or basal diet for 16 weeks. All rats were killed at the end of week 20, and the major organs were carefully examined for preneoplastic and neoplastic lesions. Immunohistochemical demonstration of glutathione S -transferase-positivc foci was also used for quantitative assessment of liver preneoplastic lesion development. Modifying effects were shown for 11 out of 14 test agents in the liver, forestomach, glandular stomach, lung, urinary bladder or thyroid, 7 of them targeting more than two organs. This was the first demonstration to our knowledge that cloflbrate possesses enhancing potential for urinary bladder carcinogenesis and an inhibiting effect on thyroid carcinogenesis. Caprolactam showed no effect in any organ, in agreement with its established inactivity. The results indicated that the system could be reliably applied as a medium-term multiple organ bioassay for assessment of the modification potential of test agents in unknown target sites.     

Initiating Activity of Diethylnitrosamine in a Rapid Production Model for Pancreatic Carcinomas in Syrian Hamsters

The potential initiating activity of diethylnitrosamine (DEN) was studied in a rapid production model for pancreatic carcinogenesis in hamsters developed in our laboratory incorporating the principle of selection based on resistance to cytotoxicity, originally demonstrated for liver carcinogenesis in rats. Female Syrian golden hamsters were given DEN at a dose of 100 mg/kg body weight or N-nitrosobis-(2-oxopropyI)amine (BOP) at a dose of 70 mg/kg body weight as initiators followed by 3 cycles of augmentation pressure (choline-deficient diet combined with DL-ethionine, L-methionine upon return to basal diet and then administration of 20 mg/kg body weight BOP), and killed 10 weeks after the beginning of the experiment. DEN followed by the augmentation pressure induced a 65% incidence of total pancreatic lesions including 15% carcinomas, while BOP followed by the augmentation pressure induced 100% incidence of total pancreatic lesions and 84.2% for carcinomas. These yields were significantly greater than those observed for augmentation pressure alone. The results thus indicate that DEN possesses weak initiating activity for pancreatic carcinogenesis under the present experimental conditions.     

Initiating activity of diethylnitrosamine in a rapid production model for pancreatic carcinomas in Syrian hamsters.

The potential initiating activity of diethylnitrosamine (DEN) was studied in a rapid production model for pancreatic carcinogenesis in hamsters developed in our laboratory incorporating the principle of selection based on resistance of cytotoxicity, originally demonstrated for liver carcinogenesis in rats. Female Syrian golden hamsters were given DEN at a dose of 100 mg/kg body weight or N-nitrosobis-(2-oxopropyl)amine (BOP) at a dose of 70 mg/kg body weight as initiators followed by 3 cycles of augmentation pressure (choline-deficient diet combined with DL-ethionine, L-methionine upon return to basal diet and then administration of 20 mg/kg body weight BOP), and killed 10 weeks after the beginning of the experiment. DEN followed by the augmentation pressure induced a 65% incidence of total pancreatic lesions including 15% carcinomas, while BOP followed by the augmentation pressure induced 100% incidence of total pancreatic lesions and 84.2% for carcinomas. These yields were significantly greater than those observed for augmentation pressure alone. The results thus indicate that DEN possesses weak initiating activity for pancreatic carcinogenesis under the present experimental conditions.     

Enhancement of DEN initiation of liver carcinogenesis by inhibitors of NAD+ ADP ribosyl transferase in rats

The effect of inhibitors of NAD⁺ ADP ribosyl transferase (ADPRT)on the early stage of liver carcinogenesis of diethylnitrosamine(DEN) was studied by estimating the number and size of -glutamyltranspeptidase(-GTP) positive foci assayed as markers of cell populationsinitiated by DEN in the rat liver. ADPRT inhibitors investigatedwere 3-amino-benzamide (ABA), 5-methylnicotinamide (MNAM), andthymidine. A single i.p. injection of ABA at > 150 mg/kgbody weight (B.W.) enhanced dose-dependently the induction of-GTP positive foci in rat liver initiated by 20 mg/kg B.W. ofDEN. The magnitude of the effect was similar to that observedwhen partial hepatectomy (PH) was performed instead of ABA administration.Single i.p. injections of MNAM or thymidine at a dose of 600mg/kg B.W. also enhanced the induction of foci in rat liverinitiated by the 20 mg/kg dose of DEN. Based on the above results,ABA was used as a representative ADPRT inhibitor for clarifyingthe mechanisms underlying the effects. Administration of ABAat a dose of 600 mg/kg B.W. was effective in enhancing the inductionof foci if given 1 day before DEN, simultaneously to DEN, and1 day after DEN initiation but it was ineffective if it wasgiven 3 days after DEN or thereafter. Liver cell necrosis wasnot detectable either by analysis of serum enzymes or histologically1, 3, 5, 7 and 14 days after 20 mg/kg B.W. of DEN with or withoutadministration of 600 mg/kg B.W. of ABA. No initiating activitywas observed for ABA administered at doses of 600 and 1200 mg/kgB.W. as assayed by development of -GTP positive foci. Long termABA administration in the diet at concentrations of 0.05, 0.1and 0.2% did not show any promoting activity for liver carcinogenesisinitiated by DEN. Furthermore, chronic administration of 0.2%ABA in the diet did not result in detectable toxicity and/orcarcinogenic effects. These results suggest that ADPRT and associatedDNA repair plays an important role in the early initiating stageof liver carcinogenesis and provide the basis for a new experimentalapproach to the analysis of the mechanisms of chemical carcinogenesisand in establishing a more sensitive assay system for livercarcinogenesis in rats.     

A single-dose protocol for azaserine initiation of pancreatic carcinogenesis in the rat

Previously, the induction of pancreatic carcinogenesis in the rat using azaserine has involved a multiple-dose treatment protocol. The objective of the present study was to determine the effect of multiple azaserine treatments on pancreatic DNA synthesis and to develop a protocol for a single-dose initiation of pancreatic carcinogenesis by azaserine in the rat. Pancreatic DNA synthesis in young rats, which was determined by measuring the amount of [³H]-thymidine incorporation into DNA, was found to be elevated at 4.3 weeks of age and to decrease to a baseline level by 6.3 weeks. Treatment of 4-week-old rats with azaserine resulted in a dose-dependent inhibition of [³H]-thymidine incorporation into both pancreatic and liver DNA. Maximum inhibition was seen at 10 mg/kg body weight. This inhibition was followed by a gradual return of incorporation to normal values over a 48 h period. One week following pretreatment with four weekly injections of azaserine at 30 mg/kg, [³H]-thymidine incorporation into pancreatic and liver DNA was significantly elevated, suggesting that multiple injection protocols cause enhanced DNA synthesis which could have a co-carcinogenic and/or promotional effect. Single-doses of azaserine (10, 30 and 60 mg/kg) given at 7 weeks of age caused the appearance of more atypical acinar cell nodules (AACN) than when given at 5 weeks of age. The most effective dose was 30 mg/kg. Using alkaline elution, we determined that this response was due to the occurrence of more DNA damage in the 7-week-old animals. Thus, these results demonstrate a rationale for the use of single-dose initiation protocols in the pancreas. An effective single-dose protocol for induction of AACN in azaserine-treated rats fed semi-synthetic diet is presented.     

Butylated hydroxytoluene lacks the activity of phenobarbital in enhancing diethylnitrosamine-induced mouse liver carcinogenesis

The effect of the food additive butylated hydroxytoluene (BHT) as an enhancer of liver carcinogenesis in mice was investigated. Liver carcinogenesis was initiated by intraperitoneal injection of diethylnitrosamine (DEN) in male B6C3F1 mice at 100 or 200 mumol/kg body weight once a week for 10 weeks (total exposure 1000 or 2000 mumol/kg body weight). After an exposure-free recovery interval of 4 weeks, groups of mice were fed either basal diet or diets containing either 5000 ppm BHT or 500 ppm phenobarbital (PB), as a positive control, for 24 weeks. Exposure to the initiating doses of DEN alone induced no liver foci at 10 weeks or at 14 weeks after the recovery period, but at termination at 38 weeks, foci and adenomas were present in a dose-related incidence. In the groups given BHT after DEN/recovery, the incidence and the multiplicity of liver foci and adenomas were not different from those in mice given only DEN/recovery, whereas, in the groups given PB after DEN, liver lesions were increased by 1.7-3.0-fold. In conclusion, BHT had no promoting or syncarcinogenic effect on DEN-induced mouse liver carcinogenesis, whereas under the same conditions, PB acted as an enhancer.