Inhibition by methionine of pancreatic carcinogenesis in hamsters after initiation with N-nitrosobis(2-oxopropyl) amine

The modifying effects of dietary L-methionine in the post-initiation phase of pancreatic carcinogenesis were investigated in hamsters treated with N-nitrosobis(2-oxopropyl)amine (BOP). Groups consisting of 20 and 30 animals, respectively, were given BOP subcutaneously, once a week five times at a dose of 10 mg/kg body wt. and then continuously fed diet supplemented with 2% (group 1) or 0% (group 2) methionine (weeks 5-32). After five subcutaneous injections of saline, group 3 animals were similarly fed diet supplemented with 2% methionine for the same period. The incidence of pancreatic ductal adenocarcinomas was significantly lower in group 1 (36.8%, P<0.05) than in group 2 (71.4%). Multiplicity of adenocarcinomas was also significantly lowered (0.52 and 1.28/hamster, P<0.05). Similarly, total numbers of combined adenocarcinomas and dysplastic lesions were significantly decreased in group 1 (2.05, P<0.05) as compared with group 2 (3.67). Methionine enhanced atrophic change of pancreatic acinar cells in hamsters given BOP, indicating that the inhibitory effects on the post-initiation stage of BOP-induced pancreatic carcinogenesis in hamsters could be generally linked to suppression of growth.     

Effects of various prostaglandin synthesis inhibitors on pancreatic carcinogenesis in hamsters after initiation with N-nitrosobis(2-oxopropyl)amine

The effects of prostaglandin synthesis inhibitors on development of N-nitrosobis(2-oxopropyl)amine (BOP)-initiated pancreatic tumors were investigated. Female Syrian golden hamsters were given five weekly s.c. injections of BOP (10 mg/kg body weight) during the first 5 weeks and then given 20 p.p.m. indomethacin in the drinking water, 0.25% phenylbutazone in the diet, 1% aspirin in the diet, or no treatment (control group). The resultant incidence of pancreatic carcinoma at week 32 was significantly lower (P less than 0.05) in animals receiving phenylbutazone (36.8%) than in the controls (71.4%) and the numbers of carcinomas per hamster were significantly reduced by indomethacin (0.63) and phenylbutazone (0.58) treatment compared with the control group value (1.29). Aspirin also showed a tendency to decrease pancreatic tumor incidence, but this was not significant. Thus, prostaglandin synthesis inhibitors reduce the development of pancreatic cancer when administered during the post-initiation phase in this animal model.     

Effects of octreotide, a somatostatin analogue, on initiation of pancreatic carcinogenesis in hamsters with N-nitrosobis(2-oxopropyl)amine

The modifying effects of octreotide acetate, a somatostatin (SMS) analogue shown to inhibit secretion of digestive enzymes, bicarbonate and pancreatic juice, on the initiation phase of pancreatic carcinogenesis were investigated in hamsters simultaneously treated with N-nitrosobis(2-oxopropyl)amine (BOP). Groups 1-3, each consisting of 20 animals, were given BOP subcutaneously once a week three times at a dose of 10 mg/kg body weight during administration of octreotide acetate for 28 days via osmotic pumps implanted subcutaneously at doses of 6 microg/day (group 1), 3 microg/day (group 2) or 0 microg/day (saline) (group 3). Group 4-6 animals (each group ten animals) were similarly administered octreotide acetate for the same period with five subcutaneous injections of saline. At the termination of experimental week 40, the incidences and multiplicities of pancreatic ductal adenocarcinomas and dysplastic lesions did not significantly differ among groups 1-3. No neoplastic lesions were found in groups 4-6. Subcutaneous administration of octreotide acetate resulted in obviously increased plasma octreotide levels. Our results thus suggest that this SMS analogue may not modulate the initiation of BOP-induced pancreatic carcinogenesis, regardless of its pharmacological action.     

Inhibitory effects of crude soybean trypsin inhibitor on pancreatic ductal carcinogenesis in hamsters after initiation with N-nitrosobis(2-oxopropyl)amine.

The effects of soybean trypsin inhibitor (SBTI) administration during the promotion phase of pancreatic carcinogenesis were investigated. Female Syrian golden hamsters were given three weekly s.c. injections of N-nitrosobis(2-oxopropyl)amine (BOP) each at a dose of 10 mg/kg and then administered 5% SBTI diet for the following 37 weeks. Additional groups of animals received the BOP injection alone or the 5% SBTI diet alone as controls. At week 40 of the experiment, all surviving animals were killed and development of pancreatic lesions was assessed histopathologically. The results showed that the incidence of dysplastic lesions in hamsters of the BOP/SBTI group was significantly decreased as compared to that of the BOP group (P < 0.01). A similar but not significant tendency was also found for pancreatic adenocarcinomas. In addition, the number of dysplastic lesions in the pancreas head portion in the BOP/SBTI group were significantly decreased as compared to the BOP group value (P < 0.05). Furthermore, atrophic changes of the pancreatic exocrine tissue were more severe in the BOP group than in the BOP/SBTI group (P < 0.01), indicating that SBTI treatment gave effective protection against the replacement process of acinar cell induced by BOP. Thus, the present experiment demonstrated that SBTI can inhibit hamster pancreatic ductal carcinogenesis when given in the promotion phase, in clear contrast to the enhancing effects reported for preneoplastic acinar lesion development in rats.     

Inhibitory effects of sulfation inhibitors on initiation of pancreatic ductal carcinogenesis by N-nitrosobis(2-oxopropyl)amine in hamsters

The effects of dehydroepiandrosterone sulfate (DHAS), a typicalhydroxysteroid sulfotransferase (HSTase) inhibitor, and of 3'-phosphoadenosine5'-phosphate (PAP), a nonspecific sulfation inhibitor on N-nitrosobis(2-oxopropyl)-amine(BOP)-induced initiation were examined in a rapid productionmodel for pancreatic carcinomas in hamsters in order to elucidatethe involvement of sulfotransferase in the metabolic activationof ß-oxypropylnitrosamines. While neither low norhigh doses of DHAS and PAP exerted any significant influenceon the incidence of ductal lesions including carcinomas, thehigh dose of DHAS (350 mg/kg body wt) and a both low (90 mg/kg)and high (180 mg/kg) doses of PAP reduced the mean numbers ofpancreatic ductal adenocarcinomas. The high dose of PAP alsoreduced the number of all ductal lesions combined. The resultsthus suggest that metabolic activation with STase is involvedin BOP-induced pancreatic ductal carcinogenesis in hamsters,and support the hypothesis that BOP is metabolized to ß-hydroxyalkylnitrosaminesfollowed by activation to proximate sulfuric acid esters byHSTase.     

Lack of influence of low blood cholesterol levels on pancreatic carcinogenesis after initiation with N-nitrosobis(2-oxopropyl)amine in Syrian golden hamsters

The effects of a cholesterol-free diet, a cholesterol-free dietsupplemented with sesamin, and a diet supplemented with sesaminon pancreatic carcinogenesis of N-nitrosobis(2-oxopropyl) amine(BOP) were investigated in 140 female Syrian golden hamsters.BOP (70 and 20 mg/kg body wt) was injected s.c. twice at aninterval of 2 weeks at the beginning of the experiment. Starting3 weeks thereafter, the animals were maintained on basal diet,cholesterol-free diet, basal diet plus sesamin, or cholesterol-freediet plus sesamin for a further 15 weeks. All surviving hamsterswere killed at week 18, and the pancreatic tissues examinedhistologically. The incidences of pancreatic neoplastic andpreneoplastic lesions in each group did not show any statisticallysignificant variation. The cholesterol-free diet significantlydecreased the cholesterol contents of the serum, pancreas andliver, and sesamin supplement significantly decreased the cholesterolcontents of the serum and liver. Both the cholesterol-free dietand sesamin decreased the serum lipoperoxide levels. The resultsthus indicated that low cholesterol per se and sesamin exertno significant influence on BOP-initiated pancreatic carcinogenesisin hamsters, at least within the 4 month period after carcinogentreatment.     

Effects of catechol and its analogs on pancreatic carcinogenesis initiated by N-nitrosobis(2-oxopropyl)amine in Syrian hamsters

The modifying effects of the phenolic antioxidant catechol (CC) and its analogs hydroquinone (HQ) and resorcinol (RN) on pancreatic carcinogenesis were evaluated in 146 female Syrian golden hamsters. Groups of animals received either saline or 70 mg/kg body wt N-nitrosobis(2-oxopropyl)amine (BOP) s.c. injections, twice with a 2 week interval, followed by basal diet or diet containing 1.5% of CC, HQ or RN, and 0.75% CC from week 4. All hamsters were killed at week 20 and histopathologically examined for development of pancreatic, liver and gall bladder lesions. The total numbers of pancreatic lesions comprising carcinomas, atypical ductal hyperplasias and ductal hyperplasias per hamster were significantly decreased in animals receiving BOP followed by CC, HQ and RN when compared to those in hamsters given BOP followed by basal diet. Incidence values for atypical ductal hyperplasias were also significantly decreased by the RN or 0.75% CC treatments. The results thus suggest that pancreatic carcinogenesis initiated by BOP in Syrian hamsters can be inhibited by treatments with phenolic antioxidants such as CC, HQ and RN for a relatively short experimental period.     

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.     

Promoting effect of truncal vagotomy on pancreatic carcinogenesis initiated with N-nitrosobis(2-oxopropyl)amine in Syrian golden hamsters

The effect of truncal vagotomy (TV) on pancreatic carcinogenesis initiated with N-nitrosobis(2-oxopropyl)amine (BOP) was investigated in 81 female Syrian golden hamsters. The animals were divided into four groups according to the treatment, groups 1 and 2 serving as non-initiated controls receiving a single s.c. injection of 0.9% NaCl followed by either a sham operation or TV respectively, at week 2. Groups 3 and 4 were given a single s.c. injection of 70 mg/kg body wt of BOP before the sham operation or TV. All hamsters were killed at week 24, and the pancreas, liver and gall bladder tissues were examined histologically. While TV itself caused no significant change in pancreatic weight, the incidence of pancreatic carcinomas in hamsters from group 4 was 48.4%, significantly higher than the 16.7% evident in hamsters from group 3 (P less than 0.05). GLC analysis of the bile acid composition of gall bladder bile from hamsters not receiving carcinogen 1 and 4 months after TV revealed significantly decreased secondary bile acids. The results thus indicated that changes in bile acid composition may be involved in enhancement of BOP-initiated pancreatic carcinogenesis in hamsters by TV.     

Inhibitory effect of butylated hydroxyanisole administration on pancreatic carcinogenesis in Syrian hamsters initiated with N-nitrosobis(2-oxopropyl)amine

The modifying potential of butylated bydroxyanisole (BHA) administrationon pancreatic carcinogenesis was evaluated in 70 female Syriangolden hamsters. Groups of animals received saline, 70 mg/kgbody weight of N-nitrosobis(2-oxopropyl)-amine (BOP) or 70 mg/kgplus 20 mg/kg body weight of BOP followed by basal diet or dietcontaining 2% BHA from week 3. Although the body weights ofhamsters receiving the 2% BHA supplement decreased, caloricrestriction was not observed. All hamsters were killed at week18 and histo-pathologically examined for lesion development.The incidences of pancreatic carcinomas in hamsters receiving70 mg/kg plus 20 mg/kg body weight of carcinogen followed by2% BHA was 7.1%, significantly lower than the 64.3% evidentin hamsters given the same doses of BOP followed by basal diet.The total numbers of pancreatic lesions including carcinomas,atypical ductal hyperplasias and ductal hyperplasias and ductularproliferations in the liver were also significantly decreasedin animals receiving BOP followed by 2% BHA. The results thusindicate that both pancreatic and cholangiocellular carcinogenesisinitiated by BOP in Syrian hamsters can be inhibited by 2% BHAtreatment for a relatively short experimental period.     

The effect of N-nitrosobis(2-oxopropyl)amine after oral administration to hamsters.

Oral administration of N-nitrosobis(2-oxopropyl)amine (BOP) in drinking water to Syrian golden hamsters for 90 days resulted in a high incidence of intra- and extrahepatic bile duct neoplasms. Only a few pancreatic neoplasms and no lung and kidney tumors developed, in contrast to results obtained after subcutaneous BOP administration.     

Chemopreventive effects of Aloe arborescens on N-nitrosobis(2-oxopropyl)amine-induced pancreatic carcinogenesis in hamsters

The modification effects of freeze-dried aloe (Aloe arborescens) whole leaf powder during the initiation phase of carcinogenesis were investigated in hamsters treated with N-nitrosobis(2-oxopropyl)amine (BOP). Female Syrian hamsters were given four weekly subcutaneous injections of BOP at a dose of 10mg/kg and then given 0, 1 or 5% aloe in their diet for 5 weeks. At week 54 of the experiment, all surviving animals were sacrificed and development of neoplastic and preneoplastic lesions was assessed histopathologically. The incidences of pancreatic adenocarcinomas, atypical hyperplasias or total atypical hyperplasias plus adenocarcinomas were significantly (P<0.05) decreased with BOP+5% aloe, and that of adenocarcinomas were also significantly (P<0.05) reduced in the BOP+1% aloe as compared to the BOP alone group. Multiplicities of pancreatic adenocarcinomas, atypical hyperplasias or total lesions were also significantly (P<0.01 or P<0.05) lower in the BOP+5% aloe group than with the BOP alone. Quantitative data for neoplastic lesions in the lung, liver, gall bladder, kidney and urinary bladder of hamsters were not significantly different among the three groups. In a satellite experiment, pretreatment with aloe significantly (P<0.01) reduced the formation of O6-methyldeoxyguanosine in epithelial cells of pancreatic ducts as compared to the BOP alone value. Our results thus indicate that aloe prevents BOP-induced pancreatic neoplasia in hamsters in relation to decreased DNA adduct formation in the target tissue.     

Chemoprevention of biliary carcinogenesis in syrian hamsters by the novel carboxamide derivative IS-741 after initiation with N-nitrosobis(2-oxopropyl)amine (BOP)

To elucidate the possible inhibitory effect of a novel carboxamide derivative (IS-741) on biliary carcinogenesis, Syrian hamsters were subjected to cholecystoduodenostomy and ligation of the distal end of the common duct, and then given a regular diet (group I) or a diet containing 200 p.p.m. of IS-741 (group II). All hamsters were subcutaneously injected with N-nitrosobis(2-oxopropyl)amine until 10 weeks after surgery, and continued to feed on their respective dietary regimen until termination of the experiment at 16 weeks after surgery. Biliary adenocarcinomas were evaluated histologically. Non-cancerous and cancerous hepatobiliary tract tissues were analyzed for phospholipase A(2) (PLA(2)) activity, myeloperoxidase (MPO) activity, and the concentrations of prostaglandin (PG), i.e., prostaglandin E(2), 6-ketoprostaglandin F(1)alpha and thromboxane B(2). IS-741 significantly inhibited the development and multiplicity of hepatobiliary adenocarcinomas and reduced the proliferating cell nuclear antigen labeling indices in non-cancerous hepatobiliary tissues, compared with group I. The anti-cancerous effect of IS-741 was associated with a significant inhibition of PLA(2) and MPO levels in non-cancerous tissues of the extrahepatic biliary tract and the liver, and in cancerous tissue of the liver. Furthermore, IS-741 reduced the production of PGs in non-cancerous hepatobiliary tissues, compared with group I. Although the precise mechanism of action of IS-741 in preventing biliary tumorigenesis remains to be elucidated, it is likely to be related to modulation of arachidonic acid metabolism and/or suppression of neutrophil accumulation.     

Inhibition by catechol and di(2-ethylhexyl)phthalate of pancreatic carcinogenesis after initiation with N-nitrosobis(2-hydroxypropyl)amine in Syrian hamsters

The effects of dietary administration of catechol (CC), paramethylcatechol(PMC) and di(2-ethylhexyl)phthalate (DEHP) were compared withthat of butylated hydroxjanisole (BHA) in Syrian hamsters initiatedwith N-nitrosobis(2-hydroxypropyl)amine (BHP). Development ofpancreatic atypical hyperplasias and adenocarcinomas in termsof combined multiplicity was significantly reduced by CC andDEHP. A similar slight but non-significant tendency was observedfor BHA, while PMC was without effect. No statistically significantreduction of liver or gall bladder lesions was observed. Theresults thus suggest that both antioxidant and peroxisome proliferatorcategories of agents can inhibit pancreatic carcinogenesis inhamsters.     

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.     

Sex differences in the effects of retinoids on carcinogenesis by N-nitrosobis(2-oxopropyl)amine in Syrian hamsters

Syrian hamsters were given in a single dose of N-nitrosobis(2-oxopropyl)-amine (BOP) (40 mg/kg, s.c.) and 1 week later were fed 1 of 4 retinoid types (13-cis-retinoic acid (13-cis-RA), N-ethylretinamide (ERA), 2-hydroxyethylretinamide (OH-ERA), or 4-hydroxyphenylretinamide (PRA)) each at 3 levels (0.05, 0.1, 0.2 mM/kg diet). The pancreatic carcinoma incidence was not influenced significantly by feeding retinoids. The pancreatic adenoma incidence, however, was reduced by feeding each of the retinoids to female hamsters, with the reduction varying with the retinoid fed (13-cis-RA greater than ERA and OH-ERA greater than PRA). In male hamsters increased numbers of pancreatic adenomas were observed after feeding OH-ERA and PRA. Tumors induced in other tissues were reduced by retinoids in females, but not in males. Females fed 13-cis-RA and ERA had a lower incidence of gall bladder polyps, and feeding OH-ERA reduced the liver tumor incidence. Food consumption and serum alkaline phosphatase ans aspartate amino transferase activities were not influenced by BOP or retinoid type or level. Body and pancreas weight were influenced by retinoid level, but the effects were not consistently dose-related.     

Inhibitory effect of meloxicam, a cyclooxygenase-2 inhibitor, on N-nitrosobis (2-oxopropyl) amine induced biliary carcinogenesis in Syrian hamsters

Pancreaticobiliary maljunction (PBM) is a high risk factor in biliary tract carcinoma. The chemopreventive action of a cyclooxygenase (COX)-2 inhibitor (meloxicam) on N-nitrosobis (2-oxopropyl) amine (BOP)-induced gallbladder cancer in hamster PBM models was investigated. In 7-week-old female Syrian golden hamsters, the extrahepatic bile duct at the distal end of the common duct was ligated and cholecystoduodenostomy was performed (group I). In group II, the same surgery was performed and from week 4 after surgery, 10 mg/kg of BOP was injected subcutaneously once a week with a 1-week interval. In group III, in addition to the measures employed in group II, 5 mg/kg/day of meloxicam was administered once a day, every weekday. Pathological findings in the gallbladder in week 20 after surgery were as follows. In group I, proper epithelium (PE) was predominant and there was no cancer. In group II, PE was predominant, but there was also hyperplasia and atypical epithelium (AE) recognized in 8 of 11 cases (72.7%); the area of AE was more extensive than that in group I. Carcinoma in situ (CIS) was recognized in 4 of 11 cases (36.4%) in group II. Group III showed the same pathological findings as group I. However, compared with group II, the incidence of AE decreased to 27.3% and no cancerous lesion was observed. In week 20 after surgery, the proliferative cell nuclear antigen labeling index in group III was statistically significantly lower than in group II (P = 0.045). No statistically significant differences were noted among the groups in terms of apoptosis labeling index in week 20 after surgery. In conclusion, it was confirmed that meloxicam suppresses carcinogenesis in hamster PBM models and its mechanism may be based on the suppression of cell growth.     

A cyclooxygenase-2 inhibitor,nimesulide, inhibits postinitiation phase of N-nitrosobis(2-oxopropyl)amine-induced pancreatic carcinogenesis in hamsters

The modification effects of nimesulide, a cyclooxygenase (COX)-2 inhibitor, administration during the postinitiation phase of pancreatic carcinogenesis were investigated in hamsters treated with N-nitrosobis(2-oxopropyl)amine (BOP). Male Syrian hamsters were given 4 weekly s.c. injections of BOP at a dose of 10 mg/kg and thereafter administered 0, 100 or 400 ppm nimesulide in the diet for 36 weeks. Additional groups of hamsters were fed 400 ppm nimesulide without prior BOP initiation or nontreated. At week 40, all surviving animals were killed and development of neoplastic and preneoplastic lesions was assessed histopathologically. The incidence of pancreatic adenocarcinomas was significantly (p < 0.05) decreased in the BOP/400 ppm nimesulide group compared to the BOP alone group. The multiplicity of total lesions of pancreatic adenocarcinoma plus atypical hyperplasia was also significantly (p < 0.05) lowered. Immunohistochemically, COX-2 was clearly expressed in pancreatic and lung tumor cells, whereas expression was not remarkably affected by the 400 ppm nimesulide treatment. Proliferating cell nuclear antigen labeling indices of pancreatic ducts were significantly (p < 0.01) reduced by nimesulide. The incidence and multiplicity of neoplastic lesions in other organs did not significantly differ among the BOP-treated groups, though only the multiplicity of lung tumors showed a tendency to decrease. No neoplastic lesions were detected in animals receiving nimesulide alone. Our results clearly indicate that nimesulide protects against BOP-induced pancreatic tumors in hamsters.     

Carcinogenicity of N-nitrosobis(2-hydroxypropyl)amine and N-nitrosobis(2-oxopropyl)amine in MRC rats.

Weekly sc injections of equitoxic doses of N-nitrosobis(2-hydroxypropyl)amine (BHP) and N-nitrosobis(2-oxopropyl)amine (BOP) to Wister-derived MRC rats induced tumors. The incidence, latency, multiplicity, morphologic type, and distribution of these tumors varied according to the compound given. The esophagus was the main target organ for BHP (100%), followed by the respiratory tract (87%), pharynx (80%), colon and liver (each 73%), kidneys (20%), thyroid gland (20%), and urinary bladder and urethra (each 7%). BOP was ineffective in the esophagus and pharynx but induced a higher incidence of tumors in the kidneys (27%), thyroid gland (60%), urinary bladder (33%), and urethra (73%) and fewer neoplasms in the respiratory tract (20%), colon (67%), and liver (53%). In addition, BOP caused a few, apparently primary, prostate squamous cell carcinomas. The results are compared with results of BHP treatment in Sprague-Dawley rats and with results of BHP and BOP treatment in Syrian golden hamsters.