Modulation of dietary fat-promoted pancreatic carcinogenesis in rats and hamsters by chronic ethanol ingestion

The effect of chronic ethanol ingestion on dietary fat-promotedpancreatic carcinogenesis was investigated in rats and hamsters.Rats were given a single i.p. injection of 30 mg azaserine perkg body wt at 19 days of age. Hamsters were injected s.c. with20 mg N-nitrosobis(2-oxopropyI)amine (BOP) per kg body wt at6 and 7 weeks of age. The animals were fed a semi-purified diethigh in unsaturated fat (25% corn oil) either separately orin combination with ethanol. Ethanol was provided in drinkingwater at a concentration of 10% (w/v). A separate group maintainedon a diet low in unsaturated fat (5% corn oil) was includedas extra controls. The rats and hamsters were given their dietsand received ethanol via their drinking water after treatmentwith carcinogen. Terminal autopsy of rats was 15 months afterazaserine treatment and of hamsters 12 months after the lastinjection with BOP. Dietary fat was found to enhance pancreaticcarcinogenesis in both rats and hamsters. In rats, ethanol slightlyenhanced the multiplicity but not the incidence of malignanttumours, while in hamsters ethanol did not show any modulatingeffect on dietary fat-promoted carcinogenesis. It was concludedthat dietary fat-promoted pancreatic carcinogenesis as observedin the animal models applied is not significantly modulatedby chronic ethanol ingestion.     

Role of cholecystokinin in dietary fat-promoted azaserine-induced pancreatic carcinogenesis in rats.

The role of cholecystokinin in dietary fat-promoted pancreatic carcinogenesis was investigated in azaserine-treated rats, using lorglumide, a highly specific cholecystokinin-receptor antagonist. The animals were killed 8 months after the start of treatment. Cholecystokinin, but not dietary unsaturated fat, increased pancreatic weight. Rats treated with cholecystokinin developed more acidophilic atypical acinar cell nodules, adenomas and adenocarcinomas than control animals. Rats maintained on the high-fat diet developed significantly more adenomas and adenocarcinomas than controls given a diet low in unsaturated fat. Lorglumide largely inhibited the enhancing effect of cholecystokinin, but not of dietary fat, on pancreatic carcinogenesis indicating that it is unlikely that the promoting effect of dietary unsaturated fat on pancreatic carcinogenesis is mediated via cholecystokinin.     

Inhibition of dietary fat-promoted colon carcinogenesis in rats by supplemental calcium or vitamin D3

A 2 x 2 x 2 factorial experimental design was used to investigatethe effects of supplemental calcium (Ca) (0.5% versus 1.0% ofdiet as Ca gluconate) and vitamin D₃ (D) (1000 IU/kg diet versus2000 IU/kg diet) on 1,2-dimethylhydrazine-induced colon carcinogenesisin male F344 rats promoted with a 20% corn oil diet. Animalson the high-fat (HF) diet had an increased tumor incidence comparedto the low-fat (LF) control diet (86% versus 53%, P < 0.05)and supplemental Ca or D reduced this to or below the LF incidence(HF + Ca: 53%, HF + D: 47%). However, supplemental Ca or D hadno inhibitory effect with LF diets (LF + Ca: 67%, LF + D: 60%).The results of this study indicate a possible role for supplementalCa or D in the prevention of colon cancer, effective only inHF diets.     

Interaction of dietary fat and protein on pancreatic carcinogenesis in Syrian golden hamsters

The role of interactions between dietary fat and protein in experimental pancreatic cancer was determined in Syrian golden hamsters treated with N-nitrosobis(2-oxopropyl)amine (BOP). Two levels of corn oil [4.5 and 18 g/385 kilocalorie (kcal)] were fed with each of two levels of casein (9 g/385 kcal and 36 g/385 kcal), either before or after a single sc injection of BOP (10 mg/kg body wt) at 8 weeks of age. Control diet was fed at other times (9 g corn oil and 18 g casein/385 kcal). The pancreatic ductular carcinoma incidence and multiplicity (average No. of tumors/tumor-bearing animals) increased as dietary fat and protein levels rose in hamsters fed the four diets after carcinogen treatment. Enhanced carcinogenesis by high-fat (HF) diets occurred only in hamsters fed the high-protein (HP) level, and protein effects were seen only with the HF diets. The low-fat-low-protein (LF-LP) diet inhibited pancreatic carcinogenesis among the hamsters given the four diets before BOP treatment. Pancreatic adenoma yields were elevated in hamsters given either HF or HP diets following BOP treatment, by comparison with the low levels. However, when diets were fed before BOP treatment, an increased yield occurred with the rise in protein, but the yield was reduced in males with the increase in fat. Acinar cell nodules were observed primarily in hamsters fed LP levels after BOP, and their multiplicity was highest in those given the HF diet. The interaction between dietary fat and protein demonstrated the interdependence of the effects of these two nutrients on pancreatic carcinogenesis in hamsters.     

Effects of sandostatin and castration on pancreatic carcinogenesis in rats and hamsters.

The effects of treatment with the somatostatin analogue Sandostatin, separately and in combination with surgical castration, on the development of azaserine-induced lesions in rat pancreas and N-nitrosobis(2-oxopropyl)amine (BOP)-induced lesions in hamster pancreas were investigated. The animals were divided in 4 groups and treated as follows: (a) controls, injected s.c. with saline solution (0.9% NaCl); (b) orchiectomy directly after the last treatment with carcinogen; (c) Sandostatin (SMS 201-995) subcutaneously; (d) orchiectomy followed by treatment with Sandostatin. No significant suppressive effects on plasma EGF or IGF-I concentrations were noted after Sandostatin treatment, but plasma gastrin levels decreased slightly in the rats, not in the hamsters. In rats, Sandostatin treatment enhanced rather than inhibited growth of acidophilic atypical acinar cell nodules. In hamster pancreas, by contrast, Sandostatin inhibited the development of putative pre-neoplastic ductular lesions. There was no interaction between treatment with Sandostatin and surgical castration. It was concluded that Sandostatin, when administered prophylactically, has an inhibitory effect on the growth of putative pre-neoplastic ductular, but not acinar, lesions.     

Inhibition of dietary fat-promoted development of (pre)neoplastic lesions in exocrine pancreas of rats and hamsters by supplemental vitamins A, C and E

The effects of vitamins A, C and E on the development of putative preneoplastic foci in exocrine pancreas were investigated in azaserine-treated rats and N-nitrosobis(2-oxoproypy)amine-treated hamsters. The animals were fed a semipurified diet high in saturated fat (20% lard) either or not supplemented with vitamin A, vitamin C or vitamin E. A separate group maintained on a diet low in saturated fat (5% lard) was incorporated as extra controls. The animals were given their diets 12 days after the last treatment with carcinogen. At 4 months postinitiation, the pancreata were quantitatively examined for both the number and size of early, putative preneoplastic lesions and the presence of neoplastic lesions. Rats as well as hamsters maintained on 5% lard exhibited a significantly lower number of putative preneoplastic pancreatic lesions than animals fed a diet containing 20% lard. Growth of acidophilic but not of basophilic foci was inhibited in rats of the high vitamin A and C group, whereas vitamin E exerted an inhibitory effect on growth of basophilic but not of acidophilic foci. In hamsters maintained on a diet high in vitamins A or C, the number of early ductular lesions was significantly decreased, whereas the number of (micro)carcinomas was increased. Vitamin E did not have any modulating effect on development of ductal lesions in hamster pancreas.     

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.     

Inhibition of mammary carcinogenesis in rats by dietary restriction

Mammary tumors were induced by 7,12-dimethylbenz[a]anthracene (DMBA) in Sprague-Dawley female rats kept under different dietary restrictions. Starting at 40 days of age, 4 groups of rats were either full-fed or fed 25%, 50% or 80% of their daily ration. At 55 days of age DMBA was given by intravenous injection. Rats were continued on the restricted diet until 150 days after carcinogen treatment. Rats on 25% diet lost weight rapidly and the experiment had to be terminated. Rats on the 50% diet maintained a lower body weight throughout the experiment; only 12% developed tumors. Rats on the 80% diet lost weight initially, but at the termination of the experiment, there was no significant difference in body weight between this group and the full-fed controls. Of the rats on 80% diet, 34% developed tumors, compared to 92% tumor incidence in the full-fed controls. Vaginal smears were normal in the animals fed the 80% diet, while some irregularity was observed in the 50% group. Breeding capability in rats on the 80% diet was not affected, since there was no observable difference in the pregnancy rate between these animals and their controls. There was also no difference in plasma level of estrogen between the 80% diet group and the full-fed controls at the time of carcinogen treatment. [3H]Thymidine labelling index was significantly affected by 50% restriction of diet while there was no significant change in the 80% group.     

Effects of chronic dietary beer and ethanol consumption on experimental colonic carcinogenesis by azoxymethane in rats

Epidemiological studies have shown an association between consumption of alcoholic beverages, particularly beer, and carcinoma of the large bowel, especially the rectum. We studied the effects of chronic dietary beer and ethanol consumption on experimental colonic carcinogenesis, fecal bile acid and neutral sterol levels, fecal bacterial flora, and colonic epithelial DNA synthesis. Ten-week-old male Fischer 344 rats were pair fed throughout the study with Lieber-DeCarli-type liquid diets providing comparable total carbohydrates, proteins, fats, and calories. The diets provided 23 or 12% of calories as alcohol in beer (Hi-Beer and Lo-Beer groups), 18 or 9% of calories as reagent ethanol (Hi-EtOH and Lo-EtOH groups), or no alcohol (control group). After 3 weeks of dietary acclimatization, 10 weekly s.c. injections of the bowel carcinogen azoxymethane, 7 mg/kg, were given (weeks 1-10). At necropsy in week 26, the high alcohol groups (Hi-Beer and Hi-EtOH) showed a significantly reduced incidence of tumors in the right colon (42 and 46% versus 81% in control, P less than 0.01 and P = 0.02) but no effect on left colonic tumorigenesis. By contrast, the low alcohol groups (Lo-Beer and Lo-EtOH) showed a trend toward increased incidence and proportion of tumors in the left colon (incidence of 42 and 35% versus 15% in control, P = 0.06 for Lo-Beer; 28 and 30% of tumors in left colon versus 11%, P = 0.08 and P = 0.07) but no effect on right colonic tumorigenesis. Numbers of right colonic tumors were inversely correlated with alcohol consumption of all rats (r = -0.350, P less than 0.001), but left colonic tumors were not correlated. Fecal bile acid and neutral sterol levels, fecal bacterial counts, and colonic epithelial DNA synthesis did not correlate with the effects of alcohol consumption on colonic tumorigenesis. Our findings suggest that: modulation of experimental colonic tumorigenesis by chronic dietary beer and ethanol consumption was due to alcohol rather than other beverage constituents; tumorigenesis in the right and left colon was affected differentially by the levels of alcohol consumption, reflecting complex interactions among the potential mechanisms for alcohol effects in the model used.     

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.     

Enhancement of experimental pancreatic cancer in Syrian golden hamsters by dietary fat

The effects of dietary fat on the induction and development of pancreatic ductular adenocarcinoma were studied in randombred Syrian golden hamsters. Diets containing low-fat (LF) or high-fat (HF) levels of corn oil [4.5 or 18.0 g/385 kilocalorie (kcal)], contributing 10 or 41% of the calories, respectively, were fed either before or after a single injection of N-nitrosobis(2-oxopropyl)amine (BOP) (10 mg/kg body wt). Control hamsters were fed corn oil at a medium-fat (MD) level (9 g/385 kcal) for life. The incidence of ductular adenocarcinomas increased in both males and females (LF diet, 16%; HF diet, 34%) when the HF diet was fed after BOP treatment. The average number of carcinomas per carcinoma-bearing animal also increased (LF diet, 1.3; HF diet, 3.0), but the carcinoma incidence was not influenced by these diets being fed before carcinogen treatment. The incidence of ductular adenomas was high with all treatments and was not influenced by diet. However, the number of adenomas was increased in animals fed HF diets. In addition, the incidence of acinar cell nodules was elevated in animals fed the MF and HF diets after BOP administration. These results showed that dietary fat modified the development of experimental ductular adenocarcinoma of the pancreas.     

Effects of sandostatin,alone and in combination with surgical castration,on pancreatic carcinogenesis in rats and hamsters

In a previous short-term study (4 months) we found that Sandostatin, when administered prophylactically, inhibited growth of putative pre-neoplastic ductular lesions induced in hamster pancreas by N-nitrosobis(2-oxopropyl)amine (BOP), but not of acinar lesions induced in rat pancreas by azaserine. The present long-term (12 months) study was carried out to investigate the effects of Sandostatin (3 μg/day), alone and in combination with orchiectomy, on pancreatic carcinogenesis in azaserine-treated rats and BOP-treated hamsters. In order to mimic therapy in humans, treatment of the animals started 4 months after the last injection with carcinogen, when(pre)neo-plastic lesions had already developed. After treatment with Sandostatin for 8 months, rats developed fewer pancreatic atypical acinar cell nodules and tumours than those not treated with Sandostatin. Moreover, multiplicity of (pre)neoplastic acinar lesions was also lower in orchiectomized rats than in intact rats. However, Sandostatin treatment did not enhance the inhibitory effect of surgical castration on pancreatic carcinogenesis in rats. In hamsters that were both orchiectomized and treated with Sandostatin, the development of borderline lesions was significantly inhibited, whereas such an effect was not present in hamsters that were either surgically castrated or treated with Sandostatin alone. In Sandostatin-treated hamsters a significantly lower number of microcarcinomas was found than in hamsters not treated with Sandostatin. The present findings suggest that Sandostatin, particularly in combination with surgical castration, might be of therapeutic value for treatment of ductular pancreatic tumours. © 1996 Wiley-Liss, Inc.     

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.     

Inhibition of PhIP-induced mammary carcinogenesis in female rats by ingestion of freeze-dried beer

This study evaluated the modulating effect of non-alcoholic constituents of beer on 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)-induced mammary carcinogenesis. Female Sprague-Dawley (SD) rats at 6 weeks of age were divided into four groups (n=26-30) and fed either a high fat diet or high fat diets containing 1, 2 or 4% freeze-dried beer (FD beer). One week after the start of feeding, rats received PhIP at a dose of 85 mg/kg by gavage four times weekly for 2 weeks. There were no differences in the body weights or diet intakes of rats between the control and the experimental groups. Weekly observation of palpable tumors indicated that tumor incidence and tumor multiplicity in the 2 and 4% FD beer groups were lower than in the control group throughout the experiment. Neoplastic lesions were pathologically examined at the end of the 22-weeks experiment. Tumor development was inhibited by FD beer intake in a dose-dependent manner. Tumor incidence (38.5%) and tumor multiplicity (0.8+/-0.4) for the group fed with a diet containing 4% FD were significantly reduced as compared with the control group (73.3% and 1.8+/-0.7). Supplementation with FD beer for 3 weeks together with the PhIP treatments resulted in increased liver GST activity, decreased liver CYP1A2 activity and a decrease in the number of DNA adducts in the mammary tissue, though these values were not significant. In conclusion, our results suggest that intake of FD beer may reduce the risk of carcinogenesis caused by heterocyclic amines.     

Effect of castration and testosterone replacement on pancreatic carcinogenesis in Syrian hamsters.

Hormonal manipulation has been proposed as a possible new approach to the treatment of pancreatic cancer. We studied the effect of orchiectomy and testosterone replacement on early stage pancreatic carcinogenesis induced by diisopropanolnitrosamine (DIPIN) in Syrian golden hamsters. Eighty-five hamsters (mean body weight, 100 g) were divided into the following treatment groups: 1) DIPN (n = 20); 2) DIPN plus orchiectomy (n = 17); 3) DIPN plus orchiectomy plus testosterone (n = 18); 4) orchiectomy (n = 10); 5) sham operation (n = 10); 6) DIPN plus testosterone (n = 10). DIPN (125 mg/kg/body wt.) was administered s.c. every week and testosterone propionate (10 micrograms/g) was administered s.c. every 3 weeks. Bilateral orchiectomy was performed 1 week after the first injection of DIPN. All animals were killed 15 weeks after starting the treatment. The whole pancreas was removed, weighted and histologically examined. There was no difference in the incidence of preneoplastic lesions among groups 1, 2, 3 and 6 (respectively 87%, 83%, 77% and 80%); 3 animals in each group developed invasive carcinoma. In control groups (4 and 5), no precancerous lesions were recorded. In this experimental model, orchiectomy and testosterone replacement had no effect on nitrosamine-induced pancreatic carcinogenesis.     

Modulation of azaserine-induced pancreatic foci by phenolic antioxidants in rats

Effects of the dietary phenolic antioxidants butylated hydroxyanisole [(BHA) CAS: 25013-16-5; (1,1-dimethylethyl)-4-methoxyphenol] and butylated hydroxytoluene [(BHT) CAS: 128-37-0; 2,6-di-tert-butyl-p-cresol] on pancreatic tumorigenesis were examined. Male LEW inbred rats were given injections of 30 mg azaserine [CAS: 115-02-6; diazoacetate (ester) serine] per kg body weight once a week for 3 weeks and maintained on either a control diet or 0.45% BHA- or 0.45% BHT-supplemented control diet throughout the initiation and post-initiation phases of the experiment. At 4 months post initiation, pancreatic tissue sections were quantitatively examined for the number and size of preneoplastic foci. BHT and BHA treatments reduced the number of acidophilic foci per pancreas by 32 and 48%, respectively, but were without effect on focal size. By contrast, basophilic foci were not subject to modulation by these antioxidants. A constellation of enzyme activities involved in carcinogen inactivation and known to be perturbed by antioxidant treatment was examined in liver and pancreas. The hepatic activities of glucose-6-phosphate dehydrogenase, glutathione reductase, and glutathione-S-transferases were markedly elevated while catalase and superoxide dismutase activities were unchanged. Glutathione peroxidase activity was diminished. In the pancreas, only glutathione peroxidase activity was affected, and it was reduced in both the BHA and BHT treatment groups. Although the pancreas is refractory to the enzyme inductive effects of these antioxidants, morphometric analysis of foci demonstrated chemoprevention by BHA and BHT of azaserine-induced foci. Whether this reduction reflected inhibition of an initiation, postinitiation , or a combination of effects was not known.     

Effect of dietary molybdenum on esophageal carcinogenesis in rats induced by N-methyl-N-benzylnitrosamine

The influence of dietary molybdenum on esophageal carcinogenesis induced by N-methyl-N-benzylnitrosamine (2.5 mg per kg of body weight once a week for 20 wk s.c.) was studied in male F344 rats. The tumor incidence and tumor development in the esophagus were significantly lower in the rats in the high-molybdenum (2 ppm) diet group than in the rats in the low-molybdenum (0.032 ppm) diet group; i.e., 44.4% (0.6 +/- 0.8) and 73.2% (2.2 +/- 2.0), respectively. The molybdenum levels in the esophagus-forestomach, liver, and serum were significantly higher in the high-molybdenum diet group than in the low-molybdenum diet group. Xanthine oxidase activity in the esophagus and forestomach in the high-molybdenum diet group was significantly higher than that in the low-molybdenum diet group, whereas liver and serum xanthine oxidase activities were not significantly different between these two groups. These results suggest that xanthine oxidase in the esophagus plays a significant role in the inhibitory effect of molybdenum on esophageal carcinogenesis.     

Enhancement of DHPN induced hepatocellular, cholangiocellular and pancreatic carcinogenesis by Opisthorchis viverrini infestation in Syrian golden hamsters

Infection with 100 Opirthorchis viverrini (OP) metacercariaeprior to two injections of dihydroxy-di-n-propyl nitrosamine(DHPN) (1000 mg/kg body weight) brought about significant enhancementof resultant preneoplastic lesion development in Syrian hamsterliver and pancreas tissue. Thus combined treatment with carcinogenand parasite was associated with pancreatic atypical (dysplastic)foci, hepatocellular nodules, cholangiofibrosis and cholangiocarcinomas.No such lesions were observed in carcinogen alone, parasitealone or untreated control groups. In addition, parasite inducedhyperplastic gall bladder epithelium was found to include areasof putative preneoplastic cells only in the DHPN-OP combinedgroup. The results strongly suggest that pancreatitis and biliarycirrhosis associated with liver fluke infestation are responsiblefor the observed enhancement of carcinogenesis, and that theresultant increased proliferation plays a major role in tumorigenesis.