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.     

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.     

Pancreatic carcinogenesis: effect of secretin in the hamster- nitrosamine model

The effect of exogenous secretin on pancreatic carcinogenesis in WO strain hamsters has been examined in the nitrosamine-ductular adenocarcinoma model. Secretin, 20 clinical U/kg, stimulated a maximal secretory response of pancreatic juice and bicarbonate when given iv. The same dose given sc for 6 weeks had no significant effect on pancreatic wet weight and DNA or RNA contents. However, when given to animals receiving N-nitrosobis(2-oxopropyl)amine [(BOP) CAS: 60599-38-4] (5 mg/kg), it reduced the latency and increased the induction rate of tumor development when compared with the carcinogen given alone to animals (secretin + BOP, 15 of 17 animals with tumors; BOP alone, 4 of 13 with tumors at 15 wk; P less than .002). These effects are consistent with secretin acting as a cocarcinogen in this model of pancreatic carcinogenesis.     

Enhancing Effects of Quinacrine on Development of Hepatopancreatic Lesions in N-Nitrosobis(2-oxopropyl)amine-initiated Hamsters

The modifying effects of quinacrine administration during the post-initiation phase of carcinogenesis were investigated in hamsters treated with N -nitrosobis(2-oxopropyl)amine (BOP). Female Syrian hamsters were given three weekly s.c. injections of BOP at a dose of 10 mg/kg and then 300 or 100 ppm quinacrine in their diet for 37 weeks. Additional groups of animals received the BOP injection alone, or only the 300 ppm quinacrine treatment as BOP-negative controls. At week 40 of the experiment, all surviving animals were killed and development of proliferative lesions was assessed histopathologically. The multiplicity of pancreatic adenocarcinomas and dysplastic lesions per hamster was significantly higher ( P <0.01 and P <0.05) in the BOP/Q100 group (1.92 and 1.78) than in the BOP-alone group (1.07 and 0.79). The incidence of hepatocellular adenomas plus carcinomas was also significantly elevated ( P <0.05) in the BOP/Q300 and BOP/Q100 groups. In contrast, the multiplicity of lung adenomas plus adenocarcinomas was significantly decreased ( P <0.05) by the Q300 treatment. Neither the incidence nor the multiplicity of renal cell tumors (adenomas and carcinomas) or nephroblastomas significantly differed between the BOP-treated groups. Electron microscopic examination revealed an abundance of myeloid lamellar bodies filling the cytoplasm of hepatocytes and pancreatic ductular and acinar cells, and epithelial cells of the gallbladder in the quinacrine-treated animals, the degree being dose-dependent. Our results indicate that quinacrine enhances pancreatic and hepatic carcinogenesis in hamsters induced by BOP.     

Modifying effects of 4-phenylbutyl isothiocyanate on N-nitrosobis(2-oxopropyl)amine-induced tumorigenesis in hamsters

The modifying effects of dietary 4-phenylbutyl isothiocyanate (PBITC), given during the initiation stage of carcinogenesis, were investigated in hamsters treated with N-nitrosobis(2-oxopropyl)amine (BOP). A total of 120 female 5-week-old hamsters were divided into six groups. Animals in groups 1–3, each consisting of 30 hamsters, were given BOP by two subcutaneous injections, 1 week apart, at a dose of 20 mg/kg body weight, plus 0, 10 or 100 μmol/animal of PBITC in corn oil by gavage 2 h prior to each carcinogen treatment. Ten animals in group 4 served as a vehicle control, and animals in groups 5 and 6, each consisting of ten hamsters, were given 10 and 100 μmol of PBITC alone in corn oil. Sacrifice was 52 weeks after the first BOP injection. The PBITC treatments significantly (P<0.05) inhibited the development of pancreatic ductal dysplasias and adenocarcinomas. Also, lung tumors (adenomas and adenocarcinomas) were significantly (P<0.05) reduced in a dose-dependent manner. In contrast, both hepatocellular and cholangiocellular tumors (adenomas and carcinomas) tended to be or were significantly increased by PBITC. These results, taken together with our previous findings, indicate that the natural isothiocyanate, phenethyl isothiocyanate (PEITC), has a more potent chemopreventive action against BOP-induced tumorigenesis than synthetic isothiocyanates with longer alkyl chains, such as 3-phenylpropyl isothiocyanate (PPITC) and PBITC. Thus, their lipophilicity does not necessarily reflect the chemopreventive potential because the strength of lipophilicity is PEITC相似文献   

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.     

Modifying effects of 4-phenylbutyl isothiocyanate on N-nitrosobis(2-oxopropyl)amine-induced tumorigenesis in hamsters

The modifying effects of dietary 4-phenylbutyl isothiocyanate (PBITC), given during the initiation stage of carcinogenesis, were investigated in hamsters treated with N-nitrosobis(2-oxopropyl)amine (BOP). A total of 120 female 5-week-old hamsters were divided into six groups. Animals in groups 1–3, each consisting of 30 hamsters, were given BOP by two subcutaneous injections, 1 week apart, at a dose of 20 mg/kg body weight, plus 0, 10 or 100 μmol/animal of PBITC in corn oil by gavage 2 h prior to each carcinogen treatment. Ten animals in group 4 served as a vehicle control, and animals in groups 5 and 6, each consisting of ten hamsters, were given 10 and 100 μmol of PBITC alone in corn oil. Sacrifice was 52 weeks after the first BOP injection. The PBITC treatments significantly (P<0.05) inhibited the development of pancreatic ductal dysplasias and adenocarcinomas. Also, lung tumors (adenomas and adenocarcinomas) were significantly (P<0.05) reduced in a dose-dependent manner. In contrast, both hepatocellular and cholangiocellular tumors (adenomas and carcinomas) tended to be or were significantly increased by PBITC. These results, taken together with our previous findings, indicate that the natural isothiocyanate, phenethyl isothiocyanate (PEITC), has a more potent chemopreventive action against BOP-induced tumorigenesis than synthetic isothiocyanates with longer alkyl chains, such as 3-phenylpropyl isothiocyanate (PPITC) and PBITC. Thus, their lipophilicity does not necessarily reflect the chemopreventive potential because the strength of lipophilicity is PEITC<PPITC<PBITC.     

Inhibitory effects of soybean trypsin inhibitor on induction of pancreatic neoplastic lesions in hamsters by N-nitrosobis(2-oxopropyl)amine

The effects of simultaneous soybean trypsin inhibitor (SBTI) treatment on initiation of pancreatic carcinogenesis by N-nitrosobis(2-oxopropyl)amine (BOP) were investigated. Female Syrian golden hamsters were given five weekly s.c. injections of BOP at a dose of 10 mg/kg while being administered a diet containing 5% SBTI for 5 weeks (BOP + SBTI group). Two other groups of 30 animals each received the s.c. injections of BOP or the 5% SBTI diet for the same period, alone (BOP and SBTI groups respectively). Total numbers of pancreatic dysplastic lesions in hamsters of the BOP+SBTI group were significantly decreased as compared to the BOP group values, though the incidences of pancreatic adenocarcinomas were not significantly different. Atrophic changes were, however, more severe in the BOP group than in the BOP+SBTI group pancreatic exocrine tissue, showing that treatment with SBTI was effective for protection of acinar cells from carcinogen toxicity.     

Enhanced thyroid carcinogenicity of N-nitrosobis(2-oxopropyl)amine in Otsuka Long-Evans Tokushima Fatty rats, a model of type II diabetes mellitus

Epidemiologic data suggest that diabetes mellitus type II is a risk factor for several types of cancer, including pancreatic, liver, colon and thyroid cancers. In the present study, effects of diabetes/hyperlipidemia on N-nitrosobis(2-oxopropyl)amine (BOP)-induced cancer development were examined in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, model animals for non-insulin-dependent diabetes mellitus and Long-Evans Tokushima Otsuka (LETO) rats, appropriate controls. Males of both strains were given four subcutaneous injections of BOP (10 mg/kg body wt) or saline on alternative days, starting at 5 weeks of age. BOP induced tumors in a variety of tissues, including the thyroid gland, colon, kidney, liver and lung. The highest yields were noted for thyroid tumors, the incidence (P = 0.0182) and multiplicity (P < 0.001) of BOP-induced thyroid cancers with marked fibrosis being significantly higher in OLETF than in LETO rats. Interestingly, anaplastic thyroid carcinomas were observed limited to the BOP-treated OLETF rats. Additionally, a greater incidence and frequency of aberrant crypt foci, putative precursor lesions for colon tumors, was observed in the BOP-treated OLETF group. However, BOP was ineffective at inducing pancreatic ductal tumors. No thyroid, liver, lung or colon tumors were found in the OLETF and LETO rats receiving the vehicle. Significant increases in serum levels of insulin, glucose, phospholipids, triglycerides and total cholesterol were detected in the OLETF rats compared with the LETO rats, regardless of the treatment. Our results indicate that diabetic/hyperlipidemic state can enhance BOP-induced carcinogenesis of the thyroid gland and to a lesser extent the colon in OLETF rats.     

Organ-dependent modifying effects of oltipraz on N-nitrosobis(2-oxopropyl)amine (BOP)-initiation of tumorigenesis in hamsters

5-(2-Pyrazinyl)-4-methyl-1,2-dithiole-thione (oltipraz), a substituted 1,2-dithiole-3-thione, is known to inhibit tumorigenesis induced by variety of carcinogens in several animal model systems. In the present experiment, the modifying effects of dietary oltipraz, given during N-nitrosobis(2-oxopropyl)amine (BOP) initiation of carcinogenesis, were investigated in Syrian hamsters. A total of 120 six-week-old females were divided into six groups. Groups 1-3 (30 animals each) were thrice given subcutaneous injections of BOP (10 mg/kg, body weight) at 1 week intervals and fed diets supplemented with 400 or 200 ppm of oltipraz or basal diet alone, starting 1 week prior and finishing 1 week after the carcinogen exposure. Groups 4-6 (10 animals each) were similarly treated without application of BOP. At the end of the 52nd experimental week, all surviving animals were autopsied and examined histopathologically for proliferative lesions of the major target organs for BOP tumorigenicity, including pancreas, liver, kidney, and lung. The incidences and multiplicity of adenocarcinomas of the pancreas were higher in groups 1 and 2 than in group 3 although without statistical significance. The incidence of pancreatic duct dysplasias was significantly (P<0.05) increased in group 2 (62.0%) but not in group 1 (50.0%) as compared with group 3 (46.6%). While the incidences of alveolar adenomas and carcinomas were significantly (P<0.05) decreased by the high dose, the multiplicities of hepatocellular adenomas, cholagiocellular carcinomas and gall bladder adenomas were elevated in the BOP/oltipraz groups (P<0.05). The results of the present study suggest that oltipraz exerts organ-dependent modifying effects on BOP-induced carcinogenesis in hamsters when given in the initiation stage.     

Effect of cholecystokinin on pancreatic carcinogenesis in the hamster model

To examine the effect of cholecystokinin (CCK) on pancreatic carcinogenicity in the hamster model, two sets of experiments were carried out. In one study, CCK (20 IDU/kg body wt) was given 3 h before, simultaneously with or 3 h after a single dose (20 mg/kg body wt) of N-nitrosobis(2-oxopropyl)amine (BOP). In another experiment, hamsters were treated similarly except that both CCK (20 IDU/kg body wt) and BOP (2.5 mg/kg body wt) were given weekly for 20 weeks. The results showed that CCK in the first experiment (single BOP dose) inhibited pancreatic cancer induction in a statistically significant fashion when given either 3 h prior to (P less than 0.05) or simultaneously with BOP (P less than 0.0005); however, CCK, when administered after BOP did not alter the cancer incidence as compared with hamsters treated with BOP alone. In the second experiment (chronic BOP treatment) the pattern and the incidence of pancreatic tumors were not affected by CCK.     

Effect of dibutyltin dichloride on incidence of pancreatic adenocarcinoma induced in hamsters by a single dose of N-nitrosobis(2-oxopropyl)amine

The effects of timing of a single intragastric application of dibutyltin dichloride, at a dosage of 30 mg/kg body wt, on N-nitrosobis(2-oxopropyl)amine (BOP)-induced pancreatic carcinomas have been studied in female Syrian golden hamsters. Dibutyltin dichloride, which has been shown to produce selected bile duct injury, was administered either 1 week before or 1 week after a single injection of BOP (20 mg/kg body wt). Control hamsters were injected with BOP alone or were given dibutyltin dichloride alone. The incidence of ductal adenocarcinomas strikingly decreased in hamsters when dibutyltin dichloride was ingested after BOP treatment, but remained unaffected when dibutyltin dichloride was given before carcinogen treatment. Two cases of sarcoma were observed in the group treated with dibutyltin dichloride before BOP injection. The incidence of insulomas, which were considered as spontaneous tumors, was not influenced by dibutyltin dichloride. These results showed that intragastric application of dibutyltin dichloride after BOP treatment significantly reduced the induction of pancreatic cancer. These findings do not support speculations based on epidemiologic studies as to a promoting effect of cholestasis.     

Effect of streptozotocin diabetes on development of nitrosamine-induced pancreatic carcinoma when diabetes induction occurs after nitrosamine exposure

Diabetes mellitus has been suggested as a possible risk factorfor the development of pancreatic cancer in humans. Previousstudies in our laboratory have shown, however, that streptozotocin(STZ) diabetes inhibits the development of cancer of the exocrinepancreas in hamsters when STZ is administered prior to treatmentwith the pancreatic carcinogen N-nitrosobis(2-oxopropyl)amine(BOP). It has been reported by others that the concurrent administrationof BOP and STZ enhances pancreatic carcinogenesis in hamsters.The purpose of the present study was to determine the effectof STZ diabetes on the development of BOP-induced pancreaticcarcinoma when STZ is given following exposure to BOP. Groupsof Syrian golden hamsters were treated with either BOP only(single s.c. injection, 40 mg/kg body wt at week 0), BOP (singles.c. injection, 40 mg/kg body wt at week 0) plus STZ (50 mg/kgbody wt x3 daily i.p. doses at weeks 10, 20 or 30), STZ only(50 mg/kg body wt x3 daily i.p. doses at weeks 10, 20 or 30),or neither BOP nor STZ. The experiment was terminated at 40weeks after BOP treatment. No significant difference was seenin the incidence of pancreatic cancer between those animalsreceiving BOP only at week 0 and those receiving BOP at week0 plus STZ at weeks 10, 20 or 30 of the study. The results wouldappear to indicate that STZ diabetes, established after BOPtumor initiation, plays no apparent role in the modulation ofpancreatic carcinogenesis.     

Enhancing effect of ethanol on esophageal tumor development in rats by initiation of diethylnitrosamine

The effects of ethanol on initiation of esophageal tumorigenesisby diethylnitrosamine (DEN) were investigated in male F344 rats.Animals were administered 50 p.p.m. DEN plus 10% ethanol (Group1), 33 p.p.m. DEN (Group 2), 50 p.p.m. DEN (Group 3) or 10%ethanol (Group 4) in the drinking water for the first 8 weeks,and were then maintained on basal diet and tap water for upto 104 weeks. The concentration of 33 p.p.m. DEN in Group 2was an adjustment to the anticipated intake in Group 1. Consequenttotal intakes of DEN in Groups 2 and 3 were respectively 80%and 134% of that in Group 1. Histopathological examination ofesophagus tissue after final sacrifice revealed incidences ofpapillomas and/or carcinomas in Groups 1, 2 and 3 to be 57.7,3.8 and 10.7% respectively. No esophageal tumors occurred inGroup 4. The incidence of hyperplasia was 100% in Group 1 incontrast to 46.2% in Group 2, 57.1% in Group 3 and 3.6% in Group4. Thus, the incidences of esophageal proliferative lesionswere significantly higher in Group 1 than in Groups 2 or 3.Our results clearly indicate that ethanol has an enhancing effecton the development of esophageal tumors induced by DEN in rats,when administered during the initiation phase.     

Modification of pancreatic carcinogenesis in the hamster model. IX. Effect of pancreatitis

The effect of acute and recurrent pancreatitis was investigated in pancreatic cancer induction by N-nitrosobis(2-oxopropyl)amine (BOP) in Syrian golden hamsters. For the correlation of the cellular alteration with carcinogenesis, BOP (20 mg/kg body wt) was injected once sc into hamsters at day 3 (group 2), week 1 (group 3), and week 8 (group 4), corresponding to cellular degeneration, regeneration, and healing, respectively. Additional groups received BOP 30 minutes before common duct ligation for 48 hours (group 1) or before repeated induction of pancreatitis at 4 weekly intervals for 4 weeks (group 5). Group 6 was a pancreatitis control. Two groups of hamsters received BOP only, at the age of 8 weeks (group 7, which served as a BOP control for groups 1-3 and 5) or at the age of 16 weeks (group 8, the control for group 4). Hamsters were killed 46 weeks after BOP injection (with the exception of group 1 animals, which were killed 52 wk after BOP) to guarantee the same postcarcinogen exposure time in each group. The results showed that BOP, when given during cellular degeneration (group 2) and healing (group 4), induced significantly fewer carcinomas than in the control groups, whereas the tumor pattern was not affected when BOP was given before pancreatitis induction (group 1) or at the time of cellular regeneration (group 3). Recurrent pancreatitis (group 5), however, resulted in carcinomas significantly larger in number and size than those in control group 8. A significantly higher incidence of carcinomas occurred in group 8 controls (treated with BOP at the age of 16 wk) compared to the incidence in group 7 controls (treated with BOP at the age of 8 wk).     

Pancreatic carcinogenesis-enhancement by cholecystokinin in the hamster-nitrosamine model

The role of the pancreaticotrophic hormone cholecystokinin (CCK) in modifying the pancreatic response to carcinogen has been examined in the hamster-nitrosamine pancreatic cancer model. Exogenous CCK, 30 IDU kg-1, stimulated a maximal pancreatic secretory response when given intravenously and caused hypertrophy and hyperplasia of the pancreas when given subcutaneously over a period of 6 weeks (pancreatic wet weight, mg per 100 g body weight, controls 295.6 +/- 61; CCK treated 466.4 +/- 77, P less than 0.001). When the same dose of CCK was given to animals receiving N-nitrosobis (2-oxopropyl)amine (BOP; 5 mg kg-1 weekly) there was a reduction in latency period and increase in induction rate of tumour development (CCK + BOP vs. BOP alone, 12 animals with tumours vs. 2 at 15 weeks; P less than 0.02). These effects are consistent with CCK acting as a co-carcinogen or promoter of pancreatic carcinogenesis in this model.     

Chronic nicotine consumption does not influence 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone-induced lung tumorigenesis

Nicotine replacement therapy is often used to maintain smoking cessation. However, concerns exist about the safety of long-term nicotine replacement therapy use in ex-smokers and its concurrent use in smokers. In this study, we determined the effect of nicotine administration on 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung tumors in A/J mice. Female mice were administered a single dose of NNK (10 μmol) and 0.44 μmol/mL nicotine in the drinking water. Nicotine was administered 2 weeks prior to NNK, 44 weeks after NNK, throughout the experiment, or without NNK treatment. The average weekly consumption of nicotine-containing water was 15 ± 3 mL per mouse, resulting in an estimated daily nicotine dose of 0.9 μmol (0.15 mg) per mouse. Nicotine administration alone for 46 weeks did not increase lung tumor multiplicity (0.32 ± 0.1 vs. 0.53 ± 0.1 tumors per mouse). Lung tumor multiplicity in NNK-treated mice was 18.4 ± 4.5 and was not different for mice consuming nicotine before or after NNK administration, 21.9 ± 5.3 and 20.0 ± 5.4 tumors per mouse, respectively. Lung tumor multiplicity in animals consuming nicotine both before and after NNK administration was 20.4 ± 5.4. Tumor size and progression of adenomas to carcinomas was also not affected by nicotine consumption. In addition, nicotine consumption had no effect on the level of O(6)-methylguanine in the lung of NNK-treated mice. These negative findings in a commonly used model of human lung carcinogenesis should lead us to question the interpretation of the many in vitro studies that find that nicotine stimulates cancer cell growth.     

Inhibitory effect of dibutyltin dichloride on pancreatic adenocarcinoma development by N-nitrosobis(2-oxopropyl)amine in the Syrian hamster

The effects of a single intragastric application of dibutyltin dichloride (DT), at a dose of 30 mg/kg body weight, on N-nitrosobis(2-oxopropyl)amine (BOP)-induced pancreatic carcinogenesis were studied in female Syrian golden hamsters. DT, which has been shown to selectively induce bile duct injury, was administered either 1 week before or after BOP initiation. BOP was injected subcutaneously once a week for 5 weeks at a dose of 10 mg/kg body weight. Controls were injected with BOP alone or given DT without carcinogen. Animals sacrificed at the end of the 25-week experimental period showed a significant inhibitory effect of DT on pancreatic carcinoma induction when DT was given before BOP treatment, although no such influence was evident with DT treatment following BOP exposure. These results indicate that the bile duct and more especially common bile-duct injury induced by DT may be relevant to the inhibition of the initiation stage of BOP-induced pancreatic carcinoma development in Syrian hamsters.     

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.