Metabolism of the Pancreatic Carcinogen N-Nitroso-bis(2-oxopropyl)amine After Oral and Intraperitoneal Administration to Syrian Golden Hamsters: Brief Communication 1, 2, 3 Ralph Gingell 4 and Parviz Pour 4,
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ABSTRACT-The levels of N-nitroso-bis(2-oxopropyl)amine (BOP) and its metabolites in the urine, blood, bile, and pancreatic juice were compared after ip and oral administration of BOP to Syrian golden hamsters to explain the differing organotropic tumor spectra resulting from treatment by these two routes. The levels of BOP and its metabolites N-nitroso(2-hydroxypropyl)(2oxopropyl)amine (HPOP) and N-nitroso-bis(2-hydroxypropyl)amine in the urine, blood, bile, and pancreatic juice were generally less after oral administration than after ip administration. The results suggested that HPOP may be a proximate pancreatic carcinogen in hamsters administered BOP, inasmuch as it was the major metabolite in the blood and pancreatic juice after ip administration. However, the results did not indicate a mechanism for the increased incidence of bile duct tumors after oral administration of BOP.-J Natl Cancer Inst 60: 911-913, 1978.
A high incidence of pancreatic duct neoplasms, similar to those in man, was induced after chronic weekly sc injections of BOP into Syrian golden hamsters (1). Lung, liver, gallbladder, and kidney tumors also developed. By the reduction of treatment frequency, the incidence of these tumors decreased and was eliminated in the liver, but the high incidence of pancreatic tumors was maintained (2). When BCP was administered chronically in drinking water at estimated weekly doses similar to those given sc, the main target organ changed. A high incidence of intrahepatic and extrahepatic bile duct neoplasms was observed, with few pancreatic and no lung or kidney tumors (3). In this report we present the results of metabolic studies done in an attempt to explain the difference in tumor response to BOP after ip and oral administration. Previous studies with the use of ip administration of BOP to mimic the sc route used in the bioassays have shown that this carcinogen is rapidly metabolized to HPOP. This HPOP metabolite can exist in a cyclic form, which has been suggested to be the proximate pancreatic carcinogen formed after administration of either BOP, BHP, or NDMM to hamsters (4,5). BOP, HPOP, and BHP have been determined in the blood and urine of the hamster after oral administration of BOP and compared to values previously obtained after ip treatment (4). Wynder et al. (6) suggested that human pancreatic cancer may be induced by the reflux of bile containing carcinogens into the pancreas. We measured the levels of BOP and metabolites in bile and pancreatic juice after oral and ip administration to determine if biliary reflux or a direct effect of nitrosamines in the pancreatic secretion is a mechanism of carcinogenesis in this animal model. VOL. 60, NO.4, APRIL 1978 Downloaded from https://academic.oup.com/jnci/article-abstract/60/4/911/1026719 by University of Durham user on 07 March 2018
911
MATERIALS AND METHODS BOP, HPOP, and BHP were obtained as described in (4). In previous metabolic studies, compounds were administered ip, instead of by the sc route used in the bioassays, to eliminate any complications of slow absorption from the injection site (4). Compounds administered ip are absorbed into the venous system, and a direct effect of BOP on the pancreas is considered unlikely. Gavage was similarly used here as an equivalent of chronic administration in the drinking water. BOP (100 mg/kg; 20 mg/ml in water) was administered by gavage to male Syrian golden hamsters. Urine and blood were collected from hamsters as in (4). In a separate experiment, bile and pancreatic juice were collected from animals briefly anesthetized with pentobarbital sodium. Bile was obtained by cannulation of the gallbladder after ligation of the common bile duct below the cystic duct. We drained pancreatic juice from the same animal by inserting a cannula into the common duct, which was ligated at its junction with the duodenum. Bile and pancreatic juice were collected continuously for 6 hours from conscious animals maintained in restraining cages. Metabolites in the urine, blood, bile, and pancreatic juice were extracted and determined as in (4), and statistical evaluations done with Student's t-test.
RESULTS AND DISCUSSION The 24-hour urine from hamsters administered BOP ip contained 1.8±0.6% of the dose as the metabolite HPOP and 4.9±3.8% of the dose as BHP (4). No unchanged BOP or any other metabolite was detected. ABBREVIATIONS USED: BOP = N-nitroso-bis(2-oxopropyl)amine; HPOP = N-nitroso(2-hydroxypropyl)(2-oxopropyl)amine; BHP = Nnitroso-bis(2-hydroxypropyl)amine; NDMM = N-nitroso-2,6-dimethylmorpholine.
Received July 8,1977; accepted October 31,1977. Supported by Public Health Service contract NOI-CP33278 from the Division of Cancer Cause and Prevention, National Cancer Institute. 3 Presented in part at the 68th Meeting of the American Association for Cancer Research held in Denver, Colorado, in May 1977. 4Eppley Institute for Research in Cancer, University of Nebraska Medical Center, 42d St. and Dewey Ave., Omaha, Nebr. 68105. "We are grateful to Katla Donnelly, Jerry Meehan, and Galen Brunk for technical assistance, and to Mardelle Susman for editorial assistance. 1
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J NATL CANCER INST
912
GINGELL AND POUR
The corresponding values after oral administration were 0.4±O.3% as HPOP and O.3%±O.2% as BHP. The rate of excretion of metabolites was greater after ip injection compared to that after oral administration. After oral administration, HPOP and BHP concentrations in the urine peaked at 2 hours and then decreased (text-fig. IA). However, after ip administration, urine metabolite levels were considerably higher and in-
I.-Concentration of BOP and metabolites in A) urine and B) blood after ip and oral administration of BOP. Male Syrian golden hamsters were administered 100 mg BOP/kg, either ip or by gavage. Blood and urine were collected at various times and the nitrosamines determined. Results are the meanS±SD for 3 animals. Results after ip administration are taken from (4).
TEXT-FIGURE
TABLE
creased with time over the 3-hour measurement period. HPOP was the major metabolite present. The blood metabolite levels also differed after BOP administration by the two routes: HPOP was again the m
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ABSTRACT-The levels of N-nitroso-bis(2-oxopropyl)amine (BOP) and its metabolites in the urine, blood, bile, and pancreatic juice were compared after ip and oral administration of BOP to Syrian golden hamsters to explain the differing organotropic tumor spectra resulting from treatment by these two routes. The levels of BOP and its metabolites N-nitroso(2-hydroxypropyl)(2oxopropyl)amine (HPOP) and N-nitroso-bis(2-hydroxypropyl)amine in the urine, blood, bile, and pancreatic juice were generally less after oral administration than after ip administration. The results suggested that HPOP may be a proximate pancreatic carcinogen in hamsters administered BOP, inasmuch as it was the major metabolite in the blood and pancreatic juice after ip administration. However, the results did not indicate a mechanism for the increased incidence of bile duct tumors after oral administration of BOP.-J Natl Cancer Inst 60: 911-913, 1978.
A high incidence of pancreatic duct neoplasms, similar to those in man, was induced after chronic weekly sc injections of BOP into Syrian golden hamsters (1). Lung, liver, gallbladder, and kidney tumors also developed. By the reduction of treatment frequency, the incidence of these tumors decreased and was eliminated in the liver, but the high incidence of pancreatic tumors was maintained (2). When BCP was administered chronically in drinking water at estimated weekly doses similar to those given sc, the main target organ changed. A high incidence of intrahepatic and extrahepatic bile duct neoplasms was observed, with few pancreatic and no lung or kidney tumors (3). In this report we present the results of metabolic studies done in an attempt to explain the difference in tumor response to BOP after ip and oral administration. Previous studies with the use of ip administration of BOP to mimic the sc route used in the bioassays have shown that this carcinogen is rapidly metabolized to HPOP. This HPOP metabolite can exist in a cyclic form, which has been suggested to be the proximate pancreatic carcinogen formed after administration of either BOP, BHP, or NDMM to hamsters (4,5). BOP, HPOP, and BHP have been determined in the blood and urine of the hamster after oral administration of BOP and compared to values previously obtained after ip treatment (4). Wynder et al. (6) suggested that human pancreatic cancer may be induced by the reflux of bile containing carcinogens into the pancreas. We measured the levels of BOP and metabolites in bile and pancreatic juice after oral and ip administration to determine if biliary reflux or a direct effect of nitrosamines in the pancreatic secretion is a mechanism of carcinogenesis in this animal model. VOL. 60, NO.4, APRIL 1978 Downloaded from https://academic.oup.com/jnci/article-abstract/60/4/911/1026719 by University of Durham user on 07 March 2018
911
MATERIALS AND METHODS BOP, HPOP, and BHP were obtained as described in (4). In previous metabolic studies, compounds were administered ip, instead of by the sc route used in the bioassays, to eliminate any complications of slow absorption from the injection site (4). Compounds administered ip are absorbed into the venous system, and a direct effect of BOP on the pancreas is considered unlikely. Gavage was similarly used here as an equivalent of chronic administration in the drinking water. BOP (100 mg/kg; 20 mg/ml in water) was administered by gavage to male Syrian golden hamsters. Urine and blood were collected from hamsters as in (4). In a separate experiment, bile and pancreatic juice were collected from animals briefly anesthetized with pentobarbital sodium. Bile was obtained by cannulation of the gallbladder after ligation of the common bile duct below the cystic duct. We drained pancreatic juice from the same animal by inserting a cannula into the common duct, which was ligated at its junction with the duodenum. Bile and pancreatic juice were collected continuously for 6 hours from conscious animals maintained in restraining cages. Metabolites in the urine, blood, bile, and pancreatic juice were extracted and determined as in (4), and statistical evaluations done with Student's t-test.
RESULTS AND DISCUSSION The 24-hour urine from hamsters administered BOP ip contained 1.8±0.6% of the dose as the metabolite HPOP and 4.9±3.8% of the dose as BHP (4). No unchanged BOP or any other metabolite was detected. ABBREVIATIONS USED: BOP = N-nitroso-bis(2-oxopropyl)amine; HPOP = N-nitroso(2-hydroxypropyl)(2-oxopropyl)amine; BHP = Nnitroso-bis(2-hydroxypropyl)amine; NDMM = N-nitroso-2,6-dimethylmorpholine.
Received July 8,1977; accepted October 31,1977. Supported by Public Health Service contract NOI-CP33278 from the Division of Cancer Cause and Prevention, National Cancer Institute. 3 Presented in part at the 68th Meeting of the American Association for Cancer Research held in Denver, Colorado, in May 1977. 4Eppley Institute for Research in Cancer, University of Nebraska Medical Center, 42d St. and Dewey Ave., Omaha, Nebr. 68105. "We are grateful to Katla Donnelly, Jerry Meehan, and Galen Brunk for technical assistance, and to Mardelle Susman for editorial assistance. 1
2
J NATL CANCER INST
912
GINGELL AND POUR
The corresponding values after oral administration were 0.4±O.3% as HPOP and O.3%±O.2% as BHP. The rate of excretion of metabolites was greater after ip injection compared to that after oral administration. After oral administration, HPOP and BHP concentrations in the urine peaked at 2 hours and then decreased (text-fig. IA). However, after ip administration, urine metabolite levels were considerably higher and in-
I.-Concentration of BOP and metabolites in A) urine and B) blood after ip and oral administration of BOP. Male Syrian golden hamsters were administered 100 mg BOP/kg, either ip or by gavage. Blood and urine were collected at various times and the nitrosamines determined. Results are the meanS±SD for 3 animals. Results after ip administration are taken from (4).
TEXT-FIGURE
TABLE
creased with time over the 3-hour measurement period. HPOP was the major metabolite present. The blood metabolite levels also differed after BOP administration by the two routes: HPOP was again the m
