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Telomerase activities in intrahepatic cholangiocarcinomas induced by N-nitrosobis(2-oxopropyl)amine (BOP) in female hamsters were determined using a telomeric repeat amplification protocol (TRAP) assay followed by densitometric quantification. Each determination was repeated to confirm the results and telomerase activity was also detected by gel electrophoresis. An increase was evident in all of 10 cholangiocarcinomas examined, with levels ranging from 2.48 to 4.40 times the normal liver value by densitometric quantification. This finding of a consistent increase suggests that telomerase activation is involved in the development of intrahepatic cholangiocarcinomas and immortalization of cancer cells.

Effects of eight heterocyclic amines (HCAs) on pancreatic duct carcinogenesis were investigated in a rapid production model in hamsters. N-Nitrosobis(2-oxopropyl)amine (BOP) was given to effect initiation, followed by augmentation pressure consisting of four daily i.p. injections of 500 mg/kg DL-ethionine, a choline-deficient (CD) diet, a single i.p. injection of 800 mg/kg L-methionine and a s.c. injection of 20 mg/kg BOP. After two cycles of augmentation pressure, the HCAs 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1), 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2), 2-amino-9H-pyrido[2,3-b]indole (AalphaC), 2-amino-3-methyl-9H-pyrido[2,3-b]indole (MeAalphaC) or 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline [4,8-DiMeIQx) were administered in the diet for 50 or 70 days. The numbers of pancreatic ductal hyperplasias (H) and a total lesions including, atypical hyperplasia (AH), carcinomas in situ (CIS) and invasive carcinomas, were increased in hamsters given the diet containing 0.02% Trp-P-1 for 50 days. This result was confirmed and extended by the finding of increased numbers of invasive carcinomas in hamsters given 0.02% Trp-P-1 for 70 days. The number and incidence of invasive carcinomas were also elevated in hamsters given the diet containing 0.06% 4,8-DiMeIQx for 50 days. These results suggest a possible involvement of Trp-P-1 and 4,8-DiMeIQx in pancreatic duct carcinogenesis.

The question of whether the changes in telomerase activity and/or the alteration of the p53 gene are involved in the development of oligo-astrocytomas induced by N-ethyl-N-nitrosourea (ENU) in rats was addressed. Telomerase activity levels of oligo-astrocytomas, including early neoplastic lesions, were significantly increased as compared to the normal controls, correlating with the degree of malignancy. In contrast, no mutations of p53 exons 5-7 were found in early neoplastic lesions or oligo-astrocytomas. These results indicate that the activation of telomerase occurs during astrocytoma carcinogenesis and contributes to the development of brain tumors, but the alterations of p53, at least on exons 5-7, may not be involved in this process.

The regulation of telomerase activity during regeneration induced by two-thirds partial hepatectomy (PH) was investigated in 6-week-old male F344 rats. Groups of animals were serially sacrificed 0, 6, 16, 24, 36 and 72 h after the operation and telomerase activity was determined by the telomeric repeat amplification protocol (TRAP) assay followed by densitometric quantification. DNA synthesis was immunohistochemically quantified in terms of bromodeoxyuridine (BrdU) incorporation. The expression levels of telomerase RNA were examined by Northern blot analysis. Telomerase activity was increased significantly from 6 to 36 h but had decreased to close to the normal levels after 72 h. DNA synthesis reached a maximum 24 h after PH. However, the expression levels of telomerase RNA did not change during regeneration. The results suggest that telomerase is actively regulated by unknown mechanisms throughout the cell cycle in regenerating rat hepatocytes.