8-hydroxyguanine and Choline-Deficiency

The effects of green tea extract (GTE) on exogenous and endogenous models of rat liver carcinogenesis using diethylnitrosamine (DEN) and a choline-deficient, L-amino acid-defined (CDAA) diet were studied. For the exogenous carcinogenesis study, male Fischer 344 rats, 6 weeks old, were given a single intraperitoneal dose of 200 mg/kg body weight of DEN, partially hepatectomized at week 3, and administered GTE at doses of 0, 0.01 and 0.1% in the drinking water from week 2 for 10 weeks. For the endogenous carcinogenesis study, rats were fed the CDAA diet and simultaneously given GTE for 12 weeks. All rats were killed at the end of week 12. After DEN-initiation, the apparent numbers of glutathione S-transferase placental form-positive foci, assayed as putative preneoplastic lesions, were decreased by the administration of GTE, though their sizes were not altered. In contrast, GTE did not significantly reduce the numbers of the lesions induced by the CDAA diet or affect their sizes. While the levels of 8-hydroxyguanine, a parameter of oxidative DNA damage, were reduced by the GTE administration in both experimental models, GTE did not protect against the CDAA-diet-associated liver tissue damage in terms of either histology or plasma marker enzyme levels. We conclude that, while GTE may be a possible chemopreventive agent for nitrosamine-initiated hepatocarcinogenesis in the absence of chronic hepatocyte damage, it does not significantly inhibit lesion development in hepatocarcinogenesis associated with the CDAA diet, a cirrhosis-associated model.

Topics: Alanine Transaminase; Animals; Choline Deficiency; Diet; Diethylnitrosamine; DNA; Glutathione Transferase; Guanine; Liver Neoplasms; Male; Plant Extracts; Precancerous Conditions; Rats; Rats, Inbred F344; Tea

Effects of N,N'-diphenyl-p-phenylenediamine (DPPD), an antioxidant, on liver carcinogenesis caused by a choline-deficient L-amino acid-defined (CDAA) diet containing ethionine were studied in Fischer 344 rats. Male animals, 6 weeks old, were fed a CDAA diet, a choline-supplemented L-amino acid-defined (CSAA) diet or a CDAA diet containing 0.05% ethionine with or without 0.2% DPPD. Histological changes and lesions positive for gamma-glutamyltransferase (GGT) were analyzed 12 weeks after the beginning of the experiment. The levels of 8-hydroxyguanine (8-OHGua) in DNA and 2-thiobarbituric acid-reacting substances (TBARS) were measured as the parameters for cellular oxidative damage after 4 and 11 days of treatment. Expression of c-myc and c-Ha-ras was also investigated in relation to cell proliferation after 2, 4, 8 and 11 days. Histologically, development of diffuse fatty liver observed in rats fed a CDAA diet was inhibited, while massive oval cell proliferation and cholangiofibrosis resulted from the addition of ethionine with/without DPPD. The sizes but not numbers of GGT-positive lesions seen in the liver of rats fed a CDAA diet were increased and the levels of 8-OHGua formation and TBARS generation were also increased by the ethionine supplement. Both numbers and sizes of GGT-positive lesions were decreased and the level of TBARS, but not 8-OHGua, was decreased by adding DPPD. The increased expression of c-myc and c-Ha-ras detected in the liver of rats fed a CDAA diet was further increased by addition of ethionine and again reduced by DPPD. These results indicate that an antioxidant DPPD can inhibit the early stage of enhanced hepatocarcinogenesis caused by coadministration of ethionine and a CDAA diet, by blocking cellular oxidative damage as well as c-myc and c-Ha-ras expression.

Topics: Amino Acids; Animals; Antioxidants; Choline Deficiency; Cocarcinogenesis; Ethionine; Guanine; Liver Neoplasms, Experimental; Male; Phenylenediamines; Rats; Rats, Inbred F344

The effects of methionine on hepatocarcinogenesis induced by coadministration of a choline-deficient L-amino acid-defined (CDAA) diet and ethionine were examined. F344 male rats were divided into 4 experimental groups. Groups 1 and 2 received the CDAA diet and a choline-supplemented L-amino acid-defined (CSAA)++ diet, respectively. Group 3 received the CDAA diet containing 0.05% ethionine, and group 4 the CDAA diet containing 0.05% ethionine and 0.47% methionine. Animals were killed after 12 weeks of treatment. Histologically, the CDAA diet induced intracellular fat accumulation and foci. In contrast, ethionine caused not only foci, but also hyperplastic nodules, cholangiofibrosis and the proliferation of oval cells without such fat accumulation. Methionine abolished the development of all of the liver lesions induced by coadministration of the CDAA diet and ethionine. To investigate the effects of methionine on induction of c-myc and c-Ha-ras expression, as well as generation of 8-hydroxyguanine (8-OHGua) and 2-thiobarbituric acid-reacting substances (TBARS), by coadministration of the CDAA diet and ethionine, subgroups of 3 to 5 animals were killed at 2, 4, 8, or 11 days after the beginning of the experiment. Coadministration of the CDAA diet and ethionine markedly enhanced the level of expression of c-myc and c-Ha-ras, 8-OHGua formation and TBARS generation as compared with the CDAA or CSAA diet within 11 days, and methionine blocks these actions. These results indicate that addition of methionine prevents the induction of c-myc and c-Ha-ras expression, 8-OHGua formation and TBARS generation, as well as hepatocellular lesions, by coadministration of the CDAA diet and ethionine in rats, and suggest a possible involvement of oxidative stress and gene expression in hepatocarcinogenesis by these agents.

Topics: Amino Acids; Animals; Carcinogens; Choline Deficiency; Cocarcinogenesis; DNA Damage; Ethionine; Food, Formulated; Gene Expression Regulation; Guanine; Liver; Liver Neoplasms, Experimental; Male; Methionine; Oncogenes; Oxidative Stress; Rats; Rats, Inbred F344; Thiobarbituric Acid Reactive Substances

The present study was performed to assess the roles of hepatocellular oxidative damage to DNA and constituents other than DNA in rat liver carcinogenesis caused by a choline-deficient, L-amino acid-defined (CDAA) diet by examining the effects of the antioxidant N,N'-diphenyl-p-phenylenediamine (DPPD). The parameters used for cellular oxidative damage were the level of 8-hydroxy-guanine (8-OHGua) for DNA and that of 2-thiobarbituric acid-reacting substance (TBARS) for constituents other than DNA. A total of 40 male Fischer 344 rats, 6 weeks old, were fed the CDAA diet for 12 weeks with or without DPPD (0.05, 0.10 or 0.20%) or butylated hydroxytoluene (BHT, 0.25%). In the livers of the rats, the numbers and sizes of glutathione S-transferase (EC 2.5.1.18) placental form (GSTP)- and/or gamma-glutamyltransferase (GGT, EC 2.3.2.2)-positive lesions and levels of 8-OHGua and TBARS were determined. The GSTP-positive lesions of 0.08 mm2 or larger were all stained positively for GGT as well in cross-sectional area, whereas the smaller lesions were generally negative for GGT. DPPD and BHT reduced the size of the GSTP-positive lesions without affecting their total numbers. At the same time, they reduced TBARS generation without affecting 8-OHGua formation in DNA. The present results indicate that oxidative DNA damage (represented by 8-OHGua formation) and damage to constituents other than DNA (represented by TBARS generation) may play different roles in rat liver carcinogenesis caused by the CDAA diet; the former appears to be involved in the induction of phenotypically altered hepatocyte populations while the latter may be related to the growth of such populations.

Topics: Animals; Antioxidants; Choline Deficiency; Diet; DNA Damage; Guanine; Liver Neoplasms; Male; Phenylenediamines; Precancerous Conditions; Rats; Rats, Inbred F344; Thiobarbituric Acid Reactive Substances