8-hydroxyguanine and Precancerous-Conditions

Oxidative DNA damage may be a risk factor for development of various pathologies, including malignancy. We studied inflammation triggered modulation of repair activity in the intestines of three weeks old rats injected i.p. with E.coli or S. typhimurium lipopolysaccharides (LPS) at doses of 1, 5 or 10 mg/kg. Subsequent formation in these animals of colonic preneoplastic lesions, aberrant crypt foci (ACF) was also investigated. Five days after LPS administration no differences were observed in repair rate of 1,N(6)-ethenoadenine (εA), 3,N(4)-ethenocytosine (εC) and 8-oxoguanine (8-oxoG) in intestines of these rats, as measured by the nicking assay. However a significant increase in all three repair activities was found within one and two months after S. typhimurium LPS treatment. E. coli LPS significantly increased only the 8-oxoG repair. S. typhimurium LPS stimulated mRNA transcription of pro-inflammatory proteins, lipooxygenase-12 and cyclooxygenase-2, as well as some DNA repair enzymes like AP-endonuclease (Ape1) and εC-glycosylase (Tdg). mRNA level of DNA glycosylases excising εA (MPG) and 8-oxoG (OGG1) was also increased by LPS treatment, but only at the highest dose. Transcription of all enzymes increased for up to 30 days after LPS, and subsequently decreased to the level observed before treatment, with the exception of APE1, which remained elevated even two months after LPS administration. Thus, the repair efficiency of εA, εC and 8-oxoG depends on the availability of APE1, which increases OGG1 and TDG turnover on damaged DNA, and presumably stimulates MPG. One and two months after administration of E. coli or S. typhimurium LPS, the number of aberrant crypt foci in rat colons increased in a dose and time dependent manner. Thus, inflammation stimulates the repair capacity for εA, εC and 8-oxoG, but simultaneously triggers the appearance of preneoplastic changes in the colons. This may be due to increased oxidative stress and imbalance in DNA repair.

Topics: Adenine; Animals; Animals, Newborn; Arachidonate 12-Lipoxygenase; Colon; Colonic Neoplasms; Cyclooxygenase 2; Cytosine; DNA Damage; DNA Repair; Escherichia coli; Guanine; Inflammation; Lipopolysaccharides; Oxidative Stress; Precancerous Conditions; Rats, Wistar; Salmonella typhimurium

Carcinogenic risk and molecular mechanisms underlying the liver tumor-promoting activity of copper gluconate, an additive of functional foods, were investigated using a rat medium-term liver carcinogenicity bioassay protocol (Ito test) and a 2-week short-term administration experiment. In the medium-term liver bioassay, Fischer 344 male rats were given a single i.p. injection of N-nitrosodiethylamine at a dose of 200 mg/kg b.w. as a carcinogenic initiator. Starting 2 weeks thereafter, rats received 0, 10, 300 or 6,000 ppm of copper gluconate in diet for 6 weeks. All rats underwent 2/3 partial hepatectomy at the end of week 3, and all surviving rats were killed at the end of week 8. In the short-term experiment, rats were given 0, 10, 300 or 6,000 ppm of copper gluconate for 2 weeks. Numbers of glutathione S-transferase placental form (GST-P) positive lesions, single GST-P-positive hepatocytes and 8-oxoguanine-positive hepatocytes, and levels of cell proliferation and apoptosis in the liver were significantly increased by 6,000 ppm of copper gluconate in the medium-term liver bioassay. Furthermore, hepatic mRNA expression of genes relating to the metal metabolism, inflammation and apoptosis were elevated by 6,000 ppm of copper gluconate both in the medium-term liver bioassay and the short-term experiments. These results indicate that copper gluconate possesses carcinogenic risk toward the liver at the high dose level, and that oxidative stress and inflammatory and pro-apoptotic signaling statuses may participate in its underlying mechanisms.

Topics: Administration, Oral; Animals; Apoptosis; Biological Assay; Carcinogenicity Tests; Carcinogens; Cell Proliferation; Diet; Dose-Response Relationship, Drug; Gene Expression Profiling; Gene Expression Regulation, Neoplastic; Gluconates; Glutathione Transferase; Guanine; Hepatectomy; Hepatocytes; Liver; Liver Neoplasms; Male; Metallothionein; Metals; Oxidative Stress; Precancerous Conditions; Rats; Rats, Inbred F344; RNA, Messenger

Basal levels of endogenously generated oxidative DNA modifications such as 7,8-dihydro-8-oxoguanine (8-oxoG) are present in apparently all mammalian cells, but their relevance for the generation of spontaneous cancers remains to be established. Both the 8-oxoG levels and the resulting spontaneous mutations are increased in the livers of Csb(m/m)/Ogg1(-/-) mice, which are deficient in the repair of 8-oxoG. In order to determine the consequences of these additional oxidative DNA modifications and mutations and thus assess the tumor initiating potency of this type of endogenous DNA damage, we treated Csb(m/m)/Ogg1(-/-) mice and repair-proficient controls with the peroxisome proliferator WY-14,643 (0.025% ad libitum), a potent inducer of liver cell proliferation. The treatment did not generate any additional oxidative DNA damage; the elevated levels of 8-oxoG in the Csb(m/m)/Ogg1(-/-) mice even decreased. Also, the spontaneous mutation frequencies observed in the lacI gene of BigBlue Csb(m/m)/Ogg1(-/-) mice, which were approximately 3-fold higher than in the repair-proficient mice, declined by 39% under the treatment, whereas the frequencies in the livers of the repair-proficient animals remained unchanged. Preneoplastic lesions (staining positive or negative for glucose-6-phoshatase) developed in the livers of both wild-type and Csb(m/m)/Ogg1(-/-) mice after 30 weeks. Both the numbers and the total volumes of the lesions were approximately 6-fold higher in the repair-deficient mice than in the wild-type mice. The results indicate that spontaneous mutations generated from endogenous oxidative DNA base damage efficiently translate into increased tumorigenesis when cell proliferation is stimulated.

Topics: Animals; Cocarcinogenesis; DNA Damage; DNA Glycosylases; DNA Repair; DNA Repair Enzymes; Guanine; Liver; Liver Neoplasms, Experimental; Mice; Mice, Inbred C57BL; Mutation; Oxidative Stress; Peroxisome Proliferators; Poly-ADP-Ribose Binding Proteins; Precancerous Conditions; Pyrimidines

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

Male F344 rats were administered 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) in the diet at doses of 200, 50, 12.5, 3.2, 0.8, 0.2 and 0.05 ppm for six weeks, and partially hepatectomized 1 week after the beginning of MeIQx administration. Quantitative values for glutathione S-transferase placental form (GST-P)-positive foci in the liver were dose-dependently increased by the MeIQx treatment. 8-Hydroxyguanine (8-OHG) levels assessed after 1 week of dietary MeIQx administration were also dose-dependently increased, although the effect was no longer observed at the end of the treatment period. The correlation between numbers of GST-P-positive foci at week 6 and 8-OHG levels at week 1 was linear, values for both parameters being higher than the control levels even in the 0.8 ppm dose group. These findings indicate that, in addition to the previously reported MeIQx-DNA adduct formation, DNA modifications due to oxidative damage may play an important role in MeIQx liver carcinogenesis in rats.

Topics: Animals; Body Weight; Carcinogens; Diet; Glutathione Transferase; Guanine; Liver; Liver Neoplasms; Male; Organ Size; Precancerous Conditions; Quinoxalines; Rats; Rats, Inbred F344

Hydroxyl radical-induced mutagenic base modifications have been linked to neoplasia in a number of biological systems, including English sole from chemically contaminated urban environments. However, virtually no information exists on the relationship between the mutagenic base modifications and preneoplastic and other lesions found in tumor-free tissues prone to cancer. We studied six hepatic lesions in immature, neoplasm-free English sole exposed to an urban and reference environment and established correlations between the lesion incidence and concentrations of the mutagenic base modifications 8-hydroxyguanine and 8-hydroxyadenine. The lesions were putatively preneoplastic basophilic foci, hepatocellular karyomegaly, megalocytic hepatosis, hepatocellular vacuolar change, hyalin droplet formation, and apoptosis. With the exception of hepatocellular vacuolar change, significant positive correlations were found between the lesions and the mutagenic base modifications. The hydroxyl radical may be a common etiological factor in the formation of the base modifications and hepatic lesions.

Topics: Adenine; Age Factors; Animals; Confounding Factors, Epidemiologic; Fish Diseases; Guanine; Liver Diseases; Liver Neoplasms; Mutagenesis; Precancerous Conditions

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