Inductions of ornithine decarboxylase and replicative DNA synthesis but not DNA single strand scission or unscheduled DNA synthesis in the pyloric mucosa of rat stomach by catechol

Human gastric cancer risk screening: From rat pepsinogen studies to the ABC method

We examined the development of gastric cancer risk screening, from rat pepsinogen studies in an experimental rat gastric carcinogenesis model induced with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and human pepsinogen studies in the 1970s and 1980s to the recent "ABC method" for human gastric cancer risk screening. First, decreased expression or absence of a major pepsinogen isozyme, PG1, was observed in the rat gastric mucosa from the early stages of gastric carcinogenesis to adenocarcinomas following treatment with MNNG. In the 1980s, decreases in PGI in the human gastric mucosa and serum were identified as markers of atrophic gastritis. In the 1990s, other researchers revealed that chronic infection with Helicobacter pylori (Hp) causes atrophic gastritis and later gastric cancer. In the 2000s, a gastric cancer risk screening method combining assays to detect serum anti-Hp IgG antibody and serum PGI and PGII levels, the "ABC method", was established. Eradication of Hp and endoscopic follow-up examination after the ABC method are recommended to prevent gastric cancer.

Sequential morphological and biological changes in the glandular stomach induced by oral administration of catechol to male F344 rats

Histogenesis and mechanisms of catechol-induced rat glandular stomach carcinogenesis were investigated in male F344 rats. Groups of 5 or 6 rats were treated with dietary catechol at doses of 1, 0.5, 0.1, and 0.01% for 12 hr or for 1, 2, 3, or 7 days or at a dose of 0.8% for 1, 2, 4, 12, and 24 wk; rats were then euthanatized. The initial morphological changes were edema of the gastric wall, inflammatory-cell infiltration, erosion in the pyloric region close to the duodenum, and considerable increase in apoptosis at 12 hr; later, changes included augmented DNA synthesis and cell proliferation, as evaluated by bromodeoxyuridine labeling index and thickness of mucosa, respectively, on day 1. Downward hyperplasia due to excess regeneration appeared at edges of ulceration at week 2. This lesion disappeared, and then submucosal hyperplasia appeared in the course of adenoma development. Only slight expression of c-myc or c-fos was apparent after 30-min oral administration or 1-, 3-, and 6-hr oral administration of catechol. No increase in lipid peroxide levels was evident in gastric epithelium fed catechol for 1 wk. The amount of catechol distributed in the glandular stomach and forestomach epithelium, which is not a target for carcinogenesis, did not differ 1, 3, 6, and 24 hr after a single intragastric dose of 75 mg/kg body weight. Amounts of catechol bound to tissue protein were also not specifically high in the glandular stomach. These results indicate that regenerative cell proliferation due to toxicity plays an important role in catechol-induced glandular stomach carcinogenesis. Protein binding and free radicals may not be largely responsible for the toxicity.

DNA single-strand scission in the pyloric mucosa of rat stomach induced by four glandular stomach carcinogens and three other chemicals

Induction of DNA single-strand scission by four glandular stomach carcinogens and three other chemicals was studied in the pyloric mucosa of rat stomach after gastric intubation. DNA single-strand scission, as was measured by the alkaline elution method, was induced by four glandular stomach carcinogens; N-nitroso N-methylurethane at doses of 1 and 9 mg/kg body wt, 4-nitroquinoline 1-oxide at 20 and 30 mg/kg body wt. N-ethyl-N'-nitro-N-nitrosoguanidine at 30 and 100 mg/kg body wt and N-propyl-N'-nitro-N-nitrosoguanidine at 30 and 100 mg/kg body wt. DNA single-strand scission was also induced dose-dependently by a direct acting mutagen, 1-nitrosoindole-3-acetonitrile at doses of 100, 500 and 800 mg/kg body wt. Omeprazole, a proton pump inhibitor, was equivocal in its effect in this assay at 30-500 mg/kg body wt: induction was statistically significant by Cochran-Armitage binomial trend test. Loxtidine, an H2-receptor antagonist, did not induce DNA single-strand breaks in the pyloric mucosa at a dose of 400 mg/kg body wt. The present results together with previous information suggest that DNA single-strand scission is a good marker for tumor-initiating activity in rat stomach mucosa.

Rat strain differences in catechol carcinogenicity to the stomach

The carcinogenic potential of catechol was compared in male Wistar, WKY, Lewis and SD strains of rats. Groups of 30 animals were treated with powdered diet containing 0.8% catechol for 104 wk and then examined histopathologically. Induction of glandular stomach adenocarcinomas occurred in 67, 73 and 77% of Wistar, Lewis and SD animals, respectively, but in only 10% of WKY rats. In addition, catechol induced forestomach papillomas in 20% (P < 0.05), and squamous cell carcinomas in 3% of SD rats. The results thus indicate that Wistar, Lewis and SD rats are much more susceptible than WKY rats to induction of glandular stomach adenocarcinomas by 0.8% catechol, and that this phenolic antioxidant also possesses weak carcinogenic activity for the SD rat forestomach.

In vivo short-term assays for tumor initiation and promotion in the glandular stomach of Fischer rats

Here we summarize the data on 55 compounds tested in in vivo short-term assays for tumor-initiating and tumor-promoting activity in the glandular stomach of male Fischer (F344) rats. Most of the data has been previously published. Tumor-initiating activity was assayed by measuring the induction of unscheduled DNA synthesis (UDS) and DNA single strand scission; tumor-promoting activity was assayed by measuring the induction of ornithine decarboxylase (ODC) activity, increased replicative DNA synthesis (RDS), and of c-fos and c-myc oncogene expression. The compounds were orally administered. Twenty-nine compounds were tested for UDS. Eight were positive, including 5 glandular stomach carcinogens; 16 were negative, including 5 liver carcinogens; and 5 were equivocal. Twenty compounds were tested for DNA single strand scission. Twelve were positive, including 6 glandular stomach carcinogens; 7 negative, including 2 liver carcinogens; and 1 was equivocal. Thirty-two compounds were tested for RDS. Twenty-six were positive, including 8 glandular stomach carcinogens and 6 glandular stomach tumor-promoters; 4 were negative, including 3 liver carcinogens and a stomach irritant; and 2 were equivocal. Forty-five compounds were tested for ODC. Thirty-seven were positive, including 8 glandular stomach carcinogens and 6 glandular stomach tumor promoters; 7 were negative, including 3 liver carcinogens; and one was equivocal. All glandular stomach carcinogens and tumor-promoters examined were positive in both RDS and ODC. Two compounds were tested for c-fos and c-myc expression; one was a glandular stomach carcinogen and one was a glandular stomach tumor promoter, and both were positive. In addition, 2 compounds inhibited the increase in RDS induced by the tumor promoter NaCl, suggesting anti-tumor-promoter activity. Thus these assays are useful for assessing potential tumor-initiating and tumor-promoting activity in the rat glandular stomach.

Potent promoting activity of dimethylitaconate on gastric carcinogenesis induced by N-methylnitrosourea

Dimethylitaconate (DMI) is one of phase II enzyme inducers suggesting a candidate for a tumor inhibitor. We tested the modifying effect of DMI on post-initiation stage of MNU induced gastric carcinogenesis in male Fischer 344 rats. Groups I and II administered N-methylnitrosourea (MNU) at a concentration of 100 ppm in the drinking water for 15 weeks. Group II was treated 0.5% DMI in the drinking water for 37 weeks after the MNU treatment. Groups III and IV were DMI alone and untreated control, respectively. DMI-treated animals showed hyperplastic changes in gastric epithelium and the incidence was 40% in the DMI alone group. MNU combined with DMI significantly increased the adenoma incidence compared with MNU alone group (P < 0.05). The concomitant administration of DMI showed a significant increase of adenocarcinoma incidence, which was 95% (P < 0.005) compared with MNU alone group (11.8%). The replicative DNA synthesis and the labelling index of bromodeoxyuridine, which are the indicators of proliferating activity, were increased in the stomach of DMI-treated rats compared with untreated control (P < 0.001 and P < 0.005, respectively). These results suggested that DMI has potent promoting potential in the post-initiation stage of gastric carcinogenesis of rats and its mechanisms are probably involved in the induction of cell proliferation including replicative DNA synthesis.

Possible tumor-initiating and -promoting activity of p-methylcatechol and methylhydroquinone in the pyloric mucosa of rat stomach

The possible tumor-promoting and tumor-initiating activities of p-methylcatechol and methylhydroquinone in the pyloric mucosa of male F344 rats were studied. Ornithine decarboxylase (ODC) and replicative DNA synthesis (RDS) were used as markers of tumor promotion and DNA single strand scission and unscheduled DNA synthesis (UDS) as markers of tumor initiation. The compounds were administered by gastric intubation and results were compared with those after administration of catechol. p-Methylcatechol at doses of 60 to 180 mg/kg body weight dose-dependently induced up to 20-fold increase in ODC activity and 9-fold increase in RDS with maxima 24 h after its administration, but it did not induce significant DNA single strand scission or UDS. Methylhydroquinone at a dose of 200 mg/kg body weight induced up to 6-fold increase in ODC activity 24 h, and 5-fold increase in RDS 16 h after its administration, but the induction was not dose-dependent. At a dose of 200 mg/kg body weight it induced DNA single strand scission, but not UDS. These results and previous findings show that the possible tumor-promoting activities of catechol are several times higher than those of p-methylcatechol and 10 times higher than those of methylhydroquinone.

Genotoxicity and cell proliferative activity of a nitrosated Oroxylum indicum Vent fraction in the pyloric mucosa of rat stomach

In vivo genotoxic activity and cell proliferative activity were examined in the stomach mucosa of male F344 rats by in vivo short-term methods after oral administration of a nitrosated Oroxylum indicum Vent (OiV) fraction, which had been found to be mutagenic without S9 mix to Salmonella typhimurium TA98 and TA100. Administration of the nitrosated OiV fraction at doses of 1 and 2 g/kg body weight induced dose-dependent DNA single-strand scission (p less than 0.02), determined by the alkaline elution method, in the stomach pyloric mucosa 2 h after its administration: a dose of 2 g/kg body weight induced an 18-fold increase in the DNA elution rate constant. Administration of the nitrosated OiV fraction at doses of 0.7-2.8 g/kg body weight also induced dose-dependent increases, up to 11-fold (p less than 0.05), in replicative DNA synthesis in the stomach pyloric mucosa 16 h after its administration. Moreover administration of the nitrosated OiV fraction at doses of 0.25-2.0 g/kg body weight induced dose-dependent increases, up to 100-fold, in ornithine decarboxylase activity in the stomach pyloric mucosa with a maximum 4 h after its administration. These results demonstrate that the nitrosated OiV fraction has genotoxic and cell proliferative activity in the pyloric mucosa of rat stomach in vivo.

Effects of sodium nitrite and catechol or 3-methoxycatechol in combination on rat stomach epithelium

The effects of sodium nitrite (NaNO2) and catechol or 3-methoxycatechol in combination were examined in male F344 rats. Animals were treated with 0.3% NaNO2 in the drinking water and 0.8% catechol or 2% 3-methoxycatechol in powdered diet for 24 weeks. While catechol or 3-methoxycatechol alone induced low incidences of mild or moderate hyperplasia, simultaneous administration of NaNO2 markedly enhanced the degree of hyperplasia and papilloma formation. In contrast, induction of submucosal hyperplasia and adenomas in the glandular epithelium was reduced. Thus, the results indicate that NaNO2 can modulate the metabolism of antioxidants, so that, possibly via production of new active moieties, targeting of forestomach epithelium is enhanced.

Gastric carcinogenesis: diet as a causative factor

Gastric cancer is a very typical cancer related to life styles, including nutrition and dietary conditions. Cigarette smoking has also been pointed out as an enhancing factor in gastric cancer development. Improvement of dietary conditions, regular dietary habits including lower salt, nitrite and nitrite intake and balanced nutritious food may be factors suppressing the incidence of gastric cancer. At the same time, advances in technology for early diagnosis and early surgical treatment have elevated the cure rate of gastric cancers. From both primary and secondary cancer prevention aspects, gastric cancer is now a conquerable disease.