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

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.

Neurotrophic and antioxidant effects of silymarin comparable to 4-methylcatechol in protection against gentamicin-induced ototoxicity in guinea pigs

BACKGROUND

Despite that gentamicin is a very effective aminoglycoside, its potential ototoxicity which is of irreversible nature makes a challenge and limitation for its use. This study was designed to investigate possible neurotrophic and antioxidant effects of silymarin comparable to 4-methylcatechol in protection against gentamicin-induced ototoxicity.

METHODS AND RESULTS

Twenty pigmented guinea pigs were divided into four equal groups, where group I served as normal control group. The other groups received gentamicin (120 mg/kg/day, ip) for 19 days where group II given vehicle of 1% CMC, group III and group IV were pre-treated 2h before gentamicin by 4-methylcatechol (10 μg/kg, ip) and silymarin (100mg/kg, oral gavage), respectively. The main findings indicated that silymarin exhibited restoration of nerve growth factor (NGF) levels and increased tropomyosin-related kinase receptors-A (Trk-A) m-RNA expression in cochlear tissue and preservation of hair cells of organ of Corti by scanning electron microscopy (SEM) with significant decrease in auditory brainstem response (ABR) threshold compared to 4-methylcatechol. Only silymarin caused significant amelioration in oxidative stress state by reducing malondialdehyde (MDA) levels and increasing catalase activity.

CONCLUSIONS

Silymarin exerts superiority over 4-methylcatechol when recommended as protective agent against gentamicin ototoxicity based on its efficient neurotrophic and antioxidant activities.

In vitro cytotoxicity of 4-methylcatechol in murine tumor cells: induction of apoptotic cell death by extracellular pro-oxidant action

Assessment of the in vitro cytotoxicity has recently been become popular as a primary screening method for evaluating the antitumor activities of various chemicals and natural substances. For example, quercetin and related phenolic compounds, present in teas, wines, and other plant products, have been shown to cause their cytotoxic effects on tumor cells in culture, proposing their protective effects against the development of cancer. However, 4-methylcatechol, a metabolite produced in the intestinal tract after ingestion, has been shown to cause the promotion rather than suppression of tumor in rat stomach despite its in vitro cytotoxic activity. To address the inconsistency between its in vivo and in vitro actions, the effect of 4-methylcatechol on the viabilities of murine tumor cells was examined, and 4-methylcatechol was shown to reduce their viabilities through the induction of apoptosis. In addition, since catechol compounds have been shown to have a complex mixture of pro-oxidant and antioxidant actions in the in vitro assay systems, the cytotoxic activity of 4-methylcatechol was reassessed in the presence of either catalase or reduced-form glutathione, and both of them were shown to protect the cells against the damage induced by 4-methylcatechol. Moreover, the generation of hydrogen peroxide was observed by incubating the drug in the growth medium with or without the cells. These findings indicate that, similar to other catechol compounds, 4-methylcatechol may induce the apoptotic death of murine tumor cells through its extracellular pro-oxidant action on the cells.

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.

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.