Toshihisa Ohta

Inhibitory effect of a prostaglandin E receptor subtype EP1 selective antagonist, ONO-8713, on development of azoxymethane-induced aberrant crypt foci in mice

We previously reported that prostaglandin E(2) contributes to colon carcinogenesis through its binding to the prostaglandin E receptor subtype EP(1) using a genetic approach in EP(1)-knockout mice and a pharmacological approach with the EP(1) selective antagonist, ONO-8711. In the present study, we examined the effects of another more selective EP(1) receptor antagonist, ONO-8713, on development of azoxymethane (AOM)-induced aberrant crypt foci (ACFs) in male C57BL/6J mice treated i.p. with 10mg/kg body weight AOM once a week for 3weeks. Administration of ONO-8713 at doses of 250, 500 and 1000ppm in diet during and post-AOM treatment for 5weeks resulted in a dose-dependent reduction of ACF formation, being 15, 30 and 36% inhibition of the control value, respectively. The level of inhibition was similar to that with ONO-8711. Moreover, ONO-8713 suppressed the development of ACF when administered at post-AOM, as in the case of ONO-8711. The data confirm EP(1) receptor involvement in colon carcinogenesis.

Chemoprevention by Nimesulide, a Selective Cyclooxygenase‐2 Inhibitor, of 2‐Amino‐1‐methyl‐6‐phenylimidazo[4,5‐b]pyridine (PhIP)‐induced Mammary Gland Carcinogenesis in Rats

Breast cancer is common in women all over the world, and exploration of chemopreventive approaches to this cancer is very important. Nimesulide, a selective inhibitor of cyclooxygenase‐2 (COX‐2), is a good candidate as a chemopreventive agent with low toxicity. We examined its effects on mammary tumor development in female Sprague‐Dawley rats induced with the environmental carcinogen 2‐amino‐1‐methyl‐6‐phenylimidazo[4,5‐b]pyridine (PhIP). Rats at 7 weeks of age received intragastric intubations of PhIP (85 mg/kg body weight) 4 times weekly for 2 weeks and were maintained on control diet (high fat diet) or experimental diet (high fat diet supplemented with 400 ppm nimesulide) throughout the experiment. COX‐2 protein was over‐expressed in epithelial cancer cells and stromal cells of the PhIP‐induced mammary carcinomas, but was weak or not apparent in normal mammary gland cells. The development of mammary carcinomas was clearly suppressed by administration of nimesulide. The carcinoma incidence was 51% as compared to 71% for the control diet group. The average multiplicity of carcinomas in the experimental diet group was 1.2±0.2 (P < 0.05), significantly smaller than the control diet group value (2.6±0.5). The size of carcinomas was also clearly decreased; 1.1±0.4 cm3/rat in experimental diet group (P < 0.05), 4.1±1.3 cm3/rat in the control diet group. The results therefore provide evidence that the selective COX‐2 inhibitor, nimesulide, possesses chemopreventive activity against PhIP‐induced mammary carcinogenesis in rats.

Suppression of azoxymethane-induced colonic aberrant crypt foci by a nitric oxide synthase inhibitor

Nitric oxide synthase (NOS), an important bioregulator of a variety of biological processes, is overexpressed in colonic tumors of humans and rodents. In this study, effects of L-N(G)-nitroarginine methyl ester (L-NAME), a NOS inhibitor, on development of aberrant crypt foci (ACF) induced by azoxymethane (AOM) in F344 male rats were investigated. Six-week-old male F344 rats were fed diets containing 0 or 100 ppm L-NAME, and given s.c. injections of AOM at 15 mg/kg body wt, once a week for 2 weeks. At 17 weeks of age, all animals were sacrificed and their colons were evaluated for numbers of ACF. Feeding of 100 ppm L-NAME inhibited the development of ACF in different sizes by 24-39%, those containing four or more crypts being most markedly affected. Assessment of silver-stained nucleolar organizer regions protein (AgNORs)/nucleus further revealed a 44% reduction by administration of L-NAME. These results suggest that the NOS inhibitor, L-NAME, may be an effective chemopreventive agent against colon carcinogenesis due to depression of cell proliferation.

Chemopreventive effects of nimesulide, a selective cyclooxygenase-2 inhibitor, against PhIP-induced mammary carcinogenesis.

Non-steroidal antiinflammatory drugs (NSAIDs) are known to decrease prostanoid synthesis through inhibition of cyclooxygenase (COX) activity, resulting in antiinflammatory effects. Two isoforms of COX-1 and —2 have been characterized in mammalian and avian species. COX-1 is constitutively expressed in most tissues to regulate prostaglandin (PG) production and maintain stable physiological conditions, including gastric cytoprotection and blood flow. In contrast, COX-2 is transiently induced by lipopolysaccharide, cytokines and growth factors, and has been indicated to produce large amount of prostanoids involved in inflammation and mitogenesis. Previous studies have revealed elevated levels of PGs in human breast cancers’. Numerous in vivo studies in rodent models of mammary carcinogenesis have indicated that NSAIDs suppress mammary tumor growth24.

Marked Enhancement by Fish Meal of Helicobacter pylori‐induced Gastritis in Mongolian Gerbils

In a search for dietary factors influencing Helicobacter pylori‐induced gastritis, the effects of fish meal in the diet were examined in Mongolian gerbils. When a conventional diet containing 10% fish meal was given to Mongolian gerbils for 4 weeks after inoculation of H. pylori, edematous thickening with severe neutrophil and mononuclear cell infiltration in both the mucosa and submucosa was observed in the glandular stomach of 19 out of the 20 animals, and hemorrhagic spots were evident in 11 cases. These gastric lesions were enhanced by a 20% fish meal supplement, and edema and hemorrhage in the gastric mucosa were observed in 19 and 17 out of 20 animals, respectively. Although almost the same levels of viable bacteria were detected independent of the diet, edema and hemorrhage were seen in only 2 and 1 of 20 gerbils fed a diet containing 10% casein, instead of 10% fish meal, respectively. Neither edema nor hemorrhage was observed in 10% beef diet animals. These results suggest that fish meal contains factors which greatly enhance H. pylori‐induced gastritis in Mongolian gerbils. Since the incidences of gastritis and gastric cancer are very high throughout the world, it is very important to identify these gastritis‐enhancing factors.