Nobuyuki Ito

Gastric and intestinal phenotypic expression of human stomach cancers as revealed by pepsinogen immunohistochemistry and mucin histochemistry

Gastric and intestinal phenotypic expression in 223 surgically obtained primary gastric cancers and their histogenetic relationship to intestinal metaplasia in the surrounding gastric mucosa were studied by mucin histochemistry and pepsinogen (Pg) immunohistochemistry. Histochemical differentiation of mucins (paradoxical concanavalin A, the galactose oxidase‐Schiff sequence and sialidase galactose oxidase Schiff) and immunohisto chemical staining of Pgs I and II, allowed differentiation of gastric cancer cells from different histological categories into gastric elements including mucous neck cells, pyloric gland cells and surface mucous cells or intestinal elements including goblet cell and intestinal absorptive cell types. Of 122 papillary and tubular adenocarcinomas, 33 (27.1%) consisted mainly of gastric type cells and 42 (34.4%) predominantly of intestinal type cells. The remainder (38.5%) consisted of mixtures of gastric‐ and intestinal‐type cells. Of 101 poorly differentiated adenocarcinomas, signet ring cell carcinomas and mucinous adenocarcinomas, 59 (58.4%) consisted mainly of gastric‐type cells and 20 (19.8%) mainly of intestinal‐type cells. Seven out of 35 papillary and tubular adenocarcinomas consisting mainly of gastric type cancer cells were surrounded by mucosa with intestinal metaplasia. Conversely, 10 out of 40 papillary and tubular adenocarcinomas consisting mainly of intestinal‐type cancer cells were observed in non metaplastic gastric mucosa. Thus no relationship as regards intestinal phenotypic expression was found between gastric cancers and surrounding gastric mucosa.

Stomach carcinogenicity of caffeic acid, sesamol and catechol in rats and mice

The carcinogenic potential of caffeic acid, sesamol and catechol was examined in male and female F344 rats and B6C3F1 mice, groups of 30 animals being treated with diets containing 2% caffeic acid, 2% sesamol or 0.8% catechol for 104 weeks (rats) or 96 weeks (mice). Histological examination revealed that caffeic acid induced forestomach squamous cell carcinoma in 57% (P<0.001 vs. controls) and 50% (P<0.001) of male and female rats, respectively, whereas sesamol was associated with squamous cell carcinoma at incidences of 31% (P<0.001) in male rats, and 38% (P<0.001) and 17% (P<0.05) in male and female mice, respectively. Catechol induced glandular stomach adenocarcinomas in 54% (P<0.001) and 43% (P<0.001) of male and female rats, respectively. The results thus clearly demonstrated that all three antioxidants are carcinogenic in rodent stomach epithelia.

Cellular differentiation and histogenesis of rat glandular stomach cancers.

The gastric and intestinal phenotypic expressions of tumor cells in 18 adenomatous hyperplasias, 33 well‐differentiated adenocarcinomas, and 16 undifferentiated adenocarcinomas (4 poorly differentiated adenocarcinomas, 10 signet‐ring cell carcinomas and 2 mucinous adenocarcinomas) induced by N‐methyl‐N’‐nitro‐N‐nitrosoguanidine or 4‐nitroquinoline‐I‐oxide in the rat glandular stomach were studied by histochemical stainings for mucin and immunohistochemical staining for pepsinogen isozyme 1 (Pg 1). By histochemical staining for mucin [by the paradoxical concanavalin A method, the modified method with labeled peanut lectin, the galactose oxidase‐Schiff (GOS) reaction, and the sialidase‐GOS reaction] and immunohistochemical staining of Pg 1, gastric cancer cells of each histological group could be clearly classified into a gastric type, including mucous neck cell pyloric gland cell, and surface mucous cell subtypes, and an intestinal type, including goblet‐cell, and intestinal absorptive cell subtypes. All tumors examined in this work consisted mainly of gastric‐type cells but intestinal‐type tumor cells were occasionally found among the gastric‐type tumor cells. The incidences of intestinal‐type cells in adenomatous hyperplasias (11.1%) and small well‐differentiated adenocarcinomas (28.6%) were significantly less (P<0.05) than that in large well‐differentiated adenocarcinomas (68.4%). The incidence of intestinal‐type cells in small undifferentiated adenocarcinomas (25.0%) was also less than that in large ones (58.3%). The present results suggest the occurrence of change of phenotypic expression of tumor cells from the gastric type to the intestinal type during growth of tumors.

Inhibitory Effects of Antioxidants on N‐Bis(2‐hydroxypropyl)nitrosamine‐induced Lung Carcinogenesis in Rats

Potential second‐stage modifying effects of 8 antioxidants on lung tumorigenesis initiated by N‐bis(2‐hydroxypropyl)nitrosamine (DHPN) were examined in male F344 rats. After an initial 2‐week treatment with DHPN (0.1% in drinking water), rats were administered one of the antioxidants supplemented in the diet for 30 weeks. Although the incidences of lung adenomas were not affected, those of carcinomas were lowered by 2% butylated hydroxyanisole (BHA, 2 rats/20 rats), 1% butylated hydroxytoluene (BHT, 1/20), 0.8% ethoxyquin (EQ, 3/20) and 1%α‐tocopherol (α‐TP, 2/20) treatments as compared to the control level (9/20), while 5% sodium l‐ascorbate (SA), 0.8% catechol (CC), 0.8% resorcinol (RN), and 0.8% hydroquinone (HQ) did not exert any significant effect on incidence. Quantitative analysis of adenomas and carcinomas (numbers and areas of lesions per unit area of lung section) revealed obvious inhibitory effects of SA, CC, and RN as well as BHA, BHT, EQ, and α‐TP. Among the antioxidants, BHT exerted the strongest inhibitory activity. In contrast, DHPN‐induced thyroid tumorigenesis was significantly enhanced by BHT (14/20) and EQ (20/20) treatments (control=5/20). Thus the antioxidants showed opposite effects on lung and thyroid carcinogenesis in the rat.

Promoting action of prolactin released from a grafted transplantable pituitary tumor (MtT/F84) on rat prostate carcinogenesis

The potential modifying effects of high prolactinemia on rat prostate carcinogenesis was investigated. Male F344 rats were treated at 5 times of 5-week intervals with s.c. injections of 3,2-dimethyl-4-aminobiphenyl (DMAB), each injection following 3 weeks pretreatment with dietary ethinyl estradiol. After completion of the carcinogen administration stage, rats received multiple s.c. transplantations of a prolactin producing transplantable pituitary tumor, MtT/F84 until sacrifice at week 51. The effects of additional or single treatment with bromocriptine, a prolactin suppressing agent, were also investigated. The body, liver and kidney but prostate weights were significantly increased in the groups given MtT/F84. Although the development of prostate carcinomas was not affected by the observed hyperprolactinemia, the incidences of atypical hyperplasia of both ventral and lateral prostate were significantly enhanced. The findings thus indicate that prolactin may have promoting potential for prostate carcinogenesis.

Structure-Activity Relations in Promotion of Rat Urinary Bladder Carcinogenesis by Phenolic Antioxidants

The urinary bladder tumor‐promoting potentials of the phenolic antioxidants, 2‐tert‐butyl‐4‐methyl‐phenol (TBMP), propylparaben, catechol, resorcinol and hydroquinone, which are structurally related to butylated hydroxyanisole (BHA), were investigated in 170 male F344 rats. The animals were initially given 0.05% N‐butyl‐N‐(4‐hydroxybutyl)nitrosamine (BBN) as an initiator in their drinking water for 4 weeks. Three days later, groups of 20 rats received diet containing 1.0% TBMP, 3% propylparaben, 0.8% catechol, 0.8% resorcinol, 0.8% hydroquinone or basal diet alone until the end of week 36. Significant increases in the incidences and average numbers of the putative preneoplastic lesions, papillary or nodular (PN) hyperplasia, and papillomas of the urinary bladder were only observed in the group given TBMP after BBN. Development of these lesions was not enhanced by diet containing the other test compounds and no induction was associated with any of the test chemicals alone. The results thus clearly showed that TBMP, which most closely resembles BHA, promoted urinary bladder carcinogenesis. The similar effects of TBMP and BHA on urinary bladder carcinogenesis suggest a direct link between chemical structure and biological potency.

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.

Carcinogenicity of Captafol in F344/DuCrj Rats

Captafol was administered at dietary levels of 0 (control), 750 and 1,500 parts per million (ppm) to groups of 50 male and 50 female F344/DuCrj rats for 104 weeks, and then all animals were maintained without captafol for a further 8 weeks, and killed in week 113. Renal cell carcinoma was found in eight of 50 male rats treated with 1,500 ppm and in one of 50 male rats treated with 750 ppm of captafol. The incidences of renal adenomas, including micro‐adenomas, and basophilic altered cell tubules were significantly higher in both sexes treated with captafol than in controls, and the increases were apparently dose‐dependent except that of adenomas in females. The incidences of neoplastic and preneoplastic lesions of the kidney in captafol‐treated animals were higher in males than in females. Captafol also induced hepatocellular carcinomas in four of 50 female rats in the 1,500 ppm group. The incidences of hyperplastic (neoplastic) nodules and foci of cellular alterations in the liver were also significantly increased in both sexes treated with captafol, the increases being dose‐dependent. In conclusion, captafol induced renal cell carcinomas in male rats and hepatocellular carcinomas in female rats.

Inhibition of rat hepatic glutathione S-transferase placental form positive foci development by concomitant administration of antioxidants to carcinogen-treated rats

Inhibition potential of concomitant butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), catechol or sodium ascorbate (Na-AsA) administration on development of diethylnitrosamine (DEN) initiated glutathione S-transferase placental form (GST-P) positive foci in rat liver under the influence of 2-acetylaminofluorene (2-AAF) or 3-methyl-4-dimethylaminoazobenzene (3-Me-DAB) plus partial hepatectomy (PH) was investigated. Whereas BHA, BHT and catechol exerted marked inhibitory effects, Na-AsA lacked any modifying potential. The compounds that demonstrated inhibition also induced GST-P in the hepatic periportal areas, suggesting that development of GST-P positive foci is negatively influenced by extra-focal increase in this enzyme form observed with BHA, BHT or catechol.

Carcinogenicity and Modification of Carcinogenic Response by Antioxidants

Synthetic or naturally occurring antioxidants such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), propyl gallate sodium L-ascorbate, and α-tocopherol have been widely used as food additives in various processed foods to prevent auto-oxidation of fatty acids. In addition, many naturally occurring antioxidants are present at appreciable levels in plants. In the light of studies which showed that antioxidants lack mutagenic activity and indeed even inhibit mutagenesis induced by carcinogens (13), they have been considered safe for use as food additives. In fact, since they have further been observed to inhibit chemical carcinogenesis in various organs when administered to rats concurrently with carcinogens (5,6,17), they have been considered as anticarcinogenic agents. However, BHA was recently found to be carcinogenic in the rat forestomach (9), and when antioxidants were given to rats after carcinogen exposure, they enhanced carcinogenesis in some organs while exerting an inhibitory influence in others (5–8). Therefore, antioxidants have both hazardous and nonhazardous effects in rodents, and by analogy also possibly in man.