Effects of butylated hydroxyanisole, butylated hydroxytoluene, and NaCl on gastric carcinogenesis initiated with N-methyl-N'-nitro-N-nitrosoguanidine in F344 rats

Promoting activities of butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and NaCl and of combinations of these antioxidants with NaCl on gastric carcinogenesis initiated by N-methyl-N'-nitro-N-nitrosoguanidine [(MNNG) (CAS: 70-25-7; 1-methyl-3-nitro-1-nitrosoguanidine] were investigated in male inbred F344 rats. Animals, 6-week old, were given an intragastric administration of MNNG at 150 mg/kg body weight by gastric tube and 1 week later were placed on a diet containing BHA (0.5%), BHT (1.0%), NaCl (5.0%), BHA (0.5%) plus NaCl (5%), or BHT (1.0%) plus NaCl (5.0%) for 51 weeks. Control rats received no further treatment after MNNG administration. A single intragastric application of MNNG to rats induced multiple epithelial tumors of the forestomach and a few epithelial tumors of the glandular stomach after 52 weeks. Squamous cell carcinomas of the forestomach were seen in 2 of 18 effective rats (11.1%) in the control groups, and the incidences in the groups receiving the subsequent treatment were 45.0% with BHA, 15.8% with BHT, 30% with NaCl, 70% with BHA plus NaCl, and 52.9% with BHT plus NaCl. Differences in the incidences of squamous cell carcinoma between the controls and groups given BHA, BHA plus NaCl, and BHT plus NaCl were statistically significant. NaCl given alone after MNNG administration also significantly increased the incidence of papillomas in the forestomach. Incidences of glandular stomach tumors, adenomas and carcinomas were not affected by any of the subsequent treatments. No tumors of the stomach developed in the groups given BHA, BHT, and NaCl without MNNG pretreatment. Thus the present experiment revealed that BHA and NaCl but not BHT exert promoting activity on MNNG-induced forestomach carcinogenesis in rats and that, when BHA and BHT were given with NaCl, promotion was more marked, suggesting a synergistic effect on tumor promotion.     

Inhibition by D-limonene of gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine in Wistar rats.

The effect of prolonged oral administration of D-limonene on gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and on the labeling and apoptotic indices of gastric cancers were investigated in Wistar rats. After 25 weeks of the carcinogen treatment, rats were given chow pellets containing 1% or 2% limonene. In week 52, long-term oral administration of 2%, but not 1%, limonene significantly decreased the incidence of gastric cancers. Limonene also significantly decreased the labeling index and significantly increased the apoptotic index of gastric cancers. No K-ras mutations were detected in gastric cancers induced by MNNG in either group. These findings indicate that limonene inhibits the development of gastric cancers through increased apoptosis and decreased DNA synthesis of gastric cancers, but not through ras oncoprotein plasma membrane association.     

Inhibition by amiloride of gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine in Wistar rats.

The effects of amiloride on the incidence and histological types of gastric cancers in Wistar rats induced by N-methyl-N''-nitro-N-nitrosoguanidine (MNNG), and on the labelling index and proliferative fraction of gastric mucosa were investigated. After oral treatment with MNNG for 25 weeks, rats received s.c. injections of amiloride (0.25 mg kg-1 or 5.0 mg kg-1 body weight) in depot form every other day until the end of the experiment. Prolonged administration of 5.0 mg kg-1, but not 2.5 mg kg-1 of amiloride significantly decreased the incidence of gastric cancers in Week 52. However, it did not influence the histological features of the gastric cancers. It also significantly decreased the labelling index and proliferative fraction of the antral mucosa. These findings indicate that amiloride inhibits the development of gastric cancers, and that its effect may be related to its effect in decreasing cell proliferation of the antral mucosa.     

Promotion by ethanol of gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine in Wistar rats

The effects of ethanol (EtOH) on the incidence and histology of gastric cancers induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) were investigated in Wistar rats. The animals received alternate-day i.p. injections of 2.5 ml kg-1 body weight of 20% EtOH in 0.9% NaCl solution after 20 weeks of oral treatment with MNNG. Prolonged administration of EtOH resulted in a significant increase in the incidence and number of gastric cancers of the glandular stomach in week 52. However, it had no influence on the histological types of the gastric cancers. Furthermore, it caused a significant increase in the labelling index of the epithelial cells of the antrum in week 52. These findings indicate that EtOH promotes gastric carcinogenesis, and that this effect may be related to its effect in increasing proliferation of the antral epithelial cells.     

Enhancement by vaso-active intestinal peptide of gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine in rats.

The effects of vaso-active intestinal peptide (VIP) on gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) were investigated in Wistar rats given VIP every other day for 27 weeks after oral administration of MNNG for 25 weeks. In week 52, administration of VIP caused a significant increase in the incidence of gastric cancers, but did not influence their histological appearance. VIP significantly increased the labeling indices of the antral mucosa. Our findings indicate that VIP enhances gastric carcinogenesis, and that this effect may be related to its effect in increasing cell proliferation of the antral epithelial cells.     

Inhibition by transforming growth factor (34-43)-alpha, a TGF-alpha antagonist, of gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine in Wistar rats.

The effect of prolonged administration of transforming growth factor (34-43)-alpha, an antagonist of TGF-alpha, on gastric carcinogenesis induced by N-methyl-N''-nitro-N-nitrosoguanidine (MNNG) and on the labelling and apoptotic indices and TGF-alpha immunoreactivity of gastric mucosa and gastric cancers was examined in Wistar rats. The rats received intraperitoneal injections of 10 or 20 microg kg(-1) body weight of TGF(34-43)-alpha every other day after oral treatment with MNNG for 25 weeks. Long-term administration of TGF(34-43)-alpha at both doses significantly reduced the incidence of gastric cancers at the end of the experiment in week 52. However, TGF(34-43)-alpha had no significant effect on the number, histological type or depth of involvement of gastric cancers. Administration of TGF(34-43)-alpha also significantly decreased the bromodeoxyuridine labelling index and TGF-alpha immunoreactivity, and significantly increased the apoptotic index of antral mucosa and gastric cancers. These findings indicate that TGF(34-43)-alpha inhibits gastric carcinogenesis, and that its effects are mediated through decreased cell proliferation and TGF-alpha immunoreactivity and increased apoptosis induction in the gastric cancers.     

Enhancement by sulpiride of the inhibitory effects of cysteamine on gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine in Wistar rats

The effects of sulpiride on cysteamine inhibition of gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and on the BUdR labelling index of gastric mucosa were investigated in inbred Wistar rats. After 25 weeks of oral treatment with MNNG, rats received one of the following alternate-day injections: cysteamine (2 doses), cysteamine (2 doses) plus sulpiride or sulpiride. At week 52, prolonged administration of cysteamine significantly reduced the incidence of adenocarcinomas of the glandular stomach. Cysteamine at low dose had no effect on the incidence of gastric cancers, but a combination of low-dose cysteamine and sulpiride caused a significantly greater reduction in the incidence of gastric cancers. Administration of sulpiride alone had no influence on gastric carcinogenesis. The labelling index of the antral mucosa was significantly lower in rats treated with high but not low doses of cysteamine. However, a combination of low-dose cysteamine and sulpiride significantly decreased the labelling index of the antral mucosa. Our findings indicate that cysteamine suppressed gastric carcinogenesis and that sulpiride enhanced this inhibition. Because sulpiride is a dopamine antagonist, these findings also indicate that dopamine may play an important role in cysteamine inhibition of gastric carcinogenesis.     

Effects of four antioxidants on N-methyl-N'-nitro-N-nitrosoguanidine initiated gastric tumor development in rats

The effects of antioxidant administration during the post initiation phase of gastric tumor development were investigated in male Wistar rats treated with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Animals (20/group) were given MNNG in the drinking water (100 mg/l) for 8 weeks, and for the duration of this treatment were also fed on diet supplemented with 10% sodium chloride. Thereafter, they were divided into 6 groups and were maintained on diet containing either 2% butylated hydroxyanisole (BHA), 1% BHA, 1% butylated hydroxytoluene (BHT), 1% ethoxyquin (EQ) or 1% DL-alpha-tocopherol (alpha-TP) for 32 weeks. A carcinogen control group was fed the basal diet without antioxidant supplementation. The experiment was terminated 40 weeks after the beginning of administration of MNNG and development of gastroduodenal tumors was determined histopathologically. EQ significantly increased the incidence of tumors in the glandular stomach. No modification of tumor development in this region of the organ were observed with 2% BHA, 1% BHA, 1% BHT or 1% alpha-TP, although both 2% BHA and 1% BHA induced and/or promoted tumor development in the forestomach. In addition, nephrocalcinosis was identified only in the kidneys of rats given EQ after MNNG treatment.     

Enhancement by tyrosine methyl ester of gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine in Wistar rats

The effect of tyrosine methyl ester (TME) on the incidence, number, and histological types of gastric cancers induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was investigated in male Wistar rats. Rats were subcutaneously given TME, 512 mg/kg body weight, every other day after 20 weeks of oral treatment with MNNG. Prolonged alternate-day administration of TME caused a significant increase in the incidence and number of gastric cancers of the glandular stomach by week 52. However, it did not affect the histology of the cancers. TME also caused a significant increase in tissue norepinephrine concentrations in the antral portion of the gastric wall and in the labelling indices of the antral epithelial cells. However, TME had no influence on the serum gastrin level and antral pH. These findings indicate that TME enhances gastric carcinogenesis, and this may be related to its effects on increasing norepinephrine levels in the gastric wall and stimulating proliferation of the antral epithelial cells.     

Low-protein diet promotes sodium chloride-enhanced gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine in Wistar rats.

Sodium chloride (NaCl) initiates and promotes experimental carcinogenesis in rats. We recently found that a high-protein diet attenuates NaCl-enhanced gastric carcinogenesis in Wistar rats. To investigate the effect of a purified low-protein diet on NaCl-enhanced gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in Wistar rats, rats were fed a purified diet with an equalized caloric content containing 1% or 2% NaCl and 25% casein (normal-protein diet) or 10% casein (low-protein diet) after oral treatment with MNNG for 25 weeks. In week 52, neither 1% nor 2% NaCl had a significant effect on gastric carcinogenesis in rats fed a normal-protein diet. However, oral administration of 2%, but not 1%, NaCl significantly increased the incidence of gastric cancers in rats fed a low-protein diet. Oral administration of 2% NaCl also significantly increased the bromodeoxyuridine (BrdU)-labeling index and the ornithine decarboxylase (ODC) activity and decreased apoptosis of gastric cancers in rats fed a low-protein diet. However, 2% NaCl had no significant effect on these three parameters in rats fed a normal-protein diet. These findings indicate that a low-protein diet enhances the effect of NaCl in gastric carcinogenesis and that this enhancement may be mediated by increased cell proliferation and reduced apoptosis of gastric cancers.     

Promotion by Nialamide of Gastric Carcinogenesis Induced by N-Methyl-N'-nitro-N-nitrosoguanidine in Wistar Rats

The effects of nialamide, a monoamine oxidase inhibitor, on the incidence, number, and histology of gastric cancers induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) were investigated in male Wistar rats. Rats were given subcutaneously 50 mg/kg body weight of nialamide in depot form every other day after 25 weeks of oral treatment with MNNG. Prolonged alternate-day administration of nialamide caused a significant increase in the incidence and number of gastric cancers of the glandular stomach in week 52, However, it did not affect the histology of the cancers. Nialamide also caused a significant increase in tissue norepinephrine concentrations in the gastric wall and in the labeling indices of the gastric mucosae. However, nialamide had no influence on serum gastrin levels in the fasting state and after re-feeding. These findings indicate that nialamide promotes gastric carcinogenesis and that this may be related to its effects in increasing norepinephrine in the gastric wall and stimulating proliferation of gastric epithelial cells.     

Promotion by nialamide of gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine in Wistar rats

The effects of nialamide, a monoamine oxidase inhibitor, on the incidence, number, and histology of gastric cancers induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) were investigated in male Wistar rats. Rats were given subcutaneously 50 mg/kg body weight of nialamide in depot form every other day after 25 weeks of oral treatment with MNNG. Prolonged alternate-day administration of nialamide caused a significant increase in the incidence and number of gastric cancers of the glandular stomach in week 52. However, it did not affect the histology of the cancers. Nialamide also caused a significant increase in tissue norepinephrine concentrations in the gastric wall and in the labeling indices of the gastric mucosae. However, nialamide had no influence on serum gastrin levels in the fasting state and after re-feeding. These findings indicate that nialamide promotes gastric carcinogenesis and that this may be related to its effects in increasing norepinephrine in the gastric wall and stimulating proliferation of gastric epithelial cells.     

Inhibition by rat C-erbB-2/neu antisense oligonucleotide of gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine in Wistar rats.

The effect of prolonged administration of a rat C-erbB-2/neu (C-erbB-2) antisense oligonucleotide on gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and on the labeling and apoptotic indices of gastric cancer was examined in Wistar rats After oral treatment with MNNG for 25 weeks, the rats received intraperitoneal injections of a C-erbB-2 antisense-liposome complex or a sense-liposome complex at a dose of 50 microgram oligonucleotide/kg body weight every other day until the end of the experiment in week 52. In week 52, the incidence of gastric cancers was significantly lover in rats treated with the C-erbB-2 antisense oligonucleotide than in rats treated with the sense oligonucleotide. Administration of the C-erbB-2 antisense oligonucleotide also significantly decreased the bromodeoxyuridine-labeling index and significantly increased the apoptotic index of gastric cancers. The mean cellular fluorescence of gastric antral cells in MNNG-treated rats was positively correlated with the dose of FITC-labeled C-erbB-2 antisense oligonucleotide. Our findings indicate that the antisense oligonucleotide inhibits gastric carcinogenesis through decreased cell proliferation and increased apoptosis induction and suggest that antisense strategies may provide new treatment for gastric cancer.     

Enhancement by aminoguanidine of gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine in Wistar rats

The effects of prolonged administration of aminoguanidine on gastric carcinogenesis induced by N-methyl-N-nitro-N-nitrosoguanidine (MNNG), the ornithine decarboxylase activity of the gastric wall, and the labeling index of the gastric mucosa were investigated in inbred Wistar rats. The rats received 12.5 or 25.0 mg/kg body weight of aminoguanidine s.c. every other day after oral MNNG treatment for 25 weeks. Prolonged administration of aminoguanidine at 25.0 mg/kg body weight, but not at 12.5 mg/kg body weight, significantly increased the incidence of gastric cancers in experimental week 52. However, it did not influence the histologic types of gastric cancers. Aminoguanidine at 25.0 mg/kg body weight also significantly increased the ornithine decarboxylase activity of the antral portion of the gastric wall and the labeling index of the antral epithelial cells. These findings indicate that aminoguanidine enhances gastric carcinogenesis and suggest that its effect may be related to increased proliferation of antral epithelial cells.     

Enhancement by thyroxine of gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine in Wistar rats.

The affects of L-thyroxine (T4) on the incidence and histology of gastric cancers induced by N-methyl-N''-nitro-N-nitrosoguanidine (MNNG), and on the labelling index of gastric mucosal epithelial cells were investigated in Wistar rats. After oral treatment with MNNG for 25 weeks, the rats received s.c. injections of T4 (0.2 microgram kg-1) in depot form every other day until the end of the experiment in Week 52. This long-term treatment with T4 significantly increased the incidence of gastric cancers in Week 52. However, it did not influence the histological type of the gastric cancers. It also caused significant increases in the labelling indices of the fundic and antral epithelial cells. These findings indicate that T4 enhances the development of gastric cancers, and that its effect may be related to its effect in increasing proliferation of gastric epithelial cells.     

Effect of ornithine decarboxylase inhibitor on tetragastrin treatment of gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine in Wistar rats

The effects of combined administration of tetragastrin and the ornithine decarboxylase inhibitor 1,3-diaminopropane (DAP) on the incidence and number of gastric cancers induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), and the BUdR labelling indices of the fundic and antral mucosae, were investigated in inbred Wistar rats. Rats were given drinking water containing 2.5 g/l of DAP ad libitum and received alternate-day injections of 1 mg/kg body weight of tetragastrin in depot form after 25 weeks of oral treatment with MNNG. At week 52, prolonged administration of tetragastrin alone resulted in a significant reduction in the incidence and number of gastric cancers and a significant increase or decrease in the labelling indices of the fundic and antral mucosae, respectively. Concomitant administration of tetragastrin and DAP had no effect on the inhibition by tetragastrin of gastric carcinogenesis. With this treatment, the labelling index was significantly reduced in the fundic mucosa but not in the antral mucosa. These results suggest that ODC inhibitor does not attenuate tetragastrin inhibition of gastric carcinogenesis, and that anti-trophic action of tetragastrin on antral mucosa may be related to tetragastrin inhibition of gastric carcinogenesis.     

Enhancing Effects of Calcium-deficient Diet on Gastric Carcinogenesis by N-Methyl-N'-nitro-N-nitrosoguanidine in Wistar Rats

The effects of ad libitum feeding of calcium-deficient diet on the incidence, number and histological types of gastric cancers induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) were investigated in male Wistar rats. Rats were fed standard pellet diet containing 0.5% (normal-calcium diet) or 0.01% calcium (calcium-deficient diet) after oral treatment with MNNG for 25 weeks. Oral administration of the calcium-deficient diet resulted in a significant increase in the incidence, hut not the number, of gastric cancers in experimental Week 52. However, it did not affect the histological types of cancer. The calcium-deficient diet also caused a significant increase in tissue norepinephrine concentration of the antral portion of the gastric wall and in the labeling index of the antral epithelial cells. These findings indicate that the calcium-deficient diet enhanced gastric carcinogenesis and suggest that its effect may be related to increase in norepinephrine in the gastric wall and consequent stimulation of proliferation of antral epithelial cells.     

Attenuating effect of the monoamine oxidase inhibitor furazolidone on the anti-carcinogenetic effect of cysteamine on gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine in Wistar rats

The effect of furazolidone on inhibition by cysteamine of gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was investigated in inbred Wistar rats. After oral treatment with MNNG for 25 weeks, rats received cysteamine, furazolidone, or both compounds. In week 52, rats treated with cysteamine had a significantly decreased incidence of gastric cancers. Concomitant treatment with furazolidone significantly attenuated the inhibitory effect of cysteamine on gastric carcinogenesis. Administration of furazolidone alone significantly increased the number, but not the incidence, of gastric cancers. The norepinephrine concentration of the antral portion of the gastric wall and the labelling index of the antral mucosa were significantly reduced in rats treated with cysteamine, and significantly higher in rats treated with both compounds than in those treated with cysteamine alone. These findings indicate that the cysteamine-induced inhibition of gastric carcinogenesis is mediated by catecholamines.     

Protection by muscimol against gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine in spontaneously hypertensive rats.

The effects of prolonged administration of the gamma-aminobutyric acid receptor agonist muscimol on enhanced induction of gastric carcinogenesis by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in spontaneously hypertensive rats (SHR), and on the norepinephrine concentration in the gastric wall and the labeling index of gastric mucosa were investigated. SHR and normotensive Wistar Kyoto (WKY) rats as controls were given a solution of MNNG (25 micrograms/ml) for 25 weeks and then i.p. injections of 0.5 mg/kg body weight of muscimol every other day. In control WKY rats, gastric cancers were found in 1 (7%) of 14 rats examined at week 52. In SHR treated with NaCl solution only, the incidence of gastric cancers was significantly increased to 50% compared with that in control WKY rats. However, treatment of SHR with muscimol significantly increased its incidence to 12% compared with the value in SHR treated with NaCl solution only. The norepinephrine concentration in the gastric wall and the labeling index of the gastric mucosa were significantly greater in SHR than in WKY rats. Prolonged administration of muscimol to SHR significantly reduced the norepinephrine concentration in the antral portion of the gastric wall or the labeling index of the antral epithelial cells. These findings indicate that long-term treatment of SHR with muscimol attenuated the enhancement of gastric carcinogenesis in SHR.     

Promotion by bombesin of gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine in Wistar rats

The effects of bombesin on the incidence, number, histological type, and depth of involvement of gastric cancers induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) were investigated in male Wistar rats. Rats received alternate-day s.c. administration of 20 or 40 micrograms/kg body weight of bombesin in depot form after p.o. treatment with the carcinogen for 25 weeks. Prolonged administration of bombesin at 40 micrograms/kg led to a significant increase in the incidence and number per rat of gastric cancers of the glandular stomach at Week 52. In rats that had received alternate-day injections of 20 micrograms/kg of bombesin, the number of gastric cancers per rat, but not the incidence of cancer, was significantly more than in untreated rats. However, bombesin at both dosages did not affect the histological appearance of the lesions or their depth of involvement. At Weeks 30 and 52, norepinephrine concentrations in the fundic and antral portion of the gastric walls and labeling indices in the antral and fundic mucosae were significantly higher in rats treated with bombesin at both dosages than in untreated rats. These findings indicate that bombesin enhances gastric carcinogenesis after administration of N-methyl-N'-nitro-N-nitrosoguanidine is stopped and that this effect may be related to its effects in increasing tissue norepinephrine concentrations in the stomach wall and increasing cell proliferation in the gastric mucosa.