Dose‐dependent promotion of rat forestomach carcinogenesis by combined treatment with sodium nitrite and ascorbic acid after initiation with N‐methyl‐N′‐nitro‐N‐nitrosoguanidine: Possible contribution of nitric oxide‐associated oxidative DNA damage

Abstract

Dose-dependent promotion effects of combined treatment with sodium nitrite (NaNO 2 ) and ascorbic acid (AsA) on gastric carcinogenesis were examined in rats pretreated with N-methyl-N′ ′ ′ ′-nitro-N-nitrosoguanidine (MNNG). Groups of 15 6-week-old F344 male rats were given 0.01% MNNG in their drinking water for 10 weeks to initiate carcinogenesis in the glandular stomach and a single intragastric administration of 100 mg/kg/ bodyweight of MNNG by stomach tube at week 9 to initiate carcinogenesis in the forestomach. From week 11, they received either drinking water containing 0.05, 0.1 or 0.2% NaNO 2 and a diet supplemented with 0.1 or 0.2% AsA in combination, each individual chemical alone or a basal diet until the end of week 42. In the forestomach, the incidence of hyperplasia was increased dose dependently by the treatment with NaNO 2 alone. Incidences of neoplastic lesions were dramatically increased by the combined treatment with NaNO 2 and AsA in a dosedependent manner, but AsA itself had no effect. In the glandular stomach, only toxicity and regenerative changes were increased by the high-dose combination. In a second short-term experiment conducted for sequential observation, necrosis and strong inflammation were found in the forestomach epithelium shortly after commencing combined treatment with 1.0% AsA and 0.2% NaNO 2 , followed by hyperplasia, whereas there were no obvious effects in the glandular stomach. In addition, after a 4 h treatment with 1.0% AsA and 0.2% NaNO 2 , a slight increase in the 8-hydroxy-deoxyguanosine levels in the forestomach epithelium was observed by high-performance liquid chromatography and an electrochemical detection system, albeit without statistical significance. In vitro, electron spin resonance demonstrated nitric oxide formation during incubation with NaNO 2 and AsA under acidic conditions. Thus, NaNO 2 was demonstrated to exert promoter action in the forestomach, with AsA acting as a strong copromoter through cytotoxicity and regenerative cell proliferation, possibly mediated by oxidative DNA damage, but the combined treatment with NaNO 2 and AsA had little influence on glandular stomach carcinogenesis. (Cancer Sci 2006; 97: 175-182) S odium nitrite is used widely as a food additive to preserve and tinge color-cured meat and fish. We intake nitrate from exogenous sources such as vegetables and water, and this is partly reduced to nitrite in vivo by microflora in the buccal cavity.(1-3) It has been shown that sodium nitrite is a precursor of N-nitroso compounds with strong genotoxic and carcinogenic potential, (4) and an increased incidence of tumors, such as forestomach papillomas and lymphoreticular tumors, has been found in rat carcinogenicity studies of NaNO 2 .(5,6) However, other studies failed to show any effects of nitrite administration on tumor incidence.(7-9) Previously, we reported that when NaNO 2 was administered simultaneously with phenolic antioxidants, such as catechol, 3-methoxycatechol, hydroquinone, tert-butylhydroquinone, gallic acid and pyrogallol...

Enhancement of Hepatocellular Proliferative Activity of Kojic Acid in Mice by a Simultaneous Administration of Ascorbic Acid

“…As several mechanisms of anti-carcinogenic effects of AA, anti-oxidant properties [13], the ability to react with nitrite as a prototype inhibitor of the nitrosation reaction [30], the regulatory role in transcription and translation [19,27,46] and cell-cycle arrest at the G 2 /M DNA damage checkpoint during oxidative stress [15] have been proposed. On the other hand, enhanced carcinogenic effects of AA have been described in several reports [12,20,36]. In the present study, the absolute and relative liver weights were significantly increased in the DEN+KA+AA group in comparison with the DEN alone group.…”

“…The anti-mutagenic, anti-clastogenic and anti-carcinogenic effects of AA [7,11,22,42] have been reported to be ascribed to several mechanisms, such as its anti-oxidant properties [13], the ability to react with nitrite as a prototype inhibitor of the nitrosation reaction [30], the regulatory role in transcription and translation [19,27,46] and cell-cycle arrest at the G 2 /M DNA damage checkpoint during oxidative stress [15]. On the other hand, in spite of the reports demonstrating that AA has anti-carcinogenic effects, it has been reported that AA enhanced the forestomach tumor-promoting activity of sodium nitrite in rats [36]. In addition, AA enhanced the rat urinary bladder carcinogenesis promotion activity of NaHCO 3 [20].…”

4‐Vinyl‐2,6‐dimethoxyphenol (canolol) suppresses oxidative stress and gastric carcinogenesis in Helicobacter pylori‐infected carcinogen‐treated Mongolian gerbils

“…13,34,35 Therefore, one of the underlying mechanisms is reduction of free radical scavenging oxidative damage. 36 In an in vitro system we could also show that canolol suppresses inflammation mediators (Fig. 5).…”

Elevated oxidative stress and DNA damage and repair levels in urinary bladder carcinomas associated with schistosomiasis

“…51 Dose-dependent promotion of rat forestomach carcinogenesis by combined treatment with sodium nitrite and ascorbic acid after initiation also showed a possible contribution of NOassociated oxidative DNA damage. 52 Schistosomal infection may also influence DNA methylation. It was shown that Schistosoma-associated urinary bladder tumors had more genes methylated than non-Schistosomal tumors, 53 and the extent of methylation in UCs was lower than in SCCs.…”