Formation of N-(Nitrosomethyl)urea in stomachs of experimental pigs and human volunteers given fish sauce in vivo

Bone marrow-derived cells may not be the original cells for carcinogen-induced mouse gastrointestinal carcinomas

AIM

It has been reported that bone marrow-derived cells (BMDC) can be original cells of mouse gastric cancers induced by Helicobacter felis (H. felis) infection. However, it is unknown whether BMDCs are also the original cells of mouse gastrointestinal cancers induced by gastric carcinogens N-nitroso-N-methylurea (NMU) and H. felis infection.

METHODS

C57BL/6 recipient mice were initially irradiated with 10Gy X-ray, reconstituted with bone marrow cells from the C57BL/6-Tg (CAG-EGFP) donor mice to label BMDCs with green fluorescence protein (GFP). After 4 weeks of recovery, the bone marrow-transplanted mice were given NMU in drinking water (240 ppm) and subsequently infected with H. felis by gavage. Eighty weeks later, all mice were euthanized for pathological examination. The BMDCs expressing GFP were detected in tissues using direct GFP fluorescence confocal microscopy analysis and immunohistochemistry staining (IHC) assays.

RESULTS

Neoplastic lesions were induced by NMU treatment and/or H. felis infection at the antrum of the glandular stomach and small intestine. In the direct GFP fluorescence confocal assay, GFP(+) epithelial cell cluster or glands were not observed in these gastrointestinal tumors, however, most GFP(+) BMDCs sporadically located in the tumor stromal tissues. Some of these GFP(+) stromal BMDCs co-expressed the hematopoietic marker CD45 or myofibroblasts markers αSMA and SRF. In the indirect GFP IHC assay, similar results were observed among 11 gastric intraepithelial neoplasia lesions and 2 small intestine tumors.

CONCLUSION

These results demonstrated that BMDCs might not be the source of gastrointestinal tumor cells induced by NMU and/or H. felis infection.

Molecular characterization of cancer reveals interactions between ionizing radiation and chemicals on rat mammary carcinogenesis

Although various mechanisms have been inferred for combinatorial actions of multiple carcinogens, these mechanisms have not been well demonstrated in experimental carcinogenesis models. We evaluated mammary carcinogenesis initiated by combined exposure to various doses of radiation and chemical carcinogens. Female rats at 7 weeks of age were γ-irradiated (0.2-2 Gy) and/or exposed to 1-methyl-1-nitrosourea (MNU) (20 or 40 mg/kg, single intraperitoneal injection) or 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) (40 mg/kg/day by gavage for 10 days) and were observed until 50 weeks of age. The incidence of mammary carcinoma increased steadily as a function of radiation dose in the absence of chemicals; mathematical analysis supported an additive increase when radiation was combined with a chemical carcinogen, irrespective of the chemical species and its dose. Hras mutations were characteristic of carcinomas that developed after chemical carcinogen treatments and were overrepresented in carcinomas induced by the combination of radiation and MNU (but not PhIP), indicating an interaction of radiation and MNU at the level of initiation. The expression profiles of seven classifier genes, previously shown to distinguish two classes of rat mammary carcinomas, categorized almost all examined carcinomas that developed after individual or combined treatments with radiation (1 Gy) and chemicals as belonging to a single class; more comprehensive screening using microarrays and a separate test sample set failed to identify differences in gene expression profiles among these carcinomas. These results suggest that a complex, multilevel interaction underlies the combinatorial action of radiation and chemical carcinogens in the experimental model.

Nucleosomes correlate with in vivo progression pattern of de novo methylation of p16 CpG islands in human gastric carcinogenesis

BACKGROUND

The exact relationship between nucleosome positioning and methylation of CpG islands in human pathogenesis is unknown.

METHODOLOGY/PRINCIPAL FINDINGS

In the present study, we characterized the nucleosome position within the p16 CpG island and established a seeding methylation-specific PCR (sMSP) assay based on bisulfite modification to enrich the p16 alleles containing methylated-CpG at the methylation "seeding" sites within its intron-1 in gastric carcinogenesis. The sMSP-positive rate in primary gastric carcinoma (GC) samples (36/40) was significantly higher than that observed in gastritis (19/45) or normal samples (7/13) (P<0.01). Extensive clone sequencing of these sMSP products showed that the density of methylated-CpGs in p16 CpG islands increased gradually along with the severity of pathological changes in gastric tissues. In gastritis lesions the methylation was frequently observed in the region corresponding to the exon-1 coding-nucleosome and the 5'UTR-nucleosome; the methylation was further extended to the region corresponding to the promoter-nucleosome in GC samples. Only few methylated-CpG sites were randomly detected within p16 CpG islands in normal tissues. The significantly inversed relationship between the p16 exon-1 methylation and its transcription was observed in GC samples. An exact p16 promoter-specific 83 bp-MSP assay confirms the result of sMSP (33/55 vs. 1/6, P<0.01). In addition, p16 methylation in chronic gastritis lesions significantly correlated with H. pylori infection; however, such correlation was not observed in GC specimens.

CONCLUSIONS/SIGNIFICANCE

It was determined that de novo methylation was initiated in the coding region of p16 exon-1 in gastritis, then progressed to its 5'UTR, and ultimately to the proximal promoter in GCs. Nucleosomes may function as the basic extension/progression unit of de novo methylation of p16 CpG islands in vivo.

RNAi technology and lentiviral delivery as a powerful tool to suppress Tpr-Met-mediated tumorigenesis

Tpr-Met, the oncogenic counterpart of the Met receptor, has been detected in gastric cancers, as well as in precursor lesions and in the adjacent normal gastric mucosa. This has prompted the suggestion that Tpr-Met may predispose to the development of gastric tumors. Given the sequence specificity of RNA interference, oncogenes activated by point mutation or rearrangements can be targeted while spearing the product of the wild-type allele. In this work, we report specific suppression of Tpr-Met expression and inhibition of Tpr-Met-mediated transformation and tumorigenesis by means of a short interfering RNA (siRNA) directed toward the Tpr-Met junction (anti-TM2). When delivered by a lentiviral vector, anti-TM2 siRNA was effective also in mouse embryonal fibroblasts or epithelial cells expressing high levels of Tpr-Met. Our results suggest that lentiviral-mediated delivery of anti-TM2 siRNA may be developed into a powerful tool to treat Tpr-Met-positive cancers.

Food groups and risk of esophageal cancer in Chaoshan region of China: a high-risk area of esophageal cancer

The current study was designed to investigate the role of common foods in the etiology of esophageal cancer in the Chaoshan region of China. A large case-control study was conducted to investigate 1248 patients with squamous cell carcinoma of the esophagus and 1248 controls matched by sex, age, and hospitals. After adjusting for the effects of sex, age, occupation, areas of residence, income, alcohol intake, and cigarette usage, a strong association with a clear dose-response relationship was observed between the fermented fish sauce eaten weekly and esophageal cancer (P for trend less than 0.001). The results for pickles were similar to those for fermented fish sauce. A protective effect of fruits on esophageal cancer was observed, and this risk decreased (P for trend less than 0.001) as frequencies of fresh fruit intake increased. The risks from sowbelly and kipper were significantly higher in consumers than in nonconsumer, but the dose-response relationship was not statistically significant. No significant effects, however, were detected from vegetables, smoked foods, and so on. To the authors' knowledge, this is the first report on the relationship between fish juice and high risk of esophageal cancer in a population. Further epidemiological and experimental study are required to find a biological causal relationship between them.

Destruction of parotid glands affects nitrate and nitrite metabolism

The role of salivary glands in nitrate and nitrite metabolism is poorly understood. The aim of the present study was to investigate the effect of parotid gland ablation on dynamic metabolism of nitrate and nitrite in miniature pigs. The parotid glands of 5 healthy miniature pigs were bilaterally ablated by methyl violet. Concentrations of nitrate and nitrite of whole saliva, serum, and urine samples were analyzed by high-performance liquid chromatography. Results showed that bilateral ablation of the parotid glands led to a significant decrease of nitrate secretion from blood to saliva (P < 0.05) and thus low nitrite levels. Dysfunction of the parotid glands temporarily increased the systemic level of nitrate in miniature pigs after nitrate loading. This study suggests that the parotid glands play an important role in the balance of nitrate and nitrite levels in both whole saliva and the body.

Pseudouridine, an antimutagenic substance in beer towards N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)

Previously we reported that beer is antimutagenic against several food-derived mutagens including heterocyclic amines. We describe here the isolation and identification of pseudouridine from beer as an antimutagenic substance against N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). All of the 17 samples of beer tested showed inhibition of the MNNG mutagenicity in Salmonella. Extensive fractionation through chromatography of the active components from a freeze-dried beer sample gave six antimutagenic fractions. One contained pseudouridine, as characterized by the UV spectra, nuclear magnetic resonance, and co-chromatography in HPLC. Pure pseudouridine inhibited the mutagenicity of MNNG in a dose-dependent manner. The amount of pseudouridine in the beer sample, estimated at about 0.4 mg/100 ml beer, can account for 3% of the total antimutagenicity of beer. Thus, the major active components in beer remain to be identified. The role of pseudouridine in inhibiting the mutagenicity of MNNG is to be studied further. Among analogs of pseudouridine, spongouridine, but not uridine, was antimutagenic against MNNG. The bacterial mutagenicity of another methylating agent N-methyl-N-nitrosourea was also inhibited by pseudouridine. Pseudouridine is the first example among nucleosides to be shown to possess an antimutagenic property.

Novel epidemiologic evidence for the association between fermented fish sauce and esophageal cancer in South China

Previous studies have suggested that fermented fish sauce is related to an increased risk for nasopharyngeal, thyroid and gastric cancers and has suspicious carcinogenic and promoting effects in the laboratory, but these reports have not investigated the association between this agent and esophageal cancer in population. Therefore, we investigated the relationship between esophageal cancer and consumption of fermented fish sauce, alcohol and tobacco after adjusting other risk factors using data from a large hospital-based case-control study in Chaoshan area of China. The subjects for analysis included 1,248 cases (median age 58.5 [range 29-82] years, 936 males, 312 females, some 50% with the habit of fermented fish sauce eating) with squamous cell carcinoma of the esophagus and the same amount of controls matched by sex and age. A significant increase in risk (OR 3.21; 95% CI 2.45-4.19) for eating fermented fish sauce compared to not eating and a significant dose-response relationship was found with the consumption of fermented fish sauce (p for trend < 0.001). In comparison based on the binary variables, the OR for the subjects with fermented fish sauce eating and current smoking was 15.5 with a 95% CI of 8.14-29.3, relative to those exposed to neither habit. The joint effect of fermented fish sauce (F) and smoking (S) was more than additive (F * S > F + S: 15.5 > 1 + (5.6 - 1) + (6.6 - 1)), but the effect for fermented fish sauce and alcohol was not found. It is concluded that risks of esophageal cancer in the population were substantially associated with fermented fish sauce. Further epidemiologic and experimental study are required to find a biologic causal relationship between them.

Formation of N-nitroso-N-methylurea in various samples of smoked/dried fish, fish sauce, seafoods, and ethnic fermented/pickled vegetables following incubation with nitrite under acidic conditions

In continuation of our previous studies on N-nitroso-N-methylurea (NMU) formation in cured meats following incubation with nitrite at gastric pH, we extended the investigation to other foods mentioned in the title of this paper. The main objective was to determine whether these foods have the potential to form NMU at pH's that can be found in the human stomach. This was done by nitrosating an aliquot (5 g for fish sauce, 10 g for the others) of each with 7.25 microM to 1.59 mM levels of sodium nitrite for 2 h at room temperature at pH 0.8--1.5 and measuring the amounts of NMU formed. Of the samples tested, fish sauce formed 2--712 ng of NMU, followed in decreasing order by herring (<0.3--688 ng); dried anchovy, shrimp, and other fishes (<0.3--134 ng); crab and lobster paté (<0.3--342 ng); sardines (6--59 ng); oysters and mussels (11--31 ng); dried squid (3--47 ng); kimchi (7--107 ng); and Japanese pickled radish (<0.3--72 ng). Incorporation of 200-2000 ppm of ascorbic acid in the fish sauce and other foods, prior to nitrosation, appreciably inhibited such NMU formation. Although previous researchers in China reported NMU formation in nitrosated samples of fish sauce, this is the first reported formation of NMU upon nitrosation of the other foods mentioned above, and the first reported inhibition of such formation by added ascorbic acid.