Possible role of mucosal damage in stomach carcinogenesis with N-methyl-N-nitro-N-nitrosoguanidine in the rat

Myenteric denervation reduces the incidence of gastric tumors in rats

The influence of myenteric denervation on the development of gastric tumors induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was studied after chemical denervation of the rat stomach with benzalkonium chloride (BAC). Three groups were evaluated: control, denervated and denervated with pyloroplasty. Random bred male Wistar rats were given MNNG in drinking water (100 mg/l) for 28 weeks. After the sacrifice of animals, the stomachs were removed for morphological study. BAC reduced myenteric neurons number, increased the gastric mucosa area and decreased the adenocarcinomas number and size. This decrease was more evident when denervation was associated with pyloroplasty. These results indicate that myenteric denervation reduces the incidence of experimentally induced gastric tumors.

7,12-DMBA-induced rat leukemia: a review with insights into future research

7,12-Dimethylbenz[a]anthracene (DMBA) elicits leukemia in Long-Evans rats (LE). This leukemia is mostly erythroblastic and 30% of leukemias have total and partial trisomy of #2 chromosome and the rest have diploid karyotype. The common duplication site is in 2q26-q34 and N-ras gene is located in 2q34. 7,8,12-Trimethylbenz[a]anthracene (TMBA) also induces similar leukemias. These leukemias reveal a highly specific mutation of N-ras gene as in human leukemias. N-ras mutation is induced 48h after DMBA treatment. Wild type N-ras allele is frequently lost in diploid leukemias but not in trisomy type. Therefore, a gene dosage problem related to the mutant N-ras gene is involved in development of leukemia. Some secondary genetic rearrangements involving abl and H-ras are also observed in cultured leukemia cells. DMBA-induced chromosome aberrations as well as leukemia are enhanced by erythropoietin and blocked by Sudan III given prior to DMBA treatment. This leukemia will provide an important tool for chemical carcinogenesis and leukemia studies.

Direct interception of mutagens and carcinogens by biomolecules

Five points are emphasized: 1. Chemical interception and mere physical exclusion of mutagens and carcinogens constitute the major means by which mutations in cellular DNA are prevented. DNA repair processes comprise critical, but relatively minor, modes of genetic protection. 2. Disruption of a mutagen-interception defense mechanism can lead to substantial increases in mutagenesis and can preordain sites to eventual tumor formation. 3. Quantitation of the relative contributions of various blocking molecules is often simplified by the fact that protection can be calculated merely through knowledge of the measured concentration of the antimutagen and its rate of reaction with specific mutagens as measured in straightforward in vitro tests. 4. Two recently recognized defensive molecules, carnosine and ergothioneine, are put ++forward as examples of interesting chemical interceptor molecules. 5. Essentially all antimutagens are in fact "double-edged swords." Situations can be artificially constructed that can lead to generation of toxic species from molecules that are normally antimutagens; in isolated cases some of these interactions can be pictured as having deleterious consequences in vivo. This may be one reason why a number of important antimutagens are often sequestered, either in different tissues or by binding to dispensable macromolecules.

Role of prostaglandins in the early phases of experimental gastric carcinogenesis in the rat

The study was initiated to evaluate the effect of N-methyl-N-nitro-N-nitrosoguanidine (NG) on gastric intraluminal prostaglandin release during a 30-day treatment period and to investigate the effect of a stable prostaglandin E1 analogue (misoprostol) on NG-induced gastric mucosal damage during the same time period. Samples of gastric juice (1 h) were obtained from 40 male Sprague-Dawley rats with chronic gastric fistulas, in basal conditions and after 5, 15 and 30 days of continuous oral administration of NG (120 mg/l) or tap water. Aliquots of gastric juice were titrated with 0.1 M NaOH. Other aliquots were extracted with ethyl acetate and subjected to specific radioimmunoassay for prostaglandin E2. The severity of gastric mucosal lesions was evaluated in 60 rats after 5 days and 30 days of continuous oral administration of NG (120 mg/l) or NG plus misoprostol (200 micrograms/kg-1/day-1) or tap water, and a histological study was carried out. Administration of NG induced a significant decrease of gastric intraluminal prostaglandin E2 concentration at 15 and 30 days. Oral administration of misoprostol, at non-antisecretory doses, protected the rats against NG-induced gastric mucosal damage. Prostaglandins may be involved in the early phases of experimental gastric carcinogenesis.

Gastric carcinogenesis: a model for the identification of risk factors

In a series of extensive studies on gastric carcinogenesis, we have used Sprague-Dawley rats to examine the morphologic, histochemical, and biochemical effects of risk and protective factors on N-methyl-N'-nitro-N-nitroso guanidine (MNNG)-induced tumors in an attempt to link early observations with the end-point lesion, gastric cancer. We have observed that the putative risk factors sodium chloride (NaCl); a mixture of bile acids; aspirin; alcohol; and nitrite enhance MNNG-induced neoplasia of the gastric mucosa. On the other hand butylated hydroxyanisol (BHA), Se and difluromethylornithine (DFMO) were protective and inhibited the induction of gastric mucosal neoplasia. In most cases, early changes detected by a number of criteria correlated with the end-point, gastric neoplasia. This model appears to be useful in screening and evaluating chemicals for risk for or protection against gastric cancer.

Chromosome aberrations in epithelial cells of the digestive tract of rats induced by 1-methyl-3-nitro-1-nitrosoguanidine

The effect of a gastrointestinal carcinogen, 1-methyl-3-nitro-1-nitrosoguanidine (MNNG), on chromosomes of rat digestive tract epithelial cells was studied. A blind loop of colorectal segment was surgically produced and the epithelial cells of this loop were treated twice with 0.5% and 0.1% MNNG solutions, respectively (5 ml each). After the first treatment, the mucosa revealed severe damage, and repair and mitoses upon regeneration were maximal on days 4-6. Chromosomal aberrations were studied 3-48 hr after the second treatment. Cells with chromosomal aberrations increased progressively from 6 hr on, reaching their maximum level at 15 hr, and gradually returned to the original level at 48 hr. Chromosomal aberrations consisted of gaps, breaks, and exchanges. The above results indicate that gastrointestinal carcinogens induce chromosomal aberrations in target epithelial cells.

Effect of bile acid gavage or vagotomy and pyloroplasty on gastrointestinal carcinogenesis

Possible promotion of MNNG-induced gastrointestinal carcinogenicity was evaluated in male Wistar rats exposed to unconjugated bile acid given as gavage or as obtained through truncal vagotomy plus pyloroplasty. No significant difference was found compared with the relevant control groups. Even though gastroduodenal erosions were found more frequently in the bile acid gavage and MNNG groups than in MNNG-treated controls, secondary deconjugated bile acids apparently did not reach optimal promoting concentrations. In contrast to partial gastrectomy, vagotomy and pyloroplasty does not increase the tumor yield in the rat.

Gastric carcinoma promoted by alkaline reflux gastritis -- with special reference to bile and other surfactants as promoters of postoperative gastric cancer

For reasons that are not known, the incidence of stomach cancer is declining in most countries. In contrast, cancer of the gastric remnant after partial gastrectomy for peptic ulcer disease seems to be increasing. "Stump cancer" has been claimed to be a separate disease entity and has recently been mentioned as an iatrogenic cancer. Alkaline bile reflux, dietary surfactants and maybe the abuse of tobacco are postulated as promoting or initiating agents, in causing malignant transformation of the operated as well as non-operated stomach. Variations in gastric pH, microflora and emptying rate may be of importance in the carcinogenic process. The decline in cancer incidence in the non-operated stomach has mainly been restricted to the intestinal type of cancer. Thus, it is important to note that stump cancer often is of the diffuse type. Different target cells and/or modes of carcinogen exposure may be of etiological importance in these histologically and clinically separate neoplastic diseases.

Effect of N-methyl-N'-nitro-N-nitrosoguanidine on the gastric mucosal barrier in rats

The gastric mucosal barrier to hydrogen ion (H+) after the administration of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) on the rat stomach was studied. Increased H+ back-diffusion was observed 3 hr after oral doses of 1 mg of MNNG over a 3-day period. MNNG in concentrations of 250 microgram/ml, 167 microgram/ml, 86 microgram/ml, and 50 microgram/ml in the presence of acid caused increased H+ back-diffusion across the gastric mucosa within 1 hr. Gastric mucosal barrier disruption by MNNG may play a pathogenic role in gastric carcinogenesis.

Sequential morphological changes of ulceration in the glandular stomach of rats induced by iodoacetamide

Two groups of 25 male Wistar rats were given 0.1% iodoacetamide (IAM) with or without 0.4% Tween 60 in their drinking water for 12 weeks. Two or three rats from each group were sacrificed at intervals for sequential morphological observations on ulceration of gastric mucosa. The ulcers invariably developed in the fundic region adjacent to the limiting ridge, and they penetrated the muscle coats and extended to the serosal lining on continuous treatment with IAM for 9 weeks. The ulcers appeared chronic, but when IAM was discontinued the healing process began rapidly and the mucosa regenerated almost completely within six weeks. Regenerating epithelium on areas of ulcer differentiated progressively, and the renewed mucosa showed pyloric metaplasia.