The effect of dietary quercetin and rutin on AOM-induced acute colonic epithelial abnormalities in mice fed a high-fat diet.

Dietary quercetin (QU) and rutin (RU), phenolic flavonoids found in many fruits and vegetables, when fed to mice on a low-fat diet successfully modified the response to azoxymethanol (AOM) by initially inhibiting hyperproliferation and the formation of foci of dysplasia (FADs) and ultimately reducing tumor incidence (Carcinogenesis 12, 1193-1196, 1991). In this study, we tested the efficacy of QU and RU when a high-fat diet was presented. An AIN 76A diet made with 20% corn oil (CO) was supplemented with QU (0.5%, 2.0%, or 5.0%) and RU (2.0% or 4.0%). These five diets, as well as a 5.0% and a 20.0% CO diet, were fed to a group of CF1 female mice for nine weeks. Both QU and RU showed nonsignificant dose-related trends toward normalization of the AOM-induced upward extension of S phase cells. Examination of 500 microns of serially sectioned distal colon revealed that 29% of mice fed the 20% CO control diet were free of FADs. Among the mice fed QU, regardless of dose, > 80% were free of FADs. When the three groups fed QU were pooled and compared with the control 20% CO-fed mice, the degree of protection was significant (p < 0.01). Mice fed RU expressed a level of protection that bordered on the significant (p < 0.08). These data suggest that, regardless of the fat content of the diet, QU and RU are capable of modifying or inhibiting events in the development of chemically induced colonic neoplasia.

Effect of N-methyl-N'-nitro-N-nitrosoguanidine on carbohydrate profiles of non-metaplastic rat gastric mucosa.

The effect of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) on the mucin phenotype of non-metaplastic gastric mucosa in the rat was studied histochemically. Animals were exposed to MNNG in drinking water (83 mg/l) for 12 weeks. Carcinogen treatment was then discontinued and the animals (27 in the treatment group and 25 in the control group) were examined after another 44 weeks. Glycosylation was analysed with histochemical stains for sialomucins and sulphomucins and with peroxidase-conjugated lectins (GS-II, SBA, DBA, UEA-I, and WGA). Sialo- and sulphomucins remained quantitatively unchanged, only a slight increase of acid mucins in the antral glands was observed. The analysis of the lectin binding patterns, however, revealed a significant increase for WGA-binding glycoproteins in the surface mucous cells and gastric pits, while DBA binding was significantly decreased (P < 0.05). GS-II lectin bound specifically to the proliferative compartment in the gastric fundus, consisting of mucous neck cells, and was significantly increased after MNNG treatment. No specific alterations were detected in lectin binding to parietal or chief cells. It is concluded, therefore, that treatment of gastric mucosa with MNNG alters the glycoprotein metabolism before intestinal metaplasia can be observed.

Effect of dietary curcumin and ascorbyl palmitate on azoxymethanol-induced colonic epithelial cell proliferation and focal areas of dysplasia.

Curcumin, a major yellow pigment of turmeric obtained from powdered rhizomes of the plant Curcuma longa Linn., is commonly used as a coloring agent in foods, drugs and cosmetics. Ascorbyl palmitate is a lipid soluble derivative of ascorbic acid. Both curcumin and ascorbyl palmitate have antioxidant activity and are potent inhibitors of 12-O-tetradecanoyl-phorbol-13-acetate-induced tumor promotion in mouse skin. The effects of dietary curcumin and ascorbyl palmitate on azoxymethanol (AOM)-induced hyperproliferation of colonic epithelial cells and the incidence of focal areas of dysplasia (FADs) were evaluated in female CF-1 mice fed an AIN 76A diet. Subcutaneous injections of AOM (10 mg/kg body wt. once weekly for 6 weeks) caused hyperplasia and the formation of FADs in the colon. Administration of 2% curcumin in the diet inhibited AOM-induced formation of FADs while administration of 2% ascorbyl palmitate in the diet did not demonstrate inhibition. This result suggests that dietary curcumin may inhibit AOM-induced colonic neoplasia in mice.

Stability of a commercially prepared fish oil (omega-3 fatty acid) laboratory rodent diet.

There is evidence that highly unsaturated omega-3 fatty acids present in fish oils can provide a cancer-protective effect; however, when added to laboratory rodent formulations, these fatty acids are subject to rapid and/or extensive oxidation and other chemical changes by exposure to air, light, or heat during processing of pellets or when stored for various lengths of time. An animal diet with 16% refined fish oil and 4% corn oil was commercially prepared with antioxidants (butylated hydroxytoluene and butylated hydroxyquinone in addition to alpha-tocopherol) present, and precautions were taken to prevent oxidation at all stages of production and handling. Fatty acid composition of dried powdered diet as well as freshly processed dried pellets was analyzed from four lots at the beginning and end of a 45-day feeding period. Additionally, fatty acid analyses were carried out on pellets dried by both vacuum and air techniques, and pellets were left exposed to air at room temperature for 96 hours. No statistical difference in overall fatty acid composition was observed among lots due to pelletization or drying procedures. Moreover, 4 days of exposure of pellets to air at ambient temperatures and 45 days of freezer storage had no significant effect on their fatty acid composition. It would appear that rodent diets containing omega-3 fatty acids can be reliably prepared commercially and safely substituted for diets prepared manually and in bulk on a weekly basis.

Quercetin and rutin as inhibitors of azoxymethanol-induced colonic neoplasia.

Dietary quercetin (QU) and rutin (RU), phenolic flavonoids commonly found in many fruits and vegetables, were provided to CF1 female mice for 50 weeks to assess the ability of these compounds to inhibit azoxymethanol (AOM)-induced colonic neoplasia. In addition to a control group fed an AIN 76A diet, five other groups received that diet to which was added either 0.1, 0.5 or 2.0% QU and 1.0 or 4.0% RU. Acute studies revealed that, among saline controls, no alteration of any proliferative parameters of colonic epithelial cells was observed among those groups receiving any dose of QU or RU. However, among the AOM-treated mice, both 2% QU and 4% RU significantly reduced hyperproliferation and inhibited the shift of S-phase cells to the middle and upper portion of crypts. Moreover, mice fed these concentrations of QU and RU had significantly fewer AOM-induced focal areas of dysplasia (FADs) than those fed the control diet (0.2 +/- 0.4 and 0.4 +/- 0.5 versus 3.6 +/- 2.3 respectively). Tumors occurred more frequently in the distal half of the colon, regardless of treatment. Compared with controls, mice fed 2% QU had a significantly reduced tumor incidence (25.0% versus 5.9%, P = 0.03). Those fed 4% RU showed only a trend toward inhibition (25% versus 9.7%, P = 0.11). Nevertheless, both 2% QU and 4% RU suppressed tumor multiplicity, i.e. fewer tumors/animal arose in these groups than in the AOM-treated control mice (1.2 versus 2.3, P = 0.005; 1.1 versus 2.3, P = 0.003 respectively). Clearly, QU and RU exhibit significant activity in reducing AOM-induced hyperproliferation of colonic epithelial cells and FAD incidence. This behavior successfully forecast the ability of both flavonoids to suppress tumor multiplicity and ultimately tumor development.

The effect of dietary omega-3 fatty acids (fish oil) on azoxymethanol-induced focal areas of dysplasia and colon tumor incidence.

MaxEPA (MA), a fish oil high in omega-3 fatty acids, was combined with various levels of corn oil (CO), rich in omega-6 fatty acids, and fed to female CF1 mice. The three fish oil blends with CO and the two CO levels of the diets studied were as follows: 16.0% CO + 4.4% MA (Diet 1); 10.2% CO + 10.2% MA (Diet 2); 4.4% CO + 16.0% MA (Diet 3); 20.4% CO (Diet 4); and 4.4% CO (Diet 5). The diets were provided 2 weeks before weekly subcutaneous injection of saline or azoxymethanol (AOM). Studies of epithelial cell proliferation and the incidence of focal areas of dysplasia (FAD) involved six weekly AOM injections. One week after the last AOM injection and 1 hour before killing, mice were injected with tritiated thymidine (3HTdR). No differences in any proliferative parameters were found among the five groups of saline-treated mice. Among the AOM-treated animals, those fed Diet 3 showed significantly fewer cells per crypt and significantly fewer labeled cells/gland than CO Diets 4 and 5. Additionally, the distribution of S-phase cells in crypts of AOM-treated mice fed Diet 3 most closely resembled that of the saline controls. The greatest alteration in the distribution of proliferative cells was observed in the high-CO diet (Diet 4) and the lowest MA level (Diet 1). Mice fed Diets 2 and 3 had significantly fewer FAD/500 microns of distal colonic serial sections than those fed the high CO diet (Diet 4). Mice involved in chronic tumor incidence studies received only three weekly injections of the same dose of AOM. Regardless of diet, approximately 88% of all tumors arose in the distal colon. A significantly larger tumor-bearing population was observed in both the high-CO Diet 4 and the lowest MaxEPA (MA) diet (Diet 1) compared with the incidence in MA Diets 2 and 3 and the low-CO Diet 5. A diet with a ratio of omega-6 to omega-3 fatty acids of approximately 1.0 apparently prevented the development of an adenoma-type proliferative pattern thereby reducing FAD numbers and subsequent tumor incidence.

Dietary butyrate (tributyrin) does not enhance AOM-induced colon tumorigenesis.

Butyrate has induced differentiation in neoplastic cells grown in vitro, among them being colon cancer cell lines. In vivo, only one major study used sodium butyrate in the drinking water and showed an elevation in 1,2-dimethylhydrazine induced colon cancer in rats. Seeking to show that it was the sodium and not the butyrate which was responsible for the enhancement, we fed tributyrin at a 5% level to mice for 48 weeks. Mice experienced normal growth and development at this dose. Analysis of short chain fatty acids in the feces after 6 months in tributyrin feeding showed a 10-fold increase in butyric acid. However no difference in AOM induced focal areas of dysplasia or colonic tumor incidence was observed between tributyrin fed and control mice. At least two conclusions have been reached by this study, (1) that the dietary use of a sodium salt can contribute to the enhancement of chemically induced colon neoplasia and (2) butyrate may be discounted as providing any major therapeutic benefit against colonic tumorigenesis.

Effect of flurbiprofen and 16,16-dimethyl prostaglandin E2 on gastrointestinal tumorigenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine in rats: glandular epithelium of stomach and duodenum.

The effect of an exogenous synthetic prostaglandin analogue, 16,16-dimethyl prostaglandin E2 (16,16-dm-PGE2), as well as the effect of endogenous prostaglandin synthesis inhibition by a cyclooxygenase inhibitor, flurbiprofen, on chemically induced gastric carcinogenesis has been investigated in rats. Carcinogenesis was induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG; CAS:70-25-7). Animals were divided into six groups: Group I, treatment with MNNG alone; Group II, treatment with 16,16-dm-PGE2 plus MNNG; Group III, treatment with flurbiprofen plus MNNG; Group IV, treatment with 16,16-dm-PGE2 alone; Group V, treatment with flurbiprofen alone; and Group VI, controls. Treatment with high doses of MNNG resulted in rapid development of malignant tumors originating from the glandular epithelium of the stomach and duodenum in animals of all groups receiving the carcinogen. The first gastric adenocarcinoma infiltrating the muscularis proper was detected after 139 days in an animal treated with a combination of MNNG and flurbiprofen. The incidence of infiltrating adenocarcinoma and the incidence of all neoplastic lesions of the glandular stomach were both significantly higher in animals treated with a combination of MNNG and flurbiprofen compared with treatment by MNNG alone or in combination with 16,16-dm-PGE2 (P less than 0.05 and P less than 0.001). The difference in tumor incidence between the last two groups was not significant. The first duodenal adenocarcinoma was detected on Day 114 in another animal of the group treated with MNNG plus flurbiprofen. When compared with the group treated with MNNG plus 16,16-dm-PGE2, significantly more animals developed duodenal adenocarcinoma when treated with MNNG plus flurbiprofen (P less than 0.005) or with MNNG alone (P less than 0.05). Results of this study indicate that inhibition of endogenous prostaglandin synthesis favors development of adenocarcinoma in the glandular stomach of rats. Vice versa, the addition of an exogenous prostaglandin analogue inhibits the development of duodenal adenocarcinoma. This protective effect of prostaglandins may be due to an increase of the thickness of the mucus gel covering the glandular epithelium, thereby preventing access of carcinogen to the mucosa.

Genetic factors controlling inheritance of susceptibility to 1,2-dimethylhydrazine.

Reciprocal crosses were made between AKR/J, a 1,2-dimethylhydrazine (DMH)-resistant mouse strain, and SWR/J, a sensitive strain. The F1 hybrids were tested with DMH and methylazoxymethanol (MAM), two colon carcinogens. Either DMH (20 mg/kg body weight) or MAM (35 mg/kg body weight), a metabolic derivative of DMH, was injected weekly for 10 weeks. In each group of 35 mice, 10 were injected with tritiated thymidine (25 microCi) 1 week after the sixth injection of DMH and MAM for the evaluation of proliferative characteristics and the number of foci of dysplasia occurring in 325 microns of distal colonic mucosa. At 27 weeks after the first injection of the carcinogen, the colons of remaining mice were opened longitudinally and the number of tumors enumerated. Compared with DMH-treated mice, the number of foci of dysplasia per mouse, the percentage of tumor-bearing mice, the number of tumors per animal, and the number of tumors per tumor-bearing animal induced by MAM were severalfold higher. This would suggest the presence of a gene(s) repressing metabolism of DMH to MAM. Moreover, differences in response to the carcinogens were observed between the sexes. In contrast to males, females treated with both DMH and MAM had significantly greater numbers of tumors per animal, tumors per tumor-bearing mice, and a greater proliferative response with extension of S-phase cells to the upper third and luminal surface of crypts. Among males, those with the XAKR/YSWR heritage appeared more resistant than XSWR/YAKR males, particularly in their response to MAM. A twofold difference in the number of foci of dysplasia per mouse, tumors per animal, and the number of tumors per tumor-bearing animals was seen. Analyses of the response to DMH and MAM by F1 reciprocal hybrids of the AKR and SWR strains have shown a complex inheritance pattern governing susceptibility to DMH. Resistance to the carcinogen is provided by at least two specific repressor genes, one governing metabolism of carcinogen from DMH to MAM, and the other controlled by gender. Genetic factors contributed by the AKR female appear to convey additional resistance to male progeny, suggesting more than one gender-related gene.

Promotion of gastric tumorigenesis by duodenal contents in rats induced with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG).

Reflux of duodenal contents into the stomach occurs in patients with pyloric incompetence and after gastric resection when bile-diverting procedures are omitted. In such settings duodenal contents have been considered to favor the development of gastric cancer. We have studied the effect of chronic duodenogastric reflux on gastric tumor promotion in rats treated with N-methyl-N'-nitrosoguanidine (MNNG) in an experimental design that avoids physical trauma to the glandular stomach. Thus the effect of trauma-induced tissue repair on carcinogenesis is eliminated, and duodenogastric reflux is isolated as an experimental parameter. To achieve such reflux the first jejunal loop was anastomosed to the forestomach in rats. Animals were exposed to MNNG in drinking water (83 mg/L) for 12 weeks before induction of reflux. Experimental groups were as follow: I, reflux plus MNNG (n = 32); II, MNNG alone (n = 27); III, reflux alone (n = 28); IV, control (n = 25). The experiment was terminated after 56 weeks. Only animals that had survived for 90 days were included in the effective number of animals, which allowed for equal chances of tumor development. In no animal that died earlier had tumors developed. Animals with reflux plus MNNG treatment had significantly more glandular neoplasms (12/32) than did animals with MNNG treatment alone (4/27; p less than 0.05). Similarly, more animals with squamous cell neoplasms were recorded in group I (9/32) than in group II (2/27; p less than 0.05). In consideration of all tumors of epithelial and mesenchymal origin, more gastric malignant tumors were observed in group I (9/32) than in group II (2/27; p less than 0.05). It is concluded that chronic exposure to duodenal contents promotes the development of gastric neoplasia.

Rectal epithelial cell proliferation in a group of young adults. Influence of age and genetic risk for colon cancer.

Twenty-one medical students with an average age of 23.3 +/- 1.5 years and no family history of large bowel cancer had a rectal biopsy taken for in vitro incorporation of tritiated thymidine (3HTdR). The number and position of labeled epithelial cells in this group was compared with an older control group of 12 and two groups of individuals at high risk for colon cancer. The latter were (1) 18 young asymptomatic individuals from familial colon cancer families without polyposis with a 50% risk for colon cancer, average age 24.1 +/- 3.7; and (2) 17 older individuals with the same genetic background and risk factor, average age 53.8 +/- 10.2 years. A group of 20 young individuals from cancer-free branches of familial colon cancer kindreds with a 25% risk for colon cancer, average age 23.1 +/- 3.6, also was studied. No overall differences in labeling index (LI) were found among the young groups, i.e., the control versus the low risk or high risk. The range of LI values was narrow regardless of risk. However age was associated with a significant increase in LI as observed among older controls and the 50% risk group as compared to younger persons; the range of LI values was wider among the older groups regardless of risk. Concerning the distribution of DNA-synthesizing cells, young controls had significantly more S-phase cells in the lower third of the crypts than either young high-risk or low-risk groups (P less than 0.05). Similarly, young controls had significantly fewer labeled cells in the middle third than the young high-risk group and young controls had significantly fewer S-phase cells in the upper third than did young low-risk or high-risk groups. When young and old members of the same group were pooled, the control group had the highest percentage of labeled cells in the lower third of the crypt (62.5%) which was significantly higher than both the low-risk (53.7%) and the pooled high-risk groups (51.6%). For the upper third of the glands, the low-risk (7.6%) and the pooled high-risk groups (6.8%) were significantly different from the controls (3.3%). Thus initial risk for colon cancer is more related to the distribution of S-phase cells than to their number, i.e., LI. Risk appears to be related to more DNA-synthesizing cells in the upper crypt, an indication that relatively early on in life the DNA switch-off mechanism shows signs of being defective.

Susceptibility to 1,2-dimethylhydrazine-induced colonic tumors and epithelial cell proliferation characteristics of F1, F2, and reciprocal backcrosses derived from SWR/J and AKR/J parental mouse strains.

Hybrid crosses were performed between SWR/J, a strain highly sensitive to 1,2-dimethylhydrazine (DMH), and AKR/J, a strain highly resistant to the carcinogen. F1 and F2 and reciprocal backcrosses were tested to determine if proliferative characteristics such as high activity, wide compartment (PC), and a large S-phase population in the middle third of crypts were linked to susceptibility and inherited as a dominant autosomal trait as was reported for DMH tumor response. A blend of resistant and sensitive tumor and proliferative characteristics was observed in the F1 and F2 crosses. A tumor incidence of 43.7% in the F1 and 52% in the F2 was obtained rather than the respective 100% and 75% expected frequencies. One week after the sixth injection of DMH, the incidence of focal areas of atypism (FAA) in the backcross to resistance (BCR) and the backcross to sensitivity (BCS) was the same (4.1 per FAA-bearing animal). This suggested that the response to the carcinogen was similar in both groups up to this point. Yet 20 weeks later, the BCR had a 7.3% tumor incidence, far lower than the 50% incidence expected. The BCS had an incidence of 98.6%, not unlike SWR frequencies and close to the expected 100% tumor incidence. Proliferative characteristics in the backcrosses, however, did not revert to parental levels. Instead, the labeling index (LI) or percentage of S-phase cells to total cells scored was significantly higher in the BCR than in the BCS (10.2% +/- 3.2% versus 8.1% +/- 2.2%, P less than 0.02). This study has shown that in crosses between these two strains (SWR/J and AKR/J), susceptibility to DMH-induced tumor is not inherited as a dominant trait. Neither are the proliferative characteristics of the colonic mucosa inherited in a simple Mendelian manner nor are the kinetic properties of the epithelial cells linked to DMH tumor susceptibility. It is suggested that the parental AKR/J strain may contribute a protective or resistant factor, that is, a repressor gene, which impedes the progression of carcinogen-induced foci of dysplasia to colonic neoplasia.

Cell proliferation and colonic neoplasia.

The preneoplastic events occurring in the mucosa of patients at risk of developing colonic cancer are described and correlate well with the histogenesis of an adenoma. Confirmatory evidence from experimental carcinogenesis systems is provided. Among individuals at 50% risk of colon cancer, proliferative abnormalities relating to the distribution of S-phase cells are present. Aging, whether among the high-risk or the unaffected control population, appears to bring about enhancement of the percentage of DNA-synthesizing cells in the crypts, indicating a similar response of colonic epithelial cells to environmental conditions over time. The combination of an already existing defect in cell proliferation among those at high risk of familial colon cancer along with an elevated rate of cell renewal increases the probability that a neoplasm will arise in this population.

Sodium transport in a mouse model of colonic carcinogenesis.

Following 4 weeks of s.c. injections of 1,2-dimethylhydrazine, a carcinogen that produces colon cancer in CF1 mice, an increase in the unidirectional mucosal to serosal flux and net absorption of sodium was observed in the distal colon. This increase in sodium transport was amiloride sensitive. 1,2-Dimethylhydrazine treatment had no effect on sodium transport in the distal colon of DBA/2 mice, a strain which does not develop colonic malignant transformation. Although stimulation of sodium transport has been observed in cultured cell systems exposed to growth factors, similar changes in sodium transport have not previously been demonstrated in an intact epithelium at an early stage of carcinogenesis. The present study in mouse distal colon demonstrates that sodium transport is altered in 1,2-dimethylhydrazine-induced malignant transformation of the large bowel.

Prolonged administration of bile salts for gallstone dissolution and its effect on rectal epithelial cell proliferation.

Bile acids and cholesterol metabolites may play a role in large bowel carcinogenesis. Currently, the bile acids chenodeoxycholic (CDCA) and ursodeoxycholic acid (UDCA) are being used for dissolution of cholesterol gallstones in surgical high-risk patients. The effect of prolonged exogenous bile acid intake on rectal epithelial cell proliferation, as a marker for preneoplasia, was evaluated in 19 patients selected for treatment. They were divided into two groups: nine patients received CDCA, 15 mg/kg/day for a mean duration of 11.0 months, while 11 patients received UDCA, 10 mg/kg/day for a mean duration of 9.2 months. Rectal biopsies taken before treatment and at one, three, six, and 12 months of treatment were analyzed and evaluated by three proliferative parameters including labeling index (LI), distribution of labeled cells, and total cells per crypt column. No significant alterations in epithelial cell proliferation were observed among patients treated with UDCA or CDCA with the exception of the number of cells per crypt column which, in the latter instance, deviated only slightly from the predicted values. The lack of major persistent alterations in the proliferative behavior of rectal epithelial cells does not justify any change in the selection of patients for gallstone therapy, but cannot exclude the potentially deleterious long-term effects of bile acid treatment.

Cell turnover and colon tumor development.

The proliferative characteristics of the large bowel are determined genetically and can vary over a wide range, the lower range being resistant to chemically induced tumors and the upper range expressing susceptibility. Basically, the colon has a relatively high level of cell renewal. It can be further elevated or depressed by a number of dietary and environmental conditions. A hyperproliferative state has been induced by the presence of carrageenan, Citrobacter freundii, nonspecific injury, or dietary factors such as high levels of bile acids. The effect of high proliferation levels is to produce more S-phase cells, which are sensitive to DNA damage, to increase the risk of neoplastic transformation and to shorten the tumor latency period. In animal models, hyperactivity has meant enhanced tumor incidence. A hypoproliferative state has been induced in the colon of man and mouse. Experimentally, the net effect of lower proliferative levels has been to reduce colon tumor incidence. It remains to be determined whether clinical trials involving hypoproliferation can be maintained chronically and are an effective means of reducing colon tumor incidence in high-risk groups.

Effect of flurbiprofen and 16,16-dimethyl-prostaglandin E2 on gastrointestinal tumorigenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine in rats. I. Squamous epithelium and mesenchymal tissue.

The effect of exogenous synthetic prostaglandins and the inhibition of endogenous prostaglandin synthesis on gastrointestinal tumorigenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine [(MNNG) CAS: 70-25-7] was studied in female Wistar rats (100 g). Animals were divided into 6 groups: Group I was treated with MNNG alone (No. = 43); group II was treated with MNNG after application of the cyclo-oxygenase inhibitor flurbiprofen (No. = 44); group III was treated with MNNG after oral administration of 16,16-dimethyl-prostaglandin E2 (16,16-dm-PGE2; No. = 43); group IV received flurbiprofen alone (No. = 15); group V was treated with 16,16-dm-PGE2 alone (No. = 11). Animals in group VI served as controls (No. = 15). All drugs were administered orally. Hyperkeratosis and hyperplasia of the forestomach developed by 10 days after the first treatment with the carcinogen. Later, benign papillomas and dysplastic lesions were noted. Progressive ingrowth of squamous epithelium from the forestomach ridge into the glandular stomach started as early as day 13 and was more frequent in animals treated with a combination of MNNG plus flurbiprofen (P less than .001). The first squamous cell carcinomas of the forestomach were detected on day 51. Their incidence was 38, 60, and 42% in groups I, II, and III, respectively. This difference was not statistically significant. The incidence of mesenchymal tumors (leiomyosarcoma) in the stomach and duodenum was higher following treatment with MNNG plus flurbiprofen as compared to the incidence following treatment with MNNG alone or in combination with 16,16-dm-PGE2 (P less than .005). No malignant tumors developed in the gastrointestinal tracts of animals treated with flurbiprofen or 16,16-dm-PGE2 alone or in controls. The higher incidence of gastric and duodenal leiomyosarcomas after treatment with flurbiprofen suggests that reduction of prostaglandin synthesis favored the development of MNNG-induced cancer in mesenchymal tissues of the upper gastrointestinal tract.

Lipid peroxidation in liver and colon of methylazoxymethanol treated rats.

Weanling male Sprague-Dawley rats were injected via the tail vein with methylazoxymethanol (MAM) acetate at a dose of 70 mg/kg body weight. Measurements of lipid peroxidation were carried out on mitochondrial and microsomal fractions of liver and colonic mucosa at various intervals over the first 24 h following delivery of the carcinogen. Significantly increased levels of peroxidation were observed 3-6 h after treatment in microsomal and mitochondrial fractions of both these tissues. A return to control levels was seen by the end of the first day. These results are discussed in relation to the role of lipid peroxidation in carcinogenesis and the proposed mechanism of tumor prevention by selenium.

The effect of selenium on cell proliferation in liver and colon.

Epidemiologic and experimental evidence support a chemoprotective role for selenium (Se) in malignancy. Many mechanisms have been proposed to explain this phenomenon. In this study, the effect of Se intake on proliferation of hepatocytes and normal colonic epithelial cells in rats was determined using autoradiographic analysis of thymidine incorporation into DNA. Hepatocyte proliferation was measured 24 h after partial hepatectomy. Selenium-dosed animals demonstrated a significant reduction in hepatocyte labeling compared to the control group (6.1±2.6 vs 29.2±15.6,p=0.003). However, Se dosing did not affect the thymidine-labeling indices or distribution of labeling in colonic epithelium. Selenium may inhibit cell proliferation when it is the result of an unusually intense stimulus. This finding could explain in part the inhibitory effect of Se in some experimental cancer models.