Inhibitory effects of epigallocatechin-3-gallate on N-nitrosomethylbenzylamine-induced esophageal tumorigenesis in F344 rats

The present study was conducted to assess the inhibitory effects of EGCG (epigallocatechin-3-gallate) on NMBA-induced rat esophageal tumorigenesis and to seek the potential mechanisms. In experiment I, 81 F344 rats were randomly divided into seven experimental groups according to the different regiments of NMBA 1 mg/kg subcutaneously (s.c.) and EGCG 4 mg/kg or 10 mg/kg orally or intraperitoneally (i.p.). The experiment was terminated at 24 weeks. In experiment II, 48 rats were allocated into two groups, each group contained 24 rats, in which the rats were injected with NMBA 1 mg/kg only or a combination of NMBA 1 mg/kg and EGCG 4 mg/kg i.p. Six rats from each group were sacrificed at the 12th, 16th, 20th and 24th week, respectively. The expression of cyclin D1 and cyclooxygenases (COX-2 and COX-1) was detected using semi-quantitative RT-PCR, and the production of prostaglandin E2 (PGE2) was measured by ELISA. In the groups which were treated with EGCG at a dose of 4 mg/kg i.p., or 10 mg/kg both orally and i.p., the mean number of tumors per rat was significantly reduced to 48, 56 and 61%, respectively (p<0.05). The incidence rate of esophageal carcinomas in the rats that were treated with EGCG 4 mg/kg i.p., was significantly lower than that in the rats which only received NMBA 1 mg/kg (p<0.05). The expression of cyclin D1 and COX-2, and the levels of PGE2 were also decreased by EGCG treatment. These results indicated that EGCG significantly inhibits the NMBA-induced rat esophageal carcinogenesis and it inhibitory effects may partly target cyclin D1 and COX-2 expression, and PGE2 production.     

香加皮三萜类化合物对甲基苄基亚硝胺诱导的食管癌大鼠调节性T细胞功能的影响

目的：探讨香加皮三萜类化合物（triterpenes compound of cortex periplocae,TCCP）对甲基苄基亚硝胺（N_nitrosomethylbenzylamine,NMBA）诱导的食管癌大鼠CD4^＋CD25^＋调节性T细胞功能的影响。方法：健康雄性F344大鼠40只,随机分为模型组（0.5mg/kg NMBA皮下注射）、治疗组（0.5mg/kg NMBA皮下注射及10mg/kg TCCP肌肉注射）、大豆油对照组（肌肉注射大豆油1ml/kg）和正常对照组,每组10只。各组每周给受试物3次,连续5周。分别在给受试物后第9周和第15周抽取4组大鼠外周血各1ml。用流式细胞仪检测大鼠外周血中CD4^＋T细胞和CD4^＋CD25^＋调节性T细胞（Tr细胞）的水平。另留取血清用ELISA法检测大鼠外周血白细胞介素IL-2、IL-10和转化生长因子TGF_β1的含量。结果：与正常对照组相比,NMBA给药后第9周和第15周,模型组外周血中CD4^＋T细胞比例均显著降低（P均〈0.05）,而CD4^＋CD25^＋Tr细胞比例均显著升高（P均〈0.05）。与同时期模型组比较,TCCP治疗组在给药后第9周和第15周外周血中CD4^＋T细胞比例升高,CD4^＋CD25^＋Tr细胞比例降低,差异均具有统计学意义（P均〈0.05）。NMBA给药后第9周和第15周,模型组大鼠外周血中IL-10、TGF-β1水平显著高于正常对照组（P均〈0.05）,经TCCP治疗后显著下降（P均〈0.05）;大鼠外周血中IL-2水平则呈现与之相反的趋势。结论：NMBA诱导大鼠食管癌后外周血中CD4^＋CD25^＋Tr细胞水平增加,TCCP可以通过抑制CD4^＋CD25^＋Tr细胞活化来纠正食管癌发生、发展过程中所致免疫细胞抑制状态,改善NMBA诱导的食管癌大鼠细胞免疫功能紊乱。     

Inhibition of N-nitrosomethylbenzylamine-induced esophageal tumorigenesis in rats by green and black tea

In this study, we investigated the effects of green tea andblack tea, when given either during or after carcinogen treatment,on esophageal tumorigenesis in male Sprague—Dawley rats.Rats were treated with N-nitrosomethylbenzylamine (NMBzA) (2.5mg/kg, s.c., twice weekly) for 5 weeks; 39 weeks after the initialdose of NMBzA, 65% of the rats had esophageal tumors with anaverage of 1.4 0.3 tumors per rat. In the groups of rats receiving0.6% of decaffeinated green tea (DGT) or decaffeinated blacktea (DBT) (6 mg tea solids/ml) as the sole source of drinkingfluid during the NMBzA-treatment period, esophageal tumor incidenceand multiplicity were reduced by     

Suppression of N-nitrosomethylbenzylamine (NMBA)-induced esophageal tumorigenesis in F344 rats by resveratrol

Resveratrol (3,5,4'-trihydroxy-trans-stilbene) is a natural product occurring in grapes and various other plants with medicinal properties associated with reduced cardiovascular disease and reduced cancer risk. To evaluate the possibility and potential mechanism(s) of which resveratrol inhibits N-nitrosomethylbenzylamine (NMBA)-induced rat esophageal tumorigenesis, 96 F344 male rats were divided into 10 groups and resveratrol (1 and 2 mg/kg) was administered orally or intraperitoneally (i.p.). In the groups in which resveratrol was administered at 2 mg/kg (orally, for 16 weeks), 1 and 2 mg/kg (i.p., for 16 weeks) and 1 mg/kg (i.p., for 20 weeks), the number of NMBA-induced esophageal tumors per rat was significantly reduced to 78, 62, 54 and 48, respectively (P < 0.05), and the size of maximum tumors in each group with resveratrol treatment was also significantly smaller than that in NMBA alone group (P < 0.05). Although the pathological examination did not indicate significantly decreased incidence of carcinomas by administering resveratrol, the tendency of carcinogensis suppression was observed (P = 0.177). Semi-quantitative RT-PCR and ELISA analysis demonstrated that following NMBA treatment, the expression of COX-1 mRNA was strongly present in tumor tissues, while weakly present in non-tissues; the expression of COX-2 mRNA was induced in both tumor and non-tumor tissues. The production of prostaglandin E(2) (PGE(2)) increased approximately 6-fold, compared with the normal esophageal mucosa. The higher expression of COX-1, the up-regulated COX-2 expression and the increased levels of PGE(2) synthesis were all significantly decreased by administering resveratrol. Our study suggests that resveratrol suppressed NMBA-induced rat esophageal tumorigenesis by targeting COXs and PGE(2), and therefore may be a promising natural anti-carcinogenesis agent for the prevention and treatment of human esophageal cancer.     

Preventive effect of fermented brown rice and rice bran on N-nitrosomethylbenzylamine-induced esophageal tumorigenesis in rats

Modifying effect of fermented brown rice by Aspergillus Oryzae (FBRA) during the initiation or post-initiation phase of N-nitrosomethylbenzylamine (NMBA)-induced esophageal tumorigenesis was investigated in rats. Five-week-old male F344 rats were divided into 7 groups, and groups 1-5 were given subcutaneous injections of NMBA (0.5 mg/kg body weight/injection 15 times) for 5 weeks starting at 7 weeks of age. Groups 2 and 4 were fed the diet containing 5 and 10% FBRA during the initiation phase, respectively, whereas groups 3 and 5 were fed these diets during the post-initiation phase. Group 6 was given the diet containing 10% FBRA throughout the experiment, and group 7 was kept on the basal diet alone and served as an untreated control. Incidence and multiplicity of esophageal neoplasms of group 1 (NMBA alone) were 89% and 1.63+/-1.01/rat, respectively. Those of groups 3 (65%, 1.04+/-1.04) and 5 (58%, 0.77+/-0.86) were significantly less than those of group 1. Furthermore, the incidence and multiplicity of esophageal preneoplastic lesions (dysplasia) of group 5 were less than those of group 1. Post-initiation feeding of 10% FBRA significantly decreased BrdU incorporation in the non-lesional esophageal tissues when compared to that of the control. In addition, the analysis of expression levels of phase I enzymes of livers at the termination of experiment showed no clear differences among the groups. These observations indicate for the first time that FBRA inhibits NMBA-induced esophageal tumor development in rats possibly through inhibition of cell proliferation in the post-initiation phase, and suggest that FBRA is a promising dietary agent for prevention of human esophageal cancer.     

Perillyl alcohol as a chemopreventive agent in N-nitrosomethylbenzylamine-induced rat esophageal tumorigenesis

Perillyl alcohol (POH) is a monoterpene found in lavender, spearmint, and cherries. Phase I clinical trials with this agent have shown a favorable toxicity profile and preliminary data indicate some chemotherapeutic efficacy in advanced cancers. Animal studies have demonstrated the ability of POH to inhibit tumorigenesis in the mammary gland, liver, and pancreas. Although the precise mechanism of action is unclear, POH has been shown to inhibit the farnesylation of small G-proteins, including Ras, up-regulate the mannose-6-phosphate receptor, and induce apoptosis. Previous studies in our laboratory using the rat model of squamous cell carcinoma of the esophagus have shown that a specific Ha-ras codon 12 mutation is important for tumor promotion and progression. Given the limited toxicity of POH in humans, its proven efficacy in several animal models and its potential to inhibit Ha-ras farnesylation, we conducted an animal study to evaluate the efficacy of POH as a chemopreventive agent for squamous cell carcinoma of the esophagus. Male Fischer-344 rats were treated s.c. with 0.25 mg/kg b.w. of N-nitrosomethylbenzylamine three times a week for 5 weeks. Three days after the final carcinogen dose, they were started either on control diet or diets containing 0.5 or 1.0% POH. At 25 weeks, the animals were sacrificed, and esophageal tumors were counted. Animals fed either dose of POH showed a significant increase in dysplasia when compared with controls (P < 0.05) and a nonsignificant trend toward increased tumor multiplicity. Additionally, 1.0% POH did not affect Ras membrane localization. These data indicate that POH has a weakly promoting effect early in nitrosamine-induced esophageal tumorigenesis and suggest that POH may not be an effective chemopreventive agent for esophageal cancer in humans.     

Suppression of N-nitrosomethylbenzylamine-induced rat esophageal tumorigenesis by dietary feeding of auraptene

The modifying effects of auraptene on N-nitrosomethylbenzylamine (NMBA)-induced esophageal tumorigenesis were investigated in male F344 rats. At 5 weeks of age, all animals, except those with the test chemical alone and control rats, received s.c. injections of NMBA (0.5 mg/kg body weight/injection, three times per week) for 5 weeks. At the end of the study (20 weeks), 75% of the rats treated with NMBA alone had esophageal neoplasms (papillomas). However, the groups who received a dose of 500 ppm auraptene during the initiation phase developed significantly reduced incidence of tumors (39%; P<0.05). Exposure to auraptene (500 ppm) during the post-initiation phase also decreased the frequency of the tumors (29%; P<0.01). The reduction of the incidence of severe dysplasia was obtained when auraptene was administered in the post-initiation phase (P<0.05). Cell proliferation in the esophageal epithelium determined by proliferating cell nuclear antigen (PCNA) was lowered by auraptene (P<0.01). Blood polyamine contents in rats who received NMBA and the test compound were also smaller than those of rats that received the carcinogen (P<0.05). These findings suggest that dietary auraptene is effective in inhibiting the development of esophageal tumors by NMBA when given during the initiation as well as post-initiation phases, and such inhibition is related to suppression of cell proliferation in the esophageal epithelium.     

The effects of L-748706, a selective cyclooxygenase-2 inhibitor, on N-nitrosomethylbenzylamine-induced rat esophageal tumorigenesis

Epidemiological studies suggest that the frequent intake of non-steroidal anti-inflammatory drugs (NSAIDs) is associated with a decreased risk of developing esophageal squamous cell carcinoma (SCC). This decrease is thought to correlate with the inhibition of cyclooxygenase (COX) activity. The production of prostaglandin E2 (PGE2), a major metabolite of COX, is increased in numerous human cancers including esophageal SCC, therefore, inhibition of COX activity and subsequent suppression of the formation of PGE2 may be chemopreventive in the esophagus. The objective of the present study was to determine whether L-748706 (L-706), a novel selective COX-2 inhibitor, would prevent N-nitrosomethylbenzylamine (NMBA)-induced esophageal tumor progression in the Fischer 344 (F344) rat. In rats pretreated with a low-dose of NMBA (0.25 mg/kg body weight), L-706 at 100 p.p.m. in the diet significantly reduced tumor multiplicity but not tumor incidence. At 150 p.p.m. in the diet, L-706 alone and in combination with 200 p.p.m. piroxicam produced significant reductions in both tumor incidence and multiplicity. Inhibition of tumor development in low-dose NMBA-treated rats was associated with reductions in esophageal cell proliferation rates and PGE2 levels in preneoplastic tissues. In contrast, in rats treated with a higher dose of NMBA (0.5 mg/kg body weight), neither L-706 alone nor in combination with piroxicam reduced esophageal tumor incidence or multiplicity in spite of the fact that they reduced esophageal PGE2 levels in preneoplastic tissues and in papillomas. Cell proliferation rates were reduced only in animals treated with L-706 + piroxicam. Our data suggest that the chemopreventive treatments were effective in inhibiting tumor development in NMBA-treated animals only when they reduced PGE2 levels in preneoplastic esophageal tissues approximately to those levels found in normal esophagus.     

Chemopreventive effect of curcumin on N-nitrosomethylbenzylamine-induced esophageal carcinogenesis in rats.

Modifying effects of curcumin (derived from the rhizome of Curcuma longa L.) during the initiation or post-initiation phase of N-nitrosomethylbenzylamine (NMBA)-induced esophageal carcinogenesis were investigated in male F344 rats. Five-week-old rats were divided into 5 groups, and groups 1, 2 and 3 were given intraperitoneal injections of NMBA (0.5 mg / kg body weight / injection 15 times) for 5 weeks from 7 weeks old to induce esophageal neoplasms. Groups 2 and 3 were fed the diet containing 500 ppm curcumin during the initiation and post-initiation phases, respectively. Group 4 was given the diet containing curcumin throughout the experiment, and group 5 was kept on the basal diet alone and served as an untreated control. Incidence and multiplicity of esophageal neoplasms of group 1 (NMBA alone) were 66.7% and 0.83 +/- 0.70, respectively. Those of groups 2 and 3 were significantly less than those of group 1 (39.3%, 0.46 +/- 0.64, P < 0.05; 33.3%, 0.36 +/- 0.56, P < 0.05, respectively). Furthermore, the incidence and multiplicity of esophageal preneoplastic lesions (moderate or severe epithelial dysplasia) of group 2 (57.1%, 0.61 +/- 0.57; 40%, 0.29 +/- 0.46) or 3 (56.7%, 0.67 +/- 0.66; 23.3%, 0.23 +/- 0.43) were less than those of group 1 (100%, 1.67 +/- 0.70; 70.8%, 0.92 +/- 0.72) (P < 0.05). In this experiment, feeding of curcumin significantly decreased the expression of cell proliferation biomarkers (5-bromo-2'-deoxyuridine labeling index) in the non-lesional esophageal epithelium (P < 0.01). These findings indicate that curcumin inhibits NMBA-induced esophageal carcinogenesis when given during the post initiation as well as initiation phase. This inhibition may be related to suppression of the increased cell proliferation induced by NMBA in the esophageal epithelium.     

Suppression of N-nitrosomethylbenzylamine-induced rat esophageal tumorigenesis by dietary feeding of 1'-acetoxychavicol acetate.

The modifying effects of 1'-acetoxychavicol acetate (ACA) on N-nitrosomethylbenzylamine (NMBA)-induced esophageal tumorigenesis were investigated in male F344 rats. At 5 weeks of age, all test animals, except those given the test chemical alone, and the control rats received s.c. injections of NMBA (0.5 mg/kg body weight/injection, three times per week) for 5 weeks. At the termination of the study (20 weeks), 75% of rats treated with NMBA alone had esophageal neoplasms (papillomas). However, the groups given a dose of 500 ppm ACA during the initiation phase developed a significantly reduced incidence of tumors (29%; P<0.01). Exposure to ACA (500 ppm) during the post-initiation phase also decreased the frequency of the tumors (38%; P<0.05). A reduction of the incidence of preneoplastic lesions (hyperplasia or dysplasia) was obtained when ACA was administered in the initiation phase (P<0.01). Cell proliferation in the esophageal epithelium, determined by assay of proliferating cell nuclear antigen (PCNA), was lowered by ACA (P<0.05). Blood polyamine contents in rats given NMBA and the test compound were also smaller than those of rats given the carcinogen (P<0.05). These findings suggest that dietary ACA is effective in inhibiting the development of esophageal tumors by NMBA when given during the initiation or post-initiation phase, and such inhibition is related to suppression of cell proliferation in the esophageal epithelium.     

Suppression of N-nitrosomethylbenzylamine (NMBA)-induced esophageal tumorigenesis in F344 rats by JTE-522, a selective COX-2 inhibitor

Recent studies have demonstrated that overexpression of cyclooxygenase-2 (COX-2) and elevation of COX-2-mediated synthesis of prostaglandin E(2) (PGE(2)) were observed in various cancers including esophageal cancer, but their roles in carcinogenesis of the esophagi still remain unclear. To address the issue, we observed the reduction of N:-nitrosomethylbenzylamine (NMBA)-induced tumorigenesis in rat esophagi via JTE-522 (4-[4-cyclohexyl-2-methyloxazol-5-yl]-2-fluorobenzenesulfonamide), a selective COX-2 inhibitor. In this study, 54 F344 male rats were divided into nine groups; JTE-522 (3, 9 and 30 mg/kg) was administered orally. We also examined the effects of JTE-522 on COX-2 mRNA and synthesis of PGE(2). In the group in which JTE-522 was administered intermittently at a daily dose of 30 mg/kg, the number of NMBA-induced esophageal tumors per rat significantly reduced, to 62% (P< 0.05), but the size of the tumors was not significantly inhibited. In the group in which JTE-522 was administered continuously five times weekly for 24 weeks at a daily dose of 9 mg/kg, both the number and size of tumors significantly reduced, to 29 and 44%, respectively (P<0.05). Furthermore, JTE-522 suppressed not only tumor formation but also developing carcinomas (P<0.0021) [corrected]. In this study, treatment with NMBA alone resulted in an approximately 5-fold rise in expression of COX-2 mRNA detected by semi-quantitative RT-PCR analysis and an approximately 7-fold increase in the production of PGE(2) measured by ELISA compared with the normal esophageal mucosa. The up-regulated COX-2 expression did not decrease with the treatment of JTE-522 at the 3, 9 and 30 mg/kg doses; however, the increased levels of PGE(2) synthesis were significantly decreased by administering JTE-522 (P<0.01). Our study suggests that COX-2-mediated PGE(2) is important in NMBA-induced esophageal tumorigenesis in rats, and therefore may be a promising chemotherapeutic target for the prevention and treatment of esophageal cancer, especially with selective COX-2 inhibitors.     

Effect of alkyl chain length on inhibition of N-nitrosomethylbenzylamine-induced esophageal tumorigenesis and DNA methylation by isothiocyanates

This study was undertaken to evaluate the inhibitory effectsof benzyl isothiocyanate (BITC), phenethyl isothiocyanate (PEITC),3-phenylpropyl isothiocyanate (PPITC) or 4- phenylbutyl isothiocyanate(PBITC) on N-nitrosomethylbenzylamine (NMBA)-induced esophagealtumorigenesis in male Fisher 344 rats. Groups of 15 male ratswere fed modified AIN-76A diet or diet containing the four isothiocyanatesat concentrations of 2.5, 1.0 and 0.4 µmol/g diet for25 weeks. After two weeks, rats were administered 0.5 mg/kgNMBA S.C. once weekly for 15 weeks. Additional controls receivedmodified AIN-76A diet only or diet containing the high concentrationof isothiocyanates (2.5 µmol/g) only. No tumors were foundin any of the groups that were not administered NMBA. Rats treatedwith NMBA only developed 6.7±0.8 tumors/animal. Tumorincidences in rats treated with 2.5 and 1.0 µmol PEITC/gdiet, and with all three dietary concentrations of PPITC wereinhibited by 60/100% compared to controls. Tumor multiplicitieswere inhibited by 83–100% by PEITC or PPITC at all dietaryconcentrations tested. PPITC clearly had a stronger inhibitoryeffect on NMBA tumorigenesis than did PEITC. Compared to PEITCand PPITC, BITC and PBITC had little inhibitory effect on tumormultiplicity and no effect on NMBA tumor incidence. In general,the occurrence of preneoplastic lesions (acanthoses, hyperkeratose,leukoplakias and leukokeratoses) was inhibited in a similarmanner as tumor incidence and multiplicity, except that no experimentaldiet resulted in a significant reduction of the incidence ofacanthoses and hyperkeratoses. As with their effects on tumorigenicityand formation of premalignant lesions, the inhibitory effectsof the isothiocyanates on NMBA-induced DNA methylation 24 hafter administration followed the order: PPITC > PEITC >PBITC > BITC.     

Enhancement of esophageal carcinogenesis in male F344 rats by dietary phenylhexyl isothiocyanate

The purpose of this study was to evaluate the potential effectsof dietary 6-phenylhexyl isothiocyanate (PHITC) on N-nitrosomethylbenzylamine(NMBA)-induced esophageal carcinogenesis in rats. Groups of15 male F344 rats received weekly s.c. injections of NMBA in20% dimethylsulfoxide or the vehicle alone for 15 consecutiveweeks. Two weeks prior to initiation of carcinogen or vehicleinjections rats were provided with modified AIN-76A diet ormodified AIN-76A diet containing PHITC at levels of 0.4, 1.0or 2.5 µmol/g diet. Experimental controls consisted ofgroups that received only the vehicle (vehicle controls), NMBA(carcinogen controls) or PHITC at the high dose level of 2.5µmol/g diet. No esophageal tumors or preneoplastic lesionswere detected in rats that received the vehicle or PHITC alone.In contrast, all rats treated with NMBA alone or PHITC + NMBAexhibited esophageal tumors and preneoplastic esophageal lesions.In groups that received PHITC + NMBA tumor multiplicity wasincreased by 21–69% when compared with rats treated withNMBA alone, indicating that PHITC enhanced esophageal tumorigenesisin this model system. These results, in conjunction with ourprevious work, demonstrate that arylalkyl isothiocyanates mayinhibit or enhance esophageal tumorigenesis in the NMBA-treatedrat. The ability of isothiocyanates to inhibit or enhance experimentaltumorigenesis may depend on alkyl chain length of the isothiocyanate,the animal species examined and the specific carcinogen employed.     

Promotion of N-methyl-N-nitrosourea-induced thyroid tumors by iodine deficiency in F344/NCr rats

Six-week-old male F344 rats were each given an injection once iv of N-methyl-N-nitrosourea [(MNU) CAS: 684-93-5] at a dose of 41.2 mg/kg body weight. Two weeks later, groups of rats were placed on iodine-deficient (ID) or iodine-adequate (IA) diets and then sacrificed at 20 and 33 weeks. Other groups received ID or IA diets without MNU. For localizing thyroid-stimulating hormone (TSH) and prolactin, sections of pituitary glands were stained by the avidin-biotin-peroxidase complex technique with the use of anti-rat TSH or prolactin antibody. At 20 weeks, rats receiving MNU and ID diets had a 100% incidence of diffuse follicular goiter and multiple follicular adenomas of the thyroid. Focal proliferative thyroid follicular lesions including focal hyperplasias and adenomas per square centimeter of thyroid gland were significantly increased in rats given MNU and ID diets in comparison with rats given MNU and IA diets. At 33 weeks, all MNU rats on ID diets had a significantly increased incidence of thyroid carcinoma of the follicular or papillary types and diffuse pituitary thyrotroph hyperplasia, hypertrophy, and vacuolar degeneration. Rats fed ID diets without MNU had diffuse follicular goiter but no tumors at any time period. MNU given alone in rats fed IA diets induced a 10% incidence of single thyroid adenomas at 20 weeks and 70% at 33 weeks and a 10% incidence of thyroid carcinoma at 33 weeks. Tumors induced in other organs by MNU were not affected by the ID diets. Thus this experiment provided evidence that ID diets are potent promoters of thyroid tumors in this system, but the ID diet itself without carcinogen was not carcinogenic under the conditions of the study.     

Sequential endoscopic findings and histological changes of N-nitrosomethylbenzylamine-induced esophageal carcinogenesis in rats

We performed a sequential endoscopic examination of esophageal carcinogenesis induced by N-nitrosomethyl-benzylamine (NMBA) in F344 rats. The endoscopic findings were consistent with the histological changes observed in the specimens obtained by a biopsy and/or an autopsy. Seven-week-old male F344 rats received a weekly subcutaneous injection of 0.5 mg/kg NMBA for 15 weeks. The first endoscopic change that was detected was redness of the musosa due to the dilatation of the submucosal blood vessels. Subsequently, the mucosal redness became obscure, and we observed a focal loss of the visible blood vessel network due to hyperkeratosis, followed by the appearance of plaque-like elevated lesions due to acanthosis. Then, smooth and irregular polyps appeared as a result of the development of papilloma without or with dysplastic potential, respectively. Finally, rough elevation appeared as a result of carcinoma in situ and invasive squamous cell carcinoma. The present endoscopic findings correlated closely with the histological changes, indicating that sequential fiberscopic examination may be useful for monitoring esophageal carcinogenesis.     

Evaluation of dietary dehydroepiandrosterone for chemoprotection against tumorigenesis in premalignant colonic epithelium of male F344 rats

Epidemiological and experimental studies suggest that dehydroepiandrosterone (DHEA), an adrenal cortical steroid, has chemoprotective properties. Rat colonic epithelium which had been induced to a premalignant state by the colonic carcinogen azoxymethane was used as a model for patients at high risk of colorectal carcinoma, and the efficacy of dietary DHEA for chemoprotection against tumorigenesis was evaluated. Ten-week-old male F344 rats (n = 100) were given 10 weekly s.c. injections of azoxymethane at a dose of 10 mg/kg/week. One day after the final dose of carcinogen, DHEA was added to the diet of 50 rats (0.5% DHEA chow), and the other rats were used as pair-fed controls. DHEA-fed rats lost body weight throughout the 17-week study, in contrast to their pair-fed controls. Serum DHEA in DHEA-fed rats at the end of the study was 6 times that of controls (120 +/- 30 versus 18 +/- 14 pmol/ml), and serum DHEA sulfate was 23 times that of controls (1311 +/- 13 versus 55 +/- 13 pmol/ml). Addition of DHEA to the diet produced no significant chemoprotection in our model. Tumor-related mortality was somewhat increased in DHEA-fed rats (20% versus 6% in week 16 of DHEA feeding, P not significant). The cumulative prevalence of left colonic tumors, identified by weekly colonoscopic examinations, was somewhat lower in DHEA-fed rats than in controls during weeks 10 through 13 (17% versus 33% in week 12, P not significant), but in week 14 the prevalence in DHEA-fed rats became similar to that in controls (39% versus 41%). Growth curves of autochthonous left colonic tumors, as assessed for 8 weeks by computerized image analysis of colonoscopic photographs, were similar for DHEA-fed and control rats. Prevalence, mean frequency, multiplicity, and diameter of colonic tumors at necropsy of colonoscopically negative rats in week 17 were somewhat lower in the DHEA-fed rats (e.g., prevalence of 47% versus 67%), but the differences from controls were not significant. Parameters of colonic epithelial proliferation after tritiated thymidine incorporation in DHEA-fed rats were similar to those in control rats (labeling index of 8.3 +/- 0.7% versus 8.4 +/- 0.6% in week 17), despite higher serum DHEA and DHEA sulfate levels. Our findings indicate that DHEA did not have significant postinduction chemoprotective activity against azoxymethane-induced colonic tumorigenesis in this model utilizing pair-fed controls. Further preclinical studies appear to be needed before dietary DHEA can be recommended for chemoprotection trials in patients with premalignant colorectal epithelium.     

Promoting effects of high-fat corn oil and high-fat mixed lipid diets on 7,12-dimethylbenz[a]anthracene-induced mammary tumorigenesis in F344 rats

Epidemiological studies and laboratory animal model assays suggest that a high intake of dietary fat promotes mammary carcinogenesis as well as colon tumorigenesis. Fat intake in the United States traditionally includes high amounts (30% of total caloric intake) of saturated fatty acids (SFAs) compared to polyunsaturated fatty acids (PUFAs). A recent study suggested that a high-fat mixed-lipid diet (HFML), which simulates the mixed-lipid and high SFAs composition of the average American diet, strongly promotes rat colon carcinogenesis, even when compared to another high-fat diet containing PUFA-rich corn oil. On the other hand, some reports suggest that a high-fat diet rich in n-6 PUFAs promotes mammary carcinogenesis more strongly than a high-fat diet rich in SFAs. Therefore, the present study was designed to compare the effects of HFML, high-fat corn oil diet (HFCO) that is rich in n-6 PUFAs, and a low-fat corn oil diet (LFCO) on 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary carcinogenesis in female F344 rats. At 7 weeks of age, female F344 rats intended for carcinogen treatment received a gavage of DMBA at a dose level of 65 mg/kg of body weight. Beginning 1 week after carcinogen treatment, groups of rats were then maintained on experimental diets containing LFCO, HFCO or HFML. All rats were evaluated weekly by palpation of mammary tumors and sacrificed 20 weeks after the DMBA treatment. Palpable tumors of mammary glands were detected at the 8, 11, and 19 weeks in the HFCO, HFML and LFCO groups, respectively. Histopathological observation revealed that the incidence and number of mammary tumors in the HFCO group were significantly higher than in the LFCO group. Rats on the HFML diet tended towards a higher incidence and number of mammary tumors compared with the LFCO group, although the correlation was not statistically significant. These results suggest that, for this animal model, both the HFCO and HFML diets promote DMBA-induced mammary carcinogenesis when compared to the LFCO diet, and that the HFCO diet is more tumor-promotional than the HFML diet.     

The effects of ellagic acid and 13-cis-retinoic acid on N-nitrosobenzylmethylamine-induced esophageal tumorigenesis in rats

Ellagic acid (EA) and 13-cis-retinoic acid (CRA), both alone and in combination, were tested for their ability to inhibit N-nitrosobenzylmethylamine-induced tumors in the rat esophagus. Groups of male rats were fed AIN-76A diet containing EA (4 g/kg), CRA (240 mg/kg), or a combination of EA and CRA (4 g/kg and 240 mg/kg), respectively, for 25 weeks. Two weeks after initiation of the diets, NBMA (0.5 mg/kg per injection) was administered s.c. once weekly for 15 weeks. After 25 weeks on the diets, the animals were necropsied. The incidence of esophageal tumors was 97-100% in all NBMA-treated groups. The multiplicity of tumors in NBMA-treated groups was reduced significantly by EA (60%), but not by CRA, or by EA + CRA. These results demonstrate that EA and CRA do not act synergistically to inhibit NBMA-induced esophageal tumorigenesis.