Preventive effects of a flavonoid myricitrin on the formation of azoxymethane-induced premalignant lesions in colons of rats

The preventive effect of dietary exposure to a flavonoid myricitrin of azoxymethane (AOM)-induced aberrant crypt foci (ACF) and beta-catenin-accumulated crypts (BCAC) formation was investigated in male F344 rats. Thirty-four rats were divided randomly into five experimental groups. Rats in groups 1-3 were given subcutaneous injections of AOM (15 mg/kg body weight) once a week for 3 weeks. Starting 1 week before the first injection of AOM, rats in groups 2 and 3 were fed a diet containing 500 or 1000 ppm myricitrin, respectively, for 11 weeks. Rats in group 4 were fed a diet containing 1000 ppm myricitrin. Rats in groups 1 and 5 were given the basal diet alone during the study. The experiment was terminated 11 weeks after the start. The frequency of ACF per colon in group 3 treated with AOM and 1000 ppm myricitrin was significantly lower than that in group 1 treated with AOM alone (p<0.01). Furthermore, dietary myricitrin at both doses (groups 2 and 3) significantly inhibited the formation of BCAC when compared to group 1 (p<0.05). These results indicate that myricitrin had possible chemopreventive effects in the present short-term colon carcinogenesis bioassays and suggest that longer exposure may cause suppression of tumor development.

Effect of Running Training on DMH-Induced Aberrant Crypt Foci in Rat Colon

PURPOSE

We examined the effects of treadmill-running training on the induction of aberrant crypt foci (ACF), which is the first step of colon cancer induction, in the colonic mucosa of rats injected with 1,2-dimethylhydrazine (DMH).

METHODS

Four-week-old F344 rats (N = 38) were randomly assigned to training (19 rats) and control (19 rats) groups. After a week, all rats were given DMH (20 mg.kg(-1) body weight) once a week for 2 wk. Running training was started at age 7 wk (speed: 10 m.min(-1), 0% grade, 120 min.d(-1), 5 d.wk(-1)). After 4 wk of training, the rats were sacrificed and the colon was removed, opened, and counted for ACF with 0.2% methylene blue staining.

RESULTS

Running training resulted in lower body- (P < 0.01) and adipose fat weight (P < 0.05). The numbers of ACF and total AC were significantly lower in the running training group than in the control group (P < 0.05). The occurrences of one, three, and five aberrant crypts per focus were also significantly lower in the running training group than in the control group (P < 0.05). The ratios of total AC/ACF did not significantly differ between the running training and control groups.

CONCLUSIONS

The results of the present investigation suggest that low-intensity running training inhibits the DMH-induced initiation of colon ACF development.

Chitosan prevents the development of AOM-induced aberrant crypt foci in mice and suppressed the proliferation of AGS cells by inhibiting DNA synthesis

We study the effect of fungal-derived chitosan on the development of chemical-induced colonic precancerous lesions in ICR mice and delineate its possible molecular mechanisms. In the 2 weeks preventive experiments, mice fed with a diet containing high molecular weight chitosan (HMWC) had significant fewer aberrant crypt foci formation than those fed with control diet. As the treatment extended to 6 weeks, both low molecular weight chitosan (LMWC)- and HMWC-fed mice contained less aberrant crypt foci when compared to control. However, such effect was not observed in mice in the 6 weeks therapeutic experiments. The anti-tumorigenesis effect of water-soluble chitosan oligomer (WSCO) was tested on four cancer cell lines. WSCO significantly suppressed AGS and to a less extent, COLO 205 cells proliferation. Flow cytometry analysis of cell cycle distribution indicated that the percentage of S phase reduced significantly in AGS cells treated with WSCO together with a decrease in DNA synthesis rate in BrdU incorporation assay. WSCO treatment also upregulated cell cycle-related genes p21/Cip and p27/Kip, whereas downregulated that of PCNA.

Mammary cancer resistance and precocious mammary differentiation in the WKY rat: Identification of 2 quantitative trait loci

The COP and WKY rat strains are resistant to mammary cancer. It has shown previously that upon chemical carcinogen treatment, COP females exhibit mammary preneoplastic lesions which disappear within a few weeks. We show here that in similar conditions, WKY females do not exhibit any visible preneoplastic lesions. WKY females are characterized by precocious mammary tissue differentiation, including active expression of the beta-casein gene in young virgin females. This trait might be critical in resistance to mammary carcinogenesis of WKY rats. To test this hypothesis, we took advantage of 2 congenic strains that contain a limited chromosome segment of WKY origin, derived either from chromosome 5 or from chromosome 18, introgressed in the susceptible genetic background (SPRD-Cu3). Each of these congenic strains has been shown to be partially resistant to chemically induced mammary carcinogenesis (reduction in tumour multiplicity with respect to the susceptible SPRD-Cu3 rats). We show here that these 2 congenic strains also exhibit precocious mammary differentiation, though to a lower extent than the WKY females. The conclusion of this study is thus 2-fold: (i) eradication of preneoplastic lesions is not a general phenomenon in mammary cancer resistance; (ii) the same segment of rat chromosomes 5 or 18 that controls mammary cancer resistance also contains a quantitative trait locus imposing precocious mammary differentiation. These 2 traits are thus associated, supporting the hypothesis that there might be a cause-effect relationship between precocious mammary differentiation and cancer resistance.

Effect of 2-(carboxyphenyl) retinamide and genistein on the formation of early lesions in 1,2-dimethylhydrazine-induced colon carcinogenesis in rats

Aberrant crypt foci (ACF) are recognized as preneoplastic lesions for colon cancer, and ACF in rodents are widely used as an intermediate biomarker to predict tumorigenicity in the colon. However, a lack of correlations between the formation of ACF and the development of colonic tumors has been reported in several studies. For example, 2-(carboxyphenyl) retinamide (2-CPR) and genistein were reported to inhibit the carcinogen-induced formation of ACF, whereas both of them were later found to enhance colon tumorigenesis in rats treated with azoxymethane (AOM). Recently, we have identified b-catenin-accumulated crypts (BCAC) in the colon of rats shortly after administration of AOM, and provided evidence that these are independent early lesions of classical ACF, and BCAC might be direct precursors for colon cancers. In the present study, we performed a comparative analysis of the modifying effects of 2-CPR and genistein on 1,2-dimethylhydrazine (DMH)-induced BCAC and ACF in male F344 rats. Dietary administration of 2-CPR (315 ppm) significantly reduced the total number, multiplicity and size of ACF in DMH-exposed colonic mucosa, while genistein (250 ppm) had no significant effects on DMH-induced ACF formation. In contrast, both of 2-CPR and genistein significantly enhanced the multiplicity and size of DMH-induced BCAC when compared with DMH alone group. In addition, both 2-CPR and genistein significantly increased the proliferating cell nuclear antigen (PCNA) index preferentially in BCAC. Together with previous findings that 2-CPR and genistein are tumor promoters in the colon, our results support the concept that BCAC are precursors of colon tumors and suggest that these lesions are more reliable short-term biomarkers for colon carcinogenesis in rodents than ACF.

Co-carcinogenic effect of cyclohexanol on the development of preneoplastic lesions in a rat hepatocarcinogenesis model

Cyclohexanol is a basic industrial chemical widely used because of its versatility as an industrial solvent. No studies have been conducted to evaluate the carcinogenic/co-carcinogenic hazards associated with cyclohexanol exposure. In male Fisher 344 rats liver preneoplastic lesions were induced by N-nitrosodiethylamine (150 mg/Kg) i.p., followed by the tumor promoter 2-acetylaminofluorene (2-AAF: 20 mg/kg) orally administered on three consecutive days before partial hepatectomy. The cyclohexanol administration in this hepatocarcinogenesis assay revealed that it has a strong tumor co-promoter potential. There is clear evidence that oxidative stress and the CYP2E1 are components of carcinogenesis. Although no changes in the lipid peroxidation levels were observed between treated and untreated animals, a significant increase in CYP2E1 expression was observed when cyclohexanol was administered 24 h after the last 2-AAF dose. On the other hand, levels of the proliferation markers PCNA and Ki-67 were not increased after treatment with cyclohexanol, but a marked downregulation of the Bax proapoptotic protein was found exclusively in mitochondrial extracts of animals treated with cyclohexanol. This study represents the first report of the ability of cyclohexanol-induced lesions, when administered simultaneously with 2-AAF, to potentiate the development of preneoplastic liver.

Low selection of preneoplastic hepatocytes after treatment with the 2-acetylaminofluorene diet-partial hepatectomy regimen in the liver of hepatocarcinogenesis-resistant DRH strain rats

In hepatocarcinogenesis-resistant DRH rats, preneoplastic hepatocytic lesions are smaller than those of usual rats during carcinogenesis. When preneoplastic hepatocytes from DRH and Donryu (original strain of DRH) were reciprocally transplanted into the livers of DRH and Donryu treated with 2-acetylaminofluorene (2-AAF) diet/two-thirds hepatectomy (PH), the Donryu cells formed small colonies within the DRH liver, whereas the DRH cells formed large colonies within the Donryu liver. The DRH liver showed less degree of oval cell proliferation after treatment with 2-AAF and PH, and DRH hepatocytes were more resistant to the growth-inhibitory effect of 2-AAF after PH. Furthermore, DRH hepatocytes were generally resistant to cytotoxicity of hepatotoxins. The tissue environment of the DRH liver, therefore, is less effective for selective growth of preneoplastic hepatocytes during the carcinogen treatment, which is probably a major cause of the hepatocarcinogenesis-resistance in DRH rats.

Effect of dietary apigenin on colonic ornithine decarboxylase activity, aberrant crypt foci formation, and tumorigenesis in different experimental models

The efficacy of dietary apigenin, a dietary flavonoid, in colon cancer prevention was investigated by evaluating the inhibition of the ornithine decarboxylase (ODC) activity and the formation of aberrant crypt foci (ACF) and by studying the ability of apigenin to block colon carcinogenesis in two mouse models. First, the activity of ODC was measured in colon cancer cells (Caco-2) and in the colon epithelium of CF-1 mice. Apigenin at 10 and 30 muM significantly inhibited the ODC activity of Caco-2 cells by 26% and 57%, respectively. Colonic ODC activity in CF-1 mice was reduced with 0.1% dietary apigenin by 42% compared with the control, but this difference was not statistically significant. Second, ACF formation was evaluated in azoxymethane (AOM)-induced CF-1 mice. Female CF-1 mice at 6 wk of age were i.p. injected with 5 mg/kg body weight (BW) AOM once to induce ACF. ACF formation in CF-1 mice was reduced by 50% (P < 0.05) with 0.1% dietary apigenin fed for 6 wk when compared with the control. Dietary apigenin inhibited ACF only in the distal region of the CF-1 mouse colon. Finally, tumorigenesis studies were conducted using two different mouse models: AOM-induced CF-1 mice and Min mice with mutant adenomatous polyposis coli (APC) gene. Female CF-1 mice at 6 wk of age were i.p. injected with 10 mg/kg BW AOM weekly for 6 (AOM Study I) or 4 (AOM Study II) wk to induce tumors. CF-1 mice were fed diets containing 0.025% or 0.1% apigenin for 23-25 wk. Female Min mice were fed diets for 10 wk beginning at 5 wk of age. In two AOM-treated mouse colon tumor studies 0.025% and 0.1% dietary apigenin modestly reduced tumors in the group fed 0.025% apigenin (25% incidence in comparison with 65% in the controls) in a non-dose response manner. Apigenin failed to inhibit adenoma formation in the Min mouse study. These results suggest that dietary apigenin showed promise in cancer prevention by reducing the ODC activity and ACF formation, however, clear evidence of cancer prevention was not obtained in mouse tumor studies. Further investigation of the potential chemopreventive effect of apigenin in carcinogenesis is warranted.

Methionine restriction inhibits colon carcinogenesis

Previously, we demonstrated that life-long methionine restriction (MR) in rats increases life span and inhibits aging-related disease processes. The present study examines the effects of MR on the formation of preneoplastic aberrant crypt foci (ACF) in the colon of azoxymethane (AOM)-treated rats. Six-week-old male F344 rats were placed on essential amino acid-defined diets containing either 0.86% Met (control diet) or 0.17% Met (MR diet) and 1 wk later were given AOM (15 mg/kg/wk, s.c.) for 2 consecutive wk. Ten weeks after the final AOM treatment, ACF formation was markedly reduced in rats fed the MR diet with ACF containing > or = 4 crypts/focus being reduced by over 80% compared to controls (P < 0.001). A similar 83% reduction in ACF containing > or = 4 crypts/focus was observed in rats fed the MR diet only during the post-initiation period (after the final dose of AOM; P < 0.001). Five weeks after AOM administration, a 12% reduction in colonic cell proliferation was observed in MR rats compared to controls (P < 0.05). These results show that MR inhibits colonic tumor development in the rat, an effect that occurs primarily during post-initiation phases of carcinogenesis and may be due, in part, to an inhibition of colonic cell proliferation.

Orphan Nuclear Receptor Constitutive Active/Androstane Receptor–Mediated Alterations in DNA Methylation during Phenobarbital Promotion of Liver Tumorigenesis

Altered DNA methylation is an epigenetic mechanism that plays a key role in the carcinogenesis process, and the nongenotoxic rodent hepatocarcinogen phenobarbital (PB) alters the methylation status of DNA in mouse liver. The constitutive active/androstane nuclear receptor (CAR) mediates half of the PB-induced hepatic gene expression changes and it is essential for liver tumor promotion in PB-treated mice. Here, a technique involving methylation-sensitive restriction digestion, arbitrarily primed PCR, and capillary electrophoresis was utilized to detect PB-induced regions of altered DNA methylation (RAMs) in CAR wildtype (WT) mice that are sensitive to promotion by PB and resistant CAR knockout (KO) mice. The CAR WT mice developed preneoplastic lesions after 23 weeks of PB treatment (precancerous) and liver tumors after 32 weeks, while the CAR KO mice did not develop tumors (Y. Yamamoto, et al., 2004, Cancer Res. 64, 7197-7200). Our goal was to discern those RAMs which are playing important roles in tumor formation by comparing the RAMs that form in sensitive and resistant groups of mice. Using this novel approach, 42 unique RAMs were identified in the precancerous as compared to the CAR KO, 23-week PB-treated tissue. Of these 42 RAMs, 14 carried forward to the tumor tissue, and additionally, 104 total unique RAMs were observed in the tumor tissue. These results indicate that there are unique RAMs occurring in the sensitive CAR WT mice and that a portion of these are seen in both the precancerous and tumor tissue. We hypothesize that these unique RAMs may be facilitating the tumorigenesis process, and these data support the view that DNA methylation plays a causative role in PB-induced tumorigenesis.

Modification of risk of arsenic-induced skin lesions by sunlight exposure, smoking, and occupational exposures in Bangladesh

BACKGROUND

The risk of skin lesions associated with arsenic exposure from drinking water in Bangladesh is considerably greater in men than in women.

METHODS

Using baseline data from 11,062 cohort members in the Health Effects of Arsenic Longitudinal Study in Araihazar, Bangladesh, we performed a cross-sectional analysis to evaluate whether the association between arsenic exposure from drinking water and the risk of skin lesions is modified by tobacco smoking, excessive sunlight, the use of fertilizer, and the use of pesticides. A time-weighted well arsenic concentration was estimated for each participant by incorporating history of well use. Relative excess risk for interaction (RERI) and its 95% confidence intervals (CIs) were estimated using adjusted prevalence odds ratios.

RESULTS

We observed a synergistic effect between the highest level of arsenic exposure (> 113 microg/L) and tobacco smoking on risk of skin lesions in men (RERI = 1.5 [95% CI = 0.3 to 2.7] overall and 1.7 [0.2 to 3.4] for the subpopulation with longer-term arsenic exposure). We also observed suggestive synergistic effects between higher levels (28.1-113.0 microg/L and 113.1-864.0 microg/L) of arsenic exposure and fertilizer use in men (RERI = 1.0 [-0.2 to 2.2] and 1.3 [-0.2 to 2.9] respectively). Furthermore, the risk of skin lesions associated with any given level of arsenic exposure was greater in men with excessive sun exposure. The patterns of effect estimates in women indicate similar-but-weaker interaction effects of arsenic exposure with tobacco smoking and fertilizer use.

CONCLUSIONS

These findings help explain why the risk of arsenic-related skin lesions was much greater in men than in women in Bangladesh. Because most arsenic-induced skin cancers arise from these skin lesions, treatment and remediation plans should take into consideration these etiologic cofactors.

Role of the Kupffer cell in mediating hepatic toxicity and carcinogenesis

Kupffer cells are resident macrophages of the liver and play an important role in its normal physiology and homeostasis as well as participating in the acute and chronic responses of the liver to toxic compounds. Activation of Kupffer cells directly or indirectly by toxic agents results in the release of an array of inflammatory mediators, growth factors, and reactive oxygen species. This activation appears to modulate acute hepatocyte injury as well as chronic liver responses including hepatic cancer. Understanding the role Kupffer cells play in these diverse responses is key to understanding mechanisms of liver injury. Idiosyncratic drug-induced liver disease results in morbidity and mortality, impacting severely on the development of new pharmacological agents. Modulation of the response of Kupffer cells by drugs has been suggested as a cause for the idiosyncratic response. Similarly, liver damage seen in chronic ethanol consumption appears to be modulated by Kupffer cell activation. More recent evidence has noted a contributory role of Kupffer cell activation in the process of hepatic carcinogenesis. Several nongenotoxic carcinogens, for example, activate Kupffer cells resulting in the release of cytokines and/or reactive oxygen species that induce hepatocyte cell proliferation and may enhance clonal expansion of preneoplastic cells leading to neoplasia. Kupffer cells therefore appear to play a central role in the hepatic response to toxic and carcinogenic agents. Taken together, the data presented in this symposium illustrate to the toxicologist the central role played by Kupffer cells in mediating hepatotoxicity.

Selected fruits reduce azoxymethane (AOM)-induced aberrant crypt foci (ACF) in Fisher 344 male rats

Phytochemicals contribute to the vibrant colors of fruits and it is suggested that the darker the fruit the higher the antioxidative or anticarcinogenic properties. In this study we investigated the possible effects of blueberries (BLU), blackberries (BLK), plums (PLM), mangoes (MAN), pomegranate juice (POJ), watermelon juice (WMJ) and cranberry juice (CBJ) on azoxymethane (AOM)-induced aberrant crypt foci (ACF) in Fisher 344 male rats. Forty-eight male Fisher 344 rats were randomly assigned to eight groups (n=6). The groups were fed AIN-93G as a control (C) diet, the rats fed fruits received AIN-93G+5% fruits and the groups that were given fruits juices received 20% fruit juice instead of water. The rats received subcutaneous injections of AOM at 16 mg/kg body weight at seventh and eighth weeks of age. At 17th week of age, the rats were killed by CO(2) asphyxiation. Total ACF numbers (mean+/-SEM) in the rats fed CON, BLU, BLK, PLM, MNG, POJ, WMJ and CBJ were 171.67+/-5.6, 11.33+/-2.85, 24.0+/-0.58, 33.67+/-0.89, 28.67+/-1.33, 15.67+/-1.86, 24.33+/-3.92 and 39.0+/-15.31. Total glutathione-S-transferase (GST) activity (mICROmol/mg) in the liver of the rats fed fruits (except BLK) and fruit juices were significantly (p<0.05) higher in the rats fed fruits and fruit juices compared with the control. Our findings suggest that among the fruits and fruit juices, BLU and POJ contributed to significant (P<0.05) reductions in the formation of AOM-induced ACF.

Catalpa seed oil rich in 9t,11t,13c-conjugated linolenic acid suppresses the development of colonic aberrant crypt foci induced by azoxymethane in rats

Catalpa (Catalpa ovata) seed oil (CPO) is a unique oil that contains a high amount of 9trans,11trans,13cis-conjugated linolenic acid. In the present study, we investigated whether dietary administration with CPO affects the development of azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) in male F344 rats to elucidate its possible cancer chemopreventive efficiency. Also, the effect of CPO on the fatty acid composition of liver tissue and colonic mucosa, the serum levels of total cholesterol and triglyceride, and the mRNA expression of cyclooxygenase (COX)-2 in the colonic mucosa were measured. In addition, the cell proliferation activity and apoptotic index in the colonic mucosa were estimated immunohistochemically. Animals were given two weekly subcutaneous injections of AOM (20 mg/kg body weight). They also received the experimental diet containing 0.01%, 0.1% or 1% CPO for 4 weeks, starting one week before the first dosing of AOM. AOM exposure produced a substantial number of ACF (99+/-28) at the end of the study (week 4). Dietary administration of CPO reduced the number of ACF (AOM + 0.01% CPO, 32+/-11, P<0.001; AOM + 0.1% CPO, 35+/-18, P<0.001; AOM + 1% CPO, 18+/-10, P<0.001). 9t,11t-conjugated linoleic acid was detected in the liver tissue and colonic mucosa of rats fed the CPO-containing diet. Additionally, dietary administration with CPO decreased the serum triglyceride level and the expression of COX-2 mRNA in the colonic mucosa. The indices of cell proliferation and apoptosis in the colonic mucosa of rats treated with AOM and 1% CPO have significant differences when compared with the AOM alone group. These findings suggest the possible chemopreventive activity of CPO in the early phase of colon carcinogenesis.

[Cystic degeneration in liver injury induced by CCl4 in SD rats]

OBJECTIVE

To explore the hepatic injury induced by CCl4in SD rat.

METHOD

40 SD rats were allocated to male and female group, consisting of 20 animals/sex/group. SD rats were given at 2 mL x kg(-1) of 10% CCl4 through celiac injection per 3 day for 12 days. All rats were killed by anaesthesia of ethyl ether and bleeding through abdominal aorta at 12th day. Liver tissue was fixed in 10% neutral formalin, embedded in paraffin, cut at a nominal thickness of 3 microm, stained with hematoxylin and eosin ( H&E) , evaluated at by microscopic examination.

RESULT

19 cases with local necrosis, 8 cases with fatty degeneration, 9 cases with cystic degeneration and 2 cases with fibrosis were seen in group male. 20 cases with local necrosis, 9 cases with fatty cases degeneration, 1 case with cystic degeneration and 1 case with fibrosis were seen in group female. The incidence of cystic degeneration in male group was found significantly higher than that in female group (P < 0. 05) , but the incidence of other lesions was no significant difference between male and female group.

CONCLUSION

CCl4 induces local necrosis , fatty degeneration, fibrosis and cystic degeneration in SD rat. The incidences of local necrosis , fatty degeneration and fibrosis were no significantly difference between male and female rat, but the incidence of cystic degeneration in male rats was significant higher than that in female rats.

Expression of ets-1 is not affected by N-ras or H-ras during oral oncogenesis

PURPOSE

To determine whether ras-activated cascades lead to activation of ets-1 expression in sequential histological stages of oral oncogenesis in an experimental animal model.

METHODS

Thirty-seven Syrian golden hamsters were divided into three experimental groups (A, B, C) and one control group. The hamsters' buccal pouches in experimental groups were treated with 0.5% 9, 10-dimethyl-1, 2-benzanthracene (DMBA) for 14 weeks and were excised at 10, 14, 19 weeks, respectively. The biopsies were classified pathologically (normal mucosa, hyperkeratosis, hyperplasia, dysplasia, early invasion, well and moderately differentiated carcinoma) and studied immunohistochemically. The two-tailed Student's t test was performed for each animal group and for each histological category.

RESULTS

The ets-1 expression increased in early stages of oral tumor formation and invasion. The expression of N-ras gradually decreased during oral oncogenesis, as previously observed with H-ras.

CONCLUSIONS

Neither N-ras nor H-ras affects ets-1 expression in contrast to other types of cancer in which N-ras and ets-1 are implicated in the same signalling pathway. Therefore, the existing pathway implicating these proteins might be somehow altered in oral cancer. It seems that ets-1 is a good prognostic marker for invasiveness and progression of oral cancer.

Chemopreventive effect of celecoxib in oral precancers and cancers

OBJECTIVES

Oral cancer has become an important health care problem in many countries. Because this disease develops slowly, early detection and intervention can greatly affect ultimate outcome. Celecoxib is a cyclooxygenase-2 inhibitor with significantly less toxicity. This study investigated the possibility of using it for chemoprevention of oral cancer at the early stages.

STUDY DESIGN

Randomized animal study.

METHODS

Dysplastic lesions were induced in the buccal pouches of 47 hamsters by a 5 week painting of 9,10-dimethl-1,2-benzanthrancene (DMBA). Basal diets or diets containing 500 or 1,500 ppm of Celecoxib were orally given for 7 weeks. The T50 (50% incidence; i.e., the time to appearance of tumors in 50% of the hamsters) was observed, and volume of tumors was measured on day 1, 9, 19, 28, 35, and 48 with the Celecoxib treatment.

RESULTS

The T50 was 9, 19, and 28 days with the treatment in the control group, in the 500 ppm group, and in the 1,500 ppm group, respectively. It indicated that the Celecoxib treatment could delay progression of early lesion. The tumor measurement showed that this treatment was also effective in delaying tumor growth in both treatment groups. There was a difference in the treatment efficacy between the 500 ppm and 1,500 ppm of Celecoxib, indicating a dose-dependent efficacy.

CONCLUSIONS

Celecoxib is effective in delaying onset of early lesions induced by DMBA and in slowing growth of the tumors in hamster cheek pouches during the postinitiation stage. Its treatment efficacy appears to be dose dependent.

Induction of mammary gland ductal hyperplasias and carcinoma in situ following fetal bisphenol A exposure

Exposure of the fetus to excess estrogen is believed to increase the risk of developing breast cancer during adult life. Fetal exposure to low doses of the xenoestrogen bisphenol A resulted in long-lasting effects in the mouse mammary gland that were manifested during adult life. It enhanced sensitivity to estradiol, decreased apoptosis, increased the number of progesterone receptor-positive epithelial cells at puberty and increased lateral branching at 4 months of age. We now report that fetal exposure to 2.5, 25, 250 and 1000 microg bisphenol A/kg body weight/day induces the development of ductal hyperplasias and carcinoma in situ at postnatal day 50 and 95 in rats. These highly proliferative lesions have an increased number of estrogen receptor-alpha positive cells. Thus, fetal bisphenol A exposure is sufficient to induce the development of preneoplastic and neoplastic lesions in the mammary gland in the absence of any additional treatment aimed at increasing tumor development.

[Prophylactic effect of a selective COX-2 inhibitor celecoxib on carcinogen-induced gastric premalignant lesions in rats]

BACKGROUND & OBJECTIVE

Although we have previously showed that a selective cyclooxygenase-2(COX-2) inhibitor celecoxib prevents gastric cancer development in a rat model of gastric carcinogenesis, the role of celecoxib on gastric premalignant lesions remains unknown. This study was to explore whether celecoxib was effective for the prevention of premalignancy, and further to clarify its mechanism.

METHODS

Ninety-four male Wistar rats were divided into 5 groups. Group A (n=12) was fed with water only; group B (n=16) with daily 10 mg/kg celecoxib; group C (n=22) with 100 microg/ml N-methyl-No-nitro-N-nitrosoguanidine (MNNG); group D (n=22) with 100 microg/ml MNNG and daily 10 mg/kg celecoxib; group E (n=22) with 100 microg/ml MNNG and daily 3 mg/kg indomethacin. The rats in groups B to E were given 10% sodium chloride in the initial 6 weeks, and the rats in groups C to E were given 100 microg/ml MNNG in drinking water to induce premalignant lesions in the stomach. Six rats in group A, 8 in group B, 10 in group C, 10 in group D, and 10 in group E were killed at week 16, and others were killed at week 24. The occurrence rates of gastric premalignant lesions in the groups were compared. The mRNA and protein levels of COX-1 and COX-2 in gastric mucosa were determined by real-time polymerase chain reaction (PCR) and immunohistochemistry; prostaglandin E2 (PGE2) level was measured by an ELISA-based assay.

RESULTS

Ninety-three rats were studied. In week 16 and week 24, the occurrence rates of glandular atrophy in groups C, D, and E had no significant difference (P>0.05). In week 16, gastric mucosal dysplasia was not detected in groups C, D, and E; at week 24, the occurrence rates of dysplasia were 75% (9/12) on group C, 25% (3/12) in group D, and 46% (5/11) in group E. The occurrence rate of gastric mucosal dysplasia was significantly lower in group D than in group C (25% vs. 75%, P=0.039); there was no significant difference between group E and group C (46% vs. 75%, P=0.214). At week 16 and week 24, there was no significant difference in COX-1 expression between treatment groups and control group. The mRNA and protein levels of COX-2 in group C (3.29+/-1.50 and 3.41+/-0.94) were significantly higher than those in other groups (P<0.001). There was no significant difference in PGE2 level between groups C, D, and E (P>0.05).

CONCLUSIONS

Celecoxib effectively inhibits the development of gastric mucosal dysplasia in rats induced by MNNG, but has no effect on the PGE2 level in the gastric mucosa, indicating that the anti-neoplastic activities of celecoxib may be independent of COX-2.

Vanadium limits the expression of proliferating cell nuclear antigen and inhibits early DNA damage during diethylnitrosamine-induced hepatocellular preneoplasia in rats

Previous studies from our laboratory have shown that vanadium stabilizes xenobiotic metabolizing enzymes and antioxidant status and suppresses DNA-protein crosslinks during chemically-induced hepatocarcinogenesis in rats. In the present study, we have further investigated the in vivo antitumor potential of this micronutrient by determining the effect of 0.5 ppm vanadium in drinking water on biomarkers for the early stages of hepatocarcinogenesis; the biomarkers included gamma-glutamyl transpeptidase (GGT)-positive foci and glycogen-storage foci, in situ expression of proliferating cell nuclear antigen (PCNA), and genotoxic DNA damage assessed by the alkaline Comet assay. Histomorphometry also was assessed during the study. Hepatocarcinogenesis was induced by treating 4-week-old male Sprague-Dawley rats with a single, necrogenic, intraperitoneal (i.p.) injection of 200 mg/kg body weight diethylnitrosamine (DEN). Compared to the carcinogen control, vanadium administration over the 32 weeks of the experiment reduced the relative liver weight by 30%, the incidence of nodules by 69.34%, the total number and multiplicity of nodules by 80.77%, and remodeled the hepatocellular premalignant architecture towards a normal phenotype. Moreover, long-term vanadium treatment reduced the development of GGT foci by 76.2% (P < 0.001), decreased periodic acid-Schiff's reactivity by 59.49% (P < 0.01), and decreased PCNA expression, with the concomitant reduction in PCNA immunolabeling index by 93.36% (P < 0.001). Finally, vanadium inhibited early DNA damage (DNA strand-breaks) in DEN-treated rat hepatocytes as expressed in the Comet assay by a 60.04% reduction in the length:width value of DNA mass (P < 0.01) and a 51.54% reduction in the tail length of the DNA comets (P < 0.001). Our results indicate that continuous supplementation with 0.5 ppm vanadium suppresses hepatocellular neoplastic transformation in rats.

E-cadherin expression during urothelial carcinogenesis induced by N-butyl-N-(4-hydroxybutyl) nitrosamine in rats

An alteration in the expression of E-cadherin has been observed in many epithelial neoplasms. No data exist, however, for the expression of this protein in an animal model for urinary bladder cancer. The present study investigated the expression of E-cadherin in rat urothelial preneoplastic lesions and tumours induced by oral administration of N-butyl-N-(4-hydroxybutyl) nitrosamine, during 10, 15 and 20 weeks. Simple hyperplasia and squamous metaplasia showed a similar E-cadherin pattern when compared with normal urothelium, with its expression confined to cell membrane. Thirty eight percent of the nodular hyperplasia, 41.4% of the dysplasia and 100% of the papillomas showed a weak E-cadherin expression. All papillary neoplasm of low malignant potential, low-and high-grade papillary carcinoma, and invasive carcinoma revealed an abnormal staining pattern with an increase in cytoplasm reactivity and discontinuous cell membrane positivity. The loss of expression for low-grade papillary carcinoma versus simple hyperplasia, nodular hyperplasia and dysplasia was statistically significant (p = 0.0001, p = 0.007 and p=0.008, respectively). There was a similar decrease in E-cadherin expression for papillary neoplasm of low malignant potential versus simple hyperplasia, nodular hyperplasia and dysplasia (p = 0.0001; p = 0.001 and p=0.0001, respectively). These results suggest that alteration in the expression of this adhesion molecule in rat may be indicative of tumour progression in N-butyl-N-(4-hydroxybutyl) nitrosamine-induced bladder cancer.

α-Tocopherol induces calnexin in renal tubular cells: Another protective mechanism against free radical-induced cellular damage

Pre-administration of alpha-tocopherol is protective against oxidative renal tubular damage and subsequent carcinogenesis by ferric nitrilotriacetate (Fe-NTA) in rats. We searched for mechanisms other than the scavenging effect of alpha-tocopherol with microarray analyses, which implicated calnexin, a chaperone for glycoproteins. Renal mRNA levels of calnexin significantly increased 3h after an injection of Fe-NTA in rats fed a standard diet whereas those fed an alpha-tocopherol-supplemented diet showed an increase prior to injection, but after injection showed a decrease in renal calnexin mRNA levels, with unaltered protein levels. In experiments using LLC-PK1 cells, addition of alpha-tocopherol was protective against oxidative stress by H2O2, concomitant with calnexin induction. Knockdown of calnexin by siRNA significantly reduced this protection. Furthermore, COS-7 cells transfected with the calnexin gene were more resistant to H2O2. Together with the fact that alpha-tocopherol induced N-acetylglucosaminyltransferase 3, our data suggest that alpha-tocopherol modifies glycoprotein metabolism partially by conferring mild ER stress. This adds another molecular mechanism of alpha-tocopherol toward cancer prevention.

Flax seed oil and flax seed meal reduce the formation of aberrant crypt foci (ACF) in azoxymethane-induced colon cancer in Fisher 344 male rats

Flax seed oil and flax seed meal are good sources of omega-3 fatty acids. The objective of this study was to explicate the effects of feeding flax seed oil and flax seed meal on AOM-induced aberrant crypt foci (ACF) in Fisher 344 male rats. Following an acclimatization period, rats were divided into six groups and fed AIN 93G diet Control (C), C+7 and 14% soybean oil (SBO), C+7 and 14% flax seed oil (FSO) and C+10 and 20% flax seed meal (FSM). All rats received 16 mg/kg body weight of AOM at 7 and 8 weeks of age. The rats were euthanized with CO2 at 17 weeks of age. FSM and FSO reduced the incidence of ACF which are putative precursor lesions in the development of colon cancer in the distal colon by 88% and 77%, in the proximal colon by 86% and 87% with a total reduction of 87.5% and 84%, respectively. Glutathione-S-transferase (GST) activities were significantly (P<0.05) higher in rats fed C+7 and 14% FSO and C+10 and 20% FSM, as compared to rats fed C+SBO diets. Results of this study showed that FSO and FSM reduced the incidence of AOM-induced ACF formation and may therefore be effective chemopreventive agents.

A prostaglandin E2 receptor subtype EP1-selective antagonist, ONO-8711, suppresses 4-nitroquinoline 1-oxide-induced rat tongue carcinogenesis

We previously reported that certain cyclooxygenase (COX) inhibitors could inhibit chemically induced tongue carcinogenesis. In the present study, we investigated the effects of prostaglandin E(2) (PGE(2)) receptor EP(1)-selective antagonist ONO-8711 on 4-nitroquinoline 1-oxide (4-NQO)-induced oral carcinogenesis to know whether an EP(1) receptor involves in oral carcinogenesis. Male Fischer 344 rats were given drinking water containing 4-NQO for 8 weeks (20 p.p.m. for the initial 2 weeks, 25 p.p.m. for 2 weeks, and then 30 p.p.m. for 4 weeks). After 4-NQO treatment, animals were given 400 or 800 p.p.m. ONO-8711 containing diets for 23 weeks. The incidence of tongue squamous cell carcinomas (SCC) in the 4-NQO-treated rats was 64%, while that in the rats given ONO-8711 after 4-NQO exposure was 29 (P<0.05) and 29% (P<0.05) in the 400 and 800 p.p.m. of ONO-8711, respectively. The multiplicity of tongue cancer was also smaller in the 4-NQO + ONO-8711 (400 p.p.m. ONO-8711, 0.35 +/- 0.61; and 800 p.p.m. ONO-8711, 0.29 +/- 0.47; P<0.05), when compared with the 4-NQO alone group (0.88 +/- 0.88). Feeding with ONO-8711 significantly reduced PGE(2) level and cell proliferation activity in the non-tumorous epithelium of the tongue. Also, treatment with ONO-8711 resulted in the decrease in EP(1) immunohistochemical expression in the tongue lesions induced by 4-NQO. The results suggest that EP(1) receptor involves in oral carcinogenesis, and that an EP1-selective antagonist ONO-8711 exerts the cancer chemopreventive effects through the suppression of EP(1) expression, PGE(2) biosynthesis and cell proliferation.

Alpha-benzene hexachloride exerts hormesis in preneoplastic lesion formation of rat hepatocarcinogenesis with the possible role for hepatic detoxifying enzymes

Recently there has been a shift in the prevailing paradigm regarding the dose dependence of carcinogen action with increasing acceptance of hormesis phenomenon, although underlying mechanisms remain to be established. To ascertain whether alpha-benzene hexachloride (alpha-BHC) might act by hormesis, rats were initiated with diethylnitrosamine and then alpha-BHC ranging from 0.01 to 500 ppm was administered in the diet for 10 weeks. The highest concentration of alpha-BHC significantly increased the number and area of glutathione S-transferase placental form (GST-P) positive foci, preneoplastic lesions in the liver, but its low dose, 0.05 ppm, caused significant reduction, showing a J-shape dose-response curve. The proliferating cell nuclear antigen positive index for GST-P positive foci in the low dose-treated group was significantly reduced. The dose response curves of CYP450 content, NADPH-P450 reductase activity and 8-hydroxydeoxyguanosine formation revealed the same pattern as GST-P positive foci data. The response curves of CYP2B1 and 3A2 in their activities, protein and mRNA expression showed a threshold but CYP2C11 activity exhibited an inverted J-shape. These results might suggest the possibility of hormesis of alpha-BHC at early stages of rat hepatocarcinogenesis. The possible mechanism involves induction of detoxifying enzymes at low dose, influencing free radical production and oxidative stress, and consequently pathological change in the liver.

Dietary artepillin C suppresses the formation of aberrant crypt foci induced by azoxymethane in mouse colon

Artepillin C, a prenylated phenylpropanoid found specifically in Brazilian propolis, has been shown to be a bioavailable antioxidant. In this study, artepillin C was tested for colon cancer-preventing activity using azoxymethane-challenged ddY mice. Oral doses of 80 and 160 mg/kg body weight of propolis or 10mg/kg of artepillin C (equi-amounts to 160 mg propolis) reduced significantly the frequency of colonic aberrant crypt foci (ACF) by 39.2, 43.7 and 43.4%, respectively. In liver of the mice, glutathione S-transferase and NADPH:quinone reductase activity increased with the doses of propolis or artepillin C, and an antioxidant-responsive element (ARE) was found to be activated for binding DNA. Artepillin C is considered to suppress the formation of colonic ACF through the activation of ARE and induction of phase II enzymes in liver.

Developmental exposure to estradiol and bisphenol A increases susceptibility to prostate carcinogenesis and epigenetically regulates phosphodiesterase type 4 variant 4

Early developmental perturbations have been linked to adult-onset prostate pathology, including excessive exposure to estrogenic compounds; however, the molecular basis for this imprinting event is not known. An important and controversial health concern is whether low-dose exposures to hormonally active environmental estrogens, such as bisphenol A, can promote human diseases, including prostate cancer. Here, we show that transient developmental exposure of rats to low, environmentally relevant doses of bisphenol A or estradiol increases prostate gland susceptibility to adult-onset precancerous lesions and hormonal carcinogenesis. We found permanent alterations in the DNA methylation patterns of multiple cell signaling genes, suggesting an epigenetic basis for estrogen imprinting. For phosphodiesterase type 4 variant 4 (PDE4D4), an enzyme responsible for cyclic AMP breakdown, a specific methylation cluster was identified in the 5'-flanking CpG island that was gradually hypermethylated with aging in normal prostates, resulting in loss of gene expression. Early and prolonged hypomethylation at this site following neonatal estradiol or bisphenol A exposure resulted in continued, elevated PDE4D4 expression. Cell line studies confirmed that site-specific methylation is involved in transcriptional silencing of the PDE4D4 gene and showed hypomethylation of this gene in prostate cancer cells. Importantly, the PDE4D4 alterations in the estrogen-exposed prostates were distinguishable before histopathologic changes of the gland, making PDE4D4 a candidate molecular marker for prostate cancer risk assessment as a result of endocrine disruptors. In total, these findings indicate that low-dose exposures to ubiquitous environmental estrogens affect the prostate epigenome during development and, in so doing, promote prostate disease with aging.

Antioxidative and modifying effects of a tropical plant Azadirachta indica (Neem) on azoxymethane-induced preneoplastic lesions in the rat colon

The purpose of the present study was to examine whether Neem leaf (Azadirachta indica) has short-term chemopreventive effects on endpoint preneoplastic lesions involved in rat colon carcinogenesis and might also exert antioxidative activity. Forty- two male F344 rats were randomly divided into 6 experimental groups. Groups 1 to 4 were given a subcutaneous injection of azoxymethane (AOM, 20 mg/kg body weight) once a week for 2 weeks. Starting one week before the first injection of AOM, rats in groups 2 to 4 received an aqueous extract of Neem leaf (20, 100, and 250 mg/kg, respectively) by gavage 3 times per week, for 5 weeks. Rats in group 5 also were given the Neem extract by gavage feeding 3 times per week for 5 weeks, while group 6 served as untreated controls. The experiment was terminated 5 weeks after the start. Dietary feeding of the Neem extract at all dose levels significantly inhibited the induction of aberrant crypt foci (ACF) (P<0.0002), when compared to the AOM-treated group (group 1). In groups 2 to 4, treatment of rats with the Neem extract also significantly decreased the proliferating cell nuclear antigen (PCNA) labeling indices (P<0.0006) of colon epithelium and ACF. Moreover, the Neem extract also showed antioxidative activity. The finding that dietary Neem has possible chemopreventive effects in the present short-term colon carcinogenesis bioassay suggests that longer-term exposure may cause suppression of tumor development.

Dual modality imaging of a novel rat model of ovarian carcinogenesis

Ovarian cancer is the fifth leading cause of cancer death in women, in part because of the limited knowledge about early stage disease. We develop a novel rat model of ovarian cancer and perform a pilot study to examine the harvested ovaries with complementary optical imaging modalities. Rats are exposed to repeated daily dosing (20 days) with 4-vinylcyclohexene diepoxide (VCD) to cause early ovarian failure (model for postmenopause), and ovaries are directly exposed to 7,12-dimethylbenz(a)anthracene (DMBA) to cause abnormal ovarian proliferation and neoplasia. Harvested ovaries are examined with optical coherence tomography (OCT) and light-induced fluorescence (LIF) at one, three, and five months post-DMBA treatment. VCD causes complete ovarian follicle depletion within 8 months after onset of dosing. DMBA induces abnormal size, cysts, and neoplastic changes. OCT successfully visualizes normal and abnormal structures (e.g., cysts, bursa, follicular remnant degeneration) and the LIF spectra show statistically significant changes in the ratio of average emission intensity at 390:450 nm between VCD-treated ovaries and both normal cycling and neoplastic DMBA-treated ovaries. Overall, this pilot study demonstrates the feasibility of both the novel animal model for ovarian cancer and the ability of optical imaging techniques to visualize ovarian function and health.

Estimated cancer risk of dioxins to humans using a bioassay and physiologically based pharmacokinetic model

The health risk of dioxins and dioxin-like compounds to humans was analyzed quantitatively using experimental data and mathematical models. To quantify the toxicity of a mixture of three dioxin congeners, we calculated the new relative potencies (REPs) for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 1,2,3,7,8-pentachlorodibenzo-p-dioxin (PeCDD), and 2,3,4,7,8- pentachlorodibenzofuran (PeCDF), focusing on their tumor promotion activity. We applied a liver foci formation assay to female SD rats after repeated oral administration of dioxins. The REP of dioxin for a rat was determined using dioxin concentration and the number of the foci in rat liver. A physiologically based pharmacokinetic model (PBPK model) was used for interspecies extrapolation targeting on dioxin concentration in liver. Toxic dose for human was determined by back-estimation with a human PBPK model, assuming that the same concentration in the target tissue may cause the same level of effect in rats and humans, and the REP for human was determined by the toxic dose obtained. The calculated REPs for TCDD, PeCDD, and PeCDF were 1.0, 0.34, and 0.05 for rats, respectively, and the REPs for humans were almost the same as those for rats. These values were different from the toxic equivalency factors (TEFs) presented previously (Van den Berg, M., Birnbaum, L., Bosveld, A.T.C., Brunstrom, B., Cook, P., Feeley, M., Giesy, J.P., Hanberg, A., Hasegawa, R., Kennedy, S.W., Kubiak, T., Larsen, J.C., Rolaf van Leeuwen, F.X., Liem, A.K.D., Nolt, C., Peterson, R.E., Poellinger. L., Safe, S., Schrenk, D., Tillitt, D, Tysklind, M., Younes, M., Waern, F., Zacharewski, T., 1998. Toxic equivalency factors (TEFs) for PCBs, PCDDs, PCDFs for humans and wildlife. Environ. Health Perspect. 106, 775-792). The relative risk of excess liver cancer for Japanese people in general was 1.7-6.5 x 10(-7) by TCDD only, and 2.9-11 x 10(-7) by the three dioxins at the present level of contamination.

[Experimental study on lung injury and cell cycle changes in mice induced by bitumen fume]

OBJECTIVE

To investigate the carcinogenic and mutagenic mechanism of bitumen fume.

METHODS

The experimental mice were forced to inhale the bitumen fume at different exposure level (55 mg/m(3), 165 mg/m(3)) and in different time (30 days, 60 days). The pathological changes of the lung tissue in mice were observed with H.E staining. The content of the DNA in the lung tissue of mice and the cell circles were determined with flow cytometry.

RESULTS

The lesion of the lung tissue in mice comprised the atypical hyperplasia of different levels and the carcinoma in situ with the increase of the containment time and dosage; the cycle index was changed: the number of the G 1 phase cells was decreased, the S phase was retarded, the cells entering the G 2/S phase were decreased, the cell proliferation index (P I) was increased and the heteroploid DNA index (DI) was increased (P < 0.05). The cell index in the 55 mg/m(3) group and the 165 mg/m(3) group was higher than that in the control group when the containment time was same. The heteroploid DNA index (DI) in the 55 mg/m(3) group was significantly higher than that in the 165 mg/m(3) group (P < 0.05 or P < 0.01). When the containment dosage was same, the DI in the 60 days treatment group (1.16 +/- 1.51 x 10(-2), 1.20 +/- 2.3 x 10(-2)) was all significantly higher than those in the 30 days treatment group (1.14 +/- 8.8 x 10(-2), 1.16 +/- 1.47 x 10(-2)) (P < 0.05).

CONCLUSION

The precancerous lesion in the lung tissue of the mice induced by the bitumen fume may be related with the changes of the cell cycle.

In vivo mutagenicity and initiation following oxidative DNA lesion in the kidneys of rats given potassium bromate

To clarify the role of 8-OHdG formation as a starting point for carcinogenesis, we examined the dose-dependence and time-course of changes of OGG1 mRNA expression, 8-OHdG levels and in vivo mutations in the kidneys of gpt delta rats given KBrO3 in their drinking water for 13 weeks. There were no remarkable changes in OGG1 mRNA in spite of some increments being statistically significant. Increases of 8-OHdG occurred after 1 week at 500 p.p.m. and after 13 weeks at 250 p.p.m. Elevation of Spi- mutant frequency, suggestive of deletion mutations, occurred after 9 weeks at 500 p.p.m. In a two-stage experiment, F344 rats were given KBrO3 for 13 weeks then, after a 2-week recovery, treated with 1% NTA in the diet for 39 weeks. The incidence and multiplicity of renal preneoplastic lesions in rats given KBrO3 at 500 p.p.m. followed by NTA treatment were significantly higher than in rats treated with NTA alone. Results suggest that a certain period of time might be required for 8-OHdG to cause permanent mutations. The two-step experiment shows that cells exposed to the alteration of the intranuclear status by oxidative stress including 8-OHdG formation might be able to form tumors with appropriate promotion.

Arsenic exposure from drinking water and risk of premalignant skin lesions in Bangladesh: baseline results from the Health Effects of Arsenic Longitudinal Study

Millions of persons around the world are exposed to low doses of arsenic through drinking water. However, estimates of health effects associated with low-dose arsenic exposure have been extrapolated from high-dose studies. In Bangladesh, many persons have been exposed to a wide range of doses of arsenic from drinking water over a significant period of time. The authors evaluated dose-response relations between arsenic exposure from drinking water and premalignant skin lesions by using baseline data on 11,746 participants recruited in 2000-2002 for the Health Effects of Arsenic Longitudinal Study in Araihazar, Bangladesh. Several measures of arsenic exposure were estimated for each participant based on well-water arsenic concentration and usage pattern of the wells and on urinary arsenic concentration. In different regression models, consistent dose-response effects were observed for all arsenic exposure measures. Compared with drinking water containing <8.1 microg/liter of arsenic, drinking water containing 8.1-40.0, 40.1-91.0, 91.1-175.0, and 175.1-864.0 microg/liter of arsenic was associated with adjusted prevalence odds ratios of skin lesions of 1.91 (95% confidence interval (CI): 1.26, 2.89), 3.03 (95% CI: 2.05, 4.50), 3.71 (95% CI: 2.53, 5.44), and 5.39 (95% CI: 3.69, 7.86), respectively. The effect seemed to be influenced by gender, age, and body mass index. These findings provide information that should be considered in future research and policy decisions.

Possible tumor development from double positive foci for TGF-alpha and GST-P observed in early stages on rat hepatocarcinogenesis

Expression of TGF-alpha during promotion of neoplastic development from GST-P-positive foci in rat chemical hepatocarcinogenesis was investigated. One-hundred male F344 rats were given a single intraperitoneal injection of DEN (200 mg/kg bodyweight) and subjected to two-thirds partial hepatectomy at week 3. Commencing 2 weeks from the start, PB at doses of 0 or 500 p.p.m. was fed to the rats for 46 weeks. Groups of 10 rats were killed at weeks 4, 8, 16, 32, 48 and their livers were immunohistochemically examined for expression of GST-P and TGF-alpha. TGF-alpha-positive foci and single positive cells were observed from week 4, partially overlapping with GST-P-positive foci but being much fewer. Numbers of TGF-alpha-positive lesions did not increase from weeks 4-48, but their areas showed increment at weeks 32 and 48, especially with PB administration. Almost all of the tumors observed at weeks 16, 32 and 48 were positive for TGF-alpha (98%). In addition, epidermal growth factor receptor overexpression was observed in most TGF-alpha-positive lesions (foci and tumors). The proliferating cell nuclear antigen labeling index in double positive foci for GST-P and TGF-alpha was significantly higher than that in TGF-alpha-negative foci. In conclusion, TGF-alpha may be closely related with promotion from altered foci to neoplasms in rat hepatocarcinogenesis. Our data suggest that double positive foci for GST-P and TGF-alpha in the early stages of rat hepatocarcinogenesis may develop into tumors with promotion.

Polyethylene glycol, unique among laxatives, suppresses aberrant crypt foci, by elimination of cells

OBJECTIVE

Polyethylene glycol (PEG), an osmotic laxative, is a potent inhibitor of colon cancer in rats. In a search for the underling mechanisms, the hypothesis that fecal bulking and moisture decrease colon carcinogenesis was tested. We also investigated the PEG effects on crypt cells in vivo.

MATERIAL AND METHODS

Fischer 344 rats (n=272) were injected with the colon carcinogen, azoxymethane. They were then randomized to a standard AIN76 diet containing one of 19 laxative agents (5% w/w in most cases): PEG 8000 and other PEG-like compounds, carboxymethylcellulose, polyvinylpyrrolidone, sodium polyacrylate, calcium polycarbophil, karaya gum, psyllium, mannitol, sorbitol, lactulose, propylene glycol, magnesium hydroxide, sodium phosphate, bisacodyl, docusate, and paraffin oil. Aberrant crypt foci (ACF) and fecal values were measured blindly after a 30-day treatment regimen. Proliferation, apoptosis, and the removal of cells from crypts were studied in control and PEG-fed rats using various methods, including TUNEL and fluorescein dextran labeling.

RESULTS

PEG 8000 reduced the number of ACF 9-fold in rats (p<0.001). The other PEGs and magnesium hydroxide modestly suppressed ACF, but not the other laxatives. ACF number did not correlate with fecal weight or moisture. PEG doubled the apoptotic bodies per crypt (p<0.05), increased proliferation by 25-50% (p<0.05) and strikingly increased (>40-fold) a fecal marker of epitheliolysis in the gut (p<0.001). PEG normalized the percentage of fluorescein dextran labeled cells on the top of ACF (p<0.001).

CONCLUSIONS

Among laxatives, only PEG afforded potent chemoprevention. PEG protection was not due to increased fecal bulking, but in all likelihood to the elimination of cells from precancerous lesions.

Preneoplastic liver cell foci expansion induced by thioacetamide toxicity in drug-primed mice

Mice primed by feeding griseofulvin or diethyl 1,4-dihydro 1,4,6-trimethyl 3,5-pyridine decarboxylate for 5 months followed by drug withdrawal for 1 month (drug-primed mice) were given thioacetamide intraperitoneally, and the livers were subsequently studied at intervals up to 7 days. The hepatocellular proliferative response was measured by immunostaining for proliferative cell nuclear antigen. Necrosis was followed by measuring ALT. Mallory bodies were identified by immunoperoxidase stains for ubiquitin and cytokeratin. Preneoplastic foci were localized using immunofluorescence stain for glutathione S-transferase (GST mu) and histochemical stain for gamma glutamyl transpeptidase (GGT). The results showed that the preneoplastic foci selectively proliferated and expanded and formed nodules as indicated by quantitation of nuclei stained positive for proliferating cell nuclear antigen after thioacetamide treatment. Data support the hypothesis that the preneoplastic foci consisted of clones of hepatocytes which preferentially express GST mu, GGT and Mallory bodies. These preneoplastic cells selectively proliferate in response to the promoter effects of necrosis-induced liver cell regeneration ("chemical partial hepatectomy").

Differential Alterations in Metabolic Pattern of the Spliceosomal UsnRNAs during Pre-Malignant Lung Lesions Induced by Benzo(a)pyrene: Modulation by Tea Polyphenols

The differential alterations of the spliceosomal UsnRNAs (U1, U2, U4, U5, and U6) were reported to be associated with cellular proliferation and development. The attempt was made in this study to analyze the metabolic pattern of the spliceosomal UsnRNAs during the development of pre-malignant lung lesions induced in experimental mice model system by benzo(a)pyrene (BP) and also to see how tea polyphenols, epigallocatechin gallate (EGCG) and epicatechin gallate (ECG), modulate the metabolism of these UsnRNAs during the lung carcinogenesis. No significant changes in the level of the UsnRNAs were seen in the inflammatory lung lesions at 9th week due to treatment of BP. However, there was significant increase in the level of U1 ( approximately 2.5 fold) and U5 ( approximately 47%) in the hyperplastic lung lesions at 17th week. But in the mild dysplastic lung lesions at 26th week, the level of UsnRNAs did not change significantly. Whereas, in the dysplastic lung lesions at 36th week there was significant increase in the level of the U2 ( approximately 2 fold), U4 ( approximately 2.5 fold) and U5 ( approximately 2 fold). Due to the EGCG and ECG treatment the lung lesions at 9th week appeared normal and in the 17th, 26th, and 36th week it appeared as hyperplasia. The level of the UsnRNAs was significantly low in the lung lesions at 9th week (only U2 and U4 by EGCG), at 17th week (only U1 by EGCG/ECG), at 26th week (U1 by ECG; U2, U4 and U5 by EGCG/ECG) and at 36th week (U1 by ECG, U2 and U4 by EGCG/ECG). Whereas, there was significant increase in the level of U5 (by EGCG/ECG) and U6 (by EGCG only) in the lung lesions at 36th and 26th week respectively. This indicates that the metabolism of the spliceosomal UsnRNAs differentially altered during the development of pre-malignant lung lesions by BP as well as during the modulation of the lung lesions by the tea polyphenols.

Red palm oil suppresses the formation of azoxymethane (AOM) induced aberrant crypt foci (ACF) in Fisher 344 male rats

Red palm oil (RPO) contains significant levels of carotenoids and Vitamin E. In this experiment we compared the inhibitory effects of RPO (7% and 14% levels) and soybean oil (7% and 14%) on azoxymethane (AOM) induced aberrant crypt foci (ACF). Thirty-two male Fisher 344 rats were randomly assigned to four groups. Two groups received AIN-93 G control (C) diet containing 7% and 14% soybean oil (SBO), respectively. Groups 3 and 4 received a treatment diet consisting of 7% and 14% RPO, respectively. The rats received subcutaneous injections of AOM at 16 mg/kg body weight at 7 and 8 weeks of age. At 17 weeks of age rats were killed by CO(2) asphyxiation. Numbers of ACF (mean+/-SE) in the proximal and distal colon were: 39.9 +/- 0.9, 53.8 +/- 2.8, 26.0 +/- 3.0, 27.5 +/- 1.5 and 118.2 +/- 1.7, 125.6 +/- 3.2, 41 +/- 7, 52.3 +/- 1.8 in rats fed 7% SBO, 14% SBO, 7% RPO and 14% RPO, respectively. The results of this study showed that RPO reduced the incidence of AOM induced ACF and may therefore have a beneficial effect in reducing the incidence of colon cancer.

Homogeneous boron targeting of heterogeneous tumors for boron neutron capture therapy (BNCT): chemical analyses in the hamster cheek pouch oral cancer model

OBJECTIVE

BNCT is a tumour cell targeted radiation therapy. Uniform targeting of heterogeneous tumours with therapeutically effective boron carriers would contribute to a therapeutic effect on all tumour cell populations and avoid radioresistant fractions. This remains an unresolved challenge. The aim of the present study was to evaluate the degree of variation in boron content delivered by boronophenylalanine (BPA), GB-10 (Na(2)(10)B(10)H(10)) and the combined administration of (BPA+GB-10) in different portions of tumour, precancerous tissue around tumour and normal pouch tissue in the hamster cheek pouch oral cancer model.

MATERIALS AND METHODS

Samples of different areas of tumour, precancerous tissue and normal pouch tissue were taken from tumour-bearing hamsters, 3h post-administration of i.p. BPA (15.5mg B/kg b.w.), or i.v. GB-10 (50mg B/kg b.w.), or 3h and 1.5h post-administration respectively of i.v. GB-10 (34.5mg B/b.w.) and sequential i.p. injections of BPA (total dose 31mg B/kg b.w.) given jointly. Boron content was evaluated by inductively coupled plasma optical emission spectroscopy (ICP-OES). The degree of homogeneity in boron targeting was assessed in terms of the coefficient of variation (V: [S.D./mean]x100) of boron values. Statistical analysis of the results was performed by one-way ANOVA and the least significant difference test.

RESULTS

GB-10 and GB-10 plus BPA achieved respectively a statistically significant 1.8- and 3.3-fold increase in targeting homogeneity over BPA.

CONCLUSIONS

The combined boron compound administration protocol contributes to homogeneous targeting of heterogeneous tumours and would be expected to increase therapeutic efficacy of BNCT.

Prevalent location of flat dysplastic aberrant crypt foci near lymphoid follicles in the colon of azoxymethane-treated rats

In the colon of F344 rats treated with 2 x 15 mg/kg body weight of azoxymethane (AOM), the density (number of lesions/cm2/rat) of flat aberrant crypt foci (ACF) was 13-fold higher (p < 0.05) in the surface area of mucosa immediately adjacent to lymphoid follicles compared with the density of these lesions in the rest of the mucosa. A similar prevalent location near lymphoid follicles was observed for tumours, but not for the classic elevated ACF. The lymphoid follicle-associated flat ACF had the same characteristics as those located in the rest of the mucosa: i.e. severe dysplasia and Wnt pathway stimulation.

Preventive effects of chrysin on the development of azoxymethane-induced colonic aberrant crypt foci in rats

The modifying effects of dietary feeding with chrysin (5,7-dihydroxyflavone) on the development of azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) were investigated in male F344 rats. We also assessed the effect of chrysin on mitosis and apoptosis in 'normal appearing' crypts. To induce ACF, rats were given two weekly subcutaneous injections of AOM (20 mg/kg body weight). They also received an experimental diet containing chrysin (0.001 or 0.01%) for 4 weeks, starting 1 week before the first dose of AOM. AOM exposure produced a substantial number of ACF (73+/-13/rat) at the end of the study (week 4). Dietary administration of chrysin caused significant reduction in the frequency of ACF: 0.001% chrysin, 37+/-17/rat (49% reduction, P<0.001); and 0.01% chrysin, 40+/-10/rat (45% reduction, P<0.001). In addition, chrysin administration significantly reduced the mitotic index and significantly increased the apoptotic index in 'normal appearing' crypts. These findings might suggest a possible chemopreventive activity of chrysin in the early step of colon tumorigenesis through modulation of cryptal cell proliferation activity and apoptosis.

Cell proliferation and apoptosis culminate in early stages of oral oncogenesis

Markers of cell proliferation (Ki-67 antigen) and apoptosis (Bax, Bcl-2) were studied in an experimental system of induced oral carcinogenesis in Syrian golden hamsters. Thirty-seven animals were divided into one control group and three experimental groups, which were treated with a carcinogen and sacrificed at 10, 14 and 19 weeks after treatment. The histological status of the lesions in the three experimental groups corresponded well with tumour advancement (from oral mucosal dysplasia to moderately differentiated squamous cell carcinoma). Tumour sections were studied using monoclonal antibodies against Bax, Bcl-2 and Ki-67 proteins. Pro-apoptotic Bax expression maintained high levels during all stages of oral carcinogenesis. Anti-apoptotic Bcl-2 expression decreased significantly in dysplastic and early invasion lesions and consequently increased almost to normal tissue level in consequent stages. Finally, Ki-67 expression increased sharply in initial stages of oral carcinogenesis, but significantly decreased in later stages.

Vanadium inhibits the development of 2-acetylaminofluorene-induced premalignant phenotype in a two-stage chemical rat hepatocarcinogenesis model

In recent years, research on the biological influence of micronutrients in cancer has grown enormously. Among these, vanadium, a dietary micronutrient present in mammalian tissues has received considerable attention as a limiting agent. In the present study, attempts have been made to investigate the in vivo antitumour potentials of this micronutrient at the 0.5 ppm dosage in drinking water in a defined model of a two-stage experimental rat hepatocarcinogenesis. The chemopreventive effect of vanadium was assessed by studying certain biomarkers, such as development of gamma-glutamyltranspeptidase (GGT)-positive foci, levels of some essential trace elements, in situ expression of proliferating cell nuclear antigen (PCNA) and chromosomal aberrations. Hepatocarcinogenesis was induced in male Sprague-Dawley rats by chronic feeding of 2-acetylaminofluorene (0.05% in basal diet) on and from week 4. Vanadium administration throughout the experiment reduced the relative liver weight, nodular incidence (66.70%), total number and multiplicity (79.93%) and restored hepatic levels of selenium (Se) and iron (Fe) (P < 0.001) when compared to the carcinogen control. Moreover, long-term vanadium treatment significantly abated the expressions of GGT (P < 0.001) and PCNA with concomitant reduction in PCNA immunolabeling index (P < 0.001; 36.62%). Finally, the anticlastogenic potential of vanadium was reflected through its ability to inhibit early chromosomal aberrations (P < 0.001; 45.17%) in 2-AAF-challenged rat hepatocytes. Our results suggest that supplementary vanadium at a dose of 0.5 ppm, when administered continuously throughout the study, than administered either in the initiation or promotion phase alone, is very much effective in suppressing neoplastic transformation in vivo. We conclude the significant role of vanadium in limiting cell proliferation and chromosomal aberrations during the preneoplastic stages of hepatocarcinogenesis in rats.

Analysis of renal cell transformation following exposure to trichloroethene in vivo and its metabolite S-(dichlorovinyl)-L-cysteine in vitro

Trichloroethene (TCE) is classified as a potential human carcinogen although there is a significant debate regarding the mechanism of TCE induced renal tumor formation. This controversy stems in part from the extremely high doses of TCE required to induce renal tumors and the potential contribution of the associated nephrotoxicity to tumorigenesis. We have used Eker rats, which are uniquely susceptible to renal carcinogens, to determine if exposures to TCE in vivo or exposure to its metabolite S-(dichlorovinyl)-L-cysteine (DCVC) in vitro can transform kidney epithelial cells in the absence of cytotoxicity. Treatment with TCE (0, 100, 250, 500, 1000 mg/kg bw by gavage, 5 days a week) for 13 weeks resulted in a significant increase in cell proliferation in kidney tubule cells, but did not enhance formation of preneoplastic lesions or tumor incidence in Eker rat kidneys as compared to controls. In vitro, concentrations of DCVC, which reduced cell survival to 50%, were able to transform rat kidney epithelial cells. However, no carcinogen-specific mutations were identified in the VHL or Tsc-2 tumor suppressor genes in the transformants. Taken together, the inability of TCE to enhance formation of preneoplastic changes or neoplasia and the absence of carcinogen-specific alteration of genes accepted to be critical for renal tumor development suggest that TCE mediated carcinogenicity may occur secondary to continuous toxic injury and sustained regenerative cell proliferation.

Role of glycogen synthase kinase 3 in squamous differentiation induced by cigarette smoke in porcine tracheobronchial epithelial cells

Epidemiological evidence suggests that cigarette smoke induces squamous metaplasia in human tracheobronchial epithelium that can progress to lung squamous carcinoma. But it is not well understood how tracheobronchial epithelial cells transduce the signals that mediate cigarette smoke-induced squamous differentiation or squamous metaplasia. In the present study, we found that in vitro cigarette smoke components notably inhibited glycogen synthase kinase 3 (GSK3) and induced the expression of involucrin, a marker of squamous differentiation. The inactivation of GSK3 by two highly selective inhibitors, lithium and SB216763, also significantly enhanced involucrin expression in cultured porcine tracheobronchial epithelial cells (PTBECs). Moreover, we demonstrated that cigarette smoke components significantly promoted activator protein-1 (AP-1) binding activities to the upstream regulatory region of involucrin gene, and similar results were observed by further studies through using GSK3 inhibitors to imitate the effects of cigarette smoke components. Taken together, we conclude that GSK3 is involved in involucrin expression induced by cigarette smoke in PTBEC probably via negatively regulating AP-1 activity, implying a possible mechanism responsible for squamous differentiation induced by cigarette smoke.

Chemopreventive efficacy of all-trans-retinoic acid in biodegradable microspheres against epithelial cancers: results in a 4-nitroquinoline 1-oxide-induced oral carcinogenesis model

Retinoids are known to suppress carcinogenesis in various epithelial tissues. Among them, all-trans-retinoic acid (atRA) is recognized as one such active retinoid. However, despite the known anticarcinogenic activity of atRA, it exhibits its short plasma half-life during repeated oral administration due to the "acute retinoid resistance" in the liver. This has been the major limitation in clinical applications of atRA. Therefore, in order to render atRA more suitable for clinical uses, sustained delivery of atRA using biodegradable microspheres is suggested in this study. When 50 mg atRA/kg of atRA-loaded microspheres were subcutaneously administered to rats once, the atRA concentration in plasma was maintained around 6.5 ng/ml for 7 weeks, with only minor signs of toxicity. When the chemopreventive efficacy of atRA-loaded microspheres was evaluated using a model of 4-nitroquinoline 1-oxide-induced oral carcinogenesis in F344 rats, a single injection of atRA-loaded microspheres significantly suppressed oral carcinogenesis. Additional injections of atRA-loaded microspheres, however, did not indicate further suppression of carcinogenesis.

Immunohistochemical study of cell proliferation, Bcl-2, p53, and caspase-3 expression on preneoplastic changes induced by cadmium and zinc chloride in the ventral rat prostate

This work was directed to evaluate immunoexpression of markers for apoptosis, resistance to apoptosis, and cell proliferation, as well as estimates of nuclear size in ventral prostate of rats treated with cadmium chloride and cadmium+zinc chloride because a possible protective effect of zinc has been postulated. The following variables were studied: volume fraction (VF) of Bcl-2 immunostaining, percentage of cells immunoreactive to proliferating cell nuclear antigen (LIPCNA) and p53 (LIp53), numerical density of caspase-3 immunoreactive cells (NV caspase-3), and estimates of volume-weighted mean nuclear volume (upsilonV). The LIPCNA and VF of Bcl-2 were significantly increased in the treated animals. The dysplasias (independent of their origin) showed a significant increase of the LIp53, NV caspase-3, and upsilonV in comparison with normal acini from treated and control animals. It can be concluded that cell proliferation is enhanced in long-term cadmium-exposed rats, and exposure to zinc combined with cadmium had no effect on any of the variables studied when comparing with normal acini. The increase of nuclear upsilonV could indicate a more aggressive behavior for pretumoral lesions.

Corrosive induced carcinoma of esophagus: report of three patients and review of literature

Patients with corrosive induced esophageal strictures have more than a 1000-fold risk of developing carcinoma of the esophagus. We report three cases of corrosion carcinoma seen by us (a team of gastroenterologists, radiologists and a surgeon) in the last 15 years. Two cases were among 156 patients with corrosive induced strictures on our follow-up, and constituted the only corrosion carcinoma out of 650 esophageal carcinomas operated on by us. Nearly all reported patients with corrosion carcinoma in the published literature had consumed an alkali, but two of our three patients had consumed an acid.

Changes in the sonographic appearance of the uterus after discontinuation of tamoxifen therapy

OBJECTIVE

The purpose of this study was to assess the duration of sonographically detected changes in the endometrium of women with a history of tamoxifen use.

METHODS

Patients with breast cancer who had a history of tamoxifen use and documented pelvic sonographic studies were identified by means of clinic databases in both the Section of Gynecological Oncology and the Section of Obstetrical and Gynecological Ultrasound, University of Chicago, between January 1, 1996, and March 30, 2004. Of the 99 patients who met study criteria, 34 had discontinued tamoxifen use before the sonographic evaluation. Each patient's age, gravity and parity, weight, ethnicity, duration and dose of drug use, interval from drug discontinuation until sonographic evaluation, and uterine pathologic findings were reviewed. Endometrial thickness as assessed by pelvic sonography was examined in relation to duration of tamoxifen use and time from discontinuation of the drug. Statistical analysis was performed with linear regression and mixed effect linear regression models.

RESULTS

Endometrial thickness increased with increasing duration of tamoxifen use at a rate of 0.75 mm/y. The mean endometrial thickness after approximately 5 years of tamoxifen use was 12 mm (range, 6-21 mm). After discontinuation of tamoxifen, endometrial thickness decreased by 1.27 mm/y.

CONCLUSIONS

Endometrial thickness as measured by pelvic ultrasound examination increases with the duration of tamoxifen use. After discontinuation of the drug, the measured thickness decreases but at a very slow rate.

Altered metaplastic response of waved-2 EGF receptor mutant mice to acute oxyntic atrophy

Metaplastic cell lineages are putative precursors for the development of gastric adenocarcinoma. The loss of parietal cells (oxyntic atrophy) is the initiating step in the evolution of gastric fundic mucosal lineage changes including metaplasia and hyperplasia. However, the intrinsic mucosal factors that promote and modulate the emergence of metaplastic phenotypes remain obscure. Over the past several years, we have studied pharmacologically induced, reversible oxyntic atrophy in rodents treated with DMP-777, a drug that acts as a parietal cell secretory membrane protonophore. DMP-777 elicits a rapid loss of parietal cells followed by the emergence of foveolar hyperplasia and spasmolytic polypeptide (SP)-expressing metaplasia (SPEM). The objective of the present study was to provide further insights into the intrinsic mucosal factors regulating the emergence of SPEM in the setting of oxyntic atrophy. We therefore studied the effects of DMP-777 administration on both SP/trefoil factor (TFF)2-deficient mice, which lack SP/TFF2, a marker of SPEM, and waved-2 mice, which harbor a point mutation in the EGF receptor that attenuates its tyrosine kinase activity. As in wild-type mice, treatment with DMP-777 for 7 days did elicit SPEM in SP/TFF2-deficient mice. These results suggest that SP/TFF2 does not impact on the development of metaplasia after the induction of parietal cell loss. In contrast, waved-2 homozygous mice displayed accelerated SPEM development by 3 days of treatment with DMP-777. These findings indicate that attenuation of EGF receptor signaling in waved-2 mice does elicit a more rapid emergence of SPEM. The results support a role for EGF receptor ligands in the regulation of gastric metaplasia.