Showing papers on "7,12-Dimethylbenz[a]anthracene published in 1999"

Cytochrome P450 CYP1B1 determines susceptibility to 7,12-dimethylbenz[a]anthracene-induced lymphomas

Abstract: CYP1B1-null mice, created by targeted gene disruption in embryonic stem cells, were born at the expected frequency from heterozygous matings with no observable phenotype, thus establishing that CYP1B1 is not required for mouse development. CYP1B1 was not detectable in cultured embryonic fibroblast (EF) or in different tissues, such as lung, of the CYP1B1-null mouse treated with the aryl hydrocarbon receptor agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin whereas the equivalent wild-type EF cells express basal and substantial inducible CYP1B1 and lung expresses inducible CYP1B1. CYP1A1 is induced to far higher levels than CYP1B1 in liver, kidney, and lung in wild-type mice and is induced to a similar extent in CYP1B1-null mice. 7,12-dimethylbenz[a]anthracene (DMBA) was toxic in wild-type EFs that express CYP1B1 but not CYP1A1. These cells effectively metabolized DMBA, consistent with CYP1B1 involvement in producing the procarcinogenic 3,4-dihydrodiol as a major metabolite, whereas CYP1B1-null EF showed no significant metabolism and were resistant to DMBA-mediated toxicity. When wild-type mice were administered high levels of DMBA intragastrically, 70% developed highly malignant lymphomas whereas only 7.5% of CYP1B1-null mice had lymphomas. Skin hyperplasia and tumors were also more frequent in wild-type mice. These results establish that CYP1B1, located exclusively at extrahepatic sites, mediates the carcinogenicity of DMBA. Surprisingly, CYP1A1, which has a high rate of DMBA metabolism in vitro, is not sufficient for this carcinogenesis, which demonstrates the importance of extrahepatic P450s in determining susceptibility to chemical carcinogens and validates the search for associations between P450 expression and cancer risk in humans.

Wakame seaweed suppresses the proliferation of 7,12-dimethylbenz(a)-anthracene-induced mammary tumors in rats.

Abstract: We examined the anti-tumor proliferation effects of wakame seaweed on 7,12-dimethylbenz(a)-anthracene (DMBA)-induced rat mammary tumor. DMBA was administered to 8-week-old female Sprague-Dawley rats, and rats which developed mammary tumors were assigned randomly to three groups. Commercial rat feed was used in a control group (group I-A), and two feed mixtures were prepared, which contained commercial rat feed blended with wakame at 1.0% (group I-B) and 5.0% (group I-C) by weight. The respective feeds were given to each group for 8 weeks, and changes in mammary tumor size were compared. At the end of the experiment, mammary tumors and thyroid glands were resected to compare their weights. Serum total iodine and thyroxin (T4) levels were measured. Immunohistochemical studies for bromodeoxyuridine (BrdU) labeling, transforming growth factor (TGF)-beta, and apoptosis were carried out in the resected tumor. Significant suppression of tumor growth was observed in groups I-B and I-C compared with I-A. In groups I-B and I-C, the weights of resected mammary tumors were significantly lower and serum total iodine concentration was significantly higher than in I-A. BrdU indices were significantly lower in groups I-B and I-C, compared with I-A. TGF-beta and apoptotic index were inversely related to BrdU. These results suggest that iodine is transported from the serum into mammary tissues and induces apoptosis through the expression of TGF-beta. In conclusion, wakame suppressed the proliferation of DMBA-induced mammary tumors.

Exposure of Sprague-Dawley rats to a 50-Hertz, 100-microTesla magnetic field for 27 weeks facilitates mammary tumorigenesis in the 7,12-dimethylbenz[a]-anthracene model of breast cancer.

Abstract: We have shown previously (W. Loscheret al., Cancer Lett., 71: 75- 81, 1993; M. Mevissen et al., Carcinogenesis (Lond.), 17: 903-910, 1996) that 50-Hz magnetic fields (MFs) of low (50 or 100 mTesla (T)) flux density enhance mammary gland tumor development and growth in the 7,12- dimethylbenz(a)anthracene (DMBA) model of breast cancer in female Sprague Dawley rats. In these previous experiments, groups of rats were given 20 mg of DMBA (four weekly gavage doses of 5 mg each) and were MF- or sham-exposed for 13 weeks. The objective of the present study was to examine whether the use of a lower dose of DMBA (10 instead of 20 mg per rat), MF exposure of the rats before DMBA injection, and the increase of the MF exposure period after DMBA application to 26 weeks enhance the effect of MF on tumor development and growth. A group 99 rats was exposed to a homogeneous, horizontally polarized 100-mT MF of 50-Hz for 24 h/day for 7 days/week; another group of 99 rats was sham-exposed under the same environmental conditions as the MF-exposed rats. The exposure chambers were identical for MF-exposed and sham-exposed animals. The age of the rats was 45- 49 days at the onset of exposure; duration of MF or sham exposure was 27 weeks. DMBA was administered p.o. at a dose of 10 mg/rat after 1 week of MF or sham exposure. The animals were palpated once weekly from week 6 onwards to assess the development of mammary tumors. At the end of the exposure period, the animals were killed for the determination of number and volume and histological verification of mammary tumors. All of the recordings were done in a blinded fashion; i.e., the investigators were not aware which animals were MF- or sham-exposed. Mammary tumor development and growth was significantly enhanced by MF exposure, the most marked effect on tumor incidence (190% above sham control) being observed 13 weeks after DMBA administration. At the time of necropsy, i.e., 26 weeks after DMBA administration, the incidence of histologically verified mam- mary tumors was 50.5% in controls and 64.7% in MF-exposed rats, the difference being statistically significant. More marked intergroup differ- ences were recorded when tumor incidence was separately evaluated for each of the six mammary complexes, the most pronounced MF effect on tumor incidence being seen in the cranial thoracic complex. The data substantiate that, at least under the experimental conditions used in our laboratory, 50-Hz, 100-mT MF exposure significantly facilitates the de- velopment and growth of mammary tumors in the DMBA rat model of breast cancer.

Heating Garlic Inhibits Its Ability to Suppress 7,12-Dimethylbenz(a)anthracene-Induced DNA Adduct Formation in Rat Mammary Tissue

Abstract: The present studies compared the impact of heating, either by microwave or convection oven, on the ability of garlic to reduce the in vivo bioactivation of 7,12-dimethylbenz(a)anthracene (DMBA) in 55-d-old female Sprague-Dawley rats. In study 1, rats were fed a semipurified casein-based diet and treated by gastric gavage thrice weekly for 2-wk with crushed garlic (0.7 g in 2 mL corn oil) or the carrier prior to DMBA treatment (50 mg/kg body weight). Providing crushed garlic reduced by 64% (P < 0.05) the quantity DMBA-induced DNA adducts present in mammary epithelial cells compared to controls. In study 2, microwave treatment for 60 s, but not 30 s, decreased (P < 0.05) the protection provided by garlic against DMBA-induced adduct formation. In study 3, allowing crushed garlic to stand for 10 min prior to microwave heating for 60 s significantly (P < 0.05) restored its anticarcinogenic activity. Microwave heating of garlic for 30 s resulted in a 90% loss of alliinase activity. Heating in a convection oven (study 4) also completely blocked the ability of uncrushed garlic to retard DMBA bioactivation. Study 5 revealed that providing either 0.105 micromol diallyl disulfide or S-allyl cysteine by gastric gavage thrice weekly for 2 wk was effective in retarding DMBA bioactivation but isomolar alliin was not. These studies provide evidence that alliinase may be important for the formation of allyl sulfur compounds that contribute to a depression in DMBA metabolism and bioactivation.

Patterns of DNA Adduct Formation in Liver and Mammary Epithelial Cells of Rats Treated with 7,12-Dimethylbenz(a)anthracene, and Selective Effects of Chemopreventive Agents

Abstract: 7,12-Dimethylbenz(a)anthracene (DMBA) is a prototype carcinogen that induces a high yield of mammary tumors in rats after a single feeding. We investigated the induction and chemoprevention of DNA adducts in female Sprague Dawley rats receiving DMBA by gavage according to a variety of treatment schedules. The patterns of 32P-postlabeled DNA adducts in liver and mammary epithelial cells were similar to those produced by the in vitro reaction of metabolically activated DMBA with calf thymus DNA. There was a high and statistically significant correlation between dose of DMBA administered to rats (0, 0.6, 2.4, and 12 mg/kg body weight) and levels of DNA adducts in both types of cells. The regression lines relating DMBA doses to total DNA adduct levels were significantly divergent and crossed at 1.5 mg/kg body weight, indicating that, at lower doses, the formation of DNA adducts is more intense in target mammary cells, whereas at higher doses, DNA adduct levels are more elevated in liver cells, presumably due to the greater metabolic capacity of this organ. When the rats were sacrificed 7 days rather than 2 days after DMBA administration, DNA adduct levels were approximately halved in both liver and mammary cells. The observed patterns can be interpreted based on toxicokinetic factors, local and distant metabolism, removal of DNA adducts by excision repair, and cell proliferation rate. Of three chemopreventive agents given with the diet to rats treated with 12 mg of DMBA, 5,6-benzoflavone (1650 ppm) was the most effective, inhibiting DNA adduct formation in liver and mammary cells by 96.5 and 83.5%, respectively. Feeding of 1,2-dithiole-3-thione (600 ppm) inhibited this biomarker by 68.5 and 50.2%, whereas butyl hydroxyanisole (BHA; 5000 ppm) showed a significant inhibition in the liver (46.5%) but was ineffective in mammary cells (29.0%, not significant). These data correlate nicely with the results of a parallel study in which 5,6-benzoflavone, 1,2-dithiole-3-thione, and BHA inhibited formation of hemoglobin adducts by 80.0, 44.0, and 0%, respectively; the incidence of mammary tumors by 82.4, 47.1, and 5.9%, respectively; and their multiplicity by 92.6, 80.0, and 7.4%, respectively. Therefore, biomarkers of biologically effective dose are highly predictive of the efficacy of chemopreventive agents in the DMBA rat mammary model. The selective inhibition by BHA of DNA adducts in the liver but not in mammary cells is consistent with the finding that this phenolic antioxidant stimulated phase II activities in the liver but not in the mammary gland (L. L. Song et al., manuscript in preparation). In any case, the broad-spectrum inducer 5,6-BF appears to be more effective than the two monofunctional phase II inducers, presumably because an enhanced activation of DMBA to reactive metabolites is coordinated with their blocking, detoxification, and excretion.

Bone marrow stromal cell cytochrome P4501B1 is required for pre-B cell apoptosis induced by 7,12-dimethylbenz[a]anthracene.

Abstract: We previously demonstrated that murine bone marrow stromal cells express high levels of cytochrome P4501B1 (CYP1B1) that metabolizes 7,12-dimethylbenza[a]anthracene (DMBA), and that DMBA activates the Ah receptor (AhR) in these cells in vitro. More recently, we reported that CYP1B1 is required for DMBA-induced lymphoblastoma formation in vivo. In this study, we addressed the hypothesis that bone marrow stromal cell CYP1B1, and not AhR activation, is required for DMBA-induced pre-B-cell apoptosis. Although DMBA did not directly cause apoptosis in pre-B cells, dose-dependent apoptosis of pre-B cells was observed when they were cocultured with a bone marrow stromal cell line. The DMBA 3,4-dihydrodiol metabolite was more potent in effecting pre-B-cell apoptosis than DMBA, whereas the potent AhR agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin was inactive. Both pre-B cells and bone marrow stromal cells contained DMBA-diol-epoxide DNA adducts, indicating that reactive metabolites were transferred from stromal cells to pre-B cells. DMBA caused apoptosis when cocultured with primary bone marrow stromal cells isolated from AhR-null mice but not CYP1B1-null mice. When cocultured with AhR-null primary bone marrow stromal cells, DMBA induced approximately 50% of the pre-B-cell apoptosis seen with stromal cells from AhR-heterozygous mice. This reduced level of apoptosis parallels the decreased CYP1B1 expression in AhR-null mouse bone marrow stromal cells. These findings provide convincing evidence that bone marrow stromal cell CYP1B1 metabolism of DMBA, but not AhR activation, is required for DMBA-induced pre-B-cell apoptosis.

Effects of tamoxifen and melatonin on mammary gland cancer induced by N-methyl-N-nitrosourea and by 7,12-dimethylbenz(a)anthracene, respectively, in female Sprague-Dawley rats.

Abstract: Chemopreventive effects were analysed of antioestrogen TAM and of MEL on NMU- or DMBA-induced mammary gland cancer, respectively, in female Sprague-Dawley rats. NMU was administered intraperitoneally in two doses each of 50 mg/kg b.w. between 46th-57th postnatal days. DMBA was given by gavage in one dose (20 mg per animal) between 50th-54th postnatal days. The treatment with MEL began 12 days and the treatment with TAM 10 days before carcinogen administration; both chemopreventive substances were administered until the end of the experiment (24 weeks after carcinogen application). TAM was administered subcutaneously twice a week in a dose 2.5 mg/kg b.w. MEL was given in tap water (20 mg/ml) daily between 3 p.m. to 8 a. m. The tumour incidence, tumour frequency per group and animal, latency period, tumour volume, body weight gain in the rats and weight of uterus (in the experiment with NMU) were evaluated. TAM suppressed carcinogenesis to 0% incidence like TAM+MEL in both the NMU and DMBA models. In NMU-induced mammary carcinogenesis MEL lowered the tumour volume (although statistically non-significantly) by 30% in comparison with the control group; in DMBA-induced mammary carcinogenesis it lowered the tumour volume (2.70 +/- 0.81 cm3 vs. 0.90 +/- 0.33 cm3) and lengthened (non-significantly) the latency period (by 12 days). The weight gain of animals in both NMU and DMBA models and relative uterus weight in the NMU model were significantly lower in the groups treated with TAM and TAM+MEL as compared to the control group and the group treated with MEL. Evaluation of the combined effect of TAM+MEL was not possible due to total suppression of carcinogenesis by TAM. TAM and TAM+MEL are highly effective agents in rat mammary carcinogenesis prevention, but the side effects of TAM in humans limits its use in clinical oncology.

Induction of lacZ mutation by 7,12-dimethylbenz[a]anthracene in various tissues of transgenic mice

Abstract: The induction of gene mutations was examined in MutaMouse after an intraperitoneal injection of 7, 8-dimethylbenz[a]anthracene (DMBA) at 20 mg/kg in a collaborative study participated by four laboratories. Although the DMBA dose used was lower than the level that has been reported to induce micronucleated erythrocytes maximally in several mouse strains, a killing effect appeared after day 9 of the post-treatment interval. Mutations in lacZ transgene were detected by the positive selection assay following in vitro packaging of phage lambda from the genomic DNA of the transgenic animals that survived. The mutant induction was evaluated in the bone marrow, liver, skin, colon, kidney, thymus, and testis 7 to 28 days after the treatment. In the bone marrow, the mutant frequency reached a maximum, approximately a 30-fold increase, 14 days after the treatment and the increased frequency persisted at least up to day 28 of the post-treatment. Induction of mutants was detected in the liver, colon, thymus, and skin to lesser extents. Marginal responses were obtained in the kidney and testis. The slight increases in the mutant frequencies in the kidney and testis observed in some laboratories were within laboratory-to-laboratory or animal-to-animal variations. In contrast to the gene mutation induction in the bone marrow, the frequency of micronucleated reticulocytes increased transiently 3 days after the treatment and returned to a control level before day 8 of the post-treatment. It was suggested that DMBA induced gene mutation is fixed in stem cells depending on cell proliferation while DNA damages responsible for chromosome breakage are not transmitted to progeny cells.

Chemopreventive action by an extract from Brassica compestris (var Sarason) on 7,12-dimethylbenz(a)anthracene induced skin papillomagenesis in mice.

Abstract: We report the chemopreventive property of an ethanolic extract of the seeds of Brassica compestris var sarason (mustard seed) on DMBA (7,12 dimethylbenz(a)anthracene induced skin papillomagenesis in male Swiss albino mice. A significant reduction in the values of tumour incidence, tumour burden and the cumulative number of papillomas was observed in mice treated orally with the seed extract of Brassica compestris var sarason, continuously at peri and post initiational stages of papillomagenesis compared with the control groups. The latency period in the experimental group significantly increased (11.3 ± 0.40 weeks) compared with the control group (7.8 ± 0.17). Copyright © 1999 John Wiley & Sons, Ltd.

Telomerase activation and cell proliferation during 7,12-dimethylbenz[a]anthracene-induced hamster cheek pouch carcinogenesis.

Abstract: Telomerase is a ribonucleoprotein complex intimately involved in cell immortalization and carcinogenesis. This enzyme is activated and stabilizes telomere length in almost all types of cancer. Telomerase may be necessary for continuous cell proliferation. In this study, we analyzed telomerase activity in hamster experimental oral lesions (starting from epithelial hyperplasia through dysplasia, carcinoma in situ, and invasive carcinoma) evoked by 7,12-dimethylbenz[a]anthracene, and in normal mucosa. We also analyzed proliferative activity in these lesions by using immunohistochemical analysis and flow cytometry. Histologically normal epithelium expressed weak telomerase activity. The telomerase activity count increased rapidly in the early stage of carcinogenesis and gradually in the late stage. Cell-proliferative activity closely correlated with progression of disease. These findings indicate that telomerase activation is an early event and that increases in telomerase activity upregulate cell proliferation in chemically induced hamster oral carcinogenesis.

Chemoprotective Effects of Neem Leaf Extract on 7,12-Dimethylbenz(a)anthracene (DMBA)-Induced Hamster Buccal Pouch Carcinogenesis.

Abstract: The chemoprotective effects of neem (Azadirachta indica A. Juss.) on hepatic and circulatory lipid peroxidation and on antioxidant and detoxifying enzyme status during 7, 12-dimethylbenz [a] anthracene (DMBA)-induced buccal pouch carcinogenesis was investigated in Syrian male hamsters. Enhanced lipid peroxidation in the liver and circulation of tumor-bearing animals was accompanied by a significant decrease in reduced glutathione (GSH) concentration and activities of the detoxifying enzymes glutathione peroxidase (GPx) and glutathione-S-transferase (GST). Administration of neem leaf extract significantly decreased the formation of lipid peroxides and enhanced the levels of antioxidants and detoxifying enzymes. We speculate that neem leaf extract exerts its effects by modulating lipid peroxidation and enhancing antioxidant and detoxification systems.

The mechanisms of antitumor effects of luteinizing hormone-releasing hormone agonist (buserelin) in 7, 12-dimethylbenz(a)anthracene-induced rat mammary cancer.

Abstract: We evaluated the mechanism of antitumor effects of buserelin, which is one of LH-RH agonists, on a hormone dependent breast cancer model, using 7,12-dimethylbenz(a)anthracene (DMBA)-induced rat mammary cancer. Rats developing solid mammary tumors within 5-7 weeks following the DMBA administration were divided into groups weekly, and treated without delay. The tumor bearing rats were randomized into five groups with regard to tumor size or average weight (15 rats per group). Each group received one of the following treatments during 4 weeks: a) no treatment (NT); b) ovariectomy (Ovx); c) buserelin; d) Ovx and 17beta-estradiol (E2) (Ovx+E2); e) Ovx+E2+buserelin. Tumor regression immediately began at one week after both buserelin treatment and ovariectomy. A significant reduction of tumor size was observed in both buserelin-treated rats and Ovx rats compared with NT rats (p<0.01). No significant difference of tumor size was observed between buserelin-treated rats and ovariectomized rats. No reduction of tumor size was observed in Ovx+E2 rats and Ovx+E2+buserelin rats. Although the mean uterine wet weight of the buserelin group was significantly higher than that of the Ovx group, it was significantly lower than that of the NT group. The mean uterine wet weight of the NT group, the Ovx+E2 group and the Ovx+E2+buserelin group was similar and was significantly higher than that of the Ovx group. Buserelin did not inhibit exogenous estrogen-dependent tumor growth in DMBA-induced rat mammary cancers. These results suggest that buserelin has no direct effects on DMBA-induced rat mammary cancers, and the main mechanism of action of buserelin for tumor-reduction is due to ovarian estrogen deficiency.

Comparison of HepG2 feeder cells generated by exposure to γ-rays, X-rays, UV-C light or mitomycin C for ability to activate 7,12-dimethylbenz[a]anthracene in a cell-mediated Chinese hamster V79/HGPRT mutation assay

Abstract: The cell-mediated Chinese hamster V79/HGPRT mutagenicity assay is an established in vitro testing method. Although gamma-irradiated human HepG2 hepatoma cells have been used recently for chemical activation, an alternative is now needed due to scheduled retirement of the available gamma-source. X-irradiation, 254 nm UV-C light and mitomycin C were examined as possible HepG2 mitotic inhibitors, and treated cells compared for activation of 7, 12-dimethylbenz[a]anthracene (DMBA). In colony-forming assays, V79 and HepG2 cells differed in sensitivity to DMBA, with V79 survival declining sharply between 1-2.5 microM (LD50=1.75 microM) while HepG2 survival decreased gradually, beginning at 0.01 microM DMBA (LD50=0.045 microM). When HepG2 feeder cells generated by each method were included in V79/HGPRT mutation assays, activation of 1 microM DMBA was found to vary according to the mitotic inhibitor used, with mutation frequencies decreasing in the order 4000 rads gamma-rays>25 microg/ml mitomycin C>4000 rads X-rays>25 J/m2 UV-C light. Only assays containing gamma-irradiated HepG2 cells generated an increase (2-3-fold) in mutation frequency when DMBA exposure was extended from 24 to 48 h. The effect of HepG2 preincubation with either Aroclor 1254 or DMBA on feeder cell activation of DMBA was also assessed using concentrations of Aroclor 1254 (10 microg/ml) or DMBA (1.0 microM) which were found to produce optimum induction of ethoxyresorufin-O-deethylase (EROD) activity (3.1-fold and 2-fold increases, respectively). Compared to results obtained with uninduced HepG2 cells, assays incorporating HepG2 cells activated by either Aroclor 1254 or DMBA produced slightly increased V79/HGPRT mutation frequencies after 24 h of exposure to mutagen; however, a 48 h incubation with mutagen in the presence of HepG2 preincubated with either Aroclor 1254 or DMBA resulted in higher mutation frequencies regardless of the mitotic inhibitor treatment. EROD activity was also induced 1.4-fold following exposure of HepG2 cells to mitomycin C alone. Although gamma-irradiation remains the treatment of choice for producing metabolically active HepG2 feeder cells, comparison of the alternatives tested suggests that mitomycin C would be a convenient and suitable replacement.

A novel aromatase inhibitor, vorozole, shows antitumor activity and a decrease of tissue insulin-like growth factor-I level in 7, 12-dimethylbenz[a]anthracene-induced rat mammary tumors.

Abstract: Effects of vorozole, a potent and specific non-steroidal aromatase inhibitor, were evaluated on female Sprague-Dawley (SD) rats with 7, 12-dimethylbenz[a]anthracene (DMBA)-induced mammary tumors. Vorozole at a dose of 0.25, 1.0 and 4.0 mg/kg was orally administered once a day for 28 consecutive days. A significant regression in tumor size was observed in each treated group at 1, 2, 3 and 4 weeks after the start of treatment compared with control group. Tissue insulin-like growth factor I (IGF-I) in the DMBA-induced tumors in each treated group significantly decreased in a dose-dependent fashion compared with control group. These results show the mechanism of vorozole in DMBA-induced rat mammary tumors.

The Effects of Sex Hormones on the Induction of Mammary Carcinomas in Male Rats by Pulse Doses of 7,12-Dimethylbenz(a) anthracene.

Abstract: Male Sprague-Dawley rats were orally dosed with 10 mg 7, 12-dimethylbenz(a)anthracene 3 or 5 times at 14-day intervals starting from 28 days of age. The male rats were treated with various hormonal treatments such as castration and/or injections (3 times/week) of various doses of 17β-estradiol or progesterone, 14 days after the last administration of 7, 12-dimethylbenz(a)anthracene. Extreme secretion in the wide lumina of the acini of the mammary glands was observed in rats given injections at high doses (0.1 mg and 1 mg) of 17β-estradiol. However, there was little lumina of acini without secretion in developed mammary glands in rats given injections of progesterone. This feature of the mammary glands suggests increased levels of progesterone and estrogens in rats given injections of progesterone because of the conversion of progesterone to estrogen. Number of rats with carcinoma and number of carcinoma per rat increased extremely and slightly in rats given injections of 0.01 mg 17β-estradiol or injections of 4 mg progesterone and in rats given injections of high doses (0.1 mg and 1 mg) of 17β-estradiol, respectively. These results indicate that suitable doses of estrogen, particularly 0.01 mg 17β-estradiol promote the progression of male mammary carcinogenesis. In rats given injections of high doses (0.1 mg and 1 mg) of 17β-estradiol, the number of carcinomas with squamous metaplasia increased significantly, and the number of estrogen receptor-positive carcinomas decreased extremely when cells with nuclei stained by immunohistochemical methods were interpreted as positive cells, and a tumor with 20% of positive cells was considered estrogen receptor-positive.

A Preliminary Study of the Effect of Plantago Ovata Forsk on the Development of 7, 12-Dimethylbenz[a]anthracene-initiated Rat Mammary Tumors under the Influence of Hypercholesterolemia

Abstract: As a preliminary study to elucidate whether Plantago ovata forsk (PO) exhibits inhibiting effects on mammary carcinogenesis under a condition of hypercholesterolemia, 50 female Sprague-Dawley rats were first given a single intragastric dose of 200 mg/kg body weight of 7, 12-dimethylbenz[a]anthracene (DMBA). Ten of 50 rats died of acute toxicity of DMBA within one week. From one week later, the survived animals were divided into 4 groups: 13 rats in group 1 and 7 in group 2 received high cholesterol diets (HC) with and without 5% PO supplementation for 26 weeks, respectively. Eleven rats in group 3 and 9 in group 4 received basal diet (BD) with and without 5% PO supplementation for the same period, respectively. One to three rats in groups 1 to 4 died of mammary tumors, lymphomas and/or adrenal impairment attributable to DMBA treatment during the treatment period. Group 1 showed a tendency to decrease in the number of palpable mammary masses as compared with group 2, whereas group 3 showed a tendency to higher values compared with group 4. At the termination of the study, the serum levels of total cholesterol in group 1 were significantly lower than those in group 2 and the number of mammary masses was significantly decreased. Histopathologically, this decrease was mainly due to the decreased incidences of mammary adenocarcinomas, while no significant difference in the multiplicity of mammary tumor was observed between BD+PO and BD alone groups. The results of the present study suggest a possibility that PO exerts inhibiting effects on mammary carcinogenesis by decreasing circulating cholesterol levels in a rat two-stage mammary carcinogenesis model.