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Showing papers on "7,12-Dimethylbenz[a]anthracene published in 2000"


Journal ArticleDOI
TL;DR: Young zebrafish are most responsive to DMBA, showing a greater diversity of neoplasm types than rainbow trout, and are a valuable model system in which to study mechanistic aspects of the carcinogenesis process.
Abstract: Using zebrafish, Danio rerio, initial pioneering work in the 1960s revealed carcinogen responsiveness of fish, yet very few subsequent tumorigenesis investigations have utilized this species. We exposed embryos (60 hours postfertilization) and fry (3 week posthatch) to 7,12-dimethylbenz[a]anthracene (DMBA) by immersion in aqueous solutions for 24 hours, at concentrations of 0-1 or 0-5 ppm (mg/L), respectively. Juvenile zebrafish 2 months posthatch were fed a diet containing 0-1,000 ppm DMBA for 4 months. Fish were sampled for histologic evaluation at 7-12 months after the onset of carcinogen treatment. Fry were most responsive to DMBA and showed the widest diversity of target tissues and histologic types of neoplasia, having several types of epithelial, mesenchymal, and neural neoplasia. The principal target tissues for carcinogenic response were liver following embryo or fry exposure, with gill and blood vessel the second and third most responsive tissues in fry. Intestine was the primary target and gill a secondary target in fish that received dietary DMBA as juveniles. These studies indicate that young zebrafish are most responsive to DMBA, showing a greater diversity of neoplasm types than rainbow trout. Thus, zebrafish are a valuable model system in which to study mechanistic aspects of the carcinogenesis process.

164 citations


Journal Article
TL;DR: Dietaries rich in soy reduce the incidence of chemically induced mammary tumors by approximately 20%.
Abstract: A study was conducted to determine the protective effects of two common dietary proteins, soy protein isolate (soy) and bovine whey, against chemically induced mammary tumors in female Sprague Dawley rats. Rats were fed AIN-93G diets having casein, soy, or whey as the sole protein source. Rats within the same dietary groups were mated to obtain the F1 and F2 generations. At age 50 days, F1 (experiment A) or F2 (experiment B) female offspring (> or =19 rats/group) were p.o. gavaged with 80 mg/kg 7,12-dimethylbenz(a)anthracene, and mammary glands were evaluated when 100% of the casein-fed group developed at least one palpable tumor. Rats grew well on all three diets, but casein-fed rats gained slightly more body weight than soy- or whey-fed rats (P < 0.05). Vaginal opening occurred 1 day earlier in soy-fed rats than in casein- or whey-fed rats, but no other differences in reproductive and developmental parameters were observed between groups. When 50% of the casein-fed rats had at least one mammary tumor, lower tumor incidences (24-34%) were observed in the soy-fed (P < 0.009) and whey-fed groups (P < 0.001). When 100% of the casein-fed rats had at least one tumor, soy-fed rats had a lower tumor incidence (77%) in experiment B (P < 0.002), but not in experiment A (P < 0.12), and there were no differences in tumor multiplicity. Whey-fed rats had lower mammary tumor incidence (54-62%; P < 0.002) and multiplicity (P < 0.007) than casein-fed rats in both experiments. Our results indicate that diets rich in soy reduce the incidence of chemically induced mammary tumors by approximately 20%. Furthermore, whey appears to be at least twice as effective as soy in reducing both tumor incidence and multiplicity.

129 citations


Journal Article
TL;DR: This study substantiates the importance of DMBA dihydrodiol epoxide generation at the site of cancer initiation and suggests that tissue-specific constitutive CYP1B1 expression may contribute to cancer susceptibility in the human population.
Abstract: Humans are exposed to polycyclic aromatic hydrocarbons (PAHs) through many environmental pollutants, especially cigarette smoke. These chemicals cause a variety of tumors and immunotoxic effects, as a consequence of bioactivation by P-450 cytochromes to dihydrodiol epoxides. The recently identified cytochrome P4501B1 (CYP1B1) bioactivates PAHs but is also a physiological regulator, as evidenced by linkage of CYP1B1 deficiency to congenital human glaucoma. This investigation demonstrates that CYP1B1 null mice are almost completely protected from the acute bone marrow cytotoxic and preleukemic effects of the prototypic PAH 7,12-dimethylbenz[a]anthracene (DMBA). CYP1B1 null mice did not produce the appreciable amounts of bone marrow DMBA dihydrodiol epoxide DNA adducts present in wild-type mice, despite comparable hepatic inductions of the prominent PAH-metabolizing P-450 cytochrome, CYP1A1. Wild-type mice constitutively expressed low levels of bone marrow CYP1B1. These findings suggest that CYP1B1 is responsible for the formation of DMBA dihydrodiol epoxides in the bone marrow. Furthermore, this study substantiates the importance of DMBA dihydrodiol epoxide generation at the site of cancer initiation and suggests that tissue-specific constitutive CYP1B1 expression may contribute to cancer susceptibility in the human population.

101 citations


Journal ArticleDOI
TL;DR: Results of the study indicate that the anticarcinogenic activity of vanadium during DMBA-initiated mammary carcinogenesis is mediated through alteration of hepatic antioxidant status as well as modulation of phase I and II drug metabolizing enzymes.
Abstract: Vanadium, a non-platinum group metal and dietary micronutrient, is now proving to act as a promising antitumor agent. The present study was conducted to ascertain its antineoplastic potential against an experimental mammary carcinogenesis. Female Sprague-Dawley rats, at 50 days of age, were treated with 7,12-dimethylbenz(a)anthracene (DMBA) (0.5 mg/100 g body weight) by a single tail vein injection in an oil emulsion. Vanadium (ammonium monovanadate) at the concentration of 0.5 ppm was supplemented in drinking water and given ad libitum to the experimental group immediately after the carcinogen treatment and it continued until the termination of the study (24 weeks for histological and biochemical observations and 35 weeks for morphological findings). It was found that vanadium treatment brought about a substantial protection against DMBA-induced mammary carcinogenesis. This was evident from histological findings that showed no sign of hyperplasia or abnormality after vanadium treatment. There was a significant reduction in incidence (P < 0.05), total number, multiplicity (P < 0.01) and size of palpable mammary tumors and delay in mean latency period of tumor appearance (P < 0.001) following vanadium supplementation compared to DMBA control. From the cumulative results of various hepatic biochemical indices namely, lipid peroxidation, reduced glutathione level, superoxide dismutase activity, cytochrome P450 content and glutathione S-transferase activity, the anticarcinogenic potential of vanadium was well reflected through stabilization of these parameters. Results of the study indicate that the anticarcinogenic activity of vanadium during DMBA-initiated mammary carcinogenesis is mediated through alteration of hepatic antioxidant status as well as modulation of phase I and II drug metabolizing enzymes. On the basis of the observed results, vanadium can be considered as a readily available, promising and novel cancer chemopreventive agent.

71 citations


Journal ArticleDOI
TL;DR: It is speculated that garlic exerts its protective effects by decreasing circulatory lipid peroxides and enhancing antioxidants and enhances antioxidants during 7,12-dimethylbenz[a]anthracene-induced hamster buccal pouch carcinogenesis in male Syrian hamsters.

53 citations


Journal Article
TL;DR: Results indicate that the adenine adducts induced by both bay-region diol epoxides of DMBA lead to the mutation at codon 61 of H-ras and, consequently, initiate tumorigenesis in mouse skin.
Abstract: We have determined the tumor-initiating activity of (+/-)syn- and (+/-)anti-7,12-dimethylbenz[a]anthracene-3,4-diol-1,2-epoxide (syn- and anti-DMBADE), the two metabolically formed bay-region diol epoxides of DMBA, and we have also analyzed mutations in the H-ras gene from tumors induced by these compounds. Using a two-stage, initiation-promotion protocol for tumorigenesis in mouse skin, we have found that both syn- and anti-DMBADE are active tumor initiators, and that the occurrence of papillomas is carcinogen dose dependent. All of the papillomas induced by syn-DMBADE (a total of 40 mice), 96% of those induced by anti-DMBADE (a total of 25 mice), and 94% of those induced by DMBA (a total of 16 mice) possessed a -CAA- to -CTA- mutation at codon 61 of H-ras. No mutations in codons 12 or 13 were detected in any tumor. Topical application of syn- and anti-DMBADE produced stable adducts in mouse epidermal DNA, most of which comigrated with stable DNA adducts formed after topical application of DMBA. Further analysis of the data showed that levels of the major syn- and anti-DMBADE-deoxyadenosine adducts formed after topical application of DMBA are sufficient to account for the tumor-initiating activity of this carcinogen on mouse skin. Previously, we showed that both the syn- and anti-DMBADE bind to the adenine (A182) at codon 61 of H-ras. Collectively, these results indicate that the adenine adducts induced by both bay-region diol epoxides of DMBA lead to the mutation at codon 61 of H-ras and, consequently, initiate tumorigenesis in mouse skin.

43 citations


Journal ArticleDOI
TL;DR: The results suggest that endothelial cells may be targets for CYP-dependent activation of such toxicants as polycyclic aromatic hydrocarbons and the possibility that chemically induced endothelial dysfunction is a risk factor in the aetiology of cardiovascular disease demands consideration.
Abstract: Autoradiography was used to investigate the cellular sites of irreversible binding of 3H-labelled 7,12-dimethylbenz[a]anthracene (DMBA) and benzo[a]pyrene (B[a]P) in mice. Autoradiograms obtained from solvent-extracted tape-sections revealed an even distribution of DMBA- and B[a]P-derived radioactivity in control mice lacking sites of selective binding in the tissues. In mice pretreated with a cytochrome P4501A (CYP1A) inducer, β-naphthoflavone (BNF) or 3,3′,4,4′,5-pentachlorobiphenyl (PCB 126), a noticeable accumulation of bound radioactivity was observed in the pulmonary alveolar region. Increased labelling was also observed in heart tissue of induced mice. As demonstrated by microautoradiography of tissues from CYP1A-induced mice treated with 3H-DMBA or 3H-B[a]P in vivo, irreversible binding in lung tissue was present in endothelial cells of arteries and veins, in the alveolar septal walls, and in type 2 pneumocytes. In heart tissue, binding was confined to endothelial cells of arteries, capillaries and veins. In liver, binding was found in the hepatocytes as well as in endothelial cells of the portal veins, whereas no binding was seen in endothelial cells of the sinusoids, central veins, or arteries. These findings were confirmed in vitro using 3H-DMBA-exposed precision-cut slices, indicating that reactive intermediates of DMBA and B(a)P were formed in situ. The addition of the CYP1A inhibitor ellipticine abolished binding in the target endothelial cells. Increased endothelial binding in the lungs and liver of CYP1A-induced mice was concomitant with increased 7-ethoxyresorufin O-deethylase (EROD) and DMBA hydroxylase activity. In heart, endothelial binding was positively correlated with EROD, but not with DMBA hydroxylase. The results suggest that endothelial cells may be targets for CYP-dependent activation of such toxicants as polycyclic aromatic hydrocarbons. Consequently, the possibility that chemically induced endothelial dysfunction is a risk factor in the aetiology of cardiovascular disease demands consideration.

42 citations


Journal ArticleDOI
TL;DR: The results suggest that DMBA is highly mutagenic to lacI in mammary tissue and that adducts with both G:C and A:T base pairs participate in forming mutations in DMBA-treated BB rats.
Abstract: Recently we compared the lacI and Hprt mutant frequencies (MFs) and types of mutations in lymphocytes of Big Blue((R)) (BB) rats exposed to 7,12-dimethylbenz[a]anthracene (DMBA) under conditions that result in mammary gland tumors. In this study, we have examined the target mammary tissue for DMBA-induced DNA adducts, lacI MF and types of lacI mutations. Seven-week-old female BB rats were given single doses of 0, 20 or 130 mg/kg DMBA by gavage and the DNA adducts and lacI MFs in the mammary tissue were measured over a period of 14 days and 18 weeks, respectively, following treatment. The lacI MF in the mammary tissue increased for 10 weeks and then remained relatively constant; 130 mg/kg DMBA produced a 14-fold increase in the MF (255 +/- 50 x 10(-6) p.f.u.) over control MF (18. 3 +/- 4 x 10(-6) p.f.u.). (32)P-post-labeling analysis of DNA from mammary tissue and splenic lymphocytes of treated rats revealed two major adducts. Comparison of these adducts with DMBA standards indicated that the adducts formed by DMBA involved both G:C and A:T base pairs. DNA sequencing revealed that the majority of DMBA-induced lacI mutations were base pair substitutions and that A:T-->T:A (44% of the independent mutations) and G:C-->T:A (24% of the independent mutations) transversions were the predominant types. Furthermore, the mutational results revealed a 'hotspot' for a G-->T mutation in codon 95 (GTG-->TTG) of the lacI gene in mammary tissue. These results suggest that DMBA is highly mutagenic to lacI in mammary tissue and that adducts with both G:C and A:T base pairs participate in forming mutations in DMBA-treated BB rats.

39 citations


Journal ArticleDOI
TL;DR: Findings show that dietary cholesterol inhibits mammary tumorigenesis induced by either MNU or DMBA and that the inhibition is independent of the type or extent of mutations in the Ha-ras gene.
Abstract: Dietary cholesterol has previously been shown to inhibit rat mammary tumorigenesis but the mechanisms remain unclear. Uptake of serum low density lipoprotein cholesterol by tissues leads to down-regulation of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase, the rate limiting enzyme in cholesterol biosynthesis that catalyzes the formation of mevalonate. In addition to being a precursor of cholesterol, mevalonate is necessary for DNA synthesis and cell proliferation. Isoprenoids, also derived from mevalonate, are required for the post-translational modification of Ras proteins that are mutated in a number of carcinogen-induced rat mammary tumors. The purpose of this study, therefore, was to determine whether inhibition of tumorigenesis by cholesterol is dependent on the frequency of mutations in the Ha-ras gene. Female Sprague-Dawley rats (30/group) were given a single dose of either N-methyl-N-nitrosourea (MNU, 50 mg/kg i.p.) or 7, 12-dimethylbenz[a]anthracene (DMBA, 100 mg/kg intragastrally), carcinogens that produce tumors with either a high (MNU) or low (DMBA) frequency of Ha-ras mutations in codon 12 or 61, respectively. Rats were fed either a control AIN-93G diet or the control diet supplemented with 0.3% cholesterol for 14 weeks. Dietary cholesterol significantly decreased the final tumor incidence in rats given DMBA (83 versus 100%, P < 0.05) or MNU (53 versus 77%, P < 0.05). HMG-CoA reductase activity was higher in mammary tumors than in normal mammary glands, but the activity of this enzyme was reduced by cholesterol feeding only in mammary glands and not in tumors. Tumors induced by MNU had a high frequency of Ha-ras mutations in both the control (65%) and cholesterol-fed (68%) groups. Tumors induced by DMBA had a low frequency of Ha-ras mutations that also did not differ between the control (21%) and cholesterol-fed (18%) groups. These findings show that dietary cholesterol inhibits mammary tumorigenesis induced by either MNU or DMBA and that the inhibition is independent of the type or extent of mutations in the Ha-ras gene.

38 citations


Journal ArticleDOI
TL;DR: The data indicate that pineal indole hormone melatonin inhibits cervical and vaginal carcinogenesis induced by DMBA in mice and possess antimutagenic and anticlastogenic effect in vitro.

36 citations


Journal ArticleDOI
TL;DR: The results of the present study suggest that garlic may exert its chemopreventive effects by modulating lipid peroxidation and enhancing the levels of GSH, GPx and GST.

Journal ArticleDOI
TL;DR: Evaluated types of mutations induced by DMBA in the autosomal thymidine kinase (Tk) gene of Tk+/− mice indicate that the predominant types of DMBA‐induced mutation detected by the autosome Tk gene are different from those detected byThe X‐linked hprt gene.
Abstract: 7,12-Dimethylbenz[a]anthracene (DMBA) is a rodent carcinogen and a potent in vivo mutagen for the X-linked hypoxanthine guanine phosphoribosyl transferase (hprt) gene of rats and for the lacl transgene of Big Blue mice and rats. Although DMBA is also a powerful clastogen, molecular analysis of these DMBA-induced hprt and lacl mutations indicates that most are single base-pair (bp) substitutions and 1- to 3-bp frameshifts. In the present study, we evaluated the types of mutations induced by DMBA in the autosomal thymidine kinase (Tk) gene of Tk +/- mice. Male and female 5-to 6-week-old animals were injected i.p. with DMBA at a dose of 30 mg/kg. Five weeks after the treatment, hprt and Tk mutant frequencies were determined using a limiting dilution clonal assay in 96-well plates. We established conditions for the automated identification of wells containing expanded lymphocyte clones using the fluorescent indicator alamarBlue. This procedure allowed the unbiased identification of viable clones and calculation of mutant frequencies. In male mice, DMBA treatment increased the frequency of hprt mutants from 1.8 ± 1.1 to 34 ± 9 × 10 6 , and Tk mutants from 33 ± 12 to 78 ± 26 × 10 6 ; treated female mice had a significant but lower increase in hprt mutant frequency than did males. Molecular analysis of DMBA-induced Tk mutants revealed that at least 75% had the entire wild-type Tk allele missing. The results indicate that the predominant types of DMBA-induced mutation detected by the autosomal Tk gene are different from those detected by the X-linked hprt gene. The Tk gene mainly detects loss of heterozygosity mutation, whereas the majority of mutations previously found in the hprt gene were point mutations. Environ. Mol. Mutagen. 36:283-291, 2000. Published 2000 Wiley-Liss, Inc.

Journal ArticleDOI
TL;DR: This is the first report demonstrating that PhIP and DMBA are capable of enhancing 8-OHdG levels in the rat mammary tissue in vivo, and the effect of the chemopreventive agent 1,4-phenylenebis(-methylene)selenocyanate (p-XSC) as an inhibitor of such damage is evaluated.

Journal ArticleDOI
TL;DR: It is found that TBAP and hemin exert concentration-related inhibition of his(+) reversion in Salmonella typhimurium TA100 induced by 7, 12-dimethylbenz[a]anthracene (DMBA), and significantly reduced both incidence and multiplicity of skin tumors when topically applied prior to treatment of 12-O-tetradecanoylphorbol-13-acetate in female ICR mice.
Abstract: Porphyrins which are widespread in nature can interfere with the actions of certain carcinogens and mutagens, and have also been used clinically in photodynamic therapy (PDT) of tumors. Porphyrins such as chlorophyll, chlorophyllin (CHL) and hemin are known to inactivate various mutagens by forming complexes with them. Tetrakis(4-benzoic acid)porphyrin (TBAP) has been developed as a photosensitizer for PDT and its metal complex, MnTBAP has been shown to be efficacious in a variety of in vitro and in vivo oxidative stress models of human diseases. In the present study, we have found that TBAP and hemin exert concentration-related inhibition of his(+) reversion in Salmonella typhimurium TA100 induced by 7, 12-dimethylbenz[a]anthracene (DMBA), and significantly reduced both incidence and multiplicity of skin tumors when topically applied prior to treatment of 12-O-tetradecanoylphorbol-13-acetate in female ICR mice. Covalent DNA binding of DMBA in mouse skin was also significantly inhibited by topical application of TBAP or hemin as well as CHL. These results suggest the chemopreventive potential of compounds containing a porphyrin nucleus.

Journal ArticleDOI
TL;DR: A 12-week treatment with I3C or beta-NF significantly increased the P450-dependent activities of ethoxy-, methoxy-, benzyloxy- and pentoxy-(with I 3C only) resorufin O-dealkylase in hepatic microsomes indicating induction of several P450s.

Journal Article
TL;DR: While the DMBA-induced gene expressions showed very different patterns, the effectiveness of the two different administrations of MBB was found to be very similar in the two sex groups, and increased p53 gene expression levels could be seen in several tissues in both sex groups.
Abstract: The cyclic chalcone analogue, E-2-(4'-methoxybenzylidene)-1-benzosuberone (MBB), has been found to show outstanding in vitro cytotoxic activity against P388, L1210, Molt 4/C8 and CEM cells, as well as against a panel of human cell lines. In order to determine whether this promising antineoplastic activity would extend to anticarcinogenic properties, the effect of MBB on the 7,12-dimethylbenz [alpha]anthracene (DMBA)-induced expression of the c-myc, Ha-ras and p53 genes in isolated RNA from the liver, lung, kidney, spleen, thymus, lymph nodes and bone marrow of CBA/Ca inbred mice was investigated. Earlier we had found that administration of MBB can reduce the DMBA-induced 24-hour gene expressions most effectively when it is administered prior to, or simultaneously with, the DMBA-treatment to female CBA/Ca inbred mice. As a continuation of this study, we investigated the effect of MBB on the DMBA-induced gene expressions according to the two protocols in a 48-hour experiment. The 48-hour experiment with female and male CBA/Ca inbred mice also determined the compound which effectively reduced the DMBA-induced c-myc and Ha-ras overexpressions in almost all tissues. While the DMBA-induced gene expressions showed very different patterns, the effectiveness of the two different administrations of MBB was found to be very similar in the two sex groups. At the same time, contrary to the 24-hour experiment, increased p53 gene expression levels could be seen in several tissues in both sex groups. In order to get a better understanding of the effects of MBB on the DMBA-induced gene expressions "long-term" and "follow-up" studies should be performed.

Journal ArticleDOI
TL;DR: Modulating CYP1A1 activity indicated this enzyme plays a significant role in metabolizing DMBA to water-soluble compounds in isolated trout liver cells, and DMBA bioactivation to DNA-binding metabolites in Trout liver cells and mouse embryo cells predominantly involve different metabolic pathways to form the DNA- binding intermediates.

Journal ArticleDOI
TL;DR: The different lacI mutation fixation times observed for bone marrow, lymphocytes and mammary tissue, and lymphocytes suggest that the lacI gene manifests a tissue‐specific mutation fixation time, which may depend on the cell proliferation rate of a tissue.
Abstract: Recently, we evaluated lacI mutations in lymphocytes and mammary tissue of Big Blue (BB) rats exposed to 7,12-dimethylbenz[a]anthracene (DMBA). The results on the time course of mutant induction suggested that the lacI gene may manifest a tissue-specific increase in mutant frequency (MF). To test whether a tissue-specific increase in lacI MF is dependent on the cell proliferation rate of a tissue, we examined rapidly proliferating bone marrow cells for DMBA-induced lacI mutations. Seven-week-old female BB rats were given single doses of 0, 20, and 130 mg/kg DMBA by gavage and the lacI MFs in the bone marrow were measured over a period of 14 weeks following treatment. Bone marrow cells had a remarkably low average background MF (3.1 ± 1.6 × 10−6 plaque-forming units) and the DMBA-induced lacI MFs were significantly higher than control MFs for both doses and at all time points (P < 0.01). The lacI MF in the bone marrow increased for 2 weeks and then remained relatively constant; 20 and 130 mg/kg DMBA produced 34- and 106-fold increases in MF over control MF. DNA sequencing revealed that the majority of DMBA-induced lacI mutations were base-pair substitutions and that A:T T:A (48%) and G:C T:A (24%) transversions were the predominant types. Thus, the different lacI mutation fixation times observed for bone marrow (2 weeks), mammary (10 weeks), and lymphocytes (6 weeks) suggest that the lacI gene manifests a tissue-specific mutation fixation time, which may depend on the cell proliferation rate of a tissue. In addition, the relatively low spontaneous MF in bone marrow compared with that in other tissues may be useful for increasing the sensitivity of the assay for detecting induced MFs in BB rats. Environ. Mol. Mutagen. 36:235–242, 2000. Published 2000 Wiley-Liss, Inc.

Journal ArticleDOI
TL;DR: Induction of xenobiotic binding capacity in cytosol of dieldrin-fed rainbow trout at least partially explained altered DMBA disposition in fish pretreated with this cyclodiene insecticide.
Abstract: Previously it was demonstrated that biliary excretion of a single dose of [14C]dieldrin or [3H]7,12-dimethylbenz[a]anthracene (DMBA) was stimulated up to 700% and 300%, respectively, in rainbow trout fed 0.3?0.4 mg dieldrin/kg/d for 9?12 wk. This was not explained by increased activities of hepatic microsomal xenobiotic-metabolizing enzymes or increased amounts of any of six cytochrome P-450 isozymes quantitated by Western blots. It was hypothesized that stimulated excretion was explained by induction of (1) cytosolic binding proteins that facilitated intracellular trafficking of DMBA to sites of metabolism, or (2) ATP-dependent proteins that transport xenobiotic metabolites from liver to bile. Binding of 15 and 60 nmol [3H]DMBA/mg protein increased about 200% in hepatic cytosol from dieldrin-fed fish. A 50-fold molar excess of unlabeled DMBA reduced binding of 15 nmol [3H]DMBA/mg protein (nonspecific binding) by the same amount in cytosol from control and dieldrin-fed fish, indicating that dieldrin induc...


Journal ArticleDOI
TL;DR: The results indicate that carcinoma cells and dysplasia cells induced by DMBA in neonatally androgenized rats differ in response to high doses of E2.
Abstract: Inbred, female Sprague-Dawley rats were neonatally androgenized at the age of 2 days by subcutaneous injections of 1.25 mg testosterone propionate and divided into 4 groups. At the age of 50 days, rats of all groups were given 20 mg 7, 12-dimethylbenz[a]anthracene (DMBA). Four weeks after the administration of DMBA, the rats in Group I remained intact, those in Group II were subjected to ovariectomy, while the animals in Groups III and IV were given 1 mg 17β-estradiol (E2) at 2-day intervals for 3 weeks. Additionally, the rats in Group IV were given 1 mg E2 at 2-day intervals for 3 weeks by intramuscular injection, starting from the 105th day after the administration of DMBA.The ovaries of the neonatally androgenized rats contained numerous large vesicular follicles and no corpora lutea, and the mammary glands of the animals in Groups I, III and IV consisted mainly of dilated acini containing milky secretions. In rats in Group I, mammary carcinomas and mammary dysplasias were induced. Rat mammary dysplasias were grossly characterized by gross cysts and solid masses. Solid masses were heteromorphic lesions and commonly consisted of several nodules with various microscopic features. These masses were subclassified into the 2 types of histological features that were predominant among the nodules: acinar adenosis and fibrotic adenosis. The induction of mammary carcinomas and mammary dysplasias was strongly suppressed by ovariectomy (Group II) as the development of mammary carcinomas and mammary dysplasias induced in neonatally androgenized rats are dependent on estrogens. The induction of mammary carcinomas was suppressed by injections of high doses of E2 for 21 days (Once in Group III and twice in Group IV). Conversely, the induction of mammary dysplasias was promoted by one time (Group III) but was suppressed by two times (Group IV) of E2. The results indicate that carcinoma cells and dysplasia cells induced by DMBA in neonatally androgenized rats differ in response to high doses of E2.

Journal ArticleDOI
TL;DR: The findings indicate that the progression of mammary carcinomas induced by a single or multiple administration of DMBA was suppressed in ovariectomized rats and in rats with injections of high doses of E2.
Abstract: The objective of this investigation was to elucidate the role of sex hormones in the progression and subsequent hormone dependency of mammary carcinomas induced by single or multiple administration of 7, 12-dimethylbenz[a]anthracene (DMBA). Ten milligrams of DMBA were administrated orally to female Sprague-Dawley (SD) rats once at the age of 42 days (Group A) and three times at the ages of 28, 42 and 56 days (Group B). All 70-day-old rats in Groups A and B were divided into 4 groups (I, II, III and IV), respectively. Rats in Groups I of A and B were intact controls. Rats in Groups II of A and B were ovariectomized (OVEX) at the age of 70 days. Rats in Group II of Group A and in Groups III of Groups A and B were divided into 4 subgroups (Group II-1, II-2, II-3 and II-4) and 3 subgroups (Group III-1, III-2 and III-3), respectively. Rats in Groups II-2 of A and III-1 of A and B, rats in Groups II-3 of A and III-2 of A and B and rats in Groups II-4 of A and III-3 of A and B were given injections of 0.01, 0.1 and 1 mg 17β-estradiol (E2), respectively. Rats in Groups IV of A and B were given injections of 4 mg progesterone (P). Injections of E2 or P were given 3 times a week between the ages of 70 and 217 days in Group A and the ages of 70 and 105 days in Group B. In Group A, there was no difference of incidence of mammary carcinomas among Groups I, II-2, II-4, III-1 and IV but the incidence of mammary carcinomas in Groups II-1, II-3, III-2 and III-3 was extremely low, compared with that in Group I. In Group B, a large number of mammary carcinomas developed and although there was no difference in the incidence of mammary carcinomas among Groups I, II, III and IV, the number of mammary carcinomas per rat decreased in Groups II, III-2 and III-3, compared with Group I. These findings indicate that the progression of mammary carcinomas induced by a single or multiple administration of DMBA was suppressed in ovariectomized rats and in rats with injections of high doses of E2. DMBA-induced mammary carcinomas in Group B were transplanted into OVEX rats (R-1), OVEX rats with injections of 0.01 mg E2 (R-2) and OVEX rats with injections of 1 mg E2 (R-3). According to tumorigenesis in those rats with various hormonal treatments (R-1, 2, 3), mammary carcinomas were classified into one of the four categories (Type A, B, C and D). Type A tumor: tumor developed greatly in R-2 but slightly or not in R-1 and R-3. Type B tumor: tumors developed greatly in R-1 but slightly or not in R-2 and R-3. Type C tumor: tumors developed greatly in R-3 but slightly or not in R-1 and R-2. Type D tumor: tumors developed greatly in R-1, R-2 and R-3. In Group B, rates of type A, B, C, D tumor were 43.2, 13.5, 24.3 and 18.9% in Group I, 26.3, 10.5, 21.1 and 42.1% in Group II, 40.0, 5.0, 45.0 and 10.0% in Group III-1, 38.5, 15.4, 30.8 and 15.4% in Group III-2, 28.6, 0, 71.4 and 0% in Group III-3 and 44.4, 33.3, 11.1 and 11.1 in Group IV, respectively. These results suggested that the hormonal status of the development process may be one of factors which affects the characteristics of hormone dependency and the multiple administration of DMBA may induce large numbers of carcinoma cells with varying dependency on hormones and carcinoma cells may be selected in hormonal conditions during progression.

Journal ArticleDOI
TL;DR: It is suggested that at least two genetic mutations are necessary for induction of adenocarcinoma with MECs in the rat submandibular gland, and the mutation is efficiently introduced to pup glands whose terminal secretory units exhibit extreme proliferative activity.
Abstract: In an attempt to induce adenocarcinoma containing myoepithelial cells (MECs) in the rat submandibular gland, we injected 7,12-dimethylbenz(a)anthracene (DMBA) dissolved in acetone into the glands of rat pups at the age of 10 days. In both male and female pups, the glands, including their developing terminal secretory units, contained far greater numbers of cells positive for proliferating cell nuclear antigen (PCNA) than did adult glands. A single administration of 1% DMBA (0.05 ml/130 g b.w.) did not produce adenocarcinoma, but did induce occasional sarcomas, such as rhabdomyosarcoma and fibrosarcoma, in 2 months. Most glands regenerated with minimal scar formation. Microscopically, these glands were atypical in that they contained increased numbers of PCNA-positive cells, underdeveloped granular ducts, and striated ducts surrounded by MECs positive for alpha smooth muscle actin (αSMA). Though these features were also observed in the regenerated glands after acetone injection, the number of PCNA-positive cells was relatively high in the glands of DMBA-treated females, especially in the terminal secretory unit. The second DMBA injection at 10 weeks of age produced adenocarcinoma made up of αSMA-positive MECs and keratin 19-positive duct cells. Such MEC-associated adenocarcinoma was induced in the glands of more than half the female but not the male animals. Replacement of either of the double DMBA treatments with acetone, or DMBA treatment, single or double, of adult glands did not produce adenocarcinoma, but did produce sarcoma and squamous cell carcinoma. These results suggest that (1) at least two genetic mutations are necessary for induction of adenocarcinoma with MECs in the rat submandibular gland, (2) the mutation is efficiently introduced to pup glands whose terminal secretory units exhibit extreme proliferative activity, and (3) the second mutation is difficult to introduce in male glands, whose proliferative activity is relatively low, and/or transformed cells need some female hormone after the mutation to propagate.

Journal ArticleDOI
TL;DR: The effects of age, gender, strain, phenobarbital treatment and pituitary influence on the regioselective metabolism of 7, 12-dimethylbenz[a]anthracene to hydroxmethyl metabolites were investigated and male predominant formation of 7OHMe12MBA was apparent following sexual maturation of the LE rats and was significantly reduced upon hypophysectomy.


Journal ArticleDOI
TL;DR: The results show that telomersase activity in the target tissue may be detected at the early stage of the DMBA-induced hamster buccal pouch tumor formation and suggests that telomerase activity may be used as a biomarker for an early clinical detection of buCCal pouch cancer.
Abstract: Objective: To investigate the roles of telomerase activity (TA) in relation to hamster buccal pouch tumor progression. Methods: male hamster were treated three times weekly with 0.5% of 7, 12-dimethyl-benzanthracene (DMBA) over a IS weeks experimental period. Hamsters were sacrificed at 3, 6, 9, 12 and 15 weeks after treatment. Telomerase activity of hamster buccal pouch tissue were measured along with the analyses of the formation of DMBA-induced hamster buccal pouch tumors. Results: DMBA-induced squamous cell carcinomas were found at the 6th week after dosing. Telomerase activity elevation began at the 3rd week and was increasing to a plateau at the 12th week. Conclusion: Our results show that telomerase activity in the target tissue may be detected at the early stage of the DMBA-induced hamster buccal pouch tumor formation and suggests that telomerase activity may be used as a biomarker for an early clinical detection of buccal pouch cancer.