Cerebellar dysgenesis in rats by diaplacental effects of 7,12-dimethylbenz[a]anthracene

7,12-Dimethylbenz[a]anthracene (DMBA) administered iv to pregnant Sparague-Dawley rats produced cerebellar malfunction in at least 10% of the offspring. The underlying morphologic basis of the cerebellar symptomatology was found in maldevelopment of cerebellar cortex, ranging from focal loss of granule and Purkinje's cell layers to extensive areas of cortical disorganization with losses of granule neurons. An interference with the proliferation of the granule cell-layer primordium was suggested as a mechanism of this cerebellar dysgenesis. After a 200-day observation, no tumors were found in the offspring of the DMBA-treated, pregnant rats.     

Seasonal influence on 7,12-dimethylbenz[a]anthracene-induced mammary carcinogenesis in Sprague-Dawley rats under controlled laboratory conditions

There is good evidence in some species, including rats, that circannual rhythms are innate and can occur even under constant environmental conditions. Such circannual rhythms, e.g. in hormone levels and immune system function, may influence tumourigenesis. This prompted us to study 7,12-dimethylbenz[a]anthracene(DMBA)-induced mammary carcinogenesis at different seasons of the year in female Sprague-Dawley rats under constant environmental conditions (photoperiod, temperature, air humidity, food). DMBA was administered orally at a dose of 5 mg per rat at the first day of the experiment and then at weekly intervals up to a total dose of 20 mg per rat. Rats were palpated once weekly for the presence of mammary tumours. After 13 weeks, they were necropsied for examination of the number and size of mammary tumours. Age-matched groups of 36-99 rats were used per experiment. When the experiment was performed twice within 2 years during the same season (spring/summer), tumour incidence (56 and 61%) and tumour burden were almost equal, indicating that data obtained in this way were reproducible. However, the same experiment performed in autumn yielded a significantly lower tumour incidence (34%) and tumour burden. When the experiment was started during winter, tumour incidence was similar to the spring/summer groups, but tumour burden was lower. The data indicate a seasonal variation in the development and growth of DMBA-induced breast cancer in Sprague-Dawley rats. One possible explanation for this phenomenon may be the seasonal variation in pineal melatonin production and immune function previously reported in rodents under constant environmental conditions.     

Induction of mammary tumors in virgin female BALB/c mice by single low doses of 7,12-dimethylbenz[a]anthracene

The induction of mammary tumors in virgin female inbred BALB/c mice after administration of 7,12-dimethylbenz[a]anthracene (DMBA) over a wide range of doses was studied. Mice were exposed at 12 weeks of age to single or multiple doses of DMBA ranging from 0.0025 to 12.0 mg by gastric intubation and were checked regularly for mammary tumors. The experiment was terminated when the mice were 800 days of age. In the dose range of 0.0025--0.125 mg DMBA, the incidence of mammary tumors was dose-dependent. At higher doses, the mammary tumor incidence became less dose-dependent and was nearly independent of doses above the 0.25-mg level. Analysis of the data for the rate of appearance of mammary tumors with age of the animals and for the age at death of non-mammary tumor-bearing animals indicated that in the low dose range induction of mammary tumors was the predominant effect of DMBA exposure, whereas at moderate to high doses the toxic and carcinogenic effects of DMBA on other tissues significantly influenced the final incidence of mammary tumors. Greater than 90% of the tumors that resulted from administration of low doses of DMBA were adenocarcinomas. In contrast, adenocarcinomas and adenoacanthomas were found in approximately equal proportions following administration of high doses of DMBA.     

Tissue distribution of DNA adducts in rats treated by intramammillary injection with dibenzo[a,l]pyrene, 7,12-dimethylbenz[a]anthracene and benzo[a]pyrene

Recombinant human bone morphogenetic protein (rhBMP-2) was examined for its in vitro effects on biochemical markers representing osteoblast phenotype. Primary cultures of fetal rat calvarial osteoblasts were used in this study. The results indicated that rhBMP-2 stimulated alkaline phosphatase activity, parathyroid hormone (PTH)-induced cyclic AMP production, and collagen biosynthesis in a dose-dependent manner in confluent cultures. The percent collagen synthesis also increased in a dose-dependent manner. Alkaline phosphatase activity was stimulated in a time-dependent manner by rhBMP-2 that reached its maximum 5 days after initiation. Cycloheximide (2 micrograms/ml) inhibited rhBMP-2-stimulated alkaline phosphatase indicating de novo protein synthesis of the enzyme. Transforming growth factor-beta 1 (TGF-beta 1)-induced inhibition of alkaline phosphatase activity observed in confluent primary cultures was completely abolished by rhBMP-2 at a concentration that was 43 times greater than the TGF-beta 1 concentration. Also, rhBMP-2 produced a small stimulation of alkaline phosphatase activity in cells grown in the absence of ascorbic acid; however, the effect was greatly enhanced in cells cultivated in the presence of ascorbic acid (50 micrograms/ml). In view of the potentiating effect of ascorbic acid on rhBMP-2-induced stimulation of alkaline phosphatase, we speculate that ascorbic acid could amplify the osteoinductive effects of rhBMP-2 and thereby augment the efficacy of the BMP when used as bone repair material in vivo. rhBMP-2 (4.3-86 ng/ml) did not exhibit mitogenic effects on cultured osteoblasts. These data suggest that rhBMP-2 has the ability to induce expression of various markers associated with the osteoblast phenotype in primary cultures of fetal rat calvarial osteoblasts. In addition, we speculate that TGF-beta 1 may play a regulatory role in BMP-induced bone formation and ascorbic acid may potentiate the effects of rhBMP-2 in vivo.     

A rice protein isolate alters 7,12-dimethylbenz[alpha]anthracene-induced mammary tumor development in female rats

The effects of a rice protein isolate (RPI) on 7,12-dimethylbenz[alpha]anthracene (DMBA)-induced mammary tumor progression were investigated in female Sprague-Dawley rats. At 6 weeks of age, rats were fed a casein, RPI or soybean protein isolate (SPI) diet, respectively. After 1 week, DMBA was administered orally at the dose of 30 mg/kg body weight. The mean tumor number per tumor-bearing rat at autopsy was significantly lower only in rats fed RPI than in those fed casein. Palpable tumors at the mid point of the experiment were significantly lower in rats fed RPI and SPI than in those fed casein. Serum estradiol-17 beta concentrations were lower in rats fed the SPI (but not in those fed RPI) than in those fed casein. In a further experiment, no differences were found in hepatic microsomal DMBA-arylhydrocarbon hydroxylase activity after 7 days of feeding the respective diets. These results suggest that RPI exerts its inhibitory effect on DMBA-induced mammary tumorigenesis irrespective of changes in circulating estrogens or modulation of hepatic DMBA metabolism.     

Antitumour activity of coumarin and 7-hydroxycoumarin against 7,12-dimethylbenz[a]anthracene-induced rat mammary carcinomas

Female SD rats with established 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary tumours were treated with coumarin (20 mg/kg body weight; six times per week) or its metabolite 7-hydroxycoumarin (20 mg/kg) for 4 weeks. The anti-oestrogen tamoxifen (8.8 mg/kg) served as the reference drug. The inhibitory effect of coumarin was similar to that of tamoxifen [mean change of tumour area: 428% (coumarin) compared to 528% (tamoxifen); control 822%]. The strongest inhibition was observed with 7-hydroxycoumarin (248%); the difference compared to the control was significant (P < 0.01). Neither coumarin nor 7-hydroxycoumarin reduced the number of tumours appearing during treatment as tamoxifen did. However, the size of the tumours treated with coumarin or its metabolite was generally much smaller than those in the tamoxifen group or in the control group. From the data obtained it appears that coumarin and 7-hydroxycoumarin inhibit the growth of tumours that have reached a certain size but do not prevent the formation of tumours after exposure to the carcinogen.     

Bone marrow stromal cells constitutively express high levels of cytochrome P4501B1 that metabolize 7,12-dimethylbenz[a]anthracene

The polycyclic aromatic hydrocarbon 7,12-dimethylbenz[a]anthracene (DMBA) is a potent carcinogen that produces immunotoxic effects in bone marrow. Here, we show that bone marrow stromal cells metabolize DMBA to such products as 3,4-dihydrodiol, the precursor to the most mutagenic DMBA metabolite. The BMS2 bone marrow stromal cell line constitutively expressed higher levels of CYP1B1 protein and mRNA than C3H10T1/2 mouse embryo fibroblasts. BMS2 cells also produced a DMBA metabolite profile that was consistent with CYP1B1 activity. Treatment with the potent aryl hydrocarbon receptor (AhR) ligand 2,3, 7,8-tetrachlorodibenzo-p-dioxin (TCDD) induced a approximately 2-fold increase in CYP1B1 mRNA, protein, and activity in BMS2 cells. Two forms of the AhR (97 and 104 kDa) and the AhR nuclear translocator were detected in BMS2 cells. The AhR translocated to the nucleus after treatment with TCDD or DMBA but was approximately 5 times slower with DMBA. Primary bone marrow stromal (BMS) cell cultures established from AhR-/- mice showed similar basal CYP1B1 expression and activity as cell cultures established from heterozygous littermates or C57BL/6 mice. However, primary BMS cells from AhR-/- mice did not exhibit increased CYP1B1 protein expression after incubation with TCDD. BMS cells therefore constitutively express functional CYP1B1 that is not dependent on the AhR. This contrasts with embryo fibroblasts from the same mouse strain, in which basal CYP1B1 expression is AhR dependent. We therefore conclude that bone marrow toxicity may be mediated by CYP1B1-dependent DMBA metabolism, which is regulated by factors other than the AhR.     

Oestradiol and progesterone receptors in the mammary tissue and tumours of female Holtzman rats following 7,12-dimethylbenz(a)anthracene administration

A single dose of the carcinogen 7,12-dimethylbenz(a)-anthracene (DMBA) when administered to 55-day-old female Holtzman rats did not produce any change in the pattern or amount of oestradiol receptors in the breast tissues, when compared to age-matched control animals. The period of observation extended up to 280 days of age. Following DMBA administration to 102 animals, only 60% developed carcinomas of the breast, of which 59 and 50% were ER- an PgR-positive, respectively. This lower yield of steroid receptor-positive tumours in this strain of rats was also reflected in a very low incidence of regression of tumours to ovariectomy. Plausible explanations for both these findings have been offered.     

Effect of dietary soy protein isolate, genistein, and 1,4-phenylenebis(methylene)selenocyanate on DNA binding of 7,12-dimethylbenz[a]anthracene in mammary glands of CD rats

We examined whether a soy protein isolate or one of its major components (genistein) influences the initiation stage of carcinogenesis via DNA binding studies of 7,12-dimethylbenz[a]anthracene (DMBA) in liver and mammary tissue of female CD rats. A semipurified high-fat diet (23.5% corn oil) containing the soy protein isolate (10%), genistein (111 ppm), or 1,4-phenylenebis(methylene)selenocyanate (p-XSC) (5 ppm as selenium) as a positive control was fed to 6-week-old virgin female CD rats for 1 week before carcinogen treatment. Neither soy nor genistein affected the extent of DMBA-DNA binding in liver. In mammary tissue, 111 ppm genistein in the diet was more effective than the soy protein isolate, although the latter contains the same amount of genistein, mainly present as a glucoside conjugate. As shown before, p-XSC inhibited DMBA-DNA binding in mammary tissue. Total binding was inhibited because of reduced formation of three major adducts: anti-diol epoxide deoxyguanosine, syn-diol epoxide deoxyadenosine, and anti-diolepoxide deoxyadenosine. Thus, an additional experiment with 111 and 222 ppm of genistein was performed; 222 ppm genistein had a weaker effect than that observed for 111 ppm. Nevertheless, 111 ppm of genistein in the diet appears to inhibit the initiation phase of DMBA-induced rat mammary tumors and may partially account for the reported inhibitory effect of soy against DMBA-induced rat mammary tumors.     

Inhibitory effects of naturally occurring coumarins on the metabolic activation of benzo[a]pyrene and 7,12-dimethylbenz[a]anthracene in cultured mouse keratinocytes

Several naturally occurring coumarins to which humans are routinely exposed have been previously found to be potent inhibitors and inactivators of cytochrome P450 (P450) 1A1-mediated monooxygenase in both murine hepatic microsomes and in a reconstituted system using purified human P450 1A1 [Cai et al. (1993) Chem. Res. Toxicol., 6, 872-879 and Cai et al. (1996) Chem. Res. Toxicol., 9, 729-736]. In the present study, several of these coumarins were investigated for their inhibitory effects on the metabolism and metabolic activation of benzo[a]pyrene (B[a]P) and 7,12-dimethylbenz[a]anthracene (DMBA) in cultured mouse keratinocytes. Initial analysis of B[a]P metabolism in cultured keratinocytes showed that imperatorin, isoimperatorin, coriandrin, and bergamottin, at concentrations of 2 nM equal with B[a]P, reduced the formation of water-soluble metabolites of B[a]P by 33% to 57%. Bergamottin and coriandrin were the most potent inhibitors of the compounds examined. HPLC analysis of organic solvent-soluble metabolites of B[a]P indicated that all the coumarins tested significantly reduced the formation of individual B[a]P metabolites (including phenols, diols and tetraols). However, the greatest effect was on the formation of B[a]P tetraols. Additional experiments determined the ability of selected coumarins to block covalent binding of B[a]P and DMBA to DNA in keratinocytes. Bergamottin preferentially inhibited the binding of B[a]P to DNA by 56%, while coriandrin preferentially inhibited the binding of DMBA to DNA by 48%. Notably, analysis of individual DNA adducts formed from B[a]P and DMBA indicated that both bergamottin and coriandrin specifically inhibited the formation of anti diol-epoxide DNA adducts derived from both hydrocarbons. The preferential inhibitory effect of bergamottin and coriandrin on the formation of anti diol-epoxide adducts derived from DMBA was further confirmed by separation of anti- and syn-diol-epoxide-DNA adducts using immobilized boronate chromatography. The current study demonstrates that certain naturally occurring coumarins inhibited metabolic activation of B[a]P and DMBA in cultured mouse keratinocytes and specifically inhibited the formation of DNA adducts derived from the anti diol-epoxide diastereomers from either hydrocarbon. The current data also suggest that certain naturally occurring coumarins may possess anticarcinogenic activity toward polycyclic aromatic hydrocarbons.     

The influence of melatonin on metabolic changes in female rats induced by continuous irradiation and/or administration of 7,12-dimethylbenz/a/anthracene

OBJECTIVE: To investigate the influence of social deprivation upon the diet, dental health behaviours and dental health status of five-year-old children in Northern Ireland. DESIGN: Cross-sectional study. SETTING: Fifty-eight primary schools in North and West Belfast. SUBJECTS: A nine per cent (240) random sample of 2,666 five-year-old children resident and attending school in North and West Belfast. MAIN OUTCOME MEASURES: Dental health status measured by dmft index; parental assessments of the child's dental health behaviours: parental dental attendance patterns and attitudes towards dental health; parental assessments of the child's diet and snacking behaviours: parental attitudes towards snack foods; and demographic profile of child's family. RESULTS: One hundred and sixty-three children were examined, a 68 per cent response. The majority of the families were either in low income employment or unemployed. Sixty-eight per cent of children had experience of dental caries. Dental decay was unrelated to parental employment status but more children from unemployed families attended when in pain. The diet of the children was related to both employment status and parental attitude and was reflected in their caries experience. Caries experience was dependent upon parental dental attendance, the consumption of carbonated drinks and sugar containing bedtime drinks. CONCLUSIONS: The results suggest that unemployment and parental attitudes are important as determinants of dental caries in five-year-old children from North and West Belfast. These factors may influence the child's dental health care as well as type of diet.     

Dietary flavonoids reduce lipid peroxidation in rats fed polyunsaturated or monounsaturated fat diets

We investigated the influence of dietary flavonoids on alpha-tocopherol status and LDL peroxidation in rats fed diets enriched in either polyunsaturated fatty acids (PUFA) or monounsaturated fatty acids (MUFA). Diets equalized for alpha-tocopherol concentrations were or were not supplemented with 8 g/kg diet of flavonoids (quercetin + catechin, 2:1). After 4 wk of feeding, plasma lipid concentrations were lower in rats fed PUFA than in those fed MUFA with a significant correlation between plasma alpha-tocopherol and cholesterol concentrations, r = 0.94, P < 0. 0001). Dietary lipids influenced the fatty acid composition of VLDL + LDL more than that of HDL or microsomes. The resistance of VLDL + LDL to copper-induced oxidation was higher in rats fed MUFA than in those fed PUFA as assessed by the lower production of conjugated dienes and thiobarbituric acid reactive substances (TBARS) and by the >100% longer lag time for dienes production. (P < 0.0001). Dietary flavonoids significantly reduced by 22% the amounts of dienes produced during 12 h of oxidation in rats fed diets rich in PUFA and lengthened lag time 43% in those fed MUFA. Microsomes of rats fed MUFA produced approximately 50% less TBARS than those of rats fed PUFA (P < 0.0001) and they contained more alpha-tocopherol in rats fed MUFA than in those fed PUFA with higher values (P < 0. 0001) in both groups supplemented with flavonoids (P < 0.0001). Our findings suggest that the intake of dietary flavonoids is beneficial not only when diets are rich in PUFA but also when they are rich in MUFA. It seems likely that these substances contribute to the antioxidant defense and reduce the consumption of alpha-tocopherol in both lipoproteins and membranes.     

Demonstration and partial characterization of a 7,12-dimethylbenz[alpha]anthracene-binding protein in rat adrenal

Rat adrenal cytosol was found to contain a 7,12-dimethylbenz[a]-anthracene (DMBA)-binding protein which is characterized by a pI of 7.2, a Kd-value of 3 microM and a maximal capacity of about 47 pmol/mg protein. The binding is highly specific for DMBA and is not displaced by 3-methylcholanthrene (MC), benz[a]pyrene (BP) or other polycyclic hydrocarbons. Likewise, various androgens, estrogens or glucocorticoids have no effect on the DMBA binding. It is proposed that the DMBA-binding protein may have a role in the toxic effects of DMBA or DMBA metabolites in adrenal and possibly in other DMBA-sensitive organs as well.     

Effects of 7,12-dimethylbenz[a]anthracene on the superantigen toxic shock syndrome toxin (TSST-1)-induced proliferation and antibody secretion by human lymphocytes

Toxic shock syndrome toxin (TSST-1), a 22-kDa exotoxin secreted by Staphylococcus aureus, can act as a nominal antigen and induce proliferation and immunoglobulin secretion in human B-cells. The purpose of the present studies was to examine the effect of 7,12-dimethylbenz[a]anthracene (DMBA), a well-characterized immunosuppressant of both cell-mediated and humoral immunity in murine lymphocytes, upon the mixed lymphocyte reaction (MLR) and TSST-1-induced immune responses in human lymphocytes. The MLR, using human tonsillar lymphocytes (HTL) from four different donors, was inhibited in a dose-dependent manner from 1 to 100 microM. The IC50 for the suppression of the MLR ranged from 10 to 40 microM. TSST-1 is a potent stimulator of T-cells bearing specific VB regions on the T-cell receptor (TCR). In contrast with the results from the MLR, DMBA inhibited TSST-1-induced T-cell proliferation only at 100 microM in HTL. A similar profile of activity was determined with splenic T-cells from a single donor. TSST-1 has also been demonstrated to induce specific B-cell proliferation and differentiation in the presence of irradiated T-cells. TSST-1-induced B-cell proliferation was only consistently and markedly inhibited by DMBA at 100 microM in tonsillar and splenic lymphocytes. In contrast, TSST-1-induced B-cell differentiation, as manifested by IgM and IgG secretion, was inhibited in a dose-dependent manner from 1 to 100 microM DMBA in B-cells from human tonsils and spleens.(ABSTRACT TRUNCATED AT 250 WORDS)     

Proliferation, development and DNA adduct levels in the mammary gland of rats given 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine and a high fat diet

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a heterocyclic amine derived from cooked meat that is a mammary gland carcinogen in rats. A carcinogenic dose-regimen of PhIP (75 mg/kg, p.o., 10 doses, once per day) was administered to 43-day old female Sprague-Dawley rats, and the rats were then placed on a defined high fat (23.5% corn oil) or low fat (5% corn oil) diet for up to 6 weeks. At various times after carcinogen and diet, and prior to carcinogenesis, we examined the percentage of proliferating cells in terminal end bud (TEB) epithelial structures of the rat mammary gland by proliferating cell nuclear antigen staining, mammary gland architecture by whole mounting, and PhIP-DNA adduct levels in mammary epithelial cells by the 32P-post-labeling assay. Immediately after dosing, the percentage of proliferating epithelial cells in TEBs was significantly higher in PhIP-treated rats than in control rats receiving vehicle only [7.5 +/- 0.9% (n = 99) versus 4.2 +/- 0.6% (n = 127), respectively]. The mammary glands of PhIP-treated rats showed a significantly lower density of alveolar buds (ABs) and a higher density of TEBs than control rats, which suggests that PhIP exposure partially inhibited the normal glandular differentiation of TEBs to ABs. After 6 weeks on the diet, proliferation in TEBs was statistically higher in rats given PhIP plus a high fat diet than in rats given vehicle plus a low fat diet. The mammary glands from rats on a high fat diet also showed a statistically higher density of TEBs when compared with rats on a low fat diet [2.08 +/- 0.34% versus 1.04 +/- 0.20%, respectively (n = 6)]. PhIP-DNA adduct levels were relatively high in mammary epithelial cells of treated rats. At 3 h after the last dose of PhIP, DNA adduct levels [relative adduct labeling (RAL) x 10(7), mean +/- SE] were 10.5 +/- 1.7 (n = 8) and 0.9 +/- 0.2 (n = 7) in epithelial cells isolated from mammary gland and in the liver, respectively. DNA adduct removal rates from the mammary gland were not different between rats on the high fat and low fat diets. Adducts were still detected after 6 weeks on either diet. Thus, events that occurred prior to neoplasia in the mammary glands of PhIP-treated rats include formation of PhIP-DNA adducts at relatively high levels, and enhanced proliferation in TEBs (putative sites of origin of mammary gland carcinomas) and partial inhibition of TEB differentiation. The high fat diet, a promoter of PhIP-induced mammary gland carcinogenesis, appeared to sustain the proliferative effect of PhIP in mammary gland TEBs at a time when PhIP-DNA adducts are still detectable. These early events may contribute to the targeting and carcinogenicity of PhIP to the mammary gland of rats.     

Inhibitory effect of TMK688 on skin tumor initiation caused by 7,12-dimethylbenz[a]anthracene in relation to inhibition of aryl hydrocarbon hydroxylase activity and Cyp1a1 mRNA induction

The effects of single and repeated (9 times) administration of two dihydropyridines (DHPs), nimodipine (NIM) and nifedipine (NIF) (5 mg/kg per 12 h and 2.5 mg/kg per 12 h, IP), on the behavior of male adult rats in the holeboard and in the plus-maze, were investigated. Besides, the effects of repeated administration of the drugs on the levels of dopamine (DA), serotonin (5-HT), and their respective major metabolites in several regions of the central nervous system (CNS) were also assessed. The effects of single and repeated administration of the drugs were similar. Both DHPs caused a significant decrease in general motor activity which was evident in both tests and more marked, with the higher doses. The two exploratory parameters measured in the holeboard, i.e. head-dipping frequency and duration, were dissociated under pharmacological treatment. The drug-treated animals did not show an increased emotionality in the holeboard. However, in the plus-maze, NIF (5 mg/kg) and to a lesser extent NIM, appeared to induce some anxiety-related responses which may be secondary, at least in part, to the depressing effect on activity and exploration. Repeated administration of NIM and NIF caused an increase in striatal DA and DOPAC levels, whilst no effects were found on serotonergic system in any of the regions of the CNS analyzed.     

Histologic characterization of rat ovarian carcinoma induced by intraovarian insertion of a 7,12-dimethylbenz[a]anthracene-coated suture: common epithelial tumors of the ovary in rats?

The frequency of the butyrylcholinesterase K mutation was calculated on the basis of data obtained by polymerase chain reaction primer-introduced restriction analysis (PCR-PIRA). The population sample was composed of 177 Brazilians: 95 whites of predominantly European ancestry and 82 admixed individuals (European and African origin). The frequencies--18.4 +/- 2.8% for whites and 17.1 +/- 2.9% for admixed--did not differ from those previously obtained in North America, Scotland, Japan, and Denmark. The occurrence of the K mutation in Europeans, East Asians, and Africans suggests a relatively old origin for this mutation, and the similar frequencies found in these populations may suggest the operation of selective forces.     

Inhibitory effects of diallyl disulfide or aspirin on 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine-induced mammary carcinogenesis in rats

Modifying effects of diallyl disulfide (DAD), aspirin or DL-alpha-difluoromethylornithine (DFMO) on 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)-induced mammary carcinogenesis in SD rats were investigated. A total of 166 female rats, 6 weeks old, were divided into 8 groups. They were fed a high fat diet throughout the experiment. Starting at 7 weeks of age, groups 1-4 were given PhIP (85 mg/kg body weight in corn oil) by gavage 8 times in 10 days, and groups 5-8 were given corn oil alone. For the beginning 4 weeks, groups 2 and 5 were given DAD at 200 ppm in diet. Similarly groups 3 and 6, and groups 4 and 7 were given aspirin (400 ppm) and DFMO (400 ppm), respectively. Mammary carcinomas were only recognized in groups 1-4 at the termination (25 weeks after the start of experiment). Multiplicity (mean number/rat) of neoplasms in group 2 (PhIP+DAD, 0.90/rat) and group 3 (PhIP+aspirin, 1.37/rat) was significantly smaller than that in group 1 (PhIP alone, 2.45/ rat) (P < 0.005 and P < 0.05, respectively). These results indicate that dietary intake of DAD or aspirin during the time corresponding to initiation phase has chemopreventive potential on PhIP-induced mammary carcinogenesis in rats.     

Inhibitory effect of a steroidal antiestrogen (EM-170) on estrone-stimulated growth of 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary carcinoma in the rat

Rats were trained on a successive delayed conditional discrimination task measuring memory for magnitude of reinforcement. In the study phase of the task, the rats were given one of two cereals. One cereal contained 25% sugar; the other 50% sugar. One of the two cereals was always designated the positive stimulus and the other the negative stimulus. This study phase was followed by the test phase in which the rat was shown an object which covered a food well. If the rat was given the negative stimulus in the study phase of the trial, no food reward was placed beneath the object. Whenever the positive stimulus was presented a food reward was available beneath the object. Performance was measured as the latency to uncover the food well. After reaching criterion level, the rats were given amygdala, hippocampal, or control lesions. Amygdala-lesioned rats showed significant deficits in performance, whereas no long-term deficits were observed for the hippocampal-lesioned groups even at longer retention delays. In additional experiments, it was shown that amygdala-lesioned, like normal, rats had similar taste preferences. Finally, normal and hippocampal-, but not amygdala-, lesioned rats transferred readily to different cereals containing 25% or 50% sugar. Thus, it appears that the amygdala, but not the hippocampus, plays a significant role in explicit data-based or working memory for affect information based on magnitude of reinforcement.     

Chemoprevention of DMBA-induced mammary carcinogenesis in rats by low-dose EPA and DHA

We investigated the effects of low-dose eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on the incidence and growth of 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary carcinoma in rats fed a high-fat (HF) diet. We also examined the effects of these treatments on the fatty acid composition of tumour and serum. Tumour incidence was significantly decreased by the administration of low-dose EPA and DHA, whereas their inhibitory effects on tumour growth did not reach significance. Serum arachidonic acid (AA) level was decreased by the administration of low-dose EPA and tended to be decreased by the administration of low-dose DHA, whereas tumour AA levels were not changed. The administration of low-dose EPA and DHA may be useful for inhibiting the incidence of breast cancer.