Biochemical alterations in 7,12-dimethylbenz[a]anthracene-induced mammary tumors from rats subjected to caloric restriction

Caloric restriction reduces the incidence and progression of a broad spectrum of neoplastic diseases, yet little is known about the biochemical and molecular mechanisms involved. Profiles of enzyme activities of importance in cellular energy utilization were examined in 7,12-dimethylbenz[a]anthracene-induced (DMBA) mammary adenocarcinomas from rats fed ad libitum or calorically restricted diets. The diets provided equal nutrients except for fewer carbohydrate-derived calories; graded caloric restriction was 10, 20, 30 and 40%. The specific activities of hexokinase, pyruvate kinase, lactate dehydrogenase, glucose-6-phosphate dehydrogenase, malic enzyme and fructose-1,6-bisphosphatase were all elevated to varying degrees in both large palpable and small, non-palpable tumors from calorically restricted hosts compared to activities in tumors from ad libitum-fed rats. Phosphofructokinase activity was increased in palpable tumors from calorically restricted hosts but markedly reduced in non-palpable tumors. These results suggest adaptive or compensatory alterations in tumor enzyme profiles in response to the altered nutritional state of the host.     

Pineal gland in rats with 7,12-dimethylbenz(a)anthracene-induced mammary tumors subjected to manipulations known as enhancers of pineal actions

The ultrastructure of pinealocytes was studied in rats with 7,12-dimethylbenz(a)anthracene-induced mammary tumors which were subjected to experimental manipulations known as enhancers of pineal actions (anosmia, underfeeding or cold exposure). In these animals we found: (I)--more nuclei with deep nuclear invaginations; (II)--a large number of cytoplasmic organelles, including lipid droplets, myeloid bodies, synaptic ribbons and lysosomes; (III)--numerous degenerative changes. In general, we found an increase in structural features related to pineal photoneuroendocrine activity. Our results indicate that pineal-dependent inhibition of neoplastic growth induced by these experimental manipulations, previously reported, can be mediated through an increase in pineal metabolic activity.     

The characteristic binding of catechol estrogens to estrogen receptors in 7,12-dimethylbenz(a)anthracene-induced rat mammary tumors

The binding of catechol estrogens (2-hydroxyestrone, 4-hydroxyestrone, 2-hydroxyestradiol, and 4-hydroxyestradiol) to estrogen receptors in 7,12-dimethylbenz(a)anthracene (DMBA)-induced rat mammary tumor cytosols was investigated. Cytosol estrogen receptors exhibited high affinities (Ka = 1.12-1.88 X 10(8) M-1) for all catechol estrogens as well as estradiol. The receptor level of catechol estrogens (46.1-97.5 fmol/mg protein) was 1.6-3.0 times higher than that of estradiol; especially the binding of 4-hydroxyestrone to estrogen receptors was the highest of all catechol estrogens and estradiol. In judging the receptor level of more than 20 fmol/mg protein to be positive, the binding of catechol estrogens to estrogen receptors was approximately correlated with that of estradiol. The positive receptor level of catechol estrogens was found in a half of tumor cytosols which showed the negative receptor level of estradiol. These results suggested that characteristic estrogen receptors indicating high affinities for catechol estrogens might be present in rat mammary tumor cytosols.     

Antioxidative effects of hesperetin against 7,12-dimethylbenz(a)anthracene-induced oxidative stress in mice

We investigated the effects of the chronic administration of hesperetin on the activation of the antioxidant defence system in mice in which oxidative stress had been induced by 7,12-dimethylbenz(a)anthracene (DMBA). Mice were divided randomly into three treatment groups. Hesperetin was administered orally to two of the three groups at 10 and 50 mg/kg body weight for 5 weeks. Subsequently, each group was subdivided randomly into DMBA-treated and untreated groups. The DMBA-treated groups were intragastrically administered a dose of 34 mg/kg BW in corn oil vehicle twice a week for 2 weeks. The TBARS value showed a tendency to decrease following hesperetin treatment; these decreases were significantly greater in the DMBA-treated than the untreated groups. Hesperetin significantly decreased the carbonyl content at the high dose in both DMBA-treated and untreated mice. Catalase and SOD activity were increased by hesperetin; this increase was more pronounced in DMBA-treated than untreated mice. Catalase, Mn-SOD, and CuZn-SOD expression analyses supported these results. Although the GSH-px and GR activity were little affected, hesperetin treatment significantly increased the GSH/GSSG ratio in the DMBA-treated group in a dose-dependent manner. These results suggest that hesperetin shows antioxidant activity and plays a protective role against DMBA-induced oxidative stress.     

Response of 7,12-dimethylbenz(a)anthracene-induced rat mammary tumor cells to tamoxifen, in vitro

Primary cell cultures from a density-defined cell subpopulation of the DMBA-induced rat mammary tumors were exposed to tamoxifen during their log phase of growth. Growth inhibition and the ultrastructure of surviving cells were examined along with the influence of this antiestrogen on the secreted proteins as determined by pulse labeling with [35S]methionine and fluorography. Cell growth was remarkably inhibited at clinically achievable concentrations. However, ultrastructural changes in the surviving cells were minimal, the most noteworthy being the accumulation of myelin bodies. Protein secretion was affected in the defined subpopulation of several tumors by the reduced production of a high-molecular-weight protein. These tumors may represent a population of estrogen-sensitive tumors within the DMBA-induced mammary tumor model.     

Consumption of a buckwheat protein extract retards 7,12-dimethylbenz[alpha]anthracene-induced mammary carcinogenesis in rats

Female rats were examined for the effects of feeding buckwheat protein extract (BWPE) on the development of mammary tumor caused by administration of 7,12-dimethylbenz[alpha]anthracene. The percentage of rats with palpable mammary tumors and serum estradiol were lower in the BWPE-fed animals than the casein-fed ones, implying that BWPE intake retarded the mammary carcinogenesis by lowering serum estradiol.     

Ultrastructure of mammary carcinomas in male rats induced by 7,12-dimethylbenz(a)anthracene

The morphology of mammary tumors induced by 7,12-dimethylbenz(a)anthracene in male rats was investigated by light and electron microscopy. All tumors induced in male rats were carcinomas with prominent epithelial growth which shows a medullary or cribriform appearance. Neither mammary dysplasias nor fibroadenomas were induced in male rats. Foci of adenoid cystic carcinoma were encountered in some parts of tumors. Papillary and/or tubular patterns, which have been observed frequently in mammary carcinomas in female rats, were not prominent histologic features in male rats. Secretory activity was not remarkable. The morphology of mammary carcinomas in male rats was unchanged in primary and transplanted tumors under various hormonal conditions. This finding supports our previously published results that the mammary carcinomas in male rats are hormone-independent, although our previous biochemical study revealed that the tumors contain both estrogen and estrogen-dependent progesterone receptors.     

Metabolism of [4-14C]estradiol by 7,12-dimethylbenz(a)anthracene-induced mammary tumor peroxidase

The peroxidase and estradiol-metabolizing activities of mammary tumors induced by 7,12-dimethylbenz(a)anthracene were determined in fresh and stored tissue. In both cases, a wide variation in peroxidase activity was observed in 47 different tumors tested. The properties of the enzyme found in the tumors were similar to those of lactoperoxidase. It is suggested that the amount of peroxidase present might reflect the ability of tumor cells to differentiate in response to hormonal stimulation and be indicative of the degree of tumor progression.     

Chemopreventive efficacy of geraniol against 7,12-dimethylbenz[a]anthracene-induced hamster buccal pouch carcinogenesis

The status of lipid peroxidation, antioxidants, and detoxification enzymes were used as biochemical end points to assess the chemopreventive potential of geraniol, a monoterpene, in 7,12-dimethylbenz[a]anthracene (DMBA)-induced hamster buccal pouch carcinogenesis. Topical application of 0.5% DMBA in liquid paraffin, three times a week, for 14 weeks developed well-differentiated squamous cell carcinoma in the buccal pouch of golden Syrian hamsters. Although 100% tumor formation was noticed in hamsters treated with DMBA alone, intragastric administration of geraniol, at a dose of 250 mg/kg body weight (b.w.) to DMBA-treated hamster completely prevented the formation of oral tumors. Furthermore, geraniol significantly reduced lipid peroxidation by-products and improved the status of enzymatic and non-enzymatic antioxidants as well as modulated the status of phase I and phase II detoxification enzymes, favoring the excretion of carcinogenic metabolite, during DMBA-induced oral carcinogenesis. The present study concludes that the chemopreventive potential of geraniol relies on its anti-lipid peroxidative and antioxidant function as well as modulatory effects on phase I and II detoxification enzymes to excrete the carcinogenic metabolite, during DMBA-induced hamster buccal pouch carcinogenesis.     

Chemopreventive efficacy of geraniol against 7,12-dimethylbenz[a]anthracene-induced hamster buccal pouch carcinogenesis

Abstract

The status of lipid peroxidation, antioxidants, and detoxification enzymes were used as biochemical end points to assess the chemopreventive potential of geraniol, a monoterpene, in 7,12-dimethylbenz[a]anthracene (DMBA)-induced hamster buccal pouch carcinogenesis. Topical application of 0.5% DMBA in liquid paraffin, three times a week, for 14 weeks developed well-differentiated squamous cell carcinoma in the buccal pouch of golden Syrian hamsters. Although 100% tumor formation was noticed in hamsters treated with DMBA alone, intragastric administration of geraniol, at a dose of 250 mg/kg body weight (b.w.) to DMBA-treated hamster completely prevented the formation of oral tumors. Furthermore, geraniol significantly reduced lipid peroxidation by-products and improved the status of enzymatic and non-enzymatic antioxidants as well as modulated the status of phase I and phase II detoxification enzymes, favoring the excretion of carcinogenic metabolite, during DMBA-induced oral carcinogenesis. The present study concludes that the chemopreventive potential of geraniol relies on its anti-lipid peroxidative and antioxidant function as well as modulatory effects on phase I and II detoxification enzymes to excrete the carcinogenic metabolite, during DMBA-induced hamster buccal pouch carcinogenesis.     

Morin augments anticarcinogenic and antiproliferative efficacy against 7,12-dimethylbenz(a)-anthracene induced experimental mammary carcinogenesis

In general, oxidative stress resulting from an imbalance between prooxidant and antioxidant systems plays an important role in the pathogenesis of cancer. Morin (3,5,7,2',4'-pentahydroxyflavone), a member of the flavanol group, has been shown to possess chemopreventive potential against hepatocellular and colon cancer in experimental animals. Given the demonstrated importance of morin, aim of the present study was to evaluate the effect of morin on antiproliferative and anticarcinogenic effect against DMBA-induced experimental mammary carcinogenesis. Oral administration of 7,12-dimethylbenz(a)-anthracene (25 mg/kg body weight) to rats resulted in significant reduction of body weight, enzymic antioxidants (superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase), and nonenzymic antioxidants (reduced glutathione, vitamin C, and vitamin E). The levels of lipid peroxidation markers (thiobarbituric acid reactive substances and hydroperoxides) and tumor markers such as CA 15-3, AFP and CEA in serum were increased significantly in cancer-induced animals as compared to control rats. Oral supplementation of morin at a dose of 50 mg/kg body weight significantly improved the body weight, enzymic, and nonenzymic antioxidants and considerably decreased the lipid peroxidation marker and tumor markers levels. Histological observations also correlated with the biochemical parameters. Tumor bearing animals showed marked increase in proliferating cell nuclear antigen-positive cells and also the number of AgNOR/nuclei compared with control rats while this expression levels were significantly reduced upon morin treatment. Thus, this study reveals the possible beneficial effect of morin as chemopreventive agent against the oxidative stress induced during mammary carcinogenesis.