Incidence and growth of mammary tumors induced by 7,12-dimethylbenz[a]anthracene as related to the dietary content of fat and antioxidant

Objective and subjective prior distributions for the Gompertz distribution

This paper takes into account the estimation for the unknown parameters of the Gompertz distribution from the frequentist and Bayesian view points by using both objective and subjective prior distributions. We first derive non-informative priors using formal rules, such as Jefreys prior and maximal data information prior (MDIP), based on Fisher information and entropy, respectively. We also propose a prior distribution that incorporate the expert's knowledge about the issue under study. In this regard, we assume two independent gamma distributions for the parameters of the Gompertz distribution and it is employed for an elicitation process based on the predictive prior distribution by using Laplace approximation for integrals. We suppose that an expert can summarize his/her knowledge about the reliability of an item through statements of percentiles. We also present a set of priors proposed by Singpurwala assuming a truncated normal prior distribution for the median of distribution and a gamma prior for the scale parameter. Next, we investigate the effects of these priors in the posterior estimates of the parameters of the Gompertz distribution. The Bayes estimates are computed using Markov Chain Monte Carlo (MCMC) algorithm. An extensive numerical simulation is carried out to evaluate the performance of the maximum likelihood estimates and Bayes estimates based on bias, mean-squared error and coverage probabilities. Finally, a real data set have been analyzed for illustrative purposes.

Estimation Parameter of R = P(Y < X) for Length-Biased Weighted Lomax Distributions in the Presence of Outliers

The concept of length-biased distribution is applied in expending proper models for lifetime data. The length-biased distribution is a special case of well-known weighted distribution. In this article, we introduce a length-biased weighted Lomax distribution (LBWLD) with k presence of outliers and estimate the parameter of R = P(Y < X) when the random variables X and Y are independent and have LBWLD in presence of outliers and without outliers, respectively. The bias and mean square error (MSE) of the estimator are examined with simulations of numerical and bootstrap resampling. Analysis of a real data set is considered for illustrative purposes.

Possibilities for Dietary Fat and antioxidants as Modulators of Mammary Carcinogenesis

The problem of defining a threshold for even a single carcinogen is both old and new. If one defines “threshold” as the quantity of carcinogen or other etiologic agent just capable of producing a tumor, then at least a common ground is described. However, this “threshold level” may be modulated upwards or downwards in the organism by various environmental and internal factors. A specific case in point is the known influence of dietary fat, especially polyunsaturated fat as an enhancer of many types of tumors, i.e., it appears to be acting to lower the threshold level of carcinogen that is required to elicit a tumorigenic response. Conversely, many dietary antioxidants such as BHT, BHA, and propyl galIate have been shown to effectively raise the threshold level, or decrease the tumorigenic response to a given level of carcinogen. The possible mechanisms through which the dietary factors modify tumorigenesis will be discussed. These will include specific influences and interactions of dietary factors on 7, 12-dimethylbenz(a) anthracene-induced mammary car-cinogenesis, carcinogen uptake and retention by the target tissue, as well as influences on glandular development which may result in an alteration of the number of possible “targets” available at the time of carcinogen exposure.

High-fat diets suppress CD3 and CD25 expression on the surface of murine lymphocytes

To determine the effects of dietary fats on surface antigen expression, we tested the effects of amount and type of dietary fat on murine lymphocytes. Mice were fed diets with 12 en%, 23 en%, or 47 en% fat containing coconut, olive, safflower, or linseed oil. After 2 wk of ad libitum feeding, the mice were killed and splenic lymphocytes were harvested. Lymphocytes were incubated with fluorescent-tagged monoclonal antibodies and assayed for mean and total surface expression using flow cytometry. Our results show that high-fat (47 en%) diets suppress expression of CD3 and CD25 antigens. We also found that linseed-oil diets suppress expression of CD11a but enhance expression of CD25 antigens. Both CD3 and CD25 are critical for lymphocyte activation, and we conclude that immunosuppression associated with high-fat diets may be associated with suppression of these surface antigens.

Dietary menhaden oil enhances mitomycin C antitumor activity toward human mammary carcinoma MX-1

In the present study, we investigated the effects of high levels of dietary fish oil on the growth of MX-1 human mammary carcinoma and its response to mitomycin C (MC) treatment in athymic mice. We found that high levels of dietary fish oil (20% menhaden oil + 5% corn oil, w/w) compared to a control diet (5% corn oil, w/w) not only lowered the tumor growth rate, but also increased the tumor response to MC treatment. We also found that high levels of dietary fish oil significantly increased the activities of tumor xanthine oxidase and DT-diaphorase, which are proposed to be involved in the bioreductive activation of MC. Since menhaden oil is highly unsaturated, its intake caused a significant increase in the degree of fatty acid unsaturation in tumor membrane phospholipids. This alteration in tumor membrane phospholipids made the tumor more susceptible to oxidative stress, as indicated by the increased levels of both endogenous lipid peroxidation and protein oxidation after feeding the host animals the menhaden oil diet. In addition, the tumor antioxidant enzyme activities, catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPOx), and glutathione S-transferase peroxidase (GSTPx), were all significantly enhanced by feeding a diet high in fish oil. MC treatment caused further increases in tumor lipid peroxidation and protein oxidation, as well as in the activities of CAT, SOD, GPOx, and GSTPx, suggesting that MC causes oxidative stress in this tumor model which is exacerbated by feeding a diet high in menhaden oil. Thus, feeding a diet rich in menhaden oil decreased the growth of human mammary carcinoma MX-1, increased its responsiveness to MC, and increased its susceptibility to endogenous and MC-induced oxidative stress, and increased the tumor activities of two enzymes proposed to be involved in the bioactivation of MC, that is, DT-diaphorase and xanthine oxidase. These findings support a role of these two enzymes in the bioactivating of MC and indicate that the type of dietary fat may be important in tumor response to therapy.

The possible role of lipid peroxidation in breast cancer risk

Breast cancer remains the commonest cause of death from cancer in women in most of the Western world. There is considerable evidence that breast cancer risk is influenced by environmental factors and can therefore potentially be modified. In this paper we describe evidence suggesting a relationship of lipid peroxidation to breast cancer risk, and propose that the method used to generate this information might usefully be applied to other disease states, and make some suggestions for further work. We have compared the urinary excretion of the mutagen malonaldehyde (MDA) in premenopausal women at different risks for breast cancer as determined by the appearance of the breast parenchyma on mammography. MDA was measured in 24-h urine samples from both groups and excretion in 30 women with mammographic dysplasia (high risk) was found to be approximately double that of 16 women without these radiological changes (p less than 0.02). These results suggest that mammographic dysplasia may be associated with lipid peroxidation. Further study of environmental factors associated with states that precede the development of breast and other cancers may lead to the identification of factors that can be modified and that may prevent the development of malignant disease.

Quantity and saturation degree of dietary fats as modulators of oxidative stress and chemically-induced liver tumours in rats

Male rats were fed, from weaning onwards, either 2, 12.5 or 25% sunflower seed oil (polyunsaturated fatty acids, PSA) or lard (saturated fatty acids, SFA) and from the age of 15 weeks subgroups were given N-nitrosodimethylamine (NDMA) for 30 weeks. Blood levels of lipids were assayed and during the study exhaled ethane was measured as an index of in vivo lipid peroxidation (LPO). At the age of 50 weeks, rats were killed and livers were analysed for tumours. PSA diets decreased plasma cholesterol and triglyceride concentrations vs. respective SFA diet; NDMA administration did not affect plasma cholesterol but enhanced triglyceride concentration. NDMA markedly enhanced LPO. An increase in dietary fat content from 2 to 25% enhanced ethane exhalation, more in rats fed PSA than the SFA diet. In the 25% PSA group, indomethacin in the diet strongly inhibited LPO. Prevalence of liver haemangiosarcomas increased from 42% to 80% (p less than 0.05) in NDMA-treated animals when PSA increased from 2 to 25%; in the group having a 25% PSA diet containing indomethacin, the NDMA-induced tumour incidence was reduced to 64%. In NDMA-treated rats fed SFA diets the prevalence of haemangiosarcoma increased from 43% (2% fat) to 67% (25% fat). The data show that NDMA modifies plasma lipids and increases LPO. The quantity and saturation degree of fats altered the frequency of chemically-induced tumours and modified LPO. As an index of free radical reactions, LPO may have an important role in carcinogenesis. Dietary fat thus appears to promote carcinogenesis through mechanisms that involve LPO.

Effects of dietary primrose oil on mammary tumorigenesis induced by 7,12-dimethylbenz(a)anthracene

The mammary tumor-promoting effect of a high-fat diet containing 20% evening primrose oil (PO) was compared to that of a 20% corn oil (CO) diet. Mammary tumors were induced in female Sprague-Dawley rats using 10 mg (Study 1) and 5 mg (Study 2) 7,12-dimethylbenz(a)anthracene (DMBA). The 10 mg dose of DMBA gave a total mammary tumor incidence of 47% in rats fed the PO diet and 80% for those fed the CO diet. When only adenocarcinomas were counted, the malignant mammary tumor incidences were 41% in rats fed the PO diet and 73% in rats fed the CO diet. In a second study using 5 mg DMBA to induce mammary tumors, total tumor incidences were 50% for PO-fed rats and 63% for those receiving a CO diet. Again, when only adenocarcinomas were counted, tumor incidences were 27% for PO- and 63% for CO-dieted rats. Analysis of plasma fatty acid profiles indicated that animals fed a 20% PO diet showed significant increases in 18:3 and 20:4 fatty acids and significant decreases in 16:0 and 18:1 compared to animals fed a 20% CO diet. These results indicate that the mammary tumor promoting effect of a diet containing 20% fat can be diminished by substituting PO for CO. Moreover, the promoting effect on mammary cancer by a high-fat diet could be depressed by feeding a source of gamma-linolenic acid (GLA).

Inhibition of bleomycin-induced DNA strand breaks in V 79 Chinese hamster cells by the antioxidant propylgallate

Bleomycin induced DNA single-strand breaks in Chinese hamster V 79 cells which were detected by the alkaline filter elution assay. In the presence of propylgallate, an antioxidant, the amount of DNA single-strand breaks was significantly reduced. The production of DNA strand breaks by methylnitronitrosoguanidine used as a positive control was not influenced by propylgallate. It is suggested that propylgallate inhibits the generation of DNA single-strand breaks by trapping reactive oxygen species produced by the bleomycin-iron(II) complex.

Can dietary fat influence hormone-induced growth responsiveness of the mammary gland?

Hormone-induced mammary gland growth responsiveness was examined in female Balb/c mice fed three different dietary levels (0, 5, and 20%) of fat (corn oil). Increasing the quantity of dietary fat enhanced hormone-induced mammary gland developmental growth processes both in vivo and in vitro. The effect of dietary fat was quite striking when comparing mice fed 0 and 5% fat diets and was less pronounced but still present when comparing mice fed 5 and 20% fat diets.

Comparison between the effects of dietary fat level and of calorie intake on methylnitrosourea-induced mammary carcinogenesis in female SD rats

The aim of this study was to separate the effects of calorie intake on tumorigenesis from those of fat content and fat composition in an animal model. Our principal observations were the following. Decreasing the calorie level by 30% significantly inhibited tumor development in any observed parameter of tumorigenesis, independently of the level of fat. The fat content of semi-synthetic diets, although varying by 44.4%, did not significantly influence mammary tumorigenesis; in fact, carcinogenic expression was discontinuously related to the fat level. A plateau of tumor incidence was observed at the level of 35 energy percentage of fat. Fat composition did not influence tumorigenesis or body weight gain. The role of caloric restriction is thus stressed in relation to possible dietary prevention of cancer.

The influence of dietary medium chain triglycerides on rat mammary tumor development

The N-nitrosomethylurea rat mammary tumor model was used to compare the tumor-promoting effects of a high-fat (HF) diet containing a 3:1 mixture of medium chain triglycerides (MCT) and corn oil with that of a HF and a low-fat (LF) corn oil diet. The serum and tumor lipid content and fatty acid (FA) composition were also determined in the three dietary groups. It was found that the MCT-containing diet failed to promote tumor development compared with the HF corn oil group. Tumor incidence in the HF-MCT group was similar to that of the LF corn oil group (5% fat, w/w), but significantly decreased compared to the HF corn oil group. Total serum cholesterol levels were significantly depressed in the HF corn oil group compared to the HF-MCT and LF corn oil groups. Analysis of serum and tumor FA profiles indicated that the HF corn oil group exhibited approximately twice the amount of linoleic acid (LA) as the other two treatment groups. Differences among the three groups in the major FA metabolite of LA, arachidonic acid, were minimal. These results are consistent with the hypothesis that tumor promotion by dietary fat is more a function of the type than the amount of fat ingested. In addition, they indicate that MCT, due at least in part to their unique structural and physiological properties, exert markedly different effects on mammary tumor development than conventional long chain unsaturated fatty acids.

The influence of different levels of dietary fat on the incidence and growth of MNU-induced mammary carcinoma in rats

This study describes the influence of isocalorically fed diets (containing different amounts of fat) on tumor incidence and parameters of fat metabolism in female Sprague-Dawley rats. Comparisons are made between rats induced with methylnitrosourea (25 mg/kg body wt) and untreated controls (Group I). The animals received either control diets (3.9% fat by weight, Groups I and II) or fat-enriched diets (10.7%, Group III; 15.6%, Group IV; 21.4%, Group V) over a period of 180 days. At the termination of the experiment, intake of the diet containing 10.7% fat by weight (24% fat per total calories) was associated with the highest tumor incidence. Comparing the different diets, liver lipid concentrations in the individual groups increased with increasing dietary fat, whereas the total lipid in plasma decreased. During the feeding period, total lipid of the liver and plasma, and plasma cholesterol, increased in all groups, but triglycerides of plasma decreased. However, when plasma cholesterol and triglycerides were calculated as a relative amount of total lipid in plasma, cholesterol was found to be significantly decreased in Groups III and IV, and triglycerides were increased in Group III but decreased significantly in Groups I, II, and V at the end of the experiment.

Diet and breast cancer in causation and therapy

The major macronutrient associated with increased breast cancer risk is dietary fat. Evidence for this association is based on epidemiologic, clinical, and laboratory animal studies. In addition, there is suggestive epidemiologic evidence that differences in postmastectomy survival rates in Japan and the United States may be attributable to differences in dietary fat intake. The importance of the type of fat consumed, as well as its amount, has emerged as an issue of major importance. Some oils, including those rich in monounsaturates, medium chain fatty acids, or omega-3 (n-3) fatty acids appear to lack tumor-promoting effects despite their presence in the diet at high levels. Possible mechanisms by which dietary fat may exert its effects could be either direct or indirect. Direct mechanisms involve dietary modification of membrane structure and function; indirect mechanisms involve alterations in the endocrine system, and/or the metabolism of essential fatty acids to biologically active eicosanoids such as prostaglandins, and suppression of immune responses. Dietary guidelines and dietary intervention trials for the primary and secondary prevention of breast cancer are discussed.

Inhibition of glutathione S-transferase P type-positive foci development by linolic acid hydroperoxides and their secondary oxidative products in a rat in vivo mid-term test for liver carcinogens

The effects of linolic acid hydroperoxides (product A) and secondary oxidative products of product A (product B), were examined in an in vivo mid-term test for hepatocarcinogens or hepatopromoters in rats. The number of placental type of glutathione S-transferase (GST-P)-positive foci of the liver was significantly reduced in rats given diethylnitrosamine (DEN) followed by products A (4.64 +/- 1.09, P less than 0.05) or B (3.62 +/- 1.65, P less than 0.01) as compared to the controls given carcinogen alone (6.31 +/- 2.82). The area of GST-P positive foci was also significantly reduced in rats given DEN followed by product B (0.30 +/- 0.21, P less than 0.05) as compared to the controls (0.47 +/- 0.23). These results suggest that linolic acid hydroperoxides or their secondary oxidative products are not hepatocarcinogens and rather may possess inhibitory potential for liver carcinogenesis.

Methods of extraction and high-performance liquid chromatographic analysis of butylated hydroxytoluene from the tissues and serum of rats

Butylated hydroxytoluene (BHT) is a phenolic antioxidant which is widely used in foods and has been shown to inhibit chemical carcinogenesis in the mammary gland induced by 7,12-dimethylbenz(a)anthracene. However, its mechanism of action as a tumor inhibitor is unclear. The purpose of this work was first to develop a method for extracting and quantitating BHT and then to determine the amounts that accumulate in the tissues and serum of rats as a starting point for looking at mechanistic possibilities in the inhibition of mammary carcinogenesis. Methodology of extracting BHT from rat tissues and serum was developed using a modified lipid extraction procedure. The sensitive nature of reverse-phase high-performance liquid chromatography proved useful in detecting and quantifying BHT after its extraction from biological tissues. All tissues were taken from animals consuming semipurified diets with and without 0.3% BHT for various periods of time (weeks). BHT was found in much higher levels in mammary tissue than in the liver and serum of rats. The lipid content in mammary tissue appears to be predictive of the amount of BHT found in this tissue, presumably because of the lipophilic character of the antioxidant.

The interaction of dietary fat and antiestrogen treatment on DMBA-induced mammary tumors in the rat

This study was designed to determine whether an estrogenic mechanism is involved in dietary fat-modulated tumor development and growth. Female Sprague-Dawley rats were placed on a semipurified low-fat (2% fat), high-saturated fat (20% fat), or high-polyunsaturated fat (20% fat) diet at 21 days of age. A single dose of 7,12-dimethylbenz[a]anthracene (DMBA, 10 mg) was administered intragastrically at 50 days of age. Two studies were performed. One tested the effectiveness of antiestrogen treatment (either tamoxifen or analog II) on tumor development when it was given one week prior to and one week after DMBA treatment in animals consuming a high-polyunsaturated fat diet. The second six-week study tested the antiestrogen effectiveness in arresting tumor growth and in producing regressions of established DMBA-induced tumors in rats consuming various levels and types of fat. The results of these studies indicate that both antiestrogens employed reduced the rate of growth and increased the number of regressions of established DMBA-induced tumors. In general, this was true in animals fed diets with a high content of either saturated or polyunsaturated fats and to a lesser extent in animals fed a low-fat diet. Tamoxifen produced a somewhat greater reduction in the growth of established tumor than did analog II. However, analog II, which is a more biologically "pure" antiestrogen, reduced the incidence of animals with mammary tumors and total tumor burden when administered one week before and one week after DMBA dosing. Tamoxifen, which is a partial estrogen-agonist, did not alter tumor incidence, but it did reduce the total tumor burden under these same experimental conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Carcinogenicity and modification of the carcinogenic response by BHA, BHT, and other antioxidants

Carcinogenicity tests showed that addition of the antioxidant BHA to the diet of F344 rats induced high incidences of papilloma and squamous cell carcinoma of the forestomach of both sexes. Male hamsters given BHA for 24 weeks also developed papilloma showing downward growth into the submucosa of the forestomach. These results indicate that BHA should be classified in the category of "sufficient evidence of carcinogenicity" as judged by IARC criteria. The 3-tert isomer of BHA seemed to be responsible for the carcinogenicity of crude BHA in the forestomach of rats. BHT was not found to be carcinogenic in rats or mice. In two-stage carcinogenesis in rats after appropriate initiation, BHA enhanced carcinogenesis in the forestomach and urinary bladder of rats, but inhibited carcinogenesis in the liver. BHT enhanced the induction of urinary bladder tumors and inhibited that of liver tumors, but had no effect on carcinogenesis in the forestomach. BHT could be a promoter of thyroid carcinogenesis. Sodium L-ascorbate enhanced forestomach and urinary bladder carcinogenesis. Ethoxyquin enhanced kidney and urinary bladder carcinogenesis, but inhibited liver carcinogenesis. Thus, these antioxidants modify two-stage chemical carcinogenesis in the forestomach, liver, kidney, urinary bladder, and thyroid, but show organ-specific differences in effects.

Effect of dietary stearic acid on the genesis of spontaneous mammary adenocarcinomas in strain A/ST mice

Strain A/ST female mice maintained on a high fat (15%) diet in which stearic acid was the major lipid component developed initial spontaneous mammary adenocarcinomas at an older age than mice fed a low fat (4.5%) stock diet. Mice placed on the SA diet at weaning developed tumors at 15.7 +/- 0.87 months compared to 12.7 +/- 0.43 months for those retained on the stock diet (p less than .05). Placing mice on the SA diet at 11.5 months resulted in a smaller but significant increase in the latency period (5.0 +/- 0.86 vs 3.0 +/- 0.57 months +/- 0.57 mo), (p less than .05). Fatty acid analyses of non-tumorous mammary tissue from mid-pregnant mice and of tumor tissues showed that feeding large amounts of 18:0 did not result in increases in the proportion of 18:0. Significant reductions in the percentages of polyunsaturated fatty acids (PUFA) was found in tissues on mice fed the SA diet. The percentage of 18:2 was reduced in both types of tissues; 20:3 and 20:4 was reduced in tumor tissues. Distribution of C18 fatty acids in plasma membranes of tumors of mice fed the two diets were similar; percentages 18:2 was higher in plasma membranes of non-tumorous tissues of mice fed the SA diet. These results suggest that dietary stearic acid interferes with the availability of certain PUFA required for tumor production.

Diet and the epidemiology of human breast cancer

There are substantial data on breast tumorigenesis in animals that suggest that diet may be an important factor in human breast cancer etiology. The promotional effects of dietary fat, and, in particular, unsaturated fats, on mammary tumors in rodents is well established. The geographic distribution of breast cancer in humans correlates with international differences in average fat intake. Differences in dietary habits among populations in the United States and their breast cancer risk also have been observed. In the United States, the trend has been toward increased total fat consumption and increased use of polyunsaturated fats. However, breast cancer incidence among white women in the United States has changed very little. Case-control studies of dietary intake and breast cancer risk have shown inconsistent results, and prospective studies of breast cancer mortality and serum cholesterol and serum lipids show no differences in risk between women with high levels of cholesterol and serum lipids compared with women with low levels. Laboratory studies also suggest the possibility that natural inhibitors of breast cancer may occur in the diet as well. Antioxidants, inducers of microsomal enzyme activity, and retinoids, all have been implicated in the metabolic epidemiology of breast cancer. Research results at Roswell Park memorial Institute have associated lower levels of intake of dietary vitamin A with a slightly elevated risk of breast cancer. To date, the epidemiologic data do not indicate with confidence that any specific dietary risk factor may be associated with breast cancer risk in the United States population. Additional epidemiologic studies on inhibition or promotion of breast cancer following the leads of previous laboratory research may clarify the nature and practical significance of the relationship between diet and breast cancer.

The effect of dietary fat on tumor growth

Experiments in animals have shown that high-fat diets can enhance tumor growth. Animals receiving high-fat diets routinely ingest up to 5 times the level of fat (by weight) found in standard chow diets. Rats given oil by gavage can triple caloric intake from fat compared to untreated controls. In laboratory animals, high-fat diets appear to play a role during the postinitiation phase of tumorigenesis. The type, level, and nature of the dietary fat may also affect the outcome of bioassays. Fat does not initiate the tumorigenic process. Additional factors must be considered when studying and interpreting the effects of dietary fat. Animal diets and dietary fats should be protected against oxidation. Antioxidants protect against oxidation but may also modify the tumorigenic process. Adequate levels of essential fatty acids must be provided. Dietary fat level can alter nutrient density and palatability; each of these factors can affect nutrient intake which can in turn influence metabolic processes.

Influence of dietary lipid upon ultraviolet-light carcinogenesis

The effects of dietary lipid level, degree of saturation, and antioxidant supplements on ultraviolet-light (UV) carcinogenesis were studied in female albino hairless mice. Twelve groups of 42 animals each received a restricted, semipurified, isocaloric diet containing 4%, 12%, or 12% (60% hydrogenated) corn oil with or without antioxidants (2%, w/w). A regimen of escalating UV irradiation was employed until a cumulative dose of 142 J/cm2 had been delivered. Tumor development time in 50% of the population (TDT50) was derived from a cumulative distribution of time to tumor formation, which was estimated for all groups. Although there were no significant differences in TDT50s between animals receiving low and high unsaturated lipid dietary regimens, animals receiving hydrogenated corn oil demonstrated a significantly (p less than 0.01) greater TDT50 and fewer tumors per animal than those receiving either level of unsaturated corn oil. Antioxidants had no effect on TDT50s within any of the dietary groups. However, greater tumor multiplicity was observed in groups receiving unsaturated lipid and antioxidants. These data demonstrate that the degree of dietary lipid saturation modifies the carcinogenic response to UV and suggest that dietary lipid may modify the previously reported inhibitory effect of antioxidants on UV carcinogenesis. It may be concluded that adherence to dietary standards is as important as other experimental parameters when comparisons of UV effects are involved.

Metabolism of benzo(a)pyrene by human epithelial and fibroblastic cells: metabolite patterns and DNA adduct formation

We demonstrate in cell culture that mammary epithelial cells from normal human breast specimens metabolize benzo(a)pyrene (BaP) and form adducts with the bases of their DNA more readily and at lower concentrations of BaP than do fibroblasts from the same specimens. BaP metabolism and adduct formation was determined in the same incubations with epithelial cells grown out in early passage from each of three specimens and with fibroblasts from one of these specimens. The metabolite pattern of the epithelial cells was indicative of preferential formation of 7, 8-dihydrodiol-9, 10-dihydroepoxybenzo(a)pyrene the ultimate carcinogen. In contrast, fibroblasts formed mainly mono- and dihydroxide derivatives of BaP. The metabolite pattern from epithelial cells was compatible with the ease in which adducts between DNA and the diolepoxide of benzo(a)pyrene were formed. These results provide evidence that chemical carcinogens should be considered as possible factors in the induction of breast cancer in women.

Comparison of the effect of butylated hydroxytoluene on N-nitrosomethylurea and 7,12-dimethylbenz[a]-anthracene-induced mammary tumors

The antioxidant butylated hydroxytoluene (BHT) when fed at a level of 0.3% in a defined semi-purified diet was found to decrease mammary tumor incidence in female Sprague-Dawley rats induced by 7,12-dimethylbenz[a]-anthracene (DMBA). however, no effect of BHT on tumor incidence was seen in animals consuming the same diet, under identical experimental conditions, but treated with the carcinogen nitrosomethylurea (NMU). Differences in effectiveness of BHT as a tumor inhibitor in the 2 model systems, and thoughts as to a possible mechanism of action with regard to BHT are discussed.

Metabolism of benzo[a]pyrene by human mammary epithelial cells: toxicity and DNA adduct formation

Pure cultures of human breast epithelial cells and of fibroblastic cells in early passage provided the opportunity to ask whether either cell type had the capability for metabolizing chemical carcinogens and, if so, was the fate of the metabolic products compatible with chemical carcinogens being a factor in the initiation of breast cancer in women. For this purpose, cells were exposed to benzo[a]pyrene (BaP), and (i) the influence on growth potential and (ii) the extent, type, and persistence of adducts between the metabolites of BaP and DNA were measured. Compared with fibroblasts, inhibition of growth by epithelial cells was 50-100 times more sensitive to BaP. Because of this differential sensitivity, epithelial cells were exposed to 0.4 microM BaP and fibroblasts were exposed to 4.0 microM BaP in the studies of DNA adduct formation. Separation by high-pressure liquid chromatography of adducts between (+/-)-7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BaP diol epoxide) and nucleosides from purified DNA revealed that epithelial cells contained modified DNA within 6 hr after adding BaP. Adducts between the 7R anti stereoisomer of BaP diol epoxide and deoxyguanosine predominated at all times. syn BaP diol epoxide adducts with deoxyguanosine and what appeared to be BaP diol epoxide adducts with deoxycytidine were consistently present but at much lower frequency. All three types of BaP diol epoxide--DNA adducts persisted in epithelial cells for 72 hr in BaP-free medium. No adducts were detected in fibroblastic cultures until 96 hr after first exposure to BaP. At this time, the type and extent of BaP diol epoxide--DNA adduct formation was similar to that in epithelial cells exposed to one-tenth the dose of BaP. The type, extent, rate of formation, and persistence of the adducts in human breast epithelial cells was similar to that in cells transformable by exposure to BaP, an indication that they may be targets for chemically induced carcinogenesis.

The consumption of seaweed as a protective factor in the etiology of breast cancer

A review of the biological properties of seaweed is presented and the role of seaweed as a breast cancer anticarcinogen is suggested. Proposed mechanisms of action are: reduction of plasma cholesterol, binding of biliary steroids, inhibition of carcinogenic fecal flora, binding of pollutants, stimulation of the immune system, and the protective effects of beta-sitosterols. In an experiment using sarcoma-180 in mice, seaweed extract appeared to have an antitumor effect. Thus it is suggested that breast cancer may be prevented and that this dietary habit among the Japanese could be an important factor in understanding the lower breast cancer rates reported in Japan.

Neoplastic growth of carcinogen-treated mammary transplants as influenced by fat intake of donor and host

Female Wistar-Furth rats were fed either a high-fat (HF) or a low fat (LF) diet from weaning. The HF and LF diets contained 20% and 0.5% corn oil, respectively. Mammary gland explants from 50-day-old rats of both dietary groups were exposed to dimethylbenz[a]anthracene in organ culture before grafting to HF- or LF-hosts. A total of 4 groups were involved: LF leads to LF, HF leads to LF, LF leads to HF, and HF leads to HF, where the designations before and after the arrow describe the dietary treatment of the donor and host, respectively. Final tumor incidences were as follows: 28%, 20%, 72% and 76%, presented in the order of the above 4 groups. Tumors also appeared earlier in the HF-hosts. Results of this experiment indicate that regardless of the nutritional status of the donor, it was the fat intake of the host that governed the subsequent neoplastic growth of transformed cells, suggesting that the action of fat is primarily exerted at the promotional stage of carcinogenesis.

The influence of dietary fat and non-specific immunotherapy on carcinogen-induced rat mammary adenocarcinoma

The incidence of mammary adenocarcinoma in Sprague-Dawley female rats, caused by the carcinogen 7,12-dimethylbenz(alpha)anthracene, was influenced by the level of dietary fat fed after exposure to carcinogen. Carcinogen was given by stomach tube to 50-day-old rats, and tumors were evaluated when rats were 9 months old. Rats on diets containing 20% unsaturated fat had a tumor incidence of 97%, while rats changed to a low-fat diet (2% unsaturated fat) three or four weeks after exposure to the carcinogen had an incidence of 45%. Some rats on each diet were given two treatments with the methanol extraction residue of Bacillus Calmette-Guerin, either three and five weeks after carcinogen or four and six weeks after carcinogen. Tumor incidence in the treated group and the untreated group was the same when rats were maintained on the high-fat diet, but tumors in the treated group were larger and the disease was more severe by histological criteria. These tumors were more anaplastic and many were extensively infiltrated with lymphocytes compared to the untreated group. Tumor incidence was significantly lower in rats changed to the low-fat diet (45%) than in those on the high-fat diet (97%), and tumor incidence was reduced to 20% when rats changed to the low-fat diet were treated with methanol extraction residue. The treated group had less severe disease than the untreated group on the low-fat diet. Only half the tumor-bearing rats in this group had malignant tumors, and none were invasive. Methanol extraction residue protected most rats on the low-fat diet against mammary adenocarcinoma, and reduced the severity of disease in those rats that did develop tumors. Methanol extraction residue treatment provided no protection, and even increased the severity of disease, in rats on the high-fat diet.