Review of the effects of dietary fat on experimental mammary gland tumorigenesis: role of lipid peroxidation

Oncogenic signaling of the free-fatty acid receptors FFA1 and FFA4 in human breast carcinoma cells

Globally, breast cancer is the most frequent type of cancer in women, and most breast cancer-associated deaths are due to metastasis and recurrence of the disease. Dietary habits, specifically dietary fat intake is a crucial risk factor involved in breast cancer development and progression. Decades of research has revealed that free-fatty acids (FFA) modulate carcinogenic processes through fatty acid metabolism and lipid peroxidation. The ground-breaking discovery of free-fatty acid receptors, which are members of the G-protein coupled receptor (GPCR) superfamily, has led to the realization that FFA can also act via these receptors to modulate carcinogenic effects. The long-chain free-fatty acid receptors FFA1 (previously termed GPR40) and FFA4 (previously termed GPR120) are activated by mono- and polyunsaturated fatty acids including ω-3, 6, and 9 fatty acids. Initial enthusiasm towards the study of these receptors focused on their insulin secretagogue and sensitization effects, and the downstream associated metabolic regulation. However, recent studies have demonstrated that abnormal expression and/or aberrant FFA1/FFA4 signaling are evident in human breast carcinomas, suggesting that FFA receptors could be a promising target in the treatment of breast cancer. The current review discusses the diverse roles of FFA1 and FFA4 in the regulation of cell proliferation, migration, invasion, and chemotherapy resistance in human breast carcinoma cells and tissue.

Silibinin loaded inhalable solid lipid nanoparticles for lung targeting

AIM

In the current study, efforts are being made to prepare Inhalable Silibinin loaded solid lipid nanoparticles (SLNs) with narrow size distribution with improved bioavailability.

METHODS

SLNs were formulated by high shear homogenisation method SLNs were characterised, including Differential Scanning Calorimetry (DSC), Fourier transform infra-red spectroscopy (FTIR), particle size analysis, entrapment efficiency with Aerodynamic behaviour. The MTT assay was performed against A549 cell line, to measure their anticancer cell activity with In vivo study.

RESULTS

Optimized formulation exhibited spherical surface with a mean particle size of 221 ± 1.251 nm, PI of 0.121 ±  0.081, zeta potential of -4.12 ± 0.744. Aerodynamic behaviour such as Mass median aerodynamic diameter (MMAD) and Geometric size distribution (GSD) were found to be 5.487 ± 0.072 and 2.321 ± 0.141 respectively proved formulation is suitable for inhalation. In vitro cellular efficacy against A549 cells, revealed that the optimised formulations were more effective and potent.

CONCLUSION

The Inhalable SLNs approach was successfully engineered and administered to the lungs safely without causing any problems.

Organoids as Complex In Vitro Models for Studying Radiation-Induced Cell Recruitment

Patients with triple negative breast cancer (TNBC) typically receive chemotherapy, surgery, and radiation therapy. Although this treatment improves prognosis for most patients, some patients continue to experience recurrence within 5 years. Preclinical studies have shown that immune cell infiltration at the irradiated site may play a significant role in tumor cell recruitment; however, little is known about the mechanisms that govern this process. This lack of knowledge highlights the need to evaluate radiation-induced cell infiltration with models that have controllable variables and maintain biological integrity. Mammary organoids are multicellular three-dimensional (3D) in vitro models, and they have been used to examine many aspects of mammary development and tumorigenesis. Organoids are also emerging as a powerful tool to investigate normal tissue radiation damage. In this review, we evaluate recent advances in mammary organoid technology, consider the advantages of using organoids to study radiation response, and discuss future directions for the applications of this technique.

Diet and risk of breast cancer

Diet may play a role in both promoting and inhibiting human breast cancer development. In this review, nutritional risk factors such as consumption of dietary fat, meat, fiber, and alcohol, and intake of phytoestrogen, vitamin D, iron, and folate associated with breast cancer are reviewed. These nutritional factors have a variety of associations with breast cancer risk. Type of fat consumed has different effects on risk of breast cancer: consumption of meat is associated with heterocyclic amine (HCA) exposure; different types of plant fiber have various effects on breast cancer risk; alcohol consumption may increase the risk of breast cancer by producing acetaldehyde and reactive oxygen species (ROS); intake of phytoestrogen may reduce risk of breast cancer through genomic and non-genomic action; vitamin D can reduce the risk of breast cancer by inhibiting the process of cancer invasion and metastasis; intake of dietary iron may lead to oxidative stress, DNA damage, and lipid peroxidation; and lower intake of folate may be linked to a higher risk of breast cancer.

Docosahexaenoic Acid Induces Growth Suppression on Epithelial Ovarian Cancer Cells More Effectively than Eicosapentaenoic Acid

Omega-3 fatty acids, especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), have been shown to possess definitively suppressive effects on the growth of epithelial ovarian cancer cells. This study investigated the differential effects of pure EPA and DHA on the growth of epithelial ovarian cancer cells and the potential molecular mechanisms that may be involved. There were significant time- and dose-dependent inhibitory effects of both EPA and DHA on cellular proliferation of the epithelial ovarian cancer cell line TOV-21G (P < 0.05). TOV-21G cells pretreated with peroxisome proliferator receptor activator gamma (PPARγ) antagonist, GW9662, markedly suppressed EPA/DHA-induced apoptosis as determined by TUNEL assay, Annexin V-FITC/PI staining, and caspase-3 activity. EPA/DHA significantly induced PPARγ and p53 overexpression as observed in immunoblotting assay and the induction of p53 by EPA/DHA was abolished by GW9662. In all cases, the effect of DHA was significantly more potent than that of EPA (P < 0.05). Our findings suggested that DHA may be more effective than EPA in growth suppression of TOV-21G cells and the biologic effects may be partly mediated by PPARγ and p53 activation. Further research is required to elucidate additional divergent mechanisms to account for apparent differences between EPA and DHA.

Prospective associations between plasma saturated, monounsaturated and polyunsaturated fatty acids and overall and breast cancer risk - modulation by antioxidants: a nested case-control study

BACKGROUND

Mechanistic data suggest that different types of fatty acids play a role in carcinogenesis and that antioxidants may modulate this relationship but epidemiologic evidence is lacking. Our aim was to investigate the association between plasma saturated, monounsaturated and polyunsaturated fatty acids (SFAs, MUFAs and PUFAs) and overall and breast cancer risk and to evaluate the potential modulatory effect of an antioxidant supplementation on these relationships.

METHODS

A nested case-control study included all first incident cancer cases diagnosed in the SU.VI.MAX study between 1994 and 2002 (n=250 cases, one matched control/case). Participants to the SU.VI.MAX randomized controlled trial received either vitamin/mineral antioxidants or placebo during this intervention period. Baseline fatty acid composition of plasma total lipids was measured by gas chromatography. Conditional logistic regression was performed overall and stratified by intervention group.

RESULTS

Dihomo-γ-linolenic acid (Ptrend=0.002), the dihomo-γ-linolenic/linoleic acids ratio (Ptrend=0.001), mead acid (Ptrend=0.0004), and palmitoleic acid (Ptrend=0.02) were inversely associated with overall cancer risk. The arachidonic/dihomo-γ-linolenic acids ratio (Ptrend=0.02) and linoleic acid (Ptrend=0.02) were directly associated with overall cancer risk. Similar results were observed for breast cancer specifically. In stratified analyses, associations were only observed in the placebo group. Notably, total PUFAs were directly associated with overall (Ptrend=0.02) and breast cancer risk in the placebo group only.

CONCLUSION

Specific SFAs, MUFAs and PUFAs were prospectively differentially associated with cancer risk. In addition, this study suggests that antioxidants may modulate these associations by counteracting the potential effects of these fatty acids on carcinogenesis.

A non-surgical method for induction of lung cancer in Wistar rats using a combination of NNK and high dietary fats

Lung cancer is one of the most common malignant neoplasms all over the world. Smoking and a number of constituents of tobacco are responsible for development of lung tumours; however, the deleterious effects of tobacco-derived carcinogen, nitrosamine 4-(methylnitrosoamino)-1-(3-pyridyl)-1-butanone (nicotine-derived nitrosamine ketone (NNK)) remain unmatched. We report the development of a novel rodent model by administering multiple doses of NNK to male Wistar rats and feeding them with high-fat and low-protein diet. Tumour cells in lungs were observed in approximately 98 % rats after 8 months of NNK treatment, as evident by histopathological analysis. This rodent model showed slow progression of lung tumours which has helped us to assess early indicators of oxidative damage in lungs by studying the levels of lipid peroxidation and antioxidant parameters. LPO was elevated by 46.94 %, SOD, CAT, GSH and GR activity was decreased by 48.67 %, 22.04 %, 21.46 % and 20.85 %, respectively in serum of NNK treated rats when compared with control. These findings suggest that increased oxidative stress can represent a risk factor for the development of chronic disease in early future. This new animal model is an attempt to greatly facilitate studies of the pathophysiology, biochemistry and therapy of lung cancer.

EPA, an omega-3 fatty acid, induces apoptosis in human pancreatic cancer cells: role of ROS accumulation, caspase-8 activation, and autophagy induction

In a recent study, we showed that eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), two common omega-3 fatty acids, can cause ROS accumulation and subsequently induce caspase-8-dependent apoptosis in human breast cancer cells (Kang et al. [2010], PLoS ONE 5: e10296). In this study, we showed that the pancreas has a unique ability to accumulate EPA at a level markedly higher than several other tissues analyzed. Based on this finding, we sought to further investigate the anticancer actions of EPA and its analog DHA in human pancreatic cancer cells using both in vitro and in vivo models. EPA and DHA were found to induce ROS accumulation and caspase-8-dependent cell death in human pancreatic cancer cells (MIA-PaCa-2 and Capan-2) in vitro. Feeding animals with a diet supplemented with 5% fish oil, which contains high levels of EPA and DHA, also strongly suppresses the growth of MIA-PaCa-2 human pancreatic cancer xenografts in athymic nude mice, by inducing oxidative stress and cell death. In addition, we showed that EPA can concomitantly induce autophagy in these cancer cells, and the induction of autophagy diminishes its ability to induce apoptotic cell death. It is therefore suggested that combination of EPA with an autophagy inhibitor may be a useful strategy in increasing the therapeutic effectiveness in pancreatic cancer.

Detection of N-(hexanoyl)lysine in the tropomyosin 1 protein in N-methyl-N'-nitro-N-nitrosoguanidine-induced rat gastric cancer cells

N^ε-(Hexanoyl)lysine, formed by the reaction of lysine with n-6 lipid hydroperoxide, is a lipid peroxidation marker during the initial stage of oxidative stress. The aim of the present study is to indentify N^ε-(hexanoyl)lysine-modified proteins in neoplastic transformed gastric mucosal cells by N-methyl-N'-nitro-N-nitrosoguanidine, and to compare the levels of these proteins between gastric mucosal cells and normal gastric cells. Much greater fluorescence of 2-[6-(4'-hydroxy)phenoxyl-3H-xanthen-3-on-9-yl]benzoic acid, an index of the intracellular levels of reactive oxygen species, was observed for gastric mucosal cells compared to normal gastric cells. N^ε-(Hexanoyl)lysine-modified proteins were detected by SDS-PAGE or two-dimensional electrophoresis and Western blotting using anti-N^ε-(hexanoyl)lysine polyclonal antibody, and a protein band of between 30–40 kDa was clearly increased in gastric mucosal cells compared to normal gastric cells. Two N^ε-(hexanoyl)lysine-modified protein spots in gastric mucosal cells were identified as the tropomyosin 1 protein by mass spectrometry using a MASCOT search. The existence of N^ε-(hexanoyl)lysine modification in tropomyosin 1 was confirmed by Western blotting of SDS-PAGE-separated or two-dimensional electrophoresis-separated proteins as well as by the immunoprecipitation with anti-tropomyosin 1 antibody. These data indicate that N^ε-(hexanoyl)lysine modification of tropomyosin 1 may be related to neoplastic transformation by N-methyl-N'-nitro-N-nitrosoguanidine in gastric epithelial cells.

Role of dietary fatty acids in mammary gland development and breast cancer

Breast cancer is the most common cancer among women worldwide. Estimates suggest up to 35% of cases may be preventable through diet and lifestyle modification. Growing research on the role of fats in human health suggests that early exposure in life to specific fatty acids, when tissues are particularly sensitive to their environment, can have long-term health impacts. The present review examines the role of dietary fat in mammary gland development and breast cancer throughout the lifecycle. Overall, n-3 polyunsaturated fatty acids have promising cancer-preventive effects when introduced early in life, and warrant further research to elucidate the mechanisms of action.

Docosahexaenoic acid induces apoptosis in MCF-7 cells in vitro and in vivo via reactive oxygen species formation and caspase 8 activation

Background

The present study sought to further investigate the in vitro and in vivo anticancer effects of a representative omega-3 fatty acid, docosahexaenoic acid (DHA), with a focus on assessing the induction of oxidative stress and apoptosis as an important mechanism for its anticancer actions.

Methodology/Principal Findings

In vitro studies showed that DHA strongly reduces the viability and DNA synthesis of MCF-7 human breast cancer cells in culture, and also promotes cell death via apoptosis. Mechanistically, accumulation of reactive oxygen species and activation of caspase 8 contribute critically to the induction of apoptotic cell death. Co-presence of antioxidants or selective inhibition or knockdown of caspase 8 each effectively abrogates the cytotoxic effect of DHA. Using athymic nude mice as an in vivo model, we found that feeding animals the 5% fish oil-supplemented diet for 6 weeks significantly reduces the growth of MCF-7 human breast cancer cells in vivo through inhibition of cancer cell proliferation as well as promotion of cell death. Using 3-nitrotyrosine as a parameter, we confirmed that the fish oil-supplemented diet significantly increases oxidative stress in tumor cells in vivo. Analysis of fatty acid content in plasma and tissues showed that feeding animals a 5% fish oil diet increases the levels of DHA and eicosapentaenoic acid in both normal and tumorous mammary tissues by 329% and 300%, respectively.

Conclusions/Significance

DHA can strongly induce apoptosis in human MCF-7 breast cancer cells both in vitro and in vivo. The induction of apoptosis in these cells is selectively mediated via caspase 8 activation. These observations call for further studies to assess the effectiveness of fish oil as a dietary supplement in the prevention and treatment of human breast cancer.

Dietary intakes of omega-6 and omega-3 polyunsaturated fatty acids and the risk of breast cancer

Experimental studies suggest detrimental effects of omega-6 polyunsaturated fatty acids (PUFA), and beneficial effects of omega-3 PUFAs on mammary carcinogenesis, possibly in interaction with antioxidants. However, PUFA food sources are diverse in human diets and few epidemiologic studies have examined whether associations between dietary PUFAs and breast cancer risk vary according to food sources or antioxidant intakes. The relationship between individual PUFA intakes estimated from diet history questionnaires and breast cancer risk was examined among 56,007 French women. During 8 years of follow-up, 1,650 women developed invasive breast cancer. Breast cancer risk was not related to any dietary PUFA overall; however, opposite associations were seen according to food sources, suggesting other potential effects than PUFA per se. Breast cancer risk was inversely associated with alpha-linolenic acid (ALA) intake from fruit and vegetables [highest vs. lowest quintile, hazard ratio (HR) 0.74; 95% confidence interval (CI) 0.63, 0.88; p trend < 0.0001], and from vegetable oils (HR 0.83; 95% CI 0.71, 0.97; p trend 0.017). Conversely, breast cancer risk was positively related to ALA intake from nut mixes (p trend 0.004) and processed foods (p trend 0.068), as was total ALA intake among women in the highest quintile of dietary vitamin E (p trend 0.036). A significant interaction was also found between omega-6 and long-chain omega-3 PUFAs, with breast cancer risk inversely related to long-chain omega-3 PUFAs in women belonging to the highest quintile of omega-6 PUFAs (p interaction 0.042). These results emphasize the need to consider food sources, as well as interactions between fatty acids and with antioxidants, when evaluating associations between PUFA intakes and breast cancer risk.

Multi-targeted therapy of cancer by omega-3 fatty acids

Omega-3 (n-3) and omega-6 (n-6) polyunsaturated fatty acids (PUFAs) are essential fatty acids necessary for human health. Currently, the Western diet contains a disproportionally high amount of n-6 PUFAs and low amount of n-3 PUFAs, and the resulting high n-6/n-3 ratio is thought to contribute to cardiovascular disease, inflammation, and cancer. Studies in human populations have linked high consumption of fish or fish oil to reduced risk of colon, prostate, and breast cancer, although other studies failed to find a significant association. Nonetheless, the available epidemiological evidence, combined with the demonstrated effects of n-3 PUFAs on cancer in animal and cell culture models, has motivated the development of clinical interventions using n-3 PUFAs in the prevention and treatment of cancer, as well as for nutritional support of cancer patients to reduce weight loss and modulate the immune system. In this review, we discuss the rationale for using long-chain n-3 PUFAs in cancer prevention and treatment and the challenges that such approaches pose in the design of clinical trials.

Dietary fat-gene interactions in cancer

Epidemiologic studies have suggested for decades an association between dietary fat and cancer risk. A large body of work performed in tissue culture and xenograft models of cancer supports an important role of various types of fat in modulating the cancer phenotype. Yet, the molecular mechanisms underlining the effects of fat on cancer initiation and progression are largely unknown. The relationships between saturated fat, polyunsaturated fat, cholesterol or phytanic acid with cancer have been reviewed respectively. However, few have considered the relationship between all of these fats and cancer. The purpose of this review is to present a more cohesive view of dietary fat-gene interactions, and outline a working hypothesis of the intricate connection between fat, genes and cancer.

The 8-epimer of prostaglandin F(2alpha), a marker of lipid peroxidation and oxidative stress, is decreased in the nipple aspirate fluid of women with breast cancer

Breast cancer (BC), a worldwide disease with increasing incidence, develops from ductal/lobular epithelium. Nipple aspirate fluid (NAF), secreted from the breast ducts and lobules, can be analyzed to assess breast metabolic activity. Whether lipid peroxidation in the mammary gland promotes or prevents tumorigenesis is unclear. Malondialdehyde (MDA) and the 8-epimer of Prostaglandin F(2alpha) (8-iso-PGF(2alpha)), two lipid peroxidation markers, were studied in milk (n = 10), NAF (n = 140) and plasma (n = 35) samples. MDA was detected in all plasma, in 80% of milk samples and in 95% of NAF samples. MDA levels in NAF and plasma were significantly higher than in milk (p = 0.016 and p = 0.029, respectively). We found no significant difference between levels of MDA in NAF samples from BC patients compared to healthy controls. 8-iso-PGF(2alpha) was detectable in all samples. 8-iso-PGF(2alpha) median levels in NAF were significantly higher than in both milk and plasma (p < 0.0001). The highest 8-iso-PGF(2alpha) levels were found in NAF from healthy women, significantly higher than in women with BC (p < 0.0001). No significant differences were found in both markers after the age-adjustment. High levels of lipid peroxidation products in NAF suggest their in situ production in the nonlactating breast. Active lipid peroxidation may have a physiologic role in the normal mammary gland. Lower levels of 8-iso-PGF(2alpha) in NAF from BC patients suggest altered production of arachidonic acid metabolites during breast carcinogenesis.

Lipid peroxidation, oxidative stress genes and dietary factors in breast cancer protection: a hypothesis

We have recently proposed that lipid peroxidation may be a common mechanistic pathway by which obesity and hypertension lead to increased renal cell cancer risk. During this exercise, we noted a risk factor swap between breast and kidney cancer (oophorectomy and increased parity, detrimental for kidney, beneficial for breast; high blood pressure, detrimental for kidney, beneficial for breast when it occurs during pregnancy; alcohol, beneficial for kidney, detrimental for breast, and so on). We have subsequently proposed the hypothesis that lipid peroxidation represents a protective mechanism in breast cancer, and reviewed the evidence of the role of lipid peroxidation on established hormonal and non-hormonal factors for breast cancer. Here, we review the evidence in support of lipid peroxidation playing a role in the relationships between dietary factors and breast cancer. Available evidence implicates increased lipid peroxidation products in the anti-carcinogenic effect of suspected protective factors for breast cancer, including soy, marine n-3 fatty acids, green tea, isothiocyanates, and vitamin D and calcium. We also review the epidemiological evidence supporting a modifying effect of oxidative stress genes in dietary factor-breast cancer relationships.

Lipid peroxidation and renal cell carcinoma: further supportive evidence and new mechanistic insights

We have recently proposed lipid peroxidation as a unifying mechanistic pathway by which several seemingly unrelated risk/protective factors (obesity, hypertension, diabetes, smoking, oophorectomy/hysterectomy, parity, antioxidants) affect renal cell carcinoma development. In experimental studies, increased lipid peroxidation is a principal mechanistic pathway in renal carcinogenesis induced by different chemicals. In this communication, we provide additional lines of evidence that further support a role for lipid peroxidation on renal cell cancer development. (1) Lipid peroxidation may explain the role of other risk (analgesic use, pre-eclampsia) or protective (alcohol intake, oral contraceptives) factors for renal cell carcinoma. (2) Additional experimental evidence supports lipid peroxidation as an important mechanism in renal carcinogenesis, and (3) Existing evidence support a cross-talk between the lipid peroxidation pathway and other pathways that are relevant to renal carcinogenesis, such as apoptosis, VHL, and possibly other pathways.

Role of Lipid Peroxidation in the Epidemiology and Prevention of Breast Cancer

We have recently proposed a common mechanistic pathway by which obesity and hypertension lead to increased renal cell cancer risk. Our hypothesis posits lipid peroxidation, which is a principal mechanism in rodent renal carcinogenesis, as an intermediate step that leads to a final common pathway shared by numerous observed risks (including obesity, hypertension, smoking, oophorectomy/hysterectomy, parity, preeclampsia, diabetes, and analgesics) or protective factors (including oral contraceptive use and alcohol) for renal cell cancer [Cancer Causes Control 2002;13:287-93]. During this exercise, we have noticed how certain risk factors for renal cell carcinoma are protective for breast cancer and how certain protective factors for renal cell carcinoma increase risk for breast cancer. Parity and oophorectomy, for example, are positively associated with renal cell carcinoma but are negatively associated with breast cancer. Similarly, obesity and hypertension are positively associated with renal cell carcinoma, but obesity is negatively associated with breast cancer in premenopausal women and hypertension during pregnancy is negatively associated with breast cancer. Furthermore, alcohol intake, negatively associated with renal cell carcinoma, is also positively associated with breast cancer. We propose here the possibility that lipid peroxidation may represent a protective mechanism in breast cancer. Although this runs counter to the conventional view that lipid peroxidation is a process that is harmful and carcinogenic, we present here the chemical and biological rationale, based on epidemiologic and biochemical data, which may deserve further consideration and investigation.

Long-chain (n-3) fatty acid intake and risk of cancers of the breast and the prostate: recent epidemiological studies, biological mechanisms, and directions for future research

The association between dietary (n-3) fatty acids and hormone-responsive cancers continues to attract considerable attention in epidemiological, clinical, and experimental studies. We previously reviewed the epidemiological literature on the association between hormone-responsive cancers and the long-chain fatty acids eicosapentaenoic acid and docosahexaenoic acid. We concluded that the compelling evidence from ecological studies, animal models, and mechanistic experiments in vitro was not supported clearly by the available epidemiological data. To various degrees, epidemiological studies published more recently attempted to address some of the methodological limitations plaguing earlier studies by using validated questionnaires, examining specific fatty acids and their interrelationships, and adjusting estimates for a wider range of potentially confounding factors than in previous studies. In this review, our aim was to update the previous review with the results of recent epidemiological studies and to discuss possible biological mechanisms and directions for future research.

Intake of specific carotenoids and essential fatty acids and breast cancer risk in Montreal, Canada

BACKGROUND

Evidence from previous investigations into the possible role of dietary and serum carotenoid concentrations in the etiology of breast cancer is inconsistent. No study has examined the combined effect of carotenoids and essential fatty acids on the risk of breast cancer.

OBJECTIVE

The objective was to assess the possible association between specific and total carotenoids and breast cancer risk and to evaluate the effect modification by diet-related fatty acids and lifestyle factors in the development of breast cancer.

DESIGN

A population-based case-control study involving 414 incident cases and 429 controls was conducted in French Canadians in Montreal. Dietary intake was estimated with the use of a validated food-frequency questionnaire in face-to-face interviews.

RESULTS

No significant association was apparent between any of the individual or total carotenoids and the risk of breast cancer after adjustment for major underlying determinants of breast cancer. In premenopausal women who ever smoked, an increased risk was related to alpha-carotene [odds ratio (OR) for the upper relative to the lowest quartiles of intake: 2.40; 95% CI: 0.90, 6.41; P for trend = 0.046]. Conversely, a reduced risk was related to beta-carotene (OR: 0.57; 95% CI: 0.26, 1.24; P for trend = 0.05) in women who never used hormone replacement therapy. In postmenopausal women, total carotenoids were positively associated with breast cancer risk in those with a high arachidonic acid intake (OR: 1.92; 95% CI: 0.93, 3.94; P = 0.028 for trend) and inversely associated in those with a high docosahexaenoic acid intake (OR: 0.52; 95% CI: 0.25, 1.07; P for trend = 0.054).

CONCLUSION

These findings suggest that the combined high intake of total carotenoids and docosahexaenoic acid may reduce the risk of breast cancer.

Olive oil consumption during pregnancy and lactation in rats influences mammary cancer development in female offspring

This study examined the effects of variety and quantity of dietary fat consumed by rats during pregnancy and lactation on female offspring's response to chemically induced mammary cancer. Groups of six female rats were fed diets containing 7% corn oil (7-CO), 15% CO (15-CO), 7% olive oil (7-OO), or 15% OO (15-OO) for 5 wk prior to, and during, pregnancy and lactation. Female offspring (n = 15 per group) were fed a 7-CO diet, and mammary cancer was induced with 7,12-dimethylbenz[a]anthracene (DMBA). Three months following cancer induction tumor incidence and size were recorded, and markers of apoptosis, serum estrogen concentrations, and hepatic phase II enzymes were measured. Tumor incidence was 47% in offspring born to mothers fed the 7-OO diet, rose to 67% in 7-CO and 15-OO offspring, and reached 86% in 15-CO. A trend toward smaller tumors was observed in the 7-OO group, and offspring of mothers fed high-fat diets had significantly more tumors. Estradiol levels at the end of lactation were significantly lower in mothers fed 7-OO but were similar in all groups of offspring. In tumor tissue, Bcl-2 expression was highest in the 15-CO offspring, and Bak expression was significantly higher in rats exposed to OO. A distinct trend toward increased caspase-3 expression (20 kDa) was observed in the 7-OO offspring, and both low-fat diets significantly elevated caspase activity. In healthy mammary tissue, rats exposed to low-fat diets had significantly higher caspase-3 (32-kDa) levels, and caspase-3 activity was significantly higher in the healthy tissue from both OO groups. Hepatic quinone reductase activity was significantly lower in offspring of mothers fed the low-fat diets. These results indicate that perinatal exposure to OO may have a protective effect against future development of mammary cancer in female offspring, whereas high-fat diets fed to pregnant and lactating rats, in particular CO, may be deleterious.

Serum fatty acids and breast cancer incidence

Fatty acid composition of the diet may be essential to the development of breast cancer. We studied the ability of several fatty acids of serum total lipids to predict breast cancer incidence in a case-control study nested within a longitudinal population study. The proportions of fatty acids in serum total lipids were determined from stored serum samples collected at baseline for 127 incident breast cancer cases and 242 matched controls. Women with a higher proportion of total polyunsaturated fatty acids (PUFAs) in serum had a reduced risk of breast cancer. The odds ratio (OR) between the highest and lowest tertiles of serum PUFA was 0.31 (95% confidence interval, CI = 0.12-0.77). This association was mainly due to n-6 PUFAs and especially to linoleic acid. The ORs were 0.35 (CI = 0.14-0.84) and 0.29 (CI = 0.12-0.73), respectively. Of the monounsaturated fatty acids (MUFAs), higher trans-11-18:1 levels were related to an increased breast cancer risk (OR = 3.69, CI = 1.35-10.06). The association was stronger in postmenopausal than in premenopausal women. The present study suggests that higher serum proportions of the n-6 PUFA linoleic acid and lower proportions of the MUFA trans-11-18:1 fatty acid predict a reduced incidence of breast cancer.

Intakes of fish and marine fatty acids and the risks of cancers of the breast and prostate and of other hormone-related cancers: a review of the epidemiologic evidence

Marine fatty acids, particularly the long-chain eicosapentaenoic and docosahexaenoic acids, have been consistently shown to inhibit the proliferation of breast and prostate cancer cell lines in vitro and to reduce the risk and progression of these tumors in animal experiments. However, whether a high consumption of marine fatty acids can reduce the risk of these cancers or other hormone-dependent cancers in human populations is unclear. Focusing primarily on the results of cohort and case-control studies, we reviewed the current epidemiologic literature on the intake of fish and marine fatty acids in relation to the major hormone-dependent cancers. Despite the many epidemiologic studies that have been published, the evidence from those studies remains unclear. Most of the studies did not show an association between fish consumption or marine fatty acid intake and the risk of hormone-related cancers. Future epidemiologic studies will probably benefit from the assessment of specific fatty acids in the diet, including eicosapentaenoic and docosahexaenoic acids, and of the ratio of these to n-6 fatty acids, dietary constituents that have not been examined individually very often.

N-3 fatty acids and lipid peroxidation in breast cancer inhibition

Long-chain n-3 fatty acids (FA) consistently inhibit the growth of human breast cancer (BC) cells both in culture and in grafts in immunosuppressed mice. Large cohort studies have, however, failed to confirm a protective effect for fish oils rich in n-3 FA against BC risk. The present review examines new evidence on biological mechanisms which may be involved in the inhibition of mammary carcinogenesis by long-chain n-3 FA, focusing on an apoptotic effect by its lipid peroxidation products. Dietary intake of n-3 FA leads to their incorporation into cell membrane lipids. Increased apoptosis in human BC cells following exposure to long-chain n-3 FA such as eicosapentaenoic and docosahexaenoic acids is generally ascribed to their inhibition of cyclooxygenase 2 which promotes mammary carcinogenesis. In addition however, long-chain n-3 FA are particularly likely to activate peroxisome proliferator-activated receptor (PPAR)-gamma, a key regulator of lipid metabolism but also capable of modulating proliferative activity in a variety of cells including mammary cells. Expression of PPAR-gamma in the nucleus is activated by second messengers such as J series prostaglandins and the latter have been shown to cause apoptosis in vivo in explants of human BC cells in immunosuppressed mice. In mammary tumours, it is observed that long-chain FA not only increase apoptosis, but also increase lipid peroxidation, and the apoptotic effect can be reversed by antioxidants. The rationale for use of n-3 FA dietary supplements in counteracting BC progression needs to be tested clinically in a phase 2 pilot study, while at the same time, the effect on whole-body lipid peroxidation needs to be monitored. Dietary supplements of fish oil rich in n-3 FA are proposed for premenopausal women over the age of 40 years who are shown to be at increased BC risk. Biological markers in breast tissue of BC progression will be monitored, and observed changes related to serial plasma levels of isoprostanes as a measure of whole-body lipid peroxidation.

Effect of varying dietary fat levels on rat growth and oxidative DNA damage

Dietary fat has previously been shown to have somewhat complicated relationships to levels of oxidative stress in rats. In this study, we examined the effects of five different dietary fat intakes on levels of oxidative DNA damage in rats. Animals fed diets containing 3%, 5%, 10%, or 15% corn oil had body weights that were similar after 20 weeks. Animals fed a 20% fat diet, however, had significantly higher mean body weight than any other group. Levels of 5-hydroxymethyl-2'-deoxyuridine, one marker of oxidative DNA damage, had different relationships to dietary fat in blood and mammary gland. In blood, levels increased with dietary fat levels, and the highest levels were observed with the 20% fat diet (65% higher levels than with the 3% fat diet). In mammary gland, a plateau-type effect was observed, with maximal levels of oxidative DNA damage being obtained using 10% fat (representing a 68% increase relative to the 3% fat diet). This could be a result of induction of compensatory mechanisms in response to a high-fat diet in mammary gland but not in the short-lived nucleated blood cells. Oxidative DNA damage levels in blood thus appear to be a marker of dietary fat intake. In mammary gland, however, levels of DNA damage are consistent with previously observed promotional effects of dietary fat on mammary gland tumorigenesis at lower levels of fat intake with little or no incremental promoting effects at higher levels of fat intake.

Oxidative DNA damage and 8-hydroxy-2-deoxyguanosine DNA glycosylase/apurinic lyase in human breast cancer

To test the hypothesis that oxidative stress is involved in breast cancer, we compared the levels of 8-hydroxy-2-deoxyguanosine (8-oxo-dG), an oxidized DNA base common in cells undergoing oxidative stress, in normal breast tissues from women with or without breast cancer. We found that breast cancer patients (N = 76) had a significantly higher level of 8-oxo-dG than control subjects (N = 49). The mean ( +/- SD) values of 8-oxo-dG/10(5) dG, as measured by high-performance liquid chromatography electrochemical detection, were 10.7 +/- 15.5 and 6.3 +/- 6.8 for cases and controls, respectively (P = 0.035). This difference also was found by immunohistochemistry with double-fluorescence labeling and laser-scanning cytometry. The average ratios (x10(6)) of the signal intensity of antibody staining to that of DNA content were 3.9 +/- 7.2 and 1.1 +/- 1.4 for cases (N = 57) and controls (N = 34), respectively (P = 0.008). There was no correlation between the ages of the study subjects and the levels of 8-oxo-dG. Cases also had a significantly higher level of 8-hydroxy-2-deoxyguanosine DNA glycosylase/apurinic lyase (hOGG1) protein expression in normal breast tissues than controls (P = 0.008). There was no significant correlation between hOGG1 expression and 8-oxo-dG. Polymorphism of the hOGG1 gene was very rare in this study population. The previously reported exon 1 polymorphism and two novel mutations of the hOGG1 gene were found in three of 168 cases and two of 55 controls. In conclusion, normal breast tissues from cancer patients had a significantly higher level of oxidative DNA damage. The elevated level of 8-oxo-dG in cancer patients was not related to age or to deficiency of the hOGG1 repair gene.

Newly recognized cytotoxic effect of conjugated trienoic fatty acids on cultured human tumor cells

We investigated the cytotoxic effect of conjugated trienoic fatty acids on various human tumor cell lines: DLD- 1, colorectal; HepG2, hepatoma; A549, lung; MCF-7, breast; and MKN-7, stomach. Conjugated linoleic acid (CLA) and conjugated linolenic acid were prepared from linoleic acid (18:2, n-6) and alpha-linolenic acid (18:3, n-3), respectively, by treatment with 6.6% or 21% potassium hydroxide. Spectrophotometric readings at 235 nm for the conjugated diene formation, and at 268 nm for the conjugated triene, were confirmed for the respective conjugated fatty acids. In addition, tung oil (Aleurites fordii) fatty acids consisting principally of a conjugated triene (eleostearic acid, approximately 80% of total fatty acids) were prepared using an alkaline saponification procedure. All tumor cells were incubated for 24 h with 5-100 microM of the conjugated fatty acids, and MTT dye reduction was measured to verify the cell viability. Among the conjugated fatty acids examined, conjugated linolenic acid and tung oil fatty acids exhibited the most intense cytotoxic effects on DLD-1, HepG2, A549, MCF-7 and MKN-7 cells, while CLA was not cytotoxic to the tumor cells. These results demonstrate that conjugated trienoic fatty acids are more cytotoxic to human tumor cells than the conjugated dienoic fatty acid, CLA.

DNA adducts in normal tissue adjacent to breast cancer: a review

To identify possible extrinsic and intrinsic DNA-damaging factors involved in breast cancer etiology, we measured the level of aromatic and lipid peroxidation-related DNA adducts in samples of normal tissue adjacent to breast tumors obtained from 87 breast cancer patients using 32P postlabeling. Twenty-nine cancer-free women who underwent reduction mammoplasty served as controls. Tissue samples from the breast cancer patients contained significantly higher levels of aromatic DNA adducts (mean +/- SEM: 97.4 +/- 23.4 x 109 nucleotides) than did samples obtained from the controls (mean +/- SEM: 23.5 +/- 6.9 x 109 nucleotides). A bulky benzo[a]pyrene (BP)-like adduct was detected in 41% of the cancer patients, but in none of the controls. The level of this adduct was extremely high in some patients (> 1/106). While 88% of the patients with a smoking history had smoking-specific DNA adducts in their breast tissues, the presence of BP-like adduct was not related to smoking history. The cancer patients also had a significantly higher level of lipid peroxidation-related DNA adducts than did controls. The level of these adducts correlated with the presence of the BP-like adduct. To further explore the origin of the BP-like adduct, we examined the level of polycyclic aromatic hydrocarbon (PAH)-DNA adducts and 8-hydroxyguanine (8-OH-G) in tissue sections obtained from 37 breast cancer patients using immunocytochemistry. We found that patients who had the BP-like adduct showed significantly greater immunostaining for PAH adducts than did those without the BP-like adduct (p = 0.04). In addition, we found that adipocytes tended to have greater immunostaining for the PAH adducts than did epithelial cells. On the other hand, epithelial cells tended to have a higher frequency and greater intensity of staining for 8-OH-G than did adipocytes. The detection of PAH adducts, lipid peroxidation-related DNA adducts, and 8-OH-G in normal breast tissues of breast cancer patients suggests that both exogenous and endogenous DNA-damaging factors may be involved in breast cancer. The exogenous source may involve the types of carcinogen exposure other than cigarette smoking, and the endogenous source may involve oxidative stress associated with normal metabolic activities.

The influence of maternal diet on breast cancer risk among female offspring

The induction of breast cancer is a long process, containing a series of biological events that drive a normal mammary cell towards malignant growth. However, it is not known when the initiation of breast cancer occurs. One hypothesis is that a high estrogenic environment during the perinatal period increases subsequent breast cancer risk. There are many sources of extragonadal estrogens, particularly in the diet. The purpose of this paper is to review the evidence that a high maternal intake of dietary fats increases serum estrogens during pregnancy and increases breast cancer risk in daughters. Our animal studies show that a high maternal consumption of corn oil consisting mainly of linoleic acid (omega-6 polyunsaturated fatty acid, PUFA), increases both circulating estradiol (E2) levels during pregnancy and the risk of developing carcinogen-induced mammary tumors among the female rat offspring. A similar increase in breast cancer risk occurs in female offspring exposed to injections of E2 through their pregnant mother. Our data suggest that the mechanisms by which an early exposure to dietary fat and/or estrogens increases breast cancer risk is related to reduced differentiation of the mammary epithelial tree and increased number of mammary epithelial cell structures that are known to the sites of neoplastic transformation. These findings may reflect our data of the reduced estrogen receptor protein levels and protein kinase C activity in the developing mammary glands of female rats exposed to a high-fat diet in utero. In summary, a high dietary linoleic acid intake can elevate pregnancy estrogen levels and this, possibly by altering mammary gland morphology and expression of fat- and/or estrogen-regulated genes, can increase breast cancer risk in the offspring. If true for women, breast cancer prevention in daughters may include modulating the mother's pregnancy intake of some dietary fats.

Omega-3 polyunsaturated fatty acids in rodent models of breast cancer

Quantitative increases in certain dietary fats promote mammary tumor growth, but the experimental data indicate that this tumor promoting capability is not equally expressed by all fatty acid families. There is a large body of evidence from experiments using either carcinogen-induced or transplanted animal mammary tumor models, as well as in vitro studies, which demonstrates that the omega-6 polyunsaturated fatty acids (PUFA) promote mammary tumor development more effectively than omega-3 PUFA. These data indicate that increases in the dietary levels of omega-6 PUFA enhance tumor development, while equivalent increases in dietary levels of omega-3 PUFA often delay or reduce tumor development. Several theoretical mechanisms have been proposed for these contrasting results, but as yet, no definitive explanation has been universally accepted.

Meta-analyses of dietary fats and mammary neoplasms in rodent experiments

We review two meta-analyses of experiments on dietary fat and mammary tumor incidence in rodents, emphasizing a recent meta-analysis on the effects of different types of dietary fatty acids. This analysis shows that n-6 polyunsaturated fatty acids most strongly enhance mammary tumors in rodents, and saturated fats also enhance these tumors but less strongly. Further, the analysis shows that energy restriction protects against mammary tumors. We show that these results agree qualitatively with estimates of effects on human breast cancer derived from international correlations.

Diet and breast cancer: studies in laboratory animals

Increasing dietary fat content increases mammary gland tumorigenesis in laboratory rodents. The effect can be attributed only in part to increasing energy intake, which itself increases tumorigenesis. Restriction of dietary or energy intake, sufficient to reduce body weight, reduces mammary gland tumorigenesis. Consideration of these effects has led to discussion of the possible need for changes in the feeding of laboratory rodents in carcinogenesis bioassays and other chronic studies. Studies of endocrine or other growth factors for the mammary gland have not identified specific effects of dietary fat or energy. In addition, tumorigenesis in other organs responds similarly to increased fat or decreased energy intake, indicating that the mechanisms are not, or not entirely, specific for the mammary gland. Extrapolations of results between species must always be made with caution, but the marked effects of dietary fat and energy in rodent tumorigenesis models must be considered in designing diet advice for humans.

Separation and quantitation of linoleic acid oxidation products in mammary gland tissue from mice fed low- and high-fat diets

We have developed an assay for the isolation and quantitation by gas chromatography-mass spectrometry (GC-MS) of free 9- and 13-hydroxyoctadecadienoic acid (9-HODE, 13-HODE) in the mammary glands of female mice. Internal standards consisting of 18O2-labeled analogs of 9- and 13-HODE are added to pulverized frozen tissue prior to extraction with ethanol. Nonlipid materials are removed in a chloroform/methanol/water step. The remaining lipid material is methylated with ethereal diazomethane, and much of the nonoxygenated fatty acid methyl esters are removed via silica solid-phase extraction. Samples are either further derivatized with bis(trimethylsilyl)trifluoroacetamide to form the trimethylsilyl ethers for quantitative analysis by GC-MS or are analyzed as the methyl esters by chiral high-performance liquid chromatography to determine the enantiomeric distribution of the 9- and 13-HODE. The extraction and quantitation protocol was applied to the analysis of mammary glands for free 9- and 13-HODE from mice fed isocaloric diets containing 20% corn oil, 5% corn oil, or 20% beef tallow. Chiral analysis of the products showed higher production of 13(S)-HODE relative to 13(R)-HODE; the enantiomeric excess is most likely due to enzymatic production of 13-HODE superimposed on a background of autoxidative production of 13(R)- plus 9(S)- and 9(R)-HODE. In addition, the effect of sample handling and storage conditions on the formation of 9- and 13-HODE in the samples was assessed by exposing aliquots of a common pool of rat mammary gland tissue to specified conditions prior to analysis. This methodology will be important during investigations of the contribution of linoleate oxidation products to the enhancement of mammary tumorigenesis by dietary fat.

Polyunsaturated fatty acids increase the sensitivity of 36B10 rat astrocytoma cells to radiation-induced cell kill

Polyunsaturated fatty acids (PUFA) such as gamma-linolenic acid (GLA, 18:3n-6), eicosapentaenoic acid (EPA, 20:5n-3), and docosahexaenoic acid (DHA, 22:6n-3) have been shown to be cytotoxic to tumor cells. The objective of this work was to study the effects of PUFA on the radiation response of a 36B10 rat astrocytoma cell line. Supplementation of the astrocytoma cells with 15-45 microM GLA, EPA, or DHA produced marked changes in the fatty acid profiles of their phospholipids and neutral lipids. The methylene bridge index of these lipids increased significantly. These PUFA also exerted cytotoxic effects, as determined using the clonogenic cell survival assay. While GLA and DHA produced a moderate cell-killing effect, EPA was extremely cytotoxic, especially at a concentration of 45 microM. The monounsaturated oleic acid (OA, 18:1n-9) did not affect cell survival. Further, all three PUFA, and particularly GLA, increased the radiation-induced cell kill; OA did not enhance the effect of radiation. alpha-Tocopherol acetate blocked the enhanced radiation sensitivity of GLA- and DHA-supplemented cells. In conclusion, GLA, EPA, and DHA supplementation prior to, during, and after irradiation can enhance the radiation-induced cytotoxicity of rat astrocytoma cells. GLA and DHA supplementation post-irradiation also enhanced the radiation response of the 36B10 cells. Because GLA maximally increases the radioresponsiveness of a rat astrocytoma, this PUFA might prove useful in increasing the therapeutic efficacy of radiation in the treatment of certain gliomas.

Human low-density lipoproteins: oxidative modification and its relation to age, gender, menopausal status and cholesterol concentrations

Recently much evidence has accumulated indicating that oxidative modification of atherogenic lipoproteins plays an important role in atherogenesis. The goal of this study was to ascertain whether any association exists between this and the previously incriminated risk factors of atherosclerotic cardiovascular disease like age, gender and cholesterol concentration. Serum lipid profile, low-density lipoprotein (LDL) composition and indicators of LDL oxidation were examined in a cohort of healthy, predominantly middle aged men and women. LDL oxidation was assessed using the copper catalysis method, and monitored routinely by the increase in conjugated dienes over 4 to 24 hours. A more objective computer-aided technique was used to estimate the oxidative indices based on the sigmoidal fit to data. No marked differences between men and women were found with respect to mean age, total and LDL cholesterol, LDL protein and oxidation of LDL. The post-menopausal as compared to pre-menopausal status was associated with a greater extent of LDL oxidation, as well as with higher total serum cholesterol and its fractions, LDL cholesterol and LDL protein. No such differences were found in the data for men appropriately separated according to age. In a group with high risk LDL cholesterol, the total LDL oxidation was higher, as well as age and total cholesterol. Lag time and half-time of LDL oxidation were significantly shorter, while the oxidation rate of LDL was significantly faster when compared with data in the lower quartile. About six percent of participants had a considerably prolonged initial oxidation phase. These persons also showed low total and LDL cholesterol. High oxidation resistance was reversible and most probably caused by very low pre-existent oxidation products. Multiple regression analysis showed that the closest association among age, gender, lipid profiles and LDL oxidation indices existed between LDL cholesterol and conjugated diene production in both sexes (men: r = 0.93; women: r = 0.81). This association remained high even if adjusted for age. As in earlier epidemiological studies using logistic regression and showing age- and gender-related rising frequency of coronary heart disease, the present paper demonstrated age- and gender-related rising frequency of highly oxidized LDL. In both cases it was closely associated with an increasing LDL cholesterol concentration.

The pH dependence of lipid peroxidation using water-soluble azo initiators

We report here the pH dependence of the rate of lipid peroxidation of methyl linoleate/Triton mixed micelles using a series of water-soluble azo initiators. The cationic initiators 2,2'-azobis(2-amidinopropane) (ABAP) and 2,2'-azobis[2-(2-imidazolin-2-yl)propane] (ABIP) exhibit similar behavior, in which increased pH results in dramatically enhanced rates of peroxidation. Rate data for ABAP and ABIP were fitted to a single proton equilibrium, which yielded apparent kinetic pKa values for the rate of approximately 7 and 6, respectively. The azo initiator 4,4'-azobis(4-cyanopentanoic acid) (ABCPA), which yields a negatively charged radical upon thermolysis at neutral pH, was also studied. In contrast to the effects observed with ABAP and ABIP, peroxidation rates with ABCPA exhibit an inverse pH dependence, in which the rates of peroxidation increase with decreasing pH, with an apparent pKa of approximately 5. By comparison, methyl linoleate oxidation rates with 2,2'-azobis (2-cyanopropane) (ABCP) display minimal changes over the pH range 5 to 7.5. Two alternatives can be advanced to account for this behavior, including either a buffer effect which is specific to the cationic initiators or an altered amidinium pKa (approximately 6 to 7) in either the initial carbon-centered radical or the subsequent peroxyl radical generated upon thermolysis of ABAP or ABIP. In the latter case, the kinetic pH dependence could thus reflect an enhanced competence of neutral radicals over charged radicals to partition into the micelles and initiate peroxidation.

Mammary carcinogenicity of diol epoxide metabolites of benzo[j]fluoranthene in female CD rats

The mammary carcinogenicity of two diol epoxide metabolites of the commonly occurring environmental carcinogen benzo[j]fluoranthene (BjF) was investigated by direct application to the tissue beneath the mammary glands of female CD rats. The compounds tested were trans-4,5-dihydroxy-anti-6,6a.epoxy-4,5,6,6a-tetrahydroBjF (BjF-4,5-DE) and trans-9,10-dihydroxy-anti-11, 12-epoxy-9,10,11,12-tetrahydroBjF (BjF-9,10-DE). The positive control was trans-3,4-dihydroxy-anti-1,2-epoxy-1,2,3,4-tetrahydrobenzo[c]phenanthren e (BcPDE). Groups of 20 female CD rats were maintained on AIN-76A-based high fat diet (23.5% corn oil) and at age 30 days were given three injections of 0.2 mumol of each compound in 0.1 ml dimethyl sulfoxide (DMSO), or DMSO alone, in the tissue underlying each of the three left thoracic nipples. The three right nipple areas were injected with DMSO alone. On the next day, each rat received three injections of 0.2 mumol of each compound in 0.1 ml DMSO, or DMSO alone, under each of the three left inguinal nipples, and DMSO alone under the three right nipples. The experiment was terminated after 44 weeks. BjF-9,10-DE, mean latent period 21.0 +/- 8.8 weeks, was more active than BjF-4,5-DE, mean latent period 36.2 +/- 8.0 weeks. BjF-9,10-DE induced tumors in 70% of the rats; a total of 38 fibroadenomas and eight adenocarcinomas was observed. BjF-4,5-DE induced tumors in 55% of the rats. These included 17 fibroadenomas, seven dysplastic fibroadenomas, and two adenocarcinomas. BcPDE induced tumors rapidly, with a mean latent period of 9.7 +/- 4.0 weeks. All BcPDE-treated rats had mammary tumors. A total of 46 adenocarcinomas, as well as other tumors, were observed. In the DMSO-treated rats, mammary tumor incidence was 15%. The results of this study demonstrate that BjF-9,10-DE is more carcinogenic in the rat mammary gland than BjF-4,5-DE and that low doses of both diol epoxide metabolites of BjF are effective mammary tumorigens in female CD rats maintained on a high fat diet.

The level of pancreatic PLA2 receptor is closely associated with the proliferative state of rat uterine stromal cells

Rat uterine stromal cells (U(III)) express pancreatic type PLA2 (PLA2-I) receptor and internalize the enzyme bound to receptors. Here, we investigate the proliferating effect and alterations in binding of PLA2-I. There is a dramatic decline in PLA2-I binding in U(III) cells as they progress from a non-confluent proliferating state (40,000 sites/cell) to a confluent state (1300 sites/cell). Intracellular concentration of PLA2-I changed with the alteration in binding, suggesting that regulation in the PLA2 binding capacity may have important implications in growth control mechanisms.

Metabolic conversion and growth effects of n-6 and n-3 polyunsaturated fatty acids in the T47D breast cancer cell line

The incorporation and conversion of polyunsaturated fatty acids (PUFA) of n-3 and n-6 families were examined in the T47D breast cancer cell line in parallel with their effects on cell proliferation. In low serum-containing medium, PUFA exerted differential growth effects, depending both on their affiliation and unsaturation degree. The study of PUFA processing suggested that T47D cells are deficient in delta 6 and delta 4-desaturation activities whereas they can process to delta 5-desaturation. Thus, the PUFA growth effect on T47D cells appeared to be associated with a lack of desaturation.

Effects of dietary fat content on the metabolism of NNK and on DNA methylation induced by NNK

The available data support the concept that high-fat diets increase cytochrome P-450 activities in the liver, leading to increased rates of carcinogen metabolism and, in some instances, DNA adduct formation. Therefore we investigated whether a high-fat diet can also influence DNA methylation by the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in the lungs of rats. Male F344 rats were fed a regular AIN-76A low-fat (5% corn oil) or AIN-76A high-fat (23.5% corn oil) diet. After three weeks on this dietary regimen, the animals were injected subcutaneously once daily for four days with NNK at 0.39 mmol/kg body wt. Groups of rats were sacrificed 4 and 24 hours after the last NNK administration; livers and lungs were excised for DNA isolation. We found that the high-fat diet significantly enhanced the formation of O6-methylguanine (O6-mGua) in the rat lung four hours (p < 0.01) after the last carcinogen administration. This may, in part, account for our previous finding in regard to the enhancing effect of the high-fat diet on NNK-induced lung carcinogenesis. There was no effect on O6-mGua or 7-mGua in the rat liver at either time point. To further elucidate the enhancing effect of the high-fat diet on DNA methylation by NNK in the lung, we determined its effect on the in vitro and in vivo metabolism of NNK. The in vitro data indicated that dietary fat has no measurable effect on liver and lung microsomal mixed-function oxidase in catalyzing the metabolic activation of NNK. The results of the metabolism study of NNK in vivo appear to be consistent with the in vitro finding, in that fat had no effect on the excretion pattern of NNK or on the distribution pattern of its urinary metabolites. It is apparent that the enhancing effect of the high-fat diet on O6-mGua in the lung of rats that was measured four hours after NNK injection requires future investigations.

Dietary conjugated linoleic acid modulation of phorbol ester skin tumor promotion

The fatty acid derivative conjugated dienoic linoleate (CLA) has been shown to inhibit initiation and postinitiation stages of carcinogenesis in several experimental animal models. The goal of the present study was to determine the role of increasing levels of dietary CLA in mouse skin tumor promotion elicited by 12-O-tetradecanoylphorbol-13-acetate (TPA). Mice were fed control (no CLA) diet during initiation, then switched to diets containing 0.0%, 0.5%, 1.0%, or 1.5% (wt/wt) CLA during skin tumor promotion by TPA. Body weights of mice fed 0.5%, 1.0%, or 1.5% CLA were similar to each other but were significantly lower (p < 0.05) than weights of mice fed no CLA (0.0%) throughout promotion. A reduction in papilloma incidence was observed in mice fed 1.5% CLA from Weeks 8 to 24 compared with mice fed diets containing 0.0-1.0% CLA (p < 0.05). Twenty-four weeks after tumor promotion was begun, diets containing 1.0% and 1.5% CLA inhibited tumor yield (4.94 and 4.35 tumors/mouse, respectively) compared with diets without CLA (0.0% CLA, 6.65 tumors/mouse, p < 0.05) or 0.5% CLA (5.92 tumors/mouse, p < 0.05). These data indicate that CLA inhibits tumor promotion in a manner that is independent of its anti-initiator activity. Further studies are warranted in identifying cellular mechanisms that are likely to be involved with the antipromoter effects of CLA.