Mechanistic studies on the inhibitory action of dietary dibenzoylmethane, a beta-diketone analogue of curcumin, on 7,12-dimethylbenz[a]anthracene-induced mammary tumorigenesis

Dietary factors play important roles in the carcinogenic process. The results of epidemiological data and some laboratory animal studies indicate that certain naturally occurring and synthetic components are able to block the carcinogenic process and inhibit the development of certain cancers. Dibenzoylmethane (DBM), a curcumin-related beta-diketone analogue has been reported to exhibit a remarkable inhibitory effect on 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary tumorigenesis in Sencar mice. The present study investigated the possible mechanisms of inhibitory action of DBM on DMBA-induced mammary tumorigenesis in mice. The summarized results indicate that: (1) in in-vitro studies. DBM inhibited DMBA metabolism and the formation of DMBA-DNA adducts in a dose-dependent manner; (2) in the assay of competitive binding to estrogen receptors with [3H]-estradiol in vitro, DBM showed weak binding affinity; (3) in vivo, feeding of 1% DBM in the diet of immature Sencar mice for 4 -5 weeks decreased the uterine and parametrial fat pad weights, and lowered the serum estrogen and triglyceride levels. This study provides insight into the mechanisms involved in the inhibitory action of DBM in mouse mammary tumorigenesis.     

Specific stimulation by estradiol of tissue-type plasminogen activator production in 7,12-dimethylbenz[a]anthracene-induced rat mammary tumor cells.

The hormonal regulation of two plasminogen activators, tissue-type plasminogen activator (t-PA) and urokinase (u-PA), was studied both in 7,12-dimethylbenz[a]anthracene (DMBA)-induced rat mammary carcinoma and in DMBA-induced rat mammary dysplasia. t-PA activity in DMBA-mammary carcinoma was decreased markedly by oophorectomy and recovered upon estradiol administration to reach the maximum level at 12 hr. In contrast to its effect on DMBA-mammary carcinoma, estradiol had no effect on t-PA activity in DMBA-mammary dysplasia. Furthermore, DMBA-mammary carcinoma cells in primary culture displayed similar estrogen-dependency in production of t-PA, while t-PA production in DMBA-mammary dysplasia cells was not under the control of estradiol in vitro. Moreover, estrogen-stimulated production of u-PA activity was not observed in DMBA-mammary carcinoma cells or DMBA-mammary dysplasia cells both in vivo and in vitro. Taken together, these results suggest that estrogen stimulates the production of t-PA but not u-PA and that this estrogen dependency of t-PA is limited to malignant DMBA-mammary tumor cells.     

Effect of human chorionic gonadotrophin on 7,12-dimethylbenz[a]anthracene-induced DNA binding and repair synthesis by rat mammary epithelial cells

The administration of the placental hormone human chorionic gonadotrophin (HCG) to 50-day-old virgin Sprague--Dawley rats has been shown to reduce the incidence of 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary cancer. We now report from studies using rat mammary epithelial cells in culture that the anti-carcinogenic effect of HCG may be related to its effect on DNA binding of DMBA and on DNA repair. The results showed that the level of excision repair in cells derived from young virgin (YV) rats grown in the presence of HCG (10 units/ml) was 2.5-4.0 times higher than the level exhibited by control YV cells and 1.5-2.5 times over that obtained for cells from old virgin and parous rats. The effect of HCG on DMBA-DNA binding was also determined in YV cells cultured in the presence of HCG (10 units/ml). Results from this study indicated that DMBA-DNA binding was inhibited by 30-40% in HCG-treated cells as compared to control cells. DNA binding of DMBA was also determined with mammary epithelial cells from YV rats which were given subcutaneous injections of HCG (5 units/rat) 5 times per week for 4 weeks. Using this in vivo-in vitro protocol, DMBA-DNA binding was 17-51% lower in cells from HCG-treated rats than in cells derived from control saline-treated rats. These results suggest that the protective effect provided by HCG against DMBA-induced mammary tumorigenesis may be attributed to its ability to inhibit binding of the carcinogen to mammary cell DNA and to its ability to increase the level of excision repair in the cells.     

Effect of dietary polyunsaturated fat and 7,12-dimethylbenz(a)-anthracene on rat splenic natural killer cells and prostaglandin E synthesis

Summary Dietary polyunsaturated fat has been shown to stimulate mammary tumorigenesis induced in rats by 7,12-dimethylbenz(a)anthracene (DMBA). Studies were undertaken to investigate the effect of polyunsaturated fat and DMBA on splenic natural killer (NK) activity and prostaglandin E (PGE) synthesis. In a first experiment, splenic NK activity at 33, 55, 75, and 110 days of age was measured in Sprague-Dawley rats fed 0.5% low fat (LF), 5% normal fat (NF), or 20% high fat (HF) corn oil diets from 23 days of age. At 55 days of age, half of the rats from the 75 and 110 day age groups were given 5 mg DMBA. Ten days after the initiation of the diets splenic NK activity against YAC-1 lymphoma was decreased from 50% cytotoxicity in rats fed NF diet to 21% cytotoxicity in rats fed HF diet, but was not affected by LF feeding. No difference in NK activity was observed among the groups at the later time periods. DMBA had no effect on NK activity at 20 or 55 days after its administration. In a second experiment, where DMBA (15 mg/rat) was given to half of the rats at 50 days of age and NF or HF diets were started 3 days later, NK activity was 35% in rats fed NF diet and 21% in rats fed HF diet, 5 days after the diets were started. No difference in NK activity in rats fed either diet was observed at later time periods. DMBA decreased both NK activity and spleen cellularity transiently. In both experiments, PGE synthesis by spleen cells cultured for 18 h was not affected by dietary fat intake, but was slightly increased 3 days after DMBA administration. Results from these experiments suggest that the stimulation of DMBA-induced mammary tumorigenesis by polyunsaturated fat and by DMBA itself may possibly be mediated by a transient decrease in splenic NK cell activity.This work was supported by grants CA-35641, CA-33240, CA-13038 and Core Grant CA-24538 from the National Cancer Institute     

Effect of curcumin and ferulic acid on modulation of expression pattern of p53 and bcl-2 proteins in 7,12-dimethylbenz[a]anthracene-induced hamster buccal pouch carcinogenesis

The modulating effect of curcumin and ferulic acid was investigated on expression pattern of apoptosis regulatory p53 and bcl-2 proteins in oral squamous cell carcinoma (OSCC). The OSCC was induced in the buccal pouch of golden Syrian hamster by painting with 0.5% 7,12-dimethylbenz[a]anthracene (DMBA) three-times a week for 14 weeks. The expression pattern of p53 and bcl-2 proteins was analyzed by immunohistochemical staining. We noticed 100% tumor formation in hamsters painted with DMBA alone for 14 weeks. Overexpression of p53 and bcl-2 proteins was observed in the buccal mucosa of tumor-bearing hamsters. Oral administration of curcumin (80 mg/kg body wt) and ferulic acid (40 mg/kg body wt) to DMBA painted hamsters on days alternate to DMBA painting for 14 weeks completely inhibited tumor formation and down-regulated the expression pattern of p53 and bcl-2 proteins. Our results thus demonstrated the protective role of curcumin and ferulic acid on DMBA-induced abnormal expression of p53 and bcl-2 proteins in the buccal mucosa of golden Syrian hamsters.     

The formation of dihydrodiols by the chemical or enzymic oxidation of benz[a] anthracene and 7,12-dimethylbenz[a] anthracene.

When benz[a] anthracene was oxidised in a reaction mixture containing ascorbic acid, ferrous sulphate and EDTA, the non-K-region dihydrodiols, trans-1,2-dihydro-1,2-dihydroxybenz[a] anthracene and trans-3,4-dihydro-3,4-dihydroxybenz[a] anthracene together with small amounts of the 8,9- and 10,11-dihydrodiols were formed. When oxidised in a similar system, 7,12-dimethylbenz[a] anthracene yielded the K-region dihydrodiol, trans-5,6-dihydro-5,6-dihydroxy-7,12-dimethylbenz[a] anthracene and the non-K-region dihydrodiols, trans-3,4-dihydro-3,4-dihydroxy-7,12-dimethylbenz[a] anthracene, trans-8,9-dihydro-8,9-dihydroxy-7,12-dimethylbenz[a] anthracene, trans-10,11-dihydro-10,11-dihydroxy-7,12-dimethylbenz[a] anthracene and a trace of the 1,2-dihydrodiol. The structures and sterochemistry of the dihydrodiols were established by comparisons of their UV spectra and chromatographic characteristics using HPLC with those of authentic compounds or, when no authentic compounds were available, by UV, NMR and mass spectral analysis. An examination by HPLC of the dihydrodiols formed in the metabolism, by rat-liver microsomal fractions, of benz[a] anthracene and 7,12-dimethylbenz[a] anthracene was carried out. The metabolic dihydriols were identified by comparisons of their chromatographic and UV or fluorescence spectral characteristics with compounds of known structures. The principle metabolic dihydriols formed from both benz[a] anthracene and 7,12-dimethylbenz[a] anthracene were the trans-5,6- and trans-8,9-dihydrodiols. The 1,2- and 10,11-dihydrodiols were identified as minor products of the metabolism of benz [a] anthracene and the tentative identification of the trans-3,4-dihydriol as a metabolite was made from fluorescence and chromatographic data. The minor metabolic dihydriols formed from 7,12-dimethylbenz[a] anthracene were the trans-3,4-dihydrodiol and the trans-10,11-dihydriol but the trans-1,2-dihydrodiol was not detected in the present study.     

Effects of dietary corn oil and salmon oil on the oxidation of fatty acids and prostaglandin E2 in rat gastric mucosa

The investigations previously carried out by Grataroli and colleagues (1) to elucidate the relationships between dietary fatty acids, lipid composition, prostaglandin E2 production and phospholipase A2 activity in the rat gastric mucosa are, here, extended. In the present investigations, fatty acid and prostaglandin E2 catabolizing enzymes were assayed in gastric mucosa from rats fed either a low fat diet (corn oil: 4.4% w/w) (referred as control group), a corn oil-enriched diet (17%) or a salmon oil-enriched diet (12.5%) supplemented with corn oil (4.5%) (referred as groups of treated animals) for eight weeks. Peroxisomal fatty acyl-CoA beta-oxidation was induced in the treated animals whereas the activities of catalase and mitochondrial tyramine oxidase were increased and normal, respectively. Mitochondrial acyl-CoA dehydrogenations occurred at higher rates and carnitine acyltransferase activities were enhanced. In addition, the induction of peroxisomal but not mitochondrial prostaglandoyl-E2-CoA beta-oxidation could be demonstrated. Induction of peroxisomal oxidation of fatty acids and prostaglandins is suggested to contribute to the decrease of prostaglandin E2 production in the treated animals, especially those receiving the salmon oil diet, that the above mentioned authors originally reported.     

Eugenol inhibit 7,12-dimethylbenz[a]anthracene-induced genotoxicity in MCF-7 cells: Bifunctional effects on CYP1 and NAD(P)H:quinone oxidoreductase

Typically, chemopreventive agents either inhibit the cytochrome P450s (CYPs) that are essential for the metabolism of carcinogens or induce phase II detoxifying enzymes. This study examined the chemopreventive effect of eugenol on 7,12-dimethylbenz[a]anthracene (DMBA)-induced DNA damage in MCF-7 cells. Eugenol inhibited the formation of the DMBA-DNA adduct in a dose dependent manner. CYP1A1 and CYP1B1 activity, which catalyze the biotransformation of DMBA, were strongly inhibited by eugenol. Eugenol also suppressed the CYP1A induction by DMBA through decreased aryl hydrocarbon receptor activation and subsequent DNA binding. Furthermore, eugenol increased the expression and activity of NAD(P)H:quinone oxidoreductase (QR), a major detoxifying enzyme for DMBA, through NF-E2 related factor2 binding to antioxidant response element in QR gene. Therefore, eugenol has a potent protective effect against DMBA-induced genotoxicity, presumably through the suppression of the DMBA activation and the induction of its detoxification. These results suggest that eugenol has potential as a chemopreventive.     

Effects of dietary lead,fish oil,and ethoxyquin on hepatic fatty acid composition in chicks

Three experiments were conducted with day-old broiler chicks reared to 18 or 19 d of age. The objective was to examine the effects of dietary oil (cottonseed oil vs fish oil), dietary antioxidant (0 vs 75 ppm ethoxyquin), and dietary lead (0 vs 1000 ppm Pb as lead acetate trihydrate) on hepatic fatty acid composition. A 2×2 factorial arrangement was used in all experiments. In Experiment 1, the factors were oil (4% of each) and Pb. In Experiments 2 and 3, the factors were ethoxyquin and Pb in diets containing 3.5% cottonseed oil (Experiment 2) or 3.5% fish oil (Experiment 3). Hepatic fatty acid profiles were measured by gas-liquid chromatography in 10 chicks/treatment (Experiment 1) or 4 chicks/treatment (Experiments 2 and 3). Dietary oils altered the profiles, with cottonseed oil producing the higher values for linoleic acid (18∶2) and arachidonic acid (20∶4). With fish oil, in addition to the lower levels of 18∶2 and 20∶4, there were significant levels of eicosapentaenoic acid (20∶5) and docosahexaenoic acid (22∶6). Pb enhanced the levels of 20∶4, but the effect was greater with cottonseed oil diets compared with fish oil diets. The enhanced 20∶4 levels resulted in lower ratios of 18∶2/20∶4. Ethoxyquin enhanced the level of 18∶2 with the cottonseed oil diet, and of 20∶5 and 22∶6 with the fish oil diet. Ethoxyquin decreased the level of hepatic 20∶4 when fish oil was fed. The results clearly show that all three factors (oil type, Pb level, and ethoxyquin level) after hepatic fatty acid composition. Both oil source and Pb level appeared to exert an effect on the metabolic conversion of 18∶2 and 20∶4. The primary effect of ethoxyquin was to enhance the levels of polyunsaturated fatty acids in liver. The data do not allow the partitioning of possible ethoxyquin effects to protection of polyunsaturated acids in feed vs protection of polyunsaturated acids in liver tissue. Use of trade names implies neither approval by the North Carolina Agricultural Research Service of products named nor criticism of products not named.     

Mutagenicity of benzo[a]pyrene 7,8-dihydrodiol and 7,12-dimethylbenz[a]anthracene 3,4-dihydrodiol in S. typhimurium mediated by microsomes from rat liver and mouse skin

The mutagenic activities of trans-7,8-dihydro-7,8-dihydroxybenzo[a]-pyrene (BP 7,8-diol) and of trans-3,4-dihydroxy-7,12-dimethylbenz[a]-anthracene (DMBA 3,4-diol) towards S. typhimurium TA100 were measured in assays that were carried out on a micro-scale in liquid medium in the presence of microsomal fractions prepared from mouse skin or rat liver. In the presence of an NADPH-generating system, microsomal enzymes converted both diols into mutagens that were probably the respective 'bay-region' diol-epoxides. The rate of the enzyme-catalysed conversion of the BP 7,8-diol into mutagens by microsomal preparations from mouse epidermis was similar to that occurring with microsomes from rat liver. Pretreatment of mice by the topical application of benz[a]anthracene (BA) or 7,12-dimethylbenz[a]-anthracene (DMBA) increased the mutagenic activity of BP 7,8-diol mediated by mouse skin microsomal preparations by 2-fold and this was paralleled by a 4-fold increase in epidermal aryl hydrocarbon (benzo[a]pyrene) hydroxylase (AHH) activity. The results are discussed in relation to the high susceptibility of mouse skin to polycyclic aromatic hydrocarbon (PAH) carcinogenesis.     

Metabolism of 7,12-dimethylbenz[a]anthracene and its methyl-hydroxylated metabolites: formation of phenolic metabolites at the 2-positions.

The 1- and 2-positions of 7,12-dimethylbenz[a]anthracene (DMBA) were thought not to be involved in biotransformation to 1,2-epoxide and 1,2-dihydrodiol because of steric hindrance from the 12-methyl group (Biochem. Biophys. Res. Commun. $\text{85}$: 357–362, 1978). However, we have identified four 2-phenols as rat liver microsomal metabolites of DMBA and its methyl-hydroxylated metabolites, 7-hydroxymethyl-12-methylbenz[a]anthracene, 7-methyl-12-hydroxymethylbenz[a]-anthracene, and 7,12-dihydroxymethylbenz[a]anthracene. Our findings suggest that neither the 12-methyl group nor the 12-hydroxymethyl group blocks the microsomal oxygenations of the 1,2 positions of DMBA or its methyl-hydroxylated derivatives. The 2-phenols may be formed as nonenzymatic rearrangement products of the 1,2-epoxide intermediates, although their formations by a direct hydroxylation mechanism cannot be ruled out.     

Differences between products of binding of 7,12-dimethylbenz[a]anthracene to DNA in mouse skin and in a rat liver microsomal system.

Hydrocarbon-deoxyribonucleoside products from the DNA of mouse skin exposed $\text{in vivo}$ to 7,12-dimethylbenz[a]anthracene are chromatographically the same as the products formed in mouse embryo cell cultures. These products, which are known to arise through the generation of a diol-epoxide in the 1,2,3,4-ring of the hydrocarbon, are chromatographically separable from products that result from reaction of the K-region oxide of this hydrocarbon with DNA. However, when 7,12-dimethylbenz[a]anthracene is bound to DNA in the presence of a microsomal system analogous to those used in various carcinogen detection systems, the hydrocarbon-deoxyribonucleoside products co-chromatograph with the K-region oxide products. Differences in the profiles of metabolites formed in mouse embryo cell cultures and rat liver microsomal systems are consistent with the differences between the DNA-bound products in these two systems.     

The contribution of specific cytochromes P-450 in the metabolism of 7,12-dimethylbenz[a]anthracene in rat and human liver microsomal membranes

The role of specific cytochrome P-450 isoenzymes in the regio-selective metabolism of 7,12-dimethylbenz[a]anthracene (DMBA) has been studied in microsomal membranes from rat and human liver. An antibody inhibition study using membranes from phenobarbital-treated rats demonstrates that a member(s) of the CYP2C family accounts for up to 90% of the formation of the proximate carcinogen, DMBA-3,4-diol, and makes significant contributions to the formation of DMBA-5,6-diol and DMBA-8,9-diol. In these membranes the formation of DMBA-5,6-diol can be entirely accounted by the combined activity of members of the CYP2C and CYP2B families. The metabolism of DMBA has been investigated in human using microsomes from 10 individuals and the metabolites formed by these membranes were found to be mainly hydroxymethyl- and -diol products. The rates of formation of each metabolite show considerable interindividual variation and there was no correlation between these rates for any pairing of metabolites. The CYP content in these membranes of specific members of families 1, 2, 3 and 4 did correlate with the rates of formation of individual metabolites. Surprisingly there was no correlation between the content of CYP2C and formation of DMBA-3,4-diol but an antibody to rat CYP2C6 partially inhibited the formation of this metabolite. The results indicate that in human both inducible sub-families of CYPs, particularly of the PB-type, and constitutively expressed CYPs may be important in DMBA metabolism and that each metabolite may be produced by the combined activity of several CYP isoforms.     

Effects of prostaglandin E 2 on rat skin: inhibition of sterol ester biosynthesis and clearing of scaly lesions in essential fatty acid deficiency

Severe scaly lesions in the skin, especially in the feet and tail, of the rat were induced by feeding a diet deficient in essential fatty acids (EFA). Analysis of the fatty acids in skin lipids of these EFA-deficient rats showed a marked increase of monoenoic acids (16:1 and 18:1) and eicosatrienoic acid (20:3), with concomitant decreases of dienoic acid (18:2) and tetraenoic acid (20:4). Topical application of prostaglandin E(2) (PGE(2)) to the scaly lesions resulted in clearance of the lesions, but did not significantly alter the composition of fatty acids in the skin. Intraperitoneal injection of PGE(2) had no observable effect on the skin lesions. Furthermore, incubation of skin specimens from the EFA-deficient rats with (14)C-labeled glucose showed a 4-5-fold increase of incorporation of glucose carbon into lipid fractions, particularly the sterol esters, and a 3-4-fold increase in pentose cycle activity. Addition of PGE(2) to the incubation mixture resulted in approximately 70% inhibition of sterol ester biosynthesis by skin of the EFA-deficient rats. These results suggest that the effects of PGE(2) in clearing the scales may be associated with its inhibitory effect on abnormal sterol esterification in the skin of the EFA-deficient rats.     

Partial replacement of dietary fish oil with blends of vegetable oils (rapeseed, linseed and palm oils) in diets for European sea bass (Dicentrarchus labrax L.) over a long term growth study: effects on muscle and liver fatty acid composition and effectiveness of a fish oil finishing diet

Triplicate groups of European sea bass (Dicentrarchus labrax L.), of initial mass 5 g, were fed one of three practical type diets for 64 weeks. The three diets differed only in the added oil and were 100% fish oil (FO; diet A), 40% FO/60% vegetable oil blend (VO; diet B) where the VO blend was rapeseed oil, linseed oil and palm oil in the ratio 10/35/15 by weight and 40% FO/60% VO blend (diet C) where the ratio was 24/24/12 by weight. After final sample collection the remaining fish were switched to a 100% FO finishing diet for a further 20 weeks. After 64 weeks fish fed 60% VO diet B had significantly lower live mass and liver mass than fish fed diets A and C although SGR, FCR and length were not different between groups. There were no differences in any of the above parameters after either 14 or 20 weeks on the FO finishing diet. Fatty acid compositions of flesh were correlated to dietary fatty acids although there was selective retention of docosahexaenoic acid (22:6n-3; DHA) regardless of dietary input. Inclusion of dietary VO resulted in significantly reduced flesh levels of DHA and eicosapentaenoic acid (20:5n-3; EPA) while 18:1n-9, 18:2n-6 and 18:3n-3 were all significantly increased in fish fed the 60% VO diets. Fatty acid compositions of liver showed broadly similar changes, as a result of dietary fatty acid composition, as was seen in flesh. However, the response of flesh and liver to feeding a FO finishing diet was different. In flesh, DHA and EPA values were not restored after 14 or 20 weeks of feeding a FO finishing diet with the values in fish fed the two 60% VO diets being around 70% of the values seen in fish fed FO throughout. Conversely, and despite liver DHA and EPA levels being reduced to only 40% of the value seen in fish fed 100% FO after 64 weeks, the levels of liver DHA and EPA were not significantly different between treatments after feeding the FO finishing diet for 14 weeks. However, a 200 g portion of sea bass flesh, after feeding the experimental diets for 64 weeks followed by a FO diet for 14 weeks, contained 1.22 and 0.95 g of EPA + DHA for fish fed FO or 60% VO, respectively. Therefore, sea bass grown for most of the production cycle using diets containing 60% VO can still contribute a significant quantity of healthy n-3 HUFA to the human consumer.     

Comparative action of 1,4-phenylenebis(methylene)selenocyanate and its metabolites against 7,12-dimethylbenz[a]anthracene-DNA adduct formation in the rat and cell proliferation in rat mammary tumor cells

1,4-phenylenebis(methylene)selenocyanate (p-XSC) inhibits 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary carcinogenesis and DMBA-DNA binding in the rat mammary gland. Tetraselenocyclophane (TSC) was identified in rat feces as a metabolite of p-XSC. This led us to postulate the metabolic pathway: p-XSC-->glutathione conjugate (p-XSeSG)-->aromatic selenol (p-XSeH)-->TSC. Whether p-XSC or one of its metabolites is responsible for cancer prevention is the focus of this study. We utilized the DMBA-DNA binding assay with p-XSC as a positive control to evaluate the chemopreventive potential of p-XSC metabolites at dietary selenium levels of 10 ppm. Rats were fed AIN-76A diet supplemented with various selenium compounds for 1 week prior to the oral administration of a single dose of [3H]DMBA (5 mg per rat, specific activity 51.3 mCi/mmol). The rats were sacrificed 24 h later and DNA was isolated from the mammary fat pads. Relative levels of total binding were: [pmol/mg DNA, mean +/- S.D., n=6]; DMBA [7.2 +/- 1.6]; DMBA+p-XSC [3.5 +/- 2.7]; DMBA+p-XSeSG [2.2 +/- 1.1]; DMBA+TSC [5.6 +/- 2.9]. All selenium compounds, except TSC, significantly inhibited DMBA-DNA adduct formation; however, the difference between p-XSC and p-XSeSG was not statistically significant. The inhibition of total binding was attributed to a reduction in the formation of the three major adducts derived from bay-region diol epoxides of DMBA. On the basis of their chromatographic characteristics, these were identified as anti-diol-epoxide:deoxyguanosine, syn-diol-epoxide:deoxyadenosine, and anti-diol-epoxide:deoxyadenosine. Our results suggest that p-XSeSG, but not TSC, is the likely inhibitor of mammary cancer. Selenium levels measured by atomic absorption spectroscopy in the target organ (mammary fat pads) and in plasma following the dietary administration of selenium compounds were in the order of p-XSeSG congruent with p-XSC>TSC. These results appear to be consistent with their order of inhibitory effects on total DMBA-DNA binding. Further in vitro studies of the effect of selenium compounds on cell proliferation suggest that, depending on the dose and time point selected, p-XSC is comparable to or better than p-XSeSG; but both are more effective than TSC. Collectively, our in vivo and in vitro results indicate that p-XSC and its conjugate are better candidates than TSC for future studies on mammary cancer chemoprevention.     

Okadaic acid and dinophysistoxin-1, non-TPA-type tumor promoters, stimulate prostaglandin E2 production in rat peritoneal macrophages

Okadaic acid and dinophysistoxin-1 isolated from a black sponge, Halichondria okadai are non-12-O-tetrade-canoylphorbol 13-acetate (non-TPA)-type tumor promoters of mouse skin. Okadaic acid at concentrations of 10-100 ng/ml stimulated prostaglandin E2 production in rat peritoneal macrophages. Dinophysistoxin-1 (35-methylokadaic acid) stimulated prostaglandin E2 production as strong as okadaic acid, but okadaic acid tetramethyl ether, an inactive compound as a tumor promoter, did not. Okadaic acid at 10 ng/ml (12.4 nM) stimulated prostaglandin E2 production as strongly as TPA at 10 ng/ml (16.2 nM) 20 h after incubation. Unlike TPA-type tumor promoters, okadaic acid required a lag phase before stimulation. The duration of this lag phase was dependent on the concentration of okadaic acid. Indomethacin inhibited okadaic acid-induced preostaglandin E2 production in a dose-dependent manner, and its inhibition was more strongly observed in okadaic acid-induced prostaglandin E2 production. Cycloheximide inhibited okadaic acid-induced release of radioactivity from [3H]arachidonic acid-labeled macrophages and prostaglandin E2 production dose dependently, suggesting that protein synthesis is a prerequisite for the stimulation of arachidonic acid metabolism. These results support our idea that tumor promoters, at very low concentrations, are able to stimulate arachidonic acid metabolism in rat peritoneal macrophages.     

Effects of dietary corn oil and salmon oil on the oxidation of fatty acids and prostaglandin E2 in rat gastric mucosa

The investigations previously carried out by Grataroli and colleagues (1) to elucidate the relationships between dietary fatty acids, lipid composition, prostaglandin E2 production and phospholipase A2 activity in the rat gastric mucosa are, here, extended. In the present investigations, fatty acid and prostaglandin E2 catabolizing enzymes were assayed in gastric mucosa from rats fed either a low fat diet (corn oil: 4.4% w/w) (referred as control group), a corn oil-enriched diet (17%) or a salmon oil-enriched diet (12.5%) supplemented with corn oil (4.5%) (referred as groups of treated animals) for eight weeks.Peroxisomal fatty acyl-CoA β-oxidation was induced in the treated animals whereas the activities of catalase and mitochondrial tyramine oxidase were increased and normal, respectively. Mitochondrial acyl-CoA dehydrogenations occured at higher rates and carnitine acyltransferase activities were enhanced. In addition, the induction of peroxisomal but not mitochondrial prostaglandoyl-E2-CoA β-oxidation could be demonstrated. Induction of peroxisomal oxidation of fatty acids and prostaglandins is suggested to contribute to the decrease of prostaglandin E2 production in the treated animals, especially those receiving the salmon oil diet, that the above mentioned authors originally reported.