Effect of ellagic acid and 3-O-decylellagic acid on the formation of benzo[a]pyrene-derived DNA adducts in vivo and on the tumorigenicity of 3-methylcholanthrene in mice

Laboratory and clinical studies of cancer chemoprevention by antioxidants in berries

Reactive oxygen species (ROS) are a major cause of cellular injury in an increasing number of diseases, including cancer. Most ROS are created in the cell through normal cellular metabolism. They can be produced by environmental insults such as ultraviolet light and toxic chemicals, as well as by the inflammatory process. Interception of ROS or limiting their cellular effects is a major role of antioxidants. Due to their content of phenolic and flavonoid compounds, berries exhibit high antioxidant potential, exceeding that of many other foodstuffs. Through their ability to scavenge ROS and reduce oxidative DNA damage, stimulate antioxidant enzymes, inhibit carcinogen-induced DNA adduct formation and enhance DNA repair, berry compounds have been shown to inhibit mutagenesis and cancer initiation. Berry constituents also influence cellular processes associated with cancer progression including signaling pathways associated with cell proliferation, differentiation, apoptosis and angiogenesis. This review article summarizes laboratory and human studies, demonstrating the protective effects of berries and berry constituents on oxidative and other cellular processes leading to cancer development.

Polyphenols as cancer chemopreventive agents

This article summarizes available data on the chemopreventive efficacies of tea polyphenols, curcumin and ellagic acid in various model systems. Emphasis is placed upon the anticarcinogenic activity of these polyphenols and their proposed mechanism(s) of action. Tea is grown in about 30 countries and, next to water, is the most widely consumed beverage in the world. Tea is manufactured as either green, black, or oolong; black tea represents approximately 80% of tea products. Epidemiological studies, though inconclusive, suggest a protective effect of tea consumption on human cancer. Experimental studies of the antimutagenic and anticarcinogenic effects of tea have been conducted principally with green tea polyphenols (GTPs). GTPs exhibit antimutagenic activity in vitro, and they inhibit carcinogen-induced skin, lung, forestomach, esophagus, duodenum and colon tumors in rodents. In addition, GTPs inhibit TPA-induced skin tumor promotion in mice. Although several GTPs possess anticarcinogenic activity, the most active is (-)-epigallocatechin-3-gallate (EGCG), the major constituent in the GTP fraction. Several mechanisms appear to be responsible for the tumor-inhibitory properties of GTPs, including enhancement of antioxidant (glutathione peroxidase, catalase and quinone reductase) and phase II (glutathione-S-transferase) enzyme activities; inhibition of chemically induced lipid peroxidation; inhibition of irradiation- and TPA-induced epidermal ornithine decarboxylase (ODC) and cyclooxygenase activities; inhibition of protein kinase C and cellular proliferation; antiinflammatory activity; and enhancement of gap junction intercellular communication. Curcumin is the yellow coloring agent in the spice tumeric. It exhibits antimutagenic activity in the Ames Salmonella test and has anticarcinogenic activity, inhibiting chemically induced preneoplastic lesions in the breast and colon and neoplastic lesions in the skin, forestomach, duodenum and colon of rodents. In addition, curcumin inhibits TPA-induced skin tumor promotion in mice. The mechanisms for the anticarcinogenic effects of curcumin are similar to those of the GTPs. Curcumin enhances glutathione content and glutathione-S-transferase activity in liver; and it inhibits lipid peroxidation and arachidonic acid metabolism in mouse skin, protein kinase C activity in TPA-treated NIH 3T3 cells, chemically induced ODC and tyrosine protein kinase activities in rat colon, and 8-hydroxyguanosine formation in mouse fibroblasts. Ellagic acid is a polyphenol found abundantly in various fruits, nuts and vegetables. Ellagic acid is active in antimutagenesis assays, and has been shown to inhibit chemically induced cancer in the lung, liver, skin and esophagus of rodents, and TPA-induced tumor promotion in mouse skin.(ABSTRACT TRUNCATED AT 400 WORDS)

Ellagic acid protects rat embryos in culture from the embryotoxic effects of N-methyl-N-nitrosourea

Ellagic acid is a naturally occurring plant phenol that has demonstrated anticarcinogenic and antimutagenic activity in several test systems. Given the common proposed etiopathogenic processes of mutagenesis, carcinogenesis, and teratogenesis induced by genotoxic chemicals, the present study was initiated to determine whether ellagic acid would protect rat embryos in culture from the teratogenic effects of N-methyl-N-nitrosourea (MNU). Ellagic acid alone (as used in these experiments; 50 microM in DMSO) was not embryotoxic. Ellagic acid (50 microM) significantly (P less than 0.01) prevented MNU (75 microM)-induced effects including mortality (absence of heart beat), abnormal formation of the cephalic neural tube derivatives, and delayed differentiation as assessed by a morphological scoring system. These embryoprotective effects were dose responsive. Sequential treatment of embryos with ellagic acid followed by MNU in fresh media also was embryoprotective with no diminution of effect. The site at which ellagic acid interrupts the critical teratogenic events induced by MNU is apparently within the embryo and/or placenta. This model of chemical embryoprotection may be useful in determining the role of cell death and/or mutation in the teratogenic mechanism of action of methylating agents.

Antimutagenicity of ellagic acid towards the food mutagen IQ: investigation into possible mechanisms of action

The ability of the plant phenol ellagic acid to inhibit the mutagenicity of the food mutagen IQ was evaluated using Salmonella typhimurium strain TA98 in the Ames mutagenicity test. Ellagic acid caused a concentration-dependent decrease in the S-9- and microsome-mediated mutagenicity of IQ. The plant phenol did not interact directly with the IQ-derived mutagenic species and did not modify the cytosol-mediated activation of the promutagen. At the concentrations used in the mutagenicity studies, ellagic acid failed to inhibit microsomal mixed-function oxidase activity, including that mediated by the P450I family responsible for the bioactivation of IQ, despite being an essentially planar molecule as indicated by computer-graphic analysis. The inhibitory effect of ellagic acid was independent of its ability to chelate Mg2+. However, pre-incubation of ellagic acid with the bacteria, followed by removal of the plant phenol, did not completely prevent the inhibitory effect of the phenol on the mutagenicity of IQ. Intraperitoneal administration of ellagic acid to rats caused a decrease in total cytochrome P-450 levels and related activities as well as in cytosolic glutathione S-transferase activity. Finally, the possibility that the reported anticarcinogenic action of ellagic acid reflects nothing more than non-selective destruction of hepatic cytochromes P-450, and thus reduced chemical activation, is considered.

The effect of ellagic acid on xenobiotic metabolism by cytochrome P-450IIE1 and nitrosodimethylamine mutagenicity

Ellagic acid (EA) is an inhibitor of the in vitro mutagenicity of N-nitrosodimethylamine (NDMA) in Salmonella typhimurium strain TA100 using pyrazole-induced rat liver 9000 x g supernatant (S-9). In order to understand this activity, the effect of EA on the metabolic hydroxylation of 4-nitrophenol, a substrate, as is NDMA, for cytochrome P-450IIE1 was studied using pyrazole induced rat S-9 and microsomal protein. It is shown that EA has an inhibitory effect on 4-nitrophenol hydroxylase with both enzyme preparations. This effect on cytochrome P-450IIE1 may be responsible, at least in part, for the inhibition of NDMA mutagenicity by EA.

Biodistribution of ellagic acid and dose-related inhibition of lung tumorigenesis in A/J mice

Ellagic acid (EA), derived from fruit ellagitannins, is known to be antimutagenic and anticarcinogenic in various animal tumor models. In this study, EA at a dose of 4 g/kg diet inhibited multiplicity of tumors induced by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in A/J mice by 54%. This inhibition was dose related between 0.06 and 4.0 g/kg diet. In contrast, two related compounds, esculin and esculetin, had no effect on lung tumorigenesis. The biodistribution of EA was studied as a function of dose and time after gavage of EA. The levels of EA in the lung were directly proportional to the dose of EA between 0.2 and 2.0 mmol. The maximum level of EA, corresponding to 21.3 nmol/g, was observed 30 minutes after gavage with 2.0 mmol of EA/kg body wt, which corresponds to only 70 ppm of the administered dose. The levels in liver tissues were 10-fold lower and reached a maximum 30 minutes after gavage. At this interval, the blood level of EA was 1 nmol/ml. The inclusion of EA in cyclodextrin doubles the level of EA in lung tissues. These results demonstrate that EA localizes preferentially in lung tissues and confirm that EA administered orally can inhibit lung tumorigenesis.

Inhibition of benzo[a]pyrene dihydrodiol epoxide mutagenicity by synthetic analogues of ellagic acid

Dibenzo[b, d]pyran-6-one, hydroxylated and methoxylated derivatives of this ring system, and some other analogues of the natural product ellagic acid have been synthesized and examined as inhibitors of benzo[a]pyrene dihydrodiol epoxide (BPDE) mutagenicity in Salmonella typhimurium strain TA100. Some of these new compounds have inhibitory effectiveness comparable to the natural product. On the basis of our results, we suggest qualitative rules for predicting inhibitory activity of ellagic acid analogues.

Prevention of cancer: vegetables and plants

1. Results of epidemiological studies indicate that a human diet rich in vegetables may lower the incidence of cancer. 2. This preventive effect of the vegetable diet against cancer could be ascribed to lowered intake of energy (joules) and its content of vitamins and carotene. 3. The consumption of vegetables means also less meat and fats as well as increased fiber content and specific chemopreventive compounds (indoles, plant phenols) present in such a diet. 4. The supposed mechanisms of prevention may include enhanced enzymatic detoxification of harmful compounds, and inhibition of their binding to cellular DNA, their adsorption on fiber, detoxification of radical forms of carcinogens by natural antioxidants in plants and probably many other ways too.

Dietary inhibitors of mutagenesis and carcinogenesis

Dietary inhibitors of mutagenesis and carcinogenesis are of particular interest because they may be useful for human cancer prevention. Several mutagenesis inhibitors have been demonstrated to be carcinogenesis inhibitors also, e.g., ellagic acid, palmitoleic acid, and N-acetylcysteine. This means that the search for mutagenesis inhibitors may be useful for discovering anticarcinogenic agents. Many mutagenesis inhibitors have been discovered by the use of short-term assays, particularly the Ames Salmonella test. This simple in vitro system has provided opportunities to elucidate the mechanisms of inhibition. The elucidation of the mechanism may allow us to infer the possible anticarcinogenic activity of the reagent. In this chapter, inhibitors of mutagenesis and carcinogenesis that can arise as components of diet have been reviewed. Most of the inhibitors have been demonstrated to be effective against a specific class of mutagens or carcinogens. Therefore, it may be argued that these inhibitors are antagonistic only to those particular agents. Here again, understanding of the mechanisms of these inhibitions is necessary for the assessment. Dietary inhibitors reviewed in this article include: (1) as inhibitors of mutagenesis: porphyllins, fatty acids, vitamins, polyphenols, and sulfhydryl compounds, (2) as inhibitors of carcinogenesis: vitamins A, E and C, ellagic acid, sulfhydryl compounds, fats, selenium, calcium, and fiber. Further studies in this area of science appear to help establish the recipe of a healthy diet.

Disposition of the plant phenol ellagic acid in the mouse following oral administration by gavage

1. The absorption, distribution and elimination of 3H-ellagic acid, a putative antimutagen and anticarcinogen, was studied in male Swiss-Webster mice following oral administration. 2. Levels of 3H-ellagic acid were highest in blood 30 min after administration, in urine and bile 120 min post-administration, and in liver, lung and kidney 15 min after administration [corrected]. 3. Free ellagic acid and its conjugates were present in urine, bile and blood. H.p.l.c. analysis of the organic solvent extracts of urine, bile and blood indicated the presence of four metabolites in urine, two in blood and one in bile. 4. Sulphate ester, glucuronide and glutathione conjugates of ellagic acid were present in urine, bile and blood. H.p.l.c. analysis of organic solvent extracts after aryl sulphatase or beta-glucuronidase treatment showed that ellagic acid was the major component present. 5. Absorption of 3H-ellagic acid occurred mostly within two hours after oral administration. Levels in blood, bile and tissues were low and almost all of the absorbed dose was excreted in urine. 6. More than 53% of the orally administered 3H-ellagic acid remained in the gastrointestinal tract at 24 h. Approximately 19% was excreted in faeces and 22% in urine at 24 h. 7. Of the 24 h faecal radioactivity 93% was extractable into organic solvents and more than 80% of this fraction was free ellagic acid. Only one metabolite was found in faeces.