The inhibition by flavonoids of 2-amino-3-methylimidazo[4,5-f]quinoline metabolic activation to a mutagen: a structure-activity relationship study

Protective Effect of Nigella sativa and Nigella damascena Fixed Oils Against Aflatoxin Induced Mutagenicity in the Classical and Modified Ames Test

The antioxidant and mutagenic/antimutagenic activities of the fixed oils from Nigella sativa (NSO) and Nigella damascena (NDO) seeds, obtained by cold press-extraction from the cultivar samples, were comparatively investigated for the first time. The antimutagenicity test was carried out using classical and modified Ames tests. The fatty acid composition of the fixed oils was characterized by gas chromatography-mass spectrometry (GC-MS) while the quantification of thymoquinone in the fixed oils was determined by UPC² . The main components of the NSO and NDO were found to be linoleic acid, oleic acid, and palmitic acid. The results of the Ames test confirmed the safety of NSO and NDO from the viewpoint of mutagenicity. The results of the three antioxidant test methods were correlated with each other, indicating NDO as having a superior antioxidant activity, when compared to the NSO. Both NSO and NDO exhibited a significant protective effect against the mutagenicity induced by aflatoxin B1 in Salmonella typhimurium TA98 and TA100 strains. When microsomal metabolism was terminated after metabolic activation of the mycotoxin, a significant increase in antimutagenic activity was observed, suggesting that the degradation of aflatoxin B1 epoxides by these oils may be a possible antimutagenic mechanism. It is worthy to note that this is the first study to assess the mutagenicity of NSO and NDO according to the OECD 471 guideline and to investigate antimutagenicity of NDO in comparison to NSO against aflatoxin.

Development of a classification model for the antigenotoxic activity of flavonoids

Genotoxic agents are capable of causing damage to genetic material and the cumulative DNA damage causes mutations, involved in the development of various pathological conditions, including cancer. Antigenotoxic agents possess the potential to counteract these detrimental cellular modifications and may aid in preventing, delaying, or decreasing the severity of these pathological conditions. An important class of natural products for which promising antigenotoxic activities have already been shown, are the flavonoids. In this research, we investigated the quantitative structure-activity relationship (QSAR) of flavonoids and their antigenotoxic activity against benzo[a]pyrene (B[a]P) and its mutagenic metabolite B[a]P-7,8-diol-9,10-epoxide-2. Random Forest classification models were developed, which could be useful as a preliminary in silico evaluation tool, before performing in vitro or in vivo experiments. The descriptors G2S and R8s. were the most significant for predicting the antigenotoxic potential.

The mutagenic and antimutagenic activity of Sutherlandia frutescens extracts and marker compounds

BACKGROUND

Sutherlandia frutescens (L.) R. Br is endemic to Southern Africa where it has been traditionally used for cancer and diabetes. In recent times it has been marketed for its reputed (but not proven) anticancer, antidiabetic and anti-HIV properties. Little is known about the mutagenic and antimutagenic potential of extracts and common marker compounds of Sutherlandia frutescens. Therefore this study aimed to investigate the putative efficacy and possible long-term adverse effects of using this herb.

METHODS

Ethylacetate (EA) and 50% Methanol (MeOH) extracts were screened for mutagenic and antimutagenic activity using the Ames assay utilising TA97a, TA98, TA100 and TA102 in the presence and absence of metabolic activation. Four compounds, L-arginine, L-canavanine, GABA and D-pinitol known to occur in sutherlandia were also included. The total polyphenolic content of the both extracts was determined using the Folin-Ciocalteau method and FRAP and ABTS were used to determine the anti-oxidant potential of the extracts.

RESULTS

The extracts and the standards did not show any cytotoxicity except in TA97a. The EA extract exhibited antimutagenicity against all the bacterial strains at all concentrations tested. The MeOH extract showed both pro-mutagenic and antimutagenic activities with 2-acetamidofluorene and aflatoxin B1 in the presence of metabolic activation of TA98 and TA100, respectively. All compounds, except L-canavanine exhibited antimutagenic activity against all strains. L-canavanine, on the other hand showed co-mutagenicity with 9-aminoacridine on TA97a, at all test concentrations. The extracts and pure compounds exhibited their antimutagenic activity in a dose response manner. L-arginine and GABA showed an some antimutagenic response. EA extract had three times the total phenolic content (12.56 μg GE / mg) observed in the MeOH extract. There was correlation between total phenolic content, antioxidant potential and antimutagenicity.

CONCLUSION

Both extracts exhibited a protective effect, with the EA extract exhibiting greater potency. L-canavanine acted as a co-mutagen in a dose response manner without metabolic activation. It is suggested that the EA extract be priotized for future development work as it showed a better risk profile and activity.

Antimutagenic and anticlastogenic effects of Turkish Black Tea on TA98 and TA100 strains of Salmonella typhimurium (in vitro) and mice (in vivo)

CONTEXT

Black tea has been reported to have significant antimutagenic and anticarcinogenic properties associated with its polyphenols theaflavins (TF) and thearubigins (TR). Similarly, Turkish black tea (TBT) also contains a considerable amount of TF and TR.

OBJECTIVE

This study investigated the mutagenic, antimutagenic and anticlastogenic properties of TBT.

MATERIALS AND METHODS

The mutagenic and antimutagenic effects of TBT (10 to 40000 μg/plate) were investigated in vitro on Salmonella strains TA98 and TA100 with and without S9 fraction. Anticlastogenic effect was studied at concentrations of 300-1200 mg/kg TBT extract by chromosomal aberrations (CA) assay from bone marrow of mice.

RESULTS

The results of this study did not reveal any mutagenic properties of TBT. On the contrary, TBT extract exhibited antimutagenic activity at >1000 μg/plate concentrations in TA98 strain with and without S9 activation (40% inhibition with S9 and 27% without S9). In TA100 strain, the antimutagenic activity was observed at >20,000 μg/plate TBT extracts without S9 activation (28% inhibition) and at >1000 μg/plate with S9 activation (59% inhibition). A significant decrease in the percentage of aberrant cells (12.33% ± 1.27) was observed in dimethylbenz(a)anthracene (DMBA) plus highest concentration (1200 mg/kg) of TBT extract-treated group when compared to only DMBA-treated group (17.00% ± 2.28).

DISCUSSION AND CONCLUSION

Results indicated that TBT can be considered as genotoxically safe, because it did not exert any mutagenic and clastogenic effects. As a result, TBT exhibited antimutagenic effects more apparently after metabolic activation in bacterial test system and had an anticlastogenic effect in mice.

Safety evaluation of styrax liquidus from the viewpoint of genotoxicity and mutagenicity

ETHNOPHARMACOLOGICAL RELEVANCE

Styrax liquidus is a resinous exudate (balsam) obtained from the wounded trunk of the Liquidambar orientalis Mill. (Hamamelidaceae). Styrax has been used for treatment of various ailments in Turkish folk medicine such as skin problems, peptic ulcers, nocturnal enuresis, parasitic infections, antiseptic or as expectorant.

AIM OF STUDY

In spite of frequent use of styrax in Turkish folk medicine as well as once as a stabilizer in perfumery industry, negative reports have been noticed by the international authority for restriction its use based on some limited evidences from an in vitro study. The aim of the present study was to evaluate the genotoxic and cytotoxic potential of styrax and its ethanolic extract using in vivo and in vitro assays, as well as an antimutagenic assay and also to determine its phenolic constituents with chromatographic analysis.

MATERIALS AND METHODS

In vitro mutagenicity and antimutagenicity of styrax and its ethanolic extract were evaluated by Ames test performed on Salmonella TA98 and TA100 strains with and without metabolic activation (10- 30,000µg/plate). The genotoxicity was also studied in vivo by chromosomal aberrations assay on bone marrow of Balb C mice with different its concentrations (500-2000mg/kg body weight). Cytotoxicity has been evaluated by the MTT assay using L929 cell line. Its phenolic constituents were determined by HPLC analysis.

RESULTS

Genotoxicological investigations of styrax or its ethanolic extract showed that none of the tested concentrations induced a significant increase in the revertant number of TA98 and TA100 strains with or without metabolic activation, indicating no mutagenicity to the tested strains. Also results indicated that up to 2000mg/kg body weight, styrax is not genotoxic in mammalian bone marrow chromosome aberration test in vivo. In cytotoxicity study, the IC₅₀ values of styrax and its ethanolic extract were found to be 50.22±1.80 and 59.69±11.77µg/mL, respectively. Among the studied reference standards the major phenolic acids in styrax balsam was found to be p-coumaric acid (2.95mg/g), while in its ethanolic extract not only p-coumaric acid (11.46mg/g), but also gallic acid (1.60mg/g) were found to the main components.

CONCLUSION

The findings of the present study provide scientific basis to the safety of styrax from the viewpoint of genotoxicity risk, and in fact, it was found to be beneficial against genotoxicity.

In vitro antioxidant, anti-diabetic and antilipemic potentials of quercetagetin extracted from marigold (Tagetes erecta L.) inflorescence residues

Quercetagetin, the major flavonoid in marigold (Tagetes erecta L.) inflorescence residues was extracted and purified. The content of quercetagetin after the purification was 89.91 ± 0.26 %. The in vitro antioxidant activity of quercetagetin and its potential in controlling diabetes mellitus and obesity were investigated and compared to quercetin and rutin. The 50 % inhibitory concentration (IC50) values of quercetagetin on scavenging 1, 1-diphenyl-2-picrylhydrazyl (DPPH), 2,2-azinobis-(3-ethylbenzothiazolin-6-sulfonic acid) (ABTS) and hydroxyl radicals were 27.12 ± 1.31 μmol/L, 12.16 ± 0.56 μmol/L and 1833.97 ± 6.66 μmol/L, respectively. The IC50 values of quercetagetin on α-glucosidase, α-amylase and pancreatic lipase were 180.11 ± 3.68 μmol/L, 137.71 ± 3.55 μmol/L and 2327.58 ± 12.37 μmol/L, respectively. These results indicated that quercetagetin exhibited strong in vitro antioxidant, anti-diabetic and antilipemic activities. Lineweaver-Burk plots analysis elucidated that quercetagetin inhibited α-glucosidase and α-amylase non-competitively, while its inhibition against pancreatic lipase was involved in a mixed-type pattern. Moreover, strong correlations were found between ABTS(·+)/DPPH(·) scavenging activities and lipase inhibitory activity (R (2) > 0.90), as well as ·OH scavenging activity and α-amylase inhibitory activity (R (2) = 0.8967).

Molecular structure, FT-IR, NBO, HOMO and LUMO, MEP and first order hyperpolarizability of (2E)-1-(2,4-Dichlorophenyl)-3-(3,4,5-trimethoxyphenyl)prop-2-en-1-one by HF and density functional methods

(2E)-1-(2,4-Dichlorophenyl)-3-(3,4,5-trimethoxyphenyl)prop-2-en-1-one is synthesized by using 2,4-dichloroacetophenone and 3,4,5-trimethoxybenzaldehyde in ethanol. The structure of the compound was confirmed by IR and single crystal X-ray diffraction studies. FT-IR spectrum of (2E)-1-(2,4-dichloro-phenyl)-3-(3,4,5-trimethoxyphenyl)prop-2-en-1-one was recorded and analyzed. The crystal structure is also described. The vibrational wavenumbers were computed using HF and DFT methods and are assigned with the help of potential energy distribution method. The first hyperpolarizability and infrared intensities are also reported. The geometrical parameters of the title compound obtained from XRD studies are in agreement with the calculated (DFT) values. The stability of the molecule arising from hyper-conjugative interaction and charge delocalization has been analyzed using NBO analysis. The HOMO and LUMO analysis are used to determine the charge transfer within the molecule. MEP was performed by the DFT method. From the MEP map of the title molecule, negative region is mainly localized over the electronegative oxygen atoms, in the carbonyl group and the oxygen atom O4 of the methoxy group and the maximum positive region is localized on the phenyl rings.

Estrogenic and chemopreventive activities of xanthones and flavones of Syngonanthus (Eriocaulaceae)

The possible benefits of some bioactive flavones and xanthones present in plants of the genus Syngonanthus prompted us to screen them for estrogenic activity. However, scientific research has shown that such substances may have undesirable properties, such as mutagenicity, carcinogenicity and toxicity, which restrict their use as therapeutic agents. Hence, the aim of this study was to assess the estrogenicity and mutagenic and antimutagenic properties. We used recombinant yeast assay (RYA), with the strain BY4741 of Saccharomyces cerevisiae, and Ames test, with strains TA100, TA98, TA97a and TA102 of Salmonella typhimirium, to evaluate estrogenicity, mutagenicity and antimutagenicity of methanolic extracts of Syngonanthus dealbatus (S.d.), Syngonanthus macrolepsis (S.m.), Syngonanthus nitens (S.n.) and Syngonanthus suberosus (S.s.), and of 9 compounds isolated from them (1=luteolin, 2=mix of A-1,3,6-trihydroxy-2-methoxyxanthone and B-1,3,6-trihydroxy-2,5-dimethoxyxanthone, 3=1,5,7-trihydroxy-3,6-dimethoxyxanthone, 4=1,3,6,8-tetrahydroxy-2,5-dimethoxyxanthone, 5=1,3,6,8-tetrahydroxy-5-methoxyxanthone, 6=7-methoxyluteolin-8-C-β-glucopyranoside, 7=7-methoxyluteolin-6-C-β-glucopyranoside, 8=7,3'-dimethoxyluteolin-6-C-β-glucopyranoside and 9=6-hydroxyluteolin). The results indicated the estrogenic potential of the S. nitens methanol extract and four of its isolated xanthones, which exhibited, respectively, 14.74±1.63 nM; 19.54±6.61; 7.20±0.37; 6.71±1.02 e 10.01±4.26 nM of estradiol-equivalents (EEQ). None of the extracts or isolated compounds showed mutagenicity in any of the test strains and all of them showed antimutagenic potential, in particular preventing mutations caused by aflatoxin B1 (AFB1) and benzo[a]pyrene (B[a]P). The results show that the xanthones, only isolated from the methanol extract of S. nitens capitula, probably were the responsible for its estrogenic activity and could be useful as phytoestrogens, providing a new opportunity to develop hormonal agents. In addition, flavones and xanthones could also be used as a new antimutagenic agent. Since, the mutagens are involved in the initiation and promotion of several human diseases, including cancer, the significance of novel bioactive phytocompounds in counteracting these pro-mutagenic and carcinogenic effects is now gaining credence.

Isorhamnetin 3-O-robinobioside from Nitraria retusa leaves enhance antioxidant and antigenotoxic activity in human chronic myelogenous leukemia cell line K562

BACKGROUND

In this report, the isorhamnetin 3-o-robinobioside and its original extract, the ethyl acetate extract, from Nitraria retusa leaves, were evaluated for their ability to induce antioxidant and antigenotoxic effects in human chronic myelogenous leukemia cell line.

METHODS

Nitraria retusa products properties were carried out by firstly evaluating their effects against lipid peroxidation induced by H2O2, using the thiobarbituric acid reactive substances species (TBARS) assay, and proceeding to the assay of cellular antioxidant activity, then doing the comet assay.

RESULTS

The isorhamnetin 3-o-robinobioside showed a protective effect against lipid peroxidation induced by H2O2. The same natural compound and ethyl acetate extract inhibited oxidation induced by 2,2'-azobis (2-amidinopropane) dihydrochloride in human chronic myelogenous leukemia cells with respectively 50% inhibitory concentration values of 0.225 mg/ml and 0.31 mg/ml, reflecting a significant antioxidant potential. The same two products inhibited the genotoxicity induced by hydroxyl radicals in the same human cell line (by 77.77% at a concentration of 800 μg/ml and by 80.55% at a concentration of 1000 μg/ml respectively).

CONCLUSIONS

The isorhamnetin 3- o-robinobioside and its original extract, the ethyl acetate extract, from Nitraria retusa leaves, have a great antioxidant and antigenotoxic potential on human chronic myelogenous leukemia cell line K562.

Evaluation of antioxidant and antigenotoxic activity of two flavonoids from Rhamnus alaternus L. (Rhamnaceae): kaempferol 3-O-β-isorhamninoside and rhamnocitrin 3-O-β-isorhamninoside

The antioxidant activity of kaempferol 3-O-β-isorhamninoside (K3O-ir) and rhamnocitrin 3-O-β-isorhamninoside (R3O-ir), isolated from the leaves of Rhamnus alaternus L., was determined by the ability of each compound to inhibit NBT photoreduction and to scavenge the free radical ABTS(+)(.). Genotoxic and antigenotoxic activities were assessed using the SOS chromotest. At a concentration of 150 μg/assay the two compounds showed the most potent inhibitory activity against superoxide anion by respectively 80.4% and 85.6%. K3O-ir was a very potent radical scavenger with an IC(50) value of 18.75 μg/ml. Moreover, these two compounds exhibit an inhibitory activity against genotoxicity induced by nitrofurantoine and aflatoxine B1 using the SOS chromotest bacterial assay system in the presence of Escherichia coli PQ37 strain. In this study, we have also evaluated correlation between antigenotoxic and antioxidant effects of K3O-ir and R3O-ir. The highest correlation was showed with R3O-ir (r=0.999).

New hypotheses for the health-protective mechanisms of whole-grain cereals: what is beyond fibre? Nutr Res Rev. 2010;23:65-134. [PMID: 20565994 DOI: 10.1017/s0954422410000041]

Epidemiological studies have clearly shown that whole-grain cereals can protect against obesity, diabetes, CVD and cancers. The specific effects of food structure (increased satiety, reduced transit time and glycaemic response), fibre (improved faecal bulking and satiety, viscosity and SCFA production, and/or reduced glycaemic response) and Mg (better glycaemic homeostasis through increased insulin secretion), together with the antioxidant and anti-carcinogenic properties of numerous bioactive compounds, especially those in the bran and germ (minerals, trace elements, vitamins, carotenoids, polyphenols and alkylresorcinols), are today well-recognised mechanisms in this protection. Recent findings, the exhaustive listing of bioactive compounds found in whole-grain wheat, their content in whole-grain, bran and germ fractions and their estimated bioavailability, have led to new hypotheses. The involvement of polyphenols in cell signalling and gene regulation, and of sulfur compounds, lignin and phytic acid should be considered in antioxidant protection. Whole-grain wheat is also a rich source of methyl donors and lipotropes (methionine, betaine, choline, inositol and folates) that may be involved in cardiovascular and/or hepatic protection, lipid metabolism and DNA methylation. Potential protective effects of bound phenolic acids within the colon, of the B-complex vitamins on the nervous system and mental health, of oligosaccharides as prebiotics, of compounds associated with skeleton health, and of other compounds such as alpha-linolenic acid, policosanol, melatonin, phytosterols and para-aminobenzoic acid also deserve to be studied in more depth. Finally, benefits of nutrigenomics to study complex physiological effects of the 'whole-grain package', and the most promising ways for improving the nutritional quality of cereal products are discussed.

Phytochemical, antibacterial, antiproliferative, and antioxidant potentials and DNA damage-protecting activity of Acacia salicina extracts

The extract enriched in total oligomer flavonoids (TOF), and the aqueous, methanol, and ethyl acetate extracts of Acacia salicina were investigated for their polyphenolic compound content, antioxidative activity in the nitro blue tetrazolium/riboflavin assay system, antibacterial activity against Gram-positive and Gram-negative bacterial reference strains, antigenotoxic activity tested with the Ames assay, and cytotoxic activity against the K562 human chronic myelogenous leukemia cell line and L1210 leukemia murine cells. TOF extract was effective at inhibiting nitro blue tetrazolium reduction by superoxide radical in a nonenzymatic O(2)(*-)-generating system. Significant activity against bacterial reference strains Staphylococcus aureus, Enterococcus faecalis, Salmonella enteritidis, and Salmonella typhimurium was shown with all the tested extracts. These extracts significantly decreased the genotoxicity induced by sodium azide and 4-nitro-o-phenylenediamine. A pronounced cytotoxic effect on both leukemia cell lines was detected in TOF, methanolic and ethyl acetate extracts. The antioxidant, antimicrobial, antigenotoxic, and cytotoxic activities exhibited by A. salicina depended on the chemical composition of the tested extracts.

Absence of antimutagenicity of Cochlospermum regium (Mart. and Schr.) Pilger 1924 by micronucleus test in mice

Cochlospermum regium (Mart. and Schr.) Pilger, popularly known as "algodãozinho do campo", is a medicinal plant that grows in the Cerrado of Brazil. This plant has been used in traditional medicine against various diseases such as leucorrhoea, gastritis and ulcers. It has also been effective in treating skin problems like pimples, boils and blotches. In the present study, the in vivo antimutagenicity of aqueous extract of C. regium was evaluated. The Micronucleus Test was performed in polychromatic erythrocytes from Swiss male mice treated with one of the four doses of extract of the plant (19, 38, 76 and 114 mg.kg-1 body weight), administered by intraperitonial injection (i.p.) simultaneously with cyclophosphamide (24 mg.kg-1 b.w.) or mitomycin C (4 mg.kg-1 b.w.). The cytotoxicity was evaluated by polychromatic and normochromatic erythrocytes ratio (PCE/NCE). The results showed no significant reduction of the micronucleated polychromatic erythrocytes frequency (P > 0.05). In conclusion, the data indicate that C. regium roots aqueous extract, for the conditions used, did not exhibit the antimutagenic effect.

The antimutagenic activity of the major flavonoids of rooibos (Aspalathus linearis): some dose-response effects on mutagen activation-flavonoid interactions

The antimutagenic properties of the most prevalent flavonoids in rooibos (Aspalathus linearis) were compared in the Salmonella typhimurium mutagenicity assay using tester strains TA98 and TA100 with, respectively, 2-acetamido-fluorene (2-AAF) and aflatoxin B(1) (AFB(1)) as mutagens in the presence of metabolic activation. The flavonoids included the dihydrochalcones aspalathin and nothofagin and their flavone analogues, orientin and isoorientin, and vitexin and isovitexin, respectively, as well as luteolin, chrysoeriol, (+)-catechin, quercetin, isoquercitrin, hyperoside and rutin. Flavonoid-mutagen interactions ranged from antimutagenic, comutagenic and promutagenic to mutagenic, while dose-response effects were mutagen-specific and ranged from typical to atypical including biphasic and threshold effects. Aspalathin and nothofagin and their structural flavonoid analogues displayed moderate antimutagenic properties while luteolin and to some extent, chrysoeriol, showed activities comparable to those of the green tea flavonoid (-) epigallocatechin gallate (EGCG). Apart from their mutagenic and promutagenic properties, quercetin and isoquercitrin exhibited concentration-dependent comutagenic and/or antimutagenic effects against 2-AAF- and AFB(1)-induced mutagenesis. Different structural parameters known to affect the antimutagenic properties of flavonoids include their hydrophilic or lipophilic nature due to the extent of hydroxylation and O-methylation, glycosylation on the A and B rings, the C4-keto group and the C2-C3 double bond. The C ring does not appear to be a prerequisite when comparing for the antimutagenic activity of the dihydrochalcones when compared of the dihydrochalcones with the structural flavone analogues.

Polyphenols and cancer cell growth

Polyphenols constitute an important group of phytochemicals that gained increased research attention since it was found that they could affect cancer cell growth. Initial evidence came from epidemiologic studies suggesting that a diet that includes regular consumption of fruits and vegetables (rich in polyphenols) significantly reduces the risk of many cancers. In the present work we briefly review the effects of polyphenols on cancer cell fate, leading towards growth, differentiation and apoptosis. Their action can be attributed not only to their ability to act as antioxidants but also to their ability to interact with basic cellular mechanisms. Such interactions include interference with membrane and intracellular receptors, modulation of signaling cascades, interaction with the basic enzymes involved in tumor promotion and metastasis, interaction with oncogenes and oncoproteins, and, finally, direct or indirect interactions with nucleic acids and nucleoproteins. These actions involve almost the whole spectrum of basic cellular machinery--from the cell membrane to signaling cytoplasmic molecules and to the major nuclear components--and provide insights into their beneficial health effects. In addition, the actions justify the scientific interest in this class of compounds, and provide clues about their possible pharmaceutical exploitation in the field of oncology.

Antimutagenicity of Stevia pilosa and Stevia eupatoria evaluated with the Ames test

Stevia pilosa and Stevia eupatoria are plants used for various purposes in traditional medicine. In this report we studied the antimutagenic effect of methanolic extracts obtained from leaves, root, and flowers of the two species using the Ames test with and without metabolic activation. We tested the effect of the extracts on the damage induced by three mutagens with the following results: 1 - we found an inhibitory effect of both species on the mutagenicity induced by 2-aminoanthracene in the strain TA98. The best antimutagenic effect was obtained with leaves of both species and the flowers of S. eupatoria (99%), 2 - the mutations induced with N-ethyl-N'-nitro-N-nitrosoguanidine in the strain TA100 was also reduced. The flowers of S. pilosa and the root of S. eupatoria showed about 93% of inhibition, 3 - finally, the mutations induced by mitomycin-C on the strain TA102 had a reduction of 87% with the leaves of S. eupatoria. Besides, we determined the radical scavenging potential of the extracts with the DPPH method, and found a potent effect produced by all extracts, with an efficacy of more than 90%. The present study showed both antimutagenic and antioxidant potential of the tested extracts, and suggest the pertinence to confirm these effects in other models, and to accurately determine their mechanism of action.

A comparative study on the antimutagenic properties of aqueous extracts of Aspalathus linearis (rooibos), different Cyclopia spp. (honeybush) and Camellia sinensis teas

Antimutagenic activity of aqueous extracts of the South African herbal teas, Aspalathus linearis (rooibos) and Cyclopia spp. (honeybush) was compared with that of Camellia sinensis (black, oolong and green) teas in the Salmonella mutagenicity assay using aflatoxin B(1) (AFB(1)) and 2-acetylaminofluorene (2-AAF) as mutagens. The present study presents the first investigation on antimutagenic properties of C. subternata, C. genistoides and C. sessiliflora. The herbal teas demonstrated protection against both mutagens in the presence of metabolic activation, with the exception of "unfermented" (green/unoxidised) C. genistoides against 2-AAF, which either protected or enhanced mutagenesis depending on the concentration. Antimutagenic activity of "fermented" (oxidised) rooibos was significantly (P<0.05) less than that of Camellia sinensis teas against AFB(1), while for 2-AAF it was less (P<0.05) than that of black tea and similar (P>0.05) to that of oolong and green teas. Antimutagenic activity of unfermented C. intermedia and C. subternata exhibited a similar protection as fermented rooibos against AFB(1). Against 2-AAF, fermented rooibos exhibited similar protective properties than unfermented C. intermedia and C. sessiliflora. Unfermented rooibos was less effective than the C. sinensis teas and fermented rooibos, but had similar (P>0.05) antimutagenicity to that of fermented C. sessiliflora against AFB(1) and fermented C. subternata against 2-AAF. Fermented C. intermedia and C. genistoides exhibited the lowest protective effect against 2-AAF, while fermented C. intermedia exhibited the lowest protection when utilising AFB(1) as mutagen. Aspalathin and mangiferin, major polyphenols in rooibos and Cyclopia spp., respectively, exhibited weak to moderate protective effects when compared to the major green tea catechin, (-)epigallocatechin gallate (EGCG). Antimutagenic activity of selected herbal tea phenolic compounds indicated that they contribute towards (i) observed antimutagenic activity of the aqueous extracts against both mutagens and (ii) enhancement of the mutagenicity of 2-AAF by unfermented C. genistoides. Antimutagenic activity of the South African herbal teas was mutagen-specific, affected by fermentation and plant material, presumably due to changes and variation in phenolic composition.

Characterization of antimutagenic mechanism of 3-allyl-5-substituted 2-thiohydantoins against 2-amino-3-methylimidazo[4,5-f]quinoline

3-Allyl-5-substituted 2-thiohydantoins (ATH-amino acids) derived from allyl isothiocyanate and amino acids can inhibit the mutagenicity of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) in the Salmonella assay. In this report, we studied possible mechanisms for the inhibition using rat liver S9 in assays for ethoxyresorufin O-deethylase (EROD), a marker activity for cytochrome P450 1A (CYP1A), which activates heterocyclic amines, and the Salmonella assays with the direct-acting mutagen 2-hydroxyamino-3-methylimidazo[4,5-f]quinoline (N-hydroxy-IQ). Quantitative analysis of ATH-amino acids and IQ during incubation with rat liver S9 fraction by HPLC showed that ATH-amino acids could act as S9-inhibitors, thereby inhibiting metabolic activation of IQ. Among the tested ATH-amino acids, ATH-Phe, ATH-Trp, ATH-Leu and ATH-Val showed a dose-dependent inhibition of EROD activity. ATH-Gly, ATH-Glu, and ATH-Asp behaved as blocking agents toward N-hydroxy-IQ, but exhibited no inhibition of EROD activity.

Inhibitory effects of beer on heterocyclic amine-induced mutagenesis and PhIP-induced aberrant crypt foci in rat colon

Anti-mutagenic and anti-carcinogenic effects of beer on heterocyclic amine (HCA)-induced carcinogenesis were studied in vitro and in vivo. Four commercial beers (two pilsner-type, black, and stout) showed inhibitory effects against five HCAs, 2-amino-3,8-dimethylimidazo [4,5-f]quinoxaline (MeIQx), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2), 2-amino-6-methyldipyrido[1,2-a:3',2'-d]imidazole (Glu-P-1) and 2-amino-3-methylimidazo[4,5-f]-quinoline (IQ), in the Ames assay using Salmonella typhimurium TA98 in the presence of rat S9 mix. The inhibitory effects of dark-colored beers (stout and black beer) were greater than those of pilsner-type beers. Dark-colored beers suppressed CYP1A2 activity in a dose-dependent manner, suggesting that inhibition of HCA activation is partly responsible for their strong anti-mutagenic effects. Anti-mutagenic effects were also observed when the pooled human S9 mix or activated IQ was used in the assay. The micronucleus test using Chinese hamster lung CHL/IU cells showed that the addition of freeze-dried samples of pilsner-type and stout beer to the culture medium significantly reduced the number of cells with micronuclei induced with PhIP or Trp-P-2. Single-cell gel electrophoresis assay (comet assay) revealed that oral ingestion of pilsner-type and stout beers for 1 week significantly inhibited DNA damage in the liver cells of male ICR mice exposed to MeIQx (13 mg/kg, i.p.). A decrease in the formation of DNA adducts was also observed using a 32P-postlabeling method. Male Fischer 344 rats orally received PhIP (75 mg/kg, five times a week for 2 weeks) and aberrant crypt foci (ACF) formation in the colon was analyzed after 5 weeks. The number of ACF was significantly reduced in rats fed a diet containing freeze-dried beer. These results suggest that beer inhibits the genotoxic effects of HCAs and may reduce the risk of carcinogenesis caused by food borne carcinogens.

Use of antioxidants to minimize the human health risk associated to mutagenic/carcinogenic heterocyclic amines in food

Heterocyclic amines (HAs) are mutagenic/carcinogenic compounds formed in meat during cooking. Several efforts have been made to minimize the risk associated to HA human exposure. Supplementation with antioxidants is considered a promising measure to reduce HA exposure because of their ability as inhibitors of HA formation or as blocking/suppressing agents on HA biotransformation/metabolism. The aim of this review is to present the current knowledge on the capability of synthetic and natural antioxidants to modulate HA-induced mutagenicity/carcinogenicity. Data show a general trend towards a reduction of HA formation both in model systems and in real foods as well as an effective modulation of biotransformation and metabolism. Phenolic compounds, particularly those from tea and olive oil, seem to be the most effective, although a great variability is observed because of the concentration-dependent pro- and antioxidant effects.

In vitro metabolism of genistein and tangeretin by human and murine cytochrome P450s

Recombinant cytochrome P450 (CYP) 1A2, 3A4, 2C9 or 2D6 enzymes obtained from Escherichia coli and human liver microsomes samples were used to investigate the ability of human CYP enzymes to metabolize the two dietary flavonoids, genistein and tangeretin. Analysis of the metabolic profile from incubations with genistein and human liver microsomes revealed the production of five different metabolites, of which three were obtained in sufficient amounts to allow a more detailed elucidation of the structure. One of these metabolites was identified as orobol, the 3'-hydroxylated metabolite of genistein. The remaining two metabolites were also hydroxylated metabolites as evidenced by LC/MS. Orobol was the only metabolite formed after incubation with CYP1A2. The two major product peaks after incubation of tangeretin with human microsomes were identical with 4'-hydroxy-5,6,7,8-tetramethoxyflavone and 5,6-dihydroxy-4',7,8-trimethoxyflavone, previously identified in rat urine in our laboratory. By comparison with UV spectra and LC/MS fragmentation patterns of previously obtained standards, the remaining metabolites eluting after 14, 17 and 20 min. were found to be demethylated at the 4',7-, 4',6-positions or hydroxylated at the 3'- and demethylated at the 4'-positions, respectively. Metabolism of tangeretin by recombinant CYP1A2, 3A4, 2D6 and 2C9 resulted in metabolic profiles that qualitatively were identical to those observed in the human microsomes. Inclusion of the CYP1A2 inhibitor fluvoxamine in the incubation mixture with human liver microsomes resulted in potent inhibition of tangeretin and genistein metabolism. Other isozymes-selective CYP inhibitors had only minor effects on tangeretin or genistein metabolism. Overall the presented observations suggest major involvement of CYP1A2 in the hepatic metabolism of these two flavonoids.

Diosmin pretreatment affects bioavailability of metronidazole

OBJECTIVE

To screen for inhibitory effects of diosmin on cytochrome P(450)-mediated metabolism of metronidazole in healthy volunteers.

DESIGN

Before/after non-blinded investigation conducted in healthy male volunteers.

METHODS

After an overnight fast, metronidazole (two 400-mg tablets) was administered to 12 volunteers, either alone or after a 9-day pretreatment period with a once-daily dose of diosmin 500-mg tablets under direct observation. Serum concentrations of metronidazole up to 48 h postdose and urinary concentrations of metronidazole and its two major metabolites up to 24 h postdose were measured using reversed-phase high-performance liquid chromatography.

RESULTS

Metronicazole plasma AUC((0- infinity )) and C(max) were significantly higher after diosmin pretreatment by (mean) 27% and 24%, respectively. However, time to reach peak concentration (t(max)) was not affected significantly. Urinary excretion of acid and hydroxy metabolites in urine was decreased significantly, while excretion of unchanged metronidazole was increased.

CONCLUSION

Diosmin pretreatment significantly altered the metabolism of metronidazole, as demonstrated by changes in plasma pharmacokinetics as well as by urinary recovery of both parent drug and its major metabolites. This may be caused by the inhibition of cytochrome P(450) enzymes.

Protection by beverages, fruits, vegetables, herbs, and flavonoids against genotoxicity of 2-acetylaminofluorene and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in metabolically competent V79 cells

Chinese hamster lung fibroblasts, genetically engineered for the expression of rat cytochrome P450 dependent monooxygenase 1A2 and rat sulfotransferase 1C1 (V79-rCYP1A2-rSULT1C1 cells), were utilized to check for possible protective effects of beverages of plant origin, fruits, vegetables, and spices against genotoxicity induced by 2-acetylaminofluorene (AAF) or 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). Antigenotoxic activities of juices from spinach and red beets against AAF could be monitored with similar effectivity by the HPRT-mutagenicity test (IC(50)=0.64%; 2.57%) and alkaline single cell gel electrophoresis (comet assay; IC(50)=0.12%; 0.89%) which detects DNA strand breaks and abasic sites. Applying the comet assay, genotoxicity of PhIP could, however, be demonstrated only in the presence of hydroxyurea and 1-[beta-D-arabinofuranosyl]cytosine, known inhibitors of DNA repair synthesis. As expected, AAF and PhIP were unable to induce any genotoxic effects in the parent V79 cells. Genotoxic activity of PhIP was strongly reduced in a dose-related manner by green tea and red wine, by blueberries, blackberries, red grapes, kiwi, watermelon, parsley, and spinach, while two brands of beer, coffee, black tea, rooibos tea, morellos, black-currants, plums, red beets, broccoli (raw and cooked), and chives were somewhat less active. One brand of beer was only moderately active while white wine, bananas, white grapes, and strawberries were inactive. Similarly, genotoxicity of AAF was strongly reduced by green, black, and rooibos tea, red wine, morellos, black-currants, kiwi, watermelon, and spinach while plums, red beets, and broccoli (raw) were less potent. Broccoli cooked exerted only moderate and white wine weak antigenotoxic activity. With respect to the possible mechanism(s) of inhibition of genotoxicity, benzo[a]pyrene-7,8-dihydrodiol (BaP-7,8-OH) and N-OH-PhIP were applied as substrates for the CYP1A family and for rSULT 1C1, respectively. Morellos, black-currants, and black tea strongly reduced the genotoxicity of BaP-7,8-OH, onions, rooibos tea, and red wine were less potent while red beets and spinach were inactive. On the other hand, red beets and spinach strongly inhibited the genotoxicity of N-OH-PhIP, rooibos tea was weakly active while all other items were inactive. These results are suggestive for enzyme inhibition as mechanism of protection by complex mixtures of plant origin. Taken together, our results demonstrate that protection by beverages, fruits, and vegetables against genotoxicity of heterocyclic aromatic amines may take place within metabolically competent mammalian cells as well as under the conditions of the Salmonella/reversion assay.

The biochemistry and medical significance of the flavonoids

Flavonoids are plant pigments that are synthesised from phenylalanine, generally display marvelous colors known from flower petals, mostly emit brilliant fluorescence when they are excited by UV light, and are ubiquitous to green plant cells. The flavonoids are used by botanists for taxonomical classification. They regulate plant growth by inhibition of the exocytosis of the auxin indolyl acetic acid, as well as by induction of gene expression, and they influence other biological cells in numerous ways. Flavonoids inhibit or kill many bacterial strains, inhibit important viral enzymes, such as reverse transcriptase and protease, and destroy some pathogenic protozoans. Yet, their toxicity to animal cells is low. Flavonoids are major functional components of many herbal and insect preparations for medical use, e.g., propolis (bee's glue) and honey, which have been used since ancient times. The daily intake of flavonoids with normal food, especially fruit and vegetables, is 1-2 g. Modern authorised physicians are increasing their use of pure flavonoids to treat many important common diseases, due to their proven ability to inhibit specific enzymes, to simulate some hormones and neurotransmitters, and to scavenge free radicals.

Antimutagenicity of some edible Thai plants, and a bioactive carbazole alkaloid, mahanine, isolated from Micromelum minutum

The antimutagenic activity against Trp-P-1 of methanolic extracts of 118 samples (108 species) of edible Thai plants was examined by the Ames Test. The activity was evaluated by the amount of plant extracts which suppressed 90% of the mutagenesis (ED90). Five plants, Micromelum minutum, Oroxylum indicum, Cuscuta chinensis, Azadirachta indica, and Litsea petiolata, exhibited significant activity with antimutagenic ED90 values lower than 5 microL/plate (0.1 mg of dry plant material equivalent). The activity-guided fractionation of the extract of M. minutum, which exhibited the highest antimutagenic activity in the screening, resulted in the isolation of an active principle, (+)-mahanine (1) as confirmed by its physicochemical properties. Compound 1 showed a wide variety of biological activity, including antimutagenicity against heterocyclic amines such as Trp-P-1 with an IC50 of 5.2 microM, cytotoxicity against a tumor cell line HL60 with a MIC100 of 4.0 microg/mL, and antimicrobial activity against Bacillus cereus and Staphylococcus aureus with MIC100 values of 6.25 and 12.5 microg/mL, respectively.

In vitro investigation of cytochrome P450-mediated metabolism of dietary flavonoids

Human and mouse liver microsomes and membranes isolated from Escherichia coli, which expressed cytochrome P450 (CYP) 1A2, 3A4, 2C9 or 2D6, were used to investigate CYP-mediated metabolism of five selected dietary flavonoids. In human and mouse liver microsomes kaempferol, apigenin and naringenin were hydroxylated at the 3'-position to yield their corresponding analogs quercetin, luteolin and eriodictyol, whereas hesperetin and tamarixetin were demethylated at the 4'-position to yield eriodictyol and quercetin, respectively. Microsomal flavonoid metabolism was potently inhibited by the CYP1A2 inhibitors, fluvoxamine and -naphthoflavone. Recombinant CYP1A2 was capable of metabolizing all five investigated flavonoids. CYP3A4 recombinant protein did not catalyze hesperetin demethylation, but showed similar metabolic profiles for the remaining compounds, as did human microsomes and recombinant CYP1A2, although the reaction rates in general were lower as compared to CYP1A2. CYP2C9 catalyzed the 4'-demethylation of tamarixetin, whereas CYP2D6 did not seem to play any role in the metabolism of the selected flavonoids. The major involvement in flavonoid metabolism of human CYP1A2, which mediates the formation of metabolites with different biochemical properties as compared to the parent compound and furthermore is known to be expressed very differently among individuals, raises the important question of whether individual differences in the CYP enzyme activity might affect the beneficial outcome of dietary flavonoids, rendering some individuals more or less refractory to the health-promoting potential of dietary flavonoids.

Genetic toxicity of a standardized mixture of citrus polymethoxylated flavones

Flavonoids are a ubiquitous family of phytochemicals that display a variety of biological effects, both beneficial and adverse depending on the individual compound. Certain flavonoids are genotoxic while others inhibit the genotoxicity of other mutagens. In the present studies, the mutagenicity of a mixture of polymethoxylated flavones (PMFs) purified from citrus peel oil was evaluated. The mixture consisted of nobiletin (32.5%), 3,3',4',5,6,7,8-heptamethoxyflavone (25.0%), tangeretin (14.0%), trimethylscutellarein (9.1%), sinensetin (3.9%), 5-demethyl-nobiletin (2.8%), hexa-O-methylquercetagetin (3.3%), 5-demethyl-tetramethylscutellarein (0.7%), 5-hydroxy-3,3',4',6,7,8-hexamethoxyflavone (0.7%), and a small quantity of unidentified flavonoid compounds (3.9%). In vitro addition of the PMF mixture over a concentration range that spanned four log doses (0.0005-5.0 mg/plate) did not reveal any evidence of mutagenicity in five bacterial tester strains (Salmonella typhimurium TA98, TA100, TA102, TA1535 and TA1537) either in the absence or presence of S9 activation. The PMF mixture exhibited a statistically significant increase in mutagenicity of L5178Y tk(+/-) mouse lymphoma cells at 0.05 (38.5 x 10(-6); P<0.05) and 0.1 mg/ml (61 x 10(-6); P<0.01) compared with vehicle-treated controls (mutation frequency=19.7 x 10(-6)). However, these responses were within historical values observed in negative control cultures and extremely small compared to the positive control (EMS 0.5 microl/ml; 1685.3 x 10(-6)). Furthermore, in the presence of S9 there was no indication of genetic toxicity in L5178Y tk(+/-) cells. These results demonstrate that the PMF mixture is not genotoxic in in vitro assay systems.

Antimutagenic activity against trp-P-1 of the edible Thai plant, Oroxylum indicum vent

A methanolic extract of Oroxylum indicum strongly inhibited the mutagenicity of Trp-P-1 in an Ames test. The major antimutagenic constituent was identified as baicalein with an IC50 value of 2.78+/-0.15 microM. The potent antimutagenicity of the extract was correlated with the high content (3.95+/-0.43%, dry weight) of baicalein. Baicalein acted as a desmutagen since it inhibited the N-hydroxylation of Trp-P-2.

Structural analysis of a novel antimutagenic compound, 4-Hydroxypanduratin A, and the antimutagenic activity of flavonoids in a Thai spice, fingerroot (Boesenbergia pandurata Schult.) against mutagenic heterocyclic amines

Six compounds were isolated from fresh rhizomes of fingerroot (Boesenbergia pandurata Schult.) as strong antimutagens toward 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) in Salmonella typhimurium TA98. These compounds were 2',4',6'-trihydroxychalcone (pinocembrin chalcone; 1), 2',4'-dihydroxy-6'-methoxychalcone (cardamonin; 2), 5,7-dihydroxyflavanone (pinocembrin; 3), 5-hydroxy-7-methoxyflavanone (pinostrobin; 4), (2,4,6-trihydroxyphenyl)-[3'-methyl-2'-(3' '-methylbut-2' '-enyl)-6'-phenylcyclohex-3'-enyl]methanone (5), and (2,6-dihydroxy-4-methoxyphenyl)-[3'-methyl-2'-(3' '-methylbut-2' '-enyl)-6'-phenylcyclohex-3'-enyl]methanone (panduratin A; 6). Compound 5 was a novel compound (tentatively termed 4-hydroxypanduratin A), and 1 was not previously reported in this plant, whereas 2-4 and 6 were known compounds. The antimutagenic IC(50) values of compounds 1-6 were 5.2 +/- 0.4, 5.9 +/- 0.7, 6.9 +/- 0.8, 5.3 +/- 1.0, 12.7 +/- 0.7, and 12.1 +/- 0.8 microM in the preincubation mixture, respectively. They also similarly inhibited the mutagenicity of 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). All of them strongly inhibited the N-hydroxylation of Trp-P-2. Thus, the antimutagenic effect of compounds 1-6 was mainly due to the inhibition of the first step of enzymatic activation of heterocyclic amines.

Anti-genotoxicity of galangin as a cancer chemopreventive agent candidate

Flavonoids are polyphenolic compounds that are present in plants. They have been shown to possess a variety of biological activities at non-toxic concentrations in organisms. Galangin, a member of the flavonol class of flavonoid, is present in high concentrations in medicinal plants (e.g. Alpinia officinarum) and propolis, a natural beehive product. Results from in vitro and in vivo studies indicate that galangin with anti-oxidative and free radical scavenging activities is capable of modulating enzyme activities and suppressing the genotoxicity of chemicals. These activities will be discussed in this review. Based on our review, galangin may be a promising candidate for cancer chemoprevention.

Modulation of multidrug resistance protein 1 (MRP1/ABCC1) transport and atpase activities by interaction with dietary flavonoids

The 190-kDa phosphoglycoprotein multidrug resistance protein 1 (MRP1) (ABCC1) confers resistance to a broad spectrum of anticancer drugs and also actively transports certain xenobiotics with reduced glutathione (GSH) (cotransport) as well as conjugated organic anions such as leukotriene C(4) (LTC(4)). In the present study, we have investigated a series of bioflavonoids for their ability to influence different aspects of MRP1 function. Most flavonoids inhibited MRP1-mediated LTC(4) transport in membrane vesicles and inhibition by several flavonoids was enhanced by GSH. Five of the flavonoids were competitive inhibitors of LTC(4) transport (K(i), 2.4-21 microM) in the following rank order of potency: kaempferol > apigenin (+ GSH) > quercetin > myricetin > naringenin (+ GSH). These flavonoids were less effective inhibitors of 17beta-estradiol 17beta-(D-glucuronide) transport. Moreover, their rank order of inhibitory potency for this substrate differed from that for LTC(4) transport inhibition but correlated with their relative lipophilicity. Several flavonoids, especially naringenin and apigenin, markedly stimulated GSH transport by MRP1, suggesting they may be cotransported with this tripeptide. Quercetin inhibited the ATPase activity of purified reconstituted MRP1 but stimulated vanadate-induced trapping of 8-azido-alpha-[(32)P]ADP by MRP1. In contrast, kaempferol and naringenin stimulated both MRP1 ATPase activity and trapping of ADP. In intact MRP1-overexpressing cells, quercetin reduced vincristine resistance from 8.9- to 2.2-fold, whereas kaempferol and naringenin had no effect. We conclude that dietary flavonoids may modulate the organic anion and GSH transport, ATPase, and/or drug resistance-conferring properties of MRP1. However, the activity profile of the flavonoids tested differed from one another, suggesting that at least some of these compounds may interact with different sites on the MRP1 molecule.

Role of plant polyphenols in genomic stability

Polyphenols are a large and diverse class of compounds, many of which occur naturally in a range of food plants. The flavonoids are the largest and best-studied group of these. A range of plant polyphenols are either being actively developed or currently sold as dietary supplements and/or herbal remedies. Although, these compounds play no known role in nutrition (non-nutrients), many of them have properties including antioxidant, anti-mutagenic, anti-oestrogenic, anti-carcinogenic and anti-inflammatory effects that might potentially be beneficial in preventing disease and protecting the stability of the genome. However not all polyphenols and not all actions of individual polyphenols are necessarily beneficial. Some have mutagenic and/or pro-oxidant effects, as well as interfering with essential biochemical pathways including topoisomerase enzyme activities, prostanoid biosynthesis and signal transduction. There is a very large amount of in vitro data available, but far fewer animal studies, and these are not necessarily predictive of human effects because of differences in bacterial and hepatic metabolism of polyphenols between species. Epidemiological studies suggest that high green tea consumption in the Japanese population and moderate red wine consumption in the French population may be beneficial for heart disease and cancer, and these effects may relate to specific polyphenols. A small number of adequately controlled human intervention studies suggest that some, but not all polyphenol extracts or high polyphenol diets may lead to transitory changes in the antioxidative capacity of plasma in humans. However, none of these studies have adequately considered long-term effects on DNA or the chromosome and unequivocally associated these with polyphenol uptake. Furthermore, clinical trials have required intravenously administered polyphenols at concentrations around 1400mg/m(2) before effects are seen. These plasma concentrations are unlikely to be achieved using the dietary supplements currently available. More focused human studies are necessary before recommending specific polyphenolic supplements at specific doses in the human population.

Extended quantitative structure-activity relationships for 80 aromatic and heterocyclic amines: structural, electronic, and hydropathic factors affecting mutagenic potency

The mutagenic/carcinogenic heterocyclic amines formed during the cooking of protein foods have been determined to be probable or possible human carcinogens. As part of a comprehensive study of the food mutagens, our laboratory has produced a series of quantitative structure-activity relationships (QSARs) of aromatic and heterocyclic amines, to attempt to elucidate the mechanisms of mutagenesis/carcinogenesis. Amines are genotoxically active only after activation by a series of reactions converting the parent compound to an electrophilic derivative, which is postulated to be a nitrenium ion that covalently binds to and damages DNA. An important agent in this conversion is cytochrome P450. In this report we develop a QSAR for 80 amines of diverse structure and a range of 10 orders of magnitude in mutagenic potency. New structural factors and quantum chemical ab initio and Hückel calculations are included. The results are interpreted to show that a main determinant of mutagenic potency is the extent of the aromatic pi-electron system. Small contributions are made by both the dipole moment and the calculated stability of the nitrenium ion. Multiple linear regression models account for nearly two-thirds of the variance in potency, leaving room for additional unknown factors. The role of cytochrome P450 1A in amine toxification is supported, and further theoretical and experimental research on its reaction mechanisms and modeling of its active site are proposed.

In vitro inhibition of human P450 enzymes by prenylated flavonoids from hops, Humulus lupulus

1. Several unique flavonoid compounds have recently been isolated from hops, Humulus lupulus, and their presence has been detected in beer. Their chemical structures are similar to other plant-derived compounds, many present in the human diet, that have been shown to have cancer chemopreventive properties due, in part, to inhibition of cytochrome P450 enzymes that activate carcinogens. Additionally, preliminary studies have shown these flavonoids (at 100 microM) to be inhibitory of P450-mediated activation reactions in a variety of in vitro systems. Thus, the in vitro effects of these phytochemicals on cDNA-expressed human CYP1A1, CYP1B1, CYP1A2, CYP3A4 and CYP2E1 were currently examined by the use of diagnostic substrates and the carcinogen AFB1. 2. At 10 microM, the prenylated chalcone, xanthohumol (XN), almost completely inhibited the 7-ethoxyresorufin O-deethylase (EROD) activity of CYP1A1. At the same concentration, other hop flavonoids decreased the EROD activity by 90.8-27.0%. 3. At 10 microM, XN completely eliminated CYP1B1 EROD activity, whereas the other hop flavonoids showed varying degrees of inhibitory action ranging from 99.3 to 1.8%. 4. In contrast, the most effective inhibitors of CYP1A2 acetanilide 4-hydroxylase activity were the two prenylated flavonoids, 8-prenylnaringenin (8PN) and isoxanthohumol (IX), which produced > 90% inhibition when added at concentrations of 10 microM. 5. CYP1A2 metabolism of the carcinogen AFB1 was also inhibited by IX and 8PN as shown by decreased appearance of dihydrodiols and AFM1 as analysed by hplc. IX and 8PN also decreased covalent binding of radiolabelled AFB1 to microsomal protein in a concomitant manner. 6. XN, IX and 8PN, however, were poor inhibitors of CYP2E1 and CYP3A4 as measured by their effect on chorzoxazone hydroxylase and nifedipine oxidase activities respectively. 7. These results suggest that the hop flavonoids are potent and selective inhibitors of human cytochrome P450 and warrant further in vivo investigations.

Quantitative structure-activity relationship of flavonoids for inhibition of heterocyclic amine mutagenicity

The mutagenic/carcinogenic heterocyclic amines formed during the cooking of protein foods have been determined to be a potential risk to human health. Therefore, mitigation measures are beginning to be studied. A recent finding is that the induction of mutation in Salmonella by these amines can be inhibited by the addition of flavonoids to the assay. This study combines data on the inhibitory process with structural, ab initio quantum chemical, hydropathic, and antioxidant factors to develop a quantitative structure-activity relationship (QSAR) database and statistical analysis. For 39 diverse flavonoids the inhibitory potency varied approximately 100-fold. Three predictive variables, in order of decreasing contribution to variance, are: (1) a large dipole moment; (2) after geometric minimization of energy, a small departure from planarity (i.e., small dihedral angle between the benzopyran nucleus and the attached phenyl ring), and a low rotational energy barrier to achieving planarity; and (3) fewer hydroxyl groups on the phenyl ring. However, these variables account for less than half of the variance in inhibitory potency of the flavonoids. Frontier orbital energies and antioxidant or radical scavenging properties showed little or no relationship to potency. We conclude that interference by the flavonoids with cytochrome P450 activation of the promutagens is the probable mechanism for inhibition of mutagenesis, and suggest avenues for further research. Environ. Mol. Mutagen. 35:279-299, 2000 Published 2000 Wiley-Liss, Inc.

Antimutagenic effects and possible mechanisms of action of vitamins and related compounds against genotoxic heterocyclic amines from cooked food

Possible antimutagenic activity of 26 vitamins and related compounds - ascorbic acid, beta-carotene, cyanocobalamin, folic acid, nicotinic acid, nicotinamide, pantothenic acid, pyridoxale, pyridoxamine, pyridoxine, retinal, retinol, retinoic acid, retinyl acetate, retinyl palmitate, riboflavin, riboflavin 5'-phosphate, flavin adenine dinucleotide (FAD), alpha-tocopherol, alpha-tocopherol acetate, vitamins K(1), K(3), K(4), 1, 4-naphthoquinone, and coenzyme Q(10) - was tested against six heterocyclic amine (HCA) mutagens, i.e., 2-amino-3-methyl-imidazo[4, 5-f]quinoline (IQ), 2-amino-3,4-dimethyl-imidazo[4,5-f]quinoline (MeIQ), 2-amino-3,8-dimethyl-imidazo[4,5-f]quinoxaline (MeIQx), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 2-amino-6-methyl-dipyrido[1,2-a:3',2'-d]imidazole (Glu-P-1) and 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) in the Salmonella/reversion assay using tester strains Salmonella typhimurium TA 98 and TA 100. Retinol, retinal, riboflavin, riboflavin 5'-phosphate, FAD, vitamins K(1), K(3), K(4), 1, 4-naphthoquinone, and coenzyme Q(10) caused a concentration-dependent decrease in the mutagenicity of all six mutagens in both tester strains. Quantification of antimutagenic potencies by calculating ID(50)1000; vitamin K(1): 401-740; vitamin K(3) (menadione): 85-590; vitamin K(4): 45-313; 1,4-naphthoquinone: 170-290; coenzyme Q(10): 490-860. In general, there were no major differences between HCAs tested except in part with Trp-P-2 nor between the two tester strains. In enzyme kinetic experiments with Salmonella, retinol, vitamins K(3), and K(4) behaved as competitive inhibitors of IQ induced mutagenesis. However, at the highest concentration of menadione (200 nmol/plate) and of riboflavin 5'-phosphate (2000 nmol/plate), non-competitive inhibition was observed. At other concentrations of riboflavin 5'-phosphate and at all concentrations of FAD, meaningful interpretation of enzyme kinetics were not possible. Reduction of the activity of 7-ethoxy- and 7-methoxyresorufin-O-dealkylases with IC(50) values of 2.03-30.8 microM indicated strong inhibition of 1A1 and 1A2 dependent monooxygenases by menadione and retinol. Riboflavin 5'-phosphate and FAD were less effective (IC(50): 110-803.7 microM). Nicotinamide-adenine-dinucleotidephosphate (NADPH) cytochrome P-450 reductase was not affected by retinoids but stimulated by naphthoquinones and both riboflavin derivatives up to about 50 and 80%, respectively. Again, the mutagenic activity of N-hydroxy-2-amino-3-methyl-imidazo[4,5-f]quinoline (N-OH-IQ) in Salmonella was not suppressed by K-vitamins but marginally reduced by retinol, retinal, and FAD but distinctly by riboflavin 5'-phosphate. In various experiments designed for modulation of the mutagenic response, inhibition of metabolic activation of IQ to N-OH-IQ was found to be the only relevant mechanism of antimutagenesis of menadione while a weak contribution of an other way seemed possible for retinol and FAD.