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

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 Non-Covalent Interactions and In Vitro Radical Scavenging Activities of the Caseinate-Galangin and Caseinate-Genistein Complexes

Non-covalent interactions and in vitro radical scavenging activities of the complexes formed by the commercial milk protein product caseinate and one of the two polyphenols (galangin and genistein) were assessed by the multi-spectroscopic techniques, molecular docking, and detection of scavenging activities against the 1,1–diphenyl-2-picryl-hydrazyl (DPPH), 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and hydroxyl radicals. The caseinate bound with the two polyphenols showed conformational changes and increased scavenging activities, compared with original caseinate. The caseinate-polyphenol binding was driven by the hydrophobic interaction and hydrogen-bonds, while hydrophobic interaction was the main binding force. Meanwhile, sodium dodecyl sulfate and urea could damage the essential hydrophobic interaction and hydrogen-bonds, respectively, and thus led to decreased apparent binding constants for the caseinate-polyphenol binding. Based on the measured values of several apparent thermodynamic parameters like ΔH, ΔS, ΔG, and donor–acceptor distance as well as the detected radical scavenging activity, galangin having more planar stereochemical structure and random B-ring rotation always had higher affinity for caseinate than genistein having location isomerism and twisted stereochemical structure, while the caseinate-galangin complex showed higher radical scavenging activity than the caseinate-genistein complex. It is thus concluded that both chemical and stereochemical structures of polyphenols are crucial to the affinity of polyphenols for protein and antioxidant activities of the protein-polyphenol complexes.

Depicting the Non-Covalent Interaction of Whey Proteins with Galangin or Genistein Using the Multi-Spectroscopic Techniques and Molecular Docking

The non-covalent interactions between a commercial whey protein isolate (WPI) and two bioactive polyphenols galangin and genistein were studied at pH 6.8 via the multi-spectroscopic assays and molecular docking. When forming these WPI-polyphenol complexes, whey proteins had changed secondary structures while hydrophobic interaction was the major driving force. Detergent sodium dodecyl sulfate destroyed the hydrophobic interaction and thus decreased apparent binding constants of the WPI-polyphenol interactions. Urea led to hydrogen-bonds breakage and protein unfolding, and therefore increased apparent binding constants. Based on the measured apparent thermodynamic parameters like ΔH, ΔS, ΔG, and donor-acceptor distance, galangin with more planar stereochemical structure and random B-ring rotation showed higher affinity for WPI than genistein with location isomerism and twisted stereochemical structure. The molecular docking results disclosed that β-lactoglobulin of higher average hydrophobicity had better affinity for the two polyphenols than α-lactalbumin of lower average hydrophobicity while β-lactoglobulin possessed very similar binding sites to the two polyphenols. It is concluded that polyphenols might have different non-covalent interactions with food proteins, depending on the crucial polyphenol structures and protein hydrophobicity.

The antioxidant activity and active sites of delphinidin and petunidin measured by DFT, in vitro chemical-based and cell-based assays

A computational DFT B3LYP method with 6-311G (d,p) basis set, the in vitro chemical-based and cellular antioxidant activity (CAA) assays were applied in this study to explain the structure-antioxidant activity relationships of delphinidin and petunidin. The compound molecular structures, spectral properties, frontier orbital energy, and transition state of delphinidin and petunidin were compared. In transition state, the result of the active site (O21-H32 and O22-H33) was consistent with the result of bond length. The frontier orbital theory results indicated that the probable antioxidant activity order was petunidin (0.09126 a.u.) > delphinidin (0.09175 a.u.), which agreed well with the cell-based antioxidant activity determined by CAA. However, the order of ABTS^•+ and DPPH radical scavenging activity was delphinidin > petunidin. Our study could help to provide a rational approach for the investigation of antioxidant activity of phytochemicals. PRACTICAL APPLICATIONS: As anthocyanins, delphinidin and petunidin with great antioxidant activity are widely found in various fruits and vegetables. However, there are many kinds of methods used to measure their antioxidant activity and the antioxidant mechanism which are not concrete and clear. Therefore, it is crucial to study the antioxidant actvity of anthocyanins utilizing the DFT method combined with in vitro chemical-based and cell-based assays. Our study could contribute not only to the elucidation of chemical mechanism of antioxidants and exploration the structural features in essence, but also to promote the further development of phytochemicals in the field of food chemistry and pharmacy.

Electrochemical and spectroscopic characteristics of p-acryloyloxybenzoyl chloride and p-acryloyloxybenzoic acid and antimicrobial activity of organic compounds

The purpose of this multidisciplinary work is to characterize title compounds, p-acryloyloxybenzoyl chloride (ABC) and p-acryloyloxybenzoic acid (ABA) by means of experimental and theoretical evidences. As experimental research, Fourier transformation-infrared spectra (in the region 400-4000 cm(-1)) and nuclear magnetic resonance (NMR) chemical shifts (with a frequency of 400 MHz) are examined for spectroscopic properties belonging to the new synthesized compounds. Moreover, the compounds are investigated for antimicrobial activity against various microorganisms (Gram-positive and Gram-negative) by means of the visual inhibition zone technique on the agar media. The experimental results observed indicate that ABA exhibits more powerful inhibitors of microorganisms due to the presence of the hydroxyl group leading to higher reactive system, one of the most striking features of the paper. As for the theoretical studies, the optimized molecular structures, vibrational frequencies, corresponding vibrational spectra interpreted with the aid of normal coordinate analysis based on scaled density functional force field, atomic charges, thermodynamic properties at different temperature, 1H NMR chemical shifts by way of density functional theory (DFT) with the standard (B3LYP) methods at 6-311G++(d,p) basis set combination for the first time. According to findings, the 1H NMR chemical shifts and vibrational frequencies are obtained to be in good agreement with the suitable experimental results. Thus, it would be more precise to say that the calculation level chosen is powerful approach for understanding in the identification of the molecules investigated. At the same time, we determine the electrochemical characteristics belonging to the samples via the simulation of translation energy (HOMO-LUMO), molecular electrostatic potential (MEP) and electrostatic potential (ESP) investigations. It is observed that the strong intra-molecular charge transfer (ICT) appears between the donor and acceptor in the both compounds (especially ABA) due to the existence of the strong electronic donating groups and effective π-π* conjugated segments with high electronic donor ability for the electrophilic attack (intermolecular interactions).

Cytotoxic, genotoxic and antigenotoxic potencies of oligorutins

Rutin has been enzymatically oligomerized by laccase from Trametes versicolor. Five fractions of oligomers were obtained from the monomers having high solubility in water, which can reach 351-times that of rutin. Cytotoxicity of rutin and oligorutin fractions was evaluated towards K562 cells. Oligorutin fractions showed a lower antiproliferative effect compared with its monomer. The genotoxic potential of rutin and oligorutin fractions was assessed, at the limit of the solubility of each molecule, using the comet test. None of the tested concentrations of either rutin or oligorutin fractions has showed a genotoxic effect. Similarly, the antigenotoxic effect of these flavonoids was tested using the same assay. The obtained results showed a higher ability of oligorutin fractions to reduce the genotoxicity induced by hydrogen peroxide compared with monomeric rutin.

A DFT STUDY ON THE ROLE OF DIFFERENT OH GROUPS IN THE RADICAL SCAVENGING PROCESS

The molecular properties of robinetin and melanoxetin which are the two naturally occurring flavonoid compounds have been studied theoretically by means of density functional theory approach (DFT) at the level of B3LYP/6-311G(d,p). The analysis of computed bond dissociation enthalpy (BDE), proton dissociation enthalpy (PDE), proton affinity (PA), electron transfer enthalpy (ETE) values for both the flavonoid compounds indicate the role of B-ring for the significant antioxidant characteristics and the instability of the A-ring. It also concerns the dominant role of BDE mechanism for antioxidant activity than PDE, PA and ETE mechanisms. Ionization potential (IP) is also found to be trustworthy in the study of antioxidant activity and the computed IP magnitudes are in agreement with the values of synthetic food additives. Further, the various molecular descriptors along with the plot of frontier molecular orbitals and Mulliken spin population analysis have been obtained and the validity of Koopmans' theorem is also verified with reference to antioxidant behavior.

Antioxidant behavior of mearnsetin and myricetin flavonoid compounds--a DFT study

The molecular characteristics of two naturally occurring flavonoid compounds mearnsetin and myricetin have been computed using density functional theory (DFT) approach with B3LYP/6-311G(d,p) level of theory. The computation and analysis of bond dissociation enthalpy magnitudes for all the OH sites for both the compounds clearly denotes the contribution of the B-ring for the antioxidant activity. The analysis has also indicated the higher values of BDE on the C5-OH radical species in both the compounds. The computed vibrational frequency analysis indicates the absence of imaginary frequency in the neutral as well as radical species of both the flavonoid compounds. The ionisation potential (IP) analysis was found to be within the range of the IP of synthetic food additives. In addition, various molecular descriptors such as electron affinity, hardness, softness, electronegativity, electrophilic index have also been calculated and the validity of Koopman's theorem is verified. The plot of frontier molecular orbital and spin density distribution analysis for neutral and the corresponding radical species for both the compounds have been computed and interpreted. The polar nature and their polarizing capacity are well established through the analysis of dipole moment and polarisability magnitudes.

Multivariate QSAR study on the antimutagenic activity of flavonoids against 3-NFA on Salmonella typhimurium TA98

A quantitative structure-activity relationship (QSAR) study of twenty flavonoid derivatives with antimutagenic activity against 3-nitrofluoranthene (3-NFA) was performed by Partial Least Squares (PLS), using Ordered Predictors Selection (OPS) algorithm for variable selection. Four descriptors (PJI2, Mor27m, G1e and R4u+) were selected and a good model (n = 19; R(2) = 0.747; SEC = 0.332; PRESS(cal) = 1.768; F((2,27)) = 23.585; Q(LOO)(2) = 0.590; SEV = 0.388; PRESS(val) = 2.858; R(pred)(2) = 0.591; SEP = 0.394; ARE(pred) = 5.230%; k = 1.005; k' = 0.990; |R(02) - R'(02)| = 0.109) was built with two latent variables describing 83.410% of the original information. Leave-N-out cross validation (LNO) and y-randomization were performed in order to confirm the robustness of the model. The topological descriptors selected indicate that the antimutagenic activity against 3-NFA depends on molecular size, shape and Sanderson electronegativity of flavonoids. The proposed model may provide a better understanding of the antimutagenic activity of flavonoids and can be used as a guidance for proposition of new chemopreventive agents.

Antioxidant mechanisms of Quercetin and Myricetin in the gas phase and in solution--a comparison and validation of semi-empirical methods

Flavonoids have long been recognized for their general health-promoting properties, of which their antioxidant activity may play an important role. In this work we have studied the properties of two flavonols, quercetin and myricetin, using semi-empirical methods in order to validate the application of the recent Parametric Model 6 and to understand the fundamental difference between the two molecules. Their geometries have been optimized and important molecular properties have been calculated. The energetic of the possible antioxidant mechanisms have also been analyzed. The two studied flavonols do not differ significantly in their molecular properties, but the antioxidant mechanisms by which they may act in solution can be rather different. Moreover, we also show that the Parametric Model 6 can produce reliable information for this type of compounds.

Antioxidant activity of the dihydrochalcones Aspalathin and Nothofagin and their corresponding flavones in relation to other Rooibos ( Aspalathus linearis ) Flavonoids, Epigallocatechin Gallate, and Trolox

The antioxidant activity of rooibos flavonoids, including the dihydrochalcones aspalathin and nothofagin and their corresponding flavone glycosides, was evaluated using the ABTS radical cation, metal chelating, and Fe(II)-induced microsomal lipid peroxidation assays. Epigallocatechin gallate (EGCG) and Trolox were used as reference standards. Optimized geometric conformers of aspalathin and nothofagin, in addition to calculated physicochemical properties, were considered to explain interaction with the microsomal membrane structure and thus relative potency of the dihydrochalcones. The most potent radical scavengers were aspalathin (IC50 = 3.33 microM) and EGCG (IC50 = 3.46 microM), followed by quercetin (IC50 = 3.60 microM) and nothofagin (IC50 = 4.04 microM). The least effective radical scavengers were isovitexin (IC50 = 1224 microM) and vitexin (IC50 > 2131 microM). Quercetin (IC50 = 17.5 microM) and EGCG (IC50 = 22.3 microM) were the most effective inhibitors of lipid peroxidation. Aspalathin (IC50 = 50.2 microM) and catechin (IC50 = 53.3 microM) displayed similar potencies. Nothofagin (IC50 = 1388 microM) was almost as ineffective as its flavone glycoside analogues.

Myricetin, quercetin, (+)-catechin and (-)-epicatechin protect against N-nitrosamines-induced DNA damage in human hepatoma cells

The aim of this study was to investigate the protective effect of myricetin, quercetin, (+)-catechin and (-)-epicatechin, against N-nitrosodibutylamine (NDBA) and N-nitrosopiperidine (NPIP)-induced DNA damage in human hepatoma cells (HepG2). DNA damage (strand breaks and oxidized purines/pyrimidines) was evaluated by the alkaline single-cell gel electrophoresis or Comet assay. (+)-Catechin at the lowest concentration (10 microM) showed the maximum reduction of DNA strand breaks (23%), the formation of endonuclease III (Endo III, 19-21%) and formamidopyrimidine-DNA glycosylase (Fpg, 28-40%) sensitive sites induced by NDBA or NPIP. (-)-Epicatechin also decreased DNA strand breaks (10 microM, 20%) and the oxidized pyrimidines/purines (33-39%) induced by NDBA or NPIP, respectively. DNA strand breaks induced by NDBA or NPIP were weakly reduced by myricetin at the lowest concentration (0.1 microM, 10-19%, respectively). Myricetin also reduced the oxidized purines (0.1 microM, 17%) and pyrimidines (0.1 microM, 15%) induced by NDBA, but not the oxidized pyrimidines induced by NPIP. Quercetin did not protect against NDBA-induced DNA damage, but it reduced the formation of Endo III and Fpg sensitive sites induced by NPIP (0.1 microM, 17-20%, respectively). In conclusion, our results indicate that (+)-catechin and (-)-epicatechin at the concentrations tested protect human derived cells against oxidative DNA damage effects of NDBA and NPIP. However, myricetin at the concentrations tested only protects human cells against oxidative DNA damage induced by NDBA and quercetin against oxidative DNA damage induced by NPIP.

In vitro investigations for the QSAR mechanism of lymphocytes apoptosis induced by substituted aromatic toxicants

The objective of this study was to assess the chemicals-induced apoptosis effects on fish lymphocytes and to use the QSAR model to interpret the relationships between apoptotic effects and chemical structures to identify the immune toxicology mechanism. By the use of a simple in vitro toxicological assay, the measured apoptotic parameter (EC50) is used in a QSAR to interpret the apoptotic effects of 25 substituted benzenes at low exposure levels. The apoptotic effects of all tested substituted aromatic chemicals with Carassius auratus lymphocytes were confirmed by DNA ladder and nucleus condensation. For both chlorobenzenes and PCBs, the EC50 values increase with increasing Cl number in the molecule, a result reflecting probably the increased p-pi conjugation of the C-Cl bonds that lowers the molecular reactivity. Furthermore, the apoptotic EC50 data were best correlated with the dipole moment (mu) and the energy of the lowest unoccupied molecular orbital (ELUMO) such that: log(1/EC50)=0.325+0.222 micro-0.163(ELUMO) (with R(2)=0.879). The dependence on the electronic ELUMO factor of the established correlation suggests that during the apoptotic process the ROS (reactive oxygen substance) produced by cells acts as a Lewis base in substituted nucleophilic reactions with toxic chemicals behaving as an electron acceptor. On the basis of the test results, the present toxicological assay offers a rapid tool for assessing the toxic effects of chemicals at low exposure levels.

Flavonoid effects on DNA oxidation at low concentrations relevant to physiological levels

Flavonoids, which are abundant in fruits and vegetables, are known to have many beneficial health effects. Antioxidant activity is likely to be a main function but has been mostly studied at high flavonoid concentrations which are not feasible at the intracellular level. In this experiment, several flavonoids (e.g., catechin, quercetin, myricetin, luteolin, morin and cyanidin) were examined at low physiologically relevant concentrations. Calf thymus DNA was treated with different flavonoids at concentrations of 0.1, 1, 10 and 100 microM using Fenton conditions to induce oxidation and several oxidative adducts including 8-hydroxy guanine (7,8-dihydro-8-oxo-2'-deoxyguanosine; 8-OH guanine) were analyzed using gas chromatography-mass spectrometry-selective ion monitoring (GC-MS-SIM). Catechin, quercetin and cyanidin inhibited 8-OH guanine formation by 92%, 33% and 45%, respectively, at low concentrations (0.1 microM). In addition catechin and quercetin showed antioxidant activities on 8-OH guanine formation over all concentrations. When the oxidative DNA adduct 4,6-diamino-5-formamidopyrimidine (fapy-adenine) was measured, however, the highest concentrations of catechin and quercetin actually increased adduct formation. These results indicate that flavonoids can act as antioxidants at low concentrations relevant to physiological levels. However measuring only one oxidative DNA adduct as a biomarker may result in misleading conclusions regarding antioxidant activities of natural products.

Effects of various plant polyphenols on bladder carcinogen benzidine-induced mutagenicity

Benzidine (Bz), a human bladder carcinogen, was strongly mutagenic to Salmonella TA102 tester strain in the Ames Salmonella microsome/mutagenicity assay in the presence of rat liver S9 mix. Various non-mutagenic plant polyphenols were included in the assay to test their inhibitory effects on the Bz-induced mutations. Coumestrol, ellagic acid (EA), (-)-epicatechin (EC), (-)-epichatechingallate (ECG), gallic acid (GA), (-)-gallocatechin (GC), plumbagin, propyl gallate (PG), taxifolin, and 2,2',4'-trihydroxychalcone were found to have a strong inhibitory effect on Bz-induced mutations. (-)-Epigallo-catechingallate (EGCG), fisetin, (-)-gallocatechingallate (GCG), and piceatannol were moderately inhibitory to the mutations; whereas, (-)-catechin, (-)-catechingallate (CG), and reseveratrol were weakly inhibitory to the mutations. (-)-Epigallocatechin (EGC) and 7,3',4'-trihydroxy isoflavon were not inhibitory to the Bz-induced mutations. Isoliquirtigenin, quercetin dihydrate, and rhein were found to be mutagenic in tester strain TA102. Benzidine mediated lipid peroxidation was conducted employing the thiobarbituric acid reactive substances (TBARS) assay using linoleic acid as a substrate. In the presence of rat liver S9 mix, Bz could cause lipid peroxidation as an outcome of production of oxygen free radicals. Incorporation of the above mentioned non-mutagenic plant polyphenols significantly inhibited benzidine mediated lipid peroxidation in a time dependent manner. These polyphenols also effectively reduced the iron mediated lipid peroxidation. Thus, it is concluded that the inhibition of oxidative mutagenicity of Bz by plant polyphenols could be due to an inhibitory effect of plant polyphenols on the bioactivating enzymes such as cytochrome P-450 and peroxidase and the chelation of iron present in the cytochrome P-450 in the S9 mix. Thus, these plant polyphenols play a significant inhibitory role on Bz-induced mutagenicity.

Antioxidative and Antigenotoxic Effects of Japanese Horse Chestnut (Aesculus turbinata) Seeds

Japanese horse chestnut seed extract (HCSE) dose-dependently inhibited the autooxidation of linoleic acid (IC(50): 0.2 mg/ml), and the inhibition was almost complete at a concentration of 1 mg/ml. The HCSE scavenged DPPH (1,1-diphenyl-2-picrylhydrazyl) radicals and superoxide anions with EC(50)s of 0.65 and 0.21 mg/ml, respectively. However, it had no effect on hydrogen peroxide. The HCSE inhibited the genotoxicities of furylfuramide, N-methyl-N-nitrosourea, methyl methanesulfonate, mitomycin C, 2-aminoanthracene and aflatoxin B1 at a concentration of 1 mg/ml or more. Total polyphenol content of the HCSE was 21 mg/g (13 mg/g-seeds). These results indicate that the Japanese horse chestnut seed is an antioxidative and antimutagenic botanical resource.

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.

Structure-Mutagenicity Study of 12 Trimethylimidazopyridine Isomers Using Orbital Energies and “Spectrum-like Representation” As Descriptors

The set of 12 trimethylimidazopyridine isomers with mutagenic potency toward two strains of Salmonella was treated in this study. Ten isomers with known mutagenic properties were taken to build the models. Fifteen molecular orbital energies, or a "spectrum-like" representation of 3D structures, were taken as descriptors. As modeling techniques the multiple linear regression and the counter propagation neural network were applied. Models were tested with the recall ability test and the leave-one-out cross-validation tests. For two isomers, which have not been synthesized yet, we report predicted values for both mutagenic potencies obtained with different models. The best models were found when unoccupied molecular orbital energies are among the descriptors.

A quantitative structure-activity relationship (QSAR) study of mutagenicity in several series of organic chemicals likely to be activated by cytochrome P450 enzymes

The results of quantitative structure-activity relationship (QSAR) studies on six series of compounds exhibiting indirect mutagenic activity are reported. These findings demonstrate the importance of frontier orbital energies and, in some cases, frontier orbital electronic populations to overall mutagenicity in diverse polyaromatic hydrocarbons, benzidines and aminobiphenyls, benzonitrofurans, nitrogenous cooked-food mutagens, benzanthracenes, and chrysenes. The correlations between structural parameters and mutagenic potency vary from R=0.81 to R=0.97, and these findings are discussed in the context of possible molecular mechanisms of mutagenicity. In particular, it is generally regarded that cytochrome P450-mediated activation of polyaromatic hydrocarbons and their amino derivatives plays an important role in mutagenic activity. In this respect, it is apparent that enzymes of the cytochrome P4501 (CYP1) family are closely associated with the metabolic activation of polyaromatic mutagens and carcinogens via the generation of reactive intermediates (usually electrophilic in nature) that attack DNA. The findings presented in this study indicate that QSAR analyses on several series of compounds are consistent with the known evidence of procarcinogen activation mechanisms, particularly for polyaromatic hydrocarbons and their heterocyclic/amino derivatives, pointing to the importance of frontier orbital energy values in particular.

Structure-activity relationships for the anti-HIV activity of flavonoids

Quantitative structure-activity relationship (QSAR) models are useful in providing a biochemical understanding of the biological activity of natural and synthetic chemicals based solely on molecular structure. One- to three-parameter multiregression equations were generated for three different groups of flavonoids to model experimental flavonoid-induced cytotoxicity and inhibition of human immunodeficiency virus I replication in lymphocyte-infected cells, using quantum chemical and geometrical parameters derived from optimized molecular structures. Both biological properties were basically dependent on electronic parameters describing charge distribution on the two fused rings of the flavonoid molecule. Atomic charges in C3 and the carbonyl carbon as well as the dipolar moment were important electronic descriptors to define the studied biological properties of flavonoids.

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.

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.