Biomedical subjects

Costas Ioannides

Publications and source records attributed to Costas Ioannides.

At least 19 recordsLinked to original sources

PubMed2006

Modulation of gene expression and DNA-adduct formation in precision-cut liver slices exposed to polycyclic aromatic hydrocarbons of different carcinogenic potency.

Polycyclic aromatic hydrocarbons (PAHs) differ markedly in their carcinogenic potencies. Differences in transcriptomic responses upon PAH exposures might improve our current understanding of the differences in carcinogenicity, and therefore gene expression modulation by six PAHs in precision-cut rat liver slices was investigated. Gene expression modulation by benzo[a]pyrene (B[a]P), dibenzo[a,l]pyrene (DB[a,l]P), benzo[b]fluoranthene (B[b]F), fluoranthene (FA), dibenzo[a,h]anthracene (DB[a,h]A) and 1-methylphenanthrene (1-MPA) was assessed after 6- (B[a]P, DB[a,l]P) and 24-h (all compounds) exposure, using oligonucleotide arrays. DNA-adduct formation was determined using (32)P-post-labelling. The effects of PAHs on gene expression and on DNA-adduct formation were much more pronounced after 24-h exposure than after a 6-h exposure. Each compound induced gene expression changes dose-dependently and gene expression profiles were generally compound-specific. B[a]P, B[b]F and DB[a,h]A displayed comparable gene expression profiles, and so did DB[a,l]P, FA and 1-MPA. Only the carcinogenic PAHs (B[a]P, B[b]F, DB[a,l]P and DB[a,h]A) induced the oxidative stress pathway. DNA-adduct levels were: DB[a,l]P >> B[a]P > B[b]F > or = DB[a,h]A > FA > or = 1-MPA. The expression of only a few genes was found to correlate significantly with DNA-adduct formation, carcinogenic potency or Ah-receptor binding capacity (the last two taken from literature). These genes differed between the parameters. Our results indicate that PAHs generally induce a compound-specific response on gene expression and that discrimination of carcinogenic from non-carcinogenic compounds is partly feasible using this approach. Only at a specific pathway level, namely oxidative stress response, PAHs with high and low carcinogenic potency could be discriminated.

Animals↗

PubMed2006

Evaluation of the precision-cut liver and lung slice systems for the study of induction of CYP1, epoxide hydrolase and glutathione S-transferase activities.

The principal objective was to ascertain whether precision-cut tissue slices can be used to evaluate the potential of chemicals to induce CYP1, epoxide hydrolase and glutathione S-transferase activities, all being important enzymes involved in the metabolism of polycyclic aromatic hydrocarbons. Precision-cut rat liver and lung slices were incubated with a range of benzo[a]pyrene concentrations for various time periods. A rise in the O-deethylation of ethoxyresorufin was seen in both liver and lung slices exposed to benzo[a]pyrene, which was accompanied by increased CYP1A apoprotein levels. Pulmonary CYP1B1 apoprotein levels and hepatic mRNA levels were similarly enhanced. Elevated epoxide hydrolase and glutathione S-transferase activities were also observed in liver slices following incubation for 24h; similarly, a rise in apoprotein levels of both enzymes was evident, peak levels occurring at the same time point. When mRNA levels were monitored, a rise in the levels of both enzymes was seen as early as 4h after incubation, but maximum levels were attained at 24 h. In lung slices, induction of epoxide hydrolase by benzo[a]pyrene was observed after a 24-h incubation, and at a concentration of 1 microM; a rise in apoprotein levels was seen at this time point. Glutathione S-transferase activity was not inducible in lung slices by benzo[a]pyrene but a modest increase was observed in hepatic slices. Collectively, these studies confirmed CYP1A induction in rat liver slices and established that CYP1B1 expression, and epoxide hydrolase and glutathione S-transferase activities are inducible in precision-cut tissue slices.

Animals↗

PubMed2006

Stability of cytochromes P450 and phase II conjugation systems in precision-cut rat lung slices cultured up to 72 h.

The objective of the present study was to evaluate the stability of cytochrome P450 enzymes and of the conjugation enzyme systems epoxide hydrolase, glucuronosyl transferase, sulphotransferase and glutathione S-transferase in precision-cut rat lung slices incubated in RPMI media for different time periods up to 72 h. Moreover, the effect of culturing of lung slices on total glutathione levels and glutathione reductase was also investigated. Monitoring of cytochrome P450 activity was achieved using established diagnostic probes, but when activity in the lung was low the maintenance of the various enzymes in culture was determined immunologically using Western blotting. The dealkylation of pentoxyresorufin declined markedly during the first 4h of incubation but in the case of ethoxyresorufin loss of activity was more gradual and less severe. Western blot analysis revealed that the rate of decrease in cytochrome P450 apoprotein levels was isoform-specific with CYP2E1 being the most stable and CYP3A the least stable. Generally, phase II activities, especially cytosolic sulphotransferase, were relatively more stable throughout the incubation period compared with cytochromes P450. Finally, glutathione reductase activity and total glutathione levels were maintained throughout the 72 h incubation. The present studies indicate that xenobiotic-metabolising enzymes in precision-cut rat lung slices decline in culture, but the rate of loss differs and depends on the nature of the enzyme.

Animals↗

PubMed2006

Mice convert melatonin to 6-sulphatoxymelatonin.

The principal objective of this study was to establish whether mice can convert melatonin to 6-sulphatoxymelatonin (aMT6s). Precision-cut liver slices from C3H/He, C57BL/6, and BALB/c mice were incubated with melatonin, and the concentration of aMT6s in the culture media was determined using a sensitive and specific radioimmunoassay procedure. All three strains of mice generated aMT6s in a time-dependent manner; no significant strain differences were observed. When samples of the media were treated with sulphatase prior to analysis, aMT6s was not detectable. In contrast, similar treatment with beta-glucuronidase had no effect. 6-Sulphatoxymelatonin was present in the urine of both control and melatonin-treated C3H/He and C57BL6 mice. Treatment with melatonin led to a dramatic rise in the urinary levels of aMT6s in both mouse strains. Pre-treatment of the urines with sulphatase, but not beta-glucuronidase, markedly decreased the levels of aMT6s. Finally, in both strains urinary excretion of aMT6s displayed diurnal rhythmicity, peak excretion occurring during the dark hours. It may be inferred that: (a) mice can convert melatonin to aMT6s, both in vivo and in vitro, and (b) mice generate aMT6s in a rhythmic manner. Finally, the present studies confirm that determination of aMT6s rhythms in mice could provide an alternative, non-invasive, approach for assessing circadian clock function.

Animals↗

PubMed2006

Cytochrome p450 expression in the liver of food-producing animals.

A number of enzyme systems participate in the metabolism of chemicals, but undoubtedly the most important are the cytochromes P450 (CYP). It is a versatile enzyme system, capable of metabolising structurally diverse chemicals. To achieve this broad substrate specificity it exists as a superfamily of enzymes, each family being characterised by different substrate specificity; families CYP1, CYP2 and CYP3 are responsible for the metabolism of exogenous chemicals. Although our current knowledge of the expression and function of cytochromes P450 in humans and laboratory animals is extensive, little is known about this enzyme system in food-producing animals, despite its dominant role in the metabolism of veterinary drugs, and the crucial role it plays in controlling the levels of drug and other chemical residues in edible tissues and food products that humans consume, a matter of major current concern. Most studies dealing with the expression of cytochromes P450 in food-producing animals utilised substrate probes defined in rats and humans and/or antibodies raised to rat or human antigens. Such an approach can prove misleading as it assumes that orthologue proteins in other animals share the same substrate specificity and, moreover, although antibodies raised to human or rat antigens may recognise epitopes in other species, they do not constitute unequivocal proof that the detected proteins are structurally identical. Despite these drawbacks, there is substantial experimental evidence that CYP1, CYP2 and CYP3 families are expressed in food-producing animals, but their role in the metabolism of veterinary drugs and other xenobiotics has not been addressed.

Animals↗

PubMed2005

Modulation of hepatic cytochromes P450 and phase II enzymes by dietary doses of sulforaphane in rats: Implications for its chemopreventive activity.

The principal objectives of our study were to ascertain whether sulforaphane, at dietary levels of intake, modulates rat hepatic cytochrome P450 and phase II enzyme systems and to evaluate the impact of such changes in the chemopreventive activity of this isothiocyanate. Animals were exposed to sulforaphane in their drinking water for 10 days, equivalent to daily doses of 3 and 12 mg/kg. Depentylation of pentoxyresorufin decreased and was paralleled by a decline in CYP2B apoprotein levels. At the higher dose, erythromycin N-demethylase activity declined and was accompanied by a similar decrease in CYP3A2 apoprotein levels. However, sulforaphane treatment upregulated CYP1A2 levels, determined immunologically, but the dealkylations of methoxy- and ethoxyresorufin were not similarly increased. Hepatic S9 preparations from sulforaphane-treated rats were less effective than control preparations in converting IQ (2-amino-3-methylimidazo-[4,5-f]quinoline) to mutagenic intermediates in the Ames test. To clarify the underlying mechanism, in vitro studies were undertaken. In beta-naphthoflavone-treated rats, the inhibition by sulforaphane of the O-dealkylations of methoxy- and ethoxyresorufin was enhanced if the isothiocyanate was preincubated in the presence of NADPH. It may be inferred that sulforaphane induces hepatic CYP1A2 but the enzyme is not catalytically competent because of bound sulforaphane metabolite(s). Finally, sulforaphane stimulated, in a dose-dependent fashion, quinone reductase but failed to influence glutathione S-transferase, epoxide hydrolase and glucuronosyl transferase activities. It is concluded that, even at dietary doses, sulforaphane can modulate the xenobiotic-metabolising enzyme systems, shifting the balance of carcinogen metabolism toward deactivation, and this may be an important mechanism of its chemopreventive activity.

Administration, Oral↗

PubMed2004

Black tea intake modulates the excretion of urinary mutagens in rats exposed to 6-aminochrysene: induction of cytochromes P450 by 6-aminochrysene in the rat.

Rats were exposed to black tea (2.5% w/v) as their sole drinking liquid for either 1 day (short-term) or 1 month (long-term), while controls received water. After exposure, all animals received a single oral dose of 6-aminochrysene and urine was collected for 72 h. Urinary mutagenicity was determined in the Ames test using an activation system comprising hepatic cytosol from Aroclor 1254-induced rats and utilizing the Salmonella typhimurium O-acetylase overexpressing bacterial strain YG1024. Both tea treatments suppressed the urinary excretion of indirect acting mutagens; no direct acting mutagenic activity was detectable. Furthermore, both tea treatments induced hepatic CYP1A2 activity, as exemplified by the O-demethylation of methoxyresorufin, when compared with the corresponding controls; similarly, an increase in CYP1A2 apoprotein levels was observed. The O-depentylation of pentoxyresorufin was also induced by the long-term tea treatment only, but the effect was less pronounced. No significant changes were seen in glutathione S-transferase and glucuronosyl transferase activities. When rats were exposed to caffeine at a dose level corresponding to that in black tea, a marked decrease was observed in the urinary excretion of indirect acting mutagens following a single oral dose of 6-aminochrysene. It is concluded that even after short-term exposure, black tea enhances the metabolism of 6-aminochrysene and that this is probably related to the up-regulation of hepatic CYP1A2 by the caffeine present in black tea. Finally, 6-aminochrysene was a potent inducer of CYP1A1, as assessed by the O-deethylation of ethoxyresorufin and immunoblot analysis. The same treatment modestly increased glutathione S-transferase activity when assessed using 1-chloro-2,4-dinitrobenzene as the accepting substrate.

Animals↗

PubMed2004

An improved method for the extraction of mutagens from human urine and cooked meat using blue rayon.

A reproducible method has been developed and validated that allows the detection of mutagenic material in human urine following the intake of a meal containing pan-fried beef patties. The mutagens are extracted from the urine with blue rayon and eluted with methanol/ammonia (100:1). Using 14C-2-amino-3-methylimidazo[4,5-f]quinoline (14C-IQ) as a tracer, the extraction efficiency of heterocyclic amines was consistently found to exceed 90%. It was observed that the critical factor in attaining high extraction efficiencies was the concentration of blue rayon, which depended on the nature of the matrix. Constituents of human urine were demonstrated to compete with IQ for the binding sites on the blue rayon. For the determination of the mutagenic activity in the extracted urine, the O-acetylase over-expressing Salmonella typhimurium strain YG1024 was utilised, and the Ames test procedure was optimised with respect to S9 concentration and incorporation of a pre-incubation step. Using the developed procedure, a marked rise in mutagenic activity, determined both in the absence and presence of an activation system, was evident in human urine following the intake of a beef patty meal. Normal mutagenicity levels were restored within 24 h. Finally, a method is described, once again employing blue rayon, for the extraction of heterocyclic amines from cooked beef patties with a 92% efficiency, as exemplified by IQ.

Animals↗

PubMed2004

Cytochromes P450 in the bioactivation of chemicals.

The initial view that the cytochrome P450 enzyme system functions simply in the deactivation of xenobiotics is anachronistic on the face of mounting evidence that this system can also transform many innocuous chemicals to toxic products. However, not all xenobiotic-metabolising cytochrome P450 subfamilies show the same propensity in the bioactivation of chemicals. For example, the CYP2C, 2B and 2D subfamilies play virtually no role in the bioactivation of toxic and carcinogenic chemicals, whereas the CYP1A, 1B and 2E subfamilies are responsible for the bioactivation of the majority of xenobiotics. Electronic and molecular structural features of organic chemicals appear to predispose them to either bioactivation by one cytochrome P450 enzyme or deactivation by another. Consequently, the fate of a chemical in the body is largely dependent on the cytochrome P450 profile at the time of exposure. Any factor that modulates the enzymes involved in the metabolism of a certain chemical will also influence its toxicity and carcinogenicity. For example, many chemical carcinogens bioactivated by CYP1, on repeated administration, selectively induce this family, thus exacerbating their carcinogenicity. CYP1 induction potency by chemicals appears to be determined by a combination of their molecular shape and electron activation. The function of cytochromes P450 in the bioactivation of chemicals is currently being exploited to design systems that can be used clinically to facilitate the metabolic conversion of prodrugs to their biologically-active metabolites in cells that poorly express them, such as tumour cells, in the so-called gene-directed prodrug therapy.

Animals↗

PubMed2004

Effect of black tea intake on the excretion of mutagens in the urine of volunteers taking a beef meal.

The objective of this study was to investigate in a crossover study conducted in human volunteers whether black tea intake modulates the metabolism of heterocyclic amines, consumed in the form of well-cooked beefburgers, as exemplified by the excretion of mutagens in the urine. Mutagens were extracted from urine with blue rayon, and mutagenic activity was determined in the Ames test, in the presence of an activation system derived from Aroclor 1254-induced rats, and employing the Salmonella typhimurium O-acetylase over-expressing YG1024 bacterial strain. Volunteers consumed three well-cooked beefburgers, whereas a concurrently cooked fourth burger was analyzed for mutagenic activity. Following intake of the burgers, an increase in urinary mutagenic activity was observed, and mutagenic activity was completely excreted within 24 hours. A good correlation was obtained between the intake and excretion of mutagenic activity. The volunteers consumed the same burger meal on two different occasions, once following intake of 10 cups of strong black tea, and the second following intake of a corresponding volume of water. Urine was collected by each volunteer for 24 hours after the meal, and compliance was ascertained utilizing the excretion of p-aminobenzoic acid. The mutagenic ratio, defined as the ratio of urinary mutagenicity over the intake of mutagenicity, was not altered by the black tea, being 0.142 and 0.135 during the water and tea intake, respectively. It is inferred that short-term intake of high levels of black tea, as part of an otherwise normal diet, does not modulate the human metabolism of heterocyclic amines.

Adult↗

PubMed2003

Cytochrome P450 expression and testosterone metabolism in the liver of deer.

Cytochrome P450 expression in cervine liver was investigated using chemical probes and Western blot analysis, and compared with the rat. Deer liver, when compared with rat liver, was characterised by high ethoxyresorufin O-deethylase, coumarin 7-hydroxylase and, to a lesser extent, erythromycin N-demethylase activities; in contrast, deer liver exhibited low debrisoquine 4-hydroxylase, chlorzoxazone 6-hydroxylase and, particularly, lauric acid hydroxylase activities. Ethoxyresorufin O-deethylase activity in deer was markedly inhibited by alpha-naphthoflavone, but was relatively resistant to inhibition by furafylline. Coumarin 7-hydroxylase was inhibited by 8-methoxypsoralen. Western blot analysis using antibodies to rat CYP1A recognised a single, highly expressed protein. Kinetic analysis indicated that a single enzyme is likely to be responsible for the high ethoxyresorufin O-deethylase activity in deer liver. Probing of cervine hepatic microsomes with antibodies to rat CYP2A2 showed that apoprotein levels were higher in the deer compared with the rat. Eadie-Hofstee plot analysis indicated that more than one enzyme catalyses the 7-hydroxylation of coumarin. Western blot analysis using antibodies to rat CYP2B, rat CYP2C11, human CYP2D6, rat CYP3A and rat CYP4A1 revealed in each case the presence of single, poorly expressed, proteins in deer liver. In contrast, when antibodies to rat CYP2E1 were used, a highly expressed single protein was observed. Cervine hepatic microsomes metabolised testosterone to generate androstenedione and a number of hydroxylated products, the major hydroxylation sites being the 2beta-, 6beta- and possibly the 12-position. In summary, this is the first study showing that deer liver expresses all xenobiotic-metabolising cytochrome P450 families, but the level of expression differs from that of the rat.

Animals↗

PubMed2003

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.

Aminobiphenyl Compounds↗

PubMed2003

Xenobiotic conjugation systems in deer compared with cattle and rat.

The ability of cattle and deer liver to catalyse xenobiotic conjugation reactions was investigated and compared with that of the rat. Marked differences in the activity of these enzymes were noted between the domestic animals and rats. Hepatic microsomal epoxide hydrolase activity in cattle and deer, determined using benzo[a]pyrene 4,5-oxide as substrate, was nearly twice that of the rat. In contrast, glutathione S-transferase activity in hepatic cytosol, determined with 1-chloro-2,4-dinitrobenzene as substrate, was significantly lower in the cattle and deer. When 1,2-dichloro-4-nitrobenzene served as the accepting substrate, no activity was detectable in the cattle and deer. Similarly, glutathione reductase activity and total glutathione levels were markedly lower in the cattle and deer compared with the rat. Cytosolic sulfotransferase activity, monitored using 2-naphthol as substrate, was higher in cattle compared with the rat. Finally, microsomal UDP-glucuronosyl transferase activity, determined using 1-napththol as substrate, did not differ significantly among the three species.

Animals↗

PubMed2003

Effects of black tea theafulvins on aflatoxin B(1) mutagenesis in the Ames test.

Black tea theafulvins, a fraction of thearubigins isolated from black tea aqueous infusions, potentiated the mutagenic activity of the mycotoxin aflatoxin B(1) in the Ames test, in the presence of a hepatic S9 activation system derived from Aroclor 1254-treated rats. In contrast, when the S9 activation system was replaced with isolated microsomes, theafulvins suppressed the mutagenicity of the mycotoxin. When microsomal metabolism was terminated after metabolic activation of the mycotoxin, incorporation of the theafulvins into the activation system reduced the mutagenic activity, whereas if it was added before termination of microsomal activity a potentiation of mutagenic response was observed. In in vitro studies, theafulvins inhibited epoxide hydrolase and glutathione S-transferase activities in a concentration-dependent manner. Finally, the mutagenicity of aflatoxin B(1) was much more pronounced in bacteria that were pre-exposed to theafulvins but from which they were subsequently washed off. It may be inferred from the above studies that the genotoxic synergy between aflatoxin B(1) and black tea theafulvins does not occur during the bioactivation of the carcinogen, but may partly be due to decreased deactivation of the reactive intermediate, aflatoxin B(1) 8,9-oxide, by conjugation with glutathione.

Aflatoxin B1↗

PubMed2003

Antimutagenic activity of tea: role of polyphenols.

PURPOSE OF REVIEW: Tea is considered to be one of the most promising dietary chemopreventive agents and, consequently, it is being studied extensively worldwide. Despite the fact that tea has proved very efficient in affording protection against chemical-induced cancer in animal models of the disease, epidemiological studies do not always support the laboratory findings, so that the value of tea as a human anticarcinogen may be considered as 'not proven'. A major mechanism of the anticarcinogenic activity of tea in animals is impairment of the interaction of carcinogens with DNA leading to mutations. The antimutagenic activity of tea as well as the underlying mechanisms will be reviewed, and the role of polyphenols, the postulated bioactive components, and caffeine will be critically evaluated. RECENT FINDINGS: In rats, exposure to tea modulated the disposition of heterocyclic amines, a major group of food-borne carcinogens, stimulating the pathways that lead to deactivation, and this is concordant with the established ability of tea to modulate the carcinogen-metabolizing enzyme systems. These observations provide a rational mechanism for the anticarcinogenic activity of tea in animals. SUMMARY: The beneficial activities of tea have always been attributed to the polyphenols, as these are present in tea at substantial concentrations and are endowed with antioxidant activity. It is becoming increasingly evident, however, that the bioavailability of these compounds is poor as a result of limited absorption and presystemic metabolism by mammalian and microbial enzymes. We propose that the biological activity of tea may be mediated by caffeine and microbial metabolites of polyphenols.

Animals↗

PubMed2003

Drug-phytochemical interactions.

Changes in dietary habits favouring diets rich in fruits and vegetables, and a meteoric rise in the consumption of dietary supplements and herbal products have substantially increased human exposure to phytochemicals. It is, therefore, not surprising that diet and herbal remedies can modulate drug-metabolising enzyme systems, such as cytochromes P450, leading to clinically relevant drug-phytochemical interactions. Phytochemicals have the potential to both elevate and suppress cytochrome P450 activity. Such effects are more likely to occur in the intestine, where high concentrations of phytochemicals may be achieved, and alteration in cytochrome P450 activity will influence, in particular, the fate of drugs that are subject to extensive first-pass metabolism as a result of intestinal cytochrome P450-mediated biotransformation. Moreover, it is becoming increasingly apparent that phytochemicals can also influence the pharmacological activity of drugs by modifying their absorption characteristics through interaction with drug transporters. Clearly, phytochemicals have the potential to alter the effectiveness of drugs, either impairing or exaggerating their pharmacological activity.

Journal Article↗

PubMed2002

Mutagenic activity of the glutathione S-transferase substrate 1-chloro-2,4-dinitrobenzene (CDNB) in the Salmonella mutagenicity assay.

The mutagenicity of the commonly used glutathione S-transferase substrates 1-chloro-2,4-dinitrobenzene (CDNB) and 1,2-dichloro-4-nitrobenzene (DCNB) was investigated in the Salmonella mutagenicity assay. CDNB induced a concentration-dependent mutagenic response in Salmonella typhimurium strain TA98. Incorporation of an activation system derived from Aroclor 1254-induced rats did not influence mutagenic response. Under the same conditions DCNB failed to display mutagenic activity. The mutagenic activity of CDNB was attenuated in bacterial strains under-expressing nitroreductase or O-acetylase activity but, in contrast, it was exaggerated in an O-acetylase over-expressing strain. It is inferred that CDNB exhibits a mutagenic response following reduction of the nitro-group to the hydroxylamine, which is further acetylated to form the acetoxy derivative that presumably breaks down spontaneously to generate the nitrenium ion, the likely ultimate mutagen.

Animals↗

PubMed2002

Evaluation of the antigenotoxic potential of monomeric and dimeric flavanols, and black tea polyphenols against heterocyclic amine-induced DNA damage in human lymphocytes using the Comet assay.

The polyphenolic dimers, epicatechin-4beta-8-catechin (B1), epicatechin-4beta-8-epicatechin (B2), catechin-4beta-8-catechin (B3), catechin-4beta-8-epicatechin (B4), and the gallate ester epicatechin-4beta-8-epicatechin gallate (B'2G) were isolated from grape seeds, and theaflavins and theafulvins from black tea brews. The ability of these naturally-occurring polyphenols to afford protection against the genotoxicity of the heterocyclic amine 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) was compared with that of the monomeric tea flavanols, (+)-catechin (C), (-)-epicatechin (EC), (-)-epicatechin gallate (ECG), (-)-epigallocatechin (EGC) and (-)-epigallocatechin gallate (EGCG). Genotoxic activity was evaluated in human peripheral lymphocytes using the Comet assay. At the concentration range of 1-100 microM, neither the monomeric nor the dimeric flavanols prevented the lymphocyte DNA damage induced by Trp-P-2. In contrast, both of the black tea polyphenols, theafulvins and theaflavins, at a dose range of 0.1-0.5 mg/ml, prevented, in a concentration-dependent manner, the DNA damage elicited by Trp-P-2. Finally, neither the monomeric and dimeric polyphenols (100 microM) nor the theafulvins and theaflavins (0.5mg/ml) caused any DNA damage in the human lymphocytes. These studies illustrate that black tea theafulvins and theaflavins, if absorbed intact, may contribute to the anticarcinogenic potential associated with black tea intake.

Antimutagenic Agents↗