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Objective: To investigate associations between nonsyndromic oral clefts and biochemical measures of folate status and the MTHFR C677T variant in the United Kingdom, where there has been no folic acid fortification program. Method: Dietary details were obtained from the mothers of 112 cases of cleft lip with or without cleft palate (CL±P), 78 cleft palate only (CP) cases, and 248 unaffected infants. Infant and parental MTHFR C677T genotype was determined. Red blood cell (RBC) and serum folate and homocysteine levels were assessed in 12-month postpartum blood samples from a subset of mothers. The data were analyzed by logistic and log-linear regression methods. Results: There was an inverse association between CL±P and maternal MTHFR CT (odds ratio [OR] = 0.5, 95% confidence interval [CI] = 0.31-0.95) and TT (OR = 0.6, 95% CI = 0.21-1.50) genotypes, with similar risk estimates for CP. There was no clear association with infant MTHFR genotype. Higher levels of maternal postpartum RBC and serum folate were associated with a lower risk for CL±P and an increased risk for CP. Higher levels of serum homocysteine were associated with a slightly increased risk for both CL±P and CP. Conclusion: While the inverse relation between the mother's having the MTHFR C677T variant and both CL±P and CP suggests perturbation of maternal folate metabolism is of etiological importance, contrasting relations between maternal postpartum levels of RBC and serum folate by type of cleft are difficult to explain. [ABSTRACT FROM AUTHOR]

We have previously reported that supplementation with folic acid (1.2 mg day(-1) for 12 week) elicited a significant improvement in the folate status of 61 healthy volunteers. We have examined effects of this supplement on markers of genomic stability. Little is known about the effect of folate supplementation on DNA stability in a cohort, which is not folate deficient. Preintervention, there was a significant inverse association between uracil misincorporation in lymphocyte DNA and red cell folate (P < 0.05). In contrast, there were no associations between folate status and DNA strand breakage, global DNA methylation or DNA base excision repair (measured as the capacity of the lymphocyte extract to repair 8-oxoGua ex vivo). Folate supplementation elicited a significant reduction in uracil misincorporation (P < 0.05), while DNA strand breakage and global DNA methylation remained unchanged. Increasing folate status significantly decreased the base excision repair capacity in those volunteers with the lowest preintervention folate status (P < 0.05). Uracil misincorporation was more sensitive to changes in folate status than other measures of DNA stability and therefore could be considered a specific and functional marker of folate status, which may also be relevant to cancer risk in healthy people. [ABSTRACT FROM AUTHOR]

Aims Dietary supplement (DS) use is actively promoted among old people but there is little evidence in favour of DS use or information about the demographic, health and cognitive characteristics of DS users. Method We examined 176 healthy, old people without dementia all born in 1921 and living independently in the community. IQ scores aged about 11 years were available for all subjects. DS users were more often female, had a lower BMI and were taking fewer prescribed medications than non-users. Results Usual dietary intake, as measured by food frequency questionnaire, did not differ between DS users and DS non-users. DS users were seen to have higher Vitamin C (p <0.05), α-carotene (p <0.05) and lower γ-tocopherol (p <0.001) and homocysteine (p <0.01). DS users did not differ from DS non-users in years of education, indices of occupational code, current socio-economic category or parameters of cardiovascular or respiratory functions. DS users had higher (p <0.05) childhood IQ scores but did not differ in current Mini-Mental State Examination (MMSE) score or performance on Raven's Progressive Matrices (RPM) either before or after adjustment for childhood IQ. Conclusions DS users may enjoy somewhat better general health than non-users but the source of this difference is unknown. Possible health benefits of DS use merit further study. Copyright © 2003 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Lymphocytes are routinely used in human biomonitoring to assess the potential toxic and cytoprotective effects of diet on both DNA damage and repair and, by implication, health. Logistically, samples may require to be cryopreserved and stored. How this affects cells used in human biomonitoring is often not considered. In this study we have evaluated the influence of cryopreservation on endogenous and induced DNA strand breakage, altered bases (oxidized purines, oxidized pyrimidines and misincorporated uracil), antioxidant capacity and DNA repair capability in human peripheral blood lymphocytes. Neither isolation nor freezing increased DNA strand breakage above endogenous levels found in freshly isolated human lymphocytes. Oxidized bases (both pyrimidines and purines) and misincorporated uracil, were similar for fresh and frozen lymphocytes. Fresh and frozen lymphocytes responded almost identically to hydrogen peroxide. Quercetin-mediated cytoprotection against hydrogen peroxide-induced strand breakage was maintained in cryopreserved lymphocytes after short-term (24 h) and longer term (2 months) storage compared with freshly isolated and treated cells. Hydrogen peroxide-induced DNA strand breakage was repaired in fresh lymphocytes. Cryopreserved lymphocytes were unable to repair oxidant-induced DNA strand breaks. Frozen human lymphocytes can therefore be successfully used for most aspects of DNA damage biomonitoring, but not for repair. [ABSTRACT FROM PUBLISHER]

DNA damage in lymphocytes, as measured by alkaline single cell gel electrophoresis (pH 12.7), is greatly increased by the concurrent lysis of whole blood in both freshly isolated samples and in PHA-stimulated cultures over a period of 7 days. Further, there is a marked progressive increase in DNA damage with time in PHA-stimulated lymphocytes cultured in whole blood even when the lymphocytes are separated before analysis; no such increase is seen in lymphocytes cultured alone. This indicates that there are components in whole blood that can cause DNA damage in lymphocytes, with granulocytes and lysis of red blood cells likely candidates. The DNA damage is greatly reduced in granulocyte-depleted whole blood cultures, but even in these significant increases are seen at later sampling times. Consequently, careful sample preparation is of paramount importance if the Comet assay is to be successfully used to assess DNA damage in human peripheral blood lymphocytes. Further, the progressive increase in DNA damage in whole blood cultures may influence other methods using lymphocytes for population biomonitoring and may be significant for in vitro genotoxicity testing. [ABSTRACT FROM PUBLISHER]

The development of certain human cancers has been linked with inadequate intake of folates. The effects of folate deficiency in vivo on DNA stability (strand breakage, misincorporated uracil and oxidative base damage) in lymphocytes isolated from rats fed a diet deficient in folic acid was determined. Because the metabolic pathways of folate and other methyl donors are closely coupled, the effects of methionine and choline deficiency alone or in combination with folate deficiency were determined. Feeding male Hooded Lister rats a folate-free diet for 10 weeks created a moderate folate deficiency (25-50% (approx.) decrease in plasma, red blood cell and hepatic folate concentrations (P < 0.05) and a 20% rise in plasma homocysteine (P < 0.05)). Lymphocyte DNA strand breakage was increased successively in all groups after 4 weeks and 8 weeks on the diet (50-100% (approx.) after 8 weeks). Only low folate specifically and progressively induced uracil misincorporation throughout the study (100% (approx.) after 8 weeks). Neither folate deficiency nor choline/methionine deficiency altered oxidative DNA base damage. In summary, moderate folate deficiency in vivo is associated with a decrease in DNA stability, measured as increased DNA strand breakage and misincorporated uracil. [ABSTRACT FROM AUTHOR]

Presents information on a study which determined the absorption and DNA protective effects of flavonoid glycosides from an onion meal. Methodology of the study; Results and discussion on the study.

Provides information on a study which examined the effects of folate deficiency on DNA stability and DNA methylation in rat colonocytes in vivo. Materials and methods used in the study; Results and discussion.

Poor folate status may be important in the aetiology of several epithelial cell malignancies including cancer of the uterine cervix. Folic acid is essential in the synthesis of purine nucleotides and the pyrimidine nucleoside thymidine and it is probable that imbalances in these DNA precursors negatively effect DNA stability and may ultimately lead to malignant transformation. The development of a modified 'comet assay' using the bacterial DNA repair enzyme uracil DNA glycosylase, to detect misincorporated uracil in human DNA is reported here. The effect of perturbing folic acid and deoxyuridine levels on uracil misincorporation in normal human lymphocytes and cultured human tumour cells was investigated using this assay. HeLa cells and peripheral human lymphocytes incubated as agarose-embedded nucleoids, with 1 unit of uracil DNA glycosylase per microg of DNA, contained low levels of uracil in their DNA. Both HeLa cells and stimulated human lymphocytes cultured in folate-deficient medium were growth arrested. Incubating human lymphocytes in folate-deficient medium significantly increased the level of uracil detected compared with control cells. HeLa cells showed an increase in non-specific DNA damage (strand breaks). Deoxyuridine (100 microM) significantly increased the level of uracil detected in the DNA of both folate-deficient and control HeLa cells. It appears that this modified comet assay specifically detects misincorporated uracil in single human cells. It should, therefore, prove valuable in determining the role of folic acid status in DNA instability and cancer. [ABSTRACT FROM PUBLISHER]

We set out to study the value of cardiotocography (CTG) performed before induction of labour for prolonged pregnancy in predicting obstetric intervention. This was a prospective observational study, based in a district general hospital. We studied 100 consecutive patients who underwent induction of labour for prolonged pregnancy. Cardiotocographs (CTGs) were performed before induction of labour on the tenth day after the estimated date of confinement (290 days). The CTGs were then reviewed without knowledge of the outcome of the induction of labour. Obstetric outcomes were then compared. The main outcome measures were the intrapartum presence or absence of meconium stained liquor and the necessity for obstetric intervention. Ninety per cent of CTGs were normal. There was no difference found between the two groups for operative delivery or the presence of meconium liquor. Caesarean section was more likely in the group with an abnormal CTG before induction of labour, but the possibility of this being due to chance is high in this study. There was one case of undiagnosed growth restriction in the abnormal CTG group. These results may be due to a true lack of difference in obstetric intervention between women with normal or abnormal CTGs prior to induction of labour or more probably an inability to detect a difference in our small study. These baseline data allow the calculations necessary for a more substantive trial. [ABSTRACT FROM AUTHOR]

There is growing interest in the potential health benefits of diets that involve regular periods of fasting. While animal studies have provided compelling evidence that feeding patterns such as alternate-day fasting can increase longevity and reduce incidence of many chronic diseases, the evidence from human studies is much more limited and equivocal. Additionally, although several candidate processes have been proposed to contribute to the health benefits observed in animals, the precise molecular mechanisms responsible remain to be elucidated. The study described here examined the effects of an extended fast on gene transcript profiles in peripheral blood mononuclear cells from ten apparently healthy subjects, comparing transcript profiles after an overnight fast, sampled on four occasions at weekly intervals, with those observed on a single occasion after a further 24 h of fasting. Analysis of the overnight fasted data revealed marked inter-individual differences, some of which were associated with parameters such as gender and subject body mass. For example, a striking positive association between body mass index and the expression of genes regulated by type 1 interferon was observed. Relatively subtle changes were observed following the extended fast. Nonetheless, the pattern of changes was consistent with stimulation of fatty acid oxidation, alterations in cell cycling and apoptosis and decreased expression of key pro-inflammatory genes. Stimulation of fatty acid oxidation is an expected response, most likely in all tissues, to fasting. The other processes highlighted provide indications of potential mechanisms that could contribute to the putative beneficial effects of intermittent fasting in humans.

Objective: To investigate associations between nonsyndromic oral clefts and biochemical measures of folate status and the MTHFR C677T variant in the United Kingdom, where there has been no folic acid fortification program., Method: Dietary details were obtained from the mothers of 112 cases of cleft lip with or without cleft palate (CL+/-P), 78 cleft palate only (CP) cases, and 248 unaffected infants. Infant and parental MTHFR C677T genotype was determined. Red blood cell (RBC) and serum folate and homocysteine levels were assessed in 12-month postpartum blood samples from a subset of mothers. The data were analyzed by logistic and log-linear regression methods., Results: There was an inverse association between CL+/-P and maternal MTHFR CT (odds ratio [OR] = 0.5, 95% confidence interval [CI] = 0.31-0.95) and TT (OR = 0.6, 95% CI = 0.21-1.50) genotypes, with similar risk estimates for CP. There was no clear association with infant MTHFR genotype. Higher levels of maternal postpartum RBC and serum folate were associated with a lower risk for CL+/-P and an increased risk for CP. Higher levels of serum homocysteine were associated with a slightly increased risk for both CL+/-P and CP., Conclusion: While the inverse relation between the mother's having the MTHFR C677T variant and both CL+/-P and CP suggests perturbation of maternal folate metabolism is of etiological importance, contrasting relations between maternal postpartum levels of RBC and serum folate by type of cleft are difficult to explain.

Benign, mucinous cystadenomatas account for 15% all ovarian neoplasms and of these, giant variants occur rarely. Ovarian masses, particularly mucinous cystadenomas, are among the largest tumours known. Surgery is the treatment of choice for a large mucinous cystadenoma. In this report we present an interesting case of an ovarian mucinous cystadenoma weighing 40 kg. Surgical treatment was successful and the patient adjusted well to her postoperative body image.

We studied 82 non-demented old people and, using MRI, derived measures of grey and white matter and intracranial volumes. Controlling for sex and intracranial volume, we related grey and white matter volumes to plasma concentrations of vitamins C, B(12), folate, homocysteine, cholesterol, triglycerides, high density and low density (LDL) lipoproteins, and to red blood cell folate and glycated haemoglobin concentrations (HbA1(c)). We found that lower grey matter volume was associated with lower plasma vitamin C and higher homocysteine, cholesterol and LDL. Lower blood cell folate was also associated with lower grey matter volume but HbA1(c) was not. These data are consistent with the putative benefits of dietary vitamin C and folate intake and the role of cholesterol in age related neurodegeneration.

Anthocyanins are secondary plant metabolites responsible for the blue, purple, and red color of many plant tissues. The phenolic structure of anthocyanins conveys marked antioxidant activity in model systems via donation of electrons or hydrogen atoms from hydroxyl moieties to free radicals. Dietary intakes of anthocyanins may exceed 200 mg/day, however, little is known about their antioxidant potency in vivo. Consequently, the aim of this study was to establish whether anthocyanins could act as putative antioxidant micronutrients. Rats were maintained on vitamin E-deficient diets for 12 weeks in order to enhance susceptibility to oxidative damage and then repleted with rations containing a highly purified anthocyanin-rich extract at a concentration of 1 g/kg diet. The extract consisted of the 3-glucopyranoside forms of delphinidin, cyanidin, petunidin, peonidin, and malvidin. Consumption of the anthocyanin-repleted diet significantly improved (p <.01) plasma antioxidant capacity and decreased (p <.001) the vitamin E deficiency-enhanced hydroperoxides and 8-Oxo-deoxyguanosine concentrations in liver. These compounds are indices of lipid peroxidation and DNA damage, respectively. Dietary consumption of anthocyanin-rich foods may contribute to overall antioxidant status, particularly in areas of habitually low vitamin E intake.

Objective: To determine the potential antioxidant effect of rutin (quercetin-3-O-beta-rutinoside) supplementation., Design: A 6-week randomized single-blind placebo controlled trial was conducted; 500 mg rutin supplement was compared to an equivalent amount of glucose placebo. In addition, a pharmacokinetic study was carried out., Setting: The Rowett Research Institute, Aberdeen, UK., Subjects: Eighteen healthy non-obese normocholesterolaemic female volunteers in the age range 18-48 y., Main Outcome Measures: Plasma flavonoids, ascorbic acid, tocopherols and carotenoids, plasma antioxidant capacity, lymphocyte DNA damage, blood chemistry and haematology, liver function tests, urinary malondialdehyde, 8-hydroxy-2-deoxyguanosine and 8-iso-prostaglandin F2alpha., Results: Eighteen volunteers completed the trial. Rutin supplementation did not induce any adverse changes in blood chemistry or indices of liver function. Plasma flavonoids were significantly elevated in the rutin-supplemented group. Endogenous oxidation of pyrimidines was significantly decreased in both rutin- and placebo-treated volunteers. There was no significant change in the level of urinary 8-hydroxy-2'-deoxyguanosine or urinary malondialdehyde in either group. A linear correlation was observed between urinary malondialdehyde and urinary 8-iso-prostaglandin F2alpha (R = 0.54, P<0.01)., Conclusion: Six weeks' rutin supplementation significantly elevated the levels of three plasma flavonoids (quercetin. kaempferol and isorhamnetin) but there was no significant change in plasma antioxidant status. The decrease in the level of endogenous base oxidation in lymphocyte DNA seen in both the placebo- and rutin-supplemented subjects may reflect seasonal changes in other dietary antioxidants.

Certain dietary antioxidants such as vitamin E and vitamin C are important for maintaining optimum health. There is now much interest in polyphenolic products of the plant phenylpropanoid pathway as they have considerable antioxidant activity in vitro and are ubiquitous in our diet. Rich sources include tea, wine, fruits and vegetables although levels are affected by species, light, degree of ripeness, processing and storage. This confounds the formulation of databases for the estimation of dietary intakes. Most attention to date has focused on the flavonoids, a generic term which includes chalcones, flavones, flavanones, flavanols and anthocyanins. There is little convincing epidemiological evidence that intakes of polyphenols are inversely related to the incidence of cancer whereas a number of studies suggest that high intakes of flavonoids may be protective against CHD. In contrast, numerous cell culture and animal models indicate potent anticarcinogenic activity by certain polyphenols mediated through a range of mechanisms including antioxidant activity, enzyme modulation, gene expression, apoptosis, upregulation of gap junction communication and P-glycoprotein activation. Possible protective effects against heart disease may be due to the ability of some polyphenols to prevent the oxidation of LDL to an atherogenic form although anti-platelet aggregation activity and vasodilatory properties are also reported. However, some polyphenols are toxic in mammalian cells. Thus, until more is known about their bioavailability, metabolism and intracellular location, increasing intakes of polyphenols by supplements or food fortification may be unwise.

Prostate cancer is one of the most common male cancers in Western countries, yet the incidence of this fatal disease remains low in Asian populations. Environmental factors such as diet play an important role in hormone-dependent cancer etiology, and a high phytoestrogen intake may be one factor contributing to the low prostate cancer mortality in Eastern populations. In this study, we investigated the effects of the phytoestrogens genistein, daidzein, coumestrol, and equol on cell growth and DNA damage (strand breakage) in two human prostate tumor cell lines: androgen receptor-positive LNCaP and androgen receptor-negative PC-3. Each compound caused growth inhibition at physiologically relevant concentrations (<10 microM). Genistein induced DNA damage in both cell lines at <10 microM. Daidzein inhibited cell growth at 10-100 microM yet had no effect on DNA damage at up to 500 microM. Thus, despite their structural similarities, different phytoestrogens inhibit prostate tumor cell growth by independent mechanisms.

Epidemiological studies have indicated that folic acid protects against a variety of cancers, particularly cancer of the colorectum. Folate is essential for efficient DNA synthesis and repair. Moreover, folate can affect cellular S-adenosylmethionine levels, which regulate DNA methylation and control gene expression. We have investigated the mechanisms through which folate affects DNA stability in immortalized normal human colonocytes (HCEC). DNA strand breakage, uracil misincorporation, and DNA repair, in response to oxidative and alkylation damage, were determined in folate-sufficient and folate-deficient colonocytes by single cell gel electrophoresis. In addition, methyl incorporation into genomic DNA was measured using the bacterial enzyme Sss1 methylase. Cultured human colonocyte DNA contained endogenous strand breaks and uracil. Folate deficiency significantly increased strand breakage and uracil misincorporation in these cells. This negative effect on DNA stability was concentration dependent at levels usually found in human plasma (1-10 ng/ml). DNA methylation was decreased in HCEC grown in the absence of folate. Conversely, hypomethylation was not concentration dependent. Folate deficiency impaired the ability of HCEC to repair oxidative and alkylation damage. These results demonstrate that folic acid modulates DNA repair, DNA strand breakage, and uracil misincorporation in immortalized human colonocytes and that folate deficiency substantially decreases DNA stability in these cells.

Background & Aims: Epidemiological studies suggest that antioxidant polyphenols in the human diet may protect against diseases such as cancer. In this study we investigated the cytoprotective potential of the flavonoids, quercetin, myricetin, kaempferol and rutin against oxidative DNA damage in human colonocytes in vitro., Methods: Caco-2 cells, which display specialised enterocyte/colonocyte cell functions, were used as an in vitro model for human colonocytes. Hydrogen peroxide was employed as the oxidant. DNA damage (strand breakage, oxidised purines and oxidised pyrimidines) was determined using the alkaline single cell gel electrophoresis or comet assay. Cell growth and viability were measured., Results: Hydrogen peroxide caused a dose-dependent increase in DNA strand breakage in human colonocytes, presumably via oxygen free radical generation. Quercetin and myricetin protected Caco-2 cells against oxidative attack. In addition, quercetin decreased hydrogen peroxide-mediated inhibition of growth. Neither rutin nor kaempferol was effective. However, quercetin, while inhibiting DNA strand breakage, did not alter the levels of oxidised bases following peroxide treatment. The antifungal agent ketoconazole, prevented quercetin cytoprotection in Caco-2 cells, indicating that P450-mediated metabolism may alter the efficacy of the flavonoids against oxidative DNA damage., Conclusion: Flavonoids, particularly quercetin, the most abundant flavonoid in the human diet, are likely to be important in defending human colonocytes from oxidative attack.

Folic acid deficiency in humans has been linked with megaloblastic anaemia, neural tube defects in the neonate, and heart disease. Folate has also been implicated in the development of cancer, especially cancer of the colorectum. There appear to be two principal mechanisms through which low folate status may increase the risk of malignancy. Folate deficiency, by reducing intracellular S-adenosylmethionine (SAM), can alter cytosine methylation in DNA, leading to inappropriate activation of proto-oncogenes and induction of malignant transformation. Alternatively, folic acid is crucial for normal DNA synthesis and repair. Folate deficiency may cause an imbalance in DNA precursors, uracil misincorporation into DNA, and chromosome breakage. This chapter briefly describes the epidemiological data supporting the involvement of folic acid in the aetiology of cancer. It also assesses the evidence from cellular, animal and human studies that folic acid can modulate DNA by such mechanisms.

Carotenoids are thought to act as antioxidants in vivo, decreasing oxidative damage to biomolecules and thus protecting against coronary heart disease and cancer. However, human intervention studies with beta-carotene have given equivocal results in terms of cancer incidence. In an alternative molecular epidemiological approach, we have employed the 'comet assay' (single cell alkaline gel electrophoresis) to measure strand breaks, oxidized pyrimidines and altered purines in the DNA of lymphocytes from volunteers supplemented with alpha/beta-carotene, lutein, lycopene or placebo. In addition, we measured concentrations of the main serum carotenoids, and vitamins E and C, by HPLC. We report a significant negative correlation between basal concentrations of total serum carotenoids and oxidized pyrimidines. A similar correlation was seen between individual carotenoids (notably lutein and beta-carotene) and oxidized pyrimidines. However, carotenoid supplementation did not have a significant effect on endogenous oxidative damage. This suggests that there are some factors in the basal diet, probably found in fruit and vegetables, that decrease oxidative damage to DNA. In this case, basal serum carotenoids may simply be markers of consumption of fruit and vegetables, they themselves having little or no protective value.

Folic acid is essential for the synthesis and repair of DNA. We report the effects of folate depletion on DNA stability in normal human lymphocytes in vitro. DNA strand breakage, uracil misincorporation, oxidative DNA base damage, and DNA repair capability were determined using variants of the comet assay (single cell gel electrophoresis). Lymphocyte proliferation was measured as an indicator of normal replication. Lymphocytes isolated from human venous blood were stimulated to grow in either complete medium containing folic acid (1 ng/ml-2 microgram/ml) or medium deficient in folic acid for up to 10 days. Cells prepared for comet analysis were treated either with the bacterial DNA repair enzyme endonuclease III to determine the level of oxidized pyrimidines in lymphocyte DNA or with uracil DNA glycosylase, which detects misincorporated uracil. Cell number and viability were measured. Normal human lymphocyte DNA contained detectable amounts of misincorporated uracil (estimated as approximately 1000 per cell). DNA strand breakage and uracil misincorporation increased in a time- and concentration-dependent manner after lymphocytes were cultured with decreasing amounts of folic acid. DNA damage was induced at folic acid concentrations routinely observed in plasma from the human population (1-10 ng/ml). Lymphocytes cultured under folate-deficient conditions failed to grow normally compared with control cells. However, all lymphocytes remained viable as measured by Trypan blue exclusion. Cells deprived of folate were unable to efficiently repair oxidative DNA damage induced by hydrogen peroxide. Inhibition of repair was maximal after 8 days in culture. Folate supply had no effect on the level of oxidized pyrimidines in lymphocyte DNA, even after 10 days in culture, suggesting that folate deficiency increases uracil misincorporation relatively specifically. These in vitro results help to determine the mechanism(s) through which folic acid maintains DNA stability.

The effects of the flavonoids quercetin and myricetin, and the antihepatotoxic agent silymarin, on hydrogen peroxide-mediated DNA damage in human lymphocytes were determined using alkaline single-cell gel electrophoresis (the comet assay). Treatment with hydrogen peroxide increased the levels of DNA strand breaks and oxidised pyrimidine bases in these cells. Quercetin was protective at concentrations above 10 microM and myricetin decreased oxidant-induced DNA strand breakage at concentrations of 100 microM. Cellular metabolism may alter the antioxidant efficacy of the flavonoids. Silymarin had no protective effect at any of the concentrations tested. None of these flavonoids was itself genotoxic. Neither alpha-tocopherol nor beta-carotene decreased hydrogen peroxide-induced DNA breakage. The differences in effectiveness of these dietary compounds against oxidative DNA damage may be explained by differences in their chemical structure or location within the cell.