Alexandra Horská

Kiwifruit Protects Against Oxidative DNA Damage in Human Cells and In Vitro

Antioxidant micronutrients may account for the beneficial effects of fruits on human health. A direct demonstration that consumption of fruit decreases oxidative DNA damage in human cells would support this hypothesis. Kiwifruit was taken as an example of a food with putative antioxidant properties, and its effectiveness at decreasing oxidative DNA damage was assessed in ex vivo as well as in vitro tests. The comet assay (single-cell gel electrophoresis) was used to measure DNA damage in lymphocytes collected during a human supplementation trial with a single 0.5-liter drink of kiwifruit juice (with water as a control). The comet assay was also modified to assess the antioxidant effect of kiwifruit in vitro by measuring the ability of an extract to interfere with oxidative damage to DNA induced by H2 O2. Ex vivo, consumption of kiwifruit led to an increased resistance of DNA to oxidative damage induced by H2 O2 in isolated lymphocytes, in comparison with lymphocytes collected after a control drink of water. No effect was seen on endogenous DNA damage. In vitro, a simple extract of kiwifruit, buffered to pH 7, was more effective than a solution of vitamin C (of equivalent concentration) at protecting DNA from damage, whereas at the highest concentrations tested, neither kiwi extract nor vitamin C had a protective effect. We have demonstrated significant antioxidant activity of kiwifruit ex vivo and in vitro, not attributable entirely to the vitamin C content of the fruit. Our dual approach is appropriate for testing other fruit and vegetable products for potential antioxidant effects.

Glutathione S-transferase polymorphisms influence the level of oxidative DNA damage and antioxidant protection in humans

Glutathione S-transferase genotypes GSTT1, GSTM1, GSTP1 were characterised in 155 middle-aged men and compared with parameters of oxidative stress at the level of DNA and lipids, with antioxidant enzymes, and with plasma antioxidants in smokers and non-smokers. Smokers had on average significantly lower levels of Vitamin C, beta-carotene and beta-cryptoxanthin and higher amounts of oxidised purines and pyrimidines in lymphocyte DNA. The GSTM1 null genotype was associated with elevated glutathione as well as with higher Vitamin C concentration in plasma. Vitamin C was higher in GSTT1+ compared with GSTT1 null--as was glucose-6-phosphate dehydrogenase activity. The homozygous GSTP1 a/a genotype was associated with significantly higher levels of GST activity measured in lymphocytes, in comparison with the b/b genotype. Using multifactorial statistical analysis we found significant associations between smoking, GSTP1 genotype, plasma Vitamin C, and purine base damage in lymphocyte DNA. The difference in Vitamin C plasma levels between smokers and non-smokers was seen only with the GSTP1 b/b genotype. This group accounted also for most of the increase in purine oxidation in smokers. In contrast, the link between smoking and oxidised pyrimidines in DNA was seen only in the GSTT1 null group. It seems that polymorphisms in the phase II metabolising enzyme glutathione S-transferase may be important determinants of commonly measured biomarkers.

Are glutathione S transferases involved in DNA damage signalling? Interactions with DNA damage and repair revealed from molecular epidemiology studies

Glutathione S-transferases (GSTs) are members of a multigene family of isoenzymes that are important in the control of oxidative stress and in phase II metabolism. Acting non-enzymically, GSTs can modulate signalling pathways of cell proliferation, cell differentiation and apoptosis. Using a molecular epidemiology approach, we have investigated a potential involvement of GSTs in DNA damage processing, specifically the modulation of DNA repair in a group of 388 healthy adult volunteers; 239 with at least 5 years of occupational exposure to asbestos, stone wool or glass fibre, and 149 reference subjects. We measured DNA damage in lymphocytes using the comet assay (alkaline single cell gel electrophoresis): strand breaks (SBs) and alkali-labile sites, oxidised pyrimidines with endonuclease III, and oxidised purines with formamidopyrimidine DNA glycosylase. We also measured GST activity in erythrocytes, and the capacity for base excision repair (BER) in a lymphocyte extract. Polymorphisms in genes encoding three GST isoenzymes were determined, namely deletion of GSTM1 and GSTT1 and single nucleotide polymorphism Ile105Val in GSTP1. Consumption of vegetables and wine correlated negatively with DNA damage and modulated BER. GST activity correlated with oxidised bases and with BER capacity, and differed depending on polymorphisms in GSTP1, GSTT1 and GSTM1. A significantly lower BER rate was associated with the homozygous GSTT1 deletion in all asbestos site subjects and in the corresponding reference group. Multifactorial analysis revealed effects of sex and exposure in GSTP1 Ile/Val heterozygotes but not in Ile/Ile homozygotes. These variants affected also SBs levels, mainly by interactions of GSTP1 genotype with exposure, with sex, and with smoking habit; and by an interaction between sex and smoking. Our results show that GST polymorphisms and GST activity can apparently influence DNA stability and repair of oxidised bases, suggesting a potential new role for these proteins in DNA damage processing via DNA damage signalling.

Metabolic gene variants associated with chromosomal aberrations in healthy humans.

Nonspecific chromosomal aberrations (CAs) are found in about 1% of lymphocytes drawn from healthy individuals. They include chromosome‐type aberrations (CSAs), which are increased in exposure to ionizing radiation, and chromatid‐type aberrations (CTAs) which in experimental systems are formed by DNA binding carcinogens and mutagens. The frequency of CAs is associated with the risk of cancer, but the causes of CAs in general population are unknown. Here, we want to test whether variants in metabolic genes associate with CAs in healthy volunteers. Cases were considered those whose total CA (CAtot) frequency was >2% and for CSA and CTA the limit was >1%. Controls had lower frequencies of CAs. Functional polymorphisms in seven genes were selected for analysis: cytochrome P450 1B1 (CYP1B1), epoxide hydrolase 1 (EPHX1), NAD(P)H:quinone oxidoreductase 1 (NQO1), each coding for phase 1 enzymes, and glutathione S‐transferase P1 (GSTP1), glutathione S‐transferases M1 (GSTM1) and T1 (GSTT1), coding for enzymes which conjugate reactive metabolites, that is, phase 2 enzymes. The number of volunteers genotyped for each gene varied from 550 to 1,500. Only EPHX1 was individually associated with CAtot; high activity genotypes decreased CAtot. A total of six significant (P < 0.01) pair‐wise interactions were observed, most including a GST variant as one of the pair. In all genotype combinations with significant odds ratios for CAs a GST variant was involved. The present data provide evidence that variants in genes coding for metabolic enzymes, which individually have small effects, interact and are associated with CA frequencies in peripheral lymphocytes of healthy volunteers.

Genetic determinants of quantitative traits associated with cardiovascular disease risk

Established risk factors for cardiovascular diseases (CVD) may be moderated by genetic variants. In 2403 unrelated individuals from general practice (mean age 40.5 years), we evaluated the influence of 15 variants in 12 candidate genes on quantitative traits (QT) associated with CVD (body mass index, abdominal obesity, glucose, serum lipids, and blood pressure). Prior to multiple testing correction, univariate analysis associated APOE rs429358, rs7412 and ATG16L1 rs2241880 variants with serum lipid levels, while LEPR rs1137100 and ATG16L1 rs2241880 variants were linked to obesity related QTs. After taking into account confounding factors and correcting for multiple comparisons only APOE rs429358 and rs7412 variants remained significantly associated with risk of dyslipidemia. APOE rs429358 variant almost tripled the risk in homozygous subjects (OR = 2.97; 95% CI 1.09-8.10, p < 0.03) and had a lesser but still highly significant association also in heterozygous individuals (OR = 1.67; 95% CI 1.24-2.10; p < 0.001). Associations with hypertension, diabetes mellitus, and metabolic syndrome were not significant after Bonferroni correction. The influence of genetic variation is more evident in dyslipidemia than in other analyzed QTs. These results may contribute to strategic research aimed at including genetic variation in the set of data required to identify subjects at high risk of CVD.