Vitamin E and genome stability

Vitamin E protects DNA from oxidative damage in human hepatocellular carcinoma cell lines

Expression of multiple drug resistant (MDR) phenotype and over-expression of P-glycoprotein (P-gp) in the human hepatocellular carcinoma (HCC) cell clone P1(0.5), derived from the PLC/PRF/5 cell line (P5), are associated with strong resistance to oxidative stress and a significant (p < 0.01) increase in intracellular vitamin E content as compared with the parental cell line. This study evaluates the role of vitamin E in conferring resistance to drugs and oxidative stress in P1(0.5) cells. Parental drug-sensitive cells, P5, were incubated in alpha-tocopherol succinate (alpha-TS, 5 microM for 24 h) enriched medium to increase intracellular vitamin E content to levels comparable to those observed in P1(0.5) cells at basal conditions. Susceptibility to lipid peroxidation and oxidative DNA damage were assessed by measuring the concentration of thiobarbituric-reactive substances (TBARS) and 8-hydroxy-2'-deoxyguanosine (8-OHdG) at basal and after experimental conditions. Cell capacity to form colonies and resistance to doxorubicin were also studied. P5 cells, treated with alpha-TS, became resistant to ADP-Fe3+ and to ionizing radiation-induced lipid peroxidation as P1(0.5) cells. Exposure to ADP-Fe3+ or ionizing radiation increased TBARS and the 8-OHdG content in the P5 cells, while vitamin E enrichment abolished these effects. Irradiation doses at 5 cGy increased TBARS and 8-OHdG. They also inhibited cell capacity to form colonies in the untreated P5 cells. Incubation with alpha-TS fully reverted this effect and significantly (p < 0.01) reduced the inhibitory effect of cell proliferation induced by irradiation doses at >500 cGy. Resistance to doxorubicin was not affected by alpha-TS. These observations demonstrate the role of vitamin E in conferring protection from lipid peroxidation, ionizing radiation and oxidative DNA damage on the human HCC cell line. They also rule out any role of P-gp over-expression as being responsible for these observations in cells with MDR phenotype expression.

Ability to activate oocytes and chromosome integrity of mouse spermatozoa preserved in EGTA Tris–HCl buffered solution supplemented with antioxidants

Potential methods for cryopreservation of mouse spermatozoa are freeze-drying, desiccation, and suspension in EGTA Tris-HCl buffered solution (ETBS: 50 mM NaCl, 50 mM EGTA, and 10 mM Tris-HCl). To determine the duration that mouse spermatozoa suspended in ETBS-based solutions could retain their normal characteristics without freezing, spermatozoa collected from the cauda epididymis were suspended in ETBS or in ETBS supplemented with the antioxidants, dimethyl sulfoxide (DMSO), or DL-alpha-tocopherol acetate (Vitamin E acetate; VEA) diluted in DMSO, then held at ambient temperature (22-24 degrees C) for up to 9 days. When oocytes were injected with spermatozoa preserved in ETBS alone, activation rates of oocytes and chromosome integrity at the first cleavage metaphase decreased at 1 day (P < 0.001) and 2-4 days (P < 0.01) following treatment. When oocytes were injected with spermatozoa preserved in ETBS supplemented with DMSO or VEA/DMSO, chromosome integrity did not decrease significantly (through 9 days of preservation). Although DMSO maintained sperm chromosome integrity more effectively than VEA/DMSO up to 2-4 days (91 and 67%, normal karyotypes in DMSO and VEA/DMSO, respectively), VEA/DMSO helped to maintain the ability of spermatozoa to activate oocytes, but did not enhance the maintenance of sperm chromosome integrity. These results suggested that deterioration of spermatozoa preserved in ETBS alone was delayed by supplementation with antioxidants.

Chronic ginseng consumption attenuates age-associated oxidative stress in rats

The antioxidant properties of North American ginseng (Panax quinquefolium) were investigated in young and old rats fed a ginseng-supplemented diet for 4 mo. Female Fischer 344 rats at 4 (Y, n = 38) or 22 (O, n = 25) mo of age were randomly divided into three groups and fed either a AIN-93G formula-based control diet (C) or a diet containing 0.5 g/kg (low dose, L) or 2.5 g/kg (high dose, H) dry ginseng power for 4 mo. Oxidant generation, measured with 2'7'-dichlorofluorescin (DCFH), was significantly lowered with ginseng feeding in the homogenates of heart, soleus, and the deep portion of vastus lateralis muscle (DVL) (P < 0.05) in both Y and O rats, and the effects were dose dependent. Superoxide dismutase activity was elevated in heart and DVL of H rats, and in soleus of L rats (P < 0.05). H rats showed higher glutathione peroxidase activity in DVL and soleus muscle (P < 0.05), and elevated citrate synthase activity in the heart of both age groups and DVL of Y rats (P < 0.05). Neither the H nor L diet affected age-dependent lipid peroxidation in the heart or muscle, but protein carbonyl content was attenuated with the H diet in the heart (P < 0.05) and with both the L and H diets in DVL (P < 0.01). We conclude that ginseng supplementation can prevent age-associated increase in oxidant production and oxidative protein damage in rats. These protective effects are explained in part by elevated antioxidant enzyme activities in the various tissues.

Oxidative damage to DNA of ovarian surface epithelial cells affected by ovulation: carcinogenic implication and chemoprevention

The majority of cancers of the ovary are thought to originate from a surface epithelial cell perturbed by ovulation. Outgrowth of a follicle destined to ovulate brings it into apposition with the ovarian epithelium. Ovarian surface cells are consequently exposed, within a limited diffusion radius, to inflammatory agents and reactive oxidants generated during periovulatory processes. Cells that overlie the formative site of follicular rupture suffer irreparable damages and undergo apoptosis. Potentially mutagenic 8-oxoguanine modifications were detected in (surviving) cells circumjacent to postovulatory ovine and human follicles. It is conceivable that clonal expansion of a cell with unrepaired DNA, but not committed to death, could be an initiating factor in the etiology of malignancy, insofar as proliferative ovulatory wound-repair responses may propagate mutations. Since the prognosis for ovarian cancer patients with invasive disease is so poor, and early detection has proven elusive, it is imperative that prospective methods of chemo-prevention be explored. Ovulation-induced oxidative base damages to the ovarian epithelium of ewes were prevented by vitamin E. Oxoguanine adducts persisted and CA-125 (a phenotype of metaplastic transformation) was expressed in cultures of cells that were distressed by ovulation in which p53 synthesis was inhibited. Vitamin E negated this reaction. Ovarian cyclicity and fertility were not altered in vitamin-treated ewes. A prophylactic benefit of a supplemental antioxidant is suggested in "ovulating" individuals designated at risk (e.g., due to a tumor suppressor malfunction) for the development of ovarian cancer.

DNA lesions and cytogenetic changes induced by N-nitrosomorpholine in HepG2, V79 and VH10 cells: the protective effects of Vitamins A, C and E

INTRODUCTION

N-Nitrosomorpholine (NMOR), present in the workplace of tyre chemical factories, is a known hepatocarcinogen. This compound belongs to the group of N-nitrosamines, which are indirect-acting and require metabolic activation. However, the mechanism of its carcinogenic effect is not completely clear.

AIMS

The objective of this study was (i) to compare the DNA-damaging and clastogenic effects of NMOR in three cell lines (HepG2, V79 and VH10) with different levels of metabolizing enzymes and (ii) to determine the protective effects of Vitamins A, C and E against deleterious effects of NMOR.

METHODS

The exponentially growing cells were pre-treated with Vitamins A, C and E and treated with NMOR. Genotoxic effects of NMOR were evaluated by single-cell gel electrophoresis (SCGE, comet assay), while the chromosomal aberration assay was used for the study of clastogenic effects.

KEY RESULTS

NMOR-induced a significant dose-dependent increase of DNA damage as analyzed by SCGE, but the extent of DNA migration in the electric field was unequal in the different cell lines. Although the results obtained by SCGE confirmed the genotoxicity of NMOR in all cell lines studied, the number of chromosomal aberrations was significantly increased only in HepG2 and V79 cells, while no changes were observed in VH10 cells. In HepG2 cells pre-treated with Vitamins A, C and E we found a significant decrease of the percentage of tail DNA induced by NMOR. The reduction of the clastogenic effects of NMOR was observed only after pretreatment with Vitamins A and E; Vitamin C did not alter the frequency of NMOR-induced chromosomal aberrations under the experimental conditions of this study.

CONCLUSIONS

The fat-soluble Vitamins A and E, which are dietary constituents, reduce the harmful effects of N-nitrosomorpholine in human hepatoma cells HepG2, which are endowed with the maximal capacity for metabolic activation of several drugs.

DNA microarray technology in nutraceutical and food safety

The quality and quantity of diet is a key determinant of health and disease. Molecular diagnostics may play a key role in food safety related to genetically modified foods, food-borne pathogens and novel nutraceuticals. Functional outcomes in biology are determined, for the most part, by net balance between sets of genes related to the specific outcome in question. The DNA microarray technology offers a new dimension of strength in molecular diagnostics by permitting the simultaneous analysis of large sets of genes. Automation of assay and novel bioinformatics tools make DNA microarrays a robust technology for diagnostics. Since its development a few years ago, this technology has been used for the applications of toxicogenomics, pharmacogenomics, cell biology, and clinical investigations addressing the prevention and intervention of diseases. Optimization of this technology to specifically address food safety is a vast resource that remains to be mined. Efforts to develop diagnostic custom arrays and simplified bioinformatics tools for field use are warranted.

Oxidative stress-dependent inhibition of yeast cell growth by farnesylamine and its possible relation to amine oxidase in the mitochondrial fraction

Among various analogs of the isoprenoid farnesol (FOH), farnesylamine (FNH2) inhibited the growth of the budding yeast Saccharomyces cerevisiae by accelerating cellular reactive oxygen species (ROS) generation. Unlike the case with FOH, however, FNH2 did not cause mitochondrial transmembrane potential (mtDeltaPsi) hyperpolarization so that FNH2-treated cells were not protected against ROS production by inhibiting the proton pumping function of mitochondrial F(O)F1-ATPase. FNH2 promoted ROS generation even in cells of a respiration-deficient mutant, indicating a yeast metabolic pathway other than mitochondrial electron transport as the origin of ROS. FNH2 oxidase activity was detected in the yeast mitochondrial fraction, which produces hydrogen peroxide (H2O2) in the reaction with either FNH2 or geranylgeranylamine (GGNH2), in addition to polyamine oxidase activity specific for spermine. GGNH2 also exhibited the growth inhibitory effect with the accompanying induction of ROS generation, while such an activity was not detected with any of the polyamines tested or geranylamine. FNH2 oxidase, which was sensitive to a typical copper-chelating agent, diethyldithiocarbamic acid (DDC), could be solubilized with Triton X-100, and detected as a single band upon activity staining with FNH2 but not with spermine in polyacrylamide gel electrophoresis. FNH2-treated cells were partly protected against ROS production by the additional supplementation of DDC in the medium. Our results suggest the involvement of H2O2 production due to direct oxidation of FNH2 by copper amine oxidase in oxidative stress-dependent inhibition of yeast cell growth.

Humic acid induces oxidative DNA damage, growth retardation, and apoptosis in human primary fibroblasts

Humic acid (HA) has been implicated as an etiological factor of Blackfoot disease endemic in the southwest coast of Taiwan. Dysfunction of endothelial cells and vasculopathy have been proposed to explain the onset of ulcerous changes at extremities. However, little is known about the effect of HA on activities of cells in these nonhealing wounds. In the present study, we demonstrate that HA adversely affects the growth properties of fibroblasts, one of the key players in wound repair. HA treatment caused growth arrest and apoptosis in human foreskin fibroblasts (HFF). This was accompanied by a significant increase in the level of 8-hydroxy-2'-deoxyguanosine (8-OHdG) in cellular DNA. The increased fluorescence in dichlorofluorescin (H2DCF)-stained and HA-treated cells suggests the involvement of reactive oxygen species (ROS) in HA-induced biological effects. Conversely, vitamin E pretreatment, which significantly reduced the 8-OHdG formation in HA-treated cells, alleviated the growth-inhibitory and apoptosis-inducing effects of HA. These results indicate that HA initiates oxidative damages to fibroblasts, and leads to their dwindling growth potential and survival. The present study suggests that HA-induced growth retardation and apoptosis of fibroblasts may play a role in the pathogenesis of Blackfoot disease.

Lipid metabolism in pregnancy and its consequences in the fetus and newborn

During early pregnancy there is an increase in body fat accumulation, associated with both hyperphagia and increased lipogenesis. During late pregnancy there is an accelerated breakdown of fat depots, which plays a key role in fetal development. Besides using placental transferred fatty acids, the fetus benefits from two other products: glycerol and ketone bodies. Although glycerol crosses the placenta in small proportions, it is a preferential substrate for maternal gluconeogenesis, and maternal glucose is quantitatively the main substrate crossing the placenta. Enhanced ketogenesis under fasting conditions and the easy transfer of ketones to the fetus allow maternal ketone bodies to reach the fetus, where they can be used as fuels for oxidative metabolism as well as lipogenic substrates. Although maternal cholesterol is an important source of cholesterol for the fetus during early gestation, its importance becomes minimal during late pregnancy, owing to the high capacity of fetal tissues to synthesize cholesterol. Maternal hypertriglyceridemia is a characteristic feature during pregnancy and corresponds to an accumulation of triglycerides not only in very low-density lipoprotein but also in low- and high-density lipoprotein. Although triglycerides do not cross the placental barrier, the presence of lipoprotein receptors in the placenta, together with lipoprotein lipase, phospholipase A2, and intracellular lipase activities, allows the release to the fetus of polyunsaturated fatty acids transported as triglycerides in maternal plasma lipoproteins. Normal fetal development needs the availability of both essential fatty acids and long chain polyunsaturated fatty acids, and the nutritional status of the mother during gestation has been related to fetal growth. However, excessive intake of certain long chain fatty acids may cause both declines in arachidonic acid and enhanced lipid peroxidation, reducing antioxidant capacity.

Effects of vitamins C and E on cytotoxicity induced by N-nitroso compounds, N-nitrosomorpholine and N-methyl-N'-nitro-N-nitrosoguanidine in Caco-2 and V79 cell lines

Since N-nitroso compounds as strong carcinogens are closely related to food and nutrition, the cytotoxic effects of N-nitrosomorpholine (NMOR) and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and their reduction by vitamins C and E were investigated in hamster V79 cells and human colon carcinoma Caco-2 cells. Cytotoxicity was evaluated by the trypan blue exclusion technique in Caco-2 cells and by the plating efficiency assay in V79 cells. NMOR caused a dose-dependent decline of viable cells in both cell lines; MNNG induced a dose-dependent cytotoxic effect only in V79 cells. Pretreatment of cells with vitamin C and vitamin E significantly reduced the cytotoxicity of NMOR, however, both vitamins had not effect on cytotoxicity induced by MNNG. These results suggest that different N-nitroso compounds react differently with cellular macromolecules. Measurement of the level of NMOR-induced DNA strand breaks and alkali-labile sites in both cell types using the alkaline comet assay also indicates a protective effect of both vitamins against the genotoxic effects of NMOR.

Micronutrients and genomic stability: a new paradigm for recommended dietary allowances (RDAs)

Diet as a key factor in determining genomic stability is more important than previously imagined because we now know that it impacts on all relevant pathways, namely exposure to dietary carcinogens, activation/detoxification of carcinogens, DNA repair, DNA synthesis and apoptosis. Current recommended dietary allowances for vitamins and minerals are based largely on the prevention of diseases of deficiency such as scurvy in the case of vitamin C. Because diseases of development, degenerative disease and aging itself are partly caused by damage to DNA it seems logical that we should focus better our attention on defining optimal requirements of key minerals and vitamins for preventing damage to both nuclear and mitochondrial DNA. To date, our knowledge on optimal micronutrient levels for genomic stability is scanty and disorganised. However, there is already sufficient evidence to suggest that marginal deficiencies in folate, vitamin B12, niacin and zinc impact significantly on spontaneous chromosome damage rate. The recent data for folate and vitamin B12 in humans with respect to micronucleus formation in blood and epithelial cells provide compelling evidence of the important role of these micronutrients in maintenance of genome integrity and the need to revise current RDAs for these micronutrients based on minimisation of DNA damage. Appropriately designed in vitro studies and in vivo placebo controlled trials with dose responses using a complementary array of DNA damage biomarkers are required to define recommended dietary allowances for genomic stability. Furthermore these studies would have to be targeted to individuals with common genetic polymorphisms that alter the bioavailability of specific micronutrients and the affinity of specific key enzymes involved in DNA metabolism for their micronutrient co-factor. That there is a need for an international collaborative effort to establish RDAs for genomic stability is self-evident.

Gene-nutrient interactions and DNA methylation

Many micronutrients and vitamins are critical for DNA synthesis/repair and maintenance of DNA methylation patterns. Folate has been most extensively investigated in this regard because of its unique function as methyl donor for nucleotide synthesis and biological methylation. Cell culture and animal and human studies showed that deficiency of folate induces disruption of DNA as well as alterations in DNA methylation status. Animal models of methyl deficiency demonstrated an even stronger cause-and-effect relationship than did studies using a folate-deficient diet alone. Such observations imply that the adverse effects of inadequate folate status on DNA metabolism are mostly due to the impairment of methyl supply. Recently, an interaction was observed between folate status and a common mutation in the gene encoding for methylenetetrahydrofolate reductase, an essential enzyme in one-carbon metabolism, in determining genomic DNA methylation. This finding suggests that the interaction between a nutritional status with a genetic polymorphism can modulate gene expression through DNA methylation, especially when such polymorphism limits the methyl supply. DNA methylation, both genome-wide and gene-specific, is of particular interest for the study of cancer, aging and other conditions related to cell-cycle regulation and tissue-specific differentiation, because it affects gene expression without permanent alterations in DNA sequence such as mutations or allele deletions. Understanding the patterns of DNA methylation through the interaction with nutrients is fundamental, not only to provide pathophysiological explanations for the development of certain diseases, but also to improve the knowledge of possible prevention strategies by modifying a nutritional status in at-risk populations.

Genetic regulation of ionizing radiation sensitivity and breast cancer risk

Genetic variability in DNA repair may contribute to hypersensitivity to ionizing radiation (IR) and susceptibility to breast cancer. We used samples collected from a clinic-based breast cancer case-control study to test the working hypothesis that amino acid substitution variants of DNA repair genes may contribute to prolonged cell-cycle delay following IR and breast cancer risk. Fluorescence-activated cell sorter (FACS) analysis was used to measure cell-cycle delay. PCR-restriction fragment length polymorphism (RFLP) assays were used to determine four genotypes of three DNA repair genes: XRCC1, 194 Arg/Trp and 399 Arg/Gln; XRCC3, 241 Thr/Met; and APE1, 148 Asp/Glu. The data showed that breast cancer patients had a significantly higher delay index than that of controls (P < 0.001); the means +/- SD for cases and controls were 36.0 +/- 13.1 (n = 118) and 31.4 +/- 11.5 (n = 225), respectively. There was a significant dose-response relationship between delay index, categorized into quartiles, and an increasing risk of breast cancer (crude odds ratios: 1.00, 1.00, 1.27, and 2.46, respectively; P(trend) = 0.002). In controls, prolonged cell-cycle delay was significantly associated with the number of variant alleles in APE1 Asp148Glu and XRCC1 Arg399Gln genotypes (P(trend) = 0.001). Although larger studies are needed to validate the results, our data suggest that an inherited hypersensitivity to IR may contribute to human breast carcinogenesis.

Vitamins/minerals and genomic stability in humans

Recommended dietary allowances (RDAs) of micronutrients have been traditionally derived as those levels necessary to prevent symptoms of deficiency diseases. There is increasing evidence that higher levels of many such micronutrients may be necessary for various DNA maintenance reactions, and that the current RDAs for some micronutrients may be inadequate to protect against genomic instability. Supplementation of a normal diet, with either vitamins and/or minerals or with isolated plant polyphenols, is becoming increasingly common in most Western populations. However, there is no clear agreement as to how much supplementation should occur, if at all, and genotypic differences are not accounted for. The 14 mini-reviews in this special issue summarise the role of specific micronutrients in various aspects of DNA maintenance: DNA synthesis, DNA repair, DNA methylation, gene mutation, chromosome breakage, chromosome segregation, gene expression, oxidative stress, necrosis and apoptosis. Evidence has been collated from mammalian and human experiments, both using in vitro cultures and in vivo approaches. Authors were asked to critically assess the strength of evidence as to whether the micronutrient can affect genomic stability in humans at realistic intake levels, and to estimate optimal dietary ranges where possible. Information on further research necessary is also documented. These reviews are an essential step towards a definition of RDAs designed to maintain genomic stability.