Sodium ascorbate induces DNA single-strand breaks in human cells in vitro

Effect of Olive Leaves or Marigold Petal Extract on Oxidative Stress, Gut Fermentative Activity, and Mucosa Morphology in Broiler Chickens Fed a Diet Rich in n-3 Polyunsaturated Fats

An experiment in broilers was conducted to investigate the effect of olive (Olea europea) leaves and marigold (Calendula officinalis) petal extract supplementation on oxidative stress, characteristics of intestinal contents, and on the morphology of the small intestine. Oxidative stress was induced by a n-3 polyunsaturated fatty acids rich diet. 1-day-old male broiler chickens, Ross 308, were housed in a deep litter system. After the first 21 days, animals were randomly divided into three groups of 16 animals in two replicates and fed, until slaughter on day 39, a diet that contained 7% linseed oil. Control diet (Cont) remained unsupplemented, while both experimental diets were supplemented with olive leaves (OliveEx) or marigold petal (MarigEx) extracts. Oxidative stress was evaluated in blood and liver by measuring markers of lipid peroxidation (malondialdehyde (MDA), isoprostanes), rate of DNA damage in lymphocytes and in blood (comet assay, 8-hydroxy-2'deoxyguanosine (8-OHdG)), and activity of antioxidant and liver enzymes in blood. In different parts of the intestine, levels of short chain fatty acids (SCFA), and viscosity of intestinal contents were measured, and the health of the gastrointestinal tract was assessed using histological measurements. OliveEx significantly (p<0.05) decreased the MDA and 8-OHdG concentration in plasma, and the level of ethanoic acid in small intestinal contents and total SCFA in caecum, indicating improved oxidative status and increased microbial activity in the intestine. MarigEx significantly (p<0.05) decreased the rate of lymphocyte DNA damage and the crypt depth in duodenum, indicating potentially beneficial effects on the immune system and the health of the small intestine. In conclusion, dietary OliveEx and MarigEx supplementation improved some markers of oxidative stress and intestinal health. However, positive effects could be more pronounced in more unfavorable environmental conditions or in cases of diseases, but further studies are needed.

High-Dose Vitamin C: Preclinical Evidence for Tailoring Treatment in Cancer Patients

Simple Summary

Vitamin C is an indispensable micronutrient in the human diet due to the multiple functions it carries out in the body. Reports of clinical studies have indicated that, when administered at high dosage by the intravenous route, vitamin C may exert beneficial antitumor effects in patients with advanced stage cancers, including those refractory to previous treatment with chemotherapy. The aim of this article is to provide an overview of the current scientific evidence concerning the different mechanisms of action by which high-dose vitamin C may kill tumor cells. A special focus will be given to those mechanisms that provide the rationale basis for tailoring vitamin C treatment according to specific molecular alterations present in the tumor and for the selection of the most appropriate companion drugs.

Abstract

High-dose vitamin C has been proposed as a potential therapeutic approach for patients with advanced tumors who failed previous treatment with chemotherapy. Due to vitamin C complex pharmacokinetics, only intravenous administration allows reaching sufficiently high plasma concentrations required for most of the antitumor effects observed in preclinical studies (>0.250 mM). Moreover, vitamin C entry into cells is tightly regulated by SVCT and GLUT transporters, and is cell type-dependent. Importantly, besides its well-recognized pro-oxidant effects, vitamin C modulates TET enzymes promoting DNA demethylation and acts as cofactor of HIF hydroxylases, whose activity is required for HIF-1α proteasomal degradation. Furthermore, at pharmacological concentrations lower than those required for its pro-oxidant activity (<1 mM), vitamin C in specific genetic contexts may alter the DNA damage response by increasing 5-hydroxymethylcytosine levels. These more recently described vitamin C mechanisms offer new treatment opportunities for tumors with specific molecular defects (e.g., HIF-1α over-expression or TET2, IDH1/2, and WT1 alterations). Moreover, vitamin C action at DNA levels may provide the rationale basis for combination therapies with PARP inhibitors and hypomethylating agents. This review outlines the pharmacokinetic and pharmacodynamic properties of vitamin C to be taken into account in designing clinical studies that evaluate its potential use as anticancer agent.

Genotoxic Effects of Pentachlorophenol, Lindane, Transfluthrin, Cyfluthrin, and Natural Pyrethrum on Human Mucosal Cells of the Inferior and Middle Nasal Conchae

Background

Animal experiments and epidemiological studies suggest that pentachlorophenol (PCP) and γ-hexachlorocyclo-hexane (lindane) should be classified as possible human carcinogens. In the past, both have had a variety of applications in the civilian and military sectors and in forestry. They have, e.g., been used to impregnate and treat uniforms and other fabrics and to control human lice. Animal experiments indicate that PCP in particular causes mutations and chromosome aberrations and thus DNA damage. Studies on whether or not this also applies to newer substances and especially to natural type I and type II pyrethroids still are not available. What is particularly lacking are data on the genotoxic effects of these substances on human target cells. Our study describes the genotoxic effects of PCP, lindane, transfluthrin, cyfluthrin, and natural pyrethrum on human mucosal cells of the inferior and middle nasal conchae.

Methods

Epithelial cells were isolated from nasal mucosa, which was removed in the surgical treatment of chronic sinusitis and nasal concha hyperplasia. After the cells had been tested for vitality using the trypan blue exclusion test, the short-term culture method was used. The material was incubated with PCP (0.3, 0.75, and 1.2 mmol), lindane (0.5, 0.75, and 1.0 mmol), transfluthrin (0.05, 0.1, 0.5, 0.75, and 1.0 mmol), cyfluthrin (0.05, 0.1, 0.5, 0.75, and 1.0 mmol), natural pyrethrum (0.001, 0.005, 0.01, 0.05, and 0.1 mmol), and N-methyl-N'-nitro-N-nitrosoguanidine for 60 minutes. Substance-induced DNA damage (single-strand and double-strand breaks) were determined using single-cell microgel electrophoresis. A fluorescence microscope was used together with an image processing system to analyze the results obtained.

Results

After exposure to all tested substances, a high percentage of the cells of the middle nasal concha in particular were found to have severely fragmented DNA as a result of strong genotoxic effects. Although the reaction of the cells of the inferior nasal concha was significantly less strong (p < 0.001), the tested substances were nevertheless found to have a notable genotoxic effect on these cells too.

Conclusions

Our study strongly suggests that exposure to PCP, lindane, transfluthrin, cyfluthrin, and natural pyrethrum has a genotoxic effect on the epithelial cells of human nasal mucosa. In addition, we have shown that nasal structures differ in susceptibility to the various pesticides used in the tests. Thus, the study provides new evidence supporting the biological plausibility of PCP- and lindane-induced effects, thereby helping evaluate potential PCP- and lindane-induced mucous membrane carcinomas of these parts of the nose. In addition, our study shows that other substances that today are widely used for controlling pests have a considerable genotoxic effect on human target cells. The results obtained indicate the need for additional studies on the genotoxicity of these substances and their adverse effects on human health.

Induction of cellular and molecular Immunomodulatory pathways by vitamin E and vitamin C

INTRODUCTION

Vitamins E and C are well known small molecules that have been used to maintain health for decades. Recent studies of the cellular and molecular pathways leading to immunomodulation by these molecules have been of interest, as have their anti-oxidant properties and signal transduction pathways for curing or improving infectious diseases and cancer. Areas covered: Herein, the authors provide a definition and the structural classification of vitamins E and C and how these molecules influence cellular function. The studies include in vitro, ex vivo and in vivo studies in animal models as well as clinical trials. The authors give particular focus to the scientifically factual and putative roles of these molecules in innate and adaptive immunomodulation and prevention or cure of diseases. Expert opinion: The antioxidant properties of vitamins E and C are well studied. However, whether there is a link between their antioxidant and immunomodulation properties is unclear. In addition, there is a strong, albeit putative, prevailing notion that vitamin C can prevent or cure infectious diseases or cancer. Presently, while there is proven evidence that vitamin E possesses immunomodulatory properties that may play a positive role in disease outcomes, this evidence is less available for vitamin C.

Effect of L-ascorbic Acid on the hsp70 Expression and Tissue Damage in the Third Instar Larvae of Transgenic Drosophila melanogaster (hsp70-lacZ) Bg(9)

All living organisms respond to various physical or chemical stressors by the induction of heat shock protein (HSP). The present study was performed on transgenic Drosophila melanogaster (hsp70-lacZ) Bg⁹ in which the transformation vector is inserted with a P-element, the line contains wild-type hsp70 sequence up to the lacZ fusion point. The effect of L-ascorbic acid on the hsp70 expression and tissue damage was studied at the doses of 1, 2, 4, and 8 × 10^–4 g/ml in the third instar larvae of transgenic D. melanogaster (hsp70-lacZ) Bg⁹. The larvae were exposed to different doses of L-ascorbic acid for 24 and 48 hours. A dose-dependent significant increase in the hsp70 expression was observed at 2, 4, and 8 × 10^–4 g/ml of L-ascorbic acid for both 24 and 48 hours. The tissue damage was observed only in the 48 hours of exposure and mostly only in the salivary glands of the third instar larvae of transgenic D. melanogaster (hsp70-lacZ) Bg⁹. The present study also validates and supports the use of transgenic D. melanogaster (hsp70-lacZ) Bg⁹ for the toxicological evaluations.

The effect of vitamin E and plant extract mixture composed of carvacrol, cinnamaldehyde and capsaicin on oxidative stress induced by high PUFA load in young pigs

The objective of our study was to determine the antioxidative potential of a plant extract (PE) mixture composed of carvacrol, capsicum oleoresin and cinnamaldehyde against high n-3 polyunsaturated fatty acid (PUFA)-induced oxidative stress in young pigs. Thirty-two weaned castrated male crossbred pigs (BW 10.9 kg; n = 32) were randomly assigned to four dietary treatments (n = 8). The negative control diet (Cont) contained 17.2% energy from fat. Oxidative stress was induced in three of the four experimental groups with the inclusion of n-3 PUFA rich linseed oil. Linseed oil substituted wheat starch in the diet to elevate the amount of energy from fat to 34.1%. One of these diets served as a positive control (Oil), one was additionally supplemented with 271.2 mg/kg of PE mixture and one with 90.4 mg/kg α-tocopheryl acetate (Vit E). After 14 days of treatment, blood and urine were collected for the determination of lipid peroxidation and DNA damage. Lipid peroxidation was studied by plasma malondialdehyde (MDA) concentrations, 24 h urinary MDA and F2-isoprostane (iPF2α-VI) excretion, total antioxidant status of plasma and glutathione peroxidase assays. Lymphocyte DNA fragmentation and 24 h urinary 8-hydroxy-2'-deoxyguanosine excretion were measured to determine DNA damage. Consumption of n-3 PUFA rich linseed oil increased the amount of MDA in plasma and urine, and induced DNA damage in lymphocytes, but did not elevate the amount of iPF2α-VI excreted in the urine. The supplementation with PE and with Vit E did not reduce MDA levels in plasma and urine, but it decreased the percentage of DNA damage in lymphocytes (P < 0.001). The PE reduced the urinary iPF2α-VI excretion in comparison to the Cont diet. The results show that PE and Vit E supplemented to pigs in concentrations of 271.2 mg/kg and 90.4 mg/kg, respectively, can effectively protect pig's blood lymphocytes against oxidative DNA damage, thus suggesting their potentially beneficial effects on the immune system under dietary-induced oxidative stress.

The comparison of in vivo antigenotoxic and antioxidative capacity of two propylene glycol extracts of Calendula officinalis (marigold) and vitamin E in young growing pigs

The objective of the study was to evaluate the protective effect of Calendula officinalis propylene glycol extracts against oxidative DNA damage and lipid peroxidation induced by high polyunsaturated fatty acid (PUFA) intake in young growing pigs. Forty young growing pigs were assigned to five treatment groups: control; oil (linseed oil supplementation); C. officinalis 1 and 2 groups (linseed oil plus 3 ml/day of C. officinalis propylene glycol extracts); and vitamin E group (linseed oil plus 100 mg/kg of vitamin E). Lymphocyte DNA fragmentation and 24-h urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG) excretion were measured to determine DNA damage. Lipid peroxidation was studied by analysing plasma and urine malondialdehyde (MDA), and urine isoprostane concentrations (iPF2α-VI), total antioxidant status of plasma and glutathione peroxidase (GPx) assays. C. officinalis 1 (extract from petals) effectively protected DNA from oxidative damage. It indicated a numerical trend towards the reduction of plasma MDA and urinary iPF2α-VI excretion. Its effect was comparable with that of vitamin E. C. officinalis 2 (extract from flower tops) showed less antioxidant potential than the extract from petals. We can conclude that the amount of C. officinalis extracts proposed for internal use by traditional medicine protects the organism against DNA damage induced by high PUFA intake.

In vivo antioxidant potential of Sweet chestnut (Castanea sativa Mill.) wood extract in young growing pigs exposed to n-3 PUFA-induced oxidative stress

BACKGROUND

Farm animals in intensive farming systems are frequently exposed to oxidative stress, which demands adequate antioxidant protection. The aim of this study was to evaluate the antioxidant potential of different concentrations of Sweet chestnut wood extract (SCW; 0.75, 1.5 and 3 g kg⁻¹) in case of n-3 PUFA-induced oxidative stress in young pigs.

RESULTS

The highest concentration (3 g kg⁻¹) of SCW decreased malondialdehyde excretion in urine by 31.7%, but had no effect on plasma malondialdehyde. A linear trend towards decrease of urine isoprostanes iPF(2α)-VI was observed with the addition of SCW. All three concentrations of SCW efficiently protected blood lymphocytes from DNA damage and lowered plasma alanine aminotransferase levels. The antioxidative and antigenotoxic effect of 3 g SCW kg⁻¹ feed was comparable to the effect of 90.4 mg kg⁻¹ of added vitamin E.

CONCLUSION

The results from this study show that, besides being known as antihelmintic, antimicrobial and antiviral agent, Sweet chestnut wood extract could also be considered as a promising natural antioxidant in animal nutrition.

Cell death by the quinoxaline dioxide DCQ in human colon cancer cells is enhanced under hypoxia and is independent of p53 and p21

INTRODUCTION

We have shown that the radio sensitizer DCQ enhances sensitivity of HCT116 human colon cancer cells to hypoxia. However, it is not known whether the p53 or p21 genes influence cellular response to DCQ. In this study, we used HCT116 that are either wildtype for p53 and p21, null for p53 or null for p21 to understand the role of these genes in DCQ toxicity.

METHODS

HCT116 cells were exposed to DCQ and incubated under normoxia or hypoxia and the viability, colony forming ability, DNA damage and apoptotic responses of these cells was determined, in addition to the modulation of HIF-1α and of p53, p21, caspase-2, and of the ataxia telangiectasia mutated (ATM) target PIDD-C.

RESULTS

DCQ decreased colony forming ability and viability of all HCT116 cells to a greater extent under hypoxia than normoxia and the p21-/-cell line was most sensitive. Cells had different HIF-1α responses to hypoxia and/or drug treatment. In p53+/+, DCQ significantly inhibited the hypoxia-induced increases in HIF-1α protein, in contrast to the absence of a significant HIF-1α increase or modulation by DCQ in p21-/- cells. In p53-/- cells, 10 μM DCQ significantly reduced HIF-1α expression, especially under hypoxia, despite the constitutive expression of this protein in control cells. Higher DCQ doses induced PreG1-phase increase and apoptosis, however, lower doses caused mitotic catastrophe. In p53+/+ cells, apoptosis correlated with the increased expression of the pro-apoptotic caspase-2 and inhibition of the pro-survival protein PIDD-C. Exposure of p53+/+ cells to DCQ induced single strand breaks and triggered the activation of the nuclear kinase ATM by phosphorylation at Ser-1981 in all cell cycle phases. On the other hand, no drug toxicity to normal FHs74 Int human intestinal cell line was observed.

CONCLUSIONS

Collectively, our findings indicate that DCQ reduces the colony survival of HCT116 and induces apoptosis even in cells that are null for p53 or p21, which makes it a molecule of clinical significance, since many resistant colon tumors harbor mutations in p53.

The antioxidant ascorbic acid mobilizes nuclear copper leading to a prooxidant breakage of cellular DNA: implications for chemotherapeutic action against cancer

PURPOSE

Ascorbic acid is an essential micronutrient and is considered to have an antioxidant function in living systems. For the past several decades, ascorbic acid has been the subject of considerable interest as an anticancer agent. Several studies have shown that ascorbic acid is cytotoxic to a variety of cancer cells, whereas normal cells are relatively resistant to such cytotoxic action. In this study, we propose a putative molecular mechanism that accounts for the preferential cytotoxicity of ascorbic acid against cancer cells.

METHODS

Standard and lysed version of alkaline single-cell gel electrophoresis (Comet assay); ferrous oxidation-xylenol orange (FOX) assay.

RESULTS

We show that ascorbic acid acts as a prooxidant and leads to oxidative DNA breakage in lymphocytes and lymphocyte nuclei. Scavengers of reactive oxygen species were able to inhibit ascorbic acid-induced DNA breakage, suggesting the involvement of reactive oxygen species in this reaction. We further show that such DNA breakage is inhibited by both iron and copper chelators in cells, whereas in nuclei, similar inhibition was achieved only by copper chelators, indicating an important role of chromatin-bound copper in the prooxidant cellular DNA breakage by ascorbic acid.

CONCLUSION

We propose that the copper-dependent cellular redox status is an important element in the cytotoxic action of ascorbic acid against cancer cells. It is well established that cellular copper levels are considerably elevated in various malignancies. Therefore, cancer cells may be more subject to electron transfer between copper and ascorbate to generate reactive oxygen species. In light of these observations and those in literature, in this paper we explain that the preferential cytotoxicity of ascorbic acid against cancer cells is the result of elevated copper levels in such cells. Further, this study identifies nuclear copper as a novel molecular target for cytotoxic action of ascorbic acid, which has implications for its chemotherapeutic properties against cancer.

The radiosensitizer 2-benzoyl-3-phenyl-6,7-dichloroquinoxaline 1,4-dioxide induces DNA damage in EMT-6 mammary carcinoma cells

Background

DCQ (2-benzoyl-3-phenyl-6,7-dichloroquinoxaline 1,4-dioxide), a synthetic quinoxaline 1,4-dioxide, enhances the cytotoxic effect of ionizing radiation (IR) in vivo and in vitro. We sought to clarify whether increased radiation-induced DNA damage, decreased rate of damage repair, and the generation of reactive oxygen species (ROS) contribute to DCQ enhancement of IR.

Methods

Murine mammary adenocarcinoma EMT-6 cells were treated with DCQ for 4 h before exposure to 10 Gy IR. Treated cells were monitored for modulations in cell cycle, induction of DNA damage, and generation of ROS.

Results

Combined DCQ and IR treatments (DCQ+IR) induced rapid cell-cycle arrests in EMT-6 cells, particularly in S and G₂/M phases. Alkaline comet assays revealed high levels of DNA damage in cells after exposure to DCQ+IR, consistent with damage-induced arrest. Unlike IR-only and DCQ-only treated cells, the damage induced by combined DCQ+IR was repaired at a slower rate. Combined treatment, compared to separate DCQ and IR treatments, activated DNA-protein kinase and induced more p-ATM, supporting a role for double strand breaks (DSBs), which are more toxic and difficult to repair than single strand breaks (SSBs). Contributing factors to DCQ radiosensitization appear to be the induction of ROS and DSBs.

Conclusion

Collectively, our findings indicate that radiosensitization by DCQ is mediated by DNA damage and decreased repair and that ROS are at least partially responsible.

DNA damage, a biomarker of carcinogenesis: its measurement and modulation by diet and environment

Free radicals and other reactive oxygen or nitrogen species are constantly generated in vivo and can cause oxidative damage to DNA. This damage has been implicated to be important in many diseases, including cancer. The assessment of damage in various biological matrices, such as tissues, cells, and urine, is vital to understanding this role and subsequently devising intervention strategies. During the last 20 years, many analytical techniques have been developed to monitor oxidative DNA base damage. High-performance liquid chromatography-electrochemical detection and gas chromatography-mass spectrometry are the two pioneering contributions to the field. Currently, the arsenal of methods available include the promising high-performance liquid chromatography-tandem mass spectrometry technique, capillary electrophoresis, 32P-postlabeling, antibody-base immunoassays, and assays involving the use of DNA repair glycosylases such as the comet assay. The objective of this review is to discuss the biological significance of oxidative DNA damage, evaluate the effectiveness of several techniques for measurement of oxidative DNA damage in various biological samples and review current research on factors (dietary and non-dietary) that influence DNA oxidative damage using these techniques.

Effect of nucleotide supplementation on lymphocyte DNA damage induced by dietary oxidative stress in pigs

The aim of the present study was to evaluate the effect of nucleotide supplementation on the oxidative stress induced by a high proportion of dietary polyunsaturated fatty acids ( PUFAs) in pigs. Twenty-four male growing pigs were penned individually and after an adaptation period divided into three groups. All groups received isocaloric daily rations composed of a basal diet supplemented with either: starch (CONT), linseed oil (LIN) and LIN and nucleotides (LIN + NUC). The experimental period lasted 21 days. Oxidative stress was evaluated by measuring the degree of lymphocyte nuclear DNA damage, the urine malondialdehyde ( MDA) excretion rate, erythrocyte glutathione peroxidase concentration and the total anti-oxidant status of plasma. Malondialdehyde concentrations in the blood and MDA urinary excretion rates were higher (P< 0·01) in animals supplemented with LIN and LIN + NUC compared with CONT animals. The degree of DNA damage in the LIN-supplemented animals was also higher (P< 0·01). Compared with the LIN-supplemented animals, nucleotide supplementation reduced (P< 0·01) the degree of DNA damage in lymphocytes to the level of the CONT group. Erythrocyte glutathione peroxidase concentration and plasma total anti-oxidant status were similar across treatments. The results of this experiment indicate that nucleotide supplementation effectively eliminates the genotoxic effects of high PUFA intakes on blood lymphocytes and demonstrates new evidence for the immunonutritive effect of nucleotides.

Investigation of the role of extracellular H2O2 and transition metal ions in the genotoxic action of ascorbic acid in cell culture models

In the presence of oxygen, ascorbic acid (AA) is unstable in aqueous media and oxidises to dehydroascorbate (DHA), generating reactive intermediates such as ascorbate free radical and H2O2. It is proposed that the cytotoxicity of AA is due to the extracellular production of H2O2 and that this is mediated by transition metal ions present in cell media. Here we investigate the role of extracellular H2O2 and metal ions in the genotoxicity of AA in cell culture models. Our preliminary results confirmed that physiological concentrations of AA were not toxic to confluent human fibroblasts, although they inhibited the proliferation of cells at low density. No inhibition was observed with ascorbic acid 2-phosphate (AA2P), a vitamin C derivative that remains stable in culture media. Furthermore, high concentrations of AA induced DNA strand breakage in a dose-dependent manner, whereas DHA and AA2P were not genotoxic. The genotoxic effect of AA was transient, required the formation of extracellular H2O2 and the presence of intracellular iron, but not of extracellular transition metal ions. These observations further clarify the pro-oxidant effect of AA solutions in cell culture models. The possibility that intravenous administration of high-dose AA may cause a similar genotoxic effect in vivo is discussed.

Prooxidant DNA breakage induced by caffeic acid in human peripheral lymphocytes: Involvement of endogenous copper and a putative mechanism for anticancer properties

Plant-derived dietary material contains several classes of polyphenols such as flavonoids, curcuminoids, stilbenes and hydroxycinnamic acids. They are recognized as naturally occurring antioxidants but also act as prooxidants catalyzing cellular DNA degradation in the presence of transition metal ions such as copper. Earlier we have shown that the stilbene resveratrol is able to mobilize endogenous copper ions leading to oxidative breakage of cellular DNA. In this paper, we show that caffeic acid (a hydroxycinnamic acid), which is a major constituent of coffee, is also capable of DNA breakage in human peripheral lymphocytes. Incubation of lymphocytes with neocuproine inhibited the DNA degradation confirming that Cu(I) is an intermediate in the DNA cleavage reaction. Further, we have also shown that caffeic acid generates oxidative stress in lymphocytes, which is inhibited by scavengers of reactive oxygen species and neocuproine. These results are in further support of our hypothesis that anticancer mechanism of plant polyphenols involves mobilization of endogenous copper, possibly chromatin bound copper, and the consequent prooxidant action.

Ascorbic acid mobilizes endogenous copper in human peripheral lymphocytes leading to oxidative DNA breakage: a putative mechanism for anticancer properties

Several decades back ascorbic acid was proposed as an effective anticancer agent. However, this idea remained controversial and the mechanism of action unclear. In this paper, we show that ascorbic acid at a concentration reported to be achievable through high doses of oral consumption is capable of cytotoxic action against normal cells. Several antioxidants of both animal as well as plant origin including ascorbic acid also possess prooxidant properties. Copper is an essential component of chromatin and can take part in redox reactions. Previously we have proposed a mechanism for the cytotoxic action of plant antioxidants against cancer cells that involves mobilization of endogenous copper ions and the consequent generation of reactive oxygen species. Using human peripheral lymphocytes and Comet assay we show here that ascorbic acid is able to cause oxidative DNA breakage in normal cells at a concentration of 100-200 microM. Neocuproine, a Cu(I) specific sequestering agent inhibited DNA breakage in a dose dependent manner indicating that Cu(I) is an intermediate in the DNA cleavage reaction. The results are in support of our above hypothesis that involves events that lead to a prooxidant action by antioxidants. The results would support the idea that even a plasma concentration of around 200 microM. would be sufficient to cause pharmacological tumor cell death particularly when copper levels are elevated. This would account for the observation of several decades back by Pauling and co-workers where oral doses of ascorbic acid in gram quantities were found to be effective in treating some cancers.

Efficiency of apples, strawberries, and tomatoes for reduction of oxidative stress in pigs as a model for humans

OBJECTIVE

The present study investigated the potency of apples, strawberries, and tomatoes in decreasing oxidative stress in pigs as a model for humans.

METHODS

Forty-eight growing pigs were individually penned in metabolic cages and divided into six groups. All groups received isocaloric daily rations composed of a basal diet supplemented with starch, linseed oil, linseed oil and apples, linseed oil and strawberries, linseed oil and tomatoes, or linseed oil, apples, strawberries and tomatoes. Oxidative stress was evaluated at the beginning and at the end of the 22-d experimental period by measuring the degree of DNA damage in mononuclear blood cells, the concentration of malondialdehyde (MDA) in plasma, the MDA excretion rate, the concentration of tocopherols in plasma, plasma total antioxidant status, and erythrocyte glutathione peroxidase concentration.

RESULTS

The results confirmed that the linseed oil diet significantly increased MDA formation in the body and DNA damage to mononuclear blood cells in comparison with the starch diet. Although the MDA concentration in plasma was significantly decreased in all fruit groups, urine MDA excretion rate was decreased only in the linseed oil/apple and linseed oil/apple/strawberry/tomato groups. Supplementation with fruit significantly decreased DNA damage, was more pronounced in the linseed oil/apple and linseed oil/apple/strawberry/tomato groups. Significantly lower glutathione peroxidase concentrations were observed only in the linseed oil/strawberry group.

CONCLUSIONS

Our findings support the hypothesis that supplementation with apples, strawberries, or tomatoes effectively decreases oxidative stress by decreasing MDA formation in the body and by protecting mononuclear blood cells against increased DNA damage. This effect was particularly pronounced in the group supplemented with a fruit mixture; among the single fruit supplements, the most beneficial effect was obtained with apples.

Plant polyphenols mobilize endogenous copper in human peripheral lymphocytes leading to oxidative DNA breakage: A putative mechanism for anticancer properties

Plant polyphenols are important components of human diet and a number of them are considered to possess chemopreventive and therapeutic properties against cancer. They are recognized as naturally occurring antioxidants but also act as prooxidants catalyzing DNA degradation in the presence of transition metal ions such as copper. Using human peripheral lymphocytes and Comet assay we have previously confirmed that resveratrol-Cu(II) is indeed capable of causing DNA degradation in cells. In this paper we show that the polyphenols alone (in the absence of added copper) are also capable of causing DNA breakage in cells. Incubation of lymphocytes with neocuproine inhibited the DNA degradation confirming that Cu(I) is an intermediate in the DNA cleavage reaction. Further, we have also shown that polyphenols generate oxidative stress in lymphocytes which is inhibited by scavengers of reactive oxygen species and neocuproine. These results are in further support of our hypothesis that anticancer mechanism of plant polyphenols involves mobilization of endogenous copper, possibly chromatin bound copper, and the consequent prooxidant action.

Inhibitory effect of ascorbic acid post-treatment on radiation-induced chromosomal damage in human lymphocytes in vitro

In the present study, the effect of exposure to ascorbic acid (vitamin C) after gamma-ray-induced chromosomal damage in cultured human lymphocytes was examined to explore the mechanism by which this antioxidant vitamin protects irradiated cells Non-irradiated lymphocytes were exposed to increasing concentrations of ascorbic acid (1-100 micro g/ml) and DNA damage was estimated using chromosomal aberration analysis and the comet assay. The results showed that ascorbic acid did not influence the frequency of chromosomal aberrations in non-irradiated cells, except at the highest concentration (20 micro g/ml), which induced breakage-type chromosomal aberrations. Vitamin C at the concentration of 50 micro g/ml caused DNA damage detected by the comet assay. A significant (34%) decrease in the frequency of chromosomal aberrations was observed in lymphocytes exposed to gamma-radiation and then cultured in the presence of ascorbic acid (1 micro g/ml). The removal of DNA breaks in cells exposed to 2 Gy of gamma-radiation was accelerated in the presence of ascorbic acid as determined by the comet assay, suggesting that it may stimulate DNA repair processes.

Vitamin C as an antioxidant: evaluation of its role in disease prevention

Vitamin C in humans must be ingested for survival. Vitamin C is an electron donor, and this property accounts for all its known functions. As an electron donor, vitamin C is a potent water-soluble antioxidant in humans. Antioxidant effects of vitamin C have been demonstrated in many experiments in vitro. Human diseases such as atherosclerosis and cancer might occur in part from oxidant damage to tissues. Oxidation of lipids, proteins and DNA results in specific oxidation products that can be measured in the laboratory. While these biomarkers of oxidation have been measured in humans, such assays have not yet been validated or standardized, and the relationship of oxidant markers to human disease conditions is not clear. Epidemiological studies show that diets high in fruits and vegetables are associated with lower risk of cardiovascular disease, stroke and cancer, and with increased longevity. Whether these protective effects are directly attributable to vitamin C is not known. Intervention studies with vitamin C have shown no change in markers of oxidation or clinical benefit. Dose concentration studies of vitamin C in healthy people showed a sigmoidal relationship between oral dose and plasma and tissue vitamin C concentrations. Hence, optimal dosing is critical to intervention studies using vitamin C. Ideally, future studies of antioxidant actions of vitamin C should target selected patient groups. These groups should be known to have increased oxidative damage as assessed by a reliable biomarker or should have high morbidity and mortality due to diseases thought to be caused or exacerbated by oxidant damage.

Antioxidants prevent the lymphocyte DNA damage induced by PMA-stimulated monocytes

Oxidative stress has been related to several degenerative diseases such as cancer and coronary heart disease. Reactive oxygen species can damage different cellular macromolecules, including DNA, which is directly responsible for mutation and carcinogenesis. In this study, monocytes that were activated by phorbol 12-myristate 13-acetate (PMA) were coincubated with lymphocytes, and the DNA damage was measured by single-cell gel electrophoresis (comet) assay. Stimulation of monocytes with PMA activates the "respiratory burst," which evokes DNA damage in lymphocytes. The extent of the damage is related to the concentration of monocytes and the exposure time. Exogenous addition of superoxide dismutase did not prevent the DNA damage, which suggests that superoxide ions are not directly responsible for the damage. Partial protection was observed when catalase was included (60% protection), which indicates that other reactive species, in addition to H2O2, are responsible for the damage. In this system, the protective activity of natural antioxidants at different concentrations was also investigated. After coincubation of PMA-activated monocytes with lymphocytes in the presence of each antioxidant for one hour at 37 degrees C, the lymphocyte DNA damage was determined. All the compounds protected the lymphocytes to a certain degree, with a maximum effect at different concentrations: 41% protection with 1 microM ascorbic acid, 55% protection with 40 microM alpha-tocopherol, 50% protection with 3 microM beta-carotene, and 56% protection with 5 microM quercetin. On the basis of these results, we maintain that this "ex vivo model," more closely related to physiological conditions, could be used to test the antioxidant activity of different compounds.

A critical assessment of some biomarker approaches linked with dietary intake

In this review many examples are given of the complexities involved in using some biomarkers in relation to assessing the effects of dietary exposure, when there is frequently a need to determine changes following long-term low level exposure to dietary components. These range from understanding why the biomarker might be valuable and how best it can be measured, to the pitfalls which can occur in the interpretation of data. Analytical technique is considered in relation to folate and selenium, and flavonoid and carotenoid species are used to illustrate how the metabolism of a compound may alter the validity or adequacy of a marker. Vitamin A is discussed in relation to the difficulties which can arise when there are several biomarkers that may be available to assess exposure to one nutrient. Vitamin B12 is discussed in relation to the dietary choices made by individuals. Possible interactions and the role of measuring total antioxidant capacity is considered in some detail. In contrast to most nutrients, there is a marked lack of biomarkers of either exposure or effect for most non-nutrients. The role of biological effect monitoring is considered for dietary contaminants, fumonisins and polyhalogenated aromatic hydrocarbons. Aflatoxins are discussed to exemplify food contaminants for which the biomarker approach has been extensively studied. Finally some compounds which are deliberately added to foods and some which appear as processing contaminants are each considered briefly in relation to the requirement for a biomarker of exposure to be developed.

Assays for DNA damage

This unit describes several assays for detecting several kinds of DNA damage (strand breaks, internal crosslinking, DNA/protein crosslinks) and repair activity following exposure to genotoxic agents. The methods include single-cell electrophoresis (comet assay), filter eluting, K-SDS precipitation, and measurement of unscheduled DNA synthesis.

Microgels for estimation of DNA strand breaks, DNA protein crosslinks and apoptosis

This report describes a part of the evolution of microgel electrophoresis in the author's laboratory for the last 15 years. It also describes the importance of estimation of DNA single and double strand breaks, DNA crosslinks and apoptosis. Some experiments based on each methodology are included here. A new protocol for rapid and efficient precipitation of DNA in microgel is included. A step by step description of laboratory protocol is also included.

Protective effect of extracts of Mesona procumbens Hemsl. on DNA damage in human lymphocytes exposed to hydrogen peroxide and UV irradiation

In the present study, the protective effect of water extracts from Hsian-tsao (WEHT) on DNA damage in human lymphocytes induced by UV-C and/or H(2)O(2) was evaluated using single-cell electrophoresis (comet assay). No toxicity was found in WEHT towards human lymphocytes. WEHT did not cause DNA damage at lower concentrations of 0.05 and 0.1 mg/ml, while it did cause slight DNA damage at a concentration of 0.5-2.5 mg/ml when compared with the control group. When WEHT was mixed with H(2)O(2) for reaction, it exhibited a slight inhibitory effect on DNA damage induced by H(2)O(2). Moreover, when WEHT and lymphocytes were irradiated by UV-C and then incubated for 35 min, the DNA damage decreased with an increase of the concentration of WEHT. Thus, WEHT could reduce UV-C-induced DNA damage, and WEHT had a more protective effect on UV-C than on H(2)O(2)-induced DNA damage. The protective effect of WEHT on DNA damage might be due to the fact that it contains polyphenol compounds and/or other active components.

A simple method for accurate estimation of apoptotic cells

A simple, sensitive, and reliable "DNA diffusion" assay for the quantification of apoptosis is described. Human lymphocytes and human lymphoblastoid cells, MOLT-4, were exposed to 0, 12.5, 25, 50, or 100 rad of X-rays. After 24 h of incubation, cells were mixed with agarose, microgels were made, and cells were lysed in high salt and detergents. DNA was precipitated in microgels by ethanol. Staining of DNA was done with an intense fluorescent dye, YOYO-1. Apoptotic cells show a halo of granular DNA with a hazy outer boundary. Necrotic cells, resulting from hyperthermia treatment, on the other hand, show an unusually large homogeneous nucleus with a clearly defined boundary. The number of cells with apoptotic and necrotic appearance can be scored and quantified by using a fluorescent microscope. Results were compared with other methods of apoptosis measurement: morphological estimations of apoptosis and DNA ladder pattern formation in regular agarose gel electrophoresis. Validation of the technique was done using some known inducers of apoptosis and necrosis (hyperthermia, hydrogen peroxide, mitoxantrone, novobiocin, and sodium ascorbate).

Antioxidant supplementation in vitro does not improve human sperm motility

OBJECTIVE

To determine the effects of supplementation of preparation media with ascorbate and alpha-tocopherol on subsequent sperm motility and reactive oxygen species production.

DESIGN

Prospective study to analyze postpreparation human sperm motility parameters and reactive oxygen species production following antioxidant supplementation.

SETTING

Andrology Laboratory, Royal Maternity Hospital, Belfast, Northern Ireland.

PATIENT(S)

Sixty patients attending the Andrology Laboratory for semen analysis.

INTERVENTION(S)

Normozoospermic and asthenozoospermic semen samples (n = 10 for each control and antioxidant group) were prepared by Percoll density centrifugation (95%-47.5%) in media supplemented with ascorbate or alpha-tocopherol to different concentrations within physiologic levels. Controls were included that were not exposed to antioxidant.

MAIN OUTCOME MEASURE(S)

Sperm motility parameters were assessed using computer-assisted semen analysis. The generation of reactive oxygen species was determined using luminol-dependent chemiluminescence.

RESULT(S)

The production of reactive oxygen species by sperm was reduced by supplementation in vitro with ascorbate and alpha-tocopherol. However, progressive motility, average path velocity, curvilinear velocity, straight-line velocity, and linearity were decreased significantly, with the greatest inhibition observed with the highest concentrations of antioxidants.

CONCLUSION(S)

Supplementation of preparation media with ascorbate and alpha-tocopherol, either singly or in combination, is not beneficial to sperm motility.

Does vitamin C act as a pro-oxidant under physiological conditions?

Vitamin C readily scavenges reactive oxygen and nitrogen species and may thereby prevent oxidative damage to important biological macromolecules such as DNA, lipids, and proteins. Vitamin C also reduces redox active transition metal ions in the active sites of specific biosynthetic enzymes. The interaction of vitamin C with 'free', catalytically active metal ions could contribute to oxidative damage through the production of hydroxyl and alkoxyl radicals; whether these mechanisms occur in vivo, however, is uncertain. To examine this issue, we reviewed studies that investigated the role of vitamin C, both in the presence and absence of metal ions, in oxidative DNA, lipid, and protein damage. We found compelling evidence for antioxidant protection of lipids by vitamin C in biological fluids, animals, and humans, both with and without iron cosupplementation. Although the data on protein oxidation in humans are sparse and inconclusive, the available data in animals consistently show an antioxidant role of vitamin C. The data on vitamin C and DNA oxidation in vivo are inconsistent and conflicting, but some of the discrepancies can be explained by flaws in experimental design and methodology. These and other important issues discussed here need to be addressed in future studies of the role of vitamin C in oxidative damage.

Single cell gel electrophoresis assay: methodology and applications

The single cell gel electrophoresis or Comet assay is a sensitive, reliable, and rapid method for DNA double- and single-strand breaks, alkali-labile sites and delayed repair site detection, in eukaryotic individual cells. Given its overall characteristics, this method has been widely used over the past few years in several different areas. In this paper we review the studies published to date about the principles, the basic methodology with currently used variations. We also explore the applications of this assay in: genotoxicology, clinical area, DNA repair studies, environmental biomonitoring and human monitoring.