Detection of in vivo genotoxicity of endogenously formed N-nitroso compounds and suppression by ascorbic acid, teas and fruit juices

Comet assay and hormesis

The paper provides the first assessment of the occurrence of hormetic dose responses using the Comet assay, a genotoxic assay. Using a priori evaluative criteria based on the Hormetic Database on peer-reviewed comet assay experimental findings, numerous examples of hormetic dose responses were obtained. These responses occurred in a large and diverse range of cell types and for agents from a broad range of chemical classes. Limited attempts were made to estimate the frequency of hormesis within comet assay experimental studies using a priori entry and evaluative criteria, with results suggesting a frequency in the 40% range. These findings are important as they show that a wide range of genotoxic chemicals display evidence that is strongly suggestive of hormetic dose responses. These findings have significant implications for study design issues, including the number of doses selected, dose range and spacing. Likewise, the widespread occurrence of hormetic dose responses in this genotoxic assay has important risk assessment implications.

Nanonitrator: novel enhancer of inorganic nitrate’s protective effects, predicated on swarm learning approach

Inorganic nitrate is an indispensable nutrient that has been used in experimental studies for the prevention and treatment of several diseases. However, the short half-life of nitrate limits its clinical application. To increase the usability of nitrate and overcome the challenges of traditional combination drug discovery through large-scale high-throughput biological experiments, we developed a swarm learning-based combination drug prediction system that identified vitamin C as the drug of choice to be combined with nitrate. Employing microencapsulation technology, we used vitamin C, sodium nitrate, and chitosan 3000 as the core materials to prepare a nitrate nanoparticle, which we named Nanonitrator. The long-circulating delivery ability of nitrate by Nanonitrator significantly increased the efficacy and effect duration of nitrate in irradiation-induced salivary gland injury, without compromising safety. Nanonitrator at the same dose could better maintain intracellular homeostasis than nitrate (with or without vitamin C), emphasizing its potential for clinical use. More importantly, our work provides a method for incorporating inorganic compounds into sustained-release nanoparticles.

Caenorhabditis elegans to Model the Capacity of Ascorbic Acid to Reduce Acute Nitrite Toxicity under Different Feed Conditions: Multivariate Analytics on Behavioral Imaging

Nitrocompounds are present in the environment and human diet and form part of vegetables and processed meat products as additives. These compounds are related to negative impacts on human and animal health. The protective effect of ascorbic acid has been demonstrated by some biological systems as regards several nitrocompounds. This work focused on studying the possibility of modeling this effect on nitrite toxicity with the model Caenorhabditis elegans. The three factors studied in this work were ascorbic acid concentration, nitrite exposure concentration, and presence/absence of food. The protective effect was evaluated by scoring lethality and its impact on behavior by means of multivariate statistical methods and imaging analytics. The effects of nitrite and the influence of food availability were evidenced. Apart from increasing lethality, nitrite had disruption effects on movements. All the observed symptoms reduced when ascorbic acid was administered, and it diminished lethality in all cases. Ascorbic acid maintained nematodes' postural capacities. The results suggest that nitrites' nonspecific toxicity in C. elegans can be mitigated by ascorbic acid, as previously evidenced in other biological systems. Thus, our results reveal the ability of C. elegans to reproduce the known protective effect of ascorbic acid against nitrite.

Inhibitory Effect of Epigallocatechin Gallate, Epigallocatechin, and Gallic Acid on the Formation of N-Nitrosodiethylamine In Vitro

This study investigated the inhibitory effect of epigallocatechin gallate (EGCG), epigallocatechin (EGC), and gallic acid (GA) on the formation of N-nitrosodiethylamine (NDEA) in vitro. Results show that the three polyphenols are capable to block NDEA formation when the molar ratio of phenols to nitrite is higher than 0.8, and a more acidic environment is prone to promote the inhibitory potential of phenols. It is also found that the inhibitory effect tends to decrease in the order: EGCG, EGC, GA, which is in accordance with the order of their DPPH scavenging activity, suggesting that the inhibitory effect of polyphenols on NDEA formation may work through a free radical way. Kinetic study further revealed the three polyphenols react with nitrite at a much faster rate than diethylamine does (P < 0.05). By scavenging nitrite at a faster rate than the nitrosation of diethylamine, polyphenols at high concentration can significantly block NDEA formation. These observations may promote a possible application of polyphenol compounds to inhibit the formation of nitrosamines in food processing. PRACTICAL APPLICATION: The presence of N-nitrosamines in human diet should be an etiological risk factor for human cancers. This work may provide a useful guideline for phenolic compounds to inhibit the formation of nitrosamines in food processing, such as in the process of curing meats. Polyphenols have been proved to block NDEA formation under normal gastric juice condition, suggesting the intake of polyphenols is a potential way to prevent diseases caused by nitrite.

Impacts of dietary exposure to sodium or potassium salts of nitrate and nitrite on the development of Drosophila melanogaster

The effects of four food additives, namely sodium nitrite (NaNO2), sodium nitrate (NaNO3), potassium nitrite (KNO2), and potassium nitrate (KNO3), on animal development were evaluated by using Drosophila melanogster, a model organism. Adult male and female flies were allowed to breed in culture medium, each containing one of 4 concentrations, i.e.10, 20, 30 or 40 mM of the above mentioned salts. The concentration of 40 mM, NaNO2 and KNO2 completely arrested the development of the flies. Of the different concentrations of the four salts tested, exposure of flies to 30 mM NaNO2 exhibited only significant delays in the initial appearances of third instar larvae, pupae and young adults, along with huge reduction in the number of pupae and young adults compared to controls. Rearrangements like inversions, deletion looping, regional shrinking, as well as highly enlarged puffing, etc. were also observed in the polytene chromosomes of the third instar larvae exposed to 30 mM NaNO2. Developmental outcomes of the flies exposed to varying concentrations of NaNO3 and KNO3 did not differ significantly from the controls. Owing to the extensive genetic homology between Drosophila and human and the successful uses of this fly as models in developmental and toxicological studies, we speculate that the experimental results exhibited by this organism in our study strongly advocate for abstaining from the dietary use of NaNO2 and KNO2 during human pregnancies to avoid possible negative developmental outcomes.

Re-evaluation of potassium nitrite (E 249) and sodium nitrite (E 250) as food additives

The Panel on Food Additives and Nutrient Sources added to Food (ANS) provided a scientific opinion re-evaluating the safety of potassium nitrite (E 249) and sodium nitrite (E 250) when used as food additives. The ADIs established by the SCF (1997) and by JECFA (2002) for nitrite were 0-0.06 and 0-0.07 mg/kg bw per day, respectively. The available information did not indicate in vivo genotoxic potential for sodium and potassium nitrite. Overall, an ADI for nitrite per se could be derived from the available repeated dose toxicity studies in animals, also considering the negative carcinogenicity results. The Panel concluded that an increased methaemoglobin level, observed in human and animals, was a relevant effect for the derivation of the ADI. The Panel, using a BMD approach, derived an ADI of 0.07 mg nitrite ion/kg bw per day. The exposure to nitrite resulting from its use as food additive did not exceed this ADI for the general population, except for a slight exceedance in children at the highest percentile. The Panel assessed the endogenous formation of nitrosamines from nitrites based on the theoretical calculation of the NDMA produced upon ingestion of nitrites at the ADI and estimated a MoE > 10,000. The Panel estimated the MoE to exogenous nitrosamines in meat products to be < 10,000 in all age groups at high level exposure. Based on the results of a systematic review, it was not possible to clearly discern nitrosamines produced from the nitrite added at the authorised levels, from those found in the food matrix without addition of external nitrite. In epidemiological studies there was some evidence to link (i) dietary nitrite and gastric cancers and (ii) the combination of nitrite plus nitrate from processed meat and colorectal cancers. There was evidence to link preformed NDMA and colorectal cancers.

Involvement of genetic factors and lifestyle on the occurrence of colorectal and gastric cancer

Gastrointestinal cancers are diseases due to genetic and environmental factors. In this present work we are interested in the influence of environmental factors on the occurrence of gastrointestinal cancers in Tunisian population. We found that the MTHFR C677T polymorphism was associated with colorectal cancer (P<0.04) but not with gastric cancer. In addition, we have shown that alcohol is associated with an increased risk of colorectal cancer, but the consumption of cheese is protective. Furthermore, we studied tymidylate synthase gene involved in folate metabolism. Indeed, we observed that the 5'UTR repeat polymorphism, is associated with risk of colorectal cancer, and the LL genotype (3R/3R) was significantly frequent in patients with colorectal cancer compared to controls (p=0.002; OR=2.7, 95% CI=1.4-5.2). While we found that SL genotype (2R/3R) was associated with risk of gastric cancer (p=0.015; OR=4.46, 95% CI=1.08-19-64). This polymorphism was also shown to be a predictor of response to chemotherapy based 5'-fluorouracil. However, we are interested in studying the GPX -1 gene involved in phase I metabolism of xenobiotics. We therefore evaluated the risk of TT genotype in GPX-1 C599T polymorphism with the onset of gastric cancer (P=0.0001; OR=5.41, 95% CI 1.98 to 15.58) and colorectal cancer (P=0.00008; OR=4.40, 95% CI 1.93 to 10.27). To clarify the possible relationship between environmental factors and the occurrence of the disease, we studied the additive effect of risk genotype and behavior in order to highlight the interaction of gene-environment factors.

Effects of heavy metal ions on N-nitrosodimethylamine (NDMA) formation

The mechanism of NDMA formation as affected by heavy metal complexes [MONO]⁺ (M = Cd, Pb, Hg) was investigated using density functional theory (DFT). Three possible NDMA formation pathways are discussed.

Dose-dependent effect of N'-Nitrosodiethylamine on hepatic architecture, RBC rheology and polypeptide repertoire in Wistar rats

N'-Nitrosodiethylamine (NDEA) is an effective hepatotoxicant, carcinogen and mutagen. NDEA-induced hepatic necrosis, through metabolic activation by CYP2E1, is an extensively used experimental model. In the present study, we analysed the dose- and time-dependent effect of NDEA on hepatic damage, RBC rheology and proteomic profile in male Wistar rats. The rats, 5-6 weeks old, were divided into four groups: Group-1 served as control and received normal saline, Group-2 received a single dose of 200 mg/kg body weight NDEA intraperitoneally (i.p.) and the animals were sacrificed after one week; the rats of Group-3 received a single dose of 100 mg/kg body weight NDEA and were sacrificed after one week; Group-4 received 100 mg/kg body weight/wk NDEA for two weeks and were then sacrificed. Various biochemical parameters such as ALT, AST, ALP and bilirubin were determined. Further, RBC rheology, histopathology (H&E staining) of liver biopsies and polypeptide profiling (SDS-PAGE) in sera and liver sections were also carried out both in control and NDEA treated groups. Our results showed a significant increase in all the biochemical parameters of the liver function test (p<0.05). In NDEA treated categories dacryocytes (tear drop cells), schistocytes (fragmented cells), codocytes (target cells), acanthocytes (spur cells) and ovalocytes (oval cells) were observed. H & E stained liver biopsies treated with NDEA showed abnormal liver architecture with severe haemorrhage, neutrophilic infiltration and dysplastic hepatocytes manifested in a dose-dependent manner. Software analysis of SDS-PAGE of control and NDEA treated rat sera and liver revealed qualitative and quantitative differences in polypeptide composition. Based on the presence/absence, polypeptides were classified in three different categories: (1) house-keeping, present in all the groups investigated; (2) novel, present in either control or NDEA treated group at any given time; (3) differential expression, showing quantitative differences. Our study indicates a dose and time-dependent hepatocellular damage and proteome profile which is likely due to NDEA-mediated oxidative stress in rats.

Quercetin 7-O-glucoside suppresses nitrite-induced formation of dinitrosocatechins and their quinones in catechin/nitrite systems under stomach simulating conditions

Catechins in foods can be transformed into dinitrosocatechins and the quinones by salivary nitrite in the stomach, and the transformation can be suppressed by flavonols including quercetin and its 7-O-glucoside.

Fruit Consumption Reduces the Risk of Esophageal Cancer in Yanting, People's Republic of China

This study aimed to investigate the contribution of fruit and family history to esophageal cancer, among residents with abnormal esophagus discovered in screening. The study was a frequency-matched case-control design in groups of normal esophagus, abnormal esophagus but not carcinoma, and esophageal squamous cell carcinoma. Odds ratio (OR) was estimated by unconditional logistic regression. Fruit intake (OR = 0.19, 95% CI = 0.06-0.56) and positive family history of esophageal cancer (OR = 3.87, 95% CI = 1.41-10.63) were associated with esophageal cancer compared to individuals with abnormal conditions of the esophagus. In individuals who consumed fruits at least once per week, the OR for family cancer history is reduced to a nonsignificant level (OR = 1.06, 95% CI = 0.07-15.91). In the individuals with abnormal esophagus at screening, fruit intake was possibly protective against esophageal cancer, even in the ones with positive family history. Local public health strategies should focus on the improvement in fruit intake.

Adverse effects of preserved vegetables on squamous cell carcinoma of esophagus and precancer lesions in a high risk area

INTRODUCTION

Squamous cell carcinoma of esophagus (ESCC) is one of the most common cancers in China. Preserved vegetables are processed foods, consumed in high amounts in the high risk areas for ESCC. This study aimed to investigate the relationships of preserved vegetable consumption with SCC and precancer lesions.

METHODS

Cases from Yanting cancer hospital with pathological diagnosis of primary cancer, along with controls and individuals diagnosed with precancer lesions by endoscopy with iodine staining were interviewed. Trained staff collected data on dietary habits 1 year before the interview. An unconditional logistic regression model was used to estimate the risk odds ratios for preserved vegetable consumption with precancer lesions and cancer.

RESULTS

Adjusting for potential confounders, intake of preserved vegetables (OR=2.92, 95%CI 1.32~6.47) and longer intake period (OR=5.78, 95%CI 2.26~14.80) were associated with higher risk of cancer. Compared with lowest intake frequency, the highest was associated with a 3.0-fold risk for precancer lesions and 3.59-fold risk for ESCC (both p<0.05).

CONCLUSION

Consumption of preserved vegetables is a risk factor for esophageal lesions in high risk areas. The carcinogenicity of preserved vegetables needs investigation in further studies and public health strategies for reduction of consumption might be initiated in high risk areas.

Measurement of deoxyinosine adduct: Can it be a reliable tool to assess oxidative or nitrosative DNA damage?

Adenosine deaminases (ADA) are key enzymes that deaminate adenosine (A) or deoxyadenosine (dA) and produce inosine or deoxyinosine (dI), respectively. While ADA only deaminates free dA, reactive nitrogen species (RNS) or reactive oxygen species (ROS) deaminate adenine base on the DNA and leave dI, which is a pre-mutagenic lesion. Therefore, dI adduct in the genomic DNA has been considered a biomarker of DNA damage caused by RNS or by ROS. In the presented study, genomic DNA was isolated from frozen calf thymus in low or room temperature, with or without an addition of antioxidant. The number of dI in the DNA was measured using liquid chromatography-tandem mass spectrometry. While low temperature (LT) work-up with an addition of antioxidant in reagents helped to prevent artifactual formation of oxidative DNA lesions in the calf thymus DNA (CTD), it also significantly inhibited activities of proteinase, which in turn resulted in significant ADA contamination in the final DNA samples. ADA remained in LT-CTD completely deaminated most dA when the DNA was subjected to enzymatic hydrolysis to single nucleosides. The ADA contamination in the DNA was significantly reduced when DNA was isolated from pre-isolated nuclear fraction rather than from entire tissue homogenates. However, enzymes used for DNA hydrolysis were confirmed to contain significant amounts of ADA. Therefore, these enzymes would increase deamination of dA during DNA hydrolysis. Artifactual dI production by contaminated ADA was dramatically reduced by an addition of EHNA (erythro-9-(2-hydroxy-3-nonyl)adenine), which is a potent inhibitor of ADA. However, time- and temperature-dependent dI production from dA in phosphate buffer solution was observed. More importantly, TEMPO, an antioxidant commonly used to prevent DNA oxidation, was found to deaminate dA independent to ADA. Overall, these findings indicate that assay methods measuring dI or other dA DNA adducts in genomic DNA should be carefully validated to minimize artificial errors caused by dA deamination. Recommendations to overcome those technical challenges were discussed in this presentation.

Investigation of cytotoxic and mutagenic effects of Malpighia glabra L. (barbados cherry) fruit pulp and vitamin C on plant and animal test systems

Fruits are important sources of nutrients in human diet, and Barbados Cherry (Malpighia glabra L.) is of particular interest due to its high content of antioxidants. Diets rich in fruits and vegetables protect individuals against diseases and cancer, but excessive intake of vitamins may act as pro-oxidant and generate changes in DNA. To evaluate the effect of different in natura (BAN) and frozen (BAF) Barbados Cherry pulp concentrations and synthetic vitamin C in liquid form (VC) on the chromosome level and the cell cycle division, root meristeme cells of Allium cepa L. and bone marrow cells of Wistar rats Rattus norvegicus, were used as test system. In Allium cepa L., BAN, at the highest concentration (0.4 mg.mL-1) and BAF, at the lowest concentration (0.2 mg.mL-1), inhibited cell division, and there was recovery of cell division after the recovery period in water only for BAN. In the Wistar rats, all treatments with Barbados Cherry, either acute or subchronic, were not cytotoxic or mutagenic; only the highest concentration of VC increased significantly the rate of chromosomal abnormalities. The data obtained are important to reinforce the use of Barbados Cherry fruit in the diet.

Use of the in vivo skin comet assay to evaluate the DNA-damaging potential of chemicals applied to the skin

The aim of the present study was to evaluate both sensitivity and specificity of an in vivo skin comet assay using chemically treated, hairless mouse dorsal skin as a model. N-methyl-N'-nitro-N-nitrosoguanidine (MNNG, 0.0125-0.2%), 4-nitroquinoline-1-oxide (4NQO, 0.01-0.25%), mitomycin C (MMC, 0.0125-0.05%), benzo[a]pyrene (B[a]P, 0.25-2%), and 7,12-dimethylbenz[a]anthracene (DMBA, 0.25-1%) were each applied once to the dorsal skin of hairless male mice; after 3h, epidermal skin cells were isolated, and the alkaline comet assay was performed. The assay was performed after 24h for only the B[a]P and DMBA. Furthermore, B[a]P and DMBA were evaluated by alkaline comet assay using liver cells after both 3 and 24h. The mean percent of DNA (%DNA) in tail in the 0.05-0.2% MNNG and 0.1-0.25% 4NQO treatment groups was markedly higher than in the control group at 3h post-application. Although the mean %DNA values in the tail in the B[a]P and DMBA groups were the same as the controls at 3h post-application, the 2% B[a]P and 1% DMBA groups showed significantly higher values versus controls 24h after application. No significant increases in the mean %DNA in the tail were observed in the MMC group. No clear increases in %DNA in the tail were observed in the B[a]P and DMBA groups at 3 or 24h after application in the liver. These results suggest that the in vivo skin comet assay is able to accurately identify DNA-damaging potential with a skin-specific response and is a useful method to detect the DNA-damaging potential of genotoxic chemicals on the skin.

Induction effect of coadministration of soybean isoflavones and sodium nitrite on DNA damage in mouse stomach

We have already found that nitrite-treated isoflavones exhibit genotoxic activities toward Salmonella typhimurium TA 100 and 98 strains (submitted: nitrite-treated genistein). However, we have not demonstrated genotoxic activity induced by simultaneous treatment with isoflavones and NaNO(2)in vivo. In the present study, we examined whether coadministration of isoflavones (such as daidzein and genistein) and NaNO(2) induces DNA damage in the stomach of ICR male mice. Mice were coadministered with isoflavones (1mg/kg body weight) and NaNO(2) (10mg/kg body weight), and dissected to collect tissues at 1, 3, and 6h after administration. We used comet assay combined with repair enzyme formamidopyrimidine-N-glycosylase (FPG) to detect FPG-sensitive sites. An HPLC-ECD system was employed to determine 8-oxo-2'-deoxyguanosine (8-oxodG) in the stomach. In addition, we observed leukocyte infiltration by histopathological investigation, and measured total superoxide dismutase (SOD) in the stomach. We confirmed that oxidative DNA damage in the stomach was significantly increased by coadministration. Total SOD activities were also significantly stimulated by coadministration. However, the induction of inflammation in the stomach was not found. These data suggest that coadministration of isoflavones and NaNO(2) can cause DNA damage in the stomach because of the formation of radicals.

Development of an in vitro system combining aqueous and lipid phases as a tool to understand gastric nitrosation

Nitrite has long been considered a potential pre-carcinogen for gastric cancer. Acidification of salivary nitrite, derived from dietary nitrate, produces nitrosative species such as NOSCN, NO(+) and N(2)O(3), which can form potentially carcinogenic N-nitroso compounds. Ascorbic acid inhibits nitrosation by converting the nitrosative species into nitric oxide (NO). However, NO diffuses rapidly to adjacent lipids, where it reacts with oxygen to reform nitrosative species. Nitrosation has been studied in vitro in aqueous systems and less frequently in organic systems; however, there is a need to investigate acid-catalysed nitrosation in a system combining aqueous and lipid environments, hence providing a physiologically relevant model. Here, we describe a two-phase system, which can be used as a tool to understand acid-catalysed nitrosation. Using gas chromatography/ion trap tandem mass spectrometry, we investigated the nitrosation of secondary amines as a function of the lipid phase composition and reaction mixing. An increased interface surface area was a driver for nitrosation, while incorporation of unsaturated fatty acids affected morpholine and piperidine nitrosation differently. Linoleic acid methyl esters did not affect morpholine nitrosation and only had a limited effect on N-nitrosopiperidine formation, while incorporation of free linoleic acid to the lipid phase significantly reduced N-nitrosopiperidine formation, but increased N-nitrosomorpholine formation at low levels. The mechanisms driving these effects are thought to involve amine partitioning, polarity and unsaturated fatty acids acting as scavengers of nitrosating species, findings relevant to the nitrosative chemistry occurring in the stomach, where the gastric acid meets a range of dietary fats which are emulsified during digestion.

Diet, fecal water, and colon cancer--development of a biomarker

Colorectal cancer (CRC) is a leading cause of cancer incidence worldwide. Lifestyle factors, especially dietary intake, affect the risk of CRC development. Suitable risk biomarkers are required in order to assess the effect that specific dietary components have on CRC risk. The relationship between dietary intake and indicators of fecal water activity has been assessed using cell and animal models as well as human studies. This review summarizes the literature on fecal water and dietary components with a view to establishing further the potential role of fecal water as a source of CRC risk biomarkers. The literature indicates that fecal water activity markers are affected by specific dietary components linked with CRC risk: red meat, saturated fats, bile acids, and fatty acids are associated with an increase in fecal water toxicity, while the converse appears to be true for calcium, probiotics, and prebiotics. However, it must be acknowledged that the study of fecal water is still in its infancy and a number of issues need to be addressed before its usefulness can be truly gauged.

The Influence of Human Neutrophils on N-nitrosodimethylamine (NDMA) Synthesis

N-nitrozodimethyloamine (NDMA) is a carcinogenic compound that can be formed in vivo. NDMA is synthesized from precursors-amines and nitrosating agents. Nitrosating agents are formed through the reaction of oxide, reactive oxygen species and nitric oxide (NO). Human neutrophils (PMN) are an important source of the most reactive oxygen species as well as of the nitric oxide. The increase in oxygen metabolism of PMN can lead to the increase nitrosating agent and nitroso-forms. Inflammatory process is associated with locally decreased pH that may favor nitrosation reaction. In the present study, we estimated the NDMA synthesis by LPS-stimulated PMN in the presence of the iNOS inhibitor--N-nitro-L-arginine methyl ester (L-NAME). In the nitrosation reaction dimethylamine (DMA) was used as substrat. The viability of the cells was measured by cytometric method. NDMA concentrations the culture media was measured by GCMS method. NO production was estimated by Griess's method. Expression of iNOS was determined by western blotting. Results obtained showed that DMA nitrosation is most effective in pH between 3-4.5. Nonstimulated PMN produced lower concentrations of NO than LPS-stimulated cells (1.27 microg/cm3 and 1.57 microg/cm3, respectively). In the culture of nonstimulated PMN supplemented with DMA, there was NDMA (mean--0.99 ng/cm3). In the culture of LPS-stimulated PMN in the presence of DMA, the concentration of NDMA was higher than in the culture of nonstimulated PMN (median--1.45 ng/cm3). In the supernatants of cells incubated without DMA and with DMA, LPS and L-NAME, no NDMA was detected. These results indicate that PMN can be one of sources of nitrosating agents and can play a role in endogenous NDMA synthesis. Stimulation of PMN can lead to the increase of NDMA concentration following the increase of NO production. Different pathological conditions associated with PMN activation as well as the decreased pH may favor endogenous NDMA synthesis.

Potential role of tryptophan derivatives in stress responses characterized by the generation of reactive oxygen and nitrogen species

To face physicochemical and biological stresses, living organisms evolved endogenous chemical responses based on gas exchange with the atmosphere and on formation of nitric oxide (NO(*)) and oxygen derivatives. The combination of these species generates a complex network of variable extension in space and time, characterized by the nature and level of the reactive oxygen (ROS) and nitrogen species (RNS) and of their organic and inorganic scavengers. Among the latter, this review focusses on natural 3-substituted indolic structures. Tryptophan-derived indoles are unsensitive to NO(*), oxygen and superoxide anion (O(2)(*-)), but react directly with other ROS/RNS giving various derivatives, most of which have been characterized. Though the detection of some products like kynurenine and nitroderivatives can be performed in vitro and in vivo, it is more difficult for others, e.g., 1-nitroso-indolic compounds. In vitro chemical studies only reveal the strong likelihood of their in vivo generation and biological effects can be a sign of their transient formation. Knowing that 1-nitrosoindoles are NO donors and nitrosating agents indicating they can thus act both as mutagens and protectors, the necessity for a thorough evaluation of indole-containing drugs in accordance with the level of the oxidative stress in a given pathology is highlighted.

Possible carcinogenic risks of copper gluconate and their prevention by co-administered green tea catechins evaluated by a rat medium-term multi-organ carcinogenicity bioassay protocol

Carcinogenic risks of copper gluconate, green tea catechins and their combined exposure were evaluated using a rat medium-term multi-organ carcinogenicity bioassay protocol. Male BrlHan:WIST@Jcl (GALAS) rats were given N-nitrosodiethylamine (DEN), N-methylnitrosourea (MNU), 1,2-dimethylhydrazine (DMH), N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) and 2,2'-dihydroxy-di-n-propylnitrosamine (DHPN) for a total multiple initiation period of 4 weeks (DMBDD treatment). Rats were then given a diet containing copper gluconate at a concentration of 0, 10, 300, 3000 or 6000 ppm with or without a co-administration of catechins starting 1 week later by admixing in the drinking water at a concentration of 5000 ppm. All survivors were sacrificed at the end of week 29. Number of putatively preneoplastic, glutathione S-transferase placental form-positive, liver lesions significantly increased by copper gluconate of 300 ppm or greater. In addition, both incidence and grade of hyperplasia in the forestomach significantly increased by copper gluconate of 6000 ppm. Catechins, exerting no effects by themselves, inhibited these effects of copper gluconate. The present results indicate that copper gluconate may possess carcinogenic risks for the liver and forestomach at its high dose level, and that co-administered green tea catechins may exert preventive effects.

Nitric oxide and acid induce double-strand DNA breaks in Barrett's esophagus carcinogenesis via distinct mechanisms

BACKGROUND & AIMS

The luminal microenvironment including acid and nitric oxide (NO) has been implicated in Barrett's esophagus carcinogenesis. We investigated the ability of acid and NO to induce DNA damage in esophageal cells.

METHODS

Transformed and primary Barrett's esophagus and adenocarcinoma cells were exposed to either acid, (pH 3.5), +/- antioxidant or NO from a donor or generated by acidification of nitrite in the presence of ascorbate +/- NO scavenger. Phosphorylation of histone H2AX and the neutral comet assay were used to detect DNA double-strand breaks (DSBs). Intracellular levels of reactive oxygen species and NO were detected with fluorescent dyes. Mitochondrial viability was measured with a rhodamine dye. Long-term survival was assessed by clonogenic assay.

RESULTS

Exposure to acid (pH 3.5) for > or =15 minutes induced DSBs in all cell lines (P < .05). There was a concomitant increase in intracellular reactive oxygen species in the absence of mitochondrial damage, and pretreatment with antioxidants inhibited DNA damage. Exposure to physiologic concentrations of NO produced from the NO donor or acidification of salivary nitrite induced DSBs in a dose- (>25 micromol/L) and cell-dependent manner (adenocarcinoma >Barrett's esophagus, P < .05). This occurred preferentially in S-phase cells consistent with stalled replication forks and was blocked with a NO scavenger. NO also induced DSBs in primary Barrett's esophagus cells treated ex vivo. Cells were able to survive when exposed to acid and NO.

CONCLUSIONS

Both acid and NO have the potential to generate DSBs in the esophagus and via distinct mechanisms.

Protective role of dietary fibre on N-nitrosopyrrolidine-induced toxicity in hypercholesterolemic rats

N-nitrosopyrrolidine (NPYR) is an important carcinogen, frequently present in the environment and food chain. Oral administration of NPYR to experimental rats evoked severe biochemical and pathological changes. In the present investigation, the protective role of dietary fibre on NPYR-induced toxicity in hypercholesterolemic rats was studied. Supplementation of chickpea seed coat fibre in the diet reduced the hepato-toxic effects of NPYR, as evident from the decreased hepatic degeneration and improved liver weight index compared to control. Administration of NPYR resulted in an increase in the osmotic fragility of erythrocytes in the experimental animals. The antioxidant potential of experimental animals decreased in the NPYR-fed group, which was evident from the increased in vitro lipid peroxidation (LPO) of erythrocytes. However, chickpea seed coat fibre considerably reduced the peroxidative damage done by NPYR. Administration of NPYR resulted in a substantial and significant increase in LPO in all tissues, to a varying degree, though the effect was maximum in the case of the liver. Inclusion of chickpea seed coat fibre considerably reduced the peroxidative damage caused by NPYR in all tissues. The effect of NPYR administration on antioxidant potential was variable in different tissues, but the effect was reduced considerably on inclusion of chickpea seed coat fibre in the diet, providing reasonable protection against NPYR-induced oxidative stress, and, hence, its toxicity. Histopathological analysis of different tissues (heart, liver, lungs, spleen and kidneys) showed mild to severe pathological changes among the control and experimental groups. However, the pathological effects of NPYR administration were markedly reduced with the addition of chickpea seed coat fibre in the diet.

The catecholic antioxidant piceatannol is an effective nitrosation inhibitor via an unusual double bond nitration

Piceatannol (1) was found to be more effective than caffeic acid, an established antinitrosating agent, in inhibiting N-nitrosation of 2,3-diaminonaphthalene. Product analysis of the reaction mixture of 1 (20 microM) with nitrite ions (80 microM) at pH 3.0 and at 37 degrees C showed conversion to a single major nitration product, (E)-3,3',4,5'-tetrahydroxy-beta-nitrostilbene (2) (68% yield). This would result from an unexpected nitration at the double bond sector via the 4-phenoxyl radical, which was analyzed at the unrestricted DFT level.

The effect of ethanol and nitric oxide on the N-nitrosodimethylamine formation in HepG2 cells overexpressing CYP2E1

The influence of lipopolysaccharide (LPS) and the nitric oxide synthase (iNOS) inhibitor--N-nitro-L-arginine methyl ester (L-NAME)--on the formation of N-nitrosodimethylamine (NDMA) by HepG2 cells, engineered to overexpress CYP2E1, was assessed and compared with data from empty vector-transfected cells. HepG2 cells produced significant amounts of NDMA but its levels in the culture media of cells overexpressing CYP2E1 was significantly lower than in empty-vector transfected cells. LPS increased the formation of NDMA, the expression of the iNOS and the production of the nitric oxide (NO). On the other hand, L-NAME significantly decreased NDMA levels. The results above indicate that the synthesis of NDMA by HepG2 cells depends on NO production. Furthermore, ethanol did not affect iNOS expression but decreased NDMA levels in CYP2E1-transfected cells below the detection limit. It is probably caused by the increased N-nitrosodimethylamine metabolism. In conclusion, HepG2 cells' ability to synthesize NO with simultaneous CYP2E1 activation may lead to an increase of carcinogenic products of the NDMA metabolism.

Apples increase nitric oxide production by human saliva at the acidic pH of the stomach: a new biological function for polyphenols with a catechol group?

Dietary inorganic nitrate is secreted in saliva and reduced to nitrite by bacterial flora. At the acidic pH of the stomach nitrite is present as nitrous acid in equilibrium with nitric oxide (*NO), and other nitrogen oxides with nitrating and nitrosating activity. *NO in the stomach exerts several beneficial effects, but nitrosating/nitrating species have been implicated as a possible cause of epithelial neoplasia at the gastroesophageal junction. We investigated the effects of apple extracts on *NO release by human saliva at pH 2. A water extract obtained from apple homogenate increased *NO release caused by acidification of saliva. Data show that polyphenols were responsible for this activity, with chlorogenic acid and (+)-catechin the most active and concentrated species. However, ferulic acid, a hydroxycinnamic acid with only one aromatic hydroxyl group, did not increase *NO release. Fructose, the most representative sugar in apples, was also inactive. Interestingly, ascorbic acid in saliva induced a SCN(-)-enhanced burst of *NO but, unlike apple, the release was transient. The simultaneous addition of ascorbic acid and apple extract caused a burst of *NO followed by the increased steady-state level characteristic of saliva containing apple extract. Chlorogenic acid and (+)-catechin, but not ferulic acid, formed o-semiquinone radicals and nitrated polyphenols, suggesting the scavenging of *NO(2) by o-semiquinones. Our results propose that some apple polyphenols not only inhibit nitrosation/nitration but also promote *NO bio-availabilty at the gastric level, a previously unappreciated function.

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.