Use of the comet assay to investigate possible interactions of nitric oxide and reactive oxygen species in the induction of DNA damage and inhibition of function in an insulin-secreting cell line

Dual Role of Nitric Oxide in Regulating the Response of β Cells to DNA Damage

SIGNIFICANCE

Cytokines released in and around pancreatic islets during islet inflammation are believed to contribute to impaired β cell function and β cell death during the development of diabetes. Nitric oxide, produced by β cells in response to cytokine exposure, controls many of the responses of β cells during islet inflammation. Recent Advances: Although nitric oxide has been shown to inhibit insulin secretion and oxidative metabolism and induce DNA damage in β cells, it also activates protective pathways that promote recovery of insulin secretion and oxidative metabolism and repair of damaged DNA. Recent studies have identified a novel role for nitric oxide in selectively regulating the DNA damage response in β cells.

CRITICAL ISSUES

Does nitric oxide mediate cytokine-induced β cell damage, or is nitric oxide produced by β cells in response to cytokines to protect β cells from damage?

FUTURE DIRECTIONS

β cells appear to be the only islet endocrine cell type capable of responding to proinflammatory cytokines with the production of nitric oxide, and these terminally differentiated cells have a limited capacity to regenerate. It is likely that there is a physiological purpose for this response, and understanding this could open new areas of study regarding the loss of functional β cell mass during diabetes development.

EPR Technology as Sensitive Method for Oxidative Stress Detection in Primary and Secondary Keratinocytes Induced by Two Selected Nanoparticles

Exogenous factors can cause an imbalance in the redox state of biological systems, promoting the development of oxidative stress, especially reactive oxygen species (ROS). To monitor the intensity of ROS production in secondary keratinocytes (HaCaT) by diesel exhaust particles and thermoresponsive nanogels (tNG), electron paramagnetic resonance (EPR) spectroscopy after 1 and 24 h of incubation, respectively, was applied. Their cytotoxicity was analyzed by a cell viability assay (XTT). For tNG an increase in the cell viability and ROS production of 10% was visible after 24 h, whereas 1 h showed no effect. A ten times lower concentration of diesel exhaust particles exhibited no significant toxic effects on HaCaT cells for both incubation times, thus normal adult human keratinocytes (NHK) were additionally analyzed by XTT and EPR spectroscopy. Here, after 24 h a slight increase of 18% in metabolic activity was observed. However, this effect could not be explained by the ROS formation. A slight increase in the ROS production was only visible after 1 h of incubation time for HaCaT (9%) and NHK (14%).

Magnesium Supplementation Diminishes Peripheral Blood Lymphocyte DNA Oxidative Damage in Athletes and Sedentary Young Man

Sedentary lifestyle is highly associated with increased risk of cardiovascular disease, obesity, and type 2 diabetes. It is known that regular physical activity has positive effects on health; however several studies have shown that acute and strenuous exercise can induce oxidative stress and lead to DNA damage. As magnesium is essential in maintaining DNA integrity, the aim of this study was to determine whether four-week-long magnesium supplementation in students with sedentary lifestyle and rugby players could prevent or diminish impairment of DNA. By using the comet assay, our study demonstrated that the number of peripheral blood lymphocytes (PBL) with basal endogenous DNA damage is significantly higher in rugby players compared to students with sedentary lifestyle. On the other hand, magnesium supplementation significantly decreased the number of cells with high DNA damage, in the presence of exogenous H₂O₂, in PBL from both students and rugby players, and markedly reduced the number of cells with medium DNA damage in rugby players compared to corresponding control nonsupplemented group. Accordingly, the results of our study suggest that four-week-long magnesium supplementation has marked effects in protecting the DNA from oxidative damage in both rugby players and in young men with sedentary lifestyle. Clinical trial is registered at ANZCTR Trial Id: ACTRN12615001237572.

Neuroprotective effect of Feronia limonia on ischemia reperfusion induced brain injury in rats

Objectives:

Brain stroke is a leading cause of death without effective treatment. Feronia limonia have potent antioxidant activity and can be proved as neuroprotective against ischemia-reperfusion induced brain injury.

Materials and Methods:

We studied the effect of methanolic extract of F. limonia fruit (250 mg/kg, 500 mg/kg body weight, p.o.) and Vitamin E as reference standard drug on 30 min induced ischemia, followed by reperfusion by testing the neurobehavioral tests such as neurodeficit score, rota rod test, hanging wire test, beam walk test and elevated plus maze. The biochemical parameters, which were measured in animals brain were catalase, superoxide dismutase (SOD), malondialdehyde and nitric oxide in control and treated rats.

Results:

The methanolic extract of F. limonia fruit (250 mg/kg, 500 mg/kg body weight, p.o.) treated groups showed a statistically significant improvement in the neurobehavioral parameters such as motor performance (neurological status, significant increase in grasping ability, forelimb strength improvement in balance and co-ordination). The biochemical parameters in the brains of rats showed a significant reduction in the total nitrite (P < 0.01) and lipid peroxidation (P < 0.01), also a significant enhanced activity of enzymatic antioxidants such as catalase (P < 0.01) and SOD (P < 0.05).

Conclusion:

These observations suggest the neuroprotective and antioxidant activity of F. limonia and Vitamin E on ischemia reperfusion induced brain injury and may require further evaluation.

Do β-cells generate peroxynitrite in response to cytokine treatment?

The purpose of this study was to determine the reactive species that is responsible for cytokine-mediated β-cell death. Inhibitors of inducible nitric oxide synthase prevent this death, and addition of exogenous nitric oxide using donors induces β-cell death. The reaction of nitric oxide with superoxide results in the generation of peroxynitrite, and this powerful oxidant has been suggested to be the mediator of β-cell death in response to cytokine treatment. Recently, coumarin-7-boronate has been developed as a probe for the selective detection of peroxynitrite. Using this reagent, we show that addition of the NADPH oxidase activator phorbol 12-myristate 13-acetate to nitric oxide-producing macrophages results in peroxynitrite generation. Using a similar approach, we demonstrate that cytokines fail to stimulate peroxynitrite generation by rat islets and insulinoma cells, either with or without phorbol 12-myristate 13-acetate treatment. When forced to produce superoxide using redox cyclers, this generation is associated with protection from nitric oxide toxicity. These findings indicate that: (i) nitric oxide is the likely mediator of the toxic effects of cytokines, (ii) β-cells do not produce peroxynitrite in response to cytokines, and (iii) when forced to produce superoxide, the scavenging of nitric oxide by superoxide is associated with protection of β-cells from nitric oxide-mediated toxicity.

Assessment of genotoxic effects of flumorph by the comet assay in mice organs

The present study investigated the genotoxic effects of flumorph in various organs (brain, liver, spleen, kidney and sperm) of mice. The DNA damage, measured as comet tail length (µm), was determined using the alkaline comet assay. The comet assay is a sensitive assay for the detection of genotoxicity caused by flumorph using mice as a model. Statistically significant increases in comet assay for both dose-dependent and duration-dependent DNA damage were observed in all the organs assessed. The organs exhibited the maximum DNA damage in 96 h at 54 mg/kg body weight. Brain showed maximum DNA damage followed by spleen > kidney > liver > sperm. Our data demonstrated that flumorph had induced systemic genotoxicity in mammals as it caused DNA damage in all tested vital organs, especially in brain and spleen.

A self-propelling cycle mediated by reactive oxide species and nitric oxide exists in LPS-activated microglia

It has been widely accepted that microglia, the innate immune cells in the brain, can be chronically activated in response to neuron death, fuelling a self-renewing cycle of microglial activation followed by further neuron damage (reactive microgliosis), which has been considered as the main reason responsible for the progressive nature of neurodegenerative diseases. In the present study, it was found that LPS (lipopolysaccharide) significantly induced the activation of N9 microglia, and the increase of NO level induced by pretreatment of LPS could last after the removal of LPS. The culture medium of activated microglia significantly decreased the viability of rat primary cortical neuron. These results can be blocked by the antioxidant N-acetylcysteine (NAC) and nicotinamide adenine dinucleotide phosphate reduced (NADPH) oxidase inhibitor diphenyleneiodonium sulfate (DPI), suggesting that intracellular reactive oxide species (iROS) released from the activated microglial cells may continue to further activate microglia. Next, it was shown that the iROS level increased rapidly after the LPS treatment in microglia cells followed by the NO production through the regulation of iNOS (inducible nitric oxide synthase) expression. The increase of iROS could be reversed by gp91phox (the critical and catalytic subunit of NADPH oxidase) siRNA. Moreover, NO released from sodium nitroprusside (SNP) was able to increase the iROS production of N9 microglia by regulating of the activity and the expression of NADPH oxidase. In conclusion, our research suggests for the first time that there may exist a self-propelling cycle in microglial cells possibly mediated by iROS and NO when they become activated by LPS. It may be responsible partially for the ongoing microglial activation and the progressive nature of neurodegenerative diseases.

Leucocytes DNA damage in mice exposed to JS-118 by the comet assay

JS-118 is an extensively used insecticide in China. The present study investigated the genotoxic effect of JS-118 on whole blood at 24, 48, 72 and 96 h by using alkaline comet assay. Male Kunming mice were given 6.25, 12.5, 25, 50 and 100 mg/kg BW of JS-118 intraperitoneally. A statistically significant increase in all comet parameters indicating DNA damage was observed at 24 h post-treatment (p < 0.05). A clear concentration-dependent increase of DNA damage was revealed as evident by the OTM (arbitrary units), tail length (µm) and tail DNA (%). From 48 h post-treatment, a gradual decrease in mean comet parameters was noted. By 96 h of post-treatment, the mean comet tail length reached control levels indicating repair of damaged DNA. This study on mice showed different DNA damage depending on the concentration of JS-118 and the period of treatment. The present study provided further information of the potential risk of the genetic damage caused by JS-118.

α-Lipoic acid and glutathione protect against the prooxidant activity of SOD/catalase mimetic manganese salen derivatives

Manganese(III) N,N'-ethylenebis(salicylideneiminato) chloride (Mn-salen chloride) and manganese(III) N,N'-ethylenebis(3-methoxysalicylideneiminato) chloride (Mn-(3,3'-MeO)salen chloride) are in vitro superoxide dismutase and catalase mimetics. They protect against free radical-related disease in animals, but Mn-salen can also be a potent prooxidant, damaging free DNA. Mn-salen protects human fibroblast DNA against hydrogen peroxide damage, however, damage to free DNA was confirmed by the comet assay. The DNA-damaging activity was dramatically reduced by co-administration with glutathione with the combination being less damaging to free DNA than either molecule alone. alpha-Lipoic acid, an antioxidant disulfide commonly used as a dietary supplement, also prevented Mn-salen prooxidant activity. Mn-(3,3'-MeO)salen protected fibroblasts against hydrogen peroxide as efficiently as Mn-salen and showed little damaging activity against free DNA. Protection was invested by both complexes in the presence and in the absence of EDTA, a potential competing chelator. Stabilities of the complexes with respect to decomposition and inactivation were studied by spectroscopic and electrochemical techniques. The complexes' binding to, and cleavage of, DNA was measured using a quartz crystal resonant sensor. Mn-salen was shown to bind strongly to DNA, prior to cleaving it; Mn-(3,3'-MeO)salen bound weakly and left DNA intact. Co-administration of either glutathione or alpha-lipoic acid appears to inhibit binding by Mn-salen thus preventing DNA-cleavage.

Evaluation of antioxidant activity and inhibitory effect on nitric oxide production of some common vegetables

The objectives of this study were to study the antioxidant activities and nitric oxide (NO) scavenging effects of vegetables in vitro systems and to study the inhibitory effects of vegetables on the NO production and NO-induced DNA damage in RAW 264.7 macrophage. The results indicated that water extracts from Indian lotus, Jew's ear, shiitake, eggplant, and winter mushroom showed stronger antioxidant activity and free-radical-scavenging ability than that of other vegetable extracts. The scavenging effects of vegetable extracts on NO derived from sodium nitroprusside (SNP) were in decreasing order of water spinach > Indian lotus > eggplant and garland chrysanthemum. In the macrophage model system, the water extracts from fresh daylily flower, sponge gourd, pea sprout, and eggplant exhibited over 80% inhibition on NO generation stimulated by lipopolysaccharide. The extract from fresh daylily flower that expressed the strongest inhibition on NO production was attributed to the ability to reduce the inducible nitric oxide synthase (iNOS) induction. However, the extracts from pea sprout and eggplant suppressed the NO production by scavenging on NO and inactivating toward iNOS enzyme. In addition, the water extracts from fresh daylily flower, sponge gourd, pea sprout, and eggplant also showed over 40% inhibitory effect on DNA damage induced by SNP in RAW 264.7 macrophage. The data also indicated that eggplant and pea sprout extracts contained higher total phenolic compounds, anthocyanins, and ascorbic acids and appeared to be responsible for their antioxidant activities and scavenging effects on NO derived from SNP.

Interaction of hyperbaric oxygen, nitric oxide, and heme oxygenase on DNA strand breaks in vivo

Hyperbaric oxygen (HBO), e.g. pure oxygen breathing at supra-atmospheric pressures, represents a well-suited model for investigating oxidative stress-induced DNA damage as well as protective mechanisms. While the induction of heme oxygenase-1 (HO-1) seems to be crucial for this protection against this DNA damage, the role of nitric oxide (NO) remains unclear. HO-1 expression is a major regulator of the inducible NO synthase (iNOS), and therefore we investigated the effect of the interaction between HBO, NO, and HO-1 on DNA damage. Prior to exposure to HBO (3 h at 3 bar ambient pressure) rats randomly received vehicle (HBO alone, 1 mL 0.9% saline, n=8), the NO donor molsidomine (SIN-10, 40 mg/kg, n=8) or the HO-1 blocker tin-mesopophyrin (Sn-MP, 50 micromol/kg, n=8). Additional groups received SIN-10 without exposure to HBO, i.e. breathing air under normobaric conditions for 3h (SIN-10 alone, 40 mg/kg, n=6), vehicle without HBO (negative controls, n=6), and ethylmethanesulfonate without HBO (EMS, 200 mg/kg) (positive controls n=4). Immediately after the 3 h HBO or air breathing period blood was analysed for DNA strand breaks (tail moment in the alkaline comet assay) and nitrite+nitrate (chemoluminescence). Whereas the tail moment was ten-fold higher after EMS than in the negative controls, there was no effect of HBO nor SIN-10 alone. Together with HBO, pretreatment with SIN-10 doubled the tail moment, and Sn-MP increased it by 50%. In contrast to Sn-MP or HBO alone, SIN-10 resulted in a five-fold increase of nitrite+nitrate concentrations. We conclude that both HO-1 blockade and excess NO release promote DNA damage during HBO exposure in vivo. The effect of HO-1 inhibition is probably independent of the regulatory function of HO-1 for iNOS.

Involvement of the cGMP signalling pathway in the regulation of viability in insulin-secreting BRIN-BD11 cells

We have evaluated the hypothesis that cGMP may serve as an intracellular messenger regulating the viability of pancreatic beta-cells. A direct activator of soluble guanylyl cyclase, YC-1, caused a time- and dose-dependent loss of viability in clonal BRIN-BD11 beta-cells. This was accompanied by a rise in cGMP and was antagonised by Rp-8-pCPT-cGMPS, a selective inhibitor of protein kinase G (PKG). Reverse transcription polymerase chain reaction analysis confirmed that BRIN-BD11 cells (and human islets) express all three known isoforms of PKG (PKG-Ialpha, -Ibeta and II). Cell death induced by YC-1 was not sensitive to cell-permeable caspase inhibitors and was not accompanied by oligonucleosomal DNA fragmentation. The response was, however, inhibited by actinomycin D, suggesting that a transcription-dependent pathway of programmed cell death is involved in the actions of cGMP.

NO-dependent phototoxicity of Roussin’s black salt against cancer cells

A metal-nitrosyl complex, Roussin's black salt (RBS), releases nitric oxide after illumination. Approximately 3.7 NO molecules were released from one RBS molecule. Both short- and long-term effects of photogenerated NO on the two neoplastic cell lines: human (SK-MEL188) and mouse (S91) have been investigated. Exogenous NO from RBS was toxic to cells in a dose-dependent manner. Apoptotic damage predominates in the response to the injury, as shown by TUNEL assay. NO and its short-lived metabolites, but not other RBS photoproducts, are responsible for cellular death. RBS in dark was toxic to cells at concentrations above 1 microM. This relatively high cytotoxicity of RBS in the dark prevents its application as a systemic anticancer agent in vivo, unless it is applied locally.

DDT induces DNA damage in blood cells. Studies in vitro and in women chronically exposed to this insecticide

In this study, DDT-induced DNA damage on blood cells was analyzed both in vitro and in vivo. Peripheral blood mononuclear cells (PBMC) were isolated from healthy donors and incubated in the presence of three different concentrations (40, 80, and 100 microg/mL) of p,p'-DDT, p,p'-DDE, and p,p'-DDD at three different treatment times (24, 48, and 72 h). Then, DNA damage was assessed by the single-cell electrophoresis assay (comet assay) as well as by flow cytometry detection of hypodiploid cells (DNA content assay). All compounds induced significant DNA damage as shown by the comet assay. Accordingly, cells exposed to DDT, DDE, and DDD showed a significant increase in the percentage of hypodiploid cells compared with untreated PBMC. In agreement with the in vitro data, a significant correlation between blood levels of DDT, DDD, and DDE and DNA damage (comet assay) was found in women with different amounts of environmental exposure. This association remained significant after controlling for nutritional status, smoking habits, alcohol ingestion, and reported exposure to other pesticides. Although the precise biological importance remains to be explained, our results strongly suggest that DDT and its metabolites are able to induce DNA damage in PBMC both in vitro and in vivo.

The mutagenic activity of the S-nitrosoglutathione/glutathione system in Salmonella typhimurium TA1535

S-nitrosoglutathine (GSNO) and reduced glutathione (GSH) were tested for mutagenicity against strain Salmonella typhimurium TA1535 in the Ames Standard plate incorporation assay. Neither GSNO not GSH were mutagenic when tested alone. In combination, the GSNO/GSH system induced a positive mutagenic response that ranged from 3 to 20 x over background at concentrations of 10 to 50 micromol (micromol)per plate, respectively. This mutagenic response can be attributable to the generation nitric oxide, among the many other reactive products generated by the reaction of GSNO with GSH.

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.

Genotoxicity, mitochondrial damage, and apoptosis in human lymphoblastoid cells exposed to peroxynitrite generated from SIN-1

SIN-1 (3-morpholinosydnonimine), the active metabolite of the vasodilator drug molsidomine, decomposes spontaneously in solution. In the presence of oxygen, NO* and O(2)(*-) are released, generating peroxynitrite, a potent oxidizing agent, at a constant rate over a 2 h period. We utilized this system to investigate mechanisms of peroxynitrite-induced cytotoxicity, genotoxicity, apoptosis, and mitochondrial damage in two human lymphoblastoid cell lines carrying either wild-type (TK6 cells) or mutant p53 (WTK-1 cells) genes. Treatment of TK6 cells with 5 mM SIN-1 for 1.5 h resulted in 28 +/- 6% survival 24 h later. Exposure in the presence of different radical scavengers significantly increased survival, as follows: cytochrome c, 96 +/- 3%; Tiron, 69 +/- 0%; SOD plus catalase, 83 +/- 5%; carboxy-PTIO, 87 +/- 3%; and uric acid, 87 +/- 2%. D-mannitol was ineffective in reducing lethality, as were SOD and catalase when added individually or in heat-inactivated form. Spontaneous as well as SIN-1-induced mutant fractions (MF) in both HPRT and TK genes were significantly higher in WTK-1 cells than in TK6 cells (p < 0.05-0.01). Exposure to 2.5 mM SIN-1 induced time-dependent apoptosis in TK6 cells, but not in WTK-1 cells. Mitochondrial membrane depolarization was also observed in both cell lines after SIN-1 treatment. Neutral comet assay demonstrated that SIN-1 treatment resulted in higher levels of DNA double-strand breaks in TK6 cells than in WTK-1 cells. Collectively, these data show that SIN-1 can be used as an effective peroxynitrite generator in cell culture experiments under these experimental conditions, in which it induced a greater apoptotic response but was less potent as a mutagen in TK6 cells compared with WTK-1 cells. Thus, p53 status was an important determinant of SIN-1 induced mutagenesis and apoptosis in these two human lymphoblastoid cell lines.

Oxidative DNA damage in human peripheral leukocytes induced by massive aerobic exercise

Reactive oxygen species produced during vigorous exercise may permeate into cell nuclei and induce oxidative DNA damage, but the supporting evidence is still lacking. By using a 42 km marathon race as a model of massive aerobic exercise, we demonstrated a significant degree of unrepaired DNA base oxidation in peripheral immunocompetent cells, despite a concurrent increase in the urinary excretion of 8-hydroxy-2'-deoxyguanosine. Single cell gel electrophoresis with the incorporation of lesion-specific endonucleases further revealed that oxidized pyrimidines (endonuclease III-sensitive sites) contributed to most of the postexercise nucleotide oxidation. The oxidative DNA damage correlated significantly with plasma levels of creatinine kinase and lipid peroxidation metabolites, and lasted for more than 1 week following the race. This phenomenon may be one of the mechanisms behind the immune dysfunctions after exhaustive exercise.

SIN-1-induced DNA damage in isolated human peripheral blood lymphocytes as assessed by single cell gel electrophoresis (comet assay)

Human lymphocytes were exposed to increasing concentrations of SIN-1, which generates superoxide and nitric oxide, and the formation of single-strand breaks (SSB) in individual cells was determined by the single-cell gel electrophoresis assay (comet assay). A dose- and time-dependent increase in SSB formation was observed rapidly after the addition of SIN-1 (0.1-15 mM). Exposure of the cells to SIN-1 (5 mM) in the presence of excess of superoxide dismutase (0.375 mM) increased the formation of SSB significantly, whereas 1000 U/ml catalase significantly decreased the quantity of SSB. The simultaneous presence of both superoxide dismutase and catalase before the addition of SIN-1 brought the level of SSB to that of the untreated cells. Moreover, pretreatment of the cells with the intracellular Ca(2+)-chelator BAPTA/AM inhibited SIN-1-induced DNA damage, indicating the involvement of intracellular Ca(2+) changes in this process. On the other hand, pretreatment of the same cells with ascorbate or dehydroascorbate did not offer any significant protection in this system. The data suggest that H2O2-induced changes in Ca(2+) homeostasis are the predominant pathway for the induction of SSB in human lymphocytes exposed to oxidants.

Nitric oxide donors induce large-scale deletion mutations in human lymphoblastoid cells: implications for mutations in T-lymphocytes from arthritis patients

Rheumatoid arthritis (RA) is an inflammatory disease in which high levels of reactive nitrogen oxygen species (RNOS) may be present in the affected joints. RNOS are known to produce small-scale mutational events (transitions, transversions, small insertions, and small deletions) but the ability of these compounds to cause deletion of large segments of genomic DNA has not been previously determined. To address this question, a human lymphoblastoid cell line (WIL2-NS) was exposed to nitric oxide (NO)-donating drugs and hypoxanthine phosphoribosyltransferase (hprt)-negative clones were selected and analyzed by multiplex-PCR. Large-scale deletions accounted for 60-80% of hprt mutations arising in drug-treated cultures compared to 12% in untreated cultures (P-values of 0.006 and 0.0001, respectively, in two experiments). Deletion mutations in untreated cultures affected exon 9, whereas 75% of drug-induced deletion mutations affected exons 2, 3, and 9, and the remainder were very large, ranging from 26 to 1200 kbp. To compare this spectrum of NO-induced mutations in a lymphoblastoid line to that arising in vivo in arthritis patients, T-cells from RA patients, osteoarthritis (OA) patients, and controls were cloned and similarly analyzed. We previously showed that the overall frequency of Hprt mutant clones from patients is appreciably elevated compared to that of control subjects. Large-scale hprt deletions (0.5 to >26 kb) were detected in mutant T-cell clones from both RA and OA patients and also from control subjects. A total of 54 mutant clones from 16 RA patients and 19 mutant clones from 6 OA patients were studied. Of these, 6 clones (from 3 RA and 1 OA patient) had suffered large-scale deletions. A total of 9 control subjects were studied and 62 mutant clones were obtained. Of these, 19 had suffered large-scale deletions, arising in 7 of 9 control subjects. In conclusion, (1) RNOS are capable of inducing large-scale deletion mutations in a human lymphoblastoid cell line and (2) large-scale deletion mutations were found in 10-30% of T-cell clones from RA and OA patients and controls, which we hypothesize may be induced by RNOS.

Beta cell destruction in the development of autoimmune diabetes in the non-obese diabetic (NOD) mouse

In the non-obese diabetic (NOD) mouse model of Type 1 (insulin-dependent) diabetes, evidence suggests that pancreatic beta cells are destroyed in part by apoptotic mechanisms. The precise mechanisms of beta cell destruction leading to diabetes remain unclear. The NOD mouse has been studied to gain insight into the cellular and molecular mediators of beta cell death, which are discussed in this review. Perforin, secreted by CD8(+) T cells, remains one of the only molecules confirmed to be implicated in beta cell death in the NOD mouse. There are many other molecules, including Fas ligand and cytokines such as interferon-gamma, interleukin-1 and tumor necrosis factor-alpha, which may lead to beta cell destruction either directly or indirectly via regulation of toxic molecules such as nitric oxide. As beta cell death can occur in the absence of perforin, these other factors, in addition to other as yet unidentified factors, may be important in the development of diabetes. Effective protection of NOD mice from beta cell destruction may therefore require inhibition of multiple effector mechanisms.

Expression of the inducible nitric oxide synthase (iNOS) in human leukocytes: responses to running exercise

INTRODUCTION

We examined the influence of two different bouts of vigorous running exercise on the expression of the inducible nitric oxide synthase (iNOS) in leukocytes (LE).

METHODS

In study 1, 10 trained runners competed in a half marathon (HM) lasting 90.5 +/- 11.0 min. In study 2, 8 untrained subjects performed a graded treadmill test followed by a continuous run (CR) until exhaustion (11.3 +/- 1.3 min). iNOS mRNA levels were assessed by RT/PCR at rest, 0, 3, and 24 h after HM and CR. In study 2, iNOS was additionally analyzed at the protein level in lympho- (L), mono- (M), and granulocytes (G) by flow cytometry at rest and up to 48 h after CR.

RESULTS

Analysis revealed a rise of the iNOS transcript directly after the HM in 8 of 10 subjects. In study 2, the expression of iNOS protein at rest differed between L (mean +/- SE: 30.9 +/- 4.5% iNOS positive cells), M (91.3 +/- 4.0%), and G (64.9 +/- 10.3%): 3 h after CR, expression of iNOS increased in L (67.3 +/- 7.4%) and G (90.3 +/- 2.9%) and was still elevated 48 h post-exercise. However, our measurements failed to detect significant changes of leukocyte iNOS mRNA in response to CR. After the HM, our findings were paralleled by elevated plasma levels of interleukin-8, myeloperoxidase (MPO), and partly of TNF-alpha, whereas CR only induced a low rise of MPO.

CONCLUSION

Our investigations revealed an increased expression of iNOS at the transcriptional and translational level in response to vigorous exercise. This reflects an inflammatory response and may contribute to an exercise-induced rise of endogenous nitric oxide production. It remains unclear if these effects serve an in-vivo immunoregulatory or cell-damaging role.

Study on DNA strand breaks induced by sodium nitroprusside, a nitric oxide donor, in vivo and in vitro

Nitric oxide (NO) as well as its donors has been shown to generate mutation and DNA damage in in vitro assays. The objective of this study was to identify that DNA single-strand breaks (SSBs) could be elicited by NO, not only in vitro but also in vivo. The alkaline single-cell gel electrophoresis (SCGE) was performed to examine the DNA damage in g12 cells and the cells isolated from the organs of mice exposed to sodium nitroprusside (SNP). A modified method, in which neither collagenase nor trypsin was necessary, was used to prepare the single-cell suspension isolated from organs of mice. Results showed that the exposure of g12 cells to 0.13-0.5 micromol/ml SNP with S9 for 1 h induced a concentration-dependent increase in DNA SSBs in g12 cells. The significant increase in DNA migration and comet frequency has appeared in the cells isolated from the spleen, thymus, and peritoneal macrophages of mice after injecting i.p. SNP in the dosage range of 0.67-6.0 mg/kg b.wt for 1 h. However, no obvious increase in DNA strand breaks was observed in the cells isolated from the liver, kidney, lung, brain and heart obtained from the same treated mice. These results suggested that DNA SSBs could be induced by NO in some cells both in vivo and in vitro. There were organ differences in sensitivity in the mice exposed to NO. Spleen, thymus, and macrophages might be the important targets of NO.

Detection of low dose radiation induced DNA damage using temperature differential fluorescence assay

A rapid and sensitive fluorescence assay for radiation-induced DNA damage is reported. Changes in temperature-induced strand separation in both calf thymus DNA and plasmid DNA (puc 19 plasmid from Escherichia coli) were measured after exposure to low doses of radiation. Exposures of between 0.004 and 1 Gy were measured with doses as low as 0.008 Gy yielding significant responses. The double-strand, sensitive dye PicoGreen was used as an indicator of DNA denaturation. Calibration plots indicate that fluorescence changes corresponding to amounts as low as 1 ng of double stranded DNA (10(6) copies for plasmid puc 19) are detected by this method.

Oxidative stress in brain ischemia

Brain ischemia initiates a complex cascade of metabolic events, several of which involve the generation of nitrogen and oxygen free radicals. These free radicals and related reactive chemical species mediate much of damage that occurs after transient brain ischemia, and in the penumbral region of infarcts caused by permanent ischemia. Nitric oxide, a water- and lipid-soluble free radical, is generated by the action of nitric oxide synthases. Ischemia causes a surge in nitric oxide synthase 1 (NOS 1) activity in neurons and, possibly, glia, increased NOS 3 activity in vascular endothelium, and later an increase in NOS 2 activity in a range of cells including infiltrating neutrophils and macrophages, activated microglia and astrocytes. The effects of ischemia on the activity of NOS 1, a Ca2+-dependent enzyme, are thought to be secondary to reversal of glutamate reuptake at synapses, activation of NMDA receptors, and resulting elevation of intracellular Ca2+. The up-regulation of NOS 2 activity is mediated by transcriptional inducers. In the context of brain ischemia, the activity of NOS 1 and NOS 2 is broadly deleterious, and their inhibition or inactivation is neuroprotective. However, the production of nitric oxide in blood vessels by NOS 3, which, like NOS 1, is Ca2+-dependent, causes vasodilatation and improves blood flow in the penumbral region of brain infarcts. In addition to causing the synthesis of nitric oxide, brain ischemia leads to the generation of superoxide, through the action of nitric oxide synthases, xanthine oxidase, leakage from the mitochondrial electron transport chain, and other mechanisms. Nitric oxide and superoxide are themselves highly reactive but can also combine to form a highly toxic anion, peroxynitrite. The toxicity of the free radicals and peroxynitrite results from their modification of macromolecules, especially DNA, and from the resulting induction of apoptotic and necrotic pathways. The mode of cell death that prevails probably depends on the severity and precise nature of the ischemic injury. Recent studies have emphasized the role of peroxynitrite in causing single-strand breaks in DNA, which activate the DNA repair protein poly(ADP-ribose) polymerase (PARP). This catalyzes the cleavage and thereby the consumption of NAD+, the source of energy for many vital cellular processes. Over-activation of PARP, with resulting depletion of NAD+, has been shown to make a major contribution to brain damage after transient focal ischemia in experimental animals. Neuronal accumulation of poly(ADP-ribose), the end-product of PARP activity has been demonstrated after brain ischemia in man. Several therapeutic strategies have been used to try to prevent oxidative damage and its consequences after brain ischemia in man. Although some of the drugs used in early studies were ineffective or had unacceptable side effects, other trials with antioxidant drugs have proven highly encouraging. The findings in recent animal studies are likely to lead to a range of further pharmacological strategies to limit brain injury in stroke patients.

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.

Neuronal death induced by SIN-1 in the presence of superoxide dismutase: protection by cyclic GMP

The nitrovasodilator 3-morpholinosydnonimine (SIN-1) slowly decomposes to release both nitric oxide (NO) and superoxide (O2-) and thereby produces peroxynitrite (ONOO-), a powerful oxidant which has been proposed to mediate the toxic actions caused by NO. Indeed, ONOO has been shown to cause neuronal death and it has been proposed to occur in different disorders of the CNS such as brain ischaemia, AIDS-associated dementia, amyothrophic lateral sclerosis, etc. We have found that SIN-1 was only slightly toxic to 1-week-old rat cortical neurones in primary culture (LC50=2.5+/-0.5 mM). Superoxide dismutase (SOD; 100 U/ml) significantly increased SIN-1-induced toxicity, an effect that was enhanced in the presence of HbO2, abolished by catalase and accompanied by the formation of hydrogen peroxide (H2O2). We have also found that 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ), a selective inhibitor of soluble guanylate cyclase, enhances cell death induced by SIN-1 (0.2-0.5 mM) + SOD (100 U/ml) in a concentration-dependent way (EC50=0.073+/-0.004 microM). Simultaneously, ODQ inhibits the elevation of cyclic GMP concentrations induced by SIN-1 + SOD in cortical cells (IC50=0.022+/-0.014 microM). Finally, we have also shown that the cyclic GMP mimetic, 8-bromo-cyclic GMP reverses the potentiating effect induced by ODQ on SIN-1 + SOD-induced neuronal death and inhibits the neurotoxicity induced by H2O2 (100 microM). Taken together, these data suggest that H2O2 is the species responsible for the potentiation by SOD of SIN-1-induced cell death and that cyclic GMP elevations confer selective cytoprotection against this H2O2-mediated component of cell death.

Factors affecting the DNA damaging activity of superoxide and nitric oxide

Nitric oxide and superoxide are formed endogenously and can react with each other and with other molecules to form a range of secondary and tertiary products. Some of these (e.g., peroxynitrite) are potent DNA-damaging agents and others (e.g., S-nitrosoglutathione) can act as reservoirs of the reactive species. Although the chemistry of these processes is now becoming understood, the question of which products are significant in vivo is not necessarily clear. To investigate these processes we have developed a cell-free version of the Comet assay, where the DNA from isolated nuclei is treated in agar on a microscope slide, following lysis. This offers an exceptionally sensitive assay for strand breakage in free DNA. Despite being present as a scavenger in the cell at millimolar levels, glutathione can act as a DNA-damaging pro-oxidant. Under appropriate conditions, glutathione-mediated damage is suppressed by superoxide dismutase and we suggest that superoxide may be a direct damaging agent, whose activity can be masked because of the involvement of superoxide in indirect mediation of damage or because of concomitant presence of hydroxyl radical.