Oxidative stress: a potential recipe for anxiety, hypertension and insulin resistance.

We recently reported involvement of oxidative stress in anxiety-like behavior of rats. Others in separate studies have demonstrated a link between oxidative stress and hypertension as well as with type 2 diabetes/insulin resistance. In the present study, we have tested a putative role of oxidative stress in anxiety-like behavior, hypertension and insulin resistance using a rat model of oxidative stress. Oxidative stress in rats was produced by xanthine (0.1%; drinking water) and xanthine oxidase (5 U/kg; i.p.). X+XO-treated rats had increased plasma and urinary 8-isoprostane levels (a marker of oxidative stress) and increased malondialdehyde (MDA) levels in the hippocampus and amygdala as compared to control rats. Serum corticosterone (a systemic marker of stress and anxiety) levels also increased with X+XO treatment. Moreover, anxiety-like behavior measured via open-field and light-dark exploration behavior tests significantly increased in X+XO-treated rats. Mean arterial blood pressure measured in anesthetized rats increased in X+XO-treated compared to control rats. Furthermore, plasma insulin but not glucose levels together with homeostasis model assessment (HOMA), an index of insulin resistance, were higher in X+XO-treated rats. Our studies suggest that oxidative stress is a common factor that link anxiety-like behavior, hypertension and insulin resistance in rats.

Extracts of Cynomorium songaricum protect human neuroblastoma cells from beta-amyloid25-35 and superoxide anion induced injury.

In Traditional Chinese Medicine a number of herbs are used to alleviate age-related diseases including memory impairment and dementia, among them stems of Cynomorium songaricum, Cynomoriaceae. In this study, we evaluated the protective effect of different extracts of aerial parts of C. songaricum on amyloid-beta peptide (Abeta) and hypoxanthine/xanthine oxidase induced cell death in SK-N-SH neuroblastoma cells. Abeta (20 microM) as well as superoxide anions generated by the hypoxanthine/xanthine oxidase system both reduced cell viability to about 60%. The methanolic extract of C. songaricum attenuated Abeta induced cell death at concentrations of 100 and 10 microg/ml, an even stronger effect was observed for the ethyl acetate fraction obtained from the crude methanolic extract. On the other hand, the dichloromethane as well as water fractions showed no protective effects. In order to further analyze the protective mode of action, the ability of extracts to protect against superoxide anions induced cell death was also evaluated. In this system, cell viability could again be restored by methanol and ethyl acetate extracts, the latter showingsignificant protective effects even at concentrations as low as 0.1 microg/ml.

Xanthine oxidase-induced neuronal death via the oxidation of NADH: prevention by micromolar EDTA.

The oxidation of xanthine by xanthine oxidase (XO) or xanthine dehydrogenase represents an important source of reactive oxygen species (ROS), which contribute to the damaging consequences of cerebral ischemia, inflammation, and neurodegenerative disorders. However, both enzymes are also able to act on reduced nicotinamide adenine dinucleotide (NADH). The FAD binding site to which NADH binds is distinct from that of the xanthine binding site. We report that the combination of xanthine oxidase and NADH is toxic to cultures of cerebellar granule neurons. Protection by superoxide dismutase (Cu,Zn-SOD or Mn-SOD) or catalase indicates mediation of the toxicity by superoxide and hydrogen peroxide. In addition, pre-incubating XO with EDTA at concentrations as low as 2 microM, prevented the toxicity, indicating that a metal contaminating XO is involved in producing the toxic effects of XO/NADH. It is possible that such a metal might play a role in the toxicity of XO in vivo.

Cruciferous dithiolethione-mediated coordinated induction of total cellular and mitochondrial antioxidants and phase 2 enzymes in human primary cardiomyocytes: cytoprotection against oxidative/electrophilic stress and doxorubicin toxicity.

3H-1,2-dithiole-3-thione (D3T), a cruciferous organosulfur compound, induces cytoprotective enzymes in animal cardiovascular cells. However, it remains unknown if D3T also upregulates antioxidants and phase 2 enzymes in human cardiomyocytes, and protects against cell injury induced by oxidative/electrophilic species as well as doxorubicin. In this study, we found that D3T (10-50 muM) potently induced a series of antioxidants and phase 2 enzymes in primary cultured human cardiomyocytes, including superoxide dismutase (SOD), glutathione (GSH), glutathione reductase (GR), glutathione peroxidase (GPx) glutathione S-transferase (GST), NAD(P)H:quinone oxidoreductase 1 (NQO1), aldose reductase (AR), and heme oxygenase (HO). D3T treatment also caused elevation of SOD, GSH, GR, GPx and GST in the isolated mitochondria. We also observed a time-dependent induction by D3T of mRNA expression for Cu,ZnSOD, MnSOD, gamma-glutamylcysteine ligase, GR, GSTA1, GSTM1, NQO1, AR, and HO-1. Pretreatment with D3T conferred concentration-dependent protection against cell injury induced by xanthine oxidase (XO)/xanthine, H(2)O(2), 3-morpholinosydnonimine, 4-hydroxy-2-nonenal, and doxorubicin. Pretreatment with D3T also reduced the formation of intracellular reactive oxygen species by XO/xanthine, H(2)O(2), and doxorubicin. In conclusion, this study demonstrated that D3T potently upregulated many antioxidants and phase 2 enzymes in human cardiomyocytes, which was accompanied by increased resistance to oxidative/electrophilic stress and doxorubicin toxicity.

Attenuating effect of daidzein on polychlorinated biphenyls-induced oxidative toxicity in mouse testicular cells.

The attenuating effect of daidzein (DAI) on oxidative toxicity induced by Aroclor 1254 (A1254) was investigated in mouse testicular cells. Cells were exposed to A1254 alone or with DAI. The oxidative damage was estimated by measuring malondialdehyde (MDA) formation, superoxide dismutase (SOD) activity and glutathione (GSH) content. Results show that A1254 induced a decrease of germ cell number, an elevation in thiobarbituric acid reactive substances (TBARS) but a decrease in SOD activity and GSH content. However, simultaneous supplementation with DAI decreased TBARS level and increased SOD activity and GSH content. Consequently, dietary DAI may restore the intracellular antioxidant system to attenuate the oxidative toxicity of A1254 in testicular cells.

Hydrogen peroxide mediates damage by xanthine and xanthine oxidase in cerebellar granule neuronal cultures.

The free radical-generating system of xanthine and xanthine oxidase is commonly used experimentally as a source of superoxide anion, which can produce oxidative stress, leading to cellular damage and death. Models of oxidative stress are important in elucidating pathologies associated with increased levels of reactive oxygen species, including stroke and neurodegenerative diseases, such as Alzheimer's and Parkinson's diseases. We therefore, examined the effect of the xanthine/xanthine oxidase system on the viability of postnatal cerebellar granule neurones obtained from 8-day old Sprague-Dawley rat pups. Xanthine (100 microM) and xanthine oxidase (0.02 U/ml) applied for 1 or 6h reduced the viability of cells at 8 div assessed using the alamar blue assay, and induced morphological changes, such as shrinkage of the cell bodies and neurites. Heat-inactivation of xanthine oxidase resulted in complete loss of its activity. Superoxide dismutase (250 U/ml) failed to modify the damage by xanthine and xanthine oxidase, while catalase (250 U/ml) completely prevented it. When applied alone, xanthine oxidase significantly lowered cell viability, an effect that was blocked by allopurinol and catalase, but not by superoxide dismutase. The results indicate that xanthine and xanthine oxidase can produce predominantly hydrogen peroxide instead of the superoxide anion. Cerebellar granule cells in culture may also possess significant levels of endogenous xanthine.

Upregulation of endogenous antioxidants and phase 2 enzymes by the red wine polyphenol, resveratrol in cultured aortic smooth muscle cells leads to cytoprotection against oxidative and electrophilic stress.

Resveratrol (3,4',5-trihydroxystilbene), a polyphenolic compound found in mulberries, grapes and red wine has been demonstrated to be capable of protecting against oxidative cardiovascular pathophysiology. However, the underlying cellular and biochemical mechanisms remain to be elucidated. This study was undertaken to determine if resveratrol could upregulate endogenous antioxidants and phase 2 enzymes in cultured aortic smooth muscle cells (ASMCs), and if such increased cellular defenses could provide protection against oxidative and electrophilic vascular cell injury. Incubation of rat ASMCs with resveratrol at low micromolar concentrations resulted in a significant induction of a scope of cellular antioxidants and phase 2 enzymes in a concentration- and/or time-dependent fashion. These cytoprotective factors include superoxide dismutase, catalase, glutathione, glutathione reductase, glutathione peroxidase, glutathione S-transferase (GST), and NAD(P)H:quinone oxidoreductase-1 (NOQ1). Notably, induction of catalase, GST, and NOQ1 was most remarkable among the above resveratrol-inducible antioxidants and phase 2 enzymes. Moreover, resveratrol treatment also significantly increased the mRNA expression of catalase, GSTA1, and NQO1 in a time-dependent manner. Pretreatment of ASMCs with resveratrol afforded a remarkable protection against xanthine oxidase (XO)/xanthine- or 4-hydroxy-2-nonenal-induced cytotoxicity, as assessed by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) reduction assay. Resveratrol pretreatment also led to a marked reduction in intracellular accumulation of reactive oxygen species in ASMCs after incubation with XO/xanthine. Taken together, this study demonstrates that a scope of key endogenous antioxidants and phase 2 enzymes in cultured ASMCs can be upregulated by resveratrol at low micromolar concentrations, and that such chemically-elevated cellular defenses rendered cells increased resistance to oxidative and electrophilic stress. The results of this study thus suggested a new mechanism, which might contribute to the cardiovascular protective effects of resveratrol.

Studies of chemical constituents and their antioxidant activities from Astragalus mongholicus Bunge.

OBJECTIVE: To evaluate the antioxidant activities of different chemical constituents from Astragalus mongholicus Bunge and their protection against xanthine (XA)/xanthine oxidase (XO)-induced toxicity in PC12 cells. METHODS: The compounds of Astragalus mongholicus Bunge were isolated by chromatography and the structures were elucidated on the basis of spectral data interpretation. Their antioxidant activities were detected by 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activities in a cell-free system. Meanwhile, the effects against XA/XO-induced toxicity were assessed using MTT assay in PC12 cells. RESULTS: Ten principal constituents were isolated and identified as formononetin (I), ononin (II), calycosin (III), calycosin-7-O-beta-D-glucoside (IV), 9,10-dimethoxypterocarpan-3-O-beta-D-glucoside (V), adenosine (VI), pinitol (VII), daucosterol (VIII), beta-sitoster (IX) and saccharose (X) from Astragalus mongholicus Bunge. The compounds I, III, and IV scavenged DPPH free radicals in vitro. Formononetin and calycosin were found to inhibit XA/XO-induced cell injury significantly, with an estimated EC50 of 50 ng/mL. CONCLUSION: Compound II, VI, and VII are first reported in this plant. Calycosin exhibits the most potent antioxidant activity both in the cell-free system and in the cell system.

Prevention of reactive oxygen species-induced oxidative stress in human microvascular endothelial cells by green tea polyphenol.

The potential protective roles played by green tea polyphenol (GTP) against the injurious effects of reactive oxygen species in human microvascular endothelial cells (HUMVECs) were investigated. Oxidative stress was induced in cultured HUMVECs, either by adding 10 mM H2O2 or by the action of 10 U/l xanthine oxidase (XO) in the presence of xanthine (250 microM). Both treatments produced a significant reduction (to 68% and 71%, respectively) in HUMVEC viability, as assessed by fluorescence double staining method followed by flow cytometric analysis. On the microscopic observations, the morphological changes and necrotic detachment were appreciably induced by both treatments. The H2O2-induced alterations were completely prevented by pre-incubating the ECs with 10 microg/ml GTP for 1 h. When the oxidative stress was induced by XO, the cell viability and morphology were also significantly maintained at the same GTP concentration. These results demonstrate that GTP can act as a biological antioxidant in a cell culture experimental model and prevent oxidative stress-induced cytotoxicity in ECs.

Dextran sulfate protects porcine but not bovine cultured endothelial cells from free radical injury.

Previous studies demonstrated that the polyanion dextran sulfate (DS) protects rat coronary and porcine aortic endothelium (PAE) from oxygen-derived free radical (OFR) injury due to hydrogen peroxide (H2O2) or xanthine/xanthine oxidase (X/XO). To determine if DS has a similar protective effect in bovine aortic endothelium (BAE) and bovine brain microvascular endothelium (BBME), H2O2 or X/XO was added to confluent cultures. Cell injury was assessed 1 d later by measuring the percentage of viable cells (by trypan blue exclusion) and the release of lactate dehydrogenase (LDH) into the medium. After H2O2 doses of 6.0 mM for BAE and BBME and 0.8 mM for PAE, and after X doses of 10 microM and XO doses of 0.3 U/mL for all cell types, approximately 50% of cells were viable. Cultures were pretreated with DS (0.001 to 500 microg/mL) 24 to 26 h prior to H2O2 or X/XO exposure. Pretreatment at concentrations of 0.5, 5, and 50 microg/mL significantly increased the percentage of viable cells and reduced LDH release in cultures of PAE, but not BAE or BBME, treated with H2O2. Similarly, pretreatment with DS concentrations of 5 and 50 microg/mL significantly increased the percentage of viable cells and reduced LDH release in cultures of PAE, but not BAE or BBME, treated with X/XO. Thus, DS protected porcine but not bovine endothelium. Catalase (10 U/mL) increased the percentage of viable cells and reduced LDH release in H2O2-treated BAE and BBME, suggesting that DS likely acts by a different mechanism and does not neutralize H2O2. These results suggest that the protective effect of DS on OFR-injured endothelium is species-dependent.

Sequential inactivation of reactive oxygen species by combined overexpression of SOD isoforms and catalase in insulin-producing cells.

Insulin-producing cells show very low activity levels of the cytoprotective enzymes catalase, glutathione peroxidase, and superoxide dismutase. This weak antioxidative defense status has been considered a major feature of the poor resistance against oxidative stress. Therefore, we analyzed the protective effect of a combined overexpression of Cu,ZnSOD or MnSOD together with different levels of catalase. Catalase alone was able to increase the resistance of transfected RINm5F insulin-producing tissue culture cells against H(2)O(2) and HX/XO, but no protection was seen in the case of menadione. In combination with an increase of the MnSOD or Cu,ZnSOD expression, the protective action of catalase overexpression could be further increased and extended to the toxicity of menadione. Thus, optimal protection of insulin-producing cells against oxidative stress-mediated toxicity requires a combined overexpression of both superoxide- and hydrogen peroxide-inactivating enzymes. This treatment can compensate for the constitutively low level of antioxidant enzyme expression in insulin-producing cells and may provide an improved protection in situations of free radical-mediated destruction of pancreatic beta cells in the process of autoimmune diabetes development.

Protective effects of curcumin against oxidative damage on skin cells in vitro: its implication for wound healing.

BACKGROUND: Curcumin, isolated from turmeric, has been known to possess many pharmacologic properties. It has been proven to exhibit remarkable anticarcinogenic, anti-inflammatory, and antioxidant properties. Turmeric curcumin may be a good potential agent for wound healing. METHODS: To further understand its therapeutic mechanisms on wound healing, the antioxidant effects of curcumin on hydrogen peroxide (H2O2) and hypoxanthine-xanthine oxidase induced damage to cultured human keratinocytes and fibroblasts were investigated. Cell viability was assessed by colorimetric assay and quantification of lactate dehydrogenase release. RESULTS: Exposure of human keratinocytes to curcumin at 10 microg/mL showed significant protective effect against hydrogen peroxide. Interestingly, exposure of human dermal fibroblasts to curcumin at 2.5 microg/mL showed significant protective effects against hydrogen peroxide. No protective effects of curcumin on either fibroblasts or keratinocytes against hypoxanthine-xanthine oxidase induced damage were found in our present studies. CONCLUSION: The findings indicate that curcumin indeed possessed powerful inhibition against hydrogen peroxide damage in human keratinocytes and fibroblasts.

Anti-oxidant effects of the extracts from the leaves of Chromolaena odorata on human dermal fibroblasts and epidermal keratinocytes against hydrogen peroxide and hypoxanthine-xanthine oxidase induced damage.

In cutaneous tissue repair, oxidants and antioxidants play very important roles. In local acute and chronic wounds, oxidants are known to have the ability to cause as cell damage and may function as inhibitory factors to wound healing. The administration of anti-oxidants or free radical scavengers is reportedly helpful, notably in order to limit the delayed sequelae of thermal trauma and to enhance the healing process. Extracts from the leaves of Chromolaena odorata have been shown to be beneficial for treatment of wounds. Studies in vitro of these extracts demonstrated enhanced proliferation of fibroblasts, endothelial cells and keratinocytes, stimulation of keratinocyte migration in an in vitro wound assay, up-regulation of production by keratinocytes of extracellular matrix proteins and basement membrane components, and inhibition of collagen lattice contraction by fibroblasts. In this study, the anti-oxidant effects of both total ethanol and polyphenolic extracts from the plant leaves on hydrogen peroxide and hypoxanthine-xanthine oxidase induced damage to human fibroblasts and keratinocytes were investigated. Cell viability was monitored by a colorimetric assay. The results showed that for fibroblasts, toxicity of hydrogen peroxide or hypoxanthine xanthine oxidase on cells was dose-dependent. Total ethanol extract (TEE) at 400 and 800 microg/ml showed maximum and consistent protective cellular effect on oxidant toxicity at low or high doses of oxidants. The 50 microg/ml concentration of TEE also had significant and slightly protective effects on fibroblasts against hydrogen peroxide and hypoxanthine-xanthine oxidase induced damage, respectively. For keratinocytes, a dose-dependent relationship of oxidant toxicity was only seen with hydrogen peroxide but the protective action of the extract correlated with oxidant dosage. TEE at 400 and 800 microg/ml showed dose-dependent effects with both low and high concentration of oxidants. TEE at 50 microg/ml had no effect on keratinocytes. Pre-treatment with the extracts did not show a protective effect on cells. Polyphenolic extract exhibited a slight anti-oxidant effect. Protection of cells against destruction by inflammatory mediators may be one of the ways in which the extracts from the plant, C. odorata, contribute to wound healing.

Melatonin protects fetal rat brain against oxidative mitochondrial damage.

Our objective was to investigate the effects of melatonin on the free radical-induced oxidative damage to mitochondria in fetal rat brain. Female Wistar rats on day 19 of pregnancy were used. Melatonin (10 mg/kg) or vehicle (control) was injected intraperitoneally 60 min prior to laparotomy for removal of the fetuses. The mitochondrial fraction was isolated from the fetal rat brain of each group. Superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities were measured. As indicators of mitochondrial respiratory activity, we determined the respiratory control index (RCI) and the adenosine 5-diphosphate/oxygen (ADP/O) ratio in the presence and absence of 2.5 microM hypoxanthine and 0.02 units/mL xanthine oxidase. Mitochondrial lipid peroxidation was determined by measuring the concentration of thiobarbituric acid reactive substances in fetal brain mitochondria in the presence or absence of 2.5 microM hypoxanthine, 0.02 units/mL xanthine oxidase, and 50 microM FeSO4. The free radical-induced rates of inhibition of mitochondrial RCI and the ADP/O ratio were both significantly lower in the fetal rat brains treated with melatonin compared with those of the controls (RCI, 44.25 +/- 15.02% vs. 25.18 +/- 5.86%, P < 0.01; ADP/O ratio, 50.74 +/- 23.05% vs. 13.90 +/- 7.80%, P < 0.001). The mitochondrial lipid peroxidation induced by free radicals was significantly reduced in the melatonin-treated group compared with the controls (484.2 +/- 147.2%) vs. 337.6 +/- 61.0%, P < 0.01). Pretreatment with melatonin significantly increased the activity of GSH-Px (20.35 +/- 5.27 to 28.93 +/- 11.01 mU/min mg(-1) protein, P < 0.05) in fetal rat brain mitochondria, but the activity of SOD did not change significantly. Results indicate that the administration of melatonin to the pregnant rat may prevent the free radical-induced oxidative mitochondrial damage to fetal rat brain by a direct antioxidant effect and the activation of GSH-Px.

Carvedilol reduces mitochondrial damage induced by hypoxanthine/xanthine oxidase: relevance to hypoxia/reoxygenation injury.

The cardioprotective properties of new pharmaceuticals such as carvedilol might be explained by enhanced mitochondrial protection. The aim of this work was to determine the role of carvedilol in the protection of heart mitochondria from oxidative damage induced by hypoxanthine/xanthine oxidase, a known source of oxidative stress in the vascular system. Carvedilol reduced oxidative-stress-induced mitochondrial injury, as seen by the delay in the loss of the mitochondrial transmembranar potential (Delta Psi), the decrease in mitochondrial swelling, and the increase in mitochondrial calcium uptake. Carvedilol improved the mitochondrial respiratory activity in state III and offered an overall protection in the respiratory control and in the P/O ratios in mitochondria under oxidative stress. The data indicated that carvedilol was able to partly protect heart mitochondria from oxidative stress-induced damage. Our results suggest that mitochondria can be important targets for some cardioprotective pharmaceuticals.

Phenolic compounds of Chromolaena odorata protect cultured skin cells from oxidative damage: implication for cutaneous wound healing.

Extracts from the leaves of Chromolaena odorata have been shown to be beneficial for treatment of wounds. The crude ethanol extract of the plant had been demonstrated to be a powerful antioxidant to protect fibroblasts and keratinocytes in vitro. In this study, the most active compounds were fractionated and identified from the crude extract using liquid chromatography coupled with UV spectroscopy and mass spectrometry. The antioxidant effects of purified fractions on cultured fibroblasts and keratinocytes were investigated using colorimetric and lactate hydrogenase release assay. The results showed that the phenolic acids present (protocatechuic, p-hydroxybenzoic, p-coumaric, ferulic and vanillic acids) and complex mixtures of lipophilic flavonoid aglycones (flavanones, flavonols, flavones and chalcones) were major and powerful antioxidants to protect cultured skin cells against oxidative damage. In conclusion, the extract from C odorata contains a mixture of powerful antioxidant compounds that may be one of potential mechanism contributing to enhanced wound healing.

Marked variation in free radical injury between bovine and porcine endothelial cells cultured in different media.

Previous studies produced models of oxygen-derived free radical (OFR) injury, using H(2)O(2) or xanthine/xanthine oxidase (X/XO), in cultured porcine aortic endothelium (PAE) and rat coronary endothelium. H(2)O(2) at 0.1 mM resulted in 50% viability in both cell types. To determine if comparable H(2)O(2) or X/XO concentrations have the same injurious effect on endothelium from other sources, models of OFR injury were developed for bovine aortic endothelium (BAE) and bovine brain microvessel endothelium (BBME). Varying concentrations of H(2)O(2) (0.01 to 6 mM) or X/XO (10 microM/0.1 to 0.3 U/mL) were added to medium 24 h prior to evaluating cell damage. Injury was assessed using the Trypan blue exclusion test (% viability) and by measuring the release of lactate dehydrogenase into medium. H(2)O(2) concentrations required to produce 50% viability were >6 mM in BAE and BBME versus 1 mM in PAE when cells were grown in Dulbecco's modified Eagle's medium (DMEM). Similarly, BAE and BBME were less sensitive than PAE to damage by X/XO. Cells from both species were more sensitive to H(2)O(2) or X/XO injury when grown in Medium 199 (M199) versus DMEM. The most profound difference was observed with PAE where 50% viability was obtained with 0.12 versus 1.05 mM H(2)O(2) in M199 versus DMEM. These results indicate that bovine endothelial cells from aorta and brain are more resistant to free radical injury than PAE. The presence or absence of key media components (iron, pyruvate, cysteine, histidine) likely influences the extent of OFR injury.

Iron, alpha-tocopherol, oxidative damage and micronucleus formation in rat splenocytes.

The influence of low and high alpha-tocopherol diets in concert with a high polyunsaturated fat content and a modest increase in dietary iron has been studied. Iron supplementation at five times the recommended dietary level was not associated with any increased sensitivity of the splenocytes to any of the oxidative challenges. Despite the significantly higher alpha-tocopherol concentrations in the plasma and liver of animals supplemented with this vitamin, there was no apparent protection against oxidative genotoxicity, as judged by the formation of micronuclei in splenocytes subjected to oxidative stress ex vivo. These results add to the evidence that vitamin E supplementation has little effect against oxidative genomic damage, at least as demonstrated by an increase in micronucleus frequency.

NMDA receptor activation: critical role in oxidant tissue injury.

The excitatory amino acid glutamate serves important neurologic functions, but overactivation of its N-methyl-D-aspartate (NMDA) receptor is toxic to neurons (excitotoxicity). We report that NMDA receptor blocker MK-801 (dizocilpine maleate) attenuated oxidant injury induced by paraquat or by xanthine oxidase. We conclude that excitotoxicity may be a key factor in oxidant tissue injury.

Influence of melatonin on free radical-induced changes in rat pancreatic beta-cells in vitro.

Free radicals may produce cytotoxicity to pancreatic islets under pathophysiological conditions. The aim of our in vitro investigations was to compare functional and morphological changes in pancreatic beta-cells induced by reactive oxygen species (ROS) generated by alloxan or xanthine oxidase/hypoxanthine (XO/HX), respectively. We demonstrate that short-term exposure to alloxan or to XO/HX leads to a temporarily elevated insulin release from isolated pancreatic islets. On application of alloxan, this effect is caused by beta-cell necrosis and can be prevented by administration of melatonin, while in contrast, XO/HX did not lead to long-term morphological changes in the majority of the cells. Among the cells destroyed by alloxan, only necrosis could be detected, while in contrast, some apoptotic cells were identified by the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) reaction and electron microscopic examinations of cells treated with XO/HX. Melatonin was able to prevent the changes caused by alloxan, but failed to influence the alterations caused by XO/HX. Using electron spin resonance and lipid peroxidation assay, respectively, it was confirmed that melatonin effectively detoxifies hydroxyl radicals. Therefore, we believe that hydroxyl radicals are the toxic principle of alloxan, but not of XO/HX toxicity.