The salicylate hydroxylation assay to measure hydroxyl free radicals induced by local application of glutamate in vivo or induced by the Fenton reaction in vitro

Boosting the activation of molecular oxygen and the degradation of tetracycline over high loading Ag single atomic catalyst

Photocatalytic activation of molecular oxygen (O₂) is a promising way in oxidative degradation of organic pollutants. However, it suffers from low efficiency mainly due to the limited active sites for O₂ activation over traditional photocatalysts. Therefore, we established a single atomic Ag-g-C₃N₄ (SAACN) catalyst with 10 wt% loading of Ag single sites for boosting the O₂ activation during the degradation of tetracycline (TC), and 10 wt% loading of nanoparticle Ag-g-C₃N₄ (NPACN) was studied as a comparison. When using SAACN, the accumulative concentration of superoxide (•O₂^-), hydroxyl radical (•OH), singlet oxygen (¹O₂) reached up to 0.66, 0.19, 0.33 mmol L^-1h^-1, respectively, within 120 min, 11.7, 5.7 and 4.9 times compared with those using NPACN, representing 17.24% of dissolved O₂ was converted to reactive oxygen species (ROS). When additionally feeding air or O_2, the accumulative concentrations of •O₂^-, •OH, ¹O₂ were even higher (air: 4.21, 0.97, 2.02 mmol L^-1 h^-1; O₂: 17.13, 1.32, 9.00 mmol L^-1 h^-1). The rate constants (k) for degrading the TC were 0.0409 min^-1 over SAACN and 0.00880 min^-1 over NPACN, respectively (mineralization rate: 95.7% vs. 59.9% after 3 h of degradation). Moreover, the degradation ability of SAACN did not decrease in a wide range of pH value (4-10) or under low temperature (10 °C). Besides the high exposure of Ag single sites, other advances of SAACN were: 1(O₂ was more energetic favorable to adsorb on single atomic Ag sites; 2) Positive Ag single sites were easier to obtain the electrons from the surrounding N atoms, and facilitated electron transfer towards adsorbed O₂.

Blockade of the renin-angiotensin system suppresses hydroxyl radical production in the rat striatum during carbon monoxide poisoning

Oxidative stress has been suggested to play a role in brain damage during carbon monoxide (CO) poisoning. Severe poisoning induced by CO at 3000 ppm, but not 1000 ppm, enhances hydroxyl radical (˙OH) production in the rat striatum, which might be mediated by NADPH oxidase (NOX) activation associated with Ras-related C3 botulinum toxin substrate (Rac) via cAMP signaling pathway activation. CO-induced ˙OH production was suppressed by antagonists of angiotensin II (AngII) type 1 receptor (AT1R) and type 2 receptor (AT2R) but not an antagonist of the Mas receptor. Suppression by an AT1R antagonist was unrelated to peroxisome proliferator-activated receptor γ. Angiotensin-converting enzyme inhibitors also suppressed CO-induced ˙OH production. Intrastriatal AngII at high concentrations enhanced ˙OH production. However, the enhancement of ˙OH production was resistant to inhibitors selective for NOX and Rac and to AT1R and AT2R antagonists. This indicates a different mechanism for ˙OH production induced by AngII than for that induced by CO poisoning. AT1R and AT2R antagonists had no significant effects on CO-induced cAMP production or ˙OH production induced by forskolin, which stimulates cAMP production. These findings suggest that the renin-angiotensin system might be involved in CO-induced ˙OH production in a manner independent of cAMP signaling pathways.

Effects of Edaravone on Nitric Oxide, Hydroxyl Radicals and Neuronal Nitric Oxide Synthase During Cerebral Ischemia and Reperfusion in Mice

BACKGROUND

The purpose of this study was to investigate the effects of edaravone on nitric oxide (NO) production, hydroxyl radical (OH^-) metabolism, and neuronal nitric oxide synthase (nNOS) expression during cerebral ischemia and reperfusion.

METHODS

Edaravone (3 mg/kg) was administered intravenously to 14 C57BL/6 mice just before reperfusion. Eleven additional mice received saline (controls). NO production and OH^- metabolism were continuously monitored using bilateral striatal in vivo microdialysis. OH^- formation was monitored using the salicylate trapping method. Forebrain ischemia was produced in all mice by bilateral occlusion of the common carotid artery for 10 minutes. Levels of NO metabolites, nitrite (NO₂^-) and nitrate (NO₃^-), were determined using the Griess reaction. Brain sections were immunostained with an anti-nNOS antibody and the fractional area density of nNOS-immunoreactive pixels to total pixels determined.

RESULTS

Blood pressure and regional cerebral blood flow were not significantly different between the edaravone and control groups. The levels of NO₂^- did not differ significantly between the 2 groups. The level of NO₃^- was significantly higher in the edaravone group compared with the control group after reperfusion. 2,3-dihydroxybenzoic acid levels were lower in the edaravone group compared with those in the control group after reperfusion. Immunohistochemistry showed nNOS expression in the edaravone group to be significantly lower than that in the control group 96 hours after reperfusion.

CONCLUSIONS

These in vivo data indicate that edaravone may have a neuroprotective effect by reducing levels of OH^- metabolites, increasing NO production and decreasing nNOS expression in brain cells.

Nucleic acid-targeted pathogen reduction technique in red blood cells by UV-generated oxygen radicals for optimising recipient safety

OBJECTIVES

A novel pathogen reduction technique based on vacuum ultraviolet (VUV) irradiation was developed to reduce pathogen numbers in red blood cell (RBC) components.

BACKGROUND

Contaminated blood components pose a great risk of infection in blood recipients. The continuous development of blood screening techniques and pathogen inactivating systems has significantly reduced this risk, but many limitations remain.

METHODS

Escherichia coli and Bacillus cereus, and bacteriophage (BP) and Lentivirus (LV) were spiked into suspended red blood cells (sRBCs) or plasma. VUV light with maximum emission at 185 nm and an average dosage of 164 μW/cm² was placed 5 cm above the targeted products to reduce the pathogen numbers.

RESULTS

Treatment for 5 minutes was effective; 3 and 10 log reductions of E coli counts were observed in sRBCs and plasma, and 2 and 3 log reductions of B cereus counts were observed in sRBCs and plasma, respectively. The BP titre was reduced by two and five log points in sRBCs and plasma, respectively; the LV titre was reduced by at least three log points in both sRBCs and plasma. VUV-based irradiation of RBCs does not cause significant structural and functional harmful effects. This novel strategy provides moderate photonic energy to generate oxygen radicals from H₂ O and O₂ and to selectively decrease DNA integrity of the potential pathogens.

CONCLUSION

The VUV-based pathogen reduction technique is a simple and fast procedure with high pathogen reduction efficacy, low toxicity and limited adverse effects on cellular blood products.

Effect of Yokukansan on Nitric Oxide Production and Hydroxyl Radical Metabolism During Cerebral Ischemia and Reperfusion in Mice

BACKGROUND

The purpose of this study was to investigate the effects of yokukansan on forebrain ischemia. Because we can measure nitric oxide production and hydroxyl radical metabolism continuously, we investigated the effect of yokukansan on nitric oxide production and hydroxyl radical metabolism in cerebral ischemia and reperfusion.

METHODS

Yokukansan (300 mg per kg per day) was mixed into feed and given to 16 mice for 10days. Sixteen additional mice received normal feed (control). Nitric oxide production and hydroxyl radical metabolism were continuously monitored using the salicylate trapping method. Forebrain ischemia was producedin all mice by occluding the common carotid artery bilaterally for 10minutes. Levels of the nitric oxide metabolites nitrite and nitrate were determined using the Griess reaction. Survival rates of hippocampal CA1 neurons were calculated and 8-hydroxydeoxyguanosine-immunopositive cells were counted to evaluate the oxidative stress in hippocampal CA1 neurons 72hours after the start of reperfusion.

RESULTS

Arterial blood pressure and regional cerebral blood flow were not significantly different between the 2 groups. The level of nitrate was significantly higher in the yokukansan group than in the control group during ischemia and reperfusion. Levels of 2,3- and 2,5-dihydroxybenzoic acid were significantly lower in the yokukansan group than in the control group during ischemia and reperfusion. Although survival rates in the CA1 did not differ significantly, there were fewer 8-hydroxydeoxyguanosine-immunopositive cells in animals that had received yokukansan than in control animals.

CONCLUSIONS

These data suggest that yokukansan exerts reducing hydroxyl radicals in cerebral ischemic injury.

Time-dependent toxicity of cadmium telluride quantum dots on liver and kidneys in mice: histopathological changes with elevated free cadmium ions and hydroxyl radicals

A complete understanding of the toxicological behavior of quantum dots (QDs) in vivo is of great importance and a prerequisite for their application in humans. In contrast with the numerous cytotoxicity studies investigating QDs, only a few in vivo studies of QDs have been reported, and the issue remains controversial. Our study aimed to understand QD-mediated toxicity across different time points and to explore the roles of free cadmium ions (Cd²⁺) and hydroxyl radicals (·OH) in tissue damage. Male ICR mice were administered a single intravenous dose (1.5 µmol/kg) of CdTe QDs, and liver and kidney function and morphology were subsequently examined at 1, 7, 14, and 28 days. Furthermore, ·OH production in the tissue was quantified by trapping · OH with salicylic acid (SA) as 2,3-dihydroxybenzoic acid (DHBA) and detecting it using a high-performance liquid chromatography fluorescence method. We used the induction of tissue metallothionein levels and 2,3-DHBA:SA ratios as markers for elevated Cd²⁺ from the degradation of QDs and ·OH generation in the tissue, respectively. Our experimental results revealed that the QD-induced histopathological changes were time-dependent with elevated Cd²⁺ and ·OH, and could recover after a period of time. The Cd²⁺ and ·OH exhibited delayed effects in terms of histopathological abnormalities. Histological assessments performed at multiple time points might facilitate the evaluation of the biological safety of QDs.

Different mechanisms of hydroxyl radical production susceptible to purine P2 receptor antagonists between carbon monoxide poisoning and exogenous ATP in rat striatum

Previous studies have suggested that carbon monoxide (CO) poisoning stimulates cAMP production via purine P2Y11-like receptors in the rat striatum, activating cAMP signaling pathways, resulting in hydroxyl radical ((•)OH) production. Extracellular ATP was thought likely to trigger the cascade, but the present study has failed to demonstrate a clear increase in the extracellular ATP due to CO poisoning. The CO-induced (•)OH production was attenuated by the P2Y11 receptor antagonist NF157, in parallel with its abilities to suppress the CO-induced cAMP production. The (•)OH production was more strongly suppressed by a non-selective P2 receptor antagonist, PPADS, which had no effect on cAMP production. More selective antagonists toward the respective P2 receptors susceptible to PPADS, including NF279, had little or no effect on the CO-induced (•)OH production. The intrastriatal administration of exogenous ATP dose-dependently stimulated (•)OH production, which was dose-dependently antagonized by PPADS and NF279 but not by NF157. Exogenous GTP and CTP dose-dependently stimulated (•)OH production, though less potently. The GTP-induced (•)OH production was susceptible to both of NF279 and PPADS, but the CTP-induced (•)OH production was resistant to PPADS. The mechanism of (•)OH production may differ between CO poisoning and exogenous ATP, while multiple P2 receptors could participate in (•)OH production. The CO-induced (•)OH production was susceptible to the inhibition of NADPH oxidase, but not xanthine oxidase. Also, the NADPH oxidase inhibition suppressed (•)OH production induced by forskolin, a stimulator of intracellular cAMP formation. It is likely that (•)OH is produced by NADPH oxidase activation via cAMP signaling pathways during CO poisoning.

Assessment of hydroxyl radical generation and radical scavenging activity of Chinese medicinal herbs using GC-MS

Aqueous extracts of ten Chinese herbs were evaluated for their radical scavenging activity by a GC-MS method based on the Fenton reaction system. Hydroxylation of salicylate and phenylalanine is widely used as an index of hydroxyl radical formation in vivo and in vitro. A problem associated with quantifying product from such reactions is the generation of complex reaction products that increase background 'noise' and reduce sensitivity for the target product. The aim of this investigation was to develop a GC-MS methodology to assess in vitro hydroxyl radical production. In this method, hydroxyl radical was trapped by p-hydroxyphenylacetic acid to form 3,4-dihydroxyphenylacetic acid (DOPAC) which was then selectively extracted from the reaction mixture using aluminium oxide and assayed by GC-MS. Selective adsorption and desorption of the catechol nucleus from aluminium oxide was shown to eliminate interference from non-catechol reaction products effectively. This system was applied to examine the hydroxyl radical scavenging activity of different herbal extracts. The results showed that the herb Dimocaepus Longan Lour exhibited the highest radical scavenging activity of all the herbs examined. With the use of a stable isotope-labelled internal standard, this system could be readily applied to in vitro methods which use 4-hydroxybenzoic acid as a substrate for the hydroxyl radical.

Study of the potential oxidative stress induced by six solvents in the rat brain

The mechanisms of action involved in the neurotoxicity of solvents are poorly understood. In vitro studies have suggested that the effects of some solvents might be due to the formation of reactive oxygen species (ROS). This study assesses hydroxyl radical (OH) generation and measures malondialdehyde (MDA) levels in the cerebral tissue of rats exposed to six solvents (n-hexane, n-octane, toluene, n-butylbenzene, cyclohexane and 1,2,4-trimethylcyclohexane). Three of these solvents have been shown to generate ROS in studies carried out in vitro on granular cell cultures from rat cerebellum. We assessed OH production by quantifying the rate of formation of 3,4-dihydroxybenzoic acid using a trapping agent, 4-hydroxybenzoic acid, infused via the microdialysis probe, into the prefrontal cortex of rats exposed intraperitoneally to the solvents. Extracellular MDA was quantified in microdialysates collected from the prefrontal cortex of rats exposed, 6h/day for ten days, to 1000ppm of the solvents (except for n-butylbenzene, generated at 830ppm) in inhalation chambers. Tissue levels of free and total MDA were measured in different brain structures for rats acutely (intraperitoneal route) and sub-acutely (inhalation) exposed to solvents. None of the six solvents studied increased the production of hydroxyl radicals in the prefrontal cortex after acute administration. Nor did they increase extracellular or tissue levels of MDA after 10 days' inhalation exposure. On the other hand, a decrease in the concentrations of free MDA in brain structures was observed after acute administration of n-hexane, 1,2,4-trimethylcyclohexane, toluene and n-butylbenzene. Therefore, data of this study carried out in vivo did not confirm observations made in vitro on cell cultures.

Dual contradictory roles of cAMP signaling pathways in hydroxyl radical production in the rat striatum

Studies have suggested that cAMP signaling pathways may be associated with the production of reactive oxygen species. In this study, we examined how modifications in cAMP signaling affected the production of hydroxyl radicals in rat striatum using microdialysis to measure extracellular 2,3-dihydroxybenzoic acid (2,3-DHBA), which is a hydroxyl radical adduct of salicylate. Up to 50 nmol of the cell-permeative cAMP mimetic 8-bromo-cAMP (8-Br-cAMP) increased 2,3-DHBA in a dose-dependent manner (there was no additional increase in 2,3-DHBA at 100 nmol). Another cAMP mimetic, dibutyryl cAMP (db-cAMP), caused a nonsignificant increase in 2,3-DHBA at 50 nmol and a significant decrease at 100 nmol. Up to 20 nmol of forskolin, which is a direct activator of adenylyl cyclase, increased 2,3-DHBA, similar to the effect of 8-Br-cAMP; however, forskolin resulted in a much greater increase in 2,3-DHBA. A potent inhibitor of protein kinase A (PKA), H89 (500 μM), potentiated the 8-Br-cAMP- and forskolin-induced increases in 2,3-DHBA and antagonized the inhibitory effect of 100 nmol of db-cAMP. Interestingly, the administration of 100 nmol of 8-bromo-cGMP alone or in combination with H89 had no significant effect on 2,3-DHBA levels. Doses of 100 nmol of a preferential PKA activator (6-phenyl-cAMP) or a preferential PKA inhibitor (8-bromoadenosine-3',5'-cyclic monophosphorothionate, Rp-isomer; Rp-8-Br-cAMPS), which also inhibits the cAMP-mediated activation of Epac (the exchange protein directly activated by cAMP), suppressed or enhanced, respectively, the formation of 2,3-DHBA. Up to 100 nmol of 8-(4-chlorophenylthio)-2'-O-methyladenosine-cAMP, which is a selective activator of Epac, dose-dependently stimulated the formation of 2,3-DHBA. These findings suggest that cAMP signaling plays contradictory roles (stimulation and inhibition) in the production of hydroxyl radicals in rat striatum by differential actions of Epac and PKA. These roles might contribute to the production of hydroxyl radicals concomitant with cAMP in carbon monoxide poisoning, because the formation of 2,3-DHBA was potentiated by the PKA inhibitor H89 and suppressed by Rp-8-Br-cAMPS, which inhibits PKA and Epac.

Ginsenoside Rd attenuates early oxidative damage and sequential inflammatory response after transient focal ischemia in rats

We previously found that ginsenoside Rd (Rd), one of the main active ingredients in Panax ginseng, attenuates neuronal oxidative damage in vitro induced by hydrogen peroxide and oxygen-glucose deprivation. In this study, we sought to investigate the potential protective effects and associated mechanisms of Rd in a rat model of focal cerebral ischemia. Rats administered with Rd (0.1-200mg/kg) or vehicle was subjected to transient middle cerebral artery occlusion. Rd at the dose of 10-50mg/kg significantly reduced the infarct volume and improved the long-term neurological outcome up to 6 weeks after ischemia. To evaluate the underlying mechanisms, in vivo free radical generation was monitored using microdialysis, oxidative DNA damage was identified by 8-hydroxy-deoxyguanosine immunostaining, oxidative protein damage was identified by the assessment of protein carbonyl and advanced glycosylation end products, and lipid peroxidation was estimated by determining the malondialdehyde and 4-hydroxynonenal formations. Microdialysis results displayed a prominent inhibitory effect of Rd on the hydroxy radical formation trapped as 2,3- and 2,5-DHBA. Early accumulations of DNA, protein and lipid peroxidation products were also suppressed by Rd treatment. Although Rd partly preserved endogenous antioxidant activities in the ischemic penumbra, in sham rats without stroke, endogenous antioxidant activities were not affected by Rd. Furthermore, we assayed sequential inflammatory response in a later phase after ischemia. Rd significantly eliminated inflammatory injury as indicated by the suppression of microglial activation, inducible nitric oxide synthase and cyclooxygenase-2 expression. Collectively, these findings demonstrated that Rd exerts neuroprotection in transient focal ischemia, which may involve early free radicals scavenging pathway and a late anti-inflammatory effect.

Cysteine-iron promotes arginase activity by driving the Fenton reaction

Impairment of nitric oxide bioavailability secondary to increased arginase activity and overproduction of reactive oxygen species (ROS) is thought to be a major cause of vascular complications in sickle cell disease (SCD). However, the role of ROS in the induction of arginase activity is unknown. This study investigated whether the mechanism of arginase activation involves the ROS produced during oxidative stress. Our study reveals that cysteine-iron dose-dependently stimulated arginase activity with a corresponding increase in (.)OH radical formation. The ()OH radicals produced were significantly inhibited by salicylic acid derivatives and superoxide dismutase. Surprisingly, the inhibition of (.)OH radicals parallels the inhibition of arginase activity, thus suggesting the role of cysteine-iron in the stimulation of arginase via the Fenton reaction. This is the first evidence demonstrating the participation of (.)OH radicals in the stimulation of arginase activity, and thus provides novel avenues for therapeutic modalities in hemoglobinopathies and other inflammation-mediated diseases.

Measurement of Hydroxyl-Radical Formation in the Rat Striatum by In Vivo Microdialysis and GC-MS

A GC-MS method was developed for measuring hydroxyl-radical capture products of salicylic acid, a common trapping agent for this reactive oxygen species, in samples obtained by in vivo cerebral microdialysis experiments. The assay employed liquid-liquid extraction followed by derivatization of 2,3- and 2,5-dihydroxybenzoic acid, along with 3,5-dihydroxybenzoic acid added as an internal standard. Due to their simple electron ionization mass spectra featuring [M - 57](+) ions through the loss of tertiary alkyl group from the corresponding molecular ions, tert-butyldimethylsilyl (TBDMS) derivatives afforded straightforward method development based on selected-ion monitoring. In addition, tandem mass spectrometry probing collision-induced dissociation of [M - 57](+) ions obtained from the isomeric tert-butyldimethylsilyl derivatives revealed characteristic differences in the resultant product-ion spectra. Our work has demonstrated the applicability of GC-MS for the assay of microdialysates for 2,3- and 2,5-dihydroxybenzoic acid by confirming that local administration of the excitotoxic glutamate into the rat striatum significantly increased in vivo hydroxyl-radical production in this brain region and that subsequent systemic administration of α-phenyl-tert-butylnitrone reversed glutamate-induced oxidative stress.

Role of nitric oxide system in hydroxyl radical generation in rat striatum due to carbon monoxide poisoning, as determined by microdialysis

We explored the possible role of the nitric oxide (NO) system in hydroxyl radical (*OH) generation induced by carbon monoxide (CO) poisoning in rat striatum by means of microdialysis with the use of NO synthase (NOS) inhibitors, N(G)-nitro-L-arginine methyl ester (L-NAME) and N(G)-monomethyl-L-arginine (L-NMMA), as well as L-arginine (L-Arg; the NOS substrate) and D-arginine (D-Arg). The CO-induced *OH generation was suppressed by both L-Arg and D-Arg. It was also suppressed by L-NAME, which inhibits generation of reactive oxygen species (ROS) via neuronal NOS (nNOS) and inducible NOS, but not via endothelial NOS. In contrast, L-NMMA, which inhibits only ROS generation via inducible NOS, potentiated the *OH generation. L-Arg completely reversed the L-NAME effect and partly reversed the L-NMMA effect. D-Arg reversed the L-NAME effect more potently than did L-Arg, resulting in much more *OH generation than was observed with CO alone, and also potentiated the L-NMMA effect. On the other hand, W-7, an antagonist of calmodulin, which is critical for nNOS activity, had no effect on the CO-induced *OH generation. These findings suggest that complex mechanisms operate in *OH generation in rat striatum upon CO poisoning and that the NO system might not be included among those mechanisms.

15-Deoxy-delta12,14-prostaglandin J2, a neuroprotectant or a neurotoxicant?

15-Deoxy-delta12,14-prostaglandin J2 (15d-PGJ2) is a potent ligand for peroxisome proliferators-activated receptor gamma (PPARgamma). However, its various effects independent of PPARgamma have recently been observed. The effect of 15d-PGJ2 on neuronal cells is still controversial. We investigated its effect on neuronal cells (N18D3 cells). When N18D3 cells were treated with 15d-PGJ2, the viability was not changed up to 8 microM, but decreased at higher than 8 microM. The expressions of survival signals, such as p85a phosphatidylinositol 3-kinase, phospho-Akt, and phospho-glycogen synthase kinase-3 beta (Ser-9), slightly increased up to 8 microM, however, decreased at higher than 8 microM. The levels of free radicals and membrane lipid peroxidation and the expression of c-Jun N-terminal Kinase increased in a dose-dependent manner, especially at higher than 8 microM. However, the expressions of death signals, such as cytosolic cytochrome c, activated caspase-3, and cleaved poly(ADP-ribose) polymerase, decreased up to 8 microM, however, increased at higher than 8 microM. In the study to evaluate whether low dose of 15d-PGJ2, up to 8 microM, had protective effect on oxidative stress-injured N18D3 cells, compared to the cells treated with only 100 microM H2O2, the pretreatment with 8 microM 15d-PGJ2 increased the viability and the expressions of the survival signals, but decreased them of the death signals. These results indicate that 15d-PGJ2 could be a neuroprotectant or a neurotoxicant, depending on its concentration. Therefore, some specific optimum dose of 15d-PGJ2 may be a new potential therapeutic candidate for oxidative stress-injury model of neurodegenerative diseases.

Reactive oxidative and nitrogen species in the nigrostriatal system following striatal 6-hydroxydopamine lesion in rats

Oxidative stress is a major contributing factor in the pathogenesis of Parkinson's disease. We therefore investigated the effect of the dopaminergic neurotoxin 6-hydroxydopamine (6-OHDA) on hydroxyl-free radical and peroxynitrite formation in the intrastriatal 6-OHDA rat model of Parkinson's disease. The hydroxylation product of salicylate (2,3-dihydroxy-benzoic acid) as well as the hydroxylation and nitration products of d-phenylalanine (2- and 3-hydroxyl-phenylalanine, nitrotyrosine and nitrophenylalanine) were assessed in tissue samples of the striatum and, for the first time, the substantia nigra of adult rats at four different time points (25 min, 2 h, 4 h and 7 days) after unilateral stereotaxic intrastriatal injection of 6-OHDA. In the striatum, maxima of hydroxylating and nitrating markers were found at early time points after 6-OHDA lesion. These results suggest a direct interrelation between 6-OHDA-autoxidation and/or the increased dopamine turnover and hydroxyl-free radical and peroxynitrite formation. In the substantia nigra, i.e., at a distance from the injection site of the neurotoxin, an increase in hydroxyl-free radical formation was observed at 7 days after 6-OHDA lesion, with this modification possibly being independent of 6-OHDA autoxidation and rather representing a long-term effect of the toxin. Furthermore, we conclude that apart from the formation of reactive oxygen species, the production of reactive nitrogen species occurs in this experimental Parkinson's disease model. Finally, the similarity between the 6-OHDA model and Parkinson's disease supports the notion that reactive oxygen species as well as reactive nitrogen species may play an important role in the pathogenesis of this neurodegenerative disorder.

Differential effects of diallyl disulfide on neuronal cells depend on its concentration

Diallyl disulfide (DADS) is one of the organosulfur compounds of garlic. The effects of DADS on neuronal cells have not clearly been established. We investigated its effects on the viability of neuronal cells (N18D3 cells), the levels of free radical and membrane lipid peroxidation, and the cell signals, such as phosphatidylinositol 3-kinase (PI3K)/Akt and glycogen synthase kinase-3 (GSK-3). When N18D3 cells were treated with several concentrations of DADS, the viability was not affected up to 25 microM, however, decreased at higher than 25 microM. The levels of free radicals and membrane lipid peroxidation were increased in a dose-dependent manner, especially at higher than 25 microM. The treatment of N18D3 cells with 25 microM DADS slightly increased the expressions of p85a PI3K, phosphorylated Akt and phosphorylated GSK-3, but the treatment with 100 microM significantly reduced them. To evaluate whether low concentration of DADS, up to 25 microM, had protective effect on oxidative stress-injured N18D3 cells, the viability of N18D3 cells (pretreated with DADS for 2h versus not pretreated) was evaluated 24h after their exposure to 100 microM H(2)O(2) for 30 min. Compared to the cells treated with only 100 microM H(2)O(2), the pretreatment with 25 microM DADS increased the viability, and the expressions of p85a PI3K, phosphorylated Akt and phosphorylated GSK-3. These results indicate that low concentration of DADS has protective effects on N18D3 cells, whereas high concentration is rather cytotoxic. Therefore, some specific optimum concentration of DADS may be a new potential therapeutic strategy for oxidative stress-injury in vitro model of neurodegenerative diseases.

Role of peroxidases in Parkinson disease: a hypothesis

Extensive research has been done to elucidate the underlying molecular events causing neurodegenerative diseases such as Parkinson disease, yet the cause and the individual steps in the progression of such diseases are still unknown. Here we advance the hypothesis that, rather than or in addition to inorganic radical molecules, heme-containing peroxidase enzymes may play a major role in the etiology of Parkinson disease. This hypothesis is based on the following considerations: (1) several heme-containing enzymes with peroxidase activity are present in the substantia nigra pars compacta; (2) these peroxidases have the ability to catalyze the oxidation of proteins and lipids; (3) certain heme peroxidases are known to destroy cells in vivo; (4) heme peroxidases have the stability and specificity that could account for the fact that specific molecules and cells are subject to damage in Parkinson disease, rather than a random destruction; (5) heme peroxidase activity could account for certain reactions in connection with parkinsonism that thus far have not been adequately explained; and (6) the participation of a heme peroxidase could explain some recent observations that are inconsistent with the oxyradical theory. The peroxidase-catalyzed oxidative pathway proposed here does not preclude the participation of apoptosis as an additional mechanism for cell destruction.

Novel method for in vivo hydroxyl radical measurement by microdialysis in fetal sheep brain in utero

Hydroxyl radical (.OH) is a reactive oxygen species produced during severe hypoxia, asphyxia, or ischemia that can cause cell death resulting in brain damage. Generation of .OH may occur in the fetal brain during asphyxia in utero. The very short half-life of .OH requires use of trapping agents such as salicylic acid or phenylalanine for detection, but their hydroxylated derivatives are either unstable, produced endogenously, or difficult to measure in the small volume of microdialysis samples. In the present study, we used terephthalic acid (TA), hydroxylation of which yields a stable and highly fluorometric isomer (excitation, 326 nm; emission, 432 nm). In vitro studies using .OH generated by the Fenton reaction showed that hydroxylated TA formed quickly (<10 s), was resistant to bleaching (<5% change in fluorescence), and permitted detection of <0.5 pmol .OH. In vivo studies were performed in fetal sheep using microdialysis probes implanted into the parasagittal cortex. The probe was perfused at 2 mul/min with artificial cerebrospinal fluid containing 5 mM TA, and samples were collected every 30 min. Fluorescence measured in 10 mul of dialysate was significantly greater than in the efflux from probes perfused without TA. High-performance liquid chromotography analysis showed that the fluorescence in dialysis samples was entirely due to hydroxylation of TA. Thus this study shows that it is possible to use TA as a trapping agent for detecting low concentrations of .OH both in vitro and in vivo and that low concentrations of .OH are present in fetal brain tissue and fluctuate with time.

Protective effect of diallyl disulfide on oxidative stress-injured neuronally differentiated PC12 cells

The effects of diallyl disulfide (DADS), a garlic-derived compound, on the viability of neuronal cells and cell signals, including phosphatidylinositol 3-kinase (PI3K)/Akt, glycogen synthase kinase-3 (GSK-3), cytochrome c, caspase-3, and poly(ADP-ribose) polymerase (PARP), were investigated in PC12 cells neuronally differentiated by nerve growth factor. To evaluate the toxicity of DADS itself, nPC12 cells were treated with several concentrations of DADS, and 3,(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and trypan blue stain revealed that the viability was not affected by low concentration of DADS, up to 20 microM, but it was decreased at higher than this concentration. The levels of free radicals and membrane lipid peroxidation were significantly increased in nPC12 cells when treated with more than 50 microM DADS, and treatment of PC12 cells with 100 microM DADS killed the cells by inhibiting PI3K/Akt and by promoting activation of GSK-3 and caspase-3, release of cytochrome c, and cleavage of PARP. To evaluate the protective effects of low concentration of DADS on oxidative stress-injured nPC12 cells, the viability of the cells (pretreated with DADS for 2 h vs. not pretreated) was evaluated 24 h after exposure to 100 microM H2O2 for 30 min. Compared to the cells treated with 100 microM H2O2 only, pretreatment of the cells with 20 microM DADS before exposure to 100 microM H2O2 increased the viability and induced activation of PI3K and Akt, inactivation of GSK-3, and inhibition of cytochrome c release, caspase-3 activation, and PARP cleavage. These results indicate that low concentration of DADS has neuroprotective effects by activating PI3K/Akt and by inhibiting GSK-3 activation, cytochrome c release, caspase-3 activation, and PARP cleavage, whereas high concentration is rather cytotoxic. Therefore, some specific optimum concentration of DADS may be a new potential therapeutic strategy for oxidative stress injured in vitro model of neurodegenerative diseases.

Characterization of hydroxyl radical generation in the striatum of free-moving rats due to carbon monoxide poisoning, as determined by in vivo microdialysis

Carbon monoxide (CO) poisoning caused by CO exposure at 3000 ppm for 40 min resulted in stimulation of hydroxyl radical (*OH) generation (estimated by measuring 2,3-dihydroxybenzoic acid (2,3-DHBA) production from salicylic acid) in the striatum of free-moving rats, as determined by means of brain microdialysis. Pretreatment with a voltage-dependent Na+ channel blocker, tetrodotoxin (TTX), lowered the basal level of 2,3-DHBA and strongly suppressed the increase in 2,3-DHBA induced by CO poisoning. CO poisoning significantly, though only slightly, increased extracellular glutamate in the striatum, and glutamate (Glu) receptor antagonists, such as MK-801 (dizocilpine) and NBQX, failed to suppress the CO-induced increase in 2,3-DHBA. These findings suggest that CO poisoning may induce Na+ influx via the voltage-dependent Na+ channels, resulting in stimulation of *OH generation in rat striatum. This effect may be independent of Glu receptor activation by increased extracellular Glu.

Lack of hydroxyl radical generation upon central administration of methamphetamine in rat caudate nucleus: a microdialysis study

The most widely accepted concept of oxidative damage centers on the formation of hydroxyl radical (*OH) which has an extremely short-life and is the major damaging free radical. It was suggested that methamphetamine (METH) toxicity is mediated via production of *OH, as measured by 2,3-dihydroxybenzoic acid (2,3-DHBA). In this study we compared the effects of local caudate nucleus perfusion of METH with systemic administration of METH on *OH generation in relation to DA release. Local perfusion of METH (5 mM, 140 min) induced a higher level of dopamine (DA) release compared to the first METH injection (10 mg/kg, 3 times, i.p.). No significant correlation was found between changes in extracellular DA levels and *OH generation when perfusing METH locally; however, both increased after systemic METH administration.

Stable nitroxide Tempol ameliorates brain injury by inhibiting lipid peroxidation in a rat model of transient focal cerebral ischemia

Oxygen free radicals have been implicated in the pathogenesis of cerebral ischemia and reperfusion injury. 4-Hydroxy-2,2,6,6-tetramethylpiperidene-1-oxyl (Tempol) has been reported as a stable nitroxide and a membrane-permeable free radical scavenger. This study was performed to investigate the mechanism of Tempol in attenuating ischemia-reperfusion injury in a rat model of transient focal cerebral ischemia. We measured the cerebral 2,3-dihydroxybenzoic acid (DHBA) level as the amount of hydroxyl radical production using a microdialysis technique with salicylic acids trapping during ischemia and reperfusion. The concentration of cerebral thiobarbituric acid reactive substances (TBARS), representing the extent of lipid peroxidation by free radicals, and the area of cerebral infarction were also measured. The level of cerebral 2,3-DHBA was increased during ischemia and reperfusion, especially during the early reperfusion stage at the periphery of the infarct area (nearly 500-fold). Intravenous administration of Tempol at the time of reperfusion reduced 2,3-DHBA production (Vehicle group: 472.2+/-196.2, Tempol group: 238.3+/-77.2) and the cerebral TBARS level (Vehicle group: 541.7+/-84.7, Tempol group: 339.0+/-147.2 nmol/g), and decreased the size of the cerebral infarction (Vehicle group: 202.2+/-98.4, Tempol group: 98.5+/-13.7 mm(3)). In contrast, Tempol administered 15 min prior to reperfusion reduced neither the TBARS level nor the size of the infarction. These results indicate that Tempol administration at the time of reperfusion reduced lipid peroxidation by scavenging free radicals, resulting in a reduction of the infarct size.

An in vitro hydroxyl radical generation assay for microdialysis sampling calibration

A xanthine oxidase hydroxyl radical (.OH)-generating system was created for sustained in vitro production of *OH. This assay was coupled with microdialysis sampling to elucidate the factors that influence microdialysis calibration during radical trapping. A *OH trapping agent, 4-hydroxybenzoic acid, was included either in the microdialysis perfusion fluid or in the medium external to the microdialysis probe. Xanthine oxidase enzymatic activity was reproducible and had an average activity measured by UV absorbance of produced uric acid of 0.037 +/- 0.005 deltaAU/min (n = 5). A considerable amount of variance in the rate and amount of the product, 3,4-dihydroxybenzoic acid (3,4-DHBA), was observed when one microdialysis probe was placed in the reaction mixture. When two microdialysis probes were placed in the reaction mixture, a greater rate and amount of 3,4-DHBA was observed. Different concentrations of 3,4-DHBA were obtained between quiescent and stirred systems.

The dopamine agonist pramipexole scavenges hydroxyl free radicals induced by striatal application of 6-hydroxydopamine in rats: an in vivo microdialysis study

Hydroxyl free radical production seems to play an important role in the pathogenesis of Parkinson's disease. In the present study, we investigated the dopamine agonists pramipexole and pergolide as well as the nitrone compound S-PBN (N-tert-butyl-alpha-(2-sulfophenyl)nitrone) to reduce hydroxyl radical formation. Microdialysis experiments were carried out in non-anaesthetized Wistar rats. Salicylate was incorporated into the perfusion fluid to measure indirectly hydroxyl radicals indicated by 2,3-dihydroxybenzoic acid (2,3-DHBA). Local perfusion with 0.2 or 2 nmol/2 microl/min 6-hydroxydopamine (6-OHDA) via the microdialysis probe significantly increased 2,3-DHBA levels 14-fold and 47-fold, respectively. Systemic application of either pergolide (0.05 mg/kg) or pramipexole (1 mg/kg) failed to significantly reduce 6-OHDA-induced hydroxyl radical production. In contrast, a 40 min pretreatment with pramipexole (2 and 10 nmol/2 microl/min via the probe) before onset of 6-OHDA perfusion, significantly attenuated 2, 3-DHBA levels compared with vehicle controls. S-PBN pretreatment (2 nmol/2 microl/min) was not effective to reduce 2,3-DHBA levels. In conclusion, pramipexole was able to reduce hydroxyl radical levels induced by 6-OHDA in vivo after local application. This property of pramipexole may be beneficial under conditions of enhanced hydroxyl radical formation in parkinsonian brains and may add to its well known dopamine D(2)-like receptor agonistic effects.