Evaluation of sodium 4-hydroxybenzoate as an hydroxyl radical trap using gas chromatography-mass spectrometry and high-performance liquid chromatography with electrochemical detection

Needle electrode design of pulsed high voltage discharge reactor for performance enhancement of 4-chlorophenol degradation in highly conductive solution

In this paper, a pulsed high voltage discharge (PHVD) reactor composed of a new type of high-voltage (HV) needle electrode and mesh grounding electrode was utilized to degrade 4-chlorophenol (4-CP). The effect of needle installation position on 4-CP degradation efficiency in solution systems with different conductivities was studied. It is verified that the recessed- and flush-tip structures could effectively overcome the main technical problem of protruded-tip HV electrode, which is that how to maintain stable discharge in the solution with high conductivity. When the conductivity of solution surpassed 116 μS cm^-1, the recessed-tip and flush-tip electrodes possessed higher energy efficiency than that of the protruded-tip electrode. Within 40 min, the flush-tip electrode had the highest 4-CP removal rate (86.2%) in pure water, which could further increased to 95.8% via increasing immersion depth of net electrode. Comprehensively considering the experimental results of 4-CP removal rate, discharge characteristic and tail gas emission, it is indicated that the optimal installation positions were 0-F and 5-R. Meanwhile, the increase in immersion depth could reduce the generation of tail gas (e.g. O₃ and NO_X) obviously. The possible mechanism of 4-CP degradation via PHVD was proposed.

Hydroxyl Radical Production in the Cortex and Striatum in a Rat Model of Focal Cerebral Ischemia

Background:

Increases in hydroxyl radical production have been used as evidence of oxidative stress in cerebral ischemia/ reperfusion. Ischemia can also induce increased dopamine release from the striatum that may contribute to hydroxyl radical formation. We have compared hydroxyl radical production in the cortex and striatum as an index of oxidative stress in a rat model of focal cerebral ischemia with cortical infarction.

Methods:

Using a three vessel occlusion model of focal cerebral ischemia combined with bilateral microdialysis, hydroxylation of 4-hydroxybenzoate (4HB) was continuously monitored in both hemispheres in either the lateral striatum or frontoparietal cortex. The ischemia protocol consisted of one hour equilibration, 30 min of three vessel occlusion, then release of the contralateral common carotid artery (CCA) for 2.5 h.

Results:

Induction of ischemia resulted in a 30-fold increase in dopamine release in the lateral striatum. Compared to the nonischemic striatum, the ratio of the hydroxylation product 3,4-dihydroxybenzoate (34DHB) to 4HB (trapping agent) in the ipsilateral striatum increased significantly 30 min after ischemia induction. In contrast, during the 30 min of three vessel occlusion there was no increase in the ratio in the cortex. Following the release of the contralateral CCA, the ratio from the ischemic cortex increased significantly compared to sham-operated animals. However, under all circumstances, the 34DHB/4HB ratio was greater in the striatum than in the cortex.

Conclusion:

The increase in the 34DHB/4HB ratio in the lateral striatum coincides with the increased dopamine release suggesting a role for dopamine oxidation in the increased production of hydroxyl radicals. The significant increase in the ratio from the ischemic cortex compared to that from the sham-operated animals is consistent with increased oxidative stress induced by ischemia. However, the lower 34DHB/4HB ratio in the cortex whichdoes not receive dopaminergic innervation compared to the striatum suggests a different mechanism for hydroxyl radical production. Such an alternate mechanism may represent a more toxic oxidative insult that contributes to infarction.

Monoamine oxidase-induced hydroxyl radical production and cardiomyocyte injury during myocardial ischemia-reperfusion in rats

To elucidate the involvement of monoamine oxidase (MAO) in hydroxyl radical production and cardiomyocyte injury during ischemia as well as after reperfusion, we applied microdialysis technique to the heart of anesthetized rats. Dialysate samples were collected during 30 min of induced ischemia followed by 60 min of reperfusion. We monitored dialysate 3,4-dihydrobenzoic acid (3,4-DHBA) concentration as an index of hydroxyl radical production using a trapping agent (4-hydroxybenzoic acid), and dialysate myoglobin concentration as an index of cardiomyocyte injury in the ischemic region. The effect of local administration of a MAO inhibitor, pargyline, was investigated. Dialysate 3,4-DHBA concentration increased from 1.9 ± 0.5 nM at baseline to 3.5 ± 0.7 nM at 20-30 min of occlusion. After reperfusion, dialysate 3,4-DHBA concentration further increased reaching a maximum (4.5 ± 0.3 nM) at 20-30 min after reperfusion, and stabilized thereafter. Pargyline suppressed the averaged increase in dialysate 3,4-DHBA concentration by ∼72% during occlusion and by ∼67% during reperfusion. Dialysate myoglobin concentration increased from 235 ± 60 ng/ml at baseline to 1309 ± 298 ng/ml at 20-30 min after occlusion. After reperfusion, dialysate myoglobin concentration further increased reaching a peak (5833 ± 1017 ng/ml) at 10-20 min after reperfusion, and then declined. Pargyline reduced the averaged dialysate myoglobin concentration by ∼56% during occlusion and by ∼41% during reperfusion. MAO plays a significant role in hydroxyl radical production and cardiomyocyte injury during ischemia as well as after reperfusion.

A rapid and sensitive method for hydroxyl radical detection on a microfluidic chip using an N-doped porous carbon nanofiber modified pencil graphite electrode

Hydroxyl radicals (˙OH) play an important role in human diseases. Traditional detection methods are time consuming and require expensive instruments. Here, we present a simple and sensitive method for the detection of hydroxyl radicals on a microfluidic chip using an electrochemical technique. Aniline monomer is electrochemically polymerized on the surface of a pencil graphite electrode and carbonized at 800 °C. The resulting N-doped porous carbon nanofiber-modified pencil graphite electrode is embedded into a microfluidic chip directly as a working electrode. 4-Hydroxybenzoic acid (4-HBA) is selected as the trapping agent owing to its unique 3,4-DHBA product and high trapping efficiency. A low detection limit of 1.0 × 10(-6) M is achieved on the microfluidic chip. As a demonstration, the microfluidic chip is successfully utilized for the detection of ˙OH in cigarette smoke. The strong π-π stacking and hydrophobic interactions between the nitrogen-doped carbon materials and the pencil graphite make the modified electrode well-suited for the microfluidic chip.

Microdialysis sampling techniques applied to studies of the foreign body reaction

Implanted materials including drug delivery devices and chemical sensors undergo what is termed the foreign body reaction (FBR). Depending on the device and its intended application, the FBR can have differing consequences. An extensive scientific research effort has been devoted to elucidating the cellular and molecular mechanisms that drive the FBR. Important, yet relatively unexplored, research includes the localized tissue biochemistry and the chemical signaling events that occur throughout the FBR. This review provides an overview of the mechanisms of the FBR, describes how the FBR affects different implanted devices, and illustrates the role that microdialysis sampling can play in further elucidating the chemical communication processes that drive FBR outcomes.

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.

Calprotectin (S100A8/S100A9) and myeloperoxidase: co-regulators of formation of reactive oxygen species

Inflammatory mediators trigger polymorphonuclear neutrophils (PMN) to produce reactive oxygen species (ROS: O₂^-, H₂O₂, ∙OH). Mediated by myeloperoxidase in PMN, HOCl is formed, detectable in a chemiluminescence (CL) assay. We have shown that the abundant cytosolic PMN protein calprotectin (S100A8/A9) similarly elicits CL in response to H₂O₂ in a cell-free system. Myeloperoxidase and calprotectin worked synergistically. Calprotectin-induced CL increased, whereas myeloperoxidase-triggered CL decreased with pH > 7.5. Myeloperoxidase needed NaCl for CL, calprotectin did not. 4-hydroxybenzoic acid, binding ∙OH, almost abrogated calprotectin CL, but moderately increased myeloperoxidase activity. The combination of native calprotectin, or recombinant S100A8/A9 proteins, with NaOCl markedly enhanced CL. NaOCl may be the synergistic link between myeloperoxidase and calprotectin. Surprisingly- and unexplained- at higher concentration of S100A9 the stimulation vanished, suggesting a switch from pro-oxidant to anti-oxidant function. We propose that the ∙OH is predominant in ROS production by calprotectin, a function not described before.

Enhanced degradation of p-chlorophenol in a novel pulsed high voltage discharge reactor

The yields of active specie such as ozone, hydrogen peroxide and hydroxyl radical were all enhanced in a novel discharge reactor. In the reactor, the original formation rate of hydroxyl radical was 2.27 x 10(-7) mol L(-1)s(-1), which was about three times than that in the contrast reactor. Ozone was formed in gas-phase and was transferred into the liquid. The characteristic of mass transfer was better in the novel reactor than that in the contrast reactor, which caused much higher ozone concentration in liquid. The dissociation of hydrogen peroxide was more evident in the former, which promoted the formations of hydroxyl radical. The p-chlorophenol (4-CP) degradation was also enhanced. Most of the ozone transferred into the liquid and hydrogen peroxide generated by discharge could be utilized by the degradation process of 4-CP. About 97% 4-CP was removed in 36 min discharge in the novel reactor. Organic acids such as formic, acetic, oxalic, propanoic and maleic acid were generated and free chloride ions were released in the degradation process. With the formation of organic acid, the pH was decreased and the conductivity was increased.

Effects of polychlorinated biphenyls on the neutrophil NADPH oxidase system

Polychlorinated biphenyls (PCBs) are reported to induce the formation of reactive oxygen species (ROS) in human neutrophil granulocytes through the activation of the NADPH oxidase. The purpose of the present study is to elucidate the cellular mechanisms responsible for the activation of the NADPH oxidase after exposure to PCB. We have previously shown that PCB activates human neutrophil granulocytes through a calcium dependent activation of phospholipase D and/or phospholipase C, followed by the activation of protein kinase C. In the present study, pharmacological characterization of Aroclor (A) 1242-induced respiratory burst in human neutrophils was conducted by the use of enzymatic inhibitors. Pre-incubation with U0126, SB203580, SP600125, cyclosporin A and FK506 attenuated the A 1242-induced respiratory burst, measured by DCF-fluorescence, and luminol-amplified chemiluminescence. Our results show that the Erk1/2 kinases and p38MAPK/JNK are involved in ROS formation in neutrophils exposed to A 1242.

In vivo microdialysis in Parkinson's research

Parkinson's disease (PD) is a progressive neurodegenerative disorder that is primarily characterized by the degeneration of dopamine (DA) neurons in the nigrostriatal system, which in turn produces profound neurochemical changes within the basal ganglia, representing the neural substrate for parkinsonian motor symptoms. The pathogenesis of the disease is still not completely understood, but environmental and genetic factors are thought to play important roles. Research into the pathogenesis and the development of new therapeutic intervention strategies that will slow or stop the progression of the disease in human has rapidly advanced by the use of neurotoxins that specifically target DA neurons. Over the years, a broad variety of experimental models of the disease has been developed and applied in diverse animal species. The two most common toxin models used employ 6-hydroxydopamine (6-OHDA) and the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/1-methyl-4-phenilpyridinium ion (MPTP/MPP+), either given systemically or locally applied into the nigrostriatal pathway, to resemble PD features in animals. Both neurotoxins selectively and rapidly destroy catecolaminergic neurons, although with different mechanisms. Since in vivo microdialysis coupled to high-performance liquid chromatography is an established technique for studying physiological, pharmacological, and pathological changes of a wide range of low molecular weight substances in the brain extracellular fluid, here we review the most prominent animal and human data obtained by the use of this technique in PD research.

An electrohydraulic discharge system of salt-resistance for p-chlorophenol degradation

An electrohydraulic discharge system of salt-resistance has been developed and analyzed for p-chlorophenol (4-CP) degradation. The discharge electrodes used in the system was consisted of four steel acupuncture needles (Ø 0.25 mm) which were covered by capillaries through which gas was supplied to the discharge region, forming gas bubbles. In the comparing system, the aeration capillaries were encapsulated and the bubbling was cancelled. It was confirmed that introducing gas into the discharge zone could reduce the affection of salt content in the pulsed high-voltage electrohydraulic discharge system. In the non-bubbling system, the formation of active species and 4-CP degradation was sharply influenced by increasing salt content. The formation rate of hydroxyl radical and hydrogen peroxide was decreased almost to zero and the 4-CP was hardly removed as the NaCl concentration was higher than 5.0 x 10(-3) mol L(-1). But in the developed system, the formation rates were changed little with increasing the salt concentration. Increasing the NaCl concentration high to 0.1 mol L(-1), the hydroxyl radical formation rate was 4.43 x 10(-7) mol L(-1)s(-1), and the removal rate of 4-CP was still high, where more than 90% was removed in 18 min.

Left ventricular dysfunction after acute intracranial hypertension is associated with increased hydroxyl free radical production, cardiac ryanodine hyperphosphorylation, and troponin I degradation

BACKGROUND

In addition to generating free radicals, stress-induced activation of the sympathetic nervous system results in hyperphosphorylation of the cardiac ryanodine receptor (RyR2)/calcium (Ca2+) release channel on the sarcoplasmic reticulum, causing leaky channels. These events may contribute to cytosolic Ca2+ overload and activation of Ca2+-dependent cytotoxic processes. Because myocardial dysfunction associated with intracranial hypertension is catecholamine mediated, we sought to determine in a rat model if hemodynamic changes are associated with an increase in oxidative stress, hyperphosphorylation of RyR2, and degradation of myofilament protein cardiac troponin I (TnI).

METHODS

In halothane-anesthetized rats treated with saline, dimethyl sulfoxide (DMSO), or the synthetic calpain inhibitor calpeptin (3,500 microg), a subdural balloon catheter was inflated to induce intracranial hypertension. Hearts were excised, and RyR2 phosphorylation status and TnI degradation was determined with Western blot analysis. In separate experiments, treated rats were challenged with increasing doses of dobutamine 30 minutes after subdural balloon inflation.

RESULTS

Elevating the intracranial pressure resulted in an increase in plasma catecholamines, as well as in 3,4-dihydroxybenzoic acid (DHBA), an indirect marker of HO. radical production, and left ventricular dysfunction in rats treated with saline or DMSO. There was evidence of hyperphosphorylation of RyR2 and TnI degradation (27 kD immunoreactive band). Calpeptin treatment improved left ventricular function; however, this had no effect on the phosphorylation status of RyR2 or TnI degradation levels. In addition, the myocardial responsiveness to dobutamine was augmented in rats with depressed myocardial function.

CONCLUSION

The present findings demonstrate that hemodynamic instability after intracranial hypertension is associated with oxidative stress and post-translational changes to RyR2 and TnI degradation. Despite this, the myocardial responsiveness to beta1 adrenergic stimulation is preserved in rats with depressed myocardial function.

Aspirin protects striatal dopaminergic neurons from neurotoxin-induced degeneration: An in vivo microdialysis study

The effect of aspirin on dopaminergic neuronal damage induced by in vivo infusion of 1-methyl-4-phenylpiridinium iodide (MPP(+)) and 6-hydroxydopamine (6-OHDA) was studied in rats, using microdialysis. Rat striata were perfused with 1 mM MPP(+) or 6-OHDA for 10 min, causing peak levels of dopamine (DA) in the dialytic fluid, after 40 min. After 24 h, 1 mM MPP(+) was perfused again for 10 min and DA levels measured in the dialytic fluid, as an index of neuronal cell integrity. Pretreatment with Aspidol (lysine acetylsalicylate), 180 mg/kg i.p., 1 h before MPP(+) or 6-OHDA perfusion, did not modify DA extracellular output, on day 1, but restored MPP(+)-induced DA release on day 2, indicating a neuroprotective effect of Aspidol. Conversion of 0.5 mM 4-hydroxybenzoic acid (4-HBA) to 3,4-dihydroxybenzoic acid (3,4-DHBA) was measured as an index of reactive oxygen species (ROS). 6-OHDA, but not MPP(+), significantly enhanced 3,4-DHBA levels in the perfusion fluid. Aspidol (180 mg/kg, i.p.) reduced 6-OHDA-dependent increase of 3,4-DHBA levels. Meloxicam (50 mg/kg, i.p.), a specific cyclooxygenase-2 (COX-2) inhibitor, was ineffective against both neurotoxins. These data suggest that the protective effect of aspirin is due to different mechanisms of action according to the neurotoxin used, and it is independent from COX-2 inhibition.

L-tyrosine contributes to (+)-3,4-methylenedioxymethamphetamine-induced serotonin depletions

The specific mechanisms underlying (+)-3,4-methylenedioxymethamphetamine (MDMA)-induced damage to 5-HT terminals are unknown. Despite the hypothesized role for dopamine (DA) and DA-derived free radicals in mediating this damage, it remains unclear why MDMA produces long-term depletions of 5-HT in brain regions that are sparsely innervated by DA neurons. We hypothesized that the precursor to DA biosynthesis, tyrosine, mediates MDMA-induced 5-HT depletions. Extracellular tyrosine concentrations increased fivefold in striatum and 2.5-fold in hippocampus during the administration of neurotoxic doses of MDMA. In vitro results show that L-tyrosine can be hydroxylated nonenzymatically to the DA precursor l-3,4-dihydroxyphenylalanine (DOPA) under pro-oxidant conditions. The local infusion of L-tyrosine into the striatum or hippocampus during MDMA administration potentiated the acute increase in extracellular DA and the long-term depletion of 5-HT after MDMA. Coinfusion of the aromatic amino acid decarboxylase (AADC) inhibitor m-hydroxybenzylhydrazine attenuated these effects in hippocampus and decreased basal extracellular DA in the striatum. In contrast, the reverse dialysis of the tyrosine hydroxylase inhibitor alpha-methyl-p-tyrosine into the hippocampus did not affect MDMA-induced increases in extracellular DA or the long-term depletion in 5-HT. These results show that MDMA increases the concentration of tyrosine in the brain to cause a long-term depletion of 5-HT via the nonenzymatic, tyrosine hydroxylase-independent, hydroxylation of tyrosine to DOPA and subsequently to DA via AADC. Overall, the findings suggest that MDMA depletes 5-HT by increasing tyrosine and its eventual conversion to DA within 5-HT terminals.

The salicylate trapping method: is oxidation of salicylic acid solution oxygen and time dependent and metal catalysed?

For a microdialytic trapping method we systematically investigated changes in concentrations of 2,5-dihydroxy-benzoic acid (2,5-DHBA) and 2,3-dihydroxy-benzoic acid (2,3-DHBA) in freshly prepared solutions of salicylic acid (SA). The solvent was 0.9% saline exposed to different atmospheric concentrations of oxygen (0, 21, and 100%). The solutions were treated by freezing-thawing and an ultrasonic bath in presence and absence of aluminium foil. Without aluminium the concentrations of 2,5-DHBA and 2,3-DHBA kept constant over an observed period of 160 min on different levels from below 20 ng/ml to about 100 ng/ml. In presence of aluminium the concentrations increased to maximum 307 ng/ml after 160 min. Ultrasonic irradiation amplified this effect to maximum 341 ng/ml. HPLC/ECD processing and quantitative analysis of dihydroxy-benzoic acids (DHBAs) in microdialysis may be artificially influenced by varying oxygen environment and metal catalysis.

Translational neurochemical research in acute human brain injury: the current status and potential future for cerebral microdialysis

Microdialysis (MD) was introduced as an intracerebral sampling method for clinical neurosurgery by Hillered et al. and Meyerson et al. in 1990. Since then MD has been embraced as a research tool to measure the neurochemistry of acute human brain injury and epilepsy. In general investigators have focused their attention to relative chemical changes during neurointensive care, operative procedures, and epileptic seizure activity. This initial excitement surrounding this technology has subsided over the years due to concerns about the amount of tissue sampled and the complicated issues related to quantification. The interpretation of mild to moderate MD fluctuations in general remains an issue relating to dynamic changes of the architecture and size of the interstitial space, blood-brain barrier (BBB) function, and analytical imprecision, calling for additional validation studies and new methods to control for in vivo recovery variations. Consequently, the use of this methodology to influence clinical decisions regarding the care of patients has been restricted to a few institutions. Clinical studies have provided ample evidence that intracerebral MD monitoring is useful for the detection of overt adverse neurochemical conditions involving hypoxia/ischemia and seizure activity in subarachnoid hemorrhage (SAH), traumatic brain injury (TBI), thromboembolic stroke, and epilepsy. There is some data strongly suggesting that MD changes precede the onset of secondary neurological deterioration following SAH, hemispheric stroke, and surges of increased ICP in fulminant hepatic failure. These promising investigations have relied on MD-markers for disturbed glucose metabolism (glucose, lactate, and pyruvate) and amino acids. Others have focused on trying to capture other important neurochemical events, such as excitotoxicity, cell membrane degradation, reactive oxygen species (ROS) and nitric oxide (NO) formation, cellular edema, and BBB dysfunction. However, these other applications need additional validation. Although these cerebral events and their corresponding changes in neurochemistry are important, other promising MD applications, as yet less explored, comprise local neurochemical provocations, drug penetration to the human brain, MD as a tool in clinical drug trials, and for studying the proteomics of acute human brain injury. Nevertheless, MD has provided new important insights into the neurochemistry of acute human brain injury. It remains one of very few methods for neurochemical measurements in the interstitial compartment of the human brain and will continue to be a valuable translational research tool for the future. Therefore, this technology has the potential of becoming an established part of multimodality neuro-ICU monitoring, contributing unique information about the acute brain injury process. However, in order to reach this stage, several issues related to quantification and bedside presentation of MD data, implantation strategies, and quality assurance need to be resolved. The future success of MD as a diagnostic tool in clinical neurosurgery depends heavily on the choice of biomarkers, their sensitivity, specificity, and predictive value for secondary neurochemical events, and the availability of practical bedside methods for chemical analysis of the individual markers. The purpose of this review was to summarize the results of clinical studies using cerebral MD in neurosurgical patients and to discuss the current status of MD as a potential method for use in clinical decision-making. The approach was to focus on adverse neurochemical conditions in the injured human brain and the MD biomarkers used to study those events. Methodological issues that appeared critical for the future success of MD as a routine intracerebral sampling method were addressed.

Evaluation of the probes 2',7'-dichlorofluorescin diacetate, luminol, and lucigenin as indicators of reactive species formation

This study attempts to provide a critical assessment of three different common approaches to identifying teactive species formed in biological systems: the 2',7'-dichlorofluorescin diacetate (DCFH-DA) assay, and the luminol- and lucigenin-amplified chemiluminescence assays. There have been several contradictory reports about the specificity of these methods. Our results show that DCFH is oxidized to the fluorescent compound 2',7'-dichlorofluorescin (DCF) in human neutrophils exposed to the following compounds: Aroclor (A)1242, hydrogen peroxide (H(2)O(2)), nitric oxide (NO), and FeSO(4). Use of a cell-free DCFH system showed increased formation of DCF by peroxynitrite (ONOO(-)), horseradish peroxidase (HRP) alone, and HRP in combination with H(2)O(2), FeSO(4) alone, and a mixture of FeSO(4) and H(2)O(2). The hydroxyl radical (z.rad;OH) scavenger formate and the iron ion chelator deferoxamine reduced the DCF formation induced by FeSO(4) in combination with H(2)O(2). DCFH was insensitive to NO and H(2)O(2) in the cell-free system. In the presence of neutrophils, the A1242-induced luminol chemiluminescence was decreased by the superoxide dismutase inhibitor diethyldithiocarbamic acid (DDC) and the myeloperoxidase inhibitor salicylhydroxamic acid (SHA). Exposure of the neutrophils to NO, FeSO(4), or H(2)O(2) alone did not have any effect. A1242-induced lucigenin chemiluminescence in the neutrophils was increased slightly by DDC, but was not affected by SHA, NO, FeSO(4), or H(2)O(2). In conclusion, we suggest that the DCF assay is only suitable for measurements of ONOO(-), H(2)O(2) in combination with cellular peroxidases, and z.rad;OH. Luminol is sensitive towards HOCl, while lucigenin is oxidized by O(2)z.rad;(-).

Hydroxyl radical formation is greater in striatal core than in penumbra in a rat model of ischemic stroke

Although hydroxyl radical ((*)OH) formation has been implicated in the pathophysiological changes of ischemic stroke, (*)OH production in the core and penumbra regions is not clear. It is extremely important to distinguish penumbra from ischemic core in focal cerebral ischemia studies, because the penumbra contains viable tissue, which can be salvaged by appropriate treatment. This study evaluated (*)OH production in both core and penumbra regions of ischemic striatum during ischemia and reperfusion. Microdialysis probes were placed in striatal tissue of rats subjected to the middle cerebral artery occlusion model of ischemic stroke. The (*)OH-trapping agent 4-hydroxybenzoic acid (4-HBA) was administered by both i.v. and probe infusion. Dialysate levels of the 4-HBA oxidation products, 3,4-dihydroxybenzoic acid (3,4-DHBA), were determined by HPLC-ECD. After microdialysis probe delivery of 4-HBA, (*)OH production was significantly increased in the striatal core during both ischemia and reperfusion. Penumbra (*)OH production increased only during reperfusion. Alterations of 3,4-DHBA concentration in dialysate following i.v. 4-HBA administration were likely related to alterations in tissue blood flow. The findings were confirmed by a greater oxidation of dihydroethidium in the ischemic core than in the penumbra as determined by fluorescent microscopy. The findings of (*)OH production in ischemic striatum are the opposite of those reported for ischemic cortex and suggest critical regional variations in (*)OH production that may have significant clinical implications in the treatment of ischemic stroke.

Hydroxyl radical in living systems and its separation methods

It has recently been shown that hydroxyl radicals are generated under physiological and pathological conditions and that they seem to be closely linked to various models of pathology putatively implying oxidative stress. It is now recognized that the hydroxyl radical is well-regulated to help maintain homeostasis on the cellular level in normal, healthy tissues. Conversely, it is also known that virtually every disease state involves free radicals, particularly the most reactive hydroxyl radical. However, when hydroxyl radicals are generated in excess or the cellular antioxidant defense is deficient, they can stimulate free radical chain reactions by interacting with proteins, lipids, and nucleic acids causing cellular damage and even diseases. Therefore, a confident analytical approach is needed to ascertain the importance of hydroxyl radicals in biological systems. In this paper, we provide information on hydroxyl radical trapping and detection methods, including liquid chromatography with electrochemical detection and mass spectrometry, gas chromatography with mass spectrometry, capillary electrophoresis, electron spin resonance and chemiluminescence. In addition, the relationships between diseases and the hydroxyl radical in living systems, as well as novel separation methods for the hydroxyl radical are discussed in this paper.

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.

Monitoring of reactive oxygen species production after traumatic brain injury in rats with microdialysis and the 4-hydroxybenzoic acid trapping method

The detection of reactive oxygen species (ROS) after traumatic brain injury (TBI) is based on indirect methods due to the high reactivity and short half-life of ROS in biological tissue. The commonly used salicylate trapping method has several disadvantages making it unsuitable for human use. We have evaluated 4-hydroxybenzoic acid (4-HBA) together with microdialysis (MD) in the rat as an alternative method. 4-HBA forms one stable adduct, 3,4-dihydroxybenzoic acid (3,4-DHBA), when reacting with ROS and has not previously been used together with MD after TBI. Twenty-seven rats were used for the assessment of 3,4-DHBA production as an indicator of ROS formation in a controlled contusion injury model using intracerebral MD with 3 mM 4-HBA in the perfusate. For comparison, salicylate trapping was used in eight rats. TBI caused a 250% increase of 3,4-DHBA that peaked at 30 min after injury in severely injured rats and remained significantly elevated as compared to baseline for 90 min after trauma. The mild injury level caused a 100% increase in 3,4-DHBA formation at 30 min after the injury. When the MD probe was placed in the perimeter of the injury site, no significant increase in ROS formation occurred. Salicylate trapping showed a similar increase in adduct formation after severe injury. In addition, high cortical concentrations of 4-HBA and salicylate were found. It is concluded that microdialysis with 4-HBA as a trapping agent appears to be a useful method for ROS detection in the rat with a potential clinical utility.

Effects of the nitrone radical scavengers PBN and S-PBN on in vivo trapping of reactive oxygen species after traumatic brain injury in rats

In previous studies, the authors showed that the nitrone radical scavenger alpha-phenyl-N- tert -butyl nitrone (PBN) and its sulfo-derivative, 2-sulfo-phenyl-N- tert -butyl nitrone (S-PBN), attenuated cognitive disturbance and reduced tissue damage after traumatic brain injury (TBI) in rats. In the current study, the production of reactive oxygen species (ROS) after TBI was monitored with microdialysis and the 4-hydroxybenzoic acid (4-HBA) trapping method. A single dose of PBN (30 mg/kg) or an equimolar dose of S-PBN (47 mg/kg) was administered intravenously 30 minutes before a controlled cortical contusion injury in rats. Plasma and brain tissue drug concentrations were analyzed at the end of the microdialysis experiment (3 hours after injury) and, in a separate experiment with S-PBN, at 30 and 60 minutes after injury. Traumatic brain injury caused a significant increase in ROS formation that lasted for 60 minutes after the injury as evidenced by increased 3,4-dihydroxybenzoic acid (3,4-DHBA) concentrations in the dialysate. PBN and S-PBN equally and significantly attenuated the posttraumatic increase in 3,4-DHBA formation. High PBN concentrations were found bilaterally in brain tissue up to 3 hours after injury. In contrast, S-PBN was rapidly cleared from the circulation and was not detectable in brain at 30 minutes after injury or at any later time point. The results suggest that scavenging of ROS after TBI may contribute to the neuroprotective properties observed with nitrone spin-trapping agents. S-PBN, which remained undetectable even in traumatized brain tissue, reduced ROS production to the same extent as PBN that readily crossed the blood-brain barrier. This finding supports an important role for ROS production at the blood-endothelial interface in TBI.

Erectile dysfunction occurs following substantia nigra lesions in the rat

Erectile function was assessed 6 weeks following uni- and bilateral injections of 6-hydroxydopamine in the substantia nigra nucleus of the brain. Behavioral apomorphine-induced penile erections were reduced (5/8) and increased (3/8) in uni- and bilateral lesioned animals. Intracavernous pressures, following electrical stimulation of the cavernous nerve, decreased in lesioned animals. Lesions of the substantia nigra were confirmed by histology. Concentration of dopamine and its metabolites were decreased in the striatum of substantia nigra lesioned rats. Lesions of the substantia nigra are therefore associated with erectile dysfunction in rats and may serve as a model to study erectile dysfunction in Parkinson's disease.

Importance of soluble metals and reactive oxygen species for cytokine release induced by mineral particles

The mechanisms for particle-induced health effects are not well understood, but inflammation seems to be of importance. Previously, we have shown that stone quarry particles with various mineral and metal content differed widely in potency to induce inflammatory cytokines (IL-6, IL-8 and TNF-alpha) in different types of lung cells. In this study we investigated if the observed cytokine responses were associated with the soluble or insoluble components of the stone particles and if there was a relationship between the differential cytokine release and generation of reactive oxygen species (ROS). Exposure of the human alveolar cell line A549 to the different particle leachates (pH 7.4 and 4.0) did not induce corresponding differential increases in the IL-8 release as observed with whole particles. Increase in ROS production, measured as dichlorofluorescein-fluorescence, was only demonstrated after exposure of A549 cells to the pH 4.0 extract from basalt. Furthermore, generation of ROS was found in neutrophils but not in A549 cells and primary macrophages after exposure to suspensions of the solid particles. However, no obvious differences in potency among the different particles were demonstrated. In summary, other mechanisms than particle-induced ROS formation seem to be responsible for the differential induction of IL-8. Furthermore, our findings indicate that the differential ability to induce IL-8 release in lung cells is attributed to the solid components of the stone particles.

Experimental and theoretical microdialysis studies of in situ metabolism

Microdialysis sampling was performed to monitor localized metabolism in vivo and in vitro. A mathematical model that accounts for analyte mass transport during microdialysis sampling was used to predict metabolite concentrations in the microdialysis probe during localized metabolism experiments. The model predicts that metabolite concentrations obtained in the microdialysis probe are a function of different experimental parameters including membrane length, perfusion fluid flow rate, and sample diffusive and kinetic properties. Different microdialysis experimental parameters including membrane length and perfusion fluid flow rate were varied to affect substrate extraction efficiency (E(d)), or loss to the sample matrix, in vivo and in vitro. Local hepatic metabolism was studied in vivo in male Sprague-Dawley rats by infusing acetaminophen through the microdialysis probe. Acetaminophen sulfate concentrations increased linearly with respect to acetaminophen E(d) in contrast to modeling predictions. Xanthine oxidase was used as an in vitro model of localized metabolism. In vitro experimental results partially matched modeling predictions for 10-mm probes. These results suggest that monitoring local metabolism using microdialysis sampling is feasible. It is important to consider system parameters such as dialysis flow rate, membrane length, and sample properties because these factors will affect analyte concentrations obtained during local metabolism experiments.

Determination of salicylate hydroxylation products as an in vivo oxidative stress marker

The in vivo measurement of highly reactive free radicals, such as the z.rad OH radical, is very difficult. New specific markers, which are based on the ability of z.rad OH to attack the benzene rings of aromatic molecules, are currently under investigation. The produced hydroxylated compounds can be measured directly. In vivo, radical metabolism of salicylic acid produces two main hydroxylated derivatives (2,3- and 2,5-dihydroxybenzoic acids). The latter acid can be also produced by enzymatic pathways through the cytochrome P-450 system, while the former acid is reported to be solely formed by direct hydroxyl radical attack. Therefore, measurement of 2, 3-DHBA, following oral administration of the drug acetyl salicylate, could be proposed for assessment of oxidative stress in vivo. In this paper, a sensitive method for the identification and quantification of hydroxylation products from the reaction of z. rad OH with salicylate in vivo is presented. It employs a high performance liquid chromatography and electrochemical detection system. A detection limit of < 1 pmol for the hydroxylation products has been achieved with linear response over at least five orders of magnitude. Using this technique, we measured plasma levels of 2,3- and 2,5-DHBA dihydroxylated derivatives and salicylic acid and determined the ratios following administration of 1 g acetyl salicylate in 20 healthy subjects.

The effects of aliphatic (n-nonane), naphtenic (1,2, 4-trimethylcyclohexane), and aromatic (1,2,4-trimethylbenzene) hydrocarbons on respiratory burst in human neutrophil granulocytes

This study investigates the effects of aliphatic (n-heptane, n-nonane), naphtenic (methylcyclohexane, 1,2,4-trimethylcyclohexane (TMCH)), and aromatic (methylbenzene, 1,2,4-trimethylbenzene (TMB)) hydrocarbons on respiratory burst in human granulocytes. The free radical formation was measured as 2,7-dichlorofluorescein diacetate-amplified (DCF) fluorescence, by electron paramagnetic resonance (EPR) spectroscopy and by hydroxylation of 4-hydroxybenzoate. The chemotactic peptide N-formyl-met-leu-phe (fMLP) and phorbol 12-myristate 13-acetate (PMA), a diacylglycerol analogue, were included as positive controls. DCF fluorescence was elevated in a concentration-dependent manner by C9 hydrocarbons. The C7 hydrocarbons did not stimulate respiratory burst in the concentration range examined. The naphtenic hydrocarbon TMCH showed the strongest effect on respiratory burst and was therefore selected for mechanistic studies of this free radical formation. In the absence of extracellular Ca(2+), fluorescence in response to TMCH and fMLP was reduced by 77 and 90%, respectively. Preincubation of the granulocytes with the protein kinase C inhibitor bisindolylmaleimide reduced the DCF fluorescence stimulated with TMCH, fMLP, and PMA by 82, 56, and 90%, respectively. The phospholipase C inhibitor U73122 lowered the TMCH- and fMLP-activated DCF fluorescence by 87 and 76%. In addition, the TMCH- and fMLP-induced DCF fluorescence, after the preincubation with the phospholipase D modulator n-butanol, was lowered by 83 and 52%, respectively. The importance of protein kinase C, phospholipase C, and phospholipase D for elevation of respiratory burst was also demonstrated by the EPR experiments using the spin trap 5-diethoxyphosphoryl-5-methyl-1-pyrroline-N-oxide (DEPMPO). Preincubation with the NADPH oxidase inhibitor diphenyleneiodonium and diethyldithiocarbamate, which inhibits superoxide dismutase, led to an almost complete reduction of DCF fluorescence in response to TMCH, fMLP, and PMA. Preincubation with diethyldithiocarbamate led to the elevation of superoxide adducts of DEPMPO. The hydrocarbons stimulated formation of mainly the superoxide (O(*-)(2)) adduct of DEPMPO (DEPMPO-OOH) but also small amounts of the hydroxyl adduct ((*)OH) (DEPMPO-OH). Using 4-hydroxybenzoate as a hydroxyl radical trap confirmed formation of (*)OH after stimulation with the hydrocarbons. In conclusion, our findings indicate that TMCH-activated respiratory burst is dependent on the Ca(2+)-dependent phospholipase C, phospholipase D, and protein kinase C prior to activation of the NADPH oxidase.

The effect of alpha-phenyl-tert-butyl nitrone (PBN) on free radical formation in transient focal ischaemia measured by microdialysis and 3,4-dihydroxybenzoate formation

alpha-phenyl-tert-butyl nitrone (PBN) reduces infarct size, improves recovery of brain energy metabolism and delays the secondary increase in extracellular potassium after focal ischaemia, presumably by trapping OH radicals. We investigated the effect of PBN on the formation of 3,4-dihydroxybenzoic acid (3,4-DHBA) as a measure of OH radical formation, during and following middle cerebral artery occlusion (MCAO). Rats, subjected to 2 h of ischaemia followed by 3 h of recirculation, were injected with either vehicle or PBN (100 mg kg-1 i.p.) prior to MCAO or immediately after recirculation, respectively. The in vivo microdialysis technique was used to collect samples for analysis of 3,4-DHBA by HPLC. The basal levels of 3,4-DHBA were 56-77 nmol L-1 in the four groups. During ischaemia, the formation of 3,4-DHBA decreased by about 50% in all groups. Upon recirculation, a 3-fold rise in 3,4-DHBA formation was seen. At 2 h of recirculation the mean value of 3,4-DHBA in the pretreated, vehicle-injected animals was 125 +/- 18 nmol L-1 and in the PBN-injected 145 +/- 48 nmol L-1, respectively. When the animals were treated after MCAO either with vehicle or PBN the values at 2 h recirculation were 155 +/- 148 and 189 +/- 145 nmol L-1, respectively. No statistically significant difference between vehicle- and PBN-injected groups was seen. We conclude that during reperfusion following MCAO, hydroxyl radical formation increases. The increase is not ameliorated by PBN which suggests that PBN does not protect the brain by a general scavenging of OH radicals, although tissue specific actions cannot be excluded.

Involvement of the serotonin transporter in the formation of hydroxyl radicals induced by 3,4-methylenedioxymethamphetamine

The mechanism of 3,4-methylenedioxymethamphetamine (MDMA)-induced depletion of brain serotonin (5-hydroxytryptamine, 5-HT) has been proposed to involve the generation of reactive oxygen species. In the present study, quantification of the extracellular concentration of 2,3-dihydroxybenzoic acid (2,3-DHBA) from salicylic acid was used as an index of hydroxyl radical generation. Although both MDMA and D-amphetamine markedly increased the extracellular concentration of dopamine in the striatum, only MDMA increased the extracellular concentration of 2,3-DHBA. Treatment with fluoxetine either 1 h prior to or 4 h following the administration of MDMA reduced the MDMA-induced formation of 2,3-DHBA and also attenuated the MDMA-induced depletion of 5-HT in the striatum. These results are supportive of the view that the MDMA-induced generation of hydroxyl radicals and, ultimately, the long-term depletion of 5-HT, is dependent, in part, on the activation of the 5-HT transporter.

Implementation of the microdialysis method in the hamster dorsal skinfold chamber

The aim of this study was to implement the microdialysis method, a well-established technique for measuring the local concentration of neurotransmitters and metabolites in the brain, in the dorsal skinfold chamber of the awake hamster. First, the effects of implanted, nonperfused microdialysis probes on the microcirculation were examined. Skinfold chambers were prepared with and without probes. Two and 3 days later, the following parameters were assessed: diameter, red blood cell (RBC) velocity, macromolecular leakage, leukocyte rolling fraction, and adherent leukocytes in venules, diameter and macromolecular leakage in arterioles, and functional capillary density (FCD). No significant differences between the animals of the two groups were observed in any of the parameters on either day. Second, the interstitial lactate concentration was measured at two perfusion rates in groups with and without a 4-h tourniquet ischemia. The induction of ischemia resulted in a significant increase in lactate concentration over the control values in the tissue within 1 h to 8000 +/- 860 microM, where it remained until the reperfusion, at which point the concentration returned to control values within 1 h. The microdialysis method provides the opportunity to measure the concentration of metabolites in the extravascular space of the hamster dorsal skinfold chamber.

Local striatal infusion of MPP+ does not result in increased hydroxylation after systemic administration of 4-hydroxybenzoate

In vivo bilateral microdialysis in the rat striatum was used to investigate hydroxyl radical formation under basal conditions and after intrastriatal administration of the neurotoxin, 1-methyl-4-phenylpyridinium (MPP+). After a short equilibration period, 4-hydroxybenzoate (4HBZ), which scavenges hydroxyl radicals to produce 3,4-dihydroxybenzoate (34DHB), was injected intraperitoneally 15 min before infusion of MPP+. To evaluate the enzymatic contribution to hydroxyl radical formation, two other series of microdialyses were performed following administration of monoamine oxidase B inhibitors, either 1-deprenyl (selegiline) or MDL 72,974A [(E)-2-(4-fluorophenethyl)-3-fluoroallylamine hydrochloride]. Microdialysate samples were analyzed by high-performance liquid chromatography for catecholamines, 3,4-dihydroxyphenylacetate (DOPAC), homovanillate (HVA), along with the hydroxyl radical adduct, 34DHB and its precursor, 4HBZ. MPP+ administration resulted in a massive release of dopamine along with a decrease in DOPAC and HVA in all three groups. A striking effect in all three groups was noted in which MPP+ resulted in a decrease in interstitial 4HBZ to < 50% of the non-MPP+ -treated side. In absolute terms, the amount of 34DHB produced was low but similar in all three groups, even after unilateral MPP+ infusion. When 34DHB was normalized to 4HBZ release to account for differences in precursor availability, there were no significant differences in the 34DHB/4HBZ ratios either with or without MAO inhibitor treatment or after local MPP+ infusion. Systemic 4HBZ administration appears to result predominantly in intra-cellular sampling of hydroxyl radicals which produces different results from local infusion of trapping agents such as salicylate.

Striatal metabolism of hexanal, a lipid peroxidation product, in the rat

Free radical induced lipid peroxidation may play a role in neurodegeneration and peroxidation leads to the formation of hexanal from omega-6 fatty acids. We have previously demonstrated in vitro that pyruvate dehydrogenase (PDH) catalyzes the condensation of saturated aldehydes with pyruvate to form acyloins. We have further shown in perfused rat heart that hexanal, presumably via PDH, is converted to 3-hydroxyoctan-2-one and that it in turn can be reduced to 2,3-octanediol. We now extend this work using intra-striatal microdialysis to show that this reaction also occurs in rat brain. The reduction of hexanal to hexanol was also evaluated. Microdialysis probes were implanted bilaterally in the striatum and were infused with hexanal with and in the absence of added pyruvate. Analysis of microdialysis samples showed a release of 3-hydroxyoctan-2-one (9.5-10.5 pmol/min), 2,3-octanediol (2.2-2.7 pmol/min) and hexanol (64-74 pmol/min). Pyruvate addition did not increase 3-hydroxyoctan-2-one or 2,3-octanediol production. In a second series of experiments where no exogenous hexanal was infused, endogenous production of 3-hydroxyoctan-2-one (1.0-1.3 pmol/min) and 2,3-octanediol (1.0-1.2 pmol/min) was still observed, although no hexanol was detected. We also investigated the possibility that oxidative stress induced by 1-methyl-4-phenylpyridinium (MPP+) would increase lipid peroxidation resulting in increased production of 3-hydroxyoctan-2-one. Analysis of samples collected following MPP+ infusion indicated no additional increase suggesting that brief exposure to MPP+ does not increase hexanal formation over baseline levels during the experimental period.

Oxidative stress is attenuated in mice overexpressing BCL-2

The protooncogene Bcl-2 inhibits apoptosis in neural cells, which may involve mitochondrial stabilization and decreased generation of reactive oxygen species. Using in vivo microdialysis we found that following administration of the mitochondrial toxin 3-nitropropionic acid (3-NP) there was a significant increase in the conversion of 4-hydroxybenzoic acid (4-HBA) to 3,4-dihydroxybenzoic acid (3,4-DHBA) in control mice, but not in Bcl-2 overexpressing mice. Striatal lesions were observed in littermate control mice, whereas, lesions were minimal or absent in Bcl-2 overexpressing mice. This shows that Bcl-2 overexpression in vivo attenuates the generation of reactive oxygen species.

Reduction of hydroxyl radical generation in a rat hindlimb model of ischemia-reperfusion injury using crosslinked hemoglobin-superoxide dismutase-catalase

The effects of PolyHb (intermolecularly crosslinked hemoglobin) and PolyHb-SOD-CAT (intermolecularly crosslinked hemoglobin, superoxide dismutase and catalase) on the production of hydroxyl radical was studied using a rat hindlimb model of ischemia-reperfusion. Hydroxyl radical generation was assessed by an indirect assay based on the hydroxylation of 4-hydroxybenzoate. The hydroxylation product, 3,4 dihydroxybenzoate (3,4 DHBA), was analyzed by high performance liquid chromatography and electrochemical detection. The identification of 3,4 DHBA was confirmed by analysis of authentic standard and an in vitro hydroxyl radical generation system. Ischemia was induced in both hindlimbs by ligation of the infrarenal aorta. After a 4hr ischemic period, hindlimbs were simultaneously perfused with PolyHb-SOD-CAT (5 g/dl) into one limb and PolyHb (5 g/dl) into the other limb via femoral arterial catheters. Each perfusate also contained the hydroxyl radical trap, 4-hydroxbenzoate (5 mM). Femoral venous effluents were analyzed for the presence of the 3,4 DHBA. Data indicates that greater 3,4 DHBA production occurs during PolyHb perfusion as compared to PolyHb-SOD-CAT. These preliminary results show that perfusion with PolyHb-SOD-CAT may alleviate oxidative stress in a model of ischemia-reperfusion.