HPLC procedure for the pharmacokinetic study of the spin-trapping agent, alpha-phenyl-N-tert-butyl nitrone (PBN)

α-Phenyl-N-tert-Butylnitrone and Analogous α-Aryl-N-alkylnitrones as Neuroprotective Antioxidant Agents for Stroke

The recent advances in research on the use of the antioxidant and neuroprotective agent α-phenyl-N-tert-butylnitrone (PBN) for the therapy of stroke have been reviewed. The protective effect of PBN in the transient occlusion of the middle cerebral artery (MCAO) has been demonstrated, although there have been significant differences in the neuronal salvaging effect between PBN-treated and untreated animals, each set of data having quite large inter-experimental variation. In the transient forebrain ischemia model of gerbil, PBN reduces the mortality after ischemia and the neuronal damage in the hippocampal cornu ammonis 1 (CA1) area of the hippocumpus caused by ischemia. However, PBN fails to prevent postischemic CA1 damage in the rat. As for focal cerebral ischemia, PBN significantly reduces cerebral infarction and decreases neurological deficit after ischemia using a rat model of persistent MCAO in rats. Similarly, the antioxidant and neuroprotective capacity of a number of PBN-derived nitrones prepared in the author's laboratory have also been summarized here, showing their high potential therapeutic power to treat stroke.

Emerging role of phenolic compounds as natural food additives in fish and fish products

Chemical and microbiological deteriorations are principal causes of quality loss of fish and fish products during handling, processing, and storage. Development of rancid odor and unpleasant flavor, changes of color and texture as well as lowering nutritional value in fish can be prevented by appropriate use of additives. Due to the potential health hazards of synthetic additives, natural products, especially antioxidants and antimicrobial agents, have been intensively examined as safe alternatives to synthetic compounds. Polyphenols (PP) are the natural antioxidants prevalent in fruits, vegetables, beverages (tea, wine, juices), plants, seaweeds, and some herbs and show antioxidative and antimicrobial activities in different fish and fish products. The use of phenolic compounds also appears to be a good alternative for sulphiting agent for retarding melanosis in crustaceans. Phenolic compounds have also been successfully employed as the processing aid for texture modification of fish mince and surimi. Thus, plant polyphenolic compounds can serve as potential additives for preventing quality deterioration or to retain the quality of fish and fish products.

Toxicokinetics of naringin and its metabolite naringenin after 180-day repeated oral administration in beagle dogs assayed by a rapid resolution liquid chromatography/tandem mass spectrometric method

Toxicokinetic characteristics of naringin and its metabolite naringenin were investigated in beagle dogs after oral administration of naringin at the doses of 20, 100, or 500 mg/kg/day in a repeated-dose study for 1, 30, 90, and 180 days. Plasma concentrations of naringin and naringenin were determined by a rapid resolution liquid chromatography/electrospray ionization/tandem mass spectrometric method. The results showed that no differences in systemic exposure were observed between male and female beagle dogs. Systematic exposure exhibited dose-dependent increase for both naringin and naringenin. No significant accumulations were observed. Results would be taken into consideration for the interpretation of toxicology findings and provide a reference for clinical safety assessment.

Hesperidin, a flavanone glycoside, on lipid peroxidation and antioxidant status in experimental myocardial ischemic rats

Myocardial infarction continues to be a leading cause of mortality world-wide. Novel therapies are needed to treat the myocardial ischemia. This study was undertaken to evaluate the cardioprotective role of hesperidin on isoproterenol-induced myocardial ischemia in rats. Myocardial ischemia was induced by subcutaneous injection of isoproterenol hydrochloride (85 mg/kg body weight), for two consecutive days. Isoproterenol-administered rats showed elevated levels of cardiac markers (aspartate transaminase, alanine transaminase, lactate dehydrogenase, creatine kinase, creatine kinase-MB, cardiac troponins T and I) when compared with control and hesperidin treatment groups (100, 200 and 400 mg/kg body weight). The serum levels of cardiac markers were significantly reduced at the doses of 200 mg and 400 mg. All further experiments were carried out at the 200 mg dose. Lipid peroxidation markers (thiobarbituric acid reactive substances, lipid hydroperoxides and conjugated dienes) were elevated significantly in the plasma and heart whereas non-enzymic antioxidants (vitamin C, vitamin E and reduced glutathione) were decreased significantly. Activities of superoxide dismutase, catalase, glutathione peroxidase, glutathione-S-transferase and glutathione reductase declined significantly in the heart of ischemic rats. However, after hesperidin treatment, all the above parameters reverted to normal levels. This study demonstrated that the cardioprotective effect of hesperidin on ischemic rats could be due to its anti-lipid peroxidative and antioxidant properties.

Modulation of ethoxyquin genotoxicity by free radical scavengers and DNA damage repair in human lymphocytes

N-tert-butyl-alpha-phenylnitrone (PBN) and its new derivative N-(Pyridine-4-ylmethylidene)-2-carboxy-tert-butylamine N-oxide (PBNC) were synthesized and used to modulate ethoxyquin (1,2-dihydro-6-ethoxy-2,2,4-trimethylquinoline, EQ) genotoxicity. Ethoxyquin, an antioxidant used mainly as a preservative in animal feeds, was shown to cause DNA breaks in human lymphocytes. The aim of the study was to evaluate the involvement of free radicals in the genotoxicity of EQ and its modulation by cellular repair systems. Human lymphocytes treated with EQ (10-50 microM) and nitrone free radical scavengers (100 microM) were tested with the comet assay. It was shown that both PBN and PBNC reduced the level of EQ-induced DNA damage, but PBN was slightly more effective. The modulation of the level of DNA damage was also observed as a result of DNA repair by cellular repair systems. Moreover, induction of oxidized bases by ethoxyquin was showed; lymphocytes exposed to ethoxyquin and treated with endonuclease III (Endo III) and formamidopyrimidine-DNA glycosylase (FpG), enzymes recognizing oxidized bases, displayed greater extent of DNA damage than those not treated with the enzymes.

Increased Susceptibility to Phenytoin Teratogenicity: Excessive Generation of Reactive Oxygen Species or Impaired Antioxidant Defense?

Phenytoin is a human and animal teratogen. Accumulating evidence suggests that the teratogenicity is associated with a potential of phenytoin to cause embryonic cardiac arrhythmia and resultant generation of toxic reactive oxygen species via hypoxia-reoxygenation mechanisms. The A/J mouse is more susceptible to phenytoin teratogenicity than other mouse strains. The aim of this study was to investigate whether A/J mice have other antioxidant enzyme activities than C57BL/6J and CD-1 mice. Also, strain differences in phenytoin effects on embryonic heart rate and rhythm were determined. Another objective was to determine whether a spin trapping agent with capacity to capture reactive oxygen species alter the developmental toxicity of phenytoin. Treatment with this agent resulted in a marked decrease in phenytoin teratogenicity, which supports the idea that reactive oxygen species are important mediators for the teratogenic action of phenytoin. The A/J mice embryos were most susceptible to the adverse cardiac effects of phenytoin and had the highest activity of superoxide dismutase and glutathione peroxidase, while the activity of catalase was the same in embryos of the three different strains. The high activities of antioxidant enzymes in the A/J stain indicate that the sensitivity to develop malformations is caused by excessive arrhythmia-related generation of reactive oxygen species rather than impaired antioxidant defense.

Neuroprotection of α-phenyl-n-tert-butyl-nitrone on the neonatal white matter is associated with anti-inflammation

Our previous study has demonstrated that alpha-phenyl-tert-butyl-nitrone (PBN) provided neuroprotection to the neonatal white matter following cerebral hypoxia-ischemia (HI). Free radical scavenging was involved in the neuroprotection of PBN. To investigate if other mechanisms contribute to the neuroprotection of PBN, postnatal day 4 SD rats were subjected to bilateral common carotid artery ligation, followed by 8% oxygen exposure for 20min. A single dose of PBN (100mg/kg, i.p.) was given prior to the hypoxic exposure. Expression of inflammatory cytokines: interleukin-1beta (IL-1beta), inducible nitric oxide synthase (iNOS) and tumor necrosis factor-alpha (TNF-alpha) was determined by RT-PCR, ELISA and immunohistochemistry. Activation of transcriptional factor nuclear factor-kappa B (NF-kappaB) was measured by ELISA. PBN significantly inhibited HI-induced up-regulation of IL-1beta, TNF-alpha and iNOS mRNA expression at 4h following HI. PBN treatment also reduced the brain concentration of IL-1beta significantly and decreased the number of IL-1beta- or iNOS-expressing cells in the white matter area at 12h following HI. Moreover, PBN suppressed the HI-induced NF-kappaB activation at 1h after HI. The overall results indicate that besides free radical scavenging, anti-inflammation might partly contribute to the neuroprotection afforded by PBN on neonatal white matter following cerebral HI.

Nitrone-related therapeutics: potential of NXY-059 for the treatment of acute ischaemic stroke

At present, none of the neurodegenerative diseases such as Parkinson's disease, Alzheimer's disease and stroke are treatable with compounds that slow or halt neuronal cell death. However, the prototype nitrone radical trap alpha-phenyl-tert-butylnitrone (PBN) has been shown to be an effective neuroprotective agent in various models of neurodegeneration. Some of these data are briefly reviewed as an introduction to an examination of the effect of the novel nitrone radical trapping agent disodium 2,4-disulfophenyl-N-tert-butylnitrone (NXY-059) in various animal models of stroke. NXY-059 has been shown to be an effective neuroprotective agent in both transient (reperfusion) and permanent focal ischaemia models in rats. In both types of model, NXY-059 has a large window of opportunity, providing effective neuroprotection when given up to 5 hours after the start of the occlusion in transient ischaemia and 4 hours after the start of permanent ischaemia. The compound is also effective in a marmoset permanent ischaemia model when administered up to 4 hours after the start of the occlusion. In this model it has been found to attenuate the problem of spatial neglect and maintain function to the paretic arm. NXY-059 administration also improves motor function in a rat haemorrhagic stroke model and has a neuroprotective effect in a rabbit thromboembolic stroke model. The compound is also well tolerated in stroke patients at plasma levels shown to provide a maximum neuroprotective effect in animal models of stroke.NXY-059, like PBN, is a nitrone with free radical trapping properties and this may be the basis of its neuroprotective action. However, experiments with PBN and NXY-059 suggest the possibility of other mechanisms being involved and these are also reviewed. Further experiments are required to fully elucidate the mechanism of action of these very effective neuroprotective agents.

Polymorphous light eruption (PLE) and a new potent antioxidant and UVA-protective formulation as prophylaxis

BACKGROUND

Polymorphous light eruption (PLE) is the most common photodermatosis. While its etiology still remains elusive, pathogenesis seems to involve UVA-induced oxidative stress and subsequent deregulation of antioxidative immune responses. Only few and often ineffective prophylactic and therapeutic measures exist to date.

METHODS

In our randomized, double-blind, placebo-controlled clinical study, we compared the efficacy of a new topical formulation, consisting of 0.25%alpha-glucosylrutin (AGR) (a natural, modified flavonoid), 1% tocopheryl acetate (vitamin E) and a broad-spectrum, highly UVA-protective sunscreen (SPF 15) in a hydrodispersion gel vehicle, to a sunscreen-only gel and vehicle. Thirty patients with a history of PLE were pretreated with either the above formulation, a similar preparation (with the same concentration for vitamin E and AGR, but a different UV filter system), placebo or a SPF 15 sunscreen-only gel, 30 min prior to daily photoprovocation with UVA irradiations of 60-100 J/cm(2) to 5 x 5 cm(2) areas on the upper arms.

RESULTS

After 4 days, results revealed a statistically highly significant difference (P<0.001) between the antioxidant containing formulations and placebo, and sunscreen-only formulation, respectively, in experimentally eliciting PLE. While only one patient developed clinical signs of PLE with accompanying itch in the area treated with the new antioxidant UV-protective gel formulation, 62.1% of the placebo-treated areas and 41.3% of the sunscreen-only treated areas showed mild to moderate signs of PLE.

CONCLUSION

Combining a potent antioxidant with a broad-spectrum, highly UVA-protective sunscreen is far more effective in preventing PLE than sunscreen alone or placebo and should thus be employed as the prophylaxis of choice for PLE.

Biological effects of epicuticular flavonoids from Primula denticulata on human leukemia cells

The biological effects of epicuticular substances in farinose exudates accumulated on inflorescence shafts and calyces of Primula denticulata on human acute myeloid leukemia cells (HL-60) were analyzed. The crude material possessed little antioxidative capacity but strong cytostatic properties. Some of its known components (5-hydroxyflavone, 2'-hydroxyflavone, 5,2'-dihydroxyflavone, and 5,8-dihydroxyflavone) were further tested to identify the biologically active compounds. The effects of these flavones on cell cycle progression, mitochondrial membrane potential, and reactive oxygen species have been investigated by flow cytometry. The flavonol quercetin was included in the study as reference compound because of its known cytostatic properties and its activity as radical scavenger. Compared to quercetin the flavones induced little apoptosis (up to 40 microM), but despite their low toxicity, the Primula flavonoids possessed strong cytostatic properties even at low concentrations. The cell cycle distribution showed a characteristic time-dependent shift, giving evidence of a generally short-lived effect of the test compounds in the exposed cells. The antioxidative properties quantified according to two different methods correlated with the number of hydroxyl groups. Whereas quercetin strongly affected the mitochondrial membrane potential, none of the Primula flavones showed a comparable effect.

Nitrones as neuroprotective agents in cerebral ischemia, with particular reference to NXY-059

Stroke is a major clinical problem, and acute pharmacological intervention with neuroprotective agents has so far been unsuccessful. Recently, there has been considerable interest in the potential therapeutic benefit of nitrone-derived free radical trapping agents as neuroprotective agents. Nitrone compounds have been shown to be beneficial in animal models of various diseases, and the prototypic compound alpha-phenyl-N-tert-butylnitrone (PBN) has been extensively demonstrated to be neuroprotective in rat models of transient and permanent focal ischemia. The nitrone radical trapping agent disodium 2,4-disulfophenyl-N-tert-butylnitrone (NXY-059) has also been shown to be neuroprotective in these models. Furthermore, it has recently been shown to improve neurological function and reduce infarct volume in a primate model of permanent focal ischemia even when given 4 hr postocclusion. While radical trapping activity is demonstrable with NXY-059 and other nitrone compounds such as PBN, this activity is weak. Arguments for and against ascribing radical trapping as the therapeutic mechanism of action are discussed. This compound is well tolerated in human stroke patients and can be administered to produce plasma concentrations exceeding those effective in animal models; crucially, at the same time, it has also been shown to be effective in animal models. NXY-059 may thus be the first compound to be examined in stroke patients using drug exposure and time to treatment that have been shown to be effective in animal models of stroke.

Influence of different oligosaccharides and inulin on heterocyclic aromatic amine formation and overall mutagenicity in fried ground beef patties

The effects of different oligosaccharides [fructooligosaccharide (FOS), galactooligosaccharide (GOS), and isomaltooligosaccharide (MOS)] and inulin on heterocyclic aromatic amine (HAA) formation and overall mutagenicity in fried ground patties were evaluated. Different oligosaccharides and inulin was added directly to ground beef. Patties (100 g) were fried at 225 degrees C (surface temperature) for 10 min per side. FOS added at levels of 0.5, 1.0, 1.5, 2.0, and 2.5 g to 100 g of ground beef inhibited total HAA formation by 19, 32, 45, 51, and 58%, respectively. The addition of 1.5 g of FOS, GOS, MOS, and inulin to ground beef patties inhibited total HAA formation by 50, 47, 46, and 54%, respectively. They also reduced overall mutagenicity by 52, 51, 48, and 59%, respectively. These studies confirm that oligosaccharides and inulin have the potential to reduce HAA formation in cooked beef patties.

The effects of PBN (phenyl-butyl-nitrone) on GLT-1 levels and on the extracellular levels of amino acids and energy metabolites in a model of iron-induced posttraumatic epilepsy

This study investigates astrocytic glutamate uptake in the iron-induced animal model of posttraumatic epilepsy. Since formation of free radicals may be involved in epileptogenesis after brain trauma and hemorrhage the effects of the nitrone radical scavenger alpha-phenyl-tert-N-butyl nitrone (PBN) were also studied. Animals received an intracortical iron injection, or were sham-operated. They were given PBN intraperitoneally or saline as control. Twenty-four hours after lesion, brain tissue was collected and the level of glial glutamate transporter (GLT-1) was analyzed using immunoblotting. The extracellular concentrations of amino acids and energy metabolites were measured using microdialysis. The results showed significantly decreased levels of GLT-1 (70 kDa), higher basal levels of glutamate, and lower levels of glutamine as well as low arginine/citrulline ratios at the lesion compared to controls. PBN significantly attenuated the decrease of 70 kDa GLT-1 in the lesioned animals and attenuated the alterations in amino acid levels but not to a significant level. PBN also increased the arginine/citrulline ratios indicating reduced nitric oxide synthase activity. Our results suggest that astrocytic uptake of glutamate is oxidatively impaired in iron-induced epileptogenesis and that the administration of a radical scavenger can attenuate this process.

Effect of two new PBN-derived phosphorylated nitrones against postischaemic ventricular dysrhythmias

Spin traps might exert antioxidant cardioprotective effects during myocardial ischaemia-reperfusion where free radicals are thought to be responsible for the occurrence of reperfusion injury. The aim of our study was to investigate the effects of two new alpha-phenyl N-tert-butylnitrone (PBN)-derived beta-phosphorylated nitrones: 2-N-oxy-N-[benzylidène amino] diéthyl propyl-2-phosphate (PPN) and 1-diethoxyphosphoryl-1-methyl-N-[(1-oxido-pyridin-1-ium-4-yl) methylidene] ethylamine N-oxide (4-PyOPN) compared with PBN on (1) the evolution of cardiovascular parameters and (2) the postischaemic recovery. Anaesthetized rats were injected with 120 micro mol/kg of the nitrones or 14 micro mol/kg of amiodarone, used as a reference antidysrhythmic drug. Ischaemia was induced in vivo through ligation of the left anterior descending coronary artery for 5 min followed by 15 min of reperfusion after release. Cardiovascular parameters and occurrence of ventricular premature beats (VPB), ventricular tachycardia (VT) and fibrillation (VF) were recorded throughout the experiment. Under nonischaemic conditions, none of the three spin traps was shown to modify cardiovascular parameters during the 25-min measurement period. Solvent-treated (NaCl 0.9%) animals challenged with ischaemia-reperfusion exhibited 39 +/- 10 VPB, 156 +/- 39 s of VT and 60% mortality caused by sustained VF. Nitrones improved slightly postischaemic recovery, reducing the occurrence of VF and mortality to 33% whereas amiodarone injection totally suppressed rhythm disturbances and mortality. Our study has shown only limited antidysrhythmic cardioprotective effects of PBN-derived beta-phosphorylated nitrones during reperfusion after a regional myocardial ischaemia but also minor antioxidant properties of these spin trapping agents.

Cocaine treatment increases expression of a 40 kDa catecholamine-regulated protein in discrete brain regions

Previous reports from our laboratory have described brain-specific catecholamine-regulated proteins, which bind dopamine and related catecholamines. Evidence from the molecular cloning of a 40 kDa catecholamine-regulated protein (CRP40) revealed that CRP40 is dopamine-inducible and has properties similar to those of the 70 kDa heat shock protein (HSP70) family. The present study investigates the effects of acute and chronic cocaine treatment on CRP40 expression in the striatum, nucleus accumbens, prefrontal cortex, and medulla. Acute treatment with cocaine increased CRP40 expression in the nucleus accumbens and striatum, whereas chronic treatment with cocaine increased CRP40 expression in the nucleus accumbens only. Neither of these treatments affected CRP40 levels in the prefrontal cortex or medulla. In addition, pretreatment with the spin-trapping agent alpha-phenyl-tert-butylnitrone did not attenuate cocaine-induced expression of CRP40, suggesting that the observed increases in CRP40 levels were not caused by free radicals. On the other hand, pretreatment with anisomycin, a protein synthesis inhibitor, blocked the cocaine-induced expression of CRP40. Thus, protein synthesis may be involved in the observed CRP40 level increases. Furthermore, neither acute nor chronic cocaine treatment affected levels of inducible or constitutively expressed HSP70, which indicates a specificity of cocaine's effects on CRP40. Since cocaine has been shown to increase extracellular dopamine levels, these findings suggest that increased expression of CRP40 is associated with high extracellular levels of dopamine (or its metabolites). Elevated levels of CRP40 could play a protective role for dopamine neurons in response to increased oxidative stress that has been shown to be induced by cocaine and that can lead to apoptosis and neurodegeneration.

In vitro blood-brain barrier permeability and cerebral endothelial cell uptake of the neuroprotective nitrone compound NXY-059 in normoxic, hypoxic and ischemic conditions

The free radical trapping nitrone compounds alpha-phenyl-N-tert-butylnitrone (PBN), 2-sulfophenyl-N-tert-butylnitrone (S-PBN) and disodium 2,4-disulfophenyl-N-tert-butyl nitrone (NXY-059) are effective neuroprotective agents in experimental models of both transient and permanent focal ischemia. A recent in vivo study suggested that NXY-059 had poor brain uptake in a transient ischemia model. We have now examined its blood-brain barrier permeability and cerebral endothelial uptake during hypoxic and ischemic conditions using an in vitro model of the blood-brain barrier. The in vitro blood-brain barrier permeability and cerebral endothelial uptake of NXY-059 and S-PBN were low during normoxic conditions. In contrast, PBN had very high blood-brain barrier penetration in vitro which confirmed earlier in vivo results. The permeability of [14C]NXY-059 increased 3.5 times after 9 h of hypoxia or 3 h of ischemia. There was, respectively, a 5-fold and more than 10-fold increase, after 6 and 9 h of ischemia. The control molecule [3H]inulin (M(r) approximately 5000) showed a similar increase in permeability under the same experimental conditions indicating a major change in the transport properties of the endothelium. There was a 60% reduction in the ATP levels of astrocytes after 3 h of ischemia and a 90% reduction after 9 h. The reduction in ATP levels in endothelial cells was somewhat lower. The uptake of NXY-059 in cerebral endothelial cells under normoxic, hypoxic or 9 h of ischemic conditions was negligible. NXY-059, S-PBN and PBN showed no effects on vesicular transport or the integrity of the blood-brain barrier in normoxic or ischemic conditions, nor did the compounds induce any change in the ATP levels of the cells. In conclusion, it is possible that the increase in blood-brain barrier permeability of [14C]NXY-059 which occurs during prolonged ischemia in vitro reflects a change which may be of importance to the neuroprotective effects of this nitrone free radical trapping agent.

Embryonic arrhythmia by inhibition of HERG channels: a common hypoxia-related teratogenic mechanism for antiepileptic drugs?

PURPOSE

There is evidence that drug-induced embryonic arrhythmia initiates phenytoin (PHT) teratogenicity. The arrhythmia, which links to the potential of PHT to inhibit a specific potassium channel (Ikr), may result in episodes of embryonic ischemia and generation of reactive oxygen species (ROS) at reperfusion. This study sought to determine whether the proposed mechanism might be relevant for the teratogenic antiepileptic drug trimethadione (TMO).

METHODS

Effects on embryonic heart rhythm during various stages of organogenesis were examined in CD-1 mice after maternal administration (125-1,000 mg/kg) of dimethadione (DMO), the pharmacologically active metabolite of TMO. Palatal development was examined after administration of a teratogenic dose of DMO and after simultaneous treatment with DMO and a ROS-capturing agent (alpha-phenyl-N-tert-butyl-nitrone; PBN). The Ikr blocking potentials of TMO and DMO were investigated in HERG-transfected cells by using voltage patch-clamping tests.

RESULTS

DMO caused stage-specific (gestation days 9-13 only) and dose-dependent embryonic bradycardia and arrhythmia at clinically relevant maternal plasma concentrations (3-11 mM). Hemorrhage in the nasopharyngeal part of the embryonic palate (within 24 h) preceded cleft palate in fetuses at term. Simultaneous treatment with PBN significantly reduced the incidence of DMO-induced cleft palate, from 40 to 13%. Voltage patch-clamping studies showed that particularly DMO (70% inhibition), but also TMO, had Ikr blocking potential at clinically relevant concentrations.

CONCLUSIONS

TMO teratogenicity, in the same way as previously shown for PHT, was associated with Ikr-mediated episodes of embryonic cardiac arrhythmia and hypoxia/reoxygenation damage.

Naringin has an antiatherogenic effect with the inhibition of intercellular adhesion molecule-1 in hypercholesterolemic rabbits

Naringin, a bioflavonoid found in citrus fruit peel, is known to have an antioxidative effect, but its effect on atherosclerosis has not been studied. This study evaluated the effect of naringin on blood lipid levels and aortic fatty streaks, and its action mechanism in hypercholesterolemic rabbits. Male New Zealand white rabbits were fed a 0.25% cholesterol diet and divided into an untreated group (n = 4), a naringin-treated group (n = 5; 500 mg/kg per day), and a lovastatin-treated group (n = 5; 20 mg/kg per day). After 8 weeks, blood was sampled and analyzed biochemically. Aorta and liver were harvested and examined histologically. Cholesterol level in rabbits fed the 0.25% cholesterol diet reached 17 times normal and decreased in the rabbits fed naringin and lovastatin, whose effects were not statistically significant (p > 0.05). However, both naringin and lovastatin effectively decreased the area of fatty streak in thoracic aorta on macroscopic analysis (p < 0.05) and significantly reduced subintimal foam cell infiltration on microscopic morphometry (p < 0.05). These foam cells were macrophages on immunohistochemical analysis. Naringin treatment inhibited hypercholesterolemia-induced intercellular adhesion molecule-1 (ICAM-1) expression on endothelial cells. Hypercholesterolemia caused fatty liver and elevation of liver enzymes, which was prevented by naringin but not by lovastatin. Naringin significantly reduced fatty streak formation and neointimal macrophage infiltration and also inhibited the expression of ICAM-1 in endothelial cells, suggesting that suppression of ICAM-1 contributed to the antiatherogenic effect. Naringin, unlike lovastatin, has a hepatoprotective action.

Free radical generation in the cochlea during combined exposure to noise and carbon monoxide: an electrophysiological and an EPR study

Ototoxicity following combined exposure to noise and carbon monoxide (CO) is known to result in more severe permanent threshold shifts than exposure to noise alone. We have previously demonstrated that such potentiation of noise-induced auditory impairment by CO can be prevented by the administration of a nitrone spin-trapping agent. Although such protection implicates injury via free radical pathways, drug-induced protection does not provide direct evidence for the presence of free radicals in the cochlea. The objective of this study was to demonstrate the actual presence of nitrone spin adducts in the cochlea following simultaneous exposure to noise and CO. Using electrophysiological end-points, the protective effects of the nitrone spin-trapping agent alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN) were assessed following combined exposure of adult male Long Evans hooded rats to noise and CO. In addition, an ex-vivo evaluation of POBN spin adducts was done by electron paramagnetic resonance spectroscopy (EPR). The noise used was octave band noise with center frequency 13.6 kHz at 100 dB(Lin) for a duration of 2 h. The level of CO used was 1200 ppm. Electrophysiological results demonstrate that POBN protects against combined exposure to noise plus CO. The EPR study demonstrates POBN spin adducts in the cochleae of animals exposed to noise plus CO. Therefore, this study provides evidence to the hypothesis that ototoxicity due to noise plus CO exposure is mediated via free radicals.

Nitric oxide is protective in listeric meningoencephalitis of rats

The bacterium Listeria monocytogenes causes meningoencephalitis in humans. In rodents, listeriosis is associated with granulomatous lesions in the liver and the spleen, but not with meningoencephalitis. Here, infant rats were infected intracisternally to generate experimental listeric meningoencephalitis. Dose-dependent effects of intracisternal inoculation with L. monocytogenes on survival and activity were noted; 10(4) L. monocytogenes organisms induced a self-limiting brain infection. Bacteria invaded the basal meninges, chorioid plexus and ependyme, spread to subependymal tissue and hippocampus, and disappeared by day 7. This was paralleled by recruitment and subsequent disappearance of macrophages expressing inducible nitric oxide synthase (iNOS) and nitrotyrosine accumulation, an indication of nitric oxide (NO.) production. Treatment with the spin-trapping agent alpha-phenyl-tert-butyl nitrone (PBN) dramatically increased mortality and led to bacterial numbers in the brain 2 orders of magnitude higher than in control animals. Treatment with the selective iNOS inhibitor L-N(6)-(1-iminoethyl)-lysine (L-NIL) increased mortality to a similar extent and led to 1 order of magnitude higher bacterial counts in the brain, compared with controls. The numbers of bacteria that spread to the spleen and liver did not significantly differ among L-NIL-treated, PBN-treated, and control animals. Thus, the infant rat brain is able to mobilize powerful antilisterial mechanisms, and both reactive oxygen and NO. contribute to Listeria growth control.

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.

Aromatic hydroxylation in PBN spin trapping by hydroxyl radicals and cytochrome P-450

Phenyl N-tert-butylnitrone (PBN) is widely used as a spin trapping agent, but is not useful detecting hydroxyl radicals because the resulting spin adduct is unstable. However, hydroxyl radicals could attack the phenyl ring to form stable phenolic products with no electron paramagnetic resonance signal, and this possibility was investigated in the present studies. When PBN was added to a Fenton reaction system composed of 25 mM H(2)O(2) and 0.1 mM FeSO(4), 4-hydroxyPBN was the primary product detected, and benzoic acid was a minor product. When the Fe(2+) concentration was increased to 1.0 mM, 4-hydroxyPBN concentrations increased dramatically, and smaller amounts of benzoic acid and 2-hydroxyPBN were also formed. Although PBN is extensively metabolized after administration to animals, its metabolites have not been identified. When PBN was incubated with rat liver microsomes and a reduced nicotinamide adenine dinculeotide phosphate (NADPH)-generating system, 4-hydroxyPBN was the only metabolite detected. When PBN was given to rats, both free and conjugated 4-hydroxyPBN were readily detected in liver extracts, bile, urine, and plasma. Because 4-hydroxyPBN is the major metabolite of PBN and circulates in body fluids, it may contribute to the pharmacological properties of PBN. But 4-hydroxyPBN formation cannot be used to demonstrate hydroxyl radical formation in vivo because of its enzymatic formation.

Methods to assess free radicals and oxidative stress in biological systems

Oxidative stress results from a disruption of the prooxidant/antioxidant cellular balance and monitoring free radical status becomes an interesting challenge in animal and human nutrition. In the present work, merits and limitations of different analytical techniques (HPLC, GC-MS, fluorometric and colourometric assays, ELISA, gel electrophoresis) for the measurement of radical mediated alterations in the cellular integrity of lipids (malondialdehyde, hydrocarbon gases, F2-isoprostanes) proteins (protein carbonyls, 3-nitrotyrosine) and DNA (8-hydroxy-2'-deoxyguanosine) are discussed. Besides these indirect methods, owing to the fact that free radicals are paramagnetic, electron paramagnetic resonance spectroscopy combined with spin trapping has become a valuable tool to directly assess and to better understand the mechanisms of free radical reactions. With this approach a radical that is too short-lived to be detected, adds to a spin-trapping agent to form a relatively long-lived radical adduct. Information obtained from the hyperfine splitting of the spin-trapped adduct can provide identification and quantification of the originally generated free radicals.

An optimal redox status for the survival of axotomized ganglion cells in the developing retina

The neuronal redox status influences the expression of genes involved in neuronal survival. We previously showed that antioxidants may reduce the number of dying ganglion cells following axotomy in chick embryos. In the present study, we show that various antioxidants, including the new spin trap azulenyl nitrone and 1,3-dimethyl-2-thiourea, protect axotomized ganglion cells, confirming that neuronal death involves an imbalance of the cellular redox status towards oxidation. However, high concentrations of antioxidants did not protect ganglion cells, suggesting that excessive reduction is detrimental for neurons. Simultaneous injections of two different antioxidants gave results only partly supporting this view. Combinations of azulenyl nitrone and N-acetyl cysteine in fact gave greater protection than either antioxidant alone, whereas N-acetyl cysteine lost its neuroprotective effects and diminished those of alpha-phenyl-N-tert-butyl nitrone when the two compounds were injected simultaneously. The results of the combined treatments suggest that azulenyl nitrone and alpha-phenyl-N-tert-butyl nitrone do not have the same chemical effects within the ganglion cells. Moreover, N-acetyl cysteine's own antioxidant properties enhance the spin trapping effects of azulenyl nitrone but potentiate the toxicity of alpha-phenyl-N-tert-butyl nitrone. Our main conclusion is that neuronal survival requires the maintenance of the redox status near an optimal set-point. "Reductive stress" may be as dangerous as oxidative stress.

High-performance liquid chromatography study of the pharmacokinetics of various spin traps for application to in vivo spin trapping

In vivo spin trapping is potentially a very useful tool to investigate the role of free radicals in physiologic processes and disease development. Unfortunately, knowledge on the stability and distribution of spin traps in living systems is limited. Therefore, in our study, we selected 11 acyclic and cyclic nitrone spin traps with diverse properties to determine their pharmacokinetics in mice. At varying times after intraperitoneal administration, we measured the concentration of the spin traps in the liver, heart, and blood. Our results showed that most spin traps were rapidly absorbed and were approximately evenly distributed throughout the mouse body. It was also found that most of the traps were relatively stable in vivo with more than half of the injected amount still available for spin trapping free radicals after an hour. Two of the 11 tested spin traps, however, decomposed after injection. These results indicate that for a successful in vivo spin trapping experiment, the stability of the spin trap is not of major concern, but the time course of distribution may be important.

Neuroprotective effects of a novel nitrone, NXY-059, after transient focal cerebral ischemia in the rat

Recent results have demonstrated that the spin trapping agent alpha-phenyl-N-tert-butyl nitrone (PBN) reduces infarct volume in rats subjected to 2 hours of middle cerebral artery occlusion, even when given 1 to 3 hours after the start of recirculation. In the current study, the authors assessed the effect of NXY-059, a novel nitrone that is more soluble than PBN. Loading doses were given of 0.30, 3.0, or 30 mg x kg(-1) followed by 0.30, 3.0, or 30 mg x kg(-1) x h(-1) for 24 or 48 hours. Dose-response studies showed that when treatment was begun 1 hour after recirculation, 0.30 mg x kg(-1) had a small and 30 mg x kg(-1) a marked effect on infarct volume. At equimolar doses (3.0 mg x kg(-1) for NXY-059 and 1.4 mg x kg(-1) for PBN), NXY-059 was more efficacious than PBN. Similar results were obtained when a recovery period of 7 days was allowed. The window of therapeutic opportunity for NXY-059 was 3 to 6 hours after the start of recirculation. Studies of the transfer constant of [14C]NXY-059 showed that, in contrast to PBN, this more soluble nitrone penetrates the blood-brain barrier less extensively. This fact, and the pronounced antiischemic effect of NXY-059, suggest that the delayed events leading to infarction may be influenced by reactions occurring at the blood-endothelial interface.

Pharmacologic properties of phenyl N-tert-butylnitrone

Phenyl N-tert-butylnitrone (PBN) is the parent of a family of nitrones used as spin-trapping agents to trap free radicals. PBN's pharmacological effects in animal models are extensive, ranging from protection against death after endotoxin shock, protection from ischemia-reperfusion injury, to increasing the life span of mice. Recent additions to the list include protection from bacterial meningitis, thalidomide-induced teratogenicity, drug-induced diabetogenesis, and choline-deficient hepatocarcinogenesis. Because PBN reacts with oxygen radicals to produce less reactive species, it has been suggested that this is the basis of its pharmacological effects. However, there has been no hard evidence for this notation. Nevertheless, many investigators have used the presence of PBN's pharmacologic effect as evidence for free radical involvement in their models. Mechanistic studies on the PBN's antisepsis action revealed that PBN inhibits expression of various pro-inflammatory genes, suggesting that the protective action involves more than a straightforward free radical-scavenging mechanism. Previous and recent developments in the investigations on the pharmacologic properties of PBN are described in this review.

Treatment with the spin-trap agent alpha-phenyl-N-tert-butyl nitrone does not enhance the survival of embryonic or adult dopamine neurons

Reactive oxygen species are thought to be involved in the death of dopaminergic neurons in Parkinson's disease as well as in transplanted embryonic dopaminergic neurons. The spin-trap agent alpha-phenyl-N-tert-butyl nitrone (PBN) reacts directly with radical species and may thereby prevent them from damaging important cellular molecules such as membrane lipids. We found that PBN does not increase the survival of cultured embryonic dopaminergic neurons subjected to serum deprivation, whereas the antioxidant and lipid peroxidation inhibitor lazaroid U-83836E does. Moreover, PBN does not increase the survival of grafted embryonic dopaminergic neurons or graft efficacy (monitored as changes in drug-induced motor asymmetry in hemiparkinsonian rats) when the spin-trap agent is given intraperitoneally to the graft recipient or is added to the solutions used when preparing tissue for transplantation. Another spin-trap agent, alpha-(4-pyridyl-1-oxide)-N-tert-butyl nitrone (POBN) also failed to protect neurons when given to graft recipients in the same experimental paradigm. Finally, we found that adult nigral neurons subjected to a progressive retrograde 6-OHDA lesion are not protected by systemic treatment with PBN. Even though reduction of oxidative stress by overexpression of superoxide dismutase or addition of lazaroids have previously been shown to enhance the survival of cultured and grafted dopaminergic neurons, spin-trap agents PBN and POBN do not provide protection in these experimental paradigms. This may be due to antioxidants and spin-trap agents interfering in different steps of free radical-induced cell damage.

The effect of the spin trapping agent α-phenyl-n-tert-butyl nitrone on dexfenfluramine-induced serotonin depletion in rat brain

Oxygen-free radical formation from either the parent compound amphetamine, its metabolites or drug-released serotonin (5-HT) has been implicated in the reduction of serotoninergic markers caused by amphetamine derivatives. Therefore, the present study investigated the effects of the spin-trapping agent α-phenyl-tert-butyl nitrone (PBN) on the 5-HT-lowering action of dexfenfluramine (DF) in rats, compared with p-chloroamphetamine (PCA). PBN (150 mg/kg, i.p, divided in two doses) almost totally prevented the reduction of 5-HT in particularly sensitive regions of the rat brain (cortex and striatum) 1 and 7 days after DF (10 mg/kg, i.p.). It also provided complete protection against the acute 5-HT-depleting action of PCA (5 mg/kg, i.p.), reducing it at 7 days in striatum, although with the higher dose (300 mg/kg, divided in two doses) there was a tendency to antagonize the long-term effects in both regions. With DF, however, the antagonistic effect of PBN was associated with a marked reduction of the plasma and brain concentrations of the parent drug, but particularly its active metabolite dexnorfenfluramine (DNF). Thus, reduced brain availability of the total active drug (DF+DNF) may explain why PBN prevents the neurochemical effects of DF (but not PCA), including the long-term one which possibly depends on the extent of the initial 5-HT lowering.

Effects of alpha-phenyl-N-tert-butyl nitrone (PBN) on compression injury of rat spinal cord

alpha-Phenyl-N-tert-butyl Nitrone (PBN) is a free radical scavenger which recently has proved to be neuroprotective in experimental studies on focal cerebral ischemia and infarction. We therefore studied the effect of this drug in a model of moderate compression injury to rat spinal cord at the midthoracic level. The compound was given intraperitoneally 0.5 h before (100 mg/kg b.w) and at 1.5 h (50 mg/kg b.w) and 3.5 h (50 mg/kg b.w) after compression. Treated animals and controls (vehicle alone) were allowed to survive for 1 or 9 days following trauma. The functional outcome was tested by the inclined plane method and the motor performance score. By using MAP2 immunostaining the number of nerve cell bodies in the ventral horn and the ratio of MAP2 immunostained area to area of whole section of the cord were assessed to detect loss of neurons and loss of dendrites in the compressed segment. beta APP and PGP9.5 immunostaining was used to demonstrate axonal lesions. Treated and control rats showed at day 1 when tested with the inclined plane method a marked reduction of the capacity angle. This abnormality recovered gradually over the following days and was normalized at day 9. The motor performance score showed a marked reduction at day 1 which almost normalized at day 9. There was no difference regarding the functional outcome between rats given PBN and controls in none one of these functional tests. The spinal cord of normal rats presented immunoreactivity to MAP2 in nerve cell bodies and dendrites but not in axons and other structures. Following compression there was at day 1 and 9 a marked loss of MAP2 immunoreactivity in dendrites and nerve cell bodies. We could not detect any difference between the PBN and the control rats regarding the degree of cell loss or degree of reduction of dendrite staining. No difference between the two groups was seen with the axonal immunostainings (beta APP and PGP9.5). In conclusion, our study did not reveal any neuroprotective effect of PBN on the functional outcome and morphology (immunostaining to MAP2, beta APP and PGP9.5) in this model of moderate compression trauma to rat spinal cord.

Optimal time and dosage of phenyl N-tert-butyl nitrone (PBN) for the inhibition of nitric oxide synthase induction in mice

We have previously reported that phenyl N-tert-butyl nitrone (PBN) inhibits the induction of inducible nitric oxide synthase (iNOS) and, thus, prevents the overproduction of nitric oxide (NO), resulting in the reduction of endotoxin-mediated death in mice. In this study, to examine the effect of PBN in detail, we investigated the dose- and administration-timing dependence of PBN on endotoxin-induced NO generation in mice. NO generation was monitored in the mouse liver after administration of lipopolysaccharide (LPS) by the in vivo NO-spin trapping method using the iron complex of N-methyl-D-glucamine dithiocarbamate (MGD) as a spin trap, followed by ex vivo EPR measurement of the liver tissue. PBN was effective in reducing liver NO generation monitored 6 h after endotoxin injection when it was administered shortly before or after LPS injection. The maximum inhibition of liver NO was obtained when PBN was administered 30 min before LPS injection. ID50 for the inhibition was estimated to be approximately 200 mg/kg when the LPS dose of 50 mg/kg was used. Expression of mRNA for iNOS in the liver as estimated by reverse transcription polymerase chain reaction was decreased when PBN was given 30 min before LPS injection, indicating that the reduction of expression of iNOS protein by PBN, which has been shown previously, is at least in part caused by a decrease in mRNA expression.

alpha-Phenyl-N-tert-butyl nitrone attenuates methamphetamine-induced depletion of striatal dopamine without altering hyperthermia

Methamphetamine (MA) administration to adult rats (4 x 10 mg/kg s.c.) induces neurotoxicity predominately characterized by a persistent reduction of neostriatal dopamine (DA) content. Hyperthermia following MA administration potentiates the resulting DA depletion. DA-derived free radicals are postulated to be a mechanism through which MA-induced neurotoxicity is produced. The spin trapping agent PBN reacts with free radicals to form nitroxyl adducts, thereby preventing damaging free radical reactions with cellular substrates. MA with saline pretreatment (Sal-MA) reduced neostriatal DA by 55% (P < 0.01 vs. Sal-Sal). MA with PBN pretreatment (PBN-MA) at 36 or 60 mg/kg reduced neostriatal DA by 36 and 22%, respectively (P < 0.05 and P < 0.01 vs Sal-MA) indicating partial protection. PBN pretreatment did not alter MA-induced hyperthermia. Thus, PBN does not attenuate MA-induced neurotoxicity by reducing MA-induced hyperthermia. These results support a role for free radicals in the generation of MA-induced dopaminergic neurotoxicity.

alpha-Phenyl N-tert-butyl nitrone (PBN) increases the cortical cerebral blood flow by inhibiting the breakdown of nitric oxide in anesthetized rats

The effects of intravenous administration of alpha-phenyl N-tert-butyl nitrone (PBN) on cortical cerebral blood flow (CBF) were examined in Wistar rats under pentobarbital anesthesia and artificial ventilation. The cortical CBF in parietal cortex was measured by laser Doppler flowmetry. Intravenous administrations of 2 mg/kg and 20 mg/kg of PBN dose-dependently produced significant increases in cortical CBF and decreases in systemic blood pressure (BP). To examine whether these increased responses in cortical CBF produced by PBN were associated with the vasodilatation system of nitric oxide (NO), the NO synthase inhibitor L-NG-nitroarginine (L-NOArg), which is an analog of L-arginine, was used to inhibit the NO-related-vasodilatative system. Since the PBN-induced responses in the cortical CBF were much attenuated in L-NOArg-treated rats (30 mg/kg, i.v.), it was inferred that NO-related vasodilatation was strongly associated with the PBN-induced increase in cortical CBF.

alpha-Phenyl-tert-butyl-nitrone reduces cortical infarct and edema in rats subjected to focal ischemia

The neuroprotective effects of the spin-trapping agent alpha-phenyl-N-tert-butyl nitrone (PBN) were evaluated in rats subjected to focal cerebral ischemia produced by permanent middle cerebral artery (MCA) and ipsilateral common carotid artery (CCA) occlusion. PBN was given i.p. at 100 mg/kg at initial times of administration of 0.5 h prior to ischemia (group 2), 0.5 (group 3), 5 (group 4) and 12 h (group 5) after ischemia. Additional doses of PBN (100 mg/kg) were administered as follows: Group 2, at 24 h; Group 3, at 5, 17, 29 and 41 h; Group 4, at 17, 29 and 41 h; Group 5, at 24 and 36 h. Animals were sacrificed 48 h after MCA occlusion and infarct volumes were calculated from triphenyetetrazolium stained 1.5 mm slices of the forebrain. PBN significantly attenuated cortical infarct volume and cerebral edema in all of the treated rats compared with those in ischemic control (group 1) rats, with no significant differences between the different PBN treated groups. The percentage of infarct volume in ischemic control rats was 22.7 +/- 1.0, while those in PBN-treated groups were: 9.6 +/- 2.0, P < 0.01 (group 2); 12.2 +/- 2.2, P < 0.01 (group 3); 11.1 +/- 2.9, P < 0.01 (group 4) and 14.4 +/- 2.5, P < 0.01 (group 5). Furthermore, neurological behavior tests showed that PBN decreased the neurological deficit scores in rats initially treated either prior to or for up to 12 h after ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

N-tert-butyl-alpha-phenylnitrone administration fails to modify alcohol dependence and alcohol induced hypervascularization

Chronic alcoholization by ethyl-alcohol inhalation was used to study the properties of a spin-trapping agent on different alcohol manifestations in rat. The spin-trapping agent, i.e. N-tert-butyl-alpha-phenylnitrone (PBN), was given at the dose of 32 mg/kg twice a day during the whole alcoholization procedure. The blood alcohol level, the hypermotility which accompanied the ethanol withdrawal, the behavioral dependence as estimated by a free-choice program and the hypervascularization which is developed after a chronic pulmonary alcoholization were quantified. The rats treated with PBN differ from the control rats only by their higher blood alcohol level at the end of the chronic alcoholization while the other quantified alcohol-induced manifestations remained unchanged.

Distribution of spin-trapping compounds in rat blood and brain: in vivo microdialysis determination

Microdialysis was utilized to determine blood and brain distribution of spin-trapping nitrone compounds in the rat following intraperitoneal administration. In vivo quantitation by high-pressure liquid chromatography (HPLC) analysis, in vitro calibration of microdialysis probes, optimum perfusion rate, and the relationship of microdialysis sample recovery to tissue levels were evaluated in detail. The microdialysis sampling and HPLC analysis provided on-line, within-animal pharmacokinetic time-course determinations. At equimolar concentrations, 150 mg/kg alpha-phenyl-N-tert-butyl nitrone (PBN) or 165 mg/kg alpha-4-pyridyl-N-oxide N-tert-butyl nitrone (POBN) reached a similar, steady-state venous blood concentration of 224 +/- 21 microM and 210 +/- 10 microM, respectively. The POBN steady-state brain concentration was 149 +/- 9 microM, a significantly (p < .05) lower concentration than in the blood. In contrast, the brain concentration of PBN was 331 +/- 25 microM, significantly (p < .05) higher than its concentration in the blood. The increased brain distribution/penetration of PBN was attributed to its greater lipophilicity as measured by its octanol/water partition coefficient. All microdialysis results were validated by direct measurement of blood and brain levels at steady-state using conventional extraction procedures and assays. Also, the amount of tissue/cell bound versus unbound nitrones was determined by comparing the microdialysis "dialyzable" fraction with the total amount from whole tissue extracts. These data demonstrate that on-line determinations of nitrone spin-trap brain penetration/levels can be carried out accurately using in vivo microdialysis. The implication of these results for potential use of the microdialysis technique for detection of free radical products in in vivo animal models is discussed.

The biochemical mechanisms of the excitotoxicity of kainic acid. Free radical formation

Kainic acid (KA) is a known potent neuroexcitotoxin, although the biochemical mechanism producing its underlying neurotoxic effect is not quite clear. Histopathological examination of gerbil brains 24 h after systemic injection of KA revealed severe neuronal lesions in different regions of the brain, especially the cerebellar and hippocampal areas. We have detected free radical formation in the brain 1 h after KA administration by using an in vivo spin trapping technique. We have also observed increased lipid peroxidation in the brain after KA-treatment by analyzing thiobarbituric acid reactive substances and conjugated diene formation. Diminished brain specific (Na+, K+)-ATPase activity was also found 2 h after KA injection and persisted to 24 h. It is possible that the free radical reaction is a primary cause of neuronal degeneration after KA administration.

Neuroprotective effects of phenyl-t-butyl-nitrone in gerbil global brain ischemia and in cultured rat cerebellar neurons

We examined the ability of phenyl-t-butyl-nitrone (PBN), an electron spin trapper, to attenuate ischemia-induced forebrain edema and hippocampal CA1 neuronal loss in gerbils, and to protect rat cerebellar neurons in primary culture from glutamate-induced toxicity. PBN, given i.p. at 75 or 150 mg/kg 30 min before ischemia (5 min occlusion), increased survival (at 7 days) of CA1 neurons from 60 +/- 14 (vehicle-treated, n = 17) to 95 +/- 15 (P less than 0.05, n = 15) and 145 +/- 3 (P less than 0.01, n = 15), respectively. When gerbils were treated with PBN (50 mg/kg, i.p.) immediately and 6 h after reperfusion, followed by b.i.d. for an additional 2 days, CA1 neurons survival improved from 35 +/- 9 (vehicle, n = 20, 6 min occlusion) to 106 +/- 17 (P less than 0.01, n = 13). In gerbils exposed to a more severe ischemia (10 min), pretreatment with 150 mg/kg PBN increased the survival of CA1 neurons from 6 +/- 6 (vehicle) to 27 +/- 10 (P less than 0.05, n = 11). Pretreatment with PBN, at 150 mg/kg, reduced forebrain edema (following 15 min ischemia) by 24.7% (P less than 0.01, n = 16). PBN at 50 mg/kg, i.p. had no hypothermic effect and at 75 or 150 mg/kg caused a transient hypothermia. The presence of PBN in the brain was confirmed in microdialysis samples and brain tissue extract using HPLC. In vitro, PBN protected rat cerebellar neurons against 100 microM glutamate-induced toxicity with an EC50 value of 2.7 mM. Our results further support the concept that free radicals contribute to brain injury following ischemia and suggest the potential therapeutic application of electron spin trappers in stroke.

The role of oxygen free radicals in the development of chronic renal failure

This study examined whether there is increased production of oxygen free radicals during chronic renal failure. Rats subjected to 3/4 nephrectomy and sham operated controls were killed after 3 weeks. Lipid extracts of plasma and renal tissue were examined by HPLC and kidney specimens were also analyzed by EPR spectroscopy. The redox capacity of blood was assessed using nitroblue tetrazolium and plasma ascorbate levels were measured with HPLC. There was no detectable renal production of oxygen free radicals in rats with chronic renal failure. Kidney parenchymal content of other oxidants and the oxidant:reductant ratio were similar in control and uremic animals. The plasma redox capacity and ascorbate levels were elevated in uremic rats. We conclude that early in the course of chronic renal failure, there is not excessive production of oxygen free radicals. There is accumulation of reductants, primarily ascorbate, in the plasma of uremic animals.

Ischemia-reperfusion induced acute renal failure in the rat is ameliorated by the spin-trapping agent alpha-phenyl-N-tert-butyl nitrone (PBN)

The spin-trapping agent alpha-phenyl-N-tert-butyl nitrone (PBN) reduced the ischemia-reperfusion induced acute renal failure in the rat. Renal ischemia was produced in unilateral nephrectomized rats by complete occlusion of the left renal artery for 60 min. Perfusion of the kidney was then reestablished, and the rats were sacrificed 48 h later. PBN (100 mg/kg i.p.) administered 30 min prior to renal artery occlusion significantly reduced the increase in serum creatinine and urea and renal failure index, as well as the decrease in urine/plasma creatinine ratio and creatinine clearance compared to saline-injected ischemic rats. PBN injected to control rats had no effect on these parameters. These data support the hypothesis of an involvement of reactive free radicals in the pathogenesis of ischemia-reperfusion induced acute renal failure in the rat and suggest that PBN may be a useful agent for the prevention of renal ischemia-reperfusion damage.

Relationship between free radical production and lipid peroxidation during ischemia-reperfusion injury in the rat brain

Forebrain ischemia was produced in the rat by bilateral occlusion of the common carotid arteries combined with hemorrhagic hypotension (30 mmHg). The whole cerebral cortex was homogenized in the presence of the spin trap agent N-tert-butyl-alpha-phenyl-nitrone, followed by a Folch extract. Spin-adducts were detected using electron spin resonance spectroscopy. The lipid peroxidation was estimated from both the amount of thiobarbituric acid reactive substance and the formation of conjugated diene. After 10 or 20 min of ischemia, reperfusion was initiated which induced an abrupt burst of free radical formation. The formation peaked at 5 min, and the peak value increased with the ischemia time. The degree of lipid peroxidation, which was measured after 20 min of reperfusion, also increased with the ischemia time. The results suggest that the lipid peroxidation may be the direct consequence of the action of free radicals formed during ischemia and reperfusion periods.

Noninvasive measures of oxidative stress status in humans

Although oxidative stress is thought to be involved in the pathophysiology of several diseases and aging, it is not routinely measured in clinical diagnosis. This is at least partly because accepted and standardized methods for measuring oxidative stress in humans are not yet established. One of the greatest needs in the field of free radical biology is the development of reliable methods for measuring oxidative stress status (OSS) in humans. A listing of some analytical approaches to measuring oxidative stress is provided as well as a listing of some noninvasive techniques that have been used in humans.

The free radical trapping agent N-tert.-butyl-alpha-phenylnitrone (PBN) attenuates cerebral ischaemic injury in gerbils

Several studies have suggested that oxygen-derived free radicals play an important role in the genesis of ischaemia-induced neuronal damage. We report here that the spin trap agent, N-tert.-butyl-alpha-phenylnitrone (PBN) reduced neuronal damage in gerbils subjected to forebrain ischaemia. PBN (100 mg/kg) administered either 30 min. prior to, or 30 min. after a 5 min. period of bilateral carotid occlusion prevented the increase in locomotor activity observed in saline-injected ischaemic animals and significantly reduced the damage to the hippocampal CAI pyramidal cell layer observed 5 days post-ischaemia. Telemetry measurements of body temperature revealed that administration of PBN and the induction of cerebral ischaemia were associated with small reductions in body temperature, but these changes were not significant. PBN (100 mg/kg) administered 2 hr post-ischaemia failed to protect against cerebral ischaemia. These findings support the hypothesis of an involvement of free radicals in ischaemia-reperfusion induced cerebral damage and suggest that spin trap agents may be useful for the prevention of cerebral ischaemic damage.