Role of antioxidants in the nitric oxide-elicited inhibition of dopamine uptake in cultured mesencephalic neurons. Insights into potential mechanisms of nitric oxide-mediated neurotoxicity

Transcranial photobiomodulation ameliorates midbrain and striatum neurochemical impairments and behavioral deficits in reserpine-induced parkinsonism in rats

Photobiomodulation (PBM) of deep brain structures through transcranial infrared irradiation might be an effective treatment for Parkinson's disease (PD). However, the mechanisms underlying this intervention should be elucidated to optimize the therapeutic outcome and maximize therapeutic efficacy. The present study aimed at investigating the oxidative stress-related parameters of malondialdehyde (MDA), nitric oxide (NO), and reduced glutathione (GSH) and the enzymatic activities of sodium-potassium-ATPase (Na+, K+-ATPase), Acetylcholinesterase (AChE), and monoamine oxidase (MAO) and monoamine levels (dopamine (DA), norepinephrine (NE) and serotonin (5-HT) in the midbrain and striatum of reserpine-induced PD in an animal model treated with PBM. Furthermore, the locomotor behavior of the animals has been determined by the open field test. Animals were divided into three groups; the control group, the PD-induced model group, and the PD-induced model treated with the PBM group. Non-invasive treatment of animals for 14 days with 100 mW, 830 nm laser has demonstrated successful attainment in the recovery of oxidative stress, and enzymatic activities impairments induced by reserpine (0.2 mg/kg) in both midbrain and striatum of adult male Wistar rats. PBM also improved the decrease in DA, NE, and 5-HT in the investigated brain regions. On a behavioral level, animals showed improvement in their locomotion activity. These findings have shed more light on some mechanisms underlying the treatment potential of PBM and displayed the safety, easiness, and efficacy of PBM treatment as an alternative to pharmacological treatment for PD.

Immunotoxicity of mercury: Pathological and toxicological effects

Mercury (Hg) is toxic and hazardous metal that causes natural disasters in the earth's crust. Exposure to Hg occurs via various routes; like oral (fish), inhalation, dental amalgams, and skin from cosmetics. In this review, we have discussed the sources of Hg and its potential for causing toxicity in humans. In addition, we also review its bio-chemical cycling in the environment; its systemic, immunotoxic, genotoxic/carcinogenic, and teratogenic health effects; and the dietary influences; as well as the important considerations in risk assessment and management of Hg poisoning have been discussed in detail. Many harmful outcomes have been reported, which will provide more awareness.

Reactive Oxygen Species: Physiological and Physiopathological Effects on Synaptic Plasticity

In the mammalian central nervous system, reactive oxygen species (ROS) generation is counterbalanced by antioxidant defenses. When large amounts of ROS accumulate, antioxidant mechanisms become overwhelmed and oxidative cellular stress may occur. Therefore, ROS are typically characterized as toxic molecules, oxidizing membrane lipids, changing the conformation of proteins, damaging nucleic acids, and causing deficits in synaptic plasticity. High ROS concentrations are associated with a decline in cognitive functions, as observed in some neurodegenerative disorders and age-dependent decay of neuroplasticity. Nevertheless, controlled ROS production provides the optimal redox state for the activation of transductional pathways involved in synaptic changes. Since ROS may regulate neuronal activity and elicit negative effects at the same time, the distinction between beneficial and deleterious consequences is unclear. In this regard, this review assesses current research and describes the main sources of ROS in neurons, specifying their involvement in synaptic plasticity and distinguishing between physiological and pathological processes implicated.

Pharmacological targeting of redox regulation systems as new therapeutic approach for psychiatric disorders: A literature overview

Redox dysregulation occurs following a disequilibrium between reactive oxygen species (ROS) producing and degrading systems, i.e. mitochondria, nicotinamide adenine dinucleotide phosphate (NADPH) oxidases and nitric oxide synthase (NOS) on one hand and the principal antioxidant system, the glutathione, on the other hand. Increasing recent evidence points towards a pathogenetic role of an altered redox state in the development of several mental disorders, such as anxiety, bipolar disorders, depression, psychosis, autism and post-traumaticstress disorders (PTSD). In this regard, pharmacological targeting of the redox state regulating systems in the brain has been proposed as an innovative and promising therapeutic approach for the treatment of these mental diseases. This review will summarize current knowledge obtained from both pre-clinical and clinical studies in order to descant "lights and shadows" of targeting pharmacologically both the producing and degrading reactive oxygen species (ROS) systems in psychiatric disorders.

Nitric oxide and DOPAC-induced cell death: from GSH depletion to mitochondrial energy crisis

The molecular mechanisms inherent to cell death associated with Parkinson's disease are not clearly understood. Diverse pathways, sequence of events and models have been explored in several studies. Recently, we have proposed an integrative mechanism, encompassing the interaction of nitric oxide (•NO) and a major dopamine metabolite, dihydroxyphenylacetic (DOPAC), leading to a synergistic mitochondrial dysfunction and cell death that may be operative in PD. In this study, we have studied the sequence of events underlying the mechanisms of cell death in PC12 cells exposed to •NO and DOPAC in terms of: a) free radical production; b) modulation by glutathione (GSH); c) energetic status and d) outer membrane mitochondria permeability. Using Electron Paramagnetic Resonance (EPR) it is shown the early production of oxygen free radicals followed by a depletion of GSH reflected by an increase of GSSG/GSH ratio in the cells treated with the mixture of •NO/DOPAC, as compared with the cells individually exposed to each of the stimulus. Glutathione ethyl ester (GSH-EE) and N-acetylcysteine (NAC) may rescue cells from death, increasing GSH content and preventing ATP loss in cells treated with the mixture DOPAC/•NO but failed to exert similar effects in the cells challenged only with •NO. The depletion of GSH is accompanied by a decreased activity of mitochondrial complex I. At a later stage, the concerted action of DOPAC and •NO include a rise in the ratio Bax/Bcl-2, an observation not evident when cells were exposed only to •NO. The results support a free radical-induced pathway leading to cell death involving the concerted action of DOPAC and •NO and the critical role of GSH in maintaining a functional mitochondria.

Nitric oxide (NO) scavenging capacity of natural antioxidants

Nitric oxide (NO)-scavenging capacities of several hydrophilic antioxidants were determined by using the PTIO method, a competitive NO-scavenging method with 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO). Relative NO-scavenging rates of antioxidants were measured with respect to PTIO and the scavenging rate constants were calculated based on PTIO's rate constant. Results indicated that NO-scavenging rate constants of the antioxidants were: uric acid (2.5)>caffeic acid (1.2)>trolox (1.0)>genistein (0.19)>glutathione (0) ≈N-acetylcysteine (0), where the numbers are expressed in trolox equivalent unit. The oxidation potentials of these antioxidants were measured and the order in the magnitude of oxidation potential was in good accordance with NO-scavenging capacity. Based on the results, we have suggested that the primary chemical process of the antioxidant reaction with NO can be characterised with the electron transfer from NO to the antioxidant.

Peroxynitrite and myocardial contractility: in vivo versus in vitro effects

Generation of peroxynitrite (ONOO-) as a result of altered redox balance has been shown to affect cardiac function; however, inconsistencies in the data exist, particularly for myocardial contractility. The hypothesis that the cardiac impact of ONOO- formation depends on its site of generation, intravascular or intramyocardial, was examined. Cardiac contractility was assessed by pressure-volume analysis to delineate vascular versus cardiac changes on direct infusion of ONOO- into the right atria of conscious dogs both with normal cardiac function and in heart failure. Additionally, ONOO- was administered to isolated murine cardiomyocytes to mimic in situ cardiac generation. When infused in vivo, ONOO- had little impact on inotropy but led to systemic arterial dilation, likely as a result of rapid decomposition to NO2- and NO3-. In contrast, infused ONOO- was long lived enough to abolish beta-adrenergic (dobutamine)-stimulated contractility/relaxation, most likely through catecholamine oxidation to aminochrome. When administered to isolated murine cardiomyocytes, ONOO- induced a rapid reduction in sarcomere shortening and whole cell calcium transients, although neither decomposed ONOO- or NaNO2 had any effect. Thus, systemic generation of ONOO- is unlikely to have primary cardiac effects, but may modulate cardiac contractile reserve, via blunted beta-adrenergic stimulation, and vascular tone, as a result of generation of NO2- and NO3-. However, myocyte generation of ONOO- may impair contractile function by directly altering Ca2+ handling. These data demonstrate that the site of generation within the cardiovascular system largely dictates the ability of ONOO- to directly or indirectly modulate cardiac pump function.

Inhibitory effect of curcumin on nitric oxide production from lipopolysaccharide-activated primary microglia

Curcumin has been shown to exhibit anti-inflammatory, antimutagenic, and anticarcinogenic activities. However, the modulatory effect of curcumin on the functional activation of primary microglial cells, brain mononuclear phagocytes causing the neuronal damage, largely remains unknown. The current study examined whether curcumin influenced NO production in rat primary microglia and investigated its underlying signaling pathways. Curcumin decreased NO production in LPS-stimulated microglial cells in a dose-dependent manner, with an IC(50) value of 3.7 microM. It also suppressed both mRNA and protein levels of inducible nitric oxide synthase (iNOS), indicating that this drug may affect iNOS gene expression process. Indeed, curcumin altered biochemical patterns induced by LPS such as phosphorylation of all mitogen-activated protein kinases (MAPKs), and DNA binding activities of nuclear factor-kappaB (NF-kappaB) and activator protein (AP)-1, assessed by reporter gene assay. By analysis of inhibitory features of specific MAPK inhibitors, a series of signaling cascades including c-Jun N-terminal kinase (JNK), p38 and NF-kappaB was found to play a critical role in curcumin-mediated NO inhibition in microglial cells. The current results suggest that curcumin is a promising agent for the prevention and treatment of both NO and microglial cell-mediated neurodegenerative disorders.

Nitric oxide donors inhibit 5-hydroxytryptamine (5-HT) uptake by the human 5-HT transporter (SERT)

1. The aim was to test the hypothesis that nitric oxide (NO) donor drugs can inhibit the 5-hydroxytryptamine (5-HT) transporter, SERT. 2. The NO donors, MAHMA/NO (a NONOate; (Z)-1-[N-methyl-N-[6-(N-methylammoniohexyl)-amino]]diazen-1-ium-1,2-diolate), SIN-1 (a sydnonimine; 5-amino-3-(4-morpholinyl)-1,2,3-oxadiazolium chloride), FK409 (an oxime; (+/-)-(4-ethyl-2E-(hydroxyimino)-5-nitro-3E-hexenamide)) and peroxynitrite, but not Angeli's salt (source of nitroxyl anion) or sodium nitrite, caused concentration-dependent inhibition of the specific uptake of [3H]-5-HT in COS-7 cells expressing human SERT. 3. Superoxide dismutase (150 U ml(-1)) plus catalase (1200 U ml(-1)), used to remove superoxide and hence prevent peroxynitrite formation, prevented the inhibitory effect of SIN-1 (which generates superoxide) but not of MAHMA/NO or FK409. 4 The inhibitory effects of the NO donors were not affected by the free radical scavenger, hydroxocobalamin (1 mM) or the guanylate cyclase inhibitor, ODQ (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one; 3 microM). 5. L-Cysteine (1 mM; source of excess thiol residues) abolished or markedly reduced the inhibitory effects of MAHMA/NO, SIN-1, FK409 and peroxynitrite. 6. It is concluded that inhibition of SERT by the NO donors cannot be attributed exclusively to NO free radical nor to nitroxyl anion. It does not involve guanosine-3',5'-cyclic monophosphate, but may involve nitrosation of cysteine residues on the SERT protein. Peroxynitrite mediates the effect of SIN-1, but not the other drugs. 7. Data in mice with hypoxic pulmonary hypertension suggest that SERT inhibitors may attenuate pulmonary vascular remodelling. Thus, NO donors may be useful in pulmonary hypertension, not only as vasodilators, but also because they inhibit SERT, provided they display this effect in vivo at appropriate doses.

Nitric oxide inhibits uptake of dopamine and N-methyl-4-phenylpyridinium (MPP+) but not release of MPP+ in rat C6 glioma cells expressing human dopamine transporter

1. Conflicting results have been reported regarding the influence of nitric oxide (NO) and peroxynitrite on dopamine (DA) uptake and release. In the present study, effects of NO donors were studied in rat C6 glioma cells expressing human DA transporter. 2. [(3)H]-DA uptake was inhibited by S-nitroso-thiol S-nitroso-N-acetylpenicillamine, spermine/NO, diethylamine/NO (DEA/NO), (Z)-1-[N-(3-ammoniopropyl)-N-(n-propyl)-amino]/NO (PAPA/NO), and 3-morphosynodiomine (SIN-1) in a rank order correlating with their half lives as NO donors, whereas no effect was observed for diethylenetriamine/NO and dipropylenetriamine/NO, which release NO very slowly. 3. Hydroxycobalamin, a NO scavenger, but not superoxide dismutase and catalase, enzymes that metabolize superoxide and hydrogen peroxide, respectively, abolished the inhibitory effect of DEA/NO and SIN-1, indicating that they inhibit DA uptake through a mechanism related to the production of NO but unrelated to the formation of peroxynitrite. In consonance, peroxynitrite did not alter DA uptake in the present system. 4. DEA/NO and PAPA/NO reduced [(3)H]-MPP(+) uptake, whereas the release of [(3)H]-MPP(+) was not modified, demonstrating that NO can inhibit uptake of DA transporter substrate without accelerating DA transporter-mediated reverse transport of substrate under the same conditions.

Aroclor 1254-induced cytotoxicity in catecholaminergic CATH.a cells related to the inhibition of NO production

The neuronal nitric oxide synthase (nNOS) specific inhibitor, 7-nitroindazole (7-NI), and the nitric oxide (NO) donor (S-nitroso-N-acetylpenicillarnine, SNAP) were used to study the role of NO in polychlorinated biphenyl (PCB: Aroclor 1254)-induced cytotoxicity in the immortalized dopaminergic cell line (CATH.a cells), derived from the central nervous system of mice. Treatment of the dopaminergic cells with various concentrations of Aroclor 1254 (0.5-10 microg/ml), a commercial PCB mixture, showed significant cytotoxicity as evaluated by lactate dehydrogenase (LDH) release and assessment of cell viability, depending on the concentration used. We also observed that Aroclor 1254 treatment reduced the level of nNOS expression. Furthermore, the cytotoxicity of Aroclor 1254 was augmented by 10 microM of 7-NI, which alone did not produce cytotoxicity, while it was protected by treatment with SNAP. Depending on the concentrations of Aroclor 1254 used, intracellular dopamine and dihydroxyphenylacetic acid (DOPAC) concentrations were significantly decreased. Therefore, these results suggest that PCBs have the potential for dopaminergic neurotoxicity, which may be related with the PCBs-mediated alteration of NO production originating from nNOS at least in part.

Oxidation of DOPAC by nitric oxide: effect of superoxide dismutase

This study aimed to characterize the redox interaction between 3,4-dihydroxyphenylacetic acid (DOPAC) and nitric oxide (.NO), and to assess the reductive and oxidative decay pathways of the DOPAC semiquinone originating from this interaction. The reaction between DOPAC and.NO led to the formation of the DOPAC semiquinone radical, detected by electron paramagnetic resonance (EPR) and stabilized by Mg(2+), and the nitrosyl anion detected as nitrosylmyoglobin. The EPR signal corresponding to the DOPAC semiquinone was modulated as follows: (i) it was suppressed by glutathione and ascorbic acid with the formation of new EPR spectra corresponding to the glutathionyl and ascorbyl radical, respectively; (ii) it was enhanced by Cu,Zn-superoxide dismutase; the enzyme also accelerated the decay of the semiquinone species to DOPAC quinone. These results are interpreted as a one-electron oxidation of DOPAC by.NO; the reductive decay of the semiquinone back to DOPAC was facilitated by reducing agents, such as glutathione and ascorbate, whereas the oxidative decay to DOPAC quinone was facilitated by superoxide dismutase. The latter effect is understood in terms of a reversible conversion of nitrosyl anion to.NO by the enzyme. The biological relevance of these reactions is also discussed in terms of the reactivity of peroxynitrite towards DOPAC as a model with implications for aerobic conditions.

Modulation of chemokine production in lung microvascular endothelial cells by dopamine is mediated via an oxidative mechanism

Serum concentrations of catecholamines are high in patients with sepsis or acute respiratory distress syndrome (ARDS). Because chemokines mediate the recruitment of neutrophils into inflammatory sites, we addressed the question of whether dopamine (DA) is able to influence chemokine production in endothelial cells under basal and proinflammatory conditions. To this end, lung microvascular endothelial cells (LMVEC) were stimulated or not for 24 h with the bacterial toxins lipopolysaccharide (LPS) (1 microg/ml) or lipoteichonic acid (LTA) (10 microg/ml) in the presence or absence of various concentrations of DA (1-100 microg/ml). Whereas under basal and stimulatory conditions, the addition of DA to endothelial cells dose-dependently increased IL-8 production, the production of ENA-78 and Gro-alpha was significantly inhibited (P < 0.01). This effect could still be demonstrated when the cells were stimulated for up to 3 h with LPS before DA administration. Similar findings were detected for the mRNA expression of these chemokines. The influence of DA on chemokine production was not receptor mediated and could be prevented by antioxidants or radical scavengers. Moreover, addition of H(2)O(2) to endothelial cells gave results similar to those observed with DA stimulation, suggesting a pivotal role for reactive oxygen species in DA-mediated modulation of chemokine production in endothelial cells. Our data thus demonstrate that DA administration results in the induction of oxidative stress, with profound effects on endothelial chemokine production.

The effects of nitric oxide on the oxidations of l-dopa and dopamine mediated by tyrosinase and peroxidase

The effects of nitric oxide (NO) on both tyrosinase/O(2)- and horseradish peroxidase/H(2)O(2)-mediated oxidations of dopamine and its o-dihydric phenol precursor l-dopa were compared with autoxidative processes and quantitatively assessed by oxidative and reductive electrochemical detection systems. In peroxidase/H(2)O(2)/NO-catalyzed reactions, significantly more substrate was oxidized than in the corresponding control incubations lacking NO. In tyrosinase/O(2)/NO-promoted reactions the total amounts of l-dopa and dopamine oxidized were significantly less than the amounts of the substrates oxidized by enzyme alone. These data indicate that the activity of the heme protein peroxidase was enhanced by NO, whereas tyrosinase, a copper-containing monoxygenase, was inhibited. The NO-mediated reduction of tyrosinase/O(2) activity may be attributed to the formation of an inhibitory copper.nitrosyl complex. An oxidized nitrodopamine derivative, considered to be either the quinone or semiquinone of 6-nitrosodopamine, was generated in peroxidase/H(2)O(2)/NO-mediated reactions with dopamine along with two oxidized melanin precursors, dopamine quinone and dopaminechrome. No corresponding nitroso compound was formed in reactions involving l-dopa or in any of the tyrosinase-mediated reactions. The formation of such a noncyclized nitrosodopamine represents an important alternative pathway in catecholamine metabolism, one that by-passes the formation of cytoprotective indole precursors of melanin. The results of this investigation suggest that cellular integrity and function can be adversely affected by NO-promoted oxidations of dopamine and other catechols, reactions that not only accelerate their conversion to reactive quinones but also form potentially cytotoxic noncyclized nitroso derivatives. Reduced levels of dopamine in the brain through NO-enhanced oxidation of the catecholamine will almost certainly be manifested by diminished levels of the dopamine-derived brain pigment neuromelanin.

Oxidation of adrenaline and its derivatives by S-nitrosoglutathione

An oxidizing effect of S-nitrosoglutathione toward adrenaline and its cyclic derivatives (adrenochrome and adrenolutin) is reported. The oxidation was monitored either spectrophotometrically or as oxygen uptake. Adrenaline was first oxidized to adrenochrome that, after isomerization to adrenolutin, was further oxidized to products monitored as fluorescence decrease. To occur to a significant extent, this oxidation requires copper ions that, in addition to a direct effect on the oxidation of the ortho-diphenol moiety, are also able to decompose nitrosothiols, giving rise to nitric oxide. The latter, after interaction with oxygen and superoxide, produces nitrogen oxides and peroxynitrite, respectively, that are important contributors to the oxidative process. In this context, catecholamines might act as regulatory factors toward nitric oxide and its derivatives.

Role of nitric oxide in the regulation of monoaminergic neurotransmission

Data accumulated in the last decade indicate that nitric oxide (NO) participates in the regulation of neurotransmission in the central nervous system. Due to its physicochemical properties, NO is an ideal mediator of nonsynaptic interactions. The importance of monoaminergic systems in the function of the brain is clearly shown by the number of severe neuropsychiatric diseases (e.g. depression, Parkinson's disease) caused by the impairment of monoaminergic neurotransmission. Because of their neuroanatomical characteristic, monoaminergic systems participate mainly in nonsynaptic interactions. Since NO is a potential nonsynaptic modulator, it may have an important role in the regulation of monoaminergic systems. The aim of the present review is to survey the literature on the effect of NO on dopaminergic, noradrenergic and serotonergic neurotransmission. The potential mechanisms of action are summarized. Since there is no agreement in the literature on the nature of the effect of NO exerted on monoaminergic neurotransmission, and there are contradictory data concerning the mechanisms involved, the possible reasons for this unusual inconsistency are also discussed.

Reactive oxygen species and reactive nitrogen species: relevance to cyto(neuro)toxic events and neurologic disorders. An overview

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are formed under physiological conditions in the human body and are removed by cellular antioxidant defense system. During oxidative stress their increased formation leads to tissue damage and cell death. This process may be especially important in the central nervous system (CNS) which is vulnerable to ROS and RNS damage as the result of the brain high O(2) consumption, high lipid content and the relatively low antioxidant defenses in brain, compared with other tissues. Recently there has been an increased number of reports suggesting the involvement of free radicals and their non-radical derivatives in a variety of pathological events and multistage disorders including neurotoxicity, apoptotic death of neurons and neural disorders: Alzheimer's (AD), Parkinson's disease (PD) and schizophrenia. Taking into consideration the basic molecular chemistry of ROS and RNS, their overall generation and location, in order to control or suppress their action it is essential to understand the fundamental aspects of this problem. In this presentation we review and summarize the basics of all the recently known and important properties, mechanisms, molecular targets, possible involvement in cellular (neural) degeneration and apoptotic death and in pathogenesis of AD, PD and schizophrenia. The aim of this article is to provide an overview of our current knowledge of this problem and to inspire experimental strategies for the evaluation of optimum innovative therapeutic trials. Another purpose of this work is to shed some light on one of the most exciting recent advances in our understanding of the CNS: the realisation that RNS pathway is highly relevant to normal brain metabolism and to neurologic disorders as well. The interactions of RNS and ROS, their interconversions and the ratio of RNS/ROS could be an important neural tissue injury mechanism(s) involved into etiology and pathogenesis of AD, PD and schizophrenia. It might be possible to direct therapeutic efforts at oxidative events in the pathway of neuron degeneration and apoptotic death. From reviewed data, no single substance can be recommended for use in human studies. Some of the recent therapeutic strategies and neuroprotective trials need further development particularly those of antioxidants enhancement. Such an approach should also consider using combinations of radical(s) scavengers rather than a single substance.

The role of adrenochrome in stimulating the oxidation of catecholamines

Adrenochrome, a stable oxidation product formed after oxidation of adrenaline, strongly stimulates oxygen uptake occurring during the autoxidation of adrenaline, other catecholamines and ascorbate. Oxygen consumed is converted to hydrogen peroxide suggesting the occurrence of a redox cycling process. The reduction of adrenochrome operated by adrenaline is accelerated by the exclusion of oxygen indicating that the oxidation of adrenaline occurs directly and superoxide anion does not necessarily mediate it. Oxygen consumption, observed in the catecholamine/adrenochrome and ascorbate/adrenochrome systems, is due to the autoxidation of leucoadrenochrome that, at variance with adrenaline, easily autoxidizes also at physiological pH. Therefore, in these systems, leucoadrenochrome appears to be the major determinant of the production of superoxide anion.

Nitric oxide modulates beta(2)-adrenergic receptor palmitoylation and signaling

To determine whether nitric oxide (NO) modulates the beta-adrenergic signaling pathway, we treated cells expressing beta(2)-adrenergic receptors (beta(2)AR) with the NO donors, 3-morpholinosydnonimine (SIN-1) and 1,2,3,4-oxatriazolium, 5-amino-3-(3-chloro-2-methylphenyl)chloride and determined the intracellular production of cAMP after exposure to beta-adrenergic receptor agonists, cholera toxin and forskolin. NO significantly decreased the potency of the beta-adrenergic agonist, isoproterenol, to stimulate cAMP production without affecting the stimulatory action of forskolin and cholera toxin, which directly activate adenylyl cyclase and G(s), respectively. Treatment with the NO donor increased the guanyl nucleotide-sensitive high affinity constant for the agonist, isoproterenol, thus suggesting that it reduced functional coupling between the receptor and G(s). Stimulation of endogenous NO production by lipopolysaccharide in RAW 264.7 macrophages also caused a significant increase in the EC(50) for isoproterenol-stimulated cAMP production. SIN-1 treatment also led to a reduction in both basal and isoproterenol-stimulated incorporation of [(3)H]palmitate into the beta(2)AR. Signaling through the nonpalmitoylated, Gly(341)beta(2)AR mutant was unchanged by SIN-1 treatment. Given the link between beta(2)AR palmitoylation and its responsiveness to agonist, these results suggest that the primary action of NO was depalmitoylation of the beta(2)AR resulting in decreased signaling through the beta(2)AR.

A rat brain fraction and different purified peroxidases catalyzing the formation of dopaminochrome from dopamine

Dopaminochrome formation is catalyzed by commercially available purified peroxidases (EC 1.11.1.7) such as horseradish, lacto- and myelo-peroxidase using dopamine, hydrogen peroxide or promethazine sulfoxide as substrates. A rat brain fraction (RBF) catalyzes a similar reaction and its catalytic power increases after preincubation with hydrogen peroxide/ascorbic acid. The activity of both the purified enzymes and the RBF preparation is inhibited by carnosine and characterized by excess substrate inhibition. The enzymes recognize different substrates but show the highest affinity for dopamine. The RBF fraction is strongly buffered against oxidation by compounds such as glutathione and by bioreductive enzymes such as DT-diaphorase (EC 1.6.99.2) which can use as a substrate menadione or dopaminochrome. The rat brain dopamine peroxidizing activity appeared to be mostly bound to the synaptosomal fraction. The reaction catalyzed by the purified peroxidases was followed by electron spin resonance spectroscopy and, unlike that catalyzed by RBF, was shown to produce the signal of a transient dopamine-o-semiquinone radical.

Redox mechanisms at the glutamate synapse and their significance: a review

This paper reviews what is currently known about the redox state of the glutamate synapse and its possible role in modulating synaptic plasticity and thus learning and neurocomputation. The hypothesis is presented that the growth or pruning of the synaptic spine is controlled in part by the balance in the synapse between neurodestructive pro-oxidants (e.g., nitric acid radical and hydrogen peroxide) and neuroprotective antioxidants (e.g., ascorbate and carnosine). In addition, there may be a role for catecholamines, in particular dopamine, related to its role in reinforcement signalling. Activation of the dopamine D2 receptor induces the synthesis of an antioxidant enzyme, possibly catalase. Dopamine may also affect the redox balance in the glutamate synapse directly by diffusion from the adjacent dopaminergic bouton-en-passage. Catecholamines are powerful antioxidants, scavengers of free radicals and iron chelators. Catecholamine-iron complexes are potent dismuters of superoxide ions. Additional agents participating in spine pruning may be neurotoxic catecholamine o-quinones present in the brain. This system may be at fault in schizophrenia and Parkinson's disease. Experiments to test the hypothesis are suggested.

The neurochemical basis of learning and neurocomputation: the redox theory

This paper presents a new theory of the biochemical basis of learning and neurocomputation. It has now been determined that excitatory synapses on dendritic spines in the brain are continually being formed and removed. This requires a neurochemical mechanism. There is evidence to suggest that the redox state of the glutamate synapse plays an important role in determining the growth or deletion of that synapse. This redox state is controlled by the balance between the pro-oxidants hydrogen peroxide and the nitric acid radical, and the antioxidants ascorbate, carnosine, the nitrosium ion and catecholamines. Key enzymes involved are prostaglandin H synthase and nitric acid synthase. Mediation of signals of reinforcing stimuli by the catecholamines may be mediated in part by their antioxidant effect on glutamate synapses. Some experiments to test the theory are suggested.

Sodium nitroprusside blocks the cat carotid chemosensory inhibition induced by dopamine, but not that by hyperoxia

We studied the effects of the nitric oxide (NO) synthase inhibitor, Nomega-nitro-L-arginine methyl ester (L-NAME), and the NO donor, sodium nitroprusside (SNP) on cat chemosensory responses to intravenous injections of NaCN (0.1-100 microg/kg) and dopamine (0. 1-20 microg/kg), and to hyperoxic ventilation (100% O2, 60-120 s). Cats were anesthetized with sodium pentobarbitone, paralyzed and artificially ventilated to prevent secondary ventilatory effects. The frequency of chemosensory discharges (fx) was recorded from one sectioned carotid sinus nerve. L-NAME (50 mg/kg i.v.) increased basal fx and slightly potentiated the responses to NaCN and dopamine. SNP (1-2 mg/kg i.v.) increased basal fx, but reduced the NaCN-induced increases of fx over baseline and the transient fx inhibitions induced by dopamine, but not those produced by hyperoxia. Present results indicate that besides the known inhibitory effect of NO on chemosensory responses to low PO2, NO also blocks the chemosensory response to dopamine, leaving hyperoxic responses largely unchanged.

The oxidative metabolism of catecholamines in the brain: a review

This paper summarizes the strong evidence that we now have that the oxidative pathway of metabolism of the catecholamines, dopamine and norepinephrine via their respective quinones occurs in vivo in the brain. This fact is not yet widely appreciated. The evidence is based on the chemical structure of neuromelanin, advanced mass spectrometry techniques and the identification of intermediates of this system, such as 5-cysteinyl dopamine, in the brain. Supportive evidence is presented from a number of sources including enzymology. A suggestion as to the possible normal function of this system is made.

Nitric oxide induces cell death in a catecholaminergic cell line derived from the central nervous system

The nitric oxide (NO) donors, sodium nitroprusside (SNP), 1-[2-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium+ ++-1,2-diolate] (DETA NONOate), and S-nitroso-N-acetyl-D,L-penicillamine (SNAP) produce a dose-dependent increase in cell death in a catecholaminergic cell line (CATH.a) derived from the central nervous system. Cell death is associated with a decrease in mitochondrial membrane potential. Dopamine also induced cell death of CATH.a cells and this was potentiated by concentrations of SNP which alone did not produce cell death. Hemoglobin, a scavenger of NO radicals, blocked SNP- and SNAP-induced cell death. Catalase and superoxide dismutase, enzymes that metabolize H2O2 and superoxide, respectively, did not inhibit SNP- or SNAP-induced cell death. These data indicate that NO donors produce cell death in CATH.a cells through a mechanism related to the production of NO and the loss of the mitochondrial membrane potential but unrelated to the production of H2O2.

Impaired mitochondrial function, oxidative stress and altered antioxidant enzyme activities following traumatic spinal cord injury

Glutamate-induced excitotoxicity involving the formation of reactive oxygen species (ROS) has been implicated in neuronal dysfunction and cell loss following ischemic and traumatic injury to the central nervous system (CNS). ROS are formed in mitochondria when energy metabolism is compromised, and are inactivated by the ROS scavengers superoxide dismutase (SOD), catalase, and glutathione (GSH). ROS can impair the function of several cellular components including proteins, nucleic acids, and lipids. In the present study, we measured indicators of mitochondrial metabolic activity, ROS formation, lipid peroxidation, and antioxidant enzyme activities in synaptosomes obtained from rat spinal cord at early times following traumatic injury. Mitochondrial metabolic activity was found to significantly decrease as early as 1 h following injury, and continued to be compromised over the remaining postinjury time points. ROS formation was found to be significantly increased at 4 and 24 h following injury, while lipid peroxidation levels were found to be significantly increased in the injured spinal cord at 1 and 24 h, but not 4 h following injury. SOD enzyme activity was unchanged at all postinjury time points, while catalase activity and GSH levels were significantly increased at 24 h following injury. These findings indicate that impaired mitochondrial function, ROS, and lipid peroxidation occur soon after traumatic spinal cord injury, while the compensatory activation of molecules important for neutralizing ROS occurs at later time points. Therapeutic strategies aimed at facilitating the actions of antioxidant enzymes or inhibiting ROS formation and lipid peroxidation in the CNS may prove beneficial in treating traumatic spinal cord injury, provided such treatments are initiated at early stages following injury.

Oxidation and nitration of catecholamines by nitrogen oxides derived from nitric oxide

The reactivity of catecholamines with nitrogen oxides formed from NO in aerated solutions, nitrite, and peroxynitrite was evaluated. Dopamine and norepinephrine in aerobic buffer (pH 7.4) were almost completely converted to their 6-nitro-derivatives by nitric oxide (NO) at room temperature, while epinephrine was nitrated and above all oxidized. The products obtained from each catecholamine treated with sodium nitrite at pH 4-7 were compared to those produced by NO at pH 7.4. Peroxynitrite, which can nitrate tyrosinyl residues, did not produce nitro-derivatives, only oxidized ones. The physiological relevance, particularly for the vascular and nervous system, is discussed. Catecholamine oxidation reactions could be relevant to physiological conditions and also explain neurotoxicity in Parkinson's disease and aging. Nitration reactions, requiring such high NO concentrations, do not seem possible to occur directly under normal physiological conditions, but could take place in acidic vesicules where nitrite, catecholamines, and their nitrated products could accumulate. Finally, the ability of dopamine to increase 2',5'-cyclic adenosine monophosphate (cAMP) formation in cultured striatal neurons was blocked by its nitration by NO or its nitrogen oxide derivatives.

The biochemical basis of synaptic plasticity and neurocomputation: a new theory

The recent finding that dendritic spines (on which 90% of all excitatory synapses on pyramidal cells are formed) are not permanent structures but are continually being formed and adsorbed has implications for the present theoretical basis of neurocomputation, which is largely based on the concept of fixed nerve nets. This evidence would tend to support the recent theories of Edelman, Freeman, Globus, Pribram and others that neuronal networks in the brain operate mainly as nonlinear dynamic, chaotic systems. This paper presents a hypothesis of a possible neurochemical mechanism underlying this synaptic plasticity based on reactive oxygen species and toxic 0-semiquinones derived from catecholamines (i) by the enzyme prostaglandin H synthetase induced by glutamatergic NMDA receptor activation and (ii) by reactive nitrogen species derived from nitric oxide in a low ascorbate environment. A key factor in this neuromodulation may be the fact that catecholamines are potent antioxidants and free radical scavengers and are thus able to affect the redox mediated balance at the glutamate receptors between synapse formation and synapse removal that may be a key factor in neurocomputational plasticity. But catecholamines are also easily oxidized to neurotoxic 0-semiquinones and this may be relevant to the pathology of several diseases including schizophrenia. The relationship between dopamine release and positive reinforcement is relevant to this hypothesis.