7-Nitroindazole prevents dopamine depletion caused by low concentrations of MPP+ in rat striatal slices

Acute restraint increases varicosity density and reduces the inter-varicosity distance in NADPH diaphorase-containing neurons in the rat dorsolateral periaqueductal gray matter

The periaqueductal gray (PAG) is important for the organization of organismal response to different types of stress and painful stimuli. Its dorsolateral (dlPAG) column is distinctly characterized by the presence of nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d), which in many brain regions, is an indication of constitutive nitric oxide (NO) synthase (NOS)-containing neurons. Different stress paradigms activate the dlPAG NOS machinery presumably by a presynaptic influence of NO on dlPAG neurons to modulate the nuclear dynamics to elicit an appropriate response. Since presynaptic components of synapses reside in axonal varicosities, this study assessed the number of varicosities and inter-varicosity spacing of NADPH-d neurons in the dlPAG of free-behaving (control) and acutely restrained male rats. The study tested the hypothesis that stress-induced increase in endogenous NO synthesis involved changes in synaptic density and inter-varicosity spacing and therefore, a non-synaptic component of NO involvement in the dlPAG response to stress. Compared with control, the number of NADPH-d-positive cells, the staining intensity and the number of varicosities per microgram tissue were significantly higher in restrained animals. Also, the inter-varicosity spacing was significantly higher in control than restrained rats, presumably due to the increase in varicosities induced by restraint. Since neural connectivity and synaptogenesis depend on mean varicosity spacing and pattern of varicosity, respectively, the present observations suggest a mechanism whereby restraint stress induces increased activity via synaptic and non-synaptic NO-mediated neurotransmission within the dlPAG.

Nitration of soluble proteins in organotypic culture models of Parkinson's disease

Protein nitration due to oxidative and nitrative stress has been linked to the pathogenesis of Parkinson's disease (PD), but its relationship to the loss of dopamine (DA) or tyrosine hydroxylase (TH) activity is not clear. Here we quantified protein-bound 3-nitrotyrosine (3-NT) by a novel gas chromatography/negative chemical ionization tandem mass spectrometry technique and DA and 3,4-dihydroxyphenylalanine (DOPA) by HPLC in tissues or medium of organotypic, mouse mesencephalon cultures after acute or chronic treatments with the peroxynitrite donor 3-morpholino-sydnonimine (SIN-1), the dopaminergic toxin 1-methyl-4-phenylpyridinium (MPP(+)) or the lipophilic complex I inhibitor rotenone. Incubation with SIN-1 (24 h) or MPP(+) treatments (48 h) caused dose-dependent protein nitration reaching a maximum of eightfold increase by 10 mM SIN-1 or twofold by 10 microM MPP(+), but significant DA depletions occurred at much lower concentrations of MPP(+) (1 microM). Chronic MPP(+) or rotenone treatments (3 weeks) caused maximum protein nitration by 1 microM (twofold) or 10nM (fourfold), respectively. Co-treatment with the nitric oxide synthase inhibitor l-NAME (300 microM) prevented protein nitration by MPP(+), but did not protect against MPP(+)-induced DA depletion or inhibition of TH activity. Acute incubation with 100 microM SIN-1 inhibited TH activity, which could be blocked by co-treatment with the tetrahydrobiopterin precursor l-sepiapterin, but tissue DA depletions required higher doses of SIN-1 (>1 mM, 24 h) and longer survival. In conclusion, protein nitration and TH activity or DA depletion are not directly related in these models.

Morroniside prevents peroxide-induced apoptosis by induction of endogenous glutathione in human neuroblastoma cells

(1) Morroniside belongs to an extensive group of natural iridorid glycosides. In the present study, using human neuroblastoma SH-SY5Y cells, we have investigated the protective effects of this compound on modifications in endogenous reduced glutathione (GSH), intracellular oxygen species (ROS) and apoptotic death on H(2)O(2)-mediated cytoxicity. (2) Incubation of cells with morroniside led to a significant dose-dependent elevation of cellular GSH accompanied by a marked protection against H(2)O(2)-mediated toxicity. Morroniside at 1-100 microM inhibited the formation of ROS and the activation of caspase-3 and 9, and the upregulation of Bcl-2, whereas no significant change occurred in Bax levels. (3) The results indicated that the anti-oxidative and anti-apoptotic properties render this natural compound potentially protective against H(2)O(2)-induced cytotoxicity. (4) This study suggested that intracellular GSH appeared to be an important factor in morroniside-mediated cytoprotection against H(2)O(2)-toxicity in SH-SY5Y cells.

[Nitric oxide, neurodegeneration, and Parkinson's disease]

<zakljucak> Brojni rezultati velikih studija pokazuju znacajnu ulogu NO u kaskadi dogadjaja koji dovode do smrti dopaminergickih neurona. Zna se da MPTP uzrokuje neurotoksicnost putem NO sintetisanog pomocu nNOS, ostecujuci primarno dopaminergicka vlakna i zavrsetke u strijatumu, dok NO stvoren uz pomoc iNOS deluje prvenstveno na tela dopaminergickih neurona u pars compacta substantia nigra. Ostecenje uzrokovano NO iz nNOS moze sluziti kao katalizator aktivacije iNOS i glioze. Slican sled dogadjaja moze se primeniti na ostecenje dopaminergickih neurona kod ljudi, bilo usled idiopatske PB ili usled intoksikacije MPTP. Znacaj ovih otkrica je ne samo u osvetljavanju cinioca koji ucestvuju u progresiji neurodegeneracije i PB vec i u upucivanju na nove terapijske mogucnosti.

Fraxetin prevents rotenone-induced apoptosis by induction of endogenous glutathione in human neuroblastoma cells

Fraxetin belongs to an extensive group of natural phenolic anti-oxidants. In the present study, using a human neuroblastoma SH-SY5Y cells, we have investigated the protective effects of this compound on modifications in endogenous reduced glutathione (GSH), intracellular oxygen species (ROS) and apoptotic death on rotenone-mediated cytoxicity. Incubation of cells with the fraxetin led to a significant elevation dose-dependent of cellular GSH and this was accompanied by a marked protection against rotenone-mediated toxicity, which was also significantly reversed in the cells with buthionine sulfoximine (BSO) co-treatment. Taken together, this study suggested that intracellular GSH appeared to be an important factor in fraxetin-mediated cytoprotection against rotenone-toxicity in SH-SY5Y cells. Fraxetin at 10-100 muM inhibited the formation of ROS, cytochrome c release, activation of caspase-3 and 9, and suppressed the up-regulation of Bax, whereas no significant change occurred in Bcl-2 levels. Our results indicated that the anti-oxidative and anti-apoptotic properties render this natural compound potentially protective against rotenone-induced cytotoxicity.

Nonsynaptic communication in the central nervous system

Classical synaptic functions are important and suitable to relatively fast and discretely localized processes, but the nonclassical receptorial functions may be providing revolutionary possibilities for dealing at the cellular level with many of the more interesting and seemingly intractable features of neural and cerebral activities. Although different forms of nonsynaptic communication (volume transmission) often appear in different studies, their importance to modulate and mediate various functions is still not completely recognized. To establish the existence and the importance of nonsynaptic communication in the nervous system, here we cite pieces of evidence for each step of the interneuronal communication in the nonsynaptic context including the release into the extracellular space (ECS) and the extrasynaptic receptors and transporters that mediate nonsynaptic functions. We are now faced with a multiplicity of chemical communication. The fact that transmitters can even be released from nonsynaptic varicosities without being coupled to frequency-coded neuronal activity and they are able to diffuse over large distances indicates that there is a complementary mechanism of interneuronal communication to classical synaptic transmission. Nonconventional mediators that are also important part of the nonsynaptic world will also be overviewed.

Peroxynitrite and mitochondrial dysfunction in the pathogenesis of Parkinson's disease

Nitric oxide (NO), in excess, behaves as a cytotoxic substance mediating the pathological processes that cause neurodegeneration. The NO-induced dopaminergic cell loss causing Parkinson's disease (PD) has been postulated to include the following: an inhibition of cytochrome oxidase, ribonucleotide reductase, mitochondrial complexes I, II, and IV in the respiratory chain, superoxide dismutase, glyceraldehyde-3-phosphate dehydrogenase; activation or initiation of DNA strand breakage, poly(ADP-ribose) synthase, lipid peroxidation, and protein oxidation; release of iron; and increased generation of toxic radicals such as hydroxyl radicals and peroxynitrite. NO is formed by the conversion of L-arginine to L-citrulline by NO synthase (NOS). At least three NOS isoforms have been identified by molecular cloning and biochemical studies: a neuronal NOS or type 1 NOS (nNOS), an immunologic NOS or type 2 NOS (iNOS), and an endothelial NOS or type 3 NOS (eNOS). The enzymatic activities of eNOS or nNOS are induced by phosphorylation triggered by Ca(2+) entering cells and binding to calmodulin. In contrast, the regulation of iNOS seems to depend on de novo synthesis of the enzyme in response to a variety of cytokines, such as interferon-gamma and lipopolysaccharide. The evidence that NO is associated with neurotoxic processes underlying PD comes from studies using experimental models of this disease NOS inhibitors can prevent 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopaminergic neurotoxicity. Furthermore, NO fosters dopamine depletion, and the said neurotoxicity is averted by nNOS inhibitors such as 7-nitroindazole working on tyrosine hydroxylase-immunoreactive neurons in substantia nigra pars compacta. Moreover, mutant mice lacking the nNOS gene are more resistant to MPTP neurotoxicity when compared with wild-type littermates. Selegiline, an irreversible inhibitor of monoamine oxidase B, is used in PD as a dopaminergic function-enhancing substance. Selegiline and its metabolite, desmethylselegiline, reduce apoptosis by altering the expression of a number of genes, for instance, superoxide dismutase, Bcl-2, Bcl-xl, NOS, c-Jun, and nicotinamide adenine nucleotide dehydrogenase. The selegiline-induced antiapoptotic activity is associated with prevention of a progressive reduction of mitochondrial membrane potential in preapoptotic neurons. As apoptosis is critical to the progression of neurodegenerative disease, including PD, selegiline or selegiline-like compounds to be discovered in the future may be efficacious in treating PD.

MPP+ increases alpha-synuclein expression and ERK/MAP-kinase phosphorylation in human neuroblastoma SH-SY5Y cells

Alpha-synuclein is a brain presynaptic protein that is linked to familiar early onset Parkinson's disease and it is also a major component of Lewy bodies in sporadic Parkinson's disease and other neurodegenerative disorders. Alpha-synuclein expression increases in substantia nigra of both MPTP-treated rodents and non-human primates, used as animal models of parkinsonism. Here we describe an increase in alpha-synuclein expression in a human neuroblastoma cell line, SH-SY5Y, caused by 5-100 microM MPP+, the active metabolite of MPTP, which induces apoptosis in SH-SY5Y cells after a 4-day treatment. We also analysed the activation of the MAPK family, which is involved in several cellular responses to toxins and stressing conditions. Parallel to the increase in alpha-synuclein expression we observed activation of MEK1,2 and ERK/MAPK but not of SAPK/JNK or p38 kinase. The inhibition of the ERK/MAPK pathway with U0126, however, did not affect the increase in alpha-synuclein. The highest increase in alpha-synuclein (more than threefold) in 4-day cultures was found in adherent cells treated with low concentrations of MPP+ (5 microM). Inhibition of ERK/MAPK reduced the damage caused by MPP+. We suggest that alpha-synuclein increase and ERK/MAPK activation have a prominent role in the cell mechanisms of rescue and damage, respectively, after MPP+ -treatment.

Nitric oxide enhances MPP(+) inhibition of complex I

There is evidence that 1-methyl-4-phenyl-1,2,3,6 tetrahydropyridine (MPTP) toxicity is mediated through both inhibition of mitochondrial complex I and free radical generation. 7-Nitroindazole protects against MPTP toxicity in vitro and in vivo, and this appears to be related to its inhibition of nitric oxide (NO(*-)) synthase. We now show that the NO(*-) generator, glutathione-N-oxide, enhances the inhibitory action of 1-methyl-4-phenylpyridinium (MPP(+)) on complex I activity in brain submitochondrial particles. We propose that the NO(*-)-induced reversible inhibition of complex IV (cytochrome oxidase) potentiates the MPP(+)-induced irreversible free radical-mediated inhibition of complex I. Thus, NO(*-) may 'prime' the respiratory chain to the effects of MPP(+). These data provide evidence for an interaction between NO(*-) and MPP(+) at the level of the respiratory chain.

Low concentrations of 1-methyl-4-phenylpyridinium ion induce caspase-mediated apoptosis in human SH-SY5Y neuroblastoma cells

There is growing evidence that apoptotic mechanisms underlie the neurodegeneration leading to Parkinson's disease. 1-Methyl-4-phenylpyridinium ion (MPP(+)), the active metabolite of the parkinsonism-inducing drug MPTP, induced apoptosis in cultures of human SH-SY5Y neuroblastoma cells. Nuclear fragmentation, DNA laddering, and a 20% decrease in viability were seen after a 4-day incubation with 5 microM MPP(+). Cell viability decreased by 40% at 100 microM MPP(+), but the degree of apoptosis was not correlatively increased. The MPP(+)-induced apoptosis was completely prevented by the broad caspase inhibitor zVAD.fmk but not by the caspase-8 inhibitor IETD.fmk. Furthermore, MPP(+) had no effect on the levels of Fas or Fas-L, suggesting lack of activation of the Fas-L/Fas/caspase-8 pathway of apoptosis. There was no evidence of mitochondrial dysfunction at 5 microM MPP(+): No differences were seen in transmembrane potential or in cytochrome c release from controls. At 100 microM MPP(+), the mitochondrial potential decreased, and cytoplasmic cytochrome c and caspase-9 activation increased slightly. At both low and high concentrations of MPP(+), VDVADase and DEVDase activities increased. We conclude that MPP(+) can induce caspase-mediated apoptosis, which is prevented by caspase inhibition, at concentrations lower than those needed to trigger mitochondrial dysfunction and closer to those found in the brains of MPTP-treated animals.

Analysis of citrulline in rat brain tissue after perfusion with haloperidol by liquid chromatography-mass spectrometry

We have investigated the potential of high-performance liquid chromatography (HPLC) coupled to mass spectrometry (MS) to determine enrichments of citrulline as a marker for in vivo nitric oxide (NO) production in brain tissue. The analysis of citrulline as the butyl ester derivative was evaluated using two types of ionization: electron spray ionization (ESI) and atmospheric pressure chemical ionization (APCI). APCI-MS appeared to be more suitable for determination of citrulline than ESI-MS, because the ion intensity of the protonated molecule ion [M+H]+, m/z 232, of citrulline in the former was about twelve times higher than in the latter. The chromatography was carried out on a reversed C8 column with the mobile phase consisting of 15% acetonitrile: 85% H2O: 0.2% acetic acid (v/v). The calibration curve had good linearity within the concentration range investigated (5 ng to 500 ng/ml). The limit of determination was estimated to be ca. 1 ng/ml of standard solution. The method was applied to the analysis of citrulline in the brain dialysate obtained from rat after perfusion of the striatum with haloperidol (HP, 0.1 mM). It is concluded that APCI-MS in combination with HPLC can be successfully applied to determination of citrulline in brain tissue, thus providing a useful tool for assessment of in vivo NO production.

Pharmacokinetics and protein binding of the selective neuronal nitric oxide synthase inhibitor 7-nitroindazole

Utilization of nitric oxide (NO) synthase (NOS) inhibitors to probe the role of NO in various central nervous system processes requires use of an inhibitor selective for neuronal NOS, and is facilitated by knowledge of the pharmacokinetics of the inhibitor. The present project was undertaken to elucidate the disposition of the selective neuronal NOS inhibitor 7-nitroindazole (7-NI). A simple, specific HPLC assay was developed with requisite sensitivity to quantitate 7-NI in serum after administration of pharmacologically relevant doses. Further experiments were performed to assess the effects of administered dose on 7-NI disposition. 7-NI displayed marked nonlinearity, consistent with saturable elimination, when administered by ip injection in peanut oil. The nonlinearity was related to total dose, but not to the concentration of 7-NI in the vehicle. Binding of 7-NI in rat serum was concentration-independent and does not contribute to the nonlinearity. Various formulations for iv administration of this water-insoluble compound were evaluated; the optimal vehicle, from the standpoint of 7-NI solubility, appeared to inhibit the clearance of 7-NI from the systemic circulation. Considering the nonlinear disposition of 7-NI, knowledge of the pharmacokinetics of this inhibitor is requisite to designing administration protocols to achieve the desired magnitude and duration of NOS inhibition.

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.

Metabolic stress in PC12 cells induces the formation of the endogenous dopaminergic neurotoxin, 3,4-dihydroxyphenylacetaldehyde

3,4-Dihydroxyphenylacetaldehyde (DOPAL) has been reported to be a toxic metabolite formed by the oxidative-deamination of dopamine (DA) catalyzed by monoamine oxidase. This aldehyde is either oxidized to 3,4-dihydroxyphenylacetic acid (DOPAC) by aldehyde dehydrogenase, an NAD-dependent enzyme or reduced to 3, 4-dihydroxyphenylethanol (DOPET) by aldehyde or aldose reductase. In the present study we examined whether levels of DOPAL are elevated by inhibition of the mitochondrial respiratory chain. Using inhibitors of mitochondrial complexes I, II, III and IV we found that inhibition of complex I and III increased levels of DOPAL and DOPET. Nerve growth factor-induced differentiation of PC12 cells markedly potentiated DOPAL and DOPET accumulation in response to metabolic stress. DOPAL was toxic to differentiated PC12 as well as to SK-N-SH cell lines. Because complex I dysfunction has been implicated in the pathogenesis of Parkinson's disease, the accumulation of DOPAL may explain the vulnerability of the dopaminergic system to complex I inhibition. The rapid appearance of DOPAL and DOPET after inhibition of complex I may be a useful early index of oxidative stress in DA-forming neurons.

Nitric oxide modulates release of noradrenaline in guinea-pig gastric fundus

The interaction between nitric oxide (NO) and the release of [(3)H]noradrenaline ([(3)H]NA) in conditions of non-activated and activated nicotinic receptors in guinea-pig gastric fundus preincubated with [(3)H]NA was studied. Nicotinic receptor agonist, 1,1-dimethyl-4-phenyl-piperazinium iodide (DMPP) (100 microM) significantly increased the resting release of [(3)H]NA. NO-synthase inhibitor, N(omega)-nitro-L-arginine (L-NNA) (100 microM) significantly decreased DMPP-induced release of [(3)H]NA. Field electrical stimulation (FES) (2Hz; 1 ms; 360 st) significantly increased the release of [(3)H]NA above the basal levels. L-NNA significantly decreased the stimulation-evoked release of [(3)H]NA. DMPP increased the stimulation-evoked release of [(3)H]NA, effect which was significantly decreased by L-NNA. The data suggests that endogenous NO increases the release of [(3)H]NA, evoked either by activation of the nicotinic receptors or by electrical stimulation in guinea-pig gastric fundus.

MPP(+)-induced mitochondrial dysfunction is potentiated by dopamine

MPP(+), the major metabolite of the Parkinsonism-inducing compound MPTP, responsible for the destruction of the nigrostriatal pathway in primates and rodents, has been assayed in isolated rat liver mitochondria in the presence of physiological concentrations of dopamine or analogous concentrations of melanin-dopamine. 5 microM MPP(+) in the presence of 70 microM dopamine or melanin-dopamine, but not alone, decreased the heat production and oxygen consumption of a mitochondrial suspension activated with succinate and ADP. Both dopamine and oxidized dopamine plus MPP(+) also decreased the mitochondrial reductive power measured with MTT. Mitochondrial swelling was observed, associated with an increase in membrane mitochondrial potential, as a synergistic effect between low concentrations of MPP(+) and dopamine. It is suggested that cytosolic dopamine, by itself or via its autooxidation products, may play a relevant role in the mitochondrial toxicity of MPP(+). A failure in the regulation of the storage/release of dopamine could aggravate a mitochondrial damage and trigger the neurodegenerative process underlying MPTP toxicity and Parkinson's disease.

Polymorphonuclear leukocyte nitrite content and antioxidant enzymes in Parkinson's disease patients

OBJECTIVE

The present study was undertaken to evaluate the alteration in the peripheral neuronal nitric oxide synthase (NOS) activity in Parkinson's disease patients. Therefore, basal nitrite content in PMNs, platelets and in the plasma of PD and control Indian population were evaluated.

MATERIALS AND METHODS

We estimated nitrite, the nitric oxide (NO) metabolite, in neutrophils (PMNs), platelets and in plasma of control and in L-dopa treated Parkinson's disease (PD) patients. We also measured the activity of catalase, superoxide dismutase (SOD) and glutathione peroxidase (GPx) in the PMNs.

RESULTS

We observed a significant increase in the basal nitrite content in PMNs of PD patients without any alteration in the plasma and platelets. Thus, the change was specific to PMNs. Catalase activity was significantly less in the PMNs of PD patients, but SOD and GPx remained unaltered.

CONCLUSION

Results obtained in the PD patients exhibit an increase in the NOS activity in PMNs. Thus, involvement of NO is suggested in PD.

Involvement of nitric oxide and nitric oxide synthase activity in anticonvulsive action

The anticonvulsant drug Diazepam (DIA-2 mg/kg b. wt), the nitric oxide (NO) donor L-Arginine (L-Arg-2000 mg/kg b. wt) and the putative nitric oxide synthase (NOS) inhibitor N(G)-Nitro-L-Arginine methyl ester (L-NAME-50 mg/kg b. wt) were used to determine the role of endogenous NO on convulsions induced by picrotoxin (PCT-5 mg/kg b. wt) in rats. Rats given a convulsant dose of PCT (5 mg/kg b. wt) had convulsion and it suppresses the NOS activity and NO concentration in brain regions. The anticonvulsant L-Arg alone significantly increases the NO concentration and NOS activity in brain regions, but not diazepam. Whereas DIA, along with L-Arg, enhances the NO and NOS activity when compared to L-Arg alone. The combination of both OIA and L-Arg completely suppressed the convulsions. L-NAME alone had no effect to produce convulsions but it completely decreased NO concentration and NOS activity and potentiated the PCT convulsions. This was reverted by pre- and post treatment of DIA plus L-Arg indicating, the increased NO concentration and NOS activity in brain regions suppresses convulsions.