Peroxynitrite inactivation of tyrosine hydroxylase: mediation by sulfhydryl oxidation, not tyrosine nitration

Echinacea purpurea root extract mitigates hepatotoxicity, genotoxicity, and ultrastructural changes induced by hexavalent chromium via oxidative stress suppression

Environmental and occupational exposure to hexavalent chromium (CrVI) is mostly renowned as a possible hepatotoxic in mammals. Echinacea purpurea (L.) Moench, a phenolic-rich plant, is recurrently used for its therapeutic properties. Therefore, this investigation was done to explore whether E. purpurea (EP) root extract would have any potential health benefits against an acute dose of CrVI-induced oxidative damage and hepatotoxicity. Results revealed that GC-MS analysis of EP root extract has 26 identified components with a significant amount of total phenolic and flavonoid contents. Twenty-four Male Wistar rats were divided into four groups: control, EP (50 mg/kg BW/day for 21 days), CrVI (15 mg/kg BW as a single intraperitoneal dosage), and EP + CrVI, respectively. Rats treated with CrVI displayed a remarkable rise in oxidative stress markers (TBARS, H2O2, PCC), bilirubin, and lactate dehydrogenase activity, and a marked decrease in enzymatic and non-enzymatic antioxidants, transaminases, and alkaline phosphatase activities, and serum protein level. Also, CrVI administration induced apoptosis and inflammation in addition to histological and ultrastructural abnormalities in the liver tissue. The examined parameters were improved significantly in rats pretreated with EP and then intoxicated with CrVI. Conclusively, EP had a potent antioxidant activity and could be used in the modulation of CrVI-induced hepatotoxicity.

Nitrosative stress in Parkinson's disease

Parkinson’s Disease (PD) is a neurodegenerative disorder characterized, in part, by the loss of dopaminergic neurons within the nigral-striatal pathway. Multiple lines of evidence support a role for reactive nitrogen species (RNS) in degeneration of this pathway, specifically nitric oxide (NO). This review will focus on how RNS leads to loss of dopaminergic neurons in PD and whether RNS accumulation represents a central signal in the degenerative cascade. Herein, we provide an overview of how RNS accumulates in PD by considering the various cellular sources of RNS including nNOS, iNOS, nitrate, and nitrite reduction and describe evidence that these sources are upregulating RNS in PD. We document that over 1/3 of the proteins that deposit in Lewy Bodies, are post-translationally modified (S-nitrosylated) by RNS and provide a broad description of how this elicits deleterious effects in neurons. In doing so, we identify specific proteins that are modified by RNS in neurons which are implicated in PD pathogenesis, with an emphasis on exacerbation of synucleinopathy. How nitration of alpha-synuclein (aSyn) leads to aSyn misfolding and toxicity in PD models is outlined. Furthermore, we delineate how RNS modulates known PD-related phenotypes including axo-dendritic-, mitochondrial-, and dopamine-dysfunctions. Finally, we discuss successful outcomes of therapeutics that target S-nitrosylation of proteins in Parkinson’s Disease related clinical trials. In conclusion, we argue that targeting RNS may be of therapeutic benefit for people in early clinical stages of PD.

Pathophysiological significance of increased α-synuclein deposition in sympathetic nerves in Parkinson's disease: a post-mortem observational study

Background

Parkinson’s disease (PD) is characterized by intra-neuronal deposition of the protein α-synuclein (α-syn) and by deficiencies of the catecholamines dopamine and norepinephrine (NE) in the brain and heart. Accumulation of α-syn in sympathetic noradrenergic nerves may provide a useful PD biomarker; however, whether α-syn buildup is pathophysiological has been unclear. If it were, one would expect associations of intra-neuronal α-syn deposition with catecholaminergic denervation and with decreased NE contents in the same samples.

Methods

We assayed immunoreactive α-syn and tyrosine hydroxylase (TH, a marker of catecholaminergic innervation) concurrently with catecholamines in coded post-mortem scalp skin, submandibular gland (SMG), and apical left ventricular myocardial tissue samples from 14 patients with autopsy-proven PD and 12 age-matched control subjects who did not have a neurodegenerative disease.

Results

The PD group had increased α-syn in sympathetic noradrenergically innervated arrector pili muscles (5.7 times control, P < 0.0001), SMG (35 times control, P = 0.0011), and myocardium (11 times control, P = 0.0011). Myocardial TH in the PD group was decreased by 65% compared to the control group (P = 0.0008), whereas the groups did not differ in TH in either arrector pili muscles or SMG. Similarly, myocardial NE was decreased by 92% in the PD group (P < 0.0001), but the groups did not differ in NE in either scalp skin or SMG.

Conclusions

PD entails increased α-syn in skin, SMG, and myocardial tissues. In skin and SMG, augmented α-syn deposition in sympathetic nerves does not seem to be pathogenic. The pathophysiological significance of intra-neuronal α-syn deposition appears to be organ-selective and prominent in the heart.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40035-022-00289-y.

Hepatoprotective potential of Rosmarinus officinalis essential oil against hexavalent chromium-induced hematotoxicity, biochemical, histological, and immunohistochemical changes in male rats

Hexavalent chromium (Cr VI) is widely known as a potential hepatotoxic in humans and animals and its toxicity is associated with oxidative stress. So, an in vivo study was outlined to assess the protective and therapeutic role of Rosmarinus officinalis essential oil (rosemary; REO) against Cr VI-induced hepatotoxicity. Male Wistar rats were assigned into five equal groups (1^st group served as control; 2^nd and 3^rd groups received 0.5 ml/kg BW REO and 2 mg/kg BW Cr VI_, respectively; 4^th group pretreated with REO then injected with K₂Cr₂O₇; and 5^th group received Cr VI then treated with REO for 3 weeks). Results revealed that rats exposed to Cr VI showed a valuable changes in hematological parameters and an increase in oxidative stress markers (Protein carbonyl, TBARS, and H₂O₂) and a noteworthy decline in glutathione (GSH) content. Furthermore, a considerable decrease in enzymatic antioxidants (SOD, CAT, GPx, and GST), transaminases (AST and ALT), and alkaline phosphatase (ALP) activities, as well as total protein and albumin levels, was detected, while serum liver function biomarkers were increased significantly. In addition, the evaluation of histopathological and immunohistochemical PCNA expression showed significant variations in the liver that confirm the biochemical results. Administration of REO pre- or post-chromium treatment restored the parameters cited above near to the normal values. Otherwise, individual intake with REO slumped lipid peroxidation and gotten better antioxidant status significantly. Conclusively, REO proved to be an effective antioxidant in modulating Cr VI-induced hepatotoxicity, especially in the pretreated rats.

Oxidative Stress, Folate Receptor Autoimmunity, and CSF Findings in Severe Infantile Autism

Background

Biomarkers such as oxidative stress, folate receptor alpha (FRα) autoimmunity, and abnormal brain serotonin turnover are common in autism.

Methods

Oxidative stress biomarkers with pro- and antioxidants were measured in the severe form of infantile autism (n = 38) and controls (n = 24). Children and parents had repeated testing for serum FR autoantibodies, spinal fluid dopamine and serotonin metabolites, pterins, and N⁵-methyltetrahydrofolate (MTHF). Statistical analysis assessed correlations between variables. Genetic analysis included the SLC6A4 and SLC29A4 genes encoding synaptic serotonin reuptake proteins.

Results

Compared to controls, the autism group showed a significant increase in oxidative DNA damage in lymphocytes, plasma ceruloplasmin and copper levels with a high copper/zinc ratio, thiol proteins, and superoxide dismutase (SOD) activity. Vitamin C levels were significantly diminished. In most autistic patients, the vitamin A (64%) and D (70%) levels were low. Serum FR autoantibodies fluctuating over 5–7 week periods presented in 68% of all autistic children, 41% of parents vs. 3.3% of control children and their parents. CSF showed lowered serotonin 5-hydroxyindole acetic acid (5HIAA) metabolites in 13 (34%), a low 5HIAA to HVA (dopamine metabolite) ratio in 5 (13%), low 5HIAA and MTHF in 2 (5%), and low MTHF in 8 patients (21%). A known SLC6A4 mutation was identified only in 1 autistic child with low CSF 5HIAA and a novel SLC29A4 mutation was identified in identical twins. Low CSF MTHF levels among only 26% of subjects can be explained by the fluctuating FR antibody titers. Two or more aberrant pro-oxidant and/or antioxidant factors predisposed to low CSF serotonin metabolites. Three autistic children having low CSF 5HIAA and elevated oxidative stress received antioxidative supplements followed by CSF 5HIAA normalisation.

Conclusion

In autism, we found diverse combinations for FR autoimmunity and/or oxidative stress, both amenable to treatment. Parental and postnatal FR autoantibodies tend to block folate passage to the brain affecting folate-dependent pathways restored by folinic acid treatment, while an abnormal redox status tends to induce reduced serotonin turnover, corrected by antioxidant therapy. Trial Registration. The case-controlled study was approved in 2008 by the IRB at Liège University (Belgian Number: B70720083916). Lay Summary. Children with severe infantile autism frequently have serum folate receptor autoantibodies that block the transport of the essential vitamin folate across the blood-brain barrier to the brain. Parents are often asymptomatic carriers of these serum folate receptor autoantibodies, which in mothers can block folate passage across the placenta to their unborn child. This folate deficiency during the child's intrauterine development may predispose to neural tube defects and autism. Oxidative stress represents a condition with the presence of elevated toxic oxygen derivatives attributed to an imbalance between the formation and protection against these toxic reactive oxygen derivatives. Oxidative stress was found to be present in autistic children where these reactive oxygen derivatives can cause damage to DNA, which changes DNA function and regulation of gene expression. In addition, excessive amounts of these toxic oxygen derivatives are likely to damage the enzyme producing the neuromessenger serotonin in the brain, diminished in about 1/3 of the autistic children. Testing children with autism for oxidative stress and its origin, as well as testing for serum folate receptor autoantibodies, could open new approaches towards more effective treatments.

Regulation of cytochrome P450 enzyme activity and expression by nitric oxide in the context of inflammatory disease

Many hepatic cytochrome P450 enzymes and their associated drug metabolizing activities are down-regulated in disease states, and much of this has been associated with inflammatory cytokines and their signaling pathways. One such pathway is the induction of inducible nitric oxide synthase (NOS2) and generation of nitric oxide (NO) in many tissues and cells including the liver and hepatocytes. Experiments in the 1990s demonstrated that NO could bind to and inhibit P450 enzymes, and suggested that inhibition of NOS could attenuate, and NO generation could mimic, the down-regulation by inflammatory stimuli of not only P450 catalytic activities but also of mRNA expression and protein levels of certain P450 enzymes. This review will summarize and examine the evidence that NO functionally inhibits and down-regulates P450 enzymes in vivo and in vitro, with a particular focus on the mechanisms by which these effects are achieved.

Improving Outcome in Infantile Autism with Folate Receptor Autoimmunity and Nutritional Derangements: A Self-Controlled Trial

Background

In contrast to multiple rare monogenetic abnormalities, a common biomarker among children with infantile autism and their parents is the discovery of serum autoantibodies directed to the folate receptor alpha (FRα) localized at blood-brain and placental barriers, impairing physiologic folate transfer to the brain and fetus. Since outcome after behavioral intervention remains poor, a trial was designed to treat folate receptor alpha (FRα) autoimmunity combined with correction of deficient nutrients due to abnormal feeding habits.

Methods

All participants with nonsyndromic infantile autism underwent a routine protocol measuring CBC, iron, vitamins, coenzyme Q10, metals, and trace elements. Serum FRα autoantibodies were assessed in patients, their parents, and healthy controls. A self-controlled therapeutic trial treated nutritional derangements with addition of high-dose folinic acid if FRα autoantibodies tested positive. The Childhood Autism Rating Scale (CARS) monitored at baseline and following 2 years of treatment was compared to the CARS of untreated autistic children serving as a reference.

Results

In this self-controlled trial (82 children; mean age ± SD: 4.4 ± 2.3 years; male:female ratio: 4.8:1), FRα autoantibodies were found in 75.6 % of the children, 34.1 % of mothers, and 29.4 % of fathers versus 3.3 % in healthy controls. Compared to untreated patients with autism (n=84) whose CARS score remained unchanged, a 2-year treatment decreased the initial CARS score from severe (mean ± SD: 41.34 ± 6.47) to moderate or mild autism (mean ± SD: 34.35 ± 6.25; paired t-test p<0.0001), achieving complete recovery in 17/82 children (20.7 %). Prognosis became less favorable with the finding of higher FRα autoantibody titers, positive maternal FRα autoantibodies, or FRα antibodies in both parents.

Conclusions

Correction of nutritional deficiencies combined with high-dose folinic acid improved outcome for autism, although the trend of a poor prognosis due to maternal FRα antibodies or FRα antibodies in both parents may warrant folinic acid intervention before conception and during pregnancy.

Administration of tetrahydrobiopterin restored the decline of dopamine in the striatum induced by an acute action of MPTP

Parkinson's disease (PD) is the second common neurodegenerative disorder. Deficit of the nigro-striatal dopaminergic neurons causes the motor symptoms of PD. While the oxidative stress is thought to be deeply involved in the etiology of PD, molecular targets for the oxidative insults has not been fully elucidated. 6R-5,6,7,8-Tetrahydrobiopterin (BH4) is a cofactor for tyrosine hydroxylase (TH), the rate-limiting enzyme for production of dopamine, and easily oxidized to its dihydro-form. In this study, we examined the alteration in the metabolism of BH4 caused by a parkinsonian neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). MPTP reduced the dopamine content and the in vivo activity of TH in the striatum prior to degeneration of the dopaminergic neurons. We found that administration of BH4 could restore the dopamine content and in vivo TH activity in the striatum of MPTP-treated mice. Unexpectedly, when BH4 was administered with MPTP, BH4 contents in the brain were far higher than those injected without MPTP even at 23 h after the last injection. Because MPTP has been shown to increase ROS production in the dopaminergic neurons, we assumed that the increased ROS oxidizes BH4 into its dihydro-form, excreted from the dopaminergic neurons, taken-up by the neighboring cells, reduced back to BH4, and then accumulated in the brain. We also investigated the action of MPTP in mice lacking quinonoid-dihydropteridine reductase (Qdpr), an enzyme catalyzing regeneration of BH4 from quinonoid dihydrobiopterin. The dopamine depletion induced by MPTP was severer in Qdpr-deficient mice than in wild-type mice. The present data suggest that perturbation of the BH4 metabolism would be the cause of early and persistent dopamine depletion in the striatum.

Neuronal nitric oxide synthase and affective disorders

Affective disorders including major depressive disorder (MDD), bipolar disorder (BPD), and general anxiety affect more than 10% of population in the world. Notably, neuronal nitric oxide synthase (nNOS), a downstream signal molecule of N-methyl-D-aspartate receptors (NMDARs) activation, is abundant in many regions of the brain such as the prefrontal cortex (PFC), hippocampus, amygdala, dorsal raphe nucleus (DRN), locus coeruleus (LC), and hypothalamus, which are closely associated with the pathophysiology of affective disorders. Decreased levels of the neurotransmitters including 5-hydroxytryptamine or serotonin (5-HT), noradrenalin (NA), and dopamine (DA) as well as hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis are common pathological changes of MDD, BPD, and anxiety. Increasing data suggests that nNOS in the hippocampus play a crucial role in the etiology of MDD whereas nNOS-related dysregulation of the nitrergic system in the LC is closely associated with the pathogenesis of BPD. Moreover, hippocampal nNOS is implicated in the role of serotonin receptor 1 A (5-HTR1 A) in modulating anxiety behaviors. Augment of nNOS and its carboxy-terminal PDZ ligand (CAPON) complex mediate stress-induced anxiety and disrupting the nNOS-CAPON interaction by small molecular drug generates anxiolytic effect. To date, however, the function of nNOS in affective disorders is not well reviewed. Here, we summarize works about nNOS and its signal mechanisms implicated in the pathophysiology of affective disorders. On the basis of this review, it is suggested that future research should more fully focus on the role of nNOS in the pathomechanism and treatment of affective disorders.

Pathologic role of nitrergic neurotransmission in mood disorders

Mood disorders are chronic, recurrent mental diseases that affect millions of individuals worldwide. Although over the past 40 years the biogenic amine models have provided meaningful links with the clinical phenomena of, and the pharmacological treatments currently employed in, mood disorders, there is still a need to examine the contribution of other systems to the neurobiology and treatment of mood disorders. This article reviews the current literature describing the potential role of nitric oxide (NO) signaling in the pathophysiology and thereby the treatment of mood disorders. The hypothesis has arisen from several observations including (i) altered NO levels in patients with mood disorders; (ii) antidepressant effects of NO signaling blockers in both clinical and pre-clinical studies; (iii) interaction between conventional antidepressants/mood stabilizers and NO signaling modulators in several biochemical and behavioral studies; (iv) biochemical and physiological evidence of interaction between monoaminergic (serotonin, noradrenaline, and dopamine) system and NO signaling; (v) interaction between neurotrophic factors and NO signaling in mood regulation and neuroprotection; and finally (vi) a crucial role for NO signaling in the inflammatory processes involved in pathophysiology of mood disorders. These accumulating lines of evidence have provided a new insight into novel approaches for the treatment of mood disorders.

Distinct effects of ketamine and acetyl L-carnitine on the dopamine system in zebrafish

Ketamine, a noncompetitive N-methyl-D-aspartic acid (NMDA) receptor antagonist is commonly used as a pediatric anesthetic. We have previously shown that acetyl L-carnitine (ALCAR) prevents ketamine toxicity in zebrafish embryos. In mammals, ketamine is known to modulate the dopaminergic system. NMDA receptor antagonists are considered as promising anti-depressants, but the exact mechanism of their function is unclear. Here, we measured the levels of dopamine (DA) and its metabolites, 3, 4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), in the zebrafish embryos exposed to ketamine in the presence and absence of 0.5 mM ALCAR. Ketamine, at lower doses (0.1-0.3 mM), did not produce significant changes in DA, DOPAC or HVA levels in 52 h post-fertilization embryos treated for 24 h. In these embryos, tyrosine hydroxylase (TH) mRNA expression remained unchanged. However, 2 mM ketamine (internal embryo exposure levels equivalent to human anesthetic plasma concentration) significantly reduced DA level and TH mRNA indicating that DA synthesis was adversely affected. In the presence or absence of 2 mM ketamine, ALCAR showed similar effects on DA level and TH mRNA, but increased DOPAC level compared to control. ALCAR reversed 2 mM ketamine-induced reduction in HVA levels. With ALCAR alone, the expression of genes encoding the DA metabolizing enzymes, MAO (monoamine oxidase) and catechol-O-methyltransferase (COMT), was not affected. However, ketamine altered MAO mRNA expression, except at the 0.1 mM dose. COMT transcripts were reduced in the 2 mM ketamine-treated group. These distinct effects of ketamine and ALCAR on the DA system may shed some light on the mechanism on how ketamine can work as an anti-depressant, especially at sub-anesthetic doses that do not affect DA metabolism and suppress MAO gene expression.

Chemical Changes in Nonthermal Plasma-Treated N-Acetylcysteine (NAC) Solution and Their Contribution to Bacterial Inactivation

In continuation of our previous reports on the broad-spectrum antimicrobial activity of atmospheric non-thermal dielectric barrier discharge (DBD) plasma treated N-Acetylcysteine (NAC) solution against planktonic and biofilm forms of different multidrug resistant microorganisms, we present here the chemical changes that mediate inactivation of Escherichia coli. In this study, the mechanism and products of the chemical reactions in plasma-treated NAC solution are shown. UV-visible spectrometry, FT-IR, NMR, and colorimetric assays were utilized for chemical characterization of plasma treated NAC solution. The characterization results were correlated with the antimicrobial assays using determined chemical species in solution in order to confirm the major species that are responsible for antimicrobial inactivation. Our results have revealed that plasma treatment of NAC solution creates predominantly reactive nitrogen species versus reactive oxygen species, and the generated peroxynitrite is responsible for significant bacterial inactivation.

Molecular, Neurochemical, and Behavioral Hallmarks of Reserpine as a Model for Parkinson's Disease: New Perspectives to a Long-Standing Model

The administration of reserpine to rodents was one of the first models used to investigate the pathophysiology and screening for potential treatments of Parkinson's disease (PD). The reserpine model was critical to the understanding of the role of monoamine system in the regulation of motor and affective disorders, as well as the efficacy of current PD treatments, such as L-DOPA and dopamine agonists. Nevertheless, with the introduction of toxin-induced and genetic models of PD, reserpine became underused. The main rationale to this drawback was the supposed absence of reserpine construct validity with PD. Here, we highlight classical and recent experimental findings that support the face, pharmacological, and construct validity of reserpine PD model and reason against the current rationale for its underuse. We also aim to shed a new perspective upon the model by discussing the main challenges and potentials for the reserpine model of PD.

The epinephrine increases tyrosine hydroxylase expression through upregulating thioredoxin-1 in PC12 cells

Epinephrine is a stress hormone which is sharply increased in response to acute stress and is continuously elevated during persistent stress. Thioredoxin-1 (Trx-1) is a redox regulating protein and is induced under various stresses. Our previous study has shown that epinephrine induces the expression of Trx-1. Tyrosine hydroxylase (TH) is the major rate-limiting enzyme in catecholamine biosynthesis in response to stress. However, how TH is regulated by epinephrine is still unknown. In the present study, we found that epinephrine increased the expression of TH in a dose- and time-dependent manner in PC12 cells, which was inhibited by propranolol (β-adrenergic receptor inhibitor), but not by phenoxybenzamine (α-adrenergic receptor inhibitor). The increase of TH was also inhibited by SQ22536 (adenylyl cyclase inhibitor), H-89(PKA inhibitor) and LY294002 (phosphatidylinositol 3 kinase inhibitor). More importantly, overexpression of Trx-1 significantly enhanced the expression of TH, while Trx-1 siRNA suppressed TH expression induced by epinephrine. These results suggest that Trx-1 is involved in TH expression induced by epinephrine in PC12 cells.

The role of parkin in the differential susceptibility of tuberoinfundibular and nigrostriatal dopamine neurons to acute toxicant exposure

Parkinson disease causes degeneration of nigrostriatal dopamine (DA) neurons, while tuberoinfundibular DA neurons remain unaffected. A similar pattern is observed following exposure to 1-methy-4-phenyl-1,2,3,6-tetrahydropyradine (MPTP). The mechanism of tuberoinfundibular neuronal recovery from MPTP is associated with up-regulation of parkin protein. Here we tested if parkin mediates tuberoinfundibular neuronal recovery from MPTP by knocking-down parkin in tuberoinfundibular neurons using recombinant adeno-associated virus (rAAV), expressing a short hairpin RNA (shRNA) directed toward parkin. Following knockdown, axon terminal DA and tyrosine hydroxylase (TH) concentrations were analyzed 24h post-MPTP administration. rAAV-shRNA-mediated knockdown of endogenous parkin rendered tuberoinfundibular neurons susceptible to MPTP induced terminal DA loss, but not TH loss, within 24h post-MPTP. To determine if the neuroprotective benefits of parkin up-regulation could be translated to nigrostriatal neurons, rAAV expressing human parkin was injected into the substantia nigra of mice and axon terminal DA and TH concentrations were analyzed 24h post-MPTP. Nigral parkin over-expression prevented loss of TH in the axon terminals and soma of nigrostriatal neurons, but had no effect on terminal DA loss within 24h post-MPTP. These data show that parkin is necessary for the recovery of terminal DA concentrations within tuberoinfundibular neurons following acute MPTP administration, and parkin can rescue MPTP-induced decreases in TH within nigrostriatal neurons.

Neurotoxicity of methamphetamine and 3,4-methylenedioxymethamphetamine

Amphetamines are a class of psychostimulant drugs that are widely abused for their stimulant, euphoric, empathogenic and hallucinogenic properties. Many of these effects result from acute increases in dopamine and serotonin neurotransmission. Subsequent to these acute effects, methamphetamine and 3,4 methylenedioxymethamphetamine (MDMA) produce persistent damage to dopamine and serotonin nerve terminals. This review summarizes the numerous interdependent mechanisms including excitotoxicity, mitochondrial damage and oxidative stress that have been demonstrated to contribute to this damage. Emerging non-neuronal mechanisms by which the drugs may contribute to monoaminergic terminal damage, as well as the neuropsychiatric consequences of this terminal damage are also presented. Methamphetamine and 3,4-methylenedioxymethamphetamine (MDMA) have similar chemical structures and pharmacologic properties compared to other abused substances including cathinone (khat), as well as a relatively new class of novel synthetic amphetamines known as 'bath salts' that have gained popularity among drug abusers.

Complexity of dopamine metabolism

: Parkinson's disease (PD) coincides with a dramatic loss of dopaminergic neurons within the substantia nigra. A key player in the loss of dopaminergic neurons is oxidative stress. Dopamine (DA) metabolism itself is strongly linked to oxidative stress as its degradation generates reactive oxygen species (ROS) and DA oxidation can lead to endogenous neurotoxins whereas some DA derivatives show antioxidative effects. Therefore, DA metabolism is of special importance for neuronal redox-homeostasis and viability.In this review we highlight different aspects of dopamine metabolism in the context of PD and neurodegeneration. Since most reviews focus only on single aspects of the DA system, we will give a broader overview by looking at DA biosynthesis, sequestration, degradation and oxidation chemistry at the metabolic level, as well as at the transcriptional, translational and posttranslational regulation of all enzymes involved. This is followed by a short overview of cellular models currently used in PD research. Finally, we will address the topic from a medical point of view which directly aims to encounter PD.

Impairment of brain redox homeostasis caused by the major metabolites accumulating in hyperornithinemia-hyperammonemia-homocitrullinuria syndrome in vivo

Ornithine, ammonia and homocitrulline are the major metabolites accumulating in hyperornithinemia-hyperammonemia-homocitrullinuria syndrome, a genetic disorder characterized by neurological regression whose pathogenesis is still not understood. The present work investigated the in vivo effects of intracerebroventricular administration of ornithine and homocitrulline in the presence or absence of hyperammonemia induced by intraperitoneal urease treatment on a large spectrum of oxidative stress parameters in cerebral cortex from young rats in order to better understand the role of these metabolites on brain damage. Ornithine increased thiobarbituric acid-reactive substances (TBA-RS) levels and carbonyl formation and decreased total antioxidant status (TAS) levels. We also observed that the combination of hyperammonemia with ornithine resulted in significant decreases of sulfhydryl levels, reduced glutathione (GSH) concentrations and the activities of catalase (CAT) and glutathione peroxidase (GPx), highlighting a synergistic effect of ornithine and ammonia. Furthermore, homocitrulline caused increases of TBA-RS values and carbonyl formation, as well as decreases of GSH concentrations and GPx activity. Hcit with hyperammonemia (urease treatment) decreased TAS and CAT activity. We also showed that urease treatment per se was able to enhance TBA-RS levels. Finally, nitric oxide production was not altered by Orn and Hcit alone or in combination with hyperammonemia. Our data indicate that the major metabolites accumulating in hyperornithinemia-hyperammonemia-homocitrullinuria syndrome provoke lipid and protein oxidative damage and a reduction of the antioxidant defenses in the brain. Therefore, it is presumed that oxidative stress may represent a relevant pathomechanism involved in the brain damage found in patients affected by this disease.

Methylphenidate exposure induces dopamine neuron loss and activation of microglia in the basal ganglia of mice

Background

Methylphenidate (MPH) is a psychostimulant that exerts its pharmacological effects via preferential blockade of the dopamine transporter (DAT) and the norepinephrine transporter (NET), resulting in increased monoamine levels in the synapse. Clinically, methylphenidate is prescribed for the symptomatic treatment of ADHD and narcolepsy; although lately, there has been an increased incidence of its use in individuals not meeting the criteria for these disorders. MPH has also been misused as a “cognitive enhancer” and as an alternative to other psychostimulants. Here, we investigate whether chronic or acute administration of MPH in mice at either 1 mg/kg or 10 mg/kg, affects cell number and gene expression in the basal ganglia.

Methodology/Principal Findings

Through the use of stereological counting methods, we observed a significant reduction (∼20%) in dopamine neuron numbers in the substantia nigra pars compacta (SNpc) following chronic administration of 10 mg/kg MPH. This dosage of MPH also induced a significant increase in the number of activated microglia in the SNpc. Additionally, exposure to either 1 mg/kg or 10 mg/kg MPH increased the sensitivity of SNpc dopaminergic neurons to the parkinsonian agent 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Unbiased gene screening employing Affymetrix GeneChip® HT MG-430 PM revealed changes in 115 and 54 genes in the substantia nigra (SN) of mice exposed to 1 mg/kg and 10 mg/kg MPH doses, respectively. Decreases in the mRNA levels of gdnf, dat1, vmat2, and th in the substantia nigra (SN) were observed with both acute and chronic dosing of 10 mg/kg MPH. We also found an increase in mRNA levels of the pro-inflammatory genes il-6 and tnf-α in the striatum, although these were seen only at an acute dose of 10 mg/kg and not following chronic dosing.

Conclusion

Collectively, our results suggest that chronic MPH usage in mice at doses spanning the therapeutic range in humans, especially at prolonged higher doses, has long-term neurodegenerative consequences.

The role of oxidative stress in neuromelanin synthesis in PC12 cells

Previous research has indicated that neuromelanin (NM) is involved in the pathogenesis of Parkinson's disease (PD). Increased reactive oxygen species (ROS) generation in PD sufferers is thought to be related to enhanced tyrosine hydroxylase (TH) activity and NM production. However, few reports have confirmed this hypothesis. In this study, PC12 cells of all experiments were exposed to 50 μmol/L levodopa (l-DOPA) to generate a model for NM synthesis. Meanwhile, PC12 cells were treated with glucose oxidase (GO) at different concentrations to generate oxidative stress. Finally, cell viability, TH activity, and NM generation in PC12 cells were measured. The results showed that GO dose-dependently stimulated oxidative stress generation in PC12 cells. Moderate increases in oxidative stress enhanced the viability of PC12 cells. However, an excessive level of oxidative stress can lead to the degeneration of PC12 cells. Notably, in the surviving PC12 cells, ROS significantly increased the TH activity, and the NM production was also upregulated. Thus, oxidative stress may upregulate the synthesis of NM, which may be a result of the increased TH activity observed in response to the elevated ROS in l-DOPA-treated PC12 cells.

Pristanic acid promotes oxidative stress in brain cortex of young rats: a possible pathophysiological mechanism for brain damage in peroxisomal disorders

Pristanic acid (Prist) is accumulated in various peroxisomal disorders characterized by severe neurological dysfunction whose pathogenesis is poorly understood. Since oxidative damage has been demonstrated in brain of patients affected by neurodegenerative disorders, in the present work we investigated the in vitro effects of Prist on important parameters of oxidative stress in cerebral cortex from young rats. Prist significantly increased malondialdehyde levels, reflecting an increase of lipid peroxidation. This effect was totally prevented by the free radical scavenger melatonin, suggesting the involvement of reactive species. Prist also provoked protein oxidative damage, as determined by increased carbonyl formation and sulfhydryl oxidation. Otherwise, it did not alter nitric oxide production, indicating that nitrogen reactive species were not implicated in the lipid and oxidative damage provoked by Prist. Furthermore, the concentration of glutathione (GSH), the major brain non-enzymatic antioxidant defense, was significantly decreased by Prist and this decrease was fully prevented by melatonin and attenuated by α-tocopherol. It is therefore presumed that Prist elicits oxidative stress in the brain probably via reactive oxygen species formation and that this pathomechanism may possibly be involved in the brain damage found in patients affected by peroxisomal disorders where Prist accumulates.

Tyrosine hydroxylase and regulation of dopamine synthesis

Tyrosine hydroxylase is the rate-limiting enzyme of catecholamine biosynthesis; it uses tetrahydrobiopterin and molecular oxygen to convert tyrosine to DOPA. Its amino terminal 150 amino acids comprise a domain whose structure is involved in regulating the enzyme's activity. Modes of regulation include phosphorylation by multiple kinases at four different serine residues, and dephosphorylation by two phosphatases. The enzyme is inhibited in feedback fashion by the catecholamine neurotransmitters. Dopamine binds to TyrH competitively with tetrahydrobiopterin, and interacts with the R domain. TyrH activity is modulated by protein-protein interactions with enzymes in the same pathway or the tetrahydrobiopterin pathway, structural proteins considered to be chaperones that mediate the neuron's oxidative state, and the protein that transfers dopamine into secretory vesicles. TyrH is modified in the presence of NO, resulting in nitration of tyrosine residues and the glutathionylation of cysteine residues.

Neurochemical evidence that phytanic acid induces oxidative damage and reduces the antioxidant defenses in cerebellum and cerebral cortex of rats

AIMS

In the present work we investigated the in vitro effects of phytanic acid (Phyt), that accumulates in Refsum disease and other peroxisomal diseases, on important parameters of oxidative stress in cerebellum and cerebral cortex from young rats.

MAIN METHODS

The parameters thiobarbituric acid-reactive substances levels (TBA-RS; lipid peroxidation), carbonyl formation and sulfhydryl oxidation (protein oxidative damage) and the concentrations of the most important nonenzymatic antioxidant defense reduced glutathione (GSH) were determined.

KEY FINDINGS

It was observed that Phyt significantly increased TBA-RS levels in both cerebral structures. This effect was prevented by the antioxidants alpha-tocopherol and melatonin, suggesting the involvement of free radicals. Phyt also provoked protein oxidative damage in both cerebellum and cerebral cortex, as determined by increased carbonyl content and sulfhydryl oxidation. Furthermore, Phyt significantly diminished the concentrations of GSH, while melatonin and alpha-tocopherol treatment totally blocked this effect. We also verified that Phyt does not behave as a direct acting oxidant, since Phyt did not oxidize commercial solutions of GSH and reduced cytochrome c to Phyt in a free cell medium.

SIGNIFICANCE

Our data indicate that oxidative stress is elicited in vitro by Phyt, a mechanism that may contribute at least in part to the pathophysiology of Refsum disease and other peroxisomal disorders where Phyt is accumulated.

Differential roles of nitric oxide synthases in regulation of ultraviolet B light-induced apoptosis

Ultraviolet B light (UVB) activates nitric oxide synthase(s) (NOSs) and nitric oxide (NO()) production, which plays a role in regulation of apoptosis. However, the role of NO() in UVB-induced apoptosis remains controversial. In this study, we analyzed expression and activation of constitutive NOSs (cNOSs) and their roles in UV-induced apoptosis of HaCaT keratinocytes. Our data showed that the expression of neuronal NOS (nNOS) was increased while endothelial NOS (eNOS) was uncoupled in the early phase (0-6 h) post-UVB. The expression of both cNOSs peaked at 12h post-UVB and NO() was transiently elevated with 30 min and then steadily rose from 6 to 18 h post-UVB. The expression of iNOS was detected at 6h post-UVB and then sturdily increased. Inhibition of cNOSs with L-NAME reduced the inducibility of NO(*) in the early and late phases of irradiation. Along with the eNOS uncoupling, an increased level of peroxynitrite (ONOO(-)) was detected in the early phase, but not in the late phase post-UVB. Inhibition of cNOSs reduced the production of ONOO(-) in the early time, but led to an increase of ONOO(-) in the late time after UVB-irradiation. The results indicate that cNOSs regulate NO()/ONOO(-) imbalance after UVB-irradiation. Our data suggested that the activation of cNOSs in the early phase post-UVB leads to NO()/ONOO(-) imbalance and promotes apoptosis via a caspase 3-independent pathway. The elevation of NO() in the late phase of UVB-irradiation is mainly produced by inducible NOS (iNOS). However, cNOSs also contribute to the NO() production and to maintain a higher NO()/ONOO(-) ratio, which reduces caspase 3 activity and protects cells from UVB-induced apoptosis.

The role of oxidative stress, metabolic compromise, and inflammation in neuronal injury produced by amphetamine-related drugs of abuse

Methamphetamine (METH) and 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) are amphetamine derivatives with high abuse liability. These amphetamine-related drugs of abuse mediate their effects through the acute activation of both dopaminergic and serotonergic neurons. Long-term abuse of these amphetamine derivatives, however, results in damage to both dopaminergic and serotonergic terminals throughout the brain. This toxicity is mediated in part by oxidative stress, metabolic compromise, and inflammation. The overall objective of this review is to highlight experimental evidence that METH and MDMA increase oxidative stress, produce mitochondrial dysfunction, and increase inflammation that converge and culminate in the long-term toxicity to dopaminergic and serotonergic neurons.

Oxygen dependence of tyrosine hydroxylase

The effects of dioxygen on tyrosine hydroxylase (TH) activity was studied, measuring the formation of DOPA from tyrosine, (3)H(2)O from 3,5-(3)H-tyrosine, or by direct oxygraphic determination of oxygen consumption. A high enzyme activity was observed during the initial 1-2 min of the reactions, followed by a decline in activity, possibly related to a turnover dependent substoichiometrical oxidation of enzyme bound Fe(II) to the inactive Fe(III) state. During the initial reaction phase, apparent K (m)-values of 29-45 microM for dioxygen were determined for all human TH isoforms, i.e. 2-40 times higher than previously reported for TH isolated from animal tissues. After 8 min incubation, the K (m) (O(2))-values had declined to an average of 20 +/- 4 microM. Thus, TH activity may be severely limited by oxygen availability even at moderate hypoxic conditions, and the enzyme is rapidly and turnover dependent inactivated at the experimental conditions commonly employed to measure in vitro activities.

Alpha-lipoic acid differently affects the reserpine-induced oxidative stress in the striatum and prefrontal cortex of rat brain

Antioxidative properties of alpha-lipoic acid (LA) are widely investigated in different in vivo and in vitro models. The aim of this study was to examine whether LA attenuates oxidative stress induced in rats by reserpine, a model substance frequently used to produce Parkinsonism in animals. Male Wistar rats were treated with reserpine (5 mg/kg) and LA (50 mg/kg) separately or in combination. The levels of reduced glutathione (GSH), glutathione disulfide (GSSG), nitric oxide (NO) and S-nitrosothiols as well as activities of glutathione peroxidase (GPx), glutathione-S-transferase (GST) and L-gamma-glutamyl transpeptidase (gamma-GT) were determined in the striatum and prefrontal cortex homogenates. In the striatum and prefrontal cortex a single dose of reserpine significantly enhanced levels of GSSG and NO but not that of S-nitrosothiols when compared with control. In the striatum, LA administered jointly with reserpine markedly increased the concentration of GSH and decreased GSSG level. In the prefrontal cortex, such treatment produced only an increasing tendency in GSH level but caused no changes in GSSG content. In both structures LA injected jointly with reserpine markedly decreased NO concentrations but did not cause significant changes in S-nitrosothiol levels when compared with control. Enzymatic activities of GPx and GST were intensified by LA in the striatum. In the prefrontal cortex, GPx activity was not altered, while that of GST was decreased. Gamma-GT activity was attenuated by reserpine in the striatum while LA reversed this effect. Such changes were not observed in the prefrontal cortex. The mode of LA action in the striatum during the reserpine-evoked oxidative stress strongly suggests that this compound may be of therapeutic value in the treatment of Parkinson's disease.

Methamphetamine-induced selective dopaminergic neurotoxicity is accompanied by an increase in striatal nitrate in the mouse

Exposure to high doses of methamphetamine (METH), a major drug of abuse, may cause neuronal damage. Previous studies have implicated the role of peroxynitrite, produced by nitric oxide (NO) and reactive oxygen species, in dopaminergic neurotoxicity produced by METH in mice. The present article was undertaken to investigate if a neurotoxic regimen of METH is associated with changes in tissue levels of nitrate and nitrite, which are the stable products of NO. Administration of METH (5 mg/kg x 3) to Swiss Webster mice resulted in marked depletion of dopamine (DA) and DA transporter (DAT) binding sites but no change in 5-hydroxytryptamine (5-HT) and 5-HT transporter (5-HTT) binding sites in the striatum, amygdala, frontal cortex, and hippocampus, suggesting that METH causes selective neurotoxicity to DA nerve terminals. The concentration of nitrate in the striatum was increased by about two-fold after METH administration; however, no changes in nitrate concentration were detected in other brain regions that endured dopaminergic neurotoxicity. These findings suggest that (a) a neurotoxic regimen of METH produces selective increase in NO in the striatum, which may generate toxic species such as peroxynitrite, and (b) toxins other than NO-related derivatives may mediate dopaminergic neurotoxicity in the amygdala and frontal cortex.

Nitric oxide and peroxynitrite in health and disease

The discovery that mammalian cells have the ability to synthesize the free radical nitric oxide (NO) has stimulated an extraordinary impetus for scientific research in all the fields of biology and medicine. Since its early description as an endothelial-derived relaxing factor, NO has emerged as a fundamental signaling device regulating virtually every critical cellular function, as well as a potent mediator of cellular damage in a wide range of conditions. Recent evidence indicates that most of the cytotoxicity attributed to NO is rather due to peroxynitrite, produced from the diffusion-controlled reaction between NO and another free radical, the superoxide anion. Peroxynitrite interacts with lipids, DNA, and proteins via direct oxidative reactions or via indirect, radical-mediated mechanisms. These reactions trigger cellular responses ranging from subtle modulations of cell signaling to overwhelming oxidative injury, committing cells to necrosis or apoptosis. In vivo, peroxynitrite generation represents a crucial pathogenic mechanism in conditions such as stroke, myocardial infarction, chronic heart failure, diabetes, circulatory shock, chronic inflammatory diseases, cancer, and neurodegenerative disorders. Hence, novel pharmacological strategies aimed at removing peroxynitrite might represent powerful therapeutic tools in the future. Evidence supporting these novel roles of NO and peroxynitrite is presented in detail in this review.

Drugs modulating the biological effects of peroxynitrite and related nitrogen species

The term "reactive nitrogen species" includes nitrogen monoxide, commonly called nitric oxide, and some other remarkable chemical entities (peroxynitrite, nitrosoperoxycarbonate, etc.) formed mostly from nitrogen monoxide itself in biological environments. Regardless of the specific mechanisms implicated in their effects, however, it is clear that an integrated pharmacological approach to peroxynitrite and related species is only just beginning to take shape. The array of affected chemical and pathological processes is extremely broad. One of the most conspicuous mechanisms observed thus far has been the scavenging of the peroxynitrite anion by molecules endowed with antioxidant activity. This discovery has in turn lent great significance to several naturally occurring and synthetic antioxidants, which usually protect not only against oxidative reactions, but also from nitrating ones, both in vitro and in vivo. This has proven to be beneficial in different tissues, especially within the central nervous system. Taking these results and those of other biochemical investigations into account, many research lines are currently in progress to establish the true potential of reactive nitrogen species deactivators in the therapy of neurological diseases, ischemia-reperfusion damage, renal failure, and lung injury, among others.

Midbrain neuronal cultures from parkin mutant mice are resistant to nitric oxide-induced toxicity

Nitric oxide (NO) is a modulator of differentiation and survival of dopamine (DA) neurons. NO may play a role in the pathogenesis of Parkinson's disease (PD) since its levels are increased in parkinsonian brains and it can nitrosylate and alter the function of key proteins involved in the pathogenesis of PD. NO producing neurons are spared in parkinsonian brains suggesting that toxicity by NO can be compensated. Furthermore, the neurotoxic or neurotrophic effects of NO on DA neurons depend on the balance between NO levels and the intracellular levels of glutathione (GSH). We have investigated the effects of NO-donating agents on midbrain neuronal cultures from parkin-deficient mice. Parkin mutations are the most common genetic deficit observed in hereditary parkinsonism. These mice have abnormal DA release and metabolism, increased production of free radicals and a compensatory elevation of GSH. Cultures from parkin knockout (PK-KO) mice were more resistant than those of wild type (WT) to the neurotoxicity by NO, and the difference of susceptibility applied equally to DA, GABA and total number of neurons, and to astrocytes. NO-induced cell death was mainly apoptotic and could be reduced by caspase inhibitors. Cultures from PK-KO had greater levels of GSH than WT and, after treatment with NO, greater levels of S-nitrosoglutathione. The differences in susceptibility disappear when the synthesis of GSH is inhibited or the GSH chelated with diethyl maleate. Our data show that, contrary to the expectations, and related to the enhanced production of GSH in parkin knockout mice, parkin-deficient dopamine neurons are less susceptible to toxicity by NO.

Cardiac sympathetic neuroprotective effect of desipramine in tachycardia-induced cardiomyopathy

Cardiac sympathetic transmitter stores are reduced in the failing heart. In this study, we proposed to investigate whether the reduction of cardiac sympathetic neurotransmitters was associated with increased interstitial norepinephrine (NE) and reactive oxygen species in congestive heart failure (CHF), using a microdialysis technique and salicylate to detect ·OH generation. Rabbits with and without rapid ventricular pacing (340 beats/min) were randomized to receive desipramine (10 mg/day) or placebo for 8 wk. Rapid pacing produced left ventricular dilation and systolic dysfunction. The failing myocardium also showed reduced tissue contents of NE and tyrosine hydroxylase protein and activity. In contrast, myocardial interstitial NE was increased in CHF (0.89 ± 0.11 ng/ml) compared with the sham-operated animals (0.26 ± 0.03 ng/ml). In addition, cardiac oxidative stress was increased in CHF animals as measured by myocardial interstitial ·OH radical, tissue oxidized glutathione, and oxidized mitochondrial DNA. Desipramine treatment produced significant NE uptake inhibition as evidence by an exaggerated pressor response and a greater increase of myocardial interstitial NE in response to intravenous NE infusion but no significant effects on cardiac function or hemodynamics in sham-operated or CHF animals. However, desipramine treatment attenuated the reductions of tissue NE and tyrosine hydroxylase protein and activity in CHF. Desipramine also prevented the reduction of tyrosine hydroxylase produced by NE in PC12 cells. Thus the reduction of cardiac sympathetic neurotransmitters is related to the increased interstitial NE and tissue oxidative stress in CHF. Also, normal neuronal uptake of NE is required for NE or its oxidized metabolites to exert their neurotoxic effects.

Role of nitrergic system in behavioral and neurotoxic effects of amphetamine analogs

Several amphetamine analogs are potent psychostimulants and major drugs of abuse. In animal models, the psychomotor and reinforcing effects of amphetamine, methamphetamine (METH), 3,4-methylenedioxymethamphetamine (MDMA; Ecstasy), and methylphenidate (MPD; Ritalin) are thought to be dependent on increased extracellular levels of dopamine (DA) in mesocorticolimbic and mesostriatal pathways. However, amphetamine analogs that increase primarily serotonergic transmission, such as p-chloroamphetamine (PCA) and fenfluramine (FEN), have no potential for abuse. High doses of METH, MDMA, PCA, and FEN produce depletions of dopaminergic and serotonergic nerve terminal markers and are considered as potential neurotoxicants. The first part of this review briefly summarizes the behavioral and neurotoxic effects of amphetamines that have a different spectrum of activity on dopaminergic and serotonergic systems. The second part discusses evidence supporting involvement of the nitrergic system in dopamine-mediated effects of amphetamines. The nitrergic system in this context corresponds to nitric oxide (NO) produced from neuronal nitric oxide synthase (nNOS) that has roles in nonsynaptic interneuronal communication and excitotoxic neuronal injury. Increasing evidence now suggests cross talk between dopamine, glutamate, and NO. Results from our laboratory indicate that dopamine-dependent psychomotor, reinforcing, and neurotoxic effects of amphetamines are diminished by pharmacological blockade of nNOS or deletion of the nNOS gene. These findings, and evidence supporting the role of NO in synaptic plasticity and neurotoxic insults, suggest that NO functions as a neuronal messenger and a neurotoxicant subsequent to exposure to amphetamine-like psychostimulants.

Nitration of tyrosine 92 mediates the activation of rat microsomal glutathione s-transferase by peroxynitrite

There is increasing evidence that protein function can be modified by nitration of tyrosine residue(s), a reaction catalyzed by proteins with peroxidase activity, or that occurs by interaction with peroxynitrite, a highly reactive oxidant formed by the reaction of nitric oxide with superoxide. Although there are numerous reports describing loss of function after treatment of proteins with peroxynitrite, we recently demonstrated that the microsomal glutathione S-transferase 1 is activated rather than inactivated by peroxynitrite and suggested that this could be attributed to nitration of tyrosine residues rather than to other effects of peroxynitrite. In this report, the nitrated tyrosine residues of peroxynitrite-treated microsomal glutathione S-transferase 1 were characterized by mass spectrometry and their functional significance determined. Of the seven tyrosine residues present in the protein, only those at positions 92 and 153 were nitrated after treatment with peroxynitrite. Three mutants (Y92F, Y153F, and Y92F, Y153F) were created using site-directed mutagenesis and expressed in LLC-PK1 cells. Treatment of the microsomal fractions of these cells with peroxynitrite resulted in an approximately 2-fold increase in enzyme activity in cells expressing the wild type microsomal glutathione S-transferase 1 or the Y153F mutant, whereas the enzyme activity of Y92F and double site mutant was unaffected. These results indicate that activation of microsomal glutathione S-transferase 1 by peroxynitrite is mediated by nitration of tyrosine residue 92 and represents one of the few examples in which a gain in function has been associated with nitration of a specific tyrosine residue.

S-thiolation of tyrosine hydroxylase by reactive nitrogen species in the presence of cysteine or glutathione

Tyrosine hydroxylase (TH) is the initial and rate-limiting enzyme in the biosynthesis of the neurotransmitter dopamine. Peroxynitrite (ONOO-) and nitrogen dioxide (NO2) inhibit TH catalytic function and cause nitration of protein tyrosine residues. Exposure of TH to either ONOO- or NO2 in the presence of cysteine (or glutathione) prevents tyrosine nitration and results in S-thiolation instead. TH catalytic activity is suppressed by S-thiolation. Dithiothreitol prevents and reverses the modification of TH by S-thiolation, and returns enzyme activity to control levels. S-Nitrosothiols, which are known to S-thiolate proteins, can be formed in the reaction of cysteine or glutathione with reactive nitrogen species. Therefore, S-nitrosoglutathione (GSNO) was tested for its ability to modify TH. Fresh solutions of GSNO did not modify TH, whereas decomposed GSNO resulted in extensive S-thiolation of the protein. Dimedone, a sulfenic acid trap, prevents S-thiolation of TH when included with GSNO during its decomposition. Taken together, these results show that TH is S-thiolated by ONOO- or NO2 in the presence of cysteine. S-Thiolation occurs at the expense of tyrosine nitration. Glutathione disulfide S-oxide, which forms spontaneously in the decomposition of GSNO and which is found in tissue undergoing oxidative stress, may be the species that S-thiolates TH.

Role of peroxidases in Parkinson disease: a hypothesis

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

Periadolescent rats (P41-50) exhibit increased susceptibility to D-methamphetamine-induced long-term spatial and sequential learning deficits compared to juvenile (P21-30 or P31-40) or adult rats (P51-60)

We have previously shown that P11-20 treatment with d-methamphetamine (MA) induces impaired spatial navigation in the Morris water maze (MWM), whereas P1-10 treatment does not. Little is known about the long-term behavioral consequences of MA during juvenile, adolescent, and early adult brain development. In dose-response experiments, we tested successive 10-day intervals of exposure to MA in rats (P21-30, P31-40, P41-50, and P51-60; four doses per day). MA dosing prior to P21 produces little or no toxicity; however, we observed an increased toxicity with advancing age. Across-age comparisons revealed no MWM acquisition or Cincinnati water maze (CWM) effects after MA treatment on P21-30 (2.5-10 mg/kg/dose), P31-40 (1.25-7.5 mg/kg/dose), or P51-60 (1.25-5.0 mg/kg/dose); however, significantly impaired MWM acquisition was observed after P41-50 MA treatment at the highest dose (6.25 mg/kg/dose). Learning in the CWM was also impaired in this group. No effects were seen at 1.25, 2.5, or 5 mg/kg/dose following P41-50 MA treatment. MWM reversal learning trials after P41-50 treatment showed a trend towards longer latency in all MA dose groups, but no effect on double-reversal trials. Reversal and double-reversal also showed no effects at the other exposure ages. No differences in straight channel swimming or cued learning in the MWM were seen after MA treatment at any exposure age. P41-50 is the periadolescent stage of brain development in rodents. The effects observed at this age may suggest a previously unrecognized period of susceptibility for MA-induced cognitive deficits.

Glutathione depletion resulting in selective mitochondrial complex I inhibition in dopaminergic cells is via an NO-mediated pathway not involving peroxynitrite: implications for Parkinson's disease

An early biochemical change in the Parkinsonian substantia nigra (SN) is reduction in total glutathione (GSH + GSSG) levels in affected dopaminergic neurons prior to depletion in mitochondrial complex I activity, dopamine loss, and cell death. We have demonstrated using dopaminergic PC12 cell lines genetically engineered to inducibly down-regulate glutathione synthesis that total glutathione depletion in these cells results in selective complex I inhibition via a reversible thiol oxidation event. Here, we demonstrate that inhibition of complex I may occur either by direct nitric oxide (NO) but not peroxinitrite-mediated inhibition of complex I or through H2O2-mediated inhibition of the tricarboxylic acid (TCA) cycle enzyme alpha-ketoglutarate dehydrogenase (KGDH) which supplies NADH as substrate to the complex; activity of both enzymes are reduced in PD. While glutathione depletion causes a reduction in spare KGDH enzymatic capacity, it produces a complete collapse of complex I reserves and significant effects on mitochondrial function. Our data suggest that NO is likely the primary agent involved in preferential complex I inhibition following acute glutathione depletion in dopaminergic cells. This may have major implications in terms of understanding mechanisms of dopamine cell death associated with PD especially as they relate to complex I inhibition.