Dopamine toxicity in neuroblastoma cells: role of glutathione depletion by L-BSO and apoptosis

Prenatal Metal Exposures and Child Social Responsiveness Scale Scores in 2 Prospective Studies

Background

Prenatal exposure to metals is hypothesized to be associated with child autism. We aim to investigate the joint and individual effects of prenatal exposure to urine metals including lead (Pb), mercury (Hg), manganese (Mn), and selenium (Se) on child Social Responsiveness Scale (SRS) scores.

Methods

We used data from 2 cohorts enriched for likelihood of autism spectrum disorder (ASD): Early Autism Risk Longitudinal Investigation (EARLI) and the Markers of Autism Risk in Babies-Learning Early Signs (MARBLES) studies. Metal concentrations were measured in urine collected during pregnancy. We used Bayesian Kernel Machine Regression and linear regression models to investigate both joint and independent associations of metals with SRS Z-scores in each cohort. We adjusted for maternal age at delivery, interpregnancy interval, maternal education, child race/ethnicity, child sex, and/or study site.

Results

The final analytic sample consisted of 251 mother-child pairs. When Pb, Hg, Se, and Mn were at their 75th percentiles, there was a 0.03 increase (95% credible interval [CI]: -0.11, 0.17) in EARLI and 0.07 decrease (95% CI: -0.29, 0.15) in MARBLES in childhood SRS Z-scores, compared to when all 4 metals were at their 50th percentiles. In both cohorts, increasing concentrations of Pb were associated with increasing values of SRS Z-scores, fixing the other metals to their 50th percentiles. However, all the 95% credible intervals contained the null.

Conclusions

There were no clear monotonic associations between the overall prenatal metal mixture in pregnancy and childhood SRS Z-scores at 36 months. There were also no clear associations between individual metals within this mixture and childhood SRS Z-scores at 36 months. The overall effects of the metal mixture and the individual effects of each metal within this mixture on offspring SRS Z-scores might be heterogeneous across child sex and cohort. Further studies with larger sample sizes are warranted.

Effect of Chronic Methylphenidate Treatment in a Female Experimental Model of Parkinsonism

Methylphenidate (MPH) is the most commonly prescribed drug for the treatment of ADHD in males and females. However, a majority of previous studies investigated the effect of MPH in only males, and little is known regarding consequences of female exposure to MPH. This is unfortunate because the few studies that have been conducted indicate that females have a greater sensitivity to MPH. Previous research in male mice has shown that chronic exposure to MPH causes dopaminergic neurons within the nigrostriatal pathway to be more sensitive to the Parkinsonian toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). However, estrogen has been shown to protect dopaminergic neurons from MPTP neurotoxicity. Therefore, in this study, we test the hypothesis that chronic MPH exposure in female mice will render dopaminergic neurons in the nigrostriatal pathway more sensitive to MPTP, and that estrogen may play a protective role. Interestingly, proestrus females exhibited greater sensitivity to MPTP, with significantly reduced dopaminergic neurons in the SN and significant increases in DA quinone production. Chronic MPH exposure contributed to GSH depletion, but surprisingly, it did not increase dopamine quinone levels or dopaminergic cell loss. There were no significant differences in anestrus animals, with the exception of a depletion in GSH seen when animals received chronic high-dose (10 mg/kg) MPH followed by MPTP. Thus, estrogen may actually sensitize neurons to MPTP in this model, and chronic MPH may contribute to GSH depletion within the striatum. This study provides insight into how chronic psychostimulant use may affect males and females differently.

Investigation into the impact of tyrosine on the product formation and quality attributes of mAbs in rCHO cell cultures

Tyrosine (Tyr) is crucial to the maintenance of the monoclonal antibody (mAb) titers and quality attributes in fed-batch cultures of recombinant Chinese hamster ovary (rCHO) cells. However, the relation between tyrosine and these aspects is not yet fully defined. In order to further elucidate such a relation, two groups of fed-batch experiments with high tyrosine (H-T) or low tyrosine (L-T) additions producing an IgG1 monoclonal antibody against CD20 were implemented to investigate the intracellular and extracellular effects of tyrosine on the culture performance. It was found that the scarcity of tyrosine led to the distinctive reduction in both viable cell density and antibody specific production rate, hence the sharply reduced titer, possibly related to the impaired translation efficiency caused by the substrate limitation of tyrosine. In addition, alterations to the critical quality attributes were detected in the L-T group, compared to those in the H-T condition. Notable decrease in the contents of intact antibody was found under the L-T condition because of the elevated reductive level in the supernatant. Moreover, the aggregate content in the L-T condition was also reduced, probably resulting from the accumulation of extracellular cystine. In particular, the lysine variant content noticeably increased with tyrosine limitation owing to the downregulation of two carboxypeptidases, i.e., CpB and CpH. Overall, understanding the role of tyrosine in these aspects is fundamental to the increase of product titers and control of critical quality attributes in the monoclonal antibody production of rCHO cell fed-batch cultures. KEY POINTS: • Tyrosine is essential in the maintenance of product titers and the control of product qualities in high cell density cultivations in rCHO cell. • This study revealed the bottleneck of decreased q_mAbupon the deficiency of tyrosine. • The impact of tyrosine on the critical product qualities and the underlying mechanisms were also thoroughly assessed.

Chronic methylphenidate induces increased quinone production and subsequent depletion of the antioxidant glutathione in the striatum

BACKGROUND

Methylphenidate (Ritalin®) is a psychostimulant used chronically to treat attention deficit hyperactivity disorder. Methylphenidate acts by preventing the reuptake of dopamine and norepinephrine, resulting in an increase in these neurotransmitters in the synaptic cleft. Excess dopamine can be autoxidized to a quinone that may lead to oxidative stress. The antioxidant, glutathione helps to protect the cell against quinones via conjugation reactions; however, depletion of glutathione may result from excess quinone formation. Chronic exposure to methylphenidate appears to sensitize dopaminergic neurons to the Parkinsonian toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). We hypothesized that oxidative stress caused by the autooxidation of the excess dopamine renders dopaminergic neurons within the nigrostriatal pathway to be more sensitive to MPTP.

METHODS

To test this hypothesis, male mice received chronic low or high doses of MPH and were exposed to saline or MPTP following a 1-week washout. Quinone formation in the striatum was examined via dot blot, and striatal GSH was quantified using a glutathione assay.

RESULTS

Indeed, quinone formation increased with increasing doses of methylphenidate. Additionally, methylphenidate dose-dependently resulted in a depletion of glutathione, which was further depleted following MPTP treatment.

CONCLUSIONS

Thus, the increased sensitivity of dopamine neurons to MPTP toxicity following chronic methylphenidate exposure may be due to quinone production and subsequent depletion of glutathione.

Buprenorphine and Methadone as Opioid Maintenance Treatments for Heroin-Addicted Patients Induce Oxidative Stress in Blood

Buprenorphine and methadone are two substances widely used in the substitution treatment of patients who are addicted to opioids. Although it is known that they partly act efficiently towards this direction, there is no evidence regarding their effects on the redox status of patients, a mechanism that could potentially improve their action. Therefore, the aim of the present investigation was to examine the impact of buprenorphine and methadone, which are administered as substitutes to heroin-dependent patients on specific redox biomarkers in the blood. From the results obtained, both the buprenorphine (n = 21) and the methadone (n = 21) groups exhibited oxidative stress and compromised antioxidant defence. This was evident by the decreased glutathione (GSH) concentration and catalase activity in erythrocytes and the increased concentrations of thiobarbituric acid reactive substances (TBARS) and protein carbonyls in the plasma, while there was no significant alteration of plasma total antioxidant capacity (TAC) compared to the healthy individuals (n = 29). Furthermore, methadone revealed more severe oxidant action compared to buprenorphine. Based on relevant studies, the tested substitutes mitigate the detrimental effects of heroin on patient redox status; still it appears that they need to be boosted. Therefore, concomitant antioxidant administration could potentially enhance their beneficial action, and most probably, buprenorphine that did not induce oxidative stress in such a severe mode as methadone, on the regulation of blood redox status.

S-Glutathionylation and Redox Protein Signaling in Drug Addiction

Drug addiction is a chronic relapsing disorder that comes at a high cost to individuals and society. Therefore understanding the mechanisms by which drugs exert their effects is of prime importance. Drugs of abuse increase the production of reactive oxygen and nitrogen species resulting in oxidative stress. This change in redox homeostasis increases the conjugation of glutathione to protein cysteine residues; a process called S-glutathionylation. Although traditionally regarded as a protective mechanism against irreversible protein oxidation, accumulated evidence suggests a more nuanced role for S-glutathionylation, namely as a mediator in redox-sensitive protein signaling. The reversible modification of protein thiols leading to alteration in function under different physiologic/pathologic conditions provides a mechanism whereby change in redox status can be translated into a functional response. As such, S-glutathionylation represents an understudied means of post-translational protein modification that may be important in the mechanisms underlying drug addiction. This review will discuss the evidence for S-glutathionylation as a redox-sensing mechanism and how this may be involved in the response to drug-induced oxidative stress. The function of S-glutathionylated proteins involved in neurotransmission, dendritic spine structure, and drug-induced behavioral outputs will be reviewed with specific reference to alcohol, cocaine, and heroin.

Toxic effects of Mn2O3 nanoparticles on rat testis and sex hormone

BACKGROUND AND OBJECTIVE

The safety of Mn2O3 nanoparticles (which are extensively used in industries) on male reproductive system is not known. Hence, we investigated the effects of Mn2O3 nanoparticles on male reproductive system.

MATERIALS AND METHODS

A total of 40 Wistar adult male rats were randomly assigned to four groups of 10 rats each. Three groups received Mn2O3 solution in concentrations of 100, 200, and 400 ppm orally for 14 days; the control group received equal volume of saline solution. Blood samples and testicles were collected for analysis.

RESULTS

Significant reduction in luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone, spermatogonial cells, primary spermatocyte, spermatid and Leydig cell was observed in the Mn2O3 nanoparticles treated groups compared with controls.

CONCLUSION

Mn2O3 nanoparticles significantly reduce FSH, LH, and testosterone levels resulting in a significant reduction in testicular cytology.

Dopamine Cytotoxicity Involves Both Oxidative and Nonoxidative Pathways in SH-SY5Y Cells: Potential Role of Alpha-Synuclein Overexpression and Proteasomal Inhibition in the Etiopathogenesis of Parkinson's Disease

Background. The cytotoxic effects of dopamine (DA) on several catecholaminergic cell lines involve DA oxidation products like reactive oxygen species (ROS) and toxic quinones and have implications in the pathogenesis of sporadic Parkinson's disease (PD). However, many molecular details are yet to be elucidated, and the possible nonoxidative mechanism of dopamine cytotoxicity has not been studied in great detail. Results. Cultured SH-SY5Y cells treated with DA (up to 400 μM) or lactacystin (5 μM) or DA (400 μM) plus N-acetylcysteine (NAC, 2.5 mM) for 24 h are processed accordingly to observe the cell viability, mitochondrial dysfunctions, oxidative stress parameters, proteasomal activity, expression of alpha-synuclein gene, and intracellular accumulation of the protein. DA causes mitochondrial dysfunction and extensive loss of cell viability partially inhibited by NAC, potent inhibition of proteasomal activity marginally prevented by NAC, and overexpression with accumulation of intracellular alpha-synuclein partially preventable by NAC. Under similar conditions of incubation, NAC completely prevents enhanced production of ROS and increased formation of quinoprotein adducts in DA-treated SH-SY5Y cells. Separately, proteasomal inhibitor lactacystin causes accumulation of alpha-synuclein as well as mitochondrial dysfunction and cell death. Conclusions. DA cytotoxicity includes both oxidative and nonoxidative modes and may involve overexpression and accumulation of alpha-synuclein as well as proteasomal inhibition.

Curcumin pretreatment induces Nrf2 and an antioxidant response and prevents hemin-induced toxicity in primary cultures of cerebellar granule neurons of rats

Curcumin is a bifunctional antioxidant derived from Curcuma longa. This study identifies curcumin as a neuroprotectant against hemin-induced damage in primary cultures of cerebellar granule neurons (CGNs) of rats. Hemin, the oxidized form of heme, is a highly reactive compound that induces cellular injury. Pretreatment of CGNs with 5–30 μM curcumin effectively increased by 2.3–4.9 fold heme oxygenase-1 (HO-1) expression and by 5.6–14.3-fold glutathione (GSH) levels. Moreover, 15 μM curcumin attenuated by 55% the increase in reactive oxygen species (ROS) production, by 94% the reduction of GSH/glutathione disulfide (GSSG) ratio, and by 49% the cell death induced by hemin. The inhibition of heme oxygenase system or GSH synthesis with tin mesoporphyrin and buthionine sulfoximine, respectively, suppressed the protective effect of curcumin against hemin-induced toxicity. These data strongly suggest that HO-1 and GSH play a major role in the protective effect of curcumin. Furthermore, it was found that 24 h of incubation with curcumin increases by 1.4-, 2.3-, and 5.2-fold the activity of glutathione reductase, glutathione S-transferase and superoxide dismutase, respectively. Additionally, it was found that curcumin was capable of inducing nuclear factor (erythroid-derived 2)-like 2 (Nrf2) translocation into the nucleus. These data suggest that the pretreatment with curcumin induces Nrf2 and an antioxidant response that may play an important role in the protective effect of this antioxidant against hemin-induced neuronal death.

LRRK2 affects vesicle trafficking, neurotransmitter extracellular level and membrane receptor localization

The leucine-rich repeat kinase 2 (LRRK2) gene was found to play a role in the pathogenesis of both familial and sporadic Parkinson’s disease (PD). LRRK2 encodes a large multi-domain protein that is expressed in different tissues. To date, the physiological and pathological functions of LRRK2 are not clearly defined. In this study we have explored the role of LRRK2 in controlling vesicle trafficking in different cellular or animal models and using various readouts. In neuronal cells, the presence of LRRK2^G2019S pathological mutant determines increased extracellular dopamine levels either under basal conditions or upon nicotine stimulation. Moreover, mutant LRRK2 affects the levels of dopamine receptor D1 on the membrane surface in neuronal cells or animal models. Ultrastructural analysis of PC12-derived cells expressing mutant LRRK2^G2019S shows an altered intracellular vesicle distribution. Taken together, our results point to the key role of LRRK2 to control vesicle trafficking in neuronal cells.

15-Deoxy-Δ12,14-prostaglandin J₂ modulates manganese-induced activation of the NF-κB, Nrf2, and PI3K pathways in astrocytes

Excessive exposure to manganese (Mn) increases levels of oxidative stressors and proinflammatory mediators, such as cyclooxygenase-2 and prostaglandin E(2). Mn also activates nuclear factor-κB (NF-κB), an important mediator of inflammation. The signaling molecule 15-deoxy-Δ12,14-prostaglandin J(2) (15 d-PGJ(2)) is an anti-inflammatory prostaglandin. Here, we tested the hypothesis that 15 d-PGJ(2) modulates Mn-induced activation of astrocytic intracellular signaling, including NF-κB and nuclear factor erythroid 2-related factor (Nrf2), a master regulator of antioxidant transcriptional responses. The results establish that 15 d-PGJ(2) suppresses Mn-induced NF-κB activation by interacting with several signaling pathways. The PI3K/Akt pathway, which is upstream of NF-κB, plays a role in this activation, because (i) pretreatment with 15 d-PGJ(2) (10 μM for 1h) significantly (p<0.01) inhibited Mn (500 μM)-induced PI3K/Akt activation and (ii) inhibition of the PI3K/Akt pathway with LY29004 significantly (p<0.05) decreased NF-κB activation. 15 d-PGJ(2) also significantly (p<0.05) attenuated Mn-induced astrocytic NF-κB activation by inhibiting the Mn-induced phosphorylation of IκB kinase and subsequent IκB-α degradation. Because Mn-induced oxidative stress is also associated with Nrf2 activation, additional studies addressed the ability of 15 d-PGJ(2) to modulate the Nrf2 pathway. 15 d-PGJ(2) significantly (p<0.01) increased Nrf2 expression in whole-cell lysates. Consistent with its pro-oxidant properties, Mn also increased Nrf2 expression. Nevertheless, cotreatment of whole-cell lysates with both Mn and 15 d-PGJ(2) partially suppressed (p<0.01) the 15 d-PGJ(2)-induced increase in astrocytic Nrf2 protein expression. Mn treatment also decreased (p<0.001) expression of DJ-1, a Parkinson disease-associated protein and a stabilizer of Nrf2, and 15 d-PGJ(2) attenuated Mn-induced astrocytic inhibition of DJ-1 expression. Collectively, these results demonstrate that 15d-PGJ(2) exerts a protective effect in astrocytes against Mn-induced inflammation and oxidative stress by modulating the activation of the NF-κB and Nrf2 signaling pathways.

Antioxidant protection: A promising therapeutic intervention in neurodegenerative disease

Oxidative stress has been consistently linked to ageing-related neurodegenerative diseases. Neurodegenerative diseases are characterized by progressive dysfunction and death of neurons. Oxidative stress is associated with dysfunction of the mitochondria and endoplasmic reticulum, inducing apoptosis and protein misfolding in neurons. Decreased activities of antioxidant enzymes like SOD, catalase, glutathione, glutathione peroxidase in neurodegenerative states signifies role of reduced antioxidant potential in neurodegeneration. Among the cellular pathways conferring protection against oxidative stress, a key role is played by vitagenes, which include Hsp70, heme oxygenase-1, thioredoxin and sirtuins. Cellular signalling pathways and molecular mechanisms that mediate hormetic responses typically involve antioxidant enzymes and transcription factors such as Nrf-2 and NFκB. Vitagenes, either individually or by acting in concert, contribute to counteract the ROS mediated damage. In this review the importance of oxidative stress and the potential use of antioxidants in the prevention and treatment of neurodegenerative disorders are discussed.

Inhibition of Respiratory Growth and Survival in Yeast by Dopamine and Counteraction with Ascorbate or Glutathione

Dopamine is a key monamine neurotransmitter, yet it can also exhibit toxicity to neuronal cells. There are suggestions that dopamine may be neurotoxic due to its propensity to induce the formation of reactive oxygen species, which may in turn adversely affect mitochondrial function and cell viability. In this study, the effects of dopamine or a dopamine reaction product on yeast growth and survival have been explored. Yeast is ideal for such a study because, unlike mammalian cells, yeast cells can be grown even when respiratory function is totally absent. Indeed, dopamine was found to be inhibitory to yeast growth in media where respiratory function was required and cytotoxic to yeast cells suspended in water. The inhibitory effects of dopamine were reduced greatly by the antioxidants ascorbate and glutathione, suggesting the involvement of reactive oxygen species in dopamine-mediated toxicity. It would appear that yeast may offer a convenient model to perform screens for further compounds that may provide protection against dopamine-mediated growth inhibition and toxicity.

Consequences of dietary manganese and copper imbalance on neuronal apoptosis in a murine model of scrapie

AIMS

Copper and manganese levels are altered in mice both lacking PrPc and prion-infected brains. The aim of this study was to analyse the effects of manganese and copper imbalance on neuronal apoptosis in a scrapie-infected Tga20 mouse model.

METHODS

Immunoreactivities for the apoptotic proteins Bax and active caspase-3 were evaluated in nine regions of the brain of scrapie-infected and control Tga20 mice treated with one of several diets: depleted cooper (-Cu), loaded manganese (+Mn), depleted copper/loaded manganese (-Cu+Mn) and regular diet. Immunohistochemical determination of NeuN was used to detect possible neuronal loss.

RESULTS

Intracellular Bax detection was significantly decreased in animals fed with modified diets, particularly in those treated with copper-depleted diets. A decrease in active caspase-3 was primarily observed in animals fed with enhanced manganese diets. Our results show that the -Cu, -Cu+Mn and +Mn diets protected against apoptosis in scrapie-infected mice. However, NeuN immunolabelling quantification revealed that no diet was sufficient to arrest neuronal death.

CONCLUSIONS

With regard to apoptosis induction, the response of Tga20 mice to prion infection was similar to that reported for other mice models. Our results demonstrate the neuroprotective effects of -Cu, -Cu+Mn and +Mn diets in a murine model of scrapie. However, neuronal death induced by infection with prions seems to be independent of apoptosis marker signalling. Moreover, copper-modified diets were neuroprotective against the possible toxicity of the prion transgene in Tga20 control and infected mice even though manganese supplementation could not counteract this toxicity.

ISTA13-catecholamine toxicity and metabolism in the ciliated protozoan, Tetrahymena pyriformis

A high throughput culture methodology of unicellular eukaryote Tetrahymena pyriformis, strain GL were used for the determination of catecholamines toxicity and their metabolism. Catecholamines exhibited acute toxicity to Tetrahymena cells where dopamine and L-DOPA showed higher toxic potential of EC(10) (0.39 and 0.63 mg/L, respectively) and EC(20) (1.1 and 1.0 mg/L, respectively). All the testing catecholamines were highly degradable in the PPY-medium due to the oxidizing environment during incubation. They were also naturally synthesized and released by Tetrahymena cells into the culture medium and increasingly accumulated with time where as noradrenalin demonstrated significant results. Cells were exposed with physiological concentration (0.12 mg/L) and one higher concentration (8.0 mg/L) of catecholamines, resulting noradrenalin depletion and in vivo generation of a metabolite in response to dopamine with higher concentration treatment. This dopamine metabolite was relatively nonpolar compared with the catecholamines and was eluted later from the reverse phase C-18 column.

Extracellular dopamine induces the oxidative toxicity of SH-SY5Y cells

Dopamine-induced neuronal cytotoxicity has been proposed as a leading pathological mechanism underlying many neuronal degenerative disorders including Parkinson disease. Various hypotheses have been proposed including oxidative stress and dopamine (DA)-induced intracellular signal disorder via DA D1 and D2 receptors. The exact mechanism involved in this process is far from clear. In this study, employing a neuronal blastoma cell line, SH-SY5Y, we tried to elucidate the roles of these different suggested mechanisms in this pathological process. The results showed that DA induced cell toxicity in a dose- and time-dependent way. Selective D1 and D2 DA receptor antagonist could not block the cytotoxic effects, whereas reductive reagent ascorbic acid but not GSH could effectively rescue the cell death, suggesting that DA-induced cell toxicity was caused by an extracellular oxidative stress. This was further supported by the enhancing effects of DA transporter blocker, GBR, which could increase the cell death when pretreated. Finally, ascorbic acid could also protect SY5Y cells from DA-induced cellular apoptotic signal changes including PARP and P53. Our studies suggested that DA exerted its cytotoxic effects via an extracellular metabolism, whereas intracellular transportation could reduce its oxidative stress. Cytotoxicity effects induced by extracellular DA could be protected by reductive agents as ascorbic acid. These results help to broaden our understanding of the mechanisms of DA-induced cell death and may provide potentially therapeutical alternative for the neurodegenerative disorders.

Estrogen and tamoxifen protect against Mn-induced toxicity in rat cortical primary cultures of neurons and astrocytes

Chronic exposure to manganese (Mn) leads to a neurological disorder, manganism, which shares multiple common features with idiopathic Parkinson disease (IPD). 17beta-Estradiol (E2) and some selective estrogen receptor modulators, including tamoxifen (TX), afford neuroprotection in various experimental models of neurodegeneration. However, the neuroprotective effects and mechanisms of E2/TX in Mn-induced toxicity have yet to be documented. Herein, we studied the ability of E2/TX to protect rat cortical primary neuronal and astroglial cultures from Mn-induced toxicity. Cell viability, Western blot, and reactive oxygen species (ROS) generation were assessed. Results established that both E2 (10nM) and TX (1 microM) attenuated Mn-induced toxicity. The protective effects of E2/TX were more pronounced in astrocytes versus neurons. The E2-mediated attenuation of Mn-induced ROS generation in astrocytes at 6-h treatment (where no cell death was detected) was mediated by a classical estrogen receptor (ER) pathway and the TX-mediated effect on Mn-induced ROS generation was not mediated via classical ER-dependent mechanisms and likely by its antioxidant properties. The phosphatidylinositol-3 kinase (PI3K)/Akt signaling pathway was involved in both E2- and TX-induced attenuation of Mn-induced ROS formation (6 h) in astrocytes. Treatments with Mn for a longer duration (24 h) led to significant cell death, and the protective effects of E2 and TX were (1) not mediated by a classical ER pathway and (2) associated with activation of both mitogen-activated protein kinase/extracellular signal-regulated kinase and PI3K/Akt signaling pathways. Taken together, the results suggest that both E2 and TX offer effective therapeutic means for neuroprotection against Mn-induced toxicity.

Growth inhibition and biodegradation of catecholamines in the ciliated protozoan Tetrahymena pyriformis

A 96-well plate culture methodology for the unicellular eukaryote Tetrahymena pyriformis, strain GL was used for the determination of toxicity and metabolism of catecholamines. Catecholamines exhibited moderate acute toxicity to Tetrahymena cells where dopamine and L-DOPA showed higher toxic potential at EC(10) (0.39 ppm and 0.63 ppm, respectively) and EC(20) (1.1 ppm and 1.0 ppm respectively) after 48 h exposure. All tested catecholamines were highly degradable in the PPY-medium due to the oxidizing environment during incubation. Also the catecholamines were naturally synthesized and released by Tetrahymena cells into the culture medium and increasingly accumulated with time where noradrenalin exhibited the highest degree of accumulation. However, the exogenous exposure of catecholamines to the cells caused the depletion of natural noradrenalin synthesis even with the addition of very low physiological concentration (0.12 ppm). Dopamine caused the higher effect on inhibiting noradrenalin synthesis. Treatment with a higher concentration (8.0 ppm) of dopamine in 96-well plates caused strong excitation of the cells and ascertained a new metabolite in vivo while the other representative catecholamines were not responsible for the production of this metabolite. This dopamine metabolite is relatively non-polar as compared to noradrenalin, adrenaline and dopamine and eluting later through the reverse phase C-18 column.

Apomorphine offers new insight into dopaminergic neuron vulnerability in mesencephalic cultures

The mechanism by which the dopamine neurons of the substantia nigra pars compacta degenerate in Parkinson's disease, is partly unknown. Dopamine could be implicated in this phenomenon, and in order to explain its toxicity several hypotheses have been suggested. The similarity between apomorphine and dopamine as regards their chemical, pharmacological and toxicological properties provided a basis for investigating the nature of the toxicity of the former agent. In this study we describe some effects of apomorphine on mouse mesencephalic cell cultures at relatively low concentrations (from 0.5 to 2.5microM), apomorphine produced a neurotrophic effect, consisting of a 60% increase in dopaminergic neuron survival as measured by [(3)H] dopamine uptake. At high concentrations (over 20microM), however, apomorphine induced an increasing cytotoxic effect, as measured by the marked decrease in [(3)H] dopamine uptake, and by the direct observation of the dopaminergic neurons after TH immunostaining. This study may offer a new strategy for investigating the mechanisms underlying DA neuron vulnerability.

Assessment of the direct and indirect effects of MPP+ and dopamine on the human proteasome: implications for Parkinson's disease aetiology

Mitochondrial impairment, glutathione depletion and oxidative stress have been implicated in the pathogenesis of Parkinson's disease (PD), linked recently to proteasomal dysfunction. Our study analysed how these factors influence the various activities of the proteasome in human SH-SY5Y neuroblastoma cells treated with the PD mimetics MPP+ (a complex 1 inhibitor) or dopamine. Treatment with these toxins led to dose- and time-dependent reductions in ATP and glutathione and also chymotrypsin-like and post-acidic like activities; trypsin-like activity was unaffected. Antioxidants blocked the effects of dopamine, but not MPP+, suggesting that oxidative stress was more important in the dopamine-mediated effects. With MPP+, ATP depletion was a prerequisite for loss of proteasomal activity. Thus in a dopaminergic neuron with complex 1 dysfunction both oxidative stress and ATP depletion will contribute independently to loss of proteasomal function. We show for the first time that addition of MPP+ or dopamine to purified samples of the human 20S proteasome also reduced proteasomal activities; with dopamine being most damaging. As with toxin-treated cells, chymotrypsin-like activity was most sensitive and trypsin-like activity the least sensitive. The observed differential sensitivity of the various proteasomal activities to PD mimetics is novel and its significance needs further study in human cells.

Glutathione prevented dopamine-induced apoptosis of melanocytes and its signaling

BACKGROUND

Dopamine (DA), a monoamine neurotransmitter, is a well-known neurotoxin and plays an etiologic role in neurodegenerative disorders such as Parkinson's disease. DA exerts its toxic effect by generation of reactive oxygen species and quinone product. Vitiligo, a depigmentary disorder of the skin and hair characterized by selective destruction of melanocytes, has been reported to show increased levels of DA with onset and progression of the disease.

OBJECTIVE

The aim of this study is to investigate the cytotoxic effect of DA on melanocytes and to search for protective antioxidants against DA-induced toxicity. In addition, molecular mechanism of cell death was also investigated.

METHODS

Cells were treated with DA and cell viabilities were measured by crystal violet staining method. To investigate the cytoprotective activity of various antioxidants, vitamin C, vitamin E, Trolox, quercetin, N-acetylcysteine (NAC) and l-glutathione (GSH) were used. To study cytoprotective effects of NAC and GSH, Mel-Ab cells and cultured normal human melanocytes were pretreated with NAC or GSH, then DA solution was added. DA-induced apoptosis and activation of c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) were also observed by flow cytometric analysis and Western blotting.

RESULTS

The viability of DA-treated Mel-Ab cells significantly decreased in a dose-dependent manner while keratinocytes were much more resistant to DA-toxicity, which was a consistent finding with the selective melanocyte loss observed in vitiligo. Among various antioxidants used in this study, only thiol-containing antioxidants such as NAC or GSH inhibited both JNK and p38 MAPK activation and apoptosis, indicating the unique protective capacity of thiol compounds. Cultured normal human melanocytes were also susceptible to DA and thiol compounds were very efficiently protective against DA-induced cytotoxicity.

CONCLUSION

DA-induced apoptosis and cytoprotective effect of thiol compounds shown in this study could be a clue to understand pathogenesis of viltigo and provide a new therapeutic strategy.

Manganese chloride stimulates rat microglia to release hydrogen peroxide

Elevated exposure to manganese is known to cause neurodegeneration in the basal ganglia and to induce movement abnormalities called manganism. However, the underlying mechanism of action is not fully understood. Activation of the resident immune cells in the brain, microglia that release a variety of neurotoxic factors, has been implicated to contribute to neurodegeneration. Of the various neurotoxic factors released by activated microglia, reactive oxygen species such as superoxide and hydrogen peroxide are particularly detrimental to the survival of the oxidative damage-prone neurons. In this study, we report that exposure of rat microglia to manganese chloride (MnCl(2)) resulted in a time- and concentration-dependent release of hydrogen peroxide (H(2)O(2)). The MnCl(2)-stimulated microglial H(2)O(2) release was sensitive to inhibitors of mitogen-activated protein kinases (MAPK) but not that of NADPH oxidase. MnCl(2)-induced a rapid activation of the extracellular signal-regulated kinase (ERK) and p38-MAPK in microglia that appeared to precede the MnCl(2)-induced H(2)O(2) release, suggesting that ERK and p38-MAPK influenced the MnCl(2)-induced H(2)O(2) release in microglia. In summary, these results demonstrate that manganese chloride is capable of activating microglia to release ROS and MAPK may, in part, be key regulators of the process. These findings may shed significant light on the potential role of microglia in the manganese-induced neurotoxicity.

Normal cellular prion protein protects against manganese-induced oxidative stress and apoptotic cell death

The normal prion protein is abundantly expressed in the central nervous system, but its biological function remains unclear. The prion protein has octapeptide repeat regions that bind to several divalent metals, suggesting that the prion proteins may alter the toxic effect of environmental neurotoxic metals. In the present study, we systematically examined whether prion protein modifies the neurotoxicity of manganese (Mn) by comparing the effect of Mn on mouse neural cells expressing prion protein (PrP(C)-cells) and prion-knockout (PrP(KO)-cells). Exposure to Mn (10microM-10mM) for 24 h produced a dose-dependent cytotoxic response in both PrP(C)-cells and PrP(KO)-cells. Interestingly, PrP(C)-cells (EC(50) 117.6microM) were more resistant to Mn-induced cytotoxicity, as compared to PrP(KO)-cells (EC(50) 59.9microM), suggesting a protective role for PrP(C) against Mn neurotoxicity. Analysis of intracellular Mn levels showed less Mn accumulation in PrP(C)-cells as compared to PrP(KO)-cells, but no significant changes in the expression of the metal transporter proteins transferrin and DMT-1. Furthermore, Mn-induced mitochondrial depolarization and reactive oxygen species (ROS) generation were significantly attenuated in PrP(C)-cells as compared to PrP(KO)-cells. Measurement of antioxidant status revealed similar basal levels of glutathione (GSH) in PrP(C)-cells and PrP(KO)-cells; however, Mn treatment caused greater depletion of GSH in PrP(KO)-cells. Mn-induced mitochondrial depolarization and ROS production were followed by time- and dose-dependent activation of the apoptotic cell death cascade involving caspase-9 and -3. Notably, DNA fragmentation induced by both Mn treatment and the oxidative stress inducer hydrogen peroxide (100microM) was significantly suppressed in PrP(C)-cells as compared to PrP(KO)-cells. Together, these results demonstrate that prion protein interferes with divalent metal Mn uptake and protects against Mn-induced oxidative stress and apoptotic cell death.

Manganese-induced neurotoxicity is differentially enhanced by glutathione depletion in astrocytoma and neuroblastoma cells

Manganese (Mn) is neurotoxic: the underlying mechanisms have not been fully elucidated. L: -Buthionine-(S,R)-sulfoximine (BSO) is an irreversible inhibitor of gamma-glutamylcysteine synthetase, an important enzyme in glutathione (GSH) synthesis. To test the hypothesis that BSO modulates Mn toxicity, we investigated the effects of treatment of U-87 or SK-N-SH cells with MnCl(2), BSO, or MnCl(2) plus BSO. We monitored cell viability using MTT assay, staining with HO-33342 to assess live and/or apoptotic cells, and staining with propidium iodide (PI) to assess necrotic cells; we also measured cellular glutathione. Our results indicate decreased viability in both cell types when treated with MnCl(2) or BSO: Mn was more toxic to SK-N-SH cells, whereas BSO was more toxic to U-87 cells. Because BSO treatment accentuated Mn toxicity in both cell lines, GSH may act to combat Mn toxicity. Thus, further investigation in oxidative stress mediated by glutathione depletion will unravel new Mn toxicity mechanism(s).

Mechanism for manganese enhancement of dopamine-induced oxidative DNA damage and neuronal cell death

Although the cause of dopaminergic cell death in Parkinson's disease is still poorly understood, there is accumulating evidence suggesting that metal ions can be involved in the processes. We investigated the effect of manganese on cell death and DNA damage in PC12 cells treated with dopamine. Mn(II) enhanced cell death induced by dopamine. Mn(II) also increased the 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) contents of DNA in PC12 cells treated with dopamine. To clarify the mechanism of cellular DNA damage, we investigated DNA damage induced by dopamine and Mn(II) using (32)P-labeled DNA fragments. Mn(II) enhanced Cu(II)-dependent DNA damage by dopamine. The Mn(II)-enhanced DNA damage was greatly increased by NADH. Piperidine and formamidopyrimidine-DNA glycosylase treatment induced cleavage sites mainly at T and G of the 5'-TG-3' sequence, respectively. Bathocuproine, a Cu(I) chelator, and catalase inhibited the DNA damage. Oxygen consumption and UV-visible spectroscopic measurements showed that Mn(II) enhanced autoxidation of dopamine with H(2)O(2) formation. These results suggest that reactive species derived from the reaction of H(2)O(2) with Cu(I) participates in Mn(II)-enhanced DNA damage by dopamine plus Cu(II). Therefore, it is concluded that oxidative DNA damage induced by dopamine in the presence of Mn(II), NADH, and Cu(II) is possibly linked to the degeneration of dopaminergic neurons.

Manganese modulates pro-inflammatory gene expression in activated glia

Redox-active metals are of paramount importance for biological functions. Their impact and cellular activities participate in the physiological and pathophysiological processes of the central nervous system (CNS), including inflammatory responses. Manganese is an essential trace element and it is required for normal biological activities and ubiquitous enzymatic reactions. However, excessive chronic exposure to manganese results in neurobehavioral deficits. Recent evidence suggests that manganese neurotoxicity involves activation of microglia or astrocytes, representative CNS immune cells. In this study, we assessed the molecular basis of the effects of manganese on the modulation of pro-inflammatory cytokines and nitric oxide (NO) production in primary rat cortical glial cells. Cultured glial cells consisted of 85% of astrocytes and 15% of microglia. Within the assayed concentrations, manganese was unable to induce tumor necrosis factor alpha (TNF-alpha) and inducible nitric oxide synthase (iNOS) expression, whereas it potentiated iNOS and TNF-alpha gene expression by lipopolysaccharide/interferon-gamma-activated glial cells. The enhancement was accompanied by elevation of free manganese, generation of oxidative stress, activation of mitogen-activated protein kinases, and increased NF-kappaB and AP-1 binding activities. The potentiated degradation of inhibitory molecule IkappaB-alpha was one of underlying mechanisms for the increased activation of NF-kappaB by manganese. However, manganese decreased iNOS enzymatic activity possibly through the depletion of cofactor since exogenous tetrahydrobiopterin reversed manganese's action. These data indicate that manganese could modulate glial inflammation through variable strategies.

A potential role for cyclized quinones derived from dopamine, DOPA, and 3,4-dihydroxyphenylacetic acid in proteasomal inhibition

We examined the ability of oxidation products of dopamine, DOPA, and 3,4-dihydroxyphenylacetic acid (DOPAC) to inhibit proteasomal activity. Dopamine, DOPA, and DOPAC underwent tyrosinase-catalyzed oxidation to generate aminochrome, dopachrome, and furanoquinone, respectively. In these studies, the oxidation of dopamine by tyrosinase generated product(s) that inhibited the proteasome, and proteasomal inhibition correlated with the presence of the UV-visible spectrum of aminochrome. The addition of superoxide dismutase and catalase did not prevent proteasomal inhibition. The addition of NADH and the quinone reductase NAD(P)H:quinone oxidoreductase 1 (NQO1) protected against aminochrome-induced proteasome inhibition. Although NQO1 protected against dopamine-induced proteasomal inhibition, the metabolism of aminochrome by NQO1 led to oxygen uptake because of the generation of a redox-labile cyclized hydroquinone, further demonstrating the lack of involvement of oxygen radicals in proteasomal inhibition. DOPA underwent tyrosinase-catalyzed oxidation to form dopachrome, and similar to aminochrome, proteasomal inhibition correlated with the presence of a dopachrome UV-visible spectrum. The inclusion of NQO1 did not protect against proteasomal inhibition induced by dopachrome. Oxidation of DOPAC by tyrosinase generated furanoquinone, which was a poor proteasome inhibitor. These studies demonstrate that oxidation products, including cyclized quinones derived from dopamine and related compounds, rather than oxygen radicals have the ability to inhibit the proteasome. They also suggest an important protective role for NQO1 in protecting against dopamine-induced proteasomal inhibition. The ability of endogenous intermediates formed during dopaminergic metabolism to cause proteasomal inhibition provides a potential basis for the selectivity of dopaminergic neuron damage in Parkinson's disease.

Alpha-synuclein facilitates the toxicity of oxidized catechol metabolites: implications for selective neurodegeneration in Parkinson's disease

Free radicals, including dopamine (DA)-oxidized metabolites, have long been implicated in pathogenesis of Parkinson's disease (PD). However, the relationships between such oxidative stresses and alpha-synuclein (alpha-S), a major constituent of Lewy bodies, remain unknown. In this study, we established neuronal cells that constitutively express alpha-S and tetracycline-regulated tyrosinase. While tyrosinase overexpression induced apoptosis, co-expression of wild type or A53T mutant human alpha-S with tyrosinase further exacerbated cell death. In this process, the formation of alpha-S oligomers and the reduction in mitochondrial membrane potential were demonstrated. This cellular model may reconstitute the pathological metabolism of alpha-S in the synucleinopathy and provide a useful tool to explore possible pathomechanisms of nigral degeneration in PD.

The effects of manganese on glutamate, dopamine and gamma-aminobutyric acid regulation

Exposure to high levels of manganese (Mn) results in a neurological disorder, termed manganism, which shares a similar phenotype to Parkinson's disease due to the involvement of the basal ganglia circuitry in both. The initial symptoms of manganism are likely due to the involvement of the globus pallidus, a region rich in gamma-aminobutyric acid (GABA) projections, while those of Parkinson's disease are related to the degeneration of the substantia nigra, a dopaminergic nucleus. Additionally, it is known that glutamate regulation is affected by increases in brain Mn levels. As Mn predominantly accumulates in the basal ganglia, it potentially could affect the regulation and interactions of all three neurotransmitters. This review will focus on the circuitry of these neurotransmitters within the basal ganglia and address potential sites for, as well as the temporal relationship, between Mn exposure and changes in the levels of these neurotransmitters. While most research has focused on perturbations in the dopaminergic system, there is evidence to support that early consequences of manganism also include disturbances in GABA regulation as well as glutamatergic-related excitotoxicity. Finally, we suggest that current research focus on the interdependence of these basal ganglial neurochemicals, with a greater emphasis on the GABAergic and glutamatergic systems.

Oxalate mediated nephronal impairment and its inhibition by c-phycocyanin: a study on urolithic rats

The assumption of oxidative stress as a mechanism in oxalate induced renal damage suggests that antioxidants might play a beneficial role against oxalate toxicity. An in vivo model was used to investigate the effect of C-phycocyanin (from aquatic micro algae; Spirulina spp.), a known antioxidant, against calcium oxalate urolithiasis. Hyperoxaluria was induced in two of the 4 groups of Wistar albino rats (n = 6 in each) by intraperitoneally injecting sodium oxalate (70 mg/kg body weight). A pretreatment of phycocyanin (100 mg/kg body weight) as a single oral dosage was given, one hour prior to oxalate challenge. An untreated control and drug control (phycocyanin alone) were employed. Phycocyanin administration resulted in a significant improvement (p < 0.001) in the thiol content of renal tissue and RBC lysate via increasing glutathione and reducing malondialdehyde levels in the plasma of oxalate induced rats (p < 0.001), indicating phycocyanin's antioxidant effect on oxalate mediated oxidative stress. Administering phycocyanin after oxalate treatment significantly increased catalase and glucose-6-phosphate dehydrogenase activity (p < 0.001) in RBC lysate suggesting phycocyanin as a free radical quencher. Assessing calcium oxalate crystal retention in renal tissue using polarization microscopy and renal ultrastructure by electron microscopy reveals normal features in phycocyanin-- pretreated groups. Thus the study presents positive pharmacological implications of phycocyanin against oxalate mediated nephronal impairment and warrants further work to tap this potential aquatic resource for its medicinal application.

Oxidative stress and inflammation in Parkinson's disease: is there a causal link?

Parkinson's disease (PD) is a neurodegenerative disorder characterized by a dramatic loss of dopaminergic neurons in the substantia nigra (SN). Among the many pathogenic mechanisms thought to contribute to the demise of these cells, dopamine-dependent oxidative stress has classically taken center stage due to extensive experimental evidence showing that dopamine-derived reactive oxygen species and oxidized dopamine metabolites are toxic to nigral neurons. In recent years, however, the involvement of neuro-inflammatory processes in nigral degeneration has gained increasing attention. Not only have activated microglia and increased levels of inflammatory mediators been detected in the striatum of deceased PD patients, but a large body of animal studies points to a contributory role of inflammation in dopaminergic cell loss. Recently, postmortem examination of human subjects exposed to the parkinsonism-inducing toxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), revealed the presence of activated microglia decades after drug exposure, suggesting that even a brief pathogenic insult can induce an ongoing inflammatory response. Perhaps not surprisingly, non-steroidal anti-inflammatory drugs (NSAIDs) have been shown to reduce the risk of developing PD. In the past few years, various pathways have come to light that could link dopamine-dependent oxidative stress and microglial activation, finally ascribing a pathogenic trigger to the chronic inflammatory response characteristic of PD.

Induction of the Protective Antioxidant Response Element Pathway by 6-Hydroxydopamine In Vivo and In Vitro

Parkinson's disease, a progressive neurodegenerative disorder, is characterized by loss of midbrain dopaminergic neurons. The etiology of sporadic Parkinson's disease is unknown; however, oxidative stress is thought to play a major role in disease pathogenesis. Little is known regarding the transcriptional changes that occur in Parkinson's disease. The antioxidant response element is a cis-acting enhancer sequence that is upstream of many phase II detoxification and antioxidant genes. Here we show that 6-hydroxydopamine, a mitochondrial inhibitor used to model Parkinson's disease, activates the antioxidant response element both in cultured neurons and in the striatum and brainstem of 6-OHDA-lesioned mice. Pretreatment with antioxidants or NMDA receptor antagonists reduced but did not abolish activation. Further induction of this pathway with tert-butylhydroquinone was able to significantly reduce cell death due to 6-OHDA in vitro. These observations indicate that 6-OHDA activates the antioxidant response element through components of oxidative stress, excitotoxicity, and potential structural factors. Further induction of this endogenous defense mechanism may suggest a novel therapeutic venue in Parkinson's disease.

Changes in antioxidant defense systems by 2,2',5,5'-tetrachlorobiphenyl exposure in neuronal SK-N-MC cells

Polychlorinated biphenyls (PCBs) are known to alter the mammalian antioxidant defense system. To determine whether similar detoxification processes are activated in human neuronal cells, we investigated activities of antioxidant enzymes and the glutathione status (i.e., the levels of reduced and oxidized glutathione, GSH and GSSG) in human neuronal SK-N-MC cells exposed to 2,2',5,5'-tetrachlorobiphenyl (PCB 52). Upon PCB 52 treatment, time- and concentration-dependent inhibitions of cell viability were observed. PCB 52 did not affect GSH contents upon increasing the concentration up to 15 microg/ml, but significant depletions in GSH were observed at the concentrations of 20 and 25 microg/ml. PCB 52 exposure increased GSSG levels in the SK-N-MC cells, while GSH levels were decreased, and these changes naturally modified the GSSG/GSH ratios. Cytosolic glutathione S-transferase (GST) activity with 1-chloro-2,4-dinitrobenzene as substrate was enhanced by two-fold in neuronal cells after exposure to PCB 52 versus controls. In contrast, neuronal cells showed a sustained decrease in glutathione peroxidase activity with increasing concentrations of PCB 52, and a sustained decrease in Cu/Zn-superoxide dismutase (SOD) activity with increasing concentrations of PCB 52. Catalase activity was increased until 12 h after exposure to PCB 52, but was decreased 24 h after exposure. Overall, these results imply a major effect of PCB 52 on GSH status and upon the activities of antioxidant enzymes in human neuronal SK-N-MC cells, and upon the overall process of detoxification in human neuronal cells.

Isatin, an endogenous monoamine oxidase inhibitor, triggers a dose- and time-dependent switch from apoptosis to necrosis in human neuroblastoma cells

Isatin is an endogenous indole that is increased in stress, inhibits monoamine oxidase (MAO) B and improves bradykinesia and striatal dopamine levels in rat models of Parkinson's disease. Consequently, it has been suggested that isatin might be a possible treatment for Parkinson's disease although little is known about its effects on neural cell growth and survival. The aim of this study was to investigate the survival of dopaminergic human neuroblastoma (SH-SY5Y) cells following treatment with increasing concentrations of isatin. SH-SY5Y cells were exposed to isatin for defined time points, after which cell survival was determined by MTT assay. A combination of Annexin V binding and propidium iodide (PI) exclusion was used to distinguish apoptosis from necrosis in flow cytometry experiments and FACS profiles of permeabilised PI-labelled cells were employed for the assessment of cell cycle distribution. Isatin treatment (1-400 microM) for 24h induced a significant dose-dependent increase in MTT metabolism by SH-SY5Y cells in culture, but this was not due to an increase in cell division. At the higher concentrations (200-400 microm) isatin triggered cell death, although MTT metabolism was still increased in the culture, suggesting that surviving cells were hypermetabolic. Following a longer (48 h) exposure, isatin was found to cause cell death in a dose-dependent manner; at lower concentrations (50 microM), the predominant mode of cell death was apoptosis while at the highest concentration (400 microm) increasing numbers of necrotic cells were also evident. Thus, in dopaminergic SH-SY5Y cells isatin induces cell death in dose- and time-dependent manner. This death occurred as a continuum of survival, apoptosis and necrosis. Our results re-emphasise that caution should be exercised when considering high doses of isatin as a putative anti-Parkinson's disease therapeutic.

Age-dependent motor deficits and dopaminergic dysfunction in DJ-1 null mice

Mutations in the DJ-1 gene were recently identified in an autosomal recessive form of early-onset familial Parkinson disease. Structural biology, biochemistry, and cell biology studies have suggested potential functions of DJ-1 in oxidative stress, protein folding, and degradation pathways. However, animal models are needed to determine whether and how loss of DJ-1 function leads to Parkinson disease. We have generated DJ-1 null mice with a mutation that resembles the large deletion mutation reported in patients. Our behavioral analyses indicated that DJ-1 deficiency led to age-dependent and task-dependent motoric behavioral deficits that are detectable by 5 months of age. Unbiased stereological studies did not find obvious dopamine neuron loss in 6-month- and 11-month-old mice. Neurochemical examination revealed significant changes in striatal dopaminergic function consisting of increased dopamine reuptake rates and elevated tissue dopamine content. These data represent the in vivo evidence that loss of DJ-1 function alters nigrostriatal dopaminergic function and produces motor deficits.

Overexpression of XIAP inhibits apoptotic cell death in an oligodendroglial cell line

1. This study describes the use of an oligodendroglial cell line (158N) to study the protective effects of X-chromosome-linked inhibitor of apoptosis (XIAP) overexpression. 2. 158N cells were transiently transfected with either pCMV-Myc-XIAP or control pCMV-Myc vector. At 48 h post-transfection, immunoblotting and immunocytochemical staining showed robust myc-XIAP overexpression in pCMV-Myc-XIAP transfected cells relative to pCMV-Myc-transfected cells and normal 158N cells. 158N cells were treated with either 100 nm staurosporine (STS) or 300 microM dopamine (DA) and cell survival/function determined using two cell viability assays. 3. Both STS and DA treatments resulted in increased apoptotic death of pCMV-Myc transfected cells. In contrast, there was significant decrease in apoptotic cell death in cells transfected with pCMV-Myc-XIAP. Finally, XIAP overexpression was found to significantly reduce caspase-3 enzyme activity levels in response to apoptotic stimuli. 4. These results provide evidence that XIAP overexpression promotes cell survival in a non-neuronal cell type derived from the central nervous system. In addition, these data suggest that the 158N oligodendroglial cell line is a suitable tool for transient transfection studies, which is a problem frequently encountered when attempting to introduce genes of interest in cultures of primary oligodendroglia.

Polychlorinated biphenyl mixture aroclor 1254-induced oxidative stress plays a role in dopaminergic cell injury

Oxidative stress (OS) is thought to participate in the pathogenesis of neurodegenerative disorders, including Parkinson's disease (PD). Excessive reactive oxygen species (ROS) production can occur during the normal aging process or following exposure to environmental toxicants. Dopamine neurons, which degenerate during PD, are particularly sensitive to oxidative stress. Polychlorinated biphenyls (PCBs), persistent and widespread pollutants, have been shown to adversely impact dopaminergic (DAergic) pathways, but the role ROS play in neurotoxicity remains unclear. To test the hypothesis that PCB exposure compromises dopamine neurons by stimulating ROS production, the direct toxicity and oxidative stress response following PCB exposure was examined both in MN9D dopamine cells and primary mesencephalic cultures. PCBs induced a time- and concentration-dependent increase in ROS production, which preceded cytotoxicity. Whereas intracellular GSH depletion exacerbated PCB effects, antioxidant pretreatment attenuated ROS production and cell death. Coincident alterations in antioxidant defense enzymes also accompanied ROS production, including decreased MnSOD and increased CuZnSOD protein levels. The robust elevation in heme oxygenase-1 levels further support the activation of oxidative stress mechanisms following PCB exposure. Furthermore, PCBs produced concentration-dependent reductions in intracellular dopamine levels and elevated dopamine turnover. Although the intracellular source of ROS remains unknown, these results suggest that sublethal PCB concentrations activate an oxidative stress-related pathway, which potentially disrupts dopamine neuron function.

Modulation of Antioxidant Defense Systems by the Environmental Pesticide Maneb in Dopaminergic Cells

A lack of evidence supporting a role of heritability in the development of idiopathic Parkinson's disease (PD) has implicated exposures to environmental contaminants in the disease etiology. Epidemiological and clinical studies, as well as animal models of the PD phenotype, have consistently linked agrichemical exposure with dopaminergic (DAergic) damage, particularly through oxidative stress mechanisms. Maneb (MB) is a dithiocarbamate (DTC) fungicide that has specifically been implicated to have adverse effects on dopamine (DA) systems, but the role MB plays in modulating the oxidative state of DAergic cells has not previously been described. Since glutathione (GSH) is a major cellular antioxidant, it was hypothesized that exposure to MB would disrupt this system. The current study primarily utilized the PC12 cell line, which displays a catecholaminergic phenotype. Low concentrations of MB (50-1000 ng/ml) had little effect on cell viability, as measured by LDH release. These same concentrations, however, led to increases in GSH and its oxidized form, GSSG. Effects on viability and GSH were correlated to a primary mesencephalic culture system. Furthermore, these effects were markedly different from those observed with the classical oxidative stressor and pesticide, paraquat (PQ). To determine how MB would affect cells in which antioxidant systems were compromised, PC12 cells were treated with L-buthionine-(S,R)-sulfoximine (BSO) to deplete cellular GSH, followed by treatment with MB. Results suggest that following an insult to the GSH antioxidant system, MB can act as an additional insult to the system and prevent the normal recovery of those defenses. Altered protein levels of heme oxygenase-1 (HO-1) further indicated an oxidative stress response elicited by MB in PC12 cells. DAergic neurons, as a population, are inherently vulnerable to oxidative stress, and the disruption of antioxidant systems by the fungicide MB may contribute to the neurodegeneration of these cells, especially with concurrent exposures to other environmentally relevant oxidative stressors, such as PQ.

Manganese exposure and induced oxidative stress in the rat brain

Neurotoxicity linked to excessive brain manganese levels can occur as a result of high level Mn exposures and/or metabolic aberrations (liver disease and decreased biliary excretion). Increased brain manganese levels have been reported to induce oxidative stress, as well as alterations in neurotransmitter metabolism with concurrent neurobehavioral and motor deficits. Two putative mechanisms in which manganese can produce oxidative stress in the brain are: (1) via its oxidation of dopamine, and (2) interference with normal mitochondrial respiration. Measurements of antioxidant species (e.g., glutathione and metallothionein), and the abundance of proteins (enzymes) exquisitely sensitive to oxidation (e.g., glutamine synthetase) have been commonly used as biomarkers of oxidative stress, particularly in rat brain tissue. This paper examines the link between manganese neurotoxicity in the rat brain and common pathways to oxidative stress.

Manganese-induced cytotoxicity in dopamine-producing cells

Manganese (Mn) is an essential metal that, at excessive levels in the brain, produces extrapyramidal symptoms similar to those in patients with Parkinson's disease (PD). In the present study, Mn toxicity was characterized in a human neuroblastoma (SK-N-SH) cell line and in a mouse catecholaminergic (CATH.a) cell line. Mn was demonstrated to be more toxic in the catecholamine-producing CATH.a cells (EC50 = 60 microM) than in non-catecholaminergic SK-N-SH cells (EC50 = 200 microM). To test the hypothesis that the sensitivity of CATH.a cells to Mn is associated with their dopamine (DA) content, DA concentrations were suppressed in these cells by pretreatment with alpha-methyl-para-tyrosine (AMPT). Treatment for 24 h with 100 microM AMPT decreased intracellular DA, but offered no significant protection from Mn exposure (EC50 = 60 microM). Additional studies were carried out to assess if Mn toxicity was dependent on glutathione (GSH) levels. CATH.a cells were significantly protected by the addition of 5mM GSH (Mn EC50 = 200 microM) and 10mM N-acetyl cysteine (NAC) (Mn EC50 = 300 microM), therefore, indirectly identifying intracellular ROS formation as a mechanism for Mn neurotoxicity. Finally, apoptotic markers of Mn-induced cell death were investigated. DNA fragmentation, caspase-3 activation, and apoptosis-related gene expression were studied in CATH.a cells. No internucleosomal fragmentation or caspase activation was evident, even in the presence of "supraphysiological" Mn concentrations. cDNA hydridization array analysis with two differing Mn concentrations and time points, identified no noteworthy mRNA inductions of genes associated with programmed cell death. In conclusion, DA content was not responsible for the enhanced sensitivity of CATH.a cells to Mn toxicity, but oxidative stress was implicated as a probable mechanism of cytotoxicity.

Dopaminergic properties and experimental anti-parkinsonian effects of IPX750 in rodent models of Parkinson disease

With a view toward improving the neural bioavailability of administered dopaminergic compounds, including dopamine, synthetic efforts have been directed toward enhancing the brain bioavailability of these compounds by accessing cellular sugar transport systems with stereoselective dopaminergic drugs. While synthesis and chemistry of the resultant class of compounds has recently been described in US Patent No. 6,548,484, the associated biologic properties have not previously been reported. One member of this new class, IPX-750, is a pro-drug dopamine-gluconamine designed to retain stereospecificity of binding at: glucose transporters (GLUT 1/GLUT 3 and intestinal Na/glucose co-transporters SGLT1), dopamine transporter (DAT); and, dopaminergic receptors of the D1/D2 families. Designed to be cleavable by tissue amidases, results reported here show that intact IPX-750 pro-drug retains dopaminergic agonist binding and biologic activities both in vitro and in vivo. IPX-750, like dopamine, exhibited predominant D5/D1 binding specificity with lower binding activity at D2. As expected, binding was highly stereo-specific, ie, IPX-760, a benzamide differing in just a hydrogen atom and keto oxygen from IPX-750, bound with 6-fold lower activity at D5. In cell culture, activation resulted from binding of IPX-750 at D1 or D5 in transfected cells was measured by increased intracellular cAMP. Interestingly, considering prior reported in vitro toxicity of dopamine oxidized and metabolic product dopamine, no evidence of in vitro toxicity was observed at up to 72 hrs in cell cultures at the EC50 of IPX-750 for increasing intracellular cAMP. IPX-750 was evaluated in the Parkinson's disease animal models, including MPTP mouse model, the 6-hydroxydopamine (6-OHDA) rat model and the Nurr1(+/-) knockout mouse model. In MPTP-lesioned and Nurr1+/- knockout mice, IPX-750 significantly increased Rota-rod time. In 6-OHDA-lesioned rats, IPX-750 significantly decreased apomorphine (APO)-induced rotation. Worthy of note, after cessation of IPX-750 treatments the anti-parkinsonian activity in MPTP-lesioned and Nurr1+/- mice required about 2 weeks to washout, suggesting a possible biologic reservoir of drug. In addition, after eight weeks of twice daily administration of 20 mg/kg IPX-750, mice did not show statistical difference in the total number of TH-positive neurons in substantia nigra (SN). These combined results suggest (i) that stereo-specific glycoconjugation may be an effective method to improve penetrability of drugs through the blood brain barrier; (ii) treatment with bioavailable IPX-750 in vitro did not show evidence for neurotoxicity; and, (iii) IPX-750 possesses dopaminergic properties and exerts anti-parkinsonian effects in three different PD rodent models, suggesting therapeutic potential for this new class of drugs in treating dopamine deficiency diseases.

Recherche d’une toxicité du 3,4-dihydroxyphénylacétaldéhyde (DOPAL) in vitro et in vivo

This work was carried out in order to evaluate the in vitro and in vivo toxicity of 3,4-dihydroxyphenylacetaldehyde (DOPAL). This aldehyde is formed from dopamine (DA) by monoamine oxidases (MAO) and is mainly oxidised to 3,4-dihydroxyphenylacetic acid by brain aldehyde dehydrogenases (ALDH), or eventually reduced to 3,4-dihydroxyphenylethanol by aldose/aldehyde reductases. In vitro, catecholaminergic SH-SY5Y cells were incubated with DA and disulfiram (DSF), an irreversible inhibitor of ALDH. As evidenced by MTT assays, a 24-h treatment with 10(-4) M DA and/or 10(-6) M DSF followed by a 24-h incubation in a drug-free medium evidenced that the toxicity of each of these drugs was potentiated by the second drug. HPLC measurements demonstrated that this drug association induced an early DOPAL production that could result in a delayed cell toxicity. For in vivo studies, male Sprague-Dawley rats were treated with L-DOPA-benserazide, which increases the production of DOPAL by MAO, and DSF. An acute injection of DSF (100mg/kg i.p.) and L-DOPA/benserazide (100mg/kg+25mg/kg, 24h later) significantly increased the DOPAL striatal level. However, a 30-day treatment with DSF (100mg/kg i.p., once every two days) and L-DOPA/benserazide (100mg/kg+25mg/kg, twice a day) did not affect both indexes used to assess the integrity of the nigro-striatal dopaminergic terminals (i.e. the striatal content in DA and the binding to the vesicular monoamine transporter on striatal membranes). These results do not support the hypothesis of a DOPAL toxicity and argue against the toxicity of L-DOPA therapy.

Co-treatment with ethanol enhances the toxicity of 6-hydroxydopamine

6-Hydroxydopamine (6-OHDA) is a widely used neural toxin in the pathogenesis research of Parkinson's disease (PD). In this work, we have studied the effect of ethanol on the toxicity of 6-OHDA on PC12 cell and SK-N-SH cell. Ethanol alone had little toxicity to these cells. However, if using 40 microM 6-OHDA along with 400 mM ethanol on PC12 cell or SK-N-SH cell for 24h, there was much more cell loss than using 40 microM 6-OHDA alone when detected by 3-(4,5-dimethylthiazal-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay or flow cytometric assay. The toxicity of 6-OHDA was enhanced only if using at least 200 mM ethanol, and the cell loss was increased with the increase of ethanol concentration. We had also found that ethanol could enhance the toxicity of 6-OHDA only when using ethanol and 6-OHDA at the same time, ethanol treatment either before or after 6-OHDA treatment did not show such effect. This effect of ethanol suggests that ethanol may contribute to the degeneration of dopaminergic cells.

Parkin attenuates manganese-induced dopaminergic cell death

Manganese as environmental factor is considered to cause parkinsonism and induce endoplasmic reticulum stress-mediated dopaminergic cell death. We examined the effects of manganese on parkin, identified as the gene responsible for familial Parkinson's disease, and the role of parkin in manganese-induced neuronal cell death. Manganese dose-dependently induced cell death of dopaminergic SH-SY5Y and CATH.a cells and cholinergic Neuro-2a cells, and that the former two cell types were more sensitive to manganese toxicity than Neuro-2a cells. Moreover, manganese increased the expression of endoplasmic reticulum stress-associated genes, including parkin, in SH-SY5Y cells and CATH.a cells, but not in Neuro-2a cells. Treatment with manganese resulted in accumulation of parkin protein in SH-SY5Y cells and its redistribution to the perinuclear region, especially aggregated Golgi complex, while in Neuro-2a cells neither expression nor redistribution of parkin was noted. Manganese showed no changes in proteasome activities in either cell. Transient transfection of parkin gene inhibited manganese- or manganese plus dopamine-induced cell death of SH-SY5Y cells, but not of Neuro-2a cells. Our results suggest that the attenuating effects of parkin against manganese- or manganese plus dopamine-induced cell death are dopaminergic cell-specific compensatory reactions associated with its accumulation and redistribution to perinuclear regions but not with proteasome system.

Oxidative stress in neurodegeneration: cause or consequence?

Oxidative stress has long been linked to the neuronal cell death that is associated with certain neurodegenerative conditions. Whether it is a primary cause or merely a downstream consequence of the neurodegenerative process is still an open question, however. The advent of a growing number of in vitro and in vivo models that emulate human disease pathology is aiding scientists in deciphering just where oxidative stress intersects with other cellular events in the emerging roadmap leading to neurodegeneration. Here I review the evidence for oxidative stress in neurodegeneration and how this relates to other cellular events.

Dose-dependent induction of apoptosis by R-apomorphine in CHO-K1 cell line in culture

A variety of mechanisms have been proposed as explanations for the distinctive neuropathology of Parkinson's disease, such as increased iron levels, increased oxidant stress or decreased antioxidant defences. The vulnerability of dopamine-containing neurons towards cell death has attracted much attention to the dopamine molecule itself as one of the probable neurotoxic factors leading to neurodegeneration. The similarity between apomorphine and dopamine with regards to their chemical, pharmacological and toxicological properties provided a basis for investigating the nature of the toxicity of the former agent. In this study the CHO-K1 cell line was exposed to different concentrations of apomorphine, and markers of cell death and apoptosis were studied. Apomorphine reduced cell proliferation in a dose-dependent fashion after 72 h incubation. Furthermore, apomorphine induced dose-dependent cell death at concentrations of 10-50 microM. The CHO-K1 line showed specific markers of apoptosis such as the typical DNA laddering phenomenon on agarose gel, morphological changes of apoptotic nuclei as described by in situ end labelling, and annexin binding. These data strongly suggest that apomorphine, like dopamine, elicits its cytotoxic effect with an apoptotic mechanism.