Copper Overload Increased Rat Striatal Levels of Both Dopamine and Its Main Metabolite Homovanillic Acid in Extracellular Fluid.

Copper is a trace element whose electronic configuration provides it with essential structural and catalytic functions. However, in excess, both its high protein affinity and redox-catalyzing properties can lead to hazardous consequences. In addition to promoting oxidative stress, copper is gaining interest for its effects on neurotransmission through modulation of GABAergic and glutamatergic receptors and interaction with the dopamine reuptake transporter. The aim of the present study was to investigate the effects of copper overexposure on the levels of dopamine, noradrenaline, and serotonin, or their main metabolites in rat's striatum extracellular fluid. Copper was injected intraperitoneally using our previously developed model, which ensured striatal overconcentration (2 mg CuCl2/kg for 30 days). Subsequently, extracellular fluid was collected by microdialysis on days 0, 15, and 30. Dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA), and noradrenaline (NA) levels were then determined by HPLC coupled with electrochemical detection. We observed a significant increase in the basal levels of DA and HVA after 15 days of treatment (310% and 351%), which was maintained after 30 days (358% and 402%), with no significant changes in the concentrations of 5-HIAA, DOPAC, and NA. Copper overload led to a marked increase in synaptic DA concentration, which could contribute to the psychoneurological alterations and the increased oxidative toxicity observed in Wilson's disease and other copper dysregulation states.

Copper increases the ability of 6-hydroxydopamine to generate oxidative stress and the ability of ascorbate and glutathione to potentiate this effect: potential implications in Parkinson's disease.

Copper is an essential metal for the function of many proteins related to important cellular reactions and also involved in the synaptic transmission. Although there are several mechanisms involved in copper homeostasis, a dysregulation in this process can result in serious neurological consequences, including degeneration of dopaminergic neurons. 6-Hydroxydopamine is a dopaminergic neurotoxin mainly used in experimental models of Parkinson's disease, whose neurotoxicity has been related to its ability to generate free radicals. In this study, we examined the effects induced by copper on 6-OHDA autoxidation. Our data show that both Cu+ and Cu2+ caused an increase in • OH production by 6-OHDA autoxidation, which was accompanied by an increase in the rate of both p-quinone formation and H2 O2 accumulation. The presence of ascorbate greatly enhanced this process by establishing a redox cycle which regenerates 6-OHDA from its p-quinone. However, the presence of glutathione did not change significantly the copper-induced effects. We observed that copper is able to potentiate the ability of 6-OHDA to cause both lipid peroxidation and protein oxidation, with the latter including a reduction in free-thiol content and an increase in carbonyl content. Ascorbate also increases the lipid peroxidation induced by the action of copper and 6-OHDA. Glutathione protects against the copper-induced lipid peroxidation, but does not reduce its potential to oxidize free thiols. These results clearly demonstrate the potential of copper to increase the capacity of 6-OHDA to generate oxidative stress and the ability of ascorbate to enhance this potential, which may contribute to the destruction of dopaminergic neurons.

Searching for Multi-Targeting Neurotherapeutics against Alzheimer's: Discovery of Potent AChE-MAO B Inhibitors through the Decoration of the 2H-Chromen-2-one Structural Motif.

The need for developing real disease-modifying drugs against neurodegenerative syndromes, particularly Alzheimer's disease (AD), shifted research towards reliable drug discovery strategies to unveil clinical candidates with higher therapeutic efficacy than single-targeting drugs. By following the multi-target approach, we designed and synthesized a novel class of dual acetylcholinesterase (AChE)-monoamine oxidase B (MAO-B) inhibitors through the decoration of the 2H-chromen-2-one skeleton. Compounds bearing a propargylamine moiety at position 3 displayed the highest in vitro inhibitory activities against MAO-B. Within this series, derivative 3h emerged as the most interesting hit compound, being a moderate AChE inhibitor (IC50 = 8.99 µM) and a potent and selective MAO-B inhibitor (IC50 = 2.8 nM). Preliminary studies in human neuroblastoma SH-SY5Y cell lines demonstrated its low cytotoxicity and disclosed a promising neuroprotective effect at low doses (0.1 µM) under oxidative stress conditions promoted by two mitochondrial toxins (oligomycin-A and rotenone). In a Madin-Darby canine kidney (MDCK)II-MDR1 cell-based transport study, Compound 3h was able to permeate the BBB-mimicking monolayer and did not result in a glycoprotein-p (P-gp) substrate, showing an efflux ratio = 0.96, close to that of diazepam.

Assessment of Oxidative Stress Markers in Hypertensive Patients under the Use of Renin-Angiotensin-Aldosterone Blockers.

As in other fields, chronotherapy applied to arterial hypertension (AHT) may have implications on oxidative stress. We compared the levels of some redox markers between hypertensive patients with morning and bedtime use of renin-angiotensin-aldosterone system (RAAS) blockers. This was an observational study that included patients older than 18 years with a diagnosis of essential AHT. Blood pressure (BP) figures were measured using twenty-four-hour ambulatory BP monitoring (24-h ABPM). Lipid peroxidation and protein oxidation were assessed using the thiobarbituric acid reactive substances (TBARS) and reduced thiols assays. We recruited 70 patients with a median age of 54 years, of whom 38 (54%) were women. In hypertensive patients with bedtime use of RAAS blockers, reduced thiol levels showed a positive correlation with nocturnal diastolic BP decrease. TBARS levels were associated with bedtime use of RAAS blockers in dipper and non-dipper hypertensive patients. In non-dipper patients, bedtime use of RAAS blockers was also associated with a decrease in nocturnal diastolic BP. Chronotherapy applied to bedtime use of some BP-lowering drugs in hypertensive patients may be linked to a better redox profile.

Implications of Inflammatory and Oxidative Stress Markers in the Attenuation of Nocturnal Blood Pressure Dipping.

To date, no model has jointly encompassed clinical, inflammatory, and redox markers with the risk of a non-dipper blood pressure (BP) profile. We aimed to evaluate the correlation between these features and the main twenty-four-hour ambulatory blood pressure monitoring (24-h ABPM) indices, as well as to establish a multivariate model including inflammatory, redox, and clinical markers for the prediction of a non-dipper BP profile. This was an observational study that included hypertensive patients older than 18 years. We enrolled 247 hypertensive patients (56% women) with a median age of 56 years. The results showed that higher levels of fibrinogen, tissue polypeptide-specific antigen, beta-2-microglobulin, thiobarbituric acid reactive substances, and copper/zinc ratio were associated with a higher risk of a non-dipper BP profile. Nocturnal systolic BP dipping showed a negative correlation with beta-globulin, beta-2-microglobulin, and gamma-globulin levels, whereas nocturnal diastolic BP dipping was positively correlated with alpha-2-globulin levels, and negatively correlated with gamma-globulin and copper levels. We found a correlation between nocturnal pulse pressure and beta-2-microglobulin and vitamin E levels, whereas the day-to-night pulse pressure gradient was correlated with zinc levels. Twenty-four-hour ABPM indices could exhibit singular inflammatory and redox patterns with implications that are still poorly understood. Some inflammatory and redox markers could be associated with the risk of a non-dipper BP profile.

Differential toxicity of 6-hydroxydopamine in SH-SY5Y human neuroblastoma cells and rat brain mitochondria: protective role of catalase and superoxide dismutase.

Oxidative stress and mitochondrial dysfunction are two pathophysiological factors often associated with the neurodegenerative process involved in Parkinson's disease (PD). Although, 6-hydroxydopamine (6-OHDA) is able to cause dopaminergic neurodegeneration in experimental models of PD by an oxidative stress-mediated process, the underlying molecular mechanism remains unclear. It has been established that some antioxidant enzymes such as catalase (CAT) and superoxide dismutase (SOD) are often altered in PD, which suggests a potential role of these enzymes in the onset and/or development of this multifactorial syndrome. In this study we have used high-resolution respirometry to evaluate the effect of 6-OHDA on mitochondrial respiration of isolated rat brain mitochondria and the lactate dehydrogenase cytotoxicity assay to assess the percentage of cell death induced by 6-OHDA in human neuroblastoma cell line SH-SY5Y. Our results show that 6-OHDA affects mitochondrial respiration by causing a reduction in both respiratory control ratio (IC(50) = 200 ± 15 nM) and state 3 respiration (IC(50) = 192 ± 17 nM), with no significant effects on state 4(o). An inhibition in the activity of both complex I and V was also observed. 6-OHDA also caused cellular death in human neuroblastoma SH-SY5Y cells (IC(50) = 100 ± 9 µM). Both SOD and CAT have been shown to protect against the toxic effects caused by 6-OHDA on mitochondrial respiration. However, whereas SOD protects against 6-OHDA-induced cellular death, CAT enhances its cytotoxicity. The here reported data suggest that both superoxide anion and hydroperoxyl radical could account for 6-OHDA toxicity. Furthermore, factors reducing the rate of 6-OHDA autoxidation to its p-quinone appear to enhance its cytotoxicity.

2-Benzazepine nitrones protect dopaminergic neurons against 6-hydroxydopamine-induced oxidative toxicity.

A number of C-3 spirocyclic 2-benzazepine analogs of α-phenyl-N-tert-butyl nitrone (PBN) were synthesized and tested for their activity in protecting rat brain mitochondria and dopaminergic (DA) neurons against 6-hydroxydopamine (6-OHDA), a toxin inducing destruction of the DA nigro-striatal pathway in rodent models of Parkinson's disease. The newly synthesized nitrone derivatives were firstly investigated for their activity in decreasing the level of hydroxyl radicals generated during 6-OHDA oxidation, and inhibit lipid peroxidation (TBARS assay) and protein carbonyl content (PCC) in rat brain mitochondria. Most of the studied 2-benzazepine nitrones showed inhibitory potencies in both TBARS and PCC assays at least two magnitude orders higher than that of PBN. The data obtained usefully complemented the known structure-activity relationships. In particular, 5 and 10, bearing C-3 spiro cyclopentyl and tetrahydropyranyl moieties, respectively, at 8 µM concentration proved to be significantly more effective than PBN in protecting cultured DA neurons exposed to 6-OHDA, which alone causes about 45% cell loss in 24 h. In addition, we found that 5 inhibited butyrylcholinesterase with an IC(50) value of 16.8 µM, which would enhance its potential as neuroprotective agent in Alzheimer's neurodegeneration. These findings extend the utility of benzazepine-based PBN analogs in the treatment of age-related free radical-mediated disorders.

Correlation between Blunted Nocturnal Decrease in Diastolic Blood Pressure and Oxidative Stress: An Observational Study.

An impaired nocturnal decrease in diastolic blood pressure (DBP) increases the blood pressure (BP) load, which is a main factor in endothelial dysfunction, atherosclerosis, and arterial stiffness. We aimed to quantify some markers of oxidative stress in hypertensive patients, to compare their levels between individuals with dipper and non-dipper DBP profiles, and to assess their correlation with the nocturnal DBP (nDBP) dipping. It was an observational study that included patients older than 18 years with a diagnosis of essential hypertension who consented to participate. The collected variables were some indices of 24-h ambulatory blood pressure monitoring, demographic, epidemiological, clinical, and laboratory variables. Plasma thiobarbituric acid reactive substances (TBARS) and reduced thiols, together with serum vitamin E, vitamin A, copper (Cu), and zinc (Zn) levels were assessed as oxidative stress markers. We recruited 248 patients with a median age of 56 years (56% women). The percentage of nDBP dipping showed a weak positive correlation with reduced thiol, vitamin E, and vitamin A levels; and a weak negative correlation with Cu levels. We also found a negative correlation between nDBP dipping and the TBARS/Thiol, TBARS/Vitamin E, and TBARS/Vitamin A ratios. After multivariate analysis, we found that increased TBARS/Thiol ratio and serum Cu levels were associated with a higher risk of a non-dipper DBP profile. As in other situations of increased cardiovascular risk, an impaired nDBP decrease may coincide with abnormalities in redox status.

Assessment of oxidative stress markers in elderly patients with SARS-CoV-2 infection and potential prognostic implications in the medium and long term.

We aimed to evaluate the correlation of plasma levels of thiobarbituric acid reactive substances (TBARS) and reduced thiols with morbidity, mortality and immune response during and after SARS-CoV-2 infection. This was an observational study that included inpatients with SARS-CoV-2 infection older than 65 years. The individuals were followed up to the twelfth month post-discharge. Plasma levels of TBARS and reduced thiols were quantified as a measure of lipid and protein oxidation, respectively. Fatal and non-fatal events were evaluated during admission and at the third, sixth and twelfth month post-discharge. Differences in oxidative stress markers between the groups of interest, time to a negative RT-qPCR and time to significant anti-SARS-CoV-2 IgM titers were assessed. We included 61 patients (57% women) with a mean age of 83 years old. After multivariate analysis, we found differences in TBARS and reduced thiol levels between the comparison groups in fatal and non-fatal events during hospital admission. TBARS levels were also correlated with fatal events at the 6th and 12th months post-discharge. One year after hospital discharge, other predictors rather than oxidative stress markers were relevant in the models. The median time to reach significant anti-SARS-CoV-2 IgM titers was lower in patients with low levels of reduced thiols. Assessment of some parameters related to oxidative stress may help identify groups of patients with a higher risk of morbidity, mortality and delayed immune response during and after SARS-CoV-2 infection.

Brain oxidative stress and selective behaviour of aluminium in specific areas of rat brain: potential effects in a 6-OHDA-induced model of Parkinson's disease.

The ability of aluminium to affect the oxidant status of specific areas of the brain (cerebellum, ventral midbrain, cortex, hippocampus, striatum) was investigated in rats intraperitoneally treated with aluminium chloride (10 mg Al3+/kg/day) for 10 days. The potential of aluminium to act as an etiological factor in Parkinson's disease (PD) was assessed by studying its ability to increase oxidative stress in ventral midbrain and striatum and the striatal dopaminergic neurodegeneration induced by 6-hydroxydopamine in an experimental model of PD.The results showed that aluminium caused an increase in oxidative stress (TBARS, protein carbonyl content, and protein thiol content) for most of the brain regions studied, which was accompanied by a decrease in the activity of some antioxidant enzymes (superoxide dismutase, catalase, glutathione peroxidase). However, studies in vitro confirmed the inability of aluminium to affect the activity of those enzymes. The reported effects exhibited a regional-selective behaviour for all the cerebral structures studied. Aluminium also enhanced the ability of 6-hydroxydopamine to cause oxidative stress and neurodegeneration in the dopaminergic system, which confirms its potential as a risk factor in the development of PD.

Copper Increases Brain Oxidative Stress and Enhances the Ability of 6-Hydroxydopamine to Cause Dopaminergic Degeneration in a Rat Model of Parkinson's Disease.

Redox properties enable copper to perform its essential role in many biological processes, but they can also convert it into a potentially hazardous element. Its dyshomeostasis may have serious neurological consequences, and its possible involvement in Parkinson's disease and other neurodegenerative disorders has been suggested. The in vitro and ex vivo ability of copper to increase oxidative stress has already been demonstrated, and the aim of the present study was to assess in vivo the capacity of copper to cause brain oxidative damage and its ability to increase the dopaminergic degeneration induced by 6-hydroxydopamine. We found that chronic copper administration (10 mg Cu2+/kg/day, IP) causes its accumulation in different brain areas (cortex, striatum, nigra) and was accompanied by an increase in TBARS levels and a decrease in protein free-thiol content in the cortex. A decrease in catalase activity and an increase in glutathione peroxidase activity were also observed in the cortex. The intrastriatal administration of Cu2+ caused an increase in some indices of oxidative stress (TBARS and protein free-thiol content) in striatum and nigra, but was unable to induce dopaminergic degeneration. However, when copper was intrastriatally coadministered with 6-hydroxydopamine, it increased dopaminergic degeneration, a fact that was also accompanied by an increase in the assayed indices of oxidative stress, a decrease in catalase activity, and an augmentation in glutathione activity. Evidently, copper cannot cause neurodegeneration per se, but may potentiate the action of other factors involved in the pathogenesis of Parkinson's disease through oxidative stress.

Synthesis and monoamine oxidase inhibitory activity of new pyridazine-, pyrimidine- and 1,2,4-triazine-containing tricyclic derivatives.

A number of condensed azines, mostly belonging to the families of indeno-fused pyridazines (1), pyrimidines (2, 3), and 1,2,4-triazines (4, 5), were synthesized and evaluated in vitro as monoamine oxidase (MAO) A and B inhibitors. Most of them showed higher inhibition potency toward MAO-B, the most effective one being 3-(3-nitrophenyl)-9H-indeno[1,2-e] [1,2,4]triazin-9-one (4c), which displayed an IC50 value of 80 nM and proved to be 10-fold more potent than its [2,1-e] fusion isomer 5. Replacing the 3-phenyl group of the known indeno[1,2-c]pyridazin-5-one MAO-B inhibitors with a flexible phenoxymethyl group enhanced the inhibitory potency. The inhibition data highlighted the importance of the aza-heterocyclic scaffold in affecting the MAO isoform selectivity. The 3-phenyl derivatives with type 1, 4, and 5 scaffolds were inhibitors of MAO-B with little or no MAO-A effect, whereas 2- or 3-phenyl derivatives of type 2 and 3 pyrimidine-containing fusion isomers inhibited both isoenzymes with a structure-dependent preference toward MAO-A.

Analysis of brain regional distribution of aluminium in rats via oral and intraperitoneal administration.

In the present work, accumulation and distribution of aluminium in the rat brain following both intraperitoneal and oral administration were studied. Electrothermal atomic absorption spectrometry was used to determine aluminium concentration in different brain areas (cerebellum, ventral midbrain, cortex, hippocampus, and striatum). Most of the brain areas showed accumulation of aluminium, but a greater and more significant increase was noted in the group receiving aluminium via intraperitoneal administration. Aluminium distribution was also dependent on the administration route.

Effects of Aluminium on Rat Brain Mitochondria Bioenergetics: an In vitro and In vivo Study.

Numerous studies have highlighted the potential of aluminium as an aetiological factor for some neurodegenerative disorders, particularly Alzheimer's disease and Parkinson's disease. Our previous studies have shown that aluminium can cause oxidative stress, reduce the activity of some antioxidant enzymes, and enhance the dopaminergic neurodegeneration induced by 6-hydroxydopamine in an experimental model of Parkinson's disease in rats. We now report a study on the effects caused by aluminium on mitochondrial bioenergetics following aluminium addition and after its chronic administration to rats. To develop our study, we used a high-resolution respirometry to test the mitochondrial respiratory capacities under the conditions of coupling, uncoupling, and non-coupling. Our study showed alterations in leakiness, a reduction in the maximum capacity of complex II-linked respiratory pathway, a decline in the respiration efficiency, and a decrease in the activities of complexes III and V in both models studied. The observed effects also included both an alteration in mitochondrial transmembrane potential and a decrease in oxidative phosphorylation capacity when relatively high concentrations of aluminium were added to the isolated mitochondria. These findings contribute to explain both the ability of aluminium to generate oxidative stress and its suggested potential to act as an etiological factor by promoting the progression of neurodegenerative disorders such as Parkinson's disease.

Reduction of dopaminergic degeneration and oxidative stress by inhibition of angiotensin converting enzyme in a MPTP model of parkinsonism.

There is growing evidence indicating that oxidative stress is a key contributor to the pathogenesis and progression of Parkinson's disease. The brain, and particularly the basal ganglia, possesses a local rennin-angiotensin system. Angiotensin activates NAD(P)H-dependent oxidases, which are a major intracellular source of superoxide, and angiotensin converting enzyme inhibitors (ACEIs) have shown antioxidant properties. We treated mice with MPTP and the ACEI captopril to study the possible neuroprotective and antioxidant effects of the latter on the dopaminergic system. Pre-treatment with captopril induced a significant reduction in the MPTP-induced loss of dopaminergic neurons in the substantia nigra and a significant reduction in the loss of dopaminergic terminals in the striatum. Furthermore, captopril reduced the MPTP-induced increase in the levels of major oxidative stress indicators (i.e. lipid peroxidation and protein oxidation) in the ventral midbrain and the striatum. Captopril did not reduce striatal MPP(+) levels, MAO-B activity or dopamine transporter activity, which may reduce MPTP neurotoxicity. Our results suggest that angiotensin-converting enzyme inhibitors may be useful for treatment of Parkinson's disease, and that further investigation should focus on the neuroprotective capacity of these compounds.

A QSAR model for in silico screening of MAO-A inhibitors. Prediction, synthesis, and biological assay of novel coumarins.

This work explores the potential of the MARCH-INSIDE methodology to seek a QSAR for MAO-A inhibitors from a heterogeneous series of compounds. A Markov model was used to quickly calculate the molecular electron delocalization, polarizability, refractivity, and n-octanol/water partition coefficients for a series of 1406 active/nonactive compounds. LDA was subsequently used to fit a classification function. The model showed 92.8% and 91.8% global accuracy and predictability in training and validation studies. This QSAR model was validated through a virtual screening of a series of coumarin derivatives. The 15 selected compounds were prepared and evaluated as in vitro MAO-A inhibitors. The theoretical prediction was compared with the experimental results and the model correctly predicted 13 compounds with only two mistakes on compounds with activities very close to the cutoff point established for the model. Consequently, this method represents a useful tool for the "in silico" screening of MAO-A inhibitors.

Structural insights into monoamine oxidase inhibitory potency and selectivity of 7-substituted coumarins from ligand- and target-based approaches.

A new series of 3-, 4-, 7-polysubstituted coumarins have been designed and evaluated for their monoamine oxidase A and monoamine oxidase B (MAO-A and MAO-B) inhibitory potency. Substituents at position 7 consisted of a bridge of different physicochemical nature linking a phenyl ring to the coumarin scaffold. Structure-affinity and structure-selectivity relationships, derived through CoMFA-GOLPE and docking studies, revealed the key physicochemical interactions responsible for the observed MAO-B and MAO-A inhibitory potency and suggested the main structural determinants for high selectivity toward one of the two enzymatic isoforms. The predictive power of our models was proved with the design of a new inhibitor demonstrating an outstanding MAO-B affinity (pIC50 = 8.29) and the highest MAO-B selectivity (DeltapIC50 = 3.39) within the entire series of ligands examined herein.

Exploring Basic Tail Modifications of Coumarin-Based Dual Acetylcholinesterase-Monoamine Oxidase B Inhibitors: Identification of Water-Soluble, Brain-Permeant Neuroprotective Multitarget Agents.

Aiming at modulating two key enzymatic targets for Alzheimer's disease (AD), i.e., acetylcholinesterase (AChE) and monoamine oxidase B (MAO B), a series of multitarget ligands was properly designed by linking the 3,4-dimethylcoumarin scaffold to 1,3- and 1,4-substituted piperidine moieties, thus modulating the basicity to improve the hydrophilic/lipophilic balance. After in vitro enzymatic inhibition assays, multipotent inhibitors showing potencies in the nanomolar and in the low micromolar range for hMAO B and eeAChE, respectively, were prioritized and evaluated in human SH-SY5Y cell-based models for their cytotoxicity and neuroprotective effect against oxidative toxins (H2O2, rotenone, and oligomycin-A). The present study led to the identification of a promising multitarget hit compound (5b) exhibiting high hMAO B inhibitory activity (IC50 = 30 nM) and good MAO B/A selectivity (selectivity index, SI = 94) along with a micromolar eeAChE inhibition (IC50 = 1.03 µM). Moreover, 5b behaves as a water-soluble, brain-permeant neuroprotective agent against oxidative insults without interacting with P-gp efflux system.

Mitochondrial angiotensin receptors in dopaminergic neurons. Role in cell protection and aging-related vulnerability to neurodegeneration.

The renin-angiotensin system (RAS) was initially considered as a circulating humoral system controlling blood pressure, being kidney the key control organ. In addition to the 'classical' humoral RAS, a second level in RAS, local or tissular RAS, has been identified in a variety of tissues, in which local RAS play a key role in degenerative and aging-related diseases. The local brain RAS plays a major role in brain function and neurodegeneration. It is normally assumed that the effects are mediated by the cell-surface-specific G-protein-coupled angiotensin type 1 and 2 receptors (AT1 and AT2). A combination of in vivo (rats, wild-type mice and knockout mice) and in vitro (primary mesencephalic cultures, dopaminergic neuron cell line cultures) experimental approaches (confocal microscopy, electron microscopy, laser capture microdissection, transfection of fluorescent-tagged receptors, treatments with fluorescent angiotensin, western blot, polymerase chain reaction, HPLC, mitochondrial respirometry and other functional assays) were used in the present study. We report the discovery of AT1 and AT2 receptors in brain mitochondria, particularly mitochondria of dopaminergic neurons. Activation of AT1 receptors in mitochondria regulates superoxide production, via Nox4, and increases respiration. Mitochondrial AT2 receptors are much more abundant and increase after treatment of cells with oxidative stress inducers, and produce, via nitric oxide, a decrease in mitochondrial respiration. Mitochondria from the nigral region of aged rats displayed altered expression of AT1 and AT2 receptors. AT2-mediated regulation of mitochondrial respiration represents an unrecognized primary line of defence against oxidative stress, which may be particularly important in neurons with increased levels of oxidative stress such as dopaminergic neurons. Altered expression of AT1 and AT2 receptors with aging may induce mitochondrial dysfunction, the main risk factor for neurodegeneration.

Effects of aluminum and zinc on the oxidative stress caused by 6-hydroxydopamine autoxidation: relevance for the pathogenesis of Parkinson's disease.

Aluminum and zinc have been related to the pathogenesis of Parkinson's disease (PD), the former for its neurotoxicity and the latter for its apparent antioxidant properties. 6-Hydroxydopamine (6-OHDA) is an important neurotoxin putatively involved in the pathogenesis of PD, its neurotoxicity often being related to oxidative stress. The potential effect of these metals on the oxidative stress induced by 6-OHDA autoxidation and the potential of ascorbic acid (AA), cysteine, and glutathione to modify this effect were investigated. Both metals, particularly Al3+, induced a significant reduction in *OH production by 6-OHDA autoxidation. The combined action of AA and a metal caused a significant and sustained increase in *OH generation, particularly with Al3+, while the effect of sulfhydryl reductants was limited to only the first few minutes of the reaction. However, both Al3+ and Zn2+ provoked a decrease in the lipid peroxidation induced by 6-OHDA autoxidation using mitochondrial preparations from rat brain, assessed by TBARS formation. In the presence of AA, only Al3+ induced a significant reduction in lipid peroxidation. After intrastriatal injections of 6-OHDA in rats, tyrosine hydroxylase immunohistochemistry revealed that Al3+ reduces 6-OHDA-induced dopaminergic lesion in the striatum, which corroborates the involvement of lipid peroxidation in 6-OHDA neurotoxicity and appears to discard the participation of this mechanism on PD by Al3+ accumulation. The previously reported antioxidant properties of Zn2+ appear to be related to the induction of Zn2+-containing proteins and not to the metal per se.