Antioxidant capacity in postmortem brain tissues of Parkinson's and Alzheimer's diseases

Transient anticonvulsant effects of time-restricted feeding in the 6-Hz mouse model

INTRODUCTION

Intermittent fasting enhances neural bioenergetics, is neuroprotective, and elicits antioxidant effects in various animal models. There are conflicting findings on seizure protection, where intermittent fasting regimens often cause severe weight loss resembling starvation which is unsustainable long-term. Therefore, we tested whether a less intensive intermittent fasting regimen such as time-restricted feeding (TRF) may confer seizure protection.

METHODS

Male CD1 mice were assigned to either ad libitum-fed control, continuous 8 h TRF, or 8 h TRF with weekend ad libitum food access (2:5 TRF) for one month. Body weight, food intake, and blood glucose levels were measured. Seizure thresholds were determined at various time points using 6-Hz and maximal electroshock seizure threshold (MEST) tests. Protein levels and mRNA expression of genes, enzyme activity related to glucose metabolism, as well as mitochondrial dynamics were assessed in the cortex and hippocampus. Markers of antioxidant defence were evaluated in the plasma, cortex, and liver.

RESULTS

Body weight gain was similar in the ad libitum-fed and TRF mouse groups. In both TRF regimens, blood glucose levels did not change between the fed and fasted state and were higher during fasting than in the ad libitum-fed groups. Mice in the TRF group had increased seizure thresholds in the 6-Hz test on day 15 and on day 19 in a second cohort of 2:5 TRF mice, but similar seizure thresholds at other time points compared to ad libitum-fed mice. Continuous TRF did not alter MEST seizure thresholds on day 28. Mice in the TRF group showed increased maximal activity of pyruvate dehydrogenase in the cortex, which was accompanied by increased protein levels of mitochondrial pyruvate carrier 1 in the cortex and hippocampus. There were no other major changes in protein or mRNA levels associated with energy metabolism and mitochondrial dynamics in the brain, nor markers of antioxidant defence in the brain, liver, or plasma.

CONCLUSIONS

Both continuous and 2:5 TRF regimens transiently increased seizure thresholds in the 6-Hz model at around 2 weeks, which coincided with stability of blood glucose levels during the fed and fasted periods. Our findings suggest that the lack of prolonged anticonvulsant effects in the acute electrical seizure models employed may be attributed to only modest metabolic and antioxidant adaptations found in the brain and liver. Our findings underscore the potential therapeutic value of TRF in managing seizure-related conditions.

Isolated Mitochondrial Preparations and In organello Assays: A Powerful and Relevant Ex vivo Tool for Assessment of Brain (Patho)physiology

Mitochondria regulate multiple aspects of neuronal development, physiology, plasticity, and pathology through their regulatory roles in bioenergetic, calcium, redox, and cell survival/death signalling. While several reviews have addressed these different aspects, a comprehensive discussion focussing on the relevance of isolated brain mitochondria and their utilities in neuroscience research has been lacking. This is relevant because the employment of isolated mitochondria rather than their in situ functional evaluation, offers definitive evidence of organelle-specificity, negating the interference from extra mitochondrial cellular factors/signals. This mini-review was designed primarily to explore the commonly employed in organello analytical assays for the assessment of mitochondrial physiology and its dysfunction, with a particular focus on neuroscience research. The authors briefly discuss the methodologies for biochemical isolation of mitochondria, their quality assessment, and cryopreservation. Further, the review attempts to accumulate the key biochemical protocols for in organello assessment of a multitude of mitochondrial functions critical for neurophysiology, including assays for bioenergetic activity, calcium and redox homeostasis, and mitochondrial protein translation. The purpose of this review is not to examine each and every method or study related to the functional assessment of isolated brain mitochondria, but rather to assemble the commonly used protocols of in organello mitochondrial research in a single publication. The hope is that this review will provide a suitable platform aiding neuroscientists to choose and apply the required protocols and tools to address their particular mechanistic, diagnostic, or therapeutic question dealing within the confines of the research area of mitochondrial patho-physiology in the neuronal perspective.

Lactulose and Melibiose Attenuate MPTP-Induced Parkinson's Disease in Mice by Inhibition of Oxidative Stress, Reduction of Neuroinflammation and Up-Regulation of Autophagy

Parkinson’s disease (PD) is a common neurodegenerative disease characterized by the progressive loss of dopaminergic (DAergic) neurons in the ventral brain. A disaccharide trehalose has demonstrated the potential to mitigate the DAergic loss in disease models for PD. However, trehalose is rapidly hydrolyzed into glucose by trehalase in the intestine, limiting its potential for clinical practice. Here, we investigated the neuroprotective potential of two trehalase-indigestible analogs, lactulose and melibiose, in sub-chronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse model of PD. Treatment with MPTP generated significant motor deficits, inhibited dopamine levels, and down-regulated dopamine transporter (DAT) in the striatum. Expression levels of genes involved in anti-oxidative stress pathways, including superoxide dismutase 2 (SOD2), nuclear factor erythroid 2-related factor 2 (NRF2), and NAD(P)H dehydrogenase (NQO1) were also down-regulated. Meanwhile, expression of the oxidative stress marker 4-hydroxynonenal (4-HNE) was up-regulated along with increased microglia and astrocyte reactivity in the ventral midbrain following MPTP treatment. MPTP also reduced the activity of autophagy, evaluated by the autophagosomal marker microtubule-associated protein 1 light chain 3 (LC3)-II. Lactulose and melibiose significantly rescued motor deficits, increased dopamine in the striatum, reduced microglia and astrocyte reactivity as well as decreased levels of 4-HNE. Furthermore, lactulose and melibiose up-regulated SOD2, NRF2, and NQO1 levels, as well as enhanced the LC3-II/LC3-I ratio in the ventral midbrain with MPTP treatment. Our findings indicate the potential of lactulose and melibiose to protect DAergic neurons in PD.

What Have We Learned from Cerebrospinal Fluid Studies about Biomarkers for Detecting LRRK2 Parkinson's Disease Patients and Healthy Subjects with Parkinson's-Associated LRRK2 Mutations?

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are the most common known cause of autosomal dominant Parkinson’s disease (PD) and sporadic PD (sPD). The clinical presentation of LRRK2 PD is similar to sPD, and except for genetic testing, no biochemical or imaging markers can differentiate LRRK2 PD from sPD. Discovery of such biomarkers could indicate neuropathological mechanisms that are unique to or increased in LRRK2 PD. This review discusses findings in 17 LRRK2 - related CSF studies found on PubMed. Most of these studies compared analyte concentrations between four diagnostic groups: LRRK2 PD patients, sPD patients, asymptomatic control subjects carrying PD-associated LRRK2 mutations (LRRK2 CTL), and healthy control subjects lacking LRRK2 mutations (CTL). Analytes examined in these studies included Aβ1-42, tau, α-synuclein, oxidative stress markers, autophagy-related proteins, pteridines, neurotransmitter metabolites, exosomal LRRK2 protein, RNA species, inflammatory cytokines, mitochondrial DNA (mtDNA), and intermediary metabolites. FINDINGS: Pteridines, α-synuclein, mtDNA, 5-hydroxyindolacetic acid, β-D-glucose, lamp2, interleukin-8, and vascular endothelial growth factor were suggested to differentiate LRRK2 PD from sPD patients; 8-hydroxy-2’-deoxyguanosine (8-OHdG), 8-isoprostane (8-ISO), 2-hydroxybutyrate, mtDNA, lamp2, and neopterin may differentiate between LRRK2 CTL and LRRK2 PD subjects; and soluble oligomeric α-synuclein, 8-OHdG, and 8-ISO might differentiate LRRK2 CTL from CTL subjects. CONCLUSIONS: The low numbers of investigations of each analyte, small sample sizes, and methodological differences limit conclusions that can be drawn from these studies. Further investigations are indicated to determine the validity of the analytes identified in these studies as possible biomarkers for LRRK2 PD patients and/or LRRK2 CTL subjects.

NFE2L2 variations reduce antioxidant response in patients with Parkinson disease

Oxidative stress has been recognized as a risk factor of Parkinson's disease (PD) development. We hypothesized that decreased function of the nuclear factor (erythroid-derived 2)-like 2 (NFE2L2)-antioxidant response element (ARE) pathway might predispose to Parkinsonism. A case-control study was performed between NFE2L2 Single Nucleotide Polymorphism (SNP) and PD in a cohort of 765 unrelated patients with diagnosis of PD and 489 matched normal individuals. We found that c.351T>A, D117E (P = 0.003, OR = 2.8) and c.351T>A, D117E (P = 0.012, OR = 1.9) were significantly associated with PD. The risk allele of both polymorphisms showed a high frequency in our PD sample (c.351A: 19.7% and c.423T: 7.8%). The association between both c.351T>A and c.423G>T and PD was further confirmed in an independent case-control cohort consisting of 210 individuals with PD and 148 normal controls. We further found that over expression of D117E and Q141H variants of NFE2L2 reduced target genes expression of Glutathione S-transferase Pi 1 (GSTP1), Glutathione S-transferase Mu 1 (GSTM1), and Heme oxygenase 1 (HO-1) genes. NFE2L2 D117E and Q141H impaired activation of ARE-driven transcriptional activity. Our findings indicate that NFE2L2 may play an important role in the pathogenesis of PD in Chinese populations.

Increased Oxidative Stress Markers in Cerebrospinal Fluid from Healthy Subjects with Parkinson's Disease-Associated LRRK2 Gene Mutations

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are the most frequent cause of inherited Parkinson’s disease (PD). The most common PD-associated LRRK2 mutation, G2019S, induces increased production of reactive oxygen species in vitro. We therefore hypothesized that individuals with PD-associated LRRK2 mutations might have increased concentrations of oxidative stress markers and/or decreased total antioxidant capacity (TAC) in their cerebrospinal fluid (CSF). We measured two oxidative stress markers, namely 8-hydroxy-2′-deoxyguanosine (8-OHdG) and 8-isoprostane (8-ISO), and TAC in CSF from LRRK2 mutation-bearing PD patients (LRRK2 PD = 19), sporadic PD patients (sPD = 31), and healthy control subjects with or without these mutations (LRRK2 CTL = 30, CTL = 27). 8-OHdG and 8-ISO levels were increased in LRRK2 CTL subjects, while TAC was similar between groups. 8-ISO was negatively correlated, and TAC was positively correlated, with Montreal Cognitive Assessment scores in LRRK2 PD, LRRK2 CTL, and CTL subjects. Correlations in both groups of PD patients between the two oxidative stress markers and Unified Parkinson Disease Rating Scale Total scores were weak, while TAC was negatively correlated with these scores. These findings suggest that oxidative stress may be increased in the CNS in healthy individuals with PD-associated LRRK2 mutations. Further, TAC may decrease in the CNS with the progression of PD, and when cognitive impairment is present regardless of the presence or absence of PD.

Alpha-synuclein-induced oxidative stress correlates with altered superoxide dismutase and glutathione synthesis in human neuroblastoma SH-SY5Y cells

Alpha-synuclein (α-syn) is a major component of Lewy bodies found in sporadic and inherited forms of Parkinson's disease (PD). Mutations in the gene encoding α-syn and duplications and triplications of wild-type (WT) α-syn have been associated with PD. Several mechanisms have been implicated in the degeneration of dopaminergic neurons in PD, including oxidative stress and mitochondrial dysfunction. Here we defined the occurrence of oxidative stress in SH-SY5Y cells overexpressing WT α-syn in a doxycycline (Dox) regulated manner, before and after exposure to iron (500 µM), and determined the changes in proteins involved in the intracellular antioxidant defense system. Data evidenced an increase in caspase-3 activation and diminished reducing capacity of -Dox cells, associated with decreased activity of mitochondria complex I and reduced mitochondrial transcription factor A (TFAM) levels in these cells. Furthermore, total and mitochondrial reactive oxygen species levels were higher under basal conditions in cells overexpressing α-syn (-Dox) and this increase was apparently correlated with diminished levels and activities of SOD1 and SOD2 in -Dox cells. Moreover, both reduced and oxidized glutathione levels were diminished in -Dox cells under basal conditions, concomitantly with decreased activity of GCL and reduced protein levels of GCLc. The effects caused by iron (500 µM) were mostly independent of α-syn expression and triggered different antioxidant responses to possibly counterbalance higher levels of free radicals. Overall, data suggest that overexpression of α-syn modifies the antioxidant capacity of SH-SY5Y cells due to altered activity and protein levels of SOD1 and SOD2, and decreased glutathione pool.

Oxidative and nitrosative stress in serum of patients with Parkinson's disease

Parkinson's disease (PD) is one of the common neurodegenerative disorders. Oxidative stress is considered as a contributing factor to the development of PD. The present study aims to investigate serum oxidative stress status in patients with PD. Oxidative stress was assessed by measuring serum nitric oxide levels, lipid hydroperoxide concentrations, and nitric oxide synthase activity. In addition, total serum antioxidant capacity (TAC) was evaluated using the serum 2,2-Diphenyl-1-picryl-hydrazyl (DPPH) free-radical scavenging method in 32 patient with Parkinson's disease and 32 control subjects. Our results indicated that serum nitric oxide and lipid hydroperoxide levels were significantly lower in patients with PD than controls. Moreover, nitric oxide levels were found to be negatively correlated with Unified Parkinson's Disease Rating Scale (UPDRS). However, no statistical difference was observed in total serum antioxidant capacities and nitric oxide synthase activities between patients and controls. The present study indicates that although antioxidant capacity was not changed, lipid hydroperoxide (LPO) level was found decreased. This might show pre-oxidative process in these patients. In addition, decreased nitric oxide (NO) level and negative correlation observed between NO level and disease rating scale implicated a role for NO in the disease process.

Glutamate excitotoxicity in neurons triggers mitochondrial and endoplasmic reticulum accumulation of Parkin, and, in the presence of N-acetyl cysteine, mitophagy

Disruption of the dynamic properties of mitochondria (fission, fusion, transport, degradation, and biogenesis) has been implicated in the pathogenesis of neurodegenerative disorders, including Parkinson's disease (PD). Parkin, the product of gene PARK2 whose mutation causes familial PD, has been linked to mitochondrial quality control via its role in regulating mitochondrial dynamics, including mitochondrial degradation via mitophagy. Models using mitochondrial stressors in numerous cell types have elucidated a PINK1-dependent pathway whereby Parkin accumulates on damaged mitochondria and targets them for mitophagy. However, the role Parkin plays in regulating mitochondrial homeostasis specifically in neurons has been less clear. We examined whether a stressor linked to neurodegeneration, glutamate excitotoxicity, elicits Parkin-mitochondrial translocation and mitophagy in neurons. We found that brief, acute exposure to glutamate causes Parkin translocation to mitochondria in neurons, in a calcium- and N-methyl-d-aspartate (NMDA) receptor-dependent manner. In addition, we found that Parkin accumulates on endoplasmic reticulum (ER) and mitochondrial/ER junctions following excitotoxicity, supporting a role for Parkin in mitochondrial-ER crosstalk in mitochondrial homeostasis. Despite significant Parkin-mitochondria translocation, however, we did not observe mitophagy under these conditions. To further investigate, we examined the role of glutamate-induced oxidative stress in Parkin-mitochondria accumulation. Unexpectedly, we found that glutamate-induced accumulation of Parkin on mitochondria was promoted by the antioxidant N-acetyl cysteine (NAC), and that co-treatment with NAC facilitated Parkin-associated mitophagy. These results suggest the possibility that mitochondrial depolarization and oxidative damage may have distinct pathways associated with Parkin function in neurons, which may be critical in understanding the role of Parkin in neurodegeneration.

Brain catalase in the streptozotocin-rat model of sporadic Alzheimer's disease treated with the iron chelator-monoamine oxidase inhibitor, M30

Low intracerebroventricular (icv) doses of streptozotocin (STZ) produce regionally specific brain neurochemical changes in rats that are similar to those found in the brain of patients with sporadic Alzheimer's disease (sAD). Since oxidative stress is thought to be one of the major pathologic processes in sAD, catalase (CAT) activity was estimated in the regional brain tissue of animals treated intracerebroventricularly with STZ and the multitarget iron chelator, antioxidant and MAO-inhibitor M30 [5-(N-methyl-N-propargylaminomethyl)-8-hydroxyquinoline]. Five-day oral pre-treatment of adult male Wistar rats with 10 mg/kg/day M30 dose was followed by a single injection of STZ (1 mg/kg, icv). CAT activity was measured colorimetrically in the hippocampus (HPC), brain stem (BS) and cerebellum (CB) of the control, STZ-, M30- and STZ + M30-treated rats, respectively, 4 weeks after the STZ treatment. STZ-treated rats demonstrated significantly lower CAT activity in all three brain regions in comparison to the controls (p < 0.05 for BS and CB, p < 0.01 for HPC). M30 pre-treatment of the control rats did not influence the CAT activity in HPC and CB, but significantly increased it in BS (p < 0.05). M30 pre-treatment of STZ-treated rats significantly increased CAT activity in the HPC in comparison to the STZ treatment alone (p < 0.05) and normalized to the control values. These findings are in line with the assumption that reactive oxygen species contribute to the pathogenesis of STZ in a rat model of sAD and indicate that multifunctional iron chelators such as M30 might also have beneficial effects in this non-transgenic sAD model.

Parkinson's disease and autophagy

It is generally accepted that a correlation between neurodegenerative disease and protein aggregation in the brain exists; however, a causal relationship has not been elucidated. In neurons, failure of autophagy may result in the accumulation of aggregate-prone proteins and subsequent neurodegeneration. Thus, pharmacological induction of autophagy to enhance the clearance of intracytoplasmic aggregate-prone proteins has been considered as a therapeutic strategy to ameliorate pathology in cell and animal models of neurodegenerative disorders. However, autophagy has also been found to be a factor in the onset of these diseases, which raises the question of whether autophagy induction is an effective therapeutic strategy, or, on the contrary, can result in cell death. In this paper, we will first describe the autophagic machinery, and we will consider the literature to discuss the neuroprotective effects of autophagy.

Defective autophagy in Parkinson's disease: role of oxidative stress

Parkinson's disease (PD) is a paradigmatic example of neurodegenerative disorder with a critical role of oxidative stress in its etiopathogenesis. Genetic susceptibility factors of PD, such as mutations in Parkin, PTEN-induced kinase 1, and DJ-1 as well as the exposure to pesticides and heavy metals, both contribute to altered redox balance and degeneration of dopaminergic neurons in the substantia nigra. Dysregulation of autophagy, a lysosomal-driven process of self degradation of cellular organelles and protein aggregates, is also implicated in PD and PD-related mutations, and environmental toxins deregulate autophagy. However, experimental evidence suggests a complex and ambiguous role of autophagy in PD since either impaired or abnormally upregulated autophagic flux has been shown to cause neuronal loss. Finally, it is generally believed that oxidative stress is a strong proautophagic stimulus. However, some evidence coming from neurobiology as well as from other fields indicate an inhibitory role of reactive oxygen species and reactive nitrogen species on the autophagic machinery. This review examines the scientific evidence supporting different concepts on how autophagy is dysregulated in PD and attempts to reconcile apparently contradictory views on the role of oxidative stress in autophagy regulation. The complex relationship between autophagy and oxidative stress is also considered in the context of the ongoing search for a novel PD therapy.

Closing the gap between clinic and cage: sensori-motor and cognitive behavioural testing regimens in neurotoxin-induced animal models of Parkinson's disease

Animal models that make use of chemical toxins to adversely affect the nigrostriatal dopaminergic pathway of rodents and primates have contributed significantly towards the development of symptomatic therapies for Parkinson's disease (PD) patients. Although their use in developing neuro-therapeutic and -regenerative compounds remains to be ascertained, toxin-based mammalian and a range of non-mammalian models of PD are important tools in the identification and validation of candidate biomarkers for earlier diagnosis, as well as in the development of novel treatments that are currently working their way into the clinic. Toxin models of PD have and continue to be important models to use for understanding the consequences of nigrostriatal dopamine cell loss. Functional assessment of these models is also a critical component for eventual translational success. Sensitive behavioural testing regimens for assessing the extent of dysfunction exhibited in the toxin models, the degree of protection or improvement afforded by potential treatment modalities, and the correlation of these findings with what is observed clinically in PD patients, ultimately determines whether a potential treatment moves to clinical trials. Here, we review existing published work that describes the use of such behavioural outcome measures associated with toxin models of parkinsonism. In particular, we focus on tests assessing sensorimotor and cognitive function, both of which are significantly and progressively impaired in PD.

DJ-1 induces thioredoxin 1 expression through the Nrf2 pathway

DJ-1, which is linked to recessively inherited Parkinson's disease when mutated, is a multi-functional protein with anti-oxidant and transcription regulatory activities. However, the mechanism(s) through which DJ-1 and the genes it regulates provide neuroprotection is not fully understood. Here, we show that wild-type DJ-1 induces the expression of thioredoxin 1 (Trx1), a protein disulfide oxidoreductase, whereas pathogenic mutant isoforms L166P and M26I cannot. Conversely, DJ-1 knockdown in SH-SY5Y cells and DJ-1 knockout in mice result in significant decrease in Trx1 protein and mRNA expression levels. The importance of Trx1 in the cytoprotective function of DJ-1 is confirmed using a pharmacological inhibitor of Trx reductase, 1-chloro-2,4-dinitrobenzene, and Trx1 siRNA. Both approaches result in partial loss of DJ-1-mediated protection. Additionally, knockdown of Trx1 significantly abrogates DJ-1-dependent, hydrogen peroxide-induced activation of the pro-survival factor AKT. Promoter analysis of the human Trx1 gene identified an antioxidant response element (ARE) that is required for DJ-1-dependent induction of Trx1 expression. The transcription factor Nuclear factor erythroid-2 related factor 2 (Nrf2), which is a critical inducer of ARE-mediated expression, is regulated by DJ-1. Overexpression of DJ-1 results in increased Nrf2 protein levels, promotes its translocation into the nucleus and enhances its recruitment onto the ARE site in the Trx1 promoter. Further, Nrf2 knockdown abolishes DJ-1-mediated Trx1 induction and cytoprotection against hydrogen peroxide, indicating the critical role of Nrf2 in carrying out the protective functions of DJ-1 against oxidative stress. These findings provide a new mechanism to support the antioxidant function of DJ-1 by increasing Trx1 expression via Nrf2-mediated transcriptional induction.

Autophagy, mitochondria and oxidative stress: cross-talk and redox signalling

Reactive oxygen and nitrogen species change cellular responses through diverse mechanisms that are now being defined. At low levels, they are signalling molecules, and at high levels, they damage organelles, particularly the mitochondria. Oxidative damage and the associated mitochondrial dysfunction may result in energy depletion, accumulation of cytotoxic mediators and cell death. Understanding the interface between stress adaptation and cell death then is important for understanding redox biology and disease pathogenesis. Recent studies have found that one major sensor of redox signalling at this switch in cellular responses is autophagy. Autophagic activities are mediated by a complex molecular machinery including more than 30 Atg (AuTophaGy-related) proteins and 50 lysosomal hydrolases. Autophagosomes form membrane structures, sequester damaged, oxidized or dysfunctional intracellular components and organelles, and direct them to the lysosomes for degradation. This autophagic process is the sole known mechanism for mitochondrial turnover. It has been speculated that dysfunction of autophagy may result in abnormal mitochondrial function and oxidative or nitrative stress. Emerging investigations have provided new understanding of how autophagy of mitochondria (also known as mitophagy) is controlled, and the impact of autophagic dysfunction on cellular oxidative stress. The present review highlights recent studies on redox signalling in the regulation of autophagy, in the context of the basic mechanisms of mitophagy. Furthermore, we discuss the impact of autophagy on mitochondrial function and accumulation of reactive species. This is particularly relevant to degenerative diseases in which oxidative stress occurs over time, and dysfunction in both the mitochondrial and autophagic pathways play a role.

Metal ion physiopathology in neurodegenerative disorders

Metal dyshomeostasis in the brain (BMD) has often been proposed as a possible cause for several neurodegenerative disorders (NDs). Nevertheless, the precise nature of the biochemical mechanisms of metal involvement in NDs is still largely unknown. Mounting evidence suggests that normal aging itself is characterized by, among other features, a significant degree of metal ion dysmetabolism in the brain. This is probably the result of a progressive deterioration of the metal regulatory systems and, at least in some cases, of life-long metal exposure and brain accumulation. Although alterations of metal metabolism do occur to some extent in normal aging, they appear to be highly enhanced under various neuropathological conditions, causing increased oxidative stress and favoring abnormal metal-protein interactions. Intriguingly, despite the fact that most common NDs have a distinct etiological basis, they share striking similarities as they are all characterized by a documented brain metal impairment. This review will primarily focus on the alterations of metal homeostasis that are observed in normal aging and in Alzheimer's disease. We also present a brief survey on BMD in other NDs (Amyotrophic Lateral Sclerosis, Parkinson's, and Prion Protein disease) in order to highlight what represents the most reliable evidence supporting a crucial involvement of metals in neurodegeneration. The opportunities for metal-targeted pharmacological strategies in the major NDs are briefly outlined as well.

Antioxidants in central nervous system diseases: preclinical promise and translational challenges

Oxidative damage is strongly implicated in the pathogenesis of neurodegenerative diseases including Alzheimer's disease, amyotrophic lateral sclerosis, Huntington's disease, Parkinson's disease and stroke (brain ischemia/reperfusion injury). The availability of transgenic and toxin-inducible models of these conditions has facilitated the preclinical evaluation of putative antioxidant agents ranging from prototypic natural antioxidants such as vitamin E (alpha-tocopherol) to sophisticated synthetic free radical traps and catalytic oxidants. Literature review shows that antioxidant therapies have enjoyed general success in preclinical studies across disparate animal models, but little benefit in human intervention studies or clinical trials. Recent high-profile failures of vitamin E trials in Parkinson's disease, and nitrone therapies in stroke, have diminished enthusiasm to pursue antioxidant neuroprotectants in the clinic. The translational disappointment of antioxidants likely arises from a combination of factors including failure to understand the drug candidate's mechanism of action in relationship to human disease, and failure to conduct preclinical studies using concentration and time parameters relevant to the clinical setting. This review discusses the rationale for using antioxidants in the prophylaxis or mitigation of human neurodiseases, with a critical discussion regarding ways in which future preclinical studies may be adjusted to offer more predictive value in selecting agents for translation into human trials.

Nrf2-induced antioxidant protection: a promising target to counteract ROS-mediated damage in neurodegenerative disease?

Neurodegenerative diseases share various pathological features, such as accumulation of aberrant protein aggregates, microglial activation, and mitochondrial dysfunction. These pathological processes are associated with generation of reactive oxygen species (ROS), which cause oxidative stress and subsequent damage to essential molecules, such as lipids, proteins, and DNA. Hence, enhanced ROS production and oxidative injury play a cardinal role in the onset and progression of neurodegenerative disorders. To maintain a proper redox balance, the central nervous system is endowed with an antioxidant defense mechanism consisting of endogenous antioxidant enzymes. Expression of most antioxidant enzymes is tightly controlled by the antioxidant response element (ARE) and is activated by nuclear factor E2-related factor 2 (Nrf2). In past years reports have highlighted the protective effects of Nrf2 activation in reducing oxidative stress in both in vitro and in vivo models of neurodegenerative disorders. Here we provide an overview of the involvement of ROS-induced oxidative damage in Alzheimer's disease, Parkinson's disease, and Huntington's disease and we discuss the potential therapeutic effects of antioxidant enzymes and compounds that activate the Nrf2-ARE pathway.

Antioxidant capacity in rat brain after intracerebroventricular treatment with streptozotocin and alloxan--a preliminary study

Intracerebroventricular (icv) administration of betacytotoxic drug streptozotocin (STZ) produces long-term and progressive cognitive deficits in rats, as well as deficits in cerebral glucose and energy metabolism. These changes resemble those found in the brain of patients with sporadic Alzheimer's disease (sAD), and therefore, STZ-icv treated rats have been proposed as an experimental model of sAD. In this study the antioxidant capacity (AC), using manual oxygen radical absorbance capacity (ORAC) assay, was measured in the rat brain frontoparietal cortex (FC) and brainstem-cerebellum region (BS-CB) after administration of STZ and another betacytotoxic drug alloxan (AL). Region-specific differences of AC were found, which were more expressed when hydroxyl radical (ORAC(-OHo)) generator was used in the assay. AC against ORAC(-OHo) was significantly lower in BS-CB than in FC of the control rats. Furthermore, ORAC(-OHo) significantly decreased in BS-CB 3-months following the icv administration of AL, but significantly increased following the TG+AL combined treatment in comparison with the controls. However, 3-months following the icv treatment of AL combination with a different glucose transport inhbitor, 3-O-methyl-D-glucose, ORAC(-OHo) values in BS-CB and ORAC(-ROOo) values in FC were significantly decreased in comparison to the controls. Our results suggest that betacytotoxic-icv treatment alters antioxidant defense systems in the brain, which particularly regarding the STZ-icv treatment, could be a useful tool in search for possible new antioxidant treatments of the neurodegenerative disorders such as sAD.

Antioxidant capacity in the lipophilic fraction of Alzheimer's brain tissues

The aim of this study was to investigate the antioxidant capacity (AC) in the lipophilic fraction of postmortem motorcortex (MC), nucleus caudatus (NC) and gyrus temporalis (GT) from controls (C) and Alzheimer's disease (AD) patients. The initial samples consisted of 50 human brain tissues of AD and C. AC of the different region of human brain were measured by using the fluorescent method of the oxygen radical absorbance capacity (ORAC). Peroxyl and hydroxyl radical generators were used in the analysis. All ORAC analysis were carried out on the Perkin-Elmer spectrofluorometer LS 55 with fluorescent filters, Ex: 485 nm; Em: 520 nm. Final results were calculated using the differences between area under the quenching curve of fluorescein (FL), blank and analyzed biological samples. AC against peroxyl radicals (ORAC-ROO degrees ) of lipophilic fraction in MC of AD was statistically significantly lower in comparison with MC of C (p < 0.008). No changes in the AC against hydroxyl radicals (ORAC- degrees OH) of lipophilic fraction of AD were found in comparison with C. Reduction of total protein in GT of AD (p < 0.03) was found. The results showed that in the MC of AD brain the balance between production of free radicals and the neutralization by a complex antioxidant system is disturbed. The manual fluorescent method for AC measurements proved to be sufficiently appropriate and sensitive for the AC measurements of lipophilic fraction of postmortem brain tissues from different patologic conditions.

Reduced brain antioxidant capacity in rat models of betacytotoxic-induced experimental sporadic Alzheimer's disease and diabetes mellitus

It is believed that oxidative stress (OS) plays a central role in the pathogenesis of metabolic diseases like diabetes mellitus (DM) and its complications (like peripheral neuropathy) as well as in neurodegenerative disorders like sporadic Alzheimer's disease (sAD). Representative experimental models of these diseases are streptozotocin (STZ)-induced diabetic rats and STZ-intracerebroventricularly (STZ-icv) treated rats, in which antioxidant capacity (AC) against peroxyl (ORAC(-ROO) (*)) and hydroxyl (ORAC(-OH) (*)) free radicals (FR) was measured in three different brain regions: the hippocampus (HPC), the cerebellum (CB), and the brain stem (BS) by means of oxygen radical absorbance capacity (ORAC) assay. In the brain of both STZ-induced diabetic and STZ-icv treated rats decreased AC has been found demonstrating regionally specific distribution. In the diabetic rats these abnormalities were not associated with the development of peripheral diabetic neuropathy (PDN). Also, these abnormalities were not prevented by the intracerebroventricularly (icv) pretreatment of glucose transport inhibitor 5-thio-D: -glucose (TG) in the STZ-icv treated rats, suggesting different mechanism of STZ-induced central effects from those at the periphery. Similarities of the OS alterations in the brain of STZ-icv rats and humans with sAD could be useful in the search for the new drugs in the treatment of sAD that have antioxidant activity. In the STZ-induced diabetic animals the existence of PDN was tested by the paw pressure test, 3 weeks following the diabetes induction. Mechanical nociceptive thresholds were measured three times at 10-min intervals by applying increased pressure to the hind paw until the paw-withdrawal or overt struggling was elicited. Only those diabetic animals which demonstrated decreased withdrawal threshold values in comparison with the control non-diabetic animals (C) were considered to have developed the PDN.

Brain antioxidant capacity in rat models of betacytotoxic-induced experimental sporadic Alzheimer's disease and diabetes mellitus

It is believed that oxidative stress plays a central role in the pathogenesis of metabolic diseases like diabetes mellitus (DM) and its complications (like peripheral neuropathy) as well as in neurodegenerative disorders like sporadic Alzheimer's disease (sAD). Representative experimental models of these diseases are streptozotocin (STZ)-induced diabetic rats and STZ-intracerebroventricularly (STZ-icv) treated rats, in which antioxidant capacity against peroxyl (ORAC(-ROO)*) and hydroxyl (ORAC(-OH)*) free radical was measured in three different brain regions (hippocampus, cerebellum, and brain stem) by means of oxygen radical absorbance capacity (ORAC) assay. In the brain of both STZ-induced diabetic and STZ-icv treated rats decreased antioxidant capacity has been found demonstrating regionally specific distribution. In the diabetic rats these abnormalities were not associated with the development of peripheral diabetic neuropathy. Also, these abnormalities were not prevented by the icv pretreatment of glucose transport inhibitor 5-thio-D-glucose in the STZ-icv treated rats, suggesting different mechanism for STZ-induced central effects from those at the periphery. Similarities in the oxidative stress alterations in the brain of STZ-icv rats and humans with sAD could be useful in the search for new drugs in the treatment of sAD that have antioxidant activity.