Immunohistochemical evidence and ultrastructural compartmentalization of a new antioxidant enzyme in the rat substantia nigra

Ascorbate and its transporter SVCT2: The dynamic duo's integrated roles in CNS neurobiology and pathophysiology

Ascorbate is a small antioxidant molecule essential for the proper development and function of the brain. Ascorbate is transported into the brain and between brain cells via the Sodium vitamin C co-transporter 2 (SVCT2). This review provides an in-depth analysis of ascorbate's physiology, including how ascorbate is absorbed from food into the CNS, emphasizing cellular mechanisms of ascorbate recycling and release in different CNS compartments. Additionally, the review delves into the various functions of ascorbate in the CNS, including its impact on epigenetic modulation, synaptic plasticity, and neurotransmission. It also emphasizes ascorbate's role on neuromodulation and its involvement in neurodevelopmental processes and disorders. Furthermore, it analyzes the relationship between the duo ascorbate/SVCT2 in neuroinflammation, particularly its effects on microglial activation, cytokine release, and oxidative stress responses, highlighting its association with neurodegenerative diseases, such as Alzheimer's disease (AD). Overall, this review emphasizes the crucial role of the dynamic duo ascorbate/SVCT2 in CNS physiology and pathology and the need for further research to fully comprehend its significance in a neurobiological context and its potential therapeutic applications.

Neuroprotective effects of Withania somnifera in the SH-SY5Y Parkinson cell model

Parkinson's disease is the most frequent neurodegenerative motor disorder. The clinical syndrome and pathology involve motor disturbance and the degeneration of dopaminergic neurons in the substantia nigra. Root extracts of Withania. somnifera, commonly called Ashwagandha, contain several major chemical constituents known as withanolides. Studies have shown that W. somnifera extracts exhibit numerous therapeutic effects including inflammation and oxidative stress reduction, memory and cognitive function improvement. This study aimed to evaluate the protective effects of KSM-66, W. somnifera root extract, on 6-hydroxydopamine (6-OHDA)-induced toxicity in the human neuroblastoma SH-SY5Y cell line, as well as the associated oxidative response protein expression and redox regulation activity focused on S-glutathionylation. SH-SY5Y cells were treated with 6-OHDA preceded or followed by treatment with the KSM-66 extract. Using KSM-66 concentrations ranging from 0.25 to 1 mg/ml before and after treatment of the cells with 6-OHDA has resulted in an increased viability of SH-SY5Y cells. Interestingly, the extract significantly increased glutathione peroxidase activity and thioltransferase activity upon pre- or post- 6-OHDA treatment. KSM-66 also modulated oxidative response proteins: peroxiredoxin-I, VGF and vimentin proteins upon 6-OHDA pre/post treatments. In addition, the extract controlled redox regulation via S-glutathionylation. Pre-treatment of SH-SY5Y cells with KSM-66 decreased protein-glutathionylation levels in the cells treated with 6-OHDA. The rescue of mitochondria with 0.5 mg/ml KSM-66 extract showed an increase in ATP levels. These findings suggest that W. somnifera root extract acts as a neuroprotectant, thereby introducing a potential agent for the treatment or prevention of neurodegenerative diseases.

Morphology, clearing efficacy, and mTOR dependency of the organelle autophagoproteasome

The interplay between autophagy (ATG) and ubiquitin proteasome (UP) cell-clearing systems was recently evidenced at biochemical and morphological levels, where subunits belonging to both pathways co-localize within a novel organelle named autophagoproteasome (APP). We previously documented that APP occurs at baseline conditions, while it is hindered by neurotoxicant administration. This is bound to the activity of the mechanistic target of rapamycin (mTOR), since APP is stimulated by mTOR inhibition, which in turn, is correlated with cell protection. In this brief report, we provide novel morphological and biochemical evidence on APP, suggesting the presence of active UP subunits within ATG vacuoles. Although a stream of interpretation considers such a merging as a catabolic pathway to clear inactive UP subunits, our data further indicate that UP-ATG merging may rather provide an empowered catalytic organelle.

Methamphetamine induces ectopic expression of tyrosine hydroxylase and increases noradrenaline levels within the cerebellar cortex

Methamphetamine produces locomotor activation and typical stereotyped motor patterns, which are commonly related with increased catecholamine activity within the basal ganglia, including the dorsal and ventral striatum. Since the cerebellum is critical for movement control, and for learning of motor patterns, we hypothesized that cerebellar catecholamines might be a target of methamphetamine. To test this experimental hypothesis we injected methamphetamine into C57 Black mice at the doses of 5 mg/kg two or three times, 2 h apart. This dosing regimen is known to be toxic for striatal dopamine terminals. However, we found that in the cerebellum, methamphetamine increased the expression of the primary transcript of the tyrosine hydroxylase (TH) gene, followed by an increased expression of the TH protein. Increased TH was localized within Purkinje cells, where methamphetamine increased the number of TH-immunogold particles, and produced a change in the distribution of the enzyme by increasing the cytoplasmic percentage. Increased TH expression was accompanied by a slight increase in noradrenaline content. This effect was highly site-specific for the cortex of posterior vermal lobules, while only slight effects were detectable in the hemispheres. The present data indicate that the cerebellum does represent a target of methamphetamine, which produces specific and fine alterations of the catecholamine system involving synthesis, amount, and compartmentalization of TH as well as increased noradrenaline levels. This may be relevant for motor alterations induced by methamphetamine. In line with this, inherited cerebellar movement disorders in various animal species including humans are associated with increased TH immunoreactivity within intrinsic neurons of the same lobules of the cerebellar cortex.

Characterization of the omega class of glutathione transferases

The Omega class of cytosolic glutathione transferases was initially recognized by bioinformatic analysis of human sequence databases, and orthologous sequences were subsequently discovered in mouse, rat, pig, Caenorhabditis elegans, Schistosoma mansoni, and Drosophila melanogaster. In humans and mice, two GSTO genes have been recognized and their genetic structures and expression patterns identified. In both species, GSTO1 mRNA is expressed in liver and heart as well as a range of other tissues. GSTO2 is expressed predominantly in the testis, although moderate levels of expression are seen in other tissues. Extensive immunohistochemistry of rat and human tissue sections has demonstrated cellular and subcellular specificity in the expression of GSTO1-1. The crystal structure of recombinant human GSTO1-1 has been determined, and it adopts the canonical GST fold. A cysteine residue in place of the catalytic tyrosine or serine residues found in other GSTs was shown to form a mixed disulfide with glutathione. Omega class GSTs have dehydroascorbate reductase and thioltransferase activities and also catalyze the reduction of monomethylarsonate, an intermediate in the pathway of arsenic biotransformation. Other diverse actions of human GSTO1-1 include modulation of ryanodine receptors and interaction with cytokine release inhibitory drugs. In addition, GSTO1 has been linked to the age at onset of both Alzheimer's and Parkinson's diseases. Several polymorphisms have been identified in the coding regions of the human GSTO1 and GSTO2 genes. Our laboratory has expressed recombinant human GSTO1-1 and GSTO2-2 proteins, as well as a number of polymorphic variants. The expression and purification of these proteins and determination of their enzymatic activity is described.

Characterization of the monomethylarsonate reductase and dehydroascorbate reductase activities of Omega class glutathione transferase variants: implications for arsenic metabolism and the age-at-onset of Alzheimer's and Parkinson's diseases

There are two functional Omega class glutathione transferase (GST) genes in humans. GSTO1 is polymorphic with several coding region alleles, including an A140D substitution, a potential deletion of E155 and an E208K substitution. GSTO2 is also polymorphic with an N142D substitution in the coding region. We investigated the effect of these variations on the enzyme's thioltransferase, dehydroascorbate reductase, monomethylarsonate reductase and dimethylarsonate reductase activities. Variant proteins were expressed in Escherichia coli and purified by Ni-agarose affinity chromatography. GSTO2-2 was insoluble and had to be dissolved and refolded from 8 M urea. The A140D and E208K substitutions in GSTO1-1 did not alter specific activity. The deletion of E155 caused a two- to three-fold increase in the specific activity with each substrate. This deletion also caused a significant decrease in the enzyme's heat stability. The E155 deletion has been linked to abnormal arsenic excretion patterns; however, the available data do not clearly identify the cause of this abnormality. We found that GSTO2-2 has activity with the same substrates as GSTO1-1, and the dehydroascorbate reductase activity of GSTO2-2 is approximately 70-100-fold higher than that of GSTO1-1. The polymorphic N142D substitution had no effect on the specific activity of the enzyme with any substrate. The most notable feature of GSTO2-2 was its very high dehydroascorbate reductase activity, which suggests that GSTO2-2 may significantly protect against oxidative stress by recycling ascorbate. A defect in ascorbate metabolism may provide a common mechanism by which the Omega class GSTs influence the age-at-onset of Alzheimer's and Parkinson's diseases.

Occurrence of neuronal inclusions combined with increased nigral expression of α-synuclein within dopaminergic neurons following treatment with amphetamine derivatives in mice

In recent years several clinical and research findings have demonstrated the involvement of the presynaptic protein alpha-synuclein in a variety of neurodegenerative disorders which are known as synucleinopathies. Although the function of this protein in the physiology of the cell remains unknown, it is evident that both genetic alterations or a mere overexpression of the native molecule produces a degeneration of nigral dopamine-containing neurons leading to movement disorders, as demonstrated in inherited Parkinson's disease. In the present study, we investigated whether widely abused drugs such as methamphetamine and methylenedioxymethamphetamine (ecstasy), which are known to damage the nigrostriatal dopamine pathway of mice, increase the expression of alpha-synuclein within dopamine neurons of the substantia nigra pars compacta. The results of this study demonstrate that nigrostriatal dopamine denervation and occurrence of intracellular inclusions in nigral neurons produced by amphetamine derivatives are related to increased expression of alpha-synuclein within dopamine neurons of the substantia nigra. This lends substance to the hypothesis that increased amounts of native alpha-synuclein may be per se a detrimental factor for the dopamine neurons.

Fine structure and biochemical mechanisms underlying nigrostriatal inclusions and cell death after proteasome inhibition

Mutation of genes encoding for various components of a metabolic pathway named the ubiquitin-proteasome system (UP) leads to inherited forms of Parkinson's disease (PD), whereas various components of the UP are constantly present within neuronal inclusions, Lewy bodies, that characterize most genetic and sporadic forms of PD. It has been hypothesized that impairment of this metabolic pathway might be a common mechanism for the onset of PD, and a recent study demonstrated a dysfunction of the UP system within the substantia nigra of patients affected by sporadic PD. In search for the mechanisms underlying the selective toxicity for nigral neurons after inhibition of the UP system, we explored the selective effects after striatal microinfusions of lactacystin or epoxomycin and potential retrograde changes within the ipsilateral substantia nigra. We found that neurotoxicity was selective for striatal dopamine (DA) components and led to retrograde apoptosis within nigral DA cells, which developed neuronal inclusions staining for antigens of the UP system. We found the same ultrastructural features characterizing inclusions obtained in vivo and in vitro after UP inhibition. In vivo, lactacystin-epoxomycin-induced toxicity was suppressed by inhibiting DA synthesis. Similarly, in vitro inclusions and apoptosis were prevented by reducing endogenous DA. On the other hand, toxicity of proteasome inhibition was enhanced by drugs augmenting DA availability: l-3,4-dihydroxyphenylalanine, monoamine oxidase blockers, and DA beta-hydroxylase blockers. These findings demonstrate that impairment of the UP system produces cell death and neuronal inclusions selectively for DA-containing neurons that depend on the occurrence of endogenous DA.

Vulnerability to DNA damage in the aging rat substantia nigra: a study with the comet assay

Oxidative DNA damage was measured in the substantia nigra (SN), cortex, hippocampus, striatum and hypothalamus of 3- and 24-month-old rats, using single-cell gel electrophoresis (SCGE, 'comet' assay) which allows the detection of DNA breaks and oxidized bases. A significant increase in basal DNA damage was selectively found in the SN of aged rats. FPG-sensitive oxidative DNA damage was also significantly increased in the SN of aged rats and, to a lesser extent, in the cortex and hypothalamus. These data show a higher vulnerability of SN to oxidative damage with aging and indicate that the detection of DNA damage within discrete brain nuclei can provide a reliable tool for investigating oxidative damage in neurodegenerative processes.