Search

The release of glutathione disulfide has been considered an important process for the maintenance of a reduced thiol redox potential in cells during oxidative stress. In cultured rat astrocytes, permanent hydrogen peroxide-induced oxidative stress caused a rapid increase in intracellular glutathione disulfide, which was followed by the appearance of glutathione disulfide in the medium. Under these conditions, the viability of the cells was not compromised. In the presence of cyclosporin A and the quinoline-derivative MK571, inhibitors of multidrug resistance proteins (MRP1 and MRP2), glutathione disulfide accumulated in cells and the release of glutathione disulfide from astrocytes during H2O2 stress was potently inhibited, suggesting a contribution of MRP1 or MRP2 in the release of glutathione disulfide from astrocytes. Using RT-PCR we amplified a cDNA from astroglial RNA with a high degree of homology to MRP1 from humans and mouse. In contrast, no fragment was amplified by using primers specific for rat MRP2. In addition, the presence of MRP1 protein in astrocytes was demonstrated by its immunolocalization in cells expressing the astroglial marker protein glial fibrillary acidic protein. Our data identify rat astrocytes as a MRP1-expressin, brain cell type and demonstrate that this transporter participates in the release of glutathione disulfide from astrocytes during oxidative stress.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) produces clinical, biochemical, and neuropathological changes reminiscent of those occurring in idiopathic Parkinson's disease (PD). Here we show that a peptide caspase inhibitor,N-benzyloxy-carbonyl-val-ala-asp-fluoromethyl ketone, or adenoviral gene transfer (AdV) of a protein caspase inhibitor, X-chromosome-linked inhibitor of apoptosis (XIAP), prevent cell death of dopaminergic substantia nigra pars compacta (SNpc) neurons induced by MPTP or its active metabolite 1-methyl-4-phenylpyridiniumin vitroandin vivo. Because the MPTP-induced decrease in striatal concentrations of dopamine and its metabolites does not differ between AdV-XIAP- and control vector-treated mice, this protection is not associated with a preservation of nigrostriatal terminals. In contrast, the combination of adenoviral gene transfer of XIAP and of the glial cell line-derived neurotrophic factor to the striatum provides synergistic effects, rescuing dopaminergic SNpc neurons from cell death and maintaining their nigrostriatal terminals. These data suggest that a combination of a caspase inhibitor, which blocks death, and a neurotrophic factor, which promotes the specific function of the rescued neurons, may be a promising strategy for the treatment of PD.

To examine the cellular distribution of radical scavenging enzymes in glia, in comparison to that in neurons and their behaviour during excitotoxically induced neurodegenerative processes, protein levels and the cellular localization of cytosolic and mitochondrial superoxide dismutase (Cu/Zn- and Mn-SOD) were investigated in the rat brain undergoing quinolinic acid (Quin)-induced neurodegeneration. Evidence for the specificity of the applied antibodies to detect immunocytochemically these SOD isoforms was obtained from electron microscopy and Western blotting. In control striatum Mn-SOD was clearly confined to neurons, whereas Cu/Zn-SOD was found, rather delicately, only in astrocytes. Microglia failed to stain with antibodies to both SOD isoforms. Quin application resulted in an initial formation of oxygen and nitrogen radicals as determined by the decline in the ratio of ascorbic to dehydroascorbic acid and by increased levels of nitrated proteins, an indicator for elevated peroxynitrite formation. Morphologically, massive neuronal damage was seen in parallel. Astroglia remained intact but showed initially decreased glutamine synthetase activities. The levels of Mn-SOD protein increased 2-fold 24 h after Quin injection (Western blotting) and declined only slowly over the time period considered (10 days). Cu/Zn-SOD levels increased only 1.3-fold. Immunocytochemical studies revealed that the increase in Mn-SOD is confined to neurons, whereas that of Cu/Zn-SOD was observed only in astroglial cells. Quiescent microglial cells were, as a rule, free of immunocytochemically detectable SOD, whereas in activated microglia a few Mn-SOD immunolabeled mitochondria occurred. Our results suggest a differential protective response in the Quin lesioned striatum in that Mn-SOD is upregulated in neurons and Cu/Zn-SOD in astroglia. Both SOD-isoforms are assumed to be induced to prevent oxidative and nitric oxide/peroxynitrite-mediated damage. In the border zone of the lesion core this strategy may contribute to resist the noxious stimulus.

Astrocytes induce blood-brain barrier (BBB) properties in brain endothelial cells (EC)*O(2)*, generated in blood and EC, opens the BBB. Hence, high activity of superoxide dismutase (SOD) is a prerequisite for normal BBB function. Therefore, the influence of rat astrocytes on the expression of manganese (Mn)SOD in rat EC was investigated in two coculture models of the BBB, allowing either exchange of soluble factors or additionally cellular contacts. Activity, protein content and mRNA expression of endothelial MnSOD were significantly increased in both coculture models in comparison to monoculture by soluble astrocytic factors, such as cytokines. High activity of endothelial MnSOD may be considered as a further essential property of the BBB, which is induced and maintained by astrocytes.

Superoxide dismutase (SOD) is considered to be a major factor in protection of nervous tissue against excitotoxic and ischemic/hypoxic lesion. Controversial reports about the localization of SOD after such an insult prompted us to re-investigate immunocytochemically the localization of the enzyme in the brain and spinal cord using specific antibodies against the manganese (Mn-SOD) and copper/zinc (Cu/Zn-SOD) containing isoenzyme in combination with cell type specific markers. CNS tissue sections were analyzed by confocal laser scanning microscopy and digital photo imaging. Cu/Zn-SOD immunoreactivity was found to be located predominantly in astrocytes throughout the CNS. The staining was found in the cytoplasm, in cellular processes and, less intensive, in the nucleus sparing the nucleolus. At a lower level the enzyme was also detectable in neuronal perikarya and in structures of the neuropil. Motoneurons of the spinal cord displayed an enhanced Cu/Zn-SOD staining intensity, when compared to brain neurons. In contrast the Mn-containing isoenzyme was predominantly localized to neurons and their processes throughout the brain and the spinal cord. Confirming the mitochondrial localization of the enzyme, a granular staining pattern sparing the nucleus was observed. Mn-SOD stained mitochondria were also seen in astroglial cells but the staining intensity was, on the whole, much lower compared to neurons, and often hardly detectable. It seems reasonable to conclude that differences in the basal content of SOD-isoenzymes may contribute to different cellular susceptibilities in neurodegenerative processes that are accompanied by oxidative stress.

The cellular distribution pattern of cellular glutathione peroxidase (GPx) was analyzed immunocytochemically in the normal rat central nervous system (CNS) and following exposure to the excitotoxin quinolinic acid (Quin). In the normal CNS, GPx was localized predominantly to microglia, identified by staining with isolectin B4 or the monoclonal antibody OX-42. Three days after intrastriatal administration of 90 pmoles Quin, GPx immunoreactivity was increased in activated microglia and also in astrocytes costained for glial fibrillary acidic protein (GFAP). Whereas GPx-positive astrocytes were seen predominantly in the environment of the lesion, most intensive immunoreactivity was located in globular-shaped microglia in the lesion core. GPx staining was generally low in neurons and failed to increase its intensity after lesion. In the case of excitotoxin-induced generation of oxygen-derived free radicals, the elevation of GPx levels in microglia, and likewise in activated astroglia, may provide an important mechanism to withstand oxidative stress.