8-hydroxyguanosine and Multiple-Sclerosis

The role of reactive oxygen species (ROS) in the progression of neurodegenerative and neuroinflammatory disorders such as multiple sclerosis (MS) has been highlighted in recent years. Due to the debilitated cellular antioxidant defense mechanism in the neurons in MS, and their vulnerability to ROS effects, the cellular components in neuronal cells are susceptible to oxidative damage. The damage due to ROS in various biomolecules including proteins and DNA has already been shown in MS lesions. Using an in situ approach we have detected hitherto unidentified RNA oxidative damage in the neuronal cells of normal appearing cortex of postmortem MS brains. We analyzed the presence of oxidative damage marker nucleoside 8-hydroxyguanosine (8-OHG) to determine the presence of oxidized RNA in MS brain. Immunohistochemical analyses with anti 8-OHG antibody showed significant oxidation in the cytoplasm and to a conspicuously lesser extent in the nucleus of neuronal cells within the normal appearing cortex of MS brain, whereas similar areas were weakly immunopositive in control brain tissues. Pretreatment with RNase 1 greatly reduced the immune reaction with anti 8-OHG antibody while it was only slightly diminished by DNase I pre-treatment, indicating extensive oxidative damage in the RNA pool of MS brain. The abundance of 8-OHG, hence the high extent of RNA oxidative damage was further confirmed by immunoprecipitation and HPLC analyses of total RNA isolated from MS brain. To our knowledge, this is the first evidence of increased RNA oxidation in normal appearing cortex of MS brain. The current study begins to define the link of RNA oxidation to MS pathophysiology.

Topics: Brain; Cell Nucleus; Cerebral Cortex; Cytoplasm; Deoxyribonuclease I; Female; Guanosine; Humans; Male; Middle Aged; Multiple Sclerosis; Neurons; Oxidation-Reduction; Oxidative Stress; Ribonucleases; RNA

Multiple sclerosis is a chronic inflammatory disease of the central nervous system, associated with demyelination and neurodegeneration. The mechanisms of tissue injury are currently poorly understood, but recent data suggest that mitochondrial injury may play an important role in this process. Since mitochondrial injury can be triggered by reactive oxygen and nitric oxide species, we analysed by immunocytochemistry the presence and cellular location of oxidized lipids and oxidized DNA in lesions and in normal-appearing white matter of 30 patients with multiple sclerosis and 24 control patients without neurological disease or brain lesions. As reported before in biochemical studies, oxidized lipids and DNA were highly enriched in active multiple sclerosis plaques, predominantly in areas that are defined as initial or 'prephagocytic' lesions. Oxidized DNA was mainly seen in oligodendrocyte nuclei, which in part showed signs of apoptosis. In addition, a small number of reactive astrocytes revealed nuclear expression of 8-hydroxy-d-guanosine. Similarly, lipid peroxidation-derived structures (malondialdehyde and oxidized phospholipid epitopes) were seen in the cytoplasm of oligodendrocytes and some astrocytes. In addition, oxidized phospholipids were massively accumulated in a fraction of axonal spheroids with disturbed fast axonal transport as well as in neurons within grey matter lesions. Neurons stained for oxidized phospholipids frequently revealed signs of degeneration with fragmentation of their dendritic processes. The extent of lipid and DNA oxidation correlated significantly with inflammation, determined by the number of CD3 positive T cells and human leucocyte antigen-D expressing macrophages and microglia in the lesions. Our data suggest profound oxidative injury of oligodendrocytes and neurons to be associated with active demyelination and axonal or neuronal injury in multiple sclerosis.

Topics: Adult; Aged; Aged, 80 and over; Antigens, CD; Axons; Brain; DNA Damage; Female; Guanosine; Humans; Inflammation; Lipids; Male; Malondialdehyde; Middle Aged; Multiple Sclerosis; Myelin Proteins; Nerve Tissue Proteins; Oligodendroglia; Oxidative Stress