Evidence of extensive RNA oxidation in normal appearing cortex of multiple sclerosis brain

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.