Redox Proteomics Identification of Oxidatively Modified Proteins in Alzheimer’s Disease Brain and in Brain from a Rodent Model of Familial Parkinson’s Disease: Insights into Potential Mechanisms of Neurodegeneration

Oxidative stress, an imbalance between the oxidant and antioxidant systems, has been implicated in the pathogenesis of numerous neurodegenerative diseases [1]. Among all the body organs, the brain is particularly vulnerable to oxidative damage because of its high utilization of oxygen, increased levels of polyunsaturated fatty acids, and relatively high levels of redox transition metal ions in certain brain regions; in addition, the brain has relatively low levels of antioxidants [2–6]. The presence of iron ion in an oxygen-rich environment can further lead to enhanced production of superoxide radicals and ultimately to a cascade of oxidative events. Either the oxidant directly or the products of oxidative stress could trigger the oxidative modification of a number of cellular macromolecular targets, including proteins, lipids, DNA, RNA, and carbohydrates, which may lead to impairment of cellular functions [2,3,5,7–9]. Among the earliest of these changes following an oxidative insult are increased levels of toxic carbonyls, 3-nitrotyrosine (3-NT), and 4-hydroxy-2trans-nonenal (HNE) [2,4,7,10–13]. HNE is derived from free radical attack on unsaturated acyl chains of phospholipids, particularly arachidonic acid. Oxidation leads to introduction of carbonyl groups to proteins [14]. Carbonyl groups are incorporated into proteins by direct oxidation of certain amino acid side chains, peptide backbone scission, or Michael addition reactions with products of lipid peroxidation or glycol oxidation [4,15,16]. Protein carbonyls can be detected by the derivatization of the carbonyl group with 2,4-dinitrophenylhydrazine (DNPH), followed by immunochemical detection of the hydrazone product [14]. Oxidative stress can stimulate additional damage via overexpression of inducible nitric oxide synthase (iNOS) and the action of constitutive