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Over the past three decades, two paradigms have been developing that largely describe the difference between normal and pathological brain aging: Namely, the twin paradigms of neural oxidative stress and neuroinflammation. These two concepts both emerged amidst an intellectual environment of either casual neglect or antipathy but have come to permeate much basic and applied neuroscience research. Current science has come to understand that these two phenomena are mutually but subtly linked to such an extent as to be practically inseparable. In Alzheimer’s disease (AD) both neural oxidative stress and neuroinflammatory events are crucial components of the neurodegenerative landscape. Both appear to arise, in part, as consequences of the classic features of AD pathology namely amyloid peptide (Aβ)-containing senile plaques and neurofibrillary tangles (NFTs). Viewed from a different perspective, however, oxidative stress and neuroinflammation also contribute fundamentally to cell biological changes that predispose the AD brain to these classic histopathologies. This review will attempt to summarize the current state of knowledge regarding neural oxidative stress in AD, with emphasis on mechanistic connections between the two phenomena, and their joint relationship to both plaques and tangles.

Oxidative posttranslational protein modifications occur as a normal process of cell biology and to a greater extent during pathogenic conditions. The detection and quantitation of protein oxidation has posed a continuing challenge to bioanalytical chemists because the products of oxidative protein damage are chemically diverse, protein oxidation generally occurs at low background levels, and the complexity of biological samples introduces high background noise when standard techniques such as immunolabeling are applied to "dirty" tissue extracts. A refinement of classic reductive amination methods has been developed, which circumvents these difficulties by incorporating a biotin label at sites of protein carbonylation. Biotin hydrazide-labeled proteins are detectable using standard streptavidin-coupled detection techniques such as peroxidase-catalyzed chemiluminescence of immunoblots. Advantages of the biotin hydrazide-labeling technique are its sensitivity and its lack of reliance upon antibodies that inevitably suffer from nonspecific background noise and contaminating endogenous immunoglobulins.

Part I. Lipids Measurement of Fat-Soluble Vitamins and Antioxidants by HPLC With Electrochemical Array Detection Paul H. Gamache, Paul A. Ullucci, Joe A. Archangelo, and Ian N. Acworth Analysis of Aldehydic Markers of Lipid Peroxidation in Biological Tissues by HPLC With Fluorescence Detection Mark A. Lovell and William R. Markesbery Measurement of Isofurans by Gas Chromatography-Mass Spectrometry/Negative Ion Chemical Ionization Joshua P. Fessel and L. Jackson Roberts, II Analysis of F2-Isoprostanes by Gas Chromatography-Mass Spectrometry/Negative Ion Chemical Ionization L. Jackson Roberts, II and Jason D. Morrow Measurement of F4-Neuroprostanes by Gas Chromatography-Mass Spectrometry/Negative Ion Chemical Ionization Nathalie Bernoud-Hubac and L. Jackson Roberts, II Immunoassays for Lipid Peroxidation End Products: One-Hour ELISA for Protein-Bound Acrolein and HNE Kimihiko Satoh and Koji Uchida Fluorometric and Colorimetric Assessment of Thiobarbituric Acid-Reactive Lipid Aldehydes in Biological Matrices Kelly S. Williamson, Kenneth Hensley, and Robert A. Floyd HPLC With Electrochemical and Photodiode Array Detection Analysis of Tocopherol Oxidation and Nitration Products in Human Plasma Kelly S. Williamson, Kenneth Hensley, and Robert A. Floyd Part II. DNA, Protein, and Amino Acids Electron Paramagnetic Resonance Spin-Labeling Analysis of Synaptosomal Membrane Protein Oxidation D. Allan Butterfield Gas Chromatography-Mass Spectrometric Analysis of Free 3-Chlorotyrosine, 3-Bromotyrosine, Ortho-Tyrosine, and 3-Nitrotyrosine in Biological Fluids Joseph P. Gaut, Jaeman Byun, and Jay W. Heinecke Isotope Dilution Gas Chromatography-Mass Spectrometric Analysis of Tyrosine Oxidation Products in Proteins and Tissues Jay W. Heinecke Single-Cell Gel Electrophoresis or Comet Assayof Intestinal Epithelial Cells Using Manual Scoring and Ridit Analysis Mark M. Huycke Detection of Aldehydic DNA Lesions Using Aldehyde Reactive Probe Jun Nakamura and James A. Swenberg Analysis of Neuroketal Protein Adducts by Liquid Chromatography-Electrospray Ionization/Tandem Mass Spectrometry Nathalie Bernoud-Hubac, Sean S. Davies, Olivier Boutaud, and L. Jackson Roberts, II Measurement of Isoketal Protein Adducts by Liquid Chromatography-Electrospray Ionization/Tandem Mass Spectrometry Sean S. Davies, Cynthia J. Brame, Olivier Boutaud, Nathalie Bernoud-Hubac, and L. Jackson Roberts, II Bioassay of 29-Deoxyguanosine/8-Hydroxy-29- Deoxyguanosine by HPLC With Electrochemical/Photodiode Array Detection Kelly S. Williamson, Kenneth Hensley, Quentin N. Pye, Scott Ferrell, and Robert A. Floyd HPLC With Electrochemical Detection Analysis of 3-Nitrotyrosine in Human Plasma Kelly S. Williamson, Kenneth Hensley, and Robert A. Floyd Part III. Reactive Oxygen Species and Reactive Nitrogen Species Protein Carbonyl Levels-An Assessment of Protein Oxidation Alessandra Castegna, Jennifer Drake, Chava Pocernich, and D. Allan Butterfield Fluorogenic Analysis of H2O2 in Biological Materials Kenneth Hensley, Kelly S. Williamson, and Robert A. Floyd Detection of Reactive Oxygen Species by Flow Cytometry Alexander Christov, Ladan Hamdheydari, and Paula Grammas Nitrite Determination by Colorimetric and Fluorometric Greiss Diazotization Assays: Simple, Reliable, High-Throughput Indices of Reactive Nitrogen Species in Cell Culture Systems Kenneth Hensley, Shenyun Mou, and Quentin N. Pye Protein Carbonyl Determination Using Biotin Hydrazide Kenneth Hensley and Kelly S. Williamson Real-Time, In Vivo Measurement of Nitric Oxide Using Electron Paramagnetic Resonance Spectroscopic Analysis of Biliary Flow

As organs age, the likelihood of severe dysfunction increases steadily. The brain is particularly sensitive to age-related, chronic and acute oxidative pathologies. An emerging paradigm holds that diverse neurodegenerative conditions share a common etiological factor, namely, enhanced brain tissue oxidation owing to exacerbated production of reactive oxygen species (ROS) or to compromise of antioxidant defense and repair mechanisms. Brain is particularly susceptible to oxidative stress owing to its high content of unsaturated lipids, high metabolic rate, relative dearth of antioxidant enzymes, and inability to regenerate lost neurons. Pathogenic ROS generation may result from metabolic enzyme dysregulation, impaired mitochondrial respiration, excitotoxic stimulation, and secondarily as a function of intracellular calcium stress (summarized in Fig. 1 and elaborated below). Natural variation in antioxidant systems may explain why humans differ so greatly with respect to pathways and rates of neurodegeneration. If this is the case, antioxidant supplementation of the aging brain may forestall certain aspects of age-related neurodegeneration. Accordingly, much research has focused on antioxidant management of aging brain and on antioxidant interdiction of postischemic brain damage. Recent findings indicate that specific antioxidants do more than scavenge ROS, but may indirectly affect cellular signal transduction, genetic response, and inflammatory events in such a way as to modulate beneficially brain response to oxidative challenge.

Alzheimer’s disease (AD) research has progressed greatly since the first description of AD by Alzheimer (1) very early in this century. Three pathological hallmarks of AD are: 1. The presence in certain brain regions of senile plaques (SP), entities composed of aggregated β-amyloid surrounded by dystrophic neurites and other moieties; 2. Neurofibrillary tangles (NFT), primarily composed of phosphorylated τ, a cytoskeletal protein, and other moieties; and 3. Loss of synapses (2–4).