Analysis of Neuroketal Protein Adducts by Liquid Chromatography-Electrospray Ionization/Tandem Mass Spectrometry

A role of free radicals has been implicated in the pathogenesis of a number of neurological disorders, including amyotrophic lateral sclerosis, Huntington’s disease (HD), Parkinson’s disease (PD), and Alzheimer’s disease (AD) (
1
–
9
). Furthermore, reactive aldehydes produced as products of lipid peroxidation are thought to be key mediators of oxidant injury because of their capacity to covalently modify proteins and
DNA
(
10
), and evidence suggests they may be involved in the pathogenesis of neurodegenerative diseases (
11
–
13
). Aggregated cross-linked proteins are characteristic features of neurodegenerative diseases (
14
). Isoprostanes (IsoPs) are prostaglandin-like compounds formed by free radical-induced peroxidation of arachidonic acid (
15
). We recently identified the formation of highly reactive γ-ketoaldehydes, now termed isoketals (IsoKs), as products of the IsoP pathway (
16
). IsoKs are orders of magnitude more reactive than other known reactive products of lipid peroxidation and exhibit a unique proclivity to cross-link proteins (
17
). Neuroprostanes (NPs) are IsoP-like compounds formed from oxidation of docosahexaenoic acid (DHA) (
5
), which is highly enriched in the brain (
18
,
19
), and levels of neuroprostanes in cerebrospinal fluid (CFS) have been found to be increased in patients with AD (
5
). Analogous to the formation of IsoKs via the isoprostane pathway, we recently identified the formation of another class of highly reactive γ-ketoaldehydes as products of the neuroprostane pathway, termed neuroketals (NKs) (
20
).