A 4-oxo-2(E)-nonenal-derived glutathione adduct from 15-lipoxygenase-1-mediated oxidation of cytosolic and esterified arachidonic acid

Identification of Protein Targets of 12/15-Lipoxygenase-Derived Lipid Electrophiles in Mouse Peritoneal Macrophages Using Omega-Alkynyl Fatty Acid

The 12/15-lipoxygenase (12/15-LOX) enzyme introduces peroxyl groups, in a position-specific manner, into polyunsaturated fatty acids to form various kinds of bioactive lipid metabolites, including lipid-derived electrophiles (LDE). The resident peritoneal macrophage is the site of highest 12/15-LOX expression in the mouse. However, the role of the enzyme in the regulation of resident macrophages is not fully understood. Here, we describe a chemoproteomic method to identify the targets of enzymatically generated LDE. By treating mouse peritoneal macrophages with omega-alkynyl arachidonic acid (aAA), we identified a series of proteins adducted by LDE generated through a 12/15-LOX catalyzed reaction. Pathway analysis revealed a dramatic enrichment of proteins involved in energy metabolism and found that glycolytic flux and mitochondrial respiration were significantly affected by the expression of 12/15-LOX. Our findings thus highlight the utility of chemoproteomics using aAA for identifying intracellular targets of enzymatically generated LDE.

The chloroplast membrane associated ceQORH putative quinone oxidoreductase reduces long-chain, stress-related oxidized lipids

Under oxidative stress conditions the lipid constituents of cells can undergo oxidation whose frequent consequence is the production of highly reactive α,β-unsaturated carbonyls. These molecules are toxic because they can add to biomolecules (such as proteins and nucleic acids) and several enzyme activities cooperate to eliminate these reactive electrophile species. CeQORH (chloroplast envelope Quinone Oxidoreductase Homolog, At4g13010) is associated with the inner membrane of the chloroplast envelope and imported into the organelle by an alternative import pathway. In the present study, we show that the recombinant ceQORH exhibits the activity of a NADPH-dependent α,β-unsaturated oxoene reductase reducing the double bond of medium-chain (C⩾9) to long-chain (18 carbon atoms) reactive electrophile species deriving from poly-unsaturated fatty acid peroxides. The best substrates of ceQORH are 13-lipoxygenase-derived γ-ketols. γ-Ketols are spontaneously produced in the chloroplast from the unstable allene oxide formed in the biochemical pathway leading to 12-oxo-phytodienoic acid, a precursor of the defense hormone jasmonate. In chloroplasts, ceQORH could detoxify 13-lipoxygenase-derived γ-ketols at their production sites in the membranes. This finding opens new routes toward the understanding of γ-ketols role and detoxification.

Cyclooxygenase- and lipoxygenase-mediated DNA damage

Cancer is a disease of aging, and so with the increasing age of the US population, the incidence of cancer is also increasing. Furthermore the global burden of cancer continues to increase largely because of aging and growth of the world population together with increasing smoking rates in economically developing countries. Tumor formation is critically dependent upon two processes--initiation and progression. The initiation step is mediated by DNA damage, which causes activating mutations in proto-oncogenes and inactivation of tumor suppressor genes in many cancers. This is then thought to facilitate tumor progression and metastasis. Cyclooxygenase-2 (COX-2) is upregulated at an early stage in tumorigenesis and has been implicated as an important mediator of proliferation through the increased formation of bioactive arachidonic acid (AA) metabolites such as prostaglandin E(2). Significantly, we have found that COX-2-mediated AA metabolism also results in the formation of heptanone-etheno (Hε)-DNA adducts. Furthermore, we showed that the Hε-DNA adducts arose from the reaction of DNA with the lipid hydroperoxide-derived bifunctional electrophile, 4-oxo-2(E)-nonenal (ONE). Similarly, 5-lipoxoygenase-mediated AA metabolism also results in the formation of ONE-derived DNA adducts. The resulting Hε-DNA adducts are highly mutagenic in mammalian cell lines suggesting that these pathways could be (in part) responsible for the somatic mutations observed in tumorigenesis. As approximately 80% of cancers arise from somatic mutations, this provides an additional link between the upregulation of COX-2 and tumorigenesis.

Chemistry and biochemistry of lipid peroxidation products

Oxidative stress and resulting lipid peroxidation is involved in various and numerous pathological states including inflammation, atherosclerosis, neurodegenerative diseases and cancer. This review is focused on recent advances concerning the formation, metabolism and reactivity towards macromolecules of lipid peroxidation breakdown products, some of which being considered as 'second messengers' of oxidative stress. This review relates also new advances regarding apoptosis induction, survival/proliferation processes and autophagy regulated by 4-hydroxynonenal, a major product of omega-6 fatty acid peroxidation, in relationship with detoxication mechanisms. The use of these lipid peroxidation products as oxidative stress/lipid peroxidation biomarkers is also addressed.

Trans-4-hydroxy-2-hexenal, a product of n-3 fatty acid peroxidation: make some room HNE

Lipid peroxidation yields multiple aldehyde species. Of these, trans-4-hydroxy-2-nonenal (HNE), derived from n-6 poly-unsaturated fatty acids (PUFA) is one of the most studied products of lipid peroxidation. On the other hand, oxidative damage to n-3 PUFA, e.g. docosahexaenoic acid (DHA; 22:6, n-3) and eicosapentaenoic acid, is now recognized as an important effector of oxidative stress and is of particular interest in n-3 rich tissues such as brain and retina. Trans-4-hydroxy-2-hexenal (HHE) is a major alpha,beta-unsaturated aldehyde product of n-3 PUFA oxidation and, like HNE, is an active biochemical mediator resulting from lipid peroxidation. HHE adducts are elevated in disease states, in some cases, at higher levels than the corresponding HNE adduct. HHE has properties in common with HNE, but there are important differences particularly with respect to adduction targets and detoxification pathways. In this review, the biochemistry and cell biology of HHE will be discussed. From this review, it is clear that further study is needed to determine the biochemical and physiological roles of HHE and its related aldehyde, trans-4-oxo-2-hexenal.

Analysis of endogenous glutathione-adducts and their metabolites

The ability to conduct validated analyses of glutathione (GSH)-adducts and their metabolites is critically important in order to establish whether they play a role in cellular biochemical or pathophysiological processes. The use of stable isotope dilution (SID) methodology in combination with liquid chromatography-tandem mass spectrometry (LC-MS/MS) provides the highest bioanalytical specificity possible for such analyses. Quantitative studies normally require the high sensitivity that can be obtained by the use of multiple reaction monitoring (MRM)/MS rather than the much less sensitive but more specific full scanning methodology. The method employs a parent ion corresponding to the intact molecule together with a prominent product ion that obtained by collision induced dissociation. Using SID LC-MRM/MS, analytes must have the same relative LC retention time to the heavy isotope internal standard established during the validation procedure, the correct parent ion and the correct product ion. This level of specificity cannot be attained with any other bioanalytical technique employed for biomarker analysis. This review will describe the application of SID LC-MR/MS methodology for the analysis of GSH-adducts and their metabolites. It will also discuss potential future directions for the use of this methodology for rigorous determination of their utility as disease and exposure biomarkers.

Stable-isotope dilution LC–MS for quantitative biomarker analysis

The ability to conduct validated analyses of biomarkers is critically important in order to establish the sensitivity and selectivity of the biomarker in identifying a particular disease. The use of stable-isotope dilution (SID) methodology in combination with LC–MS/MS provides the highest possible analytical specificity for quantitative determinations. This methodology is now widely used in the discovery and validation of putative exposure and disease biomarkers. This review will describe the application of SID LC–MS methodology for the analysis of small-molecule and protein biomarkers. It will also discuss potential future directions for the use of this methodology for rigorous biomarker analysis.