IsoLGD2−Protein Adducts Are Abundant in Vivo and Free Radical-Induced Oxidation of an Arachidonyl Phospholipid Generates This D Series Isolevuglandin in Vitro
journal contributionposted on 17.05.2004 by Eugenia Poliakov, Susan Gillette Meer, Subhas C. Roy, Clementina Mesaros, Robert G. Salomon
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Isolevuglandins (isoLGs) are a family of γ-ketoaldehydes, aka isoketals or neuroketals, that are generated by free radical-induced oxidation of polyunsaturated fatty acid-containing lipids. Because of their high reactivity toward ε-amino groups of lysyl residues, isoLGs are found as protein adducts in vivo. Plasma levels of isoLG-derived protein modifications are orders of magnitude higher than levels of the corresponding isoprostane. This suggests that while isoprostanes are rapidly cleared from the circulation, isoLG−protein adducts accumulate over the lifetime of the protein, which can be weeks, and this may provide a dosimeter for oxidant stress. We now confirm the postulated formation of the first D series isoLG, isoLGD2, by free radical-induced oxidation of 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphocholine in vitro. We also show that isoLGD2−protein adduct levels in blood are the highest known for an isoLG-derived epitope. They average 30-fold higher than isoLGE2−protein and 3-fold higher than isoLGE2−protein levels. Similarly, isoLGD2-derived epitope levels in oxidized low density lipoprotein are 20 times higher than isoLGE2−protein and five times higher than isoLGE2−protein levels. Previous studies showed that plasma levels of protein-bound E series isoLGs, i.e., isoLGE2 and isoLGE2, are elevated in individuals with atherosclerosis as compared with age-matched controls. Plasma isoLGD2−protein immunoreactivity in individuals with atherosclerosis averages 8.5 ± 3.1 nmol/mL, significantly higher (P = 0.01) than the 3.5 ± 0.1 nmol/mL in healthy controls. Plasma levels of isoLGD2−protein adducts are strongly correlated with isoLGE2− (r = 0.933) and isoLGE2−protein adducts (r = 0.877). This supports the hypothesis that isoLGs are generated in vivo by parallel competing radical-induced pathways.