Oxidized lipids: Part I. Radiochemical studies on HNE-protein adduction. Part II. Total synthesis of oxidized phospholipids and cholesterol esters.

摘要

Free radical-induced oxidation of polyunsaturated fatty acids (PUFAs) in human low density lipoproteins (LDLs) generates various reactive electrophilic products, especially α,β-unsaturated aldehydes, that covalently modify LDL protein. Some of these protein adducts have been detected in human blood plasma and tissues. Such covalent modification may result in enzyme inhibition, neurodegeneration, or receptor-mediated uptake by macrophages, e.g., of LDL, that occurs during the initial stage of atherosclerosis. The importance of oxidized phospholipids (oxPLs) is beginning to be recognized due to discoveries of their important biological activities.; Part I. (E)-4-Hydroxy-2-nonenal (HNE) is one of the major and most cytotoxic α,β-unsaturated aldehydes that are created by free-radical oxidative cleavage of arachidonate and linoleate esters. A new strategy was developed to synthesize HNE labeled with tritium at C-9, which has several advantages over labeled HNE compounds reported previously. Thus, the location of the label rules out the possibility of radiolabel loss by exchange during adduction reactions with proteins, and a stable precursor is generated which is suitable for long term storage and conveniently converted to HNE in one step. Our synthetic tritium labeled HNE, as well as two specific polyclonal antibodies against HNE-derived pyrrole and HNE-derived crosslink fluorophore epitopes were used to evaluate the nature of HNE-protein/LDL adduction chemistry. We found that the formation of pyrrole and crosslink derivatives is much slower than covalent adduction and accounts for only a small fraction of adducts formed.; Part II. Phospholipids containing a polyunsaturated fatty acyl (PUFA) residue at the sn-2 position are common constituents of cellular membranes and lipoprotein. Free radical-induced oxidation of these PUFA esters in LDL generates 2-lysophosphatidylcholine (PC) and cholesterol esters of α,β-unsaturated aldehydes. Succinct total syntheses of several of these, i.e., γ-hydroxy-α,β-unsaturated aldehydic esters of cholesterol and 2-lysophosphatidylcholine, 9-hydroxy-13-oxotridec-11-enoate ester of 2-lysophosphatidylcholine, and 13-oxotridec-9 E,11E-dienoate ester of 2-lysophosphatidylcholine were accomplished. The total syntheses provided authentic samples for biological studies.