LIGHT-EMISSION RESULTING FROM HYDROXYLAMINE-INDUCED SINGLET OXYGEN FORMATION OF OXIDIZING LDL PARTICLES

Oxidation of low-density lipoprotein (LDL) by low amounts of cupric io ns resulted in the formation of singlet oxygen (O-1(2), (1) Delta(g)) when hydroxylamine (NH2OH) was added. Direct evidence on this excited species came from partial spectral resolution of the emitted light in the red spectral region (634 nm and 703 nm), which can be attributed t o the dimol decay of singlet oxygen. Additional evidence for the exist ence of singlet oxygen came from the enhancing effect of deuterium oxi de buffer (D2O) on chemiluminescence intensity and the quenching effec t of sodium azide. A linear correlation between NH2OH-dependent chemil uminescence intensity and the amount of diene conjugates (DC) formed i n this reaction was observed, Removal of adventitious transition metal s by adequate chelators prevented chemiluminescence in this system; NH 2OH was also found to efficiently decrease metabolites of lipid peroxi dation (LPO). Our findings are consistent with a sequence of reactions in which NH2OH first converts transition metals to their reduced stat e, thereby stimulating the formation of alkoxy-and peroxyradicals. Per oxyradicals decompose in a bimolecular Russel reaction to hydroxyl com pounds and singlet oxygen while the majority of alkoxy radicals are el iminated by a secondary reaction with NH2OH. Identical effects were ob served when reducing antioxidants such as ascorbic acid or trolox C we re used instead of hydroxylamine.