Detection of vitamin C-induced singlet oxygen formation in oxidized LDL using MCLA as a chemiluminescence probe

In this study, it was observed that addition of vitamin C (vit C) to oxidized low-density lipoprotein (Ox-LDL) by cupric ions (Cu2+) could result in the formation of singlet oxygen (1O2). In experiments, 1O2 was detected by chemiluminescence method using a Cypridina luciferin analog, 2-methyl-6-(p-methoxyphenyl)-3, 7-dihydroimidazo [1, 2-a] pyrazin-3-one (MCLA), as a selective and sensitive chemiluminescence probe. Additional experimental evidence for the formation of 1O2 came from the quenching effect of sodium azide (NaN3) on vit C-induced chemiluminescence in the reaction mixture of LDL-Cu(2+)-MCLA. Analysis based on the experimental results demonstrated the plausible reaction mechanism is that vit C first converts Cu2+ to its reduced state and vit C becomes vit C radical itself, thereby stimulating the formation of peroxyl and alkoxyl radicals, and bimolecular reaction of peroxyl radicals results in 1O2 production in the systems studied.