Blue fluorescence generated during lipid oxidation of rat liver microsomes cannot be derived from malonaldehyde but can be from other aldehyde species.

Generation of blue fluorescence together with phospholipid hydroperoxides and aldehyde species in rat liver microsomes during oxidation with FeCl2-ADP-ascorbic acid was monitored, and the kind of lipid oxidation products participating in the formation of blue fluorescence was investigated. Contents of phospholipid hydroperoxides were increased in an early stage of oxidation, and were decreased in an advanced stage of oxidation. Contents of components that liberated malonaldehyde, 4-hydroxyalkenals and other unsaturated aldehydes under the acidic assay conditions were increased in the advanced stage of oxidation. Water-soluble blue fluorescence with a maximum at 440-450 nm determined after separation through gel filtration accumulated in the advanced stage of oxidation, and was characterized as resistant to borohydride treatment and to be little dependent on pH values of the solvent. Wavelength of the maximum fluorescence and characteristics of the fluorescence were similar to those of fluorescence with maxima at 440-450 nm formed by reaction of unoxidized microsomes, bovine serum albumin or methylamine with alkenals, and different from those of fluorescence with maxima at above 460 nm obtained by the reaction with a mixture containing malonaldehyde. Hence, blue fluorescence accumulated in oxidized microsomes cannot be derived from free malonaldehyde but can be from other aldehyde species including alkenals.