Assessment of the C-525 laser dye as a chemiluminescence sensitizer for lipid peroxidation in biological membranes: a comparison with chlorophyll-a.

The C-525 laser dye at micromolar concentration range is shown to enhance up to two to three orders of magnitude the chemiluminescence (CL) accompanying tert-butyl hydroperoxide (t-BHP)-induced rat liver microsome oxidation and Fe(2+)-induced lipid peroxidation (LPO) in liposomes. C-525 is shown to be a more efficient sensitizer of CL accompanying LPO in membrane systems than the known low-energy excited triplet carbonyl sensitizer, chlorophyll-alpha, (Cl-a). Regarding the sensitization mechanism, C-525 and Cl-a were compared in (a) a peroxyl radical-producing system (2,2'-azobis(2-dimethylvaleronitrile) (AMVN); (b) excited carbonyl-producing systems (3-hydroxymethyl-3,4,4-trimethyl-1,2-dioxetane (HTMD) thermal decomposition and horseradish peroxidase (HRP)-catalyzed isobutanal oxidation); and (c) excited singlet oxygen-producing system [endoperoxide of 3,3-(1,4-naphthylidene)-dipropionate (NDPO2)]. C-525 sensitized CL only in the systems where peroxyl radical and/or triplet excited carbonyls are produced, the mechanism of CL sensitization apparently is energy transfer from the excited triplet carbonyls formed in the peroxyl radical self-reaction via Russell's mechanism or by dioxetane decomposition. Cl-a was found to considerably sensitize CL related to NDPO2 thermal decomposition, a source of singlet oxygen, in addition to acting as a sensitizer of triplet carbonyl CL. The chemical stability of the C-525 laser dye in excited state-generating systems was shown to be appropriate for its application as a sensitizer of CL related to LPO reactions in membranes, but not in the HRP-catalyzed peroxidation system.