Fotosenzibilizovana oksidacija lipida u rastvoru indukovana kontinualnim UV-stresom u prisustvu kvercetina

Abstract

The aim of the present PhD thesis was to study UV(-A and -B) induced lipid peroxidation sensitized by synthetic (benzophenone) and endogenous photosensitizers (bilirubin, riboflavin) in the presence of quercetin as antioxidant. Phospholipid mixure was used as a ”protective target” and the whole process was followed in the simplest possible system – methanolic solution. Photodegradation of sensitizers and quercetin with the consequent occurrence of their degradation products both individually and in the mutual mixture, as well as in the mixture with phospholipids (where beside the mentioned processes peroxides production occurs), was followed by RP-HPLC chromatography. Unambiguous identification of degradation products was enabled by UHPLC-ESI-MS technique while free radical species were identified by EPR spectroscopy. Benzophenone was photostabile, photodegradation of bilirubin gave biliverdin and dipiroles while main degradation products of riboflavin were lumichrome and lumiflavin. Insight into the mechanism and control of lipid peroxidation provided ”conjugated diene” assay, by following the signal at 234 nm (the absorption maximum of conjugated diene structures). As typical Type I sensitizer, benzophenone generated superoxide radical anion, while riboflavin generated both superoxide and singlet oxygen by mixed Type I and II mechanisms. Irradiation of bilirubin-riboflavin mixture showed, in the indirect way, that bilirubin is typical Type II sensitizer. Photosensitizing capability of the studied sensitizers decreases in the order: riboflavin > benzophenone > bilirubin. Quercetin exhibited efficient antioxidant activity, mediated by its own degradation, in terms of its preventive (absorbing UV radition), chain-breaking activities (scavenging of generated superoxide radical anion, singlet oxygen and lipid peroxides) and besides all this effectively quenched triplet exited states of sensitizers (first of all benzophenone and riboflavin).