FLAVONOIDS AS ANTIOXIDANT AGENTS - IMPORTANCE OF THEIR INTERACTION WITH BIOMEMBRANES

Flavonoids, a group of phenolic compounds widely occurring in the plan t kingdom, have been reported to possess strong antioxidant activity. In the present study, four flavonoids (quercetin, hesperetin, naringen in, rutin), chosen according to their structural characteristics, were tested in two different in vitro experimental models: (1) Fe2+-induce d linoleate peroxidation (Fe2+-ILP), by detection of conjugated dienes ; and (2) autooxidation of rat cerebral membranes (ARCM), by using thi obarbituric acid for assay of free malondialdehyde production. The res ults obtained were also interpreted in the light of flavonoid interact ions, studied by differential scanning calorimetry, with dipalmitoylph osphatidylcholine (DPPC) vesicles as a biological membrane model. The antilipoperoxidant activity of the flavonoids tested can be classified as follows: rutin > hesperetin > quercetin much greater than naringen in in the Fe2+-ILP test; quercetin > rutin much greater than hespereti n > naringenin in the ARCM test. Quercetin, hesperetin, and naringenin interacted with DPPC liposomes causing different shifts, toward lower values, of the main transition peak temperature (T-m) typical for DPP C liposomes; however, no change in T-m of DPPC dispersion was observed in the presence of rutin. The hypothesis will be discussed that flavo noid capacity to modify membrane-dependent processes, such as free-rad ical-induced membrane lipoperoxidation, is related not only to their s tructural characteristics but also to their ability to interact with a nd penetrate the lipid bilayers.