engleski

Nonhomogeneous kinetics of very slow plasma lipoprotein oxidation

Oxidized plasma low-density lipoprotein (LDL) is implicated in atherogenesis. Oxidized LDL induces biochemical changes in arteries that in a positive feed-back mechanism induce further accumulation of oxidized LDL and subsequent formation of "foam" cells, tha constituents of fatty streaks. From the in vitro studies the lipid soluble antioxidant alpha-tocopherol seems to completely protoect LDL from the Cu(II)-initiated oxidation. In vivo studies do not confirm such a powerful antioxidant role of alpha-tocopherol. We have observed that also in the proces of very slow LDL oxidation in vitro alpha-tocopherol behaves as a prooxidant rather than antioxidant. In these processes oxygen is consumed, if present, free radicals are formed, initial increase of the peroxide level is followed by a decrease, but the alpha-tocopherol level remains unaltered. Very slow LDL oxidation takes place even under highly unfavorable conditions: in a closed system with a restricted amount or complete lack of oxygen, in apparently metal-free buffers and with presence of chelating agents. For the kinetic considerations, heterogeneous system is assumed: the reactions take place within individual particles rather in the bulk. A system of kinetic differentialequations have been set and numerically solved. The solutions fit the observations, including active rolecand at the same time preservation of alpha-tocopherol; alpha-tocopherol oscilaters between the reduced and oxidized forms.

Alpha-tocopherol; EPR; Fee radicals LDL; LDL oxidation; Oxygen consumption

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