Mild autoxidation of low density lipoproteins

The autoxidation of low density lipoproteins was investigated in a closed system, with limited amount of oxygen. The concentrations of several components were monitored: oxygen, aldehydic oxidation products and alpha-tocopherol. The concentration of lipid radicals generated in the processes of lipid peroxidation was monitored by the EPR spin trapping method. It was observed that the consumption of oxygen starts quickly after the onset of incubation at physiological temperature. After prolonged incubation, several types of trapped radicals were formed. At the same time, no consumption of alpha-tocopherol and no formation of aldehydic products of oxidation took place, indicating that the oxidation process is rather mild. The dynamics of oxidation processes were simulated by a mathematical model in which the oxidation is initiated by the degradation products of the pre-existing lipid peroxides. The best agreement between the theoretical predictions and experimental results was obtained with the rate constants which are several orders of magnitude smaller than the corresponding rate constants in "neat' lipids. The possible reasons for the behaviour observed are discussed.