Formation of Free Radicals in Oxidation of Human Low-Density Lipoprotein. An EPR Spin Trapping Study

The EPR spin trapping method with PBN as a spin trap was used to study the formation of free radicals in human low-density lipoprotein (LDL) upon ageing at 37 °C. The PBN associated radicals could be observed after 10 - 20 hours of incubation, depending on the pretreatment of LDL and the individual donor. The radicals observed in the first period of time (until about 20 - 25 hours of incubation) are related to the degradation products of PBN. After that, additional radicals associated with lipids are observed. The presence of EDTA does not prevent the process. The present experiments prove that some relatively fast oxidation process takes place in LDL incubated at physiological temperature. The process is mild, as judged from the essentially unchanged concentration of thiobarbituric acid-reactive substances (TBARS). An active role of the spin trap is not excluded