[A comparative study of the lipid phase in native and circulating multiple-modified low-density lipoproteins of human blood by the use of the spin probe method].

Different approaches based on the spin probe method were used to compare the physical state of the surface lipid monolayer in subfractions of low-density lipoproteins: in native low-density lipoproteins constituting the bulk of human blood low-density lipoproteins and in circulating multiple-modified low-density lipoproteins whose portion is minor in healthy persons but significantly increases in atherosclerotic patients. The data obtained in in vitro experiments suggest that circulating multiple-modified low-density lipoproteins possess atherogenic properties. The order parameter S, rotational correlation time tau, and hydrophobicity parameter h were calculated from electron spin resonance spectra of a series of spin probes whose paramagnetic groups are located at different depths of the lipid monolayer. These parameters characterize the molecular packing, fluidity, and polarity in the microenvironment of paramagnetic groups. The kinetics of the reduction of paramagnetic groups by ascorbate and oxidation by hypochlorite were obtained for the spin probe whose paramagnetic group is located deeply in the lipid monolayer at the level of the terminal segments of phospholipid acyl chains. No difference between native low-density lipoproteins and circulating multiple-modified low-density lipoproteins was revealed in respect of the physical properties of the lipid domain of surface proteolipid layer, as sampled by spin probes.