Effects of storage on the distribution of high density lipoprotein subfractions in human sera

The current growing interest in the separation of the high density lipoprotein (HDL) subfractions suggested a comparative analysis of the HDL2 and HDL3 distribution in fresh and stored serum samples. Human sera were processed by rate zonal ultracentrifugation in a swinging bucket rotor, immediately after collection and after a 7-day storage at 4 degrees C, both in the presence and in the absence of 5.1 M sodium bromide. Samples stored in absence of salt show a marked decrease of the HDL3 mass, a reduction of its flotation rate, and significant changes in the lipid composition. The HDL2 concentration and composition are not altered by storage. The reported findings indicate that significant HDL3 modifications may occur in serum samples stored at 4 degrees C; these changes can be prevented by the addition of high concentrations of salt before storage.