Cryopreservation and long-term storage of human low density lipoproteins.

A simple and effective technique of long-term storage of human low density lipoproteins (LDL) has been developed. The technique involves the addition of 1.4 mol/l (or 10% by volume) dimethyl sulphoxide directly to a solution of the freshly isolated LDL in high salt buffer, and subsequent freezing and storage for up to 2 years at -70 degrees C. We have shown that freshly isolated LDL, "preserved" as described above, are able to keep their native properties for a long period, i.e.: a) electrophoretic behaviour in non-denaturing (or with sodium dodecyl sulphate, 1 milligram) polyacrylamide 2-16% gradient gel electrophoresis; b) immunoreactivity of apolipoprotein B (analyzed by radial immunodiffusion, electroimmunoassay and immunoturbidimetric assay); c) immunogeneity of apolipoprotein B; d) an average size of LDL particles (analyzed by electron microscopy); e) ability to bind with B,E-receptors of human skin fibroblasts. The technique can also be applied to radiolabelled LDL samples. Taking into consideration the labour- and time-consuming procedure of obtaining and characterizing LDL, and the preferred use of single well-characterized LDL preparation, we recommend that the above technique of LDL long-term storage be applied in various clinical and biomedical studies.