Characterization of a composite gradient gel for the electrophoretic separation of lipoproteins

We describe a protocol for making a new type of gradient gel, the Composite gradient gel, that was designed to resolve plasma lipoproteins using nondenaturing gradient gel electrophoresis. The new gel format allows analysis both of high density lipoproteins (HDLs) and low density lipoproteins (LDLs) on the same gel. The gel gave highly repeatable (r2 = 0.999) size estimates. We compared lipoprotein phenotypes determined from the new gradient gel with those obtained using specialized HDL and LDL gradient gels. The comparisons indicated that the Composite gel gave lipoprotein particle size estimates for HDLs and LDLs that were virtually identical to those obtained, respectively, from the specialized HDL and LDL gradient gels. We measured median diameters, which reflect the distributions of absorbance, for LDLs and for HDLs and found that the Composite gel gave lipoprotein size distributions that were virtually identical to those measured using the specialized LDL and HDL gels. Finally, comparison of fractional absorbance for six lipoprotein size intervals obtained from the Composite and specialized gels revealed a close correlation (r2 = 0.828). Thus, it appears that both LDL and HDL size phenotypes may be evaluated simultaneously using a single gradient gel format.