Rapid separation of LDL subclasses by iodixanol gradient ultracentrifugation

A predominance of small, dense LDL (sdLDL) confers in excess of a threefold increase in coronary heart disease (CHD) risk. The conventional method for the detection of sdLDL, salt density gradient ultracentrifugation (DGUC) has been superseded by more rapid techniques. This report presents novel methodology for the separation of sdLDL by a combination of iodixanol density gradient centrifugation and digital photography.

LDL subclasses were separated in 3 h from prestained plasma on a self-forming density gradient of iodixanol. LDL subclass profiles were generated by digital photography and gel-scan software. Plasma samples from 106 normo- and dyslipidemic individuals were used to optimize the gradient for the resolution of LDL heterogeneity. A subgroup of 47 LDL profiles were then compared with LDL subclasses separated by salt DGUC.

The peak density of the predominant LDL band correlated significantly with the relative abundance (as a percentage) of sdLDL as resolved by salt DGUC (P <0.001). As shown previously, LDL isolated at a lighter density in iodixanol compared with salt gradients. A predominance of sdLDL corresponded to a peak density on iodixanol of 1.028 kg/L. This density and the area under the LDL profile lying above this density were sensitive and specific markers for the prediction of a predominance of sdLDL (P <0.001) and showed predictable associations with plasma triglycerides (r = 0.59; P <0.001) and HDL (r = -0.4; P <0.001).

This simple method for the detection of sdLDL can differentiate a predominance of sdLDL, is highly reproducible, and can be used preparatively to isolate sdLDL.