A rapid methodology for the isolation of intermediate-density lipoprotein: characterization of lipid composition and apoprotein content.

BACKGROUND

Intermediate-density lipoprotein (IDL) is a structurally related precursor of low-density lipoprotein (LDL). Although found in significantly lower levels, extensive evidence suggests that IDL shares LDL's capacity to promote atherosclerosis. To assist further investigation into IDL's composition and physiological relevance, we have established a rapid method to extract IDL from plasma.

METHODS

IDL was isolated from plasma by sequential floatation ultracentrifugation in 3 h, a significantly shorter isolation time than previously published methods. Apoproteins (apo) B100, CIII, and E, together with the level of albumin contamination, were quantified using single radial immunodiffusion. The lipid composition of IDL was measured using automated enzyme assays.

RESULTS

The percent recovery of lipid from all lipoprotein fractions (VLDL+IDL+LDL+HDL) was 97.0+/-4.9% when compared to total plasma lipid. IDL had a reduced concentration of apo CIII, apo E, triglyceride, and free cholesterol, and had a higher concentration of apo B100, cholesterol ester, and phospholipid when compared to VLDL. Pure IDL migrated in advance of LDL during agarose electrophoresis.

CONCLUSIONS

This rapid technique minimizes damage to the integrity of IDL and yields sufficient quantities to allow accurate assessment of composition and susceptibility to in vitro oxidation, and thus facilitates further investigation of IDL in the development of atherosclerosis.