Very small apolipoprotein A-I-containing particles from human plasma: Isolation and quantification by high-performance size-exclusion chromatography

Abstract

Background: Very small apolipoprotein (apo) A-I-containing lipoprotein (Sm LpA-I) particles with pre-β electrophoretic mobility may play key roles as 'nascent' and/or 'senescent' HDL; however, methods for their isolation are difficult and often semiquantitative. Methods: We developed a preparative method for separating Sm LpA-I particles from human plasma by high- performance size-exclusion chromatography (HP-SEC), using two gel permeation columns (Superdex 200 and Superdex 75) in series and measuring apo A-I content in column fractions in 30 subjects with HDL-cholesterol (HDL-C) concentrations of 0.4-3.83 mmol/L. Results: Three major sizes of apo A-I- containing particles were detected: an ~15-nm diameter (~700 kDa) species; a 7.5-12 nm (100-450 kDa) species; and a 5.8-6.3 nm species (40-60 kDa, Sm LpA-I particles), containing 0.2-3%, 80-96%, and 2-15% of plasma total apo A- I, respectively. Two subjects with severe HDL deficiency had increased relative apo A-I content in Sm LpA-I: 25% and 37%, respectively. The percentage of apo A-I in Sm LpA-I correlated positively with fasting plasma triglyceride concentrations (r = 0.581; P <0.0005) and inversely with total apo A-I (r = -0.551; P <0.0013) and HDL-C concentrations (r = -0.532; P <0.0017), although the latter two relationships were largely attributable to extremely hypoalphalipoproteinemic subjects. The percentage of apo A-I in Sm LpA-I correlated with that in pre-β-migrating species by crossed immunoelectrophoresis (r = 0.98; P <0.0001; n = 24) and with that in the d >1.21 kg/L fraction by ultracentrifugation (r = 0.86; P <0.001; n = 20). Sm LpA-I particles, on average, appear to contain two apo A-I and four phospholipid molecules but little or no apo A-II, triglyceride, or cholesterol Conclusions: We present a new HP-SEC method for size separation of native HDL particles from plasma, including Sm Lp A-I, which may play important roles in the metabolism of HDL and in its contribution(s) to protection against atherosclerosis. This method provides a basis for further studies of the structure and function of Sm Lp A-I. (C) 2000 American Association for Clinical Chemistry.