Very Small Apolipoprotein A-I-containing Particles from Human Plasma: Isolation and Quantification by High-Performance Size-Exclusion Chromatography

• Published in: Clinical chemistry (Baltimore, Md.) Vol. 46; no. 2; pp. 207 - 223
• Main Authors: Nanjee, M. Nazeem, Brinton, Eliot A
• Format: Journal Article
• Language: English
• Published: Washington, DC Am Assoc Clin Chem 01.02.2000; American Association for Clinical Chemistry
• Subjects: Adolescent; Adult; Aged; Analytical, structural and metabolic biochemistry; Apolipoprotein A-I - blood; Apolipoprotein A-I - chemistry; Apolipoprotein A-I - isolation & purification; Biological and medical sciences; Chromatography, Gel; Female; Fundamental and applied biological sciences. Psychology; Humans; Lipoproteins, myelin; Male; Middle Aged; Particle Size; Proteins; Reproducibility of Results; Human; Particle; Biochemical analysis; Small dimension; Preparation; Clinical biology; Analytical method; Apolipoprotein AI; HPLC chromatography; Isolation; High performance size exclusion chromatography; Lipoprotein HDL
• ISSN: 0009-9147; 1530-8561
• DOI: 10.1093/clinchem/46.2.207

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.