Development of homogeneous assay for simultaneous measurement of apoE-deficient, apoE-containing, and total HDL-cholesterol.

Background: Pathophysiological role for high-density lipoprotein (HDL) subclasses remains to be elucidated. Homogeneous assay for simultaneous measurements of apoE-deficient HDL-cholesterol (HDL-C), apoE-containing HDL-C, and total HDL-C is desired, because apoE plays important roles in lipid metabolism.

Methods: The proposed assay consists of a primary reaction to remove non-HDL-C, a secondary reaction to measure apoE-deficient HDL-C, and a tertiary reaction to measure apoE-containing HDL-C. The assay is completed within 10 min. For control study, 13% polyethylene glycol precipitation assay and phosphotungstate-dextran sulfate-magnesium precipitation assay were carried out.

Results: Good correlations between the control assays and the proposed assay was obtained in serum samples from patients without liver disease (n=33): r=0.987, 0.957, and 0.991 for apoE-deficient, apoE-containing, and total HDL-C, respectively. ApoE-containing HDL-C by the proposed method in healthy individuals (n=12) and patients with hyper-HDL-cholesterolemia (n=5) were 0.11±0.03 and 0.26±0.05 mmol/l (4.1±1.3 and 10.1±2.0 mg/dl), respectively. ApoE-containing HDL-C increased rapidly at >2.59 mmol/l (100 mg/dl) of total HDL-C, suggesting a unique regulating mechanism of apoE-containing HDL-C.

Conclusions: The established homogeneous assay might be useful for clinical and epidemiological studies on apoE-deficient and apoE-containing HDL subclasses.