Measurement of human high density lipoprotein apolipoprotein A-I in serum by radioimmunoassay

Abstract

A sensitive and specific double antibody radioimmunoassay for the major apolipoprotein (apo A-I) of human serum high density lipoprotein (HDL) was developed. Initial studies indicated that direct measurements of apo A-I concentration in whole untreated sera or isolated high density lipoprotein fractions yielded variable results, which were lower than those obtained in the corresponding samples which had been subjected to delipidation. Subsequently, it was observed that heating diluted sera or HDL for 3 hr at 52 °C prior to assay resulted in maximal increases in apo A-I immunoreactivity to levels comparable to those found in the delipidated specimens. This simple procedure permitted multiple sera to be assayed efficiently with full recovery of apo A-I.Serum apo A-I in healthy normolipemic males was 130 ± 3 mg/dl (range 95–165), while the values in females were significantly higher 154 ± 6 mg/dl (range 107–199) (P < 0.005). The apo A-I levels correlated with the total serum cholesterol (males r = 0.46, P < 0.005; females r = 0.58, P < 0.001).Preliminary results with sera from patients with abetalipoproteinemia, hypercholeskrdemia and Tangier disease indicated that alterations in the low density lipoprotein concentration and changes in the physical chemical properties of the high density lipoproteins did not affect the optimal conditions for mnwuring serum apo A-I. The apo A-I concentrations were abnormally low in each of the above disorders.

Keywords

• High density lipoprotein radioimmunoassay
• apolipoprotein A-I
• abetalipoproteinemia
• hypercholesterolemia
• Tangier disease