RECENT PROGRESS IN DEVELOPMENT OF RADIOIMMUNOASSAYS FOR HUMAN-SERUM LIPOPROTEINS

Abstract

A review of radioimmunoassays for measuring human apolipoprotein B (apo B), the A apolipoproteins of high density lipoprotein (apo A-I and apo A-II) and apolipoprotein C-II (apo C-II) in human plasma and isolated lipoproteins is presented. The sensitivity, specificity and validity of each of these assays is discussed. In normolipidemic subjects the reported serum apo B concentrations ranged between 0.83 .+-. 0.16-0.92 .+-. 0.21 g/l (m .+-. SD). Serum apo B concentrations were highest in Type II subjects (Type IIa homozygotes 3.83 .+-. 0.43 g/l; Type IIa heterozygotes 2.37 .+-. 0.47 g/l) and were less elevated in patients with Type IV and Type V disorders (1.32 .+-. 0.21 g/l and 1.26 .+-. 0.30 g/l, respectively). Preliminary data on the relationship between plasma apo B and cholesterol, the distribution of apo B among the lipoprotein in classes and a comparison of the lipoprotein lipid-apo B ratios in the various hyperlipidemic disorders are summarized. In contrast to apo A-II, the immunoreactivity of apo A-I was not fully exposed in whole sera and isolated lipoproteins. The different methods used to measure the apo A-I immunoreactivity are discussed. In normolipidemic subjects the serum apo A-I concentration in males and females was 1.13 .+-. 0.061 and 1.24 .+-. 0.068 g/l (m .+-. SD), respectively; the corresponding serum apo A-II values were 0.35 .+-. 0.038 g/l and 0.41 .+-. 0.046 g/l. In subjects with Tangier''s disease the serum apo A-I and apo A-II concentrations were < 1% and 5-7% of that found in controls. The serum apo A-I level was also reduced in 2 subjects with abetalipoproteinemia (0.38 g/l and 0.30 g/l) and Type II hyperlipoproteinemia (range 0.54-0.86 g/l). In normotriglyceridemic subjects and those with Type IIa hyperlipoproteinemia, the total plasma apo C-II concentrations were 0.0497 .+-. 0.0040 g/l and 0.0562 .+-. 0.0054 g/l (m .+-. SE). Plasma apo C-II levels in Type IIb, Type IV and Type V lipoproteinemic subjects were 0.0899 .+-. 0.0046, 0.0854 .+-. 0.0069 and 0.1328 .+-. 0.0021 g/l, respectively, and were significantly higher than in the normotriglyceridemic subjects. An analysis of the relationship between the apo C-II content and the lipoprotein in lipase activator properties of VLDL [very low density lipoproteins] isolated from normo- and hypertriglyceridemic plasma samples is presented.