Contents of apolipoprotein A-I, A-II and B of the human serum fractions for high-density and low-density lipoproteins prepared by common precipitation methods

Abstract

Two common precipitation methods for the determination of HDL-cholesterol in human serum were used, dextran sulphate/MgCl₂ and phosphowolframate/MgCl₂. They yield supernatants which contained almost all of the apoA-I and apoA-II lipoproteins but no lipoprotein apoB. The correlations between chol-HDL and apoA-I were about the same with these methods (r=0.79 and 0.80). The correlation between the precipitation methods and ultracentrifugal analysis for chol-HDL was highly significant (r=>0.95). Correspondingly, two common precipitation methods for the determination of LDL-cholesterol in human serum, buffered heparin, and polyvinyl sulphate procedures, produced sediments, which contained the major proportion of the apoB and only small amounts of apoA-I and apoA-II. However, yields of only 69.0–80.2% were obtained for apoB from the sediments and of 85.8–89.4% from supernatants calculated as the difference from chylomicron free serum. This difference might be due to alterations of the molecular structure of apoB by the precipitation reagents. Comparison of the results with the precipitation methods to those using the Friedewald formula showed excellent agreements (r=>0.91). Very comparable results were also obtained in the case of marked hypertriglyceridaemia provided that the serum samples were briefly centrifuged before analysis of chol, chol-HDL, and triglyceride values for the formula of chol-LDL. The precipitation methods for chol-LDL showed very good agreement with the values obtained by ultracentrifugal analysis (r=>0.93). There were no remarkable differences in the correlation of apoB and chol-LDL values measured by different methods (r=0.85).

According to the present results it was found that highly significant correlations existed between chol/chol-HDL or chol-LDL/chol-HDL and apoB/apoA-I ratios (p < 0.001). It is quite evident that apoB and apoA-I values could be used to replace chol-LDL and chol-HDL values when the risk for the cardiovascular diseases is to be assessed.

Key Words:

• cholesterol
• dextran sulphate
• phosphowolframate
• heparin
• polyvinylsulphate precipitation
• immunoturbidimetry
• ultracentrifugal analysis