Presence and Formation of ‘Free Apolipoprotein A-I–Like’ Particles in Human Plasma

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Abstract
Abstract The influence of dilution on apolipoprotein (apo) A-I–containing subpopulations was studied in human plasma. Agarose electrophoresis and two-dimensional agarose nondenaturing gradient polyacrylamide gel electrophoresis were used. Both in one- and two-dimensional electrophoresis, an increase of charge was observed that resulted in an increase of subpopulations with pre-α mobility. Dilution of plasma also resulted in a decrease in the size of apo A-I–containing pre-β 1 subpopulations. The existence of smaller pre-β 1 particles was confirmed by subjecting undiluted and 8× diluted plasma to 3% to 16% nondenaturing gradient gel electrophoresis for 4 hours. In addition to the generally observed pre-β 1 subpopulations, smaller particles similar in size to the free apo A-I were detected even in the undiluted plasma. During dilution, the proportion of larger pre-β 1 particles decreased while the smaller ones increased, and in 8× diluted plasma, almost all the pre-β 1 was present in smaller sizes. Using 3% to 35% nondenaturing polyacrylamide gels run for 24 hours, no pre-β 1 particles could be detected in 8× diluted plasma because the small pre-β 1 electrophoresed out. These studies show that pre-β 1 particles can be converted to smaller ones during dilution. It also was demonstrated that “free apo A-I–like” pre-β 1 particles are present in undiluted plasma. The presence of these particles may have important physiological and pathophysiological functions.