Presence and formation of 'free apolipoprotein A-I-like' particles in human plasma.

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-alpha mobility. Dilution of plasma also resulted in a decrease in the size of apo A-I-containing pre-beta 1 subpopulations. The existence of smaller pre-beta 1 particles was confirmed by subjecting undiluted and 8x diluted plasma to 3% to 16% nondenaturing gradient gel electrophoresis for 4 hours. In addition to the generally observed pre-beta 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-beta 1 particles decreased while the smaller ones increased, and in 8x diluted plasma, almost all the pre-beta 1 was present in smaller sizes. Using 3% to 35% nondenaturing polyacrylamide gels run for 24 hours, no pre-beta 1 particles could be detected in 8x diluted plasma because the small pre-beta 1 electrophoresed out. These studies show that pre-beta 1 particles can be converted to smaller ones during dilution. It also was demonstrated that "free apo A-I-like" pre-beta 1 particles are present in undiluted plasma. The presence of these particles may have important physiological and pathophysiological functions.