Apolipoprotein A-I inhibits transformation of high density lipoprotein subpopulations during incubation of human plasma

Abstract

We have examined the effect of added apolipoprotein A-I (apoA-I) on the changes in high density lipoprotein (HDL) particle size that occur when human plasma is incubated in vitro. In the absence of added apoA-I, incubation of plasma at 37°C resulted in a dramatic increase in HDL particle size. When these incubations contained an inhibitor of LCAT, an additional population of smaller HDL particles was formed. These changes in particle size were even more pronounced when the incubations were supplemented with an artificial triglyceride emulsion, Intralipid. All these changes in HDL particle size were markedly inhibited when incubations were supplemented with apoA-I. Even when the amount of added apoA-I was as little as 4.5% of the endogenous apolipoprotein there was an obvious inhibition of the changes in HDL particle size. The presence of added apoA-I sufficient to increase the plasma concentration by 18% virtually abolished the changes in HDL particle size. This effect did not relate to an inhibition of cholesterol esterification, nor did it appear to depend on an incorporation of the added apoA-I into the HDL.