Role of esterified cholesterol transfers in the regulation of plasma cholesterol esterification

The role of esterified cholesterol transfers in mediating the known effect of very low density lipoproteins (VLDL) on plasma cholesterol esterification has been examined. Advantage has been taken of the fact that pig plasma, in contrast to human plasma, is deficient in activity of the protein that transfers esterified cholesterol between plasma lipoproteins. The experimental protocol consisted of a pre-incubation in which VLDL-deficient pig plasma or isolated pig lipoproteins were incubated with added VLDL, in the presence or absence of an exogenous source of the esterified cholesterol transfer protein. After pre-incubation, any VLDL that may have been present was removed and rates of cholesterol esterification measured in subsequent incubations of the recovered VLDL-depleted fractions. It was, thus, possible to assess the effect of VLDL and/or transfer protein activity on the capacity of other lipoproteins to act as substrates for cholesterol esterification. In the absence of transfer protein activity, the presence of VLDL in pre-incubations had no effect on the subsequently measured rate of cholesterol esterification. However, when pig plasma was supplemented with human lipoprotein-free plasma (a source of esterified cholesterol transfer protein activity) the presence of VLDL in pre-incubations resulted in both a reduction in the esterified cholesterol content of the re-isolated VLDL-deficient fraction and a markedly enhanced rate of cholesterol esterification in subsequent incubations of this fraction.(ABSTRACT TRUNCATED AT 250 WORDS)