An effect of very low density lipoproteins on the rate of cholesterol esterification in human plasma.

ABSTRACT

Rates of esterification of plasma cholesterol have been compared in two groups of human subjects with widely differing concentrations of very low density lipoproteins (VLDL). Group 1 consisted of subjects with fasting plasma triacylglycerol concentrations over 2.0 mM and group 2 consisted of subjects with concentrations under 1.6 mM. The rate of esterified cholesterol production in incubations of whole plasma from group 1 subjects was much greater than that from group 2 subjects. A clear difference between the rates of esterification was also evident when either total lipoproteins, total high density lipoproteins (HDL) or the HDL subfraction, HDL3, from the two types of subjects were incubated in the presence of a common source of lecithincholesterol acyltransferase. Since these findings appeared to reflect fundamental differences within the HDL3 subfractions, which may have been modified by prior exposure to the high concentrations of VLDL in group 1 subjects, VLDL-deficient plasma and the plasma fraction of d greater than 1.125 g/ml (containing HDL3) from hypotriglyceridaemic subjects were preincubated at 37 degrees C with an excess of added VLDL in the presence of a reversal of the inhibition of lecithincholesterol acyltransferase, the capacity of the original fractions to esterify cholesterol had been markedly increased. These studies, therefore, show that the lecithincholesterol acyltransferase substrate capacity of particles within the HDL3 subfraction is enhanced by exposure to VLDL and that this enhancement is not dependent on the continued presence of VLDL during the actual esterification reaction.