Quantitation of the in vitro free cholesterol exchange of human red cells and lipoproteins

Steven H Quarfordt,Helen L Hilderman

doi:10.1016/s0022-2275(20)42936-0

Abstract

The exchange of free cholesterol in vitro between human red blood cells and low density lipoproteins (LDL) was quantified. The flux of sterol between LDL and red cells was relatively constant over a wide range of concentrations of free cholesterol in lipoproteins. In a system containing a suspension of red blood cells in a mixed solution of high density lipoproteins (HDL) and LDL, the fractional rate of exchange of HDL cholesterol was most rapid followed by LDL and lastly, by red cells. Increasing the ionic strength of the incubation media had no effect on the exchange of cholesterol between LDL and red cells. However, when both HDL and LDL were incubated with red cells in a buffer of increased ionic strength, total red cell cholesterol exchange was unaltered, but proportionately more exchange occurred with HDL and less with LDL. Addition of acetone to the buffer increased the exchange of cholesterol between LDL and red cells but produced no increment in red cell-HDL exchange.

Highlights

Increasing the ionic strength of the incubation media had no effect on the exchange of cholesterol between low density lipoproteins (LDL) and red cells
The supernate from the first red cell centrifugation was extracted directly when incubations involved a single lipoprotein and red cells. When both high density lipoproteins (HDL) and LDL were incubated with red cells, the lipoproteins were subsequently isolated from the supernate by a heparin-MnC12 precipitation technique [8]
A1 and A s are the fractional exchange rates of the initially labeled pool and the unlabeled pool, respectively. When both HDL and LDL were incubated with red cells, a closed three-compartment model (Fig. 16) was used for the analysis of the data

Summary

Introduction

Increasing the ionic strength of the incubation media had no effect on the exchange of cholesterol between LDL and red cells. Fractional exchange rates of red cell and lipoprotein cholesterol and free sterol flux (i.e., inass of cholesterol exchanged per minute) were derived for each study. T h e fractional red cell exchange rates (XL,R) were relatively similar within each study despite large differences in the concentrations of incubated lipoprotein.

Results

Conclusion