Studies on Human Serum High-Density Lipoproteins: VI. Studies on a Cholesterol Ester-Releasing Reaction in Vitro

Abstract

Olofsson, S.-O., Fager, G. & Gustafson, A. Studies on Human Serum High-Density Lipoproteins. VI. Studies on a Cholesterol Ester-Releasing Reaction In Vitro. Scand. J. clin. Lab. Invest. 36, 481–488, 1976.

High-density lipoproteins (HDL) turn turbid during in vitro incubation, concomitant with the formation of a cholesterol ester-rich lipoprotein, designated HDL-sup. The increase in turbidity (A) formed in relation to incubation time (t) is an asymptotic function: A=U₀(1 - e^–k₁^t), where U₀ is the amount of HDL with the property of releasing HDL-sup and k₁ the velocity constant of the reaction. The increase in turbidity and formation of HDL-sup was not related to cholesterol ester content of the incubated fraction nor to exogenous factors like bacterial growth. The in vitro incubation was accompanied by a cholesterol esterification with a mean production of 8 nmol cholesterol ester/mg HDL protein, but also by a more pronounced degradation of phosphatidyl choline, 148 nmol/mg HDL protein. These data indicate that the lipid changes are induced by a two-step lecithin:cholesterol acyltransfer (LCAT) reaction. This reaction caused in HDL lipids a consumption of surface material and an increase in ‘lipid core’, presumably leading to a weakening and disruption of the lipoprotein surface with a recombination of ‘lipid core’ material in the form of HDL-sup.

Key Words:

• Cholesterol esters
• lipoproteins
• high-density (HDL)