Cholesterol ester transfer mediated by lipid transfer protein as influenced by changes in the charge characteristics of plasma lipoproteins

H.I Nishida,H Arai,T Nishida

doi:10.1016/s0021-9258(19)85428-5

Abstract

The relationship between the cholesterol ester (CE) transfer activity of lipid transfer protein (LTP) and its affinity with lipid and lipoprotein particles was investigated. The study of the effects of chemical modification of low density lipoprotein (LDL) amino groups and carboxyl groups on the CE transfer activity showed that the maximal activity is obtained upon succinylation or acetylation of approximately 7% of LDL amino groups. Further increases in the extent of modification progressively reduced the transfer activity. The treatment of LDL with fatty acids gave results comparable to the chemical modification of LDL amino groups. The addition of low concentrations of fatty acids was stimulatory, while that of high concentrations was inhibitory. Although increases in the positive charges of LDL by the carboxyl group modification did not appreciably influence the CE transfer, the addition of cationic detergents gave a profound effect on the CE transfer. A maximal CE transfer activity was obtained upon addition of very small amounts of the detergents, with the higher concentrations sharply reducing the transfer activity. We also studied the effects of the concentrations of phosphate buffer and various salts on the CE transfer as well as the affinity of LTP for very low density lipoproteins, low density lipoproteins, high density lipoproteins 3, and high density lipoproteins 2. It appeared that the affinity of LTP for various lipoproteins is governed by a delicate balance of electrostatic and hydrophobic interactions. Optimal degrees of the interaction of LTP with both donor and acceptor particles seem to be required for the maximal degree of CE transfer.

Highlights

The relationship between the cholesterolester (CE) triglyceridesamongplasmalipoproteins (1-3)
A has yet been carried outon the lyLipid transfer protein (LTP)-lipoprotein interaction maximal CE transfer activity was obtained upon ad- in relation to the CE transfer activity
We studied the effecotsf the concen- for lipoproteinsT. he charge characteristiocf LDL wasaltered trations of phosphate buffer and varioussalts on the CE transfer as well as the affinityof LTP for verylow densitylipoproteins,lowdensitylipoproteins,high density lipoproteins3,and high density lipoprotei2n.s I t appeared that the affinityof LTP for various lipoproteins is governed by a delicate balance of electrostatic and hydrophobic interactions

Summary

EXPERIMENTAL PROCEDURES

Vesicles were prepared by rapidly injecting an ethanol solution of lipids into phosphate buffer (15, 16), and discoidal bilayer particles amino groups. Transfer assay contained PC, cholesterol, [3H]cholesteryloleate, and Preparation of Lipoprotein Sephurose 4B"Various lipoproteins apoA-I at themolar ratio of 90301.2:l.O. Buffer-Experiments were performed in 39 mM sodium phosphate recommended by Pharmacia FineChemicals. L T P Purification-LTP was purified from human plasma accord- 2.3mgof HDL, all as protein, were coupled/milliliter of packed ing to themethod recently described (6). Stand- Labeling of HDL-The labeling of HDLawas carried out by transard assay mixtures consisted of 100 pl of discoidal bilayer particles ferring [1,2,6,7-3H]cholesteryloleate from PC-cholesterol vesicles to preparations containing 90 nmol of PC, 30 nmol of cholesterol, 1.2 HDL3 using purified LTP aspreviously described (7). When LDL was modified by acetylation, succinylation, or by the lipid contents were determined by methods previously described (9)

RESULTS

CARBOXYL GROUPS

Findings

DISCUSSION