Lipopolysaccharide is transferred from high-density to low-density lipoproteins by lipopolysaccharide-binding protein and phospholipid transfer protein

Abstract

Lipopolysaccharide (LPS), the major outer membrane component of gram-negative bacteria, is a potent endotoxin that triggers cytokine-mediated systemic inflammatory responses in the host. Plasma lipoproteins are capable of LPS sequestration, thereby attenuating the host response to infection, but ensuing dyslipidemia severely compromises this host defense mechanism. We have recently reported that Escherichia coli J5 and Re595 LPS chemotypes that contain relatively short O-antigen polysaccharide side chains are efficiently redistributed from high-density lipoproteins (HDL) to other lipoprotein subclasses in normal human whole blood (ex vivo). In this study, we examined the role of the acute-phase proteins LPS-binding protein (LBP) and phospholipid transfer protein (PLTP) in this process. By the use of isolated HDL containing fluorescent J5 LPS, the redistribution of endotoxin among the major lipoprotein subclasses in a model system was determined by gel permeation chromatography. The kinetics of LPS and lipid particle interactions were determined by using Biacore analysis. LBP and PLTP were found to transfer LPS from HDL predominantly to low-density lipoproteins (LDL), in a time- and dose-dependent manner, to induce remodeling of HDL into two subpopulations as a consequence of the LPS transfer and to enhance the steady-state association of LDL with HDL in a dose-dependent fashion. The presence of LPS on HDL further enhanced LBP-dependent interactions of LDL with HDL and increased the stability of the HDL-LDL complexes. We postulate that HDL remodeling induced by LBP- and PLTP-mediated LPS transfer may contribute to the plasma lipoprotein dyslipidemia characteristic of the acute-phase response to infection.

Figures

FIG. 1.

A representative example of chromatographic profiles showing the LBP-induced (A) and PLTP-induced (B) changes in cholesterol and LPS distribution in HDL, LDL, and VLDL. After the loading of HDL with LPS, the LPS fluorescence and cholesterol distribution among the lipoprotein subclasses were measured in the absence or presence of LBP or PLTP after 24 h of incubation.

FIG. 2.

Percent change (compared to the total signal) of LBP-dependent LPS transfer from HDL (A) to LDL and VLDL (B) at different LBP concentrations over time. Corrections were made for baseline differences (

FIG. 3.

Percent change (compared to the total signal) of PLTP-dependent LPS transfer from HDL (A) to LDL and VLDL (B) at different PLTP concentrations over time. Corrections were made for baseline differences in LPS distribution (

FIG. 4.

Sensorgrams representing immobilization of HDL by anti-ApoA-I coated on a CM-5 sensor chip (A). Immobilization of HDL was with 5,150 (line 1), 2,000 (line 2), and 580 (line 3) RU bound anti-ApoA-I antibody at a flow rate of 5 μl/min. (B) Capture of LPS by HDL at three different concentrations. HDL was immobilized with a 5,150-RU anti-ApoA-I. All sensorgrams were corrected for nonspecific background.

FIG. 5.

A representative example of the sensorgrams of LDL complexation with HDL in the absence (broken lines) or presence (solid lines) of LPS and the association of LDL with HDL in the absence (curves 1 and 3) or presence of LBP (curves 2 and 4). A second injection with anti-ApoB for LDL identification in the LDL-HDL complex is indicated by region B. All sensorgrams were corrected for nonspecific background.

FIG. 6.

Effects of LBP (A) and PLTP (B) on LDL complexation with HDL, measured by Biacore analysis. The average binding signals (RU) of the association of LDL with HDL or with HDL containing bound LPS in the presence of increasing concentrations of LBP or PLTP are shown. Data are presented as means ± standard errors of the means (error bars). The P values were calculated by using the analysis of variance test for repeated measures and are indicated in the graphs.