Reconstituted high-density lipoprotein neutralizes gram-negative bacterial lipopolysaccharides in human whole blood

Antiinflammatory effects of reconstituted high-density lipoprotein during human endotoxemia

High-density lipoprotein (HDL) has been found to neutralize LPS activity in vitro and in animals in vivo. We sought to determine the effects of reconstituted HDL (rHDL) on LPS responsiveness in humans in a double-blind, randomized, placebo-controlled, cross-over study. rHDL, given as a 4-h infusion at 40 mg/kg starting 3.5 h before endotoxin challenge (4 ng/kg), reduced flu-like symptoms during endotoxemia, but did not influence the febrile response. rHDL potently reduced the endotoxin-induced release of TNF, IL-6, and IL-8, while only modestly attenuating the secretion of proinflammatory cytokine inhibitors IL-1ra, soluble TNF receptors and IL-10. In addition, rHDL attenuated LPS-induced changes in leukocyte counts and the enhanced expression of CD11b/CD18 on granulocytes. Importantly, rHDL infusion per se, before LPS administration, was associated with a downregulation of CD14, the main LPS receptor, on monocytes. This effect was biologically relevant, since monocytes isolated from rHDL-treated whole blood showed reduced expression of CD14 and diminished TNF production upon stimulation with LPS. These results suggest that rHDL may inhibit LPS effects in humans in vivo not only by binding and neutralizing LPS but also by reducing CD14 expression on monocytes.

Endotoxin and cytokines decrease serum levels and extra hepatic protein and mRNA levels of cholesteryl ester transfer protein in syrian hamsters

Endotoxin alters the metabolism of lipoproteins, including that of high density lipoprotein (HDL). Cholesteryl ester transfer protein (CETP) facilitates exchange of HDL cholesterol for very low density lipoprotein (VLDL) triglyceride, leading to catabolism of HDL. We investigated the effects of endotoxin and cytokines on CETP in Syrian hamsters. Endotoxin induced a rapid and progressive decrease in serum CETP levels, by 48 h CETP had decreased to < 20% of control levels. Endotoxin also decreased CETP mRNA and protein levels in adipose tissue, heart, and muscle, the tissues with highest levels of CETP mRNA, providing a plausible mechanism for the endotoxin-induced decrease in circulating CETP. Dexamethasone did not mimic the effects of endotoxin on CETP, but the combination of tumor necrosis factor and interleukin-1 did, indicating that these cytokines may in part mediate the effects of endotoxin on CETP. The endotoxin-induced decrease in CETP may help maintain HDL cholesterol levels during infection and inflammation when increased triglyceride levels could drive the exchange of HDL cholesteryl ester for VLDL triglyceride. Maintaining circulating HDL may be important because HDL protects against the toxic effects of endotoxin and provides cholesterol for peripheral cells involved in the immune response and tissue repair.

Low lipid concentrations in critical illness: implications for preventing and treating endotoxemia

OBJECTIVES

To determine the prevalence and clinical significance of hypolipidemia found in critically ill patients, and whether the addition of a reconstituted lipoprotein preparation could inhibit the generation of tumor necrosis factor-alpha (TNF-alpha) in acute-phase blood taken from these patients.

SETTING

Surgical intensive care unit (ICU) of a large urban university hospital.

DESIGN

Prospective case series.

PATIENTS

A total of 32 patients with a variety of critical illnesses had lipid and lipoprotein concentrations determined. Six patients and six age- and gender-matched control subjects had whole blood in vitro studies of the effect of lipoprotein on lipopolysaccharide mediated TNF-alpha production.

INTERVENTIONS

Blood samples were drawn on admission to the ICU and over a subsequent 8-day period.

MEASUREMENTS AND MAIN RESULTS

Mean serum lipid and lipoprotein values obtained from patients within 24 hrs of transfer to the surgical ICU were extremely low: mean total cholesterol was 117 mg/dL (3.03 mmol/L), low-density lipoprotein cholesterol 71 mg/dL (1.84 mmol/L), and high-density lipoprotein cholesterol 25 mg/dL (0.65 mmol/L). Only the mean triglyceride concentration of 105 mg/dL (1.19 mmol/L), and the mean lipoprotein(a) concentration of 25 mg/dL (0.25 g/L) were within the normal range. During the first 8 days following surgical ICU admission, there were trends toward increasing lipid and lipoprotein concentrations that were significant for triglycerides and apolipoprotein B. Survival did not correlate with the lipid or lipoprotein concentrations, but patients with infections had significantly lower (p = .008) high-density lipoprotein cholesterol concentrations compared with noninfected patients. Lipopolysaccharide-stimulated production of TNF-alpha in patient and control blood samples was completely suppressed by the addition of 2 mg/mL of a reconstituted high-density lipoprotein preparation.

CONCLUSIONS

Patients who are critically ill from a variety of causes have extremely low cholesterol and lipoprotein concentrations. Correction of the hypolipidemia by a reconstituted high-density lipoprotein preparation offers a new strategy for the prevention and treatment of endotoxemia.

Activation of human endothelial cells by viable or heat-killed gram-negative bacteria requires soluble CD14

In response to bacterial lipopolysaccharides (LPS; endotoxin), endothelial cells are converted to an activation phenotype expressing both proinflammatory and procoagulant properties that include the induction of leukocyte adhesion molecules and tissue factor expression. LPS-induced endothelial cell activation requires a soluble form of the monocyte LPS receptor, sCD14. We evaluated the capacity of multiple strains of gram-negative and gram-positive bacteria to induce endothelial E-selectin and tissue factor expression through sCD14-dependent pathways with cultured human umbilical vein endothelial cells (HUVE). Both viable and heat-killed gram-negative bacteria (Bacteroides fragilis, Enterobacter cloacae, Haemophilus influenzae, and Klebsiella pneumoniae) but not viable or heat-killed gram-positive bacteria (Staphylococcus aureus, Enterococcus faecalis, and Streptococcus pneumoniae) induced prominent E-selectin surface expression detected by enzyme-linked immunosorbent assay. Tissue factor activity on HUVE, indicated by factor X activation, was induced in response to gram-negative bacteria but not in response to gram-positive bacteria. Gram-negative bacteria induced transcriptional activation in HUVE, indicated by the appearance of E-selectin-specific mRNA and by the demonstration of activation of NF-kappa B, a trans-activating factor necessary for E-selectin and tissue factor gene transcription. In contrast, neither E-selectin mRNA nor activation of NF-kappa B was detected in HUVE treated with gram-positive bacteria. Endothelial cell activation by gram-negative bacteria in each of these assays was inhibited with a monoclonal antibody (60bd) against CD14. Furthermore, CHO-K1 cells, transfected with human recombinant CD14, responded to all strains of gram-negative bacteria (viable or heat killed), indicated by CHO-K1 NF-kappa B activation. We conclude that gram-negative bacteria induce endothelial cell activation through a common sCD14-dependent pathway.