SummaryHigh-density hpoprotein (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 ofproinflammatory cytokine inhibitors IL-lra, 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.T he systemic toxicity of Gram-negative sepsis is in large part mediated by endotoxin which induces an extensive inflammatory response characterized by cytokine release and activation of leukocytes. Once in the circulation, endotoxin is bound by lipopolysaccharide-binding protein (LBP) 1 which can transfer LPS to either cell-bound CD14 (causing activation of these cells), to soluble CD14 (facihtaring activation ofceUs not expressing CD14 on their surface), or to lipoproteins (1-7). Binding of LPS to lipoproteins results in inactivation of LPS (8-11). Preincubation of endotoxin with low-density lipoprotein (LDL), very-low density lipoprotein (VLDL) and chylomicrons reduced endotoxininduced lethality (12), whereas hypolipidemic animals were more sensitive to endotoxin (13). Further, transgenic mice with elevated apolipoprotein A-1 (apoA-1) and HDL levels are protected against LPS-induced mortality (14).The endotoxin-neutralizing capacity of lipoproteins is dependent on the lipid composition. Reconstituted human HDL (rHDL), containing purified apoA-1, phosphatidyl cho1Abbreviations used in this paper: apoA-1, apohpoprotein A-l; HDL, high-density hpoprotein; LBP, hpopolysaccharide-binding protein; LDL, low-density lipoprotein; rHDL, reconstituted human HDL; VLDL, very low-density lipoprotein.line and cholesterol, neutralized endotoxin in whole blood more effectively than LDL, VLDL, and natural HDL (15, 16). Pretreatment of animals with rHDL reduced endotoxininduced TNF production, leukopenia and lethality (17)(18)(19). The present study was designed to investigate the endotoxin-neutrahzing properties of rHDL (40 mg/kg) in humans in vivo. Materials and MethodsHuman Endotoxemia. Eight healthy male volunteers (mean age 24, range 20-28 yr) were enrolled in thi...

Abstract-To investigate the metabolism of nascent HDLs, apoA1/phosphatidylcholine (apoA1/PC) discs were infused IV over 4 hours into 7 healthy men. Plasma total apoA1 and phospholipid (PL) concentrations increased during the infusions. The rise in plasma apoA1 was greatest in small pre␤-migrating particles not present in the infusate. Total HDL unesterified cholesterol (UC) also increased simultaneously. After stopping the infusion, the concentrations of apoA1, PL, HDL UC, and small pre␤ HDLs decreased, whereas those of HDL cholesteryl ester (CE) and large ␣-migrating apoA1 containing HDLs increased. ApoB-containing lipoproteins became enriched in CEs. Addition of apoA1/PC discs to whole blood at 37°C in vitro also generated small pre␤ HDLs, but did not augment the transfer of UC from erythrocytes to plasma. We conclude that the disc infusions increased the intravascular production of small pre␤ HDLs in vivo, and that this was associated with an increase in the efflux and esterification of UC derived from fixed tissues. The extent to which the increase in tissue cholesterol efflux was dependent on that in pre␤ HDL production could not be determined. Infusion of discs also reduced the plasma apoB and apoA2 concentrations, and increased plasma triglycerides and apoC3.

SummaryHigh-density lipoproteins (HDL) can bind and neutralize lipopoly- saccharides (LPS) in vitro and in vivo. HDL can also affect fibrinolytic activity and can directly influence platelet function by reducing platelet aggregation. In this study, the effects of reconstituted HDL (rHDL) on LPS-induced coagulation, fibrinolysis and platelet activation in humans were investigated. In a double-blind, randomized, placebo-controlled, cross-over study, eight healthy male volunteers were injected with LPS (4 ng/kg) on two occasions, once in conjunction with rHDL (40 mg/kg, given as a 4 h infusion starting 3.5 h prior to LPS injection), and once in conjunction with placebo. rHDL significantly reduced LPS-induced activation of coagulation (plasma levels of prothrombin fragment F1+2) and fibrinolysis (plasma levels of tissue type plasminogen activator antigen, t-PA). No effect was observed on LPS-induced inhibition of the fibrinolytic pathway (PAI-1) or on the transient thrombocytopenia elicited by LPS. Furthermore, rHDL treatment significantly enhanced the inhibition of collagen-stimulated inhibition of platelet aggregation during endotoxemia, but had no such effect on arachido- nate-stimulated platelet aggregation. rHDL treatment per se also reduced collagen-induced platelet aggregation. These results indicate that rHDL modifies the procoagulant state associated with endotoxemia.

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