Serum amyloid P component prevents high-density lipoprotein-mediated neutralization of lipopolysaccharide.
Lipopolysaccharide (LPS) is an amphipathic macromolecule that is highly aggregated in aqueous preparations. LPS-binding protein (LBP) catalyzes the transfer of single LPS molecules, segregated from an LPS aggregate, to high-density lipoproteins (HDL), which results in the neutralization of LPS. When fluorescein isothiocyanate-labeled LPS (FITC-LPS) is used, this transfer of LPS monomers to HDL can be measured as an increase in fluorescence due to dequenching of FITC-LPS. Recently, serum amyloid P component (SAP) was shown to neutralize LPS in vitro, although only in the presence of low concentrations of LBP. In this study, we show that SAP prevented HDL-mediated dequenching of FITC-LPS, even in the presence of high concentrations of LBP. Human bactericidal/permeability-increasing protein (BPI), a very potent LPS-binding and -neutralizing protein, also prevented HDL-mediated dequenching of FITC-LPS. Furthermore, SAP inhibited HDL-mediated neutralization of both rough and smooth LPS in a chemiluminescence assay quantifying the LPS-induced priming of neutrophils in human blood. SAP bound both isolated HDL and HDL in serum. Using HDL-coated magnetic beads prebound with SAP, we demonstrated that HDL-bound SAP prevented the binding of LPS to HDL. We suggest that SAP, by preventing LPS binding to HDL, plays a regulatory role, balancing the amount of LPS that, via HDL, is directed to the adrenal glands.
de Haas
C J
CJ
Department of Inflammation, Eijkman Winkler Institute, University Medical Center, 3584CX Utrecht, The Netherlands. c.j.c.dehaas@lab.azu.nl
Poppelier
M J
MJ
van Kessel
K P
KP
van Strijp
J A
JA
D016632:Apolipoprotein A-I / Q000378:metabolism; D016650:Fluorescein-5-isothiocyanate; D006801:Humans; D008070:Lipopolysaccharides / Q000378:metabolism*; D008075:Lipoproteins, HDL / Q000378:metabolism*; D008163:Luminescent Measurements; D000683:Serum Amyloid P-Component / Q000378:metabolism / Q000494:pharmacology*
D016632:Apolipoprotein A-I; D008070:Lipopolysaccharides; D008075:Lipoproteins, HDL; D000683:Serum Amyloid P-Component; D016650:Fluorescein-5-isothiocyanate