title: High-density lipoprotein proteome dynamics in human endotoxemia.
abstract: BACKGROUND
  A large variety of proteins involved in inflammation, coagulation, lipid-oxidation and lipid metabolism have been associated with high-density lipoprotein (HDL) and it is anticipated that changes in the HDL proteome have implications for the multiple functions of HDL. Here, SELDI-TOF mass spectrometry (MS) was used to study the dynamic changes of HDL protein composition in a human experimental low-dose endotoxemia model. Ten healthy men with low HDL cholesterol (0.7+/-0.1 mmol/L) and 10 men with high HDL cholesterol levels (1.9+/-0.4 mmol/L) were challenged with endotoxin (LPS) intravenously (1 ng/kg bodyweight). We previously showed that subjects with low HDL cholesterol are more susceptible to an inflammatory challenge. The current study tested the hypothesis that this discrepancy may be related to differences in the HDL proteome.
  
  
  RESULTS
  Plasma drawn at 7 time-points over a 24 hour time period after LPS challenge was used for direct capture of HDL using antibodies against apolipoprotein A-I followed by subsequent SELDI-TOF MS profiling. Upon LPS administration, profound changes in 21 markers (adjusted p-value < 0.05) were observed in the proteome in both study groups. These changes were observed 1 hour after LPS infusion and sustained up to 24 hours, but unexpectedly were not different between the 2 study groups. Hierarchical clustering of the protein spectra at all time points of all individuals revealed 3 distinct clusters, which were largely independent of baseline HDL cholesterol levels but correlated with paraoxonase 1 activity. The acute phase protein serum amyloid A-1/2 (SAA-1/2) was clearly upregulated after LPS infusion in both groups and comprised both native and N-terminal truncated variants that were identified by two-dimensional gel electrophoresis and mass spectrometry. Individuals of one of the clusters were distinguished by a lower SAA-1/2 response after LPS challenge and a delayed time-response of the truncated variants.
  
  
  CONCLUSIONS
  This study shows that the semi-quantitative differences in the HDL proteome as assessed by SELDI-TOF MS cannot explain why subjects with low HDL cholesterol are more susceptible to a challenge with LPS than those with high HDL cholesterol. Instead the results indicate that hierarchical clustering could be useful to predict HDL functionality in acute phase responses towards LPS.
authors.affiliation: Department of Experimental Vascular Medicine, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands. h.levels@amc.uva.nl.
authors.forename: Johannes Hm
authors.initials: JH
authors.lastname: Levels
authors.forename: Pierre
authors.initials: P
authors.lastname: Geurts
authors.forename: Helen
authors.initials: H
authors.lastname: Karlsson
authors.forename: Raphaël
authors.initials: R
authors.lastname: Marée
authors.forename: Stefan
authors.initials: S
authors.lastname: Ljunggren
authors.forename: Louise
authors.initials: L
authors.lastname: Fornander
authors.forename: Louis
authors.initials: L
authors.lastname: Wehenkel
authors.forename: Mats
authors.initials: M
authors.lastname: Lindahl
authors.forename: Erik Sg
authors.initials: ES
authors.lastname: Stroes
authors.forename: Jan A
authors.initials: JA
authors.lastname: Kuivenhoven
authors.forename: Joost Cm
authors.initials: JC
authors.lastname: Meijers