title: A fast semi-quantitative LC-MS method for measurement of intact apolipoprotein A-I reveals novel proteoforms in serum.
abstract: BACKGROUND
  Surrogate markers for reverse cholesterol transport (RCT) efficiency such as HDL cholesterol and immune methods for apolipoprotein A-I (ApoA-I) may not fully reflect the actual efficiency of the RCT pathway. Several genetic variants and different posttranslational proteoforms of ApoA-I may unevenly affect the functionality of the HDL particle to efflux cholesterol. A method employing top-down immunoaffinity LC-MS of ApoA-I in order to characterize the most prevalent ApoA-I proteoforms in human plasma is described.
  
  
  METHODS
  Diluted plasma was directly injected into a 2D LC-MS system consisting of an affinity column and an analytical column. Enriched ApoA-I fractions were introduced into the MS and intact or fragmented ApoA-I was analyzed.
  
  
  RESULTS
  ApoA-I as detected by the described LC-MS method distributes into at least 14 major potential proteoforms exceeding detection limit in human plasma. Substantial amounts of ApoA-I in plasma were found to occur as truncated, oxidized, glycated and glycosylated proteoforms. Levels of glycated ApoA-I distinguished significantly diabetic from non-diabetic samples. In addition novel truncated and glycosylated proteoforms were detected.
  
  
  CONCLUSIONS
  ApoA-I proteoforms measured by LC-MS represent a useful approach to augment the clinical picture of ApoA-I and its function in health and disease.
authors.affiliation: Unit of Clinical Chemistry, Department of Laboratory Medicine, Lund University, S-22185 Lund, Sweden.
authors.forename: M
authors.initials: M
authors.lastname: Gåfvels
authors.affiliation: Department of Clinical Chemistry, University Health Care, Region Skåne, S-22185 Lund, Sweden. Electronic address: per.bengtson@med.lu.se.
authors.forename: P
authors.initials: P
authors.lastname: Bengtson
mesh_terms: D016632:Apolipoprotein A-I / Q000097:blood* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001774:Blood Chemical Analysis / Q000379:methods*; D002853:Chromatography, Liquid; D006442:Glycated Hemoglobin / Q000378:metabolism; D006031:Glycosylation; D006801:Humans; D013058:Mass Spectrometry; D010084:Oxidation-Reduction; D020543:Proteome / Q000378:metabolism*; D017384:Sequence Deletion; D013997:Time Factors
chemical_list: D016632:Apolipoprotein A-I; D006442:Glycated Hemoglobin; D020543:Proteome; C517652:hemoglobin A1c protein, human
keywords: Apolipoprotein A-I; Glycation; Glycosylation; Mass spectrometry; Truncation