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Clinica chimica acta; international journal of clinical chemistry

A fast semi-quantitative LC-MS method for measurement of intact apolipoprotein A-I reveals novel proteoforms in serum.


PMID 25603406

Abstract

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. 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. 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. 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.