Journal of Lipid Research, Vol 29, 77-84, Copyright © 1988 by Lipid Research, Inc.
Enzyme-linked immunosorbent assay for human proapolipoprotein A-I using specific antibodies against synthetic peptide
A Barkia, C Martin, P Puchois, JC Gesquiere, C Cachera, A Tartar and JC Fruchart
SERLIA, Institut Pasteur, Lille, France.
Apolipoprotein A-I (apoA-I), the major protein component of human high
density lipoprotein, appears intracellularly as an intermediate precursor
(proapoA-I) with a hexapeptide extension (Arg-His-Phe-Trp-Gln- Gln) at its
amino terminus. To investigate the regulation of processes that regulate
plasma apoA-I levels, a sensitive and simple assay for proapoA-I is
required. We describe a specific enzyme-linked immunosorbent assay (ELISA)
for quantification of proapoA-I using monospecific rabbit antibodies raised
against the peptide: Arg-His-Phe- Trp-Gln-Gln-Asp-Glu-Pro. The
monospecificity of antibodies to propeptide has been checked and no
cross-reaction with mature apoA-I has been found although three first
mature apoA-I amino acids (Asp-Glu- Pro) were included in the immunizing
peptide. The assay is a non- competitive sandwich ELISA in which
polystyrene microtiter plates were used with antibodies to propeptide
adsorbed on the wells. After incubation with plasma samples, the bound
proapoA-I was revealed by labeled rabbit polyclonal antibodies directed
against mature apoA-I. The working range was 10 to 100 ng/ml, recovery of
proapoA-I added to plasma was 94.6 to 106.5%, and the intra- and interassay
coefficients of variation were 3.8% and 7.9%, respectively. A delipidation
step using diisopropylether-n-butanol was necessary to expose antigen sites
of proapoA-I in native lipoproteins. Mean level of proapoA-I in normal
subjects was 87 +/- 15 micrograms/ml. It represented 7.1% of total apoA- I
while in Tangier serum it represented 29%.