An ELISA for apolipoprotein M reveals a strong correlation to total cholesterol in human plasma

Josefin Ahnström,Olof Axler,Björn Dahlbäck

doi:10.1194/jlr.m700113-jlr200

Abstract

Apolipoprotein M (apoM) is a 188 amino acid, 25 kDa protein belonging to the lipocalin protein superfamily. Although predominantly associated with high density lipoprotein, apoM is found in all major lipoprotein classes. To facilitate clinical studies of apoM, we have developed a sandwich ELISA for the measurement of apoM in human plasma. This method has been used to investigate normal apoM variation and to establish reference values for healthy individuals through the measurement of 598 samples from the Nordic Reference Interval Project Bio-bank and Database (NOBIDA) biobank. For women 18-49 years old, the reference interval for apoM was 0.58-1.18 micromol/l, whereas for women 50+ years and for men, the reference range was 0.61-1.30 micromol/l. Correlation studies of apoM with 26 common clinical chemical analytes from the NOBIDA database revealed a marked positive correlation with plasma total cholesterol (r = 0.52) and LDL and HDL cholesterol (r = 0.43 and 0.36, respectively). There was no statistically significant correlation with HDL/total cholesterol ratio or body mass index. In conclusion, a sandwich ELISA for the measurement of apoM in human plasma shows that apoM concentration is strongly correlated to total cholesterol in healthy individuals.

Highlights

Apolipoprotein M is a 188 amino acid, 25 kDa protein belonging to the lipocalin protein superfamily
The signal peptide remains uncleaved in the circulating protein, a feature that to our knowledge only has been described for two other plasma proteins, paraoxonase 1 and haptoglobin-related protein, both of which are lipoprotein-associated [7, 8]
ApoM was originally found in chylomicrons and is found in all major lipoprotein classes, the majority of Apolipoprotein M (apoM) is found in HDL in normal human and mouse plasma [4]

Summary

Introduction

Apolipoprotein M (apoM) is a 188 amino acid, 25 kDa protein belonging to the lipocalin protein superfamily. To facilitate clinical studies of apoM, we have developed a sandwich ELISA for the measurement of apoM in human plasma. This method has been used to investigate normal apoM variation and to establish reference values for healthy individuals through the measurement of 598 samples from the Nordic Reference Interval Project Bio-bank and Database (NOBIDA) biobank. A sandwich ELISA for the measurement of apoM in human plasma shows that apoM concentration is strongly correlated to total cholesterol in healthy individuals.—Axler, O., J. An ELISA for apolipoprotein M reveals a strong correlation to total cholesterol in human plasma. Overexpression of apoM in LDL receptor knockout mice protected against atherosclerosis when the mice were challenged with a cholesterol-enriched diet [9]

Methods

Results

Conclusion