Oxidized LDL is stable in human serum under extended thawed-state conditions ranging from −20 °C to room temperature

Introduction

Oxidized LDL (oxLDL) is formed by the spontaneous reaction between aldehyde byproducts of lipid peroxidation and lysine residues of apolipoprotein B within LDL. Clinically, oxLDL is used as a marker of coronary artery disease and predictor of metabolic syndrome risk. Despite its popularity as a clinical marker, no systematic studies of oxLDL stability, in which serum or plasma has been pre-analytically exposed to an array of different time and temperature conditions, have been carried out.

Objective

To systematically evaluate the stability of oxLDL in human serum samples exposed to thawed conditions (> −30 °C) for varying periods of time while monitoring a second protein/small molecule redox system as a positive control for non-enzymatic biomolecular activity.

Methods

OxLDL was measured in serum samples, from 24 different humans, that had been pre-exposed to three different time courses at 23 °C, 4 °C and −20 °C using ELISA kits from Mercodia that employ the 4E6 mouse monoclonal antibody. A liquid chromatography/mass spectrometry-based marker of serum exposure to thawed conditions known as ΔS-Cys-Albumin was employed as a positive control.

Results

OxLDL was stable in serum exposed to 23 °C for up to 48 h, 4 °C for 21 days, or −20 °C for 65 days. ΔS-Cys-Albumin changed dramatically during these time courses (p < 0.001).

Conclusions

OxLDL is remarkably stable ex vivo in human serum samples exposed to thawed conditions.