Ischaemia modified albumin (IMA) is a recently developed biomarker of transient myocardial ischaemia.¹ Circulating IMA is increased in patients with myocardial ischaemia, after percutaneous coronary intervention,^2,3 or in acute coronary syndromes.⁴ The test has recently been licensed by the US Food and Drug Administration for diagnostic use in suspected myocardial ischaemia. IMA is serum albumin in which the N-terminus has been chemically modified. The diagnostic albumin Co²⁺ binding (ACB) test is based for IMA on the observation that the affinity of serum albumin for Co²⁺ is reduced after N-terminus modifications. It has been proposed that reactive oxygen species (ROS) such as superoxide (^•O₂⁻) and hydroxyl (^•OH) radicals generated during myocardial ischaemia–reperfusion modify the N-terminus of serum albumin resulting in IMA formation but, so far, direct evidence to support this is scarce. We hypothesised that ROS generation causes the formation of IMA. Our objective was to model the formation of IMA in vitro by using chemically generated ROS and the ^•OH radical scavenger mercaptopropionylglycine (MPG).

MATERIALS AND METHODS

All reagents were obtained from Sigma-Aldrich (Poole, Dorset, UK) and normal human serum from the North London Transfusion Service (London, UK). Serum pH was 7.35–7.45 at 37°C and was unaltered by any of the reactants during the 15 minute experimental time course. Five millilitre serum aliquots (eight replicate experiments per group) were randomly selected for the following incubations for 15 minutes at 37°C. Group 1, peroxide treated (H₂O₂): serum was incubated with H₂O₂ 100 μM. Group 2, superoxide treated (^•O₂⁻): serum was incubated with a xanthine-xanthine oxidase ^•O₂⁻ generating system consisting of 100 μM xanthine plus 0.05 U/ml xanthine …