Structure and immunological function of oxidised albumin in lung cancer: its potential role as a biomarker of elevated oxidative stress

Abstract

The role of reactive oxygen species (ROS)-damaged human serum albumin (HSA) in lung cancer (LC) patients is investigated. The binding characteristics of LC antibodies with native and ROS-damaged HSA are assessed. Smoking and non-smoking LC patients (n=40) are examined by a direct binding enzyme-linked immunosorbent assay (ELISA) and the results are compared with healthy ageand gender-matched smoking and non-smoking subjects (n=38). A high degree of specific binding in approximately 70% of cancer immunoglobulin G (IgG) towards ROS-damaged HSA was observed, compared to results with its native analogue (P<0.05). Affinity purified IgG from those LC patients with a history of smoking showed substantially stronger binding to damaged HSA over native HSA. Competitive inhibition ELISA substantiated the enhanced recognition of ROS-HSA by circulating antibodies in LC patients. The increase in total serum protein carbonyl levels in the LC patients was largely due to an increase in oxidised albumin. Purified HSA from LC patients (LC-HSA) contained higher levels of carbonyls than did HSA from healthy subjects (normal-HSA; P<0.01). LC-HSA was conformationally altered and showed greater exposure of its hydrophobic regions. Collectively, the oxidation of plasma proteins, especially HSA, might enhance oxidative stress in LC patients.