Plasma glutathione peroxidase by ELISA and relationship to selenium level

Background Many assays have investigated GPx activity but there are few reports of immunoreactive methods of GPx plasma determinations and their relationship with plasma selenium. Methods A cross-sectional analysis of selenium and GPx was carried out on 170 adults randomly selected from the electoral role. Blood samples were collected and analysed for plasma GPx using a commercial enzyme-linked immunosorbent assay (ELISA) kit and plasma selenium using magnetic sector ICP–MS. Further investigations of GPx level were carried out using one-dimensional (1D) and two-dimensional (2D) polyacrylamide gel electrophoresis (PAGE). Results Plasma GPx was associated with plasma Se level (r2 = 0.24, P < 0.0001). Mean (range) Se was 108.9 (67.4–268.0) ìg/l. Mean (range) plasma GPx was 18.5 (3.8–43.8) ìg/ml, significantly higher than the theoretical mean GPx of around 6.5–6.9 ìg/ml based on ICP–MS results and the proportion of Se in intact GPx. GPx was higher in males than females and lower in current than non-smokers and ex-smokers. PAGE analysis of glycine dissociated ELISA wells revealed GPx as well as a number of unknown proteins with significant variability between high and low GPx samples. Conclusions Plasma GPx is correlated with Se status, however, there is considerable GPx variability between patients and ELISA methods appear to significantly overestimate true plasma GPx.