Fumio Furusaki

Automated Latex Photometric Immunoassay for Total Plasminogen Activator Inhibitor-1 in Plasma

Plasminogen activator inhibitor-1 (PAI-1) is a key regulator of the fibrinolytic system (1). The continuously high PAI-1 concentrations make fibrins resistant to dissolution by tissue-type plasminogen activator (tPA), which leads to multiorgan dysfunction and a bad prognosis in patients (2). Several methods have been developed for measuring the functional activity of PAI-1 in plasma samples based on the principle of adding a specified amount of tPA in excess of the PAI-1 and measuring residual tPA activity after a short incubation period (3). These methods, however, are neither completely specific nor accurate, and many other protease inhibitors in plasma inhibit tPA (4). Although several assays have also been described for PAI-1 antigen that are based on two-step enzyme immunoassays using monoclonal and/or polyclonal antibodies (5)(6), they have a narrow measurement range (0–40 μg/L) and are time-consuming (7). Because PAI-1 is a labile molecule, the utmost care is needed during blood collection and sample handling to ensure accurate measurement of PAI-1 and tPA. The half-life for the transformation from the active form of PAI-1 into the inactive latent form is ∼4 h in vitro and even shorter in vivo (8). It is therefore essential to correctly evaluate the amount of PAI-1 released from endothelial cells and adipose tissue (9) to make such methods clinically useful. We have developed a latex photometric immunoassay (LPIA) for total PAI-1 within a dynamic measurement range that can detect all forms of PAI-1 without the influence of conformational changes. Samples were obtained from 47 patients with myocardial infarction (29 men and 18 women) and 276 hospital employees, who volunteered for this study, as controls [100 men (age range, 23–63 years) and 168 women (age range, 21–57 years)]. After informed consent, blood samples were collected in a 1/10 volume of a solution containing 38 g/L sodium …