Quantitative pharmacokinetic evaluation of Subtilisin QK-2 after a bolus IV injection in a rat model using a novel sandwich enzyme-linked immunosorbent assay

Abstract

Intravascular thrombosis is a main cause of multiple cardiovascular diseases. A high thrombolytic activity of the microbial fibrinolytic enzyme Subtilisin QK-2, which is highly homologous to Nattokinase, shows great exploitable potential in thrombolytic therapy. However, the lack of a sensitive detection method limits the further analysis of Subtilisin QK-2 in vivo. We prepared a polyclonal antibody and four monoclonal antibodies (IgG1, titers of 1:500,000) to establish a sensitive sandwich ELISA for Subtilisin QK-2 detection. The limit of detection (LOD) of this ELISA was 1.160 ng/mL. The linear range of the standard curve was 1.96−250 ng/mL (R2 = 0.9912). The cut-off value was 0.236. Subsequently, a pharmacokinetic dose (IV bolus) was administered and analyzed with the established ELISA. The concentration-time profiles were best fitted to a two-compartment model. T1/2α values for doses of 2 mg/kg, 4 mg/kg, and 8 mg/kg were 29.90 ± 10.02 min, 27.17 ± 1.96 min, and 21.83 ± 9.95 min, and T1/2β values were 144.43 ± 49.73 min, 173.46 ± 52.58 min, and 159.49 ± 48.75 min, respectively. Subtilisin QK-2 was eliminated through a mechanism with first-order kinetics. In conclusion, this study provides useful data for further research and clinical applications of Subtilisin QK-2 in the treatment of cardiovascular diseases.