Immunopharmacology and InflammationNew properties of the soybean trypsin inhibitor: Inhibition of human neutrophil elastase and its effect on acute pulmonary injury

Seeds from legumes including the Gilcine max are known to be a rich source of protease inhibitors. The soybean Kunitz trypsin inhibitors (SKTIs) have been well characterised and have been found to exhibit many biological activities. However their effects on inflammatory diseases have not been studied to date. In this study, SKTI was purified using anion exchange chromatography using a Resource Q column. The purified protein was able to inhibit human neutrophil elastase (HNE) and bovine trypsin. Purified SKTI inhibited HNE with an IC50 value of 8 μg or 0.3 nM. At this concentration SKTI showed neither cytotoxic nor haemolytic effects on human blood cell populations. SKTI showed no deleterious effects on organs, blood cells or the hepatic enzymes ALT and AST in the mouse model of acute systemic toxicity. Human neutrophils incubated with SKTI released less HNE than control neutrophils when stimulated with PAF or fMLP (83.1% and 70% respectively). These results showed that SKTI affected both pathways of elastase release by PAF and fMLP stimuli, suggesting that SKTI is an antagonist of fMLP/PAF receptors. In an in vivo mouse model of LPS acute lung injury, SKTI significantly suppressed the inflammatory effects caused by elastase in a dose-dependent manner. Histological sections stained by hematoxylin/eosin confirmed this decrease in inflammation. These results showed that SKTI could be used as a pharmacological agent for the therapy of many inflammatory diseases.