Mechanism of the inhibitory effect of protease inhibitor on tumor necrosis factor α production of monocytes

If the inflammatory response becomes excessive or uncontrolled by some stimuli, inappropriate inflammatory responses occur. Monocytes are extremely important cells for regulating the cytokine network and tumor necrosis factor alpha (TNF alpha) and interleukin- (IL) 10, which are mainly synthesized by monocytes, are representative cytokines that play a central role in the cytokine network. Protease inhibitors such as gabexate mesilate (GM) and ulinastatin (UTI) have been shown to have various beneficial effects by inhibiting the activation of leukocytes, but the mechanism for this has yet to be fully elucidated. In this study we investigated the mechanism of the inhibitory effect of protease inhibitors on the proinflammatory cytokine production of lipopolysaccharide- (LPS) stimulated monocytes. LPS-stimulated monocytes were treated with G M or UTI, The value of TNF alpha and IL-10 in the cultu re medium of monocytes was measured and each mRNA expression was assayed. The inhibitory effect of protease inhibitors on the activity of intracellular signal transduction pathways such as protein kinase C (PKC) and nuclear factor kappa B (NFkappaB) were also evaluated. GM decreased the TNF alpha production of LPS-stimulated monocytes as shown by the inhibition of mRNA expression and increased the IL-10 production of LPS-stimulated monocytes. GM also suppressed the NFkappaB activity of LPS-stimulated monocytes. UTI decreased the TNF alpha production of LPS-stimulated monocytes, but did not inhibit the TN For m RNA expression. The present study shows that the inhibitory effect of GM on the TNF alpha production of activated human monocytes is mediated by the suppression of NFkappaB activation, while the mechanism of UTI inhibiting TNF alpha production of human monocytes may be due to the inhibition of either the translation or secretion of TNF alpha.