Protease inhibitors (gebexate mesylate and ulinastatin) stimulate intracellular chemiluminescence in human neutrophils.

The effect of protease inhibitors on the intracellular production of free radicals was investigated by measuring chemiluminescence (CL) elicited from phagocytosed luminol-bound microspheres (Lumispheres) in human neutrophils stimulated with formylmethionyl-leucyl-phenylalanine (fMLP), interleukin-8 (IL-8), phorbol 12-myristate 13-acetate, or diacylglycerol. Both gabexate mesylate (Foy) and ulinastatin (Miraclid), urinary trypsin inhibitor, increased intracellular CL in a dose dependent manner. Compared to control buffer without protease inhibitor, gabexate mesylate (322 micrograms/ml) caused about a 10-fold increase in intracellular CL in stimulated neutrophils, and ulinastatin (3100 U/ml) a twofold increase in neutrophils stimulated with fMLP or IL-8. When the protease inhibitors were added to the cell suspension after the phagocytosis of lumispheres, CL responses rapidly increased again to the level which was observed when both protease inhibitors and neutrophil stimulants were incubated simultaneously. In contrast, extracellular release of oxygen metabolites from stimulated neutrophils, assayed by a conventional measurement of luminol-dependent CL, was reduced by the protease inhibitors in a dose dependent fashion. When luminol-unbound microspheres were incubated with neutrophils stimulated by fMLP in luminol solution, extracellular CL was almost completely inhibited by gabexate mesylate. These results indicate that the protease inhibitors enhance the generation of intracellular CL and suppress the extracellular release of free radicals.