Vol. 291, Issue 2, 517-523, November 1999

Inhibitors of Chymase as Mast Cell-Stabilizing Agents: Contribution of Chymase in the Activation of Human Mast Cells¹

Shaoheng He, Marianna D. A. Gaça, Alan R. McEuen and Andrew F. Walls

Immunopharmacology Group, University of Southampton, Southampton General Hospital, Southampton, United Kingdom

There has long been evidence that inhibitors of chymotryptic proteinases can inhibit the degranulation of rodent mast cells, but their actions on human mast cells and the contribution of mast cell chymase itself have received little attention. We investigated the ability of the selective chymase inhibitor Z-Ile-Glu-Pro-Phe-CO₂Me and other proteinase inhibitors to inhibit chymase and cathepsin G activity, and we examined their potential to modulate the responsiveness of mast cells dispersed from human skin, lung, and tonsil tissues. IgE-dependent histamine release from skin mast cells was inhibited by up to about 80% after preincubation with Z-Ile-Glu-Pro-Phe- CO₂Me (up to 0.1 µM), 70% with chymostatin (17 µM), and 60% with soybean trypsin inhibitor (0.5 µM). The mast cell-stabilizing properties of chymase inhibitors appeared to be greater for skin mast cells than for those from lung, whereas tonsil mast cells were relatively unresponsive. There were marked differences in the time course of responses to inhibitors, and the effect was dependent on the stimulus, with calcium ionophore-induced histamine release being unaffected. Incubation of dispersed skin, lung, or tonsil cells for up to 45 min with purified chymase failed to induce histamine release, although preincubation of cells with chymase was able to suppress IgE-dependent activation. Chymase could thus contribute to mast cell degranulation and after secretion could provide a feedback mechanism to limit this process. Nevertheless, inhibitors of chymase can be potent mast cell stabilizers, particularly in the skin.