Effects of metalloproteinase inhibitors on leukotriene A 4 hydrolase in human airway epithelial cells

Abstract

Human neutrophil leukotriene A 4 (LTA 4) hydrolase is a zinc-containing metalloproteinase with aminopeptidase activity and can be inhibited by some metalloproteinase inhibitors. Human airway epithelial cells also contain an LTA 4 hydrolase enzyme that has some novel properties, suggesting that this enzyme may be functionally and structurally unique. Thus, we questioned whether the epithelial enzyme could also be inhibited by metalloproteinase inhibitors. Transformed human airway epithelial cells were studied either intact or disrupted. Of the metalloproteinase inhibitors examined, only captopril, bestatin, and fosinoprilat had appreciable inhibitory activity for LTA 4 hydrolase in disrupted epithelial cells. Concentration-inhibition curves to captopril, bestatin, and fosinoprilat revealed ic 50 values of 430 μM, 7 μM, and 1 mM, respectively, for disrupted-cell LTA 4 hydrolase activity. In contrast to its effects on neutrophils, 1,10- O-phenanthroline had no significant effect on disrupted epithelial cell hydrolase activity and had only minimal effects when this activity was partially purified (179-fold). LTA 4 hydrolase concentration-inhibition curves examined in intact cells with captopril, bestatin, and 1,10- O-phenanthroline revealed ic 50 values of 63, 70, and 920 μM, respectively. Aminopeptidase activity in disrupted epithelial cells was inhibited by amastatin, bestatin, and 1,10- O-phenanthroline ( ic 50 values of 500 nM, 1 μM, and 17 μM, respectively), but not by captopril at the highest concentration tested, 10 mM. These findings are in contrast to prior studies in neutrophils. When neutrophils were stimulated with A23187 after treatment with captopril, transcellular synthesis of LTB 4 was inhibited more effectively than direct synthesis of leukotriene B 4 (LTB 4) (43.8 ± 2.5 vs 18.5 ± 4.7%; N = 8, P < 0.02). We conclude that LTA 4 hydrolase activity of human airway epithelial cells is inhibited by some metalloproteinase inhibitors, but that the profile of inhibition is distinct from that for the neutrophil enzyme. These data provide additional information that LTA 4 hydrolase in the epithelial cell is a novel enzyme, distinct from that found in the neutrophil.