RESUMO
Human neutrophil leukotriene A4 (LTA4) hydrolase is a zinc-containing metalloproteinase with aminopeptidase activity and can be inhibited by some metalloproteinase inhibitors. Human airway epithelial cells also contain an LTA4 hydrolase enzyme that has some novel properties, suggesting that this enzyme may be functionally and structurally unique. Thus, we questioned whether the epithelial cells were studied either intact or disrupted. Of the metalloproteinase inhibitors examined, only captopril, bestatin, and fosinoprilat had appreciable inhibitory activity for LTA4 hydrolase in disrupted epithelial cells. Concentration-inhibition curves to captopril, bestatin, and fosinoprilat revealed IC50 values of 430 microM, 7 microM, and 1 mM, respectively, for disrupted-cell LTA4 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). LTA4 hydrolase concentration-inhibition curves examined in intact cells with captopril, bestatin, and 1,10-O-phenanthroline revealed IC50 values of 63, 70, and 920 microM, respectively. Aminopeptidase activity in disrupted epithelial cells was inhibited by amastatin, bestatin, and 1,10-O-phenanthroline (IC50 values of 500 nM, 1 microM, and 17 microM, 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 LTB4 was inhibited more effectively than direct synthesis of leukotriene B4 (LTB4) (43.8 +/- 2.5 vs 18.5 +/- 4.7%; N = 8, P < 0.02). We conclude that LTA4 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 LTA4 hydrolase in the epithelial cell is a novel enzyme, distinct from that found in the neutrophil.