Baker J R, Kylstra T A, Bigby T D
Department of Veterans Affairs Medical Center, San Diego, CA 92161, USA.
Biochem Pharmacol. 1995 Sep 28;50(7):905-12. doi: 10.1016/0006-2952(95)00210-q.
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.
人中性粒细胞白三烯A4（LTA4）水解酶是一种具有氨肽酶活性的含锌金属蛋白酶，可被某些金属蛋白酶抑制剂抑制。人气道上皮细胞也含有一种具有一些新特性的LTA4水解酶，这表明该酶在功能和结构上可能是独特的。因此，我们质疑上皮细胞是否是完整的或被破坏后进行研究的。在所检测的金属蛋白酶抑制剂中，只有卡托普利、贝司他汀和福辛普利拉对被破坏的上皮细胞中的LTA4水解酶具有明显的抑制活性。卡托普利、贝司他汀和福辛普利拉的浓度抑制曲线显示，对于被破坏细胞的LTA4水解酶活性，其IC50值分别为430微摩尔/升、7微摩尔/升和1毫摩尔/升。与其对中性粒细胞的作用相反，1,10 -邻菲啰啉对被破坏的上皮细胞水解酶活性没有显著影响，并且在该活性部分纯化（179倍）时只有最小的影响。用卡托普利、贝司他汀和1,10 -邻菲啰啉在完整细胞中检测的LTA4水解酶浓度抑制曲线显示，IC50值分别为63、7微摩尔/升和920微摩尔/升。被破坏的上皮细胞中的氨肽酶活性受到抑肽酶、贝司他汀和1,10 -邻菲啰啉的抑制（IC50值分别为500纳摩尔/升、1微摩尔/升和17微摩尔/升），但在最高测试浓度10毫摩尔/升的卡托普利作用下没有受到抑制。这些发现与之前在中性粒细胞中的研究结果相反。在用卡托普利处理后用A23187刺激中性粒细胞时，LTB4的跨细胞合成比白三烯B4（LTB4）的直接合成受到更有效的抑制（43.8±2.5%对18.5±4.7%；N = 8，P < 0.02）。我们得出结论，人气道上皮细胞的LTA4水解酶活性受到一些金属蛋白酶抑制剂的抑制，但抑制模式与中性粒细胞酶不同。这些数据提供了额外的信息，即上皮细胞中的LTA4水解酶是一种新型酶，与中性粒细胞中的酶不同。
