Ogushi F, Fells G A, Hubbard R C, Straus S D, Crystal R G
Pulmonary Branch, National Heart, Lung, and Blood Institute, Bethesda, Maryland 20892.
J Clin Invest. 1987 Nov;80(5):1366-74. doi: 10.1172/JCI113214.
Alpha 1-antitrypsin (alpha 1AT) deficiency resulting from homozygous inheritance of the Z-type alpha 1AT gene is associated with serum alpha 1AT levels of less than 50 mg/dl and the development of emphysema in the third to fourth decades. Despite the overwhelming evidence that the emphysema of PiZZ individuals develops because of a "deficiency" of alpha 1AT and hence an insufficient antineutrophil elastase defense of the lung, epidemiologic evidence has shown that levels of alpha 1AT of only 80 mg/dl protect the lung from an increased risk of emphysema. With this background, we hypothesized that homozygous inheritance of the Z-type may confer an added risk beyond a simple deficiency of alpha 1AT by virtue of an inability of the Z-type alpha 1AT molecule to inhibit neutrophil elastase as effectively as the common M1-type molecule. To evaluate this hypothesis, the functional status of alpha 1AT from PiZZ individuals (n = 10) was compared with that of alpha 1AT from PiM1M1 individuals (n = 7) for its ability to inhibit neutrophil elastase (percent inhibition) as well as its association rate constant for neutrophil elastase (K association). Plasma alpha 1AT concentration, measured by radial immunodiffusion, was 34 +/- 1 mg/dl in PiZZ patients vs. 237 +/- 14 mg/dl for PiM1M1 plasma, a sevenfold difference. When titrated against neutrophil elastase, the present inhibition of PiZZ plasma was significantly less than Pi M1M1 plasma (ZZ 78 +/- 1% vs. M1M1 95 +/- 1%, P less than 0.001) as was purified Z type alpha 1AT (ZZ, 63 +/- 2% vs. M1M1 86 +/- 2%, P less than 0.001). Sodium dodecyl sulfate (SDS) gel comparisons of the complexes formed with M1-type alpha 1AT and Z-type alpha 1AT with elastase demonstrated the Z alpha 1AT-elastase complexes were less stable than the M1 alpha 1AT-elastase complexes, thus releasing some of the enzyme to continue to function as a protease. Consistent with these observations, the K association of purified Z-type alpha 1AT for neutrophil elastase was lower than that of M1-type alpha 1AT (ZZ 4.5 +/- 0.3 X 10(6) M-1s-1 vs. M1M1 9.7 +/- 0.4 X 10(6) M-1s-1, P less than 0.001), suggesting that for the population of alpha 1AT molecules, the active Z-type molecules take more than twice as long as the active M1-type alpha 1AT to inhibit neutrophil elastase. Consequently, not only is there less alpha1AT in PiZZ individuals, but the population of Z-type alpha1AT molecules is less competent as an inhibitor of neutrophil elastase than M1-type alpha1AT molecules. This combination of defects suggests that PiZZ individuals have far less functional antielastase protection than suggested by the reduced concentrations of alpha1AT alone, further explaining their profound risk for development of emphysema.
Z 型α1抗胰蛋白酶（alpha 1AT）基因纯合遗传导致的α1抗胰蛋白酶（alpha 1AT）缺乏与血清 alpha 1AT 水平低于 50mg/dl 以及三、四十岁时肺气肿的发生有关。尽管有压倒性的证据表明 PiZZ 个体的肺气肿是由于 alpha 1AT“缺乏”，从而导致肺部抗中性粒细胞弹性蛋白酶防御不足，但流行病学证据表明，仅 80mg/dl 的 alpha 1AT 水平就能保护肺部免受肺气肿风险增加的影响。在此背景下，我们推测 Z 型的纯合遗传可能会因 Z 型 alpha 1AT 分子抑制中性粒细胞弹性蛋白酶的能力不如常见的 M1 型分子，而在单纯的 alpha 1AT 缺乏之外带来额外风险。为了评估这一假设，将 PiZZ 个体（n = 10）的 alpha 1AT 与 PiM1M1 个体（n = 7）的 alpha 1AT 在抑制中性粒细胞弹性蛋白酶的能力（抑制百分比）以及与中性粒细胞弹性蛋白酶的结合速率常数（K 结合）方面的功能状态进行了比较。通过放射免疫扩散法测量，PiZZ 患者的血浆 alpha 1AT 浓度为 34±1mg/dl，而 PiM1M1 血浆为 237±14mg/dl，相差七倍。当用中性粒细胞弹性蛋白酶进行滴定测定时，PiZZ 血浆的当前抑制作用明显低于 Pi M1M1 血浆（ZZ 为 78±1%，而 M1M1 为 95±1%，P＜0.001），纯化的 Z 型 alpha 1AT 也是如此（ZZ 为 63±2%，而 M1M1 为 86±2%，P＜0.001）。用十二烷基硫酸钠（SDS）凝胶对与 M1 型 alpha 1AT 和 Z 型 alpha 1AT 形成的弹性蛋白酶复合物进行比较，结果表明 Z alpha 1AT - 弹性蛋白酶复合物不如 M1 alpha 1AT - 弹性蛋白酶复合物稳定，从而使一些酶得以释放并继续作为蛋白酶发挥作用。与这些观察结果一致，纯化的 Z 型 alpha 1AT 对中性粒细胞弹性蛋白酶的 K 结合低于 M1 型 alpha 1AT（ZZ 为 4.5±0.3×10⁶M⁻¹s⁻¹，而 M1M1 为 9.7±0.4×10⁶M⁻¹s⁻¹，P＜0.001），这表明对于 alpha 1AT 分子群体而言，活性 Z 型分子抑制中性粒细胞弹性蛋白酶所需的时间是活性 M1 型 alpha 1AT 的两倍多。因此，PiZZ 个体不仅 alpha1AT 含量较少，而且 Z 型 alpha1AT 分子群体作为中性粒细胞弹性蛋白酶抑制剂的能力也不如 M1 型 alpha1AT 分子。这种缺陷的组合表明，PiZZ 个体的功能性抗弹性蛋白酶保护远低于仅由 alpha1AT 浓度降低所表明的水平，这进一步解释了他们患肺气肿的高风险。
