Huey R, Bloor C M, Kawahara M S, Hugli T E
Am J Pathol. 1983 Jul;112(1):48-60.
Carboxypeptidase N (EC 3.4.12.7) (SCPN) is a plasma enzyme that efficiently inactivates the anaphylatoxins C3a and C4a and significantly reduces C5a spasmogenic activity by removing the C-terminal arginyl residue from each of these factors. The arginine analog DL-2-mercaptomethyl-3-guanidinoethylthiopropanoic acid (SCPN-INH) is a potent competitive inhibitor of SCPN with a Ki for this carboxypeptidase in serum of 2 x 10(-9) M. Therefore, we have used the SCPN inhibitor to potentiate biologic activity of the anaphylatoxins in vivo. Infusion via the carotid artery of about 40 mg of SCPN-INH into each of 8 adult guinea pigs inactivated the SCPN for at least 3 hours and caused no measurable toxic effects. When cobra venom factor (CVF) is infused into guinea pigs, it activates the alternative pathway of complement, thereby generating the anaphylatoxins C3a and C5a. Ordinarily, infusion of CVF is nonlethal, because the generated anaphylatoxins are rapidly converted to C3a des Arg and C5a des Arg by SCPN. However, CVF (200 micrograms) plus SCPN-INH delivered intravenously in 5 animals induced a lethal reaction in less than 5 minutes. The authors conclude that the lethal effect is due largely to the anaphylatoxins. Histologic sections of the lungs from treated animals show dramatic structural changes consistent with peripheral small airway constriction, bronchial constriction, and vasoconstriction of small muscular arteries. Also, cell aggregates are present in blood vessels. Other histologic changes include severe congestion, pulmonary edema, and an interstitial infiltrate of mononuclear cells. Large doses of chlorpheniramine prevent this lethal reaction. Lethality is apparently attributable to asphyxia and is dependent on the level of CVF administered: eg, 100 micrograms CVF was not lethal in 4 animals given SCPN inhibitor, although signs of respiratory distress were observed. On histologic examination of lungs from guinea pigs given CVF and SCPN-INH, the features are similar to those described when anaphylatoxins are instilled into guinea pig lungs. Intravenous application of purified C3a plus SCPN-INH also proved lethal in 3 of the 6 animals challenged. This is the first evidence that the C3a anaphylatoxin can elicit a lethal response.
羧肽酶N（EC 3.4.12.7）（SCPN）是一种血浆酶，能有效使过敏毒素C3a和C4a失活，并通过去除这些因子中每个因子的C末端精氨酰残基，显著降低C5a的致痉挛活性。精氨酸类似物DL - 2 - 巯基甲基 - 3 - 胍基乙基硫代丙酸（SCPN - INH）是SCPN的一种强效竞争性抑制剂，其在血清中对该羧肽酶的Ki为2×10⁻⁹ M。因此，我们使用SCPN抑制剂来增强过敏毒素在体内的生物活性。通过颈动脉向8只成年豚鼠每只输注约40 mg的SCPN - INH，可使SCPN失活至少3小时，且未产生可测量的毒性作用。当将眼镜蛇毒因子（CVF）输注到豚鼠体内时，它会激活补体替代途径，从而产生过敏毒素C3a和C5a。通常情况下，输注CVF不会致死，因为产生的过敏毒素会被SCPN迅速转化为C3a des Arg和C5a des Arg。然而，在5只动物中静脉注射CVF（200微克）加SCPN - INH，在不到5分钟内就引发了致命反应。作者得出结论，这种致命效应主要归因于过敏毒素。经处理动物肺部的组织学切片显示出显著的结构变化，与外周小气道收缩、支气管收缩以及小肌性动脉血管收缩一致。此外，血管中存在细胞聚集。其他组织学变化包括严重充血、肺水肿和单核细胞间质浸润。大剂量氯苯那敏可预防这种致命反应。致死性显然归因于窒息，并且取决于所给予的CVF水平：例如，在给予SCPN抑制剂的4只动物中，100微克CVF并不致命，尽管观察到了呼吸窘迫的迹象。对给予CVF和SCPN - INH的豚鼠肺部进行组织学检查时，其特征与向豚鼠肺部滴注过敏毒素时所描述的特征相似。在6只接受挑战的动物中，静脉注射纯化的C3a加SCPN - INH在3只动物中也被证明是致命的。这是C3a过敏毒素可引发致命反应的首个证据。
