Wallace E M, Perkins S J, Sim R B, Willis A C, Feighery C, Jackson J
Department of Immunology, St. James' Hospital, Dublin, Ireland.
Mol Med. 1997 Jun;3(6):385-96.
A correct balance between protease and inhibitor activity is critical in the maintenance of homoeostasis; excessive activation of enzyme pathways is frequently associated with inflammatory disorders. Plasmin is an enzyme ubiquitously activated in inflammatory disorder, and C1-inhibitor (C1-Inh) is a pivotal inhibitor of protease activity, which is particularly important in the regulation of enzyme cascades generated in plasma. The nature of the interaction between plasmin and C1-Inh is poorly understood.
C1-Inh was immunoadsorbed from the plasma of normal individuals (n = 21), from that of patients with systemic lupus erythematosus (n = 18) or adult respiratory distress syndrome (n = 9), and from the plasma and synovial fluid of patients with rheumatoid arthritis (n = 18). As plasmin is a putative enzyme responsible for C1-Inh was examined using SDS-PAGE. In addition, peptides cleaved from C1-Inh by plasmin were isolated and sequenced and the precise cleavage sites determined from the known primary sequence of C1-Inh. Homology models of C1-Inh were then constructed.
Increased levels of cleaved and inactivated C1-Inh were found in each of the inflammatory disorders examined. Through SDS-PAGE analysis it was shown that plasmin rapidly degraded C1-Inh in vitro. The pattern of C1-Inh cleavage seen in vivo in patients with inflammatory disorders and that produced in vitro following incubation with plasmin were very similar. Homology models of C1-Inh indicate that the majority of the plasmin cleavage sites are adjacent to the reactive site of the inhibitor.
This study suggests that local C1-Inh degradation by plasmin may be a central and critical event in the loss of protease inhibition during inflammation. These findings have important implications for our understanding of pathogenic mechanisms in inflammation and for the development of more effectively targeted therapeutic regimes. These findings may also explain the efficacy of anti-plasmin agents in the treatment of C1-Inh deficiency states, as they may diminish plasmin-mediated C1-Inh degradation.
蛋白酶与抑制剂活性之间的正确平衡对于维持体内稳态至关重要；酶途径的过度激活常与炎症性疾病相关。纤溶酶是一种在炎症性疾病中普遍被激活的酶，而C1抑制剂（C1-Inh）是蛋白酶活性的关键抑制剂，在调节血浆中产生的酶级联反应中尤为重要。纤溶酶与C1-Inh之间相互作用的本质尚不清楚。
从正常个体（n = 21）、系统性红斑狼疮患者（n = 18）或成人呼吸窘迫综合征患者（n = 9）的血浆中，以及类风湿性关节炎患者（n = 18）的血浆和滑液中免疫吸附C1-Inh。由于纤溶酶是一种可能负责……的酶，使用SDS-PAGE对C1-Inh进行检测。此外，分离并测序纤溶酶从C1-Inh切割产生的肽段，并根据C1-Inh已知的一级序列确定精确的切割位点。然后构建C1-Inh的同源模型。
在所检测的每种炎症性疾病中均发现裂解和失活的C1-Inh水平升高。通过SDS-PAGE分析表明，纤溶酶在体外能迅速降解C1-Inh。炎症性疾病患者体内观察到的C1-Inh裂解模式与纤溶酶孵育后体外产生的模式非常相似。C1-Inh的同源模型表明，大多数纤溶酶切割位点与抑制剂的反应位点相邻。
本研究表明，纤溶酶对局部C1-Inh的降解可能是炎症过程中蛋白酶抑制丧失的核心关键事件。这些发现对我们理解炎症的致病机制以及开发更有效的靶向治疗方案具有重要意义。这些发现还可能解释抗纤溶酶药物在治疗C1-Inh缺乏状态中的疗效，因为它们可能减少纤溶酶介导的C1-Inh降解。
