Regulation of Complement and Contact System Activation via C1 Inhibitor Potentiation and Factor XIIa Activity Modulation by Sulfated Glycans – Structure-Activity Relationships

The serpin C1 inhibitor (C1-INH) is the only regulator of classical complement activation as well as the major regulator of the contact system. Its importance is demonstrated by hereditary angioedema (HAE), a severe disease with potentially life-threatening attacks due to deficiency or dysfunction of C1-INH. C1-INH replacement is the therapy of choice in HAE. In addition, C1-INH showed to have beneficial effects in other diseases characterized by inappropriate complement and contact system activation. Due to some limitations of its clinical application, there is a need for improving the efficacy of therapeutically applied C1-INH or to enhance the activity of endogenous C1-INH. Given the known potentiating effect of heparin on C1-INH, sulfated glycans (SG) may be such candidates. The aim of this study was to characterize suitable SG by evaluating structure-activity relationships. For this, more than 40 structurally distinct SG were examined for their effects on C1-INH, C1s and FXIIa. The SG turned out to potentiate the C1s inhibition by C1-INH without any direct influence on C1s. Their potentiating activity proved to depend on their degree of sulfation, molecular mass as well as glycan structure. In contrast, the SG had no effect on the FXIIa inhibition by C1-INH, but structure-dependently modulated the activity of FXIIa. Among the tested SG, β-1,3-glucan sulfates with a Mr ≤ 10 000 were identified as most promising lead candidates for the development of a glycan-based C1-INH amplifier. In conclusion, the obtained information on structural characteristics of SG favoring C1-INH potentiation represent an useful elementary basis for the development of compounds improving the potency of C1-INH in diseases and clinical situations characterized by inappropriate activation of complement and contact system.

丝氨酸蛋白酶抑制剂（serpin）家族的C1抑制因子（C1-INH）是经典补体激活通路的唯一调控因子，同时也是接触系统的主要调控因子。遗传性血管性水肿（hereditary angioedema, HAE）正是其生理功能重要性的直观佐证：该疾病为重症病症，可引发危及生命的急性发作，致病机制为C1-INH的缺乏或功能异常。目前，C1-INH替代疗法是HAE的首选治疗方案。此外，C1-INH在其他以补体与接触系统异常激活为特征的疾病中也展现出了显著的治疗获益。但由于其临床应用存在诸多局限，亟需优化治疗性C1-INH的药效，或增强内源性C1-INH的活性。鉴于肝素对C1-INH已知的增强活性，硫酸化聚糖（sulfated glycans, SG）有望成为此类调控分子的候选对象。本研究旨在通过构效关系分析，对具备应用潜力的SG进行系统性表征。为此，研究团队针对40余种结构各异的SG，检测其对C1-INH、补体C1s蛋白酶（C1s）及凝血因子XIIa（FXIIa）的调控作用。实验结果表明，SG可增强C1-INH对C1s的抑制活性，且不会对C1s产生直接的独立影响。进一步研究证实，SG的增强活性与其硫酸化程度、分子量及聚糖结构三者密切相关。与之形成对比的是，SG不会影响C1-INH对FXIIa的抑制活性，但可通过结构依赖性方式调控FXIIa自身的酶活性。在本次检测的SG中，分子量≤10000的β-1,3-葡聚糖硫酸酯被认定为开发基于聚糖的C1-INH增强剂的最具潜力的先导化合物。综上，本研究明确了可增强C1-INH活性的SG结构特征，为开发能够提升C1-INH药效的化合物提供了坚实的理论基础，可用于治疗补体与接触系统异常激活相关的各类疾病及临床场景。