C1-inhibitor--biochemical properties and clinical applications

C1-inhibitor (C1-INH) is an alpha-2-neuraminoglycoprotein with a molecular weight of 105,000 daltons. It has a broad spectrum control of the many blood cascades including the complement system. Inherited deficiency of this molecule has been associated with the development of hereditary angioneurotic edema (HANE), a dominant genetic disorder. The liver and monocytes are the primary sites of C1-INH synthesis. The genetic basis of dysfunctional C1-INH is a defect at the structural locus for one C1-INH gene; both the dysfunctional C1-INH gene and the normal C1-INH gene products are present in the plasma of the affected person. The absence of C1-INH permits spontaneous activation of the first component of the complement system (C1); this, in turn, activates C4 and C2. A kinin derived from C2 may be elaborated, which then increases vascular permeability. However, recent investigations have indicated that kinin activity generated from C1-INH-depleted plasma is not derived from C2 but implicates kallikrein, an enzyme which is also controlled by C1-INH, in the formation of a kinin which is most probably bradykinin. A number of therapeutic approaches have been used to treat HANE patients, including antifribrinolytic drugs such as tranexamic acid, plasma infusion, and steroids. The anabolic steroids such as danazol and stanazolol have been used widely to treat HANE patients. We discuss in this review the potential mechanisms by which danazol promotes selective synthesis of C1-INH and several other proteins in the liver.