C1 Esterase Inhibitor (C1-INH)

C1-INH is a member of the serpin family of proteases, as are alpha-antitrypsin, antithrombin III, and angiotensinogen. These proteins stoichiometrically inactivate their target proteases by forming stable, one-to-one complexes with the protein to be inhibited. Although synthesized primarily by hepatocytes, C1-INH is also synthesized by monocytes. The regulation of the protein production is not completely understood, but, since patients respond clinically to androgen therapy serum levels of C1-INH increase, it is believed that androgens may stimulate C1-INH synthesis. All C1-INH deficient patients are heterozygous; half the normal level of C1-INH is not believed sufficient to prevent attacks.\n\nAlthough named for its action on the first component of complement (C1 esterase), C1-INH also inhibits components of the fibrinolytic, clotting, and kinin pathways. Specifically, C1-INH inactivates plasmin-activated Hageman factor (factor XII), activated factor XI, PTA, and kallikrein. Within the complement system, C1-INH blocks the activation of C1 and the rest of the classic complement pathway by binding to C1r and C1s. Without C1-INH, unchecked activation of C1, C2, and C4 occur before other inhibitors (C4-binding protein and factor I) can halt the cascade.\n\nThe actual factor or factors responsible for the edema formation remain somewhat controversial. Researchers have demonstrated activation of the kinin system and increased bradykinin concentration associated with clinical flares. Bradykinin is an important inflammatory mediator that causes neutrophil chemotaxis, capillary dilation, and smooth muscle relaxation, and it has been linked to other forms of angioedema. In an animal model of C1-INH deficiency, bradykinin antagonists prevent capillary leakage. Others implicate C2 kinin, a metabolite of C2b, as the active agent in the presence of plasmin.\n\nStorage and Stability: \nMay be stored at 4 degrees C for short-term only. Aliquot to avoid repeated freezing and thawing. Store at -70 degrees C. Aliquots are stable for 6 months at -70 degrees C. For maximum recovery of product, centrifuge the original vial after thawing and prior to removing the cap. Further dilutions can be made in assay buffer.

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