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Kallistatin (Serpin A4, Kallikrein inhibitor, Peptidase inhibitor 4, PI-4, SERPINA4, KST, PI4, Serpin Peptidase Inhibitor, Clade A (Alpha-1 Antiproteinase, Antitrypsin), Member 4)

Kallistatin (Kallikrein-Binding Protein – KBP, Serpin A4) is an acidic glycoprotein composed of 427 amino acids and molecular weight of 58 kDa. It belongs to the serine proteinase inhibitor (SERPIN) superfamily and is a specific endogenous inhibitor of tissue kallikrein. Tissue kallikreins are a group of serine proteinases which are best known for their ability to process plasma kininogens to generate kinins which cause vasodilation. The kallistatin protein contains two structural elements: an active site and a heparin-binding domain. The active site is crucial for complex formation with tissue kallikrein, and thus tissue kallikrein inhibition. The inhibitory activity of kallistatin is blocked upon its binding to heparin. The heparin binding domain, however, is essential for antagonizing signaling pathways mediated by vascular endothelial growth factor (VEGF), tumor necrosis factor (TNF)-α, high mobility group box-1 (HMGB1), and transforming growth factor (TGF)-β. Kallistatin is synthesized and secreted by a wide range of human tissues including kidney, liver, eye, heart, prostate, colon, blood vessels and blood cells. Kallistatin has multiple biologic functions independent of the tissue kallikrein-kinin system and exhibits pleiotropic effects in vasodilation, inhibition of inflammation, angiogenesis, fibrosis, apoptosis, oxidative stress and cancer progression. In animal models, kallistatin administration by gene or protein delivery was observed to offer protection against a large number of pathological conditions such as hypertension, cardiovascular and organ damage, arthritis, sepsis, influenza virus infection, tumor growth and metastasis and has potential for use as a therapeutic agent or target. Kallistatin levels in circulation, body fluids or tissues are significantly lower in patients with liver disease, obesity, septic syndrome, severe pneumonia, inflammatory bowel disease, and cancer of the colon and prostate. Decreased kallistatin levels were observed in vitreous fluid of patients with diabetic retinopathy, however, circulating kallistatin serum levels were shown to be elevated in type 1 diabetes patients with vascular complications. Similar results were observed in type 2 diabetic patients in which serum kallistatin is also increased and correlates with the presence of retinopathy. A recent study demonstrated that serum kallistatin levels are significantly reduced in patients with liver cirrhosis (LC) but not in hepatocellular carcinoma and this decrease correlates with the degree of LC and disruption of normal liver function.

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