Serine protease inhibitors or “serpins” form a large family of inhibitors that regulate various physiological processes such as angiogenesis, neoplasmia, apoptosis, inflammation, coagulation, fibrinolysis and viral pathogenesis. Dysfunction of such serine protease inhibitors has been implicated in cancer, thrombosis, emphysema, cystic fibrosis, liver cirrhosis, psoriasis, arthritis, immune hypersenstivity, and mental disorders.

Some of the best characterized serpins, including alpha1-proteinase inhibitor, alaph1-antichymotrypsin, antithrombin III and alpha2-antiplasmin are inhibitors of serine proteinases. The inhibitory serpins regulate proteolysis by forming tight, equimolar complexes with a target proteinase. Once formed, the complexes are rapidly removed form the circulcaton by cellular receptors, thereby preventing proteoysis of blood and tissue proteins. Two distinct pathways for the plasma elimination of serpin complexes are a receptor designated serpin receptor 1 (SR1) which recognizes complexes of proteinases with alpha1PI, alpha1ACT, ATIII and herparin cofactor II. Similarly, SR2 recognizes and eliminates complexes of proteinases with alpha2AP. These receptors are mainly present on hepatocytes and are probably responsible for the bult removal of proteinase activity during episodes of inflammation, coagulation, and fibrinolysis. (Mast, Biochemistry, 1991, 30, 1723-1730).

Alpha 1-Antitrypsin (A1AT)(AAT)/ alpha-1 proteinase inhibitor (A1PI): is a serpine protease inhibitor belonging to the serpin superfamily. It is a glycoprotein which consists of a single polypeptide chain to which several oligosaccharide units are covalently bonded. Human alpha-1 proteinase inhibitor has a role in controlling tissue destruction by endogenous serine proteinases. It protects tissues form enzymes of inflammatory cells such as neutrophil elastase. In its absence, neutrophil elastase is free to break down elastin, which contributes to the elasticity of lungs, and can result in respiratory problems like emphysema or COPD. ?1-antitrypsin is the predominant elastase inhibitor in tissues whereas SLPI is the predmoninant elastase inhibitor in secretions. Inherited deficiency of A1AT predisposes individuals to early onset hereditary emphysema, due to the upregulated action of neutrophil elastase. Large quantities and frequent injection sof A1At are required to restore normalcy to the lungs and relieve hereditary emphysema. Presently, A1AT supplies are isolated from pooled blood products (e.g., Zemaira®, Prolastin®)., and there is a greater demand for the product relative to the available supply. A1AT may also be useful in the treatment of emphysema cuased by smoking, cystic fibrosis, pulmonary hypertension, pumonary fibrosis and CPOD.

Alpha 1-antichymotrypsin: is a serine protease inhibitor synethesized in the liver with apparent affinity toward chymotrypsin like enzymes. It is structurally related to AAT and may be useful in the treatment of pulmonary inflammation (US 4,916,117)

Alpha-2-Macroglobulin: is a large plasma protein found in blood and produced by the liver. It is composed of four identical subunits bound together by disulfide bonds. It is able to inactivate a wide variety of proteinases including serine-, cysteine-, aspartic- and metalloproteinases. It also functions as an inhibitor of coagulation by inhibiting thrombin. Alpha2M is synthesiezed as a precursor having 1474 amino acid residues. The first 23 amino acids function as a signal sequence that is cleaved to yield a mature protein with 1451 amino acid reisudes. Alpha2M promiscuously binds to proteins and peptides with nucleophilic amino acid side chains in a covalent manner. Protease interaction with alpha2M results in a complex structural rearrangement called transformation, which is the result of a cleavage within the “bait” region of alpha2M after the proteinase becomes trapped by theioesters. The conformational change exposes residues required for receptor binding, allowing the alpha2M-proteinase complex to bind to the alpha2MR.

Inter-alpha-trypsin inhibitor (ITI): is also known as inter-alpha (globulin) inhibitor. ITI is a high molecular mass glycoprotein (about 240 kDa) present in human plasma. It was first isolated in 1962. However, its function as a proteinase inhibitor was not established until 1965. When ITI is exposed to proteolytic enzymes (e.g., pancreatic trypsin or elastase), a low molecular mass compound with antiroteolytic activity, termed HI-30 appears in the reaction mixture. The molecular mass of HI-30 varies in the range between 30 and 60 kDa. The amino acid sequencing of HI-30 is identical to the acid-soluble serum-trypsin-inhibitor (STI) which appears in urine after its renal filtration and is therefore also named urinary-trypsin-inhbitor (UTI). UTI and STI have identical amino acid sequences but they may be different in their carbohyrate composition.

The I?I family in mammals refers to a group of related plasma protease inhibitors. These proteins are comprised of various multi-polypeptide molecules showing different assemblies from a group of four distinct polypeptides including 3 related heavy (H) chains H1, H2 and H3, and a light chain called bikunin. Two Kunitz-type protease inhibitor domains are present in the bikunin chain which are bound to the heavy chains through glycosaminoglycan bridges. In more detail, ITI consists of a light chain (L) serine protease inhibitor, known as bikunin or urinary trypsin inhibitor (UTI) and one or two heavy chains (H) containing von-Willebrand type A (vWA) domains. There are 5 known IAI heavy chain polypeptides, which are encoded by inter-alpha (globulin) inhibitor (ITI)H1, ITIH2, (ITIH3), ITIH4, ITIH5: The ITIs comprise a family of protease inhibitors found in the extracellular matrices of various organs, as well as in the blood circulation. Due to their isolation in complexes with hyaluranan (HA), ITIs are also referred to as SHAPs (Serum-derived HA-associated proteins). It has been shown that interaction of ITIs with HA leads to stabilization of the extracellular matrix. (Veeck, Ocogene, 27, 2008, 865-876). While IaI is most abundantly found in the liver, it is also present in the lungs.

 Plasminogen Activator Inhibitor Type-1 (PAI-1): is a serine protease inhibitor. PAI-1 is a fast-acting inhibitor of tissue-type plasminogen activator (t-PA) and urokinase-type plasminogen activator (u-PA). Studies have shown that locally elevated PAI-1 plasma levels are important for sucessor failure of thrombolytic therapy with rt-PA. For example, one study showed that TNK-t-PA which is 90 times more resistant to PAI-1 compared with wild type t-PA was also 7.5 times more potent than t-PA in lysing whole blood clots. The clinical relevance of these studies suggest that a PAI-1-resistant variant of t-PA should be used as a more potent fibrinolytic agent for thromboytic therapy as in myocardial infarction.