The direct thrombin inhibitor hirudin

Abstract

SummaryThis review discusses the pharmacology and clinical applications of hirudin, a bivalent direct thrombin inhibitor (DTI). Besides the current major indication for hirudin -anticoagulation of patients with heparin-induced thrombocytopenia (HIT) -the experience with hirudin in other indications, especially acute coronary syndromes, are briefly presented. Hirudins have been formally studied prior to their regulatory approval; however, imporKeywords Thrombin, deep vein thrombosis, hirudin, HIT tant information on their side effects and relevant preventative measures only became available later. Therefore, current recommendations and dosing schedules for hirudin differ considerably from the information given in the package inserts. Drawbacks of hirudin and important precautions for avoiding potential adverse effects are discussed in detail in the third part of this review. PharmacologyHirudin, the most potent natural thrombin inhibitor, is a 65-amino-acid polypeptide (molecular mass, ~7 kDa) produced by the parapharyngeal glands of the medicinal leech, Hirudo medicinalis. The molecule is stabilized by three disulfide bridges. Its three-dimensional structure (1) reveals three distinct regions: a central core (residues 3-30, 37-46, 56-57), a "finger" (residues 31-36), and a loop (residues 47-55).Hirudins for therapeutic use are produced by recombinant biotechnology using yeast. Recombinant hirudins (r-hirudin) differ from natural hirudin by lacking the sulfate group at Tyr-63. Although this structural change results in a lower affinity of desulfato-hirudins to thrombin, r-hirudins nevertheless are highly specific inhibitors of thrombin, with an inhibition constant for thrombin in the picomolar range (2).Effective inhibition of thrombin by antithrombin and heparin cofactor II require the catalytic actions of heparins. In contrast, hirudins effectively inhibit thrombin independently of any cofactor (3). They form noncovalent-but irreversible--1:1 complexes with thrombin. r-Hirudins bind to at least two sites on thrombin, and are thus classified as bivalent DTI's (Fig. 1). A further difference from heparin-antithrombin and heparin-heparin cofactor II is that r-hirudin inhibits both free and clot-bound thrombin (4, 5), as well as thrombin bound to fibrin split products (6). In contrast, heparinantithrombin complexes are relatively poor at accessing and inactivating clot-bound thrombin. This could explain why hirudin is more effective than heparin in promoting dissolution of mural thrombi in experimental models (7). Another important difference to heparin is that hirudin shows virtually no interaction with plasma proteins (8), whereas heparin binding to plasma proteins is the major explanation for many limitations of heparin, including its

Chinese Medicinal Leech: Ethnopharmacology, Phytochemistry, and Pharmacological Activities

“…These structural changes improve the hydrophobicity of the protein and allow the recombinant RGD-hirudin to interact more effectively with the fibrinogen recognition exosite of thrombin, resulting in a specific activity of 12,000 ATU/mg [16]. Owing to the significant anticoagulant effects [17, 18], recombinant hirudin has been approved into the market for the treatment of thrombosis-related diseases.…”

Randomized, double‐blind, placebo‐controlled, interventional phase IV investigation to assess the efficacy and safety of r‐hirudin gel (1120I.U) in patients with hematomas

“…Hirudin is the most potent naturally‐occurring direct thrombin inhibitor (DTI), and the first parenteral anticoagulant used on humans 1. Originally derived from the medicinal leech ( Hirudo medicinalis ), it consists of a 65 amino acids polypeptide chain, forming non‐covalent, equimolar, non‐reversible 1:1 complexes with α thrombin 1.…”

“…Originally derived from the medicinal leech ( Hirudo medicinalis ), it consists of a 65 amino acids polypeptide chain, forming non‐covalent, equimolar, non‐reversible 1:1 complexes with α thrombin 1. When hirudin‐bound, thrombin‐catalyzed reactions and fibrinogen clotting are blocked, and coagulation is subsequently inhibited 2.…”

Evaluating the Effect of Protein A Signal Peptide on Extracellular Expression of Recombinant Hirudin in E.Coli

“…Hirudin is a polypeptide with 65-66 amino acids, containing three disulfide bonds in the N-terminal and a set of acidic amino acids in the C-terminal region. The high specificity and binding affinity of hirudinthrombin complex has attracted the interest of investigating their reactions at molecular level (4)(5)(6)(7). Recombinant hirudin has some differences from natural hirudin.…”

“…The recombinant hirudin lacks sulfate group in tyrosine 63. Although this structural change may reduce the tendency of desulfohirudin to thrombin, recombinant hirudin is a very specific inhibitor for thrombin at picomolar level (4). Hirudin is able to block the activity of platelet-dependent thrombin in vitro and it is considered a very powerful antithrombotic agent in arterial, venous and shunts thrombosis, in vivo.…”