Screening of the Promising Direct Thrombin Inhibitors from Haematophagous Organisms. Part I: Recombinant Analogues and Their Antithrombotic Activity In Vitro

The success in treatment of venous thromboembolism and acute coronary syndromes using direct thrombin inhibitors has stimulated research aimed at finding a new anticoagulant from haematophagous organisms. This study deals with the comparison between hirudin-1 from Hirudomedicinalis(desirudin), being the first-known and most well-studied natural anticoagulant, along with recombinant analogs of haemadin from the leech Haemadipsa sylvestris, variegin from the tick Amblyomma variegatum, and anophelin from Anopheles albimanus. These polypeptides were chosen due to their high specificity and affinity for thrombin, as well as their distinctive inhibitory mechanisms. We have developed a universal scheme for the biotechnological production of these recombinant peptides as pharmaceutical substances. The anticoagulant activities of these peptides were compared using the thrombin amidolytic activity assay and prolongation of coagulation time (thrombin time, prothrombin time, and activated partial thromboplastin time) in mouse and human plasma. The preliminary results obtained suggest haemadin as the closest analog of recombinant hirudin-1, the active substance of the medicinal product Iprivask (Aventis Pharmaceuticals, USA) for the prevention of deep venous thrombosis in patients undergoing elective hip or knee replacement surgery. In contrast, variegin can be regarded as a natural analog of bivalirudin (Angiomax, The Medicines Company), a synthetic hirudin-1 derivative certified for the treatment of patients undergoing percutaneous coronary intervention and of patients with unstable angina pectoris after percutaneous transluminal coronary angioplasty.

Recombinant Hirudin Protects the Vasculature and Myocardium in Atherosclerotic Rats by Inhibiting the p38 MAPK/NF-κB Signaling Pathway

Recombinant hirudin (r-hirudin) has a good anticoagulant effect and also has a certain inhibitory effect on atherosclerosis (AS), however, its intrinsic mechanism of inhibiting AS is still unclear. In this study, we investigated the mechanism underlying the vascular and myocardial protective effects of r-hirudin in AS rats through animal experiments. A rat AS model was established by high-fat diet feeding combined with common carotid artery balloon injury. The model rats were given low, medium, or high doses of r-hirudin (0.05, 0.1, or 0.2 mg/kg/day), simvastatin tablets (1 mg/kg/day) and p38 mitogen-activated protein kinase (MAPK) pathway inhibitors (SB203580, 100 mg/kg/day) by gavage for 8 weeks. The results showed that in AS rats, r-hirudin significantly alleviated pathological changes in the common carotid artery and myocardial tissue; decreased serum total cholesterol (TC), triglyceride (TG) and low-density lipoprotein-cholesterol (LDL-C) levels; increased high-density lipoprotein-cholesterol (HDL-C) levels; decreased serum oxidized low-density lipoprotein (ox-LDL), tumor necrosis factor (TNF)-α, interleukin (IL)-6, IL-1β, and endothelin (ET)-1 levels; increased nitric oxide (NO) levels; and decreased p38 MAPK, nuclear factor-kappa B (NF-κB), caspase-9, caspase-3 mRNA and protein expression. This study showed that r-hirudin may protect blood vessels and the myocardium in AS rats by adjusting blood lipid levels and inhibiting the p38 MAPK/NF-κB signaling pathway to exert anti-inflammatory and anti-apoptotic effects and protect the vascular endothelium.

Cell-free synthesis of the hirudin variant 1 of the blood-sucking leech Hirudo medicinalis

Synthesis and purification of peptide drugs for medical applications is a challenging task. The leech-derived factor hirudin is in clinical use as an alternative to heparin in anticoagulatory therapies. So far, recombinant hirudin is mainly produced in bacterial or yeast expression systems. We describe the successful development and application of an alternative protocol for the synthesis of active hirudin based on a cell-free protein synthesis approach. Three different cell lysates were compared, and the effects of two different signal peptide sequences on the synthesis of mature hirudin were determined. The combination of K562 cell lysates and the endogenous wild-type signal peptide sequence was most effective. Cell-free synthesized hirudin showed a considerably higher anti-thrombin activity compared to recombinant hirudin produced in bacterial cells.

Self-regulated hirudin delivery for anticoagulant therapy

Pathological coagulation, a disorder of blood clotting regulation, induces a number of cardiovascular diseases. A safe and efficient system for the delivery of anticoagulants to mimic the physiological negative feedback mechanism by responding to the coagulation signal changes holds the promise and potential for anticoagulant therapy. Here, we exploit a “closed-loop” controlled release strategy for the delivery of recombinant hirudin, an anticoagulant agent that uses a self-regulated nanoscale polymeric gel. The cross-linked nanogel network increases the stability and bioavailability of hirudin and reduces its clearance in vivo. Equipped with the clot-targeted ligand, the engineered nanogels promote the accumulation of hirudin in the fibrous clots and adaptively release the encapsulated hirudin upon the thrombin variation during the pathological proceeding of thrombus for potentiating anticoagulant activity and alleviating adverse effects. We show that this formulation efficiently prevents and inhibits the clot formation on the mouse models of pulmonary embolism and thrombosis.