Hirudin is one of the most significant and most studied active ingredients in leeches and their salivary glands. It is a small molecule protein (polypeptide). Leeches are rich in hirudin, which has a strong inhibitory effect on thrombin and is the strongest natural specific inhibitor of thrombin found so far.
Structure, Function and Features
Natural hirudin is an acidic single-chain polypeptide with a relative molecular mass of about 7000. It consists of 64-66 amino acids and contains 3 disulfide bonds without the presence of polysaccharides. At present, 7 isomers have been isolated and identified, which are active High, stable structure, not easy to inactivate and so on. Natural hirudin contains six cysteine residues with similar three-dimensional structures and distribution positions, the thrombin active binding site is located at the N-terminal of its structure, and the thrombin fibrinogen binding site is located at the C-terminal of its structure. Amino acid residues in the middle region play a regulatory role. Due to the special structure of its peptide chain, natural hirudin has a strong anticoagulant effect. Its penetration ability and stability are strong, it will not be destroyed by trypsin and chymotrypsin, and it will not decompose even if the pH and temperature change slightly, it can be taken orally, and the decomposed fragments also have anticoagulant effect, But under some special conditions, such as the coexistence of strong alkali and high temperature, it will lead to irreversible inactivation.
Pharmacological Effects of Natural Hirudin
Anticoagulant and Antithrombotic Effect
In animal experiments, it was found that natural hirudin can accelerate the blood flow rate at the blood stasis site, improve the abnormal blood rheology, inhibit platelet aggregation, improve the vascular patency rate, and have a significant antithrombotic effect.
Anti-Fibrotic Effect
Some studies have found that natural hirudin can inhibit the growth of gingival fibroblasts and tendon fibroblasts, and is effective in renal interstitial fibrosis, renal tubular epithelial cell fibrosis, pulmonary fibrosis, and idiopathic interpulmonary fibrosis (IPF). Has inhibitory effect. The possible mechanisms of natural hirudin against fibrosis include three aspects: 1) Regulating the secretion of basic fibroblast growth factor (bFGF) and transforming growth factor-β1 (TGF-β1), inhibiting the growth, proliferation and further development of fibroblasts Inhibit scar formation, inhibit the production and activity of plasminogen activator inhibitor-1 (PAI-1), reduce fibrin deposition, and promote collagen dissolution; 2) Reduce monocyte Chemoattractant Protein-1 (MCP-1), intercellular adhesion molecule-1 (ICAM-1), p38 mitogen-activated protein kinase (p38MAPK) expression; 3) Decreased protein kinase B (Akt), phosphorylated Akt ( p-Akt) protein expression, slowing down the progression of IPF.
Regulates Microvascular Regeneration
Natural hirudin can promote the expression of vascular endothelial cell growth factor in random skin flaps and increase its survival rate to promote the formation of new microangiogenesis. Vascular endothelial growth factor (VEGF)/Notch signaling pathway, as a classical pro-angiogenic molecular pathway, can promote the differentiation of human pluripotent stem cells into adult microvascular endothelial cells (HMVECs). Some studies have found that natural hirudin can regulate angiogenesis. At a low concentration of 4 ATU/mL (ATU is the amount of inactivating 1 NIH unit of thrombin at 37 °C), it may promote the proliferation of HMVECs and promote the proliferation of HMVECs through the VEGF-Notch signaling pathway, and angiogenesis; at a high concentration of 7 ATU/mL, it mainly exerts antithrombin and anti-inflammatory effects, and inhibits angiogenesis by improving microcirculation. The study found that natural hirudin can also improve the survival rate of rat skin flaps through the protease-activated receptors (PARs)/p38/nuclear factor-κB (NF-κB) pathway.
Antitumor Effect
Studies have found that natural hirudin can effectively promote the apoptosis of mouse hemangioma EOMA cells and inhibit their proliferation in vitro, and there is an obvious dose-response relationship. The study found that natural hirudin may inhibit the proliferation, migration and invasion of liver cancer HepG2 cells by down-regulating the expression of VEGF. In addition, other results showed that natural hirudin may inhibit the proliferation of nasopharyngeal carcinoma CNE2 cells by inducing cancer cell apoptosis and arresting the cell cycle at G2/M, which may be related to the up-regulation of Bax and p21 mRNA expression by natural hirudin.
Improve Inflammatory Obstruction of Fallopian Tubes
The pelvic injection of natural hirudin was given to the rats with salpingitis obstructed, and metronidazole was used as the positive control group. After hematoxylin-eosin (HE) staining, the morphology and structure of the fallopian tubes of the rats before and after the experiment were observed, and the expression of VEGF protein in fallopian tubes were detected. The results showed that after pelvic injection of natural hirudin, the structure of the fallopian tubes of rats was significantly changed and improved, indicating that natural hirudin has a significant therapeutic effect on salpingitis obstruction. Treatment offers new ideas.
Anti-gout Effect
The mouse hyperuricemia model, the mouse chronic hyperuricemia model and the rat acute gout inflammation model were used, and allopurinol tablets were used as the positive control to observe the effect of natural hirudin on hyperuricemia and anti-gout effect. The results show that natural hirudin has significant anti-hyperuricemia and anti-gout effects, can reduce serum urea nitrogen levels, significantly inhibit the expression of human glucose-facilitated transporter 9 (GLUT9), and alleviate renal pathological damage.
Improve Kidney Function
Natural hirudin can reduce renal injury and improve renal function in diabetic nephropathy model mice. There are three possible mechanisms: 1) Inhibit the expression of transient receptor potential cation channel 6 (TRPC6) to reduce calcium influx, Protect renal podocytes, thereby improving renal function; 2) Reduce RhoA protein, protect podocyte cytoskeleton, and maintain podocyte cytoskeleton morphology and density; 3) Inhibit the expression of VEGF and TGF-β1 to improve renal function.
Other Function
Through the vascular ring experiment and the kinetic model of large-conductance calcium-activated potassium channel (BKCa), it was found that natural hirudin has a vasodilatory effect, which may be achieved by activating BKCa channel. In additon, studies have found that natural hirudin can reduce cerebral edema in rats with cerebral hemorrhage, reduce the rate of brain cell apoptosis, and relieve neurological impairment. Its anti-apoptotic mechanism of brain cells may be related to the inhibition of JAK2/STAT3 signaling pathway.
