Pharmacological properties of hirudin and its derivatives. Potential clinical advantages over heparin

Novel drug delivery systems for hirudin-based product development and clinical applications

Hirudin, a natural biological polypeptide macromolecule secreted by the salivary glands of medicinal leech, is a specific thrombin inhibitor with multiple favourable bioactivities, including anti-coagulation, anti-fibrotic, and anti-tumour. Despite several anticoagulants have been widely applied in clinic, hirudin shows advantages in reducing the incidence of bleeding side effects by virtue of its high specificity in binding to thrombin. As a result, hirudin has been tested in clinical practice to prevent and treat several complex diseases. However, the application of this polypeptide macromolecule is compromised by its low bioavailability and bioactivity due to poor serum stability and susceptibility to protease degradation in vivo. To overcome these drawbacks, several studies have proposed novel drug delivery systems (NDDSs) to prevent the degradation and increase the targeting efficiency of hirudin. This systematic review summarises the clinical research on hirudin, including its classification and bioactivities, and highlights the opportunities and challenges in the clinical use of hirudin. The NDDSs designed to enhance the bioavailability and bioactivity of hirudin are discussed to explore its application in the treatment of related diseases. This review may considerably contribute to the advancement of delivery science and technology, particularly in the context of polypeptide-based therapeutics.

Hirudotherapy for Venous Congestion in an Almost Completely Avulsed Earlobe without Microsurgical Repair

Venous congestion is a frequent and challenging complication after re-attachment or replantation of avulsed tissues, body parts, and flaps. It is often the reason for failure. One of the successful therapies to prevent and/or treat venous congestion is the use of medicinal leeches. There is sound evidence for its efficacy in plastic and reconstructive surgery for avulsed body parts or flaps. However, there is not enough evidence for its use in ear reconstruction or replantation, especially regarding the fragile tissue of the earlobes. The current study is the first in the literature to describe the use of hirudotherapy for venous congestion in an almost completely avulsed earlobe without microsurgical blood vessel repair, as a last resort in an otherwise healthy 38-year-old male patient who sustained trauma due to physical assault.

Direct Oral Anticoagulants (DOACs) for Therapeutic Targeting of Thrombin, a Key Mediator of Cerebrovascular and Neuronal Dysfunction in Alzheimer's Disease

Although preclinical research and observer studies on patients with atrial fibrillation concluded that direct oral anticoagulants (DOACs) can protect against dementia like Alzheimer's disease (AD), clinical investigation towards therapeutical approval is still pending. DOACs target pathological thrombin, which is, like toxic tau and amyloid-ß proteins (Aß), an early hallmark of AD. Especially in hippocampal and neocortical areas, the release of parenchymal Aß into the blood induces thrombin and proinflammatory bradykinin synthesis by activating factor XII of the contact system. Thrombin promotes platelet aggregation and catalyzes conversion of fibrinogen to fibrin, leading to degradation-resistant, Aß-containing fibrin clots. Together with oligomeric Aß, these clots trigger vessel constriction and cerebral amyloid angiopathy (CAA) with vessel occlusion and hemorrhages, leading to vascular and blood-brain barrier (BBB) dysfunction. As consequences, brain blood flow, perfusion, and supply with oxygen (hypoxia) and nutrients decrease. In parenchymal tissue, hypoxia stimulates Aß synthesis, leading to Aß accumulation, which is further enhanced by BBB-impaired perivascular Aß clearance. Aß trigger neuronal damage and promote tau pathologies. BBB dysfunction enables thrombin and fibrin(ogen) to migrate into parenchymal tissue and to activate glial cells. Inflammation and continued Aß production are the results. Synapses and neurons die, and cognitive abilities are lost. DOACs block thrombin by inhibiting its activity (dabigatran) or production (FXa-inhibitors, e.g., apixaban, rivaroxaban). Therefore, DOAC use could preserve vascular integrity and brain perfusion and, thereby, could counteract vascular-driven neuronal and cognitive decline in AD. A conception for clinical investigation is presented, focused on DOAC treatment of patients with diagnosed AD in early-stage and low risk of major bleeding.

Leech Therapy for Complex Facial Lacerations

ABSTRACT

Facial trauma can pose challenging reconstructive obstacles in both maintaining tissue viability and restoring aesthetic appearance. Medicinal leech therapy can help to promote vascular decompression in the setting of venous congestion. A retrospective chart review was conducted to identify patients who underwent medicinal leech therapy following venous stasis secondary to repair of a complex facial laceration. Three patients were identified; 2 suffered auricular avulsion, while 1 suffered a lip avulsion. All patients suffered from venous congestion and underwent medicinal leech therapy for 48 to 72 hours with reduction of edema and stasis. Decompression was successfully achieved with no further sequelae on last follow-up. Medicinal leech therapy is an adequate treatment for venous congestion following traumatic soft-tissue repair of the face. The authors advocate for the utilization of medicinal leeches to combat venous congestion after repair, particularly when arterial inflow remains intact.

A phase I, single and continuous dose administration study on the safety, tolerability, and pharmacokinetics of neorudin, a novel recombinant anticoagulant protein, in healthy subjects

The aim of this study was to evaluate the tolerability, safety, and pharmacokinetics of single and continuous dose administration of recombinant neorudin (EPR-hirudin, EH) by intravenous administration in healthy subjects, and to provide a safe dosage range for phase II clinical research. Forty-four subjects received EH as a single dose of between 0.2 and 2.0 mg/kg by intravenous bolus and drip infusion. In addition, 18 healthy subjects were randomly divided into three dose groups (0.15, 0.30, and 0.45 mg/kg/h) with 6 subjects in each group for the continuous administration trial. Single or continuous doses of neorudin were generally well tolerated by healthy adult subjects. There were no serious adverse events (SAEs), and all adverse events (AEs) were mild to moderate. Moreover, no subjects withdrew from the trial because of AEs. There were no clinically relevant changes in physical examination results, clinical chemistry, urinalysis, or vital signs. The incidence of adverse events was not significantly related to drug dose or systemic exposure. After single-dose and continuous administration, the serum EH concentration reached its peak at 5 min, and the exposure increased with the increase in the administered dose. The mean half-life (T_1/2 ), clearance (Cl), and apparent volume of distribution (Vd) of EH ranged from 1.7 to 2.5 h, 123.9 to 179.7 ml/h/kg, and 402.7 to 615.2 ml/kg, respectively. The demonstrated safety, tolerability, and pharmacokinetic characteristics of EH can be used to guide rational drug dosing and choose therapeutic regimens in subsequent clinical studies. Clinical trial registration: Chinadrugtrials.org identifier: CTR20160444.

Alzheimer's Disease-Rationales for Potential Treatment with the Thrombin Inhibitor Dabigatran

Alzheimer's disease (AD) is caused by neurodegenerative, but also vascular and hemostatic changes in the brain. The oral thrombin inhibitor dabigatran, which has been used for over a decade in preventing thromboembolism and has a well-known pharmacokinetic, safety and antidote profile, can be an option to treat vascular dysfunction in early AD, a condition known as cerebral amyloid angiopathy (CAA). Recent results have revealed that amyloid-β proteins (Aβ), thrombin and fibrin play a crucial role in triggering vascular and parenchymal brain abnormalities in CAA. Dabigatran blocks soluble thrombin, thrombin-mediated formation of fibrin and Aβ-containing fibrin clots. These clots are deposited in brain parenchyma and blood vessels in areas of CAA. Fibrin-Aβ deposition causes microvascular constriction, occlusion and hemorrhage, leading to vascular and blood-brain barrier dysfunction. As a result, blood flow, perfusion and oxygen and nutrient supply are chronically reduced, mainly in hippocampal and neocortical brain areas. Dabigatran has the potential to preserve perfusion and oxygen delivery to the brain, and to prevent parenchymal Aβ-, thrombin- and fibrin-triggered inflammatory and neurodegenerative processes, leading to synapse and neuron death, and cognitive decline. Beneficial effects of dabigatran on CAA and AD have recently been shown in preclinical studies and in retrospective observer studies on patients. Therefore, clinical studies are warranted, in order to possibly expand dabigatran approval for repositioning for AD treatment.

Pharmacological Activities and Mechanisms of Hirudin and Its Derivatives - A Review

Hirudin, an acidic polypeptide secreted by the salivary glands of Hirudo medicinalis (also known as "Shuizhi" in traditional Chinese medicine), is the strongest natural specific inhibitor of thrombin found so far. Hirudin has been demonstrated to possess potent anti-thrombotic effect in previous studies. Recently, increasing researches have focused on the anti-thrombotic activity of the derivatives of hirudin, mainly because these derivatives have stronger antithrombotic activity and lower bleeding risk. Additionally, various bioactivities of hirudin have been reported as well, including wound repair effect, anti-fibrosis effect, effect on diabetic complications, anti-tumor effect, anti-hyperuricemia effect, effect on cerebral hemorrhage, and others. Therefore, by collecting and summarizing publications from the recent two decades, the pharmacological activities, pharmacokinetics, novel preparations and derivatives, as well as toxicity of hirudin were systematically reviewed in this paper. In addition, the clinical application, the underlying mechanisms of pharmacological effects, the dose-effect relationship, and the development potential in new drug research of hirudin were discussed on the purpose of providing new ideas for application of hirudin in treating related diseases.

Study on the activity of recombinant mutant tissue-type plasminogen activator fused with the C-terminal fragment of hirudin

In the present study, bifunctional fusion proteins were designed by fusing the kringle 2 and protease domains of tissue-type plasminogen activator (tPA) to the C-terminal fragment of hirudin. The thrombolytic and anticoagulant activities of these recombinant proteins from mammalian cells were investigated using in vitro coagulation models and chromogenic assays. The results showed that all assayed tPA mutants retained catalytic activity. The C-terminal fragment of hirudin may have weak affinity to thrombin and thus was insufficient to suppress thrombin-mediated fibrin agglutination. The strength of the thrombolytic activity only relied on the selected tPA sequences, and the fibrinolytic efficiency of single-chain protein significantly decreased. Our data indicate that truncated tPA combined with a hirudin peptide may provide a framework for the further development of a new antithrombotic agent.

Safety and efficacy of herbal medicine for acute intracerebral hemorrhage (CRRICH): a multicentre randomised controlled trial

OBJECTIVE

To evaluate the safety and efficacy of removing blood stasis (RBS) herbal medicine for the treatment of acute intracerebral haemorrhage (AICH) within a 6-hour time window.

STUDY DESIGN

A randomised, multicentre, double-blind, placebo-controlled study performed in 14 hospitals in China.

PARTICIPANTS AND INTERVENTIONS

Patients with AICH were randomly assigned to receive a placebo, the ICH-1 (Intracerebral Haemorrhage) formula (eight herbs, including the RBS herbs hirudo and tabanus) or the ICH-2 formula (six herbs without the RBS herbs hirudo and tabanus) within 6 hours of ICH onset.

OUTCOMES

The primary safety outcome was the incidence of haematoma enlargement at 24 hours and at 10 days after treatment. The secondary outcome was the incidence of poor prognosis (mortality or modified Rankin Scale score ≥5) assessed at 90 days after symptom onset.

RESULTS

A total of 324 subjects were randomised between October 2013 and May 2016: 105 patients received placebo; 108 patients received the ICH-1 formula; and 111 patients received the ICH-2 formula. The incidence of haematoma enlargement at 24 hours was 7.8% in the placebo group, 12.3% in the ICH-1 group and 7.5% in the ICH-2 group; the incidence of haematoma enlargement on day 10 was 1.1% in the placebo group, 1.1% in the ICH-1 group, and 3.1% in the ICH-2 group, with no significant differences among the groups (P>0.05). The mortality rates were 3.8% in the placebo group, 2.8% in the ICH-1 group, and 0.9% in the ICH-2 group; the incidences of poor prognosis were 7.1% in the placebo group, 6.0% in the ICH-1 group and 4.8% in the ICH-2 group at 3 months, with no significant differences among the groups (p>0.05). However, the overall frequency of treatment-emergent adverse events in the ICH-1 group (12.1%) was higher among the three groups (5.8% and 2.8%, respectively, p<0.05). All three cases of serious adverse events were in the ICH-1 group.

CONCLUSIONS

Ultra-early administration of ICH-1 formula for AICH patients did not exert significant beneficial effects on clinical outcomes but increased the risk of bleeding, which probably resulted from the inclusion of RBS herbal medicines in ICH-1.

TRIALREGISTRATION NUMBER

NCT01918722.

Construction, expression and refolding of a bifunctional fusion protein consisting of C-terminal 12-residue of hirudin-PA and reteplase

To obtain a bifunctional protein simultaneously showing bioactivity of anticoagulant and fibrinolytic for use in the treatment of thrombotic diseases, we constructed a fusion protein (HV12p-rPA) containing C-terminal 12-residue of hirudin-PA (HV12p) and reteplase (rPA). The fusion protein, in which HV12p was linked to rPA via Gly-Gly-Gly, was successfully expressed in an inactive form of inclusion bodies in Escherichia coli. HV12p-rPA was identified by sodium dodecylsulfate-polyacrylamide gel electrophoresis. The expression level of HV12p-rPA was optimized by an orthogonal method and finally enhanced from 12 % to approximate 30 %. We also deeply investigated the condition of renaturation of HV12p-rPA, and the inactive protein was partly renatured through various conditions. The refolding efficacy of HV12p-rPA estimated by the recovery of fibrinolytic activity varied from 0.03 % to 16.6 % and the anticoagulant activity fluctuated in the range from 41 to 2,297 ATU/mg. Bioassays indicated that the resulted fusion protein, as expected, exhibited both fibrinolytic and anticoagulant activities. These works laid a foundation for further characterization of HV12p-rPA.

The Management of Suspected Heparin-Induced Thrombocytopenia in US Hospitals

Guidelines for the diagnosis and management of heparin-induced thrombocytopenia (HIT) vary between hospitals. Recent guidelines recommend initiating alternative anticoagulant therapy in patients with suspected HIT while awaiting laboratory test results confirming the presence of heparin–PF-4 antibodies (PF-4). This retrospective chart review was designed to assess the current state of management of patients with thrombocytopenia suspected to be due to HIT at 26 US hospitals. Most hospitals (25 of 26; 96.2%) had guidelines in place for the management of suspected HIT, with 7 (26.9%) having a “halt heparin, test, and await results” (ie, “test and wait”) policy. One-third of hospitals had a wait time for obtaining PF-4 antibodies of 3 days or more. Hospital guidelines for the management of HIT may actually discourage the use of optimal HIT management strategies.

Looking back into the future: desirudin in acute coronary syndromes and coronary stenting

Although percutaneous coronary intervention (PCI) is a highly effective modality for the management of acute coronary syndromes, it can potentiate the existing prothrombotic state around lesion areas and lead to ischaemic complications. Adjunctive pharmacologic treatment with heparin reduces the risk of ischaemic events, but the utility of heparin is limited by its unpredictable pharmacodynamic effects and its inability to modulate fibrin-bound thrombin. Additionally, a potential risk of heparin-induced thrombocytopenia is associated with heparin use. Direct thrombin inhibitors (DTIs) have emerged as potential alternatives to heparin in patients undergoing PCI. Bivalirudin is a DTI indicated for use in PCI. Results from various studies have suggested clinical benefit associated with the use of bivalirudin, driven primarily by the reduction in bleeding risks compared with the standard treatment regimens. Of concern, however, is a significant increase in acute stent thrombosis with bivalirudin monotherapy compared with heparin plus GPIIb/IIIa inhibitors following primary PCI for ST-segment elevation myocardial infarction (STEMI). Desirudin is a highly potent DTI with greater binding affinity than bivalirudin for thrombin. This report provides a comparative overview of the pharmacology and clinical utility of desirudin and bivalirudin in the setting of PCI.

Prolonged anticoagulation after discontinuation of argatroban and warfarin therapy in an obese patient with heparin-induced thrombocytopenia

A 32-year-old, morbidly obese African-American woman developed bilateral pulmonary emboli 12 days after undergoing Roux-en-Y gastric bypass surgery. Three days later, after receiving heparin and warfarin, she developed heparin-induced thrombocytopenia type II (HIT-II). An argatroban 1.5-microg/kg/minute infusion was administered for approximately 2.5 days. The patient also received four doses of warfarin, totaling 37.5 mg. The argatroban infusion was discontinued early on hospital day 6, at which time the patient's international normalized ratio (INR) was 4.36 and activated partial thromboplastin time (aPTT) 85.9 seconds. Her INR and aPTT values continued to rise after the argatroban was discontinued and peaked 3 days later at 5.28 and 123.6 seconds, respectively. At this time her platelet count had improved from 139 x 10(3)/mm(3) to 543 x 10(3)/mm(3). No additional warfarin was administered before discharge. On hospital day 11, the patient was discharged home with an INR of 4.12 and an aPTT of 67.1 seconds. Her aPTT and INR values remained elevated for 19 days after receiving her last dose of warfarin and for 20 days after argatroban discontinuation. She experienced no bleeding complications from these supratherapeutic coagulation parameters. She resumed treatment with warfarin as an outpatient and completed a 6-month course of anticoagulation without further incident. Clinicians should be aware that coagulation parameters may remain elevated longer than expected after argatroban discontinuation in certain patients taking concomitant warfarin. Patients with liver dysfunction and obesity appear most likely to be affected.

Efficient targeted anticoagulant with active RGD motif

Three anticoagulants combining large peptide recombinant hirudin variants (rHV2-K47) and Arg-Gly-Asp (RGD) motif related to platelet aggregation were generated, i.e. sequences CRFPRGDADPYCE and CNPRGDFRCI were added to the C-terminus of hirudin to obtain RGD-hirudin 1 and 2, respectively, and the sequence RGDSE was inserted between residues 53-54 of hirudin to obtain RGD-hirudin 3. All products exhibited antithrombin and antiplatelet activities, especially IC50 of RGD-hirudin 1 and 2 were much lower with respect to previously reported similar peptides. Our data suggested that RGD-hirudin 1 and 2 would be promising anticoagulants in clinic. Moreover, the triangular structure of active RGD was shown by computer simulation, which might contribute to our understanding on integrin-related peptides and proteins.

Investigation on recombinant hirudin via oral route

The possibility for oral administration of peptide recombinant hirudin variant (rHV2-K47) as an anticoagulant agent was evaluated in several aspects. The proteolytic properties of rHV2-K47 and its stability during storage were examined by in vitro experiments. Radiolabeled rHV2-K47 was infused into the duodenum of rats and rHV2-K47 absorbed into serum was shown to be intact by electrophoresis pattern. The in vivo coagulation time of blood from mouse was prolonged significantly after oral administration of rHV2-K47. The bioavailability (F) of rHV2-K47 via oral route reached 10.11% in comparison with intravenous administration as gold standard. All the results suggested that rHV2-K47 could be delivered successfully via the oral route.

Treatment of Heparin-Induced Thrombocytopenia: Is There a Role for Bivalirudin?

The recognition and management of heparin-induced thrombocytopenia (HIT) and heparin-induced thrombocytopenia with thrombosis syndrome (HITTS) has been evolving over the past several years. Although HIT is a relatively uncommon adverse event in patients receiving heparin therapy, it bears a significant risk of thrombotic events. If patients are left untreated, 50% can develop thrombosis. Several direct thrombin inhibitors have been studied as alternative anticoagulants in patients with HIT. Lepirudin and argatroban are both approved by the United States Food and Drug Administration (FDA) for the management of HIT. Lepirudin requires dosage adjustments in patients with renal insufficiency and has potential for antibody formation. Argatroban requires dosage adjustments in patients with hepatic insufficiency. Argatroban increases the international normalized ratio when coadministered with warfarin, leading to dosage difficulties when transitioning to warfarin therapy. Bivalirudin is the most recent direct thrombin inhibitor to be introduced to the market, but it is not currently FDA approved for HIT. Controversy still exists over which direct thrombin inhibitor to use, especially in acutely ill patients and in those requiring invasive or surgical procedures. Bivalirudin has a relatively short half-life and a predictable response, which makes it attractive as an anticoagulant in patients requiring invasive or surgical procedures, those who are acutely ill, or patients with both renal and hepatic insufficiency. It offers promise as an additional direct thrombin inhibitor for use in patients with HIT, but additional studies need to be performed to further define its use.

The use of intravenous recombinant hirudin in the treatment of deep vein thrombosis in a patient with an acute heparin allergy

We report a case in which intravenous heparin, given for the treatment of acute deep vein thrombosis, precipitated an acute allergic reaction, and an alternative anticoagulant, recombinant hirudin, provided rapid and successful therapeutic intervention.

Treatment of heparin-induced thrombocytopenia

OBJECTIVE

To describe heparin-induced thrombocytopenia (HIT or HIT-2), an immune-mediated adverse reaction to heparin or low-molecular-weight heparin. Available treatment options and considerations in developing a therapy approach are discussed.

DATA SOURCES

A search of the National Library of Medicine (1992-June 2001) was done to identify pertinent literature. Additional references were reviewed from selected articles.

STUDY SELECTION

Articles related to laboratory recognition and treatment options of HIT, including the use of agents in selected clinical conditions, were reviewed and included.

CONCLUSIONS

HIT is a rare but potentially severe adverse reaction to heparin that was, until recently, poorly understood and had limited treatment options. Recent advances describing the recognition and clinical manifestations of immune-mediated HIT, including recently available antithrombotic treatment options, have dramatically changed outcomes for patients having this syndrome.

Heparin-Induced Thrombocytopenia and Thrombosis: A Review of Pharmacologic Therapy

Objective:

To review pharmacological therapy in heparin-induced thrombocytopenia and thrombosis (HITT).

Data Sources:

Articles and abstracts in English published from 1966 to January 2000 were identified by MEDLINE and International Pharmaceutical Abstracts searches using the terms HIT, Hill, heparin-associated thrombocytopenia, thrombocytopenia, hirudin, lepirudin, argatroban, ancrod, heparinoids, orgaran, danaparoid, and org 10172. Additional articles were identified from the bibliographies of retrieved literature.

Data Synthesis:

HITT is a devastating drug-induced immunologic complication that occurs in 2–5% of patients on heparin. Often, HITT results in life- or limb-threatening complications. HITT is frequently diagnosed by clinical presentation, and there is no optimal drug treatment approach. The first step of treatment is to discontinue all forms of heparin. If anticoagulation is indicated, several agents have been evaluated. Lepirudin, argatroban, and danaparoid are agents available for use in HITT. Lepirudin is a recombinant hirudin that directly complexes with thrombin. Danaparoid is a heparinoid moiety that works by inactivation factor Xa. Argatroban, a direct semisynthetic thrombin inhibitor, is the newest agent available. Ancrod is derived from pit viper venom and acts as a fibrinolytic agent; its use is not recommended. No studies have evaluated the comparative efficacy and safety of these agents.

Conclusions:

Argatroban, danaparoid, and lepirudin have shown efficacy and safety in treatment of HITT. Each agent exerts differences in pharmacologic and pharmacokinetic parameters and has advantages and disadvantages in particular patient populations. Therapy must be guided on an individual basis. Further investigation is needed to ascertain an optimal treatment approach.

Successful anticoagulation with hirudin in a patient with mesenteric venous thrombosis and multiple coagulation abnormalities

A case of multiple thrombotic diatheses discovered in the setting of mesenteric venous infarction is discussed. The patient had deficiencies of protein C, protein S, antithrombin III; was heterozygous for factor V Leiden; and had polycythemia vera. Adequate anticoagulation could not be established with heparin administration and hirudin was used. The diagnosis of mesenteric venous infarction, thrombotic tendency of multiple coagulation diatheses, and use of hirudin are discussed.