Thrombin

In the internal and exterior coagulation pathways, histidine suppresses thrombin activity, deprives thrombin of its capacity to cleave fibrinogen, and stops fibrin from forming as well as the polymerization process of fibrin monomers by cross-linking [1]. By opposing thrombin, Hirudin decreases apoptosis in human microvascular endothelial cells and suppresses p-JAK2 expression [1]. At high concentrations, Hirudin suppresses the growth of human microvascular endothelial cells and the VEGF-Notch pathway [1]. TGF-β1-induced aberrant proliferation and fibrosis in HK-2 cells can be counteracted by hirudin (3–10 mg/mL) [1]. Hirudin suppresses the ERK1/2 pathway, decreases oxidative stress, inhibits angiotensin II-induced cardiac fibroblasts, and regulates variables associated to fiber in a dose-dependent manner [1].

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Li et al. reported that Hirudin exhibited antitumor effect when targeting cells of the LN229 and U251 cell lines in vitro. It significantly suppressed the growth of LN229 and U251 cell lines, with the IC 50 of 30 and 15 mM, respectively. In addition, hirudin also increased the apoptosis in these glioma cells by down-regulating the expression of Bcl-2 and increased cell cycle arrest at the G1 phase. Notably, the content of pERK1/2 was decreased after hirudin administration, as well as the level of the protein Cyclin D1, which suggested that down-regulation of ERK/MAPK signaling pathway might be a crucial mechanism of hirudin in treating gliomas (Zhao, 2015).

Recently, Hirudin was found to possess inhibitory property on hepatocellular carcinoma, and the underlying mechanism might be implicated in suppressing angiogenesis. Li et al. reported that Hirudin could inhibit the proliferation, apoptosis, migration and invasion of HepG2 cells in a dose-dependent manner. In addition, the expressions of VEGF mRNA and protein were significantly down-regulated after the treatment of hirudin (Li et al., 2016), which is consistent with previous studies that the reduction of hepatocellular carcinoma angiogenesis owes to the inactivation of VEGF pathway (Morse et al., 2019). Furthermore, hirudin is a specific inhibitor of thrombin, which can inhibit angiogenesis stimulated by thrombin and reduce the expression of VEGF. Hemangioma is a lesion caused by the abnormal proliferation of vascular endothelial cells and pericyte, which could be intervened and treated by antiangiogenic drugs (Ji et al., 2014). A study in 2015 revealed that 4 U/ml Hirudin could effectively inhibit the proliferation and promote the apoptosis of mouse EOMA hemangioma cells in vitro, which showed an obvious dose-effect relationship (Yang et al., 2015).
Besides natural Hirudin, rH was proved to have antitumor effects in Hep-2 human laryngeal cancer (LC) cells via suppressing angiogenesis. [1]

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Hirudin reduces the expression of inflammatory factors in TGF-β-induced renal tubular epithelial cells [2]
After the induction of TGF-β in human HK-2 cells, mouse IMCD3 cells and rat NRK-52E cells, the levels of IL-1β, IL-6 and TNF-α in those cells were increased, which were then gradually decreased when those cells were treated with Hirudin from 0.5 mg/ml to 1 mg/ml (Fig. 5A–C).

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Hirudin reduces the occurrence of EMT in TGF-β-induced renal tubular epithelial cells [2]
E-cad, N-cad and slug are critical proteins responsible for the occurrence of EMT. As shown in Fig. 6A–C, the expression of N-cad and slug was increased and E-cad expression was decreased when HK-2 cells, IMCD3 cells and NRK-52E cells were treated with TGF-β. What’s more, Hirudin treatment from 0.5 mg/ml to 1 mg/ml could improve the expression of N-cad and slug and depress the E-cad expression in those cells.

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Hirudin reduces the incidence of fibrosis in TGF-β induced renal tubular epithelial cells [2]
As shown in Fig. 7A–C, the expression of collagen-I, FN and α-SMA was increased in HK-2 cells, IMCD3 cells and NRK-52E cells induced by TGF-β. When those cells were treated with Hirudin from 0.5 mg/ml to 1 mg/ml, the expression of collagen-I, FN and α-SMA in cells were gradually decreased.

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Hirudin reduces the apoptosis of TGF-β-induced renal tubular epithelial cells [2]
The apoptosis of HK-2 cells, IMCD3 cells and NRK-52E cells was detected by Hoechst staining. The apoptosis of HK-2 cells, IMCD3 cells and NRK-52E cells induced by TGF-β was enhanced while alleviated when those cells were treated with Hirudin from 0.5 mg/ml to 1 mg/ml (Fig. 8A–C).

In rats, hindrin decreases the inflammatory response and boosts the survivability of random skin flaps [1]. Following laser surgery, hinddin helps SD rats' wounds recover [1]. In a mouse model of unilateral ureteral obstruction (UUO), hinddin (10 and 15 mg/kg; gavage, thrice daily for 21 days) reduces renal interstitial fibrosis to lessen tubular damage and inflammation [2].

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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. [1]

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Renal interstitial fibrosis (RIF) often occurs in many chronic kidney diseases (CKD). Hirudin now is applied to treat fibrosis in some organs. In this study, we verified the treatment effects of hirudin on RIF in vivo and in vitro with the underlying mechanism. The RIF in vivo was the unilateral ureteral obstruction (UUO) model and RIF in vitro was the renal tubular epithelial cells induced by TGF-β. The renal pathological changes and renal fibrosis were observed by hematoxylin and eosin (H&E) staining and Masson staining. The α-SMA in renal tissues was detected by immunohistochemistry. The inflammatory factors were analyzed by the ELISA assay. The cell apoptosis was observed by TUNEL assay. The related proteins of fibrosis, epithelial-mesenchymal transition (EMT) and apoptosis were assessed by western blot analysis. The experimental data demonstrated that hirudin decreased fibrosis, EMT, inflammation and cell apoptosis in renal tissues of UUO rats and TGF-β-induced renal tubular epithelial cells. Furthermore, Hirudin also reduced the expression of collgen-I, FN, α-SMA, N-cad, slug, E-cad, IL-1β, IL-6 and TNF-α in mice serum and TGF-β-induced renal tubular epithelial cells. The apoptosis related proteins (pro-caspase3, pro-caspase9, bcl2 and bax) expression was also down-regulated in renal tissues of UUO rats. In conclusion, hirudin depressed the fibrosis in renal tissues and renal tubular epithelial cells by inhibiting the inflammation, regulating the related proteins of fibrosis and ETM and decreasing the apoptosis of renal tubular epithelial cells. These findings may offer an effective treatment method for RIF [2].

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Hirudin reduces renal fibrosis in renal tissues induced by UUO model [2]
The pathologic changes of renal tissues were observed by H&E staining. UUO induced remarkable renal damage with many dilated and atrophic tubules. The hirudin intervention partially alleviated the above renal damages (Fig. 1A). There was obvious interstitial inflammation and collagen deposition in renal tissues induced by UUO model, as shown by Masson staining. The α-SMA expression assessed by immunohistochemistry was upregulated in renal tissues of UUO mice. The hirudin intervention suppressed the upregulation of α-SMA and collagen deposition in UUO mice (Fig. 1B and C).

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Hirudin regulates the expression of fibrosis-related proteins and ECM in renal tissues induced by UUO model [2]
The expression of fibrosis-related proteins and ECM were assessed by western blot analysis, and the former ones (collagen-I, FN and α-SMA) were obviously increased in renal tissues induced by UUO model while dwindled when UUO mice were treated with hirudin from 10 mg/kg to 15 mg/kg (Fig. 2A). The expression of ETM proteins was shown in Fig. 2B. The expression of N-cad and slug was increased and E-cad was decreased significantly in renal tissues induced by UUO model and hirudin gradually reversed the expression of N-cad, slug and E-cad from 10 mg/kg to 15 mg/kg.

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Hirudin decreases the expression of inflammatory factors in serum induced by UUO model [2]
The ELISA assay was used to detect the levels of IL-1β, IL-6 and TNF-α in the mouse serum. And, the levels of IL-1β, IL-6 and TNF-α in the mouse serum were upregulated in the serum of UUO mice. Hirudin treatment from 10 mg/kg to 15 mg/kg for the UUO mice could decline the levels of IL-1β, IL-6 and TNF-α in the serum (Fig. 3).

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Hirudin decreases the apoptosis of renal tubular cells in UUO mice [2]
The apoptosis of renal tubular cells in renal tissues induced by UUO model was showed by TUNEL assay. The apoptosis of renal tubular cells was increased in renal tissues of UUO mice and reduced when UUO mice were treated with hirudin from 10 mg/kg to 15 mg/kg (Fig. 4A). Accordingly, the expression of cleaved caspase3, cleaved caspase9 and bax was upregulated and the expression of bcl2 was downregulated in renal tubular cells of UUO mice. In addition, the expression of cleaved caspase3, cleaved caspase9, bax and bcl2 in renal tubular cells of UUO mice was reversed after the hirudin treatment. The expression of pro-caspase3 and pro-caspase9 in four groups was not changed (Fig. 4B).

Cell culture and cell induction [2]
The human HK-2 cells, mouse IMCD3 cells and rat NRK-52E cells were bought from ATCC. All three cell lines were incubated in the 90% high glucose DMEM and 10% FBS at 37 °C with 5% CO2. Then, the three kinds of cells were treated with 5 ng/ml TGF-β for 48 h to establish the vitro model.

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Hematoxylin and eosin (H&E) staining [2]
The kidney of mice was fixed in 4% paraformaldehyde for 48 h, then embedded in paraffin and cut into slices. The sections were put into xylene for 20 min, ethanol for 5 min and 75% ethanol for 5 min. Subsequently, the sections were put into hematoxylin for 3 min, washed with tap water and dehydrated by ethanol for 5 min. Finally, the sections were stained with eosin that was sealed with neutral gum.

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Masson staining [2]
The steps of dewaxing were the same as HE staining. The sections were soaked in potassium dichromate overnight and washed with tap water. Then, the sections were dyed with hematoxylin for 3 min, washed with tap water, dyed with ponceaux for 10 min and rinsed with tap water. Subsequently, the sections were stained with phosphomolybdic acid solution and aniline blue solution for 3 min respectively, which sealed with neutral gum.

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Immunohistochemistry [2]
The steps of dewaxing were the same as HE staining. The sections were heated for antigen retrieval at 95 °C for 30–45 min. Then, sections were cooled down at room temperature and soaked in 3% H2O2 methanol solution for 10 min. The goat serum was added to the sections to block at 25 °C for 10 min. Subsequently, the primary antibody, rabbit anti-α-SMA antibody, secondary antibody, biotin-labeled goat anti-rabbit antibody and horseradish peroxidase (HRP)-labeled streptavidin working solution were successively added to the sections. Then, the sections were colored with DAB Color Development Kit and counterstained with hematoxylin, followed by the rinse of tap water. Finally, the sections were blocked with neutral gum and observed under a microscope.

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Western blot analysis [2]
The renal tissues and renal tubular epithelial cells were obtained and lysed with the appropriate RIPA lysate. Then the supernatant of mixture was obtained after high speed centrifugation and BCA kits were used to detect the protein concentration in different groups. The required protein volume per lane was calculated according to the measured concentration and protein solution was boiled for 10 min. The proteins were separated with 10% SDS-PAGE and transferred by PVDF membrane. The PVDF membrane was sealed in the skim milk at 25 °C for 1 h. The primary antibodies for the protein detection of renal tissues were collgen-I, FN, α-SMA, E-cad, N-cad, slug, E-cad, cleaved caspase3, cleaved caspase9, pro-caspase3, pro-caspase9, bcl2 and bax. The primary antibodies for the protein detection of renal tubular epithelial cells were collgen-I, FN, α-SMA, E-cad, N-cad and slug. After PVDF membrane was incubated with primary antibodies overnight at 4 °C, PVDF membrane was washed by TBST and treated with rabbit horseradish peroxidase-linked IgG second antibody at 25 °C for 1 h. After the addition of ECL solution, PVDF membrane was exposed in dark and scanned by Bio-Rad gel documentation system. Finally, Quantity One software was used to analyze the area and gray value of each strip.

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Enzyme-linked immunosorbent assay (ELISA) [2]
Blood was taken from eyeball of mice and centrifuged at 5,000 rpm for 5 min to separate the serum. The levels of IL-1β, IL-6 and tumor necrosis factor α (TNF-α) in mice serum were determined with ELISA Kits. A Model 680 Microplate Reader was applied to obtain the optical density (OD) values at 450 nm.

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TUNEL assay The steps of dewaxing were the same as HE staining. Next, sections were incubated with Proteinase K at 25 °C for 15–30 min. After being washed by PBS twice, each section was added with 100 μL TdT reaction solution, which was incubated in a wet box at 37 °C for 1 h. Each section was washed by PBS for three times and incubated with 50 μL streptavidin fluorescein-dUTP reaction solution at 37 °C for 1 h. Finally, each section was sealed with 50 μL anti-fluorescence quenching agent for 30 min, which were then observed by a fluorescence microscopy.

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Hoechst staining [2]
The steps of dewaxing were the same as HE staining. The sections were placed in oscillating table to be washed by PBS twice. When the sections were sucked dry, they were treated with 0.5 ml Hoechst 33,258 for 5 min in oscillating table. The above cleaning procedure was repeated. Then, the sections were placed on the slide, added a drop of anti-quench sealing solution and covered with a clean slide. Blue nucleis of apoptotic cells could be observed by a fluorescence microscope.

Animal/Disease Models: Male balb/c (Bagg ALBino) mouse: with underwent unilateral ureteral ligation (UUO)[2]
Doses: 10 and 15 mg/kg
Route of Administration: po (oral gavage); 10 and 15 mg/kg, one time/day for 21 days
Experimental Results: diminished renal damages and suppressed the upregulation of α-SMA, collagen deposition in UUO mice. Increased the level of fibrosis (collagen-I, FN, α-SMA), N- cad, slug and E-cad in UUO mice. diminished the level of IL-1β, IL-6 and TNF-α, apoptosis of renal tubular cells in UUO mice. diminished the expression of inflammatory factors, the occurrence of EMT, the incidence of fibrosis and the apoptosis of TGF-β-induced renal tubular epithelial cell.

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In this experiment, mice underwent unilateral ureteral ligation (UUO) was adopted as the animal model. Forty male balb/c mice (25 g ± 3 g weight) were kept in SPF animal room with alternating light and dark for 12 h/time with humidity 60% and temperature 23 ± 3 °C and free access of water. The mice were randomly divided into four groups, including control group, UUO group, UUO + Hirudin (10 mg/kg) group and UUO + Hirudin (15 mg/kg) group, with ten mice in each group. All mice were weighed on the electronic balance to calculate the required anesthetic dose and then intraperitoneally injected with 2% pentobarbital (50 mg/kg). In the UUO group, mice were fixed on the rat board in the supine position and the abdominal skin of mice was disinfected with medical alcohol. The right abdominal incision (1.75 ± 0.25 cm) was taken and the peritoneum was opened. The right ureter was exposed and separated before its ligation with silk thread near the renal hilum and bladder. When no obvious bleeding appeared in the surgical field, the intestinal tract was rectified and the wound was sutured. In the UUO + Hirudin (10 mg/kg) group and UUO + Hirudin (15 mg/kg) group, mice were disposed with same surgery in UUO group and given the 10 mg/kg and 15 mg/kg Hirudin respectively by gavage once daily for duration of the study. The mice in the control group were not given any treatment. During the experiment, all the mice were free to eat and drink. On the 21th day after the operation, 1 ml blood was taken from eyeball of mice which then were sacrificed by cervical dislocation method and their right kidneys were obtained. [2]

Absorption, Distribution and Excretion
Lepirudin administered as a single intravenous bolus injection of 0.4 mg/kg in 9 healthy volunteers (male and female) resulted in a Cmax of 2924 ng/mL, a tmax of 0.17 h and an AUC0-∞ of 2500 ng•h/mL. When 0.1, 0.15 and 0.2 mg/kg of lepirudin was administered as a single intravenous infusion over 6 hours in healthy male volunteers, lepirudin had a corresponding Cmax of 111, 203, and 2446 ng/mL and a corresponding AUC of 612, 1184, and 1446 ng•h/mL. Bioavailability is 100% following injection. Also, it has been reported that following subcutaneous (sc) administration, the bioavailability of lepirudin is almost 100%.
Lepirudin is mostly excreted through urine (48.3%). About 35% of lepirudin is excreted unchanged, while metabolites are found in a smaller proportion (2.5% of M1, 5.4% of M2, 3.9% of M3 and 1.6% of M4).
The volume of distribution of lepirudin at steady state was 12.2 L in healthy young subjects (n=18, 18-60 years), 18.7 L in healthy elderly subjects (n=10, 65-80 years), 18.0 L in renally impaired subjects (n=16, creatinine clearance < 80 mL/min, and 32.1 L in heparin-induced thrombocytopenia patients (n=73). The distribution of lepirudin is mainly restricted to extracellular fluids.
The clearance of lepirudin is proportional to the glomerular filtration rate. On average, lepirudin clearance was 164 mL/min in healthy young subjects (n=18, 18-60 years) and 25% lower in women than in men. In healthy elderly subjects (n=10, 65-80 years), clearance was 139 mL/min, about 20% lower than in younger patients. This is possibly due to the lower creatinine clearance in elderly patients. In renally impaired subjects (n=16, creatinine clearance < 80 mL/min), clearance was 61 mL/min, and in heparin-induced thrombocytopenia patients (n=73), it was 114 mL/min.

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Metabolism / Metabolites
As a polypeptide, lepirudin is expected to be metabolized by the sequential cleavage of amino acids by kidney exoproteases, which have carboxypeptidase and dipeptidase-like activity. The C-terminal cleavage of lepirudin aminoacids (aminoacids 1 to 65) produces four metabolites with anti-thrombotic activity: M1 (aminoacids 1 to 64), M2 (aminoacids 1 to 63), M3 (aminoacids 1 to 62), and M4 (aminoacids 1 to 61).

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Biological Half-Life
Lepirudin has an initial half-life of approximately 10 minutes, and in young healthy volunteers, it has a terminal half-time of 1.3 hours. Lepirudin has a first-order elimination kinetic; plasma concentration increases proportionally as the lepirudin intravenous dose is increased. Elimination half-life values of up to 2 days were detected in patients with marked renal insufficiency (creatinine clearance < 15 mL/min).

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Pharmacokinetics [1]
Pharmacokinetic studies of Hirudin and rH have been conducted in many species, including rats, rabbits, dogs, and human; the detailed pharmacokinetic parameters of these studies are shown in Table 2. Due to the polypeptide structure of hirudin, it is difficult to achieve the effective concentration by oral administration. Thus, hirudin is usually administered parenterally for high bioavailability. The pharmacokinetic behavior of hirudin among different animals tend to be the same. After intravenous administration, the kinetics of Hirudin manifests as a two-compartment open model (Markwardt et al., 1988b; Richter et al., 1988; Kaiser et al., 1990). The absorption half-life (t1/2α) suggested that hirudin can be rapidly distributed from the central compartment to the peripheral compartment. In addition, the elimination half-life (t1/2β) was about 1 h, which indicated that hirudin can be quickly excreted and metabolized. Besides, the bioavailability of Hirudin was almost 100% after subcutaneous administration, and the concentration-time curves illustrated that its plasma pharmacokinetics was consistent with a one-compartment model (Nowak et al., 1988). Compared with intravenous administration, the elimination half-life (t1/2) was obviously prolonged in both rats (2.1 h) and dogs (3.03 h). Similar to natural hirudin, rH could be rapidly distributed into the extravascular compartment with t1/2α from 0.08 to 0.25 h. In addition, the elimination phase half-lives were relatively longer after intravenous administration. Remarkably, most of the administered hirudin and rH could be eliminated through kidney in active form in dogs (Nowak et al., 1988). Moreover, in healthy volunteers, renal clearance and degradation accounted for 90% of systemic clearance (Greinacher and Lubenow, 2001).

In addition to subcutaneous administration and intravenous administration, other routes of rH administration have been investigated. The in vivo course of rHV2 in rats fitted to the one-compartment model after intranasal administration of rHV2 spray with the relative bioavailability of 28.53% (Zhang et al., 2006). Furthermore, Zhang et al. reported that the relative bioavailability (FR) of rHV2 liposome and rHV2 saline solution after intranasal administration were 12.36 and 1.83%, respectively. These results demonstrated that the pharmacokinetics and bioavailability of rH were greatly affected by the dosage form (Zhang et al., 2007). Moreover, Liu et al. compared the pharmacokinetics of rH in rats administered through four different routes (intratracheal, buccal, nasal and rectal) and found that the pulmonary route was more suitable for systemic delivery of rHV2 than other three routes (Liu et al., 2005).

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The Preparations of Hirudin [1]
In order to reduce the adverse reactions and improve the bioavailability of Hirudin, various types of preparations have been reported in recent years, such as micelles, nanoparticles, TiO2 nanotube systems, polyamides dendrimer, and so on. Remarkably, the characteristics of these novel preparations mainly focus on prolonging circulation, thrombus targeting, continuous drug delivery, and specific disease targeting.

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Prolonging Circulation [1]
Hirudin can be rapidly distributed into the intercellular space after intravenous injection and has a short half-life; repeated injections are needed to maintain its therapeutic effect. However, several drawbacks (such as high price and bleeding risk) will be brought about after repeated injections, which greatly limited the clinical application of hirudin. The bovine serum albumin (BSA) nanoparticles are considered to be a promising carrier to address those problems (Green et al., 2006). In 2015, hirudin-BSA nanoparticles have been successfully synthesized and characterized by a desolvation technique. These nanoparticles possess good encapsulation and certain sustained-release capacity, which could control the release of hirudin to prolong the antithrombotic effect, suggesting that hirudin-BSA nanoparticles might be applied in clinic therapy for thrombosis. However, the pharmacokinetics and safety of these novel preparations need to be further studied (Jing et al., 2016). In addition to nanoparticles, polydopamine fitted TiO2 nanotube systems were also exploited to extend the release of hirudin. In 2018, Yang et al. reported that PDA fitted TiO2 nanotube systems could prolong the release of bivalirudin and improve the hemocompatibility in vitro and in vivo. Besides, the systems could effectively reduce the formation of thrombosis by inhibiting the denaturation as well as adhesion of platelets, fibrinogen, and other blood components (Yang et al., 2018). Although Hirudin could exert platelet aggregation inhibitory effect after structurally modified with platelet-targeting peptides such as RGD, the short half-life of this derivative is still a severe problem. Polyion complex (PIC) micelles have attracted extensive attention in recent years due to its complementary and unique features (Yang et al., 2009), which enables the long circulation of drugs in vivo. Recombinant hirudin variant 2 (rHV2)-loaded PIC micelles, consisting of methoxy poly (ethylene glycol)-grafted-chitosan (mPEG-g-chitosan) and Arg-Gly-Asp conjugated poly (ethylene glycol)-grafted-chitosan (RGD-PEG-g-chitosan), were prepared by Wang et al. in 2010. These rHV2-loaded PIC micelles, with the mean size of 41.9 ± 1.8 nm and the encapsulation efficiencies of 81.08 ± 0.85%, could prolong the mean retention time of rHV2 and specifically bind to platelets. Besides, efficient anticoagulant effects and platelet aggregation inhibition effects were observed in these micelles, which indicated that RGD-PIC micelles could achieve the purpose of platelet-targeted delivery and long circulation of rHV2 (Wang et al., 2010).

Effects During Pregnancy and Lactation
◉ Summary of Use during Lactation
Lepirudin is no longer marketed in the United States. Limited information indicates that lepirudin in doses up to 100 mg daily produce very low levels in milk. Because of its large molecular weight, it would not be expected to be absorbed from breastmilk by the infant. Lepirudin would not be expected to cause any adverse effects in breastfed infants, especially if the infant is older than 2 months.
◉ Effects in Breastfed Infants
One infant was breastfed for 3 months during therapeutic lepirudin use beginning at 7 weeks of age. No bleeding events occurred.
◉ Effects on Lactation and Breastmilk
Relevant published information was not found as of the revision date.

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Protein Binding
In human plasma, the protein binding of lepirudin was approximately 3%.

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Toxicity [1]
The toxic studies of Hirudin and its derivatives have been performed in several animal experiments. Previous studies revealed that after subcutaneous injection of hirudin 100 mg/kg for 8 days, the hemorrhage of pleura, pia meninges and peritoneum occurred in rats. In addition, daily doses of hirudin from 1 mg/kg to 5 mg/kg resulted in a dose-dependent increase in bleeding propensity in sub-chronic toxicity studies in rats and dogs for up to 3 months. It's worth noting that the formation of antibodies could be observed after the administration of extremely high doses of hirudin in dogs, but these antibodies did not neutralize the effect of hirudin (Nowak, 2002). Interestingly, such antibodies were also detected in humans during long-term administration of hirudin (Eichler et al., 2000), however, the antibody-bound hirudin could exert antithrombin property as before with the longer half-life, indicating that these antibodies might be a form of Hirudin storage. Moreover, the lethal dose (LD 50) of lyophilizing hirudin powder was determined to be over 10.0 g/kg when administered via orally administration, and no significant difference was observed in micronucleus rate and sperm malformation rate between hirudin groups (2.5, 5.0, and 10.0 g/kg) and control group (Huang et al., 2010). Furthermore, lyophilizing hirudin powder exhibited no maternal toxicity, embryo toxicity, and teratogenicity in rats at the dosages of 312.5, 1250, and 5000 mg/kg (Huang et al., 2011). Besides, the toxicity of rH has been investigated in some reports. Lu et al. discovered that rH (1.0, 3.0, 6.0 mg/kg) could significantly prolong the clotting time, thrombin time, and activated partial thromboplastin time in Macaca mulatta, however, these effects could be automatically reversed at 24 h after administration (Lu et al., 2004). These studies proved that hirudin rarely causes toxicity despite its minor bleeding side effect, which can be used for the prevention and treatment of more diseases with a broad development prospect.

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72941487 mammal (species unspecified) LD50 intravenous >50 mg/kg Zhongguo Yaoxue Zazhi. Chinese Pharmacuetical Journal., 26(396), 1991

[1]. Pharmacological Activities and Mechanisms of Hirudin and Its Derivatives - A Review. Front Pharmacol. 2021 Apr 16;12:660757.

[2]. Hirudin improves renal interstitial fibrosis by reducing renal tubule injury and inflammation in unilateral ureteral obstruction (UUO) mice. Int Immunopharmacol. 2020 Apr;81:106249.

Lepirudin is a heterodetic cyclic peptide composed of 65 amino acids joined in sequence and cyclised by three disulfide bridges between cysteine residues 6-14, 16-28 and 22-39. It is a highly specific inhibitor of thrombin and used as an anticoagulant in patients with heparin-induced thrombocytopenia. It has a role as an EC 3.4.21.5 (thrombin) inhibitor and an anticoagulant. It is a polypeptide, a heterodetic cyclic peptide and an organic disulfide.
Lepirudin is a recombinant hirudin formed by 65 amino acids that acts as a highly specific and direct thrombin inhibitor. Natural hirudin is an endogenous anticoagulant found in Hirudo medicinalis leeches. Lepirudin is produced in yeast cells and is identical to natural hirudin except for the absence of sulfate on the tyrosine residue at position 63 and the substitution of leucine for isoleucine at position 1 (N-terminal end). Lepirudin is used as an anticoagulant in patients with heparin-induced thrombocytopenia (HIT), an immune reaction associated with a high risk of thromboembolic complications. HIT is caused by the expression of immunoglobulin G (IgG) antibodies that bind to the complex formed by heparin and platelet factor 4. This activates endothelial cells and platelets and enhances the formation of thrombi. Bayer ceased the production of lepirudin (Refludan) effective May 31, 2012.
Lepirudin is a yeast cell-derived recombinant polypeptide related to the naturally occurring, leech-derived anticoagulant hirudin. Lepirudin directly binds to and inactivates thrombin, producing dose-dependent increases in the activated partial thromboplastin time (aPTT) and prothrombin time (PT). The mechanism of action of this agent is independent of antithrombin III and is not inhibited by platelet factor 4. Natural hirudin, a family of highly homologous isopolypeptides, is produced in trace amounts by the leech Hirudo medicinalis.

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Drug Indication
Lepirudin is indicated for anticoagulation in adult patients with acute coronary syndromes (ACS) such as unstable angina and acute myocardial infarction without ST elevation. In patients with ACS, lepirudin is intended for use with [aspirin]. Lepirudin is also indicated for anticoagulation in patients with heparin-induced thrombocytopenia (HIT) and associated thromboembolic disease in order to prevent further thromboembolic complications.
Anticoagulation in adult patients with heparin-induced thrombocytopenia type II and thromboembolic disease mandating parenteral antithrombotic therapy. The diagnosis should be confirmed by the heparin-induced platelet activation assay or an equivalent test.

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Mechanism of Action
Lepirudin is a direct thrombin inhibitor used as an anticoagulant in patients for whom heparin is contraindicated. Thrombin is a serine protease that participates in the blood-clotting cascade, and it is formed by the cleavage of pro-thrombin. Active thrombin cleaves fibrinogen and generates fibrin monomers that polymerize to form fibrin clots. Lepirudin binds to the catalytic and substrate-binding sites of thrombin, forming a stable, irreversible and non-covalent complex. This blocks the protease activity of thrombin and inhibits the coagulation process. Each molecule of lepirudin binds to a single molecule of thrombin, and unlike [heparin], it is able to inhibit thrombin in both its clot-bound or free states.

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Pharmacodynamics
Lepirudin is a recombinant hirudin that acts as a highly specific thrombin inhibitor. Its activity is measured by anti-thrombin units (ATUs) that correspond to the amount of lepirudin required to neutralize a unit of the World Health Organization α-thrombin (89/588) standard. The activity of lepirudin is 16,000 ATU/mg. A single molecule of lepirudin binds to a molecule of thrombin, blocking its thrombogenic activity. This drug increases activated partial thromboplastin time (aPTT) and PT (INR) values in a dose-dependent manner, and its mode of action is independent of antithrombin III. Platelet factor 4 does not inhibit lepirudin. The pharmacodynamic effect of lepirudin was evaluated by measuring an increase in aPTT. No saturable effect was observed at the highest tested dose (0.5 mg/kg, IV bolus). Thrombin time was considered an unsuitable routine test for lepirudin monitoring due to the high values detected (200 seconds) even at low doses. The concomitant use of thrombolytic therapy and lepirudin is not recommended due to the high risk of bleeding that may be life-threatening. In patients with a risk of bleeding, a physician should weigh the risks of lepirudin administration against its benefits. There is also an especially high risk of bleeding in patients who weigh less than 50 kg, and a lower dosage is required. Patients with renal impairment have a higher risk of hemorrhagic adverse events.

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Single-chain polypeptides of about 65 amino acids (7 kDa) from LEECHES that have a neutral hydrophobic N terminus, an acidic hydrophilic C terminus, and a compact, hydrophobic core region. Recombinant Hirudins lack tyr-63 sulfation and are referred to as 'desulfato-hirudins'. They form a stable non-covalent complex with ALPHA-THROMBIN, thereby abolishing its ability to cleave FIBRINOGEN.

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In the past few decades, notable findings of Hirudin have been gained, precisely including the clinical application, development of derivatives, exploration of novel pharmacological activities, and investigation of new preparations.
Successful Application of Derivatives of Hirudin in Clinic:
With the development of genetic engineering technology, the producing problems of natural Hirudin has been successfully solved, which greatly promoted the successfully application of lepirudin, desirudin and bivalirudin in clinic. Lepirudin has been approved as an anticoagulant for patients with heparin-induced thrombocytopenia (HIT), with the usual dose of 0.4 mg/kg IV bolus followed by 0.15 mg/kg/h IV infusion (Greinacher and Lubenow, 2001). It could reduce HIT related adverse events by 72%, providing not only effective anticoagulant therapy, but also rapid platelet recovery in HIT patients. Noticeably, the bolus and infusion rates should be scheduled according to the serum creatinine values of patients (Greinacher et al., 1999). Desirudin is used to preventing deep venous thrombosis (DVT) in patients undergoing total hip replacement (THR) and total knee replacement (TKR) surgery by subcutaneously (SC) injection. Previous studies reported that desirudin was superior in preventing VTE in patients undergoing elective hip replacement surgery at the dose of 15 mg (Q12H, SC) compared with low-dose unfractionated heparin and low-molecular-weight heparin (Eriksson et al., 1997) (Bergese et al., 2013). Another direct thrombin inhibitor, bivalirudin, is effective on preventing thromboembolic complications. It was reported that administrating bivalirudin as a 1.0 mg/kg IV bolus, followed by 2.5 mg/kg/h by IV infusion for 4 h early in the trial; later, lowering the bolus to 0.75 mg/kg, followed by a 1.75 mg/kg/h infusion over 4 h achieved procedural and clinical success in 98 and 96% of the patients, respectively (Sun et al., 2017). Additionally, bivalirudin is also being studied in phase II and III multicenter trials as an alternative anticoagulant for both on-pump and off-pump cardiac surgery for patients with or without HIT (Joseph et al., 2014). [1]

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Future Perspectives:
Although the studies of Hirudin have referred to pharmacy, pharmacology, preparation and clinical application, we find that there is still somewhat inadequate, especially studies of the dose-effect relationship, toxicity and safety of its derivatives and preparations. In this section, we focus on potential future directions for research on hirudin.
Given the multiple pharmacological activities nature of Hirudin, elaborating its dose-effect relationship is beneficial to the determination of doses for clinical treatment of different diseases in the future. Remarkably, hirudin exhibited different activities and even opposite biological effects at different concentrations. For instance, the expression of VEGF was increased when hirudin was used to treat necrosis of skin flap, but VEGF was inhibited in hirudin–treated diabetic complications and tumor. This difference may be caused by the different doses of hirudin used in these two studies. At low concentrations (1 and 4 ATU/ml), hirudin can promote cell proliferation and micro-angiogenesis by upregulating VEGF, which is quite important for wound repair. However, with higher concentration (7 ATU/ml), the promoting effect of hirudin on the VEGF/Notch signaling pathway gradually decreased and turned into an inhibitory effect. Accordingly, the expression of VEGF decreased, indicating that high concentration of hirudin can inhibit the growth of cells and exert the anti-inflammatory activity, which is conducive to the treatment of diabetic complications and tumor. Likewise, the effect of hirudin on ERK1/2 pathway is also bidirectional. At the dosage of 2ATU, Hirudin could significantly elevate the expression level of ERK1/2 phosphorylation; activated ERK promoted the transcription of VEGF signaling molecule by regulating the expression of AP-1 and c-Jun, which facilitated the neovascularization of ischemic skin flap rats. However, at other dosages (20, 40, and 80 μg/ml), hirudin could down-regulate the expression of ERK1/2 phosphorylation to participate in the treatment of fibrosis. Detailed information on the pharmacological activity, route of administration, effective dose and molecular mechanism of hirudin is provided in Table 4. It is worth noting that besides concentrations, different routes of administration and the animal models or cells used in different studies may contribute to the differences in bioactivities as well. Therefore, more in vivo researches are quite needed to clarify the dose-effect relationship of hirudin. [1]

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Although Hirudin has been successfully used for thrombosis therapy in clinic, its short half-life and the bleeding risk remain limiting factors, further researches may focus on the structural modifications. Perhaps, fusing recognition peptides identified from FXIa and FXa with these drugs might be a promising method to reduce bleeding risk. In addition, the studies associated with the derivatives and preparations of hirudin are only at the preliminary stage and further studies should be conducted to reveal the actions, toxicity and potential mechanisms.
In short, Hirudin has a wide range of pharmacological activities and enormous potential for clinic application, which is worthy of more in-depth and comprehensive study. [1]

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Hirudin has a strong inhibitory effect on thrombin with anticoagulant, antithrombotic, antitumor and anti-fibrosis functions. Hirudin reduced the deposition of fibrin-related antigens in glomerulus, decreased the proliferation of glomerular mesangial cells and glomerular sclerosis and reduced the proteinuria and low protein blood to improve the renal function. Hirudin may downregulate the expression of TGF-β and α-SMA, and reduce the proliferation and activation of fibroblast growth factors and fibroblast phenotype transformation, thereby preventing and treating renal interstitial fibrosis. In this study, hirudin decrease the inflammation and the occurrence of EMT in renal tubular epithelial cells to inhibit the fibrosis and apoptosis of renal tubular epithelial cells.
Here, hirudin suppressed the fibrosis in renal tissues and renal tubular epithelial cells by inhibiting the inflammation, regulating the fibrosis-related proteins and ECM and decreasing the apoptosis of renal tubular epithelial cells. However, natural products often have the potential liver injury. When natural products has been studied to have a protective effect on kidney injury, we also investigate the effects of natural products on liver in the future study.[2]

C287H440N80O111S6

6979.42396068573

6977.967

138068-37-8

Hirudin;8001-27-2

118856773

H-Leu-Thr-Tyr-Thr-Asp-Cys(1)-Thr-Glu-Ser-Gly-Gln-Asn-Leu-Cys(1)-Leu-Cys(2)-Glu-Gly-Ser-Asn-Val-Cys(3)-Gly-Gln-Gly-Asn-Lys-Cys(2)-Ile-Leu-Gly-Ser-Asp-Gly-Glu-Lys-Asn-Gln-Cys(3)-Val-Thr-Gly-Glu-Gly-Thr-Pro-Lys-Pro-Gln-Ser-His-Asn-Asp-Gly-Asp-Phe-Glu-Glu-Ile-Pro-Glu-Glu-Tyr-Leu-Gln-OH
L-leucyl-L-threonyl-L-tyrosyl-L-threonyl-L-alpha-aspartyl-L-cysteinyl-L-threonyl-L-alpha-glutamyl-L-seryl-glycyl-L-glutaminyl-L-asparagyl-L-leucyl-L-cysteinyl-L-leucyl-L-cysteinyl-L-alpha-glutamyl-glycyl-L-seryl-L-asparagyl-L-valyl-L-cysteinyl-glycyl-L-glutaminyl-glycyl-L-asparagyl-L-lysyl-L-cysteinyl-L-isoleucyl-L-leucyl-glycyl-L-seryl-L-alpha-aspartyl-glycyl-L-alpha-glutamyl-L-lysyl-L-asparagyl-L-glutaminyl-L-cysteinyl-L-valyl-L-threonyl-glycyl-L-alpha-glutamyl-glycyl-L-threonyl-L-prolyl-L-lysyl-L-prolyl-L-glutaminyl-L-seryl-L-histidyl-L-asparagyl-L-alpha-aspartyl-glycyl-L-alpha-aspartyl-L-phenylalanyl-L-alpha-glutamyl-L-alpha-glutamyl-L-isoleucyl-L-prolyl-L-alpha-glutamyl-L-alpha-glutamyl-L-tyrosyl-L-leucyl-L-glutamine (6->14),(16->28),(22->39)-tris(disulfide)
PEPTIDE1{L.T.Y.T.D.C.T.E.S.G.Q.N.L.C.L.C.E.G.S.N.V.C.G.Q.G.N.K.C.I.L.G.S.D.G.E.K.N.Q.C.V.T.G.E.G.T.P.K.P.Q.S.H.N.D.G.D.F.E.E.I.P.E.E.Y.L.Q}$PEPTIDE1,PEPTIDE1,6:R3-14:R3|PEPTIDE1,PEPTIDE1,16:R3-28:R3|PEPTIDE1,PEPTIDE1,22:R3-39:R3$$$

LTYTDCTESGQNLCLCEGSNVCGQGNKCILGSDGEKNQCVTGEGTPKPQSHNDGDFEEIPEEYLQ
H-LTYTDC(1)TESGQNLC(1)LC(2)EGSNVC(3)GQGNKC(2)ILGSDGEKNQC(3)VTGEGTPKPQSHNDGDFEEIPEEYLQ-OH

Typically exists as solid at room temperature

65 °C

-41.3

100

122

166

484

18600

63

S1C[C@@H](C(N[C@@H](C(C)C)C(N[C@@H]([C@@H](C)O)C(NCC(N[C@@H](CCC(=O)O)C(NCC(N[C@@H]([C@@H](C)O)C(N2CCC[C@H]2C(N[C@@H](CCCCN)C(N2CCC[C@H]2C(N[C@H](C(N[C@H](C(N[C@H](C(N[C@H](C(N[C@H](C(NCC(N[C@@H](CC(=O)O)C(N[C@@H](CC2C=CC=CC=2)C(N[C@@H](CCC(=O)O)C(N[C@@H](CCC(=O)O)C(N[C@@H]([C@@H](C)CC)C(N2CCC[C@H]2C(N[C@H](C(N[C@H](C(N[C@H](C(N[C@H](C(N[C@H](C(=O)O)CCC(N)=O)=O)CC(C)C)=O)CC2C=CC(=CC=2)O)=O)CCC(=O)O)=O)CCC(=O)O)=O)=O)=O)=O)=O)=O)=O)=O)CC(=O)O)=O)CC(N)=O)=O)CC2=CNC=N2)=O)CO)=O)CCC(N)=O)=O)=O)=O)=O)=O)=O)=O)=O)=O)=O)NC([C@H](CCC(N)=O)NC([C@H](CC(N)=O)NC([C@H](CCCCN)NC([C@H](CCC(=O)O)NC(CNC([C@H](CC(=O)O)NC([C@H](CO)NC(CNC([C@H](CC(C)C)NC([C@H]([C@@H](C)CC)NC([C@@H]2CSSC[C@@H](C(N[C@@H](CCC(=O)O)C(NCC(N[C@@H](CO)C(N[C@@H](CC(N)=O)C(N[C@@H](C(C)C)C(N[C@H](C(NCC(N[C@H](C(NCC(N[C@@H](CC(N)=O)C(N[C@H](C(N2)=O)CCCCN)=O)=O)=O)CCC(N)=O)=O)=O)CS1)=O)=O)=O)=O)=O)=O)NC([C@H](CC(C)C)NC([C@@H]1CSSC[C@@H](C(N[C@H](C(N[C@H](C(N[C@@H](CO)C(NCC(N[C@@H](CCC(N)=O)C(N[C@@H](CC(N)=O)C(N[C@H](C(N1)=O)CC(C)C)=O)=O)=O)=O)=O)CCC(=O)O)=O)[C@@H](C)O)=O)NC([C@H](CC(=O)O)NC([C@H]([C@@H](C)O)NC([C@H](CC1C=CC(=CC=1)O)NC([C@H]([C@@H](C)O)NC([C@H](CC(C)C)N)=O)=O)=O)=O)=O)=O)=O)=O)=O)=O)=O)=O)=O)=O)=O)=O)=O)=O

FIBJDTSHOUXTKV-BRHMIFOHSA-N

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(2S)-5-amino-2-[[(2S)-2-[[(2S)-2-[[(2S)-2-[[(2S)-2-[[(2S)-1-[(2S,3S)-2-[[(2S)-2-[[(2S)-2-[[(2S)-2-[[(2S)-2-[[2-[[(2S)-2-[[(2S)-4-amino-2-[[(2S)-2-[[(2S)-2-[[(2S)-5-amino-2-[[(2S)-1-[(2S)-6-amino-2-[[(2S)-1-[(2S,3R)-2-[[2-[[(2S)-2-[[2-[[(2S,3R)-2-[[(2S)-2-[[(1R,6R,9S,12S,15S,18S,24S,27S,33S,36S,39R,44R,47S,53S,56S,59S,67S,73S,76S)-15,76-bis(4-aminobutyl)-44-[[(2S)-2-[[(4R,7S,10S,13S,19S,22S,25S,28R)-28-[[(2S)-2-[[(2S,3R)-2-[[(2S)-2-[[(2S,3R)-2-[[(2S)-2-amino-4-methylpentanoyl]amino]-3-hydroxybutanoyl]amino]-3-(4-hydroxyphenyl)propanoyl]amino]-3-hydroxybutanoyl]amino]-3-carboxypropanoyl]amino]-10-(2-amino-2-oxoethyl)-13-(3-amino-3-oxopropyl)-22-(2-carboxyethyl)-25-[(1R)-1-hydroxyethyl]-19-(hydroxymethyl)-7-(2-methylpropyl)-6,9,12,15,18,21,24,27-octaoxo-1,2-dithia-5,8,11,14,17,20,23,26-octazacyclononacosane-4-carbonyl]amino]-4-methylpentanoyl]amino]-12,56,73-tris(2-amino-2-oxoethyl)-9,67-bis(3-amino-3-oxopropyl)-36-[(2S)-butan-2-yl]-18,47-bis(2-carboxyethyl)-24-(carboxymethyl)-27,53-bis(hydroxymethyl)-33-(2-methylpropyl)-8,11,14,17,20,23,26,29,32,35,38,45,48,51,54,57,60,62,65,68,71,74,77-tricosaoxo-59-propan-2-yl-3,4,41,42-tetrathia-7,10,13,16,19,22,25,28,31,34,37,46,49,52,55,58,61,63,66,69,72,75,78-tricosazabicyclo[37.22.17]octaheptacontane-6-carbonyl]amino]-3-methylbutanoyl]amino]-3-hydroxybutanoyl]amino]acetyl]amino]-4-carboxybutanoyl]amino]acetyl]amino]-3-hydroxybutanoyl]pyrrolidine-2-carbonyl]amino]hexanoyl]pyrrolidine-2-carbonyl]amino]-5-oxopentanoyl]amino]-3-hydroxypropanoyl]amino]-3-(1H-imidazol-4-yl)propanoyl]amino]-4-oxobutanoyl]amino]-3-carboxypropanoyl]amino]acetyl]amino]-3-carboxypropanoyl]amino]-3-phenylpropanoyl]amino]-4-carboxybutanoyl]amino]-4-carboxybutanoyl]amino]-3-methylpentanoyl]pyrrolidine-2-carbonyl]amino]-4-carboxybutanoyl]amino]-4-carboxybutanoyl]amino]-3-(4-hydroxyphenyl)propanoyl]amino]-4-methylpentanoyl]amino]-5-oxopentanoic acid

Lepirudin; Refludan; Lepirudin recombinant; 1-Leu-2-thr-63-desulfohirudin; Hbw 023; Lepirudin [INN:BAN]; UNII-Y43GF64R34; 138068-37-8;

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

May dissolve in DMSO (in most cases), if not, try other solvents such as H2O, Ethanol, or DMF with a minute amount of products to avoid loss of samples

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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 (Please use freshly prepared in vivo formulations for optimal results.)