In vitro and in vivo studies of AT-1362, a newly synthesized and orally active inhibitor of thrombin

An inhibitor of thrombin activated fibrinolysis inhibitor (TAFI) can reduce extracellular matrix accumulation in an in vitro model of glucose induced ECM expansion

Chronic kidney disease (CKD) is characterised by the pathological accumulation of extracellular matrix (ECM) proteins leading to progressive kidney scarring via glomerular and tubular basement membrane expansion. Increased ECM synthesis and deposition, coupled with reduced ECM breakdown contribute to the elevated ECM level in CKD. Previous pre-clinical studies have demonstrated that increased plasmin activity has a beneficial effect in the protein overload model of CKD. As plasmin activation is downregulated by the action of the thrombin activated fibrinolytic inhibitor (TAFI), we tested the hypothesis that inhibition of TAFI might increase plasmin activity and reduce ECM accumulation in an in vitro model of glucose induced ECM expansion. Treatment of NRK52E tubular epithelial cells with increasing concentrations of glucose resulted in a 40% increase in TAFI activity, a 38% reduction in plasmin activity and a subsequent increase in ECM accumulation. In this model system, application of the previously reported TAFI inhibitor UK-396082 [(2S)-5-amino-2-[(1-n-propyl-1H-imidazol-4-yl)methyl]pentanoic acid] caused a reduction in TAFI activity, increased plasmin activity and induced a parallel decrease in ECM levels. In contrast, RNAi knockdown of plasmin resulted in an increase in ECM levels. The data presented here indicate that high glucose induces TAFI activity, inhibiting plasmin activation which results in elevated ECM levels in tubular epithelial cells. The results support the hypothesis that UK-396082 is able to reduce TAFI activity, normalising plasmin activity and preventing excess ECM accumulation suggesting that TAFI inhibition may have potential as an anti-scarring strategy in CKD.

A new rat pain model of thrombus-induced ischemia

Pathophysiology of peripheral ischemic pain has not been fully demonstrated since the proper animal model has not been established. We designed this study to develop a new thrombus-induced ischemic pain (TIIP) animal model mimicking human peripheral ischemic pain by using ferrous chloride (FeCl(2)) in rats. Histological examination and Evans blue experiment revealed that the application of FeCl(2) onto the femoral artery produced an excessive thrombosis and ischemic condition in ipsilateral hind paw. Furthermore, ischemia-sensitive markers, such as hypoxia inducible factor-1 alpha (HIF-1α) and vascular endothelial growth factor (VEGF) were upregulated in the ipsilateral plantar muscles of FeCl(2)-applied rats. The mechanical allodynia was induced in bilateral hind paws from 1 day after FeCl(2) application and sustained for 30 days. However, thermal threshold of bilateral hind paws did not change in this animal model. In conclusion, we have developed a novel animal model of TIIP, which is characterized by the development of bilateral mechanical allodynia, but not thermal hyperalgesia. Thus, we suggest that this TIIP model can be useful in investigating the pathophysiological mechanisms that underlie human peripheral ischemic pain.

A new rat model for thrombus-induced ischemic pain (TIIP); development of bilateral mechanical allodynia

Patients with peripheral arterial disease (PAD) commonly suffer from ischemic pain associated with severe thrombosis. However, the pathophysiology of peripheral ischemic pain is not fully understood due to the lack of an adequate animal model. In this study, we developed a new rodent model of thrombus-induced ischemic pain (TIIP) to investigate the neuronal mechanisms underlying ischemic pain. Ischemia was induced by application of 20% FeCl(2) onto the surface of the femoral artery for 20min. Induction of peripheral ischemia was confirmed by measurement of the concentration of Evans blue and by increases in the ischemia-specific markers, hypoxia-inducible factor-1 alpha and vascular endothelial growth factor in the ipsilateral plantar muscles. Ischemic pain, as indicated by the presence of mechanical allodynia, developed bilaterally and peaked at days 3-9 post-FeCl(2) application and gradually decreased through day 31. Systemic heparin pretreatment dose dependently suppressed ischemic pain, suggesting that thrombosis-induced ischemia might be a key factor in TIIP. Intraplantar injection of BMS-182874, an ET(A) (endothelin-A) receptor antagonist, at day 3 selectively blocked ipsilateral pain, indicating that ET(A) receptor activity mediated TIIP. Spinal GFAP expression was significantly increased by FeCl(2) and intrathecal injection of carbenoxolone (an astrocyte gap junction decoupler) at day 3 significantly reduced TIIP, suggesting that spinal astrocyte activation plays an important role. However, the anti-inflammatory agent, ibuprofen, did not affect TIIP. In conclusion, we have developed a novel animal model of TIIP that should be useful in investigating the pathophysiological mechanisms that underlie human peripheral ischemic pain.

The anticoagulant fraction from the leaves ofDiospyros kaki L. has an antithrombotic activity

The leaves of Persimmon (Diospyros kaki L.) has long been used for tea in Korea since it was thought to be effective against hypertension. An anticoagulant fraction was purified through gel filtration G-100, hydrophobic, gel filtration G-150, and FPLC, Phenyl superpose column chromatographies. The purified fraction was homogenous and its Mr was estimated 10,000 Da by gel filtration and SDS-PAGE. The purified fraction was sensitive to treatment of subtilisin B, but not to heat and its activity was not changed after periodate oxidation, indicating that the activity was not due to carbohydrates. It delayed thrombin time (TT), activated partial thromboplastin time (APTT), and prothrombin time (PT) using human plasma. TT was more sensitive than APTT and PT, suggesting that the anticoagulant activity may be caused by a degradation or a defect of fibrin or thrombin. It did not cause the hydrolysis of fibrin after incubation. However, it inhibited thrombin-catalyzed fibrin formation with a competitive inhibition pattern. These results indicate that it may be an antithrombotic agent and that it is bound to fibrinogen binding sites of thrombin.

Antithrombotic effect of Glycyrrhizin, a plant-derived thrombin inhibitor

Glycyrrhizin (GL), an anti-inflammatory compound isolated from licorice (Glycyrrhiza glabra), has been previously identified as a thrombin inhibitor (Francischetti et al., Biochem Biophys Res Commun 1997;235:259-63). Here we report the in vivo effects of GL upon two experimental models of induced thrombosis in rats. Intravenous administration of GL caused a dose-dependent reduction in thrombus size on a venous thrombosis model that combines stasis and hypercoagulability. It was observed that GL doses of 180 mg/kg body weight produced 93% decrease on thrombus weight. This effect showed a time-dependent pattern being significantly reduced when the thrombogenic stimulus was applied 60 min after drug administration. GL was also able to prevent thrombosis using an arteriovenous shunt model. GL doses of 180 and 360 mg/kg decreased the thrombus weight by 35 and 90%, respectively. Accordingly, the APTT ex vivo was enhanced by 1.5- and 4.3-fold at GL doses of 180 and 360 mg/kg, respectively. In addition, GL doses above 90 mg/kg caused significant hemorrhagic effect. In contrast with heparin, GL did not potentiate the inhibitory activity of antithrombin III or heparin cofactor II towards thrombin. Altogether, data indicate that GL is an effective thrombin inhibitor in vivo, which may account for its other known pharmacological properties.

Advances in the development of thrombin inhibitors

Thromboembolic diseases are a major cause of morbidity and mortality, particularly in the Western world, which has stimulated enormous research efforts by the pharmaceutical industry to introduce new antithrombotic therapies. One strategy is the development of direct inhibitors of the serine protease thrombin, which holds a central position in the final steps of the blood coagulation cascade and in platelet activation. At present there is only limited clinical use of some parenteral preparations of thrombin inhibitors in acute situations, especially when the common antithrombotic drugs heparin, warfarin and aspirin are ineffective or associated with side effects. However, for use in prophylaxis of thrombotic diseases such inhibitors should be orally available, must be safe to avoid bleeding complications and should have an appropriate half-life, allowing once or twice daily dosing to maintain adequate antithrombotically effective blood levels. Details of several new and potent thrombin inhibitors have been published during the last years. For some of them oral bioavailability is claimed and they are effective in in vitro coagulation assays. However, most of them showed only limited efficacy in animal studies with respect to the doses administered. For that reason, effort is concentrated on the evaluation and optimisation of the overall physicochemical characteristics of the inhibitors in order to improve the pharmacokinetics and, thus, the development of promising drug candidates. Nevertheless, only careful clinical studies can give clear answers about the true therapeutical benefit of new developments in this field. This review summarises the current status of direct thrombin inhibitors which are already in clinical use and clinical development and gives an overview on recently published and promising new compounds.