Fibrinolytic potential of DS-1040, a novel orally available inhibitor of activated thrombin-activatable fibrinolysis inhibitor (TAFIa).

An activated thrombin-activatable fibrinolysis inhibitor (TAFIa) attenuates fibrinolysis by removing C-terminal lysine/arginine residues from partially degraded fibrin. We have identified a novel low-molecular-weight inhibitor of TAFIa, DS-1040, to be potentially useful for treating thrombotic diseases. In this study, we investigated its in vitro pharmacological profile and in vivo effects in animal models of microthrombosis and bleeding. DS-1040 inhibited human TAFIa and carboxypeptidase N (CPN) in vitro with IC50 values of 5.92 and 3.02 × 106 nmol/L, respectively, suggesting that DS-1040 is highly selective for TAFIa over CPN. DS-1040 did not affect platelet aggregation and coagulation time. In a tissue factor-induced rat microthrombosis model, intravenously administered DS-1040 reduced existing fibrin clots in the lung, whereas post-treatment with enoxaparin had limited effect. Both intravenously and orally administered DS-1040 elevated plasma D-dimer levels with similar plasma exposures of DS-1040. DS-1040 significantly augmented plasma D-dimer level on top of silent dose of recombinant tissue-plasminogen activator (t-PA), suggesting DS-1040 enhances fibrinolytic activity of t-PA. In addition, DS-1040 did not prolong the tail bleeding time beyond its efficacy dose. These results indicate that DS-1040 is a potent, selective, intravenously/orally available inhibitor of TAFIa with minimum risk of bleeding. DS-1040 is a potential novel fibrinolysis enhancer useful in treating thrombotic diseases.

Comparison of antithrombotic and haemorrhagic effects of edoxaban, an oral direct factor Xa inhibitor, with warfarin and enoxaparin in rats.

INTRODUCTION: Factor Xa (FXa) is a key serine protease in the coagulation cascade and a promising target for a new antithrombotic agent. Edoxaban is an oral, selective and direct FXa inhibitor. The objective of this study was to compare the antithrombotic and haemorrhagic effects of edoxaban with clinically available anticoagulants, warfarin and enoxaparin, in rat models of thrombosis and haemorrhage. METHODS: Rats were treated with single oral administration of edoxaban, repeated oral dosing of warfarin for 4 days and single subcutaneous administration of enoxaparin before thrombosis or haemorrhage induction. Thrombosis was induced by the insertion of a platinum wire into the inferior vena cava for 60 min. Tail template bleeding time was measured after making an incision on the tail. RESULTS: Edoxaban at 0.3, 1 and 3mg/kg exerted dose-dependent and significant inhibition of venous thrombus formation. The 50% thrombus inhibition dose (ED(50)) was 1.9 mg/kg. At supra-therapeutic doses (10 and 20mg/kg), edoxaban significantly but moderately (less than 2-fold) prolonged bleeding time. Warfarin and enoxaparin also dose-dependently inhibited venous thrombosis and prolonged bleeding time. The ED(50) values of warfarin and enoxaparin were 0.12 mg/kg and 500 IU/kg, and the 2-fold bleeding time prolongation doses (BT2) were 0.16 mg/kg and 1700 IU/kg, respectively. The safety margin (ratio of BT2 to ED(50)) of edoxaban (>10.5) was greater than those of warfarin (1.3) and enoxaparin (3.4). CONCLUSIONS: Edoxaban inhibited venous thrombosis comparably to warfarin and enoxaparin, and the attendant bleeding risk of edoxaban was lower than that of warfarin and enoxaparin in rats.

Serum S-100b protein as a biomarker for the assessment of neuroprotectants.

The study of biomarkers associated with stroke has proved to be of considerable utility. The astroglial protein S-100b is a candidate marker for cerebral tissue damage. We used a rat embolic model produced by injection of microspheres to demonstrate that serum S-100b is a useful biochemical marker for ischemic brain injury. Serum S-100b levels were significantly increased following microsphere injection, which was closely correlated with the development of brain edema. We found that structurally and mechanistically independent neuroprotective agents, such as 3-[2-[4-(3-chloro-2-methylphenylmethyl)-1-piperazinyl]ethyl]-5,6-dimethoxy-1-(4-imidazolylmethyl)-1H-indazole dihydrochloride 3.5 hydrate (DY-9760e), a novel calmodulin antagonist, and the N-methyl-d-aspartate (NMDA) receptor antagonist MK-801, are capable of attenuating increased serum S-100b levels and brain edema. In contrast, the hyperosmolar agent glycerol, which has no direct neuroprotective action, had little effect on serum S-100b levels, despite a significant decrease in brain water content. These results suggest that lowering of serum S-100b is mediated by neuroprotection against ischemic brain injury. Thus, serum S-100b reflects the extent of brain damage following cerebral ischemia and serves as a useful biomarker for the assessment of neuroprotectants.