The present study was designed to investigate if TAKparallel with a decrease in hepatic arterial and portal blood 044, a novel endothelin (ET) ET A /ET B receptor antagoflow. These pathological changes were reversed after ET-1 nist, inhibits ischemia-reperfusion liver injury. The iniinfusion was completed. tial study showed the presence of both ET A and ET B Several observations were derived from our previous study receptors in canine hepatic membrane fractions using using a partial liver ischemic model. 6 First, the ET levels in the specific binding assay of labeled ET-1 with ET isothe liver tissue and hepatic venous blood of the ischemic lobe mers and TAK-044. The nonselective ET A /ET B receptor increased slightly during ischemia and markedly after reperantagonist TAK-044 inhibited the specific binding of ETfusion, whereas those of the nonischemic lobe showed no sig-1 to the receptors in a concentration-dependent manner.
nificant increases. Second, the ET levels in the portal venous In subsequent studies using a canine 70% partial liver blood were significantly higher than the levels in the hepatic ischemic model (60 minutes), we found that an intravevenous blood of the ischemic lobe. Third, the intravenous nous injection of TAK-044 (3 mg/kg) before ischemia sigadministration of ET monoclonal antibody (0.5 mg/kg) before nificantly inhibited the release of serum liver enzymes reperfusion resulted in a significant inhibition of the postre-(aspartate transaminase, alanine transaminase, mitoperfusion release of the liver enzymes and improved the indochondrial glutamic oxaloacetic transaminase, and an incyanine green dye retention rate at 15 minutes. Thus, ET-1 is crease of indocyanine green retention rate after reperfustrongly involved in the pathogenesis of ischemia-reperfusion sion, compared with the control group. Elevation of the injury. portal venous pressure was also suppressed signifi-Recently, cyclic pentapeptides, BE-18257B, BQ-123, and cantly during the portal triad occlusion, and a rapid res-BQ-153, 7,8 and a tripeptide, FR139317, 9 have been shown to toration of oxygen pressure in the liver tissue after rebe specific for ET A receptor antagonists, while IRL 1038, 10 perfusion was observed in the TAK-044-treated group.
BQ-788, 11 and RES-701-1 12 were specific for ET B receptor an-Morphometric analysis revealed that the hepatocyte tagonists. These antagonists are considered to be useful for swelling and sinusoidal contraction 1 hour after reperfustudying ET A -or ET B -mediated responses separately. It resion were significantly less severe in the treated group mains to be clarified if these agents are useful in the protecthan in the control group. The sludging of erythrocytes tion of ET-1-induced liver ischemia-reperfusion injury since in the sinusoidal lumens was also minimal in the treated ET-1 has high affinity for both ET A and ET B receptors, which group. In conclusion, the significant suppression of heare responsible for ET-1-induced vasoconstriction and prespatic microcirculatory disturbance and tissue injury sor responses. 13,14 after ischemia-reperfusion were shown in the TAK-044-Nonselective ET A and ET B receptor antagonists are extreated group. This finding indicates that the pretreatpected to be of clinical use for patients who suffer from isment of TAK-044 is useful as a hepatoprotective agent chemia-reperfusion injury in a clinical setting such as hepaagainst ischemia-reperfusion injury, which is otherwise tectomy or liver transplantation. Therefore, the in vivo effect produced by a pathway involving ET-1. (HEPATOLOGY of a novel nonselective ET A /ET B receptor antagonist, TAK-1997;25:938-942.)
044, against ischemia-reperfusion injury in the liver was examined in this study. Endothelin (ET) is a potent and long-lasting vasoconstrictive peptide consisting of 21 amino acids. In 1988, Yanagi-
MATERIALS AND METHODS
sawa et al., first isolated this peptide from the supernatant Experiment 1 of cultured porcine aortic endothelial cells and determined
Preparation of the Hepatic Membrane Fraction. Adult male beaits structure. 1 In recent years, various studies have focused gles weighing 10 to 13 kg were used. The liver was excised under on ET-1-induced hepatic microcirculatory disturbance 2,3 and anesthesia introduced by an intravascular injection of pentobarbital its adverse affects on the metabolism in the liver. 4,5 Our un-(30 mg/kg). Hepatic membrane fractions were prepared according to published data have clarified that a dose-dependent intraporthe method of Kiso et al. 15 Briefly, the liver was minced and homoge- tal infusion of ET-1 (1.0, 2.5, and 5.0 ng/kg/mL) provokes an nized with a Polytron homogenizer (Kinematica, Littau-Luzern, Switzerland) (PT20, at 3 4 maximum speed, four times, for 20 seconds each) in 20 mmol/L Tris/HCl buffer solution (pH 7.4) containing 250 mmol/L sucrose, 2 mmol/L MgCl 2 , and 2 mmol/L ethylenediaminetet-Abbreviation: ET, endothelin. raacetic acid and the homogenate was centrifuged at 2,500g for 10 From the First Department of Surgery, Hyogo College of Medicine, 1-1, Mukogawa-cho, minutes. The supernatant was further centrifuged at 20,000g for 20 Nishinomiya, Japan. minutes. The pellet was homogenized using a Teflon homogenizer,