Runnegar M T, Maddatu T, Deleve L D, Berndt N, Govindarajan S
Department of Medicine, Children's Hospital, Los Angeles, California, USA.
J Pharmacol Exp Ther. 1995 Apr;273(1):545-53.
Microcystin (Mcyst) and calyculin A (CalA) in vitro inhibit protein phosphatases (PP)1 and 2A activity (IC50 0.1-2.0 nM). This study was aimed at determining the contribution of PP inhibition to Mcyst hepatotoxicity by comparing the effect of these two chemically different inhibitors in perfused rat livers. Both compounds (60 micrograms Mcyst and 6 micrograms CalA/150 ml perfusate) caused cessation of bile flow and inhibition of PP activity after 20 min of perfusion to 8% and 37% of control activity for Mcyst and CalA treatments, respectively. Histopathological findings included loss of cord sinusoidal pattern and of normal liver architecture. There also was hepatocyte swelling, pyknotic changes and necrosis. Mcyst caused a modest increase in perfusion pressure of 1.2 cm of water, whereas CalA caused a 3-fold increase. The most likely explanation for this hemodynamic effect is direct action of CalA on the vascular endothelium and/or sinusoidal and perisinusoidal cells. This possibility was explored with hepatocytes and sinusoidal endothelial cells. PP activity of both cell types was inhibited by 10 to 100 nM CalA followed later by cell lysis, whereas Mcyst (500 nM-2 microM) had no effect on sinusoidal endothelial cells, but inhibited PP activity and caused later lysis in hepatocytes (Mcyst 20-160 nM). Mcyst hepatotoxicity is therefore a direct consequence of PP inhibition in hepatocytes, the loss of sinusoidal integrity following from the primary toxic insult to the hepatocyte. Inhibition of PP activity of the cells of the presinusoidal vasculature and/or nonparenchymal cells results in hepatic hypertension.
微囊藻毒素（Mcyst）和花萼海绵诱癌素A（CalA）在体外可抑制蛋白磷酸酶（PP）1和2A的活性（半数抑制浓度为0.1 - 2.0 nM）。本研究旨在通过比较这两种化学结构不同的抑制剂在灌注大鼠肝脏中的作用，确定PP抑制对Mcyst肝毒性的影响。两种化合物（60微克Mcyst和6微克CalA/150毫升灌注液）在灌注20分钟后均导致胆汁流动停止，并抑制PP活性，Mcyst和CalA处理组的PP活性分别降至对照活性的8%和37%。组织病理学结果包括肝索窦状模式和正常肝脏结构的丧失。还存在肝细胞肿胀、核固缩变化和坏死。Mcyst使灌注压力适度升高1.2厘米水柱，而CalA使灌注压力升高3倍。对这种血流动力学效应最可能的解释是CalA对血管内皮和/或窦状隙及窦周细胞的直接作用。利用肝细胞和窦状内皮细胞对这种可能性进行了研究。两种细胞类型的PP活性均被10至100 nM的CalA抑制，随后细胞裂解，而Mcyst（500 nM - 2 microM）对窦状内皮细胞无影响，但抑制肝细胞的PP活性并在后期导致肝细胞裂解（Mcyst为20 - 160 nM）。因此，Mcyst肝毒性是肝细胞中PP抑制的直接后果，是肝细胞受到原发性毒性损伤后窦状隙完整性丧失所致。窦前血管和/或非实质细胞的PP活性受到抑制会导致肝高血压。
