In Vitro Metabolism of Isoline, a Pyrrolizidine Alkaloid from Ligularia duciformis, by Rodent Liver Microsomal Esterase and Enhanced Hepatotoxicity by Esterase Inhibitors
In Vitro Metabolism of Isoline, a Pyrrolizidine Alkaloid from Ligularia duciformis, by Rodent Liver Microsomal Esterase and Enhanced Hepatotoxicity by Esterase Inhibitors
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DOI：
10.1124/dmd.107.016311
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发表时间：
2007-10
影响因子：
3.9
通讯作者：
Jun Tang;T. Akao;N. Nakamura;Zheng-Tao Wang;K. Takagawa;M. Sasahara;M. Hattori
中科院分区：
文献类型：
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作者：
Jun Tang;T. Akao;N. Nakamura;Zheng-Tao Wang;K. Takagawa;M. Sasahara;M. Hattori
异莲心碱（Isoline）是一种主要的反枝碱型吡咯里西啶生物碱（PA），是目前已知毒性最强的PA。因此，在大鼠和小鼠肝微粒体中检测了其体外代谢，并将其毒性与小鼠腹腔注射后的君子兰碱和野百合碱进行了比较。Isoline在两种微粒体中的代谢速度均高于clivorine和野百合碱，并转化为两种极性代谢产物M1和M2，经光谱测定分别为bisline（isoline的脱乙酰代谢产物）和bisline内酯。在存在或不存在NADPH生成系统的情况下，两种代谢产物均与肝微粒体形成，但不与胞质溶胶形成。它们的形成完全被酯酶抑制剂磷酸三邻甲苯酯（TOCP）和苯甲基磺酰氟抑制，但完全或部分不被细胞色素P450（P450）抑制剂α-萘啶酮和proadifen（SKF 525 A）抑制。这些结果表明，这两种代谢产物均由微粒体酯酶产生，而非P450同工酶。在大鼠和小鼠肝微粒体中，所涉及的酯酶不仅表现出相当不同的活性，而且对不同抑制剂的反应也不同，这表明不同的关键同工酶或其组合可能负责同工酶的脱乙酰化。通过组织病理学以及血清丙氨酸氨基转移酶和天冬氨酸氨基转移酶水平判断，Isoline腹腔注射到小鼠中诱导的肝脏特异性毒性远大于clivorine或野百合碱。酯酶抑制剂TOCP可显著增强Isoline诱导的肝毒性，而P450抑制剂SKF 525 A可降低Isoline诱导的肝毒性，表明啮齿动物肝酯酶通过快速脱乙酰化在体内Isoline的解毒中起主要作用。
Isoline, a major retronecine-type pyrrolizidine alkaloid (PA) from the Chinese medicinal herb Ligularia duciformis, was suggested to be the most toxic known PA. Its in vitro metabolism was thus examined in rat and mouse liver microsomes, and its toxicity was compared with that of clivorine and monocrotaline after i.p. injection in mice. Isoline was more rapidly metabolized by both microsomes than clivorine and monocrotaline and converted to two polar metabolites M1 and M2, which were spectroscopically determined to be bisline (a deacetylated metabolite of isoline) and bisline lactone, respectively. Both metabolites were formed in the presence or absence of an NADPH-generating system with liver microsomes but not cytosol. Their formation was completely inhibited by the esterase inhibitors, triorthocresyl phosphate (TOCP) and phenylmethylsulfonyl fluoride, but not at all or partially by cytochrome P450 (P450) inhibitors, α-naphthoflavone and proadifen (SKF 525A), respectively. These results demonstrated that both metabolites were produced by microsomal esterase(s) but not P450 isozymes. The esterase(s) involved showed not only quite different activities but also responses to different inhibitors in rat and mouse liver microsomes, suggesting that different key isozyme(s) or combinations might be responsible for the deacetylation of isoline. Isoline injected i.p. into mice induced liver-specific toxicity that was much greater than that with either clivorine or monocrotaline, as judged by histopathology as well as serum alanine aminotransferase and aspartate aminotransferase levels. Isoline-induced hepatotoxicity was remarkably enhanced by the esterase inhibitor TOCP but was reduced by the P450 inhibitor SKF 525A, indicating that rodent hepatic esterase(s) played a principal role in the detoxification of isoline via rapid deacetylation in vivo.