Structure revision of isoline (ruwenine), bisline and isolinecic acid

Proteomic characterization of the possible molecular targets of pyrrolizidine alkaloid isoline-induced hepatotoxicity

Pyrrolizidine alkaloids (PAs) are distributed in plants worldwide including medicinal herbs or teas. In the present study, we investigated the effects of isoline, which is a retronecine-type PA isolated from traditional Chinese medicinal herb Ligularia duciformis, on mouse liver proteins by using proteomic approaches. Firstly, our results showed that 110mg/kg isoline increased alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities in serum, and hepatic tissue pathological observation further confirmed isoline-induced liver injury. Proteomic analysis showed that the liver samples from mice of isoline group demonstrated about 13 differentially expressed proteins compared with normal group, and those proteins may be involved in isoline-induced liver injury in mice. Next, all these 13 protein spots were identified by MALDI-TOF-TOF MS or LTQ MS; and among them 9 differentially expressed proteins are involved in the process of oxidative stress or cellular energy metabolism. Further lipid peroxidation analysis and ATPase assay confirmed the existing of oxidative injury induced by isoline and consequent disruption of energy metabolism. Furthermore, an in silico drug target searching program INVDOCK identified 2 potential protein targets of isoline, and the results are in support of proteomic analysis. In summary, the possible signaling molecules related with isoline-induced liver injury were demonstrated in this study.

In Vitro Metabolism of Isoline, a Pyrrolizidine Alkaloid fromLigularia duciformis, by Rodent Liver Microsomal Esterase and Enhanced Hepatotoxicity by Esterase Inhibitors

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, alpha-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.