clivorine and isoline

Intracellular reduced glutathione (GSH) antioxidant system is crucial for counteracting oxidative stress-induced liver injury. The present study was designed to observe the gender-dependent difference of GSH antioxidant system and its influence on hepatotoxic pyrrolizidine alkaloid (HPA) isoline-induced liver injury. Lower activities and protein expressions of glutamate-cysteine ligase (GCL) and glutathione peroxidase (GPx) were found in male mice livers than in female. Isoline is a natural HPA, our further results showed that male mice demonstrated more higher serum ALT/AST levels, less GSH amounts, lower GCL and GPx activities and proteins induced by isoline as compared to female. N-acetyl-l-cysteine (NAC), which is the precursor of cellular GSH biosynthesis, ameliorated liver injury induced by isoline. l-Buthionine-(S, R)-sulfoximine (BSO) and mercaptosuccinic acid (MA), inhibitors of GCL and GPx, both augmented isoline-induced cytotoxicity in cultured mice hepatocytes. BSO and MA also increased other natural HPAs clivorine and senecionine-induced cytotoxicity. Taken together, our results demonstrated the higher GCL and GPx activities in female mice, which indicated their crucial roles in regulating the resistance of liver injury induced by hepatotoxins in female. Meanwhile, our results also revealed the female-resistant liver injury induced by HPAs for the first time.

Topics: Acetylcysteine; Animals; Chemical and Drug Induced Liver Injury; Female; Glutamate-Cysteine Ligase; Glutathione; Glutathione Peroxidase; Liver; Male; Mice; Mice, Inbred ICR; Pyrrolizidine Alkaloids; Sex Characteristics

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.

Topics: Alanine Transaminase; Animals; Antitussive Agents; Aspartate Aminotransferases; Asteraceae; Benzoflavones; Cytochrome P-450 Enzyme Inhibitors; Drugs, Chinese Herbal; Esterases; Expectorants; Liver; Male; Mice; Mice, Inbred Strains; Microsomes, Liver; Monocrotaline; Phenylmethylsulfonyl Fluoride; Proadifen; Pyrrolizidine Alkaloids; Rats; Rats, Sprague-Dawley; Tritolyl Phosphates