Astins (including astin B) are a class of halogenated cyclic pentapeptides isolated from the medicinal herb of Aster tataricus. However, our previous works showed that the herbal medicine was hepatotoxic in vivo, and a toxicity-guided isolation method led to the identification of a cyclopeptide astin B. Astin B is structurally similar to cyclochlorotine, a well-known hepatotoxic mycotoxin. Thus, the aim of this study was to determine the potential cytotoxic effects and the underlying mechanism of astin B on human normal liver L-02 cells. We found that astin B has hepatotoxic effects in vitro and in vivo and that hepatic injury was primarily mediated by apoptosis in a mitochondria/caspase-dependent manner. Astin B provoked oxidative stress-associated inflammation in hepatocytes as evidenced by increased levels of reactive oxygen species (ROS), reduced contents of intracellular glutathione (GSH), and enhanced phosphorylation of c-Jun N-terminal kinase (JNK). Furthermore, the mitochondria-dependent apoptosis was evidenced by the depolarization of the mitochondrial membrane potential, the release of cytochrome c into cytosol, the increased ratio of Bax/Bcl-2, and the increased activities of caspases-9 and -3. Interestingly, astin B treatment also induces autophagy in L-02 cells, characterized by acidic-vesicle fluorescence, increased LC3-II and decreased p62 expression. Autophagy is a protective mechanism that is used to protect cells from apoptosis. The presence of autophagy is further supported by the increased cytotoxicity and the enhanced cleaved caspase-3 after co-treatment of cells with an autophagy inhibitor, also by increased LC3-II and decreased p62 after co-treatment with a caspase inhibitor. Taken together, astin B, most likely together with other members of astins, is the substance that is primarily responsible for the hepatotoxicity of A. tataricus.

A refined toxic fraction, Fr-2, from the ethanol extract of Aster tataricus roots was obtained by a toxic tracing isolation. The hepatotoxic effects of Fr-2 were proved by the level elevation of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (ALP) in mice serum and further confirmed by the histopathological examination on mice liver. A simple method was developed for qualitative analysis of constituents in Fr-2 fraction by high-performance liquid chromatography with diode array detection (HPLC-DAD) and electrospray ionization tandem mass spectrometry (ESI-MSn). As a result, 35 compounds were detected and identified in Fr-2. Among them, 28 compounds are pentapeptides, including 18 cyclic and 10 linear ones, and the sum of their peak area occupied about 87% (71.2% for cyclic and 15.8% for linear) of total area of chromatographic peak. Other 7 compounds are phenols, occupied about 5.9% of total area of chromatographic peak. Moreover, the structures of 10 cyclic and 2 linear peptides were reported for the first time. The results suggested that the peptides, especially the cyclic ones, are probably the principal toxic substances in Fr-2 also in A. tataricus roots.

A systematic review on chemical structures,toxic symptoms,detoxifying methods,toxic mechanisms and bioactivities of toxic natural polypeptides was given.These compounds often possess special toxicities and special bioactivities,which deserve developing and to be utilized for some difficult and complicated illnesses.