clivorine and otonecine

Plants that contain pyrrolizidine alkaloids (PAs) are widely distributed, and PAs have been shown to be genotoxic and tumorigenic in experimental animals. Our recent mechanistic studies indicated that riddelliine, a tumorigenic retronecine type PA, induced tumors via a genotoxic mechanism mediated by the formation of a set of eight 6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP)-derived DNA adducts. However, it is not known if this mechanism is general to PAs of other types. In this study, we report that the metabolism of clivorine, a tumorigenic otonecine type PA, by F344 rat liver microsomes results in DHP formation. When incubations were conducted with clivorine in the presence of calf thymus DNA, eight DHP-derived DNA adducts were formed. The Ligularia hodgsonnii Hook plant, an antitussive traditional Chinese medicine, was found to contain otonecine type PAs with clivorine being predominant. DHP and DHP-derived DNA adducts were also obtained when microsomal incubations were conducted with extracts of L. hodgsonnii Hook. This is the first report that DHP-derived DNA adducts are formed from the metabolic activation of otonecine type PA and that these DHP-derived DNA adducts are potential biomarkers of PA exposure and PA-induced tumorigenicity. These results also provide evidence that the principal metabolic activation pathway of clivorine leading to liver genotoxicity and tumorigenicity is (i) formation of the corresponding dehydropyrrolizidine (pyrrolic) derivative through oxidative N-demethylation of the necine base followed by ring closure and dehydration and (ii) binding of the pyrrolic metabolite to DNA leading to the DNA adduct formation and tumor initiation.

Topics: Animals; Asteraceae; Biomarkers; Carcinogens; Chromatography, High Pressure Liquid; Cytochrome P-450 Enzyme Inhibitors; Dihydropyridines; DNA; DNA Adducts; Male; Mass Spectrometry; Microsomes, Liver; Plant Extracts; Pyrrolizidine Alkaloids; Rats

Clivorine (1) and ligularine (2), two hepatotoxic otonecine-type pyrrolizidine alkaloids isolated from Ligularia hodgsonii, an antitussive traditional Chinese medicine, were investigated in CDCl(3) and D(2)O by various NMR techniques to delineate why this type of alkaloid displays uncharacteristic solubility properties by dissolving in both nonpolar organic and aqueous solutions. The results demonstrated that both alkaloids exist in a non-ionized form in CDCl(3), but in an ionized form in D(2)O, suggesting that this unique dual solubility may play a role in the intoxication resultant from consumption of water extracts of herbs, including herbal teas, containing otonecine-type pyrrolizidine alkaloids.

Topics: Antitussive Agents; Asteraceae; Carcinogens; Magnetic Resonance Spectroscopy; Medicine, Chinese Traditional; Phytotherapy; Pyrrolizidine Alkaloids; Solubility; Tea