Identification of the structure-dependent toxicity of hepatotoxic pyrrolizidine alkaloids

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Unsaturated pyrrolizidine alkaloids (PA) belong to the most toxic compounds; more than 400 PA have been described in a wide range of plants. They are also found in Senecio vulgaris L. PA are toxic to humans and animals. PA were detected in substantial amounts into honey and tea. Acute PA poisoning via food contamination causes severe damage to the liver; long-term, sub-lethal doses may cause cumulative damage or cancer. Animal studies revealed that PA are carcinogenic. Mutagenicity of PA was observed in several in vitro and in vivo test systems. The toxicity of these compounds is associated with enzymatic reactions by enzymes dominantly expressed in the liver and dependent on PA´s bioavailability. However, the mode of action of PA to generate hepatotoxicity is not yet identified.Based on our results for bioavailability and the molecular mode of action of the structurally different PA echimidine, heliotrine, senecionine, and senkirkine we hypothesize that PA act in a structure-dependent manner. Therefore we aimed to group the PA structure- and toxicity-dependent within this project.For that purpose bioavailability shall be further studied in an in vitro model for the human intestinal barrier with a larger set of PA (22). As endpoint for grouping the ABCB1-dependent transport/detoxification shall be investigated for the structure-dependent mode of action of PA. Additionally, the molecular mechanism of PA hepatic toxicity shall be analyzed. We already showed in our transcriptomic study with the 4 structurally different PA differences in the induction of gene expression in the liver. Therefore, in vivo analysis of the induction of hepatotoxicity in mice in real time shall be analysed using two-photon excitation microscopy. The structure-dependent induction of toxicity shall be investigated using specific liver marker in wildtype mice and in further step in Abcb1 knockout mice. The identified toxic effects on liver shall be correlated with the transcriptomics data from human primary hepatocytes. Based on these results specific genes and signalling pathways shall be verified in regard to a structure-dependent induction by PA using quantitative real time PCR and reporter gene assays, respectively.This study aimed to close gaps in regard to the structure-dependent PA bioavailability and hepatic mode of action to form PA toxicity group on the basis of its different structure. These data shall contribute to a better understanding of the toxic consequences of an acute or chronic PA uptake to enhance the protection of humans.