necic-acid and retronecine

Pyrrolizidine alkaloids (PAs) are characteristic metabolites of some plant families and form a powerful defense mechanism against herbivores. More than 600 different PAs are known. PAs are ester alkaloids composed of a necine base and a necic acid, which can be used to divide PAs in different structural subcategories. The main target organs for PA metabolism and toxicity are liver and lungs. Additionally, PAs are potentially genotoxic, carcinogenic and exhibit developmental toxicity. Only for very few PAs, in vitro and in vivo investigations have characterized their toxic potential. However, these investigations suggest that structural differences have an influence on the toxicity of single PAs. To investigate this structural relationship for a large number of PAs, a quantitative structural-activity relationship (QSAR) analysis for hepatotoxicity of over 600 different PAs was performed, using Random Forest- and artificial Neural Networks-algorithms. These models were trained with a recently established dataset specific for acute hepatotoxicity in humans. Using this dataset, a set of molecular predictors was identified to predict the hepatotoxic potential of each compound in validated QSAR models. Based on these models, the hepatotoxic potential of the 602 PAs was predicted and the following hepatotoxic rank order in 3 main categories defined (1) for necine base: otonecine > retronecine > platynecine; (2) for necine base modification: dehydropyrrolizidine ≫ tertiary PA = N-oxide; and (3) for necic acid: macrocyclic diester ≥ open-ring diester > monoester. A further analysis with combined structural features revealed that necic acid has a higher influence on the acute hepatotoxicity than the necine base.

Topics: Algorithms; Chemical and Drug Induced Liver Injury; Cyclic N-Oxides; Databases, Factual; Dicarboxylic Acids; Heterocyclic Compounds, 2-Ring; Humans; Liver; Machine Learning; Molecular Structure; Neural Networks, Computer; Pyrrolizidine Alkaloids; Quantitative Structure-Activity Relationship; Reproducibility of Results; Risk Assessment

[3H]Retronecine and [3H]necic acid-labelled senecionine and seneciphylline were prepared biosynthetically with seedlings of Senecio vulgaris L. using [2,3-3H]putrescine and [4,5-3H]isoleucine, respectively, as precursors. Lactating rats dosed with these differently labelled pyrrolizidine alkaloids (PAs) excreted within 3 h approx. 0.08% of the applied radioactivity in the milk mainly as yet not identified water-soluble retronecine-derived metabolites and with approx. 0.02% as unchanged PAs. Highest tissue levels of PAs and metabolites, 6 h after administration, were found in liver and lungs.

Topics: Animals; Dicarboxylic Acids; Female; Kinetics; Milk; Plants, Toxic; Pregnancy; Pyrrolizidine Alkaloids; Rats; Senecio; Tissue Distribution; Tritium