Pyrrolizidine alkaloids (PAs) are genotoxic carcinogenic phytotoxins mostly prevalent in the Boraginaceae, Asteraceae and Fabaceae families. Heliotropium species (Boraginaceae) are PA-producing weeds, widely distributed in the Mediterranean region, that have been implicated with lethal intoxications in livestock and humans. In Israel, H. europaeum, H. rotundifolium and H. suaveolens are the most prevalent species. The toxicity of PA-producing plants depends on the PA concentration and composition. PAs occur in plants as mixtures of dozens of various PA congeners. Hence, the risk arising from simultaneous exposure to different congeners has to be evaluated. The comparative risk evaluation of the three Heliotropium species was based on recently proposed interim relative potency (iREP) factors, which take into account certain structural features as well as in vitro and in vivo toxicity data obtained for several PAs of different classes. The aim of the present study was to determine the PA profile of the major organ parts of H. europaeum, H. rotundifolium and H. suaveolens in order to assess the plants' relative toxic potential by utilizing the iREP concept. In total, 31 different PAs were found, among which 20 PAs were described for the first time for H. rotundifolium and H. suaveolens. The most prominent PAs were heliotrine-N-oxide, europine-N-oxide and lasiocarpine-N-oxide. Europine-N-oxide displayed significant differences among the three species. The PA levels ranged between 0.5 and 5% of the dry weight. The flowers of the three species were rich in PAs, while the PA content in the root and flowers of H. europaeum was higher than that of the other species. H. europaeum was found to pose a higher risk to mammals than H. rotundifolium, whereas no differences were found between H. europaeum and H. suaveolens as well as H. suaveolens and H. rotundifolium.
Keywords: Heliotropium europaeum; interim relative potency factor; pyrrolizidine alkaloids; rotundifolium; suaveolens.