Hepatotoxicity screening and ranking of structurally different pyrrolizidine alkaloids in zebrafish

Pyrrolizidine alkaloids (PAs) are phytotoxins distributed in similar to 6000 plant species. PA-contaminated/containing foodstuffs/herbs/supplements pose a potential threat to human health. Various regulatory authorities established different PA margins of exposure assuming an equal hepatotoxic potency of structurally diverse PAs, although they exhibit different toxic potencies. Therefore, understanding hepatotoxic potencies of different PAs would facilitate a more appropriate risk assessment of PA exposure. In this study, a zebrafish model, which mimics physiological processes of absorption, distribution, metabolism, and excretion, was selected to evaluate acute hepatotoxic potency of different PAs (7 PAs and 2 PA N-oxides) and explore possible physiological pathways involved in PA-induced hepatotoxicity. After 6 h oral administration, PAs caused distinct structure-dependent hepatotoxicity with a series of biochemical and histological changes in zebrafish. Based on the measured toxicological endpoints, the relative toxic potency order of different PAs was derived as lasiocarpine similar to retrorsine > monocrotaline > riddelliine > clivorine > heliotrine > retrorsine N-oxide similar to riddelliine N-oxide >> > platyphyline. Further, compared to control group, different upregulation/downregulation of mRNA expression in PA-treated groups indicated that inflammation, apoptosis, and steatosis were involved in PA-induced hepatotoxicity in zebrafish. These findings demonstrate that zebrafish model is useful for screening and ranking hepatotoxicity of PAs with diverse structures, which would facilitate the more accurate risk assessment of PA exposure.

Automated summary

Pyrrolizidine alkaloids (PAs) are plant toxins that can be found in approximately 6000 plant species. Consuming PA-contaminated or PA-containing foodstuffs, herbs, or supplements can pose a potential threat to human health. Different regulatory authorities have established different acceptable limits for PAs, assuming equal hepatotoxic potency despite their structural diversity. This study used a zebrafish model to evaluate the hepatotoxic potency of different PAs and explore the physiological pathways involved in PA-induced liver toxicity. The results showed distinct structure-dependent hepatotoxicity and identified the involvement of inflammation, apoptosis, and steatosis in PA-induced liver toxicity.