Structure-dependent genotoxicity and cytotoxicity of eleven pyrrolizidine alkaloids in CYP3A4-proficient human liver cells

Background and Aim Pyrrolizidine alkaloids (PAs) are secondary metabolites that occur as contaminants in various plant-based foods and dietary supplements. Following metabolic activation by CYP450 enzymes, PA cause hepatotoxicity and induce DNA damage that can lead to the development of liver tumours [1]. Several lines of evidence suggest that PAs are not equally toxic and differ in their genotoxic and cytotoxic potential, which is important for their risk assessment in food and phyto-pharmaceuticals [2] [3]. The aim of the study was to detail the relative genotoxic and cytotoxic potential of eleven pyrrolizidine alkaloids in human liver cells depending on their structure and degree of esterification.

Methods CYP3A4-proficient human liver cells were used for metabolic activation of PAs. The cells were incubated with eleven different PAs for 24 h or 72 h. The cytotoxic effects of PAs were determined by the resazurin viability assay and EC₅₀ values were calculated to assess the relative cytotoxicity. The genotoxic potential was investigated using western-blot analysis of the DNA damage markers γH2AX and p53. Data were subject to BMD modelling via PROAST software to derive BMD values for assessing the relative genotoxicity.

Results In general, monoesters such as lycopsamine display the lowest and cyclic di-esters including lasiocarpine the strongest cytotoxic effects. The determined EC₅₀ values of the tested PAs are in a broad range from 4 µM up to 500 µM and above. Furthermore, a concentration-dependent formation of yH2AX and p53 was observed. The lowest BMDL values ranging from 0.2–0.8 µM were obtained for retrorsine, lasiocarpine, seneciphylline and echimidine.

The results show a concentration- and structure-dependent toxicity based on the degree of esterification. In addition, p53 was revealed as a similarly sensitive marker of genotoxicity as yH2AX. Our data support the view to classify PAs according to their relative potency, which is relevant for their risk assessment.

Publication History

Article published online:
22 June 2021

• References

• 1 Fu PP. Chem Res Toxicol 2017; 30: 81-93
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• 3 Louisse J. et al. Food Chem Toxicol 2019; 131: 110532