Elisabeth Varga Elisabeth Varga Hélène-Christine Prause Hélène-Christine Prause Matthias Riepl Matthias Riepl Nadine Hochmayr Nadine Hochmayr Deniz Berk Deniz Berk Eva Attakpah Eva Attakpah Endre Kiss Endre Kiss Nikola Medić Nikola Medić Giorgia Del Favero Giorgia Del Favero Larsen Thomas Ostenfeld Larsen Thomas Ostenfeld Per Juel Hansen Per Juel Hansen Doris Marko Doris Marko Springer 2024 Harmful algal blooms kill fish populations worldwide, as exemplified by the haptophyte microalga Prymnesium parvum. The suspected causative agents are prymnesins, categorized as A-, B-, and C-types based on backbone carbon atoms. Impacts of P. parvum extracts and purified prymnesins were tested on the epithelial rainbow trout fish gill cell line RTgill-W1 and on the human colon epithelial cells HCEC-1CT. Cytotoxic potencies ranked A > C > B-type with concentrations spanning from low (A- and C-type) to middle (B-type) nM ranges. Although RTgill-W1 cells were about twofold more sensitive than HCEC-1CT, the cytotoxicity of prymnesins is not limited to fish gills. Both cell lines responded rapidly to prymnesins; with EC50 values for B-types in RTgill-W1 cells of 110 ± 11 nM and 41.5 ± 0.6 nM after incubations times of 3 and 24 h. Results of fluorescence imaging and measured lytic effects suggest plasma membrane interactions. Postulating an osmotic imbalance as mechanisms of toxicity, incubations with prymnesins in media lacking either Cl-, Na+, or Ca2+ were performed. Cl- removal reduced morphometric rearrangements observed in RTgill-W1 and cytotoxicity in HCEC-1CT cells. Ca2+-free medium in RTgill-W1 cells exacerbated effects on the cell nuclei. Prymnesin composition of different P. parvum strains showed that analog composition within one type scarcely influenced the cytotoxic potential, while analog type potentially dictate potency. Overall, A-type prymnesins were the most potent ones in both cell lines followed by the C-types, and lastly B-types. Disturbance of Ca2+ and Cl- ionoregulation may be integral to prymnesin toxicity. A Correction to this article was published on 09 April 2024: https://doi.org/10.1007/s00204-024-03716-3 PDFDocument eng 2025-07-18T08:58:54.364767Z 2024 Harmful Algal Bloom Transport Processes Primary Cultures Ion Regulation Rainbow-Trout Toxicity Ichthyotoxicity Allelopathy Healthy Mode 1541294 b application/pdf http://creativecommons.org/licenses/by/4.0/