Work

The cytotoxic and hemolytic potential of karmitoxin from Karlodinium armiger and how it interacts with sterols

Year: 2025

Type: article

Abstract: • Karmitoxin can cause membrane damage in RTgill-W1 and HCEC-1CT cells. • Incubation with free sterols lowers hemolysis significantly. • Karmitoxin builds stable complexes with cholesterol, epicholesterol, and ergosterol. Karmitoxin, produced by Karlodinium armiger , is structurally related to karlotoxin and amphidinols, two potent ichthyotoxic hemolysins with high affinity for sterols. Given these structural similarities, karmitoxin is believed to exhibit comparable toxic effects. Cytotoxicity was assessed in the fish gill cell line RTgill-W1 and the human epithelial colon cell line HCEC-1CT. The hemolytic potential with and without added sterols was tested on fish erythrocytes to investigate possible impacts of toxin-sterol interactions. Sterol interactions were further evaluated using surface plasmon resonance. A 3-h incubation returned an EC 50 of 111 and 175 nM in RTgill-W1 and in HCEC-1CT cells, respectively. Lactate dehydrogenase (LDH) release increased with toxin concentration, reaching 11 % in the fish and 40 % in the human cell line. Extended exposure (24 h) increased the toxicity in RTgill-W1 cells (EC 50 74 nM, 40 % LDH release). In parallel, hemolytic potential of karmitoxin was confirmed, as well as its interaction with free sterols. Interaction kinetics revealed complex stabilities with k d (s −1 ) constants of 1.13 × 10 −2 (cholesterol), 5.48 × 10 −3 (epicholesterol), and 4.72 × 10 −3 (ergosterol). Interaction with cholesterol followed the single-exponential model well, while data indicated more complex binding with epicholesterol and ergosterol. Altering the RTgill-W1 cholesterol content did not impact cytotoxicity at the tested concentration. Overall, karmitoxin showed potent cytotoxic and hemolytic properties in human and fish models. Complex formation with sterols may play a role in membrane targeting, yet cellular cholesterol quantity might not affect cytotoxicity.

Source: Harmful Algae

DOI: 10.1016/j.hal.2025.102817