Identification and characterization of toxic components of Carybdea brevipedalia venom: implications for understanding box jellyfish (Cnidaria: Cubozoa) envenomation.

Jellyfish stings, particularly from cubozoans, pose a significant threat to human health worldwide. However, the major toxins responsible for the clinical symptoms following envenomation by box jellyfish (class Cubozoa) are not well understood. In this study, we investigated the major toxic components of Carybdea brevipedalia venom (CbV) as a representative model of box jellyfish venoms. We identified the key lethal toxin components (CbVLT) from crude CbV. For this, we isolated the toxic components using anion exchange chromatography and fast protein liquid chromatography (FPLC) methods, accompanied by toxicity evaluations. In vitro toxicity assays confirmed the strong cytotoxicity and hemolytic activity of CbVLT. Furthermore, CbVLT exhibited strong lethality in zebrafish, inducing notable hemorrhage and swelling, significant lactate dehydrogenase (LDH) activity, and fatal histopathological changes in vital organs (brain, gills, and heart). These results indicated that CbVLT contains the key lethal toxins in the venom. Subsequently, LC-MS/MS analysis identified 8 toxin homologs in CbVLT, including potassium channel toxins, cytolysins, hemolysins, proteases, and hydrolases. These toxins are responsible for the severe local and systemic reactions and even death caused by C. brevipedalia stings. These findings uncover and characterize the key lethal toxins in CbV, which will help reveal the molecular mechanisms of the venom's lethality and significantly aid in developing therapeutic strategies to treat stings from the cubozoa jellyfish in the future.