In silico simulations and functional cell studies evidence similar potency and distinct binding of pacific and caribbean ciguatoxins

Ciguatoxins (CTX) cause ciguatera poisoning, which is the most common reported human food poisoning related to natural marine toxins. Pacific ciguatoxins are the most abundant and studied CTX analogues; however, the growing distribution of Caribbean analogues and the limited data available on their biological effects make necessary to re-evaluate their relative potency. For decades, the guidelines established by regulatory agencies have assumed that the potency of the Caribbean CTXs were tenfold lower than the Pacific CTXs. We present here an integrated study involving Neuro-2a cells (the method used worldwide to test ciguatoxins), electrophysiological assays, and in silico simulations that evidence the similar cytotoxicity of Caribbean and Pacific ciguatoxins and their asymmetry binding within sodium channels. The binding mode of the toxins was first explored by molecular docking using the GOLD program and the resulting binary complexes were further studied by Molecular Dynamics simulation studies using the molecular mechanics force field AMBER. The simulation studies explain their distinct impact on the activation potential of the channel as experimentally observed and provide a detailed picture of the effects caused by these toxins on an atomic scaleOpen Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. The research leading to these results has received funding from the following FEDER-co-funded grants. From Conselleria de Cultura, Educacion e Ordenación Universitaria, Xunta de Galicia, GRC (ED431C 2021/01, ED431C 2021/29, and the Centro singular de investigación de Galicia accreditation 2019–2022 ED431G 2019/03). From European Union Interreg AlertoxNet EAPA-317-2016, Interreg Agritox EAPA-998-2018, and H2020 778069-EMERTOX, and the EUROCIGUA project: “Risk Characterization of Ciguatera Fish Poisoning in Europe” GP/EFSA/AFSCO/2015/03, co-funded by the European Food Safety Authority (EFSA). From Ministerio de Ciencia e Innovación PID2020-115010RB-I00/AEI/10.13039/501100011033. David Castro (D.C.) financial support for the PhD studies was obtained through EUROCIGUA project: Risk characterization of Ciguatera Fish Poisoning in Europe, framework partnership agreement GP/EFSA/AFSCO/2015/03, co-funded by the EFSA. Pablo Estevez (P.E.) acknowledges financial support from the Xunta de Galicia (Regional Government, Spain) under grant ED481A-2018/207S