Comparison of the acute inhibitory effects of Tetrodotoxin (TTX) in rat and human neuronal networks for risk assessment purposes

- TTX inhibits neuronal electrical activity in rat cortical cultures (IC50 ∼7 nM).
- TTX is equipotent in human iPSC-derived neurons (IC50 ∼10 nM).
- Our and literature data indicate that interspecies differences for TTX are limited.
- Experimental animal data could be used to derive human acute reference dose (ARfD).
- The ARfD amounts to 1.33 μg/kg bw, or 200 μg/kg TTX in shellfish.

Tetrodotoxin (TTX) is an extremely toxic marine neurotoxin. TTX inhibits voltage-gated sodium channels, resulting in a potentially lethal inhibition of neurotransmission. Despite numerous intoxications in Asia and Europe, limited (human) toxicological data are available for TTX. Additionally, the degree of interspecies differences for TTX is not well established, hampering the use of available (animal) data for human risk assessment and establishing regulatory limits for TTX concentrations in (shell)fish.We therefore used micro-electrode array (MEA) recordings as an integrated measure of neurotransmission to demonstrate that TTX inhibits neuronal electrical activity in both primary rat cortical cultures and human-induced pluripotent stem cell (hIPSC)-derived iCell® neurons in co-culture with hIPSC-derived iCell® astrocytes, with IC50 values of 7 and 10 nM, respectively.From these data combined with LD50 values and IC50 concentrations of voltage-gated sodium channels derived from literature it can be concluded that interspecies differences are limited for TTX. Consequently, we used experimental animal data to derive a human acute reference dose of 1.33 μg/kg body weight, which corresponds to maximum concentration of TTX in shellfish of 200 μg/kg.