Tetraethylammonium chloride reduces anaesthetic-induced neurotoxicity in Caenorhabditis elegans and mice.

BACKGROUND

If anaesthetics cause permanent cognitive deficits in some children, the implications are enormous, but the molecular causes of anaesthetic-induced neurotoxicity, and consequently possible therapies, are still debated. Anaesthetic exposure early in development can be neurotoxic in the invertebrate Caenorhabditis elegans causing endoplasmic reticulum (ER) stress and defects in chemotaxis during adulthood. We screened this model organism for compounds that alleviated neurotoxicity, and then tested these candidates for efficacy in mice.

METHODS

We screened compounds for alleviation of ER stress induction by isoflurane in C. elegans assayed by induction of a green fluorescent protein (GFP) reporter. Drugs that inhibited ER stress were screened for reduction of the anaesthetic-induced chemotaxis defect. Compounds that alleviated both aspects of neurotoxicity were then blindly tested for the ability to inhibit induction of caspase-3 by isoflurane in P7 mice.

RESULTS

Isoflurane increased ER stress indicated by increased GFP reporter fluorescence (240% increase, P<0.001). Nine compounds reduced induction of ER stress by isoflurane by 90-95% (P<0.001 in all cases). Of these compounds, tetraethylammonium chloride and trehalose also alleviated the isoflurane-induced defect in chemotaxis (trehalose by 44%, P=0.001; tetraethylammonium chloride by 23%, P<0.001). In mouse brain, tetraethylammonium chloride reduced isoflurane-induced caspase staining in the anterior cortical (-54%, P=0.007) and hippocampal regions (-46%, P=0.002).

DISCUSSION

Tetraethylammonium chloride alleviated isoflurane-induced neurotoxicity in two widely divergent species, raising the likelihood that it may have therapeutic value. In C. elegans, ER stress predicts isoflurane-induced neurotoxicity, but is not its cause.