In vivo evidence against clomethiazole being neuroprotective against MDMA (‘ecstasy’)-induced degeneration of rat brain 5-HT nerve terminals by a free radical scavenging mechanism

Clomethiazole is an effective neuroprotective agent against the degeneration of 5-HT neurones that follows administration of 3,4-methylenedioxymethamphetamine (MDMA or ‘ecstasy’). Since there is good evidence that free radical formation resulting from auto-oxidation of MDMA metabolites is responsible for the degeneration we have examined whether clomethiazole is a free radical scavenger. MDMA (15 mg/kg i.p.) increased the formation of 2,3- and 2,5-dihydroxybenzoic acids (2,3-DHBA and 2,5-DHBA) from salicylic acid perfused through a microdialysis tube implanted in the hippocampus, indicating increased free radical formation. Clomethiazole (50 mg/kg i.p.) administered 5 min prior and 55 min post MDMA prevented both the acute MDMA-induced hyperthermia and the rise in 2,3- and 2,5-DHBA. However, when the temperature of the MDMA+clomethiazole treated rats was kept elevated to that of the MDMA treated rats with a homeothermic blanket there was no inhibition of the MDMA-induced increase in 2,3-DHBA or 2,5-DHBA. These data suggest firstly that free radical formation is inhibited when the acute MDMA-induced hyperthermia is prevented. Secondly the data further indicate that clomethiazole has no free radical scavenging activity since the drug produces substantial neuroprotection when MDMA+clomethiazole treated rats are kept hyperthermic. This conclusion was strengthened by our observation that clomethiazole is a weak inhibitor (IC 50>1 mM) of lipid peroxidation in synaptosomes when it had been induced by addition of FeCl 2+ascorbic acid.