Mechanisms underlying seizures and hypothermia during busulphan administration

Busulphan (Bu) is used as a part of the conditioning regimen prior to HSCT. Neurotoxicity is one of Bu major adverse-effects. We investigated the kinetics of busulphan and its metabolites (tetrahydothiophene, tetrahydrothiophene-1-oxide, sulfolane, 3-OH-sulfolane) in patients and mice as well as the mechanisms underlying CNS-toxicity in mice. Busulphan metabolites were detectable in plasma and urine up to 72-h after the last Bu-dose. Sulfolane levels were high and reached maximum concentration at the time-point reported for the convulsions' occurrence. Mice were treated with either busulphan or one of its metabolites, separately. Sulfolane treated-mice showed the highest brain exposure (AUC_brain/AUC_plasma). Seizures and hypothermia were observed after sulfolane administration, accompanied with a significant decrease in calbindin-28k concentrations in the brain. Behavior changes but no signs of convulsions were seen in mice treated with lower sulfolane doses. Moreover, a reduction of spontaneous events during whole-cell patch clamp recordings from pyramidal neurons was observed following bath application of sulfolane. In conclusion, these are the first results showing that sulfolane is the major cause of seizures and hypothermia. Sulfolane concentration in plasma mirrors its concentration in the brain. The role of calbindin-D28K in CNS-toxicity and susceptibility to future neurodegenerative diseases should be investigated.