Abstracts

Rationale: Drug toxicity is a hurdle to drug development and to clinical translation of basic research. Antiepileptic drugs such as carbamazepine (CBZ) and selective serotonin reuptake inhibitors such as sertraline (SRT) are commonly co-prescribed to patients with epilepsy and co-morbid depression. Since SRT may interfere with cytochrome P450 (CYP) enzyme activity and CYPs have been implicated in the conversion of CBZ to reactive cytotoxic metabolites, we investigated in in vitro models whether SRT affects the neurotoxic potential of CBZ, and the mechanisms involved. Methods: Human fetal brain-derived dopaminergic neurons, brain endothelial cells (HBMECs), embryonic kidney (HEK) cells were used to evaluate cytotoxicity of CBZ and SRT individually and in combination. Nitrite and glutathione (GSH) levels were measured with drug exposure. To validate the role of CYP3A4 causing neurotoxicity, drug metabolism was compared to cell death in HEK CYP3A4 overexpressed and cells pretreated with CYP3A4 inhibitor ketaconazole. Results: In all cellular systems tested, exposure to CBZ (127 µM) or SRT (5 µM) alone caused negligible cytotoxicity. By contrast CBZ, tested at a much lower concentration (17 µM) in combination with SRT (5 µM), produced prominent cytotoxicity within 15 mins exposure. In neurons and HBMECs, cytotoxicity was associated with increased nitrite levels, suggesting involvement of free radicals as a pathogenetic mechanism. Pre-treatment of HBMECs with reduced GSH or with the GSH precursor N-acetyl-cysteine prevented cytotoxic response. In HEK cells, the cytotoxic response to CBZ+SRT combination correlated with the rate of CBZ biotransformation and production of 2-hydroxy CBZ, further suggesting a causative role of reactive metabolites. In the same system, cytotoxicity was potentiated by overexpression of CYP3A4, and prevented by CYP3A4 inhibitor. Conclusions: These results demonstrate an unexpected neurotoxic interaction between CBZ and SRT, apparently related to increased CYP3A4-mediated production of reactive CBZ metabolites. The potential clinical implications of these findings are important for drug therapy. Acknowledgements: Supported by R01NS078307 (N.M. and D.J.), R01NS43284, R41MH093302, R21NS077236, R42MH093302, UH3TR000491, and R21HD057256 (D.J.). AHA-SDG 13SDG13950015 and NARSAD Brain-Behavior Research Foundation (C.G).