SUMMARYObjective: 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 comorbid depression. Because 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 vitro models to determine whether SRT affects the neurotoxic potential of CBZ and the mechanisms involved. Methods: Human fetal brain-derived dopaminergic neurons, human brain microvascular endothelial cells (HBMECs), and 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 in causing neurotoxicity, drug metabolism was compared to cell death in HEK CYP3A4 overexpressed and cells pretreated with the CYP3A4 inhibitor ketoconazole. Results: In all cellular systems tested, exposure to CBZ (127 lM) or SRT (5 lM) alone caused negligible cytotoxicity. By contrast CBZ, tested at a much lower concentration (17 lM) in combination with SRT (5 lM), produced prominent cytotoxicity within 15 min exposure. In neurons and HBMECs, cytotoxicity was associated with increased nitrite levels, suggesting involvement of free radicals as a pathogenetic mechanism. Pretreatment of HBMECs with reduced GSH or with the GSH precursor N-acetyl-L-cysteine prevented cytotoxic response. In HEK cells, the cytotoxic response to the 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. Significance: 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 discussed. KEY WORDS: CYP3A4, Cytotoxicity, Drug interaction, Human, Ketoconazole, Neurotoxicity.Depression is the most frequent comorbid psychiatric disorder in epilepsy. Its lifetime prevalence has been estimated to be 6-30% in population-based studies and up to 50% among patients followed in tertiary centers. 1 Studies also indicate that a history of depression is associated with a four-to sixfold greater risk of developing epilepsy.2 Patients with epilepsy and comorbid depression are often managed by using combinations of antiepileptic drugs (AEDs) with an antidepressant. 3,4 In a study that enrolled 933 consecutive adults with refractory epilepsy, antidepressants were, together with antihypertensive agents, the drug class most

Melanocortin 4 receptor (MC4R) variants contribute to human obesity, and rats lacking functional MC4R (Mc4rK314X/K314X) are obese. We investigated the hypothesis that low energy expenditure (EE) and physical activity contribute to this obese phenotype in male rats, and determined whether lack of functional MC4R conferred protection from weight loss during 50% calorie restriction. Though Mc4rK314X/K314X rats showed low brown adipose Ucp1 expression and were less physically active than rats heterozygous for the mutation (Mc4r+/K314X) or wild-type (Mc4r+/+) rats, we found no evidence of lowered EE in Mc4rK314X/K314X rats once body weight was taken into account using covariance. Mc4rK314X/K314X rats had a significantly higher respiratory exchange ratio. Compared to Mc4r+/+ rats, Mc4rK314X/K314X and Mc4r+/K314X rats lost less lean mass during calorie restriction, and less body mass when baseline weight was accounted for. Limited regional overexpression of Mc3r was found in the hypothalamus. Although lower physical activity levels in rats with nonfunctional MC4R did not result in lower total EE during free-fed conditions, rats lacking one or two functional copies of Mc4r showed conservation of mass, particularly lean mass, during energy restriction. This suggests that variants affecting MC4R function may contribute to individual differences in the metabolic response to food restriction.

A correction has been published and is appended to both the HTML and PDF versions of this paper. The error has not been fixed in the paper.

Weight loss requires negative energy balance, which can induce adaptive thermogenesis‐the reduction of energy expenditure (EE) beyond that accounted for by the weight lost. Adaptive thermogenesis varies between individuals. Here, we measured EE and physical activity (PA) before and after 21 days of 50% calorie restriction (CR) in female rats with lean and obesity‐prone phenotypes‐rats strains selectively bred for high and low intrinsic aerobic capacity (HCR and LCR, respectively). Use of female rats minimized potentially confounding effects of group differences in body size. We found that CR decreased EE more than was predicted by loss of weight and lean mass, demonstrating adaptive thermogenesis. Both groups showed similar suppression in resting EE (HCR, 39%; LCR, 34%). The CR‐induced suppression in non‐resting EE, which includes activity EE, was significantly greater in HCR (37%) than in LCR (24%). CR also significantly suppressed PA in HCR but not LCR, but PA was still higher in HCR than in LCR even after CR. Weight loss did not differ between groups. These results suggest that individual differences in CR‐induced adaptive thermogenesis may be accounted for by variation in aerobic capacity. Moreover, it is likely activity EE, not resting or basal metabolism, accounts for individual variation in adaptive thermogenesis. Grant Funding Source: Supported by NIH R01NS055859 and NIH R15DK097644 to CMN