Abstracts

Rationale: Sertraline (SRT), a selective serotonin reuptake inhibitor (SSRI), is often prescribed to epileptic patients to manage depression. Similar to what observed with antiepileptic drugs (AEDs), sertraline s efficacy is variable. The chemical backbone of this drug is comparable to the AED carbamazepine (CBZ). Given our findings linking to extra-hepatic CBZ metabolism blood-brain barrier (BBB) cytochrome P450, we tested whether CYPs mechanism may also be responsible for the apparent drug resistance to SRT. We analyzed the pattern of SRT oxidative drug metabolism mediated by P450 enzymes in epileptic endothelial cells derived from temporal lobectomies (EPI-EC). We also investigated the involvement of nuclear receptors in the regulation of P450s enzyme expression in EPI-EC. Methods: Primary endothelial cultures were obtained from brain specimens resected from drug resistant epileptic subjects (n=4). Human brain endothelial cells (HBMEC; n=4) and non-brain endothelial cells (HUVEC) were used as controls. CYPs and nuclear receptor mRNA levels were also assessed by cDNA microarrays (from 5 additional patients). CYPs (CYP3A4, 2C9, 2C19, 2D6 and 2E1) were involved in hepatic AED metabolism were selected and their protein expression levels in EPI-EC were compared to control. The correlation of pregnane X receptor (PXR) with P450s was studied by western blot. The effects of a therapeutic dose of SRT (5 M) on CYP expression were determined after 2, 6, and 24hrs. Samples were analyzed by HPLC. Results: mRNA levels encoding nuclear receptors (aryl hydrocarbon receptor; glucocorticoid receptor; orphan receptor; retinoid x receptor) were significantly elevated in EPI-EC compared to control. cDNA microarrays also revealed significant expression increases for endothelial genes regulated by PXR and responsible for cellular detoxification. CYP3A4, 2C9, and 2E1 were overexpressed in EPI-EC; in contrast, CYP2D6 and 2C19 were down-regulated or all together absent. In EPI-EC, PXR expression did not depend on drug exposure, suggesting that, in epileptic BBB EC, PXR regulation and activity are altered. SRT treatment up regulated CYP3A4 expression in epileptic EC (*p<0.05); CYP2D6 and 2C19 remained unaltered. SRT conversion to desmethyl sertraline was consistently elevated in EPI-EC.Conclusions: The present study suggests that steady-state PXR transcriptional activity is elevated in EPI-EC; this is supported by increased expression of PXR-regulated CYPs. Unlike in normal brain EC or hepatocytes, this increased metabolic activity was not further enhanced by drug exposure. In contrast to what shown in hepatocytes, brain EPI-EC respond to SRT exposure by up regulation of CYP3A4 but not 2D6 and 2C19. Thus, in epileptic brain, steady state or disregulated PXR expression and function potentially may involve CYP3A4 to be the chief regulator of SSRI metabolism.