Abstracts

Rationale: Drug bioavailability to the brain across the blood-brain barrier in patients with drug-resistant epilepsy (DRE) is controlled by drug-metabolizing enzymes (cytochrome P450 [CYP]), drug efflux transporters (e.g., P-glycoprotein [P-gp] and breast cancer-resistance protein [BCRP]), and nuclear receptors (NRs). We recently found that NRs regulate BBB function and specific CYPs in epileptic brain endothelial cells. The present study aims (1) to determine regional specificity of CYP expression and activity; and (2) to compare drug transporters, NRs, and BBB tight junction proteins in focal (pathological) with non-focal (non-pathological) regions of the same epileptic brain. Methods: Surgically resected human brain specimens from patients with medically intractable epilepsy were used such that focal (lesional/pathological, n = 8) areas could be compared with their relatively non-focal (non-lesional/non-pathological) counterparts. Comparison of CYPs, drug transporters, NRs, and tight junction proteins from the same brain with DRE was performed by immunoblotting. Involvement of CYP was evaluated by kinetic conversion of 7-ethoxyresorufin to resorufin. Patients were compared based on prescribed antiepileptic drugs (AEDs) and CYP expression; in a cohort of 8 patients with focal cortical dysplasia, 4 patients were on lacosamide (CYP inducer) + non-CYP-inducing AED (e.g., lamotrigine or levetiracetam) and 4 on clobazam (CYP inducer) + another CYP inducer (e.g., oxcarbazepine or phenytoin). Results: In the specimens analyzed, CYP1A1, CYP2C9, and CYP2E1 expression and overall CYP involvement were significantly increased in focal compared to nonfocal counterparts in the same epileptic brain, whereas CYP2D6 levels remained unaltered in both regions. CYP3A4 was exclusively overexpressed in the focal region of patients taking clobazam + another CYP inducer. However, CYP3A4 expression was downregulated or negligible when lacosamide (CYP inducer) + a non-CYP inducer was given. Among NRs, glucocorticoid, pregnane-X, and constitutive androstane receptors were upregulated in focal brain regions, particularly when clobazam + a CYP inducer were taken together. Elevated P-gp and BCRP levels in the focal areas were identified in a majority of specimens, independent of drug intake. Simultaneous decreased expression of BBB tight junction proteins (claudin-1 and occludin-1) in the epileptic focal region was observed, suggesting an association of disease pathology with BBB alteration in that region. Conclusions: In summary our results show that (1) upregulation of specific CYPs (1A1, 2C9, and 2E1) in the focal areas is independent of co-prescribed AEDs; in contrast, increased CYP3A4 and NR expression is dependent on the AED combination used; (2) increased expression of drug efflux transporters, P-gp, and BCRP is pathology dependent, and (3) BBB properties and the CYP-NR-transporter axis in the epileptic brain could together influence future therapeutic strategies in DRE. Funding: This work is supported in part by the National Institute of Neurological Disorders and Stroke/National Institutes of Health (grants R01NS095825 and R01NS078307 to CG) and grant awards from the Brain & Behavior Foundation (NARSAD); American Heart Association National Center Scientist Development Grant (13SDG13950015); and the Alternatives Research & Development Foundation (to CG).