Modulation of glucocorticoid receptor in human epileptic endothelial cells impacts drug biotransformation in an in vitro blood-brain barrier model

Abstract

Objective: Nuclear receptors and cytochrome P450 (CYP) regulate hepatic metabolism of several drugs. Nuclear receptors are expressed at the neurovascular unit of patients with drug-resistant epilepsy. We studied whether glucocorticoid receptor (GR) silencing or inhibition in human epileptic brain endothelial cells (EPI-ECs) functionally impacts drug bioavailability across an in vitro model of the blood-brain barrier (BBB) by CYP-multidrug transporter (multidrug resistance protein 1, MDR1) mechanisms.

Methods: Surgically resected brain specimens from patients with drug-resistant epilepsy, primary EPI-ECs, and control human brain microvascular endothelial cells (HBMECs) were used. Expression of GR, pregnane X receptor, CYP3A4, and MDR1 was analyzed pre- and post-GR silencing in EPI-ECs. Endothelial cells were co-cultured with astrocytes and seeded in an in vitro flow-based BBB model (DIV-BBB). Alternatively, the GR inhibitor mifepristone was added to the EPI-EC DIV-BBB. Integrity of the BBB was monitored by measuring transendothelial electrical resistance. Cell viability was assessed by glucose-lactate levels. Permeability of [³ H]sucrose and [¹⁴ C]phenytoin was quantified. CYP function was determined by measuring resorufin formation and oxcarbazepine (OXC) metabolism.

Results: Silencing and inhibition of GR in EPI-ECs resulted in decreased pregnane X receptor, CYP3A4, and MDR1 expression. GR silencing or inhibition did not affect BBB properties in vitro, as transendothelial electrical resistance and P_sucrose were unaltered, and glucose metabolism was maintained. GR EPI-EC silencing or inhibition led to (1) increased P_phenytoin BBB permeability as compared to control; (2) decreased CYP function, indirectly evaluated by resorufin formation; (3) improved OXC bioavailability with increased abluminal (brain-side) OXC levels as compared to control.

Significance: Our results suggest that modulating GR expression in EPI-ECs at the BBB modifies drug metabolism and penetration by a mechanism encompassing P450 and efflux transporters. The latter could be exploited for future drug design and to overcome pharmacoresistance.

Keywords: P450 enzymes; bioavailability; drug-resistant epilepsy; multidrug transporter; nuclear receptors.