Molecular Mechanism of Glucocorticoid Receptor, Cytochrome P450, and P-Glycoprotein Axis on Drug Regulation at the Blood-Brain Barrier in Epilepsy with Focal Cortical Dysplasia

ABSTRACT Pharmacoresistance to antiseizure medications (ASMs) is a major clinical challenge in effective seizure management for nearly one-third of patients with epilepsy, where the blood-brain barrier (BBB) plays a fundamental role. Most ASMs are substrates of the cytochrome P450 (CYP)/P-glycoprotein (Pgp) pathway, which is transcriptionally regulated by glucocorticoid receptor (GR). We previously discovered a pivotal role for local ASM metabolism, involving CYP drug-metabolizing enzymes and efflux transporters that impede drug bioavailability across the epileptic BBB. A multiple-hurdle mechanism and its involvement of the GR-CYP-Pgp axis in the human epileptic brain has been recognized, however, there remains an unmet need to establish GR as a promising target to improve ASM bioavailability across the epileptic BBB. Our key findings suggest: 1) the GR-mediated mechanism in human epileptic brain endothelial cells (ECs) regulates other nuclear receptors and CYP-Pgp-affected drug bioavailability; 2) Novel GR and heat shock protein (Hsp) interactions (GR-Hsp) enable accelerated GR maturation in human FCD brain tissues; and, 3) Cortical dysplasia with seizure induction in rats resulted in brain GR upregulation and decreased BBB tight junction protein levels; reversed with GR inhibition and, further, both alleviated seizure activity and increased oxcarbazepine bioavailability to the brain. Thus, it becomes imperative to explicitly study GR as potential therapeutic target to improve ASM efficacy. We will test the central hypothesis that GR modulation will improve ASM bioavailability across the BBB by decreasing CYP-Pgp function in the dysplastic brain, to aid in preventing seizures and epileptogenesis. To address this hypothesis, we will use a multi-modular approach (ex vivo, in vitro and in vivo). In AIM 1 of the proposal, by comparing well-characterized specimens from dysplastic to non-dysplastic brain regions, we will study the GR-CYP-Pgp axis, ASM bioavailability, and the effect of GR modulation in a homogeneous patient population with a common drug-resistant epilepsy etiology. This will be compared to ASM levels in drug responders (e.g. non-epileptic), with or without GR modulators. We will test the hypothesis that modulation of GR in the human neurovasculature improves free brain ASM levels in epilepsy. The GR modulatory effect will be additionally correlated to clinical and demographic characteristics, facilitating eventual clinical transition. In AIM 2, the hypothesis will test if pharmacological modulation of GR in dysplastic ECs improves both BBB properties and ASM penetration across the patient-specific in vitro BBB model. In AIM 3, we will test the hypothesis that GR upregulation during epileptogenesis in CD rats, could be reversed by a combination of GR modulators and ASM. The effect of GR agonists and/or inhibitors on ASM levels across the epileptic BBB will be evaluated at each AIM. The proposed research will reveal the GR regulatory mechanism in dysplasia by repurposing existing medications, which will be significant in improving brain ASM efficacy and penetration across the BBB, in epilepsy.