Abstracts

RATIONALE: Most patients with epilepsy are effectively treated with antiepileptic drugs (AEDs); however, approximately 10-20% of them are pharmacoresistant. The mechanisms involved in antiepileptic drug resistance are not fully understood. Multiple drug resistance (multiple DR) is mediated at the cellular level by low abundance transporters expressed in normal endothelial cells (EC) and perhaps in [dsquote]epileptic[dsquote] astrocytes. Refractory epilepsy is characterized by overexpression of specific multiple DR mechanisms in EC.We investigated the expression of multiple drug resistance (MDR1), multiple drug resistance-associated (MRP1-6), cis-platin resistance-associated (CRA), and lung resistance (LRP) genes/proteins in astrocytes as well as EC isolated from epileptic brain. In addition, immunostaining was performed on tissue sections. It was our objective to study the patterns of expression and distribution of multiple DR proteins in epileptic brain.
METHODS: The methods used to investigate the expression of multiple DR genes were RT-PCR and western blot on [dsquote]epileptic[dsquote] astrocytic and endothelial cells. EC from intracranial aneurysms, umbilical cord and astrocytes from non-pathological origin were used as controls. Immunofluorescence was performed on brain tissue from patients with refractory epilepsy.
RESULTS: In endothelial cells, RT-PCR and protein analysis revealed MDR1 expression only in pathological samples. Comparable expression of MRPs, CRA and LRP occurred in all endothelia tested. RT-PCR analysis revealed that both MDR1 and LRP were expressed in astrocytes from surgical resections; MRP1 was present, but the other 5 members of multidrug resistance-associated protein family were not. Western blot experiments confirmed a high expression of MDR1 protein in astrocytes from epileptic brain compared to astrocytes from non-pathological origin. Moreover, MRP1 and LRP were present only in astrocytes from epileptic brain, even though their expression was much lower than MDR1.
CONCLUSIONS: We conclude that multiple drug resistance gene overexpression is not an exclusive property of [dsquote]epileptic[dsquote] EC, but may rather represent an endothelial and glial response to a variety of pathological or physiological conditions. Thus, outwitting the endothelial blood-brain-barrier may not be sufficient to overcome multiple DR since parenchymal cells are also likely to be involved.
[Supported by: HL51614, NS143284 and NS38195.]