Abstracts

Rationale: Drug delivery to the epileptic brain is hampered by overexpression of multiple drug resistance genes and protein in blood-brain barrier (BBB) endothelial cells. We hypothesized that BBB endothelial cells may also act as a metabolic barrier for commonly prescribed anti-epileptic drugs including carbamazepine (CBZ). CBZ is metabolized in the liver by action of the cytochrome Cyp3A4. Our preliminary results demonstrated the presence of this enzyme at the BBB. In the present study, we evaluated the functional relevance of Cyp3A4 expression on carbamazepine metabolism at the BBB. We also compared the metabolic properties of endothelial and liver cells. Methods: We used human brain microvascular endothelial cells and hepatocytes. Endothelial cells were cultured either in a dynamic in vitro blood brain barrier model (DIV-BBB; cells are exposed to flow) or in a static model (i.e., no flow present). CBZ and its metabolites were measured by HPLC-UV detection. Cyp3A4 expression was evaluated by western blotting. Results: BBB endothelial cells express a functional Cyp3A4 of potency comparable to hepatocytes. Exposure to laminar flow induces Cyp3A4 protein in human BBB endothelial cells. Exposure to CBZ also increased Cyp3A4 protein expression, but the effect was not cumulative. In other words, flow exposure occluded expression increases due to CBZ treatment. Conclusions: We conclude that human BBB endothelial cells express functional Cyp3A4. Further, in BBB endothelial cells Cyp3A4 expression is regulated by cerebral blood flow. These findings together may have functional implications for anti-epileptic drug delivery, tolerance and ultimately efficacy.