Transport of the delta-opioid receptor agonist [D-penicillamine(2,5)] enkephalin across the blood-brain barrier involves transcytosis

The delta opioid receptor antagonist [D-penicillamine(2,5)]enkephalin (DPDP E) is an enzymatically stable peptide analogue of Met-enkephalin. DPDPE use s a saturable transport mechanism to cross the blood-brain barrier (BBB), t hough the exact mechanism is not fully understood. The aim of the present s tudy was to identify the mechanism by which DPDPE enters the brain. The eff ect of phenylarsine oxide (PAO), an endocytosis inhibitor, on the transport of [H-3]DPDPE was investigated using both in vitro and in situ transport s tudies. Two in vitro models of the BBB utilizing primary bovine brain micro vascular endothelial cells (BBMEC) were studied. [H-3]DPDPE permeability ac ross monolayers of BBMEC grown on polycarbonate filters was studied. PAO si gnificantly reduced the permeability of [H-3]DPDPE across the monolayer. PA O also reduced the uptake of [H-3]DPDPE into BBMEC cells, without affecting binding to the cells. The in situ perfusion model of the BBB was also stud ied, PAO reduced DPDPE uptake by the brain in a dose-dependent manner. Thes e studies indicate that DPDPE enters the brain via an energy-dependent tran scytotic mechanism.