The ATP-binding cassette transporters ABCB1 and ABCC1 are not regulated by hypoxia in immortalised human brain microvascular endothelial cells

In order to investigate whether hypoxia might be responsible for the expression changes of ABCB1 and ABCC1 in the ischemic brain, the immortalised human brain microvascular endothelial cell line hCMEC/D3 was exposed to hypoxia (1%) or anoxia (0%). Cell lysates were analysed by Western blot to detect the protein expression of ABCB1, ABCC1, HIF-1α and HIF-2α.During hypoxia, an accumulation of HIF-1α and HIF-2α was noticed in hCMEC/D3 cells that followed different time kinetics. Both HIF-1α and HIF-2α abundance increased within 4 h of hypoxia. HIF-1α levels decreased to below detection levels within 16 h of hypoxia, whereas HIF-2α remained elevated even after 48 h. No changes of ABCB1 and ABCC1 expression were detected, neither on the mRNA nor protein level.Our data suggests that other factors than hypoxia may be responsible for the expression changes of ATP-binding cassette transporters in the ischemic brain.ATP-binding cassette (ABC) transporters are efflux proteins that are abundantly expressed at the blood-brain barrier [1,2]. ABC transporters protect the brain from toxic compounds, but at the same time they prevent the access of drugs into the brain [1,2]. In brain disease, changes of ABC transporter expression and hence function have been demonstrated to modulate barrier properties [2]. Upon ischemia, ABC transporters are regulated on brain capillary endothelial cells in a coordinated way that impedes the delivery of drugs into the brain. As such, the luminal transporter ABCB1, which transfers its substrates from the brain into the blood, was increased [3], whereas the abluminal transporter ABCC1, which carries its substrates in the opposite direction, i.e. from blood to brain was decreased [4] following middle cerebral artery occlusion (MCAO) in mice. The altered abundance had a major impact on the biodistribution of drugs in the brain and resulted in a poorer delivery of neuroprotective drugs to the post-ischaemic brain, despite a stroke-related impairment of b