An-Najah Staff

The recent identification of drug-metabolizing enzymes cytochrome P450 (CYP) in the human blood-brain barrier (BBB) raises the question of whether these enzymes act in concert with ATP-binding cassette (ABC) transporters to limit the brain distributions of drugs. We recently demonstrated several CYP genes in freshly isolated human brain microvessels; the main isoforms expressed were CYP1B1 and CYP2U1. Many studies using different experimental approaches have revealed that P-glycoprotein (P-gp, ABCB1), breast cancer resistance protein (BCRP, ABCG2) and the multidrug resistance-associated protein 4 (MRP4, ABCC4) are the main ABC transporters in the human BBB. The first part of this review covers recent studies on the expression, regulation and function of CYP450 and ABC transporters in the rodent and human BBBs. The second part focuses on the possible interplay between some CYPs and certain ABC transporters at the BBB, which makes it a determining element of brain drug concentrations and thus of the effects of centrally acting drugs.

Since the discovery of P-glycoprotein (P-gp) in brain microvessels composing the human blood-brain barrier (BBB), ATPbinding cassette (ABC) transporters have been recognized as bottlenecks in the development and delivery of neuropharmaceuticals. ABC transporters are expressed predominately at the plasma luminal membrane of brain capillary endothelial cells. These ABC transporters are responsible for the efflux of their substrates from the endothelial cells to the bloodstream against the concentration gradient and thus limit the entry of some drugs within the central nervous system (CNS). Advanced quantitative molecular biology tools allowed gene and protein quantification of the components of microvessels isolated from different species including human. Recently, positron emission tomography using radiolabelled probes that are substrates of ABC transporters allowed the determination of their functional activity at the human BBB. Here, we summarized new information regarding the relative expression, substrate recognition pattern for CNS drugs and functional activity of ABC transporters that are quantitatively expressed at the human BBB.