Functional expression of drug transporters in glial cells: potential role on drug delivery to the CNS.

Drug permeability in the central nervous system (CNS) across blood-brain and blood-cerebrospinal fluid barriers is an important determinant of neurological disorders therapeutic efficacy and is highly regulated by the expression of membrane-associated transporters belonging to the ATP-binding cassette (ABC) and solute carrier (SLC) superfamilies. Functional expression of ABC efflux transporters exists not only at the brain barriers (primary biochemical barrier) but also in astrocytes, microglia, neurons, and oligodendrocytes can significantly restrict drug penetration into these cells, thus creating a secondary biochemical barrier to permeability in brain parenchyma. In contrast, SLC members primarily contribute to the uptake of endogenous substrates (i.e., hormones, neurotransmitters) and pharmacological agents and can play a critical role in maintaining CNS homeostasis and drug response. In this chapter, we review the functional expression and localization of drug transporters in the brain, their role in CNS drug delivery, and their regulation in neuropathological conditions.