In vitro blood-brain barrier models--latest advances and therapeutic applications in a chronological perspective

The first generation of in vitro models providing successful isolation of viable brain endothelial cells from different species, which could be maintained in cell culture, have emerged around thirty years ago. However, the time consuming and the difficulty of working with primary culture cells led to the development of simpler models employing cell lines with blood-brain barrier properties. The creation, in late nineties, of a transgenic mouse harboring the temperature sensitive simian virus 40 large T-antigen as a source of conditionally immortalized brain endothelial cell lines circumvented the problems of in vitro transfection of tumour inducing gene in primary cells. These different ways to obtain cultures of brain endothelial cells have profited from the discovery of different cellular factors that allow the growth of differentiated cells on plastic filters. Although cell preparations and culture conditions of brain endothelial cells are based on the same principle, there are two main models for studying the blood-brain barrier: the static and the more recently described dynamic model. Dynamic models were created in order to replicate the physiological in vivo environment of the blood-brain barrier. The large pool of in vitro models is being enlarged since each laboratory improves its model adding small differences adapted to the research interests. The great impact of blood-brain barrier studies in the development of therapies related to the central nervous system supports the interests of this review about in vitro models.