Blood Brain Barrier Genomics Research Articles

Combinatorial approaches for the identification of brain drug delivery targets.

The blood-brain barrier (BBB) represents a large obstacle for the treatment of central nervous system diseases. Targeting endogenous nutrient transporters that transcytose the BBB is one promising approach to selectively and noninvasively deliver a drug payload to the brain. The main limitations of the currently employed transcytosing receptors are their ubiquitous expression in the peripheral vasculature and the inherent low levels of transcytosis mediated by such systems. In this review, approaches designed to increase the repertoire of transcytosing receptors which can be targeted for the purpose of drug delivery are discussed. In particular, combinatorial protein libraries can be screened on BBB cells in vitro or in vivo to isolate targeting peptides or antibodies that can trigger transcytosis. Once these targeting reagents are discovered, the cognate BBB transcytosis system can be identified using techniques such as expression cloning or immunoprecipitation coupled with mass spectrometry. Continued technological advances in BBB genomics and proteomics, membrane protein manipulation, and in vitro BBB technology promise to further advance the capability to identify and optimize peptides and antibodies capable of mediating drug transport across the BBB.

Blood—Brain Barrier Genomics and Cloning of a Novel Organic Anion Transporter

A novel organic anion transporter selectively expressed at the blood-brain barrier (BBB), originally designated BBB-specific anion transporter type 1 (BSAT1), and now classified as Slco1c1, has been cloned from a BBB genomics program as a partial cDNA; this study describes the cloning and expression of the full-length cDNA from a rat brain capillary cDNA library. Northern analysis revealed the selective expression of the transporter at the BBB, and the transporter was expressed after permanent transfection of human 293 cells with cDNA encoding either the full length or open reading frame mRNA. The full-length transporter cDNA was 2.6 kb, and the mRNA was highly expressed at the rat brain microvasculature, but not in kidney, liver, heart, or lung, or in glial cells or brain glial tumors. Blood-brain barrier-specific anion transporter type 1 expression in 293 cells was poor after the transfection of the full-length cDNA, whereas transporter expression in 293 cells was high after transfection of the open reading frame. The transporter showed asymmetric kinetic properties in comparison of the influx and efflux of model substrates, thyroxine (T4), triiodothyronine (T3), and estradiol-glucuronide (E2G). Thyroxine and T3 inhibited the influx of E2G, but E2G did not inhibit thyroxine influx, and T3 only weakly inhibited the influx of T4. Extracellular E2G stimulated the transefflux of intracellular T4. Blood-brain barrier-specific anion transporter type 1 is a novel organic anion transporter that is a sodium-independent exchanger that may participate in the active efflux of iodothyronines and steroid conjugates at the BBB.

Blood-brain barrier genomics, proteomics, and new transporter discovery

Blood-brain barrier genomics, proteomics, and new transporter discovery

Blood-brain barrier genomics.

The application of the suppressive subtraction hybridization (SSH) technique to blood-brain barrier (BBB) genomics has accelerated the discovery and identification of BBB-specific genes in humans and in experimental animals (, , ). This procedure allows for the development of gene arrays based on gene products derived from isolated brain capillaries, which represents the BBB in vivo (). The brain capillary volume is 10−3 or less than 0.1% of the total brain (). Because the sensitivity of a typical gene microarray of the brain approximates 10−4 (), the identification of BBB-specific genes from gene arrays derived from whole brain is statistically unlikely, even for BBB highly expressed transcript with relative abundance ranging 0.01–0.02% (i.e., actin, LAT1) (,). In addition, the levels of low abundant BBB-specific genes, like the p80 BBB-GLUT1 mRNA-binding protein, are less than 0.0005% of total cell proteins (), which is several log orders below the limit of detection of deoxyribonucleic acid (DNA) microarrays (). However, BBB-specific genes can be identified with a gene array derived from gene products initially obtained from isolated brain capillaries (Fig. 1). Open image in new window Fig. 1. Diagram of the blood-brain barrier genomics program. BSP, blood-brain barrier specific protein.

Rat blood-brain barrier genomics. II.

The tissue-specific gene expression at the brain microvasculature, which forms the blood-brain barrier (BBB) can be elucidated with a brain vascular genomics program, which starts with the isolation of gene products derived from purified brain microvessels. Genes commonly expressed in peripheral organs are subtracted with the suppression subtractive hybridization method using driver cDNA produced from a pool of rat liver/kidney-derived poly A+RNA. From a screen of 480 clones in the subtracted tester cDNA library, 156 clones were sequenced. The clones fell into 3 groups: known genes (51%), rat expressed sequence tags (31%), and novel rat genes not found in databases (18%). The known genes could be categorized into families of common function including vascular remodeling, signal transduction, transcription factors, biologic transport, vascular amyloid, hemostasis, myelin, lipids, secretion, cytoskeleton, and junctional complexes. Brain vascular genomics, or BBB genomics, allows for an accelerated discovery of the gene families that are differentially expressed at the microvasculature in brain.