Quantitative Proteomics-Based Blood–Brain Barrier Study

Abstract

From the viewpoint of drug discovery, it is an important issue to elucidate the drug permeability at the human central nervous system (CNS) barriers and the molecular mechanisms in the cells forming CNS barriers especially during CNS diseases. I introduced quantitative proteomics techniques into the blood-brain barrier (BBB) study, then quantitatively investigated the transport system at the human BBB and clarified the quantitative differences in protein expression levels and functions of transporters and receptors between animals and humans, or in vitro and in vivo. Based on the difference in the absolute expression level of transporters between in vitro and in vivo, I demonstrated that the drug efflux activity of P-glycoprotein (P-gp) at in vivo BBB can be accurately reconstructed from the in vitro system, not only in mouse models but also monkeys similar to humans and pathological conditions. Furthermore, I discovered Claudin-11 as another tight junction molecule expressed at the CNS barriers, and clarified that it contributes to the disruption of the CNS barriers in multiple sclerosis. Furthermore, it was also elucidated that the P-gp dysfunction causes excessive brain entry of glucocorticoid which causes a nerve damage in cerebral infarct, and it can be suppressed by targeting Abl/Src kinases. These suggest that targeting the tight junctions and transporters, which are important molecules at the CNS barriers, would potentially lead to the treatment of CNS diseases. In this review, I would like to introduce a new CNS barrier study opened by quantitative proteomics research.

Understanding the Blood‐Brain Barrier and Beyond: Challenges and Opportunities for Novel CNS Therapeutics

“…Uchida and colleagues demonstrated, for example, that P-gp functionality in in vivo BBB can be accurately predicted from data obtained from an in vitro system, in mice, monkeys, and humans (also in pathological conditions). [33][34][35] In vivo methods CSF sampling. CSF sampling can be used to assess both rate and extent of drug distribution to the CNS.…”

“…It provides a means to relate transporter protein expression levels between animals and humans (as well as between in vitro and in vivo ). Uchida and colleagues demonstrated, for example, that P‐gp functionality in in vivo BBB can be accurately predicted from data obtained from an in vitro system, in mice, monkeys, and humans (also in pathological conditions) 33–35 …”

“…Uchida and colleagues demonstrated, for example, that P‐gp functionality in in vivo BBB can be accurately predicted from data obtained from an in vitro system, in mice, monkeys, and humans (also in pathological conditions). 33 , 34 , 35 …”

Transporter Regulation in Critical Protective Barriers: Focus on Brain and Placenta

“…Other transporters that were detected and quantified by the groups cited above include the organic anion transporter (OAT) 1 (OAT1/SLC22A6), OAT2 (SLC22A7), OAT3 (SLC22A8), OAT7 (SLC22A9), the organic cation transporter (OCT) 1 (OCT1/SLC22A1), OCT3 (SLC22A3), the organic anion transporting polypeptide (OATP) 1A2 (SLCO1A2), OATP2B1 (SLCO2B1), OATP1C1 (SLCO1C1), and the multidrug resistance protein (MRP) 4 (MRP4/ABCC4). However, inconsistencies exist in terms of calculated abundance and peptide data [ 5 , 6 , 7 , 8 , 9 ]. Importantly, the quantitative data from mass spectrometry reported as “pmol transporter/mg total protein” cannot easily be compared between laboratories, as accuracy data of the proteomic methods, which allow one to distinguish between assay and population variability of the measured parameter, or method-specific scaling factors accounting for losses within the tissue preparation, are often not stated or are simply lacking [ 10 ].…”

Proteome of the Luminal Surface of the Blood–Brain Barrier

“…Mapping the expressed proteomes of the luminal BBB surface in vivo would be of pointed value for identifying highly-expressed endothelial proteins and transporters that could be exploited for brain drug delivery. Specifically, profiling luminal BBB proteins will be particularly useful to understand differences in protein expression between different species [ 22 , 23 , 24 , 25 ] and in various neurological diseases [ 26 , 27 , 28 ], which are both important considerations for the development of therapeutic delivery platforms.…”