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Drug Metabolism and Disposition Fast Forward
First published on July 20, 2005; DOI: 10.1124/dmd.105.005231

0090-9556/05/3310-1547-1554$20.00
DMD 33:1547-1554, 2005

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THE BLOOD-BRAIN BARRIER SODIUM-DEPENDENT MULTIVITAMIN TRANSPORTER: A MOLECULAR FUNCTIONAL IN VITRO-IN SITU CORRELATION

Seonghee Park, and Patrick J. Sinko

Department of Pharmaceutics, Ernest Mario School of Pharmacy, Rutgers-The State University of New Jersey, Piscataway, New Jersey

The molecular mechanism of biotin brain uptake was investigated using an in vitro bovine blood-brain barrier (BBB) cell model and an in situ mouse brain perfusion technique. A functional uptake/transport correlation of the in vitro and in situ characteristics of biotin uptake was investigated. Morphological and immunochemical characteristics (e.g., factor VIII expression) of the primary culture of brain microvessel endothelial cells (BMECs) were confirmed. Gene expression of the multidrug resistance (Mdr1) and sodium-dependent multivitamin (SMVT) transporters was also determined in BMECs. Biotin transport was saturable and Na+-dependent at the luminal side of the BBB. The estimated half-saturation concentrations (Km) of biotin uptake in vitro and in situ were 49.1 and 35.5 µM, respectively, supporting the presence of a carrier-mediated biotin transport system. Inhibition studies using various biotin derivatives and structural analogs demonstrated the structural requirements for biotin-SMVT interaction. Desthiobiotin and pantothenic acid significantly inhibited the uptake of biotin, whereas 2-iminobiotin and diaminobiotin were very weak inhibitors. Based on our results, there was a good correlation between the in vitro and in situ BBB models, suggesting that when a single membrane transporter is involved in substrate uptake, flexibility in choosing the experimental model can be afforded. The current results are also consistent with the suggestion that the properties of the BBB are likely to be organ-specific rather than species-specific. Further mechanistic and comparative studies are needed to validate these results. In conclusion, the in vitro transporter-based mechanism studies produced valuable molecular functional transport results that correlated well with in situ results.

Address correspondence to: Dr. Patrick J. Sinko, Rutgers University, Ernest Mario School of Pharmacy, 160 Frelinghuysen Road, Piscataway, NJ 08854. E-mail: sinko{at}rci.rutgers.edu




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V. S. Subramanian, J. S. Marchant, and H. M. Said
Biotin-responsive basal ganglia disease-linked mutations inhibit thiamine transport via hTHTR2: biotin is not a substrate for hTHTR2
Am J Physiol Cell Physiol, November 1, 2006; 291(5): C851 - C859.
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