The Journal of Membrane Biology

, Volume 165, Issue 3, pp 201–211

Blood-Brain Barrier Permeation: Molecular Parameters Governing Passive Diffusion


  • H.  Fischer
    • Department of Biophysical Chemistry, Biocenter of the University of Basel, Klingelbergstr, 70, CH-4056 Basel, Switzerland
  • R.  Gottschlich
    • Medicinal Chemistry Research Laboratories, CNS Department, E. Merck, Frankfurter Strasse 250, 64271 Darmstadt, Germany
  • A.  Seelig
    • Department of Biophysical Chemistry, Biocenter of the University of Basel, Klingelbergstr, 70, CH-4056 Basel, Switzerland

DOI: 10.1007/s002329900434

Cite this article as:
Fischer, H., Gottschlich, R. & Seelig, A. J. Membrane Biol. (1998) 165: 201. doi:10.1007/s002329900434


53 compounds with clinically established ability to cross or not to cross the blood-brain barrier by passive diffusion were characterized by means of surface activity measurements in terms of three parameters, i.e., the air-water partition coefficient, K aw , the critical micelle concentration, CMC D , and the cross-sectional area, A D . A three-dimensional plot in which the surface area, A D , is plotted as a function of K −1 aw and CMC D shows essentially three groups of compounds: (i) very hydrophobic compounds with large air-water partition coefficients and large cross-sectional areas, A D > 80 Å2 which do not cross the blood-brain barrier, (ii) compounds with lower air-water partition coefficients and an average cross-sectional area, A D ≅ 50 Å2 which easily cross the blood-brain barrier, and (iii) hydrophilic compounds with low air-water partition coefficients (A D < 50 Å2) which cross the blood-brain barrier only if applied at high concentrations. It was shown that the lipid membrane-water partition coefficient, K lw , measured previously, can be correlated with the air-water partition coefficient if the additional work against the internal lateral bilayer pressure, π bi = 34 ± 4 mN/m is taken into account. The partitioning into anisotropic lipid membranes decreases exponentially with increasing cross-sectional areas, A D , according to K lw =const. K aw exp(−A D π bi /kT) where kT is the thermal energy. The cross-sectional area of the molecule oriented at a hydrophilic-hydrophobic interface is thus the main determinant for membrane permeation provided the molecule is surface active and has a pK a > 4 for acids and a pK a < 10 for bases.

Key words: Blood-brain barrier — Passive diffusion — Monolayer-bilayer equivalence pressure — Internal lateral bilayer pressure — Molecular size — Cross-sectional area — Amphiphilicity — pKa— Drug screening

Copyright information

© 1998 Springer-Verlag New York Inc.