Abstract
The objective of this study was to evaluate the utility of brain tissue slices to determine the effect of plasma and brain tissue nonspecific binding on the brain-to-plasma ratio (Kp). Mouse or rat brain slices (400 μm) were prepared using a McIlwain tissue chopper (Surrey, UK) and incubated with 1 μg/ml of compound at 37°C either in a physiological buffer to determine the buffer-to-slice concentration ratio, i.e., unbound fraction in brain tissue (fu,slice), or in plasma to determine the slice-to-plasma concentration ratio (Cslice/Cplasma). The unbound fraction in plasma, fu,plasma, was determined using equilibrium dialysis. In vitro-in vivo correlation of the brain-to-plasma ratio was examined for 13 and eight model compounds in mice and rats, respectively. Cslice/Cplasma and fu,plasma/fu,slice predicted the Kp in rats, and Cslice/Cplasma predicted the Kp in FVB mice for non-P-glycoprotein substrates within 3-fold but overpredicted Kp for P-glycoprotein substrates by more than 3-fold. However, Cslice/Cplasma predicted the Kp in mdr1a/1b knockout mice for both non-P-glycoprotein and P-glycoprotein substrates. Our present study demonstrates that a brain slice method can be used to differentiate whether a compound having a low Kp is due to the effect of low nonspecific binding to brain tissue relative to plasma proteins or because of efflux transport at the blood-brain barrier.
Footnotes
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Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
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doi:10.1124/dmd.105.007914.
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ABBREVIATIONS: BBB, blood-brain barrier; BCSFB, blood-cerebrospinal fluid barrier; CNS, central nervous system; NFPS, N[3-(4′-fluorophenyl)-3-(4′-phenylphenoxy) propyl]sarcosine; CP-141938, methoxy-3-[(2-phenyl-piperadinyl-3-amino)-methyl]-phenyl-N-methyl-methane-sulfonamide; HPLC/MS/MS, high-performance liquid chromatography/tandem mass spectrometry; P-gp, P-glycoprotein.
- Received October 18, 2005.
- Accepted February 15, 2006.
- The American Society for Pharmacology and Experimental Therapeutics
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