Ohe Tomoyuki, Sato Masahiko, Tanaka Sachiko, Fujino Naoko, Hata Mikiko, Shibata Yoshihiro, Kanatani Akio, Fukami Takehiro, Yamazaki Masayo, Chiba Masato, Ishii Yasuyuki
Banyu Tsukuba Research Institute, Ibaraki, Japan.
Drug Metab Dispos. 2003 Oct;31(10):1251-4. doi: 10.1124/dmd.31.10.1251.
The ratio of drug levels in cerebrospinal fluid (CSF) to plasma (CSF/plasma) at equilibrium has been viewed as in vivo free fraction (fp) in plasma [CSF/plasma = fp], if no active transport is involved in brain penetration. We determined the CSF/plasma level following oral administration in rats and in vitro rat plasma protein binding for 20 compounds that were synthesized in our institute and have similar physicochemical properties. However, results indicated that the CSF/plasma was not only poorly correlated with fp but remarkably lower than fp in most of the compounds tested, suggesting that certain transporters such as P-glycoprotein (P-gp) located in blood-brain barrier (BBB) may decrease the unbound drug concentration in the brain. We evaluated P-gp-mediated transport activity of the 20 compounds with P-gp (mdr1a)-transfected LLC-PK1 cells and calculated P-gp efflux index (PEI), indicating the extent of P-gp-mediated transport. A plot of the CSF/plasma versus fp/PEI showed a strong correlation (r = 0.93), and the absolute values were almost identical [CSF/plasma = fp/PEI]. These results suggest that P-gp quantitatively shifts the equilibrium of unbound drugs across the BBB. Although we cannot rule out the possibility that endogenous transporters other than P-gp on BBB and/or blood-CSF barrier may affect CSF levels of compounds, the present study indicated that fp and PEI measurements may be useful in predicting in vivo CSF/plasma fractions for central nervous system-targeting drugs.
如果脑内转运过程中没有主动转运参与，那么脑脊液（CSF）与血浆中药物浓度在平衡时的比值（CSF/血浆）就被视为血浆中的体内游离分数（fp）[CSF/血浆 = fp]。我们测定了在本研究所合成的、具有相似理化性质的20种化合物经大鼠口服给药后的CSF/血浆水平以及大鼠血浆蛋白结合的体外情况。然而，结果表明CSF/血浆不仅与fp相关性较差，而且在大多数测试化合物中显著低于fp，这表明位于血脑屏障（BBB）中的某些转运蛋白，如P-糖蛋白（P-gp），可能会降低脑内未结合药物的浓度。我们用转染了P-gp（mdr1a）的LLC-PK1细胞评估了这20种化合物的P-gp介导的转运活性，并计算了P-gp外排指数（PEI），以表明P-gp介导的转运程度。CSF/血浆与fp/PEI的关系图显示出很强的相关性（r = 0.93），且绝对值几乎相同[CSF/血浆 = fp/PEI]。这些结果表明，P-gp定量地改变了未结合药物在血脑屏障两侧的平衡。虽然我们不能排除血脑屏障和/或血脑脊液屏障上除P-gp之外的内源性转运蛋白可能影响化合物脑脊液水平的可能性，但本研究表明，fp和PEI测量可能有助于预测中枢神经系统靶向药物的体内CSF/血浆分数。
