Miah Mohammad K, Chowdhury Ekram A, Bickel Ulrich, Mehvar Reza
Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Sciences Center, Amarillo, Texas 79106.
Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Sciences Center, Amarillo, Texas 79106; Center for Blood-Brain Barrier Research, School of Pharmacy, Texas Tech University Health Sciences Center, Amarillo, Texas 79106.
J Pharm Sci. 2017 Jun;106(6):1659-1669. doi: 10.1016/j.xphs.2017.02.011. Epub 2017 Feb 24.
Nonspecific quantitation of [C]sucrose in blood and brain has been routinely used as a quantitative measure of the in vivo blood-brain barrier (BBB) integrity. However, the reported apparent brain uptake clearance (K) of the marker varies widely (∼100-fold). We investigated the accuracy of the use of the marker in comparison with a stable isotope of sucrose ([C]sucrose) measured by a specific liquid chromatography-tandem mass spectrometry method. Rats received single doses of each marker, and the K values were determined. Surprisingly, the K value of [C]sucrose was 6- to 7-fold lower than that of [C]sucrose. Chromatographic fractionation after in vivo administration of [C]sucrose indicated that the majority of the brain content of radioactivity belonged to compounds other than the intact [C]sucrose. However, mechanistic studies failed to reveal any substantial metabolism of the marker. The octanol:water partition coefficient of [C]sucrose was >2-fold higher than that of [C]sucrose, indicating the presence of lipid-soluble impurities in the [C]sucrose solution. Our data indicate that [C]sucrose overestimates the true BBB permeability to sucrose. We suggest that specific quantitation of the stable isotope (C) of sucrose is a more accurate alternative to the current widespread use of the radioactive sucrose as a BBB marker.
血液和大脑中[C]蔗糖的非特异性定量已常规用作体内血脑屏障（BBB）完整性的定量指标。然而，所报道的该标志物的表观脑摄取清除率（K）差异很大（约100倍）。我们通过特定的液相色谱-串联质谱法，将该标志物与蔗糖的稳定同位素（[C]蔗糖）进行比较，研究了该标志物使用的准确性。给大鼠单次注射每种标志物，并测定K值。令人惊讶的是，[C]蔗糖的K值比[C]蔗糖的K值低6至7倍。体内注射[C]蔗糖后的色谱分离表明，大脑中放射性物质的大部分含量属于完整[C]蔗糖以外的化合物。然而，机制研究未能揭示该标志物有任何实质性的代谢。[C]蔗糖的正辛醇：水分配系数比[C]蔗糖的高2倍以上，表明[C]蔗糖溶液中存在脂溶性杂质。我们的数据表明，[C]蔗糖高估了蔗糖对血脑屏障的真实通透性。我们建议，蔗糖稳定同位素（C）的特异性定量是目前广泛使用放射性蔗糖作为血脑屏障标志物的更准确替代方法。
