Molecular mechanisms of the organic anion permeation through blood-brain barrier

血脑屏障的主要成分是紧密密封的脑毛细血管内皮细胞，其形成亲水性化合物的渗透屏障。为了向脑组织提供糖和氨基酸等必需营养素，血脑屏障因此配备了专门的运输系统。氨基酸转运系统作为氨基酸相关药物的渗透途径也很重要。血脑屏障具有有机阴离子转运系统。该系统被认为对于排出脑组织中形成的单胺代谢物和共轭化合物是必不可少的。本研究的目的是确定有机阴离子和氨基酸转运系统的分子本质，基于与有机阴离子转运蛋白OAT 1的序列同源性，我们鉴定了新的有机阴离子转运蛋白OAT 2、OAT 3和OAT 4，建立了有机阴离子转运蛋白家族。OAT 1存在于毛细血管周围的星形胶质细胞突起中。因此，OAT 1被认为介导有机阴离子从星形胶质细胞转移到毛细血管内皮细胞，这对于神经元中产生的阴离子代谢物的排泄至关重要。OAT 3接受共轭化合物作为其底物。因此，它将是合适的，作为一个有机阴离子转运系统在血脑barrier.We确定系统L转运，LAT1和LAT2，这与单一的跨膜蛋白，4F2hc。我们进一步发现了与LAT1相关的转运蛋白，并建立了异二聚体氨基酸转运蛋白家族。通过制备抗LAT1、LAT2和4F2hc蛋白的特异性抗体，证明这些蛋白存在于脑毛细血管内皮细胞上。这些蛋白质被发现存在于腔和腔外膜中。因此，LAT1和LAT2都被认为在氨基酸和氨基酸相关药物透过血脑屏障中起关键作用。

The major component of the blood-brain barrier is the tightly sealed brain capillary endothelial cells which form a permeation barrier for hydrophilic compounds. To provide brain tissues with essential nutrients such as sugars and amino acids, the blood-brain barrier is, thus, equipped with specialized transport systems. The amino acid transport systems are also important as a permeation path for amino acid-related drugs. Blood-brain barrier possesses transport systems for organic anions. This system is proposed to be essential to extrude monoamine metabolites and conjugated compounds formed in the brain tissues. The purpose of this study is to identify molecular nature of the transport systems for organic anions and amino acids.Based on the sequence homology to the organic anion transporter OAT1, we identified novel organic anion transporters OAT2, OAT3 and OAT4 and established an organic anion transporter family. OAT1 was present in astrocyte processes surrounding capillaries. OAT1 is, thus, proposed to mediate the transfer of organic anions from astrocytes to capillary endothelial cells, which is critical for the excretion of anionic metabolites produced in neurones. OAT3 accepts conjugated compounds as its substrates. It would, therefore, be suitable as an organic anion transporting system in the blood-brain barrier.We identified system L transporters, LAT1 and LAT2, which associate with single membrane spanning protein, 4F2hc. We further found transporters related LAT1 and established the heterodimeric amino acid transporter family. By gencrating specific antibodies against LAT1, LAT2 and 4F2hc, we showed that these proteins exist on the brain capillary endothelial cells. These proteins were found to be present in the luminal and abluminal membranes. Thus, both LAT1 and LAT2 are proposed to play critical roles in the permeation of amino acids and amino acid related drugs through the blood-brain barrier.