Watson Christopher P, Sekhar Gayathri Nair, Thomas Sarah A
King's College London, Institute of Pharmaceutical Science, Franklin-Wilkins Building, Stamford Street, London, UK.
Front Drug Deliv. 2023 May 23;3:1113493. doi: 10.3389/fddev.2023.1113493.
Human African Trypanosomiasis (HAT) is a neglected parasitic disease that continues to persist in sub-Saharan Africa. It is fatal if untreated. The first stage of the disease is associated with the presence of the parasite in the periphery and the second stage with the presence of the parasites in the CNS. The treatment of CNS stage HAT requires the drugs to cross the blood-brain barrier (BBB). Eflornithine is an amino acid analogue that is used to treat second stage HAT gambiense both alone and in combination with nifurtimox. Recent studies have identified that accumulation of eflornithine into the parasites (trypanosomes) involves the amino acid transporter ( AAT6). In this study we tested the hypothesis that eflornithine uses a cationic amino acid transport system to cross the BBB. We particularly focused on system-y and system-B. To do this we utilized specialist databases to compare the physicochemical characteristics of relevant molecules and an model of the BBB to explore the mechanisms of eflornithine delivery into the CNS. Our results confirmed that eflornithine is related to the endogenous amino acid, ornithine. At pH 7.4, eflornithine is predominately (92.39%) a zwitterionic (dipolar) amino acid and ornithine is predominately (99.08%) a cationic (tripolar) amino acid. In addition, the gross charge distribution at pH 7.4 of eflornithine is much smaller (+0.073) than that of ornithine (+0.99). Further results indicated that eflornithine utilized a saturable transport mechanism(s) to cross the hCMEC/D3 cell membranes and that transport was inhibited by the presence of other amino acids including ornithine. Eflornithine transport was also sodium-independent and sensitive to a y-system inhibitor, but not a B-system inhibitor. Eflornithine transport was also inhibited by pentamidine, suggestive of transport by organic cation transporters (OCT) which are expressed in this cell line. We confirmed expression of the y-system protein, CAT1, and the B-system protein, ATB, in the hCMEC/D3 cells. We conclude that eflornithine uses the cationic amino acid transporter, system y, and OCT to cross the BBB. This research highlights the potential of system-y to deliver drugs, including eflornithine, across the BBB to treat brain diseases.
人类非洲锥虫病（HAT）是一种被忽视的寄生虫病，在撒哈拉以南非洲地区持续存在。若不治疗，该病会致命。疾病的第一阶段与外周血中存在寄生虫有关，第二阶段与中枢神经系统中存在寄生虫有关。治疗中枢神经系统阶段的HAT需要药物穿过血脑屏障（BBB）。依氟鸟氨酸是一种氨基酸类似物，可单独或与硝呋莫司联合用于治疗第二阶段的冈比亚型HAT。最近的研究发现，依氟鸟氨酸在寄生虫（锥虫）中的积累涉及氨基酸转运体（AAT6）。在本研究中，我们检验了依氟鸟氨酸利用阳离子氨基酸转运系统穿过血脑屏障的假设。我们特别关注系统y和系统B。为此，我们利用专业数据库比较相关分子的物理化学特性，并利用血脑屏障模型探索依氟鸟氨酸进入中枢神经系统的机制。我们的结果证实，依氟鸟氨酸与内源性氨基酸鸟氨酸有关。在pH 7.4时，依氟鸟氨酸主要（92.39%）是两性离子（偶极）氨基酸，鸟氨酸主要（99.08%）是阳离子（三极）氨基酸。此外，依氟鸟氨酸在pH 7.4时的总电荷分布（+0.073）比鸟氨酸（+0.99）小得多。进一步的结果表明，依氟鸟氨酸利用可饱和的转运机制穿过hCMEC/D3细胞膜，并且这种转运受到包括鸟氨酸在内的其他氨基酸的抑制。依氟鸟氨酸的转运也不依赖钠，并且对y系统抑制剂敏感，但对B系统抑制剂不敏感。戊烷脒也抑制依氟鸟氨酸的转运，这表明它是通过该细胞系中表达的有机阳离子转运体（OCT）进行转运的。我们证实了y系统蛋白CAT1和B系统蛋白ATB在hCMEC/D3细胞中的表达。我们得出结论，依氟鸟氨酸利用阳离子氨基酸转运体系统y和OCT穿过血脑屏障。这项研究突出了系统y在将包括依氟鸟氨酸在内的药物穿过血脑屏障以治疗脑部疾病方面的潜力。
