Institute of Biomedical and Life Sciences, Division of Infection and Immunity, Glasgow Biomedical Research Centre, University of Glasgow, Glasgow G128TA, UK.
Malar J. 2010 Jan 29;9:36. doi: 10.1186/1475-2875-9-36.
Plasmodium parasites are unable to synthesize purines de novo and have to salvage them from the host. Due to this limitation in the parasite, purine transporters have been an area of focus in the search for anti-malarial drugs. Although the uptake of purines through the human equilibrative nucleoside transporter (hENT1), the human facilitative nucleobase transporter (hFNT1) and the parasite-induced new permeation pathway (NPP) has been studied, no information appears to exist on the relative contribution of these three transporters to the uptake of adenosine and hypoxanthine. Using the appropriate transporter inhibitors, the role of each of these salvage pathways to the overall purine transport in intraerythrocytic Plasmodium falciparum was systematically investigated.
The transport of adenosine, hypoxanthine and adenine into uninfected and P. falciparum-infected human erythrocytes was investigated in the presence or absence of classical inhibitors of the hFNT1, hENT1 and NPP. The effective inhibition of the various transporters by the classical inhibitors was verified using appropriate known substrates. The ability of high concentration of unlabelled substrates to saturate these transporters was also studied.
Transport of exogenous purine into infected or uninfected erythrocytes occurred primarily through saturable transporters rather than through the NPP. Hypoxanthine and adenine appeared to enter erythrocytes mainly through the hFNT1 nucleobase transporter whereas adenosine entered predominantly through the hENT1 nucleoside transporter. The rate of purine uptake was approximately doubled in infected cells compared to uninfected erythrocytes. In addition, it was found that the rate of adenosine uptake was considerably higher than the rate of hypoxanthine uptake in infected human red blood cells (RBC). It was also demonstrated that furosemide inhibited the transport of purine bases through hFNT1.
Collectively, the data obtained in this study clearly show that the endogenous host erythrocyte transporters hENT1 and hFNT1, rather than the NPP, are the major route of entry of purine into parasitized RBC. Inhibitors of hENT1 and hFNT1, as well as the NPP, should be considered in the development of anti-malarials targeted to purine transport.
疟原虫无法从头合成嘌呤，只能从宿主中回收利用。由于寄生虫的这种局限性，嘌呤转运体一直是寻找抗疟药物的一个重点领域。尽管已经研究了嘌呤通过人平衡核苷转运体（hENT1）、人促进核苷碱基转运体（hFNT1）和寄生虫诱导的新渗透途径（NPP）的摄取，但似乎没有关于这三种转运体对腺苷和次黄嘌呤摄取的相对贡献的信息。使用适当的转运体抑制剂，系统研究了这些补救途径对疟原虫内红细胞内整体嘌呤转运的作用。
在存在或不存在 hFNT1、hENT1 和 NPP 的经典抑制剂的情况下，研究了腺苷、次黄嘌呤和腺嘌呤进入未感染和感染疟原虫的人红细胞的转运情况。使用适当的已知底物验证了各种转运体被经典抑制剂有效抑制的情况。还研究了高浓度未标记底物饱和这些转运体的能力。
外源性嘌呤进入感染或未感染的红细胞的转运主要通过可饱和的转运体进行，而不是通过 NPP。次黄嘌呤和腺嘌呤似乎主要通过 hFNT1 核苷碱基转运体进入红细胞，而腺苷主要通过 hENT1 核苷转运体进入红细胞。与未感染的红细胞相比，感染细胞中的嘌呤摄取速度大约增加了一倍。此外，研究发现，在感染的人红细胞中，腺苷的摄取速度明显高于次黄嘌呤的摄取速度。此外，还证明了呋塞米抑制嘌呤碱基通过 hFNT1 的转运。
总的来说，本研究获得的数据清楚地表明，内源性宿主红细胞转运体 hENT1 和 hFNT1 而不是 NPP 是嘌呤进入寄生 RBC 的主要途径。hENT1 和 hFNT1 的抑制剂以及 NPP 都应考虑用于开发针对嘌呤转运的抗疟药物。
