Department of Pharmaceutics and Analytical Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark.
Br J Pharmacol. 2010 Mar;159(6):1339-53. doi: 10.1111/j.1476-5381.2009.00620.x. Epub 2010 Jan 27.
delta-Aminolevulinic acid (ALA) is used in cancer patients for photodynamic diagnosis or therapy. Oral administration of ALA has been used in patients with prostate and bladder cancer. The present aim was to investigate the mechanism of intestinal absorption of ALA and its transport via the amino acid transporter SLC36A1.
In vitro investigations of ALA affinity for and uptake via SLC36A1 and SLC15A1 were performed in Caco-2 cell monolayers. Interaction of ALA with SLC15A1 was investigated in MDCK/SLC15A1 cells, whereas interactions with SLC36A1 were investigated in COS-7 cells transiently expressing SLC36A1.
ALA inhibited SLC36A1-mediated L-[(3)H]Pro and SLC15A1-mediated [(14)C]Gly-Sar uptake in Caco-2 cell monolayers with IC(50) values of 11.3 and 2.1 mM respectively. In SLC36A1-expressing COS-7 cells, the uptake of [(14)C]ALA was saturable with a K(m) value of 6.8 +/- 3.0 mM and a V(max) of 96 +/- 13 pmol x cm(-2) x min(-1). Uptake of [(14)C]ALA was pH and concentration dependent, and could be inhibited by glycine, proline and GABA. In a membrane potential assay, translocation of ALA via SLC36A1 was concentration dependent, with a K(m) value of 3.8 +/- 1.0 mM. ALA is thus a substrate for SLC36A1. In Caco-2 cells, apical [(14)C]ALA uptake was pH dependent, but Na(+) independent, and completely inhibited by 5-hydroxy-L-tryptophan and L-4,4'-biphenylalanyl-l-proline. CONCLUSIONS AND IMPLICATIONS. ALA was a substrate for SLC36A1, and the apical absorption in Caco-2 cell was only mediated by SLC36A1 and SLC15A1. This advances our understanding of intestinal absorption mechanisms of ALA, as well as its potential for drug interactions.
δ-氨基酮戊酸（ALA）在癌症患者中用于光动力诊断或治疗。ALA 的口服给药已用于前列腺癌和膀胱癌患者。本研究旨在探讨 ALA 的肠道吸收机制及其通过氨基酸转运蛋白 SLC36A1 的转运。
在 Caco-2 细胞单层中进行 ALA 对 SLC36A1 和 SLC15A1 的亲和力和摄取的体外研究。在 MDCK/SLC15A1 细胞中研究 ALA 与 SLC15A1 的相互作用，而在瞬时表达 SLC36A1 的 COS-7 细胞中研究与 SLC36A1 的相互作用。
ALA 以分别为 11.3 和 2.1 mM 的 IC50 值抑制 Caco-2 细胞单层中 SLC36A1 介导的 L-[（3）H]Pro 和 SLC15A1 介导的 [(14)C]Gly-Sar 摄取。在表达 SLC36A1 的 COS-7 细胞中，[(14)C]ALA 的摄取呈饱和状态，K m 值为 6.8 ± 3.0 mM，V max 值为 96 ± 13 pmol x cm(-2) x min(-1)。[(14)C]ALA 的摄取与 pH 值和浓度有关，可被甘氨酸、脯氨酸和 GABA 抑制。在膜电位测定中，ALA 通过 SLC36A1 的转运与浓度有关，K m 值为 3.8 ± 1.0 mM。因此，ALA 是 SLC36A1 的底物。在 Caco-2 细胞中，ALA 的顶端摄取与 pH 值有关，但与 Na+无关，并且完全被 5-羟基-L-色氨酸和 L-4,4'-联苯丙氨酸-L-脯氨酸抑制。
ALA 是 SLC36A1 的底物，Caco-2 细胞中的顶端吸收仅由 SLC36A1 和 SLC15A1 介导。这加深了我们对 ALA 肠道吸收机制的理解，以及它在药物相互作用方面的潜力。
