Metzner Linda, Dorn Madlen, Markwardt Fritz, Brandsch Matthias
Martin Luther University Halle-Wittenberg, Halle, Germany.
Mol Pharm. 2009 May-Jun;6(3):1006-11. doi: 10.1021/mp9000684.
The orally administered creatine analogue beta-guanidinopropionic acid (beta-GPA) decreases plasma glucose levels by increasing the sensitivity to insulin. This effect is based on a beta-GPA induced expression of mRNA and total protein content of the insulin-responsive glucose transporter GLUT4. Although the oral availability of beta-GPA is well established, the underlying uptake mechanism has not yet been studied. We investigated whether the H(+)-coupled amino acid transporter PAT1, which is expressed in the apical membrane of intestinal cells, accepts guanidine derivatives as substrates. Uptake of l-[(3)H]proline into Caco-2 cells expressing hPAT1 constitutively was strongly inhibited by beta-GPA and its derivatives guanidinoacetic acid (GAA) and 4-guanidinobutyric acid (4-GBA). Competition assays revealed apparent affinity constants of about 1.5 mM. Electrophysiological measurements at hPAT1-expressing Xenopus laevis oocytes unequivocally demonstrated that beta-GPA, GAA and 4-GBA are effectively transported by this transport system in an electrogenic manner. We conclude that hPAT1 might be responsible for the intestinal absorption of beta-GPA thereby allowing its oral administration. Moreover, with beta-GPA we identified a new high affinity hPAT1 substrate that might be an interesting starting point for future drug design-drug delivery strategies.
口服肌酸类似物β-胍基丙酸（β-GPA）通过提高胰岛素敏感性来降低血糖水平。这种作用基于β-GPA诱导胰岛素反应性葡萄糖转运蛋白GLUT4的mRNA表达和总蛋白含量增加。尽管β-GPA的口服生物利用度已得到充分证实，但其潜在的摄取机制尚未得到研究。我们研究了在肠细胞顶端膜表达的H⁺偶联氨基酸转运体PAT1是否接受胍类衍生物作为底物。β-GPA及其衍生物胍基乙酸（GAA）和4-胍基丁酸（4-GBA）强烈抑制组成型表达hPAT1的Caco-2细胞对L-[(³)H]脯氨酸的摄取。竞争试验显示表观亲和常数约为1.5 mM。在表达hPAT1的非洲爪蟾卵母细胞上进行的电生理测量明确表明，β-GPA、GAA和4-GBA通过该转运系统以电生方式有效转运。我们得出结论，hPAT1可能负责β-GPA的肠道吸收，从而使其能够口服给药。此外，通过β-GPA我们鉴定出一种新的高亲和力hPAT1底物，这可能是未来药物设计-药物递送策略的一个有趣起点。
