Research School of Biology, Australian National University, Canberra, ACT 2601, Australia.
ANU Joint Mass Spectrometry Facility, Research School of Chemistry, Australian National University, Canberra, ACT 2601, Australia.
Int J Mol Sci. 2018 Nov 14;19(11):3597. doi: 10.3390/ijms19113597.
Recent studies have established that dietary protein restriction improves metabolic health and glucose homeostasis. SLC6A19 (B⁰AT1) is the major neutral amino acid transporter in the intestine and carries out the bulk of amino acid absorption from the diet. Mice lacking SLC6A19 show signs of protein restriction, have improved glucose tolerance, and are protected from diet-induced obesity. Pharmacological blockage of this transporter could be used to induce protein restriction and to treat metabolic diseases such as type 2 diabetes. A few novel inhibitors of SLC6A19 have recently been identified using in vitro compound screening, but it remains unclear whether these compounds block the transporter in vivo. To evaluate the efficacy of SLC6A19 inhibitors biomarkers are required that can reliably detect successful inhibition of the transporter in mice. A gas chromatography mass spectrometry (GC-MS)-based untargeted metabolomics approach was used to discriminate global metabolite profiles in plasma, urine and faecal samples from SLC6A19ko and wt mice. Due to inefficient absorption in the intestine and lack of reabsorption in the kidney, significantly elevated amino acids levels were observed in urine and faecal samples. By contrast, a few neutral amino acids were reduced in the plasma of male SLC6A19ko mice as compared to other biological samples. Metabolites of bacterial protein fermentation such as p-cresol glucuronide and 3-indole-propionic acid were more abundant in SLC6A19ko mice, indicating protein malabsorption of dietary amino acids. Consistently, plasma appearance rates of [C]-labelled neutral amino acids were delayed in SLC6A19ko mice as compared to wt after intra-gastric administration of a mixture of amino acids. Receiver operating characteristic (ROC) curve analysis was used to validate the potential use of these metabolites as biomarkers. These findings provide putative metabolite biomarkers that can be used to detect protein malabsorption and the inhibition of this transporter in intestine and kidney.
最近的研究表明，限制饮食中的蛋白质可以改善代谢健康和葡萄糖稳态。SLC6A19（B⁰AT1）是肠道中主要的中性氨基酸转运体，负责从饮食中吸收大部分氨基酸。缺乏 SLC6A19 的小鼠表现出蛋白质限制的迹象，葡萄糖耐量提高，并能预防饮食诱导的肥胖。该转运体的药理学阻断可用于诱导蛋白质限制，并治疗 2 型糖尿病等代谢疾病。最近通过体外化合物筛选发现了几种 SLC6A19 的新型抑制剂，但这些化合物在体内是否阻断转运体尚不清楚。为了评估 SLC6A19 抑制剂的疗效，需要能够可靠地检测到小鼠中转运体成功抑制的生物标志物。使用基于气相色谱质谱（GC-MS）的非靶向代谢组学方法来区分 SLC6A19ko 和 wt 小鼠血浆、尿液和粪便样本中的全局代谢物图谱。由于在肠道中吸收效率低且肾脏中缺乏重吸收，因此在尿液和粪便样本中观察到氨基酸水平显著升高。相比之下，与其他生物样本相比，雄性 SLC6A19ko 小鼠的血浆中一些中性氨基酸减少。细菌蛋白质发酵的代谢物，如对羟福林葡萄糖醛酸和 3-吲哚丙酸，在 SLC6A19ko 小鼠中更为丰富，表明膳食氨基酸的蛋白质吸收不良。一致地，与 wt 小鼠相比，SLC6A19ko 小鼠在胃内给予氨基酸混合物后，[C]-标记的中性氨基酸的血浆出现率延迟。接收器操作特征（ROC）曲线分析用于验证这些代谢物作为生物标志物的潜在用途。这些发现提供了潜在的代谢物生物标志物，可用于检测肠道和肾脏中的蛋白质吸收不良和该转运体的抑制。
