Development of Biomarkers for Inhibition of SLC6A19 (B⁰AT1)-A Potential Target to Treat Metabolic Disorders.

Kiran Javed,Qi Cheng,Stefan Bröer,Adam Carroll,Thy Truong

doi:10.3390/ijms19113597

Kiran Javed, Qi Cheng + Show 3 more

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https://doi.org/10.3390/ijms19113597

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Abstract

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 [14C]-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.

Highlights

Protein restriction is recognized as an important factor for the maintenance of metabolic health
Recent work published by Fontana et al [8] showed that reduction in body mass and improved glucose tolerance can be achieved by only restricting branched-chain amino acids (BCAA) in the diet in young mice
Cummings et al [9] extended those studies to obese mice and showed that a low BCAA diet was more effective in weight loss and improving glucose tolerance than low fat diet [10]

Summary

Introduction

Protein restriction is recognized as an important factor for the maintenance of metabolic health. Newgard et al [4] showed a strong correlation between the risk of developing type 2 diabetes and increased plasma levels of essential amino acids (isoleucine, leucine and valine), aromatic amino acids (phenylalanine and tyrosine) and their metabolites such as C3 and C5-acyl carnitines. To test whether BCAA restriction is necessary to achieve effects of protein restriction, Maida et al [11] replenished BCAA in a protein-restricted diet in wild type (wt) and New Zealand obese (NZO) mice and found that the metabolic effects of protein restriction was reversed in wt mice but not in obese mice This suggested that that BCAA restriction alone is not sufficient to account for all the effects of protein restriction [12]. FGF21 transcription is upregulated under conditions of protein restriction, its metabolic actions are largely restricted to lipid metabolism, such as reduction of plasma lipids and production of adiponectin and ketone body biosynthesis [19]

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