Tryptophan, glutamine, leucine, and micronutrient supplementation improves environmental enteropathy in Zambian adults: a randomized controlled trial

Abstract

Background: Environmental enteropathy (EE) refers to villus blunting, reduced absorption, and microbial translocation in children and adults in tropical or deprived residential areas. In previous work we observed an effect of micronutrients on villus height (VH).

Objective: We aimed to determine, in a randomized controlled trial, if amino acid (AA) or multiple micronutrient (MM) supplementation can improve intestinal structure or barrier dysfunction in Zambian adults with EE.

Methods: AA (tryptophan, leucine, and glutamine) and/or MM supplements were given for 16 wk in a 2 × 2 factorial comparison against placebo. Primary outcomes were changes in VH, in vivo small intestinal barrier dysfunction assessed by confocal laser endomicroscopy (CLE), and mechanistic (or mammalian) target of rapamycin complex 1 (MTORC1) nutrient responsiveness in lamina propria CD4+ lymphocytes.

Results: Over 16 wk AA, but not MM, supplementation increased VH by 16% (34.5 μm) compared with placebo (P = 0.04). Fluorescein leak, measured by CLE, improved only in those allocated to both AA and MM supplementation. No effect was seen on MTORC1 activation, but posttreatment MTORC1 and VH were correlated (ρ = 0.51; P = 0.001), and change in MTORC1 was correlated with change in VH in the placebo group (ρ = 0.63; P = 0.03). In secondary analyses no effect was observed on biomarkers of microbial translocation. Metabolomic analyses suggest alterations in a number of microbial- and host-derived metabolites including the leucine metabolite β-hydroxy-β-methylbutyrate, which was increased by AA supplementation and correlated with VH.

Conclusions: In this phase 2 trial, AA supplementation protected against a decline in VH over the supplementation period, and improved barrier function when combined with micronutrients. Leucine and MTORC1 metabolism may be involved in the mechanism of effect. This trial was registered at www.pactr.org as PACTR201505001104412.

Keywords: MTOR; Zambia; amino acids; clinical trial; confocal endomicroscopy; environmental enteropathy; metabolomics; micronutrients; morphometry.

FIGURE 3

Change in VH and villus cross-sectional surface area per unit length of mucosa after AA (top panels) or MM (bottom panels) supplementation compared with placebo. Mean ± SD changes are given together with Tukey's hinges. Two-tailed independent-samples t test, with normality confirmed by the Shapiro–Wilk test. AA, amino acid; MM, multiple micronutrient; VH, villus height.

FIGURE 4

Associations between the urinary metabolic profile and MTORC1 (upper panels) or VH (lower panels) based on the OPLS models. The NMR spectra are divided into 2 (right and left) to show the full range of δ¹H. For each comparison the upper section of the panel shows the average ¹H NMR spectrum (intensity in arbitrary units) and the lower section shows a Manhattan plot which displays the −log10(P value) for each of the spectral variables. Statistically significant peaks from the OPLS models are colored red if positively associated with MTORC1 or VH, and blue if inversely associated. n = 46 for both VH and MTORC1 models. For details of statistical analysis see the Methods. 2-HIB, 2-hydroxyisobutyrate; 2-PY, N-methyl-2-pyridone-5-carboxamide; 4-CS, 4-cresyl sulfate; DMA, dimethylamine, DMG, dimethylglycine; GAA, guanidinoacetic acid; HMB, β-hydroxy-β-methylbutyrate; MTORC1, mechanistic (or mammalian) target of rapamycin complex 1; PAG, phenylacetylglutamine; OPLS, orthogonal projection to latent structures; VH, villus height.

FIGURE 1

Examples of reproducible endomicroscopic signs of barrier dysfunction. Top left: intact mucosa; no leak; intervillous space is black (normal; Watson grade I). Top right: background luminal fluorescein (functional defect; Watson grade II) with a single apoptotic cell shedding event (nonpathological). Centre left: fluorescein plume with no mucosal defects (functional defect; Watson grade II). Center right: apical microerosion (multiple cell defect) with background fluorescein leakage (structural defect; Watson grade III). Bottom left: multiple microerosions with multiple fluorescein plumes (structural defect; Watson grade III). Bottom right: florid fluorescein leak within and out of the mucosa with multiple microerosions (structural defect; Watson grade III).

FIGURE 2

Consolidated Standards of Reporting Trials flow diagram of participants through the trial. Total numbers of participants are given, with the number of HIV-positive participants in parentheses. AA, amino acid; MM, multiple micronutrient; OGD, oesophagogastroduodenoscopy; P, placebo.