Branched Chain Amino Acids Ratio in Medical Foods

Purpose:

The purpose of this study is to use the minimally invasive Indicator Amino Acid Oxidation (IAAO) method in healthy school-aged children to determine the optimal ratio of BCAA in current medical foods used by MMA/PROP subjects. We will recruit healthy children to test our hypothesis.

Hypothesis:

1. The IAAO will be high (suggesting low protein synthesis) at high leucine levels and will be low (suggesting optimal protein synthesis) when leucine levels are reduced and at a better-balanced ratio of leucine to isoleucine and valine.

2. Children will have low levels of urine excretion of isoleucine and valine, with high leucine urinary excretion, when given the high ratio of leucine to valine and isoleucine. With the reduction of leucine intake in the diet, the urinary concentration of both isoleucine and valine will normalize.

Justification:

The use of medical foods as a sole source of energy and protein in patients with MMA/PROP has been discouraged. The recommendations state that such medical foods should be only used for patients who can't consume their RDA from natural protein. Since most of these patients are poor eaters, and at risk for malnutrition, they depend on medical foods as an easy tolerable source of energy and protein. The medical foods formulated for MMA/PROP contain imbalanced BCAA ratio (high leucine to minimal or no valine and isoleucine). The high leucine levels antagonize the other two BCAA and even suppresses their plasma and urine levels below normal. Determining the optimal ratio of BCAA is necessary to optimize protein synthesis, growth and prevent the accumulation of toxic metabolites. This proposal will focus on applying stable isotope tracers in healthy children to examine different intakes of leucine while keeping the amount of valine and isoleucine restricted as per the recommendations. Using the minimally invasive indicator amino acid technique (IAAO), and L-1-13C-Phenylalanine as the indicator amino acid for protein synthesis, the optimal amount of leucine to be added in one of the most commonly used medical food for these patients will be tested. In addition, the leucine intake which normalizes urine isoleucine and valine excretion will also be determined to be useful for patient management. Starting with the studies on healthy children ages 6-10 years to allow for characterization of the metabolic response to the different leucine intakes. Consequently, based on the results we obtain, we will be able to design the studies in MMA/PROP patients with the appropriate BCAA ratios to test.

Objectives:

1. Our primary objective is to examine the impact of reducing leucine levels from the current high doses in medical foods, sequentially, while holding isoleucine and valine at MMA/PROP recommended intakes, on protein synthesis using the IAAO technique in healthy children (6-10y).

2. Our secondary objective is to determine the impact of reducing leucine levels from the current high doses in medical foods, sequentially, while holding isoleucine and valine at MMA/PROP recommended intakes, on urinary excretion of BCAA.

Research Design:

This is a repeated measure study design involving 1 pre-study visit and 6 studies visits for each child, approximately one week apart from each other.

Statistical Analysis:

Results will be expressed as means ± SDs. Repeated Measures ANOVA will be used to assess the relationship of phenylalanine oxidation, and BCAA urinary excretion to the variable BCAA intakes using SAS statistical software (version 9.4; SAS Institute, Cary, NC). In all cases, the difference will be considered significant at P < 0.05. Repeated measure ANOVA will be used to measure the difference between means of F13CO2 oxidations in response to 6 leucine test intakes, as well as means of BCAA urinary excretions. When warranted, post hoc analysis will be performed using Tukey's multiple comparisons test to confirm where the differences occur between different conditions (leucine test intakes).