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Name of Student: Leah Cooper
Research Supervisor: Dr. Rajavel Elango
Title of Presentation: Nonessential amino acid metabolism in healthy adult males
determined using the indicator amino acid oxidation technique
Abstract
Background: Protein synthesis in the body requires all 20 amino acids (building blocks of
protein) in appropriate proportions. Throughout evolution, we have conserved
the pathways necessary for the synthesis of the nonessential amino acids
(NEAA) indicating their importance in the body. Nutritionally, there is a dietary
requirement for the 9 essential amino acids (EAA) because our body’s inability
to synthesize them. However, it is of importance to note that the requirement
for total nitrogen is the primary determinant of total protein requirement, which
includes a need for both EAA and NEAA. There is a dietary nitrogen
requirement for the de novo synthesis of the NEAA. It has been suggested that
some NEAA might be metabolically very important and may have a dietary
requirement, supplying the body with nitrogen for the synthesis of other NEAA.
The goal of this study was to determine the metabolic demand and hierarchy
among 9 of the NEAA to act as a nitrogen source for amino acid and thus
protein synthesis in the body.
Method:
Healthy adult males (n=5) were studied 10 times using the stable isotope based
indicator amino acid (IAAO) technique. Subjects maintained a protein intake of
1.0 g/kg and a caloric intake of 1.7 × resting energy expenditure (REE) during
the two days prior to each study day, provided in the form of milkshakes. The
base diet consisted of only the EAA provided at the recommended dietary
allowance as previously determined by the IAAO method. On the remaining
study days, each subject received the base diet with the addition of one NEAA
to meet the total nitrogen requirement. The study day diets were randomly
assigned. Diets were provided as eight isonitrogenous meals with a caloric
intake of 1.5 × REE. Breath and urine samples were collected at baseline and
isotopic steady state. Metabolic demand among the NEAA was determined by
measuring the oxidation of L-13C-Phenylalanine to 13CO2. The principle of
the IAAO technique is that oxidation is inversely proportional to protein
synthesis, such that a higher oxidation suggests lower protein synthesis, and
vice-versa.
Results:
Preliminary analysis conducted using repeated measures ANOVA showed a
significant difference in L-13C-Phenylalanine oxidation between all NEAA
added diets, except glutamine, compared to the base EAA diet. However no
significant differences were observed among the NEAA diets.
Conclusion: This study is the first to look at the metabolic demand among NEAA in adult
humans, and initial analysis suggests all NEAA can satisfy the metabolic
demand for total nitrogen. Whether differences exist in NEAA demand in
vulnerable populations such as pregnancy, where little is known about amino
acid requirements, remains to be determined.