Effect of Obesity and Exercise Training on Plasma Amino Acids and Amino Metabolites in American Indian Adolescents

Abstract

Context: Amino acids (AAs) and their metabolites are altered with obesity and may be predictive of future diabetes in adults, but there are fewer studies on AAs, as well as conflicting findings on how they vary with obesity, in adolescents.

Objective: To determine whether plasma AAs vary with body composition and insulin sensitivity and are altered in response to exercise training.

Design: Cross-sectional, and an exercise intervention.

Setting: Tribal wellness center.

Participants: American Indian boys and girls, 11 to 17 years of age with obesity (Ob, n = 58) or normal weight (NW, n = 36).

Intervention: The Ob group completed 16 weeks of aerobic exercise training.

Main outcome measure: A panel of 42 plasma AAs.

Results: Compared with the NW group, the Ob group had lower aerobic fitness and insulin sensitivity (interactive homeostasis model assessment 2), 17 AAs that were higher, and 7 AAs that were lower. Branched-chain AAs (+10% to 16%), aromatic AAs (+15% to 32%), and glutamate were among the higher AAs; all were positively correlated with body fat and negatively correlated with insulin sensitivity. The lysine metabolite 2-aminoadipic acid (2-AAA) and the valine metabolite β-aminoisobutyric acid (BAIBA) were 47% higher and 29% lower, respectively, in the Ob group, and were positively (2-AAA) and negatively (BAIBA) correlated with insulin sensitivity. Exercise training increased aerobic fitness by 10%, but body composition, insulin sensitivity, and AAs were not significantly changed.

Conclusions: Several plasma AAs are altered in American Indian adolescents with obesity and are associated with insulin sensitivity, but they were not altered with this exercise intervention.

Figure 1.

BCAAs in the NW and Ob groups. (A–C) Group values for valine, leucine, and isoleucine, respectively. Boxes show the median (center line) and interquartile range (IQR) for each group. Whiskers show the range of values within 1.5-fold of the IQR. Filled circles show the mean, and open circles are outlier values outside of 1.5-fold of the IQR. Between-group comparisons are shown as the percentage difference and false discovery rate–adjusted P value for a Wilcoxon rank-sum test. (D and E) Correlations between trunk fat and insulin sensitivity [iHOMA2 (%S)], respectively, and the sum of the three BCAAs. Triangles indicate normal weight; circles indicate obesity; filled symbols represent girls; open symbols represent boys. All results are for 36 normal weight participants and 58 participants with obesity at baseline, before the Ob group started the exercise program.

Figure 2.

Phenylalanine (Phe) and tyrosine (Tyr) in NW and Ob groups. (A and B) Group values for Phe and Tyr, respectively. Boxes show the median (center line) and interquartile range (IQR) for each group. Whiskers show the range of values within 1.5-fold of the IQR. Filled circles show the mean, and open circles are outlier values outside of 1.5-fold of the IQR. Between-group comparisons are shown as percentage difference and false discovery rate–adjusted P value for a Wilcoxon rank-sum test. (C–F) Correlations between trunk fat and insulin sensitivity [iHOMA2 (%S)], respectively, and Phe and Tyr. Triangles indicate normal weight; circles indicate obesity; filled symbols represent girls; open symbols represent boys. All results are for 36 normal weight participants and 58 participants with obesity at baseline, before the Ob group started the exercise program.

Figure 3.

Glutamate, glutamine, and GABA in NW and Ob groups. (A–C) Group values for glutamate, glutamine, and GABA, respectively. Boxes show the median (center line) and interquartile range (IQR) for each group. Whiskers show the range of values within 1.5-fold of the IQR. Closed circles show the mean, and open circles are outlier values outside of 1.5-fold of the IQR. Between-group comparisons are shown as percentage difference and false discovery rate–adjusted P value for Wilcoxon a rank-sum test. (D and E) Correlations between trunk fat and insulin sensitivity [iHOMA2 (%S)], respectively, and glutamate. Triangles indicate normal weight; circles indicate obesity; filled symbols represent girls; open symbols represent boys. All results are for 36 normal weight participants and 58 participants with obesity at baseline, before the Ob group started the exercise program.

Figure 4.

Amino acid metabolites, 2-AAA, and BAIBA in NW and Ob groups. (A) Group values for 2-AAA. (B) Correlation between insulin sensitivity and 2-AAA. (C) Group values for BAIBA. (D) Correlation between insulin sensitivity and BAIBA. For group comparisons in (A) and (C), boxes show the median (center line) and interquartile range (IQR) for each group. Whiskers show the range of values within 1.5-fold of the IQR. Closed circles show the mean, and open circles are outlier values outside of 1.5-fold of the IQR. Between-group comparisons are shown as percentage difference and false discovery rate–adjusted P value for a Wilcoxon rank-sum test. For scatterplots in (B) and (D), triangles indicate normal weight, circles indicate obesity, filled symbols represent girls, and open symbols represent boys. All results are for 36 normal weight participants and 58 participants with obesity at baseline, before the Ob group started the exercise program.

Figure 5.

No change in AAs or amino metabolites in response to exercise training performed by the Ob group. (A–J) For each of the selected AAs/metabolites, the figure on the left shows the preexercise and postexercise values, and the right panel shows the change in values from preexercise to postexercise. Boxes show the median (center line) and interquartile range (IQR). Whiskers show the range of values within 1.5-fold of the IQR. Closed circles show the mean, and open circles are outlier values outside of 1.5-fold of the IQR. There were no statistically significant changes from preexercise to postexercise. All results are for 42 participants.