Markers of branched-chain amino acid catabolism are not affected by exercise training in pregnant women with obesity

Authors: ALLMAN, BRITTANY - Arkansas Children'S Nutrition Research Center (ACNC); SPRAY, BEVERLY - Arkansas Children'S Nutrition Research Center (ACNC); MERCER, KELLEY - Arkansas Children'S Nutrition Research Center (ACNC); ANDRES, ALINE - University Arkansas For Medical Sciences (UAMS); BORSHEIM, ELISABET - University Arkansas For Medical Sciences (UAMS)

Submitted to: Journal of Applied Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2021
Publication Date: 1/14/2021
Citation: Allman, B.R., Spray, B.J., Mercer, K.E., Andres, A., Borsheim, E. 2021. Markers of branched-chain amino acid catabolism are not affected by exercise training in pregnant women with obesity. Journal of Applied Physiology. https://doi.org/10.1152/japplphysiol.00673.2020.
DOI: https://doi.org/10.1152/japplphysiol.00673.2020

Interpretive Summary: Some studies show that the higher an individual's blood concentrations of branched-chain amino acids (leucine, isoleucine, and valine), the higher their body's resistance to insulin (insulin resistance). However, exercise training decreases insulin resistance, but does not change blood BCAA levels. Therefore, there seems to be a disconnect in BCAA concentrations and insulin resistance when measured over the course of time. In pregnant women, there is usually an increase in insulin resistance and a decrease in blood BCAA concentrations as pregnancy progresses. It is not known how exercise training affects this relationship. Therefore, we studied the effect of an exercise intervention during pregnancy on blood BCAA concentrations, as well as markers of BCAA breakdown (acylcarnitines), to determine if insulin resistance affected these relationships. We randomly placed 80 healthy obese pregnant women into either an exercise group (aerobic and resistance from ~13 to 36 weeks gestation) or a non-exercise control group. Blood was collected at ~12 weeks and ~36 weeks to determine blood concentrations of BCAA and acylcarnitines, as well as glucose and insulin to determine insulin resistance. We found that blood concentrations of BCAA, acylcarnitines, and insulin resistance were not different between the exercise and non-exercise groups. Regardless of group, all BCAAs and acylcarnitines decreased throughout the duration of pregnancy. Importantly, these reductions in BCAA and acylcarnitines was not explained by the increase in insulin resistance throughout gestation. Therefore, insulin resistance, which is characteristic of normal pregnancy may be defended even in the face of an exercise intervention (which would normally decrease insulin resistance), to enhance the "sending" of nutrients (like BCAAs) to the growing fetus.

Technical Abstract: Exercise training does not affect resting circulating branched-chain amino acids [BCAA; leucine (Leu), isoleucine (Ile), valine (Val)] or BCAA-derived acylcarnitines (AC) [markers of BCAA catabolism: propionylcarnitine (C3), isovalerylcarnitine (C5), 3-hydroxyisovalerylcarnitine (C5-OH), 2-methylbutyrylcarnitine (MBC)], but generally decreases insulin resistance. This disconnect contrasts the current dogma of a positive relationship between BCAA and insulin resistance. These relationships have not been described in pregnant women, who experience a natural increase in insulin resistance and decrease in circulating BCAA throughout gestation. Purpose: This study aimed to determine the effect of an exercise intervention during pregnancy on circulating BCAA and BCAA-derived ACs, and if insulin resistance affects these relationships. Healthy obese (n=80, mean +/- SD; BMI: 36.9+/-5.7 kg/m2) pregnant women were randomized into an exercise (n=40, aerobic/resistance 3x/week, ~13 weeks until birth) or a non-exercise control (n=40) group. Blood was collected at ~12 and ~36 weeks and analyzed for BCAAs, ACs, and glucose and insulin [updated homeostatic model assessment of insulin resistance (HOMA2-IR)]. There were no interaction effects of group by time. There was a main effect of time for each metabolite and HOMA2-IR (deltas: Leu, -10.7+/-15.8; Ile, -4.7+/-11.2; Val, -32.3+/-40.2 µmol/L; C3, -0.30+/-0.20; C5, -0.06+/-0.15; C5-OH, -0.02+/-0.05; MBC, -0.06+/-0.14 umol/L; HOMA2-IR: 0.9+/-1.9; P<0.05 for all). The time effects remained after adjusting for HOMA2-IR. A combined moderate aerobic and resistance exercise intervention during pregnancy in women with obesity was not associated with changes in BCAAs or BCAA-derived ACs when compared to standard of care. The decrease in BCAAs and BCAA-derived ACs throughout gestation could not be explained by insulin resistance.