Increased Amino Acid Turnover and Net Protein Breakdown but Preserved Muscle and Cognitive Function in Obese Middle-Age Adults

Objectives

Skeletal muscle weakness has been observed in obese patients despite preserved or even greater lean body mass. Additionally, the presence of obesity-related comorbidities is a recognized risk factor for cognitive dysfunction and mood disturbances. Metabolism of several amino acids (AAs) including the Branched-chain Amino Acids (BCAAs) is altered in obesity but whether these disturbances are associated with muscle and cognitive dysfunction remain underexplored.

Methods

159 subjects were divided, using the BMI cut-off of 30 kg/m², into two groups: 79 non-obese (32 males/47 females, age 48.5 [43.3, 53.7], BMI 25.2 [24.6, 25.7] kg/m²) and 80 obese (31 males/49 females, age 54.3 [51.0, 57.6], BMI 38.3 [36.9, 39.6] kg/m²). Postabsorptive whole-body production (WBP) rates of several AAs were measured by IV pulse of stable isotopes including BCAAs, Phenylalanine (Phe), Tyrosine (Tyr), Glutamate (Glu), and Tryptophan (Trp). Plasma amino acid enrichments and concentrations were analyzed by LC-MS/MS. Large Neutral Amino Acids (LNAA) was calculated as the sum of BCAAs, Phe, and Tyr. Body composition (DXA), hand and leg peak strength and endurance (isokinetic dynamometer), cognitive function (Stroop, TMT), and mood (POMS, HADS) were assessed. Statistics performed by ANCOVA with age, gender, and lean body mass as covariates. Significance at P < 0.05. Results expressed as means [95% CI].

Results

Obese subjects had higher concentrations of plasma Leu (12%, P = 0.0097), Ile (7%, P = 0.0310), Tyr (23%, P < 0.0001), and Glu (40%, P = 0.0001). The obese group was also characterized by elevated WBP of BCAAs (8%, P = 0.0343), Phe (12%, P = 0.0003), Tyr (18%, P = 0.0005) and increased whole-body net protein breakdown (Phe to Tyr conversion, 11%, P = 0.0212). Both groups had similar muscle and cognitive functions but obese individuals had greater scores for self-reported depressive symptoms (P = 0.0273), anger (P = 0.0234), fatigue (P = 0.0098), and tension (P = 0.0158). No changes in Trp metabolism were found but obese subjects had elevated LNAA (7%, P = 0.0170) resulting in increased systemic Trp availability to the brain (P = 0.0014).

Conclusions

Obese subjects have preserved muscle and cognitive function despite greater whole-body net protein breakdown and increased turnover of several AAs involved in muscle metabolism and serotonin synthesis.

Funding Sources

None.

Impaired Muscle Health and Amino Acid Kinetics in Older Adults With Mild Cognitive Impairment and the Role of Comorbidities

Objectives

Recent studies suggest that mild cognitive impairment (MCI) is more prevalent in older individuals with comorbidities that negatively affect muscle mass and function. Our objective is to identify whether impaired muscle health and alterations in plasma amino acid kinetics exist in a large group of participants with MCI and to study the effects of the presence of comorbidities.

Methods

113 individuals without MCI (n = 72 with at least 1 comorbidity based on Charlson comorbidity index (CCI > 0) and n = 41 without comorbidities (CCI = 0)), and 85 individuals with MCI, based on Montreal cognitive assessment (MoCA) (n = 51: CCI > 0; n = 34: CCI = 0), were selected from the MEDIT database consisting of healthy older adults and adults with at least 1 stable chronic condition or disease. Handgrip strength was measured by dynamometry and inspiratory muscle strength by mouth pressure device. DEXA was used to analyze body composition and visceral adipose tissue (VAT). Postabsorptive kinetics of glycine were measured by pulse stable isotope administration. Plasma GLY enrichment and amino acid profile were analyzed by LC-MS/MS. Stats were done by ANCOVA (covariates BMI, sex, and age) and Pearson correlation. Significance was set at p < 0.05.

Results

MoCA scores were lower in MCI participants without comorbidities compared to those with comorbidities (p = 0.0021). Independent of the presence of comorbidities, the MCI individuals tended to have lower levels of lean mass on the whole-body level (p = 0.051) and in the extremity compartment (p = 0.0129). Both the presence of MCI and comorbidities had a negative effect on respiratory (p = 0.003) and skeletal muscle strength (p = 0.0002). MCI individuals had lower GLY plasma concentration (p = 0.016) and whole-body production (p = 0.001), independent of the presence of comorbidities or amount of VAT. MCI*comorbidity interactions were found for respiratory and skeletal muscle strength, and the plasma concentrations of hydroxyproline and the branched-chain amino acids leucine, valine, and isoleucine (all p < 0.05).

Conclusions

Impaired muscle health and disturbed amino acid kinetics exist in MCI, only partly related to the presence of comorbidities.

Funding Sources

None

Training responses of plasma beta-endorphin, adrenocorticotropin, and cortisol

The purpose of this study was to examine the effects of three different run training programs on plasma responses of beta-endorphin (beta-EP), adrenocorticotropin (ACTH), and cortisol to maximal treadmill exercise. Subjects were randomly assigned to one of three training groups: sprint intervals (SI) (N = 8), endurance (E) (N = 10), or combination (C) (N = 7). Training was monitored for 10 wk, and maximal treadmill exercise tests were administered pre-training and after 2, 4, 6, 8, and 10 wk of training. Blood samples were obtained (pre-training and after 10 wk) before, immediately after, and 5 and 15 min following the maximal exercise tests. All groups significantly (P less than 0.05) increased maximal oxygen consumption values at 8 and 10 wk of the training period. Significant exercise-induced increase in plasma beta-EP, ACTH, cortisol, and blood lactate were observed for both pre- and post-training tests in all training groups. The SI group demonstrated significant post-training increases in beta-EP, ACTH, cortisol, and 5 min post-exercise blood lactate concentrations in response to maximal exercise. No training-induced hormonal changes were observed for the E group. While exercise-induced increases were observed, the C group exhibited significant post-training reductions in plasma responses of beta-EP, ACTH, and blood lactate concentrations in response to maximal exercise. Still, resting and post-exercise increases in plasma cortisol concentrations were significantly higher in magnitude in the post-training test. Lactate was significantly correlated with beta-EP (r = 0.72), ACTH (r = 0.70), and cortisol (r = 0.64).(ABSTRACT TRUNCATED AT 250 WORDS)

Hypothalamic-pituitary-adrenal responses to short-duration high-intensity cycle exercise

beta-Endorphin (beta-EP), adrenocorticotropin (ACTH), and cortisol plasma concentrations were examined before and after maximal exercise at four intensities [36, 55, 73, and 100% of maximal leg power (MLP)] by means of a computerized cycle ergometer. All intensities were greater than those eliciting peak O2 uptake for the individual subjects. Blood samples were collected at rest, immediately after exercise, and at 5 and 15 min postexercise. Significant (P less than 0.05) increases were observed at 36% MLP for beta-EP and ACTH immediately after exercise and at 5 and 15 min postexercise. Plasma cortisol increased at 36% MLP at 15 min postexercise. Blood lactate significantly increased at all postexercise collection points for exercise intensities of 36, 55, and 73% MLP and at 5 min postexercise for 100% MLP. beta-EP concentrations at 36% MLP were significantly correlated (r = 0.75) with capillary density (mm-2), and cortisol concentrations at 36% MLP were significantly correlated (r = 0.89) with percentage of type II muscle fibers. No other significant relationships were observed. These data show that brief, high-intensity exercise up to maximal power production results in a nonlinear response pattern in peripheral blood hormone concentrations. Furthermore, blood lactate levels do not appear to be related to hypothalamic-pituitary-adrenal hormone plasma concentrations at high exercise intensities.