Amino Acids

Traumatic brain injury (TBI) is associated with sleep disturbances and cognitive impairment, with limited effective therapeutic strategies. Our previous work showed dietary supplementation with branched chain amino acids (BCAAs; isoleucine, leucine, valine), the primary substrate for de novo glutamate/GABA synthesis in the CNS, restored normal sleep-wake patterns and improved cognitive function in rodents. Our recent pilot work in humans showed preliminary feasibility/acceptability and limited efficacy for BCAAs to improve sleep in Veterans with TBI. However, these pilot data were limited in sample size, treatment dosages/duration, and therefore unable to establish efficacy or provide insight into dosing/duration parameters. The present study, SmART-TBI (supplementation with amino acid rehabilitative therapy in TBI: NCT04603443), represents a placebo-controlled, double-masked randomized clinical trial (target n = 120). Covariate adaptive randomization controlling for age, sex, TBI recency, pain, depression, and PTSD, allocated participants 1:1:1:1 to four groups comprising 3 BCAA doses b.i.d. ("high" 30 g; "medium" 20 g; and "low" 10 g) and one placebo-control (rice protein, 10 g b.i.d.). Outcomes were assessed following a 2-week baseline period; after 4 weeks, 8 weeks, and 12 weeks of intervention; and after 4 weeks and 12 weeks post-intervention. The primary outcomes are overall feasibility/acceptability metrics, and secondarily, preliminary efficacy for BCAAs to improve subjective sleep as assessed by the Insomnia Severity Index. Additional sleep measures were obtained for future analyses using a combination of actigraphy, mattress-sensors, sleep diaries, as well as pre-/post-BCAA overnight polysomnography. Additional exploratory outcomes included sweat-based biomarkers. Analyses of primary outcome measures indicated high feasibility and acceptability for this fully protocol.

Amino acids activate neutrophil phagocytosis and free radical release in vitro.

We examined the effects of amino acid supplementation on post-exercise accumulation of myeloperoxidase-positive (MPO⁺) cells in human skeletal muscle using a randomized, double-blind, placebo-controlled crossover design.

Ten young men (22 ± 2.8 years) consumed either amino acids (15 g) or an isocaloric placebo before resistance exercise. Biopsies of the vastus lateralis muscle were collected at baseline, immediately after exercise (0 h), and 24 h post-exercise.

Resistance exercise increased MPO⁺ cell infiltration (+161%, p = 0.02) and 8-hydroxy-2-deoxyguanosine (8-OHdG) levels (+66%, p = 0.02) at 24 h. Amino acid supplementation accelerated MPO⁺ cell infiltration to 0 h (+100%, p = 0.03), which diminished by 24 h post-exercise (+53%, p = 0.06). Immunofluorescence co-staining revealed that MPO⁺ cells exhibited markedly higher mitochondrial density (TOM20-labeled) and integrated with the injured regions of adjacent myofibers showing lower mitochondria. Other infiltrating MPO-negative cells also contributed mitochondria to exercised muscle tissue, resulting in an overall ~2-fold increase in mitochondrial content during 24-h recovery (p < 0.001), similar under both supplementation conditions. Cellular senescence marker p16Ink4a mRNA decreased by 58% at 24 h post-exercise, with an earlier reduction observed under amino acid treatment (0 h: -49%, p = 0.05).

These findings indicate that amino acid supplementation accelerates the resolution of inflammation in exercised human skeletal muscle. Immunofluorescence evidence further suggests that infiltrating bone marrow-derived cells contribute to fast mitochondrial gains as part of the muscle damage-response following exercise.