The effect of enteral glycine on plasma glycine and muscle structure, size, and function in the critically ill: A randomized controlled trial

BACKGROUND: Critically ill patients frequently experience severe muscle loss with subsequent physical impairment. In pre-clinical models of muscle wasting, administration of the amino acid glycine attenuates muscle loss. AIMS: To evaluate the plasma availability of enteral glycine and the impact of glycine supplementation on muscle loss in critical illness. METHODS: ). Secondary outcomes included muscle glycine concentration, myofiber diameter, quadriceps muscle thickness, physical function and length of stay. RESULTS: high-dose glycine vs placebo: 759.40 μmol/L.min; 95 % CI 219.27, 1299.54, p = 0.008) and muscle glycine concentration (Mean difference high-dose glycine vs placebo: 0.16 nmol/mg muscle wet mass; 95 % CI 0.08, 0.23, p = 0.001). Point estimates favoured attenuated loss of quadriceps muscle thickness in patients receiving high-dose glycine (Mean difference high-dose glycine vs placebo: 0.11 cm; 95 % CI: -0.10, 0.31, p = 0.299). However, glycine supplementation had no effect on myofiber diameter. Patients who received glycine had shorter ICU and hospital admissions. CONCLUSION: In critically ill patients, glycine supplementation increases plasma and muscle glycine concentrations and the effect of glycine on muscle loss warrants further evaluation in larger studies. TRIAL REGISTRATION: This trial was prospectively registered with the Australian and New Zealand Clinical Trials Registry (www.anzctr.org.au) ANZCTR ACTRN12618000409279.