Supplementing Glycine and N-Acetylcysteine (GlyNAC) in Older Adults Improves Glutathione Deficiency, Oxidative Stress, Mitochondrial Dysfunction, Inflammation, Physical Function, and Aging Hallmarks: A Randomized Clinical Trial

Abstract

Background: Elevated oxidative stress (OxS), mitochondrial dysfunction, and hallmarks of aging are identified as key contributors to aging, but improving/reversing these defects in older adults (OA) is challenging. In prior studies, we identified that deficiency of the intracellular antioxidant glutathione (GSH) could play a role and reported that supplementing GlyNAC (combination of glycine and N-acetylcysteine [NAC]) in aged mice improved GSH deficiency, OxS, mitochondrial fatty-acid oxidation (MFO), and insulin resistance (IR). To test whether GlyNAC supplementation in OA could improve GSH deficiency, OxS, mitochondrial dysfunction, IR, physical function, and aging hallmarks, we conducted a placebo-controlled randomized clinical trial.

Methods: Twenty-four OA and 12 young adults (YA) were studied. OA was randomized to receive either GlyNAC (N = 12) or isonitrogenous alanine placebo (N = 12) for 16-weeks; YA (N = 12) received GlyNAC for 2-weeks. Participants were studied before, after 2-weeks, and after 16-weeks of supplementation to assess GSH concentrations, OxS, MFO, molecular regulators of energy metabolism, inflammation, endothelial function, IR, aging hallmarks, gait speed, muscle strength, 6-minute walk test, body composition, and blood pressure.

Results: Compared to YA, OA had GSH deficiency, OxS, mitochondrial dysfunction (with defective molecular regulation), inflammation, endothelial dysfunction, IR, multiple aging hallmarks, impaired physical function, increased waist circumference, and systolic blood pressure. GlyNAC (and not placebo) supplementation in OA improved/corrected these defects.

Conclusion: GlyNAC supplementation in OA for 16-weeks was safe and well-tolerated. By combining the benefits of glycine, NAC and GSH, GlyNAC is an effective nutritional supplement that improves and reverses multiple age-associated abnormalities to promote health in aging humans. Clinical Trials Registration Number: NCT01870193.

Keywords: Clinical trials; GlyNAC; Metabolism; Oxidative stress; Successful aging.

Graphical Abstract

Figure 1.

(A) Clinical trial CONSORT flow diagram; (B) flow chart of study design.

Figure 2.

(A) Western blots for protein expression; each blot represents serial biopsies one participant from YA (0w, 2w), the OAG (0w, 2w, 16w), and OAP (0w, 2w, 16w). GCLC and GCLM = Glutamate cysteine ligase catalytic and modifier subunits; GSS = Glutathione synthetase; PGC1α = PPARG coactivator 1-alpha; SirT3 = Sirtuin 3; pAMPKα = phosphorylated AMP-activated protein kinase α subunit; AMPKα = total AMP-activated protein kinase α subunit; CPT1B = Carnitine palmitoyltransferase 1B; PPARα = Peroxisome proliferator-activated receptor α; HADHA = hydroxyacyl-CoA dehydrogenase trifunctional multienzyme complex subunit α; C-I, II, III, V = mitochondrial complexes I, II, II, V; ATP5A = mitochondrial ATP synthase F1 subunit alpha; PINK1 = PTEN-induced kinase 1; LC3AB = Microtuble-associated protein light chain 3 A and B; GLUT4 = Glucose transporter type 4; pH2AX = phospho-H2A histone family member X; PAX7 = Paired box protein 7; p16INK4α = p16; POT1 = Protection of telomeres protein 1. Additional details are in methods section. (B) Quantification of Immunoblots from 3 participants per group of YA, OAP and OAG. The figure shows average optical densities of protein expression from each group normalized to the loading control (β-actin). * = p < .05; ϕ = p < .01; θ = p < .001. GlyNAC = combination of glycine and N-acetylcysteine; YA = young adults; OAG = older adults receiving GlyNAC; OAP = older adults receiving placebo.

Figure 2.

(A) Western blots for protein expression; each blot represents serial biopsies one participant from YA (0w, 2w), the OAG (0w, 2w, 16w), and OAP (0w, 2w, 16w). GCLC and GCLM = Glutamate cysteine ligase catalytic and modifier subunits; GSS = Glutathione synthetase; PGC1α = PPARG coactivator 1-alpha; SirT3 = Sirtuin 3; pAMPKα = phosphorylated AMP-activated protein kinase α subunit; AMPKα = total AMP-activated protein kinase α subunit; CPT1B = Carnitine palmitoyltransferase 1B; PPARα = Peroxisome proliferator-activated receptor α; HADHA = hydroxyacyl-CoA dehydrogenase trifunctional multienzyme complex subunit α; C-I, II, III, V = mitochondrial complexes I, II, II, V; ATP5A = mitochondrial ATP synthase F1 subunit alpha; PINK1 = PTEN-induced kinase 1; LC3AB = Microtuble-associated protein light chain 3 A and B; GLUT4 = Glucose transporter type 4; pH2AX = phospho-H2A histone family member X; PAX7 = Paired box protein 7; p16INK4α = p16; POT1 = Protection of telomeres protein 1. Additional details are in methods section. (B) Quantification of Immunoblots from 3 participants per group of YA, OAP and OAG. The figure shows average optical densities of protein expression from each group normalized to the loading control (β-actin). * = p < .05; ϕ = p < .01; θ = p < .001. GlyNAC = combination of glycine and N-acetylcysteine; YA = young adults; OAG = older adults receiving GlyNAC; OAP = older adults receiving placebo.