Preconditioning and supplementation with glutathione ameliorates oxidative stress, mitochondrial dysfunction, and restores metabolic imbalance in insulin-resistant myotubes.

Insulin resistance, defined as the inability of the insulin-target tissues including skeletal muscles to insulin action, has been identified as a major pathophysiology associated with the development of metabolic disorders including type 2 diabetes mellitus. Palmitic acid (PA) and related saturated free fatty acids contribute significantly to the development of insulin resistance by perturbing the redox homeostasis in the cells. The deficiency of the intracellular antioxidant - glutathione (GSH) has been documented in insulin-resistant states, and dietary supplementation of GSH and its precursors has been associated with the alleviation of oxidative stress, restoration of intra-abdominal fat levels, enhancement of insulin sensitivity and glucose metabolism. However, the key metabolic pathways targeted by GSH in mediating this protection need to be identified so that they can be targeted for effective management of insulin resistance. In this study, we aimed to elucidate whether preconditioning and supplementation with GSH (0.1 and 1 mM) could alleviate the oxidative stress, mitochondrial dysfunction, and metabolic perturbations induced by PA in the L6 skeletal myotubes. Metabolic perturbations associated with the same were identified using 1H NMR spectroscopy. It was observed GSH supplementation at concentrations of 1 mM in the myotubes experiencing lipotoxicity led to the partial restoration of metabolic imbalances observed in levels of nucleotides (UMP, adenosine, AMP), GSH metabolism intermediates (glutamine, pyroglutamate), acetate, amino acids including proline, aspartate, threonine; phospholipid intermediates (o-phosphocholine, choline), niacinamide, TCA cycle intermediates (citrate), and glycerol. Thus, we believe that these metabolic pathways can be targeted for the management of lipotoxicity and insulin resistance.