Glutathione Biology in Neurodegenerative and Metabolic Diseases: Molecular Mechanisms, Pathophysiological Roles, and Therapeutic Perspectives

Glutathione is an abundant intracellular low-molecular-weight thiol that contributes importantly to cellular redox homeostasis. Besides its well-established role in the antioxidant defense of the cell, glutathione regulates mitochondrial function, metabolism of toxicants, protein thiol oxidation/reduction, redox signaling, and immunity. Disturbances in glutathione metabolism have been shown to play a role in various diseases; however, it has become clear that changes in glutathione metabolism are a part of a complex, multifactorial process. In this review, we summarize current knowledge of the molecular mechanisms governing glutathione synthesis, recycling, compartmentalization, and biological functions, with particular emphasis on redox signaling, the nuclear factor erythroid 2-related factor 2/Kelch-like ECH-associated protein 1 (Nrf2/Keap1) pathway, and reversible protein S-glutathionylation. We further examine how disturbances in glutathione homeostasis interact with mitochondrial dysfunction, chronic inflammation, metabolic stress, and impaired cellular signaling in Parkinson’s disease, Alzheimer’s disease, Huntington’s disease, multiple sclerosis, Wilson’s disease, type 2 diabetes, and nonalcoholic fatty liver disease. We also evaluate current translational interventions targeting restoration of glutathione balance through glutathione supplementation, precursor supplementation, pharmacological modulation of endogenous antioxidant mechanisms, dietary interventions, and changes in lifestyle. Despite the fact that many interventions have been promising at the mechanistic and experimental level, there are still insufficient clinical data because of the problems associated with glutathione availability, tissue specificity, disease variability, and a lack of sufficiently powered clinical trials. The conclusion of this review is that glutathione should not be viewed as a universal therapeutic target; instead, glutathione should be perceived as an important factor contributing to cellular resilience and able to help other disease-specific interventions. Future progress in glutathione-based interventions will likely depend on integrating redox biomarkers, patient stratification, and precision medicine strategies to identify individuals most likely to benefit from targeted modulation of glutathione homeostasis.