l-Cysteine-Glutathione Mixed Disulfide, a Novel Bioavailable Sulfhydryl-Modified Glutathione Precursor, Protects against Early Liver Injury Induced by Short-Term Hypercholesterolemia.

Oxidative stress contributes to the damage of biological molecules and is linked to the development of multiple diseases, including liver disorders, such as metabolic dysfunction-associated steatotic liver disease (MASLD). In mammals, reduced glutathione (GSH) is a pivotal antioxidant that regulates cellular responses to redox imbalances caused by reactive oxygen and nitrogen species. The presence of reduced GSH within mitochondria is especially crucial for preserving the organelle's routine performance by eliminating hydrogen peroxide generated under both physiological and pathological conditions. Cumulative evidence indicates that MASLD is associated with a diminished mitochondrial GSH (mGSH) pool, attributed to alterations in mitochondrial membrane fluidity due to cholesterol accumulation. Therefore, strategies aimed at boosting mGSH may offer therapeutic benefits against MASLD-associated liver injury. This study aims to investigate whether l-cysteine-glutathione disulfide (l-CySSG), a proposed GSH donor and precursor, can effectively restore total and mGSH in vitro and in vivo in mice fed cholesterol-enriched (HC) or methionine-choline-deficient (MCD) diets. Additionally, S-adenosylmethionine (SAM), a compound that serves as both a GSH precursor and a membrane fluidizer, along with N-acetylcysteine (NAC), a GSH precursor by providing cysteine, was used as the control molecules in the study. Our findings show that l-CySSG has great potential as a liver protector, especially due to its good oral bioavailability. Although it does not restore GSH levels in the mitochondria as efficiently as SAM does, l-CySSG can still offer protection against liver damage, possibly through mechanisms that are not yet fully understood. Overall, l-CySSG emerges as a promising alternative for treating conditions related to oxidative stress and mitochondrial dysfunction, paving the way for future research and therapeutic development.