Oral delivery of glutathione: antioxidant function, barriers and strategies

Glutathione (GSH) is a tripeptide with potent antioxidant activity, which is involved in numerous basic biological processes and has been used for interventions in various degenerative diseases. However, oral delivery of GSH remains challenging, similarly to that of other protein and peptide drugs, because the physicochemical barriers in the gastrointestinal (GI) tract lead to low oral bioavailability. Although several approaches have been explored to improve delivery, such as co-administration with penetration enhancers and enzymatic inhibitors, or encapsulation into nanoparticles, microemulsions and liposomes, appropriate formulations with clinical therapeutic effects remain to be developed. This review discusses approaches explored to developing an oral GSH delivery system that could provide protection against proteolytic degradation in the GI tract and enhance molecular absorption across the epithelial membrane. This system may be beneficial for the design and development of an oral formulation of GSH in the future.