Glutathione (GSH), an abundant tripeptidyl molecule, plays pivotal roles in protecting cells against oxidative stress-induced cellular damage and in detoxifying xenobiotics and drug metabolism. GSH is now entering a new era of therapeutic applications. Decreased GSH levels are associated with the common features of aging as well as of a wide range of pathological conditions, including neurodegenerative disorders. Notably, GSH depletion and/or alterations in its metabolism appear to be crucial in the onset of Parkinson's disease. Despite the fact that GSH is required for cell survival, the molecular mechanism that links GSH depletion to cell death remains poorly understood. Recently, considerable attention has been focused on a newly defined type of cell death: irondependent cell death, also referred to as "ferroptosis". The iron chelator deferoxamine nearly abolishes ferroptosis induced by inhibiting GSH synthesis or cystine uptake by the xCT transporter. Deferoxamine preferentially abrogates the intralysosomal accumulation of iron and inhibits oxidative stress-induced lysosomal membrane permeabilization and cell death. The use of GSH and a prodrug derived from it can be useful, since the dysfunction of the GSH redox system appears to cause a variety of diseases including neurodegenerative disorders. However, the effectiveness of GSH as a therapeutic agent is limited because of its low bioavailability. We also review trials that have been designed to cope with this difficulty; e.g. the use of precursors such as N-acetyl cysteine and chemical modification such as methylation.

Superoxide is a primary oxygen radical that is produced when an oxygen molecule receives one electron. Superoxide dismutase (SOD) plays a primary role in the cellular defense against an oxidative insult by ROS. However, the resulting hydrogen peroxide is still reactive and, in the presence of free ferrous iron, may produce hydroxyl radicals and exacerbate diseases. Polyunsaturated fatty acids are the preferred target of hydroxyl radicals. Ferroptosis, a type of necrotic cell death induced by lipid peroxides in the presence of free iron, has attracted considerable interest because of its role in the pathogenesis of many diseases. Radical electrons, namely those released from mitochondrial electron transfer complexes, and those produced by enzymatic reactions, such as lipoxygenases, appear to cause lipid peroxidation. While GPX4 is the most potent anti-ferroptotic enzyme that is known to reduce lipid peroxides to alcohols, other antioxidative enzymes are also indirectly involved in protection against ferroptosis. Moreover, several low molecular weight compounds that include α-tocopherol, ascorbate, and nitric oxide also efficiently neutralize radical electrons, thereby suppressing ferroptosis. The removal of radical electrons in the early stages is of primary importance in protecting against ferroptosis and other diseases that are related to oxidative stress.

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