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Abstract

The tripeptide thiol glutathione (GSH) has facile electron-donating capacity, linked to its sulfhydryl (—SH) group. Glutathione is an important water-phase antioxidant and essential cofactor for antioxidant enzymes; it provides protection also for the mitochondria against endogenous oxygen radicals. Its high electron-donating capacity combined with its high intracellular concentration endows GSH with great reducing power, which is used to regulate a complex thiol-exchange system (—SH —S-S—). This functions at all levels of cell activity, from the relatively simple (circulating cysteine/— SH thiols, ascorbate, other small molecules) to the most complex (cellular —SH proteins). Glutathione is homeostatically controlled, both inside the cell and outside. Enzyme systems synthesize it, utilize it, and regenerate it as per the gamma-glutamyl cycle. Glutathione is most concentrated in the liver (10 mM), where the “P450 Phase II” enzymes require it to convert fat-soluble substances into water-soluble GSH conjugates, in order to facilitate their excretion. While providing GSH for their specific needs, the liver parenchymal cells export GSH to the outside, where it serves as systemic source of —SH/reducing power. GSH depletion leads to cell death, and has been documented in many degenerative conditions. Mitochondrial GSH depletion may be the ultimate factor determining vulnerability to oxidant attack. Oral ascorbate helps conserve GSH; cysteine is not a safe oral supplement, and of all the oral GSH precursors probably the least flawed and most cost-effective is NAC (N-acetylcysteine). (Alt Med Rev 1997; 2(3):155-176)

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