Glutathione

Mechanism & Physiological Role

Endogenous tripeptide antioxidant. Primary substrate for glutathione peroxidase and glutathione S-transferase in phase II hepatic detoxification and reactive oxygen species neutralization.

Clinical & Research Applications

Discussed in the literature on oxidative stress and glutathione-dependent enzyme biology.

Biosynthesis, Handling & Sourcing

Glutathione is a tripeptide with an unusual bond. The link between glutamate and cysteine forms at the glutamate side chain rather than at its alpha carbon, and that gamma linkage is what makes the molecule resistant to the aminopeptidases that would otherwise clear a tripeptide quickly. Synthesis runs in two ATP-dependent steps, by glutamate-cysteine ligase and then glutathione synthetase, and the first of those is rate limiting, which is why cysteine availability rather than total protein intake is what the biosynthesis literature tends to track.

The functional unit is a ratio rather than a quantity. Reduced glutathione and its oxidized disulfide form a redox couple, and the proportion between them differs sharply between the cytosol, the mitochondria and the endoplasmic reticulum, which maintains a far more oxidizing interior to permit disulfide bond formation in folding proteins. A single number for whole-blood content therefore describes very little on its own, and published work generally reports the ratio and the compartment together.

For a compounding pharmacy the thiol group is the entire handling problem. It oxidizes readily on contact with air and more quickly at alkaline pH, converting to the disulfide, so sterile preparations are compounded under USP General Chapter 797 with headspace and pH controlled, protected from light, and carry a beyond-use date assigned at preparation rather than a manufacturer expiry. Discolouration in a solution that should be clear is a handling signal worth raising with the pharmacy rather than working around.

Injectable and intravenous glutathione has been studied in small clinical cohorts alongside a much larger body of in vitro and animal work, and reviews in the peer-reviewed literature describe its systemic pharmacokinetics as unsettled. Nothing on this page is a statement that any preparation is suitable for a given patient. Compounded medications are not FDA-approved finished drug products.