Glutathione

The liver produces more glutathione than any other organ and is the primary source of plasma GSH. Hepatic GSH serves several critical functions: it conjugates with electrophilic metabolites produced during drug metabolism (Phase II detoxification via glutathione S-transferases), neutralizes reactive oxygen species generated by cytochrome P450 enzymes (Phase I metabolism), and provides GSH for export to other tissues. Acetaminophen hepatotoxicity is the classic example of hepatic GSH depletion — the toxic metabolite NAPQI depletes GSH stores, and when GSH is exhausted, NAPQI causes oxidative damage. This mechanism is why NAC (GSH precursor) is the antidote for acetaminophen overdose.

Reduced glutathione (GSH) is a tripeptide, and the intestinal epithelium has limited transport capacity for intact peptides — most are hydrolyzed by brush border peptidases to free amino acids before absorption. Studies using isotope-labeled GSH have shown that while some intact GSH may be absorbed, most is broken down in the GI tract. The absorbed free amino acids can support intracellular GSH synthesis, but the contribution of oral GSH to tissue antioxidant capacity is less than IV or IP delivery. Liposomal formulations and specific dipeptide forms (like gamma-glutamylcysteine) have been studied for better oral bioavailability, but for research requiring defined GSH supplementation, parenteral routes are more reliable.

Lymphocytes and macrophages have particularly high GSH requirements and are sensitive to oxidative stress. GSH depletion impairs T-cell proliferation, reduces NK cell cytotoxicity, and shifts the Th1/Th2 balance toward Th2 (reducing cell-mediated immunity). HIV infection is associated with systemic GSH depletion, which has made GSH biology relevant to AIDS immunology. In research contexts, manipulating GSH levels with GSH, NAC, or GSH-depleting agents (like BSO — buthionine sulfoximine) allows investigation of redox-dependent immune cell functions. Restoring GSH in oxidatively stressed immune cells is a standard experiment in immunological research on aging and chronic disease.