Does gliotoxin react with protein thiols and disrupt glutathione balance?

Gliotoxin is an epipolythiodioxopiperazine mycotoxin whose reactive disulfide chemistry can affect both protein thiols and cellular redox systems. The central biochemical claim is well supported, whereas the broad downstream implication for cellular defense is more context-dependent.

Direct thiol and redox effects

• Protein-thiol reaction is strongly supported. Gliotoxin’s epidisulfide undergoes thiol–disulfide exchange with accessible cysteine residues, producing reducible mixed-disulfide modifications. In creatine kinase, gliotoxin association was time-dependent and reversible with dithiothreitol; mass spectrometry implicated Cys254 and Cys283.
• Glutathione disruption is supported but variable. Intracellular GSH can reduce gliotoxin to its dithiol form, consuming GSH and forming GSSG. Reoxidation in the presence of oxygen generates superoxide and hydrogen peroxide, lowering the GSH:GSSG ratio and antioxidant buffering capacity. In rat hepatocytes, 50 μM gliotoxin rapidly oxidized GSH and was associated with oxidative stress and necrosis.

Mechanistic and immune implications

• Oxidative stress can follow, particularly when GSH depletion/oxidation and oxygen-dependent redox cycling occur together. N-acetylcysteine attenuated gliotoxin-associated ROS, apoptosis, and cytotoxicity in cell models, though this does not isolate glutathione restoration as the sole protective mechanism.
• Not all effects require oxidative stress. Activated hepatic stellate cells underwent thiol-redox-dependent apoptosis at 1.5 μM without detectable oxidative stress.
• Gliotoxin also inhibits neutrophil NADPH oxidase activation/assembly at low-micromolar concentrations, more potently under hypoxia, and can inactivate the cysteine-dependent redox enzyme glutaredoxin. Thus, altered immune-cell defense may result from direct thiol targeting as well as redox disturbance.

Bottom line

• Gliotoxin demonstrably modifies protein thiols and can disrupt glutathione redox balance, increasing oxidative stress in susceptible settings. Impaired cellular defense is biologically credible, but its magnitude and direction depend on cell type, oxygen conditions, exposure level, and the specific defense function measured.