Alpha-lipoic acid (LA) and its corresponding derivative,
alpha-lipoamide (LM), have been described as
antioxidants, but the mechanisms of their putative
antioxidant effects remain largely uncharacterised. The vicinal
thiols present in the reduced forms of these compounds suggest that they might possess
metal chelating properties. We have shown previously that cell death caused by
oxidants may be initiated by lysosomal
rupture and that this latter event may involve intralysosomal
iron which catalyzes Fenton-type chemistry and resultant peroxidative damage to lysosomal membranes. Here, using cultured J774 cells as a model, we show that both LA and LM stabilize lysosomes against oxidative stress, probably by chelating intralysosomal
iron and, consequently, preventing intralysosomal Fenton reactions. In preventing
oxidant-mediated apoptosis, LM is significantly more effective than LA, as would be expected from their differing capacities to enter cells and concentrate within the acidic lysosomal compartment. As previously reported, the powerful
iron-
chelator,
desferrioxamine (Des) (which also locates within the lysosomal compartment), also provides protection against
oxidant-mediated cell death. Interestingly, although Des enhances the partial protection afforded by LA, it confers no additional protection when added with LM. Therefore, the
antioxidant actions of LA and LM may arise from intralysosomal
iron chelation, with LM being more effective in this regard.