Stimulation of Suicidal Erythrocyte Death by α-Lipoic Acid
Α-lipoic acid, a nutrient with both, antioxidant and oxidant activity induces apoptosis in a variety of cells. Owing to its proapoptotic potency Α-lipoic acid has been suggested for the therapy of cancer. Α-Lipoic acid stimulates apoptosis by induction of oxidative stress and subsequent activation of caspases. Oxidative stress could similarly trigger caspase activation and suicidal erythrocyte death or eryptosis, which is characterized by cell membrane scrambling and cell shrinkage. Eryptosis is triggered by increase of cytosolic Ca2+ concentration and/or ceramide formation. The present study explored whether Α -lipoic acid influences eryptosis. Cell membrane scrambling was estimated from binding of annexin V to phosphatidylserine at the erythrocyte surface, cell volume from forward scatter in FACS analysis, cytosolic Ca2+ concentration from Fluo3 fluorescence, caspase activation and ceramide formation utilizing respective antibodies, cytosolic ATP concentration from a luciferase-assay. Within 48 hours, exposure to Α-lipoic acid (10 - 75 mM) significantly decreased forward scatter, increased cytosolic Ca2+ concentration, decreased ATP concentration, activated caspase 3, stimulated formation of ceramide and triggered annexin V-binding. Glucose depletion (48 h) was followed by decrease of forward scatter and increase of annexin V-binding, effects significantly augmented in the presence of Α-lipoic acid (20 mM). Oxidative stress (30 min 0.3 mM tert-butylhydroperoxide) similarly triggered annexin binding, an effect slightly but significantly blunted by Α-lipoic acid. In conclusion, Α-lipoic acid triggers eryptosis but by the same token counteracts eryptosis during oxidative stress. Α-lipoic acid sensitive eryptosis may lead to anemia and derangements of microcirculation.