Lithium at 50: have the neuroprotective effects of this unique cation been overlooked?

Recent advances in cellular and molecular biology have resulted in the identification of two novel, hitherto completely unexpected targets of lithium's actions, discoveries that may have a major impact on the future use of this unique cation in biology and medicine. Chronic lithium treatment has been demonstrated to markedly increase the levels of the major neuroprotective protein, bcl-2 in rat frontal cortex, hippocampus, and striatum. Similar lithium-induced increases in bcl-2 are also observed in cells of human neuronal origin, and are observed in rat frontal cortex at lithium levels as low as approximately 0.3 mmol/L. Bcl-2 is widely regarded as a major neuroprotective protein, and genetic strategies that increase bcl-2 levels have demonstrated not only robust protection of neurons against diverse insults, but have also demonstrated an increase the regeneration of mammalian CNS axons. Lithium has also been demonstrated to inhibit glycogen synthase kinase 3 beta (GSK-3 beta), an enzyme known to regulate the levels of phosphorylated tau and beta-catenin (both of which may play a role in the neurodegeneration observed in Alzheimer's disease). Consistent with the increases in bcl-2 levels and inhibition of GSK-3 beta, lithium has been demonstrated to exert robust protective effects against diverse insults both in vitro and in vivo. These findings suggest that lithium may exert some of its long term beneficial effects in the treatment of mood disorders via underappreciated neuroprotective effects. To date, lithium remains the only medication demonstrated to markedly increase bcl-2 levels in several brain areas; in the absence of other adequate treatments, the potential efficacy of lithium in the long term treatment of certain neurodegenerative disorders may be warranted.