This hypothesis was supported by the low Ki of lithium for human pAp-phosphatase compatible within the range of therapeutic concentrations of lithium in the plasma of people (0.8–1 mM). The Ki of human pAp-phosphatase is ten times lower than that of GSK3β (glycogen synthase kinase 3β). Inhibition of pAp-phosphatase by lithium leads to increased levels of pAp (3′-5′ phosphoadenosine phosphate), which was shown to inhibit PARP-1.Another mechanism proposed in 2007 is that lithium may interact with nitric oxide (NO) signalling pathway in the central nervous system, which plays a crucial role in neural plasticity. The NO system could be involved in the antidepressant effect of lithium in the Porsolt forced swimming test in mice. It was also reported that NMDA receptor blockage augments antidepressant-like effects of lithium in the mouse forced swimming test, indicating the possible involvement of NMDA receptor/NO signaling in the action of lithium in this animal model of learned helplessness. Lithium possesses neuroprotective properties by preventing apoptosis and increasing cell longevity.Although the search for a novel lithium-specific receptor is ongoing, the high concentration of lithium compounds required to elicit a significant pharmacological effect leads mainstream researchers to believe that the existence of such a receptor is unlikely. Oxidative metabolism
Evidence suggests that mitochondrial dysfunction is present in patients with bipolar disorder.Oxidative stress and reduced levels of anti-oxidants (such as glutathione) lead to cell death. Lithium may protect against oxidative stress by up-regulating complex I and II of the mitochondrial electron transport chain.
Lithium may lead to exacerbation of pre-existing primary hyperparathyroidism or cause an increased set-point of calcium for parathyroid hormone suppression, leading to parathyroid hyperplasia. Interactions
Lithium plasma concentrations are known to be increased with concurrent use of diuretics—especially loop diuretics (such as furosemide) and thiazides—and non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen. Lithium concentrations can also be increased with concurrent use of ACE inhibitors such as captopril, enalapril, and lisinopril.Lithium is primarily cleared from the body through glomerular filtration, but some is then reabsorbed together with sodium through the proximal tubule. Its levels are therefore sensitive to water and electrolyte balance. Diuretics act by lowering water and sodium levels; this causes more reabsorption of lithium in the proximal tubules so that the removal of lithium from the body is less, leading to increased blood levels of lithium. ACE inhibitors have also been shown in a retrospective case-control study to increase lithium concentrations. This is likely due to constriction of the afferent arteriole of the glomerulus, resulting in decreased glomerular filtration rate and clearance. Another possible mechanism is that ACE inhibitors can lead to a decrease in sodium and water. This will increase lithium reabsorption and its concentrations in the body.There are also drugs that can increase the clearance of lithium from the body, which can result in decreased lithium levels in the blood. These drugs include theophylline, caffeine, and acetazolamide.