Ion homeostasis and the mechanism of action of lithium

Transcriptional and functional effects of lithium in bipolar disorder iPSC-derived cortical spheroids

Lithium (Li) is recommended for long-term treatment of bipolar disorder (BD). However, its mechanism of action is still poorly understood. Induced pluripotent stem cell (iPSC)-derived brain organoids have emerged as a powerful tool for modeling BD-related disease mechanisms. We studied the effects of 1 mM Li treatment for 1 month in iPSC-derived human cortical spheroids (hCS) from 10 healthy controls (CTRL) and 11 BD patients (6 Li-responders, Li-R, and 5 Li non-treated, Li-N). At day 180 of differentiation, BD hCS showed smaller size, reduced proportion of neurons, decreased neuronal excitability and reduced neural network activity compared to CTRL hCS. Li rescued excitability of BD hCS neurons by exerting an opposite effect in the two diagnostic groups, increasing excitability in BD hCS and decreasing it in CTRL hCS. We identified 132 Li-associated differentially expressed genes (DEGs), which were overrepresented in sodium ion homeostasis and kidney-related pathways. Moreover, Li regulated secretion of pro-inflammatory cytokines and increased mitochondrial reserve capacity in BD hCS. Through long-term Li treatment of a human 3D brain model, this study partly elucidates the functional and transcriptional mechanisms underlying the clinical effects of Li, such as rescue of neuronal excitability and neuroprotection. Our results also underscore the substantial influence of treatment duration in Li studies. Lastly, this study illustrates the potential of patient iPSC-derived 3D brain models for precision medicine in psychiatry.

Study of Lithium Biodistribution and Nephrotoxicity in Skin Melanoma Mice Model: The First Step towards Implementing Lithium Neutron Capture Therapy

Boron neutron capture therapy (BNCT) is one of the promising treatment methods for malignant melanoma. The main issue of this technology is the insufficient selectivity of ¹⁰B accumulation in tumor cells. As a result of the neutron absorption by boron, an 84% energy release occurred within the cell by the nuclear reaction ¹⁰B (n, α)⁷Li, which lead to tumor cell death. The use of lithium instead of boron brings a new unique opportunity-local 100% energy release-since all products of the ⁶Li (n, α)³H reaction have high linear energy transfer characteristics. The aim of this study was to determine the concentrations of Li in the tumor, skin, blood, brain and kidney in experimental animals with B16 melanoma and to analyze the potential Li toxicity after lithium carbonate administration at single doses of 300 and 400 mg/kg. Lithium carbonate was chosen since there is a long-term experience of its use in clinical practice for the treatment of psychiatric disorders. The inductively coupled plasma atomic emission spectrometry was used to evaluate Li concentrations in tissue samples. The accumulation efficiency of Li in the tumor was the highest at a time point of 30 min (22.4 µg/g; at a dose of 400 mg/kg). Despite the high lithium accumulation in the kidneys, the pathological changes in kidney tissues were not found. Thus, lithium may actually be used for the Li-NCT development and future studies can be conducted using ⁶Li and following irradiation of tumor cells using the schemes of lithium administration tested in this work.

Lithium in Cancer Therapy: Friend or Foe?

Lithium, a trace element important for fetal health and development, is considered a metal drug with a well-established clinical regime, economical production process, and a mature storage system. Several studies have shown that lithium affects tumor development by regulating inositol monophosphate (IMPase) and glycogen synthase kinase-3 (GSK-3). Lithium can also promote proliferation and programmed cell death (PCD) in tumor cells through a number of new targets, such as the nuclear receptor NR4A1 and Hedgehog-Gli. Lithium may increase cancer treatment efficacy while reducing side effects, suggesting that it can be used as an adjunctive therapy. In this review, we summarize the effects of lithium on tumor progression and discuss the underlying mechanisms. Additionally, we discuss lithium's limitations in antitumor clinical applications, including its narrow therapeutic window and potential pro-cancer effects on the tumor immune system.

Trinuclear Calcium Site in the C2 Domain of PKCα/γ Is Prone to Lithium Attack

Lithium (Li⁺) is the first-line therapy for bipolar disorder and a candidate drug for various diseases such as amyotrophic lateral sclerosis, multiple sclerosis, and stroke. Despite being the captivating subject of many studies, the mechanism of lithium's therapeutic action remains unclear. To date, it has been shown that Li⁺ competes with Mg²⁺ and Na⁺ to normalize the activity of inositol and neurotransmitter-related signaling proteins, respectively. Furthermore, Li⁺ may co-bind with Mg²⁺-loaded adenosine or guanosine triphosphate to alter the complex's susceptibility to hydrolysis and mediate cellular signaling. Bipolar disorder patients exhibit abnormally high cytosolic Ca²⁺ levels and protein kinase C (PKC) hyperactivity that can be downregulated by long-term Li⁺ treatment. However, the possibility that monovalent Li⁺ could displace the bulkier divalent Ca²⁺ and inhibit PKC activity has not been considered. Here, using density functional theory calculations combined with continuum dielectric methods, we show that Li⁺ may displace the native dication from the positively charged trinuclear site in the C2 domain of cytosolic PKCα/γ. This would affect the membrane-docking ability of cytosolic PKCα/γ and reduce the abnormally high membrane-associated active PKCα/γ levels, thus downregulating the PKC hyperactivity found in bipolar patients.

FROZEN! Intracellular multi-electrolyte analysis measures millimolar lithium in mammalian cells

Lithium salts are commonly used as medication for Bipolar Disorder (BD) and depression. However, there are limited methods to quantify intracellular lithium. Most methods to analyze intracellular electrolytes require tedious sample processing, specialized and often expensive machinery, sometimes involving harmful chemicals, and a bulk amount of the sample. In this work, we report a novel method (FROZEN!) based on cell isolation (from the surrounding medium) through rapid de-ionized water cleaning, followed by flash freezing for preservation. SKOV3 cells were cultured in normal medium and a medium containing 1.0 mM lithium. Lithium and other intracellular electrolytes in the isolated and preserved cells were simultaneously analyzed with laser-induced breakdown spectroscopy (LIBS) and X-ray fluorescence spectroscopy (XRF). Key electrolytes such as sodium, potassium, and magnesium, along with lithium, were detectable at the single-cell level. We found that cells cultured in the lithium medium have an intracellular lithium concentration of 0.5 mM. Concurrently, the intracellular concentrations of other positively charged electrolytes (sodium, potassium, and magnesium) were reduced by the presence of lithium. FROZEN! will greatly facilitate research in intracellular electrolyte balance during drug treatment, or other physiological stresses. In particular, the cell isolation and preservation steps can be easily performed by many laboratories worldwide, after which the samples are sent to an analytical laboratory for electrolyte analysis.

Na+/K+-ATPase and lipid peroxidation in forebrain cortex and hippocampus of sleep-deprived rats treated with therapeutic lithium concentration for different periods of time

Lithium (Li) is a typical mood stabilizer and the first choice for treatment of bipolar disorder (BD). Despite an extensive clinical use of Li, its mechanisms of action remain widely different and debated. In this work, we studied the time-course of the therapeutic Li effects on ouabain-sensitive Na⁺/K⁺-ATPase in forebrain cortex and hippocampus of rats exposed to 3-day sleep deprivation (SD). We also monitored lipid peroxidation as malondialdehyde (MDA) production. In samples of plasma collected from all experimental groups of animals, Li concentrations were followed by ICP-MS. The acute (1 day), short-term (7 days) and chronic (28 days) treatment of rats with Li resulted in large decrease of Na⁺/K⁺-ATPase activity in both brain parts. At the same time, SD of control, Li-untreated rats increased Na⁺/K⁺-ATPase along with increased production of MDA. The SD-induced increase of Na⁺/K⁺-ATPase and MDA was attenuated in Li-treated rats. While SD results in a positive change of Na⁺/K⁺-ATPase, the inhibitory effect of Li treatment may be interpreted as a pharmacological mechanism causing a normalization of the stress-induced shift and return the Na⁺/K⁺-ATPase back to control level. We conclude that SD alone up-regulates Na⁺/K⁺-ATPase together with increased peroxidative damage of lipids. Chronic treatment of rats with Li before SD, protects the brain tissue against this type of damage and decreases Na⁺/K⁺-ATPase level back to control level.

How does the mood stabilizer lithium bind ATP, the energy currency of the cell: Insights from solid-state NMR

BACKGROUND

Lithium, in the form of a salt, is a mood stabilizer and a leading drug for the treatment of bipolar disorder. It has a very narrow therapeutic range and a variety of side effects. Lithium can replace magnesium and other cations in enzymes and small molecules, among them ATP, thereby affecting and inhibiting many biochemical pathways. The form of binding of lithium ions to ATP is not known.

METHODS

Here we extract the binding environment of lithium in solid ATP using a multi-nuclear multi-dimensional solid-state NMR approach.

RESULTS

We determine that the coordination sphere of lithium includes, at a distance of 3.0(±0.4) Å, three phosphates; the two phosphates closest to the ribose ring from one ATP molecule, and the middle phosphate from another ATP molecule. A water molecule most probably completes the fourth coordination. Despite the use of excess lithium in the preparations, sodium ions still remain bound to the sample, at distances of 4.3-5.5 Å from Li, and coordinate the first phosphate and two terminal phosphates.

CONCLUSIONS

Solid-state NMR enables to unravel the exact coordination of lithium in ATP showing binding to three phosphates from two molecules, none of which are the terminal gamma phosphate.

GENERAL SIGNIFICANCE

The methods we use are applicable to study lithium bound to a variety of ATP-bound enzymes, or to other cellular targets of lithium, consequently suggesting a molecular basis for its mode of action.

Free and Bound Therapeutic Lithium in Brain Signaling

Lithium, a first-line therapy for bipolar disorder, is effective in preventing suicide and new depressive/manic episodes. Yet, how this beguilingly simple monocation with only two electrons could yield such profound therapeutic effects remains unclear. An in-depth understanding of lithium's mechanisms of actions would help one to develop better treatments limiting its adverse side effects and repurpose lithium for treating traumatic brain injury and chronic neurodegenerative diseases. In this Account, we begin with a comparison of the physicochemical properties of Li⁺ and its key native rivals, Na⁺ and Mg²⁺, to provide physical grounds for their competition in protein binding sites. Next, we review the abnormal signaling pathways and proteins found in bipolar patients, who generally have abnormally high intracellular Na⁺ and Ca²⁺ concentrations, high G-protein levels, and hyperactive phosphatidylinositol signaling and glycogen synthase kinase-3β (GSK3β) activity. We briefly summarize experimental findings on how lithium, at therapeutic doses, modulates these abnormal signaling pathways and proteins. Following this survey, we address the following aspects of lithium's therapeutic actions: (1) Can Li⁺ displace Na⁺ from the allosteric Na⁺-binding sites in neurotransmitter transporters and G-protein coupled receptors (GPCRs); if so, how would this affect the host protein's function? (2) Why are certain Mg²⁺-dependent enzymes targeted by Li⁺? (3) How does Li⁺ binding to Mg²⁺-bound ATP/GTP (denoted as NTP) in solution affect the cofactor's conformation and subsequent recognition by the host protein? (4) How do NTP-Mg-Li complexes modulate the properties of the respective cellular receptors and signal-transducing proteins? We show that Li⁺ may displace Na⁺ from allosteric Na⁺-binding sites in certain GPCRs and stabilize inactive conformations, preventing these receptors from relaying signal to the respective G-proteins. It may also displace Mg²⁺ in enzymes containing highly cationic Mg²⁺-binding sites such as GSK3β, but not in enzymes containing Mg²⁺-binding sites with low or zero charge. We further show that Li⁺ binding to Mg²⁺-NTP in water does not alter the NTP conformation, which is locked by all three phosphates binding to Mg²⁺. However, bound lithium in the form of [NTP-Mg-Li]^2- dianions can activate or inhibit the host protein depending on the NTP-binding pocket's shape, which determines the metal-binding mode: The ATP-binding pocket's shape in the P2X receptor is complementary to the native ATP-Mg solution conformation and nicely fits [ATP-Mg-Li]^2-. However, since the ATP βγ phosphates bind Li⁺, bimetallic [ATP-Mg-Li]^2- may be more resistant to hydrolysis than the native cofactor, enabling ATP to reside longer in the binding site and elicit a prolonged P2X response. In contrast, the elongated GTP-binding pockets in G-proteins allow only two GTP phosphates to bind Mg²⁺, so the GTP conformation is no longer "triply-locked". Consequently, Li⁺ binding to GTP-Mg can significantly alter the native cofactor's structure, lowering the activated G-protein level, thus attenuating hyperactive G-protein-mediated signaling in bipolar patients. In summary, we have presented a larger "connected" picture of lithium's diverse effects based on its competition as a free monocation with native cations or as a phosphate-bound polyanionic complex modulating the host protein function.

How Native and Non-Native Cations Bind and Modulate the Properties of GTP/ATP

Adenosine triphosphate (ATP) and guanosine triphosphate (GTP) exist in physiological solution mostly bound to cations. Interestingly, their cellular Mg²⁺-bound forms have been shown to bind Li⁺, a first-line drug for bipolar disorder. However, solution structures of NTP/NDP (N = A or G) bound to Li⁺ and/or Mg²⁺ have not been solved, thus precluding knowledge of how the native Mg²⁺-bound cofactor conformation changes upon binding non-native Li⁺ and/or switching its environment from aqueous solution to proteins. Using well-calibrated methods that reproduce experimental structural and thermodynamic parameters of several Mg²⁺/Li⁺-nucleotide complexes, we show that the native NTP/NDP-Mg²⁺ cofactor adopts a "folded" conformation in water that remains unperturbed upon Li⁺ binding. We further show that the ATP-binding pockets of receptors such as P2X are complementary in shape to the "folded" ATP-Mg²⁺ solution structure, whereas the elongated GTP-binding pockets found in G-proteins necessitate the GTP-Mg²⁺ cofactor to undergo a conformational change from its "folded" conformation in solution to an extended one upon G-protein binding. Implications of the findings on how Li⁺, in its bound state, can manifest its therapeutic effects are discussed.

Competition between Li+ and Na+ in sodium transporters and receptors: Which Na+-Binding sites are "therapeutic" Li+ targets?

Li⁺ (turquoise), the better charge acceptor, can displace Na⁺ (purple) bound by only one or two aa residues in buried sites. Thus, Li⁺ can displace Na⁺ bound by Asp^– and Ser in the A_2AAR/β₁AR receptor and enhance the metal site's stability, thus prohibiting structural distortions induced by agonist binding, leading to lower cytosolic levels of activated G-proteins, which are hyperactive in bipolar disorder patients.

Sodium (Na⁺) acts as an indispensable allosteric regulator of the activities of biologically important neurotransmitter transporters and G-protein coupled receptors (GPCRs), which comprise well-known drug targets for psychiatric disorders and addictive behavior. How selective these allosteric Na⁺-binding sites are for the cognate cation over abiogenic Li⁺, a first-line drug to treat bipolar disorder, is unclear. Here, we reveal how properties of the host protein and its binding cavity affect the outcome of the competition between Li⁺ and Na⁺ for allosteric binding sites in sodium transporters and receptors. We show that rigid Na⁺-sites that are crowded with multiple protein ligands are well-protected against Li⁺ attack, but their flexible counterparts or buried Na⁺-sites containing only one or two protein ligands are vulnerable to Li⁺ substitution. These findings suggest a novel possible mode of Li⁺ therapeutic action: By displacing Na⁺ bound by ≤2 protein ligands in buried GPCR sites and stabilizing the receptor's inactive state, Li⁺ could prohibit conformational changes to an active state, leading to lower cytosolic levels of activated guanine nucleotide-binding proteins, which are hyperactive/overexpressed in bipolar disorder patients.

How Native and Alien Metal Cations Bind ATP: Implications for Lithium as a Therapeutic Agent

Adenosine triphosphate (ATP), the major energy currency of the cell, exists in solution mostly as ATP-Mg. Recent experiments suggest that Mg²⁺ interacts with the highly charged ATP triphosphate group and Li⁺ can co-bind with the native Mg²⁺ to form ATP-Mg-Li and modulate the neuronal purine receptor response. However, it is unclear how the negatively charged ATP triphosphate group binds Mg²⁺ and Li⁺ (i.e. which phosphate group(s) bind Mg²⁺/Li⁺) and how the ATP solution conformation depends on the type of metal cation and the metal-binding mode. Here, we reveal the preferred ATP-binding mode of Mg²⁺/Li⁺ alone and combined: Mg²⁺ prefers to bind ATP tridentately to each of the three phosphate groups, but Li⁺ prefers to bind bidentately to the terminal two phosphates. We show that the solution ATP conformation depends on the cation and its binding site/mode, but it does not change significantly when Li⁺ binds to Mg²⁺-loaded ATP. Hence, ATP-Mg-Li, like Mg²⁺-ATP, can fit in the ATP-binding site of the host enzyme/receptor, activating specific signaling pathways.

Lithium in the treatment of bipolar disorder: pharmacology and pharmacogenetics

After decades of research, the mechanism of action of lithium in preventing recurrences of bipolar disorder remains only partially understood. Lithium research is complicated by the absence of suitable animal models of bipolar disorder and by having to rely on in vitro studies of peripheral tissues. A number of distinct hypotheses emerged over the years, but none has been conclusively supported or rejected. The common theme emerging from pharmacological and genetic studies is that lithium affects multiple steps in cellular signaling, usually enhancing basal and inhibiting stimulated activities. Some of the key nodes of these regulatory networks include GSK3 (glycogen synthase kinase 3), CREB (cAMP response element-binding protein) and Na(+)-K(+) ATPase. Genetic and pharmacogenetic studies are starting to generate promising findings, but remain limited by small sample sizes. As full responders to lithium seem to represent a unique clinical population, there is inherent value and need for studies of lithium responders. Such studies will be an opportunity to uncover specific effects of lithium in those individuals who clearly benefit from the treatment.

Wnt and lithium: a common destiny in the therapy of nervous system pathologies?

Wnt signaling is required for neurogenesis, the fate of neural progenitors, the formation of neuronal circuits during development, neuron positioning and polarization, axon and dendrite development and finally for synaptogenesis. This signaling pathway is also implicated in the generation and differentiation of glial cells. In this review, we describe the mechanisms of action of Wnt signaling pathways and their implication in the development and correct functioning of the nervous system. We also illustrate how a dysregulated Wnt pathway could lead to psychiatric, neurodegenerative and demyelinating pathologies. Lithium, used for the treatment of bipolar disease, inhibits GSK3β, a central enzyme of the Wnt/β-catenin pathway. Thus, lithium could, to some extent, mimic Wnt pathway. We highlight the possible dialogue between lithium therapy and modulation of Wnt pathway in the treatment of the diseases of the nervous system.

Lithium: Molecular interactions, clinical actions

Lithium is one of the most widely used drugs in neuropsychopharmacology. Preclinical scientists have made several advances in ascertaining the molecular mechanisms of action of this cation; such as its ability to stabilize monoamine levels, to interact with second messengers, and its neuroprotective effects, possibly over suicidal behaviors. Nevertheless, there remains a gap of knowledge between the pharmacological advances and the number of reliable clinical trials, creating a lack of evidence-based medicine to support medical prescriptions. In this review we examine lithium’s molecular mechanisms of action and evaluate their relevance in clinical applications.

Mood stabilizers for patients with bipolar disorder: the state of the art

Bipolar disorder (BD) is a prevalent and disabling condition, often comorbid with other medical and psychiatric conditions and frequently misdiagnosed. International treatment guidelines for BD recommend the use of mood stabilizers - either in monotherapy or in association - as the gold standard in both acute and long-term therapy. Commonly used in the clinical practice of BD, mood stabilizers have represented an evolving field over the last few years. The concept of stabilization, in fact, has been stressed as the ultimate objective of the treatment of BD, given the chronic and recurrent nature of the illness, which accounts for its significant levels of impairment and disability. To date, different compounds are included within the broad class of mood stabilizers, with lithium, anticonvulsants and, more recently, atypical antipsychotics being the most representative agents. This article is aimed at providing an updated review of the available literature in relation to the role of mood stabilizers in BD, with particular emphasis on their mechanism of action, main clinical aspects and specific use in the different phases of BD treatment, according to the most recently published international treatment guidelines.

Effects of brain-derived neurotrophic factor on sodium-induced apoptosis in human olfactory neuroepithelial progenitor cells

Low levels of brain-derived neurotrophic factor (BDNF) peptide are linked to the pathophysiology of mood disorders. Several single-nucleotide polymorphisms (SNPs) across the BDNF gene (BDNF) have been associated with bipolar illness. Since both elevated intracellular sodium and apoptosis are believed to contribute to cellular dysfunction in bipolar disorder, it is important to determine the effect of exogenous BDNF on apoptosis induced by the high levels of intracellular sodium seen in ill bipolar patients. Human olfactory neuroepithelial progenitor cells were treated with monensin, a sodium ionophore that increases intracellular sodium and leads to apoptosis. Apoptosis was quantified with enzyme-linked immunosorbent assay (ELISA) for mono- and oligonucleosomes. Elevation of intracellular sodium concentration by monensin induced apoptosis. BDNF 100ng/mL pretreatment or co-treatment attenuated the monensin-induced apoptosis. Pretreatment with BDNF for 24h reduced monensin-induced apoptosis by 93%. Co-treatment of BDNF and monensin increased intracellular sodium concentration and reduced apoptosis by 66%. Monensin for 24h models a process that is believed to occur during ill phases of bipolar illness. Treatment with BDNF greatly attenuates or prevents monensin-induced apoptosis. The functional consequences of BDNF SNPs, known to be associated with bipolar illness, need to be examined.

Response of sodium pump to ouabain challenge in human glioblastoma cells in culture

Bipolar disorder is a severe psychiatric condition that manifests with abnormalities in ion regulation. Previous studies have suggested that glia may be specifically involved in the pathophysiology of this condition. Since the potent sodium pump inhibitor, ouabain, has been used previously to model the ionic changes of bipolar illness, we investigated its effect of on sodium pump expression and activity in a human glioblastoma cell line. LN229 cells were grown with or without ouabain 10(-7) M for 3 days, and the effect of a therapeutic concentration of lithium was also examined. The mRNA transcription of sodium pump isoforms was determined by reverse transcriptase polymerase chain reaction (RT-PCR), and the protein expression of phosphorylated and non-phosphorylated pump isoforms was semi-quantified utilizing Western blot. Ouabain treatment caused an increase of some 6-fold in alpha1 protein expression and a doubling of alpha1 mRNA. alpha3 protein and alpha2 and alpha3 mRNA more than doubled. Lithium treatment alone had no effect, but lithium co-administered with ouabain normalized Na pump protein and mRNA expression for alpha1 and 2, but not alpha3. These results suggest that disturbance of ion regulation induces changes in glial cell sodium regulatory systems which are normalized by lithium treatment.

Lithium: bipolar disorder and neurodegenerative diseases Possible cellular mechanisms of the therapeutic effects of lithium

Bipolar illness is a major psychiatric disorder that affects 1-3% of the worldwide population. Epidemiological studies have demonstrated that this illness is substantially heritable. However, the genetic characteristics remain unknown and a clear personality has not been identified for these patients. The clinical history of lithium began in mid-19th century when it was used to treat gout. In 1940, it was used as a substitute for sodium chloride in hypertensive patients. However, it was then banned, as it had major side effects. In 1949, Cade reported that lithium could be used as an effective treatment for bipolar disorder and subsequent studies confirmed this effect. Over the years, different authors have proposed many biochemical and biological effects of lithium in the brain. In this review, the main mechanisms of lithium action are summarised, including ion dysregulation; effects on neurotransmitter signalling; the interaction of lithium with the adenylyl cyclase system; inositol phosphate and protein kinase C signalling; and possible effects on arachidonic acid metabolism. However, none of the above mechanisms are definitive, and sometimes results have been contradictory. Recent advances in cellular and molecular biology have reported that lithium may represent an effective therapeutic strategy for treating neurodegenerative disorders like Alzheimer's disease, due to its effects on neuroprotective proteins like Bcl-2 and its actions on regulators of apoptosis and cellular resilience, such as GSK-3. However, results are contradictory and more specific studies into the use of lithium in therapeutic approaches for neurodegenerative diseases are required.

Lithium normalizes elevated intracellular sodium

BACKGROUND

Both mania and bipolar depression are characterized by elevations of intracellular sodium concentrations. This observation has been purported to be central to the pathophysiology of abnormal moods in bipolar illness. Reduction of sodium influx is a proposed shared mechanism of action of effective mood stabilizers, but direct documentation of this effect for lithium has never been demonstrated.

METHODS

Flame spectroscopic determinations of intracellular sodium concentration were performed in the human glioma cell line, LN292, after treatment with the sodium pump inhibitor, ouabain, and co-treatment with ouabain and lithium.

RESULTS

Ouabain 0.1 microM doubles the intracellular sodium concentration after 3 days. Pretreatment with lithium 1 mM for 1 week normalizes intracellular sodium.

CONCLUSION

This is the first demonstration that lithium can normalize abnormally elevated intracellular sodium levels. This may be an important mechanism of lithium action.

[Lithium: 55 years of history in the therapy of bipolar affective disorder]

The clinical history of lithium began in mid-19th century when it was used to treat gout. It was subsequently administered as a substitute for sodium chloride and towards the end of 1940 its effects for the control of mania were discovered. At present it is used effectively for treatment of mania and for the prophylaxis of bipolar disorder. Though its effect on affective illnesses is evident, the same cannot be said of its mechanism of action, since in spite of the numerous studies performed to date it is still not known exactly how this ion acts. Many theories have been proposed, the most important of which are: normalisation of possible ionic alterations; interactions with the adenylyl cyclase cAMP system; effects on the phosphatidylinositol cycle; stabilisation of the levels of neuroprotective proteins; normalisation of the values of some cytosolic endopeptidases; etc. In any case, it has yet to be determined which of these is the principal factor responsible for lithium's therapeutic action, while at the same time the possibility cannot be totally ruled out that its precise mechanism of action is still to be discovered.