Different dependence of lithium and valproate on PI3K/PKB pathway

Lithium: A Promising Anticancer Agent

Lithium is a therapeutic cation used to treat bipolar disorders but also has some important features as an anti-cancer agent. In this review, we provide a general overview of lithium, from its transport into cells, to its innovative administration forms, and based on genomic, transcriptomic, and proteomic data. Lithium formulations such as lithium acetoacetate (LiAcAc), lithium chloride (LiCl), lithium citrate (Li₃C₆H₅O₇), and lithium carbonate (Li₂CO₃) induce apoptosis, autophagy, and inhibition of tumor growth and also participate in the regulation of tumor proliferation, tumor invasion, and metastasis and cell cycle arrest. Moreover, lithium is synergistic with standard cancer therapies, enhancing their anti-tumor effects. In addition, lithium has a neuroprotective role in cancer patients, by improving their quality of life. Interestingly, nano-sized lithium enhances its anti-tumor activities and protects vital organs from the damage caused by lipid peroxidation during tumor development. However, these potential therapeutic activities of lithium depend on various factors, such as the nature and aggressiveness of the tumor, the type of lithium salt, and its form of administration and dosage. Since lithium has been used to treat bipolar disorder, the current study provides an overview of its role in medicine and how this has changed. This review also highlights the importance of this repurposed drug, which appears to have therapeutic cancer potential, and underlines its molecular mechanisms.

Antidepressant-like effect of valproic acid-Possible involvement of PI3K/Akt/mTOR pathway

RATIONALE

Few studies suggest that antidepressants exert their effects by activating some signaling pathways, including the phosphatidylinositol 3-kinase (PI3K). Moreover, valproic acid (VPA) activates the PI3K pathway. Thus, here we investigated the antidepressant-like effect of VPA and if its effect is related to PI3K/Akt/mTOR activation.

METHODS

C57Bl/6 (WT) and PI3Kγ^-/- mice received VPA injections (30, 100 or 300mg/kg, i.p.) and 30min after they were submitted to the forced swimming (FS), tail suspension (TS) and open field (OF) tests. Another group was pretreated with rapamycin (5mg/kg, i.p.) 150min before VPA administration. Akt phosphorylation levels were measured by Western blotting.

RESULTS

In WT mice, VPA (30mg/kg) reduced the immobility time in both FS and TS tests. However, VPA (300mg/kg) increased the immobility time in FS test. All doses of VPA did not alter locomotor activity. In PI3Kγ^-/- mice, none of the doses revealed antidepressant-like effect. However, in the OF test, the lower dose of VPA increased the travelled distance in comparison with vehicle group. An increase in Akt phosphorylation levels was observed in WT, but not in PI3Kγ^-/- mice. Finally, the pretreatment of WT mice with rapamycin abolished the antidepressant-like effect of VPA (30mg/kg) in FS test.

CONCLUSION

These data suggest that the antidepressant-like effects of VPA might depend on PI3K and mTOR activation. Thus, more studies are necessary to investigate the mechanisms involved in the antidepressant-like effect induced by VPA in order to investigate novel therapeutic targets for the treatment of depression.

Valproic Acid Protects Primary Dopamine Neurons from MPP+-Induced Neurotoxicity: Involvement of GSK3β Phosphorylation by Akt and ERK through the Mitochondrial Intrinsic Apoptotic Pathway

Valproic acid (VPA), a drug widely used to treat manic disorder and epilepsy, has recently shown neuroprotective effects in several neurological diseases, particularly in Parkinson's disease (PD). The goal of the present study was to confirm VPA's dose-dependent neuroprotective propensities in the MPP⁺ model of PD in primary dopamine (DA) neurons and to investigate the underlying molecular mechanisms using specific mitogen-activated protein kinases (MAPKs) and phosphatidylinositol 3-kinase- (PI3K-) Akt signaling inhibitors. VPA reversed MPP⁺-induced mitochondrial apoptosis and counteracted MPP⁺-induced extracellular signal-regulated kinase (ERK) and Akt repression and inhibited glycogen synthase kinase 3β (GSK3β) activation through induction of GSK3β phosphorylation. Moreover, inhibitors of the PI3K and MAPK pathways abolished GSK3β phosphorylation and diminished the VPA-induced neuroprotective effect. These findings indicated that VPA's neuroprotective effect in the MPP⁺-model of PD is associated with GSK3β phosphorylation via Akt and ERK activation in the mitochondrial intrinsic apoptotic pathway. Thus, VPA may be a promising therapeutic candidate for clinical treatment of PD.

Valproic acid: a new candidate of therapeutic application for the acute central nervous system injuries

Acute central nervous system (CNS) injuries, including stroke, traumatic brain injury (TBI), and spinal cord injury (SCI), are common causes of human disabilities and deaths, but the pathophysiology of these diseases is not fully elucidated and, thus, effective pharmacotherapies are still lacking. Valproic acid (VPA), an inhibitor of histone deacetylation, is mainly used to treat epilepsy and bipolar disorder with few complications. Recently, the neuroprotective effects of VPA have been demonstrated in several models of acute CNS injuries, such as stroke, TBI, and SCI. VPA protects the brain from injury progression via anti-inflammatory, anti-apoptotic, and neurotrophic effects. In this review, we focus on the emerging neuroprotective properties of VPA and explore the underlying mechanisms. In particular, we discuss several potential related factors in VPA research and present the opportunity to administer VPA as a novel neuropective agent.

The role of lithium in the treatment of bipolar disorder: convergent evidence for neurotrophic effects as a unifying hypothesis

Lithium has been and continues to be the mainstay of bipolar disorder (BD) pharmacotherapy for acute mood episodes, switch prevention, prophylactic treatment, and suicide prevention. Lithium is also the definitive proof-of-concept agent in BD, although it has recently been studied in other psychoses as well as diverse neurodegenerative disorders. Its neurotrophic effects can be viewed as a unifying model to explain several integrated aspects of the pathophysiology of mood disorders and putative therapeutics for those disorders. Enhancing neuroprotection (which directly involves neurotrophic effects) is a therapeutic strategy intended to slow or halt the progression of neuronal loss, thus producing long-term benefits by favorably influencing outcome and preventing either the onset of disease or clinical decline. The present article: (i) reviews what has been learned regarding lithium's neurotrophic effects since Cade's original studies with this compound; (ii) presents human data supporting the presence of cellular atrophy and death in BD as well as neurotrophic effects associated with lithium in human studies; (iii) describes key direct targets of lithium involved in these neurotrophic effects, including neurotrophins, glycogen synthase kinase 3 (GSK-3), and mitochondrial/endoplasmic reticulum key proteins; and (iv) discusses lithium's neurotrophic effects in models of apoptosis and excitotoxicity as well as its potential neurotrophic effects in models of neurological disorders. Taken together, the evidence reviewed here suggests that lithium's neurotrophic effects in BD are an example of an old molecule acting as a new proof-of-concept agent. Continued work to decipher lithium's molecular actions will likely lead to the development of not only improved therapeutics for BD, but to neurotrophic enhancers that could prove useful in the treatment of many other illnesses.

Review of lithium effects on brain and blood

Clinicians have long used lithium to treat manic depression. They have also observed that lithium causes granulocytosis and lymphopenia while it enhances immunological activities of monocytes and lymphocytes. In fact, clinicians have long used lithium to treat granulocytopenia resulting from radiation and chemotherapy, to boost immunoglobulins after vaccination, and to enhance natural killer activity. Recent studies revealed a mechanism that ties together these disparate effects of lithium. Lithium acts through multiple pathways to inhibit glycogen synthetase kinase-3beta (GSK3 beta). This enzyme phosphorylates and inhibits nuclear factors that turn on cell growth and protection programs, including the nuclear factor of activated T cells (NFAT) and WNT/beta-catenin. In animals, lithium upregulates neurotrophins, including brain-derived neurotrophic factor (BDNF), nerve growth factor, neurotrophin-3 (NT3), as well as receptors to these growth factors in brain. Lithium also stimulates proliferation of stem cells, including bone marrow and neural stem cells in the subventricular zone, striatum, and forebrain. The stimulation of endogenous neural stem cells may explain why lithium increases brain cell density and volume in patients with bipolar disorders. Lithium also increases brain concentrations of the neuronal markers n-acetyl-aspartate and myoinositol. Lithium also remarkably protects neurons against glutamate, seizures, and apoptosis due to a wide variety of neurotoxins. The effective dose range for lithium is 0.6-1.0 mM in serum and >1.5 mM may be toxic. Serum lithium levels of 1.5-2.0 mM may have mild and reversible toxic effects on kidney, liver, heart, and glands. Serum levels of >2 mM may be associated with neurological symptoms, including cerebellar dysfunction. Prolonged lithium intoxication >2 mM can cause permanent brain damage. Lithium has low mutagenic and carcinogenic risk. Lithium is still the most effective therapy for depression. It "cures" a third of the patients with manic depression, improves the lives of about a third, and is ineffective in about a third. Recent studies suggest that some anticonvulsants (i.e., valproate, carbamapazine, and lamotrigene) may be useful in patients that do not respond to lithium. Lithium has been reported to be beneficial in animal models of brain injury, stroke, Alzheimer's, Huntington's, and Parkinson's diseases, amyotrophic lateral sclerosis (ALS), spinal cord injury, and other conditions. Clinical trials assessing the effects of lithium are under way. A recent clinical trial suggests that lithium stops the progression of ALS.

Neuroactive steroids, mood stabilizers, and neuroplasticity: alterations following lithium and changes in Bcl-2 knockout mice

Many neuroactive steroids (NS) demonstrate neurotrophic and neuroprotective actions, including protection against apoptosis via Bcl-2 protein. NS are altered in post-mortem brain tissue from subjects with bipolar disorder, and several agents with efficacy in mania elevate NS in rodents. We therefore hypothesized that lithium and valproate may elevate NS, and compensatory NS increases may occur in Bcl-2 knockout mice. NS levels (allopregnanolone, pregnenolone) were determined in frontal cortex by negative ion chemical ionization gas chromatography/mass spectrometry in male Wistar Kyoto rats treated chronically with lithium, valproate, or vehicle. NS were also investigated in heterozygous Bcl-2 knockout mice. Allopregnanolone levels are significantly elevated in lithium-treated (p<0.05), but not in valproate-treated, rats. Pregnenolone levels also tend to be higher following lithium treatment (p=0.09). Knockout of Bcl-2 significantly increases pregnenolone levels in mice (p<0.01), while allopregnanolone levels are unaltered. NS induction may be relevant to mechanisms contributing to lithium therapeutic efficacy and neuroprotection.

A systematic review of existing data on long-term lithium therapy: neuroprotective or neurotoxic?

Lithium is an efficacious agent for the treatment of bipolar disorder, but it is unclear to what extent its long-term use may result in neuroprotective or toxic consequences. Medline was searched with the combination of the word 'Lithium' plus key words that referred to every possible effect on the central nervous system. The papers were further classified into those supporting a neuroprotective effect, those in favour of a neurotoxic effect and those that were neutral. The papers were classified into research in humans, animal and in-vitro research, case reports, and review/opinion articles. Finally, the Natural Standard evidence-based validated grading rationale was used to validate the data. The Medline search returned 970 papers up to February 2006. Inspection of the abstracts supplied 214 papers for further reviewing. Eighty-nine papers supported the neuroprotective effect (6 human research, 58 animal/in vitro, 0 case reports, 25 review/opinion articles). A total of 116 papers supported the neurotoxic effect (17 human research, 23 animal/in vitro, 60 case reports, 16 review/opinion articles). Nine papers supported no hypothesis (5 human research, 3 animal/in vitro, 0 case reports, 1 review/opinion articles). Overall, the grading suggests that the data concerning the effect of lithium therapy is that of level C, that is 'unclear or conflicting scientific evidence' since there is conflicting evidence from uncontrolled non-randomized studies accompanied by conflicting evidence from animal and basic science studies. Although more papers are in favour of the toxic effect, the great difference in the type of papers that support either hypothesis, along with publication bias and methodological issues make conclusions difficult. Lithium remains the 'gold standard' for the prophylaxis of bipolar illness, however, our review suggests that there is a rare possibility of a neurotoxic effect in real-life clinical practice even in closely monitored patients with 'therapeutic' lithium plasma levels. It is desirable to keep lithium blood levels as low as feasible with prophylaxis.

DNA damage in bipolar disorder

Bipolar disorder (BD) is a prevalent, chronic, severe, and highly disabling psychiatric disorder that is associated with increased morbidity and mortality due to general medical conditions. There is an emerging body of evidence correlating chronic medical conditions with DNA damage. The present study was designed to assess DNA damage in BD patients using the comet assay (CA). Thirty-two bipolar-I outpatients diagnosed using the Structured Clinical Interview for DSM-IV were matched with 32 healthy volunteers. Manic and depressive symptoms were assessed using the Young Mania Rating Scale and the Hamilton Depression Rating Scale, respectively. Peripheral blood samples were collected and a standard protocol for CA preparation and analysis was performed. The present study showed that BD outpatients present an increased frequency of DNA damage relative to controls. The frequency of DNA damage correlated with the severity of symptoms of depression and mania.

Valproic acid prevents brain injury in a canine model of hypothermic circulatory arrest: a promising new approach to neuroprotection during cardiac surgery

BACKGROUND

The anticonvulsant valproic acid (sodium valproate, Depacon) acts as a neuroprotectant in rodents, but has never been tested in larger animals. We used valproate in our canine model of hypothermic circulatory arrest to evaluate its neuroprotective benefit in complex cardiac surgical cases.

METHODS

Thirteen dogs pretreated with valproate before 2 hours of hypothermic circulatory arrest survived for 24 hours (n = 7) or 72 hours (n = 6). Thirteen control animals (placebo only) also survived for 24 hours (n = 7) or 72 hours (n = 6) after hypothermic circulatory arrest. Blinded clinical neurologic evaluation was performed daily until sacrifice using the Pittsburgh Canine Neurologic Scoring System. Brains were harvested for blinded histopathologic analysis by a neuropathologist to determine the extent of apoptosis and necrosis in 11 brain regions (Total Brain Cell Death Score: 0 = normal, 99 = extensive neuronal death in all regions). Quantification of N-acetyl-aspartate, an established marker for brain injury, was performed with mass spectrometry.

RESULTS

Valproate dogs scored significantly better than control animals on clinical neurologic evaluation. Histopathologic examination revealed that valproate animals demonstrated less neuronal damage (by Total Brain Cell Death Score) than control animals at both 24 hours (16.4 versus 11.4; p = 0.03) and 72 hours (21.7 versus 17.7; p = 0.07). At 72 hours, the entorhinal cortex, an area involved with learning and memory, was significantly protected in valproate dogs (p < 0.05). Furthermore, the cortex, hippocampus, and cerebellum demonstrated preservation of near-normal N-acetyl-aspartate levels after valproate pretreatment.

CONCLUSIONS

These data demonstrate clinical, histologic, and biochemical improvements in dogs pretreated with valproate before hypothermic circulatory arrest. This commonly used drug may offer a promising new approach to neuroprotection during cardiac surgery.

Glycogen synthase kinase-3 is involved in the regulation of the cell cycle in cerebellar granule cells

Recent studies have demonstrated that neuronal reentry in the cell cycle and specifically the expression of the transcription factor E2F-1, constitutes a pathway that may be involved in neuronal apoptosis after serum and potassium withdrawal. Other enzymes such as glycogen synthase kinase-3beta (GSK-3beta) are also involved in this apoptotic stimulus, and thus in the process of neuronal cell death. Primary cerebellar granule cells (CGNs) were used in this study to determine whether pharmacological inhibition of GSK-3beta is involved in neuronal modulation of the cell cycle, and specifically in the regulation of E2F-1 and retinoblastoma protein (Rb). CGNs showed a dramatic increase in GSK-3beta activity after 2h of serum and potassium deprivation. Immunoblot and activity assays revealed that lithium and SB415286 inhibit fully the activation of GSK-3beta and attenuate the expression of cyclin D, cyclin E, pRb phosphorylation and the transcription factor E2F-1. These data were confirmed using AR-014418, a selective GSK-3beta inhibitor that prevents the expression of cell-cycle proteins. Our data indicate that GSK-3beta inhibition regulates, in part, the cell cycle in CGNs by inhibiting Rb phosphorylation and thus inhibiting E2F-1 activity. However, the selective inhibition of GSK-3beta with AR-A014418 had not effect on cell viability or apoptosis mediated by S/K withdrawal. Furthermore, our results suggest that selective GSK-3beta inhibition is not sufficient to protect against apoptosis in this S/K withdrawal model, indicating that Li(+) and SB415286 neuroprotective effects are mediated by the inhibition of additional targets to GSK3beta. Therefore, there is a connection between cell cycle and GSK-3beta activation and that these, along with other mechanisms, are involved in the molecular paths leading to the apoptotic process of rat CGNs triggered by S/K withdrawal.

Attenuation of phospholipid signaling provides a novel mechanism for the action of valproic acid

Valproic acid (VPA) is used to treat epilepsy and bipolar disorder and to prevent migraine. It is also undergoing trials for cancer therapy. However, the biochemical and molecular biological actions of VPA are poorly understood. Using the social amoeba Dictyostelium discoideum, we show that an acute effect of VPA is the inhibition of chemotactic cell movement, a process partially dependent upon phospholipid signaling. Analysis of this process shows that VPA attenuates the signal-induced translocation of PH(Crac)-green fluorescent protein from cytosol to membrane, suggesting the inhibition of phosphatidylinositol-(3,4,5)-trisphosphate (PIP(3)) production. Direct labeling of lipids in vivo also shows a reduction in PIP and PIP(2) phosphorylation following VPA treatment. We further show that VPA acutely reduces endocytosis and exocytosis-processes previously shown to be dependent upon PIP(3) production. These results suggest that in Dictyostelium, VPA rapidly attenuates phospholipid signaling to reduce endocytic trafficking. To examine this effect in a mammalian model, we also tested depolarization-dependent neurotransmitter release in rat nerve terminals, and we show that this process is also suppressed upon application of VPA and an inhibitor of phosphatidylinositol 3-kinase. Although a more comprehensive analysis of the effect of VPA on lipid signaling will be necessary in mammalian systems, these results suggest that VPA may function to reduce phospholipid signaling processes and thus may provide a novel therapeutic effect for this drug.

Lithium and valproate protect hippocampal slices against ATP-induced cell death

Lithium and valproate (VPA) are the most commonly prescribed mood-stabilizing drugs. Recently, several studies have reported their neuroprotective properties in several models of neural toxicity and, in some pathological conditions, large amounts of intracellular ATP can be released from damaged cells. In the present study, we investigate the potential neuroprotective effect of lithium and VPA against ATP-induced cell death in hippocampal slices of adult rats. Acute (in vitro) and chronic (in vivo) treatment at therapeutic doses with lithium or VPA significantly prevent the ATP-induced cell death. Lithium and VPA also exerted a synergic effect in the prevention of ATP-induced cell death. Moreover, hippocampal slices prepared from rats chronically treated with lithium or VPA presented a significant reduction in cell death in the presence of cytotoxic extracellular ATP. Although further investigations are necessary, our results show the neuroprotective effect of lithium and VPA against neuronal death induced by extracellular ATP, probably through a different pathway, and suggest novel uses of these drugs in neurogenerative diseases.

Lithium increases expression of p21WAF/Cip1 and survivin in human glioblastoma cells

Lithium is the most widely prescribed mood stabilizer, but the precise molecular mechanisms underlying its therapeutic function are not yet fully elucidated. Recent preclinical and clinical evidence indicates its neuroprotective and neurotrophic effects. As a tight coupling of function and metabolism in the central nervous system between glial cells and neurons has recently been detected, lithium's effect on glial cells may participate also in the total beneficial effects of this drug. The aim of the present study was to analyze molecular mechanisms induced in human glioblastoma A1235 cells by the treatment with lithium, especially its influence on the expression of apoptosis-related genes. Lower levels of lithium (0.5 mmol/L and 2 mmol/L) did not cause any cytotoxicity or changes in the cell cycle phase distribution following 72 h incubation. However, a higher dose (20 mmol/L) was cytostatic for glioblastoma cells, and caused accumulation of cells in G(2)/M phase of the cell cycle. The treatment with lithium did not alter the levels of Bcl-2 or procaspase-3 and did not cleave PARP, but increased the levels of p21(WAF/Cip1) and survivin. Thus, increased expression of p21(WAF/Cip1) (a protein with antiapoptotic function), and survivin (a protein that supports the growth of cells by suppression of apoptosis and promotion of cell proliferation) may be the early events in the long-term cell response to lithium that are involved in the beneficial effects of this drug.

Evaluation of acute antiapoptotic effects of Li+ in neuronal cell cultures

Li(+) exerts protective effect against several neurotoxins in neuronal cell preparations. Here we examined the antiapoptotic effects of GSK3beta in cerebellar granule neurons (CGNs) in the presence of several neurotoxins. Acute treatment with Li(+) protected neurons against nocodazole and serum/potassium (S/K) deprivation, but were ineffective against kainic acid and MPP(+). Li(+) 5 mM also decreased caspase-3 activation induced by nocodazole and S/K deprivation as measured by Ac-DEVD-p-nitroaniline and the breakdown of alpha-spectrin. All the neurotoxins used in the present study activated GSK3beta, evaluated with a specific antibody phospho-GSK-3beta (Ser9) by Western-blot and immunocytochemistry and were always inhibited by Li(+) 5 mM. Our results implicate Li(+) in the regulation of apoptosis mediated by caspase activation (Type I). Furthermore inhibition of GSK3beta by acute treatment with Li(+) 5 mM is not an indicator of neuroprotection. The acute antiapoptotic function of Li(+) is discussed in terms of its inhibition of Type I pathway, the intrinsic (mitochondrial) apoptotic pathway in cerebellar granule cells.

Implication of cyclin-dependent kinase 5 in the neuroprotective properties of lithium

Although numerous studies have demonstrated a neuroprotective and anti-apoptotic role of lithium in neuronal cell cultures, the precise mechanism by which this occurs, remains to be elucidated. In this study, we evaluated the lithium-mediated neuroprotection against colchicine-induced apoptosis in cultured cerebellar granule neurons. Previously, it has been demonstrated that colchicine mediates apoptosis in cerebellar granule neurons through cytoskeletal alteration and activation of an intrinsic pro-apoptotic pathway. Recently we also demonstrated a potential role of cyclin-dependent kinase 5 (cdk5) in this pathway. Here we report that colchicine induces dephosphorylation in Ser-9 and phosphorylation in Tyr-216, and thus activation, of glycogen synthase kinase-3beta in cerebellar granule neurons, and that this modification is inhibited by the presence of 5 mM lithium. However, the selective glycogen synthase kinase-3beta inhibitors SB-415286 and SB-216763 were unable to prevent colchicine-induced apoptosis in these cells, suggesting that the anti-apoptotic activity of lithium is not mediated by glycogen synthase kinase-3beta under these conditions. On the other hand, 5 mM lithium prevented the colchicine-induced increase in cdk5 expression and breakdown of cdk5/p35 to cdk5/p25. In addition, we show that up-regulation of cdk5/p25 is unrelated to inhibition of the activity of myocyte enhancer factor 2, a pro-survival transcription factor. These data suggest a previously undescribed neuroprotective mechanism of lithium associated with the modulation of cdk5/p35 or cdk5/p25 expression.

Lithium and valproic acid treatment effects on brain chemistry in bipolar disorder

BACKGROUND

Prior work reported elevated gray matter (GM) lactate and Glx (glutamate + glutamine + GABA) concentrations in unmedicated patients with bipolar disorder (BP) compared with healthy controls (HC). This study examined whether lithium (Li) and valproic acid (VPA) treatment modulated these chemicals.

METHODS

A subset of previously reported BP patients were treated with Li (n = 12, 3.6 +/- 1.9 months) or VPA (n = 9, 1.4 +/- 1.7 months) and compared untreated HC subjects (n = 12, 2.9 +/- 2.4 months) using proton echo-planar spectroscopic imaging. Regression analyses (voxel gray/white composition by chemistry) were performed at each time point, and change scores computed. Metabolite relaxation and regions of interest (ROI) were also examined.

RESULTS

Across treatment, Li-treated BP subjects demonstrated GM Glx decreases (Li-HC, p =.08; Li-VPA p =.04) and GM myo-inositol increases (Li-HC p =.07; Li-VPA p =.12). Other measures were not significant. Serum Li levels were positively correlated with Glx decreases at the trend level.

CONCLUSIONS

Li treatment of BP was associated with specific GM Glx decreases and myo-inositol increases. Findings are discussed in the context of cellular mechanisms postulated to underlie Li and VPA therapeutic efficacy.

Lithium prevents colchicine-induced apoptosis in rat cerebellar granule neurons

OBJECTIVES

Here we evaluated the neuroprotective effects of two well-known mood stabilizers, lithium and valproic acid (VPA), against colchicine neurotoxicity in cerebellar granule cells (CGNs).

METHODS

The CGNs were differentiated for 7 days, pretreated with lithium or VPA for 24 h and after colchicine 1 microM was added. Cellular damage was assessed with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium (MTT) method and apoptosis in CGNs was characterized by chromatin condensation and DNA fragmentation.

RESULTS

Incubation with lithium (1-5 mM) attenuated this apoptosis markedly, in a dose-dependent way however, the addition of VPA (0.5-2 mM) did not protect CGNs. Colchicine-induced apoptosis is mediated through the activation of caspase-3. An increase in caspase-3 activity was detected within 18 h and was blocked in presence of lithium 5 mM.

CONCLUSIONS

Our data indicate that lithium treatment is selectively neuroprotective; however, in our experimental conditions VPA did not protect CGNs from apoptosis induced by colchicine. Our results support the hypothesis that distinct pathways mediate the neuroprotective effects of lithium and VPA.