The mood cycle hypothesis: possible involvement of steroid hormones in mood regulation by means of Na+, K+-ATPase inhibition

Exploring hub genes and crucial pathways linked to oxidative stress in bipolar disorder depressive episodes through bioinformatics analysis

Background

Bipolar disorder (BD) is a complex and serious psychiatric condition primarily characterized by bipolar depression, with the underlying genetic determinants yet to be elucidated. There is a substantial body of literature linking psychiatric disorders, including BD, to oxidative stress (OS). Consequently, this study aims to assess the relationship between BD and OS by identifying key hub genes implicated in OS pathways.

Methods

We acquired gene microarray data from GSE5392 through the Gene Expression Omnibus (GEO). Our approach encompassed differential expression analysis, weighted gene co-expression network analysis (WGCNA), and Protein-Protein Interaction (PPI) Network analysis to pinpoint hub genes associated with BD. Subsequently, we utilized Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and Gene Set Enrichment Analysis (GSEA) to identify hub genes relevant to OS. To evaluate the diagnostic accuracy of these hub genes, we performed receiver operating characteristic curve (ROC) analysis on both GSE5388 and GSE5389 datasets. Furthermore, we conducted a study involving ten BD patients and ten healthy controls (HCs) who met the special criteria, assessing the expression levels of these hub genes in their peripheral blood mononuclear cells (PBMCs).

Results

We identified 411 down-regulated genes and 69 up-regulated genes for further scrutiny. Through WGCNA, we obtained 22 co-expression modules, with the sienna3 module displaying the strongest association with BD. By integrating differential analysis with genes linked to OS, we identified 44 common genes. Subsequent PPI Network and WGCNA analyses confirmed three hub genes as potential biomarkers for BD. Functional enrichment pathway analysis revealed their involvement in neuronal signal transduction, oxidative phosphorylation, and metabolic obstacle pathways. Using the Cytoscape plugin "ClueGo assay," we determined that a majority of these targets regulate neuronal synaptic plasticity. ROC curve analysis underscored the excellent diagnostic value of these three hub genes. Quantitative reverse transcription-PCR (RT-qPCR) results indicated significant changes in the expression of these hub genes in the PBMCs of BD patients compared to HCs.

Conclusion

We identified three hub genes (TAC1, MAP2K1, and MAP2K4) in BD associated with OS, potentially influencing the diagnosis and treatment of BD. Based on the GEO database, our study provides novel insights into the relationship between BD and OS, offering promising therapeutic targets.

Ouabain induces memory impairment and alter the BDNF signaling pathway in an animal model of bipolar disorder: Cognitive and neurochemical alterations in BD model

BACKGROUND

The present study aims to evaluate the effects of ouabain on memory and neurotrophic parameters in the brains of rats.

METHODS

Wistar rats received an intracerebroventricular (ICV) injection of ouabain or artificial cerebrospinal fluid (aCSF). Seven and 14 days after ICV administration, the animals were subjected to the open-field and splash tests. Furthermore, the pro-BDNF, BDNF, TrkB, and CREB were assessed in the frontal cortex and hippocampus of the rats, in both seven and 14 days after ICV injection. The memory of the animals was tested by novel object recognition test (NOR) and inhibitory avoidance task (IA), only 14 days after ICV administration.

RESULTS

Ouabain increased locomotion and exploration in the animals seven days after its administration; however, 14 days after ICV, these behavioral parameters return to the basal level. Seven days after ouabain administration increased grooming behavior in the splash test; on the other hand, seven days after ouabain injection decreased the grooming behavior, which is considered an anhedonic response. Besides, ouabain decreased recognition index in the NOR and decreased aversive memory in the IA, when compared to the control group. The levels of pro-BDNF and BDNF decreased in the frontal cortex seven days after ouabain; but its receptor (TrkB) and CREB decreased seven and 14 days after ouabain, in both cerebral structures evaluated.

CONCLUSION

Ouabain-induced animal model of BD is an excellent model to assess memory alteration, observed in bipolar patients. Besides, the memory impairment induced by ouabain seems to be related to BDNF signaling pathway alterations.

Tamoxifen has an anti-manic effect but not protect the brain against oxidative stress in an animal model of mania induced by ouabain

Studies have suggested the involvement of oxidative stress in the physiopathology of bipolar disorder. Preclinical data have shown that PKC inhibitors may act as mood-stabilizing agents and protect the brain in animal models of mania. The present study aimed to evaluate the effects of Lithium (Li) or tamoxifen (TMX) on behavioral changes and oxidative stress parameters in an animal model of mania induced by ouabain (OUA). Wistar rats received a single intracerebroventricular (ICV) injection of OUA or artificial cerebrospinal fluid (ACSF). From the day following ICV injection, the rats were treated for seven days with intraperitoneal injections of saline, Li or TMX twice a day. On the 7th day after OUA injection, locomotor activity was measured using the open-field test, and the oxidative stress parameters were evaluated in the hippocampus and frontal cortex of rats. The results showed that OUA induced hyperactivity in rats, which is considered a manic-like behavior. Also, OUA increased lipid peroxidation and oxidative damage to proteins, as well as causing alterations to antioxidant enzymes in the frontal cortex and hippocampus of rats. The Li or TMX treatment reversed the manic-like behavior induced by OUA. Besides, Li, but not TMX, reversed the oxidative damage caused by OUA. These results suggest that the manic-like effects induced by OUA and the antimanic effects of TMX seem not to be related to the oxidative stress.

Are Polyunsaturated Fatty Acids Implicated in Histaminergic Dysregulation in Bipolar Disorder?: AN HYPOTHESIS

Bipolar disorder (BD) is an extremely disabling psychiatric disease, characterized by alternate states of mania (or hypomania) and depression with euthymic states in between. Currently, patients receive pharmacological treatment with mood stabilizers, antipsychotics, and antidepressants. Unfortunately, not all patients respond well to this type of treatment. Bipolar patients are also more prone to heart and metabolic diseases as well as a higher risk of suicide compared to the healthy population. For a correct brain function is indispensable a right protein and lipids (e.g., fatty acids) balance. In particular, the amount of fatty acids in the brain corresponds to a 50–70% of the dry weight. It has been reported that in specific brain regions of BD patients there is a reduction in the content of unsaturated n-3 fatty acids. Accordingly, a diet rich in n-3 fatty acids has beneficial effects in BD patients, while their absence or high levels of saturated fatty acids in the diet are correlated to the risk of developing the disease. On the other hand, the histamine system is likely to be involved in the pathophysiology of several psychiatric diseases such as BD. Histamine is a neuromodulator involved in arousal, motivation, and energy balance; drugs acting on the histamine receptor H3 have shown potential as antidepressants and antipsychotics. The histaminergic system as other neurotransmission systems can be altered by fatty acid membrane composition. The purpose of this review is to explore how polyunsaturated fatty acids content alterations are related to the histaminergic system modulation and their impact in BD pathophysiology.

Endogenous cardiac steroids in animal models of mania

OBJECTIVES

Bipolar disorder (BD) is a complex psychiatric disorder characterized by mania and depression. Alterations in brain Na(+) , K(+) -ATPase and cardiac steroids (CSs) have been detected in BD, raising the hypothesis of their involvement in this pathology. The present study investigated the behavioral and biochemical consequences of a reduction in endogenous brain CS activity in animal models of mania.

METHODS

Amphetamine (AMPH)-induced hyperactivity in BALB/c and black Swiss mice served as a model of mania. Behavior was evaluated in the open-field test in naïve mice or in mice treated with anti-ouabain antibodies. CS levels were determined by enzyme-linked immunosorbent assay (ELISA), using sensitive and specific anti-ouabain antibodies. Extracellular signal-regulated kinase (ERK) and protein kinase B (Akt) phosphorylation levels in the frontal cortex were determined by western blot analysis.

RESULTS

Administration of AMPH to BALB/c and black Swiss mice resulted in a marked increase in locomotor activity, accompanied by a threefold increase in brain CSs. The lowering of brain CSs by the administration of anti-ouabain antibodies prevented the hyperactivity and the increase in brain CS levels. AMPH caused an increase in phosphorylated ERK (p-ERK) and phosphorylated Akt (p-Akt) levels in the frontal cortex, which was significantly reduced by administration of the antibodies. A synthetic 'functional antagonist' of CSs, 4-(3'α-15'β-dihydroxy-5'β-estran-17'β-yl) furan-2-methyl alcohol, also resulted in attenuation of AMPH-induced hyperactivity.

CONCLUSIONS

These results are in accordance with the notion that malfunctioning of the Na(+) , K(+) -ATPase/CS system may be involved in the manifestation of mania and identify this system as a potential new target for drug development.

Natriuretic hormones in brain function

Natriuretic hormones (NH) include three groups of compounds: the natriuretic peptides (ANP, BNP and CNP), the gastrointestinal peptides (guanylin and uroguanylin), and endogenous cardiac steroids. These substances induce the kidney to excrete sodium and therefore participate in the regulation of sodium and water homeostasis, blood volume, and blood pressure (BP). In addition to their peripheral functions, these hormones act as neurotransmitters or neuromodulators in the brain. In this review, the established information on the biosynthesis, release and function of NH is discussed, with particular focus on their role in brain function. The available literature on the expression patterns of each of the NH and their receptors in the brain is summarized, followed by the evidence for their roles in modulating brain function. Although numerous open questions exist regarding this issue, the available data support the notion that NH participate in the central regulation of BP, neuroprotection, satiety, and various psychiatric conditions, including anxiety, addiction, and depressive disorders. In addition, the interactions between the different NH in the periphery and the brain are discussed.

Intracerebroventricular administration of ouabain, a Na/K-ATPase inhibitor, activates mTOR signal pathways and protein translation in the rat frontal cortex

Intracerebroventricular (ICV) injection of ouabain, a specific Na/K-ATPase inhibitor, induces behavioral changes in rats in a putative animal model of mania. The binding of ouabain to Na/K-ATPase affects signaling molecules in vitro, including ERK1/2 and Akt, which promote protein translation. We have also reported that ERK1/2 and Akt in the brain are involved in the ouabain-induced hyperactivity of rats. In this study, rats were given an ICV injection of ouabain, and then their frontal cortices were examined to determine the effects of ouabain on the mTOR/p70S6K/S6 signaling pathway and protein translation, which are important in modifications of neural circuits and behavior. Rats showed ouabain-induced hyperactivity up to 8h following injection, and increased phosphorylation levels of mTOR, p70S6K, S6, eIF4B, and 4E-BP at 1, 2, 4, and 8h following ouabain injection. Immunohistochemical analyses revealed that increased p-S6 immunoreactivity in the cytoplasm of neurons by ouabain was evident in the prefrontal, cingulate, and orbital cortex. These findings suggested increased translation initiation in response to ouabain. The rate of protein synthesis was measured as the amount of [(3)H]-leucine incorporation in the cell-free extracts of frontal cortical tissues, and showed a significant increase at 8h after ouabain injection. These results suggest that ICV injection of ouabain induced activation of the protein translation initiation pathway regulated by ERK1/2 and Akt, and prolonged hyperactivity in rats. In conclusion, protein translation pathway could play an important role in ouabain-induced hyperactivity in a rodent model of mania.

Frontal lobe bioenergetic metabolism in depressed adolescents with bipolar disorder: a phosphorus-31 magnetic resonance spectroscopy study

OBJECTIVES

To compare the concentrations of high-energy phosphorus metabolites associated with mitochondrial function in the frontal lobe of depressed adolescents with bipolar disorder (BD) and healthy controls (HC).

METHODS

We used in vivo phosphorus-31 magnetic resonance spectroscopy ((31) P-MRS) at 3 Tesla to measure phosphocreatine (PCr), beta-nucleoside triphosphate (β-NTP), inorganic phosphate (Pi), and other neurometabolites in the frontal lobe of eight unmedicated and six medicated adolescents with bipolar depression and 24 adolescent HCs.

RESULTS

Analysis of covariance, including age as a covariate, revealed differences in PCr (p=0.037), Pi (p=0.017), and PCr/Pi (p=0.002) between participant groups. Percentage neurochemical differences were calculated with respect to mean metabolite concentrations in the HC group. Post-hoc Tukey-Kramer analysis showed that unmedicated BD participants had decreased Pi compared with both HC (17%; p=0.038) and medicated BD (24%; p=0.022). The unmedicated BD group had increased PCr compared with medicated BD (11%; p=0.032). The PCr/Pi ratio was increased in unmedicated BD compared with HC (24%; p=0.013) and with medicated BD (39%; p=0.002). No differences in β-NTP or pH were observed.

CONCLUSIONS

Our results support the view that frontal lobe mitochondrial function is altered in adolescent BD and may have implications for the use of Pi as a biomarker. These findings join volumetric studies of the amygdala, and proton MRS studies of n-acetyl aspartate in pointing to potential differences in neurobiology between pediatric and adult BD.

Neutralization of endogenous digitalis-like compounds alters catecholamines metabolism in the brain and elicits anti-depressive behavior

Depressive disorders are among the world's greatest public health problems. Na(+), K(+)-ATPase is the established receptor for the steroidal digitalis-like compounds (DLC). Alteration in brain Na(+), K(+)-ATPase and DLC have been detected in depressive disorders raising the hypothesis of their involvement in these pathology. The present study was designed to further elaborate this hypothesis by investigating the behavioral and biochemical consequences of neutralization in brain DLC activity attained by anti-ouabain antibodies administrations, in normal Sprague-Dawley (SD) and in the Flinders Sensitive Line (FSL) of genetically depressed rats. Chronic i.c.v. administration of anti-ouabain antibodies to FSL rats elicited anti-depressive behavior. Administration of anti-ouabain antibodies intracerebroventriculary (i.c.v.) to SD rats significantly changed the levels of catecholamines and their metabolites in the hippocampus, ventral tegmentum and nucleus accumbence. These results are in accordance with the notion that endogenous DLC may be involved in the manifestation of depressive disorders and suggests that alteration in their levels may be of significant therapeutic value.

Mitochondrial respiratory chain activity in an animal model of mania induced by ouabain

OBJECTIVES

Bipolar disorder (BD) is a mental illness associated with higher rates of suicide. The present study aims to investigate the brain mitochondrial respiratory chain activity in an animal model of mania induced by ouabain.

METHODS

Adult male Wistar rats received a single intracerebroventricular administration of ouabain (10-3 and 10-2 M) or vehicle. Locomotor activity was measured using the open field test. Mitochondrial respiratory chain activity was measured in the brain of rats 1 h and 7 days after ouabain administration.

RESULTS

Our results showed that spontaneous locomotion was increased 1 h and 7 days after ouabain administration. Complexes I, III and IV activities were increased in the prefrontal cortex, hippocampus and striatum immediately after the administration of ouabain, at the concentration of 10-3 and 10-2 M. Moreover, complex II activity was increased only in the prefrontal cortex at the concentration of 10-2 M. On the other hand, no significant alterations were observed in complex I activity 7 days after ouabain administration. However, an increase in complexes II, III and IV activities was observed only in the prefrontal cortex at the concentration of 10-2 M.

CONCLUSION

Our findings suggest an increase in the activities of mitochondrial respiratory chain in this model of mania. A possible explanation is that these findings occur as a rebound effect trying to compensate for a decrease of ATP deprivation in BD. The present findings suggest that this model may present good face validity and a limitation in construct validity.

Activation of Akt signaling in rat brain by intracerebroventricular injection of ouabain: a rat model for mania

Intracerebroventricular (ICV) injection of ouabain, a specific Na-K ATPase inhibitor, induces behavioral changes in rats resembling the manic phenotypes of bipolar disorder. The binding of ouabain to the Na-K ATPase affects signal events in vitro including Akt, a possible molecular target of mood disorders. However, the effects of ouabain on Akt in the brain need further clarification. In this study, we investigated changes in the phosphorylation state of Akt in the rat brain after ICV injection of ouabain. Consistent with our previous report, the locomotor activity of rats within 30 min after ouabain ICV injection changed according to the dose with higher doses of ouabain, 0.5 and 1 mM, inducing significant hyperactivity. In addition, ouabain administration induced a dose-dependent increase in the immunoreactivity of p-Akt (Ser473) in the frontal cortex, striatum, and hippocampus after 30 min, and reached statistical significance with 1mM of ouabain. Phosphorylation of GSK-3beta (Ser9), FOXO1 (Ser256), and eNOS (Ser1177), which are downstream molecules of Akt, was also increased in a dose-dependent manner within the same brain regions. Moreover, hyperactivity was seen for 8h after a single 1mM injection of ouabain and increased phosphorylation of Akt (Ser473), GSK-3beta (Ser9), FOXO1 (Ser256), and eNOS (Ser1177) was also observed in the cortex, striatum, and hippocampus. Thus, intrabrain injection of ouabain induces activation of Akt signaling accompanied by hyperactivity, suggesting the possible role of Akt in ouabain rat model of mania.

Association between sodium- and potassium-activated adenosine triphosphatase alpha isoforms and bipolar disorders

BACKGROUND

The sodium- and potassium-activated adenosine triphosphatase (Na+, K+-ATPase) is a major plasma membrane transporter for sodium and potassium. We recently suggested that bipolar disorders (BD) may be associated with alterations in brain Na+, K+-ATPase. We further conjectured that the differences in Na+, K+-ATPase in BD patients could result partially from genetic variations in Na+, K+-ATPase alpha isoforms.

METHODS

To test our hypothesis, we undertook a comprehensive study of 13 tagged single nucleotide polymorphisms (SNPs) across the three genes of the brain alpha isoforms of Na+, K+- ATPase (ATP1A1, ATP1A2, and ATP1A3, which encode the three alpha isoforms, alpha1, alpha2, and alpha3, respectively) identified using HapMap data and the Haploview algorithm. Altogether, 126 subjects diagnosed with BD from 118 families were genotyped (parents and affected siblings). Both individual SNPs and haplotypes were tested for association using family-based association tests as provided in the UNPHASED and PBAT set of programs.

RESULTS

Significant nominal association with BD was observed for six single SNPs (alpha1: rs11805078; alpha2: rs2070704, rs1016732, rs2854248, and rs2295623; alpha3: rs919390) in the three genes of Na+, K+-ATPase alpha isoforms. Haplotype analysis of the alpha2 isoform (ATP1A2 gene) showed a significant association with two loci haplotypes with BD (rs2295623: rs2070704; global p value = .0198, following a permutation test).

CONCLUSIONS

This study demonstrates for the first time that genetic variations in Na+, K+-ATPase are associated with BD, suggesting a role of this enzyme in the etiology of this disease.

Dose-dependent effect of intracerebroventricular injection of ouabain on the phosphorylation of the MEK1/2-ERK1/2-p90RSK pathway in the rat brain related to locomotor activity

Intracerebroventricular (ICV) injection of ouabain, a specific Na-K ATPase inhibitor, induced behavioral changes in rats, a putative animal model for bipolar disorder. The binding of ouabain to Na-K ATPase is known to affect signaling molecules in vitro such as extracellular signal-regulated kinase1/2 (ERK1/2). Although ERK has been suggested to be related to the behavioral alterations induced by various psychotomimetics, the effect of ouabain on ERK in the brain related to behavioral changes has not been examined. After ICV injection of ouabain in rats, we investigated changes in the phosphorylation of mitogen-activated protein kinase kinase1/2 (MEK1/2), ERK1/2, and p90 ribosomal s6 kinase (p90RSK) in rat striatum, frontal cortex, and hippocampus along with changes in locomotor activity. Ouabain induced the following biphasic dose-dependent changes in locomotor activity: no change with 10(-6) M, a statistically significant decrease with 10(-5) M, no change with 10(-4) M, and a statistically significant increase with 0.5x10(-3) and 10(-3) M. The phosphorylation level of MEK1/2, ERK1/2, and p90RSK in rat striatum showed dose-dependent changes similar to those observed in locomotor activity with relatively high correlation. The phosphorylation of these molecules in rat frontal cortex and hippocampus also changed in a similar dose-dependent pattern. Taken together, ouabain induced biphasic dose-dependent changes in locomotor activity and the phosphorylation of the ERK1/2 pathway. These findings suggest a possible relationship between ouabain-induced behavioral changes and ERK activity in the brain and suggest an important role of ERK in regulating locomotor activity and mood state.

The digitalis-like steroid hormones: new mechanisms of action and biological significance

Digitalis-like compounds (DLC) are a family of steroid hormones synthesized in and released from the adrenal gland. DLC, the structure of which resembles that of plant cardiac glycosides, bind to and inhibit the activity of the ubiquitous cell surface enzyme Na(+), K(+)-ATPase. However, there is a large body of evidence suggesting that the regulation of ion transport by Na(+), K(+)-ATPase is not the only physiological role of DLC. The binding of DLC to Na(+), K(+)-ATPase induces the activation of various signal transduction cascades that activate changes in intracellular Ca(++) homeostasis, and in specific gene expression. These, in turn, stimulate endocytosis and affect cell growth and proliferation. At the systemic level, DLC were shown to be involved in the regulation of major physiological parameters including water and salt homeostasis, cardiac contractility and rhythm, systemic blood pressure and behavior. Furthermore, the DLC system has been implicated in several pathological conditions, including cardiac arrhythmias, hypertension, cancer and depressive disorders. This review evaluates the evidence for the different aspects of DLC action and delineates open questions in the field.

Involvement of Na(+), K(+)-ATPase and endogenous digitalis-like compounds in depressive disorders

BACKGROUND

Sodium and potassium-activated adenosine triphosphatase (Na(+), K(+)-ATPase) and endogenous digitalis-like compounds (DLC) in the brain have been implicated in the pathogenesis of mood disorders. This hypothesis was examined by the determination of Na(+), K(+)-ATPase/DLC system in parietal cortex of patients with different mood disorders and two animal models of depression.

METHODS

Na(+), K(+)-ATPase concentrations in human brain synaptosomal fractions, from patients with mood disorders, schizophrenia, and normal individuals, were determined by (3)H-ouabain binding assay. Alpha isoforms were quantified by Western blotting. Brain DLC were measured using sensitive enzyme linked immunosorbant assay (ELISA). The effects of ouabain and ouabain-antibodies on behavior were determined in two animal models of depression.

RESULTS

(3)H-ouabain binding in bipolar patients was significantly lower than in major depressed and schizophrenic patients. Na(+), K(+)-ATPase alpha isoforms in synaptosomal fractions were not different among the groups. DLC levels in the parietal cortex of bipolar patients were significantly higher than in normal individuals and depressed patients. Injection of lipopolysaccharide (intraperitoneally) to rats elicited depression-like symptoms, which were significantly attenuated by pre-injection of ouabain-antibodies. Injection of ouabain and ouabain-antibodies (intracerebroventricular) reduced depression-like symptoms in the forced swimming test in rats.

CONCLUSIONS

The results support the possibility that Na(+), K(+)-ATPase and endogenous DLC participate in the pathogenesis of depressive disorders.

Endogenous digitalis-like ligands of the sodium pump: possible involvement in mood control and ethanol addiction

This review addresses possible involvement of endogenous digitalis-like sodium pump ligands (SPL) in the mood control and ethanol addiction. Endogenous SPL include cardenolide and bufadienolide classes. Multiple SPL and multiple isoforms of the Na/K-ATPase, one of the key membrane enzymes, comprise a complex regulatory system. In the nervous system, pattern of expression of Na/K-ATPase is based on multiple alpha/beta isoform combinations. Clinical studies demonstrate changes in the activity of Na/K-ATPase in patients with bipolar and unipolar mood disorders. The effects of ethanol on the Na/K-ATPase are concentration-dependent and are associated with both inhibition and activation of enzyme activity. Reinforcing effect of ethanol as well as its voluntary consumption may be affected by digitalis glycosides and endogenous SPL.

Endogenous digitalis-like Na+, K+-ATPase inhibitors, and brain function

Digitalis-like compounds are recently identified steroids synthesized by the adrenal gland, which resemble the structure of plant cardiac glycosides. These compounds, like the plant steroids, bind to and inhibit the activity of the Na+, K+-ATPase. The possible function of the endogenous digitalis-like compounds has to be evaluated in view of the presence of different isoforms of the Na+, K+-ATPase, which differ in their sensitivity to digitalis. This review focuses on recent published data on the Na+, K+-ATPase inhibitors, the digitalis-like compounds, regarding their structure, biosynthesis and secretion from the adrenal gland, physiological role and pathological implications in diseases such as hypertension and depression. Emphasis is given to studies describing the involvement of these compounds in brain function.