Role of endogenous ouabain in the etiology of bipolar disorder

Differentially Altered Metabolic Pathways in the Amygdala of Subjects with Schizophrenia, Bipolar Disorder and Major Depressive Disorder

Background and hypothesis

A growing number of studies implicate a key role for metabolic processes in psychiatric disorders. Recent studies suggest that ketogenic diet may be therapeutically effective for subgroups of people with schizophrenia (SCZ), bipolar disorder (BPD) and possibly major depressive disorder (MDD). Despite this promise, there is currently limited information regarding brain energy metabolism pathways across these disorders, limiting our understanding of how brain metabolic pathways are altered and who may benefit from ketogenic diets. We conducted gene expression profiling on the amygdala, a key region involved in in the regulation of mood and appetitive behaviors, to test the hypothesis that amygdala metabolic pathways are differentially altered between these disorders.

Study Design

We used a cohort of subjects diagnosed with SCZ, BPD or MDD, and non-psychiatrically ill control subjects (n=15/group), together with our bioinformatic 3-pod analysis consisting of full transcriptome pathway analysis, targeted pathway analysis, leading-edge gene analysis and iLINCS perturbagen analysis.

Study Results

We identified differential expression of metabolic pathways in each disorder. Subjects with SCZ displayed downregulation of mitochondrial respiration and nucleotide metabolism pathways. In comparison, we observed upregulation of mitochondrial respiration pathways in subjects with MDD, while subjects with BPD displayed enrichment of pathways involved in carbohydrate metabolism. Several pathways associated with brain metabolism including immune system processes and calcium ion transport were also differentially altered between diagnosis groups.

Conclusion

Our findings suggest metabolic pathways are differentially altered in the amygdala in these disorders, which may impact approaches for therapeutic strategies.

Involvement of the Na+, K+-ATPase α1 Isoform and Endogenous Cardiac Steroids in Depression- and Manic-like Behaviors

Bipolar disorder (BD) is a severe and common chronic mental illness characterized by recurrent mood swings between depression and mania. The biological basis of the disease is poorly understood, and its treatment is unsatisfactory. Na+, K+-ATPase is a major plasma membrane transporter and signal transducer. The catalytic α subunit of this enzyme is the binding site for cardiac steroids. Three α isoforms of the Na+, K+-ATPase are present in the brain. Previous studies have supported the involvement of the Na+, K+-ATPase and endogenous cardiac steroids (ECS) in the etiology of BD. Decreased brain ECS has been found to elicit anti-manic and anti-depressive-like behaviors in mice and rats. However, the identity of the specific α isoform involved in these behavioral effects is unknown. Here, we demonstrated that decreasing ECS through intracerebroventricular (i.c.v.) administration of anti-ouabain antibodies (anti-Ou-Ab) decreased the activity of α1+/- mice in forced swimming tests but did not change the activity in wild type (wt) mice. This treatment also affected exploratory and anxiety behaviors in α1+/- but not wt mice, as measured in open field tests. The i.c.v. administration of anti-Ou-Ab decreased brain ECS and increased brain Na+, K+-ATPase activity in wt and α1+/- mice. The serum ECS was lower in α1+/- than wt mice. In addition, a study in human participants demonstrated that serum ECS significantly decreased after treatment. These results suggest that the Na+, K+-ATPase α1 isoform is involved in depressive- and manic-like behaviors and support that the Na+, K+-ATPase/ECS system participates in the etiology of BD.

NMDA receptor inhibition prevents intracellular sodium elevations in human olfactory neuroepithelial precursors derived from bipolar patients

Dysregulation of ion flux across membranes and glutamate-induced excitotoxicity appear to be important pathophysiologic abnormalities in bipolar illness. Understanding ion control and responses to ionic stress is important to decipher the pathogenesis of this disorder. Monensin alone significantly increased [Na]_i in ONPs from bipolar individuals (5.08 ± 0.71 vs baseline 3.13 ± 0.93, P = 0.03) and AP5 had no effect (2.0 ± 1.2 vs baseline 3.13 ± 0.93, P = 0.27). However, the combination of AP5 and monensin resulted in normalization of [Na]_i (3.25 ± 1.28 vs baseline 3.13 ± 0.93, P = 0.89). This effect was not observed in cells from non-bipolar individuals (monensin alone, 1.72 ± 1.10 vs baseline 2.42 ± 1.80, P = 0.25; AP5 alone, 1.37 ± 0.74 vs baseline 2.42 ± 1.80; AP5 combined with monensin, 1.53 ± 0.98 vs baseline 2.42 ± 1.80, P = 0.31). Sodium regulation is central to neuronal function and may be disturbed in patients with bipolar disorder. Monensin is an ionophore, meaning that it incorporates itself into the membrane and allows sodium to enter independent of cellular membrane proteins. While the mechanism remains obscure, the observation that the NMDA receptor antagonist, AP5, normalizes [Na]_i only in olfactory neuroepithelial precursors obtained from bipolar illness may provide novel insights into ion regulation in tissues from subjects with bipolar illness.

Sleep deprivation is associated with increased circulating levels of endogenous ouabain: Potential role in bipolar disorder

Endogenously produced cardiac glycosides, like endogenous ouabain (EO), are putative hormones that have been implicated in the pathophysiology of bipolar disorder. Individuals with bipolar disorder appear to be unable to sufficiently upregulate production of EO in situations of increased need. This study was performed to determine the effect of sleep deprivation on the circulating levels of EO. Plasma EO concentrations were measured by ouabain-radioimmunoassay in heterozygote Na,K-ATPase a2 knockout (KO) mice, which have been used as an animal model of mania, and wildtype siblings at baseline and after sleep fragmentation utilizing the moving bar method. a2 KO animals had elevated endogenous ouabain concentrations compared to wild type controls (0.82 ± SD 0.22 nM vs 0.26 ± 0.02, P = 0.03). Sleep fragmentation increased ouabain concentrations in wild type mice (0.53 ± 0.08 nM sleep fragmentation vs 0.26 ± 0.02 nM baseline, P = 0.04), but not in a2 KO mice (0.60 ± 0.07 nM sleep fragmentation vs 0.82 ± 0.22 nM baseline, P > 0.05). These studies demonstrate that sleep disturbance can increase EO in control mice but animals that exhibit some manic behaviors are unable to increase EO production.

GLP-1 agonist liraglutide improves ouabain-induced mania and depressive state via GSK-3β pathway

Bipolar disorder (BD) is a severe mental illness characterized by aberrant mood changes between hypomania and mania or mixed states and depression. Metabolic changes also accompany disease progression and cause significant morbidity. Symptomatic treatment options are available, but asymptomatic patients and poor drug responders are significant problems. Based on the most common pharmacological agent that is used in the treatment, lithium and its main mechanisms of action, oxidative stress, and glycogen synthase kinase-3β (GSK-3β) signaling are extensively investigated. However, knowledge about the effects of compounds that positively affect oxidative stress and GSK-3β signaling, such as glucagon-like peptide-1 (GLP-1) mimetics, liraglutide, is still missing. Therefore, in this study, we aimed to investigate the effects of liraglutide on the ouabain-induced bipolar disease model in rats. After intracerebroventricular single dose ouabain administration, animals were treated with 100, 200, and 400 µg/kg liraglutide (s.c.) and valproic acid (200 mg/kg, i.p.) for 10 d. The locomotion and depressive states of animals were assessed by an open field, forced swimming test, and sucrose preference tests. Serum total antioxidant (TAS) and oxidant states (TOS) and glutathione, malonyl dialdehyde (MDA) levels in the brain tissue were determined. GSK-3β phosphorylation was evaluated by western blotting. Our results demonstrated that liraglutide attenuated ouabain-induced hyperlocomotion and depressive state. Additionally, liraglutide prevented oxidative stress after ouabain administration. Decreased GSK-3β phosphorylation due to the ouabain insult was alleviated by liraglutide treatment. These findings indicate that the manic and depressive-like behaviors are ameliorated by liraglutide, which exerted antioxidant action, possibly improving GSK-3β phosphorylation.

Endogenous Cardiac Steroids in Bipolar Disorder: State of the Art

Bipolar disorder (BD) is a severe psychiatric illness with a poor prognosis and problematic, suboptimal, treatments. Treatments, borne of an understanding of the pathoetiologic mechanisms, need to be developed in order to improve outcomes. Dysregulation of cationic homeostasis is the most reproducible aspect of BD pathophysiology. Correction of ionic balance is the universal mechanism of action of all mood stabilizing medications. Endogenous sodium pump modulators (collectively known as endogenous cardiac steroids, ECS) are steroids which are synthesized in and released from the adrenal gland and brain. These compounds, by activating or inhibiting Na⁺, K⁺-ATPase activity and activating intracellular signaling cascades, have numerous effects on cell survival, vascular tone homeostasis, inflammation, and neuronal activity. For the past twenty years we have addressed the hypothesis that the Na⁺, K⁺-ATPase-ECS system may be involved in the etiology of BD. This is a focused review that presents a comprehensive model pertaining to the role of ECS in the etiology of BD. We propose that alterations in ECS metabolism in the brain cause numerous biochemical changes that underlie brain dysfunction and mood symptoms. This is based on both animal models and translational human results. There are data that demonstrate that excess ECS induce abnormal mood and activity in animals, while a specific removal of ECS with antibodies normalizes mood. There are also data indicating that circulating levels of ECS are lower in manic individuals, and that patients with BD are unable to upregulate synthesis of ECS under conditions that increase their elaboration in non-psychiatric controls. There is strong evidence for the involvement of ion dysregulation and ECS function in bipolar illness. Additional research is required to fully characterize these abnormalities and define future clinical directions.

Neuronal cells from bipolar individuals are more susceptible to glutamate induced apoptosis than cells from non-bipolar subjects

BACKGROUND

Bipolar disorder (BD) is associated with marked parenchymal brain loss in a significant fraction of patients. The lack of necrosis in postmortem examination suggests an apoptotic process. Emerging evidence suggests that mood stabilizers, like lithium, have antiapoptotic actions. Glutamatergic abnormalities have been associated with BD.

METHODS

Olfactory neuroepithelial progenitors (ONPs) harvested by biopsy from type I bipolar patients (BD-ONPs, n = 3) and non-bipolar controls (non-BD-ONPs, n = 6), were treated with glutamate at concentrations sufficient to mimic the observed doubling of intracellular sodium known to occur in both mania and bipolar depression, to investigate potential differential lithium effect on both BD-ONPs and non-BD-ONPs.

RESULTS

Apoptosis was detected in BP-ONPs exposed to 0.1 M glutamate for 6 h but in non-BD-ONPs at 24 h. Moreover, after treatment with 0.1 M glutamate treated for 6 h the levels of the pro-apoptotic cleaved-caspase-3 and cleaved-PARP proteins were significantly higher in BD-ONPs compare to non-BD-ONPs. Pretreatment with a therapeutic concentration of 1 mM lithium for 3 days attenuated the glutamate induced apoptosis. Lithium pretreatment 3 days also prevented the DNA fragmentation induced by glutamate, and significantly increased the antiapoptotic phospho-B-Raf and Bcl-2 proteins in BD-ONPs compared to non-BD-ONPs.

LIMITATIONS

ONPs are obtained from subjects with and without bipolar illness, but outcome of their study may still not reflect the biology of the illness.

CONCLUSIONS

ONPs derived from BD are more susceptible to glutamate-induced apoptosis. Lithium is associated with a greater increase of anti-apoptotic B-Raf and Bcl-2 expression in BD-ONPs.