Molecular Mechanisms of Bipolar Disorder: Progress Made and Future Challenges

Methemoglobinemia as a biomarker of dapsone-induced mania severity

BACKGROUND

The underlying mechanism involved in dapsone-induced mania remains unknown.

METHODS

We report the case of a 54-year-old man with a dapsone-induced mania.

RESULTS

The maximum of manic symptoms was correlated with the maximum of methemoglobinemia and mania decreased concomitantly with the methemoglobinemia level.

LIMITATIONS

This is a single case.

CONCLUSIONS

This case shows that dapsone-induced mania severity is correlated with methemoglobinemia level, leading for the first time to the hypothesis of a physiopathological mechanism by which dapsone could induce mania.

Risk of cardiometabolic diseases among siblings of patients with bipolar disorder

BACKGROUND

Cardiometabolic diseases are suggested to be associated with bipolar disorder. However, the risk of metabolic disorders in unaffected siblings of patients with bipolar disorder remains unclear.

METHODS

From the Taiwan National Health Insurance Research Database, 7,225 unaffected siblings of bipolar probands and 28,900 age-/sex-/income-/residence-matched control individuals were included and followed until the end of 2011. Individuals who developed metabolic disorders during the follow-up period were identified.

RESULTS

The unaffected siblings of bipolar probands had a higher prevalence of dyslipidemia (5.4% vs. 4.5%, p = 0.001), younger age at diagnosis of type 2 diabetes mellitus (34.81 vs. 37.22, p = 0.024), and higher prevalence of any stroke (1.5% vs. 1.1%, p = 0.007) than the controls. Moreover, only male siblings of bipolar probands had an increased risk of dyslipidemia (odds ratio [OR]: 1.28, 95% confidence interval [CI]: 1.10-1.48) and higher rates of any stroke (OR: 1.38, 95% CI: 1.02-1.85) and ischemic stroke (OR: 2.43, 95% CI: 1.60-3.70) during the follow-up compared with the controls.

DISCUSSION

Unaffected siblings of bipolar patients, particularly brothers, had a higher prevalence of dyslipidemia and ischemic stroke compared with the controls. The result suggests the familial association between cardiometabolic diseases and bipolar disorder. Further research may be necessary to identify this shared etiology between the disorders.

A pyruvate dehydrogenase complex disorder hypothesis for bipolar disorder

Ketosis is a metabolic state in which the body uses ketones derived from breakdown of fatty acids as the primary mitochondrial fuel source instead of glucose. In recent years an accumulation of evidence for the beneficial effects of the ketotic state on the brain have heightened interest in its potential for use in neurological conditions. The ketogenic diet (KD) induces ketosis and is an effective treatment for medically resistant epilepsy. There is significant comorbidity between epilepsy and bipolar disorder (BD) and both conditions are treated by anti-convulsant drugs. In addition, reports on bipolar disease online fora have highlighted subjective mood stabilization effects associated with the KD. These KD reported effects could be explained if there was a disorder in the conversion of pyruvate into Acetyl-CoA (and subsequent impairment of oxidative phosphorylation) which was bypassed by ketones providing an alternative substrate for oxidative phosphorylation. This is consistent with growing evidence that mitochondrial dysfunction plays a causal role in BD and explains the reported TCA cycle dysfunction and elevated pyruvate levels in BD. Reduced levels of ATP affects the normal operation of the Na, K-ATPase in the brain with differing levels of reduction either leading to reduced neuronal action potential and inhibition of neurotransmitter release (consistent with the depressed state in BD) or increased neuronal resting potential and hyper-excitability (consistent with a [hypo]manic mood state). We hypothesize that the mitochondrial dysfunction is due to a disorder of the Pyruvate Dehydrogenase Complex (PDC) and/or Mitochondrial Carrier Protein (MCP) shuttle which moves intracellular pyruvate into mitochondria. The resultant reduction in ATP generation could explain mood instability and cycling in BD (through mechanisms such as those delineated by Mallakh and Peters). This proposed novel causal pathway could explain mood de-stabilization in BD and the reported positive effects of KD. If true, this hypothesis would suggest that there should be increased research attention to PDC (and in particular the E1 alpha subunit) as potential therapeutic targets and further study of a possible role of KD in BD to improve mood stability. Experimental approaches, such as through a clinical trial of KD on mood stabilization in BD, are required to further investigate this hypothesis.

Narirutin produces antidepressant-like effects in a chronic unpredictable mild stress mouse model

Depression is a highly debilitating and life-threatening mental disorder, which is accompanied by dysregulation of the peripheral and central immune system. Narirutin (NR), which has antioxidant and anti-inflammatory activities, is one of the active constituents isolated from Citrus unshiu. However, its potential antidepressant-like and anxiolytic-like effects are poorly understood. The present study was aimed to investigate whether NR confers an antidepressant-like effect in mice exposed to a chronic mild stress (CMS) model of depression. The results showed that NR treatment for 1 week significantly alleviated the depressive-like behaviours of CMS-exposed mice, as indicated by restored decreased sucrose preference and shortened floating time in the forced swimming test. Moreover, NR treatment significantly blocked the CMS-induced anxiety-like behaviors, including increased time spent in the central zone in the open field test, and shortened the latency to feeding in the novelty suppressed feeding test. Taken together, our findings suggested that NR exerted potential antidepressant-like and anxiolytic-like effects in CMS mice model of depression, which support further exploration into developing NR as a novel agent to treat depression and even other stress-related disorders.

Evidence for perturbed metabolic patterns in bipolar disorder subjects associated with lithium responsiveness

Bipolar disorder (BD) is multifactorial mood disorder characterized by alternating episodes of hyperactive mania and severe depression. Lithium is one of the most preferred drug used as mood stabilizer in treating BD. In this study, we examined the changes in plasma metabolome in BD subjects in the context of lithium responsiveness. Plasma samples from clinically defined, age and gender matched unrelated healthy controls and BD subjects (lithium responders and non-responders) were obtained and processed in positive and negative mode using untargeted liquid chromatography/mass spectrometry analysis. We identified significant alterations in plasma levels of dopamine along with its precursors (tyrosine and phenylalanine), branched chain amino acid such as valine and excitatory neurotransmitter glutamate between healthy control and BD subjects. Lipid molecules such as, eicosenoic acid and retinyl ester also showed distinguished patterns between control and BD individuals. Lithium responsiveness was markedly associated with significant differences in proline, L-gamma-glutamyl-isoleucine, dopamine, palmitic acid methyl ester, cholesterol sulfate, androsterone sulfate and 9S,12S,13S-triHOME levels. Altered metabolites enriched with key biochemical pathways associated with neuropsychiatry disorders. We hypothesize that BD pathogenesis and lithium responsiveness is associated with impaired homeostasis of amino acid and lipid metabolism.

Normal Cerebral Oxygen Consumption Despite Elevated Cerebral Blood Flow in Adolescents With Bipolar Disorder: Putative Neuroimaging Evidence of Anomalous Energy Metabolism

Background: Regional cerebral blood flow (CBF) is reportedly altered in both adolescents and adults with bipolar disorder (BD). Whether these CBF differences are part of an overall imbalance in cerebral energy homeostasis remains unknown. Therefore, we examined global cerebral metabolic rate of oxygen consumption (CMRO₂) as a physiological index of brain metabolism in adolescents with and without BD. Methods: One hundred and fifteen adolescents (mean age 17.3 ± 1.4 years), including 58 BD (type I, II, or not otherwise specified [NOS]) and 57 age-matched healthy controls (HCs) participated in this magnetic resonance imaging (MRI) study. Global estimates for venous blood oxygenation (Y_v) and grey matter CBF were measured using T2-relaxation-under-spin-tagging (TRUST) and arterial spin labeling (ASL) MRI, respectively. CMRO₂ was calculated using the Fick principle of arteriovenous difference to test for a group difference. We also examined CMRO₂ in relation to mood states (i.e. euthymic, depressed, or hypomanic/mixed). Results: Although CBF was significantly higher in BD compared to HCs, there was no group difference in global CMRO₂, nor Y_v. Meanwhile, Y_v significantly decreased with age, and females tended to have greater CBF and CMRO₂ in comparison to males. Lastly, there was no significant association between CMRO₂ and mood states. Conclusions: Our results indicate a potential mismatch between cerebral blood supply and oxygen metabolism in BD, suggesting inefficiency in energy homeostasis in the brain. Mapping CMRO₂ would provide the spatial resolution to investigate regional alterations in metabolism, particularly in the brain regions where CBF is increased.

Altered Slc25 family gene expression as markers of mitochondrial dysfunction in brain regions under experimental mixed anxiety/depression-like disorder

BACKGROUND

Development of anxiety- and depression-like states under chronic social defeat stress in mice has been shown by many experimental studies. In this article, the differentially expressed Slc25* family genes encoding mitochondrial carrier proteins were analyzed in the brain of depressive (defeated) mice versus aggressive mice winning in everyday social confrontations. The collected samples of brain regions were sequenced at JSC Genoanalytica ( http://genoanalytica.ru/ , Moscow, Russia).

RESULTS

Changes in the expression of the 20 Slc25* genes in the male mice were brain region- and social experience (positive or negative)-specific. In particular, most Slc25* genes were up-regulated in the hypothalamus of defeated and aggressive mice and in the hippocampus of defeated mice. In the striatum of defeated mice and in the ventral tegmental area of aggressive mice expression of mitochondrial transporter genes changed specifically. Significant correlations between expression of most Slc25* genes and mitochondrial Mrps and Mrpl genes were found in the brain regions.

CONCLUSION

Altered expression of the Slc25* genes may serve as a marker of mitochondrial dysfunction in brain, which accompanies the development of many neurological and psychoemotional disorders.

Eukaryotic cell survival mechanisms: Disease relevance and therapeutic intervention

Cell responds to stress by activating various modes of stress responses which aim for minimal damage to cells and speedy recovery from the insults. However, unresolved stresses exceeding the tolerance limit lead to cell death (apoptosis, autophagy etc.) that helps to get rid of damaged cells and protect cell integrity. Furthermore, aberrant stress responses are the hallmarks of several pathophysiologies (neurodegeneration, metabolic diseases, cancer etc.). The catastrophic remodulation of stress responses is observed in cancer cells in favor of their uncontrolled growth. Whereas pro-survival stress responses redirected to death signaling provokes excessive cell death in neurodegeneration. Clear understanding of such mechanistic link to disease progression is required in order to modulate these processes for new therapeutic targets. The current review explains this with respect to novel drug discoveries and other breakthroughs in therapeutics.

Peroxisome Proliferator-Activated Receptor Gamma Coactivator-1 Alpha as a Novel Target for Bipolar Disorder and Other Neuropsychiatric Disorders

Peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1 alpha) is a protein that regulates metabolism and inflammation by activating nuclear receptors, especially the family of peroxisome proliferator-activated receptors (PPARs). PGC-1 alpha and PPARs also regulate mitochondrial biogenesis, cellular energy production, thermogenesis, and lipid metabolism. Brain energy metabolism may also be regulated in part by the interaction between PGC-1 alpha and PPARs. Because neurodegenerative diseases (Huntington's disease, Parkinson's disease, and amyotrophic lateral sclerosis) and bipolar disorder have been associated with dysregulated mitochondrial and brain energy metabolism, PGC-1 alpha may represent a potential drug target for these conditions. The purpose of this article is to review the physiology of PGC-1 alpha, PPARs, and the role of PPAR agonists to target PGC-1 alpha to treat neurodegenerative diseases and bipolar disorder. We also review clinical trials of repurposed antidiabetic thiazolidines and anti-triglyceride fibrates (PPAR agonists) for neurodegenerative diseases and bipolar disorder. PGC-1 alpha and PPARs are innovative potential targets for bipolar disorder and warrant future clinical trials.

Klotho dysfunction: A pathway linking the aging process to bipolar disorder?

AIM

Although accelerated aging profile has been described in bipolar disorder (BD), the biology linking BD and aging is still largely unknown. Reduced levels and/or activity of a protein named Klotho is associated with decreased life span, premature aging and occurrence of age-related diseases. Therefore, this study was designed to evaluate plasma levels of Klotho in BD patients and controls.

METHODS

Forty patients with type 1 BD and 30 controls were enrolled in this study. After clinical evaluation, peripheral blood samples were drawn and plasma levels of Klotho were measured using enzyme-linked immunosorbent assay.

RESULTS

Patients with BD and controls presented similar age and sex distribution. The mean ± SD length of illness was 24.00 ± 12.75 years. BD patients presented increased frequency of clinical comorbidities in comparison with controls, mainly arterial hypertension, diabetes mellitus, and hypothyroidism. Both patients with BD in remission and in mania exhibited increased plasma levels of Klotho in comparison with controls. There was no significant difference between patients in mania and patients in remission regarding the levels of Klotho.

CONCLUSION

Klotho-related pathway is altered in BD. Contrary to our original hypothesis, our sample of patients with BD presented increased plasma levels of Klotho in comparison with controls. Elevated levels of Klotho in long-term BD patients may be associated with the disorder progression. Further studies are needed to better understand the role of Klotho in BD and other mood disorders.

Dysregulation of glucose metabolism since young adulthood increases the risk of cardiovascular diseases in patients with bipolar disorder

Aging patients with bipolar disorder (BD) are at a high risk of cardiovascular diseases (CVDs). However, few studies have directly examined the association between metabolic risks and CVDs in patients with BD across the lifespan. Therefore, the aim of this study was to determine lifetime metabolic risk factors for CVDs in patients with BD. We recruited BD-I patients who were more than 50 years old and had had at least one psychiatric hospitalization. Patients who had a cardiologist-confirmed CVD diagnosis (ICD-9 code 401-414) were assigned to the case group. Fifty-five cases were matched with 55 control patient without CVDs based on age and sex. Clinical data were obtained by retrospectively reviewing 30 years of hospital records. Compared to control subjects, a significantly higher proportion of cases had impaired fasting glucose between ages 31 and 40 (44.0% versus 17.4%, p = 0.046), diabetes mellitus between ages 41 and 50 (25.6% versus 8.6%, p = 0.054), and diabetes mellitus after age 51 (36.3% versus 12.7%, p = 0.005). No significant difference was found in overweight, obesity, or dyslipidemia. After adjusting for years of education, first episode as mania, and second generation antipsychotic use, lifetime diabetes mellitus remained a risk factor for CVDs (OR = 4.45, 95% CI = 1.89-10.66, p = 0.001). The findings suggest that glucose dysregulation across the adult age span is probably the major metabolic risk contributing to CVDs in patients with BD. Clinicians therefore have to notice the serum fasting glucose levels of BD patients since young adulthood.

Recent Insights into the Role of Unfolded Protein Response in ER Stress in Health and Disease

Unfolded stress response (UPR) is a conserved cellular pathway involved in protein quality control to maintain homeostasis under different conditions and disease states characterized by cell stress. Although three general schemes of and genes induced by UPR are rather well-established, open questions remain including the precise role of UPR in human diseases and the interactions between different sensor systems during cell stress signaling. Particularly, the issue how the normally adaptive and pro-survival UPR pathway turns into a deleterious process causing sustained endoplasmic reticulum (ER) stress and cell death requires more studies. UPR is also named a friend with multiple personalities that we need to understand better to fully recognize its role in normal physiology and in disease pathology. UPR interacts with other organelles including mitochondria, and with cell stress signals and degradation pathways such as autophagy and the ubiquitin proteasome system. Here we review current concepts and mechanisms of UPR as studied in different cells and model systems and highlight the relevance of UPR and related stress signals in various human diseases.