Decreased global methylation in patients with bipolar disorder who respond to lithium

Mitochondrial DNA copy number is significantly increased in bipolar disorder patients and is correlated with long-term lithium treatment

Mitochondrial dysfunctions have been reported in bipolar disorder (BD), but their role in the etiopathogenesis of BD as well as their implications in modulating response to pharmacological treatments with psychotropic medications have been scarcely explored. Mitochondrial DNA copy number (mtDNA-cn) has been linked to mitochondria functioning, and, despite some degree of inconsistence, previous findings showed that BD patients present significant differences in mtDNA-cn compared to healthy controls. Here we measured mtDNA-cn in a sample of 89 patients with BD and 78 healthy controls (HC). Patients in the BD sample were treated either with lithium (n = 47) and characterized as responders (n = 22) or non-responders (n = 25), or with other mood stabilizers (n = 42). BD patients had larger mtDNA-cn compared to HC (adjusted model: F2=9.832; p = 0.000095; contribution of diagnosis F1= 10.798; p = 0.001). When the BD sample was stratified for treatment exposure, mtDNA-cn was lower in patients treated with lithium compared to those treated with other mood stabilizers (adjusted model: F4=23.770, p = 7.0929E-13; contribution of treatment: F1=54.300, p = 1.55E-10). Moreover mtDNA-cn was higher in patients treated with other mood stabilizers compared to controls and Li-treated BD patients (F3=28.125, p = 1.36E-14; contribution of groups F2=36.156, p = 1.25E-13). Finally, there was no difference in mtDNA-cn levels in lithium responders compared to non-responders and neither between the two diagnostic groups (BD type 1 and 2). Our findings suggest that BD may be associated with mitochondrial dysfunctions, and that exposure to lithium but not to other mood stabilizers may restore these abnormalities, though this does not appear correlated with the clinical efficacy of lithium.

Evaluating Oxidative Stress Markers in At-Risk Individuals for Bipolar Disorder: A Systematic Review and Meta-Analysis

INTRODUCTION

Bipolar disorder (BD), a mood disorder with recurrent affective episodes and a strong genetic basis is frequently associated with significant comorbidities, both physical and psychiatric, yet its neurobiology remains unclear. Recent evidence underscores oxidative stress as a pivotal factor linking BD to its comorbidities, prompting an investigation into whether this is a sign of a genetic vulnerability or a consequence of the disease. In this study, we systematically reviewed oxidative stress studies conducted on individuals at risk for BD. We performed a meta-analysis on studies examining oxidative DNA damage in these individuals.

METHODS

The literature was searched across the databases PubMed, Web of Science, Scopus, Ovid MEDLINE, and Cochrane to locate studies of oxidative stress markers in relatives of patients with BD compared with healthy controls (from 1946 to March 2024). Studies were considered for inclusion based on the following criteria: (i) involvement of first- or second-degree relatives of individuals diagnosed with BD, (ii) presence of a healthy control group, (iii) reporting of oxidative stress parameters for relatives, including mean and standard deviation or median and interquartile range (25-75%) values, and (iv) publication in the English language. Studies comparing the levels of 8-hydroxy-2'-deoxyguanosine (8-OH-dG) or its tautomer 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG) in individuals at risk for BD with healthy controls were evaluated using a meta-analysis with the random-effects method. The risk of bias was evaluated using the Risk of Bias in Non-Randomized Studies of Exposure (ROBINS-E) tool.

RESULTS

Eleven studies were included in the systematic review and four studies for the meta-analysis. The meta-analysis included 543 individuals (first-degree relatives of individuals with BD = 238, control = 305). 8-OH-dG levels were found to be increased in first-degree relatives of individuals with BD compared to healthy controls (random effects: Hedges's g = 0.53, 95% CI = 0.36-0.71, p < 0.001). Findings of oxidative stress markers other than oxidative DNA damage in relatives of individuals with BD are limited and scarce.

CONCLUSION

In this meta-analysis, which consists of a limited number of studies, oxidative DNA damage seems to be a trait marker for BD. This finding could be associated with increased comorbidity and a higher risk of premature aging in individuals at risk for BD. However, further studies with larger sample sizes and longitudinal designs are warranted to confirm findings. Clarifying the changes in these markers from individuals at risk for the disorder throughout the course of the illness would help bridge the gap in understanding the role of oxidative pathways in the risk of BD.

Lithium response in bipolar disorder: Epigenome-wide DNA methylation signatures and epigenetic aging

Lithium (Li) is the first-line treatment for bipolar disorder (BD) even though only 30 % of BD patients are considered excellent responders. The mechanisms by which Li exerts its action are not clearly understood, but it has been suggested that specific epigenetic mechanisms, such as methylation processes, may play a role. In this regard, DNA methylation patterns can be used to estimate epigenetic age (EpiAge), which is accelerated in BD patients and reversed by Li treatment. Our first aim was to compare the DNA methylation profile in peripheral blood between BD patients categorized as excellent responders to Li (Ex-Rp) and non-responders (N-Rp). Secondly, EpiAge was estimated to detect differential age acceleration between the two groups. A total of 130 differentially methylated positions (DMPs) and 16 differentially methylated regions (DMRs) between Ex-Rp (n = 26) and N-Rp (n = 37) were identified (FDR adjusted p-value < 0.05). We found 122 genes mapping the DMPs and DMRs, nine of which (HOXB6, HOXB3, HOXB-AS3, TENM2, CACNA1B, ANK3, EEF2K, CYP1A1, and SORCS2) had previously been linked to Li response. We found genes related to the GSK3β pathway to be highly represented. Using FUMA, we found enrichment in Gene Ontology Cell Component for the synapse. Gene network analysis highlighted functions related to the cell cycle, nervous system development and function, and gene expression. No significant differences in age acceleration were found between Ex-Rp and N-Rp for any of the epigenetic clocks analysed. Our findings indicate that a specific methylation pattern could determine the response to Li in BD patients. We also found that a significant portion of the differentially methylated genes are closely associated with the GSK3β pathway, reinforcing the role of this system in Li response. Future longitudinal studies with larger samples will help to elucidate the epigenetic mechanisms underlying Li response.

Oxidatively-induced DNA base damage and base excision repair abnormalities in siblings of individuals with bipolar disorder DNA damage and repair in bipolar disorder

Previous evidence suggests elevated levels of oxidatively-induced DNA damage, particularly 8-hydroxy-2'-deoxyguanosine (8-OH-dG), and abnormalities in the repair of 8-OH-dG by the base excision repair (BER) in bipolar disorder (BD). However, the genetic disposition of these abnormalities remains unknown. In this study, we aimed to investigate the levels of oxidatively-induced DNA damage and BER mechanisms in individuals with BD and their siblings, as compared to healthy controls (HCs). 46 individuals with BD, 41 siblings of individuals with BD, and 51 HCs were included in the study. Liquid chromatography-tandem mass spectrometry was employed to evaluate the levels of 8-OH-dG in urine, which were then normalized based on urine creatinine levels. The real-time-polymerase chain reaction was used to measure the expression levels of 8-oxoguanine DNA glycosylase 1 (OGG1), apurinic/apyrimidinic endonuclease 1 (APE1), poly ADP-ribose polymerase 1 (PARP1), and DNA polymerase beta (POLβ). The levels of 8-OH-dG were found to be elevated in both individuals with BD and their siblings when compared to the HCs. The OGG1 and APE1 expressions were downregulated, while POLβ expressions were upregulated in both the patient and sibling groups compared to the HCs. Age, smoking status, and the number of depressive episodes had an impact on APE1 expression levels in the patient group while body mass index, smoking status, and past psychiatric history had an impact on 8-OH-dG levels in siblings. Both individuals with BD and unaffected siblings presented similar abnormalities regarding oxidatively-induced DNA damage and BER, suggesting a link between abnormalities in DNA damage/BER mechanisms and familial susceptibility to BD. Our findings suggest that targeting the oxidatively-induced DNA damage and BER pathway could offer promising therapeutic strategies for reducing the risk of age-related diseases and comorbidities in individuals with a genetic predisposition to BD.

Distinctive Patterns of 5-Methylcytosine and 5-Hydroxymethylcytosine in Schizophrenia

Schizophrenia is a highly heritable neuropsychiatric disorder characterized by cognitive and social dysfunction. Genetic, epigenetic, and environmental factors are together implicated in the pathogenesis and development of schizophrenia. DNA methylation, 5-methycytosine (5mC) and 5-hydroxylcytosine (5hmC) have been recognized as key epigenetic elements in neurodevelopment, ageing, and neurodegenerative diseases. Recently, distinctive 5mC and 5hmC pattern and expression changes of related genes have been discovered in schizophrenia. Antipsychotic drugs that affect 5mC status can alleviate symptoms in patients with schizophrenia, suggesting a critical role for DNA methylation in the pathogenesis of schizophrenia. Further exploring the signatures of 5mC and 5hmC in schizophrenia and developing precision-targeted epigenetic drugs based on this will provide new insights into the diagnosis and treatment of schizophrenia.

A comparative meta-analysis of peripheral 8-hydroxy-2'-deoxyguanosine (8-OHdG) or 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG) levels across mood episodes in bipolar disorder

OBJECTIVE

Oxidative DNA damage has been associated with the pathophysiology of bipolar disorder (BD) as one of the common pathways between increased medical comorbidity and premature aging in BD. Previous evidence shows increased levels of oxidatively induced DNA damage markers, 8-hydroxy-2'-deoxyguanosine (8-OHdG) or its tautomer 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG), in patients with BD in comparison to healthy individuals. With the current research, we aim to analyze data on peripheral (blood or urine) 8-OHdG/8-oxo-dG levels across mood states of BD using a meta-analytical approach.

METHOD

A literature search was conducted using the databases PubMed, Scopus, and Web of Science to identify eligible studies (January 1989 to July 2022). Relevant studies were systematically reviewed; a random-effects meta-analysis and a meta-regression analysis were conducted.

RESULTS

The current meta-analysis included 12 studies consisting of 808 BD patients (390 in euthymia, 156 in mania, 137 in depression, 16 in mixed episode, 109 not specified) and 563 healthy controls. BD patients that were currently depressed had significantly higher levels of 8-OHdG/8-oxo-dG than healthy controls, while euthymic or manic patients did not differ from healthy controls. A meta-regression analysis showed sex distribution (being female) and older age to be significantly related to increased 8-OHdG/8-oxo-dG levels.

CONCLUSION

Our findings suggest that 8-OHdG/8-oxo-dG may be a state-related marker of depression in BD and may be affected by older age and female gender.

Are the epigenetic changes predictive of therapeutic efficacy for psychiatric disorders? A translational approach towards novel drug targets

The etiopathogenesis of mental disorders is not fully understood and accumulating evidence support that clinical symptomatology cannot be assigned to a single gene mutation, but it involves several genetic factors. More specifically, a tight association between genes and environmental risk factors, which could be mediated by epigenetic mechanisms, may play a role in the development of mental disorders. Several data suggest that epigenetic modifications such as DNA methylation, post-translational histone modification and interference of microRNA (miRNA) or long non-coding RNA (lncRNA) may modify the severity of the disease and the outcome of the therapy. Indeed, the study of these mechanisms may help to identify patients particularly vulnerable to mental disorders and may have potential utility as biomarkers to facilitate diagnosis and treatment of psychiatric disorders. This article summarizes the most relevant preclinical and human data showing how epigenetic modifications can be central to the therapeutic efficacy of antidepressant and/or antipsychotic agents, as possible predictor of drugs response.

Osteoclasts: Other functions

Osteoclasts are the only cells that can efficiently resorb bone. They do so by sealing themselves on to bone and removing the mineral and organic components. Osteoclasts are essential for bone homeostasis and are involved in the development of diseases associated with decreased bone mass, like osteoporosis, or abnormal bone turnover, like Paget's disease of bone. In addition, compromise of their development or resorbing machinery is pathogenic in multiple types of osteopetrosis. However, osteoclasts also have functions other than bone resorption. Like cells of the innate immune system, they are derived from myeloid precursors and retain multiple immune cell properties. In addition, there is now strong evidence that osteoclasts regulate osteoblasts through a process known as coupling, which coordinates rates of bone resorption and bone formation during bone remodeling. In this article we review the non-resorbing functions of osteoclasts and highlight their importance in health and disease.

Transcriptomics and miRNomics data integration in lymphoblastoid cells highlights the key role of immune-related functions in lithium treatment response in Bipolar disorder

BACKGROUND

Bipolar Disorder (BD) is a complex mental disease characterized by recurrent episodes of mania and depression. Lithium (Li) represents the mainstay of BD pharmacotherapy, despite the narrow therapeutic index and the high variability in treatment response. However, although several studies have been conducted, the molecular mechanisms underlying Li therapeutic effects remain unclear.

METHODS

In order to identify molecular signatures and biological pathways associated with Li treatment response, we conducted transcriptome and miRNome microarray analyses on lymphoblastoid cell lines (LCLs) from 20 patients diagnosed with BD classified as Li responders (n = 11) or non-responders (n = 9).

RESULTS

We found 335 mRNAs and 77 microRNAs (miRNAs) significantly modulated in BD responders versus non-responders. Interestingly, pathway and network analyses on these differentially expressed molecules suggested a modulatory effect of Li on several immune-related functions. Indeed, among the functional molecular nodes, we found NF-κB and TNF. Moreover, networks related to these molecules resulted overall inhibited in BD responder patients, suggesting anti-inflammatory properties of Li. From the integrative analysis between transcriptomics and miRNomics data carried out using miRComb R package on the same samples from patients diagnosed with BD, we found 97 significantly and negatively correlated mRNA-miRNA pairs, mainly involved in inflammatory/immune response.

CONCLUSIONS

Our results highlight that Li exerts modulatory effects on immune-related functions and that epigenetic mechanisms, especially miRNAs, can influence the modulation of different genes and pathways involved in Li response. Moreover, our data suggest the potentiality to integrate data coming from different high-throughput approaches as a tool to prioritize genes and pathways.

Association of Oxidative Stress-Induced Nucleic Acid Damage With Psychiatric Disorders in Adults: A Systematic Review and Meta-analysis

IMPORTANCE

Nucleic acid damage from oxidative stress (NA-OXS) may be a molecular mechanism driving the severely increased morbidity and mortality from somatic causes in adults with psychiatric disorders.

OBJECTIVE

To systematically retrieve and analyze data on NA-OXS across the psychiatric disorder diagnostic spectrum.

DATA SOURCES

The PubMed, Embase, and PsycINFO databases were searched from inception to November 16, 2021. A hand search of reference lists of relevant articles was also performed.

STUDY SELECTION

Key study inclusion criteria in this meta-analysis were as follows: adult human study population, measurement of any marker of DNA or RNA damage from oxidative stress, and either a (1) cross-sectional design comparing patients with psychiatric disorders (any diagnosis) with a control group or (2) prospective intervention. Two authors screened the studies, and 2 senior authors read the relevant articles in full and assessed them for eligibility.

DATA EXTRACTION AND SYNTHESIS

The Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines were followed. Two authors performed data extraction independently, and a senior coauthor was consulted in cases of disagreement. Data were synthesized with random-effects and multilevel meta-analyses.

MAIN OUTCOMES AND MEASURES

The predefined hypothesis was that individuals with psychiatric disorders have increased NA-OXS levels. The main outcome was the standardized mean differences (SMDs) among patients and controls in nucleic acid oxidation markers compared across diagnostic groups. Analyses were divided into combinations of biological matrices and nucleic acids.

RESULTS

Eighty-two studies fulfilled the inclusion criteria, comprising 205 patient vs control group comparisons and a total of 10 151 patient and 10 532 control observations. Overall, the data showed that patients with psychiatric disorders had higher NA-OXS levels vs controls across matrices and molecules. Pooled effect sizes ranged from moderate for urinary DNA markers (SMD = 0.44 [95% CI, 0.20-0.68]; P < .001) to very large for blood cell DNA markers (SMD = 1.12 [95% CI, 0.69-1.55; P < .001). Higher NA-OXS levels were observed among patients with dementias followed by psychotic and bipolar disorders. Sensitivity analyses excluding low-quality studies did not materially alter the results. Intervention studies were few and too heterogenous for meaningful meta-analysis.

CONCLUSIONS AND RELEVANCE

The results of this meta-analysis suggest that there is an association with increased NA-OXS levels in individuals across the psychiatric disorder diagnostic spectrum. NA-OXS may play a role in the somatic morbidity and mortality observed among individuals with psychiatric disorders.

Global DNA methylation changes in adults with attention deficit-hyperactivity disorder and its comorbidity with bipolar disorder: links with polygenic scores

Genetic and environmental factors contribute to the etiology of Attention Deficit-Hyperactivity Disorder (ADHD). In this sense, the study of epigenetic mechanisms could contribute to the understanding of the disorder's neurobiology. Global DNA methylation (GMe) evaluated through 5-methylcytosine levels could be a promising epigenetic biomarker to capture long-lasting biological effects in response to environmental and hormonal changes. We conducted the first assessment of GMe levels in subjects with ADHD (n = 394) and its main comorbidities in comparison to populational controls (n = 390). Furthermore, given the high genetic contribution to ADHD (heritability of 80%), polygenic risk scores (PRS) were calculated to verify the genetic contribution to GMe levels in ADHD and the comorbidities associated with GMe levels. The GMe levels observed in patients were lower than controls (P = 1.1e-8), with women being significantly less globally methylated than men (P = 0.002). Regarding comorbidities, the presence of bipolar disorder (BD) among patients with ADHD was associated with higher methylation levels compared to patients with ADHD without BD (P = 0.031). The results did not change when pharmacological treatment was accounted for in the analyses. The ADHD and BD most predictive PRSs were negatively (P = 0.0064) and positively (P = 0.0042) correlated with GMe, respectively. This study is the first to report an association between GMe, ADHD, and its comorbidity with BD and associations between PRSs for specific psychiatric disorders and GMe. Our findings add to previous evidence that GMe may be a relevant piece in the psychiatric disorders' etiological landscape.

New Insights into TETs in Psychiatric Disorders

Psychiatric disorders are complex and heterogeneous disorders arising from the interaction of multiple factors based on neurobiology, genetics, culture, and life experience. Increasing evidence indicates that sustained abnormalities are maintained by epigenetic modifications in specific brain regions. Over the past decade, the critical, non-redundant roles of the ten-eleven translocation (TET) family of dioxygenase enzymes have been identified in the brain during developmental and postnatal stages. Specifically, TET-mediated active demethylation, involving the iterative oxidation of 5-methylcytosine to 5-hydroxymethylcytosine and subsequent oxidative derivatives, is dynamically regulated in response to environmental stimuli such as neuronal activity, learning and memory processes, and stressor exposure. Here, we review the progress of studies designed to provide a better understanding of how profiles of TET proteins and 5hmC are powerful mechanisms by which to explain neuronal plasticity and long-term behaviors, and impact transcriptional programs operative in the brain that contribute to psychiatric disorders.

Genetic and Epigenetic Markers of Lithium Response

The mood stabilizer lithium represents a cornerstone in the long term treatment of bipolar disorder (BD), although with substantial interindividual variability in clinical response. This variability appears to be modulated by genetics, which has been significantly investigated in the last two decades with some promising findings. In addition, recently, the interest in the role of epigenetics has grown significantly, since the exploration of these mechanisms might allow the elucidation of the gene-environment interactions and explanation of missing heritability. In this article, we provide an overview of the most relevant findings regarding the pharmacogenomics and pharmacoepigenomics of lithium response in BD. We describe the most replicated findings among candidate gene studies, results from genome-wide association studies (GWAS) as well as post-GWAS approaches supporting an association between high genetic load for schizophrenia, major depressive disorder or attention deficit/hyperactivity disorder and poor lithium response. Next, we describe results from studies investigating epigenetic mechanisms, such as changes in methylation or noncoding RNA levels, which play a relevant role as regulators of gene expression. Finally, we discuss challenges related to the search for the molecular determinants of lithium response and potential future research directions to pave the path towards a biomarker guided approach in lithium treatment.

A Glutathione Peroxidase Gene from Litopenaeus vannamei Is Involved in Oxidative Stress Responses and Pathogen Infection Resistance

In shrimp, several glutathione peroxidase (GPX) genes have been cloned and functionally studied. Increasing evidence suggests the genes’ involvement in white spot syndrome virus (WSSV)- or Vibrio alginolyticus-infection resistance. In the present study, a novel GXP gene (LvGPX3) was cloned in Litopenaeus vannamei. Promoter of LvGPX3 was activated by NF-E2-related factor 2. Further study showed that LvGPX3 expression was evidently accelerated by oxidative stress or WSSV or V. alginolyticus infection. Consistently, downregulated expression of LvGPX3 increased the cumulative mortality of WSSV- or V. alginolyticus-infected shrimp. Similar results occurred in shrimp suffering from oxidative stress. Moreover, LvGPX3 was important for enhancing Antimicrobial peptide (AMP) gene expression in S2 cells with lipopolysaccharide treatment. Further, knockdown of LvGPX3 expression significantly suppressed expression of AMPs, such as Penaeidins 2a, Penaeidins 3a and anti-lipopolysaccharide factor 1 in shrimp. AMPs have been proven to be engaged in shrimp WSSV- or V. alginolyticus-infection resistance; it was inferred that LvGPX3 might enhance shrimp immune response under immune challenges, such as increasing expression of AMPs. The regulation mechanism remains to be further studied.

DNA methylation signature as a biomarker of major neuropsychiatric disorders

DNA methylation is a broadly-investigated epigenetic modification that has been considered as a heritable and reversible change. Previous findings have indicated that DNA methylation regulates gene expression in the central nervous system (CNS). Also, disturbance of DNA methylation patterns has been associated with destructive consequences that lead to human brain diseases such as neuropsychiatric disorders (NPDs). In this review, we comprehensively discuss the mechanism and function of DNA methylation and its most recent associations with the pathology of NPDs-including major depressive disorder (MDD), schizophrenia (SZ), autism spectrum disorder (ASD), bipolar disorder (BD), and attention/deficit hyperactivity disorder (ADHD). We also discuss how heterogeneous findings demand further investigations. Finally, based on the recent studies we conclude that DNA methylation status may have implications in clinical diagnostics and therapeutics as a potential epigenetic biomarker of NPDs.

Mini review: Recent advances on epigenetic effects of lithium

Lithium (Li) remains the first line long-term treatment of bipolar disorders notwithstanding a high inter-individual variability of response. Significant research effort has been undertaken to understand the molecular mechanisms underlying Li cellular and clinical effects in order to identify predictive biomarkers of response. Li response has been shown to be partly heritable, however mechanisms that do not rely on DNA variants could also be involved. In recent years, modulation of epigenetic marks in relation with the level of Li response has appeared increasingly plausible. Recent results in this field of research have provided new insights into the molecular processes involved in Li effects. In this review, we examined the literature investigating the involvement of three epigenetic mechanisms (DNA methylation, noncoding RNAs and histone modifications) in Li clinical efficacy in bipolar disorder.

8-Hydroxy-2'-Deoxyguanosine and Reactive Oxygen Species as Biomarkers of Oxidative Stress in Mental Illnesses: A Meta-Analysis

OBJECTIVE

Mental illnesses may be caused by genetic and environmental factors. Recent studies reported that mental illnesses were accompanied by higher oxidative stress level. However, the results were inconsistent. Thus, present meta-analysis aimed to analyse the association between oxidative DNA damage indicated by 8-hydroxy-2'-deoxyguanosine (8-OHdG) or 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), which has been widely used as biomarker of oxidative stress, and mental illnesses, including schizophrenia, bipolar disorder and depression. As oxidative DNA damage is caused by reactive oxygen species (ROS), systematic review and meta-analysis were also conducted to analyse the relationship between ROS and these three mental illnesses.

METHODS

Studies from 1964 to 2020 (for oxidative DNA damage) and from 1907 to 2021 (for ROS) in Pubmed and Scopus databases were selected and analysed using Comprehensive Meta-Analysis version 2 respectively. Data were subjected to meta-analysis for examining the effect sizes of the results. Publication bias assessments, heterogeneity assessments and subgroup analyses based on biological specimens, patient status, illness duration and medication history were also conducted.

RESULTS

This meta-analysis revealed that oxidative DNA damage was significantly higher in patients with schizophrenia and bipolar disorder based on random-effects models whereas in depressed patients, the level was not significant. Since heterogeneity was present, results based on random-effects model was preferred. Our results also showed that oxidative DNA damage level was significantly higher in lymphocyte and urine of patients with schizophrenia and bipolar disorder respectively. Besides, larger effect size was observed in inpatients and those with longer illness duration and medication history. Significant higher ROS was also observed in schizophrenic patients but not in depressive patients.

CONCLUSION

The present meta-analysis found that oxidative DNA damage was significantly higher in schizophrenia and bipolar disorder but not in depression. The significant association between deoxyguanosines and mental illnesses suggested the possibility of using 8-OHdG or 8-oxodG as biomarker in measurement of oxidative DNA damage and oxidative stress. Higher ROS level indicated the involvement of oxidative stress in schizophrenia. The information from this study may provide better understanding on pathophysiology of mental illnesses.

Mini-review: The anti-aging effects of lithium in bipolar disorder

The medical use of lithium has grown since its initial introduction in the 1800s as a treatment for gout. Today, the divalent cation remains as the pharmacological gold standard in treatment of bipolar disorder (BD) with strong mood stabilizing effects. Lithium has demonstrated efficacy in the treatment of acute affective episodes, in the reduction of affective episode recurrence, and in significantly decreasing the risk of suicide in patients. BD has been consistently associated with clinical signs of accelerated aging, including increased rates of age-related diseases such as cardiovascular diseases, malignancies, and diabetes mellitus. This clinical scenario parallels accelerated aging mechanisms observed on a molecular basis, with studies reporting shortened telomeres, increased oxidative stress, and accelerated epigenetic aging in patients with BD compared to controls. Lithium has proved useful as a potential agent in slowing down this accelerated aging process in BD, potentially reversing effects induced by the disorder. This mini-review summarizes findings of anti-aging mechanisms associated with lithium use and provides a discussion of the clinical implications and perspectives of this evolving field. Despite many promising results, more studies are warranted in order to elucidate the exact mechanism by which lithium may act as an anti-aging agent and the extent to which these mechanisms are relevant to its mood stabilizing properties in BD.

An altered global DNA methylation status in women with depression

Sparse studies have shown that specific biomarkers of a global DNA methylation status may be related to various mental diseases and states, including: bipolar disorder (BD), anxiety and major depression disorder (MDD). The objective of this study was to analyze potential variation of the above mentioned global methylation status in women with depression. 38 women with a current and clinically confirmed depressive episode suffering from BD type I, type II or MDD and 71 women from the general population and at similar age were recruited for the study. Alu and LINE-1 methylation was assayed with the quantitative methylation-specific PCR technique with TaqMan probes, while the 5-mC and 5-hmC level was determined using the ELISA-based method. Significantly higher levels of 5-mC, Alu and LINE-1 methylation were observed in the women with depression as compared to the controls; while the 5-hmC level revealed to be significantly lower. The BD type I patients presented the highest level of 5-mC of all the women with a depressive episode. 5-mC level in the patients was positively and significantly correlated with the severity of the symptoms of depression. Relationships between Alu or LINE-1 methylation and 5-mC level were statistically significant only in the case of the control women. Alu and LINE-1 methylation do not constitute suitable biomarkers of global DNA methylation in the investigated patients. These findings require confirmation in case-control and prospective epidemiological studies.

The neuroendocrine modulation of global DNA methylation in neuropsychiatric disorders

There is an increasing body of knowledge on the influence of differential DNA methylation of specific genomic regions in psychiatric disorders. However, fewer studies have addressed global DNA methylation (GMe) levels. GMe is an estimative of biological functioning that is regulated by pervasive mechanisms able to capture the big picture of metabolic and environmental influences upon gene expression. In the present perspective article, we highlighted evidence for the relationships between cortisol and sex hormones and GMe in psychiatric disorders. We argue that the far-reaching effects of cortisol and sexual hormones on GMe may lie on the pathways linking stress and mental health. Further research on these endocrine-epigenetic links may help to explain the role of environmental stress as well as sex differences in the prevalence of psychiatric disorders.

Role of epigenetic regulatory enzymes in animal models of mania induced by amphetamine and paradoxical sleep deprivation

It is known that bipolar disorder has a multifactorial aetiology where the interaction between genetic and environmental factors is responsible for its development. Because of this, epigenetics has been largely studied in psychiatric disorders. The present study aims to evaluate the effects of histone deacetylase inhibitors on epigenetic enzyme alterations in rats or mice submitted to animal models of mania induced by dextro-amphetamine or sleep deprivation, respectively. Adult male Wistar rats were subjected to 14 days of dextro-amphetamine administration, and from the eighth to the fourteenth day, the animals were treated with valproate and sodium butyrate in addition to dextro-amphetamine injections. Adult C57BL/6 mice received 7 days of valproate or sodium butyrate administration, being sleep deprived at the last 36 hr of the protocol. Locomotor and exploratory activities of rats and mice were evaluated in the open-field test, and histone deacetylase, DNA methyltransferase, and histone acetyltransferase activities were assessed in the frontal cortex, hippocampus, and striatum. Dextro-amphetamine and sleep deprivation induced hyperactivity and increased histone deacetylase and DNA methyltransferase activities in the animal's brain. Valproate and sodium butyrate were able to reverse hyperlocomotion induced by both animal models, as well as the alterations on histone deacetylase and DNA methyltransferase activities. There was a positive correlation between enzyme activities and number of crossings for both models. Histone deacetylase and DNA methyltransferase activities also presented a positive correlation between theirselves. These results suggest that epigenetics can play an important role in BD pathophysiology as well as in its treatment.

A DNA methylation signature discriminates between excellent and non-response to lithium in patients with bipolar disorder type 1

Lithium (Li) is the cornerstone maintenance treatment for bipolar disorders (BD), but response rates are highly variable. To date, no clinical or biological marker is available to reliably define eligibility criteria for a maintenance treatment with Li. We examined whether the prophylactic response to Li (assessed retrospectively) is associated with distinct blood DNA methylation profiles. Bisulfite-treated total blood DNA samples from individuals with BD type 1 (15 excellent-responders (LiERs) versus 11 non-responders (LiNRs)) were used for targeted enrichment of CpG rich genomic regions followed by high-resolution next-generation sequencing to identify differentially methylated regions (DMRs). After controlling for potential confounders we identified 111 DMRs that significantly differ between LiERs and LiNRs with a significant enrichment in neuronal cell components. Logistic regression and receiver operating curves identified a combination of 7 DMRs with a good discriminatory power for response to Li (Area Under the Curve 0.806). Annotated genes associated with these DMRs include Eukaryotic Translation Initiation Factor 2B Subunit Epsilon (EIF2B5), Von Willebrand Factor A Domain Containing 5B2 (VWA5B2), Ral GTPase Activating Protein Catalytic Alpha Subunit 1 (RALGAPA1). Although preliminary and deserving replication, these results suggest that biomarkers of response to Li may be identified through peripheral epigenetic measures.

Dissecting the Epigenetic Changes Induced by Non-Antipsychotic Mood Stabilizers on Schizophrenia and Affective Disorders: A Systematic Review

BACKGROUND

Epimutations secondary to gene-environment interactions have a key role in the pathophysiology of major psychiatric disorders. In vivo and in vitro evidence suggest that mood stabilizers can potentially reverse epigenetic deregulations found in patients with schizophrenia or mood disorders through mechanisms that are not yet fully understood. However, their activity on epigenetic processes has made them a research target for therapeutic approaches.

METHODS

We conducted a comprehensive literature search of PubMed and EMBASE for studies investigating the specific epigenetic changes induced by non-antipsychotic mood stabilizers (valproate, lithium, lamotrigine, and carbamazepine) in animal models, human cell lines, or patients with schizophrenia, bipolar disorder, or major depressive disorder. Each paper was reviewed for the nature of research, the species and tissue examined, sample size, mood stabilizer, targeted gene, epigenetic changes found, and associated psychiatric disorder. Every article was appraised for quality using a modified published process and those who met a quality score of moderate or high were included.

RESULTS

A total of 2,429 records were identified; 1,956 records remained after duplicates were removed and were screened via title, abstract and keywords; 129 records were selected for full-text screening and a remaining of 38 articles were included in the qualitative synthesis. Valproate and lithium were found to induce broader epigenetic changes through different mechanisms, mainly DNA demethylation and histones acetylation. There was less literature and hence smaller effects attributable to lamotrigine and carbamazepine could be associated overall with the small number of studies on these agents. Findings were congruent across sample types.

CONCLUSIONS

An advanced understanding of the specific epigenetic changes induced by classic mood stabilizers in patients with major psychiatric disorders will facilitate personalized interventions. Further related drug discovery should target the induction of selective chromatin remodeling and gene-specific expression effects.

Global DNA hypomethylation and its correlation to the betaine level in peripheral blood of patients with schizophrenia

Accumulating evidence suggests that aberrant epigenetic regulation is involved in the pathophysiology of major psychiatric disorders such as schizophrenia (SZ) and bipolar disorder (BD). We previously showed that the plasma level of betaine (N,N,N-trimethylglycine), a methyl-group donor, was significantly decreased in patients with first episode schizophrenia (FESZ). In this study, we identified decrease of global DNA methylation level in FESZ (N = 24 patients vs N = 42 controls), and found that global DNA methylation level was inversely correlated with scores on the global assessment of functioning (GAF) scale, and positively correlated with plasma betaine level. Notably, correlations between levels of betaine and its metabolites (N,N-dimethylglycine and sarcosine, N-methylglycine) were lower or lost in FESZ plasma, but remained high in controls. We further examined global DNA methylation levels in patients with chronic SZ (N = 388) and BD (N = 414) as well as controls (N = 430), and confirmed significant hypomethylation and decreased betaine level in SZ. We also found that patients with BD type I, but not those with BD type II, showed significant global hypomethylation. These results suggest that global hypomethylation associated with decreased betaine level in blood cells is common to SZ and BD, and may reflect common pathophysiology such as psychotic symptoms.

Genome-wide DNA methylomic differences between dorsolateral prefrontal and temporal pole cortices of bipolar disorder

Dorsolateral prefrontal cortex (DLPFC) and temporal pole (TP) are brain regions that display abnormalities in bipolar disorder (BD) patients. DNA methylation - an epigenetic mechanism both heritable and sensitive to the environment - may be involved in the pathophysiology of BD. To study BD-associated DNA methylomic differences in these brain regions, we extracted genomic DNA from the postmortem tissues of Brodmann Area (BA) 9 (DLPFC) and BA38 (TP) gray matter from 20 BD, ten major depression (MDD), and ten control age-and-sex-matched subjects. Genome-wide methylation levels were measured using the 850 K Illumina MethylationEPIC BeadChip. We detected striking differences between cortical regions, with greater numbers of between-brain-region differentially methylated positions (DMPs; i.e., CpG sites) in all groups, most pronounced in the BD group, and with substantial overlap across groups. The genes of DMPs common to both BD and MDD (hypothetically associated with their common features such as depression) and those distinct to BD (hypothetically associated with BD-specific features such as mania) were enriched in pathways involved in neurodevelopment including axon guidance. Pathways enriched only in the BD-MDD shared list pointed to GABAergic dysregulation, while those enriched in the BD-only list suggested glutamatergic dysregulation and greater impact on synaptogenesis and synaptic plasticity. We further detected group-specific between-brain-region gene expression differences in ODC1, CALY, GALNT2, and GABRD, which contained significant between-brain-region DMPs. In each brain region, no significant DMPs or differentially methylated regions (DMRs) were found between diagnostic groups. In summary, the methylation differences between DLPFC and TP may provide molecular targets for further investigations of genetic and environmental vulnerabilities associated with both unique and common features of various mood disorders and suggest directions of future development of individualized treatment strategies.

Altered DNA methylation of the AluY subfamily in schizophrenia and bipolar disorder

Aim: To study DNA methylation patterns of AluY subfamilies in schizophrenia (SCZ) and bipolar disorder (BPD). Patients & methods: A bisulfite conversion-specific one-label extension method was employed to detect the AluY subfamily methylation levels of peripheral blood DNA from 92 SCZ patients, 99 BPD patients and 92 controls. Results: Hypermethylation of the AluY A1 and A2 CpG sites in BPD patients and hypomethylation of A3 CpG site in both of BPD and SCZ patients, and opposite age-dependent methylation alterations between SCZ and controls. Conclusion: The differentially altered DNA methylation patterns of the AluY families between BPD and SCZ suggest the role of DNA methylation in the pathogenesis of these major psychiatric disorders.

Clinical factors associated with lithium treatment response in bipolar disorder patients from India

BACKGROUND

Bipolar Disorder (BD) is a chronic and disabling psychiatric illness with waxing and waning course. Lithium is the mainstay of treatment for Bipolar disorder (BD). There is limited literature on the clinical markers of Lithium treatment response from south Asia.

METHODS

Two hundred and ten individuals with BD I and a history of at least 6 months of treatment with Lithium were recruited from the outpatient services of the National Institute of Mental Health and Neurosciences (NIMHANS) after obtaining informed consent. A diagnosis of BD I was made according to the DSM-IV criteria. The characterization of response to lithium prophylaxis was done using NIMH Retrospective Life Chart and "Retrospective Criteria of Long Term Treatment Response in Research Subjects with Bipolar Disorder" scale.

RESULTS

There were 132 (62.86%) good responders and 78 (37.14%) non-responders. Good responders were noted to have less number of hospitalizations and more onset episode of depression than non-responders. Using continuous phenotype, Lithium response was inversely correlated with total number of episodes, number of episodes of mania/ depression, number of hospitalisations and presence of suicide attempt. Multivariate analysis only revealed number of episodes and hospitalization to be associated with Lithium response.

CONCLUSION

Our Lithium response rates were higher than what have been reported in the few previous studies. Illness severity was the only factor associated with Lithium response. There is a need to examine this question in larger prospective samples and to focus on biological/ molecular markers of treatment response.

Hypomethylation of LINE-1 elements in schizophrenia and bipolar disorder

Schizophrenia (SCZ) and bipolar disorder (BPD) are severe mental illnesses with evidence of significant genetic and environmental etiological elements in their complex etiologies. 5'-Methylcytosine is the main epigenetic DNA modification that mediates the interplay between genetic and environmental components. In humans, most 5'-methylcytosine modifications are observed in CpG-rich regions within the long interspersed nuclear element (LINE-1). LINE-1 is a mobile retrotransposon that comprises ∼17% of the human genome, and its methylation levels are highly correlated with global DNA methylation levels. LINE-1 insertions are also reported to be mental illnesses-associated genomic risk factors. To examine the LINE-1 methylation levels in SCZ and BPD, this study employed a bisulfite conversion-specific one-label extension (BS-OLE) method to detect the methylation levels at three CpG sites (S1, S2 and S3) of LINE-1 in peripheral blood DNA from a Han Chinese cohort composed of 92 SCZ patients, 99 BPD patients and 92 controls (CON). The results showed a decreased S1 methylation level in SCZ, decreased S2 methylation level in BPD and decreased S3 methylation levels in both SCZ and BPD relative to those of the CON. A female-dependent positive correlation of the S3 methylation level with age in CON became non-significant in both SCZ and BPD. These findings demonstrated that LINE-1 methylation varied with development and disease status. The roles of LINE-1 methylation in the pathogenesis of SCZ and BPD remain to be elucidated.

DNA Methylation as a Biomarker of Treatment Response Variability in Serious Mental Illnesses: A Systematic Review Focused on Bipolar Disorder, Schizophrenia, and Major Depressive Disorder

So far, genetic studies of treatment response in schizophrenia, bipolar disorder, and major depression have returned results with limited clinical utility. A gene × environment interplay has been proposed as a factor influencing not only pathophysiology but also the treatment response. Therefore, epigenetics has emerged as a major field of research to study the treatment of these three disorders. Among the epigenetic marks that can modify gene expression, DNA methylation is the best studied. We performed a systematic search (PubMed) following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA guidelines for preclinical and clinical studies focused on genome-wide and gene-specific DNA methylation in the context of schizophrenia, bipolar disorders, and major depressive disorder. Out of the 112 studies initially identified, we selected 31 studies among them, with an emphasis on responses to the gold standard treatments in each disorder. Modulations of DNA methylation levels at specific CpG sites have been documented for all classes of treatments (antipsychotics, mood stabilizers, and antidepressants). The heterogeneity of the models and methodologies used complicate the interpretation of results. Although few studies in each disorder have assessed the potential of DNA methylation as biomarkers of treatment response, data support this hypothesis for antipsychotics, mood stabilizers and antidepressants.

DNA Methylation and Psychiatric Disorders

DNA methylation has been an important area of research in the study of molecular mechanism to psychiatric disorders. Recent evidence has suggested that abnormalities in global methylation, methylation of genes, and pathways could play a role in the etiology of many forms of mental illness. In this article, we review the mechanisms of DNA methylation, including the genetic and environmental factors affecting methylation changes. We report and discuss major findings regarding DNA methylation in psychiatric patients, both within the context of global methylation studies and gene-specific methylation studies. Finally, we discuss issues surrounding data quality improvement, the limitations of current methylation analysis methods, and the possibility of using DNA methylation-based treatment for psychiatric disorders in the future.

DNA redox modulations and global DNA methylation in bipolar disorder: Effects of sex, smoking and illness state

DNA redox modulations and methylation have been associated with bipolar disorder (BD) pathophysiology. We aimed to investigate DNA redox modulation and global DNA methylation and demethylation levels in patients with BD during euthymia, mania or depression in comparison to non-psychiatric controls. The roles of sex and smoking as susceptibility factors for DNA redox modulations and global DNA methylation and demethylation were also explored. Levels of 5-methylcytosine (5-mC), 5-hydroxymethylcytosine (5-hmC) and 8-hydroxy-2'-deoxyguanosine (8-OHdG) were assessed in DNA samples of 75 patients with DSM-IV BD type I (37 euthymic, 18 manic, 20 depressive) in comparison to 60 non-psychiatric controls. Levels of 5-mC and 5-hmC were assessed using Dot Blot as a screening process, and verified using ELISA. Levels of 8-OHdG were assessed using ELISA. The levels of 8-OHdG significantly differed among non-psychiatric control, euthymia, mania and depression groups [F (3,110) = 2.771, p = 0.046], whereas there were no alterations in the levels of 5-hmC and 5-mC. Linear regression analyses revealed the significant effects of smoking (p = 0.031) and sex (p = 0.012) as well as state of illness on the levels of 8-OHdG (p = 0.025) in patients with BD. Our results suggest that levels of 8-OHdG may be affected by sex, illness states and smoking in BD.

Mechanisms Underpinning the Polypharmacy Effects of Medications in Psychiatry

BACKGROUND

Bipolar disorder is a mental health condition with progressive social and cognitive function disturbances. Most patients' treatments are based on polypharmacy, but with no biological basis and little is known of the drugs' interactions. The aim of this study was to analyze the effects of lithium, valproate, quetiapine, and lamotrigine, and the interactions between them, on markers of inflammation, bioenergetics, mitochondrial function, and oxidative stress in neuron-like cells and microglial cells.

METHODS

Neuron-like cells and lipopolysaccharide-stimulated C8-B4 cells were treated with lithium (2.5 mM), valproate (0.5 mM), quetiapine (0.05 mM), and lamotrigine (0.05 mM) individually and in all possible combinations for 24 h. Twenty cytokines were measured in the media from lipopolysaccharide-stimulated C8-B4 cells. Metabolic flux analysis was used to measure bioenergetics, and real-time PCR was used to measure the expression of mitochondrial function genes in neuron-like cells. The production of superoxide in treated cells was also assessed.

RESULTS

The results suggest major inhibitory effects on proinflammatory cytokine release as a therapeutic mechanism of these medications when used in combination. The various combinations of medications also caused overexpression of PGC1α and ATP5A1 in neuron-like cells. Quetiapine appears to have a proinflammatory effect in microglial cells, but this was reversed by the addition of lamotrigine independent of the drug combination.

CONCLUSION

Polypharmacy in bipolar disorder may have antiinflammatory effects on microglial cells as well as effects on mitochondrial biogenesis in neuronal cells.

Recent trends on the role of epigenomics, metabolomics and noncoding RNAs in rationalizing mood stabilizing treatment

Mood stabilizers are the cornerstone in treatment of mood disorders, but their use is characterized by high interindividual variability. This feature has stimulated intensive research to identify predictive biomarkers of response and disentangle the molecular bases of their clinical efficacy. Nevertheless, findings from studies conducted so far have only explained a small proportion of the observed variability, suggesting that factors other than DNA variants could be involved. A growing body of research has been focusing on the role of epigenetics and metabolomics in response to mood stabilizers, especially lithium salts. Studies from these approaches have provided new insights into the molecular networks and processes involved in the mechanism of action of mood stabilizers, promoting a systems-level multiomics synergy. In this article, we reviewed the literature investigating the involvement of epigenetic mechanisms, noncoding RNAs and metabolomic modifications in bipolar disorder and the mechanism of action and clinical efficacy of mood stabilizers.

Neurobiology of Risk for Bipolar Disorder

Bipolar disorder (BD) is a chronic mental illness which follows a relapsing and remitting course and requires lifetime treatment. The lack of biological markers for BD is a major difficulty in clinical practice. Exploring multiple endophenotypes to fit in multivariate genetic models for BD is an important element in the process of finding tools to facilitate early diagnosis, early intervention, prevention of new episodes, and follow-up of treatment response in BD. Reviewing of studies on neuroimaging, neurocognition, and biochemical parameters in populations with high genetic risk for the illness can yield an integrative perspective on the neurobiology of risk for BD. The most up-to-date data reveals consistent deficits in executive function, response inhibition, verbal memory/learning, verbal fluency, and processing speed in risk groups for BD. Functional magnetic resonance imaging (fMRI) studies report alterations in the activity of the inferior frontal gyrus, medial prefrontal cortex, and limbic areas, particularly in the amygdala in unaffected first-degree relatives (FDR) of BD compared to healthy controls. Risk groups for BD also present altered immune and neurochemical modulation. Despite inconsistencies, accumulating data reveals cognitive and imaging markers for risk and to a less extent resilience of BD. Findings on neural modulation markers are preliminary and require further studies. Although the knowledge on the neurobiology of risk for BD has been inadequate to provide benefits for clinical practice, further studies on structural and functional changes in the brain, neurocognitive functioning, and neurochemical modulation have a potential to reveal biomarkers for risk and resilience for BD. Multimodal, multicenter, population-based studies with large sample size allowing for homogeneous subgroup analyses will immensely contribute to the elucidation of biological markers for risk for BD in an integrative model.

Therapeutic Mechanisms of Lithium in Bipolar Disorder: Recent Advances and Current Understanding

Lithium is the most effective and well established treatment for bipolar disorder, and it has a broad array of effects within cellular pathways. However, the specific processes through which therapeutic effects occur and are maintained in bipolar disorder remain unclear. This paper provides a timely update to an authoritative review of pertinent findings that was published in CNS Drugs in 2013. A literature search was conducted using the Scopus database, and was limited by year (from 2012). There has been a resurgence of interest in lithium therapy mechanisms, perhaps driven by technical advancements in recent years that permit the examination of cellular mechanisms underpinning the effects of lithium-along with the reuptake of lithium in clinical practice. Recent research has further cemented glycogen synthase kinase 3β (GSK3β) inhibition as a key mechanism, and the inter-associations between GSK3β-mediated neuroprotective, anti-oxidative and neurotransmission mechanisms have been further elucidated. In addition to highly illustrative cellular research, studies examining higher-order biological systems, such as circadian rhythms, as well as employing innovative animal and human models, have increased our understanding of how lithium-induced changes at the cellular level possibly translate to changes at behavioural and clinical levels. Neural circuitry research is yet to identify clear mechanisms of change in bipolar disorder in response to treatment with lithium, but important structural findings have demonstrated links to the modulation of cellular mechanisms, and peripheral marker and pharmacogenetic studies are showing promising findings that will likely inform the exploration for predictors of lithium treatment response. With a deeper understanding of lithium's therapeutic mechanisms-from the cellular to clinical levels of investigation-comes the opportunity to develop predictive models of lithium treatment response and identify novel drug targets, and recent findings have provided important leads towards these goals.

The role of DNA methylation in the pathophysiology and treatment of bipolar disorder

Bipolar disorder (BD) is a multifactorial illness thought to result from an interaction between genetic susceptibility and environmental stimuli. Epigenetic mechanisms, including DNA methylation, can modulate gene expression in response to the environment, and therefore might account for part of the heritability reported for BD. This paper aims to review evidence of the potential role of DNA methylation in the pathophysiology and treatment of BD. In summary, several studies suggest that alterations in DNA methylation may play an important role in the dysregulation of gene expression in BD, and some actually suggest their potential use as biomarkers to improve diagnosis, prognosis, and assessment of response to treatment. This is also supported by reports of alterations in the levels of DNA methyltransferases in patients and in the mechanism of action of classical mood stabilizers. In this sense, targeting specific alterations in DNA methylation represents exciting new treatment possibilities for BD, and the 'plastic' characteristic of DNA methylation accounts for a promising possibility of restoring environment-induced modifications in patients.

The Neurobiology of Bipolar Disorder: An Integrated Approach

Bipolar disorder is a heterogeneous condition with myriad clinical manifestations and many comorbidities leading to severe disabilities in the biopsychosocial realm. The objective of this review article was to underline recent advances in knowledge regarding the neurobiology of bipolar disorder. A further aim was to draw attention to new therapeutic targets in the treatment of bipolar disorder. To accomplish these goals, an electronic search was undertaken of the PubMed database in August 2015 of literature published during the last 10 years on the pathophysiology of bipolar disorder. A wide-ranging evaluation of the existing work was done with search terms such as "mood disorders and biology," "bipolar disorder and HPA axis," "bipolar disorder and cytokines," "mood disorders and circadian rhythm," "bipolar disorder and oxidative stress," etc. This endeavor showed that bipolar disorder is a diverse condition sharing neurobiological mechanisms with major depressive disorder and psychotic spectrum disorders. There is convincing evidence of crosstalk between different biological systems that act in a deleterious manner causing expression of the disease in genetically predisposed individuals. Inflammatory mediators act in concert with oxidative stress to dysregulate hormonal, metabolic, and circadian homeostasis in precipitating and perpetuating the illness. Stress, whether biologically or psychologically mediated, is responsible for the initiation and progression of the diathesis. Bipolar spectrum disorders have a strong genetic component; severe life stresses acting through various paths cause the illness phenotype.

Mood Stabilizers and the Influence on Global Leukocyte DNA Methylation in Bipolar Disorder

Little is known about the relationship between treatments for bipolar disorder (BD), their therapeutic responses and the DNA methylation status. We investigated whether global DNA methylation levels differ between healthy controls and bipolar patients under different treatments. Global DNA methylation was measured in leukocyte DNA from bipolar patients under lithium monotherapy (n = 29) or combination therapy (n = 32) and from healthy controls (n = 26). Lithium response was assessed using the Alda scale. Lithium in monotherapy was associated with hypomethylation (F = 4.63, p = 0.036). Lithium + valproate showed a hypermethylated pattern compared to lithium alone (F = 7.27, p = 0.011). Lithium response was not associated with DNA methylation levels. These data suggest that the choice of treatment in BD may lead to different levels of global DNA methylation. However, further research is needed to understand its clinical significance.

An update on the epigenetics of psychotic diseases and autism

The examination of potential roles of epigenetic alterations in the pathogenesis of psychotic diseases have become an essential alternative in recent years as genetic studies alone are yet to uncover major gene(s) for psychosis. Here, we describe the current state of knowledge from the gene-specific and genome-wide studies of postmortem brain and blood cells indicating that aberrant DNA methylation, histone modifications and dysregulation of micro-RNAs are linked to the pathogenesis of mental diseases. There is also strong evidence supporting that all classes of psychiatric drugs modulate diverse features of the epigenome. While comprehensive environmental and genetic/epigenetic studies are uncovering the origins, and the key genes/pathways affected in psychotic diseases, characterizing the epigenetic effects of psychiatric drugs may help to design novel therapies in psychiatry.

In Pursuit of New Imprinting Syndromes by Epimutation Screening in Idiopathic Neurodevelopmental Disorder Patients

Alterations of epigenetic mechanisms, and more specifically imprinting modifications, could be responsible of neurodevelopmental disorders such as intellectual disability (ID) or autism together with other associated clinical features in many cases. Currently only eight imprinting syndromes are defined in spite of the fact that more than 200 genes are known or predicted to be imprinted. Recent publications point out that some epimutations which cause imprinting disorders may affect simultaneously different imprinted loci, suggesting that DNA-methylation may have been altered more globally. Therefore, we hypothesised that the detection of altered methylation patterns in known imprinting loci will indirectly allow identifying new syndromes due to epimutations among patients with unexplained ID. In a screening for imprinting alterations in 412 patients with syndromic ID/autism we found five patients with altered methylation in the four genes studied: MEG3, H19, KCNQ1OT1, and SNRPN. Remarkably, the cases with partial loss of methylation in KCNQ1OT1 and SNRPN present clinical features different to those associated with the corresponding imprinting syndromes, suggesting a multilocus methylation defect in accordance with our initial hypothesis. Consequently, our results are a proof of concept that the identification of epimutations in known loci in patients with clinical features different from those associated with known syndromes will eventually lead to the definition of new imprinting disorders.

Is depression associated with increased oxidative stress? A systematic review and meta-analysis

BACKGROUND

It has been suggested that depressed persons have increased oxidative stress and decreased anti-oxidant defences. 8-Hydroxy-2'-deoxyguanosine (8-OHdG) and F2-isoprostanes, measures of oxidative DNA and lipid damage respectively, are among the most reliable oxidative stress markers, but studies on their association with depression show conflicting results. This meta-analysis quantifies the association between depression and these markers and explores factors that may explain inconsistencies in the results.

METHODS

A systematic literature search was conducted in PubMed, EMBASE and PsycINFO. Studies assessing the association of 8-OHdG or F2-isoprostanes with elevated depressive symptoms, major depressive disorder (MDD) or bipolar disorder (BD) were pooled in two random-effect models.

RESULTS

The pooled effect size (Hedges' g) for the association of depression with oxidative stress was 0.31 (p=0.01, I(2)=75%) for 8-OHdG (10 studies, 1308 subjects) and 0.48 (p=0.001, I(2)=73%) for F2-isoprostanes (8 studies, 2471 subjects), indicating that both markers are increased in depression. There was no indication of publication bias for either marker. The F2-isoprostane results did not differ by type of depression, biological specimen, laboratory method or quality, however subgroup analyses in the 8-OHdG studies showed significantly stronger associations in plasma/serum vs. urine samples (p<0.01), in measurements performed with immuno-assay vs. chromatography-mass spectrometry (p<0.01) and weaker associations in high quality studies vs. low (p=0.02).

CONCLUSION

This meta-analysis finds that oxidative stress, as measured by 8-OHdG and F2-isoprostanes, is increased in depression. Larger-scale studies are needed to extend the evidence on oxidative stress in depression, and examine the potential impact of treatment.

Hypothalamic-pituitary-adrenal axis dysfunction and illness progression in bipolar disorder

BACKGROUND

Impaired stress resilience and a dysfunctional hypothalamic-pituitary-adrenal (HPA) axis are suggested to play key roles in the pathophysiology of illness progression in bipolar disorder (BD), but the mechanisms leading to this dysfunction have never been elucidated. This study aimed to examine HPA axis activity and underlying molecular mechanisms in patients with BD and unaffected siblings of BD patients.

METHODS

Twenty-four euthymic patients with BD, 18 siblings of BD patients, and 26 healthy controls were recruited for this study. All subjects underwent a dexamethasone suppression test followed by analyses associated with the HPA axis and the glucocorticoid receptor (GR).

RESULTS

Patients with BD, particularly those at a late stage of illness, presented increased salivary post-dexamethasone cortisol levels when compared to controls (p = 0.015). Accordingly, these patients presented reduced ex vivo GR responsiveness (p = 0.008) and increased basal protein levels of FK506-binding protein 51 (FKBP51, p = 0.012), a co-chaperone known to desensitize GR, in peripheral blood mononuclear cells. Moreover, BD patients presented increased methylation at the FK506-binding protein 5 (FKBP5) gene. BD siblings presented significantly lower FKBP51 protein levels than BD patients, even though no differences were found in FKBP5 basal mRNA levels.

CONCLUSIONS

Our data suggest that the epigenetic modulation of the FKBP5 gene, along with increased FKBP51 levels, is associated with the GR hyporesponsiveness seen in BD patients. Our findings are consistent with the notion that unaffected first-degree relatives of BD patients share biological factors that influence the disorder, and that such changes are more pronounced in the late stages of the illness.

Current state of biomarkers in bipolar disorder

Bipolar disorder (BD) is a chronic psychiatric illness of which the etiology remains unknown. Extensive research has provided some hypotheses for the pathophysiology of this disorder; however, there are no molecular tests available to help support the diagnosis obtained by self-report and behavioral observations. A major requirement is to identify potential biomarkers that could be used for early diagnosis in patients susceptible to the disease and for its treatment. The most recently published findings regarding alterations in BD were found to be related to oxidative stress, inflammatory and trophic factor deregulation, and also polymorphisms of genes that are associated with the development of BD. Many of these targets are potential biomarkers which could help to identify the BD subgroups and to advance treatment strategies, which would beneficiate the quality of life of these patients. Therefore, the main objective of this review is to examine the recent findings and critically evaluate their potential as biomarkers for BD.

Lithium reduces the effects of rotenone-induced complex I dysfunction on DNA methylation and hydroxymethylation in rat cortical primary neurons

RATIONALE

Mitochondrial complex I dysfunction and alterations in DNA methylation levels are consistently reported in bipolar disorder (BD) and are regulated by lithium. One of the mechanisms by which lithium may exert its effects in BD is by improving mitochondrial complex I function. Therefore, we examined whether complex I dysfunction induces methylation and hydroxymethylation of DNA and whether lithium alters these effects in rat primary cortical neurons.

METHODS

Rotenone was used to induce mitochondrial complex I dysfunction. Cell viability was measured by MTT assay, and ATP levels were assessed by Cell-Titer-Glo. Complex I activity was measured using an ELISA-based assay. Apoptosis, DNA methylation, and hydroxymethylation levels were measured by immunocytochemistry.

RESULTS

Rotenone decreased complex I activity and ATP production, but increased cell death and apoptosis. Rotenone treatment increased levels of 5-methylcytosine (5mc) and hydroxymethylcytosine (5hmc), suggesting a possible association between complex I dysfunction and DNA alterations. Lithium prevented rotenone-induced changes in mitochondrial complex I function, cell death and changes to DNA methylation and hydroxymethylation.

CONCLUSIONS

These findings suggest that decreased mitochondrial complex I activity may increase DNA methylation and hydroxymethylation in rat primary cortical neurons and that lithium may prevent these effects.

Glutathione-mediated effects of lithium in decreasing protein oxidation induced by mitochondrial complex I dysfunction

The aim of this study was to elucidate whether glutathione is involved in lithium's ability to decrease carbonylation and nitration produced by complex I inhibition, which is consistently found in BD. Neuroblastoma cells were treated with rotenone, a complex I inhibitor. Our results suggest that glutathione is essential for lithium's ability to ameliorate rotenone-induced protein carbonylation, but not nitration.

Potential molecular and cellular mechanism of psychotropic drugs

Psychiatric disorders are among the most debilitating of all medical illnesses. Whilst there are drugs that can be used to treat these disorders, they give sub-optimal recovery in many people and a significant number of individuals do not respond to any treatments and remain treatment resistant. Surprisingly, the mechanism by which psychotropic drugs cause their therapeutic benefits remain unknown but likely involves the underlying molecular pathways affected by the drugs. Hence, in this review, we have focused on recent findings on the molecular mechanism affected by antipsychotic, mood stabilizing and antidepressant drugs at the levels of epigenetics, intracellular signalling cascades and microRNAs. We posit that understanding these important interactions will result in a better understanding of how these drugs act which in turn may aid in considering how to develop drugs with better efficacy or increased therapeutic reach.