Nuclear receptor rev-erb-{alpha} circadian gene variants and lithium carbonate prophylaxis in bipolar affective disorder

Differential contributions of circadian clock genes to cell survival in bipolar disorder patient derived neuronal progenitor cells distinguishes lithium responders and non-responders

Bipolar disorder (BD) is characterized by disrupted circadian rhythms and neuronal loss. Lithium is neuroprotective and used to treat BD, but outcomes are variable. Past research identified that circadian rhythms in BD patient neurons are associated with lithium response (Li-R) or non-response (Li-NR). However, the underlying cellular mechanisms remain unknown. To study interactions among circadian clock genes and cell survival, and their role in BD and predicting lithium response, we tested selected genes (PER1, BMAL1 and REV-ERBα) and small molecule modulators of ROR/REV-ERB nuclear receptors in models of cell survival using mouse neurons and stem-cell derived neuronal progenitor cells (NPC) from BD patients and controls. In apoptosis assays using staurosporine (STS), lithium was neuroprotective. Knockdown of PER1, BMAL1 and REV-ERBα modified cell survival across models. In NPCs, reduced expression of PER1 and BMAL1 led to more extensive cell death in Li-NR vs. Li-R. Reduced REV-ERBα expression caused more extensive cell death in BD vs. control NPCs, without distinguishing Li-R and Li-NR. In IMHN, The REV-ERB agonist GSK4112 had strong effects on circadian rhythm amplitude, and was neuroprotective in mouse neurons and control NPCs, but not in BD NPCs. Expression of cell survival genes following STS and GSK4112 treatments revealed BD-associated, and Li-R associated differences in expression profiles. We conclude that the neuroprotective response to lithium is similar in NPCs from Li-R and Li-NR. However, knockdown of circadian clock genes or stimulation of REV-ERBs reveal distinct contributions to cell death in BD patient NPCs, some of which distinguish Li-R and Li-NR.

Insomnia and circadian rhythm: a bibliometrics study and visualization analysis via CiteSpace

Objective

The present study aimed to use CiteSpace to analyze the status of insomnia and circadian rhythm, identify the hot spots and trends, and provide a basis for future study.

Method

The Web of Science database was searched for studies related to insomnia and circadian from its inception to 14 April 2023. CiteSpace was used to generate online maps of collaboration between countries and authors and revealed hot spots and frontiers in insomnia and circadian rhythm.

Results

We searched 4,696 publications related to insomnia and circadian rhythm. Bruno Etain was the most prolific author with most publications, i.e., with 24 articles. The USA and the University of California were the leading country and the top institution in this field of study, with 1,672 and 269 articles, respectively. There was active cooperation between institutions, countries, and authors. Hot topics focused on circadian rhythm sleep disorders, circadian clock, light therapy, melatonin, and bipolar disorder.

Conclusion

Based on the CiteSpace results, we recommend a more active collaboration between various countries, institutions, and authors to conduct clinical and basic research related to insomnia and circadian rhythm. Ongoing research focuses on the interaction of insomnia with circadian rhythms and the corresponding pathways of clock genes and by extension, the role of circadian rhythms in disorders such as bipolar disorder. Modulation of circadian rhythms may be a hot spot for future insomnia therapies (such as light therapy and melatonin).

Correction of depression-associated circadian rhythm abnormalities is associated with lithium response in bipolar disorder

BACKGROUND

Bipolar disorder (BD) is characterized by episodes of depression and mania and disrupted circadian rhythms. Lithium is an effective therapy for BD, but only 30%-40% of patients are fully responsive. Preclinical models show that lithium alters circadian rhythms. However, it is unknown if the circadian rhythm effects of lithium are essential to its therapeutic properties.

METHODS

In secondary analyses of a multi-center, prospective, trial of lithium for BD, we examined the relationship between circadian rhythms and therapeutic response to lithium. Using standardized instruments, we measured morningness, diurnal changes in mood, sleep, and energy (circadian rhythm disturbances) in a cross-sectional study of 386 BD subjects with varying lithium exposure histories. Next, we tracked symptoms of depression and mania prospectively over 12 weeks in a subset of 88 BD patients initiating treatment with lithium. Total, circadian, and affective mood symptoms were scored separately and analyzed.

RESULTS

Subjects with no prior lithium exposure had the most circadian disruption, while patients stable on lithium monotherapy had the least. Patients who were stable on lithium with another drug or unstable on lithium showed intermediate levels of disruption. Treatment with lithium for 12 weeks yielded significant reductions in total and affective depression symptoms. Lithium responders (Li-Rs) showed improvement in circadian symptoms of depression, but non-responders did not. There was no difference between Li-Rs and nonresponders in affective, circadian, or total symptoms of mania.

CONCLUSIONS

Exposure to lithium is associated with reduced circadian disruption. Lithium response at 12 weeks was selectively associated with the reduction of circadian depressive symptoms. We conclude that stabilization of circadian rhythms may be an important feature of lithium's therapeutic effects.

CLINICAL TRIALS REGISTRY

NCT0127253.

Neurobiological and behavioral mechanisms of circadian rhythm disruption in bipolar disorder: A critical multi-disciplinary literature review and agenda for future research from the ISBD task force on chronobiology

AIM

Symptoms of bipolar disorder (BD) include changes in mood, activity, energy, sleep, and appetite. Since many of these processes are regulated by circadian function, circadian rhythm disturbance has been examined as a biological feature underlying BD. The International Society for Bipolar Disorders Chronobiology Task Force (CTF) was commissioned to review evidence for neurobiological and behavioral mechanisms pertinent to BD.

METHOD

Drawing upon expertise in animal models, biomarkers, physiology, and behavior, CTF analyzed the relevant cross-disciplinary literature to precisely frame the discussion around circadian rhythm disruption in BD, highlight key findings, and for the first time integrate findings across levels of analysis to develop an internally consistent, coherent theoretical framework.

RESULTS

Evidence from multiple sources implicates the circadian system in mood regulation, with corresponding associations with BD diagnoses and mood-related traits reported across genetic, cellular, physiological, and behavioral domains. However, circadian disruption does not appear to be specific to BD and is present across a variety of high-risk, prodromal, and syndromic psychiatric disorders. Substantial variability and ambiguity among the definitions, concepts and assumptions underlying the research have limited replication and the emergence of consensus findings.

CONCLUSIONS

Future research in circadian rhythms and its role in BD is warranted. Well-powered studies that carefully define associations between BD-related and chronobiologically-related constructs, and integrate across levels of analysis will be most illuminating.

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.

Determination of genetic changes of Rev-erb beta and Rev-erb alpha genes in Type 2 diabetes mellitus by next-generation sequencing

BACKGROUND

The nuclear receptors Rev-erb alpha and Rev-erb beta are transcription factors that regulate the function of genes in glucose and lipid metabolism, and they also form a link between circadian rhythm and metabolism. We evaluated the variations in Rev-erb alpha and Rev-erb beta genes together with biochemical parameters as risk factors in type 2 diabetic (T2DM) patients.

METHODS

Molecular analyses of Rev-erb alpha and Rev-erb beta genes were performed on genomic DNA by using next-generation sequencing in 42 T2DM patients (21 obese and 21 non-obese) and 66 healthy controls.

RESULTS

We found 26 rare mutations in the study groups, including 13 missense mutations, 9 silent mutations, 3 5'UTR variations, and a 3'UTR variation, of which 9 were novel variations (5 missense and 3 silent and 1 5'UTR). Six common variations were also found in the Rev-erb genes; Rev-erb beta Chr3:24003765 A > G, Rev-erb beta rs924403442 (Chr3:24006717) G > T, Rev-erb alpha Chr17:38253751 T > C, Rev-erb alpha rs72836608 C > A, Rev-erb alpha rs2314339 C > T and Rev-erb alpha rs2102928 C > T. Of these, Rev-erb beta Chr3:24003765 A > G was a novel missense mutation (p.Q197R), while others were identified as intronic variants. T2DM patients with Rev-erb beta rs924403442 T allele had lower body surface area (BSA) than noncarriers (GG genotype) (p = 0.039). Rev-erb alpha rs72836608 A allele and Rev-erb alpha rs2314339 CC genotype were associated with decreased serum HDL-cholesterol levels in T2DM patients (p = 0.025 and p = 0.027, respectively). In our study, different effects of Rev-erbs polymorphisms were found according to gender and presence of obesity. Rev-erb alpha rs72836608 (C > A) and rs2314339 (C > T) and Rev-erb alpha rs2102928 (C > T) were associated with low HDL-C levels in male T2DM patients. In female patients, Rev-erb alpha rs2102928 (C > T) was associated with high microalbuminuria and Rev-erb beta rs9244403442 G > T was associated with low HDL and high BSA values. In addition, Rev-erb alpha Chr17: 38,253,751 (T > C), rs72836608 (C > A), and rs2314339 (C > T) and Rev-erb beta Chr3:24003765 (A > G) were associated with increased serum GGT levels in obese T2DM patients. In non-obese patients, Rev-erbs SNPs had no effect on serum GGT levels.

CONCLUSION

Our findings indicate that variations in the Rev-erb alpha and Rev-erb beta genes can affect metabolic changes in T2DM and these effects may vary depending on gender and obesity.

Pharmacogenomic Characterization in Bipolar Spectrum Disorders

The holistic approach of personalized medicine, merging clinical and molecular characteristics to tailor the diagnostic and therapeutic path to each individual, is steadily spreading in clinical practice. Psychiatric disorders represent one of the most difficult diagnostic challenges, given their frequent mixed nature and intrinsic variability, as in bipolar disorders and depression. Patients misdiagnosed as depressed are often initially prescribed serotonergic antidepressants, a treatment that can exacerbate a previously unrecognized bipolar condition. Thanks to the use of the patient's genomic profile, it is possible to recognize such risk and at the same time characterize specific genetic assets specifically associated with bipolar spectrum disorder, as well as with the individual response to the various therapeutic options. This provides the basis for molecular diagnosis and the definition of pharmacogenomic profiles, thus guiding therapeutic choices and allowing a safer and more effective use of psychotropic drugs. Here, we report the pharmacogenomics state of the art in bipolar disorders and suggest an algorithm for therapeutic regimen choice.

Twenty years of Lithium pharmacogenetics: A systematic review

Lithium is among the best proven treatments for patients diagnosed with Bipolar Disorder, however response to Lithium appears to be considerably variable among individuals and it has been suggested that this inconstancy in Lithium response could be genetically determined. Starting from this perspective, in the last few decades, a number of pharmacogenetic studies have attempted to identify genetic variants, which might be associated with response to Lithium in bipolar patients, in order to develop a pharmacogenetics test to tailor treatment on patients, identifying who will benefit the most from therapy with Lithium. Within this context, authors have critically reviewed pharmacogenetic studies of Lithium response in bipolar disorder, suggesting strategies for future work in this field. Computerized searches of PubMed and Embase databases, for studies published between 1998 and January 2018, was performed: 1162 studies were identified but only 37 relevant papers were selected for detailed review. Despite some interesting preliminary findings, the pharmacogenetics of Lithium and the development of a specific pharmacogenetics test in bipolar disorder appears to be a field still in its infancy, even though the advent of genome-wide association studies holds particular promise for future studies, which should include larger samples.

Prediction of Response to Drug Therapy in Psychiatric Disorders

Reprinted with permission from Open Biol. 8: 180031. The Royal Society.

Prediction of response to drug therapy in psychiatric disorders

Personalized medicine has become increasingly relevant to many medical fields, promising more efficient drug therapies and earlier intervention. The development of personalized medicine is coupled with the identification of biomarkers and classification algorithms that help predict the responses of different patients to different drugs. In the last 10 years, the Food and Drug Administration (FDA) has approved several genetically pre-screened drugs labelled as pharmacogenomics in the fields of oncology, pulmonary medicine, gastroenterology, haematology, neurology, rheumatology and even psychiatry. Clinicians have long cautioned that what may appear to be similar patient-reported symptoms may actually arise from different biological causes. With growing populations being diagnosed with different psychiatric conditions, it is critical for scientists and clinicians to develop precision medication tailored to individual conditions. Genome-wide association studies have highlighted the complicated nature of psychiatric disorders such as schizophrenia, bipolar disorder, major depression and autism spectrum disorder. Following these studies, association studies are needed to look for genomic markers of responsiveness to available drugs of individual patients within the population of a specific disorder. In addition to GWAS, the advent of new technologies such as brain imaging, cell reprogramming, sequencing and gene editing has given us the opportunity to look for more biomarkers that characterize a therapeutic response to a drug and to use all these biomarkers for determining treatment options. In this review, we discuss studies that were performed to find biomarkers of responsiveness to different available drugs for four brain disorders: bipolar disorder, schizophrenia, major depression and autism spectrum disorder. We provide recommendations for using an integrated method that will use available techniques for a better prediction of the most suitable drug.

The Role of Pharmacogenomics in Bipolar Disorder: Moving Towards Precision Medicine

Bipolar disorder (BD) is a common and disabling psychiatric condition with a severe socioeconomic impact. BD is treated with mood stabilizers, among which lithium represents the first-line treatment. Lithium alone or in combination is effective in 60% of chronically treated patients, but response remains heterogenous and a large number of patients require a change in therapy after several weeks or months. Many studies have so far tried to identify molecular and genetic markers that could help us to predict response to mood stabilizers or the risk for adverse drug reactions. Pharmacogenetic studies in BD have been for the most part focused on lithium, but the complexity and variability of the response phenotype, together with the unclear mechanism of action of lithium, limited the power of these studies to identify robust biomarkers. Recent pharmacogenomic studies on lithium response have provided promising findings, suggesting that the integration of genome-wide investigations with deep phenotyping, in silico analyses and machine learning could lead us closer to personalized treatments for BD. Nevertheless, to date none of the genes suggested by pharmacogenetic studies on mood stabilizers have been included in any of the genetic tests approved by the Food and Drug Administration (FDA) for drug efficacy. On the other hand, genetic information has been included in drug labels to test for the safety of carbamazepine and valproate. In this review, we will outline available studies investigating the pharmacogenetics and pharmacogenomics of lithium and other mood stabilizers, with a specific focus on the limitations of these studies and potential strategies to overcome them. We will also discuss FDA-approved pharmacogenetic tests for treatments commonly used in the management of BD.

Lithium response in bipolar disorders and core clock genes expression

OBJECTIVES

We examine whether the lithium response is associated with changes in the expression of core clock genes.

METHODS

The effect of a therapeutic concentration of lithium (1 mM) on the expression levels of 17 circadian genes was examined in lymphoblastoid cell lines (LCLs) derived from two well-characterized groups of bipolar disorder patients, defined as lithium non-responders (NR, n = 20) or excellent responders (ER, n = 16). Quantitative real-time PCR (qRT-PCR) was conducted at 2, 4 and 8 days (d2, d4 and d8) with and without lithium exposure.

RESULTS

At d2, in ER only, BHLHE41, RORA, PER1, ARNTL, CRY2, BHLHE40 and CSNK1D were upregulated, whereas NR1D1 was downregulated. At d4, in ER only, CRY1 was downregulated. At d8, in NR only, GSK3β was upregulated and DBP, TIMELESS and CRY1 were downregulated. Significant Group × Lithium interactions existed for NR1D1 at d2 (P = 0.02), and CRY1 at d4 (P = 0.02). Longitudinal analyses showed differential temporal evolutions between NR and ER (significant Time × Group interaction) for PER3, NR1D1, DBP, RORA, CSNK1D and TIMELESS; and a significant Time × Lithium interaction for NR1D1. Coexpression data analyses suggested distinct groups of circadian genes concurrently modulated by lithium.

CONCLUSIONS

In LCLs, lithium influences expression of circadian genes with differences in amplitude and kinetics according to the patient's lithium response status.

Genetic polymorphisms associated with circadian rhythm dysregulation provide new perspectives on bipolar disorder

OBJECTIVES

The objective of this study was to present a broad view of how genetic polymorphisms in genes that control the rhythmicity and function of circadian rhythm may influence the etiology, pathophysiology and treatment of bipolar disorder (BD).

METHODS

A bibliographic search was performed to identify and select papers reporting studies on variations in circadian genes and BD. A search of Medline, Google Scholar, Scopus, and Web of Science was carried out to review the literature.

RESULTS

Several studies provide evidence of contributions of variations in circadian genes to disease etiology, pathophysiological variations and lithium drug response. Dysfunction of the sleep-wake cycle, an important brain function regulator, is indicated as the primary means by which circadian gene variations act in mood disorders.

CONCLUSIONS

Investigations of the effects of circadian genes have suggested that the chronotype offers hope for guiding and improving management of patients with BD. However, BD is a disease of a complex nature and presents multiple endophenotypes determined by different associations between genetics and the environment. Thus, new genomic studies to delimit variations that may help improve the clinical condition of these patients are extremely important.

Pharmacogenomic aspects of bipolar disorder: An update

The hopes for readily implementable precision medicine are high. For many complex disorders, such as bipolar disorder, these hopes critically hinge on tangible successes in pharmacogenetics of treatment response or susceptibility to adverse events. In this article, we review the current state of pharmacogenomics of bipolar disorder including latest results from candidate genes and genome-wide association studies. The majority of studies focus on response to lithium treatment. Although a host of genes has been studied, hardly any replicated findings have emerged so far. Very small samples sizes and heterogeneous phenotype definition may be considered the major impediments to success in this field. Drawing from current experiences and successes in studies on diagnostic psychiatric phenotypes, we suggest several approaches for our way forward.

Lithium in the treatment of bipolar disorder: pharmacology and pharmacogenetics

After decades of research, the mechanism of action of lithium in preventing recurrences of bipolar disorder remains only partially understood. Lithium research is complicated by the absence of suitable animal models of bipolar disorder and by having to rely on in vitro studies of peripheral tissues. A number of distinct hypotheses emerged over the years, but none has been conclusively supported or rejected. The common theme emerging from pharmacological and genetic studies is that lithium affects multiple steps in cellular signaling, usually enhancing basal and inhibiting stimulated activities. Some of the key nodes of these regulatory networks include GSK3 (glycogen synthase kinase 3), CREB (cAMP response element-binding protein) and Na(+)-K(+) ATPase. Genetic and pharmacogenetic studies are starting to generate promising findings, but remain limited by small sample sizes. As full responders to lithium seem to represent a unique clinical population, there is inherent value and need for studies of lithium responders. Such studies will be an opportunity to uncover specific effects of lithium in those individuals who clearly benefit from the treatment.

Investigation of associations between NR1D1, RORA and RORB genes and bipolar disorder

Several genes that are involved in the regulation of circadian rhythms are implicated in the susceptibility to bipolar disorder (BD). The current study aimed to investigate the relationships between genetic variants in NR1D1 RORA, and RORB genes and BD in the Han Chinese population. We conducted a case-control genetic association study with two samples of BD patients and healthy controls. Sample I consisted of 280 BD patients and 200 controls. Sample II consisted of 448 BD patients and 1770 healthy controls. 27 single nucleotide polymorphisms in the NR1D1, RORA, and RORB genes were genotyped using GoldenGate VeraCode assays in sample I, and 492 markers in the three genes were genotyped using Affymetrix Genome-Wide CHB Array in sample II. Single marker and gene-based association analyses were performed using PLINK. A combined p-value for the joining effects of all markers within a gene was calculated using the rank truncated product method. Multifactor dimensionality reduction (MDR) method was also applied to test gene-gene interactions in sample I. All markers were in Hardy-Weinberg equilibrium (P>0.001). In sample I, the associations with BD were observed for rs4774388 in RORA (OR = 1.53, empirical p-value, P = 0.024), and rs1327836 in RORB (OR = 1.75, P = 0.003). In Sample II, there were 45 SNPs showed associations with BD, and the most significant marker in RORA was rs11639084 (OR = 0.69, P = 0.002), and in RORB was rs17611535 (OR = 3.15, P = 0.027). A combined p-value of 1.6×10−6, 0.7, and 1.0 was obtained for RORA, RORB and NR1D1, respectively, indicting a strong association for RORA with the risk of developing BD. A four way interaction was found among markers in NR1D1, RORA, and RORB with the testing accuracy 53.25% and a cross-validation consistency of 8 out of 10. In sample II, 45 markers had empirical p-values less than 0.05. The most significant markers in RORA and RORB genes were rs11639084 (OR = 0.69, P = 0.002), and rs17611535 (OR = 3.15, P = 0.027), respectively. Gene-based association was significant for RORA gene (P = 0.0007). Our results support for the involvement of RORs genes in the risk of developing BD. Investigation of the functional properties of genes in the circadian pathway may further enhance our understanding about the pathogenesis of bipolar illness.

Sleep- and circadian rhythm-associated pathways as therapeutic targets in bipolar disorder

INTRODUCTION

Disruptions in sleep and circadian rhythms are observed in individuals with bipolar disorders (BD), both during acute mood episodes and remission. Such abnormalities may relate to dysfunction of the molecular circadian clock and could offer a target for new drugs.

AREAS COVERED

This review focuses on clinical, actigraphic, biochemical and genetic biomarkers of BDs, as well as animal and cellular models, and highlights that sleep and circadian rhythm disturbances are closely linked to the susceptibility to BDs and vulnerability to mood relapses. As lithium is likely to act as a synchronizer and stabilizer of circadian rhythms, we will review pharmacogenetic studies testing circadian gene polymorphisms and prophylactic response to lithium. Interventions such as sleep deprivation, light therapy and psychological therapies may also target sleep and circadian disruptions in BDs efficiently for treatment and prevention of bipolar depression.

EXPERT OPINION

We suggest that future research should clarify the associations between sleep and circadian rhythm disturbances and alterations of the molecular clock in order to identify critical targets within the circadian pathway. The investigation of such targets using human cellular models or animal models combined with 'omics' approaches are crucial steps for new drug development.

Nuclear receptor Rev-erbα: up, down, and all around

Rev-erbα is a nuclear receptor that links circadian rhythms to transcriptional control of metabolic pathways. Rev-erbα is a potent transcriptional repressor and plays an important role in the core mammalian molecular clock while also serving as a key regulator of clock output in metabolic tissues including liver and brown adipose tissue (BAT). Recent findings have shed new light on the role of Rev-erbα and its paralog Rev-erbβ in rhythm generation, as well as additional regulatory roles for Rev-erbα in other tissues that contribute to energy expenditure, inflammation, and behavior. This review highlights physiological functions of Rev-erbα and β in multiple tissues and discusses the therapeutic potential and challenges of targeting these pathways in human disease.

Response to lithium in bipolar disorder: clinical and genetic findings

The use of lithium is a cornerstone for preventing recurrences in bipolar disorder (BD). The response of patients with bipolar disorder to lithium has different levels of magnitude. About one-third of lithium-treated patients are excellent lithium responders (ELR), showing total prevention of the episodes. A number of clinical characteristics were delineated in patients with favorable response to lithium as regards to clinical course, family history of mood disorders, and psychiatric comorbidity. We have also demonstrated that temperamental features of hypomania (a hyperthymic temperament) and a lack of cognitive disorganization predict the best results of lithium prophylaxis. A degree of prevention against manic and depressive episodes has been regarded as an endophenotype for pharmacogenetic studies. The majority of data have been gathered from so-called "candidate" gene studies. The candidates were selected on the basis of neurobiology of bipolar disorder and mechanisms of lithium action including, among others, neurotransmission, intracellular signaling, neuroprotection or circadian rhythms. We demonstrated that response to lithium has been connected with the genotype of BDNF gene and serum BDNF levels and have shown that ELR have normal cognitive functions and serum BDNF levels, even after long-term duration of the illness. A number of genome-wide association studies (GWAS) of BD have been also performed in recent years, some of which also focused on lithium response. The Consortium on Lithium Genetics (ConLiGen) has established the large sample for performing the genome-wide association study (GWAS) of lithium response in BD, and the first results have already been published.

Polymorphism of circadian clock genes and prophylactic lithium response

OBJECTIVES

The therapeutic action of lithium in bipolar mood disorder may be connected with its effect on biological rhythms. In the present study, an attempt was made to investigate an association between multiple single nucleotide polymorphisms (SNPs) and their haplotypes pertaining to four genes involved in regulation of biological rhythms [circadian locomotor output cycle kaput (CLOCK), aryl hydrocarbon receptor nuclear translocator-like (ARNTL), timeless circadian clock (TIMELESS), period circadian clock 3 (PER 3)], and the efficacy of lithium prophylaxis.

METHODS

The study was performed on 115 patients with bipolar mood disorder (45 males, 70 females) with a mean age of 52 ± 12 years, with lithium prophylaxis for 22 ± 8 years, recruited from the outpatients in the Department of Psychiatry, Poznan University of Medical Sciences. The assessment of the lithium prophylactic response was made retrospectively using the Alda scale. Genotyping was done for nine SNPs of the CLOCK gene, 18 SNPs of the ARNTL gene, six SNPs of the timeless circadian clock (TIM) gene, and nine SNPs of the PER3 gene.

RESULTS

An association with the degree of lithium prophylaxis was found for six SNPs and three haplotype blocks of the ARNTL gene, and two SNPs and one haplotype block of the TIM gene. No association with SNPs or haplotypes of the CLOCK and PER3 genes was observed.

CONCLUSIONS

The results suggest that the ARNTL and TIM genes may be associated with the lithium prophylactic response in bipolar illness. This association may be related to the role of these genes in the predisposition to bipolar mood disorder. Of special interest may be polymorphisms of these genes involved both in the predisposition to bipolar mood disorder and the lithium response.

Molecular actions and clinical pharmacogenetics of lithium therapy

Mood disorders, including bipolar disorder and depression, are relatively common human diseases for which pharmacological treatment options are often not optimal. Among existing pharmacological agents and mood stabilizers used for the treatment of mood disorders, lithium has a unique clinical profile. Lithium has efficacy in the treatment of bipolar disorder generally, and in particular mania, while also being useful in the adjunct treatment of refractory depression. In addition to antimanic and adjunct antidepressant efficacy, lithium is also proven effective in the reduction of suicide and suicidal behaviors. However, only a subset of patients manifests beneficial responses to lithium therapy and the underlying genetic factors of response are not exactly known. Here we discuss preclinical research suggesting mechanisms likely to underlie lithium's therapeutic actions including direct targets inositol monophosphatase and glycogen synthase kinase-3 (GSK-3) among others, as well as indirect actions including modulation of neurotrophic and neurotransmitter systems and circadian function. We follow with a discussion of current knowledge related to the pharmacogenetic underpinnings of effective lithium therapy in patients within this context. Progress in elucidation of genetic factors that may be involved in human response to lithium pharmacology has been slow, and there is still limited conclusive evidence for the role of a particular genetic factor. However, the development of new approaches such as genome-wide association studies (GWAS), and increased use of genetic testing and improved identification of mood disorder patients sub-groups will lead to improved elucidation of relevant genetic factors in the future.

Pharmacogenomics of bipolar disorder

Bipolar disorder (BD) is a lifelong severe psychiatric condition with high morbidity, disability and excess mortality. The longitudinal clinical trajectory of BD is significantly modified by pharmacological treatment(s), both in acute and in long-term stages. However, a large proportion of BD patients have inadequate response to pharmacological treatments. Pharmacogenomic research may lead to the identification of molecular predictors of treatment response. When integrated with clinical information, pharmacogenomic findings may be used in the future to determine the probability of response/nonresponse to treatment on an individual basis. Here we present a selective review of pharmacogenomic findings in BD. In light of the evidence suggesting a genetic effect of lithium reponse in BD, we focused particularly on the pharmacogenomic literature relevant to this trait. The article contributes a detailed overview of the current status of pharmacogenomics in BD and offers a perspective on the challenges that can hinder its transition to personalized healthcare.

Circadian rhythms in liver physiology and liver diseases

In mammals, circadian rhythms function to coordinate a diverse panel of physiological processes with environmental conditions such as food and light. As the driving force for circadian rhythmicity, the molecular clock is a self-sustained transcription-translational feedback loop system consisting of transcription factors, epigenetic modulators, kinases/phosphatases, and ubiquitin E3 ligases. The molecular clock exists not only in the suprachiasmatic nuclei of the hypothalamus but also in the peripheral tissues to regulate cellular and physiological function in a tissue-specific manner. The circadian clock system in the liver plays important roles in regulating metabolism and energy homeostasis. Clock gene mutant animals display impaired glucose and lipid metabolism and are susceptible to diet-induced obesity and metabolic dysfunction, providing strong evidence for the connection between the circadian clock and metabolic homeostasis. Circadian-controlled hepatic metabolism is partially achieved by controlling the expression and/or activity of key metabolic enzymes, transcription factors, signaling molecules, and transporters. Reciprocally, intracellular metabolites modulate the molecular clock activity in response to the energy status. Although still at the early stage, circadian clock dysfunction has been implicated in common chronic liver diseases. Circadian dysregulation of lipid metabolism, detoxification, reactive oxygen species (ROS) production, and cell-cycle control might contribute to the onset and progression of liver steatosis, fibrosis, and even carcinogenesis. In summary, these findings call for a comprehensive study of the function and mechanisms of hepatic circadian clock to gain better understanding of liver physiology and diseases.

REV-ERB-ALPHA circadian gene variant associates with obesity in two independent populations: Mediterranean and North American

SCOPE

Despite the solid connection between REV-ERB and obesity, the information about whether genetic variations at this locus may be associated with obesity traits is scarce. Therefore our objective was to study the association between REV-ERB-ALPHA1 rs2314339 and obesity in two independent populations.

METHODS AND RESULTS

Participants were 2214 subjects from Spanish Mediterranean (n = 1404) and North American (n = 810) populations. Anthropometric, biochemical, dietary, and genotype analyses were performed. We found novel associations between the REV-ERB-ALPHA1 rs2314339 genotype and obesity in two independent populations: in Spanish Mediterranean and North American groups, the frequency of the minor-allele-carriers (AA+ AG) was significantly lower in the "abdominally obese" group than in those of the "nonabdominally obese" group (p < 0.05). Minor allele carriers had lower probability of abdominal obesity than noncarriers, and the effect was of similar magnitude for both populations (OR ≈ 1.50). There were consistent associations between REV-ERB-ALPHA1 genotype and obesity-related traits (p < 0.05). Energy intake was not significantly associated with REV-ERB-ALPHA1 rs2314339. However, physical activity significantly differed by genotype. A significant interaction between the REV-ERB-ALPHA1 variant and monounsaturated-fatty-acids (MUFA) intake for obesity was also detected in the Mediterranean population.

CONCLUSION

This new discovery highlights the importance of REV-ERB-ALPHA1 in obesity and provides evidence for the connection between our biological clock and obesity-related traits.

Genetic and clinical factors predict lithium's effects on PER2 gene expression rhythms in cells from bipolar disorder patients

Bipolar disorder (BD) is associated with abnormal circadian rhythms. In treatment responsive BD patients, lithium (Li) stabilizes mood and reduces suicide risk. Li also affects circadian rhythms and expression of 'clock genes' that control them. However, the extent to which BD, Li and the circadian clock share common biological mechanisms is unknown, and there have been few direct measurements of clock gene function in samples from BD patients. Hence, the role of clock genes in BD and Li treatment remains unclear. Skin fibroblasts from BD patients (N=19) or healthy controls (N=19) were transduced with Per2::luc, a rhythmically expressed, bioluminescent circadian clock reporter gene, and rhythms were measured for 5 consecutive days. Rhythm amplitude and period were compared between BD cases and controls with and without Li. Baseline period was longer in BD cases than in controls. Li 1 mM increased amplitude in controls by 36%, but failed to do so in BD cases. Li 10 mM lengthened period in both BD cases and controls. Analysis of clock gene variants revealed that PER3 and RORA genotype predicted period lengthening by Li, whereas GSK3β genotype predicted rhythm effects of Li, specifically among BD cases. Analysis of BD cases by clinical history revealed that cells from past suicide attempters were more likely to show period lengthening with Li 1 mM. Finally, Li enhanced the resynchronization of damped rhythms, suggesting a mechanism by which Li could act therapeutically in BD. Our work suggests that the circadian clock's response to Li may be relevant to molecular pathology of BD.

Diversity of human clock genotypes and consequences

The molecular clock consists of a number of genes that form transcriptional and posttranscriptional feedback loops, which function together to generate circadian oscillations that give rise to circadian rhythms of our behavioral and physiological processes. Genetic variations in these clock genes have been shown to be associated with phenotypic effects in a repertoire of biological processes, such as diurnal preference, sleep, metabolism, mood regulation, addiction, and fertility. Consistently, rodent models carrying mutations in clock genes also demonstrate similar phenotypes. Taken together, these studies suggest that human clock-gene variants contribute to the phenotypic differences observed in various behavioral and physiological processes, although to validate this requires further characterization of the molecular consequences of these polymorphisms. Investigating the diversity of human genotypes and the phenotypic effects of these genetic variations shall advance our understanding of the function of the circadian clock and how we can employ the clock to improve our overall health.

Genetic influences on response to mood stabilizers in bipolar disorder: current status of knowledge

Mood stabilizers form a cornerstone in the long-term treatment of bipolar disorder. The first representative of their family was lithium, still considered a prototype drug for the prevention of manic and depressive recurrences in bipolar disorder. Along with carbamazepine and valproates, lithium belongs to the first generation of mood stabilizers, which appeared in psychiatric treatment in the 1960s. Atypical antipsychotics with mood-stabilizing properties and lamotrigine, which were introduced in the mid-1990 s, form the second generation of such drugs. The response of patients with bipolar disorder to mood stabilizers has different levels of magnitude. About one-third of lithium-treated patients are excellent responders, showing total prevention of the episodes, and these patients are clinically characterized by an episodic clinical course, complete remission, a bipolar family history, low psychiatric co-morbidity and a hyperthymic temperament. It has been suggested that responders to carbamazepine or lamotrigine may differ clinically from responders to lithium. The main phenotype of the response to mood stabilizers is a degree of prevention against recurrences of manic and depressive episodes during long-term treatment. The most specific scale in this respect is the so-called Alda scale, where retrospective assessment of lithium response is scored on a 0-10 scale. The vast majority of data on genetic influences on the response to mood stabilizers has been gathered in relation to lithium. The studies on the mechanisms of action of lithium and on the neurobiology of bipolar disorder have led to the identification of a number of candidate genes. The genes studied for their association with lithium response have been those connected with neurotransmitters (serotonin, dopamine and glutamate), second messengers (phosphatidyl inositol [PI], cyclic adenosine-monophosphate [cAMP] and protein kinase C [PKC] pathways), substances involved in neuroprotection (brain-derived neurotrophic factor [BDNF] and glycogen synthase kinase 3-β [GSK-3β]) and a number of other miscellaneous genes. There are no published pharmacogenomic studies of mood stabilizers other than lithium, except for one study of the X-box binding protein 1 (XBP1) gene in relation to the efficacy of valproate. In recent years, a number of genome-wide association studies (GWAS) in bipolar disorders have been performed and some of those have also focused on lithium response. They suggest roles for the glutamatergic receptor AMPA (GRIA2) gene and the amiloride-sensitive cation channel 1 neuronal (ACCN1) gene in long-term lithium response. A promise for better elucidating the genetics of lithium response has been created by the formation of the Consortium on Lithium Genetics (ConLiGen) to establish the largest sample, to date, for the GWAS of lithium response in bipolar disorder. The sample currently comprises more than 1,200 patients, characterized by their response to lithium treatment according to the Alda scale. Preliminary results from this international study suggest a possible involvement of the sodium bicarbonate transporter (SLC4A10) gene in lithium response. It is concluded that the pharmacogenetics of response to mood stabilizers has recently become a growing field of research, especially so far as the pharmacogenetics of the response to lithium is concerned. Clearly, the ConLiGen project is a highly significant step in this research. Although the results of pharmacogenetic studies are of significant scientific value, their possible practical implications are yet to be seen.

Cellular Circadian Clocks in Mood Disorders

Bipolar disorder (BD) and major depressive disorder (MDD) are heritable neuropsychiatric disorders associated with disrupted circadian rhythms. The hypothesis that circadian clock dysfunction plays a causal role in these disorders has endured for decades but has been difficult to test and remains controversial. In the meantime, the discovery of clock genes and cellular clocks has revolutionized our understanding of circadian timing. Cellular circadian clocks are located in the suprachiasmatic nucleus (SCN), the brain’s primary circadian pacemaker, but also throughout the brain and peripheral tissues. In BD and MDD patients, defects have been found in SCN-dependent rhythms of body temperature and melatonin release. However, these are imperfect and indirect indicators of SCN function. Moreover, the SCN may not be particularly relevant to mood regulation, whereas the lateral habenula, ventral tegmentum, and hippocampus, which also contain cellular clocks, have established roles in this regard. Dysfunction in these non-SCN clocks could contribute directly to the pathophysiology of BD/MDD. We hypothesize that circadian clock dysfunction in non-SCN clocks is a trait marker of mood disorders, encoded by pathological genetic variants. Because network features of the SCN render it uniquely resistant to perturbation, previous studies of SCN outputs in mood disorders patients may have failed to detect genetic defects affecting non-SCN clocks, which include not only mood-regulating neurons in the brain but also peripheral cells accessible in human subjects. Therefore, reporters of rhythmic clock gene expression in cells from patients or mouse models could provide a direct assay of the molecular gears of the clock, in cellular clocks that are likely to be more representative than the SCN of mood-regulating neurons in patients. This approach, informed by the new insights and tools of modern chronobiology, will allow a more definitive test of the role of cellular circadian clocks in mood disorders.

Impact of REV-ERB alpha gene polymorphisms on obesity phenotypes in adult and adolescent samples

BACKGROUND

REV-ERBα has been shown to regulate adipogenesis and lipid metabolism as well as to link the circadian timing system to whole body metabolic homeostasis. We thus tested whether polymorphisms in REV-ERBα could be associated with metabolic phenotypes in human population samples.

METHODS

We analyzed the associations between 5 REV-ERBα polymorphisms and anthropometric (body weight, body mass index (BMI), waist and hip circumferences), biochemical (plasma lipid, glucose and insulin levels) and clinical (systolic and diastolic blood pressure) variables in three population-based studies (MONICA Lille n=1155 adults, MONA LISA Lille n=1170 adults and HELENA n=1155 adolescents). We assessed in vitro, the potential influence of one REV-ERBα polymorphism in transient transfection assays using two different cell lines.

RESULTS

We observed significant and consistent associations between the T minor allele of the REV-ERBα rs2071427 polymorphism (located in intron 1) and higher BMI (mean allele effect=+0.33 kg m(-2)) in the MONICA Lille (P=0.02), MONA LISA (P=0.02) and HELENA (P=0.03) studies. The odds ratios for obesity associated with this allele were 1.67 (1.00-2.79) (P=0.05) in MONICA Lille, 1.29 (1.01-1.65) (P=0.04) in MONA LISA Lille and the odds ratio for overweight was 1.48 (1.08-2.03) (P=0.01) in HELENA. In transfection experiments in human hepatocyte-derived cell lines, the REV-ERBα intron 1 directed the transcription of a luciferase reporter gene independently of the rs2071427 polymorphism.

CONCLUSION

Our results suggest that the REV-ERBα rs2071427 polymorphism modulates body fat mass in both adult and young people.

Pharmacogenetics of lithium response in bipolar disorder

Bipolar disorder (BD) is a serious mental illness with well-established, but poorly characterized genetic risk. Lithium is among the best proven mood stabilizer therapies for BD, but treatment responses vary considerably. Based upon these and other findings, it has been suggested that lithium-responsive BD may be a genetically distinct phenotype within the mood disorder spectrum. This assertion has practical implications both for the treatment of BD and for understanding the neurobiological basis of the illness: genetic variation within lithium-sensitive signaling pathways may confer preferential treatment response, and the involved genes may underlie BD in some individuals. Presently, the mechanism of lithium is reviewed with an emphasis on gene-expression changes in response to lithium. Within this context, findings from genetic-association studies designed to identify lithium response genes in BD patients are evaluated. Finally, a framework is proposed by which future pharmacogenetic studies can incorporate advances in genetics, molecular biology and bioinformatics in a pathway-based approach to predicting lithium treatment response.

Functional genetic variation in the Rev-Erbα pathway and lithium response in the treatment of bipolar disorder

Bipolar disorder (BD) is characterized by disruptions in circadian rhythms such as sleep and daily activity that often normalize after lithium treatment in responsive patients. As lithium is known to interact with the circadian clock, we hypothesized that variation in circadian 'clock genes' would be associated with lithium response in BD. We determined genotype for 16 variants in seven circadian clock genes and conducted a candidate gene association study of these in 282 Caucasian patients with BD who were previously treated with lithium. We found that a variant in the promoter of NR1D1 encoding Rev-Erbα (rs2071427) and a second variant in CRY1 (rs8192440) were nominally associated with good treatment response. Previous studies have shown that lithium regulates Rev-Erbα protein stability by inhibiting glycogen synthase kinase 3β (GSK3β). We found that GSK3β genotype was also suggestive of a lithium response association, but not statistically significant. However, when GSK3β and NR1D1 genotypes were considered together, they predicted lithium response robustly and additively in proportion to the number of response-associated alleles. Using lymphoblastoid cell lines from patients with BD, we found that both the NR1D1 and GSK3β variants are associated with functional differences in gene expression. Our findings support a role for Rev-Erbα in the therapeutic mechanism of lithium and suggest that the interaction between Rev-Erbα and GSK3β may warrant further study.

Circadian biomarkers, circadian genes and bipolar disorders

Bipolar disorders are associated with circadian deregulations both during acute mood episodes and during euthymic periods, suggesting that these circadian rhythms may represent trait markers of the disease. Several arguments demonstrate that deregulations of circadian rhythms may be part of the pathophysiology of bipolar disorders. Abnormal quantitative and qualitative circadian disturbances have been repeatedly showed in bipolar patients, both during euthymic periods and acute phases, using different assessment tools such as actigraphy, polysomnography, and blood melatonin monitoring. In addition, many circadian physiological functions have been demonstrated to be altered in bipolar patients, such as secretion of hormones and other endogenous substances, core temperature, and fibroblasts activity. Furthermore, mood stabilizers efficiency could partially be explained by their impact on the regulation of the circadian rhythms. The implication of genetic vulnerability factors has long been demonstrated in bipolar disorders and several circadian genes have been tested for association in bipolar disorders. Although preliminary, interesting results have been obtained in several independent studies.

Response to treatment in bipolar disorder

PURPOSE OF REVIEW

Bipolar disorder is a complex psychiatric condition that has been shown to carry a great degree of genetic loading. This review addresses current research in the genetics of treatment response in bipolar disorder, with a focus on findings that have shaped our understanding of the changing direction of this field in light of recent technological advancements.

RECENT FINDINGS

The recent publications in bipolar disorder treatment response have helped consolidate or improve upon knowledge of susceptibility loci and genes in the field. There seems to be an increasing trend toward functionally assessing the role played by putative candidate genes and molecular factors modulating expression in bipolar disorder, as well as a movement toward more global, pathway and genome-wide-oriented research.

SUMMARY

Genetic and molecular research to date in bipolar disorder treatment response has not completely answered all the lingering questions in the field, but has contributed to the development of a more patient-based understanding of treatment. In order to apply these findings at a clinical level, more comprehensive treatment response studies are imperative, combining recent advances in high-throughput genomics with functional molecular research.