In-silico functional analyses identify TMPRSS15-mediated intestinal absorption of lithium as a modulator of lithium response in bipolar disorder

BACKGROUND

The therapeutic response to lithium in patients with bipolar disorder is highly variable and has a polygenic basis. Genome-wide association studies investigating lithium response have identified several relevant loci, though the precise mechanisms driving these associations are poorly understood. We aimed to prioritise the most likely effector gene and determine the mechanisms underlying an intergenic lithium response locus on chromosome 21 identified by the International Consortium on Lithium Genetics (ConLi+Gen).

METHODS

We conducted in-silico functional analyses by integrating and synthesising information from several publicly available functional genetic datasets and databases including the Genotype-Tissue Expression (GTEx) project and HaploReg.

RESULTS

The findings from this study highlighted TMPRSS15 as the most likely effector gene at the ConLi+Gen lithium response locus. TMPRSS15 encodes enterokinase, a gastrointestinal enzyme responsible for converting trypsinogen into trypsin and thus aiding digestion. Convergent findings from gene-based lookups in human and mouse databases as well as co-expression network analyses of small intestinal RNA-seq data (GTEx) implicated TMPRSS15 in the regulation of intestinal nutrient absorption, including ions like sodium and potassium, which may extend to lithium.

LIMITATIONS

Although the findings from this study indicated that TMPRSS15 was the most likely effector gene at the ConLi+Gen lithium response locus, the evidence was circumstantial. Thus, the conclusions from this study need to be validated in appropriately designed wet-lab studies.

CONCLUSIONS

The findings from this study are consistent with a model whereby TMPRSS15 impacts the efficacy of lithium treatment in patients with bipolar disorder by modulating intestinal lithium absorption.

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.

Longitudinal studies of bipolar patients and their families: translating findings to advance individualized risk prediction, treatment and research

BACKGROUND

Bipolar disorder is a broad diagnostic construct associated with significant phenotypic and genetic heterogeneity challenging progress in clinical practice and discovery research. Prospective studies of well-characterized patients and their family members have identified lithium responsive (LiR) and lithium non-responsive (LiNR) subtypes that hold promise for advancement.

METHOD

In this narrative review, relevant observations from published longitudinal studies of well-characterized bipolar patients and their families spanning six decades are highlighted. DSM diagnoses based on SADS-L interviews were decided in blind consensus reviews by expert clinicians. Genetic, neurobiological, and psychosocial factors were investigated in subsets of well-characterized probands and adult relatives. Systematic maintenance trials of lithium, antipsychotics, and lamotrigine were carried out. Clinical profiles that included detailed histories of the clinical course, symptom sets and disorders segregating in families were documented. Offspring of LiR and LiNR families were repeatedly assessed up to 20 years using KSADS-PL format interviews and DSM diagnoses and sub-threshold symptoms were decided by expert clinicians in blind consensus reviews using all available clinical and research data.

RESULTS

A characteristic clinical profile differentiated bipolar patients who responded to lithium stabilization from those who did not. The LiR subtype was characterized by a recurrent fully remitting course predominated by depressive episodes and a positive family history of episodic remitting mood disorders, and not schizophrenia. Response to lithium clustered in families and the characteristic clinical profile predicted lithium response, with the episodic remitting course being a strong correlate. There is accumulating evidence that genetic and neurobiological markers differ between LiR and LiNR subtypes. Further, offspring of bipolar parents subdivided by lithium response differed in developmental history, clinical antecedents and early course of mood disorders. Moreover, the nature of the emergent course bred true from parent to offspring, independent of the nature of emergent psychopathology.

CONCLUSIONS

Bipolar disorders are heterogeneous and response to long-term lithium is associated with a familial subtype with characteristic course, treatment response, family history and likely pathogenesis. Incorporating distinctive clinical profiles that index valid bipolar subtypes into routine practice and research will improve patient outcomes and advance the development and translation of novel treatment targets to improve prevention and early intervention.

Type of cycle, temperament and childhood trauma are associated with lithium response in patients with bipolar disorders

BACKGROUND

Lithium stands as the gold standard in treating bipolar disorders (BD). Despite numerous clinical factors being associated with a favorable response to lithium, comprehensive studies examining the collective influence of clinical variables alongside psychopathological dimensions are lacking. Our study aims to enhance comprehension of lithium response in individuals with BD by integrating clinical variables with psychopathological traits and early adverse events.

METHODS

We assessed 201 patients with BD for clinical characteristics, childhood trauma, temperament traits, impulsivity, and aggression. Lithium response was evaluated using the gold standard Alda scale, and predictors of lithium response were estimated through a multivariate model.

RESULTS

On the total sample, 61 (30.3%) patients were lithium responders according to the Alda scale. Comparatively, lithium responders, in contrast to non-responders, demonstrated a higher prevalence of the mania-depression-interval (MDI) cycle, a more frequent diagnosis of BD type I, and reported an earlier age of onset. They also exhibited less lifetime substance abuse, emotional, physical, and sexual abuse, while scoring higher on hyperthymic and irritable temperament scales. In multivariate analyses, only the MDI cycle (OR,3.47; 95%CI,1.61-7.50) hyperthymic (OR,1.20; 95%CI,1.02-1.41) and irritable temperament (OR,1.28; 95%CI,1.08-1.52) persisted as significant predictors of a positive response to lithium treatment, while emotional (OR,0.87; 95%CI,0.76-0.98) and physical abuse (OR,0.83; 95%CI,0.70-0.98) were predictors of non-response.

CONCLUSIONS

In evaluating lithium response in BD, our study highlights the importance of considering clinical variables alongside temperament and childhood adversities. The assessment of hyperthymic and irritable temperament, emotional and physical abuse together with the type of cycle is of particular importance. Furthermore, our findings underscore the significance of systematically assessing the type of cycle in patients with BD through the use of life charts.

Differential characteristics of bipolar I and II disorders: a retrospective, cross-sectional evaluation of clinical features, illness course, and response to treatment

BACKGROUND

The distinction between bipolar I and bipolar II disorder and its treatment implications have been a matter of ongoing debate. The aim of this study was to examine differences between patients with bipolar I and II disorders with particular emphasis on the early phases of the disorders.

METHODS

808 subjects diagnosed with bipolar I (N = 587) or bipolar II disorder (N = 221) according to DSM-IV criteria were recruited between April 1994 and March 2022 from tertiary-level mood disorder clinics. Sociodemographic and clinical variables concerning psychiatric and medical comorbidities, family history, illness course, suicidal behavior, and response to treatment were compared between the bipolar disorder types.

RESULTS

Bipolar II disorder patients were more frequently women, older, married or widowed. Bipolar II disorder was associated with later "bipolar" presentation, higher age at first (hypo)mania and treatment, less frequent referral after a single episode, and more episodes before lithium treatment. A higher proportion of first-degree relatives of bipolar II patients were affected by major depression and anxiety disorders. The course of bipolar II disorder was typically characterized by depressive onset, early depressive episodes, multiple depressive recurrences, and depressive predominant polarity; less often by (hypo)mania or (hypo)mania-depression cycles at onset or during the early course. The lifetime clinical course was more frequently rated as chronic fluctuating than episodic. More patients with bipolar II disorder had a history of rapid cycling and/or high number of episodes. Mood stabilizers and antipsychotics were prescribed less frequently during the early course of bipolar II disorder, while antidepressants were more common. We found no differences in global functioning, lifetime suicide attempts, family history of suicide, age at onset of mood disorders and depressive episodes, and lithium response.

CONCLUSIONS

Differences between bipolar I and II disorders are not limited to the severity of (hypo)manic syndromes but include patterns of clinical course and family history. Caution in the use of potentially mood-destabilizing agents is warranted during the early course of bipolar II disorder.

Decreased miR-15b-5p/miR-155-5p levels and increased miR-134-5p/miR-652-3p levels among BD patients under lithium treatment

BACKGROUND

There is an increasing interest about the role of miRNAs in the pathogenesis of bipolar disorder (BD). In this study, we aimed to examine the role of miRNAs as potential diagnostic and clinical biomarkers in BD.

METHODS

Fifteen miRNAs in plasmas obtained from BD patients (n = 66) and from the healthy control group (n = 66) were analyzed by a qPCR test. Clinical variables including lithium treatment response were assessed with various test batteries. The correlation of the miRNA levels with the clinical variables and scale scores was examined. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were performed using the DIANA-miRPath v.3.0 software to identify the possible target genes.

RESULTS

The miR-132, miR-134, miR-152, miR-607, miR-633, and miR-652 levels were significantly increased, whereas the miR-15b and miR-155 levels were found to be significantly decreased in the patient group compared to the controls. The miR-15b-5p and miR-155-5p levels and increases in the miR-134-5p and miR-652-3p levels were calculated to have 83.3 % sensitivity and 78.8 % specificity in determining the risk of BD. miR-155-5p was associated with the disease burden and severity. Fatty acid biosynthesis and metabolism, viral carcinogenesis, the EBV infection, and extracellular matrix and adhesion pathways were highlighted as target pathways.

CONCLUSION

We can conclude that miRNAs may play a role in the pathophysiology of BD through various biological pathways and that miRNAs may be used as a screening test to distinguish bipolar patients from healthy controls. Our findings will provide a basis for long-term follow-up studies with larger samples.

Association of Attention-Deficit/Hyperactivity Disorder and Depression Polygenic Scores with Lithium Response: A Consortium for Lithium Genetics Study

Response to lithium varies widely between individuals with bipolar disorder (BD). Polygenic risk scores (PRSs) can uncover pharmacogenomics effects and may help predict drug response. Patients (N = 2,510) with BD were assessed for long-term lithium response in the Consortium on Lithium Genetics using the Retrospective Criteria of Long-Term Treatment Response in Research Subjects with Bipolar Disorder score. PRSs for attention-deficit/hyperactivity disorder (ADHD), major depressive disorder (MDD), and schizophrenia (SCZ) were computed using lassosum and in a model including all three PRSs and other covariates, and the PRS of ADHD (β = -0.14; 95% confidence interval [CI]: -0.24 to -0.03; p value = 0.010) and MDD (β = -0.16; 95% CI: -0.27 to -0.04; p value = 0.005) predicted worse quantitative lithium response. A higher SCZ PRS was associated with higher rates of medication nonadherence (OR = 1.61; 95% CI: 1.34-1.93; p value = 2e-7). This study indicates that genetic risk for ADHD and depression may influence lithium treatment response. Interestingly, a higher SCZ PRS was associated with poor adherence, which can negatively impact treatment response. Incorporating genetic risk of ADHD, depression, and SCZ in combination with clinical risk may lead to better clinical care for patients with BD.

Genomic characterization and proteomic analysis of the halotolerant Micrococcus luteus SA211 in response to the presence of lithium

Micrococcus luteus SA211, isolated from the Salar del Hombre Muerto in Argentina, developed responses that allowed its survival and growth in presence of high concentrations of lithium chloride (LiCl). In this research, analysis of total genome sequencing and a comparative proteomic approach were performed to investigate the responses of this bacterium to the presence of Li. Through proteomic analysis, we found differentially synthesized proteins in growth media without LiCl (DM) and with 10 (D10) and 30 g/L LiCl (D30). Bi-dimensional separation of total protein extracts allowed the identification of 17 over-synthesized spots when growth occurred in D30, five in D10, and six in both media with added LiCl. The results obtained showed different metabolic pathways involved in the ability of M. luteus SA211 to interact with Li. These pathways include defense against oxidative stress, pigment and protein synthesis, energy production, and osmolytes biosynthesis and uptake. Furthermore, mono-dimensional gel electrophoresis revealed differential protein synthesis at equivalent NaCl and LiCl concentrations, suggesting that this strain would be able to develop different responses depending on the nature of the ion. Moreover, the percentage of proteins with acidic pI predicted and observed was highlighted, indicating an adaptation to saline environments. To the best of our knowledge, this is the first report showing the relationship between protein synthesis and genome sequence analysis in response to Li, showing the great biotechnological potential that native microorganisms present, especially those isolated from extreme environments.

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

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

Evidence towards RNA Binding Motif (RNP1, RRM) Protein 3 (RBM3) as a Potential Biomarker of Lithium Response in Bipolar Disorder Patients

Lithium has been used for more than six decades for the management of bipolar disorder (BD). In a previous transcriptomic study, we showed that patients affected by either BD or cluster headache, both disorders characterized by circadian disturbances and response to lithium in a subgroup of patients, have higher expression of the RNA binding motif (RNP1, RRM) protein 3 (RBM3) gene compared to controls. To investigate whether RBM3 could represent a biomarker of lithium response, we screened raw microarray expression data from lymphoblastoid cell lines (LCLs) derived from 20 BD patients, responders or non-responders to lithium. RBM3 was the most significantly differentially expressed gene in the list, being overexpressed in responders compared to non-responders (fold change = 2.0; p = 1.5 × 10^-16). We therefore sought to validate the microarray finding by quantitative reverse transcription polymerase chain reaction (RT-qPCR) and explore whether RBM3 expression was modulated by lithium treatment in vitro in LCLs as well as in human-derived neural progenitor cells (NPCs). Our findings confirmed the higher expression of RBM3 in responders compared to non-responders (fold change = 3.78; p = 0.0002). Lithium did not change RBM3 expression in LCLs in any of the groups, but it increased its expression in NPCs. While preliminary, our data suggest that higher levels of RBM3 might be required for better lithium response and that the expression of this gene could be modulated by lithium in a tissue-specific manner.

Bipolar disorder and socioeconomic status: what is the nature of this relationship?

Background

In psychiatric literature stretching over a century, there have been glaring discrepancies in the findings describing the relationship between bipolar disorder (BD) and socioeconomic status (SES). Early studies indicated an overall association between manic-depressive illness and higher social class. However, recent epidemiologic studies have failed to find an association between BD and SES. Instead, they report a similar distribution of BD among social classes and educational levels, and in one particular study, a lower family income was reported. The determinants of SES are complex, and the early findings are now interpreted as having been incorrect and stemming from past methodological weaknesses.

Methods

For this analysis we explored the relationship between SES and BD in a sample of patients who had participated in prior clinical and therapeutic studies. These patients met the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition criteria for BD, required long-term stabilizing treatment, and were assessed in terms of their response to lithium stabilization and a number of other clinical characteristics in accordance with research protocol. Good response to lithium stabilization (LiR) served as a proxy for identifying a subtype of manic-depressive illness, the classical form of BD. Non-responders to stabilizing lithium (LiNR) were considered belonging to other subtypes of bipolar spectrum disorder. The SES of the parents was measured upon entry into treatment using the Hollingshead SES scale, which despite its limitations has been used in psychiatry most widely to determine SES. The groups of LiR and LiNR were compared statistically in terms of SES. The influence of bipolar subtype and gender on SES was investigated.

Results and discussion

A significantly higher SES was associated with the lithium-responsive form (LiR) of BD when compared with patients continuing to relapse despite adequate lithium treatment (representing other types of bipolar spectrum). Our observation suggests that the discrepant literature findings about SES and BD may be better explained by the change in diagnostic practices: early studies describing a positive relationship included mostly classical manic-depressive disorder, while the patients in recent studies have been diagnosed according to much broader criteria, reflecting the era of bipolar spectrum disorder.