Lipid Biomarker Research in Bipolar Disorder: A Scoping Review of Trends, Challenges, and Future Directions

Bipolar disorder (BD) is a disabling disorder with heterogeneous symptom profiles and trajectories. Like many other neuropsychiatric disorders, clinical decision making related to diagnoses and choice of treatment is based on clinical assessments alone, and risk prediction for treatment success or resistance at an individual level remains sparse. An enormous effort to add biological markers to this risk prediction is ongoing. The role of lipids in normal brain functioning is well established, and several hypotheses about the role of lipids in the pathogenesis of neuropsychiatric disorders, including BD, have been made. The frequent comorbidity between neuropsychiatric disorders and cardiovascular disease, the genetic overlap of risk genes for severe mental disorders and genes involved in lipid regulation, and the lipid-altering effects of antipsychotics and mood stabilizers indicate that lipids could hold promise as biomarkers for neuropsychiatric disorders, including BD. To date, reviews of lipid biomarkers in schizophrenia and major depression have noted caveats for future investigations, while reviews of lipid biomarker research in BD is missing. In the current scoping review, we present a comprehensive overview of trends in previous research on lipid biomarkers in BD. The current literature varies greatly in the phenotypes investigated and study designs, leading to divergent findings. Small sample size; potential confounders related to physical activity, nutritional status, and medication use; and cross-sectional designs were frequently reported limitations. Future research may benefit from pivoting toward utilization of newer laboratory techniques such as lipidomics, but consistent use of study methods across cohorts is also needed.

Predicting the diagnosis of various mental disorders in a mixed cohort using blood-based multi-protein model: a machine learning approach

The lack of objective diagnostic methods for mental disorders challenges the reliability of diagnosis. The study aimed to develop an easily accessible and useable objective method for diagnosing major depressive disorder (MDD), schizophrenia (SZ), bipolar disorder (BPD), and panic disorder (PD) using serum multi-protein. Serum levels of brain-derived neurotrophic factor (BDNF), VGF (non-acronymic), bicaudal C homolog 1 (BICC1), C-reactive protein (CRP), and cortisol, which are generally recognized to be involved in different pathogenesis of various mental disorders, were measured in patients with MDD (n = 50), SZ (n = 50), BPD (n = 55), and PD along with 50 healthy controls (HC). Linear discriminant analysis (LDA) was employed to construct a multi-classification model to classify these mental disorders. Both leave-one-out cross-validation (LOOCV) and fivefold cross-validation were applied to validate the accuracy and stability of the LDA model. All five serum proteins were included in the LDA model, and it was found to display a high overall accuracy of 96.9% when classifying MDD, SZ, BPD, PD, and HC groups. Multi-classification accuracy of the LDA model for LOOCV and fivefold cross-validation (within-study replication) reached 96.9 and 96.5%, respectively, demonstrating the feasibility of the blood-based multi-protein LDA model for classifying common mental disorders in a mixed cohort. The results suggest that combining multiple proteins associated with different pathogeneses of mental disorders using LDA may be a novel and relatively objective method for classifying mental disorders. Clinicians should consider combining multiple serum proteins to diagnose mental disorders objectively.

Heightened inflammation in bipolar disorder occurs independent of symptom severity and is explained by body mass index

Inflammation is hypothesized to be a key component of bipolar disorder (BP) development and progression. However, findings linking BP prevalence and symptomology to immune functioning have been mixed, with some work suggesting that obesity may play an important role in BP-relevant inflammation. Here we investigate differences in biomarkers of inflammation [C-reactive protein (CRP), interleukin (IL)-1β, IL-6, IL-8, IL-10] between healthy controls (HC) and individuals with BP or other mental illness (MI). Adults with BP, MI, or HC (n = 545, 70% BP, 21% HC, 9% MI) self-reported depressive and manic symptoms close to a blood draw and physical exam that included measurement of height and weight. A composite score was calculated from the four cytokines measured in plasma; follow-up analyses explored a pro-inflammatory composite and IL-10, individually. BP individuals had elevated cytokine concentrations compared to HC (B = 0.197, [0.062, 0.333], t (542) = 2.855, p = .004); this difference was also evident for the pro-inflammatory composite and for IL-10. Cytokine concentrations were not associated with BP mood states. Body mass index (BMI), an indicator of obesity, was significantly higher in BP compared to HC (B = 3.780, [2.118, 5.443], t (479) = 4.457, p < .001) and differences in cytokines between the two groups was no longer significant after controlling for BMI. No differences in CRP were evident between BP and HC. These results suggest that cytokine concentrations are elevated in BP and this difference from HC is associated with obesity. Interventions targeting immune modulators in BP must carefully consider the complex relationships within the BP-inflammation-obesity triangle.

Comparative efficacy, acceptability, and tolerability of adjunctive anti-inflammatory agents on bipolar disorder: A systemic review and network meta-analysis

OBJECTIVES

We performed a network meta-analysis (NMA) with up-to-date evidence to compare different anti-inflammatory agents to improve the treatment of bipolar disorder (BD) patients.

METHODS

Four databases (i.e., the Cochrane Library, Web of Science, PubMed, and Embase) were searched for randomized controlled trials (RCTs) published between 1995 and 2022 on the use of anti-inflammatory agents in the treatment of BD. A systematic review and NMA were conducted.

RESULTS

Adjunctive N-acetylcysteine (NAC) was superior to placebo for the treatment of BD according to the endpoint scale score (SMD -0.65, 95% confidence interval (CI): - 0.99 to - 0.31), response rate (odds ratio (OR) 3.42, 95% CI: 1.23-9.52), remission rate (OR 4.94, 95% CI: 1.03-41.38) and surface under the cumulative ranking curve (SUCRA) value of the endpoint scale score (0.84). Adjunctive nonsteroidal anti-inflammatory drugs (NSAIDs) were more favorable than placebo based on the remission rate (OR 3.93, 95% CI: 1.15-13.43) and were significantly more acceptable than other treatments (OR 0.60, 95% CI: 0.36-0.99). Adjunctive coenzyme Q10 (CoQ10) was superior to other agents in terms of the response rate (OR 18.85, 95% CI: 2.63-135.00), with a SUCRA value for the response rate of 0.90 and that for the remission rate of 0.71.

CONCLUSION

Adjunctive NAC is recommended for the treatment of BD. Adjunctive NSAIDs and CoQ10 are still seen as effective, but more high-quality clinical studies are needed to verify their efficacy. Other anti-inflammatory agents may not be recommended for clinical use at present. All anti-inflammatory agents demonstrated a good safety profile. We call for further research on the combined treatment of BD with different anti-inflammatory agents to be included in future trials.

Effect of quetiapine on inflammation and immunity: a systematic review

INTRODUCTION

Knowledge about the neurobiology of psychiatric disorders is increasing in the last decades and evidence from literature suggests a central role for immuno-inflammatory mechanisms in these illnesses. The antipsychotic quetiapine acts on dopamine and serotonin signalling and well-established evidence demonstrates that these neurotransmitters can modulate immune functions in healthy and diseased conditions. Starting from this perspective, in the last few decades, a number of studies attempted to identify quetiapine effects on immune functions in order to highlight a possible additional effect of this drug in psychotic diseases, although no conclusive results were obtained.

METHODS

We critically reviewed preclinical and clinical studies evaluating quetiapine effects on immune systems, suggesting strategies for future work in this field.

RESULTS

Computerised search, in PubMed and Embase databases, was performed in March 2020: 120 studies were identified but only 29 relevant papers were selected for detailed review.

CONCLUSION

Despite some interesting preliminary findings about anti-inflammatory effects of quetiapine, mainly supported by preclinical studies, it is possible to conclude further studies are needed to investigate the immunomodulatory effects of this drug and achieve a better understanding of its relevance on clinical outcomes to finally identify new therapeutic approaches in psychiatric treatment.KeypointsMounting evidence points to a role for immuno-inflammatory mechanisms in psychiatric disorders.Quetiapine (QUE) acts on catecholamine (dopamine and norepinephrine) and serotonin signalling.The immunomodulatory effects of catecholamines are well established.Treatment with QUE in psychiatric disorders could leverage immunomodulatory effects.QUE unclear role in immune function modulation suggests future work.

Elevated atherogenic lipid profile in youth with bipolar disorder during euthymia and hypomanic/mixed but not depressive states

OBJECTIVE

Abnormal blood lipid levels are common in individuals with bipolar disorder (BD). Previous studies have revealed lipid-mood associations in adults with BD, but no data on this relationship is available in youth populations. This cross-sectional study examined the associations of lipid levels with mood states and symptoms in a cohort of youth with BD.

METHODS

Participants were youth with BD and healthy controls (HCs) between the ages of 13-20 years. We compared the levels of total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), triglycerides (TG), and TG/HDL-C ratio between 4 participant episode groups: BD-euthymic (n = 28), BD-depressed (n = 29) BD-hypomanic/mixed (n = 31), and HCs (n = 89). We also examined for dimensional associations of lipids with mania and depression scores in the overall BD group and within BD episode subgroups.

RESULTS

TG levels were significantly higher in the BD-euthymic group (p = 0.008, d = 0.59) and in the BD-mixed/hypomanic group (p = 0.03, d = 0.44) compared to the HC group. TG/HDL-C ratio was also higher in the BD-euthymic group compared to the HC group (p = 0.01, d = 0.51). No dimensional associations were found between lipids and mood symptom scores in the overall BD group. However, within the BD-mixed/hypomanic subgroup, higher mania scores were associated with higher TG (β = 0.42, p = 0.04), TG/HDL-C ratio (β = 0.59, p = 0.002), and lower HDL-C (β = 0.56 p = 0.002).

CONCLUSIONS

Youth with BD demonstrate atherogenic lipid profiles. Higher atherogenic lipids were associated with hypomanic but, contrasting adult BD studies, not depressive symptoms. Future prospective studies are warranted to evaluate the temporal association between lipids and mood among youth with BD.

Elevated C-reactive protein among symptomatic youth with bipolar disorder

RATIONALE AND OBJECTIVES

Increased levels of high-sensitivity C-reactive protein (CRP) are associated with mood symptoms in adults with bipolar disorder (BD). The few studies on this topic in youth with BD have not included controls. We, therefore, examined CRP levels in relation to symptomatic status in youth with and without BD.

METHODS

Participants included 154 youth (mean age 17 years; 48 asymptomatic BD, 39 symptomatic BD, 67 healthy controls (HC)). Rank analysis of covariance test examined group differences in CRP, controlling for age and sex. Correlation between CRP and mood symptom severity was examined using Spearman's correlation within the BD group.

RESULTS

There were significant group differences in CRP levels (F_(2,151) = 5.06, p = 0.007, ηp2=0.06); post hoc analyses showed higher CRP levels in the symptomatic BD group compared with HC (p = 0.01). In sensitivity analyses, this finding was no longer significant after controlling for body mass index (BMI). CRP was not significantly associated with symptomatic severity.

CONCLUSIONS

CRP levels are elevated among symptomatic youth with BD, partly related to BMI. As elevated BMI is associated with mood symptom burden, prospective studies are warranted to parse the associations among mood symptoms, BMI, and inflammation. Given the proportion of time that youth with BD are symptomatic, present findings raise concern about the long-term impact of elevated CRP on blood vessels, brain, and related clinical outcomes.

The Relationships between Abnormal Serum Lipid Levels, Depression, and Suicidal Ideation According to Sex

(1) Background: Serum lipid levels affect not only nutritional status but also emotional state. The purpose of this study was to examine the effects of various socio-demographic characteristics, abnormal cholesterol levels, and BMI indicators on depressive symptoms and suicidal ideation in the Korean population. (2) Methods: A total of 23,692 people were surveyed using data from the Korea National Health and Nutrition Examination Survey (KNHNES) 2014, 2016, and 2018. Data from 11,653 patients were analyzed. Age, sex, chronic disease, smoking, alcohol consumption, total cholesterol (HDL, triglycerides), BMI, depression, and suicidal ideation were measured. (3) Results: According to sex, low HDL, high triglycerides, and suicidal ideation were significant, along with low education level, smoking, binge drinking, and high BMI. High triglyceride level was shown to significantly increase the risk of depression in males (OR = 1.535, 95% CI = 1.098–2.147). Factors affecting suicidal ideation in males were age, binge drinking, and depression, while blood lipid factors were not significant. (4) Conclusions: Of the types of serum lipid factors affecting depression and suicidal ideation, high triglycerides were found to be a risk factor for depression in men. Serum lipids can be used as biomarkers to reflect depressive symptoms in men depending on cholesterol level.

Association between abnormal glycolipid level and cognitive dysfunction in drug-naïve patients with bipolar disorder

OBJECTIVES

Cognitive impairment and abnormal glycolipid metabolism are common clinical features of bipolar disorder (BD). The purpose of this study was to investigate the relationship between conventional glycolipid metabolism indicators and cognitive impairment in patients with BD.

METHODS

A total of 132 drug-naïve patients with BD and 129 healthy controls (HC) were recruited in the study. Five serum glycolipid metabolism indicators were measured and cognitive function was assessed using the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) and the Stroop Color-Word Test (Stroop test) for each participant.

RESULTS

The scores of immediate memory, attention, language and delayed memory in BD group were significantly lower than those in HC group (P < 0.05). The triglyceride (TG) level in BD group was higher than that in HC group (P = 0.011), and the total cholesterol and high-density lipoprotein cholesterol (HDL) levels were lower than those in HC group (P = 0.026; P = 0.001). Regression analysis showed that TG level was significantly correlated with RBANS total score (β = 0.245, P = 0.008), attention (β = 0.289, P = 0.03) and delayed memory (β = 0.221, P = 0.023). Fasting blood glucose (FBG) level was significantly correlated with language subscale score (β = -0.187, P = 0.046) in BD.

LIMITATIONS

Cross-sectional design and limited control variables.

CONCLUSIONS

Elevated FBG and TG levels may be associated with cognitive dysfunction in BD patients. Improving glycolipid metabolism in patients with BD may help to improve certain domain-specific cognitive functions.

Peripheral levels of C-reactive protein, tumor necrosis factor-α, interleukin-6, and interleukin-1β across the mood spectrum in bipolar disorder: A meta-analysis of mean differences and variability

IMPORTANCE

It is unclear whether differences exist in the magnitude and variability of pro-inflammatory mediators in the different phases of bipolar disorder (BD) and among subjects with BD, as compared to healthy controls.

OBJECTIVE

To run a comparative meta-analysis of C-Reactive Protein (CRP), IL-1, IL-6, TNF-α in BD vs healthy controls, measuring mean and variability effects on all subjects. Sensitivity analyses include disease activity.

DATA SOURCES

Systematic review of observational studies in PubMed and PsycInfo up to February 2nd, 2020.

STUDY SELECTION

Case-control studies reporting inflammatory mediators' levels in BD and controls.

DATA EXTRACTION AND SYNTHESIS

Summary distribution measures of circulating CRP, IL-1β, IL-6, TNF-α in participants with BD and control groups were extracted. Random-effects multivariate meta-analyses were conducted based on individual study/mediator effect sizes (Hedge's g).

MAIN OUTCOMES AND MEASURES

Co-primary outcomes were inflammatory mediators' levels (Hedge's g) and variability (coefficient of variance ratio (CVR)) differences between participants with BD across the mood spectrum and controls.

RESULTS

Out of the initial 729 papers, 72 were assessed and then excluded after full-text review, and ultimately 53 studies were included in the systematic review, while 49 were included in the meta-analysis. The mean age was 36.96 (SD: 9.29) years, and the mean female percentage was 56.31 (SD: 16.61). CRP (g = 0.70, 95% CI 0.31-1.09, k = 37, BD = 2,215 vs HC = 3,750), IL-6 (g = 0.81, 95% CI 0.46-1.16, k = 45, BD = 1,956 vs HC = 4,106), TNF-α (g = 0.49, 95% CI 0.19-0.78, k = 49, BD = 2,231 vs HC = 3,017) were elevated in subjects with BD vs HC, but not IL-1β (g = -0.28, 95% CI -0.68-0.12, k = 4, BD = 87 vs HC = 66). When considering euthymic, depressive, and manic episodes separately, CRP and TNF-α were elevated in both depressive and manic episodes, but not in euthymia, while IL-6 remained elevated regardless of the disease state. No difference in CVR emerged for CRP, IL-1β, and TNF-α, while a lower CVR was observed for IL-6. When considering disease phases, CVR was higher in BD than in HCs for CRP during depressive episodes, lower for IL-6 during euthymia, and higher during manic episodes for CRP, IL-6, and TNF-α. Sensitivity analyses after excluding outliers identified with funnel plot visual inspection, low-quality studies, and considering only studies matched per body mass index confirmed the main results. Meta-regression showed that age (IL-6, TNF-α), gender (CRP), duration of illness (CRP) moderated elevated individual inflammatory levels.

CONCLUSIONS AND RELEVANCE

Peripheral pro-inflammatory marker elevations were confirmed in BD. CRP and TNF-α could represent state markers, as they were only elevated during mood episodes, while IL-6 appeared to be a trait marker for BD. Increased variability of specific inflammatory mediators in specific disease active states suggests that a subset of subjects with BD may exhibit elevated inflammation as part of a manic or depressive episode.

Longitudinal association between CRP levels and risk of psychosis: a meta-analysis of population-based cohort studies

Meta-analyses of cross-sectional studies suggest that patients with psychosis have higher circulating levels of C-reactive protein (CRP) compared with healthy controls; however, cause and effect is unclear. We examined the prospective association between CRP levels and subsequent risk of developing a psychotic disorder by conducting a systematic review and meta-analysis of population-based cohort studies. Databases were searched for prospective studies of CRP and psychosis. We obtained unpublished results, including adjustment for age, sex, body mass index, smoking, alcohol use, and socioeconomic status and suspected infection (CRP > 10 mg/L). Based on random effect meta-analysis of 89,792 participants (494 incident cases of psychosis at follow-up), the pooled odds ratio (OR) for psychosis for participants with high (>3 mg/L), as compared to low (≤3 mg/L) CRP levels at baseline was 1.50 (95% confidence interval [CI], 1.09-2.07). Evidence for this association remained after adjusting for potential confounders (adjusted OR [aOR] = 1.31; 95% CI, 1.03-1.66). After excluding participants with suspected infection, the OR for psychosis was 1.36 (95% CI, 1.06-1.74), but the association attenuated after controlling for confounders (aOR = 1.23; 95% CI, 0.95-1.60). Using CRP as a continuous variable, the pooled OR for psychosis per standard deviation increase in log(CRP) was 1.11 (95% CI, 0.93-1.34), and this association further attenuated after controlling for confounders (aOR = 1.07; 95% CI, 0.90-1.27) and excluding participants with suspected infection (aOR = 1.07; 95% CI, 0.92-1.24). There was no association using CRP as a categorical variable (low, medium or high). While we provide some evidence of a longitudinal association between high CRP (>3 mg/L) and psychosis, larger studies are required to enable definitive conclusions.

Subsequent Dyslipidemia and Factors Associated with Mortality in Schizophrenia: A Population-Based Study in Taiwan

Background: Persons with schizophrenia are at greater risk of developing subsequent medical conditions. To date, few studies have examined comprehensively the risks, mortality and survival rates in schizophrenia and subsequent dyslipidemia over different time periods. The objective of this study was to evaluate the occurrence of subsequent dyslipidemia after the diagnosis of schizophrenia, and factors associated with mortality and survival rate in patients with schizophrenia. Methods: We used a population-based cohort from Taiwan National Health Insurance Research Database, to investigate in patients whom were first diagnosed with schizophrenia during the period from 1997 through 2009, the risk of subsequent dyslipidemia during follow-up. Cumulative incidences and hazard ratios after adjusting for competing mortality risks were calculated. Results: A total of 20,964 eligible patients were included. Risks (i.e., comorbidity) and protective factors (i.e., statin use) have significant impacts on mortality. The mortality exhibits a U-shaped pattern by age. After 50, the risk of death increases with age. Risk of mortality before 50 increases with a decrease in age. Risks differed by the duration time to subsequent dyslipidemia after schizophrenia. Mean duration was 63.55 months in the survive group, and 43.19 months in the deceased group. The 5-, 10-, and 15-year survival rates for patients with schizophrenia and subsequent dyslipidemia were 97.5, 90, and 79.18%, respectively. Conclusion: Early occurrence of subsequent dyslipidemia is associated with increased overall mortality in patients with schizophrenia.

A peripheral inflammatory signature discriminates bipolar from unipolar depression: A machine learning approach

BACKGROUND

Mood disorders (major depressive disorder, MDD, and bipolar disorder, BD) are considered leading causes of life-long disability worldwide, where high rates of no response to treatment or relapse and delays in receiving a proper diagnosis (~60% of depressed BD patients are initially misdiagnosed as MDD) contribute to a growing personal and socio-economic burden. The immune system may represent a new target to develop novel diagnostic and therapeutic procedures but reliable biomarkers still need to be found.

METHODS

In our study we predicted the differential diagnosis of mood disorders by considering the plasma levels of 54 cytokines, chemokines and growth factors of 81 BD and 127 MDD depressed patients. Clinical diagnoses were predicted also against 32 healthy controls. Elastic net models, including 5000 non-parametric bootstrapping procedure and inner and outer 10-fold nested cross-validation were performed in order to identify the signatures for the disorders.

RESULTS

Results showed that the immune-inflammatory signature classifies the two disorders with a high accuracy (AUC = 97%), specifically 92% and 86% respectively for MDD and BD. MDD diagnosis was predicted by high levels of markers related to both pro-inflammatory (i.e. IL-1β, IL-6, IL-7, IL-16) and regulatory responses (IL-2, IL-4, and IL-10), whereas BD by high levels of inflammatory markers (CCL3, CCL4, CCL5, CCL11, CCL25, CCL27, CXCL11, IL-9 and TNF-α).

CONCLUSIONS

Our findings provide novel tools for early diagnosis of BD, strengthening the impact of biomarkers research into clinical practice, and new insights for the development of innovative therapeutic strategies for depressive disorders.

Malondialdehyde and bipolar disorder: A short comprehensive review of available literature

BACKGROUND

The pathogenetic mechanisms of Bipolar Disorder (BD) have not been totally clarified. Oxidative stress seems to be involved in the etiology of BD, and malondialdehyde (MDA) represents a candidate biomarker for monitoring this aspect in different medical conditions including mood disorders. This article has the objective to critically summarize the available data about the association between MDA and BD.

METHODS

A research in Pubmed, PsycINFO and Isi Web of Knowledge was fulfilled to identify studies in which MDA levels were measured in BD patients for the purpose of securing a comprehensive review concerning the issue.

RESULTS

We detected 20 articles that satisfied the inclusion criteria: most of them observed higher MDA levels (or Thiobarbituric acid-reactive substances-TBARS) in BD patients compared to healthy controls (HC), although there are some contrasting results, depending in particular on the phase of illness or the inclusion criteria or the methodological differences.

LIMITATIONS

We included studies, exclusively in English, that used different laboratory methods to measure MDA.

CONCLUSIONS

The analysed articles suggest that MDA or TBARS are increased in BD patients with respect to HC, thus supporting the hypothesis that MDA may be a promising and potential biomarker to monitor the course of BD, although further studies are needed to confirm this hypothesis.

Inflammation as a Mechanism of Bipolar Disorder Neuroprogression

Bipolar disorder (BD) is a severe, debilitating psychiatric condition with onset in adolescence or young adulthood and often follows a relapsing and remitting course throughout life. The concept of neuroprogression in BD refers to the progressive path with an identifiable trajectory that takes place with recurrent mood episodes, which eventually leads to cognitive, functional, and clinical deterioration in the course of BD. Understanding the biological basis of neuroprogression helps to explain the subset of BD patients who experience worsening of their disorder over time. Additionally, the study of the neurobiological mechanisms underpinning neuroprogression will help BD staging based on systems biology. Replicated epidemiological studies have suggested inflammatory mechanisms as primary contributors to the neuroprogression of mood disorders. It is known that dysregulated inflammatory/immune pathways are often associated with BD pathophysiology. Hence, in this chapter, we focus on the evidence for the involvement of inflammation and immune regulated pathways in the neurobiological consequences of BD neuroprogression. Herein we put forth the evidence of immune markers from autoimmune disorders, chronic infections, and gut-brain axis that lead to BD neuroprogression. Further, we highlighted the peripheral and central inflammatory components measured along with BD progression.

Bipolar disorder and the endocannabinoid system

OBJECTIVE

Bipolar disorder (BD) is a debilitating, lifelong neuropsychiatric illness characterised by unsteady mood states which vacillate from (hypo)mania to depression. Despite the availability of pharmaceutical agents which can be effective in ameliorating the acute affective symptoms and prevent episodic relapse, BD is inadequately treated in a subset of patients. The endocannabinoid system (ECS) is known to exert neuromodulatory effects on other neurotransmitter systems critical in governing emotions. Several studies ranging from clinical to molecular, as well as anecdotal evidence, have placed a spotlight on the potential role of the ECS in the pathophysiology of BD. In this perspective, we present advantages and disadvantages of cannabis use in the management of illness course of BD and provide mechanistic insights into how this system might contribute to the pathophysiology of BD.

RESULTS

We highlight the putative role of selective cannabinoid receptor 2 (CB2) agonists in BD and briefly discuss findings which provide a rationale for targeting the ECS to assuage the symptoms of BD. Further, data encourage basic and clinical studies to determine how cannabis and cannabinoids (CBs) can affect mood and to investigate emerging CB-based options as probable treatment approaches.

CONCLUSION

The probable role of the ECS has been almost neglected in BD; however, from data available which suggest a role of ECS in mood control, it is justified to support conducting comprehensive studies to determine whether ECS manipulation could positively affect BD. Based on the limited available data, we suggest that activation of CB2 may stabilise mood in this disorder.

The association between low-grade inflammation and the clinical features of bipolar disorder in Han Chinese population

Variety of evidence suggests that low-grade inflammation may be involved in the pathophysiology of bipolar disorder (BD). However, the conclusion regarding the relationship between inflammation and BD has been inconsistent. In this study, we aimed to survey the prevalence of low-grade inflammation in a large Han Chinese population with BD and assess its impact on the clinical features of BD. 430 eligible cases were drawn from patients who were admitted or had ever been admitted for BD to the inpatient service of the psychiatric department of the Third Hospital of Sun Yat-sen University. Subjects with current active physical diseases or white blood count (WBC) >19.0 × 10⁹/L (2 times the upper reference) were excluded. Serum C-reactive protein (CRP) levels and WBC were measured with fast blood sample. Low-grade inflammation was defined as CRP>3 mg/L or WBC > 9.5 × 10⁹/L(the upper reference). Clinical features of BD were collected through semi-structural interview conducted by trained interviewers with background of psychiatric education. If defined as CRP>3 mg/L, the prevalence of low-grade inflammation among BD was 10.1% (41/404), it was positively associated with BMI (p = 0.012), comorbidity of glycolipid metabolic diseases(p = 0.018). After adjusting for BMI, it was found to be positively related to recent suicide attempt (p = 0.03), initiation with (hypo)manic episode(p = 0.047), leaden paralysis (p = 0.037) and family history of mental disorders(p = 0.012), while the association between comorbidity of glycolipid metabolic diseases and low-grade inflammation disappeared (p = 0.330). If defined as WBC > 9.5 × 10⁹/L, the prevalence of low-grade inflammation was 8.1% (33/409), it was positively associated with psychotic features (p = 0.011) and adverse life events before the onset of illness(p < 0.001), but was not significantly influenced by BMI (p = 0.077). A much lower prevalence of low-grade inflammation in BD is found among Han Chinese population than among western population. Low-grade inflammation of different definition impacts differentially on the clinical features of BD.

Neurotrophins, cytokines, oxidative stress mediators and mood state in bipolar disorder: systematic review and meta-analyses

BACKGROUND

A reliable biomarker signature for bipolar disorder sensitive to illness phase would be of considerable clinical benefit. Among circulating blood-derived markers there has been a significant amount of research into inflammatory markers, neurotrophins and oxidative stress markers.AimsTo synthesise and interpret existing evidence of inflammatory markers, neurotrophins and oxidative stress markers in bipolar disorder focusing on the mood phase of illness.

METHOD

Following PRISMA (Preferred Reporting Items for Systematic reviews and Meta-analyses) guidelines, a systematic review was conducted for studies investigating peripheral biomarkers in bipolar disorder compared with healthy controls. We searched Medline, Embase, PsycINFO, SciELO and Web of Science, and separated studies by bipolar mood phase (mania, depression and euthymia). Extracted data on each biomarker in separate mood phases were synthesised using random-effects model meta-analyses.

RESULTS

In total, 53 studies were included, comprising 2467 cases and 2360 controls. Fourteen biomarkers were identified from meta-analyses of three or more studies. No biomarker differentiated mood phase in bipolar disorder individually. Biomarker meta-analyses suggest a combination of high-sensitivity C-reactive protein/interleukin-6, brain derived neurotrophic factor/tumour necrosis factor (TNF)-α and soluble TNF-α receptor 1 can differentiate specific mood phase in bipolar disorder. Several other biomarkers of interest were identified.

CONCLUSIONS

Combining biomarker results could differentiate individuals with bipolar disorder from healthy controls and indicate a specific mood-phase signature. Future research should seek to test these combinations of biomarkers in longitudinal studies.Declaration of interestNone.

Classical Risk Factors and Inflammatory Biomarkers: One of the Missing Biological Links between Cardiovascular Disease and Major Depressive Disorder

BACKGROUND

Cardiovascular disorders (CVD) and major depressive disorder (MDD) are the most frequent diseases worldwide responsible for premature death and disability. Behavioral and immunological variables influence the pathophysiology of both disorders. We therefore determined frequency and severity of MDD in CVD and studied whether MDD without CVD or other somatic diseases influences classical and inflammatory biomarkers of cardiovascular risk. In addition, we investigated the influence of proinflammatory cytokines on antidepressant treatment outcome.

METHODS

In a case-control design, 310 adults (MDD patients without CVD, CVD patients, and cardiologically and psychiatrically healthy matched controls) were investigated. MDD patients were recruited after admission in a psychiatric university hospital. Primary outcome criteria were clinical depression ratings (HAM-D scale), vital signs, classical cardiovascular risk factors and inflammatory biomarkers which were compared between MDD patients and healthy controls.

RESULTS

We detected an enhanced cardiovascular risk in MDD. Untreated prehypertension and signs directing to a metabolic syndrome were detected in MDD. Significantly higher inflammatory biomarkers such as the high sensitivity C-reaktive protein (hsCRP) and proinflammatory acute phase cytokines interleukine-1β (IL-1β) and interleukine-6 (IL-6) underlined the higher cardiovascular risk in physically healthy MDD patients. Surprisingly, high inflammation markers before treatment were associated with better clinical outcome and faster remission. The rate of MDD in CVD patients was high.

CONCLUSIONS

Patients suffering from MDD are at specific risk for CVD. Precise detection of cardiovascular risks in MDD beyond classical risk factors is warranted to allow effective prophylaxis and treatment of both conditions. Future studies of prophylactic interventions may help to provide a basis for prophylactic treatment of both MDD and CVD. In addition, the high risk for MDD in CVD patients was confirmed and underlines the requirement for clinical attention.

Immune abnormalities across psychiatric disorders: clinical relevance

It is well established that the immune system can modulate brain functioning and influence behavioural processes. Awareness of communication between the immune and nervous systems has, over the years, progressively heightened interest in the relationship between psychiatric disorders and immune function. By reviewing findings from studies investigating inflammation in the periphery and in the central nervous systems, we summarise here the evidence linking inflammation to the development of depression, schizophrenia and bipolar disorder. We discuss how a pathophysiological role for inflammation has now been recognised across different psychiatric disorders, at least in a significant subpopulation of patients. Finally, we discuss a possible role for these findings in the development of future diagnostic classifications of psychiatric disorders as well as of new treatment strategies.

Inflammatory Compounds: Neuropeptide Substance Pand Cytokines

Inflammatory diseases represent one of the major causes of morbidity and mortality throughout the world and they affect the functions of several tissues. The pathophysiology of these diseases involves release of many pro-inflammatory mediators such as cytokines/chemokines, histamine, C3a, C5a (complement components), bradykinin, leukotrienes (LTC4, LTD4, LTE4), PAF, and substance P, in addition to anti-inflammatory molecules. Recently, it has been demonstrated that neuroimmune interactions are important in the initiation and progress of inflammatory processes. Substance P is an 11-amino acid neuropeptide that is released from nerve endings in many tissues. It acts via membrane-bound NK1 receptors (NK1R). Inflammatory and neuropeptides such as substance P stimulate the release of chemokines, in particular IL-8, a potent neutrophil chemoattractant. Expression of IL-8 is regulated mainly by the transcription factors NF-kappaB, activating protein-1. Substance P plays an important role in immunological and inflammatory states, and it is a mediator of tissue injury, asthma, arthritis, allergy and autoimmune diseases. In this article, our studies revisited the interrelationship between these two powerful inflammatory compounds: substance P and cytokines. These observations suggest that these inflammatory molecules may represent a potential therapeutic target to treat several inflammatory states.

C-reactive protein and cardiovascular risk in bipolar disorder patients: A systematic review

OBJECTIVES

New research is revealing a strong association between inflammatory markers with bipolar disorder (BD), potentially due to the high prevalence of cardiovascular disease and cardiovascular risk factors in BD. We aimed to synthesize the literature examining the association between the clinically most relevant inflammatory marker, C-reactive protein (CRP) and cardiovascular disease and cardiovascular risk factors in patients with BD.

METHODS

MEDLINE, Embase and PsychInfo were systematically searched for all relevant English language articles published prior to April 2017. Articles were included if they examined the association between CRP and cardiovascular risk factors/disease in BD.

RESULTS

Fifteen relevant articles were retrieved. Studies were mostly cross-sectional and heterogeneous in the cardiovascular risk factors investigated. Overall, elevated CRP was associated with increased risk of metabolic syndrome, elevated body mass index, higher waist circumference, and obesity. CRP was inconsistently associated with elevated fasting glucose, insulin levels, serum triglycerides, total cholesterol levels, and low high density lipoprotein (HDL) levels. Atypical antipsychotic use may mediate some of these effects. No study examined CRP's association with actual cardiovascular disease (e.g. coronary artery disease) in BD.

CONCLUSIONS

In BD, CRP is associated with increases in several cardiovascular risk factors, suggesting that systemic inflammation could be a shared driving force for both outcomes of BD and cardiovascular risk. Further longitudinal research is needed in this area to verify causality, including an examination of actual cardiovascular disease. Non-pharmacological and pharmacological treatments with anti-inflammatory effects should also be investigated, particularly in patients with increased CRP, for their potential to reduce cardiovascular risk in BD.

A systematic review of evidence for the role of inflammatory biomarkers in bipolar patients

Bipolar disorder (BD) is a neuropsychiatric disorder that is characterized by a phasic course of affective episodes interspersed with a euthymic state. Epidemiological, clinical, genetic, post-mortem and preclinical studies have shown that inflammatory reactions and immune modulation play a pivotal role in the pathophysiology of BD. It is conceptualized that biomarkers of inflammation and immune responses should be employed to monitor the disease process in bipolar patients. The objective of this systematic review is to analyse the inflammatory markers involved in human studies and to explore each individual marker for its potential clinical application and summarize evidence regarding their role in BD. A systematic review of human studies to measure inflammatory markers was conducted, and the studies were identified by searching PubMed/MEDLINE, PsycINFO, EMBASE, and Web of Science databases for peer-reviewed journals that were published until September 2015. In this review, we included peripheral markers, genetic, post-mortem and cell studies with inflammatory biomarker analysis in BD. One hundred and two (102) papers met the inclusion criteria. The pro-inflammatory cytokines were elevated and the anti-inflammatory cytokines were reduced in BD patients, particularly during manic and depressive phases when compared to the controls. These changes tend to disappear in euthymia, indicating that inflammation may be associated with acute phases of BD. Even though there are promising findings in this field, further clinical studies using more established detection techniques are needed to clearly show the benefit of using inflammatory markers in the diagnosis, follow-up and prognosis of patients with BD.

Effect of agomelatine treatment on C-reactive protein levels in patients with major depressive disorder: an exploratory study in "real-world," everyday clinical practice

OBJECTIVE

Agomelatine is a newer antidepressant but, to date, no studies have been carried out investigating its effects on C-reactive protein (CRP) levels in major depressive disorder (MDD) before and after treatment. The present study aimed (i) to investigate the effects of agomelatine treatment on CRP levels in a sample of patients with MDD and (ii) to investigate if CRP variations were correlated with clinical improvement in such patients.

METHODS

30 adult outpatients (12 males, 18 females) with a Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR) diagnosis of MDD were recruited in "real-world," everyday clinical practice and treated with a flexible dose of agomelatine for 12 weeks. The Hamilton Rating Scale for Depression (HAM-D) and the Snaith-Hamilton Pleasure Scale (SHAPS) were used to evaluate depressive symptoms and anhedonia, respectively. Moreover, serum CRP was measured at baseline and after 12 weeks of treatment.

RESULTS

Agomelatine was effective in the treatment of MDD, with a significant reduction in HAM-D and SHAPS scores from baseline to endpoint. CRP levels were reduced in the whole sample, with remitters showing a significant difference in CRP levels after 12 weeks of agomelatine. A multivariate stepwise linear regression analysis showed that higher CRP level variation was associated with higher baseline HAM-D scores, controlling for age, gender, smoking, BMI, and agomelatine dose.

CONCLUSIONS

Agomelatine's antidepressant properties were associated with a reduction in circulating CRP levels in MDD patients who achieved remission after 12 weeks of treatment. Moreover, more prominent CRP level variation was associated with more severe depressive symptoms at baseline.

C-reactive protein and white blood cell levels in schizophrenia, bipolar disorders and depression - associations with mortality and psychiatric outcomes: a population-based study

BACKGROUND

Mental disorders have been associated with increased levels of inflammatory markers, which can affect disease trajectories. We aimed to assess levels of C-reactive protein (CRP) and white blood cells (WBC) across individuals with schizophrenia, bipolar disorder, and depression, and to investigate associations with subsequent psychiatric admission and mortality.

METHODS

We identified all adults in the Central Denmark Region during 2000-2012 with a first diagnosis of schizophrenia, bipolar disorder, or depression and a baseline measurement of CRP and/or WBC count. We followed these individuals until outcome of interest (psychiatric admission or death), emigration or December 31, 2012, using Cox regression analysis to estimate hazard ratios (HRs).

RESULTS

Baseline median CRP differed significantly between mental disorders (P=0.01) being highest in individuals with bipolar disorder (3.5mg/L) (particularly during manic states, 3.9mg/L), followed by schizophrenia (3.1mg/L), and depression (2.8mg/L), while baseline WBC count did not differ (median 7.1×10⁹/L). Elevated CRP levels were associated with increased all-cause mortality by adjusted HRs of 1.56 (95% CI: 1.02-2.38) for levels 3-10mg/L and 2.07 (95% CI: 1.30-3.29) for levels above 10mg/L compared to individuals with levels below 3mg/L. WBC counts were not associated with all-cause mortality. No association was observed between levels of the inflammatory markers and subsequent psychiatric admissions.

CONCLUSIONS

People with severe mental disorders had increased inflammatory markers at first diagnosis, and elevated CRP levels were associated with increased mortality. Thorough screening for physical diseases is of utmost importance among individuals who are diagnosed with severe mental disorder.

Is Toxoplasma gondii a Trigger of Bipolar Disorder?

Toxoplasma gondii, a ubiquitous intracellular parasite, has a strong tropism for the brain tissue, where it forms intracellular cysts within the neurons and glial cells, establishing a chronic infection. Although latent toxoplasmosis is generally assumed to be asymptomatic in immunocompetent individuals, it is now clear that it can induce behavioral manipulations in mice and infected humans. Moreover, a strong relation has emerged in recent years between toxoplasmosis and psychiatric disorders. The link between T. gondii and schizophrenia has been the most widely documented; however, a significant association with bipolar disorder (BD) and suicidal/aggressive behaviors has also been detected. T. gondii may play a role in the etiopathogenesis of psychiatric disorders affecting neurotransmitters, especially dopamine, that are implicated in the emergence of psychosis and behavioral Toxoplasma-induced abnormalities, and inducing brain inflammation by the direct stimulation of inflammatory cytokines in the central nervous system. Besides this, there is increasing evidence for a prominent role of immune dysregulation in psychosis and BD. The aim of this review is to describe recent evidence suggesting a link between Toxoplasma gondii and BD, focusing on the interaction between immune responses and this infectious agent in the etiopathogenesis of psychiatric symptoms.

C-reactive protein concentrations across the mood spectrum in bipolar disorder: a systematic review and meta-analysis

BACKGROUND

Inflammatory processes and neural-immune interactions have been implicated in the pathogenesis of psychiatric conditions, but studies in bipolar disorder are inconclusive so far. We aimed to investigate whether peripheral concentrations of C-reactive protein (CRP), an acute-phase response protein of inflammatory activity, are increased in bipolar disorder across the mood spectrum.

METHODS

In this systematic review and meta-analysis, we searched MEDLINE, the Cochrane Library, Scopus, and Web of Knowledge from database inception to Aug 14, 2016, for studies that measured serum and plasma CRP concentrations in adult patients with bipolar disorder (as defined by DSM-IV-TR) and healthy controls. We extracted data from published reports. We did three between-group meta-analyses comparing CRP concentrations in patients in mania, depression, or euthymia, with those in healthy controls (cross-sectional studies), and two within-group meta-analyses comparing changes in CRP concentrations before and after treatment of an index manic or depressive episode (longitudinal studies). We used Hedges' adjusted g to calculate effect sizes and pooled results using random-effect models. We also did meta-regression analyses by mood state to investigate possible moderators of CRP concentrations.

FINDINGS

We identified 27 studies representing 2161 patients with bipolar disorder and 81 932 healthy controls. Compared with healthy individuals, CRP concentrations were moderately increased in people with bipolar disorder during depression (g 0·67, 95% CI 0·23 to 1·11; p=0·003) and euthymia (0·65, 0·40 to 0·90; p<0·0001) and more substantially increased during mania (0·87, 0·58 to 1·15; p<0·0001). The extent of the increases in CRP concentrations in mania and depression was not related to symptom severity (p=0·256 for mania and p=0·626 for depression). CRP concentrations were moderately decreased after resolution of an index manic episode (-0·36, -0·66 to -0·05; p=0·022) and slightly decreased after resolution of an index depressive episode (-0·18, -0·30 to -0·07; p=0·002).

INTERPRETATION

CRP concentrations are increased in bipolar disorder regardless of mood state, but are higher during mania than in depression and euthymia, suggesting an increased inflammatory burden in mania.

FUNDING

None.

Cytokines, brain-derived neurotrophic factor and C-reactive protein in bipolar I disorder - Results from a prospective study

BACKGROUND

Peripheral blood brain-derived neurotrophic factor (BDNF) and inflammatory markers may reflect key pathophysiological mechanisms in bipolar disorder in relation to disease activity and neuroprogression.

AIMS

To investigate whether neutrophins and inflammatory marker vary with mood states and are increased in patients with bipolar disorder type I during euthymia as well as in all affective states as a group, compared to levels in healthy control subjects.

METHODS

In a prospective 6-12 months follow-up study, we investigated state specific, intra-individual alterations in levels of BDNF, hsCRP, IL-1β, IL-6, IL-8, IL-18 and TNF-α in 60 patients with bipolar I disorder with an acute severe manic index episode and in subsequent euthymic and depressive and manic states and compared with repeated measurements in healthy control subjects. Data were analysed with linear mixed effects model and with adjustment for gender, age, BMI, alcohol intake and smoking.

RESULTS

From inclusion to end of the 6-12 months follow-up, samples of blood were drawn from the 60 patients during a total of 180 affective states, comprising 57 manic, 11 mixed, 23 depressive and 89 states of euthymia. Further, 69 blood samples were drawn from 35 healthy control subjects with three months apart. In unadjusted mixed-model analysis, levels of IL-6 and IL-8 were increased 64% (b=1.64, 95% CI: 1.31-2.05, p=<0.0001) and 24% (b=1.24, 95% CI: 1.05-1.47, p=0.013), respectively in patients with bipolar disorder overall compared with healthy control subjects. However, in adjusted models, no statistically significant differences were found in any measure between patients and control individuals. Levels of hsCRP in depressive states were decreased with 40% (95% CI: 5-62%, p=0.029) compared with euthymia and with 48% (95% CI: 17-66%, p=0.006) when compared with hypomanic/manic states after adjustment. BDNF and the other inflammatory markers did not vary according to affective state in adjusted mixed models.

LIMITATIONS

Patients were all medicated, specifically with high doses of atypical antipsychotics during the manic index episodes.

CONCLUSIONS

In a sample recruited during hospitalization for acute mania, levels of hsCRP varied according to affective state with higher levels during manic states compared with depressive states.

Clinical correlates of vitamin D deficiency in established psychosis

BACKGROUND

Suboptimal vitamin D levels have been identified in populations with psychotic disorders. We sought to explore the relationship between vitamin D deficiency, clinical characteristics and cardiovascular disease risk factors among people with established psychosis.

METHODS

Vitamin D levels were measured in 324 community dwelling individuals in England with established psychotic disorders, along with measures of mental health, cardiovascular risk and lifestyle choices. Vitamin D deficiency was defined as serum 25-hydroxyvitamin D (25-OHD) levels below 10 ng/ml (equivalent to <25 nmol/L) and "sufficient" Vitamin D as above 30 ng/ml (>50 nmol/L).

RESULTS

The mean 25-OHD serum level was 12.4 (SD 7.3) ng/ml, (range 4.0-51.7 ng/ml). Forty nine percent (n = 158) were vitamin D deficient, with only 14 % (n = 45) meeting criteria for sufficiency. Accounting for age, gender, ethnicity and season of sampling, serum 25-OHD levels were negatively correlated with waist circumference (r = -0.220, p < 0.002), triglycerides (r = -0.160, p = 0.024), total cholesterol (r = -0.144, p = 0.043), fasting glucose (r = -0.191, p = 0.007), HbA1c (r = -0.183, p = 0.01), and serum CRP levels (r = -0.211, p = 0.003) and were linked to the presence of metabolic syndrome.

CONCLUSIONS

This is the largest cross sectional study of serum 25-OHD levels in community dwelling individuals with established psychosis, indicating a high level of vitamin D deficiency. Lower vitamin D levels are associated with increased cardiovascular disease risk factors and in particular metabolic syndrome. Further research is needed to define appropriate protocols for vitamin D testing and supplementation in practice to see if this can improve cardiovascular disease risk.

TRIAL REGISTRATION

ISRCTN number is ISRCTN58667926 Date of registration: 23/04/2010.

Bipolar Depression and Cognitive Impairment: Shared Mechanisms and New Treatment Avenues

Depression and cognitive impairment are pervasive and highly disabling aspects of bipolar disorder. Although cognitive impairment is partially independent from mood episodes, depressive symptoms may increase the risk of cognitive impairment in bipolar disorder through inflammatory processes as well as health risks such as obesity and sedentary behavior. Novel treatment avenues at the intersection of bipolar depression and cognitive impairment target inflammation directly or indirectly health behaviors such as diet, physical activity, and sleep hygiene.

Elevated C-reactive protein and late-onset bipolar disorder in 78 809 individuals from the general population

BACKGROUND

No prospective studies have examined the role of C-reactive protein (CRP) in late-onset bipolar disorder.

AIMS

We tested the hypothesis that elevated levels of CRP are associated cross-sectionally and prospectively with late-onset bipolar disorder, and that such an association possibly is causal.

METHOD

We performed cross-sectional and prospective analyses with a median follow-up time of 5.9 years (interquartile range: 4.4-7.6) in 78 809 individuals from the general population, and used genetic variants influencing CRP levels to perform a Mendelian randomisation study.

RESULTS

Elevated levels of CRP were associated both cross-sectionally and prospectively with late-onset bipolar disorder. When CRP was on a continuous scale, a doubling in CRP yielded an observational odds ratio for late-onset bipolar disorder of 1.28 (1.08-1.52) with a corresponding causal odds ratio of 4.66 (0.89-24.3).

CONCLUSION

Elevated CRP is associated with increased risk of late-onset bipolar disorder in the general population which was supported by the genetic analysis.

Peripheral inflammation during abnormal mood states in bipolar I disorder

BACKGROUND

Bipolar disorder carries a substantive morbidity and mortality burden, particularly related to cardiovascular disease. Abnormalities in peripheral inflammatory markers, which have been commonly reported in case-control studies, potentially link these co-morbidities. However, it is not clear whether inflammatory markers change episodically in response to mood states or are indicative of chronic pro-inflammatory activity, regardless of mood, in bipolar disorder.

METHODS

Investigations focused on comparing concentrations of specific inflammatory cytokines associated with immune activation status (primary outcome=tumor necrosis factor alpha (TNF-α)) in 37 participants with bipolar disorder across 3 mood states (mania N=15, depression N=9, normal mood N=13) and 29 controls without a psychiatric disorder (total N=66). Cytokine levels were also compared to T1ρ, a potential neuroimaging marker for inflammation, in select brain regions in a subsample (N=39).

RESULTS

Participants with bipolar disorder and healthy controls did not differ significantly in inflammatory cytokine concentrations. However, compared to cases with normal mood, cases with abnormal mood states (mania and depression) had significantly elevated levels of TNF-α, its soluble receptors (sTNFR1/sTNFR2), other macrophage-derived cytokines (interleukin 1β (IL-1β), IL-6, IL-10, and IL-18) in addition to IL-4, interferon-γ, monocyte chemotactic protein-1, fibroblast growth factor β, and vascular endothelial growth factor. Cytokine levels were not correlated with signals from T1ρ imaging in selected structures (amygdalae, hippocampi, hypothalamus, anterior cingulate gyrus, and middle frontal gyrus).

LIMITATIONS

Participants were not followed prospectively across mood states.

CONCLUSION

Activation of inflammatory markers was found in abnormal mood states of bipolar disorder. Longitudinal study of individuals with mood disorders is needed to confirm these findings and to elucidate the time course of any such changes.

Assessment of cytokine levels and hs-CRP in bipolar I disorder before and after treatment

We aimed to assess the relationship between cytokine levels and the severity of the manic period in medication free patients. 30 Medication free patients and 28 healthy subjects (HS) were recruited. Plasma levels of pro-inflammatory, anti-inflammatory, inflammatory cytokines, and hs-CRP levels were investigated upon hospital admission, after six weeks follow up in bipolar disease manic episode and the results were compared to HS. The severity of the manic episodes was assessed according to the Young mania rating scale. TNF-α, INF-γ, IL-6 and hs-CRP levels were significantly higher in patients with manic episode of bipolar I disorder before treatment than HS. After treatment the levels of TNF-α, INF-γ, IL-6 and hs-CRP were observed to be significantly decreased. There was no difference between the levels of anti-inflammatory cytokines in patients before or after treatment of bipolar disorder and HS. hs-CRP was observed to be the only parameter correlated with clinical response. The most significant outcome of this study is the correlation between clinical outcome and hs-CRP levels in treatment naive manic episode bipolar type I patients. hs-CRP is the most consistent indicator according to pro-inflammatory, inflammatory and anti-inflammatory cytokines, in predicting treatment outcomes.

Infection and inflammation in schizophrenia and bipolar disorder: a genome wide study for interactions with genetic variation

Inflammation and maternal or fetal infections have been suggested as risk factors for schizophrenia (SZ) and bipolar disorder (BP). It is likely that such environmental effects are contingent on genetic background. Here, in a genome-wide approach, we test the hypothesis that such exposures increase the risk for SZ and BP and that the increase is dependent on genetic variants. We use genome-wide genotype data, plasma IgG antibody measurements against Toxoplasma gondii, Herpes simplex virus type 1, Cytomegalovirus, Human Herpes Virus 6 and the food antigen gliadin as well as measurements of C-reactive protein (CRP), a peripheral marker of inflammation. The subjects are SZ cases, BP cases, parents of cases and screened controls. We look for higher levels of our immunity/infection variables and interactions between them and common genetic variation genome-wide. We find many of the antibody measurements higher in both disorders. While individual tests do not withstand correction for multiple comparisons, the number of nominally significant tests and the comparisons showing the expected direction are in significant excess (permutation p=0.019 and 0.004 respectively). We also find CRP levels highly elevated in SZ, BP and the mothers of BP cases, in agreement with existing literature, but possibly confounded by our inability to correct for smoking or body mass index. In our genome-wide interaction analysis no signal reached genome-wide significance, yet many plausible candidate genes emerged. In a hypothesis driven test, we found multiple interactions among SZ-associated SNPs in the HLA region on chromosome 6 and replicated an interaction between CMV infection and genotypes near the CTNNA3 gene reported by a recent GWAS. Our results support that inflammatory processes and infection may modify the risk for psychosis and suggest that the genotype at SZ-associated HLA loci modifies the effect of these variables on the risk to develop SZ.

In Silico Post Genome-Wide Association Studies Analysis of C-Reactive Protein Loci Suggests an Important Role for Interferons

BACKGROUND

Genome-wide association studies (GWASs) have successfully identified several single nucleotide polymorphisms (SNPs) associated with serum levels of C-reactive protein (CRP). An important limitation of GWASs is that the identified variants merely flag the nearby genomic region and do not necessarily provide a direct link to the biological mechanisms underlying their corresponding phenotype. Here we apply a bioinformatics-based approach to uncover the functional characteristics of the 18 SNPs that had previously been associated with CRP at a genome-wide significant level.

METHODS AND RESULTS

In the first phase of in silico sequencing, we explore the vicinity of GWAS SNPs to identify all linked variants. In the second phase of expression quantitative trait loci analysis, we attempt to identify all nearby genes whose expression levels are associated with the corresponding GWAS SNPs. These 2 phases generate several relevant genes that serve as input to the next phase of functional network analysis. Our in silico sequencing analysis using 1000 Genomes Project data identified 7 nonsynonymous SNPs, which are in moderate to high linkage disequilibrium (r(2)>0.5) with the GWAS SNPs. Our expression quantitative trait loci analysis, which was based on one of the largest single data sets of genome-wide expression probes (n>5000) identified 23 significantly associated expression probes belonging to 15 genes (false discovery rate <0.01). The final phase of functional network analysis revealed 93 significantly enriched biological processes (false discovery rate <0.01).

CONCLUSIONS

Our post-GWAS analysis of CRP GWAS SNPs confirmed the previously known overlap between CRP and lipids biology. Additionally, it suggested an important role for interferons in the metabolism of CRP.

Depression and cardiovascular disease: an update on how course of illness may influence risk

Depression constitutes a novel and independent risk factor for cardiovascular disease, which despite extensive support in the literature has been underappreciated. While much of the evidence for depression as a risk factor for cardiovascular disease is based on studies following myocardial infarction, the elevated vascular risk conveyed by depression is not confined to periods following acute coronary syndromes. For that matter, the risk appears across mood disorders with evidence for even greater risk in bipolar disorder. This review summarizes the literature linking depressive disorders to cardiovascular mortality with a focus on how the course of illness of mood disorders may influence this risk. Mood disorders may influence risk over decades of illness in a dose-response to symptom burden, or the persistence of affective symptomatology. This may be mediated through changes in the activity of the autonomic nervous system, the hypothalamic-pituitary-adrenal axis, and inflammatory cytokines. Whether treatment of depression can mitigate this risk is not established although there are suggestions to support this contention, which could be better studied with more effective treatments of depression and larger standardized samples. Directions for future study of mechanisms and treatment are discussed. Regardless of causal mechanisms, persons with depressive disorders and other risk factors for vascular disease represent a neglected, high-risk group for cardiovascular events. In addition to the appropriate treatment for depression, screening and optimized management of traditional risk factors for cardiovascular diseases is necessary.

Elevated C-reactive protein associated with late- and very-late-onset schizophrenia in the general population: a prospective study

BACKGROUND

Individuals with autoimmune diseases and severe infections have persistent or acutely elevated inflammatory biomarkers and increased risk of schizophrenia. We tested the hypothesis that baseline elevated plasma levels of the inflammatory biomarker, C-reactive protein (CRP), associate with increased risk of late- and very-late-onset schizophrenia in the general population, and if such an association possibly is causal.

METHOD

We analyzed data from 78 810 men and women, aged 20-100 years, from 2 large population studies. Endpoints were hospitalization with schizophrenia and schizophrenia and schizophrenia-like psychosis combined. We performed prospective and cross-sectional analyses adjusted for potential confounders with up to 20 years of follow-up. Furthermore, we used genetic variants influencing plasma CRP levels to perform a Mendelian randomization study.

RESULTS

Age- and gender-adjusted hazard ratios vs individuals in the first quartile of CRP were 1.7 (95% CI: 0.3-8.9) for second quartile, 2.1 (0.4-10) for third quartile, and 11 (2.8-40) for fourth quartile individuals. The corresponding hazard ratio for fourth quartile individuals after multifactorial adjustment was 5.9 (1.4-24). Furthermore, individuals with vs without schizophrenia had 63% increased plasma levels of CRP (P = 1 × 10(-4)). Finally, when CRP was on a continuous scale, a doubling in CRP yielded an age- and gender-adjusted observational OR of 1.5 (1.3-1.8) and a corresponding causal OR of 1.4 (0.5-4.3) (observed vs causal: P = .89).

CONCLUSION

Baseline elevated plasma CRP is associated with a 6- to 11-fold increased risk of late- and very-late-onset schizophrenia in the general population. We cannot exclude that this is a causal association. These are novel findings.

Comparison of inflammatory cytokine levels among type I/type II and manic/hypomanic/euthymic/depressive states of bipolar disorder

OBJECTIVE

Inflammatory cytokines have been suggested to be the trait or state markers of bipolar disorder, but with inconsistent results. This may be related to small sample sizes and poor control of some important confounding factors.

METHODS

Gender/age-matched outpatients with bipolar disorder and normal controls were enrolled. The clinical symptoms were rated using the Montgomery Åsberg Depression Rating Scale and Young Mania Rating Scale. Inflammatory cytokines, including soluble interleukin-6 receptor (sIL-6R), soluble interleukin-2 receptor (sIL-2R), C-reactive protein (CRP), soluble tumor necrosis factor receptor type 1 (sTNF-R1), soluble P-selectin receptor (sP-selectin), and monocyte chemotactic protein-1 (MCP-1), were assessed by enzyme-linked immunosorbent assays.

RESULTS

In total, 130 patients with bipolar disorder and 130 normal subjects were enrolled. Among the patients with bipolar disorder, 77 (59.2%) had bipolar I disorder, 53 (40.8%) had bipolar II disorder; 75 (57.7%) were in a euthymic state, 14 (10.8%) were in a manic/hypomanic state, and 41 (31.5%) were in a depressive state. The 130 bipolar patients had significantly higher levels of all cytokines than the normal controls (all p<0.0001). Using multivariate regression analysis with controlling of age, gender, BMI, smoking, duration of illness, and medication grouping, the patients with bipolar II disorder had significantly lower levels of sTNF-R1 than the patients with bipolar I disorder (p=0.038); the patients in a depressive state had significantly lower levels of sTNF-R1 than the patients in manic/hypomanic and euthymic states (p=0.009).

CONCLUSION

The study supported the association of bipolar disorder with inflammatory dysregulation, and sTNF-R1 may be a potential biomarker for staging bipolar disorder.

Inflamed moods: a review of the interactions between inflammation and mood disorders

Mood disorders have been recognized by the World Health Organization (WHO) as the leading cause of disability worldwide. Notwithstanding the established efficacy of conventional mood agents, many treated individuals continue to remain treatment refractory and/or exhibit clinically significant residual symptoms, cognitive dysfunction, and psychosocial impairment. Therefore, a priority research and clinical agenda is to identify pathophysiological mechanisms subserving mood disorders to improve therapeutic efficacy. During the past decade, inflammation has been revisited as an important etiologic factor of mood disorders. Therefore, the purpose of this synthetic review is threefold: 1) to review the evidence for an association between inflammation and mood disorders, 2) to discuss potential pathophysiologic mechanisms that may explain this association and 3) to present novel therapeutic options currently being investigated that target the inflammatory-mood pathway. Accumulating evidence implicates inflammation as a critical mediator in the pathophysiology of mood disorders. Indeed, elevated levels of pro-inflammatory cytokines have been repeatedly demonstrated in both major depressive disorder (MDD) and bipolar disorder (BD) patients. Further, the induction of a pro-inflammatory state in healthy or medically ill subjects induces 'sickness behavior' resembling depressive symptomatology. Potential mechanisms involved include, but are not limited to, direct effects of pro-inflammatory cytokines on monoamine levels, dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, pathologic microglial cell activation, impaired neuroplasticity and structural and functional brain changes. Anti-inflammatory agents, such as acetyl-salicylic acid (ASA), celecoxib, anti-TNF-α agents, minocycline, curcumin and omega-3 fatty acids, are being investigated for use in mood disorders. Current evidence shows improved outcomes in mood disorder patients when anti-inflammatory agents are used as an adjunct to conventional therapy; however, further research is needed to establish the therapeutic benefit and appropriate dosage.

Increased M1/decreased M2 signature and signs of Th1/Th2 shift in chronic patients with bipolar disorder, but not in those with schizophrenia

We here present data on immune gene expression of chemokines, chemokine receptors, cytokines and regulatory T-cell (T-reg) markers in chronic patients suffering from either schizophrenia (SCZ, N=20) or bipolar disorder (BD=20) compared with healthy controls (HCs, N=20). We extracted RNA from peripheral blood mononuclear cells and performed real-time (RT)-PCR to measure mRNA levels of chemokines, chemokine receptors, cytokines and T-reg markers. All the analyses were Bonferroni-corrected. The classical monocyte activation (M1) markers il6, ccl3 were significantly increased in BD as compared with both HC and SCZ patients (P=0.03 and P=0.002; P=0.024 and P=0.021, respectively), whereas markers of alternative (M2) monocyte activation ccl1, ccl22 and il10 were coherently decreased (controls: P=0.01, P=0.001 and P=0.09; SCZ subjects: P=0.02, P=0.05 and P=0.011, respectively). Concerning T-cell markers, BD patients had compared with HC downregulated ccr5 (P=0.02) and upregulated il4 (P=0.04) and compared with both healthy and SCZ individuals downregulated ccl2 (P=0.006 and P=0.003) and tgfβ (P=0.004 and P=0.007, respectively). No significant associations were found between any immune gene expression and clinical variables (prior hospitalizations, Brief Psychiatric Rating Scale, medications' dosages and lifetime administration). Although some markers are expressed by different immune cell types, these findings suggest a coherent increased M1/decrease M2 signature in the peripheral blood of BD patients with potential Th1/Th2 shift. In contrast, all the explored immune marker levels were preserved in SCZ. Further larger studies are needed to investigate the relevance of inflammatory response in BD, trying to correlate it to psychopathology, treatment and outcome measures and, possibly, to brain connectivity.

Cytokines in bipolar disorder vs. healthy control subjects: a systematic review and meta-analysis

BACKGROUND

Bipolar disorder may be associated with peripheral immune system dysfunction; however, results in individual studies are conflicting. Our aim was to systematically review evidence of peripheral cytokine alterations in bipolar disorder integrating findings from various affective states.

METHODS

We conducted a meta-analysis of studies comparing peripheral cytokine concentrations in patients with bipolar disorder with healthy control subjects. Results were reported according to the PRISMA statement.

RESULTS

Eighteen studies with a total of 761 bipolar disorder patients and 919 healthy controls were included. Overall, concentrations of soluble Interleukin (IL)-2 receptor (sIL-2R), tumor necrosis factor-α (TNF-α), soluble tumor necrosis factor receptor type 1 (sTNFR1) (p < 0.001 each), sIL-6R (p = 0.01) and IL-4 (p = 0.04) were significantly higher in bipolar patients compared with healthy controls. There were no significant differences between bipolar disorder patients and healthy control subjects for IL-1, IL-2, IL-5, IL-6, IL-8, IL-10, IL-12, IL-1β, IL-1 receptor antagonist (IL-1RA), interferon-γ (IFN-γ), transforming growth factor-β1 (TGF-β1) and sTNFR2.

CONCLUSIONS

Employing a global approach, incorporating evidence across affective states, this meta-analysis found some support for peripheral inflammatory alterations in bipolar disorder. Results were limited by heterogeneity between studies, insufficient standardization and lacking control for confounders in individual studies. Further research exploring the role of the peripheral inflammatory system in relation to neuroinflammation is warranted.

Immunity, inflammation, and bipolar disorder: diagnostic and therapeutic implications

Bipolar disorder is now known to be associated not only with highly prevalent co-occurring psychiatric and substance use disorders but also with medical comorbidities, such as cardiovascular diseases, diabetes mellitus, obesity and thyroid dysfunction. Inflammatory disturbances repeatedly observed in bipolar disorder, can explain some of the comorbidity between bipolar disorder and medical disorder. This revised perspective of bipolar disorders should promote the development of therapeutic tools. Immuno-inflammatory dysfunction may well represent a significant component of the underlying pathophysiology of the disorder. We therefore propose to review the immuno-inflammatory hypothesis in bipolar disorder considering the co-occurence with autoimmune diseases, immunological and inflammatory markers, as well as immuno-genetic markers which could lead to personalized treatments.

Elevated immune-inflammatory signaling in mood disorders: a new therapeutic target?

Converging translational evidence has implicated elevated immune-inflammatory signaling activity in the pathoetiology of mood disorders, including major depressive disorder and bipolar disorder. This is supported in part by cross-sectional evidence for increased levels of proinflammatory eicosanoids, cytokines and acute-phase proteins during mood episodes, and prospective longitudinal evidence for the emergence of mood symptoms in response to chronic immune-inflammatory activation. In addition, mood-stabilizer and atypical antipsychotic medications downregulate initial components of the immune-inflammatory signaling pathway, and adjunctive treatment with anti-inflammatory agents augment the therapeutic efficacy of antidepressant, mood stabilizer and atypical antipsychotic medications. Potential pathogenic mechanisms linked with elevated immune-inflammatory signaling include perturbations in central serotonin neurotransmission and progressive white matter pathology. Both heritable genetic factors and environmental factors including dietary fatty-acid composition may act in concert to sustain elevated immune-inflammatory signaling. Collectively, these data suggest that elevated immune-inflammatory signaling is a mechanism that is relevant to the pathoetiology of mood disorders, and may therefore represent a new therapeutic target for the development of more effective treatments.

Selected cytokine profiles during remission in bipolar patients

OBJECTIVES

The aim of the study was to examine the cytokine status in bipolar patients during immediate remission after acute episodes of mania or depression and in patients with sustained (≥6 months) remission, compared with healthy controls.

METHODS

The study was performed on 121 bipolar patients, of whom 35 were in immediate remission after mania, 41 were in immediate remission after depression, and 45 were in >6-month remission on lithium monotherapy or lithium combined with other drugs. The control group consisted of 78 healthy individuals without any history of psychiatric or immunological illnesses. Serum concentrations of IL-1β, IL-2, IL-6, IL-10, TNF-α and IFN-γ were determined using the Human Th1/Th2 Cytometric Bead Array method.

RESULTS

The concentration of IL-10 was higher in patients in remission after mania and the concentration of IFN-γ was higher in those in remission after depression than in healthy controls. On the other hand, cytokine concentrations in patients with sustained remission were not different from those of healthy subjects.

CONCLUSIONS

The results obtained in this study show that sustained remission in bipolar patients achieved mostly by lithium maintenance brings the cytokine status to a level similar to healthy control subjects.

Cytokines in bipolar disorder: a systematic review and meta-analysis

BACKGROUND

Current research and hypothesis regarding the pathophysiology of bipolar disorder suggests the involvement of immune system dysfunction that is possibly related to disease activity. Our objective was to systematically review evidence of cytokine alterations in bipolar disorder according to affective state.

METHODS

We conducted a systemtic review of studies measuring endogenous cytokine concentrations in patients with bipolar disorder and a meta-analysis, reporting results according to the PRISMA statement.

RESULTS

Thirteen studies were included, comprising 556 bipolar disorder patients and 767 healthy controls, evaluating 15 different cytokines-, cytokine receptors- or cytokine antagonists. The levels of tumor necrosis factor-α (TNF-α), the soluble tumor necrosis factor receptor type 1 (sTNF-R1) and the soluble inlerleukin-2 receptor (sIL-2R) were elevated in manic patients compared with healthy control subjects (p<0.01 for each). Levels of sTNF-R1 and TNF-α were elevated in manic patients compared to euthymic patients (p=0.01 and p=0.04, respectively). sTNF-R1 levels were elevated in euthymic patients compared with healthy control subjects (p<0.01). There were no significant findings for other comparisons, including intra-individual alterations of cytokine levels.

LIMITATIONS

Stratification according to mood state resulted in small study numbers for some cytokines. Findings were limited by heterogeneity, small sample sizes and a lack of control for confounding factors in individual studies.

CONCLUSIONS

This meta-analysis found some support for immune dysregulation in bipolar disorder. Future research is warranted to elucidate the role of endogenous cytokine alterations in bipolar disorder. Clinical studies examining longitudinal changes within individuals are recommended.

C-Reactive Protein Level and its Relationship with Suicide Risk and Alexithymia among Newly Diagnosed, Drug-Naïve Patients with Non-Affective Psychosis

The aim of the present study was to evaluate C-Reactive Protein (CRP) levels in newly diagnosed drug-naïve patients with non-affective psychosis, testing the hypotheses that in such patients serum CRP levels would be higher than in healthy controls and related to more severe psychopathology, suicide risk and alexithymia. CRP levels of 30 adult patients and 30 sex- and age-matched healthy controls were evaluated. Patients were tested with the Scale of Suicide Ideation (SSI), the Toronto Alexithymia Scale (TAS-20), the Scale for the Assessment of Positive and Negative Symptoms (SAPS and SANS) and the Calgary Depression Scale for Schizophrenia (CDSS). Higher suicide risk patients showed higher CRP levels than lower suicide risk patients and healthy controls. Moreover, such patients showed higher SAPS, SANS and CDSS scores than lower suicide risk patients. In linear regression model, CRP was significantly associated with higher SSI and TAS-20 scores. The results of the present study support the notion that CRP, suicide risk and alexithymia are strictly linked in newly diagnosed, drug-naïve patients with non-affective psychosis, independently of depressive symptoms or general psychopathology. Limitations are discussed.

The Relationships between Cholesterol and Suicide: An Update

Cholesterol is a core component of the central nervous system, essential for the cell membrane stability and the correct functioning of neurotransmission. It has been observed that cholesterol may be somewhat associated with suicidal behaviours. Therefore, the aim of this paper was to elucidate current facts and views about the role of cholesterol levels in mood disorders. The majority of the studies reviewed in the present paper suggest an interesting relationship between cholesterol (especially lower levels) and suicidality. On the other hand, particularly during the last years, relationships between serum cholesterol and suicidality were doubted on the basis of some recent studies that have not found any correlation. However, the debate on relationships between cholesterol and suicide is open and longitudinal studies on a larger sample of patients are needed to further clarify this important issue.

Affective symptoms are associated with markers of inflammation and immune activation in bipolar disorders but not in schizophrenia

OBJECTIVE

Elevated levels of inflammation are reported in bipolar disorders (BP), but how this relates to affective symptoms is unclear. We aimed to determine if immune markers that consistently have been reported elevated in BP were associated with depressive and manic symptoms, and if this was specific for BP.

METHODS

From a catchment area, 112 BP patients were included together with 153 schizophrenia (SCZ) patients and 239 healthy controls. Depression and mania were assessed and the patients were grouped into depressed, neutral, and elevated mood. We measured the immune markers tumor necrosis factor receptor 1 (sTNF-R1), interleukin 1 receptor antagonist (IL-1Ra), interleukin 6 (IL-6), high sensitive C-reactive protein (hsCRP), osteoprotegerin (OPG) and von Willebrand factor (vWf) which have been found increased in severe mental disorders.

RESULTS

In BP all inflammatory markers were lowest in depressed state, with significant group differences after control for confounders with respect to TNF-R1 (p = 0.04), IL-1Ra (p = 0.02), OPG (p = 0.004) and IL-6 (p = 0.005). STNF-R1 was positively correlated with the item elevated mood (p = 0.02) whereas sad mood was negatively correlated with OPG (p = 0.0003), IL-1Ra (p = 0.001) and IL-6 (p = 0.006). Compared to controls the neutral mood group had significantly higher levels of OPG (p = 0.0003) and IL-6 (p = 0.005), and the elevated mood group had higher levels of TNF-R1 (p = 0.000005) and vWf (p = 0.002). There were no significant associations between affective states orsymptoms in SCZ.

CONCLUSIONS

The current associations between inflammatory markers and affective symptomatology in BP and not SCZ suggest that immune related mechanisms are associated with core psychopathology of BP.