Imbalance between pro-inflammatory and anti-inflammatory cytokines in bipolar disorder

A role for white matter abnormalities in the pathophysiology of bipolar disorder

Bipolar disorder is a chronically disabling psychiatric disorder characterized by manic states that is often interspersed with periods of depression whose neurobiology remains largely unknown. There is, however, increasing evidence that white matter (WM) abnormalities may play an important role in the neurobiology of the disorder. In this review we critically evaluate evidence for WM abnormalities in bipolar disorder obtained from neuroimaging, neuropathological, and genetic research. Increased rates of white matter hyperintensities, regional volumetric abnormalities, abnormal water diffusion along prefrontal-subcortical tracts, fewer oligodendrocytes in prefrontal WM, and alterations in the expression of myelin- and oligodendrocyte-related genes are among the most consistent findings. Abnormalities converge in the prefrontal WM and, in particular, tracts that connect prefrontal regions and subcortical gray matter structures known to be involved in emotion. Taken together, the evidence supports and clarifies a model of BD that involves disconnectivity in regions implicated in emotion generation and regulation.

Similar immune profile in bipolar disorder and schizophrenia: selective increase in soluble tumor necrosis factor receptor I and von Willebrand factor

BACKGROUND

Alterations in the inflammatory system have been associated with schizophrenia and major depression, while bipolar disorder has been less studied. Most previous studies examined small samples, and the literature is inconsistent with regard to specific underlying immune mechanisms. In the present study, we examined markers representing different inflammatory pathways, and the aim was to investigate whether the levels of inflammatory parameters in a representative sample of bipolar disorder and schizophrenia are elevated compared to healthy controls, and to investigate whether the inflammatory profile is different between the groups.

METHODS

Plasma levels of soluble tumor necrosis factor receptor 1 (sTNF-R1), interleukin-1 receptor antagonist (IL-1Ra), interleukin-6 (IL-6), high-sensitivity CRP (hs-CRP), soluble CD40L ligand (sCD40L), and von Willebrand factor (vWf) were measured with ELISA techniques in a catchment area based sample of consecutively referred patients with severe mental disorders [N = 311, comprising bipolar disorder (n = 125) and schizophrenia (n = 186)] and in healthy volunteers (n = 244).

RESULTS

Plasma levels of sTNF-R1 and vWf were statistically significantly increased in both bipolar disorder and schizophrenia compared to controls (p < 0.00001), and were also increased in unmedicated patients, but there were no major differences between the two diagnostic groups. Controlling for age, gender, ethnicity, cardiovascular disorders, kidney and liver function, and other confounders did not affect the results. There were no differences in other inflammation factors between the groups.

CONCLUSION

The present results indicate specific alterations of endothelium-related inflammation processes in both bipolar disorder and schizophrenia.

Abnormalities in serum chemokine levels in euthymic patients with bipolar disorder

The pathophysiology of bipolar disorder (BD) includes, among other processes, changes in the neuroplasticity and regulation of apoptosis, which could potentially be influenced by inflammatory mediators such as chemokines. The objectives of this study were to investigate serum chemokine levels in patients with BD and to compare results with those obtained with healthy subjects. Here, serum chemokine levels of 30 euthymic patients with BD type I and 30 healthy volunteers were investigated and compared. The chemokines assessed were CCL2, CCL3, CCL8, CCL 9, CCL10, CCL11, and CCL24. Patients with BD showed significant differences in chemokine levels when compared with healthy subjects. While serum levels of CXCL10 were increased (p=.018), CCL24 levels were lower in bipolar patients (p=.025) when compared with controls. There was no statistical difference in the serum levels of CCL2, CCL3, CCL24, CXCL9, and CXCL11 between patients and controls. The presence of chemokine abnormalities in patients with BD during euthymia suggests that these inflammatory mediators should be further investigated with regard to their potential role as longstanding markers of the disorder.

Clinical implications of a staging model for bipolar disorders

A model of staging in the field of bipolar disorder (BD) should offer a means for clinicians to predict response to treatment and more general outcome measures, such as the level of functioning and autonomy. The present staging model emphasizes the assessment of patients in the interepisodic period and includes: latent phase: individuals who present mood and anxiety symptoms and increased risk for developing threshold BD; Stage I--patients with BD who present well established periods of euthymia and absence of overt psychiatric morbidity between episodes; Stage II--patients who present rapid cycling or current axis I or II comorbidities; Stage III--patients who present a clinically relevant pattern of cognitive and functioning deterioration, as well as altered biomarkers; and Stage IV--patients who are unable to live autonomously and present altered brain scans and biomarkers. Such a model implies a longitudinal appraisal of clinical variables, as well as assessment of neurocognition and biomarkers in the interepisodic period. Staging facilitates understanding of the mechanisms underlying progression of the disorder, assists in treatment planning and prognosis and, finally, underscores the imperative for early intervention.

Neurobiological trait abnormalities in bipolar disorder

Dissecting trait neurobiological abnormalities in bipolar disorder (BD) from those characterizing episodes of mood disturbance will help elucidate the aetiopathogenesis of the illness. This selective review highlights the immunological, neuroendocrinological, molecular biological and neuroimaging abnormalities characteristic of BD, with a focus on those likely to reflect trait abnormalities by virtue of their presence in euthymic patients or in unaffected relatives of patients at high genetic liability for illness. Trait neurobiological abnormalities of BD include heightened pro-inflammatory function and hypothalamic-pituitary-adrenal axis dysfunction. Dysfunction in the intracellular signal transduction pathway is indicated by elevated protein kinase A activity and altered intracellular calcium signalling. Consistent neuroimaging abnormalities include the presence of ventricular enlargement and white matter abnormalities in patients with BD, which may represent intermediate phenotypes of illness. In addition, spectroscopy studies indicate reduced prefrontal cerebral N-acetylaspartate and phosphomonoester concentrations. Functional neuroimaging studies of euthymic patients implicate inherently impaired neural networks subserving emotional regulation, including anterior limbic, ventral and dorsal prefrontal regions. Despite heterogeneous samples and conflicting findings pervading the literature, there is accumulating evidence for the existence of neurobiological trait abnormalities in BD at various scales of investigation. The aetiopathogenesis of BD will be better elucidated by future clinical research studies, which investigate larger and more homogenous samples and employ a longitudinal design to dissect neurobiological abnormalities that are underlying traits of the illness from those related to episodes of mood exacerbation or pharmacological treatment.

Comparison of cytokine levels in depressed, manic and euthymic patients with bipolar disorder

BACKGROUND

The neurobiology of bipolar disorder is not completely understood. Cytokines have received increasing attention as potential mediators of the interaction with immune, neuroendocrine system and specific pathways involved in mood, energy, and activity control. Previous reports have suggested the association of mania and bipolar depression with a proinflammatory state. However, they did not compare cytokine levels in all phases of bipolar disorder.

METHODS

Sixty-one bipolar patients were recruited for assessment of serum cytokine levels. Of these, 14 were in euthymic state, 23 and 24 were in manic and depressive episodes, respectively. A healthy comparison group included 25 healthy volunteers. Cytokines involved in Th1/Th2 balance, such as TNF-alpha, IL-2, IL-4, IL-6, IL-10, IFN-gamma, were examined by flow cytometry.

RESULTS

During mania, proinflammatory cytokines, IL-2, IL-4 and IL-6, were increased in comparison with healthy subjects. Patients in depressive episode showed only increased IL-6 levels. There were no significant differences in cytokine levels between patients in remission and healthy subjects, except for IL-4. Mood symptoms showed a positive correlation with IL-6 and IL-2.

DISCUSSION

These findings suggest that mania, and to a less extent, depression are associated with a proinflammatory state. These changes seem to be related to mood state, as changes in cytokine profile were more pronounced during acute episodes than in euthymia. This study provides further support to investigate the immune system as a target for future treatment development.

Bipolar disorder and mechanisms of action of mood stabilizers

Bipolar disorder (BD) is a major medical and social burden, whose cause, pathophysiology and treatment are not agreed on. It is characterized by recurrent periods of mania and depression (Bipolar I) or of hypomania and depression (Bipolar II). Its inheritance is polygenic, with evidence of a neurotransmission imbalance and disease progression. Patients often take multiple agents concurrently, with incomplete therapeutic success, particularly with regard to depression. Suicide is common. Of the hypotheses regarding the action of mood stabilizers in BD, the "arachidonic acid (AA) cascade" hypothesis is presented in detail in this review. It is based on evidence that chronic administration of lithium, carbamazepine, sodium valproate, or lamotrigine to rats downregulated AA turnover in brain phospholipids, formation of prostaglandin E(2), and/or expression of AA cascade enzymes, including cytosolic phospholipase A(2), cyclooxygenase-2 and/or acyl-CoA synthetase. The changes were selective for AA, since brain docosahexaenoic or palmitic acid metabolism, when measured, was unaffected, and topiramate, ineffective in BD, did not modify the rat brain AA cascade. Downregulation of the cascade by the mood stabilizers corresponded to inhibition of AA neurotransmission via dopaminergic D(2)-like and glutamatergic NMDA receptors. Unlike the mood stabilizers, antidepressants that increase switching of bipolar depression to mania upregulated the rat brain AA cascade. These observations suggest that the brain AA cascade is a common target of mood stabilizers, and that bipolar symptoms, particularly mania, are associated with an upregulated cascade and excess AA signaling via D(2)-like and NMDA receptors. This review presents ways to test these suggestions.

Brain-derived neurotrophic factor and inflammatory markers in patients with early- vs. late-stage bipolar disorder

Bipolar I disorder (BD) has a poorer longer-term outcome than previously thought, with persistent cognitive impairment and functional decline. The neurobiological underpinnings that might underlie these changes remain unknown. Changes in brain-derived neurotrophic factor (BDNF) levels and cytokines are potential candidates. The aim of this study was to examine both cytokine and BDNF levels and their relationship in BD patients in the early and late stages of the disorder. We measured serum BDNF, TNF-alpha, IL-6 and IL-10 levels in a total of 60 patients with BD I and we compared those in early stages of illness with those in late stages of illness and also compared both groups with 60 matched healthy controls. BDNF was decreased only in those patients in the late stage of bipolar disorder. Moreover, BDNF levels were negatively correlated with length of illness. In contrast, all interleukins and TNF-alpha were increased in the early stages of BD, compared to controls. While TNF-alpha and IL-6 continued to be significantly higher than controls at late stages of BD, IL-10 did not. When levels were compared between patients at early and late stages of illness, there was a significant decrease in BDNF and IL-6 in the later stage of BD compared to the early stage. Inversely, TNF-alpha showed a significant increase at the later stage. Failure of inflammatory defences in the late stage of the disorder may account for reduction in BDNF and continued elevations in cytokines; thus these may have the potential to serve as markers of illness progression in BD.

The inflammatory & neurodegenerative (I&ND) hypothesis of depression: leads for future research and new drug developments in depression

Despite extensive research, the current theories on serotonergic dysfunctions and cortisol hypersecretion do not provide sufficient explanations for the nature of depression. Rational treatments aimed at causal factors of depression are not available yet. With the currently available antidepressant drugs, which mainly target serotonin, less than two thirds of depressed patients achieve remission. There is now evidence that inflammatory and neurodegenerative (I&ND) processes play an important role in depression and that enhanced neurodegeneration in depression may-at least partly-be caused by inflammatory processes. Multiple inflammatory-cytokines, oxygen radical damage, tryptophan catabolites-and neurodegenerative biomarkers have been established in patients with depression and these findings are corroborated by animal models of depression. A number of vulnerability factors may predispose towards depression by enhancing inflammatory reactions, e.g. lower peptidase activities (dipeptidyl-peptidase IV, DPP IV), lower omega-3 polyunsaturated levels and an increased gut permeability (leaky gut). The cytokine hypothesis considers that external, e.g. psychosocial stressors, and internal stressors, e.g. organic inflammatory disorders or conditions, such as the postpartum period, may trigger depression via inflammatory processes. Most if not all antidepressants have specific anti-inflammatory effects, while restoration of decreased neurogenesis, which may be induced by inflammatory processes, may be related to the therapeutic efficacy of antidepressant treatments. Future research to disentangle the complex etiology of depression calls for a powerful paradigm shift, i.e. by means of a high throughput-high quality screening, including functional genetics and genotyping microarrays; established and novel animal and ex vivo-in vitro models for depression, such as new transgenic mouse models and endophenotype-based animal models, specific cell lines, in vivo and ex vivo electroporation, and organotypic brain slice culture models. This screening will allow to: 1) discover new I&ND biomarkers, both at the level of gene expression and the phenotype; and elucidate the underlying molecular I&ND pathways causing depression; and 2) identify new therapeutic targets in the I&ND pathways; develop new anti-I&ND drugs for these targets; select existing anti-I&ND drugs or substances that could augment the efficacy of antidepressants; and predict therapeutic response by genetic I&ND profiles.

Cytoprotective effect of lithium against spontaneous and induced apoptosis of lymphoid cell line MOLT-4

Lithium (Li) is still useful in the treatment of bipolar disorder. Cellular mechanisms of Li action are not fully understood and include some cytoprotective properties. Data concerning Li effect on the apoptotic mechanisms in cells other than neurons are fragmentary and contradictory. We have investigated anti-apoptotic activity of Li in a lymphoid derived MOLT-4 cell line. Spontaneous and camptothecin-induced apoptosis was analyzed in cells treated with 0-20 mM Li carbonate. Early apoptosis was identified as significant mitochondrial depolarization (JC-1 staining). Later stages of apoptosis were estimated with annexin V binding and by the proportion of cells containing sub-G1 amounts of DNA (PI staining). We have observed a biphasic effect of Li on the proportion of spontaneously apoptotic cells;namely, low (therapeutic) concentrations of Li had a significant effect stabilizing the mitochondrial membrane polarization, while 10 and 20mM Li increased apoptosis. The latter could be seen both as mitochondrial depolarization as well as an increased proportion of sub-G1 cells, accompanied by reduced proportion of S phase cells. Li at concentrations above 2 mM had a significant, dose-dependent, anti-apoptotic effect on the cells undergoing camptothecin induced apoptosis. In conclusion, demonstrated cytoprotective effect of Li is at least partially related to stabilization of mitochondrial membrane potential and to the reduction of DNA damaging effects in proliferating cells; both may form part of the mechanism through which Li is useful in therapy of bipolar disorder, but may have more general consequences.

Imunologia do transtorno bipolar

OBJETIVO: Pesquisas recentes têm implicado fatores imunes na patogênese de diversos transtornos neuropsiquiátricos. O objetivo do presente trabalho é revisar os trabalhos que investigaram a associação entre transtorno bipolar e alterações em parâmetros imunes. MÉTODOS: Artigos que incluíam as palavras-chave: "bipolar disorder", "mania", "immunology", "cytokines", "chemokines", "interleukins", "interferon" e "tumor necrosis factor" foram selecionados em uma revisão sistemática da literatura. As bases de dados avaliadas foram MedLine e Scopus, entre os anos de 1980 e 2008. RESULTADOS: Foram identificados 28 trabalhos que estudaram alterações imunes em pacientes com transtorno bipolar. Seis artigos investigaram genes relacionados à resposta imune; cinco, autoanticorpos; quatro, populações leucocitárias; 13, citocinas e/ou moléculas relacionadas à resposta imune e seis, leucócitos de pacientes in vitro. CONCLUSÕES: Embora haja evidências na literatura correlacionando o transtorno bipolar a alterações imunes, os dados não são conclusivos. O transtorno bipolar parece estar associado a níveis mais elevados de autoanticorpos circulantes, assim como à tendência à ativação imune com produção de citocinas pró-inflamatórias e redução de parâmetros anti-inflamatórios.

Episode-specific differential gene expression of peripheral blood mononuclear cells in rapid cycling supports novel treatment approaches

Molecular mechanisms underlying bipolar affective disorders are unknown. Difficulties arise from genetic and phenotypic heterogeneity of patients and the lack of animal models. Thus, we focused on only one patient (n = 1) with an extreme form of rapid cycling. Ribonucleic acid (RNA) from peripheral blood mononuclear cells (PBMC) was analyzed in a three-tiered approach under widely standardized conditions. Firstly, RNA was extracted from PBMC of eight blood samples, obtained on two consecutive days within one particular episode, including two different consecutive depressive and two different consecutive manic episodes, and submitted to (1) screening by microarray hybridizations, followed by (2) detailed bioinformatic analysis, and (3) confirmation of episode-specific regulation of genes by quantitative real-time polymerase chain reaction (qRT-PCR).Secondly, results were validated in additional blood samples obtained one to two years later. Among gene transcripts elevated in depressed episodes were prostaglandin D synthetase (PTGDS) and prostaglandin D2 11-ketoreductase (AKR1C3), both involved in hibernation. We hypothesized them to account for some of the rapid cycling symptoms. A subsequent treatment approach over 5 months applying the cyclooxygenase inhibitor celecoxib (2 x 200 mg daily) resulted in reduced severity rating of both depressed and manic episodes. This case suggests that rapid cycling is a systemic disease, resembling hibernation, with prostaglandins playing a mediator role.

Promising avenues of therapeutics for bipolar illness

Basic scientific advances in understanding the neuropsychobioloqy of bipolar disorder have given us a multitude of opportunities to explore and exploit new avenues of therapeutics. Pharmacotherapeutic approaches include: neuropeptides (agonists such as thyrotropin-releasing hormone and antagonists such as corticotropin-releasing hormone), neurotrophic factors (especially brain-derived neurotrophic factor), and glutamatergic mechanisms (such as riluzole, ketamine, and antagonists of the NR-2B subunit of the glutamate receptor). Physiological interventions that would offer alternatives to electroconvulsive therapy include: repeated transcranial magnetic stimulation, especially at more intense stimulation parameters; magnetic stimulation therapy (seizures induced more focally by magnetic rather than electrical stimulation with resulting reduced meaning loss); vagal nerve stimulation, and deep brain stimulation. However, these, as well as the panoply of existing treatments, require further intensive investigation to place each of them in the proper therapeutic seguence and combination for the individual patient, based on development of better clinical and biological predictors of response. Large clinical trial networks and development of systematic research in clinical practice settings, such as that featured by the National Cancer institute for cancer chemotherapy, would greatly accelerate the progress in incorporating new, as well as existing, agents into the best treatment strategies. The bipolar disorders, which are increasingly recognized as complex, highly comorbid conditions with a high morbidity and mortality, of which the majority start in childhood and adolescence, are not likely to respond completely to any single new treatment agent, and new public health initiatives and research strategies are needed as much as any new single treatment advance.

Investigation of serum high-sensitive C-reactive protein levels across all mood states in bipolar disorder

There has been an increasing interest in the role of the immune and inflammatory systems in mood disorders. Mood episodes are associated with changes in acute phase proteins such as high-sensitivity C-reactive protein (hsCRP). The present study investigated serum hsCRP in manic, depressed, and euthymic BD patients as compared to matched healthy controls. Serum hsCRP was assessed using an ultrasensitive assay of particle-enhanced immunoturbidimetric latex agglutination. Serum hsCRP levels were increased in manic BD patients, as compared to euthymic, depressed patients and healthy controls (P < 0.001). These findings add to the notion that changes in the inflammatory system take place during acute episodes of mania.

TNF-alpha as a molecular target in bipolar disorder

The pathophysiology of bipolar disorder (BD) is poorly understood. An emerging body of evidence points to impairments in neuroplasticity, cell resilience and neuronal survival as the main neuropathological correlates of BD. It has been suggested that inflammatory cytokines, particularly TNF-alpha may play a critical role in this process. In the present review we examine the evidence suggesting that TNF-alpha regulates apoptotic cascades which may be related to neuronal and glial loss in BD. Current evidence suggests that an increase in serum levels of TNF-alpha takes place during manic and depressive episodes. The present article reviews the therapeutic implications of TNF-alpha signaling pathways involvement in the pathophysiology of BD.

Association between burnout and circulating levels of pro- and anti-inflammatory cytokines in schoolteachers

OBJECTIVE

The burnout syndrome has been associated with an increased risk of cardiovascular disease. The physiological mechanisms potentially involved in this link are underexplored. Knowing that a chronic low-grade systemic inflammatory state contributes to atherosclerosis, we investigated circulating cytokine levels in relation to burnout symptoms.

METHODS

We studied 167 schoolteachers (median, 48 years; range, 23-63 years; 67% women) who completed the Maslach Burnout Inventory with its three subscales emotional exhaustion (EE), lack of accomplishment (LA), and depersonalization (DP). Levels of the proinflammatory cytokine tumor necrosis factor (TNF)-alpha and of the anti-inflammatory cytokines interleukin (IL)-4 and IL-10 were determined in fasting morning plasma samples. The TNF-alpha/IL-4 ratio and the TNF-alpha/IL-10 ratio were computed as two indices of increased inflammatory activity. Analyses were adjusted for demographic factors, medication, lifestyle factors (including sleep quality), metabolic factors, and symptoms of depression and anxiety.

RESULTS

Higher levels of total burnout symptoms aggregating the EE, LA, and DP subscales independently predicted higher TNF-alpha levels (DeltaR(2)=.024, P=.046), lower IL-4 levels (DeltaR(2)=.021, P=.061), and a higher TNF-alpha/IL-4 ratio (DeltaR(2)=.040, P=.008). Higher levels of LA predicted decreased IL-4 levels (DeltaR(2)=.041, P=.008) and a higher TNF-alpha/IL-4 ratio (DeltaR(2)=.041, P=.007). The categorical dimensions of the various burnout scales (e.g., burnout yes vs. no) showed no independent relationship with any cytokine measure.

CONCLUSION

Burnout was associated with increased systemic inflammation along a continuum of symptom severity rather than categorically. Given that low-grade systemic inflammation promotes atherosclerosis, our findings may provide one explanation for the increased cardiovascular risk previously observed in burned-out individuals.

Chronic NMDA administration increases neuroinflammatory markers in rat frontal cortex: cross-talk between excitotoxicity and neuroinflammation

Chronic N-Methyl-D: -aspartate (NMDA) administration, a model of excitotoxicity, and chronic intracerebroventricular lipopolysaccharide infusion, a model of neuroinflammation, are reported to upregulate arachidonic acid incorporation and turnover in rat brain phospholipids as well as enzymes involved in arachidonic acid metabolism. This suggests cross-talk between signaling pathways of excitotoxicity and of neuroinflammation, involving arachidonic acid. To test whether chronic NMDA administrations to rats can upregulate brain markers of neuroinflammation, NMDA (25 mg/kg i.p.) or vehicle (1 ml saline/kg i.p.) was administered daily to adult male rats for 21 days. Protein and mRNA levels of cytokines and other inflammatory markers were measured in the frontal cortex using immunoblot and real-time PCR. Compared with chronic vehicle, chronic NMDA significantly increased protein and mRNA levels of interleukin-1beta, tumor necrosis factor alpha, glial fibrillary acidic protein and inducible nitric oxide synthase. Chronic NMDA receptor overactivation results in increased levels of neuroinflammatory markers in the rat frontal cortex, consistent with cross-talk between excitotoxicity and neuroinflammation. As both processes have been reported in a number of human brain diseases, NMDA receptor inhibitors might be of use in treating neuroinflammation in these diseases.