TNF-alpha as a molecular target in bipolar disorder

Mood disorders and obesity: understanding inflammation as a pathophysiological nexus

The aim of this review is to evaluate the evidentiary base supporting the hypothesis that the increased hazard for obesity in mood disorder populations (and vice versa) is a consequence of shared pathophysiological pathways. We conducted a PubMed search of all English-language articles with the following search terms: obesity, inflammation, hypothalamic-pituitary-adrenal axis, insulin, cognition, CNS, and neurotransmitters, cross-referenced with major depressive disorder and bipolar disorder. The frequent co-occurrence of mood disorders and obesity may be characterized by interconnected pathophysiology. Both conditions are marked by structural and functional abnormalities in multiple cortical and subcortical brain regions that subserve cognitive and/or affective processing. Abnormalities in several interacting biological networks (e.g. immuno-inflammatory, insulin signaling, and counterregulatory hormones) contribute to the co-occurence of mood disorders and obesity. Unequivocal evidence now indicates that obesity and mood disorders are chronic low-grade pro-inflammatory states that result in a gradual accumulation of allostatic load. Abnormalities in key effector proteins of the pro-inflammatory cascade include, but are not limited to, cytokines/adipokines such as adiponectin, leptin, and resistin as well as tumor necrosis factor alpha and interleukin-6. Taken together, the bidirectional relationship between obesity and mood disorders may represent an exophenotypic manifestation of aberrant neural and inflammatory networks. The clinical implications of these observations are that, practitioners should screen individuals with obesity for the presence of clinically significant depressive symptoms (and vice versa). This clinical recommendation is amplified in individuals presenting with biochemical indicators of insulin resistance and other concurrent conditions associated with abnormal inflammatory signaling (e.g. cardiovascular disease).

Cytokine levels in euthymic bipolar patients

BACKGROUND

The pathophysiology of bipolar disorder is not thoroughly understood. Several studies have investigated the possible role of cytokines in psychiatric disorders, based on their role in neuro-immune modulation; however, findings in studies on bipolar disorder remain limited and contradictory, and most studies have focused on either manic or depressive episodes. These studies suggest that both manic and depressive episodes could be pro-inflammatory states. The present study aimed to determine whether there are enduring differences in cytokine levels-unrelated to the effects of medication-between euthymic bipolar patients and healthy controls.

METHODS

The study included 31 euthymic bipolar patients-16 medication-free (MF) and 15 on lithium monotherapy (LM) and 16 healthy volunteers in whom serum cytokine levels were measured. The 3 groups were homogenous in terms of age, gender, and ethnicity. IFN-γ, TNF-α, IL-2, IL-4, IL-5, and IL-10 levels were measured in all groups using flow cytometry.

RESULTS

There were no differences in cytokine levels between MF euthymic bipolar patients and healthy controls. TNF-α and IL-4 levels in LM euthymic bipolar patients were higher than in both the MF euthymic bipolar patients and controls.

LIMITATIONS

The small and strictly selected study sample could limit the generalizability of the findings.

CONCLUSIONS

Cytokine production in MF euthymic bipolar patients was similar to that in healthy controls. The present study shows that the pro-inflammatory state resolves in euthymia and that lithium had an influence on the cytokine profile, which could create a confounding factor while investigating disease- related immunopathology of bipolar disorder.

Pathways underlying neuroprogression in bipolar disorder: focus on inflammation, oxidative stress and neurotrophic factors

There is now strong evidence of progressive neuropathological processes in bipolar disorder (BD). On this basis, the current understanding of the neurobiology of BD has shifted from an initial focus on monoamines, subsequently including evidence of changes in intracellular second messenger systems and more recently to, incorporating changes in inflammatory cytokines, corticosteroids, neurotrophins, mitochondrial energy generation, oxidative stress and neurogenesis into a more comprehensive model capable of explaining some of the clinical features of BD. These features include progressive shortening of the inter-episode interval with each recurrence, occurring in consort with reduced probability of treatment response as the illness progresses. To this end, emerging data shows that these biomarkers may differ between early and late stages of BD in parallel with stage-related structural and neurocognitive alterations. This understanding facilitates identification of rational therapeutic targets, and the development of novel treatment classes. Additionally, these pathways provide a cogent explanation for the efficacy of seemingly diverse therapies used in BD, that appear to share common effects on oxidative, inflammatory and neurotrophic pathways.

Osteoprotegerin levels in patients with severe mental disorders

BACKGROUND

Severe mental disorders are associated with elevated levels of inflammatory markers. In the present study, we investigated whether osteoprotegerin (OPG), a member of the tumour necrosis factor receptor family involved in calcification and inflammation, is elevated in patients with severe mental disorders.

METHODS

We measured the plasma levels of OPG in patients with severe mental disorders (n = 312; 125 with bipolar disorder and 187 with schizophrenia) and healthy volunteers (n = 239).

RESULTS

The mean plasma levels of OPG were significantly higher in patients than in controls (t531 = 2.6, p = 0.01), with the same pattern in bipolar disorder and schizophrenia. The increase was significant after adjustment for possible confounding variables, including age, sex, ethnic background, alcohol consumption, liver and kidney function, diabetes, cardiovascular disease, autoimmune diseases and levels of cholesterol, glucose and C-reactive protein.

LIMITATIONS

Owing to the cross-sectional design, it is difficult to determine causality.

CONCLUSION

Our results indicate that elevated OPG levels are associated with severe mental disorders and suggest that mechanisms related to calcification and inflammation may play a role in disease development.

Staging bipolar disorder

The purpose of this study was to analyze the evidence supporting a staging model for bipolar disorder. The authors conducted an extensive Medline and Pubmed search of the published literature using a variety of search terms (staging, bipolar disorder, early intervention) to find relevant articles, which were reviewed in detail. Only recently specific proposals have been made to apply clinical staging to bipolar disorder. The staging model in bipolar disorder suggests a progression from prodromal (at-risk) to more severe and refractory presentations (Stage IV). A staging model implies a longitudinal appraisal of different aspects: clinical variables, such as number of episodes and subsyndromal symptoms, functional and cognitive impairment, comorbidity, biomarkers, and neuroanatomical changes. Staging models are based on the fact that response to treatment is generally better when it is introduced early in the course of the illness. It assumes that earlier stages have better prognosis and require simpler therapeutic regimens. Staging may assist in bipolar disorder treatment planning and prognosis, and emphasize the importance of early intervention. Further research is required in this exciting and novel area.

Increased excitotoxicity and neuroinflammatory markers in postmortem frontal cortex from bipolar disorder patients

Reports of cognitive decline, symptom worsening and brain atrophy in bipolar disorder (BD) suggest that the disease progresses over time. The worsening neuropathology may involve excitotoxicity and neuroinflammation. We determined protein and mRNA levels of excitotoxicity and neuroinflammatory markers in postmortem frontal cortex from 10 BD patients and 10 age-matched controls. The brain tissue was matched for age, postmortem interval and pH. The results indicated statistically significant lower protein and mRNA levels of the N-methyl-D-aspartate receptors, NR-1 and NR-3A, but significantly higher protein and mRNA levels of interleukin (IL)-1beta, the IL-1 receptor (IL-1R), myeloid differentiation factor 88, nuclear factor-kappa B subunits, and astroglial and microglial markers (glial fibrillary acidic protein, inducible nitric oxide synthase, c-fos and CD11b) in postmortem frontal cortex from BD compared with control subjects. There was no significant difference in mRNA levels of tumor necrosis factor alpha or neuronal nitric oxide synthase in the same region. These data show the presence of excitotoxicity and neuroinflammation in BD frontal cortex, with particular activation of the IL-R cascade. The changes may account for reported evidence of disease progression in BD and be a target for future therapy.

The potential use of biomarkers as an adjunctive tool for staging bipolar disorder

Recent data show that biomarkers differ in early and late-stage bipolar disorder (BD). Here we propose a model of staging for bipolar disorder that emphasizes the potential use of biomarkers for differentiating early and late-stage BD patients in the inter-episodic period. The proposed model includes a Latent phase: patients at "ultra-high-risk" for developing BD, characterized by a family history of BD, temperament traits, mood, and anxiety symptoms as well as genetic vulnerability for developing the disorder; Stage I: patients who return to their baseline level of functioning when mood episodes resolve; Stage II: biomarkers and functioning impairment are related to comorbidities or rapid-cycling presentations; Stage III: persistent cognitive and functioning impairment in the inter-episode period as well as changes in biomarkers; and Stage IV: same findings as in Stage III associated with extreme cognitive and functioning impairment, to the point that patients are unable to live autonomously. Empirical testing will determine the ability of the present model to inform patients and clinicians about both prognosis and response to treatment.

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.

Serotonin 5-HT(2A) Receptor Function as a Contributing Factor to Both Neuropsychiatric and Cardiovascular Diseases

There are high levels of comorbidity between neuropsychiatric and cardiovascular disorders. A key molecule central to both cognitive and cardiovascular function is the molecule serotonin. In the brain, serotonin modulates neuronal activity and is actively involved in mediating many cognitive functions and behaviors. In the periphery, serotonin is involved in vasoconstriction, inflammation, and cell growth, among other processes. It is hypothesized that one component of the serotonin system, the 5-HT(2A) receptor, is a common and contributing factor underlying aspects of the comorbidity between neuropsychiatric and cardiovascular disorders. Within the brain this receptor participates in processes such as cognition and working memory, been implicated in effective disorders such as schizophrenia, and mediate the primary effects of hallucinogenic drugs. In the periphery, 5-HT(2A) receptors have been linked to vasoconstriction and hypertension, and to inflammatory processes that can lead to atherosclerosis.

State-dependent microstructural white matter changes in bipolar I depression

Abnormalities in fronto-limbic-striatal white matter (WM) have been reported in bipolar disorder (BD), but results have been inconsistent across studies. Furthermore, there have been no detailed investigations as to whether acute mood states contribute to microstructural changes in WM tracts. In order to compare fiber density and structural integrity within WM tracts between BD depression and remission, whole-brain fractional anisotropy (FA) and mean diffusivity (MD) were assessed in 37 bipolar I disorder (BD-I) patients (16 depressed and 21 remitted), and 26 healthy individuals with diffusion tensor imaging. Significantly decreased FA and increased MD in bilateral prefronto-limbic-striatal white matter and right inferior fronto-occipital, superior and inferior longitudinal fasciculi were shown in all BD-I patients versus controls, as well as in depressed BD-I patients compared to both controls and remitted BD-I patients. Depressed BD-I patients also exhibited increased FA in the ventromedial prefrontal cortex. Remitted BD-I patients did not differ from controls in FA or MD. These findings suggest that BD-I depression may be associated with acute microstructural WM changes.

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.

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.

Increased soluble tumor necrosis factor-alpha receptors in patients with major depressive disorder

AIM

Several lines of evidence suggest that major depressive disorder is associated with an inflammatory status. Tumor necrosis factor-alpha has been investigated as a potential molecular target in mood disorders. Tumor necrosis factor-alpha exerts its activity through binding to specific cell membrane receptors named as TNFR1 and TNFR2. The aim of the present study was to investigate soluble plasma TNFR1 (sTNFR1) and TNFR2 levels (sTNFR2) in major depressive disorder patients.

METHODS

Female outpatients with major depressive disorder (n = 30) were compared with a healthy control group (n = 19). Severity of depressive symptoms was evaluated on Beck Depression Inventory; post-traumatic stress disorder (PTSD) symptoms were evaluated on PTSD Checklist-Civilian Version; and childhood abuse and neglect on the Childhood Trauma Questionnaire. Plasma tumor necrosis factor-alpha and its soluble receptors were measured by ELISA.

RESULTS

Patients had no changes in tumor necrosis factor-alpha concentrations but did have increased sTNFR1 (P < 0.001) and sTNFR2 (P < 0.001) levels compared to controls. Plasma level of sTNFR1 was positively predicted by age (B = 0.25, P = 0.05) and PTSD-like symptoms (B = 0.41, P = 0.002) and plasma levels of sTNFR2 by depression severity (B = 0.67, P < 0.001).

CONCLUSIONS

Soluble tumor necrosis factor-alpha receptors could be reliable markers of inflammatory activity in major depression.

Article Commentary: The Emerging Role of Eicosapentaenoic Acid as an Important Psychoactive Natural Product: Some Answers but a Lot more Questions

Omega-3 polyunsaturated fatty acids play important roles in both the structure and communication processes of cells. Dietary deficiences of these fatty acids have been implicated in cardiac dysfunction, cancer and mood disorders. In the latter, clinical trials have strongly suggested that not all types of omega-3 PUFA are equally efficacious. In particular eicosapentaenoic acid (EPA) appears to be the most useful in ameliorating the symptoms of major depressive disorder. The mechanism by which omega-3 PUFA have these effects, and why EPA is apparently more effective in this role than the much more abundant brain lipid docosahexaenoic acid, is unclear. The available data do suggest various biologically plausible mechanisms all of which are amenable to study using straightforward experimental approaches. To progress further, a better understanding of how EPA and other omega-3 PUFA effect neurophysiological and neurosignalling processes is required.