Serum levels of brain-derived neurotrophic factor and thiobarbituric acid reactive substances in chronically medicated schizophrenic patients: a positive correlation

Concepts of Neuroinflammation and Their Relationship With Impaired Mitochondrial Functions in Bipolar Disorder

Bipolar disorder (BD) is a chronic psychiatric disease, characterized by frequent behavioral episodes of depression and mania, and neurologically by dysregulated neurotransmission, neuroplasticity, growth factor signaling, and metabolism, as well as oxidative stress, and neuronal apoptosis, contributing to chronic neuroinflammation. These abnormalities result from complex interactions between multiple susceptibility genes and environmental factors such as stress. The neurocellular abnormalities of BD can result in gross morphological changes, such as reduced prefrontal and hippocampal volume, and circuit reorganization resulting in cognitive and emotional deficits. The term "neuroprogression" is used to denote the progressive changes from early to late stages, as BD severity and loss of treatment response correlate with the number of past episodes. In addition to circuit and cellular abnormalities, BD is associated with dysfunctional mitochondria, leading to severe metabolic disruption in high energy-demanding neurons and glia. Indeed, mitochondrial dysfunction involving electron transport chain (ETC) disruption is considered the primary cause of chronic oxidative stress in BD. The ensuing damage to membrane lipids, proteins, and DNA further perpetuates oxidative stress and neuroinflammation, creating a perpetuating pathogenic cycle. A deeper understanding of BD pathophysiology and identification of associated biomarkers of neuroinflammation are needed to facilitate early diagnosis and treatment of this debilitating disorder.

Interaction of oxidative stress and BDNF on executive dysfunction in patients with chronic schizophrenia

Executive dysfunction is increasingly recognized as one of the widely observed dimensions of cognitive impairments in the course of schizophrenia (SCZ). However, the potential molecular pathological mechanisms remain elusive. Previous studies have demonstrated that decreased brain-derived neurotrophic factor (BDNF) and oxidative damage may be associated with the psychopathology and cognitive impairment of SCZ. The present study aims to assess whether the interaction between BDNF and oxidative damage is involved in the disruption of executive function (EF) in patients with chronic SCZ. Serum BDNF and plasma oxidative stress markers were measured in 189 patients and 60 control subjects. EFs were evaluated by Wisconsin card sorting tests (WCST), Stroop word/color test (Stroop), and verbal fluency tests (VFT). The results showed that patients performed worse in the VFT, WCST and Stroop tests than healthy subjects. Moreover, patients had lower activities of glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) and lower BDNF levels, but higher malondialdehyde (MDA) levels than healthy controls. In patients, BDNF was negatively correlated with SOD (p < 0.01). For patients, catalase (CAT) activity was negatively associated with WCST error score (p = 0.02) and BDNF was positively correlated to VFT score (p = 0.02). However, all these correlations between biomarkers and EF domains did not pass Bonferroni corrections. Finally, multiple regression analyses identified BDNF × SOD activity and BDNF × MDA as influencing factors for VFT score in patients (both p < 0.05). Our results highlight the complex interplay between OS parameters and BDNF in the pathophysiology of EF impairment in SCZ, consistent with its neurodevelopmental hypothesis.

Inter-relation between brain-derived neurotrophic factor and antioxidant enzymes in bipolar disorder

OBJECTIVES

Accumulating evidence indicates that oxidative stress and neurotrophins have a bidirectional relationship. In this post hoc, exploratory analysis, we investigated the association between plasma brain-derived neurotrophic factor (BDNF) levels and activities of the antioxidant enzymes glutathione peroxidase (GPx) and superoxide dismutase (SOD) in individuals with bipolar disorder (BD) and healthy controls.

METHODS

We measured plasma levels of BDNF and activities of GPx and SOD in individuals with BD (n=59) and healthy controls (n=26). Information related to current and past psychiatric/medical history, as well as to metabolic comorbidities, was also reported.

RESULTS

There were negative correlations between BDNF, GPx (r=-.449, P≤.001) and GPx/SOD ratio (r=-.503, P<.001), and a positive correlation between BDNF and SOD (r=.254, P=.020). There was a moderating effect of body mass index (BMI) on the association between BDNF and GPx/SOD rate ratio [(RR)=1.002, P=.034]; interactions between impaired glucose metabolism (IGM), GPx (RR=1.016, P=.033), and GPx/SOD ratio (RR=1.026, P=.002) were also observed. These results were significant in models that included age, gender, alcohol, tobacco and medication use.

CONCLUSIONS

There was a robust and independent correlation between peripheral BDNF and antioxidant enzyme activities in individuals with BD, which was moderated by metabolic comorbidities. These results reinforce the concept that these systems are associated and further extend knowledge of the putative effect of metabolic comorbidities in the pathophysiological substrates of BD.

Neurotrophin levels in different regions of the placenta and their association with birth outcome and blood pressure

INTRODUCTION

Our recent study in preeclampsia indicates differential oxidative stress in various regions of the placenta. Oxidative stress is known to influence neurotrophin levels. We therefore hypothesize that placental regional differences in oxidative stress will also lead to differences in neurotrophin levels.

METHODS

The current study examines the levels of neurotrophins, brain derived neurotrophic factor (BDNF) and nerve growth factor (NGF) in different regions of the placenta in 50 normotensive control women and 47 women with preeclampsia (21 delivering at term and 26 delivering preterm). Placentae were collected from four different regions: central maternal (CM), central fetal (CF), peripheral maternal (PM) and peripheral fetal (PF).

RESULTS

BDNF levels were higher in CF region as compared to CM (p < 0.01), PM (p < 0.01) and PF (p < 0.05) regions of the placenta in the control group. There was no regional change in NGF levels in any of the groups. Analysis between groups indicated higher NGF levels in CM (p < 0.01), PM (p < 0.05) and PF (p < 0.01) regions of preterm preeclampsia group as compared to control. Negative association of NGF levels in CM, CF and PM regions with baby weight and in CF, PM and PF regions with baby length was observed. NGF levels in all four regions were positively associated with systolic blood pressure.

DISCUSSION

Our data indicates regional differences in levels of BDNF only in normotensive control but not in preeclampsia group. Higher NGF levels in preterm preeclampsia may be a response to increased oxidative stress. This may have implications for altered placental development in preeclampsia.

The interplay between BDNF and oxidative stress in chronic schizophrenia

Neurodegenerative processes may be involved in the pathogenesis of schizophrenia. Brain-derived neurotrophic factor (BDNF), the most widely distributed neurotrophin and oxidative stress (OS) may be critical for several pathological manifestations of neurodegenerative disorders. Accumulating evidence suggests that both BDNF and OS may be involved in the pathophysiology of schizophrenia. However, the possible interaction between BDNF and OS has been under-investigated. Serum BDNF, plasma malondialdehyde (MDA) levels and superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase (CAT) activities were analyzed using established procedures in 164 chronic medicated schizophrenia and 50 healthy controls. Schizophrenic symptoms were assessed by the Positive and Negative Syndrome Scale (PANSS) with cognitive and depressive factors derived from the five factor model of the PANSS. Compared to the control group, the patients exhibited a significant decrease in BDNF levels, in the activities of SOD and GSH-Px but a significant increase in MDA levels. In patients, but not in controls, we observed a significant negative correlation between BDNF and SOD. Furthermore, the interaction between BDNF and CAT was associated with the PANSS cognitive factor, and the interaction between BDNF and GSH-Px with the PANSS depressive factor. Both decreased BDNF levels and OS may be implicated in the pathophysiology of chronic schizophrenia. Their inverse association only in the schizophrenia group may reflect a pathological mechanism involving an interaction of oxidative damage and neurotrophin dysfunction. Moreover, OS may interact with the BDNF system to influence the clinical symptoms and cognitive impairment in schizophrenia, which is line with the neurodevelopmental hypothesis of schizophrenia.

Antioxidant Activity of Grapevine Leaf Extracts against Oxidative Stress Induced by Carbon Tetrachloride in Cerebral Cortex, Hippocampus and Cerebellum of Rats

In recent years, it has become increasingly important to study the beneficial properties of derivatives of grapes and grapevine. The objective of this study was to determine the antioxidant activity of Vitis labrusca leaf extracts, comparing conventional and organic grapevines, in different brain areas of rats. We used male Wistar rats treated with grapevine leaf extracts for a period of 14 days, and on the 15th day, we administered in half of the rats, mineral oil and the other half, carbon tetrachloride (CCl₄). The animals were euthanized by decapitation and the cerebral cortex, hippocampus and cerebellum were removed to assess oxidative stress parameters and the activity of antioxidant enzymes. Lipid peroxidation levels (TBARS) were unchanged. However, CCl₄ induced oxidative damage to proteins in all tissues studied, and this injury was prevented by both extracts. Superoxide dismutase (SOD) activity was increased by CCl₄ in the cerebral cortex and decreased in other tissues. However, CCl₄ increased catalase (CAT) activity in the cerebellum and decreased it in the cerebral cortex. The SOD/CAT ratio was restored in the cerebellum by both extracts and only in the cerebral cortex by the organic extract.

Brain-derived neurotrophic factor as a potential biomarker of cognitive recovery in schizophrenia

Brain-derived neurotrophic factor (BDNF) has been proposed as a biomarker of schizophrenia and, more specifically, as a biomarker of cognitive recovery. Evidence collected in this review indicates that BDNF is relevant in the pathophysiology of schizophrenia and could play a role as a marker of clinical response. BDNF has been shown to play a positive role as a marker in antipsychotic treatment, and it has been demonstrated that typical antipsychotics decrease BDNF levels while atypical antipsychotics maintain or increase serum BDNF levels. Furthermore, BDNF levels have been associated with severe cognitive impairments in patients with schizophrenia. Consequently, BDNF has been proposed as a candidate target of strategies to aid the cognitive recovery process. There is some evidence suggesting that BDNF could be mediating neurobiological processes underlying cognitive recovery. Thus, serum BDNF levels seem to be involved in some synaptic plasticity and neurotransmission processes. Additionally, serum BDNF levels significantly increased in schizophrenia subjects after neuroplasticity-based cognitive training. If positive replications of those findings are published in the future then serum BDNF levels could be definitely postulated as a peripheral biomarker for the effects of intensive cognitive training or any sort of cognitive recovery in schizophrenia. All in all, the current consideration of BDNF as a biomarker of cognitive recovery in schizophrenia is promising but still premature.

Impact of peripheral levels of chemokines, BDNF and oxidative markers on cognition in individuals with schizophrenia

OBJECTIVE

To investigate possible differences in peripheral levels of chemokines, BDNF and oxidative markers between patients with Schizophrenia (SZ) and matched healthy controls, and investigate the correlation of these biomarkers with cognitive performance.

METHODS

Thirty individuals with SZ and 27 healthy controls were included and the following plasmatic biomarkers' levels were determined according to manufacturers' instructions: BDNF, TBARS, protein carbonyl content (PCC) and the chemokines CXCL-10/IP-10, CXCL-8/IL-8, CCL-11, CCL-24/Eotaxin-2, CCL-2/MCP-1, CCL-3/MIP-1. Selected neuropsychological tasks were administered to assess verbal learning (Hopkins Verbal Learning Test), verbal fluency (FAS test), working memory (Visual Working Memory Task, Keep Track Task, Letter Memory Task), set shifting (Plus-minus task, Number-letter task), inhibition (Computerized Stroop Task, Semantic Generation Task) and complex executive function tasks (Tower of London and the shortened version of the WCST-64).

RESULTS

Compared with the healthy control group, individuals with SZ presented significantly higher levels of BDNF and the chemokine CCL-11, and lower levels of TBARS and the chemokine CXCL-10/IP-10. When we examined only the SZ group, BDNF levels were positively correlated with semantic generation tasks. Working memory ability was negatively correlated with PCC. Regarding chemokines, CCL-11 was negatively correlated to performance in working memory test, and positively correlated with cognitive flexibility task. CXCL-8/IL-8 was positively correlated with verbal fluency. CCL-24/Eotaxin-2 was positively correlated with semantic generation ability and letter memory task.

CONCLUSIONS

Our results indicate that cognitive performance in SZ is associated with mediators of neuroplasticity that can be measured peripherally.

Effects of omega-3 dietary supplement in prevention of positive, negative and cognitive symptoms: a study in adolescent rats with ketamine-induced model of schizophrenia

Omega-3 has shown efficacy to prevent schizophrenia conversion in ultra-high risk population. We evaluated the efficacy of omega-3 in preventing ketamine-induced effects in an animal model of schizophrenia and its effect on brain-derived neurotrophic factor (BDNF). Omega-3 or vehicle was administered in Wistar male rats, both groups at the 30th day of life for 15days. Each group was split in two to receive along the following 7days ketamine or saline. Locomotor and exploratory activities, memory test and social interaction between pairs were evaluated at the 52nd day of life. Prefrontal-cortex, hippocampus and striatum tissues were extracted right after behavioral tasks for mRNA BDNF expression analysis. Bloods for serum BDNF were withdrawn 24h after the end of behavioral tasks. Locomotive was increased in ketamine-treated group compared to control, omega-3 and ketamine plus omega-3 groups. Ketamine group had fewer contacts and interaction compared to other groups. Working memory and short and long-term memories were significantly impaired in ketamine group compared to others. Serum BDNF levels were significantly higher in ketamine plus omega-3 group. There was no difference between groups in prefrontal-cortex, hippocampus and striatum for mRNA BDNF expression. Administration of omega-3 in adolescent rats prevents positive, negative and cognitive symptoms in a ketamine animal model of schizophrenia. Whether these findings are consequence of BDNF increase it is unclear. However, this study gives compelling evidence for larger clinical trials to confirm the use of omega-3 to prevent schizophrenia and for studies to reinforce the beneficial role of omega-3 in brain protection.

Serum levels of IL-6, IL-10 and TNF-α in patients with bipolar disorder and schizophrenia: differences in pro- and anti-inflammatory balance

OBJECTIVE

Previous reports suggest that cytokines act as potential mediators of the interaction between the immune and neuroendocrine systems, and that a proinflammatory state may be associated with bipolar disorder and schizophrenia. The aim is to compare cytokine levels in both disorders.

METHOD

Twenty euthymic bipolar disorder patients, 53 chronic stabilized schizophrenia patients and 80 healthy controls were recruited. Subjects were all non-smokers and non-obese. Cytokines TNF-α, IL-6, and IL-10 were examined by sandwich ELISA.

RESULTS

IL-6 levels were increased in schizophrenia patients when compared to controls (p < 0.0001) and euthymic bipolar disorder patients (p < 0.0001). IL-6 levels were no different in controls compared to euthymic bipolar disorder patients (p = 0.357). IL-10 was lower in controls compared to schizophrenia patients (p = 0.001) or to bipolar disorder patients (p = 0.004). There was no significant difference in TNF-α serum levels among the groups (p = 0.284). Gender-based classification did not significantly alter these findings, and no correlation was found between the antipsychotic dose administered and cytokine levels in patients with schizophrenia.

DISCUSSION

These findings evidence a chronic immune activation in schizophrenia. Bipolar disorder seems to present an episode-related inflammatory syndrome. Increased anti-inflammatory factor IL-10 in bipolar disorder and schizophrenia suggests different patterns of inflammatory balance between these two disorders. Results further support the need to investigate cytokines as possible biomarkers of disease activity or treatment response.

Similarities in serum oxidative stress markers and inflammatory cytokines in patients with overt schizophrenia at early and late stages of chronicity

Schizophrenia (SZ) is a debilitating neurodevelopmental disorder that strikes at a critical period of a young person's life. Its pathophysiology could be the result of deregulation of synaptic plasticity, with downstream alterations of inflammatory immune processes regulate by cytokines, impaired antioxidant defense and increased lipid peroxidation. The aim of this study was to examine serum oxidative stress markers and inflammatory cytokines in early and late phases of chronic SZ. Twenty-two patients at early stage (within first 10 years of a psychotic episode), 39 at late stage (minimum 10 years after diagnosis of SZ) and their respective matched controls were included. Each subject had 5 ml blood samples collected by venipuncture to examined thiobarbituric acid-reactive substances (TBARS), total reactive antioxidant potential (TRAP), protein carbonyl content (PCC), Interleukins 6 and 10 (IL-6, IL-10) and tumor necrosis factor alpha (TNF-alpha). TBARS, IL-6 and PCC levels were significantly higher in patients with SZ at early and late stages than in controls. There were no differences for TRAP and TNF-alpha levels in patients with SZ at early and late stages than in controls. IL-10 levels were decreased in patients at late stage and a decrease trend in early stage was found. Results provided evidence consistent with comparable biological markers across chronic SZ. The concept of biochemical staging proposed by others for bipolar disorder is not seen in this cohort of patients with SZ, at least for cytokines and oxidative stress markers. Our findings reinforce the need of assessment of individuals in ultra high risk to develop psychosis and first-episode population.

The role of BDNF in the pathophysiology and treatment of schizophrenia

Brain derived neurotrophic factor (BDNF) has been associated with the pathophysiology of schizophrenia (SCZ). However, it remains unclear whether alterations in BDNF observed in patients with SCZ are a core part of disease neurobiology or a consequence of treatment. In this manuscript we review existing knowledge relating the function of BDNF to synaptic transmission and neural plasticity and the relationship between BDNF and both pharmacological and non-pharmacological treatments for SCZ. With regards to synaptic transmission, exposure to BDNF or lack of this neurotrophin results in alteration to both excitatory and inhibitory synapses. Many authors have also evaluated the effects of both pharmacological and non-pharmacological treatments for SCZ in BDNF and despite some controversial results, it seems that medicated and non-medicated patients present with lower levels of BDNF when compared to controls. Further data suggests that typical antipsychotics may decrease BDNF expression whereas mixed results have been obtained with atypical antipsychotics. The authors found few studies reporting changes in BDNF after non-pharmacological treatments for SCZ, so the existing evidence in this area is limited. Although the study of BDNF provides some new insights into understanding of the pathophysiology and treatment of SCZ, additional work in this area is needed.

Brain-derived neurotrophic factor levels in schizophrenia: a systematic review with meta-analysis

Brain-derived neurotrophic factor (BDNF) regulates the survival and growth of neurons, and influences synaptic efficiency and plasticity. Several studies report reduced peripheral (blood) levels of BDNF in schizophrenia, but findings are inconsistent. We undertook the first systematic review with meta-analysis of studies examining blood BDNF levels in schizophrenia compared with healthy controls, and examined potential effects of age, gender and medication. Included are individual studies of BDNF blood (serum or plasma) levels in schizophrenia (including schizoaffective disorder, or first episode psychosis), compared with age-matched healthy controls, obtained by electronic Medline and Embase searches, and hand searching. The decision to include or exclude studies, data extraction and quality assessment were completed by two independent reviewers. The initial search revealed 378 records, of which 342 were excluded on reading the Abstract, because they did not examine BDNF blood levels in schizophrenia compared with healthy controls. Of 36 papers screened in full, 17 were eligible for inclusion, but one was subsequently removed as an outlier. The remaining 16 studies provided moderate quality evidence of reduced blood BDNF levels in schizophrenia (Hedges g=-0.458, 95% confidence interval=-0.770 to -0.146, P<0.004, random effects model). Subgroup analyses reveal reduced BDNF in both drug-naïve and medicated patients, and in males and females with schizophrenia. Meta-regressions showed an association between reduced BDNF in schizophrenia and increasing age, but no effects of medication dosage. Overall, blood levels of BDNF are reduced in medicated and drug-naïve patients with schizophrenia; this evidence is of moderate quality, that is, precise but with considerable, unexplained heterogeneity across study results.

Increased annexin-V and decreased TNF-α serum levels in chronic-medicated patients with schizophrenia

Schizophrenia (SZ) is a chronic severe mental disorder. Increased inflammatory processes have been shown in acute and chronic SZ. Apoptotic processes may alter the neuronal network and are involved in the pathogenesis of several neurodegenerative diseases, such as SZ. Annexin-V seems to have a role on inhibition of pro-inflammatory activities during apoptosis. Tumor necrosis factor (TNF-alpha) is a cytokine involved in systemic inflammation and is a member of a group of cytokines which stimulate acute phase reactions. A chronic immune activation in SZ has been shown. The aim of this study was to compare annexin-V and TNF-alpha serum levels in chronic medicated patients with SZ and healthy controls. Thirty-eight outpatients from the HCPA Schizophrenia Program and 38 healthy controls were enrolled to this study protocol. Annexin-V and TNF-alpha serum levels were measured with ELISA. Serum annexin-V levels were significantly higher in patients with SZ than in controls (p<0.001) and TNF-alpha significantly lower (p<0.001). The present result of increased annexin-V and decreased serum levels of TNF-alpha compared to controls may be a result of the stabilization phase of psychosis and a reduction in metabolic brain aggression. In this complex picture, increased levels of annexin-V and decreased levels of TNF-alpha in our sample would be explained by illness stability and chronic treatment. Our findings support the hypothesis of a state dependant process of inflammation in SZ. Further prospective studies to clarify the findings described in this paper are needed.

Serum brain-derived neurotrophic factor and clozapine daily dose in patients with schizophrenia: a positive correlation

Brain-derived neurotrophic factor (BDNF) plays a critical role in neurodevelopment and neuroplasticity. Altered BDNF signaling is thought to contribute to the pathogenesis of schizophrenia (SZ) especially in relation to cognitive deficits. Clozapine (CLZ) has been shown a beneficial effect on cognition in SZ in some studies and a detrimental effect in others. To examine serum BDNF, two groups of chronically medicated DSM-IV SZ patients (n=44), on treatment with clozapine (n=31) and typical antipsychotics (n=13) had 5ml blood samples collected by venipuncture. Serum BDNF levels were significantly correlated with CLZ daily dose (r=0.394, p=0.028), but not with typical antipsychotic daily dose (r=0.208, p=0.496). This study suggests that serum BDNF levels are correlated with CLZ daily dose, and this may lead to the cognitive enhancement as seen in patients with SZ under CLZ. Despite the strong evidence that chronic administration of CLZ is effective for patients with SZ, it is still unknown whether atypical antipsychotic drugs regulate BDNF expression. Serum BDNF levels concentration in SZ merits further investigations with regard to the role of neurotrophins in the cognitive response to treatment with CLZ and other atypical antipsychotics.

Effects of N-acetylcysteine on substance use in bipolar disorder: A randomised placebo-controlled clinical trial

OBJECTIVE

To evaluate the effect of N-acetylcysteine (NAC) on substance use in a double-blind, placebo-controlled trial of NAC in bipolar disorder. It is hypothesised that NAC will be superior to placebo for reducing scores on the Clinical Global Impressions scale for Substance Use (CGI-SU).

METHODS

Participants were randomised to a 6-months of treatment with 2 g/day NAC (n = 38) or placebo (n = 37). Substance use was assessed at baseline using a Habits instrument. Change in substance use was assessed at regular study visits using the CGI-SU.

RESULTS

Among the 75 participants 78.7% drank alcohol (any frequency), 45.3% smoked tobacco and 92% consumed caffeine. Other substances were used by fewer than six participants. Caffeine use was significantly lower for NAC-treated participants compared to placebo at week 2 of treatment but not at other study visits.

CONCLUSIONS

NAC appeared to have little effect on the participants who were using substances. A larger study on a substance-using population will be necessary to determine if NAC may be a useful treatment for substance use.

Effects of N-acetylcysteine on substance use in bipolar disorder: a randomised placebo-controlled clinical trial

OBJECTIVE

To evaluate the effect of N-acetylcysteine (NAC) on substance use in a double-blind, placebo-controlled trial of NAC in bipolar disorder. It is hypothesised that NAC will be superior to placebo for reducing scores on the Clinical Global Impressions scale for Substance Use (CGI-SU).

METHODS

Participants were randomised to 6-months of treatment with 2 g/day NAC (n = 38) or placebo (n = 37). Substance use was assessed at baseline using the Habits instrument. Change in substance use was assessed at regular study visits using the CGI-SU.

RESULTS

Amongst the 75 participants 78.7% drank alcohol (any frequency), 45.3% smoked tobacco and 92% consumer caffeine. Other substances were used by fewer than six participants. Caffeine use was significantly lower for NAC-treated participants compared with placebo at week 2 of treatment but not at other study visits.

CONCLUSION

NAC appeared to have little effect on substance use in this population. A larger study on a substance using population will be necessary to determine if NAC may be a useful treatment for substance use.

Serum brain-derived neurotrophic factor in bipolar and unipolar depression: a potential adjunctive tool for differential diagnosis

The differential diagnosis of Bipolar Disorder (BD) and Major Depressive Disorder (MDD) is a diagnostic challenge during depressive episodes. Noteworthy, the proper differentiation between BD depressive state and MDD has important treatment implications. BDNF levels may be valuable adjunctive tool for this differential diagnosis. Ten subjects with MDD, forty with BD type I and thirty healthy comparison subjects were recruited. All subjects had BDNF serum levels measured and, in patients, BDNF serum levels were assessed during acute depressive episode. Optimal sensitivity and specificity of serum BDNF for the differential diagnosis of unipolar and bipolar depression were determined by the receiver operating characteristic (ROC) curve analysis, using a nonparametric approach. Serum BDNF levels in depressive BD patients were lower compared to MDD patients and controls (0.15+/-0.08, 0.35+/-0.08, and 0.38+/-0.12, respectively, p<0.001). The area under the curve (AUC) of the ROC analysis in BD depression vs. MDD was 0.95 (ranged from 0.89 to 1.00). Overall, the AUC of the ROC analysis (BD depression vs. MDD and controls) was 0.94 (95% CI 0.89 to 0.99, p<0.001). A proposed "best" cutoff of 0.26 resulted in 88% sensitivity and 90% specificity. Serum BDNF levels appear as a promising tool to discriminate bipolar from unipolar depression. Our results suggest the role of BDNF as an adjunctive tool to promote prompt and accurate diagnosis of BD. However, further investigation and replication of these results are warranted.