Plasma BDNF and tPA are associated with late-onset geriatric depression

Differences in olfactory functional connectivity in early-onset depression and late-onset depression

Background

Late-onset depression (LOD) and early-onset depression (EOD) exhibit different pathological mechanisms and clinical phenotypes, including different extents of olfactory dysfunction. However, the brain abnormalities underlying the differences in olfactory dysfunction between EOD and LOD remain unclear.

Objective

The aim of this study was to compare the functional connectivity (FC) patterns of olfactory regions between EOD patients and LOD patients and examine their relationship with cognitive function.

Methods

One hundred and five patients with EOD, 101 patients with LOD and 160 normal controls (NCs) were recruited for the present study. Participants underwent clinical assessment, olfactory testing, cognitive assessments, and magnetic resonance imaging. Eight regions of the primary and secondary olfactory regions were selected to investigate olfactory FC.

Results

Patients with LOD exhibited decreased odor identification (OI) compared with patients with EOD and NCs. The LOD group exhibited decreased FC compared with the EOD and NC groups when primary and secondary olfactory regions were selected as the regions of interest (the piriform cortex, lateral entorhinal cortex, and orbital-frontal cortex). Additionally, these abnormal olfactory FCs were associated with decreased cognitive function scores and OI, and the FC between the left orbital-frontal cortex and left amygdala was a partial mediator of the relationship between global cognitive scores and OI.

Conclusion

Overall, patients with LOD exhibited decreased FC in both the primary and secondary olfactory cortices compared with patients with EOD, and abnormal olfactory FC was associated with OI dysfunction and cognitive impairment. The FC between the orbital-frontal cortex and amygdala mediated the relationship between global cognitive function and OI.

Pimavanserin treatment increases plasma brain-derived neurotrophic factor levels in rats

Background

Pimavanserin, a serotonin 5HT-2A receptor inverse agonist is the first-line, FDA-approved treatment of hallucinations and delusions associated with Parkinson's Disease psychosis (PDP), which occurs in up to 50% of PD patients. The neurobiological mechanism underlying the therapeutic effectiveness of Pimavanserin in PDP remains unknown. Several earlier studies have shown that treatment with 5HT-2A antagonists and other drugs acting on the serotonergic system such as SSRIs increase Brain derived neurotrophic factor (BDNF) levels in rodents. BDNF is synthesized as the precursor proBDNF, that undergoes cleavage intra or extracellularly to produce a mature BDNF (mBDNF) protein. mBDNF is believed to play a key role in neuroplasticity and neurogenesis. The present study tested the hypothesis that treatment with Pimavanserin is associated with higher and sustained elevations of mBDNF.

Methods

Adult Sprague-Dawley male rats were treated with Pimavanserin, Fluoxetine or vehicle for 4 weeks (chronic) or 2 h (acute). BDNF levels were determined by enzyme-linked Immunosorbent assay (ELISA).

Results

We found significant increases in plasma mBDNF levels in rats following chronic Pimavanserin treatment, but not in Fluoxetine-treated rats. No significant changes in mBDNF levels were found in the prefrontal cortex or hippocampus following Pimavanserin or Fluoxetine treatment.

Conclusion

These findings suggest that increase in mBDNF levels could be a contributing mechanism for the neuroprotective potential of Pimavanserin.

Blood Brain-Derived Neurotrophic Factor (BDNF) and Major Depression: Do We Have a Translational Perspective?

Major depressive disorder (MDD) affects millions of people worldwide and is a leading cause of disability. Several theories have been proposed to explain its pathological mechanisms, and the “neurotrophin hypothesis of depression” involves one of the most relevant pathways. Brain-derived neurotrophic factor (BDNF) is an important neurotrophin, and it has been extensively investigated in both experimental models and clinical studies of MDD. Robust empirical findings have indicated an association between increased BDNF gene expression and peripheral concentration with improved neuronal plasticity and neurogenesis. Additionally, several studies have indicated the blunt expression of BDNF in carriers of the Val66Met gene polymorphism and lower blood BDNF (serum or plasma) levels in depressed individuals. Clinical trials have yielded mixed results with different treatment options, peripheral blood BDNF measurement techniques, and time of observation. Previous meta-analyses of MDD treatment have indicated that antidepressants and electroconvulsive therapy showed higher levels of blood BDNF after treatment but not with physical exercise, psychotherapy, or direct current stimulation. Moreover, the rapid-acting antidepressant ketamine has presented an early increase in blood BDNF concentration. Although evidence has pointed to increased levels of BDNF after antidepressant therapy, several factors, such as heterogeneous results, low sample size, publication bias, and different BDNF measurements (serum or plasma), pose a challenge in the interpretation of the relation between peripheral blood BDNF and MDD. These potential gaps in the literature have not been properly addressed in previous narrative reviews. In this review, current evidence regarding BDNF function, genetics and epigenetics, expression, and results from clinical trials is summarized, putting the literature into a translational perspective on MDD. In general, blood BDNF cannot be recommended for use as a biomarker in clinical practice. Moreover, future studies should expand the evidence with larger samples, use the serum or serum: whole blood concentration of BDNF as a more accurate measure of peripheral BDNF, and compare its change upon different treatment modalities of MDD.

Reduced plasma Fetuin-A is a promising biomarker of depression in the elderly

Depression affects 7% of the elderly population, and it often remains misdiagnosed or untreated. Peripheral biomarkers might aid clinicians by allowing more accurate and well-timed recognition of the disease. We sought to determine if plasma protein levels predict the severity of depressive symptomatology or distinguish patients from healthy individuals. The severity of depressive symptoms and global cognitive functioning were assessed by the Geriatric Depression Scale (GDS) and Mini-Mental State Examination (MMSE) in 152 elderly subjects, 76 of which with major depressive disorder (MDD). Plasma levels of 24 proteins were measured by multiplexing and analyzed as continuous predictors or dichotomized using the median value. The association between individual plasma proteins and MDD risk or depressive symptoms severity was investigated using multiple logistic and linear regressions including relevant covariates. Sensitivity analyses were performed excluding cognitively impaired individuals or non-acute patients with MDD. After adjusting for possible confounders and false discovery rate (FDR) correction, we found lower Fetuin-A levels in MDD patients vs. controls (p_FDR = 1.95 × 10^-6). This result was confirmed by the sensitivity and dichotomized analyses. Lower prolactin (PRL) levels predicted more severe depressive symptoms in acute MDD patients (p_FDR = 0.024). Fetuin-A is a promising biomarker of MDD in the elderly as this protein was negatively associated with the disorder in our sample, regardless of the global cognitive functioning. Lower PRL levels may be a peripheral signature of impaired neuroprotective processes and serotoninergic neurotransmission in more severely depressed patients.

State-of-the-Art: Inflammatory and Metabolic Markers in Mood Disorders

Mounting evidence highlights the involvement of inflammatory/immune systems and their relationships with neurotransmitters and different metabolic processes in mood disorders. Nevertheless, there is a general agreement that available findings are still inconclusive. Therefore, further investigations are required, aimed at deepening the role of possible alterations of biomarkers in the pathophysiology of mood disorders that might lead to more focused and tailored treatments. The present study is a comprehensive review on these topics that seem to represent intriguing avenues for the development of real innovative therapeutic strategies of mood disorders.

Associations between inflammatory and neurological markers with quality of life and well-being in older adults

OBJECTIVES

Stressful experiences, poor self-rated health, and negative emotional states have been implicated with higher levels of inflammatory markers and lower levels of neurotrophic factors in some healthy adults and clinical populations, but these relationships are unclear in the elderly. This study aimed to identify the associations between systemic inflammatory and neurological markers with well-being and health-related quality of life (HR-QoL) in independently living elderly people.

DESIGN

Cross-sectional study.

SETTING AND PARTICIPANTS

A total of 268 men and women aged ≥65 years living independently in retirement communities in Melbourne, Australia.

MEASURES

Questionnaires were used to assess HR-QoL [Short Form (SF)-36 version 2] and well-being (Personal Wellbeing Index). Serum inflammatory cytokines [interleukin (IL)-4, IL-6, IL-1β, IL-8, IL-10, tumor necrosis factor (TNF)-α, and high sensitive C-reactive protein (hs-CRP)] were standardised to Z-scores and used to calculate pro- and anti-inflammatory composite score and an overall composite inflammatory index. Plasma levels of the neurological markers amyloid β (1-40) and amyloid β (1-42), brain derived neurotrophic factor (BDNF), insulin-like growth factor-1 (IGF-1) and vascular endothelial growth factor (VEGF), were also assessed.

RESULTS

No significant associations were found between any inflammatory or neurological marker with HR-OoL or well-being, with the exception that lower perceptions of the HR-QoL vitality subscale were associated with higher levels of hs-CRP [unstandardized beta-coefficient (β): -1.50; 95% CI: -2.53, -0.46; P = 0.004] and Z-scores in the pro-inflammatory composite score (β = -2.06; 95% CI: -3.49, -0.62; P = 0.005).

CONCLUSIONS/IMPLICATIONS

In elderly people residing in independent living retirement communities, there was no consistent evidence indicating that circulating inflammatory or neurological markers were associated with the key physical or mental HR-QoL domains or overall well-being. This suggests that these biomarkers may not be effective predictors in relatively healthy communities, and may be more beneficial in frail or clinical populations. Clinical Trials registry: Australian New Zealand Clinical Trials Registry (ACTRN12613001161718). http://www.anzctr.org.au/.

Prognostic effect of serum BDNF levels in late-life depression: Moderated by childhood trauma and SSRI usage?

BACKGROUND

Brain-derived neurotrophic factor (BDNF) levels decline during depression and normalise after remission, although studies in older patient samples are inconsistent. Whether BDNF serum levels predict depression remission is unclear. We hypothesize that the predictive value of serum BDNF levels in late-life depression is moderated by selective serotonin reuptake inhibitors (SSRI) usage and early traumatization.

METHODS

Our study sample was a subset of the Netherlands Study of Depression in Older persons (NESDO), a prospective cohort study. It consisted of 267 older persons with a diagnosis of depression, for which follow-up data were available. Depression diagnosis was assessed at baseline and follow up using a structured diagnostic interview (Composite International Diagnostic Interview (CIDI), volume2.1). Logistic regression was performed (adjusted for covariates) with remission of depression after two years as the dependent variable and baseline BDNF serum levels, childhood traumatization and SSRI use as independent variables. Results - The mean age of the subjects was 70.7 years, 65.6% of them were female, their mean BDNF level was 7.7 ng/ml, 80 (30.0%) of them were traumatised in their childhood,71 (26.6%) used SSRIs and 136 (50.9%) no longer had a depressive disorder at the two year follow up. The predictive value of BDNF serum levels was conditional on traumatization and SSRI usage (threeway interaction p = .010). Higher BDNF serum levels predicted remission in traumatized depressed patients without SSRI usage (OR = 1.17, 95% C.I.: 1.00-1.36; p = .048) and in non-traumatized depressed patients who used SSRIs (OR = 1.17, 95% C.I.: 1.00-1.36; p = .052), but not in the other two subgroups.

CONCLUSION

The association between BDNF serum levels and the course of late-life depression seems to depend on SSRI use and childhood trauma. Based on these results, we hypothesize that childhood trauma may permanently reduce ('blunt') the responsiveness of the neurotrophic system to SSRI usage, and that this responsiveness might be more important for depression course than the actual BDNF serum levels.

Ketamine ameliorates depressive-like behaviors by tPA-mediated conversion of proBDNF to mBDNF in the hippocampus of stressed rats

Some studies have indicated that ketamine has a rapid antidepressant effects, but the underlying molecular mechanism is still unclear. Researchers have found that mature brain-derived neurotrophic factor (mBDNF) and its precursor proBDNF are related to depression; they elicit opposite effects on cellular functions. It is clear that tissue plasminogen activator (tPA) is a key regulatory element in the conversion of proBDNF to mBDNF. The chronic unpredicted mild stress (CUMS) procedure is a classical and reliable method to establish the model of depression. This study found that sucrose preference and locomotor activity were both reduced in CUMS-treated rats while were increased in those who were injected with ketamine. The hippocampal proBDNF/mBDNF ratio was downregulated after ketamine treatment in those rats, together with an increased level of tPA in the hippocampus. However, tPA activity was unaltered after ketamine intraperitoneal injection. Intrahippocampal injection of active plasminogen activator inhibitor-1 (inhibitor of tPA) before ketamine treatment reversed the antidepressant effects and upregulated the proBDNF/mBDNF ratio. The results of this study suggest that the antidepressant action induced by ketamine may be related to tPA-mediated conversion of proBDNF to mBDNF in the hippocampus.

Altered levels of brain-derived neurotrophic factor, proBDNF and tissue plasminogen activator in children with posttraumatic stress disorder

The current study aims to compare the serum brain-derived neurotrophic factor (BDNF), proBDNF and tissue plasminogen activator (tPA) levels in cases that have developed posttraumatic stress disorder (PTSD) in consequence of sexual abuse with those in healthy control subjects. Thirty-one female patients between 8 and 18 years of age who have been diagnosed with PTSD due to sexual abuse and thirty-one healthy female volunteer controls were included in the study. Frequency, intensity and severity of PTSD symptoms were assessed on the basis of Clinician-Administered Post-Traumatic Stress Disorder Scale for Children and Adolescents (CAPS-CA). Serum BDNF, proBDNF and tPA levels were measured by Enzyme-Linked Immunosorbent Assay (ELISA) method. Results of the present study revealed that serum levels of BDNF and proBDNF in PTSD group were significantly lower but tPA level was significantly higher as compared to healthy control subjects. There were no correlations between CAPS-CA scores and BDNF, proBDNF and tPA levels. Decreased levels of BDNF, as suggested to have a role in the etiopathogenesis of PTSD, appear to be a result of the reduction in proBDNF production. The increased tPA levels in such cases, on the other hand, can be a compensatory mechanism serving to increase the BDNF levels.

Neurotrophic factors and hippocampal activity in PTSD

Although numerous studies have investigated the neurotrophic factors and hippocampal activity in posttraumatic stress disorder (PTSD) separately each other, it is unclear whether an association between neurotrophic factors and hippocampal activity is present. The aim of this study was to evaluate the functional changes in hippocampus before and after treatment with escitalopram and to associate these changes with peptides related to neuronal growth in patients with chronic PTSD and trauma survivors without PTSD. Fifteen earthquake survivors with chronic PTSD and thirteen drug naïve trauma exposed individuals without PTSD underwent fMRI scans in a block design. Serum levels of Nerve Growth Factor (NGF) and Brain Derived Neurotrophic Factor (BDNF) were measured before and after 12 weeks treatment with escitalopram. Baseline median serum level of NGF was significantly lower in patients with chronic PTSD than trauma survivors; however, 12 weeks of treatment with escitalopram significantly increased it. Higher activation was found both in left and right hippocampus for chronic PTSD group than trauma survivors. Treatment with escitalopram was significantly associated with suppression of the hyperactivation in left hippocampus in patients with chronic PTSD. Bilateral hyperactivation in hippocampus and lowered NGF may associate with neurobiological disarrangements in chronic PTSD. Treatment with escitalopram was significantly associated with both improvement in the severity of PTSD symptoms and biological alterations. Patients diagnosed with PTSD may have further and complicated deteriorations in hippocampal networks and neurotransmitter systems than individuals who had not been diagnosed with PTSD following the same traumatic experience.

BDNFVal66met polymorphism: a potential bridge between depression and thrombosis

Aims

Epidemiological studies strongly suggest a link between stress, depression, and cardiovascular diseases (CVDs); the mechanistic correlation, however, is poorly understood. A single-nucleotide polymorphism in the BDNF gene (BDNFVal66Met), associated with depression and anxiety, has been proposed as a genetic risk factor for CVD. Using a knock-in mouse carrying the BDNFVal66Met human polymorphism, which phenocopies psychiatric-related symptoms found in humans, we investigated the impact of this SNP on thrombosis.

Methods and results

BDNFMet/Met mice displayed a depressive-like phenotype concomitantly with hypercoagulable state and platelet hyperreactivity. Proteomic analysis of aorta secretome from BDNFMet/Met and wild-type (WT) mice showed differential expression of proteins involved in the coagulation and inflammatory cascades. The BDNF Met allele predisposed to carotid artery thrombosis FeCl3-induced and to death after collagen/epinephrine injection. Interestingly, transfection with BDNFMet construct induced a prothrombotic/proinflammatory phenotype in WT cells. SIRT1 activation, using resveratrol and/or CAY10591, prevented thrombus formation and restored the physiological levels of coagulation and of platelet markers in BDNFMet/Met mice and/or cells transfected with the Met allele. Conversely, inhibition of SIRT1 by sirtinol and/or by specific siRNA induced the prothrombotic/proinflammatory phenotype in WT mice and cells. Finally, we found that BDNF Met homozygosity is associated with increased risk of acute myocardial infarction (AMI) in humans.

Conclusion

Activation of platelets, alteration in coagulation pathways, and changes in vessel wall protein expression in BDNFMet/Met mice recapitulate well the features occurring in the anxiety/depression condition. Furthermore, our data suggest that the BDNFVal66Met polymorphism contribute to the individual propensity for arterial thrombosis related to AMI.

Genetic variations in the p11/tPA/BDNF pathway are associated with post stroke depression

BACKGROUND

The effects of BDNF on post stroke depression (PSD) may be influenced by genetic variations in intracellular signal transduction pathways, such as the p11/tPA/BDNF pathway. In this study, we aimed to determine the association of polymorphisms in candidate genes of the gene transduction pathway with PSD, as well as the effects of the interactions between genes in our Chinese sample.

METHODS

Two-hundred-fifty-four Chinese samples with acute ischaemic stroke included 122 PSD patients and 132 nonPSD patients. Sixty-five single nucleotide polymorphisms (SNPs) in six genes (p11, tPA, PAI-1, BDNF, TrkB and p75NTR) of the p11/tPA/BDNF pathway with minor allele frequencies > 5% were successfully genotyped from an initial series of 76 SNPs. The severity of depressive symptoms was assessed by the 17-item Hamilton Depression Rating scale score. Environmental factors were measured with the life events scale and social support rating scale for all patients. SNP and haplotype associations were analysed using gPLINK software. Gene-gene interactions were evaluated with generalized multifactor dimensionality reduction software.

RESULTS

The results showed that TrkB polymorphisms (rs11140793AC genotype, rs7047042CG genotype, rs1221CT genotype, rs2277193TC genotype and rs2277192AG genotype) were significantly associated with PSD. Three haplotypes (AT, GG, and AAT) of TrkB were significantly associated with PSD. Seven haplotypes (GC, AG, ACG, CGC, GCT, ACGC and ACAT) of BDNF were significantly correlated with PSD. We identified significant gene-gene interactions between the p11 (rs11204922 SNP), tPA (rs8178895, rs2020918 SNPs) and BDNF (rs6265, rs2049046, rs16917271, rs727155 SNPs) genes in the PSD group. We also identified significant gene-gene interactions between the BDNF (rs2049046, rs7931247 SNPs) and TrkB (rs7816 SNP) genes with increased occurrence of PSD and sig gene-gene interactions between the BDNF gene (rs6265, rs56164415, rs2049046, rs4923468, rs2883187, rs16917271, rs1491850, rs727155, rs2049048 SNPs) and p75NTR gene (rs2072446, rs11466155) in the PSD group.

CONCLUSION

These findings provides evidence that the TrkB gene, BDNF and TrkB haplotypes, and gene-gene interactions between p11, tPA and BDNF are all associated with PSD, which suggests that genetic variations in the p11/tPA/BDNF pathway may play a central role in regulating the underlying mechanism of PSD.

Role of tissue-type plasminogen activator and plasminogen activator inhibitor-1 in psychological stress and depression

Major depressive disorder is a common illness worldwide, but the pathogenesis of the disorder remains incompletely understood. The tissue-type plasminogen activator-plasminogen proteolytic cascade is highly expressed in the brain regions involved in mood regulation and neuroplasticity. Accumulating evidence from animal and human studies suggests that tissue-type plasminogen activator and its chief inhibitor, plasminogen activator inhibitor-1, are related to stress reaction and depression. Furthermore, the neurotrophic hypothesis of depression postulates that compromised neurotrophin brain-derived neurotrophic factor (BDNF) function is directly involved in the pathophysiology of depression. In the brain, the proteolytic cleavage of proBDNF, a BDNF precursor, to mature BDNF through plasmin represents one mechanism that can change the direction of BDNF action. We also discuss the implications of tissue-type plasminogen activator and plasminogen activator inhibitor-1 alterations as biomarkers for major depressive disorder. Using drugs that increase tissue-type plasminogen activator or decrease plasminogen activator inhibitor-1 levels may open new avenues to develop conceptually novel therapeutic strategies for depression treatment.

The serum protein levels of the tPA-BDNF pathway are implicated in depression and antidepressant treatment

Evidence demonstrates that brain-derived neurotrophic factor (BDNF) has a pivotal role in the pathogenesis of major depressive disorder (MDD). Precursor-BDNF (proBDNF) and mature BDNF (mBDNF) have opposing biological effects in neuroplasticity, and the tissue-type plasminogen activator (tPA)/plasmin system is crucial in the cleavage processing of proBDNF to mBDNF. However, very little is known about the role of the tPA-BDNF pathway in MDD. We examined serum protein concentrations in the tPA-BDNF pathway, including tPA, BDNF, tropomyosin receptor kinase B (TrkB), proBDNF and p75NTR, obtained from 35 drug-free depressed patients before and after 8 weeks of escitalopram (mean 12.5 mg per day) or duloxetine (mean 64 mg per day) treatment and 35 healthy controls using sandwich ELISA (enzyme-linked immunosorbent assay) methods. Serum tPA and BDNF and the ratio of BDNF/proBDNF were significantly lower in the MDD patients than in controls, whereas TrkB, proBDNF and its receptor p75NTR were higher. After 8 weeks of treatment, tPA, BDNF and proBDNF and the BDNF/proBDNF ratio were reversed, but p75NTR was higher than baseline, and TrkB was not significantly changed. tPA, BDNF, TrkB, proBDNF and p75NTR all yielded fairly good or excellent diagnostic performance (area under the receiver operating characteristic curve (AUC) >0.8 or 0.9). Combination of these five proteins demonstrated much better diagnostic effectiveness (AUC: 0.977) and adequate sensitivity and specificity of 88.1% and 92.7%, respectively. Our results suggest that the tPA-BDNF lysis pathway may be implicated in the pathogenesis of MDD and the mechanisms underlying antidepressant therapeutic action. The combination of tPA, BDNF, TrkB, proBDNF and p75NTR may provide a diagnostic biomarker panel for MDD.

Correlation between Motor Cortex Excitability Changes and Cognitive Impairment in Vascular Depression: Pathophysiological Insights from a Longitudinal TMS Study

Background. Transcranial magnetic stimulation (TMS) highlighted functional changes in dementia, whereas there are few data in patients with vascular cognitive impairment-no dementia (VCI-ND). Similarly, little is known about the neurophysiological impact of vascular depression (VD) on deterioration of cognitive functions. We test whether depression might affect not only cognition but also specific cortical circuits in subcortical vascular disease. Methods. Sixteen VCI-ND and 11 VD patients, age-matched with 15 controls, underwent a clinical-cognitive, neuroimaging, and TMS assessment. After approximately two years, all participants were prospectively reevaluated. Results. At baseline, a significant more pronounced intracortical facilitation (ICF) was found in VCI-ND patients. Reevaluation revealed an increase of the global excitability in both VCI-ND and VD subjects. At follow-up, the ICF of VCI-ND becomes similar to the other groups. Only VD patients showed cognitive deterioration. Conclusions. Unlike VD, the hyperfacilitation found at baseline in VCI-ND patients suggests enhanced glutamatergic neurotransmission that might contribute to the preservation of cognitive functioning. The hyperexcitability observed at follow-up in both groups of patients also indicates functional changes in glutamatergic neurotransmission. The mechanisms enhancing the risk of dementia in VD might be related either to subcortical vascular lesions or to the lack of compensatory functional cortical changes.

BDNF isoforms: a round trip ticket between neurogenesis and serotonin?

The brain-derived neurotrophic factor, BDNF, was discovered more than 30 years ago and, like other members of the neurotrophin family, this neuropeptide is synthetized as a proneurotrophin, the pro-BDNF, which is further cleaved to yield mature BDNF. The myriad of actions of these two BDNF isoforms in the central nervous system is constantly increasing and requires the development of sophisticated tools and animal models to refine our understanding. This review is focused on BDNF isoforms, their participation in the process of neurogenesis taking place in the hippocampus of adult mammals, and the modulation of their expression by serotonergic agents. Interestingly, around this triumvirate of BDNF, serotonin, and neurogenesis, a series of recent research has emerged with apparently counterintuitive results. This calls for an exhaustive analysis of the data published so far and encourages thorough work in the quest for new hypotheses in the field. BDNF is synthetized as a pre-proneurotrophin. After removal of the pre-region, proBDNF can be cleaved by intracellular or extracellular proteases. Mature BDNF can bind TrkB receptors, promoting their homodimerization and intracellular phosphorylation. Phosphorylated-TrkB can activate three different signaling pathways. Whereas G-protein-coupled receptors can transactivate TrkB receptors, truncated forms can inhibit mBDNF signaling. Pro-BDNF binds p75(NTR) by its mature domain, whereas the pro-region binds co-receptors.

Correlation between Motor Cortex Excitability Changes and Cognitive Impairment in Vascular Depression: Pathophysiological Insights from a Longitudinal TMS Study

Background. Transcranial magnetic stimulation (TMS) highlighted functional changes in dementia, whereas there are few data in patients with vascular cognitive impairment-no dementia (VCI-ND). Similarly, little is known about the neurophysiological impact of vascular depression (VD) on deterioration of cognitive functions. We test whether depression might affect not only cognition but also specific cortical circuits in subcortical vascular disease. Methods. Sixteen VCI-ND and 11 VD patients, age-matched with 15 controls, underwent a clinical-cognitive, neuroimaging, and TMS assessment. After approximately two years, all participants were prospectively reevaluated. Results. At baseline, a significant more pronounced intracortical facilitation (ICF) was found in VCI-ND patients. Reevaluation revealed an increase of the global excitability in both VCI-ND and VD subjects. At follow-up, the ICF of VCI-ND becomes similar to the other groups. Only VD patients showed cognitive deterioration. Conclusions. Unlike VD, the hyperfacilitation found at baseline in VCI-ND patients suggests enhanced glutamatergic neurotransmission that might contribute to the preservation of cognitive functioning. The hyperexcitability observed at follow-up in both groups of patients also indicates functional changes in glutamatergic neurotransmission. The mechanisms enhancing the risk of dementia in VD might be related either to subcortical vascular lesions or to the lack of compensatory functional cortical changes.

Neural ECM proteases in learning and synaptic plasticity

Recent studies implicate extracellular proteases in synaptic plasticity, learning, and memory. The data are especially strong for such serine proteases as thrombin, tissue plasminogen activator, neurotrypsin, and neuropsin as well as matrix metalloproteinases, MMP-9 in particular. The role of those enzymes in the aforementioned phenomena is supported by the experimental results on the expression patterns (at the gene expression and protein and enzymatic activity levels) and functional studies, including knockout mice, specific inhibitors, etc. Counterintuitively, the studies have shown that the extracellular proteolysis is not responsible mainly for an overall degradation of the extracellular matrix (ECM) and loosening perisynaptic structures, but rather allows for releasing signaling molecules from the ECM, transsynaptic proteins, and latent form of growth factors. Notably, there are also indications implying those enzymes in the major neuropsychiatric disorders, probably by contributing to synaptic aberrations underlying such diseases as schizophrenia, bipolar, autism spectrum disorders, and drug addiction.

Measurement methods of BDNF levels in major depression: a qualitative systematic review of clinical trials

There is evidence that the brain-derived neurotrophic factor (BDNF) has implications for the pathophysiology of major depressive disorders (MDD). Measures of BDNF levels are highly dependent on the methodologies used and these vary among different studies. Therefore, the aim of this study was to carry out a descriptive analysis of the methodologies used to measure BDNF in clinical trials (CT) in patients with the diagnosis of major depression. We conducted a qualitative systematic review of CT that included samples of subjects diagnosed with major depression and evaluated the BDNF levels as an outcome. The search was performed on Pubmed, Scielo, Psychinfo and Lilacs. The selected articles were analyzed according to the CONSORT Statement and their methods of BDNF collection and analysis were described. Twenty-eight studies were included in the final analysis. Of those, 6 trials (21.4%) involved non-pharmacological interventions and only half had the MDD diagnosis based on structured interview. Trials used different methods to evaluate BDNF levels: most of them verified serum BDNF levels, 17 (60.7%) trials mentioned that measured BDNF levels in duplicate and 9 (32.1%) collected blood in fasting. A variety of methods for BDNF collection and analysis was used in the different studies, making it difficult to compare results. However, despite of the methodology, BDNF seems to increase after treatment for major depression.

Association between plasma brain-derived neurotrophic factor levels and personality traits in healthy Japanese subjects

Although depression has been associated with decreased brain-derived neurotrophic factor (BDNF) levels for specific personality traits, there is a little information regarding the association between peripheral BDNF levels and such traits. The sample consisted of 178 healthy Japanese subjects (age range, 37.4 ± 11.5 years). All subjects filled out the Temperament and Character Inventory (TCI). Plasma BDNF levels were measured using the enzyme-linked immunosorbent assay. A simple regression analysis revealed that plasma BDNF levels were significantly correlated with harm avoidance (r=-0.177, p=0.018) and self-directedness scores (r=0.165, p=0.028). Our findings suggest that plasma BDNF levels are associated with depression-related personality traits.

Plasma brain-derived neurotrophic factor and prefrontal white matter integrity in late-onset depression and normal aging

OBJECTIVE

To explore the relationship between brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF), cerebral deep white matter lesions (DWMLs), and measures of white matter integrity in patients with late-onset depression, with respect to vascular risk factors.

METHOD

We examined 22 patients with late-onset depression and 22 matched controls. Quantification of plasma BDNF and VEGF levels were performed with enzyme-linked immunosorbent assay (ELISA) kits. Measures of white matter integrity comprised apparent diffusion coefficient (ADC) and fractional anisotropy (FA), obtained by diffusion tensor imaging (DTI). Effects of DWMLs, FA, ADC, and vascular risk factors on BDNF and VEGF were assessed using multiple linear regression.

RESULTS

The BDNF and VEGF levels did not differ significantly between groups. With pooled data for patients and controls, the BDNF level was positively associated with both number (t = 2.14, P = 0.039) and volume (t = 2.04, P = 0.048) of prefrontal DWMLs and negatively associated with FA in prefrontal normal-appearing white matter (t = -2.40, P = 0.02), adjusted for age and gender. Smoking and hypercholesterolemia was positively associated with the BDNF (t = 2.36, P = 0.023) and VEGF levels (t = 2.28, P = 0.028), respectively.

CONCLUSION

Our results suggest a role for BDNF in the complex pathophysiologic mechanisms underlying DWMLs in both normal aging and late-onset depression.

Involvement of brain-derived neurotrophic factor in late-life depression

Brain-derived neurotrophic factor (BDNF), one of the major neurotrophic factors, plays an important role in the maintenance and survival of neurons, synaptic integrity, and synaptic plasticity. Evidence suggests that BDNF is involved in major depression, such that the level of BDNF is decreased in depressed patients and that antidepressants reverse this decrease. Stress, a major factor in depression, also modulates BDNF expression. These studies have led to the proposal of the neurotrophin hypothesis of depression. Late-life depression is associated with disturbances in structural and neural plasticity as well as impairments in cognitive behavior. Stress and aging also play a crucial role in late-life depression. Many recent studies have suggested that not only expression of BDNF is decreased in the serum/plasma of patients with late-life depression, but structural abnormalities in the brain of these patients may be associated with a polymorphism in the BDNF gene, and that there is a relationship between a BDNF polymorphism and antidepressant remission rates. This review provides a critical review of the involvement of BDNF in major depression, in general, and in late-life depression, in particular.

A large-scale candidate gene analysis of mood disorders: evidence of neurotrophic tyrosine kinase receptor and opioid receptor signaling dysfunction

BACKGROUND

Despite proven heritability, little is known about the genetic architecture of mood disorders. Although a number of family and case-control studies have examined the genetics of mood disorders, none have carried out joint linkage-association studies and sought to validate the results with gene expression analyses in an independent cohort.

METHODS

We present findings from a large candidate gene study that combines linkage and association analyses using families and singletons, providing a systematic candidate gene investigation of mood disorder. For this study, 876 individuals were recruited, including 83 families with 313 individuals and 563 singletons. This large-scale candidate gene analysis included 130 candidate genes implicated in addictive and other psychiatric disorders. These data showed significant genetic associations for 28 of these candidate genes, although none remained significant after correction for multiple testing. To evaluate the functional significance of these 28 candidate genes in mood disorders, we examined the transcriptional profiles of these genes within the dorsolateral prefrontal cortex and anterior cingulate for 21 cases with mood disorders and 25 nonpsychiatric controls, and carried out a pathway analysis to identify points of high connectivity suggestive of particular molecular pathways that may be dysregulated.

RESULTS

Two primary gene candidates were supported by the linkage-association, gene expression profiling, and network analysis: neurotrophic tyrosine kinase receptor, type 2 (NTRK2), and the opioid receptor, κ1 (OPRK1).

CONCLUSION

This study supports a role for NTRK2 and OPRK1 signaling in the pathophysiology of mood disorder. The unique approach incorporating evidence from multiple experimental and computational modalities enhances confidence in these findings.

Hippocampus-specific deletion of tissue plasminogen activator "tPA" in adult mice impairs depression- and anxiety-like behaviors

Anxiety and depression are multifactorial disorders that have become prominent health problems all over the world. Neurotrophic factors have emerged underlying pathogenesis of these diseases. Although a number of studies indicate that the hippocampus-brain-derived neurotrophic factor (BDNF) may be involved in these psychiatric illnesses, little is known about the molecular mediators of these disorders. In this study we further investigate the role of tissue plasminogen activator (tPA), a serine protease involved in pro-BDNF cleavage to BDNF, in depression and anxiety-like behaviors in adult mice. To address this issue, we investigated the effect of hippocampus tPA manipulation, using viral vectors, on anxiety- and depression-like behaviors, including the marble burying test (MBT), elevated plus maze (EPM), tail suspension test (TST), novelty suppressed feeding (NSF) and forced swim test (FST). Our results showed that tPA knock-down - using lentiviral vectors expressing specific short hairpin RNAs (LV-shRNA) - increased the number of buried marbles together with the digging time in the MBT and decreased the time spent in open the arms of an EPM. In addition, tPA-knock down in the hippocampus increased immobility in the FST and TST, and increased time to feed in the NSF test. These effects were reversed when tPA-over-expressing vectors (LV-tPA) were injected in the hippocampus. We also found that BDNF protein levels were elevated in the hippocampus of mice receiving tPA-expressing vectors. Together, our results imply that tPA manipulation may provide an effective therapeutic intervention for depression and anxiety disorders.

Is BDNF biological link between depression and type 2 diabetes mellitus?

Epidemiological and clinical studies have demonstrated a strong association between depression and diabetes. Of note, depression is a risk factor for the development of type 2 diabetes mellitus (T2DM), while most patients with T2DM also have depression. Despite the abundance of evidence showing an epidemiological link between depression and T2DM, the cause of this association is still unknown. Brain-derived neurotrophic factor (BDNF) is widely expressed in the brain. Biological and clinical studies have repeatedly shown that BDNF is important in the pathogenesis of depression and T2DM. Therefore, we propose that BDNF may play an important role linking depression and T2DM. Studies examining the components of the BDNF system in patients with T2DM and depression may provide new understanding into the link between depression and T2DM. Such studies might also help us to identify potential treatment targets for these two common disorders.

Plasma biomarkers of depressive symptoms in older adults

The pathophysiology of negative affect states in older adults is complex, and a host of central nervous system and peripheral systemic mechanisms may play primary or contributing roles. We conducted an unbiased analysis of 146 plasma analytes in a multiplex biochemical biomarker study in relation to number of depressive symptoms endorsed by 566 participants in the Alzheimer's Disease Neuroimaging Initiative (ADNI) at their baseline and 1-year assessments. Analytes that were most highly associated with depressive symptoms included hepatocyte growth factor, insulin polypeptides, pregnancy-associated plasma protein-A and vascular endothelial growth factor. Separate regression models assessed contributions of past history of psychiatric illness, antidepressant or other psychotropic medicine, apolipoprotein E genotype, body mass index, serum glucose and cerebrospinal fluid (CSF) τ and amyloid levels, and none of these values significantly attenuated the main effects of the candidate analyte levels for depressive symptoms score. Ensemble machine learning with Random Forests found good accuracy (~80%) in classifying groups with and without depressive symptoms. These data begin to identify biochemical biomarkers of depressive symptoms in older adults that may be useful in investigations of pathophysiological mechanisms of depression in aging and neurodegenerative dementias and as targets of novel treatment approaches.

Measurements in the Blood of BDNF for RA Patients and in Response to Anti-TNF Treatment Help Us to Clarify the Magnitude of Centrally Related Pain and to Explain the Relief of This Pain upon Treatment

Brain-derived neurotrophic factor (BDNF) is a neurotrophin with functions related to neuronal survival/proliferation processes and inflammation. BDNF is also an important central pain mediator. The levels of BDNF have been found to be high for RA patients with severe disease and to become lowered in response to anti-TNF treatment. New information says that the levels of BDNF in the blood parallel the BDNF concentrations in the brain and that BDNF can pass the blood-brain barrier. Furthermore, most of the circulating BDNF is produced in the brain. Habitual and regular exercise, in contrast to temporary exercise, does also lead to a lowering of BDNF blood levels. Both anti-TNF treatment and habitual and regular exercise do have pain-relieving effects. It might be that the pain-relieving effect of anti-TNF treatment is related to an affection of central neuronal regions, hereby influencing BDNF production. Measurements of BDNF in the blood help us to clarify the magnitude of centrally related pain for RA patients and help us to explain the relief of this pain in response to anti-TNF treatment.

Association between plasma paroxetine concentration and changes in plasma brain‐derived neurotrophic factor levels in patients with major depressive disorder

Recent studies have implicated brain‐derived neurotrophic factor (BDNF) in the pathophysiology of depression and in the activities of antidepressant drugs. Serum BDNF levels are lower in depressed patients and increase in response to antidepressant medications; however, no studies have examined the association between plasma concentrations of antidepressant drugs and plasma BDNF levels. We assessed plasma BDNF levels and paroxetine concentrations in 45 patients with major depression who were being treated with paroxetine. Plasma samples were collected between 10:00 h and 12:00 h at baseline and after 1, 2 and 6 weeks of treatment. The BDNF level and paroxetine concentration of each sample were measured via enzyme immunoassay and high‐performance liquid chromatography, respectively. Plasma BDNF levels increased after 2 and 6 weeks of paroxetine treatment. Plasma BDNF levels were significantly lower in men than in women. Changes in plasma BDNF level were correlated with plasma drug concentration after 2 (r = 0.309, p < 0.05) and 6 weeks (r = 0.329, p < 0.05) but not correlated with plasma drug concentration after 1 week (r = 0.284, ns). Multiple regression analysis confirmed that this change was only significantly correlated with plasma paroxetine concentration after 2 (standardised beta = 0.343, p < 0.05) and 6 weeks (standardised beta = 0.375, p < 0.05). These results suggest that paroxetine treatment increases plasma BDNF levels and that plasma paroxetine levels play an important role in changes in plasma BDNF levels.

Brain-derived neurotrophic factor as a biomarker for mood disorders: an historical overview and future directions

Mood disorders, such as major depressive disorder (MDD) and bipolar disorder (BPD), are the most prevalent psychiatric conditions, and are also among the most severe and debilitating. However, the precise neurobiology underlying these disorders is currently unknown. One way to combat these disorders is to discover novel biomarkers for them. The development of such biomarkers will aid both in the diagnosis of mood disorders and in the development of effective psychiatric medications to treat them. A number of preclinical studies have suggested that the brain-derived neurotrophic factor (BDNF) plays an important role in the pathophysiology of MDD. In 2003, we reported that serum levels of BDNF in antidepressant-naive patients with MDD were significantly lower than those of patients medicated with antidepressants and normal controls, and that serum BDNF levels were negatively correlated with the severity of depression. Additionally, we found that decreased serum levels of BDNF in antidepressant-naive patients recovered to normal levels associated with the recovery of depression after treatment with antidepressant medication. This review article will provide an historical overview of the role played by BDNF in the pathophysiology of mood disorders and in the mechanism of action of therapeutic agents. Particular focus will be given to the potential use of BDNF as a biomarker for mood disorders. BDNF is initially synthesized as a precursor protein proBDNF, and then proBDNF is proteolytically cleaved to the mature BDNF. Finally, future perspectives on the use of proBDNF as a novel biomarker for mood disorders will be discussed.