title: BDNF blood levels after non-invasive brain stimulation interventions in major depressive disorder: a systematic review and meta-analysis.
abstract: OBJECTIVE
  To evaluate whether the antidepressant effects of novel non-invasive brain stimulation (NIBS) therapies are associated with neurotrophic effects, indexed by peripheral brain-derived neurotrophic factor (BDNF) levels.
  
  
  METHODS
  Systematic review and meta-analysis. We included trials published in PubMed/Medline from the first date available to June 2014 measuring BDNF blood levels before and after repetitive transcranial magnetic stimulation or transcranial direct current stimulation in depression.
  
  
  RESULTS
  Eight datasets (n = 259) were included. These studies enrolled mostly treatment-resistant depression patients, who received daily stimulation sessions on the left dorsolateral prefrontal cortex. BDNF did not increase after NIBS (Hedges' g = 0.03, 95% CI = -0.21 to 0.27), even when examining each intervention separately. Meta-regressions did not identify the influence of any clinical and demographic predictors on the outcome. Finally, Begg's funnel plot did not suggest publication bias and results were robust according to sensitivity analysis.
  
  
  CONCLUSIONS
  Peripheral BDNF levels do not increase after NIBS in depression. Such biomarker might, therefore, not be suitable to index NIBS antidepressant response. Further trials are needed, particularly exploring non-medicated populations, performing subsequent BDNF assessments in a larger timeframe and employing more intensive NIBS treatment protocols.
authors.affiliation: Laboratory of Neuroscience (LIM27), Department and Institute of Psychiatry, University of São Paulo , São Paulo , Brazil.
authors.forename: André R
authors.initials: AR
authors.lastname: Brunoni
authors.forename: Chris
authors.initials: C
authors.lastname: Baeken
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Machado-Vieira
authors.forename: Wagner F
authors.initials: WF
authors.lastname: Gattaz
authors.forename: Marie-Anne
authors.initials: MA
authors.lastname: Vanderhasselt
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000097:blood; D019208:Brain-Derived Neurotrophic Factor / Q000097:blood*; D003865:Major Depressive Disorder / Q000628:therapy*; D061218:Depressive Disorder, Treatment-Resistant / Q000628:therapy*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017397:Prefrontal Cortex / Q000502:physiology; D065908:Transcranial Direct Current Stimulation; D050781:Transcranial Magnetic Stimulation
chemical_list: D015415:Biomarkers; D019208:Brain-Derived Neurotrophic Factor
keywords: brain-derived neurotrophic factor; major depressive disorder; meta-analysis; neurotrophic factors; non-invasive brain stimulation