The Role of Brain-Derived Neurotrophic Factor (BDNF) in Depression: A Narrative Review

Abstract

Depression is a psychological illness defined by persistent sadness, loss of interest or pleasure in daily activities (anhedonia), hopelessness, and a range of cognitive and physical symptoms. Untreated depression can have serious implications, such as a deteriorating mental and physical state and an increased risk of suicidal behaviour. Early diagnosis and treatment can help to prevent these adverse outcomes. Traditional diagnostic approaches primarily rely on self-reported symptoms, clinical evaluations, and questionnaire-based assessments, which, although significant, may vary and depend on perspective, necessitating the exploration of biological markers. This narrative review is based on the existing literature regarding the role of Brain-Derived Neurotrophic Factor (BDNF) in the neurobiological function and evaluates its potential as a biomarker for the diagnosis, treatment, and monitoring of disease progression. The Brain-Derived Neurotrophic Factor (BDNF) is the most common neurotrophin abundantly present in the central nervous system and peripheral tissues, and it is found in both serum and plasma. In the context of depression, BDNF has a fundamental function in the serotonergic, noradrenergic, and dopaminergic pathways, which are linked to the progression of clinical depression and are implicated in mood regulation. An extensive quantity of research on BDNF supports the neurotrophic theory of depression. According to this theory, low BDNF levels cause neuroplastic alterations such as neuronal atrophy, impaired hippocampus neurogenesis, and synaptic plasticity, contributing to its inception and progression. Several clinical findings consistently established that people with depression show lower levels of BDNF, with these levels generally increasing after successful antidepressant therapy, further supporting this hypothesis. This article provides an overview of BDNF's effect on the aetiology of depression, highlighting its significance as a possible marker.