Neuroprotective factors in schizophrenia: BDNF, NGF, NT3, GDNF and their connection to the pathogenesis of schizophrenia. A narrative review

Introduction: There are several hypotheses of schizophrenia pathogenesis, including the neurodegenerative theory, which is supported by evidence for the decrease of neuroprotective factors’ serum levels. The proteins, that exert a protective effect on neurons and are researched concerning schizophrenia pathogenesis, include the brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), neurotrophin 3 (NT3), and glial cell line-derived neurotrophic factor (GDNF). This review aims to discuss the role of neuroprotective factors in the development of schizophrenia and their relevance in clinical trials. Material and methods: This review was performed by search of the PubMed, Google Scholar, and Science Direct databases from December 25th, 2022, through January 31st, 2023, using keywords: ‘schizophrenia’, ‘schizophrenia pathogenesis’, ‘neuroprotection’, ‘neurodegeneration’, ‘BDNF’, ‘NGF’, ‘NT3’, and ‘GDNF’. We considered original research papers and systematic reviews published in English or Polish. Additionally, clinical trials, which included the assessment of neuroprotective factors’ levels in schizophrenia as outcome measures, were searched for on clinicaltrials.gov. Results: Lower levels of serum BDNF have been linked to cognitive impairment in schizophrenia. In clinical trials, the assessment of serum BDNF is used as a clinical outcome measure for novel schizophrenia therapies. Schizophrenia has also been associated with reduced peripheral NGF levels. During remission, lower NGF levels correlate with higher severity of negative symptoms. Decreased NT3 and GDNF levels can also be seen, but literature reports are inconsistent. Conclusions: Neuroprotective factors are most likely related to the pathogenesis of schizophrenia. Assessing the serum level of these proteins may prove to be an invaluable element of schizophrenia management. Keywords: schizophrenia, brain-derived neurotrophic factor, nerve growth factor,neurotrophin 3, glial cell line-derived neurotrophic factor