Plasma Brain-Derived Neurotrophic Factor (BDNF) Levels and BDNF Promoters’ DNA Methylation in Workers Exposed to Occupational Stress and Suffering from Psychiatric Disorders

Abstract

Introduction: Decreased plasma BDNF (pBDNF) levels have been proposed as a biomarker in the illness phases of mood disorders. This cross-sectional study aimed to evaluate the pBDNF and BDNF promoters’ DNA methylation levels in workers exposed to occupational stress and suffering from work-related stress disorders. Methods: the pBDNF and BDNF exon I and IV promoters’ methylation levels were measured by specific immunoassays and methylation-sensitive high-resolution melting (MS-HRM) in 62 patients with adjustment disorders (AD), 79 patients with major depressive disorder (MDD) and 44 healthy controls. Occupational stress was evaluated in the patients and controls using the Job Content Questionnaire (JCQ). Results: the pBDNF levels were significantly higher in the MDD (p < 0.001) and AD (p < 0.0001) patients than in the controls. The MDD patients showed significantly lower pBDNF levels than the AD ones (p = 0.01). The BDNF exon I and IV promoters’ methylation levels were significantly higher in the MDD patients than in the AD ones (exon I promoter: p = 0.0001, exon IV promoter: p < 0.0001) and controls (exon I promoter: p = 0.0001, exon IV promoter: p < 0.0001). In the patients, but not in the controls, the BDNF promoters’ methylation levels showed significant negative correlations with occupational stress. Conclusions: BDNF could play a key role in the pathophysiology of stress-related disorders and the peripheral elevation of it observed in patients exposed to occupational stress could suggest a protective mechanism for neurons from stress-mediated damage. The elevation of the pBDNF levels, even in MDD, may characterize a “reactive” subtype of depressive episode, while the significant elevation of the BDNF promoters’ methylation levels in depressed patients could indicate a predisposition to more severe illness under stress. Further research is needed, focusing on biomarkers for stress-related disorders as a potential tool for the diagnosis and prevention of occupational diseases.