Serum levels of soluble TNF-α receptors but not BDNF are associated with apathy symptoms in mild Alzheimer's disease and amnestic mild cognitive impairment

Apathy is intimately associated with dementia. Unfortunately, its pathophysiology remains poorly understood. The motivational impairment that characterizes this disorder might share the same inflammatory mechanisms, as suggested by the sickness behavior theory. Objective: The primary aim of this study was to investigate the association between apathy symptoms and serum levels of tumor necrosis factor alpha (TNF-α) and its soluble receptors. Brain-derived neurotrophic factor (BDNF) levels were also analyzed since these have been associated with depression, a condition which shares abulic features with apathy. Methods: The sample consisted of 27 subjects with mild Alzheimer's disease or amnestic mild cognitive impairment, who were submitted to specific apathy evaluation using the Apathy Scale (AS) and provided blood samples for biomarker analysis. Participants were categorized into two groups according to median AS scores (17 points). Results: Subjects with higher apathy symptoms (n=13) displayed higher levels of TNF-α soluble receptors (type 1: p=0.03; type 2: p=0.04). No other difference was found between groups. Conclusion: These findings point to the involvement of inflammatory mediators in the genesis of apathy symptoms, as suggested by the sickness behavior theory.