Correlation of BDNF and IL-6 serum concentrations in Alzheimer's disease

Alzheimer's disease (AD) is characterized by cognitive decline and loss of neurons in specific brain regions. Recent findings have suggested an involvement of the pro-inflammatory cytokine interleukin-6 (IL-6) and brain-derived neurotrophic factor (BDNF) in the pathogenesis of AD. BDNF is an endogenous protein involved in neuronal survival and synaptic plasticity. The present pilot study assessed BDNF and IL-6 serum concentrations in 15 patients with AD in later stages with moderate to severe dementia in comparison to 10 age-matched healthy controls. As main result, we found in AD patients a significant negative correlation between the BDNF and IL-6 serum concentrations (r=-0,407, p=0,043), but not with Mini-Mental State (MMS; rBDNF-MMS=-0,152, p=0,447; rIL-6-MMS= 0,023, p=0,910). Mean BDNF serum concentration in AD patients (17,3 ng/ml) showed a tendency towards decreased values compared to healthy controls (20,7 ng/ml, p=0,086), whereas mean IL-6 serum concentration in AD patients (2,2 pg/ml) were slightly increased as compared to healthy controls (1,7 pg/ml), but without reaching statistical significance (p=0,269). In conclusion, our findings point to the possible existence of a dysbalance between neurotrophins such as BDNF and pro-inflammatory cytokines such as IL-6 in the etiology of Alzheimer's disease. There is need for further examinations, especially enrolling more patients with different stages of AD and including other differential diagnoses, to prove the specificity and sensitivity of these potential surrogate markers. Especially BDNF and IL-6 concentrations of patients with vascular dementia and traumatic brain injury have to be examined for proving the specificity of this finding to AD pathology or to brain damage in general.