Inflammatory markers and BDNF in obstructive sleep apnea (OSA) in Parkinson's disease (PD).

Objective: Obstructive sleep apnea (OSA) exacerbates Parkinson's disease (PD) manifestations including cognitive dysfunction. Both OSA and PD have been associated with inflammation. Brain-derived neurotrophic factor (BDNF) has been implicated in cognitive function. We aimed to investigate inflammatory cytokines and BDNF in relation to OSA and PD symptoms.

Methods: In a prospective observational study, patients with PD underwent overnight polysomnography. Morning serum levels of interleukin (IL)-1β, IL-6, IL-8, TNFα, and BDNF were quantified at baseline (n = 64) and 6 months (n = 38). Outcomes included non-motor and motor standard scores; Montreal Cognitive Assessment (MoCA); and Epworth Sleepiness scale (ESS). Associations were assessed using linear regression, adjusting for age, sex and body mass index.

Results: At baseline, IL-6 was associated with the Apnea-Hypopnea Index (β = 0.013, p = 0.03), and the Oxygen Desaturation Index (β = 0.028, p = 0.002). No other associations between cytokines and sleep parameters were found. Motor dysfunction was associated with IL-6 (β = 0.03, p = 0.001). ESS was associated non-significantly with IL-6 (β = 0.04, p = 0.07) and BDNF (β = 555, p = 0.06). At follow-up, change in IL-6 was associated with change in non-motor (β = 0.08, p = 0.007), and motor (β = 0.03, p = 0.001) symptoms. Change in BDNF was associated with change in ESS (β = 1450, p = 0.02).

Interpretation: We found an association between IL-6 levels and both OSA severity and PD motor dysfunction. At follow-up, increasing IL-6 correlated with deterioration of motor and non-motor PD symptoms. Increasing BDNF correlated with increasing sleepiness. Further work with a larger sample size is needed, but our results support the hypothesis that OSA-related inflammation plays a role in PD manifestations and progression.