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

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.

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.

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).

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.