Antioxidant and inflammatory biomarkers for the identification of prodromal Parkinson's disease

Objectives We explored the role of oxidative stress and inflammatory molecules as potential Parkinson (PD) biomarkers and correlated biological with non-motor abnormalities (olfactory impairment and dysautonomia), in patients with idiopathic REM behavior disorder (iRBD) (prodromal PD) and established PD. Methods We recruited 11 iRBD and 15 patients with idiopathic PD (Hohen&Yahr 1-3, on L-DOPA and dopamine agonists combination therapy) and 12 age- and sex-matched controls (CTRL). We measured total olfactory score (TOS), autonomic function [deep breathing (DB), lying to standing (LS) and Valsalva manoeuvre (VM) ratios], blood reduced glutathione (Br-GSH), oxidative stress and inflammatory markers (neopterin). Results Anosmia was similarly prevalent in iRBD (36%) and PD (33%) patients, but absent in CTRL. Orthostatic hypotension was more common among iRBD (73%) and PD (60%) than in CTRL (25%). By univariable ordinal logistic regression, TOS, Br-GSH, LS and VM ratio worsened from CTRL to iRBD and PD groups. Only reduced Br-GSH levels (p = 0.037, OR = 0.994; 95%CI 0.988-1.000) were independently associated to PD. TOS correlated with Br-GSH (R = 0.34, p = 0.037), VM ratio (R = 0.43, p = 0.015), and neopterin (rho = 0.39, p = 0.016). Conclusions Reduced systemic antioxidant capacity is found in prodromal and overt PD and may represent, in association with olfactory loss and cardiovascular dysautonomia, a useful biomarker for an integrative, early diagnosis of PD.