Oxidative stress-related biomarkers in Parkinson’s disease: A systematic review and meta-analysis

Parkinson’s disease (PD) is a neurodegenerative disease characterized with the loss of dopamine-producing neurons in a mid-brain. This loss is believed to be associated with number of environmental and genetic factors. Oxidative stress is found to be one of the factors responsible for the initiation and progression of PD. However, studies are still continued to confirm the connection and mechanism associated with oxidative stress and PD. This systematic review and meta-analysis aimed to assess the association between oxidative stress markers and PD, and explore factors that may elucidate the contradictions in these results. As per Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline systematic literature search was carried out. Meta-analysis was carried out on pooled standardized mean differences with 95% confidence interval (CI) of patients with PD and controls using random effect model in comprehensive meta-analysis statistical software. Total 17 studies were included into which 25 oxidative stress markers were analyzed. The results revealed that oxidative stress markers [nitrate and nitric oxide (NO)] and antioxidant markers [total antioxidant status (TAS) and thiols] were not statistically different between the PD and control group (P > 0.05). In case of oxidative stress markers, levels of malondialdehyde (MDA), 8-Oxo-2'-deoxyguanosine (8-oxo-dG), and lipid hydro-peroxide (LPO) were found to be high in patients with PD as compared to controls with P < 0.05, whereas lower levels of antioxidant activity of superoxide dismutase (SOD), glucose 6 phosphate dehydrogenase (G6PD), catalase (CAT), and glutathione peroxidase (GPx) were noticed in the PD group as compared to controls (P < 0.05 for all). From the results, it is concluded that patients with PD have high oxidative stress and lower antioxidant activity, and these studied biomarkers would be used as potential diagnostic tool to measure oxidative stress in patients with PD.