Multiple Hits on Cerebral Folate, Tetrahydrobiopterin and Dopamine Metabolism in the Pathophysiology of Parkinson’s Disorder: A Limited Study of Post-Mortem Human Brain Tissues

Background: Parkinson’s disorder (PD) affects around 1:500 individuals and is associated with enlarged ventricles and symptoms of normal pressure hydrocephalus (NPH). These features suggest disrupted cerebrospinal fluid (CSF) dynamics and folate metabolism. With L-DOPA treatment showing diminishing benefits over time, there is an urgent need to investigate upstream metabolic disruptions, including folate and tetrahydrobiopterin (BH4) pathways, in post-mortem CSF and brain tissue to understand their roles in PD pathogenesis. Methods: CSF and brain tissue from 20 PD patients (mean age 84 years; 55% male; disease duration 10–30 years) and 20 controls (mean age 82 years; 50% male) were analysed. Western and Dot Blots measured proteins and metabolites, spectroscopic assays assessed enzyme activities, BH4 and Neopterin levels were measured using ELISA, and levels of hydrogen peroxide, used as a proxy for reactive oxygen species, and calcium were quantified using horseradish peroxidase and flame photometry assays, respectively. ClinVar genetic data were analysed for variants in genes encoding key enzymes. Statistical significance was assessed using unpaired t-tests (p < 0.05). Results: All enzymes were significantly reduced in PD compared to controls (p < 0.01) except for methyltetrahydrofolate reductase (MTHFR), which was elevated (p < 0.0001). Enzymes were functional in control but undetectable in PD CSF except tyrosine hydroxylase (TH). BH4 and Neopterin were elevated in PD CSF (p < 0.0001, p < 0.001) but significantly reduced (p < 0.001) or unchanged in tissue. Peroxide was increased in both PD CSF (p < 0.001) and tissue (p < 0.0001) selectively inhibiting TH. Calcium was 40% higher in PD than controls (p < 0.05). No pathogenic variants in enzyme genes were found in ClinVar data searches, suggesting the observed deficiencies are physiological. Conclusions: We identified significant disruptions in folate and BH4 pathways in PD, with enzyme deficiencies, oxidative stress and calcium dysregulation pointing to choroid plexus dysfunction. These findings highlight the choroid plexus and CSF as key players in cerebral metabolism and promote further exploration of these as therapeutic targets to address dopaminergic dysfunction and ventricular enlargement in PD.