Parkinson’s disease (PD) is the second most common neurodegenerative disorder in the world. The pathological hallmarks of PD include the loss of dopaminergic neurons in the substantia nigra pars compacta and the presence of Lewy bodies. Increased oxidative stress in the brain has been hypothesised to contribute to the neurodegeneration and neuronal dysfunction in PD.
There are several markers of oxidative stress, including damaged DNA bases (e.g. 8-hydroxydeoxyguanosine), oxidised lipids, and decreased antioxidants. However, the number of these biomarkers used in clinical practice is limited, and the importance of peripheral oxidative stress markers in PD has not yet been clarified.
Vitamin C is a major antioxidant detected in various components of the peripheral blood. In lymphocytes, the vitamin C levels are 80 to 100 times higher than in plasma. Moreover, these levels are not affected by transient dietary changes and circadian rhythms. It has been suggested that vitamin C levels in the peripheral blood could serve as a biomarker of oxidative stress in various diseases.
In a recent paper (2014), researchers from the University of Shizuoka (Japan), investigated the association between lymphocyte and plasma vitamin C levels in various stages of PD. Sixty two patients with PD, being treated at Shizuoka General Hospital (Japan), were consecutively enrolled in this study, from December 2007 to August 2013. The subjects were diagnosed with PD according to the criteria of Ward and Gibb, and the severity was classified based on Hoehn-Yahr stages. It is important to note that subjects with secondary parkinsonisms including vascular and drug-induced Parkinsonism were excluded from the study. Fasting blood samples were collected, and plasma/lymphocyte vitamin C levels were measured.
The results of the foregoing study demonstrated that lymphocyte vitamin C levels were significantly (95 % CU; p <0.008) lower in subjects with severe PD, and that there was a linear correlation between plasma and lymphocyte vitamin C levels. Based on the results of the foregoing trial, lymphocyte vitamin C levels could serve as a potentially useful biomarker of PD progression. Moreover, it is suggested, that monitoring lymphocyte vitamin C levels may contribute to improved diagnostic accuracy and could prove useful in the selection of effective therapeutic approaches for various stages of PD.
Further investigations are required before such testing can be applied to clinical practice.