Abstract
Parkinson's disease is one of the most frequent diseases of the central nervous system with rather severe consequences for patients. Since the disorder can not be cured, the dopamine level in the brain needs to adjusted. Here several key enzymes of the dopamine metabolism [e. g. catechol-O-methyl transferase (COMT)] are targets for administered drugs. However, the efficiency of the treatment is decreasing with time. Consequently a monitoring of the actual activity of these enezmyes and an adjustment of the pharmaceutical treatment would be beneficial to prolong the treatment effects.
In this study, an electrochemical approach is introduced for activity determination of the COMT enzyme. As detection method differential pulse voltammetry (DPV) has been used exploiting an improved signal to noise ratio. Activity determination is based on the selective detection of one substance in the reaction scheme of the enzyme – here dopamine. As electrode material fluorine doped tin oxide (FTO) has been elucidated since it is characterized by a clear discrimination between the substrate and the product of the COMT [1]. This can be achieved without additional layers on top of the electrode. The response is characterized by a rather high stability of the dopamine signal during consecutive measurements and a linear dependency of the peak currents on the dopamine concentration in the range of the maximum reaction rate of COMT [2]. Furthermore it has been detected that redox active interferences such as ascorbic acid do not disturb the analysis.
Despite these advantageous results, it has been found that the electrochemical dopamine oxidation in the complete activity assay is influenced by each of the added essential assay components, even though none of the added components reveal a current signal at the FTO electrode itself. After adjusting the potential range of the electrochemical analysis and the solution composition, these effects can be circumvented.
Consequently, by following the dopamine concentrations during COMT action, it can be shown that the
activity of the enzyme can be detected by using DPV at a FTO electrode. Experiments with different amounts of the enzyme further demonstrate that activity quantification is feasible.
References
[1] G. Göbel, A. Talke, F. Lisdat, Electroanalysis, 2018, Vol. 30 (2), p. 225-229
[2] G. Göbel, A. Talke, U. Ahnert, F. Lisdat, ChemElectroChem, 2019, Vol. 6 (17)