Quick home test for Parkinson's medication adjustment: Detection of L-DOPA in blood using enzyme colorimetry

May 10, 2021

(This report is provided by Dr. YiChun Yeh’s research team in the Department of Chemistry) Parkinson's disease is a neurological disorder that primarily affects motor performance. L-DOPA is the precursor of dopamine (DA) synthesis in the body and is widely used in the treatment of Parkinson's disease. However, because of the side effects associated with these drugs, clinical adjustments to the medication are often required. Therefore, measuring the concentration of L-DOPA in patients is an issue of interest for many researchers. Several methods have been developed to detect the concentration of L-DOPA, such as electrochemical assay and liquid chromatography, but there are still some limitations. In this study, a simple enzymatic colorimetric method was developed to selectively identify and oxidize L-DOPA by oxidative enzymes, resulting in a yellow product that can be identified by the naked eye; the concentration of L-DOPA can be inferred from the color intensity. Therefore, it can be used as a quick and easy estimation of the L-DOPA concentration in the test body, which is expected to be used as an indicator and reference for drug formulation.   Parkinson's disease is a complex brain disorder that mainly affects motor performance, so doctors will make a judgment and diagnosis clinically based on the patient's motor development and neurological examination. According to statistics, people over the age of 65 have a prevalence rate of 1-2%, so it is estimated that more than 40,000 people in Taiwan are affected by Parkinson's disease. Parkinson's disease is a complex cause of neuronal degeneration in the brain. When the nerve cells in the brain are damaged or die, they cannot produce and send the chemical substance (dopamine) that is used to transmit information, so the movement signals associated with it cannot be transmitted. When there is not enough dopamine (DA), there is too much acetylcholine, and the balance between these two chemicals becomes abnormal, resulting in tremors and muscle stiffness in many patients. Today's treatment for Parkinson's disease focuses on increasing DA secretion, and therefore the main drug used is L-dihydroxyphenylalanine (L-DOPA). The formation of DA is catalyzed by enzymes to compensate for the lack of DA. However, because of the side effects associated with these drugs (e.g., causing hallucinations or confusion), strict clinical monitoring and adjustment of medication are often required. In the past, many monitoring methods required long periods of time and expensive equipment for effective monitoring, making it difficult for patients to manage their conditions at home. Therefore, the enzyme colorimetric method developed in this study is expected to overcome the above limitations and also has good detection capability. In this experiment, a colorimetric biosensor was designed to detect L-DOPA mainly by the production of betaine aldehyde amine. The production of betaine aldehyde amine has an obvious yellow color visible to the naked eye, and the characteristic peak at 430 nm wavelength can be clearly observed through the absorption spectrum. Selective experiments on other neurotransmitters with similar structures (e.g., dopamine, epinephrine, norepinephrine, and some metabolite intermediates) have demonstrated good selectivity of this method for L-DOPA. After confirming the good selectivity of the designed sensor for the analyte, we can further test the relationship between the absorption values obtained at different concentrations of the analyte to be detected. The color rendering showed a good linear relationship with respect to concentration in the range of 5-500 μM, with a detection limit of 2.8 μM. Next, through the chemical reaction of aldehyde amine condensation, we convert yellow betulinic acid into derivatives with green and red fluorescence to enhance the sensitivity of the detection and to reduce the background interference of the detectors. In short, this study has successfully developed a colorimetric biosensor for rapid detection, and demonstrated its sensitivity and high selectivity through experiments. This type of enzyme colorimetric method is a worthy field of development because it can achieve the purpose of instant detection without the need to carry instruments or for professional personnel.       Reference:  https://www.sciencedirect.com/science/article/pii/S0925400519309189