Noninvasive monitoring of plasma l-dopa concentrations using sweat samples in Parkinson's disease

Abstract Background l -dopa ( l -3,4-dihydroxyphenylalanine) is commonly used for treating Parkinson's disease (PD). However, regardless of its prominent effect, therapeutic range of l -dopa narrows down with disease progression, which leads to development of motor complications including wearing off and dyskinesias. In addition, intestinal absorption of l -dopa is inversely correlated with the amount of oral protein intake, and shows intra- and inter-day variability. Hence, frequent monitoring of plasma l -dopa concentrations is beneficial, but frequent venipuncture imposes physical and psychological burdens on patients with PD. Methods We investigated the usefulness of sweat samples instead of plasma samples for monitoring l -dopa concentrations. With a monolithic silica disk-packed spin column and the high-performance liquid chromatography-electrochemical detection system, l -dopa in sweat samples was successfully quantified and analyzed in 23 PD patients. Results We found that the Pearson's correlation coefficient of the plasma and sweat l -dopa concentrations was 0.678. Although the disease durations and severities were not correlated with the deviation of the actual sweat l -dopa concentrations from the fitted line, acquisition of the sweat samples under a stable condition was technically difficult in severely affected patients. The deviations may also be partly accounted for by skin permeability of l -dopa. Conclusions Measuring l -dopa concentrations in sweat is suitable to get further insights into the l -dopa metabolism.