Fluorescent-based Method May Help Measure Levels of Levodopa in Blood

The levels of levodopa, one of the gold-standard treatments in Parkinson’s disease, may be assessed using a fast, simple, low-cost, fluorescent-based method, a new study suggests.

The study, “Blue and green emission-transformed fluorescent copolymer: Specific detection of levodopa of anti-Parkinson drug in human serum,” was published in the journal Talanta.

Parkinson’s disease is a central nervous system disorder characterized by low levels of the neurotransmitter dopamine, a chemical messenger that allows nerve cells to communicate and, among other functions, helps regulate movement.

Treatment with levodopa, or L-DOPA — a precursor to dopamine — has long been one of the gold standards for Parkinson’s. However, it is important to regulate and monitor the levels of levodopa in patients to prevent undesirable side effects.

Now, a team of Chinese researchers developed a fast and simple method to measure the levels of levodopa in patients’ blood. Specifically, the method consists of mixing levodopa with a chemical solution called PEI, which results in a blue fluorescence within 10 minutes and its conversion to green fluorescence within two hours, at which time the mix is analyzed using a fluorescence spectrophotometer that emits light of a certain wavelength.

Researchers tested if the conversion in fluorescence from blue to green was highly specific for levodopa throughout time. This method was highly selective and sensitive to determine the presence of levodopa within a specific concentration rage (0 to 50 micromolar).

They then tested their method to detect levodopa in different concentrations of human diluted blood serum samples. Both fluorescence emissions showed a good correlation with levodopa levels, with the green emission showing an excellent recovery rate at the higher serum concentrations (up to 30%).

The recovery rate of a sample allows researchers to quantify the concentration of a compound present in the sample based on the fluorescence it emits.

The team then tested the method’s ability to measure the levels of levodopa present in three different levodopa-containing therapies used in Parkinson’s disease: Sinemet tablets (a controlled-release combination of levodopa and carbidopa, developed by Merck), levodopa and benserazide hydrochloride tablets (sold as Madopar or Prolopa, both by Roche), and levodopa tablets.

The results showed that both blue and green fluorescence emission correlated with the levels of levodopa, with a recovery rate ranging from 90.9% to 109.7%.

Finally, they applied their method to detect the different levodopa concentrations present in all three anti-Parkinson therapies when diluted in human blood samples. Once again, the method showed an excellent recovery of levodopa levels ranging from 91.5% to 107.4%.

Overall, “our developed dual-signal approach provided a promising platform for the diagnosis and treatment of Parkinson’s disease,” the researchers concluded.