The secret to better Parkinson’s disease treatment may sit in sweat. A new wearable patch for people with Parkinson’s disease can monitor their medication levels by sampling sweat from their fingertips.
In a new study published in the journal Proceedings of the National Academy of Sciences, researchers at the University of California, San Diego (UCSD) described how the battery-less device attained performance levels similar to those of standard laboratory tests.1 The technology could make it easier for physicians to prescribe patients personalized daily medication regimens.
The Need for Precise Parkinson’s Disease Drug Delivery
More than 25 million people worldwide are predicted to develop Parkinson’s disease by the year 2050. This trend will have a huge impact on healthcare budgets, forecast to cost tens of billions of dollars in the US alone.1
There’s no cure for Parkinson’s disease, and the top available medication for patients is the symptom-modifying drug levodopa. The compound enters the brain, where it is converted into the neurotransmitter dopamine, a chemical that people with Parkinson’s disease lack. Levodopa has been the “gold-standard” treatment for Parkinson’s since the 1960s.
The drug helps reduce the tremors and motor problems that are characteristic of the disease, but enzymes in the gut process it rapidly, reducing its efficacy. Additionally, patients who use the drug long-term can develop complications from its use. These patients need the dose they receive to be controlled very tightly. If the levels of levodopa in their body are too low, motor problems quickly re-emerge. On the other hand, if too much is given, patients can experience involuntary motor movements.
Physicians currently rely on patients’ symptom diaries to work out the correct treatment schedule and dosing level. But this approach isn’t perfect and can lead to gaps between doses. Precise lab tests, like liquid-chromatography-mass spectrometry, can measure exact drug levels, but patients often wait weeks to get results.
UCSD researchers, led by neurologist Irene Litvan and bioengineer Joseph Wang, had previously developed tests that could measure levodopa levels in blood or sweat. But these earlier platforms produced only snapshot reports and required an external power source.
The new patch instead tracks levodopa levels continuously. It consists of hydrogels and sensors sandwiched between two sheets of the rubber-like plastic material styrene-ethylene-butylene-styrene. The device is worn on the fingertip, which is packed with roughly 400 sweat glands in every square centimeter of skin. The hydrogel passively absorbs sweat from the skin through osmosis.
That sweat is absorbed into a winding channel, which contains a levodopa sensor and a transmitter. When the patient’s levodopa interacts with enzymes contained within the sensor, a chemical reaction occurs, which creates a small electrical voltage. This signal both powers the patch and is used as a proxy for levodopa levels. High amounts of the medication trigger a powerful voltage, while lower levels produce a small signal.
Proving the Patch’s Performance
To test the new monitor, the researchers asked both people with Parkinson’s disease and healthy volunteers to wear the patch.
The team first asked healthy volunteers to snack on some fava beans before putting on the patch. These beans naturally contain levodopa. The sensor worked, producing voltages that varied depending on how many beans the volunteers had eaten. The team saw similar results after healthy volunteers took levodopa tablets.
Next, they tried the patch on a group of four patients with Parkinson’s disease. Again, the levodopa levels that the patch measured strongly correlated with the precise levels detected in their blood by high-performance liquid chromatography technology. Importantly, the times when the patch measured the highest levels of levodopa were also the times when the patients had the fewest disease symptoms, showing that the patch was providing insight into what was happening in patients’ brains.
The authors hope that the patch could one day be used by patients at home, where the patch would connect with a levodopa pump that would keep the levels of the drug in patients’ bodies at the correct levels continuously. That will help patients stay well with a minimum of side effects. “Improved understanding of how L-Dopa levels correlate with motor performance will allow clinicians to define the target therapeutic range(s) for L-dopa and to treat [Parkinson’s disease] symptoms with the minimal effective L-dopa dose to prevent motor complications,” the authors wrote in their paper.
