At the root of the symptoms of Parkinson’s disease is the gradual disappearance of certain neurons producing dopamine and located in particular in the substantia nigra, a particular region of the brain. But why those, who play a role in controlling movements, and not others?
Understand why some neurons are more fragile
Because they would be more sensitive to overheating. In any case, this is a hypothesis put forward by Canadian researchers. “Like an engine running too fast, these neurons have to produce a lot of energy to function. They wear out prematurely, ”suggested, in 2015, Professor Louis-Éric Trudeau, of the University of Montreal.
Understanding this vulnerability is a key to understanding the mechanisms of the disease. But if “the different stages of the disappearance of neurons are better known, and in particular this greater fragility, the origin of the disease remains unknown », Recalls Dr. Gilles Fénelon, neurologist.
Administer treatments differently
This new light on neurons could also pave the way for new therapeutic avenues. The researchers evoke, for example, the development of drugs capable of limiting the energy consumption of these neurons, or of helping them to produce energy more efficiently.
However, in the meantime, all current drugs for Parkinson’s disease aim to supplement the missing dopamine in the brain. They reduce symptoms and maintain quality of life and independence from disease for years. But their effectiveness decreases over time with the progression of the disease. And they cause significant side effects (abnormal movements…). “To avoid them, we must achieve keep dopamine levels as constant as possible in the brain », Explains Dr Fénelon.
- Oral medications (including some extended release) containing a mixture of levodopa (L-dopa) and carbidopa, under the name Sinemet (new formulation since June 2019) and generics (Teva laboratory for example).
- Another approach, same objective: L-dopa gel pump. It delivers the same mixture, but directly into the intestine, via a catheter implanted through the abdominal wall. This solution, recent and little developed in France, is indicated for a limited number of patients, in particular because of the cost, constraints and risks associated with the equipment. For some patients, however, it represents a real improvement over oral medications.
And research continues to develop new formulations of these dopaminergic drugs, always with the aim of offering a faster or more stable effect of the drug during the day: to deliver inhaled levodopa or apomorphine in the form of lozenges under the tongue, for example.
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Directly stimulate neurons
In addition to drug treatments, over the past ten years, the deep electrical stimulation, based on the implantation of electrodes in the heart of the brain. Studies have shown that it is more effective than drugs in some patients at an early stage of the disease.
This technique, which earned its French discoverer, Pr Alim-Louis Benabid, the 2014 Lasker Prize (the American equivalent of the Nobel Prize in medicine), only concerns 10 to 15% of patients. And it remains delicate:‘surgical intervention and the stimulator settings once implantation has been carried out require great precision.
Still to boost neurons, there is also the transcranial magnetic stimulation. A magnet placed on the outside of the skull delivers a painless magnetic field for a few minutes. At the rate of several sessions per week, this technique would reduce the symptoms of a small number of patients. But “the effects remain transitory. Further research is essential to determine which patients derive the most benefit from it, ”explains Dr Fénelon.
Infrared light against degeneration of neurons?
The deep electrical stimulation is not curative because it does not completely block the progressionof Parkinson’s disease: what if this technique could be improved? This is the wish of a team of scientists from Grenoble University Hospital, the Atomic Energy Commission (CEA) and the Boston Scientific Corporation. This works on a complementary practice which is based on near infrared technology.
Following very good preclinical results obtained in 2016, a clinical trial started in March 2021 and the first patient to join it was already had a successful operation on March 24. This technique is called neuro-illumination (also called photobiomodulation), and consists of targeting the substantia nigra, the site of degeneration of dopaminergic neurons at the origin of the motor symptoms of Parkinson’s disease.
“Unlike current therapies which temporarily limit symptoms without affecting neuronal degeneration, the light could potentially stop this degeneration. Thus, this therapeutic approach could slow the loss of motor functions patients and their autonomy “, explains the CEA. The operation is performed using an implantable intracerebral device developed by the latter. This system (called Ev-NIRT) consists of a implantable neurostimulator connected to an optical generator, itself connected to an optical fiber delivering near infrared light to the brain.
Read also : Parkinson’s disease: Can we relieve dyskinesias?
Prescribe physical exercise
“We have evidence that the regular practice of sustained physical activity improves the symptoms of Parkinson’s disease ”, declares Professor Jean-Michel Gracies, neurologist and specialist in physical medicine in Créteil. One of the latest studies has shown that the benefits are all the greater the more physical activity is sustained, for example four weekly sessions of 30 minutes each of active walking on a treadmill.
Thus, to help patients move better, we can advise adapted tai chi classes, “therapeutic” tango, of capoeira. These activities reduce stiffness, increase range of motion and improve quality of life (walking, balance, etc.). Several hospitals and specialized institutes offer these activities.