Light therapy to reduce chronic neuropathic pain

How to successfully carry out daily activities when the movement of a single hair on the arm may cause severe pain? This is the question asked by the 7 to 8% of people in Europe suffering from chronic neuropathic pain.

This chronic disease is linked to a dysfunction of the nervous system processing the neurological message of pain (“the pain circuit”) and turns out to be a real nightmare for people who have it. Currently not benefiting from any truly effective treatment, this neuropathic pain can be mild or intermittent.

However, for a tiny minority of patients, the pain felt is so intense that every day-to-day activity becomes a torment to be accomplished. The pain circuit abnormality can be either central (in the spinal cord or brain) or peripheral. In this case, it is the skin’s contact with anything that causes the pain (“hyperpathy”).

Cut nerve endings in the skin

It is to these patients suffering from peripheral neuropathic pain that researchers attached to the European Molecular Biology Laboratory (EMBL) in Rome could help. Their work, published in the journal Nature Communications, relate to a series of cells called TrkB-positive and responsible for chronic pain. They also discuss the treatment they developed to relieve neuropathic pain in mice: a light-sensitive chemical that selectively binds to this type of nerve cell.

The researchers started by modifying the cells TrkB-positive in order to make them sensitive to light. They then tested their treatment on mice, applying it to a patch of sensitive skin with neuropathic pain. When exposed to infrared light, nerve cells retract from the surface of the skin, resulting in pain relief.

The use of light cuts the nerve endings of the skin: the intense pain that neuropathic patients feel at the slightest skin contact then disappears instantly. “It’s like eating a strong curry, which burns nerve endings in the mouth and desensitizes them for a period of time,” says Dr. Paul Heppenstall, EMBL researcher and lead author of the study. of our technique is that we can specifically target the small subset of neurons causing neuropathic pain. “

A test in vitro on human tissue

However, the treatment developed by Dr. Heppenstall’s team is not permanent. This is because the cut nerve endings grow back after a few weeks, causing pain again.

This does not prevent researchers from continuing their work, in particular on human skin tissue in vitro. Upon studying it, they found that its overall composition and the specificity of its neurons appeared to be similar to that of mice, indicating that the treatment might be effective in managing neuropathic pain in humans.

“Of course, a lot of work needs to be done before we can do a similar study in people with neuropathic pain, which is why we are actively seeking partners and are open to new collaborations to develop this method, with the hope that one day it will be used clinically, ”concludes Dr Heppenstall.