Light-Based Approach Manages Chronic Neuropathic Pain

Researchers have developed a light-based method that could be used to manage neuropathic pain. The technique was tested in mice.

Hairy skin of a mouse, with the nerve cells that are responsible for sensitivity to gentle touch in green. The neurons are located around the hair follicles (in light green). Courtesy of R. Dhandapani et al./Nature Communications.

Researchers from the European Molecular Biology Laboratory (EMBL) Rome identified a specific population of nerve cells in the skin that are responsible for sensitivity to gentle touch. These are also the cells that cause severe pain in neuropathic patients. The research team developed a light-sensitive chemical that selectively binds to this type of nerve cell. By first injecting the affected skin area with the chemical and then illuminating it with NIR light, the targeted nerve cells retract from the skin's surface, leading to pain relief.

By clipping off the nerve endings with light, the gentle touch that can cause severe pain in neuropathic patients is no longer felt. The skin is only desensitized to the gentlest touch — other nerve cells in the skin are not affected by the light treatment.

To test the technique, researchers used laser ablation to administer the light therapy to mice affected by neuropathic pain in their limbs. Affected mice will normally quickly withdraw their paw when it is gently touched. After the light therapy, the mice exhibited normal reflexes upon gentle touch. The effect of the therapy lasted for a few weeks, after which the nerve endings grew back and gentle touch again caused pain.

The team also investigated human skin tissue. According to the team, the overall makeup of the tissue and the specifics of the neurons of interest appear to be similar to the mouse tissue, indicating that the method could be effective in managing neuropathic pain in humans.

Previous attempts to develop drugs to treat neuropathic pain have focused on targeting single molecules. In contrast, the light-based technique targets the small subgroup of neurons causing neuropathic pain.

“We think that there’s not one single molecule responsible, there are many,” said EMBL group leader Paul Heppenstall. “You might be able to succeed in blocking one or a couple, but others would take over the same function eventually. With our new illumination method, we avoid this problem altogether.”

Heppenstall said that the team is actively seeking partners to develop the method further, with the hope of one day using it in the EMBL clinic.

The research was published in Nature Communications (doi:10.1038/s41467-018-04049-3).

Scientists at EMBL Rome have found a way to manage pain in mice using light. They discovered that the nerve cells in the skin that respond to gentle touch are the same cells that cause a type of severe pain, called neuropathic pain.