Stopping the lingering pain of shingles

Nearly one third of adults will develop shingles, also known as herpes zoster, at some point in their lifetimes, according to the Centers for Disease Control and Prevention (CDC). The disease causes a painful, blistering skin rash that can have complications for months or even years afterwards. The most common of these lingering effects is known as post-herpetic neuralgia (PHN), which is defined as severe, debilitating pain or burning in the areas of the rash several months after the rash has faded. No one entirely understands why this occurs in one out of every three shingles patients, but researchers at the Texas A&M University Baylor College of Dentistry (BCD) are trying to find out.

Phillip Kramer, PhD, a professor in the 
Department of Biomedical Sciences at TAMBCD, is developing a model for studying PHN, with the ultimate goal of creating a treatment for the pain.

It may seem strange for dentistry professors to be leading the way in shingles research, which is thought of as mostly a skin disorder. However, what many people don’t know is that many oral surgeons trained at the dental school often treat PHN.

One in five patients with PHN have opthalmic post-herpetic neuralgia, or pain in the face and around the eyes. “For some reason, the virus prefers the face,” Kramer said, and when the virus reactivates from cells in the trigeminal ganglia (an offshoot of a major cranial nerve), it causes crippling head and facial pain and eye conditions that can lead to blindness.

Although there is a vaccine for shingles, it only reduces the risk of developing the condition by 51 percent—and it is even less able to protect those over the age of 80. It is slightly better at reducing the likelihood of PHN, and so immunization is still an important preventative measure. Still, Kramer thinks there must be a better way.

“Even if every candidate receives the vaccine, which is far from being achieved, the United States would still have some half million shingles cases, many suffering from PHN,” Kramer said. “As such, both zoster and PHN are unmet in the need for better prevention and therapy.”

It has been difficult to study underlying mechanisms and better treatment strategies for opthalmic post-herpetic neuralgia because there hasn’t been a good model of the condition. Therefore, the first goal of Kramer and his team—which is made up of experts in herpes zoster, facial pain modeling and pain gene therapeutics—is to create a model to study the pain and eye problems associated with PHN. The researchers, who include Kramer’s collaborators at the University of Pittsburgh, hope that by understanding how the virus affects the nerves of the face and eyes on a molecular level, they will be able to create and test new therapies.

One of the most promising of these therapies is to use an engineered version of the herpes simplex virus to “turn on” a kind of endogenous opioid called enkephalin, which is an endorphin-type molecule produced by the body, but that can reduce pain in a similar way that morphine or other opiates can, as they bind to the same receptors.

“The goal is to develop a product to greatly reduce chronic orofacial pain in patients with PHN,” Kramer said. “It’s a debilitating condition that affects millions of people, and we expect to develop a therapy to help.”