"This protein has the potential to be a groundbreaking treatment for pain and has previously not been studied in pain-sensing neurons," said lead study author Dr. Mark J. Zylka, assistant professor of cell and molecular physiology at the University of North Carolina.
The study conducted in collaboration with researchers from the University of Helsinki has shown that this protein works by converting the chemical messengers that cause pain into ones that suppress it.
For their study, the researchers genetically engineered mice to lack PAP (prostatic acid phosphatase), a protein routinely used to diagnose prostate cancer whose levels increase in the blood of patients with metastatic prostate cancer.
The team found that the mutant mice were more sensitive than their normal counterparts to inflammatory pain and neuropathic pain, two common forms of chronic pain in humans.
The increased sensitivities diminished when researchers injected excess amounts of PAP into the spinal cords of the mutant mice.
"We were really blown away that a simple injection could have such a potent effect on pain. Not only that, but it appeared to work much better than the commonly used drug morphine," said Zylka, lead author of the study published online in the journal Neuron.
The protein suppressed pain as effectively as morphine but for substantially longer. One dose of PAP lasted for up to three days, much longer than the five hours gained with a single dose of morphine.
Zylka and his colleagues are now searching for more proteins with such an effect, and trying to develop small molecules that interact with PAP to enhance or mimic its activity.
"It is entirely possible that PAP itself could be used as a treatment for pain, through an injection just like morphine. But we would like to modify it to be taken in pill form. By taking this field in a new direction, we are encouraged and hopeful that we will be able to devise new treatments for pain," Zylka said.