New Clues About Why Sunburn Is So Painful

Researchers Put the Blame on a Protein That Triggers Pain When You're Overexposed to the Sun

July 6, 2011 -- It may come as cold comfort to those already suffering from the sting of a midsummer sunburn, but researchers have found a new clue that may help explain why sunburns are so painful.

Their study shows UVB irradiation targets a particular protein in the body called CXCL5 that plays a role in pain sensitivity. Overexposure to the sun causes the protein to be overexpressed and triggers the pain and inflammation associated with sunburn.

"These findings have shown for the first time the important role of this particular molecule in controlling pain from exposure to UVB irradiation," says researcher Steve McMahon, from the Wolfson Centre for Age-Related Diseases at King's College, in London, in a news release.

"But this study isn't just about sunburn -- we hope that we have identified a potential target which can be utilized to understand more about pain in other inflammatory conditions like arthritis and cystitis," says McMahon.

In the study, researchers analyzed samples of sunburned skin from healthy people as well as rats and found more than 90 potential pain mediators that were stimulated in response to UV radiation.

They then looked at the biology behind these markers in rats to see which of the potential pain mediators was likely triggered by UV radiation.

The results pointed to CXCLS, which is part of a family of proteins known as chemokines that attract immune cells to damaged tissue, causing inflammation and pain.

Researchers found that CXCL5 was at its highest level at the time of maximum pain in the rats. In addition, injecting the protein into healthy rat skin caused hypersensitivity to pain.

Finally, researchers found treating rats with a neutralizing antibody that targets CXCL5 reduced the sensitivity to pain caused by UVB radiation.

They say the findings, published in Science Translational Medicine, may help identify CXCL5 as a potential target for new medicines to treat other painful inflammatory conditions.

Genetic Clue to Painful Peripheral Neuropathy

Study Shows Genetic Mutation May Be a Cause of Some Cases of Peripheral Neuropathy

June 22, 2011 -- A single gene may be responsible for the pain suffered in many people diagnosed with a type of peripheral neuropathy that previously had no known cause, a study shows.

The discovery could lead to effective treatments for the disorder, which is often characterized by burning, tingling, and numbness in the hands and feet.

The study is published in the Annals of Neurology.

Peripheral nerves are any nerves located outside the spine or brain. Damage to them -- whether by injury, infection, diabetes, or other cause -- results in peripheral neuropathy.

Treating the underlying cause of peripheral neuropathy often relieves the pain. However, for nearly a third of those diagnosed with the disorder, no such underlying cause can be identified, which greatly limits treatment options.

"For millions of people, the origin of this intense pain has been a frustrating mystery," co-researcher Stephen Waxman, MD, PhD, a professor of neurobiology and of pharmacology at Yale University, says in a news release.

Now, though, Waxman and his fellow researchers at Yale, the Veterans Affairs Medical Center in West Haven, and the University Maastricht in the Netherlands believe they have found a genetic mutation that may account for as many as 30% of these mystery cases, known as idiopathic small nerve fiber neuropathy.

Twenty-eight Dutch patients were recruited for the study after being screened for any possible known causes of the disorder. Genetic analysis revealed that eight of these men had mutations in the SCN9A gene, which, the study notes, has been associated with other pain-causing disorders.

Further analysis showed that the mutation triggered hyperactivity in certain neurons, possibly leading to nerve degeneration and subsequent development of neuropathy.

"These findings will help us as clinicians to a better understanding of our patients with small fiber neuropathy and could ideally have implications for the development of future specific therapies," University Maastricht neurologist Catharina G. Faber, MD, PhD, one of study researchers, says in a news release.