May 12, 2011 -- Ultraviolet light therapy and vitamin D creams are widely prescribed treatments for psoriasis, and now a new study may help explain why they work for so many patients.
Researchers say the vitamin D-based treatments increase the binding of a peptide called cathelicidin to DNA, which, in turn, inhibits the inflammatory response that triggers psoriasis.
The finding may one day lead to better treatments for the painful skin condition that specifically target cathelicidin, study researcher Jurgen Schauber, MD, of Ludwig-Maximillian University in Munich, Germany, tells WebMD.
“We were able to identify a novel, pro-inflammatory signaling pathway which helps us understand why [vitamin D-based] treatments work,” he says.
As many as 7.5 million Americans have psoriasis, a chronic, inflammatory disease that commonly causes thick, itchy, scaly patches on the skin.
While the causes are not completely understood, it is believed that the scaly patches occur when the immune system identifies healthy cells as dangerous ones and goes into overdrive, activating protein complexes called inflammasomes.
In the newly published study, Schauber and colleagues analyzed genes in skin biopsies from psoriasis patients and healthy volunteers.
They found that a gene encoding the newly discovered protein AIM2 was highly activated in the skin of the psoriasis patients, but not the samples from people without psoriasis.
Schauber explains that along with other proteins, AIM2 is a key player in activating an inflammation-triggering inflammasome.
Topical vitamin D treatments and ultraviolet B light therapy, which promotes vitamin D production in the skin, help DNA inhibit inflammasome activation by controlling cathelicidin production.
Drugs that specifically target cathelicidin expression could prove useful in the treatment of psoriasis, the researchers conclude.
The study appears in the May 11 issue of Science Translational Medicine.
Vitamin D and Psoriasis
Henry Lim, MD, chief of dermatology at Detroit’s Henry Ford Hospital, says the study increases the understanding of the role of vitamin D in psoriasis.
“We have used these treatments for a long time, but we haven’t had a full understanding of why they work,” Lim tells WebMD. “This is one potential mechanism.”
He says UBV light therapy is an effective treatment for about 70% of patients and vitamin D creams improve symptoms in about 50% to 60% of patients with mild psoriasis.
But there is little suggestion that taking vitamin D supplements has any impact on psoriasis symptoms. Lim recommends against excess sun exposure or commercial tanning to increase vitamin D levels.
“Obviously sun exposure is associated with skin aging and skin cancer,” he says. “In the clinic exposures are controlled and much safer.”