Activating cutaneous vitamin D: Low-dose UVB strengthens epidermal barrier, antimicrobial function

Wonju, South Korea - While high-dose UVB is detrimental to the epidermal permeability barrier, low-dose UVB can be therapeutic in mending a defective epidermal barrier and antimicrobial function, such as in atopic dermatitis, according to one dermatologist.

"The activation of vitamin D in the skin plays an intricate role in strengthening these systems, " says Eung-Ho, Choi, M.D., chief professor of the department of dermatology at Yonsei University Wonju College of Medicine, Wonju, South Korea.

Dr. Choi conducted a study in which hairless mice were exposed to 40mJ/cm UVB once daily for one or three days. A sham light was exposed on the control group.

Twenty-four hours after the last exposure, epidermal barrier function was assessed and skin specimens were taken for analysis. Basal TEWL (trans-epidermal water loss) and barrier recovery rates following tape stripping were measured.

Results

Results showed that in the three-day low-dose UVB-exposed epidermis, the barrier recovery rate after acute barrier disruption by tape stripping increased when compared to the control group, without affecting basal TEWL.

Dr. Choi noticed that there was a stimulation of the vitamin D3 system and epidermal lipid synthesis enzymes, as well as an increase in both the expression of antimicrobial peptides and differentiation markers in the epidermis of those mice exposed to low-dose UVB radiation.

Validation

In order to validate the effect of vitamin D on epidermal permeability and anti-microbial peptides, 0.03 percent topical calcitriol and vehicle were applied to the murine skin at 20 minutes after the pretreatment with topical clobetasol propionate at 12-hour intervals for a total of seven treatments.

Functional and morphologic analyses performed 24 hours after the last application showed that barrier recovery after tape stripping was improved at the calcitriol sites.

"We saw that topical vitamin D could restore the impaired permeability barrier induced by the topical steroid by recovering epidermal lipid synthesis as well as restore antimicrobial peptides and cytokines reduced by the steroid, " Dr. Choi explains.

Further analysis

In a further analysis, Dr. Choi applied 2 percent ketoconazole (an inhibitor of 1 alpha-dihydroxy vitamin D3) cream immediately after UVB exposure to the murine skin. He found that the ketoconazole could inhibit the cutaneous vitamin D system, the epidermal lipid synthesis related enzymes and anti-microbial peptide expression, disrupt the basal barrier state as well as delay the permeability of the barrier.

"This shows us that many aspects of the beneficial effects of low-dose UVB are directly dependent on an activation of the cutaneous vitamin D system, " Dr. Choi says.

Steroids

Topical steroids are commonly used in patients suffering from atopic dermatitis, psoriasis and other inflammatory dermatoses, but their long-term use invariably induces skin atrophy, telangiectasis, an impairment of epidermal permeability and antimicrobial barrier. Therefore, physicians will often opt to use calcineurin inhibitors, avoiding the detrimental effects of steroids.

According to Dr. Choi, the topical or oral supplementation of vitamin D may be an option in patients suffering from atopic dermatitis, especially in those patients who have already had long-term topical steroid treatment.

"Clinical dermatologists should consider UVB therapy and topical vitamin D in order to enhance the permeability and antimicrobial barrier in inflammatory dermatoses including papulosquamous disease as well as psoriasis and atopic dermatitis," Dr. Choi says. DT

Disclosures: Dr. Choi reports no relevant financial disclosures.