Narrow-band ultraviolet B radiation induces the expression of β-endorphin in human skin in vivo.

Background: Ultraviolet radiation (UVR) from the sun and solaria has addictive properties that may develop into dependence. In mice, UVR addiction was connected to β-endorphin (β-END) formed in the skin after UVR exposure. In humans, the formation of β-END in skin keratinocytes has not been confirmed in vivo.

Objective: To determine with immunohistochemistry if sub-erythematous narrow-band UV-B (NB-UV-B) exposures stimulate p53 mediated expression of pro-opiomelanocortin (POMC), β-END and α-melanocyte stimulating hormone (α-MSH) in human skin keratinocytes in vivo.

Methods: Within 12 healthy volunteers, 7 received a single 1 standard erythema dose (SED) of NB-UV-B on their whole body, and 5 volunteers received a cumulative dose of 3 SED delivered on two subsequent days i.e., 1+2 SED. Skin biopsies were taken immediately before the first exposure and at 24h from the last UV-B exposure to assess p53, β-END, POMC, and α-MSH expression.

Results: Nuclear p53 expression increased in all samples taken at 24h after NB-UV-B exposure. UV-B irradiation also increased epidermal β-END expression in 11 out of 12 samples taken at 24h after UV-B exposure. The brownish staining was localized in the cytoplasm of keratinocytes and around the nuclei, being more pronounced in the basal cell layers. POMC and α-MSH staining showed no obvious meaningful increase since only one section of each showed any change compared with basal levels.

Conclusions: Our study is the first to show that UV-B exposures increase β-END expression in epidermal keratinocytes of human skin in vivo, which could be the link to proposed UVR addiction.