Altered epidermal lipid layers induced by long-term exposure to suberythemal-dose ultraviolet

Background Although several studies have reported on the biological effects of ultraviolet (UV) radiation, there have been only a few reports on the changes in epidermal lipids following long-term UV irradiation at suberythemal dose (SED), to which people are usually exposed during their lifetime. Objectives To investigate the changes of epidermal lipid properties after long-term UV radiation with SED. Materials and methods Hairless mice were irradiated three times weekly for 15weeks at an SED of UV (UVB: 20mJ/cm²; UVA: 14J/cm²). Every three weeks, transepidermal water loss (TEWL) was measured by a Tewameter. The morphological alterations of stratum corneum (SC) lipid lamellae were examined by electron microscopy (EM). Activities of three key enzymes for mRNA of serine palmitoyl transferase, fatty acid synthase, and HMG CoA reductase were analyzed with real time reverse transcriptase-polymerase chain reaction. We also measured the amount of ceramide, cholesterol sulfate, and free fatty acid in the SC by high-performance thin-layer chromatography with exposed times. Results The SED UV-irradiated group showed increased TEWL after 12weeks. Following the irradiation period, EM revealed incomplete and separated lamellae at SC intercellular space. mRNA of three key enzymes was increased until six weeks of UV irradiation and decreased thereafter. However, three major lipid amounts gradually decreased throughout the exposed period, with a notable decrease in ceramide. Conclusions Long-term UV irradiation even with SED influences skin barrier function and structure with prominent ceramide decrease in SC intercellular lipid.