Sodium dl‐α‐tocopheryl phosphate inhibits ultraviolet‐induced production of reactive nitrogen species in human keratinocytes

Abstract

It has been well established that UV irradiation causes various kinds of photodamage in human skin. Skin photodamage is mainly caused by reactive oxygen species (ROS), such as superoxide, hydroxyl radical, hydrogen peroxide, and singlet oxygen. Recently, it has been revealed that reactive nitrogen species (RNS), such as nitric oxide (NO) and peroxynitrite (ONOO ) ), are also an important consideration in UV-irradiated human skin. Reactive nitrogen species cause several types of skin damage, for example erythema, darkening, disruption of epidermal barrier function, and psoriasis. Therefore, it is very important to control RNS production for beautiful skin to be maintained. However, RNS are indirectly measured by stable degradation products because their life is very short. In this present study, we attempted the direct observation of RNS production in human keratinocytes. As a result, we succeeded in direct measurement of real-time UVB-induced RNS production in human keratinocytes by using a RNS-specific fluorescence probe. On the other hand, sodium dl-a-tocopheryl phosphate (VEP), a newly synthesized watersoluble vitamin E derivative, inhibited UVB-induced RNS production in human keratinocytes. Furthermore, we revealed that UVB-induced neuronal nitric oxide synthase (nNOS) mediates RNS production in human keratinocytes. These results suggest that VEP is a useful ingredient for cosmetic products, and that VEP may protect the skin from several kinds of damage caused by UV-induced RNS production.Key words: sodium dl-a-tocopheryl phosphate (VEP), reactive nitrogen species (RNS), nitric oxide (NO), peroxynitrite (ONOO ) ), neuronal nitric oxide synthase (nNOS), RNS-specific fluorescence probe, UV, keratinocytes, reactive oxygen species (ROS), skin photodamage.The phenomenon of aging can broadly be categorized into photoaging caused by exogenous factors and physiological aging that is caused by endogenous factors. Our goal was to develop a non-invasive way to assess changes taking place inside the skin for each type of aging, photoaging and physiological aging, by using near-infrared diffuse reflectance (NIR-DR) spectroscopy. For the photoaging and physiological aging effects, the outer forearm (sun-exposed) and the inner upper arm (sun-protected) skin areas were studied in eighty-six females from twentythree to sixty-nine years of age. Measurements were made using NIR-DR and subjected to Principal Component Analysis (PCA); the results suggested the possibility of distinguishing and quantifying both types of aging taking place inside the skin by using the 1670-1820 nm and 2000-2230 nm regions of NIR-DR spectra. In photoaging, structural changes in proteins occur which are reflected in the NIR-DR spectra in the form of a peak shift near 2050 nm that is due to a combination of amide A and amide II. On the other hand, physiological aging is associated with a change in collagen quantity as is reflected in the portion of the NIR-DR spectra assigned to protein. Using NIR-DR and PCA, we discovered the possibility of using a n...