Shining Light on Skin Pigmentation: The Darker and the Brighter Side of Effects of UV Radiation^†

Abstract

The term barrier function as applied to human skin often connotes the physical properties of this organ that provide protection from its surrounding environment. This term does not generally include skin pigmentation. However, skin pigmentation, which is the result of melanin produced in melanocytes residing the basal layer of the skin and exported to the keratinocytes in the upper layers, serves equally important protective function. Indeed, changes in skin pigmentation are often the most readily recognized indicators of exposure of skin to damaging agents, especially to natural and artificial radiation in the environment. Several recent studies have shed new light on a) the mechanisms of involved in selective effects of subcomponents of UV radiation on human skin pigmentation and b) the interactive influences between keratinocytes and melanocytes, acting as ‘epidermal melanin unit’, that manifest as changes in skin pigmentation in response to exposure to various forms of radiation. This article provides a concise review of our current understanding of the effects of the non-ionizing solar radiation, at cellular and molecular levels, on human skin pigmentation.

Light- or Dark-Colored, L-DOPA-Based Melanins

“…With regards to human physiology, the role of MNs to provide UV protection [51][52][53][54] and skin, hair or eye pigmentation [55][56] has been and is still studied extensively. Such functions are not applicable to the so-called internal MNs.…”

Thymol and Thymus Vulgaris L. activity against UVA- and UVB-induced damage in NCTC 2544 cell line

“…UVB is directly absorbed by the proteins and the nucleic acids and leads to the cyclobutane-pyrimidine dimers (CPDs) and pyrimidine pyrimidone photoproducts as the principal DNA lesions [13]. The incorrect repair of these products by NER (Nucleotide Excision Repair) system leads to mutations [7,15] or activation of apoptotic pathways [16]. UVB, but also UVA, has been classified as Class I carcinogen by the International Agency for the Research on Cancer [17].…”

Effect of tetracycline and UV radiation on melanization and antioxidant status of melanocytes

“…After exposure of melanocytes to UVA radiation, the induction of melanogenesis expressed by consistent increase in melanin content and Skin pigmentation is determined by over 100 genes including those that encode transcription factors, enzymes, hormones, autocrine and paracrine factors and their receptors [29]. Besides these biochemical factors, the induction of melanogenesis might be a result of the external and internal stress [30], also in form of phototoxicity.…”