Physiological Doses of Red Light Induce IL-4 Release in Cocultures between Human Keratinocytes and Immune Cells

Effects of visible light on mechanisms of skin photoaging

Human skin is not only affected by ultraviolet radiation but also by visible light wavelengths emitted by sunlight, electronic devices, and light emitting diodes. Similar to the ultraviolet radiation, visible light has been implicated in photoaging. In this review, the effects of blue light, yellow light, red light, and broad visible light are discussed in relation with photoaging. Different visible light wavelengths likely contribute beneficial and deleterious effects on photoaging by way of interaction with specific photoreceptors, ROS production, and other photon-mediated reactions. Further in vivo studies are needed to determine the mechanism and action spectrum of photoaging in humans, as well as optimal photoprotection with coverage against visible light wavelengths.

Recommendations for Reporting Methods in Phototesting Studies

The figure presented here illuminates the large number of variables that are necessary to adequately describe phototesting protocols. Each of these characteristics can be critical in understanding results presented in the photomedicine community as well as the broader photobiology and photochemistry communities. The inclusion of all of these variables within each phototesting publication will aid in discourse and further scientific discovery within our field.

Effect of Different Wavelengths of Laser Irradiation on the Skin Cells

The invention of systems enabling the emission of waves of a certain length and intensity has revolutionized many areas of life, including medicine. Currently, the use of devices emitting laser light is not only an indispensable but also a necessary element of many diagnostic procedures. It also contributed to the development of new techniques for the treatment of diseases that are difficult to heal. The use of lasers in industry and medicine may be associated with a higher incidence of excessive radiation exposure, which can lead to injury to the body. The most exposed to laser irradiation is the skin tissue. The low dose laser irradiation is currently used for the treatment of various skin diseases. Therefore appropriate knowledge of the effects of lasers irradiation on the dermal cells’ metabolism is necessary. Here we present current knowledge on the clinical and molecular effects of irradiation of different wavelengths of light (ultraviolet (UV), blue, green, red, and infrared (IR) on the dermal cells.

Physical and compositional analysis of differently cultured 3D human skin equivalents by confocal Raman spectroscopy

Three-dimensional skin equivalents are increasingly gaining acceptance as non-animal based experimental models of human skin. They are particularly suited to studying differences in physical and compositional properties of normal and diseased skin and their impact on the skin's barrier function. Typically, a culture protocol yielding a model of normal skin is modified to create a model simulating a pathology. Skin layer thicknesses and lipid/protein contents are compared using methods that are invasive, precluding further experiments on the same replicates, and which may be prone to artefacts. We show here that confocal Raman spectroscopy (CRS) is a valuable method for non-invasive discrimination of skin equivalents grown under different culture conditions. Using 3D full-thickness skin equivalents developed in-house, we measure significant differences in stratum corneum and viable epidermis apparent thicknesses resulting from a 7-day difference in the cultures' air-lift phase and from supplementation of the culture medium with interleukin 4. Furthermore, stratum corneum thicknesses obtained by CRS are up to 2.6-fold higher than values measured from histological photomicrographs. Regarding composition, CRS reveals the differential effects of the culture protocol modifications on ceramide, cholesterol and protein composition as a function of depth in the stratum corneum.

Full-Thickness Human Skin Equivalent Models of Atopic Dermatitis

Atopic dermatitis is a chronic inflammatory skin disease caused by complex multifactorial etiology. In the recent years, there have been significant advances in tissue engineering and the generation of in vitro skin models representative of healthy and diseased states. This chapter describes the methodology for the fabrication of in vitro human skin equivalent (HSE) from human keratinocytes and fibroblasts using a fibrin-based dermal matrix and serum-free culture conditions. Modification of the culture conditions with the supplementation of Th2 cytokines such as interleukin-4 induces the development of atopic dermatitis-like skin model. The chapter also describes the histological and immunohistochemical tools for characterization of the HSE model. The reconstruction of tissue-engineered HSE models that recapitulate the essential features of atopic dermatitis provides powerful tools for deeper understanding of the underlying pathological mechanisms on epidermal level, identification and testing of novel treatment options, and safety and toxicological evaluation in a pathophysiologically relevant system.

Ultraviolet radiation-induced immunosuppression and its relevance for skin carcinogenesis

The realisation that UV radiation (UVR) exposure could induce a suppressed immune environment for the initiation of carcinogenesis in the skin was first described more than 40 years ago. Van der Leun and his colleagues contributed to this area in the 1980s and 90s by experiments in mice involving UV wavelength and dose-dependency in the formation of such tumours, in addition to illustrating both the local and systemic effect of the UVR on the immune system. Since these early days, many aspects of the complex pathways of UV-induced immunosuppression have been studied and are outlined in this review. Although most experimental work has involved mice, it is clear that UVR also causes reduced immune responses in humans. Evidence showing the importance of the immune system in determining the risk of human skin cancers is explained, and details of how UVR exposure can down-regulate immunity in the formation and progression of such tumours reviewed. With increasing knowledge of these links and the mechanisms of UVR-induced immunosuppression, novel approaches to enhance immunity to skin tumour antigens in humans are becoming apparent which, hopefully, will reduce the burden of UVR-induced skin cancers in the future.

Combination of Natural Extracts and Photobiomodulation in Keratinocytes Subjected to UVA Radiation

Natural extracts (NE) with antioxidant properties can minimize the effects of photoaging. Photobiomodulation (PBM) has proven to be a useful tool for the modulation of cell metabolism. Here, we investigate the associations of antioxidants with PBM with the aim of promoting skin rejuvenation. We began with standardization of the experimental protocol. Extracts of chamomile, rosemary, blueberry, green tea, figs, pomegranate and nutwood were tested. A custom irradiation system (366 ± 10 nm) was used to simulate sun exposure. A light emitting diode system (640 ± 12.5 nm) was used for PBM. Viability assessments were performed by the (3-(4,5-Dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide) MTT assay method. Based on the results, radiant exposure to UVA was defined as 9 and 1 J cm^-2 for PBM. Extract concentrations were established on the basis of dark toxicities, which ranged from 0.01% to 0.3%. The data show that PBM is a promising therapy to restore keratinocytes after UVA damage; however, the detailed mechanism and effects require further exploration. Moreover, although the combination of PBM with NE may be a useful strategy, the choice of a NE is challenging, since the working concentration and other properties, such as photosensitivity, may bring about unwanted results.

How UV Light Touches the Brain and Endocrine System Through Skin, and Why

The skin, a self-regulating protective barrier organ, is empowered with sensory and computing capabilities to counteract the environmental stressors to maintain and restore disrupted cutaneous homeostasis. These complex functions are coordinated by a cutaneous neuro-endocrine system that also communicates in a bidirectional fashion with the central nervous, endocrine, and immune systems, all acting in concert to control body homeostasis. Although UV energy has played an important role in the origin and evolution of life, UV absorption by the skin not only triggers mechanisms that defend skin integrity and regulate global homeostasis but also induces skin pathology (e.g., cancer, aging, autoimmune responses). These effects are secondary to the transduction of UV electromagnetic energy into chemical, hormonal, and neural signals, defined by the nature of the chromophores and tissue compartments receiving specific UV wavelength. UV radiation can upregulate local neuroendocrine axes, with UVB being markedly more efficient than UVA. The locally induced cytokines, corticotropin-releasing hormone, urocortins, proopiomelanocortin-peptides, enkephalins, or others can be released into circulation to exert systemic effects, including activation of the central hypothalamic-pituitary-adrenal axis, opioidogenic effects, and immunosuppression, independent of vitamin D synthesis. Similar effects are seen after exposure of the eyes and skin to UV, through which UVB activates hypothalamic paraventricular and arcuate nuclei and exerts very rapid stimulatory effects on the brain. Thus, UV touches the brain and central neuroendocrine system to reset body homeostasis. This invites multiple therapeutic applications of UV radiation, for example, in the management of autoimmune and mood disorders, addiction, and obesity.