Abstract
Chronic exposure to solar radiation is related to an increased incidence of various skin disorders, including premature skin aging and melanoma and non-melanoma skin cancers. Ultraviolet (UV) photons in particular are responsible for skin damage. Solar UV photons mainly belong to UVA wavebands, however UVA radiation has been mostly ignored for a long time. At the cellular level, UVA photons mainly provoke indirect oxidative damage to biomolecules via the massive generation of unstable and highly reactive compounds. Human skin has several effective mechanisms that forestall, repair and eliminate damage caused by solar radiation. Regardless, some damage persists and can accumulate with chronic exposure. Therefore, conscious protection against solar radiation (UVB+UVA) is necessary. Besides traditional types of photoprotection such as sunscreen use, new strategies are being searched for and developed. One very popular protective strategy is the application of phytochemicals as active ingredients of photoprotection preparations instead of synthetic chemicals. Phytochemicals usually possess additional biological activities besides absorbing the energy of photons, and those properties (e.g. antioxidant, anti-inflammatory) magnify the protective potential of phytochemicals and extracts. Therefore, compounds of natural origin are in the interest of researchers as well as developers. In this review, only studies on UVA protection with well-documented experimental conditions are summarized. This article includes 17 well standardized plant extracts (Camellia sinensis (L.) Kuntze, Silybum marianum L. Gaertn., Punica granatum L., Polypodium aureum L., Vaccinium myrtillus L., Lonicera caerulea L., Thymus vulgaris L., Opuntia ficus-indica (L.) Mill., Morinda citrifolia L., Aloe vera (L.) Burm.f., Oenothera paradoxa Hudziok, Galinsoga parviflora Cav., Galinsoga quadriradiata Ruiz et Pavón, Hippophae rhamnoides L., Cola acuminata Schott & Endl., Theobroma cacao L. and Amaranthus cruentus L.) and 26 phytochemicals.
Highlights
Solar radiation is electromagnetic radiation produced by the Sun, ranging from about 0.25 to 4.5 μm in wavelength including infrared, visible, and ultraviolet (UV) light
This review summarises studies on pure compounds or extracts derived from natural sources that have demonstrated protective potential against UVA radiation in skin cells and/or tissue
Skin protection against solar radiation has been studied for decades, research was focused on UVB, and UVA was mostly ignored
Summary
Solar radiation is electromagnetic radiation produced by the Sun, ranging from about 0.25 to 4.5 μm in wavelength including infrared, visible, and ultraviolet (UV) light. ROS/RNS, unstable oxidised products as well as DNA lesions can affect various cellular pathways and the expression of numerous genes such as inflammatory cytokines, transcription factors, matrix metalloproteinases (MMP), mitogen-activated protein kinases (MAPK), or pro- and anti-apoptotic genes. These signalling molecules initiate the development of pathological changes in skin tissue such as altered epidermal cell proliferation and differentiation, decrease in collagen synthesis, upregulation of extracellular matrix-degrading enzymes such as collagenase (MMP-1), stromelysin (MMP-3), gelatinase (MMP-9) or elastase.
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