الفهرس 
Oxidative Stress and Skin DiseasesOnly 14 pages are availabe for public view
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Abstract
Oxidative stress is a condition of pro-oxidant/AO disequilibrium, where increased generation of oxidants overwhelms the AO defense mechanisms leading to damage of various cellular structures.
Oxidants include ROS and RNS that collectively describe free radicals and non-radical reactive derivatives. Free radicals are molecules or molecular fragments containing one or more unpaired electrons in atomic or molecular orbitals. This unpaired electron(s) usually gives a considerable degree of reactivity to the free radical. Non-radicals include H2O2, singlet oxygen, peroxynitrite and ozone. Free radicals include superoxide anion, hydroxyl, peroxyl and NO radicals.
Sources of oxidants may be exogenous as irradiation, pollution, cigarette smoke, drugs, chemicals and food additives and preservatives or endogenous as mitochondrial oxidative phosphorylation, respiratory burst, cytochrome P450 metabolism, peroxisomes, enzymatic systems as xanthine oxidase, pathological disorders as haemochromatosis and Wilson disease where there is deposition of metals in tissues that increase ROS significantly, mental and physical stress, infection, cancer and aging.
Reactive oxygen species and RNS play a dual role: beneficial and deleterious. Beneficial effects occur at low/moderate concentrations and involve defense against infectious agents, activation of some transcription factors as NF-kB, AP-1 and p53 and regulation of immune response, vascular tone, cell adhesion, cellular signaling, apoptosis and production of some hormones as erythropoietin. On the other hand, high concentrations of ROS and RNS lead to oxidative damage of all cellular structures including DNA, lipids, proteins and carbohydrates and therefore inhibiting their normal function. Because of this, oxidative stress has been implicated in a number of human diseases including skin diseases.
Oxidative stress has been found to participate in the pathogenesis of skin diseases such as skin cancer, photoaging, vitiligo, xeroderma pigmentosum, skin wounds and burns, allergic skin diseases such as AD, CD, and urticaria, and inflammatory skin diseases such as psoriasis, acne vulgaris, rosacea, SLE, lichen planus, Behcet’s disease and leprosy.
However, the skin counteracts oxidative stress by AOs which have the ability to delay, prevent or remove oxidative damage. AOs may be enzymatic or non-enzymatic. Enzymatic AOs include SOD (cytosolic Cu, Zn-SOD, mitochondrial Mn-SOD, and extracellular SOD), catalase and GPx. They work as preventive AOs where they remove most superoxides and peroxides before they react with metal ions to form more reactive free radicals. SOD enzymes catalyze the conversion of superoxide to oxygen and H2O2 then GPx and catalase decompose H2O2 to water and oxygen. GPx needs GSH, GR and NADPH for its reducing action.
Non-enzymatic AOs are either endogenous or exogenous. Endogenous AOs that can be synthesized by the body include the thiol AOs: GSH, thioredoxin system and ALA, CoQ10, melatonin, melanin, uric acid and the metal-chelating proteins as ceruloplasmin and transferrin. Exogenous AOs that can not be synthesized by the body and should be supplied from diet or taken as supplementation include lipid-soluble vitamins E and A, water-soluble vitamins B3 and C, carotenoids as β-carotene, polyphenols as flavonoids, trace elements as Se and Zn and the exogenous thiol AO NAC.
Although AOs can be supplied to skin through diet and oral supplementation, physiologic processes related to absorption, solubility, and transport limit the amount that can be delivered into skin. Direct application has therefore the added advantage of targeting the AOs to the area of skin needing the protection.
For topical application of AOs to be useful, several obstacles must be overcome including instability and deep color of some AOs that makes them difficult to formulate in an acceptable, stable composition for cosmetic use. In addition, to protect deeper layers of skin, AOs need to be formulated in a way that delivers them deep into skin. There are emerging delivery systems that can stabilize AOs and allow their simultaneous incorporation with different lipophilicities such as microemulsions or liposomes.
It is concluded that AOs due to their importance in delaying, prevention and repair of oxidative damage, are now added to a variety of skin care products including sunscreens, moisturizers, shampoos, anti-aging and skin lightening products.
It is recommended to use AOs as an adjuvant in prevention and treatment of various skin disorders. However, further research is needed to clarify the role of oxidative stress in the pathogenesis of other skin diseases and how far the use of AOs is effective in each disease.
Recommended foods rich in AOs include: fruits as berries (cherry, blackberry, strawberry, raspberry and blueberry), pomegranate, grapes especially red seeded grapes, orange, plum, apple, pineapple and kiwi, vegetables as broccoli, garlic, tomatoes, carrots, lemon, spinach and ginger, whole grains as barley, brown rice, whole wheat, pasta or couscous, bulgur, oats, and flaxseed and beverages as green tea, coffee and cinnamon in addition to curcumin, walnuts, hazelnuts, salmon fish and shellfish.