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Photochemoprotection
through botanical antioxidants
Mukhtar, Hasan1,
Ahmad, Nihal1, Katiyar, Santosh2
and Elmets, Craig2
Department of Dermatology, Case Western Reserve University, Cleveland,
OH1
Department of Dermatology, University of Alabama at Birmingham, Birmingham,
AL2
Abstract-
Because the incidence of solar ultraviolet (UV) B radiation-induced
basal- and squamous- cell cancers, grouped together as non-melanoma
skin cancers, continue to increase in the US, development of novel strategies
to reduce its occurrence is a highly desirable goal. One preventive
approach to reduce the occurrence of skin cancer is through 'Photochemoprotection',
which we define as the topical use of agents capable of counteracting
UVB-induced adverse effects on the skin. Among these agents, plant-based
antioxidants are showing promise. This approach is particularly attractive
because the antioxidants have the ability to ameliorate the deleterious
effects of UV-induced excessive generation of reactive oxygen intermediate
(ROI), which are known to play roles in both initiation and promotion
phases of photocarcinogenesis. In mouse model of photocarcinogenesis,
we have been studying the role of polyphenols from green tea (GTP),
silymarin from milk thistle, and resveratrol from grape skin, as photochemoprotective
agents. However, the relevance of these data to human situations is
unclear. We have investigated the preventive effects of topical application
of GTP and/or its major constituent (-) epigallocatechin-3-gallate (EGCG)
on UVB-mediated damages in human volunteers. Our studies have shown
that skin application of polyphenols from green tea or EGCG to human
volunteers resulted in significant inhibition of UVB-mediated i) erythema
response, ii) infiltration of leukocytes, iii) interleukin 10- positive
cells, iv) sunburn cells, v) reduced depletion of Langerhans cells,
and vi) myeloperoxidase activity, nitric oxide and hydrogen peroxide
formation, which are regarded as markers of oxidative stress. These
observations provided possible mechanisms involved in the anti-inflammatory
effects of green tea. More recently, we demonstrated that GTP treatment
of human skin inhibited both UVB-induced erythema response as well as
UVB-induced formation of cyclobutane pyrimidine dimer (CPD), an initiating
event for photocarcinogenesis. The use of photochemopreventive agents
in combination with the use of sunscreens and educational efforts to
avoid excessive sun exposure may be a successful strategy for reduction
of incidence of skin cancer and other UV-mediated damages in humans.
Keywords: Green
Tea, Photochemoprotection, Ultraviolet radiation, skin cancer
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