Carotenoids derivatives and polyphenols protect keratinocytes from UV-B induced damage
Glenda Calniquer, Yoav Sharoni, Yossi Levy
Exposure to sun radiation is the main cause of skin damage: erythema (skin inflammation), premature
skin aging, DNA damage, cell death and skin cancer. Sunscreens are used during vacation related sun
exposure to prevent skin damage. However, exposure during vacation accounts only for about 1/3 of
sun exposure within a year. Thus, using oral administration of protective compounds which will
protect skin cells from within can be an additional defending measure. Indeed, human intervention
studies have shown that the mixture of various dietary derived active components protects from UVinduced erythema formation. The goal of this study is to create an in-vitro system that will allow us
to identify specific dietary ingredients that protect the skin from UV-induced damage and to study
their mechanism of action.
We used UVB radiation (wavelength 290-320nm) which has a shorter wavelength than UVA (320400nm), and therefore is absorbed by the outer skin layers (epidermis). Keratinocytes are the most
common type of skin cells in the epidermis and thus, the study will focus on these cells. Previous
studies have shown that reactive oxygen species (ROS) are involved in damage caused by UVB and
antioxidants such as carotenoids and polyphenols protect against UV-induced damage. Previous
studies from our laboratory have shown that effects of carotenoids are mediated by their aldehyde
derivatives. These derivatives can be formed in the body as a result of a spontaneous chemical
cleavage or by enzymatic cleavage. Thus, we will focus on these derivatives.
HaCaT cells (human keratinocytes), were irradiated with UVB after overnight incubation with
carotenoids, carotenoid derivatives and polyphenols. UV-induced damage and the possible protection
were analyzed by measuring cell death (reduction in cell number by crystal violet staining) and
activation of apoptosis (PARP and caspase-3 cleavage by Western blotting). Preliminary results show
UV-induced cell death which was reduced by about 40% by treatment with the polyphenol curcumin.
The carotenoid derivatives, diapocarotene-6-14'-dial (6,14’) reduced the UV-induced cleavage of
PARP and caspase-3.
UV radiation is known to activate the NFkB transcription system, which leads to apoptosis.
Inhibition of the TNFα-induced NFkB by carotenoids derivative have been previously shown in our
laboratory and cucrcumin is also known to inhibit this pathway. Thus, we hypothesized that the
inhibition of the NFkB pathway can partially explain the protection from UV-induced apoptosis.
Indeed, UVB induced activation of NFkB transcription system, measured by a reporter gene assay,
was inhibited by the dietary compounds.
Future research will concentrate on exploring whether there is a combination of carotenoids and/or
polyphenols which demonstrate a synergistic activity. This will allow us to use lower concentrations
of the protective ingredients which are closer to the concentrations found in the blood. In addition we
will check whether these ingredients protect also against UVA-induced damage.