Celina Rocquet talks to Thierry Douki and Evelyne Sage about the latest research on UVA unveiled by the European Society for Photobiology
A lot remains to be discovered and understood about how skin reacts to light and more specifically to UV rays. Thierry Douki from the CEA Grenoble (Laboratoire Lésions des Acides Nucléiques) and Evelyne Sage from the CNRS/Institut Curie (Laboratoire de Biologie des radiations, Université de Paris-Sud XI, Orsay) and president of the European Society for Photobiology talked to SPC about their latest research.
The primary aims of the European Society for Photobiology are to co-ordinate and promote all aspects of photobiology in Europe in a way that optimises the achievements of European photobiology across a range of scientific, technological and medical arenas. This includes the liaison with and encouragement of photobiologists in other parts of the world. The Society’s aims are achieved through the publication of the peer reviewed journal Photochemical & Photobiological Sciences (PPS), the organisation of a biennial congress, the holding of regional meetings within Europe and the provision of support for meetings outside Europe. It also aims to promote joint activities between relevant societies by co-hosting symposia speakers at congresses in order to promote cross society contact and collaboration.
Here is a short overview of what Douki and Sage think are some of the hottest issues around the effects of UVA.
Oxidative stress, DNA & cancer
UVA is now known to induce global cell oxidative stress, directly linked to the oxidation of several cell components such as lipids, as well as proteins, DNA bases and carbohydrates. DNA may then be broken down and a natural phenomenon of apoptosis triggered in order to prevent the mutated cell from multiplying and propagating the mutation, or worse, inducing skin cancer (eg if the p53 protein is mutated).
Recent studies have shown that UVA may also induce DNA mutations in the form of dimers. Research teams are currently investigating the specific chemical reactions that enable cells to trigger their own protection and repair mechanisms. Kinases and phosphorylation cascades in different cell types characterise these induction phases. Cellular reparation mechanisms such as polymerase identify the mutation, cut the damaged DNA strand and build a new one, taking the non-mutated strand as a model. The proteic repair system in people suffering from Xeroderma pigmentosum (called in French ‘children of the moon’) is deficient, which can have serious consequences such as the onset of skin cancer before the age of eight.
UVA and melanocytes
UVA can also cause cell damage, which can vary according to the cell type. In fibroblasts and keratinocytes the reactions seem to be quite similar, whereas in melanocytes the biochemical reactions differ. Melanocytes are able to produce new reactive oxygen species (ROS) and singlet oxygen in particular and are particularly sensitive to UVA induced oxidative stress.
This oxidative reaction helps us understand a widespread misconception. UVA is used in tanning booths to apparently stimulate the tanning process of the skin, which in fact it does not. Only UVB can stimulate the production of melanin. When exposed to UV, the colouration of the epidermis is in reality generated by the oxidation of melanin. The colour is carrot-like and the skin becomes much more exposed. On the one hand, cutaneous cells are subject to oxidative stress; on the other, the skin if later exposed to the sun will be even more sensitive to sun induced damage.
The immune system
The last few decades have seen more and more research work on the responses of the immune system to UVA. In this area, special attention is paid to the role of Langherans cells.
Attention is also focused on vitamin D, a derivative of cholesterol obtained primarily through exposure of the skin to ultraviolet radiation in sunlight. Vitamin D is essential not only for the formation, growth and repair of the bones but also for normal calcium absorption and immune function. According to Douki and Sage, some studies suggest that higher levels of vitamin D in the blood are associated with reduced risk of colorectal, breast, prostate and pancreatic cancer. However, the research results need further investigation.
All of these subjects and more will be examined in the in-focus feature at this year’s in-cosmetics. The exhibition will take place on 17-19 April 2012 at Barcelona’s Gran Via exhibition centre. www.in-cosmetics.com
Celina Rocquet is a consultant in innovation management and teaches at the Société Française de Cosmetologie, ISIPCA and Sup’Biotech
