Scientists have given mice a tan
without exposing them to the sun.
They have developed a cream, which has
not yet been tested on humans, that switches on the tanning machinery
in skin cells. The breakthrough also raises the prospect of a
new way to protect fair-skinned people from skin cancer caused
by exposure to sunlight. The study, by Dana-Farber Cancer Institute
and Children's Hospital Boston, is published in Nature. The cream
contains a small molecule that essentially mimics the process
that occurs when skin cells are struck by ultraviolet light from
the sun.
It is thought people with fair skin and red hair cannot tan properly
because of a defect in a pouch-like receptor called MC1R on the
surface of the pigment-producing melanocyte skin cells. This leads
to reduced production of a chemical called cAMP, which stimulates
the melanocytes to produce pigment.
As a result, fair-skinned people tend to burn, rather than tan
in the sun, increasing the risk of DNA damage to skin cells which
can lead to cancer. The World Health Organization has estimated
that as many as 60,000 people a year worldwide die from skin cancer
as a result of too much exposure to the sun.
Fair-skinned mice
The researchers genetically engineered
fair-skinned, red-haired mice who did not tan when exposed to low
levels of UV radiation, but did burn when the dose was cranked up.
They then treated the skin of the animals with a compound known
to increase cAMP levels. The compound, forskolin, is derived from
the root of the forskohli plant found in India. The mice turned
dark, proving that melanocytes in redheads can make pigment if appropriately
stimulated. Further experiments showed that this sunless tanning
process was virtually indistinguishable from that in dark-haired
mice that tan naturally.
The researchers also found that the tans acquired through forskolin
treatment protected the skin against cancer caused by exposure to
UV light. Lead researcher Dr David Fisher said it was not yet clear
whether forskolin would penetrate deeply enough in human skin to
activate melanocytes. However, he said: "These studies suggest
that a drug-induced 'rescue' of the tanning mechanism may correspondingly
rescue at least some aspect of skin cancer protection. "Such
sunless tanning may also dissuade sun-seeking behaviours, which
undoubtedly contribute significantly to high skin cancer incidence."
Hazel Nunn, cancer information officer at the charity Cancer Research
UK, said the study gave new insights into why fair-skinned people
rarely tan. She said: "We welcome this advance in our understanding
of the tanning process but it is important to point out that a tan-inducing
cream alone is unlikely to be enough to protect those with fair
skin from sunburn or to prevent skin cancer. "A UV-induced
tan only provides protection equivalent to that of sunscreen with
SPF4."
