Photochemistry. Chemiexcitation of melanin derivatives induces DNA photoproducts long after UV exposure. Premi S. et al. Science. 2015 Feb 20;347(6224):842-7. doi: 10.1126/science.1256022.
-Tanning Beds mainly emit light in the Ultraviolet type A (UVA) range. They are known to increase the incidence of melanomas and they have already been banned in many countries as well as in many States in the US.
-Melanin is thought to have a protective role against sunlight (in contrast to pheomelanin)
-This article shows that sundamage is initiated by UV exposure but that its effects continue for many hours following exposure.
-UVA exposure results in the synthesis of Cyclobutane Pyrimidine Dimers (CPD) which are still present three hours afterwards. Dark CPDs arise when UV-induced reactive oxygen and nitrogen species combine to excite an electron in fragments of the pigment melanin. This creates a quantum triplet state that has the energy of a UV photon but induces CPDs by energy transfer to DNA in a radiation-independent manner
-CPDs accumulated in the dark result in C to T mutations
THE FIGURES BELOW SHOW THE ROLE OF MELANIN IN THE LIGHT (UV exposure) AND IN THE DARK
–Melanin is both an ally and an enemy: Melanin has a protective “umbrella role” to protect against sunlight but appears to have a “darker” role in the Darkness.
–The solutions may lie in either:
- interfering with the production or scavenging of the superoxide or nitric oxide radicals production
- quenching the quantum triplet state derived from the melanin degradation products.
-The study was done with both UVA and UVB
-As expected CPD’s decreased rapidly in albino melanocytes (where melanin is absent).
-As expected, the increase in CPDs was increased with pheomelanin (vs melanin) (Clinically red heads have a higher risk of melanoma)
–It remains to be seen if melanin is more of an enemy than an ally as melanin clearly has a protective role as its increasing presence is associated with a lower risk of skin cancer, corresponding clinically to Fitzpatrick phototypes.
Article selection: Prof Dr Jean-Hilaire Saurat – dermatologist. Geneva, Switzerland