Analogs of α-Melanocyte-Stimulating Hormone
Melanogenesis can also be stimulated through the use
of a-melanocyte-stimulating hormone analogs. Three
analog fragments (melanotans I, II, And III) have been
shown in vitro to be agonists of the melanocortin 1
receptor and to stimulate melanogenesis. Two of them
also promote the repair of DNA damage resulting from sun
exposure and reduce levels of UV-induced reactive oxygen
species.97 It is thought that melanotans induce tanning by
simulating the action of a-melanocyte-stimulating hormone
at melanocortin 1 receptors.98,99 Curiously, subcutaneous
injection of melanotan I stimulates the synthesis of
eumelanin in humans, inducing a tan that lasts for
a prolonged period (almost 1 month).100 Melanotan I
(the generic name for afamelanotide) is in phase III
clinical trials as a photoprotective drug for patients with
photodermatoses, such as erythropoietic protoporphyria
and polymorphic light eruption (Clinuvel Pharmaceuticals
Limited, Annual report 2008, www.clinuvel.com/resources/
pdf/annual_reports/2008/annual_report_2008.pdf). In
fact, melanotan I administered at a dose of 20 mg twice
daily for 60 days has been shown to increase sun tolerance
and decrease the adverse effects of exposure in patients
with erythropoietic protoporphyria.101