Melanotan I

Melanotan I (afamelanotide) is a synthetic linear analog of alpha-melanocyte stimulating hormone (α-MSH). It was developed at the University of Arizona alongside Melanotan II, but as a linear tridecapeptide rather than a cyclic heptapeptide. The modifications at positions 4 (Nle replaces Met) and 7 (D-Phe replaces L-Phe) enhance potency and metabolic stability.

MT-I is more selective for MC1R compared to MT-II, resulting in melanogenic effects with reduced activity at other melanocortin receptors. This selectivity made it the subject of research into erythropoietic protoporphyria (EPP), a rare genetic condition causing extreme photosensitivity.

Melanotan I acts primarily through MC1R activation:

Selective MC1R Agonism MT-I has approximately 100x greater selectivity for MC1R over MC3R/MC4R compared to MT-II. This makes it a tool for studying MC1R with little activity at the central melanocortin receptors.

Melanogenesis Pathway MC1R activation on melanocytes increases intracellular cAMP, which activates CREB and upregulates MITF (melanocyte-inducing transcription factor). MITF increases expression of melanogenic enzymes including tyrosinase, TRP-1, and TRP-2, leading to increased melanin synthesis.

Eumelanin Shift Like α-MSH, MT-I promotes eumelanin (brown/black pigment) production over pheomelanin (red/yellow). Eumelanin absorbs UV more effectively than pheomelanin, which can generate reactive oxygen species under UV exposure.

Photoprotection Research Its effect on eumelanin content is why it is studied in UV-damage and photosensitivity research.