Pharmacologic response of a controlled-release PLGA formulation for the alpha-melanocyte stimulating hormone analog, Melanotan-I

Purpose. The objective of this study was to evaluate in vitro and in vivo the melanogenic activity of one-month duration Melanotan-I (MTI) implants prepared using poly (D,L lactide-co-glycolide) polymer. Methods. The biological activity of the samples of MT-I released in vitro from the non- irradiated or gamma irradiated implants was measured using a frog skin bioassay. The effect of MT-I on skin pigmentation was measured using a Chroma meter (reflectometer) after subcutaneous administration of implants containing 4 mg MT-I to guinea pigs. Eumelanin, the black/brown melanin pigment, was quantified in skin biopsies as pyrrole-2, 3, 5-tricarboxylic acid using HPLC. Results. The MT-I released in vitro from implants after 24 hours exhibited 100% melanotropic activity in frog skins compared to an identical concentration of a freshly prepared MT-I standard. The reflectance readings demonstrated a prolonged skin darkening for up to three months as evidenced by the decrease in the luminance values from 0 to -4.82. A 2.5-fold increase in eumelanin levels was observed after one month and the increased pigmentation lasted for 3 months. Conclusions. The melanogenic response to MT-I implants persisted for three months and the increase in pigmentation, especially the increased eumelanin levels, could provide protection from ultraviolet radiation.