Approaches to Increasing Skin Melanin with MSH Analogs and Synthetic Melanins

Increased public awareness of ultraviolet (UV) radiation‐induced skin cancers has lead to new interest in technologies for protection from sun exposure. Although many sun protection formulations are available, few of them attempt to achieve that provided by melanin itself, i.e., wide‐spectrum absorbance of radiant energy coupled with anti‐oxidant activity from a single product. In that regard, technologies in two separate areas are at or near the commercialization stage: 1) hormonal enhancement of natural skin melanin content, and 2) inclusion of natural and synthetic melanins in cosmetic formulations to impart melanin‐like color to the skin. In this article, these approaches are briefly summarized using as examples Melanotans I and II®, superpotent analogs of the melanin‐stimulating hormone melanocortin (MSH), and Melasyn®, a group of plant‐derived synthetic melanins that have successfully been incorporated into cosmetic formulations for use as sun protectants and as cover‐ups for problems resulting from uneven pigmentation, such as seen in vitiligo.     

New regulatory factors for melanogenesis: developmental changes in neonatal mice of various genotypes

The biosynthesis of melanin occurs through sequential steps known as the Mason-Raper pathway. The initial steps are the conversion of tyrosine to dihydroxyphenylalanine (dopa) and of dopa to dopaquinone by the enzyme tyrosinase (EC 1.10.3.1). Until recently it was assumed that once these first two conversions were completed, the subsequent reactions occurred spontaneously. However, studies with mouse melanoma cells in culture revealed that subsequent steps in the pathway are also regulated. In this report, we demonstrate that these steps are also regulated in skins of fetal and newborn mice. The specific activities of the regulatory factors change during the first week after birth and differ in mice of different genotypes. The findings provide new insights into genetic and developmental regulation of the pigmentary system in mammals.     

L-Tyrosine stimulates induction of tyrosinase activity by MSH and reduces cooperative interactions between MSH receptors in hamster melanoma cells

L-tyrosine, a precurosr to melanin, has recently been shown to be a regulator of the melanogenic pathway in some cultured melanoma cell lines. In this paper we demonstrated that L-tyrosine, besides increasing binding capacity for MSH, decreased cooperativity between MSH receptors and increased the level of tyrosinase induction by MSH. Apparently, regulation of MSH receptor activity by L-tyrosine involves specific changes in the interactions between the receptors and modification of the cellular responsiveness to MSH.