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A review of melanin formation and the isolation of a new ingredient for products that minimize skin discolorations due to excessive melanin production
Skin color varies depending on racial background, season of the year and sex. Even a single individual doesn't exhibit the same color on all parts of the body.(7,11) While skin thickness, hemoglobin and minor pigments like carotenoids affect perceived color, the amount of melanin produced by the melanocytes primarily determines skin color. For this reason, research for the development of whitening products has focused on reducing melanin production in the melanocytes. This article reviews melanin research and the isolation of a whitening agent from paper mulberry.
Many biochemists and researchers from the cosmetic and pharmaceutical industries have studied the biosynthetic pathway of melanin. In the West, researchers hope to develop ways to treat vitiligo, albinism, and piebaldism; in the East, treatment of melasma and freckles and the development of skin-whitening products hold primary importance.
Raper and Mason(14,16) have partly established the biosynthetic pathway of melanin [ILLUSTRATION FOR FIGURE 1-1 OMITTED]; Yutaka Mishima et al have helped define the function of the cellular organelles.(9) Although organelle function and enzyme actions have been under intensive investigation, for the most part, their mechanism remains to be solved.
Synthesis route: The melanocytes synthesize melanin, the main factor determining skin color, using tyrosinase to hydroxylate tyrosine into dihydroxy phenylalanine (DOPA); this becomes the melanin polymer through a complex chain of oxidative reactions. Tyrosinase also oxidizes DOPA into dopaquinone.
Pheomelanin, a yellow or orange pigment, is synthesized via cysteinyl DOPA, glutathione DOPA and cysteinyl dopaquinone, in the presence of sulfhydryl (-SH) compounds like cysteine and glutathione. Eumelanin, the dark-brown pigment, is produced through the polymerization of dopaquinone via leucodopachrome; dopachrome; 5,6-dihydroxyindole (or 5,6-dihydroxyindole-2-carboxylic acid, DHICA); and melanochrome.
Melanin biosynthesis is influenced by genetic and environmental factors: hormones, food and medicine. Skin color relates closely to the number and the distribution pattern of melanosomes, brown cellular organelles. The number of melanosomes manufactured and their transfer to the Malpighian cells are influenced mostly by genetic factors and partly by the presence of external factors like hormones or ultraviolet light.
Tyrosinase plays the key role in melanin biosynthesis. However, many other cellular factors regulate melanin biosynthesis, including the enzymes dopachrome tautomerase (also known as TRP-2, a tyrosinase-related protein), peroxidase, catalase and glutathione reductase; metallic ions like [Cu.sup.2+], [Zn.sup.2+] and [Fe.sup.2+]; and the …