Oral communication, CS5 / C18
Official XXIst International Pigment Cell Conference website - 21-24 Sept 2011, Bordeaux - France | updated: September 04 2011
Evaluation of alkaline hydrogen peroxide oxidation to analyze eumelanin and pheomelanin
| SPEAKER | S. Ito #whois submiter ? |
| AUTHOR(s) | S. Ito, Y. Nakanishi, K. Wakamatsu |
BACKGROUND AND OBJECTIVES: Natural melanins are mixtures of eumelanin and pheomelanin. The color of hair, skin, and eyes is mainly determined by the quantity and ratio of eumelanin and pheomelanin produced in melanocytes. Furthermore, it is generally accepted that eumelanin is photoprotective, while pheomelanin is phototoxic to tissues. Eumelanin and pheomelanin in tissue samples can be specifically measured as the markers pyrrole-2,3,5-tricarboxylic acid (PTCA) and 4-amino-3-hydroxyphenylalanine (4-AHP) after acidic permanganate oxidation and reductive hydrolysis with hydroiodic acid, respectively. However, those degradative methods are not easily performed in most laboratories that do not have significant chemical expertise. METHODS: We evaluated alkaline H2O2 oxidation in 1M K2CO3 that produces, in addition to PTCA, the marker for 5,6-dihydroxyindole-2-carboxylic acid-derived eumelanin, pyrrole-2,3-dicarboxylic acid (PDCA) as a marker for 5,6-dihydroxyindole (DHI)-derived eumelanin, and thiazole-2,4,5-tricarboxylic acid (TTCA) and thiazole-4,5-dicarboxylic acid (TDCA) as markers for pheomelanin. Those four degradation products can be easily separated by HPLC and analyzed with ultraviolet detection. RESULTS: The alkaline H2O2 oxidation method is simple, reproducible and applicable to various pigmented samples such as synthetic melanins, hair, melanocytes, and skin. The ratios of TTCA/PTCA, PDCA/PTCA, and TTCA/4-AHP can be used to estimate relative contents of pheomelanin in melanin, DHI units in eumelanin, and benzothiazole units in pheomelanin, respectively. CONCLUSION: The measurement of PTCA, TTCA, PDCA, and TDCA in a single chromatographic analysis provides valuable information for characterizing mixed melanogenesis. Its application to characterize melanin in human hair shows that PTCA and TTCA serve as specific markers for eumelanin and pheomelanin, respectively, although some caution is needed regarding the artificial production of TTCA from eumelanic tissue proteins.
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