Agents to control melanogenesis are in demand for the development of cosmetics to improve pigmentation disorders of skin and hair. In this study, we examined and evaluated the effects of flavonoids on melanogenesis in the melanogenic cells model, murine B16F10 melanoma cells. In the course of this study, we found that incubation of the cells in a medium containing 10 μM of the 4'-O-methylated flavonoids, diosmetin (4'-O-methylluteolin), acacetin (4'-O-methylapigenin) or kaempferide (4'-O-methylkaempferol), increased the melanin contents of the cells 3- to 7-fold higher than the control cells. The concentration-dependence test revealed that 20 μM acacetin showed the highest effect, up to 33-fold higher than the vehicle. On the other hand, the corresponding 4'-OH-type flavonoids, luteolin, apigenin and kaempferol, had a significantly smaller effect. Furthermore, by evaluating the melanogenic proteins, we found that the cells treated with 4'-O-methylated flavonoids showed higher tyrosinase activity, as well as upregulation of tyrosinase expression, preceded by activation of cAMP response element binding protein (CREB) and extracellular signal-regulated kinases types 1 and 2 (ERK1/2). These results indicate that the 4'-O-methyl group of flavonoids plays an important role in the induction of melanogenesis by activating its major signal transduction pathway through the upregulation of phospho-CREB in murine B16F10 melanoma cells.

Hair can be exposed to oxidative environments such as hydrogen peroxide in hair dyes and bleaching agents, ultraviolet (UV) ray irradiation from sunlight, catalytic conditions with heavy metal compositions, and oxidative air pollutants. Therefore, unsaturated fatty acids present in the hair could be oxidized to form lipid peroxides and finally converted to aldehydes as their end products. Lipid peroxides and aldehydes will cause hair damage at the molecular level by denaturing hair proteins, and furthermore most of the short-chain aldehydes are sources of malodor. In the present study, we identified and quantified volatile aldehydes generated from hair by UV irradiation. Fatty acids in the hair samples were analyzed by GC-MS and 13 kinds of them detected, the ratio of saturated to unsaturated being 1 : 2. The hair was irradiated with UV light (total amount 706.8 kJ／m 2 ) in a closed container, so that the generated gas was directly trapped in a solution of 1,3-cyclohexanedione (CHD) ． The resulting aldehyde-CHD derivatives were analyzed by LC-MS. Short-chain aldehydes, formaldehyde, acetaldehyde and propanal were detected, and the amounts of them generated from 100 g of hair were 3.3, 0.3 and 0.1 mg, respectively. These low molecular weight aldehydes may have been formed by the consecutive degradation (called Norrish type II reaction) of the long-chain aldehydes which are produced by oxidative cleavage of double bonds in the unsaturated fatty acids in the hair.

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