Abstract
The organogermanium compound 3-(trihydroxygermyl)propanoic acid (THGP) has various biological activities. We previously reported that THGP forms a complex with cis-diol structures. L-3,4-Dihydroxyphenylalanine (L-DOPA), a precursor of melanin, contains a cis-diol structure in its catechol skeleton, and excessive melanin production causes skin darkening and staining. Thus, the cosmetic field is investigating substances that suppress melanin production. In this study, we investigated whether THGP inhibits melanin synthesis via the formation of a complex with L-DOPA using mushroom tyrosinase and B16 4A5 melanoma cells. The ability of THGP to interact with L-DOPA was analyzed by 1H-NMR, and the influence of THGP and/or kojic acid on melanin synthesis was investigated. We also examined the effect of THGP on cytotoxicity, tyrosinase activity, and gene expression and found that THGP interacted with L-DOPA, a precursor of melanin with a cis-diol structure. The results also showed that THGP inhibited melanin synthesis, exerted a synergistic effect with kojic acid, and did not affect tyrosinase activity or gene expression. These results suggest that THGP is a useful substrate that functions as an inhibitor of melanogenesis and that its effect is enhanced by combination with kojic acid.
Highlights
Inorganic germanium is used in semiconductors and various optical applications [1]
We evaluated the ability of L-DOPA to form a complex with THGP or 3-trimethylgermylpropanoic (TMGP), which contains a methyl group in place of the hydroxyl group on THGP, by 1H-nuclear magnetic resonance (NMR)
The mixture of THGP and L-DOPA showed the individual spectra of THGP and L-DOPA, which suggests that THGP does not form a complete complex with L-DOPA
Summary
Inorganic germanium is used in semiconductors and various optical applications [1]. The organogermanium compound poly-trans-[(2-carboxyethyl) germasesquioxane] (Ge-132; repagermanium) was first synthesized by Oikawa et al in 1967, and its structure was reported in 1976 [2,3]. Studies have shown that THGP interacts with a cis-diol structure and suggested that this interaction is involved in the physiological effects of THGP [13,14]. Substances that inhibit the production of melanin have been investigated [21]. THGP does not inhibit enzyme activity and acts on L-DOPA, which is a substrate in melanin synthesis. A synergistic effect can be expected from the combination of THGP with kojic acid, which inhibits enzyme activity. We investigated the formation of the THGP and-L-DOPA complex and the inhibition of melanin synthesis and its mechanism via complex formation. The synergistic suppressive effect obtained from the combined use of THGP and kojic acid on melanin production was examined
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