Diacylglycerol-induced melanogenesis in Skh-2 pigmented hairless mice

We investigated the effect of topically applied diacylglycerols (DG) on melanogenesis in Skh-2 pigmented hairless mouse skin. Groups of mice were treated according to 4 different regimens of either 1,2-dioctanoyl-sn-glycerol (DOG) or 1-oleyl-2-acetyl-sn-glycerol (OAG) with or without ultraviolet irradiation (UVR). After the treatment regimens were completed, separated epidermal tissue was stained with L-dopa and thin sections of whole skin were stained by the Warthin-Starry method to detect melanin deposition. Quantification of the stained areas by digital image analysis disclosed that DOG treatment without UVR increased the dopa-positive area in skin in a dose-dependent manner but had no effect on melanin deposition. DG treatment acted synergistically with UVR to enhance melanogenesis, with synergism being more pronounced for melanin deposition than for dopa staining. DOG treatment prior to UVR also resulted in an enhanced melanogenic response to UVR, suggesting that DG increases the sensitivity of melanocytes to subsequent UVR by inducing dopa oxidase activity. OAG also enhanced UVR-induced melanogenesis in a dose-dependent manner and was at least as potent an inducer as was DOG. Because DG is known to activate protein kinase C, our results suggest that a protein kinase C-dependent process is involved in melanogenesis.