In vitro Effects of the Methanolic Leaf Extract of Otholobium fruticans in Murine B16 Melanoma Cells: Implications for the Treatment of Skin Hyperpigmentation

Hyperpigmentation is a cosmetically important skin disorder which commonly affects the face and neck regions and impacts negatively on the self-esteem of affected persons. Most of the current treatment agents for hyperpigmentation are cosmetic additives and prescription medications which generally act to suppress melanogenesis. However, many of these products are known to have limited effectiveness, deleterious side effects, and induce adverse reactions especially after prolonged use, hence safe and efficacious treatments are required. Herbal formulations are a putative alternative, considering their use for generations in traditional medicine for treating many diseases, including skin-related conditions. In this study, the methanolic leaf extract of Otholobium fruticans, a gardening and ornamental plant common to the South African Cape provinces, was evaluated for its possible anti-melanogenic effects based on evidence from its traditional use. The 50 µg/mL extract concentration was found to be non-toxic to murine B16 melanoma cells, to significantly reduce tyrosinase activity, increase intracellular reactive oxygen species (iROS) levels and down-regulate some melanogenesis-related genes (TYR, TRP-1, TRP-2, MITF and MC1R), except the β-catenin gene which was upregulated. These findings tend to suggest that the depigmentation potential of the methanolic extract of O. fruticans could be mediated through an interplay of mechanisms that inhibit tyrosinase activity and the cAMP-dependent pathway, as well as increased iROS levels. Further studies involving the chemical isolation, characterization and testing of the activities of the constituent compounds in O. fruticans are recommended to fully understand the basis for the current traditional uses of Otholobium plants for the treatment of skin conditions.