Anti-melanogenic activity of ellagitannin casuarictin in B16F10 mouse melanoma cells.

Ellagitannins such as casuarictin (CAS), isolated from clove extracts, have been shown to have superior benefits such as antioxidant and anti-inflammatory activity, but there have been no reports on their capacity to inhibit melanogenesis. Inhibition of melanogenesis by novel natural products has gained attention for cosmetic applications such as skin lightening. Here, we report the effects of CAS on melanogenesis in B16F10 mouse melanoma cells. Our results showed that CAS (30 µM) significantly inhibited intracellular melanogenesis while being nontoxic to B16F10 cells or to HaCaT cells at that concentration. CAS (30 µM) also inhibited intracellular tyrosinase activity as well as mushroom tyrosinase activity; possessed robust copper chelating ability comparable to that of 500 µM kojic acid; and downregulated MITF protein levels, all of which contribute to the inhibitory mechanisms underlying its anti-melanogenic activity. In summary, our results demonstrate that CAS might hold promise as a depigmenting agent for hyperpigmentation disorders.

Organogold drug Auranofin exhibits anti-melanogenic activity in B16F10 and MNT-1 melanoma cells.

Auranofin (AF) is an organogold FDA-approved drug for treating rheumatism and has been repurposed for several pharmacological applications based on its anti-bacterial, anti-fungal and anti-inflammatory activities. To the best of our knowledge, there has been no study on effects of AF on melanogenesis yet. Hence, in this work, we studied the effect of AF on melanogenesis using B16F10 mouse melanoma cells and validated results in MNT-1 human melanoma cells. Melanogenesis assay was conducted with concentrations of AF determined to be nontoxic in B16F10 cells as well as HaCaT human epidermal cell line for a duration of 48 h, followed by various assays to delineate mechanisms of melanogenesis inhibition. Ultrastructural analysis was conducted to study further if AF affected melanosome maturation and protein levels of a key melanogenic protein, tyrosinase, and the maturation signaling molecule, cyclic adenosine monophosphate (cAMP), was estimated. Our results demonstrate that AF at nontoxic concentrations of 0.25-1 µM significantly inhibited melanin synthesis in a dose-dependent manner with significant inhibition of 32.85% at 1 µM. The study of mechanisms of melanogenesis inhibition revealed that AF inhibited tyrosinase activity in lysates of B16F10 cells but did not show a direct effect on purified mushroom tyrosinase activity or on copper chelation in a cell-free system, nor did it affect levels of B16F10 tyrosinase protein levels. However, AF significantly down-regulated cAMP levels, inhibited cellular ROS and increased number of melanosomes in immature stages, and also exhibited anti-melanogenic activity in B16F10-HaCaT cocultures. Furthermore, AF showed anti-melanogenic efficacy in MNT-1 cell monocultures and cocultures with an inhibition of intracellular tyrosinase activity. In summary, our results demonstrate a proof-of-principle for AF as a depigmenting agent for hyperpigmentation disorders and adjuvant for melanoma therapeutics.