Comparative Study of Curcumin and Its Hydrogenated Metabolites, Tetrahydrocurcumin, Hexahydrocurcumin, and Octahydrocurcumin, on Melanogenesis in B16F10 and MNT-1 Cells

Abstract

Curcumin, a bioactive from Curcuma longa, has been shown to possess anti-melanogenic activity previously; however, the effects of its hydrogenated metabolites (HMs)—Tetrahydrocurcumin (THC), Hexahydrocurcumin (HHC), and Octahydrocurcumin (OHC)—on melanogenesis have not been sufficiently explored. We have studied and compared three HMs (THC, HHC, and OHC) with the parent compound, curcumin (PC), on melanin synthesis in B16F10 mouse and MNT-1 human melanoma cells. Our results demonstrated that all the HMs were nontoxic over the concentration range 5–40 µM, while PC was nontoxic at 5 µM but induced toxicity at 20 and 40 µM in B16F10 cells. All three HMs enhanced melanin synthesis, while PC (5 µM) inhibited it. THC (40 µM) significantly stimulated melanin synthesis to a greater degree than HHC and OHC in both B16F10 and MNT-1 cells; the order of melanogenesis stimulation was THC = OHC > HHC in B16F10 mouse cells, while it was THC > HHC > OHC in MNT-1 cells. HMs stimulated melanogenesis by pathways not involving tyrosinase, as neither the intracellular tyrosinase activity nor the protein levels of tyrosinase were affected. In addition, mushroom tyrosinase activity, using L-Dihydroxyphenylalanine (L-DOPA) as the substrate, showed no direct effects of HMs. In summary, our results demonstrate that the HMs enhanced melanogenesis, which establishes that the hydrogenation of the heptadiene moiety of curcumin leads to a loss of its anti-melanogenic activity and instead results in the stimulation of melanogenesis. This stimulation is not further enhanced upon hydrogenation of the β-diketone, which was noted in MNT-1 cells, although the correlation to the number of keto groups differed in B16F10 cells where HHC was the weakest stimulator of melanogenesis. Collectively, THC with both keto groups intact is the best stimulator. Moreover, our results also validate that the electrophilicity of curcumin is necessary for its anti-melanogenic activity, as the non-electrophilic HMs did not inhibit melanogenesis. Furthermore, our results suggest that THC might hold promise as a stimulator of melanogenesis for treatment of hypopigmentation disorders and anti-graying therapies. Future studies to probe the molecular signaling mechanisms and test whether the pro-melanogenic activity of HMs is retained in primary human melanocytes are warranted.

Novel Hydrogenated Derivatives of Chemically Modified Curcumin CMC2.24 Are Potent Inhibitors of Melanogenesis in an In Vitro Model: Influence of Degree of Hydrogenation

“…The monophenolase and diphenolase activity assays were conducted similarly to the methods described in our earlier study [ 18 ]. All the test samples ( 1 – 5 ) were prepared at 2.5× concentrations in 100% DMSO, and 80 µL of each compound was combined with 100 µL of 2 mM L-tyrosine substrate solution in a 96-well microplate.…”

Novel Chemically Modified Curcumin (CMC) Derivatives Inhibit Tyrosinase Activity and Melanin Synthesis in B16F10 Mouse Melanoma Cells

“…Here, we studied four CMCs: CMC2.14, CMC2.5, CMC2.23 and CMC2.24, which differ in (i) the type of substituent on the central carbon flanked by the β-diketone (methoxycarbonyl vs. phenylaminocarbonyl) and (ii) the presence or absence of a methoxy group on the aryl rings, for their capacity to inhibit tyrosinase enzyme activity and melanin production in B16F10 cells and further elucidate mechanism of inhibition. We have also included the parent compound, pure curcumin (PC; curcumin I) as a reference, which we have shown in our previous study to inhibit melanin levels in B16F10 cells [36]. Our working hypothesis is that of the four CMCs, CMC2.24 would possess the greatest inhibitory activity towards both steps of tyrosinase-catalyzed melanin production as well as the greatest diminution of cellular melanogenesis.…”

Hyperpigmentation: Looking beyond hydroquinone

“…Tetrahydrocurcumin (THC) is a colorless polyphenolic compound. It is a major metabolite of curcumin with superior antioxidative properties in comparison with curcumin 18 . It has been shown to inhibit the melanocyte‐stimulating hormone‐induced melanin production in melanoma cells.…”

“…It is a major metabolite of curcumin with superior antioxidative properties in comparison with curcumin. 18 It has been shown to inhibit the melanocyte-stimulating hormone-induced melanin production in melanoma cells. Besides, it also reduces the expression of three main enzymes associated with the biosynthetic pathway of melanin namely tyrosinase (TYR), tyrosinaserelated protein 1 (TRP-1), and tyrosinase-related protein 2 (TRP-2).…”