Hair Coloring
Dale H. Johnson in Hair and Hair Care, 2018
The initial theory of eumelanin biosynthesis comes from the works of Raper (1) and Mason (2), who postulated that the amino acid tyrosine [1] was converted to eumelanin through a number of stages some of which were controlled en-zymically. In general terms, as shown in Figures 1 and 2, tyrosine [1] is first hydroxylated to 3,4-dihydroxyphenylalanine (DOPA) [2]. Oxidation to dopaquinone [3], followed by cyclization to leucodopachrome (cyclodopa) [4] and further oxidation, gives dopachrome [5]. Decarboxylation of dopachrome gives 5,6-dihydroxyindole [6]. Oxidation of [6] gives the quinone [7], which then polymerizes to melanin presumably through a number of oligomeric stages. The enzyme tyrosinase is an important catalyst in some of these steps.
Melanotropin Mechanisms of Action: Melanogenesis
Mac E. Hadley in The Melanotropic Peptides, 2018
From a variety of clinical and experimental observations, Lemer29 proposed several years ago that during the process of melanization, a pigment cell produces substances which are potentially autotoxic. Since that proposal, several laboratories have confirmed that the precursors of melanin biosynthesis are highly toxic to melanoma cells, probably because of their ability to generate free radicals as they co-polymerize. We showed that tyrosine and dopa are toxic to melanoma cells in culture and that the toxicity is increased significantly if the cells are preexposed to MSH.13,23 We also showed that other intermediates, i.e., dopachrome and 5,6-DHI, are even more toxic than tyrosine and dopa.23,30 However, cells that synthesize melanin possess mechanisms for protecting themselves from the cytotoxic intermediates, and our evidence indicates that in Cloudman melanoma cells, the protective mechanism is related to the relative activities of tyrosinase, dopachrome conversion factor, and indole-blocking factor.
Pigmentation Pathways and Microphtalmia-Associated Transcription Factor as New Targets in Melanoma
Sanjiv S. Agarwala, Vernon K. Sondak in Melanoma, 2008
When its expression is upregulated in normal melanocytes, MITF initiates a transcriptional program leading to melanocyte differentiation, enhanced cell cycle arrest, survival, and pigmentation (Table 1). It directly regulates the transcription of major pigmentation genes, including tyrosinase (TYR) (44–46), tyrosinase-related protein 1 (TYRP-1) (47) gene, dopachrome tautomerase (DCT)/TYRP-2 (47,48), quail neuroretina clone 71 (QNR-71) (49), silver (50,51), and absent in melanoma 1 (AIM-1) (52). The antiapoptotic protein Bcl-2 is directly transactivated by MITF and supports the survival of melanocytes since Bcl-2 knockout results in melanocyte death (53). It has also been suggested that MITF may induce cell cycle arrest during melanocytic differentiation, potentially via transcriptional targeting of the cyclin-dependent kinase (CDK) inhibitors p21, CDKN1A (54), and CDK4A (INK4A) (55). Thus, by promoting survival of the melanocyte pool and increasing pigmentation, activation of MITF would be expected to provide cutaneous photoprotection and reduced susceptibility to melanoma.
4-Arylthiosemicarbazide derivatives as a new class of tyrosinase inhibitors and anti-Toxoplasma gondii agents
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2021
Adrian Bekier, Lidia Węglińska, Agata Paneth, Piotr Paneth, Katarzyna Dzitko
In our study, we used Tyr from mushrooms (T3824, Sigma) for all experiments. All compound dilutions, L-tyrosine a Tyr substrate, and Tyr were prepared in 50 mM phosphate buffer (pH 6.5). The volume of the reaction mixture was 200 µL and contained: 80 µL of 2.5 mM L-tyrosine, 50 µL of 100 µM compound/inhibitor, and 70 µL of Tyr (10 U). First, the substrate and compound or inhibitor were added to a 96-well flat-bottom plate (Nunc MaxiSorp™, Rosklide, Denmark), next Tyr was added and the initial absorbance (A0) was measured spectrophotometrically at 492 nm. Then, the plate was incubated at 25 °C for 30 min. After incubation, the amount of dopachrome produced in the reaction mixture was determined spectrophotometrically at 492 nm (A30) using the multi-mode microplate reader SpectraMax® i3 (Syngen). 100% Tyr activity we used for the sample without addition compound/inhibitor. First, we established the inhibitory concentration of KA (IC50KA = 25 µM) for 10 U of Tyr. Then, the inhibition of Tyr activity screening test was performed at 25 µM for the studied compounds. Also, IC50Tyr for the most active compounds; 2a, 2b, 6a, and 6b was determined. The average results from three experiments are shown.
Antibacterial, Antioxidant and Melanogenesis Inhibitory Activity of Auraptene, a Coumarin from Ferula szowitsiana Root
Published in Nutrition and Cancer, 2022
Ensiyeh Charmforoshan, Ehsan Karimi, Ehsan Oskoueian, Mehrdad Iranshahi
Due to the investigation of anti-tyrosinase properties murine melanoma B16F10 cell line (ATCC CRL-6475) were cultured and grown in a 6-well plate with a density of 5 × 104 cells/ml. Then, the media was removed after 24 h, and serial concentration of auraptene and kojic acid were replaced. The cells were incubated for 72 h and the viability of the cells was determined by using 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide (MTT). The cells incubated in culture media devoid of auraptene (0 µg/ml) were considered as a negative control. The melanin content of the cells was performed base on Sun et al. (18) assay. Briefly, the cultivated cell was harvested after 72 h, of incubation and washed two times with phosphate-buffered saline. Eventually, the cells were lysed, heated for one hour (80 °C) and the melanin content was read at a wavelength of 400 nm. The expression of melanin biosynthesis-related genes namely Tyrosinase (TYR), tyrosinase-related protein 1 (TRP-1), and tyrosinase-related protein 2/DOPAchrome tautomerase (TRP-2) in the B16F10 cells was determined using real-time PCR (19).
A comprehensive review on tyrosinase inhibitors
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2019
Samaneh Zolghadri, Asieh Bahrami, Mahmud Tareq Hassan Khan, J. Munoz-Munoz, F. Garcia-Molina, F. Garcia-Canovas, Ali Akbar Saboury
Diphenolase activity can be independently studied, when tyrosinase reacts with an o-diphenol (see Figure 2). The form met-tyrosinase (Em) binds the o-diphenol (D) originating the complex EmD. This complex oxidises the o-diphenols transforming it to o-quinone and the enzyme is converted into the form deoxy-tyrosinase (Ed). Ed has a very big affinity for the molecular oxygen originating the form oxy-tyrosinase (Eox), which binds another o-diphenol molecule and originating the complex EoxD. After that, the o-diphenol is oxidised again to o-quinone and the form Em is formed again completing the catalytic cycle. However, after these enzymatic reactions, two o-quinone molecules (e.g. o-dopaquinone) react generating dopachrome and regenerating a molecule of o-diphenol.