Molecular inhibitory mechanism of dihydromyricetin on mushroom tyrosinase

Discovery of amphotericin B, an antifungal drug as tyrosinase inhibitor with potent anti-melanogenic activity

Tyrosinase, a rate-limiting enzyme for melanin production, has been the most efficient target for the development of depigmenting agents. Although hydroquinone, kojic acid, and arbutin are the most well-known tyrosinase inhibitors, their adverse effects are inevitable. In the present study, an in silico drug repositioning combined with experimental validation was performed to search for novel potent tyrosinase inhibitors. Docking-based virtual screening results revealed that, among the 3210 FDA-approved drugs available in the ZINC database, amphotericin B, an antifungal drug exhibited the highest binding efficiency against human tyrosinase. Results from tyrosinase inhibition assay demonstrated that amphotericin B could inhibit the activity of mushroom and cellular tyrosinases, especially from MNT-1 human melanoma cells. Molecular modeling results revealed that amphotericin B/human tyrosinase complex exhibited high stability in an aqueous environment. Melanin assay results demonstrated that amphotericin B significantly suppressed melanin production in α-MSH-induced B16F10 murine melanoma and MNT-1 human melanoma cell lines better than the known inhibitor, kojic acid. Mechanistically, amphotericin B treatment significantly activated ERK and Akt signaling pathways, resulting in the decreased expression of MITF and tyrosinase. The obtained results may pursue pre-clinical and clinical studies to examine the possibility of using amphotericin B as an alternative treatment for hyperpigmentation disorders.

Structure-activity relationships of antityrosinase and antioxidant activities of cinnamic acid and its derivatives

The related structure-activity relationships of cinnamic acid and its derivates have not been studied in details yet. Herein, antityrosinase and antioxidant activities of 18 compounds were evaluated. The results demonstrated that the substituents on the phenyl ring of cinnamic acid led to the enhancement of the inhibition on monophenolase and the weakening of the inhibition on diphenolase. Among these tested compounds, 9 was first discovered as a tyrosinase inhibitor in a reversible competitive manner with IC50 value of 68.6 ± 4.2 µm. Docking results demonstrated 9 located into the catalytic center of tyrosinase. Antioxidant assay indicated that only 1 hydroxyl group on the phenyl ring was not enough to possess the radical scavenging activity, and the number of hydroxyl groups may be more important. This study will be helpful in the development of new cinnamic acid derivates as tyrosinase inhibitors and antioxidants with higher efficacy.

Natural and synthetic flavonoid derivatives as new potential tyrosinase inhibitors: a systematic review

Tyrosinase is a multifunctional glycosylated and copper-containing oxidase that is highly prevalent in plants and animals and plays a pivotal role in catalyzing the two key steps of melanogenesis: tyrosine's hydroxylation to dihydroxyphenylalanine (DOPA), and oxidation of the latter species to dopaquinone. Melanin guards against the destructive effects of ultraviolet radiation which is known to produce considerable pathological disorders such as skin cancer, among others. Moreover, the overproduction of melanin can create aesthetic problems along with serious disorders linked to hyperpigmented spots or patches on skin. Several skin-whitening products which reduce melanogenesis activity and alleviate hyperpigmentation are commercially available. A few of them, particularly those obtained from natural sources and that incorporate a phenolic scaffold, have been exploited in the cosmetic industry. In this context, synthetic tyrosinase inhibitors (TIs) with elevated efficacy and fewer side effects are direly needed in the pharmaceutical and cosmetic industries owing to their protective effect against pigmentation and dermatological disorders. Furthermore, the biological significance of the chromone skeleton and its associated medicinal and bioactive properties has drawn immense interest and inspired many researchers to design and develop novel anti-tyrosinase agents based on the flavonoid core (2-arylchromone). This review article is oriented to provide an insight and a deeper understanding of the tyrosinase inhibitory activity of an array of natural and bioinspired phenolic compounds with special emphasis on flavonoids to demonstrate how the position of ring substituents and their interaction with tyrosinase could be correlated with their effectiveness or lack thereof against inhibiting the enzyme.

Evaluation of antityrosinase activity and mechanism, antioxidation, and UV filter properties of theaflavin

Tyrosinase is a key metalloenzyme for the biosynthesis of melanin that plays a critical role in the prevention of skin damage caused by ultraviolet (UV) radiation. However, the overproduction of melanin may cause a variety of skin diseases. Due to the toxicity and inefficiency of existing tyrosinase inhibitors, it is urgent to identify safe and potent alternatives from natural sources. Theaflavin, a single-component extracted from black tea, has been found to possess a variety of pharmacological activities. Herein, the inhibition kinetics of theaflavin on tyrosinase and inhibitory mechanism were determined using spectroscopy, molecular docking, and zebrafish model. The results showed that theaflavin inhibited the diphenolase activity of tyrosinase in a reversible mixed type manner with IC₅₀ of 229.75 μmol/L and hindered the synthesis of melanin in zebrafish. This may be due to the formation of eight hydrogen bonds and hydrophobic effects between theaflavin and tyrosinase according to the results of molecular docking. To study the possible effects on the prevention of free radical-mediated skin cancer and photoaging caused by UV radiation, the antioxidation and UV filter properties of theaflavin were further verified. This study demonstrates that theaflavin is a potential multifunctional compound that can be used in cosmetic and medicinal products.

Inhibition of Tyrosinase by Mercury Chloride: Spectroscopic and Docking Studies

Inorganic mercury compounds have been used in skin-lightening products since ancient times. Although a previous study demonstrated that mercury impeded the transfer of Cu²⁺ to the apotyrosinase, the effect of mercury on tyrosinase is still unclear. In the present study, the mechanism of mercury chloride (HgCl₂) induced inactivation of tyrosinase was investigated for the first time. The IC₅₀ values were 29.97 and 77.93 μmol/L for monophenolase and diphenolase, respectively. A kinetic analysis revealed that HgCl₂ inhibited tyrosinase activity in an irreversible non-competitive manner. The strong intrinsic fluorescence quenching suggested that the formation of the HgCl₂-tyrosinase complex induced conformational changes of the enzyme, and HgCl₂ had only one single binding site or a single class of binding site on tyrosinase. The molecular docking and further experiments demonstrated that HgCl₂ bound to the amino residuals (His) in the catalytic center of tyrosinase. To our knowledge, these findings presented in this paper were the first evidence of the direct interactions between HgCl₂ and tyrosinase, which provided a deep understanding of the inhibition mechanism of mercury on tyrosinase.

Identification and Characterization of the Tyrosinase Inhibitory Activity of Caffeine from Camellia Pollen

Tyrosinase inhibitors are important in cosmetic, medical, and food industries due to their regulation of melanin production. A tyrosinase inhibitor was purified from Camellia pollen using high-speed countercurrent chromatography and preparative high-performance liquid chromatography and was identified as caffeine by NMR and mass spectrometry. It showed strong mushroom tyrosinase inhibitory activity with an IC₅₀ of 18.5 ± 2.31 μg/mL in a noncompetitive model. The caffeine did not interact with copper ions in the active center of the enzyme but could quench fluorescence intensity and change the secondary conformation of this tyrosinase. A molecular dynamics simulation showed that caffeine bound this tyrosinase via Lys379, Lys 376, Asp357, Glu356, Thr308, Gln307, Asp312, and Trp358, thus changing the binding sites of l-tyrosine and the loop conformation adjacent to the active center. In vitro cell model analysis revealed that caffeine exhibited significant inhibitory effects on both intracellular tyrosinase activity and melanin production of B16-F10 melanoma cells in a concentration-dependent manner. These comprehensive results suggest that caffeine is a strong tyrosinase inhibitor that has the potential to be developed as skin-whitening agents in the cosmetics and pharmaceutical industries or as antibrowning agents in the food industry.

The Binding Affinity of Small Molecules with Yam Tyrosinase (Catechol Oxidase): A Biophysical Study

Yam tyrosinase has become an economically essential enzyme due to its ease of purification and abundant availability of yam tubers. However, an efficient biochemical and biophysical characterization of yam tyrosinase has not been reported. In the present study, the interaction of yam (Amorphophallus paeoniifolius) tyrosinase was studied with molecules such as crocin (Crocus sativus), hydroquinone, and kojic acid. Surface plasmon resonance (SPR), fluorescence spectroscopy, and circular dichroism techniques were employed to determine the binding affinities and the changes in secondary and tertiary structures of yam tyrosinase in the presence of four relevant small molecules. Hydroquinone and crocin exhibited very low binding affinities of 0.24 M and 0.0017 M. Due to their apparent weak interactions, competition experiments were used to determine more precisely the binding affinities. Structure-function interrelationships can be correlated in great detail by this study, and the results can be compared with other available tyrosinases.

Natural and Bioinspired Phenolic Compounds as Tyrosinase Inhibitors for the Treatment of Skin Hyperpigmentation: Recent Advances

One of the most common approaches for control of skin pigmentation involves the inhibition of tyrosinase, a copper-containing enzyme which catalyzes the key steps of melanogenesis. This review focuses on the tyrosinase inhibition properties of a series of natural and synthetic, bioinspired phenolic compounds that have appeared in the literature in the last five years. Both mushroom and human tyrosinase inhibitors have been considered. Among the first class, flavonoids, in particular chalcones, occupy a prominent role as natural inhibitors, followed by hydroxystilbenes (mainly resveratrol derivatives). A series of more complex phenolic compounds from a variety of sources, first of all belonging to the Moraceae family, have also been described as potent tyrosinase inhibitors. As to the synthetic compounds, hydroxycinnamic acids and chalcones again appear as the most exploited scaffolds. Several inhibition mechanisms have been reported for the described inhibitors, pointing to copper chelating and/or hydrophobic moieties as key structural requirements to achieve good inhibition properties. Emerging trends in the search for novel skin depigmenting agents, including the development of assays that could distinguish between inhibitors and potentially toxic substrates of the enzyme as well as of formulations aimed at improving the bioavailability and hence the effectiveness of well-known inhibitors, have also been addressed.