Valorization of biomass polyphenols as potential tyrosinase inhibitors

Tyrosinases (TYRs; EC 1.14.18.1) catalyze two sequential oxidative reactions of the melanin biosynthesis pathway and play an important role in mammalian pigmentation and enzymatic browning of fruit and vegetables. Inhibition of TYR activity is therefore an attractive target for new drugs and/or food ingredients. In addition, increasing evidence suggests that TYR regulation could be a novel target for treatments of cancer and Parkinson's disease. Biomasses, notably industrial byproducts and biowaste, are good sustainable sources of phytochemicals that may be valorized into bioactive compounds including TYR inhibitors. This review presents potential applications of biomass-derived polyphenols targeting TYR inhibition. Insights into structure-activity relationships of several polyphenols and their glycosides are highlighted. Finally, some remarks and perspectives on research into new TYR inhibitors from biomass waste are provided.

Natural tyrosinase enzyme inhibitors: A path from melanin to melanoma and its reported pharmacological activities

The skin containing melanin pigment acts as a protective barrier and counteracts the UVR and other environmental stressors to maintain or restore disrupted cutaneous homeostasis. The production of melanin pigment is dependent on tyrosine levels. L-tyrosine and L-dihydroxyphenylalanine (L-DOPA) can serve both as a substrates and intermediates of melanin synthetic pathway and as inducers and positive regulators of melanogenesis. The biosynthesis of melanin is stimulated upon exposure to UVR, which can also stimulate local production of hormonal factors, which can stimulate melanoma development by altering the chemical properties of eu- and pheomelanin. The process of melanogenesis can be altered by several pathways. One involves activation of POMC, with the production of POMC peptides including MSH and ACTH, which increase intracellular cAMP levels, which activates the MITF, and helps to stimulate tyrosinase (TYR) expression and activity. Defects in OCA1 to 4 affects melanogenic activity via posttranslational modifications resulting in proteasomal degradation and reducing pigmentation. Further, altering, the MITF factor, helps to regulate the expression of MRGE in melanoma, and helps to increase the TYR glycosylation in ER. CRH stimulates POMC peptides that regulate melanogenesis and also by itself can stimulate melanogenesis. The POMC, P53, ACTH, MSH, MC1R, MITF, and 6-BH4 are found to be important regulators for pigmentation. Melanogenesis can affect melanoma behaviour and inhibit immune responses. Therefore, we reviewed natural products that would alter melanin production. Our special focus was on targeting melanin synthesis and TYR enzyme activity to inhibit melanogenesis as an adjuvant therapy of melanotic melanoma. Furthermore, this review also outlines the current updated pharmacological studies targeting the TYR enzyme from natural sources and its consequential effects on melanin production.

The melanin inhibitory effect of plants and phytochemicals: A systematic review

BACKGROUND

Melanin plays an important role in protecting human skin, while excessive synthesis of melanin can cause abnormal pigmentation and induce skin diseases. Long-term use of commercial whitening agents in managing skin melanin such as kojic acid and arbutin can lead to some negative effects such as dermatitis and liver cancer. Although past studies have researched the melanin inhibitory effect of plant extracts, the effective dose and mechanisms are not well summarized and discussed. This study aims to explore the melanin inhibitory property of phytochemicals and tries to answer the following research questions: (1) Which plant extracts and phytochemicals could inhibit melanin biosynthesis in the skin? what is the mechanism of action? (2) Have human trials been conducted to confirm their melanin inhibitory effect? (3) If not, which phytochemicals are recommended for further human trials? This article would provide information for future research to develop natural and safe skin whitening products.

METHODS

A preferred reporting items for systematic reviews and meta-analyses (PRISMA) systematic review method and OHAT risk-of-bias tool were applied to screen literature from 2000 to 2021 and 50 research articles met the selection criteria.

RESULTS

Flavonoids, phenolic acids, stilbenes and terpenes are main classes of phytochemicals responsible for the melanin inhibitory effects. The in vitro/in vivo melanin inhibitory effects of these plant extracts/phytochemicals are achieved via three main mechanisms: (1) the ethyl acetate extract of Oryza sativa Indica cv., and phytochemicals such as galangin and origanoside could manage melanin biosynthesis through competitive inhibition, non-competitive inhibition or mixed-type inhibition of tyrosinase; (2) phytochemicals such as ginsenoside F1, ginsenoside Rb1 and 4‑hydroxy-3-methoxycinnamaldehyde could inhibit melanogenesis through down-regulating microphthalmia-related transcription factor (MITF) gene expression via different signalling pathways; (3) the ethanolic extracts of Dimorphandra gardneriana, Dimorphandra gardneriana, Lippia microphylla and Schinus terebinthifolius have a good ultraviolet absorption ability and high sun protective factor (SPF) values, thereby inhibiting UV induced melanogenesis in the skin.

CONCLUSION

Although many plant extracts and phytochemicals have been found to inhibit melanin production, most of the results were only proved in cellular and/or animal models. Only the ethyl acetate extract of Oryza sativa Indica cv. panicle, and ginsenoside F1 were proved effective in human trials. Animal studies proved the effectiveness of galangin, origanoside, ginsenoside Rb1 and 4‑hydroxy-3-methoxycinnamaldehyde with effective dose below 3 mM, and therefore recommended for future human trial. In addition, cellular studies have demonstrated the effectiveness of oxyresveratrol, mulberroside A, kurarinol, kuraridinol, plumbagin, (6aR,11aR)-3,8-dihydroxy-9‑methoxy pterocarpan, ginsenoside Rh4, cardamonin, nobiletin, curcumin, β-mangostin and emodin in inhibiting melanin synthesis at low concentrations of 20 µM and proved the low SPF values of Dimorphandra gardneriana, Dimorphandra gardneriana, Lippia microphylla and Schinus terebinthifolius extracts, and therefore recommended for further animal and human trials.

Crosstalk between xanthine oxidase (XO) inhibiting and cancer chemotherapeutic properties of comestible flavonoids- a comprehensive update

Gout is an inflammatory disease caused by metabolic disorder or genetic inheritance. People throughout the world are strongly dependent on ethnomedicine for the treatment of gout and some receive satisfactory curative treatment. The natural remedies as well as established drugs derived from natural sources or synthetically made exert their action by mechanisms that are closely associated with anticancer treatment mechanisms regarding inhibition of xanthine oxidase, feedback inhibition of de novo purine synthesis, depolymerization and disappearance of microtubule, inhibition of NF-ĸB activation, induction of TRAIL, promotion of apoptosis, and caspase activation and proteasome inhibition. Some anti-gout and anticancer novel compounds interact with same receptors for their action, e.g., colchicine and colchicine analogues. Dietary flavonoids, i.e., chrysin, kaempferol, quercetin, fisetin, pelargonidin, apigenin, luteolin, myricetin, isorhamnetin, phloretinetc etc. have comparable IC₅₀ values with established anti-gout drug and effective against both cancer and gout. Moreover, a noticeable number of newer anticancer compounds have already been isolated from plants that have been using by local traditional healers and herbal practitioners to treat gout. Therefore, the anti-gout plants might have greater potentiality to become selective candidates for screening of newer anticancer leads.

Polyphenols as anticancer agents: Toxicological concern to healthy cells

Polyphenols are a group of diverse chemical compounds present in a wide range of plants. Various biological properties such as antiallergic, antiviral, antibacterial, anticarcinogenic, antiinflammatory, antithrombotic, vasodilatory, and hepatoprotective effect of different polyphenols have been reported in the scientific literature. The major classes of polyphenols are flavonoids, stilbenoids, lignans, and polyphenolic acids. Flavonoids are a large class of food constituents comprising flavones, isoflavanones, flavanones, flavonols, catechins, and anthocyanins sub-classes. Even with seemingly broad biological activities, their use is minimal clinically. Among the other concurrent problems such as limited bioavailability, rapid metabolism, untargeted delivery, the toxicity associated with these polyphenols has been a topic of concern lately. These polyphenols have been reported to result in different forms of toxicity that include organ toxicity, genotoxicity, mutagenicity, cytotoxicity, etc. In the present article, we have tried to unravel the toxicological aspect of these polyphenols to healthy cells. Further high-quality studies are needed to establish the clinical efficacy and toxicology concern leading to further exploration of these polyphenols.

Dermal Drug Delivery of Phytochemicals with Phenolic Structure via Lipid-Based Nanotechnologies

Phenolic compounds are a large, heterogeneous group of secondary metabolites found in various plants and herbal substances. From the perspective of dermatology, the most important benefits for human health are their pharmacological effects on oxidation processes, inflammation, vascular pathology, immune response, precancerous and oncological lesions or formations, and microbial growth. Because the nature of phenolic compounds is designed to fit the phytochemical needs of plants and not the biopharmaceutical requirements for a specific route of delivery (dermal or other), their utilization in cutaneous formulations sets challenges to drug development. These are encountered often due to insufficient water solubility, high molecular weight and low permeation and/or high reactivity (inherent for the set of representatives) and subsequent chemical/photochemical instability and ionizability. The inclusion of phenolic phytochemicals in lipid-based nanocarriers (such as nanoemulsions, liposomes and solid lipid nanoparticles) is so far recognized as a strategic physico-chemical approach to improve their in situ stability and introduction to the skin barriers, with a view to enhance bioavailability and therapeutic potency. This current review is focused on recent advances and achievements in this area.

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.

Consistent production of kojic acid from Aspergillus sojae SSC-3 isolated from rice husk

A consistent kojic acid producing fungal strain has been isolated from rice husk using glucose-peptone medium. The isolate was identified as Aspergillus sojae SSC-3 on 18S rDNA analysis. A. sojae was capable of producing substantially good amount of kojic acid, however the production was varying from batch to batch. In order to obtain consistent, repeated and high levels of kojic acid, monospore isolation procedures was adopted. The highest production of kojic acid obtained was 12 ± 2 g/L in 120 h with sucrose (10%) and yeast extract (0.5%) as carbon and nitrogen source respectively. The process was scale up to 10 L fermenter size which repeatedly resulted in the production of 18 ± 2 g/L of kojic acid in 96 h. Kojic acid was recovered (> 82%) from the fermentation broth with > 99% purity. Best to our knowledge this is the first report were kojic acid production is reported from Aspergillus sojae strain.

Discovery of new depigmenting compounds and their efficacy to treat hyperpigmentation: Evidence from in vitro study

Human skin pigmentation is a result of constitutive and facultative pigmentation. Facultative pigmentation is frequently stimulated by UV radiation, pharmacologic drugs, and hormones whereby leads to the development of abnormal skin hyperpigmentation. To date, many state-of-art depigmenting compounds have been studied using in vitro model to treat hyperpigmentation problems for cosmetic dermatological applications; little attention has been made to compare the effectiveness of these depigmenting compounds and their mode of actions. In this present article, new and recent depigmenting compounds, their melanogenic pathway targets, and modes of action are reviewed. This article compares the effectiveness of these new depigmenting compounds to modulate several melanogenesis-regulatory enzymes and proteins such as tyrosinase (TYR), TYR-related protein-1 (TRP1), TYR-related protein-2 (TRP2), microphthalmia-associated transcription factor (MITF), extracellular signal-regulated kinase (ERK) and N-terminal kinases (JNK) and mitogen-activated protein kinase p38 (p38 MAPK). Other evidences from in vitro assays such as inhibition on melanosomal transfer, proteasomes, nitric oxide, and inflammation-induced melanogenesis are also highlighted. This article also reviews analytical techniques in different assays performed using in vitro model as well as their advantages and limitations. This article also provides an insight on recent finding and re-examination of some protocols as well as their effectiveness and reliability in the evaluation of depigmenting compounds. Evidence and support from related patents are also incorporated in this present article to give an overview on current patented technology, latest trends, and intellectual values of some depigmenting compounds and protocols, which are rarely highlighted in the literatures.

Anti-Melanogenic Effect from Submerged Mycelial Cultures of Ganoderma weberianum

Compounds from Lingzhi has been demonstrated the ability for inhibiting tyrosinase (a key enzyme in melanogenesis) activity. In this study, we investigated the anti-melanogenic activity from the submerged mycelial culture of Ganoderma weberianum and elucidated the skin lightening mechanism by B16-F10 murine melanoma cells. From the cellular context, several fractionated mycelium samples exhibited anti-melanogenic activity by reducing more than 40% extracellular melanin content of B16-F10 melanoma cells. In particular, the fractionated chloroform extract (CF-F3) inhibited both secreted and intracellular melanin with the lowest dosage (25 ppm). Further analysis demonstrated that CF-F3 inhibited cellular tyrosinase activity without altering its protein expression. Taken together, our study has demonstrated that the chemical extracts from submerged mycelial culture of G. weberianum have the potential to serve as an alternative anti-melanogenic agent.