Melanogenesis inhibitory activity of components from Salam leaf (Syzygium polyanthum) extract

Antidiabetic Activity, Phytochemical Analysis, and Acute Oral Toxicity Test of Combined Ethanolic Extract of Syzygium polyanthum and Muntingia calabura Leaves

Syzygium polyanthum is known for its capacity to regulate blood glucose levels in individuals with diabetes, while Muntingia calabura leaves have a traditional history as an alternative therapy due to their antidiabetic compounds. The combination of these two plants is expected to yield more optimized antidiabetic agents. This study aims to assess the antidiabetic activity of the combined ethanolic extract of S. polyanthum and M. calabura leaves by measuring the in vitro inhibition of the α-glucosidase enzyme and the blood glucose level in streptozotocin-induced rats and to determine the phytochemical contents of total phenolics, total flavonoids, and quercetine as marker compounds. Acute oral toxicity test was also evaluated. Both plants were extracted by maceration using 96% ethanol. Various combinations of S. polyanthum and M. calabura leaves extracts (1 : 1, 2 : 1, 3 : 1, 1 : 3, and 1 : 2) were prepared. The in vitro test, along with the total phenolic and total flavonoid content, were measured by using UV-Vis spectrophotometry, while quercetine levels were quantified through high-performance liquid chromatography (HPLC). The in vivo and acute toxicity tests were performed on rats as an animal model. The findings demonstrated that the 1 : 1 combination of S. polyanthum and M. calabura leaves ethanolic extract displayed the highest enzyme inhibitory activity with IC50 value of 36.43 µg/mL. Moreover, the combination index (CI) was found <1 that indicates the synergism effect. This combination also decreases the blood glucose level in rats after 28 days of treatments without significant difference with positive control glibenclamide (p > 0.005), and it had medium lethal doses (LD50) higher than 2000 mg/kg BW. Phytochemical analysis showed that the levels of total phenolics, total flavonoids, and quercetine were 30.81% w/w, 1.37% w/w, and 3.25 mg/g, respectively. These findings suggest the potential of combined ethanolic extracts of S. polyanthum and M. calabura leaves (1 : 1) as raw materials for herbal antidiabetic medication.

An evaluation of the antioxidant potential and in vitro enzyme inhibition profile of selected bryophytes from Northeast Anatolia (Türkiye)

Interest in the use of bryophytes in pharmaceutical, cosmetic, and food industrial applications is growing worldwide due to their secondary metabolites. In this study, n-hexane crude extracts and further fractions (aqueous, ethyl acetate and n-butanol) of aqueous ethanol (80:20, ethanol:H2O, v/v) were obtained from five different bryophytes (Pellia epiphylla, Conocephalum conicum, Porella platyphylla, Plagiomnium cuspidatum and Mnium spinulosum) collected from Trabzon, Türkiye. The total phenolic compound (TPC) content, antioxidant capacity (AC) and enzyme inhibition activity (acetylcholine esterase, butyrylcholine esterase, tyrosinase, α-amylase and α-glucosidase) of the extracts and fractions were species-specific and varied significantly between the crude extracts and fractions. Among the different bryophytes, Porella platyphylla and Pellia epiphylla in n-butanol and Plagiomnium cuspidatum and Mnium spinulosum in ethyl acetate fraction exhibited the highest TPC contents and AC values. The contents of phenolic acids liberated in free, ester and glycoside forms were also species-specific. p-Hydroxybenzoic acid (p-HBA) in free form in P. cuspidatum and P. platyphylla, p-coumaric acid (p-CoA) in ester form and m-hydroxybenzoic acid (m-HBA) in glycoside form in M. spinulosum were the major phenolic acids in the bryophytes. The n-hexane extracts of the bryophytes, in particular M. spinulosum, had IC50 values ​​almost 100 times lower than acarbose. This suggests that M. spinulosum in particular may represent a possible candidate for the production of new antidiabetic agents.Communicated by Ramaswamy H. Sarma.

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.

Natural Sources of Melanogenic Inhibitors: A Systematic Review

OBJECTIVE

Melanin gives some natural protection against the harmful effects of UV radiation, however, excessive production of melanin causes skin hyperpigmentation. Depigmenting cosmetics can be used to control this process, however, depigmenting agents commonly used have some disadvantages, such as low bioavailability, photosensitization, cellular toxicity, and insolubility. Natural sources of melanogenic inhibitors have become important alternatives to synthetic ones. The objective of this review was to summarise the results of studies on natural extracts that have been reported in the literature to inhibit the process of melanogenesis, giving a view on their suitability for potential use in new cosmetic formulations for skin-lightening.

DATA SOURCES

A systematic literature search was carried out using the descriptors: "melanogenesis", "tyrosinase", "tyrosinase inhibition", and "natural agents".

STUDY SELECTION

Publications were selected based on our designated inclusion and exclusion criteria and a total of fifteen studies were found which met these criteria.

DATA EXTRACTION

The following were used in the review of each paper which met the criteria: the name of the plant (all of the natural extracts turned out to be from plants), the method used to obtain the plant extract, the method for evaluating anti-tyrosinase activity, the main results and the conclusions.

DATA SYNTHESIS

All evaluated natural agents demonstrated anti-tyrosinase effect. The species Leathesia difformis, Morus alba, Orostachys japonicus, Heracleum moellendorffii, Coix lacryma-jobi (adlay), Inula brittanica, and Gailardia aristata stood out from the others due to their application as potential inhibitors of more than three proteins related to melanogenesis, including the cyclic adenosine monophosphate response element-binding protein (CREB), microphthalmia-associated transcription factor (MITF), tyrosinase (TYR), tyrosinase-related protein-1 (TRP-1), tyrosinase-related protein-2 (TRP-2), and dopachrome tautomerase (DCT).

CONCLUSION

The plants present an anti-tyrosinase effect that must be better explored in the new cosmetic formulations. The anti-melanogenic effects of the plant are mainly related to presence of phenolic and antioxidant compounds.

SAR and QSAR research on tyrosinase inhibitors using machine learning methods

Tyrosinase is a key rate-limiting enzyme in the process of melanin synthesis, which is closely related to human pigmentation disorders. Tyrosinase inhibitors can down-regulate tyrosinase to effectively reduce melanin synthesis. In this work, we conducted structure-activity relationship (SAR) study on 1097 diverse mushroom tyrosinase inhibitors. We applied five kinds of machine learning methods to develop 15 classification models. Model 5B built by fully connected neural networks and ECFP4 fingerprints achieved the highest prediction accuracy of 91.36% and Matthews correlation coefficient (MCC) of 0.81 on the test set. The applicability domains (AD) of classification models were defined by d S T D - P R O method. Moreover, we clustered the 1097 inhibitors into eight subsets by K-Means to figure out inhibitors' structural features. In addition, 10 quantitative structure-activity relationship (QSAR) models were constructed by four machine learning methods based on 813 inhibitors. Model 6 J, the best QSAR model, was developed by fully connected neural networks with 50 RDKit descriptors. It resulted in a coefficient of determination (r ²) of 0.770 and a root mean squared error (RMSE) of 0.482 on the test set. The AD of Model 6 J was visualized by Williams plot. The models built in this study can be obtained from the authors.

Screening of Indonesian Edible Plants for Bioactive Constituents and a New Protein Tyrosine Phosphatase 1B Inhibitory Acylbenzene Derivative from Leaves of Indonesian Syzygium polyanthum

Bioassay screening using Indonesian plants, such as traditional foods (vegetables, spices, and tea) and folk medicinal herbs, identified eight protein tyrosine phosphatase (PTP) 1B inhibitory and two antibacterial plants. The leaves of Syzygium polyanthum (Wight) Walp. were examined in more detail to define PTP1B inhibitory components, resulting in the isolation of a new active acylbenzene (1) along with four related congeners of 1 (2-5) and four oleanane triterpenes (6-9). The structure of 1 was elucidated as 12-oxo-12-(2,3,5-trihydroxy-4-methylphenyl)dodecanoic acid based on its spectroscopic data. The acylbenzenes 1 and 3-5 inhibited PTP1B activity with IC₅₀ values ranging between 9.5 and 14 µM, whereas the triterpenes 7-9 also suppressed this activity with IC₅₀ values of 3.3-5.7 µM.

Melanogenesis-inhibitory activities of limonoids and tricyclic diterpenoids from Azadirachta indica

The chemical constituents of the roots and bark of Azadirachta indica were investigated, leading to the isolation of six tricyclic diterpenoids and four limonoids including a new compound, azadirachtin J (4). The structures were elucidated on the basis of NMR spectroscopic techniques, mass spectrometry as well as comparison with the literature. Furthermore, melanogenesis-inhibitory activities of the isolated compounds were evaluated. As a result, compounds 1-3 and 10 exhibited superior inhibitory activities against melanogenesis with no, or almost no, toxicity to the cells (86.5-105.1% cell viability). Western blot analysis showed that compounds 1 and 3 exhibited melanogenesis inhibitory activities in α-MSH-stimulated B16 melanoma cells due to, at least in part, inhibition of the expression of MITF, followed by a decrease in the expression of tyrosinase, TRP-1, and TRP-2. Compounds 1 and 3 exhibited tyrosinase inhibitory activities (IC₅₀ values of 44.86 μM and 69.85 μM respectively). Docking results confirm that the active inhibitors strongly interact with tyrosinase residues.

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.