Inhibitory effects of Citrus hassaku extract and its flavanone glycosides on melanogenesis

Molecular basis of skin photoaging and therapeutic interventions by plant-derived natural product ingredients: A comprehensive review

Skin areas exposed to ultraviolet radiation (UV) from sunlight are more prone to photoaging than unexposed areas evidenced by several signs which include skin dryness, irregular pigmentation, lentigines, hyperpigmentation, wrinkling, and decreased elasticity. Plant-based natural product ingredients with therapeutic potential against skin photoaging are gaining more attention. This article aims the reviewing the research work done in exploring the cellular and molecular mechanisms involved in UV-induced skin photoaging, followed by summarizing the mechanistic insights involved in its therapeutics by natural product-based ingredients. In the mechanistic section of the convoluted procedure of photoaging, we described the effect of UV radiation (UVR) on different cellular macromolecules (direct damage) and subsequently, the deleterious consequences of UVR-generated reactive oxygen species (indirect damage) and signaling pathways activated or inhibited by UV induced ROS generation in various cellular pathologies of skin photoaging like inflammation, extracellular matrix degradation, apoptosis, mitochondrial dysfunction, and immune suppression. We also discussed the effect of UV radiation on the adipose tissue, and transient receptor potential cation channel V of photoaging skin. In the past few decades, mechanistic studies performed in this area have deciphered various therapeutic targets, opening avenues for different available therapeutic options against this pathological condition. So the remaining portion of the review deals with various natural product-based therapeutic agents available against skin photodamage.

Recent discovery of tyrosinase inhibitors in traditional Chinese medicines and screening methods

ETHNOPHARMACOLOGICAL RELEVANCE

Tyrosinase, the key rate-limiting enzyme for melanogenesis, is one of the main targets for skin senescence and some pigmented skin diseases, such as albinism and melanoma. Tyrosinase inhibitors are capable of reducing melanin generation and deposition in the skin through blocking the reaction chain of formation. Thus, it has been used for anti-melanoma and showed the potential to be developed into novel skin whitening and spot removing products. With the trend of back-to-nature, natural tyrosinase inhibitors are receiving more and more attention. Traditional Chinese medicines (TCMs) as the promising source of novel chemotypes and pharmacophores, are huge treasures for the discovery of natural tyrosinase inhibitors characterized with green, safe, and highly efficient.

AIM OF THIS REVIEW

This review aims to provide a systematic overview of natural tyrosinase inhibitors and a detailed summary of the types of TCMs from which they originate. In addition, this paper also highlights the screening methods developed for exploring tyrosinase inhibitors in recent years, compares the advantages and disadvantages of various methods under the guidance of different screening principles, and predicts their applications in the future.

MATERIALS AND METHODS

Relevant literature have been obtained using the keywords "tyrosinase inhibitors", "traditional Chinese medicines", "whitening", and "screening" in scientific databases, such as "PubMed", "SciFinder", "Web of Science", "Elsevier", "China Knowledge Resource Integrated databases". Information was also collected from Chinese pharmacopoeia, Chinese herbal classics books, "Google Scholar", "Baidu Scholar", and other literature sources, etc. RESULTS: An overview about the tyrosinase inhibitors derived from TCMs since 2002 has been compiled via the above-mentioned sources. Up to now, 186 components, mainly belonging to flavonoids, lignans, terpenoids, Diels-Alder adducts, simple phenylpropanoids and stilbenes, from 61 kinds of TCMs have been reported to possess tyrosinase inhibitory activity, among which flavonoids are mainly focused on. Furthermore, on the basis of bioactive detection strategies, the screening methods for tyrosinase inhibitors have been classified into bioaffinity-based, intrinsic enzymatic-based, and computer-aided drug design (CADD). Precisely because screening approaches are essential for rapid identification of tyrosinase inhibitors from TCMs, the principles, advantages and disadvantages, and specific applications of each method are presented along with a comparison of applicability.

CONCLUSIONS

The summary of TCMs-derived inhibitors gives a clue on the discovery of candidates with the property to whiten the skin. Meanwhile, the outlook of developed screening methods provides technical references for the efficient exploration of safer and more effective tyrosinase inhibitors from TCMs.

High-performance liquid chromatography micro-fraction bioactive evaluation combined with countercurrent chromatographic separation of antioxidants from Citrus peel and their tyrosinase inhibition activities

In the present study, high-performance liquid chromatography micro-fraction bioactive evaluation and high speed countercurrent chromatography were performed on screening, identification and isolation of antioxidants from Citrus peel. Three compounds were screened as antioxidants and tyrosinase inhibitors using 2,2'-azino-bis (3-ethyl-benzothiazoline-6-sulfonic acid) radical cation scavenging assay and tyrosinase activity test, then they were identified as eriocitrin, narirutin and hesperidin. Moreover, the solvent system ethyl acetate-n-butanol-water (6:4:10, v/v/v) was used for separation of ethyl acetate extract of Citrus peel by high speed countercurrent chromatography. In total, 0.45 mg of eriocitrin with 87.10% purity, 2.04 mg of narirutin with 95.19% purity and 1.35 mg of hesperidin with 95.19% purity were obtained from 20 mg of ethyl acetate extract of Citrus peel in a single run and then each component was subjected to 2,2'-azino-bis (3-ethyl-benzothiazoline-6-sulfonic acid) radical cation scavenging assay and tyrosinase inhibition assay. Eriocitrin showed great antioxidant activity (the half-maximum concentration: 3.65 µM) and tyrosinase inhibition activity (the half-maximum concentration: 115.67 µM), while narirutin and hesperidin exhibited moderate activity. Tyrosinase inhibition activity for eriocitrin in vitro was reported for the first time. Furthermore, molecular docking between eriocitrin and mushroom tyrosinase was also studied.

Nypa fruticans Wurmb inhibits melanogenesis in isobutylmethylxanthine‑treated melanoma via the PI3K/AKT/mTOR/CREB and MAPK signaling pathways

Malignant melanoma is responsible for 3.0 and 1.7% of cases of tumor incidence and tumor-associated mortality, respectively, in the Caucasian population. Melanoma is a type of skin cancer that occurs when melanocytes mutate and divide uncontrollably. Nypa fruticans Wurmb (NF) is abundant in phytochemicals (polyphenols and flavonoids) and is traditionally used to treat diseases of the respiratory tract. The present study investigated the inhibitory effect of the ethyl acetate fraction of NF (ENF) on melanogenesis-related factors in isobutylmethylxanthine-treated B16F10 melanoma cells. Phenolics and flavonoids (caffeic acid, catechin, epicatechin and hirsutine) in ENF were analyzed via liquid chromatography-mass spectrometry. In addition, the main factors involved in melanogenesis were identified using immunoblotting, reverse transcription-polymerase chain reaction (RT-PCR), RT-quantitative PCR and immunofluorescence. ENF significantly suppressed the expression of tyrosinase (TYR) and TYR-related proteins 1 and 2 (TYRP-1/2), which are the main factors involved in melanogenesis. ENF also inhibited the expression of microphthalmia-associated transcription factor (MITF) by phosphorylating the related cell signaling proteins (protein kinase B, mammalian target of rapamycin, phosphoinositide 3-kinase and cAMP response element-binding protein). Furthermore, ENF inhibited the phosphorylation of extracellular signal-regulated kinase and thereby downregulated melanogenesis. In conclusion, ENF inhibited melanogenesis by suppressing MITF, which controls TYRP-1/2 and TYR. These results suggested that ENF may be a natural resource that can inhibit excessive melanin expression by regulating various melanogenesis pathways.

A network pharmacology approach to evaluate the synergistic effect of dihydromyricetin and myricitrin in vine tea on the proliferation of B16F10 cells

Aim of the study

Although vine tea has demonstrated broad-spectrum anti-cancer properties, its main active compounds, dihydromyricetin (DMY) and myricitrin (MYT), exert weaker effects than the tea extracts. This study aimed to investigate the synergistic inhibitory effects of DMY and MYT on B16F10 cell proliferation and their synergistic inhibitory effects.

Methods

The effect of vine tea extracts (VTEs) and their active compounds on B16F10 cells was analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, fluorescence staining, and flow cytometry. The synergistic effects were calculated by the combination index (CI), and its mechanism was discussed by network pharmacology.

Results

Different VTEs varied in their inhibition of B16F10 cell growth, with IC₅₀ values ranging from 4.45 to 12.95 μg/mL, Among these, Guangzhou Qingyuan (Level 2), appeared to have the most potent inhibitory effect. The IC₅₀ value of mix-use of DMY and MYT was 19.94∼64.4 μM, of which DMY: MYT = 8:1 had the minimum IC₅₀ value of 19.94 μM. Combinations in the 1:1∼8:1 range had stronger effects than the isolated active compound. When they were mixed at the ratio of 1:4∼8:1, CI < 1, showing a synergistic effect. The combination of DMY and MYT also significantly inhibited the tyrosinase activity in B16F10 cells, consistent with its impact on cell proliferation. The eight potential targets were identified by network pharmacology regulating melanin metabolism, tyrosine metabolism, and melanogenesis signaling. According to the analysis of protein-protein interactions, TP53, TNF, and TYR might be critical targets for preventing and treating melanoma.

Conclusion

We found that DMY and MYT induced apoptosis of B16F10 cells, and their combined application had a significant synergistic effect. The present findings indicated that vine tea had a multi-pathway and multi-target impact on the prevention and treatment of melanoma.

Amorphigenin from Amorpha fruticosa L. Root Extract Induces Autophagy-Mediated Melanosome Degradation in mTOR-Independent- and AMPK-Dependent Manner

In this study, we investigated the depigmentation effect of Amorpha fruticosa L. root extract (RE), an herbal medicine. A. fruticosa RE significantly induced depigmentation in α-MSH-treated B16F10 cells at noncytotoxic concentrations. Further, the RE decreased the protein levels of the melanosomal proteins Tyr and Pmel without decreasing their transcript levels. We found that MG132, a proteasome complex inhibitor, was unable to rescue the protein levels, but PepA/E-64D (a lysosomal enzyme inhibitor), 3-MA (a representative autophagy inhibitor), and ATG5 knockdown effectively rescued the protein levels and inhibited the depigmentation effect following RE treatment. Among rotenoids, amorphigenin composed in the RE was identified as a functional chemical that could induce depigmentation; whereas rapamycin, an mTOR inhibitor and a nonselective autophagy inducer, could not induce depigmentation, and amorphigenin effectively induced depigmentation through the degradation of melanosomal proteins. Amorphigenin activated AMPK without affecting mTOR, and knockdown of AMPK offset the whitening effect through degradation of melanosome proteins by amorphigenin. Results from this study suggested that amorphigenin can induce degradation of the melanosome through an AMPK-dependent autophagy process, and has the potential to be used as a depigmentation agent for the treatment of hyperpigmentation.

Clinical Evidence of Effects of Green Mandarin (Putgyul) Extract on Skin Aging: A Randomized, Double Blind, Placebo-Controlled Study

Green mandarins are widely consumed unripe as mandarin oranges (Citrus unshiu Marcov.), which exhibit anti-inflammatory and anti-wrinkle effects by inhibiting the production of inflammatory cytokines and matrix metalloproteinase. A randomized, double-blind, placebo-controlled clinical study was performed to verify the skin improvement efficacy and safety of green mandarin extract (PTE). For the standardization of PTE, narirutin was set as a marker compound, and PTE with a constant narirutin content was prepared for the study. After randomizing subjects with periorbital wrinkles, they were orally administered PTE (300 mg/day) or a placebo for 12 weeks. Periorbital wrinkles were measured using PRIMOS^CR SF. Skin elasticity, moisture content, transepidermal water loss, and gloss were also measured. In the study results, the depth, volume, and skin roughness of the periorbital wrinkles were significantly improved compared to the control group (p = 0.011, 0.009, and 0.004, respectively). The survey confirmed that the skin condition improved after PTE consumption for 12 weeks. No adverse reactions associated with PTE were observed during the study period. Thus, the results demonstrate that PTE effectively improves UV-induced skin wrinkles. Therefore, it is considered that PTE has sufficient value as a functional food ingredient that can prevent skin aging.

Suppression of colorectal carcinogenesis by naringin

BACKGROUND

Colorectal cancer is the third most malignant cancer worldwide. Despite novel treatment options, the incidence and mortality rates of colon cancer continue to increase in most countries, especially in US, European and Asian countries. Colorectal carcinogenesis is multifactorial, including dietary and genetic factors, as well as lacking physical activity. Vegetables and fruits contain high amounts of secondary metabolites, which might reduce the risk for colorectal carcinogenesis. Flavonoids are important bioactive polyphenolic compounds. There are more than 4,000 different flavonoids, including flavanones, flavonoids, isoflavonoids, flavones, and catechins in a large variety of plant.

HYPOTHESIS

Among various other flavonoids, naringin in Citrus fruits has been a subject of intense scrutiny for its activity against many types of cancer, including colorectal cancer. We hypothesize that naringin is capable to inhibit the growth of transformed colonocytes and to induce programmed cell death in colon cancer cells.

RESULTS

We comprehensively review the inhibitory effects of naringin on colorectal cancers and address the underlying mechanistic pathways such as NF-κB/IL-6/STAT3, PI3K/AKT/mTOR, apoptosis, NF-κB-COX-2-iNOS, and β-catenin pathways.

CONCLUSION

Naringin suppresses colorectal inflammation and carcinogenesis by various signaling pathways. Randomized clinical trials are needed to determine their effectiveness in combating colorectal cancer.

Is Our Natural Food Our Homeostasis? Array of a Thousand Effect-Directed Profiles of 68 Herbs and Spices

The beneficial effects of plant-rich diets and traditional medicines are increasingly recognized in the treatment of civilization diseases due to the abundance and diversity of bioactive substances therein. However, the important active portion of natural food or plant-based medicine is presently not under control. Hence, a paradigm shift from quality control based on marker compounds to effect-directed profiling is postulated. We investigated 68 powdered plant extracts (botanicals) which are added to food products in food industry. Among them are many plants that are used as traditional medicines, herbs and spices. A generic strategy was developed to evaluate the bioactivity profile of each botanical as completely as possible and to straightforwardly assign the most potent bioactive compounds. It is an 8-dimensional hyphenation of normal-phase high-performance thin-layer chromatography with multi-imaging by ultraviolet, visible and fluorescence light detection as well as effect-directed assay and heart-cut of the bioactive zone to orthogonal reversed-phase high-performance liquid chromato-graphy-photodiode array detection-heated electrospray ionization mass spectrometry. In the non-target, effect-directed screening via 16 different on-surface assays, we tentatively assigned more than 60 important bioactive compounds in the studied botanicals. These were antibacterials, estrogens, antiestrogens, androgens, and antiandrogens, as well as acetylcholinesterase, butyrylcholinesterase, α-amylase, α-glucosidase, β-glucosidase, β-glucuronidase, and tyrosinase inhibitors, which were on-surface heart-cut eluted from the bioautogram or enzyme inhibition autogram to the next dimension for further targeted characterization. This biological-physicochemical hyphenation is able to detect and control active mechanisms of traditional medicines or botanicals as well as the essentials of plant-based food. The array of 1,292 profiles (68 samples × 19 detections) showed the versatile bioactivity potential of natural food. It reveals how efficiently and powerful our natural food contributes to our homeostasis.

Development of flavanone and its derivatives as topical agents against psoriasis: The prediction of therapeutic efficiency through skin permeation evaluation and cell-based assay

Flavonoids inhibit skin inflammation. Previous study suggests that the flavonoids with flavanone backbone were beneficial to penetrate into the skin. We aimed to investigate the possibility of psoriasis treatment by topically applied flavanone and its derivatives including naringenin, hesperetin, 6-hydroxyflavanone, flavanone, and 6-bromoflavone. The skin absorption of the compounds was determined by Franz cells. Molecular modeling was used to compute the physicochemical and molecular parameters of the penetrants in order to elucidate the correlation between structure and permeation. Among the compounds tested, flavanone showed the greatest skin absorption. The in vitro skin absorption predicted efficient skin targeting of 6-bromoflavone with minimal risk of circulation absorption. The permeation of naringenin was remarkably enhanced 13-fold in the barrier-defective skin mimicking inflamed skin. The penetrants with fewer hydrogen bond number, total polarity surface, and molecular volume were advantageous for facile skin absorption. In the cell-based study, IL-1β inhibition in imiquimod (IMQ)-stimulated keratinocytes was increased following the increase in compound lipophilicity. Naringenin, a flavanone analog with three hydroxyl moieties, could suppress IL-6 overexpression to baseline control. We assessed the anti-inflammatory potency of the chemicals in comparison with tacrolimus as reference in a psoriasis-like mouse model. Flavanone was found to mitigate scaling and epidermal hyperplasia at a higher level than naringenin. Flavanone lessened IL-6 overexpression by 80% in the psoriasiform plaque. The skin barrier function recorded by transepidermal water loss (TEWL) was recovered by naringenin but not flavanone. The experimental data indicate that naringenin and flavanone are potential candidates for anti-psoriatic therapy.

Insights Into the Explication of Potent Tyrosinase Inhibitors with Reference to Computational Studies

Background:

Pigment melanin has primarily a photo defensive role in human skin, its unnecessary production and irregular distribution can cause uneven skin tone ultimately results in hyper pigmentation. Melanin biosynthesis is initiated by tyrosine oxidation through tyrosinase, the key enzyme for melanogenesis. Not only in humans, tyrosinase is also widely distributed in plants and liable for browning of vegetables and fruits. Search for the inhibitors of tyrosinase have been an important target to facilitate development of therapies for the prevention of hyperpigmentary disorders and an undesired browning of vegetables and fruits.

Methods:

Different natural and synthetic chemical compounds have been tested as potential tyrosinase inhibitors, but the mechanism of inhibition is not known, and the quest for information regarding interaction between tyrosinase and its inhibitors is one of the recent areas of research. Computer based methods hence are useful to overcome such issues. Successful utilization of in silico tools like molecular docking simulations make it possible to interpret the tyrosinase and its inhibitor’s intermolecular interactions and helps in identification and development of new and potent tyrosinase inhibitors.

Results:

The present review has pointed out the prominent role of computer aided approaches for the explication of promising tyrosinase inhibitors with a focus on molecular docking approach. Highlighting certain examples of natural compounds whose antityrosinase effects has been evaluated using computational simulations.

Conclusion:

The investigation of new and potent inhibitors of tyrosinase using computational chemistry and bioinformatics will ultimately help millions of peoples to get rid of hyperpigmentary disorders as well as browning of fruits and vegetables.

Physicochemical Characterization, Microbiological Quality and Safety, and Pharmacological Potential of Hancornia speciosa Gomes

Hancornia speciosa Gomes is a fruit tree, commonly known as the mangaba tree, which is widespread throughout Brazil. The leaves of this plant are used in traditional medicine for medicinal purposes. Thus, the objective of this study was to perform a physicochemical characterization, identify the lipophilic antioxidants and fatty acids, and determine the microbiological quality and safety of H. speciosa leaves. In addition, the antioxidant, antimutagenic, and inhibitory activities of the ethanolic extract of H. speciosa leaves (EEHS) against enzymes related to neurodegenerative diseases, inflammation, obesity, and diabetes were investigated. Furthermore, this study aimed at assessing the in vivo effects of the EEHS on the glycemia of normoglycemic and diabetic Wistar rats. Physicochemical characterization was performed by colorimetry and gas-liquid chromatography with flame ionization detection (GC-FID). The total number of colonies of aerobic mesophiles, molds, and yeasts was determined. The total coliforms and Escherichia coli were counted using the SimPlates kit, and sulphite-reducing Clostridium spores were quantified using the sulphite-polymyxin-sulfadiazine agar method. Salmonella spp. were detected using the 1-2 Test. The antioxidant activity of the EEHS was measured by its inhibition of 2,2'-azobis(2-amidinopropane) dihydrochloride- (AAPH-) induced oxidative hemolysis of human erythrocytes. The antimutagenic activity was determined using the Ames test. The acetylcholinesterase, butyrylcholinesterase, tyrosinase, hyaluronidase, lipase, α-amylase, and α-glycosidase enzyme-inhibiting activities were assessed and compared with commercial controls. The in vivo effects of the EEHS were assessed using the oral glucose tolerance test in normoglycemic Wistar rats and measuring the blood glucose levels in diabetic rats. The results demonstrated physical-chemical parameters of microbiological quality and safety in the leaves of H. speciosa, as well as antioxidant and antimutagenic activities and inhibition of enzymes related to neurodegenerative diseases, inflammation, obesity, and diabetes. In in vivo assays, it was shown that the normoglycemic rats challenged with glucose overload show significantly decreased blood glucose levels when treated with the EEHS. Taken together, the results ensure the microbiological quality and safety as well as showing the contents of carotenoids and polyunsaturated fatty acids of H. speciosa leaves. Additionally, the antioxidant, antimutagenic, anti-inflammatory, anti-Alzheimer's disease, anti-Parkinson's disease, antiobesity, and antihyperglycemic activities of the EEHS were demonstrated.

Correlation between the Potency of Flavonoids on Mushroom Tyrosinase Inhibitory Activity and Melanin Synthesis in Melanocytes

Twenty-seven flavonoids isolated from Dalbergia parviflora with vast structural diversity were screened for inhibitory activity against mushroom and murine tyrosinases using l-DOPA as the substrate. Among the flavonoids tested, only four—khrinone (5), cajanin (9), (3RS)-3′-hydroxy-8-methoxy vestitol (21), and (6aR,11aR)-3,8-dihydroxy-9-methoxy pterocarpan (27)—reacted with mushroom tyrosinase, with IC₅₀ values of 54.0, 67.9, 67.8, and 16.7 μM, respectively, and only compound 27 showed inhibitory activity against murine tyrosinase. With cell-based assays, only compounds 9 and 27 effectively inhibited melanogenesis in B16-F10 melanoma cells (by 34% and 59%, respectively), at a concentration of 15 μM, without being significantly toxic to the cells. However, the crude extract of D. parviflora and some of the flavonoid constituents appeared to increase melanin production in B16-F10 cells, suggesting that there are flavonoids with both inhibitory and stimulatory melanogenesis in the crude extract. Studies on the correlation between the enzyme-based and cell-based assays showed that only the flavonoids with IC₅₀ values below 50 μM against mushroom tyrosinase could inhibit the mammalian tyrosinase, and thus, reduce melanogenesis in B16-F10. Flavonoids with the IC₅₀ values greater than 50 μM, on the other hand, could not inhibit the mammalian tyrosinase, and had either no effect or enhancement of melanogenesis. In conclusion, the tyrosinase enzyme from mushroom is not as selective as the one from mammalian source for the enzyme-based melanogenesis inhibitory screening, and the mammalian cell-based assay appears to be a more reliable model for screening than the enzyme-based one.

Antimelanogenic Effect of Urolithin A and Urolithin B, the Colonic Metabolites of Ellagic Acid, in B16 Melanoma Cells

Antimelanogenic agents from natural sources have been widely investigated. Urolithin A (UA) and B (UB), the main gut microflora metabolites of dietary ellagic acid derivatives, have various bioactivities such as anti-inflammatory and antiaging effects. In this study, the metabolites were found to possess depigmentation efficacy by suppressing tyrosinase activity. Both UA and UB could attenuate melanogenesis in B16 melanoma cells to 55.1 ± 3.8 and 76.4 ± 17.4% of control at noncytotoxic dosage, 10 μM, respectively. UA showed comparable efficacy to positive control, 5 μM of kojic acid treatment (51.2 ± 7.8). RT-PCR results revealed that UA and UB inhibited melanin formation by affecting the catalytic activity of tyrosinase rather than its mRNA expression. Kinetics for UA and UB on tyrosinase activity revealed that their inhibition behavior toward cellular tyrosinase involved competitive inhibition. UA and UB may be potent tyrosinase inhibitors and they possess significant antimelanogenesis ability as novel skin-whitening ingredients.

Phenolic compounds and biological activities of small-size citrus: Kumquat and calamondin

Kumquat and calamondin are two small-size citrus fruits. Owing to their health benefits, they are traditionally used as folk medicine in Asian countries. However, the research on flavonoids and biological activities of kumquat and calamondin have received less attention. This review summarizes the reported quantitative and qualitative data of phenolic compositions in these two fruits. Effects of maturity, harvest time, various solvent extractions and heat treatment of phenolic compositions, and bioactivities were discussed; distributions of the forms of phenolic compounds existing in kumquat and calamondin were also summarized. Furthermore, biological activities, including antioxidant, anti-tyrosinase, antimicrobial, antitumor, and antimetabolic disorder effects, have also been discussed. Effective phenolic components were proposed for a certain bioactivity. It was found that C-glycoside flavonoids are dominant phenolic compounds in kumquat and calamondin, unlike in other citrus fruits. Up to now, biological activities and chemical characteristics of C-glycoside flavonoids in kumquat and calamondin are largely unknown.

Citrus fruits as a treasure trove of active natural metabolites that potentially provide benefits for human health

Citrus fruits, which are cultivated worldwide, have been recognized as some of the most high-consumption fruits in terms of energy, nutrients and health supplements. What is more, a number of these fruits have been used as traditional medicinal herbs to cure diseases in several Asian countries. Numerous studies have focused on Citrus secondary metabolites as well as bioactivities and have been intended to develop new chemotherapeutic or complementary medicine in recent decades. Citrus-derived secondary metabolites, including flavonoids, alkaloids, limonoids, coumarins, carotenoids, phenolic acids and essential oils, are of vital importance to human health due to their active properties. These characteristics include anti-oxidative, anti-inflammatory, anti-cancer, as well as cardiovascular protective effects, neuroprotective effects, etc. This review summarizes the global distribution and taxonomy, numerous secondary metabolites and bioactivities of Citrus fruits to provide a reference for further study. Flavonoids as characteristic bioactive metabolites in Citrus fruits are mainly introduced.

Anti-metastatic effect of supercritical extracts from the Citrus hassaku pericarp via inhibition of C-X-C chemokine receptor type 4 (CXCR4) and matrix metalloproteinase-9 (MMP-9)

The fruit of hassaku (Citrus hassaku Hort. ex Tanaka) is locally known as phalsak in Korea. Recently, the fruit extract has been known to exhibit in vivo preventive effects against UVB-induced pigmentation, antiallergic activity, and enhancement of blood fluidity. However, the exact mechanisms of how supercritical extracts of phalsak peel (SEPS) inhibits tumor metastasis and invasion are still not fully understood. We found that SEPS could downregulate the constitutive expression of both CXCR4 and HER2 in human breast cancer MDA-MB-231 cells as compared with other cells. SEPS also suppressed matrix metalloproteinase-9 (MMP-9) expression and its enzymatic activity under non-cytotoxic concentrations. Neither proteasome inhibition nor lysosomal stabilization had any effect on the SEPS-induced decrease in CXCR4 expression. A detailed study of the underlying molecular mechanisms revealed that the regulation of the downregulation of CXCR4 was at the transcriptional level, as indicated by downregulation of mRNA expression, suppression of NF-κB activity, and inhibition of chromatin immunoprecipitation activity. Suppression of CXCR4 expression by SEPS correlated with the inhibition of CXCL12-stimulated invasion of MDA-MB-231 cells. Overall, our results indicate, for the first time, that SEPS can suppress CXCR4 and MMP-9 expressions through blockade of NF-κB activation and thus has the potential to suppress metastasis of breast cancer.

Search for Skin-whitening Agent from Prunus Plants and the Molecular Targets in Melanogenesis Pathway of Active Compounds

In our research program for discovering novel skin-whitening materials, screening of extracts from flowers of some Prunus species was performed using an anti-tyrosinase assay. Among the tested plants, the flowers of P. persica showed the most potent inhibitory activity. In addition, P. persica also showed suppression of melanogenesis in B16 rat melanoma cells. The active principles of tyrosinase inhibition and suppression of melanogenesis were revealed to be an afzelin (3- O-α-L-rhamnosylkaempferol) and a flavanone, naringenin. The mechanism of the anti-melanogenesis effect of these two compounds was disclosed, for the first time, as the suppression of the expression of tyrosinase protein, which was controlled by the inhibition of phosphorylation of p38 MAPK. These findings show that these compounds could be candidates for the novel molecular target for a skin-whitening agent.

Anti-degranulating activity in rat basophil leukemia RBL-2H3 cells of flavanone glycosides and their aglycones in citrus fruits

The anti-degranulating activity of flavonoids present in Citrus fruits was comprehensively evaluated. Among these, hesperetin and naringenin, respectively aglycones of hesperidin and narirutin, showed significant activity. The targets of hesperetin and naringenin were found: hesperetin inhibited phosphorylation of Syk and Akt, while naringenin suppressed the expression of Lyn and inhibited the phosphorylation of Akt. These results suggest that hesperetin and naringenin inhibit degranulation by suppression of pathway signals and reduce the symptoms of allergy by inhibiting phosphorylation of Akt, which leads to the suppression of cytokines. In addition, hesperetin showed inhibitory activity against the degranulation induced by calcium ionophores, indicating that hesperetin exerts its inhibitory activity by stabilizing the membrane structure.

Profile of non-volatiles in whisky with regard to superoxide dismutase activity

SOD (Superoxide dismutase)-like activities of 23 kinds of single malt whisky (Scotch and Japanese) were evaluated. There was a positive correlation between SOD-like activity and the maturation age of whisky that exceeded the difference resulting from the manufacturing region. The SOD-like activity of Yamazaki 18, a typical single malt whisky in Japan, was approximately 1333 U/ml and that of non-volatile components in the whisky was 388U/mg, indicating that single malt whisky generally has a very strong SOD-like activity. To elucidate their contribution to SOD-like activity, the non-volatile components of whisky (Yamazaki 18) were ultrafiltered and separated with a Diaion HP20/water-EtOH system. Elution of the fraction less than 5000 molecular weight (<5000 MW fraction) with 60% (v/v) EtOH contributed most to SOD-like activity of the whisky. As this elution contained a considerable amount of polyphenolics, the content and SOD-like specific activity of ellagic acid, gallic acid, and lyoniresinol--the main whisky polyphenolics--were evaluated. The contribution of these compounds to the SOD-like activity of whisky was approximately 15%. Polyphenolics in whisky were relatively distributed to a higher MW fraction compared to carbohydrates in whisky, and specific activity (SOD-like activity per weight) of the >10,000 MW fraction was greater than that of the <5000 MW fraction, although the content of this fraction was low. These results indicate that various polyphenolics with higher molecular weights also contribute to the SOD-like activity of whisky together with main whisky polyphenolics.

Ascorbic acid increases the activity and synthesis of tyrosinase in B16F10 cells through activation of p38 mitogen-activated protein kinase

Ascorbic acid, a potential antioxidant, is known to inhibit melanogenesis. However, there are conflicting findings that ascorbic acid has very low stability and acts as a pro-oxidant, eventually increasing proliferation and melanin content in melanoma cells. In the present study, we explored the effects of ascorbic acid on the activity and expression of tyrosinase and melanin pigmentation in the presence and absence of α-melanocyte-stimulating hormone (α-MSH) using B16F10 melanoma cells. The mechanism by which ascorbic acid stimulated the expression of tyrosinase was also investigated. No inhibitory effect on melanin content was observed in ascorbic acid-treated cells, regardless of the presence of α-MSH. Ascorbic acid stimulated the activity and expression of tyrosinase and increased the expression of melanogenic regulatory factors, such as tyrosinase-related protein-1 (TRP-1), dihydroxyphenylalaminechrome tautomerase (TRP-2), and microphthalmia-associated transcription factor (MITF). Ascorbic acid also induced phosphorylation of p38 mitogen-activated protein kinase (MAPK). The inhibition of p38 MAPK pathway by SB203580 led to the suppression of tyrosinase, TRP-1, and TRP-2 expression in cells treated with ascorbic acid. Combined treatment with N-acetyl-L: -cysteine and/or desferrioxamine mesylate attenuated the stimulating effect of ascorbic acid on tyrosinase activation in the cells. Collectively, ascorbic acid stimulates tyrosinase activity and expression in B16F10 cells via activation of p38 MAPK signaling and subsequent up-regulation of MITF, tyrosinase, and TRP expression.

Quercetin inhibits α-MSH-stimulated melanogenesis in B16F10 melanoma cells

Quercetin is known to inhibit tyrosinase activity and melanin production in melanocytes. However, several reports suggest that quercetin has different and opposite effects on melanogenesis. This study examined the precise effects of quercetin on melanogenesis using cell-free assay systems and melanocytes. Quercetin inhibited the monophenolase and diphenolase activities of tyrosinase, and melanin synthesis in cell-free assay systems. Quercetin induced mild stimulation of the tyrosinase activity and dihydroxyphenylalaminechrome tautomerase (TRP-2) expression but only at low concentrations (<20 μm) in B16F10 melanoma cells. In contrast, the addition of 50 μm quercetin to the cells led to a significant decrease in the activity and synthesis of tyrosinase, as well as a decrease in the expression of tyrosinase-related protein-1 and TRP-2 proteins, regardless of the presence or absence of α-melanocyte stimulating hormone (α-MSH). Quercetin also reduced the intracellular cAMP and the phosphorylated protein kinase A levels in α-MSH-stimulated B16F10 cells. Moreover, quercetin (20 μm) diminished the expression and activity of tyrosinase, and melanin content in cultured normal human epidermal melanocytes. These effects were not related to its cytotoxic action. Although the in vivo effects of quercetin are still unclear, these results suggest that quercetin could play important roles in controlling melanogenesis.

Effects of unripe Citrus hassaku fruits extract and its flavanone glycosides on blood fluidity

The enhancement of blood fluidity may lead to improvements in skin problems resulting from unsmooth circulation or blood stagnation. Since a 50% ethanolic extract (CH-ext) obtained from unripe Citrus hassaku fruits may be a useful ingredient in skin-whitening cosmetics, the present study was designed to examine the effect of CH-ext on blood fluidity. CH-ext concentration-dependently inhibited in vitro collagen-induced rabbit platelet aggregation and in vitro polybrene-induced rat erythrocyte aggregation. The CH-ext showed in vitro fibrinolysis activity in fibrin plate assay. Activity-guided fractionation of the CH-ext using antiplatelet activity, inhibitory activity of erythrocyte aggregation, and fibrinolysis activity revealed that these activities of CH-ext were attributable to naringenin-7-glycoside (prunin). Successive oral administration of CH-ext to rats inhibited the lipopolysaccharide (LPS)-induced decrease of blood platelets and fibrinogen, and LPS-induced increase of fibrin degradation products (FDP) in LPS-induced disseminated intravascular coagulation (DIC) model rats. Effects of CH-ext on blood fluidity were analyzed by a micro channel array flow analyzer (MC-FAN). Preventive oral administration of CH-ext to rats showed dose-dependent reduction of the passage time of whole blood flow of the DIC model rats in comparison with that of the vehicle control rats. These results imply that CH-ext may have effects which improve effects on blood fluidity.

Three new cyclic diarylheptanoids and other phenolic compounds from the bark of Myrica rubra and their melanogenesis inhibitory and radical scavenging activities

Ten cyclic diarylheptanoids (1-10), including three new compounds: myricanone 5-O-alpha-L-arabinofuranosyl-(1-->6)-beta-D-glucopyranoside (7), myricanone 17-O-beta-D-(6'-O-galloyl)-glucopyranoside (8), and 16-methoxy acerogenin B 9-O-beta-D-apiofuranosyl-(1-->6)-beta-D-glucopyranoside (10), along with two flavonoids (11, 12), were isolated from the extracts of Myrica rubra (Myricaceae) bark. The structures of new compounds were determined on the basis of spectroscopic methods. On evaluation of compounds 1-12 against the melanogenesis in the B16 melanoma cells, six compounds, 3, 5, 7, 8, 10, and 12, exhibited inhibitory effects with 30-56% reduction of melanin content at 25 microg/mL with no or very weak toxicity to the cells (82-103% of cell viability at 25 microg/mL). In addition, upon evaluation of compounds 1-12 against the scavenging activities of free radicals [against the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical], seven compounds, 1, 3, 5, 6, 8, 11, and 12, showed potent scavenging activity [IC(50) 2-21 microM (0.6-7.3 microg/mL)].

Inhibitory effects of Fortunella japonica var. margarita and Citrus sunki essential oils on nitric oxide production and skin pathogens

A number of essential oils from citrus peels are claimed to have biological activities. Citrus peel, called 'Jin-Pi', is used in traditional medicine for digestion, severe cold, and fever. However, the antibacterial activities against skin pathogens and anti-inflammatory effects of the essential oils of Citrus sunki (JinGyul) and Fortunella japonica var. margarita (GumGyul) have not yet been described. Therefore, in this study, the essential oils of the citrus species C. sunki (CSE) and F. japonica var. margarita (FJE), both native to the island of Jeju, Korea, were examined for their anti-inflammatory and antimicrobial activities against skin pathogens. Four human skin pathogenic microorganisms, Staphylococcus epidermidis CCARM 3709, Propionibacterium acnes CCARM 0081, Malassezia furfur KCCM 12679, and Candida albicans KCCM 11282, were studied. CSE and FJE exhibited strong antimicrobial activity against most of the pathogenic bacteria and yeast strains that were tested. Interestingly, CSE and FJE even showed antimicrobial activity against antibiotic-resistant S. epidermidis CCARM 3710, S. epidermidis CCARM 3711, P. acnes CCARM9009, and P. acnes CCARM9010 strains. In addition, CSE and FJE reduced the lipopolysaccharide (LPS)-induced secretion of nitric oxide (NO) in RAW 264.7 cells, indicating that they have anti-inflammatory effects. We also analysed the chemical composition of the oils by gas chromatography-mass spectrometry (GC-MS) and identified several major components, including dl-limonene (68.18%) and beta-myrcene (4.36%) for CSE, and dl-limonene (61.58%) and carvone (6.36%) for FJE. Taken together, these findings indicate that CSE and FJE have great potential to be used in human skin health applications.

An updated review of tyrosinase inhibitors

Tyrosinase is a multifunctional, glycosylated, and copper-containing oxidase, which catalyzes the first two steps in mammalian melanogenesis and is responsible for enzymatic browning reactions in damaged fruits during post-harvest handling and processing. Neither hyperpigmentation in human skin nor enzymatic browning in fruits are desirable. These phenomena have encouraged researchers to seek new potent tyrosinase inhibitors for use in foods and cosmetics. This article surveys tyrosinase inhibitors newly discovered from natural and synthetic sources. The inhibitory strength is compared with that of a standard inhibitor, kojic acid, and their inhibitory mechanisms are discussed.