Thio-barbiturate-derived compounds are novel antioxidants to prevent LPS-induced inflammation in the liver.

Liver inflammation is closely associated with metabolic syndrome. Oxidative stress plays a synergistic role in inflammation by activating nuclear factor kappa B (NF-κB) signaling in the liver. Therefore, substantial efforts have been made to develop compounds that inhibit the generation of oxidative stress and activation of NF-κB. We synthesized twenty-six novel 5-(substituted benzyl)-2-oxo- and 5-(substituted benzyl)-2-thioxo-dihydropyrimidine-4,6(1H,5H)-dione derivatives for the development of potential antioxidants and examined their biological activities in vitro and in vivo. Thio-barbiturate-derived compounds 5-[4-hydroxy-3-methoxybenzy]-2-thioxodihydropyrimidine-4,6[1H,5H]-dione (2d) and 5-[4-hydroxy-3,5-methoxybenzy]-2-thioxodihydropyrimidine-4,6[1H,5H]-dione (2l) had the strongest inhibitory effect on reactive oxygen species and peroxynitrite generation in vitro. Furthermore, oral administration of compounds 2d and 2l in mice notably suppressed lipopolysaccharide (LPS)-induced oxidative stress and NF-κB activation in the liver. Because macrophages play an essential role in liver inflammation, we investigated the effects of these compounds on inflammatory signaling in LPS-induced RAW264.7 macrophages. LPS-induced NF-κB activation and protein expression of cyclooxygenase 2 and inducible nitric oxide synthase were inhibited by pretreatment of these compounds in macrophages. In parallel with this finding, the phosphatase and tensin homolog deleted on chromosome 10 (PTEN) and AKT signalings, which are upstream activators of p65, were decreased by these compounds in macrophages. Our study suggests that compounds 2d and 2l inhibit oxidative stress and NF-кB-mediated inflammation, at least partially, through suppressing PTEN/AKT signaling. Therefore, these compounds may be useful as therapeutic agents for the amelioration of inflammatory diseases.

(Z)-5-(2,4-Dihydroxybenzylidene)thiazolidine-2,4-dione Prevents UVB-Induced Melanogenesis and Wrinkle Formation through Suppressing Oxidative Stress in HRM-2 Hairless Mice.

Background. Uncontrolled melanogenesis and wrinkle formation are an indication of photoaging. Our previous studies demonstrated that (Z)-5-(2,4-dihydroxybenzylidene)thiazolidine-2,4-dione (MHY498) inhibited tyrosinase activity and melanogenesis in vitro. Objective. To examine in vivo effects of MHY498 as an antiaging compound on UVB-induced melanogenesis and wrinkle formation, we topically applied MHY498 on dorsal skin of HRM-2 hairless mice. Methods. Using histological analysis, we evaluated effects of MHY498 on melanogenesis and wrinkle formation after UVB exposure. In addition, related molecular signaling pathways were examined using western blotting, fluorometric assay, and enzyme-linked immunosorbent assay. Results. MHY498 suppressed UVB-induced melanogenesis by inhibiting phosphorylation of CREB and translocation of MITF protein into the nucleus, which are key factors for tyrosinase expression. Consistently, tyrosinase protein levels were notably reduced in the dorsal skin of the hairless mice by MHY498 treatment. Furthermore, MHY498 inhibited UVB-induced wrinkle formation and collagen fiber destruction by increasing type 1 procollagen concentration and decreasing protein expression levels of MMPs, which play an essential role in collagen fiber degradation. As a mechanism, MHY498 notably ameliorated UVB-induced oxidative stress and NF-κB activation in the dermal skin of the hairless mice. Conclusion. Our study suggests that MHY498 can be used as a therapeutic or cosmetic agent for preventing uncontrolled melanogenesis and wrinkle formation.

Salicylideneamino-2-thiophenol modulates nuclear factor-κB through redox regulation during the aging process.

AIM: Many intracellular components have been implicated in the regulation of redox homeostasis, but homeostasis can be unbalanced by reactive species (RS), which also probably contribute to underlying inflammatory processes. Nuclear factor-κB (NF-κB) is a well-known redox-sensitive transcription factor that controls the genes responsible for regulating inflammation. METHODS: In the present study, the authors investigated the effect of short-term salicylideneamino-2-thiophenol (SAL-2) administration on the modulation of pro-inflammatory NF-κB through redox regulation in aged rats. In addition, we compared the effects of SAL-2 and caloric restriction (CR) on inflammation and redox balance. The subjects were 24-month-old (old) Fischer 344 rats administered SAL-2 (10 mg/kg/day) by dietary supplementation or placed on a 30% restricted diet for 10 days, and 6-month-old (young) rats fed ad libitum for 10 days. RESULTS: We found that NF-κB activation and the expressions of its related genes (vascular cell adhesion molecule-1, intercellular adhesion molecule-1, cyclooxygenase-2 and inducible nitric oxide synthase) were suppressed by SAL-2 supplementation in old CR rats to the levels observed in young rats. In addition, our molecular studies showed that the inhibitory effect of SAL-2 on the activation of NF-κB was mediated by the ability of SAL-2 to block the nuclear translocations of cytosolic thioredoxin and redox factor-1. CONCLUSION: These findings strongly indicate that SAL-2 stabilizes age-related redox imbalance and modulates the signal transduction pathway involved in the age-associated molecular inflammatory process.

Anti-melanogenic effect of (Z)-5-(2,4-dihydroxybenzylidene) thiazolidine-2,4-dione, a novel tyrosinase inhibitor.

We synthesized (Z)-5-(2,4-dihydroxybenzylidene)thiazolidine-2,4-dione (MHY498) as a potential tyrosinase inhibitor. MHY498 potently inhibited mushroom tyrosinase activity (mean IC50 = 3.55 µM) in a dose-dependent manner. MHY498 was more potent than the well-known tyrosinase inhibitor, kojic acid (mean IC50 = 22.79 µM). When tested in B16F10 melanoma cells treated with α-melanocyte stimulating hormone (α-MSH), MHY498 inhibited murine tyrosinase activity and decreased melanin production without inducing cytotoxicity. Docking models showed that the binding affinity of MHY498 to tyrosinase was higher than that of kojic acid, and docking simulation results indicated that the tyrosinase binding moieties of MHY498 and kojic acid were similar. Western blotting showed that tyrosinase inhibition by MHY498 partly resulted from the expressional modulations of tyrosinase and its transcription factor, microphthalmia-associated transcription factor, via the cAMP-PKA-CREB pathway. These findings suggest that MHY498 could be useful as an antimelanogenic agent for the prevention and treatment of diseases associated with skin pigmentation.

The inhibitory effect of a synthetic compound, (Z)-5-(2,4-dihydroxybenzylidene) thiazolidine-2,4-dione (MHY498), on nitric oxide-induced melanogenesis.

Nitric oxide (NO) and the NO/PKG signaling pathway play crucial roles in ultraviolet (UV)-induced melanogenesis, which is known to be related to the induction of tyrosinase. In an attempt to find a novel anti-melanogenic agent, we synthesized (Z)-5-(2,4-dihydroxybenzylidene)thiazolidine-2,4-dione (MHY498). The purpose of this study was to investigate the effect of MHY498 on NO levels and on the NO-mediated signaling pathway using an in vitro model of melanogenesis. MHY498 inhibited 200 µM sodium nitroprusside (SNP, a NO donor)-induced NO generation, dose-dependently and suppressed tyrosinase activity and melanin synthesis induced by SNP in B16F10 melanoma cells. To investigate the effect of MHY498 on NO-mediated signaling pathway, guanosine cyclic 3',5'-monophosphate (cGMP) activities were measured using a cGMP EIA Kit and western blotting was performed to determine the effects of MHY498 on the gene expressions of tyrosinase and microphthalmia-associated transcription factor (MITF). The increased activity of cGMP by SNP was reduced dose-dependently by pretreatment with MHY498. Furthermore, MHY498 suppressed the expressions of tyrosinase and MITF stimulated by SNP. This study shows that enhancement of tyrosinase gene expression via the cGMP pathway is a probable primary mechanism of NO-induced melanogenesis and that the NO-mediated signaling pathway with the expression of MITF enhances melanogenesis. In addition, MHY498 was found to scavenge NO and to suppress the activity of the NO-mediated signaling pathway, and thus, to subsequently down-regulate tyrosinase expression and melanogenesis. This study suggests that MHY498 is a promising anti-melanogenic agent that targets the NO-induced cGMP signaling pathway.

De novo tyrosinase inhibitor: 4-(6,7-dihydro-5H-indeno[5,6-d]thiazol-2-yl)benzene-1,3-diol (MHY1556).

In this study, we have synthesized and studied de novo tyrosinase inhibitor, MHY1556, which showed significantly better efficacy than other pre-existing tyrosinase inhibitors in vitro experiments. The IC50 value of MHY1556 was 0.50µM which was significantly lower than that of kojic acid (IC50=53.95µM), which is a well-known tyrosinase inhibitor and was used as a positive control in this study. We predicted the tertiary structure of tyrosinase, simulated the docking with compound MHY1556 and confirmed that the compound strongly interacts with mushroom tyrosinase residues. Substitutions with a hydroxy group at both R1 and R3 of the phenyl ring indicated that these groups play a major role in the high binding affinity to tyrosinase, especially through the hydrogen bonding interaction of the hydroxyl group at R1 with GLY281. In addition, MHY1556 showed concentration-dependent inhibitory effects in melanin content assay where B16F10 melanoma cells were treated with α-melanocyte stimulating hormone (α-MSH), and also there is no significant cytotoxicity of this compound in cell viability assay conducted in B16F10 melanoma cells. The tyrosinase activity assay results with MHY1556 also support its potent inhibitory effects. Therefore, our data strongly suggest MHY1556 suppresses the melanogenesis via a tyrosinase inhibitory effect.

Ginsenoside Rd inhibits the expressions of iNOS and COX-2 by suppressing NF-κB in LPS-stimulated RAW264.7 cells and mouse liver.

Ginsenoside Rd is a primary constituent of the ginseng rhizome and has been shown to participate in the regulation of diabetes and in tumor formation. Reports also show that ginsenoside Rd exerts anti-oxidative effects by activating anti-oxidant enzymes. Treatment with ginsenoside Rd decreased nitric oxide and prostaglandin E2 (PGE2) in lipopolysaccharides (LPS)-challenged RAW264.7 cells and in ICR mouse livers (5 mg/kg LPS; LPS + ginsenoside Rd [2, 10, and 50 mg/kg]). Furthermore, these decreases were associated with the down-regulations of inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2 and of nuclear factor (NF)-κB activity in vitro and in vivo. Our results indicate that ginsenoside Rd treatment decreases; 1) nitric oxide production (40% inhibition); 2) PGE2 synthesis (69% to 93% inhibition); 3) NF-κB activity; and 4) the NF-κB-regulated expressions of iNOS and COX-2. Taken together, our results suggest that the anti-inflammatory effects of ginsenoside Rd are due to the down-regulation of NF-κB and the consequent expressional suppressions of iNOS and COX-2.

Inhibitory action of salicylideneamino-2-thiophenol on NF-κB signaling cascade and cyclooxygenase-2 in HNE-treated endothelial cells.

In the present study, the anti-inflammatory effect of salicylideneamino-2-thiophenol (SAL-2), a derivative of salicylate, on a potent oxidant 4-hydroxynonenal (HNE)-induced oxidative stress was investigated using rat prostate endothelial (YPEN-1) cells. We focused on anti-inflammatory activity of SAL-2 which was determined by its ability to suppress COX-2 and iNOS gene expression through suppression of NF-κB and redox regulation. We found that SAL-2 effectively inhibited HNE-induced reactive species generation, while upregulated GSH/GSSG ratio. Prostagrandin (PG) E2 production stimulated by arachidonic acid was suppressed by SAL-2. SAL-2 also downregulated COX-2 and iNOS expression induced by HNE, but salicylate did not. We found that SAL-2 inhibited HNE-mediated IKK phosphorylation, IκBα degradation and nuclear translocation of p65 which are linked to NF-κB activation. Furthermore, SAL-2 inhibited HNE-induced activation of mitogen-activated protein kinases. Collectively, SAL-2 inhibited COX-2 and iNOS gene expression through suppression of NF-κB leading to the inhibition of PGE2 synthesis. Based on these data, we propose that with its combined effect on strong anti-oxidant and anti-inflammatory action, SAL-2 can be a potent anti-inflammatory agent for treatment of inflammatory-related diseases.

A novel synthesized tyrosinase inhibitor: (E)-2-((2,4-dihydroxyphenyl)diazenyl)phenyl 4-methylbenzenesulfonate as an azo-resveratrol analog.

We synthesized a novel series of (E)-2-((substituted phenyl)diazenyl)phenyl 4-methylbenzenesulfonate derivatives (2 and 3) and (E)-2-((substituted phenyl)diazenyl)phenol derivatives (4 and 5), and conducted an evaluation in order to determine their inhibitory effects on mushroom tyrosinase, with the aim of discovering a tyrosinase inhibitor. Most of the compounds (3-5) exhibited higher inhibitory effects than kojic acid (IC(50) = 49.08 µM), a representative tyrosinase inhibitor. A novel synthesized compound, (E)-2-((2,4-dihydroxyphenyl)diazenyl)phenyl 4-methylbenzenesulfonate (3), showed the best results with an IC(50) of 17.85 µM, and showed competitive inhibition on Lineweaver-Burk plots, as further confirmed by the docking results. In addition, active compounds 3-5 were not cytotoxic to cultured B16F10 cells at the concentrations tested, and inhibited both tyrosinase and melanin synthesis. Therefore the active compounds (3-5) might be considered excellent candidates for use in the development of therapeutic agents for diseases associated with hyperpigmentation.

Molecular docking studies of (1E,3E,5E)-1,6-Bis(substituted phenyl)hexa-1,3,5-triene and 1,4-Bis(substituted trans-styryl)benzene analogs as novel tyrosinase inhibitors.

We simulated the docking of the tertiary structure of mushroom tyrosinase with our compounds. From the structure-tyrosinase inhibitory activity relationship, it is notable that compounds 4, 8 and 11 showed similar or better activity rates than kojic acid which was used as a positive control. Compounds 17, 21, and 23 among benzene analogs that possess the same substituent showed significantly lower tyrosinase inhibitory effects. Therefore, we have confirmed that among the compounds showing better tyrosinase inhibitory effects than kojic acid, the compounds with triene analogs have better tyrosinase inhibitory effect than the compounds with benzene analogs. Docking simulation suggested the mechanism of compounds by several key residues which had possible hydrogen bonding interactions. The pharmacophore model underlined the features of active compounds, 4,4'-((1E,3E,5E)-hexa-1,3,5-triene-1,6-diyl)diphenol, 5,5'-((1E,3E,5E)-hexa-1,3,5-triene-1,6-diyl)bis(2-methoxy-phenol), and 5,5'-((1E,3E,5E)-hexa-1,3,5-triene-1,6-diyl)dibenzene-1,3-diol among triene derivatives which had several hydrogen bond groups on both terminal rings. The soundness of the docking results and the agreement with the pharmacophores suggest that it can be conveniently exploited to design inhibitors with an improved affinity for tyrosinase.

Identification of the dichotomous role of age-related LCK in calorie restriction revealed by integrative analysis of cDNA microarray and interactome.

Among the many experimental paradigms used for the investigation of aging, the calorie restriction (CR) model has been proven to be the most useful in gerontological research. Exploration of the mechanisms underlying CR has produced a wealth of data. To identify key molecules controlled by aging and CR, we integrated data from 84 mouse and rat cDNA microarrays with a protein-protein interaction network. On the basis of this integrative analysis, we selected three genes that are upregulated in aging but downregulated by CR and two genes that are downregulated in aging but upregulated by CR. One of these key molecules is lymphocyte-specific protein tyrosine kinase (LCK). To further confirm this result on LCK, we performed a series of experiments in vitro and in vivo using kidneys obtained from aged ad libitum-fed and CR rats. Our major significant findings are as follows: (1) identification of LCK as a key molecule using integrative analysis; (2) confirmation that the age-related increase in LCK was modulated by CR and that protein tyrosine kinase activity was decreased using a LCK-specific inhibitor; and (3) upregulation of LCK leads to NF-κB activation in a ONOO(-) generation-dependent manner, which is modulated by CR. These results indicate that LCK could be considered a target attenuated by the anti-aging effects of CR. Integrative analysis of cDNA microarray and interactome data are powerful tools for identifying target molecules that are involved in the aging process and modulated by CR.

Ferulate protects the epithelial barrier by maintaining tight junction protein expression and preventing apoptosis in tert-butyl hydroperoxide-induced Caco-2 cells.

Epithelial barrier function is determined by both transcellular and paracellular permeability, the latter of which is mainly influenced by tight junctions (TJs) and apoptotic leaks within the epithelium. We investigated the protective effects of ferulate on epithelial barrier integrity by examining permeability, TJ protein expression, and apoptosis in Caco-2 cells treated with tert-butyl hydroperoxide (t-BHP), a strong reactive species inducer. Caco-2 cells pretreated with ferulate (5 or 15 µM) were exposed to t-BHP (100 µM), and ferulate suppressed the t-BHP-mediated increases in reactive species and epithelial permeability in Caco-2 cells. Moreover, ferulate inhibited epithelial cell leakage induced by t-BHP, which was accompanied by decreased expression of the TJ proteins zonula occludens-1 and occludin. In addition, pretreatment with ferulate markedly protected cells against t-BHP-induced apoptosis, as evidenced by decreased nuclear condensation, cytochrome c release, and caspase-3 cleavage and an increased Bax/Bcl-2 ratio. These results suggest that ferulate protects the epithelial barrier of Caco-2 cells against oxidative stress, which results in increased epithelial permeability, decreased TJ protein expression, and increased apoptosis. The most significant finding of our study is the demonstration of protective, ferulate-mediated antioxidant effects on barrier integrity, with a particular focus on intracellular molecular mechanisms.

Synthesis of novel azo-resveratrol, azo-oxyresveratrol and their derivatives as potent tyrosinase inhibitors.

Ten azo compounds including azo-resveratrol (5) and azo-oxyresveratrol (9) were synthesized using a modified Curtius rearrangement and diazotization followed by coupling reactions with various phenolic analogs. All synthesized compounds were evaluated for their mushroom tyrosinase inhibitory activity. Compounds 4 and 5 exhibited high tyrosinase inhibitory activity (56.25% and 72.75% at 50 µM, respectively). The results of mushroom tyrosinase inhibition assays indicate that the 4-hydroxyphenyl moiety is essential for high inhibition and that 3,5-dihydroxyphenyl and 3,5-dimethoxyphenyl derivatives are better for tyrosinase inhibition than 2,5-dimethoxyphenyl derivatives. Particularly, introduction of hydroxyl or methoxy group into the 4-hydroxyphenyl moiety diminished or significantly reduced mushroom tryosinase inhibition. Among the synthesized azo compounds, azo-resveratrol (5) showed the most potent mushroom tyrosinase inhibition with an IC(50) value of IC(50)=36.28 ± 0.72 µM, comparable to that of resveratrol, a well-known tyrosinase inhibitor.

Design, synthesis, and evaluation of (E)-N-substituted benzylidene-aniline derivatives as tyrosinase inhibitors.

We attempted to design and synthesize (E)-N-substituted benzylidene-hydroxy or methoxy-aniline derivatives and to evaluate their inhibitory effect on tyrosinase activity and anti-melanogenesis activity in murine B16F10 melanoma cells. Derivatives with a 4-methoxy- or 4-hydroxy-anilino group exerted more potent inhibition against mushroom tyrosinase than those with a 2-hydroxyanilino group. (E)-4-((4-Hydroxyphenylimino)methyl)benzene-1,2-diol exhibited the most potent and non-competitive inhibition on mushroom tyrosinase showing an IC(50) of 17.22 ± 0.38 µM and being more effective than kojic acid (51.11 ± 1.42 µM). This compound decreased melanin production stimulated by the alpha-melanocyte-stimulating hormone and inhibited murine tyrosinase activity in a dose-dependent manner. Therefore, we propose (E)-4-((4-hydroxyphenylimino)methyl)benzene-1,2-diol as a new candidate of potent tyrosinase inhibitors that could be used as therapeutic agent with safe skin-whitening efficiency.

Suppression of melanogenesis by a newly synthesized compound, MHY966 via the nitric oxide/protein kinase G signaling pathway in murine skin.

BACKGROUND: Ultraviolet B (UVB) radiation is the main physiological stimulus for skin pigmentation. Nitric oxide (NO) and the NO/PKG signaling pathway play an important role in UVB-induced melanogenesis, which is related to the induction of expression of tyrosinase. In an attempt to find a novel anti-melanogenic agent, we synthesized a new compound, 2-bromo-4-(5-chloro-benzo[d]thiazol-2-yl) phenol (MHY966). OBJECTIVE: The purpose of this study was to investigate the action of MHY966 on NO and the NO-mediated signaling pathway using in vitro and in vivo models of melanogenesis. METHODS: NO generation, melanin synthesis, and the expression of tyrosinase and PKG were measured in B16F10 melanoma cells to verify the anti-melanogenic effect of MHY966 in vitro. Next, melanin-possessing hairless mice were pre-treated with MHY966 and then irradiated with UVB repeatedly. Morphological, histological, and biochemical analyses including the expressions of PKG, tryosinase and nuclear MITF, and productions of nitric oxide, peroxynitrite and ROS were conducted. RESULTS: MHY966 effectively inhibited NO generation and subsequent melanin synthesis induced by sodium nitroprusside, an NO donor, and suppressed the expression of tyrosinase and PKG. Topical application of MHY966 dose-dependently attenuated UVB-induced pigmentation in a mouse model. This hypopigmentation effect induced by MHY966 treatment was mediated by the down-regulation of tyrosinase, PKG, and nuclear MITF, which was accompanied by decreased NO and NO-related oxidative stress. CONCLUSION: The novel compound, MHY966 had an inhibitory effect on NO generation and the NO-mediated signaling pathway leading to the down-regulation of tyrosinase. The significance of the present study is the finding of a promising anti-melanogenic agent targeting the NO/PKG signaling pathway.

Synthesis and preliminary in vitro biological evaluation of 5-chloro-2-(substituted phenyl)benzo[d]thiazole derivatives designed as novel antimelanogenesis agents.

We describe the design, synthesis, and biological activities of 5-chloro-2-(substituted phenyl)benzo[d]thiazole derivatives as novel tyrosinase inhibitors. Among them, 4-(5-chloro-2,3-dihydrobenzo[d]thiazol-2-yl)-2,6-dimethoxyphenol (MHY884) and 2-bromo-4-(5-chloro-benzo[d]thiazol-2-yl)phenol (MHY966) showed inhibitory activity higher than or similar to kojic acid, against mushroom tyrosinase. Therefore, we carried out kinetic studies on the two compounds with potent tyrosinase inhibitory effects. Kinetic analysis of tyrosinase inhibition revealed that all of these compounds are competitive inhibitors. MHY884 and MHY966 effectively inhibited tyrosinase activity and reduced melanin levels in B16 cells treated with α-melanocyte stimulating hormone (α-MSH). These data strongly suggest that the newly synthesized compounds MHY884 and MHY966 could suppress production of melanin via inhibition of tyrosinase activity.

Inhibitory effect of mTOR activator MHY1485 on autophagy: suppression of lysosomal fusion.

Autophagy is a major degradative process responsible for the disposal of cytoplasmic proteins and dysfunctional organelles via the lysosomal pathway. During the autophagic process, cells form double-membraned vesicles called autophagosomes that sequester disposable materials in the cytoplasm and finally fuse with lysosomes. In the present study, we investigated the inhibition of autophagy by a synthesized compound, MHY1485, in a culture system by using Ac2F rat hepatocytes. Autophagic flux was measured to evaluate the autophagic activity. Autophagosomes were visualized in Ac2F cells transfected with AdGFP-LC3 by live-cell confocal microscopy. In addition, activity of mTOR, a major regulatory protein of autophagy, was assessed by western blot and docking simulation using AutoDock 4.2. In the result, treatment with MHY1485 suppressed the basal autophagic flux, and this inhibitory effect was clearly confirmed in cells under starvation, a strong physiological inducer of autophagy. The levels of p62 and beclin-1 did not show significant change after treatment with MHY1485. Decreased co-localization of autophagosomes and lysosomes in confocal microscopic images revealed the inhibitory effect of MHY1485 on lysosomal fusion during starvation-induced autophagy. These effects of MHY1485 led to the accumulation of LC3II and enlargement of the autophagosomes in a dose- and time-dependent manner. Furthermore, MHY1485 induced mTOR activation and correspondingly showed a higher docking score than PP242, a well-known ATP-competitive mTOR inhibitor, in docking simulation. In conclusion, MHY1485 has an inhibitory effect on the autophagic process by inhibition of fusion between autophagosomes and lysosomes leading to the accumulation of LC3II protein and enlarged autophagosomes. MHY1485 also induces mTOR activity, providing a possibility for another regulatory mechanism of autophagy by the MHY compound. The significance of this study is the finding of a novel inhibitor of autophagy with an mTOR activating effect.

Evaluation of in vitro and in vivo anti-melanogenic activity of a newly synthesized strong tyrosinase inhibitor (E)-3-(2,4 dihydroxybenzylidene)pyrrolidine-2,5-dione (3-DBP).

BACKGROUND: Tyrosinase inhibitors have become increasingly important because of their ability to inhibit the synthesis of the pigment melanin. A search for new agents with strong tyrosinase activity led to the synthesis of the tyrosinase inhibitor (E)-3-(2,4-dihydroxybenzylidene)pyrrolidine-2,5-dione (3-DBP). METHODS: The inhibitory effect of 3-DBP on tyrosinase activity and melanin production was examined in murine melanoma B16F10 cells. Additional experiments were performed using HRM2 hairless mice to demonstrate the effects of 3-DBP in vivo. RESULTS: The novel compound, 3-DBP, showed an inhibitory effect against mushroom tyrosinase (IC50=0.53 µM), which indicated that it was more potent than the well-known tyrosinase inhibitor kojic acid (IC50=8.2 µM). When tested in B16F10 melanoma cells treated with α-melanocyte stimulating hormone (α-MSH), 3-DBP also inhibited murine tyrosinase activity, which in turn induced a decrease in melanin production in these cells. The anti-melanogenic effect of 3-DBP was further verified in HRM2 hairless mice. The skin-whitening index (L value) of HRM2 hairless mice treated with 3-DBP before irradiation with UVB was greater than that of UVB-irradiated mice that were not treated with 3-DBP. GENERAL SIGNIFICANCE: The newly synthesized 3-DBP has a potent inhibitory effect on tyrosinase. In addition to an in vitro investigation of the effects of 3-DBP on tyrosinase, in vivo studies using an HRM2 hairless mouse model demonstrated the anti-melanogenic potency of 3-DBP. Our newly synthesized 3-DBP showed efficient tyrosinase inhibitory effect in vivo and in vitro. Our finding suggests that 3-DBP can be an effective skin-whitening agent.