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Excessive melanin formation has been linked to various skin disorders such as hyperpigmentation and skin cancer. Tyrosinase is the most prominent target for inhibitors of melanin production. In this study, we investigated whether arbutin and its prodrug, arbutin undecylenic acid ester, might inhibit phenoloxidase (PO), a tyrosinase-like enzyme. Molecular docking simulation results suggested that arbutin and arbutin undecylenic acid ester can bind to the substrate-binding pocket of PO. Arbutin undecylenic acid ester with an IC50 6.34 mM was effective to inhibit PO compared to arbutin (IC50 29.42 mM). In addition, arbutin undecylenic acid ester showed low cytotoxicity in Drosophila S2 cells and the compound inhibited the melanization reaction. Therefore, the results of this study have demonstrated that arbutin undecylenic acid ester as a potential inhibitor of PO. We successfully designed a new platform utilizing Drosophila melanogaster and Bombyx mori as animal models propounding fast, cheap, and high effectiveness in method to screen tyrosinase inhibitors.

Pseudomonas entomophila is a highly pathogenic bacterium that infects insects. It is also used as a suitable model pathogen to analyze Drosophila’s innate immunity. P. entomophila’s virulence is largely derived from Monalysin, a β-barrel pore-forming toxin that damages Drosophila tissues, inducing necrotic cell death. Here we report the first and efficient purification of endogenous Monalysin and its characterization. Monalysin is successfully purified as a pro-form, and trypsin treatment results in a cleaved mature form of purified Monalysin that kills Drosophila cell lines more effectively. Adult flies are susceptible to the injection of mature Monalysin, and humoral innate immunity is activated perhaps not by peptidoglycan, but tissue damage. Electrophysiological measurement of Monalysin in a lipid membrane with an on-chip device confirms that Monalysin forms a pore, in a cleavage-dependent manner, and provides a pore-size estimate of Monalysin using the current amplitude for a single pore. Atomic Force Microscope (AFM) analysis displays its structure in a solution and shows that active-Monalysin is stable and composed of an 8-mer complex; this observation is consistent with mass spectrometry data. AFM analysis also shows the 8-mer structure of active-Monalysin in a lipid bilayer, and real-time imaging demonstrates the moment at which Monalysin is inserted into the lipid membrane. These results collectively suggest that endogenous Monalysin is indeed a pore-forming toxin composed of a rigid structure before pore formation in the lipid membrane. The endogenous Monalysin characterized in this study could be a desirable tool for analyzing Drosophila’s immunity and the flies’ defense mechanisms against entomopathogenic bacteria.

Objective: The objective of the study was to obtain a flavone derivative compound through N-bromosuccinimide (NBS) reducing the reaction. Theantioxidant activity of the synthetic compound was then assayed by the 2,2-diphenyl-1-picrylhydrazyl method.Methods: Chalcone (3 mmol) as intermediate precursor was suspended with dimethyl sulfoxide and reacted with NBS (3 mmol), stirred at roomtemperature for 25 min and diluted in cold water. The synthesis of flavone derivatives resulted in yellow crystalline powder, freely soluble in methanoland ethanol, renamed 60% with a melting point of 87.7°C. Detection by thin-layer chromatography using hexane:chloroform (2:1) showed single spotwith Rf = 0.38 which is different from the Rf value of the starting compound (chalcone, 0.66 and 0.78).Results: The results of the characterization of the synthesized compound using ultraviolet-visible and Fourier transform-infared showed the groupcharacteristic containing C=C (1604.77 and 1639.49 cm-1), C=O (1681.93 cm-1), C-O-C (1242.16 cm-1), Ar-H (3032.1 and 3062.96 cm-1), and C-Br(663.51 cm-1) at maximum absorption of wavelength 253 nm.Conclusion: The synthesis of flavone using NBS resulted in 3-bromo-flavone with a weak antioxidant activity.