Dihydroresveratrol cellobioside and xylobioside as effective melanogenesis activators

A Fungal Versatile GH10 Endoxylanase and Its Glycosynthase Variant: Synthesis of Xylooligosaccharides and Glycosides of Bioactive Phenolic Compounds

The study of endoxylanases as catalysts to valorize hemicellulosic residues and to obtain glycosides with improved properties is a topic of great industrial interest. In this work, a GH10 β-1,4-endoxylanase (XynSOS), from the ascomycetous fungus Talaromyces amestolkiae, has been heterologously produced in Pichia pastoris, purified, and characterized. rXynSOS is a highly glycosylated monomeric enzyme of 53 kDa that contains a functional CBM1 domain and shows its optimal activity on azurine cross-linked (AZCL)-beechwood xylan at 70 °C and pH 5. Substrate specificity and kinetic studies confirmed its versatility and high affinity for beechwood xylan and wheat arabinoxylan. Moreover, rXynSOS was capable of transglycosylating phenolic compounds, although with low efficiencies. For expanding its synthetic capacity, a glycosynthase variant of rXynSOS was developed by directed mutagenesis, replacing its nucleophile catalytic residue E236 by a glycine (rXynSOS-E236G). This novel glycosynthase was able to synthesize β-1,4-xylooligosaccharides (XOS) of different lengths (four, six, eight, and ten xylose units), which are known to be emerging prebiotics. rXynSOS-E236G was also much more active than the native enzyme in the glycosylation of a broad range of phenolic compounds with antioxidant properties. The interesting capabilities of rXynSOS and its glycosynthase variant make them promising tools for biotechnological applications.

Detection and structural characterization of the metabolites of dihydroresveratrol in rats by liquid chromatography coupled to high-resolution tandem mass spectrometry

RATIONALE

Dihydroresveratrol has been demonstrated to possess a wide spectrum of bioactivities, such as anti-oxidant and anti-inflammatory effects. The aim of the present study was to investigate the metabolic profiles of dihydroresveratrol in rats.

METHODS

The in vitro metabolism was elucidated by incubating dihydroresveratrol with rat hepatocytes for 2 h at 37°C. For in vivo metabolism, dihydroresveratrol was orally administered to rats at a single dose of 50 mg/kg and the resulting biliary and urinary samples were collected. All the samples were analyzed by liquid chromatography combined with electrospray ionization high-resolution mass spectrometry. The structures of the metabolites were proposed based on their accurate masses and their MS/MS product ions.

RESULTS

A total of 16 metabolites including three phase I metabolites and 13 phase II metabolites were detected and structurally proposed. Among these metabolites, M6 and M14 were unambiguously identified as 3'-hydroxylresveratrol and resveratrol, respectively, using reference standards. Dihydroresveratrol was mainly metabolized into resveratrol (M14) and a glucuronide conjugate (M12), which were excreted into urine and bile as the major metabolites.

CONCLUSIONS

The metabolic pathways of dihydroresveratrol involved hydroxylation, dehydrogenation, glucuronidation, glutathione (GSH) conjugation and methylation. The present study provided useful information with regard to the metabolic profiles of dihydroresveratrol in rats.

Synthesis, structural revision, and tyrosinase inhibitory activity of proposed phloretin-4-O-β-D-glucopyranoside from Homalium stenophyllum

Phloretin-4-O-β-D-glucopyranoside (1), isolated from Homalium stenophyllum, was synthesized for the first time through aldol condensation and Schmidt glycosylation reactions aiming to develop a novel hydrophilic tyrosinase inhibitor. However, the specific rotation of synthetic 1 was found to be negative and different from that reported for natural product 1. Thus, L-glucoside 2 was chemically synthesized using the established synthetic route of 1, suggesting that the configuration of the natural product 1 was the same as that of 2, as their specific rotation and spectroscopic data were also the same. In addition, the evaluation of the inhibitory activity of 1 and 2 against tyrosinase indicated that 2 was 1.4 times more potent than 1, but they were both relatively weak. Therefore, the enantiomeric analogues 1 and 2 were proved to be unique tyrosinase inhibitors due to the chiral recognition from the tyrosinase active site.

Melanogenesis-Inhibitory and Cytotoxic Activities of Chemical Constituents from the Leaves of Sauropus androgynus L. Merr. (Euphorbiaceae)

A new steroid, 20-hydroxyisofucosterol (stigmasta-5,24(28)-diene-3β,20β-diol) (7), along with six known compounds 1 - 6 were isolated from the MeOH extract of the leaves of Sauropus androgynus L. Merr. (Euphorbiaceae). The structure of new steroid was determined by HR-APCI-MS and various NMR techniques in combination with literature data. Subsequently, their anti-inflammatory, cytotoxic activities against five human cell lines, as well as inhibitory activities against the α-MSH induced melanogenesis on the B16 cell line were evaluated. As the results, steroid compounds, 6 and 7 exhibited moderate cytotoxic to HL60, AZ521, SKBR3, and A549 tumor cell lines (IC₅₀ 26.9 - 45.1 μm) with high tumor selectivity for A549 relative to WI38 cell lines (SI 2.6 and 3.0, resp.). And, flavonoid compounds, 4 and 5 exhibited superior inhibitory activities against melanogenesis (67.0 - 94.7% melanin content), even with no or low toxicity to the cells (90.1 - 99.6% cell viability) at the concentrations from 10 to 100 μm. Furthermore, Western blot analysis suggested that compound 5 could inhibit melanogenesis by suppressing the protein expressions of MITF, TRP-1, TRP-2, and tyrosinase.

Upregulation of Melanogenesis and Tyrosinase Activity: Potential Agents for Vitiligo

Melanin, the compound primarily responsible in humans for hair, eye and skin pigmentation, is produced by melanocytes through a complicated process called melanogenesis that is catalyzed by tyrosinase and other tyrosinase-related proteins. The abnormal loss of melanin causes dermatological problems such as vitiligo. Hence the regulation of melanogenesis and tyrosinase activity is very important for treating hypopigmentary disorders. Many melanogenesis stimulators have been discovered during the past decade. This article reviews recent advances in research on extracts and active ingredients of plants, synthesized compounds with stimulating effect on melanin synthesis and tyrosinase activity, as well as their influence on the expression of related proteins and possible signaling pathways for the design and development of novel anti-vitiligo agents.