Laccase-mediated biotransformation of dihydroquercetin (taxifolin)

Advances in biochemistry and the biotechnological production of taxifolin and its derivatives

Taxifolin (dihydroquercetin) and its derivatives are medicinally important flavanonols with a wide distribution in plants. These compounds have been isolated from various plants, such as milk thistle, onions, french maritime, and tamarind. In general, they are commercially generated in semisynthetic forms. Taxifolin and related compounds are biosynthesized via the phenylpropanoid pathway, and most of the biosynthetic steps have been functionally characterized. The knowledge gained through the detailed investigation of their biosynthesis has provided the foundation for the reconstruction of biosynthetic pathways. Plant- and microbial-based platforms are utilized for the expression of such pathways for generating taxifolin-related compounds, either by whole-cell biotransformation or through reconfiguration of the genetic circuits. In this review, we summarize recent advances in the biotechnological production of taxifolin and its derivatives.

Laccase Catalyzed Oxidative Polymerization of Phloridzin: Polymer Characterization, Antioxidant Capacity and α-Glucosidase Inhibitory Activity

Phloridzin is a naturally occurring dihydrochalcone with various therapeutic properties. However, its low aqueous solubility and poor enzyme inhibitory capacity have limited its application in functional foods and medicines. Inspections of the properties of natural polymeric flavonoids suggest that these limitations could be mitigated by the polymerization of phloridzin, although to date, no relevant studies have been conducted. Here, oxidative polymerization was used to prepare polymeric phloridzin using laccase as the catalyst, and its structure, antioxidant capacity and α-glucosidase inhibitory activity were characterized. The results showed that laccase catalyzed polymerization via oxidative generation of phenolic radicals in the B ring of phloridzin to achieve the polymerization. The 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) radical scavenging capacity of the polymer (IC50, 0.48 mg/mL) was inferior to that of phloridzin (IC50, 0.20 mg/mL), but the α-glucosidase inhibitory activity of the polymer (IC50, 0.12 mg/mL) was significantly higher than that of phloridzin (IC50, 0.21 mg/mL). These effects could be attributed to the reduction of available phenolic groups and binding of the polymer to the enzyme, respectively.

Extracellular laccase from Monilinia fructicola: isolation, primary characterization and application

Laccases are enzymes belonging to the family of blue copper oxidases. Due to their broad substrate specificity, they are widely used in many industrial processes and environmental bioremediations for removal of a large number of pollutants. During last decades, laccases attracted scientific interest also as highly promising enzymes to be used in bioanalytics. The aim of this study is to obtain a highly purified laccase from an efficient fungal producer and to demonstrate the applicability of this enzyme for analytics and bioremediation. To select the best microbial source of laccase, a screening of fungal strains was carried out and the fungus Monilinia fructicola was chosen as a producer of an extracellular enzyme. Optimal cultivation conditions for the highest yield of laccase were established; the enzyme was purified by a column chromatography and partially characterized. Molecular mass of the laccase subunit was determined to be near 35 kDa; the optimal pH ranges for the highest activity and stability are 4.5-5.0 and 3.0-5.0, respectively; the optimal temperature for laccase activity is 30°C. Laccase preparation was successfully used as a biocatalyst in the amperometric biosensor for bisphenol A assay and in the bioreactor for bioremediation of some xenobiotics.

Laccase-Catalyzed Heterocoupling of Dihydroquercetin and p-Aminobenzoic Acid: Effect of the Reaction Product on Cultured Cells

Derivatization of the natural flavonoid dihydroquercetin with p-aminobenzoic acid was carried out in an ethyl acetate/citric buffer biphasic system using laccase from the fungus Trametes hirsuta. The main reaction product yield was ~68 mol %. The product was characterized by ¹H NMR, ¹³C NMR, and liquid chromatography-mass spectroscopy, and its structure was elucidated. The reaction product affected viability of cultured human rhabdomyosarcoma cells (RD cell line) in a dose-dependent manner and, therefore, can be of interest to pharmaceutical industry.

Inhibitory Mechanism of Taxifolin against α-Glucosidase Based on Spectrofluorimetry and Molecular Docking

The α-glucosidase inhibitory activity and behavior of taxifolin was first investigated by spectrofluorimetry and molecular docking. It was found that taxifolin inhibits α-glucosidase in a competitive manner with the IC50 value of 0.16 mg/mL. The intrinsic fluorescence quenching of α-glucosidase in the presence of taxifolin was observed by the static quenching mechanism. According to the thermodynamic study, the complex of taxifolin and α-glucosidase was maintained by van der Waals and hydrogen bonding. The binding mode provided by molecular docking simulation indicated the existence of hydrogen bonding between taxifolin and the amino acid residues of α-glucosidase (Glu429, Asp 568 and Glu771), which coincided with the result of fluorescence analysis.

Synthesis, characterization, solubilization, cytotoxicity and antioxidant activity of aminomethylated dihydroquercetin

A dihydroquercetin derivative (DHQA) was prepared through aminomethylation to overcome the low water solubility and bioavailability of dihydroquercetin (DHQ). DHQA was characterized through HPLC, nuclear magnetic resonance, scanning electron microscopy, X-ray diffraction, and thermogravimetric analyses. DHQA was converted into the amorphous form, but the major structure of DHQ remained unchanged. Solubilization and dissolution tests were also performed. Results showed that the solubility and dissolution rates of DHQA were approximately 16.28 and 6.31 times higher than those of DHQ, respectively. The MTT assay of DHQA showed a non-toxic effect against non-cancerous HEK-293T cells (EC₅₀ = 820.00 μM), and potent inhibitory activity against cancerous Hela cells (EC₅₀ = 138.17 μM). Finally, the antioxidant activity of DHQA was confirmed in vitro through DPPH and ABTS radical scavenging activity assays. DHQA displayed high antioxidant activities with low IC₅₀ values (0.043 and 0.042 mM, respectively). Reducing Fe³⁺ power assay indicated that DHQA exhibited higher reducing power than DHQ and ascorbic acid.