Different Antioxidative and Antiapoptotic Effects of Piceatannol and Resveratrol.

Resveratrol affords protection against reactive oxygen species (ROS)-related diseases via activation of SIRT1, an NAD+-dependent deacetylase. However, the low bioavailability of resveratrol limits its therapeutic applications. Since piceatannol is a hydroxyl analog of resveratrol with higher bioavailability, it could be an alternative to resveratrol. In this study, we compared the cytotoxicity, antioxidative activity, and mechanisms of cytoprotection of piceatannol with those of resveratrol. In C2C12 cells incubated with piceatannol, electrospray ionization mass spectrometry analysis showed that piceatannol was present in the intracellular fraction. A high concentration (50 µM) of piceatannol, but not resveratrol, induced mitochondrial depolarization and apoptosis. However, piceatannol at 10 µM inhibited the increase in mitochondrial ROS level induced by antimycin A, and this ROS reduction was greater than that by resveratrol. The reduction in hydrogen peroxide-induced ROS by piceatannol was also greater than that by resveratrol or vitamin C. Piceatannol reduced antimycin A-induced apoptosis more than did resveratrol. SIRT1 knockdown abolished the antiapoptotic activity of resveratrol, whereas it blocked only half of the antiapoptotic activity of piceatannol. Piceatannol, but not resveratrol, induced heme oxygenase-1 (HO1) expression, which was blocked by knockdown of the transcription factor NRF2, but not by SIRT1 knockdown. HO1 knockdown partially blocked the reduction of ROS by piceatannol. Furthermore, the antiapoptotic action of piceatannol was abolished by HO1 knockdown. Our results suggest that the therapeutic dose of piceatannol protects cells against mitochondrial ROS more than does resveratrol via SIRT1- and NRF2/HO1-dependent mechanisms. The activation of NRF2/HO1 could be an advantage of piceatannol compared with resveratrol for cytoprotection. SIGNIFICANCE STATEMENT: This study showed that piceatannol and resveratrol were different in cytotoxicity, oxidant-scavenging activities, and mechanisms of cytoprotection. Protection by piceatannol against apoptosis induced by reactive oxygen species was superior to that by resveratrol. In addition to the sirtuin 1-dependent pathway, piceatannol exerted nuclear factor erythroid 2-related factor 2/heme oxygenase-1-mediated antioxidative and antiapoptotic effects, which could be an advantage of piceatannol compared with resveratrol.

Glycosylation of Stilbene Compounds by Cultured Plant Cells.

Oxyresveratrol and gnetol are naturally occurring stilbene compounds, which have diverse pharmacological activities. The water-insolubility of these compounds limits their further pharmacological exploitation. The glycosylation of bioactive compounds can enhance their water-solubility, physicochemical stability, intestinal absorption, and biological half-life, and improve their bio- and pharmacological properties. Plant cell cultures are ideal systems for propagating rare plants and for studying the biosynthesis of secondary metabolites. Furthermore, the biotransformation of various organic compounds has been investigated as a target in the biotechnological application of plant cell culture systems. Cultured plant cells can glycosylate not only endogenous metabolic intermediates but also xenobiotics. In plants, glycosylation reaction acts for decreasing the toxicity of xenobiotics. There have been a few studies of glycosylation of exogenously administrated stilbene compounds at their 3- and 4'-positions by cultured plant cells of Ipomoea batatas and Strophanthus gratus so far. However, little attention has been paid to the glycosylation of 2'-hydroxy group of stilbene compounds by cultured plant cells. In this work, it is described that oxyresveratrol (3,5,2',4'-tetrahydroxystilbene) was transformed to 3-, 2'-, and 4'-ß-glucosides of oxyresveratrol by biotransformation with cultured Phytolacca americana cells. On the other hand, gnetol (3,5,2',6'-tetrahydroxystilbene) was converted into 2'-ß-glucoside of gnetol by cultured P. americana cells. Oxyresveratrol 2'-ß-glucoside and gnetol 2'-ß-glucoside are two new compounds. This paper reports, for the first time, the glycosylation of stilbene compounds at their 2'-position by cultured plant cells.

Synthesis of Daidzein Glycosides, α-Tocopherol Glycosides, Hesperetin Glycosides by Bioconversion and Their Potential for Anti-Allergic Functional-Foods and Cosmetics.

Daidzein is a common isoflavone, having multiple biological effects such as anti-inflammation, anti-allergy, and anti-aging. α-Tocopherol is the tocopherol isoform with the highest vitamin E activity including anti-allergic activity and anti-cancer activity. Hesperetin is a flavone, which shows potent anti-inflammatory effects. These compounds have shortcomings, i.e., water-insolubility and poor absorption after oral administration. The glycosylation of bioactive compounds can enhance their water-solubility, physicochemical stability, intestinal absorption, and biological half-life, and improve their bio- and pharmacological properties. They were transformed by cultured Nicotiana tabacum cells to 7-ß-glucoside and 7-ß-gentiobioside of daidzein, and 3'- and 7-ß-glucosides, 3',7-ß-diglucoside, and 7-ß-gentiobioside of hesperetin. Daidzein and α-tocopherol were glycosylated by galactosylation with ß-glucosidase to give 4'- and 7-ß-galactosides of daidzein, which were new compounds, and α-tocopherol 6-ß-galactoside. These nine glycosides showed higher anti-allergic activity, i.e., inhibitory activity toward histamine release from rat peritoneal mast cells, than their respective aglycones. In addition, these glycosides showed higher tyrosinase inhibitory activity than the corresponding aglycones. Glycosylation of daidzein, α-tocopherol, and hesperetin greatly improved their biological activities.

Synthesis, oxygen radical absorbance capacity, and tyrosinase inhibitory activity of glycosides of resveratrol, pterostilbene, and pinostilbene.

The stilbene compound resveratrol was glycosylated to give its 4'-O-ß-D-glucoside as the major product in addition to its 3-O-ß-D-glucoside by a plant glucosyltransferase from Phytolacca americana expressed in recombinant Escherichia coli. This enzyme transformed pterostilbene to its 4'-O-ß-D-glucoside, and converted pinostilbene to its 4'-O-ß-D-glucoside as a major product and its 3-O-ß-D-glucoside as a minor product. An analysis of antioxidant capacity showed that the above stilbene glycosides had lower oxygen radical absorbance capacity (ORAC) values than those of the corresponding stilbene aglycones. The 3-O-ß-D-glucoside of resveratrol showed the highest ORAC value among the stilbene glycosides tested, and pinostilbene had the highest value among the stilbene compounds. The tyrosinase inhibitory activities of the stilbene aglycones were improved by glycosylation; the stilbene glycosides had higher activities than the stilbene aglycones. Resveratrol 3-O-ß-D-glucoside had the highest tyrosinase inhibitory activity among the stilbene compounds tested.

Hydroxylation and Glycosylation of Phenylpropanoids by Cultured Cells of Phytolacca americana.

Hydroxylation and glycosylation of cinnamic acid, p-coumaric acid, caffeic acid, and ferulic acid were investigated using cultured plant cells of Phytolacca americana as biocatalysts. Regioselective hydroxylation at the 4-position of cinnamic acid and 3-position of p-coumaric acid was observed. Although cinnamic acid was transformed to mono-glucoside products, di-glycosylation occurred in the case of the biotransformation of p-coumaric acid, caffeic acid, and ferulic acid.

Optical Resolution of (RS)-Denopamine to (R)-Denopamine P-D- Glucoside by Glucosyltransferase from Phytolacca americana Expressed in Recombinant Escherichia coli.

The optical resolution of racemic compounds by stereoselective glucosylation was investigated using plant glucosyltransferase from Phytolacca americana expressed in recombinant Escherichia coli. The glucosyltransferase glucosylated chemoselectively the phenolic hydroxyl group of phenol compounds. The (R)-stereoselective glucosylation of (RS)-denopamine by glucosyltransferase occurred to give (R)-denopamine ß-D-glucoside.

Synthesis and pharmacological evaluation of glycosides of resveratrol, pterostilbene, and piceatannol.

To enhance their water solubility and pharmacological activities, the stilbenes resveratrol, pterostilbene, and piceatannol were glycosylated to their monoglucosides (ß-glucosides) and diglycosides (ß-maltosides) by cultured cells and cyclodextrin glucanotransferase (CGTase). Cultured cells of Phytolacca americana and glucosyltransferase (PaGT) were capable of glucosylation of resveratrol to its 3- and 4'-ß-glucosides. Pterostilbene was slightly transformed into its 4'-ß-glucoside by P. americana cells. Piceatannol was readily converted into piceatannol 4'-ß-glucoside, with the highest yield among the three substrates. The 3- and 4'-ß-glucosides of resveratrol were subjected to further glycosylation by CGTase to give 3- and 4'-ß-maltoside derivatives. The inhibitory action of resveratrol and pterostilbene toward histamine release induced with compound 48/80 from rat peritoneal mast cells was improved by ß-glucosylation and/or ß-maltosylation (i.e., the inhibitory activity for histamine release of the 3- and 4'-ß-glucosides of resveratrol, the 3- and 4'-ß-maltosides of resveratrol, and the 4'-ß-glucoside of pterostilbene was higher than that of the corresponding aglycones, resveratrol and pterostilbene, respectively). In addition, the phosphodiesterase (PDE) inhibitory activity of resveratrol and pterostilbene was enhanced by ß-glucosylation and/or ß-maltosylation (i.e., the PDE inhibitory activities of the 3- and 4'-ß-glucosides of resveratrol, the 4'-ß-maltoside of resveratrol, and the 4'-ß-glucoside of pterostilbene were higher than those of the corresponding aglycones, resveratrol and pterostilbene, respectively).

Regioselective Glycosylation of 3-, 5-, 6-, and 7-Hydroxyflavones by Cultured Plant Cells.

Regioselective glycosylation of 3-, 5-, 6-, and 7-hydroxyflavones was investigated using cultured plant cells of Eucalyptus perriniana and Phytolacca americana as biocatalysts. 3- and 7-Hydroxyflavones were practically glycosylated into the corresponding ß-D-glucosides by E. perriniana and P. americana.

Enzymatic Synthesis of Quercetin Monoglucopyranoside and Maltooligosaccharides.

Quercetin 3-O-ß-monoglucopyranoside and quercetin 3-O-ß-maltooligosaccharide were synthesized from quercetin using glucosyltransferase-3 from Phytolacca americana and cyclodextrin glucanotransferase.

Identification of Stevioside Using Tissue Culture-Derived Stevia (Stevia rebaudiana) Leaves.

Stevioside is a natural sweetener from Stevia leaf, which is 300 times sweeter than sugar. It helps to reduce blood sugar levels dramatically and thus can be of benefit to diabetic people. Tissue culture is a very potential modern technology that can be used in large-scale disease-free stevia production throughout the year. We successfully produced stevia plant through in vitro culture for identification of stevioside in this experiment. The present study describes a potential method for identification of stevioside from tissue culture-derived stevia leaf. Stevioside in the sample was identified using HPLC by measuring the retention time. The percentage of stevioside content in the leaf samples was found to be 9.6%. This identification method can be used for commercial production and industrialization of stevia through in vitro culture across the world.

Glycosylation of quercetin with cultured plant cells and cyclodextrin glucanotransferase.

Quercetin was glucosylated by cultured plant cells of lpomoea batatas to its 3- and 7-O-beta-D-glucosides, and 3,7-O-beta-D-diglucoside. On the other hand, further glycosylation of quercetin 3-O-beta-D-glucoside by cyclodextrin glucanotransferase gave the 3-O-beta-maltoside, 3-O-beta-maltotrioside, and 3-O-[beta-maltotetraosides of quercetin.

Glycosylation of artepillin C with cultured plant cells of Phytolacca americana.

Biotransformation of artepillin C was investigated using cultured plant cells as biocatalysts. Artepillin C was converted into its 4- and 9-beta-D-glucosides, and 4,9-beta-D-diglucoside by cultured cells of Phytolacca americana. In contrast, cultured lpomoea batatas cells glucosylated artepillin C to only its 4- and 9-beta-D-glucosides.