Molecular encapsulation and bioactivity of gnetol, a resveratrol analogue, for use in foods.

BACKGROUND: Gnetol is a stilbene whose characterization and bioactivity have been poorly studied. It shares some bioactivities with its analogue resveratrol, such as anti-inflammatory, anti-thrombotic, cardioprotective and anti-cancer activities. However, the low solubility of stilbenes may limit their potential applications in functional foods. Encapsulation in cyclodextrins could be a solution. RESULTS: The antioxidant activity of gnetol was evaluated by 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation and ferric reducing antioxidant power methods (Trolox equivalents 13.48 µmol L-1 and 37.08 µmol L-1 respectively at the highest concentration) and it was higher than that of resveratrol, and depending on the method, similar or higher to that of oxyresveratrol. Spectrophotometric and spectrofluorimetric characterization of gnetol is published for the first time. Moreover, its water solubility was determined and improved almost threefold after its molecular encapsulation in cyclodextrins, as well as its stability after storage for a week. A physicochemical and computational study revealed that cyclodextrins complex gnetol in a 1:1 stoichiometry, with better affinity for like 2-hydroxypropyl-ß-cyclodextrin (KF  = 4542.90 ± 227.15 mol-1  L). Temperature and pH affected the encapsulation constants. CONCLUSION: These results could increase interest of gnetol as an alternative to the most studied stilbene, resveratrol, as well as aid in the development of more stable inclusion complexes that improve its aqueous solubility and stability so that it can be incorporated into functional foods. © 2022 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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.

In silico, in vitro: antioxidant and antihepatotoxic activity of gnetol from Gnetum ula Brongn.

Introduction: Gnetum ula is a notable medicinal plant used to cure various ailments. The stem part of the plant is used traditionally to treat jaundice and other disorders. The present work is to investigate the in vitro hepatoprotective and antioxidant activity of ethanol extract of stem of G. ula (GUE) and its isolated compound gnetol. Methods: Column chromatography was carried out for GUE and various column fractions were obtained. DPPH and reducing power assays were performed for GUE and column fractions. The potent fraction was characterized, interpreted and tested for in vitro hepatoprotective activity on the BRL3A cell line. In silico docking studies of gnetol compound on the protein TGF-ß (transforming growth factor - ß) and Peroxisome proliferator-activated receptor α (PPARα) was carried out. Results: DPPH scavenging and reducing power assay showed that the fourth column fraction has antioxidant potential than other fractions. The fourth column fraction was characterized to obtain gnetol compound. BRL3A cell line was used for the toxicity study of GUE and gnetol. Both, the extract and the isolated compound were found to be nontoxic with CTC50 value more than 1000 µg/mL. At the concentration of 200 µg/mL, GUE and gnetol offered cell protection of 50.2% and 54.3%, however, silymarin showed 77.15% protection at 200 µg/mL concentration against CCl4 treated BRL3A cell line. The docking results of the ligand molecule TGF-ß showed that gnetol has the binding affinity of -7.0 and standard silymarin being -6.8. TGF-ß showed good hydrophobic interactions and formed two hydrogen bonds with the amino acids. For PPARα protein, gnetol showed the binding affinity of -8.4 and silymarin with -6.5. Hydrogen bonding and good hydrophobic interactions against the amino acid molecules in relation to the PPARα protein are shown. Conclusion: Gnetum ula stem extract and its isolated compound are safe and offered significant hepatoprotection against CCl4 induced toxicity. Isolated compound gnetol exhibited a potent antioxidant activity offering protection to liver damage. However, in vivo studies need to be carried out to validate the traditional use of G. ula .

Biological Activities of Stilbenoids.

Stilbenoids are a group of naturally occurring phenolic compounds found in various plant species. They share a common backbone structure known as stilbene, but differ in the nature and position of substituents. Stilbenoids are classified as phytoalexins, which are antimicrobial compounds produced de novo in plants to protect against fungal infection and toxins. In this review, the biological effects of stilbenoids such as resveratrol, pterostilbene, gnetol and piceatannol are discussed. Stilbenoids exert various biological activities ranging from cardioprotection, neuroprotection, anti-diabetic properties, depigmentation, anti-inflammation, cancer prevention and treatment. The results presented cover a myriad of models, from cell culture to animal studies as well as clinical human trials. Although positive results were obtained in most cell culture and animal studies, further human studies are needed to substantiate beneficial effects of stilbenoids. Resveratrol remains the most widely studied stilbenoid. However, there is limited information regarding the potential of less common stilbenoids. Therefore, further research is warranted to evaluate the salutary effects of various stilbenoids.

Preclinical Pharmacokinetics and Pharmacodynamics and Content Analysis of Gnetol in Foodstuffs.

Studies were undertaken to evaluate the bioavailability in rats and content analysis of gnetol in Gnetum gnemon products reported to contain gnetol and to examine the pharmacological properties of gnetol in in vitro models including anti-inflammatory/analgesic, antidiabetic, anti-adipogenesis, and anticancer activity. Male Sprague-Dawley rats were cannulated and dosed either intravenously with gnetol (10 mg/kg) or orally (100 mg/kg). Various methanolic extractions of G. gnemon products were quantified. Gnetol's effect on cell viability in selected cell lines with or without inflammatory stimulus was assessed. α-Amylase and α-glucosidase inhibition was evaluated. Cyclooxygenase (COX)-1, COX-2, and histone deacetylase inhibition and adipogenesis inhibition were examined. After oral and intravenous administration, gnetol was detected in both serum and urine as the parent compound and as a glucuronidated metabolite. The bioavailability of gnetol was determined to be 6%. Gnetol is rapidly glucuronidated and is excreted in urine and via nonrenal routes. Gnetol was found to exist as an aglycone and as a glycoside in G. gnemon products. Gnetol showed concentration-dependent reductions in cell viability in cancer cell lines with greatest activity in colorectal cancer and potent COX-1, histone deacetylase, and weak COX-2 activities along with limited reduction in inflammation. Gnetol also possessed concentration-dependent alpha-amylase, alpha-glucosidase, and adipogenesis activities. Pretreatment of mice with gnetol was able to increase the latency period to response in analgesia models.