Tannins as biological antioxidants

Tannic acid and zinc ion coordination of nanase for the treatment of inflammatory bowel disease by promoting mucosal repair and removing reactive oxygen and nitrogen species

Colon mucosal overexpression of reactive oxygen and nitrogen species (RONS) accelerates the development of inflammatory bowel disease (IBD) and destroys the mucosa and its barrier. IBD can be alleviated by removing RONS from the inflamed colon. The preparation of strong and efficient nanoantioxidants remains a challenge despite the development of numerous nanoantioxidants. In this paper, Zn-TA nanoparticles with fine hollow microstructure (HZn-TA) were successfully prepared and could be effectively used to treat IBD. In the first step, ZIF-8 nanoparticles were synthesized by a one-pot method. On this basis, HZn-TA nanoparticles were etched by TA, and a multifunctional nanase was developed for the treatment of IBD. RONS, including reactive oxygen species (ROS) and nitric oxide (NO), can be eliminated to increase cell survival following Hydrogen peroxide (H2O2) stimulation, including reactive oxygen species (ROS) and nitric oxide (NO with hydrogen peroxide (H2O2). In a model for preventing and delaying acute colitis, clearance of RONS has been shown to reduce intestinal inflammation in mice by reducing colon damage, proinflammatory cytokine levels, the spleen index, and body weight. Intestinal mucosal healing can be promoted by HZn-TA nanoparticles, which can upregulate zonula occludens protein 1 (ZO-1) and claudin-1 expression. Based on the results of this study, HZn-TA nanoparticles were able to effectively treat IBD with minimal adverse effects by being biocompatible, multienzyme active, and capable of scavenging RONS. Therefore, we pioneered the application of HZn-TA nanoparticles for the treatment of IBD, which are capable of clearing RONS without significant adverse effects. STATEMENT OF SIGNIFICANCE: ➢ HZn-TA nanoparticles were successfully prepared and could be effectively used to treat IBD. ➢ Intestinal mucosal healing can be promoted by HZn-TA nanoparticles, which can upregulate ZO-1 and claudin-1 expression. ➢ HZn-TA nanoparticles were able to effectively treat IBD with minimal adverse effects by being biocompatible, multienzyme active, and capable of scavenging RONS.

Analysis of Commercial Proanthocyanidins. Part 6: Sulfitation of Flavan-3-Ols Catechin and Epicatechin, and Procyanidin B-3

Proanthocyanidins (PACs) are natural plant-derived polymers consisting of flavan-3-ol monomers. Quebracho (Schinopsis lorentzii and balansae) heartwood and mimosa (Acacia mearnsii) bark extracts are the major industrial sources of PACs. These commercial extracts are often sulfited to reduce their viscosity and increase their solubility in water. The chemical process of sulfitation is still poorly understood regarding stereochemical influences during the reaction and during the cleavage of the interflavanyl bond of oligomers. To gain a better understanding of sulfitation, two diastereomeric flavan-3-ol monomers were sulfited under industrial conditions, and procyanidin B-3 (catechin-4α→8-catechin) were sulfited to investigate interflavanyl bond cleavage with sulfitation at C-4. Treatment of diastereomeric flavan-3-ols 2R,3S-catechin and 2R,3R-epicatechin with NaHSO3 at 100 °C in aqueous medium afforded the enantiomeric (1R,2S)- and (1S,2R)-1-(3,4-dihydroxyphenyl)-2-hydroxy-3-(2,4,6-trihydroxyphenyl)propane-1-sulfonic acid, respectively. Utilizing computational NMR PD4 calculations it was determined that the direction of stereoselective nucleophilic attack is controlled by the C-3 configuration of the flavan-3-ols catechin and epicatechin. Sulfitation of the catechin-4α→8-catechin dimer 7 (procyanidin B-3) under the same conditions led to the cleavage of the interflavanyl bond yielding the C-4 sulfonic acid substituted catechin momomer. From the heterocyclic ring coupling constants it was determined that nucleophilic attack occurs from the β-face of the dimer leading to the 2,3-trans-3,4-cis isomer as product.

Tannic acid acts as an agonist of the dopamine D2L receptor, regulates immune responses, and ameliorates experimentally induced colitis in mice

Tannic acid (TA) is an herbal polyphenol containing a galloyl group that has been prescribed to treat gastroenteritis, diarrhea, and irritable bowel syndrome. TA has anti-inflammatory, anti-cancer, and anti-viral properties; however, the molecular mechanisms of these potential therapeutic effects are still largely unknown. Here, we examined the ability of TA to induce anti-inflammatory responses. TA was found to be an agonist of the dopamine D2L receptor. TA reduced interferon (IFN)-γ and interleukin (IL)-1β secretion but upregulated tumor necrosis factor α and IL-10 secretion from lipopolysaccharide (LPS)-stimulated mouse splenocytes. TA also reduced IFN-γ secretion but enhanced IL-10 secretion from anti-cluster of differentiation (CD) 3/CD28 antibody-stimulated splenocytes. An immune subset study confirmed that TA regulated cytokine secretion by various types of immune cells in the context of stimulation with LPS or anti-CD3/CD28 antibodies. Administration of TA to mice with experimentally induced colitis strikingly suppressed weight loss, colon shrinkage, and IL-17 secretion from mesenteric lymph node lymphocytes in response to CD3/CD28 stimulation. These data suggest that TA suppresses inflammatory responses in colitis by regulating cytokine secretion by immune cells in the colon.

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Tannic acid is an agonist of the dopamine D2L receptor.

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Tannic acid suppresses IFN-γ secretion by LPS-stimulated splenocytes.

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Tannic acid modulates anti-CD3/CD28 antibody-stimulated cytokine levels in CD4⁺ T cells.

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Tannic acid ameliorates dextran sodium salt (DSS)-induced colitis in C57BL/6 mice.

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Tannic acid reduces production of IL-17 in DSS-induced colitis.

Effect of (-)-epigallocatechin-3-gallate on glucose-induced human serum albumin glycation

(-)-Epigallocatechin-3-gallate (EGCg) is a naturally occurring polyphenol found in plant-based foods and beverages such as green tea. Although EGCg can eliminate carbonyl species produced by glucose autoxidation and thus can inhibit protein glycation, it is also reported to be a pro-oxidant that stimulates protein glycation in vitro. To better understand the balance between antioxidant and pro-oxidant features of EGCg, we evaluated EGCg-mediated bioactivities in a human serum albumin (HSA)/glucose model by varying three different parameters (glucose level, EGCg concentration, and time of exposure to EGCg). Measurements of glycation-induced fluorescence, protein carbonyls, and electrophoretic mobility showed that the level of HSA glycation was positively related to the glucose level over the range 10-100 mM during a 21-day incubation at 37°C and pH: 7.4. Under mild glycemic pressure (10 mM), long exposure to EGCg enhanced HSA glycation, while brief exposure to low concentrations of EGCg did not. Under high glycemic pressure (100 mM glucose), long exposure to EGCg inhibited glycation. For the first time we showed that brief exposure to EGCg reversed glycation-induced fluorescence, indicating a restorative effect. In conclusion, our research identified glucose level, EGCg concentration, and time of exposure as critical factors dictating EGCg bioactivities in HSA glycation. EGCg did not affect HSA glycation under normal physiological conditions but had a potential therapeutic effect on HSA severely damaged by glycation.

Biological and biomedical functions of Penta-O-galloyl-D-glucose and its derivatives

Penta-O-galloyl-D-glucose (PGG) is a simple hydrolysable tannin in plants. PGG exists in two anomeric forms, α-PGG and β-PGG. While β-PGG can be found in a wide variety of plants, α-PGG is rather rare in nature. Numerous studies with β-PGG revealed a wide variety of biological activities, such as anti-microbial and anti-cancer functions. Until recently, studies with α-PGG were limited by the lack of its availability. Since the development of an efficient chemical synthesis of the compound, several investigations have revealed its anti-diabetic, anti-cancer, and anti-platelet-coagulation functions. Based on structure-activity-relationship (SAR) studies with α-PGG, a variety of α-PGG-related novel compounds were synthesized and some of them have been shown to possess promising therapeutic activities. In this review, the authors will survey and evaluate the biological functions of PGG with a focus on α-PGG and its derivatives.

Effects of methyl gallate and gallic acid on the production of inflammatory mediators interleukin-6 and interleukin-8 by oral epithelial cells stimulated with Fusobacterium nucleatum

Interactions between periodontal bacteria and human oral epithelial cells can lead to the activation and expression of a variety of inflammatory mediators in epithelial cells. Fusobacterium nucleatum is a filamentous human pathogen that is strongly associated with periodontal diseases. This study examined the effects of methyl gallate (MG) and gallic acid (GA) on the production of inflammatory mediators, interleukin (IL)-6 and IL-8, by oral epithelial cells stimulated by F. nucleatum. In a real-time reverse transcription-polymerase chain reaction and an enzyme-linked immunosorbent assay, live F. nucleatum induced high levels of gene expression and protein release of IL-6 and IL-8. The effects of MG and GA were examined by treating KB oral epithelial cells with MG and GA and stimulating them with F. nucleatum. MG and GA inhibited significantly the increases in the IL-6 and IL-8 gene and protein levels in a dose-dependent manner. These Compounds also inhibited the growth of F. nucleatum. No visible effects of MG and GA on the adhesion and invasion of KB cells by F. nucleatum were observed. In conclusion, both MG and GA inhibit IL-6 and IL-8 production from F. nucleatum-activated KB cells.

Experimental in vitro arterial reactivity and tissue culture solutions alter the time-dependent stability of anthocyanins from elderberry, chokeberry, and bilberry extracts

We examined the effect of solutions commonly used for in vitro assessment of blood vessel physiology and pharmacology on the half-lives of monomeric anthocyanins contained in extracts from elderberry, chokeberry, and bilberry. We observed that monomeric anthocyanin degradation in all extracts was accelerated when they were solubilized in an in vitro vascular physiological salt solution (PSS) compared with extracts in purified water. Degradation was accelerated further by increasing the temperature of the PSS to 37 degrees C and bubbling it with 95% oxygen/5% carbon dioxide. A common, complex, tissue culture media yielded similar results to the physiological salt solution at 37 degrees C. We also observed that the percentage polymeric color estimated by bisulfite bleaching corresponded to monomeric degradation in PSS. These results suggest that exposure of anthocyanins to physiological conditions that mimic those in the human body may stimulate the conversion of monomeric anthocyanins to their polymeric forms. Such conversion would probably contribute to the effects of anthocyanins on physiological functions in in vitro experiments and needs to be considered when evaluating effects of these compounds on physiological processes.