Inhibiting enzymatic starch digestion by hydrolyzable tannins isolated from Eugenia jambolana

Rumen protozoa population and carbohydrate-digesting enzymes in sheep fed a diet supplemented with hydrolysable tannins

The aim of the study was to compare the effect of adding different sources of hydrolysable tannins to the sheep diet on protozoa population and carbohydrate digestion in the rumen. The study was performed in 3 Polish Lowland ewes fistulated to the rumen in a 3 × 3 Latin -square design. Control sheep (CON) received (g/d): meadow hay (600), barley meal (300), soybean meal (100) and vitamin-mineral premix (20). Sheep from the experimental groups were additionally administered 12.6 g/kg DM oak bark extract (OAK) and 3.91 g/kg DM tannic acid (TAN). The net consumption of tannins was approx. 0.4% DM for both additives. Regarding the count of protozoa, a significant interaction between diet and sampling time was documented for all ciliates (P<0.01), with a significant effect of both factors when considered separately. Experimental diets reduced the number of total protozoa and Entodinium spp. (before, 2 and 4 h after feeding; P<0.01), while increasing the abundance of Isotricha spp. population (4 h after feeding; P<0.01) in the rumen. Interestingly, the count of Ophryoscolex spp. after feeding the TAN diet increased before feeding and 2 h after feeding in comparison to the CON and OAK groups, respectively, and subsequently decreased compared to the CON diet (4 and 8 h after feeding, P<0.01). A significant interaction between the diet and sampling time was observed for xylanolytic activity (P<0.01) in the rumen, with a significant effect of sampling time, which decreased its activity in CON (after feeding) and OAK sheep (2 h after feeding; P<0.01). For amylolytic activity (P<0.10), there was a trend towards a significant interaction between experimental factors, with a significant effect on both diet and sampling time. Detailed analysis showed that the TAN diet significantly reduced amylolytic activity 2 h after feeding compared to the CON group (P<0.05). In conclusion, the TAN diet significantly reduced the number of total protozoa and Entodinium spp., which consequently reduced amylolytic activity in the rumen, without any significant effect on pH and carbohydrate fermentation in the rumen.

Pharmacology and toxicology of tannins

Tannins are an interesting class of polyphenols, characterized, in almost all cases, by a different degree of polymerization, which, inevitably, markedly influences their bioavailability, as well as biochemical and pharmacological activities. They have been used for the process of tanning to transform hides into leather, from which their name derives. For several time, they have not been accurately evaluated, but now researchers have started to unravel their potential, highlighting anti-inflammatory, antimicrobial, antioxidant and anticancer activities, as well as their involvement in cardiovascular, neuroprotective and in general metabolic diseases prevention. The mechanisms underlying their activity are often complex, but the main targets of their action (such as key enzymes modulation, activation of metabolic pathways and changes in the metabolic fluxes) are highlighted in this review, without losing sight of their toxicity. This aspect still needs further and better-designed study to be thoroughly understood and allow a more conscious use of tannins for human health.

Evaluation of bioactive compounds, phytochemicals profile and antioxidant potential of the aqueous and ethanolic extracts of some traditional fruit tree leaves used in Brazilian folk medicine

The aim of this study was to analyze eight selected species of leaves, used in the traditional medicine of the Northeast region of Brazil obtained from several fruit trees (grageru, soursop, jambolanum, passion fruit, insulin, nogueira, pedra ume kaá and stévia), regarding their polyphenols contents and antioxidant activity. Condensed and hydrolysable tannins, phenolics and flavonoids contents were determined and the antioxidant activities measured by ABTS, FRAP and ORAC assays. Organic acids were analyzed by HPLC-DAD system. Phenolic compounds of aqueous and ethanolic extracts were determined by UHPLC-DAD-MS. The results revealed high contents of total phenolics (13.34 ± 0.19 - 127.65 ± 0.21 mg.g^-1 of GAE:QE (2:1) of sample) and flavonoids (12.30 ± 0.42 - 71.79 ± 0.00 mg.g^-1 QE of sample). The ABTS results exhibited extraordinary activity in the extracts (74.48 ± 6.23 - 1487.33 ± 2.67 µmol Trolox.g^-1 of sample). Acids quinic, tartaric, citric, gallic, chlorogenic, p-coumaric, ferulic and vanillic along with naringenin, rutin, vanillin, catechin, epicatechin, kaempferol were the most important compounds. Thus, these leaves extracts may be considered as sources of phenolics compounds having a high potential as natural antioxidants. In addition, the polyphenols present in these leaves have many beneficial effects and can also be used in medicinal and nutraceuticals products with enhanced bioactivities.

The insulin-sensitising properties of the ellagitannin geraniin and its metabolites from Nephelium lappaceum rind in 3T3-L1 cells

In this study, the insulin-like and insulin sensitising effects of the ellagitannins geraniin, corilagin, ellagic acid, gallic acid and Nephelium lappaceum rind extract in 3T3-L1 adipocytes was investigated. It was observed that non-toxic concentrations of geraniin and its metabolites (0.2-20 μM) and N. lappaceum extract (0.2-20 μg/mL) exhibited insulin-like properties in the absence of insulin and insulin-sensitising properties in the presence of insulin particularly with regards to glucose uptake in 3T3-L1 adipocytes. The compounds were further able to promote adipocyte differentiation and may be involved in the inhibition of lipolysis in 3T3-L1 adipocytes in the presence of insulin. However further study into the molecular mechanisms of action of these compounds need to be carried out to better understand the potential of these compounds/extracts to act as therapeutic agents for hyperglycaemia associated with diabetes mellitus and obesity.

Glycaemic regulation, appetite and ex vivo oxidative stress in young adults following consumption of high-carbohydrate cereal bars fortified with polyphenol-rich berries

Consumption of certain berries appears to slow postprandial glucose absorption, attributable to polyphenols, which may benefit exercise and cognition, reduce appetite and/or oxidative stress. This randomised, crossover, placebo-controlled study determined whether polyphenol-rich fruits added to carbohydrate-based foods produce a dose-dependent moderation of postprandial glycaemic, glucoregulatory hormone, appetite and ex vivo oxidative stress responses. Twenty participants (eighteen males/two females; 24 (sd 5) years; BMI: 27 (sd 3) kg/m2) consumed one of five cereal bars (approximately 88 % carbohydrate) containing no fruit ingredients (reference), freeze-dried black raspberries (10 or 20 % total weight; LOW-Rasp and HIGH-Rasp, respectively) and cranberry extract (0·5 or 1 % total weight; LOW-Cran and HIGH-Cran), on trials separated by ≥5 d. Postprandial peak/nadir from baseline (Δmax) and incremental postprandial AUC over 60 and 180 min for glucose and other biochemistries were measured to examine the dose-dependent effects. Glucose AUC0-180 min trended towards being higher (43 %) after HIGH-Rasp v. LOW-Rasp (P=0·06), with no glucose differences between the raspberry and reference bars. Relative to reference, HIGH-Rasp resulted in a 17 % lower Δmax insulin, 3 % lower C-peptide (AUC0-60 min and 3 % lower glucose-dependent insulinotropic polypeptide (AUC0-180 min) P&lt;0·05. No treatment effects were observed for the cranberry bars regarding glucose and glucoregulatory hormones, nor were there any treatment effects for either berry type regarding ex vivo oxidation, appetite-mediating hormones or appetite. Fortification with freeze-dried black raspberries (approximately 25 g, containing 1·2 g of polyphenols) seems to slightly improve the glucoregulatory hormone and glycaemic responses to a high-carbohydrate food item in young adults but did not affect appetite or oxidative stress responses at doses or with methods studied herein.

Identification of Bioactive Compounds and Analysis of Inhibitory Potential of the Digestive Enzymes from Syzygium sp. Extracts

Diabetes and obesity represent major public health problems worldwide. High cost of medicines and drug treatments propose the research for less expensive alternatives, such as enzymatic inhibitors present in medicinal plants from natural sources. An example of such medicinal plant is the jambolan Syzygium sp., which is referred to be hypoglycemic and efficient in weight loss. With this in mind, we identified the bioactive compounds from Syzygium sp. commercial teas and evaluated the inhibitory potential and the antioxidant activity of digestive enzymes from a simulated gastric fluid. Syzygium sp. samples showed low percentages of enzymatic inhibition at 1 : 200 dilution. Antioxidant activity was significant, although it was not expressive of the contents of total phenolic compounds, tannins, flavonoids, flavones, and alkaloids. Maldi-Tof spectroscopy suggested the presence of luteolin in Syzygium sp. samples. Molecular docking predicted that luteolin binds at the α-amylase catalytic site in a similar manner as acarbose, the carbohydrate inhibitor from the enzyme crystallographic structure. The phytochemical content and biological activity were distinct among samples from commercial teas. Thus, additional studies should be conducted to elucidate efficacy and safety of Syzygium sp. extracts, especially in vivo experiments. Syzygium sp. might be in the near future recommended as a medicinal plant in low cost diabetes and obesity treatments.

Phenolics from Eugenia jambolana seeds with advanced glycation endproduct formation and alpha-glucosidase inhibitory activities

Published data suggest that dietary-derived phenolics exert beneficial effects against hyperglycemia-mediated diseases, such as diabetes, through inhibiting the formation of advanced glycation endproducts (AGEs) and carbohydrate hydrolyzing enzyme activities. In the course of our investigation on the edible berry, Eugenia jambolana (known as Jamun), 21 phenolics (1-21) were isolated and identified from its seeds. Among these, one compound (1) is new and eleven compounds (3, 6, 9-13, 17, and 19-21) are being reported from E. jambolana for the first time. The anti-AGE activities of thirteen pure isolates (2-7, 9-12, 14, 15, and 20) were either comparable or superior to the synthetic anti-glycation agent, aminoguanidine, at three test concentrations (20, 50, and 100 μM) in the BSA-fructose assay. Most of these phenolics with anti-AGE activity exhibited potent free radical scavenging activity in the DPPH assay, and attenuated intracellular levels of LPS-induced reactive oxygen species in RAW264.7 macrophage. In addition, compounds 2-6, and 14 showed superior α-glucosidase inhibitory activity (IC50 = 5.0-21.2 μM) compared to the clinical α-glucosidase inhibitor, acarbose (IC50 = 289.9 μM). This is the first report of the anti-AGE effects of compounds 2-6 and 9-12, and α-glucosidase inhibitory activities of compounds 3-6, 9, 11 and 14. The current study supports the role of phenolics in the antidiabetic properties attributed to this edible berry, and warrants further animal studies to evaluate their potential as dietary agents for the prevention and/or therapy of hyperglycemia-mediated diseases.

Vine-Shoot Tannins: Effect of Post-pruning Storage and Toasting Treatment

For the first time vine-shoot tannin composition was carried out by means of HPLC-DAD-ESI-MS/MS. Two vine-shoot cultivars (Airén and Cencibel) with different post-pruning storage times were submitted to a toasting process and assayed. There were no traces of gallotannins nor ellagitannins, but a high proanthocyanidin content and a mean degree of polymerization (mDP) close to 3 were characterized. The higher concentration of proanthocyanidins corresponded to Airén after 6 months post-pruning storage and at 3 months for Cencibel. Procyanidins were the most abundant fraction (70-95%), which decreased with storage, and especially significant was the contribution of B1, B2, and B4 dimers. Prodelphinidins were also found (8-24%), increasing their % with storage time. Toasting produced a considerable reduction of proanthocyanidin content and a loss of a monomer mDP unit, suggesting that if used as oenological tannins, then they may be more bitter and less astringent when compared with the nontoasted vine-shoot samples.

Hypoglycemic Effects in Alloxan-Induced Diabetic Rats of the Phenolic Extract from Mongolian Oak Cups Enriched in Ellagic Acid, Kaempferol and Their Derivatives

Our previous reports showed that crude extract prepared with 50% ethanol (ethanol crude extract, ECE) from Mongolian oak cups possessed excellent in vitro antioxidant capacities as well as inhibitory activities against α-glucosidase, α-amylase and protein glycation caused by its enrichment in phenolics, including mainly ellagic acid, kaempferol and their derivatives. Nevertheless, few in vivo studies on antidiabetic activities of these phenolics were conducted. The present study investigated hypoglycemic effects with normal and diabetic rats being administrated orally without or with ECE at 200 and 800 mg/kg for 15 days. In normal rats, no significant differences were exhibited after ECE administration in body weight, fasting blood glucose level, levels of cholesterol, triglyceride, LDL and AST in serum, organ indexes, and levels of GSH and MDA in organs. In diabetic rats, the fasting blood glucose level, indexes of heart and liver, and levels of cholesterol and triglyceride in serum and MDA in heart tissue were significantly decreased. Moreover, HDL levels in serum and SOD activities in the four organs of diabetic rats were significantly improved after ECE administration at 800 mg/kg. Thus, in addition to inhibiting α-glucosidase, α-amylase and protein glycation reported previously, oak cups might contain novel dietary phytonutrients in preventing abnormal changes in blood glucose and lipid profile and attenuating oxidant stress in vivo. The results also implied that it is ellagic acid, kaempferol and their derivatives enriched in ECE that might play vital roles in managing type 1 as well as type 2 diabetes.

Characterizations of the endogenous starch hydrolase inhibitors in acorns of Quercus fabri Hance

The acorns of Quercus fabri Hance tree, or the mandarin duck fruits have been consumed by locals in the form of noodle, yet there is little scientific study. We found that they have much lower digestibility compared with that of rice flour. Solvent extraction using hexane, dichloromethane, and acetone-ethanol-water (AEW) mixture yielded three fractions but the starch hydrolase inhibitors were only found in the AEW fraction. Using assay-guided fractionation of the extracts, we were able to further separate the active compounds by using Sephadex LH-20 column and characterize the inhibitor chemical identities by LC-MS⁽ⁿ⁾. The main active compounds are ellagitannins including pedunculagin, punicalagin, castalagin, and eucalbanin. Our results indicate that the acorns from Quercus fabri Hance have potential for preparation of low glycemic index foods due to the endogenous starch hydrolase inhibitors.

Activities of Tannins – from in Vitro Studies to Clinical Trials

Tannins are considered as valuable plant secondary metabolites providing many benefits for human health. In this review information was gathered about bioactivity in vitro and in vivo, as well as about conducted clinical trials. The literature research was based on ScienceDirect, Scopus, and Cochrane databases and presents a wide range of tested activities of tannins. The described clinical trials verify laboratory tests and show the effective health benefits taken from supplementation with tannins.