Matrix-assisted laser desorption/ionization mass spectrometry-guided visualization analysis of intestinal absorption of acylated anthocyanins in Sprague-Dawley rats.

It is unknown whether intestinal absorption of acylated anthocyanins occurs in their intact or metabolized form. In this study, with the aid of matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) imaging, intestinal absorption of acylated anthocyanins was visually investigated. Anthocyanin extracts from purple carrots were orally administered to Sprague-Dawley rats. Acylated cyanidins were absorbed into portal and circulating blood systems in their intact form, and aglycon; cyanidin 3-O-(6-O-feruloyl-ß-d-glucopyranosyl)-(1 â†’ 6)-[ß-d-xylopyranosyl-(1 â†’ 2)]-ß-d-galactopyranoside (Cy3XFGG), and showed a high absorption of 39.3 ± 0.1 pmol/mL-plasma at 60 min after administration. MALDI-MS imaging analysis of the rat jejunum membranes showed that an organic anion transporting polypeptide (OATP) transporter was involved in Cy3XFGG transport, while deacylated anthocyanins were incorporated through both the glucose transporter 2 and OATP routes. In conclusion, acylated anthocyanin, Cy3XFGG, can be absorbed in its intact form through intestinal OATP.

Absorption and Metabolic Behavior of Hesperidin (Rutinosylated Hesperetin) after Single Oral Administration to Sprague-Dawley Rats.

We investigated the absorption and metabolic behavior of hesperidin (hesperetin-7-O-rutinoside) in the blood system of Sprague-Dawley rats by liquid chromatography- and matrix-assisted laser desorption ionization mass spectrometries (LC-MS and MALDI-MS). After a single oral administration of hesperidin (10 mg/kg), which was expected to be absorbed in its degraded hesperetin form, we detected intact hesperidin in the portal vein blood (tmax, 2 h) for the first time. We successfully detected glucuronized hesperidin in the circulating bloodstream, while intact hesperidin had disappeared. Further MS analyses revealed that homoeriodictyol and eriodictyol conjugates were detected in both portal and circulating blood systems. This indicated that hesperidin and/or hesperetin are susceptible to methylation and demethylation during the intestinal membrane transport process. Sulfated and glucuronized metabolites were also detected in both blood systems. In conclusion, hesperidin can enter into the circulating bloodstream in its conjugated forms, together with the conjugated forms of hesperetin, homoeriodictyol, and/or eriodictyol.

Brain-transportable dipeptides across the blood-brain barrier in mice.

Apart from nutrients required for the brain, there has been no report that naturally occurring peptides can cross the blood-brain barrier (BBB). The aim of this study was to identify the BBB-transportable peptides using in situ mouse perfusion experiments. Based on the structural features of Gly-N-methylated Gly (Gly-Sar), a reported BBB-transportable compound, 18 dipeptides were synthesized, and were perfused in the mouse brain for two minutes. Among the synthesized dipeptides, Gly-Sar, Gly-Pro, and Tyr-Pro were transported across the BBB with Ki values of 7.60 ± 1.29, 3.49 ± 0.66, and 3.53 ± 0.74 µL/g·min, respectively, and accumulated in the mouse brain parenchyma. Additionally, using MALDI-MS/MS imaging analysis of Tyr-Pro-perfused brain, we provide evidence for Tyr-Pro accumulation in the hippocampus, hypothalamus, striatum, cerebral cortex, and cerebellum of mouse brain.

Soybean-Derived Glycine-Arginine Dipeptide Administration Promotes Neurotrophic Factor Expression in the Mouse Brain.

Brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family, plays an important role in cognitive abilities, including memory and learning. We demonstrated that soybean protein hydrolysate (SPH) diet suppresses age-related cognitive decline via the upregulation of BDNF in a mouse model of senescence. Our purpose was to identify novel bioactive peptides in SPH, which enhance BDNF expression. We treated mouse primary astrocytes with SPH as well as with its positively charged chromatographic fraction. Significant increases in the expression of BDNF were observed in the treatment with positively charged fraction of SPH. Among the synthesized peptides, the dipeptide glycine-arginine (GR) increased BDNF expression in vitro, and LC-TOF-MS analysis showed the presence of GR in the SPH. Furthermore, its administration in vivo increased the expression of BDNF in the cerebral cortex and the number of neurons in hippocampus and cerebral cortex. These data indicate that GR might promote neurogenesis by upregulating BDNF levels.

Inhibition of Glucose Transport by Tomatoside A, a Tomato Seed Steroidal Saponin, through the Suppression of GLUT2 Expression in Caco-2 Cells.

We investigated whether tomatoside A (5α-furostane-3ß,22,26-triol-3-[O-ß-d-glucopyranosyl (1→2)-ß-d-glucopyranosyl (1→4)-ß-d-galactopyranoside] 26-O-ß-d-glucopyranoside), a tomato seed saponin, may play a role in the regulation of intestinal glucose transport in human intestinal Caco-2 cells. Tomatoside A could not penetrate through Caco-2 cell monolayers, as observed in the transport experiments using liquid chromatography-mass spectrometry. The treatment of cells with 10 µM tomatoside A for 3 h resulted in a 46.0% reduction in glucose transport as compared to untreated cells. Western blotting analyses revealed that tomatoside A significantly (p < 0.05) suppressed the expression of glucose transporter 2 (GLUT2) in Caco-2 cells, while no change in the expression of sodium-dependent glucose transporter 1 was observed. In glucose transport experiments, the reduced glucose transport by tomatoside A was ameliorated by a protein kinase C (PKC) inhibitor and a multidrug resistance-associated protein 2 (MRP2) inhibitor. The tomatoside A-induced reduction in glucose transport was restored in cells treated with apical sodium-dependent bile acid transporter (ASBT) siRNA or an ASBT antagonist. These findings demonstrated for the first time that the nontransportable tomato seed steroidal saponin, tomatoside A, suppressed GLUT2 expression via PKC signaling pathway during the ASBT-influx/MRP2-efflux process in Caco-2 cells.

Anti-prediabetic effect of rose hip (Rosa canina) extract in spontaneously diabetic Torii rats.

BACKGROUND: Prediabetes, a high-risk state for developing diabetes showing impaired glucose tolerance but a normal fasting blood glucose level, has an increasing prevalence worldwide. However, no study investigating the prevention of impaired glucose tolerance at the prediabetic stage by anti-diabetic functional foods has been reported. Thus, the present study aimed to evaluate the anti-prediabetic effect of rose hip in a prediabetic rat model. RESULTS: Spontaneously diabetic Torii (SDT) rats were supplemented with hot-water extract of rose hip at a dose of 100 mg kg-1 body weight day-1 for 12 weeks. The results obtained showed that the supplementation of rose hip extract improved impaired glucose tolerance, promoted insulin secretion, preserved pancreatic beta-cell function and suppressed plasma advanced glycation end-products formation of methylglyoxal-derived hydroimidazolone (MG-H1) residue and Nϵ -carboxymethyl-lysine residues (e.g. MG-H1, control: 465.5 ± 43.8 versus rose hip: 59.1 ± 13.0 pmol mg protein-1 , P < 0.05) in SDT rats at the prediabetic stage (12-20 weeks old). CONCLUSION: The present study provides the first evidence showing that a hot-water extract of rose hip could exert an anti-prediabetic effect in a rat model. © 2017 Society of Chemical Industry.

Condensed catechins and their potential health-benefits.

Condensed catechins are commonly present in fermented tea, and are produced by the oxidation of monomeric catechins. Due to their auto-oxidation, catechins have diverse structural features, including different binding modes and degrees of polymerization. Because of their structural complexity, their physiological functions and possible health-benefits have not yet been fully investigated. This review focuses on the physiological potentials of dimeric and trimeric catechins in the intestine (regulation of absorption across the intestinal membrane), blood vessels (vasorelaxation in vessel regulation), and muscle organs (promotion of glucose uptake resulting in an anti-diabetic effect). Furthermore, the roles of non-absorbable theaflavins (dimeric catechins), absorbable theasinensins (dimeric catechins), and absorbable procyanidins (dimeric and trimeric catechins) on target organs are discussed.

Visualized absorption of anti-atherosclerotic dipeptide, Trp-His, in Sprague-Dawley rats by LC-MS and MALDI-MS imaging analyses.

SCOPE: The basic dipeptide, Trp-His, was found to show an in vivo anti-atherosclerotic effect when orally administered to apo E-deficient mice. In addition, this dipeptide causes vasorelaxation in contracted rat aorta via suppression of intracellular Ca(2+) signaling cascades. In this study, we attempted to determine whether Trp-His can be absorbed after single oral administration in Sprague-Dawley (SD) rats. METHODS AND RESULTS: Trp-His and His-Trp (10 or 50 mg/kg) was orally administered to 8-week-old male SD rats. Both peptides in plasma were assayed by LC-MS/MS in combination with 2,4,6-trinitrobenzene sulfonate derivatization technique. In vitro transport experiments using Caco-2 cell monolayers were performed to evaluate the apparent permeability (Papp ). A phytic acid-aided MALDI-MS imaging (MSI) was conducted to visualize the distribution of dipeptides in the rat intestinal membrane. Trp-His was absorbed intact into SD rat blood, showing a maximal level at 1 h after administration at 10 mg/kg dose (Cmax , 28.7 ± 8.9 pmol/mL-plasma; area under the curve, 71.3 ± 18.7 pmol·h/mL-plasma). In contrast, His-Trp was surprisingly not detected, although the Papp was compatible to that of Trp-His. MSI analysis provided crucial evidence that Trp-His was visualized in the overall intestinal membrane. The Trp-His peptide was not visualized in the presence of Gly-Sar, which is a model peptide that is transported via the intestinal proton-coupled peptide transporter 1 (PepT1) transporter. The His-Trp molecular ion was not observed at the intestinal membrane. The MSI analysis illustrated that there is no absorption of His-Trp due to its unexpected hydrolysis by brush border proteases. CONCLUSION: To the best of our knowledge, this is the first study demonstrating that the vasoactive Trp-His is preferably transported across the rat intestinal membrane by PepT1 and is absorbed intact into the circulation. However, no absorption of His-Trp, a reverse sequence of absorbable Trp-His, is observed owing to hydrolysis by intestinal proteases. This suggests that the bioavailability of peptides may be determined in part by their protease resistance in the intestinal membrane.

Specific oligopeptides in fermented soybean extract inhibit NF-κB-dependent iNOS and cytokine induction by toll-like receptor ligands.

The ethanol extract of fermented soybean from Glycine max (chungkookjang, CHU) has been claimed to have chemopreventive and cytoprotective effects. In the present study, we examined the inhibitory effect of CHU on inducible nitric oxide synthase (iNOS) and cytokine induction by toll-like receptor (TLR) ligands treatment and attempted to identify the responsible active components. Nitric oxide (NO) content and iNOS levels in the media or RAW264.7 cells were measured using the Griess reagent and real-time polymerase chain reaction assays. CHU treatment inhibited NO production and iNOS induction elicited by lipopolysaccharide (LPS, TLR4L) in a concentration-dependent manner. Tumor necrosis factor-α and interleukin-6 productions were also diminished. Peptidoglycans (TLR2/6L) and CpG-oligodeoxynucleotides (TLR9L) from CHU inhibited iNOS induction, but not poly I:C (TLR3L) or loxoribine (TLF7L). The anti-inflammatory effect resulted from the inhibition of nuclear factor-kappa B (NF-κB) through the inhibition of inhibitory-κB degradation. Of the representative components in CHU, specific oligopeptides (AFPG and GVAWWMY) had the ability to inhibit iNOS induction by LPS, whereas others failed to do so. Daidzein, an isoflavone used for comparative purposes, was active at a relatively higher concentration. In an animal model, oral administration of CHU to rats significantly diminished carrageenan-induced paw edema and iNOS induction. Our results demonstrate that CHU has anti-inflammatory effects against TLR ligands by inhibiting NF-κB activation, which may result from specific oligopeptide components in CHU. Since CHU is orally effective, dietary applications of CHU and/or the identified oligopeptides may be of use in the prevention of inflammatory diseases.

Applicability of the DPPH assay for evaluating the antioxidant capacity of food additives - inter-laboratory evaluation study -.

An inter-laboratory evaluation study was conducted in order to evaluate the antioxidant capacity of food additives by using a 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. Four antioxidants used as existing food additives (i.e., tea extract, grape seed extract, enju extract, and d-α-tocopherol) and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox) were used as analytical samples, and 14 laboratories participated in this study. The repeatability relative standard deviation (RSD(r)) of the IC50 of Trolox, four antioxidants, and the Trolox equivalent antioxidant capacity (TEAC) were 1.8-2.2%, 2.2-2.9%, and 2.1-2.5%, respectively. Thus, the proposed DPPH assay showed good performance within the same laboratory. The reproducibility relative standard deviation (RSD(R)) of IC50 of Trolox, four antioxidants, and TEAC were 4.0-7.9%, 6.0-11%, and 3.7-9.3%, respectively. The RSD(R)/RSD(r) values of TEAC were lower than, or nearly equal to, those of IC50 of the four antioxidants, suggesting that the use of TEAC was effective for reducing the variance among the laboratories. These results showed that the proposed DPPH assay could be used as a standard method to evaluate the antioxidant capacity of food additives.

Theflavins and theasinensin A derived from fermented tea have antihyperglycemic and hypotriacylglycerolemic effects in KK-A(y) mice and Sprague-Dawley rats.

Although tea polyphenols are reported to improve serum glucose and lipid levels by inhibiting amylase activity and reducing lipid absorption, in vivo data are lacking. We evaluated in vivo the antihyperglycemic and hypotriacylglycerolemic effects of theaflavins (TFs) and theasinensin A (TSA) refined from fermented tea to purities of 12 and 59%, respectively. Feeding male KK-A(y) mice diets with 0.1% TFs or TSA for 6 weeks reduced serum glucose levels by >30% compared to a control diet. Rats fed diets containing 0.2% TFs or TSA for 4 weeks had higher fecal fat excretion and 33% lower hepatic triacylglycerol; hepatic fatty acid synthase activity was not affected. Oral administration of TFs or TSA reduced the increase in serum triacylglycerol after an oral bolus of a fat emulsion. These results indicate TFs and TSA induce antihyperglycemic responses in diabetic mice and are hypotriacylglycerolemic in rats by suppressing intestinal fat absorption.

Apple procyanidins induce hyperpolarization of rat aorta endothelial cells via activation of K+ channels.

Apple procyanidins (AP), one of the polyphenol-rich compounds, showed an endothelial-dependent vasorelaxation in rat aorta, but the mechanisms of beneficial effects are still unclear. The present study was designed to clarify the potential role of AP in rat aorta endothelial cells (RAECs). The treatment of RAECs with AP (1-10 µg/ml) resulted in a dose-dependent hyperpolarization with a maximum effect at 10 µg/ml, and for this reason, AP (10 µg/ml) was used in all the following experiments. AP-induced hyperpolarization was significantly inhibited by pretreatment of nonspecific K(+) inhibitor, tetraethyl ammonium chloride or specific K(+) channel inhibitors, iberiotoxin, glibenclamide, 4-aminopyridine and BaCl(2), as well as by high KCl or Ca(2+)-free solution. AP-induced hyperpolarization was also proved using 64-channel multielectrode dish system that can monitor a direct and real-time change of membrane potential. Furthermore, AP treatment caused a significant increase of nitric oxide (NO) production and cyclic guanosine monophosphate levels via endothelial NO synthase messenger RNA expression. The NO production was inhibited by N(G)-monoethyl-l-arginine or Ca(2+)-free solution and was completely abolished by their combination. Also, AP inhibited endothelial proliferation, while the effect was significantly abolished by N(G)-monoethyl-l-arginine or tetraethyl ammonium chloride. These findings suggest that AP induces both hyperpolarization of RAECs via multiple activation of K(+) channels and activation of NO/cyclic guanosine monophosphate pathway via increasing NO production or is responsible for antiangiogenic effect. Diminishment of hyperpolarization as well as NO production of AP in Ca(2+)-free solution implicated that AP would play a crucial role in promoting Ca(2+) influx into endothelial cells so as to promote both actions.

Polyphenol composition of a functional fermented tea obtained by tea-rolling processing of green tea and loquat leaves.

Phenolic constituents of a new functional fermented tea produced by tea-rolling processing of a mixture (9:1) of tea leaves and loquat leaves were examined in detail. The similarity of the phenolic composition to that of black tea was indicated by high-performance liquid chromatography comparison with other tea products. Twenty-five compounds, including three new catechin oxidation products, were isolated, and the structures of the new compounds were determined to be (2R)-2-hydroxy-3-(2,4,6-trihydroxyphenyl)-1-(3,4,5-trihydroxyphenyl)-1-propanone 2-O-gallate, dehydrotheasinensin H, and acetonyl theacitrin A by spectroscopic methods. In addition, theacitrinin A and theasinensin H were obtained for the first time from commercial tea products. Isolation of these new and known compounds confirms that reactions previously demonstrated by in vitro model experiments actually occur when fresh tea leaves are mechanically distorted and bruised during the production process.

Identification of a new natural vasorelaxatant compound, (+)-osbeckic acid, from rutin-free tartary buckwheat extract.

The candidates responsible for vasorelaxation action of rutin-free tartary buckwheat extract (TBSP) were examined in this study. As a result of reversed-phase high-performance liquid chromatography (HPLC) separations, five prominent peaks in the acidic fraction of TBSP were obtained at 260 nm. Among the five collected peaks, we successfully identified four compounds by nuclear magnetic resonance (NMR) and mass spectrometry (MS) measurements: (+)-osbeckic acid as a dimer ([M - H](-) m/z: 371.2 > 184.9 > 140.9), 5-hydroxymethyl-2-furoic acid, protocatechuic acid, and p-hydroxybenzoic acid. A vascular contractive measurement in 1.0 µM phenylephrine-contracted Sprague-Dawley rat thoracic aorta rings revealed that (+)-osbeckic acid dimer evoked a potent vasorelaxant effect with an EC50 value of 887 µM compared to other isolates (EC50: 5-hydroxymethyl-2-furoic acid, 3610 µM; protocatechuic acid, 2160 µM; p-hydroxybenzoic acid, no inhibition). Dimeric (+)-osbeckic acid was stable in solutions and at high temperatures, while its degraded peak on the HPLC chromatogram was observed when it was dissolved in dimethyl sulfoxide.

Hypotriacylglycerolemic and antiobesity properties of a new fermented tea product obtained by tea-rolling processing of third-crop green tea (Camellia sinensis) leaves and loquat (Eriobotrya japonica) leaves.

We manufactured a new fermented tea by tea-rolling processing of third-crop green tea (Camellia sinensis) leaves and loquat (Eriobotrya japonica) leaves. The mixed fermented tea extract inhibited pancreatic lipase activity in vitro, and effectively suppressed postprandial hypertriacylglycerolemia in rats. Rats fed a diet containing 1% freeze-dried fermented tea extract for 4 weeks had a significantly lower liver triacylglycerol concentration and white adipose tissue weight than those fed the control diet lacking fermented tea extract. The activity of fatty acid synthase in hepatic cytosol markedly decreased in the fermented tea extract group as compared to the control group. The serum and liver triacylglycerol- and body fat-lowering effects of the mixed fermented tea extract were strong relative to the level of dietary supplementation. These results suggest that the new fermented tea product exhibited hypotriacylglycerolemic and antiobesity properties through suppression of both liver fatty acid synthesis and postprandial hypertriacylglycerolemia by inhibition of pancreatic lipase.

Identification of alpha-glucosidase inhibitors from a new fermented tea obtained by tea-rolling processing of loquat (Eriobotrya japonica) and green tea leaves.

BACKGROUND: A new fermented tea produced by tea-rolling processing of loquat (Eriobotrya japonica) leaf with green tea leaf (denoted as LG tea) showed a potent antihyperglycaemic effect in maltose-loaded rats. The aim of this study, therefore, was to identify alpha-glucosidase inhibitors in the antihyperglycaemic tea product. RESULTS: LG tea had a threefold higher maltase-inhibitory activity (IC(50) 0.065 mg dried extract mL(-1)) than either the constituent loquat leaf or green tea alone. In addition, LG tea favourably inhibited maltase action rather than sucrase action. As a result of bio-guided high-performance liquid chromatography separations of LG tea, theasinensin A, theasinensin B, strictinin and 1,6-digalloylglucose were newly identified as maltase inhibitors with IC(50) values of 142, 225, 398 and 337 micromol L(-1) respectively, along with previously identified catechins and theaflavins. CONCLUSION: Judging from the magnitude of the alpha-glucosidase-inhibitory contribution of each isolated compound to the overall inhibition of LG tea, catechins were the main candidates responsible for alpha-glucosidase or maltase inhibition in LG tea, followed by theaflavins, theasinensins, strictinin and 1,6-digalloylglucose.

Suppression of blood glucose level by a new fermented tea obtained by tea-rolling processing of loquat (Eriobotrya japonica) and green tea leaves in disaccharide-loaded Sprague-Dawley rats.

BACKGROUND: In the field of food science, much interest has been focused on the development of alternative medicinal foods with the ability to regulate excess blood glucose level (BGL) rise. The authors have successfully developed a new fermented tea product (LG tea) by co-fermentation of loquat (Eriobotrya japonica) leaf and summer-harvested green tea leaf. The objective of this study was to examine the acute suppression effect of LG tea on BGL rise in disaccharide-loaded Sprague-Dawley (SD) rats and to evaluate its possible usage as an antidiabetic functional food material. RESULTS: As a result of single oral administration of hot water extract of LG tea (50 mg kg(-1)) to maltose-loaded SD rats, BGL at 30 min was significantly decreased by 23.8% (P < 0.01) compared with the control. A corresponding reduction in serum insulin secretion was also observed. The ED(50) value of LG tea (50.7 mg kg(-1)) was estimated to be about 16-fold higher than that of the therapeutic drug acarbose (3.1 mg kg(-1)). CONCLUSION: No significant change in BGL was observed when sucrose or glucose was administered, suggesting that the suppression effect of LG tea was achieved by maltase inhibition, not by sucrase inhibition or glucose transport inhibition at the intestinal membrane.

Increase of theaflavin gallates and thearubigins by acceleration of catechin oxidation in a new fermented tea product obtained by the tea-rolling processing of loquat ( Eriobotrya japonica ) and green tea leaves.

In a project to produce a new fermented tea product from non-used tea leaves harvested in the summer, we found that kneading tea leaves ( Camellia sinensis ) with fresh loquat leaves ( Eriobotrya japonica ) accelerated the enzymatic oxidation of tea catechins. The fermented tea obtained by tea-rolling processing of tea and loquat leaves had a strong, distinctive flavor and a plain aftertaste, which differed from usual black, green, and oolong teas. The phenolic constituents were similar to those of black tea. However, the concentrations of theaflavin 3-O-gallate, theaflavin 3,3'-di-O-gallate, and thearubigins were higher in the tea leaves kneaded with loquat leaves than in tea leaves kneaded without loquat leaves. The results from in vitro experiments suggested that acceleration of catechin oxidation was caused by the strong oxidation activity of loquat leaf enzymes and a coupled oxidation mechanism with caffeoyl quinic acids, which are the major phenolic constituents of loquat leaves.

Endothelium-dependent vasorelaxation effect of rutin-free tartary buckwheat extract in isolated rat thoracic aorta.

The aim of this study was to point out the potential of tartary buckwheat on vascular functions. A nonabsorbed fraction of hot-water extract of tartary buckwheat on a SP70 column (TBSP-T), which was free from rutin, was used for this aim. In a contractile experiment using Sprague-Dawley rat thoracic aorta rings contracted by 1.0 microM phenylephrine (PE) or 50 mM KCl, TBSP-T evoked a significant vasorelaxation [EC50 (mg/ml): PE; 2.2; KCl, 1.9]. By a further fractionation of TBSP-T by liquid-liquid partitioning into basic, neutral and acidic fractions, a marked enhancement of vasorelaxation effect was observed only for acidic fraction (EC50, 0.25 mg/ml). The action of acidic fraction was significantly attenuated in endothelium-denuded aortic rings and in the presence of nitric oxide synthase inhibitor, NG-monomethyl-L-arginine (100 microM). The fraction also enhanced the cyclic guanosine monophosphate (cGMP) production in aortic rings contracted with PE [cGMP (pmol/mg protein): PE, 7.2+/-2.3; PE+Acidic fraction, 35+/-8]. These results indicate that acidic fraction could mediate NO/cGMP pathways, thereby exerting endothelium-dependent vasorelaxation action. In conclusion, tartary buckwheat was proven to regulate vascular tones and have latent acidic candidates except for rutin.

Strong antihyperglycemic effects of water-soluble fraction of Brazilian propolis and its bioactive constituent, 3,4,5-tri-O-caffeoylquinic acid.

To clarify the suppression of postprandial blood glucose rise via alpha-glucosidase (AGH) inhibitory action by natural compounds, propolis was examined in this study. A single oral administration of propolis extract (50% methanol fraction on XAD-2 column chromatography) in Sprague-Dawley rats demonstrated a potent antihyperglycemic effect with the significant AUC(0-120 min) reduction of 38% at a dose of 20 mg/kg compared to that of controls. Among the active compounds isolated from the fraction, 3,4,5-tri-caffeoylquinic acid was found to be a prominent candidate that exerts the effect and shows a strong maltase-specific inhibition with an IC(50) value of 24 microM. In addition, the noncompetitive inhibition power apparently increased with the number of caffeoyl groups bound to quinic acid.