Transepithelial transport and accumulation of flavone in human intestinal Caco-2 cells

Isoflavones in food supplements: chemical profile, label accordance and permeability study in Caco-2 cells

Consumers nowadays are playing an active role in their health-care. A special case is the increasing number of women, who are reluctant to use exogenous hormone therapy for the treatment of menopausal symptoms and are looking for complementary therapies. However, food supplements are not clearly regulated in Europe. The EFSA has only recently begun to address the issues of botanical safety and purity regulation, leading to a variability of content, standardization, dosage, and purity of available products. In this study, isoflavones (puerarin, daidzin, genistin, daidzein, glycitein, genistein, formononetin, prunetin, and biochanin A) from food supplements (n = 15) for menopausal symptoms relief are evaluated and compared with the labelled information. Only four supplements complied with the recommendations made by the EC on the tolerable thresholds. The intestinal bioavailability of these compounds was investigated using Caco-2 cells. The apparent permeability coefficients of the selected isoflavonoids across the Caco-2 cells were affected by the isoflavone concentration and product matrix.

Antitumor Activity of Total Flavonoids from Daphne genkwa in Colorectal Cancer

Daphne genkwa Sieb.et Zucc. is a well-known medicinal plant. This study was designed to investigate the anticancer effects of total flavonoids in D. genkwa (TFDG) in vitro and in vivo. HT-29 and SW-480 human colorectal cancer cells were cultured to investigate the anticancer activity of TFDG. In addition, the Apc(Min/+) mouse model was applied in the in vivo experiment. Results of the cell experiment revealed that TFDG possessed significant inhibitory effects on HT-29 and SW-480 human colorectal cancer cells (both p < 0.01). Furthermore, our in vivo data showed that after treatment with TFDG, there was a significant increase in life span (both p < 0.01) and tumor numbers were reduced in the colon (both p < 0.01), which was supported by the data of tumor distribution, body weight changes and organ index. Our results also indicated that expressions of interleukin (IL)-1α, IL-1β, IL-6, granulocyte colony-stimulating factor and granulocyte-macrophage colony-stimulating factor in gut tissue were downregulated by treatments of TFDG, and immunity cytokine secretions in the serum were regulated after oral administration of TFDG. Taken together, these findings suggested that TFDG has a potential clinical utility in colorectal cancer therapeutics, and TFDG's action is likely linked to its ability to regulate immune function and inhibit the production of inflammatory cytokines.

Comparison of absorption of 1-deoxynojirimycin from mulberry water extract in rats

In this study, we compared the absorption and excretion of DNJ in mulberry leaf extract against that of the purified compound (DNJ) using GC-TOF-MS, a newly developed analytical method, when administered orally to rats. Moreover, we also compared absorption levels in small intestinal cells using the Caco-2 cell line. In the cell study, DNJ absorption from the mulberry extract seemed to be inhibited when compared to that of the purified DNJ compound. The concentration of DNJ in rat plasma was also significantly (p < 0.05) lower when the mulberry extract was administered versus the purified DNJ compound. The metabolic pattern of DNJ from the mulberry leaf extract indicated that most was excreted in the feces, whereas a lower amount was detected in the urine, which was similar to the purified DNJ compound. These findings indicate that the bioavailability of DNJ in mulberry leaf extract might be lower than that of highly purified DNJ.

The Ussing type chamber model to study the intestinal transport and modulation of specific tight-junction genes using a colonic cell line

Polyphenols in apples, such as various hydroxycinnamic acids and flavonoids, have positive health effects that strongly depend on their bioavailability. In order to show that the Ussing-type chamber is a useful model to study metabolism, transport, and tightness of cell monolayers in one experimental setup, monolayers of the T84 colon carcinoma cell line mounted in Ussing-type chambers were incubated in the presence of physiological concentrations of various hydroxycinnamic acids (including ferulic, isoferulic, cinnamic, and hydrocinnamic acids) and flavonoids for 4 h. Concentrations of each tested polyphenol in the apical chamber, basolateral chamber, and those associated with the cells were then determined using HPLC with DAD (HPLC-DAD). The transport studies showed that the amounts of the tested polyphenols that passed from the apical to the basolateral side of the T84 monolayers depended on their polarity. Metabolites, such as glucuronides and sulfates of ferulic acid, were also detected at measurable levels by HPLC-ESI-MS/MS in the model system, but only when they were supplied at supra-physiological concentrations (>100 microM). In addition, the transepithelial resistance (TER) of T84 monolayers was measured before and after the addition of polyphenols, with and without short-term exposure to apical sodium caprate (C10), a tight junction (TJ) modulator. Exposure to C10 induced a decrease in TER that was reversible by incubation with polyphenols. However, no increase in paracellular permeability of tested polyphenols was observed after apical C10 exposure, so C10 did not promote fluxes of hydroxycinnamic acids across the monolayers. Further, real-time PCR analysis of the T84 colon cell line showed that ferulic and isoferulic acids induced significant increases in expression of the TJ components zonula occludens-1 (ZO-1) and claudin-4 transcription, but reductions in occludin expression. In contrast, caffeic and p-coumaric acids had no significant effects on the transcription of either ZO-1 or occludin. Our results provide confirmation that T84 cells could be used as model system to simulate the intestinal mucosa, and that polyphenols are able to increase the TER of C10-treated and -untreated T84 monolayers.

Permeability profile estimation of flavonoids and other phenolic compounds by biopartitioning micellar capillary chromatography

This paper points out the usefulness of biopartitioning micellar chromatography (BMC) using capillary columns as a high-throughput primary screening tool providing key information about the oral absorption, skin permeability, and brain-blood distribution coefficients of 15 polyphenols (6 flavones, 2 flavonols, a flavanone, 2 flavan-3-ols, 3 phenolic acids, and a phloroglucinol) in a simple and economical way. For the compounds studied, except vicenin-2, rutin, chlorogenic acid, p-hydroxycinnamic acid, and 4-hydroxybenzoic acid, maximal oral absorption (>90%) can be expected, if there are not solubility problems or metabolic processes. On the other hand, the most retained compounds in BMC, that is, 5-hydroxyflavone, flavone, and flavanone, show the highest brain-blood distribution coefficients and skin permeability coefficients.

Characteristics of (+)-catechin and (-)-epicatechin transport across pig intestinal brush border membranes

BACKGROUND/AIMS

(+)-Catechin and (-)-epicatechin are considered as disease preventive flavan-3-ols of foods like fruits, beverages and chocolate. We investigated mechanisms and kinetics of (+)-catechin and (-)-epicatechin uptake employing a validated in vitro model with isolated pig brush border membrane vesicles.

METHODS

Vesicles were isolated from pig small intestine employing the divalent cation method. Characterization (marker enzymes, electron microscopy) confirmed their purity and function. Transport studies with (+)-catechin and (-)-epicatechin under predefined conditions [presence/absence of sodium, pH gradient, temperature (8-37 degrees C), various initial substrate concentrations (2-20 mmol/l)] revealed a measurable transport (HPLC analyses) across the brush border membrane for both substrates.

RESULTS

Catechin transport was stimulated by an outwardly directed H(+) gradient (pH(i) 5.5/pH(o) 7.5). The presence of an inwardly directed Na(+) gradient did not result in a transient overshoot in (+)-catechin and (-)-epicatechin uptake. At 37 degrees C, subtraction of diffusion from the total transport rate showed saturation kinetics.

CONCLUSION

Our in vitro study indicate that both (+)-catechin and (-)-epicatechin are transported across the basolateral membrane using a dual transport system consisting of free diffusion (dominant at low concentrations) and carrier-mediated facilitated diffusion.

Flavone initiates a hierarchical activation of the caspase-cascade in colon cancer cells

There is emerging evidence that dietary factors can prevent cancer by affecting the process of carcinogenesis. Flavonoids present in vegetarian food possess antioxidant activities, have scavenging effects on activated carcinogens and mutagens, affect cell cycle progression and alter gene and protein expression. We report here that flavone, the core structure of the flavone subgroup, potently inhibits proliferation and induces apoptosis in HCT-116 colon cancer cells. Flavone induces the activation of caspases 2, 3, 8, 9 and 10 and a decrease of mitochondrial anti-apoptotic Bcl(2) protein expression. Further analysis revealed that caspase 10 activation is mediated via caspase 1. Additionally, treatment with flavone results in release of the mitochondrial apoptosis-inducing factor (AIF), the key trigger of caspase-independent apoptosis, into the cytosol. In summary, our data show that flavone induces apoptosis in a caspase-dependent and -independent manner.

Dietary polyphenols decrease glucose uptake by human intestinal Caco-2 cells

The effect of different classes of dietary polyphenols on intestinal glucose uptake was investigated using polarised Caco-2 intestinal cells. Glucose uptake into cells under sodium-dependent conditions was inhibited by flavonoid glycosides and non-glycosylated polyphenols whereas aglycones and phenolic acids were without effect. Under sodium-free conditions, aglycones and non-glycosylated polyphenols inhibited glucose uptake whereas glycosides and phenolic acids were ineffective. These data suggest that aglycones inhibit facilitated glucose uptake whereas glycosides inhibit the active transport of glucose. The non-glycosylated dietary polyphenols appear to exert their effects via steric hindrance, and (-)-epigallochatechingallate, (-)-epichatechingallate and (-)-epigallochatechin are effective against both transporters.

In vitro digestion and lactase treatment influence uptake of quercetin and quercetin glucoside by the Caco-2 cell monolayer

BACKGROUND

Quercetin and quercetin glycosides are widely consumed flavonoids found in many fruits and vegetables. These compounds have a wide range of potential health benefits, and understanding the bioavailability of flavonoids from foods is becoming increasingly important.

METHODS

This study combined an in vitro digestion, a lactase treatment and the Caco-2 cell model to examine quercetin and quercetin glucoside uptake from shallot and apple homogenates.

RESULTS

The in vitro digestion alone significantly decreased quercetin aglycone recovery from the shallot digestate (p < 0.05), but had no significant effect on quercetin-3-glucoside recovery (p > 0.05). Digestion increased the Caco-2 cell uptake of shallot quercetin-4'-glucoside by 2-fold when compared to the non-digested shallot. Despite the loss of quercetin from the digested shallot, the bioavailability of quercetin aglycone to the Caco-2 cells was the same in both the digested and non-digested shallot. Treatment with lactase increased quercetin recovery from the shallot digestate nearly 10-fold and decreased quercetin-4'-glucoside recovery by more than 100-fold (p < 0.05), but had no effect on quercetin recovery from apple digestates. Lactase treatment also increased shallot quercetin bioavailability to the Caco-2 cells approximately 14-fold, and decreased shallot quercetin-4'-glucoside bioavailability 23-fold (p < 0.05). These Caco-2 cells had lactase activity similar to that expressed by a lactose intolerant human.

CONCLUSIONS

The increase in quercetin uptake following treatment with lactase suggests that dietary supplementation with lactase may increase quercetin bioavailability in lactose intolerant humans. Combining the digestion, the lactase treatment and the Caco-2 cell culture model may provide a reliable in vitro model for examining flavonoid glucoside bioavailability from foods.

Permeability characteristics and membrane affinity of flavonoids and alkyl gallates in Caco-2 cells and in phospholipid vesicles

Biomembrane interactions of flavonoids and alkyl gallates were investigated using transport studies on Caco-2 cells and membrane affinity experiments in phospholipid vesicles. Flavone was rapidly absorbed across the cell monolayer (P(app),380 x 10(-6) cm/s), whereas efficient uptake but no apical to basolateral transport was observed with the flavonoids with higher degree of hydroxylation (e.g., quercetin and luteolin). The transport of alkyl gallates was governed by the length of the alkyl chain, i.e., methyl and propyl gallate were absorbed while octyl gallate showed cellular uptake but no transport. Flavonoids with several hydroxyl groups exhibited highest affinity for vesicle membranes, partition coefficients being 7.1 and 7.5 microM for luteolin and quercetin, respectively. In conclusion, the degree of hydroxylation, molecular configuration, and length of the side chain of flavonoids and alkyl gallates seem to have a highly important impact on their membrane affinity as well as on their permeability characteristics in Caco-2 cells.

Absorption of quercetin-3-glucoside and quercetin-4'-glucoside in the rat small intestine: the role of lactase phlorizin hydrolase and the sodium-dependent glucose transporter

Two hypotheses on absorption mechanisms of flavonoid glucosides across the small intestine have been proposed: active uptake of the quercetin glucoside by the sodium-dependent glucose transporter (SGLT1) with subsequent deglycosylation within the enterocyte by cytosolic beta-glucosidase, or luminal hydrolysis of the glucoside by lactase phlorizin hydrolase (LPH) and absorption by passive diffusion of the released aglycone. To test the above hypotheses we employed phlorizin (as an inhibitor of SGLT1) and N-(n-butyl)-deoxygalactonojirimycin (as an inhibitor of the lactase domain of LPH) in a rat everted-jejunal sac model. Quercetin-4'-glucoside mucosal hydrolysis was 10 times greater than quercetin-3-glucoside hydrolysis in the absence of inhibitors (449 and 47 nmol g(-1) tissue, respectively), despite the similar amounts (13+/-4 and 9+/-1 nmol g(-1), respectively) being transferred to the serosal compartment during the 15 min incubation. Apical hydrolysis of both quercetin glucosides was significantly reduced in the presence of NB-DGJ (80%), and transfer of quercetin (measured as quercetin metabolites) to the serosal solution was also significantly reduced (40-50%). In the presence of phlorizin, transfer of metabolites to the serosal solution was only reduced in the case of quercetin-4'-glucoside. Evidently the mechanism of absorption of quercetin-4'-glucoside involves both an interaction with SGLT1 and luminal hydrolysis by LPH, whereas quercetin-3-glucoside appears to be absorbed only following hydrolysis by LPH.

Flavonoids and gene expression in mammalian cells

Flavonoids appear to regulate the expression of many genes. As expected, when multiple flavonoids were compared in one study, structure-specificity was always observed. Unfortunately, little information is available regarding the proportion of contribution of various structural elements. Also, we have very limited information on their molecular mechanisms of action. The affinity of flavonoids for ER could explain the stimulatory effect on genes with ERE but other modes of action apparently also exist and need to be further explored. Physiological relevance is always a concern when investigating the regulation of gene expression by environmental chemicals such as flavonoids. One factor of concern is the in vivo concentration of flavonoids. Besides intestinal cells, liver cells and skin cells, other tissues obtain flavonoids through blood circulation. Thus, plasma concentrations of flavonoids are normally discussed. Steady state plasma concentrations of flavonoids are usually not much higher than 1 microM even in populations that consume large amounts of plant material. This concentration is relatively low compared to the concentrations of flavonoids that were commonly used in cell culture systems to demonstrate their effectiveness. Nevertheless, we have evidence that some flavonoids may accumulate in the cell. The effect of quercetin on metallothionein expression in Caco-2 cells persisted for at least 24 hours after its removal from the culture medium (Kuo et al., 1998). Also, long-term treatment of cultured cells with quercetin at low concentrations led to a similar effect on metallothionein expression as one high concentration treatment (Kuo et al., 2001). If intracellular accumulation of certain flavonoids is a shared characteristic for various cell types, it implies that routine ingestion of flavonoids could lead to biological effects at the concentration lower than predicted from a single treatment. Experiments to address possible cell/tissue accumulation of flavonoids are greatly needed.

The biochemistry and medical significance of the flavonoids

Flavonoids are plant pigments that are synthesised from phenylalanine, generally display marvelous colors known from flower petals, mostly emit brilliant fluorescence when they are excited by UV light, and are ubiquitous to green plant cells. The flavonoids are used by botanists for taxonomical classification. They regulate plant growth by inhibition of the exocytosis of the auxin indolyl acetic acid, as well as by induction of gene expression, and they influence other biological cells in numerous ways. Flavonoids inhibit or kill many bacterial strains, inhibit important viral enzymes, such as reverse transcriptase and protease, and destroy some pathogenic protozoans. Yet, their toxicity to animal cells is low. Flavonoids are major functional components of many herbal and insect preparations for medical use, e.g., propolis (bee's glue) and honey, which have been used since ancient times. The daily intake of flavonoids with normal food, especially fruit and vegetables, is 1-2 g. Modern authorised physicians are increasing their use of pure flavonoids to treat many important common diseases, due to their proven ability to inhibit specific enzymes, to simulate some hormones and neurotransmitters, and to scavenge free radicals.

Potential role of dietary flavonoids in reducing microvascular endothelium vulnerability to oxidative and inflammatory insults ( small star, filled)

Although antioxidant systems help control the level of reactive oxygen species they may be overwhelmed during periods of oxidative stress. Evidence suggests that oxidative stress components as well as inflammatory mediators may be involved in the pathogenesis of vascular disorders, where localized markers of oxidative damage have been found. In this regard we investigated the putative antioxidant and anti-inflammatory effects of blueberry and cranberry anthocyanins and hydroxycinnamic acids against H(2)O(2) and TNFalpha induced damage to human microvascular endothelial cells. Polyphenols from both berries were able to localize into endothelial cells subsequently reducing endothelial cells vulnerability to increased oxidative stress at both the membrane and cytosol level. Furthermore, berry polyphenols also reduced TNFalpha induced up-regulation of various inflammatory mediators (IL-8, MCP-1 and ICAM-1) involved in the recruitment of leukocytes to sites of damage or inflammation along the endothelium. In conclusion, polyphenols isolated from both blueberry and cranberry were able to afford protection to endothelial cells against stressor induced up-regulation of oxidative and inflammatory insults. This may have beneficial actions against the initiation and development of vascular diseases and be a contributing factor in the reduction of age-related deficits in neurological impairments previously reported by us.

Evidence for consistent patterns between flavonoid structures and cellular activities

A wide variety of plant-derived compounds, including the polyphenolic flavonoids, is present in the human diet or is consumed for medicinal reasons. Epidemiological and animal studies tend to suggest a protective effect of flavonoids against cardiovascular diseases and some types of cancer. Although flavonoids have been studied for about 50 years, the cellular mechanisms involved in their biological activity are still largely unknown. Antioxidant properties of the flavonoids have been postulated as a mechanism for putative protective effect against cardiovascular disease. Nevertheless, these properties alone are not sufficient to explain the anti-carcinogenic potential of these polyphenols. The mechanisms by which the molecules interact with cells or are absorbed by them are very important for determining the intracellular concentration and distribution of the metabolites to internal organs. With the exception of the cells lining the gastrointestinal tract, all other cells in the body are only exposed to flavonoid metabolites and degradation products. No previous studies have addressed this aspect of cellular exposure, except for some methylated metabolites. Within the last decade, reports on flavonoid activities have been largely associated with enzyme inhibition and anti-proliferative activity. From our recent work on the human colon cancer cell line HT29 and comparison with published studies, structure-function relationships demonstrate that antioxidant, enzyme inhibitor or anti-proliferative activities are dependent on particular structure motifs. The present review also presents a summary of mechanistic data on a few elected compounds.

Transport of proanthocyanidin dimer, trimer, and polymer across monolayers of human intestinal epithelial Caco-2 cells

The gut absorption of proanthocyanidins (PAs) and of the related (+)-catechin monomer was investigated with colonic carcinoma (Caco-2) cells of a human origin, grown in monolayers on permeable filters. Permeability of various radiolabeled PAs differing in their molecular weight was compared with that of the radiolabeled (+)-catechin. No toxicity was observed at PA concentrations up to the physiological concentration of 1 mM. (+)-Catechin and PA dimer and trimer had similar permeability coefficients (P(app) = 0.9-2.0 x 10(-6) cm s(-1)) close to that of mannitol, a marker of paracellular transport. Paracellular transport was also indicated by the increase of absorption after reduction of the transepithelial electric resistance through calcium ion removal. In contrast, permeability of a PA polymer with an average polymerization degree of 6 (molecular weight 1,740) was approximately 10 times lower (P(app) = 0.10 +/- 0.04 x 10(-6) cm s(-1)). PAs, particularly the most astringent PA polymer, were also adsorbed on the epithelial cells. These results suggest that PA dimers and trimers could be absorbed in vivo and that polymer bioavailability is limited to the gut lumen.

Transcellular transport of genistein, a soybean-derived isoflavone, across human colon carcinoma cell line (Caco-2)

Genistein, a soybean-derived isoflavone, is thought to have an anticarcinogenic action, but little is known about the cellular mechanisms of its intestinal absorption. This study was designed to investigate the absorption mechanisms of genistein using human colon carcinoma cell line, Caco-2 cells. The apical-to-basolateral transcellular transport of genistein across a Caco-2 cell monolayer was significantly greater than that in the opposite direction. An uptake experiment revealed that cellular uptake of genistein by Caco-2 cells was concentrative. The transcellular transport of genistein was saturable and temperature-dependent, and was inhibited by other flavonoids such as rutin, quercetin, (+)-catechin and (-)-epicatechin. These results suggest that genistein is transported across Caco-2 cells by a carrier-mediated system, located on the apical membrane.

Intracellular accumulation of ascorbic acid is inhibited by flavonoids via blocking of dehydroascorbic acid and ascorbic acid uptakes in HL-60, U937 and Jurkat cells

In HL-60, U937 and Jurkat cells, the intracellular accumulation of ascorbic acid occurred via uptakes of both dehydroascorbic acid (an oxidized metabolite of ascorbic acid) and ascorbic acid (vitamin C). Dehydroascorbic acid and ascorbic acid were transported into cells by sodium-independent glucose transporters (GLUT 1 and GLUT 3) and sodium-dependent ascorbic acid transporters, respectively. Flavonoids inhibited the intracellular accumulation of ascorbic acid by blocking dehydroascorbic acid and ascorbic acid uptakes in the transformed cells. At flavonoid concentrations of 10-70 micromol/L, approximately 50% of dehydroascorbic acid uptake was inhibited in the cells. In Jurkat cells, two potent flavonoids (myricetin and quercetin) competitively inhibited dehydroascorbic acid uptake, and K(i) values were approximately 14 and 15 micromol/L, respectively. Because GLUT 1 and GLUT 3 transport dehydroascorbic acid, the inhibition of dehydroascorbic acid uptake by flavonoids was investigated by using Chinese hamster ovary cells overexpressing rat GLUT 1 or human GLUT 3. Myricetin at concentrations of 22 and 18 micromol/L, respectively, inhibited half of dehydroascorbic acid uptake in the cells overexpressing GLUT 1 and GLUT 3. Myricetin also inhibited ascorbic acid uptake; inhibition was noncompetitive with K(i) = 14 micromol/L in Jurkat cells. These data indicate that flavonoids inhibit both ascorbic acid and dehydroascorbic acid uptake but do so by different mechanisms. These data may contribute to new understanding of the biological effect of flavonoids on the intracellular accumulation of ascorbic acid in human cells.