Dietary Ellagitannins Research Articles

Urolithin A in Health and Diseases: Prospects for Parkinson's Disease Management.

Parkinson's disease (PD) is a chronic and progressive neurodegenerative disorder characterized by a complex pathophysiology and a range of symptoms. The prevalence increases with age, putting the ageing population at risk. Disease management includes the improvement of symptoms, the comfort of the patient's life, and palliative care. As there is currently no cure, growing evidence points towards the beneficial role of polyphenols on neurodegeneration. Numerous studies indicate the health benefits of the family of urolithins, especially urolithin A (UA). UA is a bacterial metabolite produced by dietary ellagitannins and ellagic acid. An expanding body of literature explores the involvement of the compound in mitochondrial health, and its anti-inflammatory, anti-oxidant, and anti-apoptotic properties. The review organizes the existing knowledge on the role of UA in health and diseases, emphasizing neurodegenerative diseases, especially PD. We gathered data on the potential neuroprotective effect in in vivo and in vitro models. We discussed the possible mechanisms of action of the compound and related health benefits to give a broader perspective of potential applications of UA in neuroprotective strategies. Moreover, we projected the future directions of applying UA in PD management.

Urolithins Modulate the Viability, Autophagy, Apoptosis, and Nephrin Turnover in Podocytes Exposed to High Glucose.

Urolithins are bioactive compounds generated in human and animal intestines because of the bacterial metabolism of dietary ellagitannins (and their constituent, ellagic acid). Due to their multidirectional effects, including anti-inflammatory, antioxidant, anti-cancer, neuroprotective, and antiglycative properties, urolithins are potential novel therapeutic agents. In this study, while considering the future possibility of using urolithins to improve podocyte function in diabetes, we assessed the results of exposing mouse podocytes cultured in normal (NG, 5.5 mM) and high (HG, 25 mM) glucose concentrations to urolithin A (UA) and urolithin B (UB). Podocytes metabolized UA to form glucuronides in a time-dependent manner; however, in HG conditions, the metabolism was lower than in NG conditions. In HG milieu, UA improved podocyte viability more efficiently than UB and reduced the reactive oxygen species level. Both types of urolithins showed cytotoxic activity at high (100 µM) concentration. The UA upregulated total and surface nephrin expression, which was paralleled by enhanced nephrin internalization. Regulation of nephrin turnover was independent of ambient glucose concentration. We conclude that UA affects podocytes in different metabolic and functional aspects. With respect to its pro-survival effects in HG-induced toxicity, UA could be considered as a potent therapeutic candidate against diabetic podocytopathy.

Ellagic Acid as a Tool to Limit the Diabetes Burden: Updated Evidence.

Oxidative stress contributes not only to the pathogenesis of type 2 diabetes (T2D) but also to diabetic vascular complications. It follows that antioxidants might contribute to limiting the diabetes burden. In this review we focus on ellagic acid (EA), a compound that can be obtained upon intestinal hydrolysis of dietary ellagitannins, a family of polyphenols naturally found in several fruits and seeds. There is increasing research on cardiometabolic effects of ellagitannins, EA, and urolithins (EA metabolites). We updated research conducted on these compounds and (I) glucose metabolism; (II) inflammation, oxidation, and glycation; and (III) diabetic complications. We included studies testing EA in isolation, extracts or preparations enriched in EA, or EA-rich foods (mostly pomegranate juice). Animal research on the topic, entirely conducted in murine models, mostly reported glucose-lowering, antioxidant, anti-inflammatory, and anti-glycation effects, along with prevention of micro- and macrovascular diabetic complications. Clinical research is incipient and mostly involved non-randomized and low-powered studies, which confirmed the antioxidant and anti-inflammatory properties of EA-rich foods, but without conclusive results on glucose control. Overall, EA-related compounds might be potential agents to limit the diabetes burden, but well-designed human randomized controlled trials are needed to fill the existing gap between experimental and clinical research.

Urolithin B suppresses tumor growth in hepatocellular carcinoma through inducing the inactivation of Wnt/β-catenin signaling.

Consumption of dietary ellagitannins (ETs) has been proven to benefit multiple chronic health disorders including cancers and cardiovascular diseases. Urolithins, gut microbiota metabolites derived from ETs, are considered as the molecules responsible for these health effects. Previous studies have demonstrated that urolithins exhibit antiproliferative effects on prostate, breast, and colon cancers. However, as for hepatocellular carcinoma (HCC), it remains elusive. Herein, we aim to investigate the function of urolithin B (UB), a member of urolithins family, in HCC. The effects of UB on cell viability, cell cycle and apoptosis were evaluated in HCC cells, and we found UB could inhibit the proliferation of HCC cells, which resulted from cell cycle arrest and apoptosis. Furthermore, UB could increase phosphorylated β-catenin expression and block its translocation from nuclear to cytoplasm, thus inducing the inactivation of Wnt/β-catenin signaling. Using a xenograft mice model, UB was found to suppress tumor growth in vivo. In conclusion, our data demonstrated that UB could inhibit the proliferation of HCC cells in vitro and in vivo via inactivating Wnt/β-catenin signaling, suggesting UB could be a promising candidate in the development of anticancer drugs targeting HCC.

Urolithin A gains in antiproliferative capacity by reducing the glycolytic potential via the p53/TIGAR axis in colon cancer cells.

Polyphenols have shown promising bioactivity in experimental in vitro and in vivo models for cancer chemoprevention. However, consumed orally, they are often transformed by gut microbes into new active principles with so far incompletely deciphered molecular mechanisms. Here, enterolacton, S-equol and urolithin A as representatives of metabolites of lignans, isoflavones and ellagitannins, respectively, were examined for their impact on HCT116 colon cancer cell growth, cooperativity with oxaliplatin and p53 dependency in vitro. Whereas enterolacton and S-equol (≤60 µM) did not elicit growth inhibition or positive cooperativity with oxaliplatin, urolithin A showed an IC50 value of 19 µM (72 h) and synergism with oxaliplatin. Urolithin A induced p53 stabilization and p53 target gene expression, and absence of p53 significantly dampened the antiproliferative effect of urolithin A (IC50(p53-/-) = 38 µM). P53 was dispensable for the G2/M arrest in HCT116 cells but required for induction of a senescence-like phenotype upon long-term exposure and for the observed synergism with oxaliplatin. Moreover, extracellular flux analyses and knockdown approaches uncovered a reduced glycolytic potential via the p53/TIGAR axis which was linked to the higher susceptibility of wildtype cells to urolithin A. Overall, the p53 status turned out to be an important determinant for the potential benefit of dietary ellagitannins in cancer chemoprevention or use in adjuvant therapy.

Ellagitannins from Pomegranate Ameliorates 5-Fluorouracil-Induced Intestinal Mucositis in Rats while Enhancing Its Chemotoxicity against HT-29 Colorectal Cancer Cells through Intrinsic Apoptosis Induction

Worldwide, colorectal cancer (CRC) is a deleterious disease causing millions of death annually. 5-Fluorouracil (5-FU) is a first-line chemotherapy for CRC, but chemoresistance and gastrointestinal mucositis limit its efficacy. Polyphenol-rich foods are increasingly popular due to their potential beneficial roles in preventing and treating cancer. Ellagitannins are a group of phenolic compounds commonly found in pomegranate, strawberries, raspberries, etc. The objective of this study was to explore whether ellagitannins from pomegranate (PETs) could ameliorate 5-FU-induced intestinal mucositis and enhance the drug's efficacy against CRC. The results showed that PETs (100 mg/kg) counteracted 5-FU-induced intestinal mucositis in rats. The number of apoptotic cells per crypt was reduced from 1.50 ± 0.21 to 0.85 ± 0.18 ( P < 0.05). Moreover, PETs induced HT-29 CRC cell death through intrinsic apoptosis, as demonstrated by dissipation of mitochondrial membrane potential, increased Bax-to-Bcl-2 ratio, and cleavage of caspase 9 and caspase 3. PETs and 5-FU combination treatments exhibited synergistic cytotoxicity against HT-29 cells with a weighted combination index of 0.3494. PETs (80 μg/mL) and 5-FU (40 μg/mL) treatments for 48 h induced 14.03 ± 0.76% and 16.42 ± 1.15% of HT-29 cells to undergo apoptosis, while the combination treatment further increased apoptosis of cells to 34.00 ± 1.54% ( P < 0.05). Combination treatment of the cells also enhanced S phase cell cycle arrest as compared with PETs or 5-FU monotherapy ( P < 0.05). These results suggest that dietary ellagitannins from pomegranate could alleviate intestinal mucositis in rats induced by 5-FU while enhancing its toxicity against HT-29 cells through potentiation of apoptosis and cell cycle arrest.

An increased autophagic flux contributes to the anti-inflammatory potential of urolithin A in macrophages

BackgroundAn extract of Phyllanthus muellerianus and its constituent geraniin have been reported to exert anti-inflammatory activity in vivo. However, orally consumed geraniin, an ellagitannin, shows low bioavailability and undergoes metabolization to urolithins by gut microbiota. This study aimed at comparing geraniin and urolithin A with respect to inhibition of M1 (LPS) polarization of murine J774.1 macrophages and shedding more light on possible underlying mechanisms. MethodsPhotometric, fluorimetric as well as luminescence-based assays monitored production of reactive oxygen species (ROS) and nitric oxide (NO), cell viability or reporter gene expression. Western blot analyses and confocal microscopy showed abundance and localization of target proteins, respectively. ResultsUrolithin A is a stronger inhibitor of M1 (LPS) macrophage polarization (production of NO, ROS and pro-inflammatory proteins) than geraniin. Urolithin A leads to an elevated autophagic flux in macrophages. Inhibition of autophagy in M1 (LPS) macrophages overcomes the suppressed nuclear translocation of p65 (NF-kB; nuclear factor kB), the reduced expression of pro-inflammatory genes as well as the diminished NO production brought about by urolithin A. The increased autophagic flux is furthermore associated with impaired Akt/mTOR (mammalian target of rapamycin) signaling in urolithin A-treated macrophages. Conclusions and general significanceIntestinal metabolization may boost the potential health benefit of widely consumed dietary ellagitannins, as suggested by side by side comparison of geraniin and urolithin A in M1(LPS) macrophages. Increased activity of the autophagic cellular recycling machinery aids the anti-inflammatory bioactivity of urolithin A.

Metabolic Fate of Ellagitannins: Implications for Health, and Research Perspectives for Innovative Functional Foods

Consumption of dietary ellagitannins (ETs) has been associated with different health benefits. Nonetheless, ETs are not bioavailable as such and are metabolized in vivo. They are partially converted into ellagic acid (EA) in the upper gastrointestinal (GI) tract, but this first metabolite is also poorly bioavailable. In the lower GI tract, EA and residual ETs are metabolized by gut microbiota to produce urolithins, which, together with their conjugate relatives, persist at relatively high concentrations in plasma and urine for days after ingestion of dietary ETs. Thus, ETs and EA may exert local health benefits on the GI tract but systemic health benefits are more likely to result from urolithins. Cellular models suggest that, at physiological concentration, urolithins are active against chronic degenerative diseases. Health benefits have been proven in animal models and during clinical studies. Even so, the crucial involvement of gut microbiota in ET bioconversion induces important variability of physiological response among humans, giving rise to the concept of high and low urolithin producers. This variability among consumers in obtaining potential health benefits from dietary ETs raises new challenges for the functional food industry. Different research perspectives are discussed to tackle this significant issue for nutritionists, food technologists, and consumers.

UV and MS Identification of Urolithins and Nasutins, the Bioavailable Metabolites of Ellagitannins and Ellagic Acid in Different Mammals

Urolithins are microbial metabolites produced from ellagic acid after the intake of dietary ellagitannins by different animals. Urolithin metabolites have distinct UV spectra that enable their detection and differentiation by HPLC coupled with UV photodiode array detectors. Correlations between structural characteristics, including conjugation, with the UV spectra and retention times are established. The production of urolithin derivatives in different animals feeding on ellagitannins, including rodents (rats and mice), humans, pigs, squirrels, beavers, sheep, bull calves, birds, and insects, was investigated. All mammals produced urolithins, and their glucuronyl and sulfate conjugates were the main metabolites detected in plasma and urine. Unconjugated urolithins were detected in feces, ruminal content, and beaver castoreum. Different urolithin hydroxylation patterns were observed for different animal species, suggesting that the microbiota responsible for the metabolism of ellagitannins in each animal species produces dehydroxylases for the removal of specific hydroxyls from the ellagic acid residue. Metabolites were characterized using HR HPLC-TOF-MS and ion trap MS/MS. Insects and birds feeding on ellagitannin-containing foods did not produce urolithins, although they released ellagic acid. Beavers and pigs were able to produce dehydroxyellagic acid derivatives (nasutin A), showing that in some cases the removal of hydroxyl groups from the ellagic acid nucleus can be carried out before the lactone ring is opened to produce urolithins.

Urolithins, Ellagic Acid-Derived Metabolites Produced by Human Colonic Microflora, Exhibit Estrogenic and Antiestrogenic Activities

Urolithins A and B (hydroxy-6H-dibenzo[b,d]pyran-6-one derivatives) are colonic microflora metabolites recently proposed as biomarkers of human exposure to dietary ellagic acid derivatives. Molecular models suggest that urolithins could display estrogenic and/or antiestrogenic activity. To this purpose, both urolithins and other known phytoestrogens (genistein, daidzein, resveratrol, and enterolactone) were assayed to evaluate the capacity to induce cell proliferation on the estrogen-sensitive human breast cancer MCF-7 cells as well as the ability to bind to alpha- and beta-estrogen receptors. Both urolithins A and B showed estrogenic activity in a dose-dependent manner even at high concentrations (40 microM), without antiproliferative or toxic effects, whereas the other phytoestrogens inhibited cell proliferation at high concentrations. Overall, urolithins showed weaker estrogenic activity than the other phytoestrogens. However, both urolithins displayed slightly higher antiestrogenic activity (antagonized the growth promotion effect of 17-beta-estradiol in a dose-dependent manner) than the other phytoestrogens. The IC(50) values for the ERalpha and ERbeta binding assays were 0.4 and 0.75 microM for urolithin A; 20 and 11 microM for urolithin B; 3 and 0.02 for genistein; and 2.3 and 1 for daidzein, respectively; no binding was detected for resveratrol and enterolactone. Urolithins A and B entered into MCF-7 cells and were metabolized to yield mainly urolithin-sulfate derivatives. These results, together with previous studies regarding absorption and metabolism of dietary ellagitannins and ellagic acid in humans, suggest that the gut microflora metabolites urolithins are potential endocrine-disrupting molecules, which could resemble other described "enterophytoestrogens" (microflora-derived metabolites with estrogenic/antiestrogenic activity). Further research is warranted to evaluate the possible role of ellagitannins and ellagic acid as dietary "pro-phytoestrogens".

The dietary hydrolysable tannin punicalagin releases ellagic acid that induces apoptosis in human colon adenocarcinoma Caco-2 cells by using the mitochondrial pathway

Polyphenol-rich dietary foodstuffs have attracted attention due to their cancer chemopreventive and chemotherapeutic properties. Ellagitannins (ETs) belong to the so-called hydrolysable tannins found in strawberries, raspberries, walnuts, pomegranate, oak-aged red wine, etc. Both ETs and their hydrolysis product, ellagic acid (EA), have been reported to induce apoptosis in tumour cells. Ellagitannins are not absorbed in vivo but reach the colon and release EA that is metabolised by the human microflora. Our aim was to investigate the effect of a dietary ET [pomegranate punicalagin (PUNI)] and EA on human colon cancer Caco-2 and colon normal CCD-112CoN cells. Both PUNI and EA provoked the same effects on Caco-2 cells: down-regulation of cyclins A and B1 and upregulation of cyclin E, cell-cycle arrest in S phase, induction of apoptosis via intrinsic pathway (FAS-independent, caspase 8-independent) through bcl-XL down-regulation with mitochondrial release of cytochrome c into the cytosol, activation of initiator caspase 9 and effector caspase 3. Neither EA nor PUNI induced apoptosis in normal colon CCD-112CoN cells (no chromatin condensation and no activation of caspases 3 and 9 were detected). In the case of Caco-2 cells, no specific effect can be attributed to PUNI since it was hydrolysed in the medium to yield EA, which entered into the cells and was metabolised to produce dimethyl-EA derivatives. Our study suggests that the anticarcinogenic effect of dietary ETs could be mainly due to their hydrolysis product, EA, which induced apoptosis via mitochondrial pathway in colon cancer Caco-2 cells but not in normal colon cells.

Metabolism of Antioxidant and Chemopreventive Ellagitannins from Strawberries, Raspberries, Walnuts, and Oak-Aged Wine in Humans: Identification of Biomarkers and Individual Variability

Ellagitannins (ETs) are dietary polyphenols, containing ellagic acid (EA) subunits, with antioxidant and cancer chemopreventive activities that might contribute to health benefits in humans. However, little is known about their metabolic fate. We investigate here the metabolism of different dietary ETs and EA derivatives in humans. Forty healthy volunteers were distributed in four groups. Each group consumed, in a single dose, a different ET-containing foodstuff, i.e., strawberries (250 g), red raspberries (225 g), walnuts (35 g), and oak-aged red wine (300 mL). After the intake, five urine fractions (F) were collected at 8 (F1), 16 (F2), 32 (F3), 40 (F4), and 56 (F5) h. Neither ETs nor EA were detected in urine after LC-MS/MS analysis. However, the microbial metabolite 3,8-dihydroxy-6H-dibenzo[b,d]pyran-6-one (urolithin B) conjugated with glucuronic acid was detected along the fractions F3-F5 in all of the subjects, independently of the consumed foodstuff. The mean percentage of metabolite excretion ranged from 2.8 (strawberries) to 16.6% (walnuts) regarding the ingested ETs. Considerable interindividual differences were noted, identifying "high and low metabolite excreters" in each group, which supported the involvement of the colonic microflora in ET metabolism. These results indicate that urolithin B (a previously described antiangiogenic and hyaluronidase inhibitor compound) is a biomarker of human exposure to dietary ETs and may be useful in intervention studies with ET-containing products. The antioxidant and anticarcinogenic effects of dietary ETs and EA should be considered in the gastrointestinal tract whereas the study of potential systemic activities should be focused on the bioavailable urolithin B derivatives.