Pilot walnut intervention study of urolithin bioavailability in human volunteers

A pilot intervention study was conducted in human volunteers (n = 4) to establish the bioavailability of urolithins, which are the terminal end-products of ellagitannin metabolism by the gastrointestinal microflora. Biospecimens (blood, feces, and urine) along with urolithins purified therefrom were analyzed for their antioxidant capacity in a range of in vitro assays. Urolithin metabolites were identified and quantitated in the biospecimens by negative ion mode HPLC-ESI-MS analysis. The data in this pilot study show that the metabolism of ellagitannins in the four volunteers gave rise to a diverse profile and a highly variable concentration of urolithins in urine. The concentration of glucuronidated urolithins in blood and urine did not correlate with antioxidant capacity. However, the antioxidant capacity of urine, but not plasma biospecimens, was highly correlated with uric acid concentration. The antioxidant capacity of fecal extracts correlated positively with the concentration of urolithin D in both the DPPH and FRAP assays, but not in the ORAC assay, which was entirely consistent with the in vitro assays for pure urolithin D.

Preparation of penta-O-galloyl-β-D-glucose from tannic acid and plasma pharmacokinetic analyses by liquid-liquid extraction and reverse-phase HPLC

The gallotannin penta-O-galloyl-beta-D-glucose (PGG) has many biological activities including in vivo anti-cancer efficacy. We present in this paper a scaled-up protocol for its preparation in high purity from tannic acid by acidic methanolysis with typical yield of 15%. We also describe a method for the analysis of PGG in mouse plasma by HPLC and its application in preliminary pharmacokinetic studies. A liquid-liquid extraction (LLE) protocol was optimized for the extraction of PGG from mouse plasma. The extraction efficiency for PGG at 1 μg/mL in mouse plasma was 70.0±1.3% (n=5). The limit of detection (LOD) for PGG was approximately 0.2 μg/mL. Preliminary pharmacokinetic parameters of PGG following a single i.p. injection with 5% ethanol/saline vehicle in mice were established. The peak plasma PGG concentrations (C(max)) were approximately 3-4 μM at a dose of 0.5 mg per mouse (∼20 mg/kg) at 2 h post-injection (T(max)).

Bioavailability of anthocyanins and ellagitannins following consumption of raspberries by healthy humans and subjects with an ileostomy

The fate of anthocyanins, ellagic acid, and ellagitannins was studied following the consumption of 300 g of raspberries by healthy human volunteers and subjects with an ileostomy. Postingestion plasma and urine from the former and ileal fluid and urine from the latter group were collected and analyzed by HPLC-PDA-MS(2). Plasma from the healthy volunteers did not contain detectable quantities of either the native raspberry polyphenolics or their metabolites. The three main raspberry anthocyanins were excreted in urine in both healthy and ileostomy volunteers 0-7 h after ingestion, in quantities corresponding to <0.1% of intake. This indicates a low level of absorption in the small intestine. With ileostomy volunteers 40% of anthocyanins and 23% of the ellagitannin sanguiin H-6 were recovered in ileal fluid with the main excretion period being the first 4 h after raspberry consumption. The recovery of ellagic acid in ileal fluid was 241%, indicating hydrolysis of ellagitannins in the stomach and/or the small intestine. Urinary excretion of ellagic acid and an ellagic acid-O-glucuronide was <1% of intake. No intact or conjugated forms of ellagitannins were detected in urine from either healthy subjects or ileostomy volunteers. However, in healthy subjects, but not the ileostomists, ellagitannins were catabolized with the appearance of urolithin A-O-glucuronide, two of its isomers, and urolithin B-O-glucuronide in urine collected 7-48 h after raspberry consumption. There was marked variation in the urolithin profile of individual volunteers, indicating differences in the colonic microflora responsible for ellagitannin degradation.

Absorption, metabolism, and antioxidant effects of pomegranate (Punica granatum l.) polyphenols after ingestion of a standardized extract in healthy human volunteers

The intake of polyphenols has been demonstrated to have health-promoting and disease-preventive effects. The pomegranate (Punica granatum L.), which is rich in several polyphenols, has been used for centuries in ancient cultures for its medicinal purposes. The potential health benefits of pomegranate polyphenols have been demonstrated in numerous in vitro studies and in vivo experiments. This study investigated the absorption and antioxidant effects of a standardized extract from pomegranate in healthy human volunteers after the acute consumption of 800 mg of extract. Results indicate that ellagic acid (EA) from the extract is bioavailable, with an observed C(max) of 33 ng/mL at t(max) of 1 h. The plasma metabolites urolithin A, urolithin B, hydroxyl-urolithin A, urolithin A-glucuronide, and dimethyl ellagic acid-glucuronide were identified by HPLC-MS. The antioxidant capacity measured with the oxygen radical absorbance capacity (ORAC) assay was increased with a maximum effect of 32% after 0.5 h, whereas the generation of reactive oxygen species (ROS) was not affected. The inflammation marker interleukin-6 (IL-6) was not significantly affected after 4 h after the consumption of the extract. Overall, this study demonstrated the absorbability of EA from a pomegranate extract high in ellagitannin content and its ex vivo antioxidant effects.

Pomegranate juice ellagitannin metabolites are present in human plasma and some persist in urine for up to 48 hours

Ellagitannins (ETs) from pomegranate juice (PJ) are reported to have numerous biological properties, but their absorption and metabolism in humans are poorly understood. To investigate the pharmacokinetics of pomegranate ETs, 18 healthy volunteers were given 180 mL of PJ concentrate, and blood samples were obtained for 6 h afterwards. Twenty-four-hour urine collections were obtained on the day before (-1), the day of (0), and the day after (+1) the study. Ellagic acid (EA) was detected in plasma of all subjects with a maximum concentration of 0.06 +/- 0.01 micromol/L, area under concentration time curve of 0.17 +/- 0.02 (micromol x h) x L(-1), time of maximum concentration of 0.98 +/- 0.06 h, and elimination half-life of 0.71 +/- 0.08 h. EA metabolites, including dimethylellagic acid glucuronide (DMEAG) and hydroxy-6H-benzopyran-6-one derivatives (urolithins), were also detected in plasma and urine in conjugated and free forms. DMEAG was found in the urine obtained from 15 of 18 subjects on d 0, but was not detected on d -1 or +1, demonstrating its potential as a biomarker of intake. Urolithin A-glucuronide was found in urine samples from 11 subjects on d 0 and in the urine from 16 subjects on d +1. Urolithin B-glucuronide was found in the urine of 3 subjects on d 0 and in the urine of 5 subjects on d +1. Urolithins, formed by intestinal bacteria, may contribute to the biological effects of PJ as they may persist in plasma and tissues and account for some of the health benefits noted after chronic PJ consumption. Whether genetic polymorphisms in EA-metabolizing enzymes (e.g., catechol-O-methyl transferase and glucuronosyl transferase) are related to variations in response to PJ remains to be established.

The potent in vitro antioxidant ellagitannins from pomegranate juice are metabolised into bioavailable but poor antioxidant hydroxy?6H?dibenzopyran?6? one derivatives by the colonic microflora of healthy humans

BACKGROUND

The antiatherogenic activity of pomegranate juice has been attributed to its antioxidant polyphenols. The most potent in vitro antioxidant polyphenol from this juice is the ellagitannin punicalagin. However, the bioavailability of ellagitannins, including punicalagin, has not been previously described in humans.

AIM OF THE STUDY

The present work aims to evaluate, in healthy humans, the bioavailability and metabolism of pomegranate juice ellagitannins, to assess their effect on several blood parameters (including cardiovascular risk disease markers) and to compare the antioxidant activity of punicalagin with that of the in vivo generated metabolites.

DESIGN

Six healthy subjects (four men and two women) consumed 1 L of pomegranate juice daily (5.58 g/L polyphenols, including 4.37 g/L punicalagin isomers) for 5 days. The polyphenols and the in vivo generated metabolites were measured by HPLC-DAD-MS-MS. Fourteen haematological and twenty serobiochemical parameters including LDL, HDL and VLDL as well as cholesterol and triglycerides in each lipoprotein were evaluated. In vitro antioxidant activity of plasma (ABTS and FRAP assays) and urine (ABTS and DPPH) were determined.

RESULTS

Neither punicalagin nor ellagic acid present in the juice were detected in both plasma and urine. Three microbial ellagitannin-derived metabolites were detected: 3,8-dihydroxy-6H-dibenzo[b,d]pyran-6-one glucuronide, an unidentified aglycone (tentatively, trihydroxy-6H-dibenzo[b,d]pyran-6-one) and hydroxy-6-H-dibenzo[b,d]pyran-6-one glucuronide. These metabolites could reach up to 18.6 microM in plasma, although a large inter-individual variability was observed. In urine, the same metabolites and their corresponding aglycones became evident after 1 day of juice consumption. Total urine excretion of metabolites ranged from 0.7 to 52.7% regarding the ingested punicalagin. No relevant effect was observed on any blood parameter. The metabolites did not show significant antioxidant activity compared to punicalagin from pomegranate juice.

CONCLUSIONS

The potential systemic biological effects of pomegranate juice ingestion should be attributed to the colonic microflora metabolites rather than to the polyphenols present in the juice.

Determination of tannic acid and its phenolic metabolites in biological fluids by high-performance liquid chromatography

A method for the identification and determination of tannic acid and its phenolic metabolites in biological fluids by high-performance liquid chromatography was developed. Tannic acid and four phenolic compounds, namely gallic acid, pyrogallol, 4-O-methylgallic acid and ellagic acid, were successfully extracted from the biological fluids by using ethyl acetate at acidic conditions. Gallic acid, pyrogallol and 4-O-methylgallic acid were found in the sheep urine, gallic acid, 4-O-methylgallic acid and ellagic acid in plasma, and gallic acid and ellagic acid in abomasal fluid after abomasal dosing of tannic acid. Tannic acid was found in the plasma apart from the abomasal fluid into which it was administered. The concentrations of tannic acid, gallic acid, pyrogallol, 4-O-methylgallic acid and ellagic acid in plasma, abomasal fluid and urine were measured. This method could be applied to measurement of other hydrolysable tannins and their phenolic metabolites in biological materials.