Novel Regioselective Synthesis of Urolithin Glucuronides─Human Gut Microbiota Cometabolites of Ellagitannins and Ellagic Acid

Abstract

Urolithins (dibenzo-pyran-[b,d]-6 one derivatives) are human gut microbiota metabolites produced from the natural food antioxidant ellagic acid. Urolithins are better absorbed than ellagic acid and demonstrate biological activities that suggest that they are responsible for the health effects observed after consuming ellagitannin-and ellagic acid-containing foods. Urolithins occur in the systemic circulation as glucuronide conjugates following phase II metabolism. These phase II conjugates are essential for testing the urolithin mechanisms of action in human cell line bioassays. Urolithin glucuronides are not commercially available, and their biosynthesis leads to mixtures of regional isomers. This study describes a novel and regioselective synthesis of urolithin A (3,8dihydroxy urolithin) 3-and 8-glucuronides and isourolithin A (3,9-dihydroxy urolithin) 3-and 9-glucuronides. The metabolites were characterized using 1 H and 13 C NMR spectroscopy and UV spectrophotometry. The presence of these metabolites in human subjects belonging to different urolithin metabotypes was also investigated.

Separation of Isomeric Forms of Urolithin Glucuronides Using Supercritical Fluid Chromatography

“…In recent years, the number of research articles devoted to investigating urolithins has increased exponentially, with significant advances in the knowledge of their physiological effects, − the metabolic pathways involved, and their presence in different biological samples (plasma, urine, feces, and tissues). − The most widely used analytical techniques rely on high- or ultra-high-performance liquid chromatography (HPLC or UHPLC, respectively) in the reverse-phase mode employing C 18 -based columns coupled to spectrophotometric (UV–vis or DAD) and mass spectrometric (MS) detectors. ,,, However, the separation of isomeric forms of glucuronide urolithins using reversed-phase liquid chromatography has not been feasible as urolithin A 3- and 8-glucuronide and isourolithin A-9-glucuronide are not resolved to enable their identification and quantification eluting as a single chromatographic peak. ,, …”

“…Three different urolithin metabotypes (0, A, and B), depending on the final urolithins produced by the gut microbiota (urolithin A, isourolithin A, and urolithin B), have been reported in humans after the intake of food containing ellagitannins and ellagic acid . Glucuronides of these urolithins are not commercially available, but some of the regioisomeric isomers have been recently synthesized . The analysis of the different metabolites is very relevant for describing the urolithin metabotypes and detecting differences in the phase II metabolites produced.…”

“…5 Glucuronides of these urolithins are not commercially available, but some of the regioisomeric isomers have been recently synthesized. 7 The analysis of the different metabolites is very relevant for describing the urolithin metabotypes and detecting differences in the phase II metabolites produced. The differences in the occurrence of these metabolites could be linked to different polymorphisms that could be related to the observed differences in the urolithinśbiological effects.…”

“…8,10,13,14 However, the separation of isomeric forms of glucuronide urolithins using reversed-phase liquid chromatography has not been feasible as urolithin A 3-and 8-glucuronide and isourolithin A-9-glucuronide are not resolved to enable their identification and quantification eluting as a single chromatographic peak. 7,13,15 Due to the resolution limitations of reversed-phase HPLC for analyzing urolithin glucuronides, other analytical methods should be explored to sufficiently separate these metabolites. A better peak resolution of urolithin glucuronides is essential to evaluate the differences in metabolites produced by the combined metabolism of gut microbiota, which leads to different final urolithins.…”

Chestnut Wood Mud as a Source of Ellagic Acid for Dermo-Cosmetic Applications

“…Despite its remarkable properties, the wide application of EA is limited by its low permeability and low solubility in aqueous solvents. To overcome these drawbacks, several approaches have been proposed, involving modulation of EA solubility properties through encapsulation or chemical derivatization [ 18 , 19 , 20 , 21 , 22 , 23 ], and different type of formulations based on e.g., pectins [ 24 , 25 ], chitosan [ 25 , 26 , 27 ], chitin [ 28 ], zein [ 5 ], cellulose [ 29 ], cyclodextrins [ 30 , 31 , 32 ], poly(lactide-co-glycolide) (PLGA) [ 33 ], graphene oxide [ 34 ], alginate [ 35 ], and microalgae [ 36 ] have been designed for the controlled release of this compound.…”