Article pubs.acs.org/JAFC
Cite This: J. Agric. Food Chem. 2017, 65, 10738−10748
Ellagitannins from Strawberries with Different Degrees of Polymerization Showed Different Metabolism through Gastrointestinal Tract of Rats Joanna Milala,*,† Monika Kosmala,† Elzḃ ieta Karlińska,† Jerzy Juśkiewicz,‡ Zenon Zduńczyk,‡ and Bartosz Fotschki‡ †
Institute of Food Technology and Analysis, Lodz University of Technology, Stefanowskiego 4/10, 90-924 Lodz, Poland Institute of Animal Reproduction and Food Research of the Polish Academy of Sciences, Division of Food Science, Tuwima 10, 10-748 Olsztyn, Poland
‡
ABSTRACT: The present paper describes a comparative study of the metabolism of (1) ellagic acid, (2) monomeric ellagitannins (a mixture of α- and β-bis-hexahydroxydiphenoyl-D-glucose), and (3) dimeric ellagitannins (mainly agrimoniin with both glucose residues being esterified with hexahydroxydiphenoyl) in rats fed polyphenol-rich diets. Their metabolites were identified and quantified in selected parts of the gastrointestinal tract, i.e., the stomach, small intestine, and cecum, on the second, fourth, and seventh days of the experiment, as well as in the rats’ feces, blood serum, and urine. Significant differences between the metabolites of strawberry ellagitannins and ellagic acid were observed in all parts of the gastrointestinal tract. Urolithin A was the predominant polyphenolic metabolite of rats fed a diet supplemented with ellagic acid. On the other hand, in rats fed low degree of polymerization (DP) ellagitannins, the main metabolite was nasutin followed by urolithin A, while ellagitannins with a higher DP led to nasutin only. KEYWORDS: ellagitannins, nasutin, urolithin, rat, agrimoniin, strawberry
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INTRODUCTION
Polyphenols are known as antioxidants but have a much wider spectrum of activity, especially considering their low bioavailability as compared to endogenous antioxidants1 like glutathione, alpha-lipoic acid, coenzyme Q, ferritin, uric acid, and bilirubin. First of all, it must be remembered that large polyphenolic molecules cannot enter the bloodstream, in contrast to some simple polyphenols which are absorbed directly. The majority of ETs are hydrolyzed by colonic microorganisms, first into ellagic acid, and then into even smaller molecules, such as urolithins. The pattern of urolithin formation seems to be as follows: HHDP acid is released from ETs and converted into poly hydroxylated dibenzopyranone and then 3,4,8,9,10-pentahydroxy-6H-dibenzo[b,d]pyran-6-one (Uro-M5). Subsequently, sequential dehydroxylation leads to tetrahydroxy- (Uro-M6 and Uro-D), trihydroxy- (Uro-M7 and Uro-C), dihydroxy- (Uro-A and IsoUro-A), and monohydroxy- (Uro-B) dibenzopyranones. These metabolites may be absorbed into the bloodstream and eventually accumulate in the urine in the form of glucuronides and sulfate conjugates; they can be also excreted in the feces.13−18 A fully validated methodology for urolithin determination in terms of linearity, sensitivity, precision, recovery, matrix effect, selectivity, stability in different biological samples, and quantí fication was developed by Garcia-Villalba et al.,18 even though not all metabolites are commercially available. Depending on the host’s species and individual characteristics, the resulting metabolites may differ.19,20 The significance
Epidemiological studies have shown that the consumption of fruits and vegetables reduces the risk of lifestyle diseases such as atherosclerosis, cancer, and neurodegenerative disorders.1−3 Berry consumption beneficially modifies the lipid profile by significantly decreasing total cholesterol, low-density lipoprotein cholesterol, and triglyceride levels,4 which is largely attributable to the activity of polyphenols. Special attention has been attracted by ellagitannins (ETs), which are the most abundant strawberry polyphenols, along with anthocyanins and flavanols.5 In the study of Juśkiewicz et al.,6 strawberry ET preparations were shown to lower lipemia and glycaemia. Ellagitannins can be defined as hexahydroxydifenoyl esters of carbohydrates of cylitols as well as compounds derived from further oxidative transformations including oligomerization processes.7,8 ETs constitute a heterogeneous group of compounds differentiated in terms of the degree of polymerization (DP) and susceptibility to hydrolysis. The elementary building blocks such as ellagic acid and hexahydroxydiphenoyl (HHDP) may exist as free compounds or may be generated as a result of hydrolysis of larger molecules. Ellagic acid is a product of spontaneous lactonization within the HHDP acid molecule.9 The main strawberry ET is agrimoniin, a GOG-type dimer composed of two α-1-O-galloyl-2,3:4,6-bis-hexahydroxydiphenoylD-glucose units linked by a C−O−C bond between two gallic acid residues.7,10 Raspberries and blackberries primarily contain sanguiin H-6 and lambertianin C, the monomeric units of which are linked with a sanguisorboyl group.7,11 These structural differences may affect the physiological activity of polyphenols from Rosaceae fruits.12 © 2017 American Chemical Society
Received: Revised: Accepted: Published: 10738
September 4, 2017 November 14, 2017 November 16, 2017 November 16, 2017 DOI: 10.1021/acs.jafc.7b04120 J. Agric. Food Chem. 2017, 65, 10738−10748
Article
Journal of Agricultural and Food Chemistry
Figure 1. Strawberry ellagitannins and ellagic acid structures.
of polyphenolic metabolites, such as urolithins, is not fully understood. It is known that they have antioxidant properties. Urolithins (especially A and C) were very active toward O2•− direct scavenging; significantly inhibited neutrophil oxidative burst (stronger than ascorbic acid)21 and/or activate phase II enzymes, which are involved in antioxidant functions or detoxification (thioredoxin reductase-1 or glutathione peroxidases);1 and show anti-inflammatory activity, antiestrogenic/estrogenic
capacity due to structural analogy to estrogens, and anticancer effects.21−24 On the other hand, nonabsorbable large compounds may influence the colonic microbiota with the result of stimulating the activity of some strains while inhibiting others.22 In our previous study, a strawberry polyphenolic extract improved the prebiotic effects of a fructooligosaccharide (FOS) diet, beneficially lowering cecal digesta pH and reducing putrefactive short-chain fatty acid production. On the other hand, the addition of 10739
DOI: 10.1021/acs.jafc.7b04120 J. Agric. Food Chem. 2017, 65, 10738−10748
Article
Journal of Agricultural and Food Chemistry dietary FOS enhanced the metabolism of the examined strawberry extracts in the cecum, thereby increasing the concentrations of polyphenolic metabolites in the cecal digesta and urine.25 Our subsequent study26 showed that the DP influenced the effectiveness of blood glucose reduction by polyphenolics, with monomers more readily mitigating sugar-induced postprandial glycemic loads. Furthermore, it was found that ETs contained in a monomeric ET-rich extract were more prone to intestinal breakdown in the cecum than those present in a dimeric ET-rich extract, and absorption of their metabolites could be increased by dietary FOS; together, they elicited strong antibacterial activity.27 Interestingly, in previous investigations, nasutin was identified as one of the ET metabolites in rats.12,27,28 This compound was previously found in the feces of some wild rodents, including beavers, and termites.13,19,29 As molecular structure is important to the physiological function of ETs, the aim of this study was to identify and quantify the metabolites of ellagic acid and strawberry polyphenol preparations with monomeric (EM) and dimeric (ED) ellagitannins (Figure 1) in selected parts of the gastrointestinal tract of rats, i.e., the stomach, small intestine, and cecum, as well as in rat feces, blood serum, and urine.
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Table 1. Chemical and Polyphenolic Composition (%) of the Strawberry Extract composition chemical composition crude protein ether extract crude ash polyphenols free ellagic acid total ellagitannins dimeric ellagitannins agrimoniina (MW 1870) ellagitanninb (MW 2038) other dimeric elagitannins monomeric ellagitanninsc (MW 784d and e MW 952 ) proanthocyanidins flavonols and anthocyanins
EM
ED
EA
4.00
