Urolithin A Explained

Urolithin A is a metabolite compound resulting from the transformation of ellagitannins by the gut bacteria.[1] It belongs to the class of organic compounds known as benzo-coumarins or dibenzo-α-pyrones. Its precursors  - ellagic acids and ellagitannins  - are ubiquitous in nature, including edible plants, such as pomegranates, strawberries, raspberries, walnuts, and others.[2]

Urolithin A is not known to be found in any food source. Its bioavailability mostly depends on individual microbiota composition, as only some bacteria are able to convert ellagitannins into urolithins.

Chemistry

Urolithin A belongs to the class of organic compounds known as benzo-coumarins or dibenzo-α-pyrones. These are polycyclic aromatic compounds containing a 1-benzopyran moiety with a ketone group at the C2 carbon atom (1-benzopyran-2-one).

Biochemistry and metabolism

Pomegranate fruits, walnuts, and raspberries are sources of ellagitannins.[3] [4] [5] Ellagitannins are hydrolyzed in the gut to release ellagic acid, which is further processed by the gut microflora into urolithins through the loss of one of its two lactones and by successive removal of hydroxyl groups.[6]

While studies have shown that Gordonibacter urolithinfaciens and Gordonibacter pamelaeae play a role in the conversion of ellagic acids and ellagitannins into urolithin A, the microorganisms responsible for the complete transformation into the final urolithins are still unknown.[7] The efficiency of the conversion of ellagitannins into urolithin A significantly varies in humans, and some individuals do not show any conversion.

When synthesized and absorbed in the intestines, urolithin A enters the systemic circulation where it becomes available to tissues throughout the body where it is further subjected to additional chemical transformations (including glucuronidation, methylation, sulfation, or a combination of them) within the enterocytes and hepatocytes.[8] Urolithin A and its derivatives - urolithin A glucuronide and urolithin A sulfate being most abundant - release into the circulation, before being excreted in the urine.[9]

Safety

In vivo studies did not determine any toxicity or specific adverse effects following dietary intake of urolithin A.[10] Safety studies in elderly humans indicated urolithin A was well tolerated.[11] In 2018, the US Food and Drug Administration listed urolithin A as a safe ingredient for food products having content in the range of 250 mg to one gram per serving.[12]

Dietary sources

Urolithin A is not known to be found in any food but rather forms as the result of transformation of ellagic acids and ellagitannins by the gut microflora in humans. Sources of ellagitannins are: pomegranates, nuts, some berries (raspberries, strawberries, blackberries, cloudberries), tea, muscadine grapes, many tropical fruits, and oak-aged wines (table below).

The conversion of the ellagic acids into urolithin A depends on individual microflora composition and can vary significantly.[13] [14]

Dietary sourceEllagic Acid[15]
Fruits (mg/100g fresh weight)
Blackberries150
Black raspberries90
Boysenberries70
Cloudberries315.1
Pomegranate269.9[16]
Raspberries270
Rose hip109.6
Strawberries 77.6
Strawberry jam24.5
Yellow raspberries1900
Nuts (mg/g)
Pecans33
Walnuts59
Beverages (mg/L)
Pomegranate juice811.1
Cognac31-55
Oak-aged red wine33
Whiskey1.2
Seeds (mg/g)
Black raspberries6.7
Red raspberries8.7
Boysenberries30
Mango1.2

See also

External links

Notes and References

  1. Garcia-Muñoz C, Vaillant F . Metabolic fate of ellagitannins: implications for health, and research perspectives for innovative functional foods . Critical Reviews in Food Science and Nutrition . 54 . 12 . 1584–98 . 2014-12-02 . 24580560 . 10.1080/10408398.2011.644643 . 5387712 .
  2. Cerdá B, Tomás-Barberán FA, Espín JC . Metabolism of antioxidant and chemopreventive ellagitannins from strawberries, raspberries, walnuts, and oak-aged wine in humans: identification of biomarkers and individual variability . Journal of Agricultural and Food Chemistry . 53 . 2 . 227–35 . January 2005 . 15656654 . 10.1021/jf049144d .
  3. Johanningsmeier SD, Harris GK . Pomegranate as a functional food and nutraceutical source . Annual Review of Food Science and Technology . 2 . 1 . 181–201 . 2011-02-28 . 22129380 . 10.1146/annurev-food-030810-153709 .
  4. Sánchez-González C, Ciudad CJ, Noé V, Izquierdo-Pulido M . Health benefits of walnut polyphenols: An exploration beyond their lipid profile . Critical Reviews in Food Science and Nutrition . 57 . 16 . 3373–3383 . November 2017 . 26713565 . 10.1080/10408398.2015.1126218 . free . 19611576 . 2445/99551 .
  5. Ludwig IA, Mena P, Calani L, Borges G, Pereira-Caro G, Bresciani L, Del Rio D, Lean ME, Crozier A . 6 . New insights into the bioavailability of red raspberry anthocyanins and ellagitannins . Free Radical Biology & Medicine . 89 . 758–69 . December 2015 . 26475039 . 10.1016/j.freeradbiomed.2015.10.400 .
  6. Espín JC, Larrosa M, García-Conesa MT, Tomás-Barberán F . Biological significance of urolithins, the gut microbial ellagic Acid-derived metabolites: the evidence so far . Evidence-Based Complementary and Alternative Medicine . 2013 . 270418 . 2013 . 23781257 . 3679724 . 10.1155/2013/270418 . free .
  7. Selma MV, Beltrán D, Luna MC, Romo-Vaquero M, García-Villalba R, Mira A, Espín JC, Tomás-Barberán FA . 6 . Isolation of Human Intestinal Bacteria Capable of Producing the Bioactive Metabolite Isourolithin A from Ellagic Acid . Frontiers in Microbiology . 8 . 1521 . 2017 . 28824607 . 5545574 . 10.3389/fmicb.2017.01521 . free .
  8. Tulipani S, Urpi-Sarda M, García-Villalba R, Rabassa M, López-Uriarte P, Bulló M, Jáuregui O, Tomás-Barberán F, Salas-Salvadó J, Espín JC, Andrés-Lacueva C . 6 . Urolithins are the main urinary microbial-derived phenolic metabolites discriminating a moderate consumption of nuts in free-living subjects with diagnosed metabolic syndrome . Journal of Agricultural and Food Chemistry . 60 . 36 . 8930–40 . September 2012 . 22631214 . 10.1021/jf301509w . free . 2445/171748 . 43139238 .
  9. Truchado P, Larrosa M, García-Conesa MT, Cerdá B, Vidal-Guevara ML, Tomás-Barberán FA, Espín JC . Strawberry processing does not affect the production and urinary excretion of urolithins, ellagic acid metabolites, in humans . Journal of Agricultural and Food Chemistry . 60 . 23 . 5749–54 . June 2012 . 22126674 . 10.1021/jf203641r .
  10. Heilman J, Andreux P, Tran N, Rinsch C, Blanco-Bose W . Safety assessment of Urolithin A, a metabolite produced by the human gut microbiota upon dietary intake of plant derived ellagitannins and ellagic acid . Food and Chemical Toxicology . 108 . Pt A . 289–297 . October 2017 . 28757461 . 10.1016/j.fct.2017.07.050 .
  11. Singh A, Andreux P, Blanco-Bose W, Ryu D, Aebischer P, Auwerx J, Rinsch C . 2017-07-01 . Orally administered urolithin A is safe and modulates muscle and mitochondrial biomarkers in elderly . Innovation in Aging . 1 . suppl_1 . 1223–1224 . 10.1093/geroni/igx004.4446 . 6183836.
  12. Web site: FDA GRAS notice GRN No. 791: urolithin A . US Food and Drug Administration . 25 August 2020 . 20 December 2018.
  13. Tomás-Barberán FA, González-Sarrías A, García-Villalba R, Núñez-Sánchez MA, Selma MV, García-Conesa MT, Espín JC . Urolithins, the rescue of "old" metabolites to understand a "new" concept: Metabotypes as a nexus among phenolic metabolism, microbiota dysbiosis, and host health status . Molecular Nutrition & Food Research . 61 . 1 . n/a . January 2017 . 27158799 . 10.1002/mnfr.201500901 .
  14. Selma MV, Romo-Vaquero M, García-Villalba R, González-Sarrías A, Tomás-Barberán FA, Espín JC . The human gut microbial ecology associated with overweight and obesity determines ellagic acid metabolism . Food & Function . 7 . 4 . 1769–74 . April 2016 . 26597167 . 10.1039/c5fo01100k .
  15. Landete JM . 2011 . Ellagitannins, ellagic acid and their derived metabolites: A review about source, metabolism, functions and health . Food Research International . 44 . 5 . 1150–1160 . 10.1016/j.foodres.2011.04.027.
  16. García-Villalba R, Espín JC, Tomás-Barberán FA . Chromatographic and spectroscopic characterization of urolithins for their determination in biological samples after the intake of foods containing ellagitannins and ellagic acid . Journal of Chromatography A . 1428 . 162–75 . January 2016 . 26341594 . 10.1016/j.chroma.2015.08.044 .

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