Location: Arkansas Children's Nutrition CenterTitle: Urinary excretion of phenolic acids in rats fed cranberry) Author
Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/13/2009
Publication Date: 4/14/2010
Citation: Prior, R.L., Rogers, T.R., Khanal, R.C., Wilkes, S.E., Wu, X., Howard, L.R. 2010. Urinary excretion of phenolic acids in rats fed cranberry. Journal of Agricultural and Food Chemistry. 58(7):3940-3946. Interpretive Summary: Complex phytochemicals in the diet can be converted into simpler compounds (i.e., phenolic acids) by bacteria in the large intestine. These bacterial products can be absorbed into the circulation and may contribute to the health-promoting effects of the parent compounds. The breakdown products can be further metabolized in other tissues. The objectives of this study were to identify and quantitate in the urine the breakdown products and other metabolites that are formed in rats fed three levels of a cranberry powder. The basic diet contained very low amounts of any of the complex phytochemicals. Nineteen phenolic acids and their metabolites were identified and quantitated. Phenolic acids produced from cranberry phytochemicals that were in the diets were indentified. Understanding the role of microbial metabolism of dietary phytochemicals in the intestine is important to understanding the health benefits observed with many foods.
Technical Abstract: Dietary flavonoids can be converted into phenolic acids by colonic microflora and be absorbed into the circulation and may contribute to the health-promoting effects of the parent compounds. The phenolic acids can be further metabolized in other tissues via methylation and conjugation with glucuronide or sulfate. The objectives of this study were to identify and quantitate in the urine catechin, epicatechin and 19 phenolic acids and their conjugates in rats fed three levels of a cranberry powder. The basic diet used was AIN93G diet containing very low amounts of any polyphenolic compounds. Amounts of catechin and epicatechin excreted in the urine in all forms (methylated plus conjugated) were highest in rats consuming the high cranberry diet. Methylation of the 4- position was higher than the 3- position for both catechin and epicatechin. Of the phenolic acids studied, the amounts excreted varied by 4-orders of magnitude with hippuric acid being excreted in the highest quantities. Amounts of 4-hydroxyphenylacetic acid (4-HPAA), 3-hydroxyphenylacetic acid (3HPAA), 3-hydroxyphenylpropionic acid (3HPPA), and 4-hydroxycinnamic acid (4HCA) excreted were in the range of 10-40 microgram/mg creatinine in animals fed the highest level of cranberry while phenylacetic acid (PAA), gallic acid (GA), 3,4-dihydroxyphenylacetic acid (34HPAA), 3,4-dihydroxybenzoic acid (34HBA), 3,4-dihydroxycinnamic acid (3,4HCA), and 4-hydroxy-3-methoxycinnamic acid (FA) were excreted in the urine in concentrations of 0.1 to 2 microgram/mg creatinine. As the amount of cranberry in the diet was increased, the percentage of conjugated 4HPPA increased (52 to 84%) and decreased for 3HBA, vanillic and hippuric acid. For other phenolic acids analyzed, the percentage excreted in the conjugated form was approximately constant across levels of cranberry in the diet and ranged from 65 to 100% for the individual phenolic acids. Studies of bioactivity and health effects need to consider more than just the compound(s) in the food, since they can be metabolized to other lower molecular weight compounds which in turn may also be methylated or conjugated in some form that may affect the perceived health effects.