Changes in Blueberry Polyphenol Metabolism Are Dependent on Dose and Food Matrix Over 90 Days in Ovariectomized Sprague-Dawley Rats

Abstract

Abstract Objectives Fruit and vegetable derived polyphenols are associated with many health benefits when consumed regularly. Blueberries are a rich source of polyphenols, leading to interest in their use as dietary supplements. With expanded use, it is critical to evaluate metabolic changes associated with repeated consumption of purified blueberry polyphenols at elevated doses relative to whole fruit. This includes potential for changes in gut microbial polyphenol metabolism and generation of putative biologically relevant phenolic metabolites. To address this, we investigated the dose-response of blueberry polyphenols and microbial metabolites produced over 90 days in rodents. Methods Five-month old, ovariectomized, Sprague-Dawley rats were orally gavaged for 90 days with either a purified extract of blueberry polyphenols (0, 50, 250, or 1000 mg total polyphenols/kg bw/d) or lyophilized blueberries (50 mg total polyphenols/kg bw/d, equivalent to 1–2 cups/d in humans). Polyphenol metabolism was assessed via 24 h urine collections on days 0, 7, 15, 30, 60, and 90 as well as collecting GI tissues, brain, liver, and kidney at sacrifice. Phenolic metabolites were extracted, purified, and quantitated via UPLC-MS/MS. Results Total phenolic content of lyophilized blueberries and the purified extract were 3.5% and 27% (w/w), respectively. A total of 38 phenolic metabolites were detected using a targeted LC MS/MS method in the urine, with 15 metabolites also found in at least one of the tissues. Metabolites were excreted in a dose-dependent manner, with total metabolite excretion ranging from 11.4–91.2 µmol/24 h. The major metabolites were cinnamic (56–87%), hippuric (6–39%), and phenylpropionic acids (4–15%). As the dose increased, metabolite production shifted from hippuric to phenolic acids (phenolic: hippuric acid ratio increased from 3.2 to 13.9), though lyophilized blueberries exhibited the opposite trend (phenolic: hippuric acid ratio 1.7). Conclusions These results indicate that ingested blueberry polyphenols are efficiently metabolized over a large range of doses, though there are clear shifts in polyphenol metabolism driven by dose and matrix. Thus, purified polyphenol extracts, as found in dietary supplements, are metabolized differently than those found in whole fruits and vegetables. Funding Sources NIH.