Abstract
Resveratrol (trans-3,4',5-trihydroxystilbene) and quercetin (3,3’,4’,5,7-pentahydroxyflavone) are two naturally occurring polyphenols with the potential to exert beneficial health effects. Since their low bioavailability is a major obstacle to biomedical applications, efforts are being made to improve their absorption and slow down phase II metabolism. An accurate evaluation of the corresponding levels in the bloodstream is important to assess delivery strategies, as well as to verify claims of efficacy based on in vitro results. In the present work we have optimized a simple method ensuring complete stabilization and extraction of resveratrol and quercetin from whole blood. The suitability of different protocols was evaluated by measuring the recovery of polyphenol and internal standard from spiked blood samples via HPLC/UV analysis. The optimized procedure ensured a satisfactory recovery of both internal standards and compounds. Comparing plasma and whole blood, up to 76% of the analyte, being associated with the cellular fraction, was unaccounted for when examining only plasma. This indicates the importance of analysing whole blood rather than plasma to avoid underestimating polyphenol absorption in bioavailability studies.
Highlights
Polyphenols are a vast class of plant-made molecules exhibiting a variety of properties and effects of relevance to many areas of health care [1]
Because of their relative abundance in foods and the potential therapeutic and disease-preventing usefulness of their multiple biological effects quercetin and resveratrol are among the polyphenols attracting most attention [2,3,4,5]
The acetone/perchloric acid and acetone/acetic acid/ascorbic acid combinations ensured the best recovery for resveratrol, and were tested with quercetin; the latter prevented oxidation of quercetin and was adopted
Summary
Polyphenols are a vast class of plant-made molecules exhibiting a variety of properties and effects of relevance to many areas of health care [1] Because of their relative abundance in foods and the potential therapeutic and disease-preventing usefulness of their multiple biological effects quercetin and resveratrol are among the polyphenols attracting most attention [2,3,4,5]. We have chosen them as model compounds. Many potentially useful effects do not take place in vivo to any significant extent because polyphenols are poorly absorbed and rapidly transformed into phase II conjugates, so that circulating levels of unmodified compounds are generally in the 10-9-10-7 M range, even after an enriched meal. Efforts are under way to modify this situation using a variety of approaches, including pro-drugs, formulations, and macromolecular vectors (liposomes, nanoparticles) [6,7,8,9]
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