Caffeic acid derivatives in artichoke extract are metabolised to phenolic acids in vivo

The purpose of this study was to investigate the absorption and metabolism of hydroxycinnamates from artichoke extract by determining the urinary excretion of the conjugates. Ten healthy, non smoking volunteers (5 female, 5 male) were given three capsules containing artichoke extract every 4 h (0, 4, 8 h) following two days of a low-polyphenol diet. One capsule contained 320 mg of artichoke extract equivalent to 34.3 +/- 0.6 mg/g hydroxycinnamates (caffeic acid derivatives) and 5.6 +/- 0.1 mg/g flavonoids. Polyphenols and phenolic acids present in the artichoke extract were not detected in the urine either as conjugates or aglycones. However, ferulic, isoferulic, dihydroferulic and vanillic acid were identified as major metabolites after beta-glucuronidase treatment of urine. The amount excreted as well as the ratio to that of creatinine, a biomarker for the general excretion rate, increased significantly on the study day compared to the pre-supplementation day. Thus, the caffeic acid esters found in the artichoke extract capsule are absorbed, metabolised and excreted as methylated phenolic acids such as ferulic, isoferulic, dihydroferulic and vanillic acid.