Absorption of N‐phenylpropenoyl‐L‐amino acids in healthy humans by oral administration of cocoa (Theobroma cacao)

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Abstract
Besides flavan‐3‐ols, a family of N‐phenylpropenoyl‐L‐amino acids (NPAs) has been recently identified as polyphenol/amino acid conjugates in the seeds of Theobroma cacao as well as in a variety of herbal drugs. Stimulated by reports on their biological activity, the purpose of this study was to investigate if these amides are absorbed by healthy volunteers after administration of a cocoa drink. For the first time, 12 NPAs were quantified in human urine by means of a stable isotope dilution analysis with LC‐MS/MS (MRM) detection. A maximum amount was found in the urine taken 2 h after the cocoa consumption. The highest absolute amount of NPAs excreted with the urine was found for N‐[4′‐hydroxy‐(E)‐cinnamoyl]‐L‐aspartic acid (5), but the highest recovery rate (57.3 and 22.8%), that means the percentage amount of ingested amides excreted with the urine, were determined for N‐[4′‐hydroxy‐(E)‐cinnamoyl]‐L‐glutamic acid (6) and N‐[4′‐hydroxy‐3′‐methoxy‐(E)‐cinnamoyl]‐L‐tyrosine (13). In order to gain first insights into the NPA metabolism in vivo, urine samples were analyzed by LC‐MS/MS before and after β‐glucuronidase/sulfatase treatment. As independent of the enzyme treatment the same NPA amounts were found in urine, there is strong evidence that these amides are metabolized neither via their O‐glucuronides nor their O‐sulfates. In order to screen for caffeic acid O‐glucuronides as potential NPA metabolites, urine samples were screened by means of LC‐MS/MS for caffeic acid 3‐O‐β‐D‐glucuronide and 4‐O‐β‐D‐glucuronide. But not even trace amounts of one of these glucuronides were detectable, thus excluding them as major NPA metabolites and underlining the importance of future investigations on a potential O‐methylation or reduction of the N‐phenylpropenoyl moiety in NPAs.

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