Lycopene bioavailability and metabolism in humans: an accelerator mass spectrometry study

Background: To our knowledge, there is no direct information on lycopene metabolism in humans. Objective: The objective of this study was to quantify the long-term human bioavailability of lycopene in plasma and skin after a single dose of C-14-lycopene and to profile the metabolites formed. Design: We preselected 2 male subjects as lycopene absorbers and gave them an oral dose of 10 mg synthetic lycopene combined with approximate to 6 mu g [6,6', 7,7'-C-14]lycopene (approximate to 30,000 Bq; 92% trans lycopene). The appearance of C-14 in plasma, plasma triacylglycerol-rich lipoprotein (TRL) fraction, urine, expired breath carbon dioxide, and skin biopsies was measured over 42 d. The C-14 in lycopene-isomer fractions from plasma and TRL fraction was measured to assess the isomerization of lycopene in vivo. Results: We quantified C-14 from C-14-lycopene in plasma, the plasma TRL fraction, expired carbon dioxide, urine, and skin. The time to maximum concentration (t(max)) of total C-14-lycopene in plasma was 6 h, and the elimination half-life (t(1/2)) was 5 d, which were different from the tmax and t1/2 of unlabeled lycopene (0.5 and 48 d, respectively). C-14-Lycopene was extensively isomerized after dosing as a 92% all-trans isomer at dosing but changed to 50% trans, 38% 5 cis, 1% 9 cis, and 11% other cis isomers after 24 h. A similar pattern of isomerization was seen in plasma TRL fractions. Conclusions: Lycopene was extensively isomerized after dosing and rapidly metabolized into polar metabolites excreted into urine with the rapid peak of (CO2)-C-14 after dosing, which implies that beta-oxidation was involved in the lycopene metabolism. Lycopene or its metabolites were detected in skin for up to 42 d. Am J Clin Nutr 2011;93:1263-73.