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 (14)C-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 ≈6 μg [6,6',7,7'-(14)C]lycopene (≈30,000 Bq; 92% trans lycopene). The appearance of (14)C in plasma, plasma triacylglycerol-rich lipoprotein (TRL) fraction, urine, expired breath carbon dioxide, and skin biopsies was measured over 42 d. The (14)C in lycopene-isomer fractions from plasma and TRL fraction was measured to assess the isomerization of lycopene in vivo. RESULTS We quantified (14)C from (14)C-lycopene in plasma, the plasma TRL fraction, expired carbon dioxide, urine, and skin. The time to maximum concentration (t(max)) of total (14)C-lycopene in plasma was 6 h, and the elimination half-life (t(1/2)) was 5 d, which were different from the t(max) and t(1/2) of unlabeled lycopene (0.5 and 48 d, respectively). (14)C-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 (14)CO(2) after dosing, which implies that β-oxidation was involved in the lycopene metabolism. Lycopene or its metabolites were detected in skin for up to 42 d.