Absorption and distribution kinetics of the ¹³c-labeled tomato carotenoid phytoene in healthy adults

Background: Phytoene is a tomato carotenoid that may contribute to the apparent health benefits of tomato consumption. Although phytoene is a less prominent tomato carotenoid than lycopene, it is a major carotenoid in various human tissues. Phytoene distribution to plasma lipoproteins and tissues differs from lycopene, suggesting the kinetics of phytoene and lycopene differ. Objective: The objective of this study was to characterize the kinetic parameters of phytoene absorption, distribution, and excretion in adults, to better understand why biodistribution of phytoene differs from lycopene. Methods: Four adults (2 males, 2 females) maintained a controlled phytoene diet (1-5 mg/d) for 42 d. On day 14, each consumed 3.2 mg 13C-phytoene, produced using tomato cell suspension culture technology. Blood samples were collected at 0, 1-15, 17, 21, and 24 h and 2, 3, 4, 7, 10, 14, 17, 21, and 28 d after 13C-phytoene consumption. Plasmaunlabeled and plasma-labeled phytoene concentrations were determined using ultra-HPLC-quadrupole time-of-flightmass spectrometry, and data were fit to a 7-compartment carotenoid kinetic model using WinSAAM 3.0.7 software. Results: Subjects were compliant with a controlled phytoene diet, consuming a mean 6 SE of 2.5 6 0.6 mg/d, resulting in a plasma unlabeled phytoene concentration of 71 6 14 nmol/L. A maximal plasma 13C-phytoene concentration of 55.6 6 5.9 nM was achieved 19.8 6 9.2 h after consumption, and the plasma half-life was 2.3 6 0.2 d. Compared with previous results for lycopene, phytoene bioavailability was nearly double at 58% 6 19%, the clearance rate from chylomicrons was slower, and the rates of deposition into and utilization by the slow turnover tissue compartment were nearly 3 times greater. Conclusions: Although only differing from lycopene by 4 double bonds, phytoene exhibitsmarkedly different kinetic characteristics in human plasma, providing insight into metabolic processes contributing to phytoene enrichment in plasma and tissues comparedwith lycopene. This trial was registered at clinicaltrials.gov as NCT01692340.