Researchers at the University of Illinois have developed a method to trace the body’s absorption, distribution and metabolism of lycopene, a pigment that gives tomatoes their color and has been shown to reduce the growth of prostate tumors in several animal models. The research paper, entitled “Compartmental and non-compartmental modeling of ¹³C-lycopene absorption, isomerization, and distribution kinetics in healthy adults,” was published in the American Journal of Clinical Nutrition and is the most complete study of lycopene to date.
In an effort that started a decade ago, the research team developed tomato plants that grow in suspension culture, with optimized production of lycopene molecules characterized by a heavier molecular weight. These molecules were “tagged” by incorporating non-radioactive carbon-13, heavier carbon atoms than the more common carbon-12, making the lycopene molecules easier to track. In this experiment, scientists studied the carbon-13 tagged lycopene in the blood of eight participants, with samples collected hourly for 10 hours after lycopene dosing, and again one, three, and 28 days later.
Lycopene, the red carotenoid in tomatoes, has been associated with disease-preventing effects, and researchers wanted to study its metabolic activity in the human body. While this compound is mainly consumed as an all-trans isomer in foods, it exists in the more flexible cis isomer form in human plasma and tissues, the isoform thought by some to be responsible for reducing disease risk. So researchers developed a mathematical model to measure the concentration of blood carbon-13 lycopene, which occurs as a consequence of all-trans being converted to cis isomeric forms as soon as lycopene is absorbed from food.
“The results provide novel information about absorption efficiency and how quickly lycopene is lost from the body. We determined its half-life in the body and now understand that the structural changes occur after the lycopene is absorbed,” Dr. John W. Erdman Jr., emeritus professor of nutrition at UI, said in a press release. “Most tomato lycopene that we eat exists as the all-trans isomer, a rigid and straight form, but in the bodies of regular tomato consumers, most lycopene exists as cis isomers, which tend to be bent and flexible. Because cis-lycopene is the form most often found in the body, some investigators think it may be the form responsible for disease risk reduction.”
Dr. Erdman added, “In the future, these new techniques could help us to better understand how lycopene reduces prostate cancer risk and severity. We will be able to develop evidence-based dietary recommendations for prostate cancer prevention.” The team is also using this technology to investigate other bioactive food components, namely phytoene, another tomato molecule, and lutein, found in green vegetables and eggs and known to be important for eye and brain health.