The study published in the American Journal of Clinical Nutrition used a specially cultured lycopene molecule with a heavier weight -C-lycopene. It is easier to trace this form's metabolism in the body.
The researchers said this may lead to future information about the anti-cancer activity of lycopene in tomatoes.
‘Heavy’ molecules
University of Illinois scientist Dr John Erdman has spent years researching the potential of lycopene, the bioactive compound in tomatoes, on prostate tumours in animal models. Yet until now, he did not have a way to trace lycopene’s metabolism in the human body.
The team at the university began developing tomato cultures with non-radioactive carbon-13 sugars ten years ago.
Most carbon in nature is carbon-12 which is a lighter molecule. They incorporated the heavier carbon molecule into the high lycopene-producing tomato plants they were growing.
The scientists felt confident that apart from improved traceability, there wouldn’t be any differences from natural tomato molecules that may influence the research.
Dr Erdman told us: “Work by others with 'heavy' labelled molecules find no differences with 12-C counterparts regarding absorption or metabolism. Thus, we do not expect differential impact of 13-C lycopene versed 12-C lycopene.”
Soon after the carbon-13 technology was established, scientists at Illinois and Ohio State conducted this first human study on eight subjects.
Participants were fed carbon -13 lycopene and their blood was tested hourly for ten hours after dosing and then at one, three and 28 days later.
Cis and trans isomers
Most lycopene in tomatoes is in the form of the all-trans isomer, but once in the body there is more of the cis isomer. The researchers wanted to understand why there is a difference between the isomers found naturally in the plant, and those in our body. Cis isomer lycopene is thought to be more likely responsible for disease reduction.
They found that after we absorb lycopene from food, there is probably a conversion from all-trans to cis lycopene.
Further research
Asked about further research into cis isomers and their potential for disease reduction, Dr Erdman said:“We have been seeking funding, so far unsuccessfully, to carry out a similar study with men with prostate cancer who have selected to have their prostate removed. We would provide 13-C lycopene prior to surgery and then evaluate the uptake into the prostate (and some surrounding fat tissue) and metabolites in the prostate, especially those in all trans compared to cis conformation.
"We would also like to study non-cancer patients with SNPs (single nucleotide polymorphisms) in various genes known to impact lycopene metabolism. Lycopene intake or blood levels have been linked to other health outcomes. Thus, this would inform that work too.”
The researchers are also looking into other phytochemicals.
“Right now our focus is on lutein uptake into the eye related to macular pigment and brain and cognitive endpoints,” Erdman said.
Whole food approach
Erdman said their laboratory has a ‘whole food’ approach.
“We have studied synergies between foods before regarding prostate carcinogenesis. For example, tomato and broccoli. However, in order to convince men to consume tomato products, we need evidence for bioactives in tomato and some indication of mechanisms of action,” he said.
Source: American Journal of Clinical Nutrition
Published online ahead of print doi: 10.3945/ajcn.114.103143
“Compartmental and noncompartmental modeling of 13C-lycopene absorption, isomerization, and distribution kinetics in healthy adults"
Authors: N.E. Moran et al.