A collaborative study by scientists at the UNC Chapel Hill Nutrition Research Institute (NRI) and the Dole Nutrition Institute (DNI), both at the NC Research Campus (NCRC) in Kannapolis, NC, provides new insight into how phytochemicals in plant-based foods optimize the regulation of the body’s natural defenses against reactive oxygen species (ROS) and free radicals.
NRI Director Steven Zeisel, MD, PhD, emphasized that these findings do not reinforce the long-held belief that all antioxidant phytochemicals “capture” or “scavenge” for free radicals and ROS to protect the body against their damaging effects. The study “Extracts of fruits and vegetables activate the antioxidant response element in IMR-32 Cells,” which was published in the Journal of Nutrition, instead focused on antioxidant response elements (AREs) on genes, which control the expression of internal defense systems that protect cells from free radical oxygen damage.
“This study changes how we can recognize constituents of fruits and vegetables that improve our antioxidant defenses,” Zeisel said. “In the past we looked for certain structures in phytochemicals that could trap free radicals, now we know that there are many ingredients in fruits and vegetables that work in a completely different way to activate our own internal defense systems.”
Determining Antioxidant Capacity
To study the impact of plant-based antioxidant phytochemicals on AREs, Zeisel’s team, which was led by Research Assistant Stephen Orena, developed an assay using IMR-32 neuroblastoma cells. The DNI laboratory prepared 134 fruit and vegetable extracts using both the flesh and peel. When the extracts were exposed to the assay, 107 of them activated the AREs. Some of the most effective activators included avocado peel, carrot, red pear peel, pineapple, lemon flesh, green pear peel, red delicious apple peel, spinach and a variety of lettuces. The assay results more effectively determined antioxidant capacity than the commonly used measures of total phenolic compound content (TP) and oxygen radical absorption capacity (ORAC).
“Our study shows at a cellular level how antioxidant phytochemicals might protect our cells and provide health benefits,” explained study co-author Nicholas Gillitt, PhD, Dole Food Company vice president of nutrition research and DNI director. “We found that more important than capturing and neutralizing oxidants and free radicals is the fact that the phytochemicals actually cause an upregulation in the expression of these AREs. This is new insight into why fruits and vegetables are healthy for us.”
Because Zeisel and Gillitt recognize that research in cell culture that examines one protection mechanism in the human body is far from definitive, they have two additional studies underway. The first is a human trial using whole fruits and vegetables blended into smoothies. AREs activation will be measured through analysis of blood draws taken before and after consuming the smoothies. The second study involves fractionating the extracts to determine the specific molecules that activate AREs.
For the NRI, an institute developing targeted nutrition, the finding is a critical step toward understanding how nutrition can be more effectively used to prevent chronic diseases.
“Now we have the tools to recognize a whole new set of healthy ingredients in fruits and vegetables, many of which we had never considered before,” Zeisel commented.
For the DNI, the research and educational arm of Dole Food Company, the study is evidence that consuming fruits and vegetables has long-lasting effects.
“Fruits and vegetables are healthy for us for a lot of reasons,” Gillitt added, “but we are showing why at a cellular level they are healthy and how important long-term exposure to phytochemicals is for our health now and thirty years from now.”