Rice is featured as a staple crop in the Asian diet, contributing about 90% of the world’s rice consumption. Brown rice, in particular, is known to have several health benefits. As a regular addition to the diet, it can help reduce body weight, lower cholesterol and suppress inflammation. Brown rice’s ability to neutralize reactive oxygen species and prevent cell damage is important for many of its health-promoting effects. Although previous studies have shown that antioxidant compounds in brown rice can protect cells against oxidative stress, knowledge of which key compounds contribute to these beneficial properties has long remained a mystery.
In a recent study led by Professor Yoshimasa Nakamura of Okayama University’s Graduate School of Environmental and Life Sciences, Japanese researchers identified cycloartenyl ferulate (CAF) as the main “cytoprotective” or cell-protecting compound in brown rice. CAF is a unique compound due to its hybrid structure. As Professor Nakamura explains, “CAF is a hybrid compound of polyphenols and phytosterols and is expected to be a potent bioactive substance with various pharmacological properties such as antioxidant effects and blood fat-lowering effects.”
The study, published Jan. 3, 2023 in Issue 1 of the International Journal of Molecular Sciences 24, was co-authored by Hongian Wu of Dalian Polytechnic University and Toshiyuki Nakamura of Okayama University’s Graduate School of Environmental and Life Sciences. In it, the researchers provide evidence for the antioxidant properties of CAF by demonstrating that it can protect cells from stress caused by hydrogen peroxide. Although hydrogen peroxide is a byproduct of a cell’s metabolic process, abnormal amounts of the compound can be toxic to cells and cause irreversible damage. Treatment of cells with CAF increases their resistance against toxic stress induced by hydrogen peroxide. Furthermore, CAF provided greater protection against hydrogen peroxide-induced stress than alpha-tocopherol and gamma-tocopherol, two other prominent antioxidant compounds previously hypothesized to be major contributors to the antioxidant capacity of brown rice.
According to study estimates, whole grains of brown rice contain five times more CAF than other antioxidant compounds found in brown rice. Also, CAF increases the concentration of heme oxygenase-1 or HO-1, an enzyme that helps produce antioxidants. “We have shown here that CAF significantly increased the mRNA level of HO-1, a small molecular weight antioxidant-producing enzyme, to the concentration required for cytoprotective effects against oxidative damage,” explains Professor Nakamura.
The researchers further explored this mechanism of action in experiments where blocking HO-1 activity using inhibitors significantly reduced the antioxidant effect of CAF. The high abundance and unique mechanism of action demonstrate that CAF are the major contributing antioxidants in brown rice.
Through this study, researchers have not only uncovered the secret behind the health benefits of brown rice, but have also locked down the ingredients that are mainly responsible for these benefits. This will allow CAF to be used in the development of better novel supplement and food products focused on consumer health. An optimistic Professor Nakamura observes, “Our study may help in the development of new functional foods and supplements based on the function of CAFs, such as CAF-based nutraceuticals.“