Effect of gamma-oryzanol on the bioaccessibility and synthesis of cholesterol

K. Mäkynen, C. Chitchumroonchokchai*, S. Adisakwattana, ML. Failla*, T. Ariyapitipun

The Medical Food Research and Development Center, Department of Transfusion Medicine, Faculty of Allied Health Sciences, Chulalongkorn University, Bangkok (Thailand)
*Department of Human Nutrition, The Ohio State University, Columbus, OH (USA)

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• Pharmacology

Background and Objectives: Gamma-oryzanol (γ-OR) is a unique mixture of triterpene alcohol and sterol ferulates present in rice bran oil. Hypocholesterolemic activity of gamma-OR has been reported in various animal and human studies. However, the mechanisms for this hypocholesterolemic activity of gamma-OR remain unclear. Therefore, the aim of this in vitro study was to examine the effect of gamma-OR on the bioaccessibility and synthesis of cholesterol.

Methods: The effects of gamma-OR on the efficiency of incorporation of cholesterol into mixed micelles during digestion and apical uptake of cholesterol by Caco-2 human intestinal cells were determined using the coupled in vitro simulated digestion/Caco-2 human intestinal cell model. The impact of gamma-OR on the HMG-CoA reductase activity was also investigated.

Results: Although incorporation of cholesterol into synthetic micelles was significantly inhibited by 15-fold molar excess of gamma-OR, efficiency of micellarization of cholesterol during simulated digestion of the rice meal was not significantly altered by the presence of as high as 20-fold molar excess of gamma-OR. Nevertheless, 20-fold molar excess of gamma-OR significantly decreased apical uptake of cholesterol into Caco-2 intestinal cells. In addition, gamma-OR inhibited 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase activity.

Conclusions: These findings suggest that the hypocholesterolemic activity of gamma-OR is due in part to impaired apical uptake of cholesterol into enterocytes and perhaps a decrease in HMG-CoA reductase activity.

Corresponding Author: Tipayanate Ariyapitipun, Ph.D.; e-mail: tipayanate@yahoo.com

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