Oryzanol decreases cholesterol absorption and aortic fatty streaks in hamsters

Oryzanol is a class of nonsaponifiable lipids of rice bran oil (RBO). More specifically, oryzanol is a group of ferulic acid esters of triterpene alcohol and plant sterols. In ex- periment 1, the mechanisms of the cholesterol-lowering action of oryzanol were investigated in 32 hamsters made hypercho- lesterolemic by feeding chow-based diets containing 5% co- conut oil and 0.1% cholesterol with or without 1% oryzanol for 7 wk. Relative to the control animals, oryzanol treatment re- sulted in a significant reduction in plasma total cholesterol (TC) (28%, P < 0.01) and the sum of IDL-C, LDL-C, and VLDL-C (NON-HDL-C) (34%, P < 0.01). In addition, the oryzanol- treated animals also exhibited a 25% reduction in percent cho- lesterol absorption vs. control animals. Endogenous cholesterol synthesis, as measured by the liver and intestinal HMG-CoA re- ductase activities, showed no difference between the two groups. To determine whether a lower dose of oryzanol was also efficacious and to measure aortic fatty streaks, 19 hamsters in experiment 2 were divided into two groups and fed for 10 wk chow-based diets containing 0.05% cholesterol and 10% co- conut oil (w/w) (control) and the control diet plus 0.5% oryzanol (oryzanol). Relative to the control, oryzanol- treated hamsters had reduced plasma TC (44%, P < 0.001), NON-HDL-C (57%, P < 0.01), and triglyceride (TG) (46%, P < 0.05) concentrations. Despite a 12% decrease in high density lipoprotein cholesterol (HDL-C) (P < 0.01), the oryzanol-treated animals maintained a more optimum NON-HDL-C/HDL-C pro- file (1.1 ± 0.4) than the control (2.5 ± 1.4; P < 0.0075). Aortic fatty streak formation, so defined by the degree of accumulation of Oil Red O-stained macrophage-derived foam cells, was re- duced 67% (P < 0.01) in the oryzanol-treated animals. From these studies, it is concluded that a constituent of the non- saponifiable lipids of RBO, oryzanol, is at least partially respon- sible for the cholesterol-lowering action of RBO. In addition, the cholesterol-lowering action of oryzanol was associated with significant reductions in aortic fatty streak formation. Lipids 32, 303-309 (1997). The cholesterol-lowering effect of rice bran oil (RBO) has re- cently been reported by several investigators (1-7). A num- ber of studies have suggested that the nonsaponifiables in the RBO may play a very important role in the cholesterol-low- ering effect of RBO (1-3,5-8). When the nonsaponifiable lipids extracted from RBO were fed to rats in an amount equivalent to that in the RBO (2), similar cholesterol-lower- ing effects were observed. When oryzanol, a constituent of the nonsaponifiable lipids in RBO, was added to a diet con- taining purified RBO (8), it further decreased the serum total cholesterol (TC) level in rats compared to purified alone, sug- gesting that the hypocholesterolemic activity of RBO is at- tributable to oryzanol and to some other components in the nonsaponifiable matter. A study in nonhuman primates demonstrated that serum cholesterol levels decreased as the level of RBO in the diet increased, and this reduction in serum cholesterol level was not entirely explained by the fatty acid composition of the dietary lipids, suggesting a component of RBO other than its fatty acid content was responsible for its hypocholesterolemic effect (5). RBO, unlike most vegetable oils, contains a relatively high proportion of nonfatty acid components (the nonsaponifiable lipids). Refined RBO may contain 1.5-2.6% of nonsaponifi- able lipids, and crude RBO may contain up to 5% of non- saponifiable lipids (9). In contrast, most common refined veg- etable oils contain only 0.3-0.9% of nonsaponifiable lipids (10). The nonsaponifiables of RBO contain sterols (43%), triterpene alcohols (28%), 4-methyl sterols (10%), and less polar components (19%) (11). In the crude oil, about 20% of the nonsaponifiables of RBO are in the form of ferulic acid es- ters, which are a mixture of esters of ferulic acid (4-hydroxy-