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Laboratory of Food Science, Kyushu University School of Agriculture, Fuluoka 812-81 and * Kawasaki University of Medical Welfare, Kurashiki 701-01, Japan
ABSTRACT
INTRODUCTION
FOOTNOTES
LITERATURE CITED
ABSTRACT 
A range of human and animal studies have shown that rice bran oil (RBO) is an edible oil of preference for improving serum cholesterol levels and lipoprotein profiles with similarity to the more commonly used vegetable oils such as corn oil and safflower oil. Of particular interest is the observation that blending RBO with safflower oil at a definite proportion (7:3, wt/wt) magnifies the hypocholesterolemic efficacy, compared with the effect of each oil alone. Although the mechanism underlying this effect is not apparent at present, the blending may have a practical significance. The blending effect was reproduced in rats fed a cholesterol-enriched diet, and there was also a decrease in liver cholesterol. The occurrence of peculiar components such as 
-oryzanol and tocotrienols could be responsible for the hypocholesterolemic effect of RBO.
-oryzanol,
humans,
rats.
INTRODUCTION
After Itoh et al. 1973a
and b.
). Rice bran oil (RBO) is not a popular oil worldwide, but it is in steady demand as a so-called "healthy oil" not only in Japan but also in Asian countries, particularly India. Approximately 80 thousand tons of RBO, corresponding to only 3.5% of total vegetable oils, is consumed annually in Japan.
, Rukmini and Raghuram 1991). In some cases, RBO lowered plasma cholesterol more effectively than other commonly used vegetable oils rich in linoleic acid (Rukmini and Raghuram 1991); this effect can be attributed to the occurrence of specific components in RBO, -oryzanol (and its constituents, triterpene alcohols) and perhaps tocotrienols (Nicolosi et al. 1994, Rukmini and Raghuram 1991).
-linolenic acid, ranging from 1 to 3% (mean value, 2%). This amount may be enough to increase the content of (n-3) highly polyunsaturated fatty acids such as eicosapentaenoic and docosahexaenoic acids in tissue phospholipids compared with other vegetable oils such as corn oil (Edwards and Radcliff 1994). The remaining major fatty acid in RBO is palmitic acid, 17%.
Table 1.
Sterol and triterpene contents in different edible oils
-oryzanol, the ferulate esters of triterpene alcohols (Table 1) (Itoh et al. 1973a and b). The content of -oryzanol differs with the source of RBO, ranging from 115 to 780 ppm, depending on the degree and possibly the method of processing (Rogers et al. 1993). Cycloartenol and 24-methylene cycloartanol are the major component terpene alcohols, followed by cycloartanol. RBO also contains campesterol and 
-sitosterol at a relatively high level. Diverse effects of -oryzanol have been reported, including the hypolipidemic effect, growth promotion, gonadotrophic action and stimulation of the hypothalamus (Kanbara et al. 1992, Nakamura 1967, Rukmini and Raghrum 1991).
). The major components are /-tocotrienols (Rogers et al. 1993). The content of tocotrienols is usually higher than that of tocopherols. The possible regulatory role of tocotrienols in cholesterol dynamics including hypocholesterolemic action has been reported (Hood and Sidhu 1992, Imaizumi et al. 1990, Qureshi et al. 1991, Watkins et al. 1993).
who compared the effects of RBO, canola and corn oil. However, the most interesting observation by Suzuki and Oshima (1970a and b) was that the blend of 7 parts of RBO with 3 parts of safflower oil unexpectedly enhanced the cholesterol-lowering potential of RBO. As shown in Figure 1, the lowering effect of the blended oil was greater than that of the respective oils alone, and other proportions of the blend were less effective in lowering serum cholesterol. Interestingly, the combination of RBO with sunflower oil did not show any additional effects on serum cholesterol levels, although safflower and sunflower oils have essentially the same fatty acid composition. This observation was confirmed repeatedly and the blended oil was commercially distributed.
Table 2.
Change of serum lipids after blended oil and egg-loading1
and 1989) observed that the blended oil exerted the hypocholesterolemic effect even when five eggs were consumed daily for 7 consecutive days (Table 2). In contrast, there was an increase in HDL-cholesterol after consumption of the blended oil, and consequently, the atherogenic index was significantly improved. Based on these observations, Tsuji and colleagues later prepared rice bran/safflower oil margarine as a cholesterol-lowering fat.
reported a unique hypocholesterolemic effect of RBO in nonhuman primates that was not attributed to the fatty acid composition of the oil.
, Kiribuchi et al. 1983), the difference in the sterol composition of safflower and sunflower oils is insufficient to cause such a contrasting effect.
Fig. 2.
Effect of rice bran oil-safflower oil blend on (A) serum and (B) liver lipid levels of rats fed cholesterol-enriched diets. The animals were fed experimental diets containg 10% fat for 3 wk. Values are means ± SEM of six rats. Chol, cholesterol, and TG, triglyceride. 
, Safflower oil group and 
, rice bran oil-safflower oil blend group (7:3, wt/wt). Dotted bars inside the cholesterol bars represent HDL-cholesterol. Significantly different at *P < 0.05 and **P < 0.01.
[View Larger Version of this Image (40K GIF file)]
reported that cycloartenol and probably 24-methylenecycloartanol magnify the cholesterol-lowering potential of soy sterols at a very low dietary level in rats. They attributed the cholesterol-lowering action to increased fecal excretion of acidic steroids. Although this observation was not confirmed in another study (Ikeda et al. 1985), the decrease in serum apo-AI as a result of cholesterol consumption was ameliorated more effectively by the combination of cycloartenol with -sitosterol than by -sitosterol alone. In addition, the combination of cycloartenol with -sitosterol did not reduce the lymphatic absorption of cholesterol as shown in Figure 3. However, cycloartenol was absorbed at a rate ~fourfold higher than that of -sitosterol, suggesting its metabolic effect after absorption.
Fig. 3.
Effect of cycloartenol and -sitosterol on lymphatic cholesterol absorption in rats. Lymph-cannulated rats received emulsions containing (A) 25 mg cholesterol, 
; 25 mg cholesterol and 25 mg -sitosterol, 
; or 25 mg cholesterol, 25 mg -sitosterol and 2.5 mg cycloartenol, 
; and (B) 50 mg -sitosterol, 
; 50 mg cycloartenol, 
. Values are means ± SEM of four rats. After Ikeda et al. (1985).
[View Larger Version of this Image (20K GIF file)]
observed increased fecal excretion of both neutral and acidic steroids in rats fed RBO compared with those fed peanut oil, in particular when cholesterol-enriched diets were given (Figure 4). Further, they showed that the cholesterol-lowering action of peanut oil in rats is magnified by adding a small portion of unsaponifiable material from RBO. The addition of oryzanol to the diet containing RBO led to a further significant decrease in serum cholesterol in rats (Seetharamaiah and Chandrasekhara 1989). In rats fed cholesterol-free diets for 18 wk, RBO reduced plasma and liver cholesterol more than peanut oil at the dietary level of 20% without influencing growth, suggesting that RBO has no deleterious effects, even at a high dietary level.
Fig. 4.
Effect of peanut oil and rice bran oil with or without cholesterol on fecal steroid excretion in rats. Values are mean ± SEM of eight rats. Peanut oil + cholesterol, 
; rice bran oil + cholesterol, 
; peanut oil, ; rice bran oil, 
. Significantly different from the corresponding peanut oil groups at *P < 0.05, **P < 0.01 and ***P < 0.001. After Sharma and Rukmini (1987).
[View Larger Version of this Image (36K GIF file)]
and 1989). The hypocholesterolemic effect of the unsaponifiable material can be attributed to the increased fecal steroid excretion through interference with cholesterol absorption (Ikeda et al. 1985, Kiribuchi et al. 1983, Sharma and Rukumini 1986). In addition, the RBO-safflower oil blend ameliorated the age-related increase in blood pressure of spontaneously hypertensive rats when it was added to a commercial nonpurified diet at the 20% level (Tsuji, E., Kawasaki University of Medical Welfare). It is also known that rice bran itself exerts a cholesterol-lowering action in hamsters (Kahloa et al. 1992).
FOOTNOTES
LITERATURE CITED
studies on the anti-atherosclerotic effect of -oryzanol in sonic stress.
Jpn. J. Atheroscler.
1992;
20:159-163-oryzanol on hepatic cholesterol biosynthesis and fecal excretion of cholesterol metabolites.
Radioisotopes
1967;
15:371-374-oryzanol components and simultaneous assessment of tocols in rice bran oil.
J. Am. Oil Chem. Soc.
1933;
70:301-307Satellite Meeting, 8th International Symposium on Atherosclerosis, pp. 37-40. CIC Edizoni Internationali, Rome, Italy.-Tocotrienol as a hypocholesterolemic and antioxidant agent in rats fed atherogenic diets. Lipids, 28, 1113-1118.
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