Cholesterol Supplementation Attenuates the Hypocholesterolemic Effect of Rice Bran Oil in Rats.

Abstract

SummaryRice bran oil (RBO), when blended with safflower oil (SFO) at the ratio of 7 to 3, has been shown to lower serum cholesterol in humans consuming cholesterol. The mechanism as to how this oil blend exerts its effect is not yet clear. This study examined the effect of cholesterol supplementation on the cholesterol-lowering ability of different RBO/SFO blends. Male Sprague Dawley rats (4wk old) were fed purified diets containing 10% fat with or without the addition of 0.5% cholesterol for 3wk. The fat was either SFO or RBO alone, or the mixture of these two oils at the ratio of 7:3 (7S/3R), 5:5 (5S/5R), or 3:7 (3S/7R). Without cholesterol supplementation, there were no significant differences in the serum and liver total cholesterol levels among different dietary fats. However, the HDL cholesterol level of rats fed the RBO-containing diets (especially in rats fed the 3S/7R diet) was higher than that of rats fed the diet containing SFO alone. This resulted in an increase in the ratio of HDL/total cholesterol-a desirable outcome. Supplementation of the diets with 0.5% cholesterol significantly increased the cholesterol level in both the serum and the liver. Increasing the proportion of RBO in the diet further raised the total cholesterol level in the serum whereas it reduced liver cholesterol. Then, the specific effect of the 3S/7R mix ture on the ratio of HDL/total cholesterol disappeared. These findings suggest that choles terol supplemented at the level of 0.5% in this study masked the cholesterol-lowering effect of RBO. Smaller percentages of polyunsaturated fatty acid (i.e., 18:2n-6) in the RBO-con taining diets than in the SFO diet might have reduced their ability to dispose the circulating serum cholesterol into the liver. Key Words rice bran oil, safflower oil, cholesterol, fatty acid profile, rats Polyunsaturated fats, such as safflower oil (SFO), are known to lower the level of serum cholesterol (1). The effect is attributed to their rich content of linoleic acid (e.g., up to 80% in SFO). On the other hand, rice bran oil (RBO), in spite of its relative low linoleic acid con tent, has also been shown to lower serum cholesterol level (2,3). The effect of RBO was attributed mainly to its high content of unsaponifiable matters, such as to cotrienols and y-oryzanol (3-5).In 1970, Suzuki and Oshima was the first group to blend SFO and RBO in different ratios and compare their cholesterol-lowering effects in human volunteers (6,7). They reported that those who consumed the oil blend of RBO and SFO at a ratio of 7:3 for 7d had a greater reduction in serum cholesterol level than those who consumed either oil alone or oil blends at different ratios. Similar effects have also been observed when a moderate amount of cholesterol was supplied as eggs (25mg/kg body weight) (8). To date, the mechanism for the cholesterol-lowering effect of SFO and RBO mix ture blended at this particular ratio is still not clear. The objective of the present study was to examine how the supplementation of cholesterol affected the hyp...

Rice Bran Oil and γ‐Oryzanol in the Treatment of Hyperlipoproteinaemias and Other Conditions

“…This is the reason why it has been proposed that the action of rice bran oil could be based on bile acids and TC complexation in the intestinal lumen (anion exchange resin-like action). This hypothesis seems to be confirmed by studies that showed a high faecal excretion of TC and bile acids in rats that underwent a hyperlipidaemic diet (Shinomiya et al, 1983), although very recent research has contradicted the same result (Koba et al, 2000). However, the antihypercholesterolaemic effect of phytosterols has been well documented in different studies on human subjects (Wang and Ng, 1999).…”

“…Thus, in addition to improving the plasma lipid profile, blending of rice bran oil with other oils can result in an economic advantage of lower prices (Sunitha et al, 1997). A somewhat contrasting effect was recently observed by Koba et al (2000) who studied the influence of a 0.5% cholesterol diet supplementation on rice bran oil's antihyperlipidaemic effect. This research examined the effect of cholesterol supplementation on the cholesterollowering ability of different rice bran oil/safflower oil blends.…”

“…In this case, the specific effect of the 3S/7R mixture on the ratio of HDL-C/TC disappeared. A explanation for this phenomenon is that smaller percentages of polyunsaturated fatty acids in the rice bran oil containing diets than in the safflower oil diet might have reduced their ability to dispose of the circulating serum cholesterol into the liver (Koba et al, 2000). Finally, a Chinese author reported that chronic oral administration of g-oryzanol is able to reduce the development of experimental coronary atherosclerosis in rats fed a hypercholesterolaemic diet from birth (Zhang, 1986).…”

Hypolipidemic Effect of Oils with Balanced Amounts of Fatty Acids Obtained by Blending and Interesterification of Coconut Oil with Rice Bran Oil or Sesame Oil

“…Earlier workers have also noticed that blending of oils improves the physicochemical ,, and nutritional properties of the oil. Koba et al have shown that feeding rats with a diet containing blended oils comprising RBO and safflower oil in the ratio of 70:30 increased the HDL concentrations and increased the HDL/TC ratio significantly . Sugano and Tsuji explained the specific cholesterol lowering effect of this blended oil based on the combined effect of the linoleic acid from sunflower oil and the unsaponifiable matter present in the RBO.…”

Characterization of oil exhibiting high γ‐linolenic acid from a genetically transformed canola strain

“…The pooled sample of each TG molecular species was transesterified with methanol and analyzed for fatty acid composition using a Hewlett-Packard 5890 II plus gas chromatograph (GC) equipped with a Supelco Omegawax 320 capillary column (30 m × 0.32 mm i.d.) as described previously (11). The purified total TG fraction and the GGL and GLO molecular species were also analyzed by high-resolution proton-decoupled 13 C nuclear magnetic resonance (NMR) for positional distribution of fatty acids in TG as previously described (12).…”