Feeding unsaponifiable compounds from rice bran oil does not alter hepaticmRNA abundance for cholesterol metabolism-related proteins in hypercholesterolemic rats

The hypocholesterolemic effect of rice bran oil (RBO) is defined in human a nd animal experiments which indicate the presence of active component(s) in the unsaponifiable fraction, but the detailed mechanism is not known yet. Exogenously hypercholesterolemic (ExHC) rats were fed for 2 weeks on a 0.5% cholesterol diet supplemented with 10% each of RBO, RBO-simulated oil (RBO SO) in its fatty acid composition, or RBOSO plus 0.25% unsaponifiable compo unds (UC) from RBO. Rats fed RBO or the UC resulted in lowing serum and liv er cholesterol concentration and preventing reduction of high density lipop roteinic-cholesterol. Dietary RBO or the UC led to an elevation of fecal ne utral sterol excretion, but no significant change in fecal bile acid excret ion or in hepatic abundance of mRNAs for 3-hydroxy-3-methylglutaryl-CoA red uctase, cholesterol-7 alpha -hydroxylase, and low density lipoprotein recep tor. Besides, serum and liver alpha -tocopherol concentrations were lowered in RBO or the UC-fed rats. These results show that the UC in RBO leads to a decreased serum cholesterol concentration by interrupting the absorption of intestinal hydrophobic compounds rather than by modifying cholesterol me tabolism in the liver.