Hypolipidemic and antioxidant properties of tocotrienol rich fraction isolated from rice bran oil in experimentally induced hyperlipidemic rats

Minhajuddin M, Beg ZH, Iqbal J.

Food Chem Toxicol. 2005 May;43(5):747-53.

We investigated a dose-dependent hypolipidemic and antioxidant effect of tocotrienol rich fraction (TRF) isolated from rice bran oil on experimentally induced hyperlipidemic rats. Feeding of atherogenic diet (5% hydrogenated fat, 0.5% cholic acid and 1% cholesterol) for three weeks resulted in a significant increase in plasma triglyceride (3.3-fold) and total cholesterol (2.4-fold) levels. There was a 5-fold increase in the level of LDL cholesterol with only a small increase in HDL cholesterol. On the other hand, HMG-CoA reductase activity was significantly reduced in these animals. The formation of TBARS, thiobarbituric acid reactive substances, (86%) and conjugated dienes (78%) were also significantly higher in these rats compared to normals. After the induction of hyperlipidemia for three weeks, rats were supplemented with different doses of TRF for one week. TRF supplementation decreased the lipid parameters in a dose-dependent manner with an optimum effect at a dose of 8 mg TRF/kg/day. HMG-CoA reductase activity, which was increased after the withdrawal of atherogenic diet, remained significantly decreased during the TRF treatment. Feeding of TRF also decreased TBARS and conjugated dienes significantly. These results suggest that TRF supplementation has significant health benefits through the modulation of physiological functions that include various atherogenic lipid profiles and antioxidants in hypercholesterolemia.

The migration of circulating monocytes into the subendothelial space occurs through the expressing of some adhesion molecules on endothelial cells. In the present study, using human aortic endothelial cells (HAECs), we investigated whether a model compound for oxysterols, 25-hydroxycholesterol, can enhance the monocyte adherence to HAECs exposed to 25-hydroxycholesterol via increasing expression of vascular cell adhesion molecule-1 (VCAM-1). We also aimed to determine the in vitro effects of tocotrienols on the enhanced interaction between monocytes and endothelial cells. We found that 25-hydroxycholesterol enhances surface expression determined by ELISA, induces VCAM-1 mRNA expression by real time-PCR, and stimulates adhesiveness of HAECs to U937 monocytic cells in a dose-dependent fashion. The combination treatment with anti-VCAM-1 and anti-CD11b monoclonal antibodies significantly reduced the monocyte adherence to 25-hydroxycholesterol-stimulated HAECs. Compared to alpha-tocopherol, tocotrienols displayed a more profound inhibitory effect on adhesion molecule expression and monocytic cell adherence. We observed that delta-tocotrienol exerted a most profound inhibitory action on monocytic cell adherence when compared to alpha-tocopherol and alpha-, beta-, and gamma-tocotrienols. Tocotrienols accumulated in HAECs to levels approximately 25-95-fold greater than that of alpha-tocopherol. In conclusion, these results indicate that a model compound 25-hydroxycholesterol can enhance the interaction between monocytes and HAECs, and that tocotrienols had a profound inhibitory effect on monocytic cell adherence to HAECs relative to alpha-tocopherol via inhibiting the VCAM-1 expression. These superior inhibitory effects of tocotrienols may be dependent on their intracellular accumulation.

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