Modulation of vascular endothelial cell function by palm oil antioxidants

Several cardiovascular risk factors including, hypercholesterolaemia and hypertension, lead to diseased blood vessels due to endothelial cell dysfunction. Recent studies also indicate that such alterations in blood vessel function may involve free radical related mechanism(s). Therefore, in the present study, two different preparations of palm oils with variable antioxidant profiles, as well as a purified antioxidant fraction extracted from unprocessed palm oil (tocotrienol-rich-factor; TRF), were tested for their ability to influence blood vessel dysfunction in the spontaneously hypertensive rat (SHR). Adult SHRs were fed a synthetic diet supplemented (5% w/w) with either physically refined palm oil (PO), golden palm cooking oil (Nutrolein; GPO) or olive oil (OO; control diet). Antioxidant rich diet (TRF diet) was prepared by supplementing the OO diet with 0.2% (w/w) TRF. After 12 weeks of pre-feeding, segments of thoracic aorta were used to evaluate vascular function. Compared to the normotensive Wistar-Kyoto (WKY) control rats, aortic rings from the SHR showed impaired endothelium dependent relaxation to acetylcholine (ACh) which was restored by dietary TRF (p<0.05, ANOVA and Tukey's test). In addition, the paradoxical increase in tension in control hypertensive vessels observed at higher doses of ACh was prevented by TRF and also by the PO and GPO diets. Although the development of thromboxane-like constrictor response, after the inhibition of nitric oxide in hypertensive vessels, was unaffected by test diets, both TRF and GPO feeding prevented the amplification of this unwanted constriction by a threshold dose (7.2x10-10 M) of noradrenaline. Results suggest a modulatory role for minor constituents of edible oils and are in agreement with the recently reported benefits of natural antioxidants against cardiovascular diseases.