Influence of dietary fat saturation on lipid peroxidation of serum and low density lipoprotein in rats

Abstract

The purpose of this study was to investigate the influence of different P/S (polyunsaturated/saturated) ratios on lipid peroxidation of plasma, liver and low-density lipoprotein (LDL) in rats, using dietary fats with different saturation levels. Male Sprague-Dawley rats weighing about 300 g were randomly divided into five groups and fed a semisynthetic diet containing 10% (w/w) fat for 6 weeks. The fat was composed of 100, 75, 50, 25, 0% corn oil and 0, 25, 50, 75, 100% lard (CO100, CO75, CO50, CO25 and LA groups, with P/S ratios of 3.81, 2.13, 1.21, 0.64, and 0.28, respectively) respectively. The body and liver weight of rats fed dietary fat with different P/S ratios were comparable among 5 groups. The CO100 group had higher plasma TBARS (thiobarbituric acid-reactive substances) than the CO25 and LA groups. The TBARS of LDL in LA and CO25 groups were lower than those of the other (CO100, CO75 and CO50) groups. In addition, the rats fed P/S ratio ≦1.21 (i.e., CO50, CO25, and LA groups) had lower LDL TBARS than rats fed P/S ratio >1.21 (i.e., CO100 and CO75 groups) when LDL were incubated with Cu 2+ at 37 °C for 2 or 5 h. On the other hand, rats fed diets with P/S ratio ≦1.21 experienced significantly increase lag time of conjugated diene formation in LDL than those fed P/S >1.21. The fatty acid content of 18:2 (n-6) in LDL was reduced by decreasing the ratio of P/S in dietary fat. The ratio of linoleic acid content to oleic acid content was inversely correlated with the lag time of LDL oxidation. However, different P/S ratio in the diet did not affect 18:1 (n − 9), vitamin E levels and the TBARS values in liver of rats. The results suggested that P/S ratios in the diet influenced the LDL oxidation, and the lipid peroxidation might have a threshold of P/S ratios between 1.21 and 0.64.