Elsevier

Nutrition Research

Volume 24, Issue 1, January 2004, Pages 73-83
Nutrition Research

Regular article
High polyunsaturated and monounsaturated fatty acid to saturated fatty acid ratio increases plasma very low density lipoprotein lipids and reduces the hepatic hypertriglyceridemic effect of dietary cholesterol in rats

https://doi.org/10.1016/j.nutres.2003.09.002Get rights and content

Abstract

To determine whether high polyunsaturated and monounsaturated fatty acid to saturated fatty acid [(P+M)/S] ratio in diets increases plasma lipoprotein lipids and reduces the hepatic hypertriglyceridemic effect of dietary cholesterol, we compared plasma lipoproteins and liver lipids in 64 rats. Rats were fed diets with the same polyunsaturated fatty acids/saturated fatty acids (P/S) ratio of 1.0, but different (P+M)/S ratios of 1.5, 2, 4, or 5.7 without (experiment 1) or with 1% cholesterol supplement (experiment 2). We found that the plasma total cholesterol (C), and low density lipoprotein (LDL)-C concentrations were significantly higher in rats fed with the (P+M)/S ratio of 5.7 compared with rats fed with the (P+M)/S ratio of 1.5 or 2.0. As to the very low density lipoprotein (VLDL)-C, rats fed with 5.7 or 4.0 ratio had higher concentration than rats fed with 1.5 or 2.0 ratio. With 1% choesterol supplement, when rats were fed with the ratio of (P+M)/S which increased from 1.5, 2, 4 to 5.7, there was a progressive increase in plasma total cholesterol (P=0.0001), total triacylglycerol (TAG, P=0.0091), total phospholipid (PL, P=0.0006), VLDL-C (P=0.0001), VLDL-TAG (P=0.0119), VLDL-PL (P=0.0013), LDL-C (P=0.0001), LDL-TAG (P=0.0006), and LDL-PL (P=0.0001) concentrations. There was also a progressive increase in liver C level (P=0.005) and decrease in liver TAG level (P=0.004) with 1% C supplement. However, without 1% cholesterol supplement, no such a trend was found for plasma total, lipoproteins, and liver lipids. We conclude that high (P+M)/S ratio increases plasma VLDL and LDL lipids and reduces the hepatic hypertriglyceridemic effect of dietary cholesterol in rats. These results suggest that the higher (P+M)/S ratio is more cholesterolemic and hepatocholesterolemic than lower (P+M)/S ratio in rats fed with high-cholesterol diet.

Introduction

Beginning in the 1950s, systematic investigations have been conducted to determine how dietary fat affected plasma cholesterol concentrations. In human studies, monounsaturated fatty acid (MUFA, M)-rich diets led to a decrease [1], [2], [3] in the plasma LDL-C concentrations when compared with polyunsaturated fatty acid (PUFA, P)- or carbohydrate-rich diets. But there have been no studies substituting monounsaturated fatty acid (MUFA, M) for either saturated fatty acid (SFA, S) or PUFA on liver lipid metabolism in human subjects with high cholesterol supplement. However, most rodent animal models did not exhibit a hypocholesterolemic response of MUFA. In contrast, compared to dietary PUFA, intake of MUFA-rich diets by rats [4], [5], [6], [7], hamsters [8], guinea pigs [9], [10], and rabbits [11] elicited a hypercholesterolemic respnse.

It has been suggested that dietary cholesterol is an increase in LDL-C, but this effect may be modified by the type and amount of fatty acids in the diets, with saturated fatty acids increasing this effect and polyunsaturated fatty acids decreasing it [12], [13]. In rats fed with high-cholesterol diets, olive oil intake resulted in the highest concentration of cholesterol in serum and liver compared with coconut or corn oil [4]. Studies in the hamsters [14] indicated that when cholesterol was added to an olive oil-containing test diet, hepatic cholesteryl ester content was increased six to nine times as compared with a safflower oil- or coconut oil-containing diet. Moreover, cholesterol feeding resulted in increased hepatic secretion of VLDL particles and increased the rate of TAG biosynthesis in rats [15], [16], [17].

In our recent studies have focused on plasma and liver cholesterol lowering by dietary high P/M ratio, low M/S ratio, and (P+M)/S ratio below 3 [5], [6]. However, whether the effect of low dietary (P+M)/S ratio on plasma lipoprotein and liver lipids metabolism in rats will be remodified by dietary cholesterol remains unclear. Therefore, in this study, we asked whether high (P+M)/S ratio increases plasma lipoprotein lipids and reduces the hepatic hypertriglyceridemic effect of dietary cholesterol in rats. To answer this question, we assessed the effects of diets with the same P/S ratio of 1.0, but different (P+M)/S ratio of 1.5, 2, 4, or 5.7, and with or without 1% cholesterol supplement on plasma and liver lipids metabolism.

Section snippets

Animals

In experiment 1, 32 male Wistar rats (Laboratory Animal Center, College of Medicine, National Taiwan University, Taipei, Taiwan), each weighing about 135g, were used for the study. All animal experimental procedures followed the Guide for the Care and Use of Laboratory Animal, National Science Council, Taiwan. Rats were divided into four groups of 8 rats in each on the basis of their weight. Rats were housed individually in a stainless steel, wire-bottomed cages and consumed a diet and water ad

Body weight gain and feed efficiency

In experiment 1 the food consumptions of rats from diet 1 to diet 4 group were Diet 1 19.4±2.6 g/day, Diet 2 18.6±3.3 g/day, Diet 3 18.5±3.2 g/day, and Diet 4 19.9±3.0 g/day. In experiment 2 the food consumptions of rats from diet 1 to diet 4 group were Diet 1 16.4±2.3 g/day, Diet 2 17.0±2.3 g/day, Diet 3 16.3±2.5 g/day, and Diet 4 17.0±2.1 g/day. However, there were no significant differences in body weight gain or feed efficiency (g weight gain/100g diet) among groups of rats in experiments 1

Discussion

The present study shows that high polyunsaturated- and monounsaturated fatty acid to saturated fatty acid [(P+M)/S] ratio increases plasma VLDL lipids and reduces the hepatic hypertriglyceridemic effect of dietary cholesterol. The evidence is that we found when the P/S ratio was held constant at 1.0 and rats fed with the ratio of (P+M)/S increased from 1.5, 2, 4, to 5.7, 1% C supplement resulted in a progressive increase in plasma total C, total TAG, total PL, VLDL-C, VLDL-TAG, VLDL-PL, LDL-C,

Acknowledgements

This work was supported by a grant (CMC90-M-17 and CMC91-M-15) from the China Medical College, Taiwan, Republic of China.

References (28)

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