Response of plasma lipids to dietary cholesterol and wine polyphenols in rats fed polyunsaturated fat diets.

This experiment was designed to evaluate the effects of dietary red wine phenolic compounds (WP) and cholesterol on lipid oxidation and transport in rats. For 5 wk, weanling rats were fed polyunsaturated fat diets (n-6/n-3 = 6.4) supplemented or not supplemented with either 3 g/kg diet of cholesterol, 5 g/kg diet of WP, or both. The concentrations of triacylglycerols (TAG, P < 0.01) and cholesterol (P < 0.0002) were reduced in fasting plasma of rats fed cholesterol despite the cholesterol enrichment of very low density lipoprotein + low density lipoprotein (VLDL + LDL). The response was due to the much lower plasma concentration of high density lipoprotein (HDL) (-35%, P < 0.0001). In contrast, TAG and cholesteryl ester (CE) accumulated in liver (+120 and +450%, respectively, P < 0.0001). However, the cholesterol content of liver microsomes was not affected. Dietary cholesterol altered the distribution of fatty acids mainly by reducing the ratio of arachidonic acid to linoleic acid (P < 0.0001) in plasma VLDL + LDL (-35%) and HDL (-42%) and in liver TAG (-42%), CE (-78%), and phospholipids (-28%). Dietary WP had little or no effect on these variables. On the other hand, dietary cholesterol lowered the alpha-tocopherol concentration in VLDL + LDL ( -40%, P < 0.003) and in microsomes (-60%, P < 0.0001). In contrast, dietary WP increased the concentration in microsomes (+21%, P < 0.0001), but had no effect on the concentration in VLDL + LDL. Cholesterol feeding decreased (P < 0.006) whereas WP feeding increased (P < 0.0001) the resistance of VLDL + LDL to copper-induced oxidation. The production of conjugated dienes after 25 h of oxidation ranged between 650 (WP without cholesterol) and 2,560 (cholesterol without WP) micromol/g VLDL + LDL protein. These findings show that dietary WP were absorbed at sufficient levels to contribute to the protection of polyunsaturated fatty acids in plasma and membranes. They could also reduce the consumption of alpha-tocopherol and endogenous antioxidants. The responses suggest that, in humans, these substances may be beneficial by reducing the deleterious effects of a dietary overload of cholesterol.

Dietary flavonoids reduce lipid peroxidation in rats fed polyunsaturated or monounsaturated fat diets.

We investigated the influence of dietary flavonoids on alpha-tocopherol status and LDL peroxidation in rats fed diets enriched in either polyunsaturated fatty acids (PUFA) or monounsaturated fatty acids (MUFA). Diets equalized for alpha-tocopherol concentrations were or were not supplemented with 8 g/kg diet of flavonoids (quercetin + catechin, 2:1). After 4 wk of feeding, plasma lipid concentrations were lower in rats fed PUFA than in those fed MUFA with a significant correlation between plasma alpha-tocopherol and cholesterol concentrations, r = 0.94, P < 0. 0001). Dietary lipids influenced the fatty acid composition of VLDL + LDL more than that of HDL or microsomes. The resistance of VLDL + LDL to copper-induced oxidation was higher in rats fed MUFA than in those fed PUFA as assessed by the lower production of conjugated dienes and thiobarbituric acid reactive substances (TBARS) and by the >100% longer lag time for dienes production. (P < 0.0001). Dietary flavonoids significantly reduced by 22% the amounts of dienes produced during 12 h of oxidation in rats fed diets rich in PUFA and lengthened lag time 43% in those fed MUFA. Microsomes of rats fed MUFA produced approximately 50% less TBARS than those of rats fed PUFA (P < 0.0001) and they contained more alpha-tocopherol in rats fed MUFA than in those fed PUFA with higher values (P < 0. 0001) in both groups supplemented with flavonoids (P < 0.0001). Our findings suggest that the intake of dietary flavonoids is beneficial not only when diets are rich in PUFA but also when they are rich in MUFA. It seems likely that these substances contribute to the antioxidant defense and reduce the consumption of alpha-tocopherol in both lipoproteins and membranes.

Interaction of transresveratrol with plasma lipoproteins.

Resveratrol (3,4',5-trihydroxystilbene) is a phytoalexin present in some red wines. Like other phenolic substances, this compound is assumed to protect against atherosclerosis by reducing the peroxidative degradation of low-density lipoproteins (LDL). The in vitro efficiency of resveratrol was found to be mainly due to its capacity to chelate copper, although it also scavenges free radicals. In this study, we examined the ability of the compound to associate with lipoproteins in vitro. Trans-resveratrol added to plasma was distributed between subsequently isolated lipoproteins with a linear dose-response curve. The concentrations as expressed on a protein basis increased with the order of their lipid content: high-density lipoproteins (HDL) < LDL < very low-density lipoproteins (VLDL). This finding reveals the lipophilic character of resveratrol. Other assays showed that resveratrol added to plasma prior to fractionation was, as expressed on a protein basis, more associated with lipoproteins (d < 1.21 g/mL) than with lipoprotein-free proteins (5.5 +/- 0.7 vs 2.2 +/- 0.4 nmol/mg protein). On the other hand, resveratrol inhibited the formation of thiobarbituric acid reactive substances (TBARS) in preparations containing phospholipid unilamellar liposomes oxidized by the water-soluble radical generator 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH). A linear dose-response curve was obtained up to 30 microM when the antioxidant was added in the final preparation and up to 200 microM when added before preparing liposomes in order to facilitate its incorporation. This suggests that the soluble fraction of resveratrol scavenged free radicals in the aqueous phase before attacking PUFA and within membranes. Taken together, the present data support the hypothesis that resveratrol may be efficient at different sites: in the protein and lipid moieties of LDL and in their aqueous environment.

Dietary sunflower oil reduces plasma and liver triacylglycerols in fasting rats and is associated with decreased liver microsomal phosphatidate phosphohydrolase activity.

Plasma and liver lipids were studied in male weanling rats fed diets containing moderate levels of fat (6% by weight) as sunflower oil (SF diet, rich in linoleic acid), salmon oil (SM diet, rich in long-chain n-3 fatty acids), or a blend of peanut and rapeseed oil (PR diet, rich in oleic acid). After nine weeks of feeding, the fasting plasma cholesterol concentrations were 49 and 24% lower in groups SM and SF, respectively, as compared to group PR. Both dietary salmon oil and sunflower oil lowered the triacylglycerol concentration of plasma and liver but, unexpectedly, the response was higher with sunflower oil. Indeed, in group SM the values were 15 and 30% lower in plasma and liver, whereas in group SF, they were 24 and 53% lower, respectively. As compared to group PR, liver triacylglycerols and microsomes contained 2.5- and 2.3-fold less oleic acid, respectively, in group SF, and they were 9.2- and 3.2-fold enriched in n-3 fatty acids, respectively, in group SM. The liver triacylglycerol concentrations were correlated with changes in the microsomal Mg(2+)-dependent phosphatidate phosphohydrolase activity (r = 0.47, P < 0.01). As oleic acid, unlike long-chain n-3 fatty acids, is considered to promote the triacylglycerol synthesis and secretion, our findings suggest that changes in the membrane fatty acid composition could affect the triacylglycerol content of liver and plasma. Moreover, the availability within the liver, of oleic acid, predominantly incorporated into triacylglycerols, might limit the triacylglycerol production in SF-fed rats.

Effects of moderate fat intake with different n-3 fatty acid sources and n-6/n-3 ratios on serum and structural lipids in rats.

The aim of this study was to compare the effects of dietary polyunsaturated fatty acids (PUFA) on serum and membrane lipids in rats fed diets containing moderate levels of fats (6% by weight). Control rats received enough PUFA to prevent any deficiency. Experimental rats were fed linseed oil, salmon oil, or sunflower oil. After 8 weeks of feeding, fasting serum triacylglycerol and cholesterol levels were not altered in the linseed oil group. In contrast, in the salmon oil group, serum cholesterol was lowered by 58% (P < 0.05) and the specific binding of heterologous LDL to liver plasma membrane was reduced by 31% (P < 0.05). Unexpectedly, serum triacylglycerol levels were not significantly lowered (-14%) whereas they decreased (-32%; P < 0.05) in the sunflower oil group. Oleic acid, which has a stimulating effect on triacylglycerol synthesis and secretion, was less incorporated in serum and liver plasma membrane in rats fed sunflower oil than in rats fed other dietary lipids. This finding suggests that the effect of dietary sunflower oil was partly mediated by the reduction of oleic acid available for triacylglycerol synthesis.

Effects of sugar beet fiber feeding on serum lipids and binding of low-density lipoproteins to liver membranes in growing pigs.

Two groups of pigs were fed either a control diet or a diet containing sugar beet fiber (SBF). After 4 wk, total serum cholesterol and high-density-lipoprotein cholesterol concentrations were similar on both diets. By contrast, the fasting triacylglycerols were 21% lower (P < 0.05) and apparent feed-conversion efficiency was 47% higher (P < 0.01) on the SBF diet than on the control diet. Accordingly, the effect of SBF did not appear to be mediated by an impairing effect on dietary lipid absorption. The results suggest that the decreasing effect of SBF on triacylglycerols was due to a reduction in very-low-density-lipoprotein synthesis without changes in the size of particles. The low-density-lipoprotein receptor activity of a liver plasma membrane-enriched fraction was not influenced by the dietary treatment; however, a significant negative relationship between cholesterol concentrations and the receptor activity was observed irrespective of the diet.

Immunological evidence for common antigenic sites in high-density lipoproteins from rainbow trout and man.

The plasma high-density lipoproteins (HDL, rho 1.085-1.21 g/ml) of rainbow trout (Salmo gairdneri) have been shown to contain large amounts of apolipoprotein (apo) AI (Mr 28,000) and several other apolipoproteins of Mr less than 14,000 (apo C-like) and of Mr 37,000-38,000, 44,000-45,000 and 53,000-54,000. Comparison of apo AI from trout and human HDL shows them to be similar in Mr and to have some cross-immunoreactivity, whereas apo AII differs in Mr but also possesses common antigenic sites. It is suggested that the major apolipoproteins of fish and human HDL may fulfil similar roles in lipid transport.

Activation of trout adipose tissue lipoprotein lipase by trout apoproteins.

In rainbow trout (Salmo gairdnerii) lipoprotein profiles change during the annual sexual cycle. Among other factors, lipoprotein lipase (LPL) activity might play a role. This enzyme is activated by trout serum suggesting the existence of a cofactor corresponding to apoprotein CII in this species. In the present study, we determined more accurately some characteristics of the enzyme activity inhibited by 0.3 M NaCl. Trout serum and high density lipoproteins (HDL) activated both rat and trout adipose tissue LPLs. A fraction of apo HDL obtained by gel filtration also activated the enzyme. The mean Mr was 10,000. Isoelectric focusing of the same fraction gave several bands of proteins with apparent pI in the range of 4.2-4.9. These results show that in trout, LPL is activated by a cofactor similar to that in mammals, the apo CII. In addition, a fraction mainly containing apo AI (+ traces of apo C) activated trout LPL and reinforced the activation by apo CII. These findings suggest that trout apo AI may promote the activating effect of apo CII on trout LPL.

Effects of a (n-3) polyunsaturated fatty acid-deficient diet on profiles of serum vitellogenin and lipoprotein in vitellogenic trout (Salmo gairdneri).

During the 6 months of vitellogenesis, 3-year-old female trout (Salmo gairdneri) were fed either an enriched (E) or an (n-3) polyunsaturated fatty acid (PUFA)-deficient (D) diet; serum vitellogenin (VG) and lipoproteins (d<1.21 g/ml) were analyzed at the third month of vitellogenesis (September) and at ovulation (December). The serum content of high density lipoproteins (HDL), the major protein class, maintained a mean value of 1500 mg/dl at both stages and with both diets. On the contrary, very low density lipoproteins (VLDL) were 90% higher during vitellogenesis than at spawning time, whereas excess vitellogenin circulated at this period (6580 mg/dl serum with diet E). The diet deficient in (n-3) lowered serum vitellogenin content by 16% in September and by 26% in December. The degree of (n-3) PUFA incorporation moderately decreased in low density lipoproteins (LDL) and in HDL with the (n-3)-deficient diet. The effect was more pronounced for 20∶5. On the other hand, essential 22∶6 was incorporated into vitellogenin at the same rate in September as in December with diet E (23% and 25%, respectively), whereas after a 3-month deficiency, the percentage fell to 12%; this percentage rose again to 19% at spawning time. These findings show that, although stored (n-3) PUFA were not exhausted after a 6-month dietary deficiency, the incorporation of essential fatty acids (EFA) into vitellogenin during the early stages of oogenesis was low, suggesting changes in egg composition that may influence hatching.