Resveratrol inhibits metal ion-dependent and independent peroxidation of porcine low-density lipoproteins

Resveratrol, a phytoalexin (3, 4', 5, trihydroxystilbene) present in some red wines, has been reported to inhibit copper-mediated low-density lipoprotein (LDL) oxidation. In this study, we examined the efficiency of this compound in inhibiting metal ion-dependent and independent peroxidation of porcine LDL. At 0.5, 1, or 1.5 microM, transresveratrol prolonged the lag time preceding the onset of conjugated diene formation in a dose-dependent manner, with a slope of the propagation phase 5-fold greater in the presence of Cu SO4 (5 microM) than in the presence of the free radical generator, AAPH [2, 2'-azobis (2-amidinopropane) dihydrochloride] (1 mM). At 1 microM, transresveratrol prolonged the lag time 3.4- and 1.4-fold in the presence of copper and AAPH, respectively. Isomerisation into cisresveratrol significantly lowered the chelating capacity, but did not alter the free radical scavenging capacity. As compared to flavonoids and trolox, transresveratrol showed a much higher ability to prolong the lag time in copper, but not in AAPH-catalyzed oxidation. The kinetics of generation of degradative products in the presence of copper confirmed the strongest protective effects of transresveratrol, because the formation of thiobarbituric acid reactive substances and hydroperoxides was almost completely inhibited at 200 min. By contrast, transresveratrol was less potent than flavonoids (but more than trolox) as a scavenger of free radicals. Our data show that, like flavonoids, resveratrol protects LDL against peroxidative degradation by both chelating and free radical scavenging mechanisms. However, transresveratrol, which is by far the most potent chelator of copper, does not chelate iron. It might contribute to the protective effects of wine polyphenols by removing copper from LDL particles and arterial tissue and, thereby, delaying the consumption of flavonoids and endogenous antioxidants.

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.

Hyperactivity in the rat is associated with spontaneous low level of n-3 polyunsaturated fatty acids in the frontal cortex

Inattention, hyperactivity and impulsiveness are the main symptoms of the heterogeneous attention-deficit/hyperactivity disorder (ADHD). It has been suggested that ADHD is associated with an imbalance in polyunsaturated fatty acid (PUFA) composition, with abnormal low levels of the main n-3 PUFA, DHA (22: 6n-3). DHA is highly accumulated in nervous tissue membranes and is implicated in neural function. Animal studies have shown that diet-induced lack of DHA in the brain leads to alterations in cognitive processes, but the relationship between DHA and hyperactivity is unclear. We examined the membrane phospholipid fatty acid profile in frontal cortex of rats characterized for attention, impulsiveness and motricity in various environmental contexts to determine the relationship between brain PUFA composition and the symptoms of ADHD. The amounts of n-3 PUFA in the PE were significantly correlated with nocturnal locomotor activity and the locomotor response to novelty: hyperactive individuals had less n-3 PUFA than hypoactive ones. We conclude that spontaneous hyperactivity in rats is the symptom of ADHD that best predicts the n-3 PUFA content of the frontal cortex. This differential model in rats should help to better understand the role of PUFA in several psychopathologies in which PUFA composition is modified.

Dietary docosahexaenoic acid [22: 6(n-3)] as a phospholipid or a triglyceride enhances the potassium chloride-evoked release of acetylcholine in rat hippocampus

We demonstrated previously that a dietary-induced depletion of docosahexaenoic acid (DHA) in cerebral phospholipids increases the spontaneous release of acetylcholine (Ach) in the rat hippocampus and reduces its potassium chloride evoked-release. In the present study, we investigated the effects in rats of DHA-enriched diets supplied by egg phospholipids (E-PL) or tuna oil (TO) on the PUFA in hippocampus membranes and on the synaptic release of Ach. Control rats were fed 3 g/kg of the DHA precursor, alpha-linolenic acid (LNA). Chronically (n-3) PUFA-deficient females were fed, starting 2 wk before mating, the deficient diet, a control diet, or a purified diet supplying 1, 2, or 3 g DHA/kg diet as E-PL or TO. Experiments were performed on the adult male progeny fed the same diet as their dams throughout life. The form of dietary DHA (TO or E-PL) did not influence its incorporation into the hippocampus. The 1 g DHA/kg diets allowed maximal incorporation into phosphatidylethanolamine (PE), but 2 g DHA/kg diet was needed for phosphatidylcholine (PC). A minimum of 2 g DHA/kg was needed to decrease the basal Ach release and to enhance the stimulated release to that of the control; the Ach release of the 1 g/kg DHA-groups did not differ from that of the deficient group. This suggests that >1 g DHA/kg diet is needed to ensure PUFA incorporation into PE and PC, and basal and stimulated Ach release in the rat hippocampus equivalent to the control group fed only LNA. PUFA incorporation into the hippocampus depends mainly on the PUFA concentration of the diet, not on the form of dietary DHA.

Simultaneous changes in lipid composition, fluidity and enzyme activity in piglet intestinal brush border membrane as affected by dietary polyunsaturated fatty acid deficiency

The effects of dietary polyunsaturated fatty acid (PUFA) deficiency on intestinal brush border membrane (BBM) fluidity, lipid composition and 5'-nucleotidase activity were examined in piglets. Cholesterol/phospholipid and sphingomyelin (SM)/phosphatidylcholine (PC) ratios were unaffected. However, fluidity was decreased in the external regions and also tended to decrease in the core of the PUFA-deficient pig membrane lipid bilayer. Therefore, the change in the membrane physical properties seemed to be due to the large diet-induced alteration in the phospholipid (PL) fatty acid composition and to the concomitant decrease in PC and increase in phosphatidylserine levels. In the membrane total PL, the arachidonic acid level was slightly lowered, while linoleic, eicosapentaenoic and docosahexaenoic acid levels markedly decreased. PC was mainly concerned by the altered distribution of unsaturated fatty acids, but not SM. However, a significant decrease in (n-6)/(n-3) ratio occurred in the latter. These structural changes were associated with a higher 5'-nucleotidase activity in the intestinal BBM of PUFA-deficient as compared to control piglets.

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.

Effects of a low dietary linoleic acid level on intestinal morphology and enterocyte brush border membrane lipid composition

The influence of low dietary linoleic acid level (an essential fatty acid deficiency) on the intestine mucosal morphology and the purified brush border membrane (BBM) lipid composition was investigated in the rat. Electron micrographs and morphometric measurements showed that villi and crypt sizes as well as the ultrastructure of epithelial cells were altered. Cholesterol (CHOL) and phospholipid (PL) levels, CHOL/PL ratio and PL class distribution were not changed by the low linoleate diet. However, the fatty acid composition of phospholipids was markedly modified in the enterocyte BBM, showing elevated amounts of palmitoleic (16:1n-7), oleic (18:1n-9) and 5,8,11-eicosatrienoic (20:3n-9) acids and, by contrast, depressed linoleic (18:2n-6) and arachidonic (20:4n-6) acid levels. Although the underlying mechanisms remain unknown the results obtained suggest that essential fatty acids (EFA) could be directly involved in the trigger action of the observed alterations, as regards both their dynamic (metabolic) and structural roles.

Phospholipid hydroperoxide glutathione peroxidase activity and vitamin E level in the liver microsomal membrane: effects of age and dietary alpha-linolenic acid deficiency

Age and diet-induced variations of phospholipid hydroperoxide glutathione peroxidase (PHGPx) activity and alpha-tocopherol concentration in the liver microsomal membrane were studied in male Wistar rats fed a semipurified diet either balanced in n-6 and n-3 polyunsaturated fatty acids (PUFA) (Control) or deprived of alpha-linolenic acid, i.e. n-3 PUFA (Deficient) over two generations. The animals were studied at the age of 6 months (adult) or 24 months (old). Both PHGPx activity and vitamin E level were significantly higher in 24-month old rats as compared to 6-month old rats. By contrast, the thiobarbituric acid reactive substances (TBARS) following stimulated in vitro peroxidation of membrane lipids were markedly lower (P < 0.01) with aging. The fatty acid composition of microsomal membrane phospholipids (PL) was also considerably modified by age. In particular, the levels of arachidonic acid and total n-6 PUFA were lower (P < 0.001) whereas n-3 PUFA levels were higher (P < 0.001) in most PL main classes. The alpha-linolenic acid deficiency markedly influenced these age-related changes. The higher PHGPx activity in the old rats as compared to the adult rats was only significant in those fed the control diet. In the 6-month old rats (but not in the 24-month old rats), the deficient diet led to a higher membrane vitamin E level and to lower TBARS production than the control diet. The results suggest that the nature of dietary PUFA may influence the age-related variations in this pair of membrane antioxidants and also in the fatty acid composition of microsomes.

Zonal high-performance affinity chromatography as a tool for protein interaction studies with special reference to the lipase-colipase complex

The technique of zonal high-performance affinity chromatography applied to the lipase-colipase system (lipase B as eluted acceptor and colipase as silica-bonded ligand) gave qualitatively the same results as conventional affinity chromatography. The elution volume of the acceptor increases with decreasing load introduced at constant volume into the column of ligand-bonded silica. This led to the use of a mathematical treatment for calculating the dissociation constant (KD) of the lipase-colipase complex. The influence of some physical and chemical chromatographic parameters was studied. Increasing temperature and flow-rate reduced the affinity of lipase for colipase, whereas it was only slightly modified by increasing the ionic strength. The KD value was minimal and equal to 0.1 X 10(-6) M at pH 4.7 and 0.38 X 10(-6) M at pH 6.5, after correction for the flow-rate. The latter value is similar to that obtained by more conventional techniques. The absence of some marked KD modifications by ionic strength and the value of delta S for the complex association obtained by temperature studies suggest the intervention of mixed hydrophobic-ionic interactions in the formation of the lipase-colipase complex. Their respective importances are discussed.