α-Linolenate reduces the dietary requirement for linoleate in the growing rat.

BACKGROUND: We hypothesized that due to the absence of a dietary source of omega-3 fatty acids, the essential fatty acid (EFA) deficiency model leads to an overestimate of linoleic acid (LA) requirements. METHODS: over 7wk, young rats consumed an EFA diet containing either 0en% linoleate (0LA) and 0en% α-linolenate (0LNA) or a diet containing 0.5en% LNA plus one of seven levels of added LA (0.12-4.0en%; n=6/group). RESULTS: Rats consuming the 0LA-0LNA diet had the lowest final body weight, 34-68% lower LA and arachidonate in plasma and liver, 87% lower LA in epididymal fat, and an 8-20 fold higher eicosatrienoate in plasma, liver and muscle lipids. 0.5LNA completely prevented the lower growth and partly prevented the rise in eicosatrienoate seen in the 0LA-0LNA group. CONCLUSION: Providing dietary LNA at 0.5 en% reduces the rat's physiological requirement for LA by an estimated factor of at least four (0.5en% instead of 2en%). Since LA requirements in humans are also based on the same flawed model of EFA deficiency, it is plausible that they too have been overestimated and should therefore be reinvestigated.

n-3 Fatty acids modulate brain glucose transport in endothelial cells of the blood-brain barrier.

We have previously shown that glucose utilization and glucose transport were impaired in the brain of rats made deficient in n-3 polyunsaturated fatty acids (PUFA). The present study examines whether n-3 PUFA affect the expression of glucose transporter GLUT1 and glucose transport activity in the endothelial cells of the blood-brain barrier. GLUT1 expression in the cerebral cortex microvessels of rats fed different amounts of n-3 PUFA (low vs. adequate vs. high) was studied. In parallel, the glucose uptake was measured in primary cultures of rat brain endothelial cells (RBEC) exposed to supplemental long chain n-3 PUFA, docosahexaenoic (DHA) and eicosapentaenoic (EPA) acids, or to arachidonic acid (AA). Western immunoblotting analysis showed that endothelial GLUT1 significantly decreased (-23%) in the n-3 PUFA-deficient microvessels compared to control ones, whereas it increased (+35%) in the microvessels of rats fed the high n-3 PUFA diet. In addition, binding of cytochalasin B indicated that the maximum binding to GLUT1 (Bmax) was reduced in deficient rats. Incubation of RBEC with 15 microM DHA induced the membrane DHA to increase at a level approaching that of cerebral microvessels isolated from rats fed the high n-3 diet. Supplementation of RBEC with DHA or EPA increased the [(3)H]-3-O-methylglucose uptake (reflecting the basal glucose transport) by 35% and 50%, respectively, while AA had no effect. In conclusion, we suggest that n-3 PUFA can modulate the brain glucose transport in endothelial cells of the blood-brain barrier, possibly via changes in GLUT1 protein expression and activity.

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.

Comparative bioavailability of dietary alpha-linolenic and docosahexaenoic acids in the growing rat.

Animal and human studies have indicated that developing mammals fed only alpha-linolenic acid (18:3n-3) have lower docosahexaenoic acid (22:6n-3) content in brain and tissue phospholipids when compared with mammals fed 18:3n-3 plus 22:6n-3. The aim of this study was to test the hypothesis that low bioavailability of dietary 18:3n-3 to be converted to 22:6n-3 could partly explain this difference in fatty acid accretion. For that purpose, we determined the partitioning of dietary 18:3n-3 and 22:6n-3 between total n-3 fatty acid body accumulation, excretion, and disappearance (difference between the intake and the sum of total n-3 fatty acids accumulated and excreted). This was assessed using the quantitative method of whole-body fatty acid balance in growing rats fed the same amount of a 5% fat diet supplying either 18:3n-3 or 22:6n-3 at a level of 0.45% of dietary energy (i.e., 200 mg/100 g diet). We found that 58.9% of the total amount of 18:3n-3 ingested disappeared, 0.4% was excreted in feces, 21.2% accumulated as 18:3n-3 (50% in total fats and 46% in the carcass-skin compartment), and 17.2% accumulated as long-chain derivatives (14% as 22:6n-3 and 3.2% as 20:5n-3 + 22:5n-3). Similar results were obtained from the docosahexaenoate balance (as % of the total amount ingested): disappearance, 64.5%; excretion, 0.5%; total accumulation, 35% with 30.1% as 22:6n-3. Thus, rats fed docosahexaenoate accumulated a twofold higher amount of 22:6n-3, which was mainly deposited in the carcass-skin compartment (68%). Similar proportions of disappearance of dietary 18:3n-3 and 22:6n-3 lead us to speculate that these two n-3 polyunsaturated fatty acids were beta-oxidized in the same amount.

Diets containing long-chain n-3 polyunsaturated fatty acids affect behaviour differently during development than ageing in mice.

The effect of a standard diet providing essential fatty acids enriched in fish oil or palm oil was studied in young, mature and old mice. Two groups of pregnant and lactating OF1 mice were fed on diets with or without high levels of long-chain n-3 polyunsaturated fatty acids. Offspring were maintained on these diets after weaning. The litter size did not differ. The weight increased more quickly in fish-oil-fed mice than palm-oil-fed mice. The fish-oil diet induced a significant increase in exploratory activity in young mice which was not found in mature and old mice. The level of locomotor activity was significantly higher in young, no different in mature, and lower in old fish-oil-fed mice than in controls. Habituation, the simpler form of learning, occurred to the same extent in the two diet groups. For the place learning protocol of the Morris water maze there was no difference between the two diet groups; however, in the probe trial, the mature fish-oil-fed mice remembered the situation well compared with the control mice. In the active avoidance test, on the first day of acquisition the young fish-oil-fed mice made more avoidances than control mice, whereas in contrast, mature and old-fish-fed mice made less avoidances than control mice. These results suggest a positive effect on arousal and learning ability of a diet enriched in long chain n-3 polyunsaturated fatty acids in young mice and a detrimental effect in old mice.

Blood lipid concentrations of docosahexaenoic and arachidonic acids at birth determine their relative postnatal changes in term infants fed breast milk or formula.

BACKGROUND: Factors other than dietary fatty acids could be involved in the variability observed in blood docosahexaenoate (22:6n-3) and arachidonate (20:4n-6) status in formula-fed infants. OBJECTIVE: We considered the 22:6n-3 and 20:4n-6 status at birth to be one of these factors and studied its influence on postnatal changes in term infants fed 4 different diets. DESIGN: The blood phospholipid composition was determined at birth and on day 42 of feeding in 83 term infants fed breast milk, nonsupplemented formula, or 2 different 22:6n-3-supplemented formulas. Relations between 22:6n-3 and 20:4n-6 status at birth and their relative postnatal changes, calculated by the difference between status at the end of the feeding period (6 wk of age) and at birth, were assessed. RESULTS: Postnatal changes in the plasma and erythrocyte phospholipids 22:6n-3 and 20:4n-6 were negatively related to their respective concentrations at birth (P < 0.01) and the slopes of the regression lines were not significantly affected by the type of milk ingested. Adjusted mean values for phospholipid 22:6n-3 in nonsupplemented-formula-fed infants and for 20:4n-6 in formula-fed infants decreased significantly more than they did in the other infant groups (P < 0.02). The status at birth and the type of milk ingested explained 33-64% and 7-47%, respectively, of the variability in postnatal changes. CONCLUSIONS: The status of 22:6n-3 and 20:4n-6 at birth in term infants is one of the major determinants of postnatal changes in these fatty acids. This finding indicates that research is required to characterize environmental, genetic, or both factors, which, in addition to maternal diet, could influence fatty acid status at birth.

n-3 and n-6 fatty acid enrichment by dietary fish oil and phospholipid sources in brain cortical areas and nonneural tissues of formula-fed piglets.

Sufficient availability of both n-3 and n-6 long-chain polyunsaturated fatty acids (LCPUFA) is required for optimal structural and functional development in infancy. The question has been raised as to whether infant formulae would benefit from enrichment with 20 and 22 carbon fatty acids. To address this issue, we determined the effect of fish oil and phospholipid (LCPUFA) sources on the fatty acid composition of brain cortical areas and nonneural tissues of newborn piglets fed artificially for 2 wk. They were fed sow milk, a control formula, or the formula enriched with n-3 fatty acids from a low-20:5n-3 fish oil added at a high or a low concentration, or the formula enriched with n-3 and n-6 fatty acids from either egg yolk- or pig brain-phospholipids. Both the fish oil- and the phospholipid-enriched formula produced significantly higher plasma phospholipid 22:6n-3 concentrations than did the control formula. The 22:6n-3 levels in the brain, hepatic, and intestinal phospholipids were significantly correlated with plasma values, whereas cardiac 22:6n-3 content appeared to follow a saturable dose-response. Feeding sow milk resulted in a much higher 20:4n-6 content in nonneural tissues than did feeding formula. Supplementation with egg phospholipid increased the 20:4n-6 content in the heart, red blood cells, plasma, and intestine in comparison to the control formula, while pig brain phospholipids exerted this effect in the heart only. The addition of 4.5% fish oil in the formula was associated with a decline in 20:4n-6 in the cortex, cerebellum, heart, liver, and plasma phospholipids, whereas using this source at 1.5% limited the decline to the cerebellum, liver, and plasma. Whatever the dietary treatment, the phosphatidylethanolamine 20:4n-6 level was 10-20% higher in the brain temporal lobe than in the parietal, frontal, and occipital lobes in the temporal lobe by administering the formula enriched with egg or brain phospholipids. In conclusion, feeding egg phospholipids to neonatal pigs increased both the 22:6n-3 content in the brain and the 20:4n-6 content in the temporal lobe cortex. This source also increased the 22:6n-3 levels in nonneural tissues with only minor alterations of 20:4n-6. These data support the notion that infant formulae should be supplemented with both 22:6n-3 and 20:4n-6 rather than with 22:6n-3 alone.

Effect of two types of fish oil supplementation on plasma and erythrocyte phospholipids in formula-fed term infants.

We studied the effect of docosahexaenoic acid (DHA) supplementation of infant formulas on fatty acid composition of blood phospholipids in term infants. Two fish oil supplemented formulas containing 0.45 wt% DHA and high (0.35%) or low (0.10%) eicosapentaenoic acid (EPA) were fed for 42 days and compared with a standard formula and breast milk. Infants fed supplemented formulas and breast milk had similar time-dependent changes for DHA from birth to day 42, i.e., slight decreases in plasma phospholipids and erythrocyte phosphatidylcholine and no change in erythrocyte phosphatidylethanolamine. Low-EPA formula prevented EPA accumulation but did not limit the significant decrease in arachidonic acid (AA) noted in infants fed high-EPA formula. These results suggest that term infant formulas should be supplemented with DHA-rich EPA, low fish oil and AA to achieve a fatty acid status in formula-fed infants similar to that of breast-fed infants.

Docosahexaenoic acid concentrations in retinal phospholipids of piglets fed an infant formula enriched with long-chain polyunsaturated fatty acids: effects of egg phospholipids and fish oils with different ratios of eicosapentaenoic acid to docosahexaenoic acid.

Docosahexaenoic acid (DHA; 22:6n-3) is the major fatty acid in the phosphatidylethanolamine of photoreceptor cells. The supply of preformed DHA in milk may play an important role in early human visual development. We examined the effect of adding dietary DHA from yolk or fish oil on its accretion in the retina of newborn piglets fed artificially for 2 wk. DHA-enriched eggs from hens fed rapeseed oil and two fish oils with a high or low ratio of eicosapentaenoic acid (EPA; 20:5n-3) to DHA were used. The basic (conventional) formula contained (% by wt of total fatty acids) 17% linoleic acid (18:2n-6) and 1.3% alpha-linolenic acid (18:3n-3). The yolk-enriched formula also contained 0.5% arachidonic acid (AA; 20:4n-6) and 0.4% DHA. The fish-oil-enriched formulas contained either 0.3% EPA and 0.2% DHA (from salmon oil) or < 0.1% EPA and 0.3% DHA (low-EPA fish oil used at a low concentration), or 0.1% AA, 0.3% EPA, and 0.9% DHA (low-EPA fish oil used at a high concentration). The low-EPA fish oil used at a low concentration can supply the DHA required without increasing the EPA status but only the yolk-enriched formula allowed the artificially reared piglets to attain the same AA status in blood lipids as with sow milk feeding. The DHA concentration plateaued in the retina when it reached 7.5% by wt of total fatty acids in plasma phospholipids. Yolk phospholipids and fish oils are equally potent sources for supplying the highest retinal DHA concentration, which was found to be 41.7% by wt of total fatty acids in phosphatidylethanolamine (compared with 35% without supplementation). Inclusion of 0.2-0.3% DHA ensures maximal DHA accretion in the retina but cosupplementation with AA is necessary to achieve the status with maternal feeding in blood lipids and to prevent any possible imbalance between n-6 and n-3 fatty acids.

Deficiency of (n-6) but not (n-3) polyunsaturated fatty acids inhibits the secretagogue effect of prolactin in lactating rat mammary epithelial cells.

The repercussions of various kinds of dietary polyunsaturated fatty acid (PUFA) deficiencies on the fatty acid composition of membranes and on the secretory activity of lactating female rat mammary epithelial cells were investigated. Primiparous female rats were fed different PUFA diets from weaning: adequate (n-6) and (n-3) PUFA supply; overall PUFA deficiency; specific (n-6) PUFA deficiency or specific (n-3) PUFA deficiency. Mammary gland phospholipids contained very low amount of (n-3) PUFA in control rats, and only 1% docosahexaenoic acid. The fatty acid composition of membrane phospholipids reflected the type of diet received by the animals, i.e., the diets deficient in the (n-3) or (n-6) PUFA series resulted in lower (n-3) or (n-6) PUFA, and the (n-3) + (n-6) deficient diet caused a true overall PUFA deficiency in the membranes. The morphology of cells from overall PUFA- or (n-6) PUFA-deficient rats showed an accumulation of secretory vesicles in the cytoplasm. Basal casein secretion was independent of the diet and of the composition of membrane phospholipids. However, prolactin did not have a secretagogue effect on cells from (n-6) PUFA- or overall PUFA-deficient rats but retained this effect on cells from (n-3)-deficient rats. These results emphasize the specific role of (n-6) PUFA in the functioning of the lactating mammary epithelial cell.

Polyunsaturated fatty acid composition of human milk in France: changes during the course of lactation and regional differences.

Milk samples were collected 2-5, 15, 30, 60 and 90 days postpartum from 41 individual mothers recruited in three French cities in order to obtain a general view of the polyunsaturated fatty acid (PUFA) composition in France. Considering the overall results, linoleic acid (18:2 n-6) represented between 11.6% and 13% of total fatty acids in human milk. In contrast alpha-linolenic acid (18:3 n-3) accounted only for about 0.6%, and hence the 18:2 n-6 to 18:3 n-3 ratio was close to 20. Amounts of n-6 and n-3 long-chain PUFAs (LCPs) regularly decreased from postpartum days 2-5 (3.09%) to day 30 (1.67%), and then remained unchanged up to postpartum day 90; the n-6/n-3 LCP ratio ranged between 2.5 and 2. According to regional areas, there were significant differences (P < 0.05) only for colostrum contents of 18:3 n-3 and LCPs, the LCP ratio remaining unchanged. These data are discussed with regard to recent data on human milk fatty acid composition from Western countries and to the mechanisms involved in milk LCP balance.

[Nutritional correction of an excess of unsaturated fatty acids in the body lipids of the growing rat]. / Correction par voie nutritionnelle d'un excès d'acides gras insaturés dans les lipides corporels du rat en croissance.

The use of hydrogenated coconut oil as a putative substance for correcting an excess of unsaturated fatty acids in reserve lipids was tested in growing rats. Young rats with a live weight of about 70 g were given diet A including 4% of sunflower oil which very rapidly created a triglyceride store containing 25 to 30% of linoleic acid (18:2 n-6). At different weights (200, 300 and 350 g), diet A was replaced by diet B containing 15% of hydrogenated coconut oil so that there was the same number of animals in each group. All the rats were killed at 400 g, and diet-A and B were compared as to final fatty acid composition of body lipids (i.e. values taken all during growth from 70 to 400 g). Hydrogenated coconut oil was a very effective substance for rapidly decreasing levels of reserve lipid linoleic acid and for increasing triglyceride melting-point. The impact on the decrease in total unsaturated fatty acid concentrations was more marked the earlier the diet was replaced. However, the latest replacements (at 300 and 350 g) still permitted 70 and 50%, respectively, of the maximal effect observed in rats eating diet B from 70 g. The present experiment shows that when coconut oil was introduced in the diet over a period corresponding to the last one-eight of total body growth in rat, the final concentrations of unsaturated fatty acids could still be considerably reduced, particularly that of linoleic acid. In the same way, there was increasing esterification of myristic acid (14:0), and especially of lauric acid (12:0), which appeared preferentially in sn-1 and sn-3 positions in triglycerides. This esterification of medium-chain fatty acids led to a modification in the mode of other fatty acid distribution. Analysis of liver phospholipids showed that when diet A was replaced above 200 g by diet B, there was no biochemical evidence of any deficiency of essential fatty acids of the n-6 series.