N-3 polyunsaturated fatty acids impair lifespan but have no role for metabolism

Although generally considered as beneficial components of dietary fats, polyunsaturated fatty acids (PUFA) have been suspected to compromise maximum lifespan (MLSP) in mammals. Specifically, high amounts of phospholipid PUFAs are thought to impair lifespan due to an increase in the susceptibility of membranes to lipid peroxidation and its damaging effect on cellular molecules. Also, there is evidence from in vitro studies suggesting that highly unsaturated PUFAs elevate basal metabolic rate (BMR). Previous comparative studies in this context were based on small sample sizes, however, and, except for one study, failed to address possible confounding influences of body weight and taxonomic relations between species. Therefore, we determined phospholipid membrane composition in skeletal muscle from 42 mammalian species to test for a relation with published data on MLSP, and with literature data on BMR (30 species). Using statistical models that adjust for the effects of body weight and phylogeny, we found that among mammals, MLSP indeed decreases as the ratio of n-3 to n-6 PUFAs increases. In contrast to previous studies, we found, however, no relation between MLSP and either membrane unsaturation (i.e. PUFA content or number of double bonds) or to the very long-chain, highly unsaturated docosahexaenoic acid (DHA). Similarly, our data set gave no evidence for any notable relation between muscle phospholipid fatty acid composition and BMR, or MLSP and BMR in mammals. These results contradict the 'membrane pacemaker theory of aging', that is, the concept of a direct link between high amounts of membrane PUFAs, elevated BMR, and thus, impaired longevity.     

Arachidonic and docosahexaenoic acids reduce the growth of A549 human lung-tumor cells increasing lipid peroxidation and PPARs

Polyunsaturated fatty acids (PUFAs) play an important role in both induction and prevention of carcinogenic process. It is well known that several types of neoplastic cells show decreased total PUFA content, contributing to their resistance to chemotherapy and lipid peroxidation. In the light of this, human lung cancer A549 cells, with low PUFA content, were exposed to arachidonic or docosahexaenoic acid to investigate the effect of n-6 and n-3 PUFAs on growth and elucidate underlying mechanisms. The bulk of the results showed that both n-6 PUFAs and n-3 PUFAs decrease human lung-tumor cell growth in a concentration-dependent manner, inducing cell death mainly evident at 100microM concentration. The mechanism underlying the antiproliferative effect of n-6 and n-3 PUFAs appeared to be the same, involving changes in fatty acid composition of biomembranes, production of cytostatic aldehydes derived from lipid peroxidation and able to affect DNA-binding activity of AP-1, and induction of PPAR. From these results it may be hypothesized that n-6 PUFAs, like n-3 PUFAs, are able to inhibit tumor growth.     

Alteration of plasma phospholipid fatty acid profile in patients with septic shock

In septic shock patients, alterations of plasma phospholipid fatty acid profile have never been described. The purpose of this monocentric, non-interventional, observational prospective study was to describe this fatty acid profile in the early phase of septic shock in intensive care unit. Thirty-seven adult patients with septic shock were included after the first day of stay in intensive care unit, before any form of artificial nutritional support. Plasma phospholipid fatty acid composition was determined by gas chromatography. All biological data from patients with septic shock were compared with laboratory reference values. Patients presented hypocholesterolemia and hypertriglyceridemia. They had low concentrations of phospholipid fatty acids specifically n-6 and n-3 polyunsaturated fatty acids (PUFAs) with a high n-6/n-3 ratio. Plasma phospholipid PUFA concentrations were strongly correlated with cholesterolemia. PUFAs/SFAs (saturated fatty acids) and PUFAs/MUFAs (monounsaturated fatty acids) ratios were low because of low percentage of n-6 and n-3 PUFAs and high percentage of SFAs and MUFAs. Low levels of plasma long chain PUFAs (≥20 carbons) were significantly associated with mortality at 28th day. In conclusion, plasma phospholipid FA profile of septic patients is very characteristic, close to that of acute respiratory distress syndrome and mortality is associated with long chain PUFA decrease. This profile could be explained by numerous non-exclusive physio-pathological processes 1) an activation of hepatic de novo lipogenesis that could contribute to hepatic steatosis, 2) an elevated adipose tissue lipolysis, 3) an increased free radical attack of FA by oxidative stress, 4) an over-production of inflammatory lipid mediators.     

Fatty acid and peptide profiles in plasma membrane and membrane rafts of PUFA supplemented RAW264.7 macrophages

The eukaryotic cell membrane possesses numerous complex functions, which are essential for life. At this, the composition and the structure of the lipid bilayer are of particular importance. Polyunsaturated fatty acids may modulate the physical properties of biological membranes via alteration of membrane lipid composition affecting numerous physiological processes, e.g. in the immune system. In this systematic study we present fatty acid and peptide profiles of cell membrane and membrane rafts of murine macrophages that have been supplemented with saturated fatty acids as well as PUFAs from the n-3, the n-6 and the n-9 family. Using fatty acid composition analysis and mass spectrometry-based peptidome profiling we found that PUFAs from both the n-3 and the n-6 family have an impact on lipid and protein composition of plasma membrane and membrane rafts in a similar manner. In addition, we found a relation between the number of bis-allyl-methylene positions of the PUFA added and the unsaturation index of plasma membrane as well as membrane rafts of supplemented cells. With regard to the proposed significance of lipid microdomains for disease development and treatment our study will help to achieve a targeted dietary modulation of immune cell lipid bilayers.     

The opposing effects of n-3 and n-6 fatty acids

Polyunsaturated fatty acids (PUFAs) can be classified in n-3 fatty acids and n-6 fatty acids, and in westernized diet the predominant dietary PUFAs are n-6 fatty acids. Both types of fatty acids are precursors of signaling molecules with opposing effects, that modulate membrane microdomain composition, receptor signaling and gene expression. The predominant n-6 fatty acid is arachidonic acid, which is converted to prostaglandins, leukotrienes and other lipoxygenase or cyclooxygenase products. These products are important regulators of cellular functions with inflammatory, atherogenic and prothrombotic effects. Typical n-3 fatty acids are docosahexaenoic acid and eicosapentaenoic acid, which are competitive substrates for the enzymes and products of arachidonic acid metabolism. Docosahexaenoic acid- and eicosapentaenoic acid-derived eicosanoids antagonize the pro-inflammatory effects of n-6 fatty acids. n-3 and n-6 fatty acids are ligands/modulators for the nuclear receptors NFkappaB, PPAR and SREBP-1c, which control various genes of inflammatory signaling and lipid metabolism. n-3 Fatty acids down-regulate inflammatory genes and lipid synthesis, and stimulate fatty acid degradation. In addition, the n-3/n-6 PUFA content of cell and organelle membranes, as well as membrane microdomains strongly influences membrane function and numerous cellular processes such as cell death and survival.     

Increased n-3 polyunsaturated fatty acid content of red blood cells from fish oil-fed rabbits increases in vitro lipid peroxidation, but decreases hemolysis.

In view of a possible relationship between fish oil, lipid peroxidation, and atherosclerosis, the in vitro lipid peroxidation susceptibility of red blood cells (RBCs) from rabbits on conventional (-FO) and fish oil-enriched diets (+FO) was investigated. The diet caused substantial increases in the RBC concentrations of n-3 polyunsaturated fatty acids (PUFAs), in combination with decreases in the concentration of oleic acid (18:1) and linoleic acid (18:2). Cumene hydroperoxide-induced oxidative stress led to increased overall fatty acid peroxidation in +FO RBCs compared with with -FO RBCs, as quantitated by GLC fatty acid analysis. However, the increased overall susceptibility to lipid peroxidation of +FO RBCs was not reflected in increased peroxidation of every individual fatty acid. This was observed for endogenous arachidonic acid (20:4) as well as, in separate experiments, for exogenously added parinaric acid (PnA). The increased cumene hydroperoxide-induced PUFA oxidation in +FO RBCs was accompanied by a lesser extent of hemolysis. To account for these observations, it is proposed that the increased n-3 PUFA content of +FO RBCs serves as an oxidizable buffer. The present data suggest that oxidation of fatty acids can occur until a critically low level of intact phospholipid in the RBC membrane is reached, after which the membrane destabilizes and hemolysis occurs. At the same time, the PUFA buffer in +FO RBCs could also prevent oxidative damage to specific membrane proteins, which could also help prevent cell lysis.     

Alteration of polyunsaturated fatty acid status and metabolism in health and disease

Essential polyunsaturated fatty acids (PUFA) cannot be synthesised in the body and must be ingested by food. A balanced intake of both n-6 and n-3 PUFA is essential for good health. PUFA are the basic constituents of phospholipid membranes and determine cellular membrane fluidity and modulate enzyme activities, carriers and membrane receptors. They are also precursors of active metabolites known collectively as eicosanoids (prostaglandins, prostacyclins, thromboxanes and leukotrienes) which regulate our cellular functions. Studies indicate that n-3 PUFA have anti-inflammatory, antithrombotic, antiarrhythmic actions and immuno-modulating properties. Erythrocyte fatty acid status is a reflection of dietary fat intake. It also explores PUFA metabolism and gives information about the integration of these fatty acids into cellular membranes. Thus, erythrocyte fatty acid analysis can detect PUFA insufficiencies and imbalances from the diet, but also metabolic abnormalities and lipid peroxidation. It can be helpful in the prevention and the control of chronic diseases in which PUFA alterations have been observed as coronary heart diseases, hypertension, cancer, diabetes, inflammatory and auto-immune disorders, atopic eczema, Alzheimer dementia, major depression, schizophrenia, multiple sclerosis, etc.     

A tale of two lipids: Lipid unsaturation commands ferroptosis sensitivity

Membrane lipids play important roles in the regulation of cell fate, including the execution of ferroptosis. Ferroptosis is a non-apoptotic cell death mechanism defined by iron-dependent membrane lipid peroxidation. Phospholipids containing polyunsaturated fatty acids (PUFAs) are highly vulnerable to peroxidation and are essential for ferroptosis execution. By contrast, the incorporation of less oxidizable monounsaturated fatty acids (MUFAs) in membrane phospholipids protects cells from ferroptosis. The enzymes and pathways that govern PUFA and MUFA metabolism therefore play a critical role in determining cellular sensitivity to ferroptosis. Here, we review three lipid metabolic processes—fatty acid biosynthesis, ether lipid biosynthesis, and phospholipid remodeling—that can govern ferroptosis sensitivity by regulating the balance of PUFAs and MUFAs in membrane phospholipids.     

Dietary n-6 PUFA deprivation for 15 weeks reduces arachidonic acid concentrations while increasing n-3 PUFA concentrations in organs of post-weaning male rats

Few studies have examined effects of feeding animals a diet deficient in n-6 polyunsaturated fatty acids (PUFAs) but with an adequate amount of n-3 PUFAs. To do this, we fed post-weaning male rats a control n-6 and n-3 PUFA adequate diet and an n-6 deficient diet for 15 weeks, and measured stable lipid and fatty acid concentrations in different organs. The deficient diet contained nutritionally essential linoleic acid (LA,18:2n-6) as 2.3% of total fatty acids (10% of the recommended minimum LA requirement for rodents) but no arachidonic acid (AA, 20:4n-6), and an adequate amount (4.8% of total fatty acids) of α-linolenic acid (18:3n-3). The deficient compared with adequate diet did not significantly affect body weight, but decreased testis weight by 10%. AA concentration was decreased significantly in serum (− 86%), brain (− 27%), liver (− 68%), heart (− 39%), testis (− 25%), and epididymal adipose tissue (− 77%). Eicosapentaenoic (20:5n-3) and docosahexaenoic acid (22:6n-3) concentrations were increased in all but adipose tissue, and the total monounsaturated fatty acid concentration was increased in all organs. The concentration of 20:3n-9, a marker of LA deficiency, was increased by the deficient diet, and serum concentrations of triacylglycerol, total cholesterol and total phospholipid were reduced. In summary, 15 weeks of dietary n-6 PUFA deficiency with n-3 PUFA adequacy significantly reduced n-6 PUFA concentrations in different organs of male rats, while increasing n-3 PUFA and monounsaturated fatty acid concentrations. This rat model could be used to study metabolic, functional and behavioral effects of dietary n-6 PUFA deficiency.     

Myogenic differentiation and lipid-raft composition of L6 skeletal muscle cells are modulated by PUFAs

Lipid composition and fatty acid analysis of the major classes of membrane phospholipids were determined during myogenic differentiation of L6 skeletal muscle cells. The cholesterol to glycerophospholipids ratio decreased during differentiation, both in total (TM) and detergent-resistant membranes (DRM). Analyses of the membrane lipids showed that differentiation had a major impact on the molecular composition of glycerophospholipids. A significant decrease in the concentration of saturated fatty acids was detected in glycerophospholipid classes, and to a lesser extent in sphingolipids, while the concentration of 16:1n-7, 18:1n-7 and 18:1n-9 increased. At the same time, the concentration of long polyunsaturated fatty acid chains decreased in TM and DRM glycerophospholipids, resulting in a lower saturated to unsaturated fatty acid ratio in myotubes as compared to myoblasts. Interestingly, the observed n-3/n-6 ratio was lower in differentiated cell membranes. PUFA supplementation of L6 cells led to an increase in myogenic differentiation correlated to an incorporation of added PUFAs in TM and DRM glycerophospholipids. As expected after n-3 PUFA supplementation, the n-3/n-6 ratio was clearly increased in TM and, surprisingly, this was also the case in isolated DRM. n-3 and n-6 PUFAs significantly and time-dependently increased the phosphorylation of kinase p70S6K1 during myogenic differentiation, revealing the activation of the upstream kinase mTORC1, a major regulator of cell cycle and protein translation. In contrast, PUFAs did not affect the phosphorylation of the kinase Akt, another pivotal regulator of cell metabolism. These results suggest that PUFA supplementation modified the membrane lipid composition and affected the differentiation of L6 cells.     

Effect of docosahexaenoic acid and alpha-tocopherol enrichment in chicken sperm on semen quality, sperm lipid composition and susceptibility to peroxidation

The aim of the present experiment was to study the effect of fish oil and Vitamin E rich diets on semen production, sperm functions and composition in broiler breeders. The following parameters were measured: semen volume and concentration, sperm motility and viability, sperm susceptibility to induced peroxidation, sperm lipid and alpha-tocopherol contents. Dietary n-3 PUFA were successfully transferred into spermatozoan phospholipid by fish oil feeding according to the following main features: (a) the C22:6n-3 and C22:5n - 3 contents were increased, but C22:4n-6 remained the peculiar and major polyunsaturate; (b) the content and proportion of total PUFA did not change; (c) the proportional increase of n-3 PUFA was compensated by the decrease of n-6 PUFA, an increase in the proportion of n-9 fatty acids was also found. The sperm content of alpha-tocopherol was doubled increasing the dietary availability of the vitamin to 300 mg/kg of feed. The specific n-3 PUFA and Vitamin E enrichment of chicken sperm affected cell functions. Significant interactions between the two treatments were also found for some parameters. The best sperm quality condition in control sperm (rich mainly in n-6 PUFA) was found supplying 200mg Vitamin E/kg of feed to the male breeders, and in contrast in n-3 rich sperm supplying 300 mg Vitamin E/kg.     

Phospholipid fatty acid composition affects enzymatic antioxidant defenses in cultured Swiss 3T3 fibroblasts

Summary

The aim of this work was to study the adaptation of enzymatic antioxidant cell defense to the nature of the membrane polyunsaturated fatty acids (PUFA). 3T3 Swiss fibroblasts were grown for 5 days in a medium supplemented with 50 μM linoleic acid (LA) or eicosapentaenoic acid (EPA) and compared t control cells (C). The phospholipid fatty acid content was evaluated: LA were enriched in n-6 PUFA (27.8%) in comparison to C (6.7%) or EPA (5.6%); EPA were enriched in n-3 PUFA (26.2%) in comparison to LA (4.4%) or C (4.6%). The fatty acid double bond index (DBI) increased from C to LA and EPA. The activities of the three key enzymatic antioxidant defenses, SOD, GPx and GST, increased with the degree of unsaturation of the phospholipid fatty acids. In the cells with fatty acids that are very sensitive to oxidative stress, the higher activities of SOD and GPx might act to limit the initiation of lipid peroxidation and the higher activities of GST and GPx to decrease the toxic effects of the various species produced from lipid degradation.     

Membrane Basis for Fish Oil Effects on the Heart: Linking Natural Hibernators to Prevention of Human Sudden Cardiac Death

The concept that diet-induced changes in membrane lipids could modify heart function partly arose from observations that membrane composition and physical properties were closely associated with the capacity of the heart to respond appropriately to torpor and hibernation. Observations of natural hibernators further revealed that behavior of key membrane-bound enzymes could be influenced through the lipid composition of the cell membrane, either by changing the surrounding fatty acids through reconstitution into a foreign lipid milieu of different composition, or by alteration through diet. Myocardial responsiveness to beta-adrenoceptor stimulation, including initiation of spontaneous dysrhythmic contractions, was altered by both hibernation and dietary modulation of membrane fatty acids, suggesting modified vulnerability to cardiac arrhythmia. Subsequent studies using whole-animal models recognized that vulnerability to ventricular fibrillation decreased as the polyunsaturated: saturated fat (P:S) ratio of the diet increased. However, dietary fish oils, which typically contain at least 30% saturated fatty acids and only 30% long-chain n-3 (omega-3) polyunsaturated fatty acids (PUFA), exhibit antiarrhythmic effects that exceed the predicted influence of the P:S ratio, suggesting properties unique to the long-chain n-3 PUFA. Large-scale clinical trials and epidemiology have confirmed the arrhythmia prevention observed in vitro in myocytes, papillary muscles, and isolated hearts and in whole-animal models of sudden cardiac death. Some progress has been made towards a biologically plausible mechanism. These developments highlight nature’s ability to provide guidance for the most unexpected applications.     

Effects of polyunsaturated fatty acids on hibernation and torpor: a review and hypothesis

Polyunsaturated fatty acids (PUFAs) can have strong effects on hibernation and daily torpor in mammals. High dietary PUFA contents were found to increase proneness for torpor, decrease body temperatures, prolong torpor bout duration, and attenuate hibernation mass loss. The mechanism by which PUFAs enhance torpor and hibernation is unknown, however. On the basis of a review of the literature, and on reexamining our own data on alpine marmots, we propose that effects on hibernation are not due to PUFAs in general, but to shifts in the ratio of n-6 PUFAs to n-3 PUFAs in membrane phospholipids. Specifically, high ratios of n-6 to n-3 PUFAs increase the activity of the Ca2+-Mg2+ pump in the sarcoplasmic reticulum of the heart (SERCA) and counteract Q10 effects on SERCA activity at low tissue temperatures. Therefore, high n-6 to n-3 PUFA ratios in cardiac myocyte membranes appear to protect the hibernating heart from arrhythmia, which in hypothermic nonhibernators is caused by massive increases in cytosolic Ca2+. The resulting reduced risk of cardiac arrest during hypothermia may explain why increased dietary uptake of n-6 PUFAs, but not of n-3 PUFAs, can strongly enhance the propensity for hibernation, and allows heterotherms to reach lower body temperatures, with associated increased energy savings. Therefore, at least for herbivorous hibernators, such as marmots, linoleic acid (C18:2 n-6)--the dietary source of all n-6 PUFAs--appears to represent a crucial and limited resource in natural environments.     

Lipid and fatty acid composition of canine lipoproteins

Lipid classes and their fatty acids were studied in the major lipoprotein fractions from canine, in comparison with human, plasma. In dogs, high-density-lipoprotein (HDL), the main carrier of plasma phospholipid (PL), cholesterol ester (CE) and free cholesterol, was the most abundant lipoprotein, followed by low and very-low density lipoproteins (LDL and VLDL). Notably, LDL and VLDL contributed similarly to the total dog plasma triacylglycerol (TG). The PL composition was similar in all three lipoproteins, dominated by phosphatidylcholine (PC). Even though the content and composition of lipids within and among lipoproteins differed markedly between dog and man, the total amount of circulating lipid was similar. All canine lipoproteins were relatively richer than those from humans in long-chain (C20-C22) n-6 and n-3 polyunsaturated fatty acids (PUFA) but had comparable proportions of total saturated and monoenoic fatty acids, with 18:2n-6 being the main PUFA in both mammals. The fatty acid profile of canine and human lipoproteins differed because they had distinct proportions of their major lipids. There were more n-3 and n-6 long-chain PUFA in canine than in human plasma, because dogs had more HDL, their HDL had more PC and CE, and both these lipids were richer in such PUFA.     

Eicosapentaenoic acid membrane incorporation impairs ABCA1-dependent cholesterol efflux via a protein kinase A signaling pathway in primary human macrophages

A diet rich in n-3/n-6 polyunsaturated fatty acids (PUFAs) is cardioprotective. Dietary PUFAs affect the cellular phospholipids composition, which may influence the function of membrane proteins. We investigated the impact of the membrane incorporation of several PUFAs on ABCA1-mediated cholesterol efflux, a key antiatherogenic pathway. Arachidonic acid (AA) (C20:4 n-6) and docosahexaenoic acid (DHA) (C22:6 n-3) decreased or increased cholesterol efflux from J774 mouse macrophages, respectively, whereas they had no effect on efflux from human monocyte-derived macrophages (HMDM). Importantly, eicosapentaenoic acid (EPA) (C20:5 n-3) induced a dose-dependent reduction of ABCA1 functionality in both cellular models (− 28% for 70 μM of EPA in HMDM), without any alterations in ABCA1 expression. These results show that PUFA membrane incorporation does not have the same consequences on cholesterol efflux from mouse and human macrophages. The EPA-treated HMDM exhibited strong phospholipid composition changes, with high levels of both EPA and its elongation product docosapentaenoic acid (DPA) (C22:5 n-3), which is associated with a decreased level of AA. In HMDM, EPA reduced the ATPase activity of the membrane transporter. Moreover, the activation of adenylate cyclase by forskolin and the inhibition of cAMP phosphodiesterase by isobutylmethylxanthine restored ABCA1 cholesterol efflux in EPA-treated human macrophages. In conclusion, EPA membrane incorporation reduces ABCA1 functionality in mouse macrophages as well as in primary human macrophages and this effect seems to be PKA-dependent in human macrophages.     

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.     

Long-chain polyunsaturated fatty acids in breast milk in La Plata, Argentina: relationship with maternal nutritional status

Milk fat is the major source of energy for breastfed infants; it also supplies polyunsaturated fatty acids (PUFAs) essential for the development of brain, retina, and other organs. Maternal nutritional status is critical for the newborn, and little information exists regarding the PUFA status of vulnerable populations living in Southern regions. We studied the relationship between maternal nourishment and milk fatty acid composition. Mother nutritional status (normal, overweight or obese) was estimated on the body mass index. Milk protein, total lipid, and fatty acid composition were determined. Milk protein was not affected by mother's nutritional status. In obese mothers an increase in lipid content, linoleic acid, total n-6 and total PUFAs was observed comparing to the other groups. Disregarding the nutritional status, the ratio n-6/n-3 fatty acids was very high and the 22:6n-3 content was very low, when compared with those of mothers from other countries. This finding led us to urge Public Health officers to promote changes in the dietary habits of nursing women.     

Dietary long-chain fatty acids and visual response in malnourished nursing infants

Polyunsaturated fatty acids (PUFAs) derived from essential fatty acids (EFAs) play an important role in prenatal visual and neural development. Protein-energy malnutrition affects PUFA supply, and hence the synthesis of structural lipids during growth. Recently, some physiological studies reported abnormalities in the visual function of formula-fed infants relative to breast-fed infants. The purpose of our study was to assess whether fatty acid composition of the malnourished infant diet modifies the visual function and erythrocyte phospholipid fatty acid composition. Three groups of full-term malnourished infants were selected. Two groups received commercial formulas. One of them supplied linoleic and alpha -linolenic acid: Formula I (FI), and the other supplied, in addition, long-chain PUFAs from n-3 and n-6 series: Formula II (FII). A reference group of breast-fed infants was also enrolled. Visual function was assessed using full-field flash electroretinography, and the erythrocyte phospholipid fatty acid composition was determined by gas-liquid chromatography. Those infants receiving the supplemented formula (FII) exhibited a similar retinal function to that of breast-fed infants. However, normal results were not achieved when infants were fed on the FI formula. In all groups, the results were correlated with the proportion of docosahexaenoic acid in erythrocyte phospholipid fatty acid composition. We conclude that in malnourished infants a nutrient formula enriched with long-chain fatty acids of n-6 and n-3 series could be helpful to achieve an erythrocyte fatty acid pattern and a visual function similar to that obtained in breast-fed infants.     

Incorporation of 14C-labelled polyunsaturated fatty acids by juvenile turbot, Scophthalmus maximus (L.) in vivo

The ability of juvenile turbot, Scophthalmus maximus (L.), to elongate and desaturate various polyunsaturated fatty acids (PUFA) was examined in relation to their lipid composition. Triacylglycerols were the most abundant lipid class present in the fish and phosphatidylcholine was the predominant phospholipid. In all lipid classes examined the levels of (n-3) PUFA exceeded that of (n-6) PUFA. 18C PUFA were minor components in comparison with 20:5(n-3) and 22:6(n-3). 20:4(n-6) was present in highest concentration in phosphatidylinositol in which it accounted for 16.9% of the fatty acids. When the fish were injected with either ¹⁴C-labelled 18:2(n-6), 18:3(n-3), 20:4(n-6), 20:5(n-3) or 22:6(n-3) the highest percentage recovery of radioactivity (69%) in body lipid was observed with 22:6(n-3). With all labelled substrates free fatty acids contained only a small proportion of the total recovered radioactivity whereas triacylglycerols were highly labelled. Phosphatidylcholine/sphingomyelin was the most highly labelled polar lipid fraction. With ¹⁴C-20:4(n-6) as injected substrate, 23.2% of the radioactivity recovered in total lipid was present in phosphatidylinositol in comparison with less than 6% with the other substrates. Only small proportions of radioactivity from ¹⁴C-18:2(n-6) and ¹⁴C-18:3(n-3) were recovered in the 20 and 22C fatty acids of triacylglycerols and total polar lipid. With ¹⁴C-20:5(n-3) as substrate, 27 and 33% of the total radioactivity recovered in the fatty acids of triacylglycerols and polar lipids respectively was present in 22C fatty acids. The corresponding values for ^l4C-20:4(n-6) as substrate were 19 and 18%. The results confirm the limited capacity of turbot to convert 18C PUFA to longer chain PUFA but demonstrate their ability to synthesize 22C PUFA from 20C PUFA. They also suggest a small but specific requirement for 20:4(n-6).