Lipids with an emphasis on long-chain polyunsaturated fatty acids

Advances in the nutrition of preterm infants

The greatly improved survival rate of infants born both preterm and low birth weight (LBW) has led to the subsequent growth and development of these infants becoming an important focus for research. Preterm infants begin life with, or acquire as a result of their prematurity, greater morbidity than term born babies, growth deficits, an increased risk of developmental delay and an increased risk of later adult diseases compared with appropriate for gestational age (AGA) term born babies.

Research in recent decades has confirmed that there are marked differences in the nutritional requirements of preterm LBW infants compared with their AGA term born counterparts, both in the neonatal period and probably for all of infancy. In addition to the increased requirement for energy and protein, preterm LBW infants demonstrate a greatly increased requirement for some of the mineral elements, particularly iron, zinc and calcium, when compared with the needs of term AGA infants. In the UK, feeding practices for preterm infants in neonatal units and throughout infancy after hospital discharge are variable and many questions remain as to the optimal nutritional regimen for preterm LBW infants (and for subgroups of these infants) at different stages of infancy. There is some concern that the 2002 World Health Organization recommendations on infant feeding may be applied to all infants, including preterm infants, without consideration of their special nutritional needs, which may further compromise their growth and development.

A brief résumé of the work of prominent researchers in the field of preterm infant nutrition in the UK, notably Lucas, Cooke and Fewtrell, is included in the review, together with information from papers published by the authors of the review. The review concludes with a summary of the generally accepted recommendations on feeding preterm LBW infants after hospital discharge and information on some practical help available to the parents of these children and to health workers in the field.

Systematic review of fatty acid composition of human milk from mothers of preterm compared to full-term infants

BACKGROUND

Fatty acid composition of human milk serves as guidance for the composition of infant formulae. The aim of the study was to systematically review data on the fatty acid composition of human milk of mothers of preterm compared to full-term infants.

METHODS

An electronic literature search was performed in English (Medline and Medscape) and German (SpringerLink) databases and via the Google utility. Fatty acid compositional data for preterm and full-term human milk were converted to differences between means and 95% confidence intervals.

RESULTS

We identified five relevant studies publishing direct comparison of fatty acid composition of preterm versus full-term human milk. There were no significant differences between the values of the principal saturated and monounsaturated fatty acids. In three independent studies covering three different time points of lactation, however, docosahexaenoic acid (DHA) values were significantly higher in milk of mothers of preterm as compared to those of full-term infants, with an extent of difference considered nutritionally relevant.

CONCLUSION

Higher DHA values in preterm than in full-term human milk underlines the importance of using own mother's milk for feeding preterm babies and raises the question whether DHA contents in preterm formulae should be higher than in formulae for full-term infants.

Has an aquatic diet been necessary for hominin brain evolution and functional development?

A number of authors have argued that only an aquatic-based diet can provide the necessary quantity of DHA to support the human brain, and that a switch to such a diet early in hominin evolution was critical to human brain evolution. This paper identifies the premises behind this hypothesis and critiques them on the basis of clinical literature. Both tissue levels and certain functions of the developing infant brain are sensitive to extreme variations in the supply of DHA in artificial feeding, and it can be shown that levels in human milk reflect maternal diet. However, both the maternal and infant bodies have mechanisms to store and buffer the supply of DHA, so that functional deficits are generally resolved without compensatory diets. There is no evidence that human diets based on terrestrial food chains with traditional nursing practices fail to provide adequate levels of DHA or other n-3 fatty acids. Consequently, the hypothesis that DHA has been a limiting resource in human brain evolution must be considered to be unsupported.

Docosahexaenoic acid, fatty acid-interacting proteins, and neuronal function: breastmilk and fish are good for you

In contrast to other tissues, the nervous system is enriched in the polyunsaturated fatty acids (PUFAs): arachidonic acid (AA, 20:4 n-6) and docosahexaenoic acid (DHA, 22:6 n-3). Despite their abundance in the nervous system, AA and DHA cannot be synthesized de novo by mammals; they, or their precursors, must be ingested from dietary sources and transported to the brain. During late gestation and the early postnatal period, neurodevelopment is exceptionally rapid, and substantial amounts of PUFAs, especially DHA, are critical to ensure neurite outgrowth as well as proper brain and retina development. Here, we review the various functions of DHA in the nervous system, the proteins involved in its internalization and metabolism into phospholipids, and its relationship to several neurological disorders, including Alzheimer's disease and depression.

Fatty acids in early human milk after preterm and full-term delivery

BACKGROUND

It has been much debated whether fatty acid composition of human milk differs after preterm as compared to full-term delivery.

SUBJECTS AND METHODS

Human milk samples were obtained from mothers of preterm (n = 8, gestational age: 28.0 [4.2] weeks, birthweight: 1,235 [420] g, median [interquartile range]) and full-term (n = 10, gestational age: 38.5 [2.7] weeks, birthweight: 3375 [282] g) infants every day during the first week and thereafter on the 14th, 21st, and 28th day of lactation. Fatty acid composition was measured by high-resolution capillary gas-liquid chromatography.

RESULTS

Maternal age and body mass index did not differ, and food frequency questionnaire did not reveal significant differences in diet between the two groups. Fat contents of human milk did not differ between the two groups. Values of linoleic acid (C18:2n-6) and alpha-linolenic acid (C18:3n-3) did not differ throughout the study. Values of the metabolites C18:3n-6 and C20:3n-6 as well as C18:4n-3 and C20:3n-3 were significantly higher after preterm as compared with full-term delivery. Values of arachidonic acid (C20:4n-6; e.g., day 4: 0.82 [0.4] vs. 0.44 [0.28]; day 7: 0.61 [0.25] vs. 0.34 [0.25]; day 21: 0.33 [0.18] vs. 0.44 [0.44]; in weight percent, preterm versus full-term, P < 0.05) and docosahexaenoic acid (C22:6n-3; e.g., day 4: 0.33 [0.23] vs. 0.15 [0.14]; day 7: 0.26 [0.16] vs. 0.13 [0.15]; day 21: 0.11 [0.08] vs. 0.21 [0.17]; P < 0.05) were significantly higher in human milk samples of mothers of preterm as compared with full-term infants.

CONCLUSION

In this study, percentage contributions of arachidonic and docosahexaenoic acids as well as the those of the intermediary metabolites of essential fatty acid metabolism were all significantly higher in early human milk samples of mothers giving birth to very low birth weight preterm as compared with full-term infants.

Early introduction of lipids to parenterally-fed preterm infants

BACKGROUND

Lipids are essential components of parenteral nutrition for preterm infants. Parenteral lipids can be administered through a peripheral vein, and their early introduction offers the potential advantages of increasing energy intake and providing essential fatty acids and fat soluble vitamins. Concerns have been raised about potential adverse effects including chronic lung disease (CLD), increase in pulmonary vascular resistance, impaired pulmonary gas diffusion, bilirubin toxicity, sepsis and free radical stress.

OBJECTIVES

To determine the safety and efficacy of 'early' (</= 5 days after birth) introduction of lipids to parenterally fed preterm infants.

SEARCH STRATEGY

Eligible studies were identified by searching MEDLINE (December 2004), EMBASE 1980 - 2004, Oxford Database of Perinatal Trials, Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 4, 2004) and CINAHL (December 1982 - December 2004). Abstracts of the Society for Pediatric Research were hand searched from 1980 to 2004 inclusive. No language restrictions were applied.

SELECTION CRITERIA

All randomised or quasi randomised controlled trials comparing 'early' versus 'no early' introduction of lipids to preterm infants.

DATA COLLECTION AND ANALYSIS

Data were sought regarding effects on growth and risk of CLD or death, other respiratory morbidities including duration of respiratory support, duration of supplemental oxygen, the need for home oxygen, pneumothorax (PTX), pulmonary haemorrhage and pulmonary interstitial emphysema (PIE), >/= stage 2 necrotizing enterocolitis (NEC), retinopathy of prematurity (ROP), patent ductus arteriosus (PDA), sepsis, intraventricular haemorrhage (IVH), clinically significant thrombocytopenia and significant jaundice. Methodological quality of eligible studies was assessed according to allocation concealment, blinding of intervention, blinding of outcome assessment and completeness of follow up. When appropriate, meta-analysis was conducted to provide a pooled estimate of effect. For categorical data the Typical relative risk (RR), Typical risk difference (RD) and number needed to treat (NNT) with 95% confidence intervals (CI) were calculated. Continuous data were analysed using weighted mean difference (WMD).

MAIN RESULTS

Five studies (n = 397) were included in the review. All studies compared the effectiveness and safety of 'early' introduction versus 'no early' introduction of lipids in preterm infants. The timing of introduction of 'early lipids' ranged from < 12 hours after birth to day five of life. The timing of introduction of lipids in the 'no early' lipid group ranged from day six after birth to day 14 after birth. The initial dose ranged from 0.5 - 1 g/kg/day with gradual daily increments up to a maximum of 2.5 - 3.5 g/kg/day. For the primary outcomes (growth, death and CLD), there was no statistically significant difference between the 'early' lipid and 'no early' lipid groups. Days to regain birth weight: [WMD 0.59 (95% CI -2.41, 3.58); two trials; N = 71]. Rate of weight gain (g/day) during period of hospital stay: [MD -2.40 (95% CI -5.30, 0.50); one trial; N = 129]Death (irrespective of time): [Typical RR 1.04 (95% CI 0.69, 1.56); Typical RD 0.01 (95% CI -0.07, 0.08); five trials; N = 397]Neonatal deaths: [Typical RR 1.35 (95% CI 0.78, 2.34); Typical RD 0.05 (95% CI -0.04, 0.13); four trials; N = 268].CLD: [Typical RR 1.10 (95% CI 0.81, 1.49); Typical RD 0.04 (95% CI -0.09, 0.17); two trials; N = 193]. For the secondary outcomes of other respiratory morbidities including duration of respiratory support, duration of supplemental oxygen, PTX, pulmonary haemorrhage, PIE, NEC, ROP, PDA, sepsis, IVH and significant jaundice, there were no statistically significant differences between 'early' and 'no early' lipid groups.

AUTHORS' CONCLUSIONS

No statistically significant effects of 'early introduction' of lipids on short term nutritional or other clinical outcomes, either benefits or adverse effects, were demonstrated in the studies reviewed. Based on the currently available evidence, 'early' initiation of lipids (</= 5 days after birth) can not be recommended for short term growth or to prevent morbidity and mortality in preterm infants.

Long-chain Acyl-CoA Synthetase 6 Preferentially Promotes DHA Metabolism

Previously we demonstrated that supplementation with the polyunsaturated fatty acids (PUFA) arachidonic acid (AA) or docosahexaenoic acid (DHA) increased neurite outgrowth of PC12 cells during differentiation, and that overexpression of rat acyl-CoA synthetase long-chain family member 6 (Acsl6, formerly ACS2) further increased PUFA-enhanced neurite outgrowth. However, whether Acsl6 overexpression enhanced the amount of PUFA accumulated in the cells or altered the partitioning of any fatty acids into phospholipids (PLs) or triacylglycerides (TAGs) was unknown. Here we show that Acsl6 overexpression specifically promotes DHA internalization, activation to DHA-CoA, and accumulation in differentiating PC12 cells. In contrast, oleic acid (OA) and AA internalization and activation to OA-CoA and AA-CoA were increased only marginally by Acsl6 overexpression. Additionally, the level of total cellular PLs was increased in Acsl6 overexpressing cells when the medium was supplemented with AA and DHA, but not with OA. Acsl6 overexpression increased the incorporation of [(14)C]-labeled OA, AA, or DHA into PLs and TAGs. These results do not support a role for Acsl6 in the specific targeting of fatty acids into PLs or TAGs. Rather, our data support the hypothesis that Acsl6 functions primarily in DHA metabolism, and that its overexpression increases DHA and AA internalization primarily during the first 24 h of neuronal differentiation to stimulate PL synthesis and enhance neurite outgrowth.

Dexamethasone treatment in the newborn rat: fatty acid profiling of lung, brain, and serum lipids

Dexamethasone is used as treatment for a variety of neonatal syndromes, including respiratory distress. The present study utilized the power of comprehensive lipid profiling to characterize changes in lipid metabolism in the neonatal lung and brain associated with dexamethasone treatment and also determined the interaction of dexamethasone with hypoxia. A 4-day tapering-dose regimen of dexamethasone was administered at 0800 on postnatal days 3 (0.5 mg/kg), 4 (0.25 mg/kg), 5 (0.125 mg/kg), and 6 (0.05 mg/kg). A subgroup of rats was exposed to hypoxia from birth to 7 days of age. Dexamethasone treatment elicited numerous specific changes in the lipid profile of the normoxic lung, such as increased concentrations of saturated fatty acids in the phosphatidylcholine and cholesterol ester classes. These increases were more profound in the lungs of hypoxic pups. Additional increases in cardiolipin concentrations were also measured in lungs of hypoxic pups treated with dexamethasone. We measured widespread increases in serum lipids after dexamethasone treatment, but the effects were not equivalent between normoxic and hypoxic pups. Dexamethasone treatment in hypoxic pups increased 20:4n6 and 22:6n3 concentrations in the free fatty acid class of the brain. Our results suggest that dexamethasone treatment in neonates elicits specific changes in lung lipid metabolism associated with surfactant production, independent of changes in serum lipids. These findings illustrate the benefits of dexamethasone on lung function but also raise the potential for negative effects due to hyperlipidemia and subtle changes in brain lipid metabolism.

Polyunsaturated fatty acids and gene expression

PURPOSE OF REVIEW

This review focuses on the effect(s) of n-3 polyunsaturated fatty acids on gene transcription as determined by data generated using cDNA microarrays. Introduced within the past decade, this methodology allows detection of the expression of thousands of genes simultaneously and, hence, is a potentially powerful tool for studying the regulation of physiological mechanisms that are triggered or inhibited by nutrients.

RECENT FINDINGS

Recent data generated with cDNA microarrays not only confirm the effects of n-3 polyunsaturated fatty acids on regulation of lipolytic and lipogenic gene expression as determined by more traditional methods but also emphasize the tissue specificity of this regulation. cDNA microarray experiments also have expanded our understanding of the role of n-3 polyunsaturated fatty acids in regulation of expression of genes involved in many other pathways. These include: oxidative stress response and antioxidant capacity; cell proliferation; cell growth and apoptosis; cell signaling and cell transduction.

SUMMARY

The cDNA microarray studies published to date show clearly that n-3 polyunsaturated fatty acids, usually provided as fish oil, modulate expression of a number of genes with such broad functions as DNA binding, transcriptional regulation, transport, cell adhesion, cell proliferation, and membrane localization. These effects, in turn, may significantly modify cell function, development and/or maturation.

New perspectives on nutrition enhance outcomes for premature infants

Significant advances have occurred during the past 20 years in the understanding of the complex relationships of the environment, the developing gut-associated immune system, the bacterial flora, the barrier functions of the gut, and the effects of nutrient intake. These advances have produced a profoundly different way of interpreting the nutritional requirements for normal growth and development of premature infants throughout their entire life.