Effects of essential fatty acid contents of lipid emulsions on erythrocyte polyunsaturated fatty acid composition in patients on long-term parenteral nutrition

The effects of different parenteral nutrition lipid formulations on clinical and laboratory endpoints in patients receiving home parenteral nutrition: A systematic review

BACKGROUND

Home parenteral nutrition (HPN) is a life-sustaining therapy for individuals with intestinal failure in a community setting. It refers to the intravenous infusion of macronutrients, micronutrients, fluids and electrolytes. Routinely used HPN solutions contain different quantities of these components. Consequently, each HPN solution may have different impacts on metabolism, inflammation and oxidative stress. Long-term use of HPN can lead to a number of adverse health outcomes including the development of metabolic bone disease, intestinal failure associated liver disease and poor quality of life but whether, and how, the composition of HPN solutions contributes to these health sequelae is poorly understood. The aim of this study is to systematically review and evaluate the evidence for the differential effects of HPN solutions and to understand what features are associated with differences in clinical endpoints.

METHODS

A systematic literature search was conducted between September and December 2020, and updated in July 2021 using the MEDLINE (Ovid), EMBASE, Scopus, and Web of Science databases. Studies were selected according to the following criteria (a) adult participants (>18 years old) dependent on HPN; (b) randomised controlled trials, prospective cohort and cross-sectional study designs; (c) primary research comparing two or more HPN solutions and (d) published in English language. Data were extracted and study quality assessed using Cochrane Collaboration's tools: Risk of Bias for Randomised Controlled Trials (RCTs); Risk of Bias in Non-Randomised Studies of Interventions; and the Newcastle Ottawa Scale for cross-sectional studies.

RESULTS

Of the 5148 articles identified, seven RCTs, two prospective cohort and one cross-sectional study were included with a total of 295 participants. Studies varied in terms of duration (one to 60 months) and sample size (n = 5 to 88). Ten studies compared lipid emulsions (LE) and one study also compared LE with lipid-free HPN. No studies were found that compared the amino acid, vitamin, trace element or electrolyte components of HPN. In general, LE were well tolerated with no significant adverse effects. LE containing olive +/or fish oil were associated with a lower ω-6:ω-3 fatty acid ratio, positive reductions in markers of liver function, and changes in blood and cell fatty acid profiles.

CONCLUSIONS

Despite the increasing use of HPN, there is surprisingly little evidence available to guide the provision of macro and micronutrients in the adult population requiring this therapy. Although LE containing olive +/or fish oil show promise with regards to liver function and blood and cell fatty acid profiles, further studies are needed before drawing definitive conclusions on the clinical value of these emulsions. It is likely that one type of HPN solution alone cannot be uniformly applied to patient care, and each patient should be assessed on an individual basis.

Influence of different intravenous lipid emulsions on fatty acid status and laboratory and clinical outcomes in adult patients receiving home parenteral nutrition: A systematic review

BACKGROUND & AIMS

Patients who have chronic intestinal failure require home parenteral nutrition (HPN) support. Intravenous lipid emulsions (IVLEs) are a vital part of HPN. The conventional IVLE is based on pure soybean oil, which contains a high concentration of omega-6 fatty acids. Alternative IVLEs are commercially available. These contain various oil blends and have different fatty acid compositions from soybean oil that could provide benefit to patients on HPN. The aim of this systematic review is to assess the effects of different IVLEs in adult patients requiring HPN.

METHODS

A systematic literature search was conducted up to October 2019 using relevant search terms in the Medline, EMBASE and CINAHL databases. Only randomised controlled trials (RCTs) in adults on HPN that compared two or more IVLEs were included. Data were extracted and the Cochrane Collaboration's tool for assessing risk of bias was used.

RESULTS

Six articles were identified for inclusion in this systematic review. Studies differed according to sample size, duration and the IVLEs compared. Four studies found no increased risk of adverse effects related to the different IVLEs, whilst one study found a higher frequency of serious adverse events with soybean oil. One study found higher serum α-tocopherol with the blend of soybean oil, medium chain triglycerides, olive oil and fish oil. Inflammatory markers were not affected by different IVLEs in three studies. Differences in liver function tests were minimal, but one study found slight abnormalities in patients receiving soybean oil. IVLEs containing olive oil or fish oil modified the blood fatty acid profile. No studies reported essential fatty acid deficiency.

CONCLUSIONS

There may be benefits of using alternative IVLEs to soybean oil-based emulsions in adults requiring HPN, although there is currently insufficient evidence to determine superiority of one formulation over another. More and larger RCTs are required in this area.

Incorporation and washout of n-3 PUFA after high dose intravenous and oral supplementation in healthy volunteers

BACKGROUND & AIMS

Although the physiological effects of n-3 polyunsaturated fatty acids (n-3PUFA) are generally thought to require several weeks of exposure to allow their incorporation into plasma membranes, intravenous (IV) n-3PUFA attenuate the cardiovascular and neuroendocrine response to stress within 3 h. Whether oral n-3 PUFA exert similar early effects remains unknown.

OBJECTIVE

To assess whether acute IV or short term oral n-3PUFA administration reproduces the metabolic effects of long term oral supplements during exercise, and how it relates to their incorporation into platelets and red blood cells (RBC) membranes.

DESIGN

Prospective single center open label study in 8 healthy subjects receiving a 3-h infusion of 0.6 g/kg body weight n-3PUFA emulsion, followed one week later by an oral administration of 0.6 g/kg over 3 consecutive days. Maximal power output (cycling exercise), maximal heart rate (HR), blood lactate at exhaustion, and platelet function were measured at baseline and after IV or 3-day oral supplementation; platelet and RBC membrane composition were assessed until 15 days after n-3PUFA administration.

RESULTS

Both IV and oral n-3PUFA significantly decreased maximal HR (-6% and -5%), maximal power output (-10%) and peak blood lactate (-47% and -52%) Platelet function tests were unchanged. The EPA and DHA membrane contents of RBC and platelets increased significantly, but only to 1.7-1.9% of fatty acid content.

CONCLUSION

The cardiovascular and metabolic effects of n-3 PUFA during exercise occur already within 1-3 days of exposure, and may be unrelated to changes in membranes composition. Effects occur within hours of administration and are unrelated to lipid membrane composition. Trial registered at clinicaltrials.gov as NCT00516178.

Rapid cellular enrichment of eicosapentaenoate after a single intravenous injection of a novel medium-chain triacylglycerol:fish-oil emulsion in humans

BACKGROUND

Dietary deficiency in n-3 (omega-3) polyunsaturated fatty acids (PUFAs) prevails in Western populations and potentially results in adverse health outcomes. To circumvent the slow n-3 PUFA incorporation in phospholipids of key cells after oral supplementation, a new preparation for intravenous bolus injection was developed with 20 g triacylglycerols/100 mL of a mixture of 80% medium-chain triacylglycerols (MCTs) and 20% fish oil (FO) (wt:wt), and 0.4 g alpha-tocopherol/100 mL of the same mixture.

OBJECTIVE

Our objective was to document the enrichment of n-3 PUFAs in leukocyte and platelet phospholipids after a bolus intravenous injection of MCT:FO in men.

DESIGN

Twelve healthy male subjects received injections over a 5-min period of 50 mL of either MCT:FO or a control MCT:long-chain triacylglycerol (MCT:LCT) emulsion containing 20 g triacylglycerols/100 mL with equal amounts (wt:wt) of MCT and soybean triacylglycerols (LCT) and containing 0.02 g alpha-tocopherol/100 mL; after an 8-wk interval, the subjects received injections of the other preparation.

RESULTS

Clinical and biological variables that assessed tolerance and safety remained unchanged. Plasma elimination was faster for MCT:FO than for MCT:LCT (half-life: 24.5 +/- 3.5 min compared with 32.9 +/- 3.0 min; P < 0.025). This was associated with a greater increase in the plasma nonesterified fatty acid concentration. The content of n-3 PUFAs, specifically eicosapentaenoic acid (20:5n-3), increased in leukocyte and platelet phospholipids within 60 min and > or =24 h after MCT:FO injection.

CONCLUSION

Bolus intravenous injection of a novel MCT:FO emulsion allows rapid enrichment of cells with n-3 PUFAs.

Fatty acid pattern of pancreatic islet lipids in Goto-Kakizaki rats

Perturbations of fatty acid content and pattern were recently documented in epididymal and parametrial lipids, as well as plasma, liver, spleen, and brain phospholipids and triglycerides of Goto-Kakizaki rats (GK). This study extends such an investigation to pancreatic islets from both control and GK rats. Groups of 5,500-14,560 islets were obtained from either control or GK rats (n = 3 in each case) and examined for their lipid fatty acid content. In the islet triglycerides, the major difference between control and GK rats, i.e., a higher C18:2ω6 content in GK rats, was similar to that found in liver triglycerides. In the islet phospholipids, however, a number of differences between control and GK rats, concerning saturated, monodesaturated, and long-chain polyunsaturated ω3 and ω6 fatty acids, were often not similar to those found in liver phospholipids. The present study reveals a number of anomalies in the fatty acid pattern of islet phospholipids in GK rats, often differing from those encountered in liver phospholipids. Such a tissue specificity was borne out by the finding that, even in control animals, the situation found in islet phospholipids differed from that recorded in liver phospholipids.

Direct effects of eicosapentaenoic and docosahexaenoic acids on phospholipid and triglyceride fatty acid pattern, glucose metabolism, 86rubidium net uptake and insulin release in BRIN-BD11 cells

The long-term metabolic and functional effects of a dietary deprivation of long-chain polyunsaturated omega3 fatty acids were recently investigated in second-generation omega3-depleted rats. This study represents the first attempt to explore the direct, but not immediate, effects of omega3 fatty acids on insulin-producing cells. For this purpose, BRIN-BD11 cells were cultured for 24 h in the absence or presence of both C20:5omega3 and C22:6omega3 (50 microM each) and, thereafter, examined for their phospholipid and triglyceride fatty acid pattern, and their metabolic, ionic, and secretory responses to D: -glucose and/or non-nutrient insulinotropic agents. The prior culture in the presence of the two omega3 fatty acids provoked an enrichment of cell lipids in such omega3 fatty acids, changes in the phospholipid fatty acid pattern of long-chain polyunsaturated omega6 fatty acids as well as saturated and monodesaturated fatty acids, and cell steatosis. It minimized the relative increase in D: -[5-(3)H]glucose utilization and D: -[U-(14)C]glucose oxidation otherwise resulting from an increase in the concentration of the hexose from 1.1 to 11.1 mM. It also minimized the changes in (86)Rb(+) net uptake otherwise provoked by rises in D: -glucose concentration and decreased the absolute values for insulin output. It is concluded that the major changes in metabolic, cationic, and secretory behavior of the omega3-enriched BRIN-BD11 cells are paradoxically similar to those encountered in pancreatic islets from omega3-depleted rats and, in both cases, possibly attributable to a phenomenon of lipotoxicity.

Effect of ALA-enriched food supply on cardiovascular risk factors in males

The outcome of a total dietary approach using a wide range of n-3 polyunsaturated fatty acids (PUFA) enriched food items on cardiovascular diseases called for further investigation. The study objective was to assess the effect of an ALA-enriched food supply on cardiovascular risk factors in healthy males. A dietary intervention (single-blind field trial with pre- and post-measurements) was performed with 59 healthy males in a Belgian prison. Over a period of 12 weeks they were supplied with an n-3 enriched diet (containing 6.5 g n-3 PUFA/day compared to 4 g n-3 PUFA/day in the standard diet) that was substituted for their regular diet, increasing mainly the alpha-linolenic acid intake (from 2.8 to around 5 g/day). The results indicated no impact on subjects waist circumference, weight and BMI or systolic blood pressure. In contrast, the diastolic blood pressure significantly decreased during the intervention period (from 74.6 +/- 8.2 to 71.7 +/- 10.1 mmHg; P < 0.02). Moreover, the HDL-cholesterol level increased in non-smoking participants (from 0.97 +/- 0.25 to 1.06 +/- 0.23 mmol/l; P < 0.03). In summary, the study demonstrated that enrichment of commonly eaten food items with n-3 fatty acids provides the opportunity to increase the n-3 fatty acid intake and to decrease the n-6/n-3 ratio which results in a decreasing diastolic blood pressure and an increase of HDL-cholesterol (in non-smokers).

Perturbation of phospholipid and triacylglycerol fatty acid positional location in the heart of rats depleted of n-3 long-chain polyunsaturates

Rats depleted of long-chain polyunsaturated n-3 fatty acids (n-3-D) display several features of the metabolic syndrome, including obesity, liver steatosis, insulin resistance, hypertension, and cardiac hypertrophy. In this study, the heart phospholipid (PL) and triacylglycerol (TG) fatty acid content and pattern were compared between female control rats (C) and n-3-D rats. The sole n-3 fatty acids found in n-3-D rats, C22:5(n-3) and C22:6(n-3), were 10 to 20 times lower than in C. The total fatty acid content of PL was lower in n-3-D rats than C. No ectopic TG accumulation was found in n-3-D rats. In both PL and TG, the C16:0/C16:1(n-7) and C18:0/C18:1(n-9) ratios suggested increased Delta9-desaturase activity in n-3-D rats. The PL C18:2(n-6)/C20:4(n-6) and C20:4(n-6)/C22:4(n-6) ratios were also lower in n-3-D rats than C. Prior intravenous injection of a medium-chain TG:fish oil emulsion to n-3-D rats 60 to 120 minutes before killing augmented the PL content in C22:5(n-3) and C22:6(n-3), minimized the age-related decrease in the PL C18:1(n-9) relative content, and increased the TG C22:4(n-6) content. The alteration of cardiac function in n-3-D rats and its improvement after injection of medium-chain TG:fish oil emulsion coincides with parallel changes in heart lipid fatty acid content and pattern.

Lipid peroxidation is not a prerequisite for the development of obesity and diabetes in high-fat-fed mice

The mechanism, by which a high-fat (HF) diet could impair glucose metabolism, is not completely understood but could be related to inflammation, lipotoxicity and oxidative stress. Lipid peroxides have been proposed as key mediators of intracellular metabolic response. The purpose of the present study was to analyse, in mice fed with a HF diet, the possible association between obesity and glucose tolerance on the one hand, and between oxidative stress and lipid peroxidation on the other hand. The present results show that a HF diet (70 % energy as fat), v. a high-carbohydrate chow diet (control), increases body weight and fat mass development, and impairs glycaemia and insulinaemia within 4 weeks. It also promotes the expression of NADPH oxidase in the liver--signing both oxidative and inflammatory stress--but decreases thiobarbituric acid-reactive substances content in the liver as well as in epididymal, subcutaneous and visceral adipose tissues. HF diet, with elevated vitamin E content, induces high concentration of alpha-tocopherol in liver and adipose tissues, which contributes to the protection against lipid peroxidation. Thus, lipid peroxidation in key organs is not necessarily related to the development of metabolic disorders associated with diabetes and obesity.

Nursing of malnourished children with emphasis on polyunsaturated fatty acids

Omega-3 (Omega-3) and omega-6 (Omega-6) fatty acids (FAs) are essential FAs needed for brain and retina development and maintenance of red blood cell (RBC) membranes. This study investigated the association between the profile of FAs in the membranes of RBCs and malnutrition in children. Demographic, anthropometric, and breast-feeding data and blood samples for analysis of FAs were obtained from malnourished and well-nourished children. The results indicate significant between-group differences in the profile of FAs. These findings support the need for adequate intake of Omega-3 FAs in promoting optimal growth and development processes and emphasize the role of nurses as providers of nutritional and anticipatory guidance for parents and caretakers.

A 3-month double-blind randomised study comparing an olive oil- with a soyabean oil-based intravenous lipid emulsion in home parenteral nutrition patients

Intravenous lipid emulsions (ILE) have demonstrated advantages including prevention of essential fatty acid (EFA) deficiency; however, too much EFA can down regulate fatty acid elongation leading to an imbalance of nutritional compounds in plasma and cell membranes. An olive oil-based ILE containing long-chain triacylglycerols (LCT) with a low content (20 %) of PUFA was administered for home parenteral nutrition (HPN) and compared with a conventional soyabean oil-based ILE (PUFA content, 60 %). Thirteen patients (26–92 years) with stable intestinal failure were randomised after a 1-month run-in period with a medium-chain triacylglycerols–LCT-based ILE, to receive 3 months of HPN with either olive oil- (n6) or soyabean oil-based (n7) ILE. The nutritional impact and safety of HPN, oral intakes and absorption rates, phospholipid fatty acids in plasma and lymphocyte cell membrane were assessed. The only clinical event reported was one case of pneumonia (soya group). In both groups, 20 : 3n-9:20:4n-6 ratios remained within normal ranges (0·03–0·07). There was a significant increase of γ-linolenic acid (γ-LA) in plasma and lymphocyte cell membrane (P=0·02) and of oleic acid in plasma (P<0·01) in the olive compared with the soya group. A significant correlation was found between γ-LA (day 90 – day 0) in plasma and PUFA parenteral intakes (P=0·02), but neither with fat intakes nor with fat absorption rates. In conclusion, plasma and lymphocyte EFA pattern remained in normal ranges without EFA deficiency with both lipid emulsions, despite a lower content ofn-3 andn-6 series with the olive oil-based ILE.

Short-term effects of parenteral nutrition of cholestatic infants with lipid emulsions based on medium-chain and long-chain triacylglycerols

OBJECTIVE

Infants with chronic cholestasis may require parenteral nutrition with lipid emulsions to provide energy and essential fatty acids but the optimal strategy is controversial.

METHODS

We studied the effects of parenteral lipid emulsions with long-chain triacylglycerols (LCTs) or a mixture of LCTs and medium-chain triacylglycerols (MCTs/LCTs) on serum bilirubin and lipid metabolism in cholestatic infants who received these 20% emulsions in alternating order for 3 d each, together with a glucose and amino acid infusion.

RESULTS

Of 11 recruited infants, two dropped out because enteral feeding could be established. In nine infants (2-8 mo of age, mean age 4.2 mo) who completed the study, serum bilirubin decreased from baseline to 6 h after the end of LCT infusion (from 8.5 +/- 2.0 to 7.8 +/- 1.8 mg/dL, mean +/- SEM, P < 0.05) and MCT/LCT infusion (7.9 +/- 6.5 to 7.1 +/- 6.5 mg/dL, P < 0.05). Cholesterol, triacylglycerol, and phospholipid concentrations in plasma and in chylomicrons, very low-density lipoprotein, low-density lipoprotein, and high-density lipoprotein were not changed by either emulsion. Total polyunsaturated fatty acid contents in high-density lipoprotein phospholipids increased during LCT infusion (from 29.8 +/- 0.9 to 35.9 +/- 1.4% wt/wt, P < 0.05) and MCT/LCT infusion (from 30.4 +/- 1.0 to 33.0 +/- 0.7%, P < 0.05). The long-chain polyunsaturated fatty acid docosahexaenoic acid increased only with the LCT infusion. Because docosahexaenoic acid availability during infancy is important for early visual and cognitive development, the use of soybean oil-based lipid emulsions may be preferable for infants with severe progressive cholestasis.

CONCLUSION

The MCT/LCT and LCT emulsions showed a good metabolic tolerance in infants with chronic cholestasis but had a differential effect on high-density lipoprotein phospholipid contents of arachidonic and docosahexaenoic acids.

Metabolism of defined structured triglyceride particles compared to mixtures of medium and long chain triglycerides intravenously infused in dogs

The present study aimed to determine whether including medium-chain fatty acids (MCFA) in specifically designed structured triglycerides (STG) with a MCFA in sn-1 and sn-3 positions and a long-chain (LC) FA in sn-2 position (MLM) would lead to different effects on plasma lipids and FA distribution into plasma and tissue lipids by comparison to a mixture of separate MCT and LCT molecules (MMM/LLL). The fatty acid (FA) composition was comparable in both lipid emulsions. Lipids were infused over 9h daily, in 2 groups of dogs (n = 6 each), for 28 days as a major component (55% of the non-protein energy intake) of total parenteral nutrition (TPN). Blood samples were obtained on specific days, before starting and just before stopping TPN. The concentration of plasma lipids was measured before starting and before stopping TPN on days 1, 2, 3, 4, 5, 8, 10, 12, 16 and 28. Biopsies were obtained from liver, muscle and adipose tissue 15 days before starting, and again on the day following cessation of TPN. In addition, the spleen was removed after the TPN period. FA composition in plasma and tissue lipids was analysed by gas liquid chromatography in different lipid components of plasma and tissues. No differences in either safety or tolerance parameters were detected between both lipid preparations. A lower rise of plasma TG (P < 0.05) was observed during MLM infusion, indicating a faster elimination rate of MLM vs MMM/LLL emulsion. In spite of the differences of TG molecules which would be assumed to affect the site of FA delivery and metabolic fate, FA distribution in phospholipids (PL) of hepatic and extrahepatic tissues did not substantially differ between both emulsions.

Specific changes in n -6 fatty acid metabolism in patients with chronic intestinal failure

BACKGROUND AND AIMS

In patients presenting severe malabsorption, essential fatty acid (EFA) deficiency can be corrected by intravenous lipids, but EFA abnormalities persist. The purpose of this study was to evaluate the role of large resection of the small bowel or malabsorption on plasma phospholipid EFA profile.

METHODS

The plasma phospholipid EFA composition was measured by gas chromatography in home parenteral nutrition patients with (n=13) or without small bowel resection (n=7) and in 14 healthy subjects.

RESULTS

The two groups of patients had the same nutritional status and comparable amounts of intravenous fat. In both groups, plasma fatty acid concentrations were significantly different from those observed in healthy subjects without EFA deficiency. Among them: a decrease in 18:2n -6, 22:5n -3, 22:6n -3 and an increase in 18:3n -3, 20:4n -6, 22:4n -6. Moreover, arachidonic acid to linoleic acid ratio was higher in both groups of patients, suggesting a stimulation of the elongation and desaturation of 18:2n -6. In multiple linear regression, 18:2n -6 and 20:4n -6 levels were not associated with the small bowel length, only 22:6n -3 concentration was correlated with small bowel length.

CONCLUSIONS

The patients with chronic intestinal failure on home parenteral nutrition presented specific change in their EFA and an increase in the n -6 fatty acid pathway. This could be related to the severe malabsorption.

Manipulation of tissue fatty acid profile by intravenous lipids in dogs

This study was undertaken to determine the effects on the fatty acid (FA) composition of various dog tissues of 4 different lipid emulsions (a 100% long-chain triacylglycerol (LCT) derived from soya bean oil emulsion, a mixed 50% medium-chain triacylglycerol (MCT)/50% LCT emulsion as well as both these emulsions supplemented with 10% fish oil (FO) triacylglycerols), when daily infused over 15 days as a substantial component of total parenteral nutrition. Lipids represented 55% of the non-protein energy. Blood samples as well as biopsies from liver, muscle and adipose tissue were taken 15 days before, and again immediately after TPN. In addition, the spleen was also removed immediately after TPN. Tissue FA composition was analysed by gas liquid chromatography of each lipid component after separation by thin layer chromatography. No differences in either safety or tolerance were detected between the different TPN preparations. In particular, infusion over 2 weeks of fat emulsions containing 10% fish oil was tolerated as well as conventional LCT and MCT/LCT emulsions. Relative linoleate content of tissue triacylglycerol (TG) was markedly increased in animals that received the LCT emulsions (e.g. from 22.6 +/- 2.5% to 32.2 +/- 0.6% in the liver), this effect being markedly reduced with MCT/LCT preparations. n-3FA were slightly incorporated into liver TG (from 0.0 +/- 0.0% to 2.3 +/- 0.7% and 1.2 +/- 0.4% for eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) respectively, with LCT + FO), but remained undetectable in extrahepatic tissue TG. Of interest, medium chain FA were found in tissue TG after infusion of the mixed MCT/LCT emulsions. As expected, changes of tissue phospholipid (PL) composition involved only long-chain FA. Infusion of soya bean oil emulsion was associated with an increased content of linoleate in liver PL (from 13.6 +/- 0.4% to 17.7 +/- 0.4%), but not in other tissues. MCT/LCT did not markedly affect PL/FA pattern in any tissue. Supplementation with fish oil was associated with an efficient incorporation of n-3FA into tissue PL, particularly in the liver (from 0.4 +/- 0.1% to 2.5 +/- 0.3% for EPA and from 3.9 +/- 0.8% to 9.1 +/- 0.4% for DHA, with the LCT + FO emulsion).

Recent advances: parenteral nutrition support

Even though there is an abundance of research related to the clinical and physiologic effects of parenteral nutrition and specific nutritional substrates, few new products have been released for clinical use. This review illustrates some of the directions being taken in the future development of parenteral nutrition products and some new perspectives related to the current effects (or lack of effects) of TPN. When considering the individual effects of specific nutrient substrates (arginine, glutamine, LCTs, MCTs, SCFAs) as reviewed here, it becomes apparent that the infusion of parenteral nutrition has the potential to produce a variety of metabolic responses that could be both beneficial and harmful. These effects depend on the type and quantity of substance infused as well as the disease and clinical condition of the patient. This also is true for those substances (GH, IGF-1) being evaluated to direct the effects of TPN infusions in a manner that improves protein accretion and supports the immunologic response of the body. At best, these investigations are producing a great amount of new and more specific information about the metabolic response to illness and the effects of TPN and individual substrate on that response.

Essential fatty acid metabolism and requirements for LBW infants

Humans are unable to synthesize linoleic acid (LA) (18:2 omega-6) and alpha-linolenic acid (LNA) (18:3 omega-3). Most formulas provide ample LA, yet infants are at risk for omega-3 deficiency unless they are fed human milk. Neonates born at 30 weeks received human milk or were randomized to three formulas: formula A, based on corn oil, similar to old commercial formula; formula B, based on soy oil supplied LNA; or formula C, a product similar to B with added marine oil to provide docosahexaenoic acid (22:6 omega-3). The fatty acids of plasma and red blood cells had marked diet-induced differences. The rod photo-receptor tests demonstrated higher threshold and decreased sensitivity in the omega-3-deficient infants. Visual acuity also showed improved function of the brain cortex in the human milk and group C infants at follow-up at 57 weeks. These results suggest that omega-3 fatty acids are needed for optimal development of visual function.

Effect of three intravenously administered fat emulsions containing different concentrations of fatty acids on the plasma fatty acid composition of premature infants

The effects of an intravenously administered lipid emulsion supplemented with gamma-linolenic acid on the fatty acid profile of premature infants were compared with those of two conventional lipid emulsions. Fifty-nine premature neonates receiving total parenteral nutrition were randomly assigned to receive either fat emulsion containing gamma-linolenic acid and long-chain triglycerides (LCT), an LCT emulsion, or a 50% (wt/wt) mixture of medium-chain triglycerides and LCT emulsion. Forty-nine infants completed the study. During the 6-day study there was a significant tenfold increase in the plasma levels of gamma-linoleic acid in the supplemented group versus the other two groups. A significant threefold to fivefold increase in the omega 6 long-chain polyunsaturated fatty acids was observed in all groups. These changes seemed to be attributable mostly to linoleic acid from the lipid emulsion, despite the 50% lower dose in the medium- and long-chain triglycerides group. The increase in the omega 3 long-chain polyunsaturated fatty acids also was mainly caused by a similar increase in the level of alpha-linolenic acid. No differences were recorded in the linoleic/alpha-linolenic acid ratio among the groups. Plasma levels of some of the semiessential fatty acids were significantly higher in the medium- and long-chain triglycerides group than in the LCT group. This may be related to slower elimination of LCT, to the difference between emulsions, or to less substrate inhibition on delta-6-desaturase, which seems to be less of a rate-limiting enzyme than previously considered. Further intravenous feeding trials are needed to identify the optimal balance of fatty acids for nutrition of these premature infants.