Effects of different lipid sources in total parenteral nutrition on whole body protein kinetics and tumor growth

Influence of feeding a fish oil-containing diet to mature, overweight dogs: Effects on lipid metabolites, postprandial glycaemia and body weight

The objective of this study was to determine the effect of feeding a fish oil (FO)-containing diet on lipid and protein metabolism, postprandial glycaemia and body weight (BW) of mature, overweight dogs. Seven female dogs were randomly assigned to one of two isonitrogenous and isocaloric diets, control (CO) or FO (FO), in a crossover design. Experimental periods were 69 day, separated by a washout period of 30 day. At the beginning of the experiment, and at 30 and 60 day of feeding the experimental diets, the dogs were infused with D-glucose (2 g/kg BW) through an intravenous catheter. Blood samples were collected for 3 hr to perform a glucose tolerance test. Nitrogen balance measurements began at 06:30 on d 63 of each experimental period and ended at 06:30 on d 69. On d 66 of each period, a single dose (7.5 mg/kg) of ¹⁵ N-glycine was administered orally for determination of protein turnover. Incremental area under the curve and glucose concentration at peak did not differ between treatments or among sampling days within treatment. Glucose half-life tended to decrease (p < .10) in the FO treatment on day 30 when compared to baseline (day 0). β-hydroxybutyrate, non-esterified fatty acid (NEFA) and triglycerides did not differ within or between treatments. Cholesterol decreased (p < .05) on the FO treatment on day 30, 60 and 69 when compared to day 0. High-density lipoprotein (HDL) decreased (p < .05) in the FO treatment on day 69 when compared to day 0. Body weight, food intake, faecal excretion, DM and N digestibilities, N balance and protein turnover were not different between diets. Overall, FO-containing diet decreases cholesterol in mature overweight dogs; however, further research is warranted to verify the effects of FO on glucose metabolism.

Structured Triglyceride Emulsions in Parenteral Nutrition

Over the past 3 decades, various concepts for IV fat emulsions (IVFE) have been developed. A randomized, structured-lipid emulsion based on an old technology has recently become available. This structured-lipid emulsion is produced by mixing medium-chain triglycerides and long-chain triglycerides, then allowing hydrolysis to form free fatty acids, followed by random transesterification of the fatty acids into mixed triglyceride molecules. Studies in animals have shown an improvement in nitrogen balance with the use of these lipid emulsions. Only 8 human clinical studies with these products have been performed. The results of these human clinical studies have been less promising than the animal studies; however, an improvement in nitrogen balance and lipid metabolism exceeds results associated with infusion of long-chain triglycerides (LCT) or a physical mixture of long-chain triglycerides and medium-chain triglycerides (LCT-MCT). Structured-lipid emulsion seems to induce less elevation in serum liver function values compared with standard IVFEs. In addition, structured-lipid emulsions have no detrimental effect on the reticuloendothelial system. Further studies are necessary in order to recommend the use of structured-lipid emulsions. The clinical community hopes that chemically defined structured triglycerides will make it possible to determine the distribution of specific fatty acids on a specific position on the glycerol core and therefore obtain specific activity for a specific clinical situation.

Influence of feeding a fish oil-containing diet to young, lean, adult dogs: effects on lipid metabolites, postprandial glycaemia and body weight

The aim of this study was to determine the effect of feeding a fish oil (FO)-containing diet on lipid and protein metabolism, postprandial glycaemia and body weight in young, lean, adult dogs. Eight female Beagles were randomly assigned to one of two isonitrogenous and isoenergetic diets, Control or FO, in a crossover design. At the beginning of the experiment and at 30 and 60 d, a baseline blood sample was collected and the dogs then were fed their daily ration. Nitrogen balance began at 07:00 h on day 63 of each experimental period and ended at 07:00 h on day 69. On day 66 of each period, a single dose (7.5 mg/kg) of (15)N-glycine was administered orally to each dog via gelatin capsule. Postprandial glycaemia did not differ between treatments or among sampling days within treatment. Cholesterol concentration was increased (p<0.05) on the Control treatment throughout the experiment when compared to values of day 0. Dogs fed the FO treatment had higher plasma triglyceride and ghrelin concentrations than those fed the Control treatment. Body weight and food intake did not differ between dietary treatments. Faecal excretion was increased (p<0.05) in the FO treatment. Dry matter digestibility was decreased (p<0.05) and fat digestibility tended (p<0.10) to decrease in the FO treatment. Overall, feeding a FO-containing diet showed a protective effect against the rise of plasma cholesterol and it increased plasma ghrelin concentration. However, FO supplementation did not appear to affect protein metabolism or postprandial glycaemia in adult lean dogs.

Effect of medium-chain triglycerides on growth performance, nutrient digestibility, plasma metabolites and antioxidant capacity in weanling pigs

The aim of this study was to investigate the effect of medium-chain triglycerides (MCTs) on growth performance, nutrient digestibility, plasma metabolites and antioxidant capacity in weanling pigs. A total of 160 weanling (Duroc × Landrace × Yorkshire) pigs (age: 21 ± 1 d; body weight: 7.50 ± 0.28 kg) were randomly allotted to 4 treatments, receiving the following diets for 28 d: control diet [containing 3.5% soybean oil (SO)], MCT1 diet (containing 0.7% MCTs and 2.8% SO), MCT2 diet (containing 1.4% MCTs and 2.1% SO) and MCT3 diet (containing 2.1% MCTs and 1.4% SO). Dietary inclusion of MCTs improved the average daily gain and feed efficiency (FE) of pigs compared with the control during the first 2 weeks post-weaning (P < 0.05). A similar positive effect was also observed for the overall FE in MCT2 group (P < 0.05). Compared with the control, apparent total tract digestibility (ATTD) of ether extract was improved by MCT2 and MCT3 treatment from day 12–14 post-weaning (P < 0.05). In addition, MCT2 treatment also exerted a beneficial effect on the ATTD of dry matter (P < 0.05). The increased total protein concentration and decreased urea nitrogen and malondialdehyde levels of plasma were observed in both MCT2 and MCT3 groups on day 14 post-weaning (P < 0.05). In conclusion, MCTs could improve growth performance, nutrients utilization, and antioxidant ability of weanling piglets.

Skeletal muscle protein metabolism in the elderly: Interventions to counteract the 'anabolic resistance' of ageing

Age-related muscle wasting (sarcopenia) is accompanied by a loss of strength which can compromise the functional abilities of the elderly. Muscle proteins are in a dynamic equilibrium between their respective rates of synthesis and breakdown. It has been suggested that age-related sarcopenia is due to: i) elevated basal-fasted rates of muscle protein breakdown, ii) a reduction in basal muscle protein synthesis (MPS), or iii) a combination of the two factors. However, basal rates of muscle protein synthesis and breakdown are unchanged with advancing healthy age. Instead, it appears that the muscles of the elderly are resistant to normally robust anabolic stimuli such as amino acids and resistance exercise. Ageing muscle is less sensitive to lower doses of amino acids than the young and may require higher quantities of protein to acutely stimulate equivalent muscle protein synthesis above rest and accrue muscle proteins. With regard to dietary protein recommendations, emerging evidence suggests that the elderly may need to distribute protein intake evenly throughout the day, so as to promote an optimal per meal stimulation of MPS. The branched-chain amino acid leucine is thought to play a central role in mediating mRNA translation for MPS, and the elderly should ensure sufficient leucine is provided with dietary protein intake. With regards to physical activity, lower, than previously realized, intensity high-volume resistance exercise can stimulate a robust muscle protein synthetic response similar to traditional high-intensity low volume training, which may be beneficial for older adults. Resistance exercise combined with amino acid ingestion elicits the greatest anabolic response and may assist elderly in producing a 'youthful' muscle protein synthetic response provided sufficient protein is ingested following exercise.

Reduction of low grade inflammation restores blunting of postprandial muscle anabolism and limits sarcopenia in old rats

Ageing is characterized by a decline in muscle mass that could be explained by a defect in the regulation of postprandial muscle protein metabolism. Indeed, the stimulatory effect of food intake on protein synthesis and its inhibitory effect on proteolysis is blunted in old muscles from both animals and humans. Recently, low grade inflammation has been suspected to be one of the factors responsible for the decreased sensitivity of muscle protein metabolism to food intake. This study was undertaken to examine the effect of long-term prevention of low grade inflammation on muscle protein metabolism during ageing. Old rats (20 months of age) were separated into two groups: a control group and a group (IBU) in which low grade inflammation had been reduced with a non-steroidal anti inflammatory drug (ibuprofen). After 5 months of treatment, inflammatory markers and cytokine levels were significantly improved in treated old rats when compared with the controls: -22.3% fibrinogen, -54.2% alpha2-macroglobulin, +12.6% albumin, -59.6% IL(6) and -45.9% IL(1beta) levels. As expected, food intake had no effect on muscle protein synthesis or muscle proteolysis in controls whereas it significantly increased muscle protein synthesis by 24.8% and significantly decreased proteolysis in IBU rats. The restoration of muscle protein anabolism at the postprandial state by controlling the development of low grade inflammation in old rats significantly decreased muscle mass loss between 20 and 25 months of age. In conclusion, the observations made in this study have identified low grade inflammation as an important target for pharmacological, nutritional and lifestyle interventions that aim to limit sarcopenia and muscle weakness in the rapidly growing elderly population in Europe and North America.

Differences in the intramolecular structure of structured oils do not affect pancreatic lipase activity in vitro or the absorption by rats of (n-3) fatty acids

The fatty acid composition and intramolecular structure of dietary triacylglycerols (TAGs) influence their absorption. We compared the in vitro pancreatic lipase activity and the lymphatic transport in rats of fish oil and 2 enzymatically interesterified oils containing 10:0 and (n-3) PUFAs of marine origin to investigate whether the positional distribution of fatty acids influenced the overall bioavailability of (n-3) PUFAs in the body. The structured oils had the (n-3) PUFA either mainly at the sn-1,3 position (LML, M = medium-chain fatty acid, L = long-chain fatty acid) or mainly at the sn-2 position (MLM). Oils were administered to lymph-cannulated rats and lymph was collected for 24 h. The fatty acid composition as well as the lipid class distribution of lymph samples was determined. In vitro pancreatic lipase activity was greater when fish oil was the substrate than when the structured oils were the substrates (P < 0.001 at 40 min). This was consistent with a greater 8-h recovery of total fatty acids from fish oil compared with the 2 structured oils (P < 0.05). The absorption profiles of MLM and LML in rats and their in vitro rates of lipase activity did not differ. This indicates that the absorption rate is highly influenced by the lipase activity, which in turn is affected by the fatty acid composition and intramolecular structure. The lipid class distribution in lymph collected from the 3 groups of rats did not differ. In conclusion, the intramolecular structure did not affect the overall absorption of (n-3) PUFAs.

Indomethacin and ibuprofen preserve gastrocnemius muscle mass in mice bearing the colon-26 adenocarcinoma

Skeletal muscle wasting is a prominent feature of cancer cachexia and involves decreased muscle protein synthesis and increased activity of the ubiquitin-proteasome pathway of protein degradation. We report that both indomethacin and ibuprofen improved body weight and weight of the gastrocnemius muscle in tumor-bearing mice. Ibuprofen increased the soluble protein content of the muscle without affecting muscle levels of phosphorylated p70 S6 kinase, a ribosomal kinase involved in protein synthesis. Paradoxically, indomethacin increased levels of ubiquitin-conjugated proteins. Further study is needed to understand the mechanism of action by which indomethacin and ibuprofen preserve body weight and muscle mass in the tumor-bearing mice. The data suggest that ibuprofen may have beneficial effects in the treatment of cancer cachexia.

Effects of fish oil in parenteral nutrition

OBJECTIVE

Fish oil is a rich source of omega-3 fatty acids (FAs), especially eicosapentaenoic acid and docosahexaenoic acid. The existing data suggest that eicosapentaenoic acid and docosahexaenoic acid are the active agents in fish oil. A number of clinical trials have shown that dietary fish oil supplementation has antiatherogenic properties and immunomodulation effects. Fish oils are not used widely in parenteral nutrition because fish oil emulsions have not been commercially available until very recently. Studies concerning the use of fish oil in parenteral route are rare.

METHODS

We reviewed the effect of parenteral fish oil infusion on lipid metabolism and immune response in normal and disease conditions.

RESULTS

Studies showed that the main effects of parenteral infusion of fish oil are: 1) incorporation of omega-3 FAs into cellular membranes of many cell populations that consequently influence the disease process of some disease conditions, 2) an effect on eicosanoid metabolism leading to a decrease in platelet aggregation and thrombosis, 3) amelioration of the severity of diet-induced hepatic steatosis, 4) less accumulation of lipid peroxidation products in liver tissue, and 5) immunomodulation effects and therapeutic benefits in animal disease models or various disease conditions of humans. Most of these studies suggested that parenteral infusion of omega-3 FAs have clinical beneficial effects comparable to those of dietary administration. However, different effects of omega-3 and omega-6 FAs in some situations has been reported. For example, plasma triacylglycerol levels were not lowered after fish oil infusion in normal or diabetic rats when compared with those of safflower oil or soybean oil infusion. The reason for the difference remain unclear.

CONCLUSION

The metabolic and immunologic effects of parenteral use of omega-3 FAs requires further evaluation, especially in some disease conditions.

Nitrogen sparing effect of structured triglycerides containing both medium-and long-chain fatty acids in critically ill patients; a double blind randomized controlled trial

BACKGROUND AND AIMS

Patients with sepsis and trauma are characterised by hypermetabolism, insulin resistance and protein catabolism. Fat emulsions containing medium chain triglycerides have been suggested to be beneficial for these patients since medium chain fatty acids are a more readily available source of energy when compared to long chain fatty acids. The aim of this study was to compare a medium and long chain triglyceride emulsion consisting of structured triglycerides (ST) with a long chain triglyceride (LCT) emulsion in terms of effects on nitrogen balance, energy metabolism and safety.

METHODS

30 ICU patients with sepsis or multiple injury received a fat emulsion with ST or 20% LCT (1.5 g triglycerides/kg body weight/day) as a component of total parenteral nutrition (TPN), for 5 days in a double blind randomised parallel group design. The main analysis was made on the 3 day per protocol population due to lack of patients at day 5.

RESULTS

There were no differences in baseline characteristics of the two groups receiving either the LCT or the ST emulsion. The efficacy analysis was performed on the per protocol population (n=9 ST, n=11 LCT). There was a significant difference between the two treatments regarding daily nitrogen balances when the first 3 days were analysed P=0.0038). This resulted in an amelioration of the nitrogen balance on day 3 in the group on ST as compared to those on LCT (0.1+/-2.4 g vs -9.9+/-2.1 g P=0.01). The 3 day cumulative nitrogen balance was significantly better in the group receiving ST compared to those on LCT (-0.7+/-6.0 vs -16.7+/-3.9 P=0.03). This better cumulative nitrogen balance on day 3 was also preserved as a tendency (P=0.061) in the analysis of the intention to treat population, but on day 5 there was no significant difference (P=0.08). The ST emulsion was well tolerated and no difference was found compared to the LCT emulsion regarding respiratory quotient, energy expenditure, glucose or triglyceride levels during infusion.

CONCLUSION

Administration of a structured triglyceride emulsion resulted in an amelioration of nitrogen balance despite no effect on energy expenditure in short term administration over 3 days to ICU patients when compared to a long chain triglyceride emulsion. No side effects linked to medium chain triglycerides were noted.

Lymphatic absorption of structured triglycerides vs. physical mix in a rat model of fat malabsorption

Comparison was made between the intestinal absorption and lymphatic transport of a randomly interesterified fish oil and medium-chain triglyceride (MCT) structured triglycerides (STG) vs. the physical mix in rat small intestine following ischemia and reperfusion (I/R) injury. Under halothane anesthesia, the superior mesenteric artery (SMA) was occluded for 20 min and then reperfused in I/R rats. The SMA was isolated but not occluded in control rats. In both treatment groups, the mesenteric lymph duct was cannulated and a gastric tube was inserted. Each treatment group received 1 ml of the fish oil-MCT STG or physical mix (7 rats/group) through the gastric tube followed by an infusion of PBS at 3 ml/h for 8 h. Lymph was collected hourly for 8 h. Lymph triglyceride, cholesterol, and decanoic and eicosapentaenoic acids increased rapidly and maintained a significantly higher output (P < 0.01) with STG compared with physical mix in control rats over 8 h. After I/R, lymphatic triglyceride output decreased 50% compared with control. Gastric infusion of STG significantly improved lipid transport by having a twofold higher triglyceride, cholesterol, and decanoic and eicosapentaenoic acids output to lymph compared with its physical mix (P < 0.01). We conclude that STG is absorbed into lymph significantly better than physical mix by both the normal intestine and the intestine injured by I/R.

The new dietary fats in health and disease

Lipids are an integral part of the routine diet of patients and the general public. In this article, the physiologic properties of various dietary lipids are reviewed, beginning with those most commonly consumed-the long-chain triglycerides (LCTs) and extending to those with special purposes: the short- and medium-chain triglycerides. The nutritional dietary management of patients typically includes physical mixtures of lipids. Recently, structured triglycerides (STs), which combine advantages from conventional fats with those of special purposes, have become available. STs are currently developed by interesterifying a mixture of conventional fats and oils, usually with medium-chain triglycerides, to achieve a specific fatty acid profile. This results in a triglyceride containing combinations of short-, medium-, and long-chain fatty acids on a single glycerol backbone. They have unique chemical, physical, or physiologic properties that are not observed by simply blending mixtures of the starting fats and oils. A number of STs are under intense laboratory and clinical investigation in models of cancer, burns, and immune dysfunction. Much interest in the fatty acids resides in the sn-2 position on the glycerol molecule. This is because the fatty acid in the sn-2 position of triglycerides is preferentially absorbed as the 2-monoglyceride and serves as the template for reesterification by intestinal cells to re-form triglycerides. The sn-2 fatty acids are also preferentially preserved as components of chylomicrons and very-low-density lipoprotein particles for ultimate incorporation in tissue membranes. Technology is evolving to create STs with a selected fatty acid in this sn-2 position. For instance, incorporating linoleic, arachidonic, or eicosapentaenoic acid at the sn-2 position is being evaluated for the specific objective of modulating serum cholesterol concentrations and essential fatty acid absorption (a review of this work is included).

The metabolic distinctiveness of emulsified lipid particles in the bloodstream and its clinical implications

The advantages of administering intravenous fat emulsions are well known. Primarily, they are important sources of essential fatty acids; they allow the administration of many calories within a small volume; and they are isotonic compared to body fluid. In this review, the metabolic distinctiveness of parenterally infused fat particles in the bloodstream is evaluated under four main headings: (1) the structure and metabolism of fat emulsion particles; (2) the metabolism of phospholipid-rich fat emulsion; (3) the interactions between fat emulsion particles and plasma lipoproteins; and (4) the acquisition of protein moieties (apolipoproteins) by fat emulsion particles and its clinical implications.

Immunostimulation following fish oil-based parenteral nutrition in tumor-bearing rats

Tumor-bearing (TB) and control rats were maintained for four to seven days on total parenteral nutrition (TPN) in which the lipid component (11.1% of total calories) was Intralipid or fish oil. Although no TB rats maintained on standard Intralipid-based TPN died prematurely in these experiments, one-third of the TB rats maintained on fish oil-based TPN died of bleeding complications by Day 4 of TPN infusion. The bleeding appeared to be due to the particle size in the fish oil emulsion, because a subsequent study employing a better emulsified TPN with smaller lipid particles exhibited fewer bleeding problems. Tumor growth, skeletal muscle atrophy, and gut hypoplasia were not reduced in the TB group maintained on fish oil-based TPN. However, immunosuppression observed in the Intralipid-based TPN group, as measured by mitogen response of cultured splenocytes, was significantly improved in the rats maintained on fish oil-based TPN. Levels of eicosapentaenoic acid were reduced in all rats receiving TPN. Although the hypothesized antitumor and anticachexia effects of fish oil administration were not realized, significant improvement in immunosuppression was noted. These results suggest that intravenously administered fish oil may have potential positive effects for the host.

Lipid-based fat substitutes

Fats and oils account for 38% of the total calories in the diet of Western populations, especially in the U.S. They provide the most concentrated source of energy, 9 kcal/g of a triacylglycerol molecule compared with 4 kcal/g provided by carbohydrate and protein. In response to consumer demands for low-calorie or calorie-free fats and their reluctance to give up the taste of fat, current research efforts have been directed toward the development of lipid-like fat substitutes. These fat substitutes contain the fatty acids found in conventional fats and oils, with all the physical and organoleptic properties of fats, but provide few or no calories in the diet. Some of the fat substitutes are modified triacylglycerols (glycerol backbone) with reduced digestion and absorption; others are digestible and nondigestible carbohydrate fatty acid esters and polyesters, respectively. Sucrose polyester (Olestra), a sucrose molecule esterified with six to either fatty acids, is the most studied of the lipid-based fat substitutes containing a carbohydrate backbone. If approved by the FDA, sucrose polyester will find application in almost all fat-containing foods. Specialty fats or fat substitutes targeted to certain individuals with special needs are being developed. Among these are the medium-chain triacylglycerols and structured lipids (glycerol backbone), or ¿nutraceuticals¿ with reduced absorption and medical applications. Enzyme biotechnology is another tool available to lipid chemists to selectively modify, esterify, transform, transesterify, and interesterify fats and oils or synthesize new lipids such as structured lipids of food, nutritional, and medical importance. These designer fats may be the trend in the future to produce medical lipids that do not occur normally in nature. The different types of lipid-based fat substitutes are reviewed with respect to their synthesis, analysis, metabolism, potential applications/uses, and the future of fat substitutes.

Metabolic effects of structured triglycerides in humans

This review considers the development of structured triglycerides as an IV nutrient source. The replacement of a portion of long-chain fatty acids in the conventional fat emulsion triglycerides confers favorable qualities on these lipids and renders them attractive as an energy source, particularly in critically ill patients. This report considers the features of structured triglycerides that may make them competitive or even more efficient as an energy source compared with conventional fat emulsions.