Vigen K. Babayan

Medium chain triglycerides and structured lipids

Lipids are an essential component of our body composition and necessary in our daily food intake. Conventional fats and oils are composed of glycerides of long chain fatty acids and are designated as long chain triglycerides (LCT). Body fat as well as the fats and oils in our daily intake fall into this category. In enteral and parenteral hyperalimentation, we can identify such LCT fats and oils. Soy, corn, safflower and sunflowerseed oils are typical of the LCT oils.In the search for alternative noncarbohydrate fuels, medium chain triglycerides (MCT) are unique and have established themselves in the areas of malabsorption syndrome cases and infant care and as a high energy, rapidly available fuel. Structure lipids with a MCT backbone and linoleic acid built into the triglyceride molecule have been developed to optimize the triglyceride structure that is best for patients, particularly the critically ill. Structured lipids with built-in essential fatty acid components or other polyunsaturated fatty acids promise greater flexibility in patient care and nitrogen support.

The Effect of Lipid Emulsions on Reticuloendothelial System Function in the Injured Animal

Use of intravenous lipid emulsions in trauma and sepsis still remains controversial. In order to examine the impact lipid emulsions have on host defense against bacterial infection during total parenteral nutrition (TPN), 56 male Sprague-Dawley rats underwent jugular cannulation and were randomly divided into three groups, each receiving one of three TPN regimens. All regimens delivered approximately 250 kcal/ kg·body weight/day, of which 12.5 g were as amino acids. Group 1 received 100% of the nonprotein calories as glucose (AA + G). Group 2 was given 50% of the nonprotein calories as a long-chain triglyceride emulsion (100% LCT). Group 3 received 50% of nonprotein calories as a mixed lipid system, composed of medium- and long-chain triglycerides (75% MCT/25% LCT). After 24 hr on intravenous nutrition, all animals received bilateral septic femur fractures and were continued on TPN for 3 days. On the last day, the level of bacteremia and the in vivo response to an intravenous challenge of 59Fe-labeled Esc...

Parenteral infusion of long- and medium-chain triglycerides and reticuloendothelial system function in man.

Previous study demonstrated that patients who received total parenteral nutrition (TPN) with standard intermittent infusion of long chain triglyceride (LCT) at 0.13 g kg-1hr-1 over 10 hr for each of three days showed a significant decline in 99Tc-sulfur colloid (TSC) clearance rate by the reticuloendothelial system (RES). The present studies evaluated eight patients who received the same total lipid dose of LCT infused continuously as in a three-in-one admixture, and another nine patients receiving the same amount of fat as a medium chain triglyceride (MCT)/LCT (75%/25%) emulsion intermittently over 10 hr at 0.13 g kg-1hr-1 for three consecutive days. Patients were given continuous total parenteral nutrition (TPN) comprised of protein, 1.5 g kg-1day-1, and dextrose, 4.5 g kg-1day-1. RES function was examined by measuring the clearance rates of intravenously injected TSC while receiving TPN containing only protein and dextrose, and again after three days of fat infusion. Mean (+/- SEM) clearance rate constants before and after continuous LCT infusion were 0.38 +/- 0.09 and 0.41 +/- 0.08 min-1, respectively, while those before and after intermittent MCT/LCT infusion were 0.50 +/- 0.18 and 0.73 +/- 0.24 min-1, respectively. In contrast to intermittent LCT infusion, the administration of continuous LCT or an intermittent MCT/LCT mixture does not impair TSC clearance by the RES. These findings suggest that condensing the daily period of LCT infusion at standard dosage may exceed the rate of metabolic utilization, resulting in increased fat removal and diminished TSC uptake by the RES.(ABSTRACT TRUNCATED AT 250 WORDS)

Structured medium-chain and long-chain triglyceride emulsions are superior to physical mixtures in sparing body protein in the burned rat

The present study was undertaken to compare the effectiveness of a physical mixture of long-chain and medium-chain triglycerides with an emulsion consisting of chemically synthesized triglycerides composed of medium-chain and long-chain fatty acids in similar proportions. Sprague-Dawley rats received a 25% body surface area full-thickness scald burn on the dorsum. For the next three days, all rats received 300 kcal/kg/day as 160 kcal/kg/day glucose, 50 kcal/kg/day amino acid, and an additional 90 kcal/kg/day lipid emulsion as either long-chain triglyceride, medium-chain triglyceride, a 1:1 physical mix of medium-chain and long-chain triglycerides or a chemically structured triglyceride made up of 60% medium-chain fatty acid and a 40% safflower oil. Rats receiving the chemically structured lipid emulsion showed the greatest gain in body weight, the greatest positive nitrogen balance, and the highest serum albumin concentration, outstripping rats receiving the long-chain triglyceride, medium-chain triglyceride, and even the physical mixture long-chain and medium-chain triglycerides (P less than 0.01). A 30% increase in oxygen consumption and 35% increase in energy expenditure in rats given the medium-chain triglyceride emulsion alone (P less than 0.01) was observed. This study confirms that the metabolism of chemically structured triglycerides composed of medium-chain and long-chain fatty acids markedly differs from similar physical mixtures. For these reasons, the new structured lipid emulsions may prove advantageous in feeding the severely injured patient.

Protein metabolism during total parenteral nutrition (TPN) in injured rats using medium-chain triglycerides

There are metabolic limitations to the infusion of large quantities of dextrose in critically ill patients receiving total parenteral nutrition. Of the alternative, nonprotein lipid sources, medium chain triglycerides (carbon chain length 8 and 10) are more rapidly oxidized and are deposited in the adipose tissue at rates much less than long chain triglycerides. In rats with burn injury receiving hypocaloric (dextrose and amino acids) parenteral feeding, we studied the changes in protein metabolism as a result of increasing the caloric intake by 33% by the addition of either dextrose, a soybean oil emulsion, a medium chain triglyceride emulsion, or a structured lipid emulsion of triglycerides synthesized from safflower oil (40%) and medium chain triglycerides (60%). Changes in body weight, blood glucose concentration, beta-hydroxybutyrate, lactate, amino acids, insulin, albumin, liver protein content, and nitrogen balance were measured during three days of feeding. Whole body leucine kinetics and muscle protein fractional synthetic rate were evaluated using a constant intravenous infusion of L-[1-14C]leucine. The addition of dextrose or soybean oil emulsion produced a significant increase in body weight and liver nitrogen but did not change albumin concentrations or leucine kinetics compared to those of the hypocaloric feeding group. Rats receiving medium chain triglycerides and structured lipid emulsions showed a reduction in branched chain amino acid concentrations and an improvement in serum albumin levels. However, the rats receiving the structured lipid emulsion also showed increased body weight, had a significant decrease in leucine oxidation, and showed a three day cumulative nitrogen balance significantly greater than zero.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration of structured lipid composed of MCT and fish oil reduces net protein catabolism in enterally fed burned rats.

The effects of enteral feeding with safflower oil or a structured lipid (SL) derived from 60% medium-chain triglyceride (MCT) and 40% fish oil (MCT/fish oil) on protein and energy metabolism were compared in gastrostomy-fed burned rats (30% body surface area) by measuring oxygen consumption, carbon dioxide production, nitrogen balance, total liver protein, whole-body leucine kinetics, and rectus muscle and liver protein fractional synthetic rates (FSR, %/day). Male Sprague-Dawley rats (195 +/- 5g) received 50 ml/day of an enteral regimen containing 50 kcal, 2 g amino acids, and 40% nonprotein calories as lipid for three days. Protein kinetics were estimated by using a continuous L-[1-14C] leucine infusion technique on day 2. Thermally injured rats enterally fed MCT/fish oil yielded significantly higher daily and cumulative nitrogen balances (p less than or equal to 0.025) and rectus muscle (39%) FSR (p less than or equal to 0.05) when compared with safflower oil. MCT/fish oil showed a 22% decrease (p less than or equal to 0.005) in per cent flux oxidized and a 7% (p less than or equal to 0.05) decrease in total energy expenditure (TEE) versus safflower oil. A 15% increase in liver FSR was accompanied by a significant elevation (p less than or equal to 0.025) in total liver protein with MCT/fish oil. This novel SL shares the properties of other structured lipids in that it reduces the net protein catabolic effects of burn injury, in part, by influencing tissue protein synthetic rates. The reduction in TEE is unique to MCT/fish oil and may relate to the ability of fish oil to diminish the injury response.

Dietary modification of Chyle composition in chylothorax

Nutrition support has played a major role in the treatment of chylothorax, both to prevent malnutrition and to minimize chyle production and flow. This report evaluates chyle composition in a patient with chylothorax who was placed on a low-fat diet, medium-chain triglyceride diet, and total parenteral nutrition in sequence. Both triglyceride content and volume of chyle declined, but drainage persisted, ultimately requiring thoracic duct ligation. The chyle triglyceride while on total parenteral nutrition, which presumably originates from both the intestine and plasma, contained more long-chain unsaturated fatty acids than the circulating serum triglyceride. Of particular interest was the detection of an appreciable amount of medium-chain fatty acids in the chyle triglyceride, constituting 20% of the triglyceride fatty acids when an enteral formulation with medium-chain triglyceride as a sole fat source was administered. The finding of almost threefold more decanoic acid (C10:0) than octanoic acid (C8:0), despite the presence of considerably more octanoic acid in the original diet, suggests that trioctanoin may be a preferable medium-chain triglyceride substrate for the nonsurgical treatment of chylothorax.

Enhanced skeletal muscle and liver protein synthesis with structured lipid in enterally fed burned rats

We assessed the effects of total enteral nutrition with long-chain triacylglycerides (LCT), medium-chain triacylglycerides (MCT), or two structured lipids, modified dairy fat (MDF) and modified MCT (Captex 810B, Capital City Products, Columbus, OH), on protein and energy metabolism in hypermetabolic burned rats (25% to 30% body surface area). Male Sprague-Dawley rats (200 +/- 10 g) were continuously gastrostomy-fed isovolemic diets that provided 50 kcal/d, 2 g amino acids/d and 40% nonprotein calories as lipid for three days. Changes in body weight, nitrogen balance, serum albumin, indirect calorimetry, whole body leucine kinetics, and rectus muscle and liver protein kinetics were determined. Whole body leucine kinetics and tissue fractional protein synthetic rates (FSR, percent per day) were estimated using a four-hour constant intravenous infusion of L-[1-14C]leucine on day 3. The group of rats enterally fed MDF lost less body weight than the other groups (P less than or equal to .05). MDF and Captex 810B produced a positive and significantly greater (P less than or equal to .05) daily and cumulative nitrogen balance than either LCT or MCT. Oxygen consumption (P less than or equal to .05) and total energy expenditure (P less than or equal to .05) were elevated approximately 22% with MDF as compared with LCT or MCT. Rectus muscle FSR and absolute rate of protein synthesis were increased 19% with MDF (P less than or equal to .05) as compared with LCT or MCT.(ABSTRACT TRUNCATED AT 250 WORDS)

Thermogenesis from intravenous medium-chain triglycerides.

Eighteen hospitalized patients dependent on total parenteral nutrition (TPN) were randomly enrolled into a prospective study comparing intravenous long-chain triglycerides (LCT) with a physical mixture of 75% medium-chain triglycerides (MCT) and 25% LCT. The TPN was given continuously as amino acids and glucose over 5 days with the respective lipid emulsion given intermittently during each day for 10 hr. Indirect calorimetry was measured on each patient before the lipid emulsion was administered in the morning and again 10 hr later near the end of the lipid infusion, on days 1, 3, and 5. Resting energy expenditure, VO2, VCO2, and calculated fat oxidation were shown to increase during MCT infusion but not during LCT administration, (resting energy expenditure 899 +/- 37 to 1085 +/- 40, compared with 978 +/- 23 to 976 +/- 39, kcal/m2 body surface area [BSA]/day, respectively, p less than 0.0002; VO2: 129.9 +/- 5.2 to 157.2 +/- 5.9, compared with 140.9 +/- 3.6 to 141.2 +/- 5.9 ml O2/min/m2 BSA, respectively, p less than 0.0005; and VCO2: 110.7 +/- 4.4 to 127.5 +/- 4.3, compared with 118.3 +/- 2.8 to 118.0 +/- 5.3, ml CO2/min/m2 BSA, respectively, p less than 0.0076; calculated fat oxidation 10.7 +/- 1.5 to 19.3 +/- 2.4, compared with 20.0 +/- 2.7 to 20.0 +/- 3.6, kcal/m2 BSA/hr, respectively, p less than 0.014). Respiratory quotient tended to fall with lipid infusion but did not change statistically. Body temperatures were unaltered by either fat infusion. It is concluded that TPN consisting of MCT causes an increased thermogenesis, most likely through increased fat oxidation, reflective of MCTs property as an obligate fuel. The increased thermogenesis occurs without an increase in body temperature.

Medium chain triglycerides and structured lipids as unique nonglucose energy sources in hyperalimentation

This brief review will discuss recent work concerning new intravenous lipid emulsions for future use in clinical patients. Intravenous lipid emulsions currently available in the United States are derived from soybean or safflower oils and serve as sources of nonglucose, nitrogen-sparing calories and the essential fatty acid linoleic acid. Because of concerns that much of the infused long chain triglyceride is not oxidized readily and that there may be some immune system impairment, newer emulsions utilizing medium chain triglycerides have been developed.