Lipoprotein metabolism during and after a 6-h infusion ofMCT/LCT vs LCT emulsion in man

Proinflammatory mediators in lipid emulsions and parenteral nutrition-associated liver disease: Review of leading factors

Lipid injectable emulsions have been in clinical use for over 60 years. The first product launched was Intralipid, which consisted of an emulsion of soybean oil in water for intravenous administration. It was a key source of essential fatty acids and an alternative source of energy for patients with gastrointestinal dysfunction requiring long-term parenteral nutrition. With clinical experience, a condition known as parenteral nutrition-associated liver disease (PNALD), or intestinal failure-associated liver disease (IFALD), was observed, with a focus on carbohydrate and fat energy. Modifying the daily doses and infusion rates had some salutary effects, but PNALD persisted. Subsequently, on closer inspection of the fatty acids profile and phytosterol concentrations, degradation products arising from chemical and physical stability issues of the available lipid injectable emulsions were implicated. Recently, the US Food and Drug Administration convened an online workshop entitled "The Role of Phytosterols in PNALD/IFALD," with an emphasis on (1) the multifactorial pathophysiology of PNALD/IFALD, (2) risk associated with phytosterols, and (3) regulatory history. The scope of this review includes the multifactorial pathophysiology of PNALD/IFALD as it relates to the pharmaceutical aspects of the various lipid injectable emulsions on the market, with respect to potential proinflammatory components, as well as physical and chemical stability issues that may also affect products' safe intravenous administration to patients.

Lipids in the intensive care unit: Recommendations from the ESPEN Expert Group

This article summarizes the presentations given at an ESPEN Workshop on "Lipids in the ICU" held in Tel Aviv, Israel in November 2014 and subsequent discussions and updates. Lipids are an important component of enteral and parenteral nutrition support and provide essential fatty acids, a concentrated source of calories and building blocks for cell membranes. Whilst linoleic acid-rich vegetable oil-based enteral and parenteral nutrition is still widely used, newer lipid components such as medium-chain triglycerides and olive oil are safe and well tolerated. Fish oil (FO)-enriched enteral and parenteral nutrition appears to be well tolerated and confers additional clinical benefits, particularly in surgical patients, due to its anti-inflammatory and immune-modulating effects. Whilst the evidence base is not conclusive, there appears to be a potential for FO-enriched nutrition, particularly administered peri-operatively, to reduce the rate of complications and intensive care unit (ICU) and hospital stay in surgical ICU patients. The evidence for FO-enriched nutrition in non-surgical ICU patients is less clear regarding its clinical benefits and additional, well-designed large-scale clinical trials need to be conducted in this area. The ESPEN Expert Group supports the use of olive oil and FO in nutrition support in surgical and non-surgical ICU patients but considers that further research is required to provide a more robust evidence base.

Immune function and leukocyte sequestration under the influence of parenteral lipid emulsions in healthy humans: a placebo-controlled crossover study

BACKGROUND

It remains unclear whether immune modulation by lipids contributes to the high risk of infectious complications that is associated with the use of parenteral nutrition. Although mixed long- and medium-chain triacylglycerol (LCT-MCT)-containing emulsions, but not pure LCT emulsions, activate neutrophils and impair crucial leukocyte functions in vitro, in vivo studies have failed to corroborate these findings.

OBJECTIVES

The present investigation was conducted to evaluate the effects of LCT and LCT-MCT on immune function in healthy humans and to assess whether the lack of in vivo effects results from sampling errors due to extravascular sequestration of activated neutrophils.

DESIGN

Saline, LCT-MCT, and LCT emulsions were administered intravenously for 4.5 h to 12 healthy volunteers in a randomized crossover design. Plasma triacylglycerol concentrations were clamped at a clinically relevant concentration of 3-5 mmol/L. Leukocyte population counts and neutrophil activation were assessed before and after infusion. Leukocyte sequestration was evaluated by monitoring the distribution of Technetium-99m-labeled autologous leukocytes during infusions.

RESULTS

Whereas LCT exerted no greater effects than did saline, LCT-MCT significantly decreased lymphocyte counts. However, no evidence for neutrophil activation was found with either lipid. Moreover, the clearance of radiolabeled leukocytes from the liver, spleen, and lungs was not altered by any lipid, which suggested that lipid emulsions do not induce leukocyte sequestration.

CONCLUSIONS

Short-term infusion of LCT-MCT (but not LCT) to healthy humans modulates leukocyte population counts but, in clear contrast with the in vitro situation, does not induce neutrophil activation. These disparate findings cannot be explained by MCT-induced leukocyte sequestration.

Clinical use of lipid emulsions

Substantial progress has been made in the understanding of the metabolism of intravenous lipid emulsions and the delivery of their various components to specific tissues or cells. Lipid emulsions should be considered not only as a means of providing energy substrates but also specific compounds that participate in the regulation of key metabolic functions. Such improved knowledge should find applications in the metabolic care of different types of patients.

Biochemical and ultra-structural reactions to parenteral nutrition with two different fat emulsions in rats

OBJECTIVE

To compare the effects on fat metabolism and Kupffer cell morphology by total parenteral nutrition (TPN) with two different fat emulsions.

DESIGN

Thirty-two male Sprague-Dawley rats, divided into three groups, were investigated. Rats fed orally were used as a reference group, and a group of rats receiving TPN with fat emulsions containing pure long-chain triglycerides (LCT) was compared to a group of rats receiving fat emulsions containing both long-chain triglycerides and medium-chain triglycerides (MCT/LCT). The TPN regimens were equicaloric and administered continuously via a jugular catheter for 10 days.

INTERVENTIONS

After suffocation, blood of the rats was collected for the determination of serum lipids. Epididymal fat and heart were collected for the analysis of lipoprotein lipase (LPL) activities, and liver specimens were saved for analyses of hepatic triglyceride concentration, as well as activities of hepatic lipase (HL) and lysosomal enzymes. Light and electron microscopy were used for examination of the Kupffer cell reaction.

RESULTS

Directly after termination of parenteral feeding, the levels of serum triglycerides and high density lipoprotein (HDL) triglycerides were higher in the MCT/LCT group than in the LCT group, while no differences concerning cholesterol and phospholipid concentrations were found. No significant difference in liver steatosis was found between the two TPN groups. Comparison of the TPN groups showed that the MCT/ LCT group had significantly decreased LPL activity in adipose tissue, while the LCT group had significantly increased LPL activity in the heart. The activity of HL was low in both groups, but significantly lower in the LCT group. Lipid accumulation and an increased number of lysosomes were found in all Kupffer cell when TPN with LCTemulsions was used. Moreover, TPN induced a pronounced increase in various liver lysosomal enzyme activities, but there was no notable difference between LCT and MCT/LCT effects.

CONCLUSIONS

Compared to treatment with pure LCTemulsions, treatment with MCT/LCT emulsions evoked weaker biochemical reactions in terms of lower activity of lipoprotein lipase in fat and heart together with higher serum and HDL triglyceride levels. Morphological signs of increased Kupffer cell activity such as the appearance of multiple lysosomes and fat vacuoles in the cytoplasm followed treatment with pure LCT emulsions. However, both TPN groups showed a marked increase in activities of liver lysosomal enzymes.