Effect of emulsions of medium and long chain triglyceride on human adipose tissue prostaglandin production in vitro

The biological actions of prostanoids in adipose tissue in physiological and pathophysiological conditions

Adipose tissue has been established as an endocrine organ that plays an important role in maintaining metabolic homeostasis. Adipose tissue releases several bioactive molecules called adipokines. Inflammation, dysregulation of adipokine synthesis, and secretion are observed in obesity and related diseases and cause adipose tissue dysfunction. Prostanoids, belonging to the eicosanoid family of lipid mediators, can be synthesized in adipose tissue and play a critical role in adipose tissue biology. In this review, we summarized the current knowledge regarding the interaction of prostanoids with adipokines, the expression of prostanoid receptors, and prostanoid synthase enzymes in adipose tissues in health and disease. Furthermore, the involvement of prostanoids in the physiological function or dysfunction of adipose tissue including inflammation, lipolysis, adipogenesis, thermogenesis, browning of adipocytes, and vascular tone regulation was also discussed by examining studies using pharmacological approaches or genetically modified animals for prostanoid receptors/synthase enzymes. Overall, the present review provides a perspective on the evidence from literature regarding the biological effects of prostanoids in adipose tissue. Among prostanoids, prostaglandin E2 (PGE₂) is prominent in regards to its substantial role in both adipose tissue physiology and pathophysiology. Targeting prostanoids may serve as a potential therapeutic strategy for preventing or treating obesity and related diseases.

Eicosanoids and fat emulsions in acute respiratory distress syndrome patients

Lipid emulsions have been associated with changes in pulmonary function. Although these changes were related to the physical effects of the infusion-induced lipemia on gas exchange, several animal and human studies suggest that the impairment in pulmonary function observed with lipid infusions was mediated by prostaglandins. Prostaglandins are synthesized enzymatically from essential fatty acids. We studied the effects of two lipid emulsions, with different amounts of essential fatty acids (20% long-chain triacylglycerols [LCT] with 55% of linoleic acid and 7% of alpha linolenic acid in 100 g of emulsion, and a physical mixture of 20% medium-chain triacyglycerols [MCT] and LCT with 26% of linoleic acid and 4% of alpha linolenic acid in 100 g of emulsion), on plasma levels of eicosanoids in patients with acute respiratory distress syndrome (ARDS). Although in patients with ARDS, plasma levels of prostanoids were higher than the reference values, neither lipid emulsion, administered at the rate of 2 mg.kg-1.min-1 induced significant changes in the eicosanoids except for a decrease in systemic-pulmonary arterial 6-keto prostaglandin F1 alpha difference.

Selection of optimal lipid sources in enteral and parenteral nutrition

The manipulation of dietary fat intake can affect the response to disease, injury, and infection. These effects include enhancement or inhibition of immune function, altered susceptibility to cardiovascular disease, promotion or maintenance of gut integrity, and prevention of total parenteral nutrition-induced hepatic dysfunction. These effects may occur as a result of changes in the fatty acid composition of biomembranes or changes in concentrations of lipid moieties such as prostaglandins or leukotrienes. Those fats that have been shown to affect physiologic function include long-chain, medium-chain, and short-chain fatty acids and omega-3 and omega-6 fatty acids. Currently available enteral and parenteral products used for nutrition support contain widely varied amounts of these different fatty acids. Therefore, the selection of the most appropriate product or nutrition support regimen for an individual patient requires an understanding of the metabolism of these different fat substrates, their therapeutic indications, and the contraindications and controversies that surround their use. This article reviews these issues and also focuses on several alternate lipid sources such as short-chain fatty acids, medium-chain fatty acids, omega-3 fatty acids, and blended and structured lipids.

Effects of anaesthesia and surgery on the immune response

Alterations have been found to occur in every component of immune response during anaesthesia and surgery. These alterations represent the body's general physiological responses and are mainly dependent on the extent of surgery, as well as other factors such as the patient's age and health status, medication and blood transfusion. Anaesthetic and operative complications have profound effects on these responses. Basically, the immune response to anaesthesia and surgery is a beneficial reaction, needed in local host defences and wound healing and in preventing the body from making autoantibodies against its own tissues. The responses may, however, contribute to the development of postoperative infections and spread of malignant disease. During uncomplicated conventional surgery, the immune response usually passes clinically unnoticed without any harmful effects. Absent responses and excessively high responses, on the other hand, harm the patient. Our understanding of immunological phenomena and our possibilities of controlling mediator activation are now lagging behind the technical advances made in operative treatment. If we want to decrease operative morbidity and mortality to below their present levels, more attention should be directed to immune responses to major surgery, injuries and operative complications with massive mediator release which place the surgical patient at risk. Experimental evidence suggests that results of treatment in injured and operated patients can in the future be improved by controlling immune responses and their mediator systems. Our current level of knowledge of immune responses is already helping us to avoid many immune-mediated complications. However, routine interference with these responses is not indicated.

Inhibition of immunoglobulin synthesis in vitro by intravenous lipid emulsion (Intralipid)

Intravenous lipid emulsions depress lymphocyte proliferative responses and granulocyte function at concentrations found in the blood circulation during their administration. The effects of Intralipid, a widely used intravenous lipid emulsion, were measured on immunoglobulin production in vitro by pokeweed mitogen-activated lymphocytes as a test of B-cell function. Intralipid decreased IgG, IgM, and IgA production at soybean oil triglyceride concentrations of 2.5-20 mg/ml occurring in the blood circulation during Intralipid infusion. The effects on IgM and IgA production were highest and that on IgG production lowest. Hydrocortisone-sensitive and concanavalin A-inducible suppressor cells were more sensitive to Intralipid than other cell populations. In vivo Ig production may not be equally disturbed, inasmuch as Intralipid concentrations in the lymph nodes and the spleen may be lower than in the blood circulation. However, care should be taken to prevent Intralipid concentrations from becoming high enough to depress immune responses.