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

Effects of parenteral lipid emulsions with different fatty acid composition on immune cell functions in vitro

BACKGROUND

Numerous studies suggest that immune function may be compromised by lipid emulsions rich in polyunsaturated fatty acids (PUFAs). In our study, we compared the effect of a new olive oil-based lipid emulsion (ClinOleic) containing a moderate level of PUFAs, with emulsions based on soybean oil (Intralipid or Ivelip), on immune functions of human cell in vitro.

METHODS

Peripheral white blood cells were collected from healthy volunteers. Lymphocyte proliferation was evaluated by [3H]-thymidine incorporation after stimulation with either phytohemagglutinin (PHA) or antibodies against T-cell specific antigens. Lymphocytes subsets and T-cell activation markers (CD25 and HLA-DR) were measured by flow cytometry. The release of cytokines (interleukin [IL]-2, IL-1beta, and tumor necrosis factor-alpha [TNF-alpha]) was measured by enzyme-linked immunosorbent assay (ELISA), after lymphocytes or monocytes/macrophages stimulation with PHA or lipopolysaccharide (LPS).

RESULTS

A significant dose-dependent inhibition of thymidine incorporation was observed with Intralipid and Ivelip (incorporation down to 39.9% of control, p < .001) whereas ClinOleic showed no inhibitory effect. Activation antigen expression on both CD4+ and CD8+ T-cells tended to decrease with Intralipid (CD25: -53.4% on CD4+ and -57.4% on CD8+; HLA-DR: -61.5% on CD4+ and -58.5% on CD8+) but not with ClinOleic (from -2.9% for CD25 on CD4+ to 16.7% for HLA-DR on CD4+). Intralipid decreased significantly IL-2 production (-39.0%, p < .05) whereas ClinOleic had little effect (-13.0%, NS). Intralipid and ClinOleic tended to inhibit to a similar extent the release of pro-inflammatory cytokines (TNF-alpha: -21.5% and -34.8%, IL-1beta: -45.1% and -40.3%; respectively).

CONCLUSIONS

Our results suggest that an olive oil-based lipid emulsion could modulate immune response selectively, maintaining protective immunity and reducing inflammatory response. Olive oil may offer an immunologically neutral alternative to soybean oil for use in parenteral lipid emulsions.

Insulin-like growth factor-I enhances immune response in dexamethasone-treated or surgically stressed rats maintained with total parenteral nutrition

BACKGROUND

New evidence suggests that insulin-like growth factor-I (IGF-I) is an important regulator of immune response. Our objective was to determine the effects of IGF-I on immune response during total parenteral nutrition (TPN) using two stress models.

METHODS

Male, Sprague-Dawley rats (230 to 250 g) were given TPN with or without coinfusion of recombinant human IGF-I (800 micrograms/d for 6 days) and subjected to either dexamethasone, a synthetic glucocorticoid, or surgical stress, in the form of a midline abdominal incision. In the dexamethasone model, immune response was assessed by total cellularity of the thymus and spleen, in vitro assays of lymphocyte proliferation, and interleukin 6 (IL-6) production, and concentrations of IL-6 and tumor necrosis factor alpha (TNF-alpha) in serum. In the surgical model, flow cytometry was used to identify and quantify splenic populations of T and B lymphocytes and macrophages.

RESULTS

In rats immunosuppressed by dexamethasone, IGF-I infusion increased mitogen-induced proliferation of thymocytes, but did not alter cellularity in the thymus; enhanced proliferation and IL-6 production in peripheral blood mononuclear cells following treatment with concanavalin A or lipopolysaccharide; and reduced the serum concentration of IL-6, but not TNF-alpha. In surgically stressed rats, IGF-I infusion restored the splenic populations of immature and mature B lymphocytes, which were decreased by TPN.

CONCLUSIONS

our data demonstrate that IGF-1 enhances immune response during TPN in rats.

Effects of propofol and Intralipid on immune response and prostaglandin E2 production

The present study evaluated the effects of propofol and its solvent Intralipid on the immune response and in vivo prostaglandin E2 production in patients during induction of anaesthesia and in healthy volunteers after Intralipid injection. Fifteen female patients (median age 48 years, ASA 1-2) scheduled for uterine dilatation and curettage were randomly assigned to two groups. In group 1 propofol (median dose 3.1 mg.kg-1) and in group 2 thiopentone (median dose 6.0 mg.kg-1) were injected intravenously over 60 s. Surgery was started after collection of the last blood sample. In the second part of this study, Intralipid 10% 0.3 ml.kg-1 was injected intravenously in eight healthy volunteers (four women and four men, median age 32 years) over 60 s. Plasma bicyclo-PGE2 concentrations increased during anaesthesia induction in both anaesthetic groups (p < 0.01). By contrast, no changes were seen in plasma bicyclo-PGE2 concentrations after Intralipid injection in volunteers. Lymphocyte proliferative responses to mitogens did not change during anaesthesia induction in patients. In volunteers, Intralipid injection caused a slight increase in T-cell percentages (p < 0.01) and unstimulated lymphocyte proliferative responses (p < 0.05), but it did not affect other lymphocyte subsets and immunoglobulin production. Intralipid and propofol were not found to be immunosuppressive at clinical doses used during anaesthesia induction.

Activated CD4+ T cells preferentially take up lipid microspheres, but resting cells do not

Lipid microspheres (LM) used as drug carriers increase the effectiveness and reduce the toxicity of incorporated drugs. The present study is designed to determine whether or not activated T lymphocytes, which were the cells chosen first from the 'inflammatory cells', can take up LM in vitro. LM were labelled with a fluorescent probe, DiI (DiI-LM), to examine the kinetics. Flow cytometric analysis demonstrated that in freshly isolated peripheral blood mononuclear cells (PBMC), monocytes principally took up DiI-LM, while lymphocytes and granulocytes did not. When PBMC were stimulated with immobilized anti-CD3 MoAb and IL-2, cells expressing CD3, CD4, CD8 and CD16 incorporated DiI-LM. Purified CD4+ T cells, obtained by positive panning selection, were stimulated with this system. They were CD25, CD71, LFA-1-positive, and also showed an ability to take up DiI-LM, which resting cells did not. The findings were confirmed by flow cytometry and quantitative analysis of DiI. Confocal micrographs showed fluorescent granules from the probe in the cytoplasm of stimulated CD4+ T cells after incubation with DiI-LM. These results suggest that immunomodulatory agents incorporated into LM might selectively regulate the function of CD4+ or CD8+ T cells when these are activated.

Nutritional support in critically ill patients

OBJECTIVE

The author reviews the newer nutritional substrates in use or under investigation for enteral and parenteral nutrition. Management of the critically ill patient remains a significant challenge to clinicians, and it is hoped that dietary manipulations, such as those outlined, may augment host barriers and immune function and improve survival.

SUMMARY BACKGROUND DATA

The role of nutrition in patient well-being has long been recognized, but until the past 25 years, the technology to artificially provide nutrients when patients could not eat was not developed. With current, new methods for enteral and vascular access, patients can be fed nonvolitionally with little difficulty. Continued efforts have been directed toward identifying optimal feeding formulations, which have resulted in a multitude of commercially available products. In the past several years, attention has been turned to evaluation of four specialized nutrients and the use of other substrates as pharmacologic agents.

METHODS

Pertinent laboratory and clinical data were reviewed to present the pros and cons for each nutritive substrate.

CONCLUSIONS

Medium-chain fatty acids, branched-chain amino acids, and glutamine have been shown to be of clinical benefit and should be in common use in the near future. Short-chain fatty acids still are under investigation. Albumin, vitamins E and C, arginine, glutamine, and omega-3 fatty acids show great promise as pharmacologic agents to manipulate the stress response. Nucleotides remain investigational. CONTENTS SUMMARY: The application of some new nutritional substrates for use in critically ill patients, both as caloric sources and as pharmacologic agents, are reviewed.

Nutrition care of patients with acute and chronic respiratory failure

Nutrition is intimately linked to pulmonary function and an understanding of these relationships have therapeutic utility. Malnutrition is known to be associated with impaired mechanical function of the lung in both chronic and acute respiratory insufficiency. Refeeding results in improvement in functional characteristics and may be critical in the weaning of patients from mechanical ventilation. In contrast, overfeeding may result in an increased ventilatory demand resulting in the inability to wean from respiratory support. This article considers the background as well as recommendations for the nutritional care of patients with acute and chronic respiratory failure.

Propofol infusion anaesthesia and immune response in minor surgery

This study was set up to evaluate the effects of propofol infusion anaesthesia on immunological function in minor surgery. Twenty-seven patients (median age 51 years, ASA 1-2) scheduled for minor breast surgery were randomly assigned to two groups. Anaesthesia was induced in group 1 with propofol 2.5 mg.kg-1 and maintained with propofol 12 mg.kg-1 x h-1 and 30% O2 in air, whereas in group 2 anaesthesia was induced with thiopentone 4 mg.kg-1 and maintained with 70% N2O in O2. Fentanyl and vecuronium were used in both groups. The percentages of T cells (p < 0.001), B cells (p < 0.01) and memory T cells increased (p < 0.01) in both groups. T helper cell percentages increased in the propofol but not in the thiopentone group (p < 0.05). The percentages of natural killer cells decreased from pre-induction values in both groups (p < 0.001). No changes were seen in lymphocyte proliferative responses. Minor breast surgery under propofol or conventional combined anaesthesia had only minor effects on the immune response. The higher percentage of T helper cells after propofol anaesthesia compared to conventional combined anaesthesia is beneficial, but its clinical importance remains to be determined.

Propofol emulsion reduces proliferative responses of lymphocytes from intensive care patients

OBJECTIVE

To test propofol lipid emulsion formulation for its immunosuppressive effects.

DESIGN

Propofol lipid emulsion and the emulsion alone were tested at increasing concentrations and compared to initial values and between each other. Propofol alone could not be tested due to its insolubility into the culture medium.

PATIENTS AND PARTICIPANTS

Lymphocytes from 12 surgical intensive care (ICU) patients (median APACHE score 16 and median TISS score 28) and 12 healthy volunteers.

MEASUREMENTS

Phytohaemagglutinin-, concanavalin A- and pokeweed mitogen-induced lymphocyte proliferative responses were measured in the presence of increasing concentrations of propofol lipid emulsion formulation or the lipid emulsion.

RESULTS

Lymphocyte proliferative responses from ICU patients were in general on a lower level than in the volunteers. The propofol lipid emulsion formulation (Diprivan) decreased pokeweed mitogen-induced proliferative responses of lymphocytes from ICU patients at propofol concentrations found in the circulation (1-10 micrograms/ml) and the lipid emulsion alon at 100 micrograms/ml triglyceride concentrations while the other mitogen-induced responses were not affected. No changes were observed in the mitogen-induced responses of lymphocytes from healthy volunteers.

CONCLUSIONS

Propofol emulsion formulation decreased in surgical intensive care patients pokeweed mitogen-induced lymphocytic responses in vitro at clinically found concentrations, indicating the need for further studies to test B-lymphocyte functions and T-B-lymphocyte co-operation during propofol lipid emulsion administration. (ICU) patients is widespread because of its good control of sedation. Propofol is currently administered in fat emulsion which is considered immunosuppressive during bolus injection or rapid infusion. Therefore, effects of a propofol fat emulsion formulation on proliferative responses of lymphocytes were studied in blood samples obtained from healthy volunteers and ICU patients known to be immunosuppressed.

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.