Employment of lipids in the measurement and modification of cellular, humoral, and immune responses

Susceptibility to fatty acid-induced β-cell dysfunction is enhanced in prediabetic diabetes-prone biobreeding rats: a potential link between β-cell lipotoxicity and islet inflammation

β-Cell lipotoxicity is thought to play an important role in the development of type 2 diabetes. However, no study has examined its role in type 1 diabetes, which could be clinically relevant for slow-onset type 1 diabetes. Reports of enhanced cytokine toxicity in fat-laden islets are consistent with the hypothesis that lipid and cytokine toxicity may be synergistic. Thus, β-cell lipotoxicity could be enhanced in models of autoimmune diabetes. To determine this, we examined the effects of prolonged free fatty acids elevation on β-cell secretory function in the prediabetic diabetes-prone BioBreeding (dp-BB) rat, its diabetes-resistant BioBreeding (dr-BB) control, and normal Wistar-Furth (WF) rats. Rats received a 48-h iv infusion of saline or Intralipid plus heparin (IH) (to elevate free fatty acid levels ~2-fold) followed by hyperglycemic clamp or islet secretion studies ex vivo. IH significantly decreased β-cell function, assessed both by the disposition index (insulin secretion corrected for IH-induced insulin resistance) and in isolated islets, in dp-BB, but not in dr-BB or WF, rats, and the effect of IH was inhibited by the antioxidant N-acetylcysteine. Furthermore, IH significantly increased islet cytokine mRNA and plasma cytokine levels (monocyte chemoattractant protein-1 and IL-10) in dp-BB, but not in dr-BB or WF, rats. All dp-BB rats had mononuclear infiltration of islets, which was absent in dr-BB and WF rats. In conclusion, the presence of insulitis was permissive for IH-induced β-cell dysfunction in the BB rat, which suggests a link between β-cell lipotoxicity and islet inflammation.

Oil-in-water lipid emulsions: implications for parenteral and ocular delivering systems

Lipid emulsions (LEs) are heterogenous dispersions of two immiscible liquids (oil-in-water or water-in-oil) and they are subjected to various instability processes like aggregation, flocculation, coalescence and hence eventual phase separation according to the second law of thermodynamics. However, the physical stability of the LE can substantially be improved with help of suitable emulsifiers that are capable of forming a mono- or multi-layer coating film around the dispersed liquid droplets in such a way to reduce interfacial tension or to increase droplet-droplet repulsion. Depending on the concentrations of these three components (oil-water-emulsifier) and the efficiency of the emulsification equipments used to reduce droplet size, the final LE may be in the form of oil-in-water (o/w), water-in-oil (w/o), micron, submicron and double or multiple emulsions (o/w/o and w/o/w). The o/w type LEs (LE) are colloidal drug carriers, which have various therapeutic applications. As an intravenous delivery system it incorporates lipophilic water non-soluble drugs, stabilize drugs that tend to undergo hydrolysis and reduce side effects of various potent drugs. When the LE is used as an ocular delivery systems they increase local bioavailability, sustain the pharmacological effect of drugs and decrease systemic side effects of the drugs. Thus, the rationale of using LE as an integral part of effective treatment is clear. Following administration of LE through these routes, the biofate of LE associated bioactive molecules are somehow related to the vehicles disposition kinetics inside blood or eyeball. However, the LE is not devoid from undergoing various bio-process while exerting their efficacious actions. The purpose of this review is therefore to give an implication of LE for parenteral and ocular delivering systems.

Lipid and lipid-free total parenteral nutrition: differential effects on macrophage phagocytosis in rats

Lipid emulsions provided with total parenteral nutrition (TPN) have been associated with mononuclear phagocytic system functional changes. The aim of the present investigation was to assess the influence of TPN with added lipid emulsions on macrophage (M phi) phagocytosis. Wistar rats (n = 70) with external jugular vein cannulation were randomized into seven groups. The rats received an oral diet or six different isocaloric (1.16 kcal/mL), isonitrogenous (1.5 g/mL), and isolipidic (30% non-protein calories) TPN regimens: (a) an oral diet with intravenous infusion of saline (OS); (b) non-lipid TPN (glucose); (c) TPN with 10% long chain triacylglycerol emulsions (LCT); (d) TPN with 90% LCT and 10% fish oil (FO) emulsion; (e) TPN with 50% LCT and 50% FO; (f) TPN with 10% lipid emulsion with 50% medium chain triacylglycerol (MCT) and 50% LCT; and (g) TPN with 45% MCT, 45% LCT, and 10% FO. After 96 h of TPN or saline infusion, colloidal carbon (Pelikan, Germany) was injected intravenously at 1.0 mL/kg body weight, and the rats were killed after 3 h. Liver, spleen, and lung were weighed and prepared by immunohistochemistry analyses with the HAM-56 anti-M phi antibody. Under light microscopy, the total M phi number (MT) and the colloidal carbon phagocytic M phi number (MP) were established, and the phagocytic index was calculated as MP/MT x 100. There were no statistical (P < 0.05) differences in liver, spleen, or lung weights among the seven groups in comparison with the OS group. Non-lipid TPN inhibited spleen and lung M phi phagocytosis when compared with the OS and lipid-TPN groups. Lipid TPN supplemented with fish oil emulsion increased total liver and lung M phi number and phagocytosis. These results indicate that TPN supplemented with fish oil increases M phi phagocytosis in rats.

Effect of total parenteral nutrition with different lipid emulsions of human monocyte and neutrophil functions

Parenteral nutrition (TPN) with lipid emulsions is claimed to be associated with impaired monocyte (M) and neutrophil (N) functions. Long-chain triglycerides (LCT) and a mixture containing 50% medium-chain triglycerides (MCT) and 50% LCT, currently used in nutritional therapy with TPN, were evaluated for their ex vivo effects on human N and M chemotaxis, phagocytosis, bacterial killing, and oxidative metabolism by nitroblue tetrazolium reduction test. Cell functions were examined in a randomized, crossover, blind trial in 10 malnourished patients with gastric cancer. Prior to the operation (2 wk), central TPN (40 kcal/kg) with 25% of caloric energy provided as LCT or MCT/LCT emulsion was infused over 48 h. After the crossover period fat-free TPN was given over 48 h. Function tests were done for N and M before and after each lipid emulsion infusion. Every cell function test performed for each patient was controlled by another test done in healthy adult volunteers and the results were compared with the normal range of values previously established for a healthy adult population. All the patients completed the studies without complications. Crossover validity was statistically established. Bacterial killing was the only function reduced in neutrophils after LCT emulsion (% killed bacteria = 79.0 +/- 8.5 versus 67.4 +/- 19.2; P < 0.05), although this function remained within the normal range values in 80% of the patients. In conclusion, the lipid emulsions did not affect any monocyte functions and only moderately decreased neutrophil bacterial killing.

Selective suppression of endothelial cell activation by arachidonic acid

Endothelial cell (EC) activation plays a key role in inflammation, thrombosis and organ rejection. Normally, EC are in a quiescent state in which their function is to prevent coagulation and thrombosis, and to participate in the regulation of leukocyte migration from the bloodstream into the tissue. Upon activation with cytokines or other stimuli, EC up-regulate a number of genes, including E-selectin (ELAM-1), intercellular adhesion molecule (ICAM)-1, vascular cell adhesion molecule (VCAM)-1, interleukin (IL)-1, IL-8, tissue factor (TF), plasminogen activator inhibitor-1 (PAI-1), MCP-1 (monocyte chemoattractant protein-1) and endothelial cell inducible gene (ECI-6). Arachidonic acid (AA) is produced by several cell types, including EC, and acts on various cells. We report here that AA inhibits the up-regulation of some, but not all genes that are induced with EC activation in a dose-dependent manner. AA suppresses TNF-alpha, IL-1 alpha, LPS or PMA-induced E-selectin expression, as well as mRNA accumulation of E-selectin, ICAM-1 and IL-8 stimulated by TNF-alpha. The inhibition appears to be at the level of transcription. At the same time under the same conditions AA does not, repress mRNA accumulation for PAI-1, ECI-6, MCP-1 and VCAM-1. We suggest that the induced expression of AA with EC activation may result in a negative feedback loop regulating further activation.

Influence of medium-chain triglyceride-based lipid emulsion on rat polymorphonuclear cell functions

Intravenous lipid emulsions are used as energy and essential fatty acids sources. There are controversial reports postulating in vitro and in vivo inhibitory effects of long-chain triglycerides (LCT) upon the blood polymorphonuclear leukocytes (PMNL) functions. In the present study the in vivo and in vitro effects of LCT and a physical mixture of medium- and long-chain triglycerides (MCT/LCT) emulsions were investigated on select PMNL functions, i.e., chemotaxis, phagocytosis, and bacterial killing. Blood from 20 rats was incubated with LCT, MCT, MCT/LCT, and saline, respectively. MCT-containing emulsions exhibited an inhibitory effect on all PMNL functions investigated, whereas LCT exerted an effect on the phagocytic index only. The administration of a parenteral supply of LCT, MCT/LCT, and saline for 30 h followed by saline infusion for 14 h in discontinuous mode did not influence any of the investigated PMNL functions. Similarly, continuous infusion over 44 h at increasing infusion rates up to 1.5 mL/h did not affect the PMNL functions. The obvious difference between in vitro and in vivo response of the PMNL model emphasizes the necessity for continuous monitoring of in vivo conditions. Appropriate interpretation of the data requires continuous circumspection and consideration of trials in a clinical setting.

The effect of increasing levels of fish oil-containing structured triglycerides on protein metabolism in parenterally fed rats stressed by burn plus endotoxin

This report investigates the effect of various levels of medium-chain/fish oil structured triglycerides on protein and energy metabolism in hypermetabolic rats. Male Sprague-Dawley rats (192 to 226 g) were continuously infused with isovolemic diets that provided 200 kcal/kg per day and 2 g of amino acid nitrogen per kilogram per day. The percentage of nonnitrogen calories as structured triglyceride was varied: no fat, 5%, 15%, or 30%. A 30% long-chain triglyceride diet was also provided as a control to compare the protein-sparing abilities of these two types of fat. Nitrogen excretion, plasma albumin, plasma triglycerides, and whole-body and liver and muscle protein kinetics were determined after 3 days of feeding. Whole-body protein breakdown, flux, and oxidation were similar in all groups. The 15% structured triglyceride diet maximized whole-body protein synthesis (p < .05). Liver fractional synthetic rate was significantly greater in animals receiving 5% of nonprotein calories as structured triglyceride (p < .05). Muscle fractional synthetic rate was unchanged. Plasma triglycerides were markedly elevated in the 30% structured triglyceride-fed rats. The 30% structured triglyceride diet maintained plasma albumin levels better than those diets containing no fat, 5% medium-chain triglyceride/fish oil structured triglyceride, or 30% long-chain triglycerides. Nitrogen excretion was lower in animals receiving 30% of nonnitrogen calories as a structured triglyceride than in those receiving 30% as long-chain triglycerides, but this difference did not reach statistical significance (p = .1). These data suggest that protein metabolism is optimized when structured triglyceride is provided at relatively low dietary fat intakes.

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.

The effect of a high fat diet on the incidence of colonic cancer after cholecystectomy in mice

An experimental study was designed to evaluate the effects of both a high fat diet and a cholecystectomy on the incidence of carcinogen-induced colon cancer in mice. Sixty pink-eyed jax (P/J) mice were divided equally into two groups. One group was fed a standard rodent diet and the other group received a diet supplemented with 20% corn oil. From each diet group, 50% of the mice had a cholecystectomy and the other 50% had a sham operation. Two weeks after surgery, each mouse received weekly subcutaneous injections of a carcinogen (dimethylhydrazine, 20 mg/kg) for 12 weeks. After the treatment period, the mice were killed and their large bowels were examined. Evaluation of the results demonstrated that the mice that had a cholecystectomy and a high fat diet had the highest incidence (P less than 0.05) of colonic adenocarcinomas.

E-rosette formation, total T-cells, and lymphocyte transformation in infants receiving intravenous safflower oil emulsion

There has been much concern about impaired immune function in children receiving infused lipid emulsions. Immunologic studies were carried out on 15 infants maintained on parenteral nutrition with intravenous safflower oil emulsion as part of the infusate. Significant increases in percentage rosette formation, total circulating T-cells, and mitogenesis to phytohemagglutinin and pokeweed mitogen were demonstrated after only 1 wk of lipid infusion. Additional parenteral nutrition did not further increase any immunologic parameter. These results suggest that infused safflower oil emulsion does not adversely alter cellular immune function.

Inhibition of lymphocyte capping by fatty acids in mouse and man

Lipid-enriched diets have been related to a high cancer incidence in experimental animals for many years, and more recently, to assorted defects on the immune response. We investigated the effect of incubating human or murine (C3H/HEJ) lymphocytes with saturated (16:0) and unsaturated (18:1, 18:2, 18:3, 20:4) fatty acids (12 micrograms for each 10(7) cells), on the ability to cap with antihuman or antimouse anti-IgM, mu-chain specific antibody. Capping was also tested in obese (ob/ob, C57BL/6J) mice. Capping at 30 and 60 min was reduced by fatty acid incubation to 10-30% of control values in humans (p less than .001), and to 30% of control values in mice (p less than .01), regardless of degree of unsaturation. ob/ob capped normally. A lymphocyte membrane effect caused by fatty acids is observed in these experiments. Whether this is related to the dysimmunity caused by lipid diets cannot be assessed from our data, especially since all fatty acids, regardless of unsaturation, reduced the capping phenomenon.

Phagocytosis of gelatin-latex particles by a murine macrophage line is dependent on fibronectin and heparin

It has been suggested that fibronectin plays a role in clearing particles from the circulation by promoting binding to phagocytes of the reticuloendothelial system. By use of a well-defined system to investigate the possible opsonic role of fibronectin, we have studied the uptake of gelatin-coated latex particles by a murine macrophage cell line (P388D1). Fibronectin promotes binding of gelatin-coated beads to these cells in both suspension and monolayer cultures. In both cases there is a requirement for heparin as a cofactor. Other glycosaminoglycans (chondroitin sulfates A and C, dermatan sulfate, and keratan sulfate) were inactive, whereas heparan sulfate was somewhat active. Proof that beads were actually endocytosed was obtained by electron microscopy, which showed beads internalized in membrane-bounded vesicles, and by immunofluorescence analyses, using antibodies to fibronectin to stain external beads. Two rapid assays for the opsonic activity of fibronectin were developed based on differential centrifugation of cell-associated beads and on the immunofluorescence procedure. Binding and endocytosis were time- and temperature-dependent and varied with the amount of gelatin on the beads and with the concentrations of fibronectin and heparin added, and could be inhibited by F(ab')2 antifibronectin. These studies provide a sound basis for a detailed analysis of the interaction of fibronectin with the cell surface and of its involvement in endocytosis.

The effect of phospholipid-containing surfactant from nickel exposed rabbits on pulmonary macrophages in vitro

Alveolar macrophages from 9 normal rabbits were incubated in vitro for 3 h with and without phospholipid-containing surfactant from nickel-treated ones. The macrophages treated with surfactant showed morphological and functional criteria of increased activity. The cell surface had many protrusions and the cytoplasma contained several lamellated structures. The oxidative metabolism, measured by the nitroblue tetrazolium (NBT)-test, at rest and after E. coli stimulation was increased, as was the attachment and ingestion of yeast particles. The NBT-values were about the same as corresponding values of macrophages lavaged from the lungs of nickel-treated rabbit. Macrophages incubated with surfactant from untreated animals, had NBT values and phagocytic activity similar to cells incubated without surfactant. As this substance was administered in excess, the difference in macrophage response would probably be due to a qualitative alteration of the surfactant after nickel exposure.

Fibronectin-mediated uptake of gelatin-coated latex particles by peritoneal macrophages

The present study demonstrates the ability of plasma fibronectin or cold-insoluble globulin (Clg) to promote the uptake of 125I-labeled, gelatin-coated latex beads (g-Ltx*) by monolayers of peritoneal macrophages (PM). The uptake of g-Ltx* by PM was enhanced by Clg in a concentration-dependent fashion and required the presence of heparin (10 U/ml) as an obligatory cofactor for maximal particle uptake. Treatment of PM monolayers with trypsin (1 mg/ml) for 15 min at 37 degrees C after particle uptake removed less than 15% of the radioactivity incorporated by the monolayers. However, a similar trypsin treatment of the monolayers before the addition of latex particles depressed Clg-dependent uptake by greater than 75%. Pretreatment of PM monolayers with inhibitors of glycolysis effectively reduced the Clg-dependent uptake of latex. Similarly, pretreatment of monolayers with either inhibitors of protein synthesis or agents that disrupt cytoskeletal elements also significantly depressed Clg-dependent particle uptake. Phagocytosis of g-Ltx* by PM in the presence of Clg and heparin was confirmed by electron microscopy. Finally, g-Ltx* could also be effectively opsonized with Clg at 37 degrees C before their addition to the monolayers. These studies suggest that the recognition of g-Ltx* in the presence of Clg required cell surface protein(s) and that subsequent phagocytosis of these particles by PM was energy dependent and required intact intracellular cytoskeleton elements. Thus, PM monolayers provide a suitable system for further studies on the function of Clg in the recognition and phagocytosis of gelatin-coated particles by phagocytic cells.

Human granulocyte and reticuloendothelial system function during intralipid infusion

In six patients, the phagocytic and catabolic functions of the RES (reticuloendothelial system), as measured by using 125I-microaggregated human serum albumin as a test substance, were not affected by Intralipid infusion. The nitroblue tetrazolium (NBT) reduction of granulocytes, the NBT reduction and the bacplasma, was significantly lower in eight patients during Intralipid infusion than before this treatment. When heat-killed E. coli were added for phagocytic stimulation in vitro, the same result was obtained only in the absence of plasma. The bactericidal capacity of granulocytes was significantly decreased in six patients during Intralipid infusion. When Intralipid was added in vitro to granulocytes, the NBT reduction, and the bactericidal capacity of these cells were decreased and the effect was mainly dose-dependent. Electron micrographs show that granulocytes phagocytize Intralipid. The loading of granulocytes with lipid particles may block the engulfment of bacteria and may be a reason for the decreased bactericidal capacity of these cells. An influence exerted by the lipid on the cell membrane is the most conceivable reason for the decreased NBT reduction.

The immunoregulatory role of cholesterol and other lipids: a hypothesis

Membrane lipids play an important role in cellular responses to exogenous signals. In immunocompetent lymphocytes, marked changes in the concentrations of membrane lipids occur following cell-antigen interaction. These changes lead to an increase in membrane fluidity, thus facilitating the microaggregation of receptor-antigen complexes. This event constitutes the inductive signal for lymphocytes. Lipid profile alterations leading to increased concentration of membrane cholesterol, of polyunsaturated lipids, or of both, bring about a decrease in membrane fluidity. The latter interferes with receptor displacement preventing delivery of an inductive signal to the responding cell. Interference with microaggregation is readily brought about in interactions involving low affinity antigens, such as tumoral antigens. We postulate that in hyperlipidemic and hypercholesterolemic states there is decreased immune responsiveness to weak antigens due to the aformentioned lipid profile alterations in the membranes of immunocompetent cells. The manner in which an increase in the concentration of the lipids mentioned can lead to decreased immune responsiveness and hence to an increased incidence of malignancies in hyperlipidemic and hypercholesterolemic states is the hypothesis presented in this paper.

Endotoxin clearance after intralipid infusion

Healthy 6-8-wk-old New Zealand white rabbits were injected with chromium-chloride- or sodium-chromate-labeled E. coli endotoxin after rapid infusion (10 ml/kg in 1 hr) or slow and repeated infusions (40 ml/kg daily for 7 consecutive days) of 10% Intralipid. Endotoxin clearance rates and RES organ uptakes were determined and the results were compared with those of the controls treated with correspondingly equal volumes of 5% D/W instead of fat. In the acute experiment, the clearance rates were similar in all animals during the first 15 min following endotoxin injection. After this phase, however, experimental animals had faster endotoxin clearance and eventually higher organ uptakes than the controls. In the chronic experiment, there was no significant difference in endotoxin clearance rates or total and per-gram organ uptakes between experimental and corresponding control animals infused with 5% D/W instead of fat. Experimental animals, particularly those having received multiple infusions of fat emulsion, showed deposition of polarizable brown pigment inside and outside the reticuloendothelial cells in the liver, spleen, and bone marrow. None of the controls had these pigments in their organs.