Phosphatidylcholine participates in the interaction between macrophages and lymphocytes

Immune Implications of Cholesterol-Containing Lipid Nanoparticles

The majority of clinically approved nanoparticle-mediated therapeutics are lipid nanoparticles (LNPs), and most of these LNPs are liposomes containing cholesterol. LNP formulations significantly alter the drug pharmacokinetics (PK) due to the propensity of nanoparticles for uptake by macrophages. In addition to readily engulfing LNPs, the high expression of cholesterol hydroxylases and reactive oxygen species (ROS) in macrophages suggests that they will readily produce oxysterols from LNP-associated cholesterol. Oxysterols are a heterogeneous group of cholesterol oxidation products that have potent immune modulatory effects. Oxysterols are implicated in the pathogenesis of atherosclerosis and certain malignancies; they have also been found in commercial liposome preparations. Yet, the in vivo metabolic fate of LNP-associated cholesterol remains unclear. We review herein the mechanisms of cellular uptake, trafficking, metabolism, and immune modulation of endogenous nanometer-sized cholesterol particles (i.e., lipoproteins) that are also relevant for cholesterol-containing nanoparticles. We believe that it would be imperative to better understand the in vivo metabolic fate of LNP-associated cholesterol and the immune implications for LNP-therapeutics. We highlight critical knowledge gaps that we believe need to be addressed in order to develop safer and more efficacious lipid nanoparticle delivery systems.

Rapid visualization of PD-L1 expression level in glioblastoma immune microenvironment via machine learning cascade-based Raman histopathology

INTRODUCTION

Combination immunotherapy holds promise for improving survival in responsive glioblastoma (GBM) patients. Programmed death-ligand 1 (PD-L1) expression in immune microenvironment (IME) is the most important predictive biomarker for immunotherapy. Due to the heterogeneous distribution of PD-L1, post-operative histopathology fails to accurately capture its expression in residual tumors, making intra-operative diagnosis crucial for GBM treatment strategies. However, the current methods for evaluating the expression of PD-L1 are still time-consuming.

OBJECTIVE

To overcome the PD-L1 heterogeneity and enable rapid, accurate, and label-free imaging of PD-L1 expression level in GBM IME at the tissue level.

METHODS

We proposed a novel intra-operative diagnostic method, Machine Learning Cascade (MLC)-based Raman histopathology, which uses a coordinate localization system (CLS), hierarchical clustering analysis (HCA), support vector machine (SVM), and similarity analysis (SA). This method enables visualization of PD-L1 expression in glioma cells, CD8+ T cells, macrophages, and normal cells in addition to the tumor/normal boundary. The study quantified PD-L1 expression levels using the tumor proportion, combined positive, and cellular composition scores (TPS, CPS, and CCS, respectively) based on Raman data. Furthermore, the association between Raman spectral features and biomolecules was examined biochemically.

RESULTS

The entire process from signal collection to visualization could be completed within 30 min. In an orthotopic glioma mouse model, the MLC-based Raman histopathology demonstrated a high average accuracy (0.990) for identifying different cells and exhibited strong concordance with multiplex immunofluorescence (84.31 %) and traditional pathologists' scoring (R2 ≥ 0.9). Moreover, the peak intensities at 837 and 874 cm-1 showed a positive linear correlation with PD-L1 expression level.

CONCLUSIONS

This study introduced a new and extendable diagnostic method to achieve rapid and accurate visualization of PD-L1 expression in GBM IMB at the tissular level, leading to great potential in GBM intraoperative diagnosis for guiding surgery and post-operative immunotherapy.

Phosphatidylcholine-Derived Lipid Mediators: The Crosstalk Between Cancer Cells and Immune Cells

To become resistant, cancer cells need to activate and maintain molecular defense mechanisms that depend on an energy trade-off between resistance and essential functions. Metabolic reprogramming has been shown to fuel cell growth and contribute to cancer drug resistance. Recently, changes in lipid metabolism have emerged as an important driver of resistance to anticancer agents. In this review, we highlight the role of choline metabolism with a focus on the phosphatidylcholine cycle in the regulation of resistance to therapy. We analyze the contribution of phosphatidylcholine and its metabolites to intracellular processes of cancer cells, both as the major cell membrane constituents and source of energy. We further extended our discussion about the role of phosphatidylcholine-derived lipid mediators in cellular communication between cancer and immune cells within the tumor microenvironment, as well as their pivotal role in the immune regulation of therapeutic failure. Changes in phosphatidylcholine metabolism are part of an adaptive program activated in response to stress conditions that contribute to cancer therapy resistance and open therapeutic opportunities for treating drug-resistant cancers.

HBsAg, Subviral Particles, and Their Clearance in Establishing a Functional Cure of Chronic Hepatitis B Virus Infection

In diverse viral infections, the production of excess viral particles containing only viral glycoproteins (subviral particles or SVP) is commonly observed and is a commonly evolved mechanism for immune evasion. In hepatitis B virus (HBV) infection, spherical particles contain the hepatitis B surface antigen, outnumber infectious virus 10 000-100 000 to 1, and have diverse inhibitory effects on the innate and adaptive immune response, playing a major role in the chronic nature of HBV infection. The current goal of therapies in development for HBV infection is a clinical outcome called functional cure, which signals a persistent and effective immune control of the infection. Although removal of spherical SVP (and the HBsAg they carry) is an important milestone in achieving functional cure, this outcome is rarely achieved with current therapies due to distinct mechanisms for assembly, secretion, and persistence of SVP, which are poorly targeted by direct acting antivirals or immunotherapies. In this Review, the current understanding of the distinct mechanisms involved in the production and persistence of spherical SVP in chronic HBV infection and their immunoinhibitory activity will be reviewed as well as current therapies in development with the goal of clearing spherical SVP and achieving functional cure.

Enhanced lipid biosynthesis in human tumor-induced macrophages contributes to their protumoral characteristics

Background

Tumor-associated macrophages (TAMs) are key components of the tumor microenvironment (TME) in non-medullary thyroid carcinoma (TC) and neuroblastoma (NB), being associated with a poor prognosis for patients. However, little is known about how tumors steer the specific metabolic phenotype and function of TAMs.

Methods

In a human coculture model, transcriptome, metabolome and lipidome analysis were performed on TC-induced and NB-induced macrophages. The metabolic shift was correlated to functional readouts, such as cytokine production and reactive oxygen species (ROS) production, including pharmacological inhibition of metabolic pathways.

Results

Based on transcriptome and metabolome analysis, we observed a strong upregulation of lipid biosynthesis pathways in TAMs. Subsequently, lipidome analysis revealed that tumor-induced macrophages have an increased total lipid content and enriched levels of intracellular lipids, especially phosphoglycerides and sphingomyelins. Strikingly, this metabolic shift in lipid synthesis contributes to their protumoral functional characteristics: blocking key enzymes of lipid biosynthesis in the tumor-induced macrophages reversed the increased inflammatory cytokines and the capacity to produce ROS, two well-known protumoral factors in the TME.

Conclusions

Taken together, our data show that tumor cells can stimulate lipid biosynthesis in macrophages to induce protumoral cytokine and ROS responses and advocate lipid biosynthesis as a potential therapeutic target to reprogram the TME.

A past and present overview of macrophage metabolism and functional outcomes

In 1986 and 1987, Philip Newsholme et al. reported macrophages utilize glutamine, as well as glucose, at high rates. These authors measured key enzyme activities and consumption and production levels of metabolites in incubated or cultured macrophages isolated from the mouse or rat intraperitoneal cavity. Metabolic pathways essential for macrophage function were then determined. Macrophages utilize glucose to generate (i) ATP in the pathways of glycolysis and mitochondrial oxidative phosphorylation, (ii) glycerol 3-phosphate for the synthesis of phospholipids and triacylglycerols, (iii) NADPH for the production of reactive oxygen species (ROS) and (iv) ribose for the synthesis of RNA and subsequently production and secretion of protein mediators (e.g. cytokines). Glutamine plays an essential role in macrophage metabolism and function, as it is required for energy production but also provides nitrogen for synthesis of purines, pyrimidines and thus RNA. Macrophages also utilize fatty acids for both energy production in the mitochondria and lipid synthesis essential to plasma membrane turnover and lipid meditator production. Recent studies utilizing metabolomic approaches, transcriptional and metabolite tracking technologies have detailed mitochondrial release of tricarboxylic acid (TCA) intermediates (e.g. citrate and succinate) to the cytosol, which then regulate pro-inflammatory responses. Macrophages can reprogramme their metabolism and function according to environmental conditions and stimuli in order to polarize phenotype so generating pro- or anti-inflammatory cells. Changes in macrophage metabolism result in modified function/phenotype and vice versa. The plasticity of macrophage metabolism allows the cell to quickly respond to changes in environmental conditions such as those induced by hormones and/or inflammation. A past and present overview of macrophage metabolism and impact of endocrine regulation and the relevance to human disease are described in this review.

The Antiinfective Effects of Velvet Antler of Formosan Sambar Deer (Cervus unicolor swinhoei) on Staphylococcus aureus-Infected Mice

We assayed the effects of velvet antler (VA) of Formosan sambar deer (Cervus unicolor swinhoei) and its extracts on the anti-infective activity against pathogenic Staphylococcus aureus in vitro and in vivo in this study. In vitro data indicated that the VA extracts stimulated the proliferation of resting splenocytes and macrophages in a dose-dependent manner up to the highest concentration used (150 μg mL(-1)). The production of proinflammatory cytokines (TNF-α, IL-6, IL-12) by lipoteichoic acid was significantly suppressed after being cocultured with the VA extracts in a dose-dependent manner. Animal test in S. aureus-infected mice demonstrated that the numbers of bacteria determined in the kidneys and peritoneal lavage fluid of S. aureus-infected mice were significantly higher than those found in the same organs of mice pretreated with the VA samples. Moreover, the highly enhanced phagocytic activity of macrophages was further verified after in vitro treatment with the VA samples. The protective mechanisms of the VA samples might include an immune enhancer and an inflammatory cytokine suppressor.

Development of a serum-free medium for in vitro expansion of human cytotoxic T lymphocytes using a statistical design

Background

Serum-containing medium (SCM), which has a number of poorly defined components with varying concentrations, hampers standardization of lymphocyte cultures. In order to develop a serum-free medium (SFM) for the expansion of human lymphocytes from peripheral blood mononuclear cells (PBMCs), a statistical optimization approach based on a fractional factorial method and a response surface method was adopted. A basal medium was prepared by supplementing RPMI1640 medium with insulin, albumin, ferric citrate, ethanolamine, fatty acids, glutamine, sodium pyruvate, 2-mercaptoethanol, 1-thioglycerol, nonessential amino acids, and vitamins. We identified additional positive determinants and their optimal concentrations for cell growth through a statistical analysis.

Results

From a statistical analysis using the fractional factorial method, cholesterol and polyamine supplement were identified as positive determinants for cell growth. Their optimal concentrations were determined by the response surface method. The maximum viable cell concentration in the developed SFM was enhanced by more than 1.5-fold when compared to that in RPMI1640 supplemented with 10% fetal bovine serum (FBS). Furthermore, a cytotoxicity assay and an enzyme-linked immunospot assay revealed that the effector function of cytotoxic T lymphocytes generated from PBMCs grown in SFM, by stimulation of peptide-presenting dendritic cells, was retained or even better than that in SCM.

Conclusions

The use of a developed SFM with cholesterol and polyamine supplement for human lymphocyte culture resulted in better growth without loss of cellular function when compared to SCM.

Lymphocytes transfer [(14)C]-labeled fatty acids to skeletal muscle in culture; modulation by exercise

Previous studies have shown that lipids are transferred from lymphocytes (Ly) to different cell types including macrophages, enterocytes, and pancreatic beta cells in co-culture. This study investigated whether [(14)C]-labeled fatty acids (FA) can be transferred from Ly to skeletal muscle (SM), and the effects of exercise on such phenomenon. Ly obtained from exercised (EX) and control (C) male Wistar rats were preloaded with the [(14)C]-labeled free FA palmitic (PA), oleic (OA), linoleic (LA), or arachidonic (AA). Radioactively loaded Ly were then co-cultured with SM from the same Ly donor animals. Substantial amounts of FA were transferred to SM being the profile PA = OA > AA > LA to the C group, and PA > OA > LA > AA to the EX group. These FA were incorporated predominantly as phospholipids (PA = 66.75%; OA = 63.09%; LA = 43.86%; AA = 47.40%) in the C group and (PA = 63.99% OA = 52.72%; LA = 55.99%; AA = 63.40%) in the EX group. Also in this group, the remaining radioactivity from AA, LA, and OA acids was mainly incorporated in structural and energetic lipids. These results support the hypothesis that Ly are able to export lipids to SM in co-culture. Furthermore, exercise modulates the lipid transference profile, and its incorporation on SM. The overall significance of this phenomenon in vivo remains to be elucidated.

Soy lecithin supplementation alters macrophage phagocytosis and lymphocyte response to concanavalin A: a study in alloxan-induced diabetic rats

Dietary soy lecithin supplementation decreases hyperlipidemia and influences lipid metabolism. Although this product is used by diabetic patients, there are no data about the effect of soy lecithin supplementation on the immune system. The addition of phosphatidylcholine, the main component of lecithin, to a culture of lymphocytes has been reported to alter their function. If phosphatidylcholine changes lymphocyte functions in vitro as previously shown, then it could also affect immune cells in vivo. In the present study, the effect of dietary soy lecithin on macrophage phagocytic capacity and on lymphocyte number in response to concanavalin A (ConA) stimulation was investigated in non-diabetic and alloxan-induced diabetic rats. Supplementation was carried out daily with 2 g kg(-1) b.w. lecithin during 7 days. After that, blood was drawn from fasting rats and peritoneal macrophages and mesenteric lymph node lymphocytes were collected to determine the phospholipid content. Plasma triacylglycerol (TAG), total and HDL cholesterol and glucose levels were also determined. Lymphocytes were stimulated by ConA. The MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) dye reduction method and flow cytometry were employed to evaluate lymphocyte metabolism and cell number, respectively. Soy lecithin supplementation significantly increased both macrophage phagocytic capacity (+29%) in non-diabetic rats and the lymphocyte number in diabetic rats (+92%). It is unlikely that plasma lipid levels indirectly affect immune cells, since plasma cholesterol, TAG, or phospholipid content was not modified by lecithin supplementation. In conclusion, lymphocyte and macrophage function were altered by lecithin supplementation, indicating an immunomodulatory effect of phosphatidylcholine.

Developing dendritic cells become 'lacy' cells packed with fat and glycogen

On maturation, dendritic cells (DCs) become highly active cells equipped for antigen uptake, migration and clustering and activation of T cells. We therefore asked whether DCs acquire fat and glycogen stores as they mature. DCs were generated from mouse bone marrow stem cells by culturing with granulocyte-macrophage colony-stimulating factor (GM-CSF) for 7-8 days. Stimulation of the DCs with lipopolysaccharide (LPS) for the last 24 hr of culture, or exposure to 1-15 ng/ml of interleukin (IL)-4 during development, resulted in production of DCs not only with an increased ability to stimulate T cells but also with an increasingly lacy appearance on transmission electron microscopy, with multiple unstained areas in the cytoplasm. This changed morphology was associated with the presence of increasing amounts of fat and glycogen, identified by Sudan Black and periodic acid leukofushin/Schiff (PAS) staining, respectively. Lacy DCs up-regulated type 1 and type 2 scavenger receptors, providing possible mechanisms contributing to these changes. Lacy DCs were found occasionally amongst freshly isolated splenic and lymph node DCs. DCs can be isolated from human adipose tissue, and we tested whether lacy DCs acquiring fat and glycogen were present in mouse omentum. CD45+ cells migrating from the omentum expressed specific DC markers CD11c and 33D1, costimulatory molecules and major histocompatibility complex (MHC) class II, and most showed darkly staining fat inclusions. Thus, during development, DCs can acquire large amounts of fat and glycogen, accumulation of which is promoted by antigen exposure and modulated by the cytokine milieu and location, and which may act as a link between energy stores and immune function.

Modification of concanavalin A-dependent proliferation by phosphatidylcholines isolated from deer antler, Cervus elaphus

OBJECTIVE

The immunomodulatory effect of deer antler, which is used as traditional medicine, has been known, but the active component of antlers from Cervus elaphus has not been identified. In this study, we identified the immunomodulator from C. elaphus and examined its biological activities on the immune system.

METHODS

To identify an immunomodulator, we used bioassay-guided fractionation after silica gel column chromatography. Structural analysis was performed with one- and two-dimensional nuclear magnetic resonance techniques and tandem mass spectrometry coupled with fast atom bombardment.

RESULTS

The subfraction, phosphatidylcholines, isolated 70% ethanol extract of C. elaphus induced the proliferation of spleen cells in synergy with concanavalin A. According to the structural analysis, phosphatidylcholines were classified as a family (1,2-alkyl-sn-glycerol-3-phosphocholines) containing arachidonyl (C20:4), stearoyl (C18:0), oleoyl (C18:1), linoleoyl (C18:2), palmitoyl (C16:0), and myristoyl (C14:0) chains in their fatty acyl chains. Because the unsaturated fatty acids showed an inhibitory effect on the immune system, dialkyl phosphatidylcholines with different chain lengths from C10:0 to C20:0 that stimulate the proliferation of spleen cells were examined extensively. Among other saturated phosphatidylcholines used, dimyristoyl phosphatidylcholine (C14:0) induced the proliferation of spleen cells more efficiently, whereas dimyristoleoyl phosphatidylcholine (C14:1) effected little change in the proliferation of spleen cells.

CONCLUSIONS

These data collectively suggest that phosphatidylcholines with saturated fatty acyl chains are immunostimulating factors. They may modify the proliferation of known mitogens. Further, chain length and saturation of the fatty acids may play important roles in the proliferation of spleen cells.

Transforming growth factor-beta, 20-HETE interaction, and glomerular injury in Dahl salt-sensitive rats

This study examined the role of transforming growth factor-beta (TGF-beta) in altering the glomerular permeability to albumin (P(alb)) during hypertension development in Dahl salt-sensitive (Dahl S) rats and whether TGF-beta acts by inhibiting the glomerular production of 20-HETE. The results indicate that the renal expression of TGF-beta doubles in Dahl S rats fed a high-salt diet for 7 days, and this is associated with a marked rise in P(alb) from 0.19+/-0.04 to 0.75+/-0.01 and changes in the ultrastructure of the glomerular filtration barrier. Chronic treatment of Dahl S rats with a TGF-beta neutralizing antibody prevented the increase in P(alb) and preserved the structure of glomerular capillaries. It had no effect on the rise in blood pressure produced by the high-salt diet. In other studies, preincubation of glomeruli isolated from Sprague Dawley rats with TGF-beta1 (10 ng/mL) for 15 minutes increased P(alb) from 0.01+/-0.01 to 0.60+/-0.02. This was associated with inhibition of the glomerular production of 20-HETE from 221+/-11 to 3.4+/-0.5 mug per 30 minutes per milligram of protein. Pretreatment of Sprague Dawley glomeruli with a stable analog of 20-HETE, 20-hydroxyeicosa-5(Z), 14(Z)-dienoic acid, reduced baseline P(alb) and opposed the effects of TGF-beta to increase P(alb). These studies indicate that upregulation of the glomerular formation of TGF-beta may contribute to the development of proteinuria and glomerular injury early in hypertension development in Dahl S rats by increasing P(alb) through inhibition of the glomerular production of 20-HETE.

Modulation of lymphocyte proliferation by macrophages and macrophages loaded with arachidonic acid

Arachidonic acid (AA) is incorporated and exported by macrophages. This fatty acid is also transferred from macrophages (Mphi) to lymphocytes (LY) in co-culture. This observation led us to investigate the effect of macrophages pre-loaded with AA on concanavalin A (Con A)-stimulated lymphocyte proliferation. The experiments were performed in co-culture. This condition reproduces the in vivo microenvironment in which the modulation of lymphocyte proliferation is dependent on the interaction with macrophages. Lymphocytes obtained from untreated rats or from intraperitoneally thioglycolate-injected rats (THIO-treated) were co-cultured with macrophages from the same rats. Firstly, macrophages were co-cultured for 48 h with Con A-stimulated lymphocytes in different proportions: 0.5, 1, 2.5, 5, 10, 20 and 30% of 5 x 10(5) lymphocytes per well. At 1% proportion, macrophages caused maximum stimulation of lymphocyte proliferation; a four- to five-fold increase, for cells from both thioglycolate-treated and untreated rats, respectively, whereas at 20% it caused maximum inhibition. In addition, 1 or 20% macrophages were pre-loaded with several AA concentrations during a period of 6 h and co-cultured with lymphocytes. At 180 microM AA and 1% macrophages, lymphocyte proliferation was inhibited (by 25%), whereas at 20% macrophages, proliferation was increased, by 25- and three-fold, respectively, for cells from untreated and THIO-treated rats. AA added directly to the medium reduced lymphocyte proliferation, also being toxic to these cells at 100 microM. No toxic effects of AA were observed on macrophages. Additional evidence suggests that nitric oxide production is involved in the modulation of lymphocyte proliferation by AA-pre-loaded macrophages. These findings support the proposition that AA can directly modulate lymphocyte proliferation and the interaction between macrophages and lymphocytes.

Transfer of arachidonic acid from lymphocytes to macrophages

The incorporation and oxidation of arachidonic acid (AA) by rat lymphocytes (LY), the transfer of AA from LY to rat macrophages (Mphi) in co-culture, and the subsequent functional impact on Mphi phagocytosis were investigated. The rate of incorporation of [1-14C]AA by untreated-LY and TG (thioglycolate treated)-LY (TG-LY) was 158 +/- 8 nmol/10(10) LY per h for both untreated-LY and TG-LY. The oxidation of AA was 3.4-fold higher in TG-LY as compared with untreated cells. LY from TG-injected rats had a 2.5-fold increase in the oxidation of palmitic (PA), oleic (OA), and linoleic (LA) acids. After 6 h of incubation, [14C] from AA was distributed mainly into phospholipids. The rate of incorporation into total lipids was 1071 nmol/10(10) cells in untreated-LY and 636 nmol/10(10) cells in TG-LY. [14C]AA was transferred from LY to co-cultured Mphi in substantial amounts (8.7 nmol for untreated and 15 nmol per 10(10) for TG cells). Exogenously added AA, PA, OA, and LA caused a significant reduction of phagocytosis by resident cells. Mphi co-cultured with AA-preloaded LY showed a significant reduction of the phagocytic capacity (about 40% at 35 microM). LY preloaded with PA, LA, and OA also induced a reduction in phagocytic capacity of co-cultured Mphi. TG treatment abolished the AA-induced inhibition of phagocytosis in Mphi co-cultured with TG-LY. Therefore, the transfer of AA between leukocytes is a modulated process and may play an important role in controlling inflammatory and immune response.

Relation between the fatty acid composition of peripheral blood mononuclear cells and measures of immune cell function in healthy, free-living subjects aged 25-72 y

BACKGROUND

There is little information about the relation between the fatty acid composition of human immune cells and the function of those cells over the habitual range of fatty acid intakes.

OBJECTIVE

The objective of the study was to determine the relation between the fatty acid composition of human peripheral blood mononuclear cell (PBMC) phospholipids and the functions of human immune cells.

DESIGN

One hundred fifty healthy adult subjects provided a fasting blood sample. The phagocytic and oxidative burst activities of monocytes and neutrophils were measured in whole blood. PBMCs were isolated and used to measure lymphocyte proliferation in response to the T cell mitogen concanavalin A and the production of cytokines in response to concanavalin A or bacterial lipopolysaccharide. The fatty acid composition of plasma and PBMC phospholipids was determined.

RESULTS

Wide variations in fatty acid composition of PBMC phospholipids and immune cell functions were identified among the subjects. The proportions of total polyunsaturated fatty acids (PUFAs), of total n-6 and n-3 PUFAs, and of several individual PUFAs in PBMC phospholipids were positively correlated with phagocytosis by neutrophils and monocytes, neutrophil oxidative burst, lymphocyte proliferation, and interferon gamma production. The ratios of saturated fatty acids to PUFAs and of n-6 to n-3 PUFAs were negatively correlated with these same immune functions. The relation of PBMC fatty acid composition to monocyte oxidative burst was the reverse of its relation to monocyte phagocytosis and neutrophil oxidative burst.

CONCLUSION

Variations in the fatty acid composition of PBMC phospholipids account for some of the variability in immune cell functions among healthy adults.

Evidence that macrophages transfer arachidonic acid and cholesterol to tissuesin vivo

Our previous studies have shown that [(14)C]-labelled cholesterol (CHOL) and arachidonic acid (AA) are transferred from macrophages (Mphi) to lymphocytes (LY) when these cells are co-cultured. In this study, we investigated whether these lipids can be transferred from control and thioglycollate-elicited Mphi (THIO-elicited Mphi) to various tissues and organs in vivo. For this purpose, control and THIO-elicited Mphi were pre-treated with [(14)C]-AA and [(3)H]-CHOL and then injected into the jugular vein of adult rats. More than 75% of the radioactivity injected was found in the liver of rats treated with [(14)C]-AA labelled-Mphi either control and THIO-stimulated. The radioactivity of [(3)H]-CHOL labelled Mphi was transferred mainly to the liver (51% in the control Mphi and 23% in the thioglycollate Mphi7) but it was also found in the kidney, lung and spleen. These results support the proposition that the transfer of lipids between cells also occurs in vivo. The full significance of this phenomenon however remains to be elucidated.

Pleiotropic effects of fatty acids on pancreatic beta-cells

Hyperlipidemia is frequently associated with insulin resistance states as found in type 2 diabetes and obesity. Effects of free fatty acids (FFA) on pancreatic beta-cells have long been recognized. Acute exposure of the pancreatic beta-cell to FFA results in an increase of insulin release, whereas a chronic exposure results in desensitization and suppression of secretion. We recently showed that palmitate augments insulin release in the presence of non-stimulatory concentrations of glucose. Reduction of plasma FFA levels in fasted rats or humans severely impairs glucose-induced insulin release. These results imply that physiological plasma levels of FFA are important for beta-cell function. Although, it has been accepted that fatty acid oxidation is necessary for its stimulation of insulin secretion, the possible mechanisms by which fatty acids (FA) affect insulin secretion are discussed in this review. Long-chain acyl-CoA (LC-CoA) controls several aspects of the beta-cell function including activation of certain types of protein kinase C (PKC), modulation of ion channels, protein acylation, ceramide- and/or nitric oxide (NO)-mediated apoptosis, and binding to nuclear transcriptional factors. The present review also describes the possible effects of FA on insulin signaling. We showed for the first time that acute exposure of islets to palmitate upregulates the intracellular insulin-signaling pathway in pancreatic islets. Another aspect considered in this review is the source of FA for pancreatic islets. In addition to be exported to the medium, lipids can be transferred from leukocytes (macrophages) to pancreatic islets in co-culture. This process consists an additional source of FA that may plays a significant role to regulate insulin secretion.

Tubulointerstitial renal disease

Tubulointerstitial damage, in progressive chronic renal disease of all types, arises because of a complex interplay between factors in the tubular lumen, tubular epithelial cells, peritubular capillaries, resident and infiltrating interstitial cells and extracellular matrix. Particularly in proteinuric renal disease, tubular epithelial cells play a central role in orchestrating these events. In response to mediators arising systemically, in the tubular lumen or from other renal cells, tubular epithelial cells undergo a complex series of structural and functional changes and produce a bewildering number of soluble and fixed mediators, which in turn lead to interstitial inflammation and fibrosis. Knowledge of these interactions has increased exponentially over the past decade, and has defined a number of new targets for treatment. Both expansion and consolidation of this knowledge is needed to determine which of these targets holds the most promise for future treatment.

Docosahexaenoic acid suppresses function of the CD28 costimulatory membrane receptor in primary murine and Jurkat T cells

(n-3) polyunsaturated fatty acids (PUFA) have been widely documented to reduce inflammation in diseases such as rheumatoid arthritis. This study sought to elucidate the mechanism whereby (n-3) PUFA downregulate T-cell proliferation. We hypothesized that membrane incorporation of dietary PUFA would alter membrane structure and consequently membrane receptor function. Female C57BL/6 mice were fed for 14 d one of three diets containing arachidonic acid (AA), fish oil or docosahexaenoic acid (DHA) that varied in lipid composition only. Spleens were harvested and T cells ( approximately 90% purity) were activated with agonists that stimulated proliferation at the receptor level [anti-CD3 (alphaCD3)/anti-CD28 (alphaCD28)], intracellularly [phorbol-12-myristate-13-acetate (PMA)/ionomycin] or with a combined receptor/intracellular agonist (alphaCD3/PMA). Although there was no significant difference (P > 0.05) in proliferative response across dietary groups within each agonist set, interleukin (IL)-2 secretion was significantly reduced (P = 0.05) in cells from DHA-fed mice stimulated with alphaCD3/alphaCD28. In parallel in vitro experiments, Jurkat T cells were incubated with 50 micromol/L linoleic acid, AA, or DHA. Similar agonists sets were employed, and cells incubated with DHA and AA had a significantly reduced (P < 0.05) IL-2 secretion in three of the agonist sets. However, only when the CD28 receptor was stimulated was there a significant difference (P < 0.05) between DHA and AA. The results of this study suggest the involvement of the CD28 receptor in reducing IL-2 secretion in DHA-fed mice and DHA-incubated Jurkat cells and that purified T cells from DHA-fed mice require accessory cells to modulate proliferative suppression.

Arachidonic acid-containing phosphatidylcholine inhibits lymphocyte proliferation and decreases interleukin-2 and interferon-gamma production from concanavalin A-stimulated rat lymphocytes

The proliferation of concanavalin A (Con A)-stimulated rat lymphocytes was markedly inhibited by phosphatidylcholine containing arachidonic and stearic acids (PC(A-S)), but not by phosphatidylcholine containing oleic and stearic acids or phosphatidylinositol containing arachidonic and stearic acids. The concentration of PC(A-S) which inhibited Con A-stimulated proliferation by 50% was 31 microM and near total inhibition was observed at 154 microM . Phosphatidylserine containing only oleic acid enhanced proliferation by 37% at a concentration of 31 microM , but phosphatidylethanolamine and phosphatidylcholine containing only oleic acid did not affect proliferation at this concentration. It is concluded that both the head group and the fatty acid composition contribute to the influence of phospholipids on lymphocyte proliferation. The effects of PC(A-S) on T-lymphocyte responses were investigated further. In parallel with the inhibition of proliferation PC(A-S) caused a concentration-dependent decrease in the production of the Th1-type cytokines interleukin (IL)-2 and interferon (IFN)-gamma; inhibition of cytokine production was >85% at the highest concentration of PC(A-S) used (154 microM ). Production of the Th2-type cytokines IL-4 and IL-10 was not affected. The possible role of prostaglandins in mediating the effects of PC(A-S) was examined by adding indomethacin into the medium and the participation of lipid peroxidation was examined by adding vitamin E and vitamin C. Indomethacin and vitamin E did not affect the inhibition caused by PC(A-S) but vitamin C caused a partial reversal. It is concluded that inhibition of T-lymphocyte proliferation by phospholipids involves both the head group and the fatty acyl chains, that this inhibition is not mediated by prostaglandins but may involve some form of oxidant stress and that some phospholipids (e.g., PC(A-S)) can markedly influence cytokine profiles.