Metabolism Of Monocytes Research Articles

Immunomodulatory Drugs Alter the Metabolism and the Extracellular Release of Soluble Mediators by Normal Monocytes.

Immunomodulatory drugs (IMiDs) are used in the treatment of hematological malignancies, especially multiple myeloma. IMiDs have direct anticancer effects but also indirect effects via cancer-supporting stromal cells. Monocytes are a stromal cell subset whose metabolism is modulated by the microenvironment, and they communicate with neighboring cells through extracellular release of soluble mediators. Toll-like receptor 4 (TLR4) is then a common regulator of monocyte metabolism and mediator release. Our aim was to investigate IMiD effects on these two monocyte functions. We compared effects of thalidomide, lenalidomide, and pomalidomide on in vitro cultured normal monocytes. Cells were cultured in medium alone or activated by lipopolysaccharide (LPS), a TLR4 agonist. Metabolism was analyzed by the Seahorse XF 96 cell analyzer. Mediator release was measured as culture supernatant levels. TLR4 was a regulator of both monocyte metabolism and mediator release. All three IMiDs altered monocyte metabolism especially when cells were cultured with LPS; this effect was strongest for lenalidomide that increased glycolysis. Monocytes showed a broad soluble mediator release profile. IMiDs decreased TLR4-induced mediator release; this effect was stronger for pomalidomide than for lenalidomide and especially thalidomide. To conclude, IMiDs can alter the metabolism and cell–cell communication of normal monocytes, and despite their common molecular target these effects differ among various IMiDs.

Elevated Glucose Levels Favor Sars-Cov-2 Infection and Monocyte Response Through a Hif-1α/Glycolysis Dependent Axis

COVID-19 can result in severe lung injury. It remained to be determined why diabetic individuals with uncontrolled glucose levels are more prone to develop the severe form of COVID-19. The molecular mechanism underlying SARS-CoV-2 infection and what determines the onset of the cytokine storm found in severe COVID-19 patients are unknown. Monocytes/macrophages are the most enriched immune cell types in the lungs of COVID-19 patients and appear to have a central role in the pathogenicity of the disease. These cells adapt their metabolism upon infection and become highly glycolytic, which facilitates SARS-CoV-2 replication. The infection triggers mitochondrial ROS production, which induces stabilization of hypoxia-inducible factor- 1α (HIF - 1α) and consequently promotes glycolysis. HIF- 1α-induced changes in monocyte metabolism by SARS-CoV-2 infection directly inhibit T cell response and reduce epithelial cell survival. Targeting HIF-1 ɑ may have great therapeutic potential for the development of novel drugs to treat COVID-19.

The Effects of β-Hydroxy-β-Methylbutyrate (HMB) on Chemotaxis, Phagocytosis, and Oxidative Burst of Peripheral Blood Granulocytes and Monocytes in Goats.

Simple SummaryThe main focus of industrial livestock production is to maximise production output without compromising the well-being of animals, which is why animal diets are supplemented with various feed additives. Feed additives boost immunity and protect animals against pathogens. The list of potential feed additives includes β-hydroxy-β-methylbutyrate (HMB) which occurs naturally in small quantities in citrus fruit, avocado, asparagus, cauliflower, selected fish species, red wine, milk, and alfalfa. However, its mechanism of action and effects on immune system cells have not been thoroughly investigated in animals, including goats. In the present study, the experimental goats whose diets were supplemented with HMB over a period of 60 days were characterised by higher levels of chemotactic and phagocytic activity and a higher rate of oxidative metabolism of peripheral blood granulocytes and monocytes than control group animals whose diets were not supplemented. Granulocytes and monocytes constitute the first line of defence against pathogens and protect animals against disease. They play a particularly important role in young animals which are more susceptible to viral and bacterial infections. Feed additives can deliver numerous benefits by boosting immunity and preventing the spread of infectious diseases in goats.The objective of this study was to determine the effect of β-hydroxy-β-methylbutyrate (HMB) on the chemotactic activity, phagocytic activity, and oxidative metabolism of peripheral blood granulocytes and monocytes in goats. Goat kids aged 30 ± 3 days were divided into two groups of 12 animals each: I—control, and II—experimental. Experimental group animals were fed a diet supplemented with HMB in the amount of 50 mg/Kg BW; whereas the diets of control goats were not supplemented. At the beginning of the experiment (day 0) and on experimental days 15, 30, and 60, blood was sampled from the jugular vein to determine and compare chemotactic activity (MIGRATEST® kit), phagocytic activity (PHAGOTEST® kit), and oxidative metabolism (BURSTTEST® kit) of peripheral blood granulocytes and monocytes by flow cytometry. The analyses of the chemotactic and phagocytic activity of granulocytes and monocytes revealed statistically higher levels of phagocytic activity in the experimental group than in the control group, as expressed by the percentage of phagocytic cells and mean fluorescence intensity. HMB also enhanced the oxidative metabolism of both granulocytes and monocytes, expressed by the rate of oxidative metabolism and mean fluorescence intensity after stimulation with Escherichia coli bacteria and PMA (4-phorbol-12-β-myristate-13-acetate).

The rheumatoid synovial environment alters fatty acid metabolism in human monocytes and enhances CCL20 secretion.

Fatty acid oxidation (FAO) and glycolysis have been implicated in immune regulation and activation of macrophages. However, investigation of human monocyte intracellular metabolism in the context of the hypoxic and inflammatory rheumatoid arthritis (RA) synovium is lacking. We hypothesized that exposure of monocytes to the hypoxic and inflammatory RA environment would have a profound impact on their metabolic state, and potential to contribute to disease pathology. Human monocytes were isolated from buffy coats and exposed to hypoxia. Metabolic profiling of monocytes was carried out by LC-MS metabolomics. Inflammatory mediator release after LPS or RA-synovial fluid (RA-SF) stimulation was analysed by ELISA. FAO was inhibited by etomoxir or enhanced with exogenous carnitine supplementation. Transcriptomics of RA blood monocytes and RA-SF macrophages was carried out by microarray. Hypoxia exacerbated monocyte-derived CCL20 and IL-1β release in response to LPS, and increased glycolytic intermediates at the expense of carnitines. Modulation of carnitine identified a novel role for FAO in the production of CCL20 in response to LPS. Transcriptional analysis of RA blood monocytes and RA-SF macrophages revealed that fatty acid metabolism was altered and CCL20 increased when monocytes enter the synovial environment. In vitro analysis of monocytes showed that RA-SF increases carnitine abundance and CCL20 production in hypoxia, which was exacerbated by exogenous carnitine. This work has revealed a novel inflammatory mechanism in RA that links FAO to CCL20 production in human monocytes, which could subsequently contribute to RA disease pathogenesis by promoting the recruitment of Th17 cells and osteoclastogenesis.

Glycolysis Is Required for LPS-Induced Activation and Adhesion of Human CD14+CD16- Monocytes.

Monocytes in humans consist of 3 subsets; CD14+CD16− (classical), CD14+CD16+ (intermediate) and CD14dimCD16+ (non-classical), which exhibit distinct and heterogeneous responses to activation. During acute inflammation CD14+CD16− monocytes are significantly elevated and migrate to the sites of injury via the adhesion cascade. The field of immunometabolism has begun to elucidate the importance of the engagement of specific metabolic pathways in immune cell function. Yet, little is known about monocyte metabolism and the role of metabolism in mediating monocyte activation and adherence to vessels. Accordingly, we aimed to determine whether manipulating the metabolism of CD14+CD16− monocytes alters their ability to become activated and adhere. We discovered that LPS stimulation increased the rate of glycolysis in human CD14+CD16− monocytes. Inhibition of glycolysis with 2-deoxy-D-glucose blunted LPS-induced activation and adhesion of monocytes. Mechanistically, we found that increased glycolysis was regulated by mTOR-induced glucose transporter (GLUT)-1. Furthermore, enhanced glycolysis increased accumulation of reactive oxygen species (ROS) and activation of p38 MAPK, which lead to activation and adhesion of monocytes. These findings reveal that glycolytic metabolism is critical for the activation of CD14+CD16− monocytes and contributes to our understanding of the interplay between metabolic substrate preference and immune cell function.

Frontline Science: Endotoxin-induced immunotolerance is associated with loss of monocyte metabolic plasticity and reduction of oxidative burst.

Secondary infections are a major complication of sepsis and associated with a compromised immune state, called sepsis‐induced immunoparalysis. Molecular mechanisms causing immunoparalysis remain unclear; however, changes in cellular metabolism of leukocytes have been linked to immunoparalysis. We investigated the relation of metabolic changes to antimicrobial monocyte functions in endotoxin‐induced immunotolerance, as a model for sepsis‐induced immunoparalysis. In this study, immunotolerance was induced in healthy males by intravenous endotoxin (2 ng/kg, derived from Escherichia coli O:113) administration. Before and after induction of immunotolerance, circulating CD14+ monocytes were isolated and assessed for antimicrobial functions, including cytokine production, oxidative burst, and microbial (Candida albicans) killing capacity, as well metabolic responses to ex vivo stimulation. Next, the effects of altered cellular metabolism on monocyte functions were validated in vitro. Ex vivo lipopolysaccharide stimulation induced an extensive rewiring of metabolism in naive monocytes. In contrast, endotoxin‐induced immunotolerant monocytes showed no metabolic plasticity, as they were unable to adapt their metabolism or mount cytokine and oxidative responses. Validation experiments showed that modulation of metabolic pathways, affected by immunotolerance, influenced monocyte cytokine production, oxidative burst, and microbial (C. albicans) killing in naive monocytes. Collectively, these data demonstrate that immunotolerant monocytes are characterized by a loss of metabolic plasticity and these metabolic defects impact antimicrobial monocyte immune functions. Further, these findings support that the changed cellular metabolism of immunotolerant monocytes might reveal novel therapeutic targets to reverse sepsis‐induced immunoparalysis.

Classical monocytes maintain ex vivo glycolytic metabolism and early but not later inflammatory responses in older adults

BackgroundInflammaging is a condition of chronic low-grade inflammation due to the aging process and is associated with a variety of chronic diseases. Monocytes are innate immune cells which contribute to inflammation and are dysregulated during aging, demonstrated reduced phagocytosis, increased inflammation, and alterations in subset proportions. Metabolism is known to determine immune cell function, with quiescent and anti-inflammatory cells primarily relying on fatty acid oxidation, while activated and inflammatory cells primarily rely on glycolysis. We have previously shown an age-related decrease in mitochondrial respiratory capacity in monocytes, so we hypothesized here that a compensatory shift toward glycolysis would occur which would also exacerbate inflammation.ResultsUsing Seahorse assays, we profiled glycolysis in classical monocytes isolated from older (60–80 yr) and younger (18–35 yr) adults. Aging did not affect parameters of basal glycolysis in the glycolysis stress test, nor did it alter glycolytic activation early (2 h) or later (24 h) post-LPS stimulation. Cytokine gene expression was unchanged between aged and young subjects at 2 h post-LPS but was reduced in older subjects at 24 h post-LPS either significantly (IL1B) or near-significantly (IL6, IL10).ConclusionsAging appears not to affect glycolytic metabolism ex vivo in classical monocytes, but may reduce cytokine expression at later timepoints. Studies examining monocytes stimulated with age-altered circulating factors or with other pattern recognition receptor agonists may shed further light on monocyte metabolism as a determinant of immunosenescence and inflammaging.

5-Lipoxygenase (ALOX5): Genetic susceptibility to type 2 diabetes and vitamin D effects on monocytes

The arachidonate 5-lipoxygenase (ALOX5) pathway has been implicated in chronic inflammatory disease which may be influenced by vitamin D due to vitamin D response elements (VDRE). We investigated an ALOX5 polymorphism (rs4987105) in patients with type 2 diabetes (T2D) and the in vitro effects of calcitriol (1,25(OH)2D3) on ALOX5 metabolism in monocytes of T2D patients and healthy controls (HC). 533 T2D and 473 HC were genotyped for the rs4987105 polymorphism. In addition, the 25(OH)D3 and 1,25(OH)2D3 plasma levels were measured in both cohorts. Further C-reactive protein (CRP) was determined in T2D patients. Our results demonstrate, that genotype CC and the allele C of ALOX5 rs4987105 polymorphism were more frequent in T2D compared to HC (OR = 1.44; 95% CI: 1.12–1.84; p < 0.05). Lower levels of both vitamin D metabolites (p < 0.0001 respectively) were found in the CC genotyped T2D patients compared to CC genotyped HC. In addition, CC genotyped T2D patients had higher levels of CRP compared to CT and TT genotyped T2D patients, (p < 0.01). In order to evaluate the impact of calcitriol in primary isolated monocytes, we isolated monocytes of 20 T2D patients and 20 HC. The cells were treated with 1,25(OH)2D3 and interleukin-1beta (IL-1β) for 24 h. The following genes were analysed for expression changes: ALOX5, leukotriene A4 hydrolase (LTA4H), leukotriene B4 receptor type 1 (LTB4R1) and CD14. Treatment with IL-1β+1,25(OH)2D3 increased ALOX5, LTA4H and LTB4R1 and CD14 mRNA in both T2D patients and HC (p < 0.0001, respectively). In addition, IL-1β+1,25(OH)2D3 treatment led to higher ALOX5, LTA4H and CD14 mRNA levels in T2D patients compared to HC (p < 0.001, p < 0.05, p ≤ 0.05, respectively). In conclusion, ALOX5 rs4987105 allele C confers susceptibility to T2D, lower vitamin D metabolites and higher CRP levels complement this association. Additionally, IL-1β+1,25(OH)2D3 treatment on, ALOX5, LTA4H and CD14 mRNA indicate a diabetes specific modulation. These findings identify a novel pathway in T2D potentially amenable for individualized therapeutic targeting.

Vitamin D effects on sphingosine 1-phosphate signaling and metabolism in monocytes from type 2 diabetes patients and controls

Elevated sphingosine 1-phopshate (S1P) concentration was observed in type 2 diabetes mellitus (T2D). On the other side, 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3) can influence the formation of sphingosine 1-phopshate (S1P) and the expression of S1P receptors, which are known to be involved in T2D. In order to evaluate mechanisms for the antiinflammatory potential of 1,25(OH)2D3, we investigated whether 1,25(OH)2D3 alters S1P signaling and metabolism in human CD14+ monocytes. Primary monocytes isolated from healthy controls (HC) and T2D patients were treated for 24 h with 10 nM 1,25(OH)2D3 in the absence or presence of 500 IU/ml interleukin-(IL)-1β. Thereafter, sphingosine kinase (SPHK)1, SPHK2 and S1P receptor 1-5 (S1P1-5) mRNA expression levels were measured by TaqMan™ analyses. Sphingolipid levels in cell supernatant were determined by high-performance liquid chromatography/tandem mass spectrometry (LC–MS/MS). 1,25(OH)2D3 treatment downregulated S1P1 and S1P2 mRNA expression compared to untreated monocytes of HC and T2D patients. In contrast, SPHK1, S1P3 and S1P4 mRNA expression levels were upregulated by 1,25(OH)2D3 treatment compared to the respective controls. Furthermore, reduced S1P2 and increased S1P3 and S1P4 mRNA expression levels upon treatment with 1,25(OH)2D3 occurred in the presence of IL-1β. Additionally, S1P levels in cell supernatants were decreased in monocytes from HC and T2D patients by 1,25(OH)2D3 with or without IL-1β costimulation. The levels of sphingosine in cell supernatants were not influenced by 1,25(OH)2D3. Overall, our results demonstrate for the first time that 1,25(OH)2D3 treatment can influence S1P receptor and SPHK expression and S1P levels in primary monocytes of both HC and subjects with T2D. These findings justify further investigations into the sphingolipid metabolism and potential benefits of vitamin D treatment in diabetes.

Trained immunity by oxidized low-density lipoprotein is defined by reprogramming of glycolytic metabolism in human monocytes

Aim: Monocyte-derived macrophages are major drives of atherosclerotic plaque development. Brief exposure of monocytes to a low concentration of oxidized low-density lipoprotein (oxLDL) induces a persis3tent, proatherogenic macrophage phenotype characterized by increased proinflammatory cytokine production, and foam cell formation. This innate immune memory has been termed trained immunity. The aim of the current study is to elucidate the intracellular mechanisms of oxLDL-mediated trained immunity.

Exosomes in Cholesterol Metabolism and Atherosclerosis.

Exosomes are small secreted membrane vesicles formed in the late endocytic compartments by inward budding. Interest in these extracellular vesicles and their role in atherosclerosis is growing, as they can affect multiple cellular processes that lead to lipid overload, cytokine secretion and cellular adhesion. Exosomes protect and transport lipids, proteins, and RNAs, fostering intercellular communication among different cell types involved in atherogenesis such as macrophages, endothelium and smooth muscle. Their molecular composition reflects their cell type of origin, but they share attributes because they are enriched in proteins of their endosomal source. This review will describe the current state of our knowledge of exosome involvement in the development of atherosclerosis. The transfer of signaling molecules, lipids, mRNAs, and microRNAs via exosomes with effects on monocyte and macrophage cholesterol metabolism, endothelial cell and platelet activation and smooth muscle proliferation will be discussed. Finally, therapeutic potential of exosomes and clinical application will be explored.

Gluten peptides drive healthy and celiac monocytes toward an M2-like polarization

Celiac disease (CD) is an immune-mediated enteropathy triggered by ingested gluten in genetically susceptible individuals and sustained by both adaptive and innate immune responses. Recent studies in murine macrophages demonstrated that the activation of arginase (ARG) metabolic pathway by gluten peptides contributes to the modulation of intestinal permeability in vitro. Here we characterize the effects of gluten on arginine metabolism and cell polarization in human monocytes from both healthy and CD subjects; both a simplified enzymatic digestion of gliadin and a physiological digestion of whole wheat have been tested. Results indicate that gluten digests induce the onset of an M2-like phenotype in activated macrophages; more precisely, both isoforms of arginase, ARG1 and ARG2, are induced likely due to the inhibition of mTOR and the consequent induction of C/EBPβ transcription factor. These effects are independent from the origin of gluten as well as from the digestive protocol employed; moreover, no statistical difference can be evidenced between healthy and CD patients, excluding a diverse predisposition of CD monocytes to gluten-triggered polarization with respect to healthy immune cells. Overall, the present findings sustain a role for arginase pathway in the immune response elicited by human monocytes toward ingested gluten that, hence, deserves particular attention when addressing the pathogenesis of CD.

THE EFFECT OF PLATELET-RICH AND PLATALET-POOR PLASMA ON METABOLIC PROFILE OF AUTOLOGOUS HUMAN MONOCYTES IN VITRO

The aim of the study was to perform the comparative investigation of the effect of platelet-rich (PRP) and platelet-poor (PPP) plasma on autologous human monocyte metabolism in vitro. Adult healthy 35–40 year old men were recruited to participate in the study. To characterize monocyte metabolism intracellular production of reactive oxygen species (ROS) and phagocytic activіty were determined by flow cytometry, with nitrite production being determined in Griess reaction and arginase activity - in colorimetric assay.The obtained results suggest that treatment of monocytes with autologous L-PRP and PPP preparations causes their anti-inflammatory metabolic activation.

Fatty Acid Oxidation Compensates for Lipopolysaccharide-Induced Warburg Effect in Glucose-Deprived Monocytes.

Monocytes enter sites of microbial or sterile inflammation as the first line of defense of the immune system and initiate pro-inflammatory effector mechanisms. We show that activation with bacterial lipopolysaccharide (LPS) induces them to undergo a metabolic shift toward aerobic glycolysis, similar to the Warburg effect observed in cancer cells. At sites of inflammation, however, glucose concentrations are often drastically decreased, which prompted us to study monocyte function under conditions of glucose deprivation and abrogated Warburg effect. Experiments using the Seahorse Extracellular Flux Analyzer revealed that limited glucose supply shifts monocyte metabolism toward oxidative phosphorylation, fueled largely by fatty acid oxidation at the expense of lipid droplets. While this metabolic state appears to provide sufficient energy to sustain functional properties like cytokine secretion, migration, and phagocytosis, it cannot prevent a rise in the AMP/ATP ratio and a decreased respiratory burst. The molecular trigger mediating the metabolic shift and the functional consequences is activation of AMP-activated protein kinase (AMPK). Taken together, our results indicate that monocytes are sufficiently metabolically flexible to perform pro-inflammatory functions at sites of inflammation despite glucose deprivation and inhibition of the LPS-induced Warburg effect. AMPK seems to play a pivotal role in orchestrating these processes during glucose deprivation in monocytes.

Research progress on metabolism of monocytes and macrophages in sepsis

During sepsis, circulating leukocytes are in a hyper inflammatory state, and with the progress of the inflammation, immune cells may become tolerated. Glycolysis and pentose phosphate pathway are up-regulated but oxidative phosphorylation is suppressed in hyper inflammatory cells, whereas during immune tolerance, glycolysis is often down-regulated. In this review, we will summarize the changes of cellular metabolic pathways in monocytes and macrophages during sepsis. We also review how the metabolism of glucose, amino acids, and fatty acids affect the function of monocytes and macrophages in sepsis. Current literature indicated that metabolism plays a significant role in regulating the functions of immune cells in sepsis, which might be a potential therapy for sepsis and deserved further research.

Differential lipid metabolism in monocytes and macrophages: influence of cholesterol loading

The influence of the hypercholesterolemia associated with atherosclerosis on monocytes is poorly understood. Monocytes are exposed to high concentrations of lipids, particularly cholesterol and lysophosphatidylcholine (lyso-PC). Indeed, in line with recent reports, we found that monocytes accumulate cholesteryl esters (CEs) in hypercholesterolemic mice, demonstrating the need for studies that analyze the effects of lipid accumulation on monocytes. Here we analyze the effects of cholesterol and lyso-PC loading in human monocytes and macrophages. We found that cholesterol acyltransferase and CE hydrolase activities are lower in monocytes. Monocytes also showed a different expression profile of cholesterol influx and efflux genes in response to lipid loading and a different pattern of lyso-PC metabolism. In monocytes, increased levels of CE slowed the conversion of lyso-PC into PC. Interestingly, although macrophages accumulated glycerophosphocholine, phosphocholine was the main water-soluble choline metabolite being generated in monocytes, suggesting a role for mono- and diacylglycerol in the chemoattractability of these cells. In summary, monocytes and macrophages show significant differences in lipid metabolism and gene expression profiles in response to lipid loading. These findings provide new insights into the mechanisms of atherosclerosis and suggest potentials for targeting monocyte chemotactic properties not only in atherosclerosis but also in other diseases.

Age‐associated changes in long‐chain fatty acid profile during healthy aging promote pro‐inflammatory monocyte polarization via PPAR γ

Differences in lipid metabolism associate with age-related disease development and lifespan. Inflammation is a common link between metabolic dysregulation and aging. Saturated fatty acids (FAs) initiate pro-inflammatory signalling from many cells including monocytes; however, no existing studies have quantified age-associated changes in individual FAs in relation to inflammatory phenotype. Therefore, we have determined the plasma concentrations of distinct FAs by gas chromatography in 26 healthy younger individuals (age<30years) and 21 healthy FA individuals (age>50years). Linear mixed models were used to explore the association between circulating FAs, age and cytokines. We showed that plasma saturated, poly- and mono-unsaturated FAs increase with age. Circulating TNF-α and IL-6 concentrations increased with age, whereas IL-10 and TGF-β1 concentrations decreased. Oxidation of MitoSOX Red was higher in leucocytes from FA adults, and plasma oxidized glutathione concentrations were higher. There was significant colinearity between plasma saturated FAs, indicative of their metabolic relationships. Higher levels of the saturated FAs C18:0 and C24:0 were associated with lower TGF-β1 concentrations, and higher C16:0 were associated with higher TNF-α concentrations. We further examined effects of the aging FA profile on monocyte polarization and metabolism in THP1 monocytes. Monocytes preincubated with C16:0 increased secretion of pro-inflammatory cytokines in response to phorbol myristate acetate-induced differentiation through ceramide-dependent inhibition of PPARγ activity. Conversely, C18:1 primed a pro-resolving macrophage which was PPARγ dependent and ceramide dependent and which required oxidative phosphorylation. These data suggest that a midlife adult FA profile impairs the switch from proinflammatory to lower energy, requiring anti-inflammatory macrophages through metabolic reprogramming.

Abstract 120: Inhibitory Effects of Cholesterol on Lysophosphatidylcholine Metabolism in Human Monocytes

Background and aims: In hypercholesterolemic conditions blood cells are exposed to high concentrations of lipids, particularly cholesterol and lysophosphatidylcholine (lyso-PtdCho). While the metabolism of lyso-PtdCho by monocytes has been studied, the effects of high cholesterol, which complexes with lyso-PtdCho, are not well understood. In this study we used a novel assay developed in our laboratory, based on the ability of lyso-PtdCho to solubilize and deliver cholesterol into the cells, to study whether cholesterol affects the metabolism of lyso-PtdCho. Methods: In THP-1 monocytes 14 C-lyso-PtdCho metabolism was analyzed by TLC and cytotoxicity by WST-1 assay. Results: Monocytes incubated with lyso-PtdCho alone metabolize the incorporated lyso-PtdCho by 4h mainly into phosphatidylcholine, with a small percentage into sphingomyelin and phosphocholine. The latter could represent PLase C reaction that would generate mono- and diacyl-glycerols, important signaling molecules. However in cells incubated with cholesterol or cholesteryl ester (CE)/lyso-PtdCho micelles, at 4h the radioactivity remained mainly in the lyso-PtdCho fraction (p&lt;0.01 and p&lt;0.001). Lyso-PtdCho decreased monocyte viability at concentrations over 30μM, but cholesterol and CE inhibited the lyso-PtdCho-induced cytotoxicity (p&lt;0.001). Lyso-PtdCho and CE/lyso-PtdCho, but not cholesterol/lyso-PtdCho, increased the gene expression of the pro-inflammatory chemokine MCP-1 (p&lt;0.05). Peripheral blood monocytes from LDL-R -/- mice on a high fat diet had higher levels of CE than monocytes from mice in a normal diet (n=10, p&lt;0.05). Monocyte CE content in these mice positively correlated with plasma LDL/HDL ratio (p&lt;0.05, R 2 =0.65). Conclusions: We show that cholesterol and CE inhibit the cytotoxic effects of lyso-PtdCho in monocytes, but only cholesterol counteracted the pro-inflammatory action of lyso-PtdCho. Since lyso-PtdCho concentrations in plasma are increased in hypercholesterolemic conditions, and its content is increased during the oxidation of LDL, the current studies might indicate that cholesterol and lyso-Ptdcho could influence each other’s metabolism. This is important as lyso-PtdCho has been suggested to influence plaque vulnerability.

Lactate promotes PGE2 synthesis and gluconeogenesis in monocytes to benefit the growth of inflammation-associated colorectal tumor.

Reprogramming energy metabolism, such as enhanced glycolysis, is an Achilles' heel in cancer treatment. Most studies have been performed on isolated cancer cells. Here, we studied the energy-transfer mechanism in inflammatory tumor microenvironment. We found that human THP-1 monocytes took up lactate secreted from tumor cells through monocarboxylate transporter 1. In THP-1 monocytes, the oxidation product of lactate, pyruvate competed with the substrate of proline hydroxylase and inhibited its activity, resulting in the stabilization of HIF-1α under normoxia. Mechanistically, activated hypoxia-inducible factor 1-α in THP-1 monocytes promoted the transcriptions of prostaglandin-endoperoxide synthase 2 and phosphoenolpyruvate carboxykinase, which were the key enzyme of prostaglandin E2 synthesis and gluconeogenesis, respectively, and promote the growth of human colon cancer HCT116 cells. Interestingly, lactate could not accelerate the growth of colon cancer directly in vivo. Instead, the human monocytic cells affected by lactate would play critical roles to 'feed' the colon cancer cells. Thus, recycling of lactate for glucose regeneration was reported in cancer metabolism. The anabolic metabolism of monocytes in inflammatory tumor microenvironment may be a critical event during tumor development, allowing accelerated tumor growth.

Glucose transporter 1-expressing proinflammatory monocytes are elevated in combination antiretroviral therapy-treated and untreated HIV+ subjects.

Monocyte activation during HIV-1 infection is associated with increased plasma levels of inflammatory markers and increased risk for premature development of age-related diseases. Because activated monocytes primarily use glucose to support cellular metabolism, we hypothesized that chronic monocyte activation during HIV-1 infection induces a hypermetabolic response with increased glucose uptake. To test this hypothesis, we evaluated glucose transporter 1 (Glut1) expression and glucose uptake by monocyte subpopulations in HIV-seropositive (HIV(+)) treatment-naive individuals (n = 17), HIV(+) individuals on combination antiretroviral therapy with viral loads below detection (n = 11), and HIV-seronegative (HIV(-)) individuals (n = 16). Surface expression of Glut1 and cellular uptake of the fluorescent glucose analog 2-(N-(7-nitrobenz-2-oxa-1, 3-diazol-4-yl) amino)-2 deoxyglucose were analyzed by flow cytometry on monocyte subpopulations. Irrespective of treatment status, monocytes from HIV(+) persons had significantly increased surface expression of Glut1 compared with those from HIV(-) controls. Nonclassical (CD14(+)CD16(++)) and intermediate (CD14(++)CD16(+)) monocyte subpopulations showed higher Glut1 expression than did classical (CD14(++)CD16(-)) monocytes. Intermediate monocytes from treatment-naive HIV(+) individuals also showed increased uptake of 2-(N-(7-nitrobenz-2-oxa-1, 3-diazol-4-yl) amino)-2 deoxyglucose compared with those from HIV(-) controls. Our results show that HIV infection is associated with increased glucose metabolism in monocytes and that Glut1 expression by proinflammatory monocytes is a potential marker of inflammation in HIV-infected subjects. However, the possibility exists whereby other Gluts such as Glut3 and Glut4 may also support the influx of glucose into activated and inflammatory monocyte populations.