Formation Of Lipid-laden Macrophages Research Articles

Lipid-Laden Macrophages in Pulmonary Diseases.

Pulmonary surfactants play a crucial role in managing lung lipid metabolism, and dysregulation of this process is evident in various lung diseases. Alternations in lipid metabolism lead to pulmonary surfactant damage, resulting in hyperlipidemia in response to lung injury. Lung macrophages are responsible for recycling damaged lipid droplets to maintain lipid homeostasis. The inflammatory response triggered by external stimuli such as cigarette smoke, bleomycin, and bacteria can interfere with this process, resulting in the formation of lipid-laden macrophages (LLMs), also known as foamy macrophages. Recent studies have highlighted the potential significance of LLM formation in a range of pulmonary diseases. Furthermore, growing evidence suggests that LLMs are present in patients suffering from various pulmonary conditions. In this review, we summarize the essential metabolic and signaling pathways driving the LLM formation in chronic obstructive pulmonary disease, pulmonary fibrosis, tuberculosis, and acute lung injury.

Long-Term Effects of Oral Eliglustat on Skeletal Manifestations of Gaucher Disease Type 1: Results from Four Completed Clinical Trials

Background:In Gaucher disease type 1 (GD1), deficient lysosomal acid β-glucosidase activity leads to accumulation of glucosylceramide and formation of lipid-laden macrophages known as Gaucher cells. Patients experience a range of disease manifestations including anemia, thrombocytopenia, hepatosplenomegaly, and debilitating bone complications that impair quality of life. Hematologists are central to disease recognition and management. Most patients, even those without overt symptoms of bone involvement, have radiologic evidence of bone disease. Eliglustat, an oral substrate-reduction therapy, is a first-line treatment for adults with GD1 who have extensive, intermediate or poor CYP2D6 metabolizer phenotypes (>90% of patients). Oral eliglustat partially inhibits glucosylceramide synthase, thereby reducing glucosylceramide accumulation, unlike enzyme replacement therapy (ERT), the historic standard of care for GD1, which augments acid β-glucosidase activity in mononuclear phagocytes and is administered in biweekly infusions.Methods:We analyzed bone mineral density T- and Z-scores and occurrence of bone pain and bone crises in 4 completed clinical trials sponsored by Sanofi Genzyme that involved 393 GD1 patients treated with eliglustat for 4-8 years: Phase 2 (NCT00358150), Phase 3 ENGAGE (NCT00891202), Phase 3 ENCORE (NCT00943111), and Phase 3 EDGE (NCT01074944). Healthy reference scores are >-1 for T-scores and >-2 for Z-scores. Bone marrow burden (BMB) scores and changes in macrophage inflammatory protein 1β (MIP-1β) were also analyzed in the 3 Phase 3 trials. BMB, an MRI-based scoring system to evaluate marrow infiltration of both the lumbar spine and femur, and MIP-1β, a biomarker produced by inflammatory phagocytes surrounding Gaucher cells, are associated with active and evolving bone disease in GD1.Results:In treatment-naïve patients (Phase 2, N=26; ENGAGE, N=40), mean spine T-scores moved from the osteopenic range (>-2.5 to ≤ -1) at baseline to the healthy reference range after 2-3 years of eliglustat, with continued improvement thereafter in both trials. Mean±SEM spine T-score increased from -1.55±0.28 to -0.59±0.34 (n=14; mean±SEM increase from baseline: 0.96±0.32), after 8 years in Phase 2, and increased to -0.53±0.27 in ENGAGE patients with bone data at 4.5 years (n=9; mean±SEM increase from baseline: 0.53±0.16). Spine Z-scores for both trials showed similar improvements; femur T- and Z-scores in both trails remained in the normal range. In the ENCORE trial of patients stabilized after a mean of 10 years of ERT (N=157), T- and Z-scores (spine and femur) remained in the reference ranges for up to 4 years; least square mean spine Z-scores improved by 0.29 (P<0.0001). In EDGE (N=170, mostly ERT switch), randomized patients stabilized on eliglustat during a 6- to 18-month Lead-In Period maintained normal T- and Z-scores (spine and femur) through the dose regimen arm of the study and the succeeding extension period. Mean total BMB scores improved from 10 (in the marked to severe range) to 8 (moderate range) in ENGAGE (treatment-naive patients), and remained stable at 8 throughout ENCORE and EDGE (switch/mostly switch patients). The proportion of patients experiencing recent (≤4 weeks) bone pain decreased after treatment in all 4 trials, and reported pain became less severe. No patient in Phase 2 or ENGAGE had a bone crisis while on eliglustat. Bone crises were reported in 3/157 (1.9%) ENCORE patients over the trial duration. In EDGE, the only trial to enroll patients with active bone disease, 6/170 (3.5%) patients had bone crises during the trial, 3 of whom had bone crises during the 6 months prior to trial entry. Bone crises decreased with increasing time on eliglustat, with only 1 bone crisis reported during the 2- to 3-year trial extension. In ENGAGE (treatment-naïve), median MIP-1β levels elevated 3-fold at baseline normalized. In ENCORE and EDGE (switch/mostly switch), MIP-1β levels remained in the normal range. Across the 4 trials, most adverse events were mild/moderate (97%) and considered unrelated to eliglustat (86%); 9 (2.3% overall) patients withdrew due to adverse events considered drug-related.Conclusions:Long-term eliglustat treatment induced continued improvement in bone parameters in treatment-naïve patients. These parameters remained stable in trials involving patients who had been previously treated. Eliglustat was generally well-tolerated. DisclosuresMistry:Sanofi Genzyme: Honoraria, Other: Principal Investigator for the eliglustat ENGAGE and ENCORE trials; ReceivedTravel Reimbursement; Member of the ICCG North American Advisory Board; , Research Funding. Charrow:Sanofi Genzyme: Honoraria, Other: Principal investigator, eliglustat EDGE trial; Member of advisory boards, Research Funding. Cox:Sanofi Genzyme: Honoraria, Other: Principal investigator for the eliglustat ENCORE trial; received travel reimbursement, Research Funding. Lukina:Sanofi Genzyme: Honoraria, Other: Principal investigator in the eliglustat Phase 2, ENGAGE, ENCORE, and EDGE trials; receives travel reimbursement; member of advisory boards, Research Funding. Marinakis:Sanofi Genzyme: Other: Principal investigator for the eliglustat EDGE trial, Research Funding. Foster:Sanofi Genzyme: Employment. Gaemers:Sanofi Genzyme: Employment. Peterschmitt:Sanofi Genzyme: Employment.

Luteolin decreases atherosclerosis in LDL receptor-deficient mice via a mechanism including decreasing AMPK-SIRT1 signaling in macrophages.

Lipid metabolism dysfunction and inflammatory infiltration into arterial walls are associated with the initiation and progression of atherosclerosis. Luteolin has been reported to possess anti-inflammatory actions and protect against tumor necrosis factor-α (TNF-α)-induced vascular inflammation, monocyte adhesion to endothelial cells and the formation of lipid-laden macrophages in vitro. However, the role of luteolin in atherosclerosis and the associated vascular inflammatory remains to be elucidated. The aim of the present study was to investigate the effects of luteolin on plaque development, lipid accumulation and macrophage inflammation low-density lipoprotein receptor-deficient (LDLR-/-) mice with atherosclerosis, as well as the underlying mechanisms in ox-induced THP-1-derived macrophages. Firstly, 9-week-old male C57BL/6 mice were fed a standard chow diet, western diet or western diet supplemented with 100 mg/kg luteolin for 14 weeks. The results of histological staining revealed that 100 mg/kg dietary luteolin ameliorated western diet-induced atherosclerotic plaque development and lipid accumulation in the abdominal aorta. Furthermore, total cholesterol, triglyceride and LDL-cholesterol levels were decreased in the plasma of western diet + luteolin mice compared with those fed with a western diet alone. Quantitative polymerase chain reaction analysis revealed that dietary luteolin inhibited the expression of cluster of differentiation 68, macrophage chemoattractant protein 2 and inflammatory cytokines, including interleukin-6 (IL-6) and TNF-α. Mechanistically, luteolin decreased the total cholesterol level as well as macrophage chemokine and inflammatory cytokine expression in THP-1-derived macrophages via AMP-activated protein kinase (AMPK)-Sirtuin (SIRT)1 signaling following induction with oxidized low-density lipoprotein. The results of the present study suggest that luteolin prevents plaque development and lipid accumulation in the abdominal aorta by decreasing macrophage inflammation during atherosclerosis, which is mediated by mechanisms including AMPK-SIRT1 signaling.

Platelets and their chemokines in atherosclerosis-clinical applications.

The concept of platelets as important players in the process of atherogenesis has become increasingly accepted due to accumulating experimental and clinical evidence. Despite the progress in understanding the molecular details of atherosclerosis, particularly by using animal models, the inflammatory and thrombotic roles of activated platelet s especially in the human system remain difficult to dissect, as often only the complications of atherosclerosis, i.e., stroke and myocardial infarction are definable but not the plaque burden. Platelet indices including platelet count and mean platelet volume (MPV) and soluble mediators released by activated platelets are associated with atherosclerosis. The chemokine CXCL4 has multiple atherogenic activities, e.g., altering the differentiation of T cells and macrophages by inhibiting neutrophil and monocyte apoptosis and by increasing the uptake of oxLDL and synergizing with CCL5. CCL5 is released and deposited on endothelium by activated platelets thereby triggering atherogenic monocyte recruitment, which can be attenuated by blocking the corresponding chemokine receptor CCR5. Atheroprotective and plaque stabilizing properties are attributed to CXCL12, which plays an important role in regenerative processes by attracting progenitor cells. Its release from luminal attached platelets accelerates endothelial healing after injury. Platelet surface molecules GPIIb/IIIa, GP1bα, P-selectin, JAM-A and the CD40/CD40L dyade are crucially involved in the interaction with endothelial cells, leukocytes and matrix molecules affecting atherogenesis. Beyond the effects on the arterial inflammatory infiltrate, platelets affect cholesterol metabolism by binding, modifying and endocytosing LDL particles via their scavenger receptors and contribute to the formation of lipid laden macrophages. Current medical therapies for the prevention of atherosclerotic therapies enable the elucidation of mechanisms linking platelets to inflammation and atherosclerosis.

Inhibitory effects of luteolin on transendothelial migration of monocytes and formation of lipid-laden macrophages

ObjectiveBecause of an initial activation of proinflammatory cytokines that facilitates leukocyte transmigration, atherosclerosis is a chronic inflammatory disease and its severity is accelerated by the occurrence of complex interactions of oxidatively modified low-density lipoprotein (LDL) with monocyte-derived macrophages. MethodsThe present study investigated whether luteolin suppresses adheren junction-associated monocyte transmigration and platelet-derived growth factor-BB–mediated foam cell formation. The involvement of monocyte integrins and macrophage scavenger receptors (SRs) also was determined. ResultsLuteolin, non-toxic at 1 to 20 μmol/L, blocked the monocyte–endothelium interactions by inhibiting the cytokine-associated monocyte induction of integrin-β2. Luteolin retarded the transendothelial migration of monocytes by firmly localizing the occludin present in paracellular endothelial junctions and by blunting the monocyte activity of matrix-degrading matrix metalloproteinase-9. Treatment with luteolin showed inhibitory effects on oxidized LDL-triggered foam cell formation by decreasing SR-A and SR-B1 induction in THP-1 cell-derived macrophages, which was confirmed by Oil red O and 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate staining. Furthermore, luteolin attenuated the oxidized LDL-induced macrophage secretion of platelet-derived growth factor-BB, entailing the induction of SR-A and SR-B1. These results demonstrate that luteolin encumbered monocyte cytokine-instigated endothelial transmigration and oxidized LDL-elicited macrophage foam cell formation. ConclusionLuteolin may qualify as an antiatherogenic agent in LDL systems, which may have implications for strategies attenuating monocyte/macrophage dysfunction-related atherosclerosis.

Vav Protein Guanine Nucleotide Exchange Factor Regulates CD36 Protein-mediated Macrophage Foam Cell Formation via Calcium and Dynamin-dependent Processes

Atherosclerosis, a chronic inflammatory disease, results in part from the accumulation of modified lipoproteins in the arterial wall and formation of lipid-laden macrophages, known as "foam cells." Recently, we reported that CD36, a scavenger receptor, contributes to activation of Vav-family guanine nucleotide exchange factors by oxidatively modified LDL in macrophages. We also discovered that CD36-dependent uptake of oxidized LDL (oxLDL) in vitro and foam cell formation in vitro and in vivo was significantly reduced in macrophages deficient of Vav proteins. The goal of the present study was to identify the mechanisms by which Vav proteins regulate CD36-dependent foam cell formation. We now show that a Vav-dynamin signaling axis plays a critical role in generating calcium signals in mouse macrophages exposed to CD36-specific oxidized phospholipid ligands. Chelation of intracellular Ca(2+) or inhibition of phospholipase C-γ (PLC-γ) inhibited Vav activation (85 and 70%, respectively, compared with vehicle control) and reduced foam cell formation (approximately 75%). Knockdown of expression by siRNA or inhibition of GTPase activity of dynamin 2, a Vav-interacting protein involved in endocytic vesicle fission, significantly blocked oxLDL uptake and inhibited foam cell formation. Immunofluorescence microscopy studies showed that Vav1 and dynamin 2 colocalized with internalized oxLDL in macrophages and that activation and mobilization of dynamin 2 by oxLDL was impaired in vav null cells. These studies identified previously unknown components of the CD36 signaling pathway, demonstrating that Vav proteins regulate oxLDL uptake and foam cell formation via calcium- and dynamin 2-dependent processes and thus represent novel therapeutic targets for atherosclerosis.

Oxidative Stress Induces Vascular Calcification through Modulation of the Osteogenic Transcription Factor Runx2 by AKT Signaling

Oxidative stress plays a critical role in the pathogenesis of atherosclerosis including the formation of lipid laden macrophages and the development of inflammation. However, oxidative stress-induced molecular signaling that regulates the development of vascular calcification has not been investigated in depth. Osteogenic differentiation of vascular smooth muscle cells (VSMC) is critical in the development of calcification in atherosclerotic lesions. An important contributor to oxidative stress in atherosclerotic lesions is the formation of hydrogen peroxide from diverse sources in vascular cells. In this study we defined molecular signaling that is operative in the H2O2-induced VSMC calcification. We found that H2O2 promotes a phenotypic switch of VSMC from contractile to osteogenic phenotype. This response was associated with an increased expression and transactivity of Runx2, a key transcription factor for osteogenic differentiation. The essential role of Runx2 in oxidative stress-induced VSMC calcification was further confirmed by Runx2 depletion and overexpression. Inhibition of Runx2 using short hairpin RNA blocked VSMC calcification, and adenovirus-mediated overexpression of Runx2 alone induced VSMC calcification. Inhibition of H2O2-activated AKT signaling blocked VSMC calcification and Runx2 induction concurrently. This blockage did not cause VSMC apoptosis. Taken together, our data demonstrate a critical role for AKT-mediated induction of Runx2 in oxidative stress-induced VSMC calcification.

Group V Secretory Phospholipase A2-modified Low Density Lipoprotein Promotes Foam Cell Formation by a SR-A- and CD36-independent Process That Involves Cellular Proteoglycans

Accumulating evidence indicates that secretory phospholipase A2 (sPLA2) enzymes promote atherogenic processes. We have previously showed the presence of Group V sPLA2 (GV sPLA2) in human and mouse atherosclerotic lesions, its hydrolysis of low density lipoprotein (LDL) particles, and the ability of GV sPLA2-modified LDL (GV-LDL) to induce macrophage foam cell formation in vitro. The goal of this study was to investigate the mechanisms involved in macrophage uptake of GV-LDL. Peritoneal macrophages from C57BL/6 mice (wild type (WT)), C57BL/6 mice deficient in LDL receptor (LDLR-/-), or SR-A and CD36 (DKO) were treated with control LDL, GV-LDL, oxidized LDL (ox-LDL) or LDL aggregated by vortexing (vx-LDL). As expected, ox-LDL induced significantly more cholesterol ester accumulation in WT and LDLR-/- compared with DKO macrophages. In contrast, there was no difference in the accumulation of GV-LDL or vx-LDL in the three cell types. 125I-ox-LDL exhibited high affinity, saturable binding to WT cells that was significantly reduced in DKO cells. Vx-LDL and GV-LDL showed low affinity, non-saturable binding that was similar for both cell types, and significantly higher compared with control LDL. GV-LDL degradation in WT and DKO cells was similar. Analyses by confocal microscopy indicated a distinct intracellular distribution of Alexa-568-labeled GV-LDL and Alexa-488-labeled ox-LDL. Uptake of GV-LDL (but not ox-LDL or vx-LDL) was significantly reduced in cells preincubated with heparin or NaClO3, suggesting a role for proteoglycans in GV-LDL uptake. Our data point to a physiological modification of LDL that has the potential to promote macrophage foam cell formation independent of scavenger receptors.

Lipoxygenases in human and bovine corneal epithelia

Oxidatively-modified low density lipoprotein (LDL) is thought to play a significant role in the formation of lipid-laden macrophages, the primary cellular component of atherosclerotic fatty lesions. Recently, lipoxygenases have been implicated as a major enzymatic pathway involved in rabbit endothelial cell-mediated LDL modification. We investigated the effect of LDL on porcine aortic endothelial cell (PAEC) and human umbilical vein (HUVEC) and aortic endothelial cell (HAEC) lipoxygenase activity. By thin layer chromatography, we observed that human LDL stimulated the metabolism of radiolabeled arachidonic acid to 12+15-hydroxyeicosatetraenoic acid (HETE) in indomethacin-treated PAEC. Furthermore, radiolabeled linoleic acid, a specific substrate for the 15-lipoxygenase, was metabolized to its respective product 13-hydroxyoctadecadienoic acid (13-HODE) in the presence of LDL. Increased product formation in both studies was inhibited by the lipoxygenase blockers nordihydroguaiaretic acid (NDGA) and RG 6866. 15-HETE was confirmed as the predominant HETE product in LDL-treated cells by high performance liquid chromatography. Both porcine- and human-derived LDL stimulated the CL release of 15-HETE from cells as determined by radioimmunoassay. Release of immunoreactive 15-HETE was inhibited by NDGA, RG 6866, and 5,8,11,14-eicosatetraynoic acid (ETYA) but not by the selective 5-lipoxygenase inhibitor RG 5901. These lipoxygenase inhibitors had similar effects on the modification of LDL. Our results suggest that the oxidative modification of LDL by endothelial cells may be mediated in part through activation of 15-lipoxygenase.

Activation of 15-lipoxygenase by low density lipoprotein in vascular endothelial cells. Relationship to the oxidative modification of low density lipoprotein

Oxidatively-modified low density lipoprotein (LDL) is thought to play a significant role in the formation of lipid-laden macrophages, the primary cellular component of atherosclerotic fatty lesions. Recently, lipoxygenases have been implicated as a major enzymatic pathway involved in rabbit endothelial cell-mediated LDL modification. We investigated the effect of LDL on porcine aortic endothelial cell (PAEC) and human umbilical vein (HUVEC) and aortic endothelial cell (HAEC) lipoxygenase activity. By thin layer chromatography, we observed that human LDL stimulated the metabolism of radiolabeled arachidonic acid to 12+15-hydroxyeicosatetraenoic acid (HETE) in indomethacin-treated PAEC. Furthermore, radiolabeled linoleic acid, a specific substrate for the 15-lipoxygenase, was metabolized to its respective product 13-hydroxyoctadecadienoic acid (13-HODE) in the presence of LDL. Increased product formation in both studies was inhibited by the lipoxygenase blockers nordihydroguaiaretic acid (NDGA) and RG 6866. 15-HETE was confirmed as the predominant HETE product in LDL-treated cells by high performance liquid chromatography. Both porcine- and human-derived LDL stimulated the CL release of 15-HETE from cells as determined by radioimmunoassay. Release of immunoreactive 15-HETE was inhibited by NDGA, RG 6866, and 5,8,11,14-eicosatetraynoic acid (ETYA) but not by the selective 5-lipoxygenase inhibitor RG 5901. These lipoxygenase inhibitors had similar effects on the modification of LDL. Our results suggest that the oxidative modification of LDL by endothelial cells may be mediated in part through activation of 15-lipoxygenase.