Lipid Accumulation In Monocytes Research Articles

Monocyte and Macrophage Lipid Accumulation Results in Down-Regulated Type-I Interferon Responses.

Macrophages are critical components of atherosclerotic lesions and their pro- and anti-inflammatory responses influence atherogenesis. Type-I interferons (IFNs) are cytokines that play an essential role in antiviral responses and inflammatory activation and have been shown to promote atherosclerosis. Although the impact of type-I IFNs on macrophage foam cell formation is well-documented, the effect of lipid accumulation in monocytes and macrophages on type-I IFN responses remains unknown. Here we examined IFN stimulated (ISG) and non-ISG inflammatory gene expression in mouse and human macrophages that were loaded with acetylated LDL (acLDL), as a model for foam cell formation. We found that acLDL loading in mouse and human macrophages specifically suppressed expression of ISGs and IFN-β secretion, but not other pro-inflammatory genes. The down regulation of ISGs could be rescued by exogenous IFN-β supplementation. Activation of the cholesterol-sensing nuclear liver X receptor (LXR) recapitulated the cholesterol-initiated type-I IFN suppression. Additional analyses of murine in vitro and in vivo generated foam cells confirmed the suppressed IFN signaling pathways and suggest that this phenotype is mediated via down regulation of interferon regulatory factor binding at gene promoters. Finally, RNA-seq analysis of monocytes of familial hypercholesterolemia (FH) patients also showed type-I IFN suppression which was restored by lipid-lowering therapy and not present in monocytes of healthy donors. Taken together, we define type-I IFN suppression as an athero-protective characteristic of foamy macrophages. These data provide new insights into the mechanisms that control inflammatory responses in hyperlipidaemic settings and can support future therapeutic approaches focusing on reprogramming of macrophages to reduce atherosclerotic plaque progression and improve stability.

Abstract 11296: Short-Term Low-Saturated Fat Diet Compared to High-Saturated Fat Diet in Patients with Hypertriglyceridemia: Lipids and Lipoproteins Associated with Monocyte Phenotypic Changes

Background: Monocyte phenotypic changes play a pivotal role in atherogenesis and can be induced by plasma lipids. We analyzed associations of monocyte phenotypes with lipid profiles and the potential of predicting monocyte phenotypes by lipid variables in subjects with hypertriglyceridemia (HTG) after short-term intake of low-saturated fat diet (LSFD) and high-saturated fat diet (HSFD). Method: Subjects with HTG (n=19, 10 men and 9 women, aged 53.9±13.7 years) received isocaloric LSFD (~25% of calories from fat, 5% from saturated fat) and HSFD (~52% of calories from fat, 25% from saturated fat) in randomized order for 4 days (days 1-4) and a test meal on day 5, separated by a 4- to 6-week washout period. Blood was taken on day 1 fasting before the diets and on day 5 fasting and 4 and 6 hours after the test meal to examine lipoprotein profile by enzymatic assay, fatty acids by nuclear magnetic resonance spectroscopy, and monocyte phenotypes by flow cytometry. Least absolute shrinkage and selection operator (LASSO) regression models were built to identify influential lipid variables for key monocyte markers that responded differently to the two diets. Results: LSFD, compared to HSFD, induced lower plasma levels of postprandial total triglyceride (TG), VLDL-TG, and LDL-TG and fasting and postprandial total cholesterol and LDL-cholesterol and altered fatty acid composition, with reduced saturated fatty acids (SFAs) but increased polyunsaturated fatty acids (PUFAs). Compared to HSFD, LSFD reduced monocyte lipid accumulation and levels of several surface markers involved in monocyte adhesion and migration including CD11c, a β2 integrin, on intermediate monocytes. Using the LASSO regression models, we identified that total cholesterol, LDL-TG, and apoB were positively correlated and n-3 PUFAs negatively correlated with lipid accumulation in intermediate monocytes and that total TG, LDL-TG, and apoCIII were positively correlated with CD11c levels on intermediate monocytes. Conclusions: In subjects with HTG, short-term LSFD compared to HSFD improves lipid profiles and monocyte phenotypes. We also identified specific plasma lipid parameters that may be reliable predictors for and contribute to specific monocyte phenotypic changes in HTG.

Sesquiterpene lactone Zaluzanin D alters MMP-9 promoter methylation in differentiated THP-1 monocytic cells and down regulates inflammatory cytokines IL-1β and TNF-α

Zaluzanin D (ZD) is a sesquiterpene lactone isolated from the leaves of Vernonia arborea. Earlier studies have highlighted the Sesquiterpene lactones (SLs) as molecules of medicinal value. The current study investigates the anti-inflammatory potential of ZD and its biotransformed derivatives in PMA differentiated human monocytic THP-1 cells. ZD and its fungal biotransformed derivatives Zaluzanin C (ZC) and 11,13- dihydrozaluzanin C (DZC) were screened for anti-inflammatory activity using their IC50 concentration. ZD showed significant ability to reduce PMA mediated THP-1 activation, while both ZC and DZC did not show any anti-inflammatory activity. Further studies revealed that ZD had ability to attenuate intracellular reactive oxygen species production in THP-1 cells as confirmed with FACS and fluorescence microscope experiments. Similarly, Oil red O (ORO) assay showed ability of ZD to inhibit lipid accumulation in monocytes. ZD also significantly reduced the expression of pro-inflammatory markers, tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, MMP (Matrix metalloproteinases)-9 and MMP-2 as observed with RT-PCR and ELISA. Interestingly the molecule ZD also partially reversed DNA methylation levels in the PMA activated THP-1 cells. This indicated the ability of ZD to influence the epigenetic machinery of the cell. Overall the current study indicates that ZD has ability to attenuate inflammation in differentiated human THP-1 cells by regulating genes involved in the atherosclerosis inflammatory pathway. Thus ZD could potentially be used to modulate inflammation in atherosclerosis like disorders wherein monocytes play a key role.

Modulation of lipid accumulation in monocytes and macrophages by cyclodextrin‐based nanocarriers for alpha‐tocopheryl phosphate

Vitamin E can modulate the CD36/FAT scavenger receptor/fatty acids transporter activity and affect lipid accumulation in monocytes and macrophages, important events for inflammation, lipotoxicity and foam cells formation during atherosclerosis. Similar to that, cyclodextrins (CD) can sequester and trigger export of lipids and influence cholesterol‐mediated signaling and gene expression leading to macrophages reprogramming and lipid lowering effects in a number of disease models. We have now combined the phosphorylated vitamin E analogue (alpha‐tocopheryl phosphate, αTP) and beta‐cyclodextrin (βCD) in a novel formulation to evaluate its regulatory effects and mechanisms of action on lipid accumulation in human monocytes/macrophages. In human THP‐1 monocytes and macrophages, the αTP/βCD complex not only increased the cellular delivery of αTP, but also reduced lipid accumulation by reducing CD36/FAT surface exposition and/or by enhancing the removal of cholesterol from the cells/membranes. A comparable activity was observed with higher order complexes of αTP/βCD with three types of modified starches or chitosan that may be useful as protective vehicle to increase oral, dermal or ocular delivery, or act as deposit‐enhancer in mucosa for delivery across epithelia. Moreover, preliminary results suggest that the αTP/βCD complex can influence signal transduction and gene expression pathways centrally involved in regulating cellular lipid homeostasis and inflammation. Thus, by acting as a Dual Action Lipid‐lowering Complex (DALC), αTP/βCD may not only increase the delivery of αTP and reduce cellular lipid accumulation by influencing CD36‐mediated signaling and gene expression relevant for lipid homeostasis, inflammation and cellular senescence, but also by stimulating βCD‐mediated lipid removal and macrophage reprogramming. In vivo, similar or better reductions of cellular lipids/cholesterol may be achieved possibly at lower concentrations as result of increased bioavailability and stability of αTP and of enhanced βCD‐mediated lipid exchange and macrophages reprogramming relevant not only for inflammation and atherosclerosis, but also for non‐alcoholic steatohepatitis (NASH), tumorigenesis and Parkinson's Disease.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Macrophages.

Macrophages.

Uncoupling between CD1d upregulation induced by retinoic acid and conduritol-B-epoxide and iNKT cell responsiveness

Gaucher disease (GD) is associated with upregulation of CD1d and MHC-class II expression by monocytes. While the physiological impact of CD1d upregulation remains uncertain, it has been proposed that MHC-class II upregulation is associated with inflammation. Hereby, we show that the decrease in MHC-class II expression seen in GD patients under therapy correlates positively with chitotriosidase activity, a marker of inflamed macrophages. We also show that retinoic acid (RA) and the β-glucocerebrosidase inhibitor conduritol-B-epoxide (CBE) lead to upregulation of CD1d expression by THP-1 cells, which correlated with an increase in mRNA expression. In vitro co-culture experiments showed that RA treated THP-1 cells were more stimulatory for CD4 + than for CD8 + T cells, as determined by CFSE loss, in comparison to untreated THP-1 cells. Interestingly, even though addition of exogenous isoglobotrihexosylceramide (iGb3), a physiological CD1d ligand, augmented the percentage of dividing CD4 + T cells, we could not detect a significant expansion of CD4 +Vα24 + invariant Natural Killer T (iNKT) cells. In contrast, addition of α-galactosylceramide (α-GC) induced expansion of Vα24 + iNKT cells as determined by using α-GC-loaded human CD1d dimers. These results strengthen the existence of a cross-talk between monocyte lipid accumulation, inflammation and changes in cell surface CD1d and MHC-class II in monocytes, which may result in inappropriate recognition events by immune cells and perpetuate chronic inflammation.

Lipid levels in monocytes of patients with moderate hyperlipoproteinemia

Recent studies suggest that circulating blood monocytes may serve as a lipid clearance system in early atherosclerotic lesions. To evaluate the influence of moderate hyperlipoproteinemia on monocyte lipid concentrations, we measured fasting serum and monocyte lipid levels in 7 healthy individuals, in 7 patients with primary hypercholesterolemia and in 17 patients with secondary dyslipidemia due to chronic renal failure; 10 of these patients were treated by hemodialysis (HD) and 7 patients by continuous ambulatory peritoneal dialysis (CAPD). The hypercholesterolemic patients had elevated serum levels of total cholesterol, LDL-cholesterol and apolipoprotein (apo) B, but normal plasma triglycerides. Patients on dialysis had elevated serum levels of triglycerides, serum cholesterol (CAPD only) and VLDL- and LDL-cholesterol (CAPD only) and apo B (CAPD only), whereas HDL-cholesterol and apo A-I levels (HD only) were decreased. In monocytes, we measured the content of free cholesterol (FC), cholesteryl esters (CE) and triglycerides (TG). The normal mean intracellular concentrations of FC, CE and TG were 48.3, 1.7 and 2.4 μg/mg cell protein, respectively. All monocyte lipid levels were similar in patients and controls, with the exception of a decreased content of FC (30.8 μg/mg) in monocytes of HD patients. We conclude that moderate increases in serum lipoprotein lipid levels are not associated with lipid accumulation in monocytes.

Oxidized low density lipoprotein suppresses the expression of tumor necrosis factor-alpha mRNA in stimulated murine peritoneal macrophages.

In the present report we have examined expression of the gene encoding the inflammatory monokine TNF-alpha in murine peritoneal macrophages treated with different forms of low density lipoprotein (LDL). LDL modified by oxidation in vitro is unable to stimulate inflammatory gene expression in peritoneal macrophages. However, treatment of macrophage cultures with oxidized LDL for 6 h or more resulted in a concentration and time-dependent suppression of TNF-alpha mRNA expression induced in response to stimulation with either LPS or maleylated BSA. This suppression was maximal after 12 h of exposure to oxidized LDL and at a concentration of 100 to 200 micrograms LDL cholesterol/ml of culture medium. The suppressive effect was restricted to oxidatively modified LDL as treatment with native LDL or acetylated LDL did not affect TNF-alpha mRNA expression, despite the fact that both acetylated and oxidized LDL lead to intracellular lipid accumulation. The expression of maleyl albumin-stimulated TNF-alpha mRNA expression could be reproduced by lipid extracts of oxidized LDL provided to macrophages at the same cholesterol concentration as from the intact lipoprotein particle. Extracts from native LDL were ineffective. These results suggest that oxidized lipid accumulation in monocytes infiltrating the arterial wall may lead to the suppression of certain inflammatory functions which, in turn, may influence the development of mature atherosclerotic lesions.