Gabriela Castilho

Advanced Glycation in macrophages induces intracellular accumulation of 7-ketocholesterol and total sterols by decreasing the expression of ABCA-1 and ABCG-1

BackgroundAdvanced glycation end products (AGE) alter lipid metabolism and reduce the macrophage expression of ABCA-1 and ABCG-1 which impairs the reverse cholesterol transport, a system that drives cholesterol from arterial wall macrophages to the liver, allowing its excretion into the bile and feces. Oxysterols favors lipid homeostasis in macrophages and drive the reverse cholesterol transport, although the accumulation of 7-ketocholesterol, 7alpha- hydroxycholesterol and 7beta- hydroxycholesterol is related to atherogenesis and cell death. We evaluated the effect of glycolaldehyde treatment (GAD; oxoaldehyde that induces a fast formation of intracellular AGE) in macrophages overloaded with oxidized LDL and incubated with HDL alone or HDL plus LXR agonist (T0901317) in: 1) the intracellular content of oxysterols and total sterols and 2) the contents of ABCA-1 and ABCG-1.MethodsTotal cholesterol and oxysterol subspecies were determined by gas chromatography/mass spectrometry and HDL receptors content by immunoblot.ResultsIn control macrophages (C), incubation with HDL or HDL + T0901317 reduced the intracellular content of total sterols (total cholesterol + oxysterols), cholesterol and 7-ketocholesterol, which was not observed in GAD macrophages. In all experimental conditions no changes were found in the intracellular content of other oxysterol subspecies comparing C and GAD macrophages. GAD macrophages presented a 45% reduction in ABCA-1 protein level as compared to C cells, even after the addition of HDL or HDL + T0901317. The content of ABCG-1 was 36.6% reduced in GAD macrophages in the presence of HDL as compared to C macrophages.ConclusionIn macrophages overloaded with oxidized LDL, glycolaldehyde treatment reduces the HDL-mediated cholesterol and 7-ketocholesterol efflux which is ascribed to the reduction in ABCA-1 and ABCG-1 protein level. This may contribute to atherosclerosis in diabetes mellitus.

ER stress is associated with reduced ABCA-1 protein levels in macrophages treated with advanced glycated albumin – Reversal by a chemical chaperone

ATP-binding cassette transporter A1 mediates the export of excess cholesterol from macrophages, contributing to the prevention of atherosclerosis. Advanced glycated albumin (AGE-alb) is prevalent in diabetes mellitus and is associated with the development of atherosclerosis. Independently of changes in ABCA-1 mRNA levels, AGE-alb induces oxidative stress and reduces ABCA-1 protein levels, which leads to macrophage lipid accumulation. These metabolic conditions are known to elicit endoplasmic reticulum (ER) stress. We sought to determine if AGE-alb induces ER stress and unfolded protein response (UPR) in macrophages and how disturbances to the ER could affect ABCA-1 content and cholesterol efflux in macrophages. AGE-alb induced a time-dependent increase in ER stress and UPR markers. ABCA-1 content and cellular cholesterol efflux were reduced by 33% and 47%, respectively, in macrophages treated with AGE-alb, and both were restored by treatment with 4-phenyl butyric acid (a chemical chaperone that alleviates ER stress), but not MG132 (a proteasome inhibitor). Tunicamycin, a classical ER stress inductor, also impaired ABCA-1 expression and cholesterol efflux (showing a decrease of 61% and 82%, respectively), confirming the deleterious effect of ER stress in macrophage cholesterol accumulation. Glycoxidation induces macrophage ER stress, which relates to the reduction in ABCA-1 and in reverse cholesterol transport, endorsing the adverse effect of macrophage ER stress in atherosclerosis. Thus, chemical chaperones that alleviate ER stress may represent a useful tool for the prevention and treatment of atherosclerosis in diabetes.

Advanced glycated albumin impairs HDL anti-inflammatory activity and primes macrophages for inflammatory response that reduces reverse cholesterol transport

OBJECTIVE We investigated the effect of advanced glycated albumin (AGE-albumin) on macrophage sensitivity to inflammation elicited by S100B calgranulin and lipopolysaccharide (LPS) and the mechanism by which HDL modulates this response. We also measured the influence of the culture medium, isolated from macrophages treated with AGE-albumin, on reverse cholesterol transport (RCT). METHODS AND RESULTS Macrophages were incubated with control (C) or AGE-albumin in the presence or absence of HDL, followed by incubations with S100B or LPS. Also, culture medium obtained from cells treated with C- or AGE-albumin, following S100B or LPS stimulation was utilized to treat naive macrophages in order to evaluate cholesterol efflux and the expression of HDL receptors. In comparison with C-albumin, AGE-albumin, promoted a greater secretion of cytokines after stimulation with S100B or LPS. A greater amount of cytokines was also produced by macrophages treated with AGE-albumin even in the presence of HDL. Cytokine-enriched medium, drawn from incubations with AGE-albumin and S100B or LPS impaired the cholesterol efflux mediated by apoA-I (23% and 37%, respectively), HDL(2) (43% and 47%, respectively) and HDL(3) (20% and 8.5%, respectively) and reduced ABCA-1 protein level (16% and 26%, respectively). CONCLUSIONS AGE-albumin primes macrophages for an inflammatory response impairing the RCT. Moreover, AGE-albumin abrogates the anti-inflammatory role of HDL, which may aggravate the development of atherosclerosis in DM.

Dietary interesterified fat enriched with palmitic acid induces atherosclerosis by impairing macrophage cholesterol efflux and eliciting inflammation

Interesterified fats are currently being used to replace trans fatty acids. However, their impact on biological pathways involved in the atherosclerosis development was not investigated. Weaning male LDLr-KO mice were fed for 16weeks on a high-fat diet (40% energy as fat) containing polyunsaturated (PUFA), TRANS, palmitic (PALM), palmitic interesterified (PALM INTER), stearic (STEAR) or stearic interesterified (STEAR INTER). Plasma lipids, lipoprotein profile, arterial lesion area, macrophage infiltration, collagen content and inflammatory response modulation were determined. Macrophage cholesterol efflux and the arterial expression of cholesterol uptake and efflux receptors were also performed. The interesterification process did not alter plasma lipid concentrations. Although PALM INTER did not increase plasma cholesterol concentration as much as TRANS, the cholesterol enrichment in the LDL particle was similar in both groups. Moreover, PALM INTER induced the highest IL-1β, MCP-1 and IL-6 secretion from peritoneal macrophages as compared to others. This inflammatory response elicited by PALM INTER was confirmed in arterial wall, as compared to PALM. These deleterious effects of PALM INTER culminate in higher atherosclerotic lesion, macrophage infiltration and collagen content than PALM, STEAR, STEAR INTER and PUFA. These events can partially be attributed to a macrophage cholesterol accumulation, promoted by apoAI and HDL2-mediated cholesterol efflux impairment and increased Olr-1 and decreased Abca1 and Nr1h3 expressions in the arterial wall. Interesterified fats containing palmitic acid induce atherosclerosis development by promoting cholesterol accumulation in LDL particles and macrophagic cells, activating the inflammatory process in LDLr-KO mice.

In Type 2 Diabetes Mellitus Glycated Albumin Alters Macrophage Gene Expression Impairing ABCA1-Mediated Cholesterol Efflux

Advanced glycation end products (AGE) are elevated in diabetes mellitus (DM) and predict the development of atherosclerosis. AGE‐albumin induces oxidative stress, which is linked to a reduction in ABCA‐1 and cholesterol efflux. We characterized the glycation level of human serum albumin (HSA) isolated from poorly controlled DM2 (n = 11) patients compared with that of control (C, n = 12) individuals and determined the mechanism by which DM2‐HSA can interfere in macrophage lipid accumulation. The HSA glycation level was analyzed by MALDI/MS. Macrophages were treated for 18 h with C‐ or DM2‐HSA to measure the 14C‐cholesterol efflux, the intracellular lipid accumulation and the cellular ABCA‐1 protein content. Agilent arrays (44000 probes) were used to analyze gene expression, and the differentially expressed genes were validated by real‐time RT‐PCR. An increased mean mass was observed in DM2‐HSA compared with C‐HSA, reflecting the condensation of at least 5 units of glucose. The cholesterol efflux mediated by apo AI, HDL3, and HDL2 was impaired in DM2‐HSA‐treated cells, which was related to greater intracellular lipid accumulation. DM2‐HSA decreased Abcg1 mRNA expression by 26%. Abca1 mRNA was unchanged, although the final ABCA‐1 protein content decreased. Compared with C‐HAS‐treated cells, NADPH oxidase 4 mRNA expression increased in cells after DM2‐HSA treatment. Stearoyl‐Coenzyme A desaturase 1, janus kinase 2, and low density lipoprotein receptor mRNAs were reduced by DM2‐HSA. The level of glycation that occurs in vivo in DM2‐HSA‐treated cells selectively alters macrophage gene expression, impairing cholesterol efflux and eliciting intracellular lipid accumulation, which contribute to atherogenesis, in individuals with DM2. J. Cell. Physiol. XXXX: XX–XX, 2015.

The impact of dietary fatty acids on macrophage cholesterol homeostasis

The impact of dietary fatty acids in atherosclerosis development may be partially attributed to their effect on macrophage cholesterol homeostasis. This process is the result of interplay between cholesterol uptake and efflux, which are permeated by inflammation and oxidative stress. Although saturated fatty acids (SAFAs) do not influence cholesterol efflux, they trigger endoplasmic reticulum stress, which culminates in increased lectin-like oxidized LDL (oxLDL) receptor (LOX1) expression and, consequently, oxLDL uptake, leading to apoptosis. Unsaturated fatty acids prevent most SAFAs-mediated deleterious effects and are generally associated with reduced cholesterol efflux, although α-linolenic acid increases cholesterol export. Trans fatty acids increase macrophage cholesterol content by reducing ABCA-1 expression, leading to strong atherosclerotic plaque formation. As isomers of conjugated linoleic acid (CLAs) are strong PPAR gamma ligands, they induce cluster of differentiation (CD36) expression, increasing intracellular cholesterol content. Considering the multiple effects of fatty acids on intracellular signaling pathways, the purpose of this review is to address the role of dietary fat in several mechanisms that control macrophage lipid content, which can determine the fate of atherosclerotic lesions.

New PPARγ partial agonist improves obesity-induced metabolic alterations and atherosclerosis in LDLr(-/-) mice.

Peroxisome proliferator-activated receptor gamma (PPARγ) regulates multiple pathways involved in the pathogenesis of obesity and atherosclerosis. Here, we evaluated the therapeutic potential of GQ-177, a new thiazolidinedione, on diet-induced obesity and atherosclerosis. The intermolecular interaction between PPARγ and GQ-177 was examined by virtual docking and PPAR activation was determined by reporter gene assay identifying GQ-177 as a partial and selective PPARγ agonist. For the evaluation of biological activity of GQ-177, low-density lipoprotein receptor-deficient (LDLr(-/-)) C57/BL6 mice were fed either a high fat diabetogenic diet (diet-induced obesity), or a high fat atherogenic diet, and treated with vehicle, GQ-177 (20mg/kg/day), pioglitazone (20mg/kg/day, diet-induced obesity model) or rosiglitazone (15mg/kg/day, atherosclerosis model) for 28 days. In diet-induced obesity mice, GQ-177 improved insulin sensitivity and lipid profile, increased plasma adiponectin and GLUT4 mRNA in adipose tissue, without affecting body weight, food consumption, fat accumulation and bone density. Moreover, GQ-177 enhanced hepatic mRNA levels of proteins involved in lipid metabolism. In the atherosclerosis mice, GQ-177 inhibited atherosclerotic lesion progression, increased plasma HDL and mRNA levels of PPARγ and ATP-binding cassette A1 in atherosclerotic lesions. GQ-177 acts as a partial PPARγ agonist that improves obesity-associated insulin resistance and dyslipidemia with atheroprotective effects in LDLr(-/-) mice.

N-acetylcysteine prevents endoplasmic reticulum stress elicited in macrophages by serum albumin drawn from chronic kidney disease rats and selectively affects lipid transporters, ABCA-1 and ABCG-1

In chronic kidney disease (CKD) nontraditional risk factors, such as oxidative stress and advanced glycation end products (AGE) contribute to cardiovascular disease. Particularly, disturbances in reverse cholesterol transport favor the development of atherosclerosis. We analyzed the influence of N-acetylcysteine (NAC) in CKD rats on plasma concentration of lipid peroxides (TBARS) and AGE and on the impact of serum albumin in the development of macrophage endoplasmic reticulum stress (ERS) and cholesterol efflux, namely apo A-I and HDL2-mediated cholesterol removal and ABCA-1 and ABCG-1 protein level. CKD was induced by 5/6 nephrectomy in 2-month old male Wistar rats. Controls (Sham) were false operated. Animals were treated or not with NAC (600 mg/L of water). After 60 days serum albumin was isolated by FPLC and purified by alcoholic extraction. J774 macrophages were incubated with serum albumin (1 mg/mL; 18 h) from all groups, and the expression of ERS markers (protein disulfide isomerase - PDI, Grp78 and Grp94), ABCA-1 and ABCG-1 determined by immunoblot. HDL2 or apo A-I were used for cholesterol efflux assays. Protein and lipid composition of total HDL from Sham and CKD was determined and these particles tested on their abilities to accept cell cholesterol. Comparisons were done by one-way ANOVA and Newman Keuls post test. After 60 days of CKD, body weight was 10% lower in CKD compared to Sham (p < 0.01). This was prevented by NAC. Urea, creatinine, total cholesterol (TC), triglycerides (TG) (mg/dL), proteinuria (mg/24 h) (Sham, n = 31; Sham + NAC, n = 20; CKD, n = 74; CKD + NAC, n = 32), total AGE and pentosidine (n = 8; fluorescence arbitrary unit) and TBARS (n = 7; nmoL/mL) were higher in CKD (122 ± 8; 0.9 ± 0.07; 151 ± 6; 83 ± 4; 46 ± 2.5; 32,620 ± 673; 16,700 ± 1,370; 6.6 ± 0.5, respectively) and in CKD + NAC (91.4 ± 5; 0.6 ± 0.02; 126 ± 7.5; 73 ± 6; 51 ± 3.5; 24,720 ± 1,114; 10,080 ± 748; 4.5 ± 0.5, respectively) in comparison to Sham (41 ± 0.9; 0.4 ± 0.03; 76 ± 2.7; 51.5 ± 3; 14 ± 0.9; 21,750 ± 960; 5,314 ± 129; 2.0 ± 0.2, respectively; p < 0.001) and Sham + NAC (40 ± 0.9; 0.3 ± 0.02; 76 ± 2.6; 68 ± 4; 18.4 ± 1.5; 20,040 ± 700; 5,050 ± 267; 1.8 ± 0.2, respectively; p < 0.001). TC, urea, creatinine, total AGE, pentosidine and TBARS were respectively, 17%, 25%, 33%, 24%, 40% and 28% (p < 0.01) lower in CKD + NAC, than in CKD. Glycemia was higher in Sham + NAC (107 ± 4.6) and CKD + NAC (107 ± 2.6) than in Sham (96 ± 1.8; p < 0.05) and CKD (98 ± 1.6; p < 0.01), respectively. In macrophages (n = 6), CKD albumin increased PDI (3 and 6 times, p < 0.01) and Grp94 (66% and 80%, p < 0.01) in comparison to Sham and CKD + NAC-albumin treated cells, respectively. ABCA-1 expression was lower (87% and 70%, p < 0.001) in macrophage treated with Sham + NAC and CKD albumin respectively in comparison to Sham albumin; ABCG-1 was higher (4 and 7 times, p < 0.001) in macrophages treated with Sham + NAC and CKD + NAC albumin, respectively in comparison to Sham and CKD albumin. Apo A-I mediated cholesterol efflux was lower (59% and 70%, p < 0.0001) in macrophage treated with Sham + NAC and CKD albumin respectively in comparison to Sham albumin, however, the HDL2 mediated cholesterol efflux was higher (54% and 25%, p < 0.0001) in macrophage treated with Sham + NAC albumin, in comparison to Sham and CKD + NAC albumin, respectively. CKD-HDL was enriched in total protein and lipids compared to Sham-HDL but preserved its capacity to remove cholesterol from macrophages. NAC reduces plasma lipid peroxidation and AGE and abrogates ERS induced by CKD-albumin. Despite diminishing ABCA-1, NAC increases ABCG-1 that counteracts the reduction in apo A-I-mediated cholesterol efflux. NAC may contribute to attenuate the deleterious effects of CKD-albumin on lipid accumulation in macrophages helping to prevent atherogenesis in CKD.

Glycated human serum albumin isolated from poorly controlled diabetic patients impairs cholesterol efflux from macrophages: an investigation by mass spectrometry

Advanced glycation end-products impair ABCA-1-mediated cholesterol efflux by eliciting inflammation, the generation of reactive oxygen species and endoplasmatic reticulum (ER) stress. The glycation level of human serum albumin (HSA) from type 1 and type 2 diabetic patients was determined by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry and related to possible impairment of ER function and cellular cholesterol efflux. Comparison of the MALDI spectra from healthy and diabetic subjects allowed us to determine an increased HSA mean mass of 1297 Da for type 1 and 890 Da for type 2. These values reflect a mean condensation of at least 8 glucose units and 5 glucose units, respectively. Mouse peritoneal macrophages were treated with HSA from control, type 1 and type 2 diabetic subjects in order to measure the expression of Grp78, Grp94, protein disulfide isomerase (PDI), calreticulin (CRT), and ABCA-1. 14C-cholesterol overloaded-J774 macrophages were treated with HSA from control and diabetic subjects and further incubated with apo A-1 to determine the cholesterol efflux. Combined analyses comprising HSA from type 1 and type 2 diabetic patients were performed in cellular functional assays. In macrophages, PDI expression increased 89% and CRT 3.4 times in comparison to HSA from the control subjects. ABCA-1 protein level and apo A-I-mediated cholesterol efflux were, respectively, 50% and 60% reduced in macrophages exposed to HSA from type 1 and type 2 diabetic patients when compared to that exposed to HSA from control subjects. We provide evidence that the level of glycation that occurs in albumin in vivo damages the ER function related to the impairment in macrophage reverse cholesterol transport, and so contributes to atherosclerosis in diabetes.

Corrigendum to “Dietary interesterified fat enriched with palmitic acid induces atherosclerosis by impairing macrophage cholesterol efflux and eliciting inflammation” [J Nutr Biochem 32C (2016) 91–100]

Lipids Laboratory (LIM10), Faculty of Medical Sciences of the University of Sao Paulo, São Paulo, Brazil Emergency Care Research Unit Laboratory (LIM51), Faculty of Medical Sciences of the University of Sao Paulo, São Paulo, Brazil Laboratory of Nutritional Genomics (LabGeN), School of Applied Science, University of Campinas (UNICAMP), Limeira, São Paulo, Brazil Department of Biochemical and Pharmaceutical Technology, Faculty of Pharmaceutical Sciences, University of Sao Paulo, São Paulo, Brazil Laboratory of Cell Biology (LIM59), Department of Pathology, Faculty of Medical Sciences of the University of Sao Paulo, São Paulo, Brazil Albert Einstein Faculty of Health Sciences, São Paulo, Brazil ⁎ Corresponding author at: Faculty of Medical Sciences of the University of Sao Paulo Lipids Laboratory (LIM10), Av Dr Arnaldo, 455, 3rd Floor, Room 3305, São Paulo, SP 01246-903, Brazil. Tel./fax: +55 11 30617263.