Advanced Glycation End Products: A Sweet Flavor That Embitters Cardiovascular Disease.

Epidemiological studies demonstrate the role of early and intensive glycemic control in the prevention of micro and macrovascular disease in both type 1 and type 2 diabetes mellitus (DM). Hyperglycemia elicits several pathways related to the etiopathogenesis of cardiovascular disease (CVD), including the generation of advanced glycation end products (AGEs). In this review, we revisit the role played by AGEs in CVD based in clinical trials and experimental evidence. Mechanistic aspects concerning the recognition of AGEs by the advanced glycosylation end product-specific receptor (AGER) and its counterpart, the dolichyl-diphosphooligosaccharide-protein glycosyltransferase (DDOST) and soluble AGER are discussed. A special focus is offered to the AGE-elicited pathways that promote cholesterol accumulation in the arterial wall by enhanced oxidative stress, inflammation, endoplasmic reticulum stress and impairment in the reverse cholesterol transport (RCT).

Plasma advanced glycation end products and soluble receptor for advanced glycation end products as indicators of sterol content in human carotid atherosclerotic plaques.

Advanced glycation end products (AGEs) are independently related to cardiovascular disease (CVD) and favor cholesterol and oxysterol accumulation in macrophage foam cells. Soluble RAGE (sRAGE) impairs cellular AGE signaling alleviating the deleterious effects of AGE in atherogenesis. The association between plasma AGEs and sRAGE with the content of cholesterol, markers of cholesterol synthesis and absorption, and oxysterols in atherosclerotic plaques was evaluated in subjects undergoing carotid endarterectomy.Plasma and carotid plaques were obtained from symptomatic (n = 23) and asymptomatic subjects (n = 40). Lipids from plaques were extracted and sterols (oxysterols, cholesterol, desmosterol, lathosterol, sitosterol, and campesterol) were determined by using gas chromatography/mass spectrometry. Plasma total AGEs and pentosidine were measured by using fluorimetry and sRAGE by using ELISA.In symptomatic subjects´ atherosclerotic plaques, an increased amount of cholesterol (3x) and oxysterols [7 α-hydroxycholesterol (1.4x); 7 ß-hydroxycholesterol (1.2x); 25-hydroxycholesterol (1.3x); 24-hydroxycholesterol (2.7x), and 27-hydroxycholesterol, (1.15x)], with exception to 7 ketocholesterol, were found in comparison to asymptomatic individuals. Plasma total AGEs and pentosidine significantly and positively correlated to sterols accumulated in the atherosclerotic lesion, including cholesterol, desmosterol, campesterol, sitosterol, and oxysterols. On the other hand, sRAGE inversely correlated to total AGEs and pentosidine in plasma, and with major species of oxysterols, cholesterol, and markers of cholesterol synthesis and absorption in the atherosclerotic lesion. In multiple regression analyses, it was observed a significant inverse correlation between sRAGE and 24-hydroxycholesterol and desmosterol, and a positive significant correlation between pentosidine and 24-hydroxycholesterol, 27-hydroxycholesterol, and campesterol.In conclusion, the plasma concentration of AGEs and sRAGE is a tool to predict the accumulation of sterols in atherosclerotic lesions in symptomatic and asymptomatic individuals, helping to prevent and improve the management of acute cardiovascular complications.

Enrichment of apolipoprotein A-IV and apolipoprotein D in the HDL proteome is associated with HDL functions in diabetic kidney disease without dialysis.

BACKGROUND AND AIMS: Diabetic kidney disease (DKD) is associated with lipid derangements that worsen kidney function and enhance cardiovascular (CVD) risk. The management of dyslipidemia, hypertension and other traditional risk factors does not completely prevent CVD complications, bringing up the participation of nontraditional risk factors such as advanced glycation end products (AGEs), carbamoylation and changes in the HDL proteome and functionality. The HDL composition, proteome, chemical modification and functionality were analyzed in nondialysis subjects with DKD categorized according to the estimated glomerular filtration rate (eGFR) and urinary albumin excretion rate (AER). METHODS: Individuals with DKD were divided into eGFR> 60 mL/min/1.73 m2 plus AER stages A1 and A2 (n = 10) and eGFR< 60 plus A3 (n = 25) and matched by age with control subjects (eGFR> 60; n = 8). RESULTS: Targeted proteomic analyses quantified 28 proteins associated with HDL in all groups, although only 2 were more highly expressed in the eGFR< 60 + A3 group than in the controls: apolipoprotein D (apoD) and apoA-IV. HDL from the eGFR< 60 + A3 group presented higher levels of total AGEs (20%), pentosidine (6.3%) and carbamoylation (4.2 x) and a reduced ability to remove 14C-cholesterol from macrophages (33%) in comparison to HDL from controls. The antioxidant role of HDL (lag time for LDL oxidation) was similar among groups, but HDL from the eGFR< 60 + A3 group presented a greater ability to inhibit the secretion of IL-6 and TNF-alpha (95%) in LPS-elicited macrophages in comparison to the control group. CONCLUSION: The increase in apoD and apoA-IV could contribute to counteracting the HDL chemical modification by AGEs and carbamoylation, which contributes to HDL loss of function in well-established DKD.

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 (14) C-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.

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.

Advanced glycated albumin isolated from poorly controlled type 1 diabetes mellitus patients alters macrophage gene expression impairing ABCA-1-mediated reverse cholesterol transport.

BACKGROUND: We evaluated the effects of albumin isolated from control individuals and from patients with poorly controlled type 1 diabetes mellitus on macrophage gene expression and on reverse cholesterol transport. METHODS: Serum albumin was purified from control subjects (n = 12) and from patients with poorly controlled type 1 diabetes mellitus (n = 13). (14)C-cholesterol-labelled J774 macrophages treated with albumin were employed to measure cholesterol efflux mediated by apo A-I, HDL(3) or HDL(2), the intracellular lipid accumulation and the cellular ABCA-1 protein content. Agilent arrays (44000 probes) were used to analyse gene expression. Several differentially expressed genes were validated by real-time reverse transcription-PCR using TaqMan Two Step RT-PCR. RESULTS: Levels of glycation-modified and (carboxymethyl)lysine-modified albumin were higher in diabetic patients than in control subjects. Apo A-I-mediated and HDL(2)-mediated cellular cholesterol efflux were impaired in macrophages treated with albumin from diabetic patients in comparison with control albumin-treated cells, which was attributed to the reduction in ABCA-1 protein content. Even in the presence of cholesterol acceptors, a higher level of intracellular lipid was observed in macrophages exposed to albumin from diabetic individuals in comparison with the control. The reduction in ABCA-1 content was associated with enhanced expression of stearoyl CoA desaturase 1 and decreased expression of janus kinase 2, which were induced by albumin from patients with type 1 diabetes mellitus. CONCLUSIONS: (Carboxymethyl)lysine-modified albumin isolated from poorly controlled type 1 diabetic patients impairs ABCA-1-mediated reverse cholesterol transport and elicits intracellular lipid accumulation, possibly contributing to atherosclerosis.

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.

Aminoguanidine and metformin prevent the reduced rate of HDL-mediated cell cholesterol efflux induced by formation of advanced glycation end products.

OBJECTIVE: The mechanisms whereby advanced glycation end products (AGE) contribute to atherogenesis in diabetes mellitus are not fully understood. In this study we analyzed in vitro the influence of advanced glycated albumin (AGE-albumin) as well as the role of the AGE inhibitors--aminoguanidine (AMG) and metformin (MF)--on the cell cholesterol efflux. METHODS: HDL3 and albumin-mediated cholesterol efflux was measured in mouse peritoneal macrophages and in SR-BI transfected cells that had been treated along time with dicarbonyl sugars or AGE-albumin, both in the presence or in the absence of AMG and MF. 125I-HDL3 cell binding and 125I-AGE-albumin cell degradation were measured. Carboxymethyllysine (CML) formation and SR-BI expressions were determined by immunoblot. RESULTS: AGE-albumin efficiently trapped cell cholesterol but impaired the HDL-mediated cell cholesterol efflux by decreasing HDL binding to the cell surface and inducing intracellular glycoxidation, without interfering with the SR-BI expression. Cell treatment with dicarbonyl sugars also disrupted the HDL-mediated cell cholesterol efflux, but this was prevented by AMG and MF that reduced CML formation. CONCLUSIONS: By adversely impairing the HDL-mediated cell cholesterol removal rate, AGE-albumin and cell glycoxidation could facilitate the development of premature atherosclerosis in diabetes mellitus (DM) and in other diseases associated with carbonyl and oxidative stress like in chronic uremia. Thus, drugs that prevent AGE formation may be useful to correct disturbances in cell cholesterol transport.