Low Density Lipoprotein Metabolism by Human Macrophages Activated with Low Density Lipoprotein Immune Complexes: A Possible Mechanism of Foam Cell Formation

Human monocytes are known to be multifunctional cells that combine a variety of functions, including phagocytosis, antigen processing and presentation to immune cells, secretion of a large number of bioactive products with significant roles in the immune and inflammatory reactions, and the ability to kill tumor cells and other abnormal cells by a variety of mechanisms, including antibody-dependent cell-mediated cytotoxicity (1-5). Tissue macrophages are believed to derive from circulating monocytes, although the two types of cells differ by a variety of morphological and functional criteria (6-10). The role of macrophages is not always well understood, since it combines potentially useful properties related to its ability to ingest and process foreign and altered materials with the capacity to secrete large amounts of mediators having the potential to cause inflammatory changes and tissue damage in general (11-14). In atherosclerosis, substantial evidence has been gathered suggesting that the foam cells seen in early atherosclerotic plaques are derived from monocytes/macrophages (15-18). The formation and subendothelial accumulation of foam cells are believed to represent a critical event in the onset of atheromatous plaque formation (19). Some interesting correlations can be drawn between the involvement of macrophages in the pathogenesis of atherosclerosis and increasing evidence suggesting that immunologic mechanisms may influence the development or evolution of this pathologic process. In the early 1970s, it was postulated that immune mechanisms involving circulating immune complexes could contribute to the pathogenesis of atherosclerosis (20). The evidence supporting this role of immune complexes was both experimental (animals undergoing serum sickness and given a lipid-rich diet developed accelerated atherosclerosis [21]) and clinical (patients with IgA myelomas with anti-lipoprotein activity had massive hyperlipemia and accelerated atherosclerosis [22]). More recently, it was also shown that immune complexes (IC)1 involving low density lipoprotein (LDL) induce profound changes on cholesterol metabolism at the cellular level (23). Further support for the involvement of IC in the pathogenesis of atherosclerosis has been recently obtained by Szondy et al. (24), who demonstrated increased levels of IC and anti-LDL antibodies in patients with clinical manifestations of coronary heart disease. The possibility that IC interactions with macrophages may lead to their activation and, therefore, play a pathogenic role in the development of atherosclerosis is extremely challenging. Until recently, the mechanism proposed to explain how monocyte-derived macrophages could be transformed into foam cells has focused upon the interaction between macrophages and modified LDL or lipoproteins of abnormal composition, such as β-very low density lipoproteins (VLDL). Modified LDL can be taken up in a nonregulated fashion via the scavenger receptor, resulting in the intracellular accumulation of cholesteryl esters (CE) and in the formation of a foam cell. In contrast, it has been observed that cultured macrophages exposed to native LDL (NLDL) do not accumulate CE due to the stringent regulation of LDL receptors. However, it has been recently shown that in certain conditions, macrophages exposed to native LDL may accumulate CE. In our laboratory, we have shown that human macrophages stimulated with microbial or microbial-related products have an increased uptake of N-LDL and accumulated CE (25). Tabas et al. (26) observed increased uptake of N-LDL and concomitant CE accumulation in J774 cells, a mouse macrophage-like tumor cell line. They postulated that this was due to the enhanced metabolic activity of this tumor cell line (26). Klimov, et al. (27) had shown excessive CE accumulation in mouse peritoneal macrophages exposed to LDL immune complexes compared with control cells. A common denominator for all these observations is the known ability of microbial products and immune complexes to activate macrophages. Therefore, we decided to examine the effect of macrophage activation on N-LDL metabolism. More specifically, we wanted to investigate the effect of LDL-anti-LDL IC on N-LDL and cholesterol metabolism in human macrophages, and determine whether this type of IC can induce the transformation of human macrophages into foam cells contributing to the development of atherosclerosis

Differential Trafficking of Oxidized LDL and Oxidized LDL Immune Complexes in Macrophages: Impact on Oxidative Stress

Oxidized low-density lipoproteins (oxLDL) and oxLDL-containing immune complexes (oxLDL-IC) contribute to formation of lipid-laden macrophages (foam cells). It has been shown that oxLDL-IC are considerably more efficient than oxLDL in induction of foam cell formation, inflammatory cytokines secretion, and cell survival promotion. Whereas oxLDL is taken up by several scavenger receptors, oxLDL-IC are predominantly internalized through the FCgamma receptor I (FCgamma RI). This study examined differences in intracellular trafficking of lipid and apolipoprotein moieties of oxLDL and oxLDL-IC and the impact on oxidative stress.Fluorescently labeled lipid and protein moieties of oxLDL co-localized within endosomal and lysosomal compartments in U937 human monocytic cells. In contrast, the lipid moiety of oxLDL-IC was detected in the endosomal compartment, whereas its apolipoprotein moiety advanced to the lysosomal compartment. Cells treated with oxLDL-IC prior to oxLDL demonstrated co-localization of internalized lipid moieties from both oxLDL and oxLDL-IC in the endosomal compartment. This sequential treatment likely inhibited oxLDL lipid moieties from trafficking to the lysosomal compartment. In RAW 264.7 macrophages, oxLDL-IC but not oxLDL induced GFP-tagged heat shock protein 70 (HSP70) and HSP70B', which co-localized with the lipid moiety of oxLDL-IC in the endosomal compartment. This suggests that HSP70 family members might prevent the degradation of the internalized lipid moiety of oxLDL-IC by delaying its advancement to the lysosome. The data also showed that mitochondrial membrane potential was decreased and generation of reactive oxygen and nitrogen species was increased in U937 cell treated with oxLDL compared to oxLDL-IC.Findings suggest that lipid and apolipoprotein moieties of oxLDL-IC traffic to separate cellular compartments, and that HSP70/70B' might sequester the lipid moiety of oxLDL-IC in the endosomal compartment. This mechanism could ultimately influence macrophage function and survival. Furthermore, oxLDL-IC might regulate the intracellular trafficking of free oxLDL possibly through the induction of HSP70/70B'

Risk Factors Related to Inflammation and Endothelial Dysfunction in the DCCT/EDIC Cohort and Their Relationship With Nephropathy and Macrovascular Complications

OBJECTIVE—Because endothelial cell dysfunction and inflammation are key contributors to the development of complications in type 1 diabetes, we studied risk factors related to endothelial dysfunction and inflammation (C-reactive protein and fibrinogen, soluble vascular cell adhesion molecule-1, intracellular adhesion molecule-1, and E-selectin, and fibrinolytic markers) in a subgroup of patients from the Diabetes Control and Complications Trial (DCCT)/Epidemiology of Diabetes Intervention and Complications (EDIC) study cohort

Prevalence of Abnormal Lipid Profiles and the Relationship With the Development of Microalbuminuria in Adolescents With Type 1 Diabetes

OBJECTIVE: To explore the prevalence of lipid abnormalities and their relationship with albumin excretion and microalbuminuria in adolescents with type 1 diabetes. RESEARCH DESIGN AND METHODS: The study population comprised 895 young subjects with type 1 diabetes (490 males); median age at the baseline assessment was 14.5 years (range 10-21.1), and median diabetes duration was 4.8 years (0.2-17). A total of 2,194 nonfasting blood samples were collected longitudinally for determination of total cholesterol, LDL cholesterol, HDL cholesterol, TG, and non-HDL cholesterol. Additional annually collected data on anthropometric parameters, A1C, and albumin-to-creatinine ratio (ACR) were available. RESULTS: Total cholesterol, LDL cholesterol, HDL cholesterol, and non-HDL cholesterol were higher in females than in males (all P 5.2 mmol/l (18.6%), non-HDL cholesterol >3.4 mmol/l (25.9%), TG >1.7 mmol/l (20.1%), and LDL cholesterol >3.4 mmol/l (9.6%). Age and duration were significantly related to all lipid parameters (P < 0.001); A1C was independently related to all parameters (P < 0.001) except HDL cholesterol, whereas BMI SD scores were related to all parameters (P < 0.05) except total cholesterol. Total cholesterol and non-HDL cholesterol were independently related to longitudinal changes in ACR (B coefficient +/- SE): 0.03 +/- 0.01/1 mmol/l, P = 0.009, and 0.32 +/- 0.014/1 mmol/l, P = 0.02, respectively. Overall mean total cholesterol and non-HDL cholesterol were higher in microalbuminuria positive (n = 115) than in normoalbuminuric subjects (n = 780): total cholesterol 4.7 +/- 1.2 vs. 4.5 +/- 0.8 mmol/l (P = 0.04) and non-HDL cholesterol 3.2 +/- 1.2 vs. 2.9 +/- 0.8 mmol/l (P = 0.03). CONCLUSIONS: In this longitudinal study of adolescents with type 1 diabetes, sustained lipid abnormalities were related to age, duration, BMI, and A1C. Furthermore, ACR was related to both total cholesterol and non-HDL cholesterol, indicating a potential role in the pathogenesis of diabetic nephropathy

Association of homocysteine and methylene tetrahydrofolate reductase (MTHFR C677T) gene polymorphism with coronary artery disease (CAD) in the population of North India

The implications of the methylene tetrahydrofolate reductase (MTHFR) gene and the level of homocysteine in the pathogenesis of coronary artery disease (CAD) have been extensively studied in various ethnic groups. Our aim was to discover the association of MTHFR (C677T) polymorphism and homocysteine level with CAD in north Indian subjects. The study group consisted of 329 angiographically proven CAD patients, and 331 age and sex matched healthy individuals as controls. MTHFR (C677T) gene polymorphism was detected based on the polymerase chain reaction and restriction digestion with HinfI. Total homocysteine plasma concentration was measured using immunoassay. T allele frequency was found to be significantly higher in patients than in the control group. We found significantly elevated levels of mean homocysteine in the patient group when compared to the control group (p = 0.00). Traditional risk factors such as diabetes, hypertension, smoking habits, a positive family history and lipid profiles (triglyceride, total cholesterol, HDL-cholesterol, LDL-cholesterol, VLDL-cholesterol), were found significantly associated through univariate analysis. Furthermore, multivariable logistics regression analysis revealed that CAD is significantly and variably associated with diabetes, hypertension, smoking, triglycerides and HDL-cholesterol. Our findings showed that MTHFR C677T polymorphism and homocysteine levels were associated with coronary artery disease in the selected population

Diets containing sea cucumber (Isostichopus badionotus) meals are hypocholesterolemic in young rats

Peer reviewedPublisher PD

Piper sarmentosum inhibits ICAM-1 and Nox4 gene expression in oxidative stress-induced human umbilical vein endothelial cells

<p>Abstract</p> <p>Background</p> <p>Aqueous extract of <it>Piper sarmentosum </it>(AEPS) is known to possess antioxidant and anti-atherosclerotic activities but the mechanism responsible for it remains unclear. In early part of atherosclerosis, nuclear factor-kappa B (NF-κB) induces the expression of cellular adhesion molecules such as vascular cell adhesion molecule-1 (VCAM-1), intracellular adhesion molecule-1 (ICAM-1) and E-selectin. NADPH oxidase 4 (Nox4) is the predominant source of superoxide in the endothelial cells whereas superoxide dismutase 1 (SOD1), catalase (CAT) and glutathione peroxidase (GPx) are the antioxidant enzymes responsible for inactivating reactive oxygen species. The present study aimed to investigate the effects of AEPS on the gene expression of NF-κB, VCAM-1, ICAM-1, E-selectin, Nox4, SOD1, CAT and GPx in cultured human umbilical vein endothelial cells (HUVECs).</p> <p>Methods</p> <p>HUVECs were divided into four groups:- control; treatment with 180 μM hydrogen peroxide (H₂O₂); treatment with 150 μg/mL AEPS and concomitant treatment with AEPS and H₂O₂for 24 hours. Total RNA was extracted from all the groups of HUVEC using TRI reagent. Subsequently, qPCR was carried out to determine the mRNA expression of NF-κB, VCAM-1, ICAM-1, E-selectin, Nox4, SOD1, CAT and GPx. The specificity of the reactions was verified using melting curve analysis and agarose gel electrophoresis.</p> <p>Results</p> <p>When stimulated with H₂O₂, HUVECs expressed higher level of ICAM-1 (1.3-fold) and Nox4 (1.2-fold) mRNA expression. However, AEPS treatment led to a reduction in the mRNA expression of ICAM-1 (p < 0.01) and Nox4 (p < 0.05) in the H₂O₂-induced HUVECs. AEPS also upregulated the mRNA expression of SOD1 (p < 0.05), CAT (p < 0.01) and GPx (p < 0.05) in oxidative stress-induced HUVECs. There was no significant change in the mRNA expression of VCAM-1 and E-selectin.</p> <p>Conclusion</p> <p>The expressional suppression of ICAM-1 and Nox4 and induction of antioxidant enzymes might be an important component of the vascular protective effect of AEPS.</p

Cardiovasc Diabetol

BACKGROUND: Advanced glycation end-products play a role in diabetic vascular complications. Their optical properties allow to estimate their accumulation in tissues by measuring the skin autofluorescence (SAF). We searched for an association between SAF and major adverse cardiovascular events (MACE) incidence in subjects with Type 1 Diabetes (T1D) during a 7 year follow-up. METHODS: During year 2009, 232 subjects with T1D were included. SAF measurement, clinical [age, sex, body mass index (BMI), comorbidities] and biological data (HbA1C, blood lipids, renal parameters) were recorded. MACE (myocardial infarction, stroke, lower extremity amputation or a revascularization procedure) were registered at visits in the center or by phone call to general practitioners until 2016. RESULTS: The participants were mainly men (59.5%), 51.5 +/- 16.7 years old, with BMI 25.0 +/- 4.1 kg/m(2), diabetes duration 21.5 +/- 13.6 years, HbA1C 7.6 +/- 1.1%. LDL cholesterol was 1.04 +/- 0.29 g/L, estimated Glomerular Filtration Rates (CKD-EPI): 86.3 +/- 26.6 ml/min/1.73 m(2). Among these subjects, 25.1% were smokers, 45.3% had arterial hypertension, 15.9% had elevated AER (>/= 30 mg/24 h), and 9.9% subjects had a history of previous MACE. From 2009 to 2016, 22 patients had at least one new MACE: 6 myocardial infarctions, 1 lower limb amputation, 15 revascularization procedures. Their SAF was 2.63 +/- 0.73 arbitrary units (AU) vs 2.08 +/- 0.54 for other patients (p = 0.002). Using Cox-model, after adjustment for age (as the scale time), sex, diabetes duration, BMI, hypertension, smoking status, albumin excretion rates, statin treatment and a previous history of MACE, higher baseline levels of SAF were significantly associated with an increased risk of MACE during follow-up (HR = 4.13 [1.30-13.07]; p = 0.02 for 1 AU of SAF) and Kaplan-Meier curve follow-up showed significantly more frequent MACE in group with SAF upper the median (p = 0.001). CONCLUSION: A high SAF predicts MACE in patients with T1D