Regulation of scavenger receptor expression in smooth muscle cells by protein kinase C: a role for oxidative stress

Knockdown of hsa_circ_0005699 attenuates inflammation and apoptosis induced by ox-LDL in human umbilical vein endothelial cells through regulation of the miR-450b-5p/NFKB1 axis

Atherosclerosis (AS) remains the leading cause of mortality throughout the world, and vascular endothelial cell dysfunction is one of the key events leading to this pathology. In recent years, there has been an increased interest in the role of circulating RNAs in various diseases; these noncoding RNAs can regulate gene products by acting as microRNA (miR) sponges. Furthermore, it has been shown that foam cells exhibit high expression levels of hsa_circ_0005699 (circ_0005699); however, to the best of our knowledge, no previous study has investigated the role of circ_0005699 in the regulation of vascular endothelial function. The present study employed human umbilical vein endothelial cells (HUVECs), which have been widely used to study vascular endothelial cell function. In addition, apolipoprotein E (ApoE)-deficient mice were used, which have been shown to rapidly develop AS and are widely used as a model of this disease. Cellular and biochemical techniques were performed, including gene transfection and short hairpin RNA-mediated gene silencing for cell transfection, luciferase reporter gene assay to confirm predicted genes, Cell Counting Kit-8 assay and flow cytometry to assess cell viability and apoptosis, and reverse transcription-quantitative PCR and western blotting for detection of mRNA and protein expression. In the present study, the expression levels of circ_0005699 were increased by oxidized low-density lipoprotein in a time- and dose-dependent manner in HUVECs; this was also associated with increased apoptosis of these cells. In addition, the expression levels of circ_0005699 were elevated, along with increased levels of inflammatory cytokines, in ApoE-deficient mice. An RNA pull-down assay indicated that circ_0005699 can bind miR-450b-5p to decrease its expression, whereas silencing of circ_0005699 resulted in increased expression of miR-450b-5p. In addition, the online bioinformatics tool starBase predicted NFKB1 as a target gene of miR-450b-5p, which was further confirmed by the luciferase reporter gene assay. Notably, knockdown of circ_0005699 resulted in the increased survival of HUVECs, which was associated with decreased protein expression levels of NFKB1 and inflammatory cytokines. By contrast, the effects of circ-0005699 silencing on survival were reversed by miR-450b-5p inhibition or NFKB1 overexpression. In conclusion, knockdown of circ_0005699 may ameliorate endothelial cell injury through regulation of the miR-450b-5P/NFKB1 signaling axis.

Smooth Muscle Cell—Macrophage Interactions Leading to Foam Cell Formation in Atherosclerosis: Location, Location, Location

Cholesterol-overloaded cells or “foam cells” in the artery wall are the biochemical hallmark of atherosclerosis, and are responsible for much of the growth, inflammation and susceptibility to rupture of atherosclerotic lesions. While it has previously been thought that macrophages are the main contributor to the foam cell population, recent evidence indicates arterial smooth muscle cells (SMCs) are the source of the majority of foam cells in both human and murine atherosclerosis. This review outlines the timeline, site of appearance and proximity of SMCs and macrophages with lipids in human and mouse atherosclerosis, and likely interactions between SMCs and macrophages that promote foam cell formation and removal by both cell types. An understanding of these SMC-macrophage interactions in foam cell formation and regression is expected to provide new therapeutic targets to reduce the burden of atherosclerosis for the prevention of coronary heart disease, stroke and peripheral vascular disease.

LDL-Based Lipid Nanoparticle Derived for Blood Plasma Accumulates Preferentially in Atherosclerotic Plaque

Apolipoprotein-based drug delivery is a promising approach to develop safe nanoparticles capable of targeted drug delivery for various diseases. In this work, we have synthesized a lipid-based nanoparticle (NPs) that we have called “Aposomes” presenting native apolipoprotein B-100 (apoB-100), the primary protein present in Low-Density Lipoproteins (LDL) on its surface. The aposomes were synthesized from LDL isolated from blood plasma using a microfluidic approach. The synthesized aposomes had a diameter of 91 ± 4 nm and a neutral surface charge of 0.7 mV ± mV. Protein analysis using western blot and flow cytometry confirmed the presence of apoB-100 on the nanoparticle’s surface. Furthermore, Aposomes retained liposomes’ drug loading capabilities, demonstrating a prolonged release curve with ∼80% cargo release at 4 hours. Considering the natural tropism of LDL towards the atherosclerotic plaques, we evaluated the biological properties of aposomes in a mouse model of advanced atherosclerosis. We observed a ∼20-fold increase in targeting of plaques when comparing aposomes to control liposomes. Additionally, aposomes presented a favorable biocompatibility profile that showed no deviation from typical values in liver toxicity markers (i.e., LDH, ALT, AST, Cholesterol). The results of this study demonstrate the possibilities of using apolipoprotein-based approaches to create nanoparticles with active targeting capabilities and could be the basis for future cardiovascular therapies.

Role of inflammatory cytokines in genesis and treatment of atherosclerosis

Atherosclerosis demonstrates an increased rate of vascular smooth muscle cells (VSMC) plasticity characterized by switching from the differentiated contractile phenotype to a de-differentiated synthetic state. In healthy blood vessels, phenotypic switching represents a fundamental property of VSMC in maintaining vascular homeostasis. However, in atherosclerosis, it is an initial and necessary step in VSMC-derived foam cell formation. These foam cells play a decisive role in atherosclerosis progression since approximately half of all the foam cells are of VSMC origin. Our recent work showed that interferon-gamma (IFN-γ), a primary inflammatory cytokine in progressive atherosclerosis, mediates VSMC phenotype switching exclusively through upregulating mini-tryptophanyl-tRNA synthetase (mini-TrpRS). Here, we discuss the pro-atherosclerotic implication of this phenomenon that inevitably occurs in the context of a more complex regulation mediated by IFN-γ. An emerging therapeutic option for patients with progressive atherosclerosis is also discussed.

Molecular Imaging of Inflammation in a Mouse Model of Atherosclerosis Using a Zirconium-89-Labeled Probe

Background

Beyond clinical atherosclerosis imaging of vessel stenosis and plaque morphology, early detection of inflamed atherosclerotic lesions by molecular imaging could improve risk assessment and clinical management in high-risk patients. To identify inflamed atherosclerotic lesions by molecular imaging in vivo, we studied the specificity of our radiotracer based on maleylated (Mal) human serum albumin (HSA), which targets key features of unstable atherosclerotic lesions.

Materials and Methods

Mal-HSA was radiolabeled with a positron-emitting metal ion, zirconium-89 (⁸⁹Zr⁴⁺). The targeting potential of this probe was compared with unspecific ⁸⁹Zr-HSA and ¹⁸F-FDG in an experimental model of atherosclerosis (Apoe^–/– mice, n=22), and compared with wild-type (WT) mice (C57BL/6J, n=21) as controls.

Results

PET/MRI, gamma counter measurements, and autoradiography showed the accumulation of ⁸⁹Zr-Mal-HSA in the atherosclerotic lesions of Apoe^–/– mice. The maximum standardized uptake values (SUV_max) for ⁸⁹Zr-Mal-HSA at 16 and 20 weeks were 26% and 20% higher (P<0.05) in Apoe^–/– mice than in control WT mice, whereas no difference in SUV_max was observed for ¹⁸F-FDG in the same animals. ⁸⁹Zr-Mal-HSA uptake in the aorta, as evaluated by a gamma counter 48 h postinjection, was 32% higher (P<0.01) for Apoe^–/– mice than in WT mice, and the aorta-to-blood ratio was 8-fold higher (P<0.001) for ⁸⁹Zr-Mal-HSA compared with unspecific ⁸⁹Zr-HSA. HSA-based probes were mainly distributed to the liver, spleen, kidneys, bone, and lymph nodes. The phosphor imaging autoradiography (PI-ARG) results corroborated the PET and gamma counter measurements, showing higher accumulation of ⁸⁹Zr-Mal-HSA in the aortas of Apoe^–/– mice than in WT mice (9.4±1.4 vs 0.8±0.3%; P<0.001).

Conclusion

⁸⁹Zr radiolabeling of Mal-HSA probes resulted in detectable activity in atherosclerotic lesions in aortas of Apoe^–/– mice, as demonstrated by quantitative in vivo PET/MRI. ⁸⁹Zr-Mal-HSA appears to be a promising diagnostic tool for the early identification of macrophage-rich areas of inflammation in atherosclerosis.

Severe hyperbilirubinemia is associated with higher risk of contrast-related acute kidney injury following contrast-enhanced computed tomography

INTRODUCTION

Contrast-induced acute kidney injury (CI-AKI) is associated with high risks of morbidity and mortality. Hyperbilirubinemia might have some renal protection but with no clear cutoff value for protection. Related studies are typically on limited numbers of patients and only in conditions of vascular intervention.

METHODS

We performed this study to elucidate CI-AKI in patients after contrast-enhanced computed tomography (CCT). The outcomes were CI-AKI, dialysis and mortality. Patients were divided to three groups based on their serum levels of total bilirubin: ≤1.2 mg/dl, 1.3-2.0 mg/dl, and >2.0 mg/dl.

RESULTS

We enrolled a total of 9,496 patients who had received CCT. Patients with serum total bilirubin >2.0 mg/dl were associated with CI-AKI. Those undergoing dialysis had the highest incidence of PC-AKI (p<0.001). No difference was found between the two groups of total bilirubin ≤1.2 and 1.3-2.0 mg/dl. Patients with total bilirubin >2mg/dl were associated with CI-AKI (OR = 1.89, 1.53-2.33 of 95% CI), dialysis (OR = 1.40, 1.01-1.95 of 95% CI) and mortality (OR = 1.63, 1.38-1.93 of 95% CI) after adjusting for laboratory data and all comorbidities (i.e., cerebrovascular disease, coronary artery disease, peripheral arterial disease, and acute myocardial infarction, diabetes mellitus, hypertension, gastrointestinal bleeding, cirrhosis, peritonitis, ascites, hepatoma, shock lung and colon cancer). We concluded that total bilirubin level >2 mg/dl is an independent risk factor for CI-AKI, dialysis and mortality after CCT. These patients also had high risks for cirrhosis or hepatoma.

CONCLUSION

This is the first study providing evidence that hyperbilirubinemia (total bilirubin >2.0 mg/dl) being an independent risk factor for CI-AKI, dialysis and mortality after receiving CCT. Most patients with total bilirubin >2.0mg/dl had cirrhosis or hepatoma.

Uptake, depuration and sublethal effects of the neonicotinoid, imidacloprid, exposure in Sydney rock oysters

The broad utilisation of imidacloprid (IMI) in agriculture poses an increasing risk to aquatic organisms. However, the potential impacts on commercially important shellfish and chemical residues after exposure, are yet to be assessed. We investigated the levels of IMI in Sydney rock oyster (SRO) tissue during a three-day uptake and four-day depuration cycle using liquid chromatography-mass spectrometry. IMI was absorbed from the water, with significantly higher concentrations in the adductor muscles than the gills and digestive glands. Depuration was also fast with a significant drop in tissue concentrations after one day in clean water and complete elimination from all tissues except the digestive gland after four days. The distribution of IMI in SRO after direct exposure using mass spectrometry imaging demonstrated uptake and spatially resolved metabolism to hydroxyl-IMI in the digestive gland and IMI-olefin in the gills. We assessed the effects of IMI on filtration rate (FR), acetylcholinesterase (AChE) activity in the gills, and gene expression profiles in the digestive gland using transcriptomics. Exposure to 2 mg/L IMI reduced the FR of oysters on the first day, while exposure to 0.5 and 1 mg/L reduced FR on day four. IMI reduced the gill AChE activity and altered the digestive gland gene expression profile. This study indicates that commercially farmed SRO can uptake IMI from the water, but negative impacts were only detected at concentrations higher than currently detected in estuarine environments and the chemical residues can be effectively eliminated using simple depuration in clean water.

Pathways of smooth muscle foam cell formation in atherosclerosis

PURPOSE OF REVIEW

Smooth muscle cells (SMCs) are the major cell type in human atherosclerosis-prone arteries and take up excess lipids, thereby contributing to luminal occlusion. Here we provide a focused review on pathways by which smooth muscle cells (SMCs) can become foam cells in atherosclerosis.

RECENT FINDINGS

A synthesis of recent and older investigations provides key mechanistic insights into SMC foam cell formation. LDL and other apoB-containing lipoproteins are modified by a diverse array of oxidative, enzymatic, and nonenzymatic processes present in the arterial intima. These modifications of LDL all promote the aggregation of LDL (agLDL), a key finding from analysis of arterial lesion particles. Scavenger receptor and phagocytic capacity of SMCs can vary greatly, perhaps related to differences in SMC phenotype or in-vitro cell culture environments, and can be increased with exposure to cytokines, growth factors, and cholesterol. Macrophages promote the formation of SMC foam cells in direct or indirect co-culture models.

SUMMARY

SMCs contribute significantly to the foam cell population in atherosclerosis. Further investigation and identification of key mechanisms of SMC foam cell formation will help drive new therapeutics to reduce cardiovascular disease.

Oxidized LDL phagocytosis during foam cell formation in atherosclerotic plaques relies on a PLD2-CD36 functional interdependence

The uptake of cholesterol carried by low-density lipoprotein (LDL) is tightly controlled in the body. Macrophages are not well suited to counteract the cellular consequences of excess cholesterol leading to their transformation into "foam cells," an early step in vascular plaque formation. We have uncovered and characterized a novel mechanism involving phospholipase D (PLD) in foam cell formation. Utilizing bone marrow-derived macrophages from genetically PLD deficient mice, we demonstrate that PLD2 (but not PLD1)-null macrophages cannot fully phagocytose aggregated oxidized LDL (Agg-Ox-LDL), which was phenocopied with a PLD2-selective inhibitor. We also report a role for PLD2 in coupling Agg-oxLDL phagocytosis with WASP, Grb2, and Actin. Further, the clearance of LDL particles is mediated by both CD36 and PLD2, via mutual dependence on each other. In the absence of PLD2, CD36 does not engage in Agg-Ox-LDL removal and when CD36 is blocked, PLD2 cannot form protein-protein heterocomplexes with WASP or Actin. These results translated into humans using a GEO database of microarray expression data from atheroma plaques versus normal adjacent carotid tissue and observed higher values for NFkB, PLD2 (but not PLD1), WASP, and Grb2 in the atheroma plaques. Human atherectomy specimens confirmed high presence of PLD2 (mRNA and protein) as well as phospho-WASP in diseased arteries. Thus, PLD2 interacts in macrophages with Actin, Grb2, and WASP during phagocytosis of Agg-Ox-LDL in the presence of CD36 during their transformation into "foam cells." Thus, this study provides new molecular targets to counteract vascular plaque formation and atherogenesis.

Serum bilirubin levels are negatively associated with diabetic retinopathy in patients with type 1 diabetes and normal renal function

INTRODUCTION

Previous studies suggested that total serum bilirubin levels are negatively associated with diabetic retinopathy (DR) and nephropathy in patients with diabetes mellitus. The objective of this study was to explore the relationship between serum total bilirubin levels and prevalence of DR in patients with type 1 diabetes (T1DM) and normal renal function.

METHODS

Study included 163 T1DM with normal renal function (urinary albumin excretion rate <30 mg/24 h, estimated glomerular filtration rate (eGFR) >60 ml min^-11.73 m^-2). Photo-documented retinopathy status was made according to the EURODIAB protocol.

RESULTS

Patients with DR were older (49 vs 42 years, p = 0.001), had higher systolic blood pressure (130 vs 120 mmHg, p = 0.001), triglycerides (0.89 vs 0.77 mmol/L, p = 0.01), and lower serum total bilirubin (12 vs 15 U/L, p = 0.02) and eGFR (100 vs 106 ml min^-11.73 m^-2, p = 0.03). In multivariate logistic regression analysis, only total serum bilirubin was significantly associated with risk of DR in our subjects (OR 0.88, CI 0.81-0.96, p = 0.006).

CONCLUSION

These data suggest that serum total bilirubin levels are independently negatively associated with DR in T1DM with normal renal function. Prospective studies are needed to confirm whether lower serum total bilirubin has predictive value for the development of DR in T1DM with normal renal function.

Cell wall glycopolymers of Firmicutes and their role as nonprotein adhesins

Cell wall glycopolymers (CWGs) of gram-positive bacteria have gained increasing interest with respect to their role in colonization and infection. In most gram-positive pathogens they constitute a large fraction of the cell wall biomass and represent major cell envelope determinants. Depending on their chemical structure they modulate interaction with complement factors and play roles in immune evasion or serve as nonprotein adhesins that mediate, especially under dynamic conditions, attachment to different host cell types. In particular, covalently peptidoglycan-attached CWGs that extend well above the cell wall seem to interact with glyco-receptors on host cell surfaces. For example, in the case of Staphylococcus aureus, the cell wall-attached teichoic acid (WTA) has been identified as a major CWG adhesin. A recent report indicates that a type-F scavenger receptor, termed SR-F1 (SREC-I), is the predominant WTA receptor in the nasal cavity and that WTA-SREC-I interaction plays an important role in S. aureus nasal colonization. Therefore, understanding the role of CWGs in complex processes that mediate colonization and infection will allow novel insights into the mechanisms of host-microbiota interaction.

Enzymatically Modified Low-Density Lipoprotein Promotes Foam Cell Formation in Smooth Muscle Cells via Macropinocytosis and Enhances Receptor-Mediated Uptake of Oxidized Low-Density Lipoprotein

OBJECTIVE

Enzyme-modified nonoxidized low-density lipoprotein (ELDL) is present in human atherosclerotic lesions. Our objective is to understand the mechanisms of ELDL uptake and its effects on vascular smooth muscle cells (SMC).

APPROACH AND RESULTS

Transformation of murine aortic SMCs into foam cells in response to ELDL was analyzed. ELDL, but not acetylated or oxidized LDL, was potent in inducing SMC foam cell formation. Inhibitors of macropinocytosis (LY294002, wortmannin, amiloride) attenuated ELDL uptake. In contrast, inhibitors of receptor-mediated endocytosis (dynasore, sucrose) and inhibitor of caveolae-/lipid raft-mediated endocytosis (filipin) had no effect on ELDL uptake in SMC, suggesting that macropinocytosis is the main mechanism of ELDL uptake by SMC. Receptor for advanced glycation end products (RAGE) is not obligatory for ELDL-induced SMC foam cell formation, but primes SMC for the uptake of oxidized LDL in a RAGE-dependent manner. ELDL increased intracellular reactive oxygen species, cytosolic calcium, and expression of lectin-like oxidized LDL receptor-1 in wild-type SMC but not in RAGE(-/-) SMC. The macropinocytotic uptake of ELDL is regulated predominantly by intracellular calcium because ELDL uptake was completely inhibited by pretreatment with the calcium channel inhibitor lacidipine in wild-type and RAGE(-/-) SMC. This is in contrast to pretreatment with PI3 kinase inhibitors which completely prevented ELDL uptake in RAGE(-/-) SMC, but only partially in wild-type SMC.

CONCLUSIONS

ELDL is highly potent in inducing foam cells in murine SMC. ELDL endocytosis is mediated by calcium-dependent macropinocytosis. Priming SMC with ELDL enhances the uptake of oxidized LDL.

MK2 inhibitory peptide delivered in nanopolyplexes prevents vascular graft intimal hyperplasia

Autologous vein grafts are commonly used for coronary and peripheral artery bypass but have a high incidence of intimal hyperplasia (IH) and failure. We present a nanopolyplex (NP) approach that efficiently delivers a mitogen-activated protein kinase (MAPK)-activated protein (MAPKAP) kinase 2 inhibitory peptide (MK2i) to graft tissue to improve long-term patency by inhibiting pathways that initiate IH. In vitro testing in human vascular smooth muscle cells revealed that formulation into MK2i-NPs increased cell internalization, endosomal escape, and intracellular half-life of MK2i. This efficient delivery mechanism enabled MK2i-NPs to sustain potent inhibition of inflammatory cytokine production and migration in vascular cells. In intact human saphenous vein, MK2i-NPs blocked inflammatory and migratory signaling, as confirmed by reduced phosphorylation of the posttranscriptional gene regulator heterogeneous nuclear ribonucleoprotein A0, the transcription factor cAMP (adenosine 3',5'-monophosphate) element-binding protein, and the chaperone heat shock protein 27. The molecular effects of MK2i-NPs caused functional inhibition of IH in human saphenous vein cultured ex vivo. In a rabbit vein transplant model, a 30-min intraoperative graft treatment with MK2i-NPs significantly reduced in vivo IH 28 days posttransplant compared with untreated or free MK2i-treated grafts. The decrease in IH in MK2i-NP-treated grafts in the rabbit model also corresponded with decreased cellular proliferation and maintenance of the vascular wall smooth muscle cells in a more contractile phenotype. These data indicate that nanoformulated MK2 inhibitors are a promising strategy for preventing graft failure.

Scavenger receptor structure and function in health and disease

Scavenger receptors (SRs) are a ‘superfamily’ of membrane-bound receptors that were initially thought to bind and internalize modified low-density lipoprotein (LDL), though it is currently known to bind to a variety of ligands including endogenous proteins and pathogens. New family of SRs and their properties have been identified in recent years, and have now been classified into 10 eukaryote families, defined as Classes A-J. These receptors are classified according to their sequences, although in each class they are further classified based in the variations of the sequence. Their ability to bind a range of ligands is reflected on the biological functions such as clearance of modified lipoproteins and pathogens. SR members regulate pathophysiological states including atherosclerosis, pathogen infections, immune surveillance, and cancer. Here, we review our current understanding of SR structure and function implicated in health and disease.

Preeclampsia serum-induced collagen I expression and intracellular calcium levels in arterial smooth muscle cells are mediated by the PLC-γ1 pathway

In women with preeclampsia (PE), endothelial cell (EC) dysfunction can lead to altered secretion of paracrine factors that induce peripheral vasoconstriction and proteinuria. This study examined the hypothesis that PE sera may directly or indirectly, through human umbilical vein ECs (HUVECs), stimulate phospholipase C-γ1-1,4,5-trisphosphate (PLC-γ1-IP₃) signaling, thereby increasing protein kinase C-α (PKC-α) activity, collagen I expression and intracellular Ca²⁺ concentrations ([Ca²⁺]_i) in human umbilical artery smooth muscle cells (HUASMCs). HUASMCs and HUVECs were cocultured with normal or PE sera before PLC-γ1 silencing. Increased PLC-γ1 and IP₃ receptor (IP₃R) phosphorylation was observed in cocultured HUASMCs stimulated with PE sera (P<0.05). In addition, PE serum significantly increased HUASMC viability and reduced their apoptosis (P<0.05); these effects were abrogated with PLC-γ1 silencing. Compared with normal sera, PE sera increased [Ca²⁺]_i in cocultured HUASMCs (P<0.05), which was inhibited by PLC-γ1 and IP₃R silencing. Finally, PE sera-induced PKC-α activity and collagen I expression was inhibited by PLC-γ1 small interfering RNA (siRNA) (P<0.05). These results suggest that vasoactive substances in the PE serum may induce deposition in the extracellular matrix through the activation of PLC-γ1, which may in turn result in thickening and hardening of the placental vascular wall, placental blood supply shortage, fetal hypoxia–ischemia and intrauterine growth retardation or intrauterine fetal death. PE sera increased [Ca²⁺]_i and induced PKC-α activation and collagen I expression in cocultured HUASMCs via the PLC-γ1 pathway.

Low serum bilirubin concentration is a predictor of chronic kidney disease

OBJECTIVE

Chronic kidney disease (CKD) is a worldwide public health problem. It is very important to identify the factors that affect CKD. Previous studies have reported that serum bilirubin concentration was positively correlated with renal function in a cross-sectional study. The aim of this study was to investigate the relationship between serum bilirubin concentration and the progression of CKD.

METHODS

A cohort study was performed on a consecutive series of 2784 subjects without CKD, defined as estimated glomerular filtration rate (eGFR) < 60 ml/min/1.73 m(2), at baseline. We analyzed the relationship between serum total bilirubin concentration at baseline and new-onset CKD in the general population.

RESULTS

We followed the subjects for a median period of 7.7 years. There were 1157 females and 1627 males, and 231 females and 370 males developed CKD during this period. Multiple Cox regression analyses revealed that serum total bilirubin concentration (hazard ratio (HR) per 1.0 μmol/L increase 0.97 (95% CI 0.95-0.99), P = 0.0084) in addition to age, gamma-glutamyl transpeptidase (GGT), uric acid (UA), creatinine and medication for hypertension in men and serum total bilirubin concentration (HR per 1.0 μmol/L increase 0.96 (95% CI 0.93-1.00), P = 0.0309) in addition to age, GGT, alanine aminotransferase, UA, creatinine and medication for dyslipidemia in women were independent predictors of new-onset CKD, after adjusting for confounders.

CONCLUSION

Our study demonstrated that serum total bilirubin concentration could be a novel risk factor for the progression of CKD, defined as eGFR <60 ml/min/1.73 m(2), in the general population.

Associations between serum total bilirubin levels and functional dependence in the elderly

BACKGROUND

Many studies support the role of bilirubin as a cytoprotector in chronic inflammatory diseases, such as stroke and atherosclerosis.

AIM

To investigate the relationship between serum total bilirubin levels and functional dependence in older adults.

METHODS

Data from the National Health and Nutrition Examination Survey (1999-2002) pertaining to 2235 old adults were analysed. All participants had given a household interview, providing information of five major domains on self-reported functional status (activities of daily living, instrumental activities of daily living, leisure and social activities, lower extremity mobility and general physical activities), had completed serum total bilirubin measurement, and a questionnaire regarding personal health. Poor performance was defined as experiencing difficulty with one or more items in a given domain. Functional dependence was defined as having three or more poor performances in the five major domains. Multiple logistic regression was performed together with quartile-based stratified odds ratio (OR) comparison and trend tests.

RESULTS

The OR of functional dependence for each standard deviation increment in the serum total bilirubin level was 0.56 (P = 0.002). After additional adjustment, the inverse association remained essentially unchanged. In quartile-based analysis, participants with higher quartiles of serum total bilirubin tended to have lower ORs of functional dependence. The trends of lower likelihood of functional dependence across increasing quartiles of the serum total bilirubin level were statistically significant (P < 0.05 for all trends).

CONCLUSIONS

Higher serum total bilirubin levels were associated with lower likelihood of functional dependence in older adults.

Scavenger receptor class A member 3 (SCARA3) in disease progression and therapy resistance in multiple myeloma

This study evaluates the role of scavenger receptor class A member 3 (SCARA3) in multiple myeloma (MM). SCARA3 expression was induced upon treatment with oxidative stressors (ionizing radiation and chemotherapeutic drugs). An epigenetic inactivation of SCARA3 was noted in MM.1S myeloma cells. Myeloma cell killing by dexamethasone and bortezomib was inhibited by up-regulation of SCARA3 while SCARA3 knockdown sensitized myeloma cells to the drugs. Clinical samples showed an inverse correlation between SCARA3 gene expression, myeloma progression, and favorable clinical prognosis. In MM, SCARA3 protects against oxidative stress-induced cell killing and can serve as predictor of MM progression and therapeutic response.

Solid-phase immunoglobulins IgG and IgM activate macrophages with solid-phase IgM acting via a novel scavenger receptor a pathway

IgG may accelerate atherosclerosis via ligation of proinflammatory Fcγ receptors; however, IgM is unable to ligate FcγR and is often considered vasculoprotective. IgM aggravates ischemia-reperfusion injury, and solid-phase deposits of pure IgM, as seen with IgM-secreting neoplasms, are well known clinically to provoke vascular inflammation. We therefore examined the molecular mechanisms by which immunoglobulins can aggravate vascular inflammation, such as in atherosclerosis. We compared the ability of fluid- and solid-phase immunoglobulins to activate macrophages. Solid-phase immunoglobulins initiated prothrombotic and proinflammatory functions in human macrophages, including NF-κB p65 activation, H(2)O(2) secretion, macrophage-induced apoptosis, and tissue factor expression. Responses to solid-phase IgG (but not to IgM) were blocked by neutralizing antibodies to CD16 (FcγRIII), consistent with its known role. Macrophages from mice deficient in macrophage scavenger receptor A (SR-A; CD204) had absent IgM binding and no activation by solid-phase IgM. RNA interference-mediated knockdown of SR-A in human macrophages suppressed activation by solid-phase IgM. IgM binding to SR-A was demonstrated by both co-immunoprecipitation studies and the binding of fluorescently labeled IgM to SR-A-transfected cells. Immunoglobulins on solid-phase particles around macrophages were found in human plaques, increased in ruptured plaques compared with stable ones. These observations indicate that solid-phase IgM and IgG can activate macrophages and destabilize vulnerable plaques. Solid-phase IgM activates macrophages via a novel SR-A pathway.

Distinct regulation of stearoyl-CoA desaturase 1 gene expression by cis and trans C18:1 fatty acids in human aortic smooth muscle cells

Consumption of trans fatty acids is positively correlated with cardiovascular diseases and with atherogenic risk factors. Trans fatty acids might play their atherogenic effects through lipid metabolism alteration of vascular cells. Accumulation of lipids in vascular smooth muscle cells is a feature of atherosclerosis and a consequence of lipid metabolism alteration. Stearoyl-CoA desaturase 1 (scd1) catalyses the production of monounsaturated fatty acids (e.g. oleic acid) and its expression is associated with lipogenesis induction and with atherosclerosis development. We were interested in analysing the regulation of delta-9 desaturation rate and scd1 expression in human aortic smooth muscle cells (HASMC) exposed to cis and trans C18:1 fatty acid isomers (cis-9 oleic acid, trans-11 vaccenic acid or trans-9 elaidic acid) for 48 h at 100 μM. Treatment of HASMC with these C18:1 fatty acid isomers led to differential effects on delta-9 desaturation; oleic acid repressed the desaturation rate more potently than trans-11 vaccenic acid, whereas trans-9 elaidic acid increased the delta-9 desaturation rate. We then correlated the delta-9 desaturation rate with the expression of scd1 protein and mRNA. We showed that C18:1 fatty acids controlled the expression of scd1 at the transcriptional level in HASMC, leading to an increase in scd1 mRNA content by trans-9 elaidic acid treatment, whereas a decrease in scd1 mRNA content was observed with cis-9 oleic acid and trans-11 vaccenic acid treatments. Altogether, this work highlights a differential capability of C18:1 fatty acid isomers to control scd1 gene expression, which presumes of different consequent effects on cell functions.

STAT3 activation in skeletal muscle links muscle wasting and the acute phase response in cancer cachexia

Background

Cachexia, or weight loss despite adequate nutrition, significantly impairs quality of life and response to therapy in cancer patients. In cancer patients, skeletal muscle wasting, weight loss and mortality are all positively associated with increased serum cytokines, particularly Interleukin-6 (IL-6), and the presence of the acute phase response. Acute phase proteins, including fibrinogen and serum amyloid A (SAA) are synthesized by hepatocytes in response to IL-6 as part of the innate immune response. To gain insight into the relationships among these observations, we studied mice with moderate and severe Colon-26 (C26)-carcinoma cachexia.

Methodology/Principal Findings

Moderate and severe C26 cachexia was associated with high serum IL-6 and IL-6 family cytokines and highly similar patterns of skeletal muscle gene expression. The top canonical pathways up-regulated in both were the complement/coagulation cascade, proteasome, MAPK signaling, and the IL-6 and STAT3 pathways. Cachexia was associated with increased muscle pY705-STAT3 and increased STAT3 localization in myonuclei. STAT3 target genes, including SOCS3 mRNA and acute phase response proteins, were highly induced in cachectic muscle. IL-6 treatment and STAT3 activation both also induced fibrinogen in cultured C2C12 myotubes. Quantitation of muscle versus liver fibrinogen and SAA protein levels indicates that muscle contributes a large fraction of serum acute phase proteins in cancer.

Conclusions/Significance

These results suggest that the STAT3 transcriptome is a major mechanism for wasting in cancer. Through IL-6/STAT3 activation, skeletal muscle is induced to synthesize acute phase proteins, thus establishing a molecular link between the observations of high IL-6, increased acute phase response proteins and muscle wasting in cancer. These results suggest a mechanism by which STAT3 might causally influence muscle wasting by altering the profile of genes expressed and translated in muscle such that amino acids liberated by increased proteolysis in cachexia are synthesized into acute phase proteins and exported into the blood.

Relationship of serum bilirubin concentration to kidney function and 24-hour urine protein in Korean adults

Background

The relationships among serum bilirubin concentration, kidney function and proteinuria have yet to be fully elucidated, nor have these relationships been investigated in Korean adults.

Method

We retrospectively reviewed the medical records of Korean adults who were evaluated at Kosin University Gospel Hospital (Busan, Republic of Korea) during a five-year period from January 2005 to December 2009. We evaluated the relationships among serum bilirubin concentration, estimated glomerular filtration rate (eGFR) and 24-hour urinary protein excretion in a sample of 1363 Korean adults aged 18 years or older.

Results

The values of eGFR <60 mL/min/1.73 m² and 24-hour urine albumin ≥150 mg/day were observed in 26.1% (n = 356) and 40.5% (n = 553) of subjects, respectively. Fasting glucose levels ≥126 mg/dL were observed in 44.9% (n = 612) of the total sample. After adjustment for potential confounding factors including demographic characteristics, comorbidities and other laboratory measures, total serum bilirubin was positively associated with eGFR and negatively associated with proteinuria both in the whole cohort and in a subgroup of diabetic individuals.

Conclusions

To our knowledge, this is the first hospital-based study specifically aimed at examining the relationships among serum total bilirubin concentration, 24-hour urine protein and kidney function in Korean adults. We demonstrated that serum total bilirubin concentration was negatively correlated with 24-hour urine protein and positively correlated with eGFR in Korean non-diabetic and diabetic adults.

Low serum bilirubin concentration in haemodialysis patients with Type 2 diabetes

AIMS

Previous studies have implicated reduced serum bilirubin concentrations in the development of cardiovascular disease. The aim of this study was to examine whether bilirubin may explain the high incidence of vascular complications in haemodialysis patients with Type 2 diabetes.

METHODS

We compared serum bilirubin concentrations, as well as other known aetiological risk factors for cardiovascular disease, in 206 Type 2 diabetes patients on haemodialysis with those in 741 Type 2 diabetes patients not receiving haemodialysis, and evaluated the association between serum bilirubin concentration and cardiovascular disease incidence.

RESULTS

Incidences of cardiovascular disease and systolic blood pressure were higher; however, BMI and serum total cholesterol were lower in haemodialysis patients compared with those in patients without haemodialysis. Serum total (0.30 ± 0.10 vs. 0.74 ± 0.26 mg/dl, 0.005 ± 0.002 vs. 0.013 ± 0.004 mmol/l, P < 0.0001) and indirect (0.17 ± 0.08 vs. 0.70 ± 0.23 mg/dl, 0.003 ± 0.001 vs. 0.012 ± 0.004 mmol/l, P < 0.0001) bilirubin were lower in haemodialysis patients compared with those in patients without haemodialysis. Stepwise regression analysis demonstrated that age (β = 0.109, F = 5.959, P < 0.05), duration of diabetes (β = -0.112, F = 6.048, P < 0.05), sex (β = -0.123, F = 8.623, P < 0.05), cardiovascular disease events (β = -0.099, F = 5.131, P < 0.05) and presence of haemodialysis (β = -0.626, F = 201.727, P < 0.01) were independent factors for serum total bilirubin. Logistic regression demonstrated that age (OR 1.089, 95% CI 1.044-1.136; P < 0.0001), duration of diabetes (OR 1.029, 95% CI 1.001-1.059; P = 0.0423), body mass index (OR 1.115, 95% CI 1.001-1.242; P = 0.0487), habit of smoking (OR 2.445, 95% CI 1.046-5.716; P = 0.0391) and serum total bilirubin (OR 0.192, 95% CI 0.037-0.989; P = 0.0484) were independent factors for cardiovascular disease events.

CONCLUSIONS

Low serum bilirubin concentration could be one of the important factors for the high incidence of cardiovascular disease in Type 2 diabetes patients receiving haemodialysis.

Aged garlic extract inhibits CD36 expression in human macrophages via modulation of the PPARgamma pathway

Expression of CD36 scavenger receptors on macrophages is involved in oxidized low-density lipoprotein uptake and foam cell formation during atherosclerotic lesion development. We examined the effects of aged garlic extract (AGE), a garlic preparation enriched in water-soluble cysteinyl moieties that increases cellular total thiols and glutathione concentrations, on CD36 expression in human monocytes/macrophages (THP-1 cells and primary human monocytes). Compared to control, AGE (1-5 mg/mL) dose-dependently and significantly suppressed CD36 expression up to by 61.8 +/- 7.4% in THP-1-derived macrophages and up to 50.5 +/- 7.1% in primary human macrophages, respectively. Furthermore, AGE prevented induction of CD36 expression by the peroxisome proliferator activator receptor (PPAR) gamma agonist troglitazone, and decreased binding of nuclear proteins to a PPARgamma response element. AGE showed a stronger inhibitory effect on CD36 expression in THP-1 cells during simultaneous incubation with phorbol 12-myristate 13-acetate (PMA) compared to cells that had been pre-incubated with PMA. Furthermore, AGE decreased CD11b expression in a dose-dependent manner. These data indicate that AGE inhibits CD36 expression by modulating the PPARgamma pathway in human macrophages and monocytes differentiation into macrophages, and suggests that the extract could be useful for the prevention of atherosclerotic lesions.

Inhibition of MMP-2 gene expression with small interfering RNA in rabbit vascular smooth muscle cells

Matrix metalloproteinase-2 (MMP-2) is constitutively expressed in vascular smooth muscle cells (VSMCs). Using small interfering RNA (siRNA), we evaluated the effect of MMP-2 inhibition in VSMCs in vitro and ex vivo. Rabbit VSMCs were transfected in vitro with 50 nmol/l MMP-2 siRNA or scramble siRNA. Flow cytometry and confocal microscopy showed cellular uptake of siRNA in ∼80% of VSMCs. MMP-2 mRNA levels evaluated by real-time RT-PCR, pro-MMP-2 activity from conditioned culture media evaluated by gelatin zymography, and VSMC migration were reduced by 44 ± 19%, 43 ± 14%, and 36 ± 14%, respectively, in MMP-2 siRNA-transfected compared with scramble siRNA-transfected VSMCs ( P < 0.005 for all). Ex vivo MMP-2 siRNA transfection was performed 2 wk after balloon injury of hypercholesterolemic rabbit carotid arteries. Fluorescence microscopy showed circumferential siRNA uptake in neointimal cells. Gelatin zymography of carotid artery culture medium demonstrated a significant decrease of pro-MMP-2 activity in MMP-2 siRNA-transfected compared with scramble siRNA-transfected arteries ( P < 0.01). Overall, our results demonstrate that in vitro MMP-2 siRNA transfection in VSMCs markedly inhibits MMP-2 gene expression and VSMC migration and that ex vivo delivery of MMP-2 siRNA in balloon-injured arteries reduces pro-MMP-2 activity in neointimal cells, suggesting that siRNA could be used to modify arterial biology in vivo.

Malondialdehyde-acetaldehyde adducts decrease bronchial epithelial wound repair

Most people who abuse alcohol are cigarette smokers. Previously, we have shown that malondialdehyde, an inflammation product of lipid peroxidation, and acetaldehyde, a component of both ethanol metabolism and cigarette smoke, form protein adducts that stimulate protein kinase C (PKC) activation in bronchial epithelial cells. We have also shown that PKC can regulate bronchial epithelial cell wound repair. We hypothesize that bovine serum albumin adducted with malondialdehyde and acetaldehyde (BSA-MAA) decreases bronchial epithelial cell wound repair via binding to scavenger receptors on bronchial epithelial cells. To test this, confluent monolayers of bovine bronchial epithelial cells were grown in serum-free media prior to wounding the cells. Bronchial epithelial cell wound closure was inhibited in a dose-dependent manner (up to 60%) in the presence of BSA-MAA than in media treated cells (Laboratory of Human Carcinogenesis [LHC]-9-Roswell Park Memorial Institute [RPMI]). The specific scavenger receptor ligand, fucoidan, also stimulated PKC activation and decreased wound repair. Pretreatment with fucoidan blocked malondialdehyde-acetaldehyde binding to bronchial epithelial cells. When bronchial epithelial cells were preincubated with a PKC alpha inhibitor, Gö 6976, the inhibition of wound closure by fucoidan and BSA-MAA was blocked. Western blot demonstrated the presence of several scavenger receptors on bronchial epithelial cell membranes, including SRA, SRBI, SRBII, and CD36. Scavenger receptor-mediated activation of PKC alpha may function to reduce wound healing under conditions of alcohol and cigarette smoke exposure where malondialdehyde-acetaldehyde adducts may be present.

Adipocytic differentiation and liver x receptor pathways regulate the accumulation of triacylglycerols in human vascular smooth muscle cells

Lipid accumulation by vascular smooth muscle cells (VSMC) is a feature of atherosclerotic plaques. In this study we describe two mechanisms whereby human VSMC foam cell formation is driven by de novo synthesis of fatty acids leading to triacylglycerol accumulation in intracellular vacuoles, a process distinct from serum lipoprotein uptake. VSMC cultured in adipogenic differentiation medium accumulated lipids and were induced to express the adipocyte marker genes adipsin, adipocyte fatty acid-binding protein, C/EBPalpha, PPARgamma, and leptin. However, complete adipocyte differentiation was not observed as numerous genes present in mature adipocytes were not detected, and the phenotype was reversible. The rate of lipid accumulation was not affected by PPARgamma agonists, but screening for the effects of other nuclear receptor agonists showed that activation of the liver X receptors (LXR) dramatically promoted lipid accumulation in VSMC. Both LXRalpha and LXRbeta were present in VSMC, and their activation with TO901317 resulted in induction of the lipogenic genes fatty acid synthetase, sterol regulatory element binding protein (SREBP1c), and stearoyl-CoA desaturase. 27-Hydroxycholesterol, an abundant oxysterol synthesized by VSMC acted as an LXR antagonist and, therefore, may have a protective role in preventing foam cell formation. Immunohistochemistry showed that VSMC within atherosclerotic plaques express adipogenic and lipogenic markers, suggesting these pathways are present in vivo. Moreover, the development of an adipogenic phenotype in VSMC is consistent with their known phenotypic plasticity and may contribute to their dysfunction in atherosclerotic plaques and, thus, impinge on plaque growth and stability.

Role of oxidative modifications in atherosclerosis

This review focuses on the role of oxidative processes in atherosclerosis and its resultant cardiovascular events. There is now a consensus that atherosclerosis represents a state of heightened oxidative stress characterized by lipid and protein oxidation in the vascular wall. The oxidative modification hypothesis of atherosclerosis predicts that low-density lipoprotein (LDL) oxidation is an early event in atherosclerosis and that oxidized LDL contributes to atherogenesis. In support of this hypothesis, oxidized LDL can support foam cell formation in vitro, the lipid in human lesions is substantially oxidized, there is evidence for the presence of oxidized LDL in vivo, oxidized LDL has a number of potentially proatherogenic activities, and several structurally unrelated antioxidants inhibit atherosclerosis in animals. An emerging consensus also underscores the importance in vascular disease of oxidative events in addition to LDL oxidation. These include the production of reactive oxygen and nitrogen species by vascular cells, as well as oxidative modifications contributing to important clinical manifestations of coronary artery disease such as endothelial dysfunction and plaque disruption. Despite these abundant data however, fundamental problems remain with implicating oxidative modification as a (requisite) pathophysiologically important cause for atherosclerosis. These include the poor performance of antioxidant strategies in limiting either atherosclerosis or cardiovascular events from atherosclerosis, and observations in animals that suggest dissociation between atherosclerosis and lipoprotein oxidation. Indeed, it remains to be established that oxidative events are a cause rather than an injurious response to atherogenesis. In this context, inflammation needs to be considered as a primary process of atherosclerosis, and oxidative stress as a secondary event. To address this issue, we have proposed an "oxidative response to inflammation" model as a means of reconciling the response-to-injury and oxidative modification hypotheses of atherosclerosis.

Proteomic identification of a novel protein regulated in CA1 and CA3 hippocampal regions during intermittent hypoxia

The CA1 and CA3 regions of the hippocampus markedly differ in their susceptibility to hypoxia in general, and more particularly to the intermittent hypoxia (IH) that characterizes sleep apnea. We used proteomic analysis to build a database of proteins expressed in normoxic CA1 and CA3. The current hippocampus protein database identifies 106 proteins. A hypothetical protein with accession number AK006737 (gimid R:12839969) was strongly upregulated in the CA1, but not CA3 hippocampal region. Bioinformatic analysis revealed that the unknown protein contained a high stringency protein kinase e binding site. Domain analysis demonstrated the presence of a conserved sequence indicative of macrophage scavenger receptors. Using proteomic analysis we have previously demonstrated that acute (6 h) IH-mediated CA1 injury results from complex interactions between pathways involving increased metabolism, induction of stress-induced proteins and apoptosis, and ultimately disruption of structural proteins and cell integrity. The current findings identify a hypothetical protein that may play a key role in the response of CA1 to IH. These findings provide initial insights into mechanisms underlying differences in susceptibility to hypoxia in neural tissue and demonstrate how proteomic analysis can be used to generate new hypotheses, which define neuronal adaptation to IH.

Oleic acid-induced PKC isozyme translocation in RAW 264.7 macrophages

Fatty acids are important second messengers that mediate various cellular functions, but their role in the formation of macrophage foam cells is not known. High plasma levels of oleic acid (OA) in obese patients are often associated with a high risk for atherosclerosis. In this study, we investigated the protein kinase C (PKC) isozymes involved in OA-induced lipid accumulation in RAW 264.7 macrophages. The results show that OA induces translocation of PKC alpha, beta1, and delta from the cytosol to the cell membrane 5 min after the treatment. After 16 h incubation with OA, PKC delta was found to be colocalized with adipose differentiation-related protein (ADRP) on the surface of lipid droplets, but immunoprecipitation experiments showed that PKC delta was not biochemically associated with ADRP. After 16 h incubation with OA plus phorbol 12-myristate 13-acetate (PMA), PKC delta staining on the lipid droplet surface was not seen, whereas the accumulation of lipid droplets was unaffected. Furthermore, downregulation of PKC delta was confirmed by immunoblotting. These results demonstrate possible involvement of specific PKC isozymes in the early phase of lipid accumulation, possibly during the uptake of OA.

Atorvastatin therapy in hypercholesterolemic patients suppresses cellular uptake of oxidized-LDL by differentiating monocytes

Atherosclerosis is characterized by macrophage foam cells formation, which originate from differentiating blood monocytes that have taken up oxidized LDL (Ox-LDL) at enhanced rate. Statin therapy exhibit pleiotropic effects on many components of atherosclerosis. We have studied the effect of atorvastatin therapy in hypercholesterolemic patients, on the cellular uptake of Ox-LDL by their monocytes during differentiation into macrophages. Eleven hypercholesterolemic men were treated with 20 mg/day of atorvastatin for a period of 1 month. Peripheral blood monocytes harvested from control subjects and from patients before and after atorvastatin therapy were allowed to differentiate in culture for up to 9 days in the presence of 20% autologous serum. In control monocytes/macrophages the cellular uptake of Ox-LDL and the scavenger receptors CD36, SRA-I and SRA-II mRNA expression were upregulated during differentiation, and this upregulation was significantly enhanced in cells from hypercholesterolemic patients. Atorvastatin therapy suppressed the upregulation in Ox-LDL degradation and scavenger receptors expression in differentiating monocytes. These effects could be related at least in part to antioxidant characteristics of atorvastatin. Reduced susceptibility of plasma to free radical-induced lipid peroxidation (by 35%), increased plasma total antioxidant status (TAS; by 30%), and increased serum paraoxonase activity (by 53%), were noted following drug therapy. We conclude that atorvastatin therapy in hypercholesterolemic patients reduces the enhanced cellular uptake of Ox-LDL during ex-vivo differentiation of monocytes into macrophages, and decreases cellular scavenger receptors gene expression. These effects may account for the attenuation of atherogenesis in hypercholesterolemic patients following atorvastatin treatment.

A genome scan for loci influencing anti-atherogenic serum bilirubin levels

Epidemiological studies have shown an association of decreased serum bilirubin levels with coronary artery disease. Two segregation analyses in large pedigrees have suggested a major gene responsible for high bilirubin levels occurring in about 12% of the population. Based on a recessive model from a previous segregation analysis, we performed a genome scan using 587 markers genotyped in 862 individuals from 48 Utah pedigrees to detect loci linked to high bilirubin levels. As a complementary approach, non-parametric linkage (NPL) analysis was performed. These two methods identified four regions showing evidence for linkage. The first region is on chromosome 2q34-37 with multipoint LOD and NPL scores of 3.01 and 3.22, respectively, for marker D2S1363. This region contains a previously described gene, uridine diphosphate glycosyltransferase 1, which has been associated with high bilirubin levels. A polymorphism in the promoter of this gene was recently shown to be responsible for Gilbert syndrome which is associated with mild hyperbilirubinemia. The other regions were found on chromosomes 9q21, 10q25-26, and 18q12 with maximum NPL scores of 2.39, 1.55, and 2.79, respectively. Furthermore, we investigated in these pedigrees the association between bilirubin levels and coronary artery disease. One-hundred and sixty-one male and 41 female subjects had already suffered a coronary artery disease event. Male patients showed significantly lower bilirubin concentrations than age-matched controls. This association, however, was not observed in females. These results provide evidence that loci influencing bilirubin variation exist on chromosomes 2q34-37, 9q21, 10q25-26, and 18q12 and confirms the association of low bilirubin levels with coronary artery disease in males.

Inhibitory effects of N-acetylcysteine on scavenger receptor class A expression in human macrophages

OBJECTIVE

The formation of foam cells from monocyte-derived macrophages involves the uptake of modified lipoproteins by scavenger receptors. Antioxidants inhibit lipoprotein oxidation and may also modulate gene expression. We investigated the effect of the antioxidant N-acetylcysteine on the expression of the class A scavenger receptor (SR-A) types I and II in human macrophages.

DESIGN

Monocytes and macrophages from healthy blood donors and plaque-derived macrophages from patients undergoing carotid endarterectomy were used for experiments. SR-A mRNA was analysed with quantitative and semiquantitative reverse transcription-polymerase chain reaction, and ligand binding and uptake were assessed with 125I-labelled acetylated low-density lipoprotein (LDL).

RESULTS

Incubation of monocytes and monocyte-derived macrophages with N-acetylcysteine decreased both SR-A I and II mRNA expression. N-Acetylcysteine also reduced SR-A mRNA in lesion-derived cells. Binding and uptake of 125I-acetylated LDL was decreased after brief incubation with N-acetylcysteine. After longer periods of incubation with N-acetylcysteine we observed an increased degradation of lipoproteins.

CONCLUSIONS

Our results imply that N-acetylcysteine leads to a decrease in SR-A mRNA and initially also to an attenuated uptake of modified lipoproteins. This adds more to the knowledge about the cellular actions of this drug.

Class A scavenger receptors, macrophages, and atherosclerosis

The scope of this review is to discuss the new advances in our understanding of the role of scavenger receptor class A in the initiation and modulation of the atherosclerotic process. Through the approaches of gene manipulation in the mouse model, a substantial body of literature has accumulated that depicts scavenger receptor class A as a central player in atherogenesis. In studies of scavenger receptor class A overexpression in macrophages through bone marrow transplantation using transgenic donor material, recipient mice with hyperlipidemia caused either by apolipoprotein E or LDL receptor deficiency did not show convincing changes in the degree of atherosclerosis development compared with controls. Conversely, the deletion of the scavenger receptor class A gene in the mouse has shown, in a consistent and significant fashion, that this receptor serves a pro-atherogenic function under hyperlipidemic conditions, as both apolipoprotein E and LDL receptor-deficient mice had reduced atherosclerosis in the absence of scavenger receptor class A. In addition, we have recently shown that C57BL/6 mice are protected from diet-induced atherosclerosis when they lack scavenger receptor class A, and that the macrophage is the cell type responsible for the effect of scavenger receptor class A deficiency in reducing lesion formation in C57BL/6 and LDL receptor null mice. Together, these results demonstrate that macrophage scavenger receptor class A contributes significantly to atherosclerotic lesion formation, and suggest that the uptake of oxidized or modified lipoproteins by vessel wall macrophages is a central process in atherogenesis.

Possible involvement of protein kinase C in the induction of adipose differentiation-related protein by Sterol ester in RAW 264.7 macrophages

The accumulation of lipid droplets in macrophages contributes to the formation of foam cells, an early event in atherosclerosis. It is, therefore, important to elucidate the mechanisms by which lipid droplets accumulate and are utilized. Sterol ester (SE)-laden RAW 264.7 macrophages accumulated lipid droplets in a time-dependent manner up to 16 h, which was enhanced by cotreatment with 0.1 microM phorbol 12-myristate 13-acetate (PMA). Inhibition of protein kinase C (PKC) activity by cotreatment with 0.3 microM calphostin C CAL for 16 h resulted in coalescence of small lipid droplets into large ones and increased accumulation of lipid droplets, although to a lesser extent than after PMA cotreatment. Immunostaining for adipose differentiation-related protein (ADRP) revealed a fluorescent rim at the surface of each medium to large lipid droplet. ADRP appearance correlated with lipid droplet accumulation and was regulated by PMA in a time-dependent manner. Induction of ADRP expression by PMA or CAL required SE, since ADRP levels in PMA- or CAL-treated non-SE-laden macrophages were comparable to those in untreated cells. Removal of SE from the incubation medium resulted in the concomitant dissolution of lipid droplets and down-regulation of ADRP. In conclusion, the above results suggest that ADRP may be an important protein in the regulation of lipid droplet metabolism in lipid-laden macrophages and that this regulation may be mediated by PKC activity.

Association of plasma bilirubin with coronary heart disease and segregation of bilirubin as a major gene trait: the NHLBI family heart study

Decreased serum bilirubin levels have been associated with coronary heart disease (CHD). It is believed that bilirubin acts as an antioxidant, preventing formation of oxidized LDL and subsequent atherosclerosis. Serum bilirubin also segregates as a major gene, with the rarer genotype associated with elevated bilirubin levels and occurring in about 12% of the population. Using a large population-based study of random and CHD high risk families, this analysis was designed to replicate the association of lower serum bilirubin levels with early CHD (onset by age 55 for males and 65 for females) using 328 case/control samples and the major gene segregation of bilirubin levels in 555 families. There were significant differences in plasma bilirubin levels between 188 males (12.5 micromol/l) and 140 females (9.3 micromol/l, P<0.0001). Higher serum albumin and lower HDL-C significantly correlated with higher plasma bilirubin levels in females but not males. In sex-specific logistic regression models of early CHD (148 cases and 180 controls), lower plasma bilirubin was associated with increased prevalence of CHD in males with borderline significance (odds ratio=0.93 for a 1 micromol/l increase in bilirubin, P=0.056) but not in females. Bilirubin was found to segregate as a major gene using all 555 families consisting of 1292 individuals, with estimates replicating those in the previously published study. The most parsimonious model was a recessive model for high bilirubin levels that occurred in about 23% of the population. The means were separated by 1.7 standard deviations and there was a significant polygenic effect (h2=0.33, P=0.0009). We conclude that decreased bilirubin is mildly related to CHD in males but not in females. Because of an inverse correlation between HDL-C and bilirubin, the protective high HDL-C levels may have counteracted the CHD risk associated with lower bilirubin levels in females. The inferred major gene for bilirubin may protect against CHD, since elevated levels, rather than lower levels, were associated with this inferred gene.

Tumor necrosis factor-alpha -mediated protein kinases in regulation of scavenger receptor and foam cell formation on macrophage

We previously reported tumor necrosis factor-alpha (TNF) modulates transcriptional and post-transcriptional down-regulation of macrophage scavenger receptor (MSR) (Hsu, H. Y., Nicholson, A. C., and Hajjar, D. P. (1996) J. Biol. Chem. 271, 7767-7773); however, TNF-mediated signaling mechanisms are unknown. Here, we demonstrate that ligation of TNF receptor stimulates activity of p21-activated protein kinase (PAK) and mitogen-activated protein kinases (MAPK) as follows: ERK, JNK, and p38 in murine macrophage J774A.1 cells. Upon activation of protein kinases (PK), TNF rapidly increases MSR message and protein; later it markedly reduces MSR expression. Studies using PK inhibitors and dominant negative constructs demonstrate phosphatidylinositol 3-kinase/Rac1/PAK/JNK and phosphatidylinositol 3-kinase/Rac1/PAK/p38 pathways contribute to important roles in the late stage of TNF down-regulation of MSR expression and taking up of OxLDL. Alternatively, the PKC/MEK1/ERK pathway in the early stage plays a significant role in up-regulation of the MSR gene. By using anti-TNF-R1 agonist antibody, we further confirm TNF-R1-mediated MAPK in regulation of MSR. Furthermore, in MSR gene promoter-driven luciferase reporter assays with TNF, PKC activator increases, but antioxidant N-acetylcysteine, PK inhibitors, and dominant negative constructs decrease luciferase activity in MSR gene promoter-transfected cells. Our current results show the first evidence of crucial roles for TNF-mediated MAPK pathways in the transcriptional regulation of MSR gene and increase MSR expression; in contrast, with TNF longer treatment the pathways down-regulate MSR and foam cell formation probably via post-transcriptional process.

Role of the cyclic AMP-dependent pathway in free radical-induced cholesterol accumulation in vascular smooth muscle cells

We have previously reported that free radical-treated vascular smooth muscle cells (SMC) lead to cholesterol accumulation in vitro. In the current study, we investigated the effects of oxidative stress on cyclic AMP concentration and cAMP-dependent enzymes involved in cholesterol homeostasis in A7r5 cells. Under our conditions of a mild oxidative stress, namely with no change in cell viability, we found that free radicals, initiated using azobis-amidinopropane dihydrochloride (AAPH), resulted in a dose-dependent decrease in cellular cAMP which was opposed by vitamin E preincubation. Although the addition of adenylate cyclase activators (carbacyclin and forskolin) increased cAMP levels it did not succeed in restoring the AAPH-induced decrease. The oxidative stress-induced increase in activities of 3-hydroxy-3-methylglutaryl coenzyme A reductase and of acyl coenzyme A: cholesterol acyltransferase and the decrease in neutral cholesteryl ester hydrolase activity were suppressed by addition of dibutyryl cAMP. Taken together, these results strongly suggest that free radicals reduce cAMP concentrations by altering cell membrane adenylate cyclase activity. The changes of cAMP-dependent enzymes induced by oxidative stress resulting in cholesterol accumulation might be one of the processes leading to SMC-derived foam cells depicted in atheroma plaque. Moreover, if extrapolated to in vivo, these data may explain in part the beneficial effects of antioxidants in the reduction of cardiovascular diseases.

Class A scavenger receptor up-regulation in smooth muscle cells by oxidized low density lipoprotein. Enhancement by calcium flux and concurrent cyclooxygenase-2 up-regulation

Oxidative stress caused by phorbol esters or reactive oxygen up-regulates the class A scavenger receptor (SR-A) in human smooth muscle cells (SMC), which normally do not express this receptor. The increase in SR-A expression correlates with activation of the redox-sensitive transcription factors activating protein-1 c-Jun and CCAAT enhancer-binding protein beta. Here we show that coincubation of SMC with macrophages or oxidized low density lipoproteins (LDL) from macrophage-conditioned medium activates these same regulatory pathways and stimulates SR-A expression. The increased SR-A gene transcription induced by cell-oxidized LDL up-regulated SR-A mRNA and increased by 30-fold the uptake of acetyl LDL, a ligand for the SR-A. Copper-oxidized LDL also increased SR-A receptor expression. Oxidized LDL with a lipid peroxide level of 80-100 nmol/mg of LDL protein and an electrophoretic mobility approximately 1.5 times that of native LDL exhibited the greatest bioactivity. Inhibition of calcium flux suppressed SR-A induction by oxidized LDL. Conversely, calcium ionophore greatly enhanced SR-A up-regulation by oxidized LDL or other treatments that promote intracellular oxidative stress. This enhancement was dependent upon concurrent up-regulation of SMC cyclooxygenase-2 expression and activity and was blocked by the cyclooxygenase-2 inhibitors NS-398 and Resveratrol. In THP-1 cells, oxidized LDL induced monocyte-to-macrophage differentiation and increased SR-A expression. These findings support a role for mildly oxidized LDL in the redox regulation of macrophage differentiation and SR-A expression and suggest that increased vascular oxidative stress may contribute to the formation of both SMC and macrophage foam cells.

Scavenger receptor regulation and atherosclerosis

Atherosclerosis and its complications, such as coronary heart disease, heart infarction and stroke, are the leading causes of death in the developed world. High blood pressure, diabetes, smoking and a diet high in cholesterol and lipids clearly increase the likelihood of premature atherosclerosis, albeit other factors, such as the individual genetic makeup, may play an additional role. During atherosclerosis, uncontrolled cholesterol and lipid accumulation in macrophages and smooth muscle cells leads to foam cell formation and to the progression of the atherosclerotic plaque. This review will focus on foam cell formation within the atherosclerotic lesion, the involvement of the scavenger receptor genes in this process, and the possibility to interfere with scavenger receptor function to reduce the progression of atherosclerosis. To date, the regulatory mechanisms for the expression of scavenger receptor genes and their role in atherosclerosis are not well characterized. Knowledge on this subject could lead to a better understanding of the process, prevention and therapy of this disease.

Macrophage specific overexpression of the human macrophage scavenger receptor in transgenic mice, using a 180-kb yeast artificial chromosome, leads to enhanced foam cell formation of isolated peritoneal macrophages

Macrophage scavenger receptors class A (MSR) are thought to play an important role in atherogenesis by mediating the unrestricted uptake of modified lipoproteins by macrophages in the vessel wall leading to foam cell formation. To investigate the in vivo role of the MSR in this process, a transgenic mouse model expressing both isoforms of the human MSR was generated. A 180-kb yeast artificial chromosome (YAC) containing the human MSR gene (MSR1) with 60- and 40-kb flanking sequence at the 5' and 3' end, respectively, was obtained by reducing the size of a 1050-kb YAC by homologous recombination. This 180-kb YAC was microinjected into mouse oocytes. In the resulting transgenic mice, high levels of mRNA for both type I and type II human MSR1 were detected in peritoneal macrophages and trace levels in other organs, known to contain macrophage-derived cells. Using an antibody against the human MSR, the Kupffer cells in the liver were shown to contain the MSR protein. In vivo clearance of acetyl-LDL was not changed in the MSR1-transgenic mice. However, in vitro studies using peritoneal macrophages from the transgenic mice showed a two-fold increased degradation of acetyl-LDL and cholesterolester accumulation concomitant with a four-fold increase in foam cell formation, as compared to wild-type macrophages. Thus, macrophage specific overexpression of the MSR may lead to increased foam cell formation, which is one of the initial and crucial steps in atherogenesis.

Structure and function of type I and II macrophage scavenger receptors

Type I and II macrophage scavenger receptors are implicated in the pathologic deposition of cholesterol during the atherogenesis. There is a charged collagen structure of type I and II receptors identified as a ligand binding domain, which can recognize a wide range of negatively charged macromolecules including oxidized LDL as well as damaged or apoptotic cells and pathogenic micro-organisms. After binding these ligands can be either internalized by endocytosis, phagocytosis, or remain at cell surface and mediate the adhesion. Under physiological condition, scavenger receptors serve to scavenge or clean up cellular debris and other related materials, as well as playing a role in the hosts defence. In pathological condition, they mediate the recruitment, activation and transformation of macrophages and other cells, which may be related to the development of atherosclerosis and to disorders caused by the accumulation of denatured materials, such as Alzheimer's disease.

Oxidant stress: the role of nutrients in cell-lipoprotein interactions

Oxidant stress is increasingly becoming an important hypothesis to explain the genesis of several pathologies, including cancer, atherosclerosis and also ageing. Beside a few rare genetic defects, dietary factors are thought to play a key role in the regulation of the production of reactive oxygenated species. An imbalance between nutrients, and in particular those involved in antioxidant status, could explain the onset of an enhanced production of free radicals. We will briefly review information concerning oxidation of lipids and lipoproteins which lead to atherothrombosis. We also present new findings supporting a role for blood platelets in generating oxidant species. New data are also described concerning the role of oxygenated derivatives of cholesterol, oxysterols, in cellular cholesterol efflux and NO production. Also, new developments relating to the influence of direct effects of free radicals on cellular cholesterol homeostasis are presented. Finally, the in vitro effects of butyrate, a natural short-chain fatty acid produced by bacterial fermentation, in the protection against free radical-mediated cytotoxicity are discussed. These data provide information on the mechanisms of dietary antioxidants in preventing oxidant stress.