The two faces of the 15-lipoxygenase in atherosclerosis

Peroxisome proliferator-activated receptor gamma in osteoarthritis

Osteoarthritis (OA) is among the most prevalent chronic human health disorders and the most common form of arthritis. It is a leading cause of disability in developed countries. This disease is characterized by cartilage deterioration, synovitis, and remodeling of the subchondral bone. There is not yet a satisfactory treatment to stop or arrest this disease process. Although several candidates for therapeutic approaches have been put forward, recent studies suggest that activation of the transcription factor peroxisome proliferator-activated receptor gamma (PPARγ) is an interesting target for this disease. PPARγ is a ligand-activated transcription factor and member of the nuclear receptor superfamily. Agonists of PPARγ inhibit inflammation and reduce synthesis of cartilage degradation products both in vitro and in vivo, and reduce the development/progression of cartilage lesions in OA animal models. This review will highlight the recent experimental studies on the presence of PPARγ in articular tissues and its effect on inflammatory and catabolic responses in chondrocytes and synovial fibroblasts, as well as the protective effects of PPARγ ligands in arthritis experimental models. Finally, the role of PPARγ polymorphism in the pathogenesis of OA and related musculoskeletal diseases will also be discussed.

Leukotrienes modulate secretion of progesterone and prostaglandins during the estrous cycle and early pregnancy in cattle: an in vivo study

Recently, we showed that leukotrienes (LTs) regulate ovarian cell function in vitro. The aim of this study was to examine the role of LTs in corpus luteum (CL) function during both the estrous cycle and early pregnancy in vivo. mRNA expression of LT receptors (BLT for LTB(4) and CYSLT for LTC(4)), and 5-lipoxygenase (5-LO) in CL tissue and their localization in the ovary were studied during the estrous cycle and early pregnancy. Moreover, concentrations of LTs (LTB(4) and C(4)) in the CL tissue and blood were measured. 5-LO and BLT mRNA expression increased on days 16-18 of the cycle, whereas CYSLT mRNA expression increased on days 16-18 of the pregnancy. The level of LTB(4) was evaluated during pregnancy compared with the level of LTC(4), which increased during CL regression. LT antagonists influenced the duration of the estrous cycle: the LTC(4) antagonist (azelastine) prolonged the luteal phase, whereas the LTB(4) antagonist (dapsone) caused earlier luteolysis in vivo. Dapsone decreased progesterone (P(4)) secretion and azelastine increased P(4) secretion during the estrous cycle. In summary, LT action in the bovine reproductive tract is dependent on LT type: LTB(4) is luteotropic during the estrous cycle and supports early pregnancy, whereas LTC(4) is luteolytic, regarded as undesirable in early pregnancy. LTs are produced/secreted in the CL tissue, influence prostaglandin function, and serve as important factors during the estrous cycle and early pregnancy in cattle.

Genome-wide expression profiling deciphers host responses altered during dengue shock syndrome and reveals the role of innate immunity in severe dengue

Background

Deciphering host responses contributing to dengue shock syndrome (DSS), the life-threatening form of acute viral dengue infections, is required to improve both the differential prognosis and the treatments provided to DSS patients, a challenge for clinicians.

Methodology/Principal Findings

Based on a prospective study, we analyzed the genome-wide expression profiles of whole blood cells from 48 matched Cambodian children: 19 progressed to DSS while 16 and 13 presented respectively classical dengue fever (DF) or dengue hemorrhagic fever grades I/II (DHF). Using multi-way analysis of variance (ANOVA) and adjustment of p-values to control the False Discovery Rate (FDR<10%), we identified a signature of 2959 genes differentiating DSS patients from both DF and DHF, and showed a strong association of this DSS-gene signature with the dengue disease phenotype. Using a combined approach to analyse the molecular patterns associated with the DSS-gene signature, we provide an integrative overview of the transcriptional responses altered in DSS children. In particular, we show that the transcriptome of DSS children blood cells is characterized by a decreased abundance of transcripts related to T and NK lymphocyte responses and by an increased abundance of anti-inflammatory and repair/remodeling transcripts. We also show that unexpected pro-inflammatory gene patterns at the interface between innate immunity, inflammation and host lipid metabolism, known to play pathogenic roles in acute and chronic inflammatory diseases associated with systemic vascular dysfunction, are transcriptionnally active in the blood cells of DSS children.

Conclusions/Significance

We provide a global while non exhaustive overview of the molecular mechanisms altered in of DSS children and suggest how they may interact to lead to final vascular homeostasis breakdown. We suggest that some mechanisms identified should be considered putative therapeutic targets or biomarkers of progression to DSS.

Common genetic variation, residential proximity to traffic exposure, and left ventricular mass: the multi-ethnic study of atherosclerosis

BACKGROUND

Elevated left ventricular mass (LVM) is a strong predictor of negative cardiovascular outcomes, including heart failure, stroke, and sudden cardiac death. A relationship between close (< 50 m compared with > 150 m) residential proximity to major roadways and higher LVM has previously been described, but the mechanistic pathways that are involved in this relationship are not known. Understanding genetic factors that influence susceptibility to these effects may provide insight into relevant mechanistic pathways.

OBJECTIVE

We set out to determine whether genetic polymorphisms in genes affecting vascular and autonomic function, blood pressure, or inflammation influence the relationship between traffic proximity and LVM.

METHODS

This was a cross-sectional study of 1,376 genotyped participants in the Multi-Ethnic Study of Atherosclerosis, with cardiac magnetic resonance imaging performed between 2000 and 2002. The impact of tagged single-nucleotide polymorphisms (tagSNPs) and inferred haplotypes in 12 candidate genes (ACE, ADRB2, AGT, AGTR1, ALOX15, EDN1, GRK4, PTGS1, PTGS2, TLR4, VEGFA, and VEGFB) on the relationship between residential proximity to major roadways and LVM was analyzed using multiple linear regression, adjusting for multiple potential confounders.

RESULTS

After accounting for multiple testing and comparing homozygotes, tagSNPs in the type 1 angiotensin II receptor (AGTR1, rs6801836) and arachidonate 15-lipoxygenase (ALOX15, rs2664593) genes were each significantly (q < 0.2) associated with a 9-10% difference in the association between residential proximity to major roadways and LVM. Participants with suboptimal blood pressure control demonstrated stronger interactions between AGTR1 and traffic proximity.

CONCLUSIONS

Common polymorphisms in genes responsible for vascular function, inflammation, and oxidative stress appear to modify associations between proximity to major roadways and LVM. Further understanding of how genes modify effects of air pollution on CVD may help guide research efforts into specific mechanistic pathways.

Oxidized LDL: diversity, patterns of recognition, and pathophysiology

Oxidative modification of LDL is known to elicit an array of pro-atherogenic responses, but it is generally underappreciated that oxidized LDL (OxLDL) exists in multiple forms, characterized by different degrees of oxidation and different mixtures of bioactive components. The variable effects of OxLDL reported in the literature can be attributed in large part to the heterogeneous nature of the preparations employed. In this review, we first describe the various subclasses and molecular composition of OxLDL, including the variety of minimally modified LDL preparations. We then describe multiple receptors that recognize various species of OxLDL and discuss the mechanisms responsible for the recognition by specific receptors. Furthermore, we discuss the contentious issues such as the nature of OxLDL in vivo and the physiological oxidizing agents, whether oxidation of LDL is a prerequisite for atherogenesis, whether OxLDL is the major source of lipids in foam cells, whether in some cases it actually induces cholesterol depletion, and finally the Janus-like nature of OxLDL in having both pro- and anti-inflammatory effects. Lastly, we extend our review to discuss the role of LDL oxidation in diseases other than atherosclerosis, including diabetes mellitus, and several autoimmune diseases, such as lupus erythematosus, anti-phospholipid syndrome, and rheumatoid arthritis.

Generation and biological activities of oxidized phospholipids

Glycerophospholipids represent a common class of lipids critically important for integrity of cellular membranes. Oxidation of esterified unsaturated fatty acids dramatically changes biological activities of phospholipids. Apart from impairment of their structural function, oxidation makes oxidized phospholipids (OxPLs) markers of "modified-self" type that are recognized by soluble and cell-associated receptors of innate immunity, including scavenger receptors, natural (germ line-encoded) antibodies, and C-reactive protein, thus directing removal of senescent and apoptotic cells or oxidized lipoproteins. In addition, OxPLs acquire novel biological activities not characteristic of their unoxidized precursors, including the ability to regulate innate and adaptive immune responses. Effects of OxPLs described in vitro and in vivo suggest their potential relevance in different pathologies, including atherosclerosis, acute inflammation, lung injury, and many other conditions. This review summarizes current knowledge on the mechanisms of formation, structures, and biological activities of OxPLs. Furthermore, potential applications of OxPLs as disease biomarkers, as well as experimental therapies targeting OxPLs, are described, providing a broad overview of an emerging class of lipid mediators.

Hydroxyoctadecadienoic acids: novel regulators of macrophage differentiation and atherogenesis

Hydroxyoctadecadienoic acids (HODEs) are stable oxidation products of linoleic acid, the generation of which is increased where oxidative stress is increased, such as in diabetes. In early atherosclerosis, 13-HODE is generated in macrophages by 15-lipoxygenase-1. This enhances protective mechanisms through peroxisome proliferator-activated receptor (PPAR)-g activation leading to increased clearance of lipid and lipid-laden cells from the arterial wall. In later atherosclerosis, both 9-HODE and 13-HODE are generated nonenzymatically. At this stage, early protective mechanisms are overwhelmed and pro-inflammatory effects of 9-HODE, acting through the receptor GPR132, and increased apoptosis predominate leading to a fragile, acellular plaque. Increased HODE levels thus contribute to atherosclerosis progression and the risk of clinical events such as myocardial infarction or stroke. Better understanding of the role of HODEs may lead to new pharmacologic approaches to modulate their production or action, and therefore lessen the burden of atherosclerotic disease in high-risk patients.

Impact of circulating esterified eicosanoids and other oxylipins on endothelial function

Eicosanoids, including epoxyeicosatrienoic acids, hydroxyeicosatetraenoic acids, and other oxylipins derived from polyunsaturated fatty acids, have emerging roles in endothelial inflammation and subsequent atherosclerosis. Unlike eicosanoids in the prostanoid series, they are known to be esterified in cell lipids such as phospholipids and triglycerides; however, our understanding of these reservoirs is in its infancy. This review focuses on recent work identifying circulating oxylipins, primarily esterified with lipoprotein lipids, and their effects on markers of endothelial dysfunction. These oxylipins are known to be released by at least one lipase (lipoprotein lipase) and to mediate increased expression of inflammatory markers in endothelial cells, which coincides with the known roles of lipoproteins in endothelial dysfunction. The implications of the lipolytic release of lipoprotein-bound oxylipins for the inflammatory response, challenges to analysis of this oxylipin compartment, and the potential importance of non-arachidonate-derived oxylipins are discussed.

Abscisic acid ameliorates atherosclerosis by suppressing macrophage and CD4+ T cell recruitment into the aortic wall

Abscisic acid (ABA) is a natural phytohormone which improves insulin sensitivity and reduces adipose tissue inflammation when supplemented into diets of obese mice. The objective of this study was to investigate the mechanisms by which ABA prevents or ameliorates atherosclerosis. apolipoprotein E-deficient (ApoE(-/-)) mice were fed high-fat diets with or without ABA for 84 days. Systolic blood pressure was assessed on Days 0, 28, 56 and 72. Gene expression, immune cell infiltration and histological lesions were evaluated in the aortic root wall. Human aortic endothelial cells were used to examine the effect of ABA on 3',5'-cyclic adenosine monophosphate (cAMP) and nitric oxide (NO) production in vitro. We report that ABA-treated mice had significantly improved systolic blood pressure and decreased accumulation of F4/80(+)CD11b(+) macrophages and CD4(+) T cells in aortic root walls. At the molecular level, ABA significantly enhanced aortic endothelial nitric oxide synthase (eNOS) and tended to suppress aortic vascular cell adhesion molecule-1 (VCAM-1) and monocyte chemoattractant protein-1 (MCP-1) expression and plasma MCP-1 concentrations. ABA also caused a dose-dependent increase in intracellular concentrations of cAMP and NO and up-regulated eNOS mRNA expression in human aortic endothelial cells. This is the first report showing that ABA prevents or ameliorates atherosclerosis-induced hypertension, immune cell recruitment into the aortic root wall and up-regulates aortic eNOS expression in ApoE(-/-) mice.

15-Lipoxygenase-2 is expressed in macrophages in human carotid plaques and regulated by hypoxia-inducible factor-1alpha

BACKGROUND

Macrophages are prominent in hypoxic areas of atherosclerotic lesions and their secreted cytokines, growth factors and activity of enzymes are involved in atherogenesis. Previously, we showed that 15-lipoxygenase (LOX)-2 is expressed in human monocyte-derived macrophages and that hypoxia increases 15-LOX-2 expression and secretion of pro-inflammatory molecules. Here we investigated whether human carotid plaque macrophages express 15-LOX-2 and whether its expression in macrophages is regulated by hypoxia through hypoxia-inducible factor 1alpha (HIF-1alpha).

MATERIALS AND METHODS

Carotid plaques from 47 patients with high-grade symptomatic carotid artery stenosis were analysed using immunohistochemistry, and stained areas were quantified by digital image analysis. Carotid plaque macrophages were isolated with anti-CD14 immunobeads using an immunomagnetic bead technique. Primary macrophages were transfected with HIF-1alpha siRNA or control siRNA before extraction of RNA and medium analysis.

RESULTS

In paired tissue sections, the extent of staining for CD68 correlated with staining for 15-LOX-2 but not for 15-LOX-1. In carotid plaque macrophages isolated with anti-CD14 immunobeads, 15-LOX-2 mRNA was expressed at high levels. In primary macrophages, 15-LOX-2 expression was significantly increased by incubation with the HIF-1alpha stabilizer dimethyloxalylglycine. Knockdown of HIF-1alpha significantly decreased production of the 15-LOX-2 enzyme products 12- and 15-hydroxyeicosatetraenoic acid. In carotid plaques, HIF-1alpha staining correlated with staining for 15-LOX-2.

CONCLUSIONS

These results demonstrate that 15-LOX-2 is highly expressed in human plaques and is correlated with the presence of macrophages and HIF-1alpha. 15-LOX-2 enzyme activity can be modulated by HIF-1alpha. Thus, increased expression of 15-LOX-2 in macrophages in hypoxic atherosclerotic plaque may enhance inflammation and the recruitment of inflammatory cells.

Immunohistochemical detection of 13(R)-hydroxyoctadecadienoic acid in atherosclerotic plaques of human carotid arteries using a novel specific antibody

13-Hydroxyoctadecadienoic acid (13-HODE) is a major component of oxidized low density lipoprotein (OxLDL), which has been shown to have a crucial role in atherogenesis. Of the 13-HODE stereoisomers, 13(S)-HODE and 13(R)-HODE, little is known about the latter in contrast to the former. To detect 13(R)-HODE in atherosclerotic lesions, we prepared a mouse monoclonal antibody against 13(R)-HODE. Competitive enzyme-linked immunosorbent assay clarified the selective reaction of a clone mAb 13H1 with both free and bovine serum albumin-conjugated forms of 13(R)-HODE but not other oxidized lipids including 13(S)-HODE. Immunohistochemical analysis revealed the colocalization of 13(R)-HODE immunoreactivity with the OxLDL marker oxidized phophatidylcholine immunoreactivity in vascular endothelial cells, macrophages and migrating vascular smooth muscle cells in atherosclerotic plaques of human carotid arteries. The present results provide in vivo evidence for the formation of 13(R)-HODE in atherosclerotic lesions of carotid arteries.

Identification of 13-hydroxy-14,15-epoxyeicosatrienoic acid as an acid-stable endothelium-derived hyperpolarizing factor in rabbit arteries

Arachidonic acid (AA) is metabolized by endothelial 15-lipoxygenase (15-LO) to several vasodilatory eicosanoids such as 11,12,15-trihydroxyeicosatrienoic acid (11,12,15-THETA) and its proposed unstable precursor 15-hydroxy-11,12-epoxyeicosatrienoic acid (15-H-11,12-EETA). In the present study, the acid-stable 13-hydroxy-trans-14,15-epoxy-eicosatrienoic acid (13-H-14,15-EETA) was identified and its vascular activities characterized. Rabbit aorta, mesenteric arteries, and the combination of 15-LO and cytochrome P450 2J2 converted AA to two distinct HEETA metabolites. The HEETA metabolites were resistant to acidic hydrolysis but were hydrolyzed by recombinant sEH to a more polar metabolite identified by mass spectrometry as 13,14,15-THETA. Mass spectrometric analyses and HPLC comigration identified the HEETAs as threo- and erythro-diastereomers of 13-H-trans-14,15-EETA. Erythro- and threo-diastereomers of 13-H-trans-14,15-EETA relaxed endothelium-denuded rabbit small mesenteric arteries with maximum relaxations of 22.6 +/- 6.0% and 8.6 +/- 4.3%, respectively. Apamin (10(-7) m) inhibited the relaxations to the erythro-isomer (maximum relaxation = 1.2 +/- 5.6%) and increasing [K(+)](o) from 4.6 to 30 mm blocked relaxations to both isomers. In cell-attached patches of mesenteric arterial smooth muscle cells (SMCs), erythro-13-H-trans-14,15-EETA (1-3 x 10(-6) m) increased mean open time of small conductance K(+) channels (13-14 pS) from 0.0007 +/- 0.0007 to 0.0053 +/- 0.0042. This activation was inhibited by apamin. The erythro, but not the threo, isomer blocked angiotensin II-stimulated aortic SMC migration. These studies demonstrate that 13-H-14,15-EETAs induces vascular relaxation via K(+) channel activation to cause SMC hyperpolarization. Thus, 13-H-14,15-EETA represents a new endothelial factor.

Targeted chiral lipidomics analysis of bioactive eicosanoid lipids in cellular systems

We have developed a targeted lipidomics approach that makes it possible to directly analyze chiral eicosanoid lipids generated in cellular systems. The eicosanoids, including prostaglandins (PGs), thromboxanes (TXs), leukotrienes (LTs) and alcohols (HETEs), have been implicated as potent lipid mediators of various biological processes. Enzymatic formations of eicosanoids are regioselective and enantioselective, whereas reactive oxygen species (ROS)-mediated formation proceeds with no stereoselectivity. To distinguish between enzymatic and non-enzymatic pathways of eicosanoid formation, it is necessary to resolve enantiomeric forms as well as regioisomers. High sensitivity is also required to analyze the eicosanoid lipids that are usually present as trace amounts (pM level) in biological fluids. A discovery of liquid chromatography-electron capture atmospheric pressure chemical ionization/mass spectrometry (LCECAPCI/MS) allows us to couple normal phase chiral chromatography without loss of sensitivity. Analytical specificity was obtained by the use of collision-induced dissociation (CID) and tandem MS (MS/MS). With combination of stable isotope dilution methodology, complex mixtures of regioisomeric and enantiomeric eicosanoids have been resolved and quantified in biological samples with high sensitivity and specificity. Targeted chiral lipidomics profiles of bioactive eicosanoid lipids obtained from various cell systems and their biological implications have been discussed.

15-oxo-Eicosatetraenoic acid, a metabolite of macrophage 15-hydroxyprostaglandin dehydrogenase that inhibits endothelial cell proliferation

The formation of 15-oxo-5,8,11,13-(Z,Z,Z,E)-eicosatetraenoic acid (15-oxo-ETE) as a product from rabbit lung 15-hydroxyprostaglandin dehydrogenase (PGDH)-mediated oxidation of 15(S)-hydroperoxy-5,8,11,13-(Z,Z,Z,E)-eicosatetraenoic acid was first reported more than 30 years ago. However, the pharmacological significance of 15-oxo-ETE formation has never been established. We have now evaluated 15-lipoxygenase (LO)-1-mediated arachidonic acid (AA) metabolism to 15-oxo-ETE in human monocytes and mouse RAW macrophages that stably express human 15-LO-1 (R15L cells). A targeted lipidomics approach was used to identify and quantify the oxidized lipids that were formed. 15-oxo-ETE was found to be a major AA-derived LO metabolite when AA was given exogenously or released from endogenous esterified lipid stores by calcium ionophore (CI) calcimycin (A-23187). This established the R15L cells as a useful in vitro model system. Pretreatment of the R15L cells with cinnamyl-3,4-dihydroxycyanocinnamate significantly inhibited AA- or CI-mediated production of 15(S)-hydroperoxy-5,8,11,13-(Z,Z,Z,E)-eicosatetraenoic acid [15(S)-HETE] and 15-oxo-ETE, confirming the role of 15-LO-1 in mediating AA metabolite formation. Furthermore, 15(S)-HETE was metabolized primarily to 15-oxo-ETE. Pretreatment of the R15L cells with the 15-hydroxyprostaglandin dehydrogenase (PGDH) inhibitor 5-[[4-(ethoxycarbonyl)phenyl]azo]-2-hydroxy-benzeneacetic acid (CAY10397) reduced AA- and 15(S)-HETE-mediated formation of 15-oxo-ETE in a dose-dependent manner. This confirmed that macrophage-derived 15-PGDH was responsible for catalyzing the conversion of 15(S)-HETE to 15-oxo-ETE. Finally, 15-oxo-ETE was shown to inhibit the proliferation of human vascular vein endothelial cells by suppressing DNA synthesis, implicating a potential antiangiogenic role. This is the first report describing the biosynthesis of 15-oxo-ETE by macrophage/monocytes and its ability to inhibit endothelial cell proliferation.

15(S)-Lipoxygenase-1 associates with neutral lipid droplets in macrophage foam cells: evidence of lipid droplet metabolism

15(S)-lipoxygenase-1 (15-LO-1) was present in the whole-cell homogenate of an acute human monocytic leukemia cell line (THP-1). Additionally, 15-LO-1 was detected on neutral lipid droplets isolated from THP-1 foam cells. To investigate if 15-LO-1 is active on lipid droplets, we used the mouse leukemic monocytic macrophage cell line (RAW 264.7), which are stably transfected with human 15-LO-1. The RAW 15-LO-1 cells were incubated with acetylated low density lipoprotein to generate foam cells. 15(S)-hydroxyeicosatetraenoic acid [15(S)-HETE], the major 15-LO-1 metabolite of arachidonic acid, was produced in the 15-LO-1 RAW but not in the mock transfected cells when incubated with arachidonic acid. Lipid droplets were isolated from the cells and incubated with arachidonic acid, and production of 15(S)-HETE was measured over 2 h. 15(S)-HETE was produced in the incubations with the lipid droplets, and this production was attenuated when the lipid droplet fraction was subjected to enzyme inactivation through heating. Efflux of 15(S)-HETE from cholesteryl ester-enriched 15-LO RAW cells, when lipid droplets are present, was significantly reduced compared with that from cells enriched with free cholesterol (lipid droplets are absent). We propose that 15-LO-1 is present and functional on cytoplasmic neutral lipid droplets in macrophage foam cells, and these droplets may act to accumulate the anti-inflammatory lipid mediator 15(S)-HETE.

Expression of 5-lipoxygenase and 15-lipoxygenase in rheumatoid arthritis synovium and effects of intraarticular glucocorticoids

Introduction

It was previously shown that lipoxygenase (LO) pathways are important in the rheumatoid arthritis (RA) inflammatory process and that synovial fluid from RA patients contains high amounts of leukotrienes. We therefore aimed to investigate the 5-LO and 15-LO-1 expression pattern in RA and ostheoarthritis (OA) synovial tissue and to study the effect of intraarticular glucocorticoid (GC) therapy on enzyme expression.

Methods

Expression of LOs was evaluated by immunohistochemistry in RA and OA synovial biopsies. Cellular localization of these enzymes was analyzed by double immunofluorescence. In synovial biopsies from 11 RA patients, 5-LO and 15-LO-1 expression was evaluated before and after triamcinolone hexacetonide knee injection and assessed by image analysis to quantify their expression. We also investigated the presence of 15-LO-1 by immunohistochemistry in synovial fluid (SF) cells as well as their ability to form 15-hydroxyeicosatetraenoic acid (15-HETE) following treatment with arachidonic acid (AA).

Results

5-LO and 15-LO-1 are present in RA and OA synovium, with 5-LO being mostly expressed in lining and sublining macrophages, neutrophils and mast cells and 15-LO-1 mainly in lining macrophages, fibroblasts and sublining endothelial cells. Intraarticular GC treatment resulted in a significant suppression of 5-LO expression, but did not influence the 15-LO-1 enzyme significantly. Also, SF cells express a functional 15-LO-1 and produce 15-HETE when challenged with AA.

Conclusions

These data demonstrate that local therapy with GC decreases 5-LO expression in RA synovium and offer an additional possible mechanism for the efficiency of intraarticular adjuvant therapy in RA.

Overexpression of human 15(S)-lipoxygenase-1 in RAW macrophages leads to increased cholesterol mobilization and reverse cholesterol transport

OBJECTIVE

The purpose of this study was to determine the effect of 15-lipoxygenase-1 (15-LO-1) on cholesterol mobilization from macrophages.

METHODS AND RESULTS

Overexpression of human 15-LO-1 in RAW mouse macrophages led to enhanced cholesterol efflux, increased cholesteryl ester (CE) hydrolysis, and increased reverse cholesterol transport (RCT). Efflux studies comparing 15-LO-1 overexpressing cells to mock-transfected RAW macrophages resulted in a 3- to 7-fold increase in cholesterol efflux to apolipoprotein A-I and a modest increase in efflux to HDL. Additional experiments revealed an increase in mRNA and protein levels of ABCA1 and ABCG1 in the RAW expressing 15-LO-1 compared to controls. Efforts to examine whether the arachidonic acid metabolite of 15-LO-1, (15S)-hydroxyeicosatetraenoic acid (HETE), was responsible for the enhanced efflux revealed this eicosanoid metabolite did not play a role. Enhanced steryl ester hydrolysis was observed in 15-LO-1 overexpressing cells suggesting that the CE produced in the 15-LO-1 expressing cells was readily mobilized. To measure RCT, RAW macrophages overexpressing 15-LO-1 or mock-transfected cells were cholesterol enriched by exposure to acetylated low-density lipoprotein and [(3)H]-cholesterol. These macrophages were injected into wild-type animals and RCT was measured as a percent of injected dose of (3)H appearing in the feces at 48 hours. We found 7% of the injected (3)H in the feces of mice that received macrophages overexpressing 15-LO-1 and 4% in the feces of mice that received mock-transfected cells.

CONCLUSIONS

These data are consistent with a model in which overexpression of human 15-LO-1 in RAW macrophages promotes RCT through increased CE hydrolysis and ABCA1-mediated cholesterol efflux.

Translational mini-review series on immunology of vascular disease: inflammation, infections and Toll-like receptors in cardiovascular disease

Cardiovascular disease, in which atherosclerosis is the major underlying cause, is currently the largest cause of death in the world. Atherosclerosis is an inflammatory disease characterized by the formation of arterial lesions over a period of several decades at sites of endothelial cell dysfunction. These lesions are composed of endothelial cells, vascular smooth muscle cells, monocytes/macrophages and T lymphocytes (CD4(+)). As the lesions progress some can become unstable and prone to disruption, resulting in thrombus formation and possibly a myocardial infarction or stroke depending upon the location. Although the exact triggers for plaque disruption remain unknown, much recent evidence has shown a link between the incidence of myocardial infarction and stroke and a recent respiratory tract infection. Interestingly, many reports have also shown a link between a family of pattern recognition receptors, the Toll-like receptors, and the progression of atherosclerosis, suggesting that infections may play a role in both the progression of atherosclerosis and in inducing the more severe complications associated with the disease.

Human articular chondrocytes express 15-lipoxygenase-1 and -2: potential role in osteoarthritis

Introduction

15-Lipoxygenases and their metabolites have been shown to exhibit anti-inflammatory and immunomodulatory properties, but little is known regarding their expression and function in chondrocytes. The objective of this study was to evaluate the expression of 15-lipoxygenase-1 and -2 in human articular chondrocytes, and to investigate the effects of their metabolites 13(S)-hydroxy octadecadienoic and 15(S)-hydroxyeicosatetraenoic acids on IL-1β-induced matrix metalloproteinase (MMP)-1 and MMP-13 expression.

Methods

The expression levels of 15-lipoxygenase-1 and -2 were analyzed by reverse transcription PCR and Western blotting in chondrocytes, and by immunohistochemistry in cartilage. Chondrocytes or cartilage explants were stimulated with IL-1β in the absence or presence of 13(S)-hydroxy octadecadienoic and 15(S)-hydroxyeicosatetraenoic acids, and the levels of MMP-1 and MMP-13 protein production and type II collagen cleavage were evaluated using immunoassays. The role of peroxisome proliferator-activated receptor (PPAR)γ was evaluated using transient transfection experiments and the PPARγ antagonist GW9662.

Results

Articular chondrocytes express 15-lipoxygenase-1 and -2 at the mRNA and protein levels. 13(S)-hydroxy octadecadienoic and 15(S)-hydroxyeicosatetraenoic acids dose dependently decreased IL-1β-induced MMP-1 and MMP-13 protein and mRNA expression as well as type II collagen cleavage. The effect on MMP-1 and MMP-13 expression does not require de novo protein synthesis. 13(S)-hydroxy octadecadienoic and 15(S)-hydroxyeicosatetraenoic acids activated endogenous PPARγ, and GW9662 prevented their suppressive effect on MMP-1 and MMP-13 production, suggesting the involvement of PPARγ in these effects.

Conclusions

This study is the first to demonstrate the expression of 15-lipoxygenase-1 and -2 in articular chondrocytes. Their respective metabolites, namely 13(S)-hydroxy octadecadienoic and 15(S)-hydroxyeicosatetraenoic acids, suppressed IL-1β-induced MMP-1 and MMP-13 expression in a PPARγ-dependent pathway. These data suggest that 15-lipoxygenases may have chondroprotective properties by reducing MMP-1 and MMP-13 expression.

15-lipoxygenase metabolites play an important role in the development of a T-helper type 1 allergic inflammation induced by double-stranded RNA

BACKGROUND

We recently demonstrated that the T-helper type 1 (Th1) immune response plays an important role in the development of non-eosinophilic inflammation induced by airway exposure of an allergen plus double-stranded RNA (dsRNA). However, the role of lipoxygenase (LO) metabolites in the development of Th1 inflammation is poorly understood.

OBJECTIVE

To evaluate the role of LO metabolites in the development of Th1 inflammation induced by sensitization with an allergen plus dsRNA.

METHODS

A Th2-allergic inflammation mouse model was created by an intraperitoneal injection of lipopolysaccharide-depleted ovalbumin (OVA, 75 microg) and alum (2 mg) twice, and the Th1 model was created by intranasal application of OVA (75 microg) and synthetic dsRNA [10 microg of poly(I : C)] four times, followed by an intranasal challenge with 50 microg of OVA four times. The role of LO metabolites was evaluated using two approaches: a transgenic approach using 5-LO(-/-) and 15-LO(-/-) mice, and a pharmacological approach using inhibitors of cysteinyl leucotriene receptor-1 (cysLTR1), LTB4 receptor (BLT1), and 15-LO.

RESULTS

We found that the Th1-allergic inflammation induced by OVA+dsRNA sensitization was similar between 5-LO(-/-) and wild-type (WT) control mice, although Th2 inflammation induced by sensitization with OVA+alum was reduced in the former group. In addition, dsRNA-induced Th1 allergic inflammation, which is associated with down-regulation of 15-hydroxyeicosateraenoic acids production, was not affected by treatment with cysLTR1 or BLT1 inhibitors, whereas it was significantly lower in 12/15-LO(-/-) mice compared with WT control mice. Moreover, dsRNA-induced allergic inflammation and the recruitment of T cells following an allergen challenge were significantly inhibited by treatment with a specific 15-LO inhibitor (PD146176).

CONCLUSION

15-LO metabolites appear to be important mediators in the development of Th1-allergic inflammation induced by sensitization with an allergen plus dsRNA. Our findings suggest that the 15-LO pathway is a novel therapeutic target for the treatment of virus-associated asthma characterized by Th1 inflammation.

No association of two functional polymorphisms in human ALOX15 with myocardial infarction

The 12/15-lipoxygenase plays a janus-role in inflammation with pro-inflammatory and anti-inflammatory effects in cell systems and even opposite effects on atherosclerosis in two different animal species. Screening of the human 15-lipoxygenase (ALOX15) gene detected a polymorphic C to T substitution at position c.-292, which led to three times higher ALOX15 activity in macrophages and showed a trend to be atheroprotective in a small case-control study for coronary artery disease (CAD). A second polymorphism at position c.1693C>T leading to an T560M exchange and an inactive enzyme was recently associated with increased CAD. We now investigated whether these polymorphisms or a certain haplotype of ALOX15 are associated with myocardial infarction (MI) in a case-control subset from the population-based MONIKA/KORA cohort S3. Six polymorphisms in ALOX15 were analyzed in 2629 participants to cover all major haplotypes with a frequency higher than 1% in the Caucasian population. None of the polymorphism was associated with MI but a rare ALOX15 haplotype showed a significant protective effect on the risk for MI (p=0.03). However, none of the polymorphisms or haplotypes was associated with CRP levels. These data suggest that ALOX15 may play a less prominent role during later stages of atherosclerosis involving atherothrombotic mechanisms than eventually during early plaque development.

Apoetm1Unc mice have impaired alveologenesis, low lung function, and rapid loss of lung function

Diminished lung function, indicated by a low forced expiratory volume in one second (FEV1), and short physical stature, predict early mortality from all causes, including cardiovascular, among smokers and never smokers. The basis for these associations is unclear, and, it is not known if there is a pulmonary morphological component to the relationship between low FEV1 and early death in a general population. Some apolipoprotein E genotypes also predict atherosclerosis and early mortality. These considerations led us to examine the Apoe tm1Unc (Apoe) mouse, in which the apolipoprotein E gene is deleted, and that develops dyslipidemia, atherosclerosis at an early age, and has a shorter life span than the founder wild-type (wt) strain. We asked if Apoe mice have a morphological or functional pulmonary phenotype. We measured the size, number, and surface area of pulmonary gas-exchange units (alveoli) and mechanical properties of the lung. Compared with wt mice, Apoe mice had: 1) diminished developmental alveologenesis, 2) increased airway resistance in early adulthood, 3) high lung volume and high dynamic and static compliance in later adulthood, 4) more rapid loss of lung recoil with age, and 5) were less long than wt mice. These findings in mice indicate the association of a low FEV1 with early death in humans may have developmental, and accelerated ageing, related pulmonary components, and that dietary, genetic, or dietary and genetic influences, on lipid metabolism may be an upstream cause of inflammation and oxidative stress, currently considered to be major risk factors for COPD.

Proteomic analysis of microsomes from lactating bovine mammary gland

Mammary gland has multiple metabolic potential including for large-scale synthesis of milk proteins, carbohydrate, and lipids including nutrient triacylglycerols. We have carried out a proteomic analysis of mammary tissue to discover proteins that affect lipid metabolism. Unfractionated microsomes from lactating bovine mammary tissue were analyzed using one-dimensional SDS-PAGE with RPLC-ESI-MS/MS. This approach gave 703 proteins including 160 predicted transmembrane proteins. Proteins were classified according to their subcellular localizations and biological functions. Over 50 proteins were associated with cellular uptake, metabolism, and secretion of lipids, including some enzymes that have been previously associated with breast cancer and potential therapeutic targets. This database develops a proteomic view of the metabolic potential of mammary gland that can be expected to contribute to a greater understanding of gene expression and tissue remodeling associated with lactation, and to further dissection of normal and pathological processes in mammary tissue.

Mechanisms by which diabetes increases cardiovascular disease

Diabetes mellitus is one of the major risk factors for cardiovascular disease which is the leading cause of death in the U.S. Increasing prevalence of diabetes and diabetic atherosclerosis makes identification of molecular mechanisms by which diabetes promotes atherogenesis an important task. Targeting common pathways may ameliorate both diseases. This review focuses on well known as well as newly discovered mechanisms which may represent promising therapeutic targets.