Lipoxygenase contributes to the oxidation of lipids in human atherosclerotic plaques

Novel Oxadiazole-Based Bioisostere of Caffeic Acid Phenethyl Ester: Synthesis, Anticancer Activity, and Inhibition of Lipoxygenase Product Biosynthesis

Caffeic acid phenethyl ester (1), a honeybee propolis component, possesses many bioactive properties, making it a useful scaffold for drug research. Further, CAPE (1) is a more effective inhibitor of the biosynthesis of 5-lipoxygenase (5-LO) products compared to Zileuton, the only clinically-approved direct 5-LO inhibitor. However, CAPE (1) suffers from a poor metabolic profile, being rapidly metabolized to caffeic acid (CA). In this study, we synthesized and performed several biological assays on a new bioisostere of CAPE (1) possessing a 1,2,4-oxadiazole ring. The new bioisostere (OB-CAPE (5)) has a similar antiproliferative effect to CAPE (1) on NCI-60 cancer cell lines and maintains the activity of CAPE (1) as an inhibitor of the biosynthesis of 5-, 12- and 15-LO products and as an iron chelator. In human polymorphonuclear leukocytes, OB-CAPE (5) inhibits the biosynthesis of 5-LO products with an IC50 of 0.93 µM compared to 1.0 µM for CAPE (1). Both compounds have similar antioxidant activity, with IC50 values of 1.2 µM for OB-CAPE (5) and 1.1 µM for CAPE (1). The new hydrogen bond predicted for the oxadiazole ring and the GLN363 amino acid in the 5-LO active site may explain the small improvement in the affinity of OB-CAPE (5) for the protein compared to CAPE (1). Finally, stability studies in human plasma reveal that OB-CAPE (5) is 25% more stable than CAPE (1). Therefore, the increase in stability associated with the replacement of the ester function with its bioisostere, while maintaining the anti-inflammatory and anticancer properties of CAPE (1), suggests that OB-CAPE (5) may be a comparable yet more stable candidate for in vivo studies in disease models.

The Interplay Between Immunity, Inflammation and Endothelial Dysfunction

The endothelium is pivotal in multiple physiological processes, such as maintaining vascular homeostasis, metabolism, platelet function, and oxidative stress. Emerging evidence in the past decade highlighted the immunomodulatory function of endothelium, serving as a link between innate, adaptive immunity and inflammation. This review examines the regulation of the immune-inflammatory axis by the endothelium, discusses physiological immune functions, and explores pathophysiological processes leading to endothelial dysfunction in various metabolic disturbances, including hyperglycemia, obesity, hypertension, and dyslipidaemia. The final section focuses on the novel, repurposed, and emerging therapeutic targets that address the immune-inflammatory axis in endothelial dysfunction.

Anti-oxidants as therapeutic agents for oxidative stress associated pathologies: future challenges and opportunities

Free radicals have been implicated in the pathogenesis of cancer along with cardiovascular, neurodegenerative, pulmonary and inflammatory disorders. Further, the relationship between oxidative stress and disease is distinctively established. Clinical trials using anti-oxidants for the prevention of disease progression have indicated some beneficial effects. However, these trials failed to establish anti-oxidants as therapeutic agents due to lack of efficacy. This is attributed to the fact that living systems are under dynamic redox control wherein their redox behavior is compartmentalized and simple aggregation of redox couples, distributed throughout the system, is of miniscule importance while determining their overall redox state. Further, free radical metabolism is intriguingly complex as they play plural roles segregated in a spatio-temporal manner. Depending on quality, quantity and site of generation, free radicals exhibit beneficial or harmful effects. Use of nonspecific, non-targeted, general ROS scavengers lead to systemic elimination of all types of ROS and interferes in cellular signaling. Failure of anti-oxidants to act as therapeutic agents lies in this oversimplification of extremely dynamic cellular redox environment as a static and non-compartmentalized redox state. Rather than generalizing the term "oxidative stress" if we can identify the "type of oxidative stress" in different types of diseases, a targeted and more specific anti-oxidant therapy may be developed. In this review, we discuss the concept of redox dynamics, role and type of oxidative stress in disease conditions, and current status of anti-oxidants as therapeutic agents. Further, we probe the possibility of developing novel, targeted and efficacious anti-oxidants with drug-like properties.

Lipid oxidation that is, and is not, inhibited by vitamin E: Consideration about physiological functions of vitamin E

Lipids are oxidized in vivo by multiple oxidizing species with different properties, some by regulated manner to produce physiological mediators, while others by random mechanisms to give detrimental products. Vitamin E plays an important role as a physiologically essential antioxidant to inhibit unregulated lipid peroxidation by scavenging lipid peroxyl radicals to break chain propagation independent of the type of free radicals which induce chain initiation. Kinetic data suggest that vitamin E does not act as an efficient scavenger of nitrogen dioxide radical, carbonate anion radical, and hypochlorite. The analysis of regio- and stereo-isomer distribution of the lipid oxidation products shows that, apart from lipid oxidation by CYP enzymes, the free radical-mediated lipid peroxidation is the major pathway of lipid oxidation taking place in humans. Compared with healthy subjects, the levels of racemic and trans,trans-hydro (pero)xyoctadecadienoates, specific biomarker of free radical lipid oxidation, are elevated in the plasma of patients including atherosclerosis and non-alcoholic fatty liver diseases. α-Tocopherol acts as a major antioxidant, while γ-tocopherol scavenges nitrogen dioxide radical, which induces lipid peroxidation, nitration of aromatic compounds and unsaturated fatty acids, and isomerization of cis-fatty acids to trans-fatty acids. It is essential to appreciate that the antioxidant effects of vitamin E depend on the nature of both oxidants and substrates being oxidized. Vitamin E, together with other antioxidants such as vitamin C, contributes to the inhibition of detrimental oxidation of biological molecules and thereby to the maintenance of human health and prevention of diseases.

The Emerging Role of COX-2, 15-LOX and PPARγ in Metabolic Diseases and Cancer: An Introduction to Novel Multi-target Directed Ligands (MTDLs)

Emerging evidence supports an intertwining framework for the involvement of different inflammatory pathways in a common pathological background for a number of disorders. Of importance are pathways involving arachidonic acid metabolism by cyclooxygenase-2 (COX-2) and 15-lipoxygenase (15-LOX). Both enzyme activities and their products are implicated in a range of pathophysiological processes encompassing metabolic impairment leading to adipose inflammation and the subsequent vascular and neurological disorders, in addition to various pro- and antitumorigenic effects. A further layer of complexity is encountered by the disparate, and often reciprocal, modulatory effect COX-2 and 15-LOX activities and metabolites exert on each other or on other cellular targets, the most prominent of which is peroxisome proliferator-activated receptor gamma (PPARγ). Thus, effective therapeutic intervention with such multifaceted disorders requires the simultaneous modulation of more than one target. Here, we describe the role of COX-2, 15-LOX, and PPARγ in cancer and complications of metabolic disorders, highlight the value of designing multi-target directed ligands (MTDLs) modifying their activity, and summarizing the available literature regarding the rationale and feasibility of design and synthesis of these ligands together with their known biological effects. We speculate on the potential impact of MTDLs in these disorders as well as emphasize the need for structured future effort to translate these early results facilitating the adoption of these, and similar, molecules in clinical research.

Arachidonic Acid Metabolites in Neurologic Disorders

BACKGROUND & OBJECTIVE

Arachidonic acid (ARA) is essential for the fluidity, selective permeability, and flexibility of the cell membrane. It is an important factor for the function of all cells, particularly in the nervous system, immune system, and vascular endothelium. ARA, after docosahexaenoic acid, is the second most common polyunsaturated fatty acid in the phospholipids of the nerve cell membrane. ARA metabolites have many kinds of physiologic roles. The major action of ARA metabolites is the promotion of the acute inflammatory response, mediated by the production of pro-inflammatory mediators such as PGE2 and PGI2, followed by the formation of lipid mediators, which have pro-resolving effects. Another important action of ARA derivatives, especially COX, is the regulation of vascular reactivity through PGs and TXA2. There is significant involvement of ARA metabolites in neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and neuropsychiatric disorders. ARA derivatives also make an important contribution to acute stroke, global ischemia, subarachnoid hemorrhage, and anticoagulation- related hemorrhagic transformation.

CONCLUSION

In this review, we discuss experimental and human study results of neurologic disorders related to ARA and its metabolites in line with treatment options.

Irradiation of the kidneys causes pathologic remodeling in the nontargeted heart: A role for the immune system

Cardiac disease is a frequent and significant adverse event associated with radiotherapy for cancer. Identifying the underlying mechanism responsible for radiation injury to the heart will allow interventions to be developed. In the present study, we tested if local kidney irradiation results in remodeling of the shielded, nontargeted heart. One kidney, two kidneys, or the total body of male WAG and Dahl SS rats were irradiated with 10 Gy of X-rays. Local kidney irradiation resulted in systemic hypertension, increased BUN, infiltration of T lymphocytes, natural killer cells, and macrophages into the renal cortex and medulla, and renal fibrosis. Local irradiation of kidneys in WAG rats resulted in remodeling in the nontargeted heart after 120 days, manifested by perivascular fibrosis and increased interventricular septal thickness, but was not seen in Dahl SS rats due to a high baseline level of fibrosis in the sham-irradiated animals. Genetic depletion of T cells mitigated the nephropathy after local kidney irradiation, indicating a role for the immune system in mediating this outcome. Local kidney irradiation resulted in a cascade of pro-inflammatory cytokines and low-molecular weight metabolites into the circulation associated with transmission of signals resulting in pathologic remodeling in the nontargeted heart. A new model is proposed whereby radiation-induced cardiac remodeling in susceptible animals is indirect, with lower hemi body organs such as the kidney exporting factors into the circulation that cause remodeling outside of the irradiated field in the shielded, nontargeted heart. This nontargeted effect appears to be mediated, in part, by the immune system.

NADPH-quinone oxidoreductase-1 mediates Benzo-[a]-pyrene-1,6-quinone-induced cytotoxicity and reactive oxygen species production in human EA.hy926 endothelial cells

Numerous studies conducted in the past have reported deaths in the human population due to cardiovascular diseases (CVD) on exposure to air particulate matter (APM). BP-1,6-quinone (BP-1,6-Q) is one of the significant components of APM. However, the mechanism(s) by which it can exert its toxicity in endothelial cells is not yet completely understood. NAD(P)H: quinone oxidoreductase-1 (NQO1) is expressed highly in myocardium and vasculature tissues of the heart and plays a vital role in maintaining vascular homeostasis. This study, demonstrated that BP-1,6-Q diminishes NQO1 enzyme activity in a dose-dependent manner in human EA.hy926 endothelial cells. The decrease in the NQO1 enzyme causes potentiation in BP-1,6-Q-mediated toxicity in EA.hy926 endothelial cells. The enhancement of NQO1 in endothelial cells showed cytoprotection against BP-1,6-Q-induced cellular toxicity, lipid, and protein damage suggesting an essential role of NQO1 in cytoprotection against BP-1,6-Q toxicity. Using various biochemical assays and genetic approaches, results from this study further demonstrated that NQO1 also plays a crucial role in BP-1,6-Q-induced production of reactive oxygen species (ROS). These findings will contribute to elucidating BP-1,6-Q mediated toxicity and its role in the development of atherosclerosis.

Formation of atherosclerotic lesions is independent of eosinophils in male mice

BACKGROUND AND AIMS

Oxidation of low-density lipoprotein (LDL) and oxidized LDL-mediated activation of the innate immune system have been recognized as early key events during the pathogenesis of atherosclerosis. Recent evidence identified eosinophils as a major source of enzymatic lipid oxidation and suggested a potential role of type 2 immunity in atherogenesis. However, the involvement of individual type 2 immune cell subsets involved in this process has been incompletely defined. We therefore sought to determine the role of eosinophils during LDL oxidation and the pathogenesis of this disease.

METHODS

Using eosinophil-deficient dblGATA1 mice, we studied the role of eosinophils in two established mouse models of atherosclerosis.

RESULTS

These experiments revealed that the presence of eosinophils did neither affect biomarkers of LDL oxidation nor atherosclerotic lesion development.

CONCLUSIONS

The obtained results show that LDL oxidation and development of atherosclerosis are largely independent of eosinophils or eosinophil-mediated LDL oxidation.

15-Lipoxygenase-1 biosynthesis of 7S,14S-diHDHA implicates 15-lipoxygenase-2 in biosynthesis of resolvin D5

The two oxylipins 7S,14S-dihydroxydocosahexaenoic acid (diHDHA) and 7S,17S-diHDHA [resolvin D5 (RvD5)] have been found in macrophages and infectious inflammatory exudates and are believed to function as specialized pro-resolving mediators (SPMs). Their biosynthesis is thought to proceed through sequential oxidations of DHA by lipoxygenase (LOX) enzymes, specifically, by human 5-LOX (h5-LOX) first to 7(S)-hydroxy-4Z,8E,10Z,13Z,16Z,19Z-DHA (7S-HDHA), followed by human platelet 12-LOX (h12-LOX) to form 7(S),14(S)-dihydroxy-4Z,8E,10Z,12E,16Z,19Z-DHA (7S,14S-diHDHA) or human reticulocyte 15-LOX-1 (h15-LOX-1) to form RvD5. In this work, we determined that oxidation of 7(S)-hydroperoxy-4Z,8E,10Z,13Z,16Z,19Z-DHA to 7S,14S-diHDHA is performed with similar kinetics by either h12-LOX or h15-LOX-1. The oxidation at C14 of DHA by h12-LOX was expected, but the noncanonical reaction of h15-LOX-1 to make over 80% 7S,14S-diHDHA was larger than expected. Results of computer modeling suggested that the alcohol on C7 of 7S-HDHA hydrogen bonds with the backbone carbonyl of Ile399, forcing the hydrogen abstraction from C12 to oxygenate on C14 but not C17. This result raised questions regarding the synthesis of RvD5. Strikingly, we found that h15-LOX-2 oxygenates 7S-HDHA almost exclusively at C17, forming RvD5 with faster kinetics than does h15-LOX-1. The presence of h15-LOX-2 in neutrophils and macrophages suggests that it may have a greater role in biosynthesizing SPMs than previously thought. We also determined that the reactions of h5-LOX with 14(S)-hydroperoxy-4Z,7Z,10Z,12E,16Z,19Z-DHA and 17(S)-hydroperoxy-4Z,7Z,10Z,13Z,15E,19Z-DHA are kinetically slow compared with DHA, suggesting that these reactions may be minor biosynthetic routes in vivo. Additionally, we show that 7S,14S-diHDHA and RvD5 have anti-aggregation properties with platelets at low micromolar potencies, which could directly regulate clot resolution.

Role of reactive oxygen species in atherosclerosis: Lessons from murine genetic models

Atherosclerosis is a multifactorial chronic and inflammatory disease of medium and large arteries, and the major cause of cardiovascular morbidity and mortality worldwide. The pathogenesis of atherosclerosis involves a number of risk factors and complex events including hypercholesterolemia, endothelial dysfunction, increased permeability to low density lipoproteins (LDL) and their sequestration on extracellular matrix in the intima of lesion-prone areas. These events promote LDL modifications, particularly by oxidation, which generates acute and chronic inflammatory responses implicated in atherogenesis and lesion progression. Reactive oxygen species (ROS) (which include both free radical and non-free radical oxygen intermediates), play a key-role at each step of atherogenesis, in endothelial dysfunction, LDL oxidation, and inflammatory events involved in the initiation and development of atherosclerosis lesions. Most advanced knowledge supporting the "oxidative theory of atherosclerosis" i.e. the nature and the cellular sources of ROS and antioxidant defences, as well as the mechanisms involved in the redox balance, is based on the use of genetically engineered animals, i.e. transgenic, genetically modified, or altered for systems producing or neutralizing ROS in the vessels. This review summarizes the results obtained from animals genetically manipulated for various sources of ROS or antioxidant defences in the vascular wall, and their relevance (advance or limitation), for understanding the place and role of ROS in atherosclerosis.

Design, Synthesis and Study of Nitrogen Monoxide Donors as Potent Hypolipidaemic and Anti-Inflammatory Agents

Inflammation and oxidative stress are involved in cardiovascular diseases. Nitrogen monoxide participates in the regulation of endothelial processes. Thus, derivatives of classic nonsteroidal anti-inflammatory drugs (NSAIDs), trolox or cinnamic acids esterified with 2-(nitrooxy)ethanol were designed and studied. It was found that the nitrogen monoxide (NO) releasing activity was comparable to that of S-nitroso-N-acetylpenicillamine. The nitrooxy derivatives decreased potently lipid indices in the plasma of hyperlipidaemic rats (30–85%). All compounds presented increased anti-inflammatory activity in vivo, inhibiting carrageenan-induced rat paw oedema as high as 76%, up to six times higher than that of the parent acids. Lipoxygenase inhibitory activity was significant for most of them, although the parent molecules exerted a minor effect (IC₅₀ > 0.2 mM). Those compounds incorporating an antioxidant structure inhibited rat microsomal membrane lipid peroxidation strongly and possessed radical scavenging activity. These results indicated that the described compounds could act at different targets in multifactorial diseases, further limiting the possible adverse effects of drug combinations.

12/15 Lipoxygenase as a Therapeutic Target in Brain Disorders

Lipoxygenases are a family of lipid-oxidizing enzymes, which generate eicosanoids and related compounds from arachidonic acid and other polyunsaturated fatty acids. These metabolites play important roles in physiology and pathogenesis of host defense mechanisms, cardiovascular diseases, cancer, inflammatory, allergic and neurodegenerative diseases. The 12/15-lipoxygenase (LOX) is special in that it can directly oxidize lipid membranes containing polyunsaturated fatty acids, without the preceding action of a phospholipase, leading to the direct attack on membranous organelles, such as mitochondria. The cytotoxic activity of human 12/15-LOX is up-regulated in neurons and endothelial cells especially after a stroke and thought to contribute to both neuronal cell death and blood-brain barrier leakage. The discovery of inhibitors that selectively target recombinant 12/15-LOX in vitro, as well as possessing activity against the murine orthologous ex vivo, could potentially support a novel therapeutic strategy for the treatment of stroke and other brain disorders related to 12/15-LOX. Here we reviewed 12/15-LOX chemistry shortly, and the diseases in which 12/15-LOX has a role in their pathophysiology and recent advances of 12/15-LOX inhibitors as a treatment option for neurological diseases.

Cholesterol Acceptors Regulate the Lipidome of Macrophage Foam Cells

Arterial foam cells are central players of atherogenesis. Cholesterol acceptors, apolipoprotein A-I (apoA-I) and high-density lipoprotein (HDL), take up cholesterol and phospholipids effluxed from foam cells into the circulation. Due to the high abundance of cholesterol in foam cells, most previous studies focused on apoA-I/HDL-mediated free cholesterol (FC) transport. However, recent lipidomics of human atherosclerotic plaques also identified that oxidized sterols (oxysterols) and non-sterol lipid species accumulate as atherogenesis progresses. While it is known that these lipids regulate expression of pro-inflammatory genes linked to plaque instability, how cholesterol acceptors impact the foam cell lipidome, particularly oxysterols and non-sterol lipids, remains unexplored. Using lipidomics analyses, we found cholesterol acceptors remodel foam cell lipidomes. Lipid subclass analyses revealed various oxysterols, sphingomyelins, and ceramides, species uniquely enriched in human plaques were significantly reduced by cholesterol acceptors, especially by apoA-I. These results indicate that the function of lipid-poor apoA-I is not limited to the efflux of cholesterol and phospholipids but suggest that apoA-I serves as a major regulator of the foam cell lipidome and might play an important role in reducing multiple lipid species involved in the pathogenesis of atherosclerosis.

Regulation and Functions of 15-Lipoxygenases in Human Macrophages

Lipoxygenases (LOXs) catalyze the stereo-specific peroxidation of polyunsaturated fatty acids (PUFAs) to their corresponding hydroperoxy derivatives. Human macrophages express two arachidonic acid (AA) 15-lipoxygenating enzymes classified as ALOX15 and ALOX15B. ALOX15, which was first described in 1975, has been extensively characterized and its biological functions have been investigated in a number of cellular systems and animal models. In macrophages, ALOX15 functions to generate specific phospholipid (PL) oxidation products crucial for orchestrating the nonimmunogenic removal of apoptotic cells (ACs) as well as synthesizing precursor lipids required for production of specialized pro-resolving mediators (SPMs) that facilitate inflammation resolution. The discovery of ALOX15B in 1997 was followed by comprehensive analyses of its structural properties and reaction specificities with PUFA substrates. Although its enzymatic properties are well described, the biological functions of ALOX15B are not fully understood. In contrast to ALOX15 whose expression in human monocyte-derived macrophages is strictly dependent on Th2 cytokines IL-4 and IL-13, ALOX15B is constitutively expressed. This review aims to summarize the current knowledge on the regulation and functions of ALOX15 and ALOX15B in human macrophages.

A pilot metabolomics study of tuberculosis immune reconstitution inflammatory syndrome

BACKGROUND

Diagnosis of paradoxical tuberculosis-associated immune reconstitution inflammatory syndrome (TB-IRIS) is challenging and new tools are needed for early diagnosis as well as to understand the biochemical events that underlie the pathology in TB-IRIS.

METHODS

Plasma samples were obtained from participants from a randomized HIV/TB treatment strategy study (AIDS Clinical Trials Group [ACTG] A5221) with (n = 26) and without TB-IRIS (n = 22) for an untargeted metabolomics pilot study by liquid-chromatography mass spectrometry. The metabolic profile of these participants was compared at the study entry and as close to the diagnosis of TB-IRIS as possible (TB-IRIS window). Molecular features with p < 0.05 and log2 fold change ≥0.58 were submitted for pathway analysis through MetaboAnalyst. We also elucidated potential metabolic signatures for TB-IRIS using a LASSO regression model.

RESULTS

At the study entry, we showed that the arachidonic acid and glycerophospholipid metabolism were altered in the TB-IRIS group. Sphingolipid and linoleic acid metabolism were the most affected pathways during the TB-IRIS window. LASSO modeling selected a set of 8 and 7 molecular features with the potential to predict TB-IRIS at study entry and during the TB-IRIS window, respectively.

CONCLUSION

This study suggests that the use of plasma metabolites may distinguish HIV-TB patients with and without TB-IRIS.

Atherosclerosis: integration of its pathogenesis as a self-perpetuating propagating inflammation: a review

This review proposes that the development of the atherosclerotic plaque is critically dependent on its inflammatory components forming a self-perpetuating and propagating positive feedback loop. The components involved are: (1) LDL oxidation, (2) activation of the endothelium, (3) recruitment of inflammatory monocytes, (4) macrophage accumulation, which induces LDL oxidation, and (5) macrophage generation of inflammatory mediators, which also activate the endothelium. Through these stages, the positive feedback loop is formed, which generates and promotes expansion of the atherosclerotic process. To illustrate this dynamic of lesion development, the author previously produced a computer simulation, which allowed realistic modelling. This hypothesis on atherogenesis can explain the existence and characteristic focal morphology of the atherosclerotic plaque. Each of the components contributing to the feedback loop is discussed. Many of these components also contain subsidiary positive feedback loops, which could exacerbate the overall process.

Emerging role of 12/15-Lipoxygenase (ALOX15) in human pathologies

12/15-lipoxygenase (12/15-LOX) is an enzyme, which oxidizes polyunsaturated fatty acids, particularly omega-6 and -3 fatty acids, to generate a number of bioactive lipid metabolites. A large number of studies have revealed the importance of 12/15-LOX role in oxidative and inflammatory responses. The in vitro studies have demonstrated the ability of 12/15-LOX metabolites in the expression of various genes and production of cytokine related to inflammation and resolution of inflammation. The studies with the use of knockout and transgenic animals for 12/15-LOX have further shown its involvement in the pathogenesis of a variety of human diseases, including cardiovascular, renal, neurological and metabolic disorders. This review summarizes our current knowledge on the role of 12/15-LOX in inflammation and various human diseases.

Regulation of monoamine oxidase A (MAO-A) expression, activity, and function in IL-13-stimulated monocytes and A549 lung carcinoma cells

Monoamine oxidase A (MAO-A) is a mitochondrial flavoenzyme implicated in the pathogenesis of atherosclerosis and inflammation and also in many neurological disorders. MAO-A also has been reported as a potential therapeutic target in prostate cancer. However, the regulatory mechanisms controlling cytokine-induced MAO-A expression in immune or cancer cells remain to be identified. Here, we show that MAO-A expression is co-induced with 15-lipoxygenase (15-LO) in interleukin 13 (IL-13)-activated primary human monocytes and A549 non-small cell lung carcinoma cells. We present evidence that MAO-A gene expression and activity are regulated by signal transducer and activator of transcription 1, 3, and 6 (STAT1, STAT3, and STAT6), early growth response 1 (EGR1), and cAMP-responsive element-binding protein (CREB), the same transcription factors that control IL-13-dependent 15-LO expression. We further established that in both primary monocytes and in A549 cells, IL-13-stimulated MAO-A expression, activity, and function are directly governed by 15-LO. In contrast, IL-13-driven expression and activity of MAO-A was 15-LO-independent in U937 promonocytic cells. Furthermore, we demonstrate that the 15-LO-dependent transcriptional regulation of MAO-A in response to IL-13 stimulation in monocytes and in A549 cells is mediated by peroxisome proliferator-activated receptor γ (PPARγ) and that signal transducer and activator of transcription 6 (STAT6) plays a crucial role in facilitating the transcriptional activity of PPARγ. We further report that the IL-13-STAT6-15-LO-PPARγ axis is critical for MAO-A expression, activity, and function, including migration and reactive oxygen species generation. Altogether, these results have major implications for the resolution of inflammation and indicate that MAO-A may promote metastatic potential in lung cancer cells.

Female mice carrying a defective Alox15 gene are protected from experimental colitis via sustained maintenance of the intestinal epithelial barrier function

Lipoxygenases (ALOXs) are involved in the regulation of cellular redox homeostasis. They also have been implicated in the biosynthesis of pro- and anti-inflammatory lipid mediators and play a role in the pathogenesis of inflammatory diseases, which constitute a major health challenge owing to increasing incidence and prevalence in all industrialized countries around the world. To explore the pathophysiological role of Alox15 (leukocyte-type 12-LOX) in mouse experimental colitis we tested the impact of systemic inactivation of the Alox15 gene on the extent of dextrane sulfate sodium (DSS) colitis. We found that in wildtype mice expression of the Alox15 gene was augmented during DSS-colitis while expression of other Alox genes (Alox5, Alox15b) was hardly altered. Systemic Alox15 (leukocyte-type 12-LOX) deficiency induced less severe colitis symptoms and suppressed in vivo formation of 12-hydroxyeicosatetraenoic acid (12-HETE), the major Alox15 (leukocyte-type 12-LOX) product in mice. These alterations were paralleled by reduced expression of pro-inflammatory gene products, by sustained expression of the zonula occludens protein 1 (ZO-1) and by a less impaired intestinal epithelial barrier function. These results are consistent with in vitro incubations of colon epithelial cells, in which addition of 12S-HETE compromised enantioselectively transepithelial electric resistance. Consistent with these data transgenic overexpression of human ALOX15 intensified the inflammatory symptoms. In summary, our results indicate that systemic Alox15 (leukocyte-type 12-LOX) deficiency protects mice from DSS-colitis. Since exogenous 12-HETE compromises the expression of the tight junction protein ZO-1 the protective effect has been related to a less pronounced impairment of the intestinal epithelial barrier function.

Biological Activities of Stilbenoids

Stilbenoids are a group of naturally occurring phenolic compounds found in various plant species. They share a common backbone structure known as stilbene, but differ in the nature and position of substituents. Stilbenoids are classified as phytoalexins, which are antimicrobial compounds produced de novo in plants to protect against fungal infection and toxins. In this review, the biological effects of stilbenoids such as resveratrol, pterostilbene, gnetol and piceatannol are discussed. Stilbenoids exert various biological activities ranging from cardioprotection, neuroprotection, anti-diabetic properties, depigmentation, anti-inflammation, cancer prevention and treatment. The results presented cover a myriad of models, from cell culture to animal studies as well as clinical human trials. Although positive results were obtained in most cell culture and animal studies, further human studies are needed to substantiate beneficial effects of stilbenoids. Resveratrol remains the most widely studied stilbenoid. However, there is limited information regarding the potential of less common stilbenoids. Therefore, further research is warranted to evaluate the salutary effects of various stilbenoids.

Oxidized Lipoprotein Uptake Through the CD36 Receptor Activates the NLRP3 Inflammasome in Human Retinal Pigment Epithelial Cells

Purpose

Accumulation of oxidized phospholipids/lipoproteins with age is suggested to contribute to the pathogenesis of AMD. We investigated the effect of oxidized LDL (ox-LDL) on human RPE cells.

Methods

Primary human fetal RPE (hf-RPE) and ARPE-19 cells were treated with different doses of LDL or ox-LDL. Assessment of cell death was measured by lactate dehydrogenase release into the conditioned media. Barrier function of RPE was assayed by measuring transepithelial resistance. Lysosomal accumulation of ox-LDL was determined by immunostaining. Expression of CD36 was determined by RT-PCR; protein blot and function was examined by receptor blocking. NLRP3 inflammasome activation was assessed by RT-PCR, protein blot, caspase-1 fluorescent probe assay, and inhibitor assays.

Results

Treatment with ox-LDL, but not LDL, for 48 hours caused significant increase in hf-RPE and ARPE-19 (P < 0.001) cell death. Oxidized LDL treatment of hf-RPE cells resulted in a significant decrease in transepithelial resistance (P < 0.001 at 24 hours and P < 0.01 at 48 hours) relative to LDL-treated and control cells. Internalized ox-LDL was targeted to RPE lysosomes. Uptake of ox-LDL but not LDL significantly increased CD36 protein and mRNA levels by more than 2-fold. Reverse transcription PCR, protein blot, and caspase-1 fluorescent probe assay revealed that ox-LDL treatment induced NLRP3 inflammasome when compared with LDL treatment and control. Inhibition of NLRP3 activation using 10 μM isoliquiritigenin significantly (P < 0.001) inhibited ox-LDL induced cytotoxicity.

Conclusions

These data are consistent with the concept that ox-LDL play a role in the pathogenesis of AMD by NLRP3 inflammasome activation. Suppression of NLRP3 inflammasome activation could attenuate RPE degeneration and AMD progression.

Atherosclerosis

In this chapter, we discuss the manner through which the immune system regulates the cardiovascular system in health and disease. We define the cardiovascular system and elements of atherosclerotic disease, the main focus in this chapter. Herein we elaborate on the disease process that can result in myocardial infarction (heart attack), ischaemic stroke and peripheral arterial disease. We have discussed broadly the homeostatic mechanisms in place that help autoregulate the cardiovascular system including the vital role of cholesterol and lipid clearance as well as the role lipid homeostasis plays in cardiovascular disease in the context of atherosclerosis. We then elaborate on the role played by the immune system in this setting, namely, major players from the innate and adaptive immune system, as well as discussing in greater detail specifically the role played by monocytes and macrophages.This chapter should represent an overview of the role played by the immune system in cardiovascular homeostasis; however further reading of the references cited can expand the reader's knowledge of the detail, and we point readers to many excellent reviews which summarise individual immune systems and their role in cardiovascular disease.

Human 15-LOX-1 active site mutations alter inhibitor binding and decrease potency

Human 15-lipoxygenase-1 (h15-LOX-1 or h12/15-LOX) reacts with polyunsaturated fatty acids and produces bioactive lipid derivatives that are implicated in many important human diseases. One such disease is stroke, which is the fifth leading cause of death and the first leading cause of disability in America. The discovery of h15-LOX-1 inhibitors could potentially lead to novel therapeutics in the treatment of stroke, however, little is known about the inhibitor/active site interaction. This study utilizes site-directed mutagenesis, guided in part by molecular modeling, to gain a better structural understanding of inhibitor interactions within the active site. We have generated eight mutants (R402L, R404L, F414I, F414W, E356Q, Q547L, L407A, I417A) of h15-LOX-1 to determine whether these active site residues interact with two h15-LOX-1 inhibitors, ML351 and an ML094 derivative, compound 18. IC₅₀ values and steady-state inhibition kinetics were determined for the eight mutants, with four of the mutants affecting inhibitor potency relative to wild type h15-LOX-1 (F414I, F414W, E356Q and L407A). The data indicate that ML351 and compound 18, bind in a similar manner in the active site to an aromatic pocket close to F414 but have subtle differences in their specific binding modes. This information establishes the binding mode for ML094 and ML351 and will be leveraged to develop next-generation inhibitors.

The double-edged role of 12/15-lipoxygenase during inflammation and immunity

12/15-Lipoxygenase (12/15-LOX) mediates the enzymatic oxidation of polyunsaturated fatty acids, thereby contributing to the generation of various bioactive lipid mediators. Although 12/15-LOX has been implicated in the pathogenesis of multiple chronic inflammatory diseases, its physiologic functions seem to include potent immune modulatory properties that physiologically contribute to the resolution of inflammation and the clearance of inflammation-associated tissue damage. This review aims to give a comprehensive overview about our current knowledge on the role of this enzyme during the regulation of inflammation and immunity. This article is part of a Special Issue entitled: Lipid modification and lipid peroxidation products in innate immunity and inflammation edited by Christoph J. Binder.

Amides of non-steroidal anti-inflammatory drugs with thiomorpholine can yield hypolipidemic agents with improved anti-inflammatory activity

Novel amides of non steroidal anti-inflammatory drugs (NSAIDs), α-lipoic acid and indole-3-acetic acid with thiomorpholine were synthesised by a simple method and at high yields (60-92%). All the NSAID derivatives highly decreased lipidemic indices in the plasma of Triton treated hyperlipidemic rats. The most potent compound was the indomethacin derivative, which decreased total cholesterol, triglycerides and LDL cholesterol by 73%, 80% and 83%, respectively. They reduced acute inflammation equally or more than most parent acids. Hence, it could be concluded that amides of common NSAIDs with thiomorpholine acquire considerable hypolipidemic potency, while they preserve or augment their anti-inflammatory activity, thus addressing significant risk factors for atherogenesis.

Structural and functional biology of arachidonic acid 15-lipoxygenase-1 (ALOX15)

Lipoxygenases (LOX) form a family of lipid peroxidizing enzymes, which have been implicated in a number of physiological processes and in the pathogenesis of inflammatory, hyperproliferative and neurodegenerative diseases. They occur in two of the three domains of terrestrial life (bacteria, eucarya) and the human genome involves six functional LOX genes, which encode for six different LOX isoforms. One of these isoforms is ALOX15, which has first been described in rabbits in 1974 as enzyme capable of oxidizing membrane phospholipids during the maturational breakdown of mitochondria in immature red blood cells. During the following decades ALOX15 has extensively been characterized and its biological functions have been studied in a number of cellular in vitro systems as well as in various whole animal disease models. This review is aimed at summarizing the current knowledge on the protein-chemical, molecular biological and enzymatic properties of ALOX15 in various species (human, mouse, rabbit, rat) as well as its implication in cellular physiology and in the pathogenesis of various diseases.

Cholesterol-Independent Suppression of Lymphocyte Activation, Autoimmunity, and Glomerulonephritis by Apolipoprotein A-I in Normocholesterolemic Lupus-Prone Mice

Apolipoprotein (Apo)A-I, the major lipid-binding protein of high-density lipoprotein, can prevent autoimmunity and suppress inflammation in hypercholesterolemic mice by attenuating lymphocyte cholesterol accumulation and removing tissue-oxidized lipids. However, whether ApoA-I mediates immune-suppressive or anti-inflammatory effects under normocholesterolemic conditions and the mechanisms involved remain unresolved. We transferred bone marrow from systemic lupus erythematosus (SLE)-prone Sle123 mice into normal, ApoA-I-knockout (ApoA-I(-/-)) and ApoA-I-transgenic (ApoA-I(tg)) mice. Increased ApoA-I in ApoA-I(tg) mice suppressed CD4(+) T and B cell activation without changing lymphocyte cholesterol levels or reducing major ApoA-I-binding oxidized fatty acids. Unexpectedly, oxidized fatty acid peroxisome proliferator-activated receptor γ ligands 13- and 9-hydroxyoctadecadienoic acid were increased in lymphocytes of autoimmune ApoA-I(tg) mice. ApoA-I reduced Th1 cells independently of changes in CD4(+)Foxp3(+) regulatory T cells or CD11c(+) dendritic cell activation and migration. Follicular helper T cells, germinal center B cells, and autoantibodies were also lower in ApoA-I(tg) mice. Transgenic ApoA-I also improved SLE-mediated glomerulonephritis. However, ApoA-I deficiency did not have the opposite effects on autoimmunity or glomerulonephritis, possibly as the result of compensatory increases in ApoE on high-density lipoprotein. We conclude that, although compensatory mechanisms prevent the proinflammatory effects of ApoA-I deficiency in normocholesterolemic mice, increasing ApoA-I can attenuate lymphocyte activation and autoimmunity in SLE independently of cholesterol transport, possibly through oxidized fatty acid peroxisome proliferator-activated receptor γ ligands, and it can reduce renal inflammation in glomerulonephritis.

Absence of an effect of vitamin E on protein and lipid radical formation during lipoperoxidation of LDL by lipoxygenase

Low-density lipoprotein (LDL) oxidation is the primary event in atherosclerosis, and LDL lipoperoxidation leads to modifications in apolipoprotein B-100 (apo B-100) and lipids. Intermediate species of lipoperoxidation are known to be able to generate amino acid-centered radicals. Thus, we hypothesized that lipoperoxidation intermediates induce protein-derived free radical formation during LDL oxidation. Using DMPO and immuno-spin trapping, we detected the formation of protein free radicals on LDL incubated with Cu(2+) or the soybean lipoxidase (LPOx)/phospholipase A2 (PLA2). With low concentrations of DMPO (1mM), Cu(2+) dose-dependently induced oxidation of LDL and easily detected apo B-100 radicals. Protein radical formation in LDL incubated with Cu(2+) showed maximum yields after 30 min. In contrast, the yields of apo B-100 radicals formed by LPOx/PLA2 followed a typical enzyme-catalyzed kinetics that was unaffected by DMPO concentrations of up to 50mM. Furthermore, when we analyzed the effect of antioxidants on protein radical formation during LDL oxidation, we found that ascorbate, urate, and Trolox dose-dependently reduced apo B-100 free radical formation in LDL exposed to Cu(2+). In contrast, Trolox was the only antioxidant that even partially protected LDL from LPOx/PLA2. We also examined the kinetics of lipid radical formation and protein radical formation induced by Cu(2+) or LPOx/PLA2 for LDL supplemented with α-tocopherol. In contrast to the potent antioxidant effect of α-tocopherol on the delay of LDL oxidation induced by Cu(2+), when we used the oxidizing system LPOx/PLA2, no significant protection was detected. The lack of protection of α-tocopherol on the apo B-100 and lipid free radical formation by LPOx may explain the failure of vitamin E as a cardiovascular protective agent for humans.

The action of peroxyl radicals, powerful deleterious reagents, explains why neither cholesterol nor saturated fatty acids cause atherogenesis and age-related diseases

Cells respond to alterations in their membrane structure by activating hydrolytic enzymes. Thus, polyunsaturated fatty acids (PUFAs) are liberated. Free PUFAs react with molecular oxygen to give lipid hydroperoxide molecules (LOOHs). In case of severe cell injury, this physiological reaction switches to the generation of lipid peroxide radicals (LOO(·)). These radicals can attack nearly all biomolecules such as lipids, carbohydrates, proteins, nucleic acids and enzymes, impairing their biological functions. Identical cell responses are triggered by manipulation of food, for example, heating/grilling and particularly homogenization, representing cell injury. Cholesterol as well as diets rich in saturated fat have been postulated to accelerate the risk of atherosclerosis while food rich in unsaturated fatty acids has been claimed to lower this risk. However, the fact is that LOO(·) radicals generated from PUFAs can oxidize cholesterol to toxic cholesterol oxides, simulating a reduction in cholesterol level. In this review it is shown how active LOO(·) radicals interact with biomolecules at a speed transcending usual molecule-molecule reactions by several orders of magnitude. Here, it is explained how functional groups are fundamentally transformed by an attack of LOO(·) with an obliteration of essential biomolecules leading to pathological conditions. A serious reconsideration of the health and diet guidelines is required.

Mammalian lipoxygenases and their biological relevance

Lipoxygenases (LOXs) form a heterogeneous class of lipid peroxidizing enzymes, which have been implicated not only in cell proliferation and differentiation but also in the pathogenesis of various diseases with major public health relevance. As other fatty acid dioxygenases LOXs oxidize polyunsaturated fatty acids to their corresponding hydroperoxy derivatives, which are further transformed to bioactive lipid mediators (eicosanoids and related substances). On the other hand, lipoxygenases are key players in the regulation of the cellular redox homeostasis, which is an important element in gene expression regulation. Although the first mammalian lipoxygenases were discovered 40 years ago and although the enzymes have been well characterized with respect to their structural and functional properties the biological roles of the different lipoxygenase isoforms are not completely understood. This review is aimed at summarizing the current knowledge on the physiological roles of different mammalian LOX-isoforms and their patho-physiological function in inflammatory, metabolic, hyperproliferative, neurodegenerative and infectious disorders. This article is part of a Special Issue entitled "Oxygenated metabolism of PUFA: analysis and biological relevance".

Apolipoprotein A-I mimetic peptide 4F rescues pulmonary hypertension by inducing microRNA-193-3p

BACKGROUND

Pulmonary arterial hypertension is a chronic lung disease associated with severe pulmonary vascular changes. A pathogenic role of oxidized lipids such as hydroxyeicosatetraenoic and hydroxyoctadecadienoic acids is well established in vascular disease. Apolipoprotein A-I mimetic peptides, including 4F, have been reported to reduce levels of these oxidized lipids and improve vascular disease. However, the role of oxidized lipids in the progression of pulmonary arterial hypertension and the therapeutic action of 4F in pulmonary arterial hypertension are not well established.

METHODS AND RESULTS

We studied 2 different rodent models of pulmonary hypertension (PH): a monocrotaline rat model and a hypoxia mouse model. Plasma levels of hydroxyeicosatetraenoic and hydroxyoctadecadienoic acids were significantly elevated in PH. 4F treatment reduced these levels and rescued preexisting PH in both models. MicroRNA analysis revealed that microRNA-193-3p (miR193) was significantly downregulated in the lung tissue and serum from both patients with pulmonary arterial hypertension and rodents with PH. In vivo miR193 overexpression in the lungs rescued preexisting PH and resulted in downregulation of lipoxygenases and insulin-like growth factor-1 receptor. 4F restored PH-induced miR193 expression via transcription factor retinoid X receptor α.

CONCLUSIONS

These studies establish the importance of microRNAs as downstream effectors of an apolipoprotein A-I mimetic peptide in the rescue of PH and suggest that treatment with apolipoprotein A-I mimetic peptides or miR193 may have therapeutic value.

OxLDL induces endothelial dysfunction and death via TRAF3IP2: inhibition by HDL3 and AMPK activators

Oxidized low-density lipoprotein (oxLDL) induces endothelial cell death through the activation of NF-κB and AP-1 pathways. TRAF3IP2 is a redox-sensitive cytoplasmic adapter protein and an upstream regulator of IKK/NF-κB and JNK/AP-1. Here we show that oxLDL-induced death in human primary coronary artery endothelial cells (ECs) was markedly attenuated by the knockdown of TRAF3IP2 or the lectin-like oxLDL receptor 1 (LOX-1). Further, oxLDL induced Nox2/superoxide-dependent TRAF3IP2 expression, IKK/p65 and JNK/c-Jun activation, and LOX-1 upregulation, suggesting a reinforcing mechanism. Similarly, the lysolipids present in oxLDL (16:0-LPC and 18:0-LPC) and minimally modified LDL also upregulated TRAF3IP2 expression. Notably, whereas native HDL3 reversed oxLDL-induced TRAF3IP2 expression and cell death, 15-lipoxygenase-modified HDL3 potentiated its proapoptotic effects. The activators of the AMPK/Akt pathway, adiponectin, AICAR, and metformin, attenuated superoxide generation, TRAF3IP2 expression, and oxLDL/TRAF3IP2-mediated EC death. Further, both HDL3 and adiponectin reversed oxLDL/TRAF3IP2-dependent monocyte adhesion to endothelial cells in vitro. Importantly, TRAF3IP2 gene deletion and the AMPK activators reversed oxLDL-induced impaired vasorelaxation ex vivo. These results indicate that oxLDL-induced endothelial cell death and dysfunction are mediated via TRAF3IP2 and that native HDL3 and the AMPK activators inhibit this response. Targeting TRAF3IP2 could potentially inhibit progression of atherosclerotic vascular diseases.

Polyoxygenated cholesterol ester hydroperoxide activates TLR4 and SYK dependent signaling in macrophages

Oxidation of low-density lipoprotein (LDL) is one of the major causative mechanisms in the development of atherosclerosis. In previous studies, we showed that minimally oxidized LDL (mmLDL) induced inflammatory responses in macrophages, macropinocytosis and intracellular lipid accumulation and that oxidized cholesterol esters (OxCEs) were biologically active components of mmLDL. Here we identified a specific OxCE molecule responsible for the biological activity of mmLDL and characterized signaling pathways in macrophages in response to this OxCE. Using liquid chromatography – tandem mass spectrometry and biological assays, we identified an oxidized cholesteryl arachidonate with bicyclic endoperoxide and hydroperoxide groups (BEP-CE) as a specific OxCE that activates macrophages in a TLR4/MD-2-dependent manner. BEP-CE induced TLR4/MD-2 binding and TLR4 dimerization, phosphorylation of SYK, ERK1/2, JNK and c-Jun, cell spreading and uptake of dextran and native LDL by macrophages. The enhanced macropinocytosis resulted in intracellular lipid accumulation and macrophage foam cell formation. Bone marrow-derived macrophages isolated from TLR4 and SYK knockout mice did not respond to BEP-CE. The presence of BEP-CE was demonstrated in human plasma and in the human plaque material captured in distal protection devices during percutaneous intervention. Our results suggest that BEP-CE is an endogenous ligand that activates the TLR4/SYK signaling pathway. Because BEP-CE is present in human plasma and human atherosclerotic lesions, BEP-CE-induced and TLR4/SYK-mediated macrophage responses may contribute to chronic inflammation in human atherosclerosis.

Indirubin-3'-monoxime exerts a dual mode of inhibition towards leukotriene-mediated vascular smooth muscle cell migration

Aims

The small molecule indirubin-3′-monoxime (I3MO) has been shown to inhibit vascular smooth muscle cell (VSMC) proliferation and neointima formation in vivo. The influence of I3MO on VSMC migration and vascular inflammation, two additional key players during the onset of atherosclerosis and restenosis, should be investigated.

Methods and results

We examined the influence of I3MO on VSMC migration, with focus on monocyte-derived leukotrienes (LTs) and platelet-derived growth factors (PDGFs) as elicitors. Exogenous LTB4 and cysteinyl leukotrienes as well as LT-enriched conditioned medium of activated primary human monocytes induced VSMC migration, which was inhibited by I3MO. I3MO also blunted migration of VSMC stimulated with the PDGF, the strongest motogen tested in this study. Induction of haem oxygenase 1 accounted for this anti-migratory activity of I3MO in VSMC. Notably, I3MO not only interfered with the migratory response in VSMC, but also suppressed the production of pro-migratory LT in monocytes. Conditioned media from monocytes that were activated in the presence of I3MO failed to induce VSMC migration. In cell-based and cell-free assays, I3MO selectively inhibited 5-lipoxygenase (5-LO), the key enzyme in LT biosynthesis, with an IC₅₀ in the low micromolar range.

Conclusion

Our study reveals a novel dual inhibitory mode of I3MO on LT-mediated VSMC migration: (i) I3MO interferes with pro-migratory signalling in VSMC and (ii) I3MO suppresses LT biosynthesis in monocytes by direct inhibition of 5-LO. These inhibitory actions on both migratory stimulus and response complement the previously demonstrated anti-proliferative properties of I3MO and may further promote I3MO as promising vasoprotective compound.

From macrophage interleukin-13 receptor to foam cell formation: mechanisms for αMβ2 integrin interference

IL-13 is a potent stimulator of alternative monocyte/macrophage activation. During alternative activation, the expression of several proteins is induced including 15-lipoxygenase (15-LO), a lipid-peroxidating enzyme and the scavenger receptor CD36. We previously reported that α(M)β(2) integrin activation or clustering suppresses the expression of both 15-LO and CD36. In this study we focused on exploring the molecular mechanisms that down-regulate CD36 expression and CD36-mediated foam cell formation in IL-13-stimulated monocytes/macrophages after α(M)β(2) activation. Our studies reveal that α(M)β(2) integrin activation inhibits the IL-13 activation of several critical pathways that are required for macrophage alternative activation; namely, blocking Jak2 and Tyk2 phosphorylation, which bind to the cytoplasmic tails of the IL-4Rα/IL-13Rα1 complex. This leads to the inhibition of tyrosine phosphorylation of Stats (Stat1, Stat3, and Stat6) and prevents the formation of a signaling complex (containing p38MAPK, PKCδ, and Stat3) that are critical for the expression of both 15-LO and CD36. Jak2-mediated Hck activation is also inhibited, thereby preventing Stats serine phosphorylation, which is essential for downstream Stat-dependent gene transcription. Moreover, inhibition of Jak2, Tyk2, or their downstream target 15-LO with antisense oligonucleotides profoundly inhibits IL-13-induced CD36 expression and CD36-dependent foam cell formation, whereas13(S) Hydroperoxyoctadecadienoic acid (HPODE), a 15-LO product and peroxisome proliferator-activated receptor-γ ligand, completely restores CD36 expression in monocytes treated with 15-LO antisense. α(M)β(2) integrin activation controls CD36 expression and foam cell formation in alternatively activated monocyte/macrophages by blocking Tyk2/Jak2 phosphorylation via a 15-LO-dependent pathway. The discovery of this mechanism helps our understanding of the potential role of alternatively activated macrophages in atherogenesis and highlights the impact of integrin α(M)β(2) on this process.

Upregulation of lectin-like oxidized low density lipoprotein receptor 1 (LOX-1) expression in human endothelial cells by modified high density lipoproteins

Lectin-like oxidized low density lipoprotein receptor-1 (LOX-1) is the main endothelial receptor for oxidized low density lipoprotein (OxLDL). LOX-1 is highly expressed in endothelial cells of atherosclerotic lesions, but also in macrophages and smooth muscle cells. LOX-1 expression is upregulated by several inflammatory cytokines (such as TNF-α), by oxidative stress, and by pathological conditions, such as dyslipidemia, hypertension, and diabetes. High density lipoprotein (HDL) possess several atheroprotective properties; however under pathological conditions associated with inflammation and oxidative stress, HDL become dysfunctional and exhibit pro-inflammatory properties. In vitro, HDL can be modified by 15-lipoxygenase, an enzyme overexpressed in the atherosclerotic lesions. Here we report that, after modification with 15-lipoxygenase, HDL(3) lose their ability to inhibit TNFα-induced LOX-1 expression in endothelial cells; in addition, 15LO-modified HDL(3) induce LOX-1 mRNA and protein expression and bind to LOX-1 with increased affinity compared to native HDL(3). Altogether these findings confirm that 15LO-modified HDL(3) possess a pro-atherogenic role.

Oxidant stress and skeletal muscle microvasculopathy in the metabolic syndrome

The evolution of the metabolic syndrome in afflicted individuals is, in part, characterized by the development of a severely pro-oxidant state within the vasculature. It has been previously demonstrated by many investigators that this increasingly pro-oxidant state can have severe negative implications for many relevant processes within the vasculature, including the coordination of dilator/constrictor tone or reactivity, the structural adaptations of the vascular wall or distal networks, as well as the integrated regulation of perfusion resistance across and throughout the vascular networks. The purpose of this review article is to present the different sources of oxidant stress within the setting of the metabolic syndrome, the available mechanism for attempts at regulation and the vascular outcomes associated with this condition. It is anticipated that this overview will help readers and investigators to more effectively design experiments and interpret their results within the extremely complicated setting of metabolic syndrome.

Fragmentation of β-hydroxy hydroperoxides

A β-hydroxy hydroperoxide was obtained through base-catalyzed disproportionation of a hydroperoxy endoperoxide available by singlet oxygenation of cyclohepta-1,4-diene. Vitamins E and C induce fragmentation of this β-hydroxy hydroperoxide generating aldehydes, especially in the presence of redox active metal ions such as those present in vivo, e.g., under conditions of "iron overload". This chemistry may contribute to the oxidative cleavage of polyunsaturated fatty acyls that produces similar aldehydes, which damage proteins and DNA through covalent adduction resulting in "oxidative injury".

Atherogenic ω-6 Lipids Modulate PPAR- EGR-1 Crosstalk in Vascular Cells

Atherogenic ω-6 lipids are physiological ligands of peroxisome proliferator-activated receptors (PPARs) and elicit pro- and antiatherogenic responses in vascular cells. The objective of this study was to investigate if ω-6 lipids modulated the early growth response-1 (Egr-1)/PPAR crosstalk thereby altering vascular function. Rat aortic smooth muscle cells (RASMCs) were exposed to ω-6 lipids, linoleic acid (LA), or its oxidized form, 13-HPODE (OxLA) in the presence or absence of a PPARα antagonist (MK886) or PPARγ antagonist (GW9662) or PPAR-specific siRNA. Our results demonstrate that ω-6 lipids, induced Egr-1 and monocyte chemotactic protein-1 (MCP-1) mRNA and protein levels at the acute phase (1-4 hrs) when PPARα was downregulated and at subacute phase (4-12 hrs) by modulating PPARγ, thus resulting in altered monocyte adhesion to RASMCs. We provide novel insights into the mechanism of action of ω-6 lipids on Egr-1/PPAR interactions in vascular cells and their potential in altering vascular function.

Electrospray MS/MS reveals extensive and nonspecific oxidation of cholesterol esters in human peripheral vascular lesions

Although LDL is rendered proatherogenic by various experimental treatments (e.g., acetylation), the exact structural changes that drive LDL transformation in vivo remain enigmatic. Among the many hypothesized targets of oxidative modification are cholesterol esters (CE). This family of neutral lipids, which carries a highly unsaturated pool of fatty acyl groups, is the main component of both LDL particles and atherosclerotic plaques. Tandem mass spectrometry (MS/MS) was employed to reveal abundant and diverse oxidized CEs (oxCE), including novel oxidation products, within human peripheral vascular lesions. These oxCE species composed up to 40% of the total CE pool, with cholesteryl linoleate being oxidized to the greatest extent. Imaging mass spectrometry studies showed that oxCE was entirely confined within the plaque, along with unmodified CE and triacylglyceride (TAG). Interestingly, we found no evidence for TAG oxidation, although polyunsaturated species were abundant. Enzymatic oxidation of cholesteryl linoleate by 15-lipoxygenase (15-LO), an enzyme often invoked in CE oxidation, initially results in a regio- and stereospecific product. Analysis of intact cholesteryl hydroxyoctadecadienoate isomers in human atheromata revealed no regio- or stereospecificity, indicating 15-LO was either not a major source of oxCE or nonenzymatic processes had eroded any product specificity.

Hck is a key regulator of gene expression in alternatively activated human monocytes

IL-13 is a Th2 cytokine that promotes alternative activation (M2 polarization) in primary human monocytes. Our studies have characterized the functional IL-13 receptor complex and the downstream signaling events in response to IL-13 stimulation in alternatively activated monocytes/macrophages. In this report, we present evidence that IL-13 induces the activation of a Src family tyrosine kinase, which is required for IL-13 induction of M2 gene expression, including 15-lipoxygenase (15-LO). Our data show that Src kinase activity regulates IL-13-induced p38 MAPK tyrosine phosphorylation via the upstream kinases MKK3 or MKK6. Our findings also reveal that the IL-13 receptor-associated tyrosine kinase Jak2 is required for the activation of both Src kinase as well as p38 MAPK. Further, we found that Src tyrosine kinase-mediated activation of p38 MAPK is required for Stat1 and Stat3 serine 727 phosphorylation in alternatively activated monocytes/macrophages. Additional studies identify Hck as the specific Src family member, stimulated by IL-13 and involved in regulating both p38 MAPK activation and p38 MAPK-mediated 15-LO expression. Finally we show that the Hck regulates the expression of other alternative state (M2)-specific genes (Mannose receptor, MAO-A, and CD36) and therefore conclude that Hck acts as a key regulator controlling gene expression in alternatively activated monocytes/macrophages.

Cannabidiol-2',6'-dimethyl ether as an effective protector of 15-lipoxygenase-mediated low-density lipoprotein oxidation in vitro

15-Lipoxygenase (15-LOX) is one of the key enzymes responsible for the formation of oxidized low-density lipoprotein (ox-LDL), a major causal factor for atherosclerosis. Both enzymatic (15-LOX) and non-enzymatic (Cu(2+)) mechanisms have been proposed for the production of ox-LDL. We have recently reported that cannabidiol-2',6'-dimethyl ether (CBDD) is a selective and potent inhibitor of 15-LOX-catalyzed linoleic acid oxygenation (Takeda et al., Drug Metab. Dispos., 37, 1733-1737 (2009)). In the LDL, linoleic acid is present as cholesteryl linoleate, the major fatty acid esterified to cholesterol, and is susceptible to oxidative modification by 15-LOX or Cu(2+). In this investigation, we examined the efficacy of CBDD on i) 15-LOX-catalyzed oxygenation of cholesteryl linoleate, and ii) ox-LDL formation catalyzed by 15-LOX versus Cu(2+)-mediated non-enzymatic generation of this important mediator. The results obtained demonstrate that CBDD is a potent and selective inhibitor of ox-LDL formation generated by the 15-LOX pathway. These studies establish CBDD as both an important experimental tool for characterizing 15-LOX-mediated ox-LDL formation, and as a potentially useful therapeutic agent for treatment of atherosclerosis.

Monocyte 15-lipoxygenase gene expression requires ERK1/2 MAPK activity

IL-13 induces profound expression of 15-lipoxygenase (15-LO) in primary human monocytes. Our studies have defined the functional IL-13R complex, association of Jaks with the receptor components, and the tyrosine phosphorylation of several Stat molecules in response to IL-13. Furthermore, we identified both p38MAPK and protein kinase Cδ as critical regulators of 15-LO expression. In this study, we report an ERK1/2-dependent signaling cascade that regulates IL-13-mediated 15-LO gene expression. We show the rapid phosphorylation/activation of ERK1/2 upon IL-13 exposure. Our results indicate that Tyk2 kinase is required for the activation of ERK1/2, which is independent of the Jak2, p38MAPK, and protein kinase Cδ pathways, suggesting bifurcating parallel regulatory pathways downstream of the receptor. To investigate the signaling mechanisms associated with the ERK1/2-dependent expression of 15-LO, we explored the involvement of transcription factors, with predicted binding sites in the 15-LO promoter, in this process including Elk1, early growth response-1 (Egr-1), and CREB. Our findings indicate that IL-13 induces Egr-1 nuclear accumulation and CREB serine phosphorylation and that both are markedly attenuated by inhibition of ERK1/2 activity. We further show that ERK1/2 activity is required for both Egr-1 and CREB DNA binding to their cognate sequences identified within the 15-LO promoter. Furthermore, by transfecting monocytes with the decoy oligodeoxyribonucleotides specific for Egr-1 and CREB, we discovered that Egr-1 and CREB are directly involved in regulating 15-LO gene expression. These studies characterize an important regulatory role for ERK1/2 in mediating IL-13-induced monocyte 15-LO expression via the transcription factors Egr-1 and CREB.

Δ9-tetrahydrocannabinol and its major metabolite Δ9-tetrahydrocannabinol-11-oic acid as 15-lipoxygenase inhibitors

15-Lipoxygenase (15-LOX) is one of the key enzymes responsible for the formation of oxidized low-density lipoprotein, a major causal factor for atherosclerosis. Δ(9)-Tetrahydrocannabinol (Δ(9)-THC), a major component of marijuana, has suggested to suppress atherosclerosis. Although Δ(9)-THC seems to be attractive for the prevention of atherosclerosis, there is no information about whether or not 15-LOX isoform can be inhibited by Δ(9)-THC. In the present study, Δ(9)-THC was found to be a direct inhibitor for 15-LOX with an IC(50) (50% inhibition concentration) value of 2.42 μM. Furthermore, Δ(9)-THC-11-oic acid, a major and nonpsychoactive metabolite of Δ(9) -THC, but not another Δ(9)-THC metabolite 11-OH-Δ(9)-THC (psychoactive), was revealed to inhibit 15-LOX. Taken together, it is suggested that Δ(9) -THC can abrogate atherosclerosis via direct inhibition of 15-LOX, and that Δ(9)-THC-11-oic acid is shown to be an "active metabolite" of Δ(9) -THC in this case.

Mechanisms of LDL oxidation

BACKGROUNDS

Many lines of evidence suggest that oxidized low-density lipoprotein (LDL) is implicated in the pathogenesis of atherosclerotic vascular diseases. This review summarizes a diversity of mechanisms proposed for LDL oxidation serving for the so-called "LDL oxidation hypothesis of atherogenesis".

METHODS AND RESULTS

We investigated the literature and our research results related to mechanisms of LDL oxidation and its atherogenesis. LDL oxidation is catalyzed by transition metal ions and several free radicals, and LDL is also oxidized by some oxidizing enzymes. In this way, LDL can be converted to a form that is recognized specifically by and with high affinity to macrophage scavenger receptors, leading to foam cell formation, the defining characteristic of fatty streak lesions.

CONCLUSIONS

Several pathways are involved in the promotion of LDL oxidation in vitro and in vivo, but it would appear that the physiologically relevant mechanisms of LDL oxidation are still imperfectly understood. The underlying mechanisms of LDL oxidation must be further explored to reveal appropriate ways for the diagnosis and treatment of atherosclerosis and its relevant diseases.

L-4F differentially alters plasma levels of oxidized fatty acids resulting in more anti-inflammatory HDL in mice

To determine in vivo if L-4F differentially alters plasma levels of oxidized fatty acids resulting in more anti-inflammatory HDL. Injecting L-4F into apoE null mice resulted in a significant reduction in plasma levels of 15-HETE, 5-HETE, 13-HODE and 9-HODE. In contrast, plasma levels of 20-HETE were not reduced and plasma levels of 14,15-EET, which are derived from the cytochrome P450 pathway, were elevated after injection of L-4F. Injection of 13(S)-HPODE into wild-type C57BL/6J mice caused an increase in plasma levels of 13-HODE and 9-HODE and was accompanied by a significant loss in the anti-inflammatory properties of HDL. The response of atherosclerosis resistant C3H/HeJ mice to injection of 13(S)-HPODE was similar but much more blunted. Injection of L-4F at a site different from that at which the 13(S)-HPODE was injected resulted in significantly lower plasma levels of 13-HODE and 9-HODE and significantly less loss of HDL anti-inflammatory properties in both strains. i) L-4F differentially alters plasma levels of oxidized fatty acids in vivo. ii) The resistance of the C3H/HeJ strain to atherosclerosis may in part be mediated by a reduced reaction of this strain to these potent lipid oxidants.