Selective uptake and efflux of cholesteryl linoleate in LDL by macrophages expressing 12/15-lipoxygenase

Exercise Prescription Improve the Rehabilitation of a Child With Viral Encephalitis Sequelae: A Case Report

This study conducted a personalized exercise prescription intervention on a child with viral encephalitis sequelae (VES). The purpose was to observe the rehabilitation process from the aspects of brain activation, and the curative effects on balance function and gait. A further aim was to explore the possible nerve biomechanical mechanisms between the extent of brain activation and the improvement in balance function and gait. A 12-week exercise prescription was used as the treatment method, and functional near-infrared spectroscopy (fNIRS), balance function test system, plantar pressure distribution system, and 3D gait system were used to assess the effects of the rehabilitation process pre and post the intervention. Following the exercise prescription intervention: (1) fNIRS showed that brain activation in the S1-D1, S1-D2, S1-D3, S2-D1, S3-D2, S3-D3, S4-D3, S5-D5, S5-D6, S5-D7, S7-D6, S7-D7, S8-D7, and S8-D8 increased significantly (P < 0.05). (2) The balance test showed that the area of motion ellipse and movement length of the child with eyes open decreased significantly and area of motion ellipse, back and forth swing, left and right swing and movement length of the child with eyes closed all decreased significantly (P < 0.05). (3) The static plantar pressure distribution demonstrated that the pressure center of the left and right foot decreased significantly (P < 0.05) from 5.3° dislocation in a straight line in the sagittal plane to 1°; an increment of the pressure loading was found on the forefoot of both feet compared with what was recorded in the pre-test. (4) The testing results of the 3D gait system showed that she had a shortened time of unilateral support phase and prolonged swing phase on the affected leg (P < 0.05), compared to that of the non-affected leg. Furthermore, the dual support phase had also been prolonged (P < 0.05). Conclusion: 12 weeks' individualized exercise training can enhance the activation in the motor areas and improve balance function and gait in a child with VES.

Lipid Peroxidation in Atherosclerotic Cardiovascular Diseases

Significance: Atherosclerotic cardiovascular diseases (ACVDs) continue to be a primary cause of mortality worldwide in adults aged 35-70 years, occurring more often in countries with lower economic development, and they constitute an ever-growing global burden that has a considerable socioeconomic impact on society. The ACVDs encompass diverse pathologies such as coronary artery disease and heart failure (HF), among others. Recent Advances: It is known that oxidative stress plays a relevant role in ACVDs and some of its effects are mediated by lipid oxidation. In particular, lipid peroxidation (LPO) is a process under which oxidants such as reactive oxygen species attack unsaturated lipids, generating a wide array of oxidation products. These molecules can interact with circulating lipoproteins, to diffuse inside the cell and even to cross biological membranes, modifying target nucleophilic sites within biomolecules such as DNA, lipids, and proteins, and resulting in a plethora of biological effects. Critical Issues: This review summarizes the evidence of the effect of LPO in the development and progression of atherosclerosis-based diseases, HF, and other cardiovascular diseases, highlighting the role of protein adduct formation. Moreover, potential therapeutic strategies targeted at lipoxidation in ACVDs are also discussed. Future Directions: The identification of valid biomarkers for the detection of lipoxidation products and adducts may provide insights into the improvement of the cardiovascular risk stratification of patients and the development of therapeutic strategies against the oxidative effects that can then be applied within a clinical setting.

From Inert Storage to Biological Activity-In Search of Identity for Oxidized Cholesteryl Esters

Esterification of cholesterol is a universal mechanism to store and transport large quantities of cholesterol between organs and tissues and to avoid toxicity of the excess of cellular cholesterol. Intended for transport and storage and thus to be inert, cholesteryl esters (CEs) reside in hydrophobic cores of circulating lipoproteins and intracellular lipid droplets. However, the inert identity of CEs is dramatically changed if cholesterol is esterified to a polyunsaturated fatty acid and subjected to oxidative modification. Post-synthetic, or epilipidomic, oxidative modifications of CEs are mediated by specialized enzymes, chief among them are lipoxygenases, and by free radical oxidation. The complex repertoire of oxidized CE (OxCE) products exhibit various, context-dependent biological activities, surveyed in this review. Oxidized fatty acyl chains in OxCE can be hydrolyzed and re-esterified, thus seeding oxidized moieties into phospholipids (PLs), with OxPLs having different from OxCEs biological activities. Technological advances in mass spectrometry and the development of new anti-OxCE antibodies make it possible to validate the presence and quantify the levels of OxCEs in human atherosclerotic lesions and plasma. The article discusses the prospects of measuring OxCE levels in plasma as a novel biomarker assay to evaluate risk of developing cardiovascular disease and efficacy of treatment.

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.

CTRP5 promotes transcytosis and oxidative modification of low-density lipoprotein and the development of atherosclerosis

BACKGROUND AND AIMS

Increased transcytosis of low-density lipoprotein (LDL) across the endothelium and oxidation of LDL deposited within the subendothelial space are crucial early events in atherogenesis. C1q/TNF-related protein (CTRP) 5 is a novel secreted glycoprotein and its biological functions are largely undefined.

METHODS

Expression of CTRP5 was analyzed in sera and atherosclerotic plaques of patients with coronary artery disease (CAD). The role of CTRP5 in atherogenesis was investigated in vitro and in vivo.

RESULTS

We found CTRP5 serum levels were higher in patients with than without CAD (247.26 ± 61.71 vs. 167.81 ± 68.08 ng/mL, p < 0.001), and were positively correlated with the number of diseased vessels (Spearman's r = 0.611, p < 0.001). Increased expression of CTRP5 was detected in human coronary endarterectomy specimens as compared to non-atherosclerotic arteries. Immunofluorescence further showed that CTRP5 was predominantly localized in the endothelium, infiltrated macrophages and smooth muscle cells in the neointima. In vivo and in vitro experiments demonstrated that CTRP5 promoted transcytosis of LDL across endothelial monolayers, as well as the oxidative modification of LDL in endothelial cells. Mechanistically, we found that CTRP5 up-regulated 12/15-lipoxygenase (LOX), a key enzyme in mediating LDL trafficking and oxidation, through STAT6 signaling. Genetic or pharmacological inhibition of 12/15-LOX dramatically attenuated the deposition of oxidized LDL in the subendothelial space and the development of atherosclerosis.

CONCLUSIONS

These data indicate that CTRP5 is a novel pro-atherogenic cytokine and promotes transcytosis and oxidation of LDL in endothelial cells via up-regulation of 12/15-LOX.

Adipocyte lipopolysaccharide binding protein (LBP) is linked to a specific lipidomic signature

OBJECTIVE

Lipopolysaccharide binding protein (LBP) is part of a family of structurally and functionally related lipid transfer proteins. This study aimed to investigate the associations of LBP with the lipid composition of human adipose tissue.

METHODS

Lipidomic analysis was performed in whole adipose tissue. To validate the associations found, LBP was knocked down (KD) in 3T3-L1 adipocytes, and lipidomic profile was evaluated by nontargeted lipidomics.

RESULTS

LBP gene expression was negatively associated with phosphatidylcholine, phosphatidylserine, and sphingomyelin relative abundance in vivo. LBP expression was also decreased in those samples with the highest docosahexanoic content, implicated in the resolution of inflammation. The KD of LBP (by ∼70%) led to sharp changes in the lipidome of adipocytes. Of note, specific plasmalogen species PE(O-16:0/22:5), PE(38:2), odd chain glycerolipids, and cholesteryl linoleate were upregulated by LBP KD. In contrast, GM3 gangliosides, several ceramides, a triacylglycerol potentially containing arachidonate, and cholesteryl palmitate were downregulated by LBP KD.

CONCLUSIONS

LBP seems to play a role in the regulation of lipid composition of adipose tissue linked to resilience to inflammation.

High-capacity selective uptake of cholesteryl ester from native LDL during macrophage foam cell formation

Macrophage foam cells are a defining pathologic feature of atherosclerotic lesions. Recent studies have demonstrated that at high concentrations associated with hypercholesterolemia, native LDL induces macrophage lipid accumulation. LDL particles are taken up by macrophages as part of bulk fluid pinocytosis. However, the uptake and metabolism of cholesterol from native LDL during foam cell formation has not been clearly defined. Previous reports have suggested that selective cholesteryl ester (CE) uptake might contribute to cholesterol uptake from LDL independently of particle endocytosis. In this study we demonstrate that the majority of macrophage LDL-derived cholesterol is acquired by selective CE uptake in excess of LDL pinocytosis and degradation. Macrophage selective CE uptake does not saturate at high LDL concentrations and is not down-regulated during cholesterol accumulation. In contrast to CE uptake, macrophages exhibit little selective uptake of free cholesterol (FC) from LDL. Following selective uptake from LDL, CE is rapidly hydrolyzed by a novel chloroquine-sensitive pathway. FC released from LDL-derived CE hydrolysis is largely effluxed from cells but also is subject to ACAT-mediated reesterification. These results indicate that selective CE uptake plays a major role in macrophage metabolism of LDL.

Fluoride in low concentration modifies expression and activity of 15 lipoxygenase in human PBMC differentiated monocyte/macrophage

Epidemiological and experimental evidences demonstrate positive correlation between environmental and occupational fluoride exposure and risk to various cardio-respiratory disorders. That fore we decided to examine the effect of fluorides on activity and expression of 15LOX enzyme which is implicated in biosynthesis of inflammatory mediators. Expression of 15LOX-1 and -2 enzymes mRNA and protein was analyzed using RT PCT and immunoblotting methods respectively whereas HPLC method was used to measure the levels of 15 lipoxygenases end products. Additionally AA and LA concentration in cells was measured using GC method. We observed that fluoride in small concentration may significantly decrease activity of 15LOX-1 and -2 in human PBMC macrophages and then concentration of its end products: 15-HETE, 12-HETE and 9+13-HODE, what may cause development of inflammation through the cholesterol arrest into the macrophages and its differentiation to foam cell. Noted by our team overexpression of the 15LOX-1 enzyme in macrophages after addition of lowest fluoride concentrations (1 and 3 μM) may be aimed at fighting inflammation development and excessive intracellular lipid accumulation. But highest fluoride concentrations (6 and 10 μM) added to cell culture slowly declined expression of this enzyme probably because of developing inflammation. Additional 15LOX-2 expression in macrophages after fluoride addition was low in 1 and 3 μM concentrations, but increased significantly after 10 μM fluoride addition what may suggest developing acute inflammation, because 15LOX-2 is associated to increased local hypoxia. This study indicated that even in small concentrations fluorides changes the amounts and activity of 15 LOX-1 and -2 enzymes taking part in the development of inflammatory process.

Oxidation-specific epitopes are danger-associated molecular patterns recognized by pattern recognition receptors of innate immunity

Oxidation reactions are vital parts of metabolism and signal transduction. However, they also produce reactive oxygen species, which damage lipids, proteins and DNA, generating "oxidation-specific" epitopes. In this review, we discuss the hypothesis that such common oxidation-specific epitopes are a major target of innate immunity, recognized by a variety of "pattern recognition receptors" (PRRs). By analogy with microbial "pathogen-associated molecular patterns" (PAMPs), we postulate that host-derived, oxidation-specific epitopes can be considered to represent "danger (or damage)-associated molecular patterns" (DAMPs). We also argue that oxidation-specific epitopes present on apoptotic cells and their cellular debris provided the primary evolutionary pressure for the selection of such PRRs. Furthermore, because many PAMPs on microbes share molecular identity and/or mimicry with oxidation-specific epitopes, such PAMPs provide a strong secondary selecting pressure for the same set of oxidation-specific PRRs as well. Because lipid peroxidation is ubiquitous and a major component of the inflammatory state associated with atherosclerosis, the understanding that oxidation-specific epitopes are DAMPs, and thus the target of multiple arcs of innate immunity, provides novel insights into the pathogenesis of atherosclerosis. As examples, we show that both cellular and soluble PRRs, such as CD36, toll-like receptor-4, natural antibodies, and C-reactive protein recognize common oxidation-specific DAMPs, such as oxidized phospholipids and oxidized cholesteryl esters, and mediate a variety of immune responses, from expression of proinflammatory genes to excessive intracellular lipoprotein accumulation to atheroprotective humoral immunity. These insights may lead to improved understanding of inflammation and atherogenesis and suggest new approaches to diagnosis and therapy.

Lipid signaling in the atherogenesis context

Normally macrophages localized in the arterial vessel wall perform the "reverse transfer" of cholesterol, which includes endocytosis of low density lipoproteins (LDL), cholesterol transfer to newly formed high density lipoprotein particles, and their following elimination by the liver. The homeostatic function of macrophages for cholesterol involves a system of lipid sensors. Oxysterol sensors LXRs, oxysterol and cholesterol sensors INSIG and SCAP acting through controlled transcription factors SREBP, as well as sensors for oxidized fatty acids and their derivatives, PPAR, are the best studied. Activation of LXR and PPAR is also accompanied by inhibition of macrophage functions related to inflammation. Accumulation of oxidized and otherwise modified LDL in the subendothelial space induced by endothelium injury, infection, or other pathogenic factors instead of stimulation of the homeostatic functions of macrophages leads to their weakening with a concurrent increase in the inflammatory potential of these cells. These shifts seem to drive the transformation of macrophages into foam cells, which form the core of sclerotic plaques. The intervention of another lipid sensor, TLR4, can trigger such a radical change in the functional activity of macrophages. The interaction of modified LDL with this signaling receptor results in inhibition of the homeostatic oxysterol signaling, induction of additional LDL transporters, and activation of the phagocytic function of macrophages. The re-establishment of cholesterol homeostasis under these circumstances can be achieved by administration of LXR and PPARgamma agonists. Therefore, it is urgent to design ligands with reduced side effects.

Functional and pathological roles of the 12- and 15-lipoxygenases

The 12/15-lipoxygenase enzymes react with fatty acids producing active lipid metabolites that are involved in a number of significant disease states. The latter include type 1 and type 2 diabetes (and associated complications), cardiovascular disease, hypertension, renal disease, and the neurological conditions Alzheimer's disease and Parkinson's disease. A number of elegant studies over the last thirty years have contributed to unraveling the role that lipoxygenases play in chronic inflammation. The development of animal models with targeted gene deletions has led to a better understanding of the role that lipoxygenases play in various conditions. Selective inhibitors of the different lipoxygenase isoforms are an active area of investigation, and will be both an important research tool and a promising therapeutic target for treating a wide spectrum of human diseases.

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.

Toll-like receptor-4 and lipoprotein accumulation in macrophages

Excessive lipid accumulation in macrophages, also known as foam cell formation, is a key process during the development of atherosclerosis, leading to vascular inflammation and plaque growth. Recent studies have identified a new mechanism of macrophage lipid accumulation in which minimally oxidized low-density lipoprotein (mmLDL) and its active components, polyoxygenated cholesteryl ester hydroperoxides, are involved in endogenous activation of toll-like receptor-4 (TLR4), leading to recruitment of spleen tyrosine kinase (Syk), robust cytoskeletal rearrangements and macropinocytosis. In hyperlipidemic environments, mmLDL-induced, TLR4- and Syk-dependent macropinocytosis leads to substantial lipid accumulation in macrophages and monocytes, which may constitute an important mechanism of foam cell formation in atherosclerosis. A novel hypercholesterolemic zebrafish model of early stages of atherosclerosis was used to demonstrate that the TLR4 deficiency significantly reduces the in vivo rate of macrophage lipid accumulation in vascular lesions.

Lipoprotein modification and macrophage uptake: role of pathologic cholesterol transport in atherogenesis

Low-density lipoprotein (LDL) is a major extracellular carrier of cholesterol and, as such, plays important physiologic roles in cellular function and regulation of metabolic pathways. However, under pathologic conditions of hyperlipidemia, oxidative stress and/or genetic disorders, specific components of LDL become oxidized or otherwise modified, and the transport of cholesterol by modified LDL is diverted from its physiologic targets toward excessive cholesterol accumulation in macrophages and the formation of macrophage "foam" cells in the vascular wall. This pathologic deposition of modified lipoproteins and the attendant pro-inflammatory reactions in the artery wall lead to the development of atherosclerotic lesions. Continued accumulation of immunogenic modified lipoproteins and a pro-inflammatory milieu result in the progression of atherosclerotic lesions, which may obstruct the arterial lumen and/or eventually rupture and thrombose, causing myocardial infarction or stroke. In this review, we survey mechanisms of LDL modification and macrophage lipoprotein uptake, including results of recent in vivo experiments, and discuss unresolved problems and controversial issues in this growing field. Future directions in studying foam cell formation may include introducing novel animal models, such as hypercholesterolemic zebrafish, enabling dynamic in vivo observation of macrophage lipid uptake.

Cholesteryl ester hydroperoxides are biologically active components of minimally oxidized low density lipoprotein

Oxidation of low density lipoprotein (LDL) occurs in vivo and significantly contributes to the development of atherosclerosis. An important mechanism of LDL oxidation in vivo is its modification with 12/15-lipoxygenase (LO). We have developed a model of minimally oxidized LDL (mmLDL) in which native LDL is modified by cells expressing 12/15LO. This mmLDL activates macrophages inducing membrane ruffling and cell spreading, activation of ERK1/2 and Akt signaling, and secretion of proinflammatory cytokines. In this study, we found that many of the biological activities of mmLDL were associated with cholesteryl ester (CE) hydroperoxides and were diminished by ebselen, a reducing agent. Liquid chromatography coupled with mass spectroscopy demonstrated the presence of many mono- and polyoxygenated CE species in mmLDL but not in native LDL. Nonpolar lipid extracts of mmLDL activated macrophages, although to a lesser degree than intact mmLDL. The macrophage responses were also induced by LDL directly modified with immobilized 12/15LO, and the nonpolar lipids extracted from 12/15LO-modified LDL contained a similar set of oxidized CE. Cholesteryl arachidonate modified with 12/15LO also activated macrophages and contained a similar collection of oxidized CE molecules. Remarkably, many of these oxidized CE were found in the extracts of atherosclerotic lesions isolated from hyperlipidemic apoE(-/-) mice. These results suggest that CE hydroperoxides constitute a class of biologically active components of mmLDL that may be relevant to proinflammatory activation of macrophages in atherosclerotic lesions.

The two faces of the 15-lipoxygenase in atherosclerosis

Chronic inflammation plays a major role in atherogenesis and understanding the role of inflammation and its resolution will offer novel approaches to interfere with atherogenesis. The 15(S)-lipoxygenase (15-LOX) plays a janus-role in inflammation with pro-inflammatory and anti-inflammatory effects in cell cultures and primary cells and even opposite effects on atherosclerosis in two different animal species. There is evidence for a pro-atherosclerotic effect of 15-LOX including the direct contribution to LDL oxidation and to the recruitment of monocytes to the vessel wall, its role in angiotensin II mediated mechanisms and in vascular smooth muscle cell proliferation. In contrast to the pro-atherosclerotic effects of 15-LOX, there is also a broad line of evidence that 15-LOX metabolites of arachidonic and linoleic acid have anti-inflammatory effects. The 15-LOX arachidonic acid metabolite 15-HETE inhibits superoxide production and polymorphonuclear neutrophil (PMN) migration across cytokine-activated endothelium and can be further metabolized to the anti-inflammatory lipoxins. These promote vasorelaxation in the aorta and counteract the action of most other pro-inflammatory factors like leukotrienes and prostanoids. Anti-atherogenic properties are also reported for the linoleic acid oxidation product 13-HODE through inhibition of adhesion of several blood cells to the endothelium. Furthermore, there is evidence that 15-LOX is involved in the metabolism of the long-chain omega-3 fatty acid docosahexaenoic acid (DHA) leading to a family of anti-inflammatory resolvins and protectins. From these cell culture and animal studies the role of the 15-LOX in human atherosclerosis cannot be predicted. However, recent genetic studies characterized the 15-LOX haplotypes in Caucasians and discovered a functional polymorphism in the human 15-LOX promoter. This will now allow large studies to investigate an association of 15-LOX with coronary artery disease and to answer the question whether 15-LOX is pro- or anti-atherogenic in humans.

Arachidonate 12-lipoxygenases with reference to their selective inhibitors

Lipoxygenase is a dioxygenase recognizing a 1-cis,4-cis-pentadiene of polyunsaturated fatty acids. The enzyme oxygenates various carbon atoms of arachidonic acid as a substrate and produces 5-, 8-, 12- or 15-hydroperoxyeicosatetraenoic acid with a conjugated diene chromophore. The enzyme is referred to as 5-, 8-, 12- or 15-lipoxygenase, respectively. Earlier we found two isoforms of 12-lipoxygenase, leukocyte- and platelet-type enzymes, which were distinguished by substrate specificity, catalytic activity, primary structure, gene intron size, and antigenicity. Recently, the epidermis-type enzyme was found as the third isoform. Attempts have been made to find isozyme-specific inhibitors of 12-lipoxygenase, and earlier we found hinokitiol, a tropolone, as a potent inhibitor selective for the platelet-type 12-lipoxygenase. More recently, we tested various catechins of tea leaves and found that (-)-gallocatechin gallate was a potent and selective inhibitor of human platelet 12-lipoxygenase with an IC50 of 0.14 microM. The compound was much less active with 12-lipoxygenase of leukocyte-type, 15-, 8-, and 5-lipoxygenases, and cyclooxygenases-1 and -2.