4-hydroxynonenal contributes to macrophage foam cell formation through increased expression of class A scavenger receptor at the level of translation

Interactions between macrophage membrane and lipid mediators during cardiovascular diseases with the implications of scavenger receptors

The onset and progression of cardiovascular diseases with the major underlying cause being atherosclerosis, occur during chronic inflammatory persistence in the vascular system, especially within the arterial wall. Such prolonged maladaptive inflammation is driven by macrophages and their key mediators are generally attributed to a disparity in lipid metabolism. Macrophages are the primary cells of innate immunity, endowed with expansive membrane domains involved in immune responses with their signalling systems. During atherosclerosis, the membrane domains and receptors control various active organisations of macrophages. Their scavenger/endocytic receptors regulate the trafficking of intracellular and extracellular cargo. Corresponding influence on lipid metabolism is mediated by their dynamic interaction with scavenger membrane receptors and their integrated mechanisms such as pinocytosis, phagocytosis, cholesterol export/import, etc. This interaction not only results in the functional differentiation of macrophages but also modifies their structural configurations. Here, we reviewed the association of macrophage membrane biomechanics and their scavenger receptor families with lipid metabolites during the event of atherogenesis. In addition, the membrane structure of macrophages and the signalling pathways involved in endocytosis integrated with lipid metabolism are detailed. This article establishes future insights into the scavenger receptors as potential targets for cardiovascular disease prevention and treatment.

Geniposide against atherosclerosis by inhibiting the formation of foam cell and lowering reverse lipid transport via p38/MAPK signaling pathways

Geniposide, the main medicinal ingredient of Gardenia jasminoides Ellis, is known to be a resistant agent to atherosclerosis. Some reports its mechanism against atherosclerosis remains completely unclear. Herein, we have investigated the protective effect of geniposide against atherosclerosis as well as clarified the mechanisms related with inhibiting the formation of foam cells and lowering reverse lipid transport via p38/MAPK signaling pathways. Macrophage Raw264.7 was induced by lysophosphatidic acid (LPA) to form foam cell as a cell model. ApoE^-/- mice were fed with a high-fat diet for 16 weeks to cause atherosclerosis in carotid artery. After treatment with geniposide, CCK-8, oil red O stain, qRT-PCR and western blot were carried out to explore the effect of geniposide. Morphological changes, histological analyses were used to evaluate atherosclerosis in ApoE^-/- mice. Geniposide significantly reduced serum total cholesterol (TC), triglyceride (TG) and LDL cholesterol levels in ApoE^-/- mice compared with vehicle control. Meanwhile, geniposide dose dependently inhibited the development of atherosclerosis in ApoE^-/- mice. Furthermore, geniposide observably inhibited the formation of foam cells induced by LPA, down-regulated the mRNA and protein levels of SR-A and up-regulated the mRNA and protein levels of ABCA1 or SR-B1 in vitro via inhibition of the p38MAPK and AKT signaling pathways. Our study shows that geniposide protected against atherosclerosis and inhibited the formation of foam cells by regulating the equilibrium on expression of diverse lipid transporters in cytomembrane which related with p38MAPK and AKT signaling pathways. Geniposide is a potential therapeutic drug for atherosclerosis.

Blocking Wnt5a signaling decreases CD36 expression and foam cell formation in atherosclerosis

BACKGROUND AND AIMS

Wnt5a is a highly studied member of the Wnt family and recently has been implicated in the pathogenesis of atherosclerosis, but its precise role is unknown. Foam cell development is a critical process to atherosclerotic plaque formation. In the present study, we investigated the role of noncanonical Wnt5a signaling in the development of foam cells.

METHODS

Human carotid atherosclerotic tissue and THP-1-derived macrophages were used to investigate the contribution of Wnt5a signaling in the formation of foam cells. Immunohistochemistry was used to evaluate protein expression of scavenger receptors and noncanonical Wnt5a receptors [frizzled 5 (Fz5) and receptor tyrosine kinase-like orphan receptor 2 (Ror2)] in human atherosclerotic macrophages/foam cells. Changes in protein expression in response to Wnt5a stimulation/inhibition were determined by Western blot, and lipid accumulation was evaluated by fluorescent lipid droplet staining.

RESULTS

Wnt5a (P<.05), Fz5 (P<.01), and Ror2 (P<.01) were significantly expressed in advanced atherosclerotic lesions compared to less advanced lesions (N=10). Wnt5a, Fz5, and Ror2 were expressed in macrophages/foam cells within the plaque. In vitro studies revealed that Wnt5a significantly increased the expression of the lipid uptake receptor CD36 (P<.05) but not the lipid efflux receptor ATP-binding cassette transporter (P>.05). rWnt5a also significantly increased lipid accumulation in THP-1 macrophages (P<.05). Furthermore, inhibition of Wnt5a signaling with Box5 prevented lipid accumulation (P<.01) and prevented CD36 up-regulation (P<.01).

CONCLUSIONS

These results suggest a direct role for Wnt5a signaling in the pathogenesis of atherosclerosis, specifically the accumulation of lipid in macrophages and the formation of foam cells.

Proatherogenic effects of 4-hydroxynonenal

4-hydroxy-2-nonenal (HNE) is a α,β-unsaturated hydroxyalkenal generated by peroxidation of n-6 polyunsaturated fatty acid. This reactive carbonyl compound exhibits a huge number of biological properties that result mainly from the formation of HNE-adducts on free amino groups and thiol groups in proteins. In the vascular system, HNE adduct accumulation progressively leads to cellular dysfunction and tissue damages that are involved in the progression of atherosclerosis and related diseases. HNE contributes to the atherogenicity of oxidized LDL, by forming HNE-apoB adducts that deviate the LDL metabolism to the scavenger receptor pathway of macrophagic cells, and lead to the formation of foam cells. HNE activates transcription factors (Nrf2, NF-kappaB) that (dys)regulate various cellular responses ranging from hormetic and survival signaling at very low concentrations, to inflammatory and apoptotic effects at higher concentrations. Among a variety of cellular targets, HNE can modify signaling proteins involved in atherosclerotic plaque remodeling, particularly growth factor receptors (PDGFR, EGFR), cell cycle proteins, mitochondrial and endoplasmic reticulum components or extracellular matrix proteins, which progressively alters smooth muscle cell proliferation, angiogenesis and induces apoptosis. HNE adducts accumulate in the lipidic necrotic core of advanced atherosclerotic lesions, and may locally contribute to macrophage and smooth muscle cell apoptosis, which may induce plaque destabilization and rupture, thereby increasing the risk of athero-thrombotic events.

Oxysterols and 4-hydroxy-2-nonenal contribute to atherosclerotic plaque destabilization

A growing bulk of evidence suggests that cholesterol oxidation products, known as oxysterols, and 4-hydroxy-2-nonenal (HNE), the major proatherogenic components of oxidized low density lipoproteins (oxLDLs), significantly contribute to atherosclerotic plaque progression and destabilization, with eventual plaque rupture. These oxidized lipids are involved in various key steps of this complex process, mainly thanks to their ability to induce inflammation, oxidative stress, and apoptosis. This review summarizes the current knowledge of the effects induced by these compounds on vascular cells, after their accumulation in the arterial wall and in the atherosclerotic plaque.

Apoptotic cell death in cultured cardiomyocytes following exposure to low concentrations of 4-hydroxy-2-nonenal

Lipid peroxidation (LP), induced by oxidative stress, is associated with degenerative processes. 4-Hydroxy-2-nonenal (HNE), a highly reactive diffusible product of LP, is considered by-product and mediator of oxidative stress. Its level increases under pathological conditions such as cardiovascular diseases. In this study, we partially characterized the mechanisms of HNE-mediated cytotoxicity in cardiomyocytes. After establishing that pathophysiological doses of HNE trigger cell death dependent on the incubation time and dose of HNE (LD50 = 4.4 μM), we tackled the mechanisms that underlie the cell death induced by HNE. Our results indicate that HNE rapidly increases intracellular Ca(2+); it also increases the rate of reactive oxygen species generation and causes a loss of mitochondrial membrane potential (ΔΨm) as well as a decrease in the ATP and GSH levels. Such alterations result in the activation of caspase-3 and DNA breakdown, both characteristic features of apoptotic cell death, as well as disruption of the cytoskeleton. Moreover, the nucleophilic compounds N-acetyl-cysteine and β-mercapto-propionyl-glycine, and the synthetic antioxidant Trolox exert a potent antioxidant action against HNE damage; this suggests its use as effective compounds in order to reduce the damage occurred as consequence of cardiovascular disorders in which oxidative stress and hence LP take place.

Chemical Atherogenesis: Role of Endogenous and Exogenous Poisons in Disease Development

Chemical atherogenesis is an emerging field that describes how environmental pollutants and endogenous toxins perturb critical pathways that regulate lipid metabolism and inflammation, thus injuring cells found within the vessel wall. Despite growing awareness of the role of environmental pollutants in the development of cardiovascular disease, the field of chemical atherogenesis can broadly include both exogenous and endogenous poisons and the study of molecular, biochemical, and cellular pathways that become dysregulated during atherosclerosis. This integrated approach is logical because exogenous and endogenous toxins often share the same mechanism of toxicity. Chemical atherogenesis is a truly integrative discipline because it incorporates concepts from several different fields, including biochemistry, chemical biology, pharmacology, and toxicology. This review will provide an overview of this emerging research area, focusing on cellular and animal models of disease.

Signaling properties of 4-hydroxyalkenals formed by lipid peroxidation in diabetes

Peroxidation of polyunsaturated fatty acids is intensified in cells subjected to oxidative stress and results in the generation of various bioactive compounds, of which 4-hydroxyalkenals are prominent. During the progression of type 2 diabetes mellitus, the ensuing hyperglycemia promotes the generation of reactive oxygen species (ROS) that contribute to the development of diabetic complications. It has been suggested that ROS-induced lipid peroxidation and the resulting 4-hydroxyalkenals markedly contribute to the development and progression of these pathologies. Recent findings, however, also suggest that noncytotoxic levels of 4-hydroxyalkenals play important signaling functions in the early phase of diabetes and act as hormetic factors to induce adaptive and protective responses in cells, enabling them to function in the hyperglycemic milieu. Our studies and others' have proposed such regulatory functions for 4-hydroxynonenal and 4-hydroxydodecadienal in insulin secreting β-cells and vascular endothelial cells, respectively. This review presents and discusses the mechanisms regulating the generation of 4-hydroxyalkenals under high glucose conditions and the molecular interactions underlying the reciprocal transition from hormetic to cytotoxic agents.

4-HNE increases intracellular ADMA levels in cultured HUVECs: evidence for miR-21-dependent mechanisms

Objective

To investigate whether 4-hydroxynonenal (4-HNE) regulates asymmetric dimethylarginine (ADMA) metabolism through pathway independent of direct adduct formation with ADMA metabolizing enzyme and the involvement of microRNA (miRNA) miR-21 in human umbilical venous endothelial cells (HUVECs).

Methods

Cultured HUVECs were treated with 4-HNE (at concentrations of 1, 5, and 10 µM, respectively) or 1‰ DMSO (vehicle control) for 24 h. MiR-21 inhibitor (final concentration of 100 nM) was transfected at 1 h before 4-HNE treatment. HUVECs were also transfected with miR-21 (at concentrations of 50 nM and 100 nM) and cultured for 12, 24, and 48 h, respectively. DDAH mRNA and miR-21 expression in the HUVECs were determined by semi-quantitative real time PCR. DDAH1 and DDAH2 protein expression were analyzed by Western blot. ADMA in the cell medium and cell lysates were analyzed by ELISA. ADMA metabolizing activity of the cell lysates was also determined.

Results

MiR-21 decreased DDAH1 and DDAH2 expression and ADMA metabolic activity significantly, while increased intracellular ADMA accumulation significantly in HUVECs. 10 µM 4-HNE treatment for 24 h increased the expression of miR-21 and intracellular ADMA concentration, decreased the expression of DDAH1/2 mRNA and protein, decreased ADMA metabolizing activity of the cell lysates significantly. MiR-21 inhibitor reversed the inhibitory effects of 4-HNE on DDAH1 expression completely, and partially reversed the changes in ADMA metabolizing activity and intracellular ADMA accumulation challenged by 10 µM 4-HNE.

Conclusion

4-HNE down-regulates DDAH1 expression and increases intracellular ADMA accumulation in HUVECs through a miR-21-dependent mechanism.

Metabolic impact of 4-hydroxynonenal on macrophage-like RAW 264.7 function and activation

Metabolic profiling of macrophage metabolic response upon exposure to 4-hydroxynonenal (HNE) demonstrates that HNE does not simply inactivate superoxide-generating enzymes but also could be responsible for the impairment of downfield signaling pathways. Multianalyte microphysiometry (MAMP) was employed to simultaneously measure perturbations in extracellular acidification, lactate production, and oxygen consumption for the examination of aerobic and anaerobic pathways. Combining the activation of oxidative burst with phorbol myristate acetate (PMA) and the immunosuppression with HNE, the complex nature of HNE toxicity was determined to be concentration- and time-dependent. Further analysis was utilized to assess the temporal effect of HNE on reactive oxygen species (ROS) production and on protein kinase C (PKC). Increased levels of HNE with decreasing PKC activity suggest that PKC is a target for HNE adductation prior to oxidative burst. Additionally, localization of PKC to the cell membrane was prevented with the introduction of HNE, demonstrating a consequence of HNE adductation on NADPH activation. The impairment of ROS by HNE suggests that HNE has a greater role in foam cell formation and tissue damage than is already known. Although work has been performed to understand the effect of HNE's regulation of specific signaling pathways, details regarding its involvement in cellular metabolism as a whole are generally unknown. This study examines the impact of HNE on macrophage oxidative burst and identifies PKC as a key protein for HNE suppression and eventual metabolic response.

Genetic and pharmacological manipulation of urotensin II ameliorate the metabolic and atherosclerosis sequalae in mice

OBJECTIVE

Urotensin II (UII) is a potent vasoactive peptide that binds to the urotensin receptor-coupled receptor-14 (known as UT) and exerts a wide range of actions in humans and experimental animals. We tested the hypothesis that UII gene deletion or UT blockade ameliorate experimental atherosclerosis.

METHODS AND RESULTS

We observed a significant reduction in weight gain, visceral fat, blood pressure, circulating plasma lipids, and proatherogenic cytokines and improvement of glucose tolerance in UII knockout mice compared with wild type (P<0.05). Deletion of UII after an apolipoprotein E knockout resulted in a significant reduction in serum cytokines, adipokines, and aortic atherosclerosis compared with apolipoprotein E knockout mice. Similarly, treatment of apolipoprotein E knockout mice fed on high-fat diet with the UT antagonist SB657510A reduced weight gain, visceral fat, and hyperlipidemia and improved glucose tolerance (P<0.05) and attenuated the initiation and progression of atherosclerosis. The UT antagonist also decreased aortic extracellular signal-regulated kinase 1/2 phosphorylation and oxidant formation and serum level of cytokines (P<0.05).

CONCLUSIONS

These findings demonstrate for the first time the role of UII gene deletion in atherosclerosis and suggest that the use of pharmaceutical agents aimed at blocking the UII pathway may provide a novel approach in the treatment of atherosclerosis and its associated precursors such as obesity, hyperlipidemia, diabetes mellitus, and hypertension.

Inflammation-related gene expression by lipid oxidation-derived products in the progression of atherosclerosis

Vascular areas of atherosclerotic development persist in a state of inflammation, and any further inflammatory stimulus in the subintimal area elicits a proatherogenic response; this alters the behavior of the artery wall cells and recruits further inflammatory cells. In association with the inflammatory response, oxidative events are also involved in the development of atherosclerotic plaques. It is now unanimously recognized that lipid oxidation-derived products are key players in the initiation and progression of atherosclerotic lesions. Oxidized lipids, derived from oxidatively modified low-density lipoproteins (LDLs), which accumulate in the intima, strongly modulate inflammation-related gene expression, through involvement of various signaling pathways. In addition, considerable evidence supports a proatherogenic role of a large group of potent bioactive lipids called eicosanoids, which derive from oxidation of arachidonic acid, a component of membrane phospholipids. Of note, LDL lipid oxidation products might regulate eicosanoid production, modulating the enzymatic degradation of arachidonic acid by cyclooxygenases and lipoxygenases; these enzymes might also directly contribute to LDL oxidation. This review provides a comprehensive overview of current knowledge on signal transduction pathways and inflammatory gene expression, modulated by lipid oxidation-derived products, in the progression of atherosclerosis.

Effects of Fufang Zhenzhu Tiaozhi Prescription (), A Chinese herbal preparation, on atherosclerosis in ApoE-/- mice and related mechanisms

OBJECTIVE: The present study was designed to observe the effects and the possible mechanisms of Fufang Zhenzhu Tiaozhi Prescription (, FZT), a Chinese herbal preparation, on atherosclerosis in apolipoprotein E deficient (ApoE-/-) mice. METHODS: ApoE-/- mice were randomized to groups orally administrated without or with FZT (4.5 and 9 g crude drug/kg body weight, respectively). Atherosclerotic plaques, lipids profifiles in serum, aortic cholesterol content, serum indices of oxidative stress were measured, and mRNA expressions of scavenger receptors CD36 and scavenger receptor-A (SR-A) in aorta were analyzed. RESULTS: FZT dose-dependently suppressed the atherosclerotic plaques and reduced the cholesterol contents in aorta (P<0.05, P<0.01). In addition, FZT decreased the levels of total cholesterol and triglyceride in serum (P<0.05, P<0.01), inhibited the production of oxidized low density lipoprotein and malonaldehyde, and increased the superoxide dismutase activity in serum (P<0.05 or P<0.01). Furthermore, FZT down-regulated the mRNA expressions of CD36 and SR-A in the aorta (P<0.05, P<0.01). CONCLUSIONS: FZT reduced the atherosclerotic formation in ApoE-/- mice. The mechanisms might be related to the decrease of serum lipid level, the improvement of oxidative stress and the down-regulated expressions of scavenger receptors CD36 and SR-A, consequently reducing the foam cell formation, the hallmark of early atherosclerosis.

Oxidative stress is associated with migraine and migraine-related metabolic risk in females

BACKGROUND AND PURPOSE

Oxidative stress is discussed to be implicated in the pathophysiology of migraine. However, data are in part controversial and the possible underlying mechanisms remain elusive to date. The aim of this study was to investigate the oxidative stress status of female patients with migraine and its implications on migraine-related metabolic alterations.

METHODS

Oxidative stress markers malondialdehyde (MDA), 4-hydroxy-2-nonenal (HNE), carbonylated proteins, parameters of associated nitric oxide stress, inflammation, lipid- and glucose-metabolism were determined in the interictal phase in female patients with migraine and controls.

RESULTS

We found significantly increased HNE levels in female migraineurs compared with controls. Logistic regression analyses of HNE revealed an odds ratio for migraine of 4.55. HNE showed significant correlations with the nitric oxide pathway, the insulin- and the lipid-metabolism.

CONCLUSIONS

We show here that increased oxidative stress is associated with migraine and contributes to migraine-related metabolic risk like nitrosative stress, an atherogenic lipid profile and hyperinsulinemia. Our data suggest that oxidative stress may represent a key event in the pathophysiology of migraine and a suitable therapeutic target.

Pathological aspects of lipid peroxidation

Lipid peroxidation (LPO) product accumulation in human tissues is a major cause of tissular and cellular dysfunction that plays a major role in ageing and most age-related and oxidative stress-related diseases. The current evidence for the implication of LPO in pathological processes is discussed in this review. New data and literature review are provided evaluating the role of LPO in the pathophysiology of ageing and classically oxidative stress-linked diseases, such as neurodegenerative diseases, diabetes and atherosclerosis (the main cause of cardiovascular complications). Striking evidences implicating LPO in foetal vascular dysfunction occurring in pre-eclampsia, in renal and liver diseases, as well as their role as cause and consequence to cancer development are addressed.

Signaling and cytotoxic functions of 4-hydroxyalkenals

The peroxidation of n-3 and n-6 polyunsaturated fatty acids (PUFAs) and of their hydroperoxy metabolites is a complex process. It is initiated by free oxygen radical-induced abstraction of a hydrogen atom from the lipid molecule followed by a series of nonenzymatic reactions that ultimately generate the reactive aldehyde species 4-hydroxyalkenals. The molecule 4-hydroxy-2E-hexenal (4-HHE) is generated by peroxidation of n-3 PUFAs, such as linolenic acid, eicosapentaenoic acid, and docosahexaenoic acid. The aldehyde product 4-hydroxy-2E-nonenal (4-HNE) is the peroxidation product of n-6 PUFAs, such as arachidonic and linoleic acids and their 15-lipoxygenase metabolites, namely 15-hydroperoxyeicosatetraenoic acid (15-HpETE) and 13-hydroperoxyoctadecadienoic acid (13-HpODE). Another reactive peroxidation product is 4-hydroxy-2E,6Z-dodecadienal (4-HDDE), which is derived from 12-hydroperoxyeicosatetraenoic acid (12-HpETE), the 12-lipoxygenase metabolite of arachidonic acid. Hydroxyalkenals, notably 4-HNE, have been implicated in various pathophysiological interactions due to their chemical reactivity and the formation of covalent adducts with macromolecules. The progressive accumulation of these adducts alters normal cell functions that can lead to cell death. The lipophilicity of these aldehydes positively correlates to their chemical reactivity. Nonetheless, at low and noncytotoxic concentrations, these molecules may function as signaling molecules in cells. This has been shown mostly for 4-HNE and to some extent for 4-HHE. The capacity of 4-HDDE to generate such "mixed signals" in cells has received less attention. This review addresses the origin and cellular functions of 4-hydroxyalkernals.

HNE-induced 5-LO expression is regulated by NF-{kappa}B/ERK and Sp1/p38 MAPK pathways via EGF receptor in murine macrophages

AIMS

5-Lipoxygenase (5-LO) has been suggested to be a modulator of atherosclerotic plaque instability and co-exists with 4-hydroxynonenal (HNE) in macrophages in atherosclerotic lesions. To determine the potential role for HNE in 5-LO expression, the molecular mechanisms of 5-LO expression were evaluated in HNE-stimulated macrophages.

METHODS AND RESULTS

A genomic sequence of the promoter 2.0 kb upstream of the transcription initiation site was amplified, and a series of sequentially deleted fragments were then fused to a luciferase reporter gene. The promoter region 213 bp upstream of the transcription start site was responsible for the HNE-enhanced transcriptional activity of 5-LO. Site-directed mutagenesis of this region showed that the transcription factors, including stimulating protein 1 (Sp1) and nuclear factor-κB (NF-κB), were associated with up-regulation of HNE-induced 5-LO transcription. Moreover, the role of Sp1 and NF-κB in HNE-induced 5-LO expression was confirmed by siRNA knockdown of Sp1 and NF-κB. The HNE-enhanced Sp1 and NF-κB activities were attenuated by SB203580, a p38 mitogen-activated protein kinase (MAPK) inhibitor, and PD98059, an extracellular signal-regulated kinase (ERK) inhibitor, respectively. In addition, the HNE-enhanced phosphorylation of p38 MAPK and ERK was inhibited by AG1478, an epidermal growth factor receptor (EGFR) antagonist, but not by AG1295, a platelet-derived growth factor receptor (PDGFR) antagonist.

CONCLUSION

5-LO expression by HNE was regulated at the transcriptional level by the EGFR-mediated activation of Sp1/p38 MAPK and NF-κB/ERK pathways in macrophages, which may lead to the development of therapeutic interventions for regulating 5-LO expression in atherosclerosis.

Lipid oxidation and peroxidation in CNS health and disease: from molecular mechanisms to therapeutic opportunities

Reactive oxygen species (ROS) are produced at low levels in mammalian cells by various metabolic processes, such as oxidative phosphorylation by the mitochondrial respiratory chain, NAD(P)H oxidases, and arachidonic acid oxidative metabolism. To maintain physiological redox balance, cells have endogenous antioxidant defenses regulated at the transcriptional level by Nrf2/ARE. Oxidative stress results when ROS production exceeds the cell's ability to detoxify ROS. Overproduction of ROS damages cellular components, including lipids, leading to decline in physiological function and cell death. Reaction of ROS with lipids produces oxidized phospholipids, which give rise to 4-hydroxynonenal, 4-oxo-2-nonenal, and acrolein. The brain is susceptible to oxidative damage due to its high lipid content and oxygen consumption. Neurodegenerative diseases (AD, ALS, bipolar disorder, epilepsy, Friedreich's ataxia, HD, MS, NBIA, NPC, PD, peroxisomal disorders, schizophrenia, Wallerian degeneration, Zellweger syndrome) and CNS traumas (stroke, TBI, SCI) are problems of vast clinical importance. Free iron can react with H(2)O(2) via the Fenton reaction, a primary cause of lipid peroxidation, and may be of particular importance for these CNS injuries and disorders. Cholesterol is an important regulator of lipid organization and the precursor for neurosteroid biosynthesis. Atherosclerosis, the major risk factor for ischemic stroke, involves accumulation of oxidized LDL in the arteries, leading to foam cell formation and plaque development. This review will discuss the role of lipid oxidation/peroxidation in various CNS injuries/disorders.

Roles of the lipid peroxidation product 4-hydroxynonenal in obesity, the metabolic syndrome, and associated vascular and neurodegenerative disorders

A rising tide of obesity and type 2 diabetes has resulted from the development of technologies that have made inexpensive high calorie foods readily available and exercise unnecessary for many people. Obesity and the metabolic syndrome (insulin resistance, visceral adiposity and dyslipidemia) wreak havoc on cells throughout the body thereby promoting cardiovascular and kidney disease, and degenerative diseases of the brain and body. Obesity and insulin resistance promote disease by increasing oxidative damage to proteins, lipids and DNA as the result of a combination of increased free radical production and an impaired ability of cells to detoxify the radicals and repair damaged molecules. By covalently modifying membrane-associated proteins, the membrane lipid peroxidation product 4-hydroxynonenal (HNE) may play particularly sinister roles in the metabolic syndrome and associated disease processes. HNE can damage pancreatic beta cells and can impair the ability of muscle and liver cells to respond to insulin. HNE may promote atherosclerosis by modifying lipoproteins and can cause cardiac cell damage by impairing metabolic enzymes. An adverse role for HNE in the brain in obesity and the metabolic syndrome is suggested by studies showing that HNE levels are increased in brain cells with aging and Alzheimer's disease. HNE can cause the dysfunction and degeneration of neurons by modifying membrane-associated glucose and glutamate transporters, ion-motive ATPases, enzymes involved in amyloid metabolism, and cytoskeletal proteins. Exercise and dietary energy restriction reduce HNE production and may also increase cellular systems for HNE detoxification including glutathione and oxidoreductases. The recent development of low molecular weight molecules that scavenge HNE suggests that HNE can be targeted in the design of drugs for the treatment of obesity, the metabolic syndrome, and associated disorders.

Participation of 5-lipoxygenase-derived LTB(4) in 4-hydroxynonenal-enhanced MMP-2 production in vascular smooth muscle cells

5-Lipoxygenase (5-LO) has been suggested as a modulator of atherosclerotic plaque instability, however, its role in MMP production in vascular smooth muscle cells (VSMC) is still unclear. Thus, this study investigated the role of 5-LO in HNE-enhanced MMP-2 production in VSMC, and the mechanisms by which this enzyme could be activated by HNE. VSMC stimulated with HNE (1 microM) produced MMP-2, which was markedly attenuated in 5-LO-deficient VSMC as well as in cells pretreated with a FLAP inhibitor, MK886, confirming a role for 5-LO metabolites in HNE-enhanced MMP-2 production. Related to these results, HNE increased nuclear translocation of 5-LO promoting 5-LO activity, which was attenuated not only by SB203580, a p38 MAPK inhibitor, but also by PD98059, an ERK inhibitor. In parallel, phosphorylation of p38 MAPK and ERK occurred as early as 15 min after exposure to HNE, suggesting a potential role for p38 MAPK and ERK pathways in HNE-induced activation of 5-LO. Among leukotriene (LT) receptor antagonists, U-75302, a BLT receptor antagonist, but not MK-571 and Rev-5901, cysLT receptor antagonists, showed an inhibitory effect on HNE-enhanced MMP-2 production. Moreover, MMP-2 production in VSMC was also significantly increased by LTB(4), but not by LTC(4) and LTD(4). Collectively, these data suggest that 5-LO mediates HNE-enhanced MMP-2 production via LTB(4)-BLT receptor pathways, consequently leading to atherosclerotic plaque instability.

Involvement of an aldo-keto reductase (AKR1C3) in redox cycling of 9,10-phenanthrenequinone leading to apoptosis in human endothelial cells

9,10-Phenanthrenequinone (9,10-PQ), a major quinone found in diesel exhaust particles, is considered to generate reactive oxygen species (ROS) through its redox cycling. Here, we show that 9,10-PQ evokes apoptosis in human aortic endothelial cells (HAECs) and its apoptotic signaling includes ROS generation and caspase activation. The 9,10-PQ-induced cytotoxicity was inhibited by ROS scavengers, indicating that intracellular ROS generation is responsible for the 9,10-PQ-induced apoptosis. Comparison of mRNA expression levels and kinetic constants in the 9,10-PQ reduction among 10 human reductases suggests that aldo-keto reductase 1C3 (AKR1C3) is a 9,10-PQ reductase in HAECs. In in vitro 9,10-PQ reduction by AKR1C3, the reduced product 9,10-dihydroxyphenanthrene and superoxide anions were formed, suggesting the enzymatic two-electron reduction of 9,10-PQ that thereby causes oxidative stress through its redox cycling. In addition, the participation of AKR1C3 in 9,10-PQ-redox cycling was confirmed by the data that AKR1C3 overexpression in endothelial cells augmented the ROS generation and cytotoxicity by 9,10-PQ, and the ROS scavengers inhibited the toxic effects. Pretreatment of the overexpressing cells with AKR1C3 inhibitors, flufenamic acid and indomethacin, suppressed the 9,10-PQ-induced GSH depletion. These results suggest that AKR1C3 is a key enzyme in the initial step of 9,10-PQ-induced cytotoxicity in HAECs.

Cilostazol Attenuates 4-hydroxynonenal-enhanced CD36 Expression on Murine Macrophages via Inhibition of NADPH Oxidase-derived Reactive Oxygen Species Production

Although anti-atherogenic effects of cilostazol have been suggested, its effects on the expression of SR in macrophages are unclear. This study investigated the role of cilostazol on CD36 expression of murine macrophages enhanced by HNE, a byproduct of lipid peroxidation. The stimulation of macrophages with HNE led to an increased expression of CD36, which was significantly attenuated by NAC, an antioxidant. Moreover, the increased production of ROS by HNE was completely abolished by NADPH oxidase inhibitors, DPI and apocynin, as well as by the 5-LO inhibitor, MK886, but not by inhibitors for other oxidases. This suggested that NADPH-oxidase and 5-LO were major sources of ROS induced by HNE. In addition, HNE-enhanced expression of CD36 was reduced by these inhibitors, which indicated a role for NADPH oxidase and 5-LO on CD36 expression. In our present study, cilostazol was a significant inhibitor of ROS production, as well as CD36 expression induced by HNE. An increase in NADPH oxidase activity by HNE was significantly attenuated by cilostazol, however cilostazol had no effect on HNE-enhanced 5-LO activity. Together, these results suggest that cilostazol attenuates HNE-enhanced CD36 expression on murine macrophages thorough inhibition of NADPH oxidase-derived ROS generation.

The core-aldehyde 9-oxononanoyl cholesterol increases the level of transforming growth factor beta1-specific receptors on promonocytic U937 cell membranes

Among the broad variety of compounds generated via oxidative reactions in low-density lipoproteins (LDL) and subsequently found in the atherosclerotic plaque are aldehydes that are still esterified to the parent lipid, termed core aldehydes. The most represented cholesterol core aldehyde in LDL is 9-oxononanoyl cholesterol (9-ONC), an oxidation product of cholesteryl linoleate. 9-ONC, at a concentration detectable in biological material, markedly up-regulates mRNA expression and protein level of both the pro-fibrogenic and pro-apoptotic cytokine transforming growth factor beta1 (TGF-beta1) and the TGF-beta receptor type I (TbetaRI) in human U937 promonocytic cells. We also observed increased membrane presentation of TGF-beta receptor type II (TbetaRII). Experiments employing the TbetaRI inhibitor SB431542, or the TGFbeta antagonist DANFc chimera, have shown that the effect on TbetaRI is directly induced by 9-ONC, while TbetaRII up-regulation seems stimulated by its specific ligand, i.e. TGFbeta1, over-secreted meanwhile by treated cells. Increased levels of the cytokine and of its specific receptors in 9-ONC-treated cells clearly occurs through stimulation of extracellular signal-regulated kinase 1 and 2 (ERK1/2), as demonstrated by ERK1/2 knockdown experiments using mitogen-activated protein kinase/extracellular signal-regulated kinase 1 and 2 (MEK1 and MEK2) siRNAs, or PD98059, a selective MEK1/2 inhibitor. 9-ONC might thus sustain further vascular remodeling due to atherosclerosis, not simply by stimulating synthesis of the pro-fibrogenic cytokine TGF-beta1 in vascular cells, but also and chiefly by enhancing the TGF-beta1 autocrine loop, because of the marked up-regulation of the cytokine's specific receptors TbetaRI and TbetaRII.

4-Hydroxynonenal enhances CD36 expression on murine macrophages via p38 MAPK-mediated activation of 5-lipoxygenase

Increased levels of 4-hydroxynonenal (HNE) and 5-lipoxygenase (5-LO) coexist in atherosclerotic lesions but their relationship in atherogenesis is unclear. This study investigated the role of 5-LO in HNE-induced CD36 expression and macrophage foam cell formation, and the link between HNE and 5-LO. In J774A.1 murine macrophages, HNE (10 microM) enhanced CD36 expression in association with an increased uptake of oxLDL, which was blunted by inhibition of 5-LO with MK886, a 5-LO inhibitor, or with 5-LO siRNA. In peritoneal macrophages from 5-LO-deficient mice, HNE-induced CD36 expression was markedly attenuated, confirming a pivotal role of 5-LO in HNE-induced CD36 expression. In an assay for 5-LO activity, stimulation of macrophages with HNE led to increased leukotriene B(4) production in the presence of exogenous arachidonic acid in association with an increased association of 5-LO to the nuclear membrane. Among the mitogen-activated protein kinase (MAPK) pathways involved in 5-LO phosphorylation, HNE predominantly activated p38 MAPK in macrophages, and the p38 MAPK inhibitor SB203580, but not an extracellular signal-regulated kinase inhibitor, suppressed HNE-induced LTB(4) production. Collectively, these data suggest that p38 MAPK-mediated activation of 5-LO by HNE might enhance CD36 expression, consequently leading to the formation of macrophage foam cells.

4-Hydroxynonenal enhances MMP-2 production in vascular smooth muscle cells via mitochondrial ROS-mediated activation of the Akt/NF-kappaB signaling pathways

4-Hydroxynonenal (HNE) accumulates at atherosclerotic lesions, but its role in the progression of atherosclerosis is not clear. Considering the role of matrix metalloproteinases (MMP) in plaque destabilization, we investigated the mechanism by which HNE induces MMP production in vascular smooth muscle cells (VSMC). VSMC stimulated by HNE (1.0 microM) produced enzymatically active MMP-2 with an increased promoter activity, which was abolished by mutation of the NF-kappaB binding site in the promoter region. The increased NF-kappaB activity with subsequent MMP-2 production by HNE was significantly attenuated by transfection with Akt siRNA as well as by pretreatment with the PI3K/Akt inhibitors LY294002 (10 microM) and SH-5 (1.0 microM). The phosphorylation of Akt occurred as early as 5 min in VSMC exposed to HNE and was markedly attenuated by inhibition of mitochondrial reactive oxygen species (ROS). Furthermore, the impact of mitochondrial ROS on HNE-induced Akt phosphorylation with subsequent MMP-2 production was also demonstrated in mitochondrial function-deficient VSMC, as well as in cells transfected with manganese superoxide dismutase. Taken together, these results suggest that HNE enhances MMP-2 production in VSMC via mitochondrial ROS-mediated activation of the Akt/NF-kappaB signaling pathways.

Inhibition of carboxylesterase 1 is associated with cholesteryl ester retention in human THP-1 monocyte/macrophages

Cholesteryl esters are hydrolyzed by cholesteryl ester hydrolase (CEH) yielding free cholesterol for export from macrophages. Hence, CEH has an important regulatory role in macrophage reverse cholesterol transport (RCT). CEH and human carboxylesterase 1 (CES1) appear to be the same enzyme. CES1 is inhibited by oxons, the bioactive metabolites of organophosphate (OP) pesticides. Here, we show that CES1 protein is robustly expressed in human THP-1 monocytes/macrophages and its biochemical activity inhibited following treatment of cell lysates and intact cells with chlorpyrifos oxon, paraoxon, or methyl paraoxon (with nanomolar IC(50) values) or after immunodepletion of CES1 protein. CES1 protein expression in cells is unaffected by a 24-h paraoxon treatment, suggesting that the reduced hydrolytic activity is due to covalent inhibition of CES1 by oxons and not down-regulation of expression. Most significantly, treatment of cholesterol-loaded macrophages with either paraoxon (a non-specific CES inhibitor) or benzil (a specific CES inhibitor) caused enhanced retention of intracellular cholesteryl esters and a "foamy" phenotype, consistent with reduced cholesteryl ester mobilization. Thus, exposure to OP pesticides, which results in the inhibition of CES1, may also inhibit macrophage RCT, an important process in the regression of atherosclerosis.