Elevated oxidative stress, iron accumulation around microvessels and increased 4-hydroxynonenal immunostaining in zone 1 of the liver acinus in hypercholesterolemic rabbits

Iron and atherosclerosis: Lessons learned from rabbits relevant to human disease

The role of iron in promoting atherosclerosis, and hence the cardiovascular, neurodegenerative and other diseases that result from atherosclerosis, has been fiercely controversial. Many studies have been carried out on various rodent models of atherosclerosis, especially on apoE-knockout (apoE-/-) mice, which develop atherosclerosis more readily than normal mice. These apoE-/- mouse studies generally support a role for iron in atherosclerosis development, although there are conflicting results. The purpose of the current article is to describe studies on another animal model that is not genetically manipulated; New Zealand White (NZW) rabbits fed a high-cholesterol diet. This may be a better model than the apoE-/- mice for human atherosclerosis, although it has been given much less attention. Studies on NZW rabbits support the view that iron promotes atherosclerosis, although some uncertainties remain, which need to be resolved by further experimentation.

Ambient fine particulate matter aggravates atherosclerosis in apolipoprotein E knockout mice by iron overload via the hepcidin-ferroportin axis

AIMS

Exposure to fine particulate matter (PM2.5) is correlated to atherosclerosis, but the mechanism remains largely undefined. Iron overload is a significant contributor to atherosclerosis, and iron homeostasis is highly regulated by the hepcidin-ferroportin (FPN) axis. Here we aimed to investigate the association between iron overload and PM2.5-induced atherosclerotic mice.

MAIN METHODS

Apolipoprotein E knockout (ApoE-/-) mice were randomly assigned to filtered air (FA group) or PM2.5 (PM2.5 group) for 3-month inhalation. Daily PM2.5 mass concentrations, serum levels of ferritin, iron, pro-atherosclerotic cytokines and lipid profiles, atherosclerotic lesion areas, hepcidin, FPN and iron depositions in atherosclerotic lesions, hepcidin, FPN mRNA and protein expressions in the aorta were detected, respectively.

KEY FINDINGS

The daily average concentration of atmospheric PM2.5 was 68.2 ± 21.8 μg/m3. Serum levels of ferritin, iron, VEGF, MCP-1, IL-6, TNF-α, TC and LDL-C, atherosclerotic lesion areas, hepcidin and iron depositions in atherosclerotic lesions, hepcidin mRNA and protein expressions in the PM2.5 group were observably higher than those in the FA group. Nevertheless, FPN deposition in atherosclerotic lesions, FPN mRNA and protein expressions in the aorta of the PM2.5 group were markedly lower than those of the FA group.

SIGNIFICANCE

PM2.5 inhalation could exacerbate the formation and development of atherosclerosis in ApoE-/- mice, the potential mechanisms may be partly associated with iron overload via the hepcidin-FPN axis, as well as iron-triggered systemic inflammation and hyperlipidemia.

Redox Signaling by Reactive Electrophiles and Oxidants

The concept of cell signaling in the context of nonenzyme-assisted protein modifications by reactive electrophilic and oxidative species, broadly known as redox signaling, is a uniquely complex topic that has been approached from numerous different and multidisciplinary angles. Our Review reflects on five aspects critical for understanding how nature harnesses these noncanonical post-translational modifications to coordinate distinct cellular activities: (1) specific players and their generation, (2) physicochemical properties, (3) mechanisms of action, (4) methods of interrogation, and (5) functional roles in health and disease. Emphasis is primarily placed on the latest progress in the field, but several aspects of classical work likely forgotten/lost are also recollected. For researchers with interests in getting into the field, our Review is anticipated to function as a primer. For the expert, we aim to stimulate thought and discussion about fundamentals of redox signaling mechanisms and nuances of specificity/selectivity and timing in this sophisticated yet fascinating arena at the crossroads of chemistry and biology.

Contribution of the HNE-immunohistochemistry to modern pathological concepts of major human diseases

Excessive production of reactive oxygen species can induce peroxidation of the polyunsaturated fatty acids thus generating reactive aldehydes like 4-hydroxy-2-nonenal (HNE), denoted as "the second messenger of free radicals". Because HNE has high binding affinity for cysteine, histidine and lysine it forms relatively stable and hardly metabolized protein adducts. By changing structure and function of diverse structural and regulatory proteins, HNE achieves not only cytotoxic, but also regulatory functions in various pathophysiological processes. Numerous animal model studies and clinical trials confirmed HNE as one of the crucial factors in development and progression of many disorders, in particular of cancer, (neuro)degenerative, metabolic and inflammatory diseases. Since HNE has multiple biological effects and is in the living system usually bound to proteins and peptides, many research groups work on development of specific immunochemical methods targeting the HNE-histidine adducts as major bioactive marker of lipid peroxidation, following the research pathway initiated by Hermann Esterbauer, who discovered HNE in 60's. Such immunohistochemical studies did not only prove the high biomedical importance of HNE, but have also given new insights into major diseases of the modern man. Immunohistochemical studies have shown reversibility of formation of the HNE-protein adducts, as well as differential onset of the HNE-mediated lipid peroxidation between age- associated atherosclerosis and photoaging, revealing eventually selective anti-cancer effects of HNE produced by non-malignant cells in vicinity of cancer. This review summarizes some of the HNE-histidine immunohistochemistry findings we believe are of broad biomedical interest and could inspire new studies in the field.

Isolation, characterization and hypolipidemic activity of ferulic acid in high-fat-diet-induced hyperlipidemia in laboratory rats

Prosopis cineraria (L.) Druce (Leguminosae) (syn. Prosopis spicigera L.) has antidiabetic and antioxidant potential. Earlier we reported its hypolipidemic activity obtained from ethanol extract (ET-PCF). Object of this work was to isolate ferulic acid (FA) from ET-PCF and evaluate hypolipidemic activity against high-fat diet (HFD)-induced hyperlipidemic laboratory rats. ET-PCF was subjected to flash column chromatography to isolate FA. The chemical structure of the isolated compound was elucidated by UV, IR, ¹H NMR,¹³C NMR and LC-MS. Further, the antihyperlipidemic effect of FA (10, 20 and 40 mg/kg, p.o.) in HFD-induced hyperlipidemic rats was investigated. Hyperlipidemia was induced in male Sprague-Dawley rats by feeding with HFD for 60 days. Lipid parameters such as total cholesterol (TC), Low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C) and triglycerides (TG) levels were measured in serum and hepatic tissue. Hepatic oxido-nitrosative stress (SOD, GSH, MDA and NO) were also determined. Histological evaluation of liver tissue was carried out. The structure of the isolated compound was characterized based on spectral data and confirmed as FA. HFD induced an alteration in serum, and hepatic lipid profile (triglyceride, cholesterol, HDL, and LDL) was significantly restored (p < 0.001) by administration of FA (20 and 40 mg/kg, p.o.). The elevated level of oxido-nitrosative stress in liver was significantly reduced (p < 0.001) by FA (20 and 40 mg/kg, p.o.). Histological aberration induced in the liver after HFD ingestion were restored by FA administration. Ferulic acid isolated from ET-PCF showed hypolipidemic effects in HFD-induced hyperlipidemic rats via modulation of elevated oxido-nitrosative stress.

Liver ergothioneine accumulation in a guinea pig model of non-alcoholic fatty liver disease. A possible mechanism of defence?

L-ergothioneine (ET), a putative antioxidant compound acquired by animals through dietary sources, has been suggested to accumulate in certain cells and tissues in the body that are predisposed to high oxidative stress. In the present study, we identified an elevation of ET in the liver of a guinea pig model of non-alcoholic fatty liver disease (NAFLD), elucidated a possible mechanism for the increased uptake and investigated the possible role for this accumulation. This increase in liver ET levels correlated with cholesterol accumulation and disease severity. We identified an increase in the transcriptional factor, RUNX1, which has been shown to upregulate the expression of the ET-specific transporter OCTN1, and could consequently lead to the observable elevation in ET. An increase was also seen in heat shock protein 70 (HSP70) which seemingly corresponds to ET elevation. No significant increase was observed in oxidative damage markers, F2-isoprostanes, and protein carbonyls, which could possibly be attributed to the increase in liver ET through direct antioxidant action, induction of HSP70, or by chelation of Fe(2+), preventing redox chemistry. The data suggest a novel mechanism by which the guinea pig fatty liver accumulates ET via upregulation of its transporter, as a possible stress response by the damaged liver to further suppress oxidative damage and delay tissue injury. Similar events may happen in other animal models of disease, and researchers should be aware of the possibility.

Oxidative and reductive metabolism of lipid-peroxidation derived carbonyls

Extensive research has shown that increased production of reactive oxygen species (ROS) results in tissue injury under a variety of pathological conditions and chronic degenerative diseases. While ROS are highly reactive and can incite significant injury, polyunsaturated lipids in membranes and lipoproteins are their main targets. ROS-triggered lipid-peroxidation reactions generate a range of reactive carbonyl species (RCS), and these RCS spread and amplify ROS-related injury. Several RCS generated in oxidizing lipids, such as 4-hydroxy trans-2-nonenal (HNE), 4-oxo-2-(E)-nonenal (ONE), acrolein, malondialdehyde (MDA) and phospholipid aldehydes have been shown to be produced under conditions of oxidative stress and contribute to tissue injury and dysfunction by depleting glutathione and other reductants leading to the modification of proteins, lipids, and DNA. To prevent tissue injury, these RCS are metabolized by several oxidoreductases, including members of the aldo-keto reductase (AKR) superfamily, aldehyde dehydrogenases (ALDHs), and alcohol dehydrogenases (ADHs). Metabolism via these enzymes results in RCS inactivation and detoxification, although under some conditions, it can also lead to the generation of signaling molecules that trigger adaptive responses. Metabolic transformation and detoxification of RCS by oxidoreductases prevent indiscriminate ROS toxicity, while at the same time, preserving ROS signaling. A better understanding of RCS metabolism by oxidoreductases could lead to the development of novel therapeutic interventions to decrease oxidative injury in several disease states and to enhance resistance to ROS-induced toxicity.

Current development in non-enzymatic lipid peroxidation products, isoprostanoids and isofuranoids, in novel biological samples

Isoprostanoids and isofuranoids are lipid mediators that can be formed from omega-3 and omega-6 polyunsaturated fatty acids (PUFAs). F2-isoprostanes formed from arachidonic acid, especially 15-F2t-isoprostane, are commonly measured in biological tissues for decades as the biomarker for oxidative stress and diseases. Recently, other forms of isoprostanoids derived from adrenic, eicosapentaenoic, and docosahexaenoic acids namely F2-dihomo-isoprostanes, F3-isoprostanes, and F4-neuroprostanes respectively, and isofuranoids including isofurans, dihomo-isofurans, and neurofurans are reported as oxidative damage markers for different metabolisms. The most widely used samples in measuring lipid peroxidation products include but not limited to the blood and urine; other biological fluids, specialized tissues, and cells can also be determined. In this review, measurement of isoprostanoids and isofuranoids in novel biological samples by gas chromatography (GC)-mass spectrometry (MS), GC-MS/MS, liquid chromatography (LC)-MS, and LC-MS/MS will be discussed.

Non-enzymatic lipid oxidation products in biological systems: assessment of the metabolites from polyunsaturated fatty acids

Metabolites of non-enzymatic lipid peroxidation of polyunsaturated fatty acids notably omega-3 and omega-6 fatty acids have become important biomarkers of lipid products. Especially the arachidonic acid-derived F2-isoprostanes are the classic in vivo biomarker for oxidative stress in biological systems. In recent years other isoprostanes from eicosapentaenoic, docosahexaenoic, adrenic and α-linolenic acids have been evaluated, namely F3-isoprostanes, F4-neuroprostanes, F2-dihomo-isoprostanes and F1-phytoprostanes, respectively. These have been gaining interest as complementary specific biomarkers in human diseases. Refined extraction methods, robust analysis and elucidation of chemical structures have improved the sensitivity of detection in biological tissues and fluids. Previously the main reliable instrumentation for measurement was gas chromatography-mass spectrometry (GC-MS), but now the use of liquid chromatography-tandem mass spectrometry (LC-MS/MS) and immunological techniques is gaining much attention. In this review, the types of prostanoids generated from non-enzymatic lipid peroxidation of some important omega-3 and omega-6 fatty acids and biological samples that have been determined by GC-MS and LC-MS/MS are discussed.

Precision-cut liver slices from diet-induced obese rats exposed to ethanol are susceptible to oxidative stress and increased fatty acid synthesis

Oxidative stress from fat accumulation in the liver has many deleterious effects. Many believe that there is a second hit that causes relatively benign fat accumulation to transform into liver failure. Therefore, we evaluated the effects of ethanol on ex vivo precision-cut liver slice cultures (PCLS) from rats fed a high-fat diet resulting in fatty liver. Age-matched male Sprague-Dawley rats were fed either high-fat (obese) (45% calories from fat, 4.73 kcal/g) or control diet for 13 mo. PCLS were prepared, incubated with 25 mM ethanol for 24, 48, and 72 h, harvested, and evaluated for ethanol metabolism, triglyceride production, oxidative stress, and cytokine expression. Ethanol metabolism and acetaldehyde production decreased in PCLS from obese rats compared with age-matched controls (AMC). Increased triglyceride and smooth muscle actin production was observed in PCLS from obese rats compared with AMC, which further increased following ethanol incubation. Lipid peroxidation, measured by thiobarbituric acid reactive substances assay, increased in response to ethanol, whereas GSH and heme oxygenase I levels were decreased. TNF-α and IL-6 levels were increased in the PCLS from obese rats and increased further with ethanol incubation. Diet-induced fatty liver increases the susceptibility of the liver to toxins such as ethanol, possibly by the increased oxidative stress and cytokine production. These findings support the concept that the development of fatty liver sensitizes the liver to the effects of ethanol and leads to the start of liver failure, necrosis, and eventually cirrhosis.

Effects of 4-hydroxynonenal on vascular endothelial and smooth muscle cell redox signaling and function in health and disease

4-hydroxynonenal (HNE) is a lipid hydroperoxide end product formed from the oxidation of n-6 polyunsaturated fatty acids. The relative abundance of HNE within the vasculature is dependent not only on the rate of lipid peroxidation and HNE synthesis but also on the removal of HNE adducts by phase II metabolic pathways such as glutathione-S-transferases. Depending on its relative concentration, HNE can induce a range of hormetic effects in vascular endothelial and smooth muscle cells, including kinase activation, proliferation, induction of phase II enzymes and in high doses inactivation of enzymatic processes and apoptosis. HNE also plays an important role in the pathogenesis of vascular diseases such as atherosclerosis, diabetes, neurodegenerative disorders and in utero diseases such as pre-eclampsia. This review examines the known production, metabolism and consequences of HNE synthesis within vascular endothelial and smooth muscle cells, highlighting alterations in mitochondrial and endoplasmic reticulum function and their association with various vascular pathologies.

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HNE is a lipid peroxidation endproduct regulating vascular redox signaling.

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HNE detoxification is tightly regulated in vascular and other cell types.

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Elevated HNE levels are associated with various vascular diseases.

Antioxidant effect of nondigestible levan and its impact on cardiovascular disease and atherosclerosis

Levan polysaccharide, a type of fructan, has been shown to favorably affect diabetes type 2 and hypercholesterolemia. Recent reports have indicated that excessive oxidative stress contributes to the development of atherosclerosis linked metabolic syndrome. The objective of this current study was to investigate the possible protection against oxidative stress linked atherosclerosis. A group of twenty four male rats was divided into four subgroups; a normal diet group (Control), normal rats received levan (L), a high-cholesterol diet group (Chol) and a high-cholesterol diet with 5% (w/w) levan group. After the treatment period, the plasma antioxidant enzymes and lipid profiles were determined. Our results show that treatment with levan positively changed plasma antioxidant enzyme activities by increasing superoxide dismutase (SOD) and catalase (CAT) by 40% and 28%, respectively, in heart. Similarly, the treatment of Chol fed groups with levan positively changed lipid profiles by decreasing total cholesterol, triglycerides and LDL-cholesterol by 50%, 38.33% and 64%, respectively. Thus may have potential antioxidant effects and could protect against oxidative stress linked atherosclerosis.

Hypolipidemic effect of diet supplementation with bacterial levan in cholesterol-fed rats

Levan polysaccharide, a type of fructan, has been shown to have industrial applications as a new industrial gum in the fields of cosmetics, foods like dietary fiber and pharmaceutical goods. The objective of this current study was to investigate the possible hypolipidemic and antioxidative effects of levan in rats fed with a high-cholesterol diet. Animals were allocated into four groups of six rats each: a normal diet group (Control), normal rats received levan (L), a high-cholesterol diet group (Chol) and a high-cholesterol diet with a daily dose of levan equivalent to 5%. Treated hypercholesterolemic rats were administrated with levan in drinking water through oral gavage for 60 days. After the treatment period, the plasma antioxidant enzymes and lipid profiles were determined. Our results show that treatment with levan polysaccharide positively changed plasma antioxidant enzyme activities and lipid profiles (total cholesterol, HDL-cholesterol, LDL-cholesterol and triglycerides) in cholesterol-rats, and thus may have potential hypolipidemic and antioxidant effects. Levan could protect against oxidative stress linked atherosclerosis and decrease the atherogenic index.

Reaction of ferritin with hydrogen peroxide induces lipid peroxidation

Lipid peroxidation is known to be an important factor in the pathologies of many diseases associated with oxidative stress. We assessed the lipid peroxidation induced by the reaction of ferritin with H2O2. When linoleic acid micelles or phosphatidyl choline liposomes were incubated with ferritin and H2O2, lipid peroxidation increased in the presence of ferritin and H2O2 in a concentration-dependent manner. The hydroxyl radical scavengers, azide and thiourea, prevented lipid peroxidation induced by the ferritin/H2O2 system. The iron specific chelator desferoxamine also prevented ferritin/H2O2 systemmediated lipid peroxidation. These results demonstrate the possible role of iron in ferritin/H2O2 system-mediated lipid peroxidation. Carnosine is involved in many cellular defense processes, including free radical detoxification. In this study, carnosine, homocarnosine, and anserine were shown to significantly prevent ferritin/H2O2 system-mediated lipid peroxidation and also inhibited the free radical-generation activity of ferritin. These results indicated that carnosine and related compounds may prevent ferritin/H2O2 system-mediated lipid peroxidation via free radical scavenging.

Hypolipidemic and antioxidant effects of dandelion (Taraxacum officinale) root and leaf on cholesterol-fed rabbits

Dandelion (Taraxacum officinale), an oriental herbal medicine, has been shown to favorably affect choleretic, antirheumatic and diuretin properties. Recent reports have indicated that excessive oxidative stress contributes to the development of atherosclerosis-linked metabolic syndrome. The objective of this current study was to investigate the possible hypolipidemic and antioxidative effects of dandelion root and leaf in rabbits fed with a high-cholesterol diet. A group of twenty eight male rabbits was divided into four subgroups; a normal diet group, a high-cholesterol diet group, a high-cholesterol diet with 1% (w/w) dandelion leaf group, and a high-cholesterol diet with 1% (w/w) dandelion root group. After the treatment period, the plasma antioxidant enzymes and lipid profiles were determined. Our results show that treatment with dandelion root and leaf positively changed plasma antioxidant enzyme activities and lipid profiles in cholesterol-fed rabbits, and thus may have potential hypolipidemic and antioxidant effects. Dandelion root and leaf could protect against oxidative stress linked atherosclerosis and decrease the atherogenic index.

Differential distribution of 4-hydroxynonenal adducts to sulfur and nitrogen residues in blood proteins as revealed using Raney nickel and gas chromatography-mass spectrometry

Quantification of 4-hydroxy-2-nonenal (HNE) bound to circulating proteins may prove to be useful in evaluating the role of this bioactive lipoperoxidation by-product in the pathogenesis of various diseases. Recently, we developed a quantitative gas chromatography-mass spectrometry (GCMS) assay of total protein-bound HNE (HNE-P) in blood after reduction with NaB(2)H(4) and cleavage with Raney nickel. Whereas it has been assumed that Raney nickel cleaves only Michael adducts of HNE to cysteine via a thioether bond (HNE-SP), results from this study demonstrate that our GCMS method also detects with precision picomoles of HNE adducts via nitrogen residues (HNE-NP). Specifically, evidence was obtained using various study models, including polyamino acids consisting of cysteine, lysine, and histidine and a biologically relevant molecule, albumin. Furthermore, we show that dinitrophenylhydrazine treatment before Raney nickel treatment can be used to discriminate and quantify the various HNE-P molecular species in plasma and blood samples from normal rats, which range between 0.15 and 3 pmol/mg protein or 10 to 600 nM. However, whereas HNE-SP predominated in whole blood, we detected HNE-NP only in plasma. We also identified another significant MS signal, which we attribute to protein-bound 1,4-dihydroxynonane (DHN-P) presumably formed from the enzymatic reduction of HNE-P. The distribution profile of all these species in plasma differed from that observed when physiologically relevant concentrations of albumin and HNE were incubated in vitro. Furthermore, interestingly, hypercholesterolemic rabbits showed higher plasma levels of HNE-NP, but not of DHN-P. Beyond documenting the presence of various types of HNE-P in circulating proteins, our results emphasize the importance of enzymatic mechanisms in situ as a factor determining their distribution in the various blood compartments under various conditions.