Lipid Peroxidation: Production, Metabolism, and Signaling Mechanisms of Malondialdehyde and 4-Hydroxy-2-Nonenal

Lipid peroxidation can be described generally as a process under which oxidants such as free radicals attack lipids containing carbon-carbon double bond(s), especially polyunsaturated fatty acids (PUFAs). Over the last four decades, an extensive body of literature regarding lipid peroxidation has shown its important role in cell biology and human health. Since the early 1970s, the total published research articles on the topic of lipid peroxidation was 98 (1970–1974) and has been increasing at almost 135-fold, by up to 13165 in last 4 years (2010–2013). New discoveries about the involvement in cellular physiology and pathology, as well as the control of lipid peroxidation, continue to emerge every day. Given the enormity of this field, this review focuses on biochemical concepts of lipid peroxidation, production, metabolism, and signaling mechanisms of two main omega-6 fatty acids lipid peroxidation products: malondialdehyde (MDA) and, in particular, 4-hydroxy-2-nonenal (4-HNE), summarizing not only its physiological and protective function as signaling molecule stimulating gene expression and cell survival, but also its cytotoxic role inhibiting gene expression and promoting cell death. Finally, overviews of in vivo mammalian model systems used to study the lipid peroxidation process, and common pathological processes linked to MDA and 4-HNE are shown.

One of the consequences of uncontrolled oxidative stress (imbalance between the prooxidant and antioxidant levels in favor of prooxidants) is cells, tissues, and organs injury caused by oxidative damage. It has long been recognized that high levels of free radicals or reactive oxygen species (ROS) can inflict direct damage to lipids. The primary sources of endogenous ROS production are the mitochondria, plasma membrane, endoplasmic reticulum, and peroxisomes [ 20 ] through a variety of mechanisms including enzymatic reactions and/or autooxidation of several compounds, such as catecholamines and hydroquinone. Different exogenous stimuli, such as the ionizing radiation, ultraviolet rays, tobacco smoke, pathogen infections, environmental toxins, and exposure to herbicide/insecticides, are sources of in vivo ROS production. The two most prevalent ROS that can affect profoundly the lipids are mainly hydroxyl radical (HO • ) and hydroperoxyl (HO • 2 ). The hydroxyl radical (HO • ) is a small, highly mobile, water-soluble, and chemically most reactive species of activated oxygen. This short-lived molecule can be produced from O 2 in cell metabolism and under a variety of stress conditions. A cell produces around 50 hydroxyl radicals every second. In a full day, each cell would generate 4 million hydroxyl radicals, which can be neutralized or attack biomolecules [ 21 ]. Hydroxyl radicals cause oxidative damage to cells because they unspecifically attack biomolecules [ 22 ] located less than a few nanometres from its site of generation and are involved in cellular disorders such as neurodegeneration [ 23 , 24 ], cardiovascular disease [ 25 ], and cancer [ 26 , 27 ]. It is generally assumed that HO • in biological systems is formed through redox cycling by Fenton reaction, where free iron (Fe 2+ ) reacts with hydrogen peroxide (H 2 O 2 ) and the Haber-Weiss reaction that results in the production of Fe 2+ when superoxide reacts with ferric iron (Fe 3+ ). In addition to the iron redox cycling described above, also a number of other transition-metal including Cu, Ni, Co, and V can be responsible for HO • formation in living cells ( Figure 1 ). The hydroperoxyl radical (HO • 2 ) plays an important role in the chemistry of lipid peroxidation. This protonated form of superoxide yields H 2 O 2 which can react with redox active metals including iron or copper to further generate HO • through Fenton or Haber-Weiss reactions. The HO • 2 is a much stronger oxidant than superoxide anion-radical and could initiate the chain oxidation of polyunsaturated phospholipids, thus leading to impairment of membrane function [ 28 – 30 ]. 2.1. Lipid Peroxidation Process Lipid peroxidation can be described generally as a process under which oxidants such as free radicals or nonradical species attack lipids containing carbon-carbon double bond(s), especially polyunsaturated fatty acids (PUFAs) that involve hydrogen abstraction from a carbon, with oxygen insertion resulting in lipid peroxyl radicals and hydroperoxides as described previously [ 31 ]. Glycolipids, phospholipids (PLs), and cholesterol (Ch) are also well-known targets of damaging and potentially lethal peroxidative modification. Lipids also can be oxidized by enzymes like lipoxygenases, cyclooxygenases, and cytochrome P450 ( see above, lipid as signaling molecules ). In response to membrane lipid peroxidation, and according to specific cellular metabolic circumstances and repair capacities, the cells may promote cell survival or induce cell death. Under physiological or low lipid peroxidation rates (subtoxic conditions), the cells stimulate their maintenance and survival through constitutive antioxidants defense systems or signaling pathways activation that upregulate antioxidants proteins resulting in an adaptive stress response. By contrast, under medium or high lipid peroxidation rates (toxic conditions) the extent of oxidative damage overwhelms repair capacity, and the cells induce apoptosis or necrosis programmed cell death; both processes eventually lead to molecular cell damage which may facilitate development of various pathological states and accelerated aging. The impact of lipids oxidation in cell membrane and how these oxidative damages are involved in both physiological processes and major pathological conditions have been analysed in several reviews [ 32 – 35 ]. The overall process of lipid peroxidation consists of three steps: initiation, propagation, and termination [ 31 , 36 , 37 ]. In the lipid peroxidation initiation step, prooxidants like hydroxyl radical abstract the allylic hydrogen forming the carbon-centered lipid radical (L • ). In the propagation phase, lipid radical (L • ) rapidly reacts with oxygen to form a lipid peroxy radical (LOO • ) which abstracts a hydrogen from another lipid molecule generating a new L • (that continues the chain reaction) and lipid hydroperoxide (LOOH). In the termination reaction, antioxidants like vitamin E donate a hydrogen

Hydroperoxides are produced during the propagation phase constituting the major primary product of lipid peroxidation process. The hydroperoxide group may be attached to various lipid structures, for example, free fatty acids, triacylglycerols, phospholipids, and sterols. Lipid hydroperoxide generation, turnover and effector action in biological systems have been reviewed [ 36 ]. In contrast to free radical, usually highly reactive and chemically unstable, at moderate reaction conditions, such as low temperature and absence of metal ions, lipid hydroperoxides are relatively more stable products. We found that lipid hydroperoxides in serum could be useful to predict the oxidative stress in tissues [ 59 ], and the levels of oxidative stress, including lipid peroxidation, increased throughout the day [ 60 ]. Once formed lipid hydroperoxides can be target of different reduction reactions, resulting in peroxidative damage inhibition or peroxidative damage induction. Peroxidative Damage Inhibition . Hydroperoxides may decompose in vivo through two-electron reduction, which can inhibit the peroxidative damage. The enzymes mainly responsible for two-electron reduction of hydroperoxides are selenium-dependent glutathione peroxidases (GPx) and selenoprotein P (SeP). GPxs are known to catalyze the reduction of H 2 O 2 or organic hydroperoxides to water or the corresponding alcohols, respectively, typically using glutathione (GSH) as reductant. Widely distributed in mammalian tissues GPx can be found in the cytosol, nuclei, and mitochondria [ 61 , 62 ]. The presence of selenocysteine (in the catalytic centre of glutathione peroxidases) as the catalytic moiety was suggested to guarantee a fast reaction with the hydroperoxide and a fast reducibility by GSH [ 61 ]. SeP is the major selenoprotein in human plasma that reduced phospholipid hydroperoxide using glutathione or thioredoxin as cosubstrate. It protected plasma proteins against peroxynitrite-induced oxidation and nitration or low-density-lipoproteins (LDL) from peroxidation [ 62 ]. Peroxidative Damage Induction . Hydroperoxides may also decompose in vivo through one-electron reduction and take part in initiation/propagation steps [ 31 , 36 , 37 ], induce new lipid hydroperoxides, and feed the lipid peroxidation process; all these mechanisms can contribute to peroxidative damage induction/expansion. Lipid hydroperoxides can be converted to oxygen radicals intermediates such as lipid peroxyl radical (LOO • ) and/or alkoxyl (LO • ) by redox cycling of transition metal (M), resulting in lipid hydroperoxide decomposition and the oxidized or reduced form of theses metal, respectively [ 63 ]. The lipid peroxyl and alkoxyl radicals can attack other lipids promoting the propagation of lipid peroxidation (1) LOOH + M n ⟶ LO • + OH − + M n + 1 (2) LOOH + M n + 1 ⟶ LOO • + H + + M n . Lipid hydroperoxides can also react with peroxynitrite (a short-lived oxidant species that is a potent inducer of cell death [ 64 ] and is generated in cells or tissues by the reaction of nitric oxide with superoxide radical) or hypochlorous acid (a high reactive species produced enzymatically by myeloperoxidase [ 65 , 66 ], which utilizes hydrogen peroxide to convert chloride to hypochlorous acid at sites of inflammation) yielding singlet molecular oxygen [ 67 , 68 ]. Singlet oxygen (molecular oxygen in its first excited singlet state 1 Δ g ; 1 O 2 ) 1 can react with amino acid, and proteins resulting in multiple effects including oxidation of side-chains, backbone fragmentation, dimerization/aggregation, unfolding or conformational changes, enzymatic inactivation, and alterations in cellular handling and turnover of proteins [ 69 , 70 ]. Major substrates for lipid peroxidation are polyunsaturated fatty acids (PUFAs) [ 31 , 36 , 37 ], which are a family of lipids with two or more double bounds, that can be classified in omega-3 ( n -3) and omega-6 ( n -6) fatty acids according to the location of the last double bond relative to the terminal methyl end of the molecule. The predominant n -6 fatty acid is arachidonic acid (AA), which can be reduced (i) via enzymatic peroxidation to prostaglandins, leukotrienes, thromboxanes, and other cyclooxygenase, lipoxygenase or cytochrome P-450 derived products [ 4 ]; or (ii) via nonenzymatic peroxidation to MDA, 4-HNE, isoprostanes, and other lipid peroxidation end-products (more stables and toxic than hydroperoxides) through oxygen radical-dependent oxidative routes [ 49 , 71 ]. The continued oxidation of fatty acid side-chains and released PUFAs, and the fragmentation of peroxides to produce aldehydes, eventually lead to loss of membrane integrity by alteration of its fluidity which finally triggers inactivation of membrane-bound proteins. Contrary to radicals that attack biomolecules located less than a few nanometres from its site of generation [ 22 ], the lipid peroxidation-derived aldehydes can easily diffuse across membranes and can covalently modify a

4-Hydroxynonenal (4-HNE), α , β -unsaturated electrophilic compounds, is the major type of 4-hydroxyalkenals end-product, generated by decomposition of arachidonic acid and larger PUFAs, through enzymatic or nonenzymatic processes [ 49 ]. 4-HNE is an extraordinarily reactive compound containing three functional groups: (i) C=C double bond that can be target to Michael additions to thiol, reduction or epoxidation, (ii) carbonyl group which can yield acetal/thio acetal or can be target to Schiff-base formation, oxidation, or reduction, and (iii) hydroxyl group which can be oxidized to a ketone [ 56 ]. 4-HNE is the most intensively studied lipid peroxidation end-product, in relation not only to its physiological and protective function as signaling molecule stimulating gene expression, but also to its cytotoxic role inhibiting gene expression and promoting the development and progression of different pathological states. In the last three years, excellent reviews have been published summarizing both signaling and cytotoxic effects of this molecule in biology, for example, overview of mechanisms of 4-HNE formation and most common methods for detecting and analyzing 4-HNE and its protein adducts [ 196 ]. Review focuses on membrane proteins affected by lipid peroxidation-derived aldehydes, under physiological and pathological conditions [ 131 ]. Jaganjac and Co-workers have described the role of 4-HNE as second messengers of free radicals that act both as signaling molecules and as cytotoxic products of lipid peroxidation involvement in the pathogenesis of diabetes mellitus (DM) [ 151 ]. Chapple and Co-workers summarized the production, metabolism and consequences of 4-HNE synthesis within vascular endothelial, smooth muscle cells and targeted signaling within vasculature [ 142 ]. Review focuses on the role of 4-HNE and Ox-PLs affecting cell signaling pathways and endothelial barrier dysfunction through modulation of the activities of proteins/enzymes by Michael adducts formation, enhancing the level of protein tyrosine phosphorylation of the target proteins, and by reorganization of cytoskeletal, focal adhesion, and adherens junction proteins [ 197 ]. An overview of molecular mechanisms responsible for the overall chemopreventive effects of sulforaphane (SFN), focusing on the role of 4-HNE in these mechanisms, which may also contribute to its selective cytotoxicity to cancer cells [ 198 ]. Perluigi and Co-workers summarized the role of lipid peroxidation, particularly of 4-HNE-induced protein modification, in neurodegenerative diseases. In this review, the authors also discuss the hypothesis that altered energy metabolism, reduced antioxidant defense, and mitochondrial dysfunction are characteristic hallmarks of neurodegenerative [ 170 ]. Zimniak described the effects of 4-HNE and other endogenous electrophiles on longevity, and its possible molecular mechanisms. The role of electrophiles is discussed, both as destabilizing factors and as signals that induce protective responses [ 199 ]. Reed showed the relationship between lipid peroxidation/4-HNE and neurodegenerative diseases. It also demonstrates how findings in current research support the common themes of altered energy metabolism and mitochondrial dysfunction in neurodegenerative disorders [ 171 ]. Fritz and Petersen summarized the generation of reactive aldehydes via lipid peroxidation resulting in protein carbonylation, and pathophysiologic factors associated with 4-HNE-protein modification. Additionally, an overview of in vitro and in vivo model systems used to study the physiologic impact of protein carbonylation, and an update of the methods commonly used in characterizing protein modification by reactive aldehydes [ 200 ]. Butterfield and Co-workers showed that several important irreversible protein modifications including protein nitration and 4-HNE modification, both which have been extensively investigated in research on the progression of Alzheimer's disease (AD) [ 201 ]. Balogh and Atkins described the cellular effects of 4-HNE, followed by a review of its GST-catalyzed detoxification, with an emphasis on the structural attributes that play an important role in the interactions with alpha-class GSTs. Additionally, a summary of the literature that examines the interplay between GSTs and 4-HNE in model systems relevant to oxidative stress is also discussed to demonstrate the magnitude of importance of GSTs in the overall detoxification scheme [ 202 ]. Like MDA, 4-HNE has high capability of reaction with multiple biomolecules such as proteins or DNA that lead to the formation of adducts [ 49 ]. 4-HNE Production by Enzymatic Processes . 4-HNE is a lipid peroxidation end-product of enzymatic transformation of n -6 PUFAs (AA, linoleic acid, and other) by 15-lipoxygenases (15-LOX). Two different 15-LOX exist, (i) 15-LOX-1 (reticulocyte type) expressed in reticulocytes, eosinophils, and macrophages; (ii) and 15-LOX-2 (epidermis type) expressed in skin,

Cellular senescence, defined as arrest during the cell cycle (G0), is involved in the complex process of the biological aging of tissues, organs, and organisms. Senescence is driven by many factors including oxidative stress, the DNA damage/repair response, inflammation, mitogenic signals, and telomere shortening. Telomeres are considered a “biological clock” of the cell and are shortened by each cell division until a critical length is reached and dysfunction ensues. Rapid telomere shortening may indicate a very high cellular activity. DNA-repair pathways are then recruited and cells enter senescence, losing their capacity to proliferate. In addition to cell division, factors causing telomere shortening include DNA damage, inflammation, and oxidative stress [ 306 ]. Activation of a DNA damage response including formation of DNA damage foci containing activated H2A.X ( γ -histone 2A.X) at either uncapped telomeres or persistent DNA strand breaks is the major trigger of cell senescence. γ H2AX is a sensitive marker of DNA damage, particularly induction of DNA double-strand breaks [ 307 ]. The length of telomeres depends on the telomerase activity and the catalytic subunit of telomerase (hTERT) which is strongly upregulated in most human cancers [ 308 ], and the major consequence of the reactivation of telomerase activity is that tumor cells escape from senescence. The expression of c- myc (an activator) , mad-1 (a repressor) and sp-1 (an activator/repressor), which have been shown to activate hTERT transcription. The formation of 4-HNE-proteins adducts in general increased as a function of age [ 309 ]. Quantitative evaluation showed that the majority of senescent hepatocytes (as measured by γ -H2A.X) were also positive for 4-HNE [ 310 , 311 ]. 4-HNE can induce premature senescence by a direct suppression of telomerase activity affecting the expression of hTERT. In endothelial cells (EC) isolated and cultured from arterial segments of patients with severe coronary artery disease, chronic treatment with an antioxidant (that significantly decreased the levels of lipid peroxidation, that is, 4-HNE expression) N-acetyl-cystein, NAC, significantly delayed cellular senescence via decrease of DNA damage marker ( γ H2AX), decrease of nuclear p53, and increase in hTERT activity [ 312 ]. In three human leukemic cell lines (HL-60, U937, and ML-1) [ 313 ] and in colon cancer cells (Caco-2 and HT-29) [ 314 ], telomerase activity and hTERT expression were downregulated by 4-HNE, as a consequence of downregulation of c- myc mRNA expression and c-Myc DNA binding activity as well as upregulation of mad-1 mRNA expression and Mad-1 DNA binding activity. On the other hand, 4-HNE may induce cellular senescence through activation of critical cell cycle sentinels that mediate this process, such as the tumor suppressor proteins p53 ( see below ), which is well known to play a central role in senescence [ 315 – 320 ]. p53 protects cells of oxidative stress and promotes DNA repair. However, when in the cells the extent of damage overwhelms repair capacities, p53 induces cell death [ 315 – 319 ]. All these data thus confirmed a cell-specific association between senescence and 4-HNE.

Apoptosis is essential programmed cell death process for cells, and its dysregulation results in too little cell death which may contribute to carcinogenesis, or too much cell death which may be a component in the pathogenesis of several diseases. The alternative to apoptosis or programmed cell death is necrosis or nonprogrammed cell death, which is considered to be a toxic process where the cell is a passive victim and follows an energy-independent mode of death. Depending on the cell type, DNA damage/repair capacity or cellular metabolic circumstances 4-HNE can activate proliferative signaling for cell division and promote cell survival or “stop” cell division, and after prolonged arrest, cells die from apoptosis. 4-HNE may induce these processes by modulating several transcription factors sensible to stress such as Nrf2, AP-1, NF- κ B, and PPAR or by modulating several signaling pathways, including MAPK (p38, Erk, and JNK), protein kinase B, protein kinase C isoforms, cell-cycle regulators, receptor tyrosine kinases, and caspases. Depending on 4-HNE concentrations the cells “end” their lives by apoptosis or necrosis. For example, the cytotoxicity of 4-HNE to HepG2 cells was evaluated by MTT assay. 4-HNE concentrations ranging from 10 to 100 μ M gradually decreased cell viability corresponding to an IC 50 value of 53 ± 2.39 μ M. 4-HNE concentrations of 5–40 μ M caused apoptotic cell death (measured by flow cytometry, caspase-3 activation, and PARP cleavage). Finally, a significant increase in necrotic cell population, that is, 31.8% and 55.4%, was observed in cells treated with 80 and 100 μ M of 4-HNE, respectively [ 350 ]. These results show that 4-HNE induces apoptosis at low concentration and necrosis at high concentration. The two main pathways of apoptosis are extrinsic and intrinsic pathways. The extrinsic signaling pathways that initiate apoptosis involve transmembrane receptor-mediated interactions. This pathway is triggered by the binding of death ligands of the tumor necrosis factor (TNF) family to their appropriate death receptors (DRs) on the cell surface; best-characterized ligands and corresponding death receptors include FasL/FasR and TNF- α /TNFR1 [ 351 , 352 ]. The intrinsic signaling pathways that initiate apoptosis involve a diverse array of non-receptor-mediated stimuli. The proapoptotic member of the Bcl-2 family of proteins, such as Bax, permeabilizes the outer mitochondrial membrane. This allows redistribution of cytochrome c from the mitochondrial intermembrane space into the cytoplasm, where it causes activation of caspase proteases and, subsequently, cell death [ 352 , 353 ]. Each apoptosis pathway requires specific triggering signals to begin an energy-dependent cascade of molecular events. Each pathway activates its own initiator caspase (8, 9) which in turn will activate the executioner caspase-3 [ 352 ]. The execution pathway results in characteristic cytomorphological features including cell shrinkage, chromatin condensation, formation of cytoplasmic blebs and apoptotic bodies, and finally phagocytosis of the apoptotic bodies by adjacent parenchymal cells, neoplastic cells or macrophages [ 352 , 353 ]. A multitude of mechanisms are employed by p53 to ensure efficient induction of apoptosis in a stage-, tissue-, and stress-signal-specific manner [ 354 ]. 4-HNE-mediated activation of p53 may be one of the mechanisms responsible for 4-HNE-induced apoptosis reported in many cell types. For example, in SH-SY5Y cells 4-HNE-induced oxidative stress was associated with increased transcriptional and translational expressions of Bax and p53; these events trigger other processes, ending in cell death [ 355 ]. In RPE cells, 4-HNE causes induction, phosphorylation, and nuclear accumulation of p53 which is accompanied with downregulation of MDM2, a negative regulator of the p53 by blocking p53 transcriptional activity directly and mediating in the p53-degradation. Associated proapoptotic genes Bax, p21, and JNK, which are all signaling components p53-mediated pathway of apoptosis, are activated in response to exposure to 4-HNE. The induction of p53 by 4-HNE can be inhibited by the overexpression of either hGSTA4 (in RPE cells) or mGsta4 (in mice) which accelerates disposition of 4-HNE [ 356 ]. In CRL25714 cell, 4-HNE induced dose-dependent increase in the expression of p53 in the cytoplasmic and nuclear compartments and increase in the expression of Bax [ 357 ]. In human osteoarthritic chondrocytes, 4-HNE treatment led to p53 upregulation, caspase-8, -9, and -3 activation, Bcl-2 downregulation, Bax upregulation, cytochrome c-induced release from mitochondria, poly (ADP-ribose) polymerase cleavage, DNA fragmentation, Fas/CD95 upregulation, Akt inhibition, and energy depletion. All these effects were inhibited by an antioxidant, N-acetyl-cysteine [ 358 ]. 4-HNE can induce apoptosis through the death receptor Fas (CD95-)mediated extrinsic pathway as well as through the p53-dependent intrinsi

The use of mammalian model in lipid peroxidation research is ideal for studying the consequences of lipid peroxidation in the context of whole organism and also to analyze their influence on biomarkers to gain more insight into what controls the lipid peroxidation and how lipid peroxidation-related diseases occur. Animal models used to investigate the genetic, physiological, or pathological consequences of lipid peroxidation should try to control the intrinsic and extrinsic influences. Genetic background, diet, environment, and health status can be strictly controlled in many model organisms. Compared with other model organisms, such as worms ( Caenorhabditis elegans ) and flies ( Drosophila melanogaster ), the mammalian model is highly comparable to the human in respect to organ systems, tissues, physiologic systems, and even behavioral traits. Finally, mammalian model in LP can be used as a first step toward possible development of drugs or interventions to control lipid peroxidation process and prevent disease progression in humans. Various mammalian models have been developed to study the lipid peroxidation process. 3.1. Cumene Hydroperoxide-Induced Lipid Peroxidation Cumene hydroperoxide (CH) a catalyst used in chemical and pharmaceutical industry [ 369 ] is a stable organic oxidizing agent with the peroxy function group, –O–O–, which induces lipid peroxidation. On the existence of transition-metal, CH can be reduced to form an alkoxyl radical, which can attack adjacent fatty acid side-chains to produce lipid radical and cumyl alcohol. The resulting lipid radical reacts with oxygen to form a lipid peroxyl radical. And a lipid peroxyl radical reacts with other fatty acid side-chains to produce a new lipid radical and lipid hydroperoxide and this chain reaction continues. These lipid hydroperoxides may undergo transition-metal mediated one-electron reduction and oxygenation to give lipid peroxyl radicals, which trigger exacerbating rounds of free radical-mediated lipid peroxidation ( Figure 7 ). In our lab we have made extensive use of membrane-soluble CH as a model compound for lipid hydroperoxides (LOOH), which are formed in the process of lipid peroxidation during oxidative stress. CH-induced lipid peroxidation in animals has been important to study the effect of lipid peroxidation on protein synthesis through mechanisms that involve regulation of eElongation Factor 2 (eEF2). It is known that eEF2 plays a key role as a cytoplasmic component of the protein synthesis machinery, where it is a fundamental regulatory protein of the translational elongation step that catalyzes the movement of the ribosome along the mRNA. One particularity of eEF2 is that it is quite sensitive to oxidative stress and is specifically affected by compounds that increase lipid peroxidation, such as cumene hydroperoxide (CH) [ 370 – 373 ]. We have previously reported that cytotoxic end-products of lipid peroxidation 4-HNE and MDA are able to form adducts with eEF2 in vitro [ 374 ] and in vivo [ 309 ], demonstrating, for the first time, that this alteration of eEF2 could contribute to decline of protein synthesis, secondary to LP increase. The formation of these peroxide-eEF2-adducts is a possible mechanism responsible of suboptimal hormone production from hypothalamic-hypophysis system (HHS) during oxidative stress and aging [ 375 ]. The protection of eEF2 alterations by end-products of lipid peroxidation must be specifically carried out by compounds with lipoperoxyl radical-scavenging features such as melatonin. We have reported the ability of melatonin to protect against the changes that occur in the eEF2 under conditions of lipid peroxidation induced by CH, as well as decline of protein synthesis rate caused by lipid peroxidation, demonstrating that melatonin can prevent the decrease of several hormones after exposure to LP [ 376 ]. In vitro studies carried out in our lab also indicated that the antioxidants have different capacities to prevent eEF2 loss caused by CH [ 377 , 378 ]. In rat hippocampal neurons and in response to lipid peroxidation induced by exposure to CH, eEF2 subcellular localization, abundance, and interaction with p53 were modified [ 379 ]. Finally, using CH-induced lipid peroxidation, we found that a unique eEF2 posttranslational modified derivative of histidine (H715) known as diphthamide plays a role in the protection of cells against the degradation of eEF2, and it is important to control the translation of IRES-dependent proteins XIAP and FGF2, two proteins that promote cell survival under conditions of oxidative stress [ 380 ]. Other labs have used cumene hydroperoxide as a model compound for lipid hydroperoxides in vivo [ 381 – 385 ].

It is a toxic, carcinogenic organic compound which is used as a general solvent in industrial degreasing operations. It is also used as pesticides and a chemical intermediate in the production of refrigerants. Carbon tetrachloride has been utilized to induce lipid peroxidation in vivo mammalian model [ 90 , 393 – 398 ].

They are essential elements which, under certain conditions, can have prooxidant effect. Redox active transition metals have ability to induce and initiate lipid peroxidation through the production of oxygen radicals, mainly hydroxyl radical, via Fenton's/Haber-Weiss reactions [ 63 , 406 ]. Transition metal, including copper [ 407 – 410 ], chromium [ 411 , 412 ], cadmium [ 413 – 416 ], nickel [ 417 , 418 ], vanadium [ 419 – 421 ], manganese [ 59 , 422 – 424 ], and iron [ 59 , 407 , 425 – 434 ] has been utilized to induce lipid peroxidation in vivo mammalian model.

As conclusion, in this review we summarized the physiological and pathophysiological role of lipid peroxides. When oxidant compounds target lipids, they can initiate the lipid peroxidation process, a chain reaction that produces multiple breakdown molecules, such as MDA and 4-HNE. Among several substrates, proteins and DNA are particularly susceptible to modification caused by these aldehydes. MDA and 4-HNE adducts play a critical role in multiple cellular processes and can participate in secondary deleterious reactions (e.g., crosslinking) by promoting intramolecular or intermolecular protein/DNA crosslinking that may induce profound alteration in the biochemical properties of biomolecules, which may facilitate development of various pathological states. Identification of specific aldehyde-modified molecules has led to the determination of which selective cellular function is altered. For instance, results obtained in our lab suggest that lipid peroxidation affects protein synthesis in all tissues during aging through a mechanism involving the adduct formation of MDA and 4-HNE with elongation factor-2. However, these molecules seem to have a dual behavior, since cell response can tend to enhance survival or promote cell death, depending of their cellular level and the pathway activated by them.