Signaling by 4-hydroxy-2-nonenal: Exposure protocols, target selectivity and degradation

Protein Haptenation and Its Role in Allergy

Humans are exposed to numerous electrophilic chemicals either as medicines, in the workplace, in nature, or through use of many common cosmetic and household products. Covalent modification of human proteins by such chemicals, or protein haptenation, is a common occurrence in cells and may result in generation of antigenic species, leading to development of hypersensitivity reactions. Ranging in severity of symptoms from local cutaneous reactions and rhinitis to potentially life-threatening anaphylaxis and severe hypersensitivity reactions such as Stephen-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN), all these reactions have the same Molecular Initiating Event (MIE), i.e. haptenation. However, not all individuals who are exposed to electrophilic chemicals develop symptoms of hypersensitivity. In the present review, we examine common chemistry behind the haptenation reactions leading to formation of neoantigens. We explore simple reactions involving single molecule additions to a nucleophilic side chain of proteins and complex reactions involving multiple electrophilic centers on a single molecule or involving more than one electrophilic molecule as well as the generation of reactive molecules from the interaction with cellular detoxification mechanisms. Besides generation of antigenic species and enabling activation of the immune system, we explore additional events which result directly from the presence of electrophilic chemicals in cells, including activation of key defense mechanisms and immediate consequences of those reactions, and explore their potential effects. We discuss the factors that work in concert with haptenation leading to the development of hypersensitivity reactions and those that may act to prevent it from developing. We also review the potential harnessing of the specificity of haptenation in the design of potent covalent therapeutic inhibitors.

Lipid Peroxidation-Related Redox Signaling in Osteosarcoma

Oxidative stress and lipid peroxidation play important roles in numerous physiological and pathological processes, while the bioactive products of lipid peroxidation, lipid hydroperoxides and reactive aldehydes, act as important mediators of redox signaling in normal and malignant cells. Many types of cancer, including osteosarcoma, express altered redox signaling pathways. Such redox signaling pathways protect cancer cells from the cytotoxic effects of oxidative stress, thus supporting malignant transformation, and eventually from cytotoxic anticancer therapies associated with oxidative stress. In this review, we aim to explore the status of lipid peroxidation in osteosarcoma and highlight the involvement of lipid peroxidation products in redox signaling pathways, including the involvement of lipid peroxidation in osteosarcoma therapies.

Dihydroartemisinin (DHA) inhibits myofibroblast differentiation through inducing ferroptosis mediated by ferritinophagy

Idiopathic pulmonary fibrosis (IPF) is caused by persistent micro-injuries and aberrant repair processes. Myofibroblast differentiation in lung is a key event for abnormal repair. Dihydroartemisinin(DHA), a well-known anti-malarial drug, have been shown to alleviate pulmonary fibrosis, but its mechanism is not clear. Ferroptosis is involved in the pathgenesis of many diseases, including IPF. Ferritinophagy is a form of cellular autophagy which regulates intracellular iron homeostasis. The function of DHA on myofibroblasts differentiation of pulmonary and whether related with ferroptosis and ferritinophagy are unknown now. Using human fetal lung fibroblast 1(HFL1) cell line and the qRT-PCR, immunofluorescent and Western blotting techniques, we found that after TGF-β1 treatment, the levels of ɑ-SMA expression and ROS increased; the mRNA and protein levels of FTH1 and NCOA4, the content of Fe2+ and 4-HNE increased significantly at 6h, then gradually reduced with time. After DHA treatment, FHL1 cells appeared ferroptosis; the levels of α-SMA mRNA and protein reduced and the levels of ROS and 4-HNE increased; the Fe2+ levels decreased sharply at 6h, then increased with time, and were higher than normal since 24h; the mRNA and protein levels of FTH1 and NCOA4 decreased, exhibited a downward trend. These results show that Fe2+, ROS and lipid peroxidation are involved in and ferritinophagy is inhibited during fibroblast-to-myofibroblast differentiation; The depletion of Fe2+ at early stage induced by DHA treatment triggers the ferritinophagy in HFL1 cells, leading to degradation of FTH1 and NCOA4 and following increase of Fe2+ levels. DHA may inhibit the fibroblast-to-myofibroblast differentiation through inducing ferroptosis mediated by ferritinophagy.

The skin sensitization adverse outcome pathway: exploring the role of mechanistic understanding for higher tier risk assessment

For over a decade, the skin sensitization Adverse Outcome Pathway (AOP) has served as a useful framework for development of novel in chemico and in vitro assays for use in skin sensitization hazard and risk assessment. Since its establishment, the AOP framework further fueled the existing efforts in new assay development and stimulated a plethora of activities with particular focus on validation, reproducibility and interpretation of individual assays and combination of assay outputs for use in hazard/risk assessment. In parallel, research efforts have also accelerated in pace, providing new molecular and dynamic insight into key events leading to sensitization. In light of novel hypotheses emerging from over a decade of focused research effort, mechanistic evidence relating to the key events in the skin sensitization AOP may complement the tools currently used in risk assessment. We reviewed the recent advances unraveling the complexity of molecular events in sensitization and signpost the most promising avenues for further exploration and development of useful assays.

Efficient scavenging of reactive carbonyl species in chloroplasts is required for light acclimation and fitness of plants

Reactive carbonyl species (RCS) derived from lipid peroxides can act as critical damage or signaling mediators downstream of reactive oxygen species by modifying target proteins. However, their biological effects and underlying mechanisms remain largely unknown in plants. Here, we have uncovered the mechanism by which the RCS 4-hydroxy-(E)-2-nonenal (HNE) participates in photosystem II (PSII) repair cycle of chloroplasts, a crucial process for maintaining PSII activity under high and changing light conditions. High Light Sensitive 1 (HLT1) is a potential NADPH-dependent reductase in chloroplasts. Deficiency of HLT1 had no impact on the growth of Arabidopsis plants under normal light conditions but increased sensitivity to high light, which resulted from a defective PSII repair cycle. In hlt1 plants, the accumulation of HNE-modified D1 subunit of PSII was observed, which did not affect D1 degradation but hampered the dimerization of repaired PSII monomers and reassembly of PSII supercomplexes on grana stacks. HLT1 is conserved in all photosynthetic organisms and has functions in overall growth and plant fitness in both Arabidopsis and rice under naturally challenging field conditions. Our work provides the mechanistic basis underlying RCS scavenging in light acclimation and suggests a potential strategy to improve plant productivity by manipulating RCS signaling in chloroplasts.

Nuclear localization of NRF2 in stroma of HER2 positive and triple-negative breast cancer

Breast cancer is one of the leading causes of cancer-related mortality in women. During tumor growth, periods of hypoxia are followed by reoxygenation due to neovascularisation leading to disturbed redox homeostasis. ROS (Reactive Oxygen Species) produced under hypoxia activate HIF1α. ROS can also activate the major antioxidant transcription factor NRF2, but also cause damage to biomolecules. Lipids are susceptible to peroxidation, as evidenced by the formation of reactive aldehydes, among which, HNE (4-hydroxynonenal) is the most studied one. Knowing that HIF1α (Hypoxia Inducing Factor 1α) is associated with breast cancer malignancy, we aimed to investigate its correlation with HNE and NRF2 (Nuclear factor erythroid 2-related factor 2). Our results show that HIF1α is activated in breast cancer, indicating an increase in ROS but not followed by HNE production. On the other hand, NRF2 was increased in all types of breast cancer suggesting that oxidative stress is present in these pathologies, but also supporting HIF1α. Interestingly, NRF2 was activated in HER2 positive and TNBC, indicating the role of stromal NRF2 in breast cancer malignancy.

The 4-Hydroxynonenal–Protein Adducts and Their Biological Relevance: Are Some Proteins Preferred Targets?

It is well known that oxidative stress and lipid peroxidation (LPO) play a role in physiology and pathology. The most studied LPO product with pleiotropic capabilities is 4-hydroxynonenal (4-HNE). It is considered as an important mediator of cellular signaling processes and a second messenger of reactive oxygen species. The effects of 4-HNE are mainly attributed to its adduction with proteins. Whereas the Michael adducts thus formed are preferred in an order of potency of cysteine > histidine > lysine over Schiff base formation, it is not known which proteins are the preferred targets for 4-HNE under what physiological or pathological conditions. In this review, we briefly discuss the methods used to identify 4-HNE–protein adducts, the progress of mass spectrometry in deciphering the specific protein targets, and their biological relevance, focusing on the role of 4-HNE protein adducts in the adaptive response through modulation of the NRF2/KEAP1 pathway and ferroptosis.

Mn(III) Porphyrin, MnTnBuOE-2-PyP5+, Commonly Known as a Mimic of Superoxide Dismutase Enzyme, Protects Cardiomyocytes from Hypoxia/Reoxygenation Induced Injury via Reducing Oxidative Stress

Myocardial ischemia-reperfusion injury (I/R) causes damage to cardiomyocytes through oxidative stress and apoptosis. We investigated the cardioprotective effects of MnTnBuOE-2-PyP5+ (BMX-001), a superoxide dismutase mimic, in an in vitro model of I/R injury in H9c2 cardiomyocytes. We found that BMX-001 protected against hypoxia/reoxygenation (H/R)-induced oxidative stress, as evident by a significant reduction in intracellular and mitochondrial superoxide levels. BMX-001 pre-treatment also reduced H/R-induced cardiomyocyte apoptosis, as marked by a reduction in TUNEL-positive cells. We further demonstrated that BMX-001 pre-treatment significantly improved mitochondrial function, particularly O2 consumption, in mouse adult cardiomyocytes subjected to H/R. BMX-001 treatment also attenuated cardiolipin peroxidation, 4-hydroxynonenal (4-HNE) level, and 4-HNE adducted proteins following H/R injury. Finally, the pre-treatment with BMX-001 improved cell viability and lactate dehydrogenase (LDH) activity in H9c2 cells following H/R injury. Our findings suggest that BMX-001 has therapeutic potential as a cardioprotective agent against oxidative stress-induced H/R damage in H9c2 cardiomyocytes.

Hsp70.1 carbonylation induces lysosomal cell death for lifestyle-related diseases

Alzheimer's disease, type 2 diabetes, and non-alcoholic steatohepatitis (NASH) constitute increasingly prevalent disorders. Individuals with type 2 diabetes are well-known to be susceptible to Alzheimer's disease. Although the pathogenesis of each disorder is multifactorial and the causal relation remains poorly understood, reactive oxygen species (ROS)-induced lipid and protein oxidation conceivably plays a common role. Lipid peroxidation product was recently reported to be a key factor also for non-alcoholic steatohepatitis, because of inducing hepatocyte degeneration/death. Here, we focus on implication of the representative lipid-peroxidation product 'hydroxynonenal' for the cell degeneration/death of brain, pancreas, and liver. Since Hsp70.1 has dual roles as a chaperone and lysosomal membrane stabilizer, hydroxynonenal-mediated oxidative injury (carbonylation) of Hsp70.1 was highlighted. After intake of high-fat diets, oxidation of free fatty acids in mitochondria generates ROS which enhance oxidation of ω-6 polyunsaturated fatty acids (PUFA) involved within biomembranes and generate hydroxynonenal. In addition, hydroxynonenal is generated during cooking deep-fried foods with vegetable oils especially containing linoleic acids. These intrinsic and exogenous hydroxynonenal synergically causes an increase in its serum and organ levels to induce Hsp70.1 oxidation. As it is amphiphilic; being water-soluble but displays strong lipophilic characteristics, hydroxynonenal can diffuse within the cells and react with targets like senile and/or atheromatous plaques outside the cells. Hydroxynonenal can deepen and expand lysosomal injuries by facilitating 'calpain-mediated cleavage of the carbonylated Hsp70.1'. Despite the unique anatomical, physiological, and biochemical characteristics of each organ for its specific disease, there should be a common cascade of the cell degeneration/death which is caused by hydroxynonenal. This review aims to implicate hydroxynonenal-mediated Hsp70.1 carbonylation for lysosomal membrane permeabilization/rupture and the resultant cathepsin leakage for inducing cell degeneration/death. Given the tremendous number of worldwide people suffering various lifestyle-related diseases, it is valuable to consider how ω-6 PUFA-rich vegetable oils is implicated for the organ disorder.

Investigation of the Captopril-Insulin Interaction by Mass Spectrometry and Computational Approaches Reveals that Captopril Induces Structural Changes in Insulin

Post-translational modifications remarkably regulate proteins' biological function. Small molecules such as reactive thiols, metabolites, and drugs may covalently modify the proteins and cause structural changes. This study reports the covalent modification and noncovalent interaction of insulin and captopril, an FDA-approved antihypertensive drug, through mass spectrometric and computation-based approaches. Mass spectrometric analysis shows that captopril modifies intact insulin, reduces it into its "A" and "B" chains, and covalently modifies them by forming adducts. Since captopril has a reactive thiol group, it might reduce the insulin dimer or modify it by reacting with cysteine residues. This was proven with dithiothreitol treatment, which reduced the abundance of captopril adducts of insulin A and B chains and intact Insulin. Liquid chromatography tandem mass spectrometric analysis identified the modification of a total of four cysteine residues, two in each of the A and B chains of insulin. These modifications were identified to be Cys6 and Cys7 of the A chain and Cys7 and Cys19 of the B chain. Mass spectrometric analysis indicated that captopril may simultaneously modify the cysteine residues of intact insulin or its subunits A and B chains. Biophysical studies involving light scattering and thioflavin T assay suggested that the binding of captopril to the protein leads to the formation of aggregates. Docking and molecular dynamics studies provided insights into the noncovalent interactions and associated structural changes in insulin. This work is a maiden attempt to understand the detailed molecular interactions between captopril and insulin. These findings suggest that further investigations are required to understand the long-term effect of drugs like captopril.

Upregulation of the TFEB-mediated lysosome function relieves 4-Hydroxynonenal-Induced apoptosis

4-Hydroxynonenal (4-HNE), the most toxic end-product of lipid peroxidation formed during oxidative stress, has been implicated in many diseases including neurodegenerative diseases, metabolic diseases, myocardial diseases, cancer and age-related diseases. 4-HNE can actively react with DNA, proteins and lipids, causing rapid cell death. The accumulation of 4-HNE leads to induction of autophagy, which clears damaged proteins and organelles. However, the underlying mechanism of 4-HNE-regulated autophagy is still not known. Transcriptional factor EB (TFEB) is a master regulator of lysosomal and autophagic functions, which we show here that TFEB is activated by 4-HNE. 4-HNE induces TFEB nuclear translocation and activated TFEB then upregulates the expression of genes required for autophagic and lysosomal biogenesis and function. Reactive oxygen species and Ca²⁺ are required in this process and TFEB activity is required for 4-HNE-mediated lysosomal function. Most importantly, genetic inhibition of TFEB (TFEB-KO) exacerbates 4-HNE-induced cell death, suggesting that TFEB is essential for cellular adaptive response to 4-HNE-induced cell damage. Hence, targeting TFEB to promote autophagic and lysosomal function may represent a promising approach to treat neurodegenerative and metabolic diseases in which 4-HNE accumulation has been implicated.

Role and Posttranslational Regulation of Cx46 Hemichannels and Gap Junction Channels in the Eye Lens

Connexins are a family of proteins that can form two distinct types of channels: hemichannels and gap junction channels. Hemichannels are composed of six connexin subunits and when open allow for exchanges between the cytoplasm and the extracellular milieu. Gap junction channels are formed by head-to-head docking of two hemichannels in series, each one from one of two adjacent cells. These channels allow for exchanges between the cytoplasms of contacting cells. The lens is a transparent structure located in the eye that focuses light on the retina. The transparency of the lens depends on its lack of blood irrigation and the absence of organelles in its cells. To survive such complex metabolic scenario, lens cells express Cx43, Cx46 and Cx50, three connexins isoforms that form hemichannels and gap junction channels that allow for metabolic cooperation between lens cells. This review focuses on the roles of Cx46 hemichannels and gap junction channels in the lens under physiological conditions and in the formation of cataracts, with emphasis on the modulation by posttranslational modifications.

The role of endogenous versus exogenous sources in the exposome of putative genotoxins and consequences for risk assessment

The “totality” of the human exposure is conceived to encompass life-associated endogenous and exogenous aggregate exposures. Process-related contaminants (PRCs) are not only formed in foods by heat processing, but also occur endogenously in the organism as physiological components of energy metabolism, potentially also generated by the human microbiome. To arrive at a comprehensive risk assessment, it is necessary to understand the contribution of in vivo background occurrence as compared to the ingestion from exogenous sources. Hence, this review provides an overview of the knowledge on the contribution of endogenous exposure to the overall exposure to putative genotoxic food contaminants, namely ethanol, acetaldehyde, formaldehyde, acrylamide, acrolein, α,β-unsaturated alkenals, glycation compounds, N-nitroso compounds, ethylene oxide, furans, 2- and 3-MCPD, and glycidyl esters. The evidence discussed herein allows to conclude that endogenous formation of some contaminants appears to contribute substantially to the exposome. This is of critical importance for risk assessment in the cases where endogenous exposure is suspected to outweigh the exogenous one (e.g. formaldehyde and acrolein).

Apoptotic mechanism in human brain microvascular endothelial cells triggered by 4'-iodo-α-pyrrolidinononanophenone: Contribution of decrease in antioxidant properties

In this study, we newly synthesized four α-pyrrolidinononanophenone (α-PNP) derivatives [4'-halogenated derivatives and α-pyrrolidinodecanophenone (α-PDP)], and then performed the structure-cytotoxicity relationship analyses. The results showed the rank order for the cytotoxic effects, α-PNP < α-PDP < 4'-fluoro-α-PNP < 4'-chrolo-α-PNP < 4'-bromo-α-PNP < 4'-iodo-α-PNP (I-α-PNP), and suggest that cytotoxicities of 4'-halogenated derivatives were more intensive than that of elongation of the hydrocarbon chain (α-PDP). We also surveyed the apoptotic mechanism of I-α-PNP in brain microvascular endothelial (HBME) cells that are utilized as the in vitro model of the blood-brain barrier. HBME cell treatment with I-α-PNP facilitated the apoptotic events (caspase-3 activation, externalization of phosphatidylserine, and DNA fragmentation), which were almost completely abolished by pretreating with antioxidants. In addition, the immunofluorescent staining revealed the enhanced production of hydroxyl radical in mitochondria by the I-α-PNP treatment, inferring that the I-α-PNP treatment triggers the apoptotic mechanism dependent on the enhanced ROS production in mitochondria. The treatment with I-α-PNP increased the production of cytotoxic aldehyde 4-hydroxy-2-nonenal and decreased the amount of reduced glutathione. Additionally, the treatment decreased the 26S proteasome-based proteolytic activities and aggresome formation. These results suggest that decrease in the antioxidant properties is also ascribable to HBME cell apoptosis elicited by I-α-PNP.

Chemistry and Biochemistry Aspects of the 4-Hydroxy-2,3-trans-nonenal

4-hydroxy-2,3-trans-nonenal (C₉H₁₆O₂), also known as 4-hydroxy-2E-nonenal (C₉H₁₆O₂; HNE) is an α,β-unsaturated hydroxyalkenal. HNE is a major aldehyde, formed in the peroxidation process of ω-6 polyunsaturated fatty acids (ω-6 PUFAs), such as linoleic and arachidonic acid. HNE is not only harmful but also beneficial. In the 1980s, the HNE was regarded as a “toxic product of lipid peroxidation” and the “second toxic messenger of free radicals”. However, already at the beginning of the 21st century, HNE was perceived as a reliable marker of oxidative stress, growth modulating factor and signaling molecule. Many literature data also indicate that an elevated level of HNE in blood plasma and cells of the animal and human body is observed in the course of many diseases, including cancer. On the other hand, it is currently proven that cancer cells divert to apoptosis if they are exposed to supraphysiological levels of HNE in the cancer microenvironment. In this review, we briefly summarize the current knowledge about the biological properties of HNE.

The interplay among oxidative stress, brain insulin resistance and AMPK dysfunction contribute to neurodegeneration in type 2 diabetes and Alzheimer disease

Alzheimer's disease (AD) is the most common form of dementia in the elderly followed by vascular dementia. In addition to clinically diagnosed dementia, cognitive dysfunction has been reported in diabetic patients. Recent studies are now beginning to recognize type 2 diabetes mellitus (T2DM), characterized by chronic hyperglycemia and insulin resistance, as a risk factor for AD and other cognitive disorders. While studies on insulin action have remained traditionally in the domain of peripheral tissues, the detrimental effects of insulin resistance in the central nervous system on cognitive dysfunction are increasingly being reported in recent clinical and preclinical studies. Brain functions require continuous supply of glucose and oxygen and a tight regulation of metabolic processes. Loss of this metabolic regulation has been proposed to be a contributor to memory dysfunction associated with neurodegeneration. Within the above scenario, this review will focus on the interplay among oxidative stress (OS), insulin resistance and AMPK dysfunctions in the brain by highlighting how these neurotoxic events contribute to neurodegeneration. We provide an overview on the detrimental effects of OS on proteins regulating insulin signaling and how these alterations impact cell metabolic dysfunctions through AMPK dysregulation. Such processes, we assert, are critically involved in the molecular pathways that underlie AD.

Variant Aldehyde Dehydrogenase 2 (ALDH2*2) as a Risk Factor for Mechanical LA Substrate Formation and Atrial Fibrillation with Modest Alcohol Consumption in Ethnic Asians

Aldehyde dehydrogenase 2 (ALDH2) rs671 polymorphism is a common genetic variant in Asians that is responsible for defective toxic aldehyde and lipid peroxidation metabolism after alcohol consumption. The extent to which low alcohol consumption may cause atrial substrates to trigger atrial fibrillation (AF) development in users with ALDH2 variants remains to be determined. We prospectively enrolled 249 ethnic Asians, including 56 non-drinkers and 193 habitual drinkers (135 (70%) as ALDH2 wild-type: GG, rs671; 58 (30%) as ALDH2 variants: G/A or A/A, rs671). Novel left atrial (LA) mechanical substrates with dynamic characteristics were assessed using a speckle-tracking algorithm and correlated to daily alcohol consumption and ALDH2 genotypes. Despite modest and comparable alcohol consumption by the habitual alcohol users (14.3 [8.3~28.6] and 12.3 [6.3~30.7] g/day for those without and with ALDH2 polymorphism, p = 0.31), there was a substantial and graded increase in the 4-HNE adduct and prolonged PR, and a reduction in novel LA mechanical parameters (including peak atrial longitudinal strain (PALS) and phasic strain rates (reservoir, conduit, and booster pump functions), p < 0.05), rather than an LA emptying fraction (LAEF) or LA volume index across non-drinkers, and in habitual drinkers without and with ALDH2 polymorphism (all p < 0.05). The presence of ALDH2 polymorphism worsened the association between increasing daily alcohol dose and LAEF, PALS, and phasic reservoir and booster functions (all P_interaction: <0.05). Binge drinking superimposed on regular alcohol use exclusively further worsened LA booster pump function compared to regular drinking without binge use (1.66 ± 0.57 vs. 1.97 ± 0.56 1/s, p = 0.001). Impaired LA booster function further independently helped to predict AF after consideration of the CHARGE-AF score (adjusted 1.68 (95% CI: 1.06–2.67), p = 0.028, per 1 z-score increment). Habitual modest alcohol consumption led to mechanical LA substrate formation in an ethnic Asian population, which was more pronounced in subjects harboring ALDH2 variants. Impaired LA booster functions may serve as a useful predictor of AF in such populations.

Oxidative Modification of Proteins: From Damage to Catalysis, Signaling, and Beyond

Significance: The systematic investigation of oxidative modification of proteins by reactive oxygen species started in 1980. Later, it was shown that reactive nitrogen species could also modify proteins. Some protein oxidative modifications promote loss of protein function, cleavage or aggregation, and some result in proteo-toxicity and cellular homeostasis disruption. Recent Advances: Previously, protein oxidation was associated exclusively to damage. However, not all oxidative modifications are necessarily associated with damage, as with Met and Cys protein residue oxidation. In these cases, redox state changes can alter protein structure, catalytic function, and signaling processes in response to metabolic and/or environmental alterations. This review aims to integrate the present knowledge on redox modifications of proteins with their fate and role in redox signaling and human pathological conditions. Critical Issues: It is hypothesized that protein oxidation participates in the development and progression of many pathological conditions. However, no quantitative data have been correlated with specific oxidized proteins or the progression or severity of pathological conditions. Hence, the comprehension of the mechanisms underlying these modifications, their importance in human pathologies, and the fate of the modified proteins is of clinical relevance. Future Directions: We discuss new tools to cope with protein oxidation and suggest new approaches for integrating knowledge about protein oxidation and redox processes with human pathophysiological conditions. Antioxid. Redox Signal. 35, 1016-1080.

Involvement of 4-hydroxy-2-nonenal in the pathogenesis of pulmonary fibrosis

Pulmonary fibrosis is a chronic progressive disease with high incidence, prevalence, and mortality rates worldwide. It is characterized by excessive accumulation of extracellular matrix in the lung parenchyma. The cellular and molecular mechanisms involved in its pathogenesis are complex, and some are still unknown. Several studies indicate that oxidative stress, characterized by overproduction of 4-hydroxy-2-nonenal (4-HNE), is an important player in pulmonary fibrosis. 4-HNE is a highly reactive compound derived from polyunsaturated fatty acids that can react with proteins, phospholipids, and nucleic acids. Thus, many of the altered cellular mechanisms that contribute to this disease can be explained by the participation of 4-HNE. Here, we summarize the current knowledge on the molecular states and signal transduction pathways that contribute to the pathogenesis of pulmonary fibrosis. Furthermore, we describe the participation of 4-HNE in various mechanisms involved in pulmonary fibrosis development, with a focus on the cell populations involved in the initiation, development, and maintenance of the fibrotic process, mainly alveolar cells, endothelial cells, macrophages, and inflammatory cells. Due to its characteristic activity as a second messenger, 4-HNE, in addition to being a consequence of oxidative stress, can support maintenance of the inflammatory and fibrotic process by spreading the effects of reactive oxygen species (ROS). Thus, regulation of 4-HNE levels could be a viable strategy to reduce its effects on the mechanisms involved in pulmonary fibrosis development.

4-Hydroxy-2-nonenal antimicrobial toxicity is neutralized by an intracellular pathogen

Pathogens encounter numerous antimicrobial responses during infection, including the reactive oxygen species (ROS) burst. ROS-mediated oxidation of host membrane poly-unsaturated fatty acids (PUFAs) generates the toxic alpha-beta carbonyl 4-hydroxy-2-nonenal (4-HNE). Although studied extensively in the context of sterile inflammation, research into 4-HNE’s role during infection remains limited. Here, we found that 4-HNE is generated during bacterial infection, that it impacts growth and survival in a range of bacteria, and that the intracellular pathogen Listeria monocytogenes induces many genes in response to 4-HNE exposure. A component of the L. monocytogenes 4-HNE response is the expression of the genes lmo0103 and lmo0613, deemed rha1 and rha2 (reductase of host alkenals), respectively, which code for two NADPH-dependent oxidoreductases that convert 4-HNE to the product 4-hydroxynonanal (4-HNA). Loss of these genes had no impact on L. monocytogenes bacterial burdens during murine or tissue culture infection. However, heterologous expression of rha1/2 in Bacillus subtilis significantly increased bacterial resistance to 4-HNE in vitro and promoted bacterial survival following phagocytosis by murine macrophages in an ROS-dependent manner. Thus, Rha1 and Rha2 are not necessary for 4-HNE resistance in L. monocytogenes but are sufficient to confer resistance to an otherwise sensitive organism in vitro and in host cells. Our work demonstrates that 4-HNE is a previously unappreciated component of ROS-mediated toxicity encountered by bacteria within eukaryotic hosts.

Lipid peroxidation derived reactive carbonyl species in free and conjugated forms as an index of lipid peroxidation: limits and perspectives

Reactive carbonyl species (RCS) formed by lipidperoxidation as free forms or as enzymatic and non-enzymatic conjugates are widely used as an index of oxidative stress. Besides general measurements based on derivatizing reactions, more selective and sensitive MS based analyses have been proposed in the last decade. Untargeted and targeted methods for the measurement of free RCS and adducts have been described and their applications to in vitro and ex vivo samples have permitted the identification of many biological targets, reaction mechanisms and adducted moieties with a particular relevance to RCS protein adducts. The growing interest in protein carbonylation can be explained by considering that protein adducts are now recognized as being involved in the damaging action of oxidative stress so that their measurement is performed not only to obtain an index of lipid peroxidation but also to gain a deeper insight into the molecular mechanisms of oxidative stress. The aim of the review is to discuss the most novel analytical approaches and their application for profiling reactive carbonyl species and their enzymatic and non-enzymatic metabolites as an index of lipid-oxidation and oxidative stress. Limits and perspectives will be discussed.

A role for aldehyde dehydrogenase (ALDH) 2 in angiotensin II-mediated decrease in angiogenesis of coronary endothelial cells

Diabetes-induced coronary endothelial cell (CEC) dysfunction contributes to diabetic heart diseases. Angiotensin II (Ang II), a vasoactive hormone, is upregulated in diabetes, and is reported to increase oxidative stress in CECs. 4-hydroxy-2-nonenal (4HNE), a key lipid peroxidation product, causes cellular dysfunction by forming adducts with proteins. By detoxifying 4HNE, aldehyde dehydrogenase (ALDH) 2 reduces 4HNE mediated proteotoxicity and confers cytoprotection. Thus, we hypothesize that ALDH2 improves Ang II-mediated defective CEC angiogenesis by decreasing 4HNE-mediated cytotoxicity. To test our hypothesis, we treated the cultured mouse CECs (MCECs) with Ang II (0.1, 1 and 10 μM) for 2, 4 and 6 h. Next, we treated MCECs with Alda-1 (10 μM), an ALDH2 activator or disulfiram (2.5 μM)/ALDH2 siRNA (1.25 nM), the ALDH2 inhibitors, or blockers of angiotensin II type-1 and 2 receptors i.e. Losartan and PD0123319 respectively before challenging MCECs with 10 μM Ang II. We found that 10 μM Ang II decreased tube formation in MCECs with in vitro angiogenesis assay (P < .0005 vs control). 10 μM Ang II downregulated the levels of vascular endothelial growth factor receptor 1 (VEGFR1) (p < .005 for mRNA and P < .05 for protein) and VEGFR2 (p < .05 for mRNA and P < .005 for protein) as well as upregulated the levels of angiotensin II type-2 receptor (AT2R) (p < .05 for mRNA and P < .005 for protein) and 4HNE-adducts (P < .05 for protein) in cultured MCECs, compared to controls. ALDH2 inhibition with disulfiram/ALDH2 siRNA exacerbated 10 μM Ang II-induced decrease in coronary angiogenesis (P < .005) by decreasing the levels of VEGFR1 (P < .005 for mRNA and P < .05 for protein) and VEGFR2 (P < .05 for both mRNA and protein) and increasing the levels of AT2R (P < .05 for both mRNA and protein) and 4HNE-adducts (P < .05 for protein) relative to Ang II alone. AT2R inhibition per se improved angiogenesis in MCECs. Additionally, enhancing ALDH2 activity with Alda 1 rescued Ang II-induced decrease in angiogenesis by increasing the levels of VEGFR1, VEGFR2 and decreasing the levels of AT2R. In summary, ALDH2 can be an important target in reducing 4HNE-induced proteotoxicity and improving angiogenesis in MCECs. Finally, we conclude ALDH2 activation can be a therapeutic strategy to improve coronary angiogenesis to ameliorate cardiometabolic diseases.

Cell line-dependent difference in glutathione levels affects the cigarette sidestream smoke-induced inhibition of nucleotide excision repair

We recently reported that cigarette sidestream smoke (CSS) induced inhibition of nucleotide excision repair (NER) and the cause was NER molecule degradation by aldehydes contained in CSS [Carcinogenesis39, 56-65, 2018; Mutat. Res.834, 42-50, 2018]. In this study, we examined the relationship between intracellular glutathione (GSH) levels and CSS-induced NER inhibition. CSS treatment decreased the intracellular GSH level in human keratinocytes HaCaT, in which the repair of pyrimidine (6-4) pyrimidone photoproducts (6-4PPs) after UVB irradiation was suppressed. We used l-buthionine-(S,R)-sulfoximine (BSO) to artificially deplete intracellular GSH level. BSO treatment remarkably accelerated the CSS-induced NER inhibition. The NER inhibition by CSS was attributed to the delay of accumulation of NER molecules (TFIIH and XPG) to DNA damaged sites, which was further enhanced by BSO treatment. CSS degraded TFIIH, and BSO promoted it as expected. Formaldehyde (FA), a major constituent of CSS, showed similar intracellular GSH reduction and NER inhibition, and BSO promoted its inhibitory effect. Five cultured cell lines showed considerable variability in intrinsic GSH levels, and CSS-induced NER inhibitory effect was significantly correlated with the GSH levels. Chemicals like aldehydes are known to react not only with proteins but also with DNA, causing DNA lesions targeted by NER. Our results suggest that the tissues and cells with low intrinsic GSH levels are susceptible to treatment with CSS and electrophilic compounds like aldehydes through NER inhibition, thus leading to higher genotoxicity and carcinogenicity.

The relevance of pathophysiological alterations in redox signaling of 4-hydroxynonenal for pharmacological therapies of major stress-associated diseases

Modern analytical methods combined with the modern concepts of redox signaling revealed 4-hydroxy-2-nonenal (4-HNE) as particular growth regulating factor involved in redox signaling under physiological and pathophysiological circumstances. In this review current knowledge of the relevance of 4-HNE as "the second messenger of reactive oxygen species" (ROS) in redox signaling of representative major stress-associated diseases is briefly summarized. The findings presented allow for 4-HNE to be considered not only as second messenger of ROS, but also as one of fundamental factors of the stress- and age-associated diseases. While standard, even modern concepts of molecular medicine and respective therapies in majority of these diseases target mostly the disease-specific symptoms. 4-HNE, especially its protein adducts, might appear to be the bioactive markers that would allow better monitoring of specific pathophysiological processes reflecting their complexity. Eventually that could help development of advanced integrative medicine approach for patients and the diseases they suffer from on the personalized basis implementing biomedical remedies that would optimize beneficial effects of ROS and 4-HNE to prevent the onset and progression of the illness, perhaps even providing the real cure.

4-Hydroxynonenal induces Cx46 hemichannel inhibition through its carbonylation

Hemichannels formed by connexins mediate the exchange of ions and signaling molecules between the cytoplasm and the extracellular milieu. Under physiological conditions hemichannels have a low open probability, but in certain pathologies their open probability increases, which can result in cell damage. Pathological conditions are characterized by the production of a number of proinflammatory molecules, including 4-hydroxynonenal (4-HNE), one of the most common lipid peroxides produced in response to inflammation and oxidative stress. The aim of this work was to evaluate whether 4-HNE modulates the activity of Cx46 hemichannels. We found that 4-HNE (100 μM) reduced the rate of 4',6-diamino-2-fenilindol (DAPI) uptake through hemichannels formed by recombinant human Cx46 fused to green fluorescent protein, an inhibition that was reversed partially by 10 mM dithiothreitol. Immunoblot analysis showed that the recombinant Cx46 expressed in HeLa cells becomes carbonylated after exposure to 4-HNE, and that 10 mM dithiothreitol reduced its carbonylation. We also found that Cx46 was carbonylated by 4-HNE in the lens of a selenite-induced cataract animal model. The exposure to 100 μM 4-HNE decreased hemichannel currents formed by recombinant rat Cx46 in Xenopus laevis oocytes. This inhibition also occurred in a mutant expressing only the extracellular loop cysteines, suggesting that other Cys are not responsible for the hemichannel inhibition by carbonylation. This work demonstrates for the first time that Cx46 is post-translationally modified by a lipid peroxide and that this modification reduces Cx46 hemichannel activity.

Investigating DNA adduct formation by flavor chemicals and tobacco byproducts in electronic nicotine delivery system (ENDS) using in silico approaches

The presence of flavors is one of the commonly cited reasons for use of e-cigarettes by youth; however, the potential harms from inhaling these chemicals and byproducts have not been extensively studied. One mechanism of interest is DNA adduct formation, which may lead to carcinogenesis. We identified two chemical classes of flavors found in tobacco products and byproducts, alkenylbenzenes and aldehydes, documented to form DNA adducts. Using in silico toxicology approaches, we identified structural analogs to these chemicals without DNA adduct information. We conducted a structural similarity analysis and also generated in silico model predictions of these chemicals for genotoxicity, mutagenicity, carcinogenicity, and skin sensitization. The empirical and in silico data were compared, and we identified strengths and limitations of these models. Good concordance (80-100%) was observed between DNA adduct formation and models predicting mammalian mutagenicity (mouse lymphoma sassy L5178Y) and skin sensitization for both chemical classes. On the other hand, different prediction profiles were observed for the two chemical classes for the modeled endpoints, unscheduled DNA synthesis and bacterial mutagenicity. These results are likely due to the different mode of action between the two chemical classes, as aldehydes are direct acting agents, while alkenylbenzenes require bioactivation to form electrophilic intermediates, which form DNA adducts. The results of this study suggest that an in silico prediction for the mouse lymphoma assay L5178Y, may serve as a surrogate endpoint to help predict DNA adduct formation for chemicals found in tobacco products such as flavors and byproducts.

Chronic Oxidative Stress Promotes Molecular Changes Associated with Epithelial Mesenchymal Transition, NRF2, and Breast Cancer Stem Cell Phenotype

Oxidative stress plays a role in carcinogenesis, but it also contributes to the modulation of tumor cells and microenvironment caused by chemotherapeutics. One of the consequences of oxidative stress is lipid peroxidation, which can, through reactive aldehydes such as 4-hydroxy-2-nonenal (HNE), affect cell signaling pathways. On the other hand, cancer stem cells (CSC) are now recognized as a major factor of malignancy by causing metastasis, relapse, and therapy resistance. Here, we evaluated whether oxidative stress and HNE modulation of the microenvironment can influence CSC growth, modifications of the epithelial to mesenchymal transition (EMT) markers, the antioxidant system, and the frequency of breast cancer stem cells (BCSC). Our results showed that oxidative changes in the microenvironment of BCSC and particularly chronic oxidative stress caused changes in the proliferation and growth of breast cancer cells. In addition, changes associated with EMT, increase in glutathione (GSH) and Nuclear factor erythroid 2-related factor 2 (NRF2) were observed in breast cancer cells grown on HNE pretreated collagen and under chronic oxidative stress. Our results suggest that chronic oxidative stress can be a bidirectional modulator of BCSC fate. Low levels of HNE can increase differentiation markers in BCSC, while higher levels increased GSH and NRF2 as well as certain EMT markers, thereby increasing therapy resistance.

Cell-based assays that predict in vivo neurotoxicity of urban ambient nano-sized particulate matter

Exposure to urban ambient particulate matter (PM) is associated with risk of Alzheimer's disease and accelerated cognitive decline in normal aging. Assessment of the neurotoxic effects caused by urban PM is complicated by variations of composition from source, location, and season. We compared several in vitro cell-based assays in relation to their in vivo neurotoxicity for NF-κB transcriptional activation, nitric oxide induction, and lipid peroxidation. These studies compared batches of nPM, a nanosized subfraction of PM2.5, extracted as an aqueous suspension, used in prior studies. In vitro activities were compared with in vivo responses of mice chronically exposed to the same batch of nPM. The potency of nPM varied widely between batches for NF-κB activation, analyzed with an NF-κB reporter in human monocytes. Three independently collected batches of nPM had corresponding differences to responses of mouse cerebral cortex to chronic nPM inhalation, for levels of induction of pro-inflammatory cytokines, microglial activation (Iba1), and soluble Aβ40 & -42 peptides. The in vitro responses of BV2 microglia for NO-production and lipid peroxidation also differed by nPM batch, but did not correlate with in vivo responses. These data confirm that batches of nPM can differ widely in toxicity. The in vitro NF-κB reporter assay offers a simple, high throughput screening method to predict the in vivo neurotoxic effects of nPM exposure.

4-Hydroxy-Trans-2-Nonenal in the Regulation of Anti-Oxidative and Pro-Inflammatory Signaling Pathways

Recent studies indicate that 4-hydroxy-trans-2-nonenal (HNE), a major oxidative stress triggered lipid peroxidation-derived aldehyde, plays a critical role in the pathophysiology of various human pathologies including metabolic syndrome, diabetes, cardiovascular, neurological, immunological, and age-related diseases and various types of cancer. HNE is the most abundant and toxic α, β-unsaturated aldehyde formed during the peroxidation of polyunsaturated fatty acids in a series of free radical-mediated reactions. The presence of an aldehyde group at C1, a double bond between C2 and C3 and a hydroxyl group at C4 makes HNE a highly reactive molecule. These strong reactive electrophilic groups favor the formation of HNE adducts with cellular macromolecules such as proteins and nucleic acids leading to the regulation of various cell signaling pathways and processes involved in cell proliferation, differentiation, and apoptosis. Many studies suggest that the cell-specific intracellular concentrations of HNE dictate the anti-oxidative and pro-inflammatory activities of this important molecule. In this review, we focused on how HNE could alter multiple anti-oxidative defense pathways and pro-inflammatory cytotoxic pathways by interacting with various cell-signaling intermediates.

Pathophysiological roles of autophagy and aldo-keto reductases in development of doxorubicin resistance in gastrointestinal cancer cells

Here, we show that incubation of three human gastrointestinal cancer cell lines (HCT15, LoVo and MKN45) with doxorubicin (DOX) provokes autophagy through facilitating production of reactive oxygen species (ROS). HCT15 cell treatment with DOX resulted in up-regulation of Beclin1, down-regulation of Bcl2, activation of AMPK and JNK, and Akt inactivation, all of which were restored by pretreating with an antioxidant N-acetyl-l-cysteine. These data suggest that all the autophagy-related alterations evoked by DOX result from the ROS production. In the DOX-resistant cancer cells, degree of autophagy elicited by DOX was milder than the parental cells, and DOX treatment hardly activated the ROS-dependent apoptotic signals [formation of 4-hydroxy-2-nonenal (HNE), cytochrome-c release into cytosol, and activation of JNK and caspase-3], inferring an inverse correlation between cellular antioxidant capacity and autophagy induction by DOX. Monitoring of expression levels of aldo-keto reductases (AKRs) in the parental and DOX-resistant cells revealed an up-regulation of AKR1B10 and/or AKR1C3 with acquiring the DOX resistance. Knockdown and inhibition of AKR1B10 or AKR1C3 in these cells enhanced DOX-elicited autophagy. Measurement of DOX-reductase activity and HNE-sensitivity assay also suggested that both AKR1B10 (via high HNE-reductase activity) and AKR1C3 (via low HNE-reductase and DOX-reductase activities) are involved in the development of DOX resistance. Combination of inhibitors of autophagy and the two AKRs overcame DOX resistance and cross-resistance of gastrointestinal cancer cells with resistance development to DOX or cis-diamminedichloroplatinum. Therefore, concomitant treatment with the inhibitors may be effective as an adjuvant therapy for elevating DOX sensitivity of gastrointestinal cancer cells.

The antioxidant components of milk and their role in processing, ripening, and storage: Functional food

The current rate of population growth is so fast that, to feed this massive population, a 2-fold increase in land is required for the production of quality food. Improved dietary products such as milk and its products with antioxidant properties and functional foods of animal origin have been utilized to prevent chronic diseases. The designer milk contains low fat and less lactose, more protein, modified level of fatty acids, and desired amino acid profiles. The importance of milk and its products is due to the presence of protein, bioactive peptides, conjugated linoleic acid, omega-3 fatty acid, Vitamin D, selenium, and calcium. These constituents are present in milk product, play a key role in the physiological activities in human bodies, and act as anti-inflammatory, anti-tumor, antioxidant, hypocholesterolemic, immune boosting, and antimicrobial activities. Consumer awareness regarding benefits of designer foods such as milk and its products is almost non-existent worldwide and needs to be established to reach the benefits of designer food technologies in the near future. The main objective of this review was to collect data on the antioxidant properties of milk and its constituents which keep milk-derived products safe and preserved.

13 reasons why the brain is susceptible to oxidative stress

The human brain consumes 20% of the total basal oxygen (O2) budget to support ATP intensive neuronal activity. Without sufficient O2 to support ATP demands, neuronal activity fails, such that, even transient ischemia is neurodegenerative. While the essentiality of O2 to brain function is clear, how oxidative stress causes neurodegeneration is ambiguous. Ambiguity exists because many of the reasons why the brain is susceptible to oxidative stress remain obscure. Many are erroneously understood as the deleterious result of adventitious O2 derived free radical and non-radical species generation. To understand how many reasons underpin oxidative stress, one must first re-cast free radical and non-radical species in a positive light because their deliberate generation enables the brain to achieve critical functions (e.g. synaptic plasticity) through redox signalling (i.e. positive functionality). Using free radicals and non-radical derivatives to signal sensitises the brain to oxidative stress when redox signalling goes awry (i.e. negative functionality). To advance mechanistic understanding, we rationalise 13 reasons why the brain is susceptible to oxidative stress. Key reasons include inter alia unsaturated lipid enrichment, mitochondria, calcium, glutamate, modest antioxidant defence, redox active transition metals and neurotransmitter auto-oxidation. We review RNA oxidation as an underappreciated cause of oxidative stress. The complex interplay between each reason dictates neuronal susceptibility to oxidative stress in a dynamic context and neural identity dependent manner. Our discourse sets the stage for investigators to interrogate the biochemical basis of oxidative stress in the brain in health and disease.

Mitochondria Alkylation and Cellular Trafficking Mapped with a Lipophilic BODIPY-Acrolein Fluorogenic Probe

Protein and DNA alkylation by endogenously produced electrophiles is associated with the pathogenesis of neurodegenerative diseases, to epigenetic alterations and to cell signaling and redox regulation. With the goal of visualizing, in real-time, the spatiotemporal response of the cell milieu to electrophiles, we have designed a fluorogenic BODIPY-acrolein probe, AcroB, that undergoes a >350-fold fluorescence intensity enhancement concomitant with protein adduct formation. AcroB enables a direct quantification of single post-translational modifications occurring on cellular proteins via recording fluorescence bursts in live-cell imaging studies. In combination with super-resolution imaging, protein alkylation events may be registered and individually counted, yielding a map of protein-electrophile reactions within the cell lipid milieu. Alkylation is predominantly observed within mitochondria, a source, yet not a sink, of AcroB adducts, illustrating that a mitochondrial constitutive excretion mechanism ensures rapid disposal of compromised proteins. Sorting within the Golgi apparatus and trafficking along microtubules and through the cell endo- and exocytic pathways can be next visualized via live-cell imaging. Our results offer a direct visualization of cellular response to a noncanonical acrolein warhead. We envision AcroB will enable new approaches for diagnosis of pathologies associated with defective cellular trafficking. AcroB may help elucidate key aspects of mitochondria electrophile adduct excretion and cell endocytic and exocytic pathways. Conceptually, AcroB provides a new paradigm on fluorescence microscopy studies where chemical perturbation is achieved and simultaneously reported by the probe.

α-Pyrrolidinononanophenone provokes apoptosis of neuronal cells through alterations in antioxidant properties

In this study, we found that exposure to α-pyrrolidinononanophenone (α-PNP), a highly lipophilic synthetic cathinone, provokes apoptosis of human neuronal SK-N-SH cells. The drug sensitivity of the cells (50% lethal concentration of 12μM) was similar to those of aortic endothelial and smooth muscle cells, and was higher than those of cells derived from colon, liver, lung and kidney, suggesting that α-PNP overdose and abuse cause serious damage in central nervous and vascular systems. SK-N-SH cell treatment with lethal concentrations (20 and 50μM) of α-PNP facilitated the reactive oxygen species (ROS) production. The treatment also prompted elevation of Bax/Bcl-2 ratio, lowering of mitochondrial membrane potential, release of cytochrome-c into cytosol, and resultant activation of caspase-9 and caspase-3. The apoptotic events (caspase-3 activation and DNA fragmentation) were abolished by pretreatment with antioxidants, N-acetyl-l-cysteine and polyethyleneglycol-conjugated catalase. These results suggest that ROS production, mitochondrial dysfunction and caspase activation are potential events in the mechanism underlying the α-PNP-triggered neuronal cell apoptosis. Intriguingly, the α-PNP treatment of SK-N-SH cells was found to promote formation of 4-hydroxynonenal, a reactive aldehyde generated from lipid peroxidation. The α-PNP treatment also decreased cellular levels of total and reduced glutathiones, expression of γ-glutamylcysteine synthetase mRNA and glutathione reductase activity. Furthermore, the α-PNP treatment resulted in both decrease in proteasomal activities and increase in expression of autophagy-related factors, which were significantly prevented by pretreating with N-acetyl-l-cysteine. Therefore, the ROS formation by α-PNP treatment may be ascribable to the decrease in glutathione level through its consumption during 4-hydroxynonenal detoxification and dysfunction of both de novo synthesis and regeneration of glutathione, in addition to impairments in proteasomal and autophagic systems that degrade cellular oxidized components.