4-Hydroxynonenal induces p53-mediated apoptosis in retinal pigment epithelial cells

Phenotypic high-throughput screening identifies aryl hydrocarbon receptor agonism as common inhibitor of toxin-induced retinal pigment epithelium cell death

The retinal pigment epithelium (RPE) is essential to maintain retinal function, and RPE cell death represents a key pathogenic stage in the progression of several blinding ocular diseases, including age-related macular degeneration (AMD). To identify pathways and compounds able to prevent RPE cell death, we developed a phenotypic screening pipeline utilizing a compound library and high-throughput screening compatible assays on the human RPE cell line, ARPE-19, in response to different disease relevant cytotoxic stimuli. We show that the metabolic by-product of the visual cycle all-trans-retinal (atRAL) induces RPE apoptosis, while the lipid peroxidation by-product 4-hydroxynonenal (4-HNE) promotes necrotic cell death. Using these distinct stimuli for screening, we identified agonists of the aryl hydrocarbon receptor (AhR) as a consensus target able to prevent both atRAL mediated apoptosis and 4-HNE-induced necrotic cell death. This works serves as a framework for future studies dedicated to screening for inhibitors of cell death, as well as support for the discussion of AhR agonism in RPE pathology.

Mediation of Ferroptosis Suppressor Protein 1 Expression via 4-Hydroxy-2-Nonenal Accumulation Contributes to Acquisition of Resistance to Apoptosis and Ferroptosis in Diffuse Large B-Cell Lymphoma

Diffuse large B-cell lymphoma (DLBCL) is the most common non-Hodgkin lymphoma. New therapeutic strategies are needed for the treatment of refractory DLBCL. 4-Hydroxy-2-nonenal (4-HNE) is a cytotoxic lipid peroxidation marker, which alters intracellular signaling and induces genetic mutations. Lipid peroxidation is associated with nonapoptotic cell death, called ferroptosis. However, the relationship between 4-HNE accumulation and feroptotic regulators in DLBCL has not been fully evaluated. Here, we aimed to evaluate the accumulation of lipid peroxide and the expression of ferroptosis suppressor protein 1 (FSP1) in DLBCL using immunohistochemistry. We found a significant increase in the expression of FSP1 in cases with nuclear 4-HNE accumulation (P = .021). Both nuclear and cytoplasmic 4-HNE accumulation and FSP1 positivity were independent predictors of worse prognosis. In vitro exposure to 4-HNE resulted in its concentration- and time-dependent intracellular accumulation and increased expression of FSP1. Furthermore, short-term (0.25 and 1.0 μM) or long-term (0.25 μM) exposure to 4-HNE induced resistance to not only apoptosis but also ferroptosis. Taken together, regulation of FSP1 through 4-HNE accumulation may attenuate resistance to cell death in treatment-resistant DLBCL and might help develop novel therapeutic strategies for refractory DLBCL.

Oxidative stress in the eye and its role in the pathophysiology of ocular diseases

Oxidative stress occurs through an imbalance between the generation of reactive oxygen species (ROS) and the antioxidant defense mechanisms of cells. The eye is particularly exposed to oxidative stress because of its permanent exposure to light and due to several structures having high metabolic activities. The anterior part of the eye is highly exposed to ultraviolet (UV) radiation and possesses a complex antioxidant defense system to protect the retina from UV radiation. The posterior part of the eye exhibits high metabolic rates and oxygen consumption leading subsequently to a high production rate of ROS. Furthermore, inflammation, aging, genetic factors, and environmental pollution, are all elements promoting ROS generation and impairing antioxidant defense mechanisms and thereby representing risk factors leading to oxidative stress. An abnormal redox status was shown to be involved in the pathophysiology of various ocular diseases in the anterior and posterior segment of the eye. In this review, we aim to summarize the mechanisms of oxidative stress in ocular diseases to provide an updated understanding on the pathogenesis of common diseases affecting the ocular surface, the lens, the retina, and the optic nerve. Moreover, we discuss potential therapeutic approaches aimed at reducing oxidative stress in this context.

Comparative mechanistic study of RPE cell death induced by different oxidative stresses

Oxidative stress is hypothesized to drive the progression of age-related macular degeneration (AMD). Retinal pigment epithelial (RPE) cell layer is important for supporting the function of retina and is particularly susceptible to oxidative stress-induced cell death. How RPE cells die in AMD, especially in geographic atrophy (GA), a late stage of dry AMD, is still controversial. The goal of this study is to compare the features and mechanisms of RPE cell death induced by different oxidative stresses, to identify potential universal therapeutic targets for GA. RPE cell death was induced both in vitro and ex vivo by 4-Hydroxynonenal (4-HNE), a major product of lipid peroxidation, sodium iodate (NaIO3) that has been widely used to model RPE cell death in dry AMD, a ferroptosis inducer RAS-selective lethal 3 (RSL3) or a necroptosis inducer shikonin. We found that RPE necroptosis and ferroptosis show common and distinct features. Common features include receptor-interacting protein kinase (RIPK)1/RIPK3 activation and lipid reactive oxygen species (ROS) accumulation, although lipid ROS accumulation is much milder during necroptosis. This supports cross talk between RPE ferroptosis and necroptosis pathways and is consistent with the rescue of RPE necroptosis and ferroptosis by RIPK1 inhibitor Necrostatin-1 (Nec-1) or in Ripk3-/- RPE explants. Distinct feature includes activated mixed lineage kinase domain like pseudokinase (MLKL) that is translocated to the cell membrane during necroptosis, which is not happening in ferroptosis. This is consistent with the failure to rescue RPE ferroptosis by MLKL inhibitor necrosulfonamide (NSA) or in Mlkl-/- RPE explants. Using this framework, we found that 4-HNE and NaIO3 induced RPE cell death likely through necroptosis based on the molecular features and the rescuing effect by multiple inhibitors. Our studies suggest that multiple markers and inhibitors are required to distinguish RPE necroptosis and ferroptosis, and that necroptosis inhibitor Nec-1 could be a potential therapeutic compound for GA since it inhibits RIPK1/RIPK3 activation and lipid ROS accumulation occurred in both necroptosis and ferroptosis pathways.

Acetaminophen-induced liver injury: Molecular mechanism and treatments from natural products

Acetaminophen (APAP) is a widely used analgesic and antipyretic over-the-counter medicine worldwide. Hepatotoxicity caused by APAP overdose is one of the leading causes of acute liver failure (ALF) in the US and in some parts of Europe, limiting its clinical application. Excessive APAP metabolism depletes glutathione and increases N-acetyl-p-benzoquinoneimide (NAPQI) levels, leading to oxidative stress, DNA damage, and cell necrosis in the liver, which in turn leads to liver damage. Studies have shown that natural products such as polyphenols, terpenes, anthraquinones, and sulforaphane can activate the hepatocyte antioxidant defense system with Nrf2 as the core player, reduce oxidative stress damage, and protect the liver. As the key enzyme metabolizing APAP into NAPQI, cytochrome P450 enzymes are also considered to be intriguing target for the treatment of APAP-induced liver injury. Here, we systematically review the hepatoprotective activity and molecular mechanisms of the natural products that are found to counteract the hepatotoxicity caused by APAP, providing reference information for future preclinical and clinical trials of such natural products.

Gamma-Muricholic Acid Inhibits Nonalcoholic Steatohepatitis: Abolishment of Steatosis-Dependent Peroxidative Impairment by FXR/SHP/LXRα/FASN Signaling

Nonalcoholic steatohepatitis (NASH) reflects the outcome of steatosis-based peroxidative impairment. Here, the effect and mechanism of γ-muricholic acid (γ-MCA) on NASH were investigated on the basis of its actions in hepatic steatosis, lipid peroxidation, peroxidative injury, hepatocyte apoptosis, and its NAFLD activity score (NAS). The agonist action of γ-MCA on farnesoid X receptor (FXR) upregulated the small heterodimer partner (SHP) expression of hepatocytes. An increase in SHP attenuated the triglyceride-dominated hepatic steatosis which was induced in vivo by a high-fat high-cholesterol (HFHC) diet and in vitro by free fatty acids depending on the inhibition of liver X receptor α (LXRα) and fatty acid synthase (FASN). In contrast, FXR knockdown abrogated the γ-MCA-dependent lipogenic inactivation. When compared to their excessive production in HFHC diet-induced rodent NASH, products of lipid peroxidation (MDA and 4-HNE) exhibited significant reductions upon γ-MCA treatment. Moreover, the decreased levels of serum alanine aminotransferases and aspartate aminotransferases demonstrated an improvement in the peroxidative injury of hepatocytes. By TUNEL assay, injurious amelioration protected the γ-MCA-treated mice against hepatic apoptosis. The abolishment of apoptosis prevented lobular inflammation, which downregulated the incidence of NASH by lowering NAS. Collectively, γ-MCA inhibits steatosis-induced peroxidative injury to ameliorate NASH by targeting FXR/SHP/LXRα/FASN signaling.

p53 Activates the Lipoxygenase Activity of ALOX15B via Inhibiting SLC7A11 to Induce Ferroptosis in Bladder Cancer Cells

Bladder cancer is a malignant tumor of the urinary system and is one of the most common cancers worldwide. Lipoxygenases are closely related to the development of various cancers. However, the relationship between lipoxygenases and p53/SLC7A11-dependent ferroptosis in bladder cancer has not been reported. Here, we aimed to investigate the roles and internal mechanisms of lipid peroxidation and p53/SLC7A11-dependent ferroptosis in the development and progression of bladder cancer. First, ultraperformance liquid chromatography-tandem mass spectrometry was performed to measure the metabolite production of lipid oxidation in patients' plasma. The metabolic changes in patients with bladder cancer were discovered, revealing that stevenin, melanin, and octyl butyrate were upregulated. Then, the expressions of lipoxygenase family members were measured to screen out candidates with significant changes in bladder cancer tissues. Among various lipoxygenases, ALOX15B was significantly downregulated in bladder cancer tissues. Moreover, p53 and 4-hydroxynonenal (4-HNE) levels were decreased in bladder cancer tissues. Next, sh-ALOX15B, oe-ALOX15B, or oe-SLC7A11 plasmids were constructed and transfected into bladder cancer cells. Then, the p53 agonist Nutlin-3a, tert-butyl hydroperoxide, iron chelator deferoxamine, and the selective ferroptosis inhibitor ferr1 were added. The effects of ALOX15B and p53/SLC7A11 on bladder cancer cells were evaluated by in vitro and in vivo experiments. We revealed that knockdown of ALOX15B promoted bladder cancer cell growth, which was also found to protect bladder cancer cells from p53-induced ferroptosis. Furthermore, p53 activated ALOX15B lipoxygenase activity by suppressing SLC7A11. Taken together, p53 activated the lipoxygenase activity of ALOX15B via inhibiting SLC7A11 to induce ferroptosis in bladder cancer cells, which provided insight into the molecular mechanism of the occurrence and development of bladder cancer.

Aldehyde Dehydrogenase 2 Ameliorates LPS-Induced Acute Kidney Injury through Detoxification of 4-HNE and Suppression of the MAPK Pathway

Lipopolysaccharide (LPS)-induced septic acute kidney injury (AKI) is determined as a devastating organ dysfunction elicited by an inappropriate response to infection with high morbidity and mortality rates. Previous evidence has illustrated an indispensable role of mitochondrial aldehyde dehydrogenase 2 (ALDH2) in the pathogenesis of sepsis-induced multiorgan abnormalities. Specifically, this study investigated the potential role of ALDH2 in sepsis-induced AKI. After LPS administration, we observed a significant decline in renal function, increased inflammatory cytokines, oxidative stress, 4-hydroxy-2-nonenal (4-HNE) accumulation, and apoptosis via MAPK activation in ALDH2^-/- mice; in contrast, pretreatment with Alda-1 (an ALDH2 activator) alleviated the LPS-induced dysfunctions in mice. Moreover, in vitro analysis revealed that ALDH2 overexpression in mouse tubular epithelial cells (mTECs) improved the inflammatory response, oxidative stress, 4-HNE accumulation, and apoptosis via MAPK inhibition, whereas ALDH2 knockdown in mTECs aggravated these parameters via MAPK activation. Therefore, ALDH2 may protect against LPS-induced septic AKI by suppressing 4-HNE/MAPK pathway.

The role of some lipids and their metabolites in programmed cell death (lipoapoptosis)

In recent years, the understanding of the mechanisms involved in the regulation of lipoapoptosis signaling pathways has expanded considerably. However, many mechanisms of apoptosis induction by lipids as well as molecules mediating intracellular and systemic signals belonging to AOS/enzyme-dependent phospholipid metabolites are not completely clear.

This review summarizes the current understanding of the mechanisms of apoptotic cell death induction by some lipid molecules. Literature search was performed in the database “PubMed”, “eLIBRARY” using key words: “apoptosis”, “lipids”, “fatty acids”, “eicosanoids”, “reactive oxygen species”.

A brief characterization of the signaling pathways of apoptosis is given. The role of reactive oxygen species and their dependent products of lipid peroxidation in the regulation of the main signaling pathways of apoptosis are shown. Particular attention is paid to the product of phospholipid metabolism – 4-hydroxynonenal.

Pro- and anti-apoptotic effects of some prostaglandins are demonstrated. Arguments are presented that prostaglandins of series J and D are pro-apoptotic in most cells, and this effect depends on activation of the prostanoid receptor DP2 and on reduction of AKT kinase activity. In contrast, the E-series prostaglandins and hydroxyecosatetraenoic acid act opposite to the J-series and D-series prostaglandins, reducing apoptosis by activating AKT and increasing Bcl-2 protein expression.

The role of individual fatty acids involved in the initiation and transduction of pro-apoptotic and anti-apoptotic signals is assessed. It was shown that saturated fatty acids have the maximum damaging potential than their unsaturated counterparts. An in-depth understanding and deciphering of the mechanisms by which lipids and their metabolites modulate the activation of signaling pathways of programmed cell death can help to develop therapeutic strategies to prevent a number of diseases associated with impaired regulation of apoptosis.

Hydroxyproline alleviates 4-hydroxy-2-nonenal-induced DNA damage and apoptosis in porcine intestinal epithelial cells

Oxidative stress has been confirmed in relation to intestinal mucosa damage and multiple bowel diseases. Hydroxyproline (Hyp) is an imino acid abundant in sow's milk. Compelling evidence has been gathered showing the potential antioxidative properties of Hyp. However, the role and mechanism of Hyp in porcine intestinal epithelial cells in response to oxidative stress remains unknown. In this study, small intestinal epithelial cell lines of piglets (IPEC-1) were used to evaluate the protective effects of Hyp on 4-hydroxy-2-nonenal (4-HNE)-induced oxidative DNA damage and apoptosis. IPEC-1 pretreated with 0.5 to 5 mmol/L Hyp were exposed to 4-HNE (40 μmol/L) in the presence or absence of Hyp. Thereafter, the cells were subjected to apoptosis detection by Hoechst staining, flow cytometry, and Western blot or DNA damage analysis by comet assay, immunofluorescence, and reverse-transcription quantitative PCR (RT-qPCR). Cell apoptosis and the upregulation of cleaved-caspase-3 induced by 4-HNE (40 μmol/L) were inhibited by 5 mmol/L of Hyp. In addition, 5 mmol/L Hyp attenuated 4-HNE-induced reactive oxygen species (ROS) accumulation, glutathione (GSH) deprivation and DNA damage. The elevation in transcription of GADD45a (growth arrest and DNA-damage-inducible protein 45 alpha) and GADD45b (growth arrest and DNA-damage-inducible protein 45 beta), as well as the phosphorylation of H2AX (H2A histone family, member X), p38 MAPK (mitogen-activated protein kinase), and JNK (c-Jun N-terminal kinase) in cells treated with 4-HNE were alleviated by 5 mmol/L Hyp. Furthermore, Hyp supplementation increased the protein abundance of Krüppel like factor 4 (KLF4) in cells exposed to 4-HNE. Suppression of KLF4 expression by kenpaulone impeded the resistance of Hyp-treated cells to DNA damage and apoptosis induced by 4-HNE. Collectively, our results indicated that Hyp serves to protect against 4-HNE-induced apoptosis and DNA damage in IPEC-1 cells, which is partially pertinent with the enhanced expression of KLF4. Our data provides an updated explanation for the nutritional values of Hyp-containing animal products.

Molecular Mechanisms of Iron Mediated Programmed Cell Death and Its Roles in Eye Diseases

Ferroptosis, a newly identified, iron-dependent type of programmed cell death, is active in several diseases, such as heart disease, brain damage, and cancer. Its main characteristics commonly involve excess iron accumulation, elevated lipid peroxides and reactive oxygen species, and reduced levels of glutathione and glutathione peroxidase 4 levels. The effects of ferroptosis in eye diseases cannot be underestimated, with ferroptosis becoming a research target in ocular disorders and emerging evidence from a series of in vivo and in vitro researches into ferroptosis revealing its role in eye conditions. However, no report provides comprehensive information on the pathophysiology of ferroptosis in eye diseases and its possible treatments. In the current review, we present an up-to-date overview of ferroptosis biology and its involvement in the pathological processes of ocular diseases. Furthermore, we pose several outstanding questions and areas for future research in this topic. We deem ferroptosis-associated cell death a pivotal new field of scientific study in ocular diseases and consider it a new therapeutic target in the treatment of some eye disorders.

Aldehyde dehydrogenase 3A1 deficiency leads to mitochondrial dysfunction and impacts salivary gland stem cell phenotype

Adult salivary stem/progenitor cells (SSPC) have an intrinsic property to self-renew in order to maintain tissue architecture and homeostasis. Adult salivary glands have been documented to harbor SSPC, which have been shown to play a vital role in the regeneration of the glandular structures postradiation damage. We have previously demonstrated that activation of aldehyde dehydrogenase 3A1 (ALDH3A1) after radiation reduced aldehyde accumulation in SSPC, leading to less apoptosis and improved salivary function. We subsequently found that sustained pharmacological ALDH3A1 activation is critical to enhance regeneration of murine submandibular gland after radiation damage. Further investigation shows that ALDH3A1 function is crucial for SSPC self-renewal and survival even in the absence of radiation stress. Salivary glands from Aldh3a1 -/- mice have fewer acinar structures than wildtype mice. ALDH3A1 deletion or pharmacological inhibition in SSPC leads to a decrease in mitochondrial DNA copy number, lower expression of mitochondrial specific genes and proteins, structural abnormalities, lower membrane potential, and reduced cellular respiration. Loss or inhibition of ALDH3A1 also elevates ROS levels, depletes glutathione pool, and accumulates ALDH3A1 substrate 4-hydroxynonenal (4-HNE, a lipid peroxidation product), leading to decreased survival of murine SSPC that can be rescued by treatment with 4-HNE specific carbonyl scavengers. Our data indicate that ALDH3A1 activity protects mitochondrial function and is important for the regeneration activity of SSPC. This knowledge will help to guide our translational strategy of applying ALDH3A1 activators in the clinic to prevent radiation-related hyposalivation in head and neck cancer patients.

Glia maturation factor-β induces ferroptosis by impairing chaperone-mediated autophagic degradation of ACSL4 in early diabetic retinopathy

Diabetic retinopathy (DR) is one of the leading causes of blindness in the world, and timely prevention and treatment are very important. Previously, we found that a neurodegenerative factor, Glia maturation factor-β (GMFB), was upregulated in the vitreous at a very early stage of diabetes, which may play an important role in pathogenesis. Here, we found that in a high glucose environment, large amounts of GMFB protein can be secreted in the vitreous, which translocates the ATPase ATP6V1A from the lysosome, preventing its assembly and alkalinizing the lysosome in the retinal pigment epithelial (RPE) cells. ACSL4 protein can be recognized by HSC70, the receptor for chaperone-mediated autophagy, and finally digested in the lysosome. Abnormalities in the autophagy–lysosome degradation process lead to its accumulation, which catalyzes the production of lethal lipid species and finally induces ferroptosis in RPE cells. GMFB antibody, lysosome activator NKH477, CMA activator QX77, and ferroptosis inhibitor Liproxstatin-1 were all effective in preventing early diabetic retinopathy and maintaining normal visual function, which has powerful clinical application value. Our research broadens the understanding of the relationship between autophagy and ferroptosis and provides a new therapeutic target for the treatment of DR.

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Glia maturation factor-β (GMFB) was upregulated in the vitreous at a very early stage of diabetes.

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Extracellular GMFB can induce ferroptosis and lysosome dysfunction in retinal RPE cells.

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ACSL4 protein can be degraded through chaperone-mediated autophagy (CMA), and finally digested in the lysosome.

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Lysosome dysfunction leads to the accumulation of ACSL4, which induces ferroptosis in RPE cells.

Long-Chain Polyunsaturated Fatty Acids and Their Metabolites Regulate Inflammation in Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a blinding eye disease, whose incidence strongly increases with ages. The etiology of AMD is complex, including aging, abnormal lipid metabolism, chronic inflammation and oxidative stress. Long-chain polyunsaturated fatty acids (LCPUFA) are essential for ocular structures and functions. This review summarizes the regulatory effects of LCPUFA on inflammation in AMD. LCPUFA are related to aging, autophagy and chronic inflammation. They are metabolized to pro- and anti-inflammatory metabolites by various enzymes. These metabolites stimulate inflammation in response to oxidative stress, causing innate and acquired immune responses. This review also discusses the possible clinical applications, which provided novel targets for the prevention and treatment of AMD and other age-related diseases.

Altered transsulfuration pathway enzymes and redox homeostasis in inherited retinal degenerative diseases

Retinal degenerative diseases result from apoptotic photoreceptor cell death. As endogenously produced gaseous molecules such as hydrogen sulfide (H₂S) and nitric oxide (NO) play a key role in apoptosis, we compared the expression levels of genes and proteins involved in the production of these molecules in the retina of normal dogs and three canine models (rcd1, crd2, and xlpra2) of human inherited retinal degeneration (IRD). Using qRT-PCR, Western blot, and immunohistochemistry (IHC), we showed that mRNA and protein levels of cystathionine β-synthase (CBS), an enzyme that produces H₂S in neurons, are increased in retinal degeneration, but those of cystathionine γ-lyase (CSE), an enzyme involved in the production of glutathione (GSH), an antioxidant, are not. Such findings suggest that increased levels of H₂S that are not counterbalanced by increased antioxidant potential may contribute to disease in affected retinas. We also studied the expression of neuronal and inducible nitric oxide synthase (nNOS and iNOS), the enzymes responsible for NO production. Western blot and IHC results revealed increased levels of nNOS and iNOS, resulting in increased NO levels in mutant retinas. Finally, photoreceptors are rich in polyunsaturated fatty acids (PUFAs) that can make these cells vulnerable to oxidative damage through reactive oxygen species (ROS). Our results showed increased levels of acrolein and hydroxynonenal (4HNE), two main toxic products of PUFAs, surrounding the membranes of photoreceptors in affected canines. Increased levels of these toxic products, together with increased NO and ROS, likely render these cells susceptible to an intrinsic apoptotic pathway involving mitochondrial membranes. To assess this possibility, we measured the levels of BCL2, an anti-apoptotic protein in the mitochondrial membrane. Western blot results showed decreased levels of BCL2 protein in affected retinas. Overall, the results of this study identify alterations in the expression of enzymes directly involved in maintaining the normal redox status of the retina during retinal degeneration, thereby supporting future studies to investigate the role of H₂S and NO in retinal degeneration and apoptosis.

Anticancer Activity of Ω-6 Fatty Acids through Increased 4-HNE in Breast Cancer Cells

Simple Summary

Epidemiological evidence suggests that breast cancer risk is lowered by Ω-3 and increased by Ω-6 polyunsaturated fatty acids (PUFAs). Paradoxically, the Ω-6 PUFA metabolite 4-hydroxynonenal (4-HNE) inhibits cancer cell growth. This duality prompted us to study whether arachidonic acid (AA) would enhance doxorubicin (dox) cytotoxicity towards breast cancer cells. We found that supplementing AA or inhibiting 4-HNE metabolism potentiated doxorubicin (dox) toxicity toward Her2-dependent breast cancer but spared myocardial cells. Our results suggest that Ω-6 PUFAs could improve outcomes of dox chemotherapy in Her2-overexpressing breast cancer.

Abstract

Her2-amplified breast cancers resistant to available Her2-targeted therapeutics continue to be a challenge in breast cancer therapy. Dox is the mainstay of chemotherapy of all types of breast cancer, but its usefulness is limited by cumulative cardiotoxicity. Because oxidative stress caused by dox generates the pro-apoptotic Ω-6 PUFA metabolite 4-hydroxynonenal (4-HNE), we surmised that Ω-6 PUFAs would increase the effectiveness of dox chemotherapy. Since the mercapturic acid pathway enzyme RALBP1 (also known as RLIP76 or Rlip) that limits cellular accumulation of 4-HNE also mediates dox resistance, the combination of Ω-6 PUFAs and Rlip depletion could synergistically improve the efficacy of dox. Thus, we studied the effects of the Ω-6 PUFA arachidonic acid (AA) and Rlip knockdown on the antineoplastic activity of dox towards Her2-amplified breast cancer cell lines SK-BR-3, which is sensitive to Her2 inhibitors, and AU565, which is resistant. AA increased lipid peroxidation, 4-HNE generation, apoptosis, cellular dox concentration and dox cytotoxicity in both cell lines while sparing cultured immortalized cardiomyocyte cells. The known functions of Rlip including clathrin-dependent endocytosis and dox efflux were inhibited by AA. Our results support a model in which 4-HNE generated by AA overwhelms the capacity of Rlip to defend against apoptosis caused by dox or 4-HNE. We propose that Ω-6 PUFA supplementation could improve the efficacy of dox or Rlip inhibitors for treating Her2-amplified breast cancer.

Identification of novel key molecular signatures in the pathogenesis of experimental diabetic retinopathy

Deep mining of the molecular mechanisms underlying diabetic retinopathy (DR) is critical for the development of novel therapeutic targets. This study aimed to identify key molecular signatures involved in experimental DR on the basis of integrated bioinformatics analysis. Four datasets consisting of 37 retinal samples were downloaded from the National Center of Biotechnology Information Gene Expression Omnibus. After batch-effect adjustment, bioinformatics tools such as Networkanalyst, Enrichr, STRING, and Metascape were used to evaluate the differentially expressed genes (DEGs), perform enrichment analysis, and construct protein-protein interaction networks. The hub genes were identified using Cytoscape software. The DEGs of interest from the meta-analysis were confirmed by quantitative reverse transcription-polymerase chain reaction in diabetic rats and a high-glucose-treated retinal cell model, respectively. A total of 743 DEGs related to lens differentiation, insulin resistance, and high-density lipoprotein (HDL) cholesterol metabolism were obtained using the meta-analysis. Alterations of dynamic gene expression in the chloride ion channel, retinol metabolism, and fatty acid metabolism were involved in the course of DR in rats. Importantly, H3K27m3 modifications regulated the expression of most DEGs at the early stage of DR. Using an integrated bioinformatics approach, novel molecular signatures were obtained for different stages of DR progression, and the findings may represent distinct therapeutic strategies for DR patients.

Cellular targets in diabetic retinopathy therapy

Despite the existence of treatment for diabetes, inadequate metabolic control triggers the appearance of chronic complications such as diabetic retinopathy. Diabetic retinopathy is considered a multifactorial disease of complex etiology in which oxidative stress and low chronic inflammation play essential roles. Chronic exposure to hyperglycemia triggers a loss of redox balance that is critical for the appearance of neuronal and vascular damage during the development and progression of the disease. Current therapies for the treatment of diabetic retinopathy are used in advanced stages of the disease and are unable to reverse the retinal damage induced by hyperglycemia. The lack of effective therapies without side effects means there is an urgent need to identify an early action capable of preventing the development of the disease and its pathophysiological consequences in order to avoid loss of vision associated with diabetic retinopathy. Therefore, in this review we propose different therapeutic targets related to the modulation of the redox and inflammatory status that, potentially, can prevent the development and progression of the disease.

Extracellular Vesicles under Oxidative Stress Conditions: Biological Properties and Physiological Roles

Under physio-pathological conditions, cells release membrane-surrounded structures named Extracellular Vesicles (EVs), which convey their molecular cargo to neighboring or distant cells influencing their metabolism. Besides their involvement in the intercellular communication, EVs might represent a tool used by cells to eliminate unnecessary/toxic material. Here, we revised the literature exploring the link between EVs and redox biology. The first proof of this link derives from evidence demonstrating that EVs from healthy cells protect target cells from oxidative insults through the transfer of antioxidants. Oxidative stress conditions influence the release and the molecular cargo of EVs that, in turn, modulate the redox status of target cells. Oxidative stress-related EVs exert both beneficial or harmful effects, as they can carry antioxidants or ROS-generating enzymes and oxidized molecules. As mediators of cell-to-cell communication, EVs are also implicated in the pathophysiology of oxidative stress-related diseases. The review found evidence that numerous studies speculated on the role of EVs in redox signaling and oxidative stress-related pathologies, but few of them unraveled molecular mechanisms behind this complex link. Thus, the purpose of this review is to report and discuss this evidence, highlighting that the analysis of the molecular content of oxidative stress-released EVs (reminiscent of the redox status of originating cells), is a starting point for the use of EVs as diagnostic and therapeutic tools in oxidative stress-related diseases.

Lipid peroxidation in brain tumors

There is a lot of evidence showing that lipid peroxidation plays very important role in development of various diseases, including neurodegenerative diseases and brain tumors. Lipid peroxidation is achieved by two main pathways, by enzymatic or by non-enzymatic oxidation, respectively. In this paper, we focus on non-enzymatic, self-catalyzed chain reaction of poly-unsaturated fatty acid (PUFA) peroxidation generating reactive aldehydes, notably 4-hydroxynonenal (4-HNE), which acts as second messenger of free radicals and as growth regulating factor. It might originate from astrocytes as well as from blood vessels, even within the blood-brain barrier (BBB), which is in case of brain tumors transformed into the blood-brain-tumor barrier (BBTB). The functionality of the BBB is strongly affected by 4-HNE because it forms relatively stable protein adducts thus allowing the persistence and the spread of lipid peroxidation, as revealed by immunohistochemical findings. Because 4-HNE can act as a regulator of vital functions of normal and of malignant cells acting in the cell type- and concentration-dependent manners, the bioactivities of this product of lipid peroxidation be should further studied to reveal if it acts as a co-factor of carcinogenesis or as natural factor of defense against primary brain tumors and metastatic cancer.

Oxidative and Nitrosative Stress in Age-Related Macular Degeneration: A Review of Their Role in Different Stages of Disease

Although the exact pathogenetic mechanisms leading to age-related macular degeneration (AMD) have not been clearly identified, oxidative damage in the retina and choroid due to an imbalance between local oxidants/anti-oxidant systems leading to chronic inflammation could represent the trigger event. Different in vitro and in vivo models have demonstrated the involvement of reactive oxygen species generated in a highly oxidative environment in the development of drusen and retinal pigment epithelium (RPE) changes in the initial pathologic processes of AMD; moreover, recent evidence has highlighted the possible association of oxidative stress and neovascular AMD. Nitric oxide (NO), which is known to play a key role in retinal physiological processes and in the regulation of choroidal blood flow, under pathologic conditions could lead to RPE/photoreceptor degeneration due to the generation of peroxynitrite, a potentially cytotoxic tyrosine-nitrating molecule. Furthermore, the altered expression of the different isoforms of NO synthases could be involved in choroidal microvascular changes leading to neovascularization. The purpose of this review was to investigate the different pathways activated by oxidative/nitrosative stress in the pathogenesis of AMD, focusing on the mechanisms leading to neovascularization and on the possible protective role of anti-vascular endothelial growth factor agents in this context.

Spermidine Attenuates Oxidative Stress-Induced Apoptosis via Blocking Ca2+ Overload in Retinal Pigment Epithelial Cells Independently of ROS

Retinal pigment epithelial (RPE) cells occupy the outer layer of the retina and perform various biological functions. Oxidative damage to RPE cells is a major risk factor for retinal degeneration that ultimately leads to vision loss. In this study, we investigated the role of spermidine in a hydrogen peroxide (H₂O₂)-induced oxidative stress model using human RPE cells. Our findings showed that 300 μM H₂O₂ increased cytotoxicity, apoptosis, and cell cycle arrest in the G2/M phase, whereas these effects were markedly suppressed by 10 μM spermidine. Furthermore, spermidine significantly reduced H₂O₂-induced mitochondrial dysfunction including mitochondrial membrane potential and mitochondrial activity. Although spermidine displays antioxidant properties, the generation of intracellular reactive oxygen species (ROS) upon H₂O₂ insult was not regulated by spermidine. Spermidine did suppress the increase in cytosolic Ca²⁺ levels resulting from endoplasmic reticulum stress in H₂O₂-stimulated human RPE cells. Treatment with a cytosolic Ca²⁺ chelator markedly reversed H₂O₂-induced cellular dysfunction. Overall, spermidine protected against H₂O₂-induced cellular damage by blocking the increase of intracellular Ca²⁺ independently of ROS. These results suggest that spermidine protects RPE cells from oxidative stress, which could be a useful treatment for retinal diseases.

Gradual Increase in Environmental Light Intensity Induces Oxidative Stress and Inflammation and Accelerates Retinal Neurodegeneration

Purpose

Retinitis pigmentosa (RP) is a blinding neurodegenerative disease of the retina that can be affected by many factors. The present study aimed to analyze the effect of different environmental light intensities in rd10 mice retina.

Methods

C57BL/6J and rd10 mice were bred and housed under three different environmental light intensities: scotopic (5 lux), mesopic (50 lux), and photopic (300 lux). Visual function was studied using electroretinography and optomotor testing. The structural and morphological integrity of the retinas was evaluated by optical coherence tomography imaging and immunohistochemistry. Additionally, inflammatory processes and oxidative stress markers were analyzed by flow cytometry and western blotting.

Results

When the environmental light intensity was higher, retinal function decreased in rd10 mice and was accompanied by light-dependent photoreceptor loss, followed by morphological alterations, and synaptic connectivity loss. Moreover, light-dependent retinal degeneration was accompanied by an increased number of inflammatory cells, which became more activated and phagocytic, and by an exacerbated reactive gliosis. Furthermore, light-dependent increment in oxidative stress markers in rd10 mice retina pointed to a possible mechanism for light-induced photoreceptor degeneration.

Conclusions

An increase in rd10 mice housing light intensity accelerates retinal degeneration, activating cell death, oxidative stress pathways, and inflammatory cells. Lighting intensity is a key factor in the progression of retinal degeneration, and standardized lighting conditions are advisable for proper analysis and interpretation of experimental results from RP animal models, and specifically from rd10 mice. Also, it can be hypothesized that light protection could be an option to slow down retinal degeneration in some cases of RP.

4-Hydroxy-7-oxo-5-heptenoic acid lactone can induce mitochondrial dysfunction in retinal pigmented epithelial cells

Oxidation of docosahexaenoate (DHA)-containing phospholipids in the cell plasma membrane leads to release of the α,β-unsaturated aldehyde 4-hydroxy-7-oxo-5-heptenoic acid (HOHA) lactone which is capable of inducing retinal pigmented epithelial (RPE) cell dysfunction. Previously, HOHA lactone was shown to induce apoptosis and angiogenesis, and to activate the alternative complement pathway. RPE cells metabolize HOHA lactone through enzymatic conjugation with glutathione (GSH). Competing with this process is the adduction of HOHA lactone to protein lysyl residues generating 2-(ω-carboxyethyl)pyrrole (CEP) derivatives that have pathological relevance to age-related macular degeneration (AMD). We now find that HOHA lactone induces mitochondrial dysfunction. It decreases ATP levels, mitochondrial membrane potentials, enzymatic activities of mitochondrial complexes, depletes GSH and induces oxidative stress in RPE cells. The present study confirmed that pyridoxamine and other primary amines, which have been shown to scavenge γ-ketoaldehydes formed by carbohydrate or lipid peroxidation, are ineffective for scavenging the α,β-unsaturated aldehydes. Histidyl hydrazide (HH), that has both hydrazide and imidazole nucleophile functionalities, is an effective scavenger of HOHA lactone and it protects ARPE-19 cells against HOHA lactone-induced cytotoxicity. The HH α-amino group is not essential for this electrophile trapping activity. The N^α-acyl L-histidyl hydrazide derivatives with 2- to 7-carbon acyl groups with increasing lipophilicities are capable of maintaining the effectiveness of HH in protecting ARPE-19 cells against HOHA lactone toxicity, which potentially has therapeutic utility for treatment of age related eye diseases.

Not All Stressors Are Equal: Mechanism of Stressors on RPE Cell Degeneration

Age-related macular degeneration (AMD) is a major cause of irreversible blindness among the elderly population. Dysfunction and degeneration of the retinal pigment epithelial (RPE) layer in the retina underscore the pathogenesis of both dry and wet AMD. Advanced age, cigarette smoke and genetic factors have been found to be the prominent risk factors for AMD, which point to an important role for oxidative stress and aging in AMD pathogenesis. However, the mechanisms whereby oxidative stress and aging lead to RPE cell degeneration are still unclear. As cell senescence and cell death are the major outcomes from oxidative stress and aging, here we review the mechanisms of RPE cell senescence and different kinds of cell death, including apoptosis, necroptosis, pyroptosis, ferroptosis, with an aim to clarify how RPE cell degeneration could occur in response to AMD-related stresses, including H₂O₂, 4-Hydroxynonenal (4-HNE), N-retinylidene-N-retinyl-ethanolamine (A2E), Alu RNA and amyloid β (Aβ). Besides those, sodium iodate (NaIO₃) induced RPE cell degeneration is also discussed in this review. Although NaIO₃ itself is not related to AMD, this line of study would help understand the mechanism of RPE degeneration.

Oxidative stress and diabetic retinopathy: Molecular mechanisms, pathogenetic role and therapeutic implications

Oxidative stress, a cytopathic outcome of excessive generation of ROS and the repression of antioxidant defense system for ROS elimination, is involved in the pathogenesis of multiple diseases, including diabetes and its complications. Retinopathy, a microvascular complication of diabetes, is the primary cause of acquired blindness in diabetic patients. Oxidative stress has been verified as one critical contributor to the pathogenesis of diabetic retinopathy. Oxidative stress can both contribute to and result from the metabolic abnormalities induced by hyperglycemia, mainly including the increased flux of the polyol pathway and hexosamine pathway, the hyper-activation of protein kinase C (PKC) isoforms, and the accumulation of advanced glycation end products (AGEs). Moreover, the repression of the antioxidant defense system by hyperglycemia-mediated epigenetic modification also leads to the imbalance between the scavenging and production of ROS. Excessive accumulation of ROS induces mitochondrial damage, cellular apoptosis, inflammation, lipid peroxidation, and structural and functional alterations in retina. Therefore, it is important to understand and elucidate the oxidative stress-related mechanisms underlying the progress of diabetic retinopathy. In addition, the abnormalities correlated with oxidative stress provide multiple potential therapeutic targets to develop safe and effective treatments for diabetic retinopathy. Here, we also summarized the main antioxidant therapeutic strategies to control this disease.

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Oxidative stress can both contribute to and result from hyperglycemia-induced metabolic abnormalities in retina.

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Genes important in regulation of ROS are epigenetically modified, increasing ROS accumulation in retina.

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Oxidative stress is closely associated with the pathological changes in the progress of diabetic retinopathy.

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Antioxidants ameliorate retinopathy through targeting multiple steps of oxidative stress.

Retinal pigment epithelium and age-related macular degeneration: A review of major disease mechanisms

Age‐related macular degeneration (AMD) is a progressive degenerative disease that is the leading cause of vision loss in the elderly population. Degeneration/dysregulation of the retinal pigment epithelium (RPE), a supportive monolayer of cells underlying the photoreceptors, is commonly seen in patients with AMD. While treatment exists for the neovascular/wet form of AMD, there is currently no cure for the non‐exudative/dry form of AMD, making it imperative to understand the pathogenesis of this disease. Although our understanding of the aetiology of AMD has increased over the years, the underlying disease mechanism has not yet been identified, mainly due to the multifactorial nature of this disease. Herein, we review some of the commonly proposed degeneration pathways of RPE cells and their role in the pathogenesis of AMD; including activation of the complement cascade, oxidative stress‐induced cell death mechanisms, dysfunctional mitochondria and the role of crystallins in AMD disease progression.

4-Hydroxy-7-oxo-5-heptenoic acid (HOHA) lactone induces apoptosis in retinal pigment epithelial cells

Retinal pigment epithelial (RPE) cell dysfunction and death play vital roles in age-related macular degeneration (AMD) pathogenesis. Previously we showed that oxidative cleavage of docosahexenoate (DHA) phospholipids generates an α,β-unsaturated aldehyde, 4-hydroxy-7-oxohept-4-enoic acid (HOHA) lactone, that forms ω-carboxyethylpyrrole (CEP) derivatives through adduction to proteins and ethanolamine phospholipids. CEP derivatives and autoantibodies accumulate in the retinas and blood plasma of individuals with AMD and are a biomarker of AMD. They promote the choroidal neovascularization of "wet AMD". Immunization of mice with CEP-modified mouse serum albumin induces "dry AMD"-like lesions in their retinas as well as interferon-gamma and interleukin-17 production by CEP-specific T cells that promote inflammatory M1 polarization of macrophages. The present study confirms that oxidative stress or inflammatory stimulus produces CEP in both the primary human ARPE-19 cell line and hRPE cells. Exposure of these cells to HOHA lactone fosters production of reactive oxygen species. Thus, HOHA lactone participates in a vicious cycle, promoting intracellular oxidative stress leading to oxidative cleavage of DHA to produce more HOHA lactone. We now show that HOHA lactone is cytotoxic, inducing apoptotic cell death through activation of the intrinsic pathway. This suggests that therapeutic interventions targeting HOHA lactone-induced apoptosis may prevent the loss of RPE cells during the early phase of AMD. We also discovered that ARPE-19 cells are more susceptible than hRPE cells to HOHA lactone cytotoxicity. This is consistent with the view that, compared to normal RPE cells, ARPE-19 cells exhibit a diseased RPE phenotype that also includes elevated expression of the mesenchymal indicator vimentin, elevated integrin a5 promotor strength and deficient secretion of the anti-VEGF molecule pigment-epithelium-derived factor fostering weaker tight junctions.

Proeryptotic Activity of 4-Hydroxynonenal: A New Potential Physiopathological Role for Lipid Peroxidation Products

Background: Eryptosis is a physiological, apoptosis-like death of injured erythrocytes crucial to prevent premature haemolysis and the pathological sequalae generated by cell-free haemoglobin. When dysregulated, the process is associated to several inflammatory-based pathologies. 4-Hydroxy-trans-2-nonenal (HNE) is an endogenous signalling molecule at physiological levels and, at higher concentrations, is involved in the pathogenesis of several inflammatory-based diseases. This work evaluated whether HNE could induce eryptosis in human erythrocytes. Methods: Measurements of phosphatidylserine, cell volume, intracellular oxidants, Ca⁺⁺, glutathione, ICAM-1, and ceramide were assessed by flow cytometry. Scanning electron microscopy evaluated morphological alterations of erythrocytes. Western blotting assessed caspases. PGE₂ was measured by ELISA. Adhesion of erythrocytes on endothelial cells was evaluated by gravity adherence assay. Results: HNE in the concentration range between 10–100 µM induces eryptosis, morphological alterations correlated to caspase-3 activation, and increased Ca⁺⁺ levels. The process is not mediated by redox-dependent mechanisms; rather, it strongly depends on PGE₂ and ceramide. Interestingly, HNE induces significant increase of erythrocytes adhesion to endothelial cells (ECs) that are in turn dysfunctionated as evident by overexpression of ICAM-1. Conclusions: Our results unveil a new physiopathological role for HNE, provide mechanistic details of the HNE-induced eryptosis, and suggest a novel mechanism through which HNE could exert pro-inflammatory effects.

Involvement of Metabolic Lipid Mediators in the Regulation of Apoptosis

Apoptosis is the physiological mechanism of cell death and can be modulated by endogenous and exogenous factors, including stress and metabolic alterations. Reactive oxygen species (ROS), as well as ROS-dependent lipid peroxidation products (including isoprostanes and reactive aldehydes including 4-hydroxynonenal) are proapoptotic factors. These mediators can activate apoptosis via mitochondrial-, receptor-, or ER stress-dependent pathways. Phospholipid metabolism is also an essential regulator of apoptosis, producing the proapoptotic prostaglandins of the PGD and PGJ series, as well as the antiapoptotic prostaglandins of the PGE series, but also 12-HETE and 20-HETE. The effect of endocannabinoids and phytocannabinoids on apoptosis depends on cell type-specific differences. Cells where cannabinoid receptor type 1 (CB1) is the dominant cannabinoid receptor, as well as cells with high cyclooxygenase (COX) activity, undergo apoptosis after the administration of cannabinoids. In contrast, in cells where CB2 receptors dominate, and cells with low COX activity, cannabinoids act in a cytoprotective manner. Therefore, cell type-specific differences in the pro- and antiapoptotic effects of lipids and their (oxidative) products might reveal new options for differential bioanalysis between normal, functional, and degenerating or malignant cells, and better integrative biomedical treatments of major stress-associated diseases.

In Vitro Aging of Human Skin Fibroblasts: Age-Dependent Changes in 4-Hydroxynonenal Metabolism

Evidence suggests that the increased production of free radicals and reactive oxygen species lead to cellular aging. One of the consequences is lipid peroxidation generating reactive aldehydic products, such as 4-hydroxynonenal (HNE) that modify proteins and form adducts with DNA bases. To prevent damage by HNE, it is metabolized. The primary metabolic products are the glutathione conjugate (GSH-HNE), the corresponding 4-hydroxynonenoic acid (HNA), and the alcohol 1,4-dihydroxynonene (DHN). Since HNE metabolism can potentially change during in vitro aging, cell cultures of primary human dermal fibroblasts from several donors were cultured until senescence. After different time points up to 30 min of incubation with 5 µM HNE, the extracellular medium was analyzed for metabolites via liquid chromatography coupled with electrospray ionization mass spectrometry (LC/ESI-MS). The metabolites appeared in the extracellular medium 5 min after incubation followed by a time-dependent increase. But, the formation of GSH-HNL and GSH-DHN decreased with increasing in vitro age. As a consequence, the HNE levels in the cells increase and there is more protein modification observed. Furthermore, after 3 h of incubation with 5 µM HNE, younger cells showed less proliferative capacity, while in older cells slight increase in the mitotic index was noticed.

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.

Aldehyde Dehydrogenase 2 and Heart Failure

Heart failure (HF) is a structural or functional cardiac abnormal syndrome characterized with series of symptoms and signs such as breathlessness, fatigue, pulmonary crackles, and peripheral edema. Being a terminal phase of most myocardial lesions, HF has become a leading cause of mobility and mortality worldwide, associated with heavy clinical burden and economic costs affecting over 23 million people [14]. There is an increase to 5.5% with systolic dysfunction and an increase to 36.0% with diastolic dysfunction in people 60 years or older [85]. The costs accompanied with heart failure stand 2-3% of the total healthcare system expenditure in high-income countries and are expected to increase >2-fold in the next 2 decades [34].

Glutathione transferase P silencing promotes neuronal differentiation of retinal R28 cells

Glutathione transferases (GSTs) play an important role in retinal pathophysiology. Within this family, the GSTP isoform is known as an endogenous regulator of cell survival and proliferation pathways and of cellular responses to oxidative stress. In the present study we silenced GSTP in R28 cells, a retinal precursor cell line with markers of both glial and neuronal origin, and obtained stable clones which were viable and, unexpectedly, characterized by a more neuronal phenotype. The degree of neuronal differentiation was inversely correlated with GSTP residual expression levels. The clone with the lowest expression of GSTP showed metabolic reprogramming, a more favorable redox status and, despite its neuronal phenotype, a sensitivity to glutamate and 4-hydroxynonenal toxicity comparable to that of control cells. Altogether, our evidence shows that near full depletion of GSTP in retinal precursor cells, triggers neuronal differentiation and prosurvival metabolic changes.

A derivative of betulinic acid protects human Retinal Pigment Epithelial (RPE) cells from cobalt chloride-induced acute hypoxic stress

The Retinal Pigment Epithelium (RPE) is a monolayer of cells located above the choroid. It mediates human visual cycle and nourishes photoreceptors. Hypoxia-induced oxidative stress to RPE is a vital cause of retinal degeneration such as the Age-related Macular Degeneration. Most of these retinal diseases are irreversible with no efficient treatment, therefore protecting RPE cells from hypoxia stress is an important way to prevent or slow down the progression of retinal degeneration. Betulinic acid (BA) and betulin (BE) are pentacyclic triterpenoids with anti-oxidative property, but little is known about their effect on RPE cells. We investigated the protective effect of BA, BE and their derivatives against cobalt chloride-induced hypoxia stress in RPE cells. Human ARPE-19 cells were exposed to BA, BE and their eighteen derivatives (named as H3H20) that we customized through replacing moieties at C3 and C28 positions. We found that cobalt chloride reduced cell viability, increased Reactive Oxygen Species (ROS) production as well as induced apoptosis and necrosis in ARPE-19 cells. Interestingly, the pretreatment of 3-O-acetyl-glycyl- 28-O-glycyl-betulinic acid effectively protected cells from acute hypoxia stress induced by cobalt chloride. Our immunoblotting results suggested that this derivative attenuated the cobalt chloride-induced activation of Akt, Erk and JNK pathways. All findings were further validated in human primary RPE cells. In summary, this BA derivate has protective effect against the acute hypoxic stress in human RPE cells and may be developed into a candidate agent effective in the prevention of prevalent retinal diseases.

Oxidative stress induces ferroptotic cell death in retinal pigment epithelial cells

The dysfunction and cell death of retinal pigment epithelial (RPE) cells are hallmarks of late-stage dry (atrophic) age-related macular degeneration (AMD), for which no effective therapy has yet been developed. Previous studies have indicated that iron accumulation is a source of excess free radical production in RPE, and age-dependent iron accumulation in RPE is accelerated in patients with dry AMD. Although the pathogenic role of oxidative stress in RPE in the development of dry AMD is widely accepted, the mechanisms of oxidative stress-induced RPE cell death remain elusive. Here, we show that ferroptotic cell death, a mode of regulated necrosis mediated by iron and lipid peroxidation, is implicated in oxidative stress-induced RPE cell death in vitro. In ARPE-19 cells we observed that the ferroptosis inhibitors ferrostatin-1 and deferoxamine (DFO) rescued tert-butyl hydroperoxide (tBH)-induced RPE cell death more effectively than inhibitors of apoptosis or necroptosis. tBH-induced RPE cell death was accompanied by the three characteristics of ferroptotic cell death: lipid peroxidation, glutathione depletion, and ferrous iron accumulation, which were all significantly attenuated by ferrostatin-1 and DFO. Exogenous iron overload enhanced tBH-induced RPE cell death, but this effect was also attenuated by ferrostatin-1 and DFO. Furthermore, mRNA levels of numerous genes known to regulate iron metabolism were observed to be influenced by oxidative stress. Taken together, our observations suggest that multiple modes of cell death are involved in oxidative stress-induced RPE cell death, with ferroptosis playing a particularly important role.

Regulatory roles of glutathione-S-transferases and 4-hydroxynonenal in stress-mediated signaling and toxicity

Glutathione-S-Transferases (GSTs) have primarily been thought to be xenobiotic metabolizing enzymes that protect cells from toxic drugs and environmental electrophiles. However, in last three decades, these enzymes have emerged as the regulators of oxidative stress-induced signaling and toxicity. 4-Hydroxy-trans 2-nonenal (HNE) an end-product of lipid peroxidation, has been shown to be a major determinant of oxidative stress-induced signaling and toxicity. HNE is involved in signaling pathways, including apoptosis, proliferation, modulation of gene expression, activation of transcription factors/repressors, cell cycle arrest, and differentiation. In this article, available evidence for a major role of GSTs in the regulation of HNE-mediated cell signaling processes through modulation of the intracellular levels of HNE is discussed.

4-hydroxynonenal-mediated signaling and aging

4-Hydroxy-2-nonenal (HNE), one of the major α, β-unsaturated aldehydes produced during lipid peroxidation, is a potent messenger in mediating signaling pathways. Lipid peroxidation and HNE production appear to increase with aging. Although the cause and effect relation remains arguable, aging is associated with significant changes in diverse signaling events, characterized by enhanced or diminished responses of specific signaling pathways. In this review we will discuss how HNE may contribute to aging-related alterations of signaling pathways.

Cardiac Cell Senescence and Redox Signaling

Aging is characterized by a progressive loss of the ability of the organism to cope with stressors and to repair tissue damage. As a result, chronic diseases, including cardiovascular disease, increase their prevalence with aging, underlining the existence of common mechanisms that lead to frailty and age-related diseases. In this frame, the progressive decline of the homeostatic and reparative function of primitive cells has been hypothesized to play a major role in the evolution of cardiac pathology to heart failure. Although initially it was believed that reactive oxygen species (ROS) were produced in an unregulated manner as a byproduct of cellular metabolism, causing macromolecular damage and aging, accumulating evidence indicate the major role played by redox signaling in physiology. Aim of this review is to critically revise evidence linking ROS to cell senescence and aging and to provide evidence of the primary role played by redox signaling, with a particular emphasis on the multifunctional protein APE1/Ref in stem cell biology. Finally, we will discuss evidence supporting the role of redox signaling in cardiovascular cells.

Nrf-2/Gst-α mediated imatinib resistance through rapid 4-HNE clearance

The advent of imatinib mesylate (IM) has dramatically improved the outcome of patients with chronic myeloid leukemia, but drug resistance, particularly in advanced stage of disease, portents eventual relapse and progression. To identify the candidate molecule responsible for resistance during IM treatment, an IM-resistant K562 cell line was generated by culturing in gradually increasing dose of IM. The expression of Nrf-2 and its downstream target, Gst-α, were significantly induced in these cells. GST-α, in turn, mediated cell survival by maintaining intracellular low level of 4-HNE. Inhibition of Nrf-2 effectively reduced the expression of Gst-α, resulting in accumulation of 4-HNE and elevated sensitiveness to IM. Moreover, in IM-sensitive K562 cells enforced Gst-α expression strikingly protected cells from the insult of IM. Finally, we also examined the levels of Nrf-2 in clinical bone morrow samples. Nrf-2 and Gst-α were more abundant in bone morrow of CML patients compared with that of healthy donors. In addition, Nrf-2 and Gst-α were further up-regulated in samples of patients with weak response to IM. In conclusion, our study shows that rapid clearance of 4-HNE by Nrf-2/GST may represents a novel molecular basis of IM resistance in CML.

Lipid radicals cause light-induced retinal degeneration

We have succeeded in detecting and scavenging lipid radicals in the retina of light induced AMD mice model.

Ptgr1 expression is regulated by NRF2 in rat hepatocarcinogenesis and promotes cell proliferation and resistance to oxidative stress

Prostaglandin reductase-1 (Ptgr1) is an alkenal/one oxidoreductase that is involved in the catabolism of eicosanoids and lipid peroxidation such as 4-hydroxynonenal (4-HNE). Recently, we reported that Ptgr1 is overexpressed in human clinical and experimentally induced samples of hepatocellular carcinoma (HCC). However, how the expression of this gene is regulated and its role in carcinogenesis are not yet known. Here, we studied parameters associated with antioxidant responses and the mechanisms underlying the induction of Ptgr1 expression by the activation of Nuclear Factor (erythroid-derived-2)-like-2 (NRF2). For these experiments, we used two protocols of induced hepatocarcinogenesis in rats. Furthermore, we determined the effect of PTGR1 on cell proliferation and resistance to oxidative stress in cell cultures of the epithelial liver cell line, C9. Ptgr1 was overexpressed during the early phase in altered hepatocyte foci, and this high level of expression was maintained in persistent nodules until tumors developed. Ptgr1 expression was regulated by NRF2, which bound to an antioxidant response element at -653bp in the rat Ptgr1 gene. The activation of NRF2 induced the activation of an antioxidant response that included effects on proteins such as glutamate-cysteine ligase, catalytic subunit, NAD(P)H dehydrogenase quinone-1 (NQO1) and glutathione-S-transferase-P (GSTP1). These effects may have produced a reduced status that was associated with a high proliferation rate in experimental tumors. Indeed, when Ptgr1 was stably expressed, we observed a reduction in the time required for proliferation and a protective effect against hydrogen peroxide- and 4-HNE-induced cell death. These data were consistent with data showing colocalization between PTGR1 and 4-HNE protein adducts in liver nodules. These findings suggest that Ptgr1 and antioxidant responses act as a metabolic adaptation and could contribute to proliferation and cell-death evasion in liver tumor cells. Furthermore, these data indicate that Ptgr1 could be used to design early diagnostic tools or targeted therapies for HCC.

4-hydroxynonenal regulates mitochondrial function in human small airway epithelial cells

Prolonged exposure to oxidative stress causes Acute Lung Injury (ALI) and significantly impairs pulmonary function. Previously we have demonstrated that mitochondrial dysfunction is a key pathological factor in hyperoxic ALI. While it is known that hyperoxia induces the production of stable, but toxic 4-hydroxynonenal (4-HNE) molecule, it is unknown how the reactive aldehyde disrupts mitochondrial function. Our previous in vivo study indicated that exposure to hyperoxia significantly increases 4-HNE-Protein adducts, as well as levels of MDA in total lung homogenates. Based on the in vivo studies, we explored the effects of 4-HNE in human small airway epithelial cells (SAECs). Human SAECs treated with 25 μM of 4-HNE showed a significant decrease in cellular viability and increased caspase-3 activity. Moreover, 4-HNE treated SAECs showed impaired mitochondrial function and energy production indicated by reduced ATP levels, mitochondrial membrane potential, and aconitase activity. This was followed by a significant decrease in mitochondrial oxygen consumption and depletion of the reserve capacity. The direct effect of 4-HNE on the mitochondrial respiratory chain was confirmed using Rotenone. Furthermore, SAECs treated with 25 μM 4-HNE showed a time-dependent depletion of total Thioredoxin (Trx) proteins and Trx activity. Taken together, our results indicate that 4-HNE induces cellular and mitochondrial dysfunction in human SAECs, leading to an impaired endogenous antioxidant response.

4-Hydroxy-2-nonenal induces apoptosis by activating ERK1/2 signaling and depleting intracellular glutathione in intestinal epithelial cells

Excessive reactive oxygen species (ROS) induces oxidative damage to cellular constituents, ultimately leading to induction of apoptotic cell death and the pathogenesis of various diseases. The molecular mechanisms for the action of ROS in intestinal diseases remain poorly defined. Here, we reported that 4-hydroxy-2-nonenal (4-HNE) treatment led to capses-3-dependent apoptosis accompanied by increased intracellular ROS level and reduced glutathione concentration in intestinal epithelial cells. These effects of 4-HNE were markedly abolished by the antioxidant L-cysteine derivative N-acetylcysteine (NAC). Further studies demonstrated that the protective effect of NAC was associated with restoration of intracellular redox state by Nrf2-related regulation of expression of genes involved in intracellular glutathione (GSH) biosynthesis and inactivation of 4-HNE-induced phosphorylation of extracellular signal-regulated protein kinases (ERK1/2). The 4-HNE-induced ERK1/2 activation was mediated by repressing mitogen-activated protein kinase phosphatase-1 (MKP-1), a negative regulator of ERK1/2, through a proteasome-dependent degradation mechanism. Importantly, either overexpression of MKP-1 or NAC treatment blocked 4-HNE-induced MKP-1 degradation, thereby protecting cell from apoptosis. These novel findings provide new insights into a functional role of MKP-1 in oxidative stress-induced cell death by regulating ERK1/2 MAP kinase in intestinal epithelial cells.

Glutathione S-transferase alpha 4 induction by activator protein 1 in colorectal cancer

Glutathione S-transferase alpha 4 (GSTA4) is a phase II detoxifying enzyme that metabolizes electrophiles and carcinogens including 4-hydroxy-2-nonenal (4-HNE), an endogenous carcinogen that contributes to colorectal carcinogenesis. In this study, we investigated GSTA4 expression and regulation in murine primary colonic epithelial cells, microbiome-driven murine colitis and human carcinomas. Exposure of YAMC cells to 4-HNE induced Gsta4 expression. Using an inflammation-associated model of colorectal cancer (CRC), Gsta4 expression increased in vivo in colon macrophages and serum after 2 weeks of colonization of IL-10 deficient (Il10^-/-) mice with Enterococcus faecalis. Increased expression was noted after 9 months of colonization in colon macrophages and epithelia in areas of inflammation. In human colon biopsies, immunohistochemistry showed no GSTA4 expression in normal epithelial cells, whereas GSTA4 was strongly expressed in the neoplastic epithelia of invasive carcinomas. For tubular adenomas, increased expression was primarily noted in stromal macrophages. Increased GSTA4 was confirmed in established human CRC cell lines and associated with 4-HNE-protein adducts in human colon adenomas and CRC. Next, we showed that 4-HNE induced activation of c-Jun and Nrf2, two components of the oncogenic transcription factor AP-1. AP-1 inhibitors and gene-specific small interfering RNAs partially suppressed GSTA4 expression. Co-immunoprecipitation confirmed interactions between c-Jun and Nrf2 supporting a role for AP-1 in regulating 4-HNE-induced GSTA4 expression. These findings demonstrate GSTA4 activation during 4-HNE-induced neoplastic transformation in colorectal carcinogenesis. GSTA4 is a potential surrogate biomarker for CRC screening and should provide novel approaches for chemoprevention.

Covalent Modification of CDK2 by 4-Hydroxynonenal as a Mechanism of Inhibition of Cell Cycle Progression

Oxidative stress is a contributing factor in a number of chronic diseases, including cancer, atherosclerosis, and neurodegenerative diseases. Lipid peroxidation that occurs during periods of oxidative stress results in the formation of lipid electrophiles, which can modify a multitude of proteins in the cell. 4-Hydroxy-2-nonenal (HNE) is one of the most well-studied lipid electrophiles and has previously been shown to arrest cells at the G1/S transition. Recently, proteomic data have shown that HNE is capable of covalently modifying CDK2, the kinase responsible for the G1/S transition. Here, we identify the sites adducted by HNE using recombinant CDK2 and show that HNE treatment suppresses the kinase activity of the enzyme. We further identify sites of adduction in HNE-treated intact human colorectal carcinoma cells (RKO) and show that HNE-dependent modification in cells is long-lived, disrupts CDK2 function, and correlates with a delay of progression of the cells into S-phase. We propose that adduction of CDK2 by HNE directly alters its activity, contributing to the cell cycle delay.

Fisetin and luteolin protect human retinal pigment epithelial cells from oxidative stress-induced cell death and regulate inflammation

Degeneration of retinal pigment epithelial (RPE) cells is a clinical hallmark of age-related macular degeneration (AMD), the leading cause of blindness among aged people in the Western world. Both inflammation and oxidative stress are known to play vital roles in the development of this disease. Here, we assess the ability of fisetin and luteolin, to protect ARPE-19 cells from oxidative stress-induced cell death and to decrease intracellular inflammation. We also compare the growth and reactivity of human ARPE-19 cells in serum-free and serum-containing conditions. The absence of serum in the culture medium did not prevent ARPE-19 cells from reaching full confluency but caused an increased sensitivity to oxidative stress-induced cell death. Both fisetin and luteolin protected ARPE-19 cells from oxidative stress-induced cell death. They also significantly decreased the release of pro-inflammatory cytokines into the culture medium. The decrease in inflammation was associated with reduced activation of MAPKs and CREB, but was not linked to NF- κB or SIRT1. The ability of fisetin and luteolin to protect and repair stressed RPE cells even after the oxidative insult make them attractive in the search for treatments for AMD.

RPE necroptosis in response to oxidative stress and in AMD

Age-related macular degeneration (AMD) is the leading cause of irreversible blindness in the elderly. The underlying mechanism of non-neovascular AMD (dry AMD), also named geographic atrophy (GA) remains unclear and the mechanism of retinal pigment epithelial (RPE) cell death in AMD is controversial. We review the history and recent progress in understanding the mechanism of RPE cell death induced by oxidative stress, in AMD mouse models, and in AMD patients. Due to the limitation of toolsets to distinguish between apoptosis and necroptosis (or necrosis), most previous research concludes that apoptosis is a major mechanism for RPE cell death in response to oxidative stress and in AMD. Recent studies suggest necroptosis as a major mechanism of RPE cell death in response to oxidative stress. Moreover, ultrastructural and histopathological studies support necrosis as major mechanism of RPE cells death in AMD. In this review, we discuss the mechanism of RPE cell death in response to oxidative stress, in AMD mouse models, and in human AMD patients. Based on the literature, we hypothesize that necroptosis is a major mechanism for RPE cell death in response to oxidative stress and in AMD.

Visible Light-Induced Lipid Peroxidation of Unsaturated Fatty Acids in the Retina and the Inhibitory Effects of Blueberry Polyphenols

The lipid peroxidation of unsaturated fatty acids (UFAs) in the retina not only threatens visual cells but also affects the physiological health of the retina. In this work, the potential damages caused by daily visible light exposure on retinal UFAs were evaluated via a simulated in vitro model. At the same time, the benefits of dietary supplementation of blueberries to the eyes were also assessed. After prolonged light exposure, lipid peroxidation occurred for both docosahexaenoic and arachidonic acids (DHA and AA, respectively). The oxidized UFAs presented obvious cytotoxicity and significantly inhibited cell growth in retinal pigment epithelium cells. Among the different blueberry polyphenol fractions, the flavonoid-rich fraction, in which quercetin was discovered as the main component, was considerably better in preventing visible light-induced DHA lipid peroxidation than the anthocyanin- and phenolic acid-rich fractions. Then the retinal protective activity of blueberry polyphenols against light-induced retinal injury was confirmed in vivo. On the basis of the above results, inhibiting lipid peroxidation of UFAs in the retina is proposed to be another important function mechanism for antioxidants to nourish eyes.

4-Acetoxyphenol Prevents RPE Oxidative Stress-Induced Necrosis by Functioning as an NRF2 Stabilizer

PURPOSE

Oxidative stress has been suggested to be a major risk factor for the pathogenesis of AMD. Retinal pigment epithelial (RPE) cells are essential for maintaining the homeostasis of the retina, and RPE cell death and the resultant photoreceptor apoptosis have been observed in dry AMD, especially in geographic atrophy. The purpose of this article was to identify and repurpose the Food and Drug Administration-approved natural compound 4-Acetoxyphenol (4-AC), and to evaluate its effect and mechanism in protecting against oxidative stress-induced RPE necrosis.

METHODS

We exposed ARPE-19 cells to tert-Butyl hydroperoxide (tBHP) after pretreatment with 4-AC, and measured cell viability by MTT assay. Aggregation of RIPK3 and HMGB1 nuclear release were analyzed by transfected reporter genes. Reactive oxygen species (ROS) were measured using a commercially available ROS detection system. The importance of the NRF2/NQO1/HO-1 pathway in mediating 4-AC function was corroborated by siRNA studies, qRT-PCR, and immunostaining.

RESULTS

We have identified a natural antioxidant, 4-AC, which demonstrates strong abilities to protect RPE cells from oxidative stress-induced necrosis. Mechanistically, 4-AC blocked the increase of cellular ROS induced by oxidative stress, and upregulated NQO1 and HO-1 genes by stabilizing and inducing the nuclear translocation of NRF2 transcription factor. The NQO1, HO-1, and NRF2 were further shown to be required for 4-AC protection of RPE cells from death induced by tBHP. The tBHQ, an NRF2 stabilizer, consistently mimicked the protective effect of 4-AC against tBHP-induced RPE death.

CONCLUSIONS

The compound 4-AC protects ARPE-19 cells from oxidative stress-induced necrosis through upregulation of NQO1 and HO-1 genes by stabilization of NRF2.