Haem oxygenase-1 overexpression alters intracellular iron distribution. Biochem J. 2013;449:189-194. [PMID: 22989377 DOI: 10.1042/bj20120936]

The significance of precisely regulating heme oxygenase-1 expression: Another avenue for treating age-related ocular disease?

Aging entails the deterioration of the body's organs, including overall damages at both the genetic and cellular levels. The prevalence of age-related ocular disease such as macular degeneration, dry eye diseases, glaucoma and cataracts is increasing as the world's population ages, imposing a considerable economic burden on individuals and society. The development of age-related ocular disease is predominantly triggered by oxidative stress and chronic inflammatory reaction. Heme oxygenase-1 (HO-1) is a crucial antioxidant that mediates the degradative process of endogenous iron protoporphyrin heme. It catalyzes the rate-limiting step of the heme degradation reaction, and releases the metabolites such as carbon monoxide (CO), ferrous, and biliverdin (BV). The potent scavenging activity of these metabolites can help to defend against peroxides, peroxynitrite, hydroxyl, and superoxide radicals. Other than directly decomposing endogenous oxidizing substances (hemoglobin), HO-1 is also a critical regulator of inflammatory cells and tissue damage, exerting its anti-inflammation activity through regulating complex inflammatory networks. Therefore, promoting HO-1 expression may act as a promising therapeutic strategy for the age-related ocular disease. However, emerging evidences suggest that the overexpression of HO-1 significantly contributes to ferroptosis due to its dual nature. Surplus HO-1 leads to excessive Fe2+ and reactive oxygen species, thereby causing lipid peroxidation and ferroptosis. In this review, we elucidate the role of HO-1 in countering age-related disease, and summarize recent pharmacological trials that targeting HO-1 for disease management. Further refinements of the knowledge would position HO-1 as a novel therapeutic target for age-related ocular disease.

Study on the differential hepatotoxicity of raw polygonum multiflorum and polygonum multiflorum praeparata and its mechanism

BACKGROUND

Polygonum multiflorum (PM), a widely used traditional Chinese medicine herb, is divided into two forms, namely raw polygonum multiflorum (RPM) and polygonum multiflorum praeparata (PMP), according to the processing procedure. Emerging data has revealed the differential hepatotoxicity of RPM and PMP, however, its potential mechanism is still unclear.

METHODS

In our study, we investigated the differential hepatotoxicity of RPM and PMP exerted in C57BL/6 mice. First, sera were collected for biochemical analysis and HE staining was applied to examine the morphological alternation of the liver. Then we treated L02 cells with 5 mg / mL of RPM or PMP. The CCK8 and EdU assays were utilized to observe the viability and proliferation of L02 cells. RNA sequencing was performed to explore the expression profile of L02 cells. Western blotting was performed to detect the expression level of ferroptosis-related protein. Flow cytometry was used to evaluate ROS accumulation.

RESULTS

In our study, a significant elevation in serum ALT, AST and TBIL levels was investigated in the RMP group, while no significant differences were observed in the PMP group, compared to that of the CON group. HE staining showed punctate necrosis, inflammatory cell infiltration and structural destruction can be observed in the RPM group, which can be significantly attenuated after processing. In addition, we also found RPM could decrease the viability and proliferation capacity of L02 cells, which can be reversed by ferroptosis inhibitor. RNA sequencing data revealed the adverse effect of PM exerted on the liver is closely associated with ferroptosis. Western blotting assay uncovered the protein level of GPX4, HO-1 and FTL was sharply decreased, while the ROS content was dramatically elevated in L02 cells treated with RPM, which can be partially restored after processing.

CONCLUSIONS

The hepatotoxicity induced by RPM was significantly lower than the PMP, and its potential mechanism is associated with ferroptosis.

Crosstalk of ferroptosis and oxidative stress in infectious diseases

Ferroptosis is a type of programmed cell death that pathogens can leverage to enhance their replication, transmission, and pathogenicity. Hosts typically combat pathogenic infections by utilizing oxidative stress as a defense mechanism. Nonetheless, some pathogens can trigger considerable oxidative stress while infecting, inducing an intense inflammatory response in the host's immune system and activating cell death. The process of ferroptosis is closely linked to oxidative stress, with their interaction exerting a substantial impact on the outcome of infectious diseases. This article presents an overview of the interrelated mechanisms of both Ferroptosis and oxidative stress in infectious diseases, identifying potential targets for treating such diseases in the context of their interaction.

Magnetospirillum magneticum triggers apoptotic pathways in human breast cancer cells

The use of bacteria in cancer immunotherapy has the potential to bypass many shortcomings of conventional treatments. The ability of anaerobic bacteria to preferentially accumulate and replicate in hypoxic regions of solid tumors, as a consequence of bacterial metabolic needs, is particularly advantageous and key to boosting their immunostimulatory therapeutic actions in situ. While several of these bacterial traits are well-studied, little is known about their competition for nutrients and its effect on cancer cells which could serve as another potent and innate antineoplastic action. Here, we explored the consequences of the iron-scavenging abilities of a particular species of bacteria, Magnetospirillum magneticum, which has been studied as a potential new class of bacteria for magnetically targeted bacterial cancer therapy. We investigated their influence in hypoxic regions of solid tumors by studying the consequential metabolic effects exerted on cancer cells. To do so, we established an in vitro co-culture system consisting of the bacterial strain AMB-1 incubated under hypoxic conditions with human breast cancer cells MDA-MB-231. We first quantified the number of viable cells after incubation with magnetotactic bacteria demonstrating a lower rate of cellular proliferation that correlated with increasing bacteria-to-cancer cells ratio. Further experiments showed increasing populations of apoptotic cells when cancer cells were incubated with AMB-1 over a period of 24 h. Analysis of the metabolic effects induced by bacteria suggest an increase in the activation of executioner caspases as well as changes in levels of apoptosis-related proteins. Finally, the level of several human apoptosis-related proteins was investigated, confirming a bacteria-dependent triggering of apoptotic pathways in breast cancer cells. Overall, our findings support that magnetotactic bacteria could act as self-replicating iron-chelating agents and indicate that they interfere with proliferation and lead to increased apoptosis of cancer cells. This bacterial feature could serve as an additional antineoplastic mechanism to reinforce current bacterial cancer therapies.

Heme oxygenase 1 alleviates nonalcoholic steatohepatitis by suppressing hepatic ferroptosis

BACKGROUND

Heme oxygenase 1 (HO-1) has an influential but insufficiently investigated effect on ferroptosis, which is a novel form of programmed cell death and may play an effect on nonalcoholic steatohepatitis (NASH). However, the understanding of the mechanism is limited. Herein, our study aimed to explore the mechanism and role of HO-1 in NASH ferroptosis.

METHODS

Hepatocyte conditional HO-1 knockout (HO-1^HEPKO) C57BL/6J mice were established and fed a high-fat diet (HFD). Additionally, wild-type mice were fed either a normal diet or a HFD. Hepatic steatosis, inflammation, fibrosis, lipid peroxidation, and iron overload were assessed. AML12 and HepG2 cells were used to investigate the underlying mechanisms in vitro. Finally, liver sections from NASH patients were used to clinically validate the histopathology of ferroptosis.

RESULTS

In mice, HFD caused lipid accumulation, inflammation, fibrosis, and lipid peroxidation, which were aggravated by HO-1^HEPKO. In line with the in vivo results, HO-1 knockdown upregulated reactive oxygen species accumulation, lipid peroxidation, and iron overload in AML12 and HepG2 cells. Additionally, HO-1 knockdown reduced the GSH and SOD levels, which was in contrast to HO-1 overexpression in vitro. Furthermore, the present study revealed that the NF-κB signaling pathway was associated with ferroptosis in NASH models. Likewise, these findings were consistent with the liver histopathology results of NASH patients.

CONCLUSION

The current study showed that HO-1 could alleviate NASH progression by mediating ferroptosis.

5-Aminolevrinic Acid Exhibits Dual Effects on Stemness in Human Sarcoma Cell Lines under Dark Conditions

5-aminolevulinic acid (ALA) is used for tumor-targeting phototherapy because it is converted to protoporphyrin IX (PPIX) upon excitation and induces phototoxicity. However, the effect of ALA on malignant cells under unexcited conditions is unclear. This information is essential when administering ALA systemically. We used sarcoma cell lines that usually arise deep in the body and are rarely exposed to light to examine the effects of ALA treatment under light (daylight lamp irradiation) and dark (dark room) conditions. ALA-treated human SW872 liposarcoma cells and human MG63 osteosarcoma cells cultured under light exhibited growth suppression and increased oxidative stress, while cells cultured in the dark showed no change. However, sphere-forming ability increased in the dark, and the expression of stem-cell-related genes was induced in dark, but not light, conditions. ALA administration increased heme oxygenase 1 (HO-1) expression in both cell types; when carbon monoxide (CO), a metabolite of HO-1, was administered to sarcoma cells via carbon-monoxide-releasing molecule 2 (CORM2), it enhanced sphere-forming ability. We also compared the concentration of biliverdin (BVD) (a co-product of HO-1 activity alongside CO) with sphere-forming ability when HO-1 activity was inhibited using ZnPPIX in the dark. Both cell types showed a peak in sphere-forming ability at 60–80 μM BVD. Furthermore, a cell death inhibitor assay revealed that the HO-1-induced suppression of sphere formation was rescued by apoptosis or ferroptosis inhibitors. These findings suggest that in the absence of excitation, ALA promotes HO-1 expression and enhances the stemness of sarcoma cells, although excessive HO-1 upregulation induces apoptosis and ferroptosis. Our data indicate that systemic ALA administration induces both enhanced stemness and cell death in malignant cells located in dark environments deep in the body and highlight the need to pay attention to drug delivery and ALA concentrations during phototherapy.

HMOX1 Promotes Ferroptosis in Mammary Epithelial Cells via FTH1 and Is Involved in the Development of Clinical Mastitis in Dairy Cows

Ferroptosis is associated with inflammatory diseases as a lethal iron-dependent lipid peroxidation; its role in the development of clinical mastitis (CM) in dairy cows is not well understood. The aim of this study was to identify differentially expressed proteins (DEPs) associated with iron homeostasis and apoptosis, and to investigate further their roles in dairy cows with CM. The results suggested that ferroptosis occurs in the mammary glands of Holstein cows with CM. Using data-independent acquisition proteomics, 302 DEPs included in 11 GO terms related to iron homeostasis and apoptosis were identified. In particular, heme oxygenase-1 (HMOX1) was identified and involved in nine pathways. In addition, ferritin heavy chain 1 (FTH1) was identified and involved in the ferroptosis pathway. HMOX1 and FTH1 were located primarily in mammary epithelial cells (MECs), and displayed significantly up-regulated expression patterns compared to the control group (healthy cows). The expression levels of HMOX1 and FTH1 were up-regulated in a dose-dependent manner in LPS induced MAC-T cells with increased iron accumulation. The expression levels of HMOX1 and FTH1 and iron accumulation levels in the MAC-T cells were significantly up-regulated by using LPS, but were lower than the levels seen with Erastin (ERA). Finally, we deduced the mechanism of ferroptosis in the MECs of Holstein cows with CM. These results provide new insights for the prevention and treatment of ferroptosis-mediated clinical mastitis in dairy animals.

A Dual Role of Heme Oxygenase-1 in Tuberculosis

Iron metabolism is vital for the survival of both humans and microorganisms. Heme oxygenase-1 (HO-1) is an essential stress-response enzyme highly expressed in the lungs, and catabolizes heme into ferrous iron, carbon monoxide (CO), and biliverdin (BV)/bilirubin (BR), especially in pathological conditions which cause oxidative stress and inflammation. Ferrous iron (Fe²⁺) is an important raw material for the synthesis of hemoglobin in red blood cells, and patients with iron deficiency are often associated with decreased cellular immunity. CO and BR can inhibit oxidative stress and inflammation. Thus, HO-1 is regarded as a cytoprotective molecule during the infection process. However, recent study has unveiled new information regarding HO-1. Being a highly infectious pathogenic bacterium, Mycobacterium tuberculosis (MTB) infection causes acute oxidative stress, and increases the expression of HO-1, which may in turn facilitate MTB survival and growth due to increased iron availability. Moreover, in severe cases of MTB infection, excessive reactive oxygen species (ROS) and free iron (Fe²⁺) due to high levels of HO-1 can lead to lipid peroxidation and ferroptosis, which may promote further MTB dissemination from cells undergoing ferroptosis. Therefore, it is important to understand and illustrate the dual role of HO-1 in tuberculosis. Herein, we critically review the interplay among HO-1, tuberculosis, and the host, thus paving the way for development of potential strategies for modulating HO-1 and iron metabolism.

Integrative analysis of the molecular mechanisms, immunological features and immunotherapy response of ferroptosis regulators across 33 cancer types

Ferroptosis is a recently described mode of cell death caused by the accumulation of intracellular iron and lipid reactive oxygen species (ROS), which play critical roles in tumorigenesis and cancer progression. However, the underlying molecular mechanisms and promising biomarkers of ferroptosis among cancers remain to be elucidated. In this study, 30 ferroptosis regulators in ferroptosis-related signaling pathways were identified and analyzed in 33 cancer types. We found transcriptomic aberrations and evaluated the prognostic value of ferroptosis regulators across 33 cancer types. Then, we predicted and validated potential transcription factors (including E2F7, KLF5 and FOXM1) and therapeutic drugs (such as cyclophosphamide, vinblastine, and gefitinib) that target ferroptosis regulators in cancer. Moreover, we explored the molecular mechanisms of ferroptosis and found that signaling pathways such as the IL-1 and IL-2 pathways are closely associated with ferroptosis. Additionally, we found that ferroptosis regulators have a close relationship with immunity-related parameters, including the immune score, immune cell infiltration level, and immune checkpoint protein level. Finally, we determined a ferroptosis score using GSVA method. We found that the ferroptosis score effectively predicted ferroptotic cell death in tumor samples. And ferroptosis score is served as an independent prognostic indicator for the incidence and recurrence of cancers. More importantly, patients with high ferroptosis scores received greater benefit from immunotherapy. We aslo created an online webserver based on the nomogram prognostic model to predict the survival in immunotherapy cohort. The reason for this outcome is partially the result of patients with a high ferroptosis rate also having high immune scores, HLA-related gene expression and immune checkpoint protein expression, such as PDL2 and TIM3. Moreover, patients with high ferroptosis scores exhibited CD8 T cell and TIL infiltration and immune-related signaling pathway enrichment. In summary, we systematically summarize the molecular characteristics, clinical relevance and immune features of ferroptosis across cancers and show that the ferroptosis score can be used as a prognostic factor and for the evaluation of immunotherapy effects.

Redox modulation of vitagenes via plant polyphenols and vitamin D: Novel insights for chemoprevention and therapeutic interventions based on organoid technology

Polyphenols are chemopreventive through the induction of nuclear factor erythroid 2 related factor 2 (Nrf2)-mediated proteins and anti-inflammatory pathways. These pathways, encoding cytoprotective vitagenes, include heat shock proteins, such as heat shock protein 70 (Hsp70) and heme oxygenase-1 (HO-1), as well as glutathione redox system to protect against cancer initiation and progression. Phytochemicals exhibit biphasic dose responses on cancer cells, activating at low dose, signaling pathways resulting in upregulation of vitagenes, as in the case of the Nrf2 pathway upregulated by hydroxytyrosol (HT) or curcumin and NAD/NADH-sirtuin-1 activated by resveratrol. Here, the importance of vitagenes in redox stress response and autophagy mechanisms, as well as the potential use of dietary antioxidants in the prevention and treatment of multiple types of cancer are discussed. We also discuss the possible relationship between SARS-CoV-2, inflammation and cancer, exploiting innovative therapeutic approaches with HT-rich aqueous olive pulp extract (Hidrox®), a natural polyphenolic formulation, as well as the rationale of Vitamin D supplementation. Finally, we describe innovative approaches with organoids technology to study human carcinogenesis in preclinical models from basic cancer research to clinical practice, suggesting patient-derived organoids as an innovative tool to test drug toxicity and drive personalized therapy.

Proteomics analysis of lung reveals inflammation and cell death induced by atmospheric H2S exposure in pig

Hydrogen sulfide (H₂S) is a popular toxic environmental gas and industrial pollutant, which can be harmful to multiple organ systems of both human and livestock, especially to the respiratory system. However, the injury mechanism of H₂S exposure to lung remains poorly understood. In this study, pig lung was selected as a H₂S exposure model for the first time. We first examined the histological damage and the mRNA expression of pro-inflammatory genes of lung in pigs exposed to H₂S. Histopathology change and increased mRNA level of pro-inflammatory cytokines demonstrated that H₂S exposure indeed induced inflammatory injury in the porcine lung. We then performed TMT-based quantitative proteomics analysis to probe the injury molecular mechanism. The proteomics results showed that 526 proteins have significant changes in abundance between control and H₂S treated swine. Further validation analysis of some H₂S responsive proteins using both Real-time quantitative PCR and western blotting demonstrated that proteomics data are reliable. KEGG pathway analysis revealed that these proteins were involved in antigen processing and presentation, complement and coagulation cascade, IL-17 signaling pathway, ferroptosis and necroptosis. Our data suggest that H₂S exposure induced immune suppression, inflammatory response and cell death. These findings provide a new insight into the complexity mechanisms of H₂S induced lung injury, and offer therapeutic potential as drug targets with a view towards curing the intoxication caused by H₂S.

Transcriptome Investigation and In Vitro Verification of Curcumin-Induced HO-1 as a Feature of Ferroptosis in Breast Cancer Cells

Ferroptosis is a form of oxidative cell death and has become a chemotherapeutic target for cancer treatment. Curcumin (CUR), a well-known cancer inhibitor, significantly inhibits the viability of breast cancer cells. Through transcriptomic analysis and flow cytometry experiments, it was found that after 48 hours of treatment of breast cancer cells at its half maximal inhibitory concentration (IC50), curcumin suppressed the viability of cancer cells via induction of ferroptotic death. Use of the ferroptosis inhibitor ferrostatin-1 and the iron chelator deferoxamine rescued cell death induced by curcumin. Furthermore, in subsequent cell validation experiments, the results showed that curcumin caused marked accumulation of intracellular iron, reactive oxygen species, lipid peroxides, and malondialdehyde, while glutathione levels were significantly downregulated. These changes are all manifestations of ferroptosis. Curcumin upregulates a variety of ferroptosis target genes related to redox regulation, especially heme oxygenase-1 (HO-1). Using the specific inhibitor zinc protoporphyrin 9 (ZnPP) to confirm the above experimental results showed that compared to the curcumin treatment group, treatment with ZnPP not only significantly improved cell viability but also reduced the accumulation of intracellular iron ions and other ferroptosis-related phenomena. Therefore, these data demonstrate that curcumin triggers the molecular and cytological characteristics of ferroptosis in breast cancer cells, and HO-1 promotes curcumin-induced ferroptosis.

Ferroptosis, a Regulated Neuronal Cell Death Type After Intracerebral Hemorrhage

Ferroptosis is a term that describes one form of regulated non-apoptotic cell death. It is triggered by the iron-dependent accumulation of lipid peroxides. Emerging evidence suggests a link between ferroptosis and the pathophysiological processes of neurological disorders, including stroke, degenerative diseases, neurotrauma, and cancer. Hemorrhagic stroke, also known as intracerebral hemorrhage (ICH), belongs to a devastating illness for its high level in morbidity and mortality. Currently, there are few established treatments and limited knowledge about the mechanisms of post-ICH neuronal death. The secondary brain damage after ICH is mainly attributed to oxidative stress and hemoglobin lysate, including iron, which leads to irreversible damage to neurons. Therefore, ferroptosis is becoming a common trend in research of neuronal death after ICH. Accumulative data suggest that the inhibition of ferroptosis may effectively prevent neuronal ferroptosis, thereby reducing secondary brain damage after ICH in animal models. Ferroptosis has a close relationship with oxidative damage and iron metabolism. This review reveals the pathological pathways and regulation mechanism of ferroptosis following ICH and then offers potential intervention strategies to mitigate neuron death and dysfunction after ICH.

Identification of PRDX6 as a regulator of ferroptosis

Ferroptosis is a newly characterized iron-dependent form of nonapoptotic regulated cell death triggered by lipid reactive oxygen species (LOOH). The dysregulation of ferroptosis is highly related to cancer, and the induction of ferroptosis is also proposed as a potential strategy for cancer therapy. Although several key regulators have been identified that are involved in ferroptosis, the molecular mechanism underlying this process remains largely unknown. Here, we report that Peroxiredoxin-6 (PRDX6) is a bona fide negative regulator of ferroptotic cell death. The knockdown of intracellular PRDX6 significantly enhances LOOH and ferroptotic cell death triggered by ferroptosis inducers (Erastin and RSL-3), which is correlated with the transcriptional activation of heme oxygenase-1. Moreover, overexpression of heme oxygenase-1 enhances both Erastin- and RSL-3-triggered LOOH, suggesting that heme oxygenase-1 mediates PRDX6 silencing-enhanced ferroptosis. More importantly, the application of a specific PRDX6 phospholipase A2 (iPLA2) inhibitor, MJ-33, synergistically enhances the ferroptosis induced by Erastin, suggesting that PRDX6 removes LOOH through its iPLA2 activity. Thus, our findings reveal an essential role of PRDX6 in protecting cells against ferroptosis and provide a potential target to improve the antitumor activity of ferroptosis-based chemotherapy.

Betula etnensis Raf. (Betulaceae) Extract Induced HO-1 Expression and Ferroptosis Cell Death in Human Colon Cancer Cells

Betula etnensis Raf. (Birch Etna) belonging to the Betulaceae family grows on the eastern slope of Etna. Many bioactive compounds present in Betula species are considered promising anticancer agents. In this study, we evaluated the effects of B. etnensis Raf. bark methanolic extract on a human colon cancer cell line (CaCo2). In order to elucidate the mechanisms of action of the extract, cellular redox status, cell cycle, and heme oxygenase-1 (HO-1) expression in ferroptosis induction were evaluated. Cell viability and proliferation were tested by tetrazolium (MTT) assayand cell cycle analysis, while cell death was evaluated by annexin V test and lactic dehydrogenase (LDH) release. Cellular redox status was assessed by measuring thiol groups (RSH) content, reactive oxygen species (ROS) production, lipid hydroperoxide (LOOH) levels and (γ-glutamylcysteine synthetase) γ-GCS and HO-1 expressions. The extract significantly reduced cell viability of CaCo2, inducing necrotic cell death in a concentration-depending manner. In addition, an increase in ROS levels and a decrease of RSH content without modulation in γ-GCS expression were detected, with an augmentation in LOOH levels and drastic increase in HO-1 expression. These results suggest that the B. etnensis Raf. extract promotes an oxidative cellular microenvironment resulting in CaCo2 cell death by ferroptosis mediated by HO-1 hyper-expression.

A Dual Role of Heme Oxygenase-1 in Cancer Cells

Heme oxygenase (HO)-1 is known to metabolize heme into biliverdin/bilirubin, carbon monoxide, and ferrous iron, and it has been suggested to demonstrate cytoprotective effects against various stress-related conditions. HO-1 is commonly regarded as a survival molecule, exerting an important role in cancer progression and its inhibition is considered beneficial in a number of cancers. However, increasing studies have shown a dark side of HO-1, in which HO-1 acts as a critical mediator in ferroptosis induction and plays a causative factor for the progression of several diseases. Ferroptosis is a newly identified iron- and lipid peroxidation-dependent cell death. The critical role of HO-1 in heme metabolism makes it an important candidate to mediate protective or detrimental effects via ferroptosis induction. This review summarizes the current understanding on the regulatory mechanisms of HO-1 in ferroptosis. The amount of cellular iron and reactive oxygen species (ROS) is the determinative momentum for the role of HO-1, in which excessive cellular iron and ROS tend to enforce HO-1 from a protective role to a perpetrator. Despite the dark side that is related to cell death, there is a prospective application of HO-1 to mediate ferroptosis for cancer therapy as a chemotherapeutic strategy against tumors.

Iron-mediated oxidative cell death is a potential contributor to neuronal dysfunction induced by neonatal hemolytic hyperbilirubinemia

The review article discusses current knowledge of iron-mediated oxidative cell death (ferroptosis) and its potential role in the pathogenesis of neuronal dysfunction induced by neonatal hemolytic hyperbilirubinemia. The connection between metabolic conditions related to hemolysis (iron and bilirubin overload) and iron-induced lipid peroxidation is highlighted. Neurotoxicity of iron and bilirubin is associated with their release from destructed erythrocytes in response to hemolytic disease. Iron overload initiates lipid peroxidation through the reactive oxygen species production resulting to oxidative damage to cells. Excessive loading of immature brain cells by iron-induced formation of reactive oxygen species contributes to the development of various neurodevelopmental disorders. The causal relationship between iron overload and susceptibility of brain cells to oxidative damage by ferroptosis appears to be associated not only with the amount of redox-active iron involved in oxidative cell damage but also with the degree of maturity of the neonatal brain. Neuronal dysfunction induced by neonatal hemolytic disease can represent a specific model of ferroptosis. The mechanism by which iron overload triggers ferroptosis is not completely explained. However, hemolysis of neonatal red blood cells appears to be a determining factor. Potential therapeutic strategy with iron-chelating agents to inhibit ferroptosis has a promising future in postnatal care.

Effect of iron on cholesterol 7α-hydroxylase expression in alcohol-induced hepatic steatosis in mice

Both iron and lipids are involved in the progression of alcoholic fatty liver disease (AFLD), but the interaction between iron and lipids in AFLD is unclear. Here, we tested the hypothesis that iron regulates the expression of genes involved in lipid metabolism through iron regulatory proteins (IRPs), which interact with the iron-responsive elements (IREs) in the untranslated regions (UTRs) of genes, resulting in lipid accumulation. Using "RNA structure software", we predicted the mRNA secondary structures of more than 100 genes involved in lipid metabolism to investigate whether the IRE structure exists in novel mRNAs. Cholesterol 7α-hydroxylase (Cyp7a1) has an IRE-like stem-loop, a noncanonical IRE structure, in its 3'-UTR. Cyp7a1 expression can be regulated by in vivo and in vitro iron treatment. In addition, the noncanonical IRE motif can efficiently bind both to IRP1 and IRP2. The results indicate that hepatic iron overloading in AFLD mice decreased Cyp7a1 expression and resulted in cholesterol accumulation, providing a new mechanism of iron-regulated gene transcription and translation through the interaction between iron and a noncanonical IRE structure in Cyp7a1 mRNA. This finding has significant implications in studying a proposed mechanism for the regulation of cholesterol homeostasis by an Fe/IRP/noncanonical IRE axis.

Heme oxygenase-1 accelerates erastin-induced ferroptotic cell death

The oncogenic RAS-selective lethal small molecule Erastin triggers a unique iron-dependent form of nonapoptotic cell death termed ferroptosis. Ferroptosis is dependent upon the production of intracellular iron-dependent reactive oxygen species (ROS), but not other metals. However, key regulators remain unknown. The heme oxygenase (HO) is a major intracellular source of iron. In this study, the role of heme oxygenase in Erastin-triggered ferroptotic cancer cell death has been investigated. Zinc protoporphyrin IX (ZnPP), a HO-1 inhibitor, prevented Erastin-triggered ferroptotic cancer cell death. Furthermore, Erastin induced the protein and mRNA levels of HO-1 in HT-1080 fibrosarcoma cells. HO-1+/+ and HO-1-/- fibroblast, HO-1 overexpression, and chycloheximide-treated experiments revealed that the expression of HO-1 has a decisive effects in Erastin-triggered cell death. Hemin and CO-releasing molecules (CORM) promote Erastin-induced ferroptotic cell death, not by biliverdin and bilirubin. In addition, hemin and CORM accelerate the HO-1 expression in the presence of Erastin and increase membranous lipid peroxidation. Thus, HO-1 is an essential enzyme for iron-dependent lipid peroxidation during ferroptotic cell death.

Molecular and Cellular Effects of Hydrogen Peroxide on Human Lung Cancer Cells: Potential Therapeutic Implications

Lung cancer has a very high mortality-to-incidence ratio, representing one of the main causes of cancer mortality worldwide. Therefore, new treatment strategies are urgently needed. Several diseases including lung cancer have been associated with the action of reactive oxygen species (ROS) from which hydrogen peroxide (H₂O₂) is one of the most studied. Despite the fact that H₂O₂ may have opposite effects on cell proliferation depending on the concentration and cell type, it triggers several antiproliferative responses. H₂O₂ produces both nuclear and mitochondrial DNA lesions, increases the expression of cell adhesion molecules, and increases p53 activity and other transcription factors orchestrating cancer cell death. In addition, H₂O₂ facilitates the endocytosis of oligonucleotides, affects membrane proteins, induces calcium release, and decreases cancer cell migration and invasion. Furthermore, the MAPK pathway and the expression of genes related to inflammation including interleukins, TNF-α, and NF-κB are also affected by H₂O₂. Herein, we will summarize the main effects of hydrogen peroxide on human lung cancer leading to suggesting it as a potential therapeutic tool to fight this disease. Because of the multimechanistic nature of this molecule, novel therapeutic approaches for lung cancer based on the use of H₂O₂ may help to decrease the mortality from this malignancy.

Potential scenarios leading to ovarian cancer arising from endometriosis

OBJECTIVES

The aim of this review was to highlight recent advances in our understanding of the pathogenesis of malignant transformation of endometriosis.

METHODS

This study reviewed the English-language literature concerning basic science studies of the potential promotion of carcinogenesis.

RESULTS

Repeated episodes of hemorrhage occur in endometriosis at the onset of menstruation. Extracellular hemoglobin, heme, and iron derivatives in endometriosis cause DNA damage and mutations, which create increased cellular susceptibility to oxidant-mediated cell killing. Excess DNA damage and mutations are linked to cell death, but not carcinogenesis. In response to an oxidative and inflammatory microenvironment, endometriotic cells and macrophages secrete antioxidants that control excess oxidative stress in the surrounding environment. Exposure of endometriotic cells to a sublethal level of oxidative stress may lead to carcinogenesis. Macrophages also secrete immunosuppressive factors that lead to promotion of malignant transformation.

DISCUSSION

At least two potential scenarios could result in ovarian cancer arising from endometriosis. The first step: extracellular hemoglobin, heme, and iron cause cellular oxidative damage by promoting reactive oxygen species formation, which results in DNA damage and mutations (ovarian cancer initiation from endometriosis). The second step: cancer progression may be associated with persistent antioxidant production favoring a protumoral microenvironment.

How Heme Oxygenase-1 Prevents Heme-Induced Cell Death

Earlier observations indicate that free heme is selectively toxic to cells lacking heme oxygenase-1 (HO-1) but how this enzyme prevents heme toxicity remains unexplained. Here, using A549 (human lung cancer) and immortalized human bronchial epithelial cells incubated with exogenous heme, we find knock-down of HO-1 using siRNA does promote the accumulation of cell-associated heme and heme-induced cell death. However, it appears that the toxic effects of heme are exerted by “loose” (probably intralysosomal) iron because cytotoxic effects of heme are lessened by pre-incubation of HO-1 deficient cells with desferrioxamine (which localizes preferentially in the lysosomal compartment). Desferrioxamine also decreases lysosomal rupture promoted by intracellularly generated hydrogen peroxide. Supporting the importance of endogenous oxidant production, both chemical and siRNA inhibition of catalase activity predisposes HO-1 deficient cells to heme-mediated killing. Importantly, it appears that HO-1 deficiency somehow blocks the induction of ferritin; control cells exposed to heme show ~10-fold increases in ferritin heavy chain expression whereas in heme-exposed HO-1 deficient cells ferritin expression is unchanged. Finally, overexpression of ferritin H chain in HO-1 deficient cells completely prevents heme-induced cytotoxicity. Although two other products of HO-1 activity–CO and bilirubin–have been invoked to explain HO-1-mediated cytoprotection, we conclude that, at least in this experimental system, HO-1 activity triggers the induction of ferritin and the latter is actually responsible for the cytoprotective effects of HO-1 activity.

Continuous de novo biosynthesis of haem and its rapid turnover to bilirubin are necessary for cytoprotection against cell damage

It is well known that haem serves as the prosthetic group of various haemoproteins that function in oxygen transport, respiratory chain, and drug metabolism. However, much less is known about the functions of the catabolites of haem in mammalian cells. Haem is enzymatically degraded to iron, carbon monoxide (CO), and biliverdin, which is then converted to bilirubin. Owing to difficulties in measuring bilirubin, however, the generation and transport of this end product remain unclear despite its clinical importance. Here, we used UnaG, the recently identified bilirubin-binding fluorescent protein, to analyse bilirubin production in a variety of human cell lines. We detected a significant amount of bilirubin with many non-blood cell types, which was sensitive to inhibitors of haem metabolism. These results suggest that there is a basal level of haem synthesis and its conversion into bilirubin. Remarkably, substantial changes were observed in the bilirubin generation when cells were exposed to stress insults. Since the stress-induced cell damage was exacerbated by the pharmacological blockade of haem metabolism but was ameliorated by the addition of biliverdin and bilirubin, it is likely that the de novo synthesis of haem and subsequent conversion to bilirubin play indispensable cytoprotective roles against cell damage.

Association of serum bilirubin and non-alcoholic fatty liver disease: A feasible therapeutic avenue?

AIM: To the look at the current strength of evidence and the potential application of anti-oxidants in this setting.

METHODS: Two electronic databases (PubMed and Web of Knowledge) were searched to January 2013 to find studies addressing serum bilirubin levels in non-alcoholic fatty liver disease (NAFLD). The search used key word combinations in relation to NAFLD and serum bilirubin specific to human adults only. After screening selected studies were reviewed in depth by two independent reviewers. Data synthesis with further meta-analysis was planned but not possible due to the heterogeneity of the outcome measures in these studies.

RESULTS: Out of 416 studies screened only seven studies were considered suitable for inclusion. All seven studies consistently reported an inverse association of bilirubin with NAFLD despite the heterogeneous sample of studies. Only two studies were prospective. No negative studies were found.

CONCLUSION: Most studies suggest a correlation between high bilirubin levels of any type are inversely correlated with NAFLD. But to date most of these studies have been poorly designed to allow meaningful conclusions, except one cohort study. There is a need for a large prospective cohort study in multiple populations to test this hypothesis fully before mechanistic associations can be established and therapeutic options of the apparent anti-oxidant effect of bilirubin be explored in NAFLD. Furthermore these studies should include analysis of UGT1A1 gene to expound upon underlying cause of unconjugated hyperbilirubinaemia.

Impaired TLR4 and HIF expression in cystic fibrosis bronchial epithelial cells downregulates hemeoxygenase-1 and alters iron homeostasis in vitro

Hemeoxygenase-1 (HO-1), an inducible heat shock protein, is upregulated in response to multiple cellular insults via oxidative stress, lipopolysaccharides (LPS), and hypoxia. In this study, we investigated in vitro the role of Toll-like receptor 4 (TLR4), hypoxia-inducible factor 1α (HIF-1α), and iron on HO-1 expression in cystic fibrosis (CF). Immunohistochemical analysis of TLR4, HO-1, ferritin, and HIF-1α were performed on lung sections of CFTR−/− and wild-type mice. CFBE41o- and 16HBE14o- cell lines were employed for in vitro analysis via immunoblotting, immunofluorescence, real-time PCR, luciferase reporter gene analysis, and iron quantification. We observed a reduced TLR4, HIF-1α, HO-1, and ferritin in CFBE41o- cell line and CF mice. Knockdown studies using TLR4-siRNA in 16HBE14o- revealed significant decrease of HO-1, confirming the role of TLR4 in HO-1 downregulation. Inhibition of HO-1 using tin protoporphyrin in 16HBE14o- cells resulted in increased iron levels, suggesting a probable role of HO-1 in iron accumulation. Additionally, sequestration of excess iron using iron chelators resulted in increased hypoxia response element response in CFBE41o- and 16HBE14o-, implicating a role of iron in HIF-1α stabilization and HO-1. To conclude, our in vitro results demonstrate that multiple regulatory factors, such as impaired TLR4 surface expression, increased intracellular iron, and decreased HIF-1α, downregulate HO-1 expression in CFBE41o- cells.

H-ferritin ferroxidase induces cytoprotective pathways and inhibits microvascular stasis in transgenic sickle mice

Hemolysis, oxidative stress, inflammation, vaso-occlusion, and organ infarction are hallmarks of sickle cell disease (SCD). We have previously shown that increases in heme oxygenase-1 (HO-1) activity detoxify heme and inhibit vaso-occlusion in transgenic mouse models of SCD. HO-1 releases Fe(2+) from heme, and the ferritin heavy chain (FHC) ferroxidase oxidizes Fe(2+) to catalytically inactive Fe(3+) inside ferritin. FHC overexpression has been shown to be cytoprotective. In this study, we hypothesized that overexpression of FHC and its ferroxidase activity will inhibit inflammation and microvascular stasis in transgenic SCD mice in response to plasma hemoglobin. We utilized a Sleeping Beauty (SB) transposase plasmid to deliver a human wild-type-ferritin heavy chain (wt-hFHC) transposable element by hydrodynamic tail vein injections into NY1DD SCD mice. Control SCD mice were infused with the same volume of lactated Ringer's solution (LRS) or a human triple missense FHC (ms-hFHC) plasmid with no ferroxidase activity. 8 weeks later, LRS-injected mice had ~40% microvascular stasis (% non-flowing venules) 1 h after infusion of stroma-free hemoglobin, while mice overexpressing wt-hFHC had only 5% stasis (p < 0.05), and ms-hFHC mice had 33% stasis suggesting vascular protection by ferroxidase active wt-hFHC. The wt-hFHC SCD mice had marked increases in splenic hFHC mRNA and hepatic hFHC protein, ferritin light chain (FLC), 5-aminolevulinic acid synthase (ALAS), heme content, ferroportin, nuclear factor erythroid 2-related factor 2 (Nrf2), and HO-1 activity and protein. There was also a decrease in hepatic activated nuclear factor-kappa B (NF-κB) phospho-p65 and vascular cell adhesion molecule-1 (VCAM-1). Inhibition of HO-1 activity with tin protoporphyrin demonstrated HO-1 was not essential for the protection by wt-hFHC. We conclude that wt-hFHC ferroxidase activity enhances cytoprotective Nrf2-regulated proteins including HO-1, thereby resulting in decreased NF-κB-activation, adhesion molecules, and microvascular stasis in transgenic SCD mice.

Are reactive oxygen species always detrimental to pathogens?

Reactive oxygen species (ROS) are deadly weapons used by phagocytes and other cell types, such as lung epithelial cells, against pathogens. ROS can kill pathogens directly by causing oxidative damage to biocompounds or indirectly by stimulating pathogen elimination by various nonoxidative mechanisms, including pattern recognition receptors signaling, autophagy, neutrophil extracellular trap formation, and T-lymphocyte responses. Thus, one should expect that the inhibition of ROS production promote infection. Increasing evidences support that in certain particular infections, antioxidants decrease and prooxidants increase pathogen burden. In this study, we review the classic infections that are controlled by ROS and the cases in which ROS appear as promoters of infection, challenging the paradigm. We discuss the possible mechanisms by which ROS could promote particular infections. These mechanisms are still not completely clear but include the metabolic effects of ROS on pathogen physiology, ROS-induced damage to the immune system, and ROS-induced activation of immune defense mechanisms that are subsequently hijacked by particular pathogens to act against more effective microbicidal mechanisms of the immune system. The effective use of antioxidants as therapeutic agents against certain infections is a realistic possibility that is beginning to be applied against viruses.

Dysregulated heme oxygenase-ferritin system in pterygium pathogenesis

PURPOSE

Cyclooxygenase (COX)-, lipoxygenase (LOX)-, and cytochrome P450 monooxygenase (CYP)-derived eicosanoids have been implicated in ocular surface inflammation and neovascularization. These eicosanoids are subjected to regulation by enzymes, such as heme oxygenases (HOs) and ferritin.

METHODS

Quantitative polymerase chain reaction and lipidomics based on liquid chromatography-tandem mass spectrometry were performed on pterygia from patients undergoing surgical pterygium excision. Control tissues consisted of donor corneas. In addition, lipidomics based on liquid chromatography-tandem mass spectrometry was performed on tears collected from patients before the surgery.

RESULTS

Messenger RNA (mRNA) expression of HO-2, the constitutive HO isoform, was upregulated by 40% in pterygia compared with control tissue, whereas the mRNA level of the inducible form, HO-1, was downregulated by more than 50%. Levels of CYP4B1 mRNA showed an approximate 2-fold increase in pterygia compared with control. Lipidomic analysis of tissues indicated a moderate elevation in Prostaglandin E2 and thromboxane B2 levels in pterygia compared with control. Among the LOX-derived metabolites, the antiinflammatory-hydroxyeicosatetraenoic acid (15-HETE) levels were significantly reduced in pterygia (79.3 ± 48.11 pg/mg protein) compared with control (586.2 ± 213.5 pg/mg protein), whereas the proinflammatory LOX- and CYP4B1-derived 12-HETE levels were 10-fold higher in pterygia (2768 ± 832.3 pg/mg protein) compared with control (231.4 ± 87.35 pg/mg protein). Prostaglandin E2 and HETEs were also present in tears from patients with pterygium but were not detected in tears from healthy volunteers. The mRNA expression levels of both light and heavy chain ferritin were 60% and 30% lower, respectively, in pterygia compared with control.

CONCLUSIONS

We believe that a dysfunctional HO-ferritin system leads to increased levels of proinflammatory mediators, thus contributing to the inflammation characteristic of pterygia.

Activation of heme oxygenase recovers motor function after spinal cord injury in rats

Characterization of auto-destructive mechanisms, leading to cell death after spinal cord injury (SCI) is important to prevent further damage to tissue. Heme oxygenase (HO) catalyzes the oxidation of heme to biliverdin and carbon monoxide (CO), as a response to cell damage. Products of HO action have biological effects, as antioxidant biliverdin. We evaluated the changes of HO activity after injury, and the effect of pharmacological treatments with hemin (an inducer) and (Sn)-protoporphyrin (an inhibitor, Sn-PPIX) of HO, upon motor recovery after SCI. Female Wistar rats were submitted to SCI by trauma and sacrificed at several times (2, 4, 8, 12 and 24h) after injury to evaluate HO activity. Additional groups of rats were treated with either hemin or Sn-PPIX, to evaluate motor recovery, spared spinal cord tissue and HO activity. Results showed that HO control activity was increased by effect of SCI, at all times evaluated, as compared to sham group values. Twenty-four hours after injury, HO activity was increased 7.2-fold by hemin treatment, as compared to SCI plus vehicle group values. In addition, animals treated with hemin 2 and 8h after SCI, showed a better motor recovery and higher spared cord tissue, as compared to control group values. Our findings indicate that activation of HO is a beneficial mechanism when attained during the acute phase after SCI.