Modulation of Inflammation and Immune Responses by Heme Oxygenase-1: Implications for Infection with Intracellular Pathogens

Untargeted metabolomics analysis reveals the metabolic disturbances and exacerbation of oxidative stress in recurrent spontaneous abortion

BACKGROUND

Recurrent spontaneous abortion (RSA) is characterized by the occurrence of two or more consecutive spontaneous abortions, with a rising prevalence among pregnant women and significant implications for their physical and mental well-being. The multifaceted etiology of RSA has posed challenges in unraveling the molecular mechanisms underlying that underlie its pathogenesis. Oxidative stress and immune response have been identified as pivotal factors in the development of its condition.

METHODS

Eleven serum samples from healthy pregnant women and 17 from RSA were subjected to liquid chromatography/mass spectrometry (LC-MS) analysis. Multivariate statistical analysis was employed to excavate system-level characterization of the serum metabolome. The measurement of seven oxidative stress products, namely superoxide dismutase (SOD), catalase (CAT), malonaldehyde (MDA), glutathione (GPx), glutathione peroxidase (GSH), oxidized glutathione (GSSG), heme oxygenase (HO-1), was carried out using ELISA.

RESULTS

Through the monitoring of metabolic and lipid alternations during RSA events, we have identified 816 biomarkers that were implicated in various metabolic pathways, including glutathione metabolism, phosphonate and phosphinate metabolism, nucleotide metabolism, sphingolipid metabolism, lysine degradation and purine metabolism, etc. These pathways have been found to be closely associated with the progression of the disease. Our finding indicated that the levels of MDA and HO-1 were elevated in the RSA group compared to the control group, whereas SOD, CAT and GPx exhibited a contrary pattern. However, no slight difference was observed in GSH and GSSG levels between the RSA group and the control group.

CONCLUSION

The manifestation of RSA elicited discernible temporal alternations in the serum metabolome and biochemical markers linked to the metabolic pathways of oxidative stress and immune response. Our investigation furnished a more comprehensive analytical framework encompassing metabolites and enzymes associated with oxidative stress. This inquiry furnished a more nuanced comprehension of the pathogenesis of RSA and established the ground work for prognostication and prophylaxis.

The Effects of Umbilical Cord Mesenchymal Stem Cells -Derived Exosomes in Oral Squamous Cell Carcinoma (In vitro Study)

OBJECTIVE

Mesenchymal stem cells (MSCs) derived exosomes offers several advantages as a cell-free therapeutic agents. In this study, Umbilical cord mesenchymal stem cells exosomes (UC-MSCs-exos) effects on oral squamous cell carcinoma (OSCC) cell line was evaluated.

METHODS

UC-MSCs-exos were isolated and co-cultured with OSCC cells and their impact on OSCC was explored by various tests. Comet assay and western blot for cleaved caspase-3 and immunocytochemistry for caspase-8 were used for apoptosis assessment. HO-1 and Nrf2 were used to determine antioxidant levels. Tumor necrosis factor-α and interleukin-6 were assessed as inflammatory biomarkers. HOX transcript antisense intergenic long noncoding RNA (HOTAIR) expression was also evaluated.

RESULTS

In a dose-dependent manner, UC-MSCs-exos reduced the levels of pro-inflammatory cytokines (IL-6 and TNF-α) and induced apoptosis of OSCC in vitro. Meanwhile, we found that UC-MSCs-exos downregulate HOTAIR.

CONCLUSION

UC-MSCs-exos conferred a suppressive role on OSCC in vitro, highlighting a promising therapeutic role. However, the exact potentially involved molecules and molecular mechanisms need to be investigated in further studies.

Transcription factor Nrf2 as a potential therapeutic target for COVID-19

The coronavirus disease 2019 (COVID-19) is caused by a novel severe acute respiratory syndrome (SARS)-like coronavirus (SARS-CoV-2). Critically ill patients with SARS-COV-2 infection frequently exhibit signs of high oxidative stress and systemic inflammation, which accounts for most of the mortality. Antiviral strategies to inhibit the pathogenic consequences of COVID-19 are urgently required. The nuclear factor erythroid 2-related transcription factor (Nrf2) is a transcription factor that is involved in antioxidant and anti-inflammatory defense in several tissues and cells. This review tries to present an overview of the role of Nrf2 in the treatment of COVID-19.

The use of carbon monoxide breath test to detect the effect of iron overload on erythrocyte lifespan in MDS

Objective

To investigate the effect of iron overload (IO) on red blood cell (RBC) lifespan in MDS patients with the use of carbon monoxide breath test

Methods

The red blood cell lifespan of 93 patients with myelodysplastic syndrome (MDS) and 22 healthy volunteers in the control group were measured by alveolar gas carbon monoxide (CO) assay, with the detection of liver iron concentration, iron metabolism index, erythropoietin (EPO) concentration, peripheral blood inflammatory cytokines, etc. The MDS patients were divided into the severe IO group, mild IO group and non IO group according to liver iron concentration. The effect of IO on RBC lifespan was analyzed in MDS patients.

Results

The RBC lifespan of MDS patients in the severe IO group was significantly lower than that in the mild IO group (p<0.05), while the RBC life span in the mild IO group was significantly lower than that in the non IO group (p<0.05). The expression of inflammatory cytokines in the severe IO group was significantly higher than that of the mild and non IO groups. After receiving iron removal treatment(ICT), the expression of inflammatory cytokines was decreased significantly, and the RBC lifespan was significantly prolonged (p<0.05).Besides, liver iron concentration was significantly positively correlated with EPO concentration, while EPO concentration was significantly negatively correlated with RBC lifespan, especially in the MDS-RS subgroup. The RBC lifespan in the EPO>1000 group was significantly lower than that in the EPO<1000 group.

Conclusion

IO can shorten RBC lifespan in MDS patients, which may be result from the increase of endogenous EPO and the over-expression of inflammatory cytokines. After ICT, the ineffective hematopoiesis caused by increased EPO may reduced and the decrease of inflammatory cytokine may significantly prolong the RBC lifespan in MDS patients.

The role of host heme in bacterial infection

Heme is an indispensable cofactor for almost all aerobic life, including the human host and many bacterial pathogens. During infection, heme and hemoproteins are the largest source of bioavailable iron, and pathogens have evolved various heme acquisition pathways to satisfy their need for iron and heme. Many of these pathways are regulated transcriptionally by intracellular iron levels, however, host heme availability and intracellular heme levels have also been found to regulate heme uptake in some species. Knowledge of these pathways has helped to uncover not only how these bacteria incorporate host heme into their metabolism but also provided insight into the importance of host heme as a nutrient source during infection. Within this review is covered multiple aspects of the role of heme at the host pathogen interface, including the various routes of heme biosynthesis, how heme is sequestered by the host, and how heme is scavenged by bacterial pathogens. Also discussed is how heme and hemoproteins alter the behavior of the host immune system and bacterial pathogens. Finally, some unanswered questions about the regulation of heme uptake and how host heme is integrated into bacterial metabolism are highlighted.

Impact of Oxidative Stress on Risk of Death and Readmission in African Children With Severe Malaria: A Prospective Observational Study

BACKGROUND

We hypothesized that oxidative stress in Ugandan children with severe malaria is associated with mortality.

METHODS

We evaluated biomarkers of oxidative stress in children with cerebral malaria (CM, n = 77) or severe malarial anemia (SMA, n = 79), who were enrolled in a randomized clinical trial of immediate vs delayed iron therapy, compared with community children (CC, n = 83). Associations between admission biomarkers and risk of death during hospitalization or risk of readmission within 6 months were analyzed.

RESULTS

Nine children with CM and none with SMA died during hospitalization. Children with CM or SMA had higher levels of heme oxygenase-1 (HO-1) (P < .001) and lower superoxide dismutase (SOD) activity than CC (P < .02). Children with CM had a higher risk of death with increasing HO-1 concentration (odds ratio [OR], 6.07 [95% confidence interval {CI}, 1.17-31.31]; P = .03) but a lower risk of death with increasing SOD activity (OR, 0.02 [95% CI, .001-.70]; P = .03). There were no associations between oxidative stress biomarkers on admission and risk of readmission within 6 months of enrollment.

CONCLUSIONS

Children with CM or SMA develop oxidative stress in response to severe malaria. Oxidative stress is associated with higher mortality in children with CM but not with SMA.

CLINICAL TRIALS REGISTRATION

NCT01093989.

Recent Advances in Host-Directed Therapies for Tuberculosis and Malaria

Tuberculosis (TB), caused by the bacterium Mycobacterium tuberculosis, and malaria, caused by parasites from the Plasmodium genus, are two of the major causes of death due to infectious diseases in the world. Both diseases are treatable with drugs that have microbicidal properties against each of the etiologic agents. However, problems related to treatment compliance by patients and emergence of drug resistant microorganisms have been a major problem for combating TB and malaria. This factor is further complicated by the absence of highly effective vaccines that can prevent the infection with either M. tuberculosis or Plasmodium. However, certain host biological processes have been found to play a role in the promotion of infection or in the pathogenesis of each disease. These processes can be targeted by host-directed therapies (HDTs), which can be administered in conjunction with the standard drug treatments for each pathogen, aiming to accelerate their elimination or to minimize detrimental side effects resulting from exacerbated inflammation. In this review we discuss potential new targets for the development of HDTs revealed by recent advances in the knowledge of host-pathogen interaction biology, and present an overview of strategies that have been tested in vivo, either in experimental models or in patients.

Crosstalk between Heme Oxygenase-1 and Iron Metabolism in Macrophages: Implications for the Modulation of Inflammation and Immunity

Heme oxygenase-1 (HO-1) is an enzyme that catalyzes the degradation of heme, releasing equimolar amounts of carbon monoxide (CO), biliverdin (BV), and iron. The anti-inflammatory and antioxidant properties of HO-1 activity are conferred in part by the release of CO and BV and are extensively characterized. However, iron constitutes an important product of HO-1 activity involved in the regulation of several cellular biological processes. The macrophage-mediated recycling of heme molecules, in particular those contained in hemoglobin, constitutes the major mechanism through which living organisms acquire iron. This process is finely regulated by the activities of HO-1 and of the iron exporter protein ferroportin. The expression of both proteins can be induced or suppressed in response to pro- and anti-inflammatory stimuli in macrophages from different tissues, which alters the intracellular iron concentrations of these cells. As we discuss in this review article, changes in intracellular iron levels play important roles in the regulation of cellular oxidation reactions as well as in the transcriptional and translational regulation of the expression of proteins related to inflammation and immune responses, and therefore, iron metabolism represents a potential target for the development of novel therapeutic strategies focused on the modulation of immunity and inflammation.

Heme Oxygenase-1: An Anti-Inflammatory Effector in Cardiovascular, Lung, and Related Metabolic Disorders

The heme oxygenase (HO) enzyme system catabolizes heme to carbon monoxide (CO), ferrous iron, and biliverdin-IXα (BV), which is reduced to bilirubin-IXα (BR) by biliverdin reductase (BVR). HO activity is represented by two distinct isozymes, the inducible form, HO-1, and a constitutive form, HO-2, encoded by distinct genes (HMOX1, HMOX2, respectively). HO-1 responds to transcriptional activation in response to a wide variety of chemical and physical stimuli, including its natural substrate heme, oxidants, and phytochemical antioxidants. The expression of HO-1 is regulated by NF-E2-related factor-2 and counter-regulated by Bach-1, in a heme-sensitive manner. Additionally, HMOX1 promoter polymorphisms have been associated with human disease. The induction of HO-1 can confer protection in inflammatory conditions through removal of heme, a pro-oxidant and potential catalyst of lipid peroxidation, whereas iron released from HO activity may trigger ferritin synthesis or ferroptosis. The production of heme-derived reaction products (i.e., BV, BR) may contribute to HO-dependent cytoprotection via antioxidant and immunomodulatory effects. Additionally, BVR and BR have newly recognized roles in lipid regulation. CO may alter mitochondrial function leading to modulation of downstream signaling pathways that culminate in anti-apoptotic, anti-inflammatory, anti-proliferative and immunomodulatory effects. This review will present evidence for beneficial effects of HO-1 and its reaction products in human diseases, including cardiovascular disease (CVD), metabolic conditions, including diabetes and obesity, as well as acute and chronic diseases of the liver, kidney, or lung. Strategies targeting the HO-1 pathway, including genetic or chemical modulation of HO-1 expression, or application of BR, CO gas, or CO donor compounds show therapeutic potential in inflammatory conditions, including organ ischemia/reperfusion injury. Evidence from human studies indicate that HO-1 expression may represent a biomarker of oxidative stress in various clinical conditions, while increases in serum BR levels have been correlated inversely to risk of CVD and metabolic disease. Ongoing human clinical trials investigate the potential of CO as a therapeutic in human disease.

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.

Citrate-capped gold nanoparticles with a diameter of 14 nm alter the expression of genes associated with stress response, cytoprotection and lipid metabolism in CaCo-2 cells

Advancements in nanotechnology have provided insight into the unique opportunities for the application of nanomaterials such as gold nanoparticles (AuNPs) in medicine due to their remarkable properties, which includes low toxicity, large surface area, and the ease of synthesis and conjugation to other molecules. Therefore, AuNPs are often preferred for bio-applications. Citrate-capped AuNPs (cAuNPs) have been reported to be non-cytotoxic and are used in numerous studies as drug delivery vehicles to treat various diseases. However, the limitations of bioassays often used to assess the toxicity of AuNPs have been well documented. Herein, we investigate the cytotoxicity of 14 nm cAuNPs in the human colorectal adenocarcinoma (Caco-2) cell line. Treatment conditions (i.e. dose and exposure time) that were established to be non-toxic to Caco-2 cells were used to investigate the effect of cAuNPs on the expression of a Qiagen panel of 86 genes involved in cytotoxicity. Out of 86 studied, 23 genes were differentially expressed. Genes involved in oxidative stress and antioxidant response, endoplasmic reticulum (ER) stress and unfolded protein response, heat shock response, and lipid metabolism were more affected than others. While low concentrations of 14 nm cAuNPs was not cytotoxic and did not cause cell death, cells treated with these nanoparticles experienced ER and oxidative stress, resulting in the activation of cytoprotective cellular processes. Additionally, several genes involved in lipid metabolism were also affected. Therefore, 14 nm cAuNPs can safely be used as drug delivery vehicles at low doses.

Heme Oxygenase 1 in Vertebrates: Friend and Foe

HO-1 is the inducible form of the enzyme heme-oxygenase. HO-1 catalyzes heme breakdown, reducing the levels of this important oxidant molecule and generating antioxidant, anti-inflammatory, and anti-apoptotic byproducts. Thus, HO-1 has been described as an important stress response mechanism during both physiologic and pathological processes. Interestingly, some findings are demonstrating that uncontrolled levels of HO-1 byproducts can be associated with cell death and tissue destruction as well. Furthermore, HO-1 can be located in the nucleus, influencing gene transcription, cellular proliferation, and DNA repair. Here, we will discuss several studies that approach HO-1 effects as a protective or detrimental mechanism in different pathological conditions. In this sense, as the major organs of vertebrates will deal specifically with distinct types of stresses, we discuss the HO-1 role in each of them, exposing the contradictions associated with HO-1 expression after different insults and circumstances.

Leishmania Parasites Differently Regulate Antioxidant Genes in Macrophages Derived From Resistant and Susceptible Mice

Macrophage-Leishmania interactions are central to parasite growth and disease outcome. Macrophages have developed various strategies to fight invaders, including oxidative burst. While some microorganisms seem to survive and even thrive in an oxidative environment, others are susceptible and get killed. To counter oxidative stress, macrophages switch the expressions of cytoprotective and detoxifying enzymes, which are downstream targets of the nuclear factor erythroid 2-related factor 2 (Nrf2), to enhance cell survival. We have explored the transcription of NRF2 and of its target genes and compared the effect of the parasite on their transcription in bone marrow-derived macrophages (BMdMs) from Leishmania-resistant and Leishmania-susceptible mice. While heme oxygenase 1 (HO-1) transcription is independent of the genetic background, the transcription of glutathione reductase (Gsr) and of cysteine/glutamate exchange transporter (Slc7a11), involved in glutathione accumulation, was differentially regulated in BMdMs from both mouse strains. We also show that, except for HO-1, known to favor the survival of the parasite, the transcription of the selected genes, including Gsr, CD36, and catalase (CAT), was actively repressed, if not at all time points at least at the later ones, by the parasite, especially in Balb/c BMdMs. Consistent with these results, we found that the silencing of NRF2 in this study increases the survival and multiplication of the parasite.

Haem oxygenase limits Mycobacterium marinum infection-induced detrimental ferrostatin-sensitive cell death in zebrafish

Iron homeostasis is essential for both sides of the host-pathogen interface. Restricting access of iron slows bacterial growth while iron is also a necessary cofactor for host immunity. Haem oxygenase 1 (HMOX1) is a critical regulator of iron homeostasis that catalyses the liberation of iron during degradation of haem. It is also a stress-responsive protein that can be rapidly upregulated and confers protection to the host. Although a protective role of HMOX1 has been demonstrated in a variety of diseases, the role of HMOX1 in Mycobacterium tuberculosis infection is equivocal across experiments with different host-pathogen combinations. Here, we use the natural host-pathogen pairing of the zebrafish-Mycobacterium marinum infection platform to study the role of zebrafish haem oxygenase in mycobacterial infection. We identify zebrafish Hmox1a as the relevant functional paralog of mammalian HMOX1 and demonstrate a conserved role for Hmox1a in protecting the host from M. marinum infection. Using genetic and chemical tools, we show zebrafish Hmox1a protects the host against M. marinum infection by reducing infection-induced iron accumulation and ferrostatin-sensitive cell death.

Interplay between membrane active host defense peptides and heme modulates their assemblies and in vitro activity

In the emerging era of antimicrobial resistance, the susceptibility to co-infections of patients suffering from either acquired or inherited hemolytic disorders can lead to dramatic increase in mortality rates. Closely related, heme liberated during hemolysis is one of the major sources of iron, which is vital for both host and invading microorganisms. While recent intensive research in the field has demonstrated that heme exerts diverse local effects including impairment of immune cells functions, it is almost completely unknown how it may compromise key molecules of our innate immune system, such as antimicrobial host defense peptides (HDPs). Since HDPs hold great promise as natural therapeutic agents against antibiotic-resistant microbes, understanding the effects that may modulate their action in microbial infection is crucial. Here we explore how hemin can interact directly with selected HDPs and influence their structure and membrane activity. It is revealed that induced helical folding, large assembly formation, and altered membrane activity is promoted by hemin. However, these effects showed variations depending mainly on peptide selectivity toward charged lipids, and the affinity of the peptide and hemin to lipid bilayers. Hemin-peptide complexes are sought to form semi-folded co-assemblies, which are present even with model membranes resembling mammalian or bacterial lipid compositions. In vitro cell-based toxicity assays supported that toxic effects of HDPs could be attenuated due to their assembly formation. These results are in line with our previous findings on peptide-lipid-small molecule systems suggesting that small molecules present in the complex in vivo milieu can regulate HDP function. Inversely, diverse effects of endogenous compounds could also be manipulated by HDPs.

Heme Oxygenase 1: A Defensive Mediator in Kidney Diseases

The incidence of kidney disease is rising, constituting a significant burden on the healthcare system and making identification of new therapeutic targets increasingly urgent. The heme oxygenase (HO) system performs an important function in the regulation of oxidative stress and inflammation and, via these mechanisms, is thought to play a role in the prevention of non-specific injuries following acute renal failure or resulting from chronic kidney disease. The expression of HO-1 is strongly inducible by a wide range of stimuli in the kidney, consequent to the kidney's filtration role which means HO-1 is exposed to a wide range of endogenous and exogenous molecules, and it has been shown to be protective in a variety of nephropathological animal models. Interestingly, the positive effect of HO-1 occurs in both hemolysis- and rhabdomyolysis-dominated diseases, where the kidney is extensively exposed to heme (a major HO-1 inducer), as well as in non-heme-dependent diseases such as hypertension, diabetic nephropathy or progression to end-stage renal disease. This highlights the complexity of HO-1's functions, which is also illustrated by the fact that, despite the abundance of preclinical data, no drug targeting HO-1 has so far been translated into clinical use. The objective of this review is to assess current knowledge relating HO-1's role in the kidney and its potential interest as a nephroprotection agent. The potential therapeutic openings will be presented, in particular through the identification of clinical trials targeting this enzyme or its products.