Potential immunoregulatory role of heme oxygenase-1 in human milk: a combined biochemical and molecular modeling approach

Non-canonical vs. Canonical Functions of Heme Oxygenase-1 in Cancer

Heme oxygenase-1 (HO-1) is a critical stress-responsive enzyme that has antioxidant and anti-inflammatory functions. HO-1 catalyzes heme degradation, which gives rise to the formation of carbon monoxide (CO), biliverdin, and iron. The upregulation of HO-1 under pathological conditions associated with cellular stress represents an important cytoprotective defense mechanism by virtue of the anti-oxidant properties of the bilirubin and the anti-inflammatory effect of the CO produced. The same mechanism is hijacked by premalignant and cancerous cells. In recent years, however, there has been accumulating evidence supporting that the upregulation of HO-1 promotes cancer progression, independently of its catalytic activity. Such non-canonical functions of HO-1 are associated with its interaction with other proteins, particularly transcription factors. HO-1 also undergoes post-translational modifications that influence its stability, functional activity, cellular translocation, etc. HO-1 is normally present in the endoplasmic reticulum, but distinct subcellular localizations, especially in the nucleus, are observed in multiple cancers. The nuclear HO-1 modulates the activation of various transcription factors, which does not appear to be mediated by carbon monoxide and iron. This commentary summarizes the non-canonical functions of HO-1 in the context of cancer growth and progression and underlying regulatory mechanisms.

Non-canonical vs. Canonical Functions of Heme Oxygenase-1 in Cancer

Heme oxygenase-1 (HO-1) is a critical stress-responsive enzyme that has antioxidant and anti-inflammatory functions. HO-1 catalyzes heme degradation, which gives rise to the formation of carbon monoxide (CO), biliverdin, and iron. The upregulation of HO-1 under pathological conditions associated with cellular stress represents an important cytoprotective defense mechanism by virtue of the anti-oxidant properties of the bilirubin and the anti-inflammatory effect of the CO produced. The same mechanism is hijacked by premalignant and cancerous cells. In recent years, however, there has been accumulating evidence supporting that the upregulation of HO-1 promotes cancer progression, independently of its catalytic activity. Such non-canonical functions of HO-1 are associated with its interaction with other proteins, particularly transcription factors. HO-1 also undergoes post-translational modifications that influence its stability, functional activity, cellular translocation, etc. HO-1 is normally present in the endoplasmic reticulum, but distinct subcellular localizations, especially in the nucleus, are observed in multiple cancers. The nuclear HO-1 modulates the activation of various transcription factors, which does not appear to be mediated by carbon monoxide and iron. This commentary summarizes the non-canonical functions of HO-1 in the context of cancer growth and progression and underlying regulatory mechanisms.

The non-canonical effects of heme oxygenase-1, a classical fighter against oxidative stress

The role of heme oxygenase-1 in resisting oxidative stress and cell protection has always been a hot research topic. With the continuous deepening of research, in addition to directly regulating redox by catalyzing the degradation of heme, HO-1 protein also participates in the gene expression level in a great diversity of methods, thereby initiating cell defense. Particularly the non-canonical nuclear-localized HO-1 and HO-1 protein interactions play the role of a warrior against oxidative stress. Besides, HO-1 may be a promising marker for disease prediction and detection in many clinical trials. Especially for malignant diseases, there may be new advances in the treatment of HO-1 by regulating abnormal ROS and metabolic signaling. The purpose of this review is to systematically sort out and describe several aspects of research to facilitate further detailed mechanism research and clinical application promotion in the future.

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The different subcellular localizations ofHO-1 implies that it has special functions.

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Nuclear HO-1 plays an indispensable role in gene regulation and other aspects.

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The interactions between HO-1 and others provide the possibility to participate in vital physiological processes.

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HO-1 may become a potential disease assessment marker.

Protocatechuic Acid, a Simple Plant Secondary Metabolite, Induced Apoptosis by Promoting Oxidative Stress through HO-1 Downregulation and p21 Upregulation in Colon Cancer Cells

Gastrointestinal cancers, particularly colorectal cancer, are mainly influenced by the dietary factor. A diet rich in fruits and vegetables can help to reduce the incidence of colorectal cancer thanks to the phenolic compounds, which possess antimutagenic and anticarcinogenic properties. Polyphenols, alongside their well-known antioxidant properties, also show a pro-oxidative potential, which makes it possible to sensitize tumor cells to oxidative stress. HO-1 combined with antioxidant activity, when overexpressed in cancer cells, is involved in tumor progression, and its inhibition is considered a feasible therapeutic strategy in cancer treatment. In this study, the effects of protocatechuic acid (PCA) on the viability of colon cancer cells (CaCo-2), annexin V, LDH release, reactive oxygen species levels, total thiol content, HO-1, γ-glutamylcysteine synthetase, and p21 expression were evaluated. PCA induced, in a dose-dependent manner, a significantly reduced cell viability of CaCo-2 by oxidative/antioxidant imbalance. The phenolic acid induced modifications in levels of HO-1, non-proteic thiol groups, γ-glutamylcysteine synthetase, reactive oxygen species, and p21. PCA induced a pro-oxidant effect in cancer cells, and the in vitro pro-apoptotic effect on CaCo-2 cells is mediated by the modulation of redox balance and the inhibition of the HO-1 system that led to the activation of p21. Our results suggest that PCA may represent a useful tool in prevention and/or therapy of colon cancer.

Increased Plasma Heme Oxygenase-1 Levels in Patients With Early-Stage Parkinson's Disease

Introduction: Heme oxygenase-1 (HO-1) is a 32 kDa stress-response protein implicated in the pathogenesis of Parkinson’s disease (PD). Biliverdin is derived from heme through a reaction mediated by HO-1 and protects cells from oxidative stress. However, iron and carbon monoxide produced by the catabolism of HO-1 exert detrimental effects on patients with PD. The purpose of this study was to determine whether plasma HO-1 levels represent a biomarker of PD and to further explore the underlying mechanism of increased HO-1 levels by applying voxel-based morphometry (VBM).Methods: We measured plasma HO-1 levels using an enzyme-linked immunosorbent assay (ELISA) in 156 subjects, including 81 patients with early- and advanced-stage PD and 75 subjects without PD. The analyses were adjusted to control for confounders such as age, sex, and medication. We analyzed T1-weighted magnetic resonance imaging (MRI) data from 74 patients with PD using VBM to elucidate the association between altered brain volumes and HO-1 levels. Then, we compared performance on MMSE sub-items between PD patients with low and high levels of HO-1 using Mann-Whitney U tests.Results: Plasma HO-1 levels were significantly elevated in PD patients, predominantly those with early-stage PD, compared with controls (p < 0.05). The optimal cutoff value for patients with early PD was 2.245 ng/ml HO-1 [area under the curve (AUC) = 0.654]. Plasma HO-1 levels were unaffected by sex, age, and medications (p > 0.05). The right hippocampal volume was decreased in the subset of PD patients with high HO-1 levels (p < 0.05). A weak correlation was observed between right hippocampal volume and plasma HO-1 levels (r = −0.273, p = 0.018). There was no difference in total MMSE scores between the low- and high-HO-1 groups (p > 0.05), but the high-HO-1 group had higher language scores than the low-HO-1 group (p < 0.05).Conclusions: Plasma HO-1 levels may be a promising biomarker of early PD. Moreover, a high plasma concentration of the HO-1 protein is associated with a reduction in right hippocampal volume.

Characterization and heme oxygenase-1 content of extracellular vesicles in human biofluids

Heme oxygenase-1 (HO-1), a highly inducible stress protein that degrades heme to biliverdin, carbon monoxide, and free ferrous iron, is increased in blood and other biofluids of subjects with various systemic and neurological disorders. HO-1 does not contain an N-terminal signal peptide and the mechanism responsible for its secretion remains unknown. Extracellular vesicles (EVs) are membrane-bound inclusions that transport microRNAs, messenger RNAs, lipids, and proteins among diverse cellular and extracellular compartments. The objective of the current study was to determine whether EVs in human biofluids contain HO-1, and whether the latter may be transported in EVs from brain to periphery. Total, L1 cell adhesion molecule protein (L1CAM)-enriched (neuron-derived), and glutamate aspartate transporter 1 (GLAST)-enriched (astrocyte-derived) EVs were purified from five different human biofluids (saliva [n = 40], plasma [n = 14], serum [n = 10], urine [n = 10], and cerebrospinal fluid [n = 11]) using polymer precipitation and immuno-affinity-based capture methods. L1CAM-enriched, GLAST-enriched, and L1CAM/GLAST-depleted (LGD) EV, along with EV-depleted (EVD), fractions were validated by nanoparticle tracking analysis, enzyme-linked immunosorbent assay (ELISA), and western blot. HO-1 was assayed in all fractions using ELISA and western blot. The majority of HO-1 protein was localized to LGD, L1CAM-enriched, and GLAST-enriched EVs of all human biofluids surveyed after adjusting for age and sex, with little HO-1 protein detected in EVD fractions. HO-1 protein in human biofluids is predominantly localized to EV compartments. A substantial proportion of EV HO-1 in peripheral human biofluids is derived from the central nervous system and may contribute to the systemic manifestations of various neurological conditions.

Clinical insights gained through metabolomic analysis of human breast milk

Introduction: Among the OMICS technologies, that have emerged in recent years, metabolomics has allowed relevant step forwards in clinical research. Several improvements in disease diagnosis and clinical management have been permitted, even in neonatology. Among potentially evaluable biofluids, breast milk (BM) results are highly interesting, representing a fluid of conjunction between mothers newborns, describing their interaction.Areas covered: in this review, updating a previous review article, we discuss research articles and reviews on BM metabolomics and found in MEDLINE using metabolomics, breast milk, neonatal nutrition, breastfeeding, human milk composition, and preterm neonates as keywords.Expert opinion: Our research group has a profound interest in metabolomics research. In 2012, we published the first metabolomic analysis on BM samples, reporting interesting data on its composition and relevant differences with formula milk (FM), useful to improve FM composition. As confirmed by successive studies, such technology can detect the specific BM composition and its dependence on several variables, including lactation stage, gestational age, maternal or environmental conditions. Moreover, since BM contaminants or drug levels can be detected, metabolomics also results useful to determine BM safety. These are only a few practical applications of BM analysis, which will be reviewed in this paper.

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.

Donor Human Milk: Effects of Storage and Heat Treatment on Oxidative Stress Markers

Mother's own milk is the first choice for the feeding and nutrition of preterm and term newborns. When mother's own milk is unavailable or in short supply donor human milk (DM) could represent a solution. Heat treatment and cold storage are common practices in Human Milk Banks (HMBs). Currently, Holder pasteurization process is the recommended heat treatment in all international guidelines. This method is thought to lead to a good compromise between the microbiological safety and nutritional/biological quality of DM. Moreover, storage of refrigerated milk is a common practice in HMBs and in NICUs. Depending on the length and on the type of storage, human milk may lose some important nutritional and functional properties. The available data on oxidative stress markers confirm that pasteurization and refrigeration affected this important elements to variable degrees, even though it is rather difficult to quantify the level of deterioration. Nonetheless, clinical practice demonstrates that many beneficial properties of human milk are preserved, even after cold storage and heat treatment. Future studies should be focused on the evaluation of new pasteurization techniques, in order to achieve a better compromise between biological quality and safety of DM.

The non-canonical functions of the heme oxygenases

Heme oxygenase (HO) isoforms catalyze the conversion of heme to carbon monoxide (CO) and biliverdin with a concurrent release of iron, which can drive the synthesis of ferritin for iron sequestration. Most of the studies so far were directed at evaluating the protective effect of these enzymes because of their ability to generate antioxidant and antiapoptotic molecules such as CO and bilirubin. Recent evidences are suggesting that HO may possess other important physiological functions, which are not related to its enzymatic activity and for which we would like to introduce for the first time the term “non canonical functions”. Recent evidence suggest that both HO isoforms may form protein-protein interactions (i.e. cytochrome P450, adiponectin, CD91) thus serving as chaperone-like protein. In addition, truncated HO-1 isoform was localized in the nuclear compartment under certain experimental conditions (i.e. excitotoxicity, hypoxia) regulating the activity of important nuclear transcription factors (i.e. Nrf2) and DNA repair. In the present review, we discuss three potential signaling mechanisms that we refer to as the non-canonical functions of the HO isoforms: protein-protein interaction, intracellular compartmentalization, and extracellular secretion. The aim of the present review is to describe each of this mechanism and all the aspects warranting additional studies in order to unravel all the functions of the HO system.

Effects of an extract of Celtis aetnensis (Tornab.) Strobl twigs on human colon cancer cell cultures

Cancers of the digestive tract, in particular colorectal cancer (CRC), are among those most responsive to dietary modification. Research has shown that approximately 75% of all sporadic cases of CRC are directly influenced by diet. Many natural compounds have been investigated for their potential usefulness as cancer chemopreventive agents as they have been thought to suppress carcinogenesis mainly during the initiation phase due to their radical scavenger activity. Since there is an increasing interest in the in vivo protective effects of natural compounds contained in plants against oxidative damage involved in several human diseases such as cancer, the aim of the present research was to test the effects of a Celtis aetnensis (Tornab.) Strobl twig extract on a human colon carcinoma cell line (Caco2). In order to elucidate the mechanisms of action of this extract, LDH release, GSH content, ROS levels, caspase-3 and γ-GCS expression were also evaluated. The results revealed that the Celtis aetnensis extract reduced the cell viability of the Caco2 cells inducing apoptosis at the lowest concentration and necrosis at higher dosages. In addition, this extract caused an increase in the levels of ROS, a decrease in RSH levels and in the expression of HO-1. The expression of γ-GCS was not modified in the Celtis aetnensis-treated Caco-2 cells. These results suggest an interference of this extract on the oxidant/antioxidant cell balance with consequent cell damage. The present study supports the growing body of data suggesting the bioactivities of Celtis aetnensis (Tornab.) Strobl and its potential impact on cancer therapy and on human health.

Combined inhibition of Hsp90 and heme oxygenase-1 induces apoptosis and endoplasmic reticulum stress in melanoma

Heat shock proteins are ubiquitous molecular chaperones involved in post-translational folding, stability, activation and maturation of many proteins that are essential mediators of signal transduction and cell cycle progression. Heat shock protein 90 (Hsp90) has recently emerged as an attractive therapeutic target in cancer treatment since it may act as a key regulator of various oncogene products and cell-signaling molecules. Heme oxygenase-1 (HO-1; also known as Hsp32) is an inducible enzyme participating in heme degradation and involved in oxidative stress resistance. Recent studies indicate that HO-1 activation may play a role in tumor development and progression. In the present study we investigated the chemotherapic effects of combining an Hsp90 inhibitor (NMS E973) and an HO-1 inhibitor (SnMP) on A375 melanoma cells. NMS E973 treatment was able to reduce cell viability and induce endoplasmic reticulum (ER) stress (i.e. Ire1α, ERO1, PDI, BIP and CHOP). Interestingly, no significant effect was observed in reactive oxygen species (ROS) formation. Finally, NMS E973 treatment resulted in a significant HO-1 overexpression, which in turn serves as a possible chemoresistance molecular mechanism. Interestingly, the combination of NMS E973 and SnMP produced an increase of ROS and reduced cell viability compared to NMS E973 treatment alone. The inhibitors combination exhibited higher ER stress, apoptosis as evidenced by bifunctional apoptosis regulator (BFAR) mRNA expression and lower phosphorylation of Akt when compared to NMS E973 alone. In conclusion, these data suggest that HO-1 inhibition potentiates NMS E973 toxicity and may be exploited as a strategy for melanoma treatment.

Relationship between post-cardiac arrest myocardial oxidative stress and myocardial dysfunction in the rat

Background

Reperfusion after resuscitation from cardiac arrest (CA) is an event that increases reactive oxygen species production leading to oxidative stress. More specifically, myocardial oxidative stress may play a role in the severity of post-CA myocardial dysfunction. This study investigated the relationship between myocardial oxidative stress and post-CA myocardial injury and dysfunction in a rat model of CA and cardiopulmonary resuscitation (CPR). Ventricular fibrillation was induced in 26 rats and was untreated for 6 min. CPR, including mechanical chest compression, ventilation, and epinephrine, was then initiated and continued for additional 6 min prior to defibrillations. Resuscitated animals were sacrificed at two h (n = 9), 4 h (n = 6) and 72 h (n = 8) following resuscitation, and plasma collected for assessment of: high sensitivity cardiac troponin T (hs-cTnT), as marker of myocardial injury; isoprostanes (IsoP), as marker of lipid peroxidation; and 8-hydroxyguanosine (8-OHG), as marker of DNA oxidative damage. Hearts were also harvested for measurement of tissue IsoP and 8-OHG. Myocardial function was assessed by echocardiography at the corresponding time points. Additional 8 rats were not subjected to CA and served as baseline controls.

Results

Compared to baseline, left ventricular ejection fraction (LVEF) was reduced at 2 and 4 h following resuscitation (p < 0.01), while it was similar at 72 h. Inversely, plasma hs-cTnT increased, compared to baseline, at 2 and 4 h post-CA (p < 0.01), and then recovered at 72 h. Similarly, plasma and myocardial tissue IsoP and 8-OHG levels increased at 2 and 4 h post-resuscitation (p < 0.01 vs. baseline), while returned to baseline 72 h later. Myocardial IsoP were directly related to hs-cTnT levels (r = 0.760, p < 0.01) and inversely related to LVEF (r = -0.770, p < 0.01). Myocardial 8-OHG were also directly related to hs-cTnT levels (r = 0.409, p < 0.05) and inversely related to LVEF (r = -0.548, p < 0.01).

Conclusions

The present study provides evidence that lipid peroxidation and DNA oxidative damage in myocardial tissue are closely related to myocardial injury and LV dysfunction during the initial hours following CA.

Heme oxygenase-2/adiponectin protein-protein interaction in metabolic syndrome

Insulin resistance with adipose tissue dysfunction and dysregulation in the production and secretion of adipokines is one of the hallmarks of metabolic syndrome. We have previously reported that increased levels of the heme oxygenase (HO) system, HO-1/HO-2 results in increased levels of adiponectin. Despite documentation of the existence of the anti-inflammatory axis HO-adiponectin, a possible protein-protein interaction between HO and adiponectin has not been examined. Here, we investigated the existence of protein interactions between HO-2 and adiponectin in the maintenance of adipocyte function during metabolic syndrome by integrating phenotypic and in silico studies. Compared to WT animals, HO-2 null mice displayed an increase in both visceral and subcutaneous fat content and reduced circulating adiponectin levels. The decrease in adiponectin was reversed by upregulation of HO-1. HO-2 depletion was associated with increased adipogenesis in cultured mesenchymal stem cells (MSCs) and decreased adiponectin levels in the culture media. In addition, HO-1 siRNA decreased adiponectin release. HO-2 was found to bind to the monomeric form of adiponectin, according to poses and calculated energies. HO-2-adiponectin interactions were validated by the two-hybrid system assay. In conclusion, protein-protein interactions between HO-2 and adiponectin highlight the role of HO-2 as a molecular chaperone for adiponectin assembly, while HO-1 increases adiponectin levels. Thus, crosstalk between HO-2 and HO-1 could be manipulated in a therapeutic approach to ameliorate the deleterious effects of obesity and the metabolic syndrome.

Human milk and formulae: neurotrophic and new biological factors

Mother milk is widely accepted to be a unique product believed to contain biological factors involved in the regulation of newborn optimal growth including brain when compared to milk-formula milks. In this setting, there is growing evidence that in milk-formula neuro-oxidative stress biomarkers, neurotrophic proteins and calcium binding proteins, known to be involved in a cascade of events leading to brain, cardiac and vascular development/damage, are to date lacking or at a lower concentration than breast milk. Therefore, this review is aimed at offering additional insights to the role in human milk of some selected biomarkers such as: i) neurotrophic factors such as Activin A; ii) Calcium binding protein such as S100B and, iii) heat shock protein known to be involved in oxidative stress response (namely hemeoxygenase-1, HO-1 or Heat shock Protein 32, HSP32).

Hsp60 and heme oxygenase-1 (Hsp32) in acute myocardial infarction

Heat shock proteins (Hsps) are produced in response to various stressors, including ischemia-reperfusion, and they can exit cells and reach the blood. In this pilot study, we determined serum levels of Hsp60 and heme-oxygenase-1 (HO-1; also named Hsp32) in subjects with acute myocardial infarction (AMI) to assess their clinical significance and potential prognostic value. We also performed a bioinformatics analysis of the 2 molecules in search of structural clues on the mechanism of their release from cells. We studied 40 patients consecutively admitted for AMI (male:female patient ratio=20:20, mean age: 64 ± 13 years) and 40 matched controls. A blood sample was drawn for biochemical analyses within 24 h of symptoms onset, and Hsp60 and HO-1 concentrations were determined by enzyme-linked immunosorbent assay (ELISA). All patients were followed up for 6 months to register adverse post-AMI cardiovascular events. A multivariate analysis demonstrated that elevated Hsp60 (P=0.0361), creatine phosphokinase-muscle brain (CK-MB) (P=0.0446), and troponin (P=0.0490) were predictive of post-AMI adverse events. In contrast, increased HO-1 showed a significant association with less severity of coronary artery diseases (P=0.0223). These findings suggest that Hsp60 and HO-1 play distinct roles in the pathogenesis of AMI and subsequent AMI-related pathology. The possibility that these proteins differ in their roles and mechanisms of action in AMI and post-AMI pathology was supported also by the bioinformatics estimates of probability of their localization in various subcellular compartments. The results clear the way for subsequent investigation on the pathogenetic role and clinical significance of Hsp60 and HO-1 in AMI.