Conversion of biliverdin to bilirubin by biliverdin reductase contributes to endothelial cell protection by heme oxygenase-1—evidence for direct and indirect antioxidant actions of bilirubin

Metabolomic profile of neuroendocrine tumors identifies methionine, porphyrin, and tryptophan metabolisms as key dysregulated pathways associated with patient survival

OBJECTIVE

Metabolic profiling is a valuable tool to characterize tumor biology but remains largely unexplored in neuroendocrine tumors (NETs). Our aim was to comprehensively assess the metabolomic profile of NETs and identify novel prognostic biomarkers and dysregulated molecular pathways.

DESIGN AND METHODS

Multiplatform untargeted metabolomic profiling (GC-MS, CE-MS, and LC-MS) was performed in plasma from 77 patients with G1-2 extra-pancreatic NETs enrolled in the AXINET trial (NCT01744249) (study cohort) and from 68 non-cancer individuals (control). The prognostic value of each differential metabolite (n = 155) in NET patients (P < .05) was analyzed by univariate and multivariate analyses adjusted for multiple testing and other confounding factors. Related pathways were explored by Metabolite Set Enrichment Analysis (MSEA) and Metabolite Pathway Analysis (MPA).

RESULTS

Thirty-four metabolites were significantly associated with progression-free survival (PFS) (n = 16) and/or overall survival (OS) (n = 27). Thirteen metabolites remained significant independent prognostic factors in multivariate analysis, 3 of them with a significant impact on both PFS and OS. Unsupervised clustering of these 3 metabolites stratified patients in 3 distinct prognostic groups (1-year PFS of 71.1%, 47.7%, and 15.4% (P = .012); 5-year OS of 69.7%, 32.5%, and 27.7% (P = .003), respectively). The MSEA and MPA of the 13-metablolite signature identified methionine, porphyrin, and tryptophan metabolisms as the 3 most relevant dysregulated pathways associated with the prognosis of NETs.

CONCLUSIONS

We identified a metabolomic signature that improves prognostic stratification of NET patients beyond classical prognostic factors for clinical decisions. The enriched metabolic pathways identified reveal novel tumor vulnerabilities that may foster the development of new therapeutic strategies for these patients.

Is Environmental Cadmium Exposure Causally Related to Diabetes and Obesity?

Cadmium (Cd) is a pervasive toxic metal, present in most food types, cigarette smoke, and air. Most cells in the body will assimilate Cd, as its charge and ionic radius are similar to the essential metals, iron, zinc, and calcium (Fe, Zn, and Ca). Cd preferentially accumulates in the proximal tubular epithelium of the kidney, and is excreted in urine when these cells die. Thus, excretion of Cd reflects renal accumulation (body burden) and the current toxicity of Cd. The kidney is the only organ other than liver that produces and releases glucose into the circulation. Also, the kidney is responsible for filtration and the re-absorption of glucose. Cd is the least recognized diabetogenic substance although research performed in the 1980s demonstrated the diabetogenic effects of chronic oral Cd administration in neonatal rats. Approximately 10% of the global population are now living with diabetes and over 80% of these are overweight or obese. This association has fueled an intense search for any exogenous chemicals and lifestyle factors that could induce excessive weight gain. However, whilst epidemiological studies have clearly linked diabetes to Cd exposure, this appears to be independent of adiposity. This review highlights Cd exposure sources and levels associated with diabetes type 2 and the mechanisms by which Cd disrupts glucose metabolism. Special emphasis is on roles of the liver and kidney, and cellular stress responses and defenses, involving heme oxygenase-1 and -2 (HO-1 and HO-2). From heme degradation, both HO-1 and HO-2 release Fe, carbon monoxide, and a precursor substrate for producing a potent antioxidant, bilirubin. HO-2 appears to have also anti-diabetic and anti-obese actions. In old age, HO-2 deficient mice display a symptomatic spectrum of human diabetes, including hyperglycemia, insulin resistance, increased fat deposition, and hypertension.

Direct bilirubin: A predictor of hematoma expansion after intracerebral hemorrhage

BACKGROUND

Previous evidence demonstrated that several biomarkers involved in the pathological process of coagulation/hemostasis dysfunction, impairment of brain vascular integrity and inflammation are associated with hematoma expansion (HE) after intracerebral hemorrhage (ICH). We aimed to explore whether there were unreported laboratory biomarkers associated with HE that were readily and commonly available in clinical practice.

METHODS

We retrospectively analyzed consecutive acute ICH patients from 2012 to 2020 with admission laboratory tests and baseline and follow-up computed tomography (CT) scans. Univariate and multivariate regression analyses were used to evaluate associations between conventional laboratory indicators and HE. The results were verified in a prospective validation cohort. The relationship of candidate biomarker and 3-month outcomes was also investigated and mediation analysis was undertaken to determine causal associations among candidate biomarker, HE and outcome.

RESULTS

Of 734 ICH patients, 163 (22.2%) presented HE. Among the included laboratory indicators, higher direct bilirubin (DBil) was associated with HE (adjusted odds ratio [OR] of per 1.0 μmol/L change 1.082; 95% confidence interval [CI] 1.011-1.158). DBil >5.65 μmol/L was a predictor of HE in validation cohort. Higher DBil was also associated with poor 3-month outcomes. The mediation analysis indicated that the association of higher DBil and poor outcomes was partially mediated by HE.

CONCLUSIONS

DBil is a predictor of HE and poor 3-month outcomes after ICH. DBil's metabolic process and involvement in the pathological mechanism of HE are likely to contribute to the association between DBil and HE. Interventions targeting DBil to improve post-ICH prognosis may be meaningful and worthy of further exploration.

Bilirubin is produced nonenzymatically in plants to maintain chloroplast redox status

Bilirubin, a potent antioxidant, is a product of heme catabolism in heterotrophs. Heterotrophs mitigate oxidative stress resulting from free heme by catabolism into bilirubin via biliverdin. Although plants also convert heme to biliverdin, they are generally thought to be incapable of producing bilirubin because they lack biliverdin reductase, the enzyme responsible for bilirubin biosynthesis in heterotrophs. Here, we demonstrate that bilirubin is produced in plant chloroplasts. Live-cell imaging using the bilirubin-dependent fluorescent protein UnaG revealed that bilirubin accumulated in chloroplasts. In vitro, bilirubin was produced nonenzymatically through a reaction between biliverdin and reduced form of nicotinamide adenine dinucleotide phosphate at concentrations comparable to those in chloroplasts. In addition, increased bilirubin production led to lower reactive oxygen species levels in chloroplasts. Our data refute the generally accepted pathway of heme degradation in plants and suggest that bilirubin contributes to the maintenance of redox status in chloroplasts.

The isothiocyanate sulforaphane prevents mitochondrial impairment and neuroinflammation in the human dopaminergic SH-SY5Y and in the mouse microglial BV2 cells: role for heme oxygenase-1

Sulforaphane (SFN) promotes protective effects in different cell types. Nonetheless, it remains to be clarified by which mechanism SFN exerts benefits in mammalian cells. Mitochondria are a major source of adenosine triphosphate (ATP) and reactive species in nucleated cells. Mitochondrial impairment result in cellular redox biology disruption, bioenergetic status collapse, and inflammation. Evidence suggest that mitochondrial dysfunction plays a role in neurological disorders. Since a cure was not discovered yet to some of these diseases, investigating strategies to promote mitochondrial protection is pharmacologically relevant and may improve life quality of patients suffering from these maladies. Natural molecules, such as SFN, are potent inducers of the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) and, consequently, stimulate the expression of genes whose products, such as heme oxygenase-1 (HO-1), induce cytoprotective actions in mammalian tissues. In this work, we investigated whether SFN (5 µM) would be capable to prevent the dysfunctions caused by chlorpyrifos (CPF) on the human dopaminergic SH-SY5Y cells. Moreover, we examined the effects of a pretreatment with SFN at the same concentration on the mouse microglial BV2 cells stimulated by lipopolysaccharide (LPS) in an experimental model of neuroinflammation. SFN prevented the mitochondrial impairment and the neuroinflammation caused by the chemical stressors in both cell types. Inhibition of heme oxygenase-1 (HO-1) suppressed the mitochondrial protection and anti-inflammatory action afforded by SFN in this experimental model. Overall, SFN promoted cytoprotection by a mechanism dependent on the HO-1 enzyme in the SH-SY5Y and BV2 cells.

Correlation Between Total Bilirubin, Total Bilirubin/Albumin Ratio with Disease Activity in Patients with Rheumatoid Arthritis

Purpose

Rheumatoid arthritis (RA) is a systemic inflammatory disorder with unknown etiology. Oxidative stress and immune imbalance play a critical role in the pathogenesis of rheumatoid arthritis. Bilirubin has recently been recognized as a potent antioxidant as well as an immunomodulatory agent of physiological importance. The aim of this study was to explore whether increased bilirubin concentrations are correlated with good clinical prognosis of rheumatoid arthritis.

Patients and Methods

In this cross-sectional study, we included 197 healthy individuals and 197 RA patients in the Affiliated Hospital of North Sichuan Medical College from October 2020 to February 2022. The latter were classified into three classes of disease activity according to DAS28-ESR: remission and low (DAS28-ESR<3.2), moderate (3.2≤DAS28-ESR≤5.1), and high (DAS28ESR>5.1). Based on the clinical and laboratory data, we evaluated the association of bilirubin levels with disease activity in RA using multivariable ordered logistic regression.

Results

The levels of total bilirubin and total bilirubin/albumin ratio were significantly lower (P < 0.001; P < 0.001) in RA patients compared with healthy controls. In RA patients, Spearman's rank correlation analysis revealed that bilirubin and total bilirubin/albumin ratio were negatively correlated with disease activity and inflammatory marker (C-reactive protein, erythrocyte sedimentation rate, Interleukin-6). In multivariable ordered logistic regression, higher total bilirubin (OR=0.77, 95% CI: 0.67-0.89, p<0.001) independently predicted lower disease activity.

Conclusion

Bilirubin levels remain associated with a reduction of disease activity, suggesting that bilirubin may be a protective factor for RA aggravation.

Nrf2 Regulates Oxidative Stress and Its Role in Cerebral Ischemic Stroke

Cerebral ischemic stroke is characterized by acute ischemia in a certain part of the brain, which leads to brain cells necrosis, apoptosis, ferroptosis, pyroptosis, etc. At present, there are limited effective clinical treatments for cerebral ischemic stroke, and the recovery of cerebral blood circulation will lead to cerebral ischemia-reperfusion injury (CIRI). Cerebral ischemic stroke involves many pathological processes such as oxidative stress, inflammation, and mitochondrial dysfunction. Nuclear factor erythroid 2-related factor 2 (Nrf2), as one of the most critical antioxidant transcription factors in cells, can coordinate various cytoprotective factors to inhibit oxidative stress. Targeting Nrf2 is considered as a potential strategy to prevent and treat cerebral ischemia injury. During cerebral ischemia, Nrf2 participates in signaling pathways such as Keap1, PI3K/AKT, MAPK, NF-κB, and HO-1, and then alleviates cerebral ischemia injury or CIRI by inhibiting oxidative stress, anti-inflammation, maintaining mitochondrial homeostasis, protecting the blood-brain barrier, and inhibiting ferroptosis. In this review, we have discussed the structure of Nrf2, the mechanisms of Nrf2 in cerebral ischemic stroke, the related research on the treatment of cerebral ischemia through the Nrf2 signaling pathway in recent years, and expounded the important role and future potential of the Nrf2 pathway in cerebral ischemic stroke.

Heme Oxygenase-1 as Therapeutic Target for Diabetic Foot Ulcers

A diabetic foot ulcer (DFU) is one of the major complications of diabetes. Wound healing under diabetic conditions is often impaired. This is in part due to the excessive oxidative stress, prolonged inflammation, immune cell dysfunction, delayed re-epithelialization, and decreased angiogenesis present at the wound site. As a result of these multifactorial impaired healing pathways, it has been difficult to develop effective therapeutic strategies for DFU. Heme oxygenase-1 (HO-1) is the rate-limiting enzyme in heme degradation generating carbon monoxide (CO), biliverdin (BV) which is converted into bilirubin (BR), and iron. HO-1 is a potent antioxidant. It can act as an anti-inflammatory, proliferative, angiogenic and cytoprotective enzyme. Due to its biological functions, HO-1 plays a very important role in wound healing, in part mediated through the biologically active end products generated by its enzymatic activity, particularly CO, BV, and BR. Therapeutic strategies involving the activation of HO-1, or the topical application of its biologically active end products are important in diabetic wound healing. Therefore, HO-1 is an attractive therapeutic target for DFU treatment. This review will provide an overview and discussion of the importance of HO-1 as a therapeutic target for diabetic wound healing.

Protective actions of nuclear factor erythroid 2-related factor 2 (NRF2) and downstream pathways against environmental stressors

Environmental risk factors, including noise, air pollution, chemical agents, ultraviolet radiation (UVR) and mental stress have a considerable impact on human health. Oxidative stress and inflammation are key players in molecular pathomechanisms of environmental pollution and risk factors. In this review, we delineate the impact of environmental risk factors and the protective actions of the nuclear factor erythroid 2-related factor 2 (NRF2) in connection to oxidative stress and inflammation. We focus on well-established studies that demonstrate the protective actions of NRF2 and its downstream pathways against different environmental stressors. State-of-the-art mechanistic considerations on NRF2 signaling are discussed in detail, e.g. classical concepts like KEAP1 oxidation/electrophilic modification, NRF2 ubiquitination and degradation. Specific focus is also laid on NRF2-dependent heme oxygenase-1 induction with detailed presentation of the protective down-stream pathways of heme oxygenase-1, including interaction with BACH1 system. The significant impact of all environmental stressors on the circadian rhythm and the interactions of NRF2 with the circadian clock will also be considered here. A broad range of NRF2 activators is discussed in relation to environmental stressor-induced health side effects, thereby suggesting promising new mitigation strategies (e.g. by nutraceuticals) to fight the negative effects of the environment on our health.

A Pretreatment with Isoorientin Attenuates Redox Disruption, Mitochondrial Impairment, and Inflammation Caused by Chlorpyrifos in a Dopaminergic Cell Line: Involvement of the Nrf2/HO-1 Axis

The C-glucosyl flavone isoorientin (ISO) is obtained by humans from the diet and exhibits several cytoprotective effects, as demonstrated in different experimental models. However, it was not previously shown whether ISO would be able to prevent mitochondrial impairment in cells exposed to a chemical stressor. Thus, we treated the human neuroblastoma SH-SY5Y cells with ISO (0.5-20 µM) for 18 h before a challenge with chlorpyrifos (CPF) at 100 µM for additional 24 h. We observed that ISO prevented the CPF-induced lipid peroxidation and protein carbonylation and nitration in the membranes of mitochondria extracted from CPF-treated cells. ISO also attenuated the CPF-elicited increase in the production of reactive species in this experimental model. Moreover, ISO prevented the CPF-induced disruption in the activity of components of the oxidative phosphorylation (OXPHOS) system in the SH-SY5Y cells. ISO also promoted an anti-inflammatory action in the cells exposed to CPF. CPF caused a decrease in the activity of the enzyme heme oxygenase-1 (HO-1), a cytoprotective agent. On the other hand, ISO upregulated HO-1 activity in SH-SY5Y cells. Inhibition of HO-1 by zinc protoporphyrin-IX (ZnPP-IX) suppressed the cytoprotection induced by ISO in the CPF-treated cells. Besides, silencing of the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) abolished the ISO-induced HO-1 upregulation and mitochondrial benefits induced by this flavone on the CPF-challenged cells. Thus, ISO protected mitochondria of the CPF-treated cells by an Nrf2/HO-1-dependent fashion in the SH-SY5Y cells.

Photomedicine based on heme-derived compounds

Photoimaging and phototherapy have become major platforms for the diagnosis and treatment of various health complications. These applications require a photosensitizer (PS) that is capable of absorbing light from a source and converting it into other energy forms for detection and therapy. While synthetic inorganic materials such as quantum dots and gold nanorods have been widely explored for their medical diagnosis and photodynamic (PDT) and photothermal (PTT) therapy capabilities, translation of these technologies has lagged, primarily owing to potential cytotoxicity and immunogenicity issues. Of the various photoreactive molecules, the naturally occurring endogenous compound heme, a constituent of red blood cells, and its derivatives, porphyrin, biliverdin and bilirubin, have shown immense potential as noteworthy candidates for clinically translatable photoreactive agents, as evidenced by previous reports. While porphyrin-based photomedicines have attracted significant attention and are well documented, research on photomedicines based on two other heme-derived compounds, biliverdin and bilirubin, has been relatively lacking. In this review, we summarize the unique photoproperties of heme-derived compounds and outline recent efforts to use them in biomedical imaging and phototherapy applications.

Biomarkers associated with rhythm status after cardioversion in patients with atrial fibrillation

Biomarkers may help to improve our knowledge about the complex pathophysiology of atrial fibrillation (AF). In this study we sought to identify significant changes in biomarkers and clinical measures in patients with and without AF recurrence after electrical cardioversion. We measured 21 conventional and new biomarkers before and 30 days after electrical cardioversion and assessed the associations of changes in biomarker levels with rhythm status at follow-up. Significant between-group changes were observed for bone morphogenetic protein 10 (BMP10), N-terminal pro-B-type natriuretic peptide (NT-proBNP) and total bilirubin. Their respective changes were − 10.4%, − 62.0% and − 25.6% in patients with sinus rhythm, and 3.1%, 1.1% and − 9.4% in patients with recurrent AF, for a between-group difference of − 13.5% (95% confidence interval [CI] − 19.3% to − 7.6%; P < 0.001), − 63.1% (95% CI − 76.6% to − 49.6%; P < 0.001) and − 16.3% (95% CI − 27.9% to − 4.7%; P = 0.007). In multivariable models, the reductions of BMP10 and NT-proBNP were significantly associated with follow-up rhythm status (β coefficient per 1 − SD decrease, − 3.85; 95% CI − 6.34 to − 1.35; P = 0.003 for BMP10 and − 5.84; 95% CI − 10.22 to − 1.47; P = 0.009 for NT-proBNP. In conclusion, changes in BMP10 und NT-proBNP levels were independently associated with rhythm status after cardioversion, suggesting that these markers may be dependent on the actual heart rhythm.

Paradoxical Association Between Baseline Apolipoprotein B and Prognosis in Coronary Artery Disease: A 36,460 Chinese Cohort Study

Background

Apolipoprotein B (ApoB) and low-density lipoprotein cholesterol (LDL-C) were identified targets for blood lipid management among coronary artery disease (CAD) patients. However, previous studies reported an inverse correlation between baseline LDL-C concentration and clinical outcomes. This study aims to explore the definite association between baseline ApoB and long-term prognosis.

Methods

A total of 36,460 CAD patients admitted to Guangdong Provincial People's Hospital were enrolled and categorized into two groups: high ApoB (≥65 mg/dL) group and low ApoB (<65 mg/dL) group. The association between baseline ApoB and long-term all-cause mortality was evaluated by the Kaplan-Meier method, Cox regression analyses and restricted cubic splines.

Results

The overall mortality was 12.49% (n = 4,554) over a median follow-up period of 5.01 years. Patients with low baseline ApoB levels were paradoxically more likely to get a worse prognosis. There was no obvious difference in risk of long-term all-cause mortality when only adjusted for age, gender, and comorbidity (aHR: 1.07, 95% CI: 0.99–1.16). When CONUT and total bilirubin were adjusted, the risk of long-term all-cause mortality would reduce in the low-ApoB (<65 mg/dL) group (aHR: 0.86, 95% CI: 0.78–0.96). In the fully covariable-adjusted model, patients in the ApoB <65 mg/d group had a 10.00% lower risk of long-term all-cause mortality comparing to patients with ApoB ≥65 mg/dL (aHR: 0.90; 95% CI:0.81–0.99).

Conclusion

This study found a paradoxical association between baseline ApoB and long-term all-cause mortality. Malnutrition and bilirubin mainly mediate the ApoB paradox. Increased ApoB concentration remained linearly associated with an increased risk of long-term all-cause mortality.

Heme in Cardiovascular Diseases: A Ubiquitous Dangerous Molecule Worthy of Vigilance

Heme, the protoporphyrin IX iron complex is widely present in the human body and it is involved in oxygen storage, electron transfer, and enzymatic reactions. However, free heme can be toxic as it catalyzes the production of reactive oxygen species, oxidizes lipids and proteins, and causes DNA damage, thereby inducing a pro-inflammatory environment. The generation, metabolism, and degradation of heme in the human body are regulated by precise mechanisms to ensure that heme remains non-toxic. However, in several types of cardiovascular diseases, impaired metabolism and exposure to heme may occur in pathological processes, including neovascularization, internal hemorrhage, ischemia, and reperfusion. Based on years of research, in this review, we aimed to summarize the underlying mechanisms by which heme contributes to the development of cardiovascular diseases through oxidative stress, relative pathway gene expression regulation and phenotypic changes in cells. Excess heme plays a detrimental role in atherosclerosis, heart failure, myocardial ischemia-reperfusion injury, degenerative aortic valve stenosis, cardiac iron overload. Recent researches revealed that in some cases heme involved in cardiac damage though ferroptosis. Thus, heme concentrations beyond normal levels are dangerous. Further research on the role of heme in cardiovascular diseases is needed.

Induction of cell apoptosis by biliverdin reductase inhibitor in MCF-7 and MDA-MB-468 breast cancer cell lines: Experimental and in silico studies

Biliverdin reductase, biliverdin and bilirubin are known as important components of cellular signaling pathways that play major roles in cell proliferation and apoptosis, although their physiological relevance is still under evaluation. This study was designed to investigate the expression and activity of BVR-A and its apoptotic effect in the breast cancer cell lines, MCF-7 and MDA-MB-468. The expression of BVR-A was examined by real-time PCR and western blot analysis. Bilirubin concentration was measured by HPLC and molecular docking was performed to identify an appropriate inhibitor for BVR-A. To detect cell apoptosis, annexin V-PI staining, caspase-3, -8, and -9 activities were evaluated. Cell viability was reduced by biliverdin, in a dose-dependent manner, and an intrinsic apoptotic response occurred which was evidenced by caspase-3 and -9 activities. The intra- and extracellular concentrations of bilirubin were higher in MCF-7 cells than those of MDA-MB-468 cells. The expression of BVR-A, at mRNA and protein levels, in MCF-7 was also higher than that of MDA-MB-468 cells. Treatment of both cell lines with biliverdin plus DTNB, a BVR-A inhibitor, increased the cell death significantly when compared with biliverdin alone. Using annexin V-PI staining and assessment of caspase-3 activity, it was confirmed that biliverdin together with DTNB increases apoptosis in breast cancer cells. In conclusion, biliverdin has an important role in cell apoptosis and inhibition of biliverdin reductase increases the apoptotic effect of biliverdin.

Heme oxygenase-1 inhibits DENV-induced endothelial hyperpermeability and serves as a potential target against dengue hemorrhagic fever

Dengue virus (DENV) is a cause of vascular endothelial dysfunction and vascular leakage, which are characterized as hallmarks of dengue hemorrhagic fever or dengue shock syndrome, which become a severe global health emergency with substantial morbidity and mortality. Currently, there are still no promising therapeutics to alleviate the dengue-associated vascular hemorrhage in a clinical setting. In the present study, we first observed that heme oxygenase-1 (HO-1) expression level was highly suppressed in severe DENV-infected patients. In contrast, the overexpression of HO-1 could attenuate DENV-induced pathogenesis, including plasma leakage and thrombocytopenia, in an AG129 mouse model. Our data indicate that overexpression of HO-1 or its metabolite biliverdin can maintain endothelial integrity upon DENV infection in vitro and in vivo. We further characterized the positive regulatory effect of HO-1 on the endothelial adhesion factor vascular endothelial-cadherin to decrease DENV-induced endothelial hyperpermeability. Subsequently, we confirmed that two medicinal plant-derived compounds, andrographolide, and celastrol, widely used as a nutritional or medicinal supplement are useful to attenuate DENV-induced plasma leakage through induction of the HO-1 expression in DENV-infected AG129 mice. In conclusion, our findings reveal that induction of the HO-1 signal pathway is a promising option for the treatment of DENV-induced vascular pathologies.

Korean Red Ginseng Improves Astrocytic Mitochondrial Function by Upregulating HO-1-Mediated AMPKα-PGC-1α-ERRα Circuit after Traumatic Brain Injury

Heme oxygenase-1 (HO-1) exerts beneficial effects, including angiogenesis and energy metabolism via the peroxisome proliferator-activating receptor-γ coactivator-1α (PGC-1α)-estrogen-related receptor α (ERRα) pathway in astrocytes. However, the role of Korean red ginseng extract (KRGE) in HO-1-mediated mitochondrial function in traumatic brain injury (TBI) is not well-elucidated. We found that HO-1 was upregulated in astrocytes located in peri-injured brain regions after a TBI, following exposure to KRGE. Experiments with pharmacological inhibitors and target-specific siRNAs revealed that HO-1 levels highly correlated with increased AMP-activated protein kinase α (AMPKα) activation, which led to the PGC-1α-ERRα axis-induced increases in mitochondrial functions (detected based on expression of cytochrome c oxidase subunit 2 (MTCO2) and cytochrome c as well as O2 consumption and ATP production). Knockdown of ERRα significantly reduced the p-AMPKα/AMPKα ratio and PGC-1α expression, leading to AMPKα-PGC-1α-ERRα circuit formation. Inactivation of HO by injecting the HO inhibitor Sn(IV) protoporphyrin IX dichloride diminished the expression of p-AMPKα, PGC-1α, ERRα, MTCO2, and cytochrome c in the KRGE-administered peri-injured region of a brain subjected to TBI. These data suggest that KRGE enhanced astrocytic mitochondrial function via a HO-1-mediated AMPKα-PGC-1α-ERRα circuit and consequent oxidative phosphorylation, O2 consumption, and ATP production. This circuit may play an important role in repairing neurovascular function after TBI in the peri-injured region by stimulating astrocytic mitochondrial biogenesis.

Bioadhesive hydrogel comprising bilirubin/β-cyclodextrin inclusion complexes promote diabetic wound healing

CONTEXT

Chronic non-healing diabetic wound therapy is an important clinical challenge. Manipulating the release of bioactive factors from an adhesive hydrogel is an effective approach to repair chronic wounds. As an endogenous antioxidant, bilirubin (BR) has been shown to promote wound healing. Nonetheless, its application is limited by its low water solubility and oxidative degradation.

OBJECTIVE

This study developed a bilirubin-based formulation for diabetic wound healing.

MATERIALS AND METHODS

Bilirubin was incorporated into β-CD-based inclusion complex (BR/β-CD) which was then loaded into a bioadhesive hydrogel matrix (BR/β-CD/SGP). Scratch wound assays were performed to examine the in vitro pro-healing activity of BR/β-CD/SGP (25 μg/mL of BR). Wounds of diabetic or non-diabetic rats were covered with BR or BR/β-CD/SGP hydrogels (1 mg/mL of BR) and changed every day for a period of 7 or 21 days. Histological assays were conducted to evaluate the in vivo effect of BR/β-CD/SGP.

RESULTS

Compared to untreated (18.7%) and BR (55.2%) groups, wound closure was more pronounced (65.0%) in BR/β-CD/SGP group. In diabetic rats, the wound length in BR/β-CD/SGP group was smaller throughout the experimental period than untreated groups. Moreover, BR/β-CD/SGP decreased TNF-α levels to 7.7% on day 3, and elevated collagen deposition and VEGF expression to 11.9- and 8.2-fold on day 14. The therapeutic effects of BR/β-CD/SGP were much better than those of the BR group. Similar observations were made in the non-diabetic model.

DISCUSSION AND CONCLUSION

BR/β-CD/SGP promotes wound healing and tissue remodelling in both diabetic and non-diabetic rats, indicating an ideal wound-dressing agent.

Bilirubin as a Therapeutic Molecule: Challenges and Opportunities

There is strong evidence that serum free bilirubin concentration has significant effects on morbidity and mortality in the most significant health conditions of our times, including cardiovascular disease, diabetes, and obesity/metabolic syndrome. Supplementation of bilirubin in animal and experimental models has reproduced these protective effects, but several factors have slowed the application bilirubin as a therapeutic agent in human patients. Bilirubin is poorly soluble in water, and is a complex molecule that is difficult to synthesize. Current sources of this molecule are animal-derived, creating concerns regarding the risk of virus or prion transmission. However, recent developments in nanoparticle drug delivery, biosynthetic strategies, and drug synthesis have opened new avenues for applying bilirubin as a pharmaceutical agent. This article reviews the chemistry and physiology of bilirubin, potential clinical applications and summarizes current strategies for safe and efficient drug delivery.

Association of Serum Bilirubin with the Severity and Outcomes of Intracerebral Hemorrhages

Intracerebral hemorrhage (ICH) is the second most common subtype of stroke, and it is often associated with a high mortality rate and significant morbidity among survivors. Recent studies have shown that bilirubin, a product of heme metabolism, can exhibit cytoprotective, antioxidant and, anti-inflammatory properties. However, little is known about the role of bilirubin in combating several pathophysiological pathways caused by intracerebral bleeding in patients with ICH. In this study, data were collected retrospectively on 276 patients with ICH who were admitted to a university hospital between 5 January 2014 and 31 December 2017. We assessed the relationship between levels of total, direct, and indirect serum bilirubin and assessments of initial stroke severity and clinical outcomes by using Spearman’s rank correlation and Kruskal-Wallis H tests. A secondary examination of the carrier protein albumin was also undertaken. Our study found that higher levels of direct bilirubin were correlated with worse admission Glasgow Coma Scales (GCS) (r_s = −0.17, p = 0.011), worse admission ICH Scores (r_s = 0.19, p = 0.008), and worse discharge modified Rankin Scales (mRS) (r_s = 0.15, p = 0.045). Direct bilirubin was still significantly correlated with discharge mRS after adjusting for temperature at admission (r_s = 0.16, p = 0.047), oxygen saturation at admission (r_s = 0.15, p = 0.048), white blood cell count (r_s = 0.18, p = 0.023), or Troponin T (r_s = 0.25, p = 0.001) using partial Spearman’s correlation. No statistical significance was found between levels of total or indirect bilirubin and assessments of stroke severity and outcomes. In contrast, higher levels of albumin were correlated with better admission GCS (r_s = 0.13, p = 0.027), discharge GCS (r_s = 0.15, p = 0.013), and discharge mRS (r_s = −0.16, p = 0.023). We found that levels of total bilirubin, direct bilirubin, and albumin were all significantly related to discharge outcomes classified by discharge destinations (p = 0.036, p = 0.014, p = 0.016, respectively; Kruskal-Wallis H tests). In conclusion, higher direct bilirubin levels were associated with greater stroke severity at presentation and worse outcomes at discharge among patients with ICH. Higher levels of albumin were associated with lower stroke severity and better clinical outcomes. Future prospective studies on the free bioactive bilirubin are needed to better understand the intricate relationships between bilirubin and ICH.

Suppression of Mitochondria-Related Bioenergetics Collapse and Redox Impairment by Tanshinone I, a Diterpenoid Found in Salvia miltiorrhiza Bunge (Danshen), in the Human Dopaminergic SH-SY5Y Cell Line Exposed to Chlorpyrifos

Tanshinone I (T-I, C₁₈H₁₂O₃) is a diterpene found in Salvia miltiorrhiza Bunge (Danshen) and promotes cytoprotection in several experimental models. Chlorpyrifos (CPF) is an agrochemical that causes bioenergetics failure, redox impairment, inflammation, and cell death in animal tissues. Here, we investigated whether T-I would be able to prevent the consequences resulting from the exposure of the human dopaminergic SH-SY5Y cells to CPF. We found that a pretreatment with T-I at 2.5 µM for 2 h suppressed lipid peroxidation and protein carbonylation and nitration on the membranes of mitochondria extracted from the CPF-treated cells. Also, T-I reduced the production of radical superoxide (O₂^-•) by the mitochondria of the CPF-challenged cells. The production of nitric oxide (NO^•) and hydrogen peroxide (H₂O₂) was also decreased by T-I in the cells exposed to CPF. The CPF-induced decrease in the activity of the complexes I-III, II-III, and V was abolished by a pretreatment with T-I. Loss of mitochondrial membrane potential (ΔΨ_m) and reduction in the production of adenosine triphosphate (ATP) were also prevented by T-I in the CPF-treated cells. T-I also induced anti-inflammatory effects in the CPF-treated cells by decreasing the levels of interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) and the activity of the nuclear factor-κB (NF-κB). Inhibition of heme oxygenase-1 (HO-1) or silencing of the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) blocked the T-I-promoted mitochondrial protection and anti-inflammatory action. Overall, T-I depended on the Nrf2/HO-1 axis to prevent the deleterious effects caused by CPF in this experimental model.

High-Resolution Proteomic Profiling Shows Sexual Dimorphism in Zebrafish Heart-Associated Proteins

Understanding the molecular basis of sexual dimorphism in the cardiovascular system may contribute to the improvement of the outcome in biological, pharmacological, and toxicological studies as well as on the development of sex-based drugs and therapeutic approaches. Label-free protein quantification using high-resolution mass spectrometry was applied to detect sex-based proteome differences in the heart of zebrafish Danio rerio. Out of almost 3000 unique identified proteins in the heart, 79 showed significant abundance differences between male and female fish. The functional differences were mapped using enrichment analyses. Our results suggest that a large amount of materials needed for reproduction (e.g., sugars, lipids, proteins, etc.) may impose extra pressure on blood, vessels, and heart on their way toward the ovaries. In the present study, the female's heart shows a clear sexual dimorphism by changing abundance levels of numerous proteins, which could be a way to safely overcome material-induced elevated pressures. These proteins belong to the immune system, oxidative stress response, drug metabolization, detoxification, energy, metabolism, and so on. In conclusion, we showed that sex can induce dimorphism at the molecular level in nonsexual organs such as heart and must be considered as an important factor in cardiovascular research. Data are available via ProteomeXchange with identifier PXD023506.

Antioxidant Therapy and Antioxidant-Related Bionanomaterials in Diabetic Wound Healing

Ulcers are a lower-extremity complication of diabetes with high recurrence rates. Oxidative stress has been identified as a key factor in impaired diabetic wound healing. Hyperglycemia induces an accumulation of intracellular reactive oxygen species (ROS) and advanced glycation end products, activation of intracellular metabolic pathways, such as the polyol pathway, and PKC signaling leading to suppression of antioxidant enzymes and compounds. Excessive and uncontrolled oxidative stress impairs the function of cells involved in the wound healing process, resulting in chronic non-healing wounds. Given the central role of oxidative stress in the pathology of diabetic ulcers, we performed a comprehensive review on the mechanism of oxidative stress in diabetic wound healing, focusing on the progress of antioxidant therapeutics. We summarize the antioxidant therapies proposed in the past 5 years for use in diabetic wound healing, including Nrf2- and NFκB-pathway-related antioxidant therapy, vitamins, enzymes, hormones, medicinal plants, and biological materials.

Heme cytotoxicity is the consequence of endoplasmic reticulum stress in atherosclerotic plaque progression

Hemorrhage and hemolysis with subsequent heme release are implicated in many pathologies. Endothelial cells (ECs) encounter large amount of free heme after hemolysis and are at risk of damage from exogenous heme. Here we show that hemorrhage aggravates endoplasmic reticulum (ER) stress in human carotid artery plaques compared to healthy controls or atheromas without hemorrhage as demonstrated by RNA sequencing and immunohistochemistry. In EC cultures, heme also induces ER stress. In contrast, if cultured ECs are pulsed with heme arginate, cells become resistant to heme-induced ER (HIER) stress that is associated with heme oxygenase-1 (HO-1) and ferritin induction. Knocking down HO-1, HO-2, biliverdin reductase, and ferritin show that HO-1 is the ultimate cytoprotectant in acute HIER stress. Carbon monoxide-releasing molecules (CORMs) but not bilirubin protects cultured ECs from HIER stress via HO-1 induction, at least in part. Knocking down HO-1 aggravates heme-induced cell death that cannot be counterbalanced with any known cell death inhibitors. We conclude that endothelium and perhaps other cell types can be protected from HIER stress by induction of HO-1, and heme-induced cell death occurs via HIER stress that is potentially involved in the pathogenesis of diverse pathologies with hemolysis and hemorrhage including atherosclerosis.

Harnessing the cardiovascular benefits of exercise: are Nrf2 activators useful?

The ability of physical activity to ameliorate cardiovascular disease and improve cardiovascular health is well accepted, but many aspects of the molecular mechanisms underlying these benefits are incompletely understood. Exercise increases the levels of reactive oxygen species (ROS) through various mechanisms. This triggers the activation of Nrf2, a redox-sensitive transcription factor activated by increases in oxidative stress. Activation of Nrf2 mitigates oxidative stress by increasing the nuclear transcription of many antioxidant genes while also mediating additional beneficial effects through the cytoprotective nature of Nrf2 signaling. Understanding the transcriptional patterns of Nrf2 caused by exercise can help in the design of pharmacological mimicry of the process in patients who are unable to exercise for various reasons.

Noise-Induced Vascular Dysfunction, Oxidative Stress, and Inflammation Are Improved by Pharmacological Modulation of the NRF2/HO-1 Axis

Vascular oxidative stress, inflammation, and subsequent endothelial dysfunction are consequences of traditional cardiovascular risk factors, all of which contribute to cardiovascular disease. Environmental stressors, such as traffic noise and air pollution, may also facilitate the development and progression of cardiovascular and metabolic diseases. In our previous studies, we investigated the influence of aircraft noise exposure on molecular mechanisms, identifying oxidative stress and inflammation as central players in mediating vascular function. The present study investigates the role of heme oxygenase-1 (HO-1) as an antioxidant response preventing vascular consequences following exposure to aircraft noise. C57BL/6J mice were treated with the HO-1 inducer hemin (25 mg/kg i.p.) or the NRF2 activator dimethyl fumarate (DMF, 20 mg/kg p.o.). During therapy, the animals were exposed to noise at a maximum sound pressure level of 85 dB(A) and a mean sound pressure level of 72 dB(A). Our data showed a marked protective effect of both treatments on animals exposed to noise for 4 days by normalization of arterial hypertension and vascular dysfunction in the noise-exposed groups. We observed a partial normalization of noise-triggered oxidative stress and inflammation by hemin and DMF therapy, which was associated with HO-1 induction. The present study identifies possible new targets for the mitigation of the adverse health effects caused by environmental noise exposure. Since natural dietary constituents can achieve HO-1 and NRF2 induction, these pathways represent promising targets for preventive measures.

The signaling pathway PI3K/Akt/Nrf2/HO-1 plays a role in the mitochondrial protection promoted by astaxanthin in the SH-SY5Y cells exposed to hydrogen peroxide

The mitochondria are the major source of reactive species in the mammalian cells. Hydrogen peroxide (H₂O₂) is a potent inducer of redox impairment by a mechanism, at least in part, dependent on its ability to impair mitochondrial function. H₂O₂ plays an important role in several pathological conditions, including neurodegeneration and cardiovascular diseases. Astaxanthin (AST) is a xanthophyll that may be found in microalgae, crustaceans, and salmon and exhibits antioxidant and anti-inflammatory effects in different cell types. Even though there is evidence pointing to a role for AST as mitochondrial protectant agent, it was not clearly demonstrated how this xanthophyll attenuates mitochondrial stress. Therefore, we investigated here whether and how AST would be able to prevent the H₂O₂-induced mitochondrial dysfunction in the human neuroblastoma SH-SY5Y cells. We found that AST (20 μM) prevented the H₂O₂-induced loss of mitochondrial membrane potential (MMP) and decrease in the activity of the Complexes I and V. AST pretreatment blocked the mitochondria-related pro-apoptotic effects elicited by H₂O₂. AST upregulated the enzyme heme oxygenase-1 (HO-1) and the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) by a mechanism dependent on the phosphoinositide 3-kinase/Akt (PI3K/Akt) signaling pathway. Inhibition of the PI3K/Akt or of the HO-1 enzyme abolished the AST-induced mitochondrial protection in cells challenged with H₂O₂. Silencing of Nrf2 caused similar effects. Thus, we suggest that AST promotes mitochondrial protection by a mechanism dependent on the PI3K/Akt/Nrf2/HO-1 signaling pathway in SH-SY5Y cells exposed to H₂O₂.

Vascular and Macrophage Heme Oxygenase-1 in Hypertension: A Mini-Review

Hypertension is one predictive factor for stroke and heart ischemic disease. Nowadays, it is considered an inflammatory disease with elevated cytokine levels, oxidative stress, and infiltration of immune cells in several organs including heart, kidney, and vessels, which contribute to the hypertension-associated cardiovascular damage. Macrophages, the most abundant immune cells in tissues, have a high degree of plasticity that is manifested by polarization in different phenotypes, with the most well-known being M1 (proinflammatory) and M2 (anti-inflammatory). In hypertension, M1 phenotype predominates, producing inflammatory cytokines and oxidative stress, and mediating many mechanisms involved in the pathogenesis of this disease. The increase in the renin-angiotensin system and sympathetic activity contributes to the macrophage mobilization and to its polarization to the pro-inflammatory phenotype. Heme oxygenase-1 (HO-1), a phase II detoxification enzyme responsible for heme catabolism, is induced by oxidative stress, among others. HO-1 has been shown to protect against oxidative and inflammatory insults in hypertension, reducing end organ damage and blood pressure, not only by its expression at the vascular level, but also by shifting macrophages toward the anti-inflammatory phenotype. The regulatory role of heme availability for the synthesis of enzymes involved in hypertension development, such as cyclooxygenase or nitric oxide synthase, seems to be responsible for many of the beneficial HO-1 effects; additionally, the antioxidant, anti-inflammatory, antiapoptotic, and antiproliferative effects of the end products of its reaction, carbon monoxide, biliverdin/bilirubin, and Fe²⁺, would also contribute. In this review, we analyze the role of HO-1 in hypertensive pathology, focusing on its expression in macrophages.

Heme oxygenase‑1 improves the survival of ischemic skin flaps (Review)

Heat shock protein 32 (Hsp32), also known as heme oxygenase‑1 (HO‑1), is an enzyme that exists in microsomes. HO‑1 can be induced by a variety of stimuli, including heavy metals, heat shock, inflammatory stimuli, heme and its derivatives, stress, hypoxia, and biological hormones. HO‑1 is the rate‑limiting enzyme of heme catabolism, which splits heme into biliverdin, carbon monoxide (CO) and iron. The metabolites of HO‑1 have anti‑inflammatory and anti‑oxidant effects, and provide protection to the cardiovascular system and transplanted organs. This review summarizes the biological characteristics of HO‑1 and the functional significance of its products, and specifically elaborates on its protective effect on skin flaps. HO‑1 improves the survival rate of ischemic skin flaps through anti‑inflammatory, anti‑oxidant and vasodilatory effects of enzymatic reaction products. In particular, this review focuses on the role of carbon monoxide (CO), one of the primary metabolites of HO‑1, in flap survival and discusses the feasibility and existing challenges of HO‑1 in flap surgery.

Bilirubin as a metabolic hormone: the physiological relevance of low levels

Recent research on bilirubin, a historically well-known waste product of heme catabolism, suggests an entirely new function as a metabolic hormone that drives gene transcription by nuclear receptors. Studies are now revealing that low plasma bilirubin levels, defined as "hypobilirubinemia," are a possible new pathology analogous to the other end of the spectrum of extreme hyperbilirubinemia seen in patients with jaundice and liver dysfunction. Hypobilirubinemia is most commonly seen in patients with metabolic dysfunction, which may lead to cardiovascular complications and possibly stroke. We address the clinical significance of low bilirubin levels. A better understanding of bilirubin's hormonal function may explain why hypobilirubinemia might be deleterious. We present mechanisms by which bilirubin may be protective at mildly elevated levels and research directions that could generate treatment possibilities for patients with hypobilirubinemia, such as targeting of pathways that regulate its production or turnover or the newly designed bilirubin nanoparticles. Our review here calls for a shift in the perspective of an old molecule that could benefit millions of patients with hypobilirubinemia.

Low Antioxidant Status of Serum Uric Acid, Bilirubin, Albumin, and Creatinine in Patients With Benign Paroxysmal Positional Vertigo

Objective: To investigate the roles of serum uric acid (UA), bilirubin (BIL), albumin (ALB), and creatinine (CRE) as major intravascular antioxidants, in benign paroxysmal positional vertigo (BPPV).

Methods: The serum levels of UA, BIL, ALB, and CRE were retrospectively analyzed in 70 patients with new-onset idiopathic BPPV and 140 age- and sex-matched healthy controls (HCs).

Results: Serum UA, BIL, ALB, and CRE levels were significantly lower in the BPPV group than the HC group. Furthermore, serum levels of BIL and ALB were significantly lower in the BPPV group when compared by sex. Multiple stepwise logistic regression revealed that a reduction in serum ALB was independently related to BPPV (odds ratio = 0.688; 95% confidence interval = 0.607– 0.780). Receiver operating characteristic analyses revealed a cut-off value of 45.15 g/L for ALB with a sensitivity of 74.29% (62.97– 83.07%) and specificity of 73.57% (65.71– 80.18%).

Conclusions: Serum levels of UA, BIL, ALB, and CRE were lower in BPPV patients, indicating a lower antioxidant status. Furthermore, a reduction in serum ALB was independently associated with BPPV. These results provide insights into the possible roles of oxidative stress in the pathogenesis of BPPV.

Heme oxygenase-1 modulation: A potential therapeutic target for COVID-19 and associated complications

Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to infect hundred thousands of people every day worldwide. Since it is a novel virus, research continues to update the possible therapeutic targets when new evidence regarding COVID-19 are gathered. This article presents an evidence-based hypothesis that activating the heme oxygenase-1 (HO-1) pathway is a potential target for COVID-19. Interferons (IFNs) have broad-spectrum antiviral activity including against SARS-CoV-2. Induction of HO-1 and increase in the heme catabolism end-product confer antiviral activity. IFN activation results in inhibition of viral replication in various viral infections. COVID-19 induced inflammation as well as acute respiratory distress syndrome (ARDS), and coagulopathies are now known major causes of mortality. A protective role of HO-1 induction in inflammation, inflammation-induced coagulation, and ARDS has been reported. Based on an association of HO-1 promoter polymorphisms and disease severity, we propose an evaluation of the status of these polymorphisms in COVID-19 patients who become severely ill. If an association is established, it might be helpful in identifying patients at high risk. Hence, we hypothesize that HO-1 pathway activation could be a therapeutic strategy against COVID-19 and associated complications.

Molecular Characterisation of Canine Osteosarcoma in High Risk Breeds

Dogs develop osteosarcoma (OSA) and the disease process closely resembles that of human OSA. OSA has a poor prognosis in both species and disease-free intervals and cure rates have not improved in recent years. Gene expression in canine OSAs was compared with non-tumor tissue utilising RNA sequencing, validated by qRT-PCR and immunohistochemistry (n = 16). Polymorphic polyglutamine (polyQ) tracts in the androgen receptor (AR/NR3C4) and nuclear receptor coactivator 3 (NCOA3) genes were investigated in control and OSA patients using polymerase chain reaction (PCR), Sanger sequencing and fragment analysis (n = 1019 Rottweilers, 379 Irish Wolfhounds). Our analysis identified 1281 significantly differentially expressed genes (>2 fold change, p < 0.05), specifically 839 lower and 442 elevated gene expression in osteosarcoma (n = 3) samples relative to non-malignant (n = 4) bone. Enriched pathways and gene ontologies were identified, which provide insight into the molecular pathways implicated in canine OSA. Expression of a subset of these genes (SLC2A1, DKK3, MMP3, POSTN, RBP4, ASPN) was validated by qRTPCR and immunohistochemistry (MMP3, DKK3, SLC2A1) respectively. While little variation was found in the NCOA3 polyQ tract, greater variation was present in both polyQ tracts in the AR, but no significant associations in length were made with OSA. The data provides novel insights into the molecular mechanisms of OSA in high risk breeds. This knowledge may inform development of new prevention strategies and treatments for OSA in dogs and supports utilising spontaneous OSA in dogs to improve understanding of the disease in people.

Heme oxygenase-1 in protozoan infections: A tale of resistance and disease tolerance

Heme oxygenase (HO-1) mediates the enzymatic cleavage of heme, a molecule with proinflammatory and prooxidant properties. HO-1 activity deeply impacts host capacity to tolerate infection through reduction of tissue damage or affecting resistance, the ability of the host to control pathogen loads. In this Review, we will discuss the contribution of HO-1 in different and complex protozoan infections, such as malaria, leishmaniasis, Chagas disease, and toxoplasmosis. The complexity of these infections and the pleiotropic effects of HO-1 constitute an interesting area of study and an opportunity for drug development.

Heme oxygenase promotes B-Raf-dependent melanosphere formation

Biosynthesis and degradation of heme, an iron-bound protoporphyrin molecule utilized by a wide variety of metabolic processes, are tightly regulated. Two closely related enzymes, heme oxygenase 1 (HMOX1) and heme oxygenase 2 (HMOX2), degrade free heme to produce carbon monoxide, Fe²⁺ , and biliverdin. HMOX1 expression is controlled via the transcriptional activator, NFE2L2, and the transcriptional repressor, Bach1. Transcription of HMOX1 and other NFE2L2-dependent genes is increased in response to electrophilic and reactive oxygen species. Many tumor-derived cell lines have elevated levels of NFE2L2. Elevated expression of NFE2L2-dependent genes contributes to tumor growth and acquired resistance to therapies. Here, we report a novel role for heme oxygenase activity in melanosphere formation by human melanoma-derived cell lines. Transcriptional induction of HMOX1 through derepression of Bach1 or transcriptional activation of HMOX2 by oncogenic B-Raf^V600E results in increased melanosphere formation. Genetic ablation of HMOX1 diminishes melanosphere formation. Further, inhibition of heme oxygenase activity with tin protoporphyrin markedly reduces melanosphere formation driven by either Bach1 derepression or B-Raf^V600E expression. Global transcriptome analyses implicate genes involved in focal adhesion and extracellular matrix interactions in melanosphere formation.

Oxidative state in equine neonates: Anti- and pro-oxidants

BACKGROUND

In newborns, exposure to the extrauterine environment with high oxygen tension and sudden pulmonary adaptation leads to an increase in reactive oxygen species (ROS). ROS have several physiological roles, which are essential for neonatal development, however, when unbalanced, these highly unstable molecules can cause cellular destabilisation, compromising vital processes.

OBJECTIVES

To characterise the oxidative status in healthy equine neonates, evaluating an indicator of lipid peroxidation and both enzymatic and nonenzymatic antioxidant systems, during the first week of life.

STUDY DESIGN

Experimental cohort.

METHODS

Twenty-four foals were evaluated, with blood collections performed at 5 minutes, 12, 72 and 168 hours after birth. The degree of lipid peroxidation was quantified using Thiobarbituric Acid Reactive Substances (TBARS). Superoxide dismutase (SOD) and glutathione peroxidase (GPx) enzymatic activities, and total, conjugated and unconjugated serum bilirubin levels were also analysed. Comparisons were performed using ANOVA followed by a Tukey's test. Additionally, dependent variables were also evaluated with Pearson's correlation tests.

RESULTS

Higher GPx activity was observed at 12 and 72 hours when compared to 5 minutes. An increase in TBARS levels was found at 5 minutes after birth, followed by a decrease at 72 hours and stabilisation through subsequent moments until 168 hours after birth. No differences were observed in SOD activity when comparing the four time points. Bilirubin concentrations were lower at 5 minutes after birth and total and unconjugated bilirubin increased at 12 hours and decreased between 72 and 168 hours after birth.

CONCLUSIONS

Lipid peroxidation at birth was high, suggesting an increase in ROS levels relating to physiological events in neonatal adaptation. Antioxidant systems, involving unconjugated bilirubin and GPx, were activated and these biomolecules act concomitantly to reduce ROS levels, thus maintaining oxidative homeostasis. Overall, our results suggest a pro-oxidant balance during the first 168 hours after birth in equine neonates.

Bilirubin in metabolic syndrome and associated inflammatory diseases: New perspectives

Diabetes mellitus is one of the major global health issues, which is closely related to metabolic dysfunction and the chronic inflammatory diseases. Multiple studies have demonstrated that serum bilirubin is negatively correlated with metabolic syndrome and associated inflammatory diseases, including atherosclerosis, hypertension, etc. However, the roles of bilirubin in metabolic syndrome and associated inflammatory diseases still remain unclear. Here, we explain the role of bilirubin in metabolic syndrome and chronic inflammatory diseases and its therapeutic potential. Understanding the role of bilirubin activities in diabetes may serve as a therapeutic target for the treatment of chronic inflammatory diseases in diabetic patients.

Biliverdin Reductase A (BVRA) Knockout in Adipocytes Induces Hypertrophy and Reduces Mitochondria in White Fat of Obese Mice

Biliverdin reductase (BVR) is an enzymatic and signaling protein that has multifaceted roles in physiological systems. Despite the wealth of knowledge about BVR, no data exist regarding its actions in adipocytes. Here, we generated an adipose-specific deletion of biliverdin reductase-A (BVRA) (Blvra^FatKO) in mice to determine the function of BVRA in adipocytes and how it may impact adipose tissue expansion. The Blvra^FatKO and littermate control (Blvra^Flox) mice were placed on a high-fat diet (HFD) for 12 weeks. Body weights were measured weekly and body composition, fasting blood glucose and insulin levels were quantitated at the end of the 12 weeks. The data showed that the percent body fat and body weights did not differ between the groups; however, Blvra^FatKO mice had significantly higher visceral fat as compared to the Blvra^Flox. The loss of adipocyte BVRA decreased the mitochondrial number in white adipose tissue (WAT), and increased inflammation and adipocyte size, but this was not observed in brown adipose tissue (BAT). There were genes significantly reduced in WAT that induce the browning effect such as Ppara and Adrb3, indicating that BVRA improves mitochondria function and beige-type white adipocytes. The Blvra^FatKO mice also had significantly higher fasting blood glucose levels and no changes in plasma insulin levels, which is indicative of decreased insulin signaling in WAT, as evidenced by reduced levels of phosphorylated AKT (pAKT) and Glut4 mRNA. These results demonstrate the essential role of BVRA in WAT in insulin signaling and adipocyte hypertrophy.

Heme-Derived Metabolic Signals Dictate Immune Responses

Heme is one of the most abundant molecules in the body acting as the functional core of hemoglobin/myoglobin involved in the O2/CO2 carrying in the blood and tissues, redox enzymes and cytochromes in mitochondria. However, free heme is toxic and therefore its removal is a significant priority for the host. Heme is a well-established danger-associated molecular pattern (DAMP), which binds to toll-like receptor 4 (TLR4) to induce immune responses. Heme-derived metabolites including the bile pigments, biliverdin (BV) and bilirubin (BR), were first identified as toxic drivers of neonatal jaundice in 1800 but have only recently been appreciated as endogenous drivers of multiple signaling pathways involved in protection from oxidative stress and regulators of immune responses. The tissue concentration of heme, BV and BR is tightly controlled. Heme oxygenase-1 (HO-1, encoded by HMOX1) produces BV by heme degradation, while biliverdin reductase-A (BLVR-A) generates BR by the subsequent conversion of BV. BLVR-A is a fascinating protein that possesses a classical protein kinase domain, which is activated in response to BV binding to its enzymatic site and initiates the downstream mitogen-activated protein kinases (MAPK) and phosphatidylinositol 3-kinase (PI3K) pathways. This links BLVR-A activity to cell growth and survival pathways. BLVR-A also contains a bZip DNA binding domain and a nuclear export sequence (NES) and acts as a transcription factor to regulate the expression of immune modulatory genes. Here we will discuss the role of heme-related immune response and the potential for targeting the heme system for therapies directed toward hepatitis and cancer.

Heme Oxygenase Dependent Bilirubin Generation in Vascular Cells: A Role in Preventing Endothelial Dysfunction in Local Tissue Microenvironment?

Among antioxidants in the human body, bilirubin has been recognized over the past 20 years to afford protection against different chronic conditions, including inflammation and cardiovascular disease. Moderate increases in plasma concentration and cellular bilirubin generation from metabolism of heme via heme oxygenase (HMOX) in virtually all tissues can modulate endothelial and vascular function and exert antioxidant and anti-inflammatory roles. This review aims to provide an up-to-date and critical overview of the molecular mechanisms by which bilirubin derived from plasma or from HMOX1 activation in vascular cells affects endothelial function. Understanding the molecular actions of bilirubin may critically improve the management not only of key cardiovascular diseases, but also provide insights into a broad spectrum of pathologies driven by endothelial dysfunction. In this context, therapeutic interventions aimed at mildly increasing serum bilirubin as well as bilirubin generated endogenously by endothelial HMOX1 should be considered.

Association between serum bilirubin and asymptomatic intracranial atherosclerosis: results from a population-based study

INTRODUCTION

The effects of bilirubin on asymptomatic intracranial atherosclerosis (aICAS) remain uncertain.

OBJECTIVES

To investigate the association between bilirubin and aICAS in rural-dwelling Chinese people.

METHODS

This population-based study included 2013 participants from the Kongcun Town Study, which aimed to investigate the prevalence of aICAS in people aged ≥ 40 years who were free of stroke and hepatic and gall disease history. Baseline data were collected via interviews, clinical examinations, and laboratory tests. Total bilirubin (Tbil), direct bilirubin (Dbil), and indirect bilirubin (Ibil) levels were divided into high-concentration group and low-concentration group, respectively. We diagnosed aICAS and moderate-to-severe aICAS (m-saICAS) (≥ 50% stenosis) by integrating transcranial Doppler ultrasound with magnetic resonance angiography. The association between bilirubin and aICAS, as well as m-saICAS, was analyzed using logistic regression.

RESULTS

Of the 2013 participants, those in the high-concentration group of Tbil (odds ratio (OR), 0.50; 95% confidence interval (CI), 0.42-0.87), Dbil (OR 0.60, 95%CI 0.41-0.87), and Ibil (OR 0.67; 95%CI 0.47-0.97) had a lower risk of aICAS than those in the low-concentration group after adjusting all confounders. The high concentrations of Tbil, Dbil, and Ibil were also negatively associated with m-saICAS. After stratification according to age, Tbil, Dbil, and Ibil were significantly negatively associated with aICAS among participants aged ≥ 60 years.

CONCLUSION

Tbil, Dbil, and Ibil might be independent protective factors for aICAS and moderate-to-severe aICAS in rural-dwelling Chinese people, especially among older participants aged ≥ 60 years.

Relationship between serum bilirubin levels and presence of fragmented QRS in patients with acute coronary syndrome

Aim: To assess the relationship between serum bilirubin levels and fragmented QRS (fQRS), and their association with adverse events in patients with acute coronary syndrome. Methods: This study included a total of 736 patients. Laboratory results such as bilirubin levels, renal and liver function tests were obtained from the first available blood sample. Results: Left ventricular ejection fraction, end-diastolic diameter and total bilirubin level were significantly lower in fQRS (+) group than in the control group (45.0 [40.0-55.0] vs 50.0 [45.0-60.0]%; p < 0.001; 4.7 [4.6-5.1] vs 4.7 [4.5-4.9] cm; p < 0.001; 0.66 [0.49-5.1] vs 0.72 [0.53-0.97] md/dl; p = 0.017); respectively. Occurrence of adverse events was significantly higher in fQRS (+) group (32.5 vs 20.5 %; p = 0.013) during mean 1-year follow-up period. Conclusion: Total bilirubin level is an independent predictor of fQRS formation, which is associated with the presence of adverse events in patients with acute coronary syndrome.

Comparison of Oxidative Stress Parameters in Heart Failure Patients Depending on Ischaemic or Nonischaemic Aetiology

Background

Abnormalities in the oxidative and antioxidant states causing oxidative stress were both found in heart failure (HF) of various aetiologies and atherosclerosis.

Aim of Study

The goals of the study were as follows: comparison of oxidative stress parameters (OSP) in ischaemic cardiomyopathy (ICM) (n = 479) and nonischaemic cardiomyopathy (nICM) (n = 295) patients; assessment of the relationships of OSP with functional capacity (NYHA class), maximal oxygen consumption (max.O2), left ventricle ejection fraction (LVEF), and NT-proBNP concentration; and determination of the mutual relations of OSP in subgroups of patients with ICM and n-ICM.

Methods

Serum concentrations of total antioxidant capacity (TAC), total oxidant status (TOS), uric acid (UA), bilirubin, albumin, protein sulfhydryl groups (PSH), and malondialdehyde (MDA) were measured. The oxidative stress index (OSI) and MDA/PSH ratio were calculated.

Results

Higher concentrations of TAC (1.14 vs 1.11 mmol/l; p < 0.001) and MDA (1.80 vs 1.70 μmol/l; p < 0.05) and higher MDA/PSH ratios (0.435 vs 0.358; p < 0,001) were observed in ICM than in nICM patients. Simultaneously, lower values of the OSI index (4.27 vs 4.6; p < 0, 05), PSH (4.10 vs 4.75 μmol/g of protein; p < 0,001), and bilirubin (12.70 vs 15.40 μmol/l; p < 0,001) concentrations were indicated in ICM patients. There were no differences in TOS, UA, and albumin between the examined groups. The NYHA class and VO2max correlate with MDA, bilirubin, and albumin in both groups, while with UA only in the ICM group. Correlations between the NYHA class, VO2max, and PSH were indicated in nICM. The association of LVEF with UA, bilirubin, and albumin has been demonstrated in the ICM group. The study showed negative correlations between TAC, MDA, and PSH and positive between TAC and MDA in both groups. In ICM patients, MDA positively correlated with UA. A negative correlation between PSH and concentrations of UA and bilirubin was expressed only in the nICM group.

Conclusion

The obtained results confirm the relationship between the severity of HF and oxidative stress. The mechanisms of oxidative stress and antioxidant defence are partially different in the ICM and the nICM patients.

CRISPR Cas9-mediated deletion of biliverdin reductase A (BVRA) in mouse liver cells induces oxidative stress and lipid accumulation

Obesity is the predominant cause of non-alcoholic fatty liver disease (NAFLD), which is associated with insulin resistance and diabetes. NAFLD includes a spectrum of pathologies that starts with simple steatosis, which can progress to non-alcoholic steatohepatitis (NASH) with the commission of other factors such as the enhancement of reactive oxygen species (ROS). Biliverdin reductase A (BVRA) reduces biliverdin to the antioxidant bilirubin, which may serve to prevent NAFLD, and possibly the progression to NASH. To further understand the role of BVRA in hepatic function, we used CRISPR-Cas9 technology to target the Blvra gene in the murine hepa1c1c7 hepatocyte cell line (BVRA KO). BVRA activity and protein levels were significantly lower in BVRA KO vs. wild-type (WT) hepatocytes. Lipid accumulation under basal and serum-starved conditions was significantly (p < 0.05) higher in BVRA KO vs. WT cells. The loss of BVRA resulted in the reduction of mitochondria number, decreased expression of markers of mitochondrial biogenesis, uncoupling, oxidation, and fusion, which paralleled reduced mitochondrial oxygen consumption. BVRA KO cells exhibited increased levels of ROS generation and decreased levels of superoxide dismutase mRNA expression. In conclusion, our data demonstrate a critical role for BVRA in protecting against lipid accumulation and oxidative stress in hepatocytes, which may serve as a future therapeutic target for NAFLD and its progression to NASH.

Associations between G6PD, OATP1B1 and BLVRA variants and susceptibility to neonatal hyperbilirubinaemia in a Chinese Han population

AIM

Hyperbilirubinaemia is a common disorder in newborns. The aim of this study was to investigate the associations between G6PD 1388 G>A, SLCO1B1 rs4149056 and BLVRA rs699512 variants and the risk of neonatal hyperbilirubinaemia in a Chinese neonate population.

METHODS

A total of 447 Chinese neonates with hyperbilirubinaemia were selected as the study group and 544 healthy subjects were recruited as the control group matched by baseline sex, age, feeding pattern and delivery mode. About 2 mL of peripheral venous blood was taken from all subjects. The single nucleotide polymorphisms (SNPs) of G6PD 1388 G>A, SLCO1B1 rs4149056 and BLVRA rs699512 loci were examined by the polymerase chain reaction and Sanger sequencing technique in the peripheral blood of all subjects.

RESULTS

For the G6PD 1388 G>A SNP, individuals carrying the A-allele were associated with a significantly increased risk of neonatal hyperbilirubinaemia (adjusted odds ratio (OR) = 1.49, P < 0.001, 95% confidence interval (CI): 1.31-1.67). This risk increased significantly in the CC genotype carriers at the rs4149056 locus of the SLCO1B1 gene (OR = 2.17, 95% CI: 1.87-2.33), whereas it decreased significantly in individuals carrying the G-allele at the rs699512 locus of the BLVRA gene (adjusted OR = 0.84, P = 0.01, 95% CI: 0.75-0.95). The G6PD 1388 G>A, SLCO1B1 rs4149056 and BLVRA rs699512 SNPs had a significant impact on serum total bilirubin levels. Moreover, individuals carrying the A-allele of G6PD 1388 G>A and BLVRA rs699512 had a significantly increased risk of developing neonatal hyperbilirubinaemia (OR = 5.01, P < 0.001, 95% CI: 3.42-7.85).

CONCLUSION

Genetic variants of bilirubin metabolism genes, including G6PD 1388 G>A, SLCO1B1 rs4149056 and BLVRA rs699512, are associated with the risk of neonatal hyperbilirubinaemia, and are potential markers for predicting the disorder.

Biochemical basis and metabolic interplay of redox regulation

Accumulated evidence strongly indicates that oxidative stress, characterized by an imbalance between reactive oxygen species (ROS) production and antioxidants in favor of oxidants, plays an important role in disease pathogenesis. However, ROS can act as signaling molecules and fulfill essential physiological functions at basal levels. Each ROS would be different in the extent to stimulate and contribute to different pathophysiological effects. Importantly, multiple ROS generators can be activated either concomitantly or sequentially by relevant signaling molecules for redox biological functions. Here, we summarized the current knowledge related to chemical and biochemical features of primary ROS species and corresponding antioxidants. Metabolic pathways of five major ROS generators and five ROS clearance systems were described, including their ROS products, specific ROS enriched tissue, cell and organelle, and relevant functional implications. We provided an overview of ROS generation and induction at different levels of metabolism. We classified 11 ROS species into three types based on their reactivity and target selectivity and presented ROS homeostasis and functional implications in pathological and physiological status. This article intensively reviewed and refined biochemical basis, metabolic signaling and regulation, functional insights, and provided guidance for the identification of novel therapeutic targets.

Bilirubin Links Heme Metabolism to Neuroprotection by Scavenging Superoxide

Bilirubin is one of the most frequently measured metabolites in medicine, yet its physiologic roles remain unclear. Bilirubin can act as an antioxidant in vitro, but whether its redox activity is physiologically relevant is unclear because many other antioxidants are far more abundant in vivo. Here, we report that depleting endogenous bilirubin renders mice hypersensitive to oxidative stress. We find that mice lacking bilirubin are particularly vulnerable to superoxide (O₂^⋅-) over other tested reactive oxidants and electrophiles. Whereas major antioxidants such as glutathione and cysteine exhibit little to no reactivity toward O₂^⋅-, bilirubin readily scavenges O₂^⋅-. We find that bilirubin's redox activity is particularly important in the brain, where it prevents excitotoxicity and neuronal death by scavenging O₂^⋅- during NMDA neurotransmission. Bilirubin's unique redox activity toward O₂^⋅- may underlie a prominent physiologic role despite being significantly less abundant than other endogenous and exogenous antioxidants.