Bilirubin, formed by activation of heme oxygenase-2, protects neurons against oxidative stress injury

Bilirubin nanotechnology: An innovative approach in biomedicine

Bilirubin, a product of heme catabolism, is toxic at elevated concentrations (>250-300 μM in blood serum), whereas at therapeutic concentrations (∼20-200 μM) exerts potent antioxidant, anti-inflammatory, immunomodulatory, cytoprotective and neuroprotective effects. Despite the therapeutic potential, its use in clinical practice is hampered by poor aqueous solubility, instability, and rapid metabolism. Nanotechnology overcomes these limitations and additionally imparts to bilirubin the advantages characteristic of nanopreparations: targeted action on the desired organ/tissue, increased therapeutic efficacy by delaying drug elimination from the body, improved transportation over biological barriers, the ability to combine therapeutic and diagnostic properties in a single agent. The review analyses the chemical synthesis, therapeutic mechanisms, and preclinical applications of nanosystems comprising bilirubin. In particular, nanostructures obtained by the covalent binding of bilirubin to macromolecules, bilirubin encapsulation in nanocarriers, bilirubin conjugation with metal nanoparticles and nanofunctionalization of inorganic compounds are considered; the data on the therapeutic trials of nanobilirubin are summarized. While studies on animal models and in vitro systems demonstrate improved biodistribution, reduced toxicity, and enhanced efficacy, no clinical trials to date have validated nanobilirubin formulations. Key barriers may include unresolved challenges in scalable synthesis, long-term biocompatibility, reproducible dosing of nanoformulations. Hence, further development of nanotherapeutic bilirubin agents for clinical practice is urgent.

Hemin-induced transient senescence via DNA damage response: a neuroprotective mechanism against ferroptosis in intracerebral hemorrhage

Intracerebral hemorrhage (ICH) poses acute fatality and long-term neurological risks, in part due to hemin and iron accumulation from hemoglobin breakdown. We observed that hemin induces DNA double-strand breaks (DSBs), prompting a senescence-like phenotype in neurons, necessitating a deeper exploration of cellular responses. Using experimental ICH models and human ICH patient tissue, we elucidate hemin-mediated DNA damage response (DDR) inducing transient senescence and delayed expression of heme oxygenase (HO-1). HO-1 co-localizes with senescence-associated β-Galactosidase (SA-β-Gal) in ICH patient tissues, emphasizing the clinical relevance of inducible HO-1 expression in senescent cells. We reveal a reversible senescence state protective against acute cell death by hemin, while repeat exposure leads to long-lasting senescence. Inhibiting early senescence expression increases cell death, supporting the protective role of senescence against hemin toxicity. Hemin-induced senescence is attenuated by a pleiotropic carbon nanoparticle that is a catalytic mimic of superoxide dismutase, but this treatment increased lipid peroxidation, consistent with ferroptosis from hemin breakdown released iron. When coupled with iron chelator deferoxamine (DEF), the nanoparticle reduces hemin-induced senescence and upregulates factors protecting against ferroptosis. Our study suggests transient senescence induced by DDR as an early potential neuroprotective mechanism in ICH, but the risk of iron-related toxicity supports a multi-pronged therapeutic approach.

Iron Overload, Microbleeding and the Role of Bilirubin in Alzheimer's Disease Brain: Revisiting the Vascular Hypothesis

Alzheimer's disease (AD) and vascular dementia (VaD) are the two most prevalent forms of dementia, sharing overlapping clinical features yet distinct pathophysiological mechanisms. While AD is primarily driven by amyloid-beta (Aβ) plaques and tau neurofibrillary tangles, VaD results from cerebrovascular pathology, including ischemic lesions and chronic hypoperfusion. However, accumulating evidence suggests that vascular dysfunction is a crucial contributor to both conditions, bridging neurodegenerative and cerebrovascular pathologies. In this review, we explore the interplay between AD and VaD, focusing on shared pathways such as blood-brain barrier (BBB) breakdown, neuroinflammation, and microvascular damage. Notably, cerebral microbleeds have emerged as a common feature in both AD and VaD, further linking vascular pathology to neurodegeneration. Microbleeding contributes to BBB disruption, iron deposition, and exacerbated oxidative stress, creating a vicious cycle that accelerates cognitive decline. We highlight the role of iron dysregulation as a key driver in AD, exacerbating Aβ accumulation, tau hyperphosphorylation, and ferroptosis. Conversely, bilirubin emerges as a molecule with theranostic potential, acting as both a biomarker and a neuroprotective agent due to its antioxidant and anti-inflammatory properties. Despite its protective role, bilirubin's dysregulation under pathological conditions may contribute to oxidative damage and neurovascular dysfunction. In this context, the accumulation of iron from recurrent microbleeds may further disrupt bilirubin homeostasis, amplifying oxidative injury and inflammation. We propose a vascular hypothesis that integrates iron metabolism and bilirubin homeostasis, suggesting that their imbalance plays a central role in AD pathogenesis and worsening. Understanding the intricate molecular interplay between neurodegeneration and vascular dysfunction could provide novel insights into targeted interventions aimed at mitigating cognitive decline. Finally, we discuss the potential of bilirubin-based therapeutic strategies, including its role in counteracting oxidative stress and modulating neuroinflammatory pathways, offering promising avenues for future research and precision medicine in dementia.

Unraveling the dual role of bilirubin in neurological Diseases: A Comprehensive exploration of its neuroprotective and neurotoxic effects

Neurodegenerative disorders are characterized by a progressive loss of neurons, causing substantial deficits in motor and cognitive functioning. Bilirubin is a yellow by-product of heme, existing in two primary isoforms namely unconjugated and conjugated, while initially produced unconjugated isomer is lipophilic and cytotoxic in nature. At physiological levels, bilirubin has an important role in brain function by acting as a powerful antioxidant, preventing brain tissues from oxidative damage by eliminating reactive oxygen species (ROS). Additionally, it contributes to immune regulation through microglial activation, cytokine release, complement system interception, fragment crystallization (Fc) receptor modulation, and major histocompatibility complex (MHC II) expression modification, which lower the risk of inflammatory and autoimmune reactions in the central nervous system (CNS). As per the literature, serum bilirubin concentrations are associated with CNS diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), ischemic stroke, hemorrhagic stroke, traumatic brain injury (TBI), multiple sclerosis (MS), epilepsy, schizophrenia and kernicterus spectrum disorder (KSD), which causes neuronal damage, especially in regions like the basal ganglia and cerebellum, which causes movement abnormalities and cognitive deficits. The aim of this article is to explore the dual role of bilirubin as neuroprotective and neurotoxic, essential for establishing effective therapeutic outcomes for neurodegenerative diseases by looking at its cellular mechanisms and discussing how bilirubin's antioxidant properties can shield neurons and, in some situations, may induce oxidative stress and apoptosis.

Bilirubin: Photophysical and photochemical properties, phototherapy, analytical methods of measurement. A short review

Bilirubin, a yellow bile pigment, plays an important role in the body, being a potent antioxidant and having anti-inflammatory, immunomodulatory, cytoprotective, and neuroprotective functions. This makes bilirubin promising as a therapeutic and diagnostic agent in biomedicine. However, excess bilirubin is toxic and should be removed from the body. Bilirubin exhibits photochemical activity, which has been the subject of numerous studies up to now. Such studies are relevant because the bilirubin photochemistry provides the basis for bilirubin removing in phototherapy of neonatal jaundice (neonatal hyperbilirubinemia) and for some therapeutic applications. Furthermore, it can model several elementary processes of molecular photonics. In particular, the bilirubin molecule is capable of ultrafast Z-E photoisomerization and contains two almost identical dipyrromethenone chromophores capable of exciton coupling. The present review considers the data on the photophysical and photochemical properties of bilirubin and ultrafast routes of its phototransformations, as well as its photochemical reactions in phototherapy of neonatal hyperbilirubinemia and the ways to decrease the possible adverse effects of the phototherapy. The main analytical methods of bilirubin measurement in biological systems are also viewed.

Bilirubinemia and retinopathy of prematurity in infants ≤ 29 weeks' gestational age

BACKGROUND

Bilirubin is a known antioxidant. We hypothesized that the degree of bilirubinemia is inversely associated with oxidative stress-mediated retinopathy of prematurity (ROP).

METHODS

A prospective study was performed to determine if bilirubinemia is associated with ROP in infants ≤ 29 wks' gestational age and birth weights ≤ 1000 g. Total serum bilirubin (TSB) levels were measured at least twice daily during the first week and at least daily during the second week to determine peak and mean TSB levels. The outcomes were the incidence and severity of ROP.

RESULTS

Of 193 infants studied, 110 developed ROP: 53 had mild (stage 1 in zone 2 or 3); 31 had moderate (stage 2 in zone 2 or 3); and 26 had severe ROP ( ≥ stage 3 in any zone or any stage in zone 1). Mean TSB levels were associated with the severity (adjusted odds ratio [AOR] 0.68, 95% confidence interval [CI]:0.47-0.98, p = 0.04), but not with the incidence of ROP (AOR 0.81, 95% CI:0.52-1.27, p = 0.3). Peak TSB levels were also associated with the severity (AOR 0.71, 95% CI:0.52-0.96, p = 0.02), but not with the incidence of ROP (AOR 0.71, 95% CI:0.48-1.01, p = 0.07).

CONCLUSIONS

Bilirubinemia may be protective against severity of ROP.

IMPACT

Retinopathy of prematurity (ROP) is a disease mediated by oxidative stress. Increasing antioxidant status may decrease the incidence and severity of ROP. Bilirubin is a known antioxidant; however, findings from observational studies evaluating the role of bilirubinemia against the incidence and/or severity of ROP in premature infants are conflicting. Our findings from this prospective study suggests that bilirubinemia may be protective against the severity of ROP.

Aging and MPTP Sensitivity Depend on Molecular and Ultrastructural Signatures of Astroglia and Microglia in Mice Substantia Nigra

Both astroglia and microglia show region-specific distribution in CNS and often maladapt to age-associated alterations within their niche. Studies on autopsied substantia nigra (SN) of Parkinson's disease (PD) patients and experimental models propose gliosis as a trigger for neuronal loss. Epidemiological studies propose an ethnic bias in PD prevalence, since Caucasians are more susceptible than non-whites. Similarly, different mice strains are variably sensitive to MPTP. We had earlier likened divergent MPTP sensitivity of C57BL/6 J and CD-1 mice with differential susceptibility to PD, based on the numbers of SN neurons. We examined whether the variability was incumbent to inter-strain differences in glial features of male C57BL/6 J and CD-1 mice. Stereological counts showed relatively more microglia and fewer astrocytes in the SN of normal C57BL/6 J mice, suggesting persistence of an immune-vigilant state. MPTP-induced microgliosis and astrogliosis in both strains suggest their involvement in pathogenesis. ELISA of pro-inflammatory cytokines in the ventral-midbrain revealed augmentation of TNF-α and IL-6 at middle age in both strains that reduced at old age, suggesting middle age as a critical, inflamm-aging-associated time point. TNF-α levels were high in C57BL/6 J, through aging and post-MPTP, while IL-6 and IL-1β were upregulated at old age. CD-1 had higher levels of anti-inflammatory cytokine TGF-β. MPTP challenge caused upregulation of enzymes MAO-A, MAO-B, and iNOS in both strains. Post-MPTP enhancement in fractalkine and hemeoxygenase-1 may be neuron-associated compensatory signals. Ultrastructural observations of elongated astroglial/microglial mitochondria vis-à-vis the shrunken ones in neurons suggest a scale-up of their functions with neurotoxic consequences. Thus, astroglia and microglia may modulate aging and PD susceptibility.

Prognostic Value of Serum Bilirubin in Aneurysmal Subarachnoid Hemorrhage Patients

BACKGROUND

Bilirubin plays a crucial role in the pathophysiological processes of strokes. However, the relationship between serum bilirubin levels and the prognosis of aneurysmal subarachnoid hemorrhage (aSAH) remains unexplored. This study aims to investigate the association between serum bilirubin levels and the mortality rate of aSAH patients.

METHODS

695 aSAH patients were included to analyze the relationship between direct bilirubin (DBil), indirect bilirubin (IDBil), total bilirubin (TBil), and mortality. The univariate and multivariate logistic regression were conducted to discover risk factors for the mortality of aSAH. The restricted cubic spline (RCS) was used to show the correlation between DBil, IDBil, TBil, and mortality. A logistic regression predictive model was developed by incorporating significant factors in the multivariate logistic regression. The receiver operating characteristic (ROC) curve was plotted to evaluate the predictive value of serum bilirubin and the developed predictive model.

RESULTS

139 aSAH patients suffered death, with a mortality of 20.0%. Non-survivors had older age (p =0.007), lower GCS (p <0.001), higher Hunt Hess (p <0.001), and mFisher (p <0.001). Both DBil (p <0.001) and TBil (p =0.011) were significantly higher among non-survivors. While the IDBil did not show a difference between survivors and non-survivors. The multivariate analysis found age (p =0.111), Glasgow Coma Scale (p =0.005), white blood cell (p <0.001), glucose (p =0.004), DBil (p =0.001), delayed cerebral ischemia (p <0.001) were significantly related with the mortality of aSAH. A logistic regression predictive model for mortality was developed incorporating these five factors, which had an area under the ROC curve (AUC) of 0.876. The AUC of DBil, IDBil, and TBil for predicting mortality was 0.607, 0.570, and 0.529, respectively.

CONCLUSION

Serum DBil level is positively associated with the mortality risk of aSAH. The predictive model incorporating DBil is beneficial for clinicians to evaluate the mortality risk of aSAH and adopt personalized therapeutics.

Andrographolide: A promising therapeutic agent against organ fibrosis

Fibrosis is the terminal pathology of chronic illness in many organs, marked by excessive accumulation of extracellular matrix proteins. These changes influence organ function, ultimately resulting in organ failure. Although significant progress has been achieved in comprehending the molecular pathways responsible for fibrosis in the last decades, effective and approved clinical therapies for the condition are still lacking. Andrographolide is a diterpenoid isolated and purified mainly from the aboveground parts of the Andrographis paniculata plant, which possesses good effects of purging heat, detoxifying, antibacterial and anti-inflammatory. In-depth research has gradually confirmed the anticancer, antioxidant, antiviral and other effects of Andro so that it can play a preventive and therapeutic role in various diseases. Over the past few years, an increasing number of research findings have indicated that Andro exerts antifibrotic effects in various organs by acting on transforming growth factor-β/small mother against decapentaplegic protein, mitogen-activated protein kinases, nuclear factor-E2-related factor 2, nuclear factor kappa-B and other signalling molecules to inhibit inflammation, oxidative stress, epithelial-mesenchymal transition, fibroblast activation and collagen buildup. This review presents a compilation of findings regarding the antifibrotic impact of Andro in tissue and cell models in vitro and in vivo. Emphasis is placed on the potential therapeutic benefits of Andro in diseases related to organ fibrosis. Existing studies and cutting-edge technologies on Andro pharmacokinetics, toxicity and bioavailability are briefly discussed to provide evidence for accelerating its clinical conversion and adoption.

Association of total bilirubin and prognosis in disorders of consciousness

Accurate prediction of the recovery of Disorders of Consciousness (DoC) is of paramount significance for clinicians and families. Serum total bilirubin (TBIL) formed by activation of heme oxygenase 2, is associated with incidence and prognosis of cardiovascular and cerebrovascular diseases. However, studies that based TBIL and DoC are limited. The study attempted to examine the association between serum TBIL levels and prognosis in patients with DoC. One hundred and sixty-eight patients with DoC in the Second hospital of Shandong University from June 2021 to June 2023 were recruited. The clinical characteristics and venous blood samples were collected within 24 h after admission. The diagnosis of DoC was determined by two skilled investigators employing various behavioral evaluations along the coma recovery scale-revised (CRS-R) and the investigators conducted follow-up assessments of diagnosis at 1, 3, and 6 months after admission. For statistical analysis, we categorized patients with an improvement in clinical diagnosis from study entry as having a "good outcome". In total, 139 individuals enrolled in the study. The median TBIL level was 8.2 μmol/L. Good recovery of DoC at 1, 3, and 6 months occurred in 25 (18.0%), 41 (29.5%), and 56 (40.3%) patients, respectively. After full adjustment, a significant association was found between TBIL levels and the prognosis of DoC at 1, 3, and 6 months. When TBIL levels were analyzed as categorical variables, an increasing trend in the tertiles of TBIL levels demonstrated a significant positive association with the recovery of DoC at 1, 3, and 6 months. Stratified analysis revealed that the association between serum TBIL levels and the recovery of DoC remained consistent across different sub-populations. A high serum TBIL level is associated with an improved likelihood of recovery of DoC. Additional research is required to elucidate the underlying pathophysiological causal association between TBIL levels and DoC.

Hemin-Induced Transient Senescence Via DNA Damage Response: A Neuroprotective Mechanism Against Ferroptosis in Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) poses acute fatality and long-term neurological risks due to hemin and iron accumulation from hemoglobin breakdown. Our observation that hemin induces DNA double-strand breaks (DSBs), prompting a senescence-like phenotype in neurons, necessitating deeper exploration of cellular responses. Using experimental ICH models and human ICH patient tissue, we elucidate hemin-mediated DNA damage response (DDR) inducing transient senescence and delayed expression of heme oxygenase (HO-1). HO-1 co-localizes with senescence-associated β-Galactosidase (SA-β-Gal) in ICH patient tissues, emphasizing clinical relevance of inducible HO-1 expression in senescent cells. We reveal a reversible senescence state protective against acute cell death by hemin, while repeat exposure leads to long-lasting senescence. Inhibiting early senescence expression increases cell death, supporting the protective role of senescence against hemin toxicity. Hemin-induced senescence is attenuated by a pleiotropic carbon nanoparticle that is a catalytic mimic of superoxide dismutase, but this treatment increased lipid peroxidation, consistent with ferroptosis from hemin breakdown released iron. When coupled with iron chelator deferoxamine (DEF), the nanoparticle reduces hemin-induced senescence and upregulates factors protecting against ferroptosis. Our study suggests transient senescence induced by DDR as an early potential neuroprotective mechanism in ICH, but the risk or iron-related toxicity supports a multi-pronged therapeutic approach.

The associations of psychopathology and metabolic parameters with serum bilirubin levels in patients with acute-episode and drug-free schizophrenia: a 5-year retrospective study using an electronic medical record system

BACKGROUND

The oxidative system plays an important role in the pathogenesis of schizophrenia. Inconsistent associations were found between hyperbilirubinemia and psychopathology as well as glycolipid metabolism in patients with schizophrenia at different episodes. This current study aimed to examine these associations in patients with acute-episode and drug-free (AEDF) schizophrenia.

METHODS

This is a retrospective study using 5 years of data from May 2017 to May 2022 extracted from the electronic medical record system of Chaohu Hospital of Anhui Medical University. Healthy controls (HCs) from the local medical screening center during the same period were also included. Participants' data of the bilirubin levels [total bilirubin (TB), conjugated bilirubin (CB), unconjugated bilirubin (UCB)], glycolipid metabolic parameters and the score of the Brief Psychiatric Rating Scale (BPRS) were collected.

RESULTS

A total of 1468 case records were identified through the initial search. After screening, 89 AEDF patients and 100 HCs were included. Compared with HCs, patients had a higher CB level, and lower levels of glycolipid metabolic parameters excluding high density lipoprotein-cholesterol (HDL-C) (all P < 0.001). Binary logistic regression analyses revealed that high bilirubin levels in the patients were independently associated with higher total and resistance subscale scores of BPRS, a higher HDL-C level, and lower total cholesterol and triglyceride levels (all P < 0.05).

CONCLUSION

Bilirubin levels are elevated in patients with AEDF schizophrenia. Patients with high bilirubin levels have more severe psychopathology and relatively optimized glycolipid metabolism. In clinical practice, regular monitoring of bilirubin levels in this patient population should be carried out.

Activation of Nrf2/HO-1 signaling pathway exacerbates cholestatic liver injury

Nuclear factor erythroid 2-related factor-2 (Nrf2) antioxidant signaling is involved in liver protection, but this generalization overlooks conflicting studies indicating that Nrf2 effects are not necessarily hepatoprotective. The role of Nrf2/heme oxygenase-1 (HO-1) in cholestatic liver injury (CLI) remains poorly defined. Here, we report that Nrf2/HO-1 activation exacerbates liver injury rather than exerting a protective effect in CLI. Inhibiting HO-1 or ameliorating bilirubin transport alleviates liver injury in CLI models. Nrf2 knockout confers hepatoprotection in CLI mice, whereas in non-CLI mice, Nrf2 knockout aggravates liver damage. In the CLI setting, oxidative stress activates Nrf2/HO-1, leads to bilirubin accumulation, and impairs mitochondrial function. High levels of bilirubin reciprocally upregulate the activation of Nrf2 and HO-1, while antioxidant and mitochondrial-targeted SOD2 overexpression attenuate bilirubin toxicity. The expression of Nrf2 and HO-1 is elevated in serum of patients with CLI. These results reveal an unrecognized function of Nrf2 signaling in exacerbating liver injury in cholestatic disease.

Unraveling the Interplay of Dopamine, Carbon Monoxide, and Heme Oxygenase in Neuromodulation and Cognition

The dopaminergic system plays important roles in neuromodulation, including prominent roles in complex neurological functions such as cognition, reward, motivation, and memory. Understandably, the highly complex nature of such physiological functions means that their regulation is intertwined with other signaling pathways, as has been demonstrated by numerous studies. Contrary to its public perception of being poisonous at all concentrations, carbon monoxide (CO) is produced endogenously from heme degradation by heme oxygenase (HO) as part of the physiological process of red blood cell turnover. Physiological concentrations of CO can reach high micromolar ranges in the hemoglobin bound form. Low-dose CO has shown therapeutic effects in numerous animal models, including traumatic brain injury via engaging various hemoprotein targets. As such, the HO-CO axis has been shown to offer beneficial effects in organ protection, anti-inflammation, and neuroprotection, among many others. Further, a large number of publications have shown the interactions among CO, HO, and the dopaminergic system. In this review, we critically examine such experimental evidence in a holistic fashion and in the context of a possible dopamine-HO-CO signaling axis. We hope that this Perspective will stimulate additional investigations into the molecular connectivity related to this possible axis and open doors to the development of novel therapeutics that impact the dopaminergic system.

A glance through the effects of CD4+ T cells, CD8+ T cells, and cytokines on Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia. Unfortunately, despite numerous studies, an effective treatment for AD has not yet been established. There is remarkable evidence indicating that the innate immune mechanism and adaptive immune response play significant roles in the pathogenesis of AD. Several studies have reported changes in CD8+ and CD4+ T cells in AD patients. This mini-review article discusses the potential contribution of CD4+ and CD8+ T cells reactivity to amyloid β (Aβ) protein in individuals with AD. Moreover, this mini-review examines the potential associations between T cells, heme oxygenase (HO), and impaired mitochondria in the context of AD. While current mathematical models of AD have not extensively addressed the inclusion of CD4+ and CD8+ T cells, there exist models that can be extended to consider AD as an autoimmune disease involving these T cell types. Additionally, the mini-review covers recent research that has investigated the utilization of machine learning models, considering the impact of CD4+ and CD8+ T cells.

Loss of Biliverdin Reductase Increases Oxidative Stress in the Cyanobacterium Synechococcus sp. PCC 7002

Oxygenic photosynthesis requires metal-rich cofactors and electron-transfer components that can produce reactive oxygen species (ROS) that are highly toxic to cyanobacterial cells. Biliverdin reductase (BvdR) reduces biliverdin IXα to bilirubin, which is a potent scavenger of radicals and ROS. The enzyme is widespread in mammals but is also found in many cyanobacteria. We show that a previously described bvdR mutant of Synechocystis sp. PCC 6803 contained a secondary deletion mutation in the cpcB gene. The bvdR gene from Synechococcus sp. PCC 7002 was expressed in Escherichia coli, and recombinant BvdR was purified and shown to reduce biliverdin to bilirubin. The bvdR gene was successfully inactivated in Synechococcus sp. PCC 7002, a strain that is naturally much more tolerant of high light and ROS than Synechocystis sp. PCC 6803. The bvdR mutant strain, BR2, had lower total phycobiliprotein and chlorophyll levels than wild-type cells. As determined using whole-cell fluorescence at 77 K, the photosystem I levels were also lower than those in wild-type cells. The BR2 mutant had significantly higher ROS levels compared to wild-type cells after exposure to high light for 30 min. Together, these results suggest that bilirubin plays an important role as a scavenger for ROS in Synechococcus sp. PCC 7002. The oxidation of bilirubin by ROS could convert bilirubin to biliverdin IXα, and thus BvdR might be important for regenerating bilirubin. These results further suggest that BvdR is a key component of a scavenging cycle by which cyanobacteria protect themselves from the toxic ROS byproducts generated during oxygenic photosynthesis.

Free Bilirubin Induces Neuro-Inflammation in an Induced Pluripotent Stem Cell-Derived Cortical Organoid Model of Crigler-Najjar Syndrome

Bilirubin-induced neurological damage (BIND), which might progress to kernicterus, occurs as a consequence of defects in the bilirubin conjugation machinery, thus enabling albumin-unbound free bilirubin (BF) to cross the blood-brain barrier and accumulate within. A defect in the UGT1A1 enzyme-encoding gene, which is directly responsible for bilirubin conjugation, can cause Crigler-Najjar syndrome (CNS) and Gilbert's syndrome. We used human-induced pluripotent stem cell (hiPSC)-derived 3D brain organoids to model BIND in vitro and unveil the molecular basis of the detrimental effects of BF in the developing human brain. Healthy and patient-derived iPSCs were differentiated into day-20 brain organoids, and then stimulated with 200 nM BF. Analyses at 24 and 72 h post-treatment point to BF-induced neuro-inflammation in both cell lines. Transcriptome, associated KEGG, and Gene Ontology analyses unveiled the activation of distinct inflammatory pathways, such as cytokine-cytokine receptor interaction, MAPK signaling, and NFκB activation. Furthermore, the mRNA expression and secretome analysis confirmed an upregulation of pro-inflammatory cytokines such as IL-6 and IL-8 upon BF stimulation. This novel study has provided insights into how a human iPSC-derived 3D brain organoid model can serve as a prospective platform for studying the etiology of BIND kernicterus.

The effects of Korean Red Ginseng on heme oxygenase-1 with a focus on mitochondrial function in pathophysiologic conditions

Korean Red Ginseng (KRG) plays a key role in heme oxygenase (HO)-1 induction under physical and moderate oxidative stress conditions. The transient and mild induction of HO-1 is beneficial for cell protection, mitochondrial function, regeneration, and intercellular communication. However, chronic HO-1 overexpression is detrimental in severely injured regions. Thus, in a chronic pathological state, diminishing HO-1-mediated ferroptosis is beneficial for a therapeutic approach. The molecular mechanisms by which KRG protects various cell types in the central nervous system have not yet been established, especially in terms of HO-1-mediated mitochondrial functions. Therefore, in this review, we discuss the multiple roles of KRG in the regulation of astrocytic HO-1 under pathophysiological conditions. More specifically, we discuss the role of the KRG-mediated astrocytic HO-1 pathway in regulating mitochondrial functions in acute and chronic neurodegenerative diseases as well as physiological conditions.

Endogenous and Exogenous Antioxidants as Agents Preventing the Negative Effects of Contrast Media (Contrast-Induced Nephropathy)

The use of conventional contrast media for diagnostic purposes (in particular, Gd-containing and iodinated agents) causes a large number of complications, the most common of which is contrast-induced nephropathy. It has been shown that after exposure to contrast agents, oxidative stress often occurs in patients, especially in people suffering from various diseases. Antioxidants in the human body can diminish the pathological consequences of the use of contrast media by suppressing oxidative stress. This review considers the research studies on the role of antioxidants in preventing the negative consequences of the use of contrast agents in diagnostics (mainly contrast-induced nephropathy) and the clinical trials of different antioxidant drugs against contrast-induced nephropathy. Composite antioxidant/contrast systems as theranostic agents are also considered.

Heme Interactions as Regulators of the Alternative Pathway Complement Responses and Implications for Heme-Associated Pathologies

Heme (Fe²⁺-protoporphyrin IX) is a pigment of life, and as a prosthetic group in several hemoproteins, it contributes to diverse critical cellular processes. While its intracellular levels are tightly regulated by networks of heme-binding proteins (HeBPs), labile heme can be hazardous through oxidative processes. In blood plasma, heme is scavenged by hemopexin (HPX), albumin and several other proteins, while it also interacts directly with complement components C1q, C3 and factor I. These direct interactions block the classical pathway (CP) and distort the alternative pathway (AP). Errors or flaws in heme metabolism, causing uncontrolled intracellular oxidative stress, can lead to several severe hematological disorders. Direct interactions of extracellular heme with alternative pathway complement components (APCCs) may be implicated molecularly in diverse conditions at sites of abnormal cell damage and vascular injury. In such disorders, a deregulated AP could be associated with the heme-mediated disruption of the physiological heparan sulphate-CFH coat of stressed cells and the induction of local hemostatic responses. Within this conceptual frame, a computational evaluation of HBMs (heme-binding motifs) aimed to determine how heme interacts with APCCs and whether these interactions are affected by genetic variation within putative HBMs. Combined computational analysis and database mining identified putative HBMs in all of the 16 APCCs examined, with 10 exhibiting disease-associated genetic (SNPs) and/or epigenetic variation (PTMs). Overall, this article indicates that among the pleiotropic roles of heme reviewed, the interactions of heme with APCCs could induce differential AP-mediated hemostasis-driven pathologies in certain individuals.

Potential ecotoxicity of substrate-enriched zinc oxide nanoparticles to Physalaemus cuvieri tadpoles

Although the ecotoxicological effects of ZnO nanoparticles (ZnO NPs) have already been reported in different taxa, little is known about their impacts on amphibians. Thus, we aimed to evaluate the potential effects of exposure of Physalaemus cuvieri tadpoles to substrates enriched with ZnO NPs (and with its ionic counterpart, Zn+2, ZnCl2 - both at 100 mg/kg) previously used in the cultivation of Panicum maximum (Guinea grass). We showed that although exposure for 21 days did not impact the survival, growth, and development of tadpoles, we noted an increase in the frequency of erythrocyte nuclear abnormalities in the "ZnCl2" and "ZnONP" groups, which was associated with suppression of antioxidant activity in the animals (inferred by SOD and CAT activity and DPPH free radical scavenging capacity). In the tadpoles of the "ZnONP" group, we also noticed a reduction in creatinine and bilirubin levels, alpha-amylase activity, and an increase in alkaline phosphatase activity. But the treatments did not alter the activity of the enzymes lactate dehydrogenase and gamma-glutamyl-transferase and total protein and carbohydrate levels. On the other hand, we report a cholinesterase and hypotriglyceridemic effect in the "ZnCl2" and "ZnONP" groups. Zn bioaccumulation in animals, from ZnO NPs, from Zn+2 released from them, or both, has been associated with causing these changes. Finally, principal component analysis (PCA) and the values of the "Integrated Biomarker Response" index revealed that the exposure of animals to substrates enriched with ZnO NPs caused more pronounced effects than those attributed to its ionic counterpart. Therefore, our study reinforces the need to consider the environmental risks of using these nanomaterials for agricultural purposes for amphibians.

Interstitial Cells of Cajal and Enteric Nervous System in Gastrointestinal and Neurological Pathology, Relation to Oxidative Stress

The enteric nervous system (ENS) is organized into two plexuses-submucosal and myenteric-which regulate smooth muscle contraction, secretion, and blood flow along the gastrointestinal tract under the influence of the rest of the autonomic nervous system (ANS). Interstitial cells of Cajal (ICCs) are mainly located in the submucosa between the two muscle layers and at the intramuscular level. They communicate with neurons of the enteric nerve plexuses and smooth muscle fibers and generate slow waves that contribute to the control of gastrointestinal motility. They are also involved in enteric neurotransmission and exhibit mechanoreceptor activity. A close relationship appears to exist between oxidative stress and gastrointestinal diseases, in which ICCs can play a prominent role. Thus, gastrointestinal motility disorders in patients with neurological diseases may have a common ENS and central nervous system (CNS) nexus. In fact, the deleterious effects of free radicals could affect the fine interactions between ICCs and the ENS, as well as between the ENS and the CNS. In this review, we discuss possible disturbances in enteric neurotransmission and ICC function that may cause anomalous motility in the gut.

Establishment of an assistive diagnostic model for schizophrenia with oxidative stress biomarkers

Objective: In this study, alterations in oxidative stress-related indicators were evaluated in drug-naïve, first-episode schizophrenia (SCZ) patients, and the effectiveness of blood serum glucose, superoxide dismutase (SOD), bilirubin in the objective assistive diagnosis of schizophrenia was explored. Materials and methods: We recruited 148 drug-naïve, first-episode SCZ patients and 97 healthy controls (HCs). Blood biochemical indexes including blood glucose, SOD, bilirubin and homocysteine (HCY) in participants were measured, the indexes were compared between patients with SCZ and HCs. The assistive diagnostic model for SCZ was established on the basis of the differential indexes. Results: In SCZ patients, the blood serum levels of glucose, total (TBIL), indirect bilirubin (IBIL) and homocysteine (HCY) were significantly higher than those in HCs (p < 0.05), and the serum levels of SOD were significantly lower than those in HCs (p < 0.05). There was a negative correlation between SOD with the general symptom scores and total scores of PANSS. After risperidone treatment, the levels of uric acid (UA) and SOD tended to increase in patients with SCZ (p = 0.02, 0.19), and the serum levels of TBIL and HCY tended to decrease in patients with SCZ (p = 0.78, 0.16). The diagnostic model based on blood glucose, IBIL and SOD was internally cross-validated, and the accuracy was 77%, with an area under the curve (AUC) of 0.83. Conclusion: Our study demonstrated an oxidative state imbalance in drug-naïve, first-episode SCZ patients, which might be associated with the pathogenesis of the disease. Our study proved that glucose, IBIL and SOD may be potential biological markers of schizophrenia, and the model based on these markers can assist the early objective and accurate diagnosis of schizophrenia.

Roles of Bilirubin in Hemorrhagic Transformation of Different Types and Severity

BACKGROUND

Hemorrhagic transformation (HT) is a severe complication in patients with acute ischemic stroke (AIS). This study was performed to explore and validate the relation between bilirubin levels and spontaneous HT (sHT) and HT after mechanical thrombectomy (tHT).

METHODS

The study population consisted of 408 consecutive AIS patients with HT and age- and sex-matched patients without HT. All patients were divided into quartiles according to total bilirubin (TBIL) level. HT was classified as hemorrhagic infarction (HI) and parenchymal hematoma (PH) based on radiographic data.

RESULTS

In this study, the baseline TBIL levels were significantly higher in the HT than non-HT patients in both cohorts (p < 0.001). Furthermore, the severity of HT increased with increasing TBIL levels (p < 0.001) in sHT and tHT cohorts. The highest quartile of TBIL was associated with HT in sHT and tHT cohorts (sHT cohort: OR = 3.924 (2.051-7.505), p < 0.001; tHT cohort: OR = 3.557 (1.662-7.611), p = 0.006).

CONCLUSIONS

Our results suggest that an increased TBIL is associated with a high risk of patients with sHT and tHT, and that TBIL is more suitable as a predictor for sHT than tHT. These findings may help to identify patients susceptible to different types and severity of HT.

Gasotransmitter modulation of hypoglossal motoneuron activity

Obstructive sleep apnea (OSA) is characterized by sporadic collapse of the upper airway leading to periodic disruptions in breathing. Upper airway patency is governed by genioglossal nerve activity that originates from the hypoglossal motor nucleus. Mice with targeted deletion of the gene Hmox2, encoding the carbon monoxide (CO) producing enzyme, heme oxygenase-2 (HO-2), exhibit OSA, yet the contribution of central HO-2 dysregulation to the phenomenon is unknown. Using the rhythmic brainstem slice preparation that contains the preBötzinger complex (preBötC) and the hypoglossal nucleus, we tested the hypothesis that central HO-2 dysregulation weakens hypoglossal motoneuron output. Disrupting HO-2 activity increased the occurrence of subnetwork activity from the preBötC, which was associated with an increased irregularity of rhythmogenesis. These phenomena were also associated with the intermittent inability of the preBötC rhythm to drive output from the hypoglossal nucleus (i.e. transmission failures), and a reduction in the input-output relationship between the preBötC and the motor nucleus. HO-2 dysregulation reduced excitatory synaptic currents and intrinsic excitability in inspiratory hypoglossal neurons. Inhibiting activity of the CO-regulated H2S producing enzyme, cystathionine-γ-lyase (CSE), reduced transmission failures in HO-2 null brainstem slices, which also normalized excitatory synaptic currents and intrinsic excitability of hypoglossal motoneurons. These findings demonstrate a hitherto uncharacterized modulation of hypoglossal activity through mutual interaction of HO-2/CO and CSE/H2S, and support the potential importance of centrally derived gasotransmitter activity in regulating upper airway control.

Mentha rotundifolia (L.) Huds. aqueous extract attenuates H2O2 induced oxidative stress and neurotoxicity

Introduction

Oxidative stress plays a causal role in neurodegenerative diseases. The aim of this study is to evaluate the antioxidant and neuroprotective effects of Mentha rotundifolia (L.) Huds (M. rotundifolia), a widely used Moroccan plant in traditional medicine.

Methods

The chemical composition of M. rotundifolia aqueous extract was analyzed by liquid chromatography coupled to mass spectrometry (LC-MS). 2,2-diphenyl 1-picrylhydrazyl (DPPH) and 2,2'-azino-bis 3-ethylbenzothiazoline-6-sulfonic acid (ABTS⁺) assays were used to assess its in vitro antioxidant activity. H₂O₂ was utilized to induce oxidative stress and neurotoxicity in vivo. Behavioral changes were evaluated using Open Field, Y-maze and Rotarod tests. Hyperalgesia was assessed using the tail immersion test.

Results and discussion

The LC-MS/MS analysis revealed high content of kaempferol glucuronide (85%) at the extract. IC₅₀ values of the DPPH and ABTS were 26.47 and 41.21 μg/mL, respectively. Pre-treatments with M. rotundifolia extract attenuated the behavioral changes induced by H₂O₂. In addition, the latency of tail withdrawal increased significantly in the treated groups suggesting central analgesic effect of M. rotundifolia extract. Moreover, the extract attenuated the deleterious effects of H₂O₂ and improved all liver biomarkers. The obtained results suggested that M. rotundifolia had remarkable antioxidant and neuroprotective effects and may prevent oxidative stress related disorders.

The dual role and mutual dependence of heme/HO-1/Bach1 axis in the carcinogenic and anti-carcinogenic intersection

INTRODUCTION

In physiological concentrations, heme is nontoxic to the cell and is essential for cell survival and proliferation. Increasing intracellular heme concentrations beyond normal levels, however, will lead to carcinogenesis and facilitate the survival of tumor cells. Simultaneously, heme in an abnormally high quantity is also a potent inducer of tumor cell death, contributing to its ability to generate oxidative stress on the cells by boosting oxidative phosphorylation and suppressing tumors through ferroptosis. During tumorigenesis and progression, therefore, heme works as a double-edged sword. Heme oxygenase 1 (HO-1) is the rate-limiting enzyme in heme catabolism, which converts heme into physiologically active catabolites of carbon monoxide (CO), biliverdin, and ferrous iron (Fe²⁺). HO-1 maintains redox equilibrium in healthy cells and functions as a carcinogenesis inhibitor. It is widely recognized that HO-1 is involved in the adaptive response to cellular stress and the anti-inflammation effect. Notably, its expression level in cancer cells corresponds with tumor growth, aggressiveness, metastasis, and angiogenesis. Besides, heme-binding transcription factor BTB and CNC homology 1 (Bach1) play a critical regulatory role in heme homeostasis, oxidative stress and senescence, cell cycle, angiogenesis, immune cell differentiation, and autoimmune disorders. Moreover, it was found that Bach1 influences cancer cells' metabolism and metastatic capacity. Bach1 controls heme level by adjusting HO-1 expression, establishing a negative feedback loop.

MATERIALS AND METHODS

Herein, the authors review recent studies on heme, HO-1, and Bach1 in cancer. Specifically, they cover the following areas: (1) the carcinogenic and anticarcinogenic aspects of heme; (2) the carcinogenic and anticarcinogenic aspects of HO-1; (3) the carcinogenic and anticarcinogenic aspects of Bach1; (4) the interactions of the heme/HO-1/Bach1 axis involved in tumor progression.

CONCLUSION

This review summarized the literature about the dual role of the heme/HO-1/Bach1 axis and their mutual dependence in the carcinogenesis and anti-carcinogenesis intersection.

The impact of heme oxygenase-2 on pharmacological research: A bibliometric analysis and beyond

Heme oxygenase (HO-2) is an enzyme mainly involved in the physiologic turnover of heme and intracellular gas sensing, and it is very abundant in the brain, testes, kidneys and vessels. Since 1990, when HO-2 was discovered, the scientific community has underestimated the role of this protein in health and disease, as attested by the small amount of articles published and citations received. One of the reason that have contributed to the lack of interest in HO-2 was the difficulty in upregulating or inhibiting this enzyme. However, over the last 10 years, novel HO-2 agonists and antagonists have been synthesized, and the availability of these pharmacological tools should increase the appeal of HO-2 as drug target. In particular, these agonists and antagonists could help explain some controversial aspects, such as the neuroprotective versus neurotoxic roles of HO-2 in cerebrovascular diseases. Furthermore, the discovery of HO-2 genetic variants and their involvement in Parkinson's disease, in particular in males, opens new avenues for pharmacogenetic studies in gender medicine.

Association between serum total bilirubin and Alzheimer's disease: A bidirectional Mendelian randomization study

Oxidative stress plays an important role in the pathogenesis of Alzheimer's disease (AD). As a potent antioxidant, serum bilirubin is decreased in AD and may be related to its pathogenesis, but the causal association between serum bilirubin and AD has not been reported. This was investigated in the present study by bidirectional two-sample Mendelian randomization (MR) analysis. Genetic instruments at the genome-wide significance level (P < 5 × 10-8) were selected from the United Kingdom Biobank (n = 342,829). Summary-level AD data were obtained from a large-scale genome-wide association study (n = 63,926). Causal estimates were evaluated using the inverse variance weighted (IVW) approach and other five complementary methods. MR-Egger, IVW and MR pleiotropy residual sum and outlier (MR-PRESSO) methods were used for sensitivity analyses. The results showed that there was no significant association between serum total bilirubin and AD (odds ratio=1.003, 95% confidence interval: 0.967-1.041, P = 0.865). Inverse MR revealed that serum total bilirubin was increased in AD (beta = 0.009, SE = 0.003, P = 0.010). These results indicate that serum total bilirubin is not causally associated with AD and cannot be used for screening or diagnosis, but can potentially serve as a biomarker of disease severity, and it needs further clinical studies.

Association of Total Bilirubin with Motor Signs in Early Parkinson's Disease in LRRK2 Variant Carriers

Oxidative stress is considered a possible mechanism in Parkinson's disease (PD) progression. Bilirubin has been recognized as a powerful antioxidant that increases due to heme-oxygenase activity. We aimed to investigate the association of total bilirubin (TB) with motor signs and asymmetry in different stages of early PD. A case-control study was performed to investigate the differences in TB levels in PD patients and healthy controls (HC) both carrying LRRK2 variants. We compared TB levels in HC and Hoehn and Yahr (HY) I and II cohorts separately, followed by multiple linear regression analysis to evaluate the association between TB and motor dysfunction in each stage. We used Movement Disorder Society-Sponsored Revision of the Unified Parkinson's Disease Rating Scale (UPDRS) part III scores and asymmetry scores to address motor disability. Asymmetry scores were calculated from the corresponding UPDRS III tasks. TB was significantly increased in HY II compared to HC (P < 0.001). Positive correlations with TB were found for UPDRS III total score (ρ = 0.303, P = 0.034) and asymmetry score (ρ = 0.418, P = 0.003) in HY I. Multiple linear regression found a significant relationship between TB and asymmetry scores in HY I (R² = 0.261, P = 0.037), but no relationship was achieved with UPDRS III total scores. Increased TB serves as an important diagnostic marker in earlier stages of PD. A significant relationship was found between TB and motor asymmetry in HY I patients. According to our findings, bilirubin mainly exhibits its protective effects in HY I population.

Preconditioning by voluntary wheel running attenuates later neuropathic pain via nuclear factor E2-related factor 2 antioxidant signaling in rats

ABSTRACT

Animal and human studies have shown that exercise prior to nerve injury prevents later chronic pain, but the mechanisms of such preconditioning remain elusive. Given that exercise acutely increases the formation of free radicals, triggering antioxidant compensation, we hypothesized that voluntary running preconditioning would attenuate neuropathic pain by supporting redox homeostasis after sciatic nerve injury in male and female rats. We show that 6 weeks of voluntary wheel running suppresses neuropathic pain development induced by chronic constriction injury across both sexes. This attenuation was associated with reduced nitrotyrosine immunoreactivity-a marker for peroxynitrite-at the sciatic nerve injury site. Our data suggest that prior voluntary wheel running does not reduce the production of peroxynitrite precursors, as expression levels of inducible nitric oxide synthase and NADPH oxidase 2 were unchanged. Instead, voluntary wheel running increased superoxide scavenging by elevating expression of superoxide dismutases 1 and 2. Prevention of neuropathic pain was further associated with the activation of the master transcriptional regulator of the antioxidant response, nuclear factor E2-related factor 2 (Nrf2). Six weeks of prior voluntary wheel running increased Nrf2 nuclear translocation at the sciatic nerve injury site; in contrast, 3 weeks of prior wheel running, which failed to prevent neuropathic pain, had no effect on Nrf2 nuclear translocation. The protective effects of prior voluntary wheel running were mediated by Nrf2, as suppression was abolished across both sexes when Nrf2 activation was blocked during the 6-week running phase. This study provides insight into the mechanisms by which physical activity may prevent neuropathic pain. Preconditioning by voluntary wheel running, terminated prior to nerve injury, suppresses later neuropathic pain in both sexes, and it is modulated through the activation of Nrf2-antioxidant signaling.

Bilirubin-Induced Neurological Damage: Current and Emerging iPSC-Derived Brain Organoid Models

Bilirubin-induced neurological damage (BIND) has been a subject of studies for decades, yet the molecular mechanisms at the core of this damage remain largely unknown. Throughout the years, many in vivo chronic bilirubin encephalopathy models, such as the Gunn rat and transgenic mice, have further elucidated the molecular basis of bilirubin neurotoxicity as well as the correlations between high levels of unconjugated bilirubin (UCB) and brain damage. Regardless of being invaluable, these models cannot accurately recapitulate the human brain and liver system; therefore, establishing a physiologically recapitulating in vitro model has become a prerequisite to unveil the breadth of complexities that accompany the detrimental effects of UCB on the liver and developing human brain. Stem-cell-derived 3D brain organoid models offer a promising platform as they bear more resemblance to the human brain system compared to existing models. This review provides an explicit picture of the current state of the art, advancements, and challenges faced by the various models as well as the possibilities of using stem-cell-derived 3D organoids as an efficient tool to be included in research, drug screening, and therapeutic strategies for future clinical applications.

Recent Advances in Reactive Oxygen Species (ROS)-Responsive Polyfunctional Nanosystems 3.0 for the Treatment of Osteoarthritis

Osteoarthritis (OA) is an inflammatory and degenerative joint disease with severe effects on individuals, society, and the economy that affects millions of elderly people around the world. To date, there are no effective treatments for OA; however, there are some treatments that slow or prevent its progression. Polyfunctional nanosystems have many advantages, such as controlled release, targeted therapy and high loading rate, and have been widely used in OA treatment. Previous mechanistic studies have revealed that inflammation and ROS are interrelated, and a large number of studies have demonstrated that ROS play an important role in different types of OA development. In this review article, we summarize third-generation ROS-sensitive nanomaterials that scavenge excessive ROS from chondrocytes and osteoclasts in vivo. We only focus on polymer-based nanoparticles (NPs) and do not review the effects of drug-loaded or heavy metal NPs. Mounting evidence suggests that polyfunctional nanosystems will be a promising therapeutic strategy in OA therapy due to their unique characteristics of being sensitive to changes in the internal environment.

Beneficial and Detrimental Roles of Heme Oxygenase-1 in the Neurovascular System

Heme oxygenase (HO) has both beneficial and detrimental effects via its metabolites, including carbon monoxide (CO), biliverdin or bilirubin, and ferrous iron. HO-1 is an inducible form of HO that is upregulated by oxidative stress, nitric oxide, CO, and hypoxia, whereas HO-2 is a constitutive form that regulates vascular tone and homeostasis. In brains injured by trauma, ischemia-reperfusion, or Alzheimer’s disease (AD), the long-term expression of HO-1 can be detected, which can lead to cytotoxic ferroptosis via iron accumulation. In contrast, the transient induction of HO-1 in the peri-injured region may have regenerative potential (e.g., angiogenesis, neurogenesis, and mitochondrial biogenesis) and neurovascular protective effects through the CO-mediated signaling pathway, the antioxidant properties of bilirubin, and the iron-mediated ferritin synthesis. In this review, we discuss the dual roles of HO-1 and its metabolites in various neurovascular diseases, including age-related macular degeneration, ischemia-reperfusion injury, traumatic brain injury, Gilbert’s syndrome, and AD.

Dysregulation of a Heme Oxygenase-Synuclein Axis in Parkinson Disease

α-Synuclein is a key driver of the pathogenesis of Parkinson disease (PD). Heme oxygenase-1 (HO-1), a stress protein that catalyzes the conversion of heme to biliverdin, carbon monoxide and free ferrous iron, is elevated in PD-affected neural tissues and promotes iron deposition and mitochondrial dysfunction in models of the disease, pathways also impacted by α-synuclein. Elevated expression of human HO-1 in astrocytes of GFAP.HMOX1 transgenic mice between 8.5 and 19 months of age elicits a parkinsonian phenotype characterized by nigrostriatal hypodopaminergia, locomotor incoordination and overproduction of neurotoxic native S129-phospho-α-synuclein. Two microRNAs (miRNA) known to regulate α-synuclein, miR-153 and miR-223, are significantly decreased in the basal ganglia of GFAP.HMOX1 mice. Serum concentrations of both miRNAs progressively decline in wild-type (WT) and GFAP.HMOX1 mice between 11 and 18 months of age. Moreover, circulating levels of miR-153 and miR-223 are significantly lower, and erythrocyte α-synuclein concentrations are increased, in GFAP.HMOX1 mice relative to WT values. MiR-153 and miR-223 are similarly decreased in the saliva of PD patients compared to healthy controls. Upregulation of glial HO-1 may promote parkinsonism by suppressing miR-153 and miR-223, which, in turn, enhance production of neurotoxic α-synuclein. The aim of the current review is to explore the link between HO-1, α-synuclein and PD, evaluating evidence derived from our laboratory and others. HO-1, miR-153 and miR-223 and α-synuclein may serve as potential biomarkers and targets for disease-modifying therapy in idiopathic PD.

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.

Heme oxygenase-2 (HO-2) binds and buffers labile ferric heme in human embryonic kidney cells

Heme oxygenases (HOs) detoxify heme by oxidatively degrading it into carbon monoxide, iron, and biliverdin, which is reduced to bilirubin and excreted. Humans express two isoforms of HO: the inducible HO-1, which is upregulated in response to excess heme and other stressors, and the constitutive HO-2. Much is known about the regulation and physiological function of HO-1, whereas comparatively little is known about the role of HO-2 in regulating heme homeostasis. The biochemical necessity for expressing constitutive HO-2 is dependent on whether heme is sufficiently abundant and accessible as a substrate under conditions in which HO-1 is not induced. By measuring labile heme, total heme, and bilirubin in human embryonic kidney HEK293 cells with silenced or overexpressed HO-2, as well as various HO-2 mutant alleles, we found that endogenous heme is too limiting a substrate to observe HO-2-dependent heme degradation. Rather, we discovered a novel role for HO-2 in the binding and buffering of heme. Taken together, in the absence of excess heme, we propose that HO-2 regulates heme homeostasis by acting as a heme buffering factor that controls heme bioavailability. When heme is in excess, HO-1 is induced, and both HO-2 and HO-1 can provide protection from heme toxicity via enzymatic degradation. Our results explain why catalytically inactive mutants of HO-2 are cytoprotective against oxidative stress. Moreover, the change in bioavailable heme due to HO-2 overexpression, which selectively binds ferric over ferrous heme, is consistent with labile heme being oxidized, thereby providing new insights into heme trafficking and signaling.

Neonatal hyperbilirubinemia and the role of unbound bilirubin

BACKGROUND

Neonatal jaundice occurs in more than 80% of newborn infants. Although mild jaundice is physiologic and possibly neuroprotective, severe hyperbilirubinemia can lead to neurologic dysfunction and death. Hyperbilirubinemia is due to an imbalance between bilirubin production and the developing excretory capacity in the first days of life. Management utilizes total serum bilirubin (TSB) levels, although recent advances suggest a role for unbound bilirubin.

GOALS

The goal of this review is to examine bilirubin biology, toxicology, and clinical effects, discuss preventive and therapeutic measures, describe neurodevelopmental consequences, and propose that, with the advent of new technology, unbound bilirubin is the optimal measurement for the management.

METHODS

Comprehensive review on neonatal hyperbilirubinemia.

RESULTS

Neonatal hyperbilirubinemia can be prevented by tin mesoporphyrin to limit heme oxygenase activity, a key enzyme in bilirubin production, or restricting bilirubin's absorption from the gastrointestinal tract. Treatment modalities include removing bilirubin from the body by exchange transfusion, binding to immunoglobulin, or converting it to a water-soluble isomer with phototherapy. While these approaches have evolved during the past decades, the diagnosis, intervention indications, and prognosis have consistently relied on TSB concentration despite its poor ability to predict an outcome.

CONCLUSIONS

Total serum bilirubin is inadequate to optimize care of the term and preterm infant with hyperbilirubinemia. A rapid, accurate, and more effective indicator of bilirubin neurotoxicity is needed to manage jaundiced infants and for the universal screening of newborn infants. Future measurements of free bilirubin unattached to albumin will improve the management of neonatal hyperbilirubinemia.

Endogenous zinc protoporphyrin formation critically contributes to hemorrhagic stroke-induced brain damage

Hemorrhagic stroke is a leading cause of death. The causes of intracerebral hemorrhage (ICH)-induced brain damage are thought to include lysis of red blood cells, hemin release and iron overload. These mechanisms, however, have not proven very amenable to therapeutic intervention, and so other mechanistic targets are being sought. Here we report that accumulation of endogenously formed zinc protoporphyrin (ZnPP) also critically contributes to ICH-induced brain damage. ICH caused a significant accumulation of ZnPP in brain tissue surrounding hematoma, as evidenced by fluorescence microscopy of ZnPP, and further confirmed by fluorescence spectroscopy and supercritical fluid chromatography-mass spectrometry. ZnPP formation was dependent upon both ICH-induced hypoxia and an increase in free zinc accumulation. Notably, inhibiting ferrochelatase, which catalyzes insertion of zinc into protoporphyrin, greatly decreased ICH-induced endogenous ZnPP generation. Moreover, a significant decrease in brain damage was observed upon ferrochelatase inhibition, suggesting that endogenous ZnPP contributes to the damage in ICH. Our findings reveal a novel mechanism of ICH-induced brain damage through ferrochelatase-mediated formation of ZnPP in ICH tissue. Since ferrochelatase can be readily inhibited by small molecules, such as protein kinase inhibitors, this may provide a promising new and druggable target for ICH therapy.

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.

Repair Mechanisms of the Neurovascular Unit after Ischemic Stroke with a Focus on VEGF

The functional neural circuits are partially repaired after an ischemic stroke in the central nervous system (CNS). In the CNS, neurovascular units, including neurons, endothelial cells, astrocytes, pericytes, microglia, and oligodendrocytes maintain homeostasis; however, these cellular networks are damaged after an ischemic stroke. The present review discusses the repair potential of stem cells (i.e., mesenchymal stem cells, endothelial precursor cells, and neural stem cells) and gaseous molecules (i.e., nitric oxide and carbon monoxide) with respect to neuroprotection in the acute phase and regeneration in the late phase after an ischemic stroke. Commonly shared molecular mechanisms in the neurovascular unit are associated with the vascular endothelial growth factor (VEGF) and its related factors. Stem cells and gaseous molecules may exert therapeutic effects by diminishing VEGF-mediated vascular leakage and facilitating VEGF-mediated regenerative capacity. This review presents an in-depth discussion of the regeneration ability by which endogenous neural stem cells and endothelial cells produce neurons and vessels capable of replacing injured neurons and vessels in the CNS.

Potential neuroprotective of trans-resveratrol a promising agent tempeh and soybean seed coats-derived against beta-amyloid neurotoxicity on primary culture of nerve cells induced by 2-methoxyethanol

Resveratrol, a natural polyphenol found in tempeh, has not been investigated especially in vitro as a neuroprotective agent against 2-methoxyethanol (2-ME)-induced beta-amyloid cytotoxicity. Beta amyloid peptides (Aβ) could initiate neurotoxic events and neuron-inflammatory response via microglial activation. However, it remains unknown whether the neurotoxic effect of beta-amyloid and/or associated with the potential of 2-ME to induce neurotoxic effects on primary culture of nerve cells induced by 2-ME. This study investigated potential neuroprotective of trans-resveratrol a promising agent tempeh and soybean seed coats-derived against beta-amyloid cytotoxicity on primary culture of nerve cells induced by 2-methoxyethanol. Biotium and MTT assays were used to analyze neurons, which were isolated from the cerebral cortex of fetal mice at gestation day 19 (GD-19). A standard solution of 2-methoxyethanol was dosed at 10 μL. The cultured cells were randomly divided into the following groups: (1) 2-ME group + resveratrol standard, (2) 2-ME group + resveratrol isolated from tempeh, (3) 2-ME group + resveratrol isolated from soybean seed coats, and (4) the control group, without the addition of either 2-ME or resveratrol. Exposure of the primary cortical neuron cells to beta-amyloid monoclonal antibody pre-incubated for 24 h with 10 µL of 4.2 µg/mL resveratrol and 7.5 mmol/l 2-methoxy-ethanol additions. Here, we report that the addition of 2-ME and resveratrol (standard and isolated from tempeh) of cell culture at concentrations of 1.4, 2.8 and 4.2 µg/mL showed that the majority of neurons grew well. In contrast, after exposure to 2-ME and Beta-amyloid, showed that glial activated. These findings demonstrate a role for resveratrol in neuroprotective-neurorescuing action.

Bach1 plays an important role in angiogenesis through regulation of oxidative stress

Bach1 is a known transcriptional repressor of the heme oxygenase-1 (HO-1) gene. The purpose of this study was to determine whether angiogenesis is accelerated by genetic ablation of Bach1 in a mouse ischemic hindlimb model. Hindlimb ischemia was surgically induced in wild-type (WT) mice, Bach1-deficient (Bach1-/-) mice, apolipoprotein E-deficient (ApoE-/-) mice, and Bach1/ApoE double-knockout (Bach1-/-/ApoE-/-) mice. Blood flow recovery after hindlimb ischemia showed significant improvement in Bach1-/- mice compared with that in WT mice. Bach1-/-/ApoE-/- mice showed significantly improved blood flow recovery compared with that in ApoE-/- mice to the level of that in WT mice. Migration of endothelial cells in ApoE-/- mice was significantly decreased compared with that in WT mice. Migration of endothelial cells significantly increased in Bach1-/-/ApoE-/- mice compared with that in ApoE-/- mice to the level of that in WT mice. The expression levels of HO-1, peroxisome proliferator-activated receptor γ co-activator-1α, angiopoietin 1, and fibroblast growth factor 2 in endothelial cells isolated from Bach1-/-/ApoE-/- mice were significantly higher than those in ApoE-/- mice. Oxidative stress assessed by anti-acrolein antibody staining in ischemic tissues and urinary 8-isoPGF2α excretion were significantly increased in ApoE-/- mice compared with those in WT and Bach1-/- mice. Oxidative stress was reduced in Bach1-/-/ApoE-/- mice compared with that in ApoE-/- mice. These findings suggest that genetic ablation of Bach1 plays an important role in ischemia-induced angiogenesis under the condition of increased oxidative stress. Bach1 could be a potential therapeutic target to reduce oxidative stress and potentially improve angiogenesis for patients with peripheral arterial disease.

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.

Heme oxygenase-2 is post-translationally regulated by heme occupancy in the catalytic site

Heme oxygenase-2 (HO2) and -1 (HO1) catalyze heme degradation to biliverdin, CO, and iron, forming an essential link in the heme metabolism network. Tight regulation of the cellular levels and catalytic activities of HO1 and HO2 is important for maintaining heme homeostasis. HO1 expression is transcriptionally regulated; however, HO2 expression is constitutive. How the cellular levels and activity of HO2 are regulated remains unclear. Here, we elucidate the mechanism of post-translational regulation of cellular HO2 levels by heme. We find that, under heme-deficient conditions, HO2 is destabilized and targeted for degradation, suggesting that heme plays a direct role in HO2 regulation. HO2 has three heme binding sites: one at its catalytic site and the others at its two heme regulatory motifs (HRMs). We report that, in contrast to other HRM-containing proteins, the cellular protein level and degradation rate of HO2 are independent of heme binding to the HRMs. Rather, under heme deficiency, loss of heme binding to the catalytic site destabilizes HO2. Consistently, an HO2 catalytic site variant that is unable to bind heme exhibits a constant low protein level and an enhanced protein degradation rate compared with the WT HO2. Finally, HO2 is degraded by the lysosome through chaperone-mediated autophagy, distinct from other HRM-containing proteins and HO1, which are degraded by the proteasome. These results reveal a novel aspect of HO2 regulation and deepen our understanding of HO2's role in maintaining heme homeostasis, paving the way for future investigation into HO2's pathophysiological role in heme deficiency response.

The Chemical Basis of Intracerebral Hemorrhage and Cell Toxicity With Contributions From Eryptosis and Ferroptosis

Intracerebral hemorrhage (ICH) is a particularly devastating event both because of the direct injury from space-occupying blood to the sequelae of the brain exposed to free blood components from which it is normally protected. Not surprisingly, the usual metabolic and energy pathways are overwhelmed in this situation. In this review article, we detail the complexity of red blood cell degradation, the contribution of eryptosis leading to hemoglobin breakdown into its constituents, the participants in that process, and the points at which injury can be propagated such as elaboration of toxic radicals through the metabolism of the breakdown products. Two prominent products of this breakdown sequence, hemin, and iron, induce a variety of pathologies including free radical damage and DNA breakage, which appear to include events independent from typical oxidative DNA injury. As a result of this confluence of damaging elements, multiple pathways of injury, cell death, and survival are likely engaged including ferroptosis (which may be the same as oxytosis but viewed from a different perspective) and senescence, suggesting that targeting any single cause will likely not be a sufficient strategy to maximally improve outcome. Combination therapies in addition to safe methods to reduce blood burden should be pursued.

Bilirubin in the Vitreous Body of the Eye of Human Fetuses

The bilirubin content in the vitreous body of the eye of human fetuses of gestation week 17-31 was measured. During gestation weeks 17-19, the mean bilirubin concentration was 8.67 μmol/liter; then, decreased to 1.37 μmol/liter (gestation weeks 20 to 31). Bilirubin, being an endogenous antioxidant, is probably involved in protection of the retina and lens from LPO processes that intensively develop in retinal neurons and lens fibers.

Spectral-domain OCT changes in retina and optic nerve in children with hypoxic-ischaemic encephalopathy

Purpose

To evaluate the effect of neonatal hypoxic–ischaemic injury on the retina and the optic nerve and to correlate ocular damage with systemic parameters, laboratory tests, neurological imaging and therapeutic hypothermia at birth.

Methods

Forty-one children with hypoxic–ischaemic encephalopathy (HIE) at birth (9.09 ± 3.78 years) and a control group of 38 healthy subjects (9.57 ± 3.47 years) were enrolled in a cohort study. The HIE population was divided into three subgroups, based on the degree of encephalopathy according to Sarnat score and the treatment with therapeutic hypothermia (TH): Sarnat score I not treated with hypothermia, Sarnat score II-III treated with TH and Sarnat score II-III not subjected to TH. Total macular thickness, individual retinal layers and peripapillary nerve fibre layer thickness were measured with spectral-domain optical coherence tomography. Clinical data of perinatal period of HIE children were collected: APGAR score, pH and base excess of funiculus blood at birth, apnoea duration, brain ultrasound, cerebral MRI ischaemic lesions and blood chemistry tests.

Results

Children with Sarnat score I did not show a reduction of peripapillary nerve fibres and ganglion cell layer compared to the control group (p = 0.387, p = 0.316). Peripapillary nerve fibre layer was 109.06 ± 7.79 μm in children with Sarnat score II-III treated with TH, 108.31 ± 7.83 μm in subjects with Sarnat score II-III not subjected to TH and 114.27 ± 6.81 μm in the control group (p = 0.028, p = 0.007). Ganglion cell layer was thinner in children with Sarnat score II-III treated with TH (50.31 ± 5.13 μm) compared to the control group (54.04 ± 2.81 μm) (p = 0.01). Inner retinal layers damage correlated with C-reactive protein and lactate dehydrogenase increase, while higher levels of total bilirubin were protective against retinal impairment (p < 0.05). Cerebral oedema was related to peripapillary nerve fibre layer damage (p = 0.046).

Conclusions

Thickness reduction of inner retinal layer and peripapillary nerve fibre impairment was related to encephalopathy severity. Ocular damage was associated with inflammation and cerebral oedema following hypoxic–ischaemic damage.

The Neuroprotective and Neurodegeneration Effects of Heme Oxygenase-1 in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disease characterized by complex pathological and biological features. Notably, extracellular amyloid-β deposits as senile plaques and intracellular aggregation of hyperphosphorylated tau as neurofibrillary tangles remain the primary premortem criterion for the diagnosis of AD. Currently, there exist no disease-modifying therapies for AD, and many clinical trials have failed to show its benefits for patients. Heme oxygenase 1 (HO-1) is a 32 kDa enzyme, which catalyzes the degradation of cellular heme to free ferrous iron, biliverdin, and carbon monoxide under stressful conditions. Several studies highlight the crucial pathological roles of HO-1 in the molecular processes of AD. The beneficial roles of HO-1 overexpression in AD brains are widely accepted due to its ability to convert pro-oxidant heme to biliverdin and bilirubin (antioxidants), which promote restoration of a suitable tissue redox microenvironment. However, the intracellular oxidative stress might be amplified by metabolites of HO-1 and exacerbate the progression of AD under certain circumstances. Several lines of evidence have demonstrated that upregulated HO-1 is linked to tauopathies, neuronal damage, and synapse aberrations in AD. Here, we review the aspects of the molecular mechanisms by which HO-1 regulates AD and the latest information on the pathobiology of AD. We further highlight the neuroprotective and neurodystrophic actions of HO-1 and the feasibility of HO-1 as a therapeutic target for AD.