The neuroprotective effect of heme oxygenase (HO) on oxidative stress in HO-1 siRNA-transfected HT22 cells

The brain heme oxygenase/biliverdin reductase system as a target in drug research and development

INTRODUCTION

The heme oxygenase/biliverdin reductase (HO/BVR) system is involved in heme metabolism. The inducible isoform of HO (HO-1) and BVR both exert cytoprotective effects by enhancing cell stress response. In this context, some xenobiotics, which target HO-1, including herbal products, behave as neuroprotectants in several experimental models of neurodegeneration. Despite this, no drug having either HO-1 or BVR as a main target is currently available.

AREAS COVERED

After a description of the brain HO/BVR system, the paper analyzes the main classes of drugs acting on the nervous system, with HO as second-level target, and their neuroprotective potential. Finally, the difficulties that exist for the development of drugs acting on HO/BVR and the possible ways to overcome these hurdles are examined.

EXPERT OPINION

Although the limited clinical evidence has restricted the translational research on the HO/BVR system, mainly because of the dual nature of its by-products, there has been growing interest in the therapeutic potential of these enzymes. Scientists should boost the translational research on the HO/BVR system which could be supported by the significant evidence provided by preclinical studies.

Cardamonin attenuates phorbol 12-myristate 13-acetate-induced pulmonary inflammation in alveolar macrophages

Pulmonary inflammation involves complex immune responses in which alveolar macrophages release pro-inflammatory proteins and cytokines. Cardamonin is a spice component that exerts anti-inflammatory and anti-oxidative properties against pulmonary inflammation. Herein, the aim of this research is to investigate the effects of cardamonin on pulmonary inflammation and its mechanism. Pulmonary inflammation in mice was induced by intratracheal administration of PMA. PMA-stimulated acute fibrosis, pulmonary edema, and inflammatory responses were ameliorated by oral administration of cardamonin in vivo. In MH-S alveolar macrophages, PMA-induced pro-inflammatory responses, including iNOS, COX-2, MMP-9 and cytokines expressions were reduced by cardamonin. The anti-oxidative Nrf2/HO-1 axis was also provoked by cardamonin in MH-S alveolar macrophages. In addition, MMP-9 expression induced by PMA is also decreased by the down-stream metabolites of HO-1, indicating that HO-1 expression partially contributes to the anti-inflammatory effect exerted by cardamonin. In this study, cardamonin demonstrates anti-inflammatory and anti-oxidative effects on PMA-induced pulmonary inflammation and activating Nrf2/HO-1 axis in alveolar macrophages. Cardamonin also ameliorates pulmonary inflammation, rapid fibrosis in vivo, suggesting powerful health benefits.

Immune Modulation by Inhibitors of the HO System

The heme oxygenase (HO) system involves three isoforms of this enzyme, HO-1, HO-2, and HO-3. The three of them display the same catalytic activity, oxidating the heme group to produce biliverdin, ferrous iron, and carbon monoxide (CO). HO-1 is the isoform most widely studied in proinflammatory diseases because treatments that overexpress this enzyme promote the generation of anti-inflammatory products. However, neonatal jaundice (hyperbilirubinemia) derived from HO overexpression led to the development of inhibitors, such as those based on metaloproto- and meso-porphyrins inhibitors with competitive activity. Further, non-competitive inhibitors have also been identified, such as synthetic and natural imidazole-dioxolane-based, small synthetic molecules, inhibitors of the enzyme regulation pathway, and genetic engineering using iRNA or CRISPR cas9. Despite most of the applications of the HO inhibitors being related to metabolic diseases, the beneficial effects of these molecules in immune-mediated diseases have also emerged. Different medical implications, including cancer, Alzheimer´s disease, and infections, are discussed in this article and as to how the selective inhibition of HO isoforms may contribute to the treatment of these ailments.

Protective Effect of Hemin Against Experimental Chronic Fatigue Syndrome in Mice: Possible Role of Neurotransmitters

Chronic fatigue syndrome (CFS) is a disorder characterized by persistent and relapsing fatigue along with long-lasting and debilitating fatigue, myalgia, cognitive impairment, and many other common symptoms. The present study was conducted to explore the protective effect of hemin on CFS in experimental mice. Male albino mice were subjected to stress-induced CFS in a forced swimming test apparatus for 21 days. After animals had been subjected to the forced swimming test, hemin (5 and 10 mg/kg; i.p.) and hemin (10 mg/kg) + tin(IV) protoporphyrin (SnPP), a hemeoxygenase-1 (HO-1) enzyme inhibitor, were administered daily for 21 days. Various behavioral tests (immobility period, locomotor activity, grip strength, and anxiety) and estimations of biochemical parameters (lipid peroxidation, nitrite, and GSH), mitochondrial complex dysfunctions (complexes I and II), and neurotransmitters (dopamine, serotonin, and norepinephrine and their metabolites) were subsequently assessed. Animals exposed to 10 min of forced swimming session for 21 days showed a fatigue-like behavior (as increase in immobility period, decreased grip strength, and anxiety) and biochemical alteration observed by increased oxidative stress, mitochondrial dysfunction, and neurotransmitter level alteration. Treatment with hemin (5 and 10 mg/kg) for 21 days significantly improved the decreased immobility period, increased locomotor activity, and improved anxiety-like behavior, oxidative defense, mitochondrial complex dysfunction, and neurotransmitter level in the brain. Further, these observations were reversed by SnPP, suggesting that the antifatigue effect of hemin is HO-1 dependent. The present study highlights the protective role of hemin against experimental CFS-induced behavioral, biochemical, and neurotransmitter alterations.

Novel Oxindole-Curcumin Hybrid Compound for Antioxidative Stress and Neuroprotection

Oxidative stress plays an important role in the pathogenesis of Parkinson's disease and other neurodegenerative disorders. The oxindole compound GIF-2165X-G1 is a hybrid molecule composed of the oxindole skeleton of the neuroprotective compound GIF-0726-r and the polyphenolic skeleton of the antioxidant curcumin. We previously reported that novel oxindole derivatives such as GIF-0726-r and GIF-2165X-G1 prevent endogenous oxidative stress-induced cell death in mouse hippocampal HT22 cells. In this study, we present a detailed investigation of the effect of GIF-2165X-G1 on endogenous oxidative stress in HT22 cells in comparison with GIF-0726-r and curcumin. GIF-2165X-G1 exhibited more potent neuroprotective activity than GIF-0726-r or curcumin and had less cytotoxicity than that observed with curcumin. Both GIF-0726-r and GIF-2165X-G1 were found to have ferrous ion chelating activity similar to that exhibited by curcumin. GIF-2165 X-G1 and curcumin induced comparable antioxidant response element transcriptional activity. Although the induction of heme oxygenase-1, an antioxidant response element-regulated gene product, was much stronger in curcumin-treated cells than in GIF-2165X-G1-treated cells, it turned out that the induction of heme oxygenase-1 is dispensable for neuroprotection. These results demonstrate that the introduction of the polyphenol skeleton of curcumin to the oxindole GIF-0726-r improves neuroprotective features. Furthermore, intrastriatal injection of GIF-2165X-G1 alleviated apomorphine-induced rotation and prevented dopaminergic neuronal loss in a 6-hydroxydopamine mouse model of Parkinson's diseases. Collectively, our novel findings indicate that the novel oxindole compound GIF-2165X-G1 serves to delay the progression of Parkinson's disease by suppressing oxidative stress.

Iduna protects HT22 cells by inhibiting parthanatos: The role of the p53-MDM2 pathway

Traumatic brain injury (TBI) is common and often fatal in current times. The role of poly(adenosine diphosphate-ribose) polymerase (PARP)-induced cell death (parthanatos) in TBI has not been well studied. Our past study showed that oxidative stress-induced cell death includes parthanatos by confirming the occurrence of PARP activation and nuclear translocation of apoptosis-inducing factor (AIF). As oxidative stress plays a key role in pathological progression after TBI, we believe TBI may also be alleviated by the expression of Iduna, which is the only known endogenous regulator of parthanatos. Thus, a transection model in HT-22 cells was established for present study. Downregulation of Iduna aggravated the cell damage caused by mechanical cell injury, whereas upregulation of Iduna reduced mitochondrial dysfunction induced by mechanical cell injury but exerted no effect on apoptosis associated with mitochondrial dysfunction. By contrast, Iduna prevented parthanatos by reducing PARP activation and nuclear translocation of AIF. We also investigated 2 novel p53-MDM2 pathway inhibitors, AMG 232 and Nutlin-3, which substantially reduced the protective effects of Iduna. These findings indicate that Iduna might prevent TBI by specifically inhibiting parthanatos and promoting mitochondrial function, with the p53-MDM2 pathway playing a critical role.

Morpho-functional effects of heat stress on the gills of Antarctic T. bernacchii and C. hamatus

The effect of increasing ocean water temperature on morpho-functional traits of Antarctic marine species is under intense attention. In this work, we evaluated the effects of acute heat stress on the gills of the Antarctic haemoglobinless Chionodraco hamatus and the red blooded Trematomus bernacchii in terms of morphology, heat shock response, antioxidant defense and NOS/NO system. We showed in both species that the exposure to high temperature (4 °C) induced structural alterations, such as epithelial lifting and oedema of secondary lamellae. By immunolocalization we also observed that HSP-90, HSP-70, Xantine Oxidase, Heme Oxigenase and NOS are expressed in both species under control conditions. After heat stress the signals increase in C. hamatus being absent/or reduced in T. bernacchii. Our preliminary results suggest a specie-specific morpho-functional response of the gills of the two Antarctic teleosts to heat stress.

HO-1 protects the nerves of rats with cerebral hemorrhage by regulating the PI3K/AKT signaling pathway

Objective: This study aimed to investigate the neuroprotective effect of heme oxygenase-1 (HO-1) on the PI3K/AKT signaling pathway in rats with cerebral hemorrhage. Materials and methods: Adult male Sprague-Dawley rats were randomly divided into: a sham group, a model group and an HO-1 inhibitor group (ZnPP group). Functional defects after surgery were scored according to the Longa5 standard. Hemotoxylin and eosin staining was used to detect whether the model was constructed successfully. Superoxide dismutase (SOD) vitality and malondialdehyde (MDA) content were calculated by the xanthine oxidase method and thiobarbituric acid method, respectively. Blood-brain barrier permeability was measured by Evans Blue. Apoptosis was detected by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling assay. The expression of Bcl-2 and BAX was evaluated by immunohistochemistry and the expression of PI3K, p-PI3K, AKT and p-AKT was tested by Western blotting. Results: The rat intracerebral hemorrhage model was successfully constructed. Compared with the model group, the bleeding in the ZnPP group was more serious, the cell edema and deformation were aggravated, and the neurological deficit score in the rat was significantly increased. In addition, the content of Evans blue, MDA, the number of apoptotic cells, the water content of brain tissue and the expression of BAX were significantly increased, while the SOD activity and the expressions of Bcl-2, p-PI3K and p-AKT protein were decreased. Conclusion: HO-1 could protect the nerves of rats with cerebral hemorrhage by regulating the PI3K/AKT signaling pathway.

Carbon Monoxide Ameliorates 6-Hydroxydopamine-Induced Cell Death in C6 Glioma Cells

Carbon monoxide (CO) is well-known as toxic gas and intrinsic signaling molecule such as neurotransmitter and blood vessel relaxant. Recently, it has been reported that low concentration of CO exerts therapeutic actions under various pathological conditions including liver failure, heart failure, gastric cancer, and cardiac arrest. However, little has been known about the effect of CO in neurodegenerative diseases like Parkinson's disease (PD). To test whether CO could exert a beneficial action during oxidative cell death in PD, we examined the effects of CO on 6-hydroxydopamine (6-OHDA)-induced cell death in C6 glioma cells. Treatment of CO-releasing molecule-2 (CORM-2) significantly attenuated 6-OHDA-induced apoptotic cell death in a dose-dependent manner. CORM-2 treatment decreased Bax/Bcl2 ratio and caspase-3 activity, which had been increased by 6-OHDA. CORM-2 increased phosphorylation of NF-E2-related factor 2 (Nrf2) which is a transcription factor regulating antioxidant proteins. Subsequently, CORM-2 also increased the expression of heme oxygenase-1 and superoxide dismutases (CuZnSOD and MnSOD), which were antioxidant enzymes regulated by Nrf2. These results suggest that CO released by CORM-2 treatment may have protective effects against oxidative cell death in PD through the potentiation of cellular adaptive survival responses via activation of Nrf2 and upregulation of heme oxygenase-1, leading to increasing antioxidant defense capacity.

Neuroprotection by aripiprazole against β-amyloid-induced toxicity by P-CK2α activation via inhibition of GSK-3β

Psychosis is reported over 30% of patients with Alzheimer's disease (AD) in clinics. Aripiprazole is an atypical antipsychotic drug with partial agonist activity at the D₂ dopamine and 5-HT_1A receptors with low side-effect profile. We identified aripiprazole is able to overcome the amyloid-β (Aβ)-evoked neurotoxicity and then increase the cell viability. This study elucidated the mechanism(s) by which aripiprazole ameliorates Aβ1-42-induced decreased neurite outgrowth and viability in neuronal cells. Pretreatment with aripiprazole increased Brain-derived neurotrophic factor (BDNF) mRNA and protein expressions in N2a cells. Additionally, phosphorylated casein kinase 2α at Y 255 (P-CK2α) was increased in time- and concentration-dependent manners. Furthermore, Aβ1-42-induced decreased BDNF and P-CK2α expression were increased over control level by aripiprazole. Subsequently, Aβ1-42-induced decreased levels of phosphorylated glycogen synthase-3β at Ser9 (P-GSK-3β) and nuclear P-β-catenin (Ser675) were elevated by aripiprazole, which were inhibited by K252A (inhibitor of BDNF receptor) and tetrabromocinnamic acid (TBCA, CK2 inhibitor), indicating that BDNF and P-CK2α activation are implicated in the aripiprazole effects. Expressions of cyclin D1 and insulin-like growth factor 2 (IGF2) mRNA were increased by aripiprazole; even in the presence of Aβ1-42, which was blocked by K252A and TBCA. In CK2α gene-silenced N2a cells, aripiprazole failed to increase P-GSK-3β and P-β-catenin expressions. Consequently, aripiprazole ameliorated Aβ1-42-induced attenuation of neurite elongation in HT22 cells, and this effect was blocked by both TBCA and imatinib. Decreased viability induced by Aβ1-42 was recovered by aripiprazole. These findings provide evidence supporting that aripiprazole can provide an effective therapeutic strategy against Aβ-induced neurotoxicity in AD-associated psychosis.

The Aminopyridinol Derivative BJ-1201 Protects Murine Hippocampal Cells against Glutamate-Induced Neurotoxicity via Heme Oxygenase-1

Glutamate is the major excitatory neurotransmitter in the brain. It can cause neuronal cell damage in the context of oxidative stress. BJ-1201 is a derivative of the compound aminopyridinol, which is known for its antioxidant activity. In this study, we examined the effect of BJ-1201, a 6-(diphenylamino)-2,4,5-trimethylpyridin-3-ol compound, on neuroprotection in HT22 cells. Our data showed that BJ-1201 can protect HT22 cells against glutamate-induced cell cytotoxicity. In addition, BJ-1201 upregulated heme oxygenase-1 (HO-1) to levels comparable to those of the CoPP-treated group. BJ-1201 treatment induced phosphorylation of JNK, but not p38-MAPK or ERK. It also increased the signal in the reporter assay based on β-galactosidase activity driven by the nuclear transcription factor erythroid-2 related factor 2 (Nrf2) promoter harboring antioxidant response elements (AREs) and induced the translocation of Nrf2. These results demonstrate that BJ-1201 may be a good therapeutic platform against neurodegenerative diseases induced by oxidative stress.

Neuroprotective effects of the Phellinus linteus ethyl acetate extract against H2O2-induced apoptotic cell death of SK-N-MC cells

Numerous studies have suggested that neuronal cells are protected against oxidative stress-induced cell damage by antioxidants, such as polyphenolic compounds. Phellinus linteus (PL) has traditionally been used to treat various symptoms in East Asian countries. In the present study, we prepared an ethyl acetate extract from the fruiting bodies of PL (PLEA) using hot water extraction, ethanol precipitation, and ethyl acetate extraction. The PLEA contained polyphenols as its major chemical component, and thus, we predicted that it may exhibit antioxidant and neuroprotective effects against oxidative stress. The results showed that the pretreatment of human brain neuroblastoma SK-N-MC cells with the PLEA (0.1-5 μg/mL) significantly and dose-dependently reduced the cytotoxicity of H2O2 and the intracellular ROS levels and enhanced the expression of HO-1 (heme oxygenase-1) and antioxidant enzymes, such as CAT (catalase), GPx-1 (glutathione peroxidase-1), and SOD-1 and -2 (superoxide dismutase-1 and -2). The PLEA also directly scavenged free radicals. PLEA pretreatment also significantly attenuated DNA fragmentation and suppressed the mRNA expression and activation of mitogen-activated protein kinases extracellular signal-regulated kinase, c-Jun N-terminal kinase, and p38 kinase, which are induced by oxidative stress and lead to cell death. PLEA pretreatment inhibited the activation of the apoptosis-related proteins caspase-3 and poly (ADP-ribose) polymerase. These results demonstrate that the PLEA has neuroprotective effects against oxidative stress (H2O2)-induced neuronal cell death via its antioxidant and anti-apoptotic properties. PLEA should be investigated in an in vivo model on its potential to prevent or ameliorate neurodegenerative disease.

Heme oxygenase-1 protects corexit 9500A-induced respiratory epithelial injury across species

The effects of Corexit 9500A (CE) on respiratory epithelial surfaces of terrestrial mammals and marine animals are largely unknown. This study investigated the role of CE-induced heme oxygenase-1 (HO-1), a cytoprotective enzyme with anti-apoptotic and antioxidant activity, in human bronchial airway epithelium and the gills of exposed aquatic animals. We evaluated CE-mediated alterations in human airway epithelial cells, mice lungs and gills from zebrafish and blue crabs. Our results demonstrated that CE induced an increase in gill epithelial edema and human epithelial monolayer permeability, suggesting an acute injury caused by CE exposure. CE induced the expression of HO-1 as well as C-reactive protein (CRP) and NADPH oxidase 4 (NOX4), which are associated with ROS production. Importantly, CE induced caspase-3 activation and subsequent apoptosis of epithelial cells. The expression of the intercellular junctional proteins, such as tight junction proteins occludin, zonula occludens (ZO-1), ZO-2 and adherens junctional proteins E-cadherin and Focal Adhesion Kinase (FAK), were remarkably inhibited by CE, suggesting that these proteins are involved in CE-induced increased permeability and subsequent apoptosis. The cytoskeletal protein F-actin was also disrupted by CE. Treatment with carbon monoxide releasing molecule-2 (CORM-2) significantly inhibited CE-induced ROS production, while the addition of HO-1 inhibitor, significantly increased CE-induced ROS production and apoptosis, suggesting a protective role of HO-1 or its reaction product, CO, in CE-induced apoptosis. Using HO-1 knockout mice, we further demonstrated that HO-1 protected against CE-induced inflammation and cellular apoptosis and corrected CE-mediated inhibition of E-cadherin and FAK. These observations suggest that CE activates CRP and NOX4-mediated ROS production, alters permeability by inhibition of junctional proteins, and leads to caspase-3 dependent apoptosis of epithelial cells, while HO-1 and its reaction products protect against oxidative stress and apoptosis.

Differentiation renders susceptibility to excitotoxicity in HT22 neurons

HT22 is an immortalized mouse hippocampal neuronal cell line that does not express cholinergic and glutamate receptors like mature hippocampal neurons in vivo. This in part prevents its use as a model for mature hippocampal neurons in memory-related studies. We now report that HT22 cells were appropriately induced to differentiate and possess properties similar to those of mature hippocampal neurons in vivo, such as becoming more glutamate-receptive and excitatory. Results showed that sensitivity of HT22 cells to glutamate-induced toxicity changed dramatically when comparing undifferentiated with differentiated cells, with the half-effective concentration for differentiated cells reducing approximately two orders of magnitude. Moreover, glutamate-induced toxicity in differentiated cells, but not undifferentiated cells, was inhibited by the N-methyl-D- aspartate receptor antagonists MK-801 and memantine. Evidently, differentiated HT22 cells expressed N-methyl-D-aspartate receptors, while undifferentiated cells did not. Our experimental findings indicated that differentiation is important for immortalized cell lines to render post-mitotic neuronal properties, and that differentiated HT22 neurons represent a better model of hippocampal neurons than undifferentiated cells.

Heme oxygenase-1 protects retinal endothelial cells against high glucose- and oxidative/nitrosative stress-induced toxicity

Diabetic retinopathy is a leading cause of visual loss and blindness, characterized by microvascular dysfunction. Hyperglycemia is considered the major pathogenic factor for the development of diabetic retinopathy and is associated with increased oxidative/nitrosative stress in the retina. Since heme oxygenase-1 (HO-1) is an enzyme with antioxidant and protective properties, we investigated the potential protective role of HO-1 in retinal endothelial cells exposed to high glucose and oxidative/nitrosative stress conditions. Retinal endothelial cells were exposed to elevated glucose, nitric oxide (NO) and hydrogen peroxide (H(2)O(2)). Cell viability and apoptosis were assessed by MTT assay, Hoechst staining, TUNEL assay and Annexin V labeling. The production of reactive oxygen species (ROS) was detected by the oxidation of 2',7'-dichlorodihydrofluorescein diacetate. The content of HO-1 was assessed by immunobloting and immunofluorescence. HO activity was determined by bilirubin production. Long-term exposure (7 days) of retinal endothelial cells to elevated glucose decreased cell viability and had no effect on HO-1 content. However, a short-time exposure (24 h) to elevated glucose did not alter cell viability, but increased both the levels of intracellular ROS and HO-1 content. Moreover, the inhibition of HO with SnPPIX unmasked the toxic effect of high glucose and revealed the protection conferred by HO-1. Oxidative/nitrosative stress conditions increased cell death and HO-1 protein levels. These effects of elevated glucose and HO inhibition on cell death were confirmed in primary endothelial cells (HUVECs). When cells were exposed to oxidative/nitrosative stress conditions there was also an increase in retinal endothelial cell death and HO-1 content. The inhibition of HO enhanced ROS production and the toxic effect induced by exposure to H(2)O(2) and NOC-18 (NO donor). Overexpression of HO-1 prevented the toxic effect induced by H(2)O(2) and NOC-18. In conclusion, HO-1 exerts a protective effect in retinal endothelial cells exposed to hyperglycemic and oxidative/nitrosative stress conditions.

Dynamic changes of heme oxygenase-1 in the hippocampus of rats after acute carbon monoxide poisoning

Heme oxygenase-1 (HO-1), an inducible enzyme, degrades heme to carbon monoxide (CO), iron, and bilirubin. We have investigated the relationship among HO-1 protein expression, HO activity, and CO concentrations in the hippocampus of CO-exposed rats. Western blotting and immunohistochemistry revealed that the enzyme is predominantly localized in hippocampal CA1 and CA3 pyramidal cells and in granule cells of the dentate gyrus. HO enzyme activity was reduced immediately following CO exposure, while expression of HO-1 protein was consistently upregulated in a time-dependent manner. Local CO concentrations in hippocampus rose immediately following exposure, but the elevation was maintained for ~20 h despite the decline in blood carboxyhemoglobin levels toward baseline. We suggest that CO initially inhibits HO enzyme activity, whereas at later time points the inhibition is released and local CO generation is maintained by the activity of the endogenous HO enzyme. And the noninducible form of heme oxygenase, HO-2, was not altered following CO administration. Together these results indicate that the HO/CO pathway in the rat hippocampus is induced by acute CO exposure; local CO production may play a regulatory role in brain injury following CO poisoning.

Induction of heme oxygenase-1 attenuates lipopolysaccharide-induced cyclooxygenase-2 expression in mouse brain endothelial cells

Background

Prostaglandin E₂ (PGE₂), an arachidonic acid metabolite converted by cyclooxygenase-2 (COX-2), plays important roles in the regulation of endothelial functions in response to bacterial infection. The enzymatic activity of COX-2 can be down-regulated by heme oxygenase-1 (HO-1) induction. However, the mechanisms underlying HO-1 modulating COX-2 protein expression are not known.

Objective

The aim of the present study was to investigate whether the up-regulation of HO-1 regulates COX-2 expression induced by lipopolysaccharide (LPS), an endotoxin produced by Gram negative bacteria, in mouse brain endothelial cells (bEnd.3)

Methods

Cultured bEnd.3 cells were used to investigate LPS-induced COX-2 expression and PGE₂ production. Cobalt protoporphyrin IX (CoPP, an HO-1 inducer), infection with a recombinant adenovirus carried with HO-1 gene (Adv-HO-1), or zinc protoporphyrin (ZnPP, an HO-1 inhibitor) was used to stimulate HO-1 induction or inhibit HO-1 activity. The expressions of COX-2 and HO-1 were evaluated by western blotting. PGE₂ levels were detected by an enzyme-linked immunoassay. Hemoglobin (a chelator of carbon monoxide, CO, one of metabolites of HO-1) and CO-RM2 (a CO releasing molecule) were used to investigate the mechanisms of HO-1 regulating COX-2 expression.

Results

We found that LPS-induced COX-2 expression and PGE₂ production were mediated through NF-κB (p65) via activation of Toll-like receptor 4 (TLR4). LPS-induced COX-2 expression was inhibited by HO-1 induction by pretreatment with CoPP or infection with Adv-HO-1. This inhibitory effect of HO-1 was reversed by pretreatment with either ZnPP or hemoglobin. Pretreatment with CO-RM2 also inhibited TLR4/MyD88 complex formation, NF-κB (p65) activation, COX-2 expression, and PGE₂ production induced by LPS.

Conclusions

We show here a novel inhibition of HO-1 on LPS-induced COX-2/PGE₂ production in bEnd.3. Our results reinforce the emerging role of cerebral endothelium-derived HO-1 as a protector against cerebral vascular inflammation triggered by bacterial infection.

Mechanism for the protective effect of resveratrol against oxidative stress-induced neuronal death

Oxidative stress can induce cytotoxicity in neurons, which plays an important role in the etiology of neuronal damage and degeneration. This study sought to determine the cellular and biochemical mechanisms underlying resveratrol's protective effect against oxidative neuronal death. Cultured HT22 cells, an immortalized mouse hippocampal neuronal cell line, were used as an in vitro model, and oxidative stress and neurotoxicity were induced in these neuronal cells by exposure to high concentrations of glutamate. Resveratrol strongly protected HT22 cells from glutamate-induced oxidative cell death. Resveratrol's neuroprotective effect was independent of its direct radical scavenging property, but instead was dependent on its ability to selectively induce the expression of mitochondrial superoxide dismutase (SOD2) and, subsequently, reduce mitochondrial oxidative stress and damage. The induction of mitochondrial SOD2 by resveratrol was mediated through the activation of the PI3K/Akt and GSK-3beta/beta-catenin signaling pathways. Taken together, the results of this study show that up-regulation of mitochondrial SOD2 by resveratrol represents an important mechanism for its protection of neuronal cells against oxidative cytotoxicity resulting from mitochondrial oxidative stress.

Mitochondrial superoxide dismutase SOD2, but not cytosolic SOD1, plays a critical role in protection against glutamate-induced oxidative stress and cell death in HT22 neuronal cells

Oxidative cell death is an important contributing factor in neurodegenerative diseases. Using HT22 mouse hippocampal neuronal cells as a model, we sought to demonstrate that mitochondria are crucial early targets of glutamate-induced oxidative cell death. We show that when HT22 cells were transfected with shRNA for knockdown of the mitochondrial superoxide dismutase (SOD2), these cells became more susceptible to glutamate-induced oxidative cell death. The increased susceptibility was accompanied by increased accumulation of mitochondrial superoxide and loss of normal mitochondrial morphology and function at early time points after glutamate exposure. However, overexpression of SOD2 in these cells reduced the mitochondrial superoxide level, protected mitochondrial morphology and functions, and provided resistance against glutamate-induced oxidative cytotoxicity. The change in the sensitivity of these SOD2-altered HT22 cells was neurotoxicant-specific, because the cytotoxicity of hydrogen peroxide was not altered in these cells. In addition, selective knockdown of the cytosolic SOD1 in cultured HT22 cells did not appreciably alter their susceptibility to either glutamate or hydrogen peroxide. These findings show that the mitochondrial SOD2 plays a critical role in protecting neuronal cells from glutamate-induced oxidative stress and cytotoxicity. These data also indicate that mitochondria are important early targets of glutamate-induced oxidative neurotoxicity.

The role of Nrf2 and MAPK pathways in PFOS-induced oxidative stress in zebrafish embryos

Perfluorooctane sulfonate (PFOS) is a persistent organic pollutant and causes oxidative stress, apoptosis, and developmental toxicity in zebrafish embryos. In the present study, we examined nuclear factor erythroid 2-related factor 2 (Nrf2)- and mitogen-activated protein kinases (MAPKs)-mediated oxidative stress pathways in zebrafish embryos upon exposure to PFOS. Four-hour postfertilization (hpf) zebrafish embryos were exposed to 0.2, 0.4, and 1.0 mg/l PFOS until 96 hpf. PFOS enhanced production of reactive oxygen species (ROS) in a concentration-dependent manner. Activity of antioxidative enzymes, including superoxide dismutase, catalase, and glutathione peroxidase, was significantly induced in zebrafish larvae in all PFOS-treated groups relative to the control. Exposure to 1.0 mg/l PFOS significantly increased malondialdehyde production in zebrafish larvae. The Nrf2 and heme oxygenase-1 (HO-1) gene expressions were both significantly upregulated compared with the control group. For MAPKs, we investigated gene expression profiles of extracellular signal-regulated protein kinase (ERK), c-Jun NH (2)-terminal kinase (JNK), and p38. The ERK gene expression levels were unchanged, whereas JNK and p38 gene expressions were significantly upregulated, which could be linked to PFOS-induced cell apoptosis in zebrafish larvae. In addition, we found that coexposure with sulforaphane, an Nrf2 activator, could significantly protect against PFOS-induced ROS generation, whereas inhibition of MAPKs did not exhibit significant effects on PFOS-induced HO-1 gene expression and ROS production. Furthermore, we showed that morpholino-mediated knockdown of Nrf2 reduced PFOS-induced HO-1 gene expression. These findings demonstrate that Nrf2 is protective against PFOS-induced oxidative stress in zebrafish larvae.

Induction of heme oxygenase-1 with hemin attenuates hippocampal injury in rats after acute carbon monoxide poisoning

Carbon monoxide (CO) poisoning is a major cause of brain injury and mortality; delayed neurological syndrome (DNS) is encountered in survivors of acute CO exposure. The toxic effects of CO have been attributed to oxidative stress induced by hypoxia. Heme oxygenase-1 (HO-1) is the inducible heme oxygenase isoform, and its induction acts as an important cellular defense mechanism against oxidative stress, cellular injury and disease. In this study, we examined the functional roles of HO-1 induction in a rat model of CO-exposured hippocampal injury. We report that acute CO exposure produces severe hippocampal injury in rats. However, hemin pretreatment reduced both the CO-induced rise in hippocampal water content and levels of neuronal damage in the hippocampus; survival rates at 24 h were significantly improved. Upregulation of HO-1 by hemin pretreatment resulted in a significant decrease in hippocampal levels of malondialdehyde (MDA), a marker of oxidative stress; levels of pro-apoptotic caspase-3 were also reduced. In contrast, inhibition of HO activity by administration of tin protoporphyrin IX (SnPP, a specific inhibitor of HO) abolished the neuroprotective effects of HO-1 induction. These data suggested that the upregulation of endogenous HO-1 expression therefore plays a pivotal protective role in CO neurotoxicity. Though the precise mechanisms underlying hemin-mediated HO-1 induction and neuroprotection are not known, these may involve the anti-oxidant and anti-apoptotic effects of HO-1 enzyme activity.

Regulation of haeme oxygenase-1 for treatment of neuroinflammation and brain disorders

Injury to the CNS elicits a host defense reaction that utilizes astrocytes, microglia, neurons and oligodendrocytes. Neuroinflammation is a major host defense mechanism designed to restore normal structure and function after CNS insult, but like other forms of inflammation, chronic neuroinflammation may contribute to pathogenesis. The inducible haeme oxygenase isoform, haeme oxygenase-1 (HO-1), is a phase 2 enzyme upregulated in response to electrophilic xenobiotics, oxidative stress, cellular injury and disease. There is emerging evidence that HO-1 expression helps mediate the resolution of inflammation, including neuroinflammation. Whether this is solely because of the catabolism of haeme or includes additional mechanisms is unclear. This review provides a brief background on the molecular biology and biochemistry of haeme oxygenases and the actions of haeme, bilirubin, iron and carbon monoxide in the CNS. It then presents our current state of knowledge regarding HO-1 expression in the CNS, regulation of HO-1 induction in neural cells and discusses the prospect of pharmacological manipulation of HO-1 as therapy for CNS disorders. Because of recognized species and cellular differences in HO-1 regulation, a major objective of this review is to draw attention to areas where gaps exist in the experimental record regarding regulation of HO-1 in neural cells. The results indicate the HO-1 system to be an important therapeutic target in CNS disorders, but our understanding of HO-1 expression in human neural cells is severely lacking.

The role of cyp1a and heme oxygenase 1 gene expression for the toxicity of 3,4-dichloroaniline in zebrafish (Danio rerio) embryos

Expression profiling of exposed cells or organisms can reveal genes sensitive to environmental contaminants or toxic compounds. However, the mechanistic relevance of altered gene expression often remains to be elucidated. Toxicant-dependent differential gene expression may indicate protection to or mediation of toxicity. Previous studies revealed a number of differentially transcribed genes in zebrafish embryos exposed to the model compound 3,4-dichloroaniline (3,4-DCA). To evaluate the significance of two of the most sensitive genes, cytochrome P 450 1a (cyp1a) and heme oxygenase 1 (hmox1), for 3,4-DCA toxicity, RNA interference-mediated knockdown and overexpression studies have been conducted. Knockdown of gene transcription by siRNA for cyp1a and hmox1 enhanced the frequency of developmental disorders in embryos exposed to 3,4-DCA. Vice versa, injection of cyp1a and hmox1 mRNA reduced the number of disorders. The opposite effects of siRNA and mRNA injection clearly indicate a protective role of the corresponding proteins. Functional studies such as the one presented could be applied to a wide variety of genes. They would be ideally suited to study the role of genes identified from toxicogenomic studies in the zebrafish embryo model.

Relationship between reactive oxygen species and heme metabolism during the differentiation of Neuro2a cells

Although neuronal cells are highly vulnerable to oxidative stress, recent studies suggest that production of reactive oxygen species (ROS) increases during and is essential for neuronal differentiation. In addition, we have previously found that heme biosynthesis is up-regulated during retinoic acid-induced differentiation of Neuro2a cells. In the current study, we showed that this up-regulation of heme biosynthesis during differentiation is ROS-dependent. Furthermore, we found that ROS-dependent induction of heme oxygenase, which degrades heme and acts as an anti-oxidant, and catalase, another anti-oxidant enzyme that contains heme as a prosthetic group, occurs during differentiation. These results suggest that heme biosynthesis following the degradation of heme protects Neuro2a cells from oxidative stress caused by ROS during differentiation.