Heme oxygenase-1 induction may explain the antioxidant profile of aspirin

Aspirin is known to exert antioxidant effects by as yet unidentified mechanisms. In cultured endothelial cells derived from human umbilical vein, aspirin (30-300 microM) increased heme oxygenase-1 (HO-1) protein levels in a concentration-dependent fashion up to fivefold over basal levels. HO-1 induction was accompanied by a marked increase in catalytic activity of the enzyme as reflected by enhanced formation of both carbon monoxide and bilirubin. Pretreatment with aspirin or bilirubin at low micromolar concentrations protected endothelial cells from hydrogen peroxide-mediated toxicity. HO-1 induction and endothelial protection by aspirin were not mimicked by indomethacin, another inhibitor of cyclooxygenase. The nitric oxide (NO) synthase blocker L-NAME prevented aspirin-dependent HO-1 induction. These findings demonstrate that aspirin targets HO-1, presumably via NO-dependent pathways. Induction of HO-1 expression and activity may be a novel mechanism by which aspirin prevents cellular injury under inflammatory conditions and in cardiovascular disease.     

Carbon monoxide and bilirubin from heme oxygenase-1 suppresses reactive oxygen species generation and plasminogen activator inhibitor-1 induction

Heme oxygenase-1 (HO-1) responds to a variety of oxidative stresses. We examined whether HO-1 expression influences pro-thrombotic processes, in which the involvement of oxidative stress has been reported. Since HO-1 knockout mice with a C57/BL6J background were not viable, embryonic cells from HO-1 deficient mice (E11.5) were used. Cell viability, the level of plasminogen activator inhibitor-1 (PAI-1) expression and reactive oxygen species (ROS) generation of HO-1 deficient cells in response to the exposures to hydrogen peroxide and oxidized LDL were compared to those with wild-type cells. We also examined the effects of glutathione (GSH), desferrioxamine (DFO) and diphenyleneiodonium (DPI: an NADPH oxidase inhibitor) as well as of the HO reaction products, bilirubin (BR) and carbon monoxide (CO) on PAI-1 expression and ROS generation. PAI-1 expression and ROS generation were markedly elevated in HO-1 deficient cells compared to wild-type cells. Exposure to oxidized LDL significantly elevated PAI-1 expression and ROS production in HO-1 deficient cells. Interestingly, these increases in HO-1 deficient cells were significantly lowered by BR, CO, GSH and DPI while DFO had little effect. Furthermore, BR and CO were effective to improve viabilities of HO-1 deficient cells. These results suggest that HO-1 may be required to suppress ROS generation and the production of pro-thrombotic molecules such as PAI-1.     

Influence of antioxidants on NO-dependent induction of heme oxygenase-1 in U937 monocytes

Thiol antioxidants are known to inhibit the nitric oxide-dependent induction of the hemoxygenase-1 gene (HOX-1). To estimate the degree to which the inhibitory effect of thiol antioxidants is accounted for by them scavenging oxidized NO derivatives or their precursors, the reactive oxygen and nitrogen species (ROS and RNS), we studied the inhibitory effect of nonthiol antioxidants: dimethyl sulfoxide, dimethylthiourea, sodium salicylate, sodium formate, uric acid, catalase, and superoxide dismutase. Partial inhibition of NO-dependent HOX-1 induction was observed in the presence of the nonpolar HO scavengers dimethyl sulfoxide and dimethylthiourea. The antioxidants which selectively bind other ROS had no effect on HOX-1 expression. To reveal the role of RNS in NO-dependent HOX-1 induction, cells were treated with the NO-generating compound DPTA-NO in the presence of 2-phenyl-4,4,5,5,-tetramethylimidazole-1-oxyl 3 oxide (PTIO), which oxidizes NO to NO₂. PTIO proved to significantly enhance NO-dependent HOX-1 induction. Thiol antioxidants completely inhibited the stimulating effect of PTIO, which is evidence that their inhibitory effect is explained by RNS scavenging. The results of this study indicate that antioxidants can be used to modulate the cell response to NO.Translated from Molekulyarnaya Biologiya, Vol. 39, No. 1, 2005, pp. 89–95.Original Russian Text Copyright © 2005 by Litvinov, Prasolov, Bouton, Drapier, Turpaev.     

A significant role for the heme oxygenase-1 gene in endothelial cell cycle progression

Heme oxygenase (HO) catalyzes the conversion of heme to biliverdin with the release of iron and carbon monoxide. HO-1 is inducible by inflammatory conditions, which cause oxidative stress in endothelial cells. Overexpression of human HO-1 in endothelial cells may have the potential to provide protection against a variety of agents that cause oxidative stress. We investigated the physiological significance of human HO-1 overexpression, using a retroviral vector, on cell cycle progression in the presence and absence of pyrrolidine dithiocarbamate (PDTC). The addition of PDTC (25 and 50 microM) to human microvessel endothelial cells over 24 h resulted in significant (P < 0.05) abnormalities in DNA distribution and cell cycle progression compared to cells overexpressing the HO-1 gene. The addition of PDTC resulted in a significantly decreased G(1) phase and an increased G(2)/M phase in the control cells, but not in cells transduced with the human HO-1 gene (P < 0.05). Further, PDTC had a potent effect on DNA distribution abnormalities in exponentially grown cells compared to subconfluent cells. Upregulation of HO activity in endothelial cells, as a result of overexpressing human HO-1, prevented PDTC-mediated abnormalities in DNA distribution. Inhibition of HO activity by tin-mesoporphyrin (SnMP) (30 microM) resulted in enhancement of PDTC-mediated abnormalities in cell cycle progression. Bilirubin or iron did not mediate DNA distribution. We conclude that an increase in endothelial cell HO-1 activity with subsequent generation of carbon monoxide, elicited by gene transfer, reversed the PDTC-mediated abnormalities in cell cycle progression and is thus a potential therapeutic means for attenuating the effects of oxidative stress-causing agents.     

Galantamine and carbon monoxide protect brain microvascular endothelial cells by heme oxygenase-1 induction

Galantamine, a reversible inhibitor of acetylcholine esterase (AChE), is a novel drug treatment for mild to moderate Alzheimer’s disease and vascular dementia. Interestingly, it has been suggested that galantamine treatment is associated with more clinical benefit in patients with mild-to-moderate Alzheimer disease compared to other AChE inhibitors. We hypothesized that the protective effects of galantamine would involve induction of the protective gene, heme oxygenase-1 (HO-1), in addition to enhancement of the cholinergic system. Brain microvascular endothelial cells (mvECs) were isolated from spontaneous hypertensive rats. Galantamine significantly reduced H₂O₂-induced cell death of mvECs in association with HO-1 induction. These protective effects were completely reversed by nuclear factor-κB (NF-κB) inhibition or HO inhibition. Furthermore, galantamine failed to induce HO-1 in mvECs which lack inducible nitric oxide synthase (iNOS), supplementation of a nitric oxide (NO) donor or iNOS gene transfection on iNOS-deficient mvECs resulted in HO-1 induction with galantamine. These data suggest that the protective effects of galantamine require NF-κB activation and iNOS expression, in addition to HO-1. Likewise, carbon monoxide (CO), one of the byproducts of HO, up-regulated HO-1 and protected mvECs from oxidative stress in a similar manner. Our data demonstrate that galantamine mediates cytoprotective effects on mvECs through induction HO-1. This pharmacological action of galantamine may, at least in part, account for the superior clinical efficacy of galantamine in vascular dementia and Alzheimer disease.     

Heme oxygenase-1 and heme oxygenase-2 have distinct roles in the proliferation and survival of olfactory receptor neurons mediated by cGMP and bilirubin,respectively

Heme oxygenase (HO) is implicated in protection against oxidative stress, proliferation and apoptosis in many cell types, including neurons. We utilized olfactory receptor neurons (ORNs) as a model to define the roles of HO-1 and HO-2 in neuronal development and survival, and to determine the mediators of these effects. The olfactory system is a useful model as ORNs display neurogenesis post-natally and do not contain nitric oxide synthase (NOS) activity, which could confound results. HO isoforms were expressed in ORNs during embryogenesis and post-natally. Mice null for either HO-1 or HO-2 displayed decreased proliferation of neuronal precursors. However, apoptosis was increased only in HO-2 null mice. Cyclic GMP immunostaining was reduced in ORNs in both genotypes, providing direct evidence that HO mediates cGMP production in vivo. Bilirubin immunostaining was reduced only in HO-2 null mice. These roles for HO-1 and HO-2 were confirmed using detergent ablation of the epithelium to observe increased neurogenesis of ORNs after target disruption in HO null mice. Primary cultures of ORNs revealed that proliferative and survival effects of HO were mediated through cGMP and bilirubin, respectively. These results support a role for HO, the CO-cGMP signaling system and bilirubin in neurodevelopment and in response to injury.     

Regulation of microglial migration,phagocytosis, and neurite outgrowth by HO‐1/CO signaling

Clearance of infected and apoptotic neuronal corpses during inflammatory conditions is a fundamental process to create a favorable environment for neuronal recovery. Microglia are the resident immune cells and the predominant phagocytic cells of the CNS, showing a multitude of cellular responses upon activation. Here, we investigated in functional assays how the CO generating enzyme heme oxygenase 1 (HO‐1) influences BV‐2 microglial migration, clearance of debris, and neurite outgrowth of human NT2 neurons. Stimulation of HO‐1 activity attenuated microglial migration in a scratch wound assay, and phagocytosis in a cell culture model of acute inflammation comprising lipopolysaccharide (LPS)‐activated microglia and apoptosis‐induced neurons. Application of a CO donor prevented the production of NO during LPS stimulation, and reduced microglial migration and engulfment of neuronal debris. LPS‐activated microglia inhibited neurite elongation of human neurons without requiring direct cell–cell surface contact. The inhibition of neurite outgrowth was totally reversed by application of exogenous CO or increased internal CO production through supply of the substrate hemin to HO. Our results point towards a vital cytoprotective role of HO‐1/CO signaling after microglial activation. In addition, they support a therapeutic potential of CO releasing chemical agents in the treatment of excessive inflammatory conditions in the CNS. © 2014 Wiley Periodicals, Inc. Develop Neurobiol 75: 854–876, 2015     

Redox regulation and oxidant activation of heme oxygenase-1

The ultraviolet A (UVA, 320–400 nm) component of sunlight has the potential to generate an oxidative stress in cells and tissue so that antioxidants (both endogenous and exogenous) strongly influence the biological effects of UVA. The expression of several genes (including heme oxygenase-1, HO-1; collagenase; the CL100 phosphatase and the nuclear oncogenes, c-fos and c-jun) is induced following physiological doses of UVA to cells and this effect can be strongly enhanced by removing intracellular glutathione or enhancing singlet oxygen lifetime. We have observed that heme is released from microsomal heme-containing proteins by UVA and other oxidants and that activation of HO-1 expression by UVA correlates with levels of heme release. UVA radiation also leads to an increase in labile iron pools (either directly or via HO-1) and eventual increases in ferritin levels. The role of heme oxygenase in protection of skin fibroblasts is probably an emergency inducible defense pathway to remove heme liberated by oxidants. The slower increase in ferritin levels is an adaptive response which serves to keep labile iron pools low and thereby reduce Fenton chemistry and oxidant-induced chain reactions involving lipid peroxidation. In keratinocytes, the primary target of UVA radiation, heme oxygenase levels are constitutively high (because of HO-2 expression). Since there is a corresponding increase in basal levels of ferritin the epidermis appears to be well protected constitutively against the oxidative stress generated by UVA.     

Guanosine stimulates neurite outgrowth in PC12 cells via activation of heme oxygenase and cyclic GMP

Undifferentiated rat pheochromocytoma (PC12) cells extend neurites when cultured in the presence of nerve growth factor (NGF). Extracellular guanosine synergistically enhances NGF-dependent neurite outgrowth. We investigated the mechanism by which guanosine enhances NGF-dependent neurite outgrowth. Guanosine administration to PC12 cells significantly increased guanosine 3,5-cyclic monophosphate (cGMP) within the first 24 h whereas addition of soluble guanylate cyclase (sGC) inhibitors abolished guanosine-induced enhancement of NGF-dependent neurite outgrowth. sGC may be activated either by nitric oxide (NO) or by carbon monoxide (CO). -Nitro-l-arginine methyl ester (l-NAME), a non-isozyme selective inhibitor of nitric oxide synthase (NOS), had no effect on neurite outgrowth induced by guanosine. Neither nNOS (the constitutive isoform), nor iNOS (the inducible isoform) were expressed in undifferentiated PC12 cells, or under these treatment conditions. These data imply that NO does not mediate the neuritogenic effect of guanosine. Zinc protoporphyrin-IX, an inhibitor of heme oxygenase (HO), reduced guanosine-dependent neurite outgrowth but did not attenuate the effect of NGF. The addition of guanosine plus NGF significantly increased the expression of HO-1, the inducible isozyme of HO, after 12 h. These data demonstrate that guanosine enhances NGF-dependent neurite outgrowth by first activating the constitutive isozyme HO-2, and then by inducing the expression of HO-1, the enzymes responsible for CO synthesis, thus stimulating sGC and increasing intracellular cGMP.     

Corticosteroid enhances heme oxygenase-1 production by circulating monocytes by up-regulating hemoglobin scavenger receptor and amplifying the receptor-mediated uptake of hemoglobin-haptoglobin complex

This study examined the relationship between steroid treatment and CD163-mediated downstream pathways linked to inflammatory resolution. Twelve patients referred for congenital heart disease surgery were divided into two groups based on the severity of intravascular hemolysis during cardiopulmonary bypass surgery. Patients with severe intravascular hemolysis were administered haptoglobin during the procedure. Flow cytometry indicated a peak in monocyte CD163 expression on post-operative day 1 in both groups. Enhanced and prolonged heme oxygenase-1 (HO-1) mRNA expression levels were observed in patients who received haptoglobin. Binding of hemoglobin-haptoglobin complex (Hb/Hp) to CD163 resulted in significant induction of HO-1 by peripheral blood mononuclear cells after exposure to dexamethasone prior to culture. This effect was significantly inhibited by anti-CD163 antibody. Our results demonstrated up-regulation of CD163 expression on the monocyte surface by steroid treatment. Steroid treatment was suggested to facilitate CD163-mediated endocytosis of hemoglobin to monocytes/macrophages and thereby induce acceleration of HO-1 synthesis.     

Hydrogen sulfide delays GA-triggered programmed cell death in wheat aleurone layers by the modulation of glutathione homeostasis and heme oxygenase-1 expression

Hydrogen sulfide (H₂S) is considered as a cellular signaling intermediate in higher plants, but corresponding molecular mechanisms and signal transduction pathways in plant biology are still limited. In the present study, a combination of pharmacological and biochemical approaches was used to study the effect of H₂S on the alleviation of GA-induced programmed cell death (PCD) in wheat aleurone cells. The results showed that in contrast with the responses of ABA, GA brought about a gradual decrease of l-cysteine desulfhydrase (LCD) activity and H₂S production, and thereafter PCD occurred. Exogenous H₂S donor sodium hydrosulfide (NaHS) not only effectively blocked the decrease of endogenous H₂S release, but also alleviated GA-triggered PCD in wheat aleurone cells. These responses were sensitive to hypotaurine (HT), a H₂S scavenger, suggesting that this effect of NaHS was in an H₂S-dependent fashion. Further experiment confirmed that H₂S, rather than other sodium- or sulphur-containing compounds derived from the decomposing of NaHS, was attributed to the rescuing response. Importantly, the reversing effect was associated with glutathione (GSH) because the NaHS triggered increases of endogenous GSH content and the ratio of GSH/oxidized GSH (GSSG) in GA-treated layers, and the NaHS-mediated alleviation of PCD was markedly eliminated by l-buthionine-sulfoximine (BSO, a selective inhibitor of GSH biosynthesis). The inducible effect of NaHS was also ascribed to the modulation of heme oxygenase-1 (HO-1), because the specific inhibitor of HO-1 zinc protoporphyrin IX (ZnPP) significantly suppressed the NaHS-related responses. By contrast, the above inhibitory effects were reversed partially when carbon monoxide (CO) aqueous solution or bilirubin (BR), two of the by-products of HO-1, was added, respectively. NaHS-triggered HO-1 gene expression in GA-treated layers was also confirmed. Together, the above results clearly suggested that the H₂S-delayed PCD in GA-treated wheat aleurone cells was associated with the modulation of GSH homeostasis and HO-1 gene expression.     

Hydrogen-rich water regulates cucumber adventitious root development in a heme oxygenase-1/carbon monoxide-dependent manner

Hydrogen gas (H₂) is an endogenous gaseous molecule in plants. Although its reputation is as a “biologically inert gas”, recent results suggested that H₂ has therapeutic antioxidant properties in animals and plays fundamental roles in plant responses to environmental stresses. However, whether H₂ regulates root morphological patterns is largely unknown. In this report, hydrogen-rich water (HRW) was used to characterize H₂ physiological roles and possible signaling transduction pathways in the promotion of adventitious root (AR) formation in cucumber explants. Our results showed that a 50% concentration of HRW was able to mimic the effect of hemin, an inducer of a carbon monoxide (CO) synthetic enzyme, and heme oxygenase-1 (HO-1), in restoring AR formation in comparison with the inhibition effect conferred by auxin-depletion treatment alone. It was further shown that the inducible effect of HRW could be further blocked by the co-treatment with N-1-naphthylphtalamic acid (NPA; an auxin transport inhibitor). The HRW-induced response, at least partially, was HO-1-dependent. This conclusion was supported by the fact that the exposure of cucumber explants to HRW up-regulates cucumber HO-1 gene expression and its protein levels. HRW-mediated induction of representative target genes related to auxin signaling and AR formation, such as CsDNAJ-1, CsCDPK1/5, CsCDC6, CsAUX22B-like, and CsAUX22D-like, and thereafter AR formation (particularly in the AR length) was differentially sensitive to the HO-1 inhibitor zinc protoporphyrin IX (ZnPP). Above blocking actions were clearly reversed by CO, further confirming that the above response was HO-1/CO-specific. However, the addition of a well-known antioxidant, ascorbic acid (AsA), failed to influence AR formation triggered by HRW, thus ruling out the involvement of redox homeostasis in this process. Together, these results indicated that HRW-induced adventitious rooting is, at least partially, correlated with the HO-1/CO-mediated responses. We also suggested that exogenous HRW treatment on plants might be a good option to induce root organogenesis.     

The − 974C>A (rs3087459) gene polymorphism in the endothelin gene (EDN1) is associated with risk of developing acute coronary syndrome in Mexican patients

Endothelial dysfunction plays an essential role in the development and progression of atherosclerotic lesions. Endothelial nitric oxide synthase (eNOS) and endothelin-1 (ET-1) are considered important molecules in the endothelial dysfunction process. The aim of the present study was to evaluate the role of eNOS and ET-1 (EDN1) gene polymorphisms as susceptibility markers for acute coronary syndrome (ACS). Six polymorphisms (rs1799983, rs2070744, rs1800783, rs3087459, rs1800541, and rs5369) of eNOS and EDN1 genes were analyzed by 5′ exonuclease TaqMan genotyping assays in a group of 452 patients with ACS and 283 healthy controls. The results showed increased frequencies of the A allele of the END1-914 C>A (rs3087459) polymorphism in ACS patients when compared to controls (OR = 1.56, Pc = 0.01). Under an additive model, the “AA” genotype was associated with an increased risk of developing ACS, adjusted for gender, hypertension, dyslipidemia, alcohol consumption, smoking, and diabetes (OR = 1.56, p = 0.045). Linkage disequilibrium analysis showed one EDN1 haplotype (AT) with increased frequency in ACS patients when compared to healthy controls (OR = 1.65, Pc = 0.0015). The “AT” haplotype was associated with the risk of developing ACS after adjusting for cardiovascular risk factors using multiple logistic analysis. In this case, the adjusted OR was 1.73 for the AT haplotype (Pc = 0.0018). In summary, resulting data suggest that the END1-914 C>A gene polymorphism could be involved in the risk of developing ACS in Mexican individuals.     

Biotechnological challenges of bioartificial kidney engineering

With the world-wide increase of patients with renal failure, the development of functional renal replacement therapies have gained significant interest and novel technologies are rapidly evolving. Currently used renal replacement therapies insufficiently remove accumulating waste products, resulting in the uremic syndrome. A more preferred treatment option is kidney transplantation, but the shortage of donor organs and the increasing number of patients waiting for a transplant warrant the development of novel technologies. The bioartificial kidney (BAK) is such promising biotechnological approach to replace essential renal functions together with the active secretion of waste products. The development of the BAK requires a multidisciplinary approach and evolves at the intersection of regenerative medicine and renal replacement therapy. Here we provide a concise review embracing a compact historical overview of bioartificial kidney development and highlighting the current state-of-the-art, including implementation of living-membranes and the relevance of extracellular matrices. We focus further on the choice of relevant renal epithelial cell lines versus the use of stem cells and co-cultures that need to be implemented in a suitable device. Moreover, the future of the BAK in regenerative nephrology is discussed.