Heme oxygenase and heme degradation

The microsomal heme oxygenase system consists of heme oxygenase (HO) and NADPH-cytochrome P450 reductase, and plays a key role in the physiological catabolism of heme which yields biliverdin, carbon monoxide, and iron as the final products. Heme degradation proceeds essentially as a series of autocatalytic oxidation reactions involving heme bound to HO. Large amounts of HO proteins from human and rat can now be prepared in truncated soluble form, and the crystal structures of some HO proteins have been determined. These advances have greatly facilitated the understanding of the mechanisms of individual steps of the HO reaction. HO can be induced in animals by the administration of heme or several other substances; the induction is shown to involve Bach1, a translational repressor. The induced HO is assumed to have cytoprotective effects. An uninducible HO isozyme, HO-2, has been identified, so the authentic HO is now called HO-1. HOs are also widely distributed in invertebrates, higher plants, algae, and bacteria, and function in various ways according to the needs of individual species.     

Involvement of heme oxygenase as antioxidant defense in soybean nodules

Objective: We have previously demonstrated that the inducible form of heme oxygenase plays a critical role in protecting against oxidative stress in mammals. To gain further insight into the functions of this enzyme in plants, we have tested its activity and expression in soybean nodules subjected to cadmium (Cd) stress.

Materials and methods: Four-weeks-old soybean nodulated plants were treated with different cadmium chloride concentrations (0, 50 and 200 μM) during 48 h. Oxidative stress parameters such as TBARS content, GSH levels and antioxidant enzyme activities were measured as well as heme oxygenase activity and expression. Besides, the effect of biliverdin and Zn-protophorphyrin IX were analized.

Results: Treatment with 200 μM Cd during 48 h caused a 67% increase in TBARS content, whereas GSH decreased 44%, and total superoxide dismutase, gluthatione reductase and guaiacol peroxidase were also inhibited 54, 20 and 60%, respectively. A total of 200 μM Cd produced the overexpression of heme oxygenase-1, as well as a 10-fold enhancement of its activity. Co-administration of biliverdin (10 μM) completely prevented the effects caused by Cd. Treatment with Zn protoporphyrin IX, a strong inhibitor of heme oxygenase, expectedly decreased heme oxygenase-1 activity to half. When the inhibitor was given together with Cd, completely prevented the enzyme induction and oxidative stress parameters were significantly enhanced.

Conclusion: Taking together, these results are indicating that heme oxygenase plays a protective role against oxidative cell damage in soybean nodules.     

Heme oxygenase activity increases after exercise in healthy volunteers

Heme oxygenase (HO) is an essential, rate-limiting protein which catalyses the breakdown of heme to iron, carbon monoxide (CO), and biliverdin. The alpha methene bridge of the heme is eliminated as CO which can be measured as blood carboxyhaemoglobin (COHb). Using blood concentrations of COHb as a measure reflecting HO activity, we tested the postulate that the activity of HO changes with exercise. Ten healthy, nonsmoking volunteers (5 females and 5 males with a mean age?±?standard deviation of 25.7?±?3.2 years), lifetime nonsmokers with no history of respiratory diseases and not taking any medication, were included in the study. Subjects were exposed to filtered air for 2?hrs while alternating exercise for 15?minutes on a cycle ergometer with rest for 15?minutes. Workload was adjusted so that subjects breathed at a ventilatory rate, normalised for body surface area, of 25?L/m²/minute. Immediately before, immediately after, and the day following exercise, blood was drawn by standard venipuncture technique. COHb was determined using the interleukin (IL) 682 Co-Oximeter (Instrumentation Laboratory, Bedford, MA). COHb increased in each participant during the exercise session with the mean value (± standard deviation) almost doubling (1.1?±?1.6 to 2.1?±?1.6%) and returned to baseline by the following day (1.3?±?1.3%). We conclude that exercise increases HO activity.     

Intracellular accumulation of bilirubin as a defense mechanism against increased oxidative stress

Antioxidant, anti-inflammatory and anti-atherogenic effects have been associated with elevations of unconjugated bilirubin (UCB) in serum and with the induction of heme oxygenase-1 (HO-1), the rate-limiting enzyme in UCB synthesis. The aim of this study was to investigate the intracellular metabolism and antioxidant properties of UCB in human hepatoblastoma HepG2 cells and tissues of Wistar rats exposed to oxidative stressors and lipopolysaccharide (LPS), respectively. Intracellular UCB concentrations in HepG2 cells correlated with its levels in culture media (p < 0.001) and diminished lipid peroxidation in a dose-dependent manner (p < 0.001). Moreover, induction of HO-1 with sodium arsenite led to 2.4-fold (p = 0.01) accumulation of intracellular UCB over basal level while sodium azide-derived oxidative stress resulted in a 60% drop (p < 0.001). This decrease was ameliorated by UCB elevation in media or by simultaneous induction of HO-1. In addition, hyperbilirubinemia and liver HO-1 induction in LPS-treated rats resulted in a 2-fold accumulation of tissue UCB (p = 0.01) associated with enhanced protection against lipid peroxidation (p = 0.02). In conclusion, hyperbilirubinemia and HO-1 induction associated with inflammation and oxidative stress increase intracellular concentrations of UCB, thus enhancing the protection of cellular lipids against peroxidation. Therefore, the previously reported protective effects of hyperbilirubinemia and HO-1 induction are at least in part due to intracellular accumulation of UCB.     

Regulation of heme oxygenase expression by alcohol, hypoxia and oxidative stress

AIM:To study the effect of both acute and chronic alcohol exposure on heme oxygenases(HOs) in the brain,liver and duodenum.METHODS:Wild-type C57BL/6 mice,heterozygous Sod2 knockout mice,which exhibit attenuated manganese superoxide dismutase activity,and liver-specific ARNT knockout mice were used to investigate the role of alcohol-induced oxidative stress and hypoxia.For acute alcohol exposure,ethanol was administered in the drinking water for 1 wk.Mice were pair-fed with regular or ethanol-containing Lieber De Carli liquid diets for 4 wk for chronic alcohol studies.HO expression was analyzed by real-time quantitative polymerase chain reaction and Western blotting.RESULTS:Chronic alcohol exposure downregulated HO-1 expression in the brain but upregulated it in the duodenum of wild-type mice.It did not alter liver HO-1 expression,nor HO-2 expression in the brain,liver or duodenum.In contrast,acute alcohol exposure decreased both liver HO-1 and HO-2 expression,and HO-2 expression in the duodenum of wild-type mice.The decrease in liver HO-1 expression was abolished in ARNT+/-mice.Sod2+/-mice with acute alcohol exposure did not exhibit any changes in liver HO-1 and HO-2 expression or in brain HO-2 expression.However,alcohol inhibited brain HO-1 and duodenal HO-2 but increased duodenal HO-1 expression in Sod2+/-mice.Collectively,these findings indicate that acute and chronic alcohol exposure regulates HO expression in a tissue-specific manner.Chronic alcohol exposure alters brain and duodenal,but not liver HO expression.However,acute alcohol exposure inhibits liver HO-1 and HO-2,and also duodenal HO-2 expression.CONCLUSION:The inhibition of liver HO expression by acute alcohol-induced hypoxia may play a role in the early phases of alcoholic liver disease progression.     

Decreased expression of heme oxygenase is associated with depressive symptoms and may contribute to depressive and hypertensive comorbidity

Background: There is strong evidence that hypertension and depression are comorbid and oxidative stress is implicated in both pathologies. We aimed to elucidate the relationship between biochemical markers of the antioxidant-pro-oxidant equilibrium and depression in hypertension.

Methods: Blood was collected from patients diagnosed with depression, hypertension, or comorbid depression and hypertension and healthy age- and sex-matched controls. Whole blood reduced glutathione, erythrocyte superoxide dismutase (SOD-1), glutathione peroxidase (GPx-1), glutathione reductase (GR), malondialdehyde (MDA), and plasma hydrogen peroxide (H₂O₂) were assayed using spectrophotometry, and heme oxygenase (HO-1) levels were determined immunoenzymatically.

Results: Both hypertension and depression were associated with altered antioxidant-pro-oxidant profiles. Decreased GPx-1 and SOD-1 activities, increased GR activity, increased levels of GSH, and increased concentrations of MDA and H₂O₂ were observed in patients compared to controls. Inducible HO-1 was specifically decreased in patients with depression and was significantly associated with both the prevalence and severity of depressive symptoms.

Conclusions: Heme oxygenase is a biological factor that might explain the relationship between inflammation, oxidative stress, and the biological and functional changes in brain activity in depression. HO-1 is a candidate depression biomarker and provides an avenue for novel preventative and diagnostic strategies against this disease.     

Heme oxygenase expression in human central nervous system disorders

In the normal mammalian CNS, heme oxygenase-2 (HO-2) is constitutively, abundantly, and fairly ubiquitously expressed, whereas heme oxygenase-1 (HO-1) mRNA and protein are confined to small populations of scattered neurons and neuroglia. Unlike ho-2, the ho-1 gene in neural (and many systemic) tissues is exquisitely sensitive to upregulation by a host of pro-oxidant and other noxious stimuli. In Alzheimer disease, HO-1 immunoreactivity is significantly augmented in neurons and astrocytes of the hippocampus and cerebral cortex relative to age-matched, nondemented controls and colocalizes to senile plaques, neurofibrillary tangles, and corpora amylacea. In Parkinson disease, HO-1 decorates Lewy bodies of affected dopaminergic neurons and is highly overexpressed in astrocytes residing within the substantia nigra. The ho-1 gene is also upregulated in glial cells within multiple sclerosis plaques; in the vicinity of human cerebral infarcts, hemorrhages, and contusions; and in various other degenerative and nondegenerative human CNS disorders. The products of the heme oxygenase reaction, free ferrous iron, carbon monoxide, and biliverdin/bilirubin, are all biologically active molecules that may profoundly influence tissue redox homeostasis under a wide range of pathophysiological conditions. Evidence adduced from whole animal and in vitro studies indicates that enhanced HO-1 activity may either ameliorate or exacerbate neural injury, effects likely contingent upon the specific model employed, the duration and intensity of HO-1 induction, and the chemistry of the local redox microenvironment. HO-1 hyperactivity also promotes mitochondrial sequestration of nontransferrin iron in oxidatively challenged astroglia and may thereby contribute to the pathological iron deposition and bioenergetic failure amply documented in aging and degenerating human neural tissues.     

Ethylene perception inhibitor 1-MCP decreases oxidative damage of leaves through enhanced antioxidant defense mechanisms in soybean plants grown under high temperature stress

Ethylene is a stress hormone involved in early senescence and abscission of vegetative and reproductive organs under stress conditions. Ethylene perception inhibitors can minimize the impact of ethylene-mediated stress. The effects of high temperature (HT) stress during flowering on ethylene production rate in leaf, flower and pod and the effects of ethylene inhibitor on ethylene production rate, oxidative damage and physiology of soybean are not understood. We hypothesize that HT stress induces ethylene production, which causes premature leaf senescence and flower and pod abscission, and that application of the ethylene perception inhibitor 1-Methyl cyclopropene (1-MCP) can minimize HT stress induced ethylene response in soybean. The objectives of this study were to (1) determine whether ethylene is produced in HT stress; (2) quantify the effects of HT stress and 1-MCP application on oxidative injury; and (3) evaluate the efficacy of 1-MCP at minimizing HT-stress-induced leaf senescence and flower abscission. Soybean plants were exposed to HT (38/28 °C) or optimum temperature (OT; 28/18 °C) for 14 d at flowering stage (R2). Plants at each temperature were treated with 1-MCP (1 μg L⁻¹) gas for 5 h or left untreated (control). High temperature stress increased rate of ethylene production in leaves, flowers and pods, production of reactive oxygen species (ROS), membrane damage, and total soluble carbohydrate content in leaves and decreased photosynthetic rate, sucrose content, F_v/F_m ratio and antioxidant enzyme activities compared with OT. Foliar spray of 1-MCP decreased rate of ethylene production and ROS and leaf senescence traits but enhanced antioxidant enzyme activities (e.g. superoxide dismutase and catalase). In conclusion, HT stress increased ethylene production rates, caused oxidative damage, decreased antioxidant enzyme activity, caused premature leaf senescence, increased flower abscission and decreased pod set percentage. Application of 1-MCP lowered ethylene and ROS production, enhanced antioxidant enzyme activity, increased membrane stability, delayed leaf senescence, decreased flower abscission and increased pod set percentage. The beneficial effects of 1-MCP were greater under HT stress compared to OT in terms of decreased ethylene production, decreased ROS production, increased antioxidant protection, decreased flower abscission and increased pod set percentage.     

Heme oxygenase 1: a novel oncogene in multiple gynecological cancers

Heme oxygenase 1 (HO-1), also known as heat shock protein 32 (HSP32), is a stress-inducible enzyme. In the past, it was believed to participate in maintaining cell homeostasis, reducing oxidative stress damage and exerting anti-apoptotic effects. When exposed to noxious stimulation, the expression of HO-1 in the body will increase, antagonizing these oxidative stresses and protecting our bodies. Recently, many studies showed that HO-1 was also highly-expressed in multiple gynecological cancers (such as ovarian cancer, cervical cancer and endometrial cancer), suggesting that it should be closely related to cell proliferation, metastasis, immune regulation and angiogenesis as an oncogene. This review summarizes the different effects of HO-1 under normal and diseased conditions with a brief discussion of its implications on the diagnosis and treatment of gynecological cancers, aiming to provide a new clue for prevention and treatment of diseases.     

Intracellular redistribution of heme in rat liver under oxidative stress: the role of heme synthesis

Heme distribution in subcellular fractions of rat liver was studied first hours under the action of several agents causing oxidative stress in vivo. Total and post-mitochondrial heme content in liver was found to depend on both the level of hemolysis products in blood and agent's capacity to modify heme and hemoproteins. The increase of activity of 5-aminolevulinate synthase (ALAS) and/or heme accumulation in mitochondria was accompanied by increase of tryptophan-2,3-dioxygenase (TDO) heme saturation. Membrane stabilisation by tocopherol or prevention of early ALAS induction by cycloheximide prevented both mitochondrial heme accumulation and increase of TDO heme saturation. Modification of heme fully prevented the alterations of total heme content even under severe hemolysis as well as the increase of TDO heme saturation if no increase of heme synthesis occurred. Thus heme synthesis can greatly contribute to heme intracellular redistribution under oxidative stress.     

Heme oxygenase induction by menadione bisulfite adduct-generated oxidative stress in rat liver

The in vivo effect of menadione bisulfite adduct on both hepatic oxidative stress and heme oxygenase induction was studied. A marked increase in lipid peroxidation was observed 1 h after menadione bisulfite adduct administration. To evaluate liver antioxidant enzymatic defenses, superoxide dismutase, catalase and glutathione peroxidase activities were determined. Antioxidant enzymes significantly decreased 3 h after menadione bisulfite adduct injection. Heme oxygenase activity appeared 6 h after treatment, peaking 9 h after menadione bisulfite adduct administration. Such induction was preceded by a decrease in the intrahepatic GSH pool and an increase in hydrogen peroxide steady-state concentration, both effects taking place some hours before induction of heme oxygenase. Iron ferritin levels and ferritin content began to increase 6 h after heme oxygenase induction, and these increases were significantly higher 15 h after treatment and remained high for at least 24 h after menadione bisulfite adduct injection. Administration of bilirubin entirely prevented heme oxygenase induction as well as the decrease in hepatic GSH and the increase in lipid peroxidation when administered 2 h before menadione bisulfite adduct treatment. These results indicate that the induction of heme oxygenase by menadione bisulfite adduct may be a general response to oxidant stress, by increasing bilirubin and ferritin levels and could therefore provide a major cellular defense mechanism against oxidative damage.     

Brain microvascular and intracranial artery resistance to atherosclerosis is associated with heme oxygenase and ferritin in Japanese quail

Oxidative stress and increased oxidation of low-density lipoprotein (oxLDL) through free radical-mediated tissue injury may be important factors in the development of extracranial atherosclerotic lesions. However, the roles of oxidative stress and hypercholesterolemia in intracranial atherosclerosis is less established. The induction of heme oxygenase (HO) is a cellular response to oxidative stress, and inducible HO (HO-1) may protect against oxidized lipids such as those produced by oxidative stress. We investigated the effects of oxLDL on cell and tissue viability, HO-1 and ferritin expression in extracranial and intracranial endothelial cells, and the arteries of cholesterol-induced atherosclerosis (CIA) Japanese quail. We report that cultured microvascular endothelial cells from the brain (QBMEC) and carotid (QCEC) differ in their response to oxidative stress. The QCECs are less responsive than QBMECs to oxidative stress induced by oxLDL, as evident by lower expression of HO-1 mRNA, HO activity, and ferritin levels. Furthermore, the higher levels of catalytic iron, thiobarbituric acid reactive substances, and lactate dehydrogenase released in QCECs indicated that these cells are more susceptible to oxidative stress than QBMECs. We also investigated the relationship between extent of atherosclerotic plaque deposition and the extracranial and intracranial arterial expression of HO-1 in quail. The common carotid and vertebral (extracranial) arteries had higher tissue cholesterol levels (starting at 2 weeks of cholesterol-supplementation) and a greater atherosclerotic plaque score (starting at 4 weeks of cholesterol-supplementation) compared with middle cerebral and basilar (intracranial) arteries, and this may be relevant to the effect of aging on the process of atherogenesis. The extracranial arteries also had early and greater levels of lipid peroxidation and catalytic iron coupled with lower expression of HO-1 protein, HO activity, and ferritin compared to the intracranial vessels. These observations suggest that the extracranial and intracranial arterial walls respond differently to oxidation of lipoproteins, and support the feasibility of increased HO-1 expression as a means of protection against oxidant injury.     

脑血红素加氧酶系统的作用研究

血红素加氧酶（HO）是降解血红素的微粒体酶系统,催化降解血红素生成一氧化碳（CO）、胆绿素和铁离子,同工酶HO-1和HO-2广泛分布于脑中,具有不同的调控机制,可能发挥着调节NO水平,抗氧化应激,参与神经元退行性变等重要作用。     

Oxidative stress and damage in liver, but not in brain, of Fischer 344 rats subjected to dietary iron supplementation with lipid-soluble [(3,5,5-trimethylhexanoyl)ferrocene

Accumulation of iron probably predisposes the aging brain to progressive neuronal loss. We examined various markers of oxidative stress and damage in the brain and liver of 3- and 24-month-old rats following supplementation with the lipophilic iron derivative [(3,5,5-trimethylhexanoyl)ferrocene] (TMHF), which is capable of crossing the blood-brain barrier. At both ages, iron concentration increased markedly in the liver but failed to increase in the brain. In the liver of TMHF-treated young rats, levels of alpha- and gamma-tocopherols and glutathione (GSH) were also higher. In contrast, the brain displayed unaltered levels of the tocopherols and GSH. Malondialdehyde (MDA) level was also higher in the cerebrospinal fluid (CSF) and the liver but not in the brain. In old rats, the absence of an increase in iron concentration in the brain was reflected by unaltered concentrations of GSH, tocopherols, and MDA as compared to that in untreated rats. In the aging liver, concentrations of GSH and MDA increased with TMHF treatment. Morphological studies revealed unaltered levels of iron, ferritin, heme oxygenase-1 (HO-1), nitrotyrosine (NT), or MDA in the brains of both young and old rats treated with TMHF. In contrast, TMHF treatment increased the level of HO-1 in Kupffer cells, NT in hepatic endothelial cells, and MDA and ferritin in hepatocytes. Although these results demonstrated an increase in the biochemical markers of oxidative stress and damage in response to increasing concentrations of iron in the liver, they also demonstrated that the brain is well protected against dietary iron overload by using iron in a lipid-soluble formulation.