The different facets of heme-oxygenase 1 in innate and adaptive immunity

Heme oxygenase (HO) enzymes are responsible for the main oxidative step in heme degradation, generating equimolar amounts of free iron, biliverdin and carbon monoxide. HO-1 is induced as a crucial stress response protein, playing protective roles in physiologic and pathological conditions, due to its antioxidant, anti-apoptotic and anti-inflammatory effects. The mechanisms behind HO-1-mediated protection are being explored by different studies, affecting cell fate through multiple ways, such as reduction in intracellular levels of heme and ROS, transcriptional regulation, and through its byproducts generation. In this review we focus on the interplay between HO-1 and immune-related signaling pathways, which culminate in the activation of transcription factors important in immune responses and inflammation. We also discuss the dual interaction of HO-1 and inflammatory mediators that govern resolution and tissue damage. We highlight the dichotomy of HO-1 in innate and adaptive immune cells development and activation in different disease contexts. Finally, we address different known anti-inflammatory pharmaceuticals that are now being described to modulate HO-1, and the possible contribution of HO-1 in their anti-inflammatory effects.

Haem oxygenases play a pivotal role in placental physiology and pathology

BACKGROUND

Haem oxygenases (HO) catabolise haem, which is the prosthetic group of numerous haemoproteins. Thus, multiple primary cellular pathways and functions rely on haem availability. HO exists in two isoforms, both expressed in the placenta, namely HO-1 and HO-2, the first being inducible. Haem oxygenases, particularly HO-1, have garnered specific interest in the field of physiological and pathological placental function. These enzymes mediate haem degradation by cleaving the alpha methene bridge to produce biliverdin, which is subsequently converted to bilirubin, carbon monoxide and iron. HO-1 has anti-inflammatory and antioxidant activities.

SEARCH METHODS

An initial literature analysis was performed using PubMed on 3 October 2018 using key terms such as 'haem oxygenase and pregnancy', 'haem oxygenase and placenta', 'HO-1 and pregnancy', 'HO-1 and placenta', 'HO and placenta', 'HO and pregnancy', 'genetic variant and HO', 'CO and pregnancy', 'CO and placenta', 'Bilirubin and pregnancy', 'Iron and pregnancy' and 'PPAR and Haem', selecting consensus conferences, recommendations, meta-analyses, practical recommendations and reviews. A second literature analysis was performed, including notable miscarriages, foetal loss and diabetes mellitus, on 20 December 2019. The three authors studied the publications independently to decipher whether they should be included in the manuscript.

OBJECTIVE AND RATIONALE

This review aimed to summarise current pieces of knowledge of haem oxygenase location, function and regulation in the placenta, either in healthy pregnancies or those associated with miscarriages and foetal loss, pre-eclampsia, foetal growth restriction and diabetes mellitus.

OUTCOMES

HO-1 exerts some protective effects on the placentation, probably by a combination of factors, including its interrelation with the PGC-1α/PPAR pathway and the sFlt1/PlGF balance, and through its primary metabolites, notably carbon monoxide and bilirubin. Its protective role has been highlighted in numerous pregnancy conditions, including pre-eclampsia, foetal growth restriction, gestational diabetes mellitus and miscarriages.

WIDER IMPLICATIONS

HO-1 is a crucial enzyme in physiological and pathological placentation. This protective enzyme is currently considered a potential therapeutic target in various pregnancy diseases.

Oxidative stress-mediated hepatotoxicity in rats induced by ethanol extracts of different parts of Chloranthus serratus

CONTEXT

Chloranthus serratus (Thunb.) Roem. et Schult. (Chloranthaceae) is an herb widely used as a folk medicine treating inflammatory diseases, although it is toxic.

OBJECTIVE

To investigate hepatotoxicity and related mechanisms induced by ethanol extracts of different parts of C. serratus in rats.

MATERIALS AND METHODS

Sprague Dawley rats were divided into control (Con), ethanol extract of roots (ER), stems (ES), and leaves (EL) groups, and acute oral toxicity studies were conducted. The rats received doses of 4.14, 3.20, and 1.16 g/kg/d extracts for 14 days, respectively. Liver index, liver function and oxidative stress biomarkers, liver pathology, ultrastructure, TNF-α, ICAM-1, and Nrf2/HO-1 proteins expression levels were determined.

RESULTS

The LD₅₀ of ER, ES, and EL were higher than 10.35, 8.05, and 2.90 g/kg/p.o., respectively. The liver indexes in the extract groups increased significantly. EL dramatically increased TP, GLB, AST, ALT, ALP, TBA, MDA, ICAM-1, and TNF-α levels (p < 0.01), and induced the most obvious pathological and ultrastructural changes. ES and EL obviously decreased the T-SOD, GSH, CAT, and CHOL levels. Nrf2 and HO-1 proteins expression was reduced significantly in ES (0.77 ± 0.06, 2.33 ± 0.20) and EL (0.23 ± 0.04, 2.14 ± 0.16) groups, and reduced slightly in ER (1.08 ± 0.10; 3.39 ± 0.21) group.

DISCUSSION AND CONCLUSION

ES and EL induce stronger hepatotoxicity than ER through oxidative stress and the Nrf2/HO-1 pathway, and the root is a better medicinal part, which provides a basis for clinical research, safe applications, and reasonable development of C. serratus.

The Effects of Exercise Training and High Triglyceride Diet in an Estrogen Depleted Rat Model: The Role of the Heme Oxygenase System and Inflammatory Processes in Cardiovascular Risk

Cardiovascular morbidity and mortality of premenopausal women are significantly lower compared to men of similar age. However, this protective effect evidently decreases after the onset of menopause. We hypothesized that physical exercise could be a potential therapeutic strategy to improve inflammatory processes and cardiovascular antioxidant homeostasis, which can be affected by the loss of estrogen and the adverse environmental factors, such as overnutrition. Ovariectomized (OVX, n= 40) and sham-operated (SO, n= 40) female Wistar rats were randomized to exercising (R) and non-exercising (NR) groups. Feeding parameters were chosen to make a standard chow (CTRL) or a high triglyceride diet (HT) for 12 weeks. Aortic and cardiac heme oxygenase (HO) activity and HO-1 concentrations significantly decreased in all of the NR OVX and SO HT groups. However, the 12-week physical exercise was found to improve HO-1 values. Plasma IL-6 concentrations were higher in the NR OVX animals and rats fed HT diet compared to SO CTRL rats. TNF-α concentrations were significantly higher in the NR OVX groups. 12 weeks of exercise significantly reduced the concentrations of both TNF-α and IL-6 compared to the NR counterparts. The activity of myeloperoxidase enzyme (MPO) was significantly increased as a result of OVX and HT diet, however voluntary wheel-running exercise restored the elevated values. Our results show that estrogen deficiency and HT diet caused a significant decrease in the activity and concentration of HO enzyme, as well as the concentrations of TNF-α, IL-6, and the activity of MPO. However, 12 weeks of voluntary wheel-running exercise is a potential non-pharmacological therapy to ameliorate these disturbances, which determine the life expectancy of postmenopausal women.

Heme oxygenase-1 protects spinal cord neurons from hydrogen peroxide-induced apoptosis via suppression of Cdc42/MLK3/MKK7/JNK3 signaling

The mechanisms by which oxidative stress induces spinal cord neuron death has not been completely understood. Investigation on the molecular signal pathways involved in oxidative stress-mediated neuronal death is important for development of new therapeutics for oxidative stress-associated spinal cord disorders. In current study we examined the role of heme oxygenase-1 (HO-1) in the modulation of MLK3/MKK7/JNK3 signaling, which is a pro-apoptotic pathway, after treating primary spinal cord neurons with H2O2. We found that MLK3/MKK7/JNK3 signaling was substantially activated by H2O2 in a time-dependent manner, demonstrated by increase of activating phosphorylation of MLK3, MKK7 and JNK3. H2O2 also induced expression of HO-1. Transduction of neurons with HO-1-expressing adeno-associated virus before H2O2 treatment introduced expression of exogenous HO-1 in neurons. Exogenous HO-1 reduced phosphorylation of MLK3, MKK7 and JNK3. Consistent with its inhibitory effect on MLK3/MKK7/JNK3 signaling, exogenous HO-1 decreased H2O2-induced neuronal apoptosis and necrosis. Furthermore, we found that exogenous HO-1 inhibited expression of Cdc42, which is crucial for MLK3 activation. In addition, HO-1-induced down-regulation of MLK3/MKK7/JNK3 signaling might be related to up-regulation of microRNA-137 (mir-137). A mir-137 inhibitor alleviated the inhibitory effect of HO-1 on JNK3 activation. This inhibitor also increased neuronal death even when exogenous HO-1 was expressed. Therefore, our study suggests a novel mechanism by which HO-1 exerted its neuroprotective efficacy on oxidative stress.

Reciprocal regulation of carbon monoxide metabolism and the circadian clock

Circadian clocks are cell-autonomous oscillators regulating daily rhythms in a wide range of physiological, metabolic and behavioral processes. Feedback of metabolic signals, such as redox state, NAD+/NADH and AMP/ADP ratios, or heme, modulate circadian rhythms and thereby optimize energy utilization across the 24-h cycle. We show that rhythmic heme degradation, which generates the signaling molecule carbon monoxide (CO), is required for normal circadian rhythms as well as circadian metabolic outputs. CO suppresses circadian transcription by attenuating CLOCK-BMAL1 binding to target promoters. Pharmacological inhibition or genetic depletion of CO-producing heme oxygenases abrogates normal daily cycles in mammalian cells and Drosophila. In mouse hepatocytes, suppression of CO production leads to a global upregulation of CLOCK-BMAL1-dependent circadian gene expression and dysregulated glucose metabolism. Together, our findings show that CO metabolism is an important link between the basic circadian-clock machinery, metabolism and behavior.

Update on Endovascular Treatment of Cerebrovascular Diseases

Several developments in endovascular technology have greatly expanded the application of these techniques to treat extra- and intracranial cerebrovascular diseases. This review explores the indications, techniques, and clinical results for endovascular treatment of ischemic stroke and intracranial stenoses, aneurysms, and arteriovenous malformations.

Heme Oxygenase-1 Mediates Up-Regulation of Adhesion Molecule Expression Induced by Peroxynitrite in Endothelial Cells

OBJECTIVE

Endothelial cell (EC) activation with up-regulation of cellular adhesion molecule (CAM) expression is a pathophysiologic feature in preeclampsia (PE). Enhanced peroxynitrite formation in the vasculature of women with PE was also reported. This study was to test whether EC oxidative stress induced by peroxynitrite could up-regulate EC CAM expression, and whether heme oxygenase-1 (HO-1) has protective effects on this peroxynitrite-induced cellular response.

METHODS

Confluent ECs were stimulated with 3-morpholinosydnonimine-HCl (SIN-1, a peroxynitrite generator) alone or combined with Mn(III) tetrakis (1-methyl-4-pyridyl) porphyrin pentachloride (MnTMPyP, a peroxynitrite scavenger) up to 4 hours. EC surface protein expressions for ICAM, VCAM, P-selectin, and E-selectin were measured by colorimetric assay. ECs were also treated with Sn(IV) mesophorphyrin IX dichloride (SnMP, a HO-1 inhibitor) to determine if HO-1 was involved in the increased CAM expression in stressed cells. Protein and mRNA expressions for HO-1 were determined by Western blot analysis and reverse-transcriptase polymerase chain reaction (RT-PCR). Data are presented as the mean +/- SE and analyzed by analysis of variance (ANOVA).

RESULTS

Endothelial CAM expressions for VCAM, P-selectin, and E-selectin, but not ICAM, were significantly increased in SIN-1-treated ECs. Protein and mRNA expressions for HO-1 were also up-regulated in cells treated with SIN-1. MnTMPyP blocked both mRNA and protein expressions for HO-1, whereas SnMP only blocked HO-1 protein expression. Both MnTMPyP and SnMP abolished SIN-1-induced up-regulation of VCAM, P-selectin, and E-selectin expression in ECs.

CONCLUSIONS

Peroxynitrite-induced EC oxidative stress produces differential effects on CAM expression, which may be mediated by HO-1 regulation. Our results suggest that increased peroxynitrite formation in the maternal vasculature may contribute to the increased CAM expression and enhanced neutrophil-endothelial interaction associated with PE.

Signaling function of heme oxygenase proteins

SIGNIFICANCE

Many reports have underscored the importance of the heme degradation pathway that is regulated by heme oxygenase (HO). This reaction releases bile pigments and carbon monoxide (CO), which are important antioxidant and signaling molecules. Thus, the reaction of HO-1 would have significant cytoprotective effects. Nevertheless, the importance of this protein goes beyond its enzymatic action. New evidence outlines significant effects of inactive forms of the HO-1 protein.

RECENT ADVANCES

In fact, the role of the HO protein in cellular signaling, including transcription factor activation, binding to proteins, phosphorylation, and modulation of protein function, among others, has started being elucidated. The mechanism by which the inducible form of HO-1, in particular, can migrate to various cellular compartments to mediate important signaling or how and why it binds to key transcription factors and other proteins that are important in DNA repair is also described in several physiologic systems.

CRITICAL ISSUES

The signaling functions of HO-1 may have particular relevance in clinical circumstances, including cancer, as redistribution of HO-1 into the nuclear compartment is observed with cancer progression and metastasis. In addition, along with oxidative stress, the pleiotropic functions of HO-1 modulate antioxidant defense. In organ transplantation, HO and its byproducts suppress rejection at multiple levels and in sepsis-induced pulmonary dysfunction, inhaled CO or modulation of HO activity can change the course of the disease in animals.

FUTURE DIRECTIONS

It is hoped that a more detailed understanding of the various signaling functions of HO will guide therapeutic approaches for complex diseases.

[Roles of heme oxygenase-1 promoting regeneration of peribiliary vascular plexus in bile duct ischemia/reperfusion injury]

OBJECTIVE

To study the effect of heme oxygenase-1 (HO-1) on peribiliary vascular plexus (PVP) in rat bile duct ischemia/reperfusion injury.

METHODS

Total 128 male SD rats were randomly divided into saline group (Saline), empty virus group (Adv), induced group (Adv-HO-1) and suppressed group (HO-1 siRNA), and there were 32 rats in each group. Rats were injected using 0.5 ml of saline, empty adenovirus, HO-1 adenovirus and siRNA adenovirus (2×10(9) TU/rat) via the dorsal penile vein 24 hours before surgery. Liver function was analyzed at 1 hour and 1, 7, 14 days after reperfusion. HO-1, hypoxiainducible factor-1α (HIF-1α), stromal cell derived factor-1α (SDF-1α) and vascular endothelial growth factor (VEGF) protein content was analyzed by Western blot. The endothelial progenitor cells (EPCs) ratio in the liver and peripheral blood was detected by flow cytometry. Small vascular around the bile duct was observed by α-smooth muscle actin and von Willebrand factor double immunofluorescence staining.

RESULTS

Reduced liver injury and higher expression of HIF-1α, SDF-1α and VEGF in the induced group after surgery (q = 5.68-7.52, P < 0.01). EPCs ratio in the liver and peripheral blood was significantly higher in the induced group than saline group (q = 12.14 and 15.26, P < 0.01), and the suppressed group at 7 days after surgery were less than saline group significantly (q = 4.83 and 5.07, P < 0.01). In comparison to the suppressed group, higher density of small vascular around the bile duct was seen in the liver tissue of induced group.

CONCLUSIONS

HO-1 can induce the expression of HIF-1α, SDF-1α and VEGF, and mobilize the release of EPCs to the peripheral from the bone marrow. EPCs migrate to the liver and promote damaged PVP repair and regeneration.

[Expression of heme oxygenase-1 and inducible nitric oxide synthase in the lungs of hyperoxia-exposed preterm rats]

OBJECTIVE

To study the expression and the role of heme oxygenase-1 (HO-1) and inducible nitric oxide synthase (iNOS) in preterm rats with hyperoxia-induced lung injuries.

METHODS

Sixty-four three-day-old preterm Sprague-Dawley rats were randomly assigned to a hyperoxia group (90% oxygen exposure) and a control group (room air exposure), with 32 rats in each group. After 3 days or 7 days of exposure, the lung activity of HO-1 and nitric oxide (NO) contents in bronchoalveolar lavage fluid (BALF), pulmonary histopathologic changes, and the cellular distribution and expression of HO-1 and iNOS in the lungs were measured.

RESULTS

After 3 days and 7 days of exposure, the hyperoxia group showed acute lung injuries characterized by the presence of hyperaemia, red cell extravasation and inflammatory infiltration. The NO contents in BALF and the iNOS expression in the lungs increased significantly in the hyperoxia group compared with those in the control group 3 and 7 days after exposure. The expression of HO-1 in macrophages in the lungs increased significantly in the hyperoxia group compared with that in the control group 3 and 7 days after exposure. The NO contents in BALF and the iNOS and HO-1 expression in the lungs increased significantly 7 days after hyperoxia exposure compared with 3 days after hyperoxia exposure.

CONCLUSIONS

iNOS and HO-1 levels in the lungs increase in preterm rats with hyperoxia-induced lung injuries, suggesting that iNOS and HO-1 may play roles in hyperoxia-induced pulmonary injuries.

Time course of heme oxygenase-1 and oxidative stress after experimental intracerebral hemorrhage

BACKGROUND

Heme oxygenase-1 (HO-1), the rate-limiting enzyme for heme catabolism and iron production, its role in intracerebral hemorrhage (ICH) is controversial. The study was to investigate correlations between brain oxidative injury and HO-1 after experimental ICH.

METHOD

Sprague-Dawley rats received intra-striatal infusions of 100 μl autologous whole blood as ICH models. HO-1 were examined by immunohistochemical and reverse transcription polymerase chain reaction (RT-PCR) analysis. Brain oxidative stress was quantitated by malondialdehyde (MDA); antioxidation were measured by copper-zinc superoxide dismutase (Cu/Zn-SOD) activity using RT-PCR assay.

RESULTS

The expression of the HO-1 upregulated and reached its peak at days 3 and 7 after ICH (P < 0.01). There was a significant increase of MDA and a top at 3-day post-ICH (P < 0.01); Cu/Zn-SOD was upregulated post-ICH and reached the top at day 7 (P < 0.001); HO-1 was correlated significantly with brain MDA content at days 7 and 14 following ICH (r = 0.435-0.501, P < 0.001) but there is no definite correlation between them on 1 to 3 days (P > 0.05); conversely, HO-1 was correlated significantly with Cu/Zn-SOD on 1 to 3 days after ICH (r = 0.433-0.621, P < 0.001) but there is no definite correlation between them at days 7 and 14 (P > 0.05).

CONCLUSIONS

HO-1 has both antioxidant and prooxidant properties in ICH. The early upregulation of HO-1 possibly fit with the events and be protective against oxidative stress, whereas its overexpression in the late stages may result in its dysfunction and be toxic. So it should be prudent to intervene ICH with the inhibitor/activator of HO-1.

[Role of HO/CO in IL-beta induced pancreatic islets apoptosis and the effect of fructose-1, 6-disphosphate]

AIM

To investigate the protective role of HO/CO systems in IL-1beta induced islest apoptosis and to explore the mechanisms of the protective effect of fructose-1, 6-disphosphate (FDP).

METHODS

The pancreases of the rats were removed to collect islets cells. The cells were incubated with IL-1beta with/or FDP. Cell activity, insulin secretion, HO-1 activity, CO content and apoptotic percentage were detected.

RESULTS

HO-1 activity and CO content of the normal control group were low. IL-1beta induced a significant decrease of cell activity and insulin release, flow cytometry analysis showed that apoptotic percentage of islet cells remarkably increased following the addition of IL-1beta, FDP obviously improved the islets cellular activity damaged by IL-1beta, and basic amount of insulin secretion and stimulated by high glucose were improved (P < 0.01). Content of CO and activity of HO-1 were higher in the IL-1beta group than the normal control group (P < 0.05), and there were significant differences between the FDP groups and IL-1beta group. FDP decreased cell apoptotic percentage. Activities of HO-1 and content of CO were higher than that in the IL-1beta group (P < 0.01).

CONCLUSION

FDP can attenuate the IL-1beta induced apoptosis of cultured beta cells, the mechanism of which may be improved HO-1 activity and CO content.

Heme oxygenase: the key to renal function regulation

Heme oxygenase (HO) plays a critical role in attenuating the production of reactive oxygen species through its ability to degrade heme in an enzymatic process that leads to the production of equimolar amounts of carbon monoxide and biliverdin/bilirubin and the release of free iron. The present review examines the beneficial role of HO-1 (inducible form of HO) that is achieved by increased expression of this enzyme in renal tissue. The influence of the HO system on renal physiology, obesity, vascular dysfunction, and blood pressure regulation is reviewed, and the clinical potential of increased levels of HO-1 protein, HO activity, and HO-derived end products of heme degradation is discussed relative to renal disease. The use of pharmacological and genetic approaches to investigate the role of the HO system in the kidney is key to the development of therapeutic approaches to prevent the adverse effects that accrue due to an impairment in renal function.

The heme oxygenase system abates hyperglycemia in Zucker diabetic fatty rats by potentiating insulin-sensitizing pathways

Emerging evidence indicates that aldosterone causes oxidative stress by stimulating proinflammatory/oxidative mediators, including nuclear factor-kappaB, activating protein (AP-1), and c-Jun N-terminal kinase. Thus, in insulin-resistant type 2 diabetes (T2D), oxidative stress generated by hyperglycemia and aldosterone would potentiate the oxidative destruction of tissue and important regulators of glucose metabolism like adiponectin and insulin. Although heme oxygenase (HO)-1 is cytoprotective, its effects on T2D have not been fully characterized. Here we report an enduring antidiabetic effect of the HO inducer, hemin, on Zucker diabetic-fatty rat (ZDF), a model of insulin-resistant T2D. Chronically applied hemin to ZDF reduced and maintained significantly low fasting and postprandial hyperglycemia for 4 months after therapy. The antidiabetic effect was accompanied by enhanced HO activity, catalase, cyclic GMP, bilirubin, ferritin, total antioxidant capacity, and insulin. In contrast, reduced aldosterone alongside markers/mediators of oxidative stress, including 8-isoprostane, c-Jun N-terminal kinase, nuclear factor-kappaB, AP-1, and AP-2 were observed. Interestingly, in hemin-treated ZDF, inhibitory proteins of insulin-signaling, such as glycogen synthase kinase-3 and protein-tyrosine phosphatase-1B were reduced, whereas agents that promote insulin signaling including adiponectin, cAMP, AMP-activated protein kinase, aldolase-B, and glucose transporter-4 (GLUT4), were robustly increased. Correspondingly, hemin improved ip glucose tolerance, reduced insulin intolerance, and lowered insulin resistance (homeostasis model assessment of insulin resistance), and the inability of insulin to enhance GLUT4 was overturned. These results suggest that the suppression of hyperglycemia and aldosterone-induced oxidative stress alongside the potentiation of insulin-sensitizing pathways may account for the 4-month enduring antidiabetic effect. The synergistic interaction between the HO system, aldolase-B, adiponectin, AMP-activated protein kinase, and GLUT4 may be explored for novel strategies against postprandial/fasting hyperglycemia and insulin-resistant T2D.

Heme oxygenase system enhances insulin sensitivity and glucose metabolism in streptozotocin-induced diabetes

Hyperglycemia-induced oxidative stress is a common phenomenon in diabetes. Since oxidative stress depletes adiponectin and insulin levels, we investigated whether an upregulated heme oxygenase (HO) system would attenuate the oxidative destruction of adiponectin/insulin and improve insulin sensitivity and glucose metabolism in streptozotocin (STZ)-induced type 1 diabetes. HO was upregulated with hemin (15 mg/kg ip) or inhibited with chromium mesoporphyrin (CrMP, 4 micromol/kg ip). Administering hemin to STZ-diabetic rats reduced hyperglycemia and improved glucose metabolism, whereas the HO inhibitor CrMP annulled the antidiabetic effects and/or exacerbated fasting/postprandial hyperglycemia. Interestingly, the antidiabetic effects of hemin lasted for 2 mo after termination of therapy and were accompanied by enhanced HO-1 and HO activity of the soleus muscle, along with potentiation of plasma antioxidants like bilirubin, ferritin, and superoxide dismutase, with corresponding elevation of the total antioxidant capacity. Importantly, hemin abated c-Jun NH2-terminal kinase (JNK), a substance known to inhibit insulin biosynthesis, and suppressed markers/mediators of oxidative stress including 8-isoprostane, nuclear-factor (NF)-kappaB, activating protein (AP)-1, and AP-2 of the soleus muscle. Furthermore, hemin therapy significantly attenuated pancreatic histopathological lesions including acinar cell necrosis, interstitial edema, vacuolization, fibrosis, and mononuclear cell infiltration. Correspondingly, hemin increased plasma insulin and potentiated agents implicated in insulin sensitization and insulin signaling such as adiponectin, adenosine monophosphate-activated protein kinase (AMPK), cAMP, cGMP, and glucose transporter (GLUT)4, a protein required for glucose uptake. These were accompanied by improved glucose tolerance [intraperitoneal glucose tolerance text (IPGTT)], decreased insulin intolerance [intraperitoneal insulin tolerance test (IPITT)], and reduced insulin resistance [homeostasis model assessment of insulin resistance (HOMA-IR) index], whereas CrMP nullified the hemin-dependent antidiabetic and insulin-sensitizing effects. In conclusion, by concomitantly enhancing insulin and paradoxically potentiating insulin sensitivity, this study unveils a novel, unique, and long-lasting antidiabetic characteristic of upregulating HO with hemin that could be exploited against insulin-resistant and insulin-dependent diabetes.

Protective effect of heme oxygenase-1 on lung injury induced by erythrocyte instillation in rats

BACKGROUND

Intratracheal instillation of blood induces self-repaired acute lung injury. However, the mechanism of repair has been unclear. Heme-oxygenase (HO)-1, which catalyzes heme breakdown, acts as an inducible defense against oxidative stress and plays an important role in inflammation. The objective of this study was to test the role of HO-1 in lung injury caused by intratracheal instillation of red cells.

METHODS

Forty healthy, male Sprague-Dawley rats were randomly divided into five groups: normal group, saline group, erythrocyte group, erythrocyte+zinc-protoporphyrin (ZnPP, HO-1 inhibitor) group and saline+ZnPP group. At 2 days after intratracheal instillation of red cells, lung tissues and lavage samples were isolated for biochemical determinations and histological measurements.

RESULTS

Histological analysis revealed that administration of ZnPP worsened the acute lung injury induced by instilled erythrocytes. HO-1 was over-expressed in the erythrocyte group and in the erythrocyte + ZnPP group. Compared with the erythrocyte + ZnPP group, the levels of total protein, lactate dehydrogenase and tumor necrosis factor-alpha in the lavage were lower (P < 0.01), while the level of interleukin-10 was higher in the erythrocyte group (P < 0.01).

CONCLUSION

HO-1 protects against erythrocyte-induced inflammatory injury in lung.

Mechanisms of heme iron absorption: current questions and controversies

Iron is a critical micronutrient, and iron derived from heme contributes a large proportion of the total iron absorbed in a typical Western diet. Heme iron is absorbed by different mechanisms than non-heme iron, but despite considerable study over many years these mechanisms remain poorly understood. This review provides an overview of the importance of heme iron in the diet and discusses the two prevailing hypotheses of heme absorption; namely receptor mediated endocytosis of heme, and direct transport into the intestinal enterocyte by recently discovered heme transporters. A specific emphasis is placed on the questions surrounding the site of heme catabolism and the identity of the enzyme that performs this task. Additionally, we present the hypothesis that a non-heme iron transport protein may be required for heme iron absorption and discuss the experiences of our laboratory in examining this hypothesis.

[Delayed protection of HO-1 in the exercise preconditioning from the myocardial relative ischemic reperfusion injury]

AIM

To explore the role of HO-1 in the exercise preconditioning protecting the rat myocardium from the relative myocardial ischemia/reperfusion injury (rI/R).

METHODS

40 Wistar rats were divided into 5 groups randomly: control group (CN), relative ischemia/reperfusion group (IR), exercise preconditioning + relative ischemia-reperfusion group (EI), HO-1 revulsant group (HE) and exercise preconditioning + HO-1 inhibitor (EZ) group. We detected the cardiac function parameter--pressure-rate product (PRP), the levels of MDA in coronary effluent and the activity of HO-1.

RESULTS

The activities of HO-1 of EI group and HE group were higher significantly than the IR group. EZ group was lower than EI group. There was significant difference between EI group and HE group. The recovery rate of PRP in the 60 min point of reperfusion of EI group was higher significantly than IR group. EZ group was lower than EI group. There was significant difference between HE group and IR group in 30 min point of reperfusion. The levels of MDA in coronary effluent after rI/R of EI group, EZ group and HE group were lower significantly than IR group. There was significant difference between EI group and EZ group.

CONCLUSION

EP can activate the HO-1 which can ameliorate the rI/R injury occurred after 24 hours.

Upregulation of heme oxygenase and collagen type III in the rat bladder after partial bladder outlet obstruction

The objective of the study was to evaluate possible changes of the gene expression and localization of the enzymes, heme oxygenase and nitric oxide synthase (NOS), with reference to increase of collagen type III in response to the partial obstruction of the bladder. Following initial obstruction, whole rat bladders were removed for real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry. Real-time RT-PCR demonstrated significantly enhanced expression of HO (p < 0.01) and collagen type III (p < 0.001) gene on postoperative day 14. Enhanced expression of NOS gene was seen only on postoperative day 4 (p < 0.01). Immunohistochemistry revealed that immunoreactivity to HO-1 had much in common in neural cells and fibers, although immunoreactivity to HO-2 and iNOS was relatively weak. This study suggested gene expression of HO, especially HO-1, was more dramatically changed than NOS, and was upregulated simultaneously with increase of collagen type III after obstruction. HO systems could be involved in the pathogenesis of bladder dysfunction related to increase of collagen type III after obstruction.

Role of oxidants in lung injury during sepsis

The role of oxidative stress has been well appreciated in the development of sepsis-induced acute lung injury (ALI). Oxidative stress in sepsis-induced ALI is believed to be initiated by products of activated lung macrophages and infiltrated neutrophils, promptly propagating to lung epithelial and endothelial cells. This leads to tissue damage and organ dysfunction. On stimulation, neutrophils (PMNs) enable their migration machinery. The lung undergoes changes favoring adhesion and transmigration of PMNs, resulting in PMN accumulation in lung, which is a characteristic of sepsis-induced ALI. Oxidative stress turns on the redox-sensitive transcription factors (NF-kappaB, AP-1), resulting in a large output of proinflammatory cytokines and chemokines, which further aggravate inflammation and oxidative stress. During the process, transcription factor nuclear factor-erythroid 2-p45-related factor 2 (Nrf2) and heme oxygenase (HO) appear to play the counterbalancing roles to limit the propagation of oxidative stress and inflammatory responses in lung. Many antioxidants have been tested to treat sepsis-induced ALI in animal models and in patients with sepsis. However, the results are inconclusive. In this article, we focus on the current understanding of the pathogenesis of sepsis-induced ALI and novel antioxidant strategies for therapeutic purposes.

Heme oxygenase-carbon monoxide pathway is involved in regulation of respiration in medullary slice of neonatal rats

Carbon monoxide (CO) is a novel biological messenger molecule. It is well known that CO can be synthesized in mammalian cells. In addition, CO is also demonstrated to participate in many physiological processes, such as vasomotion, thermoregulation and respiratory regulation. The purpose of our present study was to investigate the role of heme oxygenase-carbon monoxide (HO-CO) pathway in central regulation of respiration. The experiments were carried out on the medullary slices of neonatal Sprague-Dawley rats. The discharge activity of the hypoglossal rootlets was recorded to indicate the central rhythmic respiratory activity and its duration (DD), interval (DI), frequency (DF) and integrated amplitude (IA) were analyzed. The slices were perfused with ZnPP-9 (a potent inhibitor of heme oxygenase), CO and hemin (substrate of heme oxygenase), respectively, to observe their effects on respiratory activity. The results obtained were as follows: ZnPP-9 could decrease DD, DI and IA, and increase DF (P<0.05); exogenous CO caused a decrease in DD and DF, and an increase in DI and IA (P<0.05); in response to hemin, DI and IA decreased, DF increased (P<0.05), and DD did not change significantly (P>0.05); administration of both ZnPP-9 and hemin could decrease DI, and increase DF (P<0.05), but did not affect DD and IA significantly (P>0.05). It can be concluded from the results above that the HO-CO pathway may be involved in the regulation of rhythmic respiration at the level of medulla oblongata.

Effectiveness of novel imidazole-dioxolane heme oxygenase inhibitors in renal proximal tubule epithelial cells

To enhance our understanding of the physiological roles of heme oxygenase (HO) isozymes, HO-1 (inducible) and HO-2 (constitutive), we developed novel imidazole-based HO inhibitors. Unlike the metalloporphyrins, these imidazole-dioxolane compounds are selective for the in vitro inhibition of HO with minimal effects on other heme-dependent enzymes such as nitric oxide synthase and soluble guanylyl cyclase. In the current study, we tested the hypothesis that these novel HO inhibitors are effective in intact cells by extending their application to cultured, renal proximal tubule epithelial cells (LLC-PK1). HO-1 and HO-2 protein expression was enhanced by pretreatment of cells with hemin, transduction with adenovirus encoding human HO-1, and transfection with cDNA for HO-2, respectively. Total HO activity was measured by determining the formation of carbon monoxide (CO), whereas cell viability and apoptosis were measured by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and the expression of activated caspase-3. Gliotoxin/tumor necrosis factor-alpha (TNF-alpha) produced cytotoxicity in wild-type LLC-PK1 cells (P < 0.05) but not in HO-1 and HO-2 overexpressing or wild type cells pretreated with hemin (10 microM). The presence of imidazole-dioxolane HO inhibitors (2-25 microM) decreased cell viability (P < 0.05). A CO-releasing molecule reversed, in a dose-dependent manner, the cytotoxic effects and caspase-3 activation induced by the combination of gliotoxin/TNF-alpha and the HO inhibitors, suggesting an important role for CO in protection against renal toxicity. These data demonstrate a protective role of both HO-1 and HO-2 against gliotoxin/TNF-alpha-induced cytotoxicity in LLC-PK1 cells. The novel imidazole-dioxolane compounds can be used as effective inhibitors of HO activity in cell culture.

Propofol attenuation of renal ischemia/reperfusion injury involves heme oxygenase-1

AIM

To examine the protective effect of propofol in renal ischemia/reperfusion (I/R) injury and the role of heme oxygenase-1 (HO-1) in this process.

METHODS

Sprague-Dawley rats were randomly divided into 3 groups: (i) sham-operated group; (ii) I/R group; and (iii) propofol group. Bilateral renal warm ischemia for 45 min was performed. After 2, 6, and 24 h reperfusion, blood samples and kidneys were collected for assessment of renal injury, and HO-1 expressions were analyzed by immunohistochemical analysis, RT-PCR and Western blotting.

RESULTS

Blood urea nitrogen and serum creatinine levels in the propofol group were significantly lower than that in the I/R group at 24 h after reperfusion. The mean histological score by Palleros standard showed that propofol significantly attenuated renal I/R injury after 6 h reperfusion. Propofol increased HO-1 mRNA and protein levels 2 h after reperfusion, whereas HO-1 expressions were present at exceedingly low levels in the I/R group and the sham-operated group at same time point. Propofol also markedly increased HO-1 mRNA and protein levels than I/R at 6 and 24 h after reperfusion.

CONCLUSION

These results suggest that propofol mitigates renal I/R injury in rats. This protection may be partly through the induction of the HO-1 expression.

Influence of the heme-oxygenase pathway on cerebrocortical blood flow

Heme-oxygenase (HO)-derived carbon monoxide (CO) is generated in the cardiovascular and in the central nervous systems. Endogenous CO exerts direct vascular effects and has also been shown to inhibit nitric oxide synthase (NOS). In the current study, the heme-oxygenase blockade [zinc deuteroporphyrin 2,4-bis glycol (ZnDPBG), 45 micromol/kg intraperitoneally] decreased cerebral CO production and increased cerebrocortical blood flow (CBF) in anesthetized rats. This latter effect was abrogated by the NOS blockade (50 mg/kg L-NAME intravenously). Furthermore, inhibition of CO production had no effect on stepwise hypoxia/hypercapnia-stimulated increases in CBF. Our results indicate that endogenous CO reduces the resting CBF via inhibition of NOS but fails to influence the CBF response to hypoxia and hypercapnia in adult rats.

Roles of heme oxygenase-1 in curcumin-induced growth inhibition in rat smooth muscle cells

In vascular smooth muscle cells (VSMCs), induction of the heme oxygenase-1 (HO-1) confers vascular protection against cellular proliferation mainly via its up-regulation of the cyclin-dependent kinase inhibitor p21(WAF1/CIP1) that is involved in negative regulation of cellular proliferation. In the present study, we investigated whether the phytochemical curcumin and its metabolite tetrahydrocurcumin could induce HO-1 expression and growth inhibition in rat VSMCs and, if so, whether their antiproliferative effect could be mediated via HO-1 expression. At non-toxic concentrations, curcumin possessing two Michael-reaction acceptors induced HO-1 expression by activating antioxidant response element (ARE) through translocation of the nuclear transcription factor E2-related factor-2 (Nrf2) into the nucleus and also inhibited VSMC growth triggered by 5% FBS in a dose-dependent manner. In contrast, tetrahydrocurcumin lacking Michael-reaction acceptor showed no effect on HO-1 expression, ARE activation and VSMC growth inhibition. The antiproliferative effect of curcumin in VSMCs was accompanied by the increased expression of p21(WAF1/CIP1). Inhibition of VSMC growth and expression of p21(WAF1/CIP1) by curcumin were partially, but not completely, abolished when the cells were co- incubated with the HO inhibitor tin protoporphyrin. In human aortic smooth muscle cells (HASMCs), curcumin also inhibited growth triggered by TNF-alpha and increased p21(WAF1/CIP1) expression via HO-1-dependent manner. Our findings suggest that curcumin has an ability to induce HO-1 expression, presumably through Nrf2-dependent ARE activation, in rat VSMCs and HASMCs, and provide evidence that the antiproliferative effect of curcumin is considerably linked to its ability to induce HO-1 expression.

Intrarenal renin-angiotensin system and counteracting protective mechanisms in angiotensin II-dependent hypertension

It is now well accepted that alterations in kidney function, due either to primary renal disease or to inappropriate hormonal influences on the kidney, are a cardinal characteristic in all forms of hypertension, and lead to a reduced ability of the kidneys to excrete sodium and the consequent development of elevated arterial pressures. However, it is also apparent that many extrarenal factors are important contributors to altered kidney function and hypertension. Central to many hypertensinogenic processes is the inappropriate activation of the renin-angiotensin system (RAS) and its downstream consequences by various pathophysiologic mechanisms. There may also be derangements in arachidonic acid metabolites, endothelium derived factors such as nitric oxide and carbon monoxide, and various paracrine and neural systems that normally interact with or provide a counteracting balance to the actions of the RAS. Thus, when the capacity of the kidneys to maintain sodium balance and extracellular fluid volume within appropriate ranges is compromised, increases in arterial pressure become necessary to re-establish normal balance.

Inhibition of Heme Oxygenase-1 Protects Against Tissue Injury in Carbon Tetrachloride Exposed Livers

BACKGROUND/AIMS

During the metabolism of the hepatotoxin carbon tetrachloride (CCl(4)) by cytochrome P450, heme, and free radicals are released. Heme oxygenase (HO-1) is an enzyme that is induced by heme as well as oxidative stress and has been reported to be involved in mediating protection against toxic liver injury. The purpose of the present study was to specify the role of HO-1 in CCl(4)-hepatotoxicity.

METHODS AND RESULTS

We could demonstrate an up-regulation of HO-1 protein in CCl(4)-exposed liver tissue that reaches its maximum after 6 to 12 h, along with intrahepatic leukocyte accumulation and tissue injury. When animals were pretreated with hemin for augmentation of HO-1 expression, CCl(4)-exposure was associated with a reduction of intrahepatic leukocyte accumulation, while inhibition of CCl(4)-induced HO-1 expression by tin protoporphyrin-IX (SnPP-IX) enhanced leukocytic response. Of interest, however, liver morphology, transaminases, and bile flow as parameters of hepatocellular integrity and excretory function did not concur with reduced leukocyte numbers in the hepatic microcirculation, and revealed best organ function and tissue preservation in case of HO-1 inhibition by SnPP-IX. In contrast, hemin-treated CCl(4)-exposed livers demonstrated pathologic enzyme release and cholestasis.

CONCLUSIONS

Taken together, inhibition of HO-1 in CCl(4)-hepatotoxicity protected the liver, while higher HO-1 activity harmed liver tissue, most probably due to interference of the HO-1 pathway with CCl(4)-dependent metabolism via cytochrome P450 and heme overload-associated toxicity.

Impact of silencing HO-2 on EC-SOD and the mitochondrial signaling pathway

The contribution of heme oxygenase HO-2, the primary source of bilirubin and carbon monoxide (CO) under physiological conditions, to the regulation of vascular function has remained largely unexplored. Using siRNA HO-2, we examined the effect of suppressed levels of HO-2 on vascular antioxidant and survival proteins. In vivo HO-2 siRNA treatment decreased the basal levels of EC-SOD, pAKT proteins (serine-473 and threonine-308), without changing Akt protein expression. HO-2 siRNA treatment increased 3-nitrotyrosine (3-NT) and apoptotic signaling kinase-1 (ASK-1) (P < 0.01). HO activity was decreased by the use of siRNA HO-2. We extended these studies to the mitochondria, examining for the presence of HO-1 and its role in the regulation of pro- and anti-apoptotic proteins. HO activity was increased by the administration of CoPP resulting in the translocation of HO-1 into the mitochondria, mainly to the inner face of the mitochondrial inner membrane. These findings suggest that HO-2 is critical in the maintenance of heme homeostasis and also the regulation of apoptosis by controlling levels of EC-SOD, Akt, 3-NT, and ASK-1. In addition, localization of HO-1 in the mitochondrial compartment plays a critical role in mitochondria-mediated apoptosis.

Attenuation of oxidative injury after induction of experimental intracerebral hemorrhage in heme oxygenase-2 knockout mice

OBJECT

Experimental evidence suggests that hemoglobin degradation products contribute to cellular injury after intracerebal hemorrhage (ICH). Hemoglobin breakdown is catalyzed in part by the heme oxygenase (HO) enzymes. In the present study, the authors tested the hypothesis that HO-2 gene deletion is cytoprotective in an experimental ICH model.

METHODS

After anesthesia was induced with isoflurane, 3- to 6-month-old HO-2 knockout and wild-type mice were stereotactically injected with 15 microl autologous blood and a group of control mice were injected with an equal volume of sterile saline. Striatal protein and lipid oxidation were quantified 72 hours later using carbonyl and malondialdehyde assays. Cell viability was determined by performing a 3(4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium bromide (MTT) assay. Following blood injection, the investigators found a 3.4-fold increase in protein carbonylation compared with that in the contralateral striatum in wild-type mice; in knockout mice, the investigators found a twofold increase. The mean malondialdehyde concentration in injected striata was increased twofold in wild-type mice at this time, compared with 1.5-fold in knockout mice. Cell viability, as determined by MTT reduction, was reduced in injected striata to 38 +/- 4% of that in the contralateral striata in wild-type mice, compared with 66 +/- 5% in HO-2 knockout mice. Baseline striatal HO-1 protein expression was similar in wild-type and HO-2 knockout mice, but was induced more rapidly in the former after blood injection.

CONCLUSIONS

Deletion of HO-2 attenuates oxidative cell injury after whole-blood injection into the mouse striatum. Therapies that specifically target HO-2 may improve outcome after ICH.

Negative regulation of soluble Flt-1 and soluble endoglin release by heme oxygenase-1

BACKGROUND

Preeclampsia is characterized clinically by hypertension and proteinuria. Soluble Flt-1 (sFlt-1; also known as soluble vascular endothelial growth factor receptor-1 [VEGFR-1]) and soluble endoglin (sEng) are elevated in preeclampsia, and their administration to pregnant rats elicits preeclampsia-like symptoms. Heme oxygenase-1 (HO-1) and its metabolite carbon monoxide (CO) exert protective effects against oxidative stimuli. Thus, we hypothesized that HO-1 upregulation may offer protection against preeclampsia by inhibiting sFlt-1 and sEng release.

METHODS AND RESULTS

Preeclamptic villous explants secreted high levels of sFlt-1 and sEng. Adenoviral overexpression of HO-1 in endothelial cells inhibited VEGF-mediated sFlt-1 release and interferon-gamma- and tumor necrosis factor-alpha-induced sEng release, whereas HO-1 inhibition potentiated sFlt-1 and sEng production from endothelial cells and placental villous explants. Consistent with these findings, mice lacking HO-1 produced higher levels of sFlt-1 and sEng compared with wild-type mice. Using selective ligands (VEGF-E and placental growth factor) and a receptor-specific inhibitor (SU-1498), we demonstrated that VEGF-induced sFlt-1 release was VEGFR-2 dependent. Furthermore, CO-releasing molecule-2 (CORM-2) or CO decreased sFlt-1 release and inhibited VEGFR-2 phosphorylation. Treatment of endothelial cells with statins upregulated HO-1 and inhibited the release of sFlt-1, whereas vitamins C and E had no effect.

CONCLUSIONS

The present study demonstrates that the HO-1/CO pathway inhibits sFlt-1 and sEng release, providing compelling evidence for a protective role of HO-1 in pregnancy, and identifies HO-1 as a novel target for the treatment of preeclampsia.

Interdependence of lipoxin A4 and heme-oxygenase in counter-regulating inflammation during corneal wound healing

In the immune-privileged cornea, epithelial wounds heal rapidly with almost no scarring and, unlike in most other tissues, acute inflammation in the absence of infection is beneficial to healing. Molecular mechanisms, which account for this striking property, remain to be clearly defined, but they likely include autacoids that control leukocyte activation. Two prominent enzymes, 12/15-lipoxygenase (LOX), which generates antiinflammatory lipid autacoids, and heme-oxygenase (HO), which generates antioxidants and carbon monoxide, are highly expressed in human and mouse corneas. LXA4, an endogenous 12/15-LOX product, proved to be a potent inhibitor of exacerbated inflammation and significantly increased re-epithelialization in corneal wounds. In vivo deletion of 12/15-LOX correlated with exacerbated inflammation and impaired wound healing in 12/15-LOX(-/-) mice, a phenotype that was rescued by treatment with LXA4. More importantly, 12/15-LOX(-/-) mice demonstrated impaired induction of HO-1 in both acute and exacerbated inflammation. Topical LXA4 restored HO-1 expression in 12/15-LOX(-/-) mice and amplified HO-1 gene expression in human corneal epithelial cells. HO-2(-/-) mice, which fail to induce HO-1, also demonstrated exacerbated inflammation in response to injury, a phenotype that, notably, correlated with a 50% reduction in endogenous LXA4 formation. Collectively, results demonstrate a critical role for LXA4 in inflammatory/reparative responses and provide the first evidence that 12/15-LOX and HO systems function in concert to control inflammation.

Interactions between NO, CO and an endothelium-derived hyperpolarizing factor (EDHF) in maintaining patency of the ductus arteriosus in the mouse

BACKGROUND AND PURPOSE

Prenatal patency of ductus arteriosus is maintained by prostaglandin (PG) E(2), possibly along with nitric oxide (NO) and carbon monoxide (CO), and cyclooxygenase (COX) deletion upregulates NO. Here, we have examined enzyme source and action of NO for ductus patency and whether NO and CO are upregulated by deletion of, respectively, heme oxygenase 2 (HO-2) and COX1 or COX2.

EXPERIMENTAL APPROACH

Experiments were performed in vitro and in vivo with wild-type and gene-deleted, near-term mouse fetuses.

KEY RESULTS

N(G)-nitro-L-arginine methyl ester (L-NAME) contracted the isolated ductus and its effect was reduced by eNOS, but not iNOS, deletion. L-NAME contraction was not modified by HO-2 deletion. Zinc protoporphyrin (ZnPP) also contracted the ductus, an action unaffected by deletion of either COX isoform. Bradykinin (BK) relaxed indomethacin-contracted ductus similarly in wild-type and eNOS-/- or iNOS-/-. BK relaxation was suppressed by either L-NAME or ZnPP. However, it reappeared with combined L-NAME and ZnPP to subside again with K(+) increase or K(+) channel inhibition. In vivo, the ductus was patent in wild-type and NOS-deleted fetuses. Likewise, no genotype-related difference was noted in postnatal closure.

CONCLUSIONS AND IMPLICATIONS

NO, formed mainly via eNOS, regulates ductal tone. NO and CO cooperatively mediate BK-induced relaxation in the absence of PGE(2). However, in the absence of PGE(2), NO and CO, BK induces a relaxant substance behaving as an endothelium-derived hyperpolarizing factor. Ductus patency is, therefore, sustained by a cohort of agents with PGE(2) and NO being preferentially coupled for reciprocal compensation.

Comparative analysis of hmuO function and expression in Corynebacterium species

We have constructed defined deletions in the hmuO gene from Corynebacterium diphtheriae and Corynebacterium ulcerans and show that the C. ulcerans hmuO mutation results in a significant reduction in hemoglobin-iron utilization, whereas in C. diphtheriae strains, deletion of hmuO caused no or only partial reduction in the utilization of heme as an iron source. We also show that expression from the C. ulcerans hmuO promoter exhibits minimal regulation by iron and heme whereas transcription from the C. diphtheriae hmuO promoter shows both significant iron repression and heme-dependent activation. These findings indicate that variability in HmuO function and expression exists among Corynebacterium species.

Heme oxygenase and its role in defense system ; Paradigm shift of anti-inflammatory therapy

Heme oxygenase (HO) plays a central role in heme metabolism. At the same time, it protects cells from injury evoked by various oxidative stresses. A detailed analysis of the first human case of HO-1 deficiency revealed that HO-1 is involved in the protection of multiple tissues and organs. It is particularly important that in vivo HO-1 production is localized to selected cell types, e.g. renal tubular epithelium, reflecting the fact that HO-1 plays particularly important protective roles in these cells. In addition to renal epithelial cells and tissue macrophages, a minor subpopulation of circulating monocytes produced low, but significant levels of HO-1 and the number of these monocytes increased during episodes of acute inflammatory illnesses, indicating that monocytes play significant roles in controlling inflammation. On the other hand, excessive level of HO-1 induced by HO-1 gene transfection led to paradoxical susceptibility of the cells to oxidative injury. These results indicated that HO-1 expression is carefully controlled in vivo with regard to its location and the magnitude. Furthermore, it has been recently shown that HO-1 is involved in the immune regulation mediated by regulatory T cells. From these findings, it seems feasible to meticulously induce HO-1 protein in vivo as a novel therapeutic intervention to control various forms of inflammatory disorders.

Role of Renal Medullary Heme Oxygenase in the Regulation of Pressure Natriuresis and Arterial Blood Pressure

Recent studies have demonstrated that inhibition of renal medullary heme oxygenase (HO) activity and carbon monoxide (CO) significantly decreases renal medullary blood flow and sodium excretion. Given the crucial role of renal medullary blood flow in the control of pressure natriuresis, the present study was designed to determine whether renal medullary HO activity and resulting CO production participate in the regulation of pressure natriuresis and thereby the long-term control of arterial blood pressure. In anesthetized Sprague-Dawley rats, increases in renal perfusion pressure induced significant elevations of CO concentrations in the renal medulla. Renal medullary infusion of chromium mesoporphyrin (CrMP), an inhibitor of HO activity, remarkably inhibited HO activity and the renal perfusion pressure-dependent increases in CO levels in the renal medulla and significantly blunted pressure natriuresis. In conscious Sprague-Dawley rats, continuous infusion of CrMP into the renal medulla significantly increased mean arterial pressure (129±2.5 mm Hg in CrMP group versus 118±1.6 mm Hg in vehicle group) when animals were fed a normal salt diet (1% NaCl). After rats were switched to a high-salt diet (8% NaCl) for 10 days, CrMP-treated animals exhibited further increases in mean arterial pressure compared with CrMP-treated animals that were kept on normal salt diet (152±4.1 versus 130±4.2 mm Hg). These results suggest that renal medullary HO activity plays a crucial role in the control of pressure natriuresis and arterial blood pressure and that impairment of this HO/CO-mediated antihypertensive mechanism in the renal medulla may result in the development of hypertension.

Role of carbon monoxide in electrically induced non-adrenergic, non-cholinergic relaxations in the guinea-pig isolated whole trachea

BACKGROUND AND PURPOSE

Nitric oxide (NO) and vasoactive intestinal peptide (VIP) are considered transmitters of non-adrenergic, non-cholinergic (NANC) relaxations in guinea-pig trachea, whereas the role of carbon monoxide (CO) is unknown. This study was designed to assess the participation of CO, and to investigate the localization of haem oxygenase-2 (HO-2), the CO-producing enzyme, in tracheal neurons.

EXPERIMENTAL APPROACH

NANC responses to electrical field stimulation (EFS) at 3 and 10 Hz were evaluated in epithelium-free whole tracheal segments as intraluminal pressure changes. Drugs used were: L-nitroarginine methyl ester (L-NAME, 100 microM) to inhibit NO synthase (NOS), alpha-chymotrypsin (2 U ml(-1)) to inactivate VIP, zinc protoporphyrin-IX (ZnPP-IX, 10 microM) to inhibit HO-2, and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10 microM), a soluble guanylyl cyclase inhibitor. For immunohistochemistry, tissues were exposed to antibodies to PGP 9.5, a general neuronal marker, HO-2 and NOS, and processed with an indirect immunofluorescence method.

KEY RESULTS

alpha-Chymotrypsin did not affect NANC relaxations. ODQ inhibited NANC responses by about 60%, a value similar to that obtained by combining L-NAME and ZnPP-IX. The combination of ODQ, L-NAME and ZnPP-IX reduced the responses by 90%. Subpopulations of HO-2 positive neurons containing NOS were detected in tracheal sections.

CONCLUSIONS AND IMPLICATIONS

In the guinea-pig trachea, NANC inhibitory responses at 3 and 10 Hz use NO and CO as main transmitters. Their participation is revealed following inhibition of NOS, HO-2 and soluble guanylyl cyclase. The involvement of CO as a relaxing transmitter paves the way for novel therapeutic approaches in the treatment of airway obstruction.

Autonomic Cardiovascular Responses to Heme Oxygenase Inhibition in Conscious Rats

Carbon monoxide (CO) is produced in the course of heme degradation from biliverdin by heme oxygenase (HO) in various tissues, including the central nervous system. Recent studies suggest the inhibition of HO activity increases arterial pressure mediated by the autonomic nervous system. The present study was designed to investigate the autonomic regulation of cardiovascular responses to inhibition of endogenous CO production by the HO inhibitor Zinc deuteroporphyrin 2, 4-bis glycol (ZnDPBG) by using direct sympathetic nerve recordings in conscious, chronically instrumented rats. ZnDPBG induced increases in mean arterial pressure (MAP) (P<0.05) and renal sympathetic nerve activity (RSNA) (P<0.05) but no significant change in heart rate (P>0.05) in intact rats. In atropine-treated rats, ZnDPBG also induced increases in MAP (P<0.05) and RSNA (P<0.05) but no change in heart rate (P>0.05). In sinoaortic denervated rats, ZnDPBG induced increases in MAP (P<0.05), heart rate (P<0.05), and RSNA (P<0.05). ZnDPBG shifted the baroreflex curve for RSNA upward and to the right, which was characterized by increases in the maximum and minimum response and midpoint pressure without altering the maximum gain. These results indicate that inhibition of HO activity within the central nervous system causes sympathoexcitation, resulting in an increase in arterial pressure. We conclude that the CO/HO system plays an important role in cardiovascular regulation by modulating sympathetic tone.

Structure of the Escherichia coli O157:H7 Heme Oxygenase ChuS in Complex with Heme and Enzymatic Inactivation by Mutation of the Heme Coordinating Residue His-193

Heme oxygenases catalyze the oxidation of heme to biliverdin, CO, and free iron. For pathogenic microorganisms, heme uptake and degradation are critical mechanisms for iron acquisition that enable multiplication and survival within hosts they invade. Here we report the first crystal structure of the pathogenic Escherichia coli O157:H7 heme oxygenase ChuS in complex with heme at 1.45 A resolution. When compared with other heme oxygenases, ChuS has a unique fold, including structural repeats and a beta-sheet core. Not surprisingly, the mode of heme coordination by ChuS is also distinct, whereby heme is largely stabilized by residues from the C-terminal domain, assisted by a distant arginine from the N-terminal domain. Upon heme binding, there is no large conformational change beyond the fine tuning of a key histidine (His-193) residue. Most intriguingly, in contrast to other heme oxygenases, the propionic side chains of heme are orientated toward the protein core, exposing the alpha-meso carbon position where O(2) is added during heme degradation. This unique orientation may facilitate presentation to an electron donor, explaining the significantly reduced concentration of ascorbic acid needed for the reaction. Based on the ChuS-heme structure, we converted the histidine residue responsible for axial coordination of the heme group to an asparagine residue (H193N), as well as converting a second histidine to an alanine residue (H73A) for comparison purposes. We employed spectral analysis and CO measurement by gas chromatography to analyze catalysis by ChuS, H193N, and H73A, demonstrating that His-193 is the key residue for the heme-degrading activity of ChuS.

Pyrrolidine dithiocarbamate protects the small bowel from warm ischaemia/reperfusion injury of the intestine: the role of haem oxygenase

IR (ischaemia/reperfusion) injury of the intestine occurs commonly during abdominal surgery. We have previously shown that PDTC (pyrrolidine dithiocarbamate), an HO-1 (haem oxygenase-1) donor, improves intestinal microvascular perfusion. In the present study, we have investigated the effects of PDTC on the intestinal microcirculation following IR (ischaemia/reperfusion) injury of the intestine. Male Sprague–Dawley rats (n=72) were randomly assigned to four groups (n=18/group): (i) sham-operated group, who underwent laparotomy without induction of IR of the intestine; (ii) IR group, who were subjected to 30 min of superior mesenteric artery occlusion and 2 h of reperfusion; (iii) PDTC+IR group, who received PDTC prior to IR; and (iv) ZnPP group, who received the HO-1 inhibitor ZnPP (zinc protoporphyrin) followed by procedures as in group (iii). The ileum was evaluated for changes in tissue cytochrome c oxidase redox status, RBC (red blood cell) dynamics and leucocyte–endothelial interactions. The expression of HO-1 in the ileal tissue was examined at the end of the reperfusion. PDTC significantly improved the intestinal tissue oxygenation, mucosal perfusion index and RBC velocity compared with the IR and ZnPP groups. PDTC also decreased the leucocyte–endothelial interactions (P<0.05 compared with the IR and ZnPP groups). PDTC induced the expression of HO-1, whereas ZnPP abolished this effect.

2′,4′,6′-Tris(methoxymethoxy) chalcone attenuates hepatic stellate cell proliferation by a heme oxygenase-dependent pathway

Proliferation of hepatic stellate cells (HSCs) is central for the development of fibrosis during liver injury. We have shown previously that butein (3,4,2',4'-tetrahydroxychalcone) suppresses myofibroblastic differentiation of rat HSCs. Our aim in this study was to determine whether a new synthetic chalcone derivative, 2',4',6'-tris(methoxymethoxy) chalcone (TMMC) inhibits HSC proliferation induced by serum- or platelet-derived growth factor (PDGF). TMMC significantly inhibited growth factor-induced HSC proliferation. The inhibition of PDGF-induced proliferation by TMMC was associated with the phosphatidylinositol 3-kinase-Akt-p70(S6K) pathways. TMMC induced the expression of heme oxygenase 1 (HO-1) in HSCs. Using the chemical inhibitor tin protoporphyrin, we also found that the inhibitory action of TMMC on PDGF-induced proliferation is mediated by HO-1. Glutathione (GSH) depletion produced by TMMC activated extracellular signal-regulated kinase (ERK), which led to c-Fos expression and transactivation of activator protein 1 (AP-1) and HO-1 gene expression in the HSCs. These results demonstrate that TMMC preferentially activates ERK and that this activation leads to the transcriptional activation of AP-1 and consequently to HO-1 expression. HO-1 expression might be responsible for the antiproliferative effect of TMMC on HSCs.

Role of the peripheral heme oxygenase-carbon monoxide pathway on the nociceptive response of rats to the formalin test: evidence for a cGMP signaling pathway

The aim of the present study was to investigate the role of the peripheral heme oxygenase (HO)-carbon monoxide (CO) pathway on nociceptive response of rats to the formalin experimental model of pain. Animals were handled and adapted to the experimental environment for a few days before the formalin test was applied. For the formalin test, 50 microl of a 1% formalin solution was used and injected subcutaneously in the dorsal surface of the right hind paw. Following injections, animals were observed for 1 h, and flinching behavior was measured as the nociceptive response. Twenty minutes before the test rats were pretreated with podal injections with the HO inhibitor, zinc deuteroporphyrin 2,4-bis glycol (ZnDPBG) or heme-lysinate, which is known to induce the HO pathway. Control animals were treated with vehicles. We observed a significant increase on nociceptive response of rats treated with ZnDPBG, and a drastic reduction of flinching nociceptive behavioral response in the heme-lysinate and CO treated animals. Among the three different HO products, CO seems to account for the heme-lysinate effect because the injection of the gas attenuated the flinching response whereas biliverdine and deferoxanine (an iron chelator) failed to cause any significant change. Furthermore, CO seems to act via cGMP, since methylene blue (a soluble guanylate cyclase inhibitor) prevented the reduction of the flinching nociceptive behavioral response caused by heme-lysinate. These findings strongly indicate that CO is the HO pathway product that plays an antinociceptive role during the formalin test, acting via cGMP.

Up-regulation of heme oxygenase provides vascular protection in an animal model of diabetes through its antioxidant and antiapoptotic effects

Heme oxygenase (HO) plays a critical role in the regulation of cellular oxidative stress. The effects of the reactive oxygen species scavenger ebselen and the HO inducers cobalt protoporphyrin and stannous chloride (SnCl(2)) on HO protein levels and activity, indices of oxidative stress, and the progression of diabetes were examined in the Zucker rat model of type 2 diabetes. The onset of diabetes coincided with an increase in HO-1 protein levels and a paradoxical decrease in HO activity, which was restored by administration of ebselen. Up-regulation of HO-1 expressed in the early development of diabetes produced a decrease in oxidative/nitrosative stress as manifested by decreased levels of 3-nitrotyrosine, superoxide, and cellular heme content. This was accompanied by a decrease in endothelial cell sloughing and reduced blood pressure. Increased HO activity was also associated with a significant increase in the antiapoptotic signaling molecules Bcl-xl and phosphorylation of p38-mitogen-activated protein kinase but no significant increases in Bcl-2 or BAD proteins. In conclusion, 3-nitrotyrosine, cellular heme, and superoxide, promoters of vascular damage, are reduced by HO-1 induction, thereby preserving vascular integrity and protecting cardiac function involving an increase in antiapoptotic proteins.

Heme oxygenase protects hippocampal neurons from ethanol-induced neurotoxicity

Ethanol has deleterious effects on neuronal cells both in vivo and in vitro, but the mechanisms are unknown. Here, treatment with increasing doses of ethanol (from 20 up to 600mM) decreased the viability of a mouse hippocampal neuroblastoma cell line, HT22. The glutathione concentration decreased and intracellular reactive oxygen species (ROS) increased in a dose-and time-dependent manner, suggesting that the neurotoxicity was due to oxidative stress. Expression of heme oxygenase (HO)-1, a redox regulator and heat shock protein, increased with time after ethanol treatment, but HO-2 was expressed constitutively. The addition of 5microM zinc protoporphyrin IX (ZnPP IX), a competitive HO inhibitor, with the ethanol further reduced cell viability and increased intracellular ROS, but these effects were reversed by co-treatment with 50nM bilirubin, a well-known antioxidant and a product of HO catalysis. These results suggest that HO has a protective role in hippocampal neurons as an intrinsic factor against ethanol-induced oxidative stress and the protection depends on the degree of oxidative stress.

Redox regulation of cellular stress response in neurodegenerative disorders

There is increasing evidence that reactive oxygen species (ROS) are not only toxic but play an important role in cellular signaling and in the regulation of gene expression. A number of biochemical and physiologic stimuli, such as perturbation in redox status, expression of misfolded proteins, altered glyc(osyl)ation and glucose deprivation, overloading of products of polyunsaturated fatty acid peroxidation (Hydroxynonenals, HNE) or cholesterol oxidation and decomposition, can disrupt redox homeostasis, impose stress and subsequently lead to accumulation of unfolded or misfolded proteins in brain cells. Alzheimer's (AD), Parkinson's (PD), Huntington's disease (HD), Amyothrophic lateral sclerosis (ALS) and Friedreich ataxia (FRDA) are major neurological disorders associated with production of abnormal proteins and, as such, belong to the so called "protein conformational diseases". The Central Nervous System has evolved highly specific signaling pathways called the unfolded protein response to cope with the accumulation of unfolded or misfolded proteins. Recent discoveries of the mechanisms of cellular stress signaling have led to major new insights into the diverse processes that are regulated by cellular stress response. Thus, the pathogenic dysfunctional aggregation of proteins in non-native conformations is associated with metabolic derangements and excessive production of ROS. The brain response to detect and control metabolic or oxidative stress is accomplished by a complex network of "longevity assurance processes" integrated to the expression of genes termed vitagenes. Heat shock proteins are a highly conserved system responsible for the preservation and repair of correct protein conformation. Heme oxygenase-1, a inducible and redox-regulated enzyme, is currently considered as having an important role in cellular antioxidant defense. A neuroprotective effect, due to its heme degrading activity, and tissue-specific antioxidant effects due to its products CO and biliverdin, this latter being further reduced by biliverdin reductase in bilirubin is an emerging concept. There is a current interest in dietary compounds that can inhibit, retard or reverse the multi-stage pathophysiology of Alzheimer disease, with a chronic inflammatory response, brain injury and beta-amyloid associated pathology. Curcumin and ferulic acid, two powerful antioxidants, the first from the curry spice turmeric and the second a major constituent of fruit and vegetables, have emerged as strong inducers of the heat shock response. Food supplementation with curcumin and ferulic acid is considered a nutritional approach to reduce oxidative damage and amyloid pathology in Alzheimer disease. This review summarizes the complex regulation of cellular stress signaling and its relevance to human physiology and disease.

Heme in intestinal epithelial cell turnover, differentiation, detoxification, inflammation, carcinogenesis, absorption and motility

The gastrointestinal tract is lined by a simple epithelium that undergoes constant renewal involving cell division, differentiation and cell death. In addition, the epithelial lining separates the hostile processes of digestion and absorption that occur in the intestinal lumen from the aseptic environment of the internal milieu by defensive mechanisms that protect the epithelium from being breached. Central to these defensive processes is the synthesis of heme and its catabolism by heme oxygenase (HO). Dietary heme is also an important source of iron for the body which is taken up intact by the enterocyte. This review describes the recent literature on the diverse properties of heme/HO in the intestine tract. The roles of heme/HO in the regulation of the cell cycle/apoptosis, detoxification of xenobiotics, oxidative stress, inflammation, development of colon cancer, heme-iron absorption and intestinal motility are specifically examined.