Heme oxygenase-1: unleashing the protective properties of heme

Anti-Inflammatory Mechanisms of the Tibetan Herbal Preparation Padma 28 in the Vessel Wall

BACKGROUND

The Tibetan herbal preparation Padma 28 has been shown to act as an anti-atherosclerotic agent in advanced peripheral arterial occlusive disease. We tested the effect of aqueous Padma 28 extracts on both the Creactive protein (CRP) induced expression of the pro-inflammatory cell adhesion molecule E-selectin and the anti-atherosclerotic protective enzyme heme oxygenase- 1 (HO-1) in human aortic endothelial cells.

METHODS AND RESULTS

According to FACS analysis, quantitative RT-PCR and Western blot, CRP-induced E-selectin expression was completely prevented by aqueous Padma 28 extracts. Additionally, Padma 28 mediated an up to 60-fold upregulation of HO-1 mRNA as measured by quantitative RT-PCR. This upregulation could also be demonstrated on the protein level.

CONCLUSION

Aqueous extracts of the Tibetan herbal preparation Padma 28 inhibit CRP-induced expression of the inflammatory cell adhesion molecule E-selectin and lead to upregulation of the vascular protective enzyme HO-1 in human aortic endothelial cells. These properties may be responsible for its anti-atherosclerotic effects in peripheral arterial occlusive disease.

Hemin prevents cardiac and diaphragm mitochondrial dysfunction in sepsis

Free radical-mediated mitochondrial dysfunction may play a role in the genesis of sepsis-induced multiorgan failure. Several cellular defenses protect against free radicals, including heme oxygenase. No previous study has determined if measures that increase heme oxygenase levels reduce mitochondrial dysfunction following endotoxin. The purpose of the present study was to determine if mitochondrial dysfunction following endotoxin (LPS) administration can be attenuated by administration of hemin, a pharmacological inducer of heme oxygenase. Blood pressure, heart rate, cardiac and diaphragm mitochondrial function, plasma nitrite/nitrate levels, and tissue markers of free radical generation were compared among rats given saline, LPS, hemin, or a combination of hemin and LPS. Endotoxin (LPS) administration produced large reductions in mitochondrial function (e.g., ATP production rate decreased in both tissues, P < 0.001). Administration of hemin increased tissue heme oxygenase levels, ablated LPS-induced alterations in mitochondrial function, attenuated LPS-induced increases in plasma nitrite/nitrate levels, and prevented LPS-mediated increases in tissue markers of free radical generation. These data indicate that tissue heme oxygenase levels modulate the degree of LPS-induced mitochondrial dysfunction. Measures that increase heme oxygenase levels may provide a means of reducing sepsis-induced mitochondrial dysfunction and tissue injury.

Bilirubin derived from heme degradation suppresses MHC class II expression in endothelial cells

The enzymatic action of heme oxygenase (HO) is mediated by the cleavage of heme into carbon monoxide, ferrous iron, and biliverdin/bilirubin. Here, we show that induction of HO-1 expression, an inducible form of HO, down-regulates IFN-gamma-induced MHC class II expression in endothelial cells. Among three catalytic products of HO, bilirubin, but not carbon monoxide or ferrous iron, mediated the suppressive effects of HO through the reduction of mRNA levels of Stat-1-dependent class II transactivator. Expression of HO-1 could suppress the levels of IFN-gamma-induced Stat-1 phosphorylation. This effect could be mimicked by exposing the cells to one of its catalytic products, bilirubin. In addition, HO-1 or bilirubin could modulate the transcript activities of Stat-1-driven gene expression in luciferase reporter assays. These findings suggest an important role of HO-1 in the modulation of immune responses through suppression of MHC-II expression in antigen presenting cells. Our data provide a new line of evidence supporting HO-1-targeted therapy for immune modulation.

Potential Roles for Regulatory Oxygenases in Rickettsial Pathogenesis

Clinical and experimental evidence suggests an important role for oxidative stress and associated cellular defense mechanisms in the pathogenesis of vasculopathic rickettsioses. Our laboratory has reported that R. rickettsii infection of endothelial cells in vitro induces the expression of HO-1, the inducible isoform of the antioxidant defense enzyme heme oxygenase. HO-1 plays a critical role in maintaining the integrity of the vasculature and controls the functioning of the cyclooxygenase (COX) system. This study was undertaken to investigate the expression of COX and HO isozymes during in vitro infection of EC with two major representatives of spotted fever group Rickettsia species. The mRNA expression of COX-2 was significantly increased in endothelial cells infected with R. rickettsii and R. conorii, while that of COX-1 remained unaffected. Western blot analysis using total protein lysates from infected endothelial cells and corresponding uninfected controls further confirmed specific induction of COX-2 in response to infection. ELISA measurements on culture supernatants also suggested enhanced secretion of 6-keto PGF(1alpha) (stable hydrolysis product of PGI(2) and PGE(2). As a functional consequence of HO-1 upregulation, increased expression of the iron storage protein ferritin following R. rickettsii and R. conorii infection was also evident. Since products of HO-1 and COX-2 reactions govern a variety of physiologically important functions in the vasculature, further studies to define their regulation in the host cell should provide useful insights into the pathogenesis of rickettsial diseases.

Anti-angiogenic and anti-inflammatory effects of statins: relevance to anti-cancer therapy

Angiogenesis is indispensable for the growth of solid tumors and angiogenic factors are also involved in the progression of hematological malignancies. Targeting the formation of blood vessels is therefore regarded as a promising strategy in cancer therapy. Interestingly, besides demonstration of some beneficial effects of novel anti-angiogenic compounds, recent data on the activity of already available drugs point to their potential application in anti-angiogenic therapy. Among these are the statins, the inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A reductase. Statins are very efficient in the treatment of hypercholesterolemia in cardiovascular disorders; however, their effects are pleiotropic and some are not directly related to the inhibition of cholesterol synthesis. Some reports particularly highlight the pro-angiogenic effects of statins, which are caused by low, nanomolar concentrations and are regarded as beneficial for the treatment of cardiovascular diseases. On the other hand, the anti-angiogenic activities, observed at micromolar concentrations of statins, may be of special significance for cancer therapy. Those effects are caused by the inhibition of both proliferation and migration and induction of apoptosis in endothelial cells. Moreover, the statin-mediated inhibition of vascular endothelial growth factor synthesis, the major angiogenic mediator, may contribute to the attenuation of angiogenesis. It has been suggested that the anti-cancer effect of statins can be potentially exploited for the cancer therapy. However, several clinical trials aimed at the inhibition of tumor growth by treatment with very high doses of statins did not provide conclusive data. Herein, the reasons for those outcomes are discussed and the rationale for further studies is presented.

A physiological model to study iron recycling in macrophages

Following erythrophagocytosis (EP) of senescent red blood cells (RBCs), heme iron is recycled to the plasma by tissue macrophages. This process is critical for mammalian iron homeostasis but remains elusive. We characterized a cellular model using artificially-aged murine RBCs and murine bone marrow-derived macrophages (BMDMs) and study mRNA and protein expression of HO-1, ferroportin and ferritin after EP. In vitro ageing of RBCs was obtained by raising intracellular calcium concentration. These RBCs exhibit several features of erythrocyte senescence including externalization of phosphatidyl-serine, specific binding and phagocytosis by BMDMs. During the first hours of EP, we observed a rapid increase of HO-1 and ferroportin mRNAs and proteins, whereas ferritin protein expression was progressively induced with no major changes in RNA levels. At later stages after EP, a different pattern of expression was observed with a net decrease of ferroportin, a sustained high level of HO-1, and a strong increase in ferritins. Taken together, these results suggest that after EP, iron is rapidly extracted from heme and exported by ferroportin. Surprisingly, the gene expression profile at late stages after EP, which is indicative of iron storage, is reminiscent of what is observed in inflammation. However, phagocytosis of artificially-aged red blood cells seems to repress the proinflammatory response of macrophages.

Molecular basis of heme oxygenase-1 induction: implications for chemoprevention and chemoprotection

Heme oxygenase (HO)-1, involved in the heme degradation process, is an important antioxidant enzyme. The induction of HO-1 gene expression, in response to diverse oxidative stimuli, represents a critical event in adaptive cellular response. Experimental models of various diseases, including acute inflammation, atherosclerosis, degenerative diseases, and carcinogenesis, have demonstrated that the induction of HO-1 can prevent or mitigate the symptoms associated with these ailments. Recent progress in our understanding of cellular signaling networks as critical modulators of gene transcription sheds light on the molecular basis of HO-1 gene expression. A panel of redox-sensitive transcription factors such as activator protein-1, nuclear factor- kappaB, and nuclear factor E2-related factor-2, and some of the upstream kinases have been identified as regulators of HO-1 gene induction. The scope of this review is limited to focus on molecular mechanisms underlying HO-1 expression and the significance of targeted induction of HO-1 as a strategy to achieve chemoprevention and chemoprotection.

Carbon monoxide-releasing molecules (CO-RMs) attenuate the inflammatory response elicited by lipopolysaccharide in RAW264.7 murine macrophages

The enzyme heme oxygenase-1 (HO-1) is a cytoprotective and anti-inflammatory protein that degrades heme to produce biliverdin/bilirubin, ferrous iron and carbon monoxide (CO). The anti-inflammatory properties of HO-1 are related to inhibition of adhesion molecule expression and reduction of oxidative stress, while exogenous CO gas treatment decreases the production of inflammatory mediators such as cytokines and nitric oxide (NO). CO-releasing molecules (CO-RMs) are a novel group of substances identified by our group that are capable of modulating physiological functions via the liberation of CO. We aimed in this study to examine the potential anti-inflammatory characteristics of CORM-2 and CORM-3 in an in vitro model of lipopolysaccharide (LPS)-stimulated murine macrophages. Stimulation of RAW264.7 macrophages with LPS resulted in increased expression of inducible NO synthase (iNOS) and production of nitrite. CORM-2 or CORM-3 (10-100 microM) reduced nitrite generation in a concentration-dependent manner but did not affect the protein levels of iNOS. CORM-3 also decreased nitrite levels when added 3 or 6 h after LPS exposure. CORM-2 or CORM-3 did not cause any evident cytotoxicity and produced an increase in HO-1 expression and heme oxygenase activity; this effect was completely prevented by the thiol donor N-acetylcysteine. CORM-3 also considerably reduced the levels of tumor necrosis factor-alpha, another mediator of the inflammatory response. The inhibitory effects of CORM-2 and CORM-3 were not observed when the inactive compounds, which do not release CO, were coincubated with LPS. These results indicate that CO liberated by CORM-2 and CORM-3 significantly suppresses the inflammatory response elicited by LPS in cultured macrophages and suggest that CO carriers can be used as an effective strategy to modulate inflammation.

Hemin-activated macrophages home to the pancreas and protect from acute pancreatitis via heme oxygenase-1 induction

Hemin upregulates heme oxygenase-1 (HO-1), a stress-induced enzyme implicated in protection from a variety of injuries while its related isoform HO-2 is constitutively expressed. The role of hemin or HO-1 in the pancreas and their potential modulation of pancreatic injury are unknown. We show that HO-1 is induced in pancreatitis caused by caerulein and more prominently in severe pancreatitis caused by feeding a choline-deficient diet (CDD). Intraperitoneal hemin administration dramatically increases peritoneal and pancreas macrophages that overexpress HO-1 in association with pancreatic induction of the chemoattractants monocyte chemotactic protein-1 and macrophage inflammatory protein-1alpha but not RANTES or macrophage inflammatory protein-2. Hemin administration before CDD feeding protected 8 of 8 mice from lethality while 7 of 16 controls died. Protection is mediated by HO-1-overexpressing macrophages since hemin-primed macrophages home to the pancreas after transfer to naive mice and protect from CDD-induced pancreatitis. Suppression of hemin-primed peritoneal cell HO-1 using HO-1-specific small interfering RNA prior to cell transfer abolishes protection from CDD-induced pancreatitis. Similarly, hemin pretreatment in caerulein-induced pancreatitis reduces serum amylase and lipase, decreases pancreatic trypsin generation, and protects from lung injury. Therefore, hemin-like compounds or hemin-activated macrophages may offer novel therapeutic approaches for preventing acute pancreatitis and its pulmonary complication via upregulation of HO-1.

Heme oxygenase 1 (HO‐1) regulates osteoclastogenesis and bone resorption

Heme oxygenase 1 (HO-1) plays an important role in vascular disease, transplantation, and inflammation. In animal models of acute and chronic inflammation, induction of HO-1 has anti-inflammatory and cytoprotective properties. Since inflammation is an important trigger of osteoclastogenesis, we hypothesized that HO-1 might influence osteoclastogenesis. We investigated the effects of induction of HO-1 on osteoclast formation in vitro and in vivo. Furthermore, we addressed the role of HO-1 in inflammatory bone loss in humans. When HO-1 was induced by hemin in vitro, a significant dose-dependent inhibition of osteoclastogenesis was observed. Up-regulation of HO-1 was mediated by activation of MAPK and primarily prevented differentiation of osteoclast precursors to osteoclasts, whereas it did not affect mature osteoclasts. Anti-osteoclastogenic properties of hemin were based on a down-regulation of c-fms, RANK, TRAF-6, and c-fos. In addition, induction of HO-1 inhibited TNF-triggered osteoclast differentiation in vitro as well as LPS-driven inflammatory bone loss in vivo. Furthermore, HO-1 induction suppressed osteoclastogenesis and bone destruction in a TNF-mediated arthritis. In line, assessment of synovial tissue from rheumatoid arthritis patients revealed that osteoclasts are usually HO-1 negative. Moreover, serum levels of bilirubin, a metabolite of HO-1, were elevated in rheumatoid arthritis patients without bone damage, suggesting HO-1 affects bone loss in humans. In summary, these data indicate that HO-1 negatively regulates osteoclastogenesis, leading to a positive net balance of bone.

Increased lipopolysaccharide sensitivity in alcoholic fatty livers is independent of leptin deficiency and toll-like receptor 4 (TLR4) or TLR2 mRNA expression

BACKGROUND

Both alcoholic (AFL) and nonalcoholic (NAFL) fatty livers show increased sensitivity to endotoxin-induced injury. Lipopolysaccharide (LPS) is recognized by toll-like receptor 4 (TLR4), whereas lipopeptide triggers TLR2 to induce common downstream activation of nuclear factor (NF)-kappaB and pro-inflammatory pathways that are activated in AFL and NAFL.

METHODS

Serum alanine aminotransferase (ALT), tumor necrosis factor (TNF)-alpha, and interleukin (IL)-6 levels; hepatic NF-kappaB activity; and expression of TLR2, TLR4, inducible nitric oxide synthase (iNOS), and heme oxygenase (HO)-1 mRNAs were investigated in lean and leptin-deficient ob/ob mice after LPS challenge in combination with acute or chronic alcohol feeding.

RESULTS

Increased LPS sensitivity in AFL and NAFL was characterized by elevated serum TNF-alpha and IL-6 induction. However, there was no difference in TLR2 and TLR4 mRNA levels between lean and ob/ob livers at baseline and after acute or chronic alcohol treatment. LPS increased TLR2, but not TLR4, mRNA levels in all groups. Chronic alcohol feeding and LPS increased serum ALT and TNF-alpha levels in lean but not in ob/ob mice compared with pair-fed controls. Hepatic NF-kappaB activation was increased in both ob/ob and lean mice after chronic alcohol feeding compared with pair-fed controls. Expression of iNOS, an inducer of oxidative stress, and HO-1, a cytoprotective protein, were higher in ob/ob compared with lean mice after chronic alcohol feeding. However, LPS-induced HO-1, but not iNOS, expression was attenuated in ob/ob compared with lean mice.

CONCLUSION

These results imply that the increased sensitivity of AFL to LPS occurs without up-regulation of TLR2 or TLR4 genes and may be related to an imbalance of pro-inflammatory/oxidative and cytoprotective mechanisms.

Polymerized Hemoglobin Induces Heme Oxygenase-1 Protein Expression and Inhibits Intercellular Adhesion Molecule-1 Protein Expression in Human Lung Microvascular Endothelial Cells

BACKGROUND

Our clinical trials using a polymerized hemoglobin solution (PolyHb) as a red cell substitute in severely injured patients suggested that this hemoglobin-based oxygen carrier has a systemic antiinflammatory effect. Heme oxygenase-1 (HO-1) has recently been shown to be cytoprotective, and is known to be induced by heme moieties. We investigated the effects of this hemoglobin-based oxygen carrier on HO-1 induction and proinflammatory activation of pulmonary endothelium.

STUDY DESIGN

Human lung microvascular endothelial cells were grown to confluence and preincubated with either cell media (control) or with an equal volume mixture of polymerized hemoglobin/cell media (experimental). The cell cultures were subsequently stimulated with lipopolysaccharide. HO-1 expression was detected by protein immunoblot and further quantified by ELISA; intercellular adhesion molecule-1 protein expression was measured by flow cytometry.

RESULTS

Polymerized hemoglobin induced synthesis of HO-1 protein in human lung microvascular endothelial cells and, concurrently, inhibited lipopolysaccharide-induced intercellular adhesion molecule-1 protein cell surface expression.

CONCLUSIONS

Polymerized hemoglobin attenuates lipopolysaccharide-stimulated expression of intercellular adhesion molecule-1 protein, which is associated with upregulation of the cytoprotective protein HO-1 in human pulmonary endothelial cells. This antiinflammatory effect offers a novel mechanism by which hemoglobin-based oxygen carrier solutions may be exploited therapeutically as resuscitative fluids.

Lipopolysaccharide-Induced Heme Oxygenase-1 Expression in Human Monocytic Cells Is Mediated via Nrf2 and Protein Kinase C

Monocytes play a key role in mobilization of the immune response during sepsis. In response to LPS, monocytes produce both proinflammatory mediators and regulatory proteins that counteract the inflammation and oxidative stress. In murine macrophages, LPS stimulates expression of heme oxygenase 1 (HO-1), a cytoprotective enzyme that catalyzes the degradation of heme. The HO-1 5'-untranslated region, similarly to other cytoprotective genes, contains antioxidant-response elements (AREs) that can bind the transcription factor NF-E2-related factor 2 (Nrf2). At present, the role of Nrf2 in LPS-induced HO-1 expression in monocytic cells has not been investigated. In this study, LPS induced HO-1 mRNA and protein expression in human monocytes and THP-1 cells. Nrf2 translocated from the cytosol to the nucleus in response to LPS and bound to the ARE site in the human HO-1 promoter. In addition, a dominant negative Nrf2 mutant inhibited LPS-induced HO-1 mRNA expression but not TNF-alpha mRNA expression in THP-1 cells. Ro-31-8220, a pan-protein kinase C (PKC) inhibitor, and Go6976, a classical PKC inhibitor, blunted LPS-induced HO-1 mRNA expression in monocytes and THP-1 cells. Both PKC inhibitors also blocked LPS-induced Nrf2 binding to the ARE. These results indicate that LPS-induced HO-1 expression in human monocytic cells requires Nrf2 and PKC.

Inhibition of iNOS gene expression by quercetin is mediated by the inhibition of IkappaB kinase, nuclear factor-kappa B and STAT1, and depends on heme oxygenase-1 induction in mouse BV-2 microglia

In the present study, experiments were performed to explore the action of quercetin, the most widely distributed flavonoids, and its major metabolite, quercetin-3'-sulfate, on lipopolysaccharide (LPS)- and interferon-gamma (IFN-gamma)-induced nitric oxide (NO) production in BV-2 microglia. Quercetin could suppress LPS- and IFN-gamma-induced NO production and inducible nitric oxide synthase (iNOS) gene transcription, while quercetin-3'-sulfate had no effect. LPS-induced IkappaB kinase (IKK), nuclear factor-kappaB (NF-kappaB) and activating protein-1 (AP-1) activation, and IFN-gamma-induced NF-kappaB, signal transducer and activator of transcription-1 (STAT1) and interferon regulatory factor-1 (IRF-1) activation were reduced by quercetin. Moreover quercetin was able to induce heme oxygenase-1 expression. To address the involvement of heme oxygenase-1 induction in iNOS inhibition, heme oxygenase-1 antisense oligodeoxynucleotide was used. Quercetin-mediated inhibition of NO production and iNOS protein expression were partially reversed by heme oxygenase-1 antisense oligodeoxynucleotide, but was mimicked by hemin, a heme oxygenase-1 inducer. The involvement of signal pathways in quercetin-induced heme oxygenase-1 gene expression was associated with tyrosine kinase and mitogen-activated protein kinases activation. All these results suggest quercetin should provide therapeutic benefits for suppression of inflammatory-related neuronal injury in neurodegenerative diseases.

Nitrite is a signaling molecule and regulator of gene expression in mammalian tissues

Mammalian tissues produce nitric oxide (NO) to modify proteins at heme and sulfhydryl sites, thereby regulating vital cell functions. The majority of NO produced is widely assumed to be neutralized into supposedly inert oxidation products including nitrite (NO2(-)). Here we show that nitrite, also ubiquitous in dietary sources, is remarkably efficient at modifying the same protein sites, and that physiological nitrite concentrations account for the basal levels of these modifications in vivo. We further find that nitrite readily affects cyclic GMP production, cytochrome P450 activities, and heat shock protein 70 and heme oxygenase-1 expression in a variety of tissues. These cellular activities of nitrite, combined with its stability and abundance in vivo, suggest that this anion has a distinct and important signaling role in mammalian biology, perhaps by serving as an endocrine messenger and synchronizing agent. Thus, nitrite homeostasis may be of great importance to NO biology.

Bilirubin decreases nos2 expression via inhibition of NAD(P)H oxidase: implications for protection against endotoxic shock in rats

We investigated a possible beneficial role for bilirubin, one of the products of heme degradation by the cytoprotective enzyme heme oxygenase-1 in counteracting Escherichia coli endotoxin-mediated toxicity. Homozygous jaundice Gunn rats, which display high plasma bilirubin levels due to deficiency of glucuronyl transferase activity, and Sprague-Dawley rats subjected to sustained exogenous bilirubin administration were more resistant to endotoxin (LPS)-induced hypotension and death compared with nonhyperbilirubinemic rats. LPS-stimulated production of nitric oxide (NO) was significantly decreased in hyperbilirubinemic rats compared with normal animals; this effect was associated with reduction of inducible NO synthase (NOS2) expression in renal, myocardial, and aortic tissues. Furthermore, NOS2 protein expression and activity were reduced in murine macrophages stimulated with LPS and preincubated with bilirubin at concentrations similar to that found in the serum of hyperbilirubinemic animals. This effect was secondary to inhibition of NAD(P)H oxidase since 1) inhibition of NAD(P)H oxidase attenuated NOS2 induction by LPS, 2) bilirubin decreased NAD(P)H oxidase activity in vivo and in vitro, and 3) down-regulation of NOS2 by bilirubin was reversed by addition of NAD(P)H. These findings indicate that bilirubin can act as an effective agent to reduce mortality and counteract hypotension elicited by endotoxin through mechanisms involving a decreased NOS2 induction secondary to inhibition of NAD(P)H oxidase.

Inhibition of heme oxygenase-1 increases responsiveness of pancreatic cancer cells to anticancer treatment

Heme oxygenase-1 (HO-1) is believed to represent a key enzyme for the protection of cells against "stress." Its overexpression in different types of human cancers supports the notion that HO-1 provides a growth advantage and contributes to cellular resistance against chemotherapy and radiotherapy. Given the poor survival rates of patients with pancreatic cancer due to its aggressive growth behavior and its exceptional resistance to all known forms of anticancer treatment, we have investigated the expression of HO-1 in human pancreatic cancer cells growth behavior and prognosis. Expression of HO-1 was analyzed in human pancreatic cancer samples in comparison with normal pancreas by quantitative PCR, Western blot, and confocal microscopy. The influence of radiotherapy and chemotherapy on HO-1 expression in pancreatic cancer cell lines was evaluated. Furthermore, HO-1 expression was specifically suppressed by small interfering RNA transfection and subsequently the alterations of growth behavior and resistance to anticancer treatment were tested. Human pancreatic cancer showed a 6-fold and 3.5-fold HO-1 up-regulation in comparison to normal pancreas based on mRNA and protein level, respectively (P < 0.05). Cancer tissues revealed marked HO-1 immunoreactivity in tumor cells and in tumor associated immunocytes. Treatment of the pancreatic cancer cell lines with gemcitabine or radiation strongly induced HO-1 expression. Targeted knockdown of HO-1 expression led to pronounced growth inhibition of the pancreatic cancer cells and made tumor cells significantly more sensitive to radiotherapy and chemotherapy. Therefore, specific inhibition of HO-1 expression may be a new option in pancreatic cancer therapy and may be used as sensitizer to chemotherapy and radiotherapy.

rAAV-mediated stable expression of heme oxygenase-1 in stellate cells: a new approach to attenuate liver fibrosis in rats

Liver fibrosis is the consequence of activation of hepatic stellate cells mediated by persistent or recurrent liver injury, where oxidative stress or inflammatory response resulting from immune cells and cytokines are involved. Targeting of hepatic stellate cells could be an important strategy for the therapy of liver fibrosis. In this study, we showed a tropism of recombinant adeno-associated virus (rAAV, serotype 2) with high efficiency in transduction of a homeostatic gene, heme oxygenase-1 (HO-1), to activated stellate cells. The binding of rAAVs to stellate cells increased significantly after serum-stimulated activation compared with quiescent status. Portal injection of rAAVs to normal or carbon tetrachloride (CCl(4))-induced liver fibrosis showed a distinct distribution of rAAV binding. The majority of injected rAAVs bound to the cells in fibrotic areas that were associated with higher expression levels of fibroblast growth factor receptor-1alpha at 2 hours after administration. Isolation of different types of cells from CCl(4)-induced fibrotic livers showed predominant expression of transgene in stellate cells after rAAV/HO-1 administration on day 3 and remained stable for 12 weeks. In addition, HO-1-transduced stellate cells showed reduced transcript levels of type 1 collagen and impaired proliferative ability compared with controls. With this approach, the severity of established micronodular cirrhosis was markedly reduced. In conclusion, these findings suggest a new approach for the treatment of liver fibrosis using adeno-associated virus-mediated gene transfer.

Processes Involved in the Site-Specific Effect of Probucol on Atherosclerosis in Apolipoprotein E Gene Knockout Mice

OBJECTIVE

To elucidate processes by which the antioxidant probucol increases lesion size at the aortic sinus and decreases atherosclerosis at more distal sites in apolipoprotein E-deficient (apoE(-/-)) mice.

METHODS AND RESULTS

Male apoE(-/-) mice were fed high-fat chow with 1% (w/w) probucol or without (controls) for 6 months, before aortic sinus, arch, and descending aorta were analyzed separately for lesion size and composition. Compared with control, probucol significantly increased lesion size by 33% at the sinus, but it inhibited atherosclerosis at the descending aorta by 94%. Sites where atherosclerosis was inhibited contained substantially fewer macrophages, less lipids (cholesterol and cholesteryl esters), and endogenous antioxidant (alpha-tocopherol), but not oxidized lipids, and the extent to which probucol metabolism occurred was increased. Compared with control, aortic sinus lesions of probucol mice contained a substantially increased content of extracellular matrix, but decreased total cell and macrophage density, comparable levels of lipids and alpha-tocopherol, and decreased concentrations of oxidized lipids (cholesteryl ester hydroperoxides, F2-isoprostanes, and 7-ketocholesterol).

CONCLUSIONS

Probucol affects atherosclerosis in apoE(-/-) mice independent of the accumulation of arterial lipid oxidation products, thereby dissociating the 2 processes. Rather, probucol exerts antiinflammatory activity by decreasing accumulation of macrophages in lesions, and it promotes a more stable lesion composition at the aortic sinus.

Toll-like receptor and heme oxygenase-1 signaling in hepatic ischemia/reperfusion injury

Ischemia/reperfusion injury (IRI) represents the major problem in clinical liver transplantation. We have shown that toll-like receptor 4 (TLR4) signaling is specifically required in initiating antigen-independent IRI leading to liver inflammation, whereas local induction of anti-oxidant heme oxygenase-1 (HO-1) is cytoprotective. This study analyzes in vivo interactions between HO-1 and sentinel TLR system in the pathophysiology of liver IRI. Using a 90-min lobar warm ischemia model, wild type (WT), TLR4 KO/mutant and TLR2 KO mice were first assessed for the severity of hepatocellular damage at 6 h postreperfusion. Unlike in WT or TLR2-deficient mice, disruption/absence of TLR4 pathway reduced IRI, as manifested by liver function (serum alanine aminotransferase levels), histology (Suzuki's scores), neutrophil infiltration (myeloperoxidase activity) and local/systemic TNF-alpha production (mRNA/protein levels). Moreover, defective TLR4 but not TLR2 signaling increased mRNA/protein HO-1 expression. In contrast, tin protoporphyrin-mediated HO-1 inhibition restored hepatic damage in otherwise IRI-resistant TLR4 mutant/KO mice. CoPP-induced HO-1 overexpression ameliorated hepatic damage in IRI-susceptible TLR2 KO mice, comparable with WT controls, and concomitantly diminished TLR4 levels. In conclusion, this study highlights the importance of cross talk between HO-1 and TLR system in the mechanism of hepatic IRI. Hepatic IRI represents a case for innate immunity in which HO-1 modulates proinflammatory responses that are triggered via TLR4 signaling, a putative HO-1 repressor.

CD40: A Mediator of Pro- and Anti-Inflammatory Signals in Renal Tubular Epithelial Cells

Infiltration of immune cells into the renal interstitium is characteristic of chronic inflammatory kidney diseases. CD4+ T cells and platelets express CD40 ligand (CD40L) and are reported to mediate proinflammatory events in renal proximal tubular epithelial cells (RPTEC) via interaction with CD40. In other cell types, CD40 signals can also induce protective genes. Here, human RPTEC were treated with sCD40L to ligate CD40, and a significant increase in the generation of proinflammatory reactive oxygen species was found; however, CD40-activated cells did not undergo apoptosis. This suggests that CD40 signals may simultaneously induce antiapoptotic genes for cytoprotection of RPTEC. Heme oxygenase-1 (HO-1) expressed in RPTEC serves as a protective gene, but it is not known whether it is regulated by CD40. Next, RPTEC were transiently transfected with a full-length HO-1 promoter-luciferase construct and were treated with sCD40L. CD40 ligation was found to significantly increase HO-1 promoter activity. By electrophoretic mobility shift assay, it was confirmed that CD40 signaling induced the transcriptional activation of HO-1 through the binding of NF-kappaB to its promoter. By Western blot analysis, a marked increase in HO-1 protein expression following CD40 ligation was also found. These observations are of clinical significance because it was found that CD40 and HO-1 are induced in expression in vivo in inflamed rejecting kidney biopsies and co-expressed in renal tubules. Therefore, ligation of CD40 in RPTEC promotes both inflammatory and anti-inflammatory processes. Regulating the balance between these two events may be of importance in the prevention of tubular injury associated with renal disease.

Pharmacogenomic profiling of an oxidative stress-mediated spongiform encephalopathy

The majority of cellular superoxide is generated in the mitochondria as a by-product of normal oxidative metabolism. In the mitochondria, superoxide is detoxified by manganese superoxide dismutase (SOD2). Mice lacking SOD2 demonstrate a multifaceted neonatal lethal phenotype, including a spongiform encephalopathy that is preventable through antioxidant treatment. The molecular events behind the observed pathology in the cortex of these mice are unknown. We hypothesized that the lack of SOD2 would result in significant changes in cortical gene expression and that therapeutically beneficial antioxidant treatment would normalize the expression of some genes, providing insight into the mechanism by which mitochondrial oxidative stress results in neurodegeneration. We report the identification of gene expression profiles associated with this paradigm, which characterize the degree of response to the pharmacologic intervention. We have identified specific pathways targeted by endogenous oxidative stress, including glutathione metabolism, iron metabolism, and cell-survival pathways centering on the kinase AKT. The normalization of expression of some of these pathways by antioxidant treatment suggests approaches to treating disease in which endogenous oxidative stress plays a role.

Mitochondrial Respiratory Chain and NAD(P)H Oxidase Are Targets for theAntiproliferative Effect of Carbon Monoxide in Human Airway SmoothMuscle

Carbon monoxide (CO), one of the end products of heme oxygenase activity, inhibits smooth muscle proliferation by decreasing ERK1/2 phosphorylation and cyclin D1 expression, a signaling pathway that is known to be modulated by reactive oxygen species (ROS) in airway smooth muscle cells (ASMCs). Two important sources of ROS involved in cell signaling are the membrane NAD(P)H oxidase and the mitochondrial respiratory chain. Thus, that CO could modulate redox signaling in ASMCs by interacting with the heme moiety of NAD(P)H oxidase and/or the respiratory chain is a plausible hypothesis. Here we show that a recently identified carbon monoxide-releasing molecule, [Ru(CO)3Cl2]2 (or CORM-2) 1) inhibits NAD(P)H oxidase cytochrome b558 activity, 2) increases oxidant production by the mitochondria, and 3) inhibits ASMC proliferation and phosphorylation of the ERK1/2 mitogen-activated protein kinase and expression of cyclin D1, two critical pathways involved in muscle proliferation. No such effects were observed with the negative control (Ru(Me2SO)4Cl2), which does not contain CO groups. Because both diphenylene iodinium or apocynin (inhibitors of NAD(P)H oxidase) and rotenone (a molecule that increases mitochondrial ROS production by blocking the respiratory chain) mimicked the effect of CORM-2 on cyclin D1 expression and ASMC proliferation, the antiproliferative effect of CORM-2 is probably related to inhibition of cytochromes on both NAD(P)H oxidase and the respiratory chain. The involvement of increased mitochondria-derived oxidants is substantiated by the findings showing that the antioxidant N-acetylcysteine partially inhibited the effects of CORM-2. This study provides a new mechanism to explain redox signaling by CO.

An integral role for heme oxygenase-1 and carbon monoxide in maintaining peripheral tolerance by CD4+CD25+ regulatory T cells

Over the past decade, a great deal of interest and attention has been directed toward a population of regulatory T cells (Treg) coexpressing the markers CD4 and CD25. The hallmark phenotype of this cell population resides in its ability to dominantly maintain peripheral tolerance and avert autoimmunity. Despite robust research interest in Treg, their mechanism of action and interaction with other cell populations providing immune regulation remains unclear. In this study, we present a model for Treg activity that implicates carbon monoxide, a by-product of heme oxygenase-1 activity, as an important and underappreciated facet in the suppressive capacity of Treg. Our hypothesis is based on recent evidence supporting a role for heme oxygenase-1 in regulating immune reactivity and posit carbon monoxide to function as a suppressive molecule. Potential roles for indoleamine 2,3-dioxygenase, costimulatory molecules, and cytokines in tolerance induction are also presented. This model, if validated, could act as a catalyst for new investigations into Treg function and ultimately result in novel methods to modulate Treg biology toward therapeutic applications.

The distal sequence element of the selenocysteine tRNA gene is a tissue-dependent enhancer essential for mouse embryogenesis

Appropriate expression of the selenocysteine tRNA (tRNA(Sec)) gene is necessary for the production of an entire family of selenoprotein enzymes. This study investigates the consequence of disrupting an upstream enhancer region of the mouse tRNA(Sec) gene (Trsp) known as the distal sequence element (DSE) by use of a conditional repair gene targeting strategy, in which a 3.2-kb insertion was introduced into the promoter of the gene. In the absence of DSE activity, homozygous mice failed to develop in utero beyond embryonic day 7.5 and had severely decreased levels of selenoprotein transcript. Cre-mediated removal of the selection cassette recovered DSE regulation of Trsp, restoring wild-type levels of tRNA(Sec) expression and allowing the generation of viable rescued mice. Further analysis of targeted heterozygous adult mice revealed that the enhancer activity of the DSE is tissue dependent since, in contrast to liver, heart does not require the DSE for normal expression of Trsp. Similarly, in mouse cell lines we showed that the DSE functions as a cell-line-specific inducible element of tRNA(Sec). Together, our data demonstrate that the DSE is a tissue-dependent regulatory element of tRNA(Sec) expression and that its activity is vital for sufficient tRNA(Sec) production during mouse embryogenesis.

Identification of the receptor scavenging hemopexin-heme complexes

Heme released from heme-binding proteins on internal hemorrhage, hemolysis, myolysis, or other cell damage is highly toxic due to oxidative and proinflammatory effects. Complex formation with hemopexin, the high-affinity heme-binding protein in plasma and cerebrospinal fluid, dampens these effects and is suggested to facilitate cellular heme metabolism. Using a ligand-affinity approach, we purified the human hemopexin-heme receptor and identified it as the low-density lipoprotein receptor-related protein (LRP)/CD91, a receptor expressed in several cell types including macrophages, hepatocytes, neurons, and syncytiotrophoblasts. Binding experiments, including Biacore analysis, showed that hemopexin-heme complex formation elicits the high receptor affinity. Uptake studies of radio-labeled hemopexin-heme complex in LRP/CD91-expressing COS cells and confocal microscopy of the cellular processing of fluorescent hemopexin-heme complex established the ability of LRP/CD91 to mediate hemopexin-heme internalization resulting in cellular heme uptake and lysosomal hemopexin degradation. Uptake of hemopexin-heme complex induced LRP/CD91-dependent heme-oxygenase 1 mRNA transcription in cultured monocytes. In conclusion, hemopexin-heme complexes are removed by a receptor-mediated pathway showing striking similarities to the CD163-mediated haptoglobin-hemoglobin clearance in macrophages. Furthermore, the data indicate a hitherto unknown role of LRP/CD91 in inflammation.

Heme Oxygenase-1 Gene Activation by the NAD(P)H Oxidase Inhibitor 4-(2-Aminoethyl) Benzenesulfonyl Fluoride via a Protein Kinase B, p38-dependent Signaling Pathway in Monocytes

Heme oxygenase (HO)-1 is the inducible isoform of the rate-limiting enzyme of heme degradation and modulates the inflammatory immune response. Because HO-1 is up-regulated by NAD(P)H oxidase activators such as lipopolysaccharide and 12-O-tetradecanoylphorbol-13-acetate in monocytic cells, we investigated the gene regulation of HO-1 by the chemical NAD(P)H oxidase inhibitor 4-(2-aminoethyl) benzenesulfonyl fluoride (AEBSF). Unexpectedly, AEBSF induced endogenous gene expression and promoter activity of HO-1 in cell cultures of human and mouse monocytes. Inhibition of the phosphatidylinositol 3-kinase/protein kinase B (PKB) pathway by pharmacological inhibitors and cotransfection of an expression vector for a dominant negative mutant of PKB reduced the AEBSF-dependent induction of HO-1 gene transcription. Accordingly, overexpressed constitutively active PKB markedly up-regulated HO-1 promoter activity. AEBSF activated the mitogen-activated protein kinases (MAPK) JNK and p38. Inhibition of p38alpha and p38beta, but not that of JNK or p38gamma and p38delta, prevented the induction of HO-1 gene expression by AEBSF. p38 was stimulated by AEBSF in a PKB-dependent manner as demonstrated by a luciferase assay with a Gal4-CHOP fusion protein. Finally, AEBSF- and PKB-dependent induction of HO-1 promoter activity was reduced by simultaneous mutation of an E-box motif (-47/-42) and a cAMP response element/AP-1 element (-664/-657) of the proximal HO-1 gene promoter. Overexpression of the basic helix-loop-helix transcription factor USF2 and coactivator p300 enhanced the AEBSF-dependent response of the HO-1 promoter. The data suggest that the transcriptional induction of HO-1 gene expression by AEBSF is mediated via activation of a PKB, p38 MAPK signaling pathway.

Bilirubin and the risk of common non-hepatic diseases

Bilirubin is a potent antioxidant but can be toxic at high concentrations. This article critically reviews the reported relationships of plasma bilirubin levels to the severity and/or incidence of various common non-hepatic diseases. Plasma bilirubin levels are reportedly negatively related to the risk of atherosclerotic diseases, cancers, demyelinating neuropathies and seasonal affective disorder. By contrast, the incidence and severity of schizophrenia are increased by elevated bilirubin levels. The data strongly suggest that the level of plasma bilirubin should be considered as a risk factor for several common non-hepatic diseases. Additional studies are needed to clarify the mechanisms of this influence, which are thought to be related to unconjugated bilirubin counteracting the oxidative stress underlying these disorders.

Glutathione depletion inhibits lipopolysaccharide-induced intercellular adhesion molecule 1 synthesis

Cellular redox status is known to regulate a number of biological processes, including the activation of inflammatory genes. Our previous studies demonstrated that thiol depletion using diethyl maleate (DEM) reduced neutrophil sequestration in animal models of inflammation, an effect primarily mediated by impaired upregulation of the adhesion molecule, ICAM-1. The present studies were performed to discern the mechanism whereby DEM prevents LPS-induced ICAM-1 expression in human umbilical vein endothelial cells. DEM caused a time- and concentration-dependent inhibition of ICAM-1 expression in LPS-stimulated HUVEC by blocking induction of gene transcription. Interestingly, DEM had little effect on the degradation of the inhibitory protein IkappaB-alpha, but rather appeared to prevent translocation of the transcription factor NF-kappaB into the nucleus. Readdition of glutathione following DEM treatment restored the ability of LPS to induce NF-kappaB translocation and ICAM-1 synthesis. DEM plus LPS caused synergistic induction of heme oxygenase-1 (HO-1), suggesting its role in the inhibitory effects of DEM. However, HO-1 was shown to be neither sufficient nor necessary for the anti-inflammatory effects of glutathione depletion. These studies illustrate that thiol depletion may represent a potential therapy for inflammation, exerting its effects via a distinct mechanism on cell signaling pathways.

Interleukin 10 attenuates neointimal proliferation and inflammation in aortic allografts by a heme oxygenase-dependent pathway

Interleukin 10 (IL-10) is a pleiotropic cytokine with well known antiinflammatory, immunosuppressive, and immunostimulatory properties. Chronic allograft rejection, characterized by vascular neointimal proliferation, is a major cause of organ transplant loss, particularly in heart and kidney transplant recipients. In a Dark Agouti to Lewis rat model of aortic transplantation, we evaluated the effects of a single intramuscular injection of a recombinant adeno-associated viral vector (serotype 1) encoding IL-10 (rAAV1-IL-10) on neointimal proliferation and inflammation. rAAV1-IL-10 treatment resulted in a significant reduction of neointimal proliferation and graft infiltration with macrophages and T and B lymphocytes. The mechanism underlying the protective effects of IL-10 in aortic allografts involved heme oxygenase 1 (HO-1) because inhibition of HO activity reversed not only neointimal proliferation but also inflammatory cell infiltration. Our results indicate that IL-10 attenuates neointimal proliferation and inflammatory infiltration and strongly imply that HO-1 is an important intermediary through which IL-10 regulates the inflammatory responses associated with chronic vascular rejection.

A molecular cascade showing nitric oxide-heme oxygenase-1-vascular endothelial growth factor-interleukin-8 sequence in human endothelial cells

Heme oxygenase (HO)-1 has been shown to be an important biological target of nitric oxide (NO). NO can induce HO-1 expression and IL-8 production, particularly, in endothelial cells. Interestingly, HO-1 tends to induce the production of vascular endothelial growth factor (VEGF) that is involved in endothelial IL-8 syntheses. Whether HO-1 expression by NO may provide a link with IL-8 or VEGF synthesis was investigated in human umbilical vein endothelial cells (HUVECs). The NO donor S-nitroso-N-acetyl-penicillamine (SNAP) dose-dependently increased IL-8 and VEGF productions and HO-1 expression in HUVECs. Transfection with either HO-1 small interfering RNA or HO-1 antisense oligodeoxynucleotide abrogated the ability of SNAP to induce HO-1 expression and IL-8 and VEGF productions. Both pharmacological induction and gene transfer of HO-1 directly induced IL-8 and VEGF productions. Anti-VEGF neutralizing antibody blocked SNAP-mediated IL-8 production and VEGF itself induced IL-8 production, whereas anti-IL-8 neutralizing antibody had no effect on VEGF production in SNAP-treated HUVECs. Neither anti-VEGF nor anti-IL-8 antibodies influenced SNAP-induced HO-1 expression. Moreover, neither VEGF nor IL-8 showed an additive effect on SNAP-induced HO-1 expression. HO-1 transfection had no significant effect on productions of other CXC chemokines, such as growth-related oncogen-alpha and epithelial neutrophil activation peptide-78. Taken together, these results provide a molecular cascade showing NO-HO-1-VEGF-IL-8 sequence in human endothelial cells.

HO in pregnancy

The enzyme heme oxygenase (HO) has been implicated in several physiological functions throughout the body including control of vascular tone and regulation of the inflammatory and apoptotic cascades as well as contributing to the antioxidant capabilities in several organ systems. These various properties attributed to HO are carried out through the catalytic products of heme degradation, namely carbon monoxide (CO), biliverdin, and free iron (Fe2+). As the newly emerging roles of HO in normal organ function have come to light, researchers in several disciplines have assessed the role of this enzyme in various physiological and pathological changes taking place in the human body over a lifetime. Included in this new wave of interest is the involvement of HO, and its by-products, in the normal function of the vital organ of pregnancy, the placenta. In this review the role of HO, and its catalytic products, will be examined in the context of pregnancy. The different isoforms of the HO enzyme (HO-1, HO-2, HO-3) have been localized throughout placental tissue, and have been shown to be physiologically active. The HO protein and more specifically its catalytic by-products (CO, biliverdin, and Fe2+) have been postulated to be involved in the maintenance of uterine quiescence throughout gestation, regulation of hemodynamic control within the uterus and placenta, regulation of the apoptotic and inflammatory cascades in trophoblast cells, and the maintenance of a balance of the oxidant-antioxidant status within the placental tissues. The association between this enzyme system, and its above-noted roles throughout pregnancy, with the hypertensive disorder of pregnancy preeclampsia (PET), will also be examined. It is hypothesized that a decrease in HO expression and/or activity throughout gestation would be capable of initiating several pathological processes involved in the etiology of PET. This hypothesis has led to further discussion emphasizing the possibility of novel therapeutic designs targeting this enzyme system for the treatment of PET.

Changes in gene expression profiles of multiple myeloma cells induced by arsenic trioxide (ATO): possible mechanisms to explain ATO resistance in vivo

Multiple myeloma (MM) is an incurable plasma cell malignancy marked by eventual resistance to therapy. Although arsenic trioxide (ATO) can induce apoptosis in MM cell lines, the in vivo activity of ATO in MM has been disappointing. The existence of ATO resistance mechanisms in MM can be inferred. We sought to generate hypotheses for ATO resistance by studying the gene expression profiles of MM cells that survived in culture with 0.5 micromol/l ATO. Among the 31 genes whose quantitative levels of expression (QLE) significantly increased in ATO were haem oxygenase 1 (HO-1) and metallothionein-2A (MT-2A). Among the 56 genes whose QLE were significantly decreased were genes that modulate cell cycling [BTBD2 and IGFBP7 (mac25)] and sensitivity to reactive oxygen species (ROS) (BACH2). HO-1 exerts an anti-apoptotic effect in ischaemic cells, and MT-2A chelates ATO intracellularly. Inhibition of HO-1 with tin protoporphyrin enhances ROS in MM cells in ATO, and addition of N-acetylcysteine increases MT-2A. Protective antioxidant responses occur in MM cells exposed to ATO, and may occur in stromal cells as well, and act to quench ROS and provide diffusible anti-apoptotic factors. They may also involve cysteine-rich proteins that chelate ATO and modulate redox-sensitive residues on proteins, such as nuclear factor kappa B and p53. A better understanding of ATO resistance will enable ATO to be combined with other agents for MM.

Heme oxygenase-1-generated biliverdin ameliorates experimental murine colitis

BACKGROUND

Heme oxygenase-1 (HO-1) seems to have an important protective role in acute and chronic inflammation. The products of heme catalysis, biliverdin/bilirubin, carbon monoxide (CO), and iron (that induces apoferritin) mediate the beneficial effects of HO-1. Blockade of HO-1 activity results in exacerbation of experimental colitis. We tested whether HO-1 has protective effects in the development of colitis and determined that specific enzymatic products of HO-1 are responsible for these effects.

METHODS

Colitis was induced by oral administration of dextran sodium sulfate (5%) to C57BL/6 mice for 7 days. HO-1 was up-regulated by cobalt-protoporphyrin (5 mg/kg, intraperitoneally). Biliverdin, exogenous CO, or the iron chelator desferrioxamine was administered to other groups.

RESULTS

Cobalt-protoporphyrin treatment resulted in significant up-regulation of HO-1 protein in mucosal and submucosal cells. Induction of HO-1 was associated with significantly less loss of body weight in mice with induced colitis (-12% versus -22% in the control animals, P < 0.001). Development of diarrhea and gastrointestinal hemorrhage was substantially delayed in animals in which HO-1 was induced, and mucosal injury was significantly attenuated. Administration of CO or desferrioxamine alone had no significant effects, whereas enhanced protection with lesser evidence of bowel inflammation was observed with systemic biliverdin administration (50 micromol/kg, 3 times per day, intraperitoneally).

CONCLUSIONS

We conclude that heightened HO-1 expression or administration of biliverdin ameliorates dextran sodium sulfate-induced experimental colitis. Novel therapeutic strategies based on HO-1 and/or biliverdin administration may have use in inflammatory bowel disease.

Increased serum HO-1 in hemophagocytic syndrome and adult-onset Still's disease: use in the differential diagnosis of hyperferritinemia

Heme oxygenase-1 (HO-1), an inducible heme-degrading enzyme, is expressed by macrophages and endothelial cells in response to various stresses. Because ferritin synthesis is stimulated by Fe²⁺, which is a product of heme degradation, we examined the relation between HO-1 and ferritin levels in the serum of patients with hemophagocytic syndrome (HPS), adult-onset Still's disease (ASD), and other diseases that may cause hyperferritinemia. Seven patients with HPS, 10 with ASD, 73 with other rheumatic diseases, 20 with liver diseases, 10 recipients of repeated blood transfusion because of hematological disorders, and 22 healthy volunteers were enrolled. Serum HO-1 and ferritin levels were determined by ELISA. Expression of HO-1 mRNA and protein by peripheral blood mononuclear cells (PBMCs) was determined by real-time PCR and immunocytochemical techniques, respectively. Serum levels of HO-1 were significantly higher in patients with active HPS and ASD than in the other groups (P < 0.01). HO-1 levels were not elevated in patients with other causes of hyperferritinemia but were moderately elevated in patients with dermatomyositis/polymyositis. Among patients with HPS and ASD, serum HO-1 levels correlated closely with serum ferritin levels, and the levels of both returned to normal after therapy had induced remission. Increased expression of HO-1 mRNA was confirmed in PBMCs from some patients with HPS and ASD. Hyperferritinemia correlated closely with increased serum HO-1 in patients with HPS and ASD but not other conditions, indicating that measurement of serum HO-1 and ferritin levels would be useful in the differential diagnosis of hyperferritinemia and perhaps also in monitoring disease activity in HPS and ASD.

Paradoxical enhancement of oxidative cell injury by overexpression of heme oxygenase-1 in an anchorage-dependent cell ECV304

There has been increasing evidence suggesting the potent anti-inflammatory roles of heme oxygenase-1 (HO-1) in protecting renal tubular epithelial cells, vascular endothelial cells, and circulating monocytes. Based on these findings, novel therapeutic interventions have been proposed to control the expression of endothelial HO-1 levels to ameliorate various vascular diseases. We evaluated the effect of HO-1 gene transfer into an anchorage-dependent cell, ECV304. Effect of HO-1 production on the cell injury induced by hydrogen peroxide was evaluated after hemin stimulation and after HO-1 gene transfection. Morphological changes and the induction of various anti-apoptotic proteins were examined at the same time. Levels of HO-1 expression were variable in different clones of HO-1-transfected ECV304 cells. Among these, the clones with moderate levels of HO-1 expression were significantly more resistant to oxidative stress. In contrast, those with the highest levels of HO-1 exhibited paradoxically enhanced susceptibility to oxidative injury. Interestingly, the cell survival after oxidative stress was in parallel with the levels of Bcl-2 expression and of fibronectin receptor, alpha5 integrin. It is suggested from these results, that excessive HO-1 not only leads to enhanced cell injury, but also prolongs the repair process of the injured endothelial tissue. However, HO-1 reduces the oxidative cell injury and protects the endothelial cells, if its expression is appropriately controlled.

Upregulation of heme oxygenase-1 gene by turpentine oil-induced localized inflammation: involvement of interleukin-6

Heme oxygenase-1 (HO-1) is the inducible isoform of an enzyme family responsible for heme degradation and was suggested to be involved in the acute phase response in the liver. However, the mechanisms of the HO-1 regulation under inflammatory conditions are poorly understood. Therefore, the purpose of the current work was to study the expression of HO-1 in the liver and other organs of rats with a localized inflammation after intramuscular injection of turpentine oil (TO). Since interleukin-6 (IL-6) is known to be a principal mediator of inflammation, the levels of this cytokine were also estimated in the animal model used. HO-1 and IL-6 expression was evaluated by Northern blot, in situ hybridization, Western blot, immunohistochemistry and enzyme-linked immunosorbent assay. In the liver and injured muscle, the HO-1 mRNA levels were dramatically increased 4-6 h after TO administration. HO-1 protein levels in the liver were elevated starting from 6-12 h after the treatment. In other internal organs such as the heart, kidney and large intestine, only a slight induction of HO-1 mRNA was observed. IL-6-specific transcripts appeared only in the injured muscle and were in accordance with serum levels of IL-6. In turn, temporal expression of IL-6 in the muscle and circulatory IL-6 levels correlated well with HO-1 expression in the liver and injured muscle. In the liver of control rats HO-1 protein was detected in Kupffer cells, while in TO-injected rats also hepatocytes became strongly HO-1 positive. Conversely, in the injured muscle, HO-1 immunoreactivity was attributed only to macrophages. Our data demonstrate that during localized inflammation HO-1 expression was rapidly and strongly induced in macrophages of injured muscle and in hepatocytes, and IL-6 derived from injured muscle seems to be responsible for the HO-1 induction in the liver.

Adenovirus-Mediated Transfer and Overexpression of Heme Oxygenase 1 cDNA in Lungs Attenuates Elastase-Induced Pulmonary Emphysema in Mice

Heme oxygenase 1 (HO-1) is an inducible enzyme that catalyzes heme to generate bilirubin, ferritin, and carbon monoxide. Because enhanced expression of HO-1 provides an anti-inflammatory effect and confers cytoprotection, we examined whether HO-1 overexpression induced by inoculation of mice with an adenovirus encoding HO-1 (Ad.HO-1) in the lung would prevent pulmonary emphysema induced by porcine pancreatic elastase (PPE). Pretreatment with Ad.HO-1, which upregulated production of HO-1 in the lung, attenuated the PPE-induced increase of neutrophils in bronchoalveolar lavage fluid (BALF) and enlargement of alveoli. It also reduced PPE-induced elevated levels of tumor necrosis factor alpha, interleukin (IL)-6, and keratinocyte-derived chemokine, and increased the level of anti-inflammatory cytokine IL-10 in BALF. These results suggest that Ad.HO-1-induced HO-1 overexpression suppressed PPE-induced emphysema by attenuating neutrophilic inflammation via modulating cytokine and chemokine profiles in mouse lungs.

Small interference RNA-mediated gene silencing of human biliverdin reductase, but not that of heme oxygenase-1, attenuates arsenite-mediated induction of the oxygenase and increases apoptosis in 293A kidney cells

BVR reduces biliverdin, the HO-1 and HO-2 product, to bilirubin. Human biliverdin (BVR) is a serine/threonine kinase activated by free radicals. It is a leucine zipper (bZip) DNA-binding protein and a regulatory factor for 8/7-bp AP-1-regulated genes, including HO-1 and ATF-2/CREB. Presently, small interference (si) RNA constructs were used to investigate the role of human BVR in sodium arsenite (As)-mediated induction of HO-1 and in cytoprotection against apoptosis. Activation of BVR involved increased serine/threonine phosphorylation but not its protein or transcript levels. The peak activity at 1 h (4-5-fold) after treatment of 293A cells with 5 mum As preceded induction of HO-1 expression by 3 h. The following suggests BVR involvement in regulating oxidative stress response of HO-1: siBVR attenuated As-mediated increase in HO-1 expression; siBVR, but not siHO-1, inhibited As-dependent increased c-jun promoter activity; treatment of cells with As increased AP-1 binding of nuclear proteins; BVR was identified in the DNA-protein complex; and AP-1 binding of the in vitro translated BVR was phosphorylation-dependent and was attenuated by biliverdin. Most unexpectedly, cells transfected with siBVR, but not siHO-1, displayed a 4-fold increase in apoptotic cells when treated with 10 mum As as detected by flow cytometry. The presence of BVR small interference RNA augmented the effect of As on levels of cytochrome c, TRAIL, and DR-5 mRNA and cleavage of poly(ADP-ribose) polymerase. The findings describe the function of BVR in HO-1 oxidative response and, demonstrate, for the first time, not only that BVR advances the role of HO-1 in cytoprotection but also affords cytoprotection independent of heme degradation.

Heme oxygenase-1 (HO-1), a protective gene that prevents chronic graft dysfunction

Heme oxygenase-1 (HO-1) is a stress-responsive enzyme that acts during inflammatory reactions as the rate-limiting step in the catabolism of heme, yielding equimolar amounts of iron (Fe), biliverdin, and the gas carbon monoxide (CO). Expression of HO-1 regulates inflammatory and immune responses, such as those involved in the rejection of transplanted organs. We will discuss here accumulating evidence supporting the notion that expression of HO-1 in a transplanted organ can prevent its rejection. We will argue that the protective effects exerted by HO-1 are mediated to a large extent by the end products that it generates via the catabolism of heme. Better knowledge of how to enhance these protective effects is likely to help create new therapeutic strategies to improve the outcome of transplanted organs.

Role of Ets-2 in the Regulation of Heme Oxygenase-1 by Endotoxin

Ets proteins play a vital role in the regulation of mammalian immunity, and family members Ets-1 and Ets-2 regulate a variety of genes that participate in the propagation of an inflammatory response. Heme oxygenase (HO)-1, although acutely induced by inflammatory stimuli, has cytoprotective properties and prevents an exaggerated inflammatory response. Ets-1 and Ets-2 both induce HO-1 promoter activity; however, Ets-2 was a more potent transactivator of HO-1 in macrophages. A potent inflammatory mediator, bacterial lipopolysaccharide (LPS), induced Ets-2 at the mRNA and protein level, and this induction preceded the up-regulation of HO-1. To further delineate the role of Ets-2 in regulating HO-1 transcription, we performed HO-1 promoter analysis studies in macrophages. Deletion mutants down to -137/+74 maintained an activity analogous to that of the largest construct, -4045/+74. Further deletion constructs (starting with -117/+74) showed a significant reduction in promoter activity when co-transfected with Ets-2 or exposed to LPS. Promoter sequence analysis revealed two putative Ets binding sites (EBSs) in this region, and mutation of these sites showed that EBS -93, more than EBS -125, was critical for full HO-1 promoter activity. Additional studies showed that EBS -93 binds Ets-2 and that mutation of the DNA binding domain of Ets-2 entirely prevented transactivation of HO-1. Finally, overexpression of a dominant negative form of Ets-2 blunted HO-1 promoter induction by LPS, and kinase inhibitors (PI3K more than JNK) that reduced Ets-2 expression markedly decreased endogenous HO-1 expression. Our data provide evidence that Ets-2 contributes to the up-regulation of HO-1 by the potent inflammatory stimulus LPS in macrophages.

Heme oxygenase‐1 modulates the allo‐immune response by promoting activation‐induced cell death of T cells

Heme oxygenase-1 (HO-1), which degrades heme into three products (carbon monoxide, free iron, and biliverdin), plays a protective role in many models of disease via its anti-inflammatory, anti-apoptotic, and anti-proliferative actions. Overexpression of HO-1 has been shown to suppress immune responses and prolong the survival of allografts; however, the underlying mechanism is not clear. We demonstrate two "new" properties of HO-1 that mediate activation induced cell death (AICD) of allo-antigen-responsive murine CD4+ T cells, resulting in immunomodulation. First, it functions in vivo and in vitro to "boost" the proliferative response of CD4+ T cells to allo-antigens in the early phase of allo-antigen-driven immune responses. This "boosting" effect is accompanied with a significant increase of activation markers and IL-2 production. Second, it exerts a pro-apoptotic effect in those activated T cells after the initial burst of proliferation. We further show that the AICD effect is mediated through the Fas/CD95-FasL signal transduction pathway. Correlating with the above-mentioned findings is the observed prolongation of mouse heart graft survival when HO-1 is expressed in vivo in both donor and recipient. In conclusion, induction of HO-1 expression accelerates clonal deletion of peripheral alloreactive CD4+ T cells by promoting AICD, which is presumably a key mechanism for its immunomodulatory effects such as in prolonging the survival of transplanted organs.

Direct placental effects of cigarette smoke protect women from pre-eclampsia: the specific roles of carbon monoxide and antioxidant systems in the placenta

Pre-eclampsia is a hypertensive disorder of pregnancy characterized by shallow placentation, inadequate placental perfusion, localized placental oxidative stress, a heightened maternal inflammatory response and subsequent maternal endothelial dysfunction. This pathophysiology leads to an increase in maternal blood pressure, edema and proteinurea. Interestingly, women who smoke cigarettes throughout pregnancy are at a 33% reduced risk of developing this disorder. The exact mechanisms through which cigarette smoke reduces the risk of pre-eclampsia are not yet understood. We propose that cigarette smoke reduces the risk of developing pre-eclampsia via direct placental effects. In this review we will address, and provide evidence for, our specific hypotheses that: (a) CO increases trophoblast invasion and spiral arteriole remodeling; (b) CO decreases a localized inflammatory response at the level of the decidua; (c) CO increases utero-placental, intra-placental and feto-placental blood flow; (d) CO decreases hypoxia-induced apoptosis of the syncitiotrophoblast layer; (e) CO activates hemoproteins involved in normal endothelial functioning normally acted upon by NO; (f) compound(s) within cigarette smoke result in upregulation of antioxidant systems within the placenta. These various mechanisms of action must be further examined as they may provide valuable keys to novel therapeutic design in the realm of pre-eclampsia research.

Mechanism of concentration-dependent induction of heme oxygenase-1 by resveratrol in human aortic smooth muscle cells

Resveratrol-mediated heme oxygenase-1 (HO-1) induction has been shown to occur in primary neuronal cultures and is thought to have potential neuroprotective action. Further, antioxidant properties of resveratrol have been reported to protect against coronary heart disease. We attempted to examine resveratrol's HO-1 inducing potency and its induction regulation in human aortic smooth muscle cells (HASMC). We showed that resveratrol-mediated HO-1 induction occurred in concentration- and time-dependent manners, but only at low concentrations (1-10 microM), and that it was modulated at both the transcription and translation levels. Additionally, the results of our study showed that nuclear factor-kappa B (NF-kappaB) inhibitors eliminated resveratrol-mediated HO-1 induction and promoter activity, and that deletion of NF-kappaB binding sites in the HO-1 promoter region strongly reduced promoter activity, suggesting involvement of the NF-kappaB pathway in HO-1 induction by resveratrol. Suppression of NF-kappaB activity by resveratrol at high concentrations (> or =20 microM) has been reported to be attributed to its anti-inflammatory and anti-oxidative properties. Likewise, we showed that resveratrol at concentrations of > or =20 microM blocked the activity of NF-kappaB through suppression of I kappa-B alpha (IkappaBalpha) phosphorylation, which caused inhibition of HO-1 induction. Conversely, resveratrol in a range of 1-10 microM enhanced the phosphorylation and degradation of IkappaBalpha, a key step in NF-kappaB activation, resulting in HO-1 induction. Collectively, we suggest that resveratrol-mediated HO-1 expression occurs, at least in part, through the NF-kappaB pathway, which might contribute to resveratrol's vascular-protective effect at physiological concentrations after moderate red wine consumption.