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

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.

MicroRNAs miR-451a and Let-7i-5p Profiles in Circulating Exosomes Vary among Individuals with Different Sickle Hemoglobin Genotypes and Malaria

Sickle cell disease (SCD) occurs when two alleles of mutated hemoglobin (HbS or HbC) are inherited (HbSS and HbSC) rather than one (HbAS or HbAC), which indicates a person carries the sickle cell trait. The high prevalence of these two alleles in Africa have been associated with reduced malaria susceptibility. Recent in vitro research has been shown that microRNAs (miRNAs) miR-451a and let-7i-5p are differentially expressed in HbSS erythrocytes compared to healthy controls (HbAA) and are overexpressed in Plasmodium-infected malaria erythrocytes. However, these miRNAs have not been fully examined in the plasma of people with different sickle hemoglobin genotypes. Plasma circulating miRNAs are commonly encapsulated in extracellular vesicles, such as exosomes, and are thought to play a role in disease development. Circulating exosomal miR-451a and let-7i-5p were quantified from individuals with various hemoglobin genotypes (HbAA, HbAS, HbAC, HbSS, HbSC, and HbCC) with (+) and without (-) malaria. The results showed a higher level of exosomal let-7i-5p and miR-451a in HbSS-. Exosomal let-7i-5p and miR-451a levels were lower in HbSS+ compared to other genotypes. Based on the area under the curve (AUC) of the Receiver Operating Characteristics (ROCs), both exosomal miRNAs may be useful disease biomarkers for SCD with malaria. Finally, miR-451a and let-7i-5p modulate genes involved in inflammation, making them potential biomarkers of pathogenesis for both diseases.

Regulation of Endothelial and Vascular Functions by Carbon Monoxide via Crosstalk With Nitric Oxide

Carbon monoxide (CO), generated by heme oxygenase (HO), has been considered a signaling molecule in both the cardiovascular and central nervous systems. The biological function of the HO/CO axis is mostly related to other gaseous molecules, including nitric oxide (NO), which is synthesized by nitric oxide synthase (NOS). Healthy blood vessels are essential for the maintenance of tissue homeostasis and whole-body metabolism; however, decreased or impaired vascular function is a high-risk factor of cardiovascular and neuronal diseases. Accumulating evidence supports that the interplay between CO and NO plays a crucial role in vascular homeostasis and regeneration by improving endothelial function. Moreover, endothelial cells communicate with neighboring cells, such as, smooth muscle cells, immune cells, pericytes, and astrocytes in the periphery and neuronal vascular systems. Endogenous CO could mediate the cell-cell communication and improve the physiological functions of the cardiovascular and neurovascular systems via crosstalk with NO. Thus, a forward, positive feedback circuit between HO/CO and NOS/NO pathways can maintain cardiovascular and neurovascular homeostasis and prevent various human diseases. We discussed the crucial role of CO-NO crosstalk in the cardiovascular and neurovascular systems.

Reprogramming of Amino Acid Metabolism in Pancreatic Cancer: Recent Advances and Therapeutic Strategies

Pancreatic ductal adenocarcinoma (PDAC) is one of the most fatal malignancies with an extremely poor prognosis. Energy metabolism reprogramming, an emerging hallmark of cancer, has been implicated in the tumorigenesis and development of pancreatic cancer. In addition to well-elaborated enhanced glycolysis, investigating the role of reprogramming of amino acid metabolism has sparked great interests in recent years. The rewiring amino acid metabolism orchestrated by genetic alterations contributes to pancreatic cancer malignant characteristics including cell proliferation, invasion, metastasis, angiogenesis and redox balance. In the unique hypoperfused and nutrient-deficient tumor microenvironment (TME), the interactions between cancer cells and stromal components and salvaging processes including autophagy and macropinocytosis play critical roles in fulfilling the metabolic requirements and supporting growth of PDAC. In this review, we elucidate the recent advances in the amino acid metabolism reprogramming in pancreatic cancer and the mechanisms of amino acid metabolism regulating PDAC progression, which will provide opportunities to develop promising therapeutic strategies.

Non-canonical chemical feedback self-limits nitric oxide-cyclic GMP signaling in health and disease

Nitric oxide (NO)-cyclic GMP (cGMP) signaling is a vasoprotective pathway therapeutically targeted, for example, in pulmonary hypertension. Its dysregulation in disease is incompletely understood. Here we show in pulmonary artery endothelial cells that feedback inhibition by NO of the NO receptor, the cGMP forming soluble guanylate cyclase (sGC), may contribute to this. Both endogenous NO from endothelial NO synthase and exogenous NO from NO donor compounds decreased sGC protein and activity. This effect was not mediated by cGMP as the NO-independent sGC stimulator, or direct activation of cGMP-dependent protein kinase did not mimic it. Thiol-sensitive mechanisms were also not involved as the thiol-reducing agent N-acetyl-L-cysteine did not prevent this feedback. Instead, both in-vitro and in-vivo and in health and acute respiratory lung disease, chronically elevated NO led to the inactivation and degradation of sGC while leaving the heme-free isoform, apo-sGC, intact or even increasing its levels. Thus, NO regulates sGC in a bimodal manner, acutely stimulating and chronically inhibiting, as part of self-limiting direct feedback that is cGMP independent. In high NO disease conditions, this is aggravated but can be functionally recovered in a mechanism-based manner by apo-sGC activators that re-establish cGMP formation.

HO-1 induced autophagy protects against IL-1 β-mediated apoptosis in human nucleus pulposus cells by inhibiting NF-κB

In this study, we investigated the role of heme oxygenase-1 (HO-1) in intervertebral disc degeneration (IDD) by assessing the effects of HO-1 overexpression on IL-1β-induced apoptosis in nucleus pulposus cells (NPCs). Immunohistochemical staining showed HO-1 expression to be lower in NPCs from IDD patients than from patients with lumbar vertebral fractures (LVF). Western blot analysis showed HO-1 and LC3-II/I levels to be lower in NP tissues from IDD patients than from LVF patients, suggesting suppression of autophagy in degenerative intervertebral disc. Consistent with that idea, autophagy was increased in HO-1-overexpressing NPCs while IL-1β-induced apoptosis was reduced. These effects were reversed by treatment with the early autophagy inhibitor 3-methyl adenine, which suggests HO-1-induced autophagy suppresses IL-1β-induced apoptosis in NPCs. HO-1 overexpression promoted autophagy by increasing levels of Beclin-1/PI3KC3 complex. Phospho-P65 levels were lower in HO-1-overexpressing NPCs, suggesting inhibition of NF-κB-mediated apoptosis. Our study thus demonstrates that HO-1 promotes autophagy by enhancing formation of Beclin-1/PI3KC3 complex and suppresses IL-1β-induced apoptosis by inhibiting NF-κB. We suggest that HO-1 is a potential therapeutic target to alleviate IDD.

Role of Carbon Monoxide in Neurovascular Repair Processing

Carbon monoxide (CO) is a gaseous molecule produced from heme by heme oxygenase (HO). Endogenous CO production occurring at low concentrations is thought to have several useful biological roles. In mammals, especially humans, a proper neurovascular unit comprising endothelial cells, pericytes, astrocytes, microglia, and neurons is essential for the homeostasis and survival of the central nervous system (CNS). In addition, the regeneration of neurovascular systems from neural stem cells and endothelial precursor cells after CNS diseases is responsible for functional repair. This review focused on the possible role of CO/HO in the neurovascular unit in terms of neurogenesis, angiogenesis, and synaptic plasticity, ultimately leading to behavioral changes in CNS diseases. CO/HO may also enhance cellular networks among endothelial cells, pericytes, astrocytes, and neural stem cells. This review highlights the therapeutic effects of CO/HO on CNS diseases involved in neurogenesis, synaptic plasticity, and angiogenesis. Moreover, the cellular mechanisms and interactions by which CO/HO are exploited for disease prevention and their therapeutic applications in traumatic brain injury, Alzheimer's disease, and stroke are also discussed.

Ligustilide attenuates vascular inflammation and activates Nrf2/HO-1 induction and, NO synthesis in HUVECs

BACKGROUND

Ligustilide is a bioactive phthalide derivative isolated from Cnidii Rhizoma (Cnidium officinale, rhizome) and Angelicae Gigantis Radix (Angelica gigas Nakai, root) which are both medicinal herbs used to treat circulatory disorders. Vascular endothelium is a central spot in developing cardiovascular diseases and chronic vascular inflammation might result in atherosclerosis development.

PURPOSE

We previously found out that a traditional herbal formula, Samul-Tang (Si-Wu-Tang, containing Cnidii Rhizoma and Angelicae Gigantis Radix), attenuated vascular inflammation in human umbilical vein endothelial cells (HUVECs). However, which compound was responsible for vascular protective action remained unclear. Here, we investigated vascular protective potential of an isolated single compound, (Z)-ligustilide.

METHODS

MTT assay, western blotting, immunofluorescence, electrophoretic mobility shift assay was performed. BCECF-AM, CM-H₂DCFDA, DAF-FM diacetate were used as a fluorescent indicator.

RESULTS

Ligustilide suppressed HL-60 monocyte adhesion and CAMs (ICAM-1, VCAM-1, E-selectin) expression in HUVECs. Ligustilide significantly inhibited TNF-α-increased production of ROS and activated NF-κB signaling pathway. Also, ligustilide treated HUVECs exhibited significant HO-1 induction via Nrf2 nuclear translocation and endothelial NO synthesis.

CONCLUSION

Present study demonstrates that ligustilde attenuates vascular inflammation and activate defense system of endothelial cell. Ligustilide is a bioactive compound which might prevent cardiovascular complications such as thrombosis or atherosclerosis.

Vascular Protective Role of Samul-Tang in HUVECs: Involvement of Nrf2/HO-1 and NO

Samul-Tang (Si-Wu-Tang, SMT), composed of four medicinal herbs, is a well-known herbal formula treating hematological disorder or gynecologic disease. However, vascular protective effects of SMT and its molecular mechanisms on the vascular endothelium, known as the central spot of vascular inflammatory process, are not reported. The aim of this study was to investigate vascular protective effects of SMT water extract in human umbilical vein endothelial cells (HUVECs). Water extract of SMT was prepared and identified by HPLC-PDA analysis. Expression of cell adhesion molecules (CAMs) and heme oxygenase-1 (HO-1) and translocation of nuclear factor-kappa B (NF-κB) and nuclear factor-erythroid 2-related factor 2 (Nrf2) were determined by western blot. Nuclear localization of NF-κB and Nrf2 was visualized by immunofluorescence and DNA binding activity of NF-κB was measured. ROS production, HL-60 monocyte adhesion, and intracellular nitric oxide (NO) were also measured using a fluorescent indicator. SMT suppressed NF-κB translocation and activation as well as expression of CAMs, monocyte adhesion, and ROS production induced by TNF-α in HUVECs. SMT treated HUVECs showed upregulation of HO-1 and NO which are responsible for vascular protective action. Our study suggests that SMT, a traditionally used herbal formula, protects the vascular endothelium from inflammation and might be used as a promising vascular protective drug.

Plasmodium-infected erythrocytes (pRBC) induce endothelial cell apoptosis via a heme-mediated signaling pathway

Heme is cytotoxic to the plasmodium parasite, which converts it to an insoluble crystalline form called hemozoin (malaria pigment) in erythrocytes during replication. The increased serum levels of free heme cause tissue damage, activation of microvascular endothelial and glial cells, focal inflammation, activation of apoptotic pathways, and neuronal tissue damage. Several hypotheses have been proposed to explain how these causative factors exacerbate fatal malaria. However, none of them fully explain the detailed mechanisms leading to the high morbidity and mortality associated with malaria. We have previously reported that heme-induced brain microvascular endothelial cell (HBVEC) apoptosis is a major contributor to severe malaria pathogenesis. Here, we hypothesized that heme (at clinically relevant levels) induces inflammation and apoptosis in HBVEC, a process that is mediated by independent proinflammatory and proapoptotic signaling pathways. In this study, we determined the key signaling molecules associated with heme-mediated apoptosis in HBVEC in vitro using RT2 profiler polymerase chain reaction array technology and confirmed results using immunostaining techniques. While several expressed genes in HBVEC were altered upon heme stimulation, we determined that the apoptotic effects of heme were mediated through p73 (tumor protein p73). The results provide an opportunity to target heme-mediated apoptosis therapeutically in malaria-infected individuals.

Effect of the Acidic Dental Resin Monomer 10-methacryloyloxydecyl Dihydrogen Phosphate on Odontoblastic Differentiation of Human Dental Pulp Cells

Although 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) is frequently used as an acidic resin monomer in dental adhesives, its effect on dental pulp cells (DPCs) has been rarely reported. The purpose of this study was to examine the effects of 10-MDP on the inflammatory response and odontoblastic differentiation of DPCs at minimally toxic concentrations. We found that 10-MDP caused the release of inflammatory cytokines including NO, PGE2, iNOS, COX-2, TNF-α, IL-1β, IL-6 and IL-8 in a concentration-dependent manner. In addition, 10-MDP reduced alkaline phosphatase activity, mineralization nodule formation and mRNA expression of odontoblastic differentiation markers such as dentin sialophosphoprotein, dentin matrix protein-1, osterix and Runx2 in a concentration-dependent manner with low toxicity. In addition, 10-MDP induced activation of nuclear factor-E2-related factor 2 (Nrf2) and its target gene, haeme oxygenase-1 (HO-1). We evaluated whether the effect of 10-MDP was related to the induction of HO-1 and found that treatment with a selective inhibitor of HO-1 reversed the production of 10-MDP-mediated pro-inflammatory cytokines and the inhibition of differentiation markers. Pre-treatment with either a GSH synthesis inhibitor or antioxidants blocked 10-MDP-induced mitogen-activated protein kinases (MAPKs), Nrf2 and NF-κB pathways. Taken together, the results of this study showed that minimally toxic concentrations of 10-MDP promoted an inflammatory response and suppressed odontoblastic differentiation of DPCs by activating Nrf2-mediated HO-1 induction through MAPK and NF-κB signalling.

The multifunctional role and therapeutic potential of HO-1 in the vascular endothelium

SIGNIFICANCE

Heme oxygenases (HO-1 and HO-2) catalyze the degradation of the pro-oxidant heme into carbon monoxide (CO), iron, and biliverdin, which is subsequently converted to bilirubin. In the vasculature, particular interest has focused on antioxidant and anti-inflammatory properties of the inducible HO-1 isoform in the vascular endothelium. This review will present evidence that illustrates the potential therapeutic significance of HO-1 and its products, with special emphasis placed on their beneficial effects on the endothelium in vascular diseases.

RECENT ADVANCES

The understanding of the molecular basis for the regulation and functions of HO-1 has led to the identification of a variety of drugs that increase HO-1 activity in the vascular endothelium. Moreover, therapeutic delivery of HO-1 products CO, biliverdin, and bilirubin has been shown to have favorable effects, notably on endothelial cells and in animal models of vascular disease.

CRITICAL ISSUES

To date, mechanistic data identifying the downstream target genes utilized by HO-1 and its products to exert their actions remain relatively sparse. Likewise, studies in man to investigate the efficacy of therapeutics known to induce HO-1 or the consequences of the tissue-specific delivery of CO or biliverdin/bilirubin are rarely performed.

FUTURE DIRECTIONS

Based on the promising in vivo data from animal models, clinical trials to explore the safety and efficacy of the therapeutic induction of HO-1 and the delivery of its products should now be pursued further, targeting, for example, patients with severe atherosclerotic disease, ischemic limbs, restenosis injury, or at high risk of organ rejection.

Anti-Proliferative Effect of an Aqueous Extract of Prunella vulgaris in Vascular Smooth Muscle Cells

The abnormal proliferation of vascular smooth muscle cells (VSMCs) in arterial walls is an important pathogenic factor of vascular disorders such as diabetic atherosclerosis. We have reported the anti-inflammatory effect of an aqueous extract from Prunella vulgaris (APV) in vascular endothelial cell. In the present study, APV exhibited inhibitory effects on high glucose-stimulated VSMC proliferation, migration, and invasion activities, inducing G₁ cell cycle arrest with downregulation of cyclins and CDKs and upregulation of the CKIs, p21^waf1/cip1 and p27^kip1. Furthermore, APV dose dependently suppressed the high glucose-induced matrix metalloproteinase activity. High glucose-induced phosphorylation of ERK, p38 MAPK, was decreased by the pretreatment of APV. NF-κB activation by high glucose was attenuated by APV, as an antioxidant. APV attenuated the high glucose-induced decrease of nuclear factor E2-related factor-2 (Nrf2) translocation and heme oxygenase-1 (HO-1) expression. Intracellular cGMP level was also increased by APV treatment. These results demonstrate that APV may inhibit VSMC proliferation via downregulating ROS/NF-κB /ERK/p38 MAPK pathways. In addition, APV has a beneficial effect by the interaction of Nrf2-mediated NO/cGMP with HO-1, suggesting that Prunella vulgaris may be useful in preventing diabetic atherosclerosis.

STAT3 regulates MMP3 in heme-induced endothelial cell apoptosis

BACKGROUND

We have previously reported that free Heme generated during experimental cerebral malaria (ECM) in mice, is central to the pathogenesis of fatal ECM. Heme-induced up-regulation of STAT3 and CXCL10 promotes whereas up-regulation of HO-1 prevents brain tissue damage in ECM. We have previously demonstrated that Heme is involved in the induction of apoptosis in vascular endothelial cells. In the present study, we further tested the hypothesis that Heme reduces blood-brain barrier integrity during ECM by induction of apoptosis of brain vascular endothelial cells through STAT3 and its target gene matrix metalloproteinase three (MMP3) signaling.

METHODS

Genes associated with the JAK/STAT3 signaling pathway induced upon stimulation by Heme treatment, were assessed using real time RT(2) Profile PCR arrays. A human MMP3 promoter was cloned into a luciferase reporter plasmid, pMMP3, and its activity was examined following exposure to Heme treatment by a luciferase reporter gene assay. In order to determine whether activated nuclear protein STAT3 binds to the MMP3 promoter and regulates MMP3 gene, we conducted a ChIP analysis using Heme-treated and untreated human brain microvascular endothelial cells (HBVEC), and determined mRNA and protein expression levels of MMP3 using qRT-PCR and Western blot. Apoptosis in HBVEC treated with Heme was evaluated by MTT and TUNEL assay.

RESULTS

The results show that (1) Heme activates a variety of JAK/STAT3 downstream pathways in HBVEC. STAT3 targeted genes such as MMP3 and C/EBPb (Apoptosis-related genes), are up regulated in HBVEC treated with Heme. (2) Heme-induced HBVEC apoptosis via activation of STAT3 as well as its downstream signaling molecule MMP3 and upregulation of CXCL10 and HO-1 expressions. (3) Phosphorylated STAT3 binds to the MMP3 promoter in HBVEC cells, STAT3 transcribed MMP3 and induced MMP3 protein expression in HBVEC cells.

CONCLUSIONS

Activated STAT3 binds to the MMP3 promoter region and regulates MMP3 in Heme-induced endothelial cell apoptosis.

Dissecting plant iron homeostasis under short and long-term iron fluctuations

A wealth of information on the different aspects of iron homeostasis in plants has been obtained during the last decade. However, there is no clear road-map integrating the relationships between the various components. The principal aim of the current review is to fill this gap. In this context we discuss the lack of low affinity iron uptake mechanisms in plants, the utilization of a different uptake mechanism by graminaceous plants compared to the others, as well as the roles of riboflavin, ferritin isoforms, nitric oxide, nitrosylation, heme, aconitase, and vacuolar pH. Cross-homeostasis between elements is also considered, with a specific emphasis on the relationship between iron homeostasis and phosphorus and copper deficiencies. As the environment is a crucial parameter for modulating plant responses, we also highlight how diurnal fluctuations govern iron metabolism. Evolutionary aspects of iron homeostasis have so far attracted little attention. Looking into the past can inform us on how long-term oxygen and iron-availability fluctuations have influenced the evolution of iron uptake mechanisms. Finally, we evaluate to what extent this homeostastic road map can be used for the development of novel biofortification strategies in order to alleviate iron deficiency in human.

Pre-emptive hypoxia-regulated HO-1 gene therapy improves post-ischaemic limb perfusion and tissue regeneration in mice

AIMS

Haem oxygenase-1 (HO-1) is a haem-degrading enzyme that generates carbon monoxide, bilirubin, and iron ions. Through these compounds, HO-1 mitigates cellular injury by exerting antioxidant, anti-apoptotic, and anti-inflammatory effects. Here, we examined the influence of HO-1 deficiency and transient hypoxia/ischaemia-induced HO-1 overexpression on post-injury hindlimb recovery.

METHODS AND RESULTS

Mice lacking functional HO-1 (HO-1(-/-)) showed reduced reparative neovascularization in ischaemic skeletal muscles, impaired blood flow (BF) recovery, and increased muscle cell death compared with their wild-type littermates. Human microvascular endothelial cells (HMEC-1) transfected with plasmid vector (pHRE-HO-1) carrying human HO-1 driven by three hypoxia response elements (HREs) and cultured in 0.5% oxygen demonstrated markedly increased expression of HO-1. Such upregulated HO-1 levels were effective in conferring protection against H(2)O(2)-induced cell death and in promoting the proangiogenic phenotype of HMEC-1 cells. More importantly, when delivered in vivo, pHRE-HO-1 significantly improved the post-ischaemic foot BF in mice subjected to femoral artery ligation. These effects were associated with reduced levels of pro-inflammatory cytokines (IL-6 and CXCL1) and lower numbers of transferase-mediated dUTP nick-end labelling-positive cells. Moreover, HO-1 delivered into mouse skeletal muscles seems to influence the regenerative potential of myocytes as it significantly changed the expression of transcriptional (Pax7, MyoD, myogenin) and post-transcriptional (miR-146a, miR-206) regulators of skeletal muscle regeneration.

CONCLUSION

Our results suggest the therapeutic potential of HO-1 for prevention of adverse effects in critical limb ischaemia.

Heme mediated STAT3 activation in severe malaria

Background

The mortality of severe malaria [cerebral malaria (CM), severe malaria anemia (SMA), acute lung injury (ALI) and acute respiratory distress syndrome (ARDS)] remains high despite the availability associated with adequate treatments. Recent studies in our laboratory and others have revealed a hitherto unknown correlation between chemokine CXCL10/CXCR3, Heme/HO-1 and STAT3 and cerebral malaria severity and mortality. Although Heme/HO-1 and CXCL10/CXCR3 interactions are directly involved in the pathogenesis of CM and fatal disease, the mechanism dictating how Heme/HO-1 and CXCL10/CXCR3 are expressed and regulated under these conditions is still unknown. We therefore tested the hypothesis that these factors share common signaling pathways and may be mutually regulated.

Methods

We first clarified the roles of Heme/HO-1, CXCL10/CXCR3 and STAT3 in CM pathogenesis utilizing a well established experimental cerebral malaria mouse (ECM, P. berghei ANKA) model. Then, we further determined the mechanisms how STAT3 regulates HO-1 and CXCL10 as well as mutual regulation among them in CRL-2581, a murine endothelial cell line.

Results

The results demonstrate that (1) STAT3 is activated by P. berghei ANKA (PBA) infection in vivo and Heme in vitro. (2) Heme up-regulates HO-1 and CXCL10 production through STAT3 pathway, and regulates CXCL10 at the transcriptional level in vitro. (3) HO-1 transcription is positively regulated by CXCL10. (4) HO-1 regulates STAT3 signaling.

Conclusion

Our data indicate that Heme/HO-1, CXCL10/CXCR3 and STAT3 molecules as well as related signaling pathways play very important roles in the pathogenesis of severe malaria. We conclude that these factors are mutually regulated and provide new opportunities to develop potential novel therapeutic targets that could be used to supplement traditional prophylactics and treatments for malaria and improve clinical outcomes while reducing malaria mortality. Our ultimate goal is to develop novel therapies targeting Heme or CXCL10-related biological signaling molecules associated with development of fatal malaria.

Prunella vulgaris suppresses HG-induced vascular inflammation via Nrf2/HO-1/eNOS activation

Vascular inflammation is an important factor which can promote diabetic complications. In this study, the inhibitory effects of aqueous extract from Prunella vulgaris (APV) on high glucose (HG)-induced expression of cell adhesion molecules in human umbilical vein endothelial cells (HUVEC) are reported. APV decreased HG-induced expression of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and E-selectin. APV also dose-dependently inhibited HG-induced adhesion of HL-60 monocytic cells. APV suppressed p65 NF-κB activation in HG-treated cells. APV significantly inhibited the formation of intracellular reactive oxygen species (ROS). HG-stimulated HUVEC secreted gelatinases, however, APV inhibited it. APV induced Akt phosphorylation as well as activation of heme oxygenase-1 (HO-1), eNOS, and nuclear factor E2-related factor 2 (Nrf2), which may protect vascular inflammation caused by HG. In conclusion, APV exerts anti-inflammatory effect via inhibition of ROS/NF-κB pathway by inducing HO-1 and eNOS expression mediated by Nrf2, thereby suggesting that Prunella vulgaris may be a possible therapeutic approach to the inhibition of diabetic vascular diseases.

Changes in inflammatory gene expression induced by hyperbaric oxygen treatment in human endothelial cells under chronic wound conditions

Hyperbaric oxygen (HBO) therapy involves the inhalation of 100% oxygen, whilst inside a chamber at greater than atmospheric pressure. It is an effective treatment for chronic diabetic wounds, although the molecular mechanisms involved remain unclear. We hypothesised that HBO could alter inflammatory gene expression in human endothelial cells via a reactive oxygen/nitrogen species-mediated pathway. Endothelial cells were exposed to a chronic wound model comprising hypoxia (2% O(2) at 1 atmosphere absolute (ATA); PO(2) ~2 kPa) in the presence of lipopolysaccharide and TNF-α for 24h, then treated with HBO for 90 min (97.5% O(2) at 2.4 ATA; PO(2) ~237 kPa). 5h post-HBO, 19 genes involved in adhesion, angiogenesis, inflammation and oxidative stress were downregulated. Notably, only angiogenin gene expression, which promotes both angiogenesis and nitric oxide production (reflected by increased eNOS protein expression in this study), was upregulated. This led to a decrease in endothelial IL-8 mRNA and protein, which could help alleviate inflammatory processes during chronic wound healing. This was no longer evident 22.5h post-HBO, demonstrating the importance of daily exposures in HBO treatment protocols. These studies indicate that elevated oxygen transiently regulates inflammatory gene expression in endothelial cells, which may enhance chronic wound healing.

Heme oxygenase in the regulation of vascular biology: from molecular mechanisms to therapeutic opportunities

Heme oxygenases (HOs) are the rate-limiting enzymes in the catabolism of heme into biliverdin, free iron, and carbon monoxide. Two genetically distinct isoforms of HO have been characterized: an inducible form, HO-1, and a constitutively expressed form, HO-2. HO-1 is a kind of stress protein, and thus regarded as a sensitive and reliable indicator of cellular oxidative stress. The HO system acts as potent antioxidants, protects endothelial cells from apoptosis, is involved in regulating vascular tone, attenuates inflammatory response in the vessel wall, and participates in angiogenesis and vasculogenesis. Endothelial integrity and activity are thought to occupy the central position in the pathogenesis of cardiovascular diseases. Cardiovascular disease risk conditions converge in the contribution to oxidative stress. The oxidative stress leads to endothelial and vascular smooth muscle cell dysfunction with increases in vessel tone, cell growth, and gene expression that create a pro-thrombotic/pro-inflammatory environment. Subsequent formation, progression, and obstruction of atherosclerotic plaque may result in myocardial infarction, stroke, and cardiovascular death. This background provides the rationale for exploring the potential therapeutic role for HO system in the amelioration of vascular inflammation and prevention of adverse cardiovascular outcomes.

Heme oxygenase in the regulation of vascular biology: from molecular mechanisms to therapeutic opportunities

Heme oxygenases (HOs) are the rate-limiting enzymes in the catabolism of heme into biliverdin, free iron, and carbon monoxide. Two genetically distinct isoforms of HO have been characterized: an inducible form, HO-1, and a constitutively expressed form, HO-2. HO-1 is a kind of stress protein, and thus regarded as a sensitive and reliable indicator of cellular oxidative stress. The HO system acts as potent antioxidants, protects endothelial cells from apoptosis, is involved in regulating vascular tone, attenuates inflammatory response in the vessel wall, and participates in angiogenesis and vasculogenesis. Endothelial integrity and activity are thought to occupy the central position in the pathogenesis of cardiovascular diseases. Cardiovascular disease risk conditions converge in the contribution to oxidative stress. The oxidative stress leads to endothelial and vascular smooth muscle cell dysfunction with increases in vessel tone, cell growth, and gene expression that create a pro-thrombotic/pro-inflammatory environment. Subsequent formation, progression, and obstruction of atherosclerotic plaque may result in myocardial infarction, stroke, and cardiovascular death. This background provides the rationale for exploring the potential therapeutic role for HO system in the amelioration of vascular inflammation and prevention of adverse cardiovascular outcomes.

Carbon monoxide promotes VEGF expression by increasing HIF-1alpha protein level via two distinct mechanisms, translational activation and stabilization of HIF-1alpha protein

Carbon monoxide (CO) plays a significant role in vascular functions. We here examined the molecular mechanism by which CO regulates HIF-1 (hypoxia-inducible transcription factor-1)-dependent expression of vascular endothelial growth factor (VEGF), which is an important angiogenic factor. We found that astrocytes stimulated with CORM-2 (CO-releasing molecule) promoted angiogenesis by increasing VEGF expression and secretion. CORM-2 also induced HO-1 (hemeoxygenase-1) expression and increased nuclear HIF-1α protein level, without altering its promoter activity and mRNA level. VEGF expression was inhibited by treatment with HIF-1α siRNA and a hemeoxygenase inhibitor, indicating that CO stimulates VEGF expression via up-regulation of HIF-1α protein level, which is partially associated with HO-1 induction. CORM-2 activated the translational regulatory proteins p70(S6k) and eIF-4E as well as phosphorylating their upstream signal mediators Akt and ERK. These translational signal events and HIF-1α protein level were suppressed by inhibitors of phosphatidylinositol 3-kinase (PI3K), MEK, and mTOR, suggesting that the PI3K/Akt/mTOR and MEK/ERK pathways are involved in a translational increase in HIF-1α. In addition, CORM-2 also increased stability of the HIF-1α protein by suppressing its ubiquitination, without altering the proline hydroxylase-dependent HIF-1α degradation pathway. CORM-2 increased HIF-1α/HSP90α interaction, which is responsible for HIF-1α stabilization, and HSP90-specific inhibitors decreased this interaction, HIF-1α protein level, and VEGF expression. Furthermore, HSP90α knockdown suppressed CORM-2-induced increases in HIF-1α and VEGF protein levels. These results suggest that CO stimulates VEGF production by increasing HIF-1α protein level via two distinct mechanisms, translational stimulation and protein stabilization of HIF-1α.

Role of heme oxygenase-1 in human endothelial cells: lesson from the promoter allelic variants

OBJECTIVE

Heme oxygenase-1 (HO-1) is an antioxidative, antiinflammatory, and cytoprotective enzyme that is induced in response to cellular stress. The HO-1 promoter contains a (GT)n microsatellite DNA, and the number of GT repeats can influence the occurrence of cardiovascular diseases. We elucidated the effect of this polymorphism on endothelial cells isolated from newborns of different genotypes.

METHODS AND RESULTS

On the basis of HO-1 expression, we classified the HO-1 promoter alleles into 3 groups: short (S) (most active, GT < or = 23), medium (moderately active, GT=24 to 28), and long (least active, GT > or = 29). The presence of the S allele led to higher basal HO-1 expression and stronger induction in response to cobalt protoporphyrin, prostaglandin-J(2), hydrogen peroxide, and lipopolysaccharide. Cells carrying the S allele survived better under oxidative stress, a fact associated with the lower concentration of oxidized glutathione and more favorable oxidative status, as determined by measurement of the ratio of glutathione to oxidized glutathione. Moreover, they proliferated more efficiently in response to vascular endothelial growth factor A, although the vascular endothelial growth factor-induced migration and sprouting of capillaries were not influenced. Finally, the presence of the S allele was associated with lower production of some proinflammatory mediators, such as interleukin-1beta, interleukin-6, and soluble intercellular adhesion molecule-1.

CONCLUSIONS

The (GT)n promoter polymorphism significantly modulates a cytoprotective, proangiogenic, and antiinflammatory function of HO-1 in human endothelium.

HIF-1 induction attenuates Nrf2-dependent IL-8 expression in human endothelial cells

Through hypoxia-inducible factor 1 (HIF-1), hypoxia regulates the expression of numerous genes and is a potent inducer of angiogenesis. However, interleukin-8 (IL-8), an important angiogenic mediator, has been reported to be downregulated by HIF-1, although the mechanisms have not been elucidated. HIF-1 was induced in human endothelial cells by hypoxia and dimethyloxaloylglycine (DMOG). Interestingly, both hypoxia and DMOG attenuated IL-8 expression, and a similar effect has been obtained by adenoviral overexpression of the stable form of HIF-1alpha. Heme oxygenase-1 (HO-1) expression was also downregulated by HIF-1 induction. This suggests similar mechanisms of regulation of IL-8 and HO-1, indicating the involvement of Nrf2, a transcription factor previously linked to hypoxia-mediated inhibition of HO-1. Indeed, HIF-1-mediated downregulation of both IL-8 and HO-1 was associated with both lowered Nrf2 expression and induction of Bach1, a repressor of Nrf2 transcriptional activity. Accordingly, overexpression of Nrf2 reversed the inhibitory effect of HIF-1 on IL-8 and HO-1 expression. However, neither overexpression of HO-1 nor HO-1 inhibition affected IL-8 synthesis. The data indicate that HIF-1-dependent inhibition of IL-8 expression is caused by downregulation of Nrf2. However, expression of IL-8 is independent of HO-1. Cross-talk between HIF-1 and Nrf2 may influence the outcome of anti-angiogenic therapies aimed at targeting HIF-1. Antioxid.

Induced nitric oxide synthase as a major player in the oncogenic transformation of inflamed tissue

Nitric oxide (NO) is a free radical that is involved in the inflammatory process and carcinogenesis. There are four nitric oxide synthase enzymes involved in NO production: induced nitric oxide synthase (iNOS), endothelial NO synthase (eNOS), neural NO synthase (nNOS), and mitochondrial NOS. iNOS is an inducible and key enzyme in the inflamed tissue. Recent literatures indicate that NO as well as iNOS and eNOS can modulate cancer-related events including nitro-oxidative stress, apoptosis, cell cycle, angio-genesis, invasion, and metastasis. This chapter focuses on linking NO/iNOS/eNOS to inflammation and carcinogenesis from experimental evidence to potential targets on cancer prevention and treatment.

Solid emulsion gel as a vehicle for delivery of polyunsaturated fatty acids: implications for tissue repair, dermal angiogenesis and wound healing

The paper describes preparation and biological characterization of the solid hybrid biomaterial that was designed for cell-targeted lipid delivery in healing tissues. The material referred to as 'solid emulsion gel' combines a protein-stabilized lipid emulsion and a hydrogel structure in a single compartment. The potential of the omega-3 (n-3)-fatty acids rich solid emulsion gel for tissue repair applications was investigated at the macro-, micro-, molecular and gene expression levels, using human fibroblasts and endothelial cells and a porcine model of full-thickness wounds. Being non-cytotoxic in vitro and in vivo, the biomaterial was found to affect cell metabolism, modulate expression of certain genes, stimulate early angiogenesis and promote wound repair in vivo. The neovascular response in vivo was correlated with upregulated expression of the genes involved in lipid transport (e.g. adipophilin), anti-apoptosis (e.g. heat shock proteins, haem oxygenase 1) and angiogenesis (vascular endothelial growth factor, placental growth factor). Collectively, the results of this study provide first evidence that the angiogenic response provided by solid emulsion gel-mediated delivery of n-3 fatty acids is an alternative to the topical administration of exogenous growth factors or gene therapy, and can be advantageously used for the stimulation of tissue repair in complex wounds.

15d-PGJ2 upregulates synthesis of IL-8 in endothelial cells through induction of oxidative stress

15-Deoxy-Delta(12,14)-prostaglandin-J(2) (15d-PGJ(2)) is a cyclopentenone prostaglandin regarded as antiinflammatory mediator, which can act through peroxisome proliferator-activated receptor-gamma (PPARgamma) or through G protein-coupled surface receptors. It has been demonstrated that 15d-PGJ(2) potently increases the generation of interleukin-8 (IL-8) in human microvascular endothelial cells (HMEC-1s); however, the mechanism of this induction is not known. The aim of the study was to find the pathway involved in 15d-PGJ(2)-mediated IL-8 stimulation. Our data confirmed that the effect of 15d-PGJ(2) is independent of PPARgamma. For the first time, we excluded the activation of G proteins and the contribution of G protein-coupled surface receptors in endothelial cells treated with 15d-PGJ(2). Instead, we demonstrated that stimulation of IL-8 involved induction of oxidative stress, activation of p38 kinases, and increase in stability of IL-8 mRNA. Upregulation of IL-8 promoter, although measurable, seemed to play a less-pronounced role. Additionally, our results indicate the involvement of cAMP elevation and may suggest a role for ATF2 transcription factor. Concomitant induction of heme oxygenase-1 in HMEC-1s did not influence the synthesis of IL-8. In summary, we showed that 15d-PGJ(2), acting through oxidative stress, may exert proinflammatory effects. The upregulation of IL-8 is mostly associated with p38-mediated stabilization of mRNA.

Effects of weight loss after bariatric surgery for morbid obesity on vascular endothelial growth factor-A, adipocytokines, and insulin

BACKGROUND

Adipocytes regulate blood vessel formation, and in turn endothelial cells promote preadipocyte differentiation through the expression of proangiogenic factors, such as vascular endothelial growth factor (VEGF)-A. Some adipocytokines and hormones also have an effect on vascular development.

OBJECTIVES

Our objectives were to analyze the relationship between weight and circulating VEGF-A in morbidly obese subjects before and after bariatric surgery, and investigate the relationship between circulating VEGF-A and certain adipocytokines and hormones regulating adipocytes.

METHODS

A total of 45 morbidly obese women and nine lean females were included in the study. Patients underwent bariatric surgery: vertical banded gastroplasty (n=17), gastric bypass (n=17), and biliopancreatic diversion (n=11). Serum samples for VEGF-A, adiponectin, leptin, ghrelin, and insulin were obtained preoperatively and 9-12 months after surgery.

RESULTS

Obese patients showed significantly higher VEGF-A levels than controls (306.3+/-170.3 vs. 187.6+/-91.9 pg/ml; P=0.04), decreasing to 246.1+/-160.4 after surgery (P<0.001), with no differences among surgical procedures. In controls there was an inverse correlation between VEGF-A and ghrelin (r=-0.85; P<.01), but not in obese patients. Leptin and insulin concentrations were increased in obese patients, with a significant decrease shown after weight loss with surgery. Conversely, adiponectin concentrations were lower in obese patients, with a significant increase shown after weight loss with surgery. Ghrelin was higher in controls than obese patients, decreasing after gastric bypass and biliopancreatic diversion, but not after vertical banded gastroplasty.

CONCLUSION

Serum VEGF-A levels are significantly higher in obese patients than in lean controls, decreasing after weight loss with bariatric surgery, behaving similarly to other hormones related to adipose mass like leptin and insulin.

Possible relation of hemin-induced HO-1 expression to the upregulation of VEGF and BDNF mRNA levels in rat C6 glioma cells

Glial cells are generally considered to contribute to retaining the integrity of neural function through the protection of neuronal cells against neurodegenerative insults and also expected to play a potential role in the protection of cerebrovascular systems from various toxic insults of hemorrhaged blood, thus proposing a possible implication of glial cells in the recovery of brain function from the damage caused by cerebral hemorrhage. Based on this hypothetical idea, the direct effect of hemin on the expression of genes encoding heme oxygenase-1 (HO-1), vascular endothelial growth factor (VEGF), and brain-derived neurotrophic factor (BDNF) in glial cells was examined using rat C6 glioma cells as an in vitro model system. Hemin elevated both HO-1 and VEGF mRNA levels in the glioma cells at the concentration causing no critical damage to the cells, and the elevation of BDNF mRNA levels was also observed by exposing the cells to hemin under the same conditions. Furthermore, the elevation of VEGF and BDNF mRNA levels induced by hemin was blocked by pretreatment of the cells with the agents inhibiting not only HO-1 gene expression but also its enzymatic activity. These pharmacological studies indicate that hemin can induce the enhancement of VEGF and BDNF gene expression probably through the mechanism mediated by HO-1 activity in the glioma cells, proposing the possibility that glial cells are capable of contributing to the recovery of brain function from the damage caused by cerebral hemorrhage through the production of neurogenic and angiogenic factors.

Heme oxygenase-1 and the vascular bed: from molecular mechanisms to therapeutic opportunities

Heme oxygenase-1, an enzyme degrading heme to carbon monoxide, iron, and biliverdin, has been recognized as playing a crucial role in cellular defense against stressful conditions, not only related to heme release. HO-1 protects endothelial cells from apoptosis, is involved in blood-vessel relaxation regulating vascular tone, attenuates inflammatory response in the vessel wall, and participates in blood-vessel formation by means of angiogenesis and vasculogenesis. The latter functions link HO-1 not only to cardiovascular ischemia but also to many other conditions that, like development, wound healing, or cancer, are dependent on neovascularization. The aim of this comprehensive review is to address the mechanisms of HO-1 regulation and function in cardiovascular physiology and pathology and to demonstrate some possible applications of the vast knowledge generated so far. Recent data provide powerful evidence for the involvement of HO-1 in the therapeutic effect of drugs used in cardiovascular diseases. Novel studies open the possibilities of application of HO-1 for gene and cell therapy. Therefore, research in forthcoming years should help to elucidate both the real role of HO-1 in the effect of drugs and the clinical feasibility of HO-1-based cell and gene therapy, creating the effective therapeutic avenues for this refined antioxidant system.

Acidic pH stimulates the production of the angiogenic CXC chemokine, CXCL8 (interleukin-8), in human adult mesenchymal stem cells via the extracellular signal-regulated kinase, p38 mitogen-activated protein kinase, and NF-kappaB pathways

Blood vessel injury results in limited oxygen tension and diffusion leading to hypoxia, increased anaerobic metabolism, and elevated production of acidic metabolites that cannot be easily removed due to the reduced blood flow. Therefore, an acidic extracellular pH occurs in the local microenvironment of disrupted bone. The potential role of acidic pH and glu-leu-arg (ELR(+)) CXC chemokines in early events in bone repair was studied in human mesenchymal stem cells (hMSCs) treated with medium of decreasing pH (7.4, 7.0, 6.7, and 6.4). The cells showed a reciprocal increase in CXCL8 (interleukin-8, IL-8) mRNA levels as extracellular pH decreased. At pH 6.4, CXCL8 mRNA was induced >60x in comparison to levels at pH 7.4. hMSCs treated with osteogenic medium (OGM) also showed an increase in CXCL8 mRNA with decreasing pH; although, at a lower level than that seen in cells grown in non-OGM. CXCL8 protein was secreted into the medium at all pHs with maximal induction at pH 6.7. Inhibition of the G-protein-coupled receptor alpha, G(alphai), suppressed CXCL8 levels in response to acidic pH; whereas phospholipase C inhibition had no effect on CXCL8. The use of specific mitogen-activated protein kinase (MAPK) signal transduction inhibitors indicated that the pH-dependent increase in CXCL8 mRNA is due to activation of ERK and p38 pathways. The JNK pathway was not involved. NF-kappaB inhibition resulted in a decrease in CXCL8 levels in hMSCs grown in non-OGM. However, OGM-differentiated hMSCs showed an increase in CXCL8 levels when treated with the NF-kappaB inhibitor PDTC, a pyrrolidine derivative of dithiocarbamate.

Heme oxygenase-1 and carbon monoxide in vascular pathobiology: focus on angiogenesis

Angiogenesis involves the formation of new blood vessels and is critical for fundamental events such as development and repair after injury. Perturbances in angiogenesis contribute to the pathogenesis of diverse clinical conditions including cancer, complications of diabetes mellitus, ischemia/reperfusion injury of the heart and other organs, and preeclampsia, as well as a number of inflammatory disorders. Recent work has identified heme oxygenase-1 and its gaseous product, carbon monoxide, to possess potent proangiogenic properties in addition to well-recognized antiinflammatory, antioxidant, and antiapoptotic effects. Angiogenic factors, such as vascular endothelial growth factor and stromal cell-derived factor-1, mediate their proangiogenic effects through induction of heme oxygenase-1, making it an attractive target for therapeutic intervention. This review will provide an overview of the role of heme oxygenase-1 and carbon monoxide in angiogenesis.

Growth factors and heme oxygenase-1: perspectives in physiology and pathophysiology

Growth factors are mediators of both normal homeostasis and pathophysiology through their effects on various cellular processes. Similarly, heme oxygenase-1 (HO-1) has a role in maintaining physiologic equilibrium, by which it can either alleviate or exacerbate disease, depending on several considerations, including amount, timing, and location of expression, as well as the disease setting. Thus, the synthesis and activities of growth factors and HO-1 are intricately regulated. Interestingly, several growth factors induce HO-1, and, conversely, HO-1 can regulate the expression of some growth factors. This review focuses on the influence of growth factors and HO-1 and potential physiologic effects of the growth factor(s)-HO-1 interaction.

Heme oxygenase-1 modulates the expression of the anti-angiogenic chemokine CXCL-10 in renal tubular epithelial cells

The turnover and repair of peritubular capillaries is essential for the maintenance of normal renal tubular structure and function. Following injury, ineffective capillary repair/angiogenesis may result in chronic disease, whereas effective repair attenuates the injury process. Thus the process of healing in the kidney is likely dependent on an intricate balance between angiogenic and anti-angiogenic factors to maintain the renal microvasculature. We investigated the role of cytoprotective heme oxygenase-1 (HO-1) in the regulation of chemokines in human renal proximal tubular epithelial cells (RPTEC). Transfection of RPTEC with a HO-1 overexpression plasmid promoted a marked induction in the mRNA expression of the anti-angiogenic chemokine CXCL-10, along with angiogenic chemokines CXCL-8 and CCL-2. Utilizing a CXCL-10 promoter luciferase construct, we observed that HO-1-induced CXCL-10 expression is regulated at the transcriptional level. However, with increases in concentrations and time intervals of HO-1 induction, there was a marked decrease in CXCL-10 expression. Using pharmacological inhibitors, we found that HO-1-induced early robust CXCL-10 transcription is mediated through the PKC signaling pathway. To evaluate the functional significance of HO-1-induced CXCL-10 release, we cultured human vascular endothelial cells in the absence and presence of culture supernatants of the HO-1 plasmid-transfected RPTEC. We found that early (24 h) supernatants of the HO-1 plasmid-transfected cells (RPTEC) inhibited endothelial cell proliferation, and this effect was blocked by addition of a CXCL-10 neutralizing antibody. Thus HO-1 can regulate the expression of the anti-angiogenic CXCL-10 and may alter a critical balance between angiogenic vs. anti-angiogenic factors that are important to maintain renal microvasculature during injury.

Role of nitric oxide in chick embryonic organogenesis and dysmorphogenesis

BACKGROUND

Nitric oxide (NO), produced by the nitric oxide synthase family of enzymes, mediates multiple signaling functions, and when unchecked, NO causes pathological damage. Exposure of embryos to a variety of teratogens, including carbon monoxide (CO), has been shown to increase reactive intermediates, such as NO, and recent work showed that either the excess or absence of NO caused morphological defects. While endogenous NO is known to regulate many adult tissues, its role during embryonic organogenesis and/or in mediating responses to teratogen exposure has not been explored.

METHODS

We have examined here the presence of NO during normal chick embryonic organogenesis, and investigated the teratogenicity of NO through the application of sodium nitroprusside (SNP), which mimics NO overproduction, and NG-monomethyl-L-arginine (L-NMMA), which inhibits endogenous NOS activity.

RESULTS

Topical treatment with SNP or L-NMMA for 18 h resulted in morphological defects, specifically in the neural tube and somites, which corresponded to sites of altered apoptosis. The location of NO was histochemically correlated with the observed morphological defects. Coadministration of SNP or L-NMMA with CO showed functional coregulation and interaction between NO and CO in chick embryonic development.

CONCLUSIONS

Our results showed that regulation of NO is essential for normal axial development, that sites of altered NO expression correlate to those of altered apoptosis and dysmorphogenesis, and that CO coadministration resulted in a rectification of normal NO expression. Collectively, these results suggest that alteration in endogenous NO/CO signaling is responsible, at least in part, for the observed NO-induced teratogenesis.

Inducible nitric oxide synthase from bone marrow-derived cells plays a critical role in regulating colonic inflammation

BACKGROUND & AIMS

Nitric oxide (NO) is an important mediator of intestinal inflammation. Inducible NO synthase (iNOS) is the main source of NO in inflammation. Because iNOS is ubiquitously expressed, our aim was to determine which cellular source(s) of iNOS plays the central role in mediating intestinal inflammation.

METHODS

Chimeric lines were produced via bone marrow (BM) transplantation following irradiation. Colitis was induced with dextran sodium sulfate (DSS) or trinitrobenzene sulfonic acid (TNBS). The severity of colitis and markers of inflammation were assessed in standard fashion. Leukocyte recruitment was assessed by intravital microscopy.

RESULTS

The irradiated chimeric lines with iNOS-/- BM-derived cells were markedly more resistant to both DSS- and TNBS-induced injury. Resistance to DSS-induced colitis was lost when wild-type (wt) BM was used to reconstitute iNOS-/- mice. Neutrophils were the main source of iNOS in DSS-induced colitis. iNOS-/- chimeric lines had decreased colonic macrophage inflammatory protein 1beta and tumor necrosis factor alpha expression and increased levels of the protective growth factor, keratinocyte growth factor. LPS-mediated leukocyte recruitment was reduced in iNOS-/- mice, and there were marked changes in the inflammatory cell infiltrates between the chimeric lines with iNOS-/- vs wt BM-derived cells. Furthermore, the lamina propria CD4 +ve cells from chimeric lines with iNOS-/- BM-derived cells had reduced intracellular cytokine expression.

CONCLUSIONS

iNOS produced by BM-derived cells plays a critical role in mediating the inflammatory response during colitis. Cell-specific regulation of iNOS may represent a novel form of therapy for patients with inflammatory bowel disease.

Nitric oxide production is a proximal signaling event controlling exercise-induced mRNA expression in human skeletal muscle

Previous studies have described the magnitude and time course by which several genes are regulated within exercising skeletal muscle. These include interleukin-6 (IL-6), interleukin-8 (IL-8), heme oxygenase-1 (HO-1), and heat shock protein-72 (HSP72), which are involved in secondary signaling and preservation of intracellular environment. However, the primary signaling mechanisms coupling contraction to transcription are unknown. We hypothesized that exercise-induced nitric oxide (NO) production is an important signaling event for IL-6, IL-8, HO-1, and HSP72 expression in muscle. Twenty healthy males participated in the study. By real-time PCR, mRNA levels for 11 genes were determined in thigh muscle biopsies obtained 1) before and after 2 h knee extensor exercise without (control) and with concomitant NO synthase inhibition (nitro-L-arginine methyl ester, L-NAME, 5 mg x kg(-1)); or 2) before and after 2 h femoral artery infusion of the NO donor nitroglycerin (NTG, 1.5 microg x kg(-1) x min(-1)). L-NAME caused marked reductions in exercise-induced expression of 4 of 11 mRNAs including IL-6, IL-8, and HO-1. IL-6 protein release from the study leg to the circulation increased in the control but not in the L-NAME trial. NTG infusion significantly augmented expression of the mRNAs attenuated by L-NAME. These findings advance the novel concept that NO production contributes to regulation of gene expression in muscle during exercise. Subsequently, we sought evidence for involvement of AMP-activated kinase or nuclear factor kappa B, but found none.

3-Hydroxyanthranilic acid, one of l-tryptophan metabolites, inhibits monocyte chemoattractant protein-1 secretion and vascular cell adhesion molecule-1 expression via heme oxygenase-1 induction in human umbilical vein endothelial cells

Heme oxygenase (HO)-1 is important in the vascular system, and its genetic or pharmacological induction in endothelium would be effective for the prevention and treatment of atherosclerosis. The naturally occurring antioxidant 3-hydroxyanthranilic acid (HA), one of l-tryptophan metabolites formed in vivo along the metabolic route known as the kynurenine pathway during inflammation or infection, was found to induce HO-1 expression and to stimulate nuclear translocation of NF-E2 related factor 2 (Nrf2) in human umbilical vein endothelial cells (HUVECs). Pre-treatment with HA inhibited the secretion of monocyte chemoattractant protein (MCP)-1, the expression of vascular cell adhesion molecule (VCAM)-1 and the activation of transcriptional nuclear factor (NF)-kappaB in HUVECs stimulated with tumor necrosis factor-alpha, the major pro-inflammatory cytokine causing endothelial inflammation. Interestingly, the observed anti-inflammatory effects of HA were mimicked by a HO-1 inducer, cobalt protoporphyrin, and bilirubin, one of HO-1 enzymatic products, but abolished in the presence of a HO-1 inhibitor, tin protoporphyrin. Based on our findings, we suggest that Nrf2-dependent HO-1 expression induced by HA inhibits MCP-1 secretion, VCAM-1 expression and NF-kappaB activation associated with vascular injury and inflammation in atherosclerosis.

The role of nitric oxide in tumour progression

Nitric oxide (NO) and nitric oxide synthases are ubiquitous in malignant tumours and are known to exert both pro- and anti-tumour effects. We summarize our current understanding of the role of NO in tumour progression, especially in relation to angiogenesis and vascular functions. We also discuss potential strategies for cancer treatment that modulate NO production and/or its downstream signalling pathways.

Dual role of VEGF-induced heme-oxygenase-1 in angiogenesis

Heme-oxygenase-1 (HO-1) is an inducible cytoprotective molecule that displays antioxidant, antiapoptotic, and antiinflammatory effects. In addition, HO-1 appears to have a complex role in angiogenesis. Recent in vivo studies report that vascular endothelial growth factor (VEGF) regulates HO-1 expression and activity in vascular endothelial cells (ECs) and that inhibition of HO-1 abrogates VEGF-induced endothelial activation and subsequent angiogenesis, while promoting VEGF-induced monocyte recruitment and inflammatory angiogenesis. HO-1 may also regulate the synthesis and activity of VEGF, resulting in a positive-feedback loop. In contrast, HO-1 activity has the opposite effect on lipopolysaccharide-driven inflammatory angiogenesis, inhibiting leukocyte invasion and preventing subsequent angiogenesis. In this review, we summarize the current understanding of the role of HO-1 in angiogenesis. We conclude that further investigation, using targeted molecular approaches specifically to alter HO-1 activity, are required to develop our understanding of the role of HO-1 and its products, carbon monoxide, biliverdin, bilirubin, and free iron in angiogenesis. We propose that during chronic inflammation, HO-1 has two roles, first an antiinflammatory action inhibiting leukocyte infiltration, and second, promotion of VEGF-driven noninflammatory angiogenesis, which facilitates tissue repair. Additional studies will help determine whether modulating the activity of HO-1 and/or its products has therapeutic potential in chronic inflammatory dise.

Hydrogen sulfide inhibits nitric oxide production and nuclear factor-kappaB via heme oxygenase-1 expression in RAW264.7 macrophages stimulated with lipopolysaccharide

Hydrogen sulfide (H(2)S), a regulatory gaseous molecule that is endogenously synthesized by cystathionine gamma-lyase (CSE) and/or cystathionine beta-synthase (CBS) from L-cysteine (L-Cys) metabolism, is a putative vasodilator, and its role in nitric oxide (NO) production is unexplored. Here, we show that at noncytotoxic concentrations, H(2)S was able to inhibit NO production and inducible NO synthase (iNOS) expression via heme oxygenase (HO-1) expression in RAW264.7 macrophages stimulated with lipopolysaccharide (LPS). Both H(2)S solution prepared by bubbling pure H(2)S gas and NaSH, a H(2)S donor, dose dependently induced HO-1 expression through the activation of the extracellular signal-regulated kinase (ERK). Pretreatment with H(2)S or NaHS significantly inhibited LPS-induced iNOS expression and NO production. Moreover, NO production in LPS-stimulated macrophages that are expressing CSE mRNA was significantly reduced by the addition of L-Cys, a substrate for H(2)S, but enhanced by the selective CSE inhibitor beta-cyano-L-alanine but not by the CBS inhibitor aminooxyacetic acid. While either blockage of HO activity by the HO inhibitor, tin protoporphyrin IX, or down-regulation of HO-1 expression by HO-1 small interfering RNA (siRNA) reversed the inhibitory effects of H(2)S on iNOS expression and NO production, HO-1 overexpression produced the same inhibitory effects of H(2)S. In addition, LPS-induced nuclear factor (NF)-kappaB activation was diminished in RAW264.7 macrophages preincubated with H(2)S. Interestingly, the inhibitory effect of H(2)S on NF-kappaB activation was reversed by the transient transfection with HO-1 siRNA, but was mimicked by either HO-1 gene transfection or treatment with carbon monoxide (CO), an end product of HO-1. CO treatment also inhibited LPS-induced NO production and iNOS expression via its inactivation of NF-kappaB. Collectively, our results suggest that H(2)S can inhibit NO production and NF-kappaB activation in LPS-stimulated macrophages through a mechanism that involves the action of HO-1/CO.

Heme oxygenase-1 mediates the anti-inflammatory actions of 2′-hydroxychalcone in RAW 264.7 murine macrophages

Chalcones are a group of plant-derived polyphenolic compounds that belong to the flavonoids family, and possess a wide variety of cytoprotective and modulatory functions. Chalcones exert their cytoprotective actions via activation of specific transcriptional factors and upregulation of endogenous defensive pathways, such as phase II enzymes and the stress protein heme oxygenase-1 (HO-1). In this study, we investigated the anti-inflammatory action of 2′-hydroxychalcone (2-HC) in a model of lipopolysaccharide (LPS)-induced inflammation in RAW 264.7 macrophages and examined the role of HO-1 in this process. Our results demonstrate that 2-HC potently induces HO-1 expression and markedly reduces LPS-mediated nitrite and TNF-α production. These effects are accompanied by inhibition of inducible nitric oxide synthase protein expression and abolished by blockade of heme oxygenase activity with either tin protoporphyrin IX or HO-1 small interfering RNA. By using a pharmacological approach and siRNA technology, we also found that phosphatidylinositol 3-kinase is a major cellular mediator in 2-HC-induced HO-1 expression. These findings strongly suggest that 2-HC exerts anti-inflammatory actions via activation of the HO-1 pathway and help to elucidate the mechanisms underlying the potential therapeutic value of chalcones.

Role of Endothelial Nitric Oxide Synthase in the Regulation of SREBP Activation by Oxidized Phospholipids

Oxidized-1-palmitoyl-2-arachidonyl- sn -glycero-3-phosphorylcholine (Ox-PAPC), found in atherosclerotic lesions and other sites of chronic inflammation, activates endothelial cells (EC) to synthesize chemotactic factors, such as interleukin (IL)-8. Previously, we demonstrated that the sustained induction of IL-8 transcription by Ox-PAPC was mediated through the activation of sterol regulatory element–binding protein (SREBP). We now present evidence for the role of endothelial nitric oxide synthase (eNOS) in the activation of SREBP by Ox-PAPC. Ox-PAPC treatment of EC induced a dose- and time-dependent activation of eNOS, as measured by phosphorylation of serine 1177, dephosphorylation of threonine 495, and the conversion of l -arginine to l -citrulline. Activation of eNOS by Ox-PAPC was regulated through a phosphatidylinositol-3-kinase/Akt-mediated mechanism. These studies also demonstrated that pretreatment of EC with NOS inhibitor, N ω -nitro- l -arginine-methyl ester (L-NAME), significantly inhibited Ox-PAPC–induced IL-8 synthesis. Because SREBP activation had been previously shown to regulate IL-8 transcription by Ox-PAPC, we examined the effects of L-NAME on Ox-PAPC–induced SREBP activation. Our data demonstrated that Ox-PAPC–induced SREBP activation and expression of SREBP target genes were significantly reduced by pretreatment with L-NAME. Interestingly, treatment of EC with NO donor, S -nitroso- N -acetylpenicillamine, did not activate SREBP, suggesting that NO alone was not sufficient for SREBP activation. Rather, our findings indicated that superoxide (O 2 ·− ), in combination with NO, regulated SREBP activation by Ox-PAPC. We found that Ox-PAPC treatment generated O 2 ·− through an eNOS-mediated mechanism and that mercaptoethylguanidine, a peroxynitrite scavenger, reduced SREBP activation by Ox-PAPC. Taken together, these findings propose a novel role for eNOS in the activation of SREBP and SREBP-mediated inflammatory processes.