Ambient but not incremental oxidant generation effects intercellular adhesion molecule 1 induction by tumour necrosis factor alpha in endothelium

Phenotypic characterization of circulating endothelial cells induced by inflammation and oxidative stress in ankylosing spondylitis

Ankylosing spondylitis (AS) is a chronic auto-immune disease, affecting the spine, sacroiliac, and sometimes peripheral joints. It is also involved with cardio-vascular risk factors due to accelerated atherosclerosis. Oxidative burst, systemic inflammation coupled with endothelial dysfunction (ED), resulting in reduced bioavailability of the vasodilator nitric oxide (NO) and an increased number of circulating endothelial cells (CECs) may correlate with disease activity and its sustenance. Hence, the study was aimed to detect and quantify CECs and assess the oxidative stress and inflammatory status in AS patients vis-à-vis healthy controls, as well as relate these parameters with AS disease activity and atherosclerotic markers in patients. Our study showed an increased frequency of endothelial cells in peripheral blood of AS patients in pro-inflammatory conditions. In AS patient population, they showed significant reduction of flow-mediated dilatation (%FMD) (p < 0.05), and increased soluble adhesion molecules such as sICAM-1 (p < 0.01) and sVCAM-1 (p < 0.05) compared to healthy controls. A marked increase in pro-inflammatory markers such as TNF-α (p < 0.01) and IL-1β (p < 0.001) and reactive free radicals (p < 0.05) along with reduced serum nitrite in AS, provided a strong pro-inflammatory milieu which positively correlated with Bath ankylosing spondylitis disease activity and functional indices (BASDAI and BASFI). The observed significant upregulation in CECs (CD45^-/CD31⁺/CD105⁺/CD144⁺) in patients compared to healthy controls positively correlated with disease activity and duration as well as with markers of oxidative stress. Thus, chronic inflammation and oxidative burst induce loss of NO bioavailability, leading to ED. This may cause the derangement of CECs that may be considered as a prognostic biomarker for ED.

Extracellular methemoglobin promotes cyto-adherence of uninfected RBC to endothelial cells: Insight into cerebral malaria pathology

The endothelial cell barrier is tightly regulated, and disruption or the leaky behavior of the barrier leads to pathology. Disturbance of blood-brain barrier is observed during viral infection, cerebral malaria, and acute hemorrhagic encephalitis. Red blood cells (RBCs) bind to the endothelial cells (ECs) and their affinity towards ECs enhances in the presence of Plasmodium falciparum infection. ECs stimulated with methemoglobin (MetHb; 20 µM) for 1 hour exhibit high levels of cyto-adherence receptors CD36 and ICAM-1 on their cell surface compared with unstimulated cells. These ECs have acquired affinity towards uninfected RBCs in flow at arterial shear stress. SEM analysis indicates that EC-RBC cyto-adherence involved multiple attachment points. Initially, ECs bind single layer of RBCs and the number of RBCs increases over time to give high-order cyto-adherence with more than 30 RBCs adhered to each endothelial cell. The cyto-adherence complexes are stable to high shear stress and can withstand shear stress up to 450 dyne/cm ² . MetHb-treated ECs exhibited high reactive oxygen species level, and preincubation of ECs with antioxidant (NAC or mannitol) abolished the formation of EC-RBC cyto-adherence complexes. In addition, gallic acid (present in red wine) and green tea extract has inhibited the formation of EC-RBC cyto-adherence complex. A better understanding of gallic acid and tea polyphenol targeting pathological cyto-adherence may allow us to develop a better adjuvant therapy for cerebral malaria and other noninfectious diseases.

Association of Flavin Monooxygenase Gene E158K Polymorphism with Chronic Heart Disease Risk

We studied the relationship between the risk of chronic heart disease and FMO3 gene polymorphism E158K analyzed by PCR and restriction fragment length polymorphism (RFLP) analysis. The homozygous 158KK genotype of FMO3 gene is associated with high risk of chronic heart disease in women, but not in men. FMO3 gene polymorphism E158K is a significant predictor of predisposition to chronic heart disease in women.

The cooperative roles of inflammation and oxidative stress in the pathogenesis of hypertension

SIGNIFICANCE

Innate and adaptive immunity play fundamental roles in the development of hypertension and its complications. As effectors of the cell-mediated immune response, myeloid cells and T lymphocytes protect the host organism from infection by attacking foreign intruders with bursts of reactive oxygen species (ROS).

RECENT ADVANCES

While these ROS may help to preserve the vascular tone and thereby protect against circulatory collapse in the face of overwhelming infection, aberrant elaboration of ROS triggered by immune cells in the absence of a hemodynamic insult can lead to pathologic increases in blood pressure. Conversely, misdirected oxidative stress in cardiovascular control organs, including the vasculature, the kidney, and the nervous system potentiates inflammatory responses, augmenting blood pressure elevation and inciting target organ damage.

CRITICAL ISSUES

Inflammation and oxidative stress thereby act as cooperative and synergistic partners in the pathogenesis of hypertension.

FUTURE DIRECTIONS

Pharmacologic interventions for hypertensive patients will need to exploit this robust bidirectional relationship between ROS generation and immune activation in cardiovascular control organs to maximize therapeutic benefit, while limiting off-target side effects.

Anti-inflammatory effect of targeted delivery of SOD to endothelium: mechanism, synergism with NO donors and protective effects in vitro and in vivo

Pro-inflammatory activation of vascular endothelium is implicated in pathogenesis of severe conditions including stroke, infarction and sepsis. We have recently reported that superoxide dismutase (SOD) conjugated with antibodies (Ab/SOD) that provide targeted delivery into endothelial endosomes mitigates inflammatory endothelial activation by cytokines and agonists of Toll-like receptors (TLR). The goal of this study was to appraise potential utility and define the mechanism of this effect. Ab/SOD, but not non-targeted SOD injected in mice alleviated endotoxin-induced leukocyte adhesion in the cerebral vasculature and protected brain from ischemia-reperfusion injury. Transfection of endothelial cells with SOD, but not catalase inhibited NFκB signaling and expression of Vascular Cell Adhesion Molecule-1 induced by both cytokines and TLR agonists. These results affirmed that Ab/SOD-quenched superoxide anion produced by endothelial cells in response to proinflammatory agents mediates NFκB activation. Furthermore, Ab/SOD potentiates anti-inflammatory effect of NO donors in endothelial cells in vitro, as well as in the endotoxin-challenged mice. These results demonstrate the central role of intracellular superoxide as a mediator of pro-inflammatory activation of endothelium and support the notion of utility of targeted interception of this signaling pathway for management of acute vascular inflammation.

Aronia melanocarpa fruit extract exhibits anti-inflammatory activity in human aortic endothelial cells

Background

Altered expression of cell adhesion molecules (CAMs) has been implicated in a variety of chronic inflammatory conditions, including atherosclerosis. Regulation of adhesion molecule expression by specific redox-sensitive mechanisms has been reported. Additionally, it has been observed that the extract of Aronia melanocarpa (A. Melanocarpa) fruits, rich in polyphenols, exhibits potent anti-oxidant properties and displays cardioprotective activity.

Methods and results

Human aortic endothelial cells (HAECs) were pretreated with various concentrations (primarily 50 μg/mL) of Aronia Melanocarpa fruit extract prior to treatment with TNFα (10 ng/mL) for various periods of time. The surface protein and mRNA expression of ICAM-1 and VCAM-1 were determined using flow cytometry and real-time RT-PCR, respectively. Adhesion of peripheral blood mononuclear leucocytes (PBMLs) to TNFα-treated HAECs was evaluated by an adhesion assay. Activation of NF-κB was evaluated by measuring NF-κB p65 phosphorylation using flow cytometry. ROS production was determined by reduction in fluorescent 2′,7′-dichlorofluorescein diacetate (DCFH-DA). Tested A. Melanocarpa extract significantly inhibited the expression of ICAM-1 and VCAM-1, attenuated the phosphorylation of NF-κB p65 and decreased intracellular ROS production in TNFα-treated HAECs.

Conclusion

We conclude that A. Melanocarpa fruit extract exhibits anti-inflammatory effects in HAECs by inhibiting the expression of endothelial CAMs, activation of NF-κB and production of ROS.

Induction of ICAM-1 by Armillariella mellea is mediated through generation of reactive oxygen species and JNK activation

ETHNOPHARMACOLOGICAL RELEVANCE

Armillariella mellea is an edible mushroom that has been traditionally used as an alternative medicine in many countries because of its anti-microbial and anti-cancer effects.

AIM OF THE STUDY

In this study, we examined the ability of Armillariella mellea to induce the expression of intercellular adhesion molecule (ICAM)-1, an important cellular adhesion molecule for the recruitment of immune cells to regional inflammatory sites.

MATERIALS AND METHODS

A human monocytic cell line, THP-1 or human peripheral blood mononuclear cells (PBMC) were stimulated with Armillariella mellea extract (AME) and subjected to flow cytometry to examine the expression of ICAM-1 protein on the cell surface. Steady-state mRNA level of ICAM-1 was determined by real-time reverse transcription-polymerase chain reaction. The phosphorylation of JNK protein was examined by Western blot analysis using antibodies specific for non-phosphorylated and phosphorylated forms of JNK. For the analysis of transcription factors regulating ICAM-1 transcription, the nuclear fraction was extracted from AME-treated THP-1 cells and subjected to electrophoretic mobility shift assay.

RESULTS

AME induced expression of ICAM-1 and its mRNA in THP-1 cells in dose- and time-dependent manners. AME-induced ICAM-1 expression was also observed on CD14-positive monocytes in human PBMC. Interestingly, AME-induced ICAM-1 production was inhibited by the specific inhibitors of reactive oxygen species (ROS) and JNK, whereas no inhibitory effect was observed when inhibitors of ERK, p38 kinase, phosphatidylinositol 3-kinase, or protein kinase C were used. Concomitantly, AME increased phosphorylation of JNK in a time-dependent fashion. DNA binding activities of NF-kappaB, AP-1, SP-1, and STAT-1 were increased by AME treatment.

CONCLUSION

These results suggest that AME induces ICAM-1 expression in human monocytic cells through ROS/JNK-dependent signaling pathways leading to the activation of NF-kappaB, AP-1, SP-1, and STAT-1 transcription factors.

Suppression of Oxidative Stress in the Endothelium and Vascular Wall

There is growing evidence that oxidative stress, meaning an excessive production of reactive oxygen and nitrogen species, underlies many forms of cardiovascular disease. The major source of oxidative stress in the artery wall is an NADPH oxidase. This enzyme complex in vascular cells, including endothelium, differs from that in phagocytic leucocytes in both biochemical structure and functions. The crucial flavin-containing catalytic subunits Nox1 and Nox4 are not present in leucocytes, but are highly expressed in vascular cells and upregulated in vascular remodeling, such as that found in hypertension and atherosclerosis. This offers the opportunity to develop "vascular specific" NADPH oxidase inhibitors that do not compromise the essential physiological signaling and phagocytic function carried out by reactive oxygen and nitrogen molecules. Although many conventional antioxidants fail to significantly affect outcomes in cardiovascular disease, targeted inhibitors of NADPH oxidase that block the source of oxidative stress in the vasculature are more likely to prevent the deterioration of vascular function that leads to stroke and heart attack.

Hug tightly and say goodbye: role of endothelial ICAM-1 in leukocyte transmigration

Stable adhesion of leukocytes to endothelium is crucial for transendothelial migration (TEM) of leukocytes evoked during inflammatory responses, immune surveillance, and homing and mobilization of hematopoietic progenitor cells. The basis of stable adhesion involves expression of intercellular adhesion molecule-1 (ICAM-1), an inducible endothelial adhesive protein that serves as a counter-receptor for beta(2)-integrins on leukocytes. Interaction of ICAM-1 with beta(2)-integrins enables leukocytes to adhere firmly to the vascular endothelium and subsequently, to migrate across the endothelial barrier. The emerging paradigm is that ICAM-1, in addition to firmly capturing leukocytes, triggers intracellular signaling events that may contribute to active participation of the endothelium in facilitating the TEM of adherent leukocytes. The nature, duration, and intensity of ICAM-1-dependent signaling events may contribute to the determination of the route (paracellular vs. transcellular) of leukocyte passage; these aspects of ICAM-1 signaling may in turn be influenced by density and distribution of ICAM-1 on the endothelial cell surface, the source of endothelial cells it is present on, and the type of leukocytes with which it is engaged. This review summarizes our current understanding of the "ICAM-1 paradigm" of TEM with an emphasis on the signaling events mediating ICAM-1 expression and activated by ICAM-1 engagement in endothelial cells.

Role of NADPH oxidase in atherosclerosis

Reactive oxidant species (ROS) seem to play a key role in the atherosclerotic process via a series of molecular changes that lead to macrophage infiltration in the endothelium and eventually to plaque formation. ROS are also implicated in arterial dysfunction via inactivation of nitric oxide, a potent vasodilator and antiaggregating molecule produced by the endothelium. Owing to the relevance of endothelial dysfunction and vascular inflammation in the process of human atherosclerosis, a lot of effort has been directed towards discovering the ROS-generating pathways implicated in the ROS upregulation. Amongst the enzymatic pathways, NADPH oxidase is the most important enzyme responsible for ROS formation in human vessels. Experimental and clinical studies suggested a role for this enzyme in initiation and progression of atherosclerotic disease. The purpose of this review is to analyze whether the basic and clinical studies are consistent with this hypothesis and to point out if determination of NADPH oxidase is useful in the setting of the atherosclerosis to predict its progression and clinical complications.

Role of Reactive Oxygen Species in Tumor Necrosis Factor-alpha Induced Endothelial Dysfunction

Endothelial cell injury and dysfunction are the major triggers of pathophysiological processes leading to cardiovascular disease. Endothelial dysfunction (ED) has been implicated in atherosclerosis, hypertension, coronary artery disease, vascular complications of diabetes, chronic renal failure, insulin resistance and hypercholesterolemia. Although now recognized as a class of physiological second messengers, reactive oxygen species (ROS) are important mediators in cellular injury, specifically, as a factor in endothelial cell damage. Uncontrolled ROS production and/or decreased antioxidant activity results in a deleterious state referred to as 'oxidative stress'. A candidate factor in causing ROS production in endothelial cells is tumor necrosis factor alpha (TNF-α), a pleiotropic inflammatory cytokine. TNF-α has been shown to both be secreted by endothelial cells and to induce intracellular ROS formation. These observations provide a potential mechanism by which TNF-α may activate and injure endothelial cells resulting in ED. In this review, we focus on the relationship between intracellular ROS formation and ED in endothelial cells or blood vessels exposed to TNF-α to provide insight into the role of this important cytokine in cardiovascular disease.

Human neuronal cell protein responses to Nipah virus infection

BACKGROUND

Nipah virus (NiV), a recently discovered zoonotic virus infects and replicates in several human cell types. Its replication in human neuronal cells, however, is less efficient in comparison to other fully susceptible cells. In the present study, the SK-N-MC human neuronal cell protein response to NiV infection is examined using proteomic approaches.

RESULTS

Method for separation of the NiV-infected human neuronal cell proteins using two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) was established. At least 800 protein spots were resolved of which seven were unique, six were significantly up-regulated and eight were significantly down-regulated. Six of these altered proteins were identified using mass spectrometry (MS) and confirmed using MS/MS. The heterogenous nuclear ribonucleoprotein (hnRNP) F, guanine nucleotide binding protein (G protein), voltage-dependent anion channel 2 (VDAC2) and cytochrome bc1 were present in abundance in the NiV-infected SK-N-MC cells in contrast to hnRNPs H and H2 that were significantly down-regulated.

CONCLUSION

Several human neuronal cell proteins that are differentially expressed following NiV infection are identified. The proteins are associated with various cellular functions and their abundance reflects their significance in the cytopathologic responses to the infection and the regulation of NiV replication. The potential importance of the ratio of hnRNP F, and hnRNPs H and H2 in regulation of NiV replication, the association of the mitochondrial protein with the cytopathologic responses to the infection and induction of apoptosis are highlighted.

Gamma-irradiation-induced intercellular adhesion molecule-1 (ICAM-1) expression is associated with catalase: activation of Ap-1 and JNK

The ionizing radiation used in cancer therapy frequently produces damage to normal tissues and induces complex responses, including inflammation. The upregulation of the intercellular adhesion molecule-1 (ICAM-1) in response to numerous inducing factors is associated with inflammation. Therefore, this study examined the molecular mechanisms responsible for ICAM-1 expression induced by gamma-irradiation (gammaIR). ICAM-1 mRNA and cell surface expression were induced in A549 human lung epithelial cells after exposing them to gammaIR. Catalase expression and activity were also increased in gammaIR-treated cells. Treatment of the gammaIR-treated cells with catalase resulted in a significant increase in the ICAM-1 cell surface expression level. The catalase inhibitor 3-amino-1,2,4-triazole (AT) reduced the level of ICAM-1. Electrophoretic mobility shift assay (EMSA) analysis showed that activating protein 1 (AP-1) was activated by gammaIR, whereas NF-kappaB was not. Specific Jun N-terminal kinase (JNK) inhibition attenuated the upregulation of gammaIR stimulated ICAM-1. Western blot analysis revealed a marked elevation in activation of JNK. In addition, pretreatment with AT resulted in a decrease in the level of JNK phosphorylation and AP-1 activation. Overall, data suggest that induction of ICAM-1 expression by gammaIR is associated with catalase. Furthermore, catalase, JNKs, and AP-1 activation induce ICAM-1 upregulation through a sequential process.

Novel isoforms of NADPH-oxidase in cerebral vascular control

Reactive oxygen species (ROS) are thought to play an important role in the initiation and progression of a variety of vascular diseases. Furthermore, accumulating evidence indicates that ROS may also serve as important cell signalling molecules for the regulation of normal vascular function. Recently, a novel family of proteins (Nox1, 2 and 4) that act as the catalytic subunit of the superoxide (O2-) producing enzyme NADPH-oxidase has been discovered in vascular cells. There is now preliminary evidence suggesting that NADPH-oxidase-derived ROS may serve as a physiological vasodilator mechanism in the cerebral circulation. Moreover, the activity of NADPH-oxidase is profoundly greater in cerebral versus systemic arteries. Studies have shown that Nox1, Nox2 (also known as gp91phox) and Nox4 are all expressed in cerebral arteries, suggesting that multiple isoforms of NADPH-oxidase may be important for ROS production by cerebral arteries. Enhanced NADPH-oxidase activity is associated with several vascular-related diseases, including hypertension, stroke, subarachnoid haemorrhage and Alzheimer's dementia; however, the consequences of this for cerebral vascular function are controversial. For example, there is some evidence suggesting that NADPH-oxidase-derived O2- may play a role in endothelial dysfunction of cerebral arteries and a subsequent rise in cerebral vascular tone, associated with hypertension. However, activation of NADPH-oxidase elicits cerebral vasodilatation in vivo, and this mechanism is enhanced in chronic hypertension. While further supportive evidence is needed, it is an intriguing possibility that NADPH-oxidase-derived ROS may play a protective role in regulating cerebral vascular tone during disease.

Protective effect of erythropoietin on renal ischemia and reperfusion injury

BACKGROUND

Multiple protective effects of erythropoietin (EPO), such as antiapoptotic, antioxidant, angiogenic and neuroprotective effects, against ischemia have been demonstrated in cell culture and animal models. Genistein is also a potent tyrosine kinase inhibitor. The aims of the present study were to evaluate the effects of EPO on renal ischemia/reperfusion injury and to determine the role of the tyrosine kinase pathway on this process.

METHODS

Sprague-Dawley rats were assigned to five groups: (i) sham (Group I); (ii) control with renal ischemia (right nephrectomy and clamping on the left renal pedicle for 45 min and reperfusion; Group II); (iii) EPO + ischemia (Group III); (iv) genistein (an inhibitor of tyrosine kinase) + ischemia (Group IV); and (v) EPO + genistein + ischemia (Group V). Recombinant human EPO (1000 IU/kg) and genistein (10 mg/kg) were given 2 hours before ischemia. Blood samples and the left kidney were obtained after 45 min of reperfusion from half of the rats and after 24 h from the other half.

RESULTS

The blood urea nitrogen, creatinine, tumour necrosis factor-alpha (P < 0.05) and interleukin-2 (P < 0.01) levels, and renal tissue lipid peroxidation (P < 0.05) were significantly lower in Group III than in Group II at 45 min of reperfusion. Following 24 h of reperfusion, EPO decreased tissue peroxidation and histopathological injury, whereas genistein reversed it. The most prominent ischemic injury was observed in Group IV in which genistein was administered. There was no significant difference between Groups II and V.

CONCLUSIONS

These results suggest that EPO is effective in attenuating renal ischemia/reperfusion injury, and this effect may be related to tyrosine kinase activity.

NAD(P)H oxidase-stimulating activity of serum from type 2 diabetic patients with retinopathy mediates enhanced endothelial expression of E-selectin

Endothelial expression of E-selectin is enhanced in diabetic patients with retinopathy, however, the underlying mechanisms are unclear. Therefore, this study was aimed to determine if endothelial expression of E-selectin is stimulated with serum from type 2 diabetic patients with retinopathy, and whether this process is related to NAD(P)H oxidase-derived oxidative stress. Serum was obtained from type 2 diabetic patients with (T2DR) or without (T2DM) retinopathy, and age-matched non-diabetic healthy person (Control). Serum was added to in vitro-grown human coronary artery endothelial cells (HCAEC), after which E-selectin expression, reactive oxygen species (ROS) production, and NAD(P)H oxidase activity were measured. Serum from T2DR induced a significantly higher expression of E-selectin than serum from T2DM and control in association with an enhanced production of ROS in HCAEC. T2DR serum enhanced E-selectin expression in a ROS-dependent manner since this process was significantly attenuated not only by tiron (1 mM), a superoxide scavenger, but also by DPI (10 micromol/L) and apocynin (100 micromol/L), inhibitors of NAD(P)H oxidase. Furthermore, the activity of NADH oxidase was markedly increased by T2DR serum, and this was accompanied by the enhanced membrane translocation of p47phox, a cytosolic subunit of NAD(P)H oxidase. These findings suggest that serum from T2DR induced up-regulation of E-selectin expression in HCAEC, and this process might be dependent on activation of endothelial NADH oxidase via an enhanced membrane translocation of p47phox.

A search for genes modulated by interleukin-6 alone or with interleukin-1beta in HepG2 cells using differential display analysis

Interleukin-1 and interleukin-6 are principal cytokines involved in regulation of expression of acute-phase proteins. In the joint action of both cytokines IL-1 can suppress or enhance the IL-6-dependent induction of gene expression. Here, we report changes in the transcriptome profile of HepG2 cells exposed to IL-6 alone, or IL-1 and IL-6. Cytokine-responsive genes were identified by differential display analysis. Validation of observed changes in the transcript level was carried out using the slot blot method. Out of 88 cDNA species modulated by IL-6, only 38 represent different known genes whereas 18 clones match genomic clones in NCBI data with hypothetical cDNA sequences (the remaining 32 clones showed no homology with the database or represented several clones of the same gene). In the experiments with HepG2 cells prestimulated for 3 h with IL-1 and then stimulated with IL-6, 43 cDNA fragments were amplified. Twenty-three of them represent known genes while 10 clones have inserts matching hypothetical cDNA sequences in NCBI data. The identified transcripts modulated by IL-6 or both cytokines in HepG2 cells code for intracellular proteins of various function. The largest groups represent genes engaged in metabolism, protein synthesis and signaling pathways. Among all genes identified as differentially regulated under stimulation by IL-6, or IL-1/IL-6, six were detected in both types of stimulation. None of the typical genes coding for plasma acute phase proteins was identified in our experiments. This indicates that differential display cannot be used to characterize the profile of a given transcriptome. On the other hand, it is a useful technique for detection of new genes responding to IL-6 alone or IL-6 in combination with IL-1.

Global analysis of endothelial cell line proliferation patterns based on nutrient-depletion models: implications for a standardization of cell proliferation assays

It is known that cell populations growing in different environmental conditions may exhibit different proliferation patterns. However, it is not clear if, despite the diversity of the so-observed patterns, inherent cellular growth characteristics of the population can nevertheless be determined. This study quantifies the proliferative behaviour of the permanent endothelial human cell line, Eahy926, and establishes to which extent the estimation of the cell proliferation rate depends on variations of the experimental protocols. Cell proliferation curves were obtained for cells cultured over 16 days and the influences of cell seeding densities, foetal bovine serum content and frequency of culture medium changes were investigated. Quantitative dynamic modelling was conducted to evaluate the kinetic characteristics of this cell population. We proposed successive models and retained a nutrient-depletion toxicity dependant model, which takes into account the progressive depletion of nutrients, as well as the increase of toxicity in the cell culture medium. This model is shown to provide a very good and robust prediction of the experimental proliferation curves, whatever are the considered frequency of culture medium changes and serum concentrations. Thus, the model enables an intrinsic quantification of the parameters driving in vitro EAhy926 proliferation, including proliferation, nutrient consumption and toxicity increase rates, rather independently of the experiments design. We therefore propose that such models could provide a basis for a standardized quantification of intrinsic cell proliferation kinetics.

Hypoxia-reoxygenation-induced mitochondrial damage and apoptosis in human endothelial cells are inhibited by vitamin C

Hypoxia and hypoxia-reperfusion (H-R) play important roles in human pathophysiology because they occur in clinical conditions such as circulatory shock, myocardial ischemia, stroke, and organ transplantation. Reintroduction of oxygen to hypoxic cells during reperfusion causes an increase in generation of reactive oxygen species (ROS), which can alter cell signaling, and cause damage to lipids, proteins, and DNA leading to ischemia-reperfusion injury. Since vitamin C is a potent antioxidant and quenches ROS, we investigated the role of intracellular ascorbic acid (iAA) in endothelial cells undergoing hypoxia-reperfusion. Intracellular AA protected human endothelial cells from H-R-induced apoptosis. Intracellular AA also prevents loss of mitochondrial membrane potential and the release of cytochrome C and activation of caspase-9 and caspase-3 during H-R. Additionally, inhibition of caspase-9 activation prevented H-R-induced apoptosis, suggesting a mitochondrial site of initiation of apoptosis. We found that H-R induced an increase in ROS in endothelial cells that was abrogated in the presence of iAA. Our results indicate that vitamin C prevents hypoxia and H-R-induced damage to human endothelium.

At least 2 distinct pathways generating reactive oxygen species mediate vascular cell adhesion molecule-1 induction by advanced glycation end products

OBJECTIVE

The interaction of advanced glycation end products (AGEs) with their main receptor RAGE in endothelial cells induces intracellular generation of reactive oxygen species (ROS) and the expression of vascular cell adhesion molecule (VCAM)-1. We investigated the role of distinct sources of ROS, including the mitochondrial electron transport chain, NAD(P)H oxidase, xanthine oxidase, and arachidonic acid metabolism, in AGE-induced VCAM-1 expression.

METHODS AND RESULTS

The induction of ROS and VCAM-1 by AGEs in cultured human umbilical vein endothelial cells was specifically blocked by an anti-RAGE antibody. The inhibition of NAD(P)H oxidase by apocynin and diphenylene iodonium, and of the mitochondrial electron transport system at complex II by thenoyltrifluoroacetone (TTFA), significantly inhibited both AGE-induced ROS production and VCAM-1 expression, whereas these effects were potentiated by rotenone and antimycin A, specific inhibitors of mitochondrial complex I and III, respectively. The inhibition of Cu/Zn superoxide dismutase inhibited both ROS and VCAM-1 induction, indicating that H2O2 by this source is involved as a mediator of VCAM-1 expression by AGEs.

CONCLUSIONS

Altogether, these results demonstrate that ROS generated by both NAD(P)H-oxidase and the mitochondrial electron transport system are involved in AGE signaling through RAGE, and indicate potential targets for the inhibition of the atherogenic signals triggered by AGE-RAGE interaction.

Oxidative stress in malaria parasite-infected erythrocytes: host–parasite interactions

Experimenta naturae, like the glucose-6-phosphate dehydrogenase deficiency, indicate that malaria parasites are highly susceptible to alterations in the redox equilibrium. This offers a great potential for the development of urgently required novel chemotherapeutic strategies. However, the relationship between the redox status of malarial parasites and that of their host is complex. In this review article we summarise the presently available knowledge on sources and detoxification pathways of reactive oxygen species in malaria parasite-infected red cells, on clinical aspects of redox metabolism and redox-related mechanisms of drug action as well as future prospects for drug development. As delineated below, alterations in redox status contribute to disease manifestation including sequestration, cerebral pathology, anaemia, respiratory distress, and placental malaria. Studying haemoglobinopathies, like thalassemias and sickle cell disease, and other red cell defects that provide protection against malaria allows insights into this fine balance of redox interactions. The host immune response to malaria involves phagocytosis as well as the production of nitric oxide and oxygen radicals that form part of the host defence system and also contribute to the pathology of the disease. Haemoglobin degradation by the malarial parasite produces the redox active by-products, free haem and H(2)O(2), conferring oxidative insult on the host cell. However, the parasite also supplies antioxidant moieties to the host and possesses an efficient enzymatic antioxidant defence system including glutathione- and thioredoxin-dependent proteins. Mechanistic and structural work on these enzymes might provide a basis for targeting the parasite. Indeed, a number of currently used drugs, especially the endoperoxide antimalarials, appear to act by increasing oxidant stress, and novel drugs such as peroxidic compounds and anthroquinones are being developed.

Oxidative stress promotes blood cell-endothelial cell interactions in the microcirculation

Oxidative stress occurs when the production of reactive oxygen species (ROS) exceeds the capacity of the cell to detoxify these potentially injurious oxidants using endogenous antioxidant defense systems. Conditions associated with oxidative stress include ischemia/reperfusion, hypercholesterolemia, diabetes, and hypertension. The adhesion of circulating blood cells (leukocytes, platelets) to vascular endothelium is a key element of the pro-inflammatory and prothrombogenic phenotype assumed by the vasculature in these and other disease states that are associated with an oxidative stress. There is a growing body of evidence that links the blood cell endothelial cell interactions in these conditions to the enhanced production of ROS. Potential enzymatic sources of ROS within the microcirculation include xanthine oxidase, NAD(P)H oxidase, and nitric oxide synthase. ROS can promote a pro-inflammatory/prothrombogenic phenotype within the microvasculature by a variety of mechanisms, including the inactivation of nitric oxide, the activation of redox-sensitive transcription factors (e.g., nuclear factor-kappaB) that govern the expression of endothelial cell adhesion molecules (e.g., P-selectin), and the activation of enzymes (e.g., phospholipase A(2)) that produce leukocyte-stimulating inflammatory mediators (e.g., platelet-activating factor). The extensively documented ability of different oxidant-ablating interventions to attenuate blood cell endothelial cell interactions underscores the importance of ROS in mediating the dysfunctional microvascular responses to oxidative stress.

Superoxide dismutase mimetic M40403 improves endothelial function in apolipoprotein(E)-deficient mice

1. Overproduction of superoxide anions in the vascular wall contributes to endothelial dysfunction in vascular disease. A superoxide-generating reduced beta-nicotinamide adenine dinucleotide phosphate (NADPH) oxidase has recently been identified as a major source of oxidative radicals in vascular tissues. We studied the effects of a synthetic manganese-containing superoxide dismutase (SOD) mimetic, M40403, on NADPH oxidase-dependent superoxide generation and on endothelial dysfunction. 2. In rat aortic smooth muscle cells, NADPH (100 micro M) markedly stimulated superoxide production as detected by lucigenin (5 micro M)-enhanced chemiluminescence. M40403 reduced NADPH oxidase-dependent superoxide production in a concentration-dependent manner, with IC(50) being 31.6 micro M. In contrast, native Cu/Zn SOD (up to 300 U ml(-1)) had no effect. Angiotensin II (100 nM) increased the NADPH oxidase activity by 70%, and treatment with M40403 (10 micro M) reduced this increased superoxide to the control level. 3. In aortae from apolipoprotein(E)-deficient mice (apoE(0)) with hyperlipidemia and atherosclerosis, superoxide production is largely derived from NADPH oxidase. The attenuation of endothelial nitric oxide vasodilator function parallels the increase in vascular superoxide production at different stages of the disease. Acute incubation of such aortic rings with M40403 significantly suppressed superoxide production and improved endothelium-dependent vasorelaxation to a level comparable to that in wildtype control mice. 4. In summary, the cell-permeable SOD mimetic M40403 was found to reverse endothelial dysfunction in apoE(0) aorta ex vivo by decreasing NADPH oxidase-dependent superoxide levels. The advantages of synthetic SOD mimetics over the native Cu/Zn SOD enzyme, such as greater cell permeability and stability, confer significant therapeutic potential in vascular disease.

Intercellular adhesion molecule-1 in the heart

Intercellular adhesion molecule-1 (ICAM-1) belongs to the superfamily of immunoglobulin-like adhesion molecules. Up-regulation of ICAM-1 occurs in many different pathophysiological processes. Also, cardiomyocytes can express ICAM-1-for example, in acute myocardial infarction. Moreover, inhibition of ICAM-1 expression in the heart dramatically reduces infarct size. Hence, inhibitors of ICAM-1 may provide a novel therapeutic option for acute myocardial infarction.

Rapid upregulation of endothelial P-selectin expression via reactive oxygen species generation

Endothelial cell ICAM-1 upregulation in response to TNF-alpha is mediated in part by reactive oxygen species (ROS) generated by the endothelial membrane-associated NADPH oxidase and occurs maximally after 4 h as the synthesis of new protein is required. However, thrombin-stimulated P-selectin upregulation is bimodal, the first peak occurring within minutes. We hypothesize that this early peak, which results from the release of preformed P-selectin from within Weibel-Palade bodies, is mediated in part by ROS generated from the endothelial membrane-associated xanthine oxidase. We found that this rapid expression of P-selectin on the surface of endothelial cells was accompanied by qualitatively parallel increases in ROS generation. Both P-selectin expression and ROS generation were inhibited, dose dependently, by the exogenous administration of disparate cell-permeable antioxidants and also by the inhibition of either of the known membrane-associated ROS-generating enzymes NADPH oxidase or xanthine oxidase. This rapid, posttranslational cell signaling response, mediated by ROS generated not only by the classical NADPH oxidase but also by xanthine oxidase, may well represent an important physiological trigger of the microvascular inflammatory response.

Tumor necrosis factor-alpha selectively induces MnSOD expression via mitochondria-to-nucleus signaling, whereas interleukin-1beta utilizes an alternative pathway

Mitochondrial levels of the anti-oxidant enzyme, manganese superoxide dismutase (MnSOD), are dramatically elevated in response to stimulation with tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), and lipopolysaccharide (LPS). However, the precise intracellular signaling pathways responsible for this inducible expression are poorly understood. MnSOD expression in pulmonary epithelial and endothelial cells, treated with inflammatory mediators and various inhibitors, was studied by Northern analysis. The mitochondrial electron transport chain inhibitors, antimycin A and myxothiazol, selectively blocked TNF-alpha-inducible expression of MnSOD but not that of IL-1beta or LPS, indicating different signaling pathways. N-Acetylcysteine could reliably decrease inducible MnSOD expression by TNF-alpha, but not IL-1, linking reactive oxygen species (ROS) to the TNF-alpha signaling pathway. Elevated levels of arachidonic acid have been demonstrated previously to generate mitochondrial ROS. A specific cytoplasmic phospholipase A(2) inhibitor reduced stimulated MnSOD expression by TNF-alpha, but not by IL-1beta, further supporting the role of ROS. Other investigators have shown that MnSOD expression may be regulated by NF-kappaB. Our results with a specific inhibitory kappa-kinase inhibitor indicate that NF-kappaB modulates IL-1beta signaling but not the TNF-alpha pathway. Thus, we have demonstrated that although inducible MnSOD transcription may appear similar at the messenger RNA level, the intracellular signaling pathways are differentially regulated.

NAD(P)H oxidase-derived superoxide mediates hypercholesterolemia-induced leukocyte-endothelial cell adhesion

Experimental animals placed on a high-cholesterol diet for 2 or more weeks exhibit an inflammatory response in postcapillary venules. The aims of this study were to determine (1) whether superoxide mediates the hypercholesterolemia-induced inflammatory response and (2) whether leukocyte and/or vessel wall NAD(P)H oxidase contributes to this response. Intravital videomicroscopy was used to quantify leukocyte-endothelial cell adhesion in cremasteric postcapillary venules of wild-type (WT) mice, CuZn-superoxide dismutase transgenic (SOD TgN) mice, and mice heterozygous (p47(phox)+/-) or homozygous (p47(phox)-/-) for NAD(P)H oxidase placed on either a normal diet or high-cholesterol diet (HCD) for 2 weeks. The number of adherent and emigrated leukocytes in postcapillary venules of WT HCD mice was significantly higher than that detected in venules of their normal-diet counterparts. However, the HCD-induced recruitment of adherent and emigrated leukocytes was not observed in SOD TgN mice. Whereas hypercholesterolemic p47(phox)+/- and WT mice exhibited similar inflammatory responses, p47(phox)-/- mice did not. Bone marrow chimeras were developed to selectively delete p47(phox) from either the vessel wall or circulating leukocytes. Whereas WT marrow transplanted into WT mice produced a normal inflammatory response of venules to HCD, chimeric mice with p47(phox) deficiency in either the vessel wall or leukocytes exhibited an attenuated inflammatory response to HCD that was comparable with that observed in p47(phox)-/- HCD mice. Our findings indicate that enhanced superoxide production is a critical event that initiates the leukocyte-endothelial cell adhesion in postcapillary venules of HCD mice. NAD(P)H oxidase appears to be an important source of this superoxide.

Bilirubin impairs bactericidal activity of neutrophils through an antioxidant mechanism in vitro

BACKGROUND

Liver failure accompanied by hyperbilirubinemia after major hepatic resection is profoundly associated with septic complications. Although the immune dysfunction in cholestasis has been intensively investigated, the contribution of increased serum bilirubin to the impaired resistance to bacterial infection remains to be elucidated. Because bilirubin possesses an antioxidant activity, we hypothesized that bilirubin may scavenge reactive oxygen species (ROS) produced by neutrophils and consequently impair neutrophil bacterial killing. To address this, we evaluated the effects of bilirubin on the bactericidal activity of ROS or of neutrophils in vitro.

MATERIALS AND METHODS

The antioxidant activity of bilirubin was determined using an ROS-sensitive fluorophore, dichlorofluorescin diacetate (DCFH-DA). Bilirubin concentration in the buffer solution was monitored spectorophotometrically after incubation with ROS. The effect of bilirubin on killing of Escherichia coli by ROS or by isolated human neutrophils was determined by counting the viable E. coli after incubation on nutrient agar.

RESULTS

The bilirubin concentration in the buffer solution was decreased by the addition of hydrogen peroxide, especially in the presence of peroxidase or ferrous iron. DCFH-DA oxidation by ROS or activated neutrophils was inhibited by bilirubin in a dose-dependent manner. The bactericidal activity of ROS or of isolated neutrophils was significantly attenuated by bilirubin.

CONCLUSIONS

Bilirubin impairs bactericidal activity of neutrophils through scavenging ROS. Increased levels of serum bilirubin may well be responsible for the impaired bacterial clearance in patients with hyperbilirubinemia.

Reactive oxygen intermediates involved in cellular regulation

Reactive oxygen intermediates (ROIs) in low concentration, as released permanently by nonphagocytic cells, possess important functions in inter- and intracellular signalling. They lead to alterations in the phosphorylation pattern followed by gene activation, including the expression of proto-oncogenes. Redox-sensitive sites in membrane molecules may trigger adhesion and chemotaxis or open ion channels and activate transport processes across the cytoplasma membrane. ROIs shift the ratio of cyclic GMP to cyclic AMP giving signals to proliferation and differentiation processes. Senescence, apoptosis, and cell death can also be modulated by ROIs, depending on concentration and cell type.

Reactive oxygen species in cell signaling

Reactive oxygen species (ROS) are generated as by-products of cellular metabolism, primarily in the mitochondria. When cellular production of ROS overwhelms its antioxidant capacity, damage to cellular macromolecules such as lipids, protein, and DNA may ensue. Such a state of "oxidative stress" is thought to contribute to the pathogenesis of a number of human diseases including those of the lung. Recent studies have also implicated ROS that are generated by specialized plasma membrane oxidases in normal physiological signaling by growth factors and cytokines. In this review, we examine the evidence for ligand-induced generation of ROS, its cellular sources, and the signaling pathways that are activated. Emerging concepts on the mechanisms of signal transduction by ROS that involve alterations in cellular redox state and oxidative modifications of proteins are also discussed.

Modulation of protein kinase activity and gene expression by reactive oxygen species and their role in vascular physiology and pathophysiology

Emerging evidence indicates that reactive oxygen species, especially superoxide and hydrogen peroxide, are important signaling molecules in cardiovascular cells. Their production is regulated by hormone-sensitive enzymes such as the vascular NAD(P)H oxidases, and their metabolism is coordinated by antioxidant enzymes such as superoxide dismutase, catalase, and glutathione peroxidase. Both of these reactive oxygen species serve as second messengers to activate multiple intracellular proteins and enzymes, including the epidermal growth factor receptor, c-Src, p38 mitogen-activated protein kinase, Ras, and Akt/protein kinase B. Activation of these signaling cascades and redox-sensitive transcription factors leads to induction of many genes with important functional roles in the physiology and pathophysiology of vascular cells. Thus, reactive oxygen species participate in vascular smooth muscle cell growth and migration; modulation of endothelial function, including endothelium-dependent relaxation and expression of a proinflammatory phenotype; and modification of the extracellular matrix. All of these events play important roles in vascular diseases such as hypertension and atherosclerosis, suggesting that the sources of reactive oxygen species and the signaling pathways that they modify may represent important therapeutic targets.

NAD(P)H oxidase: role in cardiovascular biology and disease

Reactive oxygen species have emerged as important molecules in cardiovascular function. Recent work has shown that NAD(P)H oxidases are major sources of superoxide in vascular cells and myocytes. The biochemical characterization, activation paradigms, structure, and function of this enzyme are now partly understood. Vascular NAD(P)H oxidases share some, but not all, characteristics of the neutrophil enzyme. In response to growth factors and cytokines, they produce superoxide, which is metabolized to hydrogen peroxide, and both of these reactive oxygen species serve as second messengers to activate multiple intracellular signaling pathways. The vascular NAD(P)H oxidases have been found to be essential in the physiological response of vascular cells, including growth, migration, and modification of the extracellular matrix. They have also been linked to hypertension and to pathological states associated with uncontrolled growth and inflammation, such as atherosclerosis.

Secretion of MCP-1 and IL-6 by cytokine stimulated production of reactive oxygen species in endothelial cells

Endothelial cells are known to produce reactive oxygen species by several mechanisms. Functional consequences of increased production of reactive oxygen species were investigated in vitro after stimulation with several proinflammatory cytokines. Time dependent increases in DCF-fluorescence as a measure of reactive oxygen load were quantified in single cells after incubation with TNF-alpha, IL-1 and IFN-gamma. The increased DCF-fluorescence was inhibited by cell permeant antioxidative substances Tiron and Tempol. NMMA, an inhibitor of nitric oxide synthase reduced endothelial DCF-fluorescence only marginally, indicating a minor participation of nitric oxide production in this detection system. Cytokine induced endothelial DCF-fluorescence increased in the presence of NADH, whereas coincubation with NADPH or xanthine was without effect. Flavoenzyme inhibitor diphenyliodonium abolished stimulated DCF-fluorescence. Cytokine induced release of MCP-1 and IL-6 by endothelial cells was completely inhibited in the presence of Tiron and Tempol, whereas NMMA was less effective. Collectively these data indicate that cytokine stimulated endothelial cells increase their reactive oxygen species production probably via NADH oxidase and this production may critically be involved in the secretion of MCP-1 and IL-6.

Interaction of platelet activating factor, reactive oxygen species generated by xanthine oxidase, and leukocytes in the generation of hepatic injury after shock/resuscitation

OBJECTIVE

To evaluate the putative relation of platelet activating factor (PAF), xanthine oxidase, reactive oxidants, and leukocytes in the pathogenesis of hepatic injury after shock/resuscitation (S/R) in vivo.

BACKGROUND

Reactive oxygen metabolites generated by xanthine oxidase at reperfusion have been found to trigger postischemic injury in many organs, including the liver. However, the precise linear sequence of the mechanism of consequent hepatic injury after S/R remains to be characterized.

METHODS

Unheparinized male rats were bled to a mean blood pressure of 45 +/- 3 mmHg. After 2 hours of shock, they were resuscitated by reinfusion of shed blood (anticoagulated with citrate-phosphate-dextrose) and crystalloid and observed for the next 6 or 24 hours.

RESULTS

S/R caused the oxidation of hepatic glutathione and generated centrolobular leukocyte accumulation at 6 hours, followed by predominantly centrolobular hepatocellular injury at 24 hours. Each of these components was attenuated by PAF inhibition with WEB 2170, xanthine oxidase inhibition with allopurinol, antioxidant treatment with N-acetylcysteine, or severe leukopenia induced by vinblastine. In each case, the degree of leukocyte accumulation at 6 hours correlated with the hepatocellular injury seen at 24 hours. However, xanthine oxidase inhibition with allopurinol failed to attenuate further the small level of residual hepatocellular injury seen in leukopenic rats.

CONCLUSION

These findings suggest that reactive oxidants generated by xanthine oxidase at reperfusion, stimulated by PAF, mediate hepatocellular injury by triggering leukocyte accumulation, primarily within the centrolobular sinusoids.

Immunotargeting of glucose oxidase: intracellular production of H(2)O(2) and endothelial oxidative stress

Extracellular and intracellular reactive oxygen species attack different targets and may, therefore, result in different forms of oxidative stress. To specifically study an oxidative stress induced by a regulated intracellular flux of a defined reactive oxygen species in endothelium, we used immunotargeting of the H(2)O(2)-generating enzyme glucose oxidase (GOX) conjugated with an antibody to platelet-endothelial cell adhesion molecule (PECAM)-1, an endothelial surface antigen. Anti-PECAM-(125)I-GOX conjugates specifically bind to both endothelial and PECAM-transfected cells. Approximately 70% of cell-bound anti-PECAM-(125)I-GOX was internalized. The cell-bound conjugate was enzymatically active and generated H(2)O(2) from glucose. Use of the fluorescent dye dihydrorhodamine 123 revealed that 70% of H(2)O(2) was generated intracellularly, whereas 30% of H(2)O(2) was detected in the cell medium. Catalase added to the cells eliminated H(2)O(2) in the medium but had little effect on the intracellular generation of H(2)O(2) by anti-PECAM-GOX. Both H(2)O(2) added exogenously to the cell medium (extracellular H(2)O(2)) and that generated by anti-PECAM-GOX caused oxidative stress manifested by time- and dose-dependent irreversible plasma membrane damage. Inactivation of cellular catalase by aminotriazole treatment augmented damage caused by either extracellular H(2)O(2) or anti-PECAM-GOX. Catalase added to the medium protected either normal or aminotriazole-treated cells against extracellular H(2)O(2), yet failed to protect cells against injury induced by anti-PECAM-GOX. Therefore, treatment of PECAM-positive cells with anti-PECAM-GOX leads to conjugate internalization, predominantly intracellular H(2)O(2) generation and intracellular oxidative stress. These results indicate that anti-PECAM-GOX 1) provides cell-specific intracellular delivery of an active enzyme and 2) causes intracellular oxidative stress in PECAM-positive cells.

Thrombin-Induced p65 Homodimer Binding to Downstream NF-κB Site of the Promoter Mediates Endothelial ICAM-1 Expression and Neutrophil Adhesion

We investigated the mechanisms by which proinflammatory mediator, thrombin, released during intravascular coagulation and tissue injury, induces ICAM-1 (CD54) expression in endothelial cells. Stimulation of HUVEC with thrombin resulted in dose- and time-dependent increases in ICAM-1 mRNA and cell surface expression and in ICAM-1-dependent endothelial adhesivity toward polymorphonuclear leukocytes. Transient transfection of endothelial cells with ICAM-1 promoter luciferase reporter gene (ICAM-1LUC) constructs indicated that deletion of upstream NF-κB site (−533 bases from translation start site) had no effect on thrombin responsiveness, whereas mutation/deletion of downstream NF-κB site (−223 bases from the translation start site) prevented the activation of ICAM-1 promoter, indicating that the downstream NF-κB site is critical for thrombin inducibility. NF-κB-directed luciferase activity increased ∼3-fold when cells transfected with the plasmid pNF-κBLUC containing five copies of consensus NF-κB site linked to a minimal adenovirus E1B promoter-luciferase gene were exposed to thrombin, indicating that activation of NF-κB was essential for thrombin response. Gel supershift assays demonstrated that thrombin induced binding of NF-κBp65 (Rel A) to downstream NF-κB site of the ICAM-1 promoter. Thrombin receptor activation peptide, a 14-amino-acid peptide representing the new NH2 terminus of proteolytically activated receptor-1, mimicked thrombin’s action in inducing ICAM-1 expression. These data indicate that thrombin activates endothelial ICAM-1 expression and polymorphonuclear leukocyte adhesion by NF-κBp65 binding to the downstream NF-κB site of ICAM-1 promoter after proteolytically activated receptor-1 activation.