Modulation of inducible nitric oxide synthase by hypoxia in pulmonary artery endothelial cells

Anti-arthritis Effects of Zingiberaceae Extracts on Models of Inflammatory Joint Disease

Due to this becoming an aging society, the number of arthritis cases has been increasing. Unfortunately, some currently available medications can cause adverse effects. Using herbal remedies as a form of alternative medicine is becoming increasingly popular. Zingiber officinale (ZO), Curcuma longa (CL), and Kaempferia parviflora (KP) are herbal plants in the Zingiberaceae family that have potent anti-inflammatory effects. This study investigates the anti-inflammatory and chondroprotective effects of ZO, CL, and KP extracts on in vitro and ex vivo inflammatory models. The combinatorial anti-arthritis effect of each extract is also evaluated in an in vivo model. ZO extract preserves cartilaginous proteoglycans in proinflammatory cytokines-induced porcine cartilage explant in a fashion similar to that of CL and KP extracts and suppresses the expression of major inflammatory mediators in SW982 cells, particularly the COX2 gene. CL extract downregulates some inflammatory mediators and genes-associated cartilage degradation. Only KP extract shows a significant reduction in S-GAGs release in a cartilage explant model compared to the positive control, diacerein. In SW982 cells, it strongly suppresses many inflammatory mediators. The active constituents of each extract selectively downregulate inflammatory genes. The combined extracts show a reduction in inflammatory mediators to a similar degree as the combined active constituents. Reductions in paw swelling, synovial vascularity, inflammatory cell infiltration, and synovial hyperplasia are found in the combined extracts-treated arthritic rats. This study demonstrates that a combination of ZO, CL, and KP extracts has an anti-arthritis effect and could potentially be developed into an anti-arthritis cocktail for arthritis treatment.

Upregulation of iNOS Protects Cyclic Mechanical Stretch-Induced Cell Death in Rat Aorta Smooth Muscle Cells

Aortic dissection and aneurysm are associated with abnormal hemodynamic loads originating from hypertension. Our previous study demonstrated that cyclic mechanical stretch (CMS, mimicked hypertension) caused the death of rat aortic smooth muscle cells (RASMCs) in a mitogen activated-protein kinases (MAPKs)-dependent manner. The current study investigated the effects of inducible nitric oxide synthase (iNOS) on CMS-induced RASMC death. cDNA microarrays for CMS-treated RASMCs showed that iNOS expression levels were increased in response to CMS. Real-time polymerase chain reaction (PCR) analysis demonstrated that this increase was p38 MAPK (p38)-dependent. NO production was also increased. This increase could be inhibited by p38 and iNOS inhibitors. Thus, CMS-induced iNOS synthesized NO. CMS-induced cell death in RASMCs was increased by the iNOS inhibitor but abrogated by the long-acting NO donor DETA-NONOate. Increased iNOS expression was confirmed in the abdominal aortic constriction mouse model. Signal transducers and activators of transcription 1 (STAT1) was activated in stretched RASMCs, and iNOS expression and NO production were inhibited by the STAT1 inhibitor nifuroxazide. Our findings suggest that RASMCs were protected by iNOS from CMS-stimulated cell death through the STAT1 and p38 signal pathways independently.

Cryptotanshinone inhibits TNF-α-induced early atherogenic events in vitro

Endothelial dysfunction has been implicated in the pathogenesis of atherosclerosis. Salvia miltiorrhiza (danshen) is a traditional Chinese medicine that has been effectively used to treat cardiovascular disease. Cryptotanshinone (CTS), a major lipophilic compound isolated from S. miltiorrhiza, has been reported to possess cardioprotective effects. However, the anti-atherogenic effects of CTS, particularly on tumor necrosis factor-α (TNF-α)-induced endothelial cell activation, are still unclear. This study aimed to determine the effect of CTS on TNF-α-induced increased endothelial permeability, monocyte adhesion, soluble intercellular adhesion molecule 1 (sICAM-1), soluble vascular cell adhesion molecule 1 (sVCAM-1), monocyte chemoattractant protein 1 (MCP-1) and impaired nitric oxide production in human umbilical vein endothelial cells (HUVECs), all of which are early events occurring in atherogenesis. We showed that CTS significantly suppressed TNF-α-induced increased endothelial permeability, monocyte adhesion, sICAM-1, sVCAM-1 and MCP-1, and restored nitric oxide production. These observations suggest that CTS possesses anti-inflammatory properties and could be a promising treatment for the prevention of cytokine-induced early atherogenesis.

Hypoxia and reoxygenation induce endothelial nitric oxide synthase uncoupling in endothelial cells through tetrahydrobiopterin depletion and S-glutathionylation

Ischemia-reperfusion injury is accompanied by endothelial hypoxia and reoxygenation that trigger oxidative stress with enhanced superoxide generation and diminished nitric oxide (NO) production leading to endothelial dysfunction. Oxidative depletion of the endothelial NO synthase (eNOS) cofactor tetrahydrobiopterin can trigger eNOS uncoupling, in which the enzyme generates superoxide rather than NO. Recently, it has also been shown that oxidative stress can induce eNOS S-glutathionylation at critical cysteine residues of the reductase site that serves as a redox switch to control eNOS coupling. While superoxide can deplete tetrahydrobiopterin and induce eNOS S-glutathionylation, the extent of and interaction between these processes in the pathogenesis of eNOS dysfunction in endothelial cells following hypoxia and reoxygenation remain unknown. Therefore, studies were performed on endothelial cells subjected to hypoxia and reoxygenation to determine the severity of eNOS uncoupling and the role of cofactor depletion and S-glutathionylation in this process. Hypoxia and reoxygenation of aortic endothelial cells triggered xanthine oxidase-mediated superoxide generation, causing both tetrahydrobiopterin depletion and S-glutathionylation with resultant eNOS uncoupling. Replenishing cells with tetrahydrobiopterin along with increasing intracellular levels of glutathione greatly preserved eNOS activity after hypoxia and reoxygenation, while targeting either mechanism alone only partially ameliorated the decrease in NO. Endothelial oxidative stress, secondary to hypoxia and reoxygenation, uncoupled eNOS with an altered ratio of oxidized to reduced glutathione inducing eNOS S-glutathionylation. These mechanisms triggered by oxidative stress combine to cause eNOS dysfunction with shift of the enzyme from NO to superoxide production. Thus, in endothelial reoxygenation injury, normalization of both tetrahydrobiopterin levels and the glutathione pool are needed for maximal restoration of eNOS function and NO generation.

The key role of nitric oxide in hypoxia: hypoxic vasodilation and energy supply-demand matching

SIGNIFICANCE

A mismatch between energy supply and demand induces tissue hypoxia with the potential to cause cell death and organ failure. Whenever arterial oxygen concentration is reduced, increases in blood flow--hypoxic vasodilation--occur in an attempt to restore oxygen supply. Nitric oxide (NO) is a major signaling and effector molecule mediating the body's response to hypoxia, given its unique characteristics of vasodilation (improving blood flow and oxygen supply) and modulation of energetic metabolism (reducing oxygen consumption and promoting utilization of alternative pathways).

RECENT ADVANCES

This review covers the role of oxygen in metabolism and responses to hypoxia, the hemodynamic and metabolic effects of NO, and mechanisms underlying the involvement of NO in hypoxic vasodilation. Recent insights into NO metabolism will be discussed, including the role for dietary intake of nitrate, endogenous nitrite (NO₂⁻) reductases, and release of NO from storage pools. The processes through which NO levels are elevated during hypoxia are presented, namely, (i) increased synthesis from NO synthases, increased reduction of NO₂⁻ to NO by heme- or pterin-based enzymes and increased release from NO stores, and (ii) reduced deactivation by mitochondrial cytochrome c oxidase.

CRITICAL ISSUES

Several reviews covered modulation of energetic metabolism by NO, while here we highlight the crucial role NO plays in achieving cardiocirculatory homeostasis during acute hypoxia through both vasodilation and metabolic suppression.

FUTURE DIRECTIONS

We identify a key position for NO in the body's adaptation to an acute energy supply-demand mismatch.

Reactive oxygen and nitrogen species in pulmonary hypertension

Pulmonary vascular disease can be defined as either a disease affecting the pulmonary capillaries and pulmonary arterioles, termed pulmonary arterial hypertension, or a disease affecting the left ventricle, called pulmonary venous hypertension. Pulmonary arterial hypertension (PAH) is a disorder of the pulmonary circulation characterized by endothelial dysfunction, as well as intimal and smooth muscle proliferation. Progressive increases in pulmonary vascular resistance and pressure impair the performance of the right ventricle, resulting in declining cardiac output, reduced exercise capacity, right-heart failure, and ultimately death. While the primary and heritable forms of the disease are thought to affect over 5000 patients in the United States, the disease can occur secondary to congenital heart disease, most advanced lung diseases, and many systemic diseases. Multiple studies implicate oxidative stress in the development of PAH. Further, this oxidative stress has been shown to be associated with alterations in reactive oxygen species (ROS), reactive nitrogen species (RNS), and nitric oxide (NO) signaling pathways, whereby bioavailable NO is decreased and ROS and RNS production are increased. Many canonical ROS and NO signaling pathways are simultaneously disrupted in PAH, with increased expression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases and xanthine oxidoreductase, uncoupling of endothelial NO synthase (eNOS), and reduction in mitochondrial number, as well as impaired mitochondrial function. Upstream dysregulation of ROS/NO redox homeostasis impairs vascular tone and contributes to the pathological activation of antiapoptotic and mitogenic pathways, leading to cell proliferation and obliteration of the vasculature. This paper will review the available data regarding the role of oxidative and nitrosative stress and endothelial dysfunction in the pathophysiology of pulmonary hypertension, and provide a description of targeted therapies for this disease.

Inhibiting NF-κB in the developing lung disrupts angiogenesis and alveolarization

Bronchopulmonary dysplasia (BPD), a chronic lung disease of infancy, is characterized by arrested alveolar development. Pulmonary angiogenesis, mediated by the vascular endothelial growth factor (VEGF) pathway, is essential for alveolarization. However, the transcriptional regulators mediating pulmonary angiogenesis remain unknown. We previously demonstrated that NF-κB, a transcription factor traditionally associated with inflammation, plays a unique protective role in the neonatal lung. Therefore, we hypothesized that constitutive NF-κB activity is essential for postnatal lung development. Blocking NF-κB activity in 6-day-old neonatal mice induced the alveolar simplification similar to that observed in BPD and significantly reduced pulmonary capillary density. Studies to determine the mechanism responsible for this effect identified greater constitutive NF-κB in neonatal lung and in primary pulmonary endothelial cells (PEC) compared with adult. Moreover, inhibiting constitutive NF-κB activity in the neonatal PEC with either pharmacological inhibitors or RNA interference blocked PEC survival, decreased proliferation, and impaired in vitro angiogenesis. Finally, by chromatin immunoprecipitation, NF-κB was found to be a direct regulator of the angiogenic mediator, VEGF-receptor-2, in the neonatal pulmonary vasculature. Taken together, our data identify an entirely novel role for NF-κB in promoting physiological angiogenesis and alveolarization in the developing lung. Our data suggest that disruption of NF-κB signaling may contribute to the pathogenesis of BPD and that enhancement of NF-κB may represent a viable therapeutic strategy to promote lung growth and regeneration in pulmonary diseases marked by impaired angiogenesis.

Oxygen-dependent regulation of nitric oxide production by inducible nitric oxide synthase

Inducible nitric oxide synthase (iNOS) catalyzes the reaction that converts the substrates O(2) and l-arginine to the products nitric oxide (NO) and l-citrulline. Macrophages, and many other cell types, upregulate and express iNOS primarily in response to inflammatory stimuli. Physiological and pathophysiological oxygen tension can regulate NO production by iNOS at multiple levels, including transcriptional, translational, posttranslational, enzyme dimerization, cofactor availability, and substrate dependence. Cell culture techniques that emphasize control of cellular PO(2), and measurement of NO or its stable products, have been used by several investigators for in vitro study of the O(2) dependence of NO production at one or more of these levels. In most cell types, prior or concurrent exposure to cytokines or other inflammatory stimuli is required for the upregulation of iNOS mRNA and protein by hypoxia. Important transcription factors that target the iNOS promoter in hypoxia include hypoxia-inducible factor 1 and/or nuclear factor κB. In contrast to the upregulation of iNOS by hypoxia, in most cell types NO production is reduced by hypoxia. Recent work suggests a prominent role for O(2) substrate dependence in the short-term regulation of iNOS-mediated NO production.

Lung eNOS and iNOS are reoxygenation time-dependent upregulated after acute hypoxia

Nitric oxide plays a critical role in many physiological and physiopathological processes in the lung. Changes in the NO/NOS (Nitric Oxide/Nitric Oxide Synthase) system after hypoxia situations remain controversial in this organ, so that the aim of this work is to perform a complete study of this system in the hypoxic lung after different reoxygenation times ranging from 0 h to 5 days posthypoxia. This is a novel follow-up study carried out in Wistar rats submitted for 30 min to acute hypobaric hypoxia. We measured endothelial and inducible NOS (eNOS, iNOS) mRNA and protein expression, location, and in situ NOS activity as well as nitrated protein expression and location. In addition, NO levels were indirectly quantified (NOx) as well as the apoptosis level. Results showed an increase in eNOS mRNA, protein, activity as well as eNOS positive immunostaining at 0 h posthypoxia, coinciding with raised NOx levels. Contrary, iNOS, nitrated protein expression and apoptosis level augmented during the final reoxygenation times. The lung NO/NOS system provokes two responses to the hypoxia/reoxygenation processes: (i) eNOS is responsible of the immediate response, producing NO, which causes vasodilation and bronchodilation, and (ii) iNOS is related to the second late response, which seems to be involved in some of the deleterious consequences that hypoxia induces in the lung.

Direct effect of cigarette smoke on human pulmonary artery tension

The effect of chronic cigarette smoke on pulmonary artery (PA) tension has been studied extensively; nevertheless, the direct effect of cigarette smoke is poorly understood. We investigated the direct effect of cigarette smoke extract (CSE) on PA tension in non-smokers, smokers, and COPD patients in vitro. PA samples from 35 patients who underwent lung resection were examined by measuring isometric tension in response to increasing serotonin concentrations. CSE dose dependently inhibited the response to serotonin in smokers and COPD patients, and to a lesser extent in non-smokers. CSE-induced relaxation was similarly inhibited by the nonspecific nitric oxide synthase (NOS) inhibitor l-NOARG and the specific inducible NOS (iNOS) inhibitor l-NIL, mainly in non-smokers and smokers, and to a lesser extent in COPD patients. Immunostaining of iNOS in PA samples was greater for smokers and COPD patients compared with non-smokers, which explains the lesser effect of CSE on PA tension in non-smokers. Moreover, CSE induced the release of nitrite via iNOS in human PA smooth muscle cells. In conclusion, CSE inhibition of serotonin-induced PA contraction was mediated mainly by iNOS in non-smokers, smokers, and COPD patients, but in different ways, which may be explained by differential iNOS expression in the PA of these patients.

Role of src-suppressed C kinase substrate in rat pulmonary microvascular endothelial hyperpermeability stimulated by inflammatory cytokines

OBJECTIVE

The aim of the study was to investigate the role of src-suppressed C kinase substrate (SSeCKS) in the modulation of rat pulmonary microvascular endothelial cells (RPMVEC) permeability elicited by interleukin (IL)-1β and tumor necrosis factor (TNF)-α.

METHODS

The gene expression of SSeCKS was analyzed by reverse transcription-polymerase chain reaction. Immunoblotting was used to determine the SSeCKS protein expression and the activation of the protein kinase C (PKC) signaling pathway. A RPMVEC monolayer was constructed to determine changes of transendothelial electrical resistance (TER) and FITC-dextran flux (P (d)) across the monolayer. SSeCKS-specific small interfering RNA was transfected into RPMVEC.

RESULTS

IL-1β and TNF-α activated the PKC signaling pathway in RPMVEC, and up-regulated the gene and protein expression of SSeCKS. Depletion of endogenous SSeCKS in RPMVEC significantly attenuated cytokine-induced decrease in TER and increase in P (d), but not to the basal levels. PKC inhibitors also significantly decreased cytokine-induced hyperpermeability and SSeCKS expression.

CONCLUSIONS

SSeCKS is involved in the endothelial hyperpermeability induced by IL-1β and TNF-α in inflammatory process.

Physiological and hypoxic O2 tensions rapidly regulate NO production by stimulated macrophages

Nitric oxide (NO) production by inducible NO synthase (iNOS) is dependent on O(2) availability. The duration and degree of hypoxia that limit NO production are poorly defined in cultured cells. To investigate short-term O(2)-mediated regulation of NO production, we used a novel forced convection cell culture system to rapidly (response time of 1.6 s) and accurately (+/-1 Torr) deliver specific O(2) tensions (from <1 to 157 Torr) directly to a monolayer of LPS- and IFNgamma-stimulated RAW 264.7 cells while simultaneously measuring NO production via an electrochemical probe. Decreased O(2) availability rapidly (<or=30 s) and reversibly decreased NO production with an apparent K(m)O(2) of 22 (SD 6) Torr (31 microM) and a V(max) of 4.9 (SD 0.4) nmol min(-1) 10(-6) cells. To explore potential mechanisms of decreased NO production during hypoxia, we investigated O(2)-dependent changes in iNOS protein concentration, iNOS dimerization, and cellular NO consumption. iNOS protein concentration was not affected (P = 0.895). iNOS dimerization appeared to be biphasic [6 Torr (P = 0.008) and 157 Torr (P = 0.258) >36 Torr], but it did not predict NO production. NO consumption was minimal at high O(2) and NO tensions and negligible at low O(2) and NO tensions. These results are consistent with O(2) substrate limitation as a regulatory mechanism during brief hypoxic exposure. The rapid and reversible effects of physiological and pathophysiological O(2) tensions suggest that O(2) tension has the potential to regulate NO production in vivo.

TGF-beta1 reduces the heterogeneity of astrocytic cyclooxygenase-2 and nitric oxide synthase-2 gene expression in a stimulus-independent manner

Transforming growth factor-beta1 (TGF-beta1) is upregulated by inflammatory mediators in several neurological diseases/disorders where it either participates in the pathology or provides protection. Often, the biological outcome of TGF-beta1 is dependent upon changes in gene expression. Recently, we demonstrated that TGF-beta1 enhances astrocytic nitric oxide production induced by lipopolysaccharide (LPS) plus interferon-gamma (IFNgamma) by increasing the number of astrocytes in a population that express NOS-2. The purpose of this study was twofold: (1) to determine whether this effect occurs more generally by assessing the effect of TGF-beta1 on another pro-inflammatory gene, cyclooxygenase-2 (COX-2); and (2) to assess stimulus specificity. We found that TGF-beta1 augmented LPS plus IFNgamma-induced COX-2 mRNA and protein expression, by nearly tripling the number of astrocytes that express COX-2. The effect was not stimulus-specific as TGF-beta1 enhanced the number of astrocytes that expressed both COX-2 and NOS-2 protein when either IL-1beta or TNFalpha was used in lieu of LPS. Collectively, these results suggest that TGF-beta1 augments overall protein expression levels of select pro-inflammatory genes in astrocytes in a promiscuous manner by reducing the magnitude of noise in the cellular population.

Redox imbalance and ventilator-induced lung injury

Mechanical ventilation (MV) is an indispensable therapy in the care of critically ill patients with acute lung injury and the acute respiratory distress syndrome; however, it is also known to further lung injury in certain conditions of mechanical stress, leading to ventilator-induced lung injury (VILI). The mechanisms by which conventional MV exacerbates lung injury and inflammation are of considerable clinical significance. Redox imbalance has been postulated, among other mechanisms, to enhance/perpetuate susceptibility to VILI. A better understanding of these pathologic mechanisms will help not only in alleviating the side effects of mechanical forces but also in the development of new therapeutic strategies. Here, we review the relevance of oxidative stress in VILI from human studies as well as cellular and mouse models of mechanical stress. Potential therapeutic avenues for the treatment of VILI with exogenous administration of antioxidants also are discussed.

Hemodynamic and molecular response to intermittent hypoxia (IH) versus continuous hypoxia (CH) in normal humans

The hemodynamic response to hypoxia may be influenced by exposure pattern and inducible biological signals, such as nitric oxide synthase (iNOS) expression. The systemic blood pressure (BP) and heart rate (HR) response to intermittent and continuous hypoxia (IH and CH) were examined as was the relationship between these responses and iNOS expression in 10 normal subjects. BP and HR were recorded during exposure to IH or CH (total hypoxic time=60 min/dayx3 days for each exposure profile), whereas arterial oxygen saturation (SpO2) was maintained at 80-90%. Total RNA was isolated from peripheral blood lymphocytes before exposure on Day 1 and 2 hours after the last exposure on Day 3, and it was assayed for iNOS messenger RNA (mRNA) expression using quantitative polymerase chain reaction (PCR). HR, systolic BP (SBP), and diastolic BP (DBP) increased during both experimental conditions (P<0.05), with no difference by exposure pattern or evidence of facilitation over 3 days. No significant change occurred in iNOS mRNA during IH or CH when pre- and post-exposure values were compared. However, iNOS expression at the end of Day 3 was negatively correlated with the average end-exposure DBP (r=-0.79) and mean BP (MBP; r=-0.76) on Days 1-3 of the IH (P<0.05), but not CH exposure. It is concluded that both IH and CH are associated with significant but comparable hemodynamic changes. The negative correlation between BP and iNOS mRNA with IH, but not CH, may suggest differential modulation of the hemodynamic response to the 2 exposure patterns.

Acute hypoxia differentially affects the γ-aminobutyric acid type A receptor α1, α2, β2, and γ2 subunit mRNA levels in the developing chick optic tectum: Stage-dependent sensitivity

This investigation analyzes the effect of an acute hypoxic treatment on the level of four (alpha(1), alpha(2), beta(2), and gamma(2)) subunit mRNAs of the GABA(A) receptor in layer "i" of the developing chick optic tectum. Our results show that 1 hr of normobaric acute hypoxia significantly changes the subunit mRNA levels. Different subunit mRNAs display different sensitivity to hypoxia: alpha(1), beta(2), and gamma(2) mRNAs are highly sensitive, whereas alpha(2) mRNA is almost not affected. The sensitivity of the mRNA levels to hypoxia is stage dependent. The mean percentages of variation produced by the hypoxia in the level of expression of the four subunits were 20% at ED12, 5% at ED16, and only 2% at ED18. These changes in the mean percentages of expression modify the probability of coexpression. In the case of double mRNA combinations, the hypoxia produced a mean variation in the probability of coexpression of 37% at ED12, 8% at ED16, and only 4% at ED18. With regard to the triple subunit mRNAs combinations, the variations were 206% at ED12, 11% at ED16, and only 7% at ED18. The quadruple combination values were 1,500% at ED12, 21% at ED16, and only 11% at ED18. This study demonstrates that the subunit mRNA levels are highly sensitive during the early stages, suggesting that GABA(A) receptor composition might undergo environment-dependent plastic changes providing a high degree of plasticity to the GABA neurotransmitter system development.

Inducible nitric oxide synthase contributes to ventilator-induced lung injury

RATIONALE

Inducible nitric oxide synthase (iNOS) has been implicated in the development of acute lung injury. Recent studies indicate a role for mechanical stress in iNOS and endothelial NOS (eNOS) regulation.

OBJECTIVES

This study investigated changes in lung NOS expression and activity in a mouse model of ventilator-induced lung injury.

METHODS

C57BL/6J (wild-type [WT]) and iNOS-deficient (iNOS(-/-)) mice received spontaneous ventilation (control) or mechanical ventilation (MV; VT of 7 and 20 ml/kg) for 2 hours, after which NOS gene expression and activity were determined and pulmonary capillary leakage assessed by the Evans blue albumin assay.

RESULTS

iNOS mRNA and protein expression was absent in iNOS(-/-) mice, minimal in WT control mice, but significantly upregulated in response to 2 hours of MV. In contrast, eNOS protein was decreased in WT mice, and nonsignificantly increased in iNOS(-/-) mice, as compared with control animals. iNOS and eNOS activities followed similar patterns in WT and iNOS(-/-) mice. MV caused acute lung injury as suggested by cell infiltration and nitrotyrosine accumulation in the lung, and a significant increase in bronchoalveolar lavage cell count in WT mice, findings that were reduced in iNOS(-/-) mice. Finally, Evans blue albumin accumulation in lungs of WT mice was significant (50 vs. 15% increase in iNOS(-/-) mice compared with control animals) in response to MV and was prevented by treatment of the animals with the iNOS inhibitor aminoguanidine.

CONCLUSION

Taken together, our results indicate that iNOS gene expression and activity are significantly upregulated and contribute to lung edema in ventilator-induced lung injury.

Adrenomedullin expression in a rat model of acute lung injury induced by hypoxia and LPS

Adrenomedullin (ADM) is upregulated independently by hypoxia and LPS, two key factors in the pathogenesis of acute lung injury (ALI). This study evaluates the expression of ADM in ALI using experimental models combining both stimuli: an in vivo model of rats treated with LPS and acute normobaric hypoxia (9% O2) and an in vitro model of rat lung cell lines cultured with LPS and exposed to hypoxia (1% O2). ADM expression was analyzed by in situ hybridization, Northern blot, Western blot, and RIA analyses. In the rat lung, combination of hypoxia and LPS treatments overcomes ADM induction occurring after each treatment alone. With in situ techniques, the synergistic effect of both stimuli mainly correlates with ADM expression in inflammatory cells within blood vessels and, to a lesser extent, to cells in the lung parenchyma and bronchiolar epithelial cells. In the in vitro model, hypoxia and hypoxia + LPS treatments caused a similar strong induction of ADM expression and secretion in epithelial and endothelial cell lines. In alveolar macrophages, however, LPS-induced ADM expression and secretion were further increased by the concomitant exposure to hypoxia, thus paralleling the in vivo response. In conclusion, ADM expression is highly induced in a variety of key lung cell types in this rat model of ALI by combination of hypoxia and LPS, suggesting an essential role for this mediator in this syndrome.

Hepatocyte growth factor regulates angiotensin converting enzyme expression

Hepatocyte growth factor (HGF) is a mitogen, morphogen, and motogen that functions in tissue healing and acts as an anti-fibrotic factor. The mechanism for this is not well understood. Recent studies implicate somatic angiotensin-converting enzyme (ACE) in fibrosis. We examined the effects of HGF on ACE expression in bovine pulmonary artery endothelial cells (BPAEC). Short term treatment of BPAEC with HGF transiently increased both ACE mRNA (3 h) and activity (24 h), as determined by ACE protease assays and reverse transcription-PCR. Incubation of BPAEC with HGF for longer periods suppressed ACE mRNA (6 h) and activity (72 h). In contrast, phorbol ester (PMA) treatment produced sustained increase in ACE mRNA and activity. We examined the short term molecular effects of HGF on ACE using PMA for comparison. HGF and PMA increased transcription from a luciferase reporter with the core ACE promoter, which contains a composite binding site for SP1/3 and Egr-1. Immunocytochemistry and electrophoretic mobility shift assay showed that both HGF and PMA increased Egr-1 binding. HGF also increased SP3 binding, as measured by EMSA. However, HGF and PMA increased the cellular activity of only Egr-1, not SP3, as measured by luciferase reporter assays. Deletion of the Egr-1 site in the reporter construct completely abrogated HGF-induced transcription but only approximately 50% of PMA-induced activity. Expression of dominant negative Egr-1 and SP3 blocked up-regulation of the ACE promoter by HGF but only reduced up-regulation by PMA. These results show that HGF transiently increases gene transcription of ACE via activation of Egr-1, whereas PMA regulation involves Egr-1 and additional factor(s).

Nitric oxide-mediated regulation of hypoxia-induced B16F10 melanoma metastasis

Tumour hypoxia is associated with resistance to therapy and with increased invasion and metastatic potential. Recent studies in our laboratory have shown that the hypoxic up-regulation of tumour cell invasiveness and chemoresistance is in part due to reduced nitric oxide (NO) signaling. Using B16F10 murine melanoma cells, we demonstrate here that the increased metastatic potential associated with exposure to hypoxia is mediated by a reduction in cGMP-dependent NO-signaling. Pre-incubation of B16F10 cells in hypoxia (1% vs. 20% O(2)) for 12 hr increased lung colonization ability by over 4-fold. This effect of hypoxia on metastasis was inhibited by co-incubation with low concentrations of the NO-mimetic drugs glyceryl trinitrate (GTN) and diethylenetriamine NO adduct (DETA/NO). In a manner similar to hypoxia, pharmacological inhibition of NO synthesis resulted in a significant increase in lung nodule formation, an effect that was prevented by co-incubation with GTN. An important NO-signaling pathway involves the activation of soluble guanylyl cyclase and the consequential generation of cGMP. Culture in the presence of a non-hydrolysable cGMP analogue (8-Br-cGMP) abrogated the hypoxia-induced lung nodule formation, suggesting that the effects of NO on metastasis are mediated via a cGMP-dependent pathway. These findings suggest that a novel mechanism whereby hypoxia regulates metastatic potential involves a downstream inhibition of cGMP-dependent NO signaling.

Nitric oxide-dependent cytoskeletal changes and inhibition of endothelial cell migration contribute to the suppression of angiogenesis by RAD50 gene transfer

Previous reports showed that human RAD50 (hRAD50) gene delivery induced regression of an experimental rat tumor and porcine neointimal hyperplasia. In this study, we examined the effects of hRAD50 on the morphological changes and migration of endothelial cells (EC) as possible mechanisms by which hRAD50 might block angiogenesis. Quantitative image analysis revealed significant inhibition of the number and total area of blood vessels in rat tumor tissues following hRAD50 gene delivery. hRAD50 distorted actin and tubulin arrangements, and significantly reduced the F/G-actin ratio and increased the nitric oxide (NO) production in the primary cultured human EC. These effects were blocked by pretreatment with L-NAME (N(G)-nitro-L-arginine-methyl ester), a NO synthase inhibitor. FACScan analysis showed that NO was involved in the necrosis and apoptosis of EC by hRAD50. hRAD50 also inhibited EC migration in an in vitro wound-healing model. These results indicate that NO-dependent cytoskeletal changes and inhibition of EC migration contribute to the suppression of angiogenesis by hRAD50 delivery in vivo.

Effects of acute hypoxia and lipopolysaccharide on nitric oxide synthase-2 expression in acute lung injury

The potential role of nitric oxide synthase-2 (NOS2) in acute lung injury (ALI) has gained increasing attention. This study evaluates the effects of hypoxia, an important feature of ALI, on NOS2 expression in a rat model of ALI caused by exposure to hypoxia and LPS. Exposure to hypoxia alone had no effect on the expression of NOS2 in rat lungs. LPS treatment resulted in a significant increase in NOS2 in the lungs, which was further enhanced by concomitant exposure to hypoxia. Immunohistochemical analysis and in situ hybridization showed no changes in the expression of NOS2 in lung resident cells under any conditions. The increase in NOS2 levels is mainly due to the influx of NOS2-expressing inflammatory cells. By morphologic analysis, these inflammatory cells were identified as neutrophils, lymphocytes, and monocytes. In vitro experiments of lung epithelial and endothelial cell lines showed no detectable expression of NOS2 with any of the treatments. In a macrophage cell line, LPS-induced NOS2 expression was not affected by the concomitant exposure to hypoxia. In conclusion, LPS increases NOS2 expression in rat lungs through the recruitment of NOS2-producing leukocytes. Simultaneous exposure to LPS and hypoxia results in a greater influx of inflammatory cells that further enhances NOS2 expression.

Enhanced vasoconstrictor responses in eNOS deficient mice

Previous studies suggest that vasoconstriction is modulated by nitric oxide (NO). Contractions to ET-1 and/or thromboxane may be enhanced during chronic deficiency in expression or activity of NO synthase (NOS). Multiple isoforms of NOS are expressed within the vessel wall and purely pharmacological approaches cannot define the role of each. We tested the hypothesis that vasoconstriction to endothelin-1 (ET-1) and/or the thromboxane mimetic, U46619, is enhanced under conditions of chronic, selective deficiency in endothelial NOS (eNOS-/-) by examining responses in aorta from eNOS-/- mice compared to wild type (eNOS+/+). ET-1 produced dose-dependent contraction of aorta from eNOS+/+ mice that was increased twofold following acute inhibition of all NOS isoforms with N(G)-nitro-L-arginine (L-NNA). In eNOS-/- mice, contractions to ET-1 were increased twofold compared to eNOS+/+. L-NNA had no effect. Although contraction of the aorta to thromboxane mimetic U46619 was increased at lower concentrations, maximal contractions to U46619 were not increased following acute inhibition of NOS or in eNOS-/- mice. These studies provide direct evidence that vasoconstriction to ET-1 and thromboxane is augmented in the face of eNOS deficiency, demonstrating that eNOS normally inhibits vascular contractile responses.

Cytoskeletal changes in hypoxic pulmonary endothelial cells are dependent on MAPK-activated protein kinase MK2

Exposure to hypoxia causes structural changes in the endothelial cell layer that alter its permeability and its interaction with leukocytes and platelets. One of the well characterized cytoskeletal changes in response to stress involves the reorganization of the actin cytoskeleton and the formation of stress fibers. This report describes cytoskeletal changes in pulmonary microvascular endothelial cells in response to hypoxia and potential mechanisms involved in this process. The hypoxia-induced actin redistribution appears to be mediated by components downstream of MAPK p38, which is activated in pulmonary endothelial cells in response to hypoxia. Our results indicate that kinase MK2, which is a substrate of p38, becomes activated by hypoxia, leading to the phosphorylation of one of its substrates, HSP27. Because HSP27 phosphorylation is known to alter actin distribution in response to other stimuli, we postulate that it also causes the actin redistribution observed in hypoxia. This notion is supported by the observations that similar actin redistribution occurs in cells overexpressing constitutively active MK2 or phosphomimicking HSP27 mutant. Overexpressing dominant negative MK2 blocks the effects of hypoxia on the actin cytoskeleton. Taken together these results indicate that hypoxia stimulates the p38-MK2-HSP27 pathway leading to significant alteration in the actin cytoskeleton.