Microvessel damage in acute respiratory distress syndrome: the answer may not be NO

Cigarette smoke-induced pulmonary endothelial dysfunction is partially suppressed by sildenafil

Cigarette smoke mediated oxidative stress and endothelial dysfunction are important processes in the pathogenesis of several lung disorders. In this study we evaluated the effect of PDE5 inhibition on pulmonary artery endothelial dysfunction induced by cigarette smoke in vitro. Human pulmonary artery endothelial cells (HPAEC) were incubated in the absence or presence of PDE5 inhibitor sildenafil (10 nM-1 microM), PKG agonist 8-Br-cGMP (1mM), or the antioxidants dyphenyleneiodonium (DPI 1 microM) and N-acetylcysteine (NAC 1mM) for 30 min. Then, cigarette smoke extract (CSE) was added for 24h. CSE (2.5-10%)-induced ROS generation was suppressed by DPI, and partially reversed by sildenafil and 8-Br-cGMP. Decreases in intracellular levels of cGMP and extracellular NO induced by CSE were reversed by sildenafil and DPI. Furthermore, CSE-induced pg91(phox) and PDE5 mRNA overexpression were suppressed by both sildenafil and DPI. CSE (2.5-10%) induced upregulation of IL-6, IL-8 and Ang-2, and decreased Ang-1 expression in parallel to apoptosis which were partially suppressed by sildenafil, 8-Br-cGMP, DPI and NAC. This study demonstrates that PDE5 inhibition attenuates the oxidant burden and the inflammatory and remodeling effects of CSE in human HPAEC which may contribute to the therapeutic value of PDE5 inhibitors for pulmonary disorders coursing with endothelial dysfunction.

Antioxidants combined with NO donor enhance systemic inflammation in acute lung injury in rats

OBJECTIVES

Acute lung injury and acute respiratory distress syndrome (ALI, ARDS) are well-known complications of cardiac and major vascular surgery. ARDS is associated with high mortality and no effective treatment is available. Protective effects of antioxidants or nitric oxide (NO) in experimental studies were not confirmed in clinical trials, but the potential beneficial effects of their combination are poorly known. This study was designed to investigate whether concomitant administration of NO donor and antioxidants has synergic effects on lung protection in ALI.

DESIGN

ALI was induced in rats by intestinal ischemia-reperfusion. Superoxide dismutase and catalase were administered as antioxidants and arginine as NO donor. Lung wet-dry ratio, MPO activity, tissue-air ratio, airspace hemorrhage and serum TNF-alpha were used as parameters of lung injury and systemic inflammation.

RESULTS

Antioxidants and arginine significantly reduced lung damage when administered separately. However, concomitant administration of antioxidants and arginine abolished the protective effects and enhanced systemic inflammation.

CONCLUSIONS

Our data suggests that antioxidants and NO in combination should be avoided in clinical practice.

H2S-donating sildenafil (ACS6) inhibits superoxide formation and gp91phox expression in arterial endothelial cells: role of protein kinases A and G

BACKGROUND AND PURPOSE

Superoxide (O(2)(*-)), derived from nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, is associated with acute respiratory distress syndrome (ARDS). NADPH oxidase activity and expression are blocked by nitric oxide (NO) and sildenafil. As another gas, hydrogen sulphide (H(2)S) is formed by blood vessels, the effect of sodium hydrosulphide (NaHS) and the H(2)S-donating derivative of sildenafil, ACS6, on O(2)(*-) formation and the expression of gp91(phox) (a catalytic subunit of NADPH oxidase) in porcine pulmonary arterial endothelial cells (PAECs) was investigated.

EXPERIMENTAL APPROACH

PAECs were incubated with 10 ng mL(-1) tumour necrosis factor-alpha (TNFalpha) (+/-NaHS or ACS6), both of which released H(2)S, for 2 h or 16 h. O(2)(*-) was measured. Expression of gp91(phox) was measured by western blotting and the role of cyclic AMP (cAMP) and/or cyclic GMP was assessed using protein kinase inhibitors.

KEY RESULTS

After either 2- or 16-h incubations, O(2)(*-) formation by PAECs was inhibited by NaHS or ACS6, with IC(50) values of about 10 nM and less than 1 nM, respectively. Both 100 nM NaHS and 1 nM ACS6 completely inhibited gp91(phox) expression induced by TNFalpha. The effects of NaHS were blocked by the inhibition of protein kinase A (PKA), but not PKG, and not by the inhibition of guanylyl cyclase. Effects of ACS6 were blocked by inhibition of both PKA and PKG. Both NaHS and ACS6 augmented cAMP formation.

CONCLUSION AND IMPLICATIONS

H(2)S inhibited O(2)(*-) formation and upregulation of NADPH oxidase in PAECs through the adenylyl cyclase-PKA pathway. ACS6 may be effective in treating ARDS through both elevation of cAMP and inhibition of phosphodiesterase type 5 activity.

Superoxide auto-augments superoxide formation and upregulates gp91phox expression in porcine pulmonary artery endothelial cells: Inhibition by iloprost

Central to the aetiology of Acute Respiratory Distress Syndrome (ARDS) is superoxide, the principal source of which is nicotinamide adenine dinucleotide phosphate oxidase (NADPH oxidase). To test whether superoxide may influence NADPH oxidase expression directly, the effect of incubation of superoxide with porcine pulmonary arterial endothelial cells on the expression of gp91(phox) (a catalytic subunit of NADPH oxidase) and superoxide formation was investigated. Since iloprost has been purported to be potentially effective in treating ARDS, the effect of iloprost on superoxide-mediated effects was also studied. Pulmonary artery endothelial cells were incubated with xanthine/xanthine oxidase which generates superoxide, or tumour necrosis factor alpha (TNFalpha) or thromboxane A(2) analogue, U46619 (+/- superoxide dismutase [SOD] or catalase or iloprost) for 16 h. Cells were then washed and superoxide formation assessed spectrophometrically and gp91(phox) expression using Western blotting. The role of NADPH oxidase was also studied in the above settings using apocynin, an NADPH oxidase inhibitor. Superoxide, TNFalpha and U46619 elicited an increase in the formation of superoxide and induced gp91(phox) expression in pulmonary artery endothelial cells following a 16 h incubation an effect blocked by the continual presence of SOD and apocynin but not catalase. Apocynin completely inhibited superoxide formation induced with xanthine/xanthine oxidase after the 16 h incubation. Rotenone and allopurinol were without effect. Iloprost inhibited the formation of superoxide and gp91(phox) expression. These data demonstrate that superoxide upregulates gp91(phox) expression in pulmonary artery endothelial cells and thus augments superoxide formation, an effect blocked by iloprost. This constitutes a novel mechanism by which vascular superoxide creates a self-perpetuating cascade that may be of importance to the etiology of ARDS and other vasculopathies.

Penicillamine administration reverses the inhibitory effect of hyperhomocysteinaemia on endothelium-dependent relaxation and superoxide formation in the aorta of the rabbit

Although hyperhomocysteinaemia is a risk factor for cardiovascular disease, the mechanisms underlying this association have not been elucidated. It has been demonstrated, however, that copper augments the inhibitory effect of homocysteine on nitric oxide (NO)-mediated relaxation of the rat aorta through increased superoxide formation, which reacts with NO thereby reducing the bioavailability of NO. Since it follows that the administration of a copper chelator may blunt the pathogenic impact of hyperhomocysteinaemia, in vivo, the effect of penicillamine administration on NO-dependent relaxation and superoxide formation in the aortae of hyperhomocysteinaemic rabbits was studied. New Zealand White rabbits were fed a methionine-rich (20 g/kg chow) diet for 1 month+/-penicillamine administered orally (10 mg/kg/day) and aortic relaxation elicited with acetylcholine and superoxide measured. The role of NADPH oxidase was also studied using a range of inhibitors and western analysis of gp47(phox) (a catalytic subunit of NADPH oxidase). The methionine-rich diet markedly increased plasma total homocysteine levels. In hyperhomocysteinaemic rabbits there was a marked reduction of acetylcholine-stimulated relaxation and an increase in superoxide formation that were both inhibited with superoxide dismutase and apocynin, an NADPH oxidase inhibitor. Gp47(phox) expression was also increased in aortae from methionine fed rabbits. Penicillamine administration significantly reduced plasma total copper in methionine-fed rabbits compared to controls. Impaired acetylcholine-stimulated relaxation, increased superoxide formation and increased gp47(phox) expression in aortae from methionine-fed rabbits was reversed by penicillamine administration. These data indicate that hyperhomocysteinaemia augments the formation of arterial superoxide through an increase in NADPH oxidase expression/activity which in turn reduces NO bioavailability. Since these effects were reversed by penicillamine, these data consolidate the hypothesis that copper plays a role in mediating homocysteine-induced vasculopathy.

Sildenafil citrate and sildenafil nitrate (NCX 911) are potent inhibitors of superoxide formation and gp91phox expression in porcine pulmonary artery endothelial cells

Acute respiratory distress syndrome (ARDS) is associated with increased superoxide (O(2)(*-)) formation in the pulmonary vasculature and negation of the bioavailability of nitric oxide (NO). Since NO inhibits NADPH oxidase expression through a cyclic GMP-mediated mechanism, sildenafil, a type V phosphodiesterase inhibitor, may be therapeutically effective in ARDS through an augmentation of NO-mediated inhibition of NADPH oxidase. Therefore, the effect of sildenafil citrate and NO-donating sildenafil (NCX 911) on O(2)(*-) formation and gp91(phox) (active catalytic subunit of NADPH oxidase) expression was investigated in cultured porcine pulmonary artery endothelial cells (PAECs). PAECs were incubated with 10 nM TXA(2) analogue, 9,11-dideoxy-9alpha,11alpha-methanoepoxy-prostaglandin F(2alpha) (U46619) (+/-sildenafil or NCX 911), for 16 h and O(2)(*-) formation measured spectrophometrically and gp91(phox) using Western blotting. The role of the NO-cGMP axis was studied using morpholinosydnonimine hydrochloride (SIN-1), the diethylamine/NO complex (DETA-NONOate), the guanylyl cyclase inhibitor, 1H-{1,2,4}oxadiazolo{4,3-a}quinoxalin-1-one (ODQ), and the protein kinase G inhibitor, 8-bromoguanosine-3',5'-cyclic monophosphorothioate, Rp-isomer (Rp-8-Br-cGMPS). NO release was studied using a fluorescence assay and O(2)(*-)-NO interactions by measuring nitrites. After a 16-h incubation with 10 nM U46619, both NCX 911 and sildenafil elicited a concentration-dependent inhibition of O(2)(*-) formation and gp91(phox) expression, NCX 911 being more potent (IC(50); 0.26 nM) than sildenafil citrate (IC(50); 1.85 nM). These inhibitory effects were reversed by 1 microM ODQ and 10 microM Rp-8-Br-cGMPS. NCX 911 stimulated the formation of cGMP in PAECs and generated NO in a cell-free system to a greater degree than sildenafil citrate. The inhibitory effect of sildenafil was augmented by 1 muM SIN-1 and blocked partially by the eNOS inhibitor 10 microM N(5)-(1-iminoethyl)-ornithine (L-NIO). Acutely, sildenafil and NCX 911 also inhibited O(2)(*-) formation, again blocked by 1 microM ODQ. NCX 911 reacted with O(2)(*-) generated by xanthine oxidase, an effect that was inhibited by superoxide dismutase (500 U ml(-1)). Since O(2)(*-) formation plays contributory role in ARDS, both sildenafil citrate and NCX 911 may be indicated for treating ARDS through suppression of NADPH oxidase expression and therefore of O(2)(*-) formation and preservation of NO bioavailability.

The influence of iloprost on acute lung injury induced by hind limb ischemia-reperfusion in rats

The local ischemia-reperfusion (I/R) process gains a systemic nature and affects distal organs. The remote effects of I/R are most frequently observed in the lungs and pulmonary damage may vary from acute lung injury with mild dysfunction to severe respiratory failure or the acute respiratory distress syndrome. In this hind limb I/R induced experimental lung injury model two groups of rats as IR and ILO were determined. Both groups underwent 60 min of ischemia and 120 min of reperfusion. While ILO group received iloprost in saline, IR group received only saline before reperfusion period intravenously. Serum myeloperoxidase (MPO) activity, malondialdehyde (MDA) levels and total antioxidant capacity (TAC) and lung tissue MPO activity, MDA levels and Na+-K+ ATPase activity were measured and light microscopic analyses of lung specimens were performed. The MPO activities in serum and lung homogenates were found to be significantly decreased in ILO group (P < or = 0.01). The MDA levels in lung homogenates were found to be significantly decreased in ILO group (P < or = 0.01), but the decreases were not significant in serum MDA levels (P=0.052). Serum TAC and lung tissue Na+-K+ ATPase activity levels were found to be increased in ILO group compared to IR group (P < or = 0.01). Lung histology showed marked improvement by iloprost compared to the IR group in this study. Iloprost has been found to be effective in attenuating ischemia reperfusion-induced remote organ damage, in this case, lung injury, in rats.

Prednisolone augments superoxide formation in porcine pulmonary artery endothelial cells through differential effects on the expression of nitric oxide synthase and NADPH oxidase

1. Prednisolone, a potent anti-inflammatory drug, has proved ineffective in treating acute respiratory distress syndrome (ARDS). ARDS is associated with superoxide (O(2)(*-)) generation, which negates nitric oxide (NO). NO also downregulates NADPH oxidase and inhibits O(2)(*-) formation. A possible reason for the lack of effect of prednisolone may due to an inhibition of eNOS expression. In order to test this proposal, the effect of prednisolone on O(2)(*-) formation and the expression of gp91(phox) (catalytic subunit of NADPH oxidase) and eNOS in pig pulmonary artery (PA) segments and PA endothelial cells (PAECs) and PA vascular smooth muscle cells (PAVSMCs) was investigated. 2. PA segments and cells were incubated with prednisolone and tumour necrosis factor-alpha (TNF-alpha) for 16 h. O(2)(*-) formation was measured spectrophometrically and gp91(phox) and eNOS expression by Western blotting. The role of the NO-cGMP axis was studied using morpholinosydnonimine hydrochloride, the diethylamine/NO complex (DETA-NONOate), the guanylyl cyclase inhibitor, 1H-{1,2,4}oxadiazolo{4,3-a}quinoxalin-1-one (ODQ) and the stable cGMP analogues, 8-bromo cGMP and 8-(4-chlorophenylthio)-cGMP (8-pCPT-cGMP). NO release was studied using a fluorescence assay and O(2)(*-)-NO interactions with a nitrite/nitrate assay. 3. Prednisolone elicited significant increase in O(2)(*-) formation in intact PA segments and PAECs, but not PAVSMCs, in a concentration-dependent manner. In endothelium-denuded segments, prednisolone slightly enhanced O(2)(*-) release. TNF-alpha further increased prednisolone-enhanced O(2)(*-) formation in intact PA segments and PAECs. NADPH oxidase inhibitor, apocynin, inhibited O(2)(*-) formation. Increased O(2)(*-) release and gp91(phox) expression in PAECs elicited by prednisolone was blocked by SIN-1 (3-morpholinosydnonimine hydrochloride), DETA-NONOate, 8-pCPT-cGMP and 8-bromo cGMP. The effects of SIN-1 on gp91(phox) expression were reversed by ODQ. Finally, eNOS protein expression was significantly reduced by prednisolone. 4. Prednisolone increases O(2)(*-) in porcine PAECs through a downregulation of endogenous eNOS expression. Since the NO-cGMP axis inhibits gp91(phox) expression, the resultant decrease in endogenous NO formation then augments NADPH oxidase activity, which in turn results in increased O(2)(*-) formation. Since O(2)(*-) promotes inflammation, this mechanism may explain why prednisolone is ineffective in treating ARDS. Therapeutically, the coadministration of an NO donor may render prednisolone more effective in treating ARDS.

Acute hypoxia simultaneously induces the expression of gp91phox and endothelial nitric oxide synthase in the porcine pulmonary artery

BACKGROUND

The effect of hypoxia on the formation of superoxide (O2-), the expression of gp91phox and endothelial NO synthase (eNOS) were studied in pig intact pulmonary artery (PA) segments and PA vascular smooth muscle cells (PAVSMCs) and PA endothelial cells (PAECs).

METHODS

Segments and cells were incubated under hypoxic conditions for 2 hours (with or without enzyme inhibitors) and the formation of O2- measured spectrophotometrically. Protein expression was assessed using Western blotting and immunocytochemistry.

RESULTS

Hypoxia promoted the formation of O2- in PA segments, PAVSMCs and PAECs, an effect inhibited by diphenylene iodonium and apocynin (NAD[P]H oxidase inhibitors). Hypoxia induced O2- formation was enhanced by inhibition of eNOS and augmented by endotoxin and cytokines and re-oxygenation. Hypoxia also promoted the expression of gp91phox and eNOS. In intact PA segments hypoxia induced the expression of nitrotyrosine and eNOS in the endothelium.

CONCLUSIONS

The simultaneous upregulation of NAD[P]H oxidase and eNOS in response to hypoxia in the PA results in the simultaneous formation of O2-, NO, and ONOO-. This may represent either a protective mechanism designed to counter the pro-oxidant effect of hypoxia or a novel pathological mechanism underlying the progression of acute respiratory distress syndrome (ARDS).

Nitroaspirins and morpholinosydnonimine but not aspirin inhibit the formation of superoxide and the expression of gp91phox induced by endotoxin and cytokines in pig pulmonary artery vascular smooth muscle cells and endothelial cells

BACKGROUND

Although nonsteroidal antiinflammatory drugs (NSAIDs) are ineffective in treating acute respiratory distress syndrome (ARDS), inhalational NO has proved to be useful. NO-donating NSAIDs may therefore be more effective in treating ARDS than NSAIDs alone. Because oxidant stress is central to the pathophysiology of ARDS, the effect of nitroaspirins (NCX 4016, NCX 4040, and NCX 4050) compared with morpholinosydnonimine (SIN-1; an NO donor) and aspirin (ASA) on superoxide (O2*-) formation and gp91phox (an active catalytic subunit of NADPH oxidase) expression in pig pulmonary artery vascular smooth muscle cells (PAVSMCs) and endothelial cells (PAECs) was investigated.

METHODS AND RESULTS

Cultured PAVSMCs and PAECs were incubated with lipopolysaccharide (LPS), tumor necrosis factor (TNF)-alpha, and interleukin (IL)-1alpha (with or without NO-ASA, SIN-1, or ASA) for 16 hours, and O2*- release was measured by use of the reduction of ferricytochrome c. The expression of gp91(phox) was assessed by use of Western blotting. LPS, TNF-alpha, and IL-1alpha all stimulated the formation of O2*- and expression of gp91(phox) in both PAVSMCs and PAECs, an effect inhibited by NADPH oxidase inhibitors, diphenyleneiodonium, and apocynin. SIN-1, NCX 4016, and NCX 4050 but not ASA alone inhibited the formation of O2*- and expression of gp91(phox).

CONCLUSIONS

LPS and cytokines promote the formation of O2*- in PAVSMCs and PAECs through an augmentation of NADPH oxidase activity, which in turn is prevented by NO. Thus, NO may play a protective role in preventing excess O2*- formation, but its negation by O2*- may augment the progress of ARDS. The inhibitory effect of nitroaspirins suggests that they may be therapeutically useful in treating ARDS through the suppression of NADPH oxidase upregulation and O2*- formation.

Iloprost inhibits superoxide formation and gp91phox expression induced by the thromboxane A2 analogue U46619, 8-isoprostane F2alpha, prostaglandin F2alpha, cytokines and endotoxin in the pig pulmonary artery

Since the roles of thromboxane A2 (TXA2), prostacyclin (PGI2) and 8-isoprostane F2alpha in mediating vascular O2*- formation and its relation to adult respiratory distress syndrome (ARDS) is unknown, the effects of these eicosanoids on the expression of gp91phox (catalytic subunit of NADPH oxidase) and O2*- release from cultured pig pulmonary artery (PA) segments, PA vascular smooth muscle cells (PAVSMCs) and PA endothelial cells (PAECs) were investigated. PA segments, PAVSMCs and PAECs were incubated with the TXA2 analogue, U46619, (+/-LPS, tumour necrosing factor-alpha (TNF-alpha) or IL-1alpha), 8-isoprostane F2alpha and+/-iloprost (a stable PGI2 analogue) for 16 h. The formation of superoxide dismutase-inhibitable O2*- was then measured spectrophotometrically and gp91phox expression assessed using Western blotting. In parallel experiments, whole PA segments were treated with LPS, TNF-alpha and IL-alpha after which time TXA2, PGI2, PGF2alpha and 8-isoprostane F2alpha formation was measured using enzyme-linked immunoassays. U46619, PGF2alpha and 8-isoprostane F2alpha promoted the formation of O2*- in PA segments, PAVSMCs and PAECs, an effect inhibited by diphenyleneiodonium and apocynin (both NADPH oxidase inhibitors) and upregulated the expression of gp91phox in PAECs and PAVSMCs. These effects were augmented by LPS, TNF-alpha and IL-1alpha but inhibited by iloprost. Under identical incubation conditions, IL-1alpha, LPS and TNF-alpha all induced an increase in the formation of TXA2, PGF2alpha and 8-isoprostane F2alpha but reduced the concomitant formation of PGI2. These data demonstrate that LPS and cytokines influence the relative balance of TXA2, PGI2, PGF2alpha and 8-isoprostane F2alpha in pig PA, which in turn alter NADPH oxidase expression and O2*- formation. These novel findings have implications in devising effective strategies for treating ARDS.British Journal of Pharmacology (2004) 141, 488-496. doi:10.1038/sj.bjp.0705626

Role of the endothelium and nitric oxide synthases in modulating superoxide formation induced by endotoxin and cytokines in porcine pulmonary arteries

BACKGROUND

The interactive roles of cytokines, endotoxins, superoxide (O(2)(*-) ) and nitric oxide (NO) in the pathogenesis of adult respiratory distress syndrome (ARDS) have not been fully elucidated. The effects of tumour necrosis factor-alpha (TNF-alpha), interleukin 1alpha (IL-1alpha), and lipopolysaccharide (LPS) and the role of NO and the endothelium in mediating O(2)(*-) formation were therefore investigated in intact porcine pulmonary arteries in vitro.

METHODS

Intrapulmonary artery (PA) segments were obtained from White Landrace pigs (25-35 kg) and incubated with LPS, IL-1alpha, and TNF-alpha and O(2)(*-) release was measured by the superoxide dismutase (SOD) inhibitable reduction of ferricytochrome c. The source of O(2)(*-) formation was determined using a number of enzyme inhibitors. The role of NO was explored using NO synthase (NOS) inhibitors and the distribution of NOS isoforms and peroxynitrite (ONOO(-), an index of NO-O(2)(*-) interactions) assessed by immunocytochemistry.

RESULTS

LPS, IL-1alpha, and TNF-alpha promoted the formation of O(2)(*-) from PA compared with untreated controls in a time and dose dependent manner, an effect markedly enhanced by removal of the endothelium but completely inhibited by the NADPH oxidase inhibitor diphenylene iodonium chloride (DPI). L-NAME and the eNOS inhibitor N(5)-(1-iminoethyl)-ornithine (L-NIO) enhanced O(2)(*-) formation from PA (with endothelium) in response to IL-1alpha and TNF-alpha but had no effect on LPS mediated O(2)(*-) formation, whereas L-NAME and the iNOS inhibitor L-N(6)-(1-iminoethyl)-lysine-HCl (L-NIL) enhanced O(2)(*-) formation only in response to LPS.

CONCLUSIONS

LPS, IL-1alpha, and TNF-alpha promote O(2)(*-) formation through an upregulation of NADPH oxidase activity which is augmented by removal of the endothelium, as well as the inhibition of eNOS (in the case of cytokines) and iNOS (in the case of LPS). The concomitant expression of NOS isoforms (and NO formation) with that of NADPH oxidase may therefore constitute a protective system designed to remove O(2)(*-) through the formation of ONOO(-). If this is so, the integrity of the endothelium may be axiomatic in the progression and severity of ARDS.

Oxidative stress, nitric oxide, and vascular disease

Superoxide (O2-) is a key risk factor for cardiovascular disease (CVD), including atherogenesis, reperfusion injury, angina, restenosis following balloon angioplasty, and vein graft failure. Axiomatically, O2- reacts with nitric oxide (NO) to form peroxynitrite (ONOO) resulting in a depletion of endogenous vascular NO, which is now firmly associated with CVD. Furthermore, risk factors for CVD, in particular diabetes mellitus (DM), dyslipidemia, and hyperhomocysteinemia are all associated with oxidative stress OS. Antioxidant therapies, including the gene transfer of antioxidant enzymes, are potentially valuable in the treatment of CVD.