Outcomes of hospitalisation for right heart failure in pulmonary arterial hypertension.

The aim of this study was to examine the causes and outcomes of hospitalisation in patients with pulmonary arterial hypertension (PAH). 205 consecutive hospitalisations occurring between 2000 and 2009 in 90 PAH patients were studied. The leading causes for hospitalisation were right heart failure (RHF; 56%), infection (16%) and bleeding disorders (8%). For patients with RHF, in-hospital mortality was 14% overall, 46% for patients receiving inotropes and 48% for those admitted to the intensive care unit. The predictors for in-hospital mortality were the presence of connective tissue disease (CTD) (OR 4.92), systolic blood pressure <100 mmHg (OR 4.32) and Na ≤ 136 mEq · L(-1) (OR 4.29). Mortality after discharge was 13, 26 and 35% at 3, 6 and 12 months, respectively. World Health Organization functional class prior to admission, renal dysfunction, Charlson comorbidity index, and the presence of CTD were all predictors of mortality after discharge. Hyponatraemia and low systolic blood pressure upon admission and underlying CTD are the main prognostic factors for in-hospital mortality in patients with PAH admitted for RHF. The short-term outcomes after discharge are poor and remarkably worse in patients with underlying CTD or renal impairment. Early recognition of these factors may guide decisions regarding more aggressive therapy, including consideration for lung transplantation.

Disproportionate elevation of N-terminal pro-brain natriuretic peptide in scleroderma-related pulmonary hypertension.

N-terminal pro-brain natriuretic peptide (NT-proBNP) is a marker of neurohormonal activation that is useful in the diagnosis and prognosis of various forms of pulmonary arterial hypertension (PAH). We sought to characterise and compare NT-proBNP in a cohort of PAH related to systemic sclerosis (PAH-SSc) and idiopathic PAH (IPAH) patients. NT-proBNP levels, collected from PAH-SSc and IPAH patients followed prospectively, were compared and correlated with haemodynamic variables. Cox proportional hazard models were created to assess the predictive value of NT-proBNP. 98 patients (55 PAH-SSc, 43 IPAH) were included. Haemodynamics were similar, except for lower mean pulmonary arterial pressure in PAH-SSc. NT-proBNP levels were significantly higher in PAH-SSc (3,419+/-3,784 versus 1,393+/-1,633 pg x mL(-1); p<0.01) and were more closely related to haemodynamics in PAH-SSc than IPAH. 28 patients died. NT-proBNP predicted survival (hazard ratio (HR) 3.18; p<0.01) in the overall cohort; however, when stratified by group, predicted survival only in PAH-SSc (HR 3.07, p<0.01 versus 2.02, p = 0.29 in IPAH). This is the first description showing NT-proBNP levels are 1) significantly higher in PAH-SSc than IPAH despite less severe haemodynamic perturbations, and 2) stronger predictors of survival in PAH-SSc, suggesting that neurohormonal regulation may differ between PAH-SSc and IPAH. Future studies to define pertinent mechanisms are warranted.

Estimating pulmonary artery pressures by echocardiography in patients with emphysema.

In patients with emphysema being evaluated for lung volume reduction surgery, Doppler echocardiography has been used to screen for pulmonary hypertension as an indicator of increased peri-operative risk. To determine the accuracy of this test, the present authors compared the results of right heart catheterisations and Doppler echocardiograms in 163 patients participating in the cardiovascular substudy of the National Emphysema Treatment Trial. Substudy patients had both catheterisation and Doppler echocardiography performed before and after randomisation. In 74 paired catheterisations and echocardiograms carried out on 63 patients, the mean values of invasively measured pulmonary artery systolic pressures and the estimated right ventricular systolic pressures were similar. However, using the World Health Organization's definitions of pulmonary hypertension, echocardiography had a sensitivity of 60%, specificity of 74%, positive predictive value of 68% and a negative predictive value of 67% compared with the invasive measurement. Bland-Altman analysis revealed a bias of 0.37 kPa with 95% limits of agreement from -2.5-3.2 kPa. In patients with severe emphysema, echocardiographic estimates of pulmonary artery pressures correlate very weakly with right heart catheterisations, and the test characteristics (e.g. sensitivity, specificity, etc.) of echocardiographic assessments are poor.

Addition of sildenafil to bosentan monotherapy in pulmonary arterial hypertension.

Combination therapy has been recommended for the treatment of pulmonary arterial hypertension (PAH). However, there is scant information on combination therapy after failure of monotherapy, particularly in patients with scleroderma-associated PAH (PAH-SSD). From a group of 82 consecutive patients with PAH who received initial bosentan monotherapy, a total of 13 idiopathic PAH (IPAH) and 12 PAH-SSD patients requiring additional therapy with sildenafil were studied. Sildenafil was added for clinical deterioration based upon symptoms, New York Heart Association (NYHA) classification or 6-min walk distance (6MWD). Clinical data and haemodynamics were collected at baseline. Assessments were made at 1-3-month intervals. At baseline, there were no differences in demographics, NYHA classification, haemodynamics or 6MWD between the two groups. After initiation of bosentan, both groups experienced clinical improvement but ultimately deteriorated (median time to monotherapy failure 792 versus 458 days for IPAH and PAH-SSD patients, respectively). After addition of sildenafil, more IPAH patients tended to improve in NYHA class (five out of 13 versus two out of 12) and walked further (mean difference in 6MWD 47+/-77 m versus -7+/-40 m) compared with PAH-SSD patients. In conclusion, addition of sildenafil after bosentan monotherapy failure improved New York Heart Association class and 6-min walk distance in idiopathic pulmonary arterial hypertension patients but failed to improve either parameter in scleroderma-associated pulmonary arterial hypertension patients. Additional studies are needed to assess the tolerability and efficacy of this combination in patients with scleroderma-associated pulmonary arterial hypertension.

Acute respiratory distress syndrome complicating Plasmodium vivax malaria.

Malaria is one of the most common infectious diseases in the world, and severe respiratory complications have been described mainly in association with Plasmodium falciparum. We describe a case of acute respiratory distress syndrome complicating infection with P. vivax in the setting of relatively low parasitemia in a 47-yr-old woman after a brief trip to Papua New Guinea. A review of the literature shows that pulmonary complications of P. vivax are rare but occur more frequently than generally acknowledged. Pathogenic mechanisms of these complications are discussed.

Management of venous thromboembolic disease in the chronically critically ill patient.

Although PE is the most common preventable cause of death among U.S. hospital patients, proper treatment of thromboembolism and adequate prophylaxis in high-risk patients have been shown to be effective in saving lives. Because clinical symptoms and signs of thromboembolic disease are often nonspecific, early diagnosis and treatment rely on the capacity of physicians to adequately identify a patient at risk, choose the appropriate diagnostic modalities in a cost-effective fashion, and promptly initiate treatment. The diagnosis of VTE is particularly challenging in patients who are in the post acute period of a complex medical or surgical illness. Avenues that need to be further explored include various diagnostic tests such as spiral CT, MR imaging, and transesophageal echocardiography, which are less invasive than the present gold standard of pulmonary angiography. Also needed are better clinical data regarding the optimal choice of preventive therapy (e.g., unfragmented heparin or LMWH or mechanical devices) and clinical outcome of such therapy in patients with prolonged illness.

Phosphorylation of xanthine dehydrogenase/oxidase in hypoxia.

The enzyme xanthine oxidase (XO) has been implicated in the pathogenesis of several disease processes, such as ischemia-reperfusion injury, because of its ability to generate reactive oxygen species. The expression of XO and its precursor xanthine dehydrogenase (XDH) is regulated at pre- and posttranslational levels by agents such as lipopolysaccharide and hypoxia. Posttranslational modification of the protein, for example through thiol oxidation or proteolysis, has been shown to be important in converting XDH to XO. The possibility of posttranslational modification of XDH/XO through phosphorylation has not been adequately investigated in mammalian cells, and studies have reported conflicting results. The present report demonstrates that XDH/XO is phosphorylated in rat pulmonary microvascular endothelial cells (RPMEC) and that phosphorylation is greatly increased ( approximately 50-fold) in response to acute hypoxia (4 h). XDH/XO phosphorylation appears to be mediated, at least in part, by casein kinase II and p38 kinase as inhibitors of these kinases partially prevent XDH/XO phosphorylation. In addition, the results indicate that p38 kinase, a stress-activated kinase, becomes activated in response to hypoxia (an approximately 4-fold increase after 1 h of exposure of RPMEC to hypoxia) further supporting a role for this kinase in hypoxia-stimulated XDH/XO phosphorylation. Finally, hypoxia-induced XDH/XO phosphorylation is accompanied by a 2-fold increase in XDH/XO activity, which is prevented by inhibitors of phosphorylation. In summary, this study shows that XDH/XO is phosphorylated in hypoxic RPMEC through a mechanism involving p38 kinase and casein kinase II and that phosphorylation is necessary for hypoxia-induced enzymatic activation.

Lung redox homeostasis: emerging concepts.

This symposium was organized to present some aspects of current research pertaining to lung redox function. Focuses of the symposium were on roles of pulmonary endothelial NADPH oxidase, xanthine oxidase (XO)/xanthine dehydrogenase (XDH), heme oxygenase (HO), transplasma membrane electron transport (TPMET), and the zinc binding protein metallothionein (MT) in the propagation and/or protection of the lung or other organs from oxidative injury. The presentations were chosen to reflect the roles of both intracellular (metallothionein, XO/XDH, and HO) and plasma membrane (NADPH oxidase, XO/XDH, and unidentified TPMET) redox proteins in these processes. Although the lung endothelium was the predominant cell type under consideration, at least some of the proposed mechanisms operate in or affect other cell types and organs as well.

Bilateral diaphragm paralysis secondary to central von Recklinghausen's disease.

Bilateral paralysis of the diaphragm is either idiopathic or associated with several medical conditions, including trauma or thoracic surgery, viral infections, and neurologic congenital or degenerative disorders. We describe the case of a 36-year-old man with a history of neurofibromatosis who developed severe bilateral diaphragmatic paralysis from involvement of the phrenic nerve roots with neurofibromas. The patient manifested progressive exertional dyspnea and debilitating orthopnea requiring the use of noninvasive mechanical ventilation at night. A review of the literature reveals that neurofibromatosis is an unrecognized cause of diaphragmatic paralysis.

Upregulation of xanthine oxidase by lipopolysaccharide, interleukin-1, and hypoxia. Role in acute lung injury.

LPS and selected cytokines upregulate xanthine dehydrogenase/xanthine oxidase (XDH/XO) in cellular systems. However, the effect of these factors on in vivo XDH/XO expression, and their contribution to lung injury, are poorly understood. Rats were exposed to normoxia or hypoxia for 24 h after treatment with LPS (1 mg/kg) and IL-1beta (100 microg/kg) or sterile saline. Lungs were then harvested for measurement of XDH/XO enzymatic activity and gene expression, and pulmonary edema was assessed by measurement of the wet/dry lung weight ratio (W/D). Although treatment with LPS + IL-1beta or hypoxia independently produced a 2-fold elevation (p < 0. 05 versus exposure to normoxia and treatment with saline) in lung XDH/XO activity and mRNA, the combination of LPS + IL-1beta and hypoxia caused a 4- and 3.5-fold increase in these values, respectively. XDH/XO protein expression was increased 2-fold by hypoxia alone and 1.3-fold by treatment with LPS + IL-1beta alone or combination treatment. Compared with normoxic lungs, W/D was significantly increased by exposure to hypoxia, LPS + IL-1beta, or combination treatment. This increase was prevented by treatment of the animals with tungsten, which abrogated lung XDH/XO activity. In conclusion, LPS, IL-1beta, and hypoxia significantly upregulate lung XDH/XO expression in vivo. The present data support a role for this enzyme in the pathogenesis of acute lung injury.

Dietary L-arginine prevents fetal growth restriction in rats.

OBJECTIVE: Alterations in maternal plasma arginine concentration accompany normal pregnancy. Nitric oxide is synthesized from L-arginine and influences fetal growth. We hypothesized that L-arginine would influence fetal growth and hypoxia-induced uricemia in a maternal hypoxia-induced fetal growth restriction model. STUDY DESIGN: Fetal growth on day 21 of gestation was assessed in timed pregnant Wistar rats with or without exposure to maternal hypobaric hypoxia. Animals exposed to hypoxia received either no supplement or supplementation of drinking water with 0.2% L-arginine, 2% L-arginine, or 2% glycine. On day 21 of gestation, fetuses were delivered by hysterotomy and fetal and placental weights were obtained. Maternal and fetal plasma were assayed for uric acid as an index of tissue hypoxia. Xanthine oxidase and xanthine dehydrogenase, precursors of uric acid and reactive oxygen species, were assayed in maternal tissue. Results were analyzed by analysis of variance with correction for multiple comparisons. RESULTS: Exposure of rats on normal diets to hypoxia resulted in a 30% reduction in fetal weights. L-Arginine, 2% or 0.2%, prevented the reduction in fetal weight (p < 0.0001). Isocaloric and isonitrogenous supplementation with glycine did not influence hypoxia-induced fetal growth restriction. CONCLUSION: L-Arginine, but not glycine, ameliorates maternal hypoxia-induced fetal growth restriction in the rat.

Intracellular generation of reactive oxygen species in endothelial cells exposed to anoxia-reoxygenation.

Reactive oxygen species (ROS) play an important role in the pathogenesis of ischemia-reperfusion injury. Extracellular H2O2 generation from bovine pulmonary artery endothelial cells (EC) is known to increase in response to anoxia-reoxygenation (A-R). To determine potential sources of intracellular ROS formation in EC in response to A-R, a fluorometric assay based on the oxidation of 2',7'-dichlorofluorescin was used. Intracellular ROS production declined 40% during 6 h of anoxia (P < 0.05). After A-R, the rates of intracellular ROS formation increased to 148 +/- 9% (P < 0.001) that of normoxic EC (100 +/- 3%). In EC exposed to A-R, allopurinol and NG-methyl-L-arginine (L-NMMA), inhibitors of xanthine oxidase (XO) and nitric oxide synthase (NOS), respectively, reduced intracellular ROS formation by 25 +/- 1% (P < 0.001) and 36 +/- 4% (P < 0.01). Furthermore, at low doses (i.e., 20 microM), deferoxamine and diethylenetriaminepentaacetic acid (DTPA) significantly inhibited intracellular ROS formation. However, at 100 microM, only deferoxamine caused further reduction in DCF fluorescence. In summary, EC respond to A-R by generating increased amounts of XO- and NOS-derived intracellular ROS. The inhibition, to a similar extent, caused by allopurinol and L-NMMA, as well as the effect of deferoxamine and DTPA suggest that the ROS detected is peroxynitrite. Based on these findings and previous work, we conclude that EC generate ROS in response to A-R from at least two different sources: a plasma membrane-bound NADPH oxidase-like enzyme that releases H2O2 extracellularly and XO, which generates intracellular O2-, which in turn may react with nitric oxide to form peroxynitrite.

Determination of xanthine dehydrogenase mRNA by a reverse transcription-coupled competitive quantitative polymerase chain reaction assay: regulation in rat endothelial cells by hypoxia and hyperoxia.

The enzyme system xanthine dehydrogenase (XD):xanthine oxidase, which generates the superoxide anion as a by-product of action on endogenous substrates, is believed to play a role in mediating pathophysiological changes through its contribution to total superoxide production. To aid with analysis of factors that regulate XD, we have developed a reverse transcription (RT)-coupled competitive quantitative polymerase chain reaction (PCR) assay which enables XD mRNA to be determined from small amounts of cultured cells where constitutive XD levels are low. A homologous insertion mutant of wild-type XD cDNA was prepared and used as an internal standard to normalize intersample PCR efficiency differences. XD mRNA levels determined by RT-PCR also were normalized to tubulin mRNA to compensate for RT differences and loading effects among samples. We report that XD mRNA levels, determined by RT-PCR, were increased twofold in hypoxic (3% oxygen) rat pulmonary microvascular endothelial cells relative to normoxic controls (20% oxygen). Conversely, XD mRNA was decreased threefold within 24 h under hyperoxic (95% oxygen) conditions. These data support the hypothesis that XD is regulated by oxygen tension in the pulmonary vasculature.

Regulation of intracellular xanthine oxidase by endothelial-derived nitric oxide.

We have previously shown that nitric oxide (NO) donors, such as nitrosoglutathione, inhibit endothelial cell (EC) xanthine dehydrogenase (XD)/xanthine oxidase (XO) activity. The purpose of this study was to assess whether endothelial-derived NO plays any role in the regulation of intracellular XD/XO. We exposed rat pulmonary microvascular EC to L-arginine (precursor of NO) or inhibitors of nitric oxide synthase (NOS), i.e., NG-nitro-L-arginine methyl esther (L-NAME) and NG-nitro-L-arginine, in conditions of normoxia, hypoxia, and hypoxia followed by reoxygenation. Hypoxia alone caused a 1.9- and a 6.6-fold increase in XO and a 5-fold increase in XO + XD activities after 24 and 48 h of exposure, respectively. The combination of hypoxia and L-NAME (300 microM) treatment amounted at 48 h to a 10- and 7.5-fold increase in XO and XO + XD activities, respectively, compared with normoxic untreated cells. L-NAME also prevented the decline in XD/XO activity that occurred in untreated EC after hypoxia-reoxygenation. On the other hand, treatment with L-arginine caused a dose-dependent decrease in XD/XO activity in hypoxic EC compared with cells provided with L-arginine-free medium. In separate experiments, we assessed the role of L-arginine supplementation on the in vivo regulation of lung XD/XO by exposing male adult Sprague-Dawley rats for a period of 5 days to a hypoxic hypobaric atmosphere (0.5 atm). Exposure to hypoxia produced a significant increase in lung tissue XO activity and an increase in the ratio of XO to XD. L-Arginine supplementation in the drinking water prevented the increase in lung XO and the XO-to-XD ratio in hypoxic rats and caused a significant decrease in XO and XD in rats exposed to normoxia. In conclusion, this study suggests that endogenous NO has a significant role in the regulation of XD/XO both in vitro and in vivo. By inhibiting XD/XO activity, NO may have a modulating effect in conditions of hypoxia and hypoxia-reoxygenation, where this enzyme is thought to be important.

Quantification of polymerase chain reaction products: enzyme immunoassay based systems for digoxigenin- and biotin-labelled products that quantify either total or specific amplicons.

Enzyme immunoassays were developed for quantification of polymerase chain reaction (PCR) products, referred to as amplicons. Amplicons were dual labelled simultaneously by enzymatic incorporation of digoxigenin and biotin during PCR. For total amplicon quantification, Microfluor B polystyrene wells, compatible with chemiluminescent detection, were coated with streptavidin. Dual labelled amplicons were bound, treated with anti-digoxigenin antibody conjugated to alkaline phosphatase to complete the two-site sandwich immunoassay configuration, and detected by the chemiluminescence generated upon hydrolysis of a phosphate substituted dioxetane substrate, AMPPD. For specific amplicon quantification, the Microfluor B wells were coated with an unlabelled DNA probe complementary to the labelled amplicon target. Subsequent steps were performed as described above. This assay detects 2 pg of specifically amplified DNA. Chemiluminescent detection provides a linear range of four orders of magnitude for amplicon quantification. The non-radioactive labels are safe and stable. PCR as described here obviates the need for labelled primers and constitutes the initial report of concurrent dual non-radioactive labelling of DNA by a DNA polymerase.

Regulation of bovine endothelial constitutive nitric oxide synthase by oxygen.

Oxygen (O2) may regulate pulmonary vascular resistance through changes in endothelial nitric oxide (NO) production. To determine whether constitutive NO synthase (cNOS) is regulated by O2, we assessed cNOS expression and activity in bovine pulmonary artery endothelial cells exposed to different concentrations of O2. In a time-dependent manner, changes in O2 concentration from 95 to 3% produced a progressive decrease in cNOS mRNA and protein levels resulting in 4.8- and 4.3-fold reductions after 24h, respectively. This correlated with changes in cNOS activity as determined by nitrite measurements. Compared with 20% O2, cNOS activity was increased 1.5-fold in 95% O2 and decreased 1.9-fold in 3% O2. A decrease in O2 concentration from 94 to 3% shortened cNOS mRNA half-life from 46 to 24 h and caused a 20-fold repression of cNOS gene transcription. Treatment with cycloheximide produced a threefold increase in cNOS mRNA at all O2 concentrations, suggesting that cNOS mRNA expression is negatively regulated under basal condition. We conclude that O2 upregulates cNOS expression through transcriptional and post-transcriptional mechanisms. A decrease in cNOS activity in the presence of low O2 levels, therefore, may contribute to hypoxia-induced vasoconstriction in the pulmonary circulation.