An electrocardiogram-based AI algorithm for early detection of pulmonary hypertension.

BACKGROUND: Early diagnosis of pulmonary hypertension (PH) is critical for effective treatment and management. We aimed to develop and externally validate an artificial intelligence algorithm that could serve as a PH screening tool, based on analysis of a standard 12-lead ECG. METHODS: The PH Early Detection Algorithm (PH-EDA) is a convolutional neural network developed using retrospective ECG voltage-time data, with patients classified as "PH-likely" or "PH-unlikely" (controls) based on right heart catheterisation or echocardiography. In total, 39 823 PH-likely patients and 219 404 control patients from Mayo Clinic were randomly split into training (48%), validation (12%) and test (40%) sets. ECGs taken within 1 month of PH diagnosis (diagnostic dataset) were used to train the PH-EDA at Mayo Clinic. Performance was tested on diagnostic ECGs within the test sets from Mayo Clinic (n=16 175/87 998 PH-likely/controls) and Vanderbilt University Medical Center (VUMC; n=6045/24 256 PH-likely/controls). In addition, performance was tested on ECGs taken 6-18 months (pre-emptive dataset), and up to 5 years prior to a PH diagnosis at both sites. RESULTS: Performance testing yielded an area under the receiver operating characteristic curve (AUC) of 0.92 and 0.88 in the diagnostic test sets at Mayo Clinic and VUMC, respectively, and 0.86 and 0.81, respectively, in the pre-emptive test sets. The AUC remained a minimum of 0.79 at Mayo Clinic and 0.73 at VUMC up to 5 years before diagnosis. CONCLUSION: The PH-EDA can detect PH at diagnosis and 6-18 months prior, demonstrating the potential to accelerate diagnosis and management of this debilitating disease.

Electrocardiogram Detection of Pulmonary Hypertension Using Deep Learning.

BACKGROUND: Pulmonary hypertension (PH) is life-threatening, and often diagnosed late in its course. We aimed to evaluate if a deep learning approach using electrocardiogram (ECG) data alone can detect PH and clinically important subtypes. We asked: does an automated deep learning approach to ECG interpretation detect PH and its clinically important subtypes? METHODS AND RESULTS: Adults with right heart catheterization or an echocardiogram within 90 days of an ECG at the University of California, San Francisco (2012-2019) were retrospectively identified as PH or non-PH. A deep convolutional neural network was trained on patients' 12-lead ECG voltage data. Patients were divided into training, development, and test sets in a ratio of 7:1:2. Overall, 5016 PH and 19,454 patients without PH were used in the study. The mean age at the time of ECG was 62.29 ± 17.58 years and 49.88% were female. The mean interval between ECG and right heart catheterization or echocardiogram was 3.66 and 2.23 days for patients with PH and patients without PH, respectively. In the test dataset, the model achieved an area under the receiver operating characteristic curve, sensitivity, and specificity, respectively of 0.89, 0.79, and 0.84 to detect PH; 0.91, 0.83, and 0.84 to detect precapillary PH; 0.88, 0.81, and 0.81 to detect pulmonary arterial hypertension, and 0.80, 0.73, and 0.76 to detect group 3 PH. We additionally applied the trained model on ECGs from participants in the test dataset that were obtained from up to 2 years before diagnosis of PH; the area under the receiver operating characteristic curve was 0.79 or greater. CONCLUSIONS: A deep learning ECG algorithm can detect PH and PH subtypes around the time of diagnosis and can detect PH using ECGs that were done up to 2 years before right heart catheterization/echocardiogram diagnosis. This approach has the potential to decrease diagnostic delays in PH.

N-Acetylcysteine Inhibits Ventilation-Induced Collagen Accumulation in the Rat Lung.

Mechanical ventilation is the most important life supportive therapy for patients with acute respiratory distress syndrome (ARDS). However, increasing evidence from clinical studies suggests that mechanical ventilation can cause lung fibrosis, which may significantly contribute to morbidity and mortality. Recent studies also found fibroproliferation occurred in early stage of ARDS with poor outcome. We have hypothesized that mechanical ventilation-induced lung injury may be a major contributor to lung fibrosis, and antioxidant could be a potential therapeutic agent for the treatment to mechanic ventilation induced fibroproliferation. We therefore used Sprague-Dawley rats that were ventilated with large tidal volume (20 ml/kg) or low tidal volume (7 ml/kg). We analyzed the time course of collagen level in the lung and the effect of N-acetylcysteine (NAC), a thiol antioxidant, on mechanical ventilation-induced collagen accumulation. In addition, normal human lung fibroblasts (NHLF) were exposed to mechanical stretch, which mimics ventilator-induced lung inflation, to evaluate the collagen secretion in culture medium. We found that ventilation-induced collagen accumulation occurred even after 2-hour ventilation. Pretreatment with NAC (140 mg/kg) inhibited collagen accumulation in lungs of rats ventilated with large tidal volume. Moreover, mechanical stretch caused the accumulation of collagen in the culture medium of NHLF, the magnitude of which was decreased with the pretreatment with NAC (1 mM). These results indicate that mechanical ventilation can induce collagen accumulation within 2 hours. NAC alleviated the collagen accumulation induced by mechanical ventilation with high tidal volume. Therefore, NAC can be considered as a good candidate in preventing ventilation-induced lung fibrosis.

Imatinib mesylate as add-on therapy for pulmonary arterial hypertension: results of the randomized IMPRES study.

BACKGROUND: By its inhibitory effect on platelet-derived growth factor signaling, imatinib could be efficacious in treating patients with pulmonary arterial hypertension (PAH). METHODS AND RESULTS: Imatinib in Pulmonary Arterial Hypertension, a Randomized, Efficacy Study (IMPRES), a randomized, double-blind, placebo-controlled 24-week trial, evaluated imatinib in patients with pulmonary vascular resistance ≥ 800 dyne·s·cm(-5) symptomatic on ≥ 2 PAH therapies. The primary outcome was change in 6-minute walk distance. Secondary outcomes included changes in hemodynamics, functional class, serum levels of N-terminal brain natriuretic peptide, and time to clinical worsening. After completion of the core study, patients could enter an open-label long-term extension study. Of 202 patients enrolled, 41% patients received 3 PAH therapies, with the remainder on 2 therapies. After 24 weeks, the mean placebo-corrected treatment effect on 6-minute walk distance was 32 m (95% confidence interval, 12-52; P=0.002), an effect maintained in the extension study in patients remaining on imatinib. Pulmonary vascular resistance decreased by 379 dyne·s·cm(-5) (95% confidence interval, -502 to - 255; P<0.001, between-group difference). Functional class, time to clinical worsening, and mortality did not differ between treatments. Serious adverse events and discontinuations were more frequent with imatinib than placebo (44% versus 30% and 33% versus 18%, respectively). Subdural hematoma occurred in 8 patients (2 in the core study, 6 in the extension) receiving imatinib and anticoagulation. CONCLUSIONS: Imatinib improved exercise capacity and hemodynamics in patients with advanced PAH, but serious adverse events and study drug discontinuations were common. Further studies are needed to investigate the long-term safety and efficacy of imatinib in patients with PAH. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT00902174 (core study); NCT01392495 (extension).

TLR4 through IFN-ß promotes low molecular mass hyaluronan-induced neutrophil apoptosis.

Intratracheal administration of low molecular mass (LMM) hyaluronan (200 kDa) results in greater neutrophil infiltration in the lungs of TLR4(-/-) mice compared with that in wild-type mice. In general, enhanced neutrophil infiltration in tissue is due to cell influx; however, neutrophil apoptosis also plays an important role. We have assessed the effects of TLR4 in the regulation of neutrophil apoptosis in response to administration of LMM hyaluronan. We found that apoptosis of inflammatory neutrophils is impaired in TLR4(-/-) mice, an effect that depends upon the IFN-ß-mediated TRAIL/TRAILR system. IFN-ß levels were decreased in LMM hyaluronan-treated TLR4-deficient neutrophils. The treatment of inflammatory neutrophils with IFN-ß enhanced the levels of TRAIL and TRAILR 2. LMM hyaluronan-induced inflammatory neutrophil apoptosis was substantially prevented by anti-TRAIL neutralizing mAb. We conclude that decreased IFN-ß levels decrease the activity of the TRAIL/TRAILR system in TLR4-deficient neutrophils, leading to impaired apoptosis of neutrophils and resulting in abnormal accumulation of neutrophils in the lungs of LMM hyaluronan-treated mice. Thus, TLR4 plays a novel homeostatic role in noninfectious lung inflammation by accelerating the elimination of inflammatory neutrophils.

Time to diagnosis of pulmonary hypertension and diagnostic burden: A retrospective analysis of nationwide US healthcare data.

The main aim of this analysis was to investigate time from symptom onset (chronic unexplained dyspnoea [CUD]) to diagnosis of Group 1 pulmonary hypertension (PH)-pulmonary arterial hypertension (PAH)-and to characterize healthcare resource utilization leading up to diagnosis using a nationwide US claims and an electronic health record (EHR) database from Optum©. Eligible patients were ≥18 years old at first CUD diagnosis (index event) and had a PAH diagnosis on or after index date. Based on administrative codes, PAH was defined as right heart catheterization (RHC), ≥ 2 PAH diagnoses (1 within a year of RHC), and ≥1 post-RHC prescription for PAH treatment. All values are median (1st quartile-3rd quartile) unless otherwise stated. Of 854,722 patients with CUD in the claims database, 582 (0.1%) had PAH. Time from CUD to PAH diagnosis was 2.26 (0.73-4.22) years. PAH patients experienced 3 (2-4) transthoracic echocardiograms (TTEs), 6 (3-12) specialist visits, and 2 (1-4) hospitalizations during the diagnostic interval. Almost one-third of patients (29%) waited 10 months or more to have a TTE. Findings from the EHR database were broadly similar. Resource utilization during the diagnostic interval was also analyzed in an overall PH cohort: findings were generally similar to the PAH cohort (2 [1-3] TTEs, 4 [2-9] specialist visits and 2 [1-4] hospitalizations). These data indicate a delay in the diagnostic pathway for PAH, and illustrate the burden associated with PAH diagnosis.

A machine learning approach to identifying patients with pulmonary hypertension using real-world electronic health records.

BACKGROUND: This study aimed to develop a machine learning (ML) model to identify patients who are likely to have pulmonary hypertension (PH), using a large patient-level US-based electronic health record (EHR) database. METHODS: A gradient boosting model, XGBoost, was developed using data from Optum's US-based de-identified EHR dataset (2007-2019). PH and disease control adult patients were identified using diagnostic, treatment and procedure codes and were randomly split into the training (90%) or test set (10%). Model features included patient demographics, physician visits, diagnoses, procedures, prescriptions, and laboratory test results. SHapley Additive exPlanations values were used to determine feature importance. RESULTS: We identified 11,279,478 control and 115,822 PH patients (mean age, respectively: 62 and 68 years, both 53% female). The final model used 165 features, with the most important predictive features including diagnosis of heart failure, shortness of breath and atrial fibrillation. The model predicted PH with an area under the receiver operating characteristic curve (AUROC) of 0.92. AUROC remained above 0.80 for the prediction of PH up to and beyond 18 months before diagnosis. Among the PH patients, we also identified 955 pulmonary arterial hypertension (PAH) and 1432 chronic thromboembolic pulmonary hypertension (CTEPH) patients, and the range of AUROCs obtained for these cohorts was 0.79-0.90 and 0.87-0.96, respectively. CONCLUSIONS: This model to detect PH based on patients' EHR records is viable and performs well in subgroups of PAH and CTEPH patients. This approach has the potential to improve patient outcomes by reducing diagnostic delay in PH.

TLR4 is a negative regulator in noninfectious lung inflammation.

Low m.w. hyaluronan (LMW HA) has been shown to elicit the expression of proinflammatory cytokines and chemokines in various cells in vitro. However, the effects of this molecule in vivo are unknown. In this study, we report that intratracheal administration of LMW HA (200 kDa) causes inflammation in mouse lung. A lack of TLR4 is associated with even stronger inflammatory response in the lung as shown by increased neutrophil counts and elevated cytokine and chemokine concentrations. We also demonstrate that TLR4 anti-inflammatory signaling is dependent upon a MyD88-independent pathway. TLR4-mediated IL-1R antagonist production plays a negative regulatory role in LMW HA (200 kDa) induced lung inflammation. These data provide a molecular level explanation for the function of TLR4 in LMW HA (200 kDa)-induced lung inflammation, as inhibition of the beta form of pro-IL-1 promotes an anti-inflammatory response.

Regulation of lung injury and repair by Toll-like receptors and hyaluronan.

Mechanisms that regulate inflammation and repair after acute lung injury are incompletely understood. The extracellular matrix glycosaminoglycan hyaluronan is produced after tissue injury and impaired clearance results in unremitting inflammation. Here we report that hyaluronan degradation products require MyD88 and both Toll-like receptor (TLR)4 and TLR2 in vitro and in vivo to initiate inflammatory responses in acute lung injury. Hyaluronan fragments isolated from serum of individuals with acute lung injury stimulated macrophage chemokine production in a TLR4- and TLR2-dependent manner. Myd88(-/-) and Tlr4(-/-)Tlr2(-/-) mice showed impaired transepithelial migration of inflammatory cells but decreased survival and enhanced epithelial cell apoptosis after lung injury. Lung epithelial cell-specific overexpression of high-molecular-mass hyaluronan was protective against acute lung injury. Furthermore, epithelial cell-surface hyaluronan was protective against apoptosis, in part, through TLR-dependent basal activation of NF-kappaB. Hyaluronan-TLR2 and hyaluronan-TLR4 interactions provide signals that initiate inflammatory responses, maintain epithelial cell integrity and promote recovery from acute lung injury.

The effects of an anti-IL-13 mAb on cytokine levels and nasal symptoms following nasal allergen challenge.

BACKGROUND: IL-13 is a key T(H)2 cytokine that is implicated in allergic responses. OBJECTIVE: We evaluated the effects of an anti-IL-13-blocking antibody compared with placebo on repeated nasal allergen challenge responses in hay fever patients out of season. METHODS: We performed a parallel group double-blind study of anti-IL-13 (single dose, 6 mg/kg intravenously, n = 16) and placebo (n = 15), with an additional open label group given a topical nasal corticosteroid (n = 5). Subjects received intranasal timothy grass pollen (Phleum pratense P5 allergen), and serial samples of nasal mucosal lining fluid were taken by using synthetic absorptive matrix and by nasal lavage. RESULTS: Administration of anti-IL-13 on day 1 resulted in a significant decrease in IL-13 levels in synthetic absorptive matrix eluates compared with placebo (area under the curve 0-8 hours, change from baseline) during the late phase after nasal allergen challenge on day 5 (P < .05) and day 7 (P < .01). There were no apparent effects of anti-IL-13 treatment on nasal lavage eosinophil numbers or total nasal symptom scores versus placebo. However, in a subgroup with high late-phase IL-13 levels at screening, there was a trend for a decrease in total nasal symptom scores after nasal allergen challenge on day 5, when compared with subjects with low IL-13 levels (P < .10). Nasal fluticasone caused suppression of IL-13 (P < .05 on day 5) as well as IL-5 (P < .01 on day 5) levels in the late phase compared with placebo. CONCLUSIONS: Anti-IL-13 had specific pharmacodynamic action in this nasal allergen challenge model, causing profound inhibition of nasal lining fluid IL-13 responses. In addition, there was a possible effect of anti-IL-13 treatment on total nasal symptom scores in a subgroup with high late-phase nasal IL-13 levels at screening.

Heparin inhibits pulmonary artery smooth muscle cell proliferation through guanine nucleotide exchange factor-H1/RhoA/Rho kinase/p27.

Ras homolog gene family member A (RhoA) through Rho kinase kinase (ROCK), one of its downstream effectors, regulates a wide range of cell physiological functions, including vascular smooth muscle cell (SMC) proliferation, by degrading cyclin-dependent kinase inhibitor, p27. Our previous studies found that heparin inhibition of pulmonary artery SMC (PASMC) proliferation and pulmonary hypertension was dependent on p27 up-regulation. To investigate whether ROCK, a regulator of p27, is involved in regulation of heparin inhibition of PASMC proliferation, we analyzed ROCK expression in the lungs from mice and from human PASMCs exposed to hypoxia, and investigated the effect of ROCK expression in vitro by RhoA cDNA transfection. We also investigated the effect of guanine nucleotide exchange factor (GEF)-H1, an upstream regulator of RhoA, on heparin inhibition of PASMC proliferation by GEF-H1 cDNA transfection. We found that: (1) hypoxia increased ROCK expression in mice and PASMCs; (2) overexpression of RhoA diminished the inhibitory effect of heparin on PASMC proliferation and down-regulated p27 expression; and (3) overexpression of GEF-H1 negated heparin inhibition of PASMC proliferation, which was accompanied by increased GTP-RhoA and decreased p27. This study demonstrates that the RhoA/ROCK pathway plays an important role in heparin inhibition on PASMC proliferation, and reveals that heparin inhibits PASMC proliferation through GEF-H1/RhoA/ROCK/p27 signaling pathway, by down-regulating GEF-H1, RhoA, and ROCK, and then up-regulating p27.

JNK activation is responsible for mucus overproduction in smoke inhalation injury.

BACKGROUND: Increased mucus secretion is one of the important characteristics of the response to smoke inhalation injuries. We hypothesized that gel-forming mucins may contribute to the increased mucus production in a smoke inhalation injury. We investigated the role of c-Jun N-terminal kinase (JNK) in modulating smoke-induced mucus secretion. METHODS: We intubated mice and exposed them to smoke from burning cotton for 15 min. Their lungs were then isolated 4 and 24 h after inhalation injury. Three groups of mice were subjected to the smoke inhalation injury: (1) wild-type (WT) mice, (2) mice lacking JNK1 (JNK1-/- mice), and (3) WT mice administered a JNK inhibitor. The JNK inhibitor (SP-600125) was injected into the mice 1 h after injury. RESULTS: Smoke exposure caused an increase in the production of mucus in the airway epithelium of the mice along with an increase in MUC5AC gene and protein expression, while the expression of MUC5B was not increased compared with control. We found increased MUC5AC protein expression in the airway epithelium of the WT mice groups both 4 and 24 h after smoke inhalation injury. However, overproduction of mucus and increased MUC5AC protein expression induced by smoke inhalation was suppressed in the JNK inhibitor-treated mice and the JNK1 knockout mice. Smoke exposure did not alter the expression of MUC1 and MUC4 proteins in all 3 groups compared with control. CONCLUSION: An increase in epithelial MUC5AC protein expression is associated with the overproduction of mucus in smoke inhalation injury, and that its expression is related on JNK1 signaling.

High MW hyaluronan inhibits smoke inhalation-induced lung injury and improves survival.

BACKGROUND AND OBJECTIVE: High MW hyaluronan (HMW HA) as opposed to low MW hyaluronan (LMW HA) has been shown to have anti-inflammatory and anti-apoptotic effects. We hypothesized that treatment with HMW HA would block smoke inhalation lung injury by inhibiting smoke-induced lung inflammation and airway epithelial cell apoptosis. METHODS: Anesthetized, intubated male rats were randomly allocated to either control or smoke inhalation injury groups. Rats were treated with 3-mL subcutaneous normal saline solution (sham) or LMW HA (35 kDa) or HMW HA (1600 kDa) 18 h before exposure to 15 min of cotton smoke (n = 5 each). Rats were also treated post smoke inhalation with 1600 kDa HA by intra-peritoneal injection (3 mL) or intra-tracheal nebulization (200 µL). Lung neutrophil infiltration, airway apoptosis, airway mucous plugging and lung injury were assessed 4 h after smoke inhalation injury. RESULTS: Rats pretreated with 1600 kDa HA had significantly less smoke-induced neutrophil infiltration, lung oedema, airway apoptosis and mucous plugging. Pretreatment with 35 kDa HA, in contrast, increased smoke-induced neutrophil infiltration and lung injury score. Intra-tracheal administration of a single dose 1600 kDa HA, but not intra-peritoneal injection, significantly improved survival post smoke inhalation. CONCLUSIONS: High MW hyaluronan (1600 kDa) may prove to be a beneficial therapy for smoke inhalation through inhibition of smoke-induced inflammation, lung oedema, airway epithelial cell apoptosis and airway mucous plugging.

Multidetector computed tomography for acute pulmonary embolism.

BACKGROUND: The accuracy of multidetector computed tomographic angiography (CTA) for the diagnosis of acute pulmonary embolism has not been determined conclusively. METHODS: The Prospective Investigation of Pulmonary Embolism Diagnosis II trial was a prospective, multicenter investigation of the accuracy of multidetector CTA alone and combined with venous-phase imaging (CTA-CTV) for the diagnosis of acute pulmonary embolism. We used a composite reference test to confirm or rule out the diagnosis of pulmonary embolism. RESULTS: Among 824 patients with a reference diagnosis and a completed CT study, CTA was inconclusive in 51 because of poor image quality. Excluding such inconclusive studies, the sensitivity of CTA was 83 percent and the specificity was 96 percent. Positive predictive values were 96 percent with a concordantly high or low probability on clinical assessment, 92 percent with an intermediate probability on clinical assessment, and nondiagnostic if clinical probability was discordant. CTA-CTV was inconclusive in 87 of 824 patients because the image quality of either CTA or CTV was poor. The sensitivity of CTA-CTV for pulmonary embolism was 90 percent, and specificity was 95 percent. CTA-CTV was also nondiagnostic with a discordant clinical probability. CONCLUSIONS: In patients with suspected pulmonary embolism, multidetector CTA-CTV has a higher diagnostic sensitivity than does CTA alone, with similar specificity. The predictive value of either CTA or CTA-CTV is high with a concordant clinical assessment, but additional testing is necessary when the clinical probability is inconsistent with the imaging results.

The role of phosphodiesterase 3 in endotoxin-induced acute kidney injury.

BACKGROUND: Acute kidney injury frequently accompanies sepsis. Endotoxin is known to reduce tissue levels of cAMP and low levels of cAMP have been associated with renal injury. We, therefore, hypothesized that endotoxin induced renal injury by activating phosphodiesterase 3 (PDE3) which metabolizes cAMP and that amrinone an inhibitor of PDE3 would prevent the renal injury. METHODS: Animals were divided into three groups (n = 7/group): 1) Control (0.9% NaCl infusion without LPS); 2) LPS (0.9% NaCl infusion with LPS); 3) Amrinone+LPS (Amrinone infusion with LPS). Either lipopolysaccharide (LPS) or vehicle was injected via the jugular vein and the rats followed for 3 hours. We explored the expression of PDE3 isoenzymes and the concentrations of cAMP in the tissue. RESULTS: The PDE3B gene but not PDE3A was upregulated in the kidney of LPS group. Immunohistochemistry also showed that PDE3B was expressed in the distal tubule in the controls and LPS caused PDE3B expression in the proximal as well. However, PDE3A was not expressed in the kidney either in the control or LPS treated groups. Tissue level of cAMP was decreased after LPS and was associated with an increase in blood urea nitrogen, creatinine, ultrastructural proximal tubular changes, and expression of inducible nitric oxide synthase (iNOS) in the endotoxemic kidney. In septic animals the phosphodiesterase 3 inhibitor, amrinone, preserved the tissue cAMP level, renal structural changes, and attenuated the increased blood urea nitrogen, creatinine, and iNOS expression in the kidney. CONCLUSION: These findings suggest a significant role for PDE3B as an important mediator of LPS-induced acute kidney injury.

Unfractionated heparin and enoxaparin reduce high-stretch ventilation augmented lung injury: a prospective, controlled animal experiment.

INTRODUCTION: Dysregulation of coagulation and local fibrinolysis found in patients with acute lung injury often results in the need for the support of mechanical ventilation. High-tidal-volume mechanical ventilation can increase lung damage and suppression of fibrinolytic activity, but the mechanisms are unclear. We hypothesized that subcutaneous injections of unfractionated heparin and enoxaparin would decrease neutrophil infiltration, lung edema, and plasminogen-activator inhibitor-1 (PAI-1) production in mice exposed to high-tidal-volume ventilation. METHODS: Male C57BL/6 mice, weighing 20 to 25 g, were exposed to either high-tidal-volume (30 ml/kg) or low-tidal-volume (6 ml/kg) mechanical ventilation with room air for 1 to 5 hours after 200 IU/kg or 400 IU/kg unfractionated heparin and 4 mg/kg or 8 mg/kg enoxaparin administration. Nonventilated mice served as a control group. Evan blue dye, lung wet- to dry-weight ratio, histopathologic grading of epithelium, myeloperoxidase, and gene expression of PAI-1 were measured. The expression of PAI-1 was studied by immunohistochemistry. RESULTS: High-tidal-volume ventilation induced increased microvascular permeability, neutrophil influx, PAI-1 mRNA expression, production of PAI-1 protein, and positive staining of PAI-1 in epithelium in a dose-dependent manner. Lung injury induced by high-tidal-volume ventilation was attenuated with PAI-1-deficient mice and pharmacologic inhibition of PAI-1 activity by low-dose unfractionated heparin and enoxaparin. CONCLUSIONS: We conclude that high-tidal-volume mechanical ventilation increased microvascular permeability, neutrophil influx, lung PAI-1 mRNA expression, production of active PAI-1. The deleterious effects were attenuated by low-dose unfractionated heparin or enoxaparin treatment. Understanding the protective mechanism of unfractionated heparin and enoxaparin related to the reduction of PAI-1 may afford further knowledge of the effects of mechanical forces in the lung and development of possible therapeutic strategies involved in acute lung injury.

Inhibition of HA synthase 3 mRNA expression, with a phosphodiesterase 3 inhibitor, blocks lung injury in a septic ventilated rat model.

Low-molecular-weight hyaluronan produced by hyaluronan synthase 3 (HAS3) has been shown to play a role in acute lung injury secondary to high-tidal-volume ventilation. Phosphodiesterase 3 inhibitors have been shown to decrease HAS3 expression. We hypothesized that low-molecular-weight hyaluronan (LMW HA) produced by HAS3 mediates LPS-induced lung injury in the mechanically ventilated rat and that milrinone (MIL), by blocking HAS3 mRNA expression, would prevent the injury. Rats were randomized to four groups: controls with mechanical ventilation at 7 cc/kg MV, MV+LPS, MV+MIL, and MV+LPS+MIL. Rats were intubated and ventilated without PEEP for 4 h. Lipopolysaccharide (LPS) (1 mg/kg) was infused into the arterial line 1 h prior to MV. MIL 10 microg/kg/min (or an equivalent volume of saline) was infused through the venous line at the beginning of MV. Bronchoalveolar lavage fluid (BAL) was collected after 4 h of ventilation and lungs were saved for histopathology. LPS significantly increased neutrophil infiltration and protein concentration in the BAL and augmented lung injury score on histology. MIL significantly lowered alveolar protein and neutrophil infiltration as well as lung injury in response to LPS. Furthermore, MIL decreased the mRNA expression for HAS3 and MIP2 in lung tissue and decreased the protein content in BAL. MIL, a commonly used inotropic agent, inhibited LPS-induced lung inflammation and lung injury in mechanically ventilated rats. The anti-inflammatory properties of MIL may be mediated by inhibition of HAS3 and/or MIP2 and could be beneficial in the treatment of sepsis.

Deficiency of the NHE1 gene prevents hypoxia-induced pulmonary hypertension and vascular remodeling.

RATIONALE: Our previous studies found that Na(+)/H(+) exchanger (NHE) activity played an essential role in pulmonary artery smooth muscle cell (PASMC) proliferation and in the development of hypoxia-induced pulmonary hypertension and vascular remodeling. Other investigators recently observed increased expression of the NHE isoform 1 (NHE1) gene in rodents with pulmonary hypertension induced by hypoxia. However, a causal role for the NHE1 gene in pulmonary hypertension has not been determined. OBJECTIVES: To determine the causal role of the NHE1 gene in pulmonary hypertension and vascular remodeling. METHODS: We used NHE1-null mice to define the role of the NHE1 gene in the development of pulmonary hypertension and remodeling induced by hypoxia and to delineate the NHE1 regulatory pathway. MEASUREMENTS AND MAIN RESULTS: After 2 weeks of exposure to hypoxia, in contrast to wild-type hypoxic littermates, there was no significant increase in right ventricular systolic pressure, in the ratio of right ventricular to left ventricular plus septal weight [RV/(LV + S)], or in medial wall thickness of the pulmonary arterioles in homozygous mice (NHE1(-/-)). There was a significant decrease in Rho kinase (ROCK1 and ROCK2) expression, accompanied by an increase in p27 expression in NHE1(-/-) mice. CONCLUSIONS: Our study demonstrated that deficiency of the NHE1 gene prevented the development of hypoxia-induced pulmonary hypertension and vascular remodeling in mice and revealed a novel regulatory pathway associated with NHE1 signaling.

Cyclic stretch affects pulmonary endothelial cell control of pulmonary smooth muscle cell growth.

Endothelial cells are subjected to mechanical forces in the form of cyclic stretch resulting from blood pulsatility. Pulmonary artery endothelial cells (PAECs) produce factors that stimulate and inhibit pulmonary artery smooth muscle cell (PASMC) growth. We hypothesized that PAECs exposed to cyclic stretch secrete proteins that inhibit PASMC growth. Media from PAECs exposed to cyclic stretch significantly inhibited PASMC growth in a time-dependent manner. Lyophilized material isolated from stretched PAEC-conditioned media significantly inhibited PASMC growth in a dose-dependent manner. This inhibition was reversed by trypsin inactivation, which is consistent with the relevant factor being a protein(s). To identify proteins that inhibited cell growth in conditioned media from stretched PAECs, we used proteomic techniques and found that thrombospondin (TSP)-1, a natural antiangiogenic factor, was up-regulated by stretch. In vitro, exogenous TSP-1 inhibited PASMC growth. TSP-1-blocking antibodies reversed conditioned media-induced inhibition of PASMC growth. Cyclic stretched PAECs secrete protein(s) that inhibit PASMC proliferation. TSP-1 may be, at least in part, responsible for this inhibition. The complete identification and understanding of the secreted proteome of stretched PAECs may lead to new insights into the pathophysiology of pulmonary vascular remodeling.

Serine/threonine kinase-protein kinase B and extracellular signal-regulated kinase regulate ventilator-induced pulmonary fibrosis after bleomycin-induced acute lung injury: a prospective, controlled animal experiment.

INTRODUCTION: Lung fibrosis, reduced lung compliance, and severe hypoxemia found in patients with acute lung injury often result in a need for the support of mechanical ventilation. High-tidal-volume mechanical ventilation can increase lung damage and fibrogeneic activity but the mechanisms regulating the interaction between high tidal volume and lung fibrosis are unclear. We hypothesized that high-tidal-volume ventilation increased pulmonary fibrosis in acute lung injury via the serine/threonine kinase-protein kinase B (Akt) and mitogen-activated protein kinase pathways. METHODS: After 5 days of bleomycin administration to simulate acute lung injury, male C57BL/6 mice, weighing 20 to 25 g, were exposed to either high-tidal-volume mechanical ventilation (30 ml/kg) or low-tidal-volume mechanical ventilation (6 ml/kg) with room air for 1 to 5 hours. RESULTS: High-tidal-volume ventilation induced type I and type III procollagen mRNA expression, microvascular permeability, hydroxyproline content, Masson's trichrome staining, S100A4/fibroblast specific protein-1 staining, activation of Akt and extracellular signal-regulated kinase (ERK) 1/2, and production of macrophage inflammatory protein-2 and 10 kDa IFNgamma-inducible protein in a dose-dependent manner. High-tidal-volume ventilation-induced lung fibrosis was attenuated in Akt-deficient mice and in mice with pharmacologic inhibition of ERK1/2 activity by PD98059. CONCLUSION: We conclude that high-tidal-volume ventilation-induced microvascular permeability, lung fibrosis, and chemokine production were dependent, in part, on activation of the Akt and ERK1/2 pathways.