Additive effects of phosphodiesterase-4 inhibition on effects of rSP-C surfactant

Acute Lung Functional and Airway Remodeling Effects of an Inhaled Highly Selective Phosphodiesterase 4 Inhibitor in Ventilated Preterm Lambs Exposed to Chorioamnionitis

Phosphodiesterase (PDE) inhibition has been identified in animal studies as a new treatment option for neonatal lung injury, and as potentially beneficial for early lung development and function. However, our group could show that the inhaled PDE4 inhibitor GSK256066 could have dose-dependent detrimental effects and promote lung inflammation in the premature lung. In this study, the effects of a high and a low dose of GSK256066 on lung function, structure and alveolar development were investigated. In a triple hit lamb model of Ureaplasma-induced chorioamnionitis, prematurity, and mechanical ventilation, 21 animals were treated as unventilated (NOVENT) or 24 h ventilated controls (Control), or with combined 24 h ventilation and low dose (iPDE1) or high dose (iPDE10) treatment with inhaled GSK 256066. We found that high doses of an inhaled PDE4 inhibitor impaired oxygenation during mechanical ventilation. In this group, the budding of secondary septae appeared to be decreased in the preterm lung, suggesting altered alveologenesis. Ventilation-induced structural and functional changes were only modestly ameliorated by a low dose of PDE4 inhibitor. In conclusion, our findings indicate the narrow therapeutic window of PDE4 inhibitors in the developing lung.

Reduction of lung inflammation, oxidative stress and apoptosis by the PDE4 inhibitor roflumilast in experimental model of acute lung injury

Damage of alveolar-capillary barrier, inflammation, oxidative injury, and lung cell apoptosis represent the key features of acute lung injury (ALI). This study evaluated if selective phosphodiesterase (PDE)-4 inhibitor roflumilast can reduce the mentioned changes in lavage-induced model of ALI. Rabbits with ALI were divided into 2 groups: ALI without therapy (A group) and ALI treated with roflumilast i.v. (1 mg/kg; A+R group). One group of healthy animals without ALI served as ventilated controls (C group). All animals were oxygen-ventilated for further 4 h. At the end of experiment, total and differential counts of cells in bronchoalveolar lavage fluid (BALF) and total and differential counts of white blood cells were estimated. Lung edema formation was assessed from determination of protein content in BALF. Pro-inflammatory cytokines (TNFalpha, IL-6 and IL-8) and markers of oxidation (3-nitrotyrosine, thiobarbituric-acid reactive substances) were detected in the lung tissue and plasma. Apoptosis of lung cells was investigated immunohistochemically. Treatment with roflumilast reduced leak of cells, particularly of neutrophils, into the lung, decreased concentrations of cytokines and oxidative products in the lung and plasma, and reduced lung cell apoptosis and edema formation. Concluding, PDE4 inhibitor roflumilast showed potent anti-inflammatory actions in this model of ALI.

Phosphodiesterase inhibitors: Potential role in the respiratory distress of neonates

Phosphodiesterases (PDEs) are a superfamily of enzymes that catalyze the hydrolysis of phosphodiester bonds of 3',5' cyclic adenosine and guanosine monophosphate (cAMP and cGMP). PDEs control hydrolysis of cyclic nucleotides in many cells and tissues. Inhibition of PDEs by selective or nonselective PDE inhibitors represents an effective targeted strategy for the treatment of various diseases including respiratory disorders. Recent data have demonstrated that PDE inhibitors can also be of benefit in respiratory distress in neonates. This article outlines the pharmacological properties of nonselective and selective PDE inhibitors and provides up-to-date information regarding their use in experimental models of neonatal respiratory distress as well as in clinical studies.

Effects of roflumilast, a phosphodiesterase-4 inhibitor, on the lung functions in a saline lavage-induced model of acute lung injury

Acute lung injury (ALI) is associated with deterioration of alveolar-capillary lining and transmigration and activation of inflammatory cells. Whereas a selective phosphodiesterase-4 (PDE4) inhibitor roflumilast has exerted potent anti-inflammatory properties, this study evaluated if its intravenous delivery can influence inflammation, edema formation, and respiratory parameters in rabbits with a lavage-induced model of ALI. ALI was induced by repetitive saline lung lavage (30 ml/kg). Animals were divided into 3 groups: ALI without therapy (ALI), ALI treated with roflumilast i.v. (1 mg/kg; ALI+Rofl), and healthy ventilated controls (Control), and were ventilated for following 4 h. Respiratory parameters (blood gases, ventilatory pressures, lung compliance, oxygenation indexes etc.) were measured and calculated regularly. At the end of experiment, animals were overdosed by anesthetics. Total and differential counts of cells in bronchoalveolar lavage fluid (BAL) were estimated microscopically. Lung edema was expressed as wet/dry lung weight ratio. Treatment with roflumilast reduced leak of cells (P<0.01), particularly of neutrophils (P<0.001), into the lung, decreased lung edema formation (P<0.01), and improved respiratory parameters. Concluding, the results indicate a future potential of PDE4 inhibitors also in the therapy of ALI.

Surfactant

Exogenous pulmonary surfactant, widely used in neonatal care, is one of the best-studied treatments in neonatology, and its introduction in the 1990s led to a significant improvement in neonatal outcomes in preterm infants, including a decrease in mortality. This chapter provides an overview of surfactant composition and function in health and disease and summarizes the evidence for its clinical use.

Olprinone and colforsin daropate alleviate septic lung inflammation and apoptosis through CREB-independent activation of the Akt pathway

Olprinone, a specific phosphodiesterase III inhibitor, and corforsin daropate, a direct adenylate cyclase activator, are now being used in critical conditions. We investigated whether their therapeutic use provides protection against septic acute lung injury (ALI) and mortality. Polymicrobial sepsis was induced by cecal ligation and puncture (CLP) in BALB/c mice. Olprinone or colforsin daropate was continuously given through an osmotic pump that was implanted into the peritoneal cavity immediately following CLP. These treatments prevented the ALI development in CLP mice, as indicated by the findings that severe hypoxemia, increased pulmonary vascular permeability, and histological lung damage were strikingly remedied. Furthermore, continued administration of olprinone or colforsin daropate suppressed apoptosis induction in septic lungs and improved the survival of CLP mice. Olprinone and corforsin daropate enhanced Akt phosphorylation in septic lungs. Wortmannin, which inhibits the Akt upstream regulator phosphatidylinositol 3-kinase, abrogated the protective effects of olprinone and corforsin daropate on sepsis-associated lung inflammation and apoptosis. In vivo transfection of cyclic AMP response element binding protein (CREB) decoy oligodeoxynucleotide failed to negate the abilities of these agents to increase Akt phosphorylation and to inhibit IκBα degradation in septic lungs. These results demonstrate for the first time that CREB-independent Akt-mediated signaling is a critical mechanism contributing to the therapeutic effects of olprinone and corforsin daropate on septic ALI. Moreover, our data also suggest that these cyclic AMP-related agents, by blocking both nuclear factor-κB activation and apoptosis induction, may represent an effective therapeutic approach to the treatment of the septic syndrome.

The preclinical pharmacology of roflumilast--a selective, oral phosphodiesterase 4 inhibitor in development for chronic obstructive pulmonary disease

After more than two decades of research into phosphodiesterase 4 (PDE4) inhibitors, roflumilast (3-cyclopropylmethoxy-4-difluoromethoxy-N-[3,5-di-chloropyrid-4-yl]-benzamide) may become the first agent in this class to be approved for patient treatment worldwide. Within the PDE family of 11 known isoenzymes, roflumilast is selective for PDE4, showing balanced selectivity for subtypes A-D, and is of high subnanomolar potency. The active principle of roflumilast in man is its dichloropyridyl N-oxide metabolite, which has similar potency as a PDE4 inhibitor as the parent compound. The long half-life and high potency of this metabolite allows for once-daily, oral administration of a single, 500-microg tablet of roflumilast. The molecular mode of action of roflumilast--PDE4 inhibition and subsequent enhancement of cAMP levels--is well established. To further understand its functional mode of action in chronic obstructive pulmonary disease (COPD), for which roflumilast is being developed, a series of in vitro and in vivo preclinical studies has been performed. COPD is a progressive, devastating condition of the lung associated with an abnormal inflammatory response to noxious particles and gases, particularly tobacco smoke. In addition, according to the Global Initiative for Chronic Obstructive Lung Disease (GOLD), significant extrapulmonary effects, including comorbidities, may add to the severity of the disease in individual patients, and which may be addressed preferentially by orally administered remedies. COPD shows an increasing prevalence and mortality, and its treatment remains a high, unmet medical need. In vivo, roflumilast mitigates key COPD-related disease mechanisms such as tobacco smoke-induced lung inflammation, mucociliary malfunction, lung fibrotic and emphysematous remodelling, oxidative stress, pulmonary vascular remodelling and pulmonary hypertension. In vitro, roflumilast N-oxide has been demonstrated to affect the functions of many cell types, including neutrophils, monocytes/macrophages, CD4+ and CD8+ T-cells, endothelial cells, epithelial cells, smooth muscle cells and fibroblasts. These cellular effects are thought to be responsible for the beneficial effects of roflumilast on the disease mechanisms of COPD, which translate into reduced exacerbations and improved lung function. As a multicomponent disease, COPD requires a broad therapeutic approach that might be achieved by PDE4 inhibition. However, as a PDE4 inhibitor, roflumilast is not a direct bronchodilator. In summary, roflumilast may be the first-in-class PDE4 inhibitor for COPD therapy. In addition to being a non-steroid, anti-inflammatory drug designed to target pulmonary inflammation, the preclinical pharmacology described in this review points to a broad functional mode of action of roflumilast that putatively addresses additional COPD mechanisms. This enables roflumilast to offer effective, oral maintenance treatment for COPD, with an acceptable tolerability profile and the potential to favourably affect the extrapulmonary effects of the disease.

Pretreatment with olprinone hydrochloride, a phosphodiesterase III inhibitor, attenuates lipopolysaccharide-induced lung injury via an anti-inflammatory effect

PURPOSE

Acute respiratory distress syndrome is characterized by neutrophil accumulation in the lungs and the activation of several cytokines produced by macrophages. Olprinone hydrochloride, a specific phosphodiesterase III inhibitor, has anti-inflammatory effects and inhibits the activation of macrophages, in addition to its inotropic and vasodilatory effects. The purpose of this study was to examine the beneficial effects of olprinone on lipopolysaccharide (LPS)-induced pulmonary inflammation.

MATERIALS AND METHODS

Lung inflammation was produced by intravenous LPS injection into rats. The rats were divided into four groups: a vehicle group in which normal saline was injected, an olprinone group in which olprinone was injected at a dose of 0.2mg/kg, a dexamethasone group in which dexamethasone was injected at a dose of 5mg/kg, and a control group. In each group, drug was injected intraperitoneally 30 min before the intravenous administration of LPS. The blood was obtained at 1h and then animals were sacrificed at 6h and blood and lung specimen were obtained for cytokine analysis and pathological examination. On another set of experiment, bronchioloalveolar lavage (BAL) was performed for cytokine analysis of BAL fluid. The macrophages isolated from normal rat by BAL were cultured in vitro with the presence of LPS and olprinone or dexamethasone, and supernatant was collected. The levels of several cytokines in the serum, in the BAL fluid, and in the culture supernatant were determined.

RESULTS

The animals injected with LPS were found to have an influx of neutrophils in the lungs, and inflammatory cytokines, such as TNF-alpha and IL-6, and anti-inflammatory cytokine IL-10 were produced. Pretreatment with olprinone or dexamethasone significantly inhibited the LPS-induced neutrophil influx into the lungs, suppressed inflammatory cytokines TNF-alpha and IL-6. The level of anti-inflammatory cytokine IL-10 increased in an olprinone group. The inhibition of TNF-alpha and IL-6, and the augmentation of IL-10 release were also observed in in vitro culture of isolated rat alveolar macrophages when olprinone (10(-5)mol/ml) and LPS (10 microg/ml) were cultured together. However, the level of IL-10 in serum and culture supernatant was suppressed in a dexamesathone group.

CONCLUSION

LPS-induced lung inflammation is strongly inhibited by olprinone accompanying the enhancement of IL-10 and the inhibition of inflammatory cytokines. Results of the in vitro experiment suggest that alveolar macrophages may play an important role in ameliorating LPS-induced lung inflammation and the mechanism of its effect is different from that of steroid.

Intratracheal Application of Recombinant Surfactant Protein-C Surfactant to Rabbits Attenuates Acute Lung Injury Induced by Intratracheal Acidified Infant Formula

Our aim in the current study was to determine whether recombinant surfactant protein-C (rSP-C) surfactant improves acute lung injury (ALI) induced by intratracheal acidified milk products. Twenty-eight rabbits were randomly divided into four groups. ALI was induced with intratracheal acidified infant formula (0.8 mL/kg, pH 1.8) in 3 groups. The control group received intratracheal acidified saline. Therapy groups received 1 of 2 doses of intratracheal rSP-C surfactant (0.5 or 2 SP-C mg/kg) 30 min after the acidified infant formula. The lungs were ventilated with 100% oxygen for 4 h after induction of ALI. Acidified infant formula dramatically reduced oxygenation and lung compliance, and increased resistance. Both doses of rSP-C improved the variables [mean PaO(2) (mm Hg) and compliance (mL/cm H(2)O) at 4 h: 61 and 0.4 for infant formula, 162 and 1.0 for small-dose rSP-C, and 152 and 1.2 for large-dose rSP-C, respectively; P < 0.05]. Pulmonary leukosequestration and edema, and severe morphological changes were attenuated by rSP-C treatment (ALI score: 14, 7, 7 in infant formula, small-dose rSP-C, and large-dose rSP-C; P < 0.05). The efficacy was similar for the two doses of rSP-C. These findings suggest that intratracheal administration of rSP-C ameliorates ALI induced by aspiration of acidified milk products.

IMPLICATIONS

Small or large doses of recombinant surfactant protein-C surfactant given 30 min after intratracheal acidified infant formula attenuated physiological, biochemical, and morphological lung damage.

Relation between rheological properties and structural changes in monolayers of model lung surfactant under compression

rSP-C surfactant monolayers spread on a native physiological model substrate show two plateau regions in the pi/A-isotherm. The first corresponds to the main phase transition in the monolayer from a LE to a LC phase. Its course is non-horizontal because of the complex composition of the lung surfactant. The second plateau, which is much more pronounced, cannot be attributed to a change of the phase state. Brewster angle microscopy images taken in this region show a sharp apparent decrease of the aggregation degree from the LE to the LC state. This process can be considered as a change in the monolayer orientation relative to the direction of the propagated light. Such a change can be the result of monolayer folding and formation of a thicker layer, which is supported by results of rheological measurements. The dilatation elasticity obtained from oscillating barrier and longitudinal wave measurements reveals a pure elastic behaviour with a steep increase in the second plateau region. Because of the insolubility of the pure lipid components, a possible explanation is squeezing protein components of rSP-C or its complexes with lipids out of the monolayer into the bulk.

Cyclooxygenase-inhibition enhances the effects of rSP-C surfactant therapy in a rat lavage model of acute respiratory distress syndrome (ARDS)

The effects of additional i.v. therapy with a cyclooxygenase-inhibitor Eltenac to a recombinant surfactant protein C (rSP-C) based surfactant were investigated in a rat lung lavage model of acute lung injury. Treatment was done at 60 min after the induction of acute lung injury by lavage. The influence of the different treatments were tested with regard to improving oxygenation, histopathological changes (hyaline membrane formation and alveolar influx of neutrophil leukocytes). These effects were further compared to a fixed combination of Eltenac with rSP-C surfactant which was administered intratracheally (i.tr.), 60 min after lavage. To prove that fibrinogen is involved in the formation of hyaline membranes in this animal model confocal microscopy was applied. Furthermore, for selected cases the influence of Eltenac or rSP-C surfactant on fibrinogen leakage was investigated by using confocal microscopy. Results of additional i.v. therapy exhibited an improved oxygenation with rSP-C surfactant, while a high dose of Eltenacalone did not influence oxygenation as compared to untreated controls. Addition of Eltenac lead to improved oxygenation using the low dose of rSP-C surfactant. The rSP-C surfactant prevented further hyaline membrane formation. Furthemore, addition of Eltenac to the low dose of rSP-C surfactant lead to improved hyaline membrane formation at a dose of 100 micromol/kg b.w. Results of combined i.tr. therapy confirmed the results of the additional therapy. Again, rSP-C surfactant improved oxygenation and further hyaline membrane formation, while even the high dose of i.tr. administered Eltenacalone only prevented further hyaline membrane formation. Using the low dose of rSP-C surfactant, combined treatment with Eltenac showed additional effects on oxygenation and inhibition of hyaline membrane formation. The maximum therapeutic effect of combined treatment was achieved at 0.3 mg Eltenac per kg b.w. which is equivalent to approximately 1 micromol. The inflammatory cell infiltration into the lung was not influenced by any of the therapeutic approaches. Confocal microscopy gave evidence that fibrinogen is involved in hyaline membrane formation in this animal model. Furthermore, as was shown by the explorative investigations with confocal microscopy, addition of the cyclooxygenase-inhibitor decreases the diffuse interstitial leakage of fibrinogen into the lung while surfactant monotherapy did not exhibit any influence on the fibrinogen influx into the alveoli.

CONCLUSIONS

Confocal microscopy may be an effective method to investigate the connection between fibrinogen leakage and hyaline membrane formation. Effects of additional or combined treatment were superior when compared to each treatment alone leading to the conclusion that a rSP-C surfactant containing a cyclooxygenase-inhibitor, acts synergistically in this animal model of acute lung injury. Lower doses of Eltenac could be used to reach similar effects on oxygenation and prevention of hyaline membrane after combined i.tr. treatment than after additional i.v. treatment together with surfactant. This leads to the conclusion that a fixed combination of rSP-C surfactant and a cyclooxygenase-inhibitor may be an effective treatment. Further testing may be warranted to prove whether this is a promising treatment for patients with acute lung injury.

Lung surfactants for neonatal respiratory distress syndrome: animal-derived or synthetic agents?

Exogenous surfactant therapy is widely used in the management of neonatal respiratory distress syndrome. Two types of surfactants are available: synthetic surfactants, and those derived from animal sources ("natural" surfactants). Both of these surfactants have been shown to be effective. In this article, we review the evidence to compare the two types of surfactants in terms of their physical properties, physiologic effects, and clinical outcomes. Natural surfactants have been shown to have advantages over synthetic surfactants in their physical properties and physiologic effects in animals, as well as in humans. A systematic review of 11 randomized clinical trials comparing natural and synthetic surfactants demonstrated that the use of natural surfactant preparations results in greater clinical benefits compared with synthetic surfactants. These benefits include a more rapid improvement in oxygenation and lung compliance after surfactant therapy, a decrease in the risk of mortality (typical relative risk 0.87; typical risk difference -0.02), and a decrease in the risk of pneumothorax (typical relative risk 0.63; typical risk difference -0.04). Although the use of natural surfactants results in a slightly increased risk of intraventricular hemorrhage (typical relative risk 1.09; typical risk difference 0.03), there is no increase in the risk of grade 3 or 4 intraventricular hemorrhage. There are theoretical but unproven risks of natural surfactants, such as transmission of infectious agents, immunogenicity and impurities in composition. The use of natural surfactants is preferred in most situations. In addition, clinicians should determine the costs of different types of surfactants in their individual practice settings and use this information in decision-making.

Synthesis of photoreactive phosphatidic acid analogues displaying activatory properties on cyclic AMP-phosphodiesterases. Photoaffinity labeling of an isoform of phosphodiesterase

We have previously shown that phosphatidic acid (PA) is a specific activator of some isoforms of type 4 cyclic nucleotide phosphodiesterases (PDE 4) and that accumulation of endogenous PA can, in this way, influence the cAMP signaling pathway in different cell types. Enzyme activation depends on direct binding of the effector to specific sites carried by the enzyme. To identify the binding domain, photoactivatable phosphatidic acid analogues 1-azidoPA (12) and 2-azidoPA (7 and 15), potentially suitable for covalent labeling of PDE4, have been synthesized. The ability of phospholipases A(2) and D to hydrolyze unnatural phospholipids has been considered in this paper. The effect of 1-azidoPA (12) and 2-azidoPA (7 and 15) on the activity of a recombinant PA-sensitive isoform PDE4D3 was evaluated. The three compounds were able to activate the enzyme with different efficiencies. A tritiated analogue of 15 was synthesized and used in PDE4D3 labeling experiments, which showed that this PA analogue was specifically and covalently linked to the enzyme after UV irradiation. Photoactivatable analogues thus appear as suitable tools for the characterization of PA binding sites.