Phosphodiesterase 4 inhibitor cilomilast inhibits fibroblast-mediated collagen gel degradation induced by tumor necrosis factor-alpha and neutrophil elastase

Phosphodiesterases as therapeutic targets for respiratory diseases

Chronic respiratory diseases, such as chronic obstructive pulmonary disease (COPD) and asthma, affect millions of people all over the world. Cyclic adenosine monophosphate (cAMP) which is one of the most important second messengers, plays a vital role in relaxing airway smooth muscles and suppressing inflammation. Given its vast role in regulating intracellular responses, cAMP provides an attractive pharmaceutical target in the treatment of chronic respiratory diseases. Phosphodiesterases (PDEs) are enzymes that hydrolyze cyclic nucleotides and help control cyclic nucleotide signals in a compartmentalized manner. Currently, the selective PDE4 inhibitor, roflumilast, is used as an add-on treatment for patients with severe COPD associated with bronchitis and a history of frequent exacerbations. In addition, other novel PDE inhibitors are in different phases of clinical trials. The current review provides an overview of the regulation of various PDEs and the potential application of selective PDE inhibitors in the treatment of COPD and asthma. The possibility to combine various PDE inhibitors as a way to increase their therapeutic effectiveness is also emphasized.

Roflumilast Ameliorates Airway Hyperresponsiveness Caused by Diet-Induced Obesity in a Murine Model

Obese patients with asthma respond poorly to conventional asthma medications, resulting in severe symptoms and poor prognosis. Roflumilast, a phosphodiesterase-4 inhibitor that lowers the levels of various substances that are implicated in obese subjects with asthma, may be effective in the treatment of those subjects. We evaluated the potential of roflumilast as a novel therapeutic agent for obese subjects with asthma. We designed three models: diet-induced obesity (DIO); DIO with ovalbumin (OVA); and OVA. We fed C57BL/6J mice a high-fat diet for 3 months with or without OVA sensitization and challenge. Roflumilast or dexamethasone was administered orally three times at 2-day intervals in the last experimental week. Airway hyperresponsiveness resulting from DIO significantly improved in the roflumilast-treated group compared with the dexamethasone-treated groups. Although DIO did not affect the cell proliferation in bronchoalveolar lavage fluid, increased fibrosis was seen in the DIO group, which significantly improved from treatment with roflumilast. DIO-induced changes in adiponectin and leptin levels were improved by roflumilast, whereas dexamethasone aggravated them. mRNA levels and proteins of TNF-α, transforming growth factor-β, IL-1β, and IFN-γ increased in the DIO group and decreased with roflumilast. The reactive oxygen species levels were also increased in the DIO group and decreased by roflumilast. In the DIO plus OVA and OVA models, roflumilast improved Th1 and Th2 cell activation to a greater extent than dexamethasone. Roflumilast is significantly more effective than dexamethasone against airway hyperresponsiveness caused by DIO in the murine model. Roflumilast may represent a promising therapeutic agent for the treatment of obese patients with asthma.

Cyclic nucleotide signalling in kidney fibrosis

Kidney fibrosis is an important factor for the progression of kidney diseases, e.g., diabetes mellitus induced kidney failure, glomerulosclerosis and nephritis resulting in chronic kidney disease or end-stage renal disease. Cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) were implicated to suppress several of the above mentioned renal diseases. In this review article, identified effects and mechanisms of cGMP and cAMP regarding renal fibrosis are summarized. These mechanisms include several signalling pathways of nitric oxide/ANP/guanylyl cyclases/cGMP-dependent protein kinase and cAMP/Epac/adenylyl cyclases/cAMP-dependent protein kinase. Furthermore, diverse possible drugs activating these pathways are discussed. From these diverse mechanisms it is expected that new pharmacological treatments will evolve for the therapy or even prevention of kidney failure.

Clinical and molecular genetics of the phosphodiesterases (PDEs)

Cyclic nucleotide phosphodiesterases (PDEs) are enzymes that have the unique function of terminating cyclic nucleotide signaling by catalyzing the hydrolysis of cAMP and GMP. They are critical regulators of the intracellular concentrations of cAMP and cGMP as well as of their signaling pathways and downstream biological effects. PDEs have been exploited pharmacologically for more than half a century, and some of the most successful drugs worldwide today affect PDE function. Recently, mutations in PDE genes have been identified as causative of certain human genetic diseases; even more recently, functional variants of PDE genes have been suggested to play a potential role in predisposition to tumors and/or cancer, especially in cAMP-sensitive tissues. Mouse models have been developed that point to wide developmental effects of PDEs from heart function to reproduction, to tumors, and beyond. This review brings together knowledge from a variety of disciplines (biochemistry and pharmacology, oncology, endocrinology, and reproductive sciences) with emphasis on recent research on PDEs, how PDEs affect cAMP and cGMP signaling in health and disease, and what pharmacological exploitations of PDEs may be useful in modulating cyclic nucleotide signaling in a way that prevents or treats certain human diseases.

Phosphodiesterase-4 inhibition augments human lung fibroblast vascular endothelial growth factor production induced by prostaglandin E2

Lung fibroblasts are believed to be a major source of vascular endothelial growth factor (VEGF), which supports the survival of lung endothelial cells and modulates the maintenance of the pulmonary microvasculature. VEGF has been related to the pathogenesis of lung diseases, including chronic obstructive pulmonary disease (COPD). Prostaglandin E2 (PGE2) stimulates VEGF production from lung fibroblasts via the E-prostanoid (EP)-2 receptor. The EP2 signaling pathway uses cyclic adenosine monophosphate (cAMP) as a second messenger, and cAMP is degraded by phosphodiesterases (PDEs). This study investigates whether phosphodiesterase inhibition modulates the human lung fibroblast VEGF production induced by PGE2. Human fetal lung fibroblasts were cultured with PGE2 and PDE inhibitors. The PDE4 inhibitors roflumilast, roflumilast N-oxide, and rolipram with PGE2 increased VEGF release, as quantified in supernatant media by ELISA. In contrast, PDE3, PDE5, and PDE7 inhibitors did not affect VEGF release. Roflumilast increased VEGF release with either an EP2 or an EP4 agonist. Roflumilast augmented the cytosolic cAMP levels induced by PGE2 and VEGF release with other agents that use the cAMP signaling pathway. Roflumilast-augmented VEGF release was completely inhibited by a protein kinase A (PKA) inhibitor. Roflumilast with PGE2 increased VEGF mRNA levels, and the blockade of mRNA synthesis inhibited the augmented VEGF release. The stimulatory effect of roflumilast on VEGF release was replicated using primary healthy and COPD lung fibroblasts. These findings demonstrate that PDE4 inhibition can modulate human lung fibroblast VEGF release by PGE2 acting through the EP2 and EP4 receptor-cAMP/PKA signaling pathway. Through this action, PDE4 inhibitors such as roflumilast could contribute to the survival of lung endothelial cells.

Determination of 2-aryl-7(3',4'-dialkoxyphenyl)-pyrazolo [1,5-alpha] pyrimidine, a novel phosphodiesterase-4 inhibitor, in rat plasma by liquid chromatography-tandem mass spectrometry

A method for assaying a novel phosphodiesterase-4 inhibitor, 2-aryl-7(3',4'-dialkoxyphenyl)-pyrazolo [1,5-alpha] pyrimidine (PDE-310), was developed and validated in rat plasma using liquid chromatography-tandem mass spectrometry (LC-MS-MS). Rat plasma samples were processed by liquid-liquid extraction with ethyl acetate and injected onto the LC-MS-MS system for quantification. PDE-310 and imipramine (i.e., internal standard) were separated using a Gemini C18 column with mixture of acetonitrile and 0.1% formic acid (70:30, v/v) as the mobile phase. The ion transitions monitored were m/z 425.0 → 331.0 for PDE-310 and m/z 281.3 → 86.1 for imipramine in the multiple-reaction monitoring mode. The detector response was specific and linear for PDE-310 concentrations in the range of 0.1-50 µg/mL. The intra-day and inter-day precision and accuracy of the method were determined to be within the acceptance criteria for assay validation guidelines. The recoveries were approximately 85.7 and 88.2% from rat plasma for PDE-310 and imipramine, respectively. PDE-310 was stable under various processing and handling conditions. PDE-310 concentrations were readily measured in rat plasma samples up to 8 h after an intravenous administration of PDE-310, suggesting that the assay is practically useful.

Selective PDE inhibitors as novel treatments for respiratory diseases

Phosphodiesterases (PDEs) are a family of enzymes which catalyse the metabolism of the intracellular cyclic nucleotides, c-AMP and c-GMP that are expressed in a variety of cell types and in the context of respiratory diseases, It is now recognised that the use of PDE3, PDE4 and mixed PDE3/4 inhibitors can provide clinical benefit to patients with asthma or chronic obstructive pulmonary disease (COPD). The orally active PDE4 inhibitor Roflumilast-n-oxide has been approved for treatment of severe exacerbations of COPD as add-on therapy to standard drugs. This review discusses the involvement of PDEs in airway diseases and various strategies that are currently being pursued to improve efficacy and reduce side-effects of PDE4 inhibitors, including delivery via the inhaled route, mixed PDE inhibitors and/or antisense biologicals targeted towards PDE4.

PDE4: a novel target in the treatment of chronic obstructive pulmonary disease

Phosphodiesterases (PDEs) are important modulators of inflammation and wound healing. In this capacity, specific targeting of PDEs for the treatment of many diseases, including chronic obstructive pulmonary disease (COPD), has been investigated. Currently, treatment of COPD is suboptimal. PDE4 modulates the inflammatory response of the lung, and inhibition of PDE4 may be a novel, COPD-specific approach toward more effective treatment strategies. This review describes the state of PDE4-inhibitor therapy for use in COPD treatment.

Phosphodiesterase inhibitors in the treatment of inflammatory diseases

Phosphodiesterase 4 (PDE4) belongs to a family of enzymes which catalyzes the breakdown of 3, 5'-adenosine cyclic monophosphate (cAMP) and is ubiquitously expressed in inflammatory cells. There is little evidence that inflammatory diseases are caused by increased expression of this isoenzyme, although human inflammatory cell activity can be suppressed by selective PDE4 inhibitors. Consequently, there is intense interest in the development of selective PDE4 inhibitors for the treatment of a range of inflammatory diseases, including asthma, chronic obstructive pulmonary disease (COPD), inflammatory bowel disease, and psoriasis. Recent clinical trials with roflumilast in COPD have confirmed the therapeutic potential of targeting PDE4 and recently roflumilast has been approved for marketing in Europe and the USA, although side effects such as gastrointestinal disturbances, particularly nausea and emesis as well as headache and weight loss, may limit the use of this drug class, at least when administered by the oral route. However, a number of strategies are currently being pursued in attempts to improve clinical efficacy and reduce side effects of PDE4 inhibitors, including delivery via the inhaled route, development of nonemetic PDE4 inhibitors, mixed PDE inhibitors, and/or antisense biologicals targeted toward PDE4.

PDE4-inhibitors: a novel, targeted therapy for obstructive airways disease

Roflumilast is a selective once daily, oral phosphodiesterase-4 inhibitor that has recently been registered in all European Union countries as novel targeted therapy for COPD, while FDA approval for the USA market is expected in 2011. In several phase III trials in patients with moderate to (very) severe COPD and in patients with symptoms of chronic bronchitis and recurrent exacerbations, roflumilast showed sustained clinical efficacy by improving lung function and by reducing exacerbation rates. These beneficial effects have also been demonstrated when added to long-acting bronchodilators (both LABA and LAMA), underscoring the anti-inflammatory activity of roflumilast in COPD. Pooled data analysis showed overall mild to moderate, mostly self-limiting adverse events, mainly consisting of nausea, diarrhea and weight loss. In this review we discuss the results of the 4 registration studies showing promising effects of roflumilast in COPD and provide an overview of the topics that still need to be addressed.

Protease inhibitors in respiratory disease: focus on asthma and chronic obstructive pulmonary disease

Respiratory diseases, such as asthma and chronic obstructive pulmonary disease (COPD), are a major health burden on society and current treatment modalities for these diseases have not significantly changed over the past 40 years. The only major pharmacological advancement for the treatment of these diseases has been to increase the duration of action of bronchodilators (asthma: salmeterol; COPD: tiotropium bromide) and glucocorticosteroids (asthma: fluticasone propionate) and, increasingly, to formulate these agents in the same delivery device. Despite our increasing understanding of the cell and molecular biology of these diseases, the development of novel treatments remains beyond the reach of the scientific community. Proteases are a family of proteins with diverse biological activity, which are found in abundance within the airways of asthma and COPD, and have been implicated in the pathogenesis of these diseases. The targeting of proteases, including mast cell tryptase, neutrophil elastase and matrix metalloprotease with low-molecular-weight inhibitors, has highlighted the potential role of these enzymes in mediating certain aspects of the disease process in preclinical studies. Several challenges remain regarding the development of protease inhibitors, including the synthesis of highly potent and specific inhibitors, and target validation in man.

Cytokine-dependent balance of mitogenic effects in primary human lung fibroblasts related to cyclic AMP signaling and phosphodiesterase 4 inhibition

Interleukin-1beta (IL-1beta) and basic fibroblast growth factor (bFGF) are important regulators of proliferation, and their expression is increased in lungs of patients with asthma, idiopathic pulmonary fibrosis (IPF), or chronic obstructive pulmonary disease (COPD). We investigated the effect of IL-1beta and bFGF on proliferation of human lung fibroblasts and the role of COX-2, PGE(2), and cAMP in this process. Furthermore, the effect of phosphodiesterase (PDE) 3 and 4 inhibition was analyzed. In primary human lung fibroblasts low concentrations of IL-1beta (<10 pg/ml) potentiated the bFGF-induced DNA synthesis, whereas higher concentrations revealed antiproliferative effects. Higher concentrations of IL-1beta-induced COX-2 mRNA and protein associated with an increase in PGE(2) and cAMP, and all of these parameters were potentiated by bFGF. The PDE4 inhibitor piclamilast concentration-dependently reduced proliferation by a partial G1 arrest. The PDE3 inhibitor motapizone was inactive by itself but enhanced the effect of the PDE4 inhibitor. This study demonstrates that bFGF and IL-1beta act in concert to fine-tune lung fibroblast proliferation resulting in amplification or reduction. The antiproliferative effect of IL-1beta is likely attributed to the induction of COX-2, which is further potentiated by bFGF, and the subsequent generation of PGE(2) and cAMP. Inhibition of PDE4 inhibition (rather than PDE3) may diminish proliferation of human lung fibroblasts and therefore could be useful in the therapy of pathological remodeling in lung diseases.

Effects of phosphodiesterase 4 inhibition on bleomycin-induced pulmonary fibrosis in mice

Background

Pulmonary fibrosis (PF) is a group of devastating and largely irreversible diseases. Phosphodiesterase (PDE) 4 is involved in the processes of remodeling and inflammation, which play key role in tissue fibrosis. The aim of the study was, therefore, to investigate the effect of PDE4 inhibition in experimental model of PF.

Methods

PF was induced in C57BL/6N mice by instillation of bleomycin. Pharmacological inhibition of PDE4 was achieved by using cilomilast, a selective PDE4 inhibitor. Changes in either lung inflammation or remodeling were evaluated at different stages of experimental PF. Lung inflammation was assessed by bronchoalveolar lavage fluid (BALF) differential cell count and reverse transcription quantitative polymerase chain reaction (RT-qPCR) for inflammatory cytokines. Changes in tissue remodeling were evaluated by pulmonary compliance measurement, quantified pathological examination, measurement of collagen deposition and RT-qPCR for late remodeling markers. Survival in all groups was analyzed as well.

Results

PDE4 inhibition significantly reduced the total number of alveolar inflammatory cells in BALF of mice with bleomycin-induced PF at early fibrosis stage (days 4 and 7). Number of macrophages and lymphocytes, but not neutrophils, was significantly reduced as well. Treatment decreased lung tumor necrosis factor (TNF)-α mRNA level and increased mRNA level of interleukin (IL)-6 but did not influence IL-1β. At later stage (days 14 and 24) cilomilast improved lung function, which was shown by increase in lung compliance. It also lowered fibrosis degree, as was shown by quantified pathological examination of Hematoxilin-Eosin stained lung sections. Cilomilast had no significant effect on the expression of late remodeling markers such as transforming growth factor (TGF)-β1 and collagen type Ia1 (COL(I)α1). However, it tended to restore the level of lung collagen, assessed by SIRCOL assay and Masson's trichrome staining, and to improve the overall survival.

Conclusions

Selective PDE4 inhibition suppresses early inflammatory stage and attenuates the late stage of experimental pulmonary fibrosis.

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.

PDE4 inhibitors roflumilast and rolipram augment PGE2 inhibition of TGF-{beta}1-stimulated fibroblasts

Fibrotic diseases are characterized by the accumulation of extracellular matrix together with distortion and disruption of tissue architecture. Phosphodiesterase (PDE)4 inhibitors, by preventing the breakdown of cAMP, can inhibit fibroblast functions and may be able to mitigate tissue remodeling. Transforming growth factor (TGF)-beta1, a mediator of fibrosis, can potentially modulate cAMP by altering PGE(2) metabolism. The present study assessed whether PDE4 inhibitors functionally antagonize the profibrotic activity of fibroblasts stimulated by TGF-beta1. The PDE4 inhibitors roflumilast and rolipram both inhibited fibroblast-mediated contraction of three-dimensional collagen gels and fibroblast chemotaxis toward fibronectin in the widely studied human fetal lung fibroblast strain HFL-1 and several strains of fibroblasts from adult human lung. Roflumilast was approximately 10-fold more potent than rolipram. There was a trend for PDE4 inhibitors to inhibit more in the presence of TGF-beta1 (0.05 < P < 0.08). The effect of the PDE4 inhibitors was mediated through cAMP-stimulated protein kinase A (PKA), although a PKA-independent effect on gel contraction was also observed. The effect of PDE4 inhibitors depended on fibroblast production of PGE(2) and TGF-beta1-induced PGE(2) production. PDE4 inhibitors together with TGF-beta1 resulted in augmented PGE(2) production together with increased expression of COX mRNA and protein. The present study supports the concept that PDE4 inhibitors may attenuate fibroblast activities that can lead to fibrosis and that PDE4 inhibitors may be particularly effective in the presence of TGF-beta1-induced fibroblast stimulation.

PDE4 inhibitors: current status

Phosphodiesterase4 inhibitors are currently under development for the treatment of respiratory diseases including asthma and chronic obstructive pulmonary disease. The rationale for the development of this drug class stems from our understanding of the role of PDE4 in suppressing the function of a range of inflammatory and resident cells thought to contribute toward the pathogenesis of these diseases. Similarly, numerous preclinical in vivo studies have shown that PDE4 inhibitors suppress characteristic features of these diseases, namely, cell recruitment, activation of inflammatory cells and physiological changes in lung function in response to a range of insults to the airways. These potentially beneficial actions of PDE4 inhibitors have been successfully translated in phase II and III clinical trials with roflumilast and cilomilast. However, dose limiting side effects of nausea, diarrhoea and headache have tempered the enthusiasm of this drug class for the treatment of these respiratory diseases. A number of strategies are currently being pursued in attempts to improve clinical efficacy and reduce side effects, including delivery via the inhaled route, and/or development of non-emetic PDE4 inhibitors and mixed PDE inhibitors.

Reperfusion activates metalloproteinases that contribute to neurovascular injury

In this study, we examine the effects of reperfusion on the activation of matrix metalloproteinase (MMP) and assess the relationship between MMP activation during reperfusion and neurovascular injury. Ischemia was produced using suture-induced middle cerebral artery occlusion in rats. The MMP activation was examined with in situ and gel zymography. Injury to cerebral endothelial cells and basal lamina was assessed using endothelial barrier antigen (EBA) and collagen IV immunohistochemistry. Injury to neurons and glial cells was assessed using Cresyl violet staining. These were examined at 3 h after reperfusion (8 h after initiation of ischemia) and compared with permanent ischemia at the same time points to assess the effects of reperfusion. A broad-spectrum MMP inhibitor, AHA (p-aminobenzoyl-Gly-Pro-D-Leu-D-Ala-hydroxamate, 50 mg/kg intravenously) was administered 30 min before reperfusion to assess the roles of MMPs in activating gelatinolytic enzymes and in reperfusion-induced injury. We found that reperfusion accelerated and potentiated MMP-9 and MMP-2 activation and injury to EBA and collagen IV immunopositive microvasculature and to neurons and glial cells in ischemic cortex and striatum relative to permanent ischemia. Administering AHA 30 min before reperfusion decreased MMP-9 activation and neurovascular injury in ischemic cerebral cortex.

Phosphodiesterase type 4 expression and anti-proliferative effects in human pulmonary artery smooth muscle cells

Background

Pulmonary arterial hypertension is a proliferative vascular disease, characterized by aberrant regulation of smooth muscle cell proliferation and apoptosis in distal pulmonary arteries. Prostacyclin (PGI₂) analogues have anti-proliferative effects on distal human pulmonary artery smooth muscle cells (PASMCs), which are dependent on intracellular cAMP stimulation. We therefore sought to investigate the involvement of the main cAMP-specific enzymes, phosphodiesterase type 4 (PDE4), responsible for cAMP hydrolysis.

Methods

Distal human PASMCs were derived from pulmonary arteries by explant culture (n = 14, passage 3–12). Responses to platelet-derived growth factor-BB (5–10 ng/ml), serum, PGI₂ analogues (cicaprost, iloprost) and PDE4 inhibitors (roflumilast, rolipram, cilomilast) were determined by measuring cAMP phosphodiesterase activity, intracellular cAMP levels, DNA synthesis, apoptosis (as measured by DNA fragmentation and nuclear condensation) and matrix metalloproteinase-2 and -9 (MMP-2, MMP-9) production.

Results

Expression of all four PDE4A-D genes was detected in PASMC isolates. PDE4 contributed to the main proportion (35.9 ± 2.3%, n = 5) of cAMP-specific hydrolytic activity demonstrated in PASMCs, compared to PDE3 (21.5 ± 2.5%), PDE2 (15.8 ± 3.4%) or PDE1 activity (14.5 ± 4.2%). Intracellular cAMP levels were increased by PGI₂ analogues and further elevated in cells co-treated with roflumilast, rolipram and cilomilast. DNA synthesis was attenuated by 1 μM roflumilast (49 ± 6% inhibition), rolipram (37 ± 6%) and cilomilast (30 ± 4%) and, in the presence of 5 nM cicaprost, these compounds exhibited EC₅₀ values of 4.4 (2.6–6.1) nM (Mean and 95% confidence interval), 59 (36–83) nM and 97 (66–130) nM respectively. Roflumilast attenuated cell proliferation and gelatinase (MMP-2 and MMP-9) production and promoted the anti-proliferative effects of PGI₂ analogues. The cAMP activators iloprost and forskolin also induced apoptosis, whereas roflumilast had no significant effect.

Conclusion

PDE4 enzymes are expressed in distal human PASMCs and the effects of cAMP-stimulating agents on DNA synthesis, proliferation and MMP production is dependent, at least in part, on PDE4 activity. PDE4 inhibition may provide greater control of cAMP-mediated anti-proliferative effects in human PASMCs and therefore could prove useful as an additional therapy for pulmonary arterial hypertension.

Clinical Pharmacology of Cilomilast

Chronic obstructive pulmonary disease (COPD) is a multicomponent, chronic inflammatory disease of the lungs with systemic complications. The majority of the inflammation occurs in the peripheral airways and lung parenchyma. It is a progressive disease, leading to disability and eventual death, despite conventional therapy. Inflammatory activity can be reduced by increasing intracellular cyclic adenosine-3',5'-monophosphate (cAMP) through inhibition of phosphodiesterase (PDE) IV, the principal PDE isoenzyme within pro-inflammatory cells, including eosinophils, mast cells, macrophages, lymphocytes, neutrophils and epithelial cells. PDE IV inhibition also has other effects, including relaxation of airway smooth muscle, suppression of smooth muscle mitogenesis and modulation of excitatory activity in pulmonary nerves. Cilomilast is a systemically available, second-generation, selective PDE IV inhibitor. It retains the therapeutic activity of the first-generation PDE IV inhibitors but lacks their profound emetic effect. Cilomilast is the first drug to demonstrate a reduction of tissue cells considered central to the ongoing inflammatory process (macrophages and CD8+ lymphocytes) in patients with stable COPD. Cilomilast is completely absorbed following oral administration and has negligible first-pass metabolism. It exhibits linear pharmacokinetics, with low between-subject variability. Cilomilast is highly protein bound (99.4%), but this binding is concentration-independent at clinically relevant doses, and it has a small volume of distribution at steady state (17L). Plasma clearance (approximately 2 L/h) is almost entirely metabolic, through multiple parallel pathways. Its terminal elimination half-life is approximately 6.5 hours and steady state is rapidly achieved with twice-daily administration. The most abundant metabolite, formed by the action of cytochrome P450 2C8, has <10% of the activity of the parent molecule. Cilomilast pharmacokinetics in COPD patients were consistent with those in healthy subjects. Smoking, age and ethnicity had no clinically relevant effects. Total plasma cilomilast pharmacokinetic parameters did not change significantly with renal or hepatic impairment, but concentrations of unbound cilomilast increased with declining renal or hepatic function. Cilomilast had no clinically relevant interactions with a range of drugs likely to be coadministered to patients with COPD, with the exception of erythromycin where concurrent administration with cilomilast was associated with an increased incidence of gastrointestinal adverse events, a pharmacodynamic interaction predicted by their secondary pharmacology. Nausea was the principal adverse reaction seen in healthy subjects taking cilomilast, but this was reduced by administration with food or by use of simple dose-escalation regimens. Cilomilast has not shown a propensity for any of the serious cardiac or neurological adverse effects associated with theophylline. Cilomilast exhibits favourable and predictable pharmacokinetics, has few clinically relevant drug-drug interactions and has demonstrated effects on measures of inflammation of potential benefit in the treatment of COPD. It is generally well tolerated and has not generated safety concerns in any clinical study.

LPS-Induced Acute Lung Injury is Attenuated by Phosphodiesterase Inhibition: Effects on Proinflammatory Mediators, Metalloproteinases, NF-??B, and ICAM-1 Expression

BACKGROUND

Acute endotoxemia is characterized by an enhanced inflammatory response. Pentoxifylline (PTX), a phosphodiesterase inhibitor, has been shown to decrease TNF-alpha levels and to down-regulate neutrophil activation, likely because of increases in intracellular cyclic AMP. Its effects on lipopolysaccharide (LPS) induced lung injury, more specifically on tissue neutrophil infiltration and degranulation, adhesion molecule expression, and transcriptional factor activation, have not been fully investigated. We postulated that PTX treatment in acute endotoxemia downregulates the inflammatory response and may decrease lung injury.

METHODS

Male Sprague-Dawley rats were randomized into three groups: Sham (saline i.v.), LPS (5 mg/kg i.v.), and PTX + LPS (25 mg/kg and 5 mg/kg i.v., respectively; concomitant injection). After 4 hours, bronchoalveolar lavage fluid (BAL), plasma, and lungs were sampled. BAL IL-8 (ELISA), BAL MMP-2, plasma MMP-9, and BAL MMP-9 (Zymography) were measured. Lung histology (H&E), in addition to lung MPO, ICAM-1, and NF-kappaB expression evaluated by immunohistochemistry were analyzed. Lung NF-kappaB DNA binding was evaluated by electrophoretic mobility shift assay.

RESULTS

PTX treatment decreased BAL IL-8 levels, BAL MMP-2, and plasma MMP-9 activity. Lung neutrophil infiltration (MPO), ICAM-1 expression and NF-kappaB activation were decreased by PTX. In addition, PTX treatment caused a marked attenuation of LPS-induced lung injury.

CONCLUSIONS

Phosphodiesterase inhibition by PTX attenuates LPS-induced end-organ injury. In addition, proinflammatory cytokine production is also downregulated, likely because of the marked attenuation of NF-kappaB DNA binding and activation.

Roflumilast Fully Prevents Emphysema in Mice Chronically Exposed to Cigarette Smoke

RATIONALE

There is a need for new agents capable of suppressing the inflammatory response in chronic obstructive pulmonary disease.

OBJECTIVES

This study evaluated the effects of roflumilast, a phosphodiesterase 4 (PDE4) inhibitor on acute lung inflammation and chronic lung changes in models of cigarette exposure in mice.

METHODS

Roflumilast was given orally either at 1 mg/kg (R1) or at 5 mg/kg (R5). In the acute model (five cigarettes for 20 minutes), bronchoalveolar lavage fluid (BALF) changes were investigated at 4 and 24 hours. In the chronic model (three cigarettes/day for 7 months), morphometric and biochemical parameters were assessed at 7 months.

MEASUREMENTS AND MAIN RESULTS

Acute exposure caused a fivefold increase in BALF neutrophils. Both doses of roflumilast partially prevented (by 30%) this increase. In addition, after smoke exposure, R1 increased BALF interleukin-10 by 79% and R5 by 129%. Chronic smoke exposure caused a 1.8-fold increase in lung macrophage density, emphysema, an increase of the mean linear intercept (+21%), a decrease of the internal surface area (-13%), and a drop (-13%) in lung desmosine content. R1 did not have any effect, whereas R5 prevented the increase in lung macrophage density by 70% and fully prevented the other changes. In addition, in the smoke-exposure group, 63% of the mice showed goblet cell metaplasia, and neither of the doses of roflumilast had any effect.

CONCLUSIONS

This study shows for the first time that a PDE4 inhibitor partially ameliorates lung inflammation and fully prevents parenchymal destruction induced by cigarette smoke.

Evidence for a role of phosphodiesterase 4 in lipopolysaccharide-stimulated prostaglandin E2 production and matrix metalloproteinase-9 activity in human amniochorionic membranes

Chorioamniotic infection is a leading cause of preterm premature rupture of fetal membranes (amnion and chorion). Bacterial infection induces an inflammatory response characterized by elevated production of proinflammatory cytokines; the latter activate the production of both PGs that stimulate uterine contractions, and matrix metalloproteinases (MMPs) that degrade the extracellular matrix of the chorioamniotic membranes. The inflammatory response is under the control of cAMP content, which is partly regulated by phosphodiesterases (PDE). In this study, we investigated the role of the PDE4 family in the inflammatory process triggered by LPS in a model of amniochorionic explants. We found that PDE4 family is the major cAMP-PDE expressed in human fetal membranes and that PDE4 activity is increased by LPS treatment. Selective inhibition of PDE4 activity affected LPS signaling, because PDE4 inhibitors (rolipram and/or cilomilast) reduced the release of the proinflammatory cytokine TNF-alpha and increased the release of the anti-inflammatory cytokine IL-10. PDE4 inhibition reduced cyclooxygenase-2 protein expression and PGE(2) production and also modulated MMP-9, a key mediator of the membrane rupture process, by inhibiting pro-MMP-9 mRNA expression and pro-MMP-9 activity. These results demonstrate that the PDE4 family participates in the regulation of the inflammatory response associated with fetal membrane rupture during infection. The PDE4 family may be an appropriate pharmacological target for the management of infection-induced preterm delivery.

Regulation of MMP-9 gene expression for the development of novel molecular targets against cancer and inflammatory diseases

The need to pharmacologically control the proteolytic activity of matrix metalloproteinases (MMPs) has been commonly acknowledged, despite its limited efficacy in clinical trials. Among the reasons that explain this failure is our limited understanding of the signals that control the expression of MMPs in different cell types during different pathological conditions. Thus, future therapies must rely on more selective approaches. With the continually increasing body of proof implicating MMPs in a large number of diseases, it has become a priority to establish the pertinence of molecules involved in the signalling pathways leading to the expression of these enzymes. MMP-9 is a case in point: its dramatic overexpression in cancer and various inflammatory conditions clearly points to the molecular mechanisms controlling its expression as a potential target for eventual rational therapeutic intervention. In this article, recent progress in the signalling pathways that regulate MMP-9 expression is reviewed, and the latest strategies to be considered in the search for a specific inhibitor of its expression are presented.

Selective PDE4 inhibitors as potent anti-inflammatory drugs for the treatment of airway diseases

Phosphodiesterases (PDEs) are responsible for the breakdown of intracellular cyclic nucleotides, from which PDE4 are the major cyclic AMP metabolizing isoenzymes found in inflammatory and immune cells. This generated greatest interest on PDE4 as a potential target to treat lung inflammatory diseases. For example, cigarette smoke-induced neutrophilia in BAL was dose and time dependently reduced by cilomilast. Beside the undesired side effects associated with the first generation of PDE4 inhibitors, the second generation of selective inhibitors such as cilomilast and roflumilast showed clinical efficacy in asthma and chronic obstructive pulmonary diseases trials, thus re-enhancing the interest on these classes of compounds. However, the ability of PDE4 inhibitors to prevent or modulate the airway remodelling remains relatively unexplored. We demonstrated that selective PDE4 inhibitor RP 73-401 reduced matrix metalloproteinase (MMP)-9 activity and TGF-beta1 release during LPS-induced lung injury in mice and that CI-1044 inhibited the production of MMP-1 and MMP-2 from human lung fibroblasts stimulated by pro-inflammatory cytokines. Since inflammatory diseases of the bronchial airways are associated with destruction of normal tissue structure, our data suggest a therapeutic benefit for PDE4 inhibitors in tissue remodelling associated with chronic lung diseases.

PDE4 inhibition: a novel approach for the treatment of inflammatory bowel disease

Inflammation is a hallmark of inflammatory bowel disease (IBD), and elevation of cAMP levels can inhibit the pro-inflammatory and tissue-destructive properties of leukocytes. Phosphodiesterase 4 (PDE4) is the predominant enzyme that metabolizes cAMP in inflammatory cells, and the anti-inflammatory and immunomodulatory potential of PDE4 inhibitors in human leukocytes, endothelium and epithelium is well documented. Although PDE4 inhibitors have been investigated as treatments for several inflammatory diseases, this has focused mainly on asthma and chronic obstructive disease (COPD). Historically, their clinical utility has been limited by nausea and emesis. However, the PDE4 inhibitors cilomilast and roflumilast have recently shown efficacy in asthma and COPD, with a reduced propensity to cause nausea and emesis. In this review, we summarize for the first time the evidence that PDE4 inhibitors might have therapeutic benefit in IBD, and discuss mechanisms of action beyond the inhibition of inflammatory cells.

The fibroblast-populated collagen matrix as a model of wound healing: a review of the evidence

The fibroblast-populated collagen matrix (FPCM) has been utilized as an in vitro model of wound healing for more than 2 decades. It offers a reasonable approximation of the healing wound during the phases of established granulation tissue and early scar. The gross and microscopic morphology of the FPCM and the healing wound are similar at analogous phases. The processes of proliferation, survival/apoptosis, protein synthesis, and contraction act in similar directions in these two models, and the response to exogenous agents also is consistent between them. If its limitations are respected, then the FPCM can be used as a model of the healing wound.

Modulation of matrix metalloproteinase production from human lung fibroblasts by type 4 phosphodiesterase inhibitors

Over-expression of matrix metalloproteinases by lung fibroblasts has been blamed for much of the tissue destruction associated with airway inflammation. Because cyclic AMP is known to regulate fibroblast proliferation, as well as cytokine and extracellular matrix protein production, the current study was designed to evaluate the ability of three selective phosphodiesterase (PDE) type 4 inhibitors, rolipram, cilomilast and CI-1044, to inhibit extracellular matrix degradation. Using zymography and ELISA, we found that pro-MMP-2 release was enhanced following 24 h treatment of human lung fibroblast (MRC-5) with TGF-beta1 (10 ng/ml) or TNF-alpha (10 ng/ml), whereas PMA (0.02 microM) had no effect. One hour of pre-incubation with PDE4 inhibitors (10 microM) induced an inhibition of TNF-alpha-stimulated pro-MMP-2 release. Zymography and immunoblotting revealed that fibroblasts cultured with PMA or TNF-alpha released increased amounts of pro-MMP-1, whereas TGF-beta1 had no effect. Incubation with CI-1044 or cilomilast significantly prevented the TNF-alpha increase in pro-MMP-1. These results suggest that PDE4 inhibitors are effective in inhibiting the pro-MMP-2 and pro-MMP-1 secretion induced by TNF-alpha and might underline a potential therapeutic benefit of selective PDE4 inhibitors in lung diseases associated with abnormal tissue remodelling.

PDE4 inhibitors in COPD—a more selective approach to treatment

Chronic obstructive pulmonary disease (COPD) is a serious and mounting global public health problem. Although its pathogenesis is incompletely understood, chronic inflammation plays an important part and so new therapies with a novel anti-inflammatory mechanism of action may be of benefit in the treatment of COPD. Cilomilast and roflumilast are potent and selective phosphodiesterase (PDE)4 inhibitors, with an improved therapeutic index compared with the weak, non-selective PDE inhibitor, theophylline. Unlike theophylline, which is limited by poor efficacy and an unfavourable safety and tolerability profile, the selective PDE4 inhibitors are generally well tolerated, with demonstrated efficacy in improving lung function, decreasing the rate of exacerbations and improving quality of life, with proven anti-inflammatory effects in patients with COPD. Theophylline is a difficult drug to use clinically, requiring careful titration and routine plasma monitoring due to the risk of toxic side effects, such as cardiovascular and central nervous system adverse events, with dose adjustments required in many patients, including smokers, the elderly and some patients on concomitant medications. In contrast, the selective PDE4 inhibitors are convenient medications for both patient and physician alike. Hence these agents represent a therapeutic advance in the treatment of COPD, due to their novel mechanism of action and potent anti-inflammatory effects, coupled with a good safety and tolerability profile.

[Airway remodeling in asthma: mechanisms and therapeutic perspectives]

Although asthma is classically defined as reversible airflow obstruction and often remits in younger subjects with milder disease, a proportion of asthmatics experience chronic symptoms, episodic exacerbations and persistent airway obstruction, despite the continuous use of beta 2-agonists, associated with high doses of inhaled/oral corticosteroids. These patients contribute to the majority of asthma costs through hospitalization, emergency visits, absence from work or school and use of medication. Although the mechanisms behind irreversible airflow obstruction in asthma are unclear, a prominent role has been attributed to persistent structural changes of the bronchial wall, defined as airway remodeling. Studies conducted on endobronchial biopsy samples have led to the histopathological characterization of these tissue alterations, which include chronic mucosal inflammation, extensive epithelial damage, collagen deposition, subepithelial fibrosis, increased mucous glands and airway smooth muscle hypertrophy and/or hyperplasia. Several factors, such as polypeptide growth factors and their receptors, matrix metalloproteases, intracellular molecules controlling cell death and survival, adhesion molecules and their ligands, as well a large variety of cytotoxic pro-inflammatory mediators are likely to contribute to the onset and maintenance of these tissue abnormalities. However, to date, the cellular and molecular events driving specifically these phenomena and allowing asthmatics with persistent airflow limitation to be distinguished from patients who normalize their bronchial obstruction upon adequate therapeutic management have not been identified yet. Accordingly, airway remodeling represents a major research challenge, particularly in view of the development of new therapeutic strategies specifically addressed at alleviating persistent bronchial obstruction in these otherwise intractable patients.