Phosphodiesterase 4 inhibitors in chronic obstructive pulmonary disease: a new approach to oral treatment

Anti-inflammatory activity of non-selective PDE inhibitor aminophylline on the lung tissue and respiratory parameters in animal model of ARDS

Acute respiratory distress syndrome (ARDS) is a common complication of critical illness characterized by lung inflammation, epithelial and endothelial dysfunction, alveolar-capillary leakage, and worsening respiratory failure. The present study aimed to investigate the anti-inflammatory effects of non-selective phosphodiesterase (PDE) inhibitor aminophylline. New Zealand white rabbits were randomly divided into 3 groups: animals with respiratory failure defined as PaO₂/FiO₂ ratio (P/F) below < 26.7 kPa, and induced by saline lung lavage (ARDS), animals with ARDS treated with intravenous aminophylline (1 mg/kg; ARDS/AMINO), and healthy ventilated controls (Control). All animals were oxygen ventilated for an additional 4 h and respiratory parameters were recorded regularly. Post mortem, the lung tissue was evaluated for oedema formation, markers of inflammation (tumor necrosis factor, TNFα, interleukin (IL)-1β, -6, -8, -10, -13, -18), markers of epithelial damage (receptor for advanced glycation end products, RAGE) and endothelial injury (sphingosine 1-phosphate, S1P), oxidative damage (thiobarbituric acid reactive substances, TBARS, 3-nitrotyrosine, 3NT, total antioxidant capacity, TAC). Aminophylline therapy decreased the levels of pro-inflammatory cytokines, markers of epithelial and endothelial injury, oxidative modifications in lung tissue, reduced lung oedema, and improved lung function parameters compared to untreated ARDS animals. In conclusion, non-selective PDE inhibitor aminophylline showed a significant anti-inflammatory activity suggesting a potential of this drug to be a valuable component of ARDS therapy.

An Overview of PDE4 Inhibitors in Clinical Trials: 2010 to Early 2022

Since the early 1980s, phosphodiesterase 4 (PDE4) has been an attractive target for the treatment of inflammation-based diseases. Several scientific advancements, by both academia and pharmaceutical companies, have enabled the identification of many synthetic ligands for this target, along with the acquisition of precise information on biological requirements and linked therapeutic opportunities. The transition from pre-clinical to clinical phase was not easy for the majority of these compounds, mainly due to their significant side effects, and it took almost thirty years for a PDE4 inhibitor to become a drug i.e., Roflumilast, used in the clinics for the treatment of chronic obstructive pulmonary disease. Since then, three additional compounds have reached the market a few years later: Crisaborole for atopic dermatitis, Apremilast for psoriatic arthritis and Ibudilast for Krabbe disease. The aim of this review is to provide an overview of the compounds that have reached clinical trials in the last ten years, with a focus on those most recently developed for respiratory, skin and neurological disorders.

Phosphodiesterase Inhibitors in Acute Lung Injury: What Are the Perspectives?

Despite progress in understanding the pathophysiology of acute lung damage, currently approved treatment possibilities are limited to lung-protective ventilation, prone positioning, and supportive interventions. Various pharmacological approaches have also been tested, with neuromuscular blockers and corticosteroids considered as the most promising. However, inhibitors of phosphodiesterases (PDEs) also exert a broad spectrum of favorable effects potentially beneficial in acute lung damage. This article reviews pharmacological action and therapeutical potential of nonselective and selective PDE inhibitors and summarizes the results from available studies focused on the use of PDE inhibitors in animal models and clinical studies, including their adverse effects. The data suggest that xanthines as representatives of nonselective PDE inhibitors may reduce acute lung damage, and decrease mortality and length of hospital stay. Various (selective) PDE3, PDE4, and PDE5 inhibitors have also demonstrated stabilization of the pulmonary epithelial-endothelial barrier and reduction the sepsis- and inflammation-increased microvascular permeability, and suppression of the production of inflammatory mediators, which finally resulted in improved oxygenation and ventilatory parameters. However, the current lack of sufficient clinical evidence limits their recommendation for a broader use. A separate chapter focuses on involvement of cyclic adenosine monophosphate (cAMP) and PDE-related changes in its metabolism in association with coronavirus disease 2019 (COVID-19). The chapter illuminates perspectives of the use of PDE inhibitors as an add-on treatment based on actual experimental and clinical trials with preliminary data suggesting their potential benefit.

Effects of intravenous phosphodiesterase inhibitors and corticosteroids on severe meconium aspiration syndrome

BACKGROUND

Meconium aspiration syndrome (MAS) is a major cause of severe respiratory failure in near- and full-term neonates. Alleviating inflammation is key to successfully treating severe MAS. Phosphodiesterase (PDE) inhibitors are known to play a role in airway smooth muscle relaxation and alveolar inflammation inhibition. This study aimed to investigate the effects of various intravenous (IV) PDE inhibitors and corticosteroids on MAS.

METHODS

MAS was induced in newborn piglets by instilling human meconium in them. The piglets were randomly divided into five groups (n = 5 in each group): (1) control (sham treatment); (2) dexamethasone (Dex) (IV 0.6 mg/kg of dexamethasone); (3) aminophylline (Ami) (IV 6 mg/kg of aminophylline, followed by continuous infusion of 0.5 mg/kg/h of aminophylline; (4) milrinone (Mil) (IV 50 μg/kg of milrinone, followed by continuous infusion of 0.75 μg/kg/h of milrinone); and (5) rolipram (Rol) (IV 0.8 mg/kg of rolipram). The duration of the experimental period was 4 hours.

RESULTS

Compared to the control group, all the four treatment groups revealed better oxygenation 3 hours and more after the start of treatment. The Rol group had a significantly elevated heart beat (p < 0.05) and relatively lower blood pressure compared to the other groups during the first 2 hours of the experiment. The Dex group had significantly lower interleukin (IL)-1β levels in the lung tissue compared to the other groups (p < 0.05) and significantly lower IL-6 levels compared to the Ami and Mil groups (p < 0.05). Lung histology showed slightly less inflammation and atelectasis in the Dex group compared to the other groups, but lung injury scores showed no significant between-group differences.

CONCLUSION

Using IV corticosteroids or any type of PDE inhibitors has some beneficial effects in improving oxygenation in MAS. PDE inhibitors are not superior to IV corticosteroids; in fact, adverse cardiovascular effects occur with the phosphodiesterase type 4 (PDE4) inhibitor. Further investigations are required before using IV corticosteroids and PDE inhibitors in future clinical application.

Relaxant effect of Lippia origanoides essential oil in guinea-pig trachea smooth muscle involves potassium channels and soluble guanylyl cyclase

ETHNOPHARMACOLOGICAL RELEVANCE

Lippia origanoides H.B.K. is an aromatic species used in folk medicine to treat respiratory diseases, including asthma.

AIM OF THE STUDY

The aim of this work was to evaluate the relaxing potential and mechanism of action of the L. origanoides (LOO) essential oil in isolated guinea-pig trachea.

MATERIALS AND METHODS

Leaves from L. origanoides were collected at experimental fields under organic cultivation, at the Forest Garden of Universidade Estadual de Feira de Santana. Essential oil was extracted by hydrodistillation, analyzed by GC/FID and GC/MS and the volatile constituents were identified. Spasmolytic activity and relaxant mechanism of LOO were assayed in isolated guinea-pig trachea contracted with histamine, carbachol or hyperpolarizing KCl.

RESULTS

Chemical analysis revealed the presence of carvacrol (53.89%) as major constituent. LOO relaxed isolated guinea-pig trachea pre-contracted with KCl 60 mM [EC₅₀ = 30.02 μg/mL], histamine 1 µM [EC₅₀ = 9.28 μg/mL] or carbachol 1 µM [EC₅₀ = 51.80 μg/mL]. The pre-incubation of glibenclamide, CsCl, propranolol, indomethacin, hexamethonium, aminophylline or L-NAME in histamine-induced contractions did not alter significantly the relaxant effect of LOO. However, the presence of 4-aminopyridine, tetraethylammonium or methylene blue reduced LOO effect, while the presence of dexamethasone or atropine potentialized the LOO relaxant effect. LOO pre-incubation inhibited carbachol-evoked contractions, with this effect potentialized in the presence of sodium nitroprusside and blocked in the presence of ODQ.

CONCLUSIONS

The relaxant mechanism of LOO on the tracheal smooth muscle possibly involves stimulating of soluble guanylyl cyclase with consequent activation of the voltage-gated and Ca²⁺-activated K⁺ channels.

Rare Variants Association Analysis in Large-Scale Sequencing Studies at the Single Locus Level

Genetic association analyses of rare variants in next-generation sequencing (NGS) studies are fundamentally challenging due to the presence of a very large number of candidate variants at extremely low minor allele frequencies. Recent developments often focus on pooling multiple variants to provide association analysis at the gene instead of the locus level. Nonetheless, pinpointing individual variants is a critical goal for genomic researches as such information can facilitate the precise delineation of molecular mechanisms and functions of genetic factors on diseases. Due to the extreme rarity of mutations and high-dimensionality, significances of causal variants cannot easily stand out from those of noncausal ones. Consequently, standard false-positive control procedures, such as the Bonferroni and false discovery rate (FDR), are often impractical to apply, as a majority of the causal variants can only be identified along with a few but unknown number of noncausal variants. To provide informative analysis of individual variants in large-scale sequencing studies, we propose the Adaptive False-Negative Control (AFNC) procedure that can include a large proportion of causal variants with high confidence by introducing a novel statistical inquiry to determine those variants that can be confidently dispatched as noncausal. The AFNC provides a general framework that can accommodate for a variety of models and significance tests. The procedure is computationally efficient and can adapt to the underlying proportion of causal variants and quality of significance rankings. Extensive simulation studies across a plethora of scenarios demonstrate that the AFNC is advantageous for identifying individual rare variants, whereas the Bonferroni and FDR are exceedingly over-conservative for rare variants association studies. In the analyses of the CoLaus dataset, AFNC has identified individual variants most responsible for gene-level significances. Moreover, single-variant results using the AFNC have been successfully applied to infer related genes with annotation information.

Next-generation sequencing technologies have allowed genetic association studies of complex traits at the single base-pair resolution, where most genetic variants have extremely low mutation frequencies. These rare variants have been the focus of modern statistical-computational genomics due to their potential to explain missing disease heritability. The identification of individual rare variants associated with diseases can provide new biological insights and enable the precise delineation of disease mechanisms. However, due to the extreme rarity of mutations and large numbers of variants, significances of causative variants tend to be mixed inseparably with a few noncausative ones, and standard multiple testing procedures controlling for false positives fail to provide a meaningful way to include a large proportion of the causative variants. To address the challenge of detecting weak biological signals, we propose a novel statistical procedure, based on false-negative control, to provide a practical approach for variant inclusion in large-scale sequencing studies. By determining those variants that can be confidently dispatched as noncausative, the proposed procedure offers an objective selection of a modest number of potentially causative variants at the single-locus level. Results can be further prioritized or used to infer disease-associated genes with annotation information.

New drug therapies for COPD

Clinical trials with new drugs for chronic obstructive pulmonary disease (COPD) have been performed. Viruses exacerbate COPD and bacteria may play a part in severe COPD; therefore, antibiotic and antiviral approaches have a sound rationale. Antiinflammatory approaches have been studied. Advances in understanding the molecular basis of other processes have resulted in novel drugs to target reactive oxidant species, mucus, proteases, fibrosis, cachexia, and muscle wasting, and accelerated aging. Studies with monoclonal antibodies have been disappointing, highlighting the tendency for infections and malignancies during treatment. Promising future directions are lung regeneration with retinoids and stem cells.

Selective phosphodiesterase 3 inhibitor olprinone attenuates meconium-induced oxidative lung injury

Since inflammation and oxidation play a key role in the pathophysiology of neonatal meconium aspiration syndrome, various anti-inflammatory drugs have been tested in the treatment. This study evaluated whether the phosphodiesterase (PDE) 3 inhibitor olprinone can alleviate meconium-induced inflammation and oxidative lung injury. Oxygen-ventilated rabbits intratracheally received 4 ml/kg of meconium (25 mg/ml) or saline. Thirty minutes after meconium/saline instillation, meconium-instilled animals were treated by intravenous olprinone (0.2 mg/kg) or were left without treatment. All animals were oxygen-ventilated for an additional 5 h. A bronchoalveolar lavage (BAL) of the left lungs was performed and differential leukocyte count in the sediment was estimated. The right lungs were used to determine lung edema by wet/dry weight ratio, as well as to detect oxidative damage to the lungs. In the lung tissue homogenate, total antioxidant status (TAS) was determined. In isolated lung mitochondria, the thiol group content, conjugated dienes, thiobarbituric acid-reactive substances (TBARS), dityrosine, lysine-lipid peroxidation products, and activity of cytochrome c oxidase (COX) were estimated. To evaluate the effects of meconium instillation and olprinone treatment on the systemic level, TBARS and TAS were determined in the blood plasma, as well. Meconium instillation increased the relative numbers of neutrophils and eosinophils in the BAL fluid, increased edema formation and concentrations of oxidation markers, and decreased TAS. Treatment with olprinone reduced the numbers of polymorphonuclears in the BAL fluid, decreased the formation of most oxidation markers in the lungs, reduced lung edema and prevented a decrease in TAS in the lung homogenate compared to non-treated animals. In the blood plasma, olprinone decreased TBARS and increased TAS compared to the non-treated group. Conclusion, the selective PDE3 inhibitor olprinone has shown potent antioxidative and anti-inflammatory effects in the meconium-induced oxidative lung injury.

New pharmacological treatments for patients with chronic obstructive pulmonary disease (COPD)

BACKGROUND

Chronic Obstructive Pulmonary Disease (COPD) is a preventable and treatable disease characterized mainly by pulmonary airflow limitation that is not fully reversible. The airflow limitation is usually progressive and associated with abnormal inflammatory response of the lung to noxious particles or gasses. New different pharmacological approaches to decrease inflammation of the airways and consequently disease progression and increase airway obstruction reversibility have been developed.

METHODS AND RESULTS

A literature search using PubMed, Science Direct, EBSCO and free patents on line for the years 2000-2010.

CONCLUSIONS

Recent discoveries in the physiology and pathology of airways diseases have served to generate potential new drugs for the treatment of COPD patients. Several substances that block or activate specific pathways and receptors the aim of which is to decrease inflammation and increase airway obstruction reversibility are being used in different clinical protocols and hopefully will be available for patients in the near future.

Roflumilast: first phosphodiesterase 4 inhibitor approved for treatment of COPD

In April 2010, the European Medicines Agency Committee for Medicinal Products for Human Use recommended approval of roflumilast, a selective phosphodiesterase 4 inhibitor, for the “maintenance treatment of severe chronic obstructive pulmonary disease (COPD, FEV₁ postbronchodilator less than 50% predicted) associated with chronic bronchitis in adult patients with a history of frequent exacerbations as add-on to bronchodilator treatment”. This decision was based, in part, on the results of several large, international, multicenter, randomized, placebo-controlled trials of either six or 12 months’ duration that had been undertaken in COPD patients. Roflumilast 500 μg daily improved lung function and reduced exacerbations in patients with more severe COPD, especially those with chronic bronchitis, frequent exacerbations, or who required frequent rescue inhaler therapy in the placebo-controlled trials. It also improved lung function and reduced exacerbations in patients with moderately severe COPD treated with salmeterol or tiotropium. Advantages of roflumilast over inhaler therapy are that it is an oral tablet and only needs to be taken once daily. While taking roflumilast, the most common adverse effects patients experienced were gastrointestinal upset and headache. Weight loss, averaging 2.2 kg, occurred in patients treated with roflumilast. Patients taking roflumilast were more likely to drop out of the trials than patients in the control groups. Patients who discontinued therapy usually did so during the first few weeks and were more likely to have experienced gastrointestinal side effects. Roflumilast is the first selective phosphodiesterase 4 inhibitor and will offer physicians another treatment option for patients with more severe COPD.

Effect of Tanreqing Injection on treatment of acute exacerbation of chronic obstructive pulmonary disease with Chinese medicine syndrome of retention of phlegm and heat in Fei

OBJECTIVE

To explore the effect of Tanreqing Injection (TRQI) on the treatment of acute exacerbation of chronic obstructive pulmonary disease (AECOPD) with Chinese medicine syndrome of retention of phlegm and heat in Fei (RPHF).

METHODS

In a prospective randomized controlled clinical trial, 90 patients with AECOPD of RPHF syndrome were randomly assigned to 3 groups, TRQI and controls A and B, each with 30 cases. The TRQI group was administered with the intravenous injections of 20 mL TRQI once a day and conventional Western medicine treatment. Control group A was administered with the intravenous injection of 15 mg ambroxol hydrochloride twice a day and conventional Western medicine treatment, and control group B was administered with conventional Western medicine treatment only. The treatments were administered for 10 days. Chinese medical symptoms and signs were scored, and plasma concentrations of interleukin (IL)-8 and neutrophil elastase (NE) were recorded.

RESULTS

(1) The Chinese medical symptoms (cough, sputum amount, expectoration, dyspnea and fever) and signs (tongue and pulse) improved significantly in the TRQI group (P<0.05 or P<0.01), and improvements in cough, sputum amount and expectoration were better in the TRQI group than control group B (P<0.05); there was no significant difference between the TRQI group and control group A (P>0.05). The sign of tongue was also improved significantly in the TRQI group (P<0.05). (2) The overall effects in the TRQI group and control group A were significantly better than in control group B (P<0.05), with no significant differences between the TRQI group and control group A (P>0.05). There was no significant difference in the total effective rate among the three groups (P>0.05). (3) After treatment, the plasma concentrations of IL-8 and NE decreased in the TRQI group and control group A (P<0.05), and the concentration of IL-8 in control group B decreased (P<0.05). The difference in IL-8 was greater in the TRQI group than in control group A and B before and after treatment, and the change in NE was greater in control group A than in the TRQI group and control group B, but there was no statistical significance among the three groups with regards to the change in IL-8 or NE (P>0.05).

CONCLUSION

TRQI could improved the Chinese medical signs and symptoms in the patients with AECOPD, possibly because of the decreasing plasma levels of IL-8 and NE which could improve response to airway inflammation and mucus hypersecretion.

Zl-n-91, a selective phosphodiesterase 4 inhibitor, suppresses inflammatory response in a COPD-like rat model

Chronic obstructive pulmonary disease (COPD) is defined as a disease state characterized by poorly reversible airflow limitation induced by cigarette smoking and/or other noxious particle and gases. Phosphodiesterase (PDE) 4 inhibitors are known to elevated cAMP concentrations in inflammatory cells, leading to inhibition of inflammatory response, relaxation of smooth muscle in the airway, and modulation of sensory nerves in the lung as well. To investigate whether Zl-n-91, a new selective PDE4 inhibitor, could decrease inflammation and improve lung function in a COPD-like rat model, male Sprague-Dawley rats are used to challenge with lipopolysaccharide (LPS) and cigarette smoking (CS) exposure to induce COPD-like animal model. Administration of Zl-n-91 at different dosages results in decreases of inflammatory cell in bronchoalveolar lavage fluid (BALF) as compared with vehicle treatment. Zl-n-91 at 0.03, 0.3 or 3mg/kg not only dose-dependently inhibited PDE4 activity, but also decreased MMP-9 level in lungs and improved dynamic compliance (C(dyn)) as compared with vehicle treatment. Therefore, Zl-n-91 could inhibit inflammatory responses in rats after cigarette smoking exposure and LPS challenge, and it could be of some therapeutic potential as an alternative medicine in treatment of pulmonary diseases such as COPD.

New drugs for exacerbations of chronic obstructive pulmonary disease

Tobacco smoking is the dominant risk factor for chronic obstructive pulmonary disease (COPD), but viral and bacterial infections are the major causes of exacerbations in later stages of disease. Reactive oxygen species (ROS), pathogen-associated molecular patterns (PAMPs), and damage-associated molecular patterns (DAMPs) activate families of pattern recognition receptors (PRRs) that include the toll-like receptors (TLRs). This understanding has led to the hypothesis that COPD is an archetypal disease of innate immunity. COPD is characterised by abnormal response to injury, with altered barrier function of the respiratory tract, an acute phase reaction, and excessive activation of macrophages, neutrophils, and fibroblasts in the lung. The activated non-specific immune system then mediates the processes of inflammation and repair, fibrosis, and proteolysis. COPD is also associated with corticosteroid resistance, abnormal macrophage and T-cell populations in the airway, autoinflammation and autoimmunity, aberrant fibrosis, accelerated ageing, systemic and concomitant disease, and defective regeneration. Such concepts have been used to generate a range of molecular targets, and clinical trials are taking place to identify effective drugs for the prevention and treatment of COPD exacerbations.