Acute effects of sildenafil on exercise pulmonary hemodynamics and capacity in patients with COPD

Effects of Phosphodiesterase-5 Inhibitors in Patients with Chronic Obstructive Pulmonary Disease: A Systematic Review and Meta-Analysis

Chronic obstructive pulmonary disease (COPD) is a major burden of healthcare worldwide. We aimed to determine the effects of PDE-5 inhibitors on clinical outcomes and haemodynamic parameters in patients with COPD. A PROSPERO-registered systematic review and meta-analysis (identification number CRD42021227578) were performed to analyse the effects of PDE-5 inhibitors in patients with COPD. Data were sourced from MEDLINE, EMBASE, Cochrane Register of Controlled Trials and "ClinicalTrials.gov." Randomised controlled trials (RCTs) comparing PDE-5 inhibitors with control in patients with COPD were included. Quality assessment was carried out using the Cochrane Collaboration's tool for assessing the risk of bias in randomised trials. The pooled mean difference of 6-minute walk distance (6MWD) and mean pulmonary arterial pressure based on inverse variance estimation were analysed with a fixed-effect model or random-effects model meta-analysis. Nine RCTs involving 414 patients were included in the review. There was no significant difference in 6MWD (mean difference = 22.06 metres, 95% confidence interval (CI), -5.80 to 49.91). However, there was a statistically significant difference between PDE-5 inhibitor and control groups in mean pulmonary artery pressure (mean difference = -3.83 mmHg, 95% CI, -5.93 to -1.74). Headaches were the most common adverse event, occurring significantly in the PDE-5 inhibitor intervention group (odds ratio 3.83, 95% CI, 1.49 to 9.86). This systematic review indicates that PDE-5 inhibitors do not improve exercise capacity despite some possible improvements in haemodynamic parameters in COPD patients.

Secondary pulmonary arterial hypertension: to treat or not to treat?

PURPOSE OF REVIEW

The purpose of this review is to review recent literature related to mechanisms and treatment options for 'secondary' (i.e., WHO Groups 3 and 5) pulmonary arterial hypertension (PAH).

RECENT FINDINGS

Published randomized controlled trials, in general, do not support the use of approved therapies for 'primary' (i.e., WHO Group 1) PAH patients in patients with Group 3 PAH because of the small numbers of patients and inconsistent benefit. Therefore, we currently recommend against the use of these medications for Group 3 PAH. Similarly, there is limited evidence supporting the use of Group 1 PAH medications in Group 5 patients. In most patients with Group 5 PAH, treatment should be directed to the underlying disease.

SUMMARY

The utility of PAH-specific therapy in WHO Group 3 PAH is unclear because of the small numbers of patients evaluated and inconsistent beneficial effects observed. There is limited evidence supporting the use of PAH medications in Group 5 patients, and they may be harmful in some cases.

Right Heart Catheterization During Exercise in Patients with COPD-An Overview of Clinical Results and Methodological Aspects

While right heart catheterization (RHC) at rest is the gold standard to assess pulmonary hemodynamics in patients with chronic obstructive pulmonary disease (COPD) and pulmonary hypertension (PH), the invasive measurement of exercise hemodynamics is less well established in this group. Since exercise hemodynamics are increasingly recognized as important clinical information in patients with PH, our goal was to review the literature in this field to provide a basis for clinical use, further studies, and future recommendations. We identified 69 studies (published since 1968) reporting RHC data in 2819 patients with COPD, of whom 2561 underwent exercise testing. Few studies simultaneously measured gas exchange during exercise. Overall, these studies showed large variations in the patient populations and research questions studied and the methods and definitions employed. Despite these limitations, the data consistently demonstrated the presence of precapillary PH at rest in up to 38% of patients with COPD. With exercise, a relevant proportion of patients developed an abnormal hemodynamic response, depending on the definition used. Furthermore, some studies assessed right ventricular function during exercise and showed a blunted increase in right ventricular ejection fraction. Drug effects and the impact of interventional procedures were also studied. Again, due to large variations in the patients studied and the methods used, firm conclusions are difficult to derive. Despite the limitations of this dataset, several recommendations with respect to technical aspects (body position, exercise protocol, and data acquisition) can be inferred for this challenging patient population and may be helpful for further studies or recommendations.

Intravenous sildenafil acutely improves hemodynamic response to exercise in patients with connective tissue disease

Background

Hemodynamic assessment during exercise may unmask an impaired functional reserve of the right ventricle and the pulmonary vasculature in patients with connective tissue disease. We assessed the effect of intravenous sildenafil on the hemodynamic response to exercise in patients with connective tissue disease.

Methods

In this proof-of-concept study, patients with connective tissue disease and mean pulmonary arterial pressure (mPAP) >20 mm Hg were subjected to a supine exercise hemodynamic evaluation before and after administration of intravenous sildenafil 10 mg.

Results

Ten patients (four with moderately elevated mPAP 21–24 mm Hg; six with mPAP >25 mm Hg) underwent hemodynamic assessment. All of them showed markedly abnormal exercise hemodynamics. Intravenous sildenafil was well tolerated and had significant hemodynamic effects at rest and during exercise, although without pulmonary selectivity. Sildenafil reduced median total pulmonary resistance during exercise from 6.22 (IQR 4.61–8.54) to 5.24 (3.95–6.96) mm Hg·min·L^-1 (p = 0.005) and increased median pulmonary arterial capacitance during exercise from 1.59 (0.93–2.28) to 1.74 (1.12–2.69) mL/mm Hg (p = 0.005).

Conclusions

In patients with connective tissue disease who have an abnormal hemodynamic response to exercise, intravenous sildenafil improved adaption of the right ventricular-pulmonary vascular unit to exercise independent of resting mPAP. The impact of acute pharmacological interventions on exercise hemodynamics in patients with pulmonary vascular disease warrants further investigation.

Trial registration

Clinicaltrials.gov NCT01889966.

Inhaled sGC Modulator Can Lower PH in Patients With COPD Without Deteriorating Oxygenation

This study uses a highly fidelity computational simulator of pulmonary physiology to evaluate the impact of a soluble guanylate cyclase (sGC) modulator on gas exchange in patients with chronic obstructive pulmonary disease (COPD) and pulmonary hypertension (PH) as a complication. Three virtual patients with COPD were configured in the simulator based on clinical data. In agreement with previous clinical studies, modeling systemic application of an sGC modulator results in reduced partial pressure of oxygen (PaO2 ) and increased partial pressure of carbon dioxide (PaCO2 ) in arterial blood, if a drug-induced reduction of pulmonary vascular resistance (PVR) equal to that observed experimentally is assumed. In contrast, for administration via dry powder inhalation (DPI), our simulations suggest that the treatment results in no deterioration in oxygenation. For patients under exercise, DPI administration lowers PH, whereas oxygenation is improved with respect to baseline values.

Influence of dietary nitrate supplementation on lung function and exercise gas exchange in COPD patients

BACKGROUND

During exercise as pulmonary blood flow rises, pulmonary capillary blood volume increases and gas exchange surface area expands through distention and recruitment. We have previously demonstrated that pulmonary capillary recruitment is limited in COPD patients with poorer exercise tolerance. Hypoxia and endothelial dysfunction lead to pulmonary vascular dysregulation possibly in part related to nitric oxide related pathways.

PURPOSE

To determine if increasing dietary nitrate might influence lung surface area for gas exchange and subsequently impact exercise performance.

METHODS

Subjects had stable, medically treated COPD (n = 25), gave informed consent, filled out the St George Respiratory Questionnaire (SGRQ), had a baseline blood draw for Hgb, performed spirometry, and had exhaled nitric oxide (exNO) measured. Then they performed the intra-breath (IB) technique for lung diffusing capacity for carbon monoxide (DLCO) as well as pulmonary blood flow (Qc). Subsequently they completed a progressive semi-recumbent cycle ergometry test to exhaustion with measures of oxygen saturation (SpO₂) and expired gases along with DLCO and Qc measured during the 1st work load only. Subjects were randomized to nitrate supplement group (beetroot juice) or placebo group (black currant juice) for 8 days and returned for repeat of the above protocol.

RESULTS

Exhaled nitric oxide levels rose >200% in the nitrate group (p < 0.05) with minimal change in placebo group. The SGRQ suggested a small fall in perceived symptom limitation in the nitrate group, but no measure of resting pulmonary function differed post nitrate supplementation. With exercise, there was no influence of nitrate supplementation on peak VO₂ or other measures of respiratory gas exchange. There was a tendency for the exercise DLCO to increase slightly in the nitrate group with a trend towards a rise in the DLCO/Qc relationship (p = 0.08) but not in the placebo group. The only other significant finding was a fall in the exercise blood pressure in the nitrate group, but not placebo group (p < 0.05).

CONCLUSION

Despite evidence of a rise in exhaled nitric oxide levels with nitrate supplementation, there was minimal evidence for improvement in exercise performance or pulmonary gas exchange surface area in a stable medically treated COPD population.

Pulmonary hypertension associated with lung diseases and hypoxemia

Pulmonary hypertension that develops in the setting of underlying lung diseases such as COPD or idiopathic pulmonary fibrosis (IPF) is associated with decreased functional status, worsening hypoxemia and quality of life, and increased mortality. This complication of lung disease is complex in its origin and carries a unique set of diagnostic and therapeutic issues. This review attempts to provide an overview of mechanisms associated with the onset of pulmonary hypertension in COPD and IPF, touches on appropriate evaluation, and reviews the state of knowledge on treating pulmonary hypertension related to underlying lung disease.

Pulmonary hypertension

In 2015, more than 800 papers were published in the field of pulmonary hypertension. A Clinical Year in Review article cannot possibly incorporate all this work and needs to be selective. The recently published European guidelines for the diagnosis and treatment of pulmonary hypertension contain an inclusive summary of all published clinical studies conducted until very recently. Here, we provide an overview of papers published after the finalisation of the guideline. In addition, we summarise recent advances in pulmonary vasculature science. The selection we made from the enormous amount of published work undoubtedly reflects our personal views and may not include all papers with a significant impact in the near or more distant future. The focus of this paper is on the diagnosis of pulmonary arterial hypertension, understanding the success of combination therapy on the right ventricle and scientific breakthroughs.

Severe pulmonary hypertension in lung disease: phenotypes and response to treatment

Pulmonary hypertension (PH) due to lung disease (World Health Organization (WHO) group 3) is common, but severe PH, arbitrarily defined as mean pulmonary artery pressure ≥35 mmHg is reported in only a small proportion. Whether these should be treated as patients in WHO group 1 (i.e.pulmonary arterial hypertension) with PH-targeted therapies is unknown.

We compared the phenotypic characteristics and outcomes of 118 incident patients with severe PH and lung disease with 74 idiopathic pulmonary arterial hypertension (IPAH) patients, all treated with pulmonary vasodilators.

Lung disease patients were older, more hypoxaemic, and had lower gas transfer, worse New York Heart Association functional class and lower 6-min walking distance (6MWD) than IPAH patients. Poorer survival in those with lung disease was driven by the interstitial lung disease (ILD) cohort.

In contrast to IPAH, where significant improvements in 6MWD and N-terminal pro-brain natruiretic peptide (NT-proBNP) occurred, PH therapy in severe PH lung disease did not lead to improvement in 6MWD or functional class, but neither was deterioration seen. NT-proBNP decreased from 2200 to 1596 pg·mL−1(p=0.015). Response varied by lung disease phenotype, with poorer outcomes in patients with ILD and emphysema with preserved forced expiratory volume in 1 s. Further study is required to investigate whether vasodilator therapy may delay disease progression in severe PH with lung disease.

Cigarette Smoke-Induced Emphysema and Pulmonary Hypertension Can Be Prevented by Phosphodiesterase 4 and 5 Inhibition in Mice

Rationale

Chronic obstructive pulmonary disease (COPD) is a widespread disease, with no curative therapies available. Recent findings suggest a key role of NO and sGC-cGMP signaling for the pathogenesis of the disease. Previous data suggest a downregulation/inactivation of the cGMP producing soluble guanylate cyclase, and sGC stimulation prevented cigarette smoke-induced emphysema and pulmonary hypertension (PH) in mice. We thus aimed to investigate if the inhibition of the cGMP degrading phosphodiesterase (PDE)5 has similar effects. Results were compared to the effects of a PDE 4 inhibitor (cAMP elevating) and a combination of both.

Methods

C57BL6/J mice were chronically exposed to cigarette smoke and in parallel either treated with Tadalafil (PDE5 inhibitor), Piclamilast (PDE4 inhibitor) or both. Functional measurements (lung compliance, hemodynamics) and structural investigations (alveolar and vascular morphometry) as well as the heart ratio were determined after 6 months of tobacco smoke exposure. In addition, the number of alveolar macrophages in the respective lungs was counted.

Results

Preventive treatment with Tadalafil, Piclamilast or a combination of both almost completely prevented the development of emphysema, the increase in lung compliance, tidal volume, structural remodeling of the lung vasculature, right ventricular systolic pressure, and right ventricular hypertrophy induced by cigarette smoke exposure. Single, but not combination treatment prevented or reduced smoke-induced increase in alveolar macrophages.

Conclusion

Cigarette smoke-induced emphysema and PH could be prevented by inhibition of the phosphodiesterases 4 and 5 in mice.

Exercise-induced pulmonary artery hypertension in a patient with compensated cardiac disease: hemodynamic and functional response to sildenafil therapy

We describe the case of a 54-year-old man who presented with exertional dyspnea and fatigue that had worsened over the preceding 2 years, despite a normally functioning bioprosthetic aortic valve and stable, mild left ventricular dysfunction (left ventricular ejection fraction, 0.45). His symptoms could not be explained by physical examination, an extensive biochemical profile, or multiple cardiac and pulmonary investigations. However, abnormal cardiopulmonary exercise test results and a right heart catheterization-combined with the use of a symptom-limited, bedside bicycle ergometer-revealed that the patient's exercise-induced pulmonary artery hypertension was out of proportion to his compensated left heart disease. A trial of sildenafil therapy resulted in objective improvements in hemodynamic values and functional class.

The role of phosphodiesterase inhibitors in the management of pulmonary vascular diseases

Phosphodiesterase inhibitors (PDE) can be used as therapeutic agents for various diseases such as dementia, depression, schizophrenia and erectile dysfunction in men, as well as congestive heart failure, chronic obstructive pulmonary disease, rheumatoid arthritis, other inflammatory diseases, diabetes and various other conditions. In this review we will concentrate on one type of PDE, mainly PDE5 and its role in pulmonary vascular diseases.

Cyclic nucleotide-based therapeutics for chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) defines a group of chronic inflammatory disorders of the airways that are characterised by a progressive and largely irreversible decline in expiratory airflow. Drugs used to treat COPD through actions mediated by cyclic AMP (cAMP) are restricted to long-acting and short-acting β2-adrenoceptor agonists and, in a subset of patients with chronic bronchitis, a phosphodiesterase 4 inhibitor, roflumilast. These agents relax airway smooth muscle and suppress inflammation. At the molecular level, these effects in the airways are mediated by two cAMP effectors, cAMP-dependent protein kinase and exchange proteins activated by cAMP. The pharmacology of newer agents, acting through these systems, is discussed here with an emphasis on their potential to interact and increase therapeutic effectiveness.

Pharmacologic treatments for pulmonary hypertension: exploring pharmacogenomics

Pulmonary hypertension (PH) is a disease with multiple etiologies and is categorized into five broad groups. Of these groups, pulmonary arterial hypertension (PAH) is the most studied and, therefore, all of the currently available drug classes (prostacyclin analogs, endothelin receptor antagonists and phosphodiesterase type 5 inhibitors) were developed to treat PAH. Thus, limited treatment data exist for the less-studied non-PAH forms of PH. Pharmacogenomics can be a tool to better understand the pathways involved in PH, as well as to improve personalization of therapy. However, little pharmacogenomic research has been carried out on this disease. New treatments for PH are on the horizon, deriving from both repurposed currently available drugs and novel therapeutics.

Ventilatory and cardiocirculatory exercise profiles in COPD: the role of pulmonary hypertension

BACKGROUND

Pulmonary hypertension (PH) is a well-recognized complication of COPD. The impact of PH on exercise tolerance is largely unknown. We evaluated and compared the circulatory and ventilatory profiles during exercise in patients with COPD without PH, with moderate PH, and with severe PH.

METHODS

Forty-seven patients, GOLD (Global Initiative for Chronic Obstructive Lung Disease)stages II to IV, underwent cardiopulmonary exercise testing and right-sided heart catheterization at rest and during exercise. Patients were divided into three groups based on mean pulmonary artery pressure (mPAP) at rest: no PH (mPAP, < 25 mm Hg), moderate PH (mPAP, 25-39 mm Hg),and severe PH (mPAP, ≥ 40 mm Hg). Mixed venous oxygen saturation (S VO 2 ) was used for evaluating the circulatory reserve. Pa CO 2 and the calculated breathing reserve were used for evaluation of the ventilatory reserve.

RESULTS

Patients without PH (n = 24) had an end-exercise S VO 2 of 48%± 9%, an increasing Pa CO 2 with exercise, and a breathing reserve of 22% ± 20%. Patients with moderate PH (n = 14) had an exercise S VO 2 of 40% ± 8%, an increasing Pa CO 2 , and a breathing reserve of 26% ± 15%. Patients with severe PH (n =9) had a significantly lower end-exercise S VO 2 (30% ± 6%), a breathing reserve of 37% ± 11%, and an absence of Pa CO 2 accumulation.

CONCLUSION

Patients with severe PH showed an exhausted circulatory reserve at the end of exercise.A profile of circulatory reserve in combination with ventilatory impairments was found inpatients with COPD and moderate or no PH. The results suggest that pulmonary vasodilation might only improve exercise tolerance in patients with COPD and severe PH.

Pulmonary arterial lesions in explanted lungs after transplantation correlate with severity of pulmonary hypertension in chronic obstructive pulmonary disease

BACKGROUND

Pulmonary vascular findings are largely unreported in end-stage chronic obstructive pulmonary disease (COPD).

METHODS

Pulmonary vascular lesions in explanted lungs from 70 patients with COPD/emphysema or α-1-antitrypsin deficiency were analyzed retrospectively. Patients were stratified by the presence and severity of pulmonary hypertension (PH) assessed by right-heart catheterization in 3 hemodynamically distinct groups: (1) non-PH (mean pulmonary arterial pressure [mPAP]<25 mm Hg), (2) mild to moderate PH (mPAP, 25-34 mm Hg), and (3) severe PH (mPAP≥35 mm Hg). The control group comprised 18 patients with idiopathic pulmonary arterial hypertension (IPAH). Vascular lesions were graded 1-6 according to a modified Heath and Edwards (HE) scale.

RESULTS

All COPD patients were in New York Heart Association Functional Class III-IV (forced expiratory volume in 1 second, 23%±8%; total lung capacity, 128%±20% of predicted). Non-PH group: 30 patients (60% women) aged 54±6 years; mPAP, 17.2±3.8 mm Hg; median HE Grade 1 (range, 0-3), with medial hypertrophy of muscular pulmonary arteries and muscularization of pulmonary arterioles. Mild-moderate PH group: 30 patients (50% women) aged 53±6 years; mPAP, 28.6±2.8 mm Hg; median HE Grade 3 (range, 1-3), with additional cellular intimal proliferation. Severe PH group: 10 patients (50% women) aged 54±6 years; mPAP, 40.7±5.2 mm Hg; median HE Grade 3 (range, 2-5), with additional intimal fibrosis. IPAH controls: 18 patients (67% women) aged 36±4 years; mPAP,>50 mm Hg; median HE Grade 4 (range 3-6), with generalized arterial dilatation and plexiform lesions.

CONCLUSIONS

The extent of pulmonary vascular lesions in COPD correlate with the severity of PH. Morphologic lesions similar to those characteristic of IPAH can be observed as PH in COPD progresses to levels characteristic of IPAH.

World Health Organization Group III pulmonary hypertension

Pulmonary hypertension in the setting of parenchymal lung disease and conditions associated with chronic hypoxemia is commonly encountered in clinical practice and may adversely affect patients' function and mortality. Diagnosis of this subgroup of pulmonary hypertension has evolved but still requires right heart catheterization for confirmation. The primary treatment goal is optimization of the underlying parenchymal lung or hypoxemia-associated condition prior to consideration of pharmacologic therapy. Limited published experience with pulmonary hypertension-specific medications for treatment of WHO Group 3 pulmonary hypertension suggests symptomatic and functional benefit in selected individuals. The potential for worsening ventilation-perfusion matching must be considered in these cases, however, since there is a paucity of data regarding the optimal approach to treatment selection. Ongoing medication trials and further investigation of mechanisms of hypoxic pulmonary vasoconstriction provide hope for these patients who in the past often had only lung transplantation as a potential treatment option.

Udenafil improves exercise capacity in patients with chronic obstructive pulmonary disease: a prospective study

Pulmonary hypertension (PH) is a serious complication of chronic obstructive pulmonary disease (COPD), and there is no effective pharmacological treatment for COPD-associated PH. We evaluated the effect of udenafil, a phosphodiesterase-5 (PDE-5) inhibitor, on the exercise capacity of patients with severe COPD. Patients with severe and very severe COPD (forced expiratory volume in one second (FEV(1)) <50% of predicted) received udenafil (50 mg daily) for 8 weeks. A 6-min walk test (6MWT), lung function test, Doppler echocardiography, and Saint George's Respiratory Questionnaire (SGRQ) were completed before and after therapy. The primary outcome was a change in the 6-min walk distance (6MWD). Thirty-eight patients were screened for eligibility, and 23 completed the study. After 8 weeks of udenafil treatment, the mean 6MWD increased from 315 to 348 m (p = 0.02), and median PASP decreased from 36 to 30 mmHg (p = 0.02). There were no changes in the SGRQ score, Borg dyspnea score, or pulmonary function parameters. The PDE-5 inhibitor udenafil improved exercise capacity and decreased pulmonary artery pressure in patients with severe COPD. However, due to the small sample size, uncontrolled design and high dropout rate, the efficacy of udenafil in severe COPD needs to be confirmed in a large-scale randomized controlled study. This study was registered at ClinicalTrials.gov (number: NCT01364181).

Pulmonary Hypertension Secondary to COPD

The development of pulmonary hypertension in COPD adversely affects survival and exercise capacity and is associated with an increased risk of severe acute exacerbations. Unfortunately not all patients with COPD who meet criteria for long term oxygen therapy benefit from it. Even in those who benefit from long term oxygen therapy, such therapy may reverse the elevated pulmonary artery pressure but cannot normalize it. Moreover, the recent discovery of the key roles of endothelial dysfunction and inflammation in the pathogenesis of PH provides the rationale for considering specific pulmonary vasodilators that also possess antiproliferative properties and statins.

Sildenafil for chronic obstructive pulmonary disease: a randomized crossover trial

RATIONALE

Pulmonary hypertension with exercise is common in chronic obstructive pulmonary disease (COPD) and may contribute to exercise limitation in this disease. We aimed to determine the effects of treatment with sildenafil on exercise capacity in patients with COPD and emphysema.

METHODS

We performed a randomized, double-blind, placebo-controlled 2-period crossover trial of sildenafil thrice daily in ten adults with COPD and emphysema on CT scan without pulmonary hypertension. We randomized study participants to 4 weeks of sildenafil (or placebo) followed by a 1-week washout and then 4 weeks of placebo (or sildenafil). The 2 primary outcomes were the 6-minute walk distance and oxygen consumption at peak exercise.

RESULTS

Sildenafil had no effect on 6-minute walk distance (placebo-corrected difference = -7.8 m, 95% confidence interval, -23.2 to 7.5 m, p = 0.35) or oxygen consumption at peak exercise (placebo-corrected difference = -0.1 ml/kg/min, 95% confidence interval -2.1 to 1.8 ml/kg/min, p = 0.89). Sildenafil increased the alveolar-arterial oxygen gradient (p = 0.02), worsened symptoms (p = 0.04), and decreased quality-of-life (p = 0.03). Adverse events were more frequent while receiving sildenafil (p = 0.005).

CONCLUSIONS

Routine sildenafil administration did not have a beneficial effect on exercise capacity in patients with COPD and emphysema without pulmonary hypertension. Sildenafil significantly worsened gas exchange at rest and quality of life. (clinicaltrials.gov NCT00104637).

Chronic obstructive pulmonary disease: a concise review

Globally, chronic obstructive pulmonary disease (COPD) is a major cause of significant morbidity and mortality, and is now the third leading cause of death in the United States. Over the past 15 years there has been a surge of bench and translational research regarding the genetics and pathogenesis of COPD, and several large-scale clinical trials have introduced new treatment paradigms for COPD. Current research also demonstrates that COPD is not just a lung disease and that there are several potential extrapulmonary manifestations and comorbidities that should be evaluated and treated when one identifies an individual as having COPD.

Harnessing the clinical efficacy of phosphodiesterase 4 inhibitors in inflammatory lung diseases: dual-selective phosphodiesterase inhibitors and novel combination therapies

Phosphodiesterase (PDE) 4 inhibitors have been in development as a novel anti-inflammatory therapy for more than 20 years, with asthma and chronic obstructive pulmonary disease (COPD) being primary indications. Despite initial optimism, only one selective PDE4 inhibitor, roflumilast (Daxas (®)), has been approved for use in humans and available in Canada and the European Union in 2011 for the treatment of a specific population of patients with severe COPD. In many other cases, the development of PDE4 inhibitors of various structural classes has been discontinued due to lack of efficacy and/or dose-limiting adverse events. Indeed, for many of these compounds, it is likely that the maximum tolerated dose is either subtherapeutic or at the very bottom of the efficacy dose-response curve. Thus, a significant ongoing challenge that faces the pharmaceutical industry is to synthesize compounds with therapeutic ratios that are superior to roflumilast. Several strategies are being considered, but clinically effective compounds with an optimal pharmacophore have not, thus far, been reported. In this chapter, alternative means of harnessing the clinical efficacy of PDE4 inhibitors are described. These concepts are based on the assumption that additive or synergistic anti-inflammatory effects can be produced with inhibitors that target either two or more PDE families or with a PDE4 inhibitor in combination with other anti-inflammatory drugs such as a glucocorticoid.

Update on the clinical utility of sildenafil in the treatment of pulmonary arterial hypertension

Sildenafil is an orally administered phosphodiesterase type 5 inhibitor that is approved for the treatment of pulmonary arterial hypertension (PAH). The hemodynamic effects of sildenafil are mitigated primarily via potentiating the effects of endogenous nitric oxide, leading to smooth muscle cell relaxation and reductions in pulmonary arterial pressures and pulmonary vascular resistance. When added to standard background therapy in patients with idiopathic or associated PAH from congenital heart disease, anorexigen use, or connective tissue disease, sildenafil treatment results in improved exercise capacity as measured by 6 minute walk distance, improved hemodynamics, and favorable changes in quality of life. Sildenafil use is contraindicated with concomitant nitrate administration, and caution should be exercised when used in combination with antihypertensive agents due to risks of precipitating hypotension. Side effects are generally mild, and include flushing, headaches, and epistaxis. The combination of sildenafil with intravenous epoprostenol is safe and well tolerated, and further improves exercise capacity. Sildenafil is approved only for treatment of PAH, and although emerging data suggest a potential role in treating other types of pulmonary hypertension, larger trials are required to confirm these findings.

Update on pulmonary hypertension complicating chronic obstructive pulmonary disease

Pulmonary hypertension (PH) is the hemodynamic manifestation of various pathological processes that result in elevated pulmonary artery pressures (PAP). The National Institutes of Health Registry defined pulmonary arterial hypertension as the mean PAP of more than 25 mm Hg with a pulmonary capillary wedge pressure or left atrial pressure equal to or less than 15 mm Hg. This definition remains the currently accepted definition of PH that is used to define PH related to multiple clinical conditions including chronic obstructive pulmonary disease (COPD). The estimated US prevalence of COPD by the National Health Survey in 2002 in people aged >25 was 12.1 million. There is a lack of large population-based studies in COPD to document the correct prevalence of PH and outcome. The major cause of PH in COPD is hypoxemia leading to vascular remodeling. Echocardiogram is the initial screening tool of choice for PH. This simple noninvasive test can provide an estimate of right ventricular systolic and right atrial pressures. Right heart catheterization remains the gold standard to diagnose PH. It provides accurate measurement of mean PAP and pulmonary capillary wedge pressure. Oxygen therapy remains the cornerstone therapeutic for hypoxemia in COPD patients. Anecdotal reports suggest utility of PDE5-inhibitors and prostacyclin to treat COPD-related PH. Large randomized clinical trials are needed before the use of these drugs can be recommended.

Impact of pulmonary artery pressure on exercise function in severe COPD

BACKGROUND

Although pulmonary hypertension commonly complicates COPD, the functional consequences of increased pulmonary artery pressures in patients with this condition remain poorly defined.

METHODS

We conducted a cross-sectional analysis of a cohort of 362 patients with severe COPD who were evaluated for lung transplantation. Patients with pulmonary hemodynamics measured by cardiac catheterization and available 6-min walk test results were included. The association of mean pulmonary artery pressure (mPAP) with pulmonary function, echocardiographic variables, and 6-min walk distance was assessed.

RESULTS

The prevalence of pulmonary hypertension (mPAP, > 25 mm Hg; pulmonary artery occlusion pressure [PAOP], < 16 mm Hg) was 23% (95% confidence interval, 19 to 27%). In bivariate analysis, higher mPAP was associated with lower FVC and FEV(1), higher Pco(2) and lower Po(2) in arterial blood, and more right heart dysfunction. Multivariate analysis demonstrated that higher mPAP was associated with shorter distance walked in 6 min, even after adjustment for age, gender, race, height, weight, FEV(1), and PAOP (-11 m for every 5 mm Hg rise in mPAP; 95% confidence interval, -21 to -0.7; p = 0.04).

CONCLUSIONS

Higher pulmonary artery pressures are associated with reduced exercise function in patients with severe COPD, even after controlling for demographics, anthropomorphics, severity of airflow obstruction, and PAOP. Whether treatments aimed at lowering pulmonary artery pressures may improve clinical outcomes in COPD, however, remains unknown.