Functional desensitization of the β 2 adrenoceptor is not dependent on agonist efficacy

ROS-mediated regulation of β2AR function: Does oxidation play a meaningful role towards β2-agonist tachyphylaxis in airway obstructive diseases?

β2-adrenergic receptor (β2AR) agonists are the clinical gold standard for treatment and prophylaxis of airway constriction in pulmonary obstructive diseases such as asthma and COPD. Inhaled β2-agonists elicit rapid bronchorelaxation of the airway smooth muscle, yet, clinical tachyphylaxis to this response can occur over repeated and chronic use, which reduces the bronchodilatory effectiveness. Several mechanisms have been proposed to impart β2-agonist tachyphylaxis, most notably β2AR desensitization. However, airway tissue is known to be highly oxidative, particularly in obstructive disease states where reactive oxygen species (ROS) generation is upregulated and ROS degradation is suboptimal yielding a large oxidative burden. Recent evidence demonstrates that β2AR can regulate ROS generation and that ROS can post-translationally alter β2AR cysteine residues via oxidation, leading to distinct functional receptor outcomes. Herein, we discuss the growing evidence for β2AR mediated ROS generation in airway cells and the role of ROS in regulating β2AR via cysteine-oxidation of the receptor. Given the functional consequence of the β2AR-ROS signaling axis in the airways, we also discuss the potential role of ROS in mediating β2-agonist tachyphylaxis.

Key aspects of modern GPCR drug discovery

G-protein-coupled receptors (GPCRs) are the largest and most versatile cell surface receptor family with a broad repertoire of ligands and functions. We've learned an enormous amount about discovering drugs of this receptor class since the first GPCR was cloned and expressed in 1986, such that it's now well-recognized that GPCRs are the most successful target class for approved drugs. Here we take the reader through a GPCR drug discovery journey from target to the clinic, highlighting the key learnings, best practices, challenges, trends and insights on discovering drugs that ultimately modulate GPCR function therapeutically in patients. The future of GPCR drug discovery is inspiring, with more desirable drug mechanisms and new technologies enabling the delivery of better and more successful drugs.

Beta-blockers reduce severe exacerbation in patients with mild chronic obstructive pulmonary disease with atrial fibrillation: a population-based cohort study

BACKGROUND AND OBJECTIVE

Beta-blockers (BBs) decrease mortality and acute exacerbation (AE) rates in patients with chronic obstructive pulmonary disease (COPD) and cardiovascular disease; however, information on their effects in patients with COPD and atrial fibrillation (AF) is limited. We aimed to assess the AE risk in patients with different severities of COPD and AF receiving BBs compared with that in patients receiving calcium channel blockers (CCBs).

METHODS

This retrospective cohort study used data from the Taiwan National Health Insurance Database from 2009 to 2018. Outcomes included AE-related emergency room visits and hospitalisation. HRs and 95% CIs were estimated using the Cox proportional hazards model. COPD severity was classified as mild or severe based on exacerbation history. Sensitivity analyses included treatment and subgroup analyses, and competing risk adjustment.

RESULTS

After propensity score matching, 4486 pairs of BB and CCB users from 13 462 eligible patients were included. The exacerbation risk for BB users was lower (HR 0.80; 95% CI 0.72 to 0.89) than that of CCB users. After stratification, BB benefits persisted in the mild COPD group (HR 0.75; 95% CI 0.66 to 0.85), unlike the severe COPD group (HR 0.95; 95% CI 0.75 to 1.20). The results of the subgroup analysis showed consistent protective effects even in patients without heart failure or myocardial infarction (adjusted HR 0.82; 95% CI 0.71 to 0.94).

CONCLUSION

We found that BB use in patients with mild COPD and AF was associated with a lower exacerbation risk than CCB use, and that close monitoring of BB use in patients with severe COPD and AF is warranted.

"As-Needed" Inhaled Corticosteroids for Patients With Asthma

Prevention of severe asthma exacerbations is a primary management goal for asthma across the severity spectrum. Inhaled corticosteroids (ICSs) decrease the risk of asthma exacerbations, but patient adherence to ICS-containing medications as a daily maintenance therapy is poor, and many patients overuse short-acting beta2-agonist relievers; both are associated with increased risk of severe exacerbations and death. Airway inflammation also varies over time, influenced by exposures such as viral infections and allergen. As-needed ICS strategies, in which patients receive ICSs (or additional ICSs, if already taking controller therapy) whenever they take their reliever inhaler, empower patients to adjust their ICS intake in response to symptom fluctuation. These strategies can improve asthma morbidity outcomes, particularly by reducing severe exacerbations and reducing the risk of adverse effects of oral corticosteroids. In this review, the evidence for combination ICS-formoterol in a single inhaler, ICS and short-acting beta2-agonists in separate inhalers, and combination ICS-albuterol in a single inhaler is presented, along with practical considerations, evidence gaps, and implications for clinical practice for each strategy, presented by level of asthma severity and age group. Improving access to such strategies on a global scale is imperative to improve asthma outcomes and achieve equity across populations.

Angiotensin II Type 1 Receptor Tachyphylaxis Is Defined by Agonist Residence Time

Several GPCRs (G-protein-coupled receptors) have been reported to exhibit tachyphylaxis, which is an acute loss of functional receptor response after repeated stimuli with an agonist. GPCRs are important clinical targets for a wide range of disorders. Therefore, elucidation of the ligand features that contribute to receptor tachyphylaxis and signaling events underlying this phenomenon is important for drug discovery and development. In this study, we examined the role of ligand-binding kinetics in the tachyphylaxis of AT₁R (angiotensin II type 1 receptor) using bioluminescence resonance energy transfer assays to monitor signaling events under both kinetic and equilibrium conditions. We investigated AT₁R signal transduction and translocation promoted by the endogenous tachyphylactic agonist Ang II (angiotensin II) and its analogs, described previously for inducing reduced receptor tachyphylaxis. Estimation of binding kinetic parameters of the ligands revealed that the residence time of Ang II was higher than that of the analogs, resulting in more sustained G_q protein activation and recruitment of β-arrestin than that promoted by the analogs. Furthermore, we observed that Ang II led to more sustained internalization of the receptor, thereby retarding its recycling to the plasma membrane and preventing further receptor responses. These results show that the apparent lack of tachyphylaxis in the studied analogs resulted from their short residence time at the AT₁R. In addition, our data highlight the relevance of complete characterization of novel GPCR drug candidates, taking into account their receptor binding kinetics as well.

Short- and long-term effects of fluticasone furate/vilaterol in exercising asthmatic adolescents: a randomized and open label trial

PURPOSE

Relvar® (Fluticasone furoate (FF)/Vilanterol (VI)) is a once-daily inhaler with bronchodilator effect lasting 24 hours. Our aim was to investigate the short- and long-term effects of FF/VI on exercise-induced asthma (EIA) in adolescents.

METHODS

Ninety-three adolescent asthmatics aged 12-18 years were referred for evaluation of EIA. Following a positive exercise challenge test (ECT), 22/44 were allocated to a single administration of salbutamol (400 μg) and 22/44 to FF/VI (92/22 μg) in a double-blind method. Thirty-five subjects were reassessed by repeat ECT 30-60 days of FF/VI.

RESULTS

Median FEV1 change post-ECT at baseline was -22.8% predicted (IQR -26.1 and -18.0) for salbutamol and -21.0 (IQR -30.7 and -16.8) for FF/VI. Following bronchodilator, FEV1 improved similarly in both groups. Repeat ECT following 30-60 days of FF/VI resulted in negative exercise challenge test in 33/35 subjects; the median decrease in FEV1 of these 35 subjects was 22.6% predicted (IQR 29-18) before, and 4.6% predicted (IQR 8.7-2.5) after 30-60 days of FF/VI treatment; p<0.0001).

CONCLUSIONS

FF/VI is effective in reversing EIA after 15 minutes in adolescents and in protecting EIA after 30-60 days in adolescents. Larger studies are needed to assess the effect of FF/VI on EIA.

Fluticasone furoate/vilanterol versus fluticasone propionate in patients with asthma and exercise-induced bronchoconstriction

Objective: To investigate whether once-daily (OD) fluticasone furoate (FF)/vilanterol (VI) provides greater long-term protection from postexercise fall in forced expiratory volume in 1 s (FEV₁) than twice-daily (BD) fluticasone propionate (FP) in patients with asthma and exercise-induced bronchoconstriction. Methods: A randomized, double-blind, crossover study was conducted in patients (aged 12-50 years) on low-/mid-dose maintenance inhaled corticosteroid. Following a 4-week run-in period (FP 250 µg BD), patients with a ≥ 20% decrease in postexercise FEV₁ received FF/VI 100/25 µg OD or FP 250 µg BD for 2 weeks. Exercise challenges were carried out 23 h after the first dose of study medication, and 12 and 23 h after evening clinic dose at the end of the 2-week treatment period. After a 2-week washout period (FP 250 µg), patients crossed over treatments, with procedures and tests repeated. The primary endpoint was mean maximal percentage decrease from pre-exercise FEV₁ following exercise challenge 12-h postevening dose on Day 14. Results: The mean maximal percentage decrease from pre-exercise FEV₁ after the 12-h exercise challenge (Day 14) was 15.02% with FF/VI, and 16.71% with FP (difference, -1.69; 95% confidence interval, -3.76 to 0.39; p = 0.109). After the 23-h exercise challenge (Day 14), respective mean maximal decreases were 11.90% and 14.05% (difference, -2.15; 95% confidence interval, -4.31 to 0.01). Conclusion: The study failed to show a difference between FF/VI and FP at providing long-term protection from exercise-induced bronchoconstriction.

The inhibition of human lung fibroblast proliferation and differentiation by Gs-coupled receptors is not predicted by the magnitude of cAMP response

Background

Idiopathic pulmonary fibrosis (IPF) is a chronic and progressive fibrotic lung disease for which there is no cure. Current therapeutics are only able to slow disease progression, therefore there is a need to explore alternative, novel treatment options. There is increasing evidence that the 3′, 5′ cyclic adenosine monophosphate (cAMP) pathway is an important modulator in the development of fibrosis, with increasing levels of cAMP able to inhibit cellular processes associated with IPF. In this study we investigate the expression of G_s-coupled G protein-coupled receptors (GPCR) on human lung fibroblasts (HLF), and explore which can increase cAMP levels, and are most efficacious at inhibiting proliferation and differentiation.

Methods

Using TaqMan arrays we determined that fibroblasts express a range of G_s-coupled GPCR. The function of selected agonists at expressed receptors was then tested in a cAMP assay, and for their ability to inhibit fibroblast proliferation and differentiation.

Results

Expression analysis of GPCR showed that the prostacyclin, prostaglandin E₂ (PGE₂) receptor 2 and 4, melanocortin-1, β₂ adrenoceptor, adenosine 2B, dopamine-1, and adenosine 2A receptors were expressed in HLF. Measuring cAMP accumulation in the presence of selected G_s-coupled receptor ligands as well as an adenylyl cyclase activator and inhibitors of phosphodiesterase showed formoterol, PGE₂, treprostinil and forskolin elicited maximal cAMP responses. The agonists that fully inhibited both fibroblast proliferation and differentiation, BAY60–6583 and MRE-269, were partial agonists in the cAMP accumulation assay.

Conclusions

In this study we identified a number of ligands that act at a range of GPCR that increase cAMP and inhibit fibroblast proliferation and differentiation, suggesting that they may provide novel targets to develop new IPF treatments. From these results it appears that although the cAMP response is important in driving the anti-fibrotic effects we have observed, the magnitude of the acute cAMP response is not a good predictor of the extent of the inhibitory effect. This highlights the importance of monitoring the kinetics and localisation of intracellular signals, as well as multiple pathways when profiling novel compounds, as population second messenger assays may not always predict phenotypic outcomes.

Electronic supplementary material

The online version of this article (10.1186/s12931-018-0759-2) contains supplementary material, which is available to authorized users.

A luminescent assay for real-time measurements of receptor endocytosis in living cells

Ligand-mediated endocytosis is a key autoregulatory mechanism governing the duration and intensity of signals emanating from cell surface receptors. Due to the mechanistic complexity of endocytosis and its emerging relevance in disease, simple methods capable of tracking this dynamic process in cells have become increasingly desirable. We have developed a bioluminescent reporter technology for real-time analysis of ligand-mediated receptor endocytosis using genetic fusions of NanoLuc luciferase with various G-protein-coupled receptors (GPCRs). This method is compatible with standard microplate formats, which should decrease work flows for high-throughput screens. This article also describes the application of this technology to endocytosis of epidermal growth factor receptor (EGFR), demonstrating potential applicability of the method beyond GPCRs.