Case for continuing community NIV and CPAP during the COVID-19 epidemic

Dear Editor, Recent clinical guidelines regarding the use of home non-invasive ventilation (NIV) and continuous positive airway pressure (CPAP) during the COVID-19 epidemic have tried to balance the risks of stopping NIV or CPAP against the unknown potential risk of increased aerosol-related transmission to family and carers. We read with interest views put forward by Barker et al but feel that wider aspects need consideration, and for NIV and CPAP separately

Impact of polymorphic variants on the molecular pharmacology of the two-agonist conformations of the human β1-adrenoceptor

β-blockers are widely used to improve symptoms and prolong life in heart disease primarily by inhibiting the actions of endogenous catecholamines at the β1-adrenoceptor. There are two common naturally occurring polymorphisms within the human β1-adrenoceptor sequence: Ser or Gly at position 49 in the N-terminus and Gly or Arg at position 389 in the C-terminus and some clinical studies have suggested that expression of certain variants may be associated with disease and affect response to treatment with β-blockers. The β1-adrenoceptor also exists in two agonist conformations - a high affinity catecholamine conformation and a low affinity secondary agonist conformation. Receptor-effector coupling and intracellular signalling from the different conformations may be affected by the polymorphic variants. Here, we examine in detail the molecular pharmacology of the β1-adrenoceptor polymorphic variants with respect to ligand affinity, efficacy, activation of the different agonist conformations and signal transduction and determine whether the polymorphic variants do indeed affect this secondary conformation. Stable cell lines expressing the wildtype and polymorphic variants were constructed and receptor pharmacology examined using whole cell binding and intracellular secondary messenger techniques. There was no difference in affinity for agonists and antagonists at the human wildtype β1-adrenoceptor (Ser49/Gly389) and the polymorphic variants Gly49/Gly389 and Ser49/Arg389. Furthermore, the polymorphic variant receptors both have two active agonist conformations with pharmacological properties similar to the wildtype receptor. Although the polymorphism at position 389 is thought to occur in an intracellular domain important for Gs-coupling, the two agonist conformations of the polymorphic variants stimulate intracellular signalling pathways, including Gs-cAMP intracellular signalling, in a manner very similar to that of the wildtype receptor

Similarity- and substructure-based development of β2-adrenergic receptor ligands based on unusual scaffolds

The β2-adrenergic receptor (β2AR) is a G protein-coupled receptor (GPCR) and a well-explored target. Here, we report the discovery of 13 ligands, ten of which are novel, of this particular GPCR. They have been identified by similarity- and substructure-based searches using multiple ligands, which were described in an earlier study, as starting points. Of note, two of the molecules used as queries here distinguish themselves from other β2AR antagonists by their unique scaffold. The molecules described in this work allow us to explore the ligand space around the previously reported molecules in greater detail, leading to insights into their structure−activity relationship. We also report experimental binding and selectivity data and putative binding modes for the novel molecules

The selectivity of α-adrenoceptor agonists for the human α1A, α1B, and α1D-adrenoceptors

Highly selective drugs offer a way to minimize side-effects. For agonist ligands, this could be through highly selective affinity or highly selective efficacy, but this requires careful measurements of intrinsic efficacy. The α1-adrenoceptors are important clinical targets, and α1-agonists are used to manage hypotension, sedation, attention deficit hypersensitivity disorder (ADHD), and nasal decongestion. With 100years of drug development, there are many structurally different compounds with which to study agonist selectivity. This study examined 62 α-agonists at the three human α1-adrenoceptor (α1A, α1B, and α1D) stably expressed in CHO cells. Affinity was measured using whole-cell 3H-prazosin binding, while functional responses were measured for calcium mobilization, ERK1/2-phosphorylation, and cAMP accumulation. Efficacy ratios were used to rank compounds in order of intrinsic efficacy. Adrenaline, noradrenaline, and phenylephrine were highly efficacious α1-agonists at all three receptor subtypes. A61603 was the most selective agonist and its very high α1A-selectivity was due to selective α1A-affinity (>660-fold). There was no evidence of Gq-calcium versus ERK-phosphorylation biased signaling at the α1A, α1B, or α1D-adrenoceptors. There was little evidence for α1A calcium versus cAMP biased signaling, although there were suggestions of calcium versus cAMP bias the α1B-adrenoceptor. Comparisons of the rank order of ligand intrinsic efficacy suggest little evidence for selective intrinsic efficacy between the compounds, with perhaps the exception of dobutamine which may have some α1D-selective efficacy. There seems plenty of scope to develop affinity selective and intrinsic efficacy selective drugs for the α1-adrenoceptors in future

The signaling and selectivity of α-adrenoceptor agonists for the human α2A, α2B and α2C-adrenoceptors and comparison with human α1 and β-adrenoceptors

α2-adrenoceptors, (α2A, α2B and α2C-subtypes), are Gi-coupled receptors. Central activation of brain α2A and α2C-adrenoceptors is the main site for α2-agonist mediated clinical responses in hypertension, ADHD, muscle spasm and ITU management of sedation, reduction in opiate requirements, nausea and delirium. However, despite having the same Gi-potency in functional assays, some α2-agonists also stimulate Gs-responses whilst others do not. This was investigated. Agonist responses to 49 different α-agonists were studied (CRE-gene transcription, cAMP, ERK1/2-phosphorylation and binding affinity) in CHO cells stably expressing the human α2A, α2B or α2C-adrenoceptor, enabling ligand intrinsic efficacy to be determined (binding KD/Gi-IC50). Ligands with high intrinsic efficacy (e.g., brimonidine and moxonidine at α2A) stimulated biphasic (Gi-Gs) concentration responses, however for ligands with low intrinsic efficacy (e.g., naphazoline), responses were monophasic (Gi-only). ERK1/2-phosphorylation responses appeared to be Gi-mediated. For Gs-mediated responses to be observed, both a system with high receptor reserve and high agonist intrinsic efficacy were required. From the Gi-mediated efficacy ratio, the degree of Gs-coupling could be predicted. The clinical relevance and precise receptor conformational changes that occur, given the structural diversity of compounds with high intrinsic efficacy, remains to be determined. Comparison with α1 and β1/β2-adrenoceptors demonstrated subclass affinity selectivity for some compounds (e.g., α2:dexmedetomidine, α1:A61603) whilst e.g., oxymetazoline had high affinity for both α2A and α1A-subtypes, compared to all others. Some compounds had subclass selectivity due to selective intrinsic efficacy (e.g., α2:brimonidine, α1:methoxamine/etilefrine). A detailed knowledge of these agonist characteristics is vital for improving computer-based deep-learning and drug design

The affinity and selectivity of α‐adrenoceptor antagonists, antidepressants and antipsychotics for the human α2A, α2B, and α2C‐adrenoceptors and comparison with human α1 and β‐adrenoceptors

α2-adrenoceptors, subdivided into α2A, α2B and α2C subtypes and expressed in heart, blood vessels, kidney, platelets and brain, are important for blood pressure, sedation, analgesia and platelet aggregation. Brain α2C-adrenoceptor blockade has also been suggested to be beneficial for antipsychotic action. However, comparing α2-adrenoceptor subtype affinity is difficult due to significant species and methodology differences in published studies. Here, 3H-rauwolscine whole cell binding was used to determine the affinity and selectivity of 99 α-antagonists (including antidepressants and antipsychotics) in CHO cells expressing human α2A, α2B or α2C-adrenoceptors, using an identical method to β and α1-adrenoceptor measurements, thus allowing direct human receptor comparisons. Yohimbine, RX821002, RS79948 and atipamezole are high affinity non-selective α2-antagonists. BRL44408 was the most α2A-selective antagonist, although its α1A-affinity (81nM) is only 9-fold greater than its α2C-affinity. MK-912 is the highest-affinity, most α2C-selective antagonist (0.15nM α2C-affinity) although its α2C-selectivity is only 13-fold greater than at α2A. There are no α2B-selective antagonists. A few α-ligands with significant β-affinity were detected, e.g. naftopidil where its clinical α1A-affinity is only 3-fold greater than off-target β2-affinity. Antidepressants (except mirtazapine) and first generation antipsychotics have higher α1A than α2-adrenoceptor affinity but poor β-affinity. Second generation antipsychotics varied widely in their α2-adrenoceptor affinity. Risperidone (9nM) and paliperidone (14nM) have the highest α2C-adrenoceptor affinity however this is only 5-fold selective over α2A, and both have higher affinity for α1A (2nM and 4nM respectively). So, despite a century of yohimbine use, and decades of α2-subtype studies, there remains plenty of scope to develop α2-subtype selective antagonists

Salmeterol's Extreme b2 Selectivity Is Due to Residues in Both Extracellular Loops and Transmembrane Domains

ABSTRACT Salmeterol is a long-acting b2-agonist, widely used as an inhaled treatment of asthma and chronic obstructive pulmonary disease. It has very high b2-affinity (log K D 28.95) and is very selective for the b2-adrenoceptor (1000-fold selectivity over the b1-adrenoceptor). This study used a mutagenesis approach to determine the exact amino acids in the human b2-adrenoceptor responsible for this very high selectivity. Wild-type b2-and b1-adrenoceptors, chimeric b2/b1-adrenoceptors, and receptors with single-point mutations were transfected into Chinese hamster ovary-K1 cells, and affinity and function were studied using [ ]cAMP accumulation. Extracellular loop 3 (and specifically amino acid K305) had the largest single effect by reducing salmeterol's affinity for the b2-adrenoceptor by 31-fold. H296 in transmembrane 6 also had a major effect (18-fold reduction in salmeterol affinity). Combining these, in the double mutant b2-H296K-K305D, reduced salmeterol's affinity by 275-fold, to within 4-fold of that of the b1-adrenoceptor, without affecting the affinity or selectivity of other b2-agonists (salbutamol, formoterol, fenoterol, clenbuterol, or adrenaline). Another important amino acid was Y308 in transmembrane 7, although this also affected the affinity and selectivity of other agonists. F194 in extracellular loop 2 and R304 in extracellular loop 3 also had minor effects. None of these mutations (including the double mutant b2-H296K-K305D) affected the efficacy or duration of action of salmeterol. This suggests that the high affinity and selectivity of salmeterol are due to specific amino acids within the receptor itself, but that the duration of action is at least in part due to other factors, for example lipophilicity