Three generations of ongoing controversies concerning the use of short acting beta-agonist therapy in asthma: a review

Feline asthma: what's new and where might clinical practice be heading?

PRACTICAL RELEVANCE

Feline bronchial asthma is one of the most commonly diagnosed respiratory conditions of cats. Clinical signs range from intermittent wheezing and coughing, which can compromise quality of life, to episodes of severe dyspnea that can be life-threatening.

CLINICAL CHALLENGES

Feline asthma can be easily disregarded as a simplistic condition. However, much about its pathophysiology remains obscure. There is no gold standard method of diagnosis, and current approaches are associated with various limitations. Also, feline asthma is typically treated with long-term glucocorticoid therapy, which can have significant consequences.

AUDIENCE

Because of its prevalence, general practitioners encounter asthma regularly. Refractory cases are often managed by veterinary internists and pulmonologists.

PATIENT GROUP

Asthma can be diagnosed in cats of any age but is usually seen in young to middle-aged adults (mean 4 years, range 1-15 years). There is no sex predilection, but the Siamese breed appears to be overrepresented.

EVIDENCE BASE

While the standard clinical approach to feline asthma has changed little in recent years, new research has provided greater insight into many aspects of this complex disease and new strategies are being studied. This article reviews the current literature in order to raise awareness of how advances in the understanding of the pathophysiology, diagnosis and treatment of feline asthma may be determining the future direction of clinical practice.

Functional selectivity of GPCR ligand stereoisomers: new pharmacological opportunities

It is now well established that any given ligand for a G-protein-couple receptor (GPCR) does not simply possess a single defined efficacy. Rather, a ligand possesses multiple efficacies, depending on the specific down-stream signal transduction pathway analyzed. This diversity may be based on ligand-specific GPCR conformations and is often referred to as "functional selectivity." It has been known for a century that stereoisomers of catecholamines differ in their potency and, in some systems, also in their efficacy. However, the molecular basis for efficacy differences of GPCR ligand stereoisomers has remained poorly defined. In an elegant study published in this issue of Molecular Pharmacology, Woo et al. (p. 158) show that stereoisomers of the beta(2)-adrenoceptor selective agonist fenoterol differentially activates G(s)- and G(i)-proteins in native rat cardiomyocytes. This study is so important because it is the first report to show that even the subtle structural differences within a ligand stereoisomer pair are sufficient to discriminate between GPCR conformations with distinct G-protein coupling properties. The study highlights of how important it is to examine the "more active" (eutomer) and the "less active" (distomer) stereoisomer to understand the mechanisms of action and the cellular effects of GPCR ligands. The study by Woo et al. will ignite a renaissance of the analysis of ligand stereoisomers, using sensitive pharmacological and biophysical assays. The available literature supports the notion that meticulous analysis of ligand stereoisomers is a goldmine for understanding mechanisms of GPCR activation, analysis of signal transduction pathways, development of new therapies for important diseases, and drug safety.