Different in vitro and in vivo profiles of substituted 3-aminopropylphosphinate and 3-aminopropyl(methyl)phosphinate GABA(B) receptor agonists as inhibitors of transient lower oesophageal sphincter relaxation

Peripheral antitussives affect temporal features of tracheobronchial coughing in cats

The influence of peripheral antitussive drugs on spatiotemporal features of coughing has not been reported. We hypothesized that this class of compounds would alter the cough motor pattern, in part, by lengthening cough phases. Peripherally acting antitussives, 3-aminopropylphosphinic acid (3APPi, 5 mg/kg) and levodropropizine (Levo, 3 mg/kg) were injected intravenously in anesthetized spontaneously breathing cats (13 males, 2 females; 4.38 ± 0.19 kg). Spatio-temporal analysis of cough induced by mechanical stimulation of the trachea showed significant reductions in cough number and expiratory cough efforts after the administration of each drug. A significant reduction in inspiratory cough efforts occurred after Levo. Both drugs induced temporal changes in the cough motor pattern, including prolongations of inspiratory phase, inspiratory-expiratory transition, total cough diaphragm activity, and total cough cycle duration. Levo also significantly lengthened the expiratory phase of cough. A shortening of the overlap between diaphragm and abdominal activity and cough abdominal electromyogram (EMG) activity was observed after the administration of 3APPi. No significant changes in cardiorespiratory data were seen, with the exception of prolonged expiratory phase after 3APPi and lower blood pressure after Levo. Peripherally induced cough suppression is accompanied with changes in cough temporal characteristics that are not observed after the administration of centrally acting antitussives. The motor output produced by the cough central pattern generator differs significantly when coughing is perturbed by peripherally and centrally acting antitussives.NEW & NOTEWORTHY In a study on anesthetized cats, peripherally acting antitussives 3-aminopropylphosphinic acid (3APPi) and levodropropizine (Levo) significantly reduced cough number and expiratory efforts, with Levo also reducing inspiratory efforts. Both antitussives altered the cough motor pattern, extending various cough phases. 3APPi shortened diaphragm-abdominal activity overlap, whereas Levo decreased the respiratory rate. These changes contrast with those induced by centrally acting antitussives.

Novel antitussive strategies

Acute and chronic cough represent one of the most common symptoms of medical importance but effective pharmacotherapy is, to all intents and purposes, absent. Numerous initiatives targeting the recently discovered tussive pathways are in progress. Here, we review the current antitussive armamentarium and provide an update on the novel strategies and compounds in development.

Antitussive effects of the peripherally restricted GABAB receptor agonist lesogaberan in guinea pigs: comparison to baclofen and other GABAB receptor-selective agonists

BACKGROUND

Gastroesophageal reflux disease (GERD) is a common cause of chronic cough. Both acid and nonacid reflux is thought to play a role in the initiation of coughing and cough hypersensitivity. The GABAB receptor agonist lesogaberan was developed as a peripherally restricted anti-reflux therapy that reduces the frequency of transient lower esophageal sphincter relaxations (TLESR; the major cause of reflux) in animals and in patients with GERD. GABAB receptor agonists have also been shown to possess antitussive effects in patients and in animals independent of their effects on TLESR, suggesting that lesogaberan may be a promising treatment for chronic cough.

METHODS

We have assessed the direct antitussive effects of lesogaberan (AZD3355). The effects of other GABAB receptor agonists were also determined. Coughing was evoked in awake guinea pigs using aerosol challenges with citric acid.

RESULTS

Lesogaberan dose-dependently inhibited citric acid evoked coughing in guinea pigs. Comparable effects of the GABAB receptor agonists baclofen and 3-aminopropylphosphinic acid (3-APPiA) on cough were also observed. Baclofen produced obvious signs of sedation and respiratory depression. By contrast, both lesogaberan and 3-APPiA (both inactivated centrally by GABA transporters) were devoid of sedative effects and did not alter respiratory rate.

CONCLUSIONS

Together, the data suggest that lesogaberan and related GABAB receptor agonists may hold promise as safe and effective antitussive agents largely devoid of CNS side effects.