Robbie L. McLeod

Central antitussive activity of the NK1 and NK2 tachykinin receptor antagonists, CP-99,994 and SR 48968, in the guinea-pig and cat.

The purpose of this study was to investigate the antitussive activity and sites of action of the NK1 and NK2 tachykinin receptor antagonists, CP‐99,994, SR 48968, and the racemate of SR 48968, SR 48212A in the cat and guinea‐pig. Guinea‐pigs were dosed subcutaneously (s.c.) with CP‐99,994, SR 48212A or SR 48968 one hour before exposure to aerosols of capsaicin (0.3 mM) to elicit coughing. Coughs were detected with a microphone and counted. Intracerebroventricular (i.c.v.) cannulae were placed in the lateral cerebral ventricles of anaesthetized guinea‐pigs. Approximately one week later, the animals were dosed with CP‐99,994 or SR 48212A (i.c.v.) and exposed to aerosols of capsaicin (0.3 mM) to elicit coughing. Cough was produced in anaesthetized cats by mechanical stimulation of the intrathoracic trachea and was monitored from electromyograms of respiratory muscle activity. Cannulae were placed for intravenous (i.v.) or, in separate groups of animals, intravertebral arterial (i.a.) administration of CP‐99,994, SR 48212A or SR 48968. Dose‐response relationships for i.v. and i.a. administration of each drug were generated to determine a ratio of i.v. ED50 to i.a. ED50, known as the effective dose ratio (EDR). The EDR will be 20 or greater for a centrally active drug and less than 20 for a peripherally active drug. In the guinea‐pig, CP‐99,994 (0.1–30 mg kg−1, s.c.), SR 48212A (1.0–30 mg kg−1, s.c.), and SR 48968 (0.3–3.0 mg kg−1, s.c.) inhibited capsaicin‐induced cough in a dose‐dependent manner. Capsaicin‐induced cough was also inhibited by i.c.v. administration of CP‐99,994 (10 and 100 μg) or SR 48212A (100 μg). In the cat, both CP‐99,994 (0.0001–0.3 mg kg−1, i.a., n=5; 0.003–3.0 mg kg−1, i.v., n=5) and SR 48212A (0.003–1.0 mg kg−1, i.a., n=5; 0.01–3.0 mg kg−1, i.v., n=5) inhibited mechanically induced cough by either the i.v. or i.a. routes in a dose‐dependent manner. SR 48968 (0.001–0.3 mg kg−1, i.a., n=5; 0.03–1.0 mg kg−1, i.v., n=5) inhibited cough when administered by the i.a. route in a dose‐dependent manner, but had no effect by the i.v. route up to a dose of 1.0 mg kg−1. Intravenous antitussive potencies (ED50, 95% confidence interval (CI)) of these compounds were: CP‐99,994 (0.082 mg kg−1, 95% CI 0.047–0.126), SR 48212A (2.3 mg kg−1, 95% CI 0.5–20), and SR 48968 (>1.0 mg kg−1, 95% CI not determined). The intra‐arterial potencies of these compounds were: CP‐99,994 (1.0 μg kg−1, 95% CI 0.4–1.8), SR 48212A (25 μg kg−1, 95% CI 13–52), and SR 48968 (8.0 μg kg−1, 95% CI 1–32). The derived EDRs for each compound were: CP‐99,994, 82; SR 48212A, 92; and SR 48968, >125. We concluded that CP‐99,994 and SR 48968 inhibit cough in the guinea‐pig and cat by a central site of action. In the cat, the antitussive action of these compounds appears to be solely by a central site.

Nociceptin inhibits cough in the guinea‐pig by activation of ORL1 receptors

We studied the central and peripheral antitussive effect of ORL1 receptor activation with nociceptin/orphanin FQ in conscious guinea‐pigs. In guinea‐pig cough studies, nociceptin/orphanin FQ (10, 30, and 90u2003μg) given directly into the CNS by an intracerebroventricular (i.c.v.) route inhibited cough elicited by capsaicin exposure by approximately 23, 29 and 52%, respectively. The antitussive activity of nociceptin/orphanin FQ (90u2003μg, i.c.v.) was blocked by the selective ORL1 antagonist [Phe1γ(CH2‐NH)Gly2]nociceptin‐(1‐13)‐NH2 (180u2003μg, i.c.v.) and J113397 (10u2003mgu2003kg−1, i.p.) but not by the opioid antagonist, naltrexone (3u2003mgu2003kg−1, i.p.). Furthermore, intravenous (i.v.) nociceptin/orphanin FQ (1.0 and 3.0u2003mgu2003kg−1) also inhibited cough approximately by 25 and 42%, respectively. These findings indicate that selective ORL1 agonists display the potential to inhibit cough by both a central and peripheral mechanism, and potentially represent a novel therapeutic approach for the treatment of cough.

Anandamide induces cough in conscious guinea‐pigs through VR1 receptors

Endogenous neuronal lipid mediator anandamide, which can be synthesized in the lung, is a ligand of both cannabinoid (CB) and vanilloid receptors (VR). The tussigenic effect of anandamide has not been studied. The current study was designed to test the direct tussigenic effect of anandamide in conscious guinea‐pigs, and its effect on VR1 receptor function in isolated primary guinea‐pig nodose ganglia neurons. Anandamide (0.3–3 mg·ml−1), when given by aerosol, induced cough in conscious guinea‐pigs in a concentration dependent manner. When guinea‐pigs were pretreated with capsazepine, a VR1 antagonist, the anandamide‐induced cough was significantly inhibited. Pretreatment with CB1 (SR 141716A) and CB2 (SR 144528) antagonists had no effect on anandamide‐induced cough. These results indicate that anandamide‐induced cough is mediated through the activation of VR1 receptors. Anandamide (10–100 μM) increased intracellular Ca2+ concentration estimated by Fluo‐4 fluorescence change in isolated guinea‐pig nodose ganglia cells. The anandamide‐induced Ca2+ response was inhibited by two different VR1 antagonists: capsazepine (1 μM) and iodo‐resiniferatoxin (I‐RTX, 0.1 μM), indicating that anandamide‐induced Ca2+ response was through VR1 channel activation. In contrast, the CB1 (SR 141716A, 1 μM) and CB2 (SR 144528, 0.1 μM) receptor antagonists had no effect on Ca2+ response to anandamide. In conclusion, these results provide evidence that anandamide activates native vanilloid receptors in isolated guinea‐pig nodose ganglia cells and induces cough through activation of VR1 receptors.

Antitussive action of nociceptin in the cat

Experiments were conducted to determine the influence of the specific ORL1 receptor agonist, nociceptin, on the cough reflex in the cat. Cats were anesthetized and allowed to breathe spontaneously. Cough was elicited by mechanical stimulation of the intrathoracic airway. Intravenous administration of nociceptin (0.001-3.0 mg x kg(-1)) inhibited cough number and the magnitude of abdominal muscle electromyogram (EMG) discharge during cough in a dose-dependent manner. Nociceptin had no effect on the magnitude of the inspiratory muscle EMG during cough. These effects of nociceptin were antagonized by pretreatment with the ORL1 receptor antagonist, 1-[(3R,4R)-1-cyclooctylmethyl-3-hydroxymethyl-4-piperidyl]-3-ethyl-1, 3-dihydro-2H-benzimidazol-2-one (J-113397, 0.1 mg x kg(-1), i.v.). We conclude that intravenous nociceptin inhibits cough in the cat.

TRPV1 antagonists attenuate antigen-provoked cough in ovalbumin sensitized guinea pigs

We examined the molecular pharmacology and in vivo effects of a TRPV1 receptor antagonist, N-(4-Tertiarybutylphenyl)-4(3-cholorphyridin-2-yl)-tetrahydro-pyrazine1(2H) – carboxamide (BCTC) on the guinea pig TRPV1 cation channel. BCTC antagonized capsaicin-induced activation and PMA-mediated activation of guinea pig TRPV1 with IC50 values of 12.2 ± 5.2 nM, and 0.85 ± 0.10 nM, respectively. In addition, BCTC (100 nM) completely blocked the ability of heterologously expressed gpTRPV1 to respond to decreases in pH. Thus, BCTC is able to block polymodal activation of gpTRPV1. Furthermore, in nodose ganglia cells, capsaicin induced Ca2+ influx through TRPV1 channel was inhibited via BCTC in a concentration dependent manner. In in vivo studies capsaicin (10 – 300 μM) delivered by aerosol to the pulmonary system of non-sensitized guinea pigs produced an increase in cough frequency. In these studies, the tussigenic effects of capsaicin (300 μM) were blocked in a dose dependent fashion when BCTC (0.01–3.0 mg/kg, i.p.) was administered 30 minutes before challenge. The high dose of BCTC (3.0 mg/kg, i.p) produced a maximum inhibition of capsaicin-induced cough of 65%. We also studied the effects of BCTC (0.03 and 3.0) when administered 60 minutes before capsaicin. Under these conditions, BCTC (3.0 mg/kg, i.p) produced a maximum decrease in capsaicin-induced cough of 31%. In ovalbumin passively sensitized guinea pigs, we found that BCTC (1 and 3 mg/kg, i.p.) attenuated antigen ovalbumin (0.3%) cough responses by 27% and 60%, respectively. We conclude that TRPV1 channel activation may play role in cough mediated by antigen in sensitized guinea pigs. Our results supports increasing evidence that TRPV1 may play a role in the generation of the cough response.

SCH 206272: a potent, orally active tachykinin NK1, NK2, and NK3 receptor antagonist

Experiments were performed to characterize the pharmacology of SCH 206272 [(R,R)-1[5-[(3,5-dichlorobenzoyl)methylamino]-3-(3,4-dichlorophenyl)-4(Z)-(methoxyimino)pentyl]-N-methyl-2-oxo-[1,4bipiperidine]-3-acetamide] as a potent and selective antagonist of tachykinin (NK) NK(1), NK(2), and NK(3) receptors. SCH 206272 inhibited binding at human tachykinin NK(1), NK(2), and NK(3) receptors (K(i) = 1.3, 0.4, and 0.3 nM, respectively) and antagonized [Ca(2+)](i) mobilization in Chinese hamster ovary (CHO) cells expressing the cloned human tachykinin NK(1), NK(2), or NK(3) receptors. SCH 206272 inhibited relaxation of the human pulmonary artery (pK(b) = 7.7 +/- 0.3) induced by the tachykinin NK(1) receptor agonist, [Met-O-Me] substance P and contraction of the human bronchus (pK(b = 8.2 +/- 0.3) induced by the tachykinin NK(2) receptor agonist, neurokinin A. In isolated guinea pig tissues, SCH 206272 inhibited substance P-induced enhancement of electrical field stimulated contractions of the vas deferens, (pK(b = 7.6 +/- 0.2), NKA-induced contraction of the bronchus (pK(b) = 7.7 +/- 0.2), and senktide-induced contraction of the ileum. In vivo, oral SCH 206272 (0.1-10 mg/kg, p.o.) inhibited substance P-induced airway microvascular leakage and neurokinin A-induced bronchospasm in the guinea pig. In a canine in vivo model, SCH 206272 (0.1-3 mg/kg, p.o.) inhibited NK(1) and NK(2) activities induced by exogenous substance P and neurokinin A. Furthermore, in guinea pig models involving endogenously released tachykinins, SCH 206272 inhibited hyperventilation-induced bronchospasm, capsaicin-induced cough, and airway microvascular leakage induced by nebulized hypertonic saline. These data demonstrate that SCH 206272 is a potent, orally active tachykinin NK(1), NK(2), and NK(3) receptor antagonist. This compound may have beneficial effects in diseases thought to be mediated by tachykinins, such as cough, asthma, and chronic obstructive pulmonary disease.

TRPV1 Antagonists as Potential Antitussive Agents

Cough is an important defensive pulmonary reflex that removes irritants, fluids, or foreign materials from the airways. However, when cough is exceptionally intense or when it is chronic and/or nonproductive it may require pharmacologic suppression. For many patients, antitussive therapies consist of OTC products with inconsequential efficacies. On the other hand, the prescription antitussive market is dominated by older opioid drugs such as codeine. Unfortunately, “codeine-like” drugs suppress cough at equivalent doses that also often produce significant ancillary liabilities such as GI constipation, sedation, and respiratory depression. Thus, the discovery of a novel and effective antitussive drug with an improved side effect profile relative to codeine would fulfill an unmet clinical need in the treatment of cough. Afferent pulmonary nerves are endowed with a multitude of potential receptor targets, including TRPV1, that could act to attenuate cough. The evidence linking TRPV1 to cough is convincing. TRPV1 receptors are found on sensory respiratory nerves that are important in the generation of the cough reflex. Isolated pulmonary vagal afferent nerves are responsive to TRPV1 stimulation. In vivo, TRPV1 agonists such as capsaicin elicit cough when aerosolized and delivered to the lungs. Pertinent to the debate on the potential use of TRPV1 antagonist as antitussive agents are the observations that airway afferent nerves become hypersensitive in diseased and inflamed lungs. For example, the sensitivity of capsaicin-induced cough responses following upper respiratory tract infection and in airway inflammatory diseases such as asthma and COPD is increased relative to that of control responses. Indeed, we have demonstrated that TRPV1 antagonism can attenuate antigen-induced cough in the allergic guinea pig. However, it remains to be determined if the emerging pharmacologic profile of TRPV1 antagonists will translate into a novel human antitussive drug. Current efforts in clinical validation of TRPV1 antagonists revolve around various pain indications; therefore, clinical evaluation of TRPV1 antagonists as antitussive agents will have to await those outcomes.

The Efficacy of a NOP1 Agonist (SCH486757) in Subacute Cough

Currently, opiates are widely used as antitussives but have substantial side effects. Recently, it has been proposed that NOP1 receptor agonists may be useful as a novel approach to cough suppression. Therefore, we compared the effect of NOP1 receptor agonist SCH486757 with matched placebo and codeine in a multicentre, double-blind, parallel-group study in patients with subacute cough. The primary outcome was change in cough severity scores, with the key secondary outcome change in objective daytime cough counts. We studied 91 subjects with subacute cough [59 (65%) female, median agexa0=xa041 (rangexa0=xa018–64) years, and median cough durationxa0=xa033 (rangexa0=xa016–99) days]. Subjects were randomised to receive either SCH486757 100xa0mg, codeine 30xa0mg, or matched placebo twice daily for 5xa0days. Cough severity was scored throughout using a diary card and objective cough frequency recorded for 8xa0h at baseline and on the first and last treatment days. There were no significant differences in changes in average cough severity scores from baseline to treatment between SCH486757 and placebo [mean changexa0=xa0−0.57 (−30.1%) vs. mean changexa0=xa0−0.49 (−19.7%); Pxa0=xa00.56] or between codeine and placebo [mean changexa0=xa0−0.72 (−33.2%); Pxa0=xa00.07 compared to placebo). Changes in objective cough counts also showed no differences between the three treatment groups. There were some hints of possible limited antitussive efficacy with SCH486757. Unfortunately, the maximum clinical dose is limited by its tendency to produce somnolence. If the therapeutic ratio of NOP1 agonists could be improved, these drugs may still prove to contain effective antitussives.

Treatment of acute lung injury by targeting MG53-mediated cell membrane repair

Injury to lung epithelial cells has a role in multiple lung diseases. We previously identified mitsugumin 53 (MG53) as a component of the cell membrane repair machinery in striated muscle cells. Here we show that MG53 also has a physiological role in the lung and may be used as a treatment in animal models of acute lung injury. Mice lacking MG53 show increased susceptibility to ischemia-reperfusion and over-ventilation induced injury to the lung when compared with wild type mice. Extracellular application of recombinant human MG53 (rhMG53) protein protects cultured lung epithelial cells against anoxia/reoxygenation-induced injuries. Intravenous delivery or inhalation of rhMG53 reduces symptoms in rodent models of acute lung injury and emphysema. Repetitive administration of rhMG53 improves pulmonary structure associated with chronic lung injury in mice. Our data indicate a physiological function for MG53 in the lung and suggest that targeting membrane repair may be an effective means for treatment or prevention of lung diseases.

Antitussive Action of Antihistamines Is Independent of Sedative and Ventilation Activity in the Guinea Pig

We studied the oral actions of antihistamines from six chemical classes, namely: the ethanolamines (ENA, diphenhydramine and clemastine); ethylenediamines (EDA, pyrilamine and tripelennamine); piperidines (PPD, terfenadine and astemizole); piperazines (PPZ, hydroxyzine and cetirizine); phenothiazines (PTZ, promethazine), and the alkylamines (ALA, chlorpheniramine and bromopheniramine) on cough reflexes, pentobarbital-induced sedation and minute ventilation in the conscious guinea pig. Antihistamines of the ENA class had minimal effects on capsaicin-induced cough although both diphenhydramine (30 and 100 mg/kg p.o.) and clemastine (30 and 100 mg/kg p.o.) increased sedation time (ST). The PPZ class demonstrated both antitussive and sedating activity. The minimum effective oral antitussive dose (MED) of cetirizine and hydroxyzine was 30 and 10 mg/kg, respectively. The EDA did not exhibit antitussive activity. Tripelennamine (10, 30 and 100 mg/kg p.o.) but not pyrilamine enhanced ST. The MED for the PTZ, promethazine, was 10 mg/kg, and at 100 mg/kg promethazine increased ST. The ALA group displayed antitussive activity but only chlorpheniramine (10 mg/kg p.o.) had any effects on ST. The MED for chlorpheniramine and bromopheniramine was 3 and 10 mg/kg p.o., respectively. The PPD antihistamines, namely terfenadine and astemizole, inhibited cough (MED 30 and 10 mg/kg p.o.) without sedative effects. Of the antihistamines tested only promethazine (100 mg/kg p.o.) depressed ventilation responses; however, this dose of promethazine was associated with adverse behavioral effects. The present findings indicate that the antitussive actions of antihistamines are not directly related to histamine H1-receptor blockade because several antihistamines did not antagonize capsaicin-induced cough. In addition, the antitussive actions of antihistamines are independent of their sedative or ventilation effects.