Action of moguisteine on the activity of tracheobronchial rapidly adapting receptors in the dog

Effects of four antitussives on airway neurogenic inflammation in a guinea pig model of chronic cough induced by cigarette smoke exposure

OBJECTIVE

The effects of four antitussives, including codeine phosphate (CP), moguisteine, levodropropizine (LVDP) and naringin, on airway neurogenic inflammation and enhanced cough were investigated in guinea pig model of chronic cough.

METHODS

Guinea pigs were exposed to CS for 8 weeks. At the 7th and 8th week, the animals were treated with vehicle, CP (4.8 mg/kg), moguisteine (24 mg/kg), LVDP (14 mg/kg) and naringin (18.4 mg/kg) respectively. Then the cough and the time-enhanced pause area under the curve (Penh-AUC) during capsaicin challenge were recorded. The substance P (SP) content, NK-1 receptor expression and neutral endopeptidase (NEP) activity in lung were determined.

RESULTS

Chronic CS exposure induced a bi-phase time course of cough responsiveness to capsaicin. Eight weeks of CS exposure significantly enhanced the airway neurogenic inflammation and cough response in guinea pigs. Two weeks of treatment with CP, moguisteine, LVDP or naringin effectively attenuated the chronic CS-exposure enhanced cough. Only naringin exerted significant effect on inhibiting Penh-AUC, SP content and NK-1 receptor expression, as well as preventing the declining of NEP activity in lung.

CONCLUSIONS

Chronic CS-exposed guinea pig is suitable for studying chronic pathological cough, in which naringin is effective on inhibiting both airway neurogenic inflammation and enhanced cough.

Antitussive effect of NS-398, a selective cyclooxygenase-2 inhibitor, in guinea pigs

Several reports have demonstrated that the number of capsaicin-induced coughs is increased in the presence of prostaglandins in the airway. Moreover, it has been reported that the expression of cyclooxygenase-2, which converts arachidonic acid to prostaglandins, was found in cultured human airway epithelial cells in the absence of inflammatory cytokine stimulation. Thus, it is possible that cyclooxygenase-2 inhibitor may produce an antitussive effect. To test this hypothesis, we investigated the effects of N-[2-(cyclohexyloxy)-4-nitrofenyl]-methane sulfonamide (NS-398), a selective cyclooxygenase-2 inhibitor, and 5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-trifluoromethyl-pyrazole (SC-560), a selective cyclooxygenase-1 inhibitor, on capsaicin-induced coughs in guinea pigs. NS-398 (1-10 mg/kg, p.o.) dose-dependently and significantly reduced the number of capsaicin-induced coughs. In contrast, SC-560 (10 mg/kg, p.o.) did not reduce the number of capsaicin-induced coughs. The antitussive effect of NS-398 (10 mg/kg, p.o.) was not antagonized by pretreatment with methysergide (3 mg/kg, i.p.), a non-selective serotonin (5-HT) receptor antagonist, or glibenclamide (10 mg/kg, i.p.), an ATP-sensitive K(+) channel blocker. Furthermore, although NS-398 did not significantly affect the cough reflex induced by substance P (10(-16) M), it significantly reduced the capsaicin-induced release of substance P in bronchoalveolar lavage fluid (BALF). The present findings clearly show that cyclooxygenase-2 inhibitor, but not cyclooxygenasez-1 inhibitor, has a potent antitussive effect. Furthermore, it is possible that the antitussive action of NS-398 does not depend on centrally acting mechanisms, since 5-HT receptors play an important role in the cough-depressant activities of centrally acting antitussive drugs. NS-398 may exert peripheral antitussive effects by inhibiting the release of substance P from capsaicin-sensitive afferent C-fibers in the airways. These results suggest that cyclooxygenase-2 inhibitors may have a therapeutic benefit in reducing coughs.

Antitussive principles of Glycyrrhizae radix, a main component of the Kampo preparations Bakumondo-to (Mai-men-dong-tang)

We attempted to elucidate the antitussive principles of Glycyrrhizae radix, a main component of Bakumondo-to (Mai-men-dong-tang). Although the 50% methanol-eluted fraction (100 mg/kg, p.o.) caused a more than 60% reduction in the number of capsaicin-induced coughs, neither the water-eluted nor 100% ethanol-eluted fractions of water extract of G. radix had antitussive effects. The water extract of G. radix contained high levels of liquiritin, liquiritin apioside, isoliquiritin, isoliquiritin apioside and glycyrrhizin. On the other hand, the 50% methanol-eluted fraction contained mainly liquiritin and liquiritin apioside, but not the other compounds. Liquiritin apioside (3-30 mg/kg, p.o.), but not liquiritin, isoliquiritin, isoliquiritin apioside or glycyrrhizin, dose-dependently inhibited the number of coughs. Methysergide, a serotonin receptor antagonist, antagonized the antitussive effect of liquiritin apioside. However, the antitussive effect of liquiritin apioside was not antagonized by naloxone. Pretreatment with glibenclamide (3 mg/kg, i.p.), an ATP-sensitive potassium channel blocker, also significantly reduced the antinociceptive effect of liquiritin apioside. These results suggest that G. radix contains a potent antitussive compound, liquilitin apioside, whose antitussive effect may depend on both peripheral and central mechanisms.

Inhaled pinacidil, an ATP-sensitive K+ channel opener, and moguisteine have potent antitussive effects in guinea pigs

We investigated whether inhaled pinacidil and moguisteine inhibit capsaicin-induced coughs in guinea pigs. Inhaled pinacidil (15 - 60 microg/ml), an ATP-sensitive K+ channel opener, and moguisteine (15 - 60 microg/ml) each dose-dependently inhibited the number of capsaicin-induced coughs. The antitussive effects of pinacidil and moguisteine were significantly antagonized by pretreatment with glibenclamide (10 mg/kg, i.p.), an ATP-sensitive K+ channel blocker. However, pretreatment with naloxone methiodide (10 mg/kg, s.c.) had no significant effect on the antitussive effects of either pinacidil or moguisteine. On the other hand, inhaled dihydrocodeine (15 - 60 microg/ml) also dose-dependently suppressed the number of capsaicin-induced coughs. The antitussive effect of inhaled dihydrocodeine was significantly antagonized by pretreatment with naloxone methiodide (10 mg/kg, s.c.), but not by glibenclamide (10 mg/kg, i.p.). These results indicate that inhaled pinacidil and moguisteine both attenuate capsaicin-induced coughs. Pinacidil and moguisteine may exert their antitussive effects through the activation of ATP-sensitive K+ channels in the tracheobronchial tract. Furthermore, it is possible that ATP-sensitive K+ channels may be involved in the antitussive effects of peripherally acting non-narcotic antitussive drugs.

Involvement of ATP-sensitive K(+) channels in the anti-tussive effect of moguisteine

The effect of glibenclamide, an ATP-sensitive K(+) channel blocker, on the anti-tussive effect of moguisteine and of pinacidil, an ATP-sensitive K(+) channel opener in guinea pigs was studied. Pinacidil (1 and 5 mg/kg, subcutaneous (s.c.)) dose-dependently reduced the number of coughs. The anti-tussive effect of pinacidil was significantly and dose-dependently antagonized by pre-treatment with glibenclamide (3 and 10 mg/kg, i.p.). Moguisteine (1 and 5 mg/kg, s.c.) dose-dependently reduced the number of coughs. The anti-tussive effect of moguisteine was also reduced by pre-treatment with glibenclamide, in a dose-dependent manner. However, pre-treatment with glibenclamide had no effect on the anti-tussive effects of dihydrocodeine and dextromethorphan. Glibenclamide (10 mg/kg, i.p.), by itself, had no significant effect on the number of coughs. These results suggest that pinacidil and moguisteine may exert their anti-tussive effects through the activation of ATP-sensitive K(+) channels. Furthermore, it is possible that ATP-sensitive K(+) channels may be involved in the anti-tussive effect of peripherally acting non-narcotic anti-tussive drugs.

Effects of moguisteine on the cough reflex induced by afferent electrical stimulation of the superior laryngeal nerve in guinea pigs

The study aimed to further demonstrate the peripheral antitussive properties of moguisteine. Firstly, the antitussive effect of moguisteine on the cough reflex induced by inhalation of citric acid aerosol was evaluated in conscious guinea pigs. Secondly, the effects of both moguisteine and codeine on the centrally mediated cough reflex induced by afferent electrical stimulation of the superior laryngeal nerve were investigated in anesthetized guinea pigs. Moguisteine (2.5-10 mg/kg, intravenously, i.v.) reduced the cough reflex induced by 7.5% citric acid aerosol in a dose-dependent manner, with an ED50 value of 0.55 mg/kg. Both i.v. (0.5-4 mg/kg) and intracerebroventricular (i.c.v., 5-20 microg) injection of codeine dose dependently inhibited the cough reflex induced by afferent electrical stimulation of the superior laryngeal nerve; the ED50 values were 0.91 mg/kg and 7.90 microg, respectively. The inhibitory effect of codeine (4 mg/kg i.v.) was abolished by pretreatment with naloxone (2 mg/kg intraperitoneally). In contrast to codeine, neither i.v. (4 and 20 mg/kg) nor i.c.v. (20 microg) injection of moguisteine affected the cough reflex. These results suggest that the antitussive effect of codeine is mediated by central opioid mechanisms, whereas the antitussive effect of moguisteine is mediated by peripheral mechanisms.

Modulation of sensory nerve function in the airways

Several clinical studies document a greater discrimination between asthmatic and healthy subjects in bronchial responsiveness to a range of stimuli such as cold air, distilled water and sodium metabisulphite, than to conventional bronchoconstrictor agonists including histamine and methacholine. One of the mechanisms thought to account for the bronchoconstriction induced by these agents is via reflex activation of the cholinergic pathway. An increase in sensory nerve (afferent) activity in asthma might account for the increased responsiveness to these agents. If so, a number of strategies are available to inhibit the function of afferent nerves which could lead to a suppression of bronchial hyperresponsiveness, including (1) inhibition of afferent activity, (2) inhibition of neuropeptide release and (3) antagonism of tachykinin receptors. As there are numerous reviews dealing with the latter, in this review Domenico Spina, Saloni Shah and Selena Harrison focus on the first two strategies.