Bronchodilatory effects of S-isopetasin, an antimuscarinic sesquiterpene of Petasites formosanus, on obstructive airway hyperresponsiveness.
In the presence of neostigmine (0.1 microM), S-isopetasin competitively antagonized cumulative acetylcholine-induced contractions in guinea pig trachealis, because the slope [1.18+/-0.15 (n=6)] of Schild's plot did not significantly differ from unity. The pA2 value of S-isopetasin was calculated to be 4.62+/-0.05 (n=18). The receptor binding assay for muscarinic receptors of cultured human tracheal smooth muscle cells (HTSMCs) was performed using [3H]-N-methylscopolamine ([3H]-NMS). Saturation binding assays were carried out with [3H]-NMS in the presence (non-specific binding) and absence (total binding) of atropine (1 microM). Analysis of the Scatchard plot (y=0.247-1.306x, r2=0.95) revealed that the muscarinic receptor binding sites in cultured HTSMCs constituted a single population (n(H)=1.00). The equilibrium dissociation constant (Kd) and the maximal receptor density (B(max)) for [3H]-NMS binding were 766 pM and 0.189 pmol/mg of protein, respectively. The -logIC50 values of S-isopetasin, methoctramine, and 1,1-Dimethyl-4-diphenylacetoxypiperidinium iodide (4-DAMP) for displacing 0.4 nM [3H]-NMS-specific binding were 5.05, 6.25, and 8.56, respectively, which suggests that [3H]-NMS binding is predominantly on muscarinic M3 receptors of cultured HTSMCs. The inhibitory effects of S-isopetasin on enhanced pause (P(enh)) value were similar to that of ipratropium bromide, a reference drug. The duration of action of S-isopetasin (20 microM), also similar to that of ipratropium bromide (20 microM), was 3 h. In contrast to ipratropium bromide, which non-selectively acts on muscarinic receptors, S-isopetasin preferentially acts on muscarinic M3 receptors. In conclusion, S-isopetasin may be beneficial as a bronchodilator in the treatment of chronic obstructive pulmonary disease and asthma exacerbations.
Lin
Ling-Hung
LH
Department of Dentistry, Taipei Medical University Hospital, Taipei 110, Taiwan.
Huang
Tzu-Jung
TJ
Wang
Sheng-Hao
SH
Lin
Yun-Lian
YL
Wu
Sheng-Nan
SN
Ko
Wun-Chang
WC
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D001667:Binding, Competitive; D016535:Bronchial Hyperreactivity / Q000378:metabolism / Q000517:prevention & control*; D016085:Bronchoconstrictor Agents / Q000494:pharmacology; D001993:Bronchodilator Agents / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology*; D002478:Cells, Cultured; D002800:Cholinesterase Inhibitors / Q000494:pharmacology; D003959:Diamines / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D006801:Humans; D009241:Ipratropium / Q000494:pharmacology; D008297:Male; D018727:Muscarinic Antagonists / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology*; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism; D019832:N-Methylscopolamine / Q000378:metabolism; D009388:Neostigmine / Q000494:pharmacology; D036901:Petasites / Q000737:chemistry; D010880:Piperidines / Q000378:metabolism; D011485:Protein Binding; D043587:Receptor, Muscarinic M3 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D012717:Sesquiterpenes / Q000302:isolation & purification / Q000494:pharmacology*; D013997:Time Factors; D014132:Trachea / Q000187:drug effects* / Q000378:metabolism
D016085:Bronchoconstrictor Agents; D001993:Bronchodilator Agents; D002800:Cholinesterase Inhibitors; D003959:Diamines; D018727:Muscarinic Antagonists; D010880:Piperidines; D043587:Receptor, Muscarinic M3; D012717:Sesquiterpenes; D009388:Neostigmine; D001285:Atropine; C042375:4-diphenylacetoxy-1,1-dimethylpiperidinium; C418728:isopetasin; D009241:Ipratropium; D000109:Acetylcholine; C054938:methoctramine; D019832:N-Methylscopolamine