Comparative GC Analysis, Bronchodilator Effect and the Detailed Mechanism of Their Main Component—Cinnamaldehyde of Three Cinnamon Species

Cinnamon is one of the most commonly used spices worldwide. In some Arab countries, cinnamon is used with other ingredients to relieve bronchospasm and treatment of airways-related disorders. In the current study, GC, GC-MS and tracheal relaxant effect comparison were performed using the three available types in Saudi Arabia, Cinnamomum verum (Ceylon cinnamon), C. cassia (Chinese cinnamon) and C. loureiroi (Vietnamese cinnamon). The essential oil of C. verum was the most potent in the relaxation of guinea pig isolated tracheal muscles against carbachol (CCh, 1 uM)-evoked bronchospasm at the concentration range from 0.03 to 3 mg/mL followed by C. bureiroi at 0.03 to 5 mg/mL; whereas, C. cassia was the least potent oil. Cinnamaldehyde (1), isolated as the main component of the three oils induced complete relaxation of low K⁺ (25 mM)-evoked contractions, with mild effect on the contractions evoked by high K⁺ (80 mM). Pre-incubation of the tracheal tissues with glibenclamide (10 μM) significantly opposed the relaxation of low K⁺ by cinnamaldehyde. The standard drug, cromakalim also inserted glibenclamide-sensitive inhibition of low K⁺ without relaxing high K⁺. These results indicate that cinnamaldehyde acts predominantly by ATP-specific K⁺ channel opening followed by weak Ca⁺⁺ antagonistic effects. The obtained results justify the medicinal value of cinnamon oil in respiratory disorders.