Abstract
The health benefits of Allium cepa (A. cepa) have been proclaimed for centuries. Various pharmacological and therapeutic effects on respiratory, allergic, and immunologic disorders are shown by A. cepa and its constituents. Flavonoids such as quercetin and kaempferol, alk(en)yl cysteine sulfoxides including S-methyl cysteine sulfoxide and S-propyl cysteine sulfoxide, cycloalliin, thiosulfinates, and sulfides are the main compounds of the plant. A. cepa displays broad-spectrum pharmacological activities including antioxidant, anti-inflammatory, antihypertensive, and antidiabetic effects. Our objective in this review is to present the effects of A. cepa and its constituents on respiratory, allergic, and immunologic disorders. Different online databases were searched to find articles related to the effect of A. cepa extracts and its constituents on respiratory, allergic, and immunologic disorders until the end of December 2020 using keywords such as onion, A. cepa, constituents of A. cepa, therapeutic effects and pharmacological effects, and respiratory, allergic, and immunologic disorders. Extracts and constituents of A. cepa showed tracheal smooth muscle relaxant effects, indicating possible bronchodilator activities or relieving effects on obstructive respiratory diseases. In experimental animal models of different respiratory diseases, the preventive effect of various extracts and constituents of A. cepa was induced by their antioxidant, immunomodulatory, and anti-inflammatory effects. The preventive effects of the plant and its components on lung disorders induced by exposure to noxious agents as well as lung cancer, lung infection, and allergic and immunologic disorders were also indicated in the experimental and clinical studies. Therefore, this review may be considered a scientific basis for development of therapies using this plant, to improve respiratory, allergic, and immunologic disorders.
Highlights
Allium cepa L. (A. cepa) or onion species are used as vegetables and employed in traditional medicine as therapeutic agents [1,2,3]
A. cepa extracts (AcE), (2, 4, 8, 16, 32, and 64 mg/ml) showed concentrationdependent relaxant effects on tracheal smooth muscle (TMS) of rats contracted by KCl or methacholine. ere was no significant difference in the relaxant effects of AcE between nonincubated and incubated tissues with glibenclamide, atropine, chlorpheniramine, and indomethacin
Various experimental studies showed the relaxant effects of A. cepa and its constituents mainly Qt on tracheal smooth muscle (TSM). e relaxant effects of the plant and Qt were possibly mediated by different mechanisms including β2-adrenoceptor stimulation, muscarinic and histamine H1 receptor inhibition, calcium channel blocking, and phosphodiesterase enzyme-like mechanisms. ese results suggest the possible bronchodilatory effects of the plant and Qt on obstructive respiratory diseases
Summary
Allium cepa L. (A. cepa) or onion species are used as vegetables and employed in traditional medicine as therapeutic agents [1,2,3]. Common cold is mainly caused by viruses and does not require antimicrobial treatment unless it is complicated by acute otitis media with effusion, tonsillitis, sinusitis, and lower respiratory tract infection. Treatments used against respiratory, allergic, and immunologic disorders with synthetic drugs do not fully cure these diseases and may cause various adverse side effects [33]. Erefore, using natural products such as some medicinal herbs, flavonoids, lactones, alkaloids, polysaccharides, diterpenoids, and glucosides, with immune-modulating and antiinflammatory properties, may potentially help in treatment of respiratory, allergic, and immunologic disorders [34]. Other sulfur compounds in onions include c-glutamyl peptides, S-substituted cysteines, and cycloaline, which are nonvolatile and have no effect on onion taste [46]
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