Anti-asthmatic and anti-cough activities of the essential oil Of Eucalyptus Grandis W. Hill Ex Maiden
Asthma is a chronic inflammatory disorder of the airways. It is characterized by an inflammation of the airways causing airway dysfunction. Asthma is associated with widespread airflow obstruction, with an associated increase in airway responsiveness to a variety of stimuli. An asthma attack is accompanied by wheezing, shortness of breath, chest tightness and coughing. This project aims to investigate the essential oil of Eucalyptus grandis, a medicinal plant used by Zulu traditional healers for its antiasthmatic and anti-cough activities in the treatment of respiratory tract infections. The anti-asthmatic and anti-cough activities of the essential oils and 1, 8-cineole on rats were assessed. These activities were induced and challenged with histamine and acetylcholine using an ultrasonic nebulizer for asthma and exposure to ammonia for coughs. The assessment of the chemical composition of the essential oils hydrodistilled from the fresh and dry leaves of Eucalyptus grandis was carried out using a GC and GC-MS analysis. Column chromatography was used to isolate 1,8-cineole and terpinen- 4-ol components of the essential oils. Agar well diffusion was used to access antibacterial (Klebsiella pneumoniae, Staphylococcus aureus and Moraxella catarrhalis) susceptibility to the essential oil. Cytosolic LDH was released and efflux pump inhibition activity was monitored to determine the apparent bactericidal mechanism of the essential oils. Antioxidant activity (free radical scavenging of nitric oxide, hydroxyl radical, superoxide anion, and also the sulfhydryl, NADH as well as the malondialdehyde (MDA)—TBARS contents) was determined. vi Anti-inflammatory activities of the essential oils and 1,8-cineole were determined using the cotton pellet granuloma test. Biochemical estimates were carried out on the catalase activity, superoxide dismutase, in vitro COX-1 and COX-2 inhibition assay and the acetylcholinesterase inhibitory activity. Muscle contraction studies where carried out using the vascular reactivity on aortic smooth muscle, and cytotoxicity assay done using the MTT assay on human embryonic kidney cells (HEK293) and human hepatocellular carcinoma cells (HepG2). The percentage yield of the essential oils from the fresh and dry leave was 0.19% and 0.40% respectively. The identified main components of the essential oil of the fresh leaves constituted 99.25% and the major constituents were: α- pinene (29.69%), p-cymene (19.89%), 1,8-cineole (12.80%), α-terpineol (6.48%), borneol (3.48%) and d-limonene (3.14%). The identified main components of the essential oil of the dry leaves was 92.63%, with the major constituents being: 1,8- cineole (47.44%), d- limonene (13.34%), α-pinene (7.49%), (-)-spathulenol (7.13%) and benzene,1-methyl-4-(1-methylethyl)-(5.42%). The oils exhibited concentration dependent anti-asthma and anti-cough activities. Significantly, 1,8-cineole isolated and purified from the essential oil showed a concentration dependent anti-inflammatory, anti-cough and anti-asthma activity. The oils inhibited the growth of the microorganisms studied. The minimum inhibitory concentration (MIC) ranged from 0.3125 mg/ml to 1.25 mg/ml, and the minimum bactericidal concentration (MBC) ranged from 0.625 mg/ml to >5 mg/ml. The LDH release assay (membrane damage) revealed bacterial membrane damage ranging from 1% to 11% in comparison with the standard tritonX-100. Accumulation of rhodamine 6G in bacterial cells, which was used to determine the activity of the essential oils as drug efflux pump inhibitors (EPIs), showed that the vii essential oils were effective as EPIs; the essential oils were also seen to be concentration dependent in inhibiting the activity of COX 2, with no significant effect on COX 1. The essential oils showed weak antioxidant activity in scavenging free radicals (IC50 for nitric oxide scavenging of 4.34 µg/ml and 3.65 µg/ml for the fresh and dry respectively, and >5 µg/ml for hydroxyl radical). Sulfhydryl contents were 9.00 µg/g(w/w) and 13.14 µg/g(w/w) for the oils from the fresh and dry leaves respectively. The essential oils showed vasorelaxant activity; cytotoxicity levels of the oils indicated that the oils were not toxic on cell lines, with IC50 of 2291, 2189 on HEK 293 cell, HEPG2 for the essential oils from the fresh leaves and 1875 and 1942 for the essential oils from the dry leaves on HEK293 and HEPG2 respectively. It is concluded that the essential oils have the potential to be used as an anti-asthma and anti-cough therapy. This study also justifies its use by traditional healers in the treatment of asthma and coughs in Zulu folklore medicine.
asthma --cough activities --essential oils --Eucalyptus Grandis W. Hill Ex Maiden
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