[Elevated expression of endothelin 2 in lung tissues of asthmatic rats after exposed to cigarette smoke and its mechanism].

Objective To study the effect of cigarette smoke exposure on the expression of endothelin 2 (ET-2) in bronchial epithelium of asthmatic rats. Methods Asthma models were established through intraperitoneal injection of 1 mL chicken ovalbumin (OVA)/Al(OH)3 mixture (asthma model group, n=6); based on the asthma models, exposure to smoking gas lasted four weeks with 10 cigarettes per day (smoke-exposed asthma group, n=6); based on the smoke-exposed asthma models, the rats were treated with intraperitoneal injection of dexamethasone 2 mg/(kg.d), intragastric administration of ET receptor inhibitor bosentan 100 mg/(kg.d) and combined use, respectively named dexamethasone treated group, bosentan treated group, and dexamethasone-bosentan treated group, 6 rats in every group. What's more, other 6 rats were only subjected to intraperitoneal injection of 1 mL normal saline as normal controls; in addition to the injection of saline, cigarette smoke control group (n=6) was set up by the exposure to smoking gas for four weeks with 10 cigarettes per day. Bronchoalveolar lavage fluid (BALF) was collected from the upper lobe of the left lung for cell counting and classification. Pathological changes of the right upper lung lobe tissues were observed by HE staining. In other lung tissues, the expression of JNK1/2 was detected by Western blotting; ET-2 was tested by Western blotting and immunohistochemistry; thiobarbituric acid reactive substances (TBARS) assay and trace enzyme standard method were used to measure malondialdehyde (MDA) and glutathione (GSH), respectively. Results Compared with normal control group, the number of airway inflammation cells increased in the BALF, and the expressions of ET-2, JNK1/2, MDA and GSH increased in the lung tissues of cigarette smoke control group, asthma model group and cigarette smoke-exposed asthma group. Compared with cigarette smoke-exposed asthma group, the number of airway inflammation cells decreased in the BALF, and the expressions of ET-2, JNK1/2, MDA and GSH decreased in the lung tissues of the dexamethasone treated group, bosentan treated group, and dexamethasone-bosentan treated group. Airway inflammation was attenuated and the staining intensity of ET-2 in the lung tissue was reduced in the dexamethasone treated group, bosentan treated group, and dexamethasone-bosentan treated group, which were more obvious in the dexamethasone-bosentan treated group. Conclusion Cigarette smoke exposure obviously aggravates airway inflammation in asthmatic rats, and bosentan can effectively alleviate the airway inflammation. The mechanism of the inflammation may be related to ET-2 and JNK1/2 signaling pathway.