Background There is evidence that tumour necrosis factor alpha (TNFα) may be an important mediator in initiating asthmatic airway inflammation. It has been proposed that endothelin-1 (ET-1) is involved in bronchoconstriction and airway remodelling in asthma. It is not known, however, if there is any interaction between TNFα and ET in perpetuating airway inflammation in asthma.
Objective The present study aimed to determine the activities of ET-1 and TNFα in ovalbumin-sensitized guinea pigs and their roles in the development of airway inflammation.
Method Twelve guinea pigs were sensitized by ovalbumin injection and aerosol inhalation. ET-1 levels were measured in both bronchoalveolar lavage fluid (BALF) and plasma by 125-labelled endothelin-1 (ET-1) radioimmunoassay. The TNFα activity released from alveolar macrophage (AM) in BALF was estimated by ELISA. Cultured bovine airway smooth muscle cells (BASMCs) were treated with TNFα (1000 units/5 ± 104 cells) for different times. ET-1 levels in harvested medium from these cells were measured by radioimmunoassay. Cultured human fetal lung fibroblasts (HFLFs) were incubated with ET-1(10–8–10–6M), then 3HTdR incorporation to these cells and cell counting were performed. The effects of ET-1 stimulation on the granulocyte macrophage colony stimulating factor (GM CSF) gene expression in HFLFs were estimated by using RT- PCR method.
Results ET-1 levels in both plasma and BALF were significantly higher in ovalbumin- sensitized guinea-pigs compared with those in controls (422.27 × 175.0pg/mL vs 277.311 × 88.0pg/mL, P < 0.05, 81.22 × 16.15 vs 49.81 × 12.64pg/mL, P < 0.05) while TNFα activity was also significantly increased in the OVA-sensitized group compared with that in the control group (6010 ± 1900pg/mL vs 2810 × 450 pg/mL, P < 0.05). The ET-1 level in harvested medium of BASMCs rose significantly in 12 h in the TNF-α treated group (from < 5pg/mL to53.72 × 14.3pg/mL, P < 0.001), and remained at a similar level for 24 h in the TNFα treated group. It was shown that ET-1 not only stimulated cell proliferation but also induced GM-CSF mRNA expression in HFLFs.
Conclusion ET-1 levels in both plasma and BALF and TNFα release from macrophage are increased significantly in ovalbumin-sensitized guinea-pigs. TNFα stimulates ET-1 secretion from cultured BASMCsw; ET-1 accelerates cell proliferation and induces GM- CSF mRNA expression in the human fetal lung fibroblast.