The interaction of tumour necrosis factor alpha and endothelin-1 in pathogenetic models of asthma

Abstract

Background: There is evidence that tumour necrosis factor alpha (TNF alpha) 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 TNF alpha and ET in perpetuating airway inflammation in asthma.

Objective: The present study aimed to determine the activities of ET-1 and TNF alpha 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 TNF alpha activity released from alveolar macrophage (AM) in BALF was estimated by ELISA. Cultured bovine airway smooth muscle cells (BASMCs) were treated with TNF alpha (1000 units/5 x 10(4) 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) approximately 10(-6)M), 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 +/- 175.0 pg/mL vs 277.311 +/- 88.0 pg/mL, P < 0.05, 81.22 +/- 16.15 vs 49.81 +/- 12.64 pg/mL, P < 0.05) while TNF alpha activity was also significantly increased in the OVA-sensitized group compared with that in the control group (6010 +/- 1900 pg/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-alpha treated group (from < 5 pg/mL to 53.72 +/- 14.3 pg/mL, P < 0.001), and remained at a similar level for 24 h in the TNF alpha 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 TNF alpha release from macrophage are increased significantly in ovalbumin-sensitized guinea-pigs. TNF alpha stimulates ET-1 secretion from cultured BASMCsw; ET-1 accelerates cell proliferation and induces GM-CSF mRNA expression in the human fetal lung fibroblast.