Objective: To investigate whether the endothelin (ET) receptor antagonists have protective role in the development of emphysema.
Methods: Sprague-Dawley rats (n = 24) were divided into four groups: control group, cigarette smoke extract (CSE) group, BQ123 group and Bosentan group. CSE was injected intraperitoneally once a week for three weeks and BQ123 and Bosentan were administered daily for the same duration. TdT-mediated dUTP nick end labeling (TUNEL) was performed to observe the deoxyribonucleic acid (DNA) damaged cells and the expression of caspase-3 was determined by immunohistochemistry and Western blot. Matrix metalloproteinase-2 (MMP-2) and MMP-9 activities were investigated by gelatin zymography and tumor necrosis factor α (TNFα) and interleukin-1ß (IL-1ß) concentrations were measured by enzyme linked immunosorbent assay (ELISA).
Results: We confirmed the emphysematous destruction in the lungs of experimental rats induced by the intraperitoneal injection of CSE within 3 weeks. The mean lining interval (MLI) and damage index (DI) were significantly increased in the CSE group compared with control group. However, the MLI and DI were significantly decreased in the BQ123 and bosentan groups compared with CSE rats (P < 0.01, respectively). The TUNEL-positive cells were markedly distributed in the peri-bronchioles, intra-alveoli, and septal areas of the emphysematous lungs in CSE rats comparing with the lungs of control rats. The apoptosis index (AI) was significantly higher in CSE group than control group. And the AI was significantly reduced in BQ123 group and bosentan group compared with that in CSE group. The caspase-3 positive cells were markedly distributed in the emphysematous lungs of CSE group comparing with the stained cells in the lungs of control rats. These positive cells were apparently reduced in the BQ123 and bosentan groups compared with the stained cells in CSE group. Comparing with the control group, expression of caspase-3 was prominently enhanced in CSE groups, but both BQ123 and bosentan treatments markedly inhabited the increases of the cleaved caspase-3 protein levels in rats injected with CSE. Rats injected with CSE showed increased MMP-2 and MMP-9 activities in their lung tissue homogenates and MMP-2 and MMP-9 activities were reduced significantly in both BQ123 and bosentan groups. The levels of TNFα and IL-1ß were significantly increased in the CSE group in comparison to those in controls. BQ123 and bosentan significantly prevented the increases of the levels of TNFα and IL-1ß in lungs of rats with injection of CSE.
Conclusions: ET-1 may have an important role in the pathological process of emphysema and ET receptor antagonists protect against the development of emphysema probably by decelerating apoptosis, inhibiting proteolytic enzyme activity and reducing inflammatory cytokine levels.