[Hydrogen sulfide attenuates bronchial epithelial cell apoptosis by inhibiting endoplasmic reticulum stress]

To explore the effects of hydrogen sulfide on nicotine-induced bronchial epithelial cell endoplasmic reticulum (ER) stress and apoptosis.

Nicotine was used to establish the apoptotic model in human bronchial epithelial cell line (16HBE) for mimicing the effect of cigarette smoke on apoptosis. The 16HBE cells were grouped by the concentration gradients of 0 (control), 5, 10, 20, 40, 80 µmol/L nicotine dosing. All groups were treated for 72 h. And 16HBE cells were grouped by the time gradients of 0 (control), 24, 48, 72 h of nicotine dosing. For control group, the nicotine concentration was 40 µmol/L. Then the protein expression level of CCAAT/enhancer binding protein homologous protein (CHOP) was measured by Western blot to define the effect of various concentrations of nicotine and different dosing periods of nicotine on the protein expression level of CHOP. For observing the role of hydrogen sulfide in ER stress-mediated apoptosis, 16HBE cells were divided into 6 groups of control, 40 µmol/L nicotine, 100 µmol/L sodium hydrosulfide (NaHS) + 40 µmol/L nicotine, 200 µmol/L NaHS + 40 µmol/L nicotine, 400 µmol/L NaHS + 40 µmol/L nicotine and 10 mmol/L taurine + 40 µmol/L nicotine. NaHS or taurine was pretreated for 30 min and then nicotine dosed for 72 h. The protein expression levels of GRP78 and ER stress-mediated apoptosis markers, such as cleaved caspase-12 and CHOP, were measured by Western blot. And chromatin dye Hoechst 33258 was used to detect the morphological changes of apoptotic 16HBE cells and apoptotic index calculated.

Nicotine could concentration and time-dependently improve the expression of CHOP in 16HBE cells. The ratio of CHOP to average absorbance of glyceraldehyde phosphate dehydrogenase (GAPDH) was significantly higher in 40 µmol/L nicotine group than that in control group (1.04 ± 0.32 vs 0.30 ± 0.17, P < 0.05). The ratio of GRP78 to average absorbance of β-actin (0.59 ± 0.19 vs 1.00 ± 0.08), cleaved caspase-12 to average absorbance of procaspase-12 (0.06 (0.01, 6.06) vs 20.30(12.79, 23.78)) and CHOP to average absorbance of β-actin (0.18 ± 0.10 vs 0.53 ± 0.09) in 200 µmol/L NaHS + 40 µmol/L nicotine group were all significantly lower than those in 40 µmol/L nicotine group (all P < 0.05). The apoptotic index in 200 µmol/L NaHS + 40 µmol/L nicotine group (3.04 ± 1.83 vs 16.60 ± 3.32) and apoptotic index in 10 mmol/L taurine + 40 µmol/L nicotine group (4.08 ± 2.04 vs 16.60 ± 3.32) were significantly lower than those in 40 µmol/L nicotine group (all P < 0.01).

NaHS exerts its protection against nicotine-induced bronchial epithelial cell apoptosis through suppressing ER stress. And the underlying mechanism may be through a down-regulation of ER stress-mediated apoptosis markers of cleaved caspase-12 and CHOP.