OBJECTIVETo investigate the effects of bleomycin (BLM) on the apoptosis of type II alveolar epithelial cell (AT II) in lung fibrotic rats and its possible mechanisms.

METHODSTotally 32 male Sprague-Dawley rats were randomly divided into sham group (n = 8) and BLM group (n = 24). Rats in sham group or BLM group were intratracheally instillated with saline or 5 mg/kg of bleomycin, respectively. One, three, and seven days after the instillation of bleomycin, 8 rats in BLM group were taken for AT II isolation and purification. Rats in sham group were used to isolate and purify AT II on 7 days after the instillation of saline. The cell cycle and apoptosis, intracellular free calcium concentration, and mitochondrial membrane potential (MMP) in AT II were determined by flow cytometry. Immunohistochemistry was performed to observe the expressions of Bax, Bcl-2, and Fas. Caspase-3, Caspase-8, and Caspase-9 activities were measured by Caspase activity detection kit.

RESULTSThe ratio of S phase AT II in BLM group was significantly lower than in sham group (P < 0.05). AT II apoptosis rates on day 1 and 3 were significantly higher in BLM group than in sham group (P < 0.01). Intracellular free calcium concentrations in BLM group were significantly higher than in sham group (P < 0.05). However, MMP was significantly lower than sham group (P < 0.05). The positive rates of Bax, Fas and Caspase-3, Caspase-8, and Caspase-9 activities of BLM group were significantly higher than those of sham group (P < 0.05, P < 0.01). The positive rates of Bcl-2 on day 1 and 3 were significantly lower than those of sham group (P < 0.05).

CONCLUSIONEarly AT II apoptosis may be induced by bleomycin, which may be explained by the increase of intracellular free calcium concentration, depression of MMP, increased expressions of Fas and Bax, and increase of Caspase-3, Caspase-8, and Caspase-9 activities.